TW201808643A - Hard coat film - Google Patents

Abstract

A hard coat film 1 is provided which comprises a substrate film 2 and a hard coat layer 3 laminated on at least one principal surface of the substrate film 2, wherein the substrate film 2 is a polyimide film, the absolute value of the difference between the refractive index of the polyimide film and the refractive index of the hard coat layer 3 is less than or equal to 0.04, and the thickness of the hard coat layer 3 is 0.5-10 [mu]m. The hard coat film 1 has flex resistance enabling resisting repeated bending, and is not prone to generate interference fringes.

Description

Hard-coated film

The present invention relates to a hard coat film including a substrate film and a hard coat layer, and more particularly to a hard coat film suitable for use in a flexible display.

Various electronic devices are widely used in liquid crystal displays (LCD), organic EL displays (OELD), and various displays including touch panels. In order to prevent damage to the surface of such various displays, a hard-coated film in which a hard-coat layer is provided on a base film is often provided.

In recent years, as the display described above, a display capable of being bent, that is, a so-called flexible display has been developed. Flexible displays are expected to be used in a wide range of applications, for example, for a display that is bent and placed on a columnar pillar, or for a portable display that is bent or rounded and can be carried. As a hard-coated film for a flexible display, Patent Documents 1 and 2 disclose a hard-coated film.

Here, the flexible display is not only curved once, but may be repeatedly bent (bent) as described in Patent Document 3.

Prior art literature Patent literature

[Patent Document 1] Japanese Patent No. 5468167

[Patent Document 2] Japanese Patent Laid-Open No. 2015-69197

[Patent Document 3] Japanese Patent Laid-Open No. 2016-2764

However, when the conventional hard-coated film is used in a flexible display such as the one described above, there are problems in that a portion where the film is repeatedly bent is bent or whitened to reduce the appearance, and the visibility of the display is also deteriorated.

On the other hand, in hard-coated films, interference fringes may occur due to various important reasons. When interference fringes are generated on the hard-coated film, the appearance is still low and the visibility as a display is also low.

The present invention has been made in view of such an actual situation, and an object thereof is to provide a hard-coated film that has bending resistance that can withstand repeated bending and at the same time does not easily generate interference fringes.

In order to achieve the above object, the first system of the present invention provides a hard coating film, which is a hard coating film including a base film and a hard coating layer laminated on at least one main surface side of the base film, which is characterized in that: The base film is a polyimide film, and the absolute value of the difference between the refractive index of the polyimide film and the refractive index of the hard coating layer is 0.04 or less, and the thickness of the hard coating layer is 0.5 μm or more and 10 μm or less. (Invention 1).

In the hard coating film of the above invention (Invention 1), the base film is a polyimide film, and since the thickness of the hard coating layer is within the above range, it has excellent bending resistance and scratch resistance. In addition, the hard coat film is based on the refractive index difference as described above. This range is not easy to produce interference fringes.

In the above invention (Invention 1), the refractive index of the hard coat layer is preferably 1.40 or more and 1.85 or less (Invention 2).

In the above invention (Inventions 1, 2), the thickness of the polyimide film is preferably 5 μm or more and 300 μm or less (Invention 3).

In the above inventions (Inventions 1 to 3), the hard coat layer is preferably formed of a material obtained by hardening a composition containing an active energy ray-curable component and transition metal oxide fine particles (Invention 4).

The hard-coated film of the above inventions (Inventions 1 to 4) is used as a flexible member constituting a flexible display (Invention 5)

In the above inventions (Inventions 1 to 5), an adhesive layer is preferably laminated on at least one main surface side of the base film (Invention 6).

The hard-coated film of the present invention has bending resistance that can withstand repeated bending, and at the same time, it is not easy to generate interference fringes.

1, 1A, 1B‧‧‧‧Hard-coated film

2‧‧‧ substrate film

3‧‧‧hard coating

4‧‧‧ 2nd hard coating

5‧‧‧ Adhesive layer

FIG. 1 is a cross-sectional view of a hard-coated film according to an embodiment of the present invention.

Fig. 2 is a sectional view of a hard-coated film according to another embodiment of the present invention.

Fig. 3 is a sectional view of a hard-coated film according to another embodiment of the present invention.

Forms used to implement the invention

Hereinafter, embodiments of the present invention will be described.

FIG. 1 is a cross-sectional view of a hard-coated film according to an embodiment of the present invention. Authentic The hard-coated film 1 of this embodiment includes a base film 2 and a hard-coat layer 3 laminated on at least one main surface side (upper side in FIG. 1) of the base film.

In the hard coat film 1, the base film 2 is a polyimide film. When the base film 2 is a polyimide film, when the hard coating film 1 is applied to a flexible display and repeatedly bent, it is possible to suppress the occurrence of bending marks or whitening of the base film 2 and to have excellent bending resistance. Sex. Therefore, in the flexible display using the hard-coated film 1 of this embodiment, when a predetermined portion is repeatedly bent, it is possible to suppress the appearance of the bent portion from being deteriorated or the visibility from being deteriorated.

The absolute value of the difference between the refractive index of the polyfluorene imine film and the refractive index of the hard coat layer 3 is 0.04 or less. In the hard-coated film 1 of this embodiment, since the absolute value of the difference between the refractive index of the polyimide film and the hard-coat layer 3 is 0.04 or less, the difference between the hard-coat layer 3 and the base film 2 can be suppressed. Light reflection occurs at the interface, and it is difficult for the surface of the hard coat layer 3 to interfere with the reflected light, thereby suppressing the occurrence of interference fringes. The measurement wavelength of the refractive index in this specification is 589 nm, and the measurement temperature is 25 ° C. The detailed refractive index measurement method is disclosed in the test examples described later.

From the viewpoint of suppressing the occurrence of interference fringes, the absolute value of the difference between the refractive index of the polyfluorene imine film and the refractive index of the hard coat layer 3 is preferably 0.03 or less, and particularly preferably 0.02 or less.

The thickness of the hard coat layer 3 is 0.5 μm or more and 10 μm or less. When the thickness of the hard coat layer 3 is more than 10 μm, the flexibility of the hard coat film 1 is reduced. On the other hand, when the thickness of the hard-coat layer 3 is less than 0.5 μm, the surface hardness of the hard-coat layer 3 becomes low and the scratch resistance is poor. That is, when the thickness of the hard coating layer 3 is within the above range, the hard coating film 1 is excellent in bending resistance and abrasion resistance. Trauma.

From the viewpoint described above, the thickness of the hard coat layer 3 is preferably 0.75 μm or more, and particularly preferably 1 μm or more. The thickness of the hard coat layer 3 is preferably 8 μm or less, and particularly preferably 6 μm or less.

(1) Components of hard-coated film

(1-1) Substrate film

The base film 2 of the hard coat film 1 of this embodiment is a polyimide film. In the case of a display, a transparent polyimide film with less yellowing is preferred. This makes it possible to obtain a display (particularly a flexible display) that displays a transparent and color-reproducible image.

Specifically, as the polyimide film used in this embodiment, from the viewpoint of transparency, the transmittance at a wavelength of 550 nm is preferably 75% or more, more preferably 80% or more, and 85 More than% is particularly good. The method for measuring the transmittance in this specification is disclosed in Examples described later.

In addition, as the polyimide film used in this embodiment, the absolute value of b * in the L * a * b * colorimetric system using a transmission measurement method is 10 or less from the viewpoint of reducing yellowing. Preferably, 5 or less is preferred, and 3 or less is particularly preferred. The method for measuring b * in this specification is disclosed in Examples described later.

The term "polyimide film" as used herein means the content of polyimide, that is, a polymer having a fluorene imine bond in the main chain, preferably 50% by mass or more, particularly preferably 80% by mass or more, More preferably, the film is 90% by mass or more. In addition, because poly (meth) acrylic acid imine does not have a fluorene imine bond in the main chain, it is not polyimide, and this poly (meth) acrylic acid imine film is repeatedly bent. As a result, whitening occurs.

Polyfluorene imide film is generally capable of polymerizing a tetracarboxylic anhydride (preferably an aromatic tetracarboxylic dianhydride) and a diamine (preferably an aromatic diamine) in a solution to form a polyamidic acid. This polyamic acid is formed into a thin film, and secondly, it is obtained by dehydrating and closing the polyamino acid site, but it is not limited thereto.

Polyimide in polyimide films can also be modified. For example, the aromatic ring usually contained in polyimide can also be modified with an aliphatic hydrocarbon, whereby the base film 2 has excellent adhesion with the hard coat layer 3.

The lower limit of the refractive index of the polyfluoreneimide film is usually 1.50 or more, preferably 1.55 or more, and more preferably 1.60 or more. The upper limit of the refractive index of the polyfluoreneimide film is usually 1.85 or less, preferably 1.80 or less, and more preferably 1.75 or less.

The polyimide film can be treated with a primer and oxidized as required for the purpose of improving the adhesion with the layer (hard coat layer 3 or an adhesive layer described later) provided on the surface thereof. Method, bumping method and other surface treatment on one or both sides. Examples of the oxidation method include corona discharge treatment, chromic acid treatment, flame treatment, hot air treatment, and ozone. Ultraviolet treatment and the like include, for example, a sandblasting method, a solvent treatment method, and the like.

The lower limit of the thickness of the polyfluoreneimide film is preferably 5 μm or more, particularly preferably 7.5 μm or more, and further preferably 10 μm or more. When the thickness of the polyimide film is the above, the hard-coated film 1 can exhibit a predetermined mechanical strength, and even when it is repeatedly bent, cracks and the like are unlikely to occur. On the other hand, as the upper limit of the thickness of the polyfluoreneimide film, 300 μm or less is preferred, 90 μm or less is particularly preferred, and 50 μm or less is more preferred. good. Since the polyfluorene imide film is easy to be colored, the thickness of the polyfluorene imide film is the following or less, which can ensure transparency and can suppress the b * value to be low, and can be suitably used for optical applications. In addition, when the thickness of the polyimide film is the following or less, the hard-coated film 1 is a person who can exhibit a predetermined flexibility and easily bend it.

(1-2) Hard coating

The hard coat layer 3 of the hard coat film 1 of this embodiment is laminated on one main surface side (upper side in FIG. 1) of the base film 2, and gives the hard coat film 1 a high surface hardness.

The lower limit of the refractive index of the hard coat layer 3 is preferably 1.40 or more, particularly preferably 1.45 or more, and more preferably 1.56 or more. The upper limit of the refractive index of the hard coat layer 3 is preferably 1.85 or less, particularly preferably 1.80 or less, and even more preferably 1.75 or less. When the refractive index of the hard coat layer 3 is in the above range, the difference in refractive index between the polyimide films can easily become 0.04 or less.

The hard coat layer 3 is not particularly limited as long as it satisfies the above-mentioned refractive index difference and has a predetermined hardness. It is preferably formed of a material obtained by hardening a composition containing an active energy ray-curable component. A material formed by hardening a composition containing an active energy ray-curable component and fine particles of transition metal oxides (hereinafter referred to as a "composition for a hard coat layer").

(1-2-1) Active energy ray hardening component

The active energy ray-hardening component is preferably one that can be hardened by irradiating the active energy ray and exhibits a predetermined hardness, and that the refractive index difference can be achieved by the relationship with the transition metal oxide fine particles.

Specific examples of the active energy ray-curable component include polyfunctional (meth) acrylate-based monomers, (meth) acrylate-based prepolymers, and active energy ray-curable polymers. A polyfunctional (meth) acrylate-based monomer and / or a (meth) acrylate-based prepolymer are preferred, and a polyfunctional (meth) acrylate-based monomer is more preferred. The polyfunctional (meth) acrylate-based monomer and the (meth) acrylate-based prepolymer may be used alone or in combination. In addition, in this specification, a (meth) acrylate means both an acrylate and a methacrylate. The same applies to other similar terms.

Examples of the polyfunctional (meth) acrylate-based monomer include 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, and neopentyl Glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, hydroxytrimethyl acetate neopentyl glycol di (meth) acrylate, dicyclopentyl di (meth) acrylate, Caprolactone modified dicyclopentenyl di (meth) acrylate, ethylene oxide modified phosphoric acid di (meth) acrylate, allyl cyclohexyl di (meth) acrylate, trimeric isocyanate di (Meth) acrylate, trimethylolpropane tri (meth) acrylate, dineopentaerythritol tri (meth) acrylate, propionic acid modified dinepentaerythritol tri (meth) acrylate, Neopentaerythritol tri (meth) acrylate, propylene oxide modified trimethylolpropane tri (meth) acrylate, trimeric isocyanate (propylene ethoxyethyl) ester, propionic acid modified Dinepentaerythritol penta (meth) acrylate, dinepentaerythritol hexa (meth) acrylate, ethylene oxide modified dinepentaerythritol hexa (meth) acrylate, caprolactone modification Dinepentaerythritol hexa (meth) acrylate, etc. Polyfunctional (meth) acrylate. These may be used individually by 1 type, and may be used in combination of 2 or more type. Among the above, from the viewpoint of dispersibility and scratch resistance of the transition metal oxide fine particles, it is modified with dipentaerythritol hexa (meth) acrylate and ethylene oxide. Dipentaerythritol hexa (meth) acrylate, or a mixture of these is preferred.

On the other hand, examples of the (meth) acrylate-based prepolymer include polyester acrylate-based, epoxy acrylate-based, urethane acrylate-based, and polyol acrylate-based prepolymers. .

As the polyester acrylate-based prepolymer, for example, a hydroxyl group of a polyester oligomer having hydroxyl groups at both ends of a polycarboxylic acid and a polyhydric alcohol obtained by condensation can be esterified by using (meth) acrylic acid. Or, a terminal hydroxyl group of an oligomer obtained by adding an alkylene oxide to a polycarboxylic acid is obtained by esterification using (meth) acrylic acid.

The epoxy acrylate-based prepolymer is, for example, an ester capable of reacting (meth) acrylic acid with an ethylene oxide ring such as a bisphenol epoxy resin or a novolac epoxy resin having a relatively low molecular weight. To get.

The urethane acrylate-based prepolymer is, for example, a polyurethane oligomer obtained by reacting a polyether polyol or a polyester polyol with a polyisocyanate, and esterified by using (meth) acrylic acid. To get.

The polyol acrylate-based prepolymer can be obtained, for example, by esterifying a hydroxyl group of a polyether polyol with (meth) acrylic acid.

The above prepolymers may be used singly or in combination of two or more kinds.

(1-2-2) Transition metal oxide fine particles

The composition for a hard coat layer constituting the hard coat layer 3 of this embodiment is preferably one containing fine particles of a transition metal oxide. By including the transition metal oxide fine particles, the refractive index of the hard coat layer 3 can be made close to the refractive index of the polyfluorene imine film, and the absolute value of the refractive index difference can be easily made 0.04 or less. also, It is also possible to impart a high surface hardness to the hard coat layer 3.

As the transition metal oxide fine particles, fine particles such as zirconia, titanium oxide, tantalum oxide, zinc oxide, hafnium oxide, cerium oxide, and niobium oxide are preferable. These systems can be used alone or in combination of two or more. Among the above, it is possible to impart a high refractive index to the hard coat layer 3, and at the same time, it is not easy to increase the haze of the hard coat layer 3. The oxide fine particles of the group 4 element, specifically, the zirconia fine particles and the oxide Titanium particles are particularly preferred. The crystal structure of the titanium oxide fine particles is not particularly limited, and a rutile type is preferred. By being of the rutile type, deterioration of the hard coat layer 3 with time due to photocatalytic activity can be suppressed.

The zirconia particles and titanium oxide particles may be surface-treated. For example, it may be covered with an oxide such as aluminum or silicon, or may be modified with an organic compound. Examples of the organic compound include a polyol, an alkanolamine, stearic acid, a silane coupling agent, and a titanate coupling agent. By such a surface treatment, dispersibility and the like can be improved and the above-mentioned effects can be made more excellent.

The shape of the transition metal oxide fine particles may be spherical or non-spherical.

The lower limit of the average particle diameter of the transition metal oxide fine particles is preferably 1 nm or more, particularly preferably 3 nm or more, and further preferably 5 nm or more. When the average particle diameter of the transition metal oxide fine particles is 1 nm or more, the dispersibility is improved, and at the same time, the obtained hard coat layer 3 has a high surface hardness. The upper limit of the average particle diameter of the transition metal oxide fine particles is preferably 500 nm or less, particularly preferably 200 nm or less, and more preferably 50 nm or less. When the average particle diameter of the transition metal oxide fine particles is 500 nm or less, light scattering is unlikely to occur in the obtained hard coat layer 3, and Transparency becomes high. The average particle diameter of the transition metal oxide fine particles is a primary particle diameter measured by a Zeta-potential measurement method.

The content of the transition metal oxide fine particles in the hard coat layer 3 in this embodiment is the lower limit of the hard coat layer 3, preferably 5 mass% or more, particularly preferably 10 mass% or more, and further 40 mass. More than% is preferred. When the content of the transition metal oxide fine particles is 5% by mass or more, the refractive index of the hard coating layer 3 can be easily approached to the refractive index of the polyimide film, and at the same time, the surface hardness of the hard coating layer 3 can be easily imparted. On the other hand, the content of the transition metal oxide fine particles is the upper limit of the hard coat layer 3, preferably 95% by mass or less, more preferably 85% by mass or less, and even more preferably 75% by mass or less. When the content of the transition metal oxide fine particles is 95% by mass or less, the refractive index of the hard coat layer 3 can be made close to the refractive index of the polyimide film in the same manner as described above, and the composition for the hard coat layer can be easily formed. Into layers.

The content of the transition metal oxide fine particles can be determined from the blending ratio. When the blending ratio is unclear, it can be determined as follows. That is, a part of the hard coat layer 3 of the hard coat film 1 is separated from the base film 2 by a piece or the like, and the separated pieces of the hard coat layer 3 are burned with organic components in accordance with JIS 7250-1. Then, the mass% of the transition metal oxide fine particles can be determined from the obtained ash.

Here, in order to improve the dispersibility of the transition metal oxide fine particles in the composition for a hard coat layer, a dispersant may be used. The dispersant is preferably an acrylic resin from the viewpoint of compatibility with the active energy ray-curable component.

(1-2-3) Photopolymerization initiator

When an ultraviolet ray is used as the active energy ray for curing the active energy ray-curable component, the composition for a hard coat layer preferably contains a photopolymerization initiator. By containing the photopolymerization initiator in this way, the active energy ray-curable component can be efficiently polymerized, and the polymerization hardening time and the amount of ultraviolet radiation can be reduced.

Examples of such a photopolymerization initiator include benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin-n-butyl ether, benzoin isobutyl ether, Acetophenone, dimethylaminoacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxy-2-phenylacetophenone, 2-hydroxy- 2-methyl-1-phenylpropane-1-one, 1-hydroxycyclohexylphenyl ketone, 2-methyl-1- [4- (methylthio) phenyl] -2-morpholine-propane- 1-ketone, 4- (2-hydroxyethoxy) phenyl-2- (hydroxy-2-propyl) ketone, diphenyl ketone, p-phenyldiphenyl ketone, 4,4'-diethylamine Diphenyl ketone, dichlorodiphenyl ketone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, 2-aminoanthraquinone, 2-methyl 9-oxyl sulfur 2-ethyl 9-oxysulfur , 2-chloro9-oxysulfur 2,4-dimethyl 9-oxosulfur , 2,4-diethyl 9-oxysulfur , Benzyl dimethyl ketal, acetophenone dimethyl ketal, p-dimethylamino benzoate, oligo [2-hydroxy-2-methyl-1 [4- (1-methylvinyl) Phenyl] acetone], 2,4,6-trimethylbenzylidene-diphenyl-phosphine oxide, and the like. These may be used alone or in combination of two or more.

The content of the photopolymerization initiator in the composition for a hard coat layer is preferably 0.01 parts by mass or more and particularly preferably 0.1 parts by mass or more with respect to 100 parts by mass of the active energy ray-curable component. It is more preferably 1 part by mass or more. The upper limit value is preferably 20 parts by mass or less, particularly preferably 10 parts by mass or less, and further preferably 5 parts by mass or less.

(1-2-4) Other ingredients

The composition for a hard coat layer constituting the hard coat layer 3 of the present embodiment may contain various additives in addition to the aforementioned components. Examples of the various additives include ultraviolet absorbers, antioxidants, light stabilizers, antistatic agents, silane coupling agents, anti-aging agents, thermal polymerization inhibitors, colorants, surfactants, storage stabilizers, plasticizers, Lubricants, defoamers, organic fillers, wetting improvers, coating improvers, etc.

(2) Manufacturing method of hard coating film

The hard-coated film 1 according to this embodiment can be produced by using the following method. In this method, as an example, it is a product produced using a composition for a hard coat layer containing an active energy ray-curable component.

First, a composition layer composed of a composition for a hard coat layer is formed on one main surface of the base film 2. At this time, the composition for a hard coat layer may be directly applied to one main surface of the base film 2 to form a composition layer, or the composition for a hard coat layer may be applied to a cover sheet and then attached to the substrate. The composition layer of the cover sheet is bonded to one main surface of the base film 2.

As the cover sheet, a desired resin film can be used. Moreover, you may use the peeling sheet which peeled off one side or both sides of these resin films with a peeling agent.

The composition layer can be formed by preparing a coating liquid containing a composition for a hard coat layer and a solvent as required, applying the coating liquid to the base film 2 or a cover sheet, and drying the coating layer. The application of the coating liquid may be performed using a commonly used method, for example, a bar coating method, a doctor blade coating method, a Mayer bar method, a roll coating method, or a blade coating method. Die coating method, gravure coating method can. Drying can be performed, for example, by heating at 40 to 180 ° C. for about 30 seconds to 5 minutes.

Examples of the solvent include aliphatic hydrocarbons such as hexane and heptane, aromatic hydrocarbons such as toluene and xylene, halogenated hydrocarbons such as dichloromethane and dichloroethane, methanol, ethanol, propanol, and butanol Alcohols such as propylene glycol monomethyl ether, acetone, methyl ethyl ketone, methyl isobutyl ketone, 2-pentanone, isophorone, cyclohexanone and other ketones, ethyl acetate, butyl acetate, etc. Solvents such as esters, ethylcellulose and the like. The solvent may be used singly or in combination of two or more kinds. The concentration of the coating solution. The viscosity is not particularly limited as long as it can be applied, and can be appropriately selected depending on the situation.

Next, the composition layer is irradiated with active energy rays to harden the composition layer to become the hard coat layer 3.

As the active energy ray, ultraviolet rays, electron rays, and the like can be used. The ultraviolet irradiation can be performed using a high-pressure mercury lamp, a Fusion H lamp, a xenon lamp, and the like. The ultraviolet irradiation amount is preferably about 50 to 1,000 mW / cm ² and 50 to 1000 mJ / cm ² . On the other hand, the electron beam irradiation system can be performed using an electron beam accelerator or the like, and the irradiation amount of the electron beam is preferably about 10 to 1000 krad.

When ultraviolet rays are used as the active energy rays, the composition layer is preferably irradiated with ultraviolet rays in a state of being isolated from oxygen. Thereby, the hard coating layer 3 having a high surface hardness is effectively formed without being hindered by the hardening caused by oxygen.

In order to isolate the composition layer from oxygen, when a cover sheet is added to the composition layer, it is assumed that the cover sheet is maintained in an added state. In the case where no cover sheet is added to the above composition layer, a new cover sheet is laminated on the above composition layer, or the laminated body of the base film 2 and the composition layer is kept in an environment with a low oxygen concentration. It is preferable to keep it under a nitrogen atmosphere.

(3) Physical properties of hard coating film

(3-1) Maximum reflectance difference

As described above, in the hard-coated film 1 of this embodiment, the occurrence of interference fringes can be suppressed. This case can be determined not only by visual evaluation but also by the measured value of the maximum reflectance difference. To measure the maximum reflectance difference, first set the normal direction of the film to 0 °, and irradiate the light from the direction of the incident angle of 8 °. The reflected light is collected by an integrating sphere and detected as reflected light. In addition, irradiation of light is performed by changing the wavelength to detect reflected light corresponding to each wavelength.

The reflected light is set as a relative value of 100 (hereinafter, referred to as "reflectance") to reflect light generated from barium sulfate crystals, and is detected at each measurement wavelength. That is, a graph in which the horizontal axis is the measurement wavelength and the vertical axis is the reflectance can be obtained. The graph is usually a shape having fluctuations of a plurality of minimum values and maximum values.

Here, in the graph for measuring the reflectance at a wavelength of 500 to 600 nm, among the differences between the adjacent maximum and minimum values, the largest difference is measured as the "maximum reflectance difference". The maximum reflectance difference is preferably 1.5 or less, particularly preferably 1.1 or less, and further preferably 0.6 or less. When the reflectance is 1.5 or less, interference fringes can be suppressed.

(3-2) Minimum mandrel diameter

As mentioned above, the hard coating film 1 of this embodiment can withstand repeated bending Those having excellent bending resistance can judge the degree of bending based on the minimum mandrel diameter.

The hard-coated film 1 of this embodiment is subjected to the bending resistance test of the cylindrical mandrel method in accordance with JIS K5600-5-1. The hard mandrel 3 has the smallest diameter among the mandrels that do not cause cracking and peeling. The diameter of the mandrel (the minimum mandrel diameter) is preferably 14 mm or less, particularly preferably 6 mm or less, and further preferably 4 mm or less.

(3-3) Image sharpness

In the hard-coated film 1 of this embodiment, interference fringes are prevented. Instead of adding fine particles, it is solved by reducing the refractive index difference between the hard-coat layer 3 and the base film 2. Therefore, the hard-coated film 1 of this embodiment can be a film having more excellent image sharpness than the case where interference fringes are prevented by adding fine particles of a minute level.

When a hard-coated film having excellent image sharpness is applied to a display, a display capable of displaying an image with excellent contrast can be obtained. From this point of view, the image sharpness is preferably at least 400%, more preferably at least 430%, and particularly preferably at least 450%.

The image sharpness can be obtained in accordance with JIS K7374 by setting the total value of each image sharpness measured in five types of slits (slit width: 0.125mm, 0.25mm, 0.5mm, 1mm, and 2mm). .

(3-4) Haze value

When applied to a monitor, from the viewpoint of displaying a more vivid image, it is preferable to set the haze value of the hard-coated film 1 measured in accordance with JIS K7136 to 1% or less, and more preferably 0.8% or less. It is particularly preferable to set it to 0.5% or less.

(3-5) 60 ° gloss

When applied to a monitor, from the viewpoint of making the display more vivid, the hard coat film 3 of the hard coat film 1 is set to have a 60 ° gloss (Gloss value) according to JIS Z8741-1997 set to 100%. The above values are good, a value of 120% or more is preferable, and a value of 140% or more is particularly good.

(4) Other Embodiments-1

On the other main surface side of the base film 2 of the hard-coated film 1 (the surface side opposite to the side on which the hard-coat layer 3 is laminated), as shown in FIG. 2, a second hard layer can also be laminated. Coating 4 (the symbol of the hard-coated film shown in FIG. 2 is referred to as "1A"). By laminating the second hard coat layer 4, the abrasion resistance on the other main surface side of the base film 2 is improved, and at the same time, the hard coat layer 3 is hardened by the hardening shrinkage of the second hard coat layer 4. Cancellation of shrinkage can suppress curling of the hard-coated film 1A.

The second hard coat layer 4 may be formed of the same material as the hard coat layer 3 described above, or may be formed of a different material. The thickness of the second hard coat layer 4 may be the same as that of the hard coat layer 3 described above, or may be a different thickness.

The hard-coated film 1A of this embodiment can be basically manufactured in the same manner as the hard-coated film 1 described above. However, the hard coat layer 3 and the second hard coat layer 4 may be hardened at the same time, or a composition layer of the hard coat layer 3 (or the second hard coat layer 4) may be formed and hardened to form a second hard coat layer. The composition layer of the hard coat layer 4 (or the hard coat layer 3) is hardened.

(5) Other embodiment-2

On the other main surface side of the base film 2 of the hard coating film 1 (the surface side opposite to the surface on which the hard coating layer is laminated), as shown in FIG. 3, an adhesive layer 5 may also be laminated. (The symbol of the hard-coated film shown in FIG. 3 is described as "1B"). By laminating the adhesive layer 5 in this manner, the hard-coated film 1B can be easily attached to any place. Adhesives needed. Similarly, an adhesive layer may be laminated on the second hard coat layer 4 of the hard coat film 1A on the opposite side to the base film 2 side.

The adhesive constituting the adhesive layer 5 is not particularly limited, and a conventional adhesive such as an acrylic adhesive, a rubber adhesive, or a silicone adhesive can be used. The thickness of the adhesive layer 5 is not particularly limited, but it is usually 5 to 100 μm, and preferably 10 to 60 μm.

The hard-coated film 1B of this embodiment can be produced basically in the same manner as the hard-coated film 1 described above. The adhesive layer 5 may be formed using a commonly used method.

In addition, on the exposed surface of the adhesive layer 5 (the surface opposite to the base film 2 side), a release sheet may be laminated.

(6) Other Embodiments-3

The hard coating film 1 of this embodiment may also be laminated with other layers, such as an adhesive layer, a barrier layer, a conductive layer, a low reflection layer, an easy-printing layer, an antifouling layer, and the like.

(7) Use of hard coating film

The hard-coated films 1, 1A, and 1B of the above embodiments are, for example, flexible displays that can be suitably used in various electronic devices, especially portable electronic devices, and specifically, liquid crystal displays (LCDs) and organic EL displays. Various flexible displays such as (OELD) and electronic paper modules (film-like electronic paper) are used as the flexible member of the surface layer (protective film) or intermediate layer.

The embodiments described above are described for easy understanding of the present invention, and are not described for limiting the present invention. Therefore, each element disclosed in the above embodiment also includes all design changes and equivalents belonging to the technical scope of the present invention.

For example, other layers may be provided between the base film 2 of the hard coating film 1, 1A, and 1B, and the hard coating layer 3, the second hard coating layer 4, or the adhesive layer 5.

[Example]

Hereinafter, the present invention will be described more specifically with reference to examples, but the scope of the present invention is not limited by these examples and the like.

[Production Example 1] (Production of Substrate Film 1)

In a N, N-dimethylacetamide solvent, 2,2'-bis (trifluoromethyl) -4,4'-diaminobiphenyl, biphenyltetracarboxylic dianhydride, and 2 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropionic dianhydride was mixed and dissolved under cooling, and then a polyamic acid solution was obtained by stirring at normal temperature for 10 hours.

Acetic anhydride and pyridine were added to the obtained polyamic acid solution, and after fully stirring, it was apply | coated on the glass plate, and it heated up slowly from normal temperature to 180 degreeC. After reaching 180 ° C, the volatiles were completely removed by heating for a certain period of time, followed by evacuation. Finally, the polyimide film A having a film thickness of 25 μm was obtained by cooling to normal temperature under vacuum. When measured for this polyfluoreneimide film A, b * was 0.61, the refractive index was 1.62, and the transmittance at a wavelength of 550 nm was 90%.

The film thickness of the polyimide film was measured in accordance with JIS K7130 using a constant-pressure thickness measuring device (manufactured by Teclock Corporation, product name "PG-02").

Regarding the above b *, a spectrophotometric colorimeter (manufactured by Nippon Denshoku Industries Co., Ltd., product name "SQ-2000") was used as a measuring device in accordance with JIS Z8722, and a C light source 2 ° field of view (C / 2) was used As a light source, b * in the L * a * b * color system was measured using a transmission measurement method.

The transmittance at the above wavelength of 550nm is based on the use of ultraviolet visible near infrared It was measured with a light transmittance meter (manufactured by Shimadzu Corporation, product name "UV3600").

[Production Example 2] (Production of Substrate Film 2)

In the N, N-dimethylacetamide solvent, in addition to 2,2'-bis (trifluoromethyl) -4,4'-diaminobiphenyl, biphenyltetracarboxylic dianhydride, and Except for adjusting the concentration of 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropionic dianhydride and adjusting the concentration of the obtained polyimide coating solution, the same procedures as in Production Example 1 were performed. To obtain a polyimide film B having a film thickness of 15 μm, b * of 2.25, a refractive index of 1.70, and a transmittance of 87% at a wavelength of 550 nm (the measurement method is as described above).

[Example 1]

100 parts by mass of dipentaerythritol hexaacrylate, which is an active energy ray-curable component (solid content conversion; the same applies hereinafter), and surface-modified zirconia particles (made by CIK Nanotec Corporation, product names) as transition metal oxide particles "ZRMIBK15WT% -F85", average particle size: 15 nm) 150 parts by mass and 5 parts by mass of 1-hydroxycyclohexylphenyl ketone as a photopolymerization initiator, methyl isobutyl was mixed at a mass ratio of 1: 1 A mixed solvent of a base ketone and cyclohexanone is stirred and mixed to obtain a coating liquid of a composition for a hard coat layer.

Next, the coating liquid of the composition for a hard-coat layer was coated on one side of a polyimide film A as a base film using a wire rod, and heated and dried at 70 ° C for 1 minute to form a hard-coat layer Use the composition layer of the composition.

Subsequently, under the following conditions, ultraviolet rays were irradiated from the composition layer side to harden the composition layer of the composition for a hard coat layer to form a hard coat layer (thickness: 3 μm) to obtain a hard coat film.

<UV irradiation conditions>

． Ultraviolet irradiation device: Ultraviolet irradiation made by GS Yuasa Corporation Shooting device

． Light source: high pressure mercury lamp

． Lamp power: 1.4kW

． Illumination: 100mW / cm ²

． Light quantity: 240mJ / cm ²

． Conveyor speed: 1.2m / min

． UV radiation in a nitrogen environment (oxygen concentration below 1%)

[Examples 2 to 8, Comparative Examples 1 to 5]

It manufactured similarly to Example 1 except having changed the kind and compounding quantity of each component which comprises the composition for hard-coat layers, the thickness of a hard-coat layer, and the kind and thickness of a base film as shown in Table 1. Hard-coated film.

The details of the abbreviations and the like described in Table 1 are as follows.

A: Dinepentaerythritol hexaacrylate

B: ethylene oxide modified dinepentaerythritol hexaacrylate (introduced with ethylene oxide 12 mol)

C: Surface-modified zirconia fine particles (manufactured by CIK Nanotec, product name "ZR MIBK15WT% -F85", average particle size: 15nm)

D: Surface-modified titanium oxide fine particles (manufactured by Tayca, product name "ND139", average particle diameter: 10 nm)

E: 1-hydroxycyclohexylphenyl ketone

PI-25: Polyimide film A

PI-15: Polyimide film B

PET: Polyethylene terephthalate film (manufactured by Mitsubishi Resin Corporation, product name "Diafoil T-60", thickness: 50 μm)

[Test Example 1] (Measurement of refractive index)

(1) Refractive index of substrate film

Under the conditions of a measurement wavelength of 589 nm and a measurement temperature of 25 ° C., an Abbe refractometer (manufactured by ATAGO, product name “Multi-Wavelength Abbe Refractometer DR-M2”) was used, and measurements were performed in the Examples and in accordance with JIS K7142 (2008). The refractive index of the base film used in the comparative example. The results are shown in Table 2.

(2) refractive index of hard coating

The untreated side of a polyethylene terephthalate film (manufactured by Toyobo Co., Ltd., product name "COSMOSHINE A4100", thickness: 50 µm) was processed on one side in the same manner as in Examples and Comparative Examples to form a thickness of 200 nm. Hard coating. Next, the easy-to-adhere surface of the polyethylene terephthalate film was rubbed with sand paper, and painted with black using an oil-based pen (manufactured by ZEBRA, product name "Mckee Black").

Subsequently, the refractive index of the hard coat layer was measured in accordance with JIS K7142 (2008) using a spectroscopic ellipsometer (manufactured by JAWOOLLAM, product name "M-2000") under a measurement wavelength of 589 nm and a measurement temperature of 25 ° C. rate. The results are shown in Table 2.

(3) Calculation of refractive index difference

The refractive index difference is calculated by subtracting the refractive index of the hard coat layer from the refractive index of the substrate film measured above. The results are shown in Table 2.

[Test Example 2] (Evaluation of interference fringes)

(1) Visual evaluation

The hard-coated films produced in the examples and comparative examples were passed through a double-sided adhesive sheet (manufactured by LINTEC, product name "OPTERIA MO-3006C", thickness: 25 μm) It was attached to a black acrylic board (manufactured by Mitsubishi Rayon, under the product name "Acrylight L502"). At this time, the base film of the hard-coated film is attached so as to contact the acrylic plate.

The obtained laminated body was visually checked for interference fringes from a hard-coat layer side under a 3-wavelength fluorescent lamp, and evaluated in accordance with the following criteria. The results are shown in Table 2.

Good (◎): Interference fringes are hardly seen

Fair (○): Interference fringes are not easy to see

Slightly bad (△): interference fringes can be seen

Bad (×): interference fringes can be clearly seen

(2) Measurement of maximum reflectance difference

For the multilayer body obtained in (1), the maximum reflectance difference between the wavelengths of the reflectance spectrum of 500 to 600 nm was measured using a spectrophotometer under the following conditions. The results are shown in Table 2.

<Measurement conditions>

． Spectrophotometer: manufactured by Shimadzu Corporation, product name "UV-Visible Near-Infrared Spectrophotometer UV-3600"

． Sample holder: "Major sample chamber MPC-3100" manufactured by Shimadzu Corporation

． Integrating sphere: Made by Shimadzu Corporation, product name "Integrating sphere attachment ISR-3100"

． Angle of incidence: 8 °

[Test Example 3] (Evaluation of Scratch Resistance)

The hard-coated surfaces of the hard-coated films produced in the examples and comparative examples were subjected to reciprocating friction 10 times using a steel wool of # 0000 under a load of 125 g weight / cm ² , and a range of length 100 mm and width 20 mm was set. Test range. The number of flaws in the test range was visually confirmed under a 3-wavelength fluorescent lamp, and the scratch resistance was evaluated in accordance with the following criteria. The results are shown in Table 2.

○: The number of flaws is less than 20.

×: The number of flaws is 20 or more.

[Test Example 4] (Spindle Test)

The hard-coated films produced in the examples and comparative examples were subjected to a mandrel test according to JIS K5600-5-1 using a cylindrical mandrel bending tester (manufactured by CORTEC). This mandrel test was performed with the hard coat of the hard coat film on the outside. The diameter of the smallest mandrel (minimum mandrel diameter) among the defective mandrels in which the hard coat layer does not crack or peel is determined. The results are shown in Table 2.

[Test Example 5] (Bending resistance test)

For the hard-coated films manufactured in the examples and comparative examples, a durability tester (manufactured by YUASA SYSTEM, Inc., product name "Flat-body Unloaded U-shaped Stretch Tester DLDMLH-FS") was used, and the hard coat layer was made to be outside. The test speed was 60 mm / s, and the number of tests (reciprocation number) and the bending diameter were variously changed to repeat the bending. Next, it was confirmed whether or not cracking of the hard coating occurred. Peeling and whitening of hard coating film. For defects such as bending marks, bending resistance was evaluated in accordance with the following criteria. The results are shown in Table 2.

：: The bending diameter is 5 mm or less, and no defect occurs even if the number of tests is 20,000 or more.

○: The bending diameter is 10 mm or less, and no defect occurs even if the number of tests is 20,000 or more.

×: The level of the benchmark of ○ was not reached.

[Test Example 6] (Evaluation of image sharpness)

For the hard-coated films produced in the examples and comparative examples, an image sharpness measuring device (manufactured by SUGA Testing Machine Co., Ltd., product name "ICM-10P") was used to measure the image sharpness (%) in accordance with JIS K7374 5 Total types of slits (slit width: 0.125mm, 0.25mm, 0.5mm, 1mm, and 2mm). Based on the results, the image sharpness was rated as less than 400%, ×, 400% or more and less than 450%, and ○, and 450% or more as ◎. The results are shown in Table 2.

[Test Example 7] (Evaluation of Haze Value)

For the hard-coated films produced in the examples and comparative examples, the haze value (%) was measured in accordance with JIS K7136 using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name "NDH5000"). Based on the results, a haze value of more than 1% was evaluated as ×, 1% or less and more than 0.5% was evaluated as ○, and 0.5% or less was evaluated as ◎. The results are shown in Table 2.

[Test Example 8] (Evaluation of 60 ° gloss)

With respect to the hard-coated films produced in the examples and comparative examples, a gloss meter (manufactured by Nippon Denshoku Industries Co., Ltd.) was used to measure the 60 ° gloss (Gloss value) in accordance with JIS Z8741-1997. Based on the results, a gloss of 60 ° is less than 100% and is rated as X, 100% or more and less than 140% is rated as ○, and 140% or more is rated as ◎. The results are shown in Table 2.

[Table 1]

As can be clearly understood from Table 2, the hard-coated film obtained in the examples has excellent scratch resistance and optical characteristics, and also has excellent bending resistance, and it is difficult to generate interference fringes.

Industrial availability

The hard-coated film of the present invention is suitable as a flexible member constituting a flexible display that is repeatedly bent, and is particularly a protective film on the surface layer.

1‧‧‧hard-coated film

2‧‧‧ substrate film

3‧‧‧hard coating

Claims (6)

A hard coating film is a hard coating film comprising a base film and a hard coating layer laminated on at least one main surface side of the base film, wherein the base film is a polyimide film, and The absolute value of the difference between the refractive index of the polyimide film and the refractive index of the hard coat layer is 0.04 or less, and the thickness of the hard coat layer is 0.5 μm or more and 10 μm or less. The hard coating film according to item 1 of the scope of the patent application, wherein the refractive index of the hard coating layer is 1.40 or more and 1.85 or less. The hard coating film according to item 1 of the scope of patent application, wherein the thickness of the polyimide film is 5 μm or more and 300 μm or less. The hard coating film according to item 1 of the scope of the patent application, wherein the hard coating layer is formed by hardening a composition containing an active energy ray-curable component and transition metal oxide fine particles. The hard-coated film described in item 1 of the scope of patent application is used as a flexible member constituting a flexible display. The hard-coated film according to any one of claims 1 to 5, wherein an adhesive layer is laminated on at least one main surface side of the substrate film.