Foldable display and portable terminal device

Abstract

To provide a foldable display that is suitable for mass production and does not cause any disturbance in an image displayed at a folded portion after being repeatedly folded, and a portable terminal device equipped with such a foldable display.SOLUTION: A foldable display has a hard coat film arranged on at least a part of a surface, where in the hard coat film, a polyester film with an intrinsic viscosity of 0.65 to 1.0 dl / g is used as a base film, and the base film has a polyimide resin-based hardened layer with a thickness of 0.5 to 3.0 μm and a hard coat layer in this order at least on the surface side of the foldable display.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a foldable display and a portable terminal device, which are related to a foldable display and a portable terminal device with a film surface of high hardness, in which even when repeatedly folded, the image is less likely to be disturbed due to the deformation of the film located on the surface.

Background Art

[0002] The thin film of portable terminal devices has been made lighter, and portable terminal devices represented by smartphones have been widely popularized. While various functions are required for portable terminal devices, convenience is also sought. Therefore, popular portable terminal devices can be operated with one hand for simple operations, and furthermore, since it is assumed that they can be stored in clothes pockets etc., it is necessary to have a small screen size of about 6 inches.

[0003] On the other hand, tablet terminals with a screen size of 7 inches to 10 inches are assumed to be used not only for video content and music but also for business applications, drawing applications, reading, etc., and have high functionality. However, they cannot be operated with one hand, have poor portability, and have problems with convenience.

[0004] To achieve these, a method of making it compact by connecting multiple displays has been proposed, but since the bezel part remains, the video becomes interrupted, and the reduction in visibility becomes a problem and it has not been popularized.

[0005] Therefore, in recent years, portable terminals incorporating flexible displays and foldable displays have been proposed. With this method, it is possible to carry a portable terminal device equipped with a large-screen display conveniently without the image being interrupted.

[0006] Here, for displays and mobile terminal devices that do not have a conventional folding structure, the surface of the display could be protected with a non-flexible material such as glass. However, in a foldable display, when making a single-sided display through the folding part, it is necessary to use a hard coat film or the like that is flexible and can protect the surface. However, in a foldable display, since the portion corresponding to a certain folding part is repeatedly bent, the film at that portion is deformed over time, causing problems such as distorting the image displayed on the display.

[0007] Also, a method of making the thickness of the folded part and the non-folded part different has been proposed. However, although the flexural resistance is improved in the thin part of the film thickness, there is a problem that the pencil hardness decreases (see Patent Document 1).

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0009] The present invention aims to solve the problems of the conventional displays as described above, and provides a foldable display with excellent mass productivity, no possibility of disturbing the image displayed at the folding part after repeated folding, and high hardness, and a mobile terminal device equipped with such a foldable display.

Means for Solving the Problems

[0010] That is, the present invention has the following configuration. 1. A foldable display having a hard coat film disposed on at least a part of the surface, wherein the hard coat film uses a polyester film having an intrinsic viscosity of 0.65 to 1.0 dl / g as a base film, and on at least the surface side of the foldable display of the base film, there are successively provided a cured layer of a polyimide resin having a thickness of 0.5 to 3.0 μm and a hard coat layer. 2. The foldable display according to the first aspect, wherein the thickness of the polyester film as the base film is 10 to 75 μm. 3. The foldable display according to the first or second aspect, wherein the thickness of the hard coat layer is 1 to 40 μm. 4. The foldable display according to any one of the first to third aspects, wherein a single continuous hard coat film is disposed through the folding portion of the foldable display. 5. The foldable display according to any one of the first to fourth aspects, wherein the polyester film is a biaxially stretched polyethylene terephthalate film. 6. The pencil hardness of the hard coat layer measured at a load of 750 g in accordance with JIS K5600-5-4:1999 is 2H or more. The foldable display according to any one of the first to fifth aspects. 7. The foldable display according to any one of the first to sixth aspects, wherein the bending radius when folded is 5 mm or less. 8. A portable terminal device having the foldable display according to any one of the first to seventh aspects.

Advantages of the Invention

[0011] The foldable display of the present invention, while maintaining mass productivity, does not cause deformation after repeated folding of the hard coat film located on the surface, and does not cause image distortion at the folding portion of the high-hardness display. A portable terminal device equipped with the foldable display as described above provides beautiful images, is highly resistant to scratches due to its high hardness, is rich in functionality, and is excellent in convenience such as portability.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Mode for Carrying Out the Invention

[0013] (Display) The display referred to in the present invention generally refers to a display device. As types of displays, there are LCD, organic EL display, inorganic EL display, LED, FED, etc. Among them, an LCD, organic EL, or inorganic EL having a foldable structure is preferable. In particular, organic EL and inorganic EL that can reduce the layer structure are particularly preferable, and organic EL with a wide color gamut is even more preferable.

[0014] (Foldable Display) The foldable display preferably has a structure in which a single continuous display is folded in half or more than three folds when carried, thereby reducing the size by half or further reducing it, and improving portability. At the same time, it is preferably thin and lightweight. Therefore, the bending radius of the foldable display is preferably 5 mm or less, and more preferably 3 mm or less. If the bending radius is 5 mm or less, it is possible to reduce the thickness in the folded state. Although it can be said that the smaller the bending radius, the better, it may be 0.1 mm or more, or 0.5 mm or more. Even if it is 1 mm or more, the practicality is sufficiently good compared to a conventional display without a folding structure. The bending radius when folded is measured at the location of reference numeral 11 in the schematic diagram of FIG. 1, and means the radius inside the folded portion when folded.

[0015] (Organic EL) A general configuration of an organic EL display includes an organic EL layer composed of an electrode / electron transport layer / light emitting layer / hole transport layer / transparent electrode, a retardation plate for improving image quality, and a polarizing plate.

[0016] (Portable terminal device having a touch panel) When an organic EL display is used, for example, in a portable terminal device having a touch panel, the touch panel module is disposed on the upper portion of the organic EL display or between the organic EL layer and the retardation plate. At this time, when an impact is applied from above, there is a risk that the circuits of the organic EL and the touch panel may be disconnected, so it is preferable that a film for protecting the surface is provided. It is preferable that at least a part of the surface of the foldable display is provided with a hard coat film as a film for protecting the surface, and it is preferable that this mainly includes the surface of the image display portion of the foldable display. The hard coat layer is preferably located on the outer surface side of the display.

[0017] Note that the image display portion of the foldable display may be located inside or outside when folded. In other words, the hard coat film, which is a film for protecting the surface of the foldable display of the present invention, may be located on the inner surface or the outer surface of the foldable display when folded.

[0018] In the present invention, the hard coat film disposed on at least a part of the surface of the foldable display preferably has a cured layer of a polyimide-based resin and a hard coat layer laminated in this order on at least one side of the base film.

[0019] As the base film constituting the hard coat film, any film having high light transmittance and low haze, such as a polyimide film, a polyester film, a polycarbonate film, an acrylic film, a triacetyl cellulose film, and a cycloolefin polymer film, can be used. Among them, a polyimide film and a polyester film having high impact resistance and sufficient pencil hardness are preferable, and a polyester film that can be manufactured at low cost is particularly preferable.

[0020] Figure 2 shows a schematic cross-sectional view of one embodiment of the hard coat film in the present invention. The hard coat film preferably has a cured layer (reference numeral 22) of polyimide resin and a hard coat layer (reference numeral 23) laminated in this order on a polyester film (reference numeral 21) as a base film. The hard coat film is located on the surface of the foldable display, and the hard coat layer is preferably arranged to be located on the outer surface of the foldable display. Although not shown, it can be said that the surface of the hard coat layer (reference numeral 23) usually coincides with the surface of the foldable display.

[0021] In the present invention, the polyester film, which is the base film of the hard coat film, may be a single-layer film composed of one or more polyester resins, or when two or more types of polyesters are used, it may be a multilayer structure film or a super-multilayer laminated film with a repeating structure.

[0022] Examples of the polyester resin include polyester films made of polyethylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate, or copolymers mainly composed of the constituent components of these resins. Among them, a biaxially stretched polyethylene terephthalate film is particularly preferred in terms of mechanical properties, heat resistance, transparency, price, etc.

[0023] When using a polyester copolymer for the base film, examples of the dicarboxylic acid component of the polyester include aliphatic dicarboxylic acids such as adipic acid and sebacic acid; aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, and 2,6-naphthalenedicarboxylic acid; and polyfunctional carboxylic acids such as trimellitic acid and pyromellitic acid. Examples of the glycol component include fatty acid glycols such as ethylene glycol, diethylene glycol, 1,4-butanediol, propylene glycol, and neopentyl glycol; aromatic glycols such as p-xylene glycol; alicyclic glycols such as 1,4-cyclohexanedimethanol; and polyethylene glycol with an average molecular weight of 150 to 20,000. The mass ratio of the copolymer components of the preferred copolymer is less than 20% by mass. When it is less than 20% by mass, it is preferable because the film strength, transparency, and heat resistance are maintained.

[0024] In the production of the polyester film, the intrinsic viscosity of at least one type of resin pellet is preferably in the range of 0.65 to 1.0 dl / g. When the intrinsic viscosity is 0.65 dl / g or more, it is preferable because deformation is less likely to occur after repeatedly folding the obtained film, and there is no risk of deteriorating the image quality. On the other hand, when the intrinsic viscosity is 1.00 dl / g or less, it is preferable because the increase in the filtration pressure of the molten fluid does not become too large, and it is easy to stably operate the film production.

[0025] Regardless of whether the film is a single-layer structure or a laminated structure, the intrinsic viscosity of the film is preferably 0.65 dl / g or more. More preferably, it is 0.68 dl / g or more. If it is 0.65 dl / g or more, the effect of sufficient flex resistance can be obtained. On the other hand, a film with an intrinsic viscosity of 1.00 dl / g or less can be preferably produced with good operability.

[0026] The thickness of the polyester film is preferably 10 to 75 μm, more preferably 25 to 75 μm. When the thickness is 10 μm or more, the effect of improving the pencil hardness is easily obtained, which is preferable. On the other hand, when the thickness is 75 μm or less, it is advantageous for weight reduction, and it is also preferable because it is excellent in flexibility, processability, handling properties, etc.

[0027] The surface of the polyester film in the present invention may be smooth or may have irregularities. However, since it is used for the surface cover of a display, a decrease in optical properties due to irregularities is not preferable. The haze is preferably 3% or less, more preferably 2% or less, and most preferably 1% or less. If the haze is 3% or less, the visibility of the image can be improved. The lower limit of the haze is preferably as small as possible, but it may be 0.1% or more, or 0.3% or more.

[0028] For the purpose of reducing the haze as described above, the irregularities on the film surface are preferably not too large. However, from the viewpoint of handling properties, in order to give a certain degree of slipperiness, as a method of forming irregularities, a filler can be blended in the surface polyester resin layer, or a coating layer containing a filler can be formed by coating during film formation.

[0029] As a method of blending particles into the polyester film, a known method can be adopted. For example, it can be added at any stage of manufacturing polyester, but preferably at the esterification stage, or at the stage after the transesterification reaction and before the start of the polycondensation reaction, as a slurry dispersed in ethylene glycol or the like, and the polycondensation reaction may be advanced. Also, it can be carried out by a method of blending a slurry of particles dispersed in ethylene glycol or water and a polyester raw material using a kneading extruder with a vent, or a method of blending dried particles and a polyester raw material using a kneading extruder.

[0030] Among these, a method is preferred in which, after uniformly dispersing aggregated inorganic particles in a monomer liquid that is part of the polyester raw material and then filtering it, the filtered product is added to the remaining portion of the polyester raw material before, during, or after the esterification reaction. According to this method, since the monomer liquid has a low viscosity, uniform dispersion of the particles and highly accurate filtration of the slurry can be easily performed. Also, when adding to the remaining portion of the raw material, the dispersibility of the particles is good and new aggregates are less likely to form. From such a viewpoint, it is particularly preferable to add to the remaining portion of the raw material at a low temperature state before the esterification reaction.

[0031] Further, after obtaining a polyester containing particles in advance, the number of protrusions on the film surface can be further reduced by a method such as kneading and extruding the pellets containing the particles and the pellets not containing the particles (masterbatch method).

[0032] Also, the polyester film may contain various additives within a range where light transmittance is satisfactory. Examples of the additives include antistatic agents, UV absorbers, and stabilizers.

[0033] The total light transmittance of the polyester film is preferably 85% or more, more preferably 87% or more. If the transmittance is 85% or more, sufficient visibility can be ensured. Although it can be said that the higher the total light transmittance of the polyester film, the better, it may be 99% or less, or 97% or less.

[0034] On the surface of the polyester film of the present invention, a treatment can be performed to improve the adhesion to a resin such as a cured layer of a polyimide-based resin.

[0035] Examples of the method by surface treatment include roughening treatment such as sandblasting treatment and solvent treatment, and oxidation treatment such as corona discharge treatment, electron beam irradiation treatment, plasma treatment, ozone-ultraviolet irradiation treatment, flame treatment, chromic acid treatment, and hot air treatment, and they can be used without particular limitation.

[0036] Although not shown in Fig. 2, it is also preferable that an easy - adhesion layer is laminated on the polyester film. The adhesion can also be improved by an adhesion - improving layer such as an easy - adhesion layer. As the easy - adhesion layer, acrylic resin, polyester resin, polyurethane resin, polyether resin, etc. can be used without particular limitation, and it can be formed by a general coating method, preferably by a so - called in - line coat formulation.

[0037] The above - mentioned polyester film can be manufactured, for example, through a polymerization step of homogeneously dispersing inorganic particles in a monomer solution that is part of the polyester raw material, filtering it, then adding it to the remaining part of the polyester raw material to carry out the polymerization of the polyester, and a film - forming step of melt - extruding the polyester in a sheet form through a filter, cooling this, and then stretching it to form a base film.

[0038] Next, regarding the manufacturing method of the polyester film, an example using polyethylene terephthalate (hereinafter sometimes referred to as PET) pellets as the raw material of the base film will be described in detail, but it is not limited to these. Also, the number of layers such as single - layer configuration and multi - layer configuration is not limited.

[0039] After mixing and drying PET pellets at a predetermined ratio, they are supplied to a known extrusion machine for melt lamination, extruded in a sheet form from a slit - shaped die, and cooled and solidified on a casting roll to form an unstretched film. In the case of a single - layer, one extrusion machine is sufficient, but when manufacturing a multi - layer film, two or more extrusion machines, a manifold or a merging block with two or more layers (for example, a merging block having a square merging part) are used to laminate a plurality of film layers constituting each outermost layer, extrude two or more sheets from the die, and cool them with a casting roll to form an unstretched film.

[0040] In this case, during melt extrusion, it is preferable to perform high-precision filtration at an arbitrary location where the molten resin is maintained at about 280°C in order to remove foreign matter contained in the resin. The filter medium used for the high-precision filtration of the molten resin is not particularly limited, but a filter medium made of a sintered stainless steel body is preferable because it has excellent performance in removing aggregates mainly composed of Si, Ti, Sb, Ge, Cu and high-melting-point organic substances.

[0041] Furthermore, the filtration particle size of the filter medium (initial filtration efficiency 95%) is preferably 20 μm or less, particularly preferably 15 μm or less. When the filtration particle size of the filter medium (initial filtration efficiency 95%) exceeds 20 μm, foreign matter with a size of 20 μm or more cannot be sufficiently removed. Although the productivity may decrease when performing high-precision filtration of the molten resin using a filter medium with a filtration particle size of 20 μm or less (initial filtration efficiency 95%), it is preferable for obtaining a film with fewer protrusions caused by coarse particles.

[0042] Specifically, for example, after sufficiently vacuum-drying PET pellets, they are supplied to an extruder, melt-extruded into a sheet shape at about 280°C, and cooled and solidified to form an unstretched PET sheet. The obtained unstretched sheet is stretched 2.5 to 5.0 times in the longitudinal direction with a roll heated to 80 to 120°C to obtain a uniaxially oriented PET film. Furthermore, the end of the film is gripped with clips and guided into a hot air zone heated to 80 to 180°C. After drying, it is stretched 2.5 to 5.0 times in the width direction. Subsequently, it is guided into a heat treatment zone at 160 to 240°C and heat-treated for 1 to 60 seconds to complete the crystal orientation. During this heat treatment process, if necessary, a relaxation treatment of 1 to 12% may be performed in the width direction or the longitudinal direction.

[0043] (Cured layer of polyimide-based resin) The polyester film that is positioned on the surface of the foldable display to protect the display preferably has a cured layer of a polyimide-based resin between the polyester film / hard coat layers. The polyimide-based resin preferably includes a polyimide resin or a polyamide-imide resin and a resin having reactive functional groups. Having reactive functional groups is preferable because it forms a crosslinked structure, improves the elastic modulus of the coating film, and has the effect of improving the pencil hardness.

[0044] The polyimide resin is also available as a solution. Examples include "Polyamic Acid Type Polyimide Resin-HCI Series" manufactured by Hitachi Chemical Co., Ltd. and "Neoprim (registered trademark)" manufactured by Mitsubishi Gas Chemical Co., Ltd. Examples of the polyamide-imide resin solution include "Bylomax (registered trademark)" manufactured by Toyobo Co., Ltd. and "Polyamide-imide Resin-HPC Series" manufactured by Hitachi Chemical Co., Ltd.

[0045] (Crosslinking agent) It is also preferable to use a crosslinking agent in combination to cure the polyimide-based resin. As the crosslinking agent, an isocyanate-based crosslinking agent, an epoxy-based crosslinking agent, a chelate-based crosslinking agent, an aziridine-based crosslinking agent, an oxazoline-based crosslinking agent, etc. can be used without particular limitation.

[0046] (Additive) In addition to additives such as an adhesion improving material for improving the adhesion to the hard coat layer and an ultraviolet absorber for improving the light resistance, a filler etc. can also be added.

[0047] (Film thickness) The film thickness of the cured layer of the polyimide-based resin is preferably 0.5 to 3 μm. If the thickness is 0.5 μm or more, the effect of improving the pencil hardness becomes remarkable, which is preferable. Also, if the thickness is 3 μm or less, the effect of improving the pencil hardness is remarkable without reducing the flex resistance, which is preferable.

[0048] (Coating method) As a method for applying the cured layer of the polyimide-based resin, a Mayer bar, gravure coating, die coater, knife coater, etc. can be used without particular limitation, and can be appropriately selected according to the viscosity and film thickness.

[0049] (Curing conditions) As a method for curing the polyamideimide layer, an energy ray such as ultraviolet ray or electron beam, or a curing method by heat can be used, and it can be used in a method compatible with the crosslinking agent. In the case of curing by heat, 150 °C or lower is preferable, and 130 °C or lower is particularly preferable.

[0050] (Hard coat layer) The polyester film that is located on the surface of the foldable display to protect the display preferably has a hard coat layer on its surface. As the resin for forming the hard coat layer, (meth)acrylate-based, siloxane-based, inorganic hybrid-based, urethane (meth)acrylate-based, polyester (meth)acrylate-based, epoxy-based, etc. can be used without particular limitation. Also, two or more kinds of materials can be mixed and used, and particles such as inorganic fillers and organic fillers can be added.

[0051] (Film thickness) The film thickness of the hard coat layer is preferably 1 to 40 μm. When the thickness is 1 μm or more, it is preferable to obtain good pencil hardness. Also, when the thickness is 40 μm or less, curl due to the curing shrinkage of the hard coat can be suppressed, and the handleability of the film can be improved.

[0052] (Coating method) As a method for applying the hard coat layer, a Mayer bar, gravure coating, die coater, knife coater, etc. can be used without particular limitation, and can be appropriately selected according to the viscosity and film thickness.

[0053] (Curing conditions) As a method for curing the hard coat layer, an energy ray such as ultraviolet ray or electron beam, or a curing method by heat can be used, but ultraviolet ray, electron beam, etc. are preferable in order to reduce damage to the film.

[0054] (Pencil hardness) As the pencil hardness of the hard coat layer of the hard coat film, 2H or more is preferable, and 3H or more is more preferable. If the pencil hardness is 2H or more, it will not be easily scratched and will not reduce visibility. Generally, the higher the pencil hardness of the hard coat layer, the better, but it may be 10H or less, 8H or less, or 6H or less, and it can be used without practical problems.

[0055] (Type of hard coat layer) The hard coat layer in the present invention may have other functions added thereto as long as it can be used for the purpose of protecting the display by increasing the pencil hardness of the surface as described above. For example, a hard coat layer added with functions such as an antiglare layer, an antiglare antireflection layer, an antireflection layer, a low reflection layer, and an antistatic layer having a certain pencil hardness as described above is also preferably applied in the present invention.

[0056] As the haze of the hard coat film in the present invention, 3% or less is preferable, 2% or less is more preferable, and 1% or less is most preferable, similar to the polyester film. If the haze is 3% or less, the visibility of the image can be improved. The lower limit of the haze is preferably as small as possible, but it may be 0.1% or more or 0.3% or more.

[0057] As the total light transmittance of the hard coat film in the present invention, 85% or more is preferable, and 87% or more is more preferable, similar to the polyester film. If the transmittance is 85% or more, sufficient visibility can be ensured. It can be said that the higher the total light transmittance, the better, but it may be 99% or less or 97% or less.

Examples

[0058] Next, the effects of the present invention will be described using examples and comparative examples. First, the evaluation methods of the characteristic values used in the present invention are shown below.

[0059] (1) Intrinsic viscosity After the film or polyester resin was pulverized and dried, it was dissolved in a mixed solvent of phenol / tetrachloroethane = 60 / 40 (mass ratio). After subjecting this solution to centrifugation to remove inorganic particles, using an Ubbelohde viscometer, the flow-down time of a solution with a concentration of 0.4 (g / dl) at 30°C and the flow-down time of only the solvent were measured. From the ratio of those times, assuming that the Huggins constant is 0.38, the intrinsic viscosity was calculated using Huggins' equation. In the case of a laminated film, according to the laminated thickness, by scraping off the corresponding polyester layer of the film, the intrinsic viscosity of each layer alone was evaluated.

[0060] (2) Flexural resistance Prepare a sample with a size of 50 mm in the width direction × 100 mm in the flow direction. Using a non-load U-shaped expansion and contraction testing machine (manufactured by Yuasa System Co., Ltd., DLDMLH-FS), set the bending radius to 3 mm and bend it 50,000 times at a speed of 1 time / second. At that time, the sample was fixed at positions 10 mm from both ends on the long side, and the bending part was 50 mm × 80 mm. After the bending treatment, place the sample flat with the inner side of the bend facing down and conduct a visual inspection. In each of the following examples and comparative examples, the flexural resistance of the hard coat film was evaluated. It was evaluated by bending it so that the hard coat layer faces the outside of the bend. ◎: Deformation of the sample cannot be confirmed. ○: There is deformation of the sample, but when placed horizontally, the maximum height of the lift is less than 5 mm. ×: There is a crease in the sample or when placed horizontally, the maximum height of the lift is 5 mm or more.

[0061] (3) Pencil hardness In accordance with JIS K 5600-5-4:1999, the hard coat layer of the hard coat film was measured with a load of 750 g and a speed of 0.5 mm / s.

[0062] (4) Total light transmittance, haze The hard coat film was measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., NDH5000) and

[0063] (5) Thickness of the polyester film Three 5 cm square samples were cut from three arbitrary locations of the film. Using an electric micrometer (manufactured by Fine Reuleaux, Millitron 1245D), five measurements were taken at five points on each sample (15 points in total), and the average value was taken as the thickness of the polyester film.

[0064] (6) Thickness of the cured layer of the polyimide resin and thickness of the hard coat layer Sections were cut from three arbitrary locations of the hard coat film. The end face surface of one side of each section was made uniform with a microtome. This end face was magnified 600 times and observed with a digital microscope RH - 2000 (manufactured by Highrox Co., Ltd.). The thickness of the cured layer of the polyimide resin and the thickness of the hard coat layer at five points on each end face (15 points in total) were measured, and the average value of each was calculated.

[0065] (Preparation of Polyimide Resin Coating Solution 1) 100 parts by weight of a polyamideimide resin solution (manufactured by Toyobo Co., Ltd., BYROMAC (registered trademark) HR - 15ET, solid content concentration 25%) and 2.5 parts by weight of a cross - linking agent (manufactured by Mitsubishi Gas Chemical Co., Ltd., product name: Tetrad X, solid content concentration: 100% by weight) were mixed and diluted with a solvent of toluene / MEK = 1 / 1 to prepare Coating Solution 1 with a concentration of 15%.

[0066] (Preparation of Hard Coat Coating Solution 2) 95 parts by weight of a urethane acrylate - based hard coat agent (manufactured by Arakawa Chemical Industries, Ltd., Beam Set (registered trademark) 577, solid content concentration 100%), 5 parts by weight of a photo - radical polymerization initiator (manufactured by IGM Resi ns Co., Ltd., product name: Omnirad907, solid content concentration: 100% by weight), and 0.1 part by weight of a leveling agent (manufactured by BYK - Chemie Japan Co., Ltd., BYK307, solid content concentration 100%) were mixed and diluted with a solvent of toluene / MEK = 1 / 1 to prepare Coating Solution 1 with a concentration of 40%.

[0067] (Preparation of Polyethylene Terephthalate Pellets (a)) As an esterification reactor, a continuous esterification reactor consisting of three stages of completely mixed tanks having a stirring device, a partial condenser, a raw material inlet, and a product outlet was used. TPA was set at 2 tons / hr, EG was set at 2 moles per 1 mole of TPA, antimony trioxide was set at an amount such that the Sb atom was 160 ppm with respect to the produced PET, and these slurries were continuously supplied to the first esterification reactor of the esterification reactor and reacted at 255 °C with an average residence time of 4 hours under normal pressure. Next, the reaction product in the first esterification reactor was continuously taken out of the system and supplied to the second esterification reactor. EG distilled off from the first esterification reactor was supplied to the second esterification reactor in an amount of 8% by mass with respect to the produced polymer (produced PET). Further, an EG solution containing magnesium acetate in an amount such that the Mg atom was 65 ppm with respect to the produced PET and an EG solution containing TMPA in an amount such that the P atom was 20 ppm with respect to the produced PET were added, and the reaction was carried out at 260 °C with an average residence time of 1.5 hours under normal pressure. Next, the reaction product in the second esterification reactor was continuously taken out of the system and supplied to the third esterification reactor. Further, an EG solution containing TMPA in an amount such that the P atom was 20 ppm with respect to the produced PET was added, and the reaction was carried out at 260 °C with an average residence time of 0.5 hours under normal pressure. The esterification reaction product produced in the third esterification reactor was continuously supplied to a three-stage continuous polycondensation reactor for polycondensation, and further filtered with a filter medium of a stainless steel sintered body (nominal filtration accuracy: 90% cut for 5 μm particles) to obtain polyethylene terephthalate pellets (a) having an intrinsic viscosity of 0.62 dl / g.

[0068] (Preparation of polyethylene terephthalate pellets (b)) The polyethylene terephthalate pellets (a) were subjected to solid-phase polymerization at 220 °C for varying times under a reduced pressure of 0.5 mmHg using a rotary vacuum polymerization apparatus to prepare polyethylene terephthalate pellets (b) having an intrinsic viscosity of 0.67 dl / g.

[0069] (Preparation of polyethylene terephthalate pellets (c)) Polyethylene terephthalate pellets (a) were subjected to solid-phase polymerization at 220 °C under a reduced pressure of 0.5 mmHg for varying times using a rotary vacuum polymerization apparatus to produce polyethylene terephthalate pellets (c) with an intrinsic viscosity of 0.75 dl / g.

[0070] (Preparation of polyethylene terephthalate pellets (d)) Polyethylene terephthalate pellets (a) were subjected to solid-phase polymerization at 220 °C under a reduced pressure of 0.5 mmHg for varying times using a rotary vacuum polymerization apparatus to produce polyethylene terephthalate pellets (d) with an intrinsic viscosity of 0.83 dl / g.

[0071] The above polyethylene terephthalate master pellets (a) were dried under reduced pressure (3 Torr) at 180 °C for 8 hours, and then polyethylene terephthalate pellets (a) were fed into an extruder and fed into the extruder respectively, and melted at 285 °C. This polymer was filtered through a stainless steel sintered filter medium (nominal filtration accuracy: 95% cut-off for 10 μm particles), extruded into a sheet form from a die, and then cooled and solidified by contacting a casting drum with a surface temperature of 30 °C using an electrostatic application casting method to produce an unstretched film. This unstretched film was stretched 3.4 times in the longitudinal direction at 85 °C. This uniaxially stretched film was stretched 4.2 times in the width direction at 95 °C using a tenter and heat-treated at 220 °C for 5 seconds to obtain the polyethylene terephthalate film of No. 1 in Table 1. Polyethylene terephthalate master pellets (b) to (d) were supplied to substantially the same process as above with some condition adjustments to obtain the polyethylene terephthalate films of No. 2 to 5 in Table 1.

[0072] (Example 1) On one side of a polyethylene terephthalate film No. 3, using a Mayer bar, a polyimide-based resin coating solution 1 was applied so that the film thickness after drying would be 2.0 μm, and it was dried at 120°C for 1 minute to obtain a cured layer of the polyimide-based resin. Next, on the cured layer of the polyimide-based resin, using a Mayer bar, a hard coat coating solution 2 was applied so that the film thickness after drying would be 10 μm. After drying at 80°C for 30 seconds, ultraviolet rays were irradiated (integrated light quantity 200 mJ / cm 2 ), and a hard coat film was obtained.

[0073] (Examples 2 to 5, Comparative Examples 1 to 3) A hard coat film was prepared under the conditions shown in Table 2 in the same manner as in Example 1.

[0074] The prepared film was bonded to an organic EL module via an adhesive layer with a thickness of 25 μm, and a smartphone-type foldable display that could be folded in half at the center with a corresponding radius of the bending radius in FIG. 1 of 3 mm was created. The hard coat film was arranged on the surface of a single continuous display through the folding part, and the hard coat layer was arranged so as to be located on the surface of the display. Those using the hard coat film of each example satisfied the operation and visibility as a smartphone that could be folded in half at the center and carried around. On the other hand, the foldable displays using the hard coat films of Comparative Examples 2 and 3 seemed to have image distortion at the folding part of the display as the usage frequency increased, and were not very preferable. Also, Comparative Example 1 was somewhat unsatisfactory in terms of the pencil hardness of the hard coat film.

[0075]

Table 1

[0076]

Table 2

Industrial Applicability

[0077] According to the present invention, while maintaining mass productivity, there is provided a foldable display having a high pencil hardness on the surface, being less likely to deform the surface hard coat film after repeated folding, and being less likely to cause image disturbance over time, and a portable terminal device equipped with such a foldable display.

Explanation of Signs

[0078] 1: Foldable display 11: Bending radius 2: Hard coat film 21: Polyester film 22: Cured layer of polyimide-based resin 23: Hard coat layer

Claims

1. A folding organic electroluminescence display comprising an organic electroluminescence module and a hard coat film, the hard coat film being disposed on at least a part of a surface thereof, the hard coat film is disposed on an upper portion of an organic electroluminescence module; The hard coat film has a polyethylene terephthalate film as a base film, and has an easy-adhesion layer, a cured layer, and a hard coat layer in this order on at least the front surface side of the base film of the foldable organic EL display, the cured layer contains either a polyimide resin or a polyamide-imide resin; The bending radius when folded is 5 mm or less, In a no-load U-shaped stretch test in which the cable was bent 50,000 times at a bending radius of 3 mm and a speed of 1 time per second, after bending, the cable was placed horizontally on a flat surface with the inside of the bend facing down. The maximum lift is less than 5 mm, or there is no deformation. Foldable OLED display.

2. The total light transmittance of the hard coat film is 85% or more, The haze of the hard coat film is 3% or less; The thickness of the hard coat layer is 1 to 40 μm, The thickness of the base film is 10 to 75 μm, and the intrinsic viscosity of the base film is 0.65 to 0.80 dl / g, 2. The foldable organic electroluminescence display according to claim 1, wherein the thickness of the cured layer is 1.0 to 2.0 μm.

3. A foldable organic electroluminescence display as described in claim 1, wherein a continuous single hard coat film is arranged throughout the folding portion of the foldable organic electroluminescence display.

4. A foldable organic electroluminescence display as described in claim 1, wherein the pencil hardness of the hard coat layer measured under a load of 750 g in accordance with JIS K5600-5-4:1999 is 2H or more.

5. A mobile terminal device having the foldable organic EL display described in claim 1.

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