Foldable glass cover plate and hole filling protection method thereof

Abstract

The invention discloses a foldable glass cover plate and a hole filling protection method thereof, the foldable glass cover plate comprises a glass cover plate and a plurality of rows of through holes arranged in parallel at a bending area of the glass cover plate, the through holes are uniformly distributed in the whole bending area of the glass cover plate, and the through holes are of a bamboo book structure or a regular quadrangle or a circle or a rhombus or a regular triangle. According to the invention, the through hole is filled, and even the surface and the edge of the cover plate are covered with the colorless transparent high polymer material with the refractive index consistent with that of the glass cover plate, so that the foldable glass cover plate which is free of hole marks and not easy to pollute is obtained, and compared with a traditional foldable cover plate, the strength of a bending area of the filled and protected foldable glass cover plate is higher, and the service life of the foldable glass cover plate is prolonged. And the bending resistance is better.

Description

Technical Field

[0001] The present invention relates to the technical field of foldable glass cover plate processing technology, and in particular to a foldable glass cover plate and a hole filling and protection method thereof. Background Art

[0002] Foldable devices have attracted widespread attention from users because of their advantages of large screens and portability. The cover is both an interface for human-computer interaction and a protective barrier for flexible OLEDs, which deeply affects the user experience. It is also one of the bottleneck materials restricting the development of foldable device technology.

[0003] The glass cover of the folding device is foldable by using TGV (through-hole glass) technology to evenly punch holes in the bending area of ​​glass with a thickness of 100 to 500um or more; for example, patent CN 218585541 U discloses a foldable glass cover, in which holes of uniform size are set in the bending area of ​​the glass cover; the foldable glass cover can be bent up to 20w times or more while having high impact resistance, and can achieve both inner and outer bending of the glass at the same time, without being restricted by the bending direction of the glass. However, this type of design destroys the integrity of the glass in the bending area and has low impact resistance. The difference in refractive index between the through hole and the glass will leave obvious hole marks in the bending area, and the through hole area is easily contaminated, thereby affecting the quality of the foldable glass cover. Summary of the invention

[0004] The purpose of the present invention is to address the deficiencies of the prior art and provide a foldable glass cover and a hole filling protection method thereof, by adopting a special through-hole morphology and filling the through-hole with a colorless and transparent polymer material having a refractive index consistent with that of the glass cover, thereby obtaining a glass cover without hole marks and not easy to be contaminated.

[0005] To achieve the above object, the present invention first provides a foldable glass cover, comprising a glass cover and a plurality of rows of through holes arranged in parallel at a bending area of ​​the glass cover, wherein the through holes are evenly distributed over the entire bending area of ​​the glass cover, and the shape of the through holes is an equilateral triangle, a regular quadrilateral, a circle, or a rhombus;

[0006] The through holes are in the shape of regular triangles, with a side length of 400 to 900 μm, a spacing of 400 to 900 μm between adjacent through holes in each row, and a spacing of 200 to 400 μm between two adjacent rows of through holes in the upper and lower parts; the base of the regular triangle of each row of through holes is parallel to the base of the bending area, and the vertex of the next row of through holes corresponds to the midpoint between the two through holes in the previous row;

[0007] The through holes are in the shape of a regular quadrilateral, with a side length of 400 to 800 μm, a spacing of 300 to 800 μm between adjacent through holes in each row, and a spacing of 200 to 400 μm between two adjacent rows of through holes in each row; the bottom sides of the regular quadrilaterals of the through holes in each row are parallel to the bottom sides of the bending areas, and the vertical symmetry axis of the through holes in the next row is staggered by 200 to 400 μm with the vertical symmetry axis of the through holes in the previous row;

[0008] The through holes are circular in shape, with a through hole radius of 500-1000 μm, a spacing of 300-600 μm between adjacent through holes in each row, a spacing of 200-400 μm between two adjacent rows of through holes, and a vertical symmetry axis of the next row of through holes staggered by 300-600 μm with a vertical symmetry axis of the previous row of through holes;

[0009] The through holes are in a diamond shape with a side length of 300 to 600 μm. The spacing between adjacent through holes in each row is 200 to 400 μm. The spacing between two adjacent rows of through holes is 200 to 400 μm. The line connecting the two opposite vertices of each row of through holes is parallel to the bottom edge of the bending area, and the vertical symmetry axis of the next row of through holes is staggered by 200 to 400 μm with the vertical symmetry axis of the previous row of through holes.

[0010] The present invention also provides a foldable glass cover plate with a bamboo book structure, comprising a glass cover plate and a plurality of grooves arranged in parallel at a bending area of ​​the glass cover plate, wherein the intervals between the grooves are 200 to 400 μm; the grooves are obtained by yellow light etching or printing acid-resistant peelable adhesive.

[0011] Specifically, the glass cover plate has a thickness of 200-500 μm.

[0012] On the basis of the above technical solution, the foldable glass cover plate further includes a transparent polymer material protective layer, and the transparent polymer material protective layer is filled in the through hole and wraps the entire outer surface of the glass cover plate.

[0013] Furthermore, according to actual production and processing requirements, the transparent polymer material protection layer can also be filled in the through hole and only cover the bending area of ​​the glass cover plate.

[0014] Specifically, a functional coating is also provided on the upper surface of the transparent polymer material protective layer, and the functional coating includes an anti-glare hardened coating and an anti-reflective and anti-fingerprint hardened coating, so that the glass cover plate can have practical functions such as anti-glare, anti-reflection and anti-fingerprint after being applied to a foldable device.

[0015] It should be noted that in the above technical solution, the functional coating only lists anti-glare hardened coating and anti-reflective anti-fingerprint hardened coating. In fact, depending on the specific application equipment, the functional coating can also be an anti-blue light coating, an oleophobic coating, etc.

[0016] Specifically, the material of the transparent polymer material protective layer is acrylic polymer or silicone resin or epoxy resin or polyurethane resin, the refractive index of the material is 1.50-1.53, the transmittance is greater than 90%, the haze is less than 0.5%, and the elongation at break after curing is greater than 10%; the thickness of the transparent polymer material protective layer is 5-50μm; the thickness of the functional coating is 5-35μm; the refractive index of the transparent polymer material is consistent with that of the glass cover.

[0017] Secondly, the present invention also provides a foldable glass cover plate hole filling protection method, which is used for the above-mentioned foldable glass cover plate hole filling protection, comprising the following steps:

[0018] Step S1, cleaning the glass cover plate to be punched;

[0019] Step S2, using through-hole glass (TGV) technology to evenly punch holes in the bending area of ​​the glass cover plate;

[0020] Step S3, cleaning the punched glass cover again;

[0021] Step S4, selecting a hole filling protection scheme;

[0022] Step S5, filling the punched and cleaned glass cover with transparent polymer material according to the selected protection scheme, and performing a curing treatment to form a transparent polymer material protection layer;

[0023] Step S6: spray the functional coating on the surface of the transparent polymer material protective layer, bake it at 60-100°C for 15-30min, and 2 UV exposure at an energy of , to obtain a foldable glass cover;

[0024] Step S7: performing a bending test on the obtained foldable glass cover to verify its performance.

[0025] Specifically, the hole filling protection scheme is selected in step S4, and the hole filling protection scheme includes:

[0026] Hole filling protection solution 1: fill the transparent polymer material inside the through hole and wrap the entire outer surface of the glass cover;

[0027] Hole filling protection solution 2: Fill the transparent polymer material inside the through hole and cover the bending area of ​​the glass cover.

[0028] Specifically, the curing treatment method in step S5 is one or two of thermal curing, moisture curing, and UV curing.

[0029] Specifically, the bending test in step S7 has the following test conditions: bending 200,000 times at R1.0-20°C & 60°C / 90% RH & 70°C without breakage.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. The present invention adopts a special through-hole morphology and fills the through-hole with a colorless transparent polymer material having a refractive index consistent with that of glass, thereby obtaining a glass cover plate with no hole marks and not easy to be contaminated. This solves the problem that the traditional foldable glass cover plate has obvious hole marks in the bending area due to the refractive index difference between the through-hole and the glass, and the through-hole area is easily contaminated, which affects the quality of the foldable glass cover plate.

[0032] 2. The present invention fills the through hole with transparent polymer material and further extends it to the bending area of ​​the glass cover plate, and even to the entire surface of the glass cover plate and its edge, so as to maintain the bending performance of the through-hole glass, effectively improve the impact strength of the bending area, and solve the problem of insufficient strength of the edge of the glass in the through-hole area and easy breakage due to collision.

[0033] 3. The present invention also provides a functional coating outside the transparent polymer material protective layer, which can make the foldable cover more functional while achieving a better touch feeling. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a schematic structural diagram of a foldable glass cover plate of the present invention when the through hole is in the shape of an equilateral triangle;

[0035] Figure 2 This is a schematic structural diagram of a foldable glass cover plate of the present invention when the through hole is in a regular quadrilateral shape;

[0036] Figure 3 This is a schematic structural diagram of a foldable glass cover plate of the present invention when the through hole is circular in shape;

[0037] Figure 4 This is a schematic structural diagram of a foldable glass cover plate of the present invention when the through hole is in a diamond shape;

[0038] Figure 5 This is a schematic structural diagram of a foldable glass cover with a bamboo book structure according to the present invention;

[0039] Figure 6 The process flow chart of the yellow light etching method used in the foldable glass cover plate of the bamboo book structure of the present invention;

[0040] Figure 7 The process flow chart of the method for printing acid-resistant peelable adhesive for the foldable glass cover plate with bamboo book structure of the present invention;

[0041] Figure 8 This is a schematic diagram of the process flow when the foldable glass cover plate of the present invention adopts the hole filling protection solution 1;

[0042] Fig. 9This is a schematic diagram of the process flow when the foldable glass cover of the present invention adopts the hole filling protection solution 2.

[0043] In the figure: 1. Glass cover; 2. Through hole; 3. Transparent polymer material protective layer; 4. Functional coating; 5. Anti-glare hardened coating; 6. Anti-reflective and anti-fingerprint hardened coating; 7. Groove. DETAILED DESCRIPTION

[0044] In order to better reflect the advantages and innovations of the present invention and clearly demonstrate the technical solution of the present invention, the present invention will be further described in detail below in conjunction with specific embodiments.

[0045] Example

[0046] The present invention provides a foldable glass cover plate, comprising a glass cover plate 1 and a plurality of through holes 2 arranged in parallel at a bending area of ​​the glass cover plate 1, wherein the through holes 2 are evenly distributed over the entire bending area of ​​the glass cover plate 1, and the shape of the through holes 2 is an equilateral triangle, a regular quadrilateral, a circle, or a rhombus;

[0047] like Figure 1 As shown, the through hole 2 is in the shape of an equilateral triangle, the side length of the through hole 2 is 400-900 μm, the spacing between adjacent through holes 2 in each row is 400-900 μm, and the spacing between two adjacent rows of through holes 2 is 200-400 μm; the base of the equilateral triangle of each row of through holes 2 is parallel to the base of the bending area, and the vertex of the next row of through holes 2 corresponds to the midpoint between the two through holes 2 in the previous row;

[0048] like Figure 2 As shown, the through hole 2 is in the shape of a regular quadrilateral, the side length of the through hole 2 is 400-800 μm, the spacing between adjacent through holes 2 in each row is 300-800 μm, and the spacing between two adjacent rows of through holes 2 is 200-400 μm; the bottom side of the regular quadrilateral of each row of through holes 2 is parallel to the bottom side of the bending area, and the vertical symmetry axis of the next row of through holes 2 is staggered by 200-400 μm with the vertical symmetry axis of the previous row of through holes 2;

[0049] like Figure 3 As shown, the through hole 2 is circular in shape, the radius of the through hole 2 is 500-1000 μm, the spacing between adjacent through holes 2 in each row is 300-600 μm, the spacing between two adjacent rows of through holes 2 is 200-400 μm, and the vertical symmetry axis of the next row of through holes 2 is staggered by 300-600 μm with the vertical symmetry axis of the previous row of through holes 2;

[0050] like Figure 4As shown, the through hole 2 is in the shape of a diamond, the side length of the through hole 2 is 300-600 μm, the spacing between adjacent through holes 2 in each row is 200-400 μm, the spacing between two adjacent rows of through holes 2 is 200-400 μm, the line connecting the two opposite vertices of each row of through holes 2 is parallel to the bottom edge of the bending area, and the vertical symmetry axis of the next row of through holes 2 is staggered by 200-400 μm with the vertical symmetry axis of the previous row of through holes 2.

[0051] like Figure 5 As shown, this embodiment also provides a foldable glass cover with a bamboo book structure, including a glass cover 1 and a plurality of grooves 7 arranged in parallel at the bending area of ​​the glass cover 1, wherein the grooves 7 are spaced 200 to 400 μm apart; the grooves 7 are formed by Figure 6 The yellow photolithography method shown in FIG. 1 is obtained, or by Figure 7 The printed acid-resistant peelable adhesive is obtained by the method shown.

[0052] Specifically, the glass cover plate 1 has a thickness of 200-500 μm.

[0053] In this embodiment, the glass cover plate 1 further includes a transparent polymer material protective layer 3 , which is filled in the through hole 2 and wraps the entire outer surface of the glass cover plate 1 .

[0054] Furthermore, according to actual production and processing requirements, the transparent polymer material protection layer can also be filled in the through hole and only cover the bending area of ​​the glass cover plate.

[0055] Furthermore, a functional coating 4 is also provided on the upper surface of the transparent polymer material protection layer 3 , and the functional coating 4 includes an anti-glare hardening coating 5 and an anti-reflection and anti-fingerprint hardening coating 6 .

[0056] In this embodiment, the material of the transparent polymer material protective layer 3 is acrylic polymer or silicone resin or epoxy resin or polyurethane resin, the refractive index of the material is 1.50-1.53, the transmittance is greater than 90%, the haze is less than 0.5%, and the elongation at break after curing is greater than 10%; the thickness of the transparent polymer material protective layer 3 is 5-50μm; the thickness of the functional coating 4 is 5-35μm.

[0057] It should be emphasized that in order to avoid the problem of obvious hole marks in the bending area of ​​the traditional foldable glass cover due to the difference in refractive index between the through hole and the glass, in this embodiment, the refractive index of the transparent polymer material is consistent with that of the glass cover 1.

[0058] The present invention also provides a method for filling holes and protecting a foldable glass cover, which is used for filling holes and protecting the foldable glass cover, and comprises the following steps:

[0059] Step S1, cleaning the glass cover plate 1 to be punched;

[0060] Step S2, using through-hole glass TGV technology to evenly punch holes in the bending area of ​​the glass cover plate 1;

[0061] Step S3, cleaning the punched glass cover plate 1 again;

[0062] Step S4, selecting a hole filling protection scheme;

[0063] Step S5, filling the punched and cleaned glass cover plate 1 with transparent polymer material according to the selected protection scheme, and performing a curing treatment to form a transparent polymer material protection layer 3;

[0064] Step S6: spray the functional coating 4 on the surface of the transparent polymer material protective layer 3, and bake it at 60-100°C for 15-30 minutes at 500-1500mJ / cm 2 UV exposure under energy of , to obtain a foldable glass cover;

[0065] Step S7: performing a bending test on the obtained foldable glass cover to verify its performance.

[0066] In this embodiment, the hole filling protection scheme includes:

[0067] like Figure 8 The figure shows the first hole filling protection scheme: a transparent polymer material is filled into the through hole 2 and wraps the entire outer surface of the glass cover plate 1;

[0068] like Fig. 9 The second hole filling protection scheme is shown: a transparent polymer material is filled into the through hole 2 and covers the bending area of ​​the glass cover plate 1 .

[0069] Preferably, the curing treatment method in step S5 is one or two of thermal curing, moisture curing, and UV curing.

[0070] The bending test in step S7 has the following test conditions: bending 200,000 times at R1.0-20°C & 60°C / 90% RH & 70°C without breakage.

[0071] The performance of the foldable glass cover after hole filling and protection of the present invention is further tested and explained through comparative tests.

[0072] 1. Appearance inspection

[0073] 20 observers were randomly selected to observe the bending areas of the foldable glass cover plate after hole filling protection of the present invention and the traditional foldable glass cover plate, and the number of observers who observed obvious hole marks in the bending areas was counted. The results are shown in Table 1 below.

[0074] Table 1. Appearance test results

[0075]

[0076]

[0077] Note: "0" indicates no hole marks were observed; "1" indicates obvious hole marks were observed.

[0078] It can be seen from the results in the above table that the present invention can effectively solve the problem of obvious hole marks in the bending area of ​​the traditional foldable glass cover due to the difference in refractive index between the through hole and the glass by filling the through hole with a colorless transparent polymer material whose refractive index is consistent with that of the glass cover.

[0079] 2. Drop ball test

[0080] A 35g steel ball is used for dropping. The ball-dropping jig is made of stainless steel, with a smooth surface and no scratches, dents, convex spots or other surface defects. The steel ball is dropped from a height of 5cm at the center of the drop hole area. Each height is tested 5 times. After the test is completed, it is confirmed that the product appearance is not broken. The height is increased by 5cm intervals until it breaks, and the height value before breaking is recorded.

[0081] The above method was used to perform a drop ball test on the foldable glass cover plate after hole filling protection, the TGV foldable glass cover plate and the ultra-thin glass, and the results are shown in Table 2 below.

[0082] Table 2. Ball drop test results

[0083]

[0084]

[0085] It can be seen from the results in the above table that the present invention greatly improves the ball drop strength of the bending zone by filling the through hole with a colorless transparent polymer material whose refractive index is consistent with that of the glass cover plate, which can effectively solve the problem that the traditional foldable glass cover plate has weak ball drop strength and cannot be used for the first surface of human-machine contact.

[0086] 3. Bending test of foldable glass cover after hole filling protection

[0087] As shown in Table 3 below, the fracture conditions of the bending zone of the foldable glass cover plate after hole filling protection of the present invention and the traditional foldable glass cover plate after being bent 200,000 times at R1.0 are shown.

[0088] Table 3. Bending test results

[0089]

[0090]

[0091] Note: “ / ” indicates that the sample did not break after being bent 200,000 times; “*” indicates that the sample broke after being bent 200,000 times.

[0092] It can be seen from the above table that the bending performance of the bending zone of the foldable glass cover plate after hole filling and protection according to the method of the present invention is not significantly different from that of the traditional foldable glass, and the bending performance is not reduced.

[0093] 4. Effect of through-hole morphology on the bending performance of the foldable glass cover after hole filling protection

[0094] As shown in Table 4 below, the fracture conditions of the bending zone of the foldable glass cover plate after being bent 200,000 times at R1.0 for different through-hole morphologies after hole filling and protection according to the present invention.

[0095] Table 4. Bending test results

[0096]

[0097]

[0098] Note: “ / ” indicates that the sample did not break after being bent 200,000 times; “*” indicates that the sample broke after being bent 200,000 times.

[0099] It can be seen from the above table that there is no obvious difference in the bending performance of the bending zone of the foldable glass cover after the hole filling protection according to different through-hole morphologies, indicating that the hole filling protection method proposed in the present invention is applicable to foldable glass cover plates with various through-hole morphologies, and different through-hole morphologies will not affect the bending performance of the glass cover plate.

[0100] In summary, the present invention fills the through holes with a colorless and transparent polymer material having a refractive index consistent with that of the glass cover plate. Compared with the traditional foldable cover plate, a foldable glass cover plate with no hole marks and not easy to be contaminated is obtained. At the same time, the bending zone of the foldable glass cover plate after filling and protection has higher strength and better bending resistance.

[0101] It should be understood that the above description of the preferred embodiment is relatively detailed and cannot be regarded as limiting the scope of patent protection of the present invention. Under the enlightenment of the present invention, ordinary technicians in this field can also make substitutions or modifications without departing from the scope of protection of the claims of the present invention, which all fall within the scope of protection of the present invention. The scope of protection requested for the present invention shall be based on the attached claims.

Claims

1. A foldable glass cover, characterized in that: It comprises a glass cover plate (1) and a plurality of rows of through holes (2) arranged in parallel at a bending area of ​​the glass cover plate (1), wherein the through holes (2) are evenly distributed over the entire bending area of ​​the glass cover plate (1), and the shape of the through holes (2) is an equilateral triangle, a regular quadrilateral, a circle, or a rhombus; The through holes (2) are in the shape of an equilateral triangle, with a side length of 400 to 900 μm. The spacing between adjacent through holes (2) in each row is 400 to 900 μm, and the spacing between two adjacent rows of through holes (2) is 200 to 400 μm. The base of the equilateral triangle of each row of through holes (2) is parallel to the base of the bending area, and the vertex of the next row of through holes (2) corresponds to the midpoint between the two through holes (2) in the previous row. The through holes (2) are in the shape of a regular quadrilateral, with a side length of 400-800 μm, a spacing of 300-800 μm between adjacent through holes (2) in each row, and a spacing of 200-400 μm between two adjacent rows of through holes (2) above and below; the bottom side of the regular quadrilateral of each row of through holes (2) is parallel to the bottom side of the bending area, and the vertical symmetry axis of the next row of through holes (2) is staggered by 200-400 μm with the vertical symmetry axis of the previous row of through holes (2); The through holes (2) are circular in shape, with a radius of 500-1000 μm, a spacing of 300-600 μm between adjacent through holes (2) in each row, a spacing of 200-400 μm between two adjacent rows of through holes (2) above and below, and a vertical symmetry axis of the through holes (2) in the next row is staggered by 300-600 μm from the vertical symmetry axis of the through holes (2) in the previous row; The through holes (2) are in a diamond shape, with a side length of 300-600 μm. The spacing between adjacent through holes (2) in each row is 200-400 μm, and the spacing between two adjacent rows of through holes (2) is 200-400 μm. The line connecting the two opposite vertices of each row of through holes (2) is parallel to the bottom edge of the bending area, and the vertical symmetry axis of the next row of through holes (2) is staggered by 200-400 μm from the vertical symmetry axis of the previous row of through holes (2).

2. The foldable glass cover according to claim 1, wherein: The glass cover plate (1) has a thickness of 100-500 μm.

3. The foldable glass cover according to claim 1, wherein: It also includes a transparent polymer material protective layer (3), which is filled in the through hole (2) and wraps the entire outer surface of the glass cover plate (1).

4. The foldable glass cover according to claim 1, wherein: It also includes a transparent polymer material protective layer (3), which is filled in the through hole (2) and covers the bending area of ​​the glass cover plate (1).

5. The foldable glass cover according to any one of claims 3 or 4, characterized in that: The upper surface of the transparent polymer material protective layer (3) is also provided with a functional coating (4), and the functional coating (4) comprises an anti-glare hardening coating (5) and an anti-reflection and anti-fingerprint hardening coating (6).

6. The foldable glass cover according to any one of claims 3 to 5, characterized in that: The transparent polymer material protective layer (3) is made of an acrylic polymer, a silicone resin, an epoxy resin, or a polyurethane resin, and has a refractive index of 1.50 to 1.53, a light transmittance of more than 90%, a haze of less than 0.5%, and an elongation at break after curing of more than 10%. The transparent polymer material protective layer (3) has a thickness of 5 to 50 μm. The functional coating (4) has a thickness of 5 to 35 μm. The refractive index of the transparent polymer material is consistent with that of the glass cover plate (1).

7. A method for filling holes in a foldable glass cover for protecting the foldable glass cover according to any one of claims 1 to 6, characterized in that: The following steps are involved: Step S1, cleaning the glass cover plate (1) to be punched; Step S2, using through-hole glass (TGV) technology to uniformly punch holes in the bending area of ​​the glass cover plate (1); Step S3, cleaning the punched glass cover plate (1) again; Step S4: Select a hole filling protection scheme; Step S5: filling the punched and cleaned glass cover plate (1) with a transparent polymer material according to the selected protection scheme, and performing a curing process to form a transparent polymer material protective layer (3); Step S6: spraying the functional coating (4) on the surface of the transparent polymer material protective layer (3); baking the coating at 60-100°C for 15-30 minutes; and UV exposure at an energy of 500-1500 mJ / cm² to obtain a foldable glass cover; Step S7: performing a bending test on the obtained foldable glass cover to verify its performance.

8. The method for filling holes and protecting a foldable glass cover according to claim 7, wherein: In step S4, a hole filling protection scheme is selected, which includes: Hole filling protection solution 1: Fill the inside of the through hole (2) with a transparent polymer material and wrap the entire outer surface of the glass cover plate (1); Hole filling protection solution 2: Fill the inside of the through hole (2) with a transparent polymer material and cover the bending area of ​​the glass cover plate (1).

9. The method for filling holes and protecting a foldable glass cover according to claim 7, wherein: The curing treatment method in step S5 is one or two of thermal curing, moisture curing, and UV curing.

10. The method for filling holes and protecting a foldable glass cover according to claim 7, wherein: The bending test in step S7 is conducted under the following conditions: R1.0 -20°C & 60°C / 90%RH & 70°C, and the device is bent 200,000 times without breaking.

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