Chemically strengthened glass having no optical orange peel and method for producing the same

Abstract

To provide a chemically toughened glass article with a thickness of at most 0.07 mm and has no optical orange skin when inspected under reflection light, and a method for producing the same.SOLUTION: A method for chemical toughening a thin glass article with a thickness of at most 0.07 mm comprises the following steps: immersing the glass article into a bath of molten salt having a certain toughening temperature for a certain toughening time, lifting the toughened glass article out of the salt bath, post-toughening dwelling the toughened glass article for a certain dwelling time, wherein the dwelling temperature is selected to be higher than a melting point of the salt bath and lower than a transition temperature (Tg) of the toughened glass article, and cooling and cleaning the toughened glass article.SELECTED DRAWING: Figure 16

Description

Technical Field

[0001] The present invention relates to a chemically strengthened glass article having no optical orange peel when a glass article has a thickness of up to 0.07 mm and is inspected under reflected light, and a method for manufacturing such a chemically strengthened glass article.

Background Art

[0002] Thin glasses having various compositions are suitable substrate materials for many applications where transparency, high chemical and heat resistance, and defined chemical and physical properties are important. For example, alkali-free glass can be used for display panels and as an electronic packaging material in wafer form. Alkali-containing silicate glass is used for filter coating substrates, touch sensor substrates, and covers for fingerprint sensor modules.

[0003] Aluminosilicate (AS) glass, lithium aluminosilicate (LAS) glass, borosilicate glass, and soda-lime glass are widely used for applications such as covers for fingerprint sensors (FPS), protective covers, and display covers. In those applications, the glass is usually chemically strengthened to achieve high mechanical strength measured by special tests such as two-point bending (2PB), ball drop, pen drop, sharp object impact resistance, sharp object contact resistance, scratch resistance, and others.

[0004] Currently, due to the continuous demands for new functionality and a wider range of applications of products, there is a need for even thinner, lighter glass substrates and cover glasses with high strength and flexibility. A suitable glass is ultra-thin glass (UTG). The fields where ultra-thin glass (UTG) is typically applied are protective covers for precision electronic devices. For example, UTG can be used as a flexible and foldable display glass for consumer electronic devices. Currently, due to the increasing demands for new functionality of products and the exploration of new and extensive applications, there is a need for new characteristics, such as thinner and lighter glass substrates with flexibility. Due to the flexibility of UTG, such glass has been investigated and developed as cover glasses and displays for devices such as smartphones, tablets, watches, and other wearable devices. Such glass can also be used as a cover glass for fingerprint sensor modules and as a lens cover for cameras.

[0005] However, some of the mechanical properties and performance of pure glass (such as impact resistance and bendability) are not sufficient due to the very thin thickness of UTG. One effective means to enhance mechanical performance is chemical strengthening, that is, surface modification by ion exchange.

[0006] Chemical strengthening is a well-known method for glass to increase the strength of glass such as soda-lime glass or aluminosilicate (AS) glass or lithium aluminosilicate (LAS) glass or borosilicate glass used as cover glass for display applications. Under this situation, the surface compressive stress (CS) is typically 100 - 1000 MPa, and the depth of the ion exchange layer depends on the thickness of the glass.

[0007] However, when the glass sheet becomes thinner than 0.5 mm, handling becomes increasingly difficult mainly due to defects that cause breakage, such as cracks and chips at the glass edges. Also, the overall mechanical strength, i.e., the strength reflected in the bending strength or impact strength, significantly decreases. Therefore, strengthening of the glass is extremely important for thin glass. However, strengthening of ultra-thin glass always involves the risk of self-destruction due to the high internal tensile stress of the glass.

[0008] Typically, ultra-thin glass sheets with a thickness of less than 0.4 mm can be manufactured by direct hot forming methods, such as down-draw, overflow fusion, or special float methods. The redraw method is also possible. Compared to thin glass post-treated by chemical or physical methods (e.g., manufactured by grinding and polishing), directly hot-formed thin glass has much better surface uniformity and surface roughness because the surface is cooled from a high-temperature molten state to room temperature. Using the down-draw method, glass thinner than 0.3 mm, or even thinner than 0.07 mm, such as aluminosilicate glass, lithium aluminosilicate glass, alkali borosilicate glass, soda-lime glass, or alkali-free aluminoborosilicate glass, can be manufactured.

[0009] The chemical strengthening of UTG has been described (e.g., International Publication No. 2014 / 139147 (WO2014 / 139147A1)).

[0010] For chemical strengthening, the glass article is placed in a special bath of at least one molten salt having a predetermined temperature for a defined time. During strengthening, ion exchange occurs at the surface of the glass article, where smaller cations (especially monovalent cations) are replaced by cations having a larger radius. After the strengthening process, the glass article is lifted out of the salt bath and subsequently cooled and washed.

[0011] Surprisingly, it has been found that standard ion-exchange procedures can result in undesirable optical features in the form of an "optical orange skin" (OOS) on the surface of the strengthened glass article. This effect can be observed when the glass article has a thickness of 0.07 mm or less and is inspected under reflected light.

[0012] Under such reflection conditions, or even upon inspection with the naked eye in some cases, the surface of the glass article appears to have small irregularities (dots or bumps), similar to the orange skin of a fruit.

[0013] OOS is undesirable as it disrupts the optical appearance of electronic devices using glass articles with such surface effects.

Prior Art Documents

Patent Documents

[0014]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0015] The problem of the present invention is to provide a chemically strengthened glass article having a maximum thickness of 0.07 mm and not having an optical orange skin when inspected under reflected light, and a method for manufacturing a chemically strengthened glass article having a maximum thickness of 0.07 mm and not having a visible optical orange skin when inspected under reflected light.

Means for Solving the Problems

[0016] Explanation of Technical Terms Glass article: The glass article can be of any size. For example, it can be a long, thin, rolled-up glass ribbon (glass roll), or an individual smaller glass member cut from the glass roll, or a separate glass sheet, or an individual small glass article (e.g., cover glass for an FPS or a display), etc.

[0017] Ultra-thin glass: For the purposes of the present invention, the ultra-thin glass is flexible, preferably foldable glass, having a thickness of 0.4 mm or less, preferably 0.14 mm or less, particularly more preferably 0.1 mm or less, preferably 0.07 mm or less, preferably 0.05 mm or less, preferably 0.03 mm or less.

[0018] Thickness (t): The thickness of the glass article is the arithmetic mean of the thicknesses of the samples measured.

[0019] Compressive stress (CS): Compression induced between the glass network after ion exchange on the surface layer of the glass. Such compression cannot be relaxed by deformation of the glass and is maintained as stress. Commercially available testing machines, such as the FSM6000 (Lucio Corporation, Japan / Tokyo), can measure CS by means of a waveguide mechanism.

[0020] Depth of layer (DoL): The thickness of the ion exchange layer of the region of the glass where CS is present. Commercially available testing machines, such as the FSM6000 (Lucio Corporation, Japan / Tokyo), can measure DoL by means of a waveguide mechanism.

[0021] Internal tensile stress (CT): When CS is induced on one or both sides of a single glass sheet, in order to balance the stress according to the third principle of Newton's law, tensile stress must be induced in the central region of the glass, which is referred to as internal tensile stress. CT can be calculated from the measured CS and DoL.

[0022] Surface roughness (R a): Scale of the surface texture. This is quantified by the vertical deviation from the ideal form of the actual surface. Conventionally, amplitude parameters characterize the surface based on the vertical deviation from the center line of the roughness profile. R a is the arithmetic mean of the absolute values of those vertical deviations.

[0023] Total thickness variation (TTV): The maximum variation in the thickness of the substrate, coating, or salt residue layer. The total thickness variation is generally determined by measuring a glass article, sheet, or layer at about 20 - 200 points in a cross pattern (so as not to be too close to the edges of the article) and calculating the maximum difference in the measured thicknesses, i.e., TTV = T max - T min where.

[0024] Detailed Description of the Invention According to the present invention, a method for manufacturing a chemically strengthened glass article having a glass article with a thickness of at most 0.07 mm and having no visible optical orange peel (OOS) when inspected under reflected light provides a more homogeneous ion exchange process by providing a controlled thickness and distribution of salt residues on the glass surface.

[0025] In the prior art, it has been considered that only the strengthening time, temperature, and type of salt bath mainly affect / act on the performance of the strengthened glass article. However, chemical strengthening of UTG articles is more difficult. Surprisingly, the inventors have found that when dealing with ultra-thin glass articles, it is important to control and accurately set each of the subsequent post-ion exchange processes before the salt residue solidifies when the strengthened glass is lifted from the salt bath.

[0026] The aforementioned OOS effect (see Figure 1b compared to Figure 1a) may be seen on chemically strengthened glass articles having a thickness of less than 0.07 mm under reflected light inspection. In this test method, a strong white light source, such as the white light source of a vein inspection system, is used. For the present invention, a 500 W xenon lamp (CHF-XM-500W) was used. The sample of the glass article to be inspected is oriented with respect to the light source such that it acts as a mirror, and the light reflected by the glass article is projected onto an inspection surface (such as a screen, a horizontal and flat wall, etc.). The distance between the glass article and the inspection surface should be about 10 cm. The optical and geometric distortions (such as warping, deformation, optical effects, such as OOS) of the glass article will appear to be greatly magnified by this test method. For the present invention, the projected image is visually inspected and documented by taking a photograph of the reflected image. Furthermore, the photograph of the reflected image can be further evaluated using a computer-based image evaluation system (for example, evaluating variations in different gray levels and / or brightness). A suitable image evaluation program is "ImageJ".

[0027] Looking at the reflected images of strengthened thin glass articles having a thickness of 70 μm or less, small surface irregularities are seen (Figure 1b, 3b, 4b, 5b), which are referred to as optical orange peel (OOS). OOS can appear in various ways: the surface may appear to have a wavy or wrinkled structure (Figure 1b, 3b), or the surface may appear to have a (localized) structure in the form of bumps or depressions (Figure 4b, 5b). Due to the thin thickness of the glass, the OOS effect may be visible to the naked eye for some strengthened glass articles.

[0028] The inventors have found that the surface irregularities of strengthened UTG that are visible under reflected light, referred to as OOS, do not correspond to changes in surface topology. Surface topology analysis does not show changes in height at the frequency that is the characteristic size of OOS (see Figures 2a and 2b).

[0029] OOS is considered to be an optical effect that appears to be caused by inhomogeneities in the ion exchange that can lead to inhomogeneities in the slope of the specific refractive index. In relation to the present invention, the inventors have found that visible OOS can be correlated with a non-uniform ion exchange process between the glass and the salt residue adhering to the glass surface, while and after lifting the glass article from the salt bath and before the salt residue solidifies. Due to the gravity and rheology of the molten salt, the thickness of the salt residue adhering to the glass surface is not uniform. When strengthened in the same salt bath, the thicker the residual salt, the worse the appearance of the optical surface called OOS (see FIGS. 3a, 3b and FIGS. 4a, 4b).

[0030] Furthermore, the inventors have found that strengthened thin glass articles having a thickness greater than 70 μm, having the same composition and strengthened under the same strengthening conditions, do not exhibit OOS under the corresponding reflected light inspection as described in the following description of the drawings (see FIG. 6).

[0031] To avoid or minimize OOS, the following procedure is proposed using only the methods described or in combination with other described means: According to one aspect of the present invention, a method for chemically strengthening a thin glass article having a maximum thickness of 0.07 mm includes the following steps: · Immersing the glass article in a bath of molten salt having a specific strengthening temperature for a specific strengthening time; · Lifting the strengthened glass article out of the salt bath; · Holding the strengthened glass article for a specific holding time after strengthening, where the holding temperature is selected to be higher than the melting point of the salt bath and lower than the transition temperature (T g ) of the strengthened glass article; · Cooling and washing the strengthened glass article.

[0032] While lifting the strengthened glass article out of the salt bath, maintain the temperature of the space above the salt bath at a high temperature higher than the melting point of the salt bath. Preferably, the temperature of the said space corresponds to or is near the holding temperature in the subsequent holding stage after strengthening. In an advantageous aspect of the present invention, the part of the strengthened glass emerging from the salt bath during the lifting process is not cooled below the defined holding temperature. In a preferred embodiment, the holding process after strengthening is carried out directly above the salt bath. Optionally, transport the lifted strengthened glass article to a holding position where the lifted glass article is maintained at a high temperature preferably corresponding to or near the defined holding temperature.

[0033] Carry out the holding stage after strengthening preferably using a heating furnace capable of setting the holding temperature. According to the present invention, immediately after leaving the salt bath, hold the glass article at the holding temperature for a specific holding time, and then cool and wash it. (Compared with the procedure in which the strengthened glass article can be directly cooled after leaving the salt bath) Due to the higher holding temperature, the viscosity of the salt residue adhering to the surface of the strengthened glass article is maintained at a low level, so the salt residue moves under the influence of gravity, and a thin, preferably homogeneous layer of residual salt is formed on the surface of the strengthened glass article. Under inspection by reflected light, such a strengthened glass article having a thickness of 70 μm or less does not have OOS.

[0034] Regarding the present invention, the lifting time is the time required to completely lift the glass article out of the salt bath. The lifting time starts when the upper end of the glass article emerges from the salt bath and ends when the lower end just leaves the salt bath.

[0035] The holding time after strengthening starts after the lifting time, that is, when the lower end of the glass article emerges from the salt bath. The holding process is a processing stage that affects the entire glass article after leaving the strengthening salt bath. During the holding time (also referred to as the hold time), preferably maintain the entire glass article at a temperature higher than the melting point of the salt bath.

[0036] Preferably, the holding time is >0 seconds, preferably >5 seconds, preferably >15 seconds, preferably >30 seconds, preferably >1 minute, preferably ≥2 minutes. Preferably, the holding time is longer than the lifting time.

[0037] The holding time ends when the glass article is finally cooled to a temperature below the melting point of the salt bath.

[0038] The salts most commonly used for chemical strengthening are Na + -containing molten salts or K + -containing molten salts, or mixtures thereof. Conventionally used salts are NaNO3, KNO3, NaCl, KCl, K2SO4, Na2SO4, Na2CO3 and K2CO3. Additives such as NaOH, KOH and other sodium or potassium salts can also be used to better control the rate of ion exchange, CS and DoL during chemical strengthening.

[0039] The preferred strengthening temperature of the strengthening bath is in the range of 340°C to 460°C. More preferably, the strengthening time is in the range of 1 minute to 600 minutes. The strengthening time, strengthening temperature and type of molten salt bath used should be selected taking into account the type of glass of the article to be strengthened and the intended strengthening result. Preferably, the strengthened glass article has a CS in the range of 100 MPa to 2000 MPa. Preferably, the strengthened glass article has a DoL of 1 μm to t / 3 μm, preferably 2 μm to t / 4 μm, preferably 3 μm to t / 5 μm, where t is the thickness of the strengthened glass article in μm.

[0040] In an advantageous aspect of the method, the strengthened glass article is lifted from the salt bath at a lifting speed of <10 m / min, preferably <5 m / min, more preferably <1 m / min, preferably <0.8 m / min, more preferably <0.6 m / min, and even more preferably <0.5 m / min. When a reduced lifting speed is applied, there is sufficient time for the residual salt adhering to the surface of the strengthened glass article to flow off the surface under the influence of gravity and the surface tension of the salt bath and the glass. The low lifting speed helps to form a thinner layer of residual salt on the surface of the strengthened glass article. Since an increase in impurities in the salt bath (e.g., exchanged ions derived from the glass composition) changes the rheology (e.g., viscosity) of the salt bath, it may be recommended to modify the lifting setting during the life of the salt bath used. When the viscosity increases, a smaller lifting speed should be applied to reduce unwanted residual salt on the surface of the strengthened glass article.

[0041] With respect to the present invention, the lifting speed is indicated as an average speed. It can be advantageous for the glass article to be lifted at a substantially constant lifting speed, i.e., the lifting speed does not substantially change during the lifting process.

[0042] In an advantageous aspect, the lifting speed is >0.001 m / min, preferably >0.005 m / min, preferably >0.01 m / min, preferably >0.03 m / min, preferably >0.05 m / min.

[0043] To provide a strengthened glass article having no visible OOS, it is advantageous if the difference between the post-strengthening holding temperature and the strengthening temperature is <200 °C, preferably <100 °C. The said difference may be selected to be <70 °C or <55 °C or <40 °C or <20 °C or <10 °C, where the indicated difference values are absolute values, i.e., the holding temperature may be higher or lower than the strengthening temperature. Since impurities in the salt bath (e.g., exchanged ions derived from the glass composition) change the rheology (e.g., viscosity) of the salt bath, it may be recommended to correct the applied temperature difference during the life of the salt bath used. If the viscosity increases, a higher temperature difference (absolute value) can be applied to reduce unwanted residual salts on the surface of the strengthened glass article.

[0044] In an advantageous aspect of the present invention, the post-strengthening holding temperature is >350 °C, preferably >360 °C, preferably >370 °C, preferably >380 °C, preferably >390 °C, preferably >400 °C, preferably >410 °C, preferably >420 °C. The holding temperature is selected to be significantly higher than the melting point of the salt. The inventors have found that a holding temperature close to the melting point of the salt used in the strengthening bath can result in a strengthened glass article having visible OOS. Without being bound by the following attempt at explanation, this may be because a lower holding temperature, closer to the melting point of the salt, can result in a greater variation in ion mobility, making the ion exchange during holding more non-uniform.

[0045] To obtain a strengthened glass article having no visible OOS, it is further advantageous if the holding time after strengthening is < 120 minutes, preferably < 80 minutes, preferably < 40 minutes, preferably < 20 minutes, preferably < 10 minutes, preferably ≦ 5 minutes. If the holding time is too long, this can result in a decrease in CS due to relaxation. Since impurities in the salt bath (e.g., exchanged ions derived from the glass composition) change the rheology (e.g., viscosity) of the salt bath, it may be recommended to modify the applied holding time during the life of the salt bath used. If the viscosity increases, a longer holding time can be applied to reduce unwanted residual salt on the surface of the strengthened glass article.

[0046] In a further advantageous aspect, the strengthening setting, lifting setting and / or post-strengthening holding setting are selected such that the thickness of the salt residue adhering to one surface of the strengthened glass article is < 9 / 10×t (i.e., multiply t by 9 / 10), preferably < 7 / 10×t, preferably < 5 / 10×t, preferably < 3 / 10×t, preferably < 1 / 10×t, where t is the thickness of the glass article. Thus, the total of the salt residues for both sides (surfaces) of a plate-shaped glass article is < 18 / 10×t, preferably < 14 / 10×t, preferably < 10 / 10×t, preferably < 6 / 10×t, preferably < 2 / 10×t.

[0047] In another advantageous embodiment, the homogeneity of the salt residue on the glass surface is set. Preferably, the TTV (total thickness variation) of the salt residue adhering to one surface of the strengthened glass article is < 9 / 10×t (i.e., multiply t by 9 / 10), preferably < 7 / 10×t, preferably < 5 / 10×t, preferably < 3 / 10×t, preferably < 1 / 10×t, where t is the thickness of the plate-shaped glass article. A homogeneous thickness (small TTV) of the layer of salt residue on one surface, preferably both surfaces, of the glass article is advantageous for obtaining a strengthened glass article having no OOS.

[0048] In another advantageous aspect, the method includes the step of controlling the impurity content (molar concentration of monovalent ions) in the salt bath to be <5000 ppm, preferably <3000 ppm, preferably <2000 ppm, preferably <1000 ppm, preferably <700 ppm, preferably <500 ppm, preferably <400 ppm, preferably <300 ppm, preferably <200 ppm, preferably <100 ppm, preferably <50 ppm, preferably <20 ppm. By this means, the rheology of the molten salt bath can be improved, as will be described in more detail below.

[0049] As described above, in order to produce a strengthened thin glass article without OOS, it is an important and preferred means to hold it at a high temperature after strengthening. However, a glass article without OOS or with reduced OOS can also be produced without using the holding step after strengthening, as described herein. Of course, the methods described below can be used alone or in combination. Furthermore, the methods described below can be combined with and improved upon the advantageous means (holding step, lifting speed, thickness of residual salt, etc.) already described above.

[0050] It is important to control the speed applied when lifting the glass article from the strengthening salt bath. According to a first advantageous means, the speed at which the holder supporting the glass article during strengthening is lifted is 0.5 m / min or less. The inventors have found that the morphology and thickness of the salt residue on the surface of the strengthened glass article can be significantly affected by the lifting speed. A slower lifting speed significantly reduces the amount of salt residue adhering to the glass surface by shear thinning because the surface tension changes (see FIGS. 7a and 7b). Therefore, an effective way to limit the inhomogeneous ion exchange process is to reduce the amount of salt residue adhering to the glass during lifting.

[0051] Furthermore, it is recommended to control the rheology of the molten salt bath. According to a second advantageous means, the rheology of the molten salt bath is controlled by limiting the content rate (calculated as molar concentration) of impurities in the salt bath. In particular, the content rate of impurities of monovalent metal ions should be controlled to be less than 5000 ppm, preferably less than 3000 ppm, preferably less than 2000 ppm, preferably less than 1000 ppm, preferably less than 700 ppm, preferably less than 500 ppm, preferably less than 400 ppm, preferably less than 300 ppm, preferably less than 200 ppm, preferably less than 100 ppm, preferably less than 50 ppm, preferably less than 20 ppm. The inventors have found that impurities in the strengthening salt bath, such as sodium, can change the rheology of the molten salt and, consequently, affect the morphology of the salt residues adhering to the glass surface after lifting from the salt bath (see Figure 7c compared to Figure 7b). For example, sodium can lower the melting point of the salt because the sodium nitrate / potassium nitrate system has a eutectic point. An increase in the content rate of Na ions in the KNO3 salt bath due to ion exchange of Na ions for K ions during chemical strengthening of glass articles is considered to modify the rheology of the molten salt bath and, consequently, the morphology of the salt residues formed on the glass surface. An increase in the Na ion content rate in the salt bath results in an increase in the visible OOS of the strengthened glass articles (see Figures 8a - 8d).

[0052] Therefore, an advantageous means for reducing OOS is to reduce the sodium content rate in the KNO3 salt bath in mass production.

[0053] To control and reduce the sodium content rate in the strengthening bath containing KNO3, preferably, a special zeolite can be applied as a selective absorbent for sodium ions in the salt bath during production.

[0054] According to a further advantageous means, an annealing step before chemical strengthening can be carried out to reduce OOS. This means will be described in detail later in connection with Figures 11a, 11b and 11c.

[0055] According to a further advantageous measure, before the reflected light inspection and further procedures, storage of the strengthened glass article can be carried out to reduce visible OOS. This measure will be explained in detail later in connection with FIGS. 12a, 12b, 12c and FIGS. 13a, 13b, 13c.

[0056] According to a further advantageous measure, bonding of the strengthened glass article to a transparent medium can be carried out to reduce visible OOS. This measure will be explained in detail later in connection with FIGS. 14a and 14b.

[0057] In order to achieve a strengthened glass article that is free of OOS or has reduced OOS, the molten salt should have a low viscosity (i.e., at least one measure selected from the group consisting of selecting a higher salt bath temperature, selecting a higher holding temperature after strengthening, and reducing the impurity concentration should be employed). Further, the molten salt should be given sufficient time to flow under gravity to form a preferably uniform thin layer on the glass (i.e., a slower lifting rate and / or a longer holding time after strengthening should be used). As described above, the strengthening and lifting settings are more limited for salt baths with a higher impurity content.

[0058] According to another aspect of the invention, the problem shown above is solved by a chemically strengthened article having a thickness of at most 0.07 mm and having no optical orange skin (OOS) when the glass article is inspected under reflected light using a strong white light source. The measurement procedure has already been described above. Having no OOS means that there is little variation in the gray level or brightness of the reflected image of the strengthened glass article.

[0059] In an advantageous embodiment of the present invention, the toughened glass article has a variation in gray level of ≦9%, preferably ≦8%, preferably ≦7%, preferably ≦6%, preferably ≦5%, as defined as standard deviation / mean (StdDev / Mean)×100%. The variation in gray level is a measure of the degree of optical orange skin (OOS).

[0060] The standard deviation / mean×100% can be determined using an image processing program, such as "ImageJ".

[0061] For evaluation, a reflected image of the glass article is created using the method described above, for example via "ImageJ". A photograph of the reflected image is taken, where the photograph should have a resolution of at least 500 pixels per inch of the sample. The photograph is cropped so that only the reflection from the glass is within the relevant area, i.e., the end regions, fingerprints, and reflections from other objects should be excluded. Furthermore, the measurement is performed in an area that is flat and has no recognizable warping and / or deformation. Without further adjustment, the photograph should have an average gray value of 80 - 100 (measured in InageJ).

[0062] Next, the standard deviation (StdDev) of the gray values of the photograph is determined. The standard deviation is calculated from all the individual pixels within the photograph. The variation in gray level is calculated as the standard deviation / mean multiplied by 100%.

[0063] It is advantageous to measure the degree of optical orange skin at various surface positions on the toughened glass article. Preferably, the toughened glass article has a high homogeneity with respect to the degree of optical orange skin. Preferably, the entire measurable surface (i.e., without end regions, regions with reflections from fingerprints and / or other articles, regions with recognizable warping and / or deformation, etc.) has a variation in gray level of <9%, preferably <8%, preferably <7%, preferably <6%, preferably <5%.

[0064] The ultra-thin glass article according to the present invention has a thickness of 70 μm or less, more preferably 65 μm or less, more preferably 60 μm or less, more preferably 55 μm or less, still more preferably 50 μm or less, more preferably 45 μm or less, more preferably 40 μm or less, more preferably 35 μm or less, still more preferably 30 μm or less, more preferably 25 μm or less, more preferably 20 μm or less, still more preferably 10 μm or less. Such particularly thin glass articles are desirable for the various applications described above. In particular, a thin thickness imparts flexibility to the glass. The thickness may be at least 5 μm.

[0065] The surface compressive stress (CS) of the glass article according to the present invention is at least 100 MPa. Preferably, CS exceeds 200 MPa, more preferably exceeds 300 MPa, more preferably exceeds 400 MPa, more preferably exceeds 500 MPa, more preferably exceeds 600 MPa. According to a preferred embodiment of the present invention, CS is 700 MPa or more preferably exceeds 700 MPa, more preferably exceeds 800 MPa, more preferably exceeds 900 MPa, still more preferably exceeds 1000 MPa. However, CS must not be too high because otherwise the glass may be prone to self-destruction. Preferably, CS is 2000 MPa or less, preferably 1600 MPa or less, advantageously 1500 MPa or less, more preferably 1400 MPa or less. Some advantageous embodiments even have a CS of 1300 MPa or less, or 1200 MPa or less.

[0066] Preferably, the strengthened glass article has a layer depth (DoL) of 1 μm to t / 3 μm, preferably 2 μm to t / 4 μm, preferably 3 μm to t / 5 μm, where t is the thickness of the strengthened glass article in μm.

[0067] In order to achieve good chemical strengthening performance, the glass should contain a significant amount of alkali metal ions, preferably Na2O. Furthermore, adding a smaller amount of K2O to the glass composition can also improve the chemical strengthening rate. Additionally, it has been found that adding Al2O3 to the glass composition can significantly improve the strengthening performance of the glass.

[0068] SiO2 is the main glass network-forming component in the glass of the present invention. Furthermore, Al2O3, B2O3, and P2O5 can also be used as glass network-forming components. The total content of SiO2, B2O3, and P2O5 should not be less than 40% for conventional manufacturing methods. Otherwise, the glass sheet may be difficult to form, and may become brittle and lose transparency. A high SiO2 content requires a high melting temperature and working temperature for glass production, which should usually be less than 90%. In a preferred embodiment, the SiO2 content in the glass is 40 - 75% by mass, more preferably 50 - 70% by mass, even more preferably 55 - 68% by mass. In another preferred embodiment, the SiO2 content in the glass is 55 - 69% by mass, more preferably 57 - 66% by mass, even more preferably 57 - 63% by mass. In a further preferred embodiment, the SiO2 content in the glass is 60 - 85% by mass, more preferably 63 - 84% by mass, even more preferably 63 - 83% by mass. In yet another further preferred embodiment, the SiO2 content in the glass is 40 - 81% by mass, more preferably 50 - 81% by mass, even more preferably 55 - 76% by mass. Adding B2O3 and P2O5 to SiO2 can modify the network properties and lower the melting temperature and working temperature of the glass. The glass network-forming components also have a significant impact on the CTE of the glass.

[0069] Furthermore, B2O3 in the glass network forms two different polyhedral structures, thereby increasing the compatibility with the externally applied force. The addition of B2O3 usually results in a lower thermal expansion and a lower Young's modulus, which leads to good thermal shock resistance and a slower chemical strengthening rate, through which low CS and low DoL can be easily obtained. Therefore, the addition of B2O3 to the ultra-thin glass can greatly improve the window of the chemical strengthening process and the ultra-thin glass, and can expand the practical applications of the chemically strengthened ultra-thin glass. In a preferred embodiment, the amount of B2O3 in the glass of the present invention is 0 to 20% by mass, more preferably 0 to 18% by mass, and even more preferably 0 to 15% by mass. In some embodiments, the amount of B2O3 may be 0 to 5% by mass, preferably 0 to 2% by mass. In other embodiments, the amount of B2O3 may be 5 to 20% by mass, preferably 5 to 18% by mass. If the amount of B2O3 is too large, the melting point of the glass may become too high. Furthermore, the chemical strengthening performance may decrease if the amount of B2O3 is too large. An embodiment without B2O3 may be preferred.

[0070] Al2O3 acts as both a network - forming component and a network - modifying component of the glass. [AlO4] tetrahedra and [AlO6] hexahedra are formed depending on the amount of Al2O3 in the glass network, and they can adjust the ion - exchange rate by changing the size of the space for ion exchange inside the glass network. Generally, the content rate of this component varies depending on the type of each glass. Therefore, some glasses of the present invention preferably contain Al2O3 in an amount of at least 2% by mass, more preferably at least 10% by mass, and even more preferably at least 15% by mass. However, if the content rate of Al2O3 is too high, the melting temperature and working temperature of the glass will also become very high, and crystals are likely to be formed, causing the glass to lose transparency and flexibility. Therefore, some glasses of the present invention preferably contain Al2O3 in an amount of at most 30% by mass, more preferably at most 27% by mass, and even more preferably at most 25% by mass. Some advantageous embodiments may contain Al2O3 in an amount of at most 20% by mass, preferably at most 15% by mass or at most 10% by mass, or even more preferably at most 8% by mass, preferably at most 7% by mass, preferably at most 6% by mass, preferably at most 5% by mass. Some glass embodiments may be free of Al2O3. Other advantageous glass embodiments may contain at least 15% by mass, preferably at least 18% by mass of Al2O3, and / or at most 25% by mass, preferably at most 23% by mass, and even more preferably at most 22% by mass of Al2O3.

[0071] Alkali oxides, such as K2O, Na2O, and Li2O, act as network - modifying components of the glass. They can break the glass network and form non - bridging oxides inside the glass network. Adding alkali can lower the working temperature of the glass and increase the CTE of the glass. Na + / Li + 、Na + / K + 、Li + / K +Ion exchange is an essential step for strengthening, so the sodium and lithium contents are important for ultra-thin flexible glass that can be chemically strengthened. Without the presence of alkali itself, the glass cannot be strengthened. However, sodium is more preferable than lithium because lithium may significantly reduce the diffusion rate of the glass. Therefore, some glasses of the present invention preferably contain Li2O in an amount of up to 7% by mass, preferably up to 5% by mass, more preferably up to 4% by mass, more preferably up to 2% by mass, more preferably up to 1% by mass, and more preferably up to 0.1% by mass. Some preferred embodiments are even free of Li2O. Depending on the type of glass, the lower limit for Li2O may be 3% by mass, preferably 3.5% by mass.

[0072] The glass of the present invention preferably contains Na2O in an amount of at least 4% by mass, more preferably at least 5% by mass, more preferably at least 6% by mass, more preferably at least 8% by mass, and more preferably at least 10% by mass. Sodium is very important for chemical strengthening performance because chemical strengthening preferably involves ion exchange between sodium in the glass and potassium in the chemical strengthening medium. However, the sodium content should not be too high because the glass network may be severely deteriorated and the glass may become extremely difficult to form. Another important factor is that the ultra-thin glass should have a low CTE, and the glass should not contain too much Na2O to meet such requirements. Therefore, the glass preferably contains Na2O in an amount of up to 30% by mass, more preferably up to 28% by mass, more preferably up to 27% by mass, more preferably up to 25% by mass, and more preferably up to 20% by mass.

[0073] The glass of the present invention may contain K2O. However, since the glass is preferably chemically strengthened by exchanging sodium ions in the glass with potassium ions in the chemical strengthening medium, too much K2O in the glass may impair the chemical strengthening performance. Therefore, the glass of the present invention preferably contains K2O in an amount of up to 10% by mass, more preferably up to 8% by mass. Some preferred embodiments contain up to 7% by mass, and other preferred embodiments contain up to 4% by mass, more preferably up to 2% by mass, more preferably up to 1% by mass, more preferably up to 0.1% by mass. Some preferred embodiments are even free of K2O.

[0074] However, since the network of the glass may deteriorate severely and the glass may become extremely difficult to form, the total alkali content should preferably be 35% by mass or less, preferably 30% by mass or less, more preferably 28% by mass or less, more preferably 27% by mass or less, and even more preferably 25% by mass or less. Some embodiments have an alkali content of up to 16% by mass, preferably up to 14% by mass. Another important factor is that the ultra-thin glass should have a low CTE, and in order to meet such requirements, the glass should not contain too many alkali elements. However, as described above, in order to facilitate chemical strengthening, the glass should contain alkali elements. Therefore, the glass of the present invention preferably contains alkali metal oxides in an amount of at least 2% by mass, more preferably at least 3% by mass, more preferably at least 4% by mass, more preferably at least 5% by mass, more preferably at least 6% by mass.

[0075] Alkaline earth oxides, such as MgO, CaO, SrO, and BaO, act as network modifying components and lower the glass forming temperature. Adding these oxides can adjust the CTE and Young's modulus of the glass. Alkaline earth oxides have a very important function of being able to change the refractive index of the glass to meet special requirements. For example, MgO can lower the refractive index of the glass, and BaO can increase the refractive index. The mass content of the alkaline earth oxides should preferably be 40% by mass or less, preferably 30% by mass or less, preferably 25% by mass or less, also preferably 20% by mass or less, more preferably 15% by mass or less, more preferably 13% by mass or less, and more preferably 12% by mass or less. Some aspects of the glass may contain up to 10% by mass, preferably up to 5% by mass, more preferably up to 4% by mass of alkaline earth oxides. If the amount of alkaline earth oxides is too large, the chemical strengthening performance may deteriorate. The lower limit for the alkaline earth oxides may be 1% by mass or 5% by mass. Furthermore, if the amount of alkaline earth oxides is too large, the crystallization tendency may increase. Some advantageous aspects may be free of alkaline earth oxides.

[0076] Some transition metal oxides in the glass, such as ZnO and ZrO2, have functions similar to those of alkaline earth oxides and may be included in some embodiments. Other transition metal elements, such as Nd2O3, Fe2O3, CoO, NiO, V2O5, MnO2, TiO2, CuO, CeO2, and Cr2O3, function as colorants for producing glasses with specific optical or photonic functions, such as color filters or light converters. As2O3, Sb2O3, SnO2, SO3, Cl, and / or F can also be added as fining agents in an amount of 0 to 2% by mass. Rare earth oxides can be added in an amount of 0 to 5% by mass to impart magnetic or photonic or optical functions to the glass sheet.

[0077] The following advantageous compositions relate to various types of glass before strengthening.

[0078] In one embodiment, the ultra-thin flexible glass is an alkali metal aluminosilicate glass containing the following components in the indicated amounts (mass%): [Table 1]

[0079] Optionally, coloring oxides such as Nd2O3, Fe2O3, CoO, NiO, V2O5, MnO2, CuO, CeO2, Cr2O3 can be added. As2O3, Sb2O3, SnO2, SO3, Cl and / or F can also be added as fining agents in an amount of 0 to 2 mass%. Rare earth oxides can be added in an amount of 0 to 5 mass% to impart magnetic or photonic or optical functions to the glass sheet.

[0080] The alkali metal aluminosilicate glass of the present invention preferably contains the following components in the indicated amounts (mass%): [Table 2]

[0081] Optionally, coloring oxides such as Nd2O3, Fe2O3, CoO, NiO, V2O5, MnO2, CuO, CeO2, Cr2O3 can be added. 0 to 2 mass% of As2O3, Sb2O3, SnO2, SO3, Cl and / or F can also be added as fining agents. 0 to 5 mass% of rare earth oxides can be added to impart magnetic or photonic or optical functions to the glass sheet.

[0082] Most preferably, the alkali metal aluminosilicate glass of the present invention contains the following components in the indicated amounts (mass%): [Table 3]

[0083] Optionally, coloring oxides such as Nd2O3, Fe2O3, CoO, NiO, V2O5, MnO2, CuO, CeO2, Cr2O3 can be added. 0 to 2% by mass of As2O3, Sb2O3, SnO2, SO3, Cl and / or F can also be added as fining agents. 0 to 5% by mass of rare earth oxides can be added to impart magnetic or photonic or optical functions to the glass sheet.

[0084] In one embodiment, the ultra-thin flexible glass is soda-lime glass containing the following components in the indicated amounts (by mass): [Table 4]

[0085] Optionally, coloring oxides such as Nd2O3, Fe2O3, CoO, NiO, V2O5, MnO2, CuO, CeO2, Cr2O3 can be added. 0 to 2% by mass of As2O3, Sb2O3, SnO2, SO3, Cl and / or F can also be added as fining agents. 0 to 5% by mass of rare earth oxides can be added to impart magnetic or photonic or optical functions to the glass sheet.

[0086] The soda-lime glass of this invention preferably contains the following components in the indicated amounts (by mass): [Table 5]

[0087] Optionally, coloring oxides such as Nd2O3, Fe2O3, CoO, NiO, V2O5, MnO2, CuO, CeO2, Cr2O3 can be added. 0 to 2% by mass of As2O3, Sb2O3, SnO2, SO3, Cl and / or F can also be added as fining agents. 0 to 5% by mass of rare earth oxides can be added to impart magnetic or photonic or optical functions to the glass sheet.

[0088] The soda-lime glass of this invention preferably contains the following components in the indicated amounts (mass%): [Table 6]

[0089] Optionally, coloring oxides such as Nd2O3, Fe2O3, CoO, NiO, V2O5, MnO2, CuO, CeO2, Cr2O3 can be added. 0 to 2 mass% of As2O3, Sb2O3, SnO2, SO3, Cl and / or F can also be added as fining agents. 0 to 5 mass% of rare earth oxides can be added to impart magnetic or photonic or optical functions to the glass sheet.

[0090] The soda-lime glass of this invention preferably contains the following components in the indicated amounts (mass%): [Table 7]

[0091] Optionally, coloring oxides such as Nd2O3, Fe2O3, CoO, NiO, V2O5, MnO2, CuO, CeO2, Cr2O3 can be added. 0 to 2 mass% of As2O3, Sb2O3, SnO2, SO3, Cl and / or F can also be added as fining agents. 0 to 5 mass% of rare earth oxides can be added to impart magnetic or photonic or optical functions to the glass sheet.

[0092] Most preferably, the soda-lime glass of this invention contains the following components in the indicated amounts (mass%): [Table 8]

[0093] Optionally, coloring oxides such as Nd2O3, Fe2O3, CoO, NiO, V2O5, MnO2, CuO, CeO2, Cr2O3 can be added. 0 to 2% by mass of As2O3, Sb2O3, SnO2, SO3, Cl and / or F can also be added as fining agents. 0 to 5% by mass of rare earth oxides can be added to impart magnetic or photonic or optical functions to the glass sheet.

[0094] Most preferably, the soda-lime glass of the present invention contains the following components in the indicated amounts (mass%):

Table 9

[0095] Optionally, coloring oxides such as Nd2O3, Fe2O3, CoO, NiO, V2O5, MnO2, CuO, CeO2, Cr2O3 can be added. 0 to 2% by mass of As2O3, Sb2O3, SnO2, SO3, Cl and / or F can also be added as fining agents. 0 to 5% by mass of rare earth oxides can be added to impart magnetic or photonic or optical functions to the glass sheet.

[0096] In one embodiment, the ultra-thin flexible glass is a lithium aluminosilicate glass containing the following components in the indicated amounts (mass%):

Table 10

[0097] Optionally, coloring oxides such as Nd2O3, Fe2O3, CoO, NiO, V2O5, MnO2, CuO, CeO2, Cr2O3 can be added. As2O3, Sb2O3, SnO2, SO3, Cl and / or F can also be added as fining agents in an amount of 0 to 2% by mass. Rare earth oxides can be added in an amount of 0 to 5% by mass to impart magnetic or photonic or optical functions to the glass sheet.

[0098] The lithium aluminosilicate glass of the present invention preferably contains the following components in the indicated amounts (mass%): [Table 11]

[0099] Optionally, coloring oxides such as Nd2O3, Fe2O3, CoO, NiO, V2O5, MnO2, CuO, CeO2, Cr2O3 can be added. 0 to 2 mass% of As2O3, Sb2O3, SnO2, SO3, Cl and / or F can also be added as fining agents. 0 to 5 mass% of rare earth oxides can be added to impart magnetic or photonic or optical functions to the glass sheet.

[0100] Most preferably, the lithium aluminosilicate glass of the present invention contains the following components in the indicated amounts (mass%): [Table 12]

[0101] Optionally, coloring oxides such as Nd2O3, Fe2O3, CoO, NiO, V2O5, MnO2, CuO, CeO2, Cr2O3 can be added. 0 to 2 mass% of As2O3, Sb2O3, SnO2, SO3, Cl and / or F can also be added as fining agents. 0 to 5 mass% of rare earth oxides can be added to impart magnetic or photonic or optical functions to the glass sheet.

[0102] In one embodiment, the ultra-thin flexible glass is a borosilicate glass containing the following components in the indicated amounts (mass%): [Table 13]

[0103] Optionally, coloring oxides such as Nd2O3, Fe2O3, CoO, NiO, V2O5, MnO2, CuO, CeO2, Cr2O3 can be added. 0 to 2% by mass of As2O3, Sb2O3, SnO2, SO3, Cl and / or F can also be added as fining agents. 0 to 5% by mass of rare earth oxides can be added to impart magnetic or photonic or optical functions to the glass sheet.

[0104] The borosilicate glass of the present invention preferably contains the following components in the indicated amounts (mass%):

Table 14

[0105] Optionally, coloring oxides such as Nd2O3, Fe2O3, CoO, NiO, V2O5, MnO2, CuO, CeO2, Cr2O3 can be added. 0 to 2% by mass of As2O3, Sb2O3, SnO2, SO3, Cl and / or F can also be added as fining agents. 0 to 5% by mass of rare earth oxides can be added to impart magnetic or photonic or optical functions to the glass sheet.

[0106] The borosilicate glass of the present invention preferably contains the following components in the indicated amounts (mass%):

Table 15

[0107] Optionally, coloring oxides such as Nd2O3, Fe2O3, CoO, NiO, V2O5, MnO2, CuO, CeO2, Cr2O3 can be added. 0 to 2% by mass of As2O3, Sb2O3, SnO2, SO3, Cl and / or F can also be added as fining agents. 0 to 5% by mass of rare earth oxides can be added to impart magnetic or photonic or optical functions to the glass sheet.

[0108] Typically, the ultra-thin glass according to the present invention can be manufactured by thinning a thicker glass by polishing or etching. These two methods are not economical and result in poor surface quality quantified, for example, by R a oughness.

[0109] Direct hot forming manufacturing, such as the down-draw method and the overflow fusion method, is preferable for mass production. The redraw method is also advantageous. These described methods are economical and the quality of the glass surface is high.

[0110] Generally, strengthening is referred to as strengthening and can be carried out by immersing the glass in a molten salt bath having potassium ions, or by coating the glass with a paste containing potassium ions or other alkali metal ions and heating at a high temperature for a specific time. Alkali metal ions having a larger ionic radius in the salt bath or paste are exchanged with alkali metal ions having a smaller radius in the glass article, and a surface compressive stress is formed due to the ion exchange. As described above, immersing the glass article in a bath of molten salt is applied here. The strengthened glass is lifted out of the salt bath, and after a further advantageous stage, the glass article is cooled and washed using known procedures.

[0111] The chemically strengthened glass article of the present invention is obtained by chemically strengthening a chemically strengthenable glass article. The strengthening process can be carried out by immersing an ultra-thin glass article in a salt bath containing monovalent ions and exchanging them with alkali ions inside the glass. The monovalent ions in the salt bath have a larger radius than the alkali ions inside the glass. The compressive stress on the glass is formed after ion exchange due to the intrusion of larger ions into the network of the glass. Surprisingly, the strength and flexibility of the ultra-thin glass are significantly improved after ion exchange. Furthermore, the CS induced by chemical strengthening can improve the bending properties of the strengthened glass article and enhance the scratch resistance and impact resistance of the glass, so that the strengthened glass is not easily scratched, and the DoL can increase the scratch tolerance, and the glass is not easily broken even if it is scratched.

[0112] The most commonly used salts for chemical strengthening are Na + -containing molten salts or K + -containing molten salts, or mixtures thereof. Commonly used salts are NaNO3, KNO3, NaCl, KCl, K2SO4, Na2SO4, Na2CO3 and K2CO3. Additives such as NaOH, KOH and other sodium salts or potassium salts can also be used to better control the rate of ion exchange, CS and DoL during chemical strengthening. Ag + -containing or Cu 2+ -containing salt baths can be used to add antibacterial functions to ultra-thin glass.

[0113] Chemical strengthening is not limited to one step. It can include multiple steps in salt baths with various concentrations of alkali metal ions to achieve better strengthening performance. Therefore, the chemically strengthened glass article according to the present invention can be strengthened in a one-step or multiple-step process, such as a two-step process.

[0114] The chemically strengthened glass article according to the present invention can have only one surface (the first surface) in which a compressive stress region extends from the first surface to a first depth of layer (DoL) within the glass article, said region being defined by a compressive stress (CS). In this case, the glass article includes only one strengthened side. Preferably, the chemically strengthened glass article according to the present invention also includes a second surface (opposite to the first surface) in which a compressive stress region extends from the second surface to a second depth of layer (DoL) within the glass article, said region being defined by a compressive stress (CS). This preferred glass article is strengthened on both sides.

[0115] CS mainly depends on the composition of the glass. A higher Al2O3 content can help achieve a higher CS. After strengthening, the ultra-thin glass should have a sufficiently high CS to achieve high strength. Therefore, CS is 100 MPa or more, preferably above 100 MPa, preferably above 200 MPa, more preferably above 300 MPa, still more preferably above 400 MPa, still more preferably above 500 MPa. In a particularly preferred embodiment, CS is above 600 MPa, more preferably above 700 MPa, and even more preferably above 800 MPa.

[0116] Generally, DoL depends on the composition of the glass, but it can increase almost infinitely with an increase in the strengthening time and temperature. A defined DoL is essential to ensure the stable strength of the strengthened glass, but a too high DoL should be preferably controlled because it increases the self-destruction rate and strength performance when the ultra-thin glass article is under compressive stress.

[0117] In some embodiments, a high resistance to sharp object contact of the bare glass is required and a low DoL is preferred. To achieve the defined low DoL, the tempering temperature and / or the tempering time are decreased. Optionally, a lower tempering temperature may be recommended because the DoL is more sensitive to temperature and it is easier to set a longer tempering time during mass production. However, it is also possible to reduce the tempering time to lower the DoL of the glass article.

[0118] The advantageous values of the DoL depend, in each case, on the glass composition, thickness and the applied CS of each glass article. Generally, glass articles according to the advantageous embodiments described above have a very low DoL. By reducing the DoL, the CT is reduced. When a high impact force and / or pressing load is applied by a sharp object in such an embodiment, the resulting defect is only on the glass surface. Since the CT is significantly reduced, the resulting defect cannot overcome the internal strength of the glass article, and thus the glass article is not broken into two or more pieces. Such glass articles with a low DoL have an improved resistance to sharp object contact.

[0119] As described above, the CS, DoL and CT depend on the glass composition (type of glass), the thickness of the glass and the tempering conditions.

[0120] The chemically strengthened glass article can be used in the fields of flexible and foldable electronic products, such as image sensors, display covers, covers for screen protectors, and substrates. Further, it can be used in, for example, the following application fields: substrates or protective covers for displays, fingerprint sensor covers, substrates or covers for general sensors, cover glasses for consumer electronics, protective covers for displays and other surfaces, especially curved surfaces. Furthermore, the glass article can be used in substrates and covers for displays, substrates or covers for fingerprint sensor modules, semiconductor packages, substrates and covers for thin-film batteries, and applications for foldable displays. In certain embodiments, the glass article can be used as a cover film for resistive screens, and disposable protective films for display screens, mobile phones, cameras, gaming gadgets, tablets, laptops, TVs, mirrors, windows, aircraft windows, furniture, and white goods.

[0121] The present invention is particularly suitable for use in substrates and covers for displays, fragile sensors, substrates or covers for fingerprint sensor modules, semiconductor packages, substrates and covers for thin-film batteries, and applications for foldable displays. Further, it can be used in flexible electronic devices (such as curved displays, wearable devices) having thin, lightweight, and flexible characteristics. Such flexible devices also require, for example, flexible substrates for holding or mounting components. Furthermore, flexible displays with high contact resistance and small bending radii are possible.

[0122] In one embodiment, the glass is an alkali-containing glass, such as alkali aluminosilicate glass, alkali silicate glass, alkali borosilicate glass, alkali aluminoborosilicate glass, alkali borate glass, alkali germanate glass, alkali borogermanate glass, alkali soda lime glass, and combinations thereof.

[0123] This aspect and other aspects of the present invention will become apparent from the following description, the accompanying drawings, and the scope of the claims.

Brief Description of the Drawings

[0124]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Example

[0125] The following is the description of the figures in the attached drawings.

[0126] Unless otherwise specified, the samples described below are as-manufactured 30-μm glass articles having the same composition. "As-manufactured" means that the glass articles were manufactured via the down-draw method. The size of the tested samples was mainly 50 mm × 50 mm. The strengthening bath was based on KNO3. For some experiments, NaNO3 salt was subsequently added to the salt bath to simulate the aging process of the strengthening bath. The strengthening time was 10 minutes and the strengthening temperature was 420 °C. The resulting DoL was approximately 10 μm. The resulting CS was in the range of 600 - 800 MPa.

[0127] Figure 1a shows a reflected image (i.e., an image projected using the reflected light inspection method described above) of a pre-strengthened 30-μm glass article in the form of a plate made of aluminosilicate glass with a size of 50 mm × 50 mm. The plate-shaped glass article has two large main surfaces on opposite sides connected by small ends. Under reflected light inspection, the surface appears smooth without any irregularities.

[0128] Figure 1b shows a reflected image of a strengthened 30-μm glass article made of aluminosilicate glass with a size of 50 mm × 50 mm. The glass article was strengthened in a KNO3 salt bath containing 2500 ppm of sodium. Using reflected light inspection, a surface with irregularities that appear like a wavy or wrinkled structure can be seen (see arrows). This optical appearance is referred to as "optical orange skin (OOS)". The curved upper end is due to a slight warp of the strengthened sample and not due to glass breakage. The inventors have found that the visible surface irregularities, referred to as OOS of the strengthened UTG, do not correspond to changes in the surface topology but rather are optical problems.

[0129] Figure 2a shows the analysis results of the surface topology using a "stylus profiler". The surface topologies of various unstrengthened AS glass samples a, b, c and strengthened AS glass samples d, e were measured. The stylus profiler shows the surface height variation in the range of 0.5 μm within a scanning range of 10 mm.

[0130] Figure 2b shows the analysis results of the surface topology using white light interferometry (WLI). WLI is a non-contact optical method for measuring the surface height in a 3D structure with a surface profile varying from several tens of nanometers to several centimeters. It is often used as an alternative name for coherence scanning interferometry regarding the surface topology measurement of a surface based on spectrally broadband visible wavelength light (white light). The WLI results of unstrengthened AS glass sample x and strengthened AS glass sample y (each 30 μm thick) show the surface height variation in the range of 5 μm within a scanning range of 10 mm.

[0131] Figures 3a, 4a and 5a show photographs of three pieces of strengthened 30-μm AS glass after being lifted from a strengthening salt bath containing KNO₃. The three samples have the same glass composition and were strengthened under the same strengthening conditions. Salt residues are seen on the surface of the samples. There are areas on the glass surface with a very thin and homogeneous salt film, while there are also areas with higher residual molten salt where ion exchange can proceed for a longer time. This results in non-uniform ion exchange across the glass surface region. Figures 3b, 4b and 5b show the reflection images of the same samples after cleaning, inspected under reflected light. Figure 3b shows an OOS structure similar to that in Figure 1b (wavy / wrinkled structure, refer to the arrow). In Figures 4b and 5b, the surface appears to have a (localized) structure in the form of small bumps or dents, also referred to as OOS (refer to the arrow). As can be seen, the surface irregularities visible under reflected light coincide with the pattern of the salt residues on the strengthened glass article. Therefore, the OOS effect correlates with the distribution of the residual salt on the sample surface rather than the composition of the raw glass.

[0132] Figure 6 shows a reflected image of a 75 μm strengthened AS glass article strengthened in a KNO₃ salt bath having 10,000 ppm of sodium. Here, under reflected light inspection, no characteristic surface irregularities (OOS) can be observed.

[0133] Figure 7a shows a strengthened glass article quickly lifted from a strengthening salt bath consisting of pure KNO₃. The lifting speed was about 5 cm / second. As a result, thick and non-uniformly distributed salt residues are attached to the glass surface. In contrast, Figure 7b shows a strengthened glass article of the same glass composition slowly lifted from a strengthening salt bath consisting of pure KNO₃. The lifting speed was about 5 mm / second. Here, a more uniform distribution of salt residues can be observed. When inspected under reflected light, a sample lifted so slowly does not show OOS.

[0134] Figure 7c shows a strengthened glass article slowly lifted from a strengthening salt bath consisting of KNO₃ having 300 ppm of sodium. Comparing Figure 7b and Figure 7c, it can be seen that impurities such as Na ions can change the morphology of the salt residues.

[0135] Figures 8a - 8d show the effect of increasing Na ion content in the KNO3 bath on the OOS effect under reflected light inspection of 30 μm thick strengthened glass articles of the same composition. To simulate the increase in Na ion content in the salt bath during the life of the salt bath, Na - containing salt (here NaNO3) was added. When using a pure new KNO3 salt bath, no OOS is seen in the reflected image (Figure 8a). Figure 8b shows the reflected image for a sample strengthened in a new KNO3 salt bath containing 100 ppm of sodium. Figure 8c shows the reflected image for a sample strengthened in a new KNO3 salt bath containing 200 ppm of sodium. Figure 8d shows the reflected image for a sample strengthened in a new KNO3 salt bath containing 300 ppm of sodium. As can be seen, OOS deteriorates with the increase in sodium content in the strengthening bath. When more sodium is added to the KNO3 bath, the salt residue formed on the strengthened glass article increases (for the same lifting and holding settings). Thus, OOS deteriorates.

[0136] Figures 9a - 9c show the results of an experiment regarding maintaining the sodium impurity content of the salt bath at a specific level (200 ppm) by adding K3PO4 salt to a KNO3 salt bath containing 300 ppm of sodium in order to limit OOS. Figure 9a shows the reflected image of a 30 μm thick AS glass article strengthened in a KNO3 salt bath containing 300 ppm. In Figure 9b (reflected image), 0.5 mass% of K3PO4 was added to the strengthening bath. In Figure 9c (reflected image), 1 mass% of K3PO4 was added to the strengthening bath. All samples have the same composition, thickness, and applied strengthening conditions (strengthening temperature 420 °C, strengthening time about 10 minutes). As can be seen, the addition of K3PO4 to the salt bath was unable to suppress OOS. On the contrary, this additive seems to promote OOS.

[0137] Figure 10a shows a reflected image of an unstrengthened 30 μm AS glass article produced by thinning (by acid etching) from a drawn 75 μm thick glass. There is no OOS. Figure 10b shows the glass article from Figure 10a under reflected light inspection after chemical strengthening. The sample shows some OOS. The deformation at the ends of the photograph is due to the slightly higher deformation of the thinned glass compared to the as-produced UTG. For comparison, Figure 10c shows, as a reflected image, an as-produced strengthened 30 μm AS glass article strengthened under the same strengthening conditions. Comparing Figure 10b and Figure 10c, the OOS effect of the thinned 30 μm strengthened glass was not as prominent as that of the as-produced strengthened glass of the same thickness. This can be explained as follows: The outer part of the newly drawn glass ribbon has a higher virtual temperature than the inner part. Therefore, the thinned glass should have a denser structure at the surface than the drawn glass (the energy barrier for ion exchange is higher). Therefore, the ion exchange between the well-thinned glass and the salt residue is somewhat suppressed. Furthermore, the surface roughness of the thinned glass can vary the amount of salt residue due to the different contact angles between the glass surface and the molten salt. A rougher surface can hold a thicker salt residue.

[0138] A further advantageous means for reducing OOS could be to carry out an annealing step before chemical strengthening. Preferably, the annealing is above the glass's T g Figure 11a shows a reflected image of an unstrengthened 30 μm AS glass article heated to 637 °C. After a holding time of 1 hour, the glass article was cooled to a temperature >567 °C using a rate of 1 °C / min. Figure 11b shows the sample of Figure 11a after chemical strengthening with salt residue on the surface. Figure 11c shows a reflected image of the annealed and strengthened 30 μm AS glass article of Figure 11a. Before strengthening, T gWhen annealed above, no further OOS surface effect can be observed on the strengthened 30 μm glass. There are no new features resulting from the chemical strengthening process in either the reflected light or visual inspection with the naked eye. In Figures 11a and 11c, slight deformation of the annealed sample results in non-uniform features in the reflected light image.

[0139] A further advantageous means for reducing visible OOS could be to store the strengthened glass article prior to reflected light inspection and further procedures. Figures 12a, 12b, and 12c show three samples of a 30 μm AS glass article immediately after chemical strengthening under reflected light. The samples exhibit unwanted OOS effects. Figures 13a, 13b, and 13c show the same samples after 7 days under reflected light. After one week, the OOS effects are clearly less prominent. Thus, a longer storage time reduces the unwanted OOS effects to some extent.

[0140] According to a further advantageous means, as can be seen in the reflected images of Figures 14a and 14b, visible OOS can be removed by bonding the strengthened glass article to a transparent medium. Figure 14a shows the reflected image of a strengthened 30 μm AS glass sample. The OOS is visible. Figure 14b shows the same glass article after bonding onto a transparent medium (here silicone glue). Here there is no visible OOS. Bonding onto the silicone glue removes the reflected light from below the strengthened glass article. This indicates that OOS is an optical effect. This can be explained, without being limited to this attempt at explanation, as follows: OOS can be caused by inhomogeneities in the specific refractive index gradient caused by ion exchange of residual salts and by the short optical path difference between the reflected light from the upper and lower parts of the glass article.

[0141] Figure 15 shows the influence of the thickness of salt residues adhering to the surface of the strengthened glass article on the degree of OOS. Here, the thickness of the glass is 32 μm each. The sum of the "glass thickness" and the "salt thickness" (where the latter is the total of the salt thickness on the first surface of the plate-shaped glass article + the salt thickness on the second surface) is 50 μm for the left reflection image (A), 65 μm for the reflection image at the center (B), and 80 μm for the right reflection image (C). The sum was measured before washing the strengthened glass. While reflection image A does not show OOS, reflection image C has OOS. Therefore, an increase in the thickness of salt residues adhering to the glass surface after chemical strengthening promotes the generation of OOS.

[0142] Figure 16 shows the reflection images of 30-μm-thick AS glass articles that were subjected to a holding treatment at a high temperature after being lifted from the strengthening salt bath (KNO₃). The strengthening temperature was about 420 °C, the holding temperature was about 380 °C, and the holding time was about 12 minutes. No OOS was observed on the strengthened glass articles. The inventors have found that when the strengthening procedure includes a post-strengthening holding stage, it is possible to produce OOS-free strengthened glass articles from a salt bath that has been used for a very long time (i.e., contains a high content of impurities due to ion exchange). Furthermore, the inventors have found that a holding time in the range of 2 - 5 minutes is sufficient and advantageous for 30-μm-thick AS glass articles. A strengthened glass article without OOS corresponding to the article shown in Figure 16 can be produced under the same holding conditions (strengthening temperature about 420 °C, holding temperature about 380 °C) but with a holding time of about 3 minutes.

[0143] The experiments and evaluations described above were carried out on samples of the AS glass type. However, it is clear that the observations and results can also be transferred to other types of glass (see also Table 1, such as lithium aluminosilicate glass, soda-lime glass, borosilicate glass, etc.).

[0144] The variation in gray level, defined as standard deviation / mean × 100%, was determined as a measure of the degree of OOS for the samples in FIGS. 1 to 16 using "ImageJ 1.52d" and the evaluation method described above. The determined values are shown in each figure. Each square schematically shows the corresponding area on the sample, and they schematically show the position of the measured degree of OOS. However, the size of each individual square does not indicate the exact size of the area examined and measured by ImageJ and is not correlated with it.

[0145] A small variation in gray level, specifically up to 9 mass%, indicates no OOS or no significant OOS. Higher gray level variations indicate visible OOS.

[0146] For example, FIGS. 1b, 3b, 9c, 10c show strengthened glass articles with a very high degree of OOS. The strengthened glass articles shown in FIGS. 4b, 5b have low homogeneity with respect to the degree of OOS. FIGS. 6, 8a, 13b, 13c, 16 are examples of strengthened glass articles that have no OOS or no significant OOS and have very high homogeneity with respect to the degree of OOS.

[0147]

Table 16

Claims

1. A chemically strengthened glass article having a thickness of at most 0.07 mm, wherein when the glass article is inspected under reflected light using a white light source, it does not have an optical orange skin (OOS), and the chemically strengthened glass article is not laminated.

2. Not having an optical orange skin (OOS) means that when the glass article is inspected under reflected light using a white light source, the gray level variation of the glass article is small, and the gray level variation defined as standard deviation / average × 100% is ≦ 9%. The chemically strengthened glass article according to Claim 1.

3. The glass article has a thickness < 0.07 mm and / or ≧ 0.005 mm. The chemically strengthened glass article according to Claim 1 or 2.

4. The glass article has a thickness of 0.05 mm or less. The chemically strengthened glass article according to Claim 1 or 2.

5. The glass article has a layer depth (DoL) of 1 μm to t / 3 μm, where t is the thickness of the strengthened glass article in μm. The chemically strengthened glass article according to any one of Claims 1 to 4.

6. The surface compressive stress CS of the glass article is greater than 300 MPa. The chemically strengthened glass article according to any one of Claims 1 to 5.

7. The glass has the following components in the amounts shown in mass%: Component (mass%) SiO 2 40 - 75 Al 2 O 3 10 - 30 B 2 O 3 0 - 20 Li 2 O + Na 2 O + K 2 O 4 - 30 MgO + CaO + SrO + BaO + ZnO 0 - 15 TiO 2 + ZrO 2 0 - 15 P 2 O 5 0 - 10 The chemically strengthened glass article according to any one of claims 1 to 6, which is an alkali metal aluminosilicate glass containing

8. The chemically strengthened glass article is in the following stages: - Preparing a glass article having a thickness of at most 0.07 mm; - Immersing the glass article in a bath of molten salt having a specific strengthening temperature for a specific strengthening time; - Lifting the strengthened glass article out of the bath of molten salt; - Holding the strengthened glass article for a specific holding time after strengthening, where the holding time is less than 20 minutes and the holding temperature is selected to be higher than the melting point of the bath of molten salt and lower than the transition temperature (T g ) of the strengthened glass article, so that the salt residue of the molten salt moves under the influence of gravity and a homogeneous layer of the salt residue of the molten salt is formed on the surface of the strengthened glass article; - Cooling and washing the strengthened glass article The chemically strengthened glass article according to any one of claims 1 to 7, which is manufactured by a method including

9. The chemically strengthened glass article is in the following stages: - Preparing a glass article having a thickness of at most 0.07 mm; - Immersing the glass article in a bath of molten salt having a specific strengthening temperature for a specific strengthening time; - Lifting the strengthened glass article from the molten salt bath at a controlled lifting speed of less than 0.5 m / min, such that the salt residue of the molten salt flows down from the surface of the strengthened glass article under the influence of gravity and the surface tension between the molten salt bath and the glass article, and a homogeneous layer of the salt residue of the molten salt is formed on the surface of the strengthened glass article; - Cooling and washing the strengthened glass article; The chemically strengthened glass article according to any one of claims 1 to 8, produced by a method comprising the above steps.

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