Transparent resin substrates for flexible displays and hard coat films

Abstract

Provided is a transparent resin substrate that is for a flexible display, that contains a (meth)acrylic resin which has a weight-average molecular weight of 200,000 or greater, that has a glass transition temperature of 110°C or higher, and that has a photoelastic constant of -5.0×10-12 to 5.0×10-12 Pa-1. Also provided are: a hard coat film obtained by forming a hard coat layer on at least one of the primary surfaces of said transparent resin substrate; and a flexible display having said transparent resin substrate.

Description

[Technical Field]

[0001] The present disclosure relates to a transparent resin substrate for a flexible display, and a hard coat film having a hard coat layer on at least one main surface of the transparent resin substrate. [Background technology]

[0002] Rapid advances in electronic devices such as displays, touch panels, and solar cells have led to demands for thinner, lighter, and more flexible devices. In response to these demands, consideration has been given to replacing glass materials used in substrates, cover windows, and the like with plastic film materials. For these applications, plastic films are required to have high heat resistance, high dimensional stability at high temperatures, high mechanical strength, and the like. Furthermore, curved displays and foldable flexible displays (foldable displays, bendable displays, etc.) have been developed in recent years, and plastic films used in cover windows, etc., in particular, are required to have excellent transparency, flexibility (bending ability), and the like in addition to the above-mentioned properties.

[0003] A known candidate for such a plastic film is, for example, a transparent polyimide film. Patent Document 1 discloses an optical film containing a polyimide polymer used for the front panel of a flexible device component. While transparent polyimide films have excellent heat resistance and mechanical strength, they have problems such as a narrow molding processability due to their high heat resistance and high material costs, which increase the price of the entire display.

[0004] Patent Document 2 discloses a hard coat film for use as a surface protection film for flexible displays, which uses a polyester film. Polyester films have excellent mechanical strength and dimensional stability, and are inexpensive materials, but have the problem of low light extraction efficiency due to high birefringence, resulting in reduced visibility due to rainbow unevenness and light leakage.

[0005] Acrylic resins have high transparency and excellent optical properties, and are therefore used in a variety of display applications, such as liquid crystal displays and organic electroluminescence (EL) displays. In recent years, attempts have been made to use acrylic films as front panels (cover windows) for flexible displays in order to improve the optical properties of polyethylene terephthalate (PET) films.

[0006] Patent Document 3 relates to a hard-coated film for use as a front panel, in which an acrylic hard-coat layer is applied to a protective resin layer made of acrylic resin, and discloses a technology for reducing the difference in refractive index between the protective resin layer and the hard-coat layer to eliminate unevenness when viewed.

[0007] Patent Document 4 describes that an optical film having high toughness can be obtained by including a predetermined acrylic resin and rubber particles as an optical film such as a polarizer protective film. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2021-120762 [Patent Document 2] Japanese Patent Publication No. 2020-12087 [Patent Document 3] International Publication No. 2021 / 182383 [Patent Document 4] International Publication No. 2020 / 203833 Summary of the Invention [Problem to be solved by the invention]

[0009] However, there has been no proposal for a transparent resin substrate that has excellent optical properties and flexibility (bending ability) and that also provides excellent image quality even under conditions of use in which an external force is applied, for use in flexible devices such as organic electroluminescence (EL) display devices. Furthermore, there is still room for improvement in the bending ability of the hard coat film formed on the transparent resin substrate.

[0010] In view of the above, an object of the present disclosure is to provide a transparent resin substrate that is excellent in optical properties and flexibility (bendability) and that exhibits excellent image quality even under use conditions in which external forces are repeatedly applied, and a hard coat film that is excellent in bendability and that has a hard coat layer formed on at least one main surface of the transparent resin substrate. [Means for solving the problem]

[0011] Specific means for solving the above problems include the following embodiments. <1> A transparent resin substrate for a flexible display, Contains a (meth)acrylic resin having a weight average molecular weight of 200,000 or more, The glass transition temperature is 110°C or higher, and the photoelastic constant is -5.0×10 -12 ~5.0×10 -12 Pa -1 A transparent resin substrate.

[0012] <2> Orientation birefringence is -2.0×10 -4 ~2.0×10 -4 That is, <1> The transparent resin substrate according to claim 1.

[0013] <3> The absolute value of the in-plane retardation Re is 10.0 nm or less, and the absolute value of the thickness direction retardation Rth is 20.0 nm or less. <1> or <2> The transparent resin substrate according to claim 1.

[0014] <4> The (meth)acrylic resin is a (meth)acrylic resin having, as constituent units, 30 to 100% by weight of methyl methacrylate units and 0 to 70% by weight of other monomer units copolymerizable with the methyl methacrylate units. <1> ~ <4> The transparent resin substrate according to any one of the above items.

[0015] <5> the other monomer unit is at least one selected from the group consisting of an N-substituted maleimide-based monomer unit, a methacrylic acid ester unit in which the ester moiety is a primary or secondary hydrocarbon group or an aromatic hydrocarbon group having 2 to 20 carbon atoms, a methacrylic acid ester unit in which the ester moiety is a saturated hydrocarbon group having 7 to 16 carbon atoms and having a condensed ring structure, a methacrylic acid ester unit in which the ester moiety is a linear or branched group containing an ether bond, and a styrene-based monomer unit; <4> The transparent resin substrate according to claim 1.

[0016] <6> the (meth)acrylic resin is a graft copolymer comprising crosslinked (meth)acrylic polymer particles (a) having an average particle size of 150 nm or less and a glass transition temperature of -10°C or less, and a non-crosslinked methacrylic polymer component (b) having a weight-average molecular weight of 200,000 or more, wherein at least a portion of the non-crosslinked methacrylic polymer component (b) is graft-bonded to the crosslinked (meth)acrylic polymer particles (a), and the proportion of the crosslinked (meth)acrylic polymer particles (a) in the total of the crosslinked (meth)acrylic polymer particles (a) and the non-crosslinked methacrylic polymer component (b) is 1% by weight or more but less than 50% by weight; <1> ~ <4> The transparent resin substrate according to any one of the above items.

[0017] <7> Produced by solution casting, <1> ~ <6> The transparent resin substrate according to any one of the above items.

[0018] <8> Haze is less than 1.5%; <1> ~ <7> The transparent resin substrate according to any one of the above items.

[0019] <9> A hard coat layer is laminated on at least one of the main surfaces. <1> ~ <8> The transparent resin substrate according to any one of the above items.

[0020] <10> <1> ~ <9> 1. A hard coat film comprising the transparent resin substrate according to any one of claims 1 to 9, and a hard coat layer on at least one main surface of the transparent resin substrate.

[0021] <11> and an easy-adhesion layer between the transparent resin substrate and the hard coat layer, the easy-adhesion layer being made of an easy-adhesion composition containing a polyurethane resin having a carboxyl group and a tri- or higher-functional polyfunctional epoxy-based crosslinking agent. <10> 2. The hard coat film according to claim 1.

[0022] <12> The hard coat layer is made of a cured product of a hard coat composition containing a polyorganosiloxane compound. <10> or <11> 2. The hard coat film according to claim 1.

[0023] <13> the polyorganosiloxane compound is a condensate of a silane compound represented by the following formula (1), and the weight-average molecular weight of the condensate is 500 to 20,000; The molar ratio of the constitutional unit represented by the following formula (3) to the constitutional unit represented by the following formula (4) contained in the condensate ([constituent unit represented by formula (3)] / [constituent unit represented by formula (4)]) is less than 5. <12> 2. The hard coat film according to claim 1. [ka] (In formula (1), R 1 represents an alkylene group having 2 to 16 carbon atoms, and R 2 represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R 3 represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 25 carbon atoms, or an aralkyl group having 7 to 12 carbon atoms, x represents 2 or 3, and Y represents a glycidyloxy group represented by the following formula (2-1) or an alicyclic epoxy group represented by the following formula (2-2). [ka] (In formulas (2-1) and (2-2), * represents R 1 ) [ka] (In formula (3), R 1and Y have the same meaning as in formula (1). [ka] (In formula (4), R 1 and Y are as defined in the formula (1). Z represents a hydrogen atom, an alkoxy group having an alkyl moiety of 1 to 10 carbon atoms, an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 25 carbon atoms, or an aralkyl group having 7 to 12 carbon atoms.

[0024] <14> The total thickness is 40 to 500 μm, and the total light transmittance is 80% or more. <10> ~ <13> 10. The hard coat film according to claim 1, wherein the hard coat film is a hard coat film having a thickness of 100 nm or less.

[0025] <15> The thickness of the hard coat layer is 10 to 100 μm. <10> ~ <14> 10. The hard coat film according to claim 1, wherein the hard coat film is a hard coat film having a thickness of 100 nm or less.

[0026] <16> <1> ~ <9> 1. A flexible display comprising the transparent resin substrate according to any one of claims 1 to 9. [Effects of the Invention]

[0027] According to the present disclosure, it is possible to provide a transparent resin substrate for flexible displays that has excellent optical properties and flexibility (bendability) and can reproduce excellent image quality even when deformed by external force. Furthermore, by forming a hard coat layer on at least one main surface of this transparent resin substrate, it is also possible to provide a hard coat film with excellent bendability. Such a transparent resin substrate and hard coat film are suitable for use as films for flexible displays. DETAILED DESCRIPTION OF THE INVENTION

[0028] The present disclosure relates to a transparent resin substrate (transparent resin film) for flexible displays, and a hard coat film having a hard coat layer on at least one main surface of the transparent resin substrate. Here, a flexible display refers to a single continuous display that has a structure that can be deformed depending on the application, and examples include curved displays; foldable or bendable displays that are bendable or foldable displays; and rollable or slidable displays that are rollable displays. These displays can be suitably used as organic EL displays with a flexible light-emitting layer.

[0029] <Transparent resin base material> The transparent resin substrate of the present disclosure contains a (meth)acrylic resin having a weight-average molecular weight of 200,000 or more. The weight-average molecular weight of the (meth)acrylic resin is preferably 400,000 or more, more preferably 500,000 or more, even more preferably 1,000,000 or more, particularly preferably 1,500,000 or more, and extremely preferably 2,000,000 or more. From the viewpoint of moldability, the weight-average molecular weight of the (meth)acrylic resin is preferably 5,000,000 or less, more preferably 3,500,000 or less. When the weight-average molecular weight of the (meth)acrylic resin is within the above-mentioned preferred range, the toughness and flexibility (bending) of the substrate are increased, making it possible to obtain a strong substrate that is resistant to deformation. Note that when the weight-average molecular weight of the (meth)acrylic resin is less than 200,000, the substrate does not immediately become brittle or easily breakable, but it becomes difficult to obtain the high toughness and flexibility (bending) required for flexible display applications.

[0030] The proportion of the (meth)acrylic resin having a weight-average molecular weight of 200,000 or more is preferably 50% by weight or more, more preferably more than 50% by weight, even more preferably 70% by weight or more, particularly preferably 80% by weight or more, extremely preferably 90% by weight or more, and most preferably 95% by weight or more, relative to 100% by weight of the transparent resin substrate. The upper limit of the proportion of the (meth)acrylic resin may be 100% by weight, 99% by weight, 98% by weight, or 97% by weight.

[0031] [Method of manufacturing transparent resin substrate] Although the method for producing the transparent resin substrate of the present disclosure is not particularly limited, from the viewpoint of molding a high-molecular-weight (meth)acrylic resin, it is preferable to produce it by a solution casting method. Transparent resin substrates made of general (meth)acrylic resins are often produced by a melt extrusion method, but the transparent resin substrate of the present disclosure has a high molecular weight, so when molded by a melt extrusion method, the melt viscosity becomes high and the molding load becomes large.

[0032] Furthermore, in applications where repeated external forces are applied, such as substrates for flexible displays, it is necessary to minimize the amount of foreign matter in the substrate, as foreign matter can become the starting point for cracks and other problems. With the melt extrusion method, if a filtration filter is installed during the process to remove foreign matter, significant processing restrictions are imposed, such as the need to increase the processing temperature to reduce the filter differential pressure, and there is also the disadvantage that the amount of foreign matter can actually increase due to the effects of thermal decomposition. On the other hand, with the solution casting method, even if a filtration filter is installed during the process, operation can be performed at low temperatures and with little pressure loss, making it relatively easy to obtain transparent resin substrates with few foreign matters.

[0033] An example of the solution casting method will be described below, but the method is not limited to this example. First, a (meth)acrylic resin and, if necessary, other components are mixed with a solvent that dissolves the (meth)acrylic resin well, i.e., a good solvent, to prepare a dope in which each component is dissolved or dispersed in the solvent. In this case, the dope may be prepared by dissolving or dispersing each component in the solvent simultaneously or sequentially, or multiple dopes in which at least one component is dissolved or dispersed in a solvent may be prepared and mixed. The dissolving or dispersing step can be carried out by appropriately adjusting the temperature and pressure. After the above steps, the obtained dope can be filtered or degassed.

[0034] Next, the prepared dope is sent to a pressure die by a liquid feed pump, and the dope is cast from the slit of the pressure die onto the surface (mirror surface) of a metal or synthetic resin support (endless belt, drum, etc.) to form a dope membrane (cast membrane).

[0035] The doped film is then heated on the support to evaporate the solvent, forming a film. The conditions for evaporating the solvent can be determined appropriately depending on the boiling point of the solvent used.

[0036] The film thus obtained is peeled off from the surface of the support, and may then be subjected to a drying step, a heating step, a stretching step, or the like, as appropriate.

[0037] The type of good solvent is not particularly limited as long as it dissolves the (meth)acrylic resin, and examples thereof include chlorine-based organic solvents such as methylene chloride, and non-chlorine-based organic solvents such as methyl acetate, ethyl acetate, acetone, methyl ethyl ketone, tetrahydrofuran, etc. Among these, methylene chloride is preferred because it can dissolve the (meth)acrylic resin well.

[0038] In addition to the good solvent, alcohols, which are poor solvents, can also be added to the dope. Examples of alcohols that can be used include linear or branched aliphatic alcohols having 1 to 4 carbon atoms. Among these, ethanol and / or methanol are preferred. Adding such alcohols not only improves the drying efficiency of the dope, but also allows the evaporated alcohols to create numerous voids in the film, making the film thin, resulting in a transparent resin substrate with excellent releasability from the support. When alcohols are added, the amount of alcohol added is preferably 1 to 25 wt %, more preferably 2 to 20 wt %, and even more preferably 3 to 15 wt %, of the total amount of solvents added to the dope.

[0039] [Glass transition temperature] The preferred glass transition temperature of the transparent resin substrate of the present disclosure is described below. From the viewpoints of improving the dimensional stability of the substrate under the usage environment and preventing deformation due to heat generated during processing steps such as module assembly, the glass transition temperature of the transparent resin substrate of the present disclosure is preferably 110°C or higher, more preferably 115°C or higher, even more preferably 120°C or higher, particularly preferably 123°C or higher, extremely preferably 124°C or higher, and most preferably 125°C or higher.

[0040] [Orientation birefringence, photoelastic constant] Preferred aspects of orientation birefringence and photoelastic constant in the transparent resin substrate of the present disclosure are described below. Birefringence is one of the important optical properties that must be considered when manufacturing optical components using optical resins. Polymers are composed of elongated, directionally-dependent ellipsoids. Therefore, when the polymer is deformed to orient the molecular chains, birefringence occurs due to the difference in refractive index between the orientation direction and the perpendicular direction. In other words, a birefringent state refers to a state in which the speed of light traveling through a material differs depending on the direction of the vibration plane, resulting in optical anisotropy. In optical components such as liquid crystal display devices, optical disk drives, and projection screens, the presence of birefringent films or lenses in the optical path affects image quality and signal reading performance. Therefore, it is desirable to use optical components made of optical resins with as little birefringence as possible. Similarly, for optical resins used in optical devices such as flexible displays, low birefringence is desirable from the perspective of improving image quality and light extraction efficiency.

[0041] As is well known in the art, the birefringence exhibited by optical resins can be classified into "orientation birefringence," which is primarily caused by the orientation of the polymer main chain, and "photoelastic birefringence," which is caused by stress. The signs of orientation birefringence and photoelastic birefringence are derived from the chemical structure of the polymer and are properties inherent to each polymer.

[0042] In other words, orientation birefringence is birefringence that generally occurs when the main chain (polymer chain) of a chain-like polymer is oriented, and this orientation of the main chain occurs in processes that involve material flow, such as the extrusion molding or stretching process when manufacturing a polymer film, or the injection molding process when making an optical component, and occurs when the material remains fixed in the optical component. Here, when the refractive index increases in the direction parallel to the orientation direction of the polymer chain, it is said that "orientation birefringence is positive," and when the refractive index increases in the direction perpendicular to it, it is said that "orientation birefringence is negative."

[0043] Here, we will explain the definition of orientation birefringence in this specification. As mentioned above, orientation birefringence is birefringence that occurs due to the orientation of polymer chains. However, since the degree of orientation of polymer chains varies depending on the processing and molding conditions of the polymer, in order to uniformly discuss orientation birefringence, it is necessary to measure it in a state where the film has been manufactured under the same processing and molding conditions. Therefore, in this specification, orientation birefringence is defined as the orientation birefringence of a film obtained by preheating for 5 minutes at a temperature 10°C above the glass transition temperature, followed by uniaxial stretching at a fixed width of 1.5 times at a speed of 100 mm / min.

[0044] From the viewpoint of improving the image quality and light extraction efficiency of a display, the orientation birefringence of the transparent resin substrate of the present disclosure is set to be −2.0×10 -4 ~2.0×10 -4 is preferably -1.5 x 10 -4 ~1.5×10 -4 It is more preferable that the -4 ~1.0×10 -4 More preferably, it is -0.8 × 10 -4 ~0.8×10 -4 It is particularly preferable that -4 ~0.5×10 -4 It is highly preferable that -4 ~0.2×10 -4 It is most preferable that:

[0045] Photoelastic birefringence is birefringence caused by elastic deformation (strain) of a polymer. In optical components using polymers, for example, when the polymer is cooled from near its glass transition temperature to a temperature below it, volume shrinkage occurs, causing elastic deformation (strain) to remain in the material, which causes photoelastic birefringence. In addition, when an optical component is used at a temperature below its glass transition temperature, such as the temperature in a typical operating environment, the material will also elastically deform due to external forces, etc., while fixed to the device, which will cause photoelastic birefringence.

[0046] Photoelastic birefringence is birefringence that occurs when stress is applied to a polymer molded body due to elastic deformation (strain) of the polymer in the molded body, and in fact, the degree of photoelastic birefringence of a material can be evaluated by determining the photoelastic constant specific to the polymer. The photoelastic constant is defined as the coefficient γ when birefringence Δn occurs due to a stress difference Δσ, as shown in the following formula. Δn=γ×Δσ

[0047] Furthermore, if the refractive index increases in the direction parallel to the direction in which tensile stress is applied (the orientation direction of the polymer chains), it is said that the "photoelastic birefringence is positive," and if the refractive index increases in the perpendicular direction, it is said that the "photoelastic birefringence is negative."

[0048] The photoelastic constant of the transparent resin substrate of the present disclosure is −5.0×10 -12 ~5.0×10 -12 Pa -1 is preferably -3.0 x 10 -12 ~3.0×10 -12 Pa -1 It is more preferable that the -12 ~2.5×10 -12 Pa -1 More preferably, it is -1.5 × 10 -12 ~1.5×10 -12 Pa -1 It is particularly preferable that -12 ~1.0×10 -12 Pa -1 It is particularly preferable that -12 ~0.8×10 -12 Pa -1 It is particularly preferable that -12 ~0.5×10 -12 Pa -1 It is highly preferable that -12 ~0.3×10 -12 Pa -1If the photoelastic constant is within the above range, when the transparent resin substrate of the present disclosure is used as a film for a flexible display, even if external forces are applied due to various deformations such as bending, folding, folding, and winding, the birefringence generated is extremely small, and there is no need to worry about uneven phase difference, deterioration of image quality or contrast in the peripheral area of ​​deformation, light leakage, etc. The same applies even when the film is deformed and stressed in a usage environment such as high temperature and high humidity.

[0049] Here, we will discuss optical design related to the orientation birefringence and photoelastic birefringence of (meth)acrylic resins. As mentioned above, the properties of orientation birefringence and photoelastic birefringence are derived from the chemical structure of the polymer (constituent monomer), and their signs are properties inherent to each polymer (constituent monomer). From the perspective of being used in optical displays, the transparent resin substrate of the present disclosure is required to have low photoelastic birefringence, and it is desirable that both the orientation birefringence and photoelastic birefringence be low. When designing a (meth)acrylic resin, it is preferable to incorporate polymers (constituent monomers) with orientation birefringence and photoelastic birefringence having opposite signs (positive and negative) by copolymerization or modification. This allows birefringences of opposite signs to cancel each other out based on the principle of additivity, making it possible to obtain a (meth)acrylic resin with low orientation birefringence and photoelastic birefringence.

[0050] For example, methyl methacrylate, a constituent monomer of polymethyl methacrylate (PMMA), a typical (meth)acrylic resin, exhibits both negative orientation birefringence (intrinsic birefringence) and photoelastic birefringence. Note that intrinsic birefringence refers to the orientation birefringence when the polymer is completely oriented in one direction. On the other hand, N-substituted maleimide monomers such as N-phenylmaleimide and N-cyclohexylmaleimide, and methacrylate ester monomers with aromatic hydrocarbon groups, such as benzyl methacrylate, exhibit positive orientation birefringence (intrinsic birefringence) and photoelastic birefringence. Therefore, by combining these monomers in copolymerization and adjusting the ratio of their introduction, the orientation birefringence and photoelastic birefringence, which have opposite signs, can be mutually offset, resulting in a polymer with low orientation birefringence and photoelastic birefringence.

[0051] The optical design described above also applies to crosslinked polymer particles (such as the graft copolymer of the second embodiment, polymer particles (I) described later, etc.). In the monomers constituting the crosslinked polymer or the non-crosslinked polymer that is not graft-bonded to the crosslinked polymer, monomers having orientation birefringence (intrinsic birefringence) and photoelastic birefringence of different signs are combined by copolymerization and the ratio of introduction is adjusted, whereby the orientation birefringence and photoelastic birefringence of different signs cancel each other out, making it possible to obtain crosslinked polymer particles having small orientation birefringence and photoelastic birefringence.

[0052] [Hayes] A preferred embodiment of haze in the transparent resin substrate of the present disclosure will now be described. When a transparent resin substrate is used in a liquid crystal display device, an organic EL display device, or the like, it goes without saying that it is preferable to use a substrate with high transparency and low haze from the viewpoint of effectively utilizing incident light from a light source unit. However, in displays such as organic EL display devices that aim for high contrast between light and dark areas (black and white areas), the haze of the transparent resin substrate used becomes even more important.

[0053] In organic EL display devices that do not have a backlight and are equipped with light-emitting elements, the elements do not emit any light when reproducing black, which allows them to provide images with better black reproduction and higher contrast than liquid crystal display devices, which reproduce black by blocking the backlight.Though organic EL display devices have better contrast than liquid crystal display devices, there has been a demand in recent years for further improvements in contrast, as exemplified by the HDR (High Dynamic Range) standard.

[0054] On the other hand, for example, organic EL display devices for foldable displays have multiple functional film layers, such as a cover window, a cover window protective film, an impact absorbing layer, and a backing film. When multiple functional film layers are stacked on a light source unit in this way, if the functional film layer has a light scattering effect, the influence of interference between adjacent light-emitting elements cannot be ignored. For example, if the functional film layer has a high haze and a scattering source, when light incident from a certain light-emitting element passes through the functional film layer, light scattering or diffusion occurs within the layer or on the surface, and light is emitted from the adjacent non-emitting element, causing light to leak from the black area that is not supposed to emit light, resulting in a decrease in black-and-white contrast. Therefore, if higher contrast is desired, a low haze is required for the functional film layer.

[0055] There are various causes of haze in functional film layers, but since light scattering and diffusion occur at the interface between materials with different refractive indices, it is desirable that the materials that make up the functional film layer be made up of materials with as similar refractive indices as possible.

[0056] In transparent resin substrates, possible causes of scattering include scattering between different polymers that form the base material, scattering by various additives and particles added to improve functionality, scattering by trace amounts of residual monomers, solvents, moisture, foreign matter, etc. from the polymer raw materials, and scattering by voids that occur in the base material. To minimize the effects of scattering at the interfaces between these substances, possible measures include using substances with similar refractive indices, reducing the amount of additives to a level that does not impair functionality, and reducing the size of the substances and voids that are scattering sources to a size where the effect is negligible.

[0057] By taking the measures listed above as an example, the haze of the transparent resin substrate of the present disclosure can be reduced by minimizing the influence of light scattering. The haze of the transparent resin substrate of the present disclosure is preferably less than 1.5%, more preferably less than 1.2%, even more preferably less than 1.0%, particularly preferably less than 0.8%, extremely preferably less than 0.5%, and most preferably less than 0.3%. By keeping the haze of the transparent resin substrate of the present disclosure within the above range, it is possible to provide optical performance as an optical display and reproduce high contrast when used in an organic EL display device or the like. For these reasons, the transparent resin substrate of the present disclosure can be suitably used when a hard coat layer is laminated on at least one of its main surfaces.

[0058] As with transparent resin substrates, it is important to consider the effects of light scattering in hard-coated films that have a hard-coat layer on at least one major surface of a transparent resin substrate, and in hard-coated films with an easy-adhesion layer that has an easy-adhesion layer between the transparent resin substrate and the hard-coat layer. In these films, the effects of light scattering between various layers, such as the transparent resin substrate, the hard-coat layer, and the easy-adhesion layer, are likely to be considered. Therefore, it is preferable that the refractive indices of the materials forming each layer are as close as possible. Furthermore, the key to reducing the effects of scattering is to firmly adhere the layers to each other so that even small voids do not form between the layers. As described above, reducing the effects of scattering not only in the transparent resin substrate but also in the hard-coat layer and easy-adhesion layer provided therein can be said to be a design that enhances contrast when viewed as a whole display.

[0059] [Phase difference] A preferred embodiment of retardation in the transparent resin substrate of the present disclosure will be described. Retardation is an index value calculated based on birefringence, and the in-plane retardation (Re) and thickness direction retardation (Rth) can be calculated by the following formulas. In an ideal molded body that is completely optically isotropic in three-dimensional directions, both the in-plane retardation (Re) and thickness direction retardation (Rth) are zero. Re=(nx-ny)×d Rth = [(nx + ny) / 2 - nz] × d In the above formula, nx, ny, and nz represent the refractive index in the respective axial directions, where the in-plane stretching direction (the orientation direction of the polymer chain) is the X axis, the direction perpendicular to the X axis is the Y axis, and the thickness direction of the substrate is the Z axis. Also, d represents the thickness of the substrate, and nx-ny represents the orientation birefringence. The MD direction of the substrate is the X axis, but in the case of a stretched substrate, the stretching direction is the X axis.

[0060] When the transparent resin substrate of the present disclosure is used as a substrate film for a flexible display, it is preferable that the optical isotropy is small, and it is preferable that the optical isotropy is small not only in the in-plane directions (length direction and width direction) but also in the thickness direction. More specifically, the absolute value of the in-plane retardation is preferably 10.0 nm or less, more preferably 5.0 nm or less, and even more preferably 3.0 nm or less. Furthermore, the absolute value of the thickness direction retardation is preferably 20.0 nm or less, more preferably 10.0 nm or less, and even more preferably 5.0 nm or less. A transparent resin substrate having such a retardation can be suitably used as a substrate film for a flexible display such as an organic electroluminescence (EL) display device.

[0061] [(Meth)acrylic resin of the first embodiment] A first embodiment of the (meth)acrylic resin contained in the transparent resin substrate of the present disclosure is a (meth)acrylic resin having, as constituent units, 30 to 100% by weight of methyl methacrylate units and 0 to 70% by weight of other monomer units copolymerizable with the methyl methacrylate units.

[0062] (methyl methacrylate units) The methyl methacrylate unit is a structural unit represented by the following formula:

[0063] [ka]

[0064] From the viewpoints of appearance, weather resistance, etc., the (meth)acrylic resin of the first embodiment preferably has a methyl methacrylate unit content of 50% by weight or more, more preferably 60% by weight or more, even more preferably 70% by weight or more, and particularly preferably 80% by weight or more. Furthermore, from the viewpoints of optical properties, heat resistance, etc., the (meth)acrylic resin of the first embodiment preferably has a methyl methacrylate unit content of 99.9% by weight or less, more preferably 99% by weight or less, even more preferably 97% by weight or less, and particularly preferably 95% by weight or less.

[0065] (other monomer units) The other monomer unit copolymerizable with the methyl methacrylate unit is preferably at least one selected from the group consisting of N-substituted maleimide monomer units, methacrylic acid ester units in which the ester moiety is a primary or secondary hydrocarbon group or an aromatic hydrocarbon group having 2 to 20 carbon atoms, methacrylic acid ester units in which the ester moiety is a saturated hydrocarbon group having 7 to 16 carbon atoms and a fused ring structure, methacrylic acid ester units in which the ester moiety is a linear or branched group containing an ether bond, and styrene monomer units. The inclusion of such a monomer unit can increase the evaporation rate of the solvent from the dope film without reducing the heat resistance of the (meth)acrylic resin, for example, when producing a transparent resin substrate by a solution casting method. Hereinafter, these monomer units are also referred to as "drying-accelerating comonomer units."

[0066] Examples of N-substituted maleimide monomer units include N-phenylmaleimide units, N-benzylmaleimide units, N-cyclohexylmaleimide units, N-methylmaleimide units, etc. Among these, maleimide monomer units having a cyclic substituent on the nitrogen atom, i.e., N-phenylmaleimide units, N-benzylmaleimide units, and N-cyclohexylmaleimide units, are preferred.

[0067] Examples of methacrylic acid ester units in which the ester moiety is a primary or secondary hydrocarbon group or an aromatic hydrocarbon group having 2 to 20 carbon atoms include ethyl methacrylate units, propyl methacrylate units, n-butyl methacrylate units, hexyl methacrylate units, cyclohexyl methacrylate units, 2-ethylhexyl methacrylate units, octyl methacrylate units, stearyl methacrylate units, phenyl methacrylate units, benzyl methacrylate units, etc. Among these, ethyl methacrylate units, n-butyl methacrylate units, cyclohexyl methacrylate units, 2-ethylhexyl methacrylate units, phenyl methacrylate units, and benzyl methacrylate units are preferred.

[0068] Examples of methacrylic acid ester units in which the ester moiety is a saturated hydrocarbon group having 7 to 16 carbon atoms and a fused ring structure include a dicyclopentanyl methacrylate unit and an isobornyl methacrylate unit. The saturated hydrocarbon group preferably has 8 to 14 carbon atoms, more preferably 9 to 12. The fused ring structure is preferably a structure in which two 5-membered rings are fused together by three consecutive carbon atoms.

[0069] Examples of methacrylic acid ester units in which the ester moiety is a linear or branched group containing an ether bond include 2-methoxyethyl methacrylate units.

[0070] Examples of the styrene-based monomer unit include a styrene unit, an α-methylstyrene unit, a monochlorostyrene unit, a dichlorostyrene unit, etc. Among these, a styrene unit is preferred.

[0071] [(Meth)acrylic resin of second aspect] A second embodiment of the (meth)acrylic resin contained in the transparent resin substrate of the present disclosure is a graft copolymer (hereinafter also referred to as a "specific graft copolymer") that includes crosslinked (meth)acrylic polymer particles (a) having an average particle size of 150 nm or less and a glass transition temperature of -10°C or less, and a non-crosslinked methacrylic polymer component (b) having a weight-average molecular weight of 200,000 or more, in which at least a portion of the non-crosslinked methacrylic polymer component (b) is graft-bonded to the crosslinked (meth)acrylic polymer particles (a), and in which the proportion of the crosslinked (meth)acrylic polymer particles (a) in the total of the crosslinked (meth)acrylic polymer particles (a) and the non-crosslinked methacrylic polymer component (b) is 1% by weight or more but less than 50% by weight.

[0072] When the (meth)acrylic resin contained in the transparent resin substrate of the present disclosure is a specific graft copolymer, a high-strength transparent resin substrate can be formed even if the resin component is solely the specific graft copolymer. Furthermore, since there is no need to additionally blend and disperse a graft copolymer having a core-shell structure, a low-haze transparent resin substrate can be easily formed. Furthermore, the specific graft copolymer has excellent storage stability despite containing a rubber component, and therefore has the advantage that when the dope is prepared by dissolving it in a solvent in a solution casting method, the dope is less likely to become cloudy. As a result, the haze of the transparent resin substrate produced by the solution casting method can be reduced.

[0073] The specific graft copolymer contains crosslinked (meth)acrylic polymer particles (a) and a non-crosslinked methacrylic polymer component (b). The crosslinked (meth)acrylic polymer particles (a) are a rubber component, which can contribute to improving strength. Furthermore, the non-crosslinked methacrylic polymer component (b) can achieve excellent heat resistance. Compared to conventional systems in which a core-shell graft copolymer is blended with a (meth)acrylic resin, the crosslinked (meth)acrylic polymer particles (a) correspond to the core rubber component in the core-shell graft copolymer, and the non-crosslinked methacrylic polymer component (b) corresponds to the matrix (meth)acrylic resin.

[0074] At least a portion of the non-crosslinked methacrylic polymer component (b) is graft-bonded to the crosslinked (meth)acrylic polymer particles (a). This graft-bonding can be achieved by producing a graft copolymer by emulsion polymerization, as described below. Due to this production method, the specific graft copolymer may also contain a non-crosslinked methacrylic polymer component (b) that is not graft-bonded to the crosslinked (meth)acrylic polymer particles (a).

[0075] The specific graft copolymer can have a configuration in which small-sized crosslinked (meth)acrylic polymer particles (a) are dispersed in a high-molecular-weight non-crosslinked methacrylic polymer component (b), and therefore aggregation of the crosslinked (meth)acrylic polymer particles (a) is unlikely to proceed within the specific graft copolymer. As a result, the specific graft copolymer has good stability when stored in powder form or as a dope dissolved in a solvent. Furthermore, because aggregation of the crosslinked (meth)acrylic polymer particles (a) is suppressed, the specific graft copolymer has the advantage of being easily soluble in solvents.

[0076] (Crosslinked (meth)acrylic polymer particles (a)) The crosslinked (meth)acrylic polymer particles (a) are (meth)acrylic rubber particles. By including the crosslinked (meth)acrylic polymer particles (a), the specific graft copolymer can achieve high strength when used, for example, as a transparent resin substrate.

[0077] The crosslinked (meth)acrylic polymer particles (a) have a relatively small particle size, specifically an average particle size of 150 nm or less. By using crosslinked (meth)acrylic polymer particles with such a small particle size, low haze can be achieved when the specific graft copolymer is formed into a film, for example. Furthermore, by reducing the size of the crosslinked (meth)acrylic polymer particles, it is no longer necessary to match the refractive index of the crosslinked (meth)acrylic polymer particles (a) with the refractive index of the non-crosslinked methacrylic polymer component (b). As a result, a monomer composition that lowers the glass transition temperature of the crosslinked (meth)acrylic polymer particles (a) can be adopted without considering the refractive index. This allows high strength to be achieved when the specific graft copolymer is formed into, for example, a transparent resin substrate. The average particle size can be adjusted by the type and amount of emulsifier, stirring conditions, etc.

[0078] From the viewpoint of achieving low haze, the average particle size of the crosslinked (meth)acrylic polymer particles (a) is preferably 130 nm or less, more preferably 120 nm or less, even more preferably 110 nm or less, and particularly preferably 100 nm or less. There are no particular restrictions on the lower limit of the average particle size, but from the viewpoint of the strength of the transparent resin substrate or the ease of production of the specific graft copolymer, it is preferably 30 nm or more, more preferably 50 nm or more, and even more preferably 60 nm or more. The average particle size is a volume average particle size and can be measured by a known particle size measurement method.

[0079] The crosslinked (meth)acrylic polymer particles (a) have a glass transition temperature of -10°C or lower. By using crosslinked (meth)acrylic polymer particles with a low glass transition temperature, high strength can be achieved when the specific graft copolymer is used in, for example, a transparent resin substrate. The glass transition temperature can be adjusted by the type and ratio of the monomers constituting the crosslinked (meth)acrylic polymer particles (a).

[0080] The glass transition temperature of the crosslinked (meth)acrylic polymer particles (a) is preferably −20° C. or lower, more preferably −30° C. or lower, even more preferably −40° C. or lower, and particularly preferably −45° C. or lower. There are no particular restrictions on the lower limit of the glass transition temperature, but for example, it is preferably −130° C. or higher, more preferably −110° C. or higher, even more preferably −100° C. or higher, particularly preferably −80° C. or higher, and extremely preferably −70° C. or higher. The glass transition temperature of the crosslinked (meth)acrylic polymer particles (a) is a value calculated using the Fox formula using values ​​listed in the Polymer Handbook (J. Brandrup, Interscience 1989) (for example, the glass transition temperature of poly(n-butyl acrylate) is −54° C.).

[0081] The crosslinked (meth)acrylic polymer particles (a) are particles formed from a crosslinked (meth)acrylic polymer obtained by polymerizing a monomer component containing a (meth)acrylic monomer and a polyfunctional monomer. The monomer component excluding the polyfunctional monomer contains an acrylic monomer and / or a methacrylic monomer, and preferably contains at least an acrylic monomer.

[0082] The acrylic monomer contained in the crosslinked (meth)acrylic polymer particles (a) is preferably an acrylic acid alkyl ester having an alkyl moiety with 1 to 8 carbon atoms. Specific examples include ethyl acrylate, n-butyl acrylate, n-octyl acrylate, and 2-ethylhexyl acrylate. The acrylic acid alkyl ester may be used alone or in combination of two or more. Of these, n-butyl acrylate is preferred.

[0083] As the optional methacrylic monomer that can be contained in the crosslinked (meth)acrylic polymer particles (a), a methacrylic acid alkyl ester having an alkyl moiety with 1 to 8 carbon atoms is preferred. Specific examples include methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, and octyl methacrylate. The methacrylic acid alkyl ester may be used alone or in combination of two or more. Among these, a methacrylic acid alkyl ester having an alkyl moiety with 1 to 4 carbon atoms is preferred, and methyl methacrylate is particularly preferred.

[0084] In the crosslinked (meth)acrylic polymer particles (a), monomers other than the above-mentioned alkyl acrylates and alkyl methacrylates may be used. Examples of such monomers include acrylic esters other than alkyl acrylates, methacrylic esters other than alkyl methacrylates, aromatic vinyl monomers, and other copolymerizable vinyl monomers. Examples of acrylic esters other than alkyl acrylates include phenyl acrylate, benzyl acrylate, cyclohexyl acrylate, and isobornyl acrylate. Examples of methacrylic esters other than alkyl methacrylates include phenyl methacrylate, benzyl methacrylate, cyclohexyl methacrylate, and isobornyl methacrylate. Examples of aromatic vinyl monomers include styrene, α-methylstyrene, chlorostyrene, and other styrene derivatives. Examples of other copolymerizable vinyl monomers include unsaturated nitrile monomers such as acrylonitrile and methacrylonitrile; α,β-unsaturated carboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid; olefin monomers such as vinyl acetate, ethylene, and propylene; halogenated vinyl monomers such as vinyl chloride, vinylidene chloride, and vinylidene fluoride; and maleimide monomers such as N-ethylmaleimide, N-propylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide, and No-chlorophenylmaleimide. These may be used alone or in combination of two or more.

[0085] From the viewpoint of strength and heat resistance, the content of acrylic acid esters (particularly acrylic acid alkyl esters having 1 to 8 carbon atoms in the alkyl moiety) among the monomer components constituting the crosslinked (meth)acrylic polymer particles (a) is preferably 70% by weight or more, more preferably 80% by weight or more, even more preferably 90% by weight or more, and particularly preferably 95% by weight or more, among the monomer components excluding polyfunctional monomers.

[0086] The crosslinked (meth)acrylic polymer particles (a) are formed by polymerizing the above-mentioned monomer components in the presence of a polyfunctional monomer. The polyfunctional monomer, also known as a crosslinking agent or crosslinkable monomer, is a compound having two or more unsaturated bonds in one molecule that are copolymerizable with the (meth)acrylic monomer. Specific examples include allyl methacrylate, allyl acrylate, diallyl maleate, diallyl fumarate, diallyl itaconate, monoallyl maleate, monoallyl fumarate, butadiene, divinylbenzene, triallyl isocyanurate, alkylene glycol dimethacrylate, and alkylene glycol diacrylate. These may be used alone or in combination of two or more. Allyl methacrylate is preferred.

[0087] The amount of the polyfunctional monomer used can be appropriately set from the viewpoint of strength, and specifically, it may be about 0.1 to 5.0 parts by weight per 100 parts by weight of the monomer components (excluding the polyfunctional monomer) constituting the crosslinked (meth)acrylic polymer particles (a). From the viewpoint of strength of the specific graft copolymer, the amount of the polyfunctional monomer used is preferably 0.2 to 3.5 parts by weight, more preferably 0.2 to 3.0 parts by weight, even more preferably 0.3 to 2.0 parts by weight, and particularly preferably 0.4 to 1.5 parts by weight per 100 parts by weight of the monomer components (excluding the polyfunctional monomer) constituting the crosslinked (meth)acrylic polymer particles (a).

[0088] (Non-crosslinked methacrylic polymer component (b)) The non-crosslinked methacrylic polymer component (b) is primarily composed of methacrylic monomers polymerized and does not have a crosslinked structure (i.e., is obtained by polymerization without using a polyfunctional monomer). At least a portion of the non-crosslinked methacrylic polymer component (b) is graft-bonded to the crosslinked (meth)acrylic polymer particles (a), which makes the crosslinked (meth)acrylic polymer particles (a) less likely to aggregate. As a result, the storage stability of the specific graft copolymer is improved, and low haze can be achieved when it is used as a transparent resin substrate.

[0089] The non-crosslinked methacrylic polymer component (b) is a high-molecular-weight polymer, specifically one having a weight-average molecular weight of 200,000 or more. The high molecular weight of the non-crosslinked methacrylic polymer component (b) enables the transparent resin substrate to achieve high heat resistance and, when used as a substrate for a flexible display, to obtain excellent flexibility (bending ability). The weight-average molecular weight of the non-crosslinked methacrylic polymer component (b) is preferably 500,000 or more, more preferably 1,000,000 or more, even more preferably 1,500,000 or more, and particularly preferably 2,000,000 or more. From the viewpoint of moldability, the weight-average molecular weight of the non-crosslinked methacrylic polymer component (b) is preferably 5,000,000 or less, more preferably 3,500,000 or less. When the weight-average molecular weight of the non-crosslinked methacrylic polymer component (b) is within the above-described preferred range, the toughness and flexibility (bending ability) of the transparent resin substrate are increased, resulting in a substrate that is resistant to deformation and is strong. If the weight-average molecular weight of the non-crosslinked methacrylic polymer component (b) is less than 200,000, the substrate will not immediately become brittle or easily breakable, but it will be difficult to obtain the high toughness and flexibility (bendability) required for flexible displays.

[0090] From the viewpoint of the heat resistance of the specific graft copolymer, the glass transition temperature of the non-crosslinked methacrylic polymer component (b) is preferably 115°C or higher, more preferably 118°C or higher, and even more preferably 120°C or higher. The upper limit of the glass transition temperature is not particularly limited, but may be, for example, 160°C or lower, or 150°C or lower. The glass transition temperature can be controlled by adjusting the type and ratio of the monomers constituting the non-crosslinked methacrylic polymer component (b). The glass transition temperature of the non-crosslinked methacrylic polymer component (b) can also be calculated using the Fox formula using values ​​listed in the Polymer Handbook (J. Brandrup, Interscience 1989) (for example, the glass transition temperature of polymethyl methacrylate is 105°C).

[0091] The non-crosslinked methacrylic polymer component (b) is a polymer mainly composed of methacrylic monomer units. From the viewpoint of the heat resistance of the graft copolymer and film formation, methyl methacrylate units are preferred as the methacrylic monomer units. In particular, the content of methyl methacrylate units among the monomer components constituting the non-crosslinked methacrylic polymer component (b) is preferably 70 to 99 wt %. This improves heat resistance and makes it easier to form a film by solution casting. The content of methyl methacrylate units is more preferably 75 to 98 wt %, even more preferably 80 to 97 wt %, particularly preferably 85 to 96 wt %, extremely preferably 88 to 95 wt %, and most preferably 90 to 95 wt %.

[0092] The non-crosslinked methacrylic polymer component (b) can use, as a monomer unit other than the methyl methacrylate unit, the same materials as the "drying-accelerating comonomer unit" in the first embodiment described above.

[0093] Among the monomer components constituting the non-crosslinked methacrylic polymer component (b), the content of the drying-accelerating comonomer unit is preferably 1 to 30 wt%, more preferably 2 to 25 wt%, even more preferably 3 to 20 wt%, particularly preferably 4 to 18 wt%, particularly preferably 4 to 15 wt%, extremely preferably 4 to 12 wt%, and most preferably 5 to 10 wt%. When two or more types of drying-accelerating comonomer units are contained, the content of the drying-accelerating comonomer unit refers to the proportion of the total of all the drying-accelerating comonomer units contained in the non-crosslinked methacrylic polymer component (b) to the total monomer components constituting the non-crosslinked methacrylic polymer component (b). By achieving such a content, the specific graft copolymer can have excellent heat resistance while accelerating the solvent evaporation rate in the solution casting method. The content of each of these units can be determined by proton nuclear magnetic resonance spectroscopy.

[0094] The non-crosslinked methacrylic polymer component (b) may be a copolymer that does not contain other comonomer units that do not fall under the category of drying-accelerating comonomer units, or may be a copolymer that contains other comonomer units that do not fall under the category of drying-accelerating comonomer units. Examples of other comonomers include methacrylic acid esters such as glycidyl methacrylate, epoxycyclohexylmethyl methacrylate, dimethylaminoethyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2,2,2-trifluoroethyl methacrylate, 2,2,2-trichloroethyl methacrylate, methacrylamide, and N-methylolmethacrylamide; methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, benzyl acrylate, octyl acrylate, glycidyl acrylate; Examples of such other comonomer units include acrylic esters such as epoxycyclohexylmethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, acrylamide, and N-methylol acrylamide; carboxylic acids such as methacrylic acid and acrylic acid and their salts; vinyl cyanides such as acrylonitrile and methacrylonitrile; maleic acid, fumaric acid, and their esters; vinyl halides such as vinyl chloride, vinyl bromide, and chloroprene; vinyl esters such as vinyl formate, vinyl acetate, and vinyl propionate; and alkenes such as ethylene, propylene, butylene, butadiene, and isobutylene. The proportion of such other comonomer units in the total monomer components constituting the non-crosslinked methacrylic polymer component (b) is preferably 10% by weight or less, more preferably 8% by weight or less, and even more preferably 5% by weight or less.

[0095] In the specific graft copolymer, the proportion of the crosslinked (meth)acrylic polymer particles (a) in the total of the crosslinked (meth)acrylic polymer particles (a) and the non-crosslinked methacrylic polymer component (b) is 1% by weight or more and less than 50% by weight, and the proportion of the non-crosslinked methacrylic polymer component (b) is more than 50% by weight and 99% by weight or less. By containing such a high proportion of the non-crosslinked methacrylic polymer component (b), the specific graft copolymer makes the crosslinked (meth)acrylic polymer particles (a) less likely to aggregate, making it possible to form a film with high strength and low haze, and further improving the storage stability of the specific graft copolymer or a dope thereof.

[0096] When the specific graft copolymer is used as a transparent resin substrate, taking into consideration the balance with the elastic modulus and surface hardness of the substrate, the proportion of the crosslinked (meth)acrylic polymer particles (a) in the total of the crosslinked (meth)acrylic polymer particles (a) and the non-crosslinked methacrylic polymer component (b) is preferably 3 to 45% by weight, more preferably 4 to 40% by weight, even more preferably 5 to 35% by weight, and particularly preferably 6 to 30% by weight.

[0097] From the viewpoints of the moisture permeability, elastic modulus, and bending resistance of the resulting film, the proportion of the crosslinked (meth)acrylic polymer particles (a) in the total of the crosslinked (meth)acrylic polymer particles (a) and the non-crosslinked methacrylic polymer component (b) is preferably 5% by weight or more, more preferably 6% by weight or more, and even more preferably 7% by weight or more. From the same viewpoint, the upper limit of the proportion is preferably 25% by weight or less, more preferably 20% by weight or less, even more preferably 15% by weight or less, particularly preferably 12% by weight or less, and extremely preferably 10% by weight or less.

[0098] (Method for producing (meth)acrylic resin according to second embodiment) The method for producing the (meth)acrylic resin of the second aspect is not particularly limited as long as it is a method that can exhibit the effects of the invention. However, from the viewpoints of the degree of freedom in designing the structure of the (meth)acrylic polymer used as the (meth)acrylic resin, the ease of polymerization, productivity, etc., it is preferable that the (meth)acrylic resin be produced by an emulsion polymerization method or a suspension polymerization method.

[0099] When producing a transparent resin substrate by a solution casting method, from the viewpoint of producing a highly transparent film with excellent appearance and being less likely to produce foam marks on the surface or inside of the film during film drying, it is preferable to produce it by an emulsion polymerization method in which polymerization is carried out in the presence of an ionic emulsifier. In particular, in the production of a (meth)acrylic polymer containing a maleimide ring structure in the main chain, maleimide monomers remaining during the polymerization process tend to hydrolyze and discolor the (meth)acrylic polymer, but emulsion polymerization is preferable because it can effectively reduce the amount of these remaining maleimide monomers.

[0100] As the polymerization initiator for polymerizing the (meth)acrylic polymer, known initiators can be used, and examples thereof include persulfates such as potassium persulfate, sodium persulfate, and ammonium persulfate; and organic peroxides such as t-butyl hydroperoxide, t-butylperoxyisopropyl carbonate, cumene hydroperoxide, p-menthane hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, di(8,5,5-trimethylhexanoyl) peroxide, dilauroyl peroxide, and benzoyl peroxide.

[0101] [Polymer particles (I)] The transparent resin substrate of the present disclosure may further contain polymer particles (I). The polymer particles (I) are crosslinked (meth)acrylic polymer particles having a weight-average molecular weight of less than 200,000. The form of the polymer particles (I) is not limited, and examples thereof include graft copolymers having a core-shell structure. The graft copolymers having a core-shell structure can impart mechanical strength, such as bending resistance and crack resistance, to the transparent resin substrate. When producing the transparent resin substrate by a solution casting method, a dope may be prepared by mixing a solution in which a (meth)acrylic resin is dissolved in a solvent with a solution in which a graft copolymer having a core-shell structure is dissolved in a solvent.

[0102] Graft copolymers having a core-shell structure are also called multistage polymers, multilayer polymers, or core-shell polymers. These polymers have a polymer layer (shell layer) obtained by polymerizing a monomer mixture in the presence of crosslinked polymer particles (core layer). The core layer and shell layer may each consist of one layer or two or more layers. Such graft copolymers are not particularly limited, and known graft copolymers can be used as appropriate. One example is a graft copolymer obtained by polymerizing a monomer mixture containing an acrylic ester as the main component with a crosslinking agent to form an acrylic ester-based rubber-like polymer, and then polymerizing a monomer mixture containing a methacrylic ester as the main component in the presence of the acrylic ester-based rubber-like polymer.

[0103] The graft copolymer can be produced by ordinary emulsion polymerization using a known emulsifier. When producing a transparent resin substrate by a solution casting method, from the viewpoint of suppressing foaming marks that may occur during the drying process, it is preferable to produce the graft copolymer by emulsion polymerization using an ionic emulsifier that is soluble in an alcohol solvent. Furthermore, for example, when the graft copolymer is granulated using a coagulant such as calcium chloride or magnesium chloride, the ionic emulsifier will exist as a salt of a polyvalent cation. Therefore, from the viewpoint of suppressing foaming marks on the transparent resin substrate, it is preferable to wash the graft copolymer using a known washing method to reduce the salt content in the graft copolymer.

[0104] When the crosslinked (meth)acrylic polymer particles have a structure similar to that of a graft copolymer obtained by polymerizing a monomer mixture containing a methacrylic acid ester as a main component in the presence of an acrylic acid ester rubber-like polymer, the addition of the crosslinked (meth)acrylic polymer particles tends to improve the mechanical strength of the transparent resin substrate while decreasing the physical properties of the substrate, such as the elastic modulus and hardness.

[0105] In particular, when used as a hard-coated film having a hard-coat layer on a transparent resin substrate, such as for cover window applications, if the substrate contains a large amount of the above-mentioned graft copolymer, the elastic modulus and surface hardness of the hard-coated film as a whole tend to decrease. Therefore, from the viewpoint of improving mechanical strength while maintaining properties such as elastic modulus and surface hardness, the content of polymer particles (I) is preferably 50% by weight or less, more preferably less than 50% by weight, even more preferably 30% by weight or less, particularly preferably 20% by weight or less, extremely preferably 10% by weight or less, and most preferably 5% by weight or less, relative to 100% by weight of the transparent resin substrate. Furthermore, the content of polymer particles (I) is preferably 1% by weight or more, and may be 2% by weight or more, or even 3% by weight or more, relative to 100% by weight of the transparent resin substrate.

[0106] From the viewpoint of the balance between the mechanical strength of the transparent resin substrate and the modulus of elasticity and surface hardness, the polymer particles (I) to be added may have a hard polymer composition with a high glass transition temperature, or the amount of crosslinking agent used may be adjusted to obtain crosslinked polymer particles with a high degree of crosslinking.

[0107] When a transparent resin substrate containing polymer particles (I) is produced by a solution casting method, it is preferable to use a solvent that does not easily swell the polymer particles (I) when preparing a dope. For example, a graft copolymer with a high crosslink density in the crosslinked polymer of the core layer prevents solvent penetration into the core layer and suppresses swelling of the graft copolymer, so that the density of the molecular chains in the shell layer does not decrease and the steric repulsion effect between particles is maintained, resulting in good particle dispersibility.

[0108] <Hard coat film> The transparent resin substrate of the present disclosure is also used as a hard-coated film having a hard-coat layer on at least one of its main surfaces. For example, in applications such as a cover window (front panel) for a foldable display, high surface hardness is required, so even if it is a thin glass or plastic film, a hard-coated film having a hard-coat layer that is a cured product of a hard-coat composition is generally used. The hard-coat layer may be formed on only one main surface (one side) of the transparent resin substrate, or on both main surfaces (both sides).

[0109] [Hard Coat Composition] Examples of hard coat compositions that form the hard coat layer include (meth)acrylic acid ester-based, polyorganosiloxane-based, inorganic hybrid-based, urethane acrylate-based, polyester acrylate-based, and epoxy-based compositions. These may be mixed together, or particles of organic or inorganic fillers may be added. Among these, hard coat compositions containing a polyorganosiloxane compound having an epoxy group are preferred, as they provide a hard coat film with an excellent balance between flexibility (flexibility) and surface hardness. Hard coat films produced using hard coat compositions containing a polyorganosiloxane compound having an epoxy group are suitable for use in applications requiring a balance between high flexibility (flexibility) and surface hardness, such as cover windows (front panels) for foldable displays.

[0110] (Polyorganosiloxane compound) The polyorganosiloxane compound is, for example, a condensate of a silane compound represented by the following formula (1), wherein the weight-average molecular weight of the condensate is 500 to 20,000, and the molar ratio of the constituent unit represented by the following formula (3) to the constituent unit represented by the following formula (4) contained in the condensate ([constituent unit represented by formula (3)] / [constituent unit represented by formula (4)]) is less than 5.

[0111] [ka] (In formula (1), R 1 represents an alkylene group having 2 to 16 carbon atoms, and R 2 represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R 3 represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 25 carbon atoms, or an aralkyl group having 7 to 12 carbon atoms, x represents 2 or 3, and Y represents a glycidyloxy group represented by the following formula (2-1) or an alicyclic epoxy group represented by the following formula (2-2).

[0112] [ka] (In formulas (2-1) and (2-2), * represents R 1 )

[0113] [ka] (In formula (3), R 1 and Y are defined as in formula (1) above.

[0114] [ka] (In formula (4), R 1 and Y are defined as in the above formula (1). Z represents a hydrogen atom, an alkoxy group having an alkyl moiety of 1 to 10 carbon atoms, an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 25 carbon atoms, or an aralkyl group having 7 to 12 carbon atoms.

[0115] In the above formula (1), R 1 represents an alkylene group having 2 to 16 carbon atoms, and preferably represents a linear alkylene group. Examples of linear alkylene groups include an ethylene group, a trimethylene group, a tetramethylene group, a pentamethylene group, a hexamethylene group, a heptamethylene group, an octamethylene group, a decamethylene group, a dodecamethylene group, a tetradecamethylene group, and a hexadecamethylene group. R 1 may further have a substituent having 1 to 6 carbon atoms. Examples of the substituent having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a cyclohexyl group, and a phenyl group.

[0116] In the above formula (1), R 2 represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an isopropyl group, an isobutyl group, a cyclohexyl group, and an ethylhexyl group. From the viewpoint of facilitating hydrolysis and condensation of a silane compound having a hydrolyzable silyl group, R 2The alkyl group is preferably a methyl group, an ethyl group, or a propyl group, and more preferably a methyl group.

[0117] In the above formula (1), R 3 represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 25 carbon atoms, or an aralkyl group having 7 to 12 carbon atoms. 3 Examples of the alkyl group include a hydrogen atom, a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an isopropyl group, an isobutyl group, a cyclohexyl group, an ethylhexyl group, a benzyl group, a phenyl group, a tolyl group, a xylyl group, a naphthyl group, and a phenethyl group.

[0118] In the above formula (1), x represents 2 or 3, and is appropriately selected depending on the physical properties required for the hard coat.

[0119] The polyorganosiloxane compound has an alkylene group having a specific chain length between the epoxy group and the silicon atom that connects the epoxy group by a chemical bond. Therefore, a hard coat film having a hard coat layer containing the polyorganosiloxane compound exhibits excellent flexibility. From the viewpoint of improving the flexibility of the hard coat film, R 1 R preferably represents an alkylene group having 6 to 14 carbon atoms, and more preferably represents an alkylene group having 8 to 12 carbon atoms. 1 If the number of carbon atoms in R is 3 or less, the surface hardness of the cured product will be improved, but the flexibility of the cured product may be less exhibited. 1 When mixing silane compounds with a large number of carbon atoms, or when R 1 By using a method such as co-condensation with a silane compound having a large number of carbon atoms, it is possible to obtain a polyorganosiloxane compound that provides an excellent balance between surface hardness and flexibility of the cured product.

[0120] The weight-average molecular weight of the polyorganosiloxane compound is preferably 500 or more from the viewpoint of increasing the hardness of the cured product. Furthermore, the weight-average molecular weight of the siloxane compound is preferably 500 or more from the viewpoint of suppressing volatilization of the siloxane compound. On the other hand, if the molecular weight is too large, cloudiness may occur due to reduced compatibility with other components. Therefore, the weight-average molecular weight of the siloxane compound is preferably 20,000 or less.

[0121] The weight average molecular weight of the polyorganosiloxane compound can be controlled by appropriately selecting the amount of water used in the reaction and the type and amount of catalyst. For example, the weight average molecular weight can be increased by increasing the amount of water initially charged.

[0122] The polyorganosiloxane compound may contain a structural unit represented by the formula (3) or (4) above, which is formed by the hydrolysis and condensation reaction of the silane compound represented by the formula (1). The structural unit represented by the formula (3) above (hereinafter referred to as [SiO 3 / 2 The structural unit represented by the above formula (4) (hereinafter referred to as [SiO 2 / 2 The ratio of [SiO 3 / 2 body] / [SiO 2 / 2 The SiO 2 content is preferably less than 5, more preferably 4 or less, and even more preferably 3 or less, and the lower limit may be 0. 3 / 2 Body and SiO 2 / 2 The ratio of [SiO 3 / 2 body] / [SiO 2 / 2 By making the SiO condensate less than 5, the hard coat film having a hard coat layer made of a cured product of the polyorganosiloxane compound exhibits excellent flexibility. 3 / 2 The content of [SiO 3 / 2 body] / [SiO 2 / 2 If the [molecule ratio] is 5 or more, the resulting condensation product will have a dense structure and will have reduced flexibility, resulting in reduced flexibility when made into a hard coat film.

[0123] SiO in polyorganosiloxane compounds 3 / 2 body and SiO 2 / 2 The content and proportion of the body, e.g. 29 It can be calculated by Si-NMR measurement. 29 In Si-NMR measurements, SiO 3 / 2 Chemical shift of silicon atoms in the SiO 2 / 2 Unlike the chemical shift of silicon atoms in the solid, the signals are at different positions in the spectrum, so the above ratio [SiO 3 / 2 body] / [SiO 2 / 2 body] can be obtained.

[0124] In addition, SiO in the polyorganosiloxane compound 3 / 2 Body and SiO 2 / 2 The ratio of [SiO 3 / 2 body] / [SiO 2 / 2 The ratio [SiO ] can be controlled by appropriately selecting the amount of water used in the reaction and the type and amount of catalyst. For example, by increasing the amount of catalyst initially charged, 3 / 2 body] / [SiO 2 / 2 body] can be made larger.

[0125] The amount of water required for the hydrolysis and condensation reactions is determined by the amount of OR bonded directly to the silicon atom. 2 group (OR in the above formula (1) 2 The amount of water is preferably 0.3 to 3 equivalents, more preferably 0.5 to 2 equivalents, per equivalent of the OR group. 2 On the other hand, if the amount of water exceeds 3 equivalents, the reaction rates of the hydrolysis and condensation reactions become too high, resulting in the formation of high molecular weight condensates, which may reduce the physical properties and transparency of the cured film.

[0126] Residual OR in polyorganosiloxane compounds 2The number of groups is preferably 2 or less, more preferably 1 or less, even more preferably 0.5 or less, particularly preferably 0.1 or less, and it is extremely preferable that there are substantially no groups remaining in one molecule of the polyorganosiloxane compound.

[0127] From the viewpoint of increasing the crosslinking density and improving the hardness of the cured product, it is preferable that the residual rate of epoxy structure-containing groups in the polyorganosiloxane compound obtained by the hydrolysis and condensation reaction of the silane compound represented by the above formula (1) is high.

[0128] The residual rate of epoxy structure-containing groups, that is, the ratio of the number of moles of epoxy structure-containing groups in the polyorganosiloxane compound obtained by condensation to the number of moles of epoxy structure-containing groups in the silane compound represented by the above formula (1), which is the raw material, is preferably 20% or more, more preferably 40% or more, and even more preferably 60% or more. Here, the residual rate of epoxy structure-containing groups is 1 It can be calculated by H-NMR measurement.

[0129] The hydrolysis and condensation reactions are carried out, for example, in the presence of a neutral salt catalyst. By carrying out the hydrolysis and condensation reactions in the presence of a neutral salt catalyst, a polyorganosiloxane compound can be obtained without deactivating the epoxy groups before, after, or during storage of the hydrolysis and condensation reactions.

[0130] Furthermore, the neutral salt catalyst itself does not corrode the production vessel or storage vessel, so it can be used without being restricted by the material of the production or storage equipment. This is because, in general, acid catalysts and base catalysts react electrophilically or nucleophilically with various substances, or change the hydrogen ion concentration or hydroxide ion concentration in the reaction solution, so that these ions contribute to the reaction, whereas neutral salts have extremely low reactivity as described above.

[0131] Furthermore, when an acid catalyst or a base catalyst is used in the hydrolysis and condensation reactions, a step of removing the acid or base or a step of neutralization is required for the reasons mentioned above. These steps are undesirable because they are cumbersome and reduce the yield. Neutral salt catalysts are preferable because they do not require these steps.

[0132] In the production of the polyorganosiloxane compound, in consideration of safety during production, it is preferable to carry out the production while refluxing the dilution solvent, alcohol generated by hydrolysis, etc.

[0133] The dilution solvent used in the production of the polyorganosiloxane compound is preferably a water-soluble alcohol compound or ether compound. This is because many silane compounds represented by the above formula (1) have low compatibility with the neutral salt and water used for hydrolysis, and it is preferable for the reaction solution to be compatible with them in order to smoothly proceed with the reaction.

[0134] When a polyorganosiloxane compound is obtained by condensation of a silane compound, in addition to the silane compound (1) represented by the above formula (1) having an epoxy group, a silane compound represented by the following formula (5) having no epoxy group may be used.

[0135] [ka] (In formula (5), R 4 represents a monovalent group having no epoxy group selected from the group consisting of substituted or unsubstituted alkyl groups having 1 to 10 carbon atoms, alkenyl groups, aryl groups having 6 to 25 carbon atoms, and aralkyl groups having 7 to 12 carbon atoms, and R 5 represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R 6 represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 25 carbon atoms, or an aralkyl group having 7 to 12 carbon atoms, and x represents 2 or 3.

[0136] However, from the viewpoint of improving the mechanical strength of the cured product, the more epoxy groups contained in one molecule of the polyorganosiloxane compound, the better. In the reaction of the silane compound, the molar ratio of the silane compound represented by the formula (5) to the silane compound represented by the formula (1) is preferably 2 or less, more preferably 1 or less, even more preferably 0.4 or less, and particularly preferably 0.2 or less. The molar ratio of the silane compound represented by the formula (5) to the silane compound represented by the formula (1) may be 0.

[0137] From the viewpoint of forming a hard coat layer having excellent mechanical strength, the content of the polyorganosiloxane compound in the hard coat composition is preferably 40 parts by weight or more, more preferably 50 parts by weight or more, and even more preferably 60 parts by weight or more, per 100 parts by weight of the total solid content.

[0138] (Cationic photopolymerization initiator) The hard coat composition preferably contains a photocationic polymerization initiator. The photocationic polymerization initiator is a compound (photoacid generator) that generates an acid upon irradiation with active energy rays. The acid generated from the photoacid generator promotes a ring-opening reaction and a polymerization reaction of the epoxy groups of the polyorganosiloxane compound, forming intermolecular crosslinks and curing the hard coat composition.

[0139] Examples of the photocationic polymerization initiator include strong acids such as toluenesulfonic acid and boron tetrafluoride; onium salts such as sulfonium salts, ammonium salts, phosphonium salts, iodonium salts, and selenium salts; iron-allene complexes; silanol-metal chelate complexes; sulfonic acid derivatives such as disulfones, disulfonyldiazomethanes, disulfonylmethanes, sulfonylbenzoylmethanes, imidosulfonates, and benzoin sulfonates; and organic halogen compounds.

[0140] The content of the photocationic polymerization initiator in the hard coat composition is preferably 0.05 to 10 parts by weight, more preferably 0.1 to 5 parts by weight, and even more preferably 0.2 to 2 parts by weight, relative to 100 parts by weight of the polyorganosiloxane compound.

[0141] (reactive diluent) The hard coat composition may further contain a cationic curable compound other than a polyorganosiloxane compound as a reactive diluent. As a reactive diluent for photocationic polymerization, a compound having a cationic polymerizable functional group such as an epoxy group, a vinyl ether group, an oxetane group, or an alkoxysilyl group is used. Among these, a reactive diluent having an epoxy group is preferred because of its high reactivity with the epoxy group of the polyorganosiloxane compound. The cationic curable compound may be used alone or in combination of two or more.

[0142] The content of the reactive diluent in the hard coat composition is preferably 100 parts by weight or less, and more preferably 50 parts by weight or less, per 100 parts by weight of the polyorganosiloxane compound.

[0143] (photosensitizer) The hard coat composition may contain a photosensitizer for the purpose of improving the photosensitivity of the cationic photopolymerization initiator.

[0144] (solvent) The hard coat composition may contain a solvent. When a solvent is contained, it is preferable that the solvent does not dissolve the transparent resin substrate. The content of the solvent in the hard coat composition is preferably 500 parts by weight or less, more preferably 300 parts by weight or less, and even more preferably 100 parts by weight or less, relative to 100 parts by weight of the polyorganosiloxane compound.

[0145] (additives) The hard coat composition may contain additives such as inorganic pigments, organic pigments, surface conditioners, surface modifiers, plasticizers, dispersants, wetting agents, thickeners, and antifoaming agents. The hard coat composition may also contain a thermoplastic or thermosetting resin material other than the polyorganosiloxane compound. When the siloxane compound and / or the resin material other than the siloxane compound is radically polymerizable, the hard coat composition may contain a radical polymerization initiator in addition to the photocationic polymerization initiator.

[0146] [Hard coat film manufacturing method] The hard coat film of the present disclosure can be obtained by applying a hard coat composition to a transparent resin substrate, drying and removing the solvent as necessary, and then irradiating the hard coat composition with active energy rays to cure it.

[0147] Before applying the hard coat layer, the surface of the transparent resin substrate may be subjected to a surface treatment such as a corona treatment or a plasma treatment. In addition, an easy-adhesion layer (primer layer) described later may be provided on the surface of the transparent resin substrate.

[0148] When the hard coat composition is irradiated with active energy rays, an acid is generated from the photocationic polymerization initiator, and the epoxy groups of the polyorganosiloxane compound undergo ring-opening and cationic polymerization, thereby proceeding with curing. When the hard coat composition contains a reactive diluent, in addition to the polymerization reaction between the siloxane compounds, a polymerization reaction between the epoxy groups of the siloxane compound and the reactive diluent also occurs.

[0149] Examples of active energy rays irradiated during photocuring include visible light, ultraviolet light, infrared light, X-rays, α-rays, β-rays, γ-rays, and electron beams. Ultraviolet light is preferred as the active energy ray because it has a high curing reaction rate and excellent energy efficiency. The cumulative irradiation dose of the active energy ray is, for example, 50 to 10,000 mJ / cm. 2 The curing temperature is about 100° C., and may be set depending on the type and amount of the photocationic polymerization initiator, the thickness of the hard coat layer, etc. The curing temperature is not particularly limited, and is usually 100° C. or lower.

[0150] The thickness of the transparent resin substrate is not particularly limited and can be appropriately selected, for example, within the range of 1 to 1000 μm, preferably 5 to 500 μm, more preferably 10 to 200 μm, and even more preferably 15 to 150 μm.

[0151] The thickness of the hard coat layer is preferably 10 μm or more, more preferably 20 μm or more, even more preferably 30 μm or more, and particularly preferably 40 μm or more. The thickness of the hard coat layer is preferably 100 μm or less, more preferably 80 μm or less. If the thickness of the hard coat layer is less than 10 μm, mechanical properties such as surface hardness and dent resistance may not be sufficiently improved. On the other hand, if the thickness of the hard coat layer is more than 100 μm, transparency and flexibility may be reduced.

[0152] The total thickness of the hard coat film of the present disclosure can be appropriately selected from the range of 40 to 500 μm, and is preferably 80 to 250 μm, and more preferably 100 to 200 μm.

[0153] In the hard coat film of the present disclosure, the ratio of the thickness of the hard coat layer to the thickness of the transparent resin substrate (thickness of hard coat layer / thickness of transparent resin substrate) is not particularly limited and may be appropriately selected, for example, from the range of 1 / 10 to 10 / 1.

[0154] The hard coat layer in the hard coat film of the present disclosure preferably has a polymer matrix crosslinked by ring-opening and polymerization reaction of the epoxy group of the polyorganosiloxane compound, and in this case, it can achieve a surface hardness comparable to that of glass. The pencil hardness of the hard coat layer-forming surface of the hard coat film of the present disclosure is preferably HB or higher, more preferably H or higher, even more preferably 2H or higher, and particularly preferably 4H or higher.

[0155] The total light transmittance of the hard coat film of the present disclosure is preferably 80% or more, more preferably 85% or more, and even more preferably 88% or more. The haze of the hard coat film of the present disclosure is preferably 1.5% or less, more preferably 0.9% or less, even more preferably 0.6% or less, and particularly preferably 0.5% or less.

[0156] [Easy adhesive layer] The hard coat film of the present disclosure may have an easy-adhesion layer between the transparent resin substrate and the hard coat layer. The easy-adhesion layer may have any easy-adhesion composition. For example, an easy-adhesion layer containing a water-based urethane resin and a crosslinking agent is known. Examples of the crosslinking agent include oxazoline-based and epoxy-based crosslinking agents.

[0157] Among these, from the viewpoint of improving the adhesion between the (meth)acrylic transparent resin substrate and the hard coat layer, an adhesive layer made of an adhesive composition containing a polyurethane resin having a carboxyl group and a multifunctional epoxy crosslinking agent having three or more functional groups can be preferably used. The multifunctional epoxy crosslinking agent preferably has four or more epoxy functional groups.

[0158] <Application> The transparent resin substrate of the present disclosure has high flexibility (bendability) and excellent optical properties, and can therefore be used as a substrate for various flexible displays. Examples include curved displays; foldable or bendable displays, which are bent or folded displays; and rollable or slidable displays, which are rollable displays. Display devices for realizing flexible displays include, but are not limited to, organic electroluminescence (EL) displays having a flexible light-emitting layer.

[0159] Transparent resin substrates used in flexible organic EL displays include, for example, films for cover windows. The transparent resin substrates of the present disclosure have high flexibility (bendability) and excellent optical properties, so that hard coat films formed by forming a hard coat layer on the transparent resin substrate also have high flexibility (bendability).

[0160] In addition, high flexibility (bending ability) is required for the functional film layers that constitute flexible organic EL displays. For this reason, for example, the transparent resin substrate of the present disclosure is also suitable for use as an impact absorbing film, a backing film, or a laminated protective film for the surface of other substrates. The laminated protective film can be used to protect the surface of substrates such as thin-film glass, TAC (triacetyl cellulose), and COP (cycloolefin polymer) from scratches, or to prevent thin-film glass from breaking and shattering. [Example]

[0161] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples. The number of parts of each substance is based on weight.

[0162] (polymerization conversion rate) The polymerization conversion rate of the (meth)acrylic resin and polymer particles (I) was determined by the following method. Approximately 2 g of latex and suspension slurry containing the polymer was collected from the polymerization system and precisely weighed. After drying in a hot air dryer at 120°C for 1 hour, the weight after drying was precisely weighed as the solid content. Next, the ratio of the weighing results before and after drying was determined as the solid content ratio in the sample. Finally, using this solid content ratio, the polymerization conversion rate was calculated according to the following formula. In this formula, the polyfunctional monomer and chain transfer agent were treated as charged monomers. Polymerization conversion rate (%) = {(total weight of charged raw materials x solid content ratio - total weight of raw materials other than water and monomers) / weight of charged monomer} x 100

[0163] (Volume average particle size of polymerized latex) Using Microtrac UPA150 (manufactured by Nikkiso Co., Ltd.), the volume average particle size of the polymerized latex of the (meth)acrylic resin was determined based on the principle of dynamic light scattering.

[0164] (Volume average particle size of bead-shaped particles) Using a Microtrac MT3300EXII (manufactured by Nikkiso Co., Ltd.), the volume average particle size of the bead-shaped particles of the (meth)acrylic resin was determined based on the principle of the laser diffraction scattering method.

[0165] (glass transition temperature (Tg)) The glass transition temperature (Tg) of the transparent resin substrate was measured using a differential scanning calorimeter (DSC, model Q1000, manufactured by TA Instruments). The sample was placed under a nitrogen flow and heated to 200°C at a heating rate of 10°C / min, then rapidly cooled to 40°C, and heated again to 200°C at a heating rate of 10°C / min. The glass transition observed during the second heating was averaged between the extrapolated glass transition onset temperature and the extrapolated glass transition end temperature, and this value was taken as the glass transition temperature (Tg).

[0166] (Haze measurement of transparent resin substrate) The haze of the obtained transparent resin substrate was measured using a haze meter (HZ-V3, manufactured by Suga Test Instruments Co., Ltd.) according to the method described in JIS K7105.

[0167] (Internal haze measurement of transparent resin substrate) To measure the haze occurring only inside the transparent resin substrate (internal haze), the haze was measured while canceling the influence of surface scattering from the transparent resin substrate. Glycerin, which has a refractive index close to that of the (meth)acrylic transparent resin substrate, was dropped onto both sides of the film and sandwiched between glass plates, so that the interface between the transparent resin substrate and the glass plates was filled with glycerin. The haze was then measured as described above, and the haze value of the glass plate alone, which had been measured previously, was subtracted to determine the internal haze of the transparent resin substrate.

[0168] (Stretching) The transparent resin substrate was preheated for 5 minutes using a stretching machine equipped with a drying oven at a temperature 10°C higher than the glass transition temperature of the substrate before stretching, and then uniaxially stretched at a fixed width of 1.5 times at a speed of 100 mm / min.

[0169] (Thickness) The thickness of the transparent resin substrate was measured using a Digimatic Indicator (manufactured by Mitutoyo Corporation).

[0170] (phase difference) A test specimen was cut from the center of a 40 μm-thick transparent resin substrate after uniaxial stretching. The in-plane retardation Re of this test specimen was measured using an automatic birefringence meter (KOBRA-WR, manufactured by Oji Measurement Co., Ltd.) under conditions of a wavelength of 590 nm and an incident angle of 0°. Measurement was also performed at an incident angle of 40°, and the thickness direction retardation Rth was also measured. Measurements were performed three times each while moving the test specimen to change the measurement location, and the average value was calculated. In addition to the transparent resin substrate of the present disclosure, the retardation of a 38 μm-thick transparent PET film (Cosmoshine A4300, manufactured by Toyobo Co., Ltd.) was also measured and converted to a value equivalent to a thickness of 40 μm.

[0171] (orientation birefringence) The orientation birefringence of the transparent resin substrate was determined by dividing the in-plane retardation Re measured by the above method by the thickness of the transparent resin substrate.

[0172] (Photoelastic Constant) Before uniaxial stretching, a transparent resin substrate in an unstretched state was used to cut out a 15 mm x 85 mm rectangular test piece (cut so that the long side was in the TD direction). Using this test piece, the in-plane retardation Re was measured using an automatic birefringence meter (KOBRA-WR, manufactured by Oji Measurement Co., Ltd.) at a wavelength of 590 nm and an incident angle of 0°. One of the long sides of the test piece was fixed, and the other side was measured while changing the load (stress) in 0.5 kgf increments from no load to 4 kgf. The proportionality constant was calculated from the relationship between the obtained stress and the in-plane retardation Re, and used as the photoelastic constant. The sign of the photoelastic constant was determined as positive or negative based on the change in orientation angle relative to stress. In addition to the transparent resin substrate of the present disclosure, the photoelastic constant of a 38 μm thick transparent PET film (Cosmoshine A4300, manufactured by Toyobo Co., Ltd.) was also measured.

[0173] (2D birefringence evaluation) A 15 mm x 85 mm test piece was cut from a 40 μm thick transparent resin substrate, and both ends were joined with tape to create a cylindrical test piece. The curved cylindrical test piece was placed perpendicular to the imaging direction, with the joint facing downward. With stress applied to the test piece, a two-dimensional birefringence evaluation device (Photonic Lattice Co., Ltd., WPA-200-L) was used to visualize the phase difference of the entire test piece at a wavelength of 543 nm. While referring to the visualized image, the cursor was positioned on the highest and lowest phase difference portions of the cylindrical test piece, the phase difference was read, and the difference (Δ phase difference) was calculated. In addition to the transparent resin substrate of the present disclosure, the Δ phase difference of a 38 μm thick transparent PET film (Cosmoshine A4300, manufactured by Toyobo Co., Ltd.) was also measured and converted to a value per 40 μm thickness.

[0174] (Surface hardness) According to JIS K5600-5-4:1999, the pencil hardness of the surface on which the hard coat layer was formed was measured under a load of 750 g to evaluate the surface hardness of the hard coat film.

[0175] (Flexibility test) Using a bending durability tester (manufactured by Yuasa System Co., Ltd.), a 25mm x 130mm bending test sample cut out from the hard coat film was subjected to a repeated bending test at room temperature, with a bending radius of 1.5R and one bending per second, with the hard coat layer formed on one main surface (main surface 1) facing outward, and the number of bending cycles was measured. The test was judged to be out when the hard coat film broke or showed even a slight crack.

[0176] (Weight average molecular weight) The weight-average molecular weight of the transparent resin substrate was calculated using gel permeation chromatography (GPC) in terms of standard polystyrene. The GPC column was packed with cross-linked polystyrene gel (model: TSK gel Super HZM-H, manufactured by Tosoh Corporation), and tetrahydrofuran (THF) was used as the GPC solvent. The sample solution was a clear supernatant obtained by centrifuging a solution consisting of 20 mg of each substrate piece and 10 mL of THF at 43,000 G for 30 minutes. The GPC column temperature was set to 40°C.

[0177] (Imidization rate) The imidization rate was calculated using IR as follows: Pellets of the (meth)acrylic resin were dissolved in methylene chloride, and the IR spectrum of the solution was measured at room temperature using a TravelIR manufactured by SensIR Technologies. -1 The absorption intensity attributable to the ester carbonyl group (Absester) and the absorption intensity at 1660cm -1 The imidization rate (Im%(IR)) was calculated from the ratio of the absorption intensity (Absimide) attributed to the imide carbonyl group to the absorption intensity (Im%) attributed to the imide carbonyl group. Here, the "imidization rate" refers to the proportion of imide carbonyl groups in all carbonyl groups.

[0178] (Glutarimide unit content) 1 H-NMR BRUKER AvanceIII (400MHz) was used to measure the 1H-NMR measurement was performed to determine the content (mol%) of each monomer unit, such as glutarimide unit and ester unit, in the resin, and the content (mol%) was converted to content (wt%) using the molecular weight of each monomer unit.

[0179] (acid number) 0.3 g of the obtained glutarimide acrylic resin was dissolved in a mixed solvent of 37.5 mL of methylene chloride and 37.5 mL of methanol. Two drops of phenolphthalein ethanol solution were added, followed by 5 mL of 0.1 N aqueous sodium hydroxide solution. The excess base was titrated with 0.1 N hydrochloric acid, and the acid value was calculated as the difference in milliequivalents between the added base and the amount of hydrochloric acid used to achieve neutralization.

[0180] Examples of producing the (meth)acrylic resin and polymer particles (I) are described below. The abbreviations in the descriptions represent the following substances, respectively. MMA: methyl methacrylate n-BMA: n-butyl methacrylate 2-EHMA: 2-ethylhexyl methacrylate PhMI: N-phenylmaleimide BA: butyl acrylate St: styrene ALMA: Allyl methacrylate n-OM: n-octyl mercaptan DSS: Dioctyl sodium sulfosuccinate NPS: Sodium persulfate KPS: Potassium persulfate SFS: Sodium sulfoxylate formaldehyde ED: Ethylenediaminetetraacetic acid disodium salt FeSO4: Ferrous sulfate heptahydrate 2-EHTG: 2-ethylhexyl thioglycolate LPO: Lauroyl peroxide t-BHP: t-butyl hydroperoxide HPMC: Hydroxypropyl methylcellulose PLEP: Polyoxyethylene lauryl ether phosphate

[0181] [Production of (meth)acrylic resin] (Production Example 1: Production of (meth)acrylic resin A) An 8-liter glass reactor equipped with a paddle stirrer was charged with 170 parts of deionized water and 0.1 parts of anhydrous disodium hydrogen phosphate. The contents were then stirred at 300 rpm and the reactor was heated to 40°C while being purged with nitrogen. After 0.3 parts of LPO was charged into the reactor, a monomer mixture consisting of 85 parts of MMA, 5 parts of 2-EHMA, and 10 parts of PhMI was continuously added to the reactor over 30 minutes. Thirty minutes after the completion of the monomer mixture addition, 0.4 parts of HPMC (Metolose 60SH50, manufactured by Shin-Etsu Chemical Co., Ltd.) was continuously added to the reactor over 30 minutes. After 30 minutes, the reactor was heated, and the reaction was initiated when the internal temperature reached 65°C. 100 minutes after the start of the reaction, the internal temperature of the reactor reached a maximum of 85°C, after which the internal temperature gradually decreased. The internal temperature of the reactor was then raised to 95°C and maintained at that temperature for 60 minutes to complete the polymerization. The polymerization conversion rate was 99.5%. The volume average particle diameter of the resulting bead-like particles was 50 μm. The suspension slurry containing the bead-like particles was dehydrated and washed, and then dried in a hot air oven at 50°C for 24 hours to obtain a white powdery (meth)acrylic resin A.

[0182] (Production Example 2: Production of (meth)acrylic resin B) An 8-liter glass reactor equipped with a paddle stirrer was charged with 102 parts of deionized water, 0.01 parts of sodium hydroxide, and 0.15 parts of DSS. The contents were then stirred at 175 rpm and the reactor was heated to 85°C while being purged with nitrogen. After reaching 85°C, 0.022 parts of NPS and 0.0005 parts of SFS were added. A monomer mixture consisting of 85 parts of MMA, 5 parts of 2-EHMA, 10 parts of PhMI, and 0.05 parts of 2-EHTG was then continuously added to the reactor over 80 minutes to conduct the reaction. 15 minutes after the addition of the monomer mixture, 0.55 parts of DSS was added dropwise and continuously added to the reactor in parallel with the addition of the monomer mixture. The stirring speed was increased to 200 rpm 55 minutes after the start of the monomer mixture addition and to 240 rpm 70 minutes later. After the addition of the monomer mixture was completed, a mixed aqueous solution of 0.0055 parts of ED and 0.0015 parts of FeSO4, 0.03 parts of SFS, 0.3 parts of DSS, and 0.03 parts of t-BHP were added to the reactor in this order. The reaction was then continued for 60 minutes to complete the polymerization, yielding a polymerized latex. The polymerization conversion was 99.9%, and the average particle size was 2000 Å. The resulting polymerized latex was then evaporated to dryness in a drying oven at 50°C for 24 hours, yielding a white powdery (meth)acrylic polymer B.

[0183] (Production Example 3: Production of (meth)acrylic resin C) An 8-liter glass reactor equipped with a paddle stirrer was charged with 105 parts of deionized water, 0.004 parts of sodium hydroxide, and 0.2 parts of DSS. The contents were then stirred at 175 rpm and the reactor was heated to 80°C while being purged with nitrogen. After reaching 80°C, 0.03 parts of NPS and 0.0005 parts of SFS were added. A monomer mixture consisting of 8 parts of BA and 0.04 parts of ALMA was then continuously added to the reactor over 20 minutes to conduct the reaction. The reaction was then continued for 30 minutes to obtain crosslinked (meth)acrylic polymer particles. The polymerization conversion rate was 99.5%, and the average particle diameter was 600 Å. A monomer mixture consisting of 84 parts of MMA, 1 part of n-BMA, 7 parts of PhMI, and 0.02 parts of 2-EHTG was then continuously added to the reactor over 70 minutes to conduct the reaction. Furthermore, 15 minutes after the addition of the monomer mixture, 0.7 parts of DSS were added dropwise and continuously to the reactor in parallel with the addition of the monomer mixture. The stirring speed was increased to 200 rpm 55 minutes after the start of the monomer mixture addition and to 240 rpm 70 minutes later. After the addition of the monomer mixture was completed, a mixed aqueous solution of 0.0055 parts of ED and 0.0015 parts of FeSO4, 0.06 parts of SFS, 0.2 parts of DSS, and 0.06 parts of t-BHP were added to the reactor in this order. The reaction was then continued for 60 minutes to complete the polymerization, yielding a polymerized latex. The polymerization conversion was 99.9%, and the average particle size was 1250 Å. The resulting polymerized latex was then evaporated to dryness in a drying oven at 50°C for 24 hours to yield a white powdery (meth)acrylic polymer C.

[0184] (Production Example 4: Production of (meth)acrylic resin D) (Meth)acrylic resin D is a glutarimide acrylic resin produced using polymethyl methacrylate as the raw resin and monomethylamine as the imidization agent. A tandem-type reactive extruder with two extrusion reactors arranged in series was used for this production. The first and second extruders in the tandem-type reactive extruder were intermeshing co-rotating twin-screw extruders with a diameter of 75 mm and an L / D (ratio of the extruder length L to diameter D) of 74. A constant-weight feeder (manufactured by Kubota Corporation) was used to supply the raw resin to the raw material supply port of the first extruder. The pressure reduction level of each vent in the first and second extruders was set to -0.095 MPa. Furthermore, the first and second extruders were connected by a 38 mm diameter, 2 m long pipe, and a constant-flow pressure valve was used as the internal pressure control mechanism connecting the resin discharge port of the first extruder to the raw material supply port of the second extruder. The resin (strand) discharged from the second extruder was cooled on a cooling conveyor and then cut into pellets using a pelletizer. Here, in order to adjust the pressure inside the part connecting the resin discharge port of the first extruder and the raw material supply port of the second extruder or to determine extrusion fluctuations, resin pressure gauges were installed at the discharge port of the first extruder, the center of the connecting part between the first extruder and the second extruder, and the discharge port of the second extruder.

[0185] In the first extruder, polymethyl methacrylate (weight average molecular weight: 105,000) was used as the raw resin and monomethylamine was used as the imidizing agent to produce imide resin intermediate 1. The temperature of the highest temperature part of the extruder was 280°C, the screw rotation speed was 55 rpm, the raw resin feed rate was 150 kg / hour, and the amount of monomethylamine added was 2.0 parts per 100 parts of raw resin. A constant flow pressure valve was installed immediately before the raw material feed port of the second extruder, and the pressure at the monomethylamine injection section of the first extruder was adjusted to 8 MPa.

[0186] Next, in the second extruder, the remaining imidizing agent and by-products were devolatilized through the rear vent and vacuum vent, and then dimethyl carbonate was added as an esterifying agent to produce imide resin intermediate 2. At this time, the temperature of each barrel of the extruder was 260°C, the screw rotation speed was 55 rpm, and the amount of dimethyl carbonate added was 3.2 parts per 100 parts of the raw material resin. Furthermore, after the esterifying agent was removed through a vent, the mixture was extruded through a strand die, cooled in a water tank, and pelletized in a pelletizer to obtain pellets of (meth)acrylic resin D, which is a glutarimide acrylic resin.

[0187] The imidization rate, glutarimide unit content, acid value, and glass transition temperature of (meth)acrylic resin D were measured according to the above-mentioned methods. The imidization rate was 13%, the glutarimide unit content was 7% by weight, the acid value was 0.4 mmol / g, and the glass transition temperature was 123°C.

[0188] (Production Example 5: Production of polymer particles (I); polymer particles A) An 8-liter glass reactor equipped with a three-way, swept-back blade stirrer was charged with 165 parts of deionized water, 0.5 parts of boric acid, 0.05 parts of sodium carbonate, and 0.003 parts of polyoxyethylene lauryl ether phosphate. The contents were then stirred at 600 rpm and purged with nitrogen while the reactor was heated to 80°C. After reaching 80°C, 0.01 parts of sodium hydroxide and 0.03 parts of KPS were added. A monomer mixture consisting of 25 parts of MMA, 1.5 parts of BA, 0.5 parts of St, 0.15 parts of ALMA, 0.3 parts of n-OM, and 0.1 parts of polyoxyethylene lauryl ether phosphate was then continuously added to the reactor over 80 minutes, and the reaction was continued. The reaction was then continued for 60 minutes, and 0.03 parts of sodium hydroxide and 0.08 parts of KPS were added. Next, a monomer mixture consisting of 40 parts BA, 10 parts St, 0.75 parts ALMA, and 0.2 parts polyoxyethylene lauryl ether phosphate was continuously added to the reactor over 150 minutes. Immediately after the addition of the monomer mixture was completed, 0.02 parts KPS was added and the reaction was continued for 120 minutes. Then, 0.02 parts KPS was added, and a monomer mixture consisting of 18 parts MMA and 5 parts BA was continuously added to the reactor over 60 minutes. The reaction was then continued for 60 minutes, yielding polymer particles (I) with an average particle size of 2400 Å. The polymerization conversion rate was 99.5%. The weight-average molecular weight of the polymer particles (I) was 60,000.

[0189] [Manufacturing transparent resin substrates] (Production Example 1: Production of Transparent Resin Substrate A) A transparent dope solution was prepared by adding (meth)acrylic resin A at a concentration of 8 wt% to a mixed solvent of methylene chloride and ethanol (90 wt%:10 wt%) and stirring and mixing with a magnetic stirrer. The resulting dope solution was left to stand for 24 hours, degassed, and then cast onto a 125 μm-thick PET film (Cosmoshine A4100, manufactured by Toyobo Co., Ltd.) and applied to a uniform film with an applicator. The clearance was adjusted so that the coating film would have a thickness of approximately 60 μm after drying. The coating film, together with the PET film, was dried in a dry atmosphere at 40°C for 1 hour and then peeled off from the PET film. The resulting semi-dried film of (meth)acrylic resin A was fixed to a stainless steel frame and dried in a dry atmosphere at 140°C for 60 minutes to remove residual solvent, yielding a dried film of (meth)acrylic resin A. The dried film of acrylic resin A was then preheated for 5 minutes using a stretching machine equipped with a drying oven at a temperature 10°C higher than the glass transition temperature of acrylic resin A, and then uniaxially stretched 1.5 times at a fixed width at a speed of 100 mm / min to obtain a transparent resin substrate A with a thickness of 40 μm. The weight-average molecular weight of transparent resin substrate A was 1,980,000.

[0190] (Production Example 2: Production of transparent resin substrate B) A transparent resin substrate B having a thickness of 40 μm was obtained in the same manner as in Production Example 1, except that the (meth)acrylic resin used in Production Example 1 was changed from (meth)acrylic resin A to (meth)acrylic resin B. The weight-average molecular weight of the transparent resin substrate B was 460,000.

[0191] (Production Example 3: Production of transparent resin substrate C) A transparent resin substrate C having a thickness of 40 μm was obtained in the same manner as in Production Example 1, except that the (meth)acrylic resin used in Production Example 1 was changed from (meth)acrylic resin A to (meth)acrylic resin C. The weight-average molecular weight of the transparent resin substrate C was 690,000.

[0192] (Production Example 4: Production of Transparent Resin Substrate D) Pellets of (meth)acrylic resin D were melt-extruded using a single-screw extruder equipped with a leaf disc filter with 5 μm openings and a T-die connected to the outlet. The temperature setting in the extruder's temperature control zone was 260°C, the screw rotation speed was 20 rpm, and the pellets were fed at a rate of 10 kg / hour to obtain a film with a thickness of 60 μm. The (meth)acrylic resin D film was then preheated for 5 minutes at a temperature 10°C above the glass transition temperature of the acrylic resin D using a stretching machine equipped with a drying oven, and then uniaxially stretched at a fixed width of 1.5 times at a speed of 100 mm / min to obtain a transparent resin substrate D with a thickness of 40 μm. The weight-average molecular weight of the transparent resin substrate D was 100,000.

[0193] (Production Example 5: Production of Transparent Resin Substrate E) Using a single-screw extruder with a 40 mm diameter full-flight screw, the temperature setting in the extruder's temperature control zone was set to 255°C, the screw rotation speed was set to 52 rpm, and a mixture consisting of 90 wt% pellets of (meth)acrylic resin D and 10 wt% crosslinked (meth)acrylic microparticles was fed into the extruder at a rate of 10 kg / hour. The resin emerging as strands from the die at the extruder outlet was cooled in a water bath and pelletized using a pelletizer. The resulting pellets were melt-extruded into a 60 μm thick film using a single-screw extruder equipped with a leaf disc filter with a 5 μm opening and a T-die connected to the outlet. The temperature setting in the extruder's temperature control zone was set to 260°C, the screw rotation speed was set to 20 rpm, and the pellets were fed at a rate of 10 kg / hour. The glass transition temperature of the film was 122°C. Thereafter, the film was preheated for 5 minutes at a temperature condition of +10°C above the glass transition temperature using a stretching machine equipped with a drying oven, and then uniaxially stretched at a width fixed by 1.5 times at a speed of 100 mm / min to obtain a 40 μm-thick transparent resin substrate E. The weight-average molecular weight of the transparent resin substrate E was 100,000.

[0194] (Production Example 6: Production of Transparent Resin Substrate F) Using a single-screw extruder with a 40 mm diameter full-flight screw, the temperature setting in the extruder's temperature control zone was set to 255°C, the screw rotation speed was set to 52 rpm, and a mixture consisting of 80 wt% pellets of (meth)acrylic resin D and 20 wt% crosslinked (meth)acrylic microparticles was fed into the extruder at a rate of 10 kg / hour. The resin emerging as strands from the die at the extruder outlet was cooled in a water bath and pelletized using a pelletizer. The resulting pellets were melt-extruded into a 60 μm thick film using a single-screw extruder equipped with a leaf disc filter with a 5 μm opening and a T-die connected to the outlet. The temperature setting in the extruder's temperature control zone was set to 260°C, the screw rotation speed was set to 20 rpm, and the pellets were fed at a rate of 10 kg / hour. The glass transition temperature of the film was 121°C. Thereafter, the film was used in a stretching machine equipped with a drying oven, preheated at a temperature condition of +10°C above the glass transition temperature for 5 minutes, and then uniaxially stretched at a width fixed by 1.5 times at a speed of 100 mm / min to obtain a 40 μm-thick transparent resin substrate F. The weight-average molecular weight of the transparent resin substrate F was 95,000.

[0195] [Synthesis of polyorganosiloxane compounds] 8-Glycidyloxyoctyltrimethoxysilane (KBM-4803, manufactured by Shin-Etsu Chemical Co., Ltd.) (67.4 g; 220 mmol) and methanol (11.6 g) were charged into a 200 mL flask reaction vessel equipped with a thermometer, a stirrer, and a reflux condenser, and stirred until homogeneous. A solution of magnesium chloride (0.010 g; 0.11 mmol) dissolved in a mixture of water (11.9 g; 660 mmol) and methanol (4.7 g) was added dropwise to this mixture over 5 minutes, and the mixture was stirred until homogeneous. The temperature was then raised to 70°C, and the polycondensation reaction was carried out for 6 hours with stirring. After completion of the reaction, the mixture was subjected to devolatilization and concentration under reduced pressure using a rotary evaporator, and the methanol and water in the condensate were removed. Analysis of the resulting condensate revealed that the weight-average molecular weight Mn was 4,500, and the condensate had a molecular weight of 1,000. 29 SiO calculated by Si-NMR measurement 3 / 2 Body and SiO 2 / 2 Body and ratio [SiO 3 / 2body] / [SiO 2 / 2 body] is 2.1, 1 The residual rate of epoxy groups calculated by H-NMR measurement was 95% or more. The content of magnesium chloride (neutral salt catalyst) calculated based on the above-mentioned charged weight was 191 ppm.

[0196] [Preparation of Hard Coat Composition] For 100 parts of the polyorganosiloxane compound synthesized above, triarylsulfonium P(R f ) n F 6-n A hard coat composition was obtained by blending 0.5 parts by solid content of a 50% propylene carbonate solution of silane (manufactured by San-Apro Co., Ltd.; CPI-200K) and 0.5 parts by solid content of a 52% xylene / isobutanol solution of polyether-modified polydimethylsiloxane (manufactured by BYK Co., Ltd.; BYK-300) as a leveling agent.

[0197] [Preparation of Easy-Adhesive Composition] To 100 parts of an aqueous polyurethane having a carboxyl group (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., trade name: Superflex 210, solid content: 35% by weight), 2.02 parts of a tetrafunctional epoxy crosslinking agent (manufactured by Nagase ChemteX Corporation, trade name: Denacol EX-512, solid content: 100% by weight, epoxy equivalent: 168 g / eq) and 250 parts of pure water were added, and the mixture was mixed with a magnetic stirrer to obtain an easy-adhesive composition with a solid content concentration of 10.5% by weight.

[0198] [Hard coat film manufacturing] (Example 1: Production of hard coat film 1) The hard coat composition was applied to the main surface 1 of a 40 μm-thick transparent resin substrate A using a bar coater so that the dry film thickness was 40 μm, and the coating was heated at 120° C. for 10 minutes. Thereafter, a high-pressure mercury lamp was used to apply UVA (wavelength range: 320 to 400 nm) with an integrated light intensity of 880 mJ / cm 2 . 2 , the irradiation intensity is 220mW / cm 2The hard coat composition on main surface 1 was cured by irradiating it with ultraviolet light so that the hard coat composition became 40 μm thick on main surface 2 of transparent resin substrate A. After 24 hours, the hard coat composition was applied to main surface 2 of transparent resin substrate A using a bar coater in the same manner as for main surface 1, so that the dry film thickness was 40 μm. The hard coat composition was heated under the same conditions as for main surface 1, and then irradiated with ultraviolet light to cure the hard coat composition on main surface 2. After 24 hours, the obtained film was heated at 60°C for 24 hours, to obtain hard coat film 1 having hard coat layers on both main surfaces 1 and 2. The surface hardness of hard coat film 1 was measured and found to be 2H.

[0199] (Example 2: Production of hard coat film 2) An easy-adhesive composition was applied to the main surface 1 of a 40 μm-thick transparent resin substrate B using a bar coater so that the dry film thickness was 1 μm, and the coating was heated at 100° C. for 10 minutes. Thereafter, a hard coat composition was applied to the surface to which the easy-adhesive composition had been applied, and cured in the same manner as in Example 1. After 24 hours, the easy-adhesive composition and the hard coat composition were applied in this order to the main surface 2 of the transparent resin substrate B, and cured in the same manner as for the main surface 1. After 24 hours, the obtained film was heated at 60° C. for 24 hours, and a hard coat film 2 having hard coat layers on both the main surface 1 and the main surface 2 was obtained.

[0200] (Example 3: Production of hard coat film 3) A hard coat film 3 having hard coat layers on both the principal surface 1 and the principal surface 2 was obtained in the same manner as in Example 1, except that a transparent resin substrate C having a thickness of 40 μm was used.

[0201] (Comparative Example 1: Production of Hard Coat Film 4) The adhesive composition was applied to the main surface 1 of a 40 μm-thick transparent resin substrate D using a bar coater so that the dry film thickness was 1 μm, and the applied film was heated at 100° C. for 10 minutes. Thereafter, the surface to which the adhesive composition was applied was irradiated with discharge electrons at a dose of 80 W / m 2A corona discharge treatment was performed at an irradiation intensity of 1 / min. Thereafter, a hard coat composition was applied to the surface coated with the easy-adhesive composition in the same manner as in Example 1, and cured. 24 hours later, a corona discharge treatment was performed on main surface 2 of transparent resin substrate D at the same irradiation intensity as main surface 1. Thereafter, a hard coat composition was applied to the main surface 2 of transparent resin substrate D in the same manner as main surface 1, and cured. After 24 hours, the obtained film was heated at 60°C for 24 hours, and a hard coat film 4 having hard coat layers on both main surfaces 1 and 2 was obtained.

[0202] Comparative Example 2: Production of hard-coated film 5 A hard-coated film 5 having hard-coating layers on both main surfaces 1 and 2 was obtained in the same manner as in Comparative Example 1, except that a transparent resin substrate E having a thickness of 40 μm was used.

[0203] (Comparative Example 3: Production of Hard Coat Film 6) The discharge electron irradiation dose was 80 W / m for the main surface 1 of the transparent resin substrate F with a thickness of 40 μm. 2 A corona discharge treatment was performed at an irradiation intensity of 1 / min. Thereafter, a hard coat composition was applied to main surface 1 in the same manner as in Example 1 and cured. 24 hours later, a corona discharge treatment was performed on main surface 2 of transparent resin substrate F at the same irradiation intensity as main surface 1. Thereafter, a hard coat composition was applied to main surface 2 in the same manner as main surface 1 and cured. After 24 hours, the obtained film was heated at 60°C for 24 hours to obtain hard coat film 4 having hard coat layers on both main surfaces 1 and 2.

[0204] [Table 1]

[0205] [Table 2]

[0206] Tables 1 and 2 reveal the following: The transparent resin substrates of Examples 1 to 3 have low haze (internal haze), orientation birefringence, photoelastic constant, in-plane retardation Re, and thickness direction retardation Rth, and are therefore transparent resin substrates with excellent optical properties. Furthermore, hard coat films 1 to 3, which are formed by providing a hard coat layer on the transparent resin substrates of Examples 1 to 3, exhibit excellent flexing times. Furthermore, hard coat film 1 is found to have an excellent balance between flexing times and surface hardness.

[0207] On the other hand, although the transparent resin substrates of Comparative Examples 1 to 3 exhibited optical properties comparable to those of the transparent resin substrates of Examples 1 to 3, hard coat films 4 to 6, which had a hard coat layer on the transparent resin substrates of Comparative Examples 1 to 3, had a low number of flexions.

[0208] [Table 3]

[0209] The following can be seen from Table 3. The transparent resin substrates of Examples 1 to 3 were all low in orientation birefringence, photoelastic constant, in-plane retardation Re, and thickness direction retardation Rth, and the Δ phase difference in the two-dimensional birefringence evaluation was also very small. Furthermore, the retardation images obtained by retardation imaging in the two-dimensional birefringence evaluation showed continuous high and low phase differences. That is, with transparent resin substrates having excellent optical properties such as those of Examples 1 to 3, the retardation (optical distortion) generated by deformation of the substrate is small and the change is continuous, so it is presumed that even when external forces such as bending or winding are applied in a flexible display or the like, there will be very little change in image quality (image quality).

[0210] On the other hand, the transparent PET film of Comparative Example 4 had very large orientation birefringence, photoelastic constant, in-plane retardation Re, and thickness direction retardation Rth, and also had a very large Δ phase difference in the two-dimensional birefringence evaluation. Furthermore, in the retardation imaging image in the two-dimensional birefringence evaluation, high and low phase differences were observed in a repeated striped pattern or a spotted pattern. When such a substrate is used, when an external force such as bending or winding is applied in a flexible display, the change in phase difference is very large around the stressed area, which is presumably resulting in significant light leakage and changes in image quality.

Claims

1. A transparent resin substrate for a flexible display, Contains a (meth)acrylic resin having a weight average molecular weight of 200,000 or more, the (meth)acrylic resin is a graft copolymer comprising crosslinked (meth)acrylic polymer particles (a) having an average particle size of 150 nm or less and a glass transition temperature of −10° C. or less, and a non-crosslinked methacrylic polymer component (b) having a weight-average molecular weight of 200,000 or more, in which at least a portion of the non-crosslinked methacrylic polymer component (b) is graft-bonded to the crosslinked (meth)acrylic polymer particles (a), and the proportion of the crosslinked (meth)acrylic polymer particles (a) in the total of the crosslinked (meth)acrylic polymer particles (a) and the non-crosslinked methacrylic polymer component (b) is 1% by weight or more and less than 50% by weight, The glass transition temperature is 110°C or higher, and the photoelastic constant is -5.0 x 10 －１２ ~5.0 x 10 －１２ Pa －１ A transparent resin substrate.

2. Orientation birefringence is −2.0×10 －４ ~2.0 x 10 －４ The transparent resin substrate according to claim 1 ,

3. 2. The transparent resin substrate according to claim 1, wherein the absolute value of the in-plane retardation Re is 10.0 nm or less, and the absolute value of the thickness direction retardation Rth is 20.0 nm or less.

4. The transparent resin substrate according to claim 1 , which is produced by a solution casting method.

5. The transparent resin substrate according to claim 1 , which has a haze of less than 1.5%.

6. The transparent resin substrate according to claim 1 , which has a hard coat layer laminated on at least one of its main surfaces.

7. A hard coat film comprising the transparent resin substrate according to any one of claims 1 to 6 and a hard coat layer on at least one main surface thereof.

8. 8. The hard coat film according to claim 7, further comprising an easy-adhesion layer between the transparent resin substrate and the hard coat layer, the easy-adhesion layer being made of an easy-adhesion composition containing a polyurethane resin having a carboxyl group and a tri- or higher functional polyfunctional epoxy-based crosslinking agent.

9. 8. The hard coat film according to claim 7, wherein the hard coat layer is made of a cured product of a hard coat composition containing a polyorganosiloxane compound.

10. The polyorganosiloxane compound is a condensate of a silane compound represented by the following formula (1), and the weight average molecular weight of the condensate is 500 to 20,000:

10. The hard coat film according to claim 9, wherein the molar ratio of the structural unit represented by the following formula (3) to the structural unit represented by the following formula (4) contained in the condensate ([structural unit represented by formula (3)] / [structural unit represented by formula (4)]) is less than 5: 【Chemistry 1】 (In formula (1), R １ represents an alkylene group having 2 to 16 carbon atoms, and R ２ represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R ３ represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 25 carbon atoms, or an aralkyl group having 7 to 12 carbon atoms, x represents 2 or 3, and Y represents a glycidyloxy group represented by the following formula (2-1) or an alicyclic epoxy group represented by the following formula (2-2). 【Chemistry 2】 (In formulas (2-1) and (2-2), * represents R １ indicates the bonding position with 【Transformation 3】 (In formula (3), R １ and Y have the same meaning as in formula (1). 【Chemistry 4】 (In formula (4), R １ and Y are the same as those in formula (1). Z represents a hydrogen atom, an alkoxy group having an alkyl portion of 1 to 10 carbon atoms, an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 25 carbon atoms, or an aralkyl group having 7 to 12 carbon atoms.

11. 8. The hard coat film according to claim 7, which has a total thickness of 40 to 500 μm and a total light transmittance of 80% or more.

12. 8. The hard coat film according to claim 7, wherein the hard coat layer has a thickness of 10 to 100 μm.

13. A flexible display comprising the transparent resin substrate according to any one of claims 1 to 6.

14. A hard coat film comprising a transparent resin substrate for a flexible display and a hard coat layer provided on at least one main surface of the transparent resin substrate, the transparent resin substrate contains a (meth)acrylic resin having a glass transition temperature of 110° C. or higher, a photoelastic constant of −5.0×10 −12 to 5.0×10 −12 Pa −1 , and a weight-average molecular weight of 200,000 or higher; the (meth)acrylic resin is a (meth)acrylic resin whose constituent units are 30 to 100% by weight of methyl methacrylate units and 0 to 70% by weight of other monomer units copolymerizable with the methyl methacrylate units, the other monomer unit is at least one selected from the group consisting of an N-substituted maleimide-based monomer unit, a methacrylic acid ester unit in which the ester moiety is a primary or secondary hydrocarbon group or an aromatic hydrocarbon group having 2 to 20 carbon atoms, a methacrylic acid ester unit in which the ester moiety is a saturated hydrocarbon group having 7 to 16 carbon atoms and having a condensed ring structure, a methacrylic acid ester unit in which the ester moiety is a linear or branched group containing an ether bond, and a styrene-based monomer unit; the hard coat layer is made of a cured product of a hard coat composition containing a polyorganosiloxane compound, The polyorganosiloxane compound is a condensate of a silane compound represented by the following formula (1), and the weight average molecular weight of the condensate is 500 to 20,000: The hard coat film has a molar ratio of the structural unit represented by the following formula (3) to the structural unit represented by the following formula (4) contained in the condensate ([structural unit represented by formula (3)] / [structural unit represented by formula (4)]) of less than 5: 【Transformation 5】 (In formula (1), R 1 represents an alkylene group having 8 to 12 carbon atoms, R 2 represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, R 3 represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 25 carbon atoms, or an aralkyl group having 7 to 12 carbon atoms, x represents 2 or 3, and Y represents a glycidyloxy group represented by the following formula (2-1) or an alicyclic epoxy group represented by the following formula (2-2). 【Transformation 6】 (In formulas (2-1) and (2-2), * indicates the bonding position with R 1 .) 【Transformation 7】 (In formula (3), R 1 and Y have the same meanings as in formula (1).) 【Transformation 8】 (In formula (4), R 1 and Y are defined as in formula (1). Z represents a hydrogen atom, an alkoxy group having an alkyl portion having 1 to 10 carbon atoms, an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 25 carbon atoms, or an aralkyl group having 7 to 12 carbon atoms.)

15. A hard coat film according to claim 14, having a total thickness of 40 to 500 μm and a total light transmittance of 80% or more.

16. The hard coat film according to claim 14, wherein the thickness of the hard coat layer is 10 to 100 μm.

Images