Polyamide film, method for producing same, laminated film, and display

Abstract

The purpose of the present invention is to provide a polyamide film having improved bending resistance, a method for producing the same, and a laminated film and a display having the polyamide film. This polyamide film contains a semi-aromatic polyamide, has a refractive index in the longitudinal direction and / or the width direction of 1.600 or less, and has a difference between the refractive index in the longitudinal direction and the refractive index in the width direction of 0.030 or more.

Description

Polyamide film and its manufacturing method, laminated film, display

[0001] The present invention relates to a polyamide film that is suitably used as a surface protection film.

[0002] 2. Description of the Related Art Surface protective films are used to protect displays of mobile terminal devices and the like from scratches, impacts, and the like.

[0003] In recent years, mobile terminals incorporating flexible displays or foldable displays have been developed, and surface protection films for foldable displays have also been developed (see, for example, Patent Document 1).

[0004] JP 2023-061931 A

[0005] Surface protection films for foldable displays must be flex-resistant enough to withstand repeated bending, but conventional surface protection films have insufficient flex-resistance. Therefore, there has been a demand for the development of a surface protection film with excellent flex-resistance.

[0006] The present invention has been made in view of the above problems, and has as its object to provide a polyamide film with improved flex resistance, a method for producing the same, and a laminate film and a display that include the polyamide film.

[0007] The present invention provides the following aspects. <1> A polyamide film containing a semi-aromatic polyamide, wherein the polyamide film has a refractive index in the longitudinal direction and / or width direction of 1.600 or less and a difference between the refractive index in the longitudinal direction and the width direction of 0.030 or more. <2> The polyamide film according to <1>, wherein the polyamide film has a 0.2% yield strain in the longitudinal direction and / or width direction of 2.30% or more. <3> The polyamide film according to <1> or <2>, wherein the polyamide film has a haze of 1.0% or less. <4> The polyamide film according to any one of <1> to <3>, wherein the polyamide film has a total light transmittance of 85.0% or more. <5> The polyamide film according to any one of <1> to <4>, wherein the polyamide film has a thickness of 100 μm or less. <6> A laminate film comprising the polyamide film according to any one of <1> to <5> and a hard coat layer laminated together. <7> A display having the polyamide film according to any one of <1> to <5>. <8> A display having the laminate film according to <6>, wherein the laminate film is disposed with the hard coat layer facing outward. <9> A method for producing a polyamide film according to any one of <1> to <5>, comprising a stretching step of uniaxially stretching an unstretched film containing a semi-aromatic polyamide in the longitudinal direction or width direction at a stretching ratio of 1.5 to 4.0. <10> A method for producing a polyamide film according to <9>, wherein neither a heat setting treatment nor a relaxation treatment is performed after the stretching step. <11> A method for producing a polyamide film according to <9> or <10>, wherein the unstretched film has a heat of crystallization of 20 J / g or more.

[0008] The polyamide film of the present invention has excellent flex resistance and is resistant to deformation even when repeatedly folded, for example, 250,000 times or more, so that when used as a surface protection film for a folding display, image distortion at the folded portion can be effectively suppressed. Furthermore, the polyamide film of the present invention has excellent transparency, so that it is suitable for use as a surface protection film for a display.

[0009] 1. Polyamide Film The polyamide film of the present invention contains a semi-aromatic polyamide, has a refractive index of 1.600 or less in the longitudinal direction and / or the width direction, and has a difference between the refractive index in the longitudinal direction and the refractive index in the width direction of 0.030 or more. The polyamide film of the present invention is described in detail below.

[0010] <Semi-aromatic Polyamide> The semi-aromatic polyamide constituting the polyamide film of the present invention is composed of at least an aromatic dicarboxylic acid component and an aliphatic diamine component.

[0011] The aromatic dicarboxylic acid component is not particularly limited, and examples thereof include terephthalic acid, isophthalic acid, and naphthalenedicarboxylic acid (1,2-isomer, 1,3-isomer, 1,4-isomer, 1,5-isomer, 1,6-isomer, 1,7-isomer, 1,8-isomer, 2,3-isomer, 2,6-isomer, and 2,7-isomer). These may be used alone or in combination of two or more kinds. Of these, terephthalic acid is preferred.

[0012] From the viewpoint of improving the heat resistance and reducing the water absorption of the polyamide film, the aromatic dicarboxylic acid component preferably contains 60 mol% or more of terephthalic acid, more preferably 70 mol% or more, even more preferably 85 mol% or more, even more preferably 90 mol% or more, and particularly preferably 100 mol%.

[0013] The semi-aromatic polyamide may contain other dicarboxylic acid components in addition to the aromatic dicarboxylic acid components as long as the effects of the present invention are not impaired, but it is preferable that the semi-aromatic polyamide does not contain other dicarboxylic acid components. Examples of other dicarboxylic acids include aliphatic dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, dodecanedioic acid, tetradecanedioic acid, and octadecanedioic acid. These may be used alone or in combination of two or more.

[0014] The aliphatic diamine component is not particularly limited, but preferably contains as the main component an aliphatic diamine having 6 to 12 carbon atoms, more preferably contains as the main component an aliphatic diamine having 9 to 12 carbon atoms, and even more preferably contains as the main component an aliphatic diamine having 9 or 10 carbon atoms. Incidentally, "containing as the main component" means containing 50 mol % or more.

[0015] From the viewpoint of achieving both heat resistance and productivity of the polyamide film, the content of the aliphatic diamine having 6 to 12 carbon atoms in the aliphatic diamine component is preferably 60 mol% or more, more preferably 75 mol% or more, even more preferably 90 mol% or more, and particularly preferably 100 mol%. The aliphatic diamine having 6 to 12 carbon atoms may be used alone or in combination of two or more. When two or more types are used in combination, the content is the total amount thereof.

[0016] Examples of the aliphatic diamine having 6 to 12 carbon atoms include linear aliphatic diamines such as 1,6-hexanediamine, 1,7-heptanediamine, 1,8-octanediamine, 1,9-nonanediamine, 1,10-decanediamine, 1,11-undecanediamine, and 1,12-dodecanediamine; and branched aliphatic diamines such as 2-methyl-1,8-octanediamine, 4-methyl-1,8-octanediamine, 5-methyl-1,9-nonanediamine, 2,2,4- / 2,4,4-trimethyl-1,6-hexanediamine, 2-methyl-1,5-pentanediamine, 2-methyl-1,6-hexanediamine, and 2-methyl-1,7-heptanediamine.

[0017] Examples of the aliphatic diamine other than the aliphatic diamine having 6 to 12 carbon atoms include linear aliphatic diamines such as 1,4-butanediamine and 1,5-pentanediamine.

[0018] The semi-aromatic polyamide may contain other diamine components besides the aliphatic diamine components as long as the effects of the present invention are not impaired, but it is preferable that the semi-aromatic polyamide does not contain other diamine components. Examples of other diamine components include alicyclic diamines such as isophorone diamine, norbornane dimethylamine, and tricyclodecane dimethylamine; and aromatic diamines such as meta-xylylene diamine, para-xylylene diamine, meta-phenylene diamine, and para-phenylene diamine. These may be used alone or in combination of two or more.

[0019] The semi-aromatic polyamide may be copolymerized with one or more lactams such as ε-caprolactam, ζ-enantholactam, η-capryllactam, and ω-laurolactam, within the range that does not impair the effects of the present invention.

[0020] The types and copolymerization ratios of the monomers constituting the semi-aromatic polyamide are preferably selected so that the melting point (Tm) of the resulting semi-aromatic polyamide is in the range of 270 to 350°C and the glass transition temperature (Tg) is in the range of 100 to 135°C. Tm is more preferably 280 to 330°C, and even more preferably 280 to 310°C. Tg is more preferably 110 to 130°C, and even more preferably 120 to 125°C. When the Tm and Tg are in the above ranges, the semi-aromatic polyamide has sufficient heat resistance and can effectively suppress thermal decomposition when processed into a film.

[0021] The semi-aromatic polyamide may contain an end-capping agent and a polymerization catalyst. Examples of the end-capping agent include acetic acid, lauric acid, benzoic acid, octylamine, cyclohexylamine, and aniline. Examples of the polymerization catalyst include phosphoric acid, phosphorous acid, hypophosphorous acid, and salts thereof.

[0022] The intrinsic viscosity of the semi-aromatic polyamide is not particularly limited, but from the viewpoint of efficiently producing a polyamide film having excellent mechanical strength, it is preferably 0.8 to 2.0 dL / g, more preferably 0.9 to 1.8 dL / g, even more preferably 1.0 to 1.5 dL / g, and even more preferably 1.0 to 1.3 dL / g.

[0023] <Method of Manufacturing Semi-Aromatic Polyamides> Semi-aromatic polyamides can be produced using methods known for producing crystalline polyamides. Examples include solution polymerization or interfacial polymerization (Method A) using an acid chloride and a diamine component as raw materials; a method (Method B) using a dicarboxylic acid component and a diamine component as raw materials to obtain a low-molecular-weight polymer and then polymerizing the resulting low-molecular-weight polymer by melt polymerization or solid-state polymerization; a method (Method C) using a dicarboxylic acid component and a diamine component as raw materials to obtain a crushed mixture of salt and low-molecular-weight polymer and then solid-state polymerizing the resulting crushed mixture; and a method (Method D) using a dicarboxylic acid component and a diamine component as raw materials to obtain a salt and then solid-state polymerizing the resulting salt. Of these methods, Methods C and D are preferred, with Method D being more preferred. Compared to Method B, Methods C and D can produce a crushed mixture of salt and low-molecular-weight polymer or a salt at a lower temperature and do not require a large amount of water during production of the crushed mixture of salt and low-molecular-weight polymer or the salt. This reduces the occurrence of gel-like bodies and reduces fisheyes.

[0024] In Method B, for example, a nylon salt prepared by mixing a diamine component, a dicarboxylic acid component, and a polymerization catalyst all at once is thermally polymerized at 200 to 250°C to obtain a low polymer. The intrinsic viscosity of the low polymer is preferably 0.1 to 0.6 dL / g. By setting the intrinsic viscosity of the low polymer within this range, the molar balance between the carboxyl groups in the dicarboxylic acid component and the amino groups in the diamine component is not disrupted during subsequent melt polymerization or solid-state polymerization, and the polymerization rate can be increased. If the intrinsic viscosity of the low polymer is less than 0.1 dL / g, the polymerization time may be prolonged, resulting in poor productivity. On the other hand, if the intrinsic viscosity of the low polymer exceeds 0.6 dL / g, the resulting semi-aromatic polyamide may become discolored.

[0025] The solid-state polymerization of the oligomer is preferably carried out under reduced pressure or in an inert gas flow. The temperature of the solid-state polymerization is preferably 200 to 280°C. By setting the temperature of the solid-state polymerization within the above range, discoloration and gelation of the resulting semi-aromatic polyamide can be suppressed. If the temperature of the solid-state polymerization is less than 200°C, the polymerization time becomes long, which may result in poor productivity. On the other hand, if the temperature of the solid-state polymerization exceeds 280°C, the resulting semi-aromatic polyamide may become discolored or gel.

[0026] The melt polymerization of the oligomer is preferably carried out at 350°C or less. If the polymerization temperature exceeds 350°C, decomposition or thermal degradation of the semi-aromatic polyamide may be accelerated. Therefore, the polyamide film obtained from such a semi-aromatic polyamide may be inferior in strength and appearance. The melt polymerization also includes melt polymerization using a melt extruder.

[0027] In Method C, for example, a suspension containing a molten aliphatic diamine component and a solid aromatic dicarboxylic acid component is stirred and mixed to obtain a mixture. Then, in this mixture, a salt-forming reaction between the aromatic dicarboxylic acid component and the aliphatic diamine component and a oligomer-forming reaction between the resulting salt and the resulting oligomer are carried out at a temperature below the melting point of the semi-aromatic polyamide to be ultimately produced, thereby obtaining a mixture of the salt and the oligomer. In this case, crushing may be carried out during the reaction, or the reaction may be carried out after the reaction and then removed and crushed. The resulting reaction product is then solid-phase polymerized at a temperature below the melting point of the semi-aromatic polyamide to obtain a predetermined molecular weight, thereby obtaining a semi-aromatic polyamide. Solid-phase polymerization is preferably carried out in a stream of inert gas such as nitrogen, at a polymerization temperature of 180 to 270°C and a reaction time of 0.5 to 10 hours.

[0028] In Method D, for example, a powder of an aromatic dicarboxylic acid component is preheated to a temperature above the melting point of the aliphatic diamine component and below the melting point of the aromatic dicarboxylic acid. The aliphatic diamine component is then added to the aromatic dicarboxylic acid component powder at this temperature, while maintaining the powder state, without substantially containing water, to obtain a salt. The resulting salt is then solid-state polymerized at a temperature below the melting point of the semi-aromatic polyamide to obtain a semi-aromatic polyamide, resulting in a high molecular weight to a predetermined molecular weight. The solid-state polymerization is preferably carried out in a stream of an inert gas such as nitrogen, at a polymerization temperature of 180 to 270°C for a reaction time of 0.5 to 10 hours.

[0029] The semi-aromatic polyamide may be a virgin semi-aromatic polyamide, or may be a mixture of scraps such as off-spec films or edge trimmings obtained during the production of semi-aromatic polyamide films, or may be prepared by adding virgin semi-aromatic polyamide to the scrap mixture. These may be mixed by known methods such as dry blending using a known device or melt-kneading using a single-screw or twin-screw extruder.

[0030] Commercially available semi-aromatic polyamides may be used, such as "Genesta (registered trademark)" manufactured by Kuraray Co., Ltd., "Zecot (registered trademark)" manufactured by Unitika Ltd., "Reny (registered trademark)" manufactured by Mitsubishi Engineering-Plastics Corporation, "Arlen (registered trademark)" manufactured by Mitsui Chemicals, Inc., and "Ultramid (registered trademark)" manufactured by BASF.

[0031] <Characteristics of Polyamide Film> The polyamide film of the present invention has a refractive index in the longitudinal direction (machine flow direction, hereinafter also referred to as "MD direction") and / or width direction (direction perpendicular to the longitudinal direction, hereinafter also referred to as "TD direction") of 1.600 or less, preferably 1.580 or less, more preferably 1.570 or less. The lower limit of the refractive index is not particularly limited, but is, for example, 1.500 or more. Furthermore, the polyamide film of the present invention has a refractive index in one of the MD direction and the TD direction within the above range, and the refractive index in the other direction is preferably more than 1.600, more preferably 1.610 or more. The upper limit of the other refractive index is not particularly limited, but is, for example, 1.700 or less.

[0032] When the refractive index in the MD direction and / or TD direction is 1.600 or less, the semi-aromatic polyamide is highly oriented in the plane direction, so that deformation when the polyamide film is repeatedly folded is reduced, cracks are less likely to occur, and breakage does not occur, so that the visibility of the display can be maintained good.

[0033] The polyamide film of the present invention has a difference between the refractive index in the MD direction and the refractive index in the TD direction of 0.030 or more, preferably 0.035 or more, more preferably 0.040 or more, even more preferably 0.045 or more, and particularly preferably 0.050 or more. The upper limit of the refractive index difference is not particularly limited, but is, for example, 0.500 or less.

[0034] When the difference between the refractive index in the MD direction and the refractive index in the TD direction is 0.030 or more, the semi-aromatic polyamide is highly oriented in one axial direction, so that deformation when the polyamide film is repeatedly folded is reduced and cracks are less likely to occur.

[0035] From the viewpoint of further improving flex resistance, the polyamide film of the present invention preferably has a 0.2% proof strain in the MD direction and / or TD direction of 2.30% or more, more preferably 2.40% or more, and even more preferably 2.50% or more. The upper limit of the 0.2% proof strain is not particularly limited, but is, for example, 3.50% or less. The 0.2% proof strain is a value used as a substitute for the yield point, regardless of whether a yield point appears or does not appear in the stress-strain curve, and is used as an indicator of the elastic region. In the present invention, the 0.2% proof strain is a value calculated by obtaining a stress-strain curve using a tensile tester and setting the strain to 0.2% using autograph software.

[0036] From the viewpoint of the transparency and visibility required for a surface protection film for a display, the polyamide film of the present invention preferably has a haze of 1.0% or less, more preferably 0.5% or less, even more preferably 0.3% or less, and still more preferably 0.2% or less. In the present invention, the haze is a value measured in accordance with JIS K7136:2000 (Method of determining haze of plastic transparent materials).

[0037] From the viewpoint of the visibility required for a surface protection film for a display, the polyamide film of the present invention preferably has a total light transmittance of 85.0% or more, more preferably 90.0% or more. In the present invention, the total light transmittance is a value measured in accordance with JIS K 7361-1:1997 (Plastics - Test methods for total light transmittance of transparent materials - Part 1: Single beam method).

[0038] The thickness of the polyamide film of the present invention is not particularly limited, but from the viewpoint of preventing the folding marks caused by repeated folding at the part corresponding to the folding portion from being easily left, it is preferably 100 μm or less, more preferably 75 μm or less, and even more preferably 50 μm or less.

[0039] 2. Method for Producing Polyamide Film The method for producing the polyamide film of the present invention is not particularly limited, but the polyamide film of the present invention having the above-described characteristics can be obtained, for example, by adjusting the crystalline state of the unstretched film and the stretching conditions.

[0040] The polyamide film of the present invention can be produced, for example, by uniaxially stretching an unstretched film containing a semi-aromatic polyamide in the MD or TD direction at a stretching ratio of 1.5 to 4.0 times.

[0041] The unstretched film contains at least a semi-aromatic polyamide. To improve the film's properties, the unstretched film may optionally contain additives such as lubricants, colorants such as pigments and dyes (e.g., titanium dioxide), color inhibitors, heat stabilizers, hindered phenols, antioxidants such as phosphates and phosphites, weather resistance improvers such as benzotriazole compounds, bromine-based and phosphorus-based flame retardants, plasticizers, release agents, reinforcing agents such as talc, modifiers, antistatic agents, UV absorbers, antifogging agents, and various resins. These additives may be used alone or in combination. A resin layer containing the additives may also be laminated onto the unstretched or stretched film.

[0042] The resin constituting the resin layer is not particularly limited, and various resins can be used. Examples of the resin include polyamide-based resins, polyester-based resins, polyurethane-based resins, acrylic-based resins, and epoxy-based resins. Among these, polyamide-based resins, polyester-based resins, polyurethane-based resins, and acrylic-based resins are preferred from the viewpoint of excellent adhesion to the hard coat layer.

[0043] Examples of lubricants that improve the sliding properties include inorganic particles such as silica, alumina, titanium dioxide, calcium carbonate, kaolin, and barium sulfate, and organic particles such as acrylic resin particles, melamine resin particles, silicone resin particles, and cross-linked polystyrene particles. The average particle size of the lubricant is preferably 0.03 to 5.0 μm.

[0044] The content of the lubricant can be adjusted as appropriate depending on the frictional properties, optical properties, and other required properties of the polyamide film, but in order to keep the haze of the polyamide film at 1.0% or less, if the polyamide film is a single layer, it is preferable to set it at 0.2 mass% or less.

[0045] When the polyamide film of the present invention is a multilayer film formed by laminating multiple films, it is preferable to control the content of lubricant in the entire multilayer film. For example, a multilayer film may be obtained by laminating a thin film containing a high concentration of lubricant with a film containing no lubricant.

[0046] Various methods can be used to incorporate the additives into the unstretched film. Representative methods include the following: (A) A method of adding the additives during polymerization of the semi-aromatic polyamide; (B) A masterbatch method of adding the additives directly to the semi-aromatic polyamide and preparing melt-kneaded pellets; (C) A method of adding the additives directly to the semi-aromatic polyamide during film formation and melt-kneading in an extruder; and (D) A method of adding the additives directly to the extruder during film formation and melt-kneading.

[0047] Examples of methods for laminating a resin layer containing the additive onto a film containing a semi-aromatic polyamide include, but are not limited to, a method of applying a solution or aqueous dispersion of various solvents that form the resin layer onto a film containing a semi-aromatic polyamide, a method of heat-melting a composition that forms the resin layer and extrusion-coating it onto a film containing a semi-aromatic polyamide, and a method of forming a resin layer on the outermost layer when extruding a film containing a semi-aromatic polyamide into multiple layers.

[0048] The unstretched film preferably has a crystallization heat of 20 J / g or more, more preferably 25 J / g or more. If the crystallization heat of the unstretched film is less than 20 J / g, crystallization will progress, causing frequent breakage and making it impossible to stretch, and a higher stretching force will be required at the beginning of stretching, making it difficult to obtain a stretched film with a uniform thickness. Even if a stretched film is obtained, the haze may be high and the transparency may be poor. The upper limit of the crystallization heat is not particularly limited, but is, for example, 30 J / g or less.

[0049] An unstretched film having a heat of crystallization of 20 J / g or more can be produced, for example, by melt-mixing a semi-aromatic polyamide in an extruder at a temperature of 280 to 340° C., extruding the resulting polyamide into a sheet using a mold such as a T-die, and then cooling the sheet by placing it in close contact with a cooling body (e.g., a roll) whose temperature is adjusted to 20 to 40° C. If the temperature of the cooling body exceeds 40° C., the resulting unstretched film is likely to have a heat of crystallization of less than 20 J / g, making it more likely to experience the above-mentioned problems after stretching.

[0050] The unstretched film is then stretched, and the semi-aromatic polyamide is highly oriented by the stretching. The stretching method is not particularly limited, and examples thereof include a roll stretching method, a tenter stretching method, and a tubular method.

[0051] The stretching is preferably uniaxially stretched in the MD or TD direction. The uniaxial stretching direction is preferably the direction in which the polyamide film is repeatedly folded. By uniaxially stretching in this direction, the semi-aromatic polyamide is highly oriented in the stretching direction, and the polyamide film of the present invention having the above-mentioned characteristics is obtained.

[0052] In the case of uniaxial stretching, the stretching ratio is preferably 1.5 to 4.0 times, more preferably 2.0 to 4.0 times, and even more preferably 2.4 to 3.8 times, from the viewpoint of facilitating the production of the polyamide film of the present invention having the above-mentioned characteristics.

[0053] The stretching may be biaxial in both the MD and TD directions, but in the case of biaxial stretching, in order to obtain the polyamide film of the present invention having the above-mentioned characteristics, it is necessary to adjust the stretching ratio in one direction to 1.2 or less, and the stretching ratio in the other direction is preferably 1.5 to 4.0, more preferably 2.0 to 4.0, and even more preferably 2.4 to 3.8.

[0054] The stretching temperature is preferably within ±20°C of the glass transition temperature (Tg) of the semi-aromatic polyamide, more preferably within ±10°C of Tg, from the viewpoint of suppressing film breakage and stably producing a polyamide film, and from the viewpoint of suppressing uneven stretching and highly orienting the semi-aromatic polyamide in the stretching direction.

[0055] After the stretching step, a heat setting treatment may be performed. However, since the heat setting treatment may relax the orientation of the semi-aromatic polyamide, it is preferable not to perform the heat setting treatment. The heat setting temperature is preferably 250°C or less, more preferably 200°C or less, and even more preferably Tg or less. The heat setting time is not particularly limited, but is, for example, 20 to 120 seconds.

[0056] Examples of the heat setting method include known methods such as a method of blowing hot air, a method of irradiating infrared rays, and a method of irradiating microwaves.

[0057] After the heat setting, a relaxation treatment may be carried out. However, since the relaxation treatment may relax the orientation of the semi-aromatic polyamide and reduce the 0.2% yield strain, it is preferable not to carry out the relaxation treatment. The relaxation rate when carrying out the relaxation treatment is, for example, 2% or less.

[0058] The obtained polyamide film may be in the form of a sheet or may be wound on a winding roll to form a film roll. From the viewpoint of productivity when used for various applications, the film roll is preferable. When forming a film roll, the film may be slit to a desired width.

[0059] The polyamide film may be a single-layer film consisting of one type of layer, or may have a multilayer structure consisting of two or more layers laminated together. In the case of a multilayer structure, for example, a two-layer film preferably contains a lubricant in any one layer, and a three-layer film preferably contains a lubricant in each of the layers located on both surfaces. The type and content of the lubricant to be contained can be independently designed. By using such a multilayer structure, the surface roughness of each side of the polyamide film can be independently controlled.

[0060] The surface of the polyamide film may be subjected to corona treatment, plasma treatment, acid treatment, flame treatment, or the like in order to improve adhesion to other materials.

[0061] 3. Laminated Film The laminated film of the present invention is obtained by laminating the polyamide film of the present invention and a hard coat layer.

[0062] Examples of resins that form the hard coat layer include acrylic resins, siloxane resins, inorganic hybrid resins, urethane acrylate resins, polyester acrylate resins, and epoxy resins. These may be used alone or in combination of two or more. The hard coat layer may also contain particles such as inorganic fillers and organic fillers.

[0063] The thickness of the hard coat layer is not particularly limited, but from the viewpoint of surface protection function, suppression of curling, and improvement of film handling properties, it is preferably 1 to 50 μm, more preferably 1 to 40 μm, and even more preferably 3 to 20 μm.

[0064] The hard coat layer can be formed, for example, by applying a resin composition for forming the hard coat layer using a coating machine such as a Mayer bar, a gravure coater, a die coater, or a knife coater, and then curing the applied resin composition by irradiating it with energy rays such as ultraviolet rays and electron beams, or by heating.

[0065] 4. Display A display is, for example, a display device in a mobile terminal device, and specific examples include LCDs, organic EL displays, inorganic EL displays, LEDs, and FEDs. An organic EL display may be, for example, one that includes an organic EL layer consisting 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. The mobile terminal device may also have a touch panel.

[0066] The display of the present invention has the polyamide film or laminate film of the present invention. When the display of the present invention has the laminate film of the present invention, the hard coat layer of the laminate film is disposed on the outside.

[0067] The display of the present invention is preferably a flexible display or a foldable display, more preferably a foldable display. A foldable display is a single continuous display that can be folded into two or more parts. The polyamide film or laminate film of the present invention may be provided on the outside or inside of the folded part of the foldable display.

[0068] The display of the present invention has the polyamide film of the present invention, which has excellent flex resistance, and therefore, even when repeatedly folded, for example, 250,000 times or more, or even 300,000 times or more, image distortion is unlikely to occur at the folded portion.

[0069] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0070] 1. Evaluation Method (1) Intrinsic Viscosity The intrinsic viscosity (ηinh) of the resin in concentrated sulfuric acid at 30°C at concentrations of 0.05, 0.1, 0.2, and 0.4 g / dL was calculated using the following formula, and the value extrapolated to a concentration of 0 was taken as the intrinsic viscosity [η]: ηinh = [ln(t1 / t0)] / c (where ηinh is the intrinsic viscosity (dL / g), t0 is the flow time of the solvent (seconds), t1 is the flow time of the resin solution (seconds), and c is the concentration of the resin in the solution (g / dL).)

[0071] (2) Melting point, glass transition temperature, crystallization heat quantity Using a differential scanning calorimeter (PerkinElmer, DSC-7), the prepared film was heated from 20 ° C. to 350 ° C. at 10 ° C. / min under a nitrogen atmosphere and held for 5 minutes (1st scan), then cooled from 350 ° C. to 20 ° C. at 100 ° C. / min and held for 5 minutes. Further, the glass transition temperature in the process of reheating from 20 ° C. to 350 ° C. at 10 ° C. / min (2nd scan) was taken as Tg, and the peak top temperature of the crystalline melting peak was taken as the melting point Tm. Similarly, the integrated value of the temperature-rising crystallization peak observed in the 2nd scan was taken as the heat of crystallization.

[0072] (3) Refractive Index Using an Abbe refractometer manufactured by Atago Co., Ltd., a polarizing plate analyzer was attached to the eyepiece side, and the refractive index of the film in the MD and TD directions was measured at a temperature of 23°C using monochromatic NaD light as the light source and methylene iodide as the mounting liquid. The sample used for the measurement was taken from the center of the entire width of the prepared film. When measuring the refractive index in the MD direction, a strip measuring 40 mm in the MD direction and 8.0 mm in the TD direction was taken, and when measuring the refractive index in the TD direction, a strip measuring 40 mm in the TD direction and 8.0 mm in the MD direction was taken. The average value of n = 5 measurements was taken as the refractive index.

[0073] (4) 0.2% Proof Strain The prepared film was conditioned for 1 day at a temperature of 23 ° C. and a humidity of 50% RH, after which test pieces (10 mm wide x 100 mm long) were cut out and subjected to a tensile test at a tensile speed of 100 mm / min using a tensile tester (Shimadzu Corporation, AUTOGRAPH AG-X Plus). From the obtained stress-strain curve, using Shimadzu Corporation's autograph software TRAPEZIUM X, the strain at the intersection of the stress-strain curve and a parallel line obtained by translating the approximation line with a slope of 0.2 to 0.5% in the stress-strain curve so that it passes through a strain of 0.2% was calculated as the 0.2% proof strain.

[0074] (5) Haze and Total Light Transmittance According to JIS K7136:2000 (Method for determining the haze of plastic transparent materials), the haze of the prepared film was measured using a haze meter (NDH 2000) manufactured by Nippon Denshoku Co., Ltd. Furthermore, according to JIS K 7361-1:1997 (Test method for total light transmittance of plastic transparent materials - Part 1: Single beam method), the total light transmittance of the prepared film was measured using the haze meter.

[0075] (6) Flexibility of Film The prepared film was cut into a 30 x 100 mm rectangle to prepare a sample. The short sides of the sample were fixed to a durability tester (Yuasa System Co., Ltd., DLDMLH-FS) so that the minimum distance between the two opposing sides was 1.5 mm. The sample was then bent 300,000 times under the conditions of a bending radius of 1.0 mm, a bending angle of 0 to 180°, and a test speed of 60 times / min. The bent portion was visually inspected for cracks, breaks, creases, and whitening, and the flexibility was evaluated according to the following criteria. Note that, for practical purposes, evaluation criteria A or B are required, with evaluation criteria A being particularly preferred. [Evaluation Criteria] A: After 300,000 flexes, there were no cracks or breaks in the bent portion, and no creases or whitening occurred. B: After 300,000 flexes, there were no cracks or breaks in the bent portion, and creases remained but no whitening occurred. C: After 200,000 bending cycles, there was no cracking or breakage at the bent portion, and no crease marks or whitening occurred. However, after 300,000 bending cycles, there was no cracking or breakage at the bent portion, but crease marks remained and whitening occurred. D: After 200,000 bending cycles, there was no cracking or breakage at the bent portion, but crease marks remained and whitening occurred. E: After 200,000 bending cycles, there was cracking or breakage at the bent portion, and crease marks remained and whitening occurred.

[0076] 2. Raw Materials (1) Resin Semi-Aromatic Polyamide The semi-aromatic polyamide obtained in the following Production Example was used. Production Example Terephthalic acid (TA), 1,9-nonanediamine (NDA), 2-methyl-1,8-octanediamine (MODA), and benzoic acid (BA) (TA / BA / NDA / MODA = 99 / 2 / 80 / 20 (molar ratio)) were placed in a reactor, and sodium hypophosphite monohydrate (0.1% by mass based on the total amount of the polyamide raw materials) and distilled water were then placed in the reactor, followed by nitrogen substitution. The contents of the reactor were stirred at 100°C for 30 minutes, and then the internal temperature was raised to 210°C over 2 hours. At this time, the inside of the reactor was pressurized to 2.12 MPa (22 kg / cm). 2 The reaction was continued for 1 hour, and then the temperature was raised to 230°C. The temperature was then maintained at 230°C for 2 hours, and the steam was gradually released to reduce the pressure to 2.12 MPa (22 kg / cm). 2 The reaction was carried out while maintaining the pressure at 0.98 MPa (10 kg / cm) over 30 minutes. 2 ), and reacted for another hour to obtain a prepolymer. The prepolymer was dried at 100°C under reduced pressure for 12 hours and then pulverized to a size of 2 mm or less. The pulverized prepolymer was then subjected to solid-state polymerization at a temperature of 230°C and a pressure of 13.3 Pa (0.1 mmHg) for 10 hours to obtain a polymer. The polymer was fed to a twin-screw extruder (TEX44C, manufactured by The Japan Steel Works, Ltd.), melt-kneaded and extruded at a cylinder temperature of 320°C, cooled, and cut to produce pellets of semi-aromatic polyamide.

[0077] The melting points, glass transition temperatures, and intrinsic viscosities of the produced semi-aromatic polyamides and the polyethylene terephthalate used in Comparative Example 4 are shown in Table 1.

[0078]

[0079] (2) Microparticles Master chips containing 2% by mass of silica were prepared by the following method: 98 parts by mass of the semi-aromatic polyamide and 2 parts by mass of silica particles (Fuji Silysia Chemical Ltd., Sylysia 310P, average particle size 2.7 μm) were melt-kneaded to prepare master chips containing 2% by mass of silica particles.

[0080] (3) Hindered phenol-based heat stabilizer GA: 3,9-bis[2-{3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy}-1,1-dimethylethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane (Sumitomo Chemical Co., Ltd., Sumilizer GA-80, thermal decomposition temperature 392°C) was used.

[0081] Example 1: Semi-aromatic polyamide and GA were mixed so that GA was 0.2 parts by mass per 100 parts by mass of semi-aromatic polyamide. This mixture was melt-mixed in an extruder at a temperature of 320 ° C., extruded into a sheet from a T-die set at 320 ° C., and cooled by electrostatically adhering it to a cooling roll set at a surface temperature of 40 ° C. to obtain a 190 μm thick unoriented unstretched film. The obtained unstretched film was cut into a 12 × 12 cm square and set in a batch-type biaxial stretching machine (KARO IV, manufactured by Bruckner Maschinenbau) and uniaxially stretched (TD direction) to obtain a 50 μm thick polyamide film. The stretching conditions were a preheating and stretching temperature of 115 ° C. and a stretch ratio of 3.4 times. The TD direction is the direction perpendicular to the flow direction (MD direction) during the production of the unstretched film.

[0082] Example 2 A polyamide film was obtained in the same manner as in Example 1, except that the stretching ratio was changed to 2.4 times.

[0083] Example 3 An unstretched film produced in the same manner as in Example 1 was uniaxially stretched (in the MD direction) by 2.4 times using longitudinal stretching rolls heated to 115°C to obtain a polyamide film having a thickness of 50 µm.

[0084] Examples 4, 5, 8, 9 and 13 Polyamide films were obtained in the same manner as in Example 3, except that the stretching ratio, stretching temperature and film thickness were changed to those shown in Table 2.

[0085] Example 6: An unstretched film produced in the same manner as in Example 1 was stretched 2.4 times (MD direction) using longitudinal stretching rolls heated to 115°C to obtain a film. The obtained film was cut into a 12 x 12 cm square and set in a batch-type biaxial stretching machine (KARO IV, manufactured by Bruckner Maschinenbau) and stretched in the TD direction to obtain a polyamide film with a thickness of 50 μm. The TD stretching conditions were a preheating and stretching temperature of 115°C and a stretch ratio of 1.1 times.

[0086] Example 7 A polyamide film was obtained in the same manner as in Example 6, except that the stretching ratio in the TD direction was changed to 1.2 times.

[0087] Example 10 A polyamide film produced in the same manner as in Example 5 was further heat-treated at 250°C for 50 seconds to obtain a uniaxially stretched and heat-set polyamide film.

[0088] Example 11 A polyamide film was obtained in the same manner as in Example 1, except that the semi-aromatic polyamide, GA, and master chips were mixed so that the amount of GA was 0.2 part by mass and the amount of silica was 0.1 part by mass per 100 parts by mass of the semi-aromatic polyamide.

[0089] Example 12 A polyamide film produced in the same manner as in Example 11 was further heat-treated at 250°C for 50 seconds to obtain a uniaxially stretched and heat-set polyamide film.

[0090] Comparative Example 1 A polyamide film was obtained in the same manner as in Example 6, except that the stretching ratio was changed to that shown in Table 3.

[0091] Comparative Example 2 An unstretched film produced in the same manner as in Example 1 was stretched 2.5 times (MD direction) using longitudinal stretching rolls heated to 115 ° C to obtain a film. The obtained film was cut into a 12 × 12 cm square and set in a batch-type biaxial stretching machine (KARO IV, manufactured by Bruckner Maschinenbau) and stretched in the TD direction. The stretching conditions in the TD direction were a preheating and stretching temperature of 115 ° C and a stretch ratio of 3.4 times. After stretching, the film was heat-set at 275 ° C for 10 seconds, and then relaxed at a relaxation rate of 3.0% in the MD direction and 2.2% in the TD direction to obtain a polyamide film with a thickness of 50 μm.

[0092] Comparative Example 3: An unstretched film produced in the same manner as in Example 1 was cut into 12 x 12 cm squares and placed in a batch-type biaxial stretching machine (KARO IV, manufactured by Bruckner Maschinenbau) for simultaneous biaxial stretching. The stretching conditions were a preheating and stretching temperature of 115°C, a stretch ratio of 3.0 in the MD direction, and a stretch ratio of 3.3 in the TD direction. After stretching, the film was heat-set at 275°C for 10 seconds, and then relaxed at a relaxation rate of 1.0% in the MD direction and 8.0% in the TD direction to obtain a polyamide film with a thickness of 25 μm.

[0093] Comparative Example 4 Polyethylene terephthalate pellets were extruded into a sheet from a T-die set at 280°C, and cooled by electrostatically contacting it with a cooling roll set at a surface temperature of 40°C, to obtain a non-oriented unstretched film with a thickness of 180 µm. The obtained unstretched film was stretched 3.3 times (MD direction) with a longitudinal stretching roll heated to 80°C, to obtain a polyester film with a thickness of 50 µm.

[0094] Comparative Example 5 An attempt was made to produce a polyamide film in the same manner as in Example 1, except that the stretching ratio was changed to 4.2 times. However, because the stretching ratio was too high, the film broke, and it was not possible to produce a polyamide film.

[0095] Tables 2 and 3 show the composition of the pellets used, the film production conditions, and the properties of the obtained film.

[0096]

[0097]

[0098] The polyamide films of Examples 1 to 6 and 9 were particularly excellent in flex resistance and transparency, and also had very good visibility. The polyamide films of Examples 7, 8, 10 and 13 were excellent in flex resistance and transparency, and also had good visibility. The polyamide films of Examples 11 and 12 were excellent in flex resistance.

[0099] On the other hand, the polyamide films of Comparative Examples 1 to 3 were stretched under inappropriate conditions, resulting in a small difference between the refractive index in the MD direction and the refractive index in the TD direction, and thus had poor flex resistance. The polyester film of Comparative Example 4, which was made of polyethylene terephthalate, also had poor flex resistance.

Claims

1. A polyamide film containing a semi-aromatic polyamide, wherein the polyamide film has a refractive index in the longitudinal direction and / or width direction of 1.600 or less, and the difference between the refractive index in the longitudinal direction and the refractive index in the width direction is 0.030 or more.

2. The polyamide film according to claim 1, wherein the polyamide film has a 0.2% yield strain in the longitudinal direction and / or the width direction of 2.30% or more.

3. The polyamide film according to claim 1, wherein the polyamide film has a haze of 1.0% or less.

4. The polyamide film according to claim 1, wherein the polyamide film has a total light transmittance of 85.0% or more.

5. The polyamide film according to claim 1, wherein the polyamide film has a thickness of 100 μm or less.

6. A laminated film comprising the polyamide film according to any one of claims 1 to 5 and a hard coat layer.

7. A display comprising the polyamide film according to any one of claims 1 to 5.

8. A display having the laminated film according to claim 6, wherein the hard coat layer of the laminated film is disposed on the outside.

9. A method for producing a polyamide film according to any one of claims 1 to 5, comprising a stretching step in which an unstretched film containing a semi-aromatic polyamide is uniaxially stretched in the longitudinal direction or width direction at a stretching ratio of 1.5 to 4.

0.

10. The method for producing a polyamide film according to claim 9, wherein the stretching step is not followed by a heat setting treatment or a relaxation treatment.

11. The method for producing a polyamide film according to claim 9, wherein the unstretched film has a heat of crystallization of 20 J / g or more.

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