WO2018070523A1

WO2018070523A1 - Optical film and image display device

Info

Publication number: WO2018070523A1
Application number: PCT/JP2017/037193
Authority: WO
Inventors: 征一磯嶋; 篤弘小林; 橋本　裕介
Original assignee: 大日本印刷株式会社
Priority date: 2016-10-14
Filing date: 2017-10-13
Publication date: 2018-04-19
Also published as: TWI734849B; JPWO2018070523A1; JP7155472B2; TW201827231A

Abstract

According to one aspect of the present invention, an optical film 10, which can be used in an image display device, is foldable, and is light transmissive, is provided, the optical film 10 being provided with: a base material 11; and a resin layer 12 having a multilayer structure in which first to nth (n is an integer of 3 or more) layers are laminated, in that order starting from the side of the base material 11, on one surface 11A of the base material, wherein the indentation hardness of the first to nth layers of the resin layer 12 increases in the order from the first layer to the nth layer.

Description

Optical film and image display device

Reference to related applications

This application enjoys the benefit of the priority of Japanese Patent Application No. 2016-203116 (filing date: October 14, 2016), which is a prior Japanese application, the entire disclosure of which is incorporated herein by reference. To be part of

The present invention relates to an optical film and an image display device.

Conventionally, image display devices such as smartphones and tablet terminals are known, but a foldable image display device is currently being developed. Usually, smartphones and tablet devices are covered with a cover glass, but glass generally does not bend although it has excellent hardness, so if you use a cover glass for the image display device, try to fold it. Then there is a high risk of breaking. For this reason, it has been studied to use a foldable optical film including a base material to be bent and a resin layer instead of a cover glass for a foldable image display device (for example, Japanese Patent Application Laid-Open No. 2016-125063). See the official gazette).

An optical film used in such a foldable image display device is required to have excellent foldability, pencil hardness, and impact resistance. In impact resistance, when an impact is applied to the surface of the optical film, the surface of the optical film may be recessed, and in the image display device, a member that exists inside the optical film (for example, an organic light-emitting diode panel or the like). Display panel) may be damaged, so that when the impact is applied to the surface of the optical film, the dent on the surface of the film is suppressed, and the members existing inside the image display device are damaged more than the optical film. There is a need for impact resistance that is not affected.

On the other hand, if the optical film is folded so that the resin layer is on the inside, wrinkles and fine cracks may occur on the surface of the resin layer. For this reason, in an optical film, the outstanding flexibility is further calculated | required. A wrinkle here is a wrinkle observed in the bending part of an optical film when an optical film is folded, and is not a wrinkle observed when an optical film is folded and an optical film is returned to a flat shape again.

Furthermore, unlike large televisions, image display devices such as smartphones and tablet terminals are sometimes stored in clothes pockets or bags. The display surface may be rubbed by stored items. For this reason, the optical film is further required to have excellent scratch resistance.

However, the present situation is that an optical film having excellent bendability and excellent scratch resistance in addition to excellent foldability, excellent pencil hardness, and excellent impact resistance has not been obtained.

The present invention has been made to solve the above problems. That is, an object is to provide a foldable optical film having excellent foldability, excellent pencil hardness, excellent impact resistance, excellent bendability, and excellent scratch resistance, and an image display device including the foldable optical film. And

As a result of diligent research on the above problems, the inventors of the present invention laminated three or more resin layers and gradually increased the indentation hardness of the resin layer toward the surface side of the optical film. It has been found that excellent foldability, excellent pencil hardness, excellent impact resistance, excellent flexibility, and excellent scratch resistance can be obtained. The present invention has been completed based on such findings.

According to one aspect of the present invention, there is a foldable light-transmitting optical film used in an image display device, from the first layer to the n-th layer (n is an integer of 3 or more) in this order. A resin layer having a multilayered structure, and the indentation hardness of each of the first layer to the n-th layer in the resin layer increases in order from the first layer to the n-th layer. A film is provided.

The optical film may further include a substrate provided on the first layer side of the resin layer.

In the optical film, n is 3, and in the resin layer, the indentation hardness of the first layer is 1 MPa or more and 100 MPa or less, and the indentation hardness of the second layer is 10 MPa or more and 500 MPa or less. The indentation hardness of the third layer may be 100 MPa or more and 1000 MPa or less.

In the optical film, n is 4, and in the resin layer, the indentation hardness of the first layer is 1 MPa or more and 100 MPa or less, and the indentation hardness of the second layer is 10 MPa or more and 300 MPa or less. The indentation hardness of the third layer may be 50 MPa or more and 500 MPa or less, and the indentation hardness of the fourth layer may be 100 MPa or more and 1000 MPa or less.

In the optical film, the optical film may have a Young's modulus of 3 GPa or more.

In the optical film, a yellow index of the optical film may be 15 or less.

In the optical film, the optical film is placed on a soda glass plate having a thickness of 0.7 mm so that the first layer is positioned closer to the soda glass plate than the n layer, and the nth layer of the resin layer is formed. When an iron ball having a weight of 100 g and a diameter of 30 mm is dropped from a position with a height of 30 cm with respect to the surface, it is preferable that no depression is generated on the surface of the n-th layer and no crack is generated on the soda glass plate. .

In the optical film, when the surface of the n-th layer of the resin layer is subjected to a steel wool test in which the steel layer is rubbed 10 times while applying a load of 1 kg / cm ² , the surface of the n-th layer It is preferable that neither cracks nor scratches are confirmed.

In the above optical film, it is preferable that no cracking or breakage occurs when the test of folding 180 ° so that the distance between the opposing sides of the optical film is 6 mm is repeated 100,000 times at 25 ° C.

In the optical film, the base material may be a base material made of a polyimide resin, a polyamide resin, or a mixture thereof.

According to another aspect of the present invention, there is provided a foldable image display device, comprising: a display panel; and the optical film disposed closer to an observer than the display panel, and the resin of the optical film The n-th layer in the layer is located closer to the viewer than the first layer. An image display device is provided.

In the above image display device, the display panel may be an organic light emitting diode panel.

According to one embodiment of the present invention, a foldable optical film having excellent foldability, excellent pencil hardness, excellent impact resistance, excellent bendability, and excellent scratch resistance can be provided. Moreover, according to the other aspect of this invention, an image display apparatus provided with such an optical film can be provided.

It is a schematic block diagram of the optical film which concerns on 1st Embodiment. It is the figure which showed the mode of the folding test typically. It is a schematic block diagram of the other optical film which concerns on 1st Embodiment. 1 is a schematic configuration diagram of an image display device according to a first embodiment. It is a schematic block diagram of the optical film with a release film which concerns on 2nd Embodiment. It is a schematic block diagram of the other optical film with a release film which concerns on 2nd Embodiment. It is a schematic block diagram of the image display apparatus which concerns on 2nd Embodiment.

[First Embodiment]
Hereinafter, an optical film and an image display device according to a first embodiment of the present invention will be described with reference to the drawings. In this specification, terms such as “film” and “sheet” are not distinguished from each other only based on the difference in designation. Therefore, for example, “film” is used to include a member that is also called a sheet. FIG. 1 is a schematic configuration diagram of an optical film according to the present embodiment, FIG. 2 is a diagram schematically illustrating a folding test, and FIG. 3 is a schematic configuration diagram of another optical film according to the present embodiment. It is.

<<< Optical film >>>
The optical film 10 shown in FIG. 1 is used for an image display device, is foldable, and has optical transparency. The “light transmittance” in the present specification means a property of transmitting light. For example, the total light transmittance is 50% or more, preferably 70% or more, more preferably 80% or more, and particularly preferably 90%. Including that. The light transmissive property does not necessarily need to be transparent, and may be translucent.

The optical film 10 shown in FIG. 1 includes a base material 11 and one surface 11A side of the base material 11 from the first layer to the n-th layer (n is an integer of 3 or more) from the base material 11 side. And a resin layer 12 having a multilayer structure laminated in order. In addition, although the optical film 10 is provided with the base material 11, the optical film does not need to be provided with the base material so that it may demonstrate in 2nd Embodiment.

The surface 10A of the optical film 10 is the surface 12A of the resin layer 12. In the optical film 10, since the third layer 12D of the resin layer 12 is the uppermost layer as will be described later, the surface 10A of the optical film 10 is the surface of the third layer 12D. In the present specification, the surface of the optical film is used as meaning the surface of one side of the optical film, so that the surface opposite to the surface of the optical film is distinguished from the back surface in order to distinguish it from the surface of the optical film. Shall be called. The back surface 10 B of the optical film 10 is the other surface 11 B that is the surface opposite to the one surface 11 A of the base material 11.

Although the optical film 10 can be folded, specifically, even when the folding test described below is repeated 100,000 times on the optical film 10, the optical film is cracked or broken. Even when the folding test is repeated 200,000 times, it is more preferable that the optical film 10 is not cracked or broken, and even when the folding test is repeated 1,000,000 times, More preferably, no cracking or breakage occurs. When the folding test is repeated 100,000 times on the optical film 10, if the optical film 10 is cracked or the like, the folding property of the optical film 10 becomes insufficient. The folding test may be performed so that the optical film 10 is folded so that the resin layer 12 is inside, or may be performed so that the optical film 10 is folded so that the resin layer 12 is outside. In any case, it is preferable that the optical film is not cracked or broken.

When another film such as a polarizing plate is provided on one surface side of the optical film 10 via an adhesive layer or an adhesive layer, the other film is peeled off together with the adhesive layer or the adhesive layer, and then a folding test. Shall be performed. Other films can be peeled as follows, for example. First, a laminate in which another film is attached to an optical film through an adhesive layer or an adhesive layer is immersed in warm water at 80 ° C. for 10 seconds, and then taken out and cooled to about room temperature. After repeating this several times, put the cutting edge of the cutter in the part that seems to be the interface between the optical film and other film, create a trigger, and peel off slowly to peel off the adhesive layer, adhesive layer and other film be able to. In addition, even if there exists such a peeling process, there is no big influence on the result of a folding test.

The folding test is performed as follows. As shown in FIG. 2A, in the folding test, first, the side portion 10C of the optical film 10 cut out to a size of 30 mm × 100 mm and the side portion 10D facing the side portion 10C are arranged in parallel. The fixing portions 15 are fixed respectively. Further, as shown in FIG. 2A, the fixing portion 15 is slidable in the horizontal direction.

Next, as shown in FIG. 2 (B), the fixing portion 15 is moved so as to be close to each other, thereby deforming the optical film 10 so as to be folded. Further, as shown in FIG. After moving the fixing part 15 to a position where the distance between two opposing side parts fixed by the fixing part 15 of the film 10 is 6 mm, the fixing part 15 is moved in the reverse direction to eliminate the deformation of the optical film 10. Let

As shown in FIGS. 2A to 2C, the optical film 10 can be folded by 180 ° by moving the fixing portion 15. In addition, a folding test is performed so that the bent portion 10E of the optical film 10 does not protrude from the lower end of the fixed portion 15, and the distance when the fixed portion 15 is closest is controlled to 6 mm. The distance between the two sides can be 6 mm. In this case, the outer diameter of the bent portion 10E is regarded as 6 mm. In addition, since the thickness of the optical film 10 is a sufficiently small value as compared with the interval (6 mm) between the fixing portions 15, the result of the folding test of the optical film 10 is affected by the difference in the thickness of the optical film 10. It can be regarded as not.

The optical film 10 is placed on a soda glass plate having a thickness of 0.7 mm, the optical film 10 cut into a size of 100 mm × 100 mm so that the first layer is closer to the soda glass plate than the nth layer, and a resin layer When an iron ball having a weight of 100 g and a diameter of 30 mm is dropped from a position of 30 cm in height with respect to the surface of the 12th n-th layer, no dent is formed on the surface of the n-th layer and a soda glass plate is cracked. Preferably not.

The surface 10A of the optical film 10 (the surface 12A of the resin layer 12) has a hardness (pencil hardness) of 3H or more as measured by a pencil hardness test specified in JIS K5600-5-4: 1999. Preferably, it is 5H, more preferably 6H or more. In the pencil hardness test, a pencil hardness tester (product name “Pencil Scratch Coating Film Hardness Tester (Electric))” manufactured by Toyo Seiki Seisakusho Co., Ltd. is applied to the surface of an optical film cut out to a size of 50 mm × 100 mm. The pencil is moved at a moving speed of 1 mm / second while applying a load of 750 g to the pencil (product name “Uni”, manufactured by Mitsubishi Pencil Co., Ltd.). The pencil hardness is the highest hardness at which the surface of the optical film was not damaged in the pencil hardness test. The pencil hardness is measured using a plurality of pencils having different hardnesses. The pencil hardness test is performed five times for each pencil, and the surface of the optical film is scratched four times or more out of the five times. If not, it is determined that the surface of the optical film was not scratched with the pencil having this hardness. The above-mentioned scratches refer to those that are visually observed through transmission observation of the surface of the optical film subjected to the pencil hardness test under a fluorescent lamp.

In the optical film 10, when a flexibility test is performed in which the surface on the resin layer 12 side is folded 180 ° so that the resin layer 12 is on the inner side and the distance between two opposing side portions of the optical film 10 is 6 mm. It is preferable that no wrinkles are observed in the bent portion of the optical film 10, and it is preferable that no fine cracks are observed in the optical film 10 in a state where the optical film is returned to a flat shape. In the bendability test, similar to the folding test (see FIG. 2C), the opposing side portions of the optical film 10 cut out to a size of 30 mm × 100 mm are fixed by the fixing portions 15 respectively. . The wrinkle is confirmed by visual observation under a fluorescent lamp with the surface on the resin layer 12 side folded by 180 °. Further, since a fine crack is a crack that cannot be visually confirmed, it is observed with an optical microscope (product name “VHX-5000”, manufactured by KEYENCE).

The optical film 10 is reciprocated 10 times against the surface of the nth layer of the resin layer 12 while applying a load of 1 kg / cm ² using # 0000 steel wool (product name “Bonstar”, manufactured by Nippon Steel Wool Co., Ltd.). It is preferable that neither a crack nor a scratch is confirmed on the surface of the n-th layer when a scratch resistance test is performed. The scratch resistance test uses an optical film cut out to a size of 50 mm × 100 mm, and the optical film is made of Nichiban cello tape (registered trademark) so that the optical film is not folded or wrinkled. It shall be performed in a fixed state.

The Young's modulus of the optical film 10 is preferably 3 GPa or more. If the Young's modulus of the optical film 10 is less than 3 GPa, the optical film may have insufficient hardness. The Young's modulus of the optical film 10 is obtained as follows. First, both ends of a sample cut into a predetermined size (for example, 2 mm × 150 mm) from the optical film 10 are used for chucking attached to a Tensilon universal testing machine (product name “RTC-1310A”, manufactured by Orientec). The sample is fixed to a jig or the like so that the longitudinal direction of the sample is in the tensile direction, and using the Tensilon universal testing machine, the measured values of the elongation and load of the sample when the sample is pulled at a test speed of 25 mm / min are set as strain. In terms of stress, Young's modulus was determined by determining the slope of a straight line connecting the stress when the strain was 0.5% and the stress when the strain was 1%. The Young's modulus is the arithmetic average value of the values obtained by measuring three times. The upper limit of the Young's modulus of the optical film 10 is more preferably 7 GPa or less.

Moreover, when other films, such as a polarizing plate, are provided in the one surface side of the optical film 10 via the adhesion layer or the contact bonding layer, another film with an adhesion layer and an adhesion layer by the method similar to the above is carried out. The Young's modulus shall be measured after peeling. In addition, even if there exists such a peeling process, there is no big influence on the measurement of Young's modulus.

The optical film 10 preferably has a yellow index (YI) of 15 or less. If the YI of the optical film 10 exceeds 15, the yellow color of the optical film is conspicuous and may not be applicable to uses where transparency is required. The yellow index (YI) is measured on an optical film cut into a size of 50 mm × 100 mm using a spectrophotometer (product name “UV-3100PC”, manufactured by Shimadzu Corporation, light source: tungsten lamp and deuterium lamp). The chromaticity tristimulus values X, Y, Z are calculated from the obtained values according to the arithmetic expression described in JIS Z8722: 2009, and the tristimulus values X, Y, Z are calculated according to the arithmetic expression described in ASTM D1925: 1962. Value. The yellow index (YI) is measured three times for one optical film, and is the arithmetic average value of the values obtained by measuring three times. The upper limit of the yellow index (YI) of the optical film 10 is more preferably 10 or less.

Moreover, when other films, such as a polarizing plate, are provided in the one surface side of the optical film 10 via the adhesion layer or the contact bonding layer, another film with an adhesion layer and an adhesion layer by the method similar to the above is carried out. The yellow index (YI) shall be measured after peeling. Even if there is such a peeling process, there is no significant influence on the measurement of the yellow index (YI).

In order to adjust the yellow index (YI) of the optical film 10, for example, the base material 11 or the resin layer 12 may contain a blue pigment that is a complementary color of yellow. Even if yellowishness becomes a problem due to the use of a polyimide base material as the base material, the yellow index of the optical film can be obtained by including a blue pigment in the base material 11 or the resin layer 12. (YI) can be reduced.

The blue pigment may be either a pigment or a dye. For example, when the optical film 10 is used in an organic light emitting diode display device, it is preferable to have both light resistance and heat resistance. As the above-mentioned blue pigment, polycyclic organic pigments, metal complex organic pigments, etc. are used in applications where light resistance is required because the degree of molecular breakage due to ultraviolet rays is small compared to the molecular dispersion of dyes and the light resistance is remarkably superior More specifically, phthalocyanine-based organic pigments and the like are preferable. However, since the pigment is particle-dispersed with respect to the solvent, transparency inhibition due to particle scattering exists, and therefore it is preferable to put the particle size of the pigment dispersion in the Rayleigh scattering region. On the other hand, when the transparency of the optical film is regarded as important, it is preferable to use a dye that is molecularly dispersed in a solvent as the blue pigment.

The transmittance of light having a wavelength of 380 nm of the optical film 10 is preferably 8% or less. When the transmittance of the optical film exceeds 8%, when the optical film is used in a mobile terminal, the polarizer may be exposed to ultraviolet rays and may be easily deteriorated. The transmittance can be measured using a spectrophotometer (product name “UV-3100PC”, manufactured by Shimadzu Corporation, light source: tungsten lamp and deuterium lamp). The said transmittance | permeability is measured 3 times with respect to the optical film cut out to the magnitude | size of 50 mm x 100 mm, and is taken as the arithmetic average value of the value obtained by measuring 3 times. The upper limit of the transmittance of the optical film 10 is more preferably 5%. In addition, the said transmittance | permeability of the optical film 10 can be achieved by adjusting the addition amount of the ultraviolet absorber mentioned later in the resin layer 12, etc.

The haze value (total haze value) of the optical film 10 is preferably 2.5% or less. If the haze value of the optical film exceeds 2.5%, the image display surface may be whitened when the optical film is used for a mobile terminal. The haze value is more preferably 1.5% or less, and more preferably 1.0% or less. In addition, the said haze value of the optical film 10 can be achieved by adjusting the addition amount of the ultraviolet absorber mentioned later in the resin layer 12.

The haze value can be measured by a method in accordance with JIS K7136: 2000 using a haze meter (product name “HM-150”, manufactured by Murakami Color Research Laboratory). The above haze value is cut out to a size of 50 mm × 100 mm, and installed so that the surface side of the optical film becomes the non-light source side without curling or wrinkling, and without fingerprints or dust. Is measured three times, and the arithmetic average value of the values obtained by measuring three times is used. In this specification, “measuring three times” means not measuring the same place three times, but measuring three different places. In the optical film 10, the visually observed surface 10A is flat, the resin layer 12 is also flat, and the variation in film thickness is within ± 10%. Therefore, it is thought that the average value of the haze value of the approximate whole in-plane of an optical film is obtained by measuring a haze value in three different places of the cut-out optical film. The variation in the haze value is within ± 10% regardless of whether the measurement target is as long as 1 m × 3000 m or the size of a 5-inch smartphone. In the case where the optical film cannot be cut out to the above size, for example, HM-150 has an inlet opening for measurement of 20 mm.phi., So that the sample size needs to be 21 mm or more in diameter. For this reason, you may cut out an optical film suitably in the magnitude | size of 22 mm x 22 mm or more. When the size of the optical film is small, the measurement points are set to three positions by gradually shifting within a range where the light source spot is not removed or changing the angle.

Moreover, when other films, such as a polarizing plate, are provided in the one surface side of the optical film 10 via the adhesion layer or the contact bonding layer, another film with an adhesion layer and an adhesion layer by the method similar to the above is carried out. After peeling, the haze value shall be measured. In addition, even if there exists such a peeling process, there is no big influence on the measurement of a haze value.

In recent years, a light emitting diode (Light Emitting Diode) has been actively adopted as a light source for a backlight of an image display device such as a personal computer or a tablet terminal. The light emitting diode strongly emits light called blue light. . This blue light is a light with a wavelength of 380 to 495 nm and has properties close to ultraviolet rays, and has strong energy. Therefore, the blue light reaches the retina without being absorbed by the cornea or the crystalline lens. It is said to cause serious fatigue and adverse effects on sleep. For this reason, when an optical film is applied to an image display device, it is preferable that the optical film has excellent blue light shielding properties without affecting the color of the display screen. Therefore, from the viewpoint of shielding blue light, the optical film 10 has a spectral transmittance of less than 1% at a wavelength of 380 nm, a spectral transmittance of less than 10% at a wavelength of 410 nm, and a spectral transmittance of 70 at a wavelength of 440 nm. % Or more is preferable. If the spectral transmittance at a wavelength of 380 nm is 1% or more or the spectral transmittance at a wavelength of 410 nm is 10% or more, the problem due to blue light may not be solved, and the spectral transmittance at a wavelength of 440 nm is 70%. This is because if it is less than the range, the color of the display screen of the image display device using the optical film may be affected. The optical film 10 sufficiently absorbs light in the wavelength region of 410 nm or less of the wavelength of blue light, while sufficiently transmitting light of wavelength 440 nm or more without affecting the color of the display screen. Blue light shielding properties can be improved. Moreover, when the optical film 10 having excellent blue light shielding properties is applied to an organic light emitting diode (OLED) display device as an image display device, it is also effective in suppressing deterioration of the organic light emitting diode element.

The light transmittance of the optical film 10 is almost 0% up to a wavelength of 380 nm, it is preferable that the light transmission gradually increases from a wavelength of 410 nm, and the light transmission rapidly increases in the vicinity of a wavelength of 440 nm. Specifically, for example, it is preferable that the spectral transmittance changes between a wavelength of 410 nm and 440 nm so as to draw a sigmoid curve. The spectral transmittance at a wavelength of 380 nm is more preferably less than 0.5%, still more preferably less than 0.2%, and the spectral transmittance at a wavelength of 410 nm is more preferably less than 7%, more preferably less than 5%. The spectral transmittance at a wavelength of 440 nm is more preferably 75% or more, and still more preferably 80% or more. The optical film 10 preferably has a spectral transmittance of less than 50% at a wavelength of 420 nm. By satisfying such a spectral transmittance relationship, the optical film 10 has a sharply improved transmittance around a wavelength of 440 nm, and has an excellent blue light shielding property without affecting the color of the display screen. Can be obtained.

The spectral transmittance at a wavelength of 380 nm in the optical film 10 is more preferably less than 0.1%, the spectral transmittance at a wavelength of 410 nm is more preferably less than 7%, and the spectral transmittance at a wavelength of 440 nm is 80% or more. It is more preferable that

The optical film 10 preferably has an inclination a of a transmission spectrum in a wavelength range of 415 to 435 nm obtained by using the least square method such that a> 2.0. If the slope a is 2.0 or less, light cannot be sufficiently cut in the blue light wavelength region, for example, the wavelength region of 415 to 435 nm, and the blue light cut effect may be weakened. Further, there is a possibility that the light wavelength region of blue light (wavelength 415 to 435 nm) is cut too much. In that case, the backlight of the image display device or the light emission wavelength region (for example, light emission from the wavelength 430 nm of the OLED) There is a possibility that a problem such as a problem that the color becomes worse due to interference with the color is increased. The slope a is, for example, transmittance data for at least 5 points between 1 nm before and after using a spectroscope (product name “UV-2450”, manufactured by Shimadzu Corporation) that can be measured in 0.5% increments. Can be calculated by measuring between 415 and 435 nm.

The optical film 10 preferably has a blue light shielding rate of 40% or more. If the blue light shielding rate is less than 40%, the above-described problems caused by blue light may not be sufficiently solved. The blue light shielding rate is, for example, a value calculated according to JIS T7333: 2005. Such a blue light shielding rate can be achieved, for example, when the resin layer 12 contains a sesamol type benzotriazole-based monomer described later.

The use of the optical film 10 is not particularly limited. Examples of the use of the optical film 10 include image display devices such as smartphones, tablet terminals, personal computers (PCs), wearable terminals, digital signage, televisions, and car navigation systems. Can be mentioned. The optical film 10 is also suitable for in-vehicle use. The form of each image display device is also preferable for applications that require flexibility such as foldable and rollable.

The optical film 10 may be cut into a desired size, but may be in a roll shape. When the optical film 10 is cut into a desired size, the size of the optical film is not particularly limited, and is appropriately determined according to the size of the display surface of the image display device. Specifically, the size of the optical film 10 may be, for example, not less than 2.8 inches and not more than 500 inches. In the present specification, “inch” means the length of a diagonal line when the optical film has a quadrangular shape, means the diameter when the optical film is circular, and has the short diameter when it is elliptical. And the average value of the sum of the major axes. Here, when the optical film has a quadrangular shape, the aspect ratio of the optical film when obtaining the inch is not particularly limited as long as there is no problem as a display screen of the image display device. For example, length: width = 1: 1, 4: 3, 16:10, 16: 9, 2: 1, and the like. However, the aspect ratio is not particularly limited in in-vehicle applications and digital signage that are rich in design. Moreover, when the magnitude | size of the optical film 10 is large, after cutting out to A5 size (148 mm x 210 mm) from arbitrary positions, it shall cut out to the magnitude | size of each measurement item.

The location of the optical film 10 in the image display device may be inside the image display device, but is preferably near the surface of the image display device. When used near the surface of the image display device, the optical film 10 functions as a cover film used instead of the cover glass.

<< Base material >>
The substrate 11 is a substrate having optical transparency. The thickness of the substrate 11 is preferably 10 μm or more and 100 μm or less. When the thickness of the substrate is less than 10 μm, the curl of the optical film becomes large, the hardness is insufficient, and the pencil hardness may not be 3H or more. Further, when the optical film is manufactured by Roll to Roll Since wrinkles are likely to occur, the appearance may be deteriorated. On the other hand, when the thickness of the substrate exceeds 100 μm, the folding performance of the optical film becomes insufficient, and the requirements for the folding test described later may not be satisfied, and the optical film becomes heavy, which is not preferable in terms of weight reduction. . The thickness of the base material is obtained by taking a cross-section of the base material using a scanning electron microscope (SEM), measuring the thickness of the base material at 20 locations in the cross-sectional image, and calculating the arithmetic average value of the thickness at the 20 locations. To do. The lower limit of the substrate 11 is more preferably 25 μm or more, and the upper limit of the substrate 11 is more preferably 80 μm or less.

Examples of the constituent material of the substrate 11 include resins such as polyimide resins, polyamideimide resins, polyamide resins, and polyester resins (for example, polyethylene terephthalate and polyethylene naphthalate). Among these, in addition to not easily cracking or breaking in the folding test, it also has excellent hardness and transparency, is also excellent in heat resistance, and is further improved in hardness and transparency by firing. From the viewpoint of imparting, a polyimide resin, a polyamide resin, or a mixture thereof is preferable.

The polyimide resin is obtained by reacting a tetracarboxylic acid component and a diamine component. It is preferable to obtain imidization by obtaining a polyamic acid by polymerization of a tetracarboxylic acid component and a diamine component. The imidization may be performed by thermal imidization or chemical imidization. Moreover, it can also manufacture by the method which used thermal imidation and chemical imidization together. The polyimide resin may be an aliphatic polyimide resin, but is preferably an aromatic polyimide resin containing an aromatic ring. The aromatic polyimide resin contains an aromatic ring in at least one of the tetracarboxylic acid component and the diamine component.

As specific examples of the tetracarboxylic acid component, tetracarboxylic dianhydride is preferably used. Cyclohexanetetracarboxylic dianhydride, cyclopentanetetracarboxylic dianhydride, dicyclohexane-3,4,3 ′, 4 '-Tetracarboxylic dianhydride, pyromellitic dianhydride, 3,3', 4,4'-benzophenone tetracarboxylic dianhydride, 2,2 ', 3,3'-benzophenone tetracarboxylic dianhydride 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 2,2 ′, 3,3′-biphenyltetracarboxylic dianhydride, 2,2-bis (3,4-dicarboxy) Phenyl) propane dianhydride, 2,2-bis (2,3-dicarboxyphenyl) propane dianhydride, bis (3,4-dicarboxyphenyl) ether dianhydride, bis ( , 4-dicarboxyphenyl) sulfone dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, bis (3 4-Dicarboxyphenyl) methane dianhydride, 2,2-bis (3,4-dicarboxyphenyl) -1,1,1,3,3,3-hexafluoropropane dianhydride, 2,2-bis (2,3-dicarboxyphenyl) -1,1,1,3,3,3-hexafluoropropane dianhydride, 1,3-bis [(3,4-dicarboxy) benzoyl] benzene dianhydride, 1,4-bis [(3,4-dicarboxy) benzoyl] benzene dianhydride, 2,2-bis {4- [4- (1,2-dicarboxy) phenoxy] phenyl} propane dianhydride, , 2-bis {4- [3- ( , 2-dicarboxy) phenoxy] phenyl} propane dianhydride, bis {4- [4- (1,2-dicarboxy) phenoxy] phenyl} ketone dianhydride, bis {4- [3- (1,2 -Dicarboxy) phenoxy] phenyl} ketone dianhydride, 4,4'-bis [4- (1,2-dicarboxy) phenoxy] biphenyl dianhydride, 4,4'-bis [3- (1,2 -Dicarboxy) phenoxy] biphenyl dianhydride, bis {4- [4- (1,2-dicarboxy) phenoxy] phenyl} ketone dianhydride, bis {4- [3- (1,2-dicarboxy) Phenoxy] phenyl} ketone dianhydride, bis {4- [4- (1,2-dicarboxy) phenoxy] phenyl} sulfone dianhydride, bis {4- [3- (1,2-dicarboxy) phenoxy] Phenyl} Sulfone dianhydride, bis {4- [4- (1,2-dicarboxy) phenoxy] phenyl} sulfide dianhydride, bis {4- [3- (1,2-dicarboxy) phenoxy] phenyl} sulfide Anhydride, 4,4 '-(Hexafluoroisopropylidene) diphthalic anhydride, 3,4'-(hexafluoroisopropylidene) diphthalic anhydride, 3,3 '-(hexafluoroisopropylidene) diphthalic anhydride 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, , 2,3,4-Benzenetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 2,3,6,7-anthracenetetracarbo Dianhydride, 1,2,7,8-phenanthrene tetracarboxylic acid dianhydride, and the like. These may be used alone or in combination of two or more.

Specific examples of the diamine component include p-phenylenediamine, m-phenylenediamine, o-phenylenediamine, 3,3′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether, 4,4′-diaminodiphenyl ether, 3,3 '-Diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone 3,3′-diaminobenzophenone, 4,4′-diaminobenzophenone, 3,4′-diaminobenzophenone, 4,4′-diaminobenzanilide, 3,3′-diaminodiphenylmethane, 4,4′-diaminodiphenylmethane, 3, 4 -Diaminodiphenylmethane, 2,2-di (3-aminophenyl) propane, 2,2-di (4-aminophenyl) propane, 2- (3-aminophenyl) -2- (4-aminophenyl) propane, 2 , 2-di (3-aminophenyl) -1,1,1,3,3,3-hexafluoropropane, 2,2-di (4-aminophenyl) -1,1,1,3,3,3 -Hexafluoropropane, 2- (3-aminophenyl) -2- (4-aminophenyl) -1,1,1,3,3,3-hexafluoropropane, 1,1-di (3-aminophenyl) -1-phenylethane, 1,1-di (4-aminophenyl) -1-phenylethane, 1- (3-aminophenyl) -1- (4-aminophenyl) -1-phenylethane, 1,3- Bis (3-aminophenoxy) , 1,3-bis (4-aminophenoxy) benzene, 1,4-bis (3-aminophenoxy) benzene, 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (3-amino) Benzoyl) benzene, 1,3-bis (4-aminobenzoyl) benzene, 1,4-bis (3-aminobenzoyl) benzene, 1,4-bis (4-aminobenzoyl) benzene, 1,3-bis (3 -Amino-α, α-dimethylbenzyl) benzene, 1,3-bis (4-amino-α, α-dimethylbenzyl) benzene, 1,4-bis (3-amino-α, α-dimethylbenzyl) benzene, 1,4-bis (4-amino-α, α-dimethylbenzyl) benzene, 1,3-bis (3-amino-α, α-ditrifluoromethylbenzyl) benzene, 1,3-bis (4-a No-α, α-ditrifluoromethylbenzyl) benzene, 1,4-bis (3-amino-α, α-ditrifluoromethylbenzyl) benzene, 1,4-bis (4-amino-α, α-ditrifluoro) Methylbenzyl) benzene, 2,6-bis (3-aminophenoxy) benzonitrile, 2,6-bis (3-aminophenoxy) pyridine, N, N′-bis (4-aminophenyl) terephthalamide, 9,9 -Bis (4-aminophenyl) fluorene, 2,2'-dimethyl-4,4'-diaminobiphenyl, 2,2'-ditrifluoromethyl-4,4'-diaminobiphenyl, 3,3'-dichloro-4 , 4'-diaminobiphenyl, 3,3'-dimethoxy-4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminobiphenyl, 4,4 -Bis (3-aminophenoxy) biphenyl, 4,4'-bis (4-aminophenoxy) biphenyl, bis [4- (3-aminophenoxy) phenyl] ketone, bis [4- (4-aminophenoxy) phenyl] Ketone, bis [4- (3-aminophenoxy) phenyl] sulfide, bis [4- (4-aminophenoxy) phenyl] sulfide, bis [4- (3-aminophenoxy) phenyl] sulfone, bis [4- (4 -Aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] ether, bis [4- (4-aminophenoxy) phenyl] ether, 2,2-bis [4- (3-aminophenoxy) Phenyl] propane, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 2,2-bis [3- (3-Aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane, 2,2-bis [4- (4-aminophenoxy) phenyl] -1,1,1,3 3,3-hexafluoropropane, 1,3-bis [4- (3-aminophenoxy) benzoyl] benzene, 1,3-bis [4- (4-aminophenoxy) benzoyl] benzene, 1,4-bis [ 4- (3-aminophenoxy) benzoyl] benzene, 1,4-bis [4- (4-aminophenoxy) benzoyl] benzene, 1,3-bis [4- (3-aminophenoxy) -α, α-dimethyl [Benzyl] benzene, 1,3-bis [4- (4-aminophenoxy) -α, α-dimethylbenzyl] benzene, 1,4-bis [4- (3-aminophenoxy) -α, α-dimethylbenzyl Benzene, 1,4-bis [4- (4-aminophenoxy) -α, α-dimethylbenzyl] benzene, 4,4′-bis [4- (4-aminophenoxy) benzoyl] diphenyl ether, 4,4′- Bis [4- (4-amino-α, α-dimethylbenzyl) phenoxy] benzophenone, 4,4′-bis [4- (4-amino-α, α-dimethylbenzyl) phenoxy] diphenylsulfone, 4,4 ′ -Bis [4- (4-aminophenoxy) phenoxy] diphenylsulfone, 3,3′-diamino-4,4′-diphenoxybenzophenone, 3,3′-diamino-4,4′-dibiphenoxybenzophenone, 3, 3′-diamino-4-phenoxybenzophenone, 3,3′-diamino-4-biphenoxybenzophenone, 6,6′-bis (3-amino Enoxy) -3,3,3 ′, 3′-tetramethyl-1,1′-spirobiindane, 6,6′-bis (4-aminophenoxy) -3,3,3 ′, 3′-tetramethyl-1 , 1′-spirobiindane, 1,3-bis (3-aminopropyl) tetramethyldisiloxane, 1,3-bis (4-aminobutyl) tetramethyldisiloxane, α, ω-bis (3-aminopropyl) poly Dimethylsiloxane, α, ω-bis (3-aminobutyl) polydimethylsiloxane, bis (aminomethyl) ether, bis (2-aminoethyl) ether, bis (3-aminopropyl) ether, bis (2-aminomethoxy) Ethyl] ether, bis [2- (2-aminoethoxy) ethyl] ether, bis [2- (3-aminoprotoxy) ethyl] ether, trans Rhohexanediamine, trans-1,4-bismethylenecyclohexanediamine, 2,6-bis (aminomethyl) bicyclo [2,2,1] heptane, 2,5-bis (aminomethyl) bicyclo [2,2,1 Heptane, and diamines obtained by substituting some or all of the hydrogen atoms on the aromatic ring of the diamine with a substituent selected from a fluoro group, a methyl group, a methoxy group, a trifluoromethyl group, or a trifluoromethoxy group Can be used. These may be used alone or in combination of two or more.

From the viewpoint of improving light transmittance and improving rigidity, the polyimide-based resin includes an aromatic ring, and (i) a fluorine atom, (ii) an aliphatic ring, and (iii) an aromatic ring. It is preferable that it is a polyimide resin containing at least one selected from the group consisting of a linking group that cleaves the electron conjugation between each other, and it is a polyimide resin containing at least one of (i) and (iii). More preferred. When the polyimide resin contains an aromatic ring, the orientation is improved and the rigidity is improved, but the transmittance tends to be lowered depending on the absorption wavelength of the aromatic ring. When the polyimide resin contains (i) a fluorine atom, the light transmittance is improved because the electronic state in the polyimide skeleton can be hardly transferred. Further, when the polyimide resin contains (ii) an aliphatic ring, light transmittance is improved because the transfer of charges in the skeleton can be inhibited by breaking the π electron conjugation in the polyimide skeleton. . Furthermore, when the polyimide resin includes (iii) a linking group that cleaves the electron conjugation between aromatic rings, the transfer of charge in the skeleton may be inhibited by breaking the π electron conjugation in the polyimide skeleton. The light transmittance is improved from the point where it can be done. Examples of the linking group that cleaves the electron conjugation between aromatic rings include, for example, ether bond, thioether bond, carbonyl bond, thiocarbonyl bond, amide bond, sulfonyl bond, sulfinyl bond, and fluorine-substituted. And a divalent linking group such as an alkylene group.

Among these, a polyimide resin containing an aromatic ring and containing a fluorine atom is preferably used from the viewpoint of improving light transmittance and improving rigidity. The content ratio of fluorine atoms in the polyimide resin containing fluorine atoms is the ratio (F / C) of the number of fluorine atoms (F) and the number of carbon atoms (C) measured on the surface of the polyimide resin by X-ray photoelectron spectroscopy. , 0.01 or more, and more preferably 0.05 or more. On the other hand, if the content ratio of fluorine atoms is too high, the inherent heat resistance of the polyimide resin may be lowered, so the ratio of the number of fluorine atoms (F) to the number of carbon atoms (C) (F / C). Is preferably 1 or less, more preferably 0.8 or less. Here, the said ratio by the measurement of X-ray photoelectron spectroscopy (XPS) can be calculated | required from the value of atomic% of each atom measured using an X-ray photoelectron spectrometer (for example, Thermo Scientific Theta Probe). .

Further, it is a polyimide resin in which 70% or more of the hydrogen atoms bonded to the carbon atoms contained in the polyimide resin are hydrogen atoms directly bonded to the aromatic ring. It is preferably used from the point of improving. The proportion of hydrogen atoms (number) directly bonded to the aromatic ring in the total hydrogen atoms (number) bonded to the carbon atoms contained in the polyimide resin is preferably 80% or more, more preferably 85% or more. It is more preferable that When 70% or more of the hydrogen atoms bonded to the carbon atoms contained in the polyimide are polyimide atoms that are bonded directly to the aromatic ring, the film is stretched at, for example, 200 ° C. or higher even after a heating step in the atmosphere. Is preferable from the viewpoint of little change in optical characteristics, particularly total light transmittance and yellow index (YI). In the case where polyimide, which is a hydrogen atom bonded directly to an aromatic ring, is 70% or more of hydrogen atoms bonded to carbon atoms contained in the polyimide resin, the reactivity with oxygen is low. It is presumed that the chemical structure is difficult to change. A substrate made of a polyimide resin utilizes its high heat resistance, and is often used for devices that require a heating process, but 70% of the hydrogen atoms bonded to the carbon atoms contained in the polyimide resin. When the above is a polyimide resin that is a hydrogen atom directly bonded to an aromatic ring, it is not necessary to carry out these subsequent steps in an inert atmosphere in order to maintain transparency. There is an advantage that the cost for control can be suppressed. Here, the ratio of the hydrogen atoms (number) directly bonded to the aromatic ring in the total hydrogen atoms (number) bonded to the carbon atoms contained in the polyimide resin is determined by high-performance liquid chromatography, gas chromatography It can be determined using a tomograph mass spectrometer and NMR. For example, a sample is decomposed with an alkaline aqueous solution or supercritical methanol, and the resulting decomposition product is separated by high performance liquid chromatography, and a qualitative analysis of each separated peak is performed using a gas chromatograph mass spectrometer and NMR. The ratio of hydrogen atoms (numbers) directly bonded to the aromatic ring in the total hydrogen atoms (numbers) contained in the polyimide can be determined by performing determination using high performance liquid chromatography.

Moreover, from the point which improves a light transmittance and improves a rigidity, as a polyimide-type resin, it is chosen from the group which consists of a structure represented by the following general formula (1) and the following general formula (3) especially. It preferably has at least one structure.

In the general formula (1), R ¹ is a tetravalent group which is a tetracarboxylic acid residue, R ² is a trans-cyclohexanediamine residue, a trans-1,4-bismethylenecyclohexanediamine residue, 4,4 It represents at least one divalent group selected from the group consisting of a '-diaminodiphenylsulfone residue, a 3,4'-diaminodiphenylsulfone residue, and a divalent group represented by the following general formula (2). . n represents the number of repeating units and is 1 or more. In this specification, the “tetracarboxylic acid residue” means a residue obtained by removing four carboxyl groups from tetracarboxylic acid, and a residue obtained by removing an acid dianhydride structure from tetracarboxylic dianhydride; Represents the same structure. The “diamine residue” refers to a residue obtained by removing two amino groups from a diamine.

In the general formula (2), R ³ and R ⁴ each independently represent a hydrogen atom, an alkyl group, or a perfluoroalkyl group.

In the general formula (3), R ⁵ represents a cyclohexanetetracarboxylic acid residue, a cyclopentanetetracarboxylic acid residue, a dicyclohexane-3,4,3 ′, 4′-tetracarboxylic acid residue, and 4,4 ′. At least one tetravalent group selected from the group consisting of-(hexafluoroisopropylidene) diphthalic acid residues, R ⁶ represents a divalent group that is a diamine residue. n ′ represents the number of repeating units and is 1 or more.

In the general formula (1), R ¹ is a tetracarboxylic acid residue, and can be a residue obtained by removing the acid dianhydride structure from the tetracarboxylic dianhydride as exemplified above. R ¹ in the general formula (1) is, among others, 4,4 ′-(hexafluoroisopropylidene) diphthalic acid residue, 3,3 ′, from the viewpoint of improving light transmittance and improving rigidity. 4,4'-biphenyltetracarboxylic acid residue, pyromellitic acid residue, 2,3 ', 3,4'-biphenyltetracarboxylic acid residue, 3,3', 4,4'-benzophenonetetracarboxylic acid residue Selected from the group consisting of a group, 3,3 ′, 4,4′-diphenylsulfonetetracarboxylic acid residue, 4,4′-oxydiphthalic acid residue, cyclohexanetetracarboxylic acid residue, and cyclopentanetetracarboxylic acid residue At least one selected from the group consisting of 4,4 '-(hexafluoroisopropylidene) diphthalic acid residue, 4,4'-oxydiphthalic acid residue, and 3,3', 4,4'- The It is preferable to include at least one selected from the group consisting of phenylsulfonetetracarboxylic acid residues.

In R ¹ , these suitable residues are preferably contained in a total amount of 50 mol% or more, more preferably 70 mol% or more, and still more preferably 90 mol% or more.

R ¹ is selected from the group consisting of 3,3 ′, 4,4′-biphenyltetracarboxylic acid residue, 3,3 ′, 4,4′-benzophenonetetracarboxylic acid residue, and pyromellitic acid residue. A group of tetracarboxylic acid residues (group A) suitable for improving rigidity such as at least one selected from 4,4 ′-(hexafluoroisopropylidene) diphthalic acid residues, 2,3 ′ , 3,4′-biphenyltetracarboxylic acid residue, 3,3 ′, 4,4′-diphenylsulfonetetracarboxylic acid residue, 4,4′-oxydiphthalic acid residue, cyclohexanetetracarboxylic acid residue, and cyclohexane It is also preferable to use a mixture of a tetracarboxylic acid residue group (group B) suitable for improving transparency, such as at least one selected from the group consisting of pentanetetracarboxylic acid residues. There.

In this case, the content ratio of the tetracarboxylic acid residue group (group A) suitable for improving the rigidity and the tetracarboxylic acid residue group (group B) suitable for improving transparency is, 0.05 mol of the tetracarboxylic acid residue group (group A) suitable for improving the rigidity is 1 mol per 1 mol of the tetracarboxylic acid residue group (group B) suitable for improving the transparency. It is preferably 9 mol or less, more preferably 0.1 mol or more and 5 mol or less, still more preferably 0.3 mol or more and 4 mol or less.

R ² in the general formula (1) is, among others, 4,4′-diaminodiphenylsulfone residue, 3,4′-diaminodiphenylsulfone residue from the viewpoint of improving light transmittance and improving rigidity. And at least one divalent group selected from the group consisting of a divalent group represented by the general formula (2), and is preferably a 4,4′-diaminodiphenylsulfone residue, 3 , 4′-diaminodiphenylsulfone residue, and at least one divalent group selected from the group consisting of divalent groups represented by the above general formula (2), wherein R3 and R4 are perfluoroalkyl groups It is preferable that

R ⁵ in the general formula (3) is, among others, 4,4 ′-(hexafluoroisopropylidene) diphthalic acid residue, 3,3 ′, from the viewpoint of improving light transmittance and improving rigidity. It preferably contains a 4,4′-diphenylsulfone tetracarboxylic acid residue and an oxydiphthalic acid residue.

In R ⁵ , these suitable residues are preferably contained in an amount of 50 mol% or more, more preferably 70 mol% or more, and even more preferably 90 mol% or more.

R ⁶ in the general formula (3) is a diamine residue, and can be a residue obtained by removing two amino groups from the diamine as exemplified above. R6 in the general formula (3) is, among others, a 2,2′-bis (trifluoromethyl) benzidine residue, bis [4- (4- Aminophenoxy) phenyl] sulfone residue, 4,4′-diaminodiphenylsulfone residue, 2,2-bis [4- (4-aminophenoxy) phenyl] hexafluoropropane residue, bis [4- (3-amino Phenoxy) phenyl] sulfone residue, 4,4′-diamino-2,2′-bis (trifluoromethyl) diphenyl ether residue, 1,4-bis [4-amino-2- (trifluoromethyl) phenoxy] benzene Residue, 2,2-bis [4- (4-amino-2-trifluoromethylphenoxy) phenyl] hexafluoropropane residue, 4,4′-diamino-2- (tri Fluoromethyl) diphenyl ether residue, 4,4′-diaminobenzanilide residue, N, N′-bis (4-aminophenyl) terephthalamide residue, and 9,9-bis (4-aminophenyl) fluorene residue It preferably contains at least one divalent group selected from the group consisting of 2,2′-bis (trifluoromethyl) benzidine residue, bis [4- (4-aminophenoxy) phenyl] sulfone residue. The group preferably contains at least one divalent group selected from the group consisting of a group and a 4,4′-diaminodiphenylsulfone residue.

In R ⁶ , these suitable residues are preferably contained in a total amount of 50 mol% or more, more preferably 70 mol% or more, and still more preferably 90 mol% or more.

R ⁶ is a bis [4- (4-aminophenoxy) phenyl] sulfone residue, 4,4′-diaminobenzanilide residue, N, N′-bis (4-aminophenyl) terephthalamide residue, A group of diamine residues suitable for improving the rigidity such as at least one selected from the group consisting of a paraphenylenediamine residue, a metaphenylenediamine residue, and a 4,4′-diaminodiphenylmethane residue (group) C), 2,2′-bis (trifluoromethyl) benzidine residue, 4,4′-diaminodiphenylsulfone residue, 2,2-bis [4- (4-aminophenoxy) phenyl] hexafluoropropane residue Group, bis [4- (3-aminophenoxy) phenyl] sulfone residue, 4,4′-diamino-2,2′-bis (trifluoromethyl) diphenyl Ether residue, 1,4-bis [4-amino-2- (trifluoromethyl) phenoxy] benzene residue, 2,2-bis [4- (4-amino-2-trifluoromethylphenoxy) phenyl] hexa As at least one selected from the group consisting of fluoropropane residues, 4,4′-diamino-2- (trifluoromethyl) diphenyl ether residues, and 9,9-bis (4-aminophenyl) fluorene residues It is also preferable to use a mixture with a diamine residue group (group D) suitable for improving the transparency.

In this case, the content ratio of the diamine residue group (group C) suitable for improving the rigidity and the diamine residue group (group D) suitable for improving transparency improves transparency. The diamine residue group (group C) suitable for improving the rigidity is 0.05 mol or more and 9 mol or less with respect to 1 mol of the diamine residue group (group D) suitable for the treatment. More preferably, it is preferably 0.1 mol or more and 5 mol or less, and more preferably 0.3 mol or more and 4 mol or less.

In the structures represented by the general formula (1) and the general formula (3), n and n 'each independently represent the number of repeating units and are 1 or more. The number of repeating units n in the polyimide is not particularly limited as long as it is appropriately selected depending on the structure so as to exhibit a preferable glass transition temperature described later. The average number of repeating units is usually 10 to 2000, and more preferably 15 to 1000.

Moreover, the polyimide resin may contain a polyamide structure in a part thereof. Examples of the polyamide structure that may be included include a polyamideimide structure containing a tricarboxylic acid residue such as trimellitic anhydride and a polyamide structure containing a dicarboxylic acid residue such as terephthalic acid.

The polyimide resin preferably has a glass transition temperature of 250 ° C. or higher, and more preferably 270 ° C. or higher, from the viewpoint of heat resistance. On the other hand, the glass transition temperature is preferably 400 ° C. or lower, and more preferably 380 ° C. or lower, from the viewpoint of easy stretching and reduction of the baking temperature.

Specifically, examples of the polyimide base material include compounds having a structure represented by the following formula. In the following formula, n is a repeating unit and represents an integer of 2 or more.

Polyamide resin is a concept including not only aliphatic polyamide but also aromatic polyamide (aramid). The polyamide-based resin generally has a skeleton represented by the following formulas (21) and (22). Examples of the polyamide-based resin include compounds represented by the following formula (23). Can be mentioned. In the following formula, n is a repeating unit and represents an integer of 2 or more.

Commercially available polyimide resins or polyamide resins represented by the above formulas (4) to (20) and (23) may be used. Examples of the commercially available base material made of the polyimide-based resin include Neoprim manufactured by Mitsubishi Gas Chemical Co., Ltd., and examples of the commercially available base material made of the polyamide-based resin include Mikutron manufactured by Toray Industries, Inc. Is mentioned.

The polyimide resin or polyamide resin represented by the above formulas (4) to (20) and (23) may be synthesized by a known method. For example, a method for synthesizing a polyimide film represented by the above formula (4) is described in JP-A-2009-132091. Specifically, 4,4′-hexafluoro represented by the following formula (21) is described. It can be obtained by reacting propylidenebisphthalic dianhydride (FPA) with 2,2′-bis (trifluoromethyl) -4,4′-diaminobiphenyl (TFDB).

The weight average molecular weight of the polyimide resin or polyamide resin is preferably in the range of 3,000 to 500,000, more preferably in the range of 5,000 to 300,000, and in the range of 10,000 to 200,000. More preferably. When the weight average molecular weight is less than 3000, sufficient strength may not be obtained. When the weight average molecular weight exceeds 500,000, the viscosity increases and the solubility decreases, so that a substrate having a smooth surface and a uniform film thickness can be obtained. It may not be obtained. In the present specification, the “weight average molecular weight” is a polystyrene conversion value measured by gel permeation chromatography (GPC).

Among the polyimide resins and polyamide resins, a polyimide base material or polyamide resin having a structure in which charge transfer within a molecule or between molecules hardly occurs is preferable because it has excellent transparency. Specifically, Fluorinated polyimide films of the above formulas (4) to (11), polyimide resins having an alicyclic structure such as the above formulas (13) to (15), and polyamide resins having a halogen group such as the above formula (23) Is mentioned.

In addition, the fluorinated polyimide resins such as the above formulas (4) to (11) have a fluorinated structure and thus have high heat resistance, and heat during the production of the substrate made of the polyimide resin. Since it is not colored by, it has the outstanding transparency.

The base material 11 has a hardness measured on the surface 12A of the resin layer 12 under the conditions of a pencil hardness test (load: 750 g, speed: 1 mm / second) specified in JIS K5600-5-4: 1999 of 3H or more. From a possible viewpoint, a base material composed of a fluorinated polyimide resin represented by the above formulas (4) to (11) or a base material composed of a polyamide resin having a halogen group such as the above formula (23) is used. It is preferable to use it. Especially, since the said pencil hardness can provide very excellent hardness of 3H or more, it is more preferable to use the base material which consists of a polyimide-type resin represented by the said Formula (4).

Examples of the polyester-based resin include resins having at least one of polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate as constituent components.

<< Resin layer >>
The resin layer 12 has a multilayer structure in which layers from the first layer to the n-th layer (n is an integer of 3 or more) are stacked. Needless to say, the first to nth layers are layers mainly made of a resin, but may contain particles, additives and the like in addition to the resin.

The indentation hardness of each of the first to nth layers in the resin layer 12 increases in order from the first layer to the nth layer. That is, in the resin layer 12, when the indentation hardness of the first layer, the second layer,..., The nth layer is H _IT1 , H _IT2 _,. ) Is satisfied.
H _IT1 <H _IT2 <... <H _ITn (A)

Specifically, since the resin layer 12 has a multilayer structure in which the first layer 12B to the third layer 12D are laminated in this order from the substrate 11 side, the first layer 12B, the second layer 12C, The indentation hardness of each of the three layers 12D increases in order from the first layer 12B to the third layer 12D. That is, when the indentation hardness of the first layer 12B, the second layer 12C, and the third layer 12D is set to H _IT1 , H _IT2 and H _IT3 , the following relational expression (B) is satisfied.
H _IT1 <H _IT2 <H _IT3 (B)

In the present specification, the “indentation hardness” is the hardness when an indenter is pressed 100 nm into each resin layer by the hardness measurement by the nanoindentation method. The measurement of the indentation hardness by the nanoindentation method is performed using “TI950 TriboIndenter” manufactured by HYSITRON. Specifically, first, a block in which an optical film cut out to 1 mm × 10 mm is embedded with an embedding resin is prepared, and a uniform thickness without a hole or the like is obtained from this block by a general section manufacturing method. Cut the following sections. “Ultramicrotome EM UC7” (Leica Microsystems) can be used for preparing the slice. The remaining block from which a uniform section without holes or the like is cut out is taken as a measurement sample. Next, at the center of the cross section of each resin layer obtained by cutting out the section in such a measurement sample, a Berkovich indenter (triangular pyramid) is pushed in as a indenter about 100 nm at a maximum load of 40 μN and a speed of 10 μN / s, and constant. After holding and relaxing the residual stress, unloading and measuring the maximum load after relaxation, the maximum load (P _max (μN)) and the projected contact area between the indenter and the sample (each layer) ( Indentation hardness is calculated from P _max / A _p using A _p (nm ² )). The indentation hardness is the arithmetic average value of the values measured 10 times.

In the optical film 10, since the resin layer 12 is composed of the first layer 12B, the second layer 12C, and the third layer 12D, the n is 3, but the n of the n-th layer is 3 If it is more, it will not specifically limit. The upper limit of n is preferably 10 or less from the viewpoint of productivity.

When the resin layer 12 has a three-layer structure, each indentation hardness of the first layer 12B, the second layer 12C, and the third layer 12D is not particularly limited as long as the relational expression (B) is satisfied. The indentation hardness of the first layer 12B is 1 MPa or more and 100 MPa or less, the indentation hardness of the second layer 12C is 10 MPa or more and 500 MPa or less, and the indentation hardness of the third layer 12D is It is preferably 100 MPa or more and 1000 MPa or less. When the indentation hardness of the first layer is 1 MPa or more, the pencil hardness can be further improved, and when the indentation hardness of the first layer is 100 MPa or less, the impact resistance is further improved. be able to. When the indentation hardness of the second layer is 10 MPa or more, cracking of the resin layer is less likely to occur when the optical film is folded, and the indentation hardness of the second layer is 500 MPa or less. When the optical film is folded, wrinkles of the resin layer are less likely to occur. When the indentation hardness of the third layer is 100 MPa or more, the scratch resistance can be further improved, and when the indentation hardness of the third layer is 1000 MPa or less, the optical film is folded. In addition, cracks in the resin layer are less likely to occur.

<First layer>
The first layer 12B is a layer having the lowest indentation hardness among the first layer 12B to the third layer 12D, and mainly has a function of improving pencil hardness and impact resistance. The film thickness of the first layer 12B is preferably 50 μm or more and 300 μm or less. When the film thickness of the first layer is 50 μm or more, the hardness of the resin layer can be further improved. When the film thickness is 300 μm or less, the film thickness is not too thick and is suitable for thinning, and processability is improved. Is also good. The film thickness of the first layer 12B is obtained by photographing a cross section of the first layer 12B using a scanning electron microscope (SEM), measuring the film thickness of the first layer 12B in 20 positions in the image of the cross section, The arithmetic average value of the film thickness at the location is used. The lower limit of the first layer 12B is more preferably in the order of 80 μm or more, 100 μm or more, and 150 μm or more (higher values are preferable), and the upper limit of the first layer 12B is more preferable in the order of 250 μm or less, 220 μm or less, 200 μm or less. Is preferable).

The film thickness of the first layer is obtained by photographing a cross section of the first layer using a scanning electron microscope (SEM), measuring 20 film thicknesses of the first layer in the image of the cross section, The arithmetic average value of the film thickness is used. A specific method for taking a cross-sectional photograph is described below. First, a block is prepared by embedding an optical film cut into 1 mm × 10 mm with an embedding resin, and a uniform section having a thickness of 70 nm or more and 100 nm or less without holes is cut out from this block by a general section preparation method. . For the preparation of the section, “Ultra Microtome EM UC7” (Leica Microsystems Co., Ltd.) or the like can be used. The remaining block from which a uniform section without holes or the like is cut out is taken as a measurement sample. Thereafter, a cross-sectional photograph of the measurement sample is taken using a scanning electron microscope (SEM) (product name “S-4800”, manufactured by Hitachi High-Technologies Corporation). When taking a cross-sectional photograph using the S-4800, the cross-section is observed with the detector set to “SE”, the acceleration voltage set to “5 kV”, and the emission current set to “10 μA”. The magnification is appropriately adjusted from 100 to 100,000 times while adjusting the focus and observing whether each layer can be distinguished. When taking a cross-sectional photograph using the above S-4800, the aperture is set to “beam monitor aperture 3”, the objective lens aperture is set to “3”, and the W.S. D. May be set to “8 mm”. When measuring the thickness of the first layer, it is important that the interface contrast between the first layer and another layer (for example, the second layer) can be observed as clearly as possible when the cross-section is observed. If it is difficult to see this interface due to insufficient contrast, a dyeing process such as osmium tetroxide, ruthenium tetroxide, or phosphotungstic acid can be used to easily see the interface between the organic layers. Also, the interface contrast may be difficult to understand when the magnification is high. In that case, the low magnification is also observed at the same time. For example, observe at two magnifications of high and low, such as 25,000 times and 50,000 times, and 50,000 times and 100,000 times, and obtain the arithmetic average value described above at both magnifications. The value of the film thickness.

The resin constituting the first layer 12B is not particularly limited as long as the indentation hardness of the first layer 12B is lower than the indentation hardness of the second layer 12C. Examples of such a resin include urethane resins, epoxy resins, silicone resins, and the like. Among these, since the urethane-based resin is excellent in toughness, the urethane-based resin is preferable from the viewpoint of obtaining excellent folding performance and obtaining excellent hardness with a pencil hardness of 3H or more. In addition, the resin layer 12 may contain rubber | gum and a thermoplastic elastomer other than urethane type resin, an epoxy resin, etc.

Urethane resin is a resin having a urethane bond. Examples of the urethane resin include a cured product of an ionizing radiation curable urethane resin composition and a cured product of a thermosetting urethane resin composition. Among these, a cured product of an ionizing radiation-curable urethane-based resin composition is preferable from the viewpoint that scratch resistance and high hardness are obtained, and the curing rate is high and the mass productivity is excellent.

The ionizing radiation curable urethane resin composition contains urethane (meth) acrylate, and the thermosetting urethane resin composition contains a polyol compound and an isocyanate compound. The urethane (meth) acrylate, polyol compound, and isocyanate compound may be any of a monomer, an oligomer, and a prepolymer. The “urethane (meth) acrylate” means both “urethane acrylate” and “urethane methacrylate”.

The number (functional group number) of (meth) acryloyl groups in urethane (meth) acrylate is preferably 2 or more and 6 or less. If the number of (meth) acryloyl groups in the urethane (meth) acrylate is less than 2, the pencil hardness may be low, and if it exceeds 6, the curing shrinkage increases and the optical film curls. In addition, there is a risk of cracks in the resin layer during bending. The upper limit of the number of (meth) acryloyl groups in the urethane (meth) acrylate is more preferably 3 or less. The “(meth) acryloyl group” means to include both “acryloyl group” and “methacryloyl group”.

The weight average molecular weight of urethane (meth) acrylate is not particularly limited, but is preferably 1500 or more and 20000 or less. If the weight average molecular weight of the urethane (meth) acrylate is less than 1500, the impact resistance may be lowered. If it exceeds 20000, the viscosity of the ionizing radiation-curable urethane resin composition increases, and the coating is applied. May deteriorate. The lower limit of the weight average molecular weight of the urethane (meth) acrylate is more preferably 2000 or more, and the upper limit is more preferably 15000 or less.

Moreover, as a repeating unit which has a structure derived from urethane (meth) acrylate, the structure etc. which are represented by the following general formula (25), (26), (27) or (28) are mentioned, for example.

In the general formula (25), R ⁷ represents a branched alkyl group, R ⁸ represents a branched alkyl group or a saturated cycloaliphatic group, R ⁹ represents a hydrogen atom or a methyl group, and R ¹⁰ represents , A hydrogen atom, a methyl group or an ethyl group, m represents an integer of 0 or more, and x represents an integer of 0 to 3.

In the general formula (26), R ⁷ represents a branched alkyl group, R ⁸ represents a branched alkyl group or a saturated cycloaliphatic group, R ⁹ represents a hydrogen atom or a methyl group, and R ¹⁰ represents , Represents a hydrogen atom, a methyl group or an ethyl group, n represents an integer of 1 or more, and x represents an integer of 0 to 3.

In the general formula (27), R ⁷ represents a branched alkyl group, R ⁸ represents a branched alkyl group or a saturated cycloaliphatic group, R ⁹ represents a hydrogen atom or a methyl group, and R ¹⁰ represents , A hydrogen atom, a methyl group or an ethyl group, m represents an integer of 0 or more, and x represents an integer of 0 to 3.

In the general formula (28), R ⁷ represents a branched alkyl group, R ⁸ represents a branched alkyl group or a saturated cycloaliphatic group, R ⁹ represents a hydrogen atom or a methyl group, and R ¹⁰ represents , Represents a hydrogen atom, a methyl group or an ethyl group, n represents an integer of 1 or more, and x represents an integer of 0 to 3.

The structure of the resin constituting the first layer 12B and the like is defined by the structure of the polymer chain (repeating unit) by, for example, the first layer 12B and the like by pyrolysis GC-MS and FT-IR. Judgment can be made by analysis. In particular, pyrolysis GC-MS is useful because it can detect monomer units contained in the first layer 12B and the like as monomer components.

If the indentation hardness is lower than the indentation hardness of the second layer 12C, the first layer 12B may contain a Hz ultraviolet absorber, a spectral transmittance adjusting agent, and the like.

<Ultraviolet absorber>
The optical film is particularly preferably used for a mobile terminal such as a foldable smartphone or tablet terminal. However, such a mobile terminal is often used outdoors, and therefore, the optical film is disposed closer to the display element than the optical film. There is a problem that the polarizer is easily deteriorated by being exposed to ultraviolet rays. However, since the first layer is disposed on the display screen side of the polarizer, if the ultraviolet absorber is contained in the first layer, deterioration due to exposure of the polarizer to ultraviolet rays can be suitably prevented. it can. The ultraviolet absorbent (UVA) may be contained in at least one of the base material 11 and the second to nth layers. In this case, the ultraviolet absorber (UVA) may not be contained in the first layer 12B.

Examples of ultraviolet absorbers include triazine-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, and benzotriazole-based ultraviolet absorbers.

Examples of the triazine ultraviolet absorber include 2- (2-hydroxy-4- [1-octyloxycarbonylethoxy] phenyl) -4,6-bis (4-phenylphenyl) -1,3,5-triazine. 2- [4-[(2-hydroxy-3-dodecyloxypropyl) oxy] -2-hydroxyphenyl] -4,6-bis (2,4-dimethylphenyl) -1,3,5-triazine, 2 , 4-Bis [2-hydroxy-4-butoxyphenyl] -6- (2,4-dibutoxyphenyl) -1,3,5-triazine, 2- [4-[(2-hydroxy-3-tridecyl) Oxypropyl) oxy] -2-hydroxyphenyl] -4,6-bis (2,4-dimethylphenyl) -1,3,5-triazine, and 2- [4-[(2-hydroxy-3- ( '- ethyl) hexyl) oxy] -2-hydroxyphenyl] -4,6-bis (2,4-dimethylphenyl) -1,3,5-triazine. Examples of commercially available triazine ultraviolet absorbers include TINUVIN 460, TINUVIN 477 (both manufactured by BASF), LA-46 (manufactured by ADEKA), and the like.

Examples of the benzophenone ultraviolet absorber include 2-hydroxybenzophenone, 2,4-dihydroxybenzophenone, 2,2′-dihydroxy-4,4′-dimethoxybenzophenone, 2,2 ′, 4,4′-tetrahydroxy. Examples thereof include benzophenone, 2-hydroxy-4-methoxybenzophenone, hydroxymethoxybenzophenone sulfonic acid and its trihydrate, hydroxymethoxybenzophenone sulfonate sodium, and the like. Examples of commercially available benzophenone ultraviolet absorbers include CHMASSORB81 / FL (manufactured by BASF).

Examples of the benzotriazole ultraviolet absorber include 2-ethylhexyl-3- [3-tert-butyl-4-hydroxy-5- (5-chloro-2H-benzotriazol-2-yl) phenyl] propionate, 2 -(2H-benzotriazol-2-yl) -6- (linear and side chain dodecyl) -4-methylphenol, 2- [5-chloro (2H) -benzotriazol-2-yl] -4-methyl- 6- (tert-butyl) phenol, 2- (2H-benzotriazol-2-yl) -4,6-di-tert-pentylphenol, 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, 2- (2′-hydroxy-3 ′, 5′-di-tert-butylphenyl) benzotriazole, 2- (2′-hydroxy-3) -Tert-butyl-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3 ', 5'-di-tert-butylphenyl) -5-chlorobenzotriazole, 2- (2'-hydroxy- 3 ′-(3 ″, 4 ″, 5 ″, 6 ″ -tetrahydrophthalimidomethyl) -5′-methylphenyl) benzotriazole, 2,2-methylenebis (4- (1,1,3,3 -Tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol) and 2- (2'-hydroxy-3'-tert-butyl-5'-methylphenyl) -5-chlorobenzotriazole Etc. Examples of commercially available benzotriazole ultraviolet absorbers include KEMISORB71D, KEMISORB79 (all manufactured by Chemipro Kasei Co., Ltd.), JF-80, JAST-500 (all manufactured by Johoku Chemical Co., Ltd.), ULS-1933D (one side) And RUVA-93 (manufactured by Otsuka Chemical Co., Ltd.).

Among these, triazine ultraviolet absorbers and benzotriazole ultraviolet absorbers are preferably used as the ultraviolet absorber. It is preferable that the ultraviolet absorber has high solubility with the resin component constituting the resin layer, and it is preferable that the bleed-out after the above-described durability folding test is small. The ultraviolet absorber is preferably polymerized or oligomerized. As the ultraviolet absorber, a polymer or oligomer having a benzotriazole, triazine, or benzophenone skeleton is preferable. Specifically, (meth) acrylate having a benzotriazole or benzophenone skeleton and methyl methacrylate (MMA) at an arbitrary ratio. It is preferable that it has been heat copolymerized. In addition, when an optical film is applied to an organic light emitting diode (OLED) display device, the ultraviolet absorber can also serve to protect the OLED from ultraviolet rays.

Although it does not specifically limit as content of a ultraviolet absorber, It is preferable that they are 1 mass part or more and 6 mass parts or less with respect to 100 mass parts of solid content of the composition for 1st layers. If the amount is less than 1 part by mass, the effect of containing the above-described ultraviolet absorber in the first layer may not be sufficiently obtained. Sometimes. The minimum with more preferable content of the said ultraviolet absorber is 2 mass parts or more, and a more preferable upper limit is 5 mass parts or less.

<Spectral transmittance adjusting agent>
The spectral transmittance adjusting agent adjusts the spectral transmittance of the optical film. For example, when the sesamol type benzotriazole monomer represented by the following general formula (29) is included in the first layer, the above-described spectral transmittance can be preferably satisfied.

In the formula, R ¹¹ represents a hydrogen atom or a methyl group. R ¹² represents a linear or branched alkylene group having 1 to 6 carbon atoms or a linear or branched oxyalkylene group having 1 to 6 carbon atoms.

The sesamol type benzotriazole monomer is not particularly limited, but specific substance names include 2- [2- (6-hydroxybenzo [1,3] dioxol-5-yl) -2H-benzo Triazol-5-yl] ethyl methacrylate, 2- [2- (6-hydroxybenzo [1,3] dioxol-5-yl) -2H-benzotriazol-5-yl] ethyl acrylate, 3- [2- (6 -Hydroxybenzo [1,3] dioxol-5-yl) -2H-benzotriazol-5-yl] propyl methacrylate, 3- [2- (6-hydroxybenzo [1,3] dioxol-5-yl) -2H -Benzotriazol-5-yl] propyl acrylate, 4- [2- (6-hydroxybenzo [1,3] dioxol-5-yl -2H-benzotriazol-5-yl] butyl methacrylate, 4- [2- (6-hydroxybenzo [1,3] dioxol-5-yl) -2H-benzotriazol-5-yl] butyl acrylate, 2- [ 2- (6-Hydroxybenzo [1,3] dioxol-5-yl) -2H-benzotriazol-5-yloxy] ethyl methacrylate, 2- [2- (6-hydroxybenzo [1,3] dioxol-5- Yl) -2H-benzotriazol-5-yloxy] ethyl acrylate, 2- [3- {2- (6-hydroxybenzo [1,3] dioxol-5-yl) -2H-benzotriazol-5-yl} prop Noyloxy] ethyl methacrylate, 2- [3- {2- (6-hydroxybenzo [1,3] dioxol-5-yl -2H-benzotriazol-5-yl} propanoyloxy] ethyl acrylate, 4- [3- {2- (6-hydroxybenzo [1,3] dioxol-5-yl) -2H-benzotriazol-5-yl } Propanoyloxy] butyl methacrylate, 4- [3- {2-(6-hydroxybenzo [1,3] dioxol-5-yl) -2H-benzotriazol-5-yl} propanoyloxy] butyl acrylate, 2 -[3- {2- (6-hydroxybenzo [1,3] dioxol-5-yl) -2H-benzotriazol-5-yl} propanoyloxy] ethyl methacrylate, 2- [3- {2- (6 -Hydroxybenzo [1,3] dioxol-5-yl) -2H-benzotriazol-5-yl} propanoyloxy] ethyl acrylate 2- (methacryloyloxy) ethyl 2- (6-hydroxybenzo [1,3] dioxol-5-yl) -2H-benzotriazole-5 carboxylate, 2- (acryloyloxy) ethyl 2- (6- Hydroxybenzo [1,3] dioxol-5-yl) -2H-benzotriazole-5-carboxylate, 4- (methacryloyloxy) butyl 2- (6-hydroxybenzo [1,3] dioxol-5-yl)- 2H-benzotriazole-5-carboxylate, 4- (acryloyloxy) butyl 2- (6-hydroxybenzo [1,3] dioxol-5-yl) -2H-benzotriazole-5-carboxylate, etc. it can. Further, these sesamol type benzotriazole monomers may be used alone or in combination of two or more.

The sesamol type benzotriazole-based monomer may be contained in the first layer 12B, but it may be contained in at least one of the first layer to the n-th layer so as to satisfy the requirements for the spectral transmittance. Good. For example, the first layer contains the sesamol type benzotriazole monomer so that only the spectral transmittance at a wavelength of 380 nm can be achieved, and the spectral transmittance conditions at a wavelength of 410 nm and a wavelength of 440 nm can be achieved in the other layers. The structure etc. which contain the said sesamol type | mold benzotriazole type monomer are mentioned.

When the sesamol type benzotriazole monomer is contained in the first layer 12B, for example, the sesamol type benzotriazole monomer is contained at 15 to 30% by mass in the first layer 12B layer. It is preferable. When the sesamol type benzotriazole monomer is contained in such a range, the above-described spectral transmittance can be satisfied. The sesamol type benzotriazole-based monomer may be contained in the first layer 12B by reacting with the resin component constituting the first layer 12B, and the resin constituting the first layer 12B. You may contain independently, without reacting with a component.

<Second layer>
The second layer 12C is a layer having indentation hardness between the first layer 12B and the third layer 12D, and mainly has a function of improving flexibility and scratch resistance. The film thickness of the second layer 12C is preferably 1 μm or more and 50 μm or less. When the thickness of the second layer is 1 μm or more, the resin layer is less likely to be wrinkled when the optical film is folded, and when it is 50 μm or less, the resin layer is cracked when the optical film is folded. Is less likely to occur. The film thickness of the second layer 12C is determined by the same method as the film thickness of the first layer 12B. The lower limit of the second layer 12C is more preferable in the order of 3 μm or more, 5 μm or more, and 7 μm or more (the larger the value, the more preferable), and the upper limit of the second layer 12C is further preferable in the order of 30 μm or less, 25 μm or less, 20 μm or less. Is preferable).

The material constituting the second layer 12C is not particularly limited as long as the indentation hardness of the second layer 12C is higher than the indentation hardness of the first layer 12B. In the second layer 12C, for example, the indentation hardness may be made higher than that of the first layer 12B by adding inorganic particles and / or organic particles to the resin described in the column of the first layer 12B. Further, in addition to urethane (meth) acrylate, an ionizing radiation polymerizable compound that increases the indentation hardness may be added to make the indentation hardness higher than that of the first layer 12B.

(Inorganic particles)
The inorganic particles are a component that increases the indentation hardness of the second layer 12C. Examples of the inorganic particles include inorganic oxide particles such as silica (SiO ₂ ) particles, alumina particles, titania particles, tin oxide particles, antimony-doped tin oxide (abbreviation: ATO) particles, and zinc oxide particles. Among these, silica particles are preferable from the viewpoint of further increasing the hardness. Examples of the silica particles include spherical silica particles and irregular silica particles. Among these, irregular silica particles are preferable. In the present specification, “spherical particles” mean, for example, particles such as true spheres and ellipsoids, and “irregular particles” mean particles having potato-like random irregularities on the surface. Since the irregular shaped particles have a larger surface area than the spherical particles, the inclusion of such irregular shaped particles increases the contact area with the resin, and the pencil hardness of the resin layer 12 is more excellent. can do. Whether or not the silica particles contained in the second layer 12C are irregular-shaped silica particles is determined by observing the cross section of the second layer 12C with a transmission electron microscope (TEM) or a scanning transmission electron microscope (STEM). Can be confirmed. When using spherical silica particles, the smaller the particle diameter of the spherical silica particles, the higher the hardness of the light transmissive functional layer. On the other hand, the deformed silica particles can achieve the same hardness as that of spherical silica particles, even if they are not as small as the commercially available spherical silica particles having the smallest particle diameter.

The average primary particle diameter of the silica particles is preferably 1 nm or more and 100 nm or less. When the silica particles are irregular-shaped silica particles, the average primary particle diameter of the irregular-shaped silica particles is determined from the cross-sectional image of the light-transmitting functional layer taken using a transmission electron microscope (TEM) or a scanning transmission electron microscope (STEM). The maximum value (major axis) and the minimum value (minor axis) of the distance between two points on the outer periphery of the particle are measured and averaged to obtain the particle size, which is the arithmetic average value of the particle size of 20 particles. In addition, when the silica particles are spherical silica particles, the average particle diameter of the spherical silica particles is 20 from the cross-sectional image of the particles taken using a transmission electron microscope (TEM) or a scanning transmission electron microscope (STEM). The particle diameter of the particles is measured and taken as the arithmetic average value of the particle diameters of 20 particles.

The content of inorganic particles in the second layer 12C is preferably 20% by mass or more and 70% by mass or less. When the content of the inorganic particles is less than 20% by mass, it becomes difficult to ensure sufficient hardness, and when the content of the inorganic particles exceeds 70% by mass, the filling rate increases too much, and the inorganic particles Adhesiveness with the resin component is deteriorated, and rather the hardness of the second layer is lowered.

As the inorganic particles, it is preferable to use inorganic particles (reactive inorganic particles) having a photopolymerizable functional group on the surface. Such inorganic particles having a photopolymerizable functional group on the surface can be prepared by surface-treating the inorganic particles with a silane coupling agent or the like. As a method of treating the surface of the inorganic particles with a silane coupling agent, a dry method in which the silane coupling agent is sprayed on the inorganic particles, or a wet method in which the inorganic particles are dispersed in a solvent and then the silane coupling agent is added and reacted. Etc.

(Organic particles)
Organic particles are also a component that increases the indentation hardness of the second layer 12C. Examples of the organic particles include plastic beads. Specific examples of the plastic beads include polystyrene beads, melamine resin beads, acrylic beads, acrylic-styrene beads, silicone beads, benzoguanamine beads, benzoguanamine / formaldehyde condensation beads, polycarbonate beads, polyethylene beads, and the like.

(Ionizing radiation polymerizable compound)
The ionizing radiation polymerizable compound is also a component that increases the indentation hardness of the second layer 12C. The ionizing radiation polymerizable compound is used by mixing with urethane (meth) acrylate. Examples of such ionizing radiation polymerizable compounds that can increase the indentation hardness include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and the like. Monomers containing hydroxyl groups, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, tetramethylene glycol di (meth) acrylate, triethylene glycol Methylolpropane tri (meth) acrylate, trimethylolethane tri (meth) acrylate, pentaerythritol di (meth) acrylate, pentaerythritol tri (meth) acrylate, pen Pentaerythritol tetra (meth) acrylate, dipentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, (meth) acrylate monomers such as glycerol (meth) acrylate.

<Third layer>
The third layer 12D is a layer having the highest indentation hardness among the first layer 12B to the third layer 12D, and mainly has a function of improving scratch resistance. The film thickness of the third layer 12D is preferably 0.05 μm or more and 5 μm or less. When the thickness of the third layer is 0.05 μm or more, the scratch resistance can be further improved, and when it is 5 μm or less, the resin layer is less likely to be cracked when the optical film is folded. Become. The thickness of the third layer 12D is determined by the same method as the thickness of the first layer 12B. The lower limit of the third layer 12D is more preferably in the order of 0.1 μm or more, 0.5 μm or more, and 0.8 μm or more (the larger the numerical value, the more preferable), and the upper limit of the third layer 12D is 3 μm or less, 2 μm or less, and 1 μm or less. More preferable (the smaller the value, the better).

The material constituting the third layer 12D is not particularly limited as long as the indentation hardness of the third layer 12D is higher than the indentation hardness of the second layer 12C. In the third layer 12D, by using the ionizing radiation polymerizable compound described in the column of the second layer 12C without using the resin described in the column of the first layer 12B, the indentation hardness is higher than that of the second layer 12C. The height may be increased. In addition, the third layer 12D may further contain a solvent-drying resin or an antifouling agent.

(Solvent drying resin)
The solvent-drying resin is a resin that forms a film only by drying a solvent added to adjust the solid content during coating, such as a thermoplastic resin. When the solvent-drying type resin is added, coating defects on the coating surface of the coating liquid can be effectively prevented when forming the third layer 12D. It does not specifically limit as solvent dry type resin, Generally, a thermoplastic resin can be used.

Examples of thermoplastic resins include styrene resins, (meth) acrylic resins, vinyl acetate resins, vinyl ether resins, halogen-containing resins, alicyclic olefin resins, polycarbonate resins, polyester resins, polyamide resins. , Cellulose derivatives, silicone resins and rubbers or elastomers.

(Anti-fouling agent)
As for the antifouling agent, the antifouling agent may be uniformly dispersed in the third layer 12D. However, from the viewpoint of obtaining sufficient antifouling properties with a small addition amount and suppressing the strength reduction of the third layer 12D. It is preferable that it is unevenly distributed on the surface side of the three layers 12D. As a method of unevenly distributing the antifouling agent on the surface side of the third layer 12D, for example, when forming the third layer 12D, a coating film formed using a third resin composition described later is dried and cured. Before, the coating film is heated, the fluidity is increased by lowering the viscosity of the resin component contained in the coating film, and the antifouling agent is unevenly distributed on the surface side of the third layer 12D, or the surface tension is low. By selecting and using an antifouling agent, the antifouling agent is floated on the surface of the coating film without applying heat when the coating film is dried, and then the coating film is cured, so that the antifouling agent is applied to the third layer 12D. For example, a method of uneven distribution on the surface side can be mentioned.

The antifouling agent is not particularly limited, and examples thereof include silicone antifouling agents, fluorine antifouling agents, silicone and fluorine antifouling agents, which may be used alone or in combination. May be. The antifouling agent may be an acrylic antifouling agent.

The content of the antifouling agent is preferably 0.01 to 3.0 parts by weight with respect to 100 parts by weight of the resin component described above. If it is less than 0.01 part by weight, sufficient antifouling performance may not be imparted to the third layer, and if it exceeds 3.0 parts by weight, the hardness of the third layer may be reduced.

The antifouling agent preferably has a weight average molecular weight of 5000 or less, and is a compound having preferably 1 or more, more preferably 2 or more reactive functional groups in order to improve the durability of the antifouling performance. Among them, excellent scratch resistance can be imparted by using an antifouling agent having two or more reactive functional groups.

When the antifouling agent does not have a reactive functional group, the antifouling agent is transferred to the back surface of the optical film when it is stacked, whether it is a roll or a sheet. When an attempt is made to attach or apply another layer to the back surface, the other layer may be peeled off and may be easily peeled off by performing a plurality of folding tests.

Furthermore, the antifouling agent having the reactive functional group has good antifouling performance durability (durability), and among them, the resin layer containing the above-mentioned fluorine-based antifouling agent is difficult to have a fingerprint ( Less noticeable) and good wiping property. Furthermore, since the surface tension at the time of application of the resin layer composition can be lowered, the leveling property is good and the appearance of the resin layer to be formed is good.

The resin layer containing a silicone antifouling agent has good sliding properties and good steel wool resistance. A touch sensor in which an optical film containing such a silicone antifouling agent is mounted on the resin layer has a good tactile sensation because of good sliding when touched with a finger or a pen. Further, fingerprints are hardly attached to the resin layer (not easily noticeable), and the wiping property is improved. Furthermore, since the surface tension at the time of application of the resin layer composition can be lowered, the leveling property is good and the appearance of the resin layer to be formed is good.

Examples of commercially available silicone antifouling agents include SUA1900L10 (manufactured by Shin-Nakamura Chemical Co., Ltd.), SUA1900L6 (manufactured by Shin-Nakamura Chemical Co., Ltd.), Ebecryl 1360 (manufactured by Daicel Cytec Co., Ltd.), UT3971 (manufactured by Nippon Gosei Co., Ltd.), and BYKUV3500 (BIC Chemie). BYKUV3510 (manufactured by Big Chemie), BYKUV3570 (manufactured by Big Chemie), X22-164E, X22-174BX, X22-2426, KBM503. KBM5103 (manufactured by Shin-Etsu Chemical Co., Ltd.), TEGO-RAD2250, TEGO-RAD2300. TEGO-RAD2200N, TEGO-RAD2010, TEGO-RAD2500, TEGO-RAD2600, TEGO-RAD2700 (manufactured by Evonik Japan), MegaFac RS854 (manufactured by DIC) and the like can be mentioned.

Commercially available fluorine-based antifouling agents include, for example, OPTOOL DAC, OPTOOL DSX (manufactured by Daikin Industries, Ltd.), Megafuck RS71, Megafuck RS74 (manufactured by DIC), LINC152EPA, LINC151EPA, and LINC182UA (manufactured by Kyoeisha Chemical Co., Ltd.) Examples of the solvent include 650A, 601ENT, 602, and 602.

Examples of commercially available antifouling agents having fluorine-based and silicone-based reactive functional groups include, for example, MegaFac RS851, MegaFac RS852, MegaFac RS853, MegaFac RS854 (manufactured by DIC), Opstar TU2225, Opstar TU2224 ( JSR), X71-1203M (Shin-Etsu Chemical Co., Ltd.) and the like.

<<< Other optical films >>>
In the optical film 10 shown in FIG. 1, the resin layer 12 has a three-layer structure, but may have a four-layer structure. Specifically, as shown in FIG. 3, the optical film is formed in this order from the base material 11 side to the base material 11 and the one surface 11A side of the base material 11 from the first layer 21B to the fourth layer 21E. The optical film 20 provided with the resin layer 21 of the four-layer structure laminated | stacked by may be sufficient. The surface 20A of the optical film 20 is the surface 21A of the resin layer 21 (the surface of the fourth layer 21E). Since the physical properties of the optical film 20 are the same as the physical properties of the optical film 10, the description thereof will be omitted here. Since the base material 11 of the optical film 20 is the same as the base material 11 of the optical film 10, the description thereof will be omitted.

<< Resin layer >>
In the resin layer 21, the indentation hardness of each of the first layer 21B, the second layer 21C, the third layer 21D, and the fourth layer 21E increases in order from the first layer 21B to the fourth layer 21E. That is, when the indentation hardnesses of the first layer 21B, the second layer 21C, the third layer 21D, and the fourth layer 21E are respectively H _IT1 , H _IT2 , H _IT3, and H _IT4 , the above relational expression (A ) Is satisfied. That is, the resin layer 21 satisfies the following relational expression (C).
H _IT1 <H _IT2 <H _IT3 <H _IT4 (C)

In the resin layer 21, the indentation hardness of the first layer 21B, the second layer 21C, the third layer 21D, and the fourth layer 21E is not particularly limited as long as the relational expression (C) is satisfied. The indentation hardness of the first layer 21B is 1 MPa or more and 100 MPa or less, the indentation hardness of the second layer 21C is 10 MPa or more and 300 MPa or less, and the indentation hardness of the third layer 21D is The indentation hardness of the fourth layer 21E is preferably 100 MPa or more and 1000 MPa or less. When the indentation hardness of the first layer is 1 MPa or more, the pencil hardness can be further improved, and when the indentation hardness of the first layer is 100 MPa or less, the impact resistance is further improved. be able to. When the indentation hardness of the second layer is 10 MPa or more, cracking of the resin layer is less likely to occur when the optical film is folded, and the indentation hardness of the second layer is 300 MPa or less. When the optical film is folded, wrinkles of the resin layer are less likely to occur. When the indentation hardness of the third layer is 50 MPa or more, cracking of the resin layer is less likely to occur when the optical film is folded, and the indentation hardness of the third layer is 500 MPa or less. When the optical film is folded, wrinkles of the resin layer are less likely to occur. When the indentation hardness of the fourth layer is 100 MPa or more, the scratch resistance can be further suppressed, and when the indentation hardness of the fourth layer is 1000 MPa or less, the resin layer is folded when the optical film is folded. Cracks are less likely to occur.

<First layer>
The film thickness of the first layer 21B is preferably 50 μm or more and 300 μm or less. When the film thickness of the first layer is 50 μm or more, the hardness of the resin layer can be further improved. When the film thickness is 300 μm or less, the film thickness is not too thick and is suitable for thinning, and processability is improved. Is also good. The film thickness of the first layer 21B is measured by the same method as the film thickness of the first layer 12B. The lower limit of the first layer 21B is more preferable in the order of 80 μm or more, 100 μm or more, and 150 μm or more (the higher the numerical value), and the upper limit of the first layer 21B is more preferable in the order of 250 μm or less, 220 μm or less, 200 μm or less (the numerical value is small). Is preferable). Since the first layer 21B can be formed of the same resin as the first layer 12B, description thereof will be omitted here.

<Second layer and third layer>
The film thicknesses of the second layer 21C and the third layer 21D are preferably 1 μm or more and 50 μm or less, respectively. When the thickness of the second layer and the third layer is 1 μm or more, wrinkles of the resin layer are less likely to occur when the optical film is folded, and when the thickness is 50 μm or less, the optical film is folded. Cracks in the resin layer are less likely to occur. The film thicknesses of the second layer 21C and the third layer 21D are determined by the same method as the film thickness of the first layer 12B. The lower limit of the film thickness of the second layer 21C and the third layer 21D is more preferably in the order of 3 μm or more, 5 μm or more, and 7 μm or more (the larger the value, the more preferable), and the upper limit of the film thickness of the second layer 21C and the third layer 21D. Are more preferable in the order of 40 μm or less, 30 μm or less, and 20 μm or less (the smaller the value, the better). The second layer 21C can be formed by adding inorganic particles and / or organic particles to the resin described in the column of the first layer 12B, for example, as described in the column of the second layer 12C. The third layer 21D can be formed by using a resin layer composition containing urethane (meth) acrylate and an ionizing radiation polymerizable compound that increases the indentation hardness.

<Fourth layer>
The film thickness of the fourth layer 21E is preferably 0.05 μm or more and 5 μm or less. When the thickness of the fourth layer is 0.05 μm or more, the scratch resistance can be further improved, and when it is 5 μm or less, the resin layer is less likely to crack when the optical film is folded. Become. The film thickness of the fourth layer 21E is determined by the same method as the film thickness of the first layer 12B. The lower limit of the fourth layer 21E is more preferably in the order of 0.1 μm or more, 0.5 μm or more, and 0.8 μm or more (the higher the numerical value, the more preferable), and the upper limit of the fourth layer 21E is 3 μm or less, 2 μm or less, and 1 μm or less. Further preferred. The fourth layer 21E can be formed from the ionizing radiation polymerizable compound described in the column of the third layer 12D.

<<< Optical Film Manufacturing Method >>>
The optical film 10 can be produced by various methods depending on the type of resin constituting the first layer 12B to the third layer 12D. For example, when the first layer 12B and the second layer 12C are layers made of a urethane resin, they can be manufactured as follows. First, the first resin composition is applied onto one surface 11A of the substrate 11 by a coating device such as a bar coater to form a coating film of the first resin composition.

<First resin composition>
The 1st composition for resin layers contains urethane (meth) acrylate or a polyol compound, and an isocyanate compound. In addition, the 1st resin composition may contain the ultraviolet absorber, the spectral transmittance regulator, the leveling agent, the solvent, and the polymerization initiator as needed.

The first resin composition preferably has a total solid content of 25 to 95%. If it is lower than 25%, residual solvent may remain or whitening may occur. If it exceeds 95%, the viscosity of the composition for the first layer will increase, the coatability may decrease, and unevenness and streaks may appear on the surface. The solid content is more preferably 30 to 90%.

(solvent)
Examples of the solvent include alcohols (eg, methanol, ethanol, propanol, isopropanol, n-butanol, s-butanol, t-butanol, benzyl alcohol, PGME, ethylene glycol, diacetone alcohol), ketones (eg, acetone, methyl ethyl ketone, Methyl isobutyl ketone, cyclopentanone, cyclohexanone, heptanone, diisobutyl ketone, diethyl ketone, diacetone alcohol), ester (methyl acetate, ethyl acetate, butyl acetate, n-propyl acetate, isopropyl acetate, methyl formate, PGMEA), aliphatic Hydrocarbons (eg, hexane, cyclohexane), halogenated hydrocarbons (eg, methylene chloride, chloroform, carbon tetrachloride), aromatic hydrocarbons (eg, benzene, toluene, xylene), Amide (eg, dimethylformamide, dimethylacetamide, n-methylpyrrolidone), ether (eg, diethyl ether, dioxane, tetrahydrofuran), ether alcohol (eg, 1-methoxy-2-propanol), carbonate (dimethyl carbonate, diethyl carbonate, Ethyl methyl carbonate), and the like. These solvents may be used alone or two or more of them may be used in combination. Especially, as said solvent, components, such as urethane (meth) acrylate, and another additive are melt | dissolved or disperse | distributed, and the point which can apply the said 1st resin composition suitably, methyl isobutyl ketone, methyl ethyl ketone Is preferred.

(Polymerization initiator)
The polymerization initiator is a component that is decomposed by irradiation with ionizing radiation or heat to generate radicals to initiate or advance polymerization (crosslinking) of the polymerizable compound.

The polymerization initiator is not particularly limited as long as it can release a substance that initiates radical polymerization by irradiation with ionizing radiation or heat. The polymerization initiator is not particularly limited, and known ones can be used. Specific examples include, for example, acetophenones, benzophenones, Michler benzoylbenzoate, α-amyloxime ester, thioxanthones, propiophenone. , Benzyls, benzoins, acylphosphine oxides. Further, it is preferable to use a mixture of photosensitizers, and specific examples thereof include n-butylamine, triethylamine, poly-n-butylphosphine and the like.

After forming a coating film of the first resin composition, it is dried, and then irradiated with ionizing radiation or heated to semi-cure (half cure) the coating film of the first resin composition. The term “semi-cured” in the present specification means that curing proceeds substantially when irradiated or heated with ionizing radiation. However, at this stage, the coating film of the first resin composition may be completely cured (full cure). The term “fully cured” in the present specification means that curing does not substantially proceed even when ionizing radiation is further irradiated or heated.

After semi-curing the coating film of the first resin composition, the second resin composition is applied onto the semi-cured coating film of the first resin composition by a coating device such as a bar coater. Then, a coating film of the second resin composition is formed.

<Second resin composition>
The second resin composition contains urethane (meth) acrylate and inorganic particles and / or organic particles or the ionizing radiation polymerizable compound. In addition, the composition for 1st layer may contain the ultraviolet absorber, the spectral transmittance adjusting agent, the leveling agent, the solvent, and the polymerization initiator as needed.

After forming a coating film of the second resin composition, it is dried, and then irradiated with ionizing radiation, so that the coating film of the second resin composition is semi-cured (half-cured). However, at this stage, the coating film of the first resin composition may be completely cured (full cure).

After semi-curing the coating film of the second resin composition, the third resin composition is applied onto the semi-cured coating film of the second resin composition by a coating device such as a bar coater. Then, a coating film of the third resin composition is formed.

<Third resin composition>
The third resin composition contains the ionizing radiation polymerizable compound. In addition, the first resin composition may contain a solvent-drying resin, an antifouling agent, an ultraviolet absorber, a spectral transmittance adjusting agent, a leveling agent, a solvent, and a polymerization initiator, if necessary.

After forming a coating film of the third resin composition, it is dried and then irradiated with ionizing radiation to completely cure (full cure) the coating film of the composition for the third layer. Thereby, the optical film 10 provided with the resin layer 12 in which the first layer 12B, the second layer 12C, and the third layer 12D are laminated in this order on the one surface 11A side of the substrate 11 is obtained.

When the resin layer has a single layer structure composed of a relatively soft resin layer, excellent foldability, impact resistance and pencil hardness can be obtained, but since the resin layer is relatively soft, excellent scratch resistance is obtained. There is a risk of not being able to. In order to obtain excellent scratch resistance, the surface of the resin layer needs to be hardened to some extent. However, if the surface of the resin layer is too hard, there is a possibility that excellent foldability and impact resistance cannot be obtained. In addition, when the resin layer has a two-layer structure of a relatively soft first layer and a hard second layer, excellent foldability, impact resistance, and excellent pencil hardness can be obtained, but the relatively soft first layer can be obtained. Since the hard second layer is formed on the layer, when the optical film is folded at 180 °, fine cracks are generated in the resin layer. There is a risk of sinking into two layers and breaking the second layer. Furthermore, when the resin layer has a three-layer structure including a first layer, a second layer softer than the first layer, and a third layer harder than the first layer and the second layer, excellent foldability, Although impact properties and excellent pencil hardness can be obtained, when the optical film is folded at 180 °, wrinkles and fine cracks are generated in the resin layer. There is a risk of sinking into the layer and breaking the third layer. From such knowledge, the present inventors have obtained an optical film satisfying all of excellent foldability, excellent pencil hardness, excellent impact resistance, excellent flexibility, and excellent scratch resistance. The present inventors have found that the resin layer has a structure of three or more layers and the hardness needs to be gradually increased from the first layer to the n-th layer. According to this embodiment, the resin layer has a structure of three or more layers, and the indentation hardness of each of the first layer to the n-th layer increases in order from the first layer to the n-th layer. That is, since the above relational expression (A) is satisfied, excellent foldability, excellent pencil hardness, excellent impact resistance, excellent flexibility, and excellent scratch resistance can be obtained.

<<< Image display device >>>
The optical film 10 can be used by being incorporated in a foldable image display device. FIG. 4 is a schematic configuration diagram of the image display apparatus according to the present embodiment. As shown in FIG. 4, the image display device 30 mainly has a housing 31 in which a battery and the like are stored, a protective film 32, a display panel 33, a touch sensor 34, and a circularly polarizing plate 35 toward the viewer. , And the optical film 10 are laminated in this order. Between the display panel 33 and the touch sensor 34, between the touch sensor 34 and the circularly polarizing plate 35, and between the circularly polarizing plate 35 and the optical film 10, for example, optical transparency such as OCA (Optical Clear Adhesive). An adhesive layer 36 is disposed, and these members are fixed to each other by a light-transmitting adhesive layer 36. The “adhesive layer” in the present specification is a concept including an adhesive layer. A black layer 37 is provided on a part of the back surface 10 B of the optical film 10.

The optical film 10 is arranged so that the resin layer 12 is closer to the viewer than the base material 11. In the image display device 30, the surface 12 A of the resin layer 12 of the optical film 10 constitutes the surface 30 A of the image display device 30.

In the image display device 30, the display panel 33 is an organic light emitting diode panel including an organic light emitting diode. The touch sensor 34 is disposed closer to the display panel 33 than the circularly polarizing plate 35, but may be disposed between the circularly polarizing plate 35 and the optical film 10. The touch sensor 34 may be an on-cell method or an in-cell method.

[Second Embodiment]
Hereinafter, an optical film and an image display device according to a second embodiment of the present invention will be described with reference to the drawings. FIG. 5 is a schematic configuration diagram of an optical film with a release film according to this embodiment, and FIG. 6 is a schematic configuration diagram of another optical film with a release film according to this embodiment.

<<< Optical film with release film >>>
The optical film 50 with a release film shown in FIG. 5 includes a release film 51, an optical film 60, and a release film 52 in this order. The optical film 60 includes a multi-layered resin layer 61 laminated from the first layer to the n-th layer (n is an integer of 3 or more).

<< Release film >>
The

release films

51 and 52 can be peeled from the optical film 60. Although it does not specifically limit as the

release films

51 and 52, It is preferable that it is a film from which the peeling force at the time of peeling will be 0.01 N / 25mm or more and 0.5 N / 25mm or less. If the peeling force is 0.01 N / 25 mm or more, since the adhesive force between the

release films

51 and 52 and the optical film 60 is large, the partial release of the

release films

51 and 52 can be suppressed. Moreover, if the peeling force is 0.5 N / 25 mm or less, the

release films

51 and 52 can be easily peeled from the optical film 60. As the

release films

51 and 52, a film formed from a polyethylene resin, a polypropylene resin, a polystyrene resin, a polyethylene terephthalate resin, or the like is used from the viewpoint of easy handling and securing a certain degree of transparency. it can. The release film may be a single film or a laminated film having an adhesive layer on a base film. Examples of the release film include Sanitect (registered trademark, manufactured by Sanei Kaken Co., Ltd.) in which an adhesive layer is formed on the surface of a polyethylene film, and E-mask (registered trademark) in which an adhesive layer is formed on the surface of a polyethylene terephthalate film. And commercial products such as MASTACK (registered trademark, manufactured by Fujimori Kogyo Co., Ltd.) in which an adhesive layer is formed on the surface of a polyethylene terephthalate film.

<< Optical film >>
Similar to the optical film 10, the optical film 60 shown in FIG. 5 is used for an image display device, is foldable and has light transmittance, but does not include a base material. And different from the optical film 10. In addition, since the

release films

51 and 52 are finally peeled from the optical film 60, they are not regarded as base materials.

The surface 60A of the optical film 60 is the surface 61A of the resin layer 61. In the optical film 60, since the third layer 61D of the resin layer 61 is the uppermost layer as will be described later, the surface 60A of the optical film 60 is the surface of the third layer 61D. The back surface 60B of the optical film 60 is a surface opposite to the surface on the second layer 61C side in the first layer 61B.

The physical properties of the optical film 60 are the same as the physical properties of the optical film 10. However, the physical properties of the optical film 60 are measured in a state where both the

release films

51 and 52 are peeled from the optical film 50 with the release film.

<< Resin layer >>
The resin layer 61 has a multilayer structure in which the first layer to the n-th layer (n is an integer of 3 or more) are stacked. Needless to say, the first to nth layers are layers mainly made of a resin, but may contain particles, additives and the like in addition to the resin.

The indentation hardness of each of the first layer to the n-th layer in the resin layer 61 increases in order from the first layer to the n-th layer. That is, the resin layer 61 also satisfies the relational expression (A).

Specifically, since the resin layer 61 has a multilayer structure in which the first layer 61B to the third layer 61D are laminated in this order, each of the first layer 61B, the second layer 61C, and the third layer 61D. The indentation hardness increases in order from the first layer 61B to the third layer 61D. That is, when the indentation hardness of the first layer 61B, the second layer 61C, and the third layer 61D is H _IT1 , H _IT2 , and H _IT3 , the above relational expression (B) is satisfied.

In the optical film 60, since the resin layer 61 is composed of the first layer 61B, the second layer 61C, and the third layer 61D, the n is 3, but the n of the n-th layer is 3 If it is more, it will not specifically limit. The upper limit of n is preferably 10 or less from the viewpoint of productivity.

When the resin layer 61 has a three-layer structure, the indentation hardness of each of the first layer 61B, the second layer 61C, and the third layer 61D is not particularly limited as long as the relational expression (B) is satisfied. For the same reason as described in the first embodiment, the indentation hardness of the first layer 61B is 1 MPa or more and 100 MPa or less, and the indentation hardness of the second layer 61C is 10 MPa or more and 500 MPa or less. The indentation hardness of the third layer 61D is preferably 100 MPa or more and 1000 MPa or less.

<First to third layers>
Since the first layer 61B is the same as the first layer 12B, the second layer 61C is the same as the second layer 12C, and the third layer 61D is the same as the third layer 12D, the description is omitted here. And

<<< Optical film with other release film >>>
The optical film 70 with a release film shown in FIG. 6 includes a release film 51, an optical film 80, and a release film 52 in this order.

<< Optical film >>
The optical film 80 shown in FIG. 6 includes a resin layer 81 having a four-layer structure that is laminated in this order from the first layer 81B to the fourth layer 81E. The surface 80A of the optical film 80 is the surface 81A of the resin layer 81 (the surface of the fourth layer 81E). The back surface 80B of the optical film 80 is a surface opposite to the surface on the second layer 81C side in the first layer 81B. In FIG. 6, members having the same reference numerals as those in FIG. 5 are the same as the members shown in FIG.

The physical properties of the optical film 80 are the same as the physical properties of the optical film 10. However, the physical property of the optical film 80 shall be measured in the state which peeled both the

release films

51 and 52 from the optical film 70 with a release film.

<< Resin layer >>
In the resin layer 81, the indentation hardness of each of the first layer 81B, the second layer 81C, the third layer 81D, and the fourth layer 81E increases in order from the first layer 81B to the fourth layer 81E. That is, when the indentation hardnesses of the first layer 81B, the second layer 81C, the third layer 81D, and the fourth layer 81E are respectively H _IT1 , H _IT2 , H _IT3, and H _IT4 , the above relational expression (A Specifically, the above relational expression (C) is satisfied.

In the resin layer 81, the indentation hardness of each of the first layer 81B, the second layer 81C, the third layer 81D, and the fourth layer 81E is not particularly limited as long as the relational expression (C) is satisfied. For the same reason as described in the first embodiment, the indentation hardness of the first layer 81B is 1 MPa or more and 100 MPa or less, and the indentation hardness of the second layer 81C is 10 MPa or more and 300 MPa or less. The indentation hardness of the third layer 81D is preferably 50 MPa or more and 500 MPa or less, and the indentation hardness of the fourth layer 81E is preferably 100 MPa or more and 1000 MPa or less.

<First to fourth layers>
The first layer 81B is the same as the first layer 21B, the second layer 81C is the same as the second layer 21C, the third layer 81D is the same as the third layer 21D, and the fourth layer 81E is the fourth layer. Since it is the same as 21E, the description is omitted here.

According to this embodiment, the resin layer has a structure of three or more layers, and the indentation hardness of each of the first layer to the n-th layer increases in order from the first layer to the n-th layer. That is, since the relational expression (A) is satisfied, for the same reason as described in the first embodiment, excellent foldability, excellent pencil hardness, excellent impact resistance, excellent flexibility, In addition, excellent scratch resistance can be obtained.

<<< Image display device >>>
The optical film 60 can be used by being incorporated in a foldable image display device. FIG. 7 is a schematic configuration diagram of the image display apparatus according to the present embodiment. As shown in FIG. 7, the image display device 90 mainly has a housing 31 in which a battery or the like is stored, a protective film 32, a display panel 33, a touch sensor 34, and a circularly polarizing plate 35 toward the viewer. The foldable film 91 and the optical film 60 are laminated in this order. Light transmissive adhesive such as OCA (Optical Clear Adhesive) is provided between the display panel 33 and the touch sensor 34, between the touch sensor 34 and the circularly polarizing plate 35, and between the circularly polarizing plate 35 and the film 91. A layer 36 is disposed, and these members are fixed to each other by a light-transmitting adhesive layer 36. A black layer 37 is provided on a part of the back surface of the film 91.

The optical film 60 is in a state where the

release films

51 and 52 are peeled off, and is affixed to the film 91 via the light-transmitting adhesive layer 36. Therefore, the optical film 60 is disposed such that the third layer 61D is closer to the viewer than the first layer 61B. In the image display device 90, the surface 61 A of the resin layer 61 of the optical film 60 constitutes the surface 90 A of the image display device 90.

The film 91 is a foldable film. Examples of the film 91 include a film made of a resin similar to the resin described in the column of the base material 11.

In order to describe the present invention in detail, examples will be described below, but the present invention is not limited to these descriptions.

<Preparation of resin layer composition>
First, each component was mix | blended so that it might become the composition shown below, and the composition for resin layers was obtained.

(Resin composition 1)
-Urethane acrylate (product name "RUA-051", manufactured by Asia Industries, trifunctional): 90 parts by mass-Phenoxyethyl acrylate (product name "Biscoat # 192", manufactured by Osaka Organic Chemical Industry): 10 parts by mass Initiator (1-hydroxycyclohexyl phenyl ketone, product name “Irgacure (registered trademark) 184”, manufactured by BASF Japan Ltd.): 5 parts by mass / methyl isobutyl ketone: 10 parts by mass

(Resin composition 2)
-Urethane acrylate (product name "RUA-051", manufactured by Asia Kogyo Co., Ltd., trifunctional): 90 parts by mass-Phenoxyethyl acrylate (product name "Biscoat # 192", manufactured by Osaka Organic Chemical Industry Co., Ltd.): 10 parts by mass Silica fine particles (average particle size 25 nm, manufactured by JGC Catalysts & Chemicals): 50 parts by mass Polymerization initiator (1-hydroxycyclohexyl phenyl ketone, product name “Irgacure (registered trademark) 184”, manufactured by BASF Japan): 5 parts by mass・ Methyl isobutyl ketone: 100 parts by mass

(Resin composition 3)
・ Urethane acrylate (product name “RUA-051”, manufactured by Asia Kogyo Co., Ltd., trifunctional): 90 parts by mass • Phenoxyethyl acrylate (product name “Biscoat # 192”, manufactured by Osaka Organic Chemical Industry Co., Ltd.): 10 parts by mass Pentaerythritol EO-modified hexaacrylate (product name “A-DPH-6E”, Shin-Nakamura Chemical Co., Ltd.): 10 parts by mass / polymerization initiator (1-hydroxycyclohexyl phenyl ketone, product name “Irgacure (registered trademark) 184” , Manufactured by BASF Japan Ltd.): 5 parts by massMethyl isobutyl ketone: 100 parts by mass

(Resin composition 4)
・ Urethane acrylate (Product name “8UX-015A”, Taisei Fine Chemical Co., Ltd.): 30 parts by mass ・ Polyfunctional acrylate polymer (Product name “8KX-012C”, Taisei Fine Chemical Co., Ltd.): 70 parts by mass Name “X-71-1203M” (manufactured by Shin-Etsu Chemical Co., Ltd.): 0.5 parts by mass / polymerization initiator (product name “Irgacure (registered trademark) 127”, manufactured by BASF Japan): 5 parts by mass / methyl isobutyl ketone : 200 parts by mass

<Example 1>
A polyimide substrate (product name “Neoprim”, manufactured by Mitsubishi Gas Chemical Co., Inc.) having a thickness of 30 μm was prepared as a substrate, and the resin composition 1 was applied to one surface of the polyimide substrate with a bar coater. Formed. Then, the solvent in the coating film is evaporated by heating the formed coating film at 70 ° C. for 1 minute, and ultraviolet rays are removed from the air using an ultraviolet irradiation device (Fusion UV System Japan, light source H bulb). The coating film was semi-cured by irradiation so that the integrated light amount was 200 mJ / cm ² .

And the resin composition 2 was apply | coated to the semi-hardened coating film with the bar coater, and the coating film was formed. Then, the solvent in the coating film is evaporated by heating the formed coating film at 70 ° C. for 1 minute, and ultraviolet rays are removed from the air using an ultraviolet irradiation device (Fusion UV System Japan, light source H bulb). The coating film was semi-cured by irradiation so that the integrated light amount was 100 mJ / cm ² .

Next, the resin composition 4 was applied to the semi-cured coating film with a bar coater to form a coating film. Then, the solvent in the coating film is evaporated by heating the formed coating film at 70 ° C. for 1 minute, and ultraviolet rays are removed from the air using an ultraviolet irradiation device (Fusion UV System Japan, light source H bulb). The coating film was completely cured by irradiation so that the integrated light amount was 600 mJ / cm ² . As a result, a first layer having a thickness of 200 μm, a second layer having a thickness of 20 μm, and a third layer having a thickness of 1 μm were laminated in this order on one surface of the polyimide substrate from the polyimide substrate side. An optical film having a layered resin layer was obtained.

The film thickness of each layer is obtained by photographing a cross section of each layer using a scanning electron microscope (SEM), measuring the film thickness of each layer at 20 points in the image of the cross section, and calculating the arithmetic average value of the film thicknesses at the 20 points. It was. The specific cross-sectional photography method was as follows. First, a block is prepared by embedding an optical film cut into 1 mm × 10 mm with an embedding resin, and a uniform section having a thickness of 70 nm or more and 100 nm or less without holes is cut out from this block by a general section preparation method. . For the preparation of the sections, “Ultra Microtome EM UC7” (Leica Microsystems Co., Ltd.) or the like was used. The remaining block from which a uniform section having no holes or the like was cut out was used as a measurement sample. Thereafter, a cross-sectional photograph of the measurement sample was taken using a scanning electron microscope (SEM) (product name “S-4800”, manufactured by Hitachi High-Technologies Corporation). When taking a cross-sectional photograph using the S-4800, the cross-section was observed with the detector set to “SE”, the acceleration voltage set to “5 kV”, and the emission current set to “10 μA”. The magnification was appropriately adjusted from 100 to 100,000 times while adjusting the focus and observing whether each layer could be distinguished. Further, the aperture is set to “beam monitor aperture 3”, the objective lens aperture is set to “3”, and D. Was set to “8 mm”. Moreover, the thickness of the polyimide base material was also measured by the same method as the film thickness of each layer. In Examples 2 to 5 and Comparative Examples 1 to 4, the thickness of the base material and the thickness of the resin layer were measured by the same method as in Example 1.

<Example 2>
In Example 2, an optical film was obtained in the same manner as in Example 1 except that the second layer was formed using the resin composition 3 instead of the resin composition 2.

<Example 3>
A polyimide base material having a polyimide skeleton represented by the above formula (1) with a thickness of 30 μm is prepared as a base material, and the resin composition 1 is applied to one surface of the polyimide base material with a bar coater. Formed. Then, the solvent in the coating film is evaporated by heating the formed coating film at 70 ° C. for 1 minute, and ultraviolet rays are removed from the air using an ultraviolet irradiation device (Fusion UV System Japan, light source H bulb). The coating film was semi-cured by irradiation so that the integrated light amount was 200 mJ / cm ² .

Next, the resin composition 2 was applied to the semi-cured coating film with a bar coater to form a coating film. Then, the solvent in the coating film is evaporated by heating the formed coating film at 70 ° C. for 1 minute, and ultraviolet rays are removed from the air using an ultraviolet irradiation device (Fusion UV System Japan, light source H bulb). The coating film was semi-cured by irradiation so that the integrated light amount was 100 mJ / cm ² .

And the resin composition 3 was apply | coated to the semi-hardened coating film with the bar coater, and the coating film was formed. Then, the solvent in the coating film is evaporated by heating the formed coating film at 70 ° C. for 1 minute, and ultraviolet rays are removed from the air using an ultraviolet irradiation device (Fusion UV System Japan, light source H bulb). The coating film was semi-cured by irradiation so that the integrated light amount was 100 mJ / cm ² .

Next, the resin composition 4 was applied to the semi-cured coating film with a bar coater to form a coating film. Then, the solvent in the coating film is evaporated by heating the formed coating film at 70 ° C. for 1 minute, and ultraviolet rays are removed from the air using an ultraviolet irradiation device (Fusion UV System Japan, light source H bulb). The coating film was completely cured by irradiation so that the integrated light amount was 600 mJ / cm ² . Thereby, on one surface of the polyimide substrate, the first layer having a thickness of 200 μm, the second layer having a thickness of 20 μm, the third layer having a thickness of 5 μm, and the first layer having a thickness of 1 μm are formed from the polyimide substrate side. An optical film having a resin layer having a four-layer structure in which four layers were laminated in this order was obtained.

<Example 4>
In Example 4, an optical film was prepared in the same manner as in Example 1 except that an aramid base material having an aramid skeleton represented by the above formula (22) having a thickness of 30 μm was used instead of the polyimide base material. Obtained.

<Example 5>
In Example 5, first, a polyethylene terephthalate (PET) film (product name “Cosmo Shine A4100”, manufactured by Toyobo Co., Ltd.) having a thickness of 100 μm and subjected to one-side easy adhesion treatment was used as a release film instead of a polyimide base material. A first layer having a thickness of 200 μm made of a cured product of the resin composition 1 and a thickness of 20 μm made of a cured product of the resin composition 2 are prepared on the untreated surface of the PET film in the same procedure as in Example 1. The second layer and the third layer having a thickness of 1 μm made of a cured product of the resin composition 4 were sequentially formed. And PET film was peeled and the optical film was obtained. Thereafter, a polyethylene film having a pressure-sensitive adhesive layer (product name “SANITECT (registered trademark), manufactured by Sanei Kaken Co., Ltd.)” is attached to each of the surfaces of the first layer and the third layer of the optical film as a release film. An optical film with a release film was obtained.

<Comparative Example 1>
In Comparative Example 1, the second layer and the third layer in the resin layer were not formed, that is, the optical layer was the same as in Example 1 except that the resin layer had a single-layer structure including only the first layer. A film was obtained.

<Comparative example 2>
In Comparative Example 2, the optical film was formed in the same manner as in Example 1 except that the third layer in the resin layer was not formed, that is, the resin layer had a two-layer structure of the first layer and the second layer. Obtained.

<Comparative Example 3>
A polyimide substrate (product name “Neoprim”, manufactured by Mitsubishi Gas Chemical Co., Inc.) having a thickness of 30 μm was prepared as a substrate, and the resin composition 1 was applied to one surface of the polyimide substrate with a bar coater. Formed. Then, the solvent in the coating film is evaporated by heating the formed coating film at 70 ° C. for 1 minute, and ultraviolet rays are removed from the air using an ultraviolet irradiation device (Fusion UV System Japan, light source H bulb). The coating film was semi-cured by irradiation so that the integrated light amount was 200 mJ / cm ² .

Next, the resin composition 4 was applied to the semi-cured coating film with a bar coater to form a coating film. Then, the solvent in the coating film is evaporated by heating the formed coating film at 70 ° C. for 1 minute, and ultraviolet rays are removed from the air using an ultraviolet irradiation device (Fusion UV System Japan, light source H bulb). The coating film was completely cured by irradiation so that the integrated light amount was 600 mJ / cm ² . Thereby, on one surface of the polyimide base material, an optical film having a resin layer having a two-layer structure in which a first layer having a thickness of 200 μm and a second layer having a thickness of 1 μm are laminated in this order from the polyimide base material side. Got.

<Comparative example 4>
As a base material, a 30 μm-thick polyimide base material (product name “Neoprim”, manufactured by Mitsubishi Gas Chemical Co., Ltd.) was prepared, and the resin composition 2 was applied to one surface of the polyimide base material with a bar coater. Formed. Then, the solvent in the coating film is evaporated by heating the formed coating film at 70 ° C. for 1 minute, and ultraviolet rays are removed from the air using an ultraviolet irradiation device (Fusion UV System Japan, light source H bulb). The coating film was semi-cured by irradiation so that the integrated light amount was 200 mJ / cm ² .

And the resin composition 1 was apply | coated to the semi-hardened coating film with the bar coater, and the coating film was formed. Then, the solvent in the coating film is evaporated by heating the formed coating film at 70 ° C. for 1 minute, and ultraviolet rays are removed from the air using an ultraviolet irradiation device (Fusion UV System Japan, light source H bulb). The coating film was semi-cured by irradiation so that the integrated light amount was 200 mJ / cm ² .

Next, the resin composition 4 was applied to the semi-cured coating film with a bar coater to form a coating film. Then, the solvent in the coating film is evaporated by heating the formed coating film at 70 ° C. for 1 minute, and ultraviolet rays are removed from the air using an ultraviolet irradiation device (Fusion UV System Japan, light source H bulb). The coating film was completely cured by irradiation so that the integrated light amount was 600 mJ / cm ² . As a result, a first layer having a thickness of 20 μm, a second layer having a thickness of 200 μm, and a third layer having a thickness of 1 μm were laminated in this order on one surface of the polyimide substrate from the polyimide substrate side. An optical film having a layered resin layer was obtained.

<Indentation hardness>
In the optical films according to Examples and Comparative Examples, the indentation hardness of each layer of the base material and the resin layer was measured. Specifically, in the optical films according to Examples 1 to 5 and Comparative Examples 1 to 4, first, a block in which an optical film cut into 1 mm × 10 mm was embedded with an embedding resin was prepared, and a general block was prepared from this block. A uniform slice having a thickness of 70 nm or more and 100 nm or less without a hole or the like was cut out by a typical slice preparation method. On the other hand, in the optical film which concerns on Example 5, first, both release films were peeled from the optical film with a release film, and the optical film single-piece | unit was obtained. Then, the optical film is cut out to 1 mm × 10 mm, and a block in which the optical film of this size is embedded with an embedding resin is produced. Sections of 100 nm or less were cut out. For the preparation of the section, “Ultra Microtome EM UC7” (Leica Micro Systems Co., Ltd.) or the like was used. The remaining block from which a uniform section having no holes or the like was cut out was used as a measurement sample. Next, at the center of the cross section of each layer of the base material and the resin layer obtained by cutting out the above-mentioned section in such a measurement sample, using a “TI950 TriboIndenter” manufactured by HYSITRON (Heiditron), a Berkovich indenter ( (Triangular pyramid) was pushed in at 100 nm at a maximum load of 40 μN and a speed of 10 μN / s and held constant to relieve the residual stress, then unloading, measuring the maximum load after relaxation, and measuring the maximum load P _max (μN ) And the projected contact area A _p (nm ² ) between the indenter and the sample (each layer), and calculated by P _max / A _p . The indentation hardness was the arithmetic average value of the values measured 10 times.

<Flexibility>
Flexibility tests were performed on optical films according to Examples and Comparative Examples. Specifically, in the optical films according to Examples 1 to 4 and Comparative Examples 1 to 4, first, the optical film was cut into a 30 mm × 100 mm rectangle to prepare a measurement sample. On the other hand, in the optical film which concerns on Example 5, first, both release films were peeled from the optical film with a release film, and the optical film single-piece | unit was obtained. Next, a polyimide film having a thickness of 30 μm (a product name “Panaclean (registered trademark) PD-S1”, manufactured by Panac Co., Ltd.) is provided on the back surface (surface on the first layer side) of the optical film via a 25 μm-thick optical adhesive layer (product name “Panaclean (registered trademark) PD-S1”). A laminate was formed by pasting to a product name “Neoprim” (Mitsubishi Gas Chemical Co., Ltd.). And this laminated body was cut into the rectangle of 30 mm x 100 mm, and the measurement sample was obtained. Next, the measurement sample is fixed to an endurance tester (product name “DLDMMLH-FS”, manufactured by Yuasa System Equipment Co., Ltd.) with the short side (30 mm) side of the measurement sample fixed by the fixing portion, and the two opposing side portions are fixed. The surface on the resin layer side of the measurement sample was folded by 180 ° so that the interval was 6 mm (outer diameter of bent portion 6.0 mm). In this state, it was observed by visual observation under a fluorescent lamp whether wrinkles were generated in the bent portion of the measurement sample. Thereafter, the sample was removed from the fixing portion, and in the state where the sample was flattened, it was observed with an optical microscope (product name “VHX-5000”, manufactured by KEYENCE Corp.) whether a fine crack was generated in the bent portion. The evaluation results were as follows.
(Wrinkle evaluation)
○: Wrinkles were not observed.
X: Wrinkles were observed.
(Crack evaluation)
○: No fine cracks were observed.
X: Fine cracks were observed.

<Abrasion resistance>
The optical films according to the examples and comparative examples were subjected to a scratch resistance test. Specifically, in the optical films according to Examples 1 to 4 and Comparative Examples 1 to 4, first, the optical film was cut into a size of 50 mm × 100 mm to prepare a measurement sample. On the other hand, in the optical film which concerns on Example 5, first, both release films were peeled from the optical film with a release film, and the optical film single-piece | unit was obtained. Next, the optical film was cut into a size of 50 mm × 100 mm to prepare a measurement sample. After obtaining the measurement sample, it was fixed with a cello tape (registered trademark) manufactured by Nichiban Co., Ltd. so that the resin layer would be on the upper side so that there was no break or wrinkle on the glass plate. Next, the surface of the measurement sample (the surface of the resin layer) was rubbed 10 times while applying a load of 1 kg / cm ² using # 0000 steel wool (product name “Bonstar”, manufactured by Nippon Steel Wool). A scratch test was conducted to observe whether cracks or scratches were observed on the surface of the resin layer. The evaluation results were as follows.
○: Neither cracks nor scratches were observed.
X: Either cracks or scratches were observed.

<Foldability>
A folding test was performed on the optical films according to the examples and the comparative examples, and the folding property was evaluated. Specifically, in the optical films according to Examples 1 to 4 and Comparative Examples 1 to 4, first, a measurement sample was prepared by cutting into 30 mm × 100 mm rectangles. On the other hand, in the optical film which concerns on Example 5, first, both release films were peeled from the optical film with a release film, and the optical film single-piece | unit was obtained. Next, a polyimide film (product name “Neoprim” is provided on the back surface (first layer side surface) of the optical film via an optical adhesive layer (product name “Panaclean (registered trademark) PD-S1”, manufactured by Panac Co., Ltd.) having a thickness of 25 μm. “Mitsubishi Gas Chemical Co., Ltd.)” to form a laminate. And this laminated body was cut into the rectangle of 30 mm x 100 mm, and the measurement sample was produced. After preparing the measurement sample, the short side (30 mm) side of the measurement sample is fixed to the endurance tester (product name “DLDMMLH-FS”, Yuasa System Equipment Co., Ltd.) with the fixing part, respectively, as shown in FIG. As shown in the test, the minimum distance between two opposing sides is 6 mm (outside diameter of bent portion is 6.0 mm), and the surface on the resin layer side of the measurement sample is folded 180 ° (resin layer is The test of folding the base material or the polyimide film so as to be on the inside was performed 100,000 times, and it was examined whether cracks or breaks occurred in the bent portion. In addition, a new sample prepared in the same manner as described above with the optical films according to Examples and Comparative Examples is attached to the above durability tester in the same manner as described above, and the test sample (resin layer) is folded 180 degrees on the substrate side surface of the measurement sample. The test was carried out 100,000 times so that the base material or the polyimide film was on the inside, and whether or not the bent portion was cracked or broken was examined. The results of the folding test were evaluated according to the following criteria.
○: In any of the folding tests, the bent portion was not cracked or broken.
X: In any of the folding tests, the bent portion was cracked or broken.

<Impact resistance>
In the optical films according to Examples and Comparative Examples, impact resistance was evaluated. Specifically, in the optical films according to Examples 1 to 4 and Comparative Examples 1 to 4, first, the optical film was cut into a size of 100 mm × 100 mm to prepare a measurement sample. On the other hand, in the optical film with a release film according to Example 5, first, both release films were peeled to obtain a single optical film. Next, the optical film was cut into a size of 100 mm × 100 mm to prepare a measurement sample. After preparing the measurement sample, place the measurement sample on a soda glass plate with a thickness of 0.7 mm so that the first layer is closer to the soda glass plate than the nth layer, and weigh from a position of 30 cm in height. A test of dropping an iron ball having a diameter of 100 g and a diameter of 30 mm onto the surface of the resin layer of the optical film was performed three times. The position where the iron ball is dropped is changed each time. And while evaluating whether the dent was confirmed on the surface of the resin layer by visual observation, it was evaluated whether the soda glass plate had cracked. The evaluation results were as follows.
(Evaluation of dents on the surface of the resin layer)
(Double-circle): The dent was not confirmed by the surface of the resin layer in both the case where the resin layer was observed from the front and diagonally.
○: When the resin layer was observed from the front, no dent was observed on the surface of the resin layer, but when observed obliquely, a level of dent that had no practical problem was confirmed on the surface of the resin layer.
X: A clear dent was observed on the surface of the resin layer both when the resin layer was observed from the front and obliquely.
(Soda glass crack evaluation)
A: Soda glass was not broken.
○: Soda glass was scratched but not broken.
Δ: Cracking occurred in the soda glass once or twice.
X: The soda glass was cracked three times.

<Pencil hardness>
The pencil hardness on the surface of the optical film according to the example and the comparative example (surface of the resin layer) was measured based on JIS K5600-5-4: 1999. Specifically, the optical films according to Examples 1 to 4 and Comparative Examples 1 to 4 were first cut into a size of 50 mm × 100 mm to prepare measurement samples. On the other hand, in the optical film which concerns on Example 5, first, both release films were peeled from the optical film with a release film, and the optical film single-piece | unit was obtained. Next, the optical film was cut into a size of 50 mm × 100 mm to prepare a measurement sample. After preparing the measurement sample, the measurement sample was fixed on a glass plate having a thickness of 2 mm with cello tape (registered trademark) manufactured by Nichiban Co., Ltd. so as not to be folded or wrinkled. Then, using a pencil hardness tester (product name “Pencil Scratch Coating Film Hardness Tester (Electric Type)”, manufactured by Toyo Seiki Seisakusho Co., Ltd.), a pencil (product name “Uni”, manufactured by Mitsubishi Pencil Co., Ltd.) While applying a load of 750 g, the pencil was moved at a speed of 1 mm / sec. The pencil hardness was the highest hardness at which the surface of the measurement sample (the surface of the resin layer) was not damaged in the pencil hardness test. The pencil hardness is measured using a plurality of pencils having different hardnesses. The pencil hardness test is performed five times for each pencil, and the surface of the measurement sample is measured under a fluorescent lamp four times or more out of five times. When the scratch was not visually recognized on the surface of the measurement sample when the sample was observed through transmission, it was judged that the surface of the measurement sample was not scratched with the pencil having this hardness.

The results are shown in Tables 1 and 2.

The following describes the results. In the optical films according to Comparative Examples 1 and 2, since the resin layer had a relatively soft single-layer structure or a two-layer structure, cracks and scratches were confirmed in the scratch resistance test. In the optical film according to Comparative Example 3, since the second layer was too hard for the first layer, cracks occurred during folding in the flexibility test, and the steel wool was formed in the second layer in the scratch resistance test. Sunk and cracks occurred in the second layer. In the optical film according to Comparative Example 4, although the resin layer had a three-layer structure, the second layer was softer than the first layer, so that wrinkles and cracks occurred during folding in the flexibility test, and the scratch resistance. In the property test, steel wool sank into the third layer, and cracks occurred in the third layer.

In contrast, in the optical films according to Examples 1 to 5, the resin layer has a three-layer structure or a four-layer structure, and the indentation hardness of each layer extends from the substrate side or polyimide film side to the surface side of the optical film. Therefore, wrinkles and fine cracks did not occur in the flexibility test, and no cracks or scratches occurred in the scratch resistance test.

In the optical films according to Examples 1 to 5, the impact resistance and folding test results were good, and the pencil hardness was high.

In the optical films according to Examples 1 and 3, the surface of the optical film (the surface of the resin layer) is 1 kg / # using steel wool of # 0000 (product name “Bonstar”, manufactured by Nippon Steel Wool Co., Ltd.). When the scratch resistance test was performed by reciprocating 20 strokes while applying a load of cm ^{2, in} the optical film according to Example 1, either cracks or scratches were confirmed, but in the optical film according to Example 3, Neither cracks nor scratches were observed. From this result, it was confirmed that the optical film according to Example 3 was superior in scratch resistance to the optical film according to Example 1.

Further, when the Young's modulus was measured for the optical films according to Examples 1 to 4, the Young's modulus was all 3 GPa. In the measurement of Young's modulus, first, each optical film was cut into a size of 2 mm × 150 mm to obtain a sample. Then, fix both ends of this sample to the chucking jig etc. attached to the Tensilon universal testing machine (product name “RTC-1310A”, manufactured by Orientec Co., Ltd.) so that the longitudinal direction of the sample is the tensile direction. Then, using the Tensilon universal testing machine, the sample elongation and load measurements when the sample was pulled at a test speed of 25 mm / min were converted into strain and stress, and the stress when the strain was 0.5% The Young's modulus was obtained by obtaining the slope of the straight line connecting the stress when the strain was 1%. The Young's modulus was an arithmetic average value obtained by measuring three times.

In the optical films according to Examples 1 to 5, when the yellow index (YI) was measured, Example 1 to 4 was 5, and Example 5 was 1. The yellow index is a value measured for an optical film cut into a size of 50 mm × 100 mm using a spectrophotometer (product name “UV-3100PC”, manufactured by Shimadzu Corporation, light source: tungsten lamp and deuterium lamp). The chromaticity tristimulus values X, Y, Z are calculated according to the arithmetic expression described in JIS Z8722: 2009, and the values calculated according to the arithmetic expression described in ASTM D1925: 1962 from the tristimulus values X, Y, Z. It was. The yellow index was an arithmetic average value obtained by measuring three times.

10, 20, 60, 80 ...

Optical films

10A, 12A, 20A, 21A, 60A, 61A, 80A, 81A ... Surface 11 ...

Base material

12, 21, 61, 81 ... Resin layers 12B, 21B, 61B, 81B ...

No. 1st layer

12C, 21C, 61C, 81C ...

2nd layer

12D, 21D, 61D, 81D ...

3rd layer

21E, 81E ...

4th layer

30, 90 ... Image display device 33 ... Display panel

Claims

A foldable light transmissive optical film used in an image display device,
A multilayered resin layer laminated in this order from the first layer to the nth layer (n is an integer of 3 or more);
An optical film in which the indentation hardness of each of the first layer to the n-th layer in the resin layer increases in order from the first layer to the n-th layer.
The optical film according to claim 1, further comprising a base material provided on the first layer side of the resin layer.
n is 3, in the resin layer, the indentation hardness of the first layer is 1 MPa or more and 100 MPa or less, the indentation hardness of the second layer is 10 MPa or more and 500 MPa or less, The optical film of Claim 1 whose indentation hardness is 100 MPa or more and 1000 MPa or less.
n is 4, and in the resin layer, the indentation hardness of the first layer is 1 MPa or more and 100 MPa or less, the indentation hardness of the second layer is 10 MPa or more and 300 MPa or less, The optical film according to claim 1, wherein the indentation hardness is 50 MPa or more and 500 MPa or less, and the indentation hardness of the fourth layer is 100 MPa or more and 1000 MPa or less.
The optical film according to claim 2, wherein the optical film has a Young's modulus of 3 GPa or more.
The optical film according to claim 1, wherein a yellow index of the optical film is 15 or less.
The optical film is placed on a soda glass plate having a thickness of 0.7 mm so that the first layer is positioned closer to the soda glass plate than the n layer, and the surface of the resin layer is higher than the surface of the nth layer. 2. The optical device according to claim 1, wherein when an iron ball having a weight of 100 g and a diameter of 30 mm is dropped from a position of 30 cm in length, the surface of the n-th layer is not depressed, and the soda glass plate is not cracked. the film.
When a scratch resistance test was performed on the surface of the n-th layer of the resin layer by 10 reciprocating rubs while applying a load of 1 kg / cm 2 using steel wool, the surface of the n-th layer was cracked and scratched. The optical film according to claim 1, wherein none is confirmed.
2. The optical film according to claim 1, wherein a crack or break does not occur when a test of folding 180 ° so that a distance between opposing sides of the optical film is 6 mm is repeated 100,000 times at 25 ° C. 2.
The optical film according to claim 2, wherein the substrate is a substrate made of a polyimide resin, a polyamide resin, or a mixture thereof.
A foldable image display device, comprising: a display panel; and the optical film according to claim 1 disposed closer to an observer than the display panel, wherein the nth in the resin layer of the optical film. An image display device, wherein the layer is located closer to the viewer than the first layer.
The image display device according to claim 11, wherein the display panel is an organic light emitting diode panel.