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

Abstract

The present disclosure relates to a glass substrate multilayer structure, a method for manufacturing the same, and a flexible display panel including the same, and more particularly, to a glass substrate multilayer structure which is remarkably improved in a surface hardness reduction phenomenon, has remarkably improved impact resistance, can ensure safety of a user by improving a flying phenomenon at the time of breakage of a glass substrate, and has excellent optical characteristics, a method for manufacturing the same, and a flexible display panel including the same.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2021-0066650, filed with the Korean Intellectual Property Office on May 25, 2021, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] This disclosure relates to multilayer structures of glass substrates, methods for manufacturing the same, and flexible display panels including the same. Background Technology

[0004] Recently, with the development of mobile devices such as smartphones and tablets, there has been a need to reduce the thickness of display devices. In particular, flexible display devices that can be bent or folded when needed by the user, or flexible display devices with bending or folding steps in the manufacturing process, are attracting attention.

[0005] Such a display device may include a transparent window covering the display screen, which serves to protect the display device from external impacts and scratches during use.

[0006] Display windows are typically made of glass or tempered glass, which are materials with excellent mechanical properties. However, traditional glass has the problem of lacking flexibility and increasing the weight of the display device due to its weight.

[0007] To address these issues, flexible glass substrate thinning technology has been developed, but it is still insufficient to achieve flexible properties that allow for bending or folding, and the problem of susceptibility to damage from external impacts remains unresolved.

[0008] In particular, for flexible display devices, there is a problem that the glass substrate window is prone to breakage due to external impact or during bending or folding, and the fragments of the glass substrate window can scatter, potentially injuring users. Efforts have been made to solve this problem by forming an anti-scattering layer with a flexible structure on the flexible glass film.

[0009] However, when an anti-shatter layer (hereinafter also called a shatterproof layer) is formed, there is a problem that due to pressing, marks are produced on the glass substrate itself or on the surface hardening layer on the glass substrate, and the physical properties of the glass multilayer structure itself may decrease, such as a decrease in surface hardness.

[0010] Therefore, there is a need for a novel glass multilayer structure that significantly improves the problem of reduced surface hardness or markings when pressed or penned, even when forming an anti-scattering layer including a soft polymer. Furthermore, there is a need to develop a novel glass substrate multilayer structure that significantly improves impact resistance, ensures user safety by mitigating scattering when the glass substrate breaks, and possesses excellent optical properties. Summary of the Invention

[0011] Technical problems to be solved

[0012] One embodiment aims to provide a multilayer structure of a glass substrate that does not experience a decrease in surface hardness or leave marks when pressed or subjected to a pen drop test.

[0013] Another embodiment of the present invention aims to provide a multilayer structure of a glass substrate. When using a thin glass substrate as the substrate, even if the multilayer structure of the glass substrate has a multilayer structure including an anti-scattering layer formed on one side of the glass substrate and a hard coating formed on the other side as its reverse side, there will be no reduction in the surface hardness of the glass substrate or the hard coating or indentation. It has significantly improved impact resistance, can ensure user safety by further improving the scattering phenomenon when the glass substrate breaks, and has excellent optical properties. Therefore, it can be used in flexible display devices.

[0014] Another embodiment of the present invention aims to provide a multilayer structure of a glass substrate with excellent surface properties, which, even if the multilayer structure of the glass substrate has a multilayer structure including an anti-scattering layer formed on one side of the glass substrate and a hard coating formed on the other side as its reverse side, will not produce pen marks on the surface of the glass substrate or the surface of the hard coating when a pen drop test is performed at a specified position (height).

[0015] Another embodiment of the present invention aims to provide a multilayer structure of glass substrate that has excellent durability and anti-scattering properties and is flexible, so that the glass will not break or crack even if it is repeatedly folded or bent, and therefore can be used in flexible display devices.

[0016] Another embodiment of the present invention aims to provide a multilayer structure of a glass substrate having excellent optical properties, such as yellowness index (YI), transmittance, and thickness-direction phase difference R. th Furthermore, visibility and transparency are significantly improved, making it suitable for flexible display devices.

[0017] Technical solution

[0018] To achieve the above objectives, according to one aspect, the flexible glass substrate multilayer structure may employ a polyimide layer comprising a (meth)acrylic acid crosslinked polymer (or a multifunctional (meth)acrylic acid crosslinked polymer) as an anti-scattering layer.

[0019] According to one aspect, a multilayer structure of a glass substrate is provided, comprising: a flexible glass substrate and an anti-scattering layer formed on one side of the flexible glass substrate, wherein the anti-scattering layer comprises a multifunctional (meth)acrylic acid crosslinked polymer and a polyimide polymer.

[0020] In one embodiment, the glass substrate multilayer structure may further include a hard coating formed on the other side of the flexible glass substrate.

[0021] In one embodiment, the multifunctional (meth)acrylic acid crosslinked polymer may further include alkenyl, ether, urethane group, ester group, or combinations thereof.

[0022] In one embodiment, the multifunctional (meth)acrylic acid crosslinked polymer may include structural units derived from multifunctional (meth)acrylic acid compounds having 3 to 6 (meth)acrylic acid groups.

[0023] In one embodiment, the polyfunctional (meth)acrylate compound may include trimethylolpropane trimethacrylate, trimethylolethane trimethacrylate, 1,2,4-cyclohexane trimethacrylate, pentaglycerol trimethacrylate, pentaerythritol tetramethacrylate, pentaerythritol trimethacrylate, dipentaerythritol trimethacrylate, dipentaerythritol pentamethacrylate, dipentaerythritol tetramethacrylate, dipentaerythritol hexamethacrylate, tripentaerythritol trimethacrylate, tripentaerythritol hexamethacrylate, polyfunctional urethane (meth)acrylate, polyfunctional polyester (meth)acrylate, or combinations thereof.

[0024] In one embodiment, the polyimide polymer may include units derived from aromatic diamines containing fluorine atoms and units derived from aromatic dianhydrides.

[0025] In one embodiment, the hard coating may include a (meth)acrylic hard coating.

[0026] In one embodiment, the thickness of the flexible glass substrate can be from 1 μm to 100 μm.

[0027] In one embodiment, the thickness of the anti-scattering layer can be from 1 μm to 20 μm.

[0028] In one embodiment, the thickness of the hard coating can be from 1 μm to 15 μm.

[0029] In one embodiment, the glass substrate multilayer structure may have a pencil hardness of 4H or higher according to ASTM D3363, specifically, it may be 4H to 9H.

[0030] In one embodiment, the impact resistance of the multilayer glass substrate structure can be above 10 cm according to the pen drop test.

[0031] According to another aspect, a method for manufacturing a multilayer structure of a glass substrate can be provided, which includes the step of coating and curing an anti-scattering composition comprising a polyimide precursor and a polyfunctional (meth)acrylic acid compound on one side of a flexible glass substrate to form an anti-scattering layer.

[0032] In one embodiment, the method for manufacturing a multilayer structure of a glass substrate may further include the step of coating and curing a hard coating composition on the other side of the flexible glass substrate to form a hard coating.

[0033] In one embodiment, the polyfunctional (meth)acrylic acid compound may include alkenyl, ether, carbamate, ester, or combinations thereof.

[0034] In one embodiment, the polyfunctional (meth)acrylic acid compound may have 3 to 6 (meth)acrylic acid groups.

[0035] In one embodiment, the polyfunctional (meth)acrylate compound may include trimethylolpropane trimethacrylate, trimethylolethane trimethacrylate, 1,2,4-cyclohexane trimethacrylate, pentaglycerol trimethacrylate, pentaerythritol tetramethacrylate, pentaerythritol trimethacrylate, dipentaerythritol trimethacrylate, dipentaerythritol pentamethacrylate, dipentaerythritol tetramethacrylate, dipentaerythritol hexamethacrylate, tripentaerythritol trimethacrylate, tripentaerythritol hexamethacrylate, polyfunctional urethane (meth)acrylate, polyfunctional polyester (meth)acrylate, or combinations thereof.

[0036] In one embodiment, the polyimide precursor may include units derived from aromatic diamines containing fluorine atoms and units derived from aromatic dianhydrides.

[0037] In one embodiment, the hard coating composition may include a polyfunctional (meth)acrylic acid compound.

[0038] According to another aspect, a flexible display panel comprising a multilayer structure of a glass substrate can be provided.

[0039] Technical effect

[0040] One aspect is to provide a multilayer glass substrate structure that does not exhibit a decrease in surface hardness or leave marks when pressed or written, even when including a soft polymer.

[0041] According to one aspect of the glass substrate multilayer structure, even with a multilayer structure including an anti-scattering layer formed on one side of the glass substrate and a hard coating formed on the other side as its reverse side, the problem of reduced surface hardness or indentation when writing is significantly improved, as well as the problem of marks when writing, the impact resistance is significantly improved, the scattering phenomenon when the glass substrate breaks is improved, thereby ensuring the safety of the user, and it can have excellent optical properties.

[0042] Furthermore, according to one aspect of the glass substrate multilayer structure, even if it has a multilayer structure including an anti-scattering layer formed on one side of the glass substrate and a hard coating formed on the other side as its reverse side, no pen marks will be generated on the surface of the glass substrate or the surface of the hard coating when a pen drop test is performed at a specified position (height).

[0043] Furthermore, according to one aspect, the multilayer structure of the glass substrate has excellent durability and anti-scattering properties and flexible characteristics that allow it to be bent or folded. Therefore, even repeated folding or bending operations will not cause the glass to break or crack, and thus it can be used in flexible display devices.

[0044] Furthermore, based on one aspect of the multilayer glass substrate structure, it possesses excellent optical properties, such as yellowness index (YI), transmittance, and thickness-direction phase difference R. th This results in significantly improved visibility and transparency, making it suitable for flexible display devices. Attached Figure Description

[0045] Figure 1 This is an exploded perspective view schematically showing an example of a cross-section of a glass substrate multilayer structure according to one embodiment. Figure 1 The glass substrate multilayer structure 100 shown includes a flexible glass substrate 10, an anti-scattering layer 20, and a hard coating 30. Detailed Implementation

[0046] The following will describe in detail an embodiment of a multilayer glass substrate structure, its manufacturing method, and a flexible display panel including the same.

[0047] Unless otherwise defined, all technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of effectively describing particular embodiments only and is not intended to limit the invention.

[0048] In addition, additives not specifically described in the instructions may be expressed in parts by weight.

[0049] Furthermore, unless the context clearly indicates otherwise, the singular form used in the specification and appended claims is also used to include the plural form.

[0050] Throughout the specification, the phrase "includes" a certain component means, unless otherwise stated, that other components may be further included, rather than excluded.

[0051] Unless otherwise defined in this specification, when describing a part of a layer, membrane, film, region, plate, etc. as being "above" or "on top of" another part, this may include not only the case where it is "directly" above the other part, but also the case where there is another part between the two.

[0052] Unless otherwise defined in this specification, the term "combination thereof" may refer to a mixture or copolymerization of the components. Furthermore, "combination thereof" may refer to two or more of the elements defined above that are used simultaneously or provided.

[0053] Unless otherwise stated in this specification, “A and / or B” may refer to a situation that includes both A and B, or a situation that chooses one of A and B.

[0054] Unless otherwise stated below, "derivative" can refer to a structure or composition formed by a reaction involving compounds, or it can refer to the modification of at least one functional group of a compound, specifically including the modification or departure of reactive and / or leaving groups of the compound as a result of a reaction. Furthermore, when the structures derived from different compounds are identical, it can also include cases where the structure derived from one compound is identical to the structure derived from another compound.

[0055] Unless otherwise stated in this specification, "polymer" refers to a relatively high molecular weight molecule whose structure may include multiple repetitions of units derived from low molecular weight molecules. In one embodiment, the polymer may be an alternating copolymer, block copolymer, random copolymer, branched copolymer, crosslinked copolymer, or a copolymer comprising all of these copolymers (e.g., a copolymer comprising more than one monomer). In another embodiment, the polymer may be a homopolymer (e.g., a copolymer comprising one monomer).

[0056] Unless otherwise defined in this specification, "oligomery" can refer to a molecule comprising a small number of units derived from a low molecular weight molecule or the same repeating units. An oligomer may comprise fewer monomer units than a polymer (e.g., fewer than 30 monomer units), and a polymer may comprise more monomer units than an oligomer (e.g., more than 30 monomer units). In one embodiment, an oligomer may comprise 2 to 20 monomer units.

[0057] Unless otherwise defined in this specification, the term "flexible" may refer to a flexible component that can be rolled, bent, and / or folded.

[0058] Unless otherwise defined in this specification, the term "hard coating" may be used as including "(meth)acrylic hard coating".

[0059] Unless otherwise defined in this specification, “(meth)acrylic acid” may be used as a meaning that includes “methacrylic acid” and / or “acrylic acid”.

[0060] In the following text, unless otherwise defined in this specification, “polyimide” is a polymer that includes an imide structure and may be used to mean “polyimide” or “polyamide-imide”.

[0061] Unless otherwise defined in this specification, "(meth)acrylic acid crosslinking polymer" may refer to a crosslinking polymer formed by crosslinking together (meth)acrylic acid compounds having (meth)acrylic acid groups, and the (meth)acrylic acid crosslinking polymer may or may not contain (meth)acrylic acid groups, such as (meth)acrylate groups.

[0062] Unless otherwise defined in this specification, “about” can be considered as a value within 30%, 25%, 20%, 15%, 10%, or 5% of the explicitly stated value.

[0063] According to one embodiment, a multilayer glass substrate structure can be provided that does not experience a decrease in surface hardness or leave marks even when the structure, which includes a soft polymer, is pressed or pen-written.

[0064] Figure 1 The diagram shows a multi-layered glass structure that prevents surface hardness reduction and minimizes structural changes or marks when subjected to pressure or external impact. Figure 1 An example of a glass multilayer structure shown includes a flexible glass substrate 10, an anti-scattering layer 20 bonded to one side (e.g., the lower side) of the flexible glass substrate 10, and a hard coating 30 bonded to the other side (e.g., the upper side).

[0065] According to one embodiment, a multilayer structure of a glass substrate can be provided, which, when using a thin glass substrate as the substrate, does not exhibit a decrease in surface hardness or indentation even when having a structure including an anti-scattering layer made of a flexible polymer formed on one side of the glass substrate and a hard coating formed on the other side, which is its reverse side, and / or can be used in flexible display devices.

[0066] The following is a detailed explanation of an implementation plan.

[0067] One aspect may provide a multilayer structure of a glass substrate, comprising:

[0068] Flexible glass substrates; and

[0069] An anti-scattering layer is formed on one side of the flexible glass substrate, wherein the anti-scattering layer comprises a multifunctional (meth)acrylic acid crosslinked polymer and a polyimide polymer.

[0070] Alternatively, another aspect may provide a multilayer glass substrate structure comprising:

[0071] Flexible glass substrate;

[0072] An anti-scattering layer formed on one side of the flexible glass substrate; and

[0073] A hard coating formed on the other side of the flexible glass substrate, wherein the anti-scattering layer comprises a multifunctional (meth)acrylic acid crosslinked polymer and a polyimide polymer.

[0074] According to one aspect of a glass substrate multilayer structure, an anti-scattering layer may be included on one side of the flexible glass substrate, particularly an anti-scattering layer comprising a multifunctional (meth)acrylic acid crosslinked polymer and a polyimide polymer. While not limited to a specific theory, an embodiment of a glass substrate multilayer structure including an anti-scattering layer achieves flexible properties (e.g., excellent flexibility) and significantly improves the trade-off between reduced surface hardness and reduced impact resistance as measured by a pen drop test, exhibiting excellent optical properties, thus making it suitable for use as a cover window for flexible display panels.

[0075] In a multilayer glass substrate structure according to one aspect, the multifunctional (meth)acrylic acid crosslinked polymer can be formed by inducing crosslinking polymerization of the multifunctional (meth)acrylic acid compound by means of heating or the like. The crosslinking polymerization can be all or part of the multifunctional (meth)acrylic acid compound crosslinked, but is not limited thereto. The multifunctional (meth)acrylic acid compound is a compound having multifunctional (meth)acrylic acid groups, and the (meth)acrylic acid groups can be, for example, acrylic acid groups or methacrylic acid groups.

[0076] In one embodiment, the multifunctional (meth)acrylic acid crosslinked polymer can be dispersed in the polyimide matrix resin of the anti-scattering layer to form a composite. However, the bond between the multifunctional (meth)acrylic acid crosslinked polymer and the polyimide polymer may not include chemical bonds; for example, the multifunctional (meth)acrylic acid crosslinked polymer and the polyimide polymer may not be covalently bonded to each other.

[0077] In a glass substrate multilayer structure according to one aspect, the multifunctional (meth)acrylic acid crosslinked polymer may also include alkenyl, ether, urethane, ester or combination thereof, but is not limited thereto.

[0078] Furthermore, in a glass substrate multilayer structure according to one aspect, the multifunctional (meth)acrylic acid crosslinking polymer may comprise, but is not limited to, structural units derived from multifunctional (meth)acrylic acid compounds having 3 to 6, for example 4 to 6, or for example 5 or 6 (meth)acrylic acid groups. Here, the (meth)acrylic acid groups may, for example, be acrylic acid groups or methacrylic acid groups.

[0079] In one embodiment, the polyfunctional (meth)acrylic acid crosslinking polymer may include, but is not limited to, structural units derived from polyfunctional (meth)acrylic acid compounds such as monomers having polyfunctional (meth)acrylic acid groups and oligomers having polyfunctional (meth)acrylic acid groups.

[0080] In one embodiment, the anti-scattering layer may comprise a multifunctional (meth)acrylic acid crosslinked polymer and a polyimide polymer that satisfy the above-described properties. While not limited to a specific theory, the glass substrate multilayer structure according to one embodiment can achieve flexible properties and significantly improve the trade-off between reduced surface hardness and reduced impact resistance as measured by pen drop tests. The glass substrate multilayer structure according to one embodiment can possess excellent optical properties, thus making it further suitable as a cover window for flexible display panels.

[0081] More specifically, a multilayer glass substrate structure according to one aspect may have a pencil hardness of about 4H or higher according to ASTM D3363, specifically a pencil hardness of about 4H to about 9H, more specifically a pencil hardness of about 5H to about 6H, but not necessarily limited thereto.

[0082] Furthermore, according to one aspect, the glass substrate multilayer structure can exhibit impact resistance when subjected to a pen drop test at heights of approximately 10 cm or more, approximately 15 cm or more, approximately 20 cm or more, approximately 10 cm to approximately 25 cm, or approximately 10 cm to approximately 20 cm, but is not necessarily limited to the aforementioned height ranges. In this case, the impact resistance according to the pen drop test refers to the state where no surface dents or indentations are formed when a ballpoint pen with a diameter of approximately 0.7 mm and a weight of approximately 0.5 g is dropped vertically from a designated position (height) on the glass substrate multilayer structure.

[0083] Although not limited to a specific theory, by having surface hardness and impact resistance properties within the aforementioned range, a multilayer structure of a glass substrate can ensure flexibility while better maintaining the original hardness, impact resistance, and durability of the glass substrate.

[0084] Furthermore, according to one aspect, the glass substrate multilayer structure may have a bending characteristic within approximately ±0.4 mm, for example, within approximately ±0.3 mm, or for example, within approximately ±0.25 mm, but is not necessarily limited to this. Here, the bending characteristic is measured by placing the glass substrate multilayer structure on a vibration isolation table and measuring the bending of the glass substrate multilayer structure at room temperature. Here, when the substrate bends towards the vibration isolation table and the center of the glass substrate bends towards the air layer, the difference in bending distance from the uppermost bending point to the center is measured relative to the edge and expressed as a negative (stress) value (mm); conversely, when both ends (edges) of the glass substrate bend towards the air layer on the vibration isolation table, the difference in edge rise is measured relative to the center and expressed as a positive (tensile) value (mm).

[0085] Although not limited to a specific theory, by having bending characteristics within the aforementioned range, a multilayer glass substrate structure according to one aspect has foldable or bendable flexible characteristics, so that the glass will not break or crack even with repeated folding or bending operations, and therefore can be more suitable for flexible display devices.

[0086] Furthermore, the multilayer glass substrate structure according to one aspect may have a yellowness index (YI) measured according to ASTM E313, for example, which may be from about 0.1 to about 5.0, from about 0.1 to about 3.0, from about 0.1 to about 2.0, and a b* value, for example, which may be from about 0.1 to about 2.0, from about 0.1 to about 1.5, from about 0.1 to about 1.0, but is not necessarily limited thereto.

[0087] Furthermore, the total transmittance of the glass substrate multilayer structure, measured according to ASTM D1746 at 400 nm to 700 nm, may be, for example, about 85% to about 99.9%, about 90% to about 99.9%, but is not necessarily limited thereto.

[0088] In one embodiment, the glass substrate multilayer structure exhibits a certain degree of optical birefringence. Therefore, to compensate for the phase difference between two orthogonally polarized rays in the glass substrate multilayer structure, the phase difference between the two orthogonally polarized rays can be measured. This can be measured as follows: for the glass substrate multilayer structure, the film is cut to a certain size using an Axoscan and the film thickness is measured. Then, the phase difference is measured using an Axoscan. To compensate for the value of the phase difference, the measurement is performed while correcting towards the C-plate direction. The phase difference is the delay between two orthogonally polarized rays corresponding to the two orthogonally polarized states of light passing through the material at the highest and lowest refractive indices, and can be represented by phase or distance. In one embodiment, the measured phase difference R... th For example, it could be approximately 10 μm to approximately 40 μm, or approximately 10 μm to approximately 30 μm, but it is not limited to these. The phase difference (R) th (at 550nm) is calculated using the following formula 1.

[0089] [Formula 1]

[0090] R th =[(n x +n y ) / 2-n z ]×d

[0091] (In Equation 1, n) x It is the largest refractive index among in-plane refractive indices, n y It is the in-plane refractive index that is related to n x Vertical refractive index, n z (This is the vertical refractive index, and d is the value calculated by converting the thickness of the multilayer glass substrate structure to 10 μm.)

[0092] Although not limited to a specific theory, due to the optical properties described above, multilayer glass substrate structures are excellent in terms of visibility and transparency, and are therefore more suitable for flexible display devices.

[0093] See below Figure 1 The composition of the flexible glass substrate 10, the anti-scattering layer 20, and the hard coating 30 included in the glass substrate multilayer structure 100 according to one embodiment of the present invention will be described in more detail. However, this is merely exemplary, and the present invention is not limited to the specific embodiments illustrated herein.

[0094] Flexible glass substrate

[0095] First, we will explain one aspect of flexible glass substrates.

[0096] In one embodiment, a flexible glass substrate refers to a foldable or curved glass substrate that can function as a window in a display device, has good durability, and possesses excellent surface smoothness and transparency.

[0097] In one embodiment, a flexible glass substrate that is bent due to pressure or force may have excellent recovery properties that allow it to return to its original shape after the pressure or force is removed.

[0098] In one embodiment, the glass substrate multilayer structure 100 can be formed on one side of the flexible display panel and can be bent or folded in response to bending or folding. Here, in order to allow the glass substrate multilayer structure 100 to deform to the extent of bending or folding with a small radius of curvature, the flexible glass substrate 10 can be formed from an ultrathin glass substrate.

[0099] In the glass substrate multilayer structure 100 according to one aspect, the flexible glass substrate 10 can be an ultrathin glass substrate with a thickness of about 100 μm or less, specifically about 1 μm to about 100 μm, more specifically about 30 μm to about 100 μm, but not necessarily limited thereto.

[0100] In the glass substrate multilayer structure 100 according to one aspect, the flexible glass substrate 10 may further include a chemically strengthened layer, which can be formed by chemically strengthening one or more of the first or second surfaces of the flexible glass substrate 10. Therefore, the strength of the flexible glass substrate 10 can be further significantly improved.

[0101] There are various methods for forming ultrathin flexible glass substrates that have undergone the chemical strengthening treatment described above. For example, an ultrathin glass (UTG) with a thickness of 100 μm or less can be prepared and processed into a predetermined shape through cutting, chamfering, and firing before undergoing chemical strengthening. Alternatively, a ledger glass of general thickness can be prepared and thinned to a thickness of approximately 100 μm or less before shape processing and chemical strengthening. However, this is merely a non-limiting example and is not intended to be limiting. Here, any one and / or two methods selected from mechanical and / or chemical methods can be used for the thinning operation, but this is not a limitation.

[0102] <Anti-scattering layer>

[0103] Next, we will explain the anti-scattering layer based on one aspect.

[0104] In addition to its basic function of absorbing the energy generated when the flexible glass substrate 10 is damaged to prevent fragments from scattering, the anti-scattering layer 20, as a non-limiting aspect of the invention, is formed on the opposite side of the surface that is opposite to the direction of forming the hard coating to further improve the phenomenon of reduced surface hardness and can further improve impact resistance.

[0105] In a glass substrate multilayer structure 100 according to one aspect, the anti-scattering layer 20 may include various suitable materials, for example, it may include a multifunctional (meth)acrylic acid crosslinked polymer and a polyimide polymer.

[0106] In a glass substrate multilayer structure 100 according to one aspect, the polyfunctional (meth)acrylic acid crosslinked polymer can be formed by inducing crosslinking polymerization of the polyfunctional (meth)acrylic acid compound through heating or other means, and the crosslinking polymerization can be all or part of the polyfunctional (meth)acrylic acid compound crosslinked, but is not limited thereto. The polyfunctional (meth)acrylic acid compound is a compound having polyfunctional (meth)acrylic acid groups, such as acrylic acid groups or methacrylic acid groups.

[0107] In one embodiment, the multifunctional (meth)acrylic acid crosslinked polymer can be dispersed in the polyimide matrix resin of the anti-scattering layer to form a composite. However, the bonding between the multifunctional (meth)acrylic acid crosslinked polymer and the polyimide polymer may not include chemical bonding; for example, the multifunctional (meth)acrylic acid crosslinked polymer and the polyimide polymer may not be covalently bonded to each other.

[0108] In the glass substrate multilayer structure 100 according to one aspect, the multifunctional (meth)acrylic acid crosslinked polymer may further include alkenyl, ether, urethane, ester or combinations thereof, but is not limited thereto.

[0109] Furthermore, in a glass substrate multilayer structure according to one aspect, the multifunctional (meth)acrylic acid crosslinking polymer may comprise, but is not limited to, structural units derived from multifunctional (meth)acrylic acid compounds having 3 to 6, for example 4 to 6, or for example 5 or 6 (meth)acrylic acid groups. Here, the (meth)acrylic acid groups may, for example, be acrylic acid groups or methacrylic acid groups.

[0110] More specifically, the multifunctional (meth)acrylic acid crosslinked polymer may include, but is not limited to, structural units derived from multifunctional (meth)acrylic acid compounds such as monomers having multifunctional (meth)acrylic acid groups and oligomers having multifunctional (meth)acrylic acid groups. In a glass substrate multilayer structure 100 according to one aspect of the present invention, the polyfunctional (meth)acrylate compound may include trimethylolpropane trimethacrylate, trimethylolethane trimethacrylate, 1,2,4-cyclohexane trimethacrylate, pentaglycerol trimethacrylate, pentaerythritol tetramethacrylate, pentaerythritol trimethacrylate, dipentaerythritol trimethacrylate, dipentaerythritol pentamethacrylate, dipentaerythritol tetramethacrylate, dipentaerythritol hexamethacrylate, tripentaerythritol trimethacrylate, tripentaerythritol hexamethacrylate, polyfunctional urethane (meth)acrylate, polyfunctional polyester (meth)acrylate, or combinations thereof. For example, the polyfunctional (meth)acrylate compound may include, but is not limited to, pentaerythritol hexa(meth)acrylate, pentaerythritol tetra(meth)acrylate, polyfunctional urethane (meth)acrylate, polyfunctional polyester (meth)acrylate, or combinations thereof.

[0111] In a glass substrate multilayer structure 100 according to one aspect, the polyfunctional urethane (meth)acrylate is prepared by reacting a (meth)acrylate containing hydroxyl groups and a compound containing isocyanate groups in the presence of a catalyst according to methods known in the art. An example of a commercially available polyfunctional urethane (meth)acrylate is urethane acrylate (PU9020, Miwon Special Chemical), but this is only a non-limiting example and is not intended to be limited thereto.

[0112] Here, as an example of a (meth)acrylate containing a hydroxyl group in the molecule, it can be any one of the following: a mixture of 2-hydroxyethyl (meth)acrylate, 2-hydroxyisopropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, caprolactone open-ring hydroxy acrylate and pentaerythritol tri / tetra(meth)acrylate or a mixture of dipentaerythritol penta / hexa(meth)acrylate or a combination thereof, but is not limited thereto.

[0113] Furthermore, examples of compounds containing isocyanate groups include those selected from 1,4-diisocyanobutane, 1,6-diisocyanohexane, 1,8-diisocyanooctane, 1,12-diisocyanododecane, 1,5-diisocyano-2-methylpentane, trimethyl-1,6-diisocyanohexane, 1,3-bis(isocyanomethyl)cyclohexane, trans-1,4-cyclohexene diisocyanate, 4,4'-methylenebis(cyclohexylisocyanate), and isoflavone. The following are all of the following: ketone diisocyanate, toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, xylene-1,4-diisocyanate, tetramethylxylene-1,3-diisocyanate, 1-chloromethyl-2,4-diisocyanate, 4,4'-methylenebis(2,6-dimethylphenylisocyanate), 4,4'-oxybis(phenylisocyanate), trifunctional isocyanates derived from hexamethylene diisocyanate, or combinations thereof, but not necessarily limited thereto.

[0114] Furthermore, in the glass substrate multilayer structure 100 according to one aspect, the multifunctional polyester (meth)acrylate is produced by reacting polyester polyol and acrylic acid according to a method known in the art. As a commercial example, it may be polyester acrylate (PS2500, Miwon Special Chemical), but this is only a non-limiting example and is not required to be limited thereto.

[0115] Examples of the multifunctional polyester (meth)acrylates may include polyester diacrylate, polyester tetraacrylate, polyester hexaacrylate, polyester pentaerythritol triacrylate, polyester pentaerythritol tetraacrylate, polyester pentaerythritol hexaacrylate, or combinations thereof, but are not necessarily limited thereto.

[0116] In a glass substrate multilayer structure 100 according to one aspect, the polyimide polymer may include units derived from fluorinated aromatic diamines and units derived from aromatic dianhydrides. Although not limited to a specific theory, in this case, optical and mechanical properties are superior, elasticity and resilience are further improved, and the effect of preventing deformation of the glass substrate can be further enhanced, but the invention is not limited thereto.

[0117] In the glass substrate multilayer structure 100 according to one aspect, the aromatic diamine containing fluorine atoms may be any one or a mixture of two 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), etc., but is not limited thereto. Furthermore, the aromatic diamine containing fluorine atoms may also be used in combination with other known aromatic diamine components containing or not containing fluorine atoms, but is not limited thereto.

[0118] In a glass substrate multilayer structure 100 according to one aspect, the aromatic dianhydride may be selected from 4,4'-hexafluoroisopropylidene phthalic anhydride (6FDA), biphenyl tetracarboxylic anhydride (BPDA), oxyphthalic anhydride (ODPA), sulfonyl phthalic anhydride (SO2DPA), (isopropylidene diphenoxy)bis(phthalic anhydride) (6HDBA), 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic anhydride (TDA), 1,2,4,5-benzenetetracarboxylic anhydride (PMDA), benzophenone tetracarboxylic anhydride (BTDA), bis(carboxyphenyl)dimethylsilane dianhydride (SiDA), bis(dicarboxyphenoxy)diphenyl sulfide dianhydride (BDSDA), and ethylene glycol bis(triphenylene)trihydride. It may be any one or a mixture of two or more of the following, but is not limited to: bis(anhydrotrimellitate), TMEG100, etc.

[0119] In the glass substrate multilayer structure 100 according to one aspect, although not limited to a specific theory, by forming an anti-scattering layer 20 on the back side of the flexible glass substrate 10, the problem that the glass substrate is easily broken during external impact or bending and folding, and the fragments may scatter, can be solved. At the same time, since the anti-scattering layer 20 includes a polyfunctional (meth)acrylic acid crosslinked polymer, the problem of reduced surface hardness, impact resistance and durability, which have a trade-off relationship with the flexibility properties, can be significantly improved.

[0120] In particular, the anti-scattering layer 20, which includes the multifunctional (meth)acrylic acid crosslinked polymer, and the hard coating 30, which is formed together by curing a compound having (meth)acrylic acid groups, are formed on both sides of the flexible glass substrate 10, thereby further improving the dent resistance and impact resistance according to the pen drop test.

[0121] In the glass substrate multilayer structure 100 according to one aspect, the thickness of the anti-scattering layer 20 is not particularly limited, but can be from about 1 μm to about 20 μm, more specifically from about 2 μm to about 10 μm, and more specifically from about 5 μm to about 10 μm, but is not limited thereto.

[0122] Hard coating

[0123] The following describes a hard coating according to one aspect of the present invention.

[0124] Although not limited to a specific theory, the hard coating 30 can protect the glass substrate multilayer structure 100 from external physical and chemical damage and can have excellent optical and mechanical properties.

[0125] In one aspect, the hard coating 30 may be formed on the other side (e.g., the reverse side) of the flexible glass substrate 10 on which the anti-scattering layer 20 is formed. For example, the surface of the flexible glass substrate 10 may be chemically strengthened, and the hard coating 30 may be formed on the surface of the chemically strengthened flexible glass substrate 10.

[0126] Furthermore, in the glass substrate multilayer structure 100 according to one aspect, the hard coating 30 may have the same properties as the shrinkage phenomenon of the anti-scattering layer 20 formed on the back side of the flexible glass substrate 10, and more specifically may be a (meth)acrylic hard coating, but is not limited thereto.

[0127] Furthermore, in the glass substrate multilayer structure 100 according to one aspect, the thickness of the hard coating 30 can be, for example, from about 1 μm to about 15 μm, from about 1 μm to about 10 μm, or from about 1 μm to about 5 μm, but is not necessarily limited thereto. When having a thickness within the above range, the hard coating 30 is preferred because it is able to maintain excellent hardness and flexibility.

[0128] In a glass substrate multilayer structure 100 according to one embodiment, the hard coating 30 may further include inorganic particles, which may include any one or a combination of two or more selected from silicon dioxide, metal oxides, etc., but are not limited thereto.

[0129] In addition, the inorganic particles include hydroxides such as aluminum hydroxide, magnesium hydroxide, and potassium hydroxide; metal particles such as gold, silver, copper, nickel, and their alloys; conductive particles such as carbon, carbon nanotubes, and fullerenes; glass; ceramics, etc., but are not limited thereto.

[0130] In one embodiment, the inorganic particles may have an average particle diameter of about 1 nm to about 200 nm, or about 10 nm to about 200 nm. Two or more inorganic particles with different average particle sizes may be used within this range, but are not limited to this. In one embodiment, including the inorganic particles can improve the surface hardness of the hard coating 30.

[0131] Flexible display panel

[0132] Another aspect provides a flexible display panel or flexible display device including a glass substrate multilayer structure 100 according to one aspect above.

[0133] For example, in a flexible display device, the multilayer glass substrate structure 100 can be used as the outermost window substrate of the flexible display panel. Flexible display devices can be various image display devices such as general liquid crystal displays, electroluminescent displays, plasma displays, and field emission displays, but are not limited to these.

[0134] <Methods for Manufacturing Multilayer Structures on Glass Substrates>

[0135] The following provides a detailed description of a method for manufacturing a multilayer glass substrate structure 100 according to another aspect.

[0136] A method for manufacturing a multilayer structure 100 of a glass substrate according to one aspect may include the step of forming an anti-scattering layer 20 by coating and curing an anti-scattering composition comprising one or more polyimide precursors and one or more polyfunctional (meth)acrylic acid compounds on one side of a flexible glass substrate.

[0137] Furthermore, a method for manufacturing a multilayer glass substrate structure 100 according to another aspect may include:

[0138] The steps of forming an anti-scattering layer 20 by coating and curing an anti-scattering composition comprising a polyimide precursor and a polyfunctional (meth)acrylic acid compound on one side of a flexible glass substrate; and

[0139] The step of coating and curing a hard coating composition on the other side of the flexible glass substrate to form a hard coating 30.

[0140] First, in a method for manufacturing a multilayer structure 100 of a glass substrate according to one aspect, the anti-scattering composition for forming the anti-scattering layer 20 will be described.

[0141] First, the anti-scattering composition may be a composition comprising one or more polyimide precursors and one or more polyfunctional (meth)acrylic acid compounds. Here, the polyimide precursor contained in the anti-scattering composition may be a substance comprising units derived from aromatic diamines containing fluorine atoms and units derived from aromatic dianhydrides, wherein the fluorinated aromatic diamines and aromatic dianhydrides may be the same as those described above in the description of the anti-scattering layer 20.

[0142] Furthermore, the polyfunctional (meth)acrylic acid compound according to one embodiment may also include alkenyl, ether, carbamate, ester or combination thereof, but is not limited thereto.

[0143] Furthermore, in the method of manufacturing a glass substrate multilayer structure 100 according to one aspect, at least one of the more than one polyfunctional (meth)acrylic acid compounds may have 3 to 6, for example 4 to 6, for example 5 or 6 (meth)acrylic acid groups, but is not necessarily limited thereto. Here, the (meth)acrylic acid groups may be, for example, acrylic acid groups or methacrylic acid groups.

[0144] More specifically, the polyfunctional (meth)acrylic acid compound according to one embodiment may include monomers having polyfunctional (meth)acrylic acid groups and oligomers having polyfunctional (meth)acrylic acid groups, etc., and the same compound as described above in the description of the anti-scattering layer 20 may be used.

[0145] In a method of manufacturing a glass substrate multilayer structure 100 according to one aspect, based on a total of 100 parts by weight of the one or more polyimide precursors and polyfunctional (meth)acrylic acid compounds, the content of the polyfunctional (meth)acrylic acid compound may be from about 1 to about 50 parts by weight, specifically from about 10 to about 40 parts by weight, more specifically from about 20 to about 40 parts by weight, but is not limited thereto.

[0146] When the content of the polyfunctional (meth)acrylic acid compound meets the above range, the effect of preventing the decrease in surface hardness or indentation caused by pen drop test can be further improved, and / or the problem of surface condition deterioration such as decrease in durability due to excessive decrease in impact resistance can be further improved.

[0147] The polyimide precursor can be obtained by dissolving an aromatic diamine containing fluorine atoms in an organic solvent and adding an aromatic dianhydride to the mixed solution for polymerization. The polymerization reaction can be carried out under an inert gas or nitrogen flow, or under anhydrous conditions. Furthermore, the polymerization reaction can be carried out at temperatures from about -20°C to about 200°C, or from about 0°C to about 180°C, but is not limited to these temperatures. Additionally, the organic solvent used in the polymerization reaction can be any one or a mixture of two or more selected from N,N-diethylacetamide (DEAc), N,N-diethylformamide (DEF), N-ethylpyrrolidone (NEP), dimethylpropionamide (DMPA), and diethylpropionamide (DEPA), but is not limited to these.

[0148] Here, according to one embodiment, the polyimide precursor may be present in the form of a solution dissolved in an organic solvent. In one embodiment, the polyimide precursor solution may include the polyimide precursor dissolved in one or more organic solvents (e.g., two, three, or four organic solvents). In one embodiment, the polyimide precursor may be present in an organic solvent, and a second organic solvent may be added to the solution to dilute the polyimide precursor. In one embodiment, the polyimide precursor may be added to the organic solvent in the form of a solid powder, whereby the polyimide precursor may dissolve upon mixing with the organic solvent to form a polyimide precursor solution.

[0149] According to one aspect, the anti-scattering composition can be prepared by adding one or more of the polyfunctional (meth)acrylic acid compounds to the polyimide precursor solution.

[0150] In a method for manufacturing a glass substrate multilayer structure 100 according to one aspect, the addition of one or more polyfunctional (meth)acrylic acid compounds can be carried out, for example, by adding the polyfunctional (meth)acrylic acid compounds in a diluted state in a solvent to the polyimide precursor solution and stirring at room temperature.

[0151] Furthermore, crosslinking and / or imidization can be induced by heating during the stirring. Here, the reaction conditions are not limited as long as the solubility of the anti-scattering composition in the solvent increases during the crosslinking reaction and the crosslinked polymer can be uniformly dispersed in the solution. The heating temperature can be from about 50°C to about 200°C, but is not limited to this.

[0152] The solvent for diluting the polyfunctional (meth)acrylic acid compound may be any one or a mixture of two or more of N,N-diethylacetamide (DEAc), N,N-diethylformamide (DEF), N-ethylpyrrolidone (NEP), dimethylpropionamide (DMPA), and diethylpropionamide (DEPA), but is not limited thereto.

[0153] In one aspect of the method for manufacturing a multilayer structure 100 of a glass substrate, the imidization process can employ known imidization methods without limitation, but specific examples include chemical imidization methods, thermal imidization methods, etc. As one aspect, an azeotropic thermal imidization method or a chemical imidization method can be used, but the present invention is not limited to these.

[0154] The azeotropic thermal imidization method may, for example, involve adding toluene or xylene to a polyimide precursor solution containing the polyfunctional (meth)acrylic acid compound and stirring, and carrying out an imidization reaction at about 160°C to about 200°C for about 6 hours to about 24 hours. The water released during the formation of the imide ring can be separated as an azeotrope of toluene or xylene, but is not necessarily limited thereto.

[0155] In a method for manufacturing a glass substrate multilayer structure 100 according to one aspect, the polyfunctional (meth)acrylic acid compound in the anti-scattering composition may be further crosslinked at the temperature at which the imidization reaction is performed.

[0156] The method for forming the anti-scattering layer 20 is described below.

[0157] In a method of manufacturing a multilayer structure 100 of a glass substrate according to one aspect, the anti-scattering layer 20 can be formed by coating the anti-scattering composition onto one side of the flexible glass substrate 10 and curing it. Here, the coating method can be any one of bar coating, dip coating, die coating, gravure coating, comma coating, and slit coating, or a combination thereof, but is not limited to these methods.

[0158] The curing process may be performed at a temperature of about 50°C to about 250°C, and the heat treatment may be performed more than once, or at the same temperature or within different temperature ranges, but this is only a non-limiting example and is not required to be limited thereto. Furthermore, the heat treatment time may be from about 1 minute to about 60 minutes, but is not required to be limited thereto.

[0159] When heat-treated as described above, crosslinking of the polyfunctional (meth)acrylic acid compound in the anti-scattering composition can be carried out without an additional initiator. Since no initiator is included, stability at room temperature can also be improved. When the polyfunctional (meth)acrylic acid compound exists in the anti-scattering composition in a partially crosslinked state, the isotropy of the composition can be further improved.

[0160] Next, in a method for manufacturing a multilayer structure 100 of a glass substrate according to one aspect, a method for preparing the hard coating composition for forming the hard coating 30 will be described.

[0161] In one embodiment, the hard coating 30 can be made from a known hard coating composition having the same shrinkage properties as the multifunctional (meth)acrylic crosslinked polymer of the anti-scattering layer, and can be made by curing a composition containing a multifunctional (meth)acrylic compound, but is not limited thereto.

[0162] One method for manufacturing a glass substrate multilayer structure 100 includes the steps of coating and curing an anti-scattering layer composed of a flexible polymer formed on one side of a glass substrate. This process causes bending of the multilayer structure, leading to reduced bending characteristics, durability, and other issues. However, when a hard coating is formed on the opposite side of the anti-scattering layer by coating and curing a hard coating composition comprising a (meth)acrylic acid material having the same or similar shrinkage characteristics as the multifunctional (meth)acrylic acid crosslinked polymer of the anti-scattering layer, the bending phenomenon caused by the anti-scattering layer is more significantly counteracted, thereby obtaining a glass substrate multilayer structure 100 with superior bending characteristics, durability, and other properties.

[0163] In a method for manufacturing a glass substrate multilayer structure 100 according to one aspect, when the hard coating 30 is formed by curing a composition containing a polyfunctional (meth)acrylic acid compound, the hard coating 30 can be formed by a step of photocuring or thermal curing after applying the hard coating composition, but is not limited thereto.

[0164] Furthermore, in a method of manufacturing a multilayer structure 100 of a glass substrate according to one aspect, the hard coating composition may also include a photoinitiator or a thermal initiator.

[0165] In one embodiment, the photoinitiator may be a ium salt and / or organometallic salt, etc., as a photocation initiator, such as any one or a combination of two or more of diaryliodoium salts, triarylthioium salts, aryl diazonium salts and iron-aromatic complexes, but this is only a non-limiting example and is not required to be limited thereto.

[0166] The content of the photoinitiator is not particularly limited. For example, based on 100 parts by weight of the hard coating composition, it may include, for example, about 0.01 to about 10 parts by weight, specifically about 0.1 to about 10 parts by weight, more specifically about 0.5 to about 5 parts by weight of the photoinitiator. Although not limited to a specific theory, when the content of the photoinitiator is within the above range, the curing efficiency of the hard coating composition can be maintained better, and the reduction of physical properties due to residual components after curing can be further prevented.

[0167] As the thermal initiator, a cationic thermal initiator can be used, and based on 100 parts by weight of the hard coating composition, it can contain about 0.01 to about 15 parts by weight, specifically about 0.1 to about 15 parts by weight, more specifically about 0.3 to about 10 parts by weight, but is not limited thereto. Although not limited to a specific theory, when the content of the thermal initiator is within the above range, the thermosetting reaction can proceed at a more efficient rate, and the decrease in the mechanical properties of the hard coating 30 due to the reduction in the content of other components of the hard coating composition can be further prevented.

[0168] In a method of manufacturing a glass substrate multilayer structure 100 according to one aspect, the hard coating composition may further include a crosslinking agent. The crosslinking agent can cure the hard coating composition and further increase the hardness of the hard coating 30. Examples of crosslinking agents include diamines (which can promote condensation reactions with the carbonyl groups of (meth)acrylate compounds), polyvinyl compounds, and small molecule crosslinkers (e.g., formaldehyde, glutaraldehyde, potassium dichromate, osmium tetroxide, and potassium permanganate).

[0169] The content of the crosslinking agent according to the embodiment is not particularly limited. For example, the hard coating composition based on 100 parts by weight may contain about 1 to about 30 parts by weight, specifically about 5 to about 20 parts by weight, but is not limited thereto.

[0170] According to one aspect, the hard coating composition may further include a thermosetting agent.

[0171] The thermosetting agent may include amine-based thermosetting agents, imidazole-based thermosetting agents, acid anhydride-based thermosetting agents, amide-based thermosetting agents, etc. Acid anhydride-based thermosetting agents can be used to prevent discoloration and achieve high hardness. These can be used alone or in combination of two or more, but are not limited to this.

[0172] In a method for manufacturing a multilayer structure 100 of a glass substrate according to one aspect, the rigid coating composition can be prepared by diluting the solid components with a solvent. Here, the solvent can be any one or a combination of two or more of the following solvents: alcohol-based solvents such as methanol, ethanol, isopropanol, butanol, methylcellulose, and ethylcellulose; ketone-based solvents such as methyl ethyl ketone, methyl butyl ketone, methyl isobutyl ketone, diethyl ketone, diacetone, and cyclohexanone; hexane-based solvents such as hexane, heptane, and octane; and benzene-based solvents such as benzene, toluene, and xylene. However, these are merely non-limiting examples and are not intended to limit the scope.

[0173] In a method of manufacturing a glass substrate multilayer structure 100 according to one aspect, the hard coating composition may further include inorganic particles, which may be any one or a combination of two or more selected from silicon dioxide and metal oxides, but are not limited thereto.

[0174] Furthermore, the inorganic particles may further include hydroxides such as aluminum hydroxide, magnesium hydroxide, and potassium hydroxide; metal particles such as gold, silver, copper, nickel, and their alloys; conductive particles such as carbon, carbon nanotubes, and fullerenes; glass; ceramics, etc., but are not limited thereto.

[0175] Here, the average particle size of the inorganic particles can be from about 1 nm to about 200 nm, specifically from about 10 nm to about 200 nm. Within this average particle size range, inorganic particles having two or more different average particle sizes can be used, but are not limited to this. By including the aforementioned inorganic particles, the surface hardness of the hard coating 30 can be further improved.

[0176] In a method of manufacturing a multilayer structure 100 of a glass substrate according to one aspect, the hard coating composition may further include a lubricant. The lubricant may further improve winding efficiency, anti-blocking properties, abrasion resistance, scratch resistance, etc. Specific examples of the lubricant may be waxes such as polyethylene wax, paraffin wax, synthetic wax, or lignite wax; synthetic resins such as silicone resins and fluorine resins, etc., which may be used alone or in combination of two or more, but are not limited thereto.

[0177] The method for forming the hard coating 30 is described below.

[0178] In a method for manufacturing a multilayer structure 100 of a glass substrate according to one aspect, the hard coating 30 is formed by applying the hard coating composition to the opposite side of the surface on which the anti-scattering layer 20 is formed and then curing it. Here, the coating method can be selected from any one of bar coating, dip coating, die coating, gravure coating, comma coating, and slit coating, or a combination thereof, but is not limited to this.

[0179] In a method for manufacturing a multilayer structure 100 of a glass substrate according to one aspect, the curing method may include a method of performing light curing or thermal curing alone, a method of performing thermal curing after light curing, or a method of performing light curing after thermal curing, but is not limited to these methods.

[0180] In addition, in one aspect, a step may be included in which the composition for forming the hard coating is pretreated by heating prior to the photocuring, the pretreatment being performed at a temperature lower than that of the heat curing, but not necessarily limited thereto.

[0181] The following describes one embodiment in more detail based on examples and comparative examples. However, the following examples and comparative examples are only used to illustrate one embodiment in more detail, and an embodiment is not limited to the following examples and comparative examples.

[0182] Methods for measuring physical properties

[0183] 1) Surface hardness

[0184] Based on ASTM D3363, the pencil hardness of the surfaces of the glass substrate multilayer structures fabricated in the examples and comparative examples was measured using a pencil hardness tester (Gibei E&T) under a load of 750 gf with pencils of different hardness (Mitsubishi). Here, the surface of the glass substrate multilayer structure was measured with respect to the surface in the direction where the hard coating is formed.

[0185] 2) Impact resistance (pen drop)

[0186] A BIC Orange 0.7mm pen was placed vertically on the glass substrate multilayer structure samples prepared in the following examples and comparative examples and dropped from a specified position (height). The condition of the glass substrate multilayer structure was evaluated according to the following criteria. Here, the drop direction is measured on the surface in which the hard coating is formed.

[0187] <Evaluation Criteria>

[0188] ◎: No dents or indentations

[0189] ○: There are dents and indentations.

[0190] X: Broken

[0191] 3) Curl

[0192] The glass substrate multilayer structure prepared in the following embodiments and comparative examples is placed on a flat surface, and the degree of bending of the glass substrate multilayer structure in the upward or downward direction is measured. The upward bending of the edge portion of the glass substrate is represented by a + value, and the downward bending or curling is represented by a - value.

[0193] Specifically, after coating and curing the various compositions used to form the anti-scattering layer and the hard coating on a glass substrate with a width of 180 mm × a length of 76 mm × a thickness of 40 μm, the multilayer structure of the glass substrate was placed on a precisely leveled vibration isolation table, and then the bending of the multilayer structure of the glass substrate was measured at room temperature. Here, when the substrate bends towards the vibration isolation table, so that the center of the glass substrate bends towards the air layer, the discontinuity of the highest bending point from the edge is measured with reference to the edge and expressed as a negative (stress) value (mm). Conversely, when both ends of the glass substrate bend towards the air layer on the vibration isolation table, the discontinuity of the edge rise is measured with reference to the center and expressed as a positive (tensile) value (mm).

[0194] 4) Yellowness Index (YI)

[0195] The yellowness index was measured using a spectrophotometer (Nippon Denshoku, COH-5500) based on the ASTM E313 standard.

[0196] 5) Light transmittance

[0197] Based on ASTM D1746 standard, the total transmittance of a 50 μm thick film was measured in the full wavelength range of 400 nm to 700 nm using a spectrophotometer (Nippon Denshoku, COH-400). The unit is %.

[0198] 6) Phase difference R th

[0199] Phase difference is measured using Axoscan. The film is cut to a certain size and its thickness is measured using Axoscan. Then, in order to measure the phase difference and compensate for the phase difference value via Axoscan, the thickness (nm) measured simultaneously is input for correction in the C-plate direction.

[0200] [Formula 1]

[0201] R th =[(n x +n y ) / 2-n z ]×d

[0202] (In Equation 1, n) x It is the largest refractive index among in-plane refractive indices, n y It is the in-plane refractive index that is related to n xVertical refractive index, n z (This is the vertical refractive index; d is a value calculated by converting the thickness of the multilayer glass substrate structure to 100 μm.)

[0203] [Preparation of the anti-scattering composition]

[0204] [Preparation Example 1]

[0205] After filling 230 g of N,N-dimethylpropionamide (DMPA) into a stirrer under nitrogen flow, 41 g of 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether (6FODA) was dissolved while maintaining the reactor temperature at 25°C. At the same temperature, 50 g of ethylene glycol bis-anhydro trimellitate (TMEG100) was added and dissolved while stirring for a certain time to prepare a polyimide precursor solution containing the polyimide precursor. A solution of dipentaerythritol hexaacrylate diluted in N,N-dimethylpropionamide (DMPA) solvent to a solids concentration of 50 parts by weight was added to the polyimide precursor solution at 25°C and then stirred for a certain time. Here, based on a total of 100 parts by weight of polyimide precursor and dipentaerythritol hexaacrylate, 30 parts by weight of dipentaerythritol hexaacrylate were included. Then, dimethylpropionamide (DMPA) is added to make the concentration of solids 20 parts by weight to prepare an anti-scattering composition.

[0206] [Preparation Example 2]

[0207] The anti-scattering composition was prepared in the same manner as in Preparation Example 1, except that it contained 20 parts by weight of dipentaerythritol hexaacrylate, based on a total of 100 parts by weight of polyimide precursor and dipentaerythritol hexaacrylate.

[0208] [Preparation Example 3]

[0209] The anti-scattering composition was prepared in the same manner as in Preparation Example 1, except that, based on a total of 100 parts by weight of polyimide precursor and pentaerythritol tetraacrylate, 30 parts by weight of pentaerythritol tetraacrylate were included instead of dipentaerythritol hexaacrylate.

[0210] [Preparation Example 4]

[0211] The anti-scattering composition was prepared in the same manner as in Preparation Example 1, except that, based on a total of 100 parts by weight of polyimide precursor and urethane acrylate, 30 parts by weight of urethane acrylate (PU9020, Miwon Special Chemical) was used instead of dipentaerythritol hexaacrylate.

[0212] [Preparation Example 5]

[0213] The anti-scattering composition was prepared in the same manner as in Preparation Example 1, except that, based on a total of 100 parts by weight of polyimide precursor and polyester acrylate, 30 parts by weight of polyester acrylate (PS2500, Miwon Special Chemical) was used instead of dipentaerythritol hexaacrylate.

[0214] [Comparative Preparation Example 1]

[0215] After filling 230 g of N,N-dimethylpropionamide (DMPA) into a nitrogen-fluidized stirrer, 41 g of 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether (6FODA) was dissolved while maintaining the reactor temperature at 25°C. At the same temperature, 50 g of ethylene glycol bis-anhydro trimellitate (TMEG100) was added and dissolved while stirring for a certain period of time to prepare a polyimide precursor solution containing the polyimide precursor. Dimethylpropionamide (DMPA) was then added to achieve a solids concentration of 20 parts by weight to obtain an anti-scattering composition.

[0216] [Preparation of Hard Coating Compositions]

[0217] [Preparation Example 6]

[0218] A composition for forming an acrylic hard coating was prepared by diluting 91 g of pentaerythritol triacrylate (PETA), 3 g of fine silica particles with a particle size of 15 nm (surface treatment: 3-methacryloyloxypropylmethyldimethoxysilane), and 1.95 g of photoinitiator (Irgacure 184, Ciba) solids in methyl ethyl ketone (MEK) solvent to a solids concentration of 35 parts by weight.

[0219] [Manufacturing of Multilayer Structures on Glass Substrates]

[0220] [Example 1]

[0221] The anti-scattering composition prepared in Preparation Example 1 was coated onto one side of a glass substrate (UTG 40 μm) using a #20 Mayer rod. The substrate was dried at 80°C for 15 minutes under N2 atmosphere, followed by drying at 230°C for 20 minutes to form an anti-scattering layer with a thickness of 5 μm. Then, the hard coating composition prepared in Preparation Example 6 was coated onto the uncoated side of the glass substrate using a #10 rod, dried at 65°C for 3 minutes, and then irradiated with 300 mJ / cm². 2 Ultraviolet light is used to prepare a multilayer structure of a glass substrate with a hard coating of 5 μm thickness.

[0222] [Example 2]

[0223] Except that the thickness of the anti-scattering layer is 8 μm, the glass substrate multilayer structure is manufactured in the same manner as in Example 1.

[0224] [Example 3]

[0225] Except that the thickness of the anti-scattering layer is 2 μm, the glass substrate multilayer structure is manufactured in the same manner as in Example 1.

[0226] [Example 4]

[0227] A multilayer glass substrate structure was manufactured in the same manner as in Example 1, except that the anti-scattering composition prepared in Preparation Example 2 was used instead of the anti-scattering composition prepared in Preparation Example 1 to form the anti-scattering layer.

[0228] [Example 5]

[0229] A multilayer glass substrate structure was manufactured in the same manner as in Example 1, except that the anti-scattering composition prepared in Preparation Example 3 was used instead of the anti-scattering composition prepared in Preparation Example 1 to form the anti-scattering layer.

[0230] [Example 6]

[0231] A multilayer glass substrate structure was prepared in the same manner as in Example 1, except that the anti-scattering composition prepared in Preparation Example 4 was used instead of the anti-scattering composition prepared in Preparation Example 1 to form the anti-scattering layer.

[0232] [Example 7]

[0233] A multilayer structure of a glass substrate was prepared in the same manner as in Example 1, except that the anti-scattering composition prepared in Preparation Example 5 was used instead of the anti-scattering composition prepared in Preparation Example 1 to form the anti-scattering layer.

[0234] [Comparative Example 1]

[0235] A multilayer structure of a glass substrate was prepared in the same manner as in Example 1, except that the anti-scattering composition prepared in Comparative Preparation Example 1 was used instead of the anti-scattering composition prepared in Preparation Example 1 to form the anti-scattering layer.

[0236] The physical properties of the glass substrate multilayer structures prepared in Examples 1 to 7 and Comparative Example 1 were measured and are shown in Table 1 below.

[0237] [Table 1]

[0238]

[0239] Referring to Table 1 above, the glass substrate multilayer structures of Examples 1 to 7, including the anti-scattering layer containing (meth)acrylic acid crosslinked polymer and polyimide polymer, have excellent surface hardness of 5H or higher, and according to the pen drop test results, it can be confirmed that even if the pen is dropped from a height of 15 cm or higher (e.g., 20 cm), no dents or indentations will be produced, demonstrating very excellent surface properties.

[0240] Furthermore, it can be confirmed that the bending of the glass substrate multilayer structure in all embodiments is less than 0.1 mm, less than 0.2 mm, or less than 0.3 mm, effectively suppressing bending and making it suitable for use as a flexible glass substrate multilayer structure.

[0241] On the other hand, the glass substrate multilayer structure of Comparative Example 1, which includes an anti-scattering layer without (meth)acrylic acid crosslinked polymer, has a lower surface hardness than that of Examples 1 to 7, and according to the pen drop test results, it is prone to breakage when the pen is dropped from a height of 15 cm. In addition, it has been confirmed to have significantly reduced surface properties and low bending properties of less than 0.05 mm.

[0242] Furthermore, it was confirmed that the glass substrate multilayer structures of Examples 1 to 7 possess excellent optical properties, such as yellowness index (YI), transmittance, and phase difference R. th wait.

[0243] Therefore, according to one embodiment, the glass substrate multilayer structure having an anti-scattering layer comprising a multifunctional (meth)acrylic acid crosslinked polymer and a polyimide polymer does not exhibit a decrease in surface hardness or indentation, and can ensure user safety by significantly improving impact resistance, and has excellent optical properties.

[0244] As described above, the present invention has described a multilayer structure of a glass substrate, its manufacturing method, and a flexible display panel including the same through specific details and limited embodiments. However, these descriptions are provided only to aid in a complete understanding of the invention. Therefore, the invention is not limited to the above embodiments, and those skilled in the art can make various modifications and variations based on these descriptions.

[0245] Therefore, the concept of the present invention should not be limited to the above embodiments, and all that is the same as or equivalent to the scope of the appended claims is intended to fall within the scope of the present invention.

Claims

1. A multilayer glass substrate structure, comprising: Flexible glass substrate; An anti-scattering layer is formed on one side of the flexible glass substrate, and A hard coating is formed on the other side of the flexible glass substrate. The anti-scattering layer comprises a multifunctional (meth)acrylic acid crosslinked polymer and a polyimide polymer, wherein the multifunctional (meth)acrylic acid crosslinked polymer and the polyimide polymer are not covalently bonded to each other, and The hard coating includes a (meth)acrylic hard coating.

2. The multilayer glass substrate structure according to claim 1, wherein, The multifunctional (meth)acrylic acid crosspolymer includes alkenyl, ether, urethane, ester, or combinations thereof.

3. The multilayer glass substrate structure according to claim 1, wherein, The multifunctional (meth)acrylic acid crosslinked polymer comprises structural units derived from multifunctional (meth)acrylic acid compounds having 3 to 6 (meth)acrylic acid groups.

4. The multilayer glass substrate structure according to claim 3, wherein, The polyfunctional (meth)acrylate compounds include trimethylolpropane trimethacrylate, trimethylolethane trimethacrylate, 1,2,4-cyclohexane trimethacrylate, pentaglycerol trimethacrylate, pentaerythritol tetramethacrylate, pentaerythritol trimethacrylate, dipentaerythritol trimethacrylate, dipentaerythritol pentamethacrylate, dipentaerythritol tetramethacrylate, dipentaerythritol hexamethacrylate, tripentaerythritol trimethacrylate, tripentaerythritol hexamethacrylate, polyfunctional urethane (meth)acrylate, polyfunctional polyester (meth)acrylate, or combinations thereof.

5. The multilayer glass substrate structure according to claim 1, wherein, The polyimide polymer includes units derived from aromatic diamines containing fluorine atoms and units derived from aromatic dianhydrides.

6. The multilayer glass substrate structure according to claim 1, wherein, The thickness of the flexible glass substrate is from 1 μm to 100 μm.

7. The multilayer glass substrate structure according to claim 1, wherein, The thickness of the anti-scattering layer is 1 μm to 20 μm.

8. The multilayer glass substrate structure according to claim 1, wherein, The thickness of the hard coating is 1 μm to 15 μm.

9. The multilayer glass substrate structure according to claim 1, wherein, The multilayer structure of the glass substrate has a pencil hardness of 4H to 9H according to ASTM D3363.

10. The multilayer glass substrate structure according to claim 1, wherein, According to the pen drop test, the impact resistance of the multilayer structure of the glass substrate is above 10cm. The impact resistance of the pen drop test refers to the state in which no surface dents or indentations are left when a ballpoint pen with a diameter of 0.7mm and a weight of 0.5g is dropped vertically from a specified height on the multilayer structure of the glass substrate.

11. A method for manufacturing a multilayer structure of a glass substrate, comprising: The step of coating one side of a flexible glass substrate with a composition comprising a polyimide precursor and a polyfunctional (meth)acrylic acid compound; The step of curing the composition comprising a polyimide precursor and a polyfunctional (meth)acrylic acid compound to form an anti-scattering layer, wherein the anti-scattering layer comprises a polyfunctional (meth)acrylic acid crosslinked polymer and a polyimide polymer, The step of coating the other side of the flexible glass substrate with a hard coating composition, wherein the hard coating composition comprises a polyfunctional (meth)acrylic acid compound; and The step of curing the hard coating composition to form a hard coating.

12. The method for manufacturing a multilayer structure of a glass substrate according to claim 11, wherein, The polyfunctional (meth)acrylic acid compounds also include alkenyl, ether, carbamate, ester, or combinations thereof.

13. The method for manufacturing a multilayer structure of a glass substrate according to claim 11, wherein, The polyfunctional (meth)acrylic acid compound comprises 3 to 6 (meth)acrylic acid groups.

14. The method for manufacturing a multilayer structure of a glass substrate according to claim 11, wherein, The polyfunctional (meth)acrylate compounds include trimethylolpropane trimethacrylate, trimethylolethane trimethacrylate, 1,2,4-cyclohexane trimethacrylate, pentaglycerol trimethacrylate, pentaerythritol tetramethacrylate, pentaerythritol trimethacrylate, dipentaerythritol trimethacrylate, dipentaerythritol pentamethacrylate, dipentaerythritol tetramethacrylate, dipentaerythritol hexamethacrylate, tripentaerythritol trimethacrylate, tripentaerythritol hexamethacrylate, polyfunctional urethane (meth)acrylate, polyfunctional polyester (meth)acrylate, or combinations thereof.

15. The method for manufacturing a multilayer structure of a glass substrate according to claim 11, wherein, The polyimide precursor includes units derived from aromatic diamines containing fluorine atoms and units derived from aromatic dianhydrides.

16. A flexible display panel comprising a multilayer glass substrate structure as described in any one of claims 1 to 10.

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