KR20220094505A - Method for processing ultra-thin glass and ultra-thin glass processed thereby - Google Patents

Abstract

The present invention comprises the steps of (a) preparing a plurality of cells by cutting the original glass in cell units; (b) physically grinding the cut surface of the cell; (c-1) etching the polished cell; and (c-2) healing the polished cut surface of the cell.

Description

Manufacturing method of ultra-thin glass and ultra-thin glass manufactured by the method

The present invention relates to a method for manufacturing an ultra-thin glass and to an ultra-thin glass manufactured by the method.

With the recent development of display technology, a foldable display, a rollable display, a stretchable display, etc. are being developed, and in order to protect these various types of displays, a flexible characteristic is Research on improved ultra-thin glass is being actively conducted.

Since this ultra-thin glass has flexible properties, excellent flexural strength is required to be used in various types of displays, and surface roughness is required to improve display quality.

In general, in order to reduce the possibility of scratching the glass surface of the window glass when using the display and the possibility of breakage due to dropping during use, the window glass used in the mobile display uses ion substitution chemical strengthening to improve the strength.

In the above method, the displacement of the surface compressive stress is determined according to the physical properties and thickness of the glass under the same chemical strengthening conditions. In addition, since the depth of layer and the surface compressive stress of ion displacement chemical strengthening have opposite tendencies, it cannot have a result exceeding the surface compressive stress determined by the glass properties determined during glass manufacturing.

On the other hand, in the ultra-thin tempered glass processing process up to now, as disclosed in Korean Patent No. 10-1417993, after laminating glass using a laminated material, cutting and grinding the edge surface (cross-section) by abrasive processing, the edge After undergoing a chemical polishing process by chemical etching to remove chipping and microcracks, a process for separating the cells by removing the layered material, cleaning the separated cells and dipping them in a strengthening solution to chemically strengthen them This is known

However, if the ultra-thin glass is cut in cell units, the thickness of the glass is so thin that it is easily broken during processing. There is a problem in that the process is complicated as it has to go through a number of steps, such as having to discard the entire amount, and having to go through a separate process to apply and remove it because the laminated material is used during lamination. In addition, residues may remain on the surface even after cleaning the laminated material, and even if the treatment time is slightly exceeded during chemical polishing of the side of the glass, the side becomes sharp and stability is lowered, thereby increasing the possibility of damage in the subsequent process.

On the other hand, when cutting the ultra-thin glass without laminating it, a masking process is essential to prevent thickness reduction due to surface etching or healing.

Republic of Korea Patent No. 10-1417993

An object of the present invention is to improve the problems of the prior art described above, and to provide a method for manufacturing an ultra-thin glass capable of simplifying an ultra-thin glass manufacturing process while lowering the possibility of breakage in a post-processing process, and tracing each cell.

In addition, by processing the ultra-thin glass by the above method, it is intended to provide an ultra-thin glass that is healed in a gentle round shape in which the cell side has a predetermined curvature.

However, the problems to be solved by the present application are not limited to the problems mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the following description.

In order to achieve the above object, the present invention comprises the steps of (a) preparing a plurality of cells by cutting the original glass cell unit; (b) physically grinding the cut surface of the cell; (c-1) etching the polished cell; and (c-2) healing the polished cut surface of the cell.

In addition, the present invention provides an ultra-thin glass manufactured by the above method.

The manufacturing method of the ultra-thin glass of the present invention can improve the yield by reducing the possibility of breakage in the post-treatment process while simplifying the process, it is possible to trace each cell, and a gentle round shape (curved edge) with a cut surface having a predetermined curvature ) to provide a healing ultra-thin glass.

In addition, the manufacturing method of ultra-thin glass according to the present invention does not use a separate masking process or laminated material (eg, adhesive, adhesive, etc.), and can heal the side while etching the glass to a target thickness. Compared to that, the process can be shortened, and defects and defects that occur during the physical polishing process can be minimized.

1 is a process flow chart of the ultra-thin glass manufacturing method of the present invention.
2 is a schematic schematic diagram for explaining a method of manufacturing an ultra-thin glass of the present invention.
3 is a cross-sectional photograph of the edge portion of the ultra-thin glass processed according to the embodiment of the present application.
4 is a cross-sectional photograph of the edge portion of the ultra-thin glass processed by the conventional method.
5 is a cross-sectional side view of the cell in step (b), in one embodiment, showing an edge portion having a predetermined curvature.
6 is a cross-sectional view illustrating a side form of an ultra-thin glass having one curved edge.
7 is a cross-sectional view illustrating a side form of an ultra-thin glass having two curved edges.

The present invention relates to a method of manufacturing an ultra-thin glass applicable to a flexible display with improved surface roughness and flexural strength, and to an ultra-thin glass manufactured by the method, wherein the method according to the present invention simplifies the process and post-processing It is possible to improve the yield by lowering the possibility of breakage in the process, it is possible to trace each cell, and it is possible to manufacture an ultra-thin glass healed in a gentle round shape (curved edge) with a predetermined curvature on the cell side.

Hereinafter, with reference to the accompanying drawings, embodiments and examples of the present invention will be described in detail so that those of ordinary skill in the art to which the present invention pertains can easily carry out. However, the present application may be embodied in several different forms and is not limited to the embodiments and examples described herein. And in order to clearly explain the present invention in the drawings, parts irrelevant to the description are omitted, and similar reference numerals are attached to similar parts throughout the specification.

< Manufacturing method of ultra-thin glass >

1 is a process flow chart of an ultra-thin glass manufacturing method according to an embodiment of the present invention, and FIG. 2 is a schematic schematic diagram for explaining the ultra-thin glass manufacturing method of the present invention.

Hereinafter, a method of manufacturing the ultra-thin glass of the present invention will be described in detail with reference to the drawings.

The manufacturing method of the ultra-thin glass of the present invention comprises the steps of: (a) preparing a plurality of cells 20 by cutting the original glass 10 in cell units; (b) grinding the cut surfaces 11 of the cells; and (c) etching the polished cell 20 and healing the polished cut surface 21 of the cell. After step (c), (d) cleaning; (e) chemical fortification; and/or (f) chemical polishing.

(a) step of cutting the original glass in units of cells

First, (a) a plurality of cells 10 are prepared by cutting the original glass 100 in units of cells.

The step (a) of cutting the original glass 100 in units of cells is a step for forming a shape according to the design of the device to use the original glass 100, and cutting the original glass 100 to a plurality of It may be to form a cell (cell) (10). This step may be a step performed without stacking the original glass 100 in a plurality of layers. This enables cell tracking when defects occur, simplifies the manufacturing process by omitting the lamination process, reduces the defect rate for residues that may occur during the lamination process, and has the advantage of being able to freely select the shape of the glass side .

The original glass refers to a thick film before thickness etching, and the thickness 13 of the original glass may be 50 to 700 μm, and preferably 100 to 400 μm.

The cutting step (a) is not particularly limited as long as a plurality of cells 10 can be formed by cutting the original glass 100, and in one embodiment, a diamond cutting wheel or a laser It may be to form a plurality of cells showing a certain shape using the mounted CNC cutting machine.

(b) grinding the cut surface of the unit cell

Then, the present invention includes the step of (b) grinding the cut surface 11 of the cell, wherein the polishing is preferably physical polishing, and most preferably physical polishing so that the cut surface 11 of the cell is round. may be polished with The cut surface 11 of the cell means a side surface of the cell. In this case, the thickness 23 of the cut cell may be the same as the thickness 13 of the original glass.

The physical polishing step (b) includes physically polishing the chipping of the cut surface after the cutting step and processing the cell side into a desired shape. At this time, the thickness 23 of the cut cell may be the same as the thickness 13 of the original glass before cutting.

The polished cut surface 21, that is, the side of the cell may have a gentle round shape having a predetermined curvature in terms of stability to reduce the possibility of damage during post-processing, and 'curvature' in the present invention means the degree of curvature, and 'curvature' The radius (R)' means the radius of the circle forming the curved curve.

5, when the thickness of the original glass is "T1" and the thickness of the final manufactured ultra-thin glass cell is "T2", for example, T2 is 1/10 of T1. When manufacturing an ultra-thin glass cell with a thickness, it is preferable to grind it so that the radius of curvature (R) based on the most end (outermost part) of the round-shaped cut surface becomes T1/20.

The physical polishing step (b) is not particularly limited as long as it is a method capable of physically polishing the chipping generated during cutting, and in one embodiment, the cut surface of the cell cut using a chamfering tool of 400 mesh or less Grinding the, roughing step; a medium grinding step of grinding the cut surface of the cell that has undergone the roughing step using a chamfering tool of about 500 to 800 mesh; Grinding the cross section of the cell that has undergone the intermediate grinding step using a chamfering tool of 1200 mesh or more, may be performed including a finishing step.

(c) etching of the polished cell and healing of the polished cut surface of the polished cell

Subsequently, (c-1) etching of the polished cell and (c-2) healing of the polished cut surface of the polished cell may be included. The above step of the present invention includes performing the etching of the polished cell and the healing step of the polished cut surface of the polished cell at the same time. In addition, the healed cut surface 31 refers to the side of the ultra-thin glass cell finally manufactured.

In step (c) of the present invention, the cell 20 polished in step (b) can be etched without a protective material to prevent impact on the glass during the process, such as resin or film, or to mask the etchant.

(c) The polished cell 20 is made ultra-thin through a chemical etching process, and at the same time, the polished cut surface 21 of the cell is healed to obtain an ultra-thin glass 30 in a cell unit.

Specifically, (c-1) the etching step of the polished cell includes, but is not limited to, chemical etching. The cell can be made ultrathin through the (c-1) etching step of the polished cell. The ultra-thinning refers to a process of making the glass thin to a thickness of 100 μm or less.

(c-1) etching of the polished cell and (c-2) healing of the polished cut surface of the polished cell may be performed separately, respectively, but the (c-2) healing step of the polished cut surface of the cell is It is more preferable in terms of simplification of the process to be performed by the same method simultaneously with the step (c-1) of etching the polished cell.

When the etching and healing step (c) of the present invention are simultaneously performed, the cell 20 in the thick film state is made ultra-thin and at the same time it is performed to improve the edge strength of the cut cell, and the healed cut surface ( 31) may be processed into a round shape that is smoother than the shape of the polished cut surface 21, and defects such as chipping of the cut surface due to physical polishing are removed by healing, and the roughness is lowered, so that the bending It is possible to suppress the destruction of the surface, and it is preferable that the surface processed into the round shape forms a gentle curve.

The healed cut surface 31 may have one curved edge having a predetermined radius of curvature based on the outermost portion of the side surface of the ultra-thin glass cell. For example, as shown in FIG. 6 , when the thickness 33 of the ultra-thin glass cell is T, the radius of curvature R of the curved edge may be T/2.

In addition, the healed cut surface 31 may have two or more curved edges having a predetermined radius of curvature. For example, as shown in FIG. 7 , when the thickness 33 of the ultra-thin glass cell is T, the two curved edges may be vertically symmetrical, and in this case, the radius of curvature (R) of the curved edge may be T/4.

In the chemical etching step (c-1), a dipping method of dipping a cell in an etchant may be used, and in one embodiment, a cell jig fixing step of fixing the cell to a jig for handling the cell Wow; a jig dipping step of dipping the cell into the etchant in the etchant bath filled with the etchant; a chemical etching step of uniformly chemically etching the thickness and the cut surface at a constant etching rate in a dipped state; a jig discharging step of discharging the jig from the etchant bath when the chemical etching is completed; It may be carried out including one or more of the cell separation step of separating the cell in which the chemical etching is completed in the jig.

In addition to the dipping method in which the cell is immersed in the etching solution, a side spray method or a top spray method may be additionally performed to help the etching.

Without the dipping method in which the cell is all immersed in the etchant, only the side spray method or the top spray method may be performed. At this time, since the glass is cut in cell units, the etching solution can be adsorbed to the surface of the glass cell by the surface tension of the sprayed etching solution, so that etching and side healing are possible.

In the etching and healing step (c) of the present invention, the contact between the respective glass cells may be minimized by performing etching and healing while moving the plurality of glass cells through the upper and lower jigs, respectively.

The thickness 33 of the ultra-thin glass can be appropriately adjusted according to the intended use, for example, may be 20 to 200 μm, preferably 30 to 100 μm.

The etching solution, in one or more embodiments, hydrofluoric acid (HF), ammonium fluoride (NH ₄ F), ammonium hydrogen fluoride (NH ₄ HF ₂ ), sodium fluoride (NaF), sodium hydrogen fluoride (NaHF ₂ ), Lithium fluoride (LiF), potassium fluoride (KF) and calcium fluoride (CaF ₂ ) It may include one or more selected from the group consisting of.

When the (c-1) etching of the polished cell and (c-2) the healing of the polished cut surface of the polished cell are performed as separate steps, as described above, through the chemical etching step (c-1) After the cell is etched, the healing step of the polished cut surface of the polished cell may be further performed by applying the same method as the above-described chemical etching step (c-2).

(d) cleaning, (e) chemical strengthening, and/or (f) chemical polishing.

In addition, the method of manufacturing an ultra-thin glass of the present invention may further include (d) cleaning, (e) chemical strengthening, and/or (f) chemical polishing. The order of the cleaning step, chemical strengthening step, and chemical polishing step may be changed, added, or omitted as necessary.

The cleaning step (d) may be for removing residual foreign substances and etchant from the previous process. The cleaning process for removing the remaining foreign substances and the etchant may be one using a commonly used process, and in one embodiment, a spray method of cleaning using a washing solution and spraying the washing solution or the water A dipping method of immersing in the washing solution may be used.

The washing solution is not particularly limited as long as it serves to clean the ultra-thin glass surface, and in one or more embodiments, pure water (DI Water), or potassium hydroxide (KOH) or sodium hydroxide (NaOH) It may be an alkaline washing solution.

The chemical strengthening step (e) is to strengthen the ultra-thin glass by exchanging alkali ions in the molten salt with alkali ions inside the ultra-thin glass by immersing the ultra-thin glass in molten salt, and in one embodiment, the ultra-thin glass A preheating step of gradually increasing the temperature; chemical strengthening of the preheated ultra-thin glass by ion substitution; and slowly cooling the strengthened ultra-thin glass at room temperature.

In the preheating step of gradually increasing the temperature of the ultra-thin glass, in order to prevent damage due to a sudden temperature change of the ultra-thin glass in the chemical strengthening step proceeding at a high temperature of 350 to 500 ° C, the temperature is lowered before immersing the ultra-thin glass in the ion replacement solution. It may be carried out to gradually increase the temperature.

In the chemical strengthening step, when a glass containing Na ⁺ is brought into contact with a salt containing K ⁺ ions, Na ⁺ and K ⁺ ion exchange on the surface proceeds inwardly, in this case the position occupied by Na ⁺ in the ultra-thin glass structure K ⁺ ions enter the ion, and since the ionic radius of K ⁺ is larger than that of Na ⁺ , a compressive force is generated around the network structure, which may be why the glass is strengthened.

The depth at which K ⁺ ions are substituted by the chemical strengthening is not particularly limited, but may be a depth of 5% to 40% of the cell thickness 33 in terms of improving bending resistance, specifically, 10% to 35% Preferably, it is 15% to 30%, more preferably.

In addition, the target depth of chemical strengthening may vary depending on the thickness of the glass, for example, as shown in Table 1 below, the depth (thickness) of chemical strengthening may vary according to the thickness of the glass.

cell thickness Chemical strengthening depth (thickness) 5% 10% 15% 20% 30% 40% 30 μm 1.5 μm 3 μm 4.5 μm 6 μm 9 μm 12 μm 50 μm 2.5 μm 5 μm 7.5 μm 10 μm 15 μm 20 μm 70 μm 3.5 μm 7 μm 10.5 μm 14 μm 21 μm 28 μm

The ion replacement solution used for the chemical strengthening may be a commonly used ion replacement solution, and in one embodiment, may include potassium nitrate (KNO ₃ ).

After the chemical strengthening process, a slow cooling step and a process for removing impurities may be additionally performed. The process for slow cooling and removal of impurities may be one using a commonly used process, and in one embodiment, after the process of natural slow cooling in contact with outside air, to remove impurities, such as potassium nitrate, a washing process may include.

The chemical polishing step (f) is to polish the ultra-thin glass through a chemical polishing solution, and the chemical polishing thickness is, in terms of improving bending resistance, the thickness of the ultra-thin glass after chemical polishing is 80 of the thickness of the ultra-thin glass before chemical polishing % or more and less than 100% may be polished, preferably, may be 90% or more and less than 100%.

The chemical polishing solution is not particularly limited as long as it is typically used in a process of polishing ultra-thin glass, but may include at least one of hydrofluoric acid (HF) and ammonium fluoride (NH ₄ F).

In addition, after the chemical polishing step, if necessary, a cleaning step may be additionally performed.

< Ultra-thin glass >

In addition, the present invention includes the ultra-thin glass manufactured by the method for manufacturing the ultra-thin glass described above, and the ultra-thin glass of the present invention has an advantage of excellent stability in a gentle round shape with no polygonal vertices. The gentle round shape is preferably a circular or elliptical shape having no vertices of a polygon that significantly increases the possibility of damage caused by external impact.

For the ultra-thin glass according to the present invention, all of the contents described for the method for manufacturing the ultra-thin glass according to the present invention can be applied, and detailed descriptions of overlapping parts are omitted, but the same can be applied even if the description is omitted. have.

Hereinafter, the present invention will be described in more detail through examples. However, the following examples are provided to explain the present invention in more detail, and the scope of the present invention is not limited by the following examples.

<Example>

Example 1: Preparation of ultra-thin glass cell 1

An aluminosilicate glass disc with a thickness of 400 μm was cut in a cell unit with a diamond wheel in a size of 70x160 mm 2 . The cut surface of the cell was sequentially polished so that the glass side had a semicircular shape with a 600-mesh and 1200-mesh R=T/2 type groove grinder. The polished cell was immersed in an etchant having a composition of 20 wt% hydrogen fluoride and 15 wt% sulfuric acid and etched to a thickness of 50 μm to prepare an ultra-thin glass cell according to Example 1.

After cleaning the ultra-thin glass, to perform chemical strengthening, the cell is fixed to a strengthening jig, preheated in the air at 400°C for 60 minutes, immersed in a potassium nitrate solution at 400°C for 10 minutes, then slowly cooled in the air, washed, and the side is curved An ultra-thin glass of a cell unit having an edge was prepared.

Example 2: Preparation of ultra-thin glass cell 2

An ultra-thin glass cell according to Example 2 having a curved edge was prepared in the same manner as in Example 1, except that the cut surface of the cell was sequentially polished with a groove grinder of R=T/4 type.

Example 3: Preparation of ultra-thin glass cells 3

An ultra-thin glass cell according to Example 3 was prepared in the same manner as in Example 1, except that chemical polishing was additionally performed after chemical strengthening.

The chemical polishing was performed by immersing a chemically strengthened ultra-thin glass cell in a water bath containing hydrofluoric acid or ammonium fluoride, polishing both surfaces of 1.0 μm, respectively, followed by washing and drying.

Comparative Example 1: Preparation of ultra-thin glass cell 4

After attaching aluminosilicate glass with a thickness of 400 μm, 300 mm in width, and 400 mm in length, to an etching jig by taping the upper and lower portions of the glass by 10 mm, the thickness after primary etching in an etchant composed of 20 wt% hydrogen fluoride and 15 wt% sulfuric acid It was slimmed to a thickness of 200 μm, a thickness of 100 μm after the second etching, and a thickness of 50 μm after the third etching. In order to remove the upper and lower portions of the non-etched glass by taping, 20 mm of the upper and lower portions of the glass were removed using a laser cutting equipment.

After that, 20 sheets were laminated by repeating the operation of applying a separation layer on the upper part of the dummy glass and bonding the slimmed glass, then the separation layer was applied and the dummy glass was bonded to the top. The laminated glass was cut to a size of 70x160 ㎟, and the cut side was polished at a right angle with a 600 mesh and further polished with a 1200 mesh.

The polished glass laminate was immersed in a healing solution of 10 wt% hydrogen fluoride and 7.5 wt% sulfuric acid for 10 minutes to alleviate side chipping and cracking of the glass during polishing. Then, to remove the separation layer, the glass laminate was immersed in hot water to separate the separation layer and the glass.

Thereafter, cleaning and strengthening methods were performed in the same manner as in Example 1 to prepare an ultra-thin glass cell according to Comparative Example 1.

Comparative Example 2: Preparation of ultra-thin glass cell 5

An ultra-thin glass cell according to Comparative Example 2 was prepared in the same manner as in Example 1, except that the cut surface of the cell was sequentially polished on the glass side with a polygon-shaped groove grinder.

Comparative Example 3: Preparation of ultra-thin glass cell 6

An ultra-thin glass cell according to Comparative Example 3 was manufactured in the same manner as in Example 1, except that the cut surface of the cell was sequentially polished on the glass side with a planar groove grinder.

<Experimental example>

(1) Lateral condition evaluation

The states of the ultra-thin glass cells prepared in Examples and Comparative Examples were photographed to confirm the state, and the results are shown in Table 2 below.

3 is a photograph of the ultra-thin glass prepared in Example 1, and FIG. 4 is a photograph of the ultra-thin glass prepared in Comparative Example 1.

(2) Fracture evaluation during the strengthening process

When the ultra-thin glass cells prepared in Examples and Comparative Examples were inserted into the reinforcing jig and reinforced and cleaned, the degree of breakage due to contact between the reinforcing jig and the cell side was measured, and the results are shown in Table 2 below.

(3) Flexural repeatability evaluation

Table 2 below shows the results of evaluating the bending repeatability of the ultra-thin glass cells prepared in Examples and Comparative Examples using a 2.0R bending device at room temperature for 200,000 times.

[Table 2]

* In Table 2, T means the thickness of the final manufactured ultra-thin glass.

As can be seen in Table 2, the ultra-thin glass prepared according to Examples 1 and 2 was manufactured in the form of a smooth curved edge, the fracture evaluation during the strengthening process was less than 5%, and the bending evaluation was 93% or more showed excellent performance.

On the other hand, as in Comparative Examples 1 to 3, it was confirmed that the relatively sharp side cells were easily cracked and destroyed first.

The above description of the present application is for illustration, and those of ordinary skill in the art to which the present application pertains will understand that it can be easily modified into other specific forms without changing the technical spirit or essential features of the present application. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive. For example, each component described as a single type may be implemented in a dispersed form, and likewise components described as distributed may also be implemented in a combined form.

The scope of the present application is indicated by the following claims rather than the above detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included in the scope of the present application.

100: original glass
10, 20, 30: cell unit glass
11, 21, 31: cut plane
13, 23, 33: glass height

Claims (11)

(a) preparing a plurality of cells by cutting the original glass in cell units;
(b) physically grinding the cut surface of the cell;
(c-1) etching the polished cell; and
(c-2) healing the polished cut surface of the cell
A method of manufacturing an ultra-thin glass comprising a. The method according to claim 1,
The thickness of the ultra-thin glass is 20 to 200 μm, the method of manufacturing an ultra-thin glass. The method according to claim 1,
The thickness of the original glass is 100 to 700 μm, the method of manufacturing an ultra-thin glass. The method according to claim 1,
The step (b) comprises processing the cut surface of the cell in a round shape, a method of manufacturing an ultra-thin glass. The method according to claim 1,
In the step (c-1), the polished cell is ultra-thinned with an etchant, a method of manufacturing an ultra-thin glass. 6. The method of claim 5,
The etching solution is hydrofluoric acid (HF), ammonium fluoride (NH ₄ F), ammonium hydrogen fluoride (NH ₄ HF ₂ ), sodium fluoride (NaF), sodium hydrogen fluoride (NaHF ₂ ), lithium fluoride (LiF), potassium fluoride (KF) ) and calcium fluoride (CaF ₂ ) The method for producing an ultra-thin glass comprising at least one selected from the group consisting of. The method according to claim 1,
A method of manufacturing an ultra-thin glass comprising simultaneously performing the step (c-1) and the step (c-2). The method according to claim 1,
After step (c-2), (d) washing; (e) chemical fortification; (f) chemical polishing, and at least one step selected from a combination thereof, the method for producing an ultra-thin glass. 9. The method of claim 8,
The (f) chemical polishing step, characterized in that the polishing step so that the thickness of the ultra-thin glass after chemical polishing is 80% or more and less than 100% of the thickness of the ultra-thin glass before chemical polishing, the ultra-thin glass manufacturing method. The ultra-thin glass manufactured by the method according to any one of claims 1 to 9. 11. The method of claim 10,
The ultra-thin glass has a thickness of 20 to 200 μm, and is characterized in that the side has a round shape having a predetermined curvature, the ultra-thin glass.

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