JP6930100B2 - Optical film - Google Patents

Description

The present invention relates to an optical film.

Liquid crystal displays and organic EL displays are widely used in televisions, notebook computers, smartphones, and the like. As the light-transmitting optical film used for these displays, a cycloolefin-based resin film having excellent water resistance is used.

Further, in recent years, the optical film has been used not only as an electrode film such as a touch panel and a barrier film having a gas barrier property, but also as a flexible film and the like. With the expansion of such applications, optical films are required to have improved processing suitability such as solvent resistance and oil resistance.

Patent Document 1 describes a cycloolefin-based resin by forming a layer having a thickness of 0.1 μm or more and 20 μm or less obtained by applying an aqueous dispersion of non-chlorine-based polymer particles on the surface of a cycloolefin-based resin film. It is stated that the solvent resistance and oil resistance of the film can be improved. Patent Document 1 describes that a copolymer containing a styrene-based monomer as a main component can be used as the non-chlorine-based polymer particles.

In addition, Patent Document 2 describes that a polymer containing a cyclic olefin-based monomer such as norbornene and a fluorene-based compound having a polymerizable unsaturated bond as a polymerization component is excellent in heat resistance and the like.

Japanese Unexamined Patent Publication No. 2001-96673 Japanese Unexamined Patent Publication No. 2012-111942

However, according to the findings of the present inventors, even with the method described in Patent Document 1, a cycloolefin-based resin film satisfying the higher solvent resistance and seborrheic oil resistance (oil resistance) required in recent years could not be obtained. ..

Here, it is considered that solvent resistance and oil resistance can be improved by using a polymer having a rigid structure derived from the fluorene compound described in Patent Document 2.

Further, in recent years, optical films have also been made thinner in order to produce thinner displays. However, the optical film tends to be particularly brittle when it is thinned. Therefore, if an attempt is made to thin the optical film, there is a possibility that the film may have punching defects such as cracks, cracks, and chips during the production of the optical film, stretching, roll transfer, and the like.

On the other hand, even if the non-chlorine polymer particles described in Patent Document 1 are copolymerized resins having a structural unit derived from a styrene-based monomer and a structural unit derived from a fluorene-based monomer, an optical film can be used. On the other hand, the transparency of the optical film was lowered, and when the film was thinned, the optical film was liable to be punched poorly.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical film having high solvent resistance and transparency, and capable of sufficiently suppressing punching defects when a thin film is formed.

[1] A cycloolefin-based resin having a polar group and a copolymer resin having a structural unit derived from a styrene-based monomer having a proton-donating group and a structural unit derived from a fluorene-based monomer, as described above. An optical film in which the ratio of the copolymer resin to the total mass of the cycloolefin resin and the copolymer resin is 5% by mass or more and 95% by mass or less.
[2] The optical film according to [1], wherein the proton donating group is a hydroxyl group.
[3] The ratio of the mass of the copolymer resin to the total mass of the cycloolefin resin and the copolymer resin is 20% by mass or more and 80% by mass or less, according to [1] or [2]. Optical film.
[4] The optical film according to any one of [1] to [3], wherein the cycloolefin-based resin has a structural unit derived from a norbornene-based monomer having a polar group.
[5] The copolymer according to any one of [1] to [4], wherein the copolymer resin is a random copolymer of the styrene-based monomer having a proton-donating group and the fluorene-based monomer. Optical film.
[6] The optical film according to any one of [1] to [5], wherein the film thickness is 10 μm or more and 25 μm or less.
[7] A polarizing plate comprising a polarizing element and the optical film according to any one of [1] to [6] arranged on at least one surface thereof.
[8] A display device including the polarizing plate according to [7].
[9] A cycloolefin-based resin having a polar group, a copolymer resin having a structural unit derived from a styrene-based monomer having a proton-donating group and a structural unit derived from a fluorene-based monomer, and a solvent. An optical film including a step of obtaining a dope containing the mixture, a step of casting the dope onto a support and then drying it to obtain a film-like substance, and a step of peeling the film-like substance from the support. Manufacturing method.

The present invention can provide an optical film having high solvent resistance and transparency, and which can sufficiently suppress punching defects when the film is thinned.

FIG. 1 is a schematic view showing an example of a basic configuration of a liquid crystal display.

The present inventors have a cycloolefin-based resin and a copolymer resin having a structural unit derived from a styrene-based monomer and a structural unit derived from a fluorene-based monomer (hereinafter, also simply referred to as "copolymerized resin". ), In the optical film containing, the cycloolefin resin has a polar group, and the structural unit derived from the styrene monomer of the copolymer resin has a proton donating group. It has been found that while improving the solvent resistance and transparency of the optical film, punching defects when the film is thinned can be sufficiently suppressed.

The reason for this is not clear, but it is speculated as follows. That is, in order to improve the oil resistance of the fluorene compound and suppress punching defects more sufficiently, it is effective to entangle the copolymer resin obtained by converting the fluorene compound into a copolymer and the cycloolefin resin. .. However, since the cycloolefin resin and the above-mentioned copolymer resin are incompatible with each other, they are not sufficiently mixed when the optical film is produced. Therefore, in the optical film produced from these materials, it is difficult to sufficiently exhibit the improvement of the solvent resistance due to the structural unit derived from the fluorene-based monomer in the entire optical film. Further, in the optical film produced from these materials, especially when the film is thinned, breakage is likely to occur at the interface between the above-mentioned resins dispersed with each other. Further, in the optical film produced from these materials, light is easily refracted at the interface between the above-mentioned resins dispersed with each other, so that the transparency is not easily increased.

On the other hand, the cycloolefin-based resin has a polar group, and the constituent unit derived from the styrene-based monomer of the copolymer resin has a proton-donating group. The polar group of the copolymer and the proton-donating group of the copolymerized resin interact with each other, and these resins are easily compatible with each other. As a result, the solvent resistance of the structural unit derived from the fluorene-based monomer can be sufficiently improved and the punching defect can be suppressed in the entire optical film, and the transparency can be improved at the same time.

Further, the fluorene skeleton contained in the above-mentioned copolymer resin can make the phase difference of the optical film smaller, but the cycloolefin resin and the copolymer resin are easily compatible with each other, so that the phase difference of the optical film is also increased. It can be made smaller.

1. 1. Optical film The optical film of the present invention is a copolymerization of a cycloolefin-based resin having a polar group and a structural unit derived from a styrene-based monomer having a proton-donating group and a structural unit derived from a fluorene-based monomer. Contains with resin.

The ratio of the mass of the copolymer resin to the total mass of the cycloolefin resin and the copolymer resin is 5% by mass or more and 95% by mass or less. When the mass ratio of the copolymerized resin is 5% by mass or more, the effect of improving the oil resistance of the copolymerized resin can be more sufficiently exhibited. When the mass ratio of the copolymerized resin is 95% by mass or less, the characteristics of the cycloolefin are not easily impaired, and the phase difference is unlikely to be excessively expressed. From the viewpoint of further increasing the transparency, sufficiently suppressing punching defects, and further reducing the phase difference, the mass ratio of the above-mentioned copolymer resin is 20% by mass or more and 80% by mass or less. It is more preferably 30% by mass or more and 70% by mass or less, and more preferably 40% by mass or more and 60% by mass or less.

The total mass of the cycloolefin resin and the copolymer resin is more preferably 80% by mass or more and 100% by mass or less, and 90% by mass or more and 100% by mass or less, based on the total mass of the optical film. Is more preferable.

1-1. Cycloolefin-based resin The cycloolefin-based resin contained in the optical film of the present invention is a homopolymer of a cycloolefin monomer or a copolymer of a cycloolefin monomer and another copolymerizable monomer. It has a polar group.

Examples of the polar group include a carboxy group, a hydroxy group, an alkoxy group, an alkoxycarbonyl group, an allyloxycarbonyl group, a cyano group, an amino group and an amide group. The polar group may be added to a structural unit derived from the cycloolefin monomer, or may be added to a structural unit derived from a copolymerizable monomer copolymerizable with the cycloolefin monomer. You may.

The cycloolefin monomer is preferably a cycloolefin monomer (norbornene-based monomer) having a norbornene skeleton having a polar group, and is a norbornene-based monomer represented by the following general formula (A). Is preferable.

^{R 1 to} R ⁴ of the general formula (A) independently represent a hydrogen atom, a halogen atom, a hydrocarbon group having 1 or more and 5 or less carbon atoms, or the above-mentioned polar group. However, ^{at least one of R 1 to} R ⁴ is the above-mentioned polar group.

Examples of the halogen atom include a fluorine atom, a chlorine atom and the like. Examples of the hydrocarbon group having 1 or more and 5 or less carbon atoms include a methyl group, an ethyl group, a propyl group, a butyl group and the like. The above-mentioned hydrocarbon group having 1 or more carbon atoms and 5 or less carbon atoms includes a linking group containing a halogen atom, an oxygen atom, a nitrogen atom, a sulfur atom or a silicon atom (for example, a carbonyl group, an imino group, an ether bond, a silyl ether bond, a thioether bond, etc. It may further have a divalent linking group).

R ² and R ³ may combine with each other to form an aromatic ring or an aliphatic ring.

Further, ^{among R 1 to} R ⁴ , R ¹ and R ² may be hydrogen atoms at the same time, or R ¹ , R ² and R ³ may be hydrogen atoms at the same time. Since such norbornene-based monomers have low molecular symmetry, they can promote the diffusion motion between the resin and the additive during solvent volatilization in the solution casting film forming step.

P in the general formula (A) represents an integer of 0 or more and 2 or less. From the viewpoint of making the obtained resin bulky, increasing the glass transition temperature of the resin, and further enhancing the heat resistance of the optical film, p is preferably 1 or more and 2 or less.

Specific examples of the norbornene-based monomer having a polar group represented by the general formula (A) are shown below.

The content ratio of the structural units derived from the norbornene-based monomer having a polar group is, for example, 50 mol% or more, preferably 50 mol% or more, based on the total of the structural units derived from the cycloolefin monomers constituting the cycloolefin-based resin. It can be 70 mol% or more, more preferably 100 mol%.

At this time, examples of the copolymerizable monomer copolymerizable with the cycloolefin monomer include a norbornene-based monomer, a ring-open copolymerizable copolymerizable monomer, and a norbornene-based monomer. A copolymerizable monomer capable of addition copolymerization is included.

Examples of the copolymerizable monomer capable of ring-opening copolymerization with the norbornene-based monomer include cycloolefins containing cyclobutene, cyclopentene, cycloheptene, cyclooctene, dicyclopentadiene and the like.

Examples of copolymerizable monomers that can be additionally copolymerized with the norbornene-based monomers include unsaturated double bond-containing compounds, vinyl-based cyclic hydrocarbon monomers, and (meth) acrylates.

Examples of the unsaturated double bond-containing compound include an olefin compound having 2 or more and 12 or less carbon atoms (preferably 2 or more and 8 or less), and specifically, ethylene, propylene, and butene. ..

Examples of the vinyl-based cyclic hydrocarbon monomer include 4-vinylcyclopentene, and vinylcyclopentene-based monomers including 2-methyl-4-isopropenylcyclopentene and the like.

Examples of the (meth) acrylate include an alkyl (meth) acrylate having 1 to 20 carbon atoms including methyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate and the like.

The content ratio of the structural units derived from the norbornene-based monomer in the copolymer of the above-mentioned norbornene-based monomer and the other copolymerizable monomer is the total of the structural units constituting the cycloolefin-based resin. On the other hand, it may be 50 mol% or more and 100 mol% or less, preferably 60 mol% or more and 100 mol% or less, and more preferably 70 mol% or more and 100 mol% or less.

As described above, the cycloolefin-based resin is a polymer obtained by polymerizing or copolymerizing a cycloolefin monomer, preferably a norbornene-based monomer represented by the general formula (A). The polymerization or copolymerization may be ring-opening polymerization or ring-opening copolymerization, or addition polymerization or addition copolymerization. Examples of polymers include:
(1) Ring-opened copolymer of norbornene-based monomer (2) Ring-opened copolymer of norbornene-based monomer and a copolymerizable copolymer thereof (3) The above (1) or (2) Hydrogenated Ring-Opened (Co) Polymer (4) The ring-opened (co) polymer of (1) or (2) above was cyclized by the Friedercrafts reaction and then hydrogenated (co). ) Polymer (5) Add-copolymer of norbornene-based monomer and unsaturated double bond-containing compound (6) Add-copolymer of norbornene-based monomer with vinyl-based cyclic hydrocarbon monomer and its Hydrogen additive (7) Addition copolymer of norbornene-based monomer and (meth) acrylate

The polymers (1) to (7) can all be obtained by known methods, for example, the methods described in JP-A-2008-107534 and JP-A-2005-227606. For example, as the catalyst and solvent used for the ring-opening copolymerization of (2), those described in paragraphs 0019 to 0024 of JP-A-2008-107534 can be used. As the catalyst used for hydrogenation of (3) and (6), those described in paragraphs 0025 to 0028 of JP-A-2008-107534 can be used. As the acidic compound used in the Friedel-Crafts reaction of (4), those described in paragraph 0029 of JP-A-2008-107534 can be used. As the catalyst used for the addition polymerization of (5) to (7), for example, paragraphs 0058 to 0063 of JP-A-2005-227606 can be used. The alternating copolymerization reaction of (7) can be carried out by the method described in paragraphs 0071 and 0072 of JP-A-2005-227606.

Among them, (1) to (3) and (5) are preferable, and (1) to (3) are more preferable. That is, the cycloolefin-based resin is preferably a ring-opening polymer or a ring-opening copolymer of a norbornene-based monomer, or a hydrogenated product thereof. Such a cycloolefin resin may contain, for example, a structural unit represented by the following general formula (B). The structural unit represented by the general formula (B) is derived from the ring-opened product of the norbornene-based monomer represented by the general formula (A) described above.

X in the general formula (B) is, -CH = CH- or _-CH 2 CH ₂ -.

^R 1 to R ⁴ and p in the general formula (B) are respectively ^R 1 to R ⁴ and p in the general formula (A) synonymous.

The cycloolefin-based resin may be a ring-opening polymer, a ring-opening copolymer, an addition copolymer, a hydrogenated product thereof, or the like of a cycloolefin monomer other than the above-mentioned norbornene-based monomer. good.

The cycloolefin resin may be a commercially available product. Examples of commercially available cycloolefin resins include Arton G (eg, G7810, etc.), Arton F, Arton R (eg, R4500, R4900, R5000, etc.), and Arton RX, manufactured by JSR Corporation.

The intrinsic viscosity [η] inh of the cycloolefin resin ^{is preferably 0.2 cm 3} / g or more and 5 cm ³ / g or less, and ^{more preferably 0.3 cm 3} / g or more and 3 cm ³ / g or less. It is more preferably 0.4 cm ³ / g or more and 1.5 cm ³ / g or less.

The number average molecular weight (Mn) of the cycloolefin resin is preferably 8,000 or more and 100,000 or less, more preferably 10,000 or more and 80,000 or less, and further preferably 12,000 or more and 50,000 or less. The weight average molecular weight (Mw) of the cycloolefin resin is preferably 20,000 or more and 300,000 or more, more preferably 30,000 or more and 250,000 or less, and further preferably 40,000 or more and 200,000 or more. The number average molecular weight and the weight average molecular weight of the cycloolefin resin can be measured by gel permeation chromatography (GPC) in terms of polystyrene.

When the intrinsic viscosity [η] inh, the number average molecular weight and the weight average molecular weight are in the above ranges, the heat resistance, water resistance, chemical resistance, mechanical properties and molding processability as a film of the cycloolefin resin are improved. ..

The glass transition temperature (Tg) of the cycloolefin resin is usually 110 ° C. or higher, preferably 110 ° C. or higher and 350 ° C. or lower, more preferably 120 ° C. or higher and 250 ° C. or lower, and 120 ° C. or higher and 220 ° C. or higher. It is more preferably ° C. or lower. When Tg is 110 ° C. or higher, deformation under high temperature conditions can be easily suppressed. On the other hand, when the Tg is 350 ° C. or lower, the molding process becomes easy, and the deterioration of the resin due to the heat during the molding process is also easily suppressed.

1-2. Copolymerization Resin The copolymerization resin contained in the optical film of the present invention is a copolymerization resin of a styrene-based monomer having a proton-donating group and a fluorene-based monomer, and is a styrene-based monomer having the proton-donating group. It has a structural unit derived from a monomer and a structural unit derived from the above-mentioned styrene-based monomer.

Examples of the proton donating group include a hydroxy group, a thiol group, a carboxy group and the like. Of these, from the viewpoint of further enhancing the compatibility between the cycloolefin resin and the copolymer resin, a hydroxy group that easily interacts with the polar group of the cycloolefin resin is preferable.

The proton donating group may be added to any of the o-position, the m-position, and the p-position with respect to the vinyl group of styrene. Of these, the effect of steric hindrance due to the constituent units derived from the fluorene-based monomer is reduced, and the proton-donating group and the polar group of the cycloolefin-based resin can easily interact with each other to facilitate the interaction between the cycloolefin-based resin. From the viewpoint of making the copolymerization resin more compatible with the copolymer resin, it is preferably added at the p-position.

Examples of styrene-based monomers include styrene, α-methylstyrene, β-methylstyrene, pt-butylstyrene, vinyltoluene and the like.

The fluorene-based monomer is a monomer having a fluorene skeleton and a functional group having a polymerizable unsaturated bond.

The fluorene skeleton may be fluorene without a substituent, but is preferably a substituted fluorene having a substituent at the 9-position, more preferably a 9,9-bisarylfluorene skeleton, and a 9,9-bisphenol fluorene skeleton. Is more preferable.

The polymerizable unsaturated bond is preferably a carbon-carbon unsaturated bond containing a (meth) acryloyl group or the like. The functional group having a polymerizable unsaturated bond may be directly bonded to the fluorene skeleton, but may be bonded to a substituent added to the fluorene skeleton (for example, a substituent added to the 9-position of the fluorene skeleton). It is preferable to have.

Examples of the fluorene-based monomer include 9,9-bis ((meth) acryloyloxyaryl) fluorene, 9,9-bis ((meth) acryloyloxy (poly) alkoxyaryl) fluorene and the like.

Specific examples of the above 9,9-bis ((meth) acryloyloxyaryl) fluorene include
9,9-bis ((meth) acryloyloxyphenyl) fluorene, such as 9,9-bis (4- (meth) acryloyloxyphenyl) fluorene,
9,9-Bis (4- (meth) acryloyloxy-3-methylphenyl) fluorene and 9,9-bis (4- (meth) acryloyloxy-3,5-dimethylphenyl) fluorene and the like 9,9- Bis (alkyl- (meth) acryloyloxyphenyl) fluorene,
9,9-bis (aryl (meth) acryloyloxyphenyl) fluorene, such as 9,9-bis (4- (meth) acryloyloxy-3-phenylphenyl) fluorene,
9,9-Bis [3,4-di ((meth) acryloyloxy) phenyl] fluorene, and 9,9-bis [3,4,5-tri ((meth) acryloyloxy) phenyl] fluorene, etc. 9-Bis (poly (meth) acryloyloxyphenyl) fluorene, as well as,
9,9-bis [6- (2- (meth) acryloyloxynaphthyl)] fluorene, and 9,9-bis [1- (5- (meth) acryloyloxynaphthyl)] fluorene, etc.] Bis ((meth) acryloyloxynaphthyl) fluorene and the like are included.

Specific examples of the above 9,9-bis ((meth) acryloyloxy (poly) alkoxyaryl) fluorene include
9,9-bis ((meth) acryloyloxyalkoxyphenyl) fluorene, such as 9,9-bis (4- (2- (meth) acryloyloxyethoxy) phenyl) fluorene,
9,9-bis ((meth) acryloyloxydialkoxyphenyl) fluorene, such as 9,9-bis {4- [2- (2- (meth) acryloyloxyethoxy) ethoxy] phenyl} fluorene, etc.]
9,9-bis (4- (2- (meth) acryloyloxyethoxy) -3-methylphenyl) fluorene, and 9,9-bis (4- (2- (meth) acryloyloxyethoxy) -3,5- 9,9-bis (alkyl- (meth) acryloyloxyalkoxyphenyl) fluorene, such as dimethylphenyl) fluorene,
9,9-bis (aryl- (meth) acryloyloxyalkoxyphenyl) fluorene, such as 9,9-bis (4- (2- (meth) acryloyloxyethoxy) -3-phenylphenyl) fluorene,
9,9-bis [3,4-di (2- (meth) acryloyloxyethoxy) phenyl] fluorene, 9,9-bis [3,4,5-tri (2- (meth) acryloyloxyethoxy) phenyl] 9,9-bis [di or tri ((meth) acryloyloxyalkoxy) phenyl] fluorene such as fluorene, and
9,9-bis ((meth) acryloyloxyalkoxynaphthyl) fluorene and the like, 9,9-bis ((meth) acryloyloxyalkoxynaphthyl) fluorene and the like are included.

The mole of the structural unit derived from the styrene-based monomer with respect to the total number of moles of the structural unit derived from the styrene-based monomer and the structural unit derived from the fluorene-based monomer contained in the copolymer resin. The ratio of numbers is preferably 10 mol% or more and 30 mol% or less. When the ratio of the number of moles of the structural unit derived from the styrene-based monomer is 10 mol% or more, the phase difference of the optical film can be further reduced. Further, when the ratio of the number of moles of the constituent units derived from the styrene-based monomer is 30 mol% or less, the compatibility with the cycloolefin-based resin is further enhanced, and in particular, the transparency of the optical film is enhanced. be able to.

The molar ratio of the structural unit derived from the styrene-based monomer and the structural unit derived from the fluorene-based monomer can be measured by known methods such as ^{1 1} H-NMR and ^{13 C-MNR.}

The weight average molecular weight (Mw) of the copolymerized resin is preferably 2000 or more and 1500,000 or less, more preferably 5000 or more and 1,000,000 or less, and further preferably 12,000 or more and 50,000 or less. The weight average molecular weight of the copolymer resin can be measured by gel permeation chromatography (GPC) in terms of polystyrene.

The copolymer resin may be any copolymer such as a block copolymer, a random copolymer and a graft copolymer, but between the polar group of the cycloolefin resin and the proton donor group. A random copolymer is preferable from the viewpoint of causing an interaction in the entire copolymer resin and facilitating compatibility with the cycloolefin-based resin.

The copolymer resin is other than the structural unit derived from the styrene-based monomer and the structural unit derived from the fluorene-based monomer, as long as the solvent resistance, transparency and brittleness of the optical film are not significantly deteriorated. , Other building blocks may be included. The ratio of the number of moles of the other constituent units to the copolymer resin is preferably 0 mol% or more and 20 mol% or less, more preferably 0 mol% or more and 10 mol% or less, and the copolymer resin is the above. It is further preferred that it is substantially free of other building blocks.

1-3. Other Components The optical film may further contain other components as long as the effects of the present invention are not impaired. Examples of the other components include resins other than the cycloolefin resin or the copolymer resin, an ultraviolet absorber, an antioxidant and the like.

1-4. Film physical characteristics (haze)
The haze of the optical film is preferably 0.01 or more and 2.0 or less. When the haze of the optical film is 2.0 or less, the contrast of the display image on the display can be increased. The haze of the optical film is more preferably 0.01 or more and 1.0 or less. The haze of the optical film can be measured with a haze meter (model NDH 2000, manufactured by Nippon Denshoku Co., Ltd.).

The haze of the optical film can be adjusted mainly by the content of (meth) acrylic resin fine particles and inorganic fine particles. In order to reduce the haze of the optical film, for example, it is preferable to keep the content of (meth) acrylic resin fine particles and inorganic fine particles below a certain level.

(Phase difference Ro and Rt)
When the optical film is used as a polarizing plate protective film or a retardation film for a flexible display, it may have retardation values Ro and Rt depending on the application.

For example, when an optical film is used as a zero retardation film, the in-plane retardation Ro measured in an environment with a measurement wavelength of 590 nm and 23 ° C. and 55% RH preferably satisfies 0 nm ≦ Ro ≦ 5 nm. More preferably, 0 nm ≦ Ro ≦ 3 nm. The phase difference Rt in the thickness direction measured in an environment with a measurement wavelength of 590 nm and 23 ° C. and 55% RH preferably satisfies −10 nm ≦ Rt ≦ 10 nm, and more preferably −5 nm ≦ Ro ≦ 5 nm.

Ro and Rt of the optical film are defined by the following formulas, respectively.
Equation (1a): Ro = (nx-ny) × d
Equation (1b): Rt = ((nx + ny) /2-nz) × d
(During the ceremony,
nx represents the refractive index in the in-plane slow-phase axial direction (the direction in which the refractive index is maximized) of the optical film.
ny represents the refractive index in the direction orthogonal to the in-plane slow phase axis of the optical film.
nz represents the refractive index in the thickness direction of the optical film.
d represents the thickness (nm) of the optical film. )

The in-plane slow-phase axis of the optical film means the axis having the maximum refractive index on the film surface. The in-plane slow-phase axis of the optical film can be confirmed by an automatic birefringence meter Axoscan (AxoScan Mueller Matrix Polarimeter: manufactured by Axometrics).

The Ro and Rt of the optical film can be measured by the following method.
1) The optical film is humidity-controlled for 24 hours in an environment of 23 ° C. and 55% RH. The average refractive index of this optical film is measured with an Abbe refractometer, and the thickness d is measured with a commercially available micrometer.
2) The retardation Ro and Rt of the optical film after humidity control at a measurement wavelength of 590 nm were measured at 23 ° C. and 55% RH using an automatic birefringence meter Axoscan (AxoScan Mueller Matrix Polarimeter). Measure in the environment.

The phase difference Ro and Rt of the optical film can be adjusted mainly by the draw ratio. In order to increase the phase difference Ro and Rt of the optical film, it is preferable to increase the draw ratio.

(Thickness)
The thickness of the optical film is, for example, preferably 5 μm or more and 40 μm or less, and more preferably 10 μm or more and 25 μm or less. The thicker the film thickness, the more a certain level of optical film strength can be exhibited, and the crack resistance of the optical film and the crack resistance of the polarizing plate using the optical film can be further enhanced. The thinner the film thickness, the smaller the phase difference of the optical film, and the thinner the polarizing plate and the display device can be.

2. Method for Producing Optical Film The optical film of the present invention can be produced by any method, but it is preferably produced by a solution film forming method (casting method).

That is, in the optical film of the present invention, 1) a step of obtaining a dope containing at least the above-mentioned cycloolefin resin, a copolymer resin, and a solvent, and 2) the obtained dope is cast on a metal support. It can be produced through a step of drying and peeling to obtain a film-like substance, and 3) a step of drying the obtained film-like substance or stretching while drying.

About the step 1) The dope may be obtained by directly adding a cycloolefin resin and a copolymer resin to a solvent and mixing them, or a solution in which a cycloolefin resin is dissolved in a solvent and a copolymer resin. May be obtained by mixing with a solution prepared by dissolving the above in a solvent.

The solvent used for doping preferably contains an organic solvent (good solvent) capable of dissolving both the cycloolefin resin and the copolymer resin described above. Examples of such a good solvent include a chlorine-based organic solvent containing methylene chloride (methylene chloride) and the like, and a non-chlorine-based organic solvent containing methyl acetate, ethyl acetate, acetone, toluene, tetrahydrofuran and the like. Of these, methylene chloride (methylene chloride) is preferable.

The solvent used for doping may further contain an organic solvent (poor solvent) that does not dissolve either the cycloolefin resin or the copolymer resin. Examples of the poor solvent include straight-chain or branched-chain aliphatic alcohols having 1 to 4 carbon atoms. When the ratio of alcohol in the dope is high, the film-like substance tends to gel and peels off from the metal support easily. Examples of the linear or branched aliphatic alcohol having 1 or more and 4 or less carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, and tert-butanol. Of these, ethanol is preferable because it has relatively low dope stability, a relatively low boiling point, and good drying properties.

The dope obtained in step 2) is cast on a metal support. Dope casting can be performed by discharging from a casting die.

The solvent in the dope cast on the metal support is then evaporated and dried. The dried dope is stripped from the metal support to give a film. The residual solvent amount of the dope when peeling from the metal support (residual solvent amount S ₀ at the time of peeling) is 50% by mass or more and 120% by mass in terms of facilitating reduction of the phase difference Ro and Rt of the obtained optical film. The following is preferable. When the residual solvent amount S ₀ at the time of peeling is 50% by mass or more, the cycloolefin resin and the copolymer resin tend to flow easily and become non-oriented during drying or stretching, so that Ro and Rt of the obtained optical film are reduced. Cheap. When the residual solvent amount S ₀ at the time of peeling is 120% by mass or less, the force required for peeling the dope is unlikely to be excessively large, so that it is easy to suppress the breakage of the dope.

The amount of residual solvent in the dope is defined by the following formula. The same applies to the following.
Residual solvent amount of dope (mass%) = (mass before heat treatment of dope-mass after heat treatment of dope) / mass after heat treatment of dope × 100
The heat treatment for measuring the amount of residual solvent means a heat treatment at 120 ° C. for 60 minutes.

About the step 3) The obtained film-like substance is dried or stretched while being dried. Stretching can be done in at least one direction. The stretching direction may be any of the longitudinal direction of the film-like object (MD direction), the width direction orthogonal to the longitudinal direction of the film-like object (TD direction), and the oblique direction with respect to the longitudinal direction of the film-like object. good.

The draw ratio is set according to the required optical performance, but from the viewpoint of making the optical film function as a λ / 4 film or a retardation film for VA, it should be, for example, 1.31 times or more and 5.0 times or less. From the viewpoint of functioning as a retardation film for IPS, for example, it can be 1.01 times or more and 1.3 times or less. The stretch ratio is defined as (size of the film after stretching in the stretching direction) / (size of the film before stretching in the stretching direction).

The stretching temperature is preferably (Tg-10) ° C. or higher (Tg + 50) ° C. or lower, preferably (Tg−50) ° C., where Tg is the glass transition temperature of the optical film to be produced, which contains the cycloolefin resin and the copolymer resin. 5) More preferably, it is ℃ or more (Tg + 40) ℃ or less. When the stretching temperature is (Tg-10) ° C. or higher, the tension applied to the film-like material during drying or stretching is unlikely to be excessively increased, so that Ro and Rt of the obtained optical film are unlikely to be excessively increased. When the stretching temperature is (Tg + 50) ° C. or lower, it is easy to highly suppress the generation of bubbles due to the vaporization of the solvent in the film-like material. Specifically, the stretching temperature can be 120 ° C. or higher and 200 ° C. or lower.

_{The amount of residual solvent S 1 in} the film-like material at the start of stretching is preferably 5% by mass or more and 20% by mass or less. When the residual solvent amount S ₁ at the start of stretching is 5% by mass or more, the substantial Tg of the film-like substance at the time of stretching is lowered due to the plasticizing effect of the residual solvent, so that Ro and Rt of the optical film are increased. It's hard to do. When the residual solvent amount S ₁ at the start of stretching is 20% by mass or less, the generation of bubbles due to the vaporization of the solvent in the film-like material can be highly suppressed. _{The amount of residual solvent S 1 in} the film-like material at the start of stretching is more preferably 8% by mass or more and 15% by mass or less.

Stretching of the film-like material in the MD direction can be performed, for example, by a method (roll method) in which a plurality of rolls are provided with a peripheral speed difference and the roll peripheral speed difference is used between them. Stretching of the film-like object in the TD direction can be performed, for example, by fixing both ends of the film-like object with clips or pins and widening the distance between the clips or pins in the traveling direction (tenter method).

3. 3. Applications As described above, the optical film of the present invention is highly transparent and can be thinned. Therefore, the optical film of the present invention includes transparent plastic film substrates, optical films (for example, polarizing plate protective films, retardation films, etc.), touch panel films (electrode films), and most of the displays including liquid crystal displays and organic EL displays. It can be preferably used as a protective film or the like arranged on the surface on the viewing side. Further, the optical film of the present invention can be preferably used for a flexible display or the like. Furthermore, the optical film of the present invention can be preferably used as a sealing substrate for an organic EL device, a sealing film (barrier film) for an organic thin-film solar cell, and the like.

(Liquid crystal display)
In one example of the application of the optical film of the present invention, the liquid crystal display includes a liquid crystal cell and a pair of polarizing plates sandwiching the liquid crystal cell.

FIG. 1 is a schematic view showing an example of a basic configuration of a liquid crystal display. As shown in FIG. 1, the liquid crystal display 10 includes a liquid crystal cell 20, a first polarizing plate 30 and a second polarizing plate 40 sandwiching the liquid crystal cell 20, and a backlight 50.

The display mode of the liquid crystal cell 20 is not particularly limited, and may be any of, for example, TN (Twisted Nematic), VA (Visual Alginment), IPS (In Plane Switching), and the like.

The liquid crystal cell 20 has a pair of transparent plastic film substrates 21 and 23, and a liquid crystal layer 25 arranged between them and containing liquid crystal molecules. The pixel electrode may be arranged on one of the pair of transparent plastic film substrates 21 and 23 (for example, the transparent plastic film substrate 21). The counter electrode may be further arranged on the transparent plastic film substrate 21 on which the pixel electrode is arranged, or may be further arranged on the other transparent plastic film substrate 23.

Then, by applying an electric field between the pixel electrode and the counter electrode, the liquid crystal molecules are oriented in a predetermined direction, so that the transmittance and reflectance of each sub-pixel are changed to display an image.

The first polarizing plate 30 is arranged on the surface of the liquid crystal cell 20 on the viewing side, and the first polarizing element 31 and the polarized light arranged on the surface of the first polarizing element 31 opposite to the liquid crystal cell. The plate protective film 33 (F1) and the polarizing plate protective film 35 (F2) arranged on the surface of the first polarizing element 31 on the liquid crystal cell side are included.

The second polarizing plate 40 is arranged on the surface of the liquid crystal cell 20 on the backlight side, and is arranged on the surface of the second polarizing element 41 and the second polarizing element 41 on the liquid crystal cell side to protect the polarizing plate. The film 43 (F3) and the polarizing plate protective film 45 (F4) arranged on the surface of the second polarizer 41 opposite to the liquid crystal cell are included. The absorption axis of the second polarizer 41 is preferably orthogonal to the absorption axis of the first polarizer 41.

The optical film of the present invention can be preferably used as a transparent plastic film substrate 21 or 23, or a polarizing plate protective film 33 (F1), 35 (F2), 43 (F3) or 45 (F4). Above all, since the optical film of the present invention can function as a zero retardation film, it is preferable to use it as a protective film 35 (F2) or 43 (F3).

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited thereto.

1. 1. Optical film material 1-1. Cycloolefin resin (Cycloolefin resin COP1)
A hydrogenated norbornene resin (manufactured by JSR Corporation, Arton G7810 (“Arton” is a registered trademark of JSR Corporation)) was used as the cycloolefin-based resin having a polar group. Hereinafter, this cycloolefin resin is referred to as COP1.

(Cycloolefin resin COP2)
As the cycloolefin-based resin having no polar group, the resin synthesized by the method described in Synthesis Example 1 below was used. Hereinafter, this cycloolefin resin is referred to as COP2.

<Synthesis example 1>
50 parts by mass of dicyclopentadiene, 35 parts by mass of tetracyclododecene and 15 parts by mass of methanotetrahydrofluorene are mixed, and the amount of 1- is 0.85 mol% based on 100 mol% of the above confusion. Docosen was added to prepare a raw material mixture.

Substituting the glass container with nitrogen, 7 parts by mass of the above raw material mixture, 1,600 parts by mass of cyclohexane, 1.3 parts by mass of diisopropyl ether, 0.33 parts by mass of isobutyl alcohol, 0.84 parts by mass. Triisobutylaluminum and 30 parts by mass of tungsten hexachloride 0.66% cyclohexane solution were added, and the mixture was stirred for 7 hours while heating at 70 ° C. Then, while stirring at 55 ° C., 693 parts by mass of the above raw material mixture and 72 parts by mass of a 0.77% tungsten hexachloride solution of cyclohexane were continuously added dropwise over 150 minutes, and after further stirring for 30 minutes, 1 The polymerization reaction was stopped by adding 0.0 parts by mass of isopropyl alcohol to obtain a polymer solution.

Then, 300 parts by mass of the above polymer solution was transferred to an autoclave equipped with a stirrer, and 100 parts by mass of cyclohexane and 2.0 parts by mass of a diatomaceous earth-supported nickel catalyst (manufactured by Nikki Kagaku Co., Ltd., T8400RL, nickel-supporting ratio 58%) were added. After replacing the inside of the autoclave with hydrogen, a hydrogenation reaction was carried out at 180 ° C. under a hydrogen pressure of 4.5 MPa for 6 hours.

After the hydrogenation reaction is completed, a pressure filter (IHI, Fundafilter) is used with diatomaceous earth (Showa Kagaku Kogyo Co., Ltd., Radiolite # 500 ("Radiolite" is a registered trademark of the company) ") as a filtration bed. Then, pressure filtration was performed at a pressure of 0.25 MPa to obtain a colorless and transparent solution of a cycloolefin-based resin (norbornene-based ring-opening copolymer hydride).

Then, in the obtained solution, 0.5 parts by mass of Ciba Specialty Chemicals, Inc., Irganox 1010 (“Irganox” is a registered trademark of BASF) with respect to 100 parts by mass of the cycloolefin resin. Was added and dissolved, and foreign matter was removed by filtering using a metal fiber filter (manufactured by Nichidai Co., Ltd., pore diameter 0.4 μm).

Then, using a cylindrical concentrator / dryer (manufactured by Hitachi, Ltd.), cyclohexane and other volatile components were removed from the above filtrate at a temperature of 260 ° C. and a pressure of 1 kPa or less, and the strands were melted from a die directly connected to the concentrator. It was extruded into a shape, cooled with water, and then cut with a pelletizer (OSP-2 manufactured by Nagata Seisakusho Co., Ltd.) to obtain pellets of the above cycloolefin resin.

The molecular weight of the cycloolefin resin was 35,000 for Mw, 2.2 for Mw / Mn, 99.7% for hydrogenation, and 124 ° C for Tg.

1-2. Copolymerized resin (copolymerized resin 1)
As the copolymer resin having a proton-donating group, the copolymer resin synthesized by the method described in Synthesis Example 2 below was used. Hereinafter, this copolymer resin will be referred to as a copolymer resin 1.

<Synthesis example 2>
200 mL of dichloromethane was taken into a glass container for reaction, in which 7.79 g of 9,9-bis (4-hydroxyphenyl) fluorene and 0.11 g of hydroquinone were dissolved to prepare a raw material solution. 10.45 g of methacryloyl chloride was added dropwise to the raw material solution while cooling from the dropping device, and after the dropping was completed, the mixture was stirred for 5 hours. Then, it was mixed with 200 mL of pure water to separate the target product extracted into the organic layer. The separated target product is concentrated with an evaporator, mixed with hexane, recrystallized, and 9,9-bis (4-methacryloyloxyphenyl) fluorene represented by the following general formula (1) (hereinafter, copolymer resin). The above-mentioned fluorene-based monomer used for the synthesis of the above-mentioned fluorene-based monomer is also referred to as "monomer 1").

Another reaction glass container was replaced with nitrogen, and 250 mL of degassed tetrahydrofuran was taken into the glass container under a nitrogen flow, and 24.33 g of monomer 1 and 0.32 g of p-hydroxystyrene ( Hereinafter, (hereinafter, the styrene-based monomer used for the synthesis of the copolymer resin is also referred to as “monomer 2”, and the styrene-based monomer having a proton-donating group is also simply referred to as “H-styrene”, and in particular. Unless otherwise stated, H-styrene means p-hydroxystyrene), and 0.086 g of azobisisobutyronitrile (AIBN) were added and dissolved. These solutions were heated to 70 ° C. 7 After stirring for a time, the mixture was allowed to cool at room temperature to prepare a reaction solution. Then, the reaction solution was concentrated, added dropwise to methanol and reprecipitated, and the copolymerization represented by the following general formula (2) was carried out. Resin 1 was obtained. The molecular weight Mn of the copolymerized resin 1 was 43000, the molecular weight Mw was 138,000, and the Mw / Mn was 3.209.

(Copolymerized resin 2)
As a copolymer resin having a proton-donating group, the same method as the synthesis of the copolymer resin 1 was performed except that the amount of the monomer 1 used for preparing the reaction solution was changed to 24.33 g and the amount of the monomer 2 was changed to 1.50 g. The synthesized copolymer resin was used. Hereinafter, this copolymer resin will be referred to as a copolymer resin 2. The molecular weight Mn of the copolymer resin 2 was 48,000, the molecular weight Mw was 136000, and the molecular weight Mw / Mn was 2.833.

(Copolymerized resin 3)
As a copolymer resin having a proton-donating group, the same method as in the synthesis of the copolymer resin 1 except that the amount of the monomer 1 used for preparing the reaction solution was changed to 24.33 g and the amount of the monomer 2 was changed to 4.01 g. The synthesized copolymer resin was used. Hereinafter, this copolymer resin will be referred to as a copolymer resin 3. The molecular weight Mn of the copolymer resin 3 was 45,000, the molecular weight Mw was 141000, and the molecular weight Mw / Mn was 3.133.

(Copolymerized resin 4)
As another copolymer resin having a proton-donating group, a copolymer resin synthesized by the same method as the synthesis of the copolymer resin 1 was used except that the monomer 2 was changed to 4-mercaptostyrene. Hereinafter, this copolymer resin will be referred to as a copolymer resin 4. The molecular weight Mn of the copolymer resin 4 was 55,000, the molecular weight Mw was 178,000, and the molecular weight Mw / Mn was 3.236.

(Copolymerized resin 5)
As the copolymer resin having no proton donating group, a copolymer resin synthesized by the same method as the synthesis of the copolymer resin 1 was used except that the monomer 2 was changed to styrene. Hereinafter, this copolymer resin will be referred to as a copolymer resin 5. The molecular weight Mn of the copolymer resin 5 was 69000, the molecular weight Mw was 198000, and the molecular weight Mw / Mn was 2.870.

1-3. Other resins (fluorene-based homopolymers)
As the homopolymer obtained by polymerizing the fluorene-based monomer alone, a homopolymer synthesized by the same method as the synthesis of the copolymer resin 1 except that the monomer 2 was not used was used. Hereinafter, this homopolymer will be referred to as a fluorene-based homopolymer. The molecular weight Mn of the fluorene-based homopolymer was 78,000, the molecular weight Mw was 255,000, and Mw / Mn was 3.269.

(Styrene homopolymer)
As a homopolymer obtained by independently polymerizing a styrene-based monomer having no proton-donating group, the same method as in the synthesis of the copolymer resin 1 is used except that the monomer 1 is not used and the monomer 2 is changed to styrene. The synthesized copolymer was used. Hereinafter, this homopolymer will be referred to as a styrene homopolymer. The molecular weight Mn of the styrene homopolymer was 68,000, the molecular weight Mw was 185,000, and Mw / Mn was 2.721.

(H-styrene homopolymer)
As the homopolymer obtained by independently polymerizing the styrene-based monomer having a proton-donating group, a homopolymer synthesized by the same method as the synthesis of the copolymer resin 1 except that the monomer 1 was not used was used. Hereinafter, this homopolymer will be referred to as an H-styrene homopolymer. The molecular weight Mn of the above H-styrene homopolymer was 45,000, the molecular weight Mw was 131000, and Mw / Mn was 2.911.

2. Preparation of Optical Film Optical film 1 to optical film 20 were produced by the following procedure.

(Preparation of optical film 1)
<Preparation of dope>
The following ingredients were placed in a closed container, heated, and completely dissolved with stirring. This is referred to as Azumi Filter Paper No. manufactured by Azumi Filter Paper Co., Ltd. Filtration was obtained using 24 to obtain a dope.
COP1 (Cycloolefin resin): 95 parts by mass Copolymerized resin 1: 5 parts by mass Dichloromethane: 200 parts by mass Ethanol: 10 parts by mass

<Film formation>
The resulting dope was kept at 30 ° C. and uniformly cast on a stainless steel belt, which is an endless metal support kept at 30 ° C. The cast dope was dried until the residual solvent amount became 50% by mass, and then peeled off from the stainless belt to obtain a film-like substance.

<Stretching and drying>
The obtained film-like substance was dried at 40 ° C. until the residual solvent amount became 10% by mass, and then stretched in the width direction at a stretching ratio of 1.1 times (10%). The obtained film-like material was further dried at 150 ° C. while being conveyed by a large number of rolls to obtain an optical film 1 having a length of 3000 m and a thickness of 20 μm.

(Preparation of optical film 2)
The optical film 2 was formed in the same manner as the optical film 1 except that the amount of COP1 charged into the closed container was changed to 5 parts by mass and the amount of the copolymer resin 1 charged into the closed container was changed to 95 parts by mass. Obtained.

(Preparation of optical film 3)
The optical film 3 was formed in the same manner as the optical film 1 except that the amount of COP1 charged into the closed container was changed to 80 parts by mass and the amount of the copolymer resin 1 charged into the closed container was changed to 20 parts by mass. Obtained.

(Preparation of optical film 4)
The optical film 4 was formed in the same manner as the optical film 1 except that the amount of COP1 charged into the closed container was changed to 20 parts by mass and the amount of the copolymer resin 1 charged into the closed container was changed to 80 parts by mass. Obtained.

(Preparation of optical film 5)
The optical film 5 was formed in the same manner as the optical film 1 except that the amount of COP1 charged into the closed container was changed to 50 parts by mass and the amount of the copolymer resin 1 charged into the closed container was changed to 50 parts by mass. Obtained.

(Preparation of optical film 6)
An optical film 6 was obtained in the same manner as the optical film 1 except that the copolymer resin 1 was changed to the copolymer resin 2.

(Preparation of optical film 7)
An optical film 7 was obtained in the same manner as the optical film 1 except that the copolymer resin 1 was changed to the copolymer resin 3.

(Preparation of optical film 8)
An optical film 8 was obtained in the same manner as the optical film 3 except that the copolymer resin 1 was changed to the copolymer resin 4.

(Preparation of optical film 9)
An optical film 9 was obtained in the same manner as the optical film 2 except that the thickness was changed to 5 μm.

(Preparation of optical film 10)
An optical film 10 was obtained in the same manner as the optical film 2 except that the thickness was changed to 10 μm.

(Preparation of Optical Film 11)
An optical film 11 was obtained in the same manner as the optical film 2 except that the thickness was changed to 40 μm.
(Preparation of Optical Film 12)
The optical film 12 was formed in the same manner as the optical film 1 except that the amount of COP1 charged into the closed container was changed to 99 parts by mass and the amount of the copolymer resin 2 charged into the closed container was changed to 1 part by mass. Obtained.
(Preparation of optical film 13)
The optical film 13 was formed in the same manner as the optical film 1 except that the amount of COP1 charged into the closed container was changed to 1 part by mass and the amount of the copolymer resin 2 charged into the closed container was changed to 99 parts by mass. Obtained.

(Preparation of optical film 14)
An optical film 14 was obtained in the same manner as the optical film 1 except that the copolymer resin was not put into the closed container at the time of preparing the dope.

(Preparation of optical film 15)
The copolymer resin was changed to the fluorene-based homopolymer, the amount of COP1 charged in the closed container was changed to 60 parts by mass, and the amount of the fluorene-based homopolymer charged in the closed container was changed to 40 parts by mass. An optical film 15 was obtained in the same manner as in the optical film 1 except for the above.

(Preparation of optical film 16)
Except that the copolymer resin was changed to the styrene homopolymer, the amount of COP1 charged in the closed container was changed to 60 parts by mass, and the amount of the styrene homopolymer charged in the closed container was changed to 40 parts by mass. Obtained an optical film 16 in the same manner as the optical film 1.

(Preparation of optical film 17)
Optical except that the copolymer resin was changed to the copolymer resin 5, the amount of COP1 charged into the closed container was changed to 60 parts by mass, and the amount of the copolymer resin 5 charged into the closed container was changed to 40 parts by mass. An optical film 17 was obtained in the same manner as in film 1.

(Preparation of optical film 18)
The copolymer resin 2 was melt-kneaded at a resin temperature of 210 ° C. using an extruder, and the obtained strands were cut with a pelletizer to obtain resin pellets containing the copolymer resin 2.

The pellet of COP2 obtained in Synthesis Example 2 containing 60 parts by mass of COP2 and the above resin pellet containing 40 parts by mass of the copolymer resin 2 were mixed by a blender. Then, a twin-screw kneader (manufactured by Toshiba Machine Co., Ltd., TEM-35B) was used for kneading and extruding under the following kneading conditions to obtain pellets of these resins.
Kneading conditions: Screw diameter 37 mm, L / D = 32
Screw rotation speed 250 rpm
Resin temperature 250 ℃
Feed rate 15 kg / hour

The pellets obtained were obtained by using a hanger manipulation type T-die film melt extrusion molding machine having a resin melt kneader equipped with a screw having a screw diameter of 50 mmφ, a compression ratio of 2.5, and L / D = 30. T-die molding was performed under molding conditions, and the thickness was adjusted to be taken up by a roll so as to have a thickness of 20 μm to obtain an optical film 18.
Molding conditions: Die gap 300 μm
Molten resin temperature 210 ℃
T-die width 300 mm
Cooling roll 40 ° C
Cast roll 40 ℃

(Preparation of Optical Film 19)
Optical film except that the amount of COP1 charged in the closed container was 60 parts by mass and the copolymer resin charged in the closed container was changed to 20 parts by mass of the fluorene-based homopolymer and 20 parts by mass of the styrene homopolymer. An optical film 19 was obtained in the same manner as in 1.

(Preparation of optical film 20)
Except that the amount of COP1 charged into the closed container was 60 parts by mass, and the copolymer resin charged into the closed container was changed to 20 parts by mass of the fluorene-based homopolymer and 20 parts by mass of the H-styrene homopolymer. An optical film 20 was obtained in the same manner as the optical film 1.

The materials used for producing the optical films 1 to 20 and their ratios are shown in Tables 1 and 2.

3. 3. Evaluation of Optical Films The phase difference (Ro), phase difference (Rt), oil resistance, transparency (haze) and brittleness of the obtained optical films 1 to 20 were evaluated by the following methods.

(Phase difference (Ro), phase difference (Rt))
The optical films 1 to 20 were humidity-controlled for 24 hours in an environment of 23 ° C. and 55% RH. The measured wavelength of the optical film after humidity control was 590 nm, and the three-dimensional refractive index was measured. ) Was measured in an environment of 23 ° C. and 55% RH, and the calculation was made by applying the above formulas (1a) and (1b).

(Oil resistance)
After wrapping the optical film 1 to the optical film 20 around a 30 mmφ steel tube and fixing them with tape, apply beef tallow to the surface of the optical film and leave it at 20 ° C for 1 hour to check if there are any minute cracks in the film. It was visually observed and evaluated according to the following criteria.
○ No cracks have occurred in the optical film △ Minor cracks have occurred in a part of the optical film × Cracks have occurred in the entire optical film

(Transparency (haze))
The haze of the optical films 1 to 20 was measured with a haze meter (model NDH 2000, manufactured by Nippon Denshoku Co., Ltd.).

(Brittleness (crack occurrence rate))
By observing the outer peripheral portion of a cut piece obtained by stacking five optical films 1 to 20 and punching 100 pieces with a 10 cm square Thomson blade, a punching defect such as a crack, a crack, or a chip was detected. The number of parts (n) was divided by the number of observed outer peripheral parts (m), and the crack occurrence rate was shown as a percentage as shown below.
Crack occurrence rate (%) = 100 x (n / m)

The evaluation results of the optical films 1 to 20 are shown in Tables 3 and 4.

The cycloolefin-based resin having a polar group and a copolymer resin having a structural unit derived from a styrene-based monomer having a proton-donating group and a structural unit derived from a fluorene-based monomer, and having the above-mentioned cyclo The optical films 1 to 11 in which the ratio of the copolymer resin to the total mass of the olefin resin and the copolymer resin is 5% by mass or more and 95% by mass or less have solvent resistance and transparency (compatibility). In addition, punching defects such as cracks were sufficiently suppressed.

In particular, the optical films 3 to 5 in which the ratio of the mass of the copolymer resin to the total mass of the cycloolefin resin and the copolymer resin is 20% by mass or more and 80% by mass or less are the same cycloolefin. In the combination of the based resin and the copolymer resin, the phase difference is smaller than that of the optical film 1 having a lower mass ratio of the copolymer resin, and the solvent resistance is smaller than that of the optical film 2 having a higher mass ratio of the copolymer resin. Was increased, punching defects such as cracks were further suppressed, and the phase difference became smaller.

Further, the ratio of the number of moles of the structural unit derived from the styrene-based monomer to the total number of moles of the structural unit derived from the styrene-based monomer and the structural unit derived from the fluorene-based monomer is 10 mol%. The optical film 6 using the copolymer resin having a content of 30 mol% or more has a smaller phase difference than the optical film 1 having a lower ratio of the number of moles of the constituent units derived from the styrene-based monomer, and is a styrene-based monomer. It was more transparent than the optical film 7, which had a higher ratio of the number of moles of the constituent units derived from the merits.

Further, as compared with the optical film 2, the optical film 9, the optical film 10 and the optical film 11 in which the film thickness was changed in the combination of the same cycloolefin resin and the copolymer resin, the thicker the film thickness, the more cracks and the like. Punching defects were less likely to occur, and the thinner the film, the smaller the phase difference tended to be.

On the other hand, the optical films 12 and 13 having the ratio of the copolymer resin to less than 5% by mass or more than 95% by mass with respect to the total mass of the cycloolefin resin and the copolymer resin have a larger phase difference. Was there.

Further, the optical film 14 not containing the copolymer resin probably does not have a fluorene skeleton, so that the oil resistance is difficult to increase and the phase difference is larger than that of other optical films containing a fluorene skeleton.

In addition, the optical film 15 using a fluorene-based homopolymer instead of the copolymer resin had low transparency, probably because the resins were not compatible with each other. Further, probably because the resins are not compatible with each other, the improvement of oil resistance by the fluorene skeleton is not sufficiently achieved, and punching defects such as cracks are likely to occur.

In addition, the optical film 16 using a styrene homopolymer instead of the copolymer resin had low transparency, probably because the resins were not compatible with each other. Further, probably because the fluorene skeleton does not exist, the oil resistance of the optical film is difficult to increase, and punching defects such as cracks are likely to occur.

Further, the optical film 17 using the copolymer resin having no proton donating group probably had low transparency because the resins did not dissolve with each other. Further, probably because the resins are not compatible with each other, the improvement of oil resistance by the fluorene skeleton is not sufficiently achieved, and punching defects such as cracks are likely to occur.

Further, the optical film 18 using a cycloolefin-based resin having no polar group had low transparency, probably because the resins were not compatible with each other. Further, probably because the resins are not compatible with each other, the improvement of oil resistance by the fluorene skeleton is not sufficiently achieved, and punching defects such as cracks are likely to occur.

Further, the optical film 19 and the optical film 20 using the fluorene-based homopolymer and the styrene homopolymer or the H-styrene homopolymer probably had low transparency because the resins were not sufficiently compatible with each other. Further, probably because the resins are not sufficiently compatible with each other, the improvement of oil resistance by the fluorene skeleton is not sufficiently achieved, and punching defects such as cracks are likely to occur.

According to the present invention, it is possible to provide an optical film having high solvent resistance and transparency, and capable of sufficiently suppressing punching defects such as cracks when the film is thinned. Such optical films are used as display devices such as liquid crystal displays and organic EL displays widely used in televisions, notebook computers, smartphones, etc., electrode films such as touch panels, barrier films having gas barrier properties, flexible films, and the like. Can also be preferably used.

10 Liquid crystal display 20 Liquid crystal cells 21, 23 Transparent plastic film substrate 25 Liquid crystal layer 30 First polarizing plate 31 First polarizing element 33 Polarizing plate protective film (F1)
35 Polarizing plate protective film (F2)
40 Second polarizing plate 41 Second polarizing element 43 Polarizing plate protective film (F3)
45 Polarizing plate protective film (F4)
50 backlight

Claims (8)

It has a cycloolefin-based resin having a polar group, a structural unit derived from a styrene-based monomer having a proton-donating group, and a structural unit derived from a fluorene-based monomer having a 9,9-bisarylfluorene skeleton. Including with polymer resin
The ratio of the copolymer resin to the total mass of the cycloolefin resin and the copolymer resin is 5% by mass or more and 95% by mass or less.
Optical film. The optical film according to claim 1, wherein the proton donating group is a hydroxy group. The optical film according to claim 1 or 2, wherein the ratio of the mass of the copolymer resin to the total mass of the cycloolefin resin and the copolymer resin is 20% by mass or more and 80% by mass or less. The optical film according to any one of claims 1 to 3, wherein the cycloolefin-based resin has a structural unit derived from a norbornene-based monomer having a polar group. The optical film according to any one of claims 1 to 4, wherein the copolymer resin is a random copolymer of the styrene-based monomer having a proton-donating group and the fluorene-based monomer. The optical film according to any one of claims 1 to 5, wherein the film thickness is 10 μm or more and 25 μm or less. A polarizing plate comprising a polarizing element and an optical film according to any one of claims 1 to 6 arranged on at least one surface thereof. A display device including the polarizing plate according to claim 7.

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