Glass substrate multilayer structure, method of manufacturing the same, and flexible display panel including the same

Abstract

The present application provides a glass substrate multilayer structure, a manufacturing method thereof, and a flexible display panel including the same. Specifically, a glass substrate multilayer structure including a flexible glass substrate and a polyimide-based anti-shatter layer formed on one surface of the flexible glass substrate, and a flexible display panel including the same are provided.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority from Korean Patent Application No. 10-2020-0112018 filed on September 3, 2020, with the Korean Intellectual Property Office (KIPO), the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to a glass substrate multilayer structure, a manufacturing method thereof and a flexible display panel comprising the same. Background Art

[0004] In recent years, with the development of mobile devices such as smartphones and tablets, thinner display devices are required, among which flexible display devices that can be bent or folded according to user needs or flexible display devices whose manufacturing process includes bending or folding are attracting attention.

[0005] The display device includes a transparent window covering a display screen, and the window has a function of protecting the display device from external impacts, scratches applied during use, and the like.

[0006] Glass or tempered glass, which is a material having excellent mechanical properties, is generally used for a window of a display, but glass has no flexibility and causes a higher weight of the display device due to its weight.

[0007] To address these issues, thinning technologies for flexible glass substrates have been developed. However, these technologies are insufficient to achieve sufficient flexibility to bend or fold, and the issue of susceptibility to damage from external impacts has not yet been addressed. In the case of flexible display devices, in particular, the glass substrate window is susceptible to external impacts or damage during bending or folding, resulting in shattered fragments and potential injuries to users.

[0008] To solve the above-mentioned problem, attempts have been made to form an anti-shatter layer on a flexible glass film. However, the anti-shatter layer is generally formed of an acrylic resin adhesive or an adhesive is inserted to form the anti-shatter layer. Therefore, the anti-shatter resistance and impact resistance are insufficient, and the cost increases with the increase in process steps. It is also difficult to remove the acrylic adhesive during the subsequent reproduction of the glass substrate.

[0009] Furthermore, conventional anti-shatter layers, including acrylic anti-shatter layers, suffer from issues such as pen marks on the anti-shatter layer during a pen drop test, insufficient adhesion, and insufficient bendability. To address these issues, increasing the surface hardness of the anti-shatter layer may prevent the glass substrate multilayer structure from being fully bent or folded.

[0010] Therefore, there is a need to develop a new type of flexible glass substrate multilayer structure, which has excellent flexibility, such as almost no breakage after thousands of folding and unfolding, further improved durability, such as impact resistance and shatter resistance, excellent heat resistance and optical properties, and in a pen drop test, for example, even if the pen is dropped from a height of 10 cm, 20 cm or 25 cm, there is still an effect of no pen drop mark, has a bending value within ±0.2 mm or within ±0.15 mm, provides excellent physical properties in terms of adhesion to glass, reduces manufacturing costs by simplifying the process, and is easy to reproduce. Summary of the Invention

[0011] Embodiments of the present invention may be achieved by providing a glass substrate multi-layer structure applicable to a flexible display device, the glass substrate multi-layer structure having excellent durability and shatter resistance to ensure user safety.

[0012] Another embodiment of the present invention can be achieved by providing a glass substrate multilayer structure that can be applied to a flexible display device, the glass substrate multilayer structure having excellent surface properties so that no pen marks appear even when the pen is dropped from a height, and also having flexibility to allow bending or folding, so that the glass does not break or crack even when repeatedly bent or folded.

[0013] Another embodiment of the present invention can be achieved by providing an excellent glass substrate multi-layer structure having further improved surface hardness, shatter resistance, and flexibility compared to conventional technologies and having no pen marks in a pen drop test because an anti-shatter layer formed of a polyimide-based resin, particularly a polyimide-based resin containing a fluorine element, is formed on a flexible glass substrate.

[0014] Another embodiment of the present invention may be achieved by providing a flexible glass substrate multi-layer structure having a value within ±0.2 mm or within ±0.15 mm in bending properties and providing excellent physical properties in terms of adhesion to glass.

[0015] Yet another embodiment of the present invention is a glass substrate multi-layer structure which has a low manufacturing cost and can be easily reproduced after its use.

[0016] In one general aspect, a glass substrate multi-layer structure includes a flexible glass substrate; and a polyimide-based anti-shatter layer formed on one surface of the flexible glass substrate.

[0017] In an exemplary embodiment of the present invention, the polyimide-based anti-shatter layer may be formed of a polyimide-based resin including a unit derived from a fluorine-based aromatic diamine and a unit derived from an aromatic dianhydride.

[0018] In an exemplary embodiment of the present invention, the flexible glass substrate may have a thickness of 1-100 μm.

[0019] In an exemplary embodiment of the present invention, the polyimide-based anti-shatter layer may have a thickness of 100 nm to 10 μm.

[0020] In an exemplary embodiment of the present invention, the glass substrate multi-layer structure may have a pencil hardness of 4H to 6H measured according to ASTM D3363.

[0021] In an exemplary embodiment of the present invention, the glass substrate multi-layer structure may have an impact resistance of 20 cm or more measured by a pen drop test.

[0022] In an exemplary embodiment of the present invention, the glass substrate multi-layer structure may have a value within ±0.2 mm in bending properties and an adhesion of 5B measured according to ASTM D3359, wherein the bending properties are measured by placing the glass substrate multi-layer structure on a calibrated vibration isolation table immediately after forming an anti-shatter layer and a hard coating layer, respectively, on a glass substrate having a size of 180 mm in width, 76 mm in length, and 40 μm in thickness.

[0023] In another general aspect, a method of making a glass substrate multilayer structure includes coating an anti-shatter composition on a rear surface of a flexible glass substrate and curing the anti-shatter composition to form a polyimide-based anti-shatter layer.

[0024] In an exemplary embodiment of the present invention, the anti-shatter composition may include a fluorine-based aromatic diamine and an aromatic dianhydride.

[0025] In yet another general aspect, a flexible display includes a glass substrate multilayer structure.

[0026] Other features and aspects will become apparent from the following detailed description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is an exploded perspective view schematically showing a cross section of a glass substrate multilayer structure according to an exemplary embodiment of the present invention.

[0028] [Detailed description of main components]

[0029] 10: Flexible glass substrate

[0030] 20: Polyimide-based anti-shatter layer

[0031] 100: Glass substrate multilayer structure DETAILED DESCRIPTION

[0032] The meanings of the terms used in the present invention are the same as those generally understood by those skilled in the art. In addition, the terms used herein are only used to effectively describe a specific example and are not used to limit the present invention.

[0033] As used in the description of the invention and the appended claims, singular forms may be intended to include plural forms as well, unless the context indicates otherwise.

[0034] Throughout this specification in describing the present invention, unless explicitly described to the contrary, “comprising” any elements will be understood to imply the further inclusion of other elements rather than the exclusion of any other elements.

[0035] The term "flexible" in the present invention means curved, bent or folded.

[0036] The term "anti-shatter layer" in the present invention is used to mean including a "polyimide-based anti-shatter layer".

[0037] The term "within" in the present invention is used to refer to an inclusive range, and as a specific example, "within ±0.2 mm" is used to refer to a range including +0.2 mm and -0.2 mm.

[0038] The inventors of the present invention conducted extensive research to solve the above-mentioned problems and discovered a glass substrate multilayer structure. By forming a polyimide-based anti-shatter layer on one surface of a flexible glass substrate, the structure has bending properties, adhesion and excellent pen-drop performance, as well as excellent flexibility, while having significantly improved shatter resistance, impact resistance and optical properties. Therefore, the structure is suitable for use as a cover window for a flexible display panel, thus completing the present invention.

[0039] In addition, the polyimide-based anti-shatter layer is formed of a polyimide resin, particularly a fluorine-containing polyimide resin, and thus, compared with conventional anti-shatter layers formed of acrylic resins or other resins, the present invention exhibits a surprising effect of excellent adhesion to a flexible display device, and does not form pen marks when a pen is dropped from a height in a pen drop test, and does not lose bending performance or folding performance.

[0040] Hereinafter, each component of the present invention will be described in detail with reference to the accompanying drawings. However, these are only exemplary, and the present invention is not limited to the specific embodiments exemplarily described in the present invention.

[0041] Figure 1 Schematic diagram showing a glass substrate multilayer structure according to an exemplary embodiment of the present invention. Figure 1As shown, the glass substrate multi-layer structure 100 according to an exemplary embodiment of the present invention includes a polyimide-based anti-shatter layer 20 formed on one surface of a flexible glass substrate 10 .

[0042] The glass substrate multilayer structure according to an exemplary embodiment of the present invention may have a pencil hardness of 3H or more, specifically 4H or more, as measured according to ASTM D3363, and the upper limit is not particularly limited, but may be 6H. In addition, the impact resistance measured by the pen drop test may be 10 cm or more, specifically 20 cm or more, more specifically 25 cm or more, and even more specifically 30 cm or more. Here, the impact resistance measured by the pen drop test refers to a state in which there are no scratches or indentations on the surface when a ballpoint pen with a diameter of 0.7 mm and a weight of 5.3 g is dropped vertically.

[0043] The glass substrate multi-layer structure according to the exemplary embodiment of the present invention may have a bending property within ±0.2 mm and an adhesion of 5B measured according to ASTM D3359, wherein the bending property is measured by placing the glass substrate multi-layer structure on a calibrated vibration isolation table immediately after forming an anti-shatter layer and a hard coating layer on a glass substrate having a width of 180 mm, a length of 76 mm, and a thickness of 40 μm.

[0044] When the glass substrate multilayer structure according to an exemplary embodiment of the present invention is produced to have a polyimide film forming a polyimide-based anti-shatter layer, the glass substrate multilayer structure has a modulus of 5 GPa or less, 3 GPa or less, or 2.5 GPa or less, as measured in accordance with ASTM E1111, an elongation at break of 10% or more, 20% or more, or 30% or more, a light transmittance at 388 nm of 5% or more or 5-80% and a light transmittance at 400-700 nm of 87% or more, 88% or more, or 89% or more, as measured in accordance with ASTM D1746, a haze of 2.0% or less, 1.5% or less, or 1.0% or less, as measured in accordance with ASTM D1003, a yellowness index of 5.0 or less, 3.0 or less, or 0.4-3.0, as measured in accordance with ASTM E313, and a b* value of 2.0 or less, 1.3 or less, or 0.4-1.3.

[0045] The glass substrate multilayer structure according to an exemplary embodiment of the present invention uses a fluorine-containing polyimide as the anti-shatter layer-forming material to form a polyimide-based anti-shatter layer on one surface of a flexible glass substrate. This provides excellent surface properties, including no traces left by a pen drop test, even when the pen is dropped from a height, while also maintaining the glass substrate's excellent bending and folding properties. Furthermore, the glass substrate multilayer structure easily achieves flexible properties with excellent flexibility, exhibits excellent impact resistance and shatter resistance, ensuring user safety, and is transparent, exhibiting excellent optical properties, making it suitable for use as a window cover for flexible display panels.

[0046] In addition, when a flexible display device is formed on the polyimide-based anti-shatter layer of the glass substrate multi-layer structure according to an exemplary embodiment of the present invention, its bonding strength with the device is excellent, and when defective products occur due to process errors, the defective products can be easily removed, thereby having excellent reworkability.

[0047] In the following, reference Figure 1 , the flexible glass substrate 10 forming the glass substrate multi-layer structure 100 according to an exemplary embodiment of the present invention and the polyimide-based anti-shatter layer 20 formed on one surface of the flexible glass substrate 10 will be described in more detail.

[0048] <Flexible glass substrate>

[0049] Flexible glass substrate refers to a foldable or bendable glass substrate that can serve as a window for a display device and has good durability and excellent surface smoothness and transparency.

[0050] In the exemplary embodiment of the present invention, the flexible glass substrate is not limited as long as it includes glass, but specifically may be selected from ordinary glass, soda-lime glass, tempered glass, and the like.

[0051] In an exemplary embodiment of the present invention, the glass substrate multilayer structure 100 may be formed on one surface of a flexible display panel, or may be bent or folded in response to bending or folding. Here, in order to deform the glass substrate multilayer structure 100 so as to bend with a relatively small radius of curvature or fold significantly, the flexible glass substrate 10 should be formed of an ultra-thin glass substrate. In an exemplary embodiment of the present invention, the flexible glass substrate 10 may be an ultra-thin glass substrate and may have a thickness of 100 μm or less, specifically 1-100 μm or 30-100 μm.

[0052] In an exemplary embodiment of the present invention, the flexible glass substrate may further include a chemically strengthened layer, and the chemically strengthened layer may be formed by performing a chemical strengthening treatment on any one or more surfaces of the first surface and the second surface of the glass substrate included in the flexible glass substrate, thereby improving the strength of the flexible glass substrate.

[0053] There are various methods for forming such chemically strengthened ultra-thin flexible glass substrates. For example, a method may include the following steps: preparing a raw long glass having a thickness of 100 μm or less, processing the glass into a predetermined shape through cutting, chamfering, sintering, etc., and chemically strengthening the processed glass. Another example is preparing a raw long glass of normal thickness and thinning it to a thickness of 100 μm or less, followed by sequential shaping and chemical strengthening. Here, thinning can be performed by any one of mechanical and chemical methods, or a combination of the two.

[0054] <Polyimide-based anti-shatter layer>

[0055] The polyimide-based anti-shatter layer of the present invention should absorb the energy generated when the glass substrate 10 breaks to prevent the fragments of the glass substrate 10 from shattering, and should also provide excellent surface properties that prevent damage due to external impact. For example, the polyimide-based anti-shatter layer should provide excellent surface properties such as no pen marks in a pen drop test performed from a height of 10 cm, 20 cm, or 30 cm or more.

[0056] In addition, the polyimide-based anti-shatter layer of the present invention can be further endowed with better surface properties by forming polyimide, especially polyimide containing fluorine element as the anti-shatter layer, which has excellent adhesion to the flexible display device formed on the anti-shatter layer and is easier to remove than the conventional anti-shatter layer formed of acrylic resin.

[0057] In an exemplary embodiment of the present invention, the polyimide-based anti-shatter layer may be formed from a polyimide-based resin comprising units derived from aromatic diamines and units derived from aromatic dianhydrides, as known in the art. In particular, as an exemplary embodiment of the present invention, the polyimide-based anti-shatter layer is formed from a polyimide-based resin comprising units derived from fluorine-based aromatic diamines and units derived from aromatic dianhydrides. Specifically, the polyimide resin is polymerized from monomers comprising fluorine-based aromatic diamines and aromatic dianhydrides, and has excellent optical and mechanical properties, as well as excellent elasticity and resilience.

[0058] In one exemplary embodiment of the present invention, the fluorine-based aromatic diamine may be any one or more selected from 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (6FAPB), 2,2'-bis(trifluoromethyl)benzidine (TFMB), 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether (6FODA), and the like. Furthermore, the fluorine-based aromatic diamine may be used in combination with other known aromatic diamine components, but the present invention is not limited thereto. The use of such a fluorine-based aromatic diamine can further enhance the anti-shatter properties of the resulting polyimide-based anti-shatter layer, further improve its optical properties, and improve its yellowness index.

[0059] In an exemplary embodiment of the present invention, the aromatic dianhydride may be selected from 4,4'-hexafluoroisopropylidene diphthalic anhydride (6FDA), biphenyltetracarboxylic dianhydride (BPDA), oxydiphthalic dianhydride (ODPA), sulfonyl diphthalic anhydride (SO2DPA), (isopropylidene diphenoxy) di(phthalic anhydride) (6HDBA), 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic dianhydride (TDA), 1,2,4,5-pyromellitic dianhydride (PMDA), benzophenone tetracarboxylic dianhydride (BTDA), bis(dicarboxyphenyl) dimethylsilane dianhydride (SiDA), bis(dicarboxyphenoxy) diphenyl sulfide dianhydride (BDSDA), ethylene glycol bis(trimellitic anhydride) (TMEG100, ethylene glycol bis(anhydrotrimellitate)), and the like, but is not limited thereto.

[0060] In an exemplary embodiment of the present invention, the fluorine-based aromatic diamine and the aromatic dianhydride may be used in a molar ratio of 1.5:1 to 1:1.5, specifically 1.3:1 to 1:1.3, or 1.2:1 to 1:1.2, but is not limited thereto.

[0061] In the exemplary embodiment of the present invention, the polyimide-based anti-shatter layer may have a thickness of 10 μm or less or 8 μm or less, and the lower limit is not particularly limited, but may be 10 nm.

[0062] <Flexible Display Panel>

[0063] In an exemplary embodiment of the present invention, a flexible display panel or a flexible display device including the glass substrate multi-layer structure according to the exemplary embodiment as a window cover may be provided.

[0064] In an exemplary embodiment of the present invention, the glass substrate multilayer structure 100 in a flexible display device can serve as the outermost window substrate of the flexible display panel. As a specific exemplary embodiment, the flexible display panel can have a structure in which the flexible display device is formed on the polyimide-based anti-shatter layer 20 of the glass substrate multilayer structure 100 of the present invention. When a flexible display panel has such a multilayer structure, the bonding strength between the glass substrate multilayer structure 100 and the flexible display device is improved, preventing the flexible glass substrate 100 from shattering when damaged, thereby protecting the flexible display device.

[0065] The flexible display device may be various image display devices, such as common liquid crystal display devices, electroluminescent display devices, plasma display devices, and field emission display devices.

[0066] <Method for Manufacturing Glass Substrate Multilayer Structure>

[0067] Hereinafter, a method of manufacturing a glass substrate multi-layer structure according to an exemplary embodiment of the present invention will be described in detail.

[0068] A method of manufacturing a glass substrate multi-layer structure according to an exemplary embodiment of the present invention may include coating an anti-shatter composition on one surface of a glass substrate and curing the anti-shatter composition to form a polyimide-based anti-shatter layer.

[0069] First, the anti-shatter composition forming the polyimide-based anti-shatter layer will be described.

[0070] In an exemplary embodiment of the present invention, the anti-shatter composition may include a fluorine-based aromatic diamine and an aromatic dianhydride, and the fluorine-based aromatic diamine and the aromatic dianhydride may be the same as those described above. As a specific exemplary embodiment, the anti-shatter composition may be a polyimide precursor, which is prepared by the following method: dissolving the fluorine-based aromatic diamine in an organic solvent to obtain a mixed solution, and adding an aromatic dianhydride thereto to carry out a polymerization reaction. Here, the reaction can be carried out under an inert gas or nitrogen flow, or under anhydrous conditions. In addition, the temperature during the polymerization reaction can be -20°C to 200°C or 0°C to 180°C, and the organic solvent that can be used in the polymerization reaction can be selected from N,N-diethylacetamide (DEAc), N,N-diethylformamide (DEF), N-ethylpyrrolidone (NEP), dimethylpropionamide (DMPA), diethylpropionamide (DEPA) or a mixture thereof.

[0071] Here, the polyimide precursor solution may be in the form of a solution dissolved in an organic solvent, or may be a dilution of the solution in other solvents. In addition, when the polyimide precursor is obtained as a solid powder, it may be dissolved in an organic solvent to form a solution.

[0072] Thereafter, the polyimide precursor may be imidized to prepare a polyimide solution (anti-shatter composition). Here, as the imidization process, a known imidization method may be used without limitation, but specific examples include a chemical imidization method, a thermal imidization method, and the like, and as an exemplary embodiment of the present invention, specifically, an azeotropic thermal imidization method may be used.

[0073] In the azeotropic thermal imidization method, toluene or xylene is added to a polyimide precursor (polyamic acid solution) and stirred to carry out an imidization reaction at 160°C to 200°C for 6 to 24 hours, during which water released when imide rings are generated can be separated as an azeotropic mixture of toluene or xylene.

[0074] The polyimide solution prepared according to the above-mentioned preparation method may include a certain amount of solid content to have a suitable viscosity in consideration of workability such as coatability.

[0075] According to exemplary embodiments, the solid content of the anti-shatter composition (polyimide solution) may be 1-30 wt %, specifically 5-25 wt %, or 8-20 wt %.

[0076] Hereinafter, a method of forming a polyimide-based anti-shatter layer will be described.

[0077] In an exemplary embodiment of the present invention, the polyimide-based anti-shatter layer can be formed by coating an anti-shatter composition on one surface of a flexible glass substrate and curing the anti-shatter composition. Here, the coating method is not limited, and various methods such as rod coating, dip coating, die coating, gravure coating, comma coating, slit coating, or a combination thereof can be used.

[0078] The curing may be performed by heat treatment at a temperature of 40° C. to 250° C., the number of heat treatments may be one or more, and the heat treatment may be performed once or more at the same temperature or in different temperature ranges. In addition, the heat treatment time may be 1 minute to 60 minutes, but is not limited thereto.

[0079] In addition, the polyimide-based anti-shatter layer may be formed of one or more layers, but is not limited thereto.

[0080] Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the following Examples and Comparative Examples are merely examples for describing the present invention in more detail and do not limit the present invention in any way.

[0081] In the following, the physical properties were measured as follows:

[0082] 1) Pencil hardness

[0083] The pencil hardness of the surface of the glass substrate multilayer structure produced in Examples and Comparative Examples was measured using a pencil hardness tester (Kipae E&T Co., Ltd.) under a load of 1 kg using a pencil (Mitsubishi Pencil Co., Ltd.) in accordance with ASTM D3363. This surface refers to the surface opposite to the surface on which the anti-shatter layer is formed.

[0084] 2) Evaluation of impact resistance (pen drop test)

[0085] A 0.7 mm BICOrange pen (5.3 g) was placed vertically on a designated position on a glass substrate multilayer structure sample prepared in the following Examples and Comparative Examples, and the substrate condition was evaluated according to the following criteria:

[0086] <Evaluation Criteria>

[0087] ◎: No scratches or indentations

[0088] ○: Scratches and indentations are present

[0089] ×: Destroyed (not crushed)

[0090] ▲: The two evaluation results are different

[0091] 3) Adhesion

[0092] Adhesion was measured by the method of ASTM D3359. The adhesion between the polyimide-based anti-shatter layer and the glass substrate was measured. A grid groove was made on the coating film with a knife, the coating film was soaked in a hot water bath at 80°C for 5 hours, the moisture on the surface was wiped off, 3M tape was tightly attached to it, and then separated several times with constant force to observe the degree of adhesion between the coating and the substrate. 11×11 cross cuts were made at intervals of 1 mm on the surface of the coated support to make 100 squares, and the tape (3M tape) was attached thereto, and then the tape was quickly pulled to evaluate the surface. The number of remaining 100 squares was represented as 5B, more than 95 was represented as 4B, more than 85 was represented as 3B, more than 65 was represented as 2B, more than 35 was represented as 1B, and less than 35 was represented as 0B.

[0093] 4) Bending performance

[0094] The glass substrate multilayer structures produced in the following Examples and Comparative Examples were placed on a flat ground, and the degree to which the glass substrate multilayer structures were bent upward or downward was measured. When the edge portion of the glass substrate was bent upward, the value was expressed as +, and when the portion was bent or curved downward, the value was expressed as -.

[0095] Specifically, an anti-shatter layer-forming composition and a hard coat layer-forming composition were each applied and cured onto a glass substrate measuring 180 mm wide, 76 mm long, and 40 μm thick. The glass substrate multilayer structure was then immediately placed on a correctly leveled vibration isolation table, and the bending of the glass substrate multilayer structure was measured at room temperature. Here, when the glass substrate multilayer structure was bent in the direction of the vibration isolation table, with the center of the glass substrate bent toward the air layer, the step difference at the highest bending point at the center was measured from the edge and expressed as a negative (stress) value (mm). Conversely, when both ends (edges) of the glass substrate were bent toward the air layer on the vibration isolation table, the step difference at the raised edge was measured from the center and expressed as a positive (tension) value (mm).

[0096] [Preparation Example 1] Preparation of a fluorine-containing polyimide anti-shatter layer forming composition

[0097] A nitrogen-flowing stirrer was filled with 153 g of N,N-dimethylpropionamide (DMPA), and 41 g of 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether (6FODA) was dissolved therein while maintaining the reactor temperature at 25°C. 50 g of ethylene glycol bis(trimellitic anhydride) (TMEG100) was added to the 6FODA solution at the same temperature and stirred for a predetermined time to dissolve. 70 g of toluene was added to the polyimide precursor solution prepared by the above reaction, and the mixture was refluxed at 180°C for 6 hours to remove moisture. DMPA was then added to a solids concentration of 20% by weight to prepare an anti-shatter layer-forming composition (polyimide solution).

[0098] [Preparation Example 2] Preparation of a urethane acrylic anti-shatter layer forming composition

[0099] 60 g of urethane acrylate (UV-6100B, a product of "Nippon Gosei", available from Nippon Gosei Kagakusha KK), 20 g of 2-hydroxypropyl acrylate ("Light Ester HOP-A", available from Kyoeisha Kagakusha KK), 20 g of 1,6-hexanediol diacrylate (HDODA, available from Dial UCB Co.), and 1 g of Darocure 1174 (trade name, available from Ciba-Geigy Co.) as an initiator were uniformly mixed to prepare an anti-shatter layer-forming composition.

[0100] [Example 1]

[0101] The anti-shatter layer-forming composition prepared in Preparation Example 1 was coated on one surface of a glass substrate (UTG 40 μm) using a #20 Mayer bar, dried at 50° C. for 1 minute and at 230° C. for 10 minutes to form a polyimide-based anti-shatter layer having a thickness of 3 μm.

[0102] [Example 2]

[0103] A glass substrate multilayer structure was manufactured in the same manner as in Example 1, except that the polyimide-based anti-shatter layer was formed to have a thickness of 5 μm.

[0104] [Example 3]

[0105] A glass substrate multilayer structure was manufactured in the same manner as in Example 1, except that the polyimide-based anti-shatter layer was formed to have a thickness of 10 μm.

[0106] [Comparative Example 1]

[0107] A glass substrate multilayer structure was manufactured in the same manner as in Example 1, except that the anti-shatter layer-forming composition of Preparation Example 2 was used. 2 The 360nm ultraviolet rays are irradiated at an intensity of 100 nm to form an anti-shatter layer.

[0108] Physical properties of the glass substrate multilayer structures prepared in Examples 1 to 3 and Comparative Example 1 were measured and shown in Table 1 below.

[0109] [Table 1]

[0110]

[0111] As shown in Table 1, Examples 1 to 3 were found to have an excellent surface hardness of 4H or more, and excellent chipping resistance, excellent impact resistance, and excellent adhesion even at 15 cm or more.

[0112] However, Comparative Example 1 was confirmed to have remarkably poor surface hardness, impact resistance, and adhesion.

[0113] Furthermore, Examples 1 to 3 confirmed that the manufactured glass substrate multilayer structures had a curvature within ±0.15 mm and excellent curvature performance. However, Comparative Example 1 confirmed a relatively large curvature of 1.5 mm.

[0114] The glass substrate multilayer structure of the present invention has high surface hardness, is flexible, and has excellent heat resistance and optical properties, while providing a surface on which handwriting is difficult to form.

[0115] Furthermore, the glass substrate multilayer structure of the present invention utilizes a polyimide-based anti-shatter layer, particularly a fluorinated polyimide, on one surface of a flexible glass substrate. This layer, despite being a thin coating of less than 10 μm, exhibits significantly improved shatter resistance and impact resistance compared to conventional anti-shatter layers formed from acrylic resins. Furthermore, the layer exhibits excellent flexibility and impact resistance, making it suitable for flexible display windows. Specifically, the polyimide anti-shatter layer formed on the back of the glass substrate provides excellent adhesion to flexible display panels. Conventional acrylic anti-shatter layers are formed by laminating thick films, resulting in reduced surface hardness after lamination. However, the multilayer structure of the present process, formed by coating with a thin film at a low thickness, maintains both shatter resistance and impact resistance while maintaining the surface hardness of the substrate itself.

[0116] Furthermore, the glass substrate multilayer structure according to the present invention realizes a polyimide-based anti-shatter layer through a single coating, thereby simplifying the process steps to reduce costs, and can also maintain the surface hardness of the glass substrate while having the above effects.

[0117] Although the present invention has been described above by way of specific matters, limited exemplary embodiments and accompanying drawings, these are provided only to facilitate an overall understanding of the present invention. The present invention is not limited to the exemplary embodiments, and those skilled in the art may make various modifications and changes based on this description.

[0118] Therefore, the spirit of the present invention should not be limited to the above-described exemplary embodiments, but the appended claims and all modifications that are the same as or equivalent to the claims will fall within the scope and spirit of the present invention.

Claims

1. A glass substrate multilayer structure comprising: Flexible glass substrate; and a polyimide-based anti-shatter layer formed on one surface of the flexible glass substrate, The polyimide-based anti-shatter layer is formed of a polyimide-based resin, and the polyimide-based resin includes a unit derived from 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether and a unit derived from ethylene glycol bis(trimellitic anhydride). 2 . The glass substrate multi-layer structure according to claim 1 , wherein the flexible glass substrate has a thickness of 1 to 100 μm. 3 . The glass substrate multi-layer structure according to claim 1 , wherein the polyimide-based anti-shatter layer has a thickness of 100 nm to 10 μm.

4. The glass substrate multilayer structure according to claim 1, wherein The glass substrate multi-layer structure has a pencil hardness of 4H to 6H measured according to ASTM D3363. The glass substrate multi-layer structure according to claim 1 , wherein the glass substrate multi-layer structure has an impact resistance of 20 cm or more as measured by a pen drop test.

6. The glass substrate multi-layer structure according to claim 1 , wherein the glass substrate multi-layer structure has a bending property within ±0.2 mm and an adhesion of 5B measured according to ASTM D3359, wherein the bending property is measured by placing the glass substrate multi-layer structure on a calibrated vibration isolation table immediately after forming an anti-shatter layer and a hard coating layer, respectively, on a glass substrate having a size of 180 mm in width, 76 mm in length, and 40 μm in thickness.

7. A method for manufacturing a glass substrate multilayer structure, the method comprising: coating an anti-shatter composition on a rear surface of a flexible glass substrate and curing the anti-shatter composition to form a polyimide-based anti-shatter layer, The anti-shatter composition comprises 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether and ethylene glycol bis(trimellitic anhydride). 8 . A flexible display panel comprising the glass substrate multilayer structure according to claim 1 .

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