KR20210070722A - Ultra thin glass that protecting the flexible display surfaces - Google Patents

Abstract

The present invention relates to an ultra-thin glass that protects the surface of a flexible display used for a display of an in-folding method smart phone. The thickness of the ultra-thin glass is 15 to 65 μm, and the ultra-thin glass is strengthened by heating, aging, and cooling steps. In order to protect the surface of the flexible display used as a smartphone screen by using the ultra-thin glass having the thickness of 15 to 65 μm, an optimized heat treatment process with improved properties of the ultra-thin glass is secured.

Description

ULTRA THIN GLASS THAT PROTECTING THE FLEXIBLE DISPLAY SURFACES

The present invention relates to an ultra-thin glass that protects the surface of a flexible display, and chemically polishes a relatively thin glass of about 70-400 μm produced for smartphones to have a thickness of 15-65 μm. It relates to an ultra-thin glass that protects the surface of a flexible display to be made of a protective glass that protects the flexible display after being made of thin glass, UTG) and then subjected to heat treatment to strengthen the ultra-thin glass.

Since 2019, global smartphone manufacturers have started developing and mass-producing foldable phones in earnest, and interest in companies that supply parts related to foldable phones is growing. Therefore, domestic and foreign companies are preparing parts for foldable smartphones, and there are currently many companies that use transparent polyimide (Colorless PI, CPI) rather than glass for the cover that protects the display surface due to the nature of the foldable. In the case of glass, the elastic limit is low, so the current technology is not suitable as a cover for a foldable display. In fact, metal and glass show a low elastic limit of less than 0.5%, but in the case of plastic film, it is 5%, showing an elastic limit 10 times that of metal and glass.

However, in order to produce a CPI film with film characteristics, a hard coating operation is required on the base film. However, even after hard coating, as long as the matrix is a film, there are limitations no matter how good the CPI film is.

Of course, in Korean Patent Registration No. 10-1557307, "In the display cover glass; it consists of tempered glass and a printed film bonded to the tempered glass, wherein the printed film is attached to the tempered glass through a glass adhesive layer, and the The printing film forms a printing layer on the edge of the opposite side of the glass adhesive layer by printing, and a printing release paper is attached to the upper surface of the printing layer, and the central part of the printing film corresponding to the screen projection area of the display and the printing layer in the central part of the printing film It provides a display cover glass, characterized in that it forms a screen projection area to cut and remove the inner edge of the print layer, and is formed of a print release paper adhered by a print adhesive layer on the upper surface of the print layer.

In addition, in Korean Patent Laid-Open No. 10-2015-0131550, "Glass that forms the exterior of a touch screen panel; an adhesive layer that is transparent and has adhesive properties, one side of which is attached to the surface of the glass 500; the other side of the adhesive layer A printed layer attached to some areas and printed with letters, numbers, patterns, or patterns, and the remaining areas to which the printed layer is not attached are filled with the adhesive layer, so that the area to which the printed layer is attached and the area to which the printed layer is not attached Provides a touch screen panel with a thermal transfer adhesive layer, characterized in that there is no step difference at the boundary between the printed layer and the adhesive layer due to the uniform thickness of the panel.

However, all of the above techniques are related to glass protecting the surface of a conventional flat smartphone display, and thus the above technique cannot be applied to a flexible display.

However, since a product for applying a flexible display to a smartphone has already been released, the development of glass for protecting the surface of the flexible display for a smartphone is urgently needed.

Cited Document 1: Republic of Korea Patent No. 10-1557307, registration date (September 25, 2015) Cited Document 2: Korea Patent Publication No. 10-2015-0131550, publication date (November 25, 2015)

An object of the present invention is to provide a glass for protecting the surface of the flexible display in a smart phone employing a flexible display, and for this purpose, a thin glass is chemically polished to make ultra thin glass (UTG) and plastic properties This is to provide an ultra-thin glass capable of protecting the surface of the flexible display by going through a processing process such as heat treatment to have it as a result.

The object is, in the ultra-thin glass to protect the surface of the flexible display used for the display of the in-folding method smart phone, the thickness of the ultra-thin glass is 15 ~ 65 ㎛, the ultra-thin glass is a temperature raising step, This is achieved by strengthening the aging phase and cooling phase.

And, the stress of the ultra-thin glass is characterized in that 400 Mpa ~ 800 Mpa, the elastic limit of the ultra-thin glass is 1.5% to 5%.

In addition, when the side surface of the ultra-thin glass is etched at the boundary of the ultra-thin glass when the edge is processed, let L be the distance at which the ultra-thin glass is etched, and let the thickness of the ultra-thin glass be T, the ratio between the L value and the T value is

1/6 ≤ L/T ≤ 1/2.

In addition, the thickness of the coating to be coated to strengthen the surface of the ultra-thin glass is

1/30 ≤ T1 (thickness of reinforcing coating)/T (thickness of ultra-thin glass) ≤ 15/30

to be.

Meanwhile, in the heat treatment process to strengthen the ultra-thin glass, the cooling rate is from 7.5°C per minute to 25°C per minute.

According to the present invention, an optimized heat treatment process that improves the properties of the ultra-thin glass is secured so that the surface of a flexible display used as a smartphone screen can be protected by using an ultra-thin glass having a thickness of 15 to 65 μm. .

1 is a view of an embodiment showing a method of folding a flexible glass,
FIG. 2 is a diagram of another embodiment of FIG. 1A .
3 is a view of another embodiment when the ultra-thin glass is folded.
4 is a diagram of an embodiment showing a heat treatment step.
5 is a view of an embodiment showing the side processing of the ultra-thin glass.
6 is a view of an embodiment showing a reliability test method in the folding and unfolding process.
7 is a view showing an ultra-thin glass having a multilayer structure.
8 is a diagram of an embodiment showing a practical application example of the present invention.
9 is a view of an embodiment showing the extent to which the ultra-thin glass is stretched.

Hereinafter, an embodiment according to the present invention will be described in detail with reference to the accompanying drawings. The configuration of the present invention and the effects thereof will be clearly understood through the following detailed description.

In addition, a detailed description of the known technical configuration may be omitted.

Meanwhile, in order to obtain the result of the present invention, some of the methods of performing chemical etching or heat treatment may follow conventional general methods.

1 is a view of an embodiment showing a method of folding a flexible glass,

As shown in the figure, in order for the flexible display applied to the in-folding method to be folded, the folding and unfolding operations of the flexible display are performed while the flexible display is relatively fixed to the fixed substrate 20 . will wake up

In addition, the ultra-thin glass of the present invention, which protects the surface of the flexible display applied to the in-folding method, is also fixed to the fixed substrate 20 (a substrate fixed without bending of a metal or plastic material) so that folding and unfolding operations occur. it can only be

Therefore, experiments such as measuring the radius of curvature of the ultra-thin glass 10 developed in the present invention and some reliability tests were conducted in the method of the embodiment of FIG. 1 .

And, the value of the gap G between the substrates shown in FIG. 1A is determined according to the radius of curvature of the ultra-thin glass 10 . That is, as shown in FIGS. 1 (B) and 1 (C), the two fixed substrates 20 are rotated and moved to be folded, and the ultra-thin film attached to the two fixed substrates 20 The glass 10 is also folded together.

However, in the ultra-thin glass 10 , since one substrate is folded, the G value exists because the radius of curvature must exist at least.

That is, even in the process in which the ultra-thin glass 10 is completely folded, there is a region that maintains a flat state as it is, and there is a folded region, where the distance of the folded region of the ultra-thin glass 10 is the G value.

FIG. 2 is a diagram of another embodiment of FIG. 1 ;

1 (A) is an embodiment in which the interval between the two fixed substrates 20 is spaced apart by G, but FIG. 2 is an embodiment in which the two fixed substrates 20 are in contact with each other. However, the gap G also exists in FIG. 2 .

That is, when the two fixed substrates 20 are in contact with each other, the fixed region and the non-fixed region by the interval G exist. In the fixed area shown in FIG. 2, the ultra-thin glass 10 is fixed to the fixed substrate 20 by an adhesive or fixing means, but in the non-fixed area (gap G) shown in FIG. 2, the ultra-thin glass 10 is fixed. It is not fixed to the substrate 20 (or is not adhered), but only in a state of being placed on it.

And, in the embodiment of Fig. 2, as in Figs. 1 (B) and (C), when the two fixed substrates 20 are rotated and folded, the ultra-thin glass 10 provided on the fixed substrate 20. will also be folded.

On the other hand, if the two fixed substrates 20 are spaced apart from each other by a distance less than the G value, the ultra-thin glass 10 and the fixed substrate 20 are fixed to each other in the region existing within the G value. It is not attached (not glued).

3 is a view of another embodiment when the ultra-thin glass is folded.

In order for the ultra-thin glass 10 of the present invention to be used in an actual flexible display, the ultra-thin glass 10 is placed on the display unit 50 to be used.

In this case, the display unit 50 shown in FIG. 3 of the present invention means a foldable flexible display and an input device (touch panel) provided thereon.

And, when the two fixed substrates 20 are rotated and folded in the embodiment of FIG. 3 as in the embodiment of FIG. 1 , the ultra-thin glass 10 and the display unit 50 are also folded together.

On the other hand, since the achieved R value is 5.0 or 4.6 in the case of an in-folding flexible display that has already been commercialized and released, the R value of the ultra-thin glass 10 developed in the present invention must also be at least 5.0 or 4.6 or less.

In addition, in the embodiment of Fig. 3, the fixed substrate 20 can be set as the example of the embodiment of Fig. 2, and in this case, the adhesive is not coated between the display unit 50 and the fixed substrate 20 in the non-fixed area. do.

- Manufacture of ultra-thin glass -

Although the thickness of the glass sold by companies that produce glass used to protect the surface of the smartphone display is generally about 400 μm, recently, it is produced and sold to 200 μm or less or even 70 μm.

However, the glass having the above thickness does not serve as a glass that protects the surface of the flexible display. Therefore, it is necessary to manufacture the ultra-thin glass 10 having a desired thickness through an additional polishing process.

For the polishing process, physical polishing is also used, and although physical polishing is a very difficult and laborious task, it is a technique that can be performed by a company that has been in our processing industry for a long time.

On the other hand, a polishing process mainly used to make ultra-thin glass is a method of chemical etching using a hydrofluoric acid solution, which is a process generally used in the prior art. Therefore, it is possible to make the glass having a thickness of 400 μm, 200 μm, or 70 μm into ultra-thin glass having a desired thickness by a conventional chemical polishing method.

However, in order to protect the surface of the flexible display while the ultra-thin glass has plastic properties and is folded to an R value of 5.0 R or 4.6 R or less or less, the etched and polished ultra-thin glass must be strengthened. .

- Reinforcement process of ultra-thin glass -

The conventionally generally known strengthening process of ultra-thin glass is a process of precipitating ultra-thin glass processed to a desired thickness in a reinforcing solution and then performing heat treatment in 5 minutes.

As the fortification solution, sodium nitrate (NaNO ₃ ), potassium nitrate (KNO ₃ ) are mainly used, _{and a small amount of silicic acid (H 2} SiO ₃ ), etc. is added and used.

4 is a diagram of an embodiment showing a heat treatment step.

As shown in FIG. 4 , the heat treatment process is divided into three steps: a temperature increase process, an aging process, and a cooling process. And, since this process is a conventional process, in the present invention, a method of a new temperature condition is found to improve the properties of the ultra-thin glass.

Through various trials and errors in the past, the optimized heat treatment conditions were found for 2 hours of heating time, 2 hours of aging at 400° C., and cooling within 30 minutes. And, in the present invention, in order to drastically reduce the number of experiments, an appropriate R value and an appropriate thickness are determined in advance to manufacture an ultra-thin glass 10 having a suitable thickness, and the manufactured ultra-thin glass can have an appropriate R value. A method of developing process conditions for heat treatment was used.

An appropriate thickness of the ultra-thin glass 10 was set to 30 μm, and an appropriate R value was set to 2. The predetermined value of 30 μm is a value determined in consideration of the thickness of the protective film used in the flexible display, and the determined 2 R value is 5, 0 or 4.6, so that the R value of the commercially available flexible display is 5, 0 or 4.6, so that it is applicable here. An appropriate R value was determined.

On the other hand, with the sold glass having a thickness of 100 μm or more, a polishing process is performed using a hydrofluoric acid solution, and the ultra-thin glass having a thickness of 30 μm is manufactured by repeatedly performing several times.

At this time, as described above, the optimized heat treatment temperature and aging time conditions are as follows.

- Time of temperature increase step: 2 hours

- Aging temperature: 2 hours at 400 ℃

- Time of cooling phase: 30 minutes to room temperature (25℃)

That is, the temperature increase rate in the temperature raising step is 3.13 °C per minute, and the cooling rate per minute in the cooling stage is 12.5 °C.

On the other hand, the environment of the heat-treated paper oven is an environment in which a vacuum or an inert gas is present.

- Reinforcement Experiment -

After immersing 30 μm thick ultra-thin glass in the reinforcing solution, heat treatment of 30 μm-thick ultra-thin glass under the above temperature conditions, and then folding it to a value of 2 R, cracked and failed.

In order to overcome the failure, I thought of quenching the iron, and eventually came to think of a method of repeated heat treatment.

And, by repeating the heat treatment process from 1 to n times, the ultra-thin glass was found to be folded without cracking even at a value of 2R.

1) After cutting the ultra-thin glass having a thickness of 30 μm into 10 cm and 15 cm in width and length, respectively, a heat treatment process is performed.

2) After performing the heat treatment process once, the ultra-thin glass was folded to a value of 2R, but cracks occurred,

3) After repeating the experiment 2) 5 times, the ultra-thin glass was folded to a value of 2 R, and as a result, the ultra-thin glass was folded to a value of 2 R.

That is, as a result of performing the heat treatment process 5 times with the ultra-thin glass having a thickness of 30 μm, the result of folding the ultra-thin glass to a value of 2 R was obtained.

When repeated 6 times, more stable folding results were obtained, but no significant problems were observed even after repeated 5 times.

4) The aging temperature may vary depending on the conditions for n repeated experiments. And the aging temperature is not necessarily limited to the 400 ℃, that is, the temperature for one heat treatment may be 450 ℃, the second heat treatment temperature may be 390 ℃. And from the third time, the heat treatment temperature can be set to 400°C, and can be changed based on 400°C.

- How to get the optimized thickness -

1) Ultra-thin glass with a thickness of 65 μm:

As a result of performing the heat treatment process 8 times, it was successful in folding to a value of 4.6R,

However, the 65 μm thickness can be seen as the limit thickness for commercialization, and it was determined that there is a problem in commercialization to make it thicker, so that the experiment was conducted only up to a thickness of 65 μm.

2) Ultra-thin glass with a thickness of 50 μm

As a result of performing the heat treatment process 7 times, it was successful in folding to a value of 4.6R.

3) Ultra-thin glass with a thickness of 40 μm

As a result of performing the heat treatment process 6 times, it was successful in folding to a value of 3.5R.

3) Ultra-thin glass with a thickness of 20 μm

As a result of performing the heat treatment process 6 times, it was successful in folding to a value of 2.0R.

3) Ultra-thin glass having a thickness of 15 μm

As a result of performing the heat treatment process 7 times, it was successful in folding to a value of 2.0R.

4) Ultra-thin glass with a thickness of 10 μm

Even when the heat treatment process was tested up to 8 times, cracks occurred in the process of folding to a value of 2.0R.

Therefore, when the ultra-thin glass (thickness of 15 μm to 65 μm) is heat-treated by the above method to have a value of 2 R or less than 5,0 R or 4.6 R, which has already been commercialized as a flexible display, the above-mentioned R value is was found to be achievable.

On the other hand, in the case of the substrate capable of 2R, it was only folded up to 2R in consideration of stability, and when it was folded stably in 2R, it was stably folded even at 1.5 R. This was the case in the patent 20 μm substrate.

- Various temperature conditions -

When the heat treatment temperature of ultra-thin glass with a thickness of 30 μm was 400° C., the cooling rate was changed.

The temperature increase rate in the temperature increasing step used in the heat treatment process in the previous embodiment of the present invention is 3.13 °C per minute, and the cooling rate per minute in the cooling step is 12.5 °C. And the aging temperature was 2 hours at 400 degreeC.

The temperature at which the glass is heat treated is not necessarily limited to 400°C, and the temperature could be achieved from 250°C to 450°C.

1) In the previous embodiment of the present invention, the aging temperature was 400°C. And, the cooling time reached from 400°C to 25°C was changed to 40 minutes. When the cooling time was changed to 40 minutes, the cooling rate was 9.4°C per minute.

And, when the cooling rate is 9.4°C per minute and the other heat treatment is performed under the same conditions, the temperature raising step, the aging step, and the cooling step are 1 cycle, and the 1 cycle is repeated 7 times. As a result, a thickness of 30 μm is obtained. It was possible to fold the excitation ultra-thin glass to 2R.

2) The cooling time from 400°C to 25°C was changed to 50 minutes. When the cooling time was changed to 50 minutes, the cooling rate was 7.5° C. per minute.

In addition, when the cooling rate is 7.5° C. per minute and other heat treatments are performed under the same conditions, the temperature raising step, aging step, and cooling step are 1 cycle, and as a result of repeating the 1 cycle 10 times, the thickness of 30 μm It was possible to fold the excitation ultra-thin glass to 2R.

However, repeating up to 10 times is reasonable, considering that there is a problem with practicality. However, it can be said that folding with 2 R was successful.

3) The cooling time from 400°C to 25°C was changed to 20 minutes. When the cooling time was changed to 20 minutes, the cooling rate was 18.75° C. per minute.

And, when the cooling rate is 18.75° C. per minute and other heat treatment is performed under the same conditions, the temperature rising step, aging step, and cooling step are 1 cycle, and the result of repeating the 1 cycle 4 times is 30 μm thick. It was possible to fold the excitation ultra-thin glass to 2R.

3) The cooling time from 400°C to 25°C was changed to 15 minutes. In this case, the cooling rate was 25.0° C. per minute.

And, when the cooling rate is 25.0° C. per minute and other heat treatment is performed under the same conditions, the temperature raising step, aging step, and cooling step are 1 cycle, and the result of repeating the 1 cycle 3 times is 2 R. it was possible But soon cracks arose. However, folding with 2 R can be said to have been successful.

4) The cooling time from 400°C to 25°C was changed to 10 minutes. In this case, the ultra-thin glass was cracked. The cooling rate was 37.0° C. per minute.

As a result, after performing the aging process in the present invention, the cooling rate for cooling was appropriate at 7.5°C to 25°C per minute. And it can be expressed as follows.

7.5°C per minute ≤ Cooling rate ≤ 25°C per minute

On the other hand, in the case of the substrate capable of 2R, it was only folded up to 2R in consideration of stability, and when it was folded stably in 2R, it was stably folded even at 1.5 R. This was the case in the patent 20 μm substrate.

5 is a view of an embodiment showing the side processing of the ultra-thin glass.

In order to prevent cracking of the glass, it is also one of the important issues to process the edge of the glass side.

Edge processing on the side of the glass will also use a conventional general method. That is, the etching is performed using the hydrofluoric acid solution, but the portion that does not require etching is masked so that the etching is not performed.

Patent In this case, instead of using only one glass, 10 or 20 ultra-thin glasses are stacked, and then the side part is immersed in hydrofluoric acid to etch.

As shown in FIG. 5 , when the thickness of the ultra-thin glass 10 is T and the distance L is etched at the boundary of the ultra-thin glass, the correlation ratio is important.

When the thickness of the glass is 30 μm, the value of the distance L is preferably 10 μm. Therefore, the value of L/T becomes 1/3.

However, when the side surface of the ultra-thin glass is actually processed, errors in the machining process exist, and thus, these errors can be considered and the level of the degree to which the problem caused by the edges of the ultra-thin glass is eliminated. That is, even if the L value was 5 μm, there was no problem in actual use, and even 15 μm was not obtained at a level that was too difficult.

No problem above means that folding from 2R (or 1.5R) to 5R does not cause cracking. Cracks are the biggest cause of breakage in the process of folding ultra-thin glass, and even very small micro-cracks can cause breakage.

Accordingly, the range of the L value is 5 µm to 15 µm.

As a result, in the processing of the side edge of the ultra-thin glass, when the thickness of the ultra-thin glass is T and the distance at which the etching is performed at the boundary of the ultra-thin glass is L, the value of the ratio of the T value and the L value is as follows same.

1/6 ≤ L/T ≤ 1/2 (L/T value is greater than or equal to 1/6 and less than or equal to 1/2)

6 is a view of an embodiment showing a reliability test method in the folding and unfolding process.

A reliability test may be performed by actually applying the ultra-thin glass of the present invention to a smart phone employing a flexible display, but since it may be difficult in reality, the reliability test may be performed by imitating the structure when applied to a flexible display.

That is, the drawing of FIG. 6 is a diagram of an embodiment showing a reliability test method manufactured by imitating the structure of a folding smartphone that is actually folded and unfolded.

Two test boards 70 that can be folded and unfolded by rotating 180 degrees and 0 degrees are provided, and on the test board, the ultra-thin glass 10 is mounted as in the embodiment of FIG. 1 (or the embodiment of FIG. 2 ) do.

And, as shown in FIG. 6 , the test protrusion 71 is mounted on the boundary of the test substrate 70 . The test protrusion 71 is a protrusion protruding to a certain height, therefore, due to the test protrusion 71 . As in the embodiment of FIG. 1(C) or the embodiment of FIG. 2(C), the ultra-thin glass 10 is folded with a predetermined value of curvature. In addition, the height value of the test protrusion 71 is adjustable,

In addition, the presence of the second protrusion 72 prevents the folded ultra-thin glass 10 from contacting each other.

As a result, the second protrusion 72 is formed to be higher than the ultra-thin glass 10, and the first protrusion 71 is formed to be higher than the second protrusion.

The ultra-thin glass 10 of the present invention is mounted (attached with a thermoplastic resin) to the device of the embodiment of FIG. 6 . Therefore, when heat is applied, the ultra-thin glass 10 can be easily separated from the test substrate 70 . ), and by connecting the electric device to the test board 70 and repeating folding and unfolding operations, it is possible to determine reliability.

At this time, considering the process of the operation of actually opening and closing the flexible display user, the time taken to fold and unfold the unfolded ultra-thin glass 10 was set to 1.5 seconds, and a reliability test was conducted.

On the other hand, assuming that it is opened and closed 20 times a day and used for 3 years, reliability can be secured by repeating the folding and unfolding operations up to 20,000 times in the method shown in the embodiment of FIG. 6 . And, it takes 8.33 hours to repeat the folding and unfolding action 20,000 times within 1.5 seconds.

And, the experiment of the present invention is to fold continuously for 20,000, and thus, in the folding process, the vibration energy generated when folding before is not zero, that is, in a state in which the vibration energy remaining when previously folded exists. The vibrational energy that is generated will be generated again. Therefore, it can be said that the continuous test of 20,000 times shows reliability when folded 40,000 times (more than twice as much as 20,000 times) in actual use. Of course, continuous numerical experiments will be necessary for this.

- Characteristic values of ultra-thin glass -

1) Stress value

The stress value of the glass that protects the conventional smartphone display was requested by the set company at 650 Mpa and 800 Mpa, respectively. However, the stress value of the ultra-thin glass that protects the flexible display cannot be as high as the stress value that protects the conventional smartphone display.

In the present invention, as a result of testing as an ultra-thin glass having 30 μm, it had a stress value of 450 Mpa, and as a result of testing the operation of folding and unfolding by the method of the embodiment of FIG. 6 (based on 3 R), the folding and unfolding operation 20,000 rounds were possible.

Therefore, the stress value of the ultra-thin glass 10 for protecting the flexible display is preferably 250 Mpa or more. However, the maximum value can be said to be 800 Mpa because it does not need to be greater than the stress value that protects the conventional smartphone display screen.

As a result, it can be said that the stress value of the ultra-thin glass presented in the present invention is 450 Mpa to 800 Mpa.

For the measurement of the stress value, a measuring device manufactured by RIHARA (Surface Stress Merer) of Japan is generally used, and the same is true in the present invention.

In the present invention, the DOL value was also measured. And the measured values for each thickness were as follows.

15 µm: 5 to 7. 20 µm: 6 to 8, 30 µm: 7 to 10, 40 µm: 9 to 13, 50 µm: 10 to 15, 65 µm: 14 to 17

Therefore, the range of the DOL value in the present invention is 5 to 17 when the range of the ultra-thin glass is 15 µm to 65 µm.

2) Elastic limit

Glass generally shows a low elastic limit of less than 0.5%, but in the case of a plastic film, it shows an elastic limit 10 times that of glass at 5%. Therefore, even if the elastic limit of the ultra-thin glass 10 manufactured in the present invention is not as high as the plastic film, it should be at a level exceeding the range of the elastic limit of the conventional glass.

As a result of measuring the elastic limit of the 30 μm thick ultra-thin glass prepared in the present invention, it was found that the value was increased to 1.5%, and folded and unfolded up to 20,000 times in the experiment by the method of the example of FIG. 6 . was possible.

And, the heat treatment process used in the previous embodiment of the present invention was performed more than 5 times. That is, as a result of repeated experiments up to 10 times, the elastic limit was increased to 2.5%.

As a result, it was found that the properties of the ultra-thin glass were improved by repeating the heat treatment process.

On the other hand, since the elastic limit of the glass cannot go beyond the level of the plastic film, in the present invention, it can be said that the elastic limit value of the ultra-thin glass protecting the flexible display surface is from 1.5% to 5%.

- Surface coating -

Since the glass that protects the display surface in the smartphone is exposed to the outside as it is, the glass should be coated on the surface.

As the type of coating, a protective film may exist to protect consumers when the ultra-thin glass ruptures, AF coating, etc. may be applied, and a reinforcing coating may also be applied.

On the other hand, the level of the reinforced coating thickness of the conventional smartphone was 20 μm to 45 μm. However, since the thickness of the ultra-thin glass protecting the flexible display is thin, the thickness of the reinforcing coating cannot be used as it is.

Reinforcement coating was applied with ultra-thin glass having a thickness of 30 μm. 2 When folded at the R level, the range was set to a level where there was no uniformity, and the range was set.

The thickness of the reinforcing coating was coated at a level of 1 μm, and the coating was performed in 2 μm steps from 2 μm to 16 μm, and then it was judged whether cracks occurred when folded at the 2 R level.

When the thickness of the reinforcing coating was varied from 2 μm to 12 μm, cracks did not occur when folded at the 2 R level, but cracks occurred when the coating was 16 μm. Naturally, even at the time of 1 μm coating, it was folded to the level of 2 R.

Therefore, in the present invention, when the thickness of the reinforcing coating was from 1 μm to 15 μm, an ultra-thin glass that protects the surface of the flexible display was possible.

As a result, the range of the thickness for applying the reinforcement coating is as follows.

1/30 ≤ T1 (thickness of reinforcing coating)/T (thickness of ultra-thin glass) ≤ 15/30

In this case, the coating may be a film attached to the ultra-thin glass. That is, various types of transparent films may be used, and for example, a CPI film may also be used.

7 is a view showing an ultra-thin glass having a multilayer structure.

A common common knowledge known to those who study film layers is that "even if the total thickness is the same, the tensile strength is better when two or three films are used and overlapped rather than one film".

In the present invention, an attempt was also made for this.

That is, as in FIG. 7 , the first ultra-thin glass 10-1 and the second ultra-thin glass 10-2 are provided, and the first ultra-thin glass 10-1 and the second ultra-thin glass 10 are provided. The adhesive layer 15 is formed between -2).

In addition, another resin film layer may be present in the adhesive layer.

At this time, in the present invention, it is an object to manufacture an ultra-thin glass for protecting the flexible display surface, and thus, the ultra-thin glass 10 (10-1) (10-2) of the present invention is also folded. Accordingly, in the ultra-thin glass 10, 10-1, and 10-2 of the present invention, there are a folded region (non-fixed region) and an unfolded region (fixed region).

And, in FIG. 7 , the folded area (non-fixed area) is a section marked with G shown in the embodiment of FIG. 1 .

Naturally, the adhesive must also show a difference in adhesive strength in the folded area (non-fixed area) and the non-folded area (fixed area). That is, it can be expressed as

Adhesive force of the adhesive in the folded area (non-fixed area) < Adhesive force of the adhesive in the unfolded area (fixed area)

That is, the "adhesive force of the adhesive in the folded region (non-fixed region)" is weaker than the "adhesive force of the adhesive in the non-folded region (fixed region)".

On the other hand, when actually coating the adhesive, it becomes difficult to accurately distinguish and coat the boundary between the folded region (non-fixed region) and the non-folded region (fixed region). Visible does not mean exactly dividing boundaries. That is, it will be understood that the adhesive force of the adhesive mainly coated on the folded region (non-fixed region) is weaker.

8 is a diagram of an embodiment showing a practical application example of the present invention.

Attaching the ultra-thin glass 10 (or the ultra-thin glass 10-1, 10-2) having multiple layers of the present invention to the display unit 50 (the part including the display and the input device) of the flexible display will do

At this time, as in the embodiment of FIG. 7 , there are a fixed region and a non-fixed region, and even at this time, the adhesive force of the adhesive used in the non-fixed region is weaker as in the embodiment of FIG. 7 .

9 is a view of an embodiment showing the extent to which the ultra-thin glass is stretched.

If R is 1.5 and the thickness of the ultra-thin glass is 30 μm, the length of the ultra-thin glass on the outer surface is compared to the distance between the inner surface of the ultra-thin glass and the outer ultra-thin glass. should be increased by 4% compared to the length of the ultra-thin glass present on the inner surface,

In addition, when R is 5 and the thickness of the ultra-thin glass is 65 μm, when comparing the distance between the surface of the ultra-thin glass existing inside and the ultra-thin glass existing on the outside, the The length should be increased by 2.6% over the length of the ultra-thin glass present on the inner surface,

As a result, in the present invention, the outer surface should be increased by 2.6% to 4% than the inner surface as it is folded.

10: ultra-thin glass 20: fixed substrate
50: display unit 70: test board
71: test protrusion 10-1: first ultra-thin glass
10-2: second ultra-thin glass 15: adhesive

Claims (6)

In the ultra-thin glass that protects the surface of the flexible display used in the display of the in-folding method smartphone,
The thickness of the ultra-thin glass is 15 μm to 65 μm,
The ultra-thin glass is an ultra-thin glass for protecting the surface of a flexible display, characterized in that it is strengthened by a temperature raising step, an aging step, and a cooling step. The ultra-thin glass for protecting the flexible display surface according to claim 1, wherein the stress of the ultra-thin glass is 450 Mpa to 800 Mpa. The ultra-thin glass for protecting the flexible display surface according to claim 1, wherein the elastic limit of the ultra-thin glass is 1.5% to 5%. According to claim 1, When the ultra-thin glass side is processing the edge,
When the etched distance at the boundary of the ultra-thin glass is L and the thickness of the ultra-thin glass is T, the ratio between the L value and the T value is
1/6 ≤ L/T ≤ 1/2
Ultra-thin glass to protect the surface of the flexible display, characterized in that. According to claim 1, wherein the thickness of the coating coating the surface of the ultra-thin glass is
1/30 ≤ T1 (thickness of coating)/T (thickness of ultra-thin glass) ≤ 15/30
Ultra-thin glass to protect the surface of the flexible display, characterized in that. The ultra-thin glass for protecting the flexible display surface according to claim 1, wherein, in the heat treatment process to strengthen the ultra-thin glass, the cooling rate is from 7.5°C per minute to 25°C per minute. .

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