CN109073789B

CN109073789B - Hard coating film

Info

Publication number: CN109073789B
Application number: CN201680085288.4A
Authority: CN
Inventors: 星野弘气; 大类知生; 所司悟
Original assignee: Lintec Corp
Current assignee: Lintec Corp
Priority date: 2016-08-23
Filing date: 2016-08-23
Publication date: 2021-07-13
Anticipated expiration: 2036-08-23
Also published as: CN113009602B; KR20190039466A; JPWO2018037489A1; JP6216907B1; KR102619222B1; TW201808607A; TWI759298B; CN113009602A; CN109073789A; WO2018037489A1

Abstract

The present invention provides a hard coat film (1) comprising a base film (2), a first hard coat layer (3) laminated on at least one main surface side of the base film (2), and a second hard coat layer (4) laminated on the main surface side of the first hard coat layer (3) opposite to the base film (2), wherein the base film (2) is a polyimide film, the first hard coat layer (3) and the second hard coat layer (4) are made of different materials, the difference between the refractive index of the first hard coat layer (3) and the refractive index of the second hard coat layer (4) is 0.04 or less in absolute value, and the total of the thickness of the first hard coat layer (3) and the thickness of the second hard coat layer (4) is 7 [ mu ] m or more and 35 [ mu ] m or less. The hard coating film (1) has bending resistance to withstand repeated bending, and is less likely to warp and further less likely to generate interference fringes.

Description

Hard coating film

Technical Field

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

Background

Various displays such as a Liquid Crystal Display (LCD), an organic EL display (OELD), and a touch panel are widely used in various electronic devices. In order to prevent damage, 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.

In recent years, however, as the display described above, a display capable of being bent, that is, a so-called flexible display, is being developed. Flexible displays are expected to be used in a wide range of applications, for example, as a stationary display that is provided on a column-shaped support by bending the display, or as a portable display that can be carried by bending or rounding the display. As a hard coat film for a flexible display, hard coat films disclosed in

patent documents

1 and 2 are proposed.

Here, the flexible display may be repeatedly bent (bent) as described in patent document 3, instead of being formed with only 1-fold curved surface.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 5468167

Patent document 2: japanese patent laid-open publication No. 2015-69197

Patent document 3: japanese patent laid-open publication No. 2016-2764

Disclosure of Invention

Technical problem to be solved by the invention

However, when the conventional hard coat film is used for a flexible display for such applications, there is a problem that a bend mark or whitening occurs in a repeatedly bent portion to deteriorate the appearance and the visibility of the display is reduced.

When the above-mentioned bending resistance to withstand repeated bending is required, there is a problem in optical characteristics such as yellowing and the like and transparency depending on the kind of the base film to be used. In addition, when the film thickness of the base film is reduced to improve this problem, the ratio of the hard coat layer to the entire hard coat film is relatively increased, and warpage is generated when the hard coat film is formed.

On the other hand, interference fringes may be generated in the hard coating film for various important reasons. If interference fringes occur in the hard coat film, the appearance deteriorates and the visibility of the display device deteriorates.

The present invention has been made in view of such circumstances, and an object thereof is to provide a hard coating film which has bending resistance to withstand repeated bending, is less likely to warp, and is less likely to generate interference fringes.

Means for solving the problems

In order to achieve the above object, a first aspect of the present invention provides a hard coat film comprising a base film, a first hard coat layer laminated on at least one main surface side of the base film, and a second hard coat layer laminated on a main surface side of the first hard coat layer opposite to the base film side, wherein the base film is a polyimide film, the first hard coat layer and the second hard coat layer are made of different materials, a difference between a refractive index of the first hard coat layer and a refractive index of the second hard coat layer is 0.04 or less in absolute value, and a total of a thickness of the first hard coat layer and a thickness of the second hard coat layer is 7 μm or more and 35 μm or less (invention 1).

The hard coat film of the invention (invention 1) is excellent in bending resistance by using a polyimide film as the base film and setting the total thickness of the first hard coat layer and the second hard coat layer within the above range. Further, when the difference between the refractive index of the first hard coat layer and the refractive index of the second hard coat layer is within the above range and the sum of the thickness of the first hard coat layer and the thickness of the second hard coat layer is within the above range, interference fringes are not easily generated in the hard coat film. Further, when the first hard coat layer and the second hard coat layer are formed of different materials and the total thickness of the first hard coat layer and the second hard coat layer is in the above range, the hard coat film is less likely to warp and has excellent scratch resistance.

In the above invention (invention 1), it is preferable that the first hard coat layer and the second hard coat layer are formed of a material obtained by curing a composition containing an active energy ray-curable component, and the first hard coat layer is formed of a material softer than the second hard coat layer (invention 2).

In the above inventions (inventions 1 and 2), it is preferable that: the first hard coat layer is formed of a material obtained by curing a composition containing an active energy ray-curable component modified with an alkylene oxide (alkylene oxide); the second hard coat layer is formed of a material obtained by curing a composition containing an active energy ray-curable component which is not modified with an alkylene oxide (invention 3).

In the above inventions (inventions 2 and 3), the active energy ray-curable component is preferably a polyfunctional (meth) acrylate monomer (invention 4).

In the above inventions (inventions 1 to 4), the refractive index of the first hard coat layer is preferably 1.40 or more and 1.80 or less (invention 5).

In the above inventions (inventions 1 to 5), the refractive index of the second hard coat layer is preferably 1.40 or more and 1.80 or less (invention 6).

In the above inventions (inventions 1 to 6), it is preferable that the thickness of the first hard coat layer is 3 μm or more and 30 μm or less (invention 7).

In the above inventions (inventions 1 to 7), it is preferable that the thickness of the second hard coat layer is 0.75 μm or more and 10 μm or less (invention 8).

In the above inventions (inventions 1 to 8), the thickness of the polyimide film is preferably 5 μm or more and 300 μm or less (invention 9).

The hard coat film of the above invention (inventions 1 to 9) is preferably used as a flexible member constituting a flexible display (invention 10)

In the above inventions (inventions 1 to 10), an adhesive layer is preferably laminated on at least one main surface side of the base film (invention 11).

Effects of the invention

The hard coat film of the present invention has excellent scratch resistance, has bending resistance to withstand repeated bending, and is less likely to warp and to generate interference fringes.

Drawings

Fig. 1 is a sectional view of a hard coat film according to an embodiment of the present invention.

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

Detailed Description

Hereinafter, embodiments of the present invention will be described.

Fig. 1 is a sectional view of a hard coat film according to an embodiment of the present invention. The hard coat film 1 of the present embodiment is configured to include a base film 2, a first hard coat layer 3 laminated on at least one main surface side (upper side in fig. 1) of the base film, and a second hard coat layer 4 laminated on a main surface side (upper side in fig. 1) of the first hard coat layer 3 opposite to the base film 2 side. The first hard coat layer 3 and the second hard coat layer 4 are formed of different materials.

In the hard coat film 1, the base film 2 is a polyimide film. When the base film 2 is a polyimide film and the hard coat film 1 is applied to a flexible display and repeatedly bent, occurrence of bending marks or whitening on the base film 2 can be suppressed, and excellent bending resistance can be obtained. Therefore, in the flexible display using the hard coat film 1 of the present embodiment, when a predetermined portion is repeatedly bent, deterioration in appearance or reduction in visibility of the bent portion can be suppressed.

The difference between the refractive index of the first hard coat layer 3 and the refractive index of the second hard coat layer 4 is 0.04 or less in absolute terms, and the total of the thickness of the first hard coat layer 3 and the thickness of the second hard coat layer 4 is 7 μm or more and 35 μm or less. By setting the difference between the refractive index of the first hard coat layer 3 and the refractive index of the second hard coat layer 4 to 0.04 or less in absolute value, reflection of light at the interface between the first hard coat layer 3 and the second hard coat layer 4 can be suppressed, and interference with reflected light on the surface of the second hard coat layer 4 is less likely to occur. Further, by making the total of the thickness of the first hard coat layer 3 and the thickness of the second hard coat layer 4 to be 7 μm or more, the thickness is considerably large compared with the wavelength of light, and light reflected at the interface between the first hard coat layer 3 and the base material film 2 does not easily interfere with light reflected at the surface of the second hard coat layer 4. Further, since the intensity of light reflected at the interface between the first hard coat layer 3 and the base film 2 (reflection intensity) is weak when passing through the first hard coat layer 3 and the second hard coat layer 4, interference with the reflected light from the surface of the second hard coat layer 4 is less likely to occur from the side surface. By these actions, the hard coat film 1 can be inhibited from generating interference fringes. In the present specification, the measurement wavelength of the refractive index is 589nm, and the measurement temperature is 25 ℃. The detailed method of measuring the refractive index is shown in the test examples described later.

From the viewpoint of suppressing the occurrence of interference fringes, the difference in absolute value between the refractive index of the first hard coat layer 3 and the refractive index of the second hard coat layer 4 is preferably 0.02 or less, and particularly preferably 0.01 or less.

Further, by making the total of the thickness of the first hard coat layer 3 and the thickness of the second hard coat layer 4 7 μm or more, the hard coat film 1 is also excellent in scratch resistance. From the viewpoint of suppressing the occurrence of interference fringes and scratch resistance, the total of the thickness of the first hard coat layer 3 and the thickness of the second hard coat layer 4 is preferably 9 μm or more, and particularly preferably 10m or more.

On the other hand, when the total of the thickness of the first hard coat layer 3 and the thickness of the second hard coat layer 4 is 35 μm or less, the hard coat film 1 is easily bent, and the bending resistance is excellent. From this viewpoint, the total of the thickness of the first hard coat layer 3 and the thickness of the second hard coat layer 4 is preferably 30 μm or less, and particularly preferably 25 μm or less.

Further, when the total of the thickness of the first hard coat layer 3 and the thickness of the second hard coat layer 4 is within the above range, and the first hard coat layer 3 and the second hard coat layer 4 are formed of different materials from each other, particularly, the first hard coat layer 3 is formed of a material softer than the second hard coat layer 4, warpage is not likely to occur at the time of producing the hard coat film 1.

(1) Hard coating film constituting member

(1-1) base Material film

The base film 2 of the hard coat film 1 of the present embodiment is a polyimide film, and in the case of a display, a transparent polyimide film with little yellowing is preferable. This makes it possible to obtain a display (particularly, a flexible display) that displays a clear image with high color reproducibility.

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

In addition, the polyimide film used in the present embodiment has an absolute value of L × a × b in a color system by a transmission measurement method, preferably 10 or less, more preferably 5 or less, and particularly preferably 3 or less, from the viewpoint of reducing yellowing. The measurement method of b in the present specification is shown in examples described later.

The polyimide film in the present specification means a film containing preferably 50% by mass or more, particularly preferably 80% by mass or more, and further preferably 90% by mass or more of polyimide, that is, a polymer having an imide bond in the main chain. Further, poly (meth) acrylimide is not polyimide because it has no imide bond in the main chain, and whitening occurs when such a poly (meth) acrylimide film is repeatedly bent.

The polyimide film can be obtained in the following manner, but is not limited thereto: the polyamic acid is produced by polymerizing tetracarboxylic acid anhydride (preferably aromatic tetracarboxylic acid dianhydride) and diamine (preferably aromatic diamine) in a solution to produce polyamic acid, and then forming the polyamic acid into a film, followed by dehydration ring closure of the polyamic acid portion.

The polyimide in the polyimide film may also be modified. For example, aromatic rings generally contained in polyimide may be modified with aliphatic hydrocarbons, and thus, the adhesion between the substrate film 2 and the second hard coat layer 4 becomes excellent.

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. The upper limit of 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.

In the polyimide film, one or both surfaces of the polyimide film may be subjected to a surface treatment by a primer treatment, an oxidation method, an embossing method, or the like as necessary for the purpose of improving adhesion to a layer (the second hard coat layer 4, an adhesive agent layer described later, or the like) provided on the surface thereof. Examples of the oxidation method include corona discharge treatment, chromic acid treatment, flame treatment, hot air treatment, and ozone/ultraviolet treatment, and examples of the concavo-convex method include sand blast treatment and solvent treatment.

The lower limit of 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. By setting the thickness of the polyimide film to be equal to or greater than the above, the hard coat film 1 exhibits a predetermined mechanical strength and is less likely to be broken 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, more preferably 50 μm or less, and most preferably 30 μm or less. Since the polyimide film is easily colored, when the thickness of the polyimide film is set to the above-mentioned value or less, the transparency can be secured, and the value of b can be suppressed to a low value, and thus the polyimide film can be suitably used for optical applications. When the thickness of the polyimide film is less than the above, the hard coat film 1 can exhibit predetermined flexibility and can be easily bent.

(1-2) first hard coat layer

The first hard coat layer 3 of the hard coat film 1 of the present embodiment is laminated on one main surface side (upper side in fig. 1) of the base film 2, and functions to suppress the occurrence of interference fringes and to exhibit scratch resistance in cooperation with the second hard coat layer 4 as described above.

The material of the first hard coat layer 3 is not particularly limited as long as the refractive index difference from the refractive index of the second hard coat layer 4 is within the above range and the second hard coat layer 4 exhibits the desired scratch resistance. The first hard coat layer 3 is preferably formed of a material obtained by curing a composition containing an active energy ray-curable component, and particularly preferably formed of a material softer than the second hard coat layer 4. Specifically, the curable composition is preferably formed of a material obtained by curing a composition containing an active energy ray-curable component modified with an alkylene oxide. By constituting the first hard coat layer 3 of a material softer than the second hard coat layer 4, the bending resistance becomes excellent. Further, the curing shrinkage of the first hard coat layer 3 is reduced, and even if the total thickness of the first hard coat layer 3 and the second hard coat layer 4 is thick, warpage can be suppressed from occurring at the time of producing the hard coat film 1.

(1-2-1) active energy ray-curable component

Examples of the active energy ray-curable component include a polyfunctional (meth) acrylate monomer, a (meth) acrylate prepolymer, and an active energy ray-curable polymer, and among them, a polyfunctional (meth) acrylate monomer and/or a (meth) acrylate prepolymer are preferable, and a polyfunctional (meth) acrylate monomer is more preferable. The polyfunctional (meth) acrylate monomer and the (meth) acrylate prepolymer may be used alone or in combination. In the present specification, the term (meth) acrylate refers to both acrylate and methacrylate. Other similar terms are also the same.

Examples of the polyfunctional (meth) acrylate monomer 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, 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, tris (acryloyloxyethyl) isocyanurate, and the like, Polyfunctional (meth) acrylates such as propionic acid-modified dipentaerythritol penta (meth) acrylate, dipentaerythritol hexa (meth) acrylate, dipentaerythritol tetra (meth) acrylate, caprolactone-modified dipentaerythritol hexa (meth) acrylate, and alkylene oxide-modified products thereof. These may be used alone or in combination of two or more.

Among the above, polyfunctional (meth) acrylate monomers modified with alkylene oxide are preferable from the viewpoint of the bending resistance and suppression of warpage of the obtained hard coat film. Specific examples thereof include preferably alkylene oxide-modified trimethylolpropane tri (meth) acrylate, alkylene oxide-modified dipentaerythritol hexa (meth) acrylate and alkylene oxide-modified dipentaerythritol tetra (meth) acrylate, particularly preferred are ethylene oxide-modified trimethylolpropane tri (meth) acrylate, propylene oxide-modified trimethylolpropane tri (meth) acrylate, ethylene oxide-modified dipentaerythritol hexa (meth) acrylate, propylene oxide-modified dipentaerythritol hexa (meth) acrylate, ethylene oxide-modified dipentaerythritol tetra (meth) acrylate, and propylene oxide-modified dipentaerythritol tetra (meth) acrylate, and further preferred are ethylene oxide-modified dipentaerythritol hexa (meth) acrylate and ethylene oxide-modified dipentaerythritol tetra (meth) acrylate. The polyfunctional (meth) acrylate modified with an alkylene oxide has a long distance between crosslinking points, exhibits relatively soft physical properties after curing, and has a small curing shrinkage. By forming the first hard coat layer 3 of such a material, even if the total thickness of the first hard coat layer 3 and the second hard coat layer 4 is thick, the bending resistance is excellent, and the occurrence of warpage in the production of the hard coat film 1 can be effectively suppressed.

The amount of the alkylene oxide introduced with respect to 1 mole of the polyfunctional (meth) acrylate is preferably 2 moles or more, particularly preferably 6 moles or more, and more preferably 20 moles or more. The amount of the compound to be introduced is preferably 50 mol or less, particularly preferably 45 mol or less, and more preferably 40 mol or less. When the amount of the alkylene oxide to be introduced is 2 moles or more, the curing shrinkage of the alkylene oxide-modified polyfunctional (meth) acrylate is small. When the alkylene oxide-modified polyfunctional (meth) acrylate is cured by adjusting the amount of the alkylene oxide to 50 mol or less, the desired hardness can be obtained.

The proportion of the alkylene oxide-modified polyfunctional (meth) acrylate in the active energy ray-curable component is preferably 30% by mass or more, more preferably 50% by mass or more, particularly preferably 80% by mass or more, and even more preferably 90% by mass or more, from the viewpoint of bending resistance and suppression of warpage. The ratio may be 100% by mass.

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

The polyester acrylate prepolymer can be obtained, for example, by: esterifying hydroxyl groups of a polyester oligomer having hydroxyl groups at both ends, which is obtained by condensing a polyvalent carboxylic acid with a polyvalent alcohol, with (meth) acrylic acid; alternatively, the hydroxyl group at the end of an oligomer obtained by adding an alkylene oxide to a polycarboxylic acid is esterified using (meth) acrylic acid.

The epoxy acrylate-based prepolymer can be obtained, for example, by: (meth) acrylic acid is reacted with an oxirane ring of a bisphenol type epoxy resin or a novolak type epoxy resin having a relatively low molecular weight and esterified.

The urethane acrylate prepolymer can be obtained, for example, by: the polyurethane oligomer obtained by the reaction of polyether polyol or polyester polyol with polyisocyanate is esterified using (meth) acrylic acid.

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

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

(1-2-2) photopolymerization initiator

When the first hard coat layer 3 is formed of a material obtained by curing a composition containing an active energy ray-curable component, when ultraviolet rays are used as active energy rays, the composition preferably contains a photopolymerization initiator. By containing the photopolymerization initiator in this manner, the active energy ray-curable component can be efficiently polymerized, and the polymerization curing time and the amount of ultraviolet radiation can be reduced.

Examples of such photopolymerization initiators include benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin n-butyl ether, benzoin isobutyl ether, acetophenone, dimethylaminoacetophenone, 2-dimethoxy-2-phenylacetophenone, 2-diethoxy-2-phenylacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-hydroxycyclohexylphenyl ketone, 2-methyl-1- [4- (methylthio) phenyl ] -2-morpholin-propan-1-one, 4- (2-hydroxyethoxy) phenyl-2- (hydroxy-2-propyl) ketone, benzophenone, p-phenylbenzophenone, and mixtures thereof, 4, 4' -diethylaminobenzophenone, dichlorobenzophenone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, 2-aminoanthraquinone, 2-methylthioxanthone, 2-ethylthioxanthone, 2-chlorothioxanthone, 2, 4-dimethylthioxanthone, 2, 4-diethylthioxanthone, benzyldimethylketal, acetophenone dimethylketal, p-dimethylaminobenzoate, oligo [ 2-hydroxy-2-methyl-1 [4- (1-methylvinyl) phenyl ] acetone ], 2,4, 6-trimethylbenzoyl-diphenyl-phosphine oxide, and the like. These may be used alone or in combination of two or more.

The lower limit of the content of the photopolymerization initiator in the composition is preferably 0.01 part by mass or more, particularly preferably 0.1 part by mass or more, and more preferably 1 part by mass or more, per 100 parts by mass of the active energy ray-curable component. The upper limit 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.

(1-2-3) silica nanoparticles

The composition constituting the first hard coat layer 3 may also contain silica nanoparticles. Thereby, the curing shrinkage of the first hard coat layer 3 can be further reduced.

The lower limit of the average particle diameter of the silica nanoparticles is preferably 2nm or more, particularly preferably 6nm or more, and further preferably 8nm or more. The upper limit is preferably 300nm or less, particularly preferably 100nm or less, and more preferably 50nm or less. If the average particle diameter of the silica nanoparticles is 2nm or more, the effect of reducing the curing shrinkage of the first hard coat layer 3 can be more easily obtained. When the average particle diameter of the silica nanoparticles is 300nm or less, scattering of light is less likely to occur in the obtained first hard coat layer 3, and the transparency of the first hard coat layer 3 is increased. In addition, the average particle diameter of the silica nanoparticles was measured by Zeta potential measurement.

Silica nanoparticles generally have silanol groups on the surface, and these silanol groups may reduce dispersibility in an organic solvent or resin having low polarity. The silica nanoparticles may also be modified with organic substances for the purpose of improving dispersibility and the like. Further, it is preferable to use silica nanoparticles in the form of an organosol (colloidal). By using the organic sol, the dispersibility of the silica nanoparticles becomes good, and the uniformity and light transmittance of the obtained first hard coat layer 3 are improved.

Modification with an organic substance can be performed using a conventional method. For example, by mixing CH₂＝C(CH₃)COO(CH₂)₃Si(OCH₃)₃The silane coupling agent having such a structure is added to an organosol of silica nanoparticles, heated to about 50 ℃, and stirred for several hours, thereby modifying the surface of the silica particles. The structure and amount of the silane coupling agent used can be appropriately selected depending on the degree of dispersibility of the silica nanoparticles.

As the organic solvent used in the organosol, methyl ethyl ketone, methyl isobutyl ketone, and the like, which are excellent in compatibility with the active energy ray-curable component and volatility when the first hard coat layer 3 is formed, are preferable.

When the first hard coat layer 3 of the present embodiment contains silica nanoparticles, the lower limit of the content thereof in the first hard coat layer 3 is preferably 5% by mass or more, particularly preferably 10% by mass or more, and more preferably 30% by mass or more. By setting the content of the silica nanoparticles to 5 mass% or more, the curing shrinkage of the first hard coat layer 3 can be easily further reduced. On the other hand, in the first hard coat layer 3, the upper limit of the content of the silica nanoparticles is preferably 80% by mass or less, particularly preferably 75% by mass or less, and more preferably 70% by mass or less. By setting the content of the silica nanoparticles to 80 mass% or less, the refractive index of the first hard coat layer 3 can be easily set to a value close to the refractive index of the second hard coat layer 4, and a layer using the composition for a hard coat layer can be easily formed.

The content of the silica nanoparticles can be determined from the blending ratio, and when the blending ratio is not clear, the content can be determined as follows. That is, a part of the first hard coat layer 3 of the hard coat film 1 is separated from the base film 2 as a piece or the like, and the separated piece of the first hard coat layer 3 is burned with an organic component in accordance with JIS 7250-1. Then, the mass% of the silica nanoparticles can be determined from the obtained ash.

(1-2-4) other Components

The composition constituting the first hard coat layer 3 of the present embodiment may contain various additives in addition to the above components. Examples of the various additives include ultraviolet absorbers, antioxidants, light stabilizers, antistatic agents, silane coupling agents, antioxidants, thermal polymerization inhibitors, colorants, surfactants, storage stabilizers, plasticizers, lubricants, antifoaming agents, organic fillers, wettability modifiers, and coating surface modifiers.

(1-2-5) physical Properties

The lower limit of the refractive index of the first hard coat layer 3 is preferably 1.40 or more, particularly preferably 1.43 or more, and more preferably 1.45 or more. The upper limit of the refractive index of the first hard coat layer 3 is preferably 1.80 or less, particularly preferably 1.70 or less, and more preferably 1.60 or less. By setting the refractive index of the first hard coat layer 3 within the above range, the refractive index difference from the refractive index of the second hard coat layer 4 can be easily set within the above range.

The thickness of the first hard coat layer 3 is preferably 3 μm or more, particularly preferably 4 μm or more, and further preferably 5 μm or more. The thickness of the first hard coat layer 3 is preferably 30 μm or less, particularly preferably 20 μm or less, and further preferably 15 μm or less. By setting the thickness of the first hard coat layer 3 to 3 μm or more, the occurrence of warpage in the production of the hard coat film 1 can be easily suppressed, and the scratch resistance of the first hard coat layer 3 becomes further excellent. When the thickness of the first hard coat layer 3 is 30 μm or less, the hard coat film 1 is easily bent and has further excellent bending resistance.

(1-3) second hard coat layer

The second hard coat layer 4 of the hard coat film 1 of the present embodiment imparts a high surface hardness to the hard coat film 1 and is excellent in scratch resistance. The second hard coat layer 4 and the first hard coat layer 3 are not particularly limited as long as they have a predetermined hardness while satisfying the above-described relationship in refractive index. The second hard coat layer 4 is preferably formed of a material obtained by curing a composition containing an active energy ray-curable component, and particularly preferably formed of a material obtained by curing a composition containing an active energy ray-curable component that is not modified with an alkylene oxide, from the viewpoint of obtaining more excellent scratch resistance.

As the active energy ray-curable component, the same active energy ray-curable component as that used for the first hard coat layer 3 can be used. Among them, active energy ray-curable components which are not modified with alkylene oxide are preferably used. Specifically, polyfunctional (meth) acrylates, urethane acrylate prepolymers, and mixtures thereof which are not modified with alkylene oxide are preferred, and particularly, aliphatic polyfunctional (meth) acrylates such as dipentaerythritol hexa (meth) acrylate and dipentaerythritol tetra (meth) acrylate, urethane acrylate prepolymers, and mixtures thereof are preferred from the viewpoint of obtaining bending resistance without impairing scratch resistance.

When the second hard coat layer 4 is formed of an active energy ray-curable component containing an alkylene oxide-modified polyfunctional (meth) acrylate, the content of the alkylene oxide-modified polyfunctional (meth) acrylate in the entire active energy ray-curable component used in the second hard coat layer 4 is preferably 60% by mass or less, more preferably 30% by mass or less, and particularly preferably 10% by mass or less, from the viewpoint of scratch resistance. The lower limit is 0 mass%.

When ultraviolet rays are used as the active energy rays to be irradiated for curing the active energy ray-curable component, the composition preferably contains a photopolymerization initiator. As the photopolymerization initiator, the same photopolymerization initiator as that used in the first hard coat layer 3 can be used.

The second hard coat layer 4 in the present embodiment may also contain a filler. This can impart a higher surface hardness to the second hard coat layer 4, and can further improve the scratch resistance.

The filler may be either an organic filler or an inorganic filler, and from the viewpoint of imparting higher surface hardness to the second hard coat layer 4, it is preferable to use an inorganic filler, and particularly preferable to use an inorganic filler chemically modified with an organic compound having a polymerizable functional group that is polymerized by irradiation with active energy rays. The filler may be used alone or in combination of two or more.

Examples of the inorganic filler include metal oxides such as silica, alumina, zirconia, titania, zinc oxide, germanium oxide, indium oxide, tin oxide, Indium Tin Oxide (ITO), antimony oxide, and cerium oxide; and a filler made of a metal fluoride such as magnesium fluoride or sodium fluoride. Among them, silica and alumina are preferable, and silica is particularly preferable, from the viewpoint of less influence on optical characteristics.

The surface of the filler, particularly silica filler, may also be chemically modified, and particularly preferably chemically modified by an organic compound having a polymerizable functional group that is polymerized by irradiation with active energy rays. The specific structure of the chemical modification is not limited, and examples thereof include a structure in which a polymerizable functional group is added via a silane coupling agent. In the case of such a structure, the filler and the active energy ray-curable component are chemically bonded by irradiation with the active energy ray, and peeling between them is less likely to occur, and the hardness of the second hard coat layer 4 is likely to increase. The filler chemically modified with the organic compound having a polymerizable functional group in this way is referred to as a reactive filler, and for example, if the filler is silica, it is referred to as a reactive silica filler.

The filler may be spherical or non-spherical in shape. When the shape is non-spherical, the shape may be indefinite, or may be a shape having a high aspect ratio such as a needle shape or a scale shape. The filler is preferably spherical from the viewpoint of ensuring the transparency of the second hard coat layer 4.

The lower limit of the average particle diameter of the filler is preferably 1nm or more, particularly preferably 3nm or more, and further preferably 5nm or more. By making the average particle diameter of the filler 1nm or more, the dispersibility is improved. The upper limit of the average particle diameter of the filler is preferably 500nm or less, particularly preferably 200nm or less, and further preferably 50nm or less. When the average particle diameter of the filler is 500nm or less, scattering of light is not easily generated in the obtained second hard coat layer 4, and transparency of the second hard coat layer 4 is increased. The average particle diameter of the filler is a primary particle diameter measured by Zeta potential measurement.

When the second hard coat layer 4 of the present embodiment contains a filler, the lower limit of the content thereof is preferably 5% by mass or more, particularly preferably 20% by mass or more, and more preferably 50% by mass or more. By setting the filler content to 5 mass% or more, the hardness of the second hard coat layer 4 can be effectively increased. On the other hand, in the second hard coat layer 4, the upper limit of the content of the filler is preferably 90% by mass or less, particularly preferably 80% by mass or less, and more preferably 70% by mass or less. By setting the content of the filler to 90 mass% or less, layer formation becomes easy.

The second hard coat layer 4 of the present embodiment may contain various additives similar to those used for the first hard coat layer 3, in addition to the above components.

The lower limit of the refractive index of the second hard coat layer 4 is preferably 1.40 or more, particularly preferably 1.43 or more, and more preferably 1.45 or more. The upper limit of the refractive index of the second hard coat layer 4 is preferably 1.80 or less, particularly preferably 1.70 or less, and more preferably 1.60 or less. By setting the refractive index of the second hard coat layer 4 within the above range, the refractive index difference from the refractive index of the first hard coat layer 3 can be easily set within the above range.

The thickness of the second hard coat layer 4 is preferably 0.75 μm or more, particularly preferably 1 μm or more, and further preferably 1.5 μm or more. The thickness of the second hard coat layer 4 is preferably 10 μm or less, particularly preferably 8 μm or less, and more preferably 6 μm or less. By setting the thickness of the second hard coat layer 4 to 0.75 μm or more, the scratch resistance of the second hard coat layer 4 becomes more excellent. When the thickness of the second hard coat layer 4 is 10 μm or less, the occurrence of warpage in the hard coat film 1 can be further suppressed.

The ratio of the thickness of the first hard coat layer 3 to the thickness of the second hard coat layer 4 is preferably 10:90 to 90:10, particularly preferably 40:60 to 80:20, and further preferably 50:50 to 80: 20. When the ratio is within the above range, the hard coating film 1 obtained is more excellent in scratch resistance and bending resistance, and the occurrence of warpage can be further suppressed.

(2) Method for producing hard coat film

The hard coat film 1 of the present embodiment can be produced by the following method. In the present method, as an example, a composition containing an active energy ray-curable component is used for forming the first hard coat layer 3 and the second hard coat layer 4.

First, a coating liquid containing a composition constituting the first hard coat layer 3 (composition for the first hard coat layer 3) and, if necessary, a composition for the first hard coat layer 3 further containing a solvent is prepared. Further, a coating liquid containing a composition constituting the second hard coat layer 4 (composition for the second hard coat layer 4), and a composition for the second hard coat layer 4 further containing a solvent as necessary, is prepared in the same manner.

Examples of the solvent include aliphatic hydrocarbons such as hexane and heptane, aromatic hydrocarbons such as toluene and xylene, halogenated hydrocarbons such as methylene chloride and dichloroethane, 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 solvents such as ethyl cellosolve. One solvent may be used alone, or two or more solvents may be used in combination. The concentration and viscosity of the coating liquid are not particularly limited as long as they are in a range in which the coating liquid can be applied, and can be appropriately selected according to the situation.

After a coating liquid of the composition for the first hard coat layer 3 is applied to one main surface of the base material film 2 and dried, the coating liquid is irradiated with an active energy ray under the conditions described later. Thereby, the coating film of the composition for the first hard coat layer 3 is cured and the first hard coat layer 3 is formed. Next, a coating liquid of the composition for the second hard coat layer 4 was applied on the obtained first hard coat layer and dried, and then irradiated with active energy rays in accordance with the conditions described later. Thereby, the coating film of the composition for the second hard coat layer 4 is cured, and the second hard coat layer 4 is formed. The method for forming the first hard coat layer 3 and the second hard coat layer 4 is not limited to the above-described method, and the first hard coat layer 3 and the second hard coat layer 4 may be formed simultaneously by sequentially applying and drying the coating liquids of the two layers and irradiating the coating liquids with primary active energy rays.

The coating liquid may be applied by a conventional method, and for example, it may be applied by a bar coating method, a blade coating method, a meyer bar method, a roll coating method, a blade coating method, a die coating method, or a gravure coating method. The coating film can be dried by heating at 40 to 180 ℃ for about 30 seconds to 5 minutes, for example.

As the active energy ray, ultraviolet rays, electron beams, or the like can be used. The ultraviolet irradiation can be performed by using a high pressure mercury lamp, a photo-curing H lamp (fusion H lamp), a xenon lamp, or the like, and the irradiation amount of the ultraviolet is preferably 50 to 1000mW/cm in terms of illuminance²Preferably 50 to 1000mJ/cm in light amount²Left and right. On the other hand, the electron beam irradiation can be performed by 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 coating film of the composition for the first hard coat layer 3 and the coating film of the composition for the second hard coat layer 4 are preferably irradiated with ultraviolet rays in a state isolated from oxygen. Thus, a hard coat film having excellent bending resistance and high surface hardness can be efficiently formed without being inhibited by curing by oxygen.

In order to isolate the coating film of the composition for the first hard coat layer 3 and the coating film of the composition for the second hard coat layer 4 from oxygen, it is preferable to laminate a cover sheet on the coating films or to maintain an atmosphere having a low oxygen concentration, for example, a nitrogen atmosphere.

(3) Physical Properties of hard coating film

(3-1) maximum reflectance difference

As described above, in the hard coat film 1 of the present embodiment, the occurrence of interference fringes can be suppressed. This can be evaluated not only visually but also by the measurement value of the maximum reflectance difference. For measuring the maximum reflectance difference, light is first irradiated from the direction of an incident angle of 8 ° with the film normal direction set to 0 °, and the light reflected by the light is condensed by an integrating sphere to be detected as reflected light. The light is irradiated by changing the wavelength, and the reflected light corresponding to each wavelength is detected.

The reflected light is detected for each measurement wavelength so that the reflected light generated by the barium sulfate crystal has a relative value of 100 (hereinafter referred to as "reflectance"). That is, a graph with the horizontal axis representing the measurement wavelength and the vertical axis representing the reflectance can be obtained. The graph is typically an undulating shape having a plurality of minima and maxima.

In the graph for measuring the reflectance at a wavelength of 500 to 600nm, the maximum 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 further preferably 0.6 or less. By setting the reflectance to 1.5 or less, the occurrence of interference fringes can be suppressed.

(3-2) image sharpness

The hard coat film 1 of the present embodiment solves the problem of preventing interference fringes by providing the first hard coat layer 3 and the second hard coat layer 4 having a predetermined refractive index difference and thickness, without adding fine particles (micro order). Therefore, the hard coat film 1 of the present embodiment can provide more excellent image clarity than when interference fringes are prevented by adding fine-order fine particles.

When a hard coat film having excellent image sharpness is applied to a display, a display having an image with excellent contrast can be obtained. From such a viewpoint, the image sharpness is preferably 400% or more, more preferably 430% or more, and particularly preferably 450% or more.

The image sharpness was obtained as a total value of the sharpness of each image measured in 5 types of slits (slit width: 0.125mm, 0.25mm, 0.5mm, 1mm, and 2mm) according to JIS K7374.

(3-3) haze value

In the case of application to a display, the haze value of the hard coat film 1 measured according to JIS K7136 is preferably 1% or less, more preferably 0.8% or less, and particularly preferably 0.5% or less, from the viewpoint of displaying a clearer image.

(3-4)60 ℃ gloss

In the case of application to a display, from the viewpoint of displaying a clearer image, the 60 ° Gloss (Gloss value) according to JIS Z8741-1997 on the second hard coat layer 4 side in the hard coat film 1 is preferably set to a value of 100% or more, more preferably 120% or more, and particularly preferably 140% or more.

(4) Other embodiments

As shown in fig. 2, an adhesive layer 5 (the symbol of the hard coat film shown in fig. 2 is denoted by "1A") may be laminated on the other main surface side (the surface side opposite to the surface on which the first hard coat layer 3 and the second hard coat layer 4 are laminated) of the base film 2 of the hard coat film 1. By laminating such an adhesive layer 5, the hard coat film 1A can be easily attached to a desired adherend.

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 5 to 100 μm, preferably 10 to 60 μm.

The hard coat film 1A of the present embodiment can be produced basically in the same manner as the hard coat film 1 described above. The adhesive layer 5 may be formed by a conventional method.

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

(5) Other embodiment mode-2

The

hard coat films

1 and 1A of the present embodiment may be laminated with other layers such as a pressure-sensitive adhesive layer, a barrier layer (barrier layer), a conductive layer, a low reflection layer, an easy-to-print layer, and an antifouling layer.

(6) Use of hard coat film

The

hard coat films

1 and 1A of the above embodiments can be preferably used as, for example, flexible members of surface layers (protective films) of various flexible displays in various electronic devices, particularly mobile electronic devices, specifically, Liquid Crystal Displays (LCDs), organic EL displays (OELDs), electronic paper modules (film-like electronic paper), and the like.

When the

hard coat films

1 and 1A or the flexible display according to the present embodiment are bent, it is preferable that the

hard coat films

1 and 1A are bent with the side where the first hard coat layer 3 and the second hard coat layer 4 are present as the inner side. This makes it difficult for defects such as cracks to occur in the first hard coat layer 3 and the second hard coat layer 4.

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 embodiments is intended to include all design modifications and equivalents that fall within the technical scope of the present invention.

For example, another layer may be present between the

hard coat films

1 and 1A as long as the effects of the present embodiment are not hindered.

Examples

The present invention will be described in more detail with reference to examples and the like, but the scope of the present invention is not limited to these examples and the like.

[ production example 1] (production of base Material film)

In an N, N-dimethylacetamide solvent, 2 '-bis (trifluoromethyl) -4, 4' -diaminobiphenyl, biphenyltetracarboxylic dianhydride, and 2, 2-bis (3, 4-dicarboxyphenyl) hexafluoropropanoic dianhydride were 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 sufficiently stirring, the polyamic acid solution was coated on a glass plate, and the temperature was gradually raised from room temperature to 180 ℃. After reaching 180 ℃, heating was performed for a certain time, followed by vacuum, whereby volatile components were completely removed. Finally, the film was cooled to room temperature under vacuum to obtain a polyimide film having a thickness of 25 μm. The polyimide film was measured, and as a result, b was 0.61, the refractive index was 1.62, and the transmittance at a wavelength of 550nm was 90%.

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

B in the above-mentioned color system was measured by a transmission measurement method using a simultaneous measurement type spectrocolorimeter (NIPPON DENSHOKU INDUSTRIES co., ltd., product name "SQ-2000") as a measurement device and a C light source 2 ° field of view (C/2) as a light source according to JIS Z8722.

The transmittance at a wavelength of 550nm was measured using an ultraviolet-visible near-infrared spectral transmittance meter (manufactured by Shimadzu Corporation, product name "UV 3600").

[ example 1]

100 parts by mass (in terms of solid content; the same applies hereinafter) of ethylene oxide-modified dipentaerythritol hexaacrylate (12 moles of ethylene oxide introduced) as an active energy ray-curable component and 5 parts by mass of 1-hydroxycyclohexyl phenyl ketone as a photopolymerization initiator were stirred and mixed in a mixed solvent in which methyl isobutyl ketone and cyclohexanone were mixed in a mass ratio of 1:1 to obtain a coating liquid of the first hard coat layer composition.

In addition, a mixture of 40 parts by mass of dipentaerythritol hexaacrylate as an active energy ray-curable component, 60 parts by mass of a reactive silica filler (average particle diameter: 15nm) as a filler, and 10 parts by mass of 1-hydroxycyclohexyl phenyl ketone as a photopolymerization initiator was stirred in a mixed solvent in which methyl isobutyl ketone and cyclohexanone were mixed in a mass ratio of 1:1 to obtain a coating liquid of the second hard coat layer composition.

Next, a coating liquid of the first hard coat composition was applied to one surface of the polyimide film as the base film obtained in production example 1 using a meyer rod, and heated and dried at 70 ℃ for 1 minute to form a coating film of the first hard coat composition. Then, the coating film of the first hard coat layer composition was cured by irradiating ultraviolet rays from the coating film side of the first hard coat layer composition under the following conditions, thereby forming a first hard coat layer having a thickness of 5 μm.

Next, a coating liquid of the second hard coat layer composition was applied on the obtained first hard coat layer, and dried by heating at 70 ℃ for 1 minute to form a coating film of the second hard coat layer composition. Then, the coating film of the second hard coat layer composition was cured by irradiating ultraviolet rays from the coating film side of the second hard coat layer composition under the following conditions, thereby forming a second hard coat layer having a thickness of 5 μm. Thus, a hard coat film was obtained in which a first hard coat layer (thickness: 5 μm) and a second hard coat layer (thickness: 5 μm) were sequentially formed on a polyimide film (thickness: 25 μm) as a base film.

< ultraviolet irradiation conditions >

Ultraviolet irradiation apparatus: ultraviolet irradiation device manufactured by GS Yuasa Corporation

Light source: high pressure mercury lamp

Lamp power: 1.4kW

Illuminance: 100mW/cm²

Light amount: 240mJ/cm²

Conveyor belt speed: 1.2m/min

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

Examples 2 to 5 and comparative examples 1 to 6

A hard coat film was produced in the same manner as in example 1, except that the kind and blending ratio of each component constituting the first hard coat layer composition and the second hard coat layer composition, the thicknesses of the first hard coat layer and the second hard coat layer, and the kind and thickness of the base material film were changed as shown in table 1.

Here, the total thickness of the first hard coat layer and the thickness of the second hard coat layer was calculated and shown in table 1.

The abbreviations and the like shown in table 1 are as follows.

A: ethylene oxide-modified dipentaerythritol hexaacrylate (12 mol ethylene oxide introduced)

B: ethylene oxide-modified dipentaerythritol hexaacrylate (6 moles ethylene oxide introduced)

C: ethylene oxide modified pentaerythritol tetraacrylate (35 mol ethylene oxide introduced)

D: vinyl ester resin (Hitachi Chemical Co., Ltd., product name "Hitaloid 7663" by Ltd.)

E: dipentaerythritol hexaacrylate

F: silica nanoparticles (silica sol) (manufactured by Nissan Chemical Corporation, product name "MIBK-ST", average particle diameter: 10nm)

G: 1-hydroxycyclohexyl phenyl ketones

H: a mixture of 40 parts by mass of dipentaerythritol hexaacrylate, 60 parts by mass of a reactive silica filler (average particle diameter: 15nm), and 10 parts by mass of 1-hydroxycyclohexyl phenyl ketone

1: mixture of 50 parts by mass of 6-functional urethane acrylate prepolymer, 50 parts by mass of pentaerythritol tetraacrylate and 10 parts by mass of 1-hydroxycyclohexyl phenyl ketone

The details of the abbreviation symbols and the like described in table 2 are as follows.

PI: polyimide film

PET: polyethylene terephthalate film (manufactured by Mitsubishi Plastics, Inc., product name "Diafil T-60" thickness: 50 μm)

[ test example 1] (measurement of refractive index)

(1) Refractive index of substrate film

The refractive index of the substrate films used in examples and comparative examples was measured using an abbe refractometer (ATAGO co., LTD, product name "multi-wavelength abbe refractometer DR-M2"), according to JIS K7142(2008), under conditions of a measurement wavelength of 589nm and a measurement temperature of 25 ℃. The results are shown in Table 2.

(2) Refractive index of hard coating

In the same manner as in examples and comparative examples, a first hard coat layer or a second hard coat layer having a thickness of 200nm was formed on an untreated side of a polyethylene terephthalate film (TOYOBO CO., LTD., product name "COSMOSHINE A4100", thickness: 50 μm) having one side subjected to an easy adhesion treatment. Next, the easy adhesion treated face of the polyethylene terephthalate film was rubbed with sandpaper and painted black with an oil pen (ZEBRA co., ltd., product name "Mckee black").

Then, the refractive indices of the first hard coat layer and the second hard coat layer were measured according to JIS K7142(2008) using a spectroscopic ellipsometer (product name "M-2000" manufactured by j.a. woollam co.) under conditions that the measurement wavelength was 589nm and the measurement temperature was 25 ℃. 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 second hard coat layer from the refractive index of the first hard coat layer measured above. The results are shown in Table 2.

[ test example 1] (evaluation of interference fringe)

(1) Visual evaluation

The hard coat films produced in examples and comparative examples were applied to a black acrylic plate (MITSUBISHI ray co., ltd., product name "acrylic L502") via a double-sided adhesive sheet (manufactured by LINTEC CORPORATION, product name "OPTERIA MO-3006C", thickness: 25 μm). At this time, the base film of the hard coat film was attached so as to be in contact with the acrylic plate.

The obtained laminate was evaluated by visually checking interference fringes from the hard coat layer side under a 3-wavelength fluorescent lamp according to the following criteria. The results are shown in Table 2.

Good (excellent): interference fringes are hardly visible

Substantially good (∘): interference fringes are not easy to see

Slightly poor (Δ): see interference fringes

Poor (x): interference fringes are clearly seen

(2) Determination of maximum reflectance difference

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

< measurement conditions >

Spectrophotometer: manufactured by Shimadzu corporation, product name "ultraviolet-visible near-infrared spectrophotometer UV-3600"

Sample holder (specimen holder): manufactured by Shimadzu corporation, product name "Large Scale laboratory MPC-3100"

Integrating sphere: manufactured by Shimadzu corporation, product name "integrating sphere attachment ISR-3100"

Angle of incidence: 8 degree

[ test example 3] (evaluation of scratch resistance)

Hard materials produced in examples and comparative examplesThe hard coat surface of the coating film was coated with a steel wool of #0000 at a weight of 125 g/cm²The test range was defined as a range of 100mm in length and 20mm in width. The number of scratches in this test range was visually confirmed under a 3-wavelength fluorescent lamp, and the scratch resistance was evaluated according to the following criteria. The results are shown in Table 2.

O: the number of the scar strips is less than 20.

X: the number of the scar strips is more than 20.

[ test example 4] (warpage evaluation)

The hard coat films produced in examples and comparative examples were cut to 100 × 100mm so that each side was parallel to the MD direction (the line direction in the production of a polyimide film) or the TD direction (the direction orthogonal to the MD direction), and then the hard coat films were placed on a flat glass plate so that the substrate film became the glass plate side. Next, the height of the rise from the upper surface of the glass plate to the apex of each corner of the hard coat film was measured, and the warpage was evaluated based on the following criteria. The results are shown in Table 2.

Very good (verycirco): of the 10 samples, the total of the floating heights of the corners of the 10 samples was less than 20mm

Good (∘): in 10 samples, the total of the buoyed-up of each corner of 9-6 samples is less than 20mm

Poor (x): in 10 samples, the total of the buoyed-up of each corner of 5-0 samples is less than 20mm

[ test example 5] (bending resistance test)

The hard coat films produced in examples and comparative examples were repeatedly bent at a test speed of 60mm/s while changing the number of tests (round trip number) and the bending diameter variously using a durability tester (YUASA SYSTEM co., ltd., product name "plane body no-load U-shaped elongation tester DLDMLH-FS") with the hard coat layer on the inner side. Then, whether or not defects such as cracking and peeling of the hard coat layer, whitening of the hard coat film, and occurrence of a bending mark were caused was checked, and the bending resistance was evaluated according to the following criteria. The results are shown in Table 2.

Very good: the bending diameter is 5mm or less, and no trouble occurs even if the number of tests is 2 ten thousand or more.

O: the bending diameter is 10mm or less, and no trouble occurs even if the number of tests is 2 ten thousand or more.

X: the reference value of O is not reached.

[ test example 6] (evaluation of image clarity)

The hard coat films produced in examples and comparative examples were measured for the total value of 5 types of slits (slit width: 0.125mm, 0.25mm, 0.5mm, 1mm, and 2mm) as the image clarity (%) according to JIS K7374 using an image clarity measuring instrument (manufactured by Suga Test Instruments co., ltd., product name "ICM-10P"). Based on the results, the image clarity was rated "x" when the image clarity was less than 400%, rated "o" when the image clarity was 400% or more and less than 450%, and rated "excellent" when the image clarity was 450% or more. The results are shown in Table 2.

(test example 7) (evaluation of haze value)

The hard coat films produced in examples and comparative examples were measured for haze value (%) in accordance with JIS K7136 using a haze meter (NIPPON DENSHOKU INDUSTRIES co., ltd., product name "NDH 5000"). Based on the results, the haze value of more than 1% was rated as x, the haze value of 1% or less and more than 0.5% was rated as o, and the haze value of 0.5% or less was rated as excellent. The results are shown in Table 2.

(test example 8) (evaluation of 60 ℃ gloss)

The hard coat films produced in examples and comparative examples were measured for 60 ° gloss in accordance with JIS Z8741-1997 using a gloss meter (NIPPON DENSHOKU indestandards co., ltd. Based on the results, the 60 ° gloss was rated "x" when it was less than 100%, rated "o" when it was 100% or more and less than 140%, and rated "excellent" when it was 140% or more. The results are shown in Table 2.

As is clear from table 2, the hard coat films obtained in the examples have excellent scratch resistance and optical characteristics, and also have excellent bending resistance and are less likely to cause interference fringes and warpage.

Industrial applicability

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

Description of the reference numerals

1. 1A: hard coating; 2: a substrate film; 3: a first hard coat layer; 4: a second hard coat layer; 5: an adhesive layer.

Claims

1. A hard coat film comprising a base film, a first hard coat layer laminated on at least one main surface side of the base film, and a second hard coat layer laminated on a main surface side of the first hard coat layer opposite to the base film side,

the substrate film is a polyimide film,

the first hard coating layer and the second hard coating layer are formed of different materials from each other,

the first hard coat layer is formed of a material obtained by curing a composition containing an active energy ray-curable component modified with an alkylene oxide,

the second hard coat layer is formed of a material obtained by curing a composition containing an active energy ray-curable component that is not modified with an alkylene oxide,

the difference between the refractive index of the first hard coat layer and the refractive index of the second hard coat layer is 0.04 or less in absolute value,

the sum of the thickness of the first hard coat layer and the thickness of the second hard coat layer is 7 to 35 μm,

the hard coat film is used as a flexible member constituting a flexible display.

2. The hard coating film according to claim 1,

the first hard coat layer and the second hard coat layer are formed of a material obtained by curing a composition containing an active energy ray-curable component,

the first hard coating layer is formed of a softer material than the second hard coating layer.

3. The hard coat film according to claim 1, wherein the active energy ray-curable component is a polyfunctional (meth) acrylate monomer.

4. The hard coat film according to claim 1, wherein the refractive index of the first hard coat layer is 1.40 or more and 1.80 or less.

5. The hard coat film according to claim 1, wherein the refractive index of the second hard coat layer is 1.40 or more and 1.80 or less.

6. The hard coat film according to claim 1, wherein the thickness of the first hard coat layer is 3 μm or more and 30 μm or less.

7. The hard coat film according to claim 1, wherein the thickness of the second hard coat layer is 0.75 μm or more and 10 μm or less.

8. The hard coat film according to claim 1, wherein the thickness of the polyimide film is 5 μm or more and 300 μm or less.

9. The hard coat film according to claim 1, wherein an adhesive layer is laminated on at least one main surface side of the base film.