Polyester film for supporting display unit display light-emitting element back side and display unit with the film

Abstract

To provide a film which has superior static flexibility as a polyester film for supporting a display unit display light-emitting element back side, and also to provide a display unit mounted with the film for supporting the display light-emitting element back side.SOLUTION: There is provided a polyester film for supporting a display unit display light-emitting element back side characterized in that when stress in a 5% stretched state is F0 m and stress after the 5% stretched state is maintained for 30 minutes is F30 m, F30 m / F0 m (stress relief degree) obtained by dividing F30 m by F0 m is 0.5 or more and 1.0 or less in both length and width directions, and a refractive index of at least one of the length and width directions is 1.625 or more and less than 1.67.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polyester film for supporting the back side of a display light-emitting element, and more particularly to a film that can be used as a polyester film for supporting the back side of a display light-emitting element by controlling the film stretching characteristics within a specific range, and to a display on which the film is mounted. [Background technology]

[0002] In recent years, the practical application of image display devices using self-emissive materials called organic light-emitting diodes (hereinafter referred to as "organic electroluminescent display devices") has been progressing. Compared to conventional liquid crystal display devices, these organic electroluminescent display devices are superior in terms of visibility and response speed because they use self-emissive materials. Furthermore, because they do not require auxiliary lighting devices such as backlights, they can be made into thinner and more flexible display devices. For this reason, the development of flexible display devices that can be folded or rolled up is accelerating.

[0003] In the development of flexible display devices, efforts are being made to achieve large screens and improve miniaturization and weight reduction by reducing the bezel area, which is the non-display area surrounding the display area, and by developing foldable display devices that can be opened and closed in a folding manner. In these developments, thin-film flexible substrates that can maintain display performance even when bent are mainly used. Because the display devices using flexible substrates are too thin, a backplate capable of supporting the display panel is attached to the bottom of the flexible substrate (for example, Patent Document 1). The back-side support member of the display light-emitting element is sometimes called a backplate.

[0004] Furthermore, as a film for folding, films with controlled refractive indices in the bending direction, the folded portion, and the thickness direction have been considered (for example, Patent Document 2). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2021-521034 [Patent Document 2] Japanese Patent Publication No. 2021-9349 [Overview of the project] [Problems that the invention aims to solve]

[0006] In Patent Document 1, polyimide is used as a backplate. Polyimide is generally expensive and difficult to mass-produce, so polyethylene terephthalate (hereinafter sometimes referred to as PET), which has good handling and mechanical properties, is sometimes used as an alternative. Furthermore, while Patent Document 2 is designed with flexibility in mind among polyester films, as described in paragraphs

[0081] and

[0082] , only dynamic flexibility is considered, and the fact that it is mostly folded and left unattended when not in use is not taken into consideration. In other words, the design does not take into consideration static flexibility, and there is a problem in that it has poor static flexibility. [Means for solving the problem]

[0007] The polyester film for supporting the back side of a display light-emitting element of the present invention employs the following means to solve the above problem. (1) A polyester film for supporting the back side of a display light-emitting element, wherein when the stress at which 5% elongation is reached is F0m (MPa) and the stress after holding the 5% elongation state for 30 minutes is F30m (MPa), the F30m / F0m (degree of stress relaxation) obtained by dividing F30m by F0m is 0.5 or more and 1.0 or less in both the longitudinal and width directions, and the refractive index in at least one of the longitudinal or width directions is 1.625 or more and less than 1.67. (2) The polyester film for supporting the back side of a display light-emitting element as described in (1), wherein the dimensional change (CL30) when a stress (F-5) in at least one direction is applied for 30 minutes is 0 mm or more and 60 mm or less. (3) A polyester film for supporting the back side of a display light-emitting element according to (1) or (2), characterized in that the bending rigidity in at least one direction is 0.8g or more and 1.5g or less. (4) A polyester film for supporting the back side of a display light-emitting element according to (1) or (2) above, wherein the acid component constituting the polyester is mainly terephthalic acid or 2,6-naphthalenedicarboxylic acid. (5) A display equipped with a polyester film for supporting the back side of the display light-emitting element as described in (1) or (2) above. (6) The display according to (5), wherein the display includes a polarizing plate, a display light-emitting element, a polyester film for supporting the back side of the display light-emitting element, and an image sensor arranged in this order. (7) The display according to (6), wherein the display is a foldable image display device, and the slow phase axis direction of the polyester film for supporting the back side of the display light-emitting element is orthogonal to the bending direction of the display screen of the foldable image display device. (8) The display according to (6) or (7), wherein the image sensor has an aspect ratio of 1.05 or more, and the angle between the long side direction of the image sensor and the slow phase axis direction of the polyester film for supporting the back side of the display light-emitting element is 45° or more and 90° or less. (9) The display according to (6) or (7), wherein an adhesive layer is further disposed between the display light-emitting element and the polyester film for supporting the back side of the display light-emitting element. (10) The display according to (10), wherein the adhesive layer is in contact with the back plate via an easy-adhesion layer having a refractive index of 1.45 or more and 1.55 or less. (11) A method for manufacturing a polyester film for supporting the back side of a display light-emitting element, comprising performing at least the following steps (1) to (3) in this order. (1) A step of stretching 2.9 times or more and 3.3 times or less in the longitudinal extension direction (2) A step of stretching 3.7 times or more and 4.5 times or less in the lateral extension direction (3) A step of heat-treating at 220°C or higher and 245°C or lower [Advantages of the Invention]

[0008] According to the present invention, as a polyester film for supporting the back side of a display emission element, a film excellent in static bending resistance can be provided. Further, a display equipped with the film for supporting the back side of a display emission element has excellent static bending resistance. [Brief Description of the Drawings]

[0009] [Figure 1] It is a schematic diagram for explaining a visibility test. [Figure 2] It is a schematic diagram for explaining a bending test. [Figure 3] It is a front schematic view showing an example of the display of the present invention. [Figure 4] It is an exploded view of a screen area portion where an imaging element is arranged on the back side of an image display surface in an example of the display of the present invention. [Figure 5] It is a diagram for explaining the measurement of the network stretch ratio (λnet). [Modes for Carrying Out the Invention]

[0010] Hereinafter, the polyester film for supporting the back side of a display emission element according to the present invention will be described in detail together with embodiments.

[0011] The polyester film for supporting the back side of the display light-emitting element of the present invention has a stress relaxation degree of F30m / F0m (where F0m is the stress at the time of reaching 5% elongation and F30m is the stress after holding the 5% elongation state for 30 minutes) of 0.5 or more and 1.0 or less in both the longitudinal direction and the width direction. By controlling within this range, when used as a polyester film for supporting the back side of the display light-emitting element, excellent static bending resistance can be indirectly obtained when incorporated into a module. Here, the static bending resistance can be evaluated by the method described in the evaluation method (15) module performance determination of the examples. In the present invention, a module refers to a display in which at least a polarizer, a display light-emitting element (also called a light-emitting element for image display if an image display is assumed), and a film for supporting the back side of the display light-emitting element are mounted in this order. Incidentally, a photosensitive element for acquiring information on the image display side may be further provided on the back of the film for supporting the light-emitting element for image display as viewed from the display light-emitting element side. Also, the photosensitive element for acquiring information on the image display side includes, for example, an imaging element. The imaging element refers to an element having a photoelectric conversion function, and usually has a plurality of pixels arranged in a planar manner. Examples of the wavelength range are image sensors such as cameras that acquire information on light from near ultraviolet to visible light and near infrared, about 300 nm to 1500 nm. The imaging element may be at least one of a camera and a sensor. Also, a plurality of imaging elements may be arranged. Examples of the image sensor include a CMOS sensor and a CCD sensor. As the CMOS sensor, a back-illuminated CMOS sensor and a front-illuminated CMOS sensor can be mentioned. In terms of reducing light scattering and reflection and improving sensitivity by arranging the optical sensor on the back side, the back-illuminated CMOS sensor is preferable.

[0012] The image sensor used in the present invention can generally be formed as a rectangular surface in which photoelectric conversion elements are arranged at equal intervals along two orthogonal axes. As an example, the aspect ratio of a rectangular image sensor can be 1.05 or greater. Since the screen shape of a typical image display device is rectangular, if the image sensor is a camera, for example, by matching the aspect ratio of the image sensor to the screen area in order to effectively utilize the screen area to display information, it is possible to miniaturize the image sensor, which is also economically advantageous.

[0013] F30m / F0m is an index that indicates the degree of stress relaxation when a film is held at its F-5 value for 30 minutes. A higher value indicates that the film is less prone to plastic deformation and has superior static flexural resistance. Therefore, a value of 0.6 or higher is preferable from the viewpoint of static flexural resistance, and 1.0 is ideal. To control the value within this range, it is important to perform at least the following steps (1) to (3) in order. If the film is sampled by any other method, it may not be possible to control the value to F30m / F0m. Process (1) A process of stretching in the longitudinal direction by 2.9 times or more and 3.3 times or less. Process (2) A process of stretching in the transverse direction to a length of 3.7 times or more and 4.5 times or less. Process (3) A process of heat treatment at a temperature of 220°C or higher and 245°C or lower. Furthermore, we will explain the details of each process with examples.

[0014] Regarding step (1): the step of stretching in the longitudinal direction by 2.9 times or more and 3.3 times or less, in order to obtain the more remarkable effects of the present invention, it is important to stretch in three stages, and furthermore, it is important that the stretching ratios of the first, second, and third stages satisfy the following conditions. First row: ≤1.3 times Second row: ≤1.5 times 3rd stage: 2.0 times or more and 2.3 times or less Regarding step (2): In order to obtain a more remarkable effect of the present invention in the step of stretching in the transverse direction to a ratio of 3.7 to 4.5 times, it is important to stretch in three stages, and furthermore, it is important that the stretch ratios of the first, second, and third stages satisfy the following conditions. 1st stage: 2.0 times or more and 2.5 times or less Second row: ≤1.5 times Third row: ≤1.5 times Regarding step (3): the process of heat treatment relaxation at 220°C to 245°C, in order to obtain the more remarkable effects of the present invention, it is important to perform the heat treatment relaxation in three stages, and furthermore, it is important that the heat treatment temperatures of the first, second, and third stages and the relaxation rates in the longitudinal and transverse directions satisfy the following conditions. 1st stage: 150℃ or higher and 245℃ or lower 2nd stage: 220℃ or higher and 245℃ or lower 3rd tier: 100℃ or more and 180℃ or less Longitudinal relaxation rate: 1% to 8% Lateral relaxation rate: 1% to 8% In this invention, from the viewpoint of controlling F30m / F0m and CL30 (described later) to a preferred range, it is preferable that the longitudinal stretching direction is 2.95 times or more and 3.2 times or less, and the transverse stretching direction is 3.85 times or more and 4.15 times or less.

[0015] Furthermore, in order to obtain the effects of the present invention, it is important that the stretch ratio in the longitudinal direction and the width direction (longitudinal / width stretch ratio) be 0.7 or more and 0.81 or less, and that the area stretch ratio, which is the product of the longitudinal and width direction stretch ratios, be 10 or more and 14 or less. In particular, from the viewpoint of making F30m / F0m 0.6 or more, it is preferable that the area stretch ratio be 12 or more and 13 or less, and that the manufacturing is carried out within the range that satisfies the above steps (1) to (3).

[0016] The polyester film for supporting the back side of the display light-emitting element of the present invention preferably has a birefringence Δn, which is the difference in refractive index between the longitudinal and width directions, of 0.02 or more and 0.05 or less. Since birefringence Δn is the difference in refractive index between the longitudinal and width directions, it is what is known as the anisotropy of the film. By setting the birefringence Δn within this range, it becomes easier to control F30m / F0m within the range of the present invention. In the present invention, if the surface orientation coefficient is less than 0.15 and the birefringence Δn exceeds 0.05, the anisotropy is too strong, and the dynamic bending resistance determined from the number of MIT bending fractures may be poor. The method for controlling the birefringence Δn to 0.02 or more and 0.05 or less is to manufacture as described in steps (1) to (3) above. Furthermore, from the viewpoint of visibility, which will be discussed later, it is preferable that the birefringence Δn be 0.03 or more, and more preferably 0.05 or more.

[0017] The polyester film for supporting the back side of the display light-emitting element of the present invention has a refractive index of 1.625 or more and less than 1.67 in at least one of the longitudinal and width directions. In the present invention, in addition to the control range of F30m / F0m, it is essential to simultaneously satisfy the condition that the refractive index in either the longitudinal or width direction is 1.625 or more and less than 1.67 in order to achieve the effect of static bending resistance. The control method is as described in steps (1) to (3) above. If the refractive index in either the longitudinal or width direction is not 1.625 or more and less than 1.67, the static bending resistance will be inferior.

[0018] The polyester film for supporting the back side of the display light-emitting element of the present invention preferably has a MIT bending and breaking count of 30,000 or more. By controlling it within this range, burr suppression in secondary processing such as punching and excellent dynamic flexibility are achieved. The control method is as described in steps (1) to (3) above.

[0019] The polyester film for supporting the back side of the display light-emitting element of the present invention preferably has a dimensional change (CL30) of 0 mm or more and 60 mm or less when a stress (F-5) in at least one direction is applied for 30 minutes. If it exceeds 60 mm or measurement becomes impossible, the number of MIT bending fractures, i.e., secondary processability and dynamic bending resistance may be inferior. The control method is preferably obtained by the method described in steps (1) to (3) above.

[0020] The polyester film for supporting the back side of the display light-emitting element of the present invention preferably has a bending stiffness of 0.8g or more and 1.5g or less in at least one direction. It is more preferable that the bending stiffness in both the longitudinal and width directions is 0.8g or more and 1.5g or less. Note that gr is a unit of weight referring to grains, and 1 gram is equivalent to 15.432g. By setting the bending stiffness within this range, excellent compatibility between the preferred range of MIT bending fracture resistance and static bending performance can be achieved. To set the bending stiffness within this range, the steps (1) to (3) described above should be followed.

[0021] The polyester film for supporting the back side of the display light-emitting element of the present invention preferably has a film thickness of 20 μm to 80 μm. From the viewpoint of achieving both back support and static bending resistance, it is preferably 30 μm to 70 μm. From the above viewpoint, it is most preferably 40 μm to 60 μm.

[0022] The polyester film for supporting the back side of the display light-emitting element of the present invention preferably has a total light transmittance of 90% or more, from the viewpoint of use in displays.

[0023] Examples of glycols or derivatives thereof that yield polyesters in the present invention include aliphatic dihydroxy compounds such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, and neopentyl glycol; polyoxyalkylene glycols such as diethylene glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol; alicyclic dihydroxy compounds such as 1,4-cyclohexanedimethanol and spiroglycol; aromatic dihydroxy compounds such as bisphenol A and bisphenol S; and derivatives thereof.

[0024] Furthermore, examples of dicarboxylic acids or their derivatives that provide polyesters for use in the present invention include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenylsulfondicarboxylic acid, diphenoxyethanedicarboxylic acid, and 5-sodiumsulfondicarboxylic acid; aliphatic dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, sebacic acid, dimer acid, maleic acid, and fumaric acid; alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid; oxycarboxylic acids such as parahydroxybenzoic acid; and derivatives thereof. Examples of dicarboxylic acid derivatives include esterified products such as dimethyl terephthalate, diethyl terephthalate, 2-hydroxyethyl methyl terephthalate, dimethyl 2,6-naphthalenedicarboxylic acid, dimethyl isophthalate, dimethyl adipate, diethyl maleate, and dimethyl dimerate.

[0025] In this invention, from the viewpoint of low cost and excellent productivity, it is preferable that the acid component constituting the polyester is mainly terephthalic acid or 2,6-naphthalenedicarboxylic acid. Here, "main component" means that the component accounts for 70 mol% or more. Furthermore, copolymerizing the acid component constituting the polyester with terephthalic acid as the main component and 2,6-naphthalenedicarboxylic acid in a proportion of 3 to 30 mol% is preferable because it provides excellent static flexural resistance.

[0026] The polyester film of the present invention has an inter-entanglement density N of 4 × 10 26 (m -3 ) Above, 12 x 10 26 (m -3 It is preferable that the value be less than or equal to the value. By setting it within this range, the dynamic bending resistance is further improved. In order to control the inter-entanglement density N within the above range, it is preferable to use a resin with an intrinsic viscosity of 0.7 or higher and to carry out steps (1) to (3) described later in this order.

[0027] The polyester film for supporting the back side of the display light-emitting element of the present invention preferably has a layer containing a curable resin on at least one side. For example, this can be done as described in paragraphs

[0013] to

[0017] of Japanese Patent Application Publication No. 2018-124367. As for the manufacturing method when a curable resin layer is provided, for example, this can be done as described in paragraphs

[0025] to

[0026] of Japanese Patent Application Publication No. 2018-124367.

[0028] Next, we will describe the polyester film for supporting the back side of the display light-emitting element of the present invention and an example of a specific manufacturing method for the polyester film for supporting the back side of the display light-emitting element of the present invention. Here, polyethylene terephthalate is used as the resin constituting the film as an example, but the present invention is not limited to such examples.

[0029] First, polyethylene terephthalate resin, used as the resin for the film, is dried and pre-crystallized, then supplied to a single-screw extruder and melt-extruded. At this stage, the resin temperature is preferably controlled to 265-295°C. Next, foreign matter is removed and the extrusion volume is equalized through filters and gear pumps, respectively, and the resin is discharged in a sheet-like form onto a cooling drum from a T-die. At this stage, the sheet-like polymer is adhered to the casting drum using electrostatic application (using electrodes with high voltage to create static electricity to bond the resin to the cooling drum), a casting method (creating a water film between the casting drum and the extruded polymer sheet), a method (setting the casting drum temperature to the glass transition temperature of the polyester resin ~ (glass transition temperature - 20°C) to adhere the extruded polymer), or a combination of these methods. The sheet-like polymer is then cooled and solidified to obtain an unstretched film. Among these casting methods, when using polyester, the electrostatic application method is preferred from the viewpoint of productivity and flatness.

[0030] This can be obtained by stretching the unstretched film obtained in the casting process by a sequential biaxial stretching method in which the film is stretched longitudinally and then in the width direction, or by stretching it in the width direction and then in the longitudinal direction, or by a simultaneous biaxial stretching method in which the film is stretched longitudinally and in the width direction almost simultaneously.

[0031] In this invention, it is important to obtain the product by sequentially performing at least the following steps (1) to (3). Process (1) A process of stretching in the longitudinal direction by 2.9 times or more and 3.3 times or less. Process (2) A process of stretching in the transverse direction to a length of 3.7 times or more and 4.5 times or less. Process (3) A process of heat treatment at a temperature of 220°C or higher and 245°C or lower. Furthermore, details of each process are described below. Regarding step (1): the step of stretching in the longitudinal direction by 2.9 times or more and 3.3 times or less, in order to obtain the more remarkable effects of the present invention, it is important to stretch in three stages, and furthermore, it is important that the stretching ratios of the first, second, and third stages satisfy the following conditions. First row: ≤1.3 times Second row: ≤1.5 times 3rd stage: 2.0 times or more and 2.3 times or less Regarding step (2): In order to obtain a more remarkable effect of the present invention in the step of stretching in the transverse direction to a ratio of 3.7 to 4.5 times, it is important to stretch in three stages, and furthermore, it is important that the stretch ratios of the first, second, and third stages satisfy the following conditions. 1st stage: 2.0 times or more and 2.5 times or less Second row: ≤1.5 times Third row: ≤1.5 times Regarding step (3): the step of heat treatment relaxation at 220°C to 245°C, in order to obtain the more remarkable effects of the present invention, it is important to perform the heat treatment relaxation in three stages, and furthermore, it is important that the heat treatment temperatures and the relaxation rates in the longitudinal and transverse directions of the first, second, and third stages satisfy the following conditions. It is preferable to heat treat each stage for 1 second to 60 seconds, and to heat treat in total for 1 second to 180 seconds. 1st stage: 150℃ or higher and 245℃ or lower 2nd stage: 220℃ or higher and 245℃ or lower 3rd tier: 100℃ or more and 180℃ or less Longitudinal relaxation rate: 1% to 8% Lateral relaxation rate: 1% to 8% In the present invention, from the viewpoint of controlling F30m / F0m and CL30 to a preferred range, it is preferable that the longitudinal stretching direction is 2.95 times or more and 3.2 times or less, and the transverse stretching direction is 3.85 times or more and 4.15 times or less.

[0032] Furthermore, in order to obtain the effects of the present invention, it is important that the stretch ratio in the longitudinal direction and the width direction (longitudinal / width stretch ratio) be 0.7 or more and 0.81 or less, and that the area stretch ratio, which is the product of the stretch ratios in the longitudinal direction and the width direction, be 10 or more and 14 or less, and particularly preferably 12 or more and 13 or less.

[0033] Furthermore, the stretching temperature in the longitudinal stretching process should preferably be set to a level that does not cause uneven stretching. For example, when employing a sequential biaxial stretching method in which the material is stretched in the longitudinal direction first and then in the width direction, it is preferable that the preheating temperature in the longitudinal direction be at least -20°C above the glass transition temperature of the resin and at least +0°C above the glass transition temperature, and the stretching temperature be at least the glass transition temperature of the resin and at least +20°C above the glass transition temperature. It is also preferable that the preheating temperature in the width direction be at least the glass transition temperature of the resin and at least +20°C above the glass transition temperature, and the stretching temperature be at least +10°C above the glass transition temperature of the resin and at least +60°C above the glass transition temperature. In addition, stretching may be performed multiple times in each direction.

[0034] Furthermore, the polyester film for supporting the back side of the display light-emitting element of the present invention is preferably heat-treated after being stretched in the width direction. The heat treatment can be carried out by any conventionally known method, such as in an oven or on a heated roll. The heat treatment is preferably performed at a temperature of 160°C to 245°C, and the temperature of the highest heat treatment zone is preferably 220°C to 245°C. In addition, the heat treatment can be carried out by dividing it into multiple zones and gradually raising and lowering the temperature, or by slightly stretching it in the width direction to about 1.01 to 1.2 times during the heat treatment process. The heat treatment time can be any range that does not degrade the properties, preferably 10 to 60 seconds, more preferably 15 to 30 seconds. Furthermore, the heat treatment may be carried out while relaxing the film in the longitudinal and / or width directions.

[0035] The polyester film for supporting the back side of the display light-emitting element of the present invention may be manufactured by subjecting it to additional heat treatments such as annealing or aging, to the extent that the properties of the present invention are not impaired. By subjecting it to annealing or aging, the thermal shrinkage characteristics of the polyester film can be controlled, which is advantageous in suppressing problems caused by differences in thermal shrinkage characteristics with other components during the heat processing process when incorporating it as an image display device component.

[0036] Furthermore, the polyester film for supporting the back side of the display light-emitting element of the present invention preferably has an easily adhesive resin layer laminated on at least one side, having a thickness of 10 nm to 500 nm and a surface free energy of 38 mN / m or more, from the viewpoint of adhesion to the layer containing a curable resin. Methods for forming the easily adhesive resin layer include coating the film surface with the easily adhesive resin (composite melt extrusion method, hot melt coating method, in-line or off-line coating method from a solvent other than water, water-soluble or water-dispersible resin, etc.), or surface lamination methods of similar compositions or blends thereof. The thickness of the easily adhesive resin layer is preferably 10 nm to 500 nm, more preferably 20 nm or more as the lower limit, even more preferably 50 nm or more, particularly preferably 90 nm or more, and preferably 300 nm or less as the upper limit, more preferably 200 nm or less, and particularly preferably 130 nm or less. By having the thickness of the easily adhesive resin layer within the above range, good adhesive strength can be achieved, problems such as the detachment of added particles can be suppressed, and the accuracy of the information obtained from the image sensor can be improved. In particular, an in-line coating method is preferred for uniform film formation and industrially, in which a coating agent is applied to one side of the film before orientation crystallization is completed, the film is stretched in at least one direction, and heat-treated to complete orientation crystallization. Furthermore, when an easily adhesive resin layer is provided by coating, the resin used to provide the easily adhesive resin layer is not particularly limited, but for example, acrylic resins, urethane resins, polyester resins, olefin resins, fluororesins, vinyl resins, chlorine resins, styrene resins, various graft resins, epoxy resins, silicone resins, etc., can be used, and mixtures of these resins can also be used. From the viewpoint of adhesion, polyester resins, acrylic resins, or urethane resins are preferred. When polyester resin is used as an aqueous coating solution, a water-soluble or water-dispersible polyester resin is used, and for such water solubility or water dispersion, it is preferable to copolymerize a compound containing a sulfonic acid base or a compound containing a carboxylic acid base. Furthermore, when using acrylic resin as an aqueous coating solution, it is necessary to dissolve or disperse it in water, and a surfactant (for example, polyether compounds, but not limited to these) is used as an emulsifier.) may be used.

[0037] Furthermore, to further improve adhesion, various crosslinking agents can be used in combination with the resin in the easily adhesive resin layer used in the present invention. Melamine-based, epoxy-based, and oxazoline-based resins are commonly used as crosslinking agent resins. The particles contained in the resin layer of the present invention can be inorganic particles or organic particles, but inorganic particles are more preferred because they improve slipperiness and blocking resistance. Examples of inorganic particles include silica, alumina, kaolin, talc, mica, calcium carbonate, and titanium.

[0038] Furthermore, the refractive index of the easy-adhesion resin layer is preferably 1.45 or higher and 1.55 or lower in order to improve the accuracy of the information obtained by the image sensor. The refractive index of the easy-adhesion resin can be adjusted to the above range by changing the composition of the resin used. Polyester resins, acrylic resins, or urethane resins are preferred, and the inclusion of an acrylic resin is particularly preferable from the viewpoint of controlling the refractive index. The upper limit of the refractive index is more preferably 1.53 or lower, and even more preferably 1.52 or lower.

[0039] The display of the present invention is preferably a display equipped with a polyester film for supporting the back side of the display light-emitting element of the present invention. In the present invention, "display" refers to display devices in general, and examples of display types include organic EL displays, inorganic EL displays, micro-LEDs, mini-LEDs, and FEDs. Organic ELs and inorganic ELs, which can reduce the number of layers, are particularly preferred, and organic ELs with a wide color gamut are even more preferred.

[0040] The display in this invention is a display in which at least a polarizer, a display light-emitting element, and a film for supporting the back side of the display light-emitting element are mounted in the order shown, from the side that displays the image (viewing side) toward the direction of the display light-emitting element. The film for supporting the image display light-emitting element may also be expressed as a backplate. Furthermore, a photosensitive element such as an image sensor for acquiring information from the image display side may be provided on the back of the film for supporting the back side of the display light-emitting element as viewed from the display light-emitting element side.

[0041] The display using the polyester film for supporting the back side of the display light-emitting element of the present invention is preferably a foldable display that can be bent with a bending diameter of 1 to 10 mm. A more preferable range for the bending diameter is an upper limit of 8 mm or less, more preferably 6 mm or less, and even more preferably 5 mm or less. If the bending diameter is 10 mm or less, it is possible to make the display thin when folded. It can be said that a smaller bending diameter is better, but a smaller bending diameter makes it easier for creases to form. A bending diameter of 0.1 mm or more is preferable, but it may also be 1 mm or more. Even with a bending diameter of 1 mm, it is possible to achieve a sufficiently thin design for practical use when carrying the device. Furthermore, the foldable display may be tri-fold, quad-fold, or even a rollable type, and all of these fall within the range of a foldable display as defined in the present invention. A foldable display is a display in which a single continuous screen is configured to be bent at a certain line (folding part) in the display screen, like a hinge. The bending direction is the direction perpendicular to the line of the folding part.

[0042] In this specification, "orthogonal" means not only when two straight lines intersect perpendicularly, but also when two straight lines parallel to each other intersect perpendicularly.

[0043] In the image display device of the present invention, when the image display device is a foldable image display device, it is preferable to position the backplate with the slow axis perpendicular to the bending direction. Positioning the backplate with the slow axis perpendicular to the bending direction in the present invention means positioning it so that the angle between the slow axis and the bending direction is 90 ± 10° (i.e., a deviation of within 10° from the state in which the slow axis of the backplate and the bending direction are perpendicular).

[0044] In the image display device of the present invention, it is preferable that the angle between the absorption axis direction of the polarizer of the polarizer plate and the slow axis direction of the backplate is 0±10° (i.e., a deviation of within 10° from the state in which the absorption axis of the polarizer and the slow axis of the backplate coincide) or 90±10°, as this improves the accuracy of the information collected by the image sensor. In particular, from the viewpoint of flexibility, it is preferable that the angle be set to 0±10°. Here, the slow axis is the axis determined by "(17) Film slow axis" described later. When the slow axis direction and the bending direction in a foldable image display device are perpendicular, fatigue due to compressive stress applied to the inside of the fold during folding can be reduced. Fatigue due to compressive stress is thought to occur mainly in the crystalline portion, and the fewer crystals there are in the bending direction, the less fatigue progresses. Therefore, it is thought that by lowering the refractive index, the amount of oriented crystals in the bending direction is reduced, and compressive fatigue is suppressed. In addition, the creep phenomenon caused by tensile stress applied to the outside of the fold during folding can be suppressed by lowering the refractive index. Fatigue due to tensile stress is thought to occur mainly in the amorphous portion, and deformation occurs due to alignment of molecular chains caused by repeated stress. It can be inferred that the fewer molecular chains aligned in the bending direction, the less deformation due to alignment. Also, since fatigue due to tension can be suppressed if there is less amorphous portion, it is preferable that the polyester film for supporting the back side of the display light-emitting element of the present invention has a high degree of crystallinity, i.e., a high density.

[0045] The display has a polarizer positioned at the bottom of the cover member to prevent a decrease in visibility and contrast ratio caused by light incident from the outside into the inside of the display device. The polarizer in the image display device of the present invention, when applied to an organic electroluminescent display device, etc., as a circular polarizer used together with an optical film (λ / 4 phase difference film), exhibits the effect of shielding specular reflections of metal electrodes of the organic electroluminescent device, etc., across all wavelengths of visible light, thereby preventing reflections during observation and improving black color representation. The circular polarizer consists of a polarizer that converts light to linear polarization upon transmission and a phase difference plate that converts linearly polarized light to circular polarization upon transmission.

[0046] The polarizer can be any polarizer or coated polarizing film used in the relevant art, as appropriate. Typical polarizers include those made by dyeing a dichroic material such as iodine onto a polyvinyl alcohol film, but are not limited to this, and known and future polarizers can be appropriately selected and used.

[0047] The phase difference plate can be any phase difference plate used in the art as appropriate. As the phase difference plate, a plastic film stretched in a specific direction can be used, such as polycarbonate, polyester, polysulfone, polystyrene, or polymethyl methacrylate. While the phase difference plate can be formed from a single birefringent film, it may also be formed by laminating multiple birefringent films to reduce the wavelength dependence of the phase difference and to function across the entire visible light wavelength range.

[0048] Furthermore, the polarizer and phase difference plate can be bonded together using an acrylic-based transparent adhesive or bonding agent that does not exhibit optical anisotropy.

[0049] Furthermore, to improve the effect of preventing external light reflection, an anti-reflective film can be provided on the surface of the circular polarizer. For example, in addition to directly forming a multilayer film on the surface of the circular polarizer, it is also possible to attach an anti-reflective film. Alternatively, a microstructure such as a moth-eye structure may be provided, or an appropriate anti-glare treatment may be applied.

[0050] The display light-emitting element used in the present invention can be any image display light-emitting element used in the art, selected as appropriate. Typical image display light-emitting elements include organic electroluminescent elements, inorganic electroluminescent elements, organic light-emitting diodes, and microlight-emitting diodes, but are not limited to these, and any known or future-developed image display light-emitting elements can be selected as appropriate. However, it is preferable to use an organic electroluminescent element because it can achieve high contrast and form a clear image.

[0051] The configuration of the display light-emitting element, using an organic electroluminescent element as an example, is not particularly limited, but includes a light-emitting element substrate, a thin-film transistor, an organic electroluminescent element, and a sealing layer, and the organic electroluminescent element includes an anode, a light-emitting layer, and a cathode. For example, it may have the layer structure described in (i) to (vi) below. Furthermore, the light-emitting layer described below may consist of a blue light-emitting layer, a green light-emitting layer, and a red light-emitting layer. Note that the light-emitting element substrate may be the same as the film described later.

[0052] The following shows a typical example of the pixel configuration of an organic electroluminescent element. (i) Anode / Hole injection transport layer / Emitting layer / Electron injection transport layer / Cathode (ii) Anode / Hole injection transport layer / Emitting layer / Hole blocking layer / Electron injection transport layer / Cathode (iii) Anode / Hole Injection Transport Layer / Electron Blocking Layer / Emitting Layer / Hole Blocking Layer / Electron Injection Transport Layer / Cathode (iv) Anode / Hole injection layer / Hole transport layer / Emitting layer / Electron transport layer / Electron injection layer / Cathode (v) Anode / Hole injection layer / Hole transport layer / Emitting layer / Hole blocking layer / Electron transport layer / Electron injection layer / Cathode (vi) Anode / Hole Injection Layer / Hole Transport Layer / Electron Blocking Layer / Emitting Layer / Hole Blocking Layer / Electron Transport Layer / Electron Injection Layer / Cathode A light-emitting element substrate is a base material for supporting various elements of a display light-emitting element and can be formed from an insulating material. For example, a light-emitting element substrate may be a glass substrate or a plastic substrate. For example, the plastic substrate may be selected from, but is not limited to, polyester, polyimide, polyethersulfone, and polycarbonate.

[0053] The display of the present invention exhibits excellent static bending resistance by arranging the polyester film for back-side support of the display light-emitting element of the present invention as a support member, as a backplate below the display light-emitting element, thereby enabling the creation of a flexible display, for example. Within the limits that do not impair the objectives of the present invention, the material used for the backplate may be a single material or a combination of two or more materials, and may be an inorganic material such as glass, or a plastic material such as polymethyl methacrylate, polycarbonate, or polyvinyl alcohol. Among these, the use of a polyester film is preferable from the viewpoint of effectively controlling retardation, which will be explained later.

[0054] The display of the present invention is an image display device in which a polarizing plate, an image display light-emitting element, a back plate, and an image sensor are arranged in this order, and it is preferable that the back plate is a polyester film for supporting the back side of the display light-emitting element of the present invention. With this configuration, the image display light-emitting element is supported so as not to sag, and the image display light-emitting element is protected from moisture, heat, shock, etc., while the display can be made to have excellent static bending resistance.

[0055] Furthermore, it is preferable that the image sensor has an aspect ratio of 1.05 or more, and that the angle between the long side direction of the image sensor and the slow-phase axis direction of the polyester film for supporting the back side of the display light-emitting element of the present invention is 45° or more and 90° or less. Such an arrangement is preferable because it improves the accuracy of the information obtained from the image sensor. In other words, by arranging the angle between the slow-phase axis of the back plate and the long side of the image sensor within the above range, it is possible to suppress the reflection of rainbow-like unevenness that occurs at the end of the back plate in the slow-phase axis direction onto the image sensor, thereby improving visibility.

[0056] In this invention, an adhesive layer or tack layer can be placed between the image display light-emitting element and the backplate to bond them together. The adhesive layer may be, but is not limited to, a light-transparent adhesive or a vacuum adhesive. The tack layer mainly consists of a tacky resin, and examples of tacky resins include acrylic adhesives and silicone adhesives. In particular, it is preferable to use a silicone adhesive from the viewpoint of heat resistance and transparency. Because the image display light-emitting element and the backplate are bonded together via a tacky resin, the layer of air between the image display light-emitting element and the backplate can be eliminated, thereby suppressing reflection at the interface and further improving the accuracy of the information obtained by the image sensor. The image sensor of this invention preferably has a diagonal field of view of 60 to 140°, which is the maximum angle at which external light irradiated onto the image display device can be collected and identified, more preferably 70° or more as the lower limit, and even more preferably 75° or more. Since productivity may decrease if the diagonal field of view is too high, the upper limit is preferably 140° or less, more preferably 130° or less, and even more preferably 120° or less. The mechanism that suppresses the occurrence of rainbow-like unevenness described above allows for the use of image sensors with particularly large diagonal fields of view in image display devices, enabling accurate collection and identification of image information over a wider range. The diagonal angle can be controlled by focusing light with an appropriate lens group. Multiple lenses can be used as the lens group to correct optical distortion and image distortion over a wide field of view. The lens group is positioned between the backplate and the image sensor, focusing the light rays that have passed through the backplate onto the image sensor.

[0057] Figure 3 is a schematic diagram illustrating the display (image display device) of the present invention. As shown in Figure 3, the display j includes a screen area k in which the image sensor is located on the back side of the image display surface, an excess screen area l, and an image sensor m. The screen area k in which the image sensor is located on the back side of the image display surface may be arranged according to highly transparent image display light-emitting elements, in which transparent materials are used for the cathode, anode, and light-emitting element substrate. The excess screen area l may be arranged with either low-transparency or highly transparent image display light-emitting elements.

[0058] Since this screen area k has high transparency, the image sensor can pass through the screen area and collect information outside the screen, and the display can achieve full-screen display. In addition to the camera, other image sensors m may be further arranged below the screen area k in the above-mentioned display, such as multiple cameras with different viewing angles, a fingerprint sensor, a light sensor, a distance sensor, etc., which need to collect light rays.

[0059] Figure 4 is an exploded view illustrating the arrangement of each component in the screen area where the image sensor is located on the back of the image display surface, for an example of the display (image display device) of the present invention. As shown in Figure 4, in the image display device n, the polarizer u, image display light-emitting element v, backplate a, and image sensor q are arranged in that order when viewed from the side where the image is displayed (viewing side). In the image display device of the present invention, it is preferable that the backplate and image sensor are arranged such that the angle between the slow axis direction p of the backplate and the direction r of the long side of the image sensor is 45° or more and 90° or less. This arrangement is preferable because it improves the accuracy of the information obtained from the image sensor. That is, by arranging the angle between the slow axis of the backplate and the long side of the image sensor within the above range, it is possible to suppress the reflection of rainbow unevenness t, which occurs in the slow axis direction of the backplate and at the edges of the image circle s, which is a circular area created on the focal plane by light that has passed through a lens or the like, onto the image sensor. [Examples]

[0060] The present invention will be described below with reference to examples, but the present invention is not intended to be limited by these examples. The various characteristics were measured by the following methods.

[0061] (1) Film thickness To measure the overall thickness of the film, a dial gauge was used to measure the thickness at five arbitrary locations on a sample cut from the film, and the arithmetic mean was calculated.

[0062] (2) Thickness of the curable resin layer and the easy-to-bond resin layer The thickness of the curable resin layer on the film was measured by observing the cross-section using a transmission electron microscope (TEM). The thickness of the curable resin layer was read from images taken with the TEM at a magnification of 100,000x. The thickness of a total of 10 curable resin layers and easy-to-adhere resin layers was measured, and the arithmetic mean was calculated. Note that the observation magnification can be other than 100,000x as long as the thickness can be measured.

[0063] (3) Total light transmittance Measurements were taken using a direct-reading haze computer (UGV-5D) manufactured by Suga Test Instruments Co., Ltd., in accordance with JIS K-73615. Each measurement was performed three times, and the arithmetic mean was used.

[0064] (4) Main orientation axis A sample measuring 100mm x 100mm was cut from an arbitrary point on the film, and a molecular orientation analyzer MOA-7015 (frequency 15GHz) manufactured by Oji Instruments Co., Ltd. was used.

[0065] (5) Longitudinal direction, width direction In this invention, the direction of film flow during film manufacturing is defined as the longitudinal direction, and the direction perpendicular to the longitudinal direction is defined as the width direction. If the longitudinal and width directions are unknown, an arbitrary direction is used as the reference 0°, and the refractive index is measured in 15° increments from 0 to 360°. The direction with the lowest refractive index is defined as the longitudinal direction, and the direction perpendicular to it is defined as the width direction. The refractive index is measured using an Abbe refractometer with sodium D line (wavelength 589 nm) as the light source.

[0066] (6) Film refractive index and surface orientation coefficient Using a sodium D line (wavelength 589 nm) as the light source and methylene iodide as the mounting solution, the refractive indices (nMD, nTD, and nZD, respectively) in the longitudinal, widthwise, and thicknesswise directions of the film were measured at 25°C using an Abbe refractometer 4T (manufactured by Atago Co., Ltd.) in accordance with JIS K7142 (2014) Method A. The refractive index of the test piece used was 1.74. From the obtained refractive indices, the surface orientation coefficient (fn) was calculated using the following formula (1). fn=(nMD+nTD) / 2-nZD ···(1) (7) Composition of the resin that makes up the film Dissolve the film in hexafluoroisopropanol (HFIP), 1 H-NMR and 13 The content of each monomer residue and by-product diethylene glycol is quantified using 1C-NMR.

[0067] (8) Glass transition temperature of resin Measurements and analyses were performed in accordance with JIS K-7121 (1987 edition) using a differential scanning calorimetry robot DSC-RDC6220 manufactured by Seiko Instruments Inc., and the thermal analysis rheology system software "Muse" manufactured by SII Nanotechnology Inc. for data analysis. Specifically, the stepwise transition portion of the glass transition in the differential scanning calorimetry chart obtained from the DSC curve when a 5 mg sample was heated from 25 °C to 300 °C at a rate of 20 °C / min was determined from the point where a line equidistant in the vertical direction from the extended line of each baseline intersects with the curve of the stepwise transition portion of the glass transition.

[0068] (9) Heat shrinkage rate at 150℃ The film was cut into rectangular pieces measuring 150 mm in length and 10 mm in width along both the longitudinal and transverse directions to create samples. Markings were drawn on the samples at 100 mm intervals (50 mm from the center to both ends), and the samples were heat-treated by suspending a 3 g weight and placing them in a hot air oven (GPH-2, manufactured by espec Co., Ltd.) heated to 150°C for 30 minutes. The distance between the markings was measured after heat treatment, and the thermal shrinkage rate was calculated from the change in the distance between the markings before and after heating using the following formula. Thermal shrinkage rate (%) = {(gauge distance before heat treatment) - (gauge distance after heat treatment)} / (gauge distance before heat treatment) × 100.

[0069] (10) Elongation 5% stress A strip-shaped sample measuring 150 mm in length and 10 mm in width was measured using an Instron-type tensile testing machine according to the method specified in JIS Z1702 (1994). The measurement was performed under the following conditions, and the stress at 5% elongation was measured for 10 samples and calculated as the arithmetic mean. Note that the value not divided by the cross-sectional area is the load [N]. Measuring device: Orientec Co., Ltd. automatic film strength and elongation measuring device "Tensilon" (registered trademark) AMF / RTA-100 Sample size: 10mm wide x 50mm long Pulling speed: 300 mm / min Measurement environment: temperature 23℃, humidity 65%RH.

[0070] (11) Bending stiffness Using a loop stiffness tester manufactured by Toyo Seiki Seisakusho Co., Ltd., a sample was cut to a length of 120 mm and a width of 5 mm in the measurement direction, with a loop circumference of 100 mm and a crushing distance of 5 mm. The peak value was taken as the bending stiffness (gr). Subsequently, measurements were taken five times each in the longitudinal and lateral directions, and the arithmetic mean value for each measurement direction was taken as the bending stiffness.

[0071] (12) F0m, F30m F0m was defined as the stress [MPa] at the point when the elongation reached 5%, obtained by the method described in (10). F30m was defined as the stress [MPa] after maintaining the state of 5% elongation for 30 minutes.

[0072] (13)CL30 First, the load [N] at a film elongation of 5% is determined by the method described in (10). Next, tension is applied to the sample using the Tensilon with the load value at a film elongation of 5%, and the dimensional change after 30 minutes is measured and set to CL30 [mm]. For example, if the load at a film elongation of 5% is 50N using the method described in (10), the load is set to 50N and applied using the Tensilon, and the dimensional change after 30 minutes is measured.

[0073] (14) Static bending test lift angle Figure 2 shows an overview of the experiment.

[0074] Using a U-shaped stretch tester (DLDMLH-FS, manufactured by Yuasa Systems Equipment), a film sample a, cut to 60 mm in length and 25 mm in width, was attached to the end of the tilt clamp with the tilt clamp in a horizontal position and the stroke direction being the length direction of the sample. The film was left undisturbed for 24 hours in the most bent state, with the center h of the film bending at a distance of 1.5 mm between faces. After 24 hours, the bending state was released and the sample was removed from the device, placed undisturbed with the bent outer side facing downwards, and the angle i formed by the film sample was measured. This measurement was repeated 5 times in both the longitudinal and width directions, and the average value was calculated as the static bending test lift angle. The angle was read with 0° representing the completely folded state and 180° representing the state in which the film returns to its original unfolded state.

[0075] (15) Static bending resistance The static bending resistance was determined using the results of the static bending test lift angle measurement in the longitudinal and width directions obtained in (14). The determination was made by comparing criteria from A to D, and the first determination that was found to be satisfactory was adopted. Determinations A, B, and C are levels that have excellent static bending resistance and can be suitably used as a foldable display, with A being the best. Determination D indicates that when used as a foldable display, wrinkles may form and the static bending resistance is poor.

[0076] A: The lift angle in the static bending test in both the longitudinal and width directions is 150° or more.

[0077] B: The lift angle in both the longitudinal and widthwise directions of the static bending test is 140° or greater.

[0078] C: The lift angle in both the longitudinal and widthwise directions of the static bending test is 120° or greater.

[0079] D: The lift angle in either the longitudinal or transverse static bending test is less than 120°.

[0080] (16) MIT flexure fracture count (dynamic flexure) A film sample was cut into a rectangle measuring 110 mm (in the test direction) x 15 mm in width. Using an MIT flexure resistance tester (MAYZ Corporation, tester No. 702), a flexure test was performed on the film sample in accordance with JIS P-8115 (2001 edition) with a load of 1,000 g, a bending angle of 135° to the left and right (R: +135°, L: -135°), a bending speed of 175 times / min, and a chuck tip radius of 0.38 mm. The number of flexures at which the film sample broke was defined as the number of flexures to break. Three tests were performed in both the MD and TD directions, and the average value was used. For the evaluation below, the value with the higher number of flexures to break in either the MD or TD direction was used. Repeated flexure resistance levels A and B are considered suitable for use as foldable displays.

[0081] A: The number of bending cycles to reach fracture was over 30,000, demonstrating excellent resistance to repeated bending.

[0082] B: The number of bending cycles to reach fracture is less than 30,000, making it usable as an image display device, but it is less practical as a foldable display.

[0083] (17) Film slow axis The main orientation axis of the film was determined by cutting a 100mm x 100mm sample at an arbitrary point on the film and using a KS Systems (now Oji Instruments Co., Ltd.) microwave molecular orientation meter MOA-2001A (frequency 4GHz) to find the slow phase axis within the film plane. The slow phase axis is the axis in which the phase lags and the speed of light propagation is slowest when light propagates through a birefringent crystal, and it is the direction with the highest refractive index.

[0084] (18) Visibility Figure 1 shows a schematic diagram of a visibility test in a model device configuration of an image display device in which the image sensor is positioned below the image display surface.

[0085] A 50mm x 50mm piece of film a was cut and placed on top of a polarizing plate b (manufactured by Kenis Co., Ltd., thin polarizing film, S size, transmittance 0.43, polarization rate 0.9999, product code 1-115-0820) to create a measurement sample. To bond film a and polarizing plate b, the following materials were mixed, and the resulting adhesive layer composition was applied to one side of film a using a gravure roll so that the coating thickness after drying was 20 μm. The adhesive layer formed by drying at 100°C for 3 minutes was then used to bond film a to polarizing plate b. "SD4580PSA" (manufactured by Toray Dow Corning Co., Ltd., hydrosilylation reaction curing agent) 100 parts by mass Toluene 50 parts by mass "NC-25" (Platinum-based catalyst manufactured by Toray Dow Corning Co., Ltd.) 0.9 parts by mass.

[0086] The sample was placed horizontally on a surface light source f (Tritech Co., Ltd., Triviewer A4-100) with the polarizing plate b side of the sample facing downwards. A camera-integrated device c (Samsung Galaxy S10®) with an ultra-wide-angle lens d (diagonal field of view 122°) was used to take a picture horizontally relative to film a, and the image was observed when the entire field of view was illuminated by the backlight f. The visibility was judged as follows. At this time, the image sensor of the camera-integrated device c has an aspect ratio of 1.33, and the direction of the long side of the image sensor is parallel to the direction of the long side of the camera-integrated device c. Visibility levels A, B, and C were considered acceptable levels that are sufficiently usable even in image display devices. A: Interference colors are hardly visible overall. B: Although some interference colors are visible at the edges of the image, it does not pose a practical problem. C: Interference colors are visible throughout, but it is still usable. D: The interference colors are very noticeable, making it unsuitable for practical use.

[0087] (19) Refractive index of the easily bonded resin layer The refractive index of a film approximately 100 μm thick, prepared by drying and solidifying the resin or curing it with active radiation, was measured using a PRISM COUPLER & LOSS MEASUREMENT (SPA-4000) manufactured by SAIRON TECHNOLOGY, INC. The refractive index was measured in two directions parallel and perpendicular to the film surface, and the average value was defined as the refractive index. The measurement wavelength was 589 nm.

[0088] If the above measurement method cannot be used, the resin may be subjected to compositional analysis, and the measurement may be performed using a replica of the resin based on the analysis results, with the results being used as a substitute.

[0089] (20) Intrinsic viscosity Weigh 0.100 g of the sample with an accuracy within 0.001 g, and dissolve it by heating at 100 °C for 30 minutes using 10 mL of o-chlorophenol. Cool the solution to room temperature, charge 8 mL of this solution into an Ostwald viscometer placed in a 25 °C water bath, and measure the number of seconds (A (seconds)) it takes to pass through the calibration line. Also, measure the number of seconds (B (seconds)) it takes for only 8 mL of o-chlorophenol to pass through the calibration line using an Ostwald viscometer placed in a 25 °C water bath in the same manner as above. The intrinsic viscosity was calculated using the following formula. IV = {[1 + 4 × K × {(A / B) - 1}] 0.5 - 1} / (2 × K × C) Here, K is 0.343 and C is the concentration of the sample solution (g / 100 mL).

[0090] (21) Density between crosslinking points Measure the peak value σ of the thermal shrinkage stress of the sample by the method described in (24) below, measure the network stretch ratio λnet by the method described in (22) below, and calculate it using the following formula. N = σ / kT(λnet 2 - λnet -1 ) Here, N: Density between crosslinking points (m -3 ) σ: Peak value of thermal shrinkage stress (N / m 2 ) k: Boltzmann constant (1.380649 × 10 -23 [J / K]) T: Temperature (298.16 (K)).

[0091] (22) Network stretch ratio (λnet) First, prepare a reference sample. Since the reference sample requires the film to be in an unstretched state, first measure the intrinsic viscosity of the sample to be measured, and use a resin with the same composition that has an equivalent intrinsic viscosity (within ±0.3) as the resin for the reference sample. In the following examples and comparative examples, the resin for the reference sample was the one obtained by mixing the main raw materials, (if used) auxiliary raw materials, and particle master specified in each raw material composition at a predetermined mixing ratio.

[0092] For the reference sample, an unstretched sheet with a thickness of 400 μm was obtained by melt extrusion of the resin, and this was used as the reference sample. The unstretched sheet used as the reference sample had a thickness variation of ±5% or less at the five measurements taken in the measurement method described in (1) above. For example, if it was a 400 μm film, the thickness should be within 380 to 420 μm.

[0093] Next, the elongation and load of the reference sample were measured using a universal testing machine. The measurement method is as described in (23) Elongation-Stress Curve below. Subsequently, the nominal strain, true strain, nominal stress, and true stress at each elongation were calculated from the obtained elongation and load as follows.

[0094] Nominal strain = elongation (mm) / initial length (mm) *Elongation (%) = Elongation (mm) / Initial length (mm) × 100 True strain = ln(1 + nominal strain) Nominal stress (MPa) = Load (N) / Initial cross-sectional area (mm²) 2 ) True stress = Nominal stress × (1 + Nominal strain) A true strain-true stress curve was created using the calculated true strain as the X-axis and the true stress as the Y-axis.

[0095] On the other hand, elongation-stress curves were obtained for each film of the examples and comparative examples (represented as measurement samples in Figure 5) in the same manner as above, and true strain-true stress curves were calculated. As shown in Figure 5, the obtained true strain-true stress curves were shifted to overlap with the fracture point of the reference sample, and the amount of shift in the true strain value at the start of elongation was defined as the network elongation ratio λnet, with 0 as the reference.

[0096] For example, if the nominal strain at fracture of the reference sample is 5.0 and the nominal stress is 40 MPa, then the true strain is ln(1+5.0)=1.791759 and the true stress is 40×(1+5)=240. When the true stresses are superimposed so that they are the same as the true stress at the fracture point of each film in the examples and comparative examples and their corresponding reference sample, and the true strain value at the start of elongation is 1.3, then the shift amount is calculated to be 1.3.

[0097] (23) Elongation at break, stress at break Strip-shaped samples measuring 150 mm in length and 10 mm in width were measured using an Instron-type tensile testing machine (Orientec Co., Ltd.'s "Tensilon" (registered trademark) AMF / RTA-100 automatic film strength and elongation measuring device) according to the method specified in JIS Z1702 (1994). The measurements were performed under the following conditions, and 20 samples were measured.

[0098] From the obtained measurement results, 5 points with the lowest fracture elongation and 5 points with the highest fracture elongation were removed from the data, for a total of 10 points. Based on the remaining 10 points, the fracture elongation was calculated as the arithmetic mean of the values ​​of the above 10 points. On the other hand, for the fracture stress, only the samples from the remaining 10 points whose fracture elongation was equal to or greater than the arithmetic mean calculated above were considered, and the fracture stress was calculated as the arithmetic mean of the fracture stress of these samples. Sample size: 10mm wide x 50mm long Pulling speed: 300 mm / min Measurement environment: temperature 23℃, humidity 65%RH.

[0099] (24) Peak value of thermal contraction stress σ The film was cut into rectangular pieces measuring 50 mm in length and 4 mm in width as samples, and the peak thermal shrinkage stress σ (N / m) was measured under the following conditions using a thermomechanical analyzer (Seiko Instruments, TMA EXSTAR6000). 2 ) was measured. Chuck spacing: 15mm Load: 19.6mN Heating rate: 5°C / min Measurement temperature range: 25~220℃.

[0100] (Polyester manufacturing) The polyester resin used for film formation was prepared as follows:

[0101] (Polyester A) A polyethylene terephthalate resin (intrinsic viscosity 0.65) containing 100 mol% terephthalic acid as the dicarboxylic acid component and 100 mol% ethylene glycol as the glycol component.

[0102] (Polyester B) A polyethylene terephthalate resin (intrinsic viscosity 0.80) containing 100 mol% terephthalic acid as the dicarboxylic acid component and 100 mol% ethylene glycol as the glycol component.

[0103] (Polyester C) A copolymer polyethylene terephthalate resin (intrinsic viscosity 0.65) in which terephthalic acid is present as the dicarboxylic acid component at a concentration of 90 mol%, 2,6-naphthalenedicarboxylic acid at a concentration of 10 mol%, and ethylene glycol at a concentration of 100 mol%.

[0104] (Polyester D) A copolymer polyethylene terephthalate resin (intrinsic viscosity 0.80) in which terephthalic acid is present as the dicarboxylic acid component at a concentration of 90 mol%, 2,6-naphthalenedicarboxylic acid at a concentration of 10 mol%, and ethylene glycol at a concentration of 100 mol%.

[0105] (Formulation of easy-to-adhere resin P) The easily adhering resin layer to be laminated on the surface of the film was prepared as follows.

[0106] Resin solution (a): A solution obtained by mixing 70 parts by weight of a water-soluble coating solution of polyester resin consisting of acidic components such as terephthalic acid (88 mol%), 5-sodium sulfisoisophthalic acid (12 mol%), and diol components such as ethylene glycol (100 mol%), with 30 parts by weight of an aqueous dispersion of polyester resin consisting of acidic components such as terephthalic acid (50 mol%), isophthalic acid (49 mol%), and 5-sodium sulfisoisophthalic acid (1 mol%), and diol components such as ethylene glycol (55 mol%), neopentyl glycol (44 mol%), and polyethylene glycol (molecular weight: 4000) (1 mol%). Crosslinking agent (b): Methylol-based melamine crosslinking agent Crosslinking agent (c): Oxazoline group-containing crosslinking agent Particle (d): Aqueous dispersion of 150 nm diameter corodile silica particles. Particle (e): Aqueous dispersion of 300 nm diameter corodile silica particles. Fluorine-based surfactant (f): Megafac F-444 manufactured by DIC Corporation These are expressed by solid content weight ratio as (a) / (b) / (c) / (d) / (e) / (f) = 47 parts by weight. The mixture was prepared in the following proportions: 19 parts by weight, 20 parts by weight, 4.9 parts by weight, 0.7 parts by weight, and 0.1 parts by weight. The refractive index was 1.57.

[0107] (Examples 1-11, Comparative Examples 1-3) As shown in Table 1, the resin types were mixed in the quantities listed in Table 1 and fed into an extruder. The mixture was then melted at the extruder temperature listed in Table 1 and extruded in a sheet form from the T-die onto a cooling drum controlled to the temperature listed in Table 1. At this time, electrostatic discharge was applied using a wire electrode with a diameter of 0.1 mm to ensure close contact with the cooling drum and obtain an unstretched sheet. Subsequently, the sheet was rapidly cooled on a cooling roll controlled to 20°C, and then stretched longitudinally at the stretching temperature and stretching ratio listed in Tables 2 and 3, after which it was cooled. Next, corona discharge treatment was applied to both sides of this uniaxially oriented film to achieve a wetting tension of 55 mN / m. The easily adhesive resin P was then applied to both sides of the film, and then stretched in the width direction at the stretching temperature and stretching ratio listed in Tables 2 and 3. Finally, it was heat-treated in a tenter at the heat treatment temperature listed in Table 3 and relaxed in the width direction to obtain a film with the thickness listed in Table 1. The physical properties of the obtained film are shown in Tables 4 to 6, and the example showed excellent static flexibility.

[0108] Furthermore, using the film of the present invention, visibility was evaluated with the angle between the slow-motion axis direction and the long-side direction of the image sensor set to 90°, and good results were obtained.

[0109] On the other hand, Comparative Examples 1 to 3 were inferior in static flexibility because their F30m / F0m and refractive index were outside the scope of the present invention, and Comparative Example 3 also had inferior dynamic flexibility due to its birefringence exceeding 0.05.

[0110] [Table 1]

[0111] [Table 2]

[0112] [Table 3]

[0113] [Table 4]

[0114] [Table 5]

[0115] [Table 6] [Industrial applicability]

[0116] The polyester film for supporting the back side of a display light-emitting element of the present invention and the display using the film exhibit a small lifting angle when held at a predetermined bending radius for a predetermined time, and are particularly suitable for use as a back-side support film for displays that use organic electroluminescence as a light-emitting element. [Explanation of symbols]

[0117] a. Film (backplate) b Polarizing plate c. Camera-integrated device d camera e Shooting angle f surface light source g bending direction h Film center (bent section) i. The angle formed by the film sample (recovery angle) j display k: Screen area where the image sensor is located on the back of the image display surface. l Surplus screen area m image sensor n Image display device p slow axis direction q Image sensor r Long side direction of the image sensor s Image Circle t Rainbow pattern u polarizer v Image display light-emitting element

Claims

1. When the stress at 5% elongation is F0m (MPa) and the stress after maintaining the 5% elongation state for 30 minutes is F30m (MPa), F30m / F0m (stress relaxation degree), obtained by dividing F30m by F0m, is 0.5 or more and 1.0 or less in both the longitudinal direction and the width direction, and the refractive index in at least one of the longitudinal direction and the width direction is 1.625 or more and less than 1.

67.

2. 2. The polyester film for supporting the rear side of a display light-emitting element according to claim 1, wherein the dimensional change (CL30) when stress (F-5) in at least one direction is applied for 30 minutes is 0 mm or more and 60 mm or less.

3. 3. The polyester film for supporting the rear side of a display light-emitting element according to claim 1, wherein the flexural rigidity in at least one direction is 0.8 gr or more and 1.5 gr or less.

4. 3. The polyester film for supporting the rear side of a display light emitting element according to claim 1, wherein the acid component constituting the polyester is mainly terephthalic acid or 2,6-naphthalenedicarboxylic acid.

5. A display comprising the polyester film for supporting the rear side of a display light-emitting element according to claim 1 or 2.

6. 6. The display according to claim 5, wherein the display comprises a polarizer, a display light-emitting element, a polyester film for supporting the rear side of the display light-emitting element, and an imaging element, arranged in this order.

7. The display is a foldable image display device, and the slow axis direction of the polyester film for supporting the rear side of the display light-emitting element of the display and the bending direction of the display screen of the foldable image display device are perpendicular to each other.

8. The display described in claim 6, wherein the imaging element has an aspect ratio of 1.05 or more, and the angle between the long side direction of the imaging element and the slow axis direction of the polyester film for supporting the rear side of the display light-emitting element of the display is 45° or more and 90° or less.

9. 7. The display according to claim 6, further comprising an adhesive layer disposed between the display light emitting element and the polyester film for supporting the rear side of the display light emitting element.

10. 10. The display according to claim 9, wherein the adhesive layer is in contact with the polyester film for supporting the rear side of the display light-emitting element of the display via an easy-adhesion layer having a refractive index of 1.45 or more and 1.55 or less.

11. A method for producing a polyester film for supporting the rear side of a display light-emitting element, comprising carrying out at least the following steps (1) to (3) in this order: (1) A step of stretching the film in the longitudinal stretching direction by 2.9 times or more and 3.3 times or less (2) A step of stretching the film in the transverse stretching direction by 3.7 times or more and 4.5 times or less (3) A step of heat treating at 220°C or higher and 245°C or lower

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