KR20220028493A - Cover window for flexible diplay - Google Patents

Abstract

The present invention relates to: protective glass for a flexible display, which is provided in a multilayer structure to be used as protective glass for a flexible device; a manufacturing method thereof; and a multilayer glass structure using the same. The present invention is to reduce display quality deterioration caused by wrinkle marks in a bent part, which have been pointed out as disadvantages of conventional flexible glass, and different refractive indices appearing in multi-thickness glass to compensate the same. Specifically, flexible glass is formed by stacking a plurality of glass sheets with a transparent adhesive material such as an optically clear adhesive (OCA), an optically clear resin (OCR), and poly vinyl butyral (PVB), and thus resilience after bending is increased and display quality is increased in comparison with the existing flexible display structure. In addition, as materials of the same thickness are laminated rather than materials of multiple thicknesses, an excellent touch feeling can be provided during use with an electronic pen and the like, and the present invention can contribute to speeding up arrival of various flexible display markets (smartphones, tablet PCs, laptops, wearable devices, etc.). The cover window comprises a plurality of glass sheets and one or more adhesive layers.

Description

COVER WINDOW FOR FLEXIBLE DIPLAY

The present invention relates to a cover window for a display, and more particularly, to a glass-based cover window applied to a flexible display.

Recently, as a major change in the display market, a field using a flexible display is in the spotlight. Flexible displays are being commercialized in various forms, such as stretchable, rollable, or foldable devices, and it has become possible to manufacture smartphones, tablet PCs, notebooks, etc. using the flexible displays. By implementing the flexible display, it is possible to dramatically reduce the volume of the user to carry and use various electronic products.

Such a flexible display should be formed to be flexible not only the display panel but also the cover window for protecting it. That is, the cover window for a flexible display should have excellent flexibility and should not generate marks on the folding part even after repeated folding. Initially, flexible polymer sheets such as PET were attempted to be applied as cover window materials for flexible displays, but whitening occurred in the bent part due to repeated bending. CPI (Clear Polyimide) with improved characteristics was applied. However, due to the limitations of polymer properties, when applied to touch screens, these materials have poorer touch and texture compared to glass, and their low hardness makes them vulnerable to external shocks such as scratches, as well as low light transmittance and wrinkle marks due to folding. There are several problems with poor quality, and a lot of research and development has been made on the application of a tempered glass-based cover window, which has been most widely applied as a smartphone cover, as a cover window for a flexible display, and it has been applied to an initial foldable phone.

Currently, in the case of a glass-based flexible display cover window, the bending radius of the folding part can be bent to 2 mm or less, and it is known that it is suitable for commercialization only when it has durability that does not break at 200,000 repeated bending times. In order to realize a radius of curvature of 2 mm, the thickness of the glass must be very thin, about 30 μm. However, if the thickness of the glass is thinned to about 30 μm and applied to the cover glass in order to give flexibility, it cannot sufficiently withstand the compressive or impact stress applied when using the pen for handwriting recognition, so that the cover glass is more likely to be destroyed. do. When a protective film is attached to the upper surface or upper and lower surfaces of the cover glass in order to prevent the glass breakage, the elastic restoring force of the glass is relatively weakened, so it is difficult to avoid the side effect of leaving wrinkles in the folding part due to the repeated bending operation. Therefore, in order not to break when applying such a writing implement and to prevent wrinkles occurring during repeated bending, it is preferable that the thickness of the glass be about 100 μm, but the thickness of the chemically strengthened aluminosilicate-based glass applied as a flexible display cover is 100 μm. In order to implement a 2.0 mm radius of curvature, it is very difficult to actually implement it because it is a task to simultaneously improve two opposite properties of flexibility and rigidity.

An example of a method for overcoming the limitations of conventional glass-based flexible display product development and commercialization is disclosed in Korean Patent Nos. 10-2068685 and 10-2069040. According to the patents, a transparent resin such as OCR ( 300) to maintain the inherent strength and texture of glass to some extent and to satisfy both flexibility and restoration properties in the folding part, which is a problem in applying to flexible displays or their cover windows, at the same time. there is. 1 shows a cross-sectional structural diagram of a glass-based cover window in which the resin 300 is filled in the folding part of the thinly processed tempered glass 200 according to the Republic of Korea Patent Nos. 10-2068685 and 10-2069040 .

However, in the case of the flexible cover window according to the Republic of Korea Patent Nos. 10-2068685 and No. 10-2069040, a process of selectively processing only the folding part should be added, and the resin 300 and the tempered glass ( 200) due to the difference in refractive index between the interface, the display quality in the corresponding folding part may be sharply deteriorated by recognizing the interface or distorting the image. Also, during repeated folding operations, the resin 300 and the tempered glass ( 200) It is difficult to become a realistic method for commercialization of a glass-based flexible display because another problem, such as the tempered glass 200 may be damaged, may be complicatedly accompanied by interfacial separation between the 200).

Republic of Korea Patent No. 10-2069040 Republic of Korea Patent Registration No. 10-2068685

The present invention maintains the inherent strength, texture (touch feeling) and display quality of glass, has sufficient bendability and flexibility to be applied to a flexible display cover, and has impact resistance so that it is not damaged even when an external impact is applied by a writing input tool, etc. It is to provide this reinforced glass-based cover window.

In the process of researching and developing the glass-based cover window related to the above-mentioned problem, the present inventors have discovered that the damage that occurs when an external shock is applied by a writing recognition tool in the cover window disposed on the front of the flexible display is the thickness of the glass. For example, since it is an excessively thin phenomenon of about 30 μm or less, in order to improve this, it is ideal to improve the tempered glass component and the manufacturing process. Focusing on the multi-layer stacking of a plurality of relatively thin glass sheets, in the case of a cover window structure including the multi-layered glass sheets, each glass sheet layer is thin, so it can be bent with excellent flexibility and usually The present invention was reached by discovering that impact strength could be increased similarly to laminated glass used by bonding two or more sheets of glass. The gist of the present invention based on the recognition and conception of these problems is the same as described in the claims as follows.

(1) A cover window for a glass-based flexible display, comprising: a plurality of glass sheets; and one or more adhesive layers provided between the plurality of glass sheets to integrally bond adjacent glass sheets to each other, wherein the thickness of the glass sheet composite in which the plurality of glass sheets and the adhesive layer are integrated is 65 to 180 μm Features a cover window.

(2) The cover window of (1), characterized in that each of the glass sheets has a thickness of 30 ~ 65㎛.

(3) When one of the plurality of glass sheets that is to be adhered to the display is used as the lower glass sheet, and the outermost one is the upper glass sheet after being adhered to the display, the thickness of the lower glass sheet is thicker than the upper glass sheet The cover window of (1) above.

(4) When one of the plurality of glass sheets that is to be adhered to the display is used as the lower glass sheet and the outermost one is the upper glass sheet after being adhered to the display, the thickness of the upper glass sheet is thicker than the lower glass sheet The cover window of (1) above.

(5) The cover window of (1), wherein the adhesive layer is a transparent bonding material selected from optically clear adesive (OCA), optically clear resin (OCR), and poly vinyl butyral (PVB).

(6) The cover window of (1), characterized in that the thickness of the adhesive layer is 5 ~ 50㎛.

According to the present invention, as a cover window that maintains the inherent strength, texture (touch feeling) and display quality of glass, in particular, it satisfies sufficient flexibility to enable folding to a very small radius of curvature of less than 2.0 mm, which is commercially available. At the same time, it is possible to provide a glass-based cover window that can be advantageously applied to a flexible display by improving the impact resistance so as not to be damaged even by an impact by a writing recognition tool or the like. In addition, the glass-based cover window according to the present invention is easy to manufacture and can have an excellent product yield because it does not involve a high-difficulty processing process of locally producing different thicknesses of tempered glass, unlike in the prior art.

1 is a cross-sectional structural view of a glass-based flexible display cover window in a form in which a resin is filled in a folding part of a thinly processed tempered glass according to the prior art;
2 is a structure of a cover window for a glass-based flexible display according to an embodiment of the present invention;
3 to 5 are views showing results of a ball drop test, a compressive stress test, and a bending test for a cover window according to an embodiment of the present invention and a comparative example;

Hereinafter, the present invention will be described in detail through examples. Prior to this, the terms or words used in the present specification and claims should not be construed as being limited to conventional or dictionary meanings, and the inventor should properly understand the concept of the term in order to best describe his invention. Based on the principle that can be defined, it should be interpreted as meaning and concept consistent with the technical idea of the present invention. Accordingly, since the configuration of the embodiments described in this specification is only one of the most preferred embodiments of the present invention and does not represent all the technical spirit of the present invention, various equivalents that can be substituted for them at the time of filing of the present invention It should be understood that there may be variations and variations. On the other hand, in the drawings, the same or similar reference numbers are given to the same or equivalents, and in the entire specification, when it is said that a part "includes" a certain element, it is a different element unless otherwise stated. It does not exclude, but means that other components may be further included.

Structure of Glass-Based Cover Window

2 shows a structural diagram of a cover window 1 for a glass-based flexible display according to an embodiment of the present invention. The cover window 1 is provided between a plurality of glass sheets 2; 21 and 22; and the plurality of glass sheets 2; 21, 22 to integrally bond adjacent glass sheets 2; 21, 22. At least one adhesive layer (3); includes.

The glass-based cover window 1 according to the present invention is intended to protect the front surface of the display panel, and in particular, it is intended to constitute a flexible display together with the display panel. In this specification, "front" refers to a surface in a direction in which an image is output from the display surface, and the opposite side is referred to as "rear". In addition, "folding area" means an area that is folded or bent in a state applied to a flexible display, and an area excluding this "folding area" is referred to as a "flat area".

The cover window 1 basically has a uniform thickness in the entire area of the folding area and the flat area, but has a flexibility applicable to a flexible display, that is, a glass sheet so that it can be bent and deformed with a radius of curvature of 2.0 mm or less in the folding area. By controlling the thickness of (2; 21, 22) while stacking the glass sheets 2; 21, 22 whose thickness is adjusted in this way in a plurality of layers rather than a single layer, the inherent texture and touch feeling of glass are secured accordingly. , It is characterized in that durability is maintained even with repeated folding operations of more than 200,000 times, and at the same time, damage to the glass is minimized even when an external shock is applied by a writing recognition tool or the like. In some cases, the cover window 1 configured by stacking the plurality of glass sheets 2; 21 and 22 is referred to as a “glass sheet composite”.

The total number of the glass sheets (2; 21, 22) stacked may vary depending on the product for which the display is to be used, and at least two or more are provided. In the case of a mobile product requiring a bending radius of curvature of 2.0 mm in general, two sheets are appropriate, and in the embodiment, two upper and lower glass sheets (2; 21, 22) are stacked with an adhesive layer (3) interposed therebetween. has been For convenience of explanation in the present specification, the glass that is scheduled to be adhered to the display among the plurality of glass sheets 2; 21, 22 is referred to as “lower glass sheet”, and the glass positioned at the outermost portion after being adhered to the display is referred to as “upper glass sheet 21”. called ", respectively.

Each of the plurality of glass sheets 2; 21, 22 does not involve separate processing on the front or back surface of the glass sheet 2 in the folding area, and has a uniform thickness in the entire area including the folding area and the flat area. The thickness of the glass sheets (2; 21, 22) applied to the glass sheet composite is preferably as thick as possible at the same radius of curvature if each glass sheet (2; 21, 22) can implement a radius of curvature of 1.0 to 2.0 mm. . For example, in order not to break the glass sheets (2; 21, 22) at a radius of curvature of 1.0 mm, the thickness of the glass sheets (2; 21, 22) is generally about 30 μm, but if it is possible with a thickness of 38 μm, it is applied to the glass sheet composite. It means 38㎛.

The thickness of each glass that can be applied to the glass sheet composite is based on the experimental results of Table 1 to be described later, and is controlled to be 30 ~ 65㎛ considering the thickness of 30㎛ reported that the radius of curvature is usually 1.0mm. desirable. When the thickness of each glass sheet (2; 21, 22) exceeds 65 μm, the possibility of glass breakage increases when bending to a curvature of 2.0 mm, which is undesirable. It is undesirable because it increases the possibility of breakage.

On the other hand, the adhesive layer 3 serves to protect and buffer the glass sheets 2; 21 and 22 from impacts caused by external forces such as bending while bonding two adjacent glass sheets 2; 21, 22 to each other. . As a material of the adhesive layer 3, it has adhesive properties such as acrylic, urethane, urethane compound, epoxy, and siloxane, which are widely used as adhesive materials for displays such as OCA (Optically clear adhesive), OCR (Optically clear resin), etc. It may be a polymer material. In addition, a material such as poly vinyl butyral (PVA), which is most widely applied to conventional laminated glass, may be used.

The thickness of the adhesive layer 3 is preferably selected in consideration of physical properties such as viscoelasticity of the adhesive material and strength after curing, and the manufacturing process. As an example of a typical adhesive layer 3 material, OCA is advantageous in reducing the radius of curvature of the glass sheet composite as its thickness increases. Considering that wrinkles appear in foldable phones to which two or more 25 μm OCA adhesive layers 3 are applied, it may be appropriate to set the OCA thickness to 50 μm or less. In the case of OCR, if the thickness of the adhesive layer 3 is less than 5 μm, the workability is not good, so the adhesion of the glass is incomplete, and the possibility of partial non-adhesion increases. For the OCA bonding process, a conventional laminating process can be applied, and for OCR, an injection-type coating and inkjet process can be applied. Considering the above-mentioned characteristics of OCA and OCR, it is appropriate to maintain the thickness of the adhesive layer 3 to about 5-50 μm.

It is preferable that the total thickness of the glass sheet composite using the above-described glass sheets 2; 21 and 22 and the adhesive is 65 to 180 μm. In this case, with respect to the thickness of each of the glass sheets 2; 21 and 22 applied to the glass sheet composite, for example, 30 µm + 30 µm, 65 + 65 µm, the thickness of the upper glass sheet 21 and the lower glass sheet 22 is The thickness may be the same, but the thickness may be different between the two in consideration of the required physical properties of the glass sheet composite. For example, by making the lower glass sheet 22 thicker than the upper glass sheet 21 by 30 + 50 μm, the bending load of the lower glass sheet 22 bonded to the display during bending deformation is relatively reduced, thereby making the glass sheet composite of the same thickness. It is possible to lower the radius of curvature compared to , or, conversely, by making the upper glass sheet 21 thicker than the lower glass sheet 22 by 50 + 30 μm, resistance to external stress such as pen impact can be increased.

physical test

In order to secure the glass sheet according to the present invention, using Shot's 100㎛ thick aluminosilicate chemically strengthened glass as a raw material, the size 160mm*65mm through cutting, grinding, slimming, and chemical strengthening processes commonly used in the manufacture of thin plate glass , a 30-70 μm thick glass was prepared. Table 1 below shows the test results by dividing the thickness of the glass into three groups, placing it by bending it between two sheet steel plates, and narrowing the gap until it breaks. In Table 1, the radius of curvature is defined as the radius of curvature, which is 1/2 of the distance between the plates when the glass is inserted between two flat steel plates and pressed in parallel until broken, and each group tested three samples. It is expressed as an average value. The glass sheet manufactured by this test method was 38㎛ thick, and it was possible to bend at a radius of curvature of 1.0mm, and it was confirmed that it was possible to realize a radius of curvature of 2.0mm with a glass thickness of 65㎛.

Correlation between the thickness of the glass sheet and the bending radius of curvature radius of curvature (mm) Thickness (㎛) group 1 1.0 38 group 2 2.0 50 group 3 2.5 65

The glass sheet composite of the present invention was prepared by the laminating method using the two prepared glass sheets and OCA. After manufacturing the 'glass sheet composite' specimen according to the embodiment of the present invention and the 'glass sheet' specimen according to the comparative example, the specimens were subjected to a ball drop test, a compressive stress test, and a bending test. After performing the test, the comparison results are shown in FIGS. 3 to 5 .

In this case, the glass sheet composite has a structure in which two glass sheets are bonded by an adhesive layer, and the thickness of each of the two glass sheets is 30 μm, the thickness of the adhesive layer is 25 μm, and the total thickness is 85 μm. The thickness of the glass sheet used in the test was set to 30 μm, so that it was the same as the thickness of the glass sheet used in the glass sheet composite.

3 is a view showing a ball drop test result of the glass sheet and the glass sheet composite specimen. In the ball drop test of FIG. 3 , the steel ball used for the test had a diameter of 20 mm and a weight of 30 g, and was repeatedly performed while increasing the height of the falling ball until the specimen was damaged. The height of the falling ball at the time of failure was measured to be 30 mm for single glass and 380 mm for double glass. From these results, it was confirmed that the durability against impact of double glass was increased by more than 10 times compared to single glass.

4 is a view showing the results of the compressive stress test for the glass sheet and the glass sheet composite specimen. The device used for the compressive stress test in Fig. 4 is a HF500 push & pull gauge from Tripod, and it is designed to apply a concentrated load to the test object by installing a 0.35mm diameter steel tip with a 60 degree taper. The test was performed by measuring the applied load at the time of failure, and the average value was calculated after repeating the test 5 times for each specimen. As a result, the average load applied at the time of failure was 7.12N for single glass and 7.72N for double glass. From these results, it was confirmed that the durability of the double glass to compressive stress was increased by about 8.4% compared to the single glass. The reason why the strength increase rate of double glass tends to be relatively low compared to the steel ball test result is that when OCA used as an adhesive applies a concentrated load to the top of the glass like a steel tip, it is relatively less effective at dispersing stress.

5 is a view showing a bending test result of the glass sheet and the glass sheet composite specimen. The bending test is performed by bending the test sample glass sheet and glass sheet composite in half between two parallel steel plates, and when bending for each specimen, the distance between the two steel plates is 1/ 2 The numerical value was used as the radius of curvature, and this was compared. As a result, the bending curvature at the time of failure was measured to be 0.6 mm for the glass sheet and 1.4 mm for the radius of curvature of the glass sheet composite. These measurement results may be seen as indicating that the flexibility of the glass sheet composite is relatively low because the glass sheet composite is broken at a larger bending curvature value than that of the glass sheet, but this means that the overall thickness of the glass sheet composite is more than twice that of the glass sheet. It can be seen as a natural phenomenon that occurs because it is thick. That is, in the case of the glass sheet composite, although the overall thickness of the cover window is thickened to improve impact resistance and touch texture, the decrease in flexibility due to the increase in thickness is not large. Since the radius of curvature of 2.0 mm can be sufficiently satisfied, the glass sheet composite according to an embodiment of the present invention exhibits opposite characteristics such as flexibility and impact durability, which were difficult to achieve with a conventional glass-based cover window such as the glass sheet of Comparative Example. At the same time, it can be seen that it can be improved.

As described above, according to the present invention, as a cover window that maintains the inherent strength, texture (touch feeling) and display quality of glass, in particular, it satisfies sufficient flexibility to enable folding with a very small radius of curvature of 2.0 mm or less. At the same time, it is possible to provide a glass-based cover window that can be advantageously applied to a flexible display by improving the impact resistance so as not to be damaged even by an impact caused by a writing recognition tool or the like. In addition, the glass-based cover window according to the present invention is easy to manufacture and can have an excellent product yield because it does not involve a high-difficulty processing process of locally producing different thicknesses of tempered glass, unlike in the prior art.

The above description relates to specific embodiments of the present invention. As described above, the embodiments according to the present invention are disclosed for the purpose of explanation and are not to be construed as limiting the scope of the present invention, and those skilled in the art will not depart from the essence of the present invention. It should be understood that various changes and modifications are possible. Accordingly, all such modifications and variations can be understood to correspond to the scope of the invention disclosed in the claims or equivalents thereof.

1: Cover window
2: Glass sheet
21: upper glass sheet
22: lower glass sheet
3: adhesive layer

Claims (6)

A cover window for a glass-based flexible display, comprising: a plurality of glass sheets; and one or more adhesive layers provided between the plurality of glass sheets to integrally bond adjacent glass sheets; Features a cover window.
The cover window according to claim 1, wherein each glass sheet has a thickness of 30 to 65 μm.
The thickness of the lower glass sheet according to claim 1, wherein when a lower glass sheet among the plurality of glass sheets to be adhered to a display is used as a lower glass sheet and an upper glass sheet positioned at the outermost side after being adhered to the display is used as the lower glass sheet. A cover window, characterized in that it is thick.
The thickness of the upper glass sheet according to claim 1, wherein when a lower glass sheet among the plurality of glass sheets to be adhered to a display is used as a lower glass sheet, and an upper glass sheet positioned at the outermost side after being adhered to the display is used as the upper glass sheet. A cover window, characterized in that it is thick.
The cover window of claim 1, wherein the adhesive layer is a transparent bonding material selected from optically clear adesive (OCA), optically clear resin (OCR), and poly vinyl butyral (PVB).
The cover window according to claim 1, wherein the adhesive layer has a thickness of 5 to 50 µm.

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