KR102610461B1 - hard coat film - Google Patents

Abstract

It has a base film (2) and a hard coat layer (3) laminated on at least one main surface side of the base film (2), the base film (2) is a polyimide film, and the polyimide film A hard coat film (1) is provided in which the difference between the refractive index of and the refractive index of the hard coat layer (3) is 0.04 or less in absolute value, and the thickness of the hard coat layer (3) is 0.5 μm or more and 10 μm or less. This hard coat film 1 has bending resistance that can withstand repeated bending, and interference arcs are unlikely to occur.

Description

hard coat film

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

In various electronic devices, various displays such as liquid crystal display (LCD), organic EL display (OELD), and touch panel are widely used. To prevent scratches, the surfaces of these various displays are often provided with a hard coat film in which a hard coat layer is provided on a base film.

However, recently, a bendable display, a so-called flexible display, has been developed as a display similar to the above. Flexible displays are expected to have a wide range of uses, for example, as a stationary display that is curved and installed on a cylindrical pillar, or as a mobile display that is bent or rounded and transported. As a hard coat film for flexible displays, the hard coat films disclosed in Patent Documents 1 and 2 have been proposed.

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

Japanese Patent No. 5468167 Publication Japanese Patent Application Publication No. 2015-69197 Japanese Patent Application Publication No. 2016-2764

However, when a conventional hard coat film is used in a flexible display for the above purpose, bending marks or whitening occur in the repeatedly bent portion, which causes the problem of deteriorating the appearance and lowering visibility as a display.

On the other hand, in hard coat films, interference arcs may occur due to various factors. If an interference signal occurs in the hard coat film, the problem of not only deteriorating the appearance but also deteriorating visibility as a display occurs.

The present invention was made in view of such actual conditions, and its purpose is to provide a hard coat film that has bending resistance that can withstand repeated bending and is less likely to generate interference arcs.

In order to achieve the above object, firstly, the present invention is a hard coat film comprising a base film and a hard coat layer laminated on at least one main surface side of the base film, wherein the base film is polyimide. It is a film, and the difference between the refractive index of the polyimide film and the refractive index of the hard coat layer is 0.04 or less in absolute value, and the thickness of the hard coat layer is 0.5 μm or more and 10 μm or less. Provided (invention 1).

The hard coat film according to the invention (invention 1) has excellent bending resistance and scratch resistance because the base film is a polyimide film and the thickness of the hard coat layer is within the above range. . In addition, the hard coat film has a refractive index difference within the above-described range, making it difficult for interference arcs to occur.

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

In the above inventions (inventions 1 and 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), it is preferable that the hard coat layer is made of a material obtained by curing a composition containing an active energy ray-curable component and transition metal oxide fine particles (invention 4).

The hard coat film according to the above inventions (inventions 1 to 4) is preferably used as a flexible member constituting a flexible display (invention 5).

In the above inventions (inventions 1 to 5), it is preferable that an adhesive layer is laminated on at least one main surface side of the base film (invention 6).

The hard coat film according to the present invention has bending resistance that can withstand repeated bending and is less likely to generate interference arcs.

1 is a cross-sectional view of a hard coat film according to an embodiment of the present invention.
Figure 2 is a cross-sectional view of a hard coat film according to another embodiment of the present invention.
Figure 3 is a cross-sectional view of a hard coat film according to another embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described.

1 is a cross-sectional view of a hard coat film according to an embodiment of the present invention. The hard coat film 1 according to this embodiment is comprised of a base film 2 and a hard coat layer 3 laminated on 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. Since the base film 2 is a polyimide film, when the hard coat film 1 is applied to a flexible display and repeatedly bent, bending marks or whitening of the base film 2 are suppressed, and the bending resistance is improved. This is excellent. Therefore, when the flexible display using the hard coat film 1 according to the present embodiment is repeatedly bent at a predetermined portion, deterioration in appearance or visibility at the bent portion is suppressed.

Additionally, the difference between the refractive index of the polyimide film and the refractive index of the hard coat layer 3 is 0.04 or less in absolute value. In the hard coat film 1 according to the present embodiment, the difference between the refractive index of the polyimide film and the refractive index of the hard coat layer 3 is 0.04 or less in absolute value, so that the base film of the hard coat layer 3 ( Reflection of light at the interface with 2) is suppressed, and interference with reflected light on the surface of the hard coat layer 3 is less likely to occur, thereby suppressing the generation of interference arcs. In addition, the measurement wavelength of the refractive index in this specification is 589 nm, and the measurement temperature is 25°C. Details of the refractive index measurement method are as shown in the test examples described later.

From the viewpoint of suppressing the generation of interference arcs, the difference between the refractive index of the polyimide film and the refractive index of the hard coat layer 3 is preferably 0.03 or less in absolute value, and especially preferably 0.02 or less.

Additionally, 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 exceeds 10 μm, the flexibility of the hard coat film 1 decreases. On the other hand, if 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 coat layer 3 is within the above range, the hard coat film 1 has excellent bending resistance and scratch resistance.

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

(1) Constituent absence of hard coat film

(1-1) Base film

The base film 2 of the hard coat film 1 according to the present embodiment is a polyimide film, and when used for displays, it is preferably a polyimide film that is transparent and has little yellowish taste. As a result, it is possible to obtain a display (particularly a flexible display) that displays images that are clear and have high color reproducibility.

Specifically, from the viewpoint of transparency, the polyimide film used in this embodiment preferably has a transmittance of 75% or more, more preferably 80% or more, and especially preferably 85% or more at a wavelength of 550 nm. The transmittance measurement method in this specification is as shown in the Examples described later.

In addition, for the polyimide film used in this embodiment, from the viewpoint of reducing yellowness, the absolute value of b* in the L*a*b* colorimetric system by transmission measurement is preferably 10 or less, and more preferably 5 or less. And, it is particularly preferable that it is 3 or less. The measuring method of b* in this specification is as shown in the Examples described later.

The polyimide film in this specification refers to polyimide, that is, containing a polymer having an imide bond in the main chain, preferably 50% by mass or more, particularly preferably 80% by mass or more, more preferably 90% by mass or more. refers to a film that In addition, poly(meth)acrylimide is not a polyimide because it does not have an imide bond in the main chain, and when such a poly(meth)acrylimide film is repeatedly bent, it whitens.

Polyimide films are usually made by polymerizing tetracarboxylic acid anhydride (preferably aromatic tetracarboxylic dianhydride) and diamine (preferably aromatic diamine) in a solution to produce polyamic acid, and then forming the polyamic acid into a film. It can be obtained by molding and then dehydrating and ring-closing the polyamic acid portion, but it is not limited to this.

The polyimide in the polyimide film may be modified. For example, the aromatic ring usually contained in polyimide may be modified with an aliphatic hydrocarbon, and thereby the base film 2 has excellent adhesion to the hard coat layer 3.

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

In the polyimide film, primer treatment, oxidation, Surface treatment can be performed by a concave-convex method, etc. Examples of oxidation methods include corona discharge treatment, chromic acid treatment, flame treatment, hot air treatment, ozone/ultraviolet treatment, etc., and examples of roughening methods include sandblasting, solvent treatment, etc.

As a lower limit, the thickness of the polyimide film is preferably 5 μm or more, particularly preferably 7.5 μm or more, and more preferably 10 μm or more. When the thickness of the polyimide film is more than the above, the hard coat film 1 exhibits a predetermined mechanical strength and becomes prone to fracture or the like even when repeatedly bent. On the other hand, the upper limit of the thickness of the polyimide film is preferably 300 μm or less, particularly preferably 90 μm or less, and more preferably 50 μm or less. Since the polyimide film is easy to color, when the thickness of the polyimide film is less than the above, transparency is ensured, and the b* value is suppressed low, so that it can be suitably used for optical purposes. In addition, if the thickness of the polyimide film is the above or less, the hard coat film 1 exhibits a certain amount of flexibility and is easy to bend.

(1-2) Hard coat layer

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

As a lower limit, 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. Moreover, the refractive index of the hard coat layer 3 is preferably 1.85 or less as an upper limit, particularly preferably 1.80 or less, and more preferably 1.75 or less. When the refractive index of the hard coat layer 3 is within the above range, the difference from the refractive index of the polyimide film easily becomes 0.04 or less in absolute value.

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, but is preferably made of a material obtained by curing a composition containing an active energy ray curable component, especially, It is preferably made of a material obtained by curing a composition containing an active energy ray-curable component and transition metal oxide fine particles (hereinafter sometimes referred to as “composition for hard coat layer”).

(1-2-1) Active energy ray curable ingredient

As the active energy ray-curable component, it is preferable that the component cured by irradiation of active energy rays exhibits a predetermined hardness and can achieve the above-mentioned refractive index difference in relation to the transition metal oxide fine particles.

Specific active energy ray-curable components include polyfunctional (meth)acrylate-based monomers, (meth)acrylate-based prepolymers, and active energy ray-curable polymers. Among them, polyfunctional (meth)acrylate-based monomers and/ Alternatively, it is preferable that it is a (meth)acrylate-based prepolymer, and it is more preferable that it is a multifunctional (meth)acrylate-based monomer. The polyfunctional (meth)acrylate-based monomer and (meth)acrylate-based prepolymer may be used individually, or both may be used in combination. In addition, in this specification, (meth)acrylate means both acrylate and methacrylate. The same goes for other similar terms.

Examples of polyfunctional (meth)acrylate monomers include 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, Polyethylene glycol di(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate, dicyclopentanyl di(meth)acrylate, caprolactone modified dicyclopentenyl di(meth)acrylate, ethylene oxide modified phosphoric acid. Di(meth)acrylate, allylated cyclohexyl di(meth)acrylate, isocyanurate di(meth)acrylate, trimethylolpropane tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, Propionic acid-modified dipentaerythritol tri(meth)acrylate, pentaerythritol tri(meth)acrylate, propylene oxide-modified trimethylolpropane tri(meth)acrylate, tris(acryloxyethyl)isocyanurate, propionic acid-modified di Pentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ethylene oxide modified dipentaerythritol hexa(meth)acrylate, caprolactone modified dipentaerythritol hexa(meth)acrylate, etc. and polyfunctional (meth)acrylates. These may be used individually by 1 type, or may be used in combination of 2 or more types. Among the above, dipentaerythritol hexa(meth)acrylate, ethylene oxide modified dipentaerythritol hexa(meth)acrylate, or mixtures thereof are preferred from the viewpoint of dispersibility and scratch resistance of the transition metal oxide fine particles. .

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

As a polyester acrylate-based prepolymer, for example, it is obtained by condensation of a polyhydric carboxylic acid and a polyhydric alcohol, by esterifying the hydroxyl groups of a polyester oligomer having hydroxyl groups at both ends with (meth)acrylic acid, or by esterifying the polyester oligomer with an alkyl group to the polyhydric carboxylic acid. It can be obtained by esterifying the terminal hydroxyl group of the oligomer obtained by adding lene oxide with (meth)acrylic acid.

The epoxy acrylate-based prepolymer can be obtained, for example, by reacting (meth)acrylic acid with the oxilane ring of a relatively low molecular weight bisphenol-type epoxy resin or novolac-type epoxy resin to esterify it.

A urethane acrylate-based prepolymer can be obtained, for example, by esterifying a polyurethane oligomer obtained by the reaction of polyether polyol or polyester polyol with polyisocyanate with (meth)acrylic acid.

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

The above prepolymers may be used individually, or may be used in combination of two or more types.

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

It is preferable that the hard coat layer composition constituting the hard coat layer 3 of this embodiment contains transition metal oxide fine particles. By containing transition metal oxide fine particles, the refractive index of the hard coat layer 3 can be brought close to the refractive index of the polyimide film, and the refractive index difference can easily be set to 0.04 or less in absolute value. Additionally, high surface hardness can be provided to the hard coat layer 3.

Preferred examples of the transition metal oxide fine particles include zirconium oxide, titanium oxide, tantalum oxide, zinc oxide, hafnium oxide, cerium oxide, and niobium oxide. These are used individually or in combination of two or more types. Among the above, oxide fine particles of a Group 4 element, specifically, zirconium oxide fine particles, which can provide a high refractive index to the hard coat layer 3 and are difficult to improve the haze of the hard coat layer 3. and titanium oxide fine particles are particularly preferred. The crystal structure of the titanium oxide fine particles is not particularly limited, but is preferably of a rutile type. By being of the rutile type, deterioration of the hard coat layer 3 due to photocatalytic activity over time can be suppressed.

The zirconium oxide fine particles and titanium oxide fine 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 organic compounds include polyol, alkanolamine, stearic acid, silane coupling agent, and titanate coupling agent. By such surface treatment, dispersibility, etc. 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.

As a lower limit, the average particle diameter of the transition metal oxide fine particles is preferably 1 nm or more, particularly preferably 3 nm or more, and more 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 the resulting hard coat layer 3 has a higher surface hardness. Additionally, 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, scattering of light becomes less likely to occur in the resulting hard coat layer 3, and transparency of the hard coat layer 3 increases. In addition, the average particle size of the transition metal oxide fine particles is assumed to be the primary particle size measured by the zeta potential measurement method.

The content of transition metal oxide fine particles in the hard coat layer 3 of the present embodiment is preferably 5% by mass or more, and particularly preferably 10% by mass or more, as a lower limit in the hard coat layer 3, It is more preferable that it is 40 mass% or more. When the content of transition metal oxide fine particles is 5% by mass or more, it becomes easy to make the refractive index of the hard coat layer 3 close to that of the polyimide film, and it is easy to provide high surface hardness to the hard coat layer 3. Lose. On the other hand, the upper limit of the content of transition metal oxide fine particles in the hard coat layer 3 is preferably 95% by mass or less, particularly preferably 85% by mass or less, and more preferably 75% by mass or less. As the content of the transition metal oxide fine particles is 95% by mass or less, it becomes easy to bring the refractive index of the hard coat layer 3 close to that of the polyimide film as described above, and it is easy to form a layer using the composition for the hard coat layer. It becomes.

In addition, the content of transition metal oxide fine particles can be determined from the mixing ratio, but when the mixing 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 into fragments, etc., and the separated fragments of the hard coat layer 3 are in accordance with JIS 7250-1. The organic components are burned accordingly. Then, the mass percent of the transition metal oxide fine particles can be determined from the obtained batch.

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

(1-2-3) Photopolymerization initiator

When using ultraviolet rays as an active energy ray for curing the active energy ray curable component, it is preferable that the composition for the hard coat layer contains a photopolymerization initiator. By containing the photopolymerization initiator in this way, the active energy ray-curable component can be polymerized efficiently, and the polymerization curing time and the amount of ultraviolet irradiation can be reduced.

Such photopolymerization initiators include, for example, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin-n-butyl ether, benzoin isobutyl ether, acetophenone, and dimethylaminoacetophenone. , 2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxy-2-phenylacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-hydroxycyclo Hexylphenylketone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propan-1-one, 4-(2-hydroxyethoxy)phenyl-2-(hydroxy- 2-propyl) ketone, benzophenone, p-phenylbenzophenone, 4,4'-diethylaminobenzophenone, dichlorobenzophenone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-tertiary-butylanthraquinone , 2-aminoanthraquinone, 2-methylthioxanthone, 2-ethylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, benzyldimethyl ketal, acetophenone dimethyl ketal , p-dimethylaminobenzoic acid ester, oligo[2-hydroxy-2-methyl-1[4-(1-methylvinyl)phenyl]propanone], 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide etc. can be mentioned. These may be used individually, or two or more types may be used in combination.

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

(1-2-4) Other ingredients

The composition for hard coat layers constituting the hard coat layer 3 of this embodiment may contain various additives in addition to the components mentioned above. Various additives include, for example, ultraviolet absorbers, antioxidants, light stabilizers, antistatic agents, silane coupling agents, anti-aging agents, thermal polymerization inhibitors, colorants, surfactants, storage stabilizers, plasticizers, lubricants, anti-foaming agents, organic fillers, and wettability improvers. , drawing improvement agents, etc.

(2) Manufacturing method of hard coat film

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

First, a composition layer consisting of a hard coat layer composition is formed on one main surface of the base film 2. At this time, the composition for the hard coat layer may be applied directly to one main surface of the base film 2 to form a composition layer, or after the composition for the hard coat layer is applied to the cover sheet, the composition layer attached to the cover sheet is applied to the base film. It may be bonded to one main surface of (2).

As the cover sheet, any desired resin film can be used. Additionally, a release sheet in which one or both sides of the resin film has been subjected to a release treatment with a release agent can also be used.

The composition layer is formed by preparing a coating liquid further containing the composition for the hard coat layer and a solvent as desired, applying this to the base film 2 or the cover sheet, and drying it. The application of the coating liquid may be performed by a normal method, for example, a bar coat method, a knife coat method, a Meyer bar method, a roll coat method, a blade coat method, a die coat method, or a gravure coat method. Drying can be performed, for example, by heating at 40 to 180°C for about 30 seconds to 5 minutes.

Examples of solvents include aliphatic hydrocarbons such as hexane and heptane, aromatic hydrocarbons such as toluene and xylene, halogenated hydrocarbons such as methylene chloride and ethylene chloride, alcohols such as methanol, ethanol, propanol, butanol, and propylene glycol monomethyl ether, Ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, 2-pentanone, isophorone, and cyclohexanone, esters such as ethyl acetate and butyl acetate, and cellosolve-based solvents such as ethyl cellosolve. . Only one type of solvent may be used, or two or more types may be mixed and used. The concentration and viscosity of the coating solution are not particularly limited as long as it is within a range that can be coated, and can be appropriately selected depending on the situation.

Next, by irradiating the composition layer with active energy rays, the composition layer is cured to form the hard coat layer 3.

As the active energy ray, ultraviolet rays, electron beams, etc. can be used. Ultraviolet irradiation can be performed by a high-pressure mercury lamp, fusion H lamp, xenon lamp, etc., and the irradiation amount of ultraviolet rays is preferably about 50 to 1000 mW/cm2 and 50 to 1000 mJ/cm2. On the other hand, electron beam irradiation can be performed using an electron beam accelerator or the like, and the amount of electron beam irradiation is preferably about 10 to 1000 krad.

In addition, when using ultraviolet rays as an active energy ray, it is preferable to irradiate the composition layer with ultraviolet rays while it is blocked from oxygen. As a result, the hard coat layer 3 with high surface hardness is effectively formed without being inhibited from curing by oxygen.

In order to block the composition layer from oxygen, if the cover sheet is floating in the composition layer, the cover sheet is attached as is, and if the cover sheet is not floating in the composition layer, a new cover sheet is attached. It is preferable to laminate the composition layer, or to place the laminate of the base film 2 and the composition layer in an atmosphere with a low oxygen concentration, preferably in a nitrogen atmosphere.

(3) Physical properties of hard coat film

(3-1) Maximum reflectance difference

As described above, in the hard coat film 1 according to this embodiment, the generation of interference arcs is suppressed. In addition to visual evaluation, this can be judged by the measured value of the maximum reflectance difference. To measure the maximum reflectance difference, first, the film normal direction is set to 0°, light is irradiated from the direction of the incident angle of 8°, and the reflected light is collected by an integrating sphere and detected as reflected light. Additionally, light irradiation is performed by changing the wavelength, and reflected light corresponding to each wavelength is detected.

The reflected light is detected corresponding to each measurement wavelength as a relative value (hereinafter referred to as “reflectance”) where the reflected light by the barium sulfate crystal is set to 100. In other words, you can obtain a chart where the horizontal axis is the measurement wavelength and the vertical axis is the reflectance. The chart usually has a wavy shape with multiple minimum and maximum values.

Here, in the reflectance chart at a measurement wavelength of 500 to 600 nm, the largest difference among the differences between adjacent maximum and minimum values is measured as the “maximum reflectance difference.” The maximum reflectance difference is preferably 1.5 or less, particularly preferably 1.1 or less, and more preferably 0.6 or less. It can be said that the generation of interference arcs is suppressed because the reflectance is 1.5 or less.

(3-2) Minimum mandrel diameter

As described above, the hard coat film 1 according to the present embodiment has excellent bending resistance that can withstand repeated bending, but the degree of bending can be judged by the minimum mandrel diameter.

The hard coat film 1 according to the present embodiment has a diameter among the mandrels in which no cracks or peeling occurred in the hard coat layer 3 in a bending resistance test using a cylindrical mandrel method in accordance with JIS K5600-5-1. The minimum mandrel diameter (minimum mandrel diameter) is preferably 14 mm or less, particularly preferably 6 mm or less, and more preferably 4 mm or less.

(3-3) Image clarity

The hard coat film 1 according to the present embodiment solves the problem of preventing interference signals by reducing the difference in refractive index between the hard coat layer 3 and the base film 2, rather than by adding micro-order fine particles. . For this reason, the hard coat film 1 according to the present embodiment can be made into a film with superior image clarity compared to the case where interference signals are prevented by adding micro-order fine particles.

When a hard coat film with excellent image clarity is applied to a display, a display that displays images with excellent contrast can be obtained. From this viewpoint, the image clarity is preferably 400% or more, more preferably 430% or more, and especially preferably 450% or more.

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

(3-4) Haze value

When applied to a display, from the viewpoint of displaying a clearer image, the haze value of the hard coat film (1) measured in accordance with JIS K7136 is preferably 1% or less, and more preferably 0.8% or less. , it is particularly desirable to set it to 0.5% or less.

(3-5) 60° glossiness

From the viewpoint of displaying a clearer image when applied to a display, the 60° glossiness (gloss value) based on JIS Z8741-1997 of the hard coat layer 3 in the hard coat film 1 is set to 100%. It is preferable to set it as a value above, more preferably at least 120%, and especially preferably at least 140%.

(4) Other Embodiment-1

As shown in FIG. 2, on the other main surface side of the base film 2 in the hard coat film 1 (the surface side opposite to the surface on which the hard coat layer 3 is laminated), a second hard layer is provided. The coat layer 4 may be laminated (the code for the hard coat film shown in Fig. 2 is written as “1A”). By laminating this second hard coat layer 4, the scratch resistance on the other main surface side of the base film 2 is improved, and the curing shrinkage of the second hard coat layer 4 causes hard Curing shrinkage of the coat layer 3 can be offset and curl of the hard coat film 1A can be suppressed.

The second hard coat layer 4 may be made of the same material as the hard coat layer 3 described above, or may be made of different materials. In addition, the thickness of the second hard coat layer 4 may be the same as or different from that of the hard coat layer 3 described above.

The hard coat film 1A according to the present embodiment can be basically manufactured in the same manner as the hard coat film 1 described above. However, the curing of the hard coat layer 3 and the second hard coat layer 4 may be performed simultaneously, and the composition layer of the hard coat layer 3 (or the second hard coat layer 4) is formed and cured. After this, a composition layer of the second hard coat layer 4 (or hard coat layer 3) may be formed and cured.

(5) Other Embodiment-2

As shown in FIG. 3, on the other main surface side of the base film 2 in the hard coat film 1 (the surface side opposite to the surface on which the hard coat layer 3 is laminated), an adhesive layer 5 is applied. ) may be laminated (the code for the hard coat film shown in FIG. 3 is written as “1B”). By laminating such an adhesive layer 5, the hard coat film 1B can be easily attached to a desired adherend. Additionally, similarly, an adhesive layer may be laminated on the side of the second hard coat layer 4 in the hard coat film 1A opposite to the base film 2 side.

The adhesive constituting the adhesive layer 5 is not particularly limited, and known adhesives such as acrylic adhesives, rubber adhesives, and silicone adhesives can be used. The thickness of the adhesive layer 5 is not particularly limited, but is usually in the range of 5 to 100 μm, preferably 10 to 60 μm.

The hard coat film 1B according to the present embodiment can be basically manufactured in the same manner as the hard coat film 1 described above. The adhesive layer 5 may be formed by a normal method.

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

(6) Other Embodiment-3

Other layers, such as an adhesive layer, a barrier layer, a conductive layer, a low-reflection layer, an easy-to-print layer, an antifouling layer, etc., may be laminated on the hard coat film 1 according to this embodiment.

(7) Uses of hard coat film

The hard coat films 1, 1A, and 1B according to the above embodiments are, for example, flexible displays in various electronic devices, especially mobile electronic devices, specifically, liquid crystal displays (LCDs) and organic EL displays ( It can be suitably used as a flexible member of the surface layer (protective film) or middle layer of various flexible displays such as OELD) and electronic paper modules (electronic paper on film).

The embodiments described above are described to facilitate understanding of the present invention, and are not intended to limit the present invention. Therefore, each element disclosed in the above embodiment is intended to include all design changes and equivalents that fall within the technical scope of the present invention.

For example, between the base film 2 and the hard coat layer 3, the second hard coat layer 4, or the adhesive layer 5 in the hard coat films 1, 1A, and 1B, Other layers may intervene.

(Example)

Hereinafter, the present invention will be described in more detail through examples, etc., but the scope of the present invention is not limited to these examples.

[Production Example 1] (Production of base film 1)

In N,N-dimethylacetamide solvent, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, biphenyltetracarboxylic dianhydride, and 2,2-bis(3,4 -dicarboxyphenyl)hexafluoropropanoic acid dianhydride was mixed and dissolved under cooling, and then stirred at room temperature for 10 hours to obtain a polyamic acid solution.

Acetic anhydride and pyridine were added to the obtained polyamic acid solution, and after sufficient stirring, the solution was coated on a glass plate and the temperature was slowly raised from room temperature to 180°C. After reaching 180°C, it was heated for a certain period of time and then vacuum evacuated to completely remove volatile components. Finally, polyimide film A with a film thickness of 25 μm was obtained by cooling to room temperature under vacuum. When the polyimide film A was measured, b* was 0.61, the refractive index was 1.62, and the transmittance at a wavelength of 550 nm was 90%.

In addition, the film thickness of the polyimide film was measured using a constant pressure thickness meter (product name "PG-02", manufactured by Techrocsha) in accordance with JIS K7130.

For the above b*, in accordance with JIS Z8722, a simultaneous measurement spectroscopic colorimeter (manufactured by Nippon Denshoku Kogyo Corporation, product name "SQ-2000") was used as the measuring device, and a C light source 2° field of view (C/2) was used as the light source. Then, b* in the L*a*b* colorimetric system was measured using the transmission measurement method.

The transmittance at the wavelength of 550 nm was measured using an ultraviolet-visible-near-infrared spectral transmittance meter (manufactured by Shimadzu Seisakujo, product name "UV3600").

[Production Example 2] (Production of base film 2)

In N,N-dimethylacetamide solvent, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, biphenyltetracarboxylic dianhydride, and 2,2-bis(3,4 -Dicarboxyphenyl)Hexafluoropropanoic acid dianhydride was changed in the mixing ratio and the concentration of the resulting polyimide coating solution was adjusted. By carrying out the same production method as in Production Example 1, the film thickness was reduced. Polyimide film B was obtained with 15 μm, b* of 2.25, refractive index of 1.70, and transmittance of 87% at a wavelength of 550 nm (the measurement method was as described above).

[Example 1]

100 parts by mass of dipentaerythritol hexaacrylate as an active energy ray-curable component (converted to solid content; the same applies below), and surface-modified zirconium oxide fine particles as transition metal oxide fine particles (manufactured by CIK Nanotech, product name "ZRMIBK15WT%-F85", average particle size) : 15 nm) 150 parts by mass and 5 parts by mass of 1-hydroxycyclohexylphenyl ketone as a photopolymerization initiator were stirred and mixed in a mixed solvent containing methyl isobutyl ketone and cyclohexanone at a mass ratio of 1:1, and a hard coat was prepared. A coating liquid for the layer composition was obtained.

Next, the coating liquid of the hard coat layer composition was applied to one side of the polyimide film A as the base film using a Meyer bar and dried by heating at 70°C for 1 minute to form a composition layer of the hard coat layer composition.

After that, ultraviolet rays were irradiated from the composition layer side under the following conditions to cure the composition layer of the hard coat layer composition to form a hard coat layer (thickness: 3 μm), thereby obtaining a hard coat film.

<Ultraviolet irradiation conditions>

·UV irradiation device: UV irradiation device made by DS Yuasa Corporation

·Light source: high pressure mercury lamp

·Lamp power: 1.4kW

·Illuminance: 100mW/㎠

·Light quantity: 240mJ/㎠

·Conveyor speed: 1.2m/min

·Ultraviolet irradiation under nitrogen atmosphere (oxygen concentration 1% or less)

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

A hard coat film was made in the same manner as in Example 1, except that the type and mixing of each component constituting the composition for the hard coat layer, the thickness of the hard coat layer, and the type and thickness of the base film were changed as shown in Table 1. manufactured.

In addition, details such as abbreviations listed in Table 1 are as follows.

A: Dipentaerythritol hexaacrylate

B: Ethylene oxide modified dipentaerythritol hexaacrylate (12 moles of ethylene oxide introduced)

C: Surface-modified zirconium oxide fine particles (manufactured by CIK Nanotech, product name “ZRMIBK15WT%-F85”, average particle size: 15 nm)

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

E: 1-hydroxycyclohexylphenylketone

PI-25: Polyimide Film A

PI-15: Polyimide film B

PET: Polyethylene terephthalate film (Mitsubishi Juushi Co., Ltd., product name “Diafoil T-60”, thickness: 50㎛)

[Test Example 1] (Measurement of refractive index)

(1) Refractive index of the base film

The refractive index of the base film used in the examples and comparative examples was measured by JIS using an Abbe refractometer (manufactured by Atago Corporation, product name "Multiple Wavelength Abbe Refractometer DR-M2") under the conditions of a measurement wavelength of 589 nm and a measurement temperature of 25°C. Measurements were made based on K7142 (2008). The results are shown in Table 2.

(2) Refractive index of hard coat layer

On the untreated side of a polyethylene terephthalate film (manufactured by Toyobo Corporation, product name “Cosmo Shine A4100”, thickness: 50 μm), on which one side has been treated with easy adhesion, a hard layer with a thickness of 200 nm is applied in the same manner as in the examples and comparative examples. A coat layer was formed. Next, the easily adhesive treated surface of the polyethylene terephthalate film was rubbed with sandpaper and thoroughly painted black with an oil-based pen (made by Zebrasha, product name "Maki Black").

Thereafter, the refractive index of the hard coat layer was measured using a spectroscopic ellipsometer (manufactured by J.A.WOOLLAM, product name “M-2000”) under the conditions of a measurement wavelength of 589 nm and a measurement temperature of 25°C, according to JIS K7142 (2008). It was measured based on . The results are shown in Table 2.

(3) Calculation of refractive index difference

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

[Test Example 2] (Evaluation of interference)

(1) Visual evaluation

The hard coat film manufactured in the examples and comparative examples was spread over a black acrylic plate (manufactured by Mitsubishi Rayon Corporation, product name "Acrylite L502") through a double-sided adhesive sheet (manufactured by Lintech, product name "OPTERIA MO-3006C", thickness: 25㎛). 」). At this time, the base film of the hard coat film was attached so that it was in contact with the acrylic plate.

With respect to the obtained laminate, the interference signal was visually confirmed from the hard coat layer side under a three-wavelength fluorescent lamp, and evaluated based on the following criteria. The results are shown in Table 2.

Good (◎): Interference lines are barely visible.

Approximately good (○): Interference lines are difficult to see

Slightly defective (△): Interference signs are visible

Poor (×): Interference signal is clearly visible

(2) Measurement of maximum reflectance difference

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

<Measurement conditions>

・Spectrophotometer: Shimadzu Seisakujo Co., Ltd., product name: “Ultraviolet/Visible/Near-Infrared Spectrophotometer UV-3600”

・Sample folder: Shimadzu Seisakujo Co., Ltd., product name “Large sample chamber MPC-3100”

Integrating sphere: Shimadzu Seisakujo Co., Ltd., product name: “Integrating sphere attachment device ISR-3100”

·Angle of incidence: 8°

[Test Example 3] (Evaluation of scratch resistance)

The surface of the hard coat layer of the hard coat film manufactured in the examples and comparative examples was subjected to 10 reciprocal friction using #0000 steel wool at a load of 125 g/cm2, and the range was 100 mm in length and 20 mm in width. This was set as the test range. The number of scratches in the test range was confirmed visually under a three-wavelength fluorescent lamp, and the scratch resistance was evaluated based on the following standards. The results are shown in Table 2.

○: The number of scratches was less than 20.

×: The number of scratches was 20 or more.

[Test Example 4] (Mandrel test)

For the hard coat films manufactured in Examples and Comparative Examples, a mandrel test based on JIS K5600-5-1 was performed using a cylindrical mandrel bending tester (manufactured by Kotecsha). The mandrel test was conducted with the hard coat layer of the hard coat film facing the outside. Among the mandrels that did not have defects such as cracks or peeling in the hard coat layer, the diameter of the mandrel with the smallest diameter (minimum mandrel diameter) was obtained. The results are shown in Table 2.

[Test Example 5] (Bending resistance test)

For the hard coat films manufactured in the Examples and Comparative Examples, the hard coat layer was tested on the outer side using a durability tester (Yasa Systems Kikisha, product name: "Flat No-Load U-shaped Stretch Tester DLDMLH-FS"). In this way, the test speed was 60 mm/s, the number of tests (reciprocations) and bending diameter were changed variously, and bending was repeated. Then, the presence or absence of defects such as cracks and peeling of the hard coat layer and whitening and bending marks of the hard coat film was confirmed, and the bending resistance was evaluated based on the following standards. The results are shown in Table 2.

◎: No defects occurred even when the bending diameter was 5 mm or less and the number of tests was 20,000 or more.

○: No defects occurred even when the bending diameter was 10 mm or less and the number of tests was 20,000 or more.

×: It did not meet the standard of ○

[Test Example 6] (Evaluation of image clarity)

For the hard coat films manufactured in Examples and Comparative Examples, five types of slits (slits) were made in accordance with JIS K7374 using an image quality measuring device (manufactured by Suga Chemical Co., product name “ICM-10P”). The total value (width: 0.125 mm, 0.25 mm, 0.5 mm, 1 mm, and 2 mm) was measured as image clarity (%). Based on the results, image clarity of less than 400% was evaluated as ×, image clarity of 400% to less than 450% was evaluated as ○, and image clarity of 450% or more was evaluated as ◎. The results are shown in Table 2.

[Test Example 7] (Evaluation of haze value)

For the hard coat films manufactured in the examples and comparative examples, the haze value (%) was measured using a haze meter (manufactured by Nippon Denshoku Kogyo Corporation, product name "NDH5000") based on JIS K7136. Based on the results, a haze value of more than 1% was evaluated as ×, a haze value of 1% or less but more than 0.5% was evaluated as ○, and a haze value of 0.5% or less was evaluated as ◎. The results are shown in Table 2.

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

For the hard coat films manufactured in Examples and Comparative Examples, 60° glossiness (gloss value) was measured using a glossmeter (manufactured by Nippon Denshoku Kogyo Corporation) based on JIS Z8741-1997. Based on the results, 60° glossiness of less than 100% was evaluated as ×, 100% to less than 140% as ○, and 140% or more as ◎. The results are shown in Table 2.

[Table 1]

[Table 2]

As is clear from Table 2, the hard coat films obtained in the Examples had excellent scratch resistance and optical properties, excellent bending resistance, and were less likely to generate interference arcs.

The hard coat film of the present invention is suitable as a flexible member constituting a flexible display that is bent repeatedly, especially as a protective film located in the surface layer.

1, 1A, 1B: Hard coat film
2: Base film
3: Hard coat layer
4: Second hard coat layer
5: Adhesive layer

Claims (6)

A flexible display that is repeatedly bent,
The flexible display includes a hard coat film,
The hard coat film includes a base film and a hard coat layer laminated on at least one main surface side of the base film,
The base film is a polyimide film,
The difference between the refractive index of the polyimide film and the hard coat layer is 0.04 or less in absolute value,
The thickness of the polyimide film is 5 μm or more and 50 μm or less,
The hard coat layer is made of a material cured from a composition containing an active energy ray curable component and transition metal oxide fine particles,
The transition metal oxide fine particles are one or two types of zirconium oxide fine particles and titanium oxide fine particles,
The thickness of the hard coat layer is 0.5 μm or more and 10 μm or less.
A flexible display that is repeatedly bent, characterized in that. According to paragraph 1,
A flexible display that is repeatedly bent, characterized in that the refractive index of the hard coat layer is 1.40 or more and 1.85 or less. delete delete delete According to paragraph 1,
A flexible display that is repeatedly bent, characterized in that an adhesive layer is laminated on at least one main surface side of the base film.

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