KR102559467B1 - Optical film, process for producing the optical film, and polarizing plate - Google Patents

Abstract

An object of the present invention is to provide an optical film having excellent durability against heat and cold cycles, a manufacturing method thereof, and a polarizing plate.
The optical film of the present invention is an optical film containing an acrylic resin (A), elastic fine particles (B), and a resin (C) different from the acrylic resin (A),
The said acrylic resin (A) is a main component, has N-substituted maleimide as a structural unit, and has a weight average molecular weight of 300000 or more,
The elastic fine particles (B) have an average particle diameter in the range of 50 to 500 nm and a content in the range of 5 to 25% by mass,
The resin (C) is an acetyl cellulose or cycloolefin polymer having an average degree of substitution of 2.70 or more, and the content thereof satisfies specific formula (1).

Description

Optical film, its manufacturing method and polarizing plate

The present invention relates to an optical film, a manufacturing method thereof, and a polarizing plate. More specifically, the present invention relates to an optical film having excellent durability against heat and cold cycles, a manufacturing method thereof, and a polarizing plate.

In recent years, a liquid crystal display device as a display device, an organic electroluminescent display device, an optical film such as a polarizing plate protective film or a retardation film, a base film such as a base film for a touch panel or a gas barrier base film, as well as a base film such as a substrate film for nanoimprinting or a substrate film for flexible electronic circuits.

Acrylic resins have been utilized in optical films because, in addition to low hygroscopicity, they exhibit excellent transparency, dimensional stability and low birefringence.

As a further enhancement of the functionality of acrylic resins, copolymerization of N-substituted maleimide monomer units is also preferably performed for designing heat resistance and birefringence.

In this case, since hard brittleness, which is a drawback of the acrylic resin, becomes more of a problem, it is usually performed to increase the molecular weight of the resin to make it more robust and to add elastic fine particles for shock absorption.

For example, in Patent Literature 1, it is said that an acrylic film having excellent flexibility is obtained by solution-casting an acrylic resin and acrylic particles, which are elastic fine particles, in a predetermined mixed organic solvent and subjecting to a predetermined heat treatment. It is also described that ductile fracture and cutting properties are further improved by further containing a cellulose ester resin in this acrylic film at a mass ratio of acrylic resin:cellulose ester resin = 95:5 to 30:70 in a commercial state.

However, with the expansion of active scenes such as mobile and vehicle-mounted displays, more diverse durability is required for optical films. Specifically, by being exposed to outdoor heat and cold cycles, the optical film repeats expansion and contraction in a long-term range. At this time, since the action of stress and relaxation occurs repeatedly in the resin polymer constituting the film, the dimensional change of the optical film and the residual stress accompanying it may cause optical design deviations in other constituent members of the display. This phenomenon may be a greater problem in a stretched film in which the residual stress is originally high.

For this reason, an optical film made of an acrylic resin having excellent durability that can withstand outdoor heat and cold cycles has been demanded.

International Publication No. 2009/150926

This invention was made|formed in view of the said problem and situation, and the problem to be solved is to provide the optical film excellent in durability with respect to a heat and cold cycle, its manufacturing method, and a polarizing plate.

As a result of examining the causes of the above problems in order to solve the above problems, the inventors of the present invention found out that a polymer different from the acrylic resin had a different action due to the presence of a very small amount of a specific amount, and reached the present invention.

That is, the said subject concerning this invention is solved by the following means.

1. An optical film containing an acrylic resin (A), elastic fine particles (B), and a resin (C) different from the acrylic resin (A),

The said acrylic resin (A) is a main component, has N-substituted maleimide as a structural unit, and has a weight average molecular weight of 300000 or more,

The elastic fine particles (B) have an average particle diameter in the range of 50 to 500 nm and a content in the range of 5 to 25% by mass,

The resin (C) is an acetyl cellulose or cycloolefin polymer having an average substitution degree of 2.70 or more, and the content satisfies the following formula (1).

Equation (1)

0.00001 ≤ content of resin (C) in unit area of optical film (g) / sum of particle surface areas of elastic fine particles (B) contained in unit area of optical film (m 2) ≤ 0.001

2. The optical film according to claim 1, wherein the heat shrinkage rate by heating at 150°C for 8 hours is in the range of -65 to -2% in at least one of the MD direction and the TD direction.

3. The optical film according to 1st or 2nd term characterized by containing an ultraviolet absorber.

4. The optical film according to item 3, wherein the ultraviolet absorber is a benzotriazole-based ultraviolet absorber.

5. The optical film according to any one of items 1 to 4, which contains methanol.

6. It is a manufacturing method of the optical film which manufactures the optical film in any one of Claims 1-5,

A step of preparing a dope containing the acrylic resin (A), the elastic fine particles (B) and a resin (C) and a step of solution casting the dope to form a film,

In the dope, the content (g) of the resin (C) contains an amount that satisfies the following formula (2),

Further, in the step of preparing the dope, the elastic fine particles (B) and the resin (C) are mixed prior to mixing the acrylic resin (A).

Equation (2)

0.00001 ≤ content of resin (C) in dope unit amount (g) / sum of particle surface areas of elastic fine particles (B) contained in dope unit amount (m 2) ≤ 0.001

7. A polarizing plate comprising the optical film according to any one of claims 1 to 5.

According to the above means of the present invention, it is possible to provide an optical film having excellent durability against heat and cold cycles, a manufacturing method thereof, and a polarizing plate.

Although the expression mechanism or action mechanism of the effect of the present invention is not clear, it is estimated as follows.

In the optical film of the present invention, the acrylic resin (A) serving as a matrix and the elastic fine particles (B) are heterogeneous components, and it is considered that the action of stress/relaxation caused by the different components acts on the interface.

When a trace amount of a resin (C), which is a heterogeneous polymer such as triacetyl cellulose (TAC) or a cycloolefin polymer, is added to the optical film, it is considered that the resin (C) is more present at the interface between the elastic fine particles than in the matrix of the acrylic resin (A). It is presumed that the action of acts and the durability increases.

1 is a conceptual diagram of the state of covering the elastic fine particles (B) in the optical film of the present invention. A case where the resin (C) different from the acrylic resin (A) as a heterogeneous component is TAC will be described as an example.

(a) of FIG. 1 shows a case where the addition amount of TAC, which is a heterogeneous component, resin (C) is small. The elastic fine particles (B) 2a in the acrylic resin (A) 1a are partially covered by the resin (C) 3a, and an interface between the three exists. Further, when the addition amount of TAC is increased, as shown in FIG.

In (c) of FIG. 1 , when the addition amount of TAC is further increased, the periphery of the elastic fine particles (B) (2a) is covered with TAC, and the interface between the elastic fine particles (B) (2a) and the acrylic resin (A) (1a) disappears, and a thick layer of TAC, which is the resin (C) (3a), exists.

1(d) is a case where TAC as the resin (C) (3a) and acrylic resin (A) as the matrix resin are commercially available. A resin 4a in which the acrylic resin (A) and the resin (C) are mixed is present around the elastic fine particles (B) 2a.

In the cases shown in FIGS. 1(b) to (d), there is no interface between three parties on the elastic fine particles (B) (2a).

The addition amount of the resin (C) (3a) in the present invention corresponds to FIG.

Regarding the elastic fine particles (B), when TAC is in such a coated state (added amount), it is effective in stress propagation and relaxation, and it is estimated that the durability is excellent in heat and cold cycles.

In addition, both TAC and cycloolefin polymer differ greatly in polarity, but in the middle of the acrylic resin (A), both are considered to have the same effect as resins having different polarities.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a conceptual diagram of the covered state of elastic fine particles (B) in an optical film of the present invention.
Fig. 2 is a diagram schematically showing a step of preparing a dope and a step of forming a film by solution casting in a solution casting film forming method suitable for the present invention.

The optical film of the present invention is an optical film containing an acrylic resin (A), elastic fine particles (B), and a resin (C) different from the acrylic resin (A),

The said acrylic resin (A) is a main component, has N-substituted maleimide as a structural unit, and has a weight average molecular weight of 300000 or more,

The elastic fine particles (B) have an average particle diameter in the range of 50 to 500 nm and a content in the range of 5 to 25% by mass,

The resin (C) is an acetyl cellulose or cycloolefin polymer having an average substitution degree of 2.70 or more, and the content satisfies the above formula (1). This feature is a technical feature common to or corresponding to each of the following embodiments (modes).

As an embodiment of the present invention, from the viewpoint of effect expression of the present invention, the heat shrinkage rate by heating at 150 ° C. for 8 hours is -65 to -2% in at least one of the MD direction (softening direction) and the TD direction (width direction). It is preferable because cracking after durability of the polarizing plate can be suppressed.

Moreover, since the dimensional change rate and haze fluctuation before and after heat cycle durability can be suppressed by containing a ultraviolet absorber, it is preferable.

Moreover, it is preferable that the said ultraviolet absorber is a benzotriazole type ultraviolet absorber because the said effect is high.

In addition, from the viewpoint of effect expression of the present invention, containing methanol is preferable because the rate of dimensional change before and after heat cycle durability can be suppressed.

As a method for producing an optical film for producing an optical film of the present invention, a step of preparing a dope containing the acrylic resin (A), the elastic fine particles (B), and a resin (C), and a step of solution casting the dope to form a film,

In the dope, the content (g) of the resin (C) contains an amount that satisfies the above formula (2),

Further, in the step of preparing the dope, mixing the elastic fine particles (B) and the resin (C) prior to mixing the acrylic resin (A) is preferable from the viewpoint of suppressing the rate of dimensional change before and after heat cycle durability.

The optical film of the present invention may be suitably provided for a polarizing plate.

Hereinafter, detailed explanation is given about the form and aspect for implementing this invention, its component, and this invention. In addition, in this application, "to" is used by the meaning which includes the numerical value described before and after that as a lower limit value and an upper limit value.

<<Optical film of the present invention>>

The optical film of the present invention is an optical film containing an acrylic resin (A), elastic fine particles (B), and a resin (C) different from the acrylic resin (A),

The said acrylic resin (A) is a main component, has N-substituted maleimide as a structural unit, and has a weight average molecular weight of 300000 or more,

The elastic fine particles (B) have an average particle diameter in the range of 50 to 500 nm and a content in the range of 5 to 25% by mass,

The resin (C) is an acetyl cellulose or cycloolefin polymer having an average substitution degree of 2.70 or more, and the content thereof satisfies the following formula (1).

Equation (1)

0.00001 ≤ content of resin (C) in unit area of optical film (g) / sum of particle surface areas of elastic fine particles (B) contained in unit area of optical film (m 2) ≤ 0.001

When the content (g) of the resin (C) in the unit area of the optical film satisfies the above formula (1), as described above, the interface between the acrylic resin (A), the elastic fine particles (B), and the resin (C) is preferably present. Since it is effective in stress propagation and relaxation, it is thought that an optical film excellent in durability against heat and cold cycles can be obtained.

In Formula (1), when “the content of resin (C) in the unit area of the optical film (g) / the total surface area of the particles of the elastic fine particles (B) contained in the unit area of the optical film (m 2 )” represented by the formula (1) is less than 0.00001 g / m and greater than 0.001 g / m, it is considered that the effect of stress propagation and relaxation due to the generation of the three-part interface is reduced, which is not preferable.

(Method for Calculating Surface Area of Elastomer Fine Particles (B))

The “content of C in the unit area of the optical film (g)/the total surface area of the particles of B contained in the unit area of the optical film (m 2 )” defined in the present invention is defined as Cov1 (g/m 2), and this Cov1 is calculated in the following procedure.

First, a cross section of the optical film is observed by TEM to extract 20 or more elastic fine particles. From each cross-sectional area, the average particle diameter D (m) by circular conversion is calculated. After that, all the elastic fine particles are regarded as uniform spherical particles and calculated.

Surface area per elastic fine particle s = 4 × π × (D / 2) ² (㎡)

Volume v = 4/3 × π × (D / 2) ³ (m3) per elastic fine particle

The mass per unit area of the optical film is defined as W (g/m), the mass ratio Pb (ununit) occupied by the elastic fine particles in the optical film, and the specific gravity d (g/m) of the elastic fine particles, and the number N (piece/m) of the elastic fine particles (B) contained per unit area of the optical film is represented by the following formula.

N=W×Pb÷(v×d)

On the other hand, if the C content rate Pc (no unit) in the optical film is used, the content of the resin (C) in the unit area of the optical film will be W×Pc (g/m 2 ).

From the above, if Cov1 (g/m 2 ) is calculated,

Cov1=W×Pc÷(s×N)

=W×Pc÷(s×(W×Pb÷(v×d)))

=Pc/Pb×(v×d/s)

=Pc×d×D/(6Pb)

, and as a conclusion, "the total amount of the particle surface area of the elastic fine particles (B) contained in the content (g) of the resin (C) in the unit area of the optical film (g) / unit area of the optical film (m 2)" can be obtained by the following formula.

Cov1=Pc×d×D/(6×Pb)

As image analysis software, WinROOF (provided by Shoji Mitani Co., Ltd.), aVision (provided by Image Sense Co., Ltd.), etc. can be used, for example.

[Acrylic Resin (A)]

The optical film of the present invention has an acrylic resin (A) as a main component, has an N-substituted maleimide as a structural unit, and has a weight average molecular weight of 300,000 or more.

The fact that the acrylic resin (A) is the main component means that 50% by mass or more of the optical film contains the acrylic resin (A). Preferably it exists in the range of 50-95 mass %.

It is preferable that the acrylic resin (A) concerning this invention has the following structure.

MMA-PMI-XA

Here, MMA represents the unit of methyl methacrylate, PMI represents the unit of phenyl maleimide, and XA represents the other copolymerizable unit. As other copolymerizable units, there are descriptions exemplified in paragraph numbers [0020] to [0025] of Japanese Unexamined Patent Publication No. 2015-86250, and among these, all except MMA and PMI are included. Preferred units are BMA (butyl methacrylate), BA (butyl acrylate), and MA (methyl acrylate).

It is preferable that the acrylic resin (A) concerning this invention is a tertiary copolymer resin containing a methyl methacrylate unit, a phenyl maleimide unit, and other copolymerizable units, and each said monomeric unit is contained as a repeating unit.

Considering optical properties, transparency, compatibility, processability and productivity, it is preferable to include 70 to 93 parts by mass of MMA units, 5 to 10 parts by mass of PMI units, and 2 to 20 parts by mass of other copolymerizable units based on 100 parts by mass of the acrylic resin (A). This is because excellent retardation characteristics and optical characteristics can be obtained when the content of the methyl methacrylate unit is within the above range. When the content of the methyl methacrylate unit is 70 parts by mass or more, the optical performance of the protective film is not deteriorated, and when it is 93 parts by mass or less, the uniformity of the thickness of the protective film is not lowered.

In addition, in the resin composition, the PMI unit serves to impart an appropriate retardation value and compatibility between the MMA unit and other copolymerizable units, and relative to 100 parts by mass of the acrylic resin (A), the PMI unit is preferably about 5 to 10 parts by mass. When the content of the PMI unit is within the above range, necessary retardation characteristics can be obtained.

Moreover, it is preferable that content of other copolymerizable units contains 2-20 mass parts with respect to 100 mass parts of acrylic resins (A).

The molecular weight of the acrylic resin (A) concerning this invention is 300000 or more. Preferably, it is preferable that it is 500000 to 2500000. If the molecular weight is 300000 or more, the production efficiency of the film will not decrease, and if the molecular weight is 2500000 or less, the molding process is easy. Moreover, it is preferable that the glass transition temperature (Tg) of the acrylic resin (A) concerning this invention is 120 degreeC or more. When the glass transition temperature is within the above range, the handleability is good, which is preferable.

(Measurement of Weight Average Molecular Weight)

The weight average molecular weight of the acrylic resin (A) according to the present invention can be obtained as follows.

The weight average molecular weight (Mw) of the acrylic resin (A) according to the present invention is obtained by polystyrene conversion using gel permeation chromatography (GPC) according to the following measurement conditions.

Measurement system: "GPC system HLC-8220" manufactured by Tosoh Corporation

Developing solvent: chloroform (manufactured by Wako Pure Chemical Industries, Ltd.; special grade)

Solvent flow: 0.6 mL/min

Standard sample: TSK standard polystyrene ("PS-oligomer kit" from Tosoh)

Measurement-side column configuration: Tosoh Corporation’s “TSK-GEL super HZM-M 6.0x150” 2 units in series connection, Tosoh Corporation’s “TSK-GEL super HZ-L 4.6x35” 1 unit

Reference-side column configuration: Tosoh Corporation's "TSK-GEL SuperH-RC 6.0x150" 2pcs serial connection

Column temperature: 40°C

(Polymerization method of acrylic resin (A))

As a method for producing the acrylic resin (A) according to the present invention, commonly used polymerization methods such as cast polymerization, bulk polymerization, suspension polymerization, solution polymerization, emulsion polymerization, and anionic polymerization can be used. Among them, bulk polymerization or solution polymerization without using a suspending agent or an emulsifying agent is preferable because it is possible to reduce the inclusion of microscopic foreign matters that are unsuitable for optical applications.

<Solution Polymerization>

In the case of solution polymerization, a solution prepared by dissolving a mixture of monomers in an aromatic hydrocarbon solvent such as toluene or ethylbenzene can be used.

As the initiator used in the polymerization reaction, any initiator used in radical polymerization can be used, and examples thereof include azo compounds such as azobisisobutyronitrile; Organic peroxides such as benzoyl peroxide, lauroyl peroxide, and t-butyl peroxy-2-ethylhexanoate can be used.

In particular, when polymerization is carried out at a high temperature of 90°C or higher, solution polymerization is common, so peroxides, azobis initiators, and the like that have a 10-hour half-life temperature of 80°C or higher and are soluble in the organic solvent used are preferable. Specifically, 1,1-bis (t-butyl peroxy) -3,3,5-trimethylcyclohexane, cyclohexane peroxide, 2,5-dimethyl-2,5-di (benzoyl peroxy) hexane, 1,1-azobis (1-cyclohexane carbonitrile), 2- (carbamoyl azo) isobutyronitrile and the like. It is preferable to use these initiators in the range of 0.005-5 mass % with respect to 100 mass % of all monomers, for example.

In the polymerization reaction, as the molecular weight modifier used as necessary, any generally used in radical polymerization can be used, and examples thereof include mercaptan compounds such as butyl mercaptan, octyl mercaptan, dodecyl mercaptan, and thioglycolic acid 2-ethylhexyl as particularly preferable ones. These molecular weight modifiers are added in a concentration range in which the molecular weight of the acrylic resin (A) is controlled within the above preferred range.

<Block polymerization>

Bulk polymerization is carried out, for example, by continuously supplying a monomer component, a polymerization initiator, etc. into a reaction vessel while allowing them to stay in the reaction vessel for a predetermined time and continuously extracting a partial polymer obtained, thereby producing a copolymer with high productivity.

The polymerization initiator used when polymerizing the monomer components is not particularly limited, and examples thereof include azo compounds such as azobisisobutyronitrile, 1,1-di(tert-butylperoxy)cyclohexane, benzoylperoxide, p-chlorobenzoylperoxide, diisopropylperoxycarbonate, di-2-ethylhexylperoxycarbonate, t-butylperoxypivalate, t-butylperoxy(2-ethylhexanoate) Known radical polymerization initiators such as peroxides of the like can be used. A polymerization initiator may use only 1 type, and may use it in combination of 2 or more types. In addition, the amount used is usually 0.01 to 5% by mass with respect to the total amount of the mixture. The heating temperature in thermal polymerization is usually 40 to 200°C, and the heating time is usually about 30 minutes to 8 hours.

When polymerizing a monomer component, a chain transfer agent can be used as needed. Although the chain transfer agent is not particularly limited, suitable examples thereof include mercaptans such as n-butyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan, and 2-ethylhexylthioglycolate. A chain transfer agent may use only 1 type, and may use it in combination of 2 or more types.

<Suspension polymerization>

In the case of suspension polymerization, those used in normal suspension polymerization can be used, and examples thereof include organic peroxides and azo compounds.

Also, as the suspension stabilizer, commonly used known ones can be used, and examples thereof include organic colloidal high molecular substances, inorganic colloidal high molecular substances, inorganic fine particles, and combinations of these with surfactants.

Examples of the aqueous medium for polymerizing the monomer mixture include water or a mixed medium of water and a water-soluble solvent such as alcohol (eg, methanol or ethanol). The amount of the aqueous medium used is usually 100 to 1000 parts by mass with respect to 100 parts by mass of the monomer mixture in order to stabilize the crosslinked resin particles.

In addition, in order to suppress the generation of emulsified particles in the aqueous system, a water-soluble polymerization inhibitor such as nitrites, sulfites, hydroquinones, ascorbic acids, water-soluble B vitamins, citric acid, and polyphenols may be used.

Moreover, you may add other suspension stabilizers as needed. For example, phosphates such as calcium phosphate, magnesium phosphate, aluminum phosphate, zinc phosphate, pyrophosphates such as calcium phosphate, magnesium pyrophosphate, aluminum pyrophosphate, zinc pyrophosphate, calcium carbonate, magnesium carbonate, calcium hydroxide, magnesium hydroxide, aluminum hydroxide, calcium metasilicate, calcium sulfate, barium sulfate, and the like, and polyvinyl alcohol. A dispersion stabilizer of , etc. are mentioned.

Moreover, it is also possible to use together the said suspension stabilizer and surfactant, such as an anionic surfactant, a cationic surfactant, an amphoteric surfactant, and a nonionic surfactant.

A monomer mixture is added to the aqueous medium prepared in this way to carry out polymerization.

As a method for dispersing the monomer mixture, for example, a method in which the monomer mixture is directly added to an aqueous medium and dispersed in the aqueous medium as monomer droplets by the stirring force of a propeller blade or the like, a method of dispersing using a homomixer, which is a disperser using high shear force composed of a rotor and a stator, or a method of dispersing using an ultrasonic disperser or the like.

Next, polymerization is initiated by heating the aqueous suspension in which the monomer mixture is dispersed as spherical droplets. During the polymerization reaction, it is preferable to stir the aqueous suspension, and the stirring may be performed slowly enough to prevent, for example, the floating of spherical water droplets and the settling of particles after polymerization.

The polymerization temperature is preferably about 30 to 100°C, more preferably about 40 to 80°C. And as time to hold this polymerization temperature, about 0.1 to 20 hours is preferable.

After polymerization, the particles are separated as a water-containing cake by a method such as suction filtration, centrifugal dehydration, centrifugation, and pressurized dehydration, and further, the obtained water-containing cake is washed with water and dried to obtain target particles. Here, the average particle diameter of the particles can be adjusted by adjusting the mixing conditions of the monomer mixture and water, the addition amount of the suspension stabilizer or surfactant, and the stirring conditions and dispersion conditions of the agitator.

[Elastic fine particles (B)]

The said elastic fine particle (B) has an average particle diameter in the range of 50-500 nm, and its content exists in the range of 5-25 mass % with respect to an optical film.

When the average particle diameter is in the range of 50 to 500 nm, it is preferable from the viewpoint of not only improving slipperiness but also imparting flexibility.

There are various intentions of using the elastic fine particles (B) in the film, and there are so-called mat agents that increase slipperiness by providing irregularities on the surface of the film, phase difference control fine particles using birefringence of crystalline fine particles, and the like. In addition to these, in the present invention, flexible flexibility is imparted to the acrylic resin-containing film, which is brittle and easily cracked, by using the elastic fine particles (B) (hereinafter also referred to as rubber particles).

The optical film of the present invention preferably contains rubber particles having a core-shell structure (multilayer structure). It may be a two-layer structure including a core layer and a shell layer, or a three-layer structure of a core layer/middle layer/shell layer, or a three-layer structure of a seed particle layer/core layer/shell layer. However, the shell layer is the outermost layer.

As conventionally known, it becomes possible to impart toughness to an optical film containing a brittle acrylic resin by adding rubber particles, which are an elastic body. The rubber particle content in the optical film containing an acrylic resin is preferably 5 to 25% by mass, more preferably 5 to 35% by mass, and most preferably 5 to 20% by mass. When the content of the elastic fine particles (B) is in the range of 5 to 25% by mass, it is preferable because both the fragility and rigidity of the optical film can be achieved.

(layer structure of elastic fine particles (B))

The elastic fine particles (B) (rubber particles) preferably have a multilayer structure including a core portion and a shell portion formed by further polymerizing a (meth)acrylic acid ester as a shell portion to a particulate polymer serving as a core portion within an average particle diameter in the range of 0.01 to 1 μm.

The rubber particle has a structure derived from a polyfunctional compound only in the central portion (core), and in a portion (shell) surrounding the central portion, it is preferable to have a structure similar in polarity to the acrylic resin (A) constituting the optical film within a range that does not impair the effect of the present invention. From this, the rubber particles can be more uniformly dispersed in the acrylic resin (A), and by-products of foreign matter generated by aggregation of the rubber particles or the like can be further suppressed.

Hereinafter, the shell part and the core part of the core-shell structure will be described.

<Shellbu>

The shell portion is not particularly limited as long as it is a structure having high compatibility with the acrylic resin (A) constituting the optical film.

<Core part>

The core portion is not particularly limited as long as it exhibits an effect of improving the flexibility of the acrylic resin (A) constituting the optical film, and examples thereof include a structure having crosslinking. Moreover, as a structure which has crosslinking, it is preferable that it is a crosslinked rubber structure.

The above crosslinked rubber structure means a rubber structure in which a polymer having a glass transition point in the range of -100°C to 25°C is used as a main chain and the main chain is crosslinked with a polyfunctional compound to provide elasticity. Examples of the crosslinked rubber structure include structures (repeating structural units) of acrylic rubber, polybutadiene rubber, and olefin rubber. Among these, acrylic rubber is preferable because it is easy to control the average particle diameter to 0.3 μm or less and has good optical properties such as transparency of the film when uniformly dispersed in resin.

As a structure which has the said bridge|crosslinking, the structure derived from the polyfunctional compound mentioned above is mentioned, for example. Among the above polyfunctional compounds, 1,4-butanediol dimethacrylate, diethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, divinylbenzene, allyl methacrylate, allyl acrylate, and dicyclopentenyl methacrylate are more preferable.

The amount of the polyfunctional monomer used during production of the core portion is preferably in the range of 0.01 to 15% by mass, and more preferably in the range of 0.1 to 10% by mass of the monomer composition to be used. By using a polyfunctional monomer within the above range, the resulting film exhibits good bending resistance.

(constituting material)

As a material of a rubber particle, a butadiene type crosslinked polymer, a (meth)acryl type crosslinked polymer, an organosiloxane type crosslinked polymer, etc. are mentioned, for example. Among them, from the viewpoint of weather resistance (light resistance) and transparency of the optical film, a (meth)acrylic crosslinked polymer (in the present specification, a rubber portion containing a (meth)acrylic copolymer is also referred to as an acrylic rubber particle) is particularly preferred.

Examples of the acrylic rubber particles include ABS resin rubber particles, ASA resin rubber particles, and acrylic acid ester rubber particles.

As the multilayered particles, multilayered particles obtained by graft polymerization using a desired monomer to form a shell layer on the surface of these acrylic rubber particles are preferable.

From the viewpoint of the transparency of the obtained optical film, etc., as the multilayered particles, acrylic graft copolymer particles obtained by performing graft polymerization on the surface of particles of an acrylic acid ester-based rubbery polymer shown below are preferable.

The acrylic graft copolymer particles can be obtained by polymerizing a monomer mixture containing methacrylic acid ester as a main component in the presence of acrylic acid ester rubbery polymer particles.

<monofunctional>

The acrylic acid ester-based rubber-like polymer, which is the material of the rubber part, is a rubber-like polymer containing acrylic acid ester as a main component. Specifically, a monomer mixture (100% by mass) containing 50 to 100% by mass of an acrylic acid ester and 50 to 0% by mass of another copolymerizable vinylic monomer, and a polyfunctional monomer having two or more non-conjugated reactive double bonds per molecule is preferably formed by polymerization.

The polyfunctional monomer is used in a desired amount so that the degree of crosslinking of the rubber part is in the range of 2.3 to 4.0% by mass.

All the monomers may be mixed and used, or the monomer composition may be changed and used in two or more stages.

As acrylic acid ester, it is preferable to use the C1-C12 thing of an alkyl group from the point of polymerizability or cost. Examples thereof include methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, sec-butyl acrylate, isobutyl acrylate, benzyl acrylate, cyclohexyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, phenyl acrylate, and 2-phenoxyethyl acrylate.

These acrylic acid esters may use together 2 or more types.

The amount of acrylic acid ester is preferably 50 to 100% by mass, more preferably 60 to 99% by mass, still more preferably 70 to 99% by mass, and most preferably 80 to 99% by mass based on 100% by mass of the monomer mixture. If it is less than 50% by mass, impact resistance decreases, elongation at tensile fracture decreases, and cracks tend to occur easily when the film is cut.

As another vinylic monomer copolymerizable with acrylic acid ester, methacrylic acid esters are particularly preferable from the viewpoint of weather resistance and transparency. Examples of methacrylic acid esters include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, n-butyl methacrylate, sec-butyl methacrylate, isobutyl methacrylate, benzyl methacrylate, cyclohexyl methacrylate, 2-phenoxyethyl methacrylate, 2-ethylhexyl methacrylate, phenyl methacrylate, and n-octyl methacrylate.

Also preferred are aromatic vinyls and their derivatives, and vinyl cyanides. Examples of these vinyl monomers include styrene, methyl styrene, acrylonitrile, and methacrylonitrile. In addition, substituted or unsubstituted maleic anhydrides, (meth)acrylamides, vinyl esters, vinylidene halides, (meth)acrylic acid and salts thereof, and (hydroxyalkyl)acrylic acid esters are exemplified.

The multilayer structure polymer may have another polymer layer inside (center side) of the rubber part. From the viewpoint of anti-blocking property, it is preferable to have a methacrylic crosslinked polymer layer obtained by polymerizing 0.01 to 10 parts by mass of a polyfunctional monomer with respect to a monomer mixture containing 40 to 100% by mass of an alkyl methacrylate ester and 60 to 0% by mass of another monomer having a double bond copolymerizable with this, and 100 parts by mass of the monomer mixture. As a monomer having a double bond that can be copolymerized, the other vinyl-based monomers and acrylic acid esters that can be copolymerized described above are exemplified similarly.

The acrylic graft copolymer comprising a rubber portion and a shell layer formed on the surface of the rubber portion by graft polymerization is preferably obtained by polymerizing 95 to 25 parts by mass of a monomer mixture containing a methacrylic acid ester as a main component in at least one step in the presence of 5 to 90 parts by mass (more preferably 5 to 75 parts by mass) of acrylic acid ester rubbery polymer particles.

The methacrylic acid ester in the graft copolymer composition (monomer mixture) is preferably 50% by mass or more. If it is less than 50% by mass, the hardness and rigidity of the obtained film tend to decrease.

As the monomer used in the graft copolymerization, the above-described methacrylic acid esters and acrylic acid esters and vinyl-based monomers capable of copolymerizing these can be used similarly, and methacrylic acid esters and acrylic acid esters are preferably used. From the viewpoint of compatibility with the acrylic resin, methyl methacrylate, and from the viewpoint of suppressing zipper depolymerization, methyl acrylate, ethyl acrylate, and n-butyl acrylate are preferred.

<Multifunctional compound>

As the rubber particle having the above crosslinked structure, it can be obtained by, for example, polymerizing a monomer composition containing a polyfunctional compound having two or more non-conjugated double bonds per molecule.

Examples of the polyfunctional compound include divinylbenzene, allyl methacrylate, allyl acrylate, dicyclopentenyl methacrylate, dicyclopentenyl acrylate, 1,4-butanediol dimethacrylate, ethylene glycol dimethacrylate, triallyl cyanurate, triallyl isocyanurate, diallyl phthalate, diallyl maleate, divinyl adipate, divinylbenzene ethylene glycol dimethacrylate, dibi Nylbenzene ethylene glycol diacrylate, diethylene glycol dimethacrylate, diethylene glycol diacrylate, triethylene glycol dimethacrylate, triethylene glycol diacrylate, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, tetramethylolmethane tetramethacrylate, tetramethylolmethane tetraacrylate, dipropylene glycol dimethacrylate and dipropylene glycol diacrylate. It may be, and you may use 2 or more types together.

(synthetic method)

As the method for producing the core-shell type elastic fine particles (B) (rubber particles) in the present invention, any suitable method capable of producing core-shell type rubber particles can be employed.

For example, a polymerizable monomer forming the rubbery polymer constituting the core layer is subjected to suspension or emulsion polymerization to prepare a suspension or emulsion dispersion containing rubbery polymer particles, and then a polymerizable monomer forming the glassy polymer constituting the shell layer is added to the suspension or emulsion dispersion to radically polymerize, thereby obtaining a core-shell elastomer having a multilayer structure in which the surface of the rubbery polymer particle is coated with the glassy polymer. Here, the polymerizable monomer that forms the rubbery polymer and the polymerizable monomer that forms the glassy polymer may be polymerized in one step or in two or more steps by changing the composition ratio.

In order to secure the physical property balance of the optical film of the present invention, it is preferable to appropriately control the structure of the core-shell type rubber particles.

Preferred structures of the core/shell elastomer include, for example, (a) a soft rubber core layer and a hard glass shell layer, the core layer having a (meth)acrylic crosslinking elastomer layer, (b) the rubber core layer having a multilayer structure having at least one glass layer therein, and having a glass shell layer on the outside of the core layer. By appropriately selecting the monomer species of each layer, the physical properties (mechanical properties, optical properties, particularly orientation birefringence and photoelastic coefficient) of the (meth)acrylic resin can be arbitrarily controlled. The soft rubbery layer preferably has a polymer glass transition temperature of less than 20°C, preferably less than 0°C, and the hard glassy layer preferably has a polymer glass transition temperature of 0°C or higher, preferably 20°C or higher.

As specific examples of a more preferable structure of the core/shell type rubber particles, for example, (i) the shell layer of the core/shell type rubber particles is a non-crosslinked methacrylic resin containing preferably 3% by mass or more, more preferably 10% by mass or more, still more preferably 15% by mass or more of an alkyl acrylate, (ii) the shell layer of the core/shell type rubber particles contains two or more multilayers with different alkyl acrylate content, and alkyl acrylate is preferred as a total Preferably, it is a non-crosslinked methacrylic resin containing 10% by mass or more, more preferably 15% by mass or more, (iii) the core layer of the core/shell type rubber particles has a multilayer structure in which a mixture of acrylacrylate, a polyfunctional monomer, an alkylmercaptan, and appropriately other monomers is polymerized in the presence of a glassy polymer layer obtained by polymerizing a mixture of alkyl methacrylate, a polyfunctional monomer, an alkylmercaptan, and other monomers as appropriate. (iv) a core layer of the core/shell type rubber particles having a multilayer structure in which a rubbery polymer layer polymerized using a peracid (persulfuric acid, superphosphate, etc.) as a thermal decomposition type initiator is formed in the presence of a glassy polymer layer polymerized using an organic peroxide as a redox type polymerization initiator; and the like.

In addition, the total amount of alkyl acrylate used in the shell layer is preferably 60% by mass or less, more preferably 50% by mass or less, still more preferably 40% by mass or less. When it exceeds 60% by mass, the dispersibility of the core/shell type rubber particles in the matrix tends to deteriorate, mechanical strength and transparency deteriorate, and furthermore, it is likely to cause foreign matter such as fish eye. Further, also in terms of the productivity of the core/shell type rubber particles, the product tends to become granulated, and the like tends to cause problems. As for such a preferred structural design element of the core/shell type rubber particle, only one or a plurality of design elements of two or more may be used in combination. By having such a structure, the core-shell type rubber particles are easily dispersed well in the acrylic resin (A) according to the present invention, and when forming a film, there are few defects due to microdispersion or aggregation, and strength, toughness, heat resistance, transparency, and appearance are excellent, and whitening due to temperature change or stress is suppressed, and a quality optical film can be obtained.

In the case of producing the core/shell type rubber particles in the present invention by emulsion polymerization, suspension polymerization or the like, a known polymerization initiator can be used.

When the core/shell type rubber particles of the present invention are produced by emulsion polymerization, they can be produced by ordinary emulsion polymerization using a known emulsifier.

[Resin (C)]

The optical film of the present invention is characterized in that the resin (C) is an acetyl cellulose or cycloolefin polymer having an average substitution degree of 2.70 or more, and the content satisfies the above formula (1).

(acetyl cellulose)

The acetyl cellulose used as the resin (C) in the optical film of the present invention has an average degree of substitution of 2.70 or more. An average substitution degree of less than 2.70 is not preferable because the haze of the optical film increases.

The ratio of acetyl cellulose synthesized from cotton linters is preferably 60% by mass or more, more preferably 85% by mass or more, and most preferably 100% by mass. The synthesis method of acetyl cellulose is not particularly limited, but it can be synthesized by, for example, the method described in Japanese Unexamined Patent Publication No. 10-45804. The method for measuring the degree of substitution of an acetyl group can be measured according to ASTM-D817-96. The number average molecular weight of acetyl cellulose is preferably within the range of 70000 to 300000, more preferably within the range of 80000 to 200000, in order to obtain mechanical strength suitable as a protective film for polarizing plates.

(cycloolefin polymer)

The cycloolefin polymer (also referred to as COP) according to the present invention is preferably a homopolymer or copolymer of a cycloolefin monomer represented by the following general formula (A-1) or (A-2).

The cycloolefin monomer represented by general formula (A-1) is demonstrated.

R ¹ to R ⁴ in the general formula (A-1) each represent a hydrogen atom, a halogen atom, a substituted or unsubstituted hydrocarbon group having 1 to 30 carbon atoms, or a polar group. However, it is assumed that there is no case where R ¹ and R ² simultaneously become a hydrogen atom, or R ³ and R ⁴ become ^a hydrogen atom at the same time, except for the case where both R 1 to R ⁴ become a hydrogen atom.

A halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom. Examples of the hydrocarbon group of 1 to 30 carbon atoms include an alkyl group of 1 to 30 carbon atoms. Examples of the polar group include a carboxy group, a hydroxy group, an alkoxycarbonyl group, an aryloxycarbonyl group, an amino group, an amide group, a cyano group, a group in which these groups are bonded through a linking group such as a methylene group, a hydrocarbon group in which a divalent organic group having polarity such as a linking group such as a carbonyl group, an ether group, a silyl ether group, a thioether group, and an imino group is bonded. Among these, a carboxy group, a hydroxy group, an alkoxycarbonyl group, or an aryloxycarbonyl group is preferable, and an alkoxycarbonyl group or an aryloxycarbonyl group is particularly preferable from the viewpoint of ensuring solubility during solution film formation.

At least one of R ¹ to R ⁴ is preferably a polar group from the viewpoint of ensuring the solubility of the cycloolefin polymer during solution film formation.

p in the general formula (A-1) represents an integer of 0 to 2; From a viewpoint of improving the heat resistance of an optical film, it is preferable that p is 1-2. It is because when p is 1-2, the resin obtained becomes bulky and the glass transition temperature tends to improve.

Next, the cycloolefin monomer represented by general formula (A-2) is demonstrated.

R ⁵ in the general formula (A-2) represents a hydrogen atom, a hydrocarbon group having 1 to 5 carbon atoms, or an alkylsilyl group having an alkyl group having 1 to 5 carbon atoms. Especially, it is preferable that R ^<5> is a C1-C3 hydrocarbon group.

R ⁶ in the general formula (A-2) represents a polar group or a halogen atom. It is preferable that a polar group is a carboxy group, a hydroxyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, an amino group, an amide group, or a cyano group. A halogen atom is a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom. Among them, R ⁶ is preferably a polar group, preferably a carboxy group, a hydroxy group, an alkoxycarbonyl group, or an aryloxycarbonyl group, and particularly preferably an alkoxycarbonyl group or an aryloxycarbonyl group from the viewpoint of ensuring solubility during solution film formation.

By using the cycloolefin monomer represented by the general formula (A-2), the molecular symmetry is lowered, and the diffusion motion of the resin at the time of solvent volatilization is easily promoted.

In general formula (A-2), p represents the integer of 0-2.

Below, the specific example of the structure of general formula (A-1) and (A-2) is shown.

Examples of the copolymerizable monomer copolymerizable with the cycloolefin monomer represented by the formula (A-1) or formula (A-2) include a copolymerizable monomer capable of ring-opening copolymerization with the cycloolefin monomer represented by the formula (A-1) or formula (A-2), and a copolymerizable monomer capable of addition copolymerization with the cycloolefin monomer represented by the formula (A-1) or formula (A-2).

Examples of the copolymerizable monomer capable of ring-opening copolymerization with the cycloolefin monomer represented by formula (A-1) or formula (A-2) include other cycloolefin monomers such as cyclobutene, cyclopentene, cycloheptene, cyclooctene, and dicyclopentadiene.

Examples of the copolymerizable monomer capable of addition copolymerization with the cycloolefin monomer represented by Formula (A-1) or Formula (A-2) include unsaturated double bond-containing compounds, vinyl-based cyclic hydrocarbon compounds, and (meth)acrylates. An example of the unsaturated double bond-containing compound is an olefinic compound having 2 to 12 (preferably 2 to 8) carbon atoms, and examples thereof include ethylene, propylene, and butene. Examples of the vinyl-based cyclic hydrocarbon compound include vinylcyclopentene-based monomers such as 4-vinylcyclopentene and 2-methyl-4-isopropenylcyclopentene. Examples of the (meth)acrylate include C1-C20 alkyl (meth)acrylates such as methyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and cyclohexyl (meth)acrylate.

The content of the structural unit derived from the cycloolefin monomer represented by the formula (A-1) or the formula (A-2) can be 50 to 100 mol%, preferably 60 to 100 mol%, and more preferably 70 to 100 mol% with respect to the total structural units constituting the cycloolefin polymer.

[Other additives]

In the optical film of the present invention, known additives such as ultraviolet absorbers, plasticizers, surfactants, and matting agents can be used as additives.

(ultraviolet ray absorbent)

The optical film of the present invention preferably contains a UV absorber. The ultraviolet absorber aims to improve light resistance by absorbing ultraviolet rays of 400 nm or less, and in particular, the transmittance at a wavelength of 370 nm is preferably in the range of 2 to 30%, more preferably in the range of 4 to 20%, still more preferably in the range of 5 to 10%.

The ultraviolet absorbers preferably used in the present invention are benzotriazole-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, and triazine-based ultraviolet absorbers, which are nitrogen-containing heterocyclic compounds, and particularly preferably benzotriazole-based ultraviolet absorbers and benzophenone-based ultraviolet absorbers.

Examples include 5-chloro-2-(3,5-di-sec-butyl-2-hydroxyphenyl)-2H-benzotriazole, (2-2H-benzotriazol-2-yl)-6-(linear and branched chain dodecyl)-4-methylphenol, 2-hydroxy-4-benzyloxybenzophenone, 2,4-benzyloxybenzophenone, etc., and also Tinuvin 109, Tinuvin 171, Tinuvin 234, Tinuvin 326, Tinuvin 327, Tinuvin 328, and Tinuvin 928.

Among these, benzotriazole-based ultraviolet absorbers are preferable.

All of these are commercial items manufactured by BASF Japan Co., Ltd. and can be preferably used.

In addition to this, discoid compounds such as compounds having a 1,3,5-triazine ring are also preferably used as ultraviolet absorbers.

The optical film of this invention may contain 2 or more types of ultraviolet absorbers.

Moreover, as a ultraviolet absorber, a polymeric ultraviolet absorber can also be used suitably, and especially the polymer type ultraviolet absorber described in Unexamined-Japanese-Patent No. 6-148430 is used preferably. Moreover, it is preferable that the ultraviolet absorber does not have a halogen group.

It is also preferable to use a UV absorber and a so-called HALS (hindered amine stabilizer) in combination. Examples of HALS include Adeka Staff LA-52, LA-57, LA-63P, LA-68, LA-72, LA-77, LA-81 (manufactured by ADEKA Co., Ltd.), Tinuvin PA 144, Tinuvin 765, Tinuvin 770 DF, Tinuvin XT 55 FB, Chimassorb 2020 FDL, Chimassorb 944 FDL, Chimas Sorb 944 LD, Tinuvin 622 SF (product of BASF Japan Co., Ltd.), etc. are mentioned.

The addition method of the ultraviolet absorber is to dissolve the ultraviolet absorber in an alcohol such as methanol, ethanol, or butanol, or an organic solvent such as methylene chloride, methyl acetate, acetone, or dioxolane, or a mixed solvent thereof, and then add it to the dope, or it may be added directly in the dope composition.

A substance insoluble in an organic solvent, such as an inorganic powder, is dispersed in an organic solvent and cellulose acylate using a dissolver or a sand mill, and then added to the dope.

The amount of the ultraviolet absorber used is not uniform depending on the type of ultraviolet absorber, conditions of use, etc., but when the dry film thickness of the optical film is 15 to 50 μm, the range of 0.5 to 10% by mass is preferable, and the range of 0.6 to 4% by mass is more preferable.

≪Physical properties of optical film≫

(1) thickness of optical film

The thickness of the finished (after drying) optical film of the present invention varies depending on the purpose of use, but is usually in the range of 5 to 500 μm, preferably in the range of 10 to 150 μm, and preferably in the range of 20 to 110 μm for liquid crystal display devices, and particularly preferably in the range of 20 to 60 μm considering recent thinning.

(2) optical properties of optical films

Preferred optical properties of the optical film of the present invention vary depending on the use of the film. In the case of a polarizing plate protective film use, the absolute value of in-plane retardation (Ro) is preferably 10 nm or less, and more preferably 5 nm or less. The absolute value of thickness direction retardation (Rt) is also preferably 50 nm or less, more preferably 35 nm or less, and particularly preferably 10 nm or less.

When the optical film is used as an optical compensation film (retardation film), the range of Ro or Rt varies depending on the type of the retardation film, and although there are various requirements, it is preferable that 0 nm ≤ Ro ≤ 100 nm and -30 nm ≤ Rt ≤ 400 nm. 0 nm ≤ Ro ≤ 20 nm and 40 nm ≤ Rt ≤ 80 nm in the TN mode, 0 nm ≤ Ro ≤ 20 nm and -30 nm ≤ Rt ≤ 30 nm in the case of the IPS mode, and 20 nm ≤ Ro ≤ 80 nm and 80 nm ≤ Rt ≤ 400 nm in the VA mode. In the case of the IPS mode, the ranges of 0 nm ≤ Ro ≤ 5 nm and -10 nm ≤ Rt ≤ 10 nm are particularly preferred.

The optical film of the present invention can realize desired optical properties by appropriately adjusting process conditions such as the polymer structure used, the type and amount of additives, the stretching ratio, and the residual volatile matter at the time of peeling.

(Retardation Ro, Rt)

In this specification, Ro and Rt respectively represent in-plane retardation and retardation in the thickness direction at a wavelength λ. Ro is measured by making light with a wavelength of λ nm incident in a film normal direction in KOBRA 21ADH (manufactured by Oji Scientific Instruments Co., Ltd.). Rt is the retardation value measured by incident light with a wavelength of λ nm from a direction inclined by +40 ° with respect to the film normal direction with the above Ro, the in-plane slow axis (determined by KOBRA 21ADH) as the inclined axis (rotation axis), and the in-plane slow axis (Rotation axis). Based on the data values, KOBRA 21ADH calculates. Here, as the assumed value of the average refractive index, values in the polymer handbook (JOHN WILEY & SONS, INC) and catalogs of various optical films can be used. If the value of the average refractive index is not known, it can be measured with an Abbe refractometer. By inputting these assumed values of average refractive index and film thickness, KOBRA 21ADH calculates n _x , n _y , n _z and calculates retardation based on the following formulas (i) and (ii).

Formula (i): Ro=(n _x -n _y )×d (nm)

Equation (ii): Rt={(n _x +n _y )/2-n _z }×d (nm)

(Wherein, Ro represents the in-plane retardation value within the film, and Rt represents the retardation value in the thickness direction within the film. In addition, d represents the thickness (nm) of the optical film, n _x represents the maximum in-plane refractive index of the film, and is also referred to as the refractive index in the slow axis direction. n _y represents the refractive index in the film plane in the direction perpendicular to the slow axis, and n _z represents the refractive index of the film in the thickness direction. All measurements at a wavelength of 590 nm value)

The photoelastic modulus of the optical film of the present invention is preferably 10×10 ^-12 /Pa or less, and more preferably 3×10 ^-12 /Pa or less.

(3) Total light transmittance and haze

The optical film of the present invention is characterized by high transparency, and has a total light transmittance of 80% or more, preferably 85% or more, more preferably 90% or more, particularly preferably 95% or more, measured after humidity control in an environment of 23°C/55% RH. The total light transmittance can be measured in accordance with JIS7573 "Plastic - method for determining total light transmittance and total light reflectance".

It is preferable that it is less than 1 %, and, as for the internal haze of the optical film of this invention, it is more preferable that it is less than 0.5 %. By setting the haze to less than 1%, there is an advantage that the transparency of the film becomes higher and it becomes easier to use as a film for optical applications. Furthermore, if it is less than 0.1%, since polarization depolarization by light scattering does not arise as a film inside the polarizer of a liquid crystal display (inside of the crossed nicol comprised with two polarizers), it is used especially preferably.

In the measurement of the internal haze, it is usually performed to apply a liquid having a refractive index equal to that of the film and cover it with smooth glass in order to cancel surface scattering of the film. The measurement is performed with a haze meter (Type 1001DP, manufactured by Nippon Denshoku Kogyo Co., Ltd.) after humidity control of the sample film in an environment of 23°C and 55% RH for 5 hours or more.

The total light transmittance, haze, and internal haze can be adjusted to a preferred range by basically removing scattering materials in the film. It is also preferably performed to match the refractive index of the additive material to the resin of the film so as not to become a scattering material. In order to keep the surface of the film smooth so as not to cause surface scattering, it is also preferable to adjust the surface roughness of the casting belt or the contacting conveying roll, or to adjust the surface shape change due to stretching by the stretching temperature and magnification.

(4) Equilibrium moisture content

It is preferable that the equilibrium moisture content in the optical film concerning this invention in 25 degreeC and 60% of relative humidity is 3 % or less, and it is more preferable that it is 1 % or less. By setting the equilibrium moisture content to 3% or less, it is preferable to easily respond to changes in humidity and to make the optical properties and dimensions less likely to change.

The equilibrium moisture content is determined by the Karl Fischer method after leaving the sample film in a room regulated at 23 ° C. and a relative humidity of 20% for 4 hours or more, then left for 24 hours in a room conditioned at 23 ° C. and 80% RH, drying and evaporating moisture at a temperature of 150 ° C.

(5) Permeability

The water vapor transmission rate (regulated in JIS K 7129) of the optical film of the present invention is preferably 200 g/m 2 ·d (40°C · 90% RH) or less. As a polarizer protective film, the range of 50-200g/m<2>*d is preferable in order to maintain the water|moisture content of a polarizer appropriately, and less than 50 g/m<2>d is preferable as other optical films and electronic circuit board films. In order to adjust the moisture permeability, adjusting the film thickness (inversely proportional) is most effective, but it is also possible to adjust by adding a more hydrophilic and hydrophobic additive to the resin of the film.

(6) Expansion coefficient

The linear expansion coefficient of the optical film of the present invention is preferably 50 to 100 ppm/°C in the range of 30°C to 80°C. The humidity expansion coefficient for humidity change is preferably less than 50 ppm/% RH (in the range of 20% at 23°C to 80% at 23°C).

(7) Heat shrinkage rate

It was left to stand in an oven at 150°C for 8 hours, and immediately after taking out from the oven, another glass plate was pressed from above to correct wrinkles in the optical film. It is preferable that the heat shrinkage rate (refer to the following formula) before and after this treatment is in the range of -65 to -2%, more preferably in the range of -55 to -2%.

Heat shrinkage rate (%) = (Dimension after treatment - Dimension before treatment) ÷ Dimension before treatment × 100

≪Applications of Optical Films≫

The optical film of the present invention is a display device, such as a liquid crystal display device or an organic electroluminescent display device, an optical film such as a polarizing plate protective film or a retardation film, a substrate film such as a base film for a touch panel or a gas barrier base film, and a substrate film such as a substrate film for nanoimprint or a substrate film for flexible electronic circuits. It can be suitably used.

<< Manufacturing method of optical film >>

The method for producing an optical film of the present invention includes a step of preparing a dope containing an acrylic resin (A), an elastic fine particle (B), and a resin (C), and a step of solution casting the dope to form a film, wherein the content (g) of the resin (C) in the dope contains an amount satisfying the following formula (2), and in the step of preparing the dope, prior to mixing the acrylic resin (A), the elastic fine particles (B) and the resin (C ) are mixed.

Equation (2)

0.00001 ≤ content of resin (C) in dope unit amount (g) / sum of particle surface areas of elastic fine particles (B) contained in dope unit amount (m 2) ≤ 0.001

Cov2 (g / m) is defined as “the total amount of the particle surface area of the elastic fine particles (B) contained in the content (g) / dope unit amount of the resin (C) in the dope unit amount” as Cov2 (g / m), and this Cov2 is calculated in the following procedure.

Similar to Cov1 described above, TEM observation of the elastic fine particles (B) is performed, 20 or more of the elastic fine particles (B) are extracted, and the average particle diameter D (m) by circular conversion is calculated from each cross-sectional area. After that, all the elastic fine particles are regarded as uniform spherical particles and calculated. After that, as described above, the surface area per elastic fine particle and the volume per elastic fine particle are calculated, and Cov2 can be calculated in the same way as Cov1.

<< the details of the manufacturing method >>

As a film forming method of the optical film of the present invention, a manufacturing method such as an inflation method, a T-die method, a calender method, a cutting method, a casting method, an emulsion method, a hot press method, etc. can be used. However, from the viewpoint of suppressing coloring, foreign matter defects, and suppressing optical defects such as die lines, solution film forming by a casting method is preferable. It has at least the process of preparing dope, and the process of solution-casting the said dope and forming into a film.

(organic solvent)

An organic solvent useful for forming a dope in the case of producing the optical film of the present invention by a solution casting method may be used without limitation as long as it simultaneously dissolves the acrylic resin (A), acetyl cellulose, and other additives.

For example, as the chlorine-based organic solvent, methylene chloride, as the non-chlorine-based organic solvent, methyl acetate, ethyl acetate, amyl acetate, acetone, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, cyclohexanone, ethyl formate, 2,2,2-trifluoroethanol, 2,2,3,3-hexafluoro-1-propanol, 1,3-difluoro-2-propanol Panol, 1,1,1,3,3,3-hexafluoro-2-methyl-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol, nitroethane, etc. are mentioned, and methylene chloride, methyl acetate, ethyl acetate, and acetone can be used preferably.

It is preferable to make dope contain 1-40 mass % of C1-C4 linear or branched aliphatic alcohol other than the said organic solvent. When the ratio of alcohol in the dope is high, the web is gelled and peeling from the metal support is facilitated, and when the ratio of alcohol is small, the dissolution of the acrylic resin (A) and acetyl cellulose in a non-chlorine organic solvent system is promoted.

In particular, in a solvent containing methylene chloride and a linear or branched chain aliphatic alcohol having 1 to 4 carbon atoms, an acrylic resin (A), acetyl cellulose, and three types of acrylic particles are dissolved at least in a total amount of 15 to 45% by mass. It is preferable that it is a dope composition.

Examples of the straight-chain or branched-chain aliphatic alcohol having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, and tert-butanol. Methanol or ethanol is preferable because of their dope resistance, relatively low boiling point, and good drying properties.

It is difficult to completely remove the above organic solvents in the process of forming a film, and it is common that several tens to hundreds of ppm remain in the optical film.

Although the mechanism is unclear, it has been found that this trace amount of residual organic solvent also has a slight effect on the effect of the present invention. Since the effect was seen in the dimensional change rate of an optical film by selecting methanol rather than ethanol as alcohol at the time of dope adjustment specifically, as alcohol, methanol is more preferable.

Hereinafter, a preferred film forming method for the optical film of the present invention will be described.

1) Process of preparing dope

This is a step of preparing a dope containing an acrylic resin (A), elastic fine particles (B), and resin (C) in a melting pot in an organic solvent mainly composed of a good solvent, and other additives may be dissolved while stirring.

The resin is dissolved in various ways such as a method carried out under normal pressure, a method carried out below the boiling point of the main solvent, a method carried out by applying pressure above the boiling point of the main solvent, a method carried out by a cooling melting method as described in Japanese Unexamined Patent Publication No. 9-95544, 9-95557, or 9-95538, and a method performed at high pressure as described in Japanese Unexamined Patent Publication No. 11-21379 Although any method can be used, a method of applying pressure above the boiling point of the main solvent is particularly preferred.

In the present invention, the resin (C) in the dope is used in an amount that satisfies the above formula (2), and is characterized in that the elastic fine particles (B) and the resin (C) are mixed in advance prior to mixing the acrylic resin (A).

By mixing the elastic fine particles (B) and the resin (C) in advance, the resin (C) can be efficiently attached to a part of the surface of the elastic fine particles (B), and the acrylic resin (A), the elastic fine particles (B), and the resin (C) can prepare an elastic fine particle dispersion liquid having a three-way interface. Additives are added to the dope during or after dissolution, and after dissolution and dispersion, the solution is filtered with a filter medium, defoamed, and sent to the next step by a liquid feeding pump.

For filtration, it is preferable to use a filter medium having a collection particle diameter of 0.5 to 5 μm and a filtering time of 10 to 25 sec/100 mL.

In this method, only aggregates can be removed by using a filter medium having a collected particle size of 0.5 to 5 µm and a filtering time of 10 to 25 sec/100 mL for aggregates. In the main soup, since the concentration of the elastic fine particles (B) is sufficiently softer than that of the additive solution, the filtration pressure does not rise rapidly due to the sticking of aggregates during filtration.

Fig. 2 is a diagram schematically showing a step of preparing a dope and a step of forming a film by solution casting in a solution casting film forming method suitable for the present invention. The process of forming a film by solution casting includes a casting process, a drying process, a solution evaporation process, a peeling process, and a drying process. You may include an extending process as needed.

The acrylic resin (A) is dissolved in an appropriate amount of organic solvent in the charging pot 41, and the solution is sent to the filter 44 to remove large aggregates, and the solution is sent to the stock tank 42. Thereafter, from the stock tank 42 to the main soup melting kiln 1, a dispersion of elastic fine particles prepared by mixing the elastic fine particles (B) and the resin (C) in advance, and various additives (for example, plasticizer, mat agent, ultraviolet absorber, etc.) are added to the main soup melting kiln 1 to prepare a main soup.

As conditions for mixing the elastic fine particles (B) and the resin (C) in advance, it is preferable to disperse under conditions of 500 to 3000 rpm using a dispersing machine such as a milder dispersing machine (manufactured by Daiheiyo Gikou Co., Ltd.).

As an additive, a plasticizer, a matting agent, an ultraviolet absorber, etc. are stirred and diluted with a solvent in an additive loading pot to obtain an additive solution, and then added to the loading pot 41 as appropriate.

2) Flexible process

Dope is fed to the pressure die 30 via a liquid feed pump (e.g., a pressure-type metering gear pump), and endless metal belt 31, for example, a stainless steel belt or a rotating metal drum, is a step of casting the dope from a pressure die slit to a casting position on a metal support such as a rotating metal drum.

A pressure die that can adjust the slit shape of the mouthpiece portion of the die and easily makes the film thickness uniform is preferable. There exist a coat hanger die, a T die, etc. as a pressure die, and all are used suitably. The surface of the metal support is mirror-finished. In order to increase the film forming speed, two or more pressure dies may be provided on the metal support, and the dope amount may be divided and layered. Alternatively, it is also preferable to obtain a film having a laminated structure by a covalent casting method in which a plurality of dopes are simultaneously casted.

3) Solvent evaporation process

This is a step of heating a web (a dope film formed by casting dope on a casting support body is referred to as a web) on a casting support body to evaporate the solvent.

In order to evaporate the solvent, there are a method of blowing wind from the web side, a method of transferring heat with a liquid from the back side of the support, a method of transferring heat from the front and back by radiant heat, etc. Moreover, the method of combining them is also used preferably. It is preferable to dry the web on a support body after casting|flow_spreading on a support body in the atmosphere of 40-100 degreeC. In order to maintain in the atmosphere of 40-100 degreeC, it is preferable to apply warm air of this temperature to the upper surface of a web, or to heat by infrared rays or other means.

From the viewpoint of cotton quality, moisture permeability, and peelability, it is preferable to peel the web from the support within 30 to 120 seconds.

4) Peeling process

It is the process of peeling the web from which the solvent evaporated on the metal support body at a peeling position. The peeled web is sent to the next process.

The temperature at the peeling position on the metal support is preferably 10 to 40°C, more preferably 11 to 30°C.

In addition, when peeling the web on the metal support at the time of peeling, the amount of residual solvent is preferably in the range of 50 to 120% by mass depending on the strength and weakness of the drying conditions, the length of the metal support, etc., but when peeling at a higher amount of residual solvent, if the web is too soft, flatness is damaged during peeling, or it is easy to cause bias or vertical stripes due to peeling tension, so the amount of residual solvent at the time of peeling is determined by the balance between economic speed and quality.

The residual solvent amount of the web is defined by the following formula.

Residual solvent amount (%) = (mass of web before heat treatment - mass of web after heat treatment) / (mass of web after heat treatment) × 100

In addition, heat treatment at the time of measuring the amount of residual solvent means performing heat treatment at 115 degreeC for 1 hour.

The peeling tension at the time of peeling the metal support and the film is usually 196 to 245 N/m, but when wrinkles tend to occur during peeling, it is preferable to peel at a tension of 190 N/m or less, and it is preferable to peel at a minimum tension capable of peeling to 166.6 N/m, and then at a minimum tension to 137.2 N/m, but particularly preferably at a minimum tension to 100 N/m. is to peel

In the present invention, the temperature at the peeling position on the metal support is preferably -50 to 40°C, more preferably 10 to 40°C, and most preferably 15 to 30°C.

5) Drying and stretching process

After peeling, the web is dried using a roller drying device 35 that conveys the web by alternately passing it through a plurality of rolls arranged in a drying device, or a tenter stretching device 34 that clips and conveys both ends of the web with a clip.

As a drying means, it is common to blow hot air on both sides of the web, but there is also a means to heat by applying microwaves instead of wind. Too rapid drying is likely to damage the flatness of the finished film. Drying by high temperature is preferably performed from about 8 mass % or less of residual solvent. Overall, drying is done at approximately 40 to 250°C. It is preferable to dry especially at 40-160 degreeC.

When a tenter stretching device is used, it is preferable to use a device capable of independently controlling the gripping length of the film (the distance from the start of gripping to the end of gripping) on the left and right sides by the left and right gripping means of the tenter. Further, in the tenter process, it is also desirable to intentionally create sections having different temperatures in order to improve flatness.

Moreover, it is also preferable to provide a neutral zone between different temperature zones so that each zone may not cause interference.

In addition, the stretching operation may be divided into multiple stages and performed, and it is also preferable to perform biaxial stretching in the casting direction and the width direction. In addition, when performing biaxial stretching, simultaneous biaxial stretching may be performed, and you may carry out stepwise.

In this case, stepwise means, for example, that stretching in different stretching directions can be sequentially performed, or stretching in the same direction can be divided into multiple stages, and stretching in different directions can be added to any stage. That is, for example, the following stretching step is also possible.

Stretching in the softening direction - Stretching in the width direction - Stretching in the softening direction - Stretching in the softening direction

Stretching in the width direction - Stretching in the width direction - Stretching in the softening direction - Stretching in the softening direction

In addition, the simultaneous biaxial stretching also includes a case where stretching is performed in one direction and the tension is relieved and contracted in the other direction. A preferable draw ratio for simultaneous biaxial stretching can be taken in the range of ×1.01 to ×1.5 in both the width direction and the longitudinal direction.

The amount of residual solvent on the web in the case of tenter is preferably 20 to 100% by mass at the start of the tenter, and drying is preferably carried out while applying a tenter until the amount of residual solvent in the web is 10% by mass or less, more preferably 5% by mass or less.

The drying temperature in the case of performing the tenter is preferably 30 to 150°C, more preferably 50 to 120°C, and most preferably 70 to 100°C.

In the tenter step, the temperature distribution in the width direction of the atmosphere is preferably small from the viewpoint of increasing the uniformity of the film, and the temperature distribution in the width direction in the tenter step is preferably within ±5 ° C, more preferably within ± 2 ° C, and most preferably within ± 1 ° C.

6) winding process

It is a process of winding up with the winding machine 37 as an optical film after the amount of residual solvent in the web becomes 2% by mass or less, and a film having good dimensional stability can be obtained by setting the amount of residual solvent to 0.4% by mass or less.

As the winding method, a generally used one may be used, and there are constant torque method, constant tension method, taper tension method, program tension control method with constant internal stress, and the like, and these may be used separately.

The optical film of the present invention is preferably a long film, specifically, about 100 m to 5000 m, and is usually provided in a roll form. Moreover, it is preferable that it is 1.3-4 m, and, as for the width|variety of a film, it is more preferable that it is 1.4-2 m.

[Polarizer]

The polarizing plate according to the present invention can be produced by a general method. It is preferable to provide an adhesive layer on the back side of the film containing the acrylic resin (A) according to the present invention, and bond it to at least one side of a polarizer produced by dipping and stretching in an iodine solution.

On the other side, the film may be used, or another polarizing plate protective film may be used. For example, commercially available cellulose ester films (for example, Konica Minolta TAC KC8UX, KC4UX, KC5UX, KC8UY, KC4UY, KC12UR, KC8UCR-3, KC8UCR-4, KC8UCR-5, KV8UY-HA, KV8UX-RHA, manufactured by Konica Minolta Co., Ltd.) and the like are preferably used.

A polarizer, which is the main component of a polarizing plate, is an element that transmits only light of a plane of polarization in a certain direction, and a representative polarizing film currently known is a polyvinyl alcohol-based polarizing film, which is a polyvinyl alcohol-based film.

The polarizer forms a film of polyvinyl alcohol aqueous solution, uniaxially stretches and dyes this, or after uniaxially stretches after dyeing, what preferably performed durability treatment with a boron compound is used.

As the pressure-sensitive adhesive used in the pressure-sensitive adhesive layer, a pressure-sensitive adhesive having a storage elastic modulus at 25 ° C. in at least a portion of the pressure-sensitive adhesive layer in the range of 1.0 × 10 ⁴ to 1.0 × 10 ⁹ Pa is preferably used, and a curable pressure-sensitive adhesive that forms a high molecular weight body or a crosslinked structure by various chemical reactions after applying and bonding the pressure-sensitive adhesive is suitably used.

Specific examples include, for example, urethane-based adhesives, epoxy-based adhesives, water-based polymer-isocyanate-based adhesives, curable adhesives such as thermosetting acrylic adhesives, moisture-curing urethane adhesives, polyether methacrylate-type, ester-based methacrylate-type, oxidized polyether methacrylate, etc. anaerobic adhesives, cyanoacrylate-based instant adhesives, acrylate and peroxide-based two-component instant adhesives I can lift my back.

The pressure-sensitive adhesive may be of a one-component type or of a type in which two or more liquids are mixed before use.

Further, the pressure-sensitive adhesive may be a solvent-based adhesive using an organic solvent as a medium, may be a water-based adhesive such as an emulsion type, colloidal dispersion type, or aqueous solution type, which is a medium containing water as a main component, or may be a non-solvent type. The concentration of the pressure-sensitive adhesive liquid may be appropriately determined depending on the film thickness after adhesion, the coating method, and the coating conditions, and is usually 0.1 to 50% by mass.

[Example]

Hereinafter, the present invention will be described in detail with examples, but the present invention is not limited thereto. In Examples, "parts" or "%" are used, but "parts by mass" or "% by mass" are used unless otherwise specified.

[Example 1]

The following acrylic resin (A), elastic fine particles (B), resin (C), and elastic fine particle dispersion were prepared.

<Acrylic resin (A)>

Acrylic resin A-1: What copolymerized 90 parts by mass of MMA units, 5 parts by mass of PMI units, and 5 parts by mass of BMA units (weight average molecular weight: 1,120,000)

Acrylic resin A-2: What copolymerized 95 parts by mass of MMA units and 5 parts by mass of MA units (weight average molecular weight: 1,080,000)

Acrylic resin A-3: What copolymerized 90 parts by mass of MMA units, 5 parts by mass of PMI units, and 5 parts by mass of BMA units (weight average molecular weight: 200,000)

<Elastic fine particles (B)>

(Preparation of elastic fine particles B-1 to B-6)

38.2 liters of ion-exchanged water and 111.6 g of sodium dioctylsulfosuccinate were put into a reactor with an internal volume of 60 liters and equipped with a reflux condenser, and the temperature was raised to 75° C. under a nitrogen atmosphere while stirring at a rotational speed of 250 rpm, so that the effect of oxygen was virtually absent. After adding 0.36 g of ammonium persulfate (APS) and stirring for 5 minutes, a monomer mixture (c1) containing 1657 g of methyl methacrylate (MMA), 21.6 g of butyl acrylate (BA), and 1.68 g of allyl methacrylate (ALMA) was added at once, and after detection of an exothermic peak, the mixture was maintained for another 20 minutes to complete polymerization of the innermost hard layer.

Next, 3.48 g of ammonium persulfate (APS) was added, and after stirring for 5 minutes, a monomer mixture (a1) containing 1961 g of butyl acrylate (BA), 346 g of methyl methacrylate (MMA), and 264.0 g of allyl methacrylate (ALMA) (BA/MMA = 85/15 mass ratio) was continuously added over 120 minutes, and maintained for another 120 minutes after completion of the addition, The polymerization of the vaginal layer was completed.

Next, 1.32 g of ammonium persulfate (APS) was added, and after stirring for 5 minutes, a monomer mixture (b1) containing 2106 g of methyl methacrylate (MMA) and 201.6 g of butyl acrylate (BA) was continuously added over 20 minutes. After the addition, the mixture was maintained for another 20 minutes to complete polymerization of the hard layer 1.

Next, 1.32 g of ammonium persulfate (APS) was added, and after 5 minutes, a monomer mixture (b2) containing 3148 g of methyl methacrylate (MMA), 201.6 g of butyl acrylate (BA), and 10.1 g of n-octyl mercaptan (n-OM) was continuously added over 20 minutes, and maintained for another 20 minutes after the addition was completed. Next, the temperature was raised to 95°C and maintained for 60 minutes to complete polymerization of the hard layer 2.

The remaining latex was put into a 3% by mass sodium sulfate warm water solution, salted out and coagulated, and then, after repeating dehydration and washing, it was dried to obtain acrylic particles having a four-layer structure (rubber particle B-1). The glass transition temperature (Tg) of the obtained rubber particle B-1 was -30 degreeC. Elastic fine particles B-2 to B-6 having different particle diameters were prepared in the same manner while adjusting the amount of sodium dioctylsulfosuccinate.

The average particle diameters of the elastic fine particles B-1 to B-6 were measured by the method described above by TEM observation, and are shown in Table I.

<Resin (C)>

Resin (C) was prepared.

Resin C-1: triacetyl cellulose resin having an average acetyl group substitution (DS) of 2.86 (weight average molecular weight: 200000)

Resin C-2: Arton G7810 manufactured by JSR

<Preparation of Elastomer Fine Particle Dispersion>

22.6 parts by mass of rubber particles B-1, 0.0289 parts by mass of resin C-1, and 400 parts by mass of methylene chloride were stirred and mixed with a dissolver for 50 minutes, and then dispersed under conditions of 1500 rpm using a milder dispersing machine (manufactured by Daiheiyo Gikou Co., Ltd.) to obtain a rubber particle dispersion.

<Ultraviolet absorber>

A UV absorber was prepared.

UV-1: Made by ADEKA, LA-F70, triazine-based UV absorber

UV-2: BASF product, Tinuvin 928, benzotriazole-based ultraviolet absorber

<<Manufacture of Optical Film>>

[Manufacture of optical film 1]

<Preparation of Elastomer Fine Particle Dispersion>

A dispersion of elastic fine particles in which the elastic fine particles (B) and the resin (C) were mixed was prepared as follows.

22.6 parts by mass of elastic fine particles B-1, 0.0289 parts by mass of resin C-1, and 400 parts by mass of methylene chloride were stirred and mixed with a dissolver for 50 minutes, and then dispersed under 1500 rpm conditions using a milder disperser (manufactured by Daiheiyo Kikou Co., Ltd.), and the elastic fine particles dispersion in which the elastic fine particles B-1 and the resin C-1 were mixed in advance got the liquid

<Process of preparing dope>

A dope obtained by mixing and dissolving the following composition was first prepared.

Acrylic resin A-1: 88 parts by mass

Methylene chloride: 70 parts by mass

Ethanol: 50 parts by mass

Elastomer fine particle dispersion: 183 parts by mass

<Film forming process>

Next, using an endless belt casting machine, the dope was uniformly cast on a stainless belt support at a temperature of 31°C and a width of 1800 mm. The temperature of the stainless belt was controlled at 28 degreeC.

On a stainless steel belt support, the solvent was evaporated until the amount of residual solvent in the casted (cast) film became 30%. Next, it was peeled from the stainless belt support body at a peel tension of 128 N/m. While conveying the peeled film with many rollers, the obtained membranous material was conveyed without extending|stretching, maintaining width with a tenter. Thereafter, it was further dried while being conveyed with a roll, and the edge clamped with a tenter clip was slit and wound up with a laser cutter to obtain an optical film 1 having a thickness of 40 μm.

[Production of Optical Films 2 to 6 and 12 to 22]

In the production of optical film 1, the type of acrylic resin (A) used for preparing the dope, and the type and amount of elastic fine particles (B) and resin (C) were changed as shown in Table I, and optical films 2 to 6 and optical films 2 to 6 and 12 to 22 were prepared in the same manner as in optical film 1.

[Manufacture of optical film 7]

In the manufacture of the optical film 1, stretching was performed in the TD direction with a tenter after the film forming step. The stretching temperature was set to 130°C and the stretching ratio was set to 2.0 times.

[Production of Optical Films 8 and 9]

In the production of the optical film 7, in the step of preparing the dope, 3 parts by mass of the ultraviolet absorber (UV-1) is added in the form of substituting a part of the mass of the acrylic resin (A) to prepare a dope, and the optical film 8 is prepared in the same manner as in the optical film 7, and similarly, 3 parts by mass of the ultraviolet absorber (UV-2) is added in the form of substituting a part of the mass of the acrylic resin (A) to prepare a dope, and the optical film 9 is prepared in the same manner as in the optical film 7 did

[Manufacture of optical film 10]

In the manufacture of the optical film 7, in the step of preparing the dope, the type of alcohol used was changed from ethanol (EtOH) to methanol (MeOH) as shown in Table I, and the optical film 10 was prepared in the same manner as in the optical film 7.

[Manufacture of optical film 11]

In the manufacture of the optical film 7, in the process of preparing dope, the optical film 11 was manufactured in the same manner as in the optical film 7 without using the resin (C).

[Manufacture of optical film 23]

In the production of the optical film 1, the order of addition of the resin (C) was changed. That is, resin C-1 was not added during preparation of the dispersion of elastic fine particles. Instead, after preparing and dissolving additives other than Resin C-1, 0.0244 parts by mass of Resin C-1 was further added, and a dope dissolved again was used.

In Table I, "-" in the type of material indicates that the material was not used.

<Average Particle Diameter of Elastomer Fine Particles>

About the obtained optical film, the cross section was observed as described above, and the average particle diameter of the elastic fine particles was calculated from image analysis. The same value as the average particle diameter obtained at the time of producing the elastic fine particles B-1 to B-6 was obtained.

<<Production of polarizing plate>>

A polyvinyl alcohol film having a thickness of 120 μm was uniaxially stretched (temperature: 110° C., draw ratio: 5 times). This was immersed for 60 seconds in an aqueous solution containing 0.075 g of iodine, 5 g of potassium iodide and 100 g of water, and then immersed in an aqueous solution at 68°C containing 6 g of potassium iodide, 7.5 g of boric acid and 100 g of water. This was washed with water and dried to obtain a polarizer.

Next, each optical film prepared above on one side of the polarizer was surface-treated under conditions of 12 W min / m 2 using a corona discharge treatment device (HFS-202) manufactured by Kasuga Denki Co., Ltd., and then bonded using a urethane-based adhesive having the following composition.

<Urethane adhesive>

100 parts by mass of aqueous emulsion of urethane resin

(Hydran AP-20, manufactured by Dainippon Ink Kagaku Kogyo Co., Ltd.)

5 parts by mass of polyfunctional glycidyl ether

(CR-5L, manufactured by Dainippon Ink Kagaku Kogyo Co., Ltd.)

On the other side of the polarizer, the surface in contact with the polarizer of Konica Minolta TAC KC4UY (cellulose ester film manufactured by Konica Minolta Co., Ltd.) was immersed in a 2 mol/L sodium hydroxide solution at 60 ° C. for 90 seconds, then washed with water, dried and saponified, and bonded using a polyvinyl alcohol adhesive having a solid content of 2% by mass.

What was bonded above was dried in a dryer at 80° C. to produce polarizing plates 1 to 23 corresponding to optical films 1 to 23.

<<Evaluation of optical film and polarizing plate>>

(1) The prepared optical film and polarizing plate were subjected to a heat cycle test, and the rate of dimensional change of the optical film, brittleness of the optical film, and cracking of the polarizing plate were evaluated.

<Dimension change rate of optical film>

The obtained optical film was subjected to a heat cycle test. Heat cycle conditions are as follows.

70℃ 10 hours

-30℃ 10 hours

200 cycles of the above were performed alternately.

With respect to the test piece before and after the heat cycle, the rate of dimensional change specified below in the TD direction was measured. The criterion for passing the dimensional change rate (%) is that the absolute value is 1.00 or less.

Dimensional change rate (%) = (Dimension after treatment - Dimension before treatment) ÷ Dimension before treatment × 100

<Brittleness of optical film>

With respect to the test piece after the said heat cycle, the crack when it bent so that the fold line might be in the TD direction was evaluated according to the following criteria. (triangle|delta) or more is a pass level.

◎: It is completely bent, and a crease is formed, but there is no crack.

○: It cracks when completely bent, but does not crack until the radius of curvature is 0.5 mm.

△: Cracked between 0.5 mm and 1 mm of curvature radius

×: Cracked before reaching a radius of curvature of 1 mm

<Cracks in the polarizer>

The obtained polarizing plate was subjected to a heat cycle test in the same manner as described above, and the test piece after the heat cycle was evaluated for cracks when bent so that the folded line became the TD direction according to the following criteria. (triangle|delta) or more is a pass level.

◎: It is completely bent, and a crease is formed, but there is no crack.

○: It cracks when completely bent, but does not crack until the radius of curvature is 0.5 mm.

△: Cracked between 0.5 mm and 1 mm of curvature radius

×: Cracked before reaching a radius of curvature of 1 mm

The above evaluation results are shown in Table I.

[Table I]

(2) Among the optical films prepared above, the heat shrinkage rate and the Δ haze before and after the heat cycle test were evaluated for the optical film 1 and the stretched optical films 7 to 11.

<Heat shrinkage rate of optical film>

Baby powder was applied on a smooth glass plate, the obtained optical film was placed horizontally thereon, and left to stand in an oven at 150°C for 8 hours. Immediately after taking out from the oven, another glass plate was pressed from above to correct wrinkles in the film. Heat shrinkage in the TD direction before and after this treatment was measured.

Heat shrinkage rate (%) = (Dimension after treatment - Dimension before treatment) ÷ Dimension before treatment × 100

<Δ haze of optical film>

The haze value (%) was measured for the test piece before and after the heat cycle, and was expressed as an increase with respect to before the heat cycle shown below.

Δ Haze (%) = haze value after treatment (%) - haze value before treatment (%)

The above results are shown in Table II.

[Table II]

From Table I and Table II, the optical film of the present invention has a small heat shrinkage rate, excellent dimensional change rate after heat cycle, brittleness, and haze, and also excellent resistance to cracking of a polarizing plate provided therewith, It can be seen that durability against heat and cold cycles is excellent.

1a: acrylic resin (A)
2a: elastic fine particles (B)
3a: Resin (C)
4a: resin in which acrylic resin (A) and resin (C) are commonly used
1: melting kiln
2: pump
3, 6, 12, 15: filter
4, 13: stock tank
5, 14: liquid delivery pump
8, 16: Conduit
10: UV absorber input kiln
20: confluence pipe
21: mixer
30: pressure die
31: unauthorized metal belt
32: web
33: peeling position
34: tenter stretching device
35: roller drying device
36: conveying roller
37: winding device
41: input kiln
42: stock tank
43: pump
44: filter

Claims (7)

An optical film containing an acrylic resin (A), elastic fine particles (B), and a resin (C) different from the acrylic resin (A),
The acrylic resin (A) has a content of 50% by mass or more, has an N-substituted maleimide as a structural unit, and has a weight average molecular weight of 300000 or more,
The elastic fine particles (B) have an average particle diameter in the range of 50 to 500 nm and a content in the range of 5 to 25% by mass,
The resin (C) is an acetyl cellulose or cycloolefin polymer having an average substitution degree of 2.70 or more, and the content satisfies the following formula (1).
Equation (1)
0.00001 ≤ content of resin (C) in unit area of optical film (g) / sum of particle surface areas of elastic fine particles (B) contained in unit area of optical film (m 2) ≤ 0.001 According to claim 1,
An optical film characterized in that the heat shrinkage rate by heating at 150°C for 24 hours is within a range of -65 to -2% in at least one of the MD direction and the TD direction. According to claim 1 or 2,
An optical film characterized by containing an ultraviolet absorber. According to claim 3,
An optical film, characterized in that the ultraviolet absorber is a benzotriazole-based ultraviolet absorber. According to claim 1 or 2,
An optical film characterized by containing methanol. A manufacturing method of an optical film for manufacturing the optical film according to claim 1 or 2,
A step of preparing a dope containing the acrylic resin (A), the elastic fine particles (B) and a resin (C) and a step of solution casting the dope to form a film,
In the dope, the content (g) of the resin (C) contains an amount that satisfies the following formula (2),
Further, in the step of preparing the dope, the elastic fine particles (B) and the resin (C) are mixed prior to mixing the acrylic resin (A).
Equation (2)
0.00001 ≤ content of resin (C) in dope unit amount (g) / sum of particle surface areas of elastic fine particles (B) contained in dope unit amount (m 2) ≤ 0.001 A polarizing plate comprising the optical film according to claim 1 or 2.

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