Glass Structure and Cover Glass

Abstract

The present invention provides a glass structure comprising a glass substrate in which a stepped surface formed by the difference in level between a thick sheet portion and a thin sheet portion is not readily visually recognizable. A glass structure (1) is provided with: a glass substrate which has a thick sheet portion (3) and a thin sheet portion (4); and a filler (6) that covers a stepped surface (5) formed by the difference in level between the thick sheet portion (3) and the thin sheet portion (4). The difference in the refractive index between the glass substrate (2) and the filler (6) at a wavelength of 555 nm is 0.008 or less in absolute value, and the difference in the refractive index between the glass substrate (2) and the filler (6) at a wavelength of 507 nm is 0.008 or less in absolute value.

Description

[Technical Field]

[0001] The present invention relates to a glass structure and a cover glass. [Background technology]

[0002] BACKGROUND ART Conventionally, a glass substrate having a structure in which portions of different thicknesses are connected to each other has been used as a cover glass in a display device such as an in-vehicle display device (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Chinese Patent Application Publication No. 109081561 Summary of the Invention [Problem to be solved by the invention]

[0004] A glass substrate having a configuration in which portions with different plate thicknesses are connected to each other has a thick plate portion and a thin plate portion that is thinner (has a smaller plate thickness) than the thick plate portion. When such a glass substrate is used as a cover glass, it is assembled into an in-vehicle display device or the like, for example, in a state in which at least a part of the thin plate portion is elastically deformed.

[0005] However, the present inventors have found that a step surface formed by a step between a thin plate portion and a thick plate portion may be visible in some cases. Since high aesthetic quality is required for cover glasses used in in-vehicle display devices, it is undesirable for the step surface to be visible.

[0006] Therefore, an object of the present invention is to provide a glass structure including a glass substrate in which a step surface formed by a step between a thick plate portion and a thin plate portion is difficult to see. [Means for solving the problem]

[0007] As a result of extensive investigation, the present inventors have found that the above problems can be solved by employing the following configuration. That is, the present invention provides the following [1] to [7]. [1] A glass structure comprising: a glass substrate having a thick portion and a thin portion thinner than the thick portion; and a filler covering a step surface formed by a step between the thick portion and the thin portion, wherein the difference in refractive index between the glass substrate and the filler at a wavelength of 555 nm is an absolute value of 0.008 or less, and the difference in refractive index between the glass substrate and the filler at a wavelength of 507 nm is an absolute value of 0.008 or less. [2] The glass structure according to [1] above, wherein the thickness t3 of the thick portion is 0.2 mm or more, and the thickness t4 of the thin portion is smaller than the thickness t3 of the thick portion. [3] The glass structure according to [2] above, wherein the plate thickness t4 of the thin plate portion is less than 0.5 mm. [4] The glass structure according to any one of the above [1] to [3], wherein the glass substrate is a chemically strengthened glass. [5] The glass structure according to any one of [1] to [4] above, wherein the filler is filled in a recess formed by disposing one of the thin plate portions between two of the thick plate portions. [6] A cover glass for covering a display panel of an in-vehicle display device, comprising the glass structure according to any one of the above [1] to [5]. [7] An in-vehicle display device comprising: a display panel; and the glass structure according to any one of [1] to [5] above, which covers the display panel, and the thin plate portion is bonded to the display panel in an elastically deformed state. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a glass structure including a glass substrate in which a step surface formed by a step between a thick plate portion and a thin plate portion is difficult to see. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view showing a glass structure. [Figure 2] FIG. 2 is a cross-sectional view showing a modified example of the glass structure. [Figure 3] FIG. 3 is a cross-sectional view showing the display device. [Figure 4] FIG. 4 is a cross-sectional view showing another display device. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiment. Various modifications and substitutions can be made to the following embodiment without departing from the scope of the present invention.

[0011] Hereinafter, ranges expressed using "to" include both ends of the range. For example, a range expressed as "A to B" includes A and B. In this specification, "mass" is synonymous with "weight."

[0012] [Glass structure] The glass structure 1 will be described with reference to FIGS.

[0013] FIG. 1 is a cross-sectional view showing a glass structure 1. As shown in FIG. The glass structure 1 has a glass base 2. The glass base 2 has a thick plate portion 3 and a thin plate portion 4. The plate thickness t4 of the thin plate portion 4 is smaller than the plate thickness t3 of the thick plate portion 3. The thick plate portion 3 has a first main surface 3a which is one of the main surfaces and a second main surface 3b which is the other main surface. The thin plate portion 4 has a first main surface 4a which is one of the main surfaces and a second main surface 4b which is the other main surface. The main surfaces such as the first main surface 3a are illustrated as flat surfaces in FIG. 1, but may also be curved surfaces. The step between the thick plate portion 3 and the thin plate portion 4 forms a step surface 5 . Although the step surface 5 is shown in FIG. 1 as a surface inclined with respect to a main surface such as the first main surface 3a, it may be a surface perpendicular to a main surface such as the first main surface 3a. Although the step surface 5 is shown as a flat surface in Fig. 1, it may be a curved surface. The radius of curvature of the curved step surface 5 is not particularly limited and is, for example, 100 to 500 µm. The radius of curvature is measured using a contour measuring device (for example, a Contour Record manufactured by Tokyo Seimitsu Co., Ltd.) at a magnification of, for example, 100 to 200 times.

[0014] When such a glass substrate 2 is used as, for example, a cover glass for an in-vehicle display device, a display panel is disposed on the side of the first main surfaces 3a and 4a (see FIG. 3 ), and a user of the in-vehicle display device views it from the side of the second main surfaces 3b and 4b. At this time, as described above, the step surface 5, which is the boundary between the thick plate portion 3 and the thin plate portion 4, may be visible to the user.

[0015] Therefore, a filler 6 is disposed on the first main surface 4a of the thin plate portion 4. The filler 6 covers the first main surface 4a and the step surface 5 of the thin plate portion 4, and reaches the height of the first main surface 3a of the thick plate portion 3. The difference in refractive index between the glass substrate 2 and the filler 6 at a wavelength of 555 nm is an absolute value of 0.008 or less, and the difference in refractive index between the glass substrate 2 and the filler 6 at a wavelength of 507 nm is an absolute value of 0.008 or less. This makes the step surface 5 less visible.

[0016] The circumstances that led to this configuration and effect will be explained below.

[0017] First, the inventors considered that light from a display panel or the like is reflected by the stepped surface 5, and the stepped surface 5 is visible when the reflected light is recognized. The inventors then approached the refractive index difference between the glass substrate 2 and the filler 6 at a wavelength of 589 nm to 0 (zero) in order to prevent the step surface 5 from being visible. The wavelength of 589 nm is a typical measurement wavelength used in devices for measuring refractive index. However, this did not result in preventing the step surface 5 from being visible. In light of this situation, the inventors further investigated and focused on the standard luminous efficiency (standard luminous efficiency for photopic and scotopic vision) established by the International Commission on Illumination (CIE). According to the standard luminous efficiency, humans are most sensitive to light around 555 nm in bright places and to light around 507 nm in dark places. Therefore, the inventors set the absolute value of the difference in refractive index between the glass base 2 and the filler 6 at a wavelength of 555 nm to 0.008 or less, and the absolute value of the difference in refractive index between the glass base 2 and the filler 6 at a wavelength of 507 nm to 0.008 or less, and as a result, the step surface 5 became less visible. It is thought that the reflected light from the step surface 5 became less noticeable in bright or dark places, and as a result, the step surface 5 was prevented from being visible.

[0018] Unlike fixed-position display devices, in-vehicle display devices mounted on vehicles are used in frequently changing locations, often alternately switching between bright and dark places in short bursts. For this reason, the above-described effects are extremely useful when glass structure 1 is used as a cover glass for an in-vehicle display device.

[0019] If the filler 6 comes into contact with another filler, it is susceptible to the generation of bubbles due to the difference in thermal expansion between the materials and to the influence of ultraviolet rays. However, since the object that the filler 6 comes into contact with is glass (glass substrate 2), it is unlikely to be affected by these factors, and it is presumed that the visibility of the step surface 5 can be sufficiently reduced.

[0020] For reasons that can further reduce visibility of the step surface 5, the refractive index difference at a wavelength of 555 nm between the glass substrate 2 and the filler 6 is preferably 0.006 or less, more preferably 0.003 or less, and even more preferably 0.001 or less, in absolute value. For the same reason, the difference in refractive index between the glass substrate 2 and the filler 6 at a wavelength of 507 nm is preferably 0.006 or less, more preferably 0.003 or less, and even more preferably 0.001 or less, in absolute value.

[0021] The refractive index is measured in accordance with the measurement method described in the Examples below.

[0022] <Explanation of filler> The filler 6 is not particularly limited as long as it satisfies the refractive index difference described above. Examples of the filler 6 include a cured product of an adhesive (transparent adhesive) such as a thermosetting adhesive or an ultraviolet curing adhesive. Commercially available adhesives can be used, including, for example, UV-curable adhesives such as NORLAND Optical Adhesive NBA107 and NORLAND Optical Adhesive NOA65 (both manufactured by Edmund Optics Japan Co., Ltd.). Adhesives that cure quickly and cause minimal dimensional change upon curing are preferred.

[0023] The filler 6 may be in a liquid form depending on the shape and amount of the filling portion. Examples of the liquid filler 6 include water, oil, organic solvents, liquid polymers, ionic liquids, and mixtures thereof. More specifically, examples of the solvent include propylene glycol, dipropylene glycol, tripropylene glycol, straight silicone oil (dimethyl silicone oil, methylphenyl silicone oil, methylhydrogen silicone oil, etc.), modified silicone oil, acrylic acid polymer, liquid polybutadiene, glycerin paste, fluorine-based solvent, fluorine-based resin, acetone, ethanol, xylene, toluene, water, mineral oil, and mixtures thereof.

[0024] <<How to arrange fillers>> The method for arranging the filler 6 is not particularly limited, and for example, the filler 6 is arranged on the first main surface 4a of the thin plate portion 4. When the filler 6 reaches the height of the first main surface 3a of the thick plate portion 3, the step surface 5 is covered with the filler 6. When the filler 6 is liquid, a device such as a dispenser capable of uniformly supplying a fixed amount of liquid may be used. In this case, it is preferable to provide a highly viscous sealing member (not shown) or the like on the periphery of the stepped surface 5 (for example, on the edge of the first main surface 4a of the thin plate portion 4) in advance. This prevents the liquid filler 6 from seeping out.

[0025] <Explanation of glass substrate> The glass base 2 is preferably glass that has been subjected to a chemical strengthening treatment (chemically strengthened glass). From the viewpoint of strength, it is preferable that the compressive stress value (CS) of the compressive stress layer of the glass substrate 2 is large. By increasing CS to improve strength, scratch resistance and crack resistance are improved, and further, flexibility is improved because the glass substrate 2 is less likely to break even when bent. Therefore, CS of the glass substrate 2 is preferably 400 MPa or more, more preferably 450 MPa or more, and even more preferably 500 MPa or more. On the other hand, if CS becomes too large, it may become difficult to reduce the internal tensile stress (CT) described later. Therefore, CS of the glass substrate 2 is preferably 1200 MPa or less, more preferably 1100 MPa or less, and even more preferably 1000 MPa or less. In order to improve the strength of the glass base 2 and improve scratch resistance, crack resistance, and flexibility, the depth of the compressive stress layer (DOL) of the glass base 2 is preferably 3 μm or more, more preferably 5 μm or more, even more preferably 7 μm or more, and particularly preferably 8 μm or more. On the other hand, if the DOL is too large, it may be difficult to reduce the internal tensile stress (CT) described later. Therefore, the DOL of the glass substrate 2 is preferably 25 μm or less, more preferably 20 μm or less, and even more preferably 18 μm or less. The compressive stress value (CS) and depth of the compressive stress layer (DOL) of the compressive stress layer of the glass are determined by measurement using a surface stress meter (FSM-6000) manufactured by Orihara Seisakusho Co., Ltd.

[0026] The internal tensile stress (CT) of the glass substrate 2 is preferably 160 MPa or less, more preferably 135 MPa or less, even more preferably 110 MPa or less, particularly preferably 100 MPa or less, and most preferably 75 MPa or less, in order to prevent fragments from flying violently when crushed. The internal tensile stress (CT) of glass is calculated from CS, DOL and plate thickness t according to the following formula. CT=CS[MPa]×DOL[mm] / (t[mm]-2×DOL[mm])

[0027] The thickness t3 of the thick plate portion 3 is preferably 0.2 mm or more, and more preferably 0.5 mm or more, because the thick plate portion 3 has excellent impact resistance. On the other hand, the thickness t3 of the thick plate portion 3 is preferably 2.5 mm or less, and more preferably 2.0 mm or less. The thickness t4 of the thin plate portion 4 is preferably less than 0.5 mm, and more preferably 0.25 mm or less, because this facilitates elastic deformation of the thin plate portion 4. On the other hand, the thickness t4 of the thin plate portion 4 is preferably 0.05 mm or more, and more preferably 0.10 mm or more. The glass plate thickness (average plate thickness) is determined by measurement using a micrometer.

[0028] <Method for manufacturing glass substrate> A method for manufacturing the glass substrate 2 will now be described. First, a raw plate (not shown) of the glass substrate 2 is prepared. The base plate is, for example, a glass plate, and examples of the glass type include soda lime glass and aluminosilicate glass (SiO2-Al2O3-Na2O-based glass).

[0029] Examples of the glass composition of the raw plate include the following compositions: All of the following compositions are expressed in mole percent based on oxides. (1) Glass containing 50-80% SiO2, 2-25% Al2O3, 0-10% Li2O, 0-18% Na2O, 0-10% K2O, 0-15% MgO, 0-5% CaO, and 0-5% ZrO2. (2) Glass containing 50-74% SiO2, 1-10% Al2O3, 6-14% Na2O, 3-11% K2O, 2-15% MgO, 0-6% CaO, and 0-5% ZrO2, with the total content of SiO2 and Al2O3 being 75% or less, the total content of Na2O and K2O being 12-25%, and the total content of MgO and CaO being 7-15%. (3) Glass containing 68-80% SiO2, 4-10% Al2O3, 5-15% Na2O, 0-1% K2O, 4-15% MgO, and 0-1% ZrO2. (4) A glass containing 67-75% SiO2, 0-4% Al2O3, 7-15% Na2O, 1-9% K2O, 6-14% MgO, and 0-1.5% ZrO2, with the total content of SiO2 and Al2O3 being 71-75%, the total content of Na2O and K2O being 12-20%, and if CaO is contained, its content is less than 1%. (5) Glass containing 65 to 75% SiO2, 0.1 to 5% Al2O3, 1 to 6% MgO, 1 to 15% CaO, and the total content of Na2O and K2O is 10 to 18%. (6) A glass containing 60 to 72% SiO2, 1 to 10% Al2O3, 5 to 12% MgO, 0.1 to 5% CaO, 13 to 19% Na2O, and 0 to 5% K2O, with RO / (RO+RO) being 0.20 to 0.42 (wherein RO is the total content of alkaline earth metal oxides, and RO is the total content of alkali metal oxides). (7) Glass containing 55.5 to 80% SiO2, 12 to 20% Al2O3, 8 to 25% Na2O, 2.5% or more P2O5, and 1% or more alkaline earth metal RO (RO is MgO + CaO + SrO + BaO). (8) Glass containing 57 to 76.5% SiO2, 12 to 18% Al2O3, 8 to 25% Na2O, 2.5 to 10% P2O5, and 1% or more alkaline earth metal RO. (9) Glass containing 56-72% SiO2, 8-20% Al2O3, 3-20% B2O3, 8-25% Na2O, 0-5% K2O, 0-15% MgO, 0-15% CaO, 0-15% SrO2, 0-15% BaO, and 0-8% ZrO2.

[0030] When chemical strengthening treatment, which will be described later, is carried out, for example, chemically strengthened glass based on aluminosilicate glass (for example, "Dragontrail (registered trademark)") is preferably used. The size of the raw plate (plate thickness, etc.) is appropriately selected taking into consideration the size of the glass substrate 2 to be finally obtained.

[0031] Slimming Next, the prepared blank is slimmed by, for example, at least one method selected from the group consisting of polishing and etching.

[0032] When polishing a raw plate, for example, polishing is performed so as to reduce the thickness of a portion of the raw plate. Thus, for example, the unpolished portion becomes a thick plate portion 3, and the polished portion becomes a thin plate portion 4. The polishing method is not particularly limited, and a conventionally known polishing pad or the like can be used as appropriate.

[0033] When etching a blank, first, the portions that do not need to be etched (for example, the portions that will become the thick plate portion 3) are masked using a mask material. The material of the mask material is not particularly limited as long as it is resistant to the etching solution described below, and any conventionally known material can be appropriately selected and used. An example of such a mask material is a resist material. In this case, the resist material is exposed through a photomask with a desired shape pattern, and the exposed resist material is developed to form a resist pattern in the portions that do not need to be etched. Next, the masked blank is etched, which dissolves the unmasked portions of the blank. Thus, for example, the dissolved portions become the thin plate portions 4, and the masked portions that remain undissolved become the thick plate portions 3. The etching method is not particularly limited, but a method in which the masked substrate is immersed in an etching solution is preferred. The etching solution may be an aqueous solution containing an acid. Examples of the acid include hydrogen fluoride (HF), sulfuric acid, nitric acid, hydrochloric acid, and hexafluorosilicic acid, with hydrogen fluoride being preferred. The content of the acid, such as hydrogen fluoride, in the etching solution is preferably 2 to 10 mass %.

[0034] After etching, the mask material such as the resist material (resist pattern) is stripped off. Examples of a resist material stripping solution include an alkaline solution containing an alkali such as KOH or NaOH. The base plate may be masked with a resist pattern and then etched, and after the resist pattern is removed, the entire base plate may be further etched.

[0035] Chemical strengthening treatment The slimmed raw plate may be subjected to a chemical strengthening treatment. When chemical strengthening treatment is performed, glass for chemical strengthening is used as the base plate. In the chemical strengthening treatment, the glass for chemical strengthening is brought into contact with an inorganic salt composition containing alkali metal ions with a larger ionic radius than the alkali metal ions contained in the glass, whereby the alkali metal ions (Li ions and / or Na ions) contained in the glass are exchanged for the larger alkali metal ions (Na ions and / or K ions) contained in the inorganic salt composition, forming a high-density compressive stress layer. The density of chemically strengthened glass increases gradually from the outer edge of the non-ion-exchanged region (intermediate layer) in the center of the glass toward the surface of the compressive stress layer. There is no clear boundary between the intermediate layer and the compressive stress layer where the density changes suddenly.

[0036] Examples of methods for bringing the inorganic salt composition into contact with the glass for chemical strengthening include a method of applying a paste-like inorganic salt composition to the glass for chemical strengthening; a method of spraying an aqueous solution of the inorganic salt composition onto the glass for chemical strengthening; and a method of immersing the glass for chemical strengthening in an inorganic salt composition (hereinafter also referred to as "molten salt") that has been melted by heating it to or above its melting point. Of these, the method of immersing the glass for chemical strengthening in a molten salt is preferred.

[0037] When the glass for chemical strengthening contains Na ions, an inorganic salt composition containing potassium nitrate (KNO3) and at least one flux selected from the group consisting of K2CO3, Na2CO3, KHCO3, NaHCO3, K3PO4, Na3PO4, K2SO4, Na2SO4, KOH, and NaOH may be used. The melting point of potassium nitrate is 330°C, which is lower than the strain point of chemically strengthened glass (usually 500 to 600°C).

[0038] When immersing the glass for chemical strengthening in the molten salt, the glass for chemical strengthening is preheated to, for example, 100°C or higher, then immersed in the heated molten salt, and then removed from the molten salt and allowed to cool. The chemical strengthening temperature (temperature of the molten salt) may be equal to or lower than the strain point of the glass for chemical strengthening (usually 500 to 600°C), but in order to obtain a deep compressive stress layer, a temperature of 350°C or higher is preferable, and from the viewpoint of shortening the treatment time, a temperature of 400°C or higher is more preferable, and a temperature of 430°C or higher is even more preferable. In consideration of the balance between the strength of the resulting chemically strengthened glass and the depth of the compressive stress layer, the immersion time of the chemically strengthened glass in the molten salt is preferably 1 minute or more, more preferably 5 minutes or more, and even more preferably 10 minutes or more, while it is preferably 10 hours or less, more preferably 8 hours or less, and even more preferably 4 hours or less.

[0039] After the chemical strengthening treatment, the glass (chemically strengthened glass) is preferably washed with a cleaning liquid. Examples of the cleaning liquid include industrial water that has been treated as necessary and ion-exchanged water, and among these, ion-exchanged water is preferred. The preferred washing conditions vary depending on the washing solution used, but in order to thoroughly remove salts adhering to the glass, washing is preferably carried out at a temperature of 0 to 100°C when using ion-exchanged water, for example. Cleaning methods include immersing the glass in a tank containing ion-exchanged water, exposing the glass surface to running water, and spraying cleaning liquid onto the glass surface using a shower.

[0040] <Modification of Glass Substrate> FIG. 2 is a cross-sectional view showing a modified example of the glass structure 1. As shown in FIG. In FIG. 2, the same parts as those in FIG. 1 are denoted by the same reference numerals, and the description thereof will be omitted. In the glass substrate 21 shown in Fig. 2, one thin plate portion 4 is disposed between two thick plate portions 3. A recess 7 is formed by the two step surfaces 5 and the first main surface 4a of the thin plate portion 4. A filler 6 is filled in the recess 7. 2, the difference in refractive index between the glass substrate 21 and the filler 6 also satisfies the above-mentioned range, thereby making the step surface 5 less visible.

[0041] [Display device] FIG. 3 is a cross-sectional view showing the display device 11. As shown in FIG. Display device 11 has multiple display panels (i.e., display panel 12, display panel 13, display panel 14, and display panel 15), which are held by panel holder 16 having an uneven shape. At this time, the three display panels 12, 13, and 14 are arranged in recesses in panel holder 16.

[0042] Fig. 4 is a cross-sectional view showing another display device 17. The same components as those in the display device 11 of Fig. 3 are designated by the same reference numerals, and the description thereof will be omitted. The display device 17 has one display panel 18 having an uneven shape, which is held by a panel holding portion 16 having an uneven shape.

[0043] Each display panel is, for example, a liquid crystal panel. In this case, a backlight unit is disposed on the rear side of each liquid crystal panel. Each display panel may be, for example, an organic EL (ElectroLuminescence) panel, a PDP (Plasma Display Panel), an electronic ink panel, or the like. It may also have a touch panel, etc.

[0044] The above-described glass structure 1 (see FIG. 1) is assembled to such display device 11 and display device 17. 3, the first main surface 3a of the thick plate portion 3 of the glass base 2 is bonded to the display panel 15 via an OCA (Optical Clear Adhesive) (not shown). Furthermore, in a state in which the thin plate portion 4 of the glass base 2 is elastically deformed, the first main surface 4a of the thin plate portion 4 is bonded to the display panels 12, 13, and 14 via the OCA (not shown). In the display device 17 shown in FIG. 4, the glass base 2 is bonded to a display panel 18 via an OCA (not shown) in a state in which the thin plate portion 4 of the glass base 2 is elastically deformed. In the display device 11 and the display device 17, the glass structure 1 functions as a cover glass that covers each display panel.

[0045] The display device 11 and the display device 17 each include an in-vehicle display device that is mounted on a vehicle for use. More specifically, examples include in-vehicle display devices that have an instrument cluster (cluster) located in front of the driver's seat, and a center information display (CID) located in front of the driver's seat and passenger seat. In an in-vehicle display device, for example, the concave portion is a cluster and the convex portion is a CID, in which case the thin plate portion 4 functions as a cover glass for the cluster and the thick plate portion 3 functions as a cover glass for the CID.

[0046] A user of the display device 11 (display device 17) views the display device 11 (display device 17) from the side of the second main surface 3b and the second main surface 4b of the glass structure 1, which is the cover glass. At this time, since the glass structure 1 is used as the cover glass, the step surface 5, which is the boundary between the thick plate portion 3 and the thin plate portion 4, is prevented from being visible to the user. [Example]

[0047] The present invention will be specifically described below with reference to examples, although the present invention is not limited to the following examples.

[0048] Examples 1 to 3 are working examples, and Examples 4 and 5 are comparative examples.

[0049] Example 1 A glass structure (see Figure 1) was fabricated as described below.

[0050] <<Production of Glass Substrate>> First, a 120 mm×60 mm piece of chemically strengthened glass (AGC Corporation's "Dragontrail Pro," plate thickness: 0.2 mm) was prepared as a raw plate to serve as the glass substrate. Next, the prepared base plate was slimmed. More specifically, the base plate was polished using a polishing pad to reduce the thickness of the thin plate portion to 0.1 mm, and a concave curved surface (radius of curvature: 300 μm) was formed as the step surface. The slimmed raw plate was then subjected to a chemical strengthening treatment. More specifically, the slimmed raw plate was immersed in a KNO molten salt at 380°C for 15 minutes, and then washed with water. In this way, a glass substrate was obtained, which had a thick portion having a thickness t3 of 0.2 mm, a thin portion having a thickness t4 of 0.1 mm, a compressive stress value (CS) of the compressive stress layer of 950 MPa, and a depth of the compressive stress layer (DOL) of 5 μm.

[0051] <<Filler placement>> Next, silicone oil (KF-54, manufactured by Shin-Etsu Silicones Co., Ltd., methylphenyl silicone oil) was placed as a filler on the first main surface of the thin plate portion of the obtained glass substrate, and filled up to the height of the first main surface of the thick plate portion. In this way, the stepped surface of the glass substrate was covered with the filler. Before filling with silicone oil, a sealing member (not shown) was provided on the edge of the first main surface of the thin plate portion of the glass substrate to prevent the silicone oil from leaking out. In this way, a glass structure (see FIG. 1) was obtained.

[0052] Example 2 As the silicone oil filler, KF-56 (methylphenyl silicone oil, manufactured by Shin-Etsu Silicone Co., Ltd.) was used. Otherwise, the glass structure was produced in the same manner as in Example 1.

[0053] Example 3 The silicone oil filler used was a mixture of KF-56 and HIVAC F-5 (methylphenyl silicone oil, manufactured by Shin-Etsu Silicones Co., Ltd.) with a mass ratio of 8 / 2 (KF-56 / HIVACF-5). Otherwise, the glass structure was produced in the same manner as in Example 1.

[0054] Example 4: The silicone oil filler used was a mixture of KF-96 (dimethyl silicone oil, manufactured by Shin-Etsu Silicones Co., Ltd.) and KF-56. The mass ratio of the mixture (KF-96 / KF-56) was 2 / 8.

[0055] Example 5 A mixture of KF-56 and HIVAC F-5 was used as the silicone oil filler, with a mass ratio of 6 / 4 (KF-56 / HIVAC F-5). Otherwise, the glass structure was produced in the same manner as in Example 1.

[0056] <Refractive index difference> For each of the obtained glass structures, the refractive index difference between the glass substrate and the filler at a wavelength of 555 nm and the refractive index difference between the glass substrate and the filler at a wavelength of 507 nm were determined. The results are shown in Table 1 below. First, the refractive index of the glass substrate was measured at multiple wavelengths under the following conditions, and the measured values ​​were plotted on a graph (vertical axis: refractive index, horizontal axis: wavelength). The refractive indexes at wavelengths of 555 nm and 507 nm were then calculated from an approximate curve (polynomial approximation). The refractive index of the filler was also determined in the same manner at wavelengths of 555 nm and 507 nm.

[0057] <<Measurement conditions for refractive index of glass substrate>> Measurement equipment: Kalnew precision refractometer KPR-2000 (accuracy: ±0.00003 (23°C)) ·Measurement wavelength: d(587.562nm), C(656.273nm), F(486.133nm), e(546.074nm), g(435.834nm), C′(643.847nm), F′(479.991nm)

[0058] <Measurement conditions for refractive index of filler: Examples 1 to 5> Measurement equipment: Kalnew Precision Refractometer KPR-3000 (Accuracy: ±0.00002 (23°C)) ·Measurement wavelength: h (404.656nm), F (486.133nm), d (587.294nm), r (706.519nm), LD785 (785nm)

[0059] <Visibility of step surfaces> Each of the resulting glass structures was observed in light and in the dark. When adapted to an environment of 500 lux, which is the general standard for indoor brightness, it becomes photopic vision and has wavelength sensitivity based on 555 nm. In addition, when adapted to an environment of 10 lux or less, it becomes scotopic (or dim light) vision and has wavelength sensitivity based on 507 nm. Therefore, each glass structure was observed under 500 lux as an illuminance in a bright place and 5 lux as an illuminance in a dark place.

[0060] The glass structure observed under each illuminance was evaluated according to the following criteria. The evaluation results are shown in Table 1 below. From a practical standpoint, A, B or C is preferred, A or B is more preferred, and A is even more preferred. A: The stepped surface of the glass substrate was not visible. B: The stepped surface of the glass substrate was slightly visible. C: The stepped surface of the glass substrate was somewhat clearly visible. D: The stepped surface of the glass substrate was clearly visible.

[0061] [Table 1]

[0062] <Summary of evaluation results> As shown in Table 1 above, in Examples 1 to 3, in which the refractive index difference at a wavelength of 555 nm was 0.008 or less in absolute value and the refractive index difference at a wavelength of 507 nm was 0.008 or less in absolute value, the visibility of the step surface of the glass substrate was reduced more than in Examples 4 to 5, in which the refractive index difference did not satisfy the above range.

[0063] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application (Patent Application No. 2020-106291) filed on June 19, 2020, the contents of which are incorporated herein by reference. [Explanation of symbols]

[0064] 1: Glass structure 2: Glass substrate 3: Thick plate section 3a: First main surface of the thick plate 3b: Second main surface of the thick plate 4: Thin plate part 4a: First main surface of the thin plate 4b: Second main surface of the thin plate 5: Step surface 6: Filler 7: Recess 11:Display device 12, 13, 14, 15: Display panel 16: Panel holder 17:Display device 18: Display panel 21: Glass substrate (variant) t3: Thickness of the thick plate t4: thickness of thin plate

Claims

1. a glass substrate having a thick portion and a thin portion thinner than the thick portion; a filler that covers a step surface formed by a step between the thick plate portion and the thin plate portion, the thickness of the glass substrate is partially changed, thereby forming the thick portion, the thin portion, and the step surface; The plate thickness t 3 of the thick plate portion is 0.5 mm or more and 2.0 mm or less, a glass structure in which the difference in refractive index between the glass substrate and the filler at a wavelength of 555 nm is 0.008 or less in absolute value, and the difference in refractive index between the glass substrate and the filler at a wavelength of 507 nm is 0.008 or less in absolute value; Cover glass that covers the display panel of an in-vehicle display device.

2. The plate thickness t of the thin plate portion ４ is the plate thickness t of the thick plate portion ３ The cover glass of claim 1 , wherein the cover glass is smaller than

3. The thickness t of the thin plate portion ４ The cover glass according to claim 1 or 2, wherein the thickness is 0.1 mm or more and less than 0.5 mm.

4. The cover glass according to any one of claims 1 to 3, wherein the glass substrate is chemically strengthened glass.

5. The cover glass according to any one of claims 1 to 4, wherein the filler is filled into a recess formed by placing one thin plate portion between two thick plate portions.

6. A display panel; The cover glass according to any one of claims 1 to 5, which covers the display panel; Equipped with The thin plate portion is attached to the display panel in an elastically deformed state.

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