JP7242166B2 - Optical film and method for producing optical film - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical film and a method for producing an optical film.

In a device having a display such as a smart phone and a tablet PC, the design of the optical path around the edge of the film is becoming important as the frame of the display is required to be narrowed. It is possible to use reflected light by using a white member at the end, or to absorb unnecessary light by using a black member. It has been proposed to increase brightness and reduce brightness unevenness by designing the colors of members (see Patent Document 1).

In flexible devices, a transparent resin film is being studied as a front plate.
For example, the use of a film containing a polyimide-based polymer as the front panel has been studied (see Patent Document 2).

JP-A-09-5740 JP 2016-93992 A

Even in flexible devices, it is necessary to design so that brightness unevenness at the edge of the display, reduction in efficiency due to light leakage from the vicinity of the edge, and deterioration in design due to unnecessary light leakage to the outside.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an optical film capable of suppressing light leakage from the end face of a flexible device, and a flexible device using the same.

An optical film according to the present invention is a transparent optical film containing a polyimide polymer, and the edge of the optical film is colored.

According to the present invention, the coloration of the end portion suppresses the leakage of light from the inside to the outside through the end face. Therefore, it is possible to suppress the light from escaping from the end portion to the outside regardless of the member of the frame.

Here, the coloring of the ends may have a hue of 2YR to 3Y on a white background in the Munsell color system, or may be achromatic.

Further, the coloring of the ends may have a hue of 3YR to 10YR on a white background in the Munsell color system.

Also, the thickness can be 20 to 100 μm.

The present invention also relates to a method for producing an optical film in which edges are colored by laser irradiation. In this manufacturing method, the optical film may be a transparent optical film containing a polyimide polymer.

A front panel for a flexible device according to the present invention has any one of the optical films described above.

A flexible device according to the present invention has a flexible functional layer and any one of the optical films described above.

ADVANTAGE OF THE INVENTION According to this invention, the optical film which can suppress the light leakage from the edge surface in a flexible device, and a flexible device using the same are provided.

FIG. 1 is a perspective view showing one example of an optical film according to an embodiment of the invention. FIG. 2 is a perspective view showing one example of a flexible display according to an embodiment of the invention.

The optical film 10 according to this embodiment is a transparent optical film containing a polyimide-based polymer, and as shown in FIG. 1, the end portion EP of the optical film 10 is colored.
The edge portion EP is a portion along the edge surface EF of the optical film 10 . The width W of the edge EP can be 10 to 500 μm when viewed from the direction perpendicular to the surface of the optical film 10 . Although the entire annular end EP along all the end faces EF may be colored, only a portion of the annular end EP (for example, a portion along one end face EF) may be colored. .

Coloring is expressed in the Munsell color system. The term “colored” means that the edge of the film is colored when placed against a background color of white (N9 in the Munsell color system) or against a background color of light green (10GY8/6 in the Munsell color system). It means that the part EP is determined to be substantially the same color in the Munsell color system. Determining to be substantially the same color means that the difference in hue is within 5 (for example, for the edge where the hue is determined to be 7YR when the background color is white, the background color is light green and 2YR to 10YR or 1Y to 2Y) and the difference in both chroma and brightness is within 2.

More preferably, the difference in hue is within 3, the difference in saturation and brightness is within 1, and it is most preferable to determine that they are all the same value.

On the other hand, the edge EP of a conventional transparent polyimide film that is not colored has a certain level of transmittance or higher, and thus is determined to have different colors depending on the background color. Specifically, the Munsell evaluation value in the case of a white background and the Munsell evaluation value in the case of a light green background have (a) a difference of 6 or more in hue, (b) a difference of 3 or more in saturation, and (c) a difference in lightness. When at least one of 3 or more different is satisfied, it is uncolored.

The coloring may be chromatic (saturation greater than 0) or achromatic N (saturation 0).

Preferred hues are 2YR to 3Y or neutral (N) on a white background in the Munsell color system. A more preferred hue is 3YR to 10YR. Such edge coloring is preferable because it can be easily obtained by laser cutting.

From the viewpoint of making the color of the edge portion EP inconspicuous, the hue, saturation, and brightness can be appropriately adjusted within these ranges to make the color similar to that of the members arranged around the optical film 10 .

The evaluation of the color of the edge EP in the Munsell color system can be performed by comparing the color sample of the Munsell color system with the color of the edge EP. Observation of the color of the edge EP of the optical film 10 is performed by observing the edge EP from a direction perpendicular to the surface of the optical film 10 . When observing the edge EP, it is observed with a microscope. Place the film against a background color of white (N9 in the Munsell color system) and compare with the color sample to determine the hue, saturation, and lightness in the Munsell color system, then light green (Munsell color system The hue, saturation, and lightness in the Munsell color system are compared with the color sample placed on the background color of 10GY8/6), and the edge EP is substantially the same color for any background color, i.e. , the difference in hue is within 5 and the difference in saturation and lightness is within 2, it is determined that the film is colored.

The optical film 10 has a refractive index of usually 1.45 to 1.7, preferably 1.5 to 1.66.

The thickness of the optical film 10 is appropriately adjusted according to the type of flexible device, etc., and is usually 10 to 500 μm, preferably 15 to 200 μm, more preferably 20 to 100 μm.

The optical film 10 generally has a total light transmittance of 85% or more, preferably 90% or more, according to JIS K 7105:1981.

The optical film 10 may have a Haze of 1 or less, or 0.9 or less, according to JIS K 7105:1981.

The refractive index, total light transmittance, and haze are values measured in the thickness direction of the optical film.

The size of the optical film 10 can be appropriately adjusted according to the size of the flexible device used. Also, the shape of the optical film 10 is not limited to a rectangle, and can be appropriately adjusted to an ellipse, trapezoid, circle, or the like according to the flexible device.

(film material)
(transparent resin)
The optical film contains a transparent resin such as a polyimide polymer.

(polyimide polymer)
As used herein, polyimide is a polymer containing repeating structural units containing imide groups, and polyamide is a polymer containing repeating structural units containing amide groups. Polyimide-based polymers refer to polyimides and polymers containing repeating structural units containing both imide and amide groups.

The polyimide-based polymer according to the present embodiment can be produced using a tetracarboxylic acid compound and a diamine compound, which will be described later, as main raw materials, and has a repeating structural unit represented by formula (10). Here, G is a tetravalent organic group and A is a divalent organic group. Two or more types of structures represented by formula (10) in which G and/or A are different may be included.
In addition, the polyimide polymer according to the present embodiment contains a structure represented by any one of formulas (11) to (13) within a range that does not impair various physical properties of the obtained polyimide polymer film. good too.

The polyimide-based polymer preferably has a repeating structural unit represented by formula (10) as the main structural unit of the polyimide-based polymer from the viewpoint of film strength and transparency. The repeating structural unit represented by formula (10) is preferably 40 mol% or more, more preferably 50 mol% or more, and still more preferably 70 mol% of the total repeating structural units of the polyimide polymer. More preferably, it is 90 mol % or more, and even more preferably 98 mol % or more. The repeating structural unit represented by formula (10) may be 100 mol %.

G and G ¹ are a tetravalent organic group, preferably an organic group optionally substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group, represented by formulas (20) to (29) and a tetravalent chain hydrocarbon group having 6 or less carbon atoms. * in the formula represents a bond, Z is a single bond, -O-, -CH ₂ -, -CH ₂ -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -Ar-, -SO ₂ -, -CO-, -O-Ar-O-, -Ar-O-Ar-, -Ar-CH ₂ -Ar-, -Ar- represents C(CH ₃ ) ₂ -Ar- or -Ar-SO ₂ -Ar-. Ar represents an arylene group having 6 to 20 carbon atoms which may be substituted with a fluorine atom, and specific examples include a phenylene group. G and G ¹ are preferably groups represented by formulas (20) to (27) because they tend to suppress the yellowness of the resulting film.

G ² is a trivalent organic group, preferably an organic group optionally substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group, represented by formulas (20) to (29) is substituted with a hydrogen atom, and a trivalent chain hydrocarbon group having 6 or less carbon atoms.

G ³ is a divalent organic group, preferably an organic group optionally substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group, represented by formulas (20) to (29) and two non-adjacent bonds are replaced with hydrogen atoms, and chain hydrocarbon groups having 6 or less carbon atoms are exemplified.

A, A ¹ , A ² and A ³ are each a divalent organic group, preferably a hydrocarbon group or an organic group optionally substituted with a fluorine-substituted hydrocarbon group, represented by formula (30) - groups represented by formula (38); groups substituted with methyl group, fluoro group, chloro group or trifluoromethyl group, and chain hydrocarbon groups having 6 or less carbon atoms are exemplified.
* in the formula represents a bond, and Z ¹ , Z ² and Z ³ each independently represent a single bond, —O—, —CH ₂ —, —CH ₂ —CH ₂ —, —CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -SO ₂ - or -CO-. One example is when Z ¹ and Z ³ are —O— and Z ² is —CH ₂ —, —C(CH ₃ ) ₂ —, —C(CF ₃ ) ₂ — or —SO ₂ —. be. Z ¹ and Z ² and Z ² and Z ³ are each preferably meta or para to each ring.

The polyamide according to this embodiment is a polymer mainly composed of repeating structural units represented by formula (13). Preferred examples and specific examples are the same as ^G3 and ^A3 in the polyimide polymer. Two or more types of structures represented by formula (13) in which G ³ and/or A ³ are different may be included.

Polyimide-based polymers, for example, are obtained by polycondensation of a diamine and a tetracarboxylic acid compound (tetracarboxylic dianhydride, etc.), for example, described in JP-A-2006-199945 or JP-A-2008-163107. can be synthesized according to the method Commercial products of polyimide include Neoprim manufactured by Mitsubishi Gas Chemical Co., Ltd., and the like.

Examples of the tetracarboxylic acid compound used for polyimide synthesis include aromatic tetracarboxylic acid compounds such as aromatic tetracarboxylic dianhydrides and aliphatic tetracarboxylic acid compounds such as aliphatic tetracarboxylic dianhydrides. A tetracarboxylic acid compound may be used independently and may use 2 or more types together. The tetracarboxylic acid compound may be a dianhydride or a tetracarboxylic acid compound analog such as an acid chloride compound.

Specific examples of aromatic tetracarboxylic dianhydrides include 4,4′-oxydiphthalic dianhydride, 3,3′,4,4′-benzophenonetetracarboxylic dianhydride, 2,2′,3, 3'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 3,3 ',4,4'-diphenylsulfonetetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis(2,3-dicarboxyphenyl)propane dianhydride, 2,2-bis(3,4-dicarboxyphenoxyphenyl)propane dianhydride, 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride, 1,2-bis(2,3 -dicarboxyphenyl)ethane dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,2-bis(3,4-dicarboxyphenyl)ethane dianhydride, 1, 1-bis(3,4-dicarboxyphenyl)ethane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, 4,4 '-(p-phenylenedioxy)diphthalic dianhydride, 4,4'-(m-phenylenedioxy)diphthalic dianhydride and 2,3,6,7-naphthalenetetracarboxylic dianhydride. preferably 4,4'-oxydiphthalic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,2',3,3'-benzophenonetetracarboxylic dianhydride , 3,3′,4,4′-biphenyltetracarboxylic dianhydride, 2,2′,3,3′-biphenyltetracarboxylic dianhydride, 3,3′,4,4′-diphenylsulfonetetra Carboxylic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, 2,2-bis (2,3-dicarboxyphenyl) propane dianhydride, 2,2-bis ( 3,4-dicarboxyphenoxyphenyl)propane dianhydride, 4,4′-(hexafluoroisopropylidene)diphthalic dianhydride, 1,2-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,2-bis(3,4-dicarboxyphenyl)ethane dianhydride, 1,1-bis(3,4-dicarboxy Phenyl)ethane dianhydride , bis(3,4-dicarboxyphenyl)methane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, 4,4′-(p-phenylenedioxy)diphthalic dianhydride and 4 , 4′-(m-phenylenedioxy)diphthalic dianhydride. These can be used individually or in combination of 2 or more types.

Aliphatic tetracarboxylic dianhydrides include cyclic or acyclic aliphatic tetracarboxylic dianhydrides. The cyclic aliphatic tetracarboxylic dianhydride is a tetracarboxylic dianhydride having an alicyclic hydrocarbon structure, and specific examples thereof include 1,2,4,5-cyclohexanetetracarboxylic dianhydride. 1,2,3,4-cyclobutanetetracarboxylic dianhydride, cycloalkanetetracarboxylic dianhydride such as 1,2,3,4-cyclopentanetetracarboxylic dianhydride, bicyclo[2.2 .2] oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, dicyclohexyl 3,3′-4,4′-tetracarboxylic dianhydride and positional isomers thereof . These can be used individually or in combination of 2 or more types. Specific examples of the acyclic aliphatic tetracarboxylic dianhydride include 1,2,3,4-butanetetracarboxylic dianhydride and 1,2,3,4-pentanetetracarboxylic dianhydride. and these can be used alone or in combination of two or more.

Among the above tetracarboxylic dianhydrides, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, bicyclo[2.2.2]oct-7-ene, from the viewpoint of high transparency and low coloring -2,3,5,6-tetracarboxylic dianhydride and 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride are preferred.

The polyimide-based polymer according to the present embodiment contains, in addition to the anhydride of tetracarboxylic acid used in the polyimide synthesis, tetracarboxylic acid, Further reaction of tricarboxylic acids and dicarboxylic acids and their anhydrides and derivatives may also be used.

Examples of tricarboxylic acid compounds include aromatic tricarboxylic acids, aliphatic tricarboxylic acids, their analogous acid chloride compounds, acid anhydrides, and the like, and two or more of them may be used in combination.
Specific examples include the anhydride of 1,2,4-benzenetricarboxylic acid; 2,3,6-naphthalenetricarboxylic acid-2,3-anhydride; a single bond between _phthalic anhydride and benzoic acid; -, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -SO ₂ -, or compounds linked by a phenylene group.

Examples of dicarboxylic acid compounds include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, their analogous acid chloride compounds, acid anhydrides, and the like, and two or more of them may be used in combination. Specific examples include terephthalic acid; isophthalic acid; naphthalenedicarboxylic acid; 4,4′-biphenyldicarboxylic acid; 3,3′-biphenyldicarboxylic acid; Examples include compounds in which two benzoic acids are linked via a single bond, —CH ₂ —, —C(CH ₃ ) ₂ —, —C(CF ₃ ) ₂ —, —SO ₂ — or a phenylene group.

Aliphatic diamines, aromatic diamines, or mixtures thereof may be used as the diamines used in polyimide synthesis. In this embodiment, the term "aromatic diamine" refers to a diamine in which an amino group is directly bonded to an aromatic ring, and part of its structure may contain an aliphatic group or other substituents. The aromatic ring may be a single ring or a condensed ring, and examples include, but are not limited to, benzene ring, naphthalene ring, anthracene ring and fluorene ring. Among these, a benzene ring is preferred. The term "aliphatic diamine" refers to a diamine in which an amino group is directly bonded to an aliphatic group, and part of its structure may contain an aromatic ring or other substituents.

Aliphatic diamines include, for example, acyclic aliphatic diamines such as hexamethylenediamine, 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, norbornanediamine, 4,4'- Cycloaliphatic diamines such as diaminodicyclohexylmethane and the like can be mentioned, and these can be used alone or in combination of two or more.

Examples of aromatic diamines include p-phenylenediamine, m-phenylenediamine, 2,4-toluenediamine, m-xylylenediamine, p-xylylenediamine, 1,5-diaminonaphthalene and 2,6-diaminonaphthalene. aromatic diamines having one aromatic ring, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylpropane, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,3' -diaminodiphenyl ether, 4,4'-diaminodiphenylsulfone, 3,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfone, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis( 4-aminophenoxy)benzene, 4,4'-diaminodiphenylsulfone, bis[4-(4-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)phenyl]sulfone, 2,2-bis[ 4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(3-aminophenoxy)phenyl]propane, 2,2'-dimethylbenzidine, 2,2'-bis(trifluoromethyl)benzidine , 4,4′-bis(4-aminophenoxy)biphenyl, 4,4′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether, 4,4′-diaminodiphenylmethane, 9,9-bis(4-aminophenyl) Fluorene, 9,9-bis(4-amino-3-methylphenyl)fluorene, 9,9-bis(4-amino-3-chlorophenyl)fluorene, 9,9-bis(4-amino-3-fluorophenyl) Examples thereof include aromatic diamines having two or more aromatic rings such as fluorene, and these can be used alone or in combination of two or more.

Among the above diamines, it is preferable to use one or more selected from the group consisting of aromatic diamines having a biphenyl structure from the viewpoint of high transparency and low coloration. 1 selected from the group consisting of 2,2'-dimethylbenzidine, 2,2'-bis(trifluoromethyl)benzidine, 4,4'-bis(4-aminophenoxy)biphenyl and 4,4'-diaminodiphenyl ether More preferably, the above is used, and even more preferably 2,2'-bis(trifluoromethyl)benzidine is included.

Polyimide-based polymers and polyamides, which are polymers containing at least one repeating structural unit represented by any one of formulas (10) to (13), are composed of a diamine and a tetracarboxylic acid compound (acid chloride compound, tetracarboxylic acid tetracarboxylic acid compound analogues such as acid dianhydrides), tricarboxylic acid compounds (acid chloride compounds, tricarboxylic acid compound analogues such as tricarboxylic anhydride) and dicarboxylic acid compounds (dicarboxylic acid compound analogues such as acid chloride compounds) It is a condensation-type polymer that is a polycondensation product with at least one compound included in the group consisting of In addition to these, dicarboxylic acid compounds (including analogues such as acid chloride compounds) may also be used as starting materials. The repeating structural unit represented by formula (11) is usually derived from diamines and tetracarboxylic acid compounds. A repeating structural unit represented by formula (12) is usually derived from a diamine and a tricarboxylic acid compound. A repeating structural unit represented by formula (13) is usually derived from a diamine and a dicarboxylic acid compound. Specific examples of diamines and tetracarboxylic acid compounds are as described above.

The standard polystyrene equivalent weight average molecular weight of the polyimide polymer and polyamide according to the present embodiment is usually 10,000 to 500,000, preferably 50,000 to 500,000, more preferably 100,000. ~400,000. The higher the weight-average molecular weight of the polyimide-based polymer and the polyamide, the higher the flexibility tends to be when formed into a film. It tends to be high and workability tends to decrease.

Polyimide-based polymers and polyamides tend to improve the elastic modulus and reduce the YI value when formed into a film by containing fluorine-containing substituents. When the elastic modulus of the film is high, the occurrence of scratches and wrinkles tends to be suppressed. From the viewpoint of film transparency, the polyimide polymer and the polyamide preferably have a fluorine-containing substituent. Specific examples of fluorine-containing substituents include a fluoro group and a trifluoromethyl group.

The content of fluorine atoms in the polyimide polymer and polyamide is preferably 1% by mass or more and 40% by mass or less, more preferably 5% by mass or more and 40% by mass or less, based on the mass of the polyimide polymer or polyamide. is.

In the optical film according to this embodiment, the content of the polyimide polymer is 40% by mass or more, preferably 50% by mass or more, and more preferably 60% by mass or more.

(Inorganic particles)
The optical film according to this embodiment may further contain an inorganic material such as inorganic particles in addition to the polyimide polymer and/or polyamide.

Preferred inorganic materials include silicon compounds such as silica particles and quaternary alkoxysilanes such as tetraethyl orthosilicate (TEOS), and silica particles are preferred from the viewpoint of varnish stability.

The silica particles preferably have an average primary particle size of 10 to 100 nm, more preferably 20 to 80 nm. When the average primary particle size of the silica particles is 100 nm or less, the transparency tends to be improved. When the average primary particle size of the silica particles is 10 nm or more, the cohesive force of the silica particles is weakened, which tends to facilitate handling.

The silica fine particles according to the present embodiment may be a silica sol in which silica particles are dispersed in an organic solvent or the like, or may be a silica fine particle powder produced by a gas phase method. Preferably.

The (average) primary particle size of the silica particles in the optical film can be determined by observation with a transmission electron microscope (TEM). The particle size distribution of silica particles before forming the optical film can be determined by a commercially available laser diffraction particle size distribution meter.

In the optical film according to this embodiment, the inorganic material is 0% by mass or more and 90% by mass or less. It is preferably 10% by mass or more and 60% by mass or less, more preferably 20% by mass or more and 50% by mass or less. When the compounding ratio of the polyimide-based polymer or polyamide and the inorganic material (silicon material) is within the above range, it tends to be easy to achieve both transparency and mechanical strength of the optical film.

(Ultraviolet absorber)
The optical film may contain one or more UV absorbers. The ultraviolet absorber can be appropriately selected from those commonly used as ultraviolet absorbers in the field of resin materials. The ultraviolet absorber may contain a compound that absorbs light with a wavelength of 400 nm or shorter. Examples of the ultraviolet absorber include at least one compound selected from the group consisting of benzophenone-based compounds, salicylate-based compounds, benzotriazole-based compounds, and triazine-based compounds.
In addition, in this specification, a "system compound" refers to the derivative of the compound to which the said "system compound" is attached. For example, a "benzophenone-based compound" refers to a compound having benzophenone as a parent skeleton and a substituent attached to the benzophenone.

(other additives)
The optical film may further contain other additives as long as the transparency and flexibility are not impaired. Other components include, for example, antioxidants, release agents, stabilizers, colorants such as bluing agents, flame retardants, lubricants, thickeners, leveling agents, and the like.

Components other than the resin component and the inorganic material are preferably 0% or more and 20% or less by mass with respect to the mass of the optical film. More preferably, it is more than 0% and 10% by mass or less.

(Production method)
Next, an example of the method for manufacturing the optical film of this embodiment will be described.

The varnish used to prepare the optical film according to the present embodiment is, for example, selected from the tetracarboxylic acid compound, the diamine, and the other raw materials, and is obtained by reacting the polyimide-based polymer and/or the reaction of the polyamide. It can be prepared by mixing and stirring the liquid, the solvent, and optionally the ultraviolet absorber and the other additives. A solution of a purchased polyimide polymer or the like, or a solution of a purchased solid polyimide polymer or the like may be used instead of the reaction liquid of the polyimide polymer or the like.

Next, by a known roll-to-roll or batch method, the above solution is applied on a resin substrate, stainless steel belt, or glass substrate to form a coating film, and the coating film is dried, A film containing a polyimide polymer is obtained by peeling from the substrate. After peeling, the film may be further dried.

The coating film is dried at a temperature of 50 to 350° C. by evaporating the solvent. Drying may be performed under air, inert atmosphere, or under reduced pressure.

Examples of resin substrates include PET, PEN, polyimide, and polyamideimide.
Resins with excellent heat resistance are preferred. In particular, a PET base material is preferable from the viewpoint of adhesion to the film and cost.

Subsequently, the edge EP of the film is colored. Coloring can be performed, for example, by dyeing the end portion EP with a dye.

For example, the edge can be dyed by applying a dye solution to the edge EP. There are no particular restrictions on the dye. Coloring mode can be easily controlled by blending the dye in the dye solution and adjusting the concentration.

Moreover, the coloring of the end portion EP can also be performed by irradiating with a laser. A preferred laser is a _CO2 laser. Specifically, by cutting the raw film into a desired size with a CO ₂ laser, a colored end portion EP is formed along the end face EF. Although the principle of the coloration of the edge EP due to laser irradiation is unknown, it is believed that the modification of the components in the film, for example, the polyimide compound, contributes to the coloring.
When a laser is used, it is also possible to cut the laser-irradiated portion, so that the end portion can be colored at the same time as the film is cut out, and the process can be simplified.

Methods for controlling coloration by laser include a method of changing the structure of polyimide, a method of controlling laser output, and the like. For example, a polyimide containing an aliphatic structure in part of its main chain tends to be colored with high brightness. In the case of a wholly aromatic polyimide, the end portions tend to be colored with a low brightness. When the laser power is lowered, the brightness of the coloring tends to increase, so the brightness of the coloring can be made lower when the laser power is increased.
The wholly aromatic polyimide refers to a polyimide in which both G and A in the structural formulas (10) to (13) above have aromatic groups.

(Application)
Such an optical film can be suitably used as a front plate of a flexible device. A flexible device according to this embodiment has a flexible functional layer and the optical film described above that is superimposed on the flexible functional layer and functions as a front panel. That is, the front panel of the flexible device is positioned on the viewing side above the flexible functional layer. This front plate has the function of protecting the flexible functional layer.

Examples of flexible devices include image display devices (flexible displays, electronic paper, etc.), solar cells, and the like. For example, a display functional layer and a solar cell functional layer are flexible functional layers.

An example of a flexible display is shown in FIG. This flexible display 100 is composed of front plate 110/polarizing plate protective film 120B/polarizer 120A/polarizing plate protective film 120B/touch sensor film 130/organic EL element layer 140/TFT substrate 150 in this order from the surface side (viewing side). have A layer other than the front plate 110 in the flexible display 100 is the flexible functional layer 190 . Polarizing plate protective film 120B/polarizer 120A/polarizing plate protective film 120B constitute polarizing plate 120. FIG. A hard coat layer, an adhesive layer, an adhesive layer, a retardation layer, and the like may be included on the surface of each layer and between the layers. The optical film 10 described above can be used as the front plate 110 . Such a flexible display can be used as an image display unit for tablet PCs, smart phones, portable game machines, and the like.

According to the flexible device of this embodiment, the optical film 10 described above is used as the front plate 110 . The edge EP of the optical film 10 is colored, and light leakage from the edge EF to the outside can be suppressed.

Coloring of the edge EP makes it possible to suppress the phenomenon that light passing through the center of the film in the thickness direction is scattered and escapes from the edge. It is thought that light directed toward the end face EF is attenuated by light reflection, absorption, or the like in the colored portion, and as a result, light leakage from the end is suppressed.

It is also possible to form a laminate in which various functional layers such as an ultraviolet absorbing layer, a hard coat layer, an adhesive layer, a hue adjusting layer and a refractive index adjusting layer are added to the surface of this optical film.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to the following examples.

(Example 1)
A commercially available polyimide polymer solution ("Neoplim C6A20" manufactured by Mitsubishi Gas Chemical Co., Ltd.) (Varnish 1) was cast on the base material to form a film, and a polyimide polymer film raw fabric (called polyimide A) having a thickness of 50 μm was formed. (sometimes). The refractive index of the original film was 1.56. After that, a rectangular area (100 mm×100 mm) was cut out from the original film with a CO ₂ laser to obtain an optical film.
_CO2 laser irradiation was under the following conditions.
Device: ML-Z9510T manufactured by Keyence Corporation
Wavelength: 9.3 μm
Output: 80%
Processing speed: 150 mm/sec Edge EP of the film was colored. The edge EP of the film on the white background and the light green background had a hue of 5YR, a lightness of 9, and a saturation of 2 in the Munsell color system.

(Preparation of varnish 2)
Mitsubishi Gas Chemical Co., Ltd. polyimide-based polymer solution "Neoplim C6A20" (γ-butyrolactone solvent, 22% by mass), a solution in which silica particles with a solid content concentration of 30% by mass are dispersed in γ-butyrolactone, alkoxy having an amino group A dimethylacetamide solution of silane and water were mixed and stirred for 30 minutes to obtain a polymer solution (varnish 2). Here, the mass ratio of silica and polyimide polymer is 30:70, the amount of alkoxysilane having an amino group is 1.67 parts with respect to the total 100 parts by mass of silica and polyimide polymer, and the amount of water is silica and polyimide. 10 parts by mass with respect to the total 100 parts by mass.

(Example 2)
The procedure was the same as in Example 1, except that a raw polymer film (sometimes referred to as polyimide B) was obtained from Varnish 2. The edge EP of the film was colored. The edge EP of the film on the white background and the light green background had a hue of 5YR, a lightness of 9, and a saturation of 2 in the Munsell color system. The refractive index of the original film was 1.57.

(Preparation of varnish 3)
A polyimide polymer (KPI-MX300F manufactured by Kawamura Sangyo Co., Ltd.) was dissolved in γ-butyrolactone to obtain a polymer solution (varnish 3) having a polymer concentration of 18% by mass.
(Example 3)
Example 1 was the same as Example 1, except that varnish 3 was used, the thickness of the original film (referred to as polyimide C) was 80 μm, and the CO ₂ laser irradiation was performed under the following conditions. The refractive index of the original film was 1.56.
Device: E400iCL manufactured by COHERENT
Optical system: Digital scanner fθ lens 70 mm × 70 mm
Wavelength: 9.4 μm
Output: 17W
Machining speed: 400 mm/sec Frequency: 60 kHz
The edge EP of the film was colored. The edge EP of the film on the white background and the light green background had a hue of 7.5 YR, a brightness of 2, and a saturation of 4 in the Munsell color system.

(Comparative example 1)
The procedure was the same as in Example 2, except that a rectangular region was cut out from the original film with a blade (a shear blade). The edge EP of the film was not colored. Table 1 shows Munsell evaluation values on a white background and a light green background.

(Comparative example 2)
The procedure was the same as in Example 3, except that a rectangular region was cut out from the original film with a blade (a shear blade). The edge EP of the film was not colored. Table 1 shows Munsell evaluation values on a white background and a light green background.

(evaluation)
The light leakage from the end face EF was evaluated as follows. A 10 cm square film was sandwiched between two stainless steel frames of 10 cm square, 1 cm wide and 1.5 mm thick, and the frames were fixed with clips. Using LA-HDF15T (LED light source) manufactured by Hayashi Tokei Kogyo Co., Ltd. with the lens removed, and maximizing the output of the device, the central portion of the frame was irradiated with light in a darkroom. The frame was observed from the side, and light leakage from the end face EF of the film sandwiched between the frames was observed. Those in which light leakage was observed were evaluated as ×, and those in which light leakage was suppressed were evaluated as ○. Table 1 shows the results. In the example in which the end EP was colored, light leakage from the end face EF was suppressed as compared with the comparative example.

10... Optical film, 100... Flexible display.

Claims (7)

A transparent optical film containing a polyimide-based polymer, wherein only the edge along the edge of the optical film is colored,
The coloring of the ends has a hue of 2YR to 3Y on a white background in the Munsell color system, or is achromatic on a white background ,
For the coloring of the edge, the edge of the optical film is placed on a background color of white (N9 in the Munsell color system) and compared with a color sample to determine the hue, saturation, and lightness in the Munsell color system. Then, the edge of the optical film is placed on a background color of light green (10GY8/6 in the Munsell color system) and compared with a color sample to determine the hue, saturation, and lightness in the Munsell color system. An optical film having a hue difference of 5 or less and a chroma and brightness difference of 2 or less . 2. The optical film according to claim 1, wherein the coloring of the edges has a hue of 3YR to 10YR on a white background in the Munsell color system. 3. The optical film according to claim 1, which has a thickness of 20 to 100 μm. A method for producing an optical film, in which the edges are colored by laser irradiation,
The coloring of the ends has a hue of 2YR to 3Y on a white background in the Munsell color system, or is achromatic on a white background ,
For the coloring of the edge, the edge of the optical film is placed on a background color of white (N9 in the Munsell color system) and compared with a color sample to determine the hue, saturation, and lightness in the Munsell color system. Then, the edge of the optical film is placed on a background color of light green (10GY8/6 in the Munsell color system) and compared with a color sample to determine the hue, saturation, and lightness in the Munsell color system. A method for producing an optical film , wherein the difference in hue is within 5 and the difference in saturation and brightness is within 2 . 5. The method for producing an optical film according to claim 4, wherein the optical film is a transparent optical film containing a polyimide polymer. A flexible device front panel comprising the optical film according to any one of claims 1 to 3. A flexible device comprising a flexible functional layer and the optical film according to any one of claims 1 to 3.

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