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

Abstract

This invention relates to a multilayer glass substrate structure, its manufacturing method, and a flexible display panel comprising the same. More specifically, it relates to a multilayer glass substrate structure, its manufacturing method, and a flexible display panel comprising the same, which significantly improves the phenomenon of reduced surface hardness, has significantly improved impact resistance, can ensure user safety by reducing the scattering phenomenon when the glass substrate breaks, and has excellent optical properties.

Description

[Technical Field]

[0001] This invention relates to a multilayer structure of a glass substrate, a method for manufacturing the same, and a flexible display panel including the same. [Previous Technology]

[0002] Recently, with the development of mobile devices such as smartphones and tablets, it has become necessary 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 that have bending or folding steps in the manufacturing process, are attracting attention.

[0003] Such a display device may include a transparent window covering the display screen, which has the function of protecting the display device from external impacts and scratches during use.

[0004] Display windows are typically made of glass or tempered glass, which are materials with excellent mechanical properties. However, traditional glass has the problem of lack of flexibility and its weight increases the weight of the display device.

[0005] In order to solve the above problems, flexible glass substrate thinning technology has been developed, but it is still insufficient to achieve the flexible characteristics of bendable or foldable glass, and the problem of being easily damaged by external impact has not been solved.

[0006] 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 may scatter, potentially causing injury to the user. Efforts have been made to solve this problem by forming an anti-scattering layer designed as a flexible structure on the flexible glass film.

[0007] However, when forming an anti-scattering layer (hereinafter also called a shatterproof layer), there is a problem that due to pressing, marks may be produced on the glass substrate itself or on the surface hardness layer on the glass substrate, which further causes a decrease in the physical properties of the glass multilayer structure itself, such as a decrease in surface hardness.

[0008] 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 pen-dropped, even when an anti-scattering layer including a soft polymer is formed. Furthermore, there is a need to develop a novel glass substrate multilayer structure that has significantly improved impact resistance, ensures user safety by reducing scattering when the glass substrate breaks, and possesses excellent optical properties.

[0009] The description provided in this section is intended to generally present the content of this disclosure. Within the scope of the description in this section, the work of the inventors listed and any embodiments described that are not identified as prior art are not expressly and unintentionally acknowledged as prior art to this disclosure. [Summary of the Invention]

[0010] Technical problems to be solved

[0011] One embodiment of the present invention 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 when a pen drop test is performed.

[0012] 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 phenomenon of reduced surface hardness of the glass substrate or hard coating or indentation due to pressure. It has significantly improved impact resistance, and can ensure user safety by further improving the scattering phenomenon when the glass substrate breaks. It also has excellent optical properties and can therefore be used in flexible display devices.

[0013] 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).

[0014] Another embodiment of the present invention aims to provide a multilayer structure of glass substrate, which has excellent durability and scattering resistance and flexible properties, 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.

[0015] Another embodiment of the present invention aims to provide a multilayer glass substrate structure with excellent optical properties, such as yellowness index (YI), transmittance, and thickness direction retardation (Rth), and significantly improved visibility and transparency, thus making it suitable for flexible display devices. Technical Solution

[0016] To achieve the above objective, according to one embodiment, the flexible glass substrate multilayer structure may employ a polyimide layer comprising a (meth)acrylic crosslinked polymer (or a multifunctional (meth)acrylic crosslinked polymer) as an anti-scattering layer.

[0017] According to one embodiment, a multilayer structure of a glass substrate can be 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.

[0018] In one embodiment, the glass substrate multilayer structure may further include a hard coating formed on the other side of the flexible glass substrate.

[0019] In one embodiment, the multifunctional (meth)acrylic acid crosslinker may include alkylene group, ether group, urethane group, ester group or combination thereof.

[0020] In one embodiment, the multifunctional (meth)acrylic acid crosslinking polymer may include structural units derived from multifunctional (meth)acrylic acid compounds having 3 to 6 (meth)acrylic acid groups.

[0021] In one embodiment, the polyfunctional (meth)acrylate compound may include trimethylolpropane tri(meth)acrylate, trimethylolethane tri(meth)acrylate, 1,2,4-cyclohexane tri(meth)acrylate, pentaglycerol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, dinepentetrine tri(meth)acrylate, dinepentetrine penta(meth)acrylate, dinepentetrine tetra(meth)acrylate, dinepentetrine hexa(meth)acrylate, trinepentetrine tri(meth)acrylate, trinepentetrine hexa((meth)acrylate, polyfunctional urethane (meth)acrylate, polyfunctional polyester (meth)acrylate, or combinations thereof.

[0022] In one embodiment, the polyimide polymer may include units derived from aromatic diamines containing fluorine atoms and units derived from aromatic dianhydrides.

[0023] In one embodiment, the hard coating may include a (meth)acrylic hard coating.

[0024] In one embodiment, the thickness of the flexible glass substrate can be from 1 micrometer to 100 micrometers.

[0025] In one embodiment, the thickness of the anti-scattering layer can be from 1 micrometer to 20 micrometers.

[0026] In one embodiment, the thickness of the hard coating may be from 1 micrometer to 15 micrometers.

[0027] In one embodiment, the glass substrate multilayer structure may have a pencil hardness of 4H or higher according to ASTM D3363, and more specifically, may have a pencil hardness of 4H to 9H according to ASTM D3363.

[0028] In one embodiment, according to the pen drop test, the impact resistance of the glass substrate multilayer structure can be 10 cm or more.

[0029] According to another aspect of the present invention, a method for manufacturing a multilayer structure of a glass substrate is 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.

[0030] In one embodiment, the method of 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.

[0031] In one embodiment, the polyfunctional (meth)acrylic acid compound may include alkyl, ether, urethane, ester, or combinations thereof.

[0032] In one embodiment, the polyfunctional (meth)acrylic acid compound may have 3 to 6 (meth)acrylic acid groups.

[0033] In one embodiment, the polyfunctional (meth)acrylate compound may include trimethylolpropane tri(meth)acrylate, trimethylolethane tri(meth)acrylate, 1,2,4-cyclohexane tri(meth)acrylate, pentaglycerol tri(meth)acrylate, neopentyltetroxide tetra(meth)acrylate, neopentyltetroxide tri(meth)acrylate, dinepentyltetroxide penta(meth)acrylate, dinepentyltetroxide tetra(meth)acrylate, dinepentyltetroxide hexa(meth)acrylate, trinepentyltetroxide tri(meth)acrylate, trinepentyltetroxide hexa(meth)acrylate, polyfunctional urethane (meth)acrylate, polyfunctional polyester (meth)acrylate, or combinations thereof.

[0034] In one embodiment, the polyimide precursor may include units derived from aromatic diamines containing fluorine atoms and units derived from aromatic dianhydrides.

[0035] In one embodiment, the hard coating composition may include a polyfunctional (meth)acrylic compound.

[0036] According to another aspect of the present invention, a flexible display panel comprising a multilayer structure of a glass substrate can be provided. Technical Effects

[0037] According to one solution, a multilayer glass substrate structure can be provided that does not experience a decrease in surface hardness when pressed or when writing, even when including a flexible polymer, and does not produce marks when pressed or when writing.

[0038] According to another embodiment, the multilayer structure of the glass substrate, even having 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, significantly improves the problem of reduced surface hardness or indentation when the pen is applied, as well as the problem of marks when the pen is applied, significantly improves impact resistance, improves the scattering phenomenon when the glass substrate breaks, thereby ensuring the safety of the user, and has excellent optical properties.

[0039] Furthermore, according to one embodiment 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).

[0040] Furthermore, according to one embodiment, the multilayer structure of the glass substrate has excellent durability and anti-scattering properties, and has 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 it can be used in flexible display devices.

[0041] Furthermore, according to one embodiment, the multilayer structure of the glass substrate has excellent optical properties, such as yellowness index (YI), transmittance and thickness direction phase difference (Rth), thereby significantly improving visibility and transparency, and thus can be used in flexible display devices.

Implementation Method

[0043] The following will describe in detail the glass substrate multilayer structure according to an embodiment of the present invention, its manufacturing method and the flexible display panel including the same.

[0044] 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.

[0045] In addition, the units for additives not specifically described in the instructions may be parts by weight.

[0046] In addition, unless the context clearly indicates otherwise, the singular form used in the specification and the claims is also used to include the plural form.

[0047] Throughout the specification, the phrase "a part includes" or "contains" a certain component element, unless otherwise stated, may mean that other components may be further included, rather than excluding other components.

[0048] 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.

[0049] Unless otherwise defined in this specification, the term "combination thereof" may refer to a mixture or copolymerization of the components. In addition, "combination thereof" may refer to two or more of the elements defined above the term that may be used simultaneously or provided.

[0050] 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.

[0051] Unless otherwise stated below, "derivative" may refer to a structure or composition resulting from a reaction involving compounds, or may refer to the modification of at least one functional group of a compound, specifically including the modification or departure of reactive and / or dissociative groups of the compound as a result of the reaction. Furthermore, when the structures derived from different compounds are identical, it may also include cases where the structure derived from one compound is identical to the structure derived from another compound.

[0052] 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, a block copolymer, a random copolymer, a branched copolymer, a 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).

[0053] Unless otherwise defined in this specification, "oligomer" may 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.

[0054] Unless otherwise defined in this specification, the term "flexible" may refer to a flexible component that can be rolled, bent and / or folded.

[0055] Unless otherwise defined in this specification, the term "hard coating" may be used as including "(meth)acrylic hard coating".

[0056] Unless otherwise defined in this specification, "(meth)acrylic acid" may be used as a meaning that includes "methacrylic acid" and / or "acrylic acid".

[0057] In the following text, unless otherwise defined in this specification, "polyimide" is a polymer that includes a amide structure and may be used to mean "polyimide" or "polyamide amide".

[0058] Unless otherwise defined in this specification, "(meth)acrylic acid crosslinking polymer" may refer to a crosslinking polymer formed by crosslinking (meth)acrylic acid compounds having (meth)acrylic acid groups with each other, and the (meth)acrylic acid crosslinking polymer may or may not contain (meth)acrylic acid groups, such as (meth)acrylate groups.

[0059] Unless otherwise defined in this specification, “about” can be considered as a value within 30%, 25%, 20%, 15%, 10% or 5% of the value explicitly stated.

[0060] According to one embodiment, a multilayer glass substrate structure can be provided that does not experience a decrease in surface hardness or leave marks during pressing or writing, even when the structure includes a flexible polymer.

[0061] Figure 1 illustrates a glass multilayer structure that prevents surface hardness reduction and minimizes structural changes or marks under pressure or external impact. An example of the glass multilayer structure shown in Figure 1 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). Therefore, the glass multilayer structure system in Figure 1 places the flexible glass substrate 10 between the anti-scattering layer 20 and the hard coating 30.

[0062] According to one embodiment, when using a thin glass substrate as the substrate, even if the multilayer structure of the glass substrate has 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 as its reverse side, there will be no reduction in surface hardness and / or no structural changes or marks caused by pressing or folding, and it can be used in flexible display devices.

[0063] The embodiments of the present invention will be described in detail below.

[0064] One solution may provide a multilayer structure of a glass substrate, 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.

[0065] Alternatively, another approach may provide a multilayer glass substrate structure comprising: a flexible glass substrate; an anti-scattering layer formed on one side of the flexible glass substrate; and a hard coating formed on the other (e.g., opposite) side of the flexible glass substrate, wherein the anti-scattering layer comprises a multifunctional (meth)acrylic acid crosslinked polymer and a polyimide polymer.

[0066] According to one embodiment 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. Although not limited to a particular theory, an embodiment of a glass substrate multilayer structure including an anti-scattering layer can provide flexible properties (e.g., excellent flexibility) and significantly improve the phenomena of reduced surface hardness and reduced impact resistance measured by pen drop test, which have a trade-off relationship with it, providing the desired excellent optical properties, thus making it suitable for use as a cover window for a flexible display panel.

[0067] In a glass substrate multilayer structure according to one embodiment, the multifunctional (meth)acrylic acid crosslinking 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 crosslinking of the multifunctional (meth)acrylic acid compound, 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.

[0068] 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 a chemical bond; for example, the multifunctional (meth)acrylic acid crosslinked polymer and the polyimide polymer may not be covalently bonded to each other.

[0069] In a glass substrate multilayer structure according to one embodiment, the multifunctional (meth)acrylic acid crosslinked polymer may further include alkyl groups, ether groups, urethane groups, ester groups or combinations thereof, but is not limited thereto.

[0070] Furthermore, in a glass substrate multilayer structure according to one embodiment, the multifunctional (meth)acrylic acid crosslinking polymer may include, but is not limited to, structural units derived from multifunctional (meth)acrylic acid compounds having 3 to 6 (e.g., 4 to 6, or, for example, 5 or 6) (meth)acrylic acid groups. Here, the (meth)acrylic acid groups may be, for example, acrylic acid groups or methacrylic acid groups.

[0071] In one embodiment, the multifunctional (meth)acrylic acid crosslinking polymer may include structural units derived from, for example, monomers having multifunctional (meth)acrylic acid groups and oligomers having multifunctional (meth)acrylic acid groups, but is not necessarily limited thereto.

[0072] 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. Although not limited to a specific theory, the glass substrate multilayer structure according to one embodiment can provide flexible properties and can significantly improve the phenomena of reduced surface hardness and reduced impact resistance measured by pen drop tests, which have a trade-off with it. The glass substrate multilayer structure according to one embodiment can have excellent optical properties, and is therefore further suitable for use as a cover window for flexible display panels.

[0073] More specifically, the glass substrate multilayer structure according to one embodiment 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 limited thereto.

[0074] Furthermore, according to one embodiment, 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) above the glass substrate multilayer structure.

[0075] Although not limited to a specific theory, by means of the surface hardness and impact resistance properties within the above range, a multilayer structure of a glass substrate according to a certain scheme can better maintain the original hardness, impact resistance and durability of the glass substrate while ensuring flexibility.

[0076] Furthermore, the glass substrate multilayer structure according to one embodiment 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 step difference from the uppermost bending point of the center is measured with reference 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 step difference of the edge rise is measured with reference to the center and expressed as a positive (tensile) value (mm).

[0077] Although not limited to a specific theory, by having the bending characteristics within the above range, a multilayer structure of a glass substrate according to one embodiment has the flexibility to be folded or bent, so that the glass will not break or crack even if repeated folding or bending operations occur, and therefore it can be more suitable for flexible display devices.

[0078] Furthermore, the glass substrate multilayer structure according to one embodiment may have a yellowness index (YI) measured according to ASTM E313 in several ranges, such as about 0.1 to about 5.0, about 0.1 to about 3.0, about 0.1 to about 2.0, and the b* value may be, for example, about 0.1 to about 2.0, about 0.1 to about 1.5, about 0.1 to about 1.0, but is not necessarily limited thereto.

[0079] Furthermore, the total transmittance of the glass substrate multilayer structure according to one embodiment, 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 limited thereto.

[0080] 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 and the thickness of the film is measured using an Axoscan (phase difference meter). 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 corresponds to the delay between two orthogonally polarized rays in two orthogonally polarized states of light passing through the material at the highest and lowest refractive indices, and can be expressed by phase (degrees) or distance. In one embodiment, the measured phase difference (Rth) can be, for example, from about 10 micrometers to about 40 micrometers, or from about 10 micrometers to about 30 micrometers, but is not limited to these values. The phase difference (Rth) (at 550 nanometers) is calculated by the following Equation 1. [Formula 1] Rth= [(nx+ ny) / 2- nz] × d

[0081] In Equation 1, nx is the largest in-plane refractive index, ny is the in-plane refractive index perpendicular to nx, nz is the perpendicular refractive index, and d is the value calculated by converting the thickness of the multilayer structure of the glass substrate to 10 micrometers (i.e., in 10 micrometers).

[0082] Although not limited to a specific theory, due to the optical properties within the above range, the multilayer structure of the glass substrate according to one scheme is excellent in terms of visibility and transparency, and is therefore more suitable for use in flexible display devices.

[0083] The following description, with reference to FIG1, details the composition of the flexible glass substrate 10, the anti-scattering layer 20, and the hard coating 30 included in a glass substrate multilayer structure 100 according to an embodiment of the present invention. However, this is merely exemplary, and the present invention is not limited to the specific embodiments illustrated herein.

[0084] <Flexible Glass Substrate>

[0085] First, the flexible glass substrate in one embodiment will be described.

[0086] In one embodiment, a flexible glass substrate refers to a foldable or curved glass substrate that can be used as a window for a display device, has good durability, and has excellent surface smoothness and transparency.

[0087] In one embodiment, a flexible glass substrate that bends due to pressure or force can have excellent recovery properties that allow it to return to its original shape after the pressure or force is removed.

[0088] 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 enable the glass substrate multilayer structure 100 to undergo deformation sufficient for bending or folding with a small radius of curvature, the flexible glass substrate 10 can be formed from an ultrathin glass substrate.

[0089] In the glass substrate multilayer structure 100 according to one embodiment, the flexible glass substrate 10 may be an ultrathin glass substrate with a thickness of about 100 micrometers or less, specifically about 1 micrometer to about 100 micrometers, more specifically about 30 micrometers to about 100 micrometers, but not necessarily limited thereto.

[0090] In a glass substrate multilayer structure 100 according to one embodiment, the flexible glass substrate 10 may further include a chemically strengthened layer, which may be formed by chemically strengthening one or more surfaces of the first or second surface of the flexible glass substrate 10. Therefore, the strength of the flexible glass substrate 10 can be further significantly improved.

[0091] 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 micrometers or less can be prepared and processed into a predetermined shape by cutting, chamfering, and firing before undergoing chemical strengthening treatment. Alternatively, glass of normal thickness can be prepared and thinned to approximately 100 micrometers or less before shape processing and / or chemical strengthening treatment. However, this is merely a non-limiting example and is not intended to be limiting. Here, any one or two methods selected from mechanical and / or chemical methods can be used for the thinning operation, but this is not a limitation.

[0092] <Anti-scattering layer>

[0093] Next, the anti-scattering layer according to one scheme will be explained.

[0094] In addition to improving the 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 according to one embodiment of the invention, as a non-limiting embodiment, further improves the phenomenon of reduced surface hardness by being formed on the opposite side to the surface on which the hard coating is formed, and can further improve impact resistance.

[0095] In a glass substrate multilayer structure 100 according to one embodiment, 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.

[0096] In a glass substrate multilayer structure 100 according to one embodiment, the multifunctional (meth)acrylic acid crosslinking polymer can be formed by inducing crosslinking polymerization of the multifunctional (meth)acrylic acid compound through heating or other means, and the crosslinking polymerization can be all or part of the crosslinking of the multifunctional (meth)acrylic acid compound, but is not limited thereto. The multifunctional (meth)acrylic acid compound is a compound having multifunctional (meth)acrylic acid groups, such as acrylic acid groups or methacrylic acid groups.

[0097] 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 bonding; for example, the multifunctional (meth)acrylic acid crosslinked polymer and the polyimide polymer may not be covalently bonded to each other.

[0098] In a glass substrate multilayer structure 100 according to one embodiment, the multifunctional (meth)acrylic acid crosslinked polymer may further include alkyl, ether, urethane, ester or combinations thereof, but is not limited thereto.

[0099] Furthermore, in a glass substrate multilayer structure according to one embodiment, the multifunctional (meth)acrylic acid crosslinking polymer may include structural units derived from a multifunctional (meth)acrylic acid compound having 3 to 6 (e.g., 4 to 6, or e.g., 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.

[0100] More specifically, the polyfunctional (meth)acrylic acid crosslinked polymer may include 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, but is not necessarily limited thereto. 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, neopentyltetroxide tetramethacrylate, neopentyltetroxide trimethacrylate, dinepentyltetroxide pentamethacrylate, dinepentyltetroxide tetramethacrylate, dinepentyltetroxide hexamethacrylate, trinepentyltetroxide trimethacrylate, trinepentyltetroxide 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, dinepentylenetetroxide hexa(meth)acrylate, neopentylenetetroxide tetra(meth)acrylate, polyfunctional urethane (meth)acrylate, polyfunctional polyester (meth)acrylate, or combinations thereof.

[0101] In a glass substrate multilayer structure 100 according to one embodiment, the polyfunctional urethane (meth)acrylate can be 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.

[0102] Here, as an example of a (meth)acrylate containing a hydroxyl group in the molecule, it may be any one of the following: a mixture of 2-hydroxyethyl (meth)acrylate, 2-hydroxyisopropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, caprolactone ring-opened hydroxy acrylate and neopentyl tetrol tri / tetra(meth)acrylate or a mixture of dinepentyl tetrol penta / hexa(meth)acrylate, or a combination thereof, but is not limited thereto.

[0103] 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, and 4,4'-methylenebis(cyclohexylisocyanate). (e.g., isophorone 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 any combination thereof, but not necessarily limited thereto.)

[0104] Furthermore, in the glass substrate multilayer structure 100 according to one embodiment, 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 include polyester acrylate (PS2500, Mihara Special Chemicals), but this is only a non-limiting example and is not required to be limited thereto.

[0105] Herein, examples of the multifunctional polyester (meth) acrylate may include polyester diacrylate, polyester tetraacrylate, polyester hexaacrylate, polyester neopentyl terephthalate triacrylate, polyester neopentyl terephthalate tetraacrylate, polyester neopentyl terephthalate hexaacrylate or combinations thereof, but are not limited thereto.

[0106] In a glass substrate multilayer structure 100 according to one embodiment, the polyimide polymer may include units derived from aromatic diamines containing fluorine atoms and units derived from aromatic dianhydrides. Although not limited to a specific theory, in this case, the optical and mechanical properties are superior, and the elasticity and resilience are further improved, which can further enhance the effect of preventing deformation of the glass substrate, but the invention is not limited thereto.

[0107] In a glass substrate multilayer structure 100 according to one embodiment, the aromatic diamine containing fluorine atoms may be selected from any one or a mixture of two or more of 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.

[0108] In a glass substrate multilayer structure 100 according to one embodiment, the aromatic dianhydride may be selected from 4,4'-hexafluoroisopropylidene diphthalic anhydride (6FDA), biphenyltetracarboxylic dianhydride (BPDA), oxydiphthalic dianhydride (ODPA), sulfonyl diphthalic anhydride (SO2DPA), and (isopropylidenediphenoxy)bis(phthalic anhydride). (6HDBA), 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic dianhydride (TDA), 1,2,4,5-benzene tetracarboxylic dianhydride (PMDA), benzophenone tetracarboxylic dianhydride (BTDA), bis(carboxyphenyl) dimethyl silane dianhydride (SiDA), bis(dicarboxyphenoxy) diphenyl sulfide dianhydride (SiDA) The product may contain any one or a mixture of two or more of the following: dianhydride (BDSDA) and ethylene glycol bis(anhydrotrimellitate) (TMEG100), but is not limited thereto.

[0109] In a glass substrate multilayer structure 100 according to one embodiment, 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 multifunctional (meth)acrylic acid crosslinked polymer, the problem of reduced surface hardness, impact resistance and durability, which have a trade-off relationship with the flexible properties, can be significantly improved.

[0110] In one embodiment of the present invention, the anti-scattering layer 20 comprising the multifunctional (meth)acrylic acid crosslinked polymer can be formed together with the hard coating 30 on both sides of the flexible glass substrate 10, especially by curing the hard coating formed by a compound having (meth)acrylic acid groups, thereby further improving the dent resistance and impact resistance according to the pen drop test.

[0111] In a glass substrate multilayer structure 100 according to one embodiment, the thickness of the anti-scattering layer 20 is not particularly limited, but can be from about 1 micrometer to about 20 micrometers, specifically from about 2 micrometers to about 10 micrometers, more specifically from about 5 micrometers to about 10 micrometers, but not necessarily limited thereto.

[0112] <Hard Coating>

[0113] The following describes a hard coating according to one aspect of the present invention.

[0114] 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.

[0115] In one embodiment, 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.

[0116] Furthermore, in a glass substrate multilayer structure 100 according to one embodiment, the hard coating 30 may be designed to have the same characteristics as, for example, 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.

[0117] Furthermore, in the glass substrate multilayer structure 100 according to one embodiment, the thickness of the hard coating 30 can be, for example, from about 1 micrometer to about 15 micrometers, from about 1 micrometer to about 10 micrometers, or from about 1 micrometer to about 5 micrometers, but is not necessarily limited thereto. When having a thickness within the above range, the hard coating 30 is preferable because it can maintain excellent hardness and flexibility.

[0118] 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.

[0119] In addition, the inorganic particles may further include hydroxides such as aluminum hydroxide, magnesium hydroxide, potassium hydroxide, etc.; metal particles such as gold, silver, copper, nickel and their alloys, etc.; conductive particles such as carbon, carbon nanotubes, fullerene, etc.; glass; ceramics, etc., but are not limited thereto.

[0120] In one embodiment, the inorganic particles may have an average particle diameter of about 1 nanometer to about 200 nanometers, specifically about 10 nanometers to about 200 nanometers. Within the range of average particle diameters, two or more types of inorganic particles with different average particle sizes may be used, but are not limited thereto. In one embodiment, by including the inorganic particles, the surface hardness of the hard coating 30 can be improved.

[0121] <Flexible Display Panel>

[0122] Another solution provides a flexible display panel or flexible display device including a glass substrate multilayer structure 100 according to one of the above solutions.

[0123] 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. The flexible display device can be, for example, a general liquid crystal display device, an electroluminescence display device, a plasma display device, and a field emission display device, etc., but is not limited thereto.

[0124] <Method for Manufacturing Multilayer Structures of Glass Substrates>

[0125] The following describes in detail a method for manufacturing a multilayer structure 100 of a glass substrate according to yet another embodiment.

[0126] A method for manufacturing a glass substrate multilayer structure 100 according to one embodiment 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.

[0127] Furthermore, a method for manufacturing a multilayer structure 100 of a glass substrate according to another embodiment may include: a 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 20; and a step of coating and curing a hard coating composition on the other side of the flexible glass substrate to form a hard coating 30.

[0128] First, in a method for manufacturing a glass substrate multilayer structure 100 according to one embodiment, the anti-scattering composition for forming the anti-scattering layer 20 will be described.

[0129] According to one embodiment, 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 aromatic diamines containing fluorine atoms and the aromatic dianhydrides may be the same as those described above in the description of the anti-scattering layer 20.

[0130] In addition, the polyfunctional (meth)acrylic acid compound according to one embodiment may also include alkyl, ether, urethane, ester or combination thereof, but is not limited thereto.

[0131] Furthermore, in a method for manufacturing a glass substrate multilayer structure 100 according to one embodiment, at least one of the more than one polyfunctional (meth)acrylic acid compounds may have 3 to 6 (e.g., 4 to 6, or e.g., 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.

[0132] 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.

[0133] In a method for manufacturing a glass substrate multilayer structure 100 according to one embodiment, based on a total of 100 parts by weight of 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.

[0134] 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.

[0135] 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 to carry out a polymerization reaction. Here, 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 a temperature of about -20°C to about 200°C, or specifically at a temperature of about 0°C to about 180°C, but is not necessarily limited to these temperatures. Furthermore, the organic solvent that can be used in the polymerization reaction may be any one or a mixture of two or more of N,N-diethylformamide (DEAc), N,N-diethylformamide (DEF), N-ethylpyrrolidone (NEP), dimethylpropionamide (DMPA), and diethylpropanamide (DEPA), but is not limited thereto.

[0136] Here, according to one embodiment, the polyimide precursor may exist 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, in which case the polyimide precursor may dissolve upon mixing with the organic solvent to form a polyimide precursor solution.

[0137] The anti-scattering composition according to one embodiment can be prepared by adding one or more of the polyfunctional (meth)acrylic acid compounds to the polyimide precursor solution.

[0138] In a method for manufacturing a glass substrate multilayer structure 100 according to one embodiment, the addition of one or more polyfunctional (meth)acrylic acid compounds may 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.

[0139] Furthermore, crosslinking and / or amide formation can be induced by heating during the stirring. Here, the reaction conditions are not limited as long as the solubility of the anti-spreading composition in the solvent increases during the crosslinking reaction and the crosslinking 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.

[0140] 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-diethylmethylamine (DEF), N-ethylpyrrolidone (NEP), dimethylpropionamide (DMPA), diethylpropionamide (DEPA), etc., but is not limited thereto.

[0141] In a method for manufacturing a glass substrate multilayer structure 100 according to one embodiment, the amide process can employ conventional amide methods without limitation, but specific examples include chemical amide methods, thermal amide methods, etc. As an embodiment, an azeotropic thermal amide method or a chemical amide method can be used, but the present invention is not limited to these.

[0142] 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 the 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 may be separated as an azeotrope of toluene or xylene, but is not necessarily limited thereto.

[0143] In a method of manufacturing a glass substrate multilayer structure 100 according to one embodiment, the polyfunctional (meth)acrylic acid compound in the anti-scattering composition may be further crosslinked at the temperature at which the methimization reaction is performed.

[0144] The method for forming the anti-scattering layer 20 will be described below.

[0145] In a method for manufacturing a multilayer structure 100 of a glass substrate according to one embodiment, 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 thereto.

[0146] The curing may be performed by heat treatment 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 in different temperature ranges more than once, but this is only a non-limiting example and is not required to be limited thereto. In addition, the heat treatment time may be from about 1 minute to about 60 minutes, but is not required to be limited thereto.

[0147] When heat treatment is performed as described above, the 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 contained, the 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.

[0148] Next, in a method for manufacturing a glass substrate multilayer structure 100 according to one embodiment, a method for preparing the hard coating composition for forming the hard coating 30 will be described.

[0149] In one embodiment, the hard coating 30 can be made using a conventional hard coating composition. Here, the hard coating composition has 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.

[0150] A method for manufacturing a glass substrate multilayer structure 100 according to one embodiment includes the steps of coating and curing an anti-scattering layer made of a flexible polymer to form on one side of a glass substrate, thereby causing bending of the multilayer structure and resulting in a reduction in bending characteristics, durability, etc. Here, when a hard coating composition comprising a (meth)acrylic material having the same or similar shrinkage characteristics as the multifunctional (meth)acrylic crosslinked polymer of the anti-scattering layer is coated and cured on the opposite side to form a hard coating, the bending phenomenon caused by the anti-scattering layer is more significantly offset, thereby obtaining a glass substrate multilayer structure 100 with superior bending characteristics, durability, etc.

[0151] In a method of manufacturing a glass substrate multilayer structure 100 according to one embodiment, when the hard coating 30 is formed by curing a composition containing a polyfunctional (meth)acrylic acid compound, the hard coating 30 may be formed by a photocuring or thermal curing step after coating the hard coating composition, but is not limited thereto.

[0152] Furthermore, in a method of manufacturing a glass substrate multilayer structure 100 according to one embodiment, the hard coating composition may further include a photoinitiator or a thermal initiator.

[0153] In one embodiment, the photoinitiator may be an onion salt and / or an organometallic salt, etc., as a photocation initiator. For example, it may be any one or a combination of two or more of the following: diaryliodonium salt, triarylsulfonium salt, aryldiazonium salt, and iron-arene complex. However, this is only a non-limiting example and is not required to be limited thereto.

[0154] 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.

[0155] As the thermal initiator, a cationic thermal initiator can be used, and based on 100 parts by weight of the hard coating composition, it may 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 of the thermal initiator, 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.

[0156] In a method of manufacturing a glass substrate multilayer structure 100 according to one embodiment, 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).

[0157] The content of the crosslinking agent according to the embodiment is not particularly limited. For example, based on 100 parts by weight of the hard coating composition, it may contain about 1 to about 30 parts by weight, specifically about 5 to about 20 parts by weight of the crosslinking agent, but is not limited thereto.

[0158] According to one embodiment, the hard coating composition may further include a thermosetting agent.

[0159] The thermosetting agent may include amine thermosetting agents, imidazole thermosetting agents, acid anhydride thermosetting agents, amide thermosetting agents, etc. Acid anhydride 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.

[0160] In a method for manufacturing a multilayer structure 100 of a glass substrate according to one embodiment, the hard 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 solvents such as methanol, ethanol, isopropanol, butanol, methylcellulose, and ethylcellulose; ketone solvents such as methyl ethyl ketone, methyl butyl ketone, methyl isobutyl ketone, diethyl ketone, dipropyl ketone, and cyclohexanone; hexane solvents such as hexane, heptane, and octane; and benzene solvents such as benzene, toluene, and xylene. However, these are only non-limiting examples and are not intended to be limited thereto.

[0161] In a method of manufacturing a glass substrate multilayer structure 100 according to one embodiment, 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.

[0162] In addition, the inorganic particles may further include hydroxides such as aluminum hydroxide, magnesium hydroxide, potassium hydroxide, etc.; 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.

[0163] Here, the average particle size of the inorganic particles can be from about 1 nanometer to about 200 nanometers, specifically from about 10 nanometers to about 200 nanometers. Within the range of average particle size, inorganic particles having two or more different average particle sizes can be used, but are not limited thereto. By including the above-mentioned inorganic particles, the surface hardness of the hard coating 30 can be further improved.

[0164] In a method for manufacturing a multilayer structure 100 of a glass substrate according to one embodiment, the hard coating composition may further include a lubricant. The lubricant may further improve winding efficiency, blocking resistance, abrasion resistance, scratch resistance, etc. Specific examples of the lubricant may include 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.

[0165] The method for forming the hard coating 30 will be described below.

[0166] In a method for manufacturing a multilayer structure 100 of a glass substrate according to one embodiment, the hard coating 30 can be formed by applying the hard coating composition to the reverse 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 rod coating, dip coating, die coating, gravure coating, comma coating and slot coating or a combination thereof, but is not limited to this.

[0167] In a method for manufacturing a glass substrate multilayer structure 100 according to one embodiment, the curing method may be 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, etc., but is not limited to these.

[0168] Furthermore, in one embodiment, a step of pretreatment may be included by heating the composition used to form the hard coating prior to the photocuring, the pretreatment being performed at a temperature lower than that of the heat curing, but not necessarily thereto.

[0169] The embodiments and comparative examples of the present invention will be described in more detail below. However, the embodiments and comparative examples below are only used to illustrate the embodiments in more detail, and the present invention is not limited to the embodiments and comparative examples below.

[0170] [Methods for measuring physical properties]

[0171] (1) Surface hardness

[0172] Based on ASTM D3363, the pencil hardness of the surfaces of the glass substrate multilayer structures manufactured in the examples and comparative examples was measured using a pencil hardness tester (Gibei E&T) under a load of 750 gf using pencils of different hardness (Mitsubishi Corporation). Here, the surface of the glass substrate multilayer structure was measured towards the surface on which the hard coating is formed.

[0173] (2)Impact resistance (pen drop)

[0174] A BIC Orange 0.7 mm pen was placed vertically above 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 was taken with the surface with the hard coating formed as the drop direction. <Evaluation Criteria> ◎: No dents or indentations ○: Dents and indentations X: Broken

[0175] (3) Bend

[0176] The glass substrate multilayer structure prepared in the following examples 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 positive value (+), and the downward bending or curling is represented by a negative value (-).

[0177] 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 × length of 76 mm × thickness of 40 μm, the glass substrate multilayer structure is placed on a precisely leveled vibration isolation table, and then the bending of the glass substrate multilayer structure is measured 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 step difference between the highest bending point and the center 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 step difference of the edge rise is measured with reference to the center and expressed as a positive (tensile) value (mm).

[0178] (4)Yellowness Index (YI)

[0179] The yellowness index was measured using a spectrophotometer (Nippon Denshoku, COH-5500) based on the ASTM E313 standard.

[0180] (5)Transmittance

[0181] Based on ASTM D1746 standard, the total transmittance of a 50-micron thick film was measured in the full wavelength range from 400 nm to 700 nm using a spectrophotometer (Nippon Denshoku Co., Ltd., COH-400). The unit is %.

[0182] (6)Phase difference Rth

[0183] Phase difference measurement using Axoscan. The film is cut to a certain size and the thickness is measured using Axoscan. Then, in order to measure the phase difference and compensate for the phase difference value by Axoscan, the thickness (nanometers) measured while correcting towards the C-plate direction is input. [Equation 1] Rth= [(nx+ ny) / 2 - nz] ×d

[0184] In Equation 1, nx is the largest refractive index in the plane, ny is the refractive index in the plane that is perpendicular to nx, nz is the perpendicular refractive index, and d is the value calculated by converting the thickness of the multilayer structure of the glass substrate to 10 micrometers (that is, in 10 micrometers as the unit).

[0185] [Preparation of the anti-scattering composition]

[0186] [Preparation Example 1]

[0187] After filling 230 g of N,N-dimethylpropionic acid (DMPA) into a stirrer with 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(trimethicone) anhydride (TMEG100) was added and stirred for a certain time to dissolve it, thus preparing a polyimide precursor solution containing the polyimide precursor. A solution obtained by diluting dipentylenetetrol hexaacrylate in N,N-dimethylpropionic acid (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 dipentylenetetrol hexaacrylate, 30 parts by weight of dipentylenetetrol hexaacrylate were included. Then, dimethylpropionamide (DMPA) is added to make the concentration of solids 20 parts by weight to prepare an anti-scattering composition.

[0188] [Preparation Example 2]

[0189] An anti-scattering composition was prepared in the same manner as in Preparation Example 1, except that it contained 20 parts by weight of dinepentylenetetramethylol hexaacrylate, based on a total of 100 parts by weight of polyimide precursor and dinepentylenetetramethylol hexaacrylate.

[0190] [Preparation Example 3]

[0191] An 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 neopentyl tertrate, 30 parts by weight of neopentyl tertrate was included instead of dinepentyl tertrate hexaacrylate.

[0192] [Preparation Example 4]

[0193] An anti-scattering composition was prepared in the same manner as in Preparation Example 1, except that 30 parts by weight of urethane acrylate (PU9020, Mihara Special Chemicals) was used instead of dinepentylenetetrol hexaacrylate, based on a total of 100 parts by weight of polyimide precursor and urethane acrylate.

[0194] [Preparation Example 5]

[0195] An 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, Mihara Special Chemicals) was used instead of dinepentylenetetrol hexaacrylate.

[0196] [Comparative Preparation Example 1]

[0197] After filling 230 g of N,N-dimethylpropionic acid (DMPA) into a nitrogen-flowing stirrer, 41 g of 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether (6FODA) was dissolved while the reactor temperature was maintained at 25°C. At the same temperature, 50 g of ethylene glycol bis(trimethicone) anhydride (TMEG100) was added and stirred for a certain time to dissolve it, thus preparing a polyimide precursor solution containing the polyimide precursor. Next, dimethylpropionic acid (DMPA) was added to bring the solids concentration to 20 parts by weight to obtain an anti-scattering composition.

[0198] [Preparation of Hard Coating Compositions]

[0199] [Preparation Example 6]

[0200] A composition for forming an acrylic hard coating was prepared by diluting 91 g of pentaerythritol triacrylate (PETA), 3 g of first silica fine particles with a particle size of 15 nanometers (surface treatment: 3-methacryloxypropylmethyldimethoxysilane), 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.

[0201] [Manufacturing of Multilayer Structures on Glass Substrates]

[0202] [Example 1]

[0203] 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 bar. The substrate was then dried in a convection oven under N2 atmosphere at 80°C for 15 minutes and 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 Mayer bar, dried at 65°C for 3 minutes, and then irradiated with 300 mJ / cm² (millijoules per square centimeter) of ultraviolet light to prepare a multilayer glass substrate structure with a hard coating thickness of 5 μm.

[0204] [Example 2]

[0205] Except that the thickness of the anti-scattering layer is 8 micrometers, the glass substrate multilayer structure is manufactured in the same manner as in Example 1.

[0206] [Example 3]

[0207] Except that the thickness of the anti-scattering layer is 2 micrometers, the glass substrate multilayer structure is manufactured in the same manner as in Example 1.

[0208] [Example 4]

[0209] A multilayer structure of a glass substrate 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.

[0210] [Example 5]

[0211] A multilayer structure of a glass substrate 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.

[0212] [Example 6]

[0213] 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 4 was used instead of the anti-scattering composition prepared in Preparation Example 1 to form the anti-scattering layer.

[0214] [Example 7]

[0215] 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.

[0216] [Comparative Example 1]

[0217] 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.

[0218] 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.

[0219] [Table 1] Anti-scattering layer Hard coating surface hardness Impact resistance (Result / Altitude) bending (millimeters) Yellowness Index (YI) Light transmittance (%) Phase difference (R) th ) Example 1 thickness (micrometer) 5 5 6H ◎ / 15 cm 0.1 1.54 91.2 16 Composition Preparation Example 1 Preparation Example 6 2 thickness (micrometer) 8 5 6H ◎ / 20 cm 0.3 1.45 92.8 34 Composition Preparation Example 1 Preparation Example 6 3 thickness (micrometer) 2 5 5H ◎ / 20 cm 0.15 1.31 91.3 twenty four Composition Preparation Example 1 Preparation Example 6 4 thickness (micrometer) 5 5 5H ◎ / 20 cm 0.2 1.28 92.1 36 Composition Preparation Example 2 Preparation Example 6 5 thickness (micrometer) 5 5 6H ◎ / 20 cm 0.21 1.34 91.5 35 Composition Preparation Example 3 Preparation Example 6 6 thickness (micrometer) 5 5 6H ◎ / 20 cm 0.17 1.45 92.4 25 Composition Preparation Example 4 Preparation Example 6 7 thickness (micrometer) 5 5 5H ◎ / 20 cm 0.19 1.4 92.4 26 Composition Preparation Example 5 Preparation Example 6 Comparative example 1 thickness (micrometer) 5 5 4H X / 15 cm 0.05 1.5 93.0 50 Composition Comparative Preparation Example 1 Preparation Example 6

[0220] Referring to Table 1 above, the glass substrate multilayer structures of Examples 1 to 7, which include an anti-scattering layer containing a (meth)acrylic acid crosslinked polymer and a polyimide polymer, can have an excellent surface hardness of 5H or higher. Furthermore, based on the pen drop test results, it can be confirmed that even if a pen is dropped from a height of 15 cm or more (e.g., 20 cm), no dents or pen marks will be produced, demonstrating very excellent surface properties.

[0221] Furthermore, it can be confirmed that the bending characteristics of the glass substrate multilayer structure in all embodiments are less than 0.1 mm, less than 0.2 mm, or less than 0.3 mm, making it suitable for use as a flexible glass substrate multilayer structure.

[0222] On the other hand, the glass substrate multilayer structure system of Comparative Example 1, which includes an anti-scattering layer that does not contain a (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 distance of 15 cm. In addition, it was confirmed that it has significantly reduced surface properties and low bending properties of less than 0.05 mm.

[0223] Furthermore, it has been confirmed that the glass substrate multilayer structure of Examples 1 to 7 has excellent optical properties, such as yellowness index (YI), transmittance, phase difference (Rth), etc.

[0224] 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 show a decrease in surface hardness or traces, and can ensure user safety by significantly improving impact resistance, and has excellent optical properties.

[0225] 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.

[0226] As described above, the present invention has described a multilayer structure of a glass substrate, a method for manufacturing the same, 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 present invention is not limited to the above embodiments, and those skilled in the art to which this invention pertains can make various modifications and variations based on these descriptions.

[0227] Therefore, the ideas of the present invention should not be limited to the above embodiments, and all that are the same as or have equivalent transformations of the scope of the patent application are intended to fall within the scope of the ideas of the present invention. [Simplified Explanation of the Diagram]

[0042] FIG1 is an exploded perspective view schematically showing an example of a cross-section of a glass substrate multilayer structure according to one embodiment. The glass substrate multilayer structure 100 shown in FIG1 includes a flexible glass substrate 10, an anti-scattering layer 20, and a hard coating 30.

Claims

1. A multilayer glass substrate structure, comprising: A flexible glass substrate; comprising an anti-scattering layer of a flexible polymer formed on one side of the flexible glass substrate, and a hard coating formed on the other side of the flexible glass substrate, wherein the anti-scattering layer comprises a (meth)acrylic crosslinked polymer and a polyimide polymer, and wherein the hard coating comprises a (meth)acrylic hard coating.

2. The multilayer glass substrate structure as described in claim 1, wherein, The (meth)acrylic acid crosspolymer includes alkylene group, ether group, urethane group, ester group, or a combination thereof.

3. The multilayer glass substrate structure as described in claim 1, wherein, The (meth)acrylic acid crosslinker comprises structural units derived from (meth)acrylic acid compounds having 3 to 6 (meth)acrylic acid groups.

4. The multilayer glass substrate structure as described in claim 3, wherein, The (meth)acrylic acid compounds include trimethylolpropane tri(meth)acrylate, trimethylolethane tri(meth)acrylate, 1,2,4-cyclohexane tri(meth)acrylate, pentaglycerol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, dinepentetrine tri(meth)acrylate, dinepentetrine penta(meth)acrylate, dinepentetrine tetra(meth)acrylate, dinepentetrine hexa(meth)acrylate, trinepentetrine tri(meth)acrylate, trinepentetrine hexa(meth)acrylate, polyfunctional urethane (meth)acrylate, polyfunctional polyester (meth)acrylate, or combinations thereof.

5. The multilayer glass substrate structure as described in claim 1, wherein, The polyimide polymer comprises units derived from aromatic diamines containing fluorine atoms and units derived from aromatic dianhydrides.

6. The multilayer glass substrate structure as described in claim 1, wherein, The thickness of the flexible glass substrate ranges from 1 micrometer to 100 micrometers.

7. The multilayer glass substrate structure as claimed in claim 1, wherein, The thickness of the anti-scattering layer is 1 micrometer to 20 micrometers.

8. The multilayer glass substrate structure as claimed in claim 1, wherein, The thickness of the hard coating ranges from 1 micrometer to 15 micrometers.

9. The multilayer glass substrate structure as claimed in 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 as claimed in claim 1, wherein, According to the pen drop test, the impact resistance of this multilayer glass substrate structure is over 10 cm.

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

12. The method for manufacturing a multilayer structure of a glass substrate as described in claim 11, wherein, The (meth)acrylic acid compound also includes alkyl groups, ether groups, ethyl carbamate groups, ester groups, or combinations thereof.

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

14. The method for manufacturing a multilayer structure of a glass substrate as described in claim 11, wherein, The (meth)acrylic acid compounds include trimethylolpropane tri(meth)acrylate, trimethylolethane tri(meth)acrylate, 1,2,4-cyclohexane tri(meth)acrylate, pentaglycerol tri(meth)acrylate, neopentyltetroxide tetra(meth)acrylate, neopentyltetroxide tri(meth)acrylate, dinepentyltetroxide penta(meth)acrylate, dinepentyltetroxide tetra(meth)acrylate, dinepentyltetroxide hexa(meth)acrylate, trinepentyltetroxide tri(meth)acrylate, trinepentyltetroxide hexa(meth)acrylate, polyfunctional urethane (meth)acrylate, polyfunctional polyester (meth)acrylate, or combinations thereof.

15. The method for manufacturing a multilayer structure of a glass substrate as described in 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 structure of a glass substrate as described in any one of claims 1 to 10.

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