WO2020203833A1

WO2020203833A1 - Optical film, polarizing plate, and production method for optical film

Info

Publication number: WO2020203833A1
Application number: PCT/JP2020/014179
Authority: WO
Inventors: 治加増田
Original assignee: コニカミノルタ株式会社
Priority date: 2019-03-29
Filing date: 2020-03-27
Publication date: 2020-10-08
Also published as: JPWO2020203833A1; KR20210125543A

Abstract

This optical film includes a (meth)acrylic resin that has a glass transition temperature of at least 115°C and a weight average molecular weight of 600,000–3,000,000, residual monomers from the (meth)acrylic resin, and rubber particles. The residual monomer content of the optical film is 0.1–2 mass%.

Description

Manufacturing method of optical film, polarizing plate and optical film

The present invention relates to an optical film, a polarizing plate, and a method for producing an optical film.

Optical films such as polarizing plate protective films are used in display devices such as liquid crystal display devices and organic EL display devices. As such an optical film, a (meth) acrylic resin film such as polymethylmethacrylate may be used because it has excellent transparency, dimensional stability, and low hygroscopicity.

The (meth) acrylic resin film is usually manufactured by a melt film forming method (melt film forming method). In the melt film formation method, if the monomer remains in the (meth) acrylic resin that is the raw material, the fluidity during melt film formation is lowered, and the color tone and heat resistance of the film are lowered ( For example, Patent Documents 1 to 3), it has been studied to reduce the amount of residual monomers in a (meth) acrylic resin or an optical film.

For example, in Patent Document 1, a (meth) acrylic resin layer (I) containing a specific (meth) acrylic resin (α) and a simple adhesive layer (II) are included, and a (meth) acrylic resin layer (meth). A film in which the amount of residual maleimide-based monomer in I) is reduced to 0.01 to 0.5% by mass is disclosed.

Patent Document 2 discloses an optical film containing a specific acrylic copolymer having a residual monomer amount of 5% by mass or less, and Patent Document 3 discloses an optical film containing a specific acrylic copolymer and having a residual monomer amount of 5% by mass or less. A resin composition for an optical film having a concentration of 2000 ppm or less is disclosed.

Japanese Unexamined Patent Publication No. 2016-79194 Japanese Unexamined Patent Publication No. 2014-133858 Special Table 2014-514611

By the way, in recent years, with the demand for larger display devices, thinner and more flexible display devices, and higher functionality of polarizing plates, it is desired that optical films have high toughness (mechanical strength). However, in the melt film forming method as shown in Patent Documents 1 to 3, a high molecular weight resin cannot be used, so that the obtained optical film does not have sufficient toughness.

On the other hand, in the solution film forming method (cast film forming method), a high molecular weight resin can be used, so that a (meth) acrylic resin film having sufficient toughness can be obtained. In the solution film forming method, a dope (solution) in which a resin is dissolved in a solvent is cast on a support, and then the solvent is removed (dried) to obtain a film. However, since the (meth) acrylic resin has high hydrophobicity, it has a high affinity with a solvent, and it takes time to remove the solvent, that is, it has a problem of low drying property.

The present invention has been made in view of the above circumstances, and although it contains a (meth) acrylic resin as a main component, it can be obtained with high production efficiency due to its high drying property, and is sufficient. It is an object of the present invention to provide an optical film having toughness, a polarizing plate, and a method for producing an optical film.

The above problem can be solved by the following configuration.

The optical film of the present invention contains a (meth) acrylic resin having a glass transition temperature of 115 ° C. or higher and a weight average molecular weight of 600,000 to 3 million, and a residual monomer derived from the (meth) acrylic resin. An optical film containing rubber particles, the content of the residual monomer is 0.1 to 2% by mass with respect to the optical film.

The polarizing plate of the present invention includes a polarizing element and an optical film of the present invention arranged on at least one surface of the polarizing element.

The method for producing an optical film of the present invention is derived from a (meth) acrylic resin having a glass transition temperature of 115 ° C. or higher and a weight average molecular weight of 600,000 to 3 million, and the (meth) acrylic resin. A dope containing a residual monomer and rubber particles and having a content of the residual monomer of more than 0.1% by mass and less than 3% by mass based on the total amount of the (meth) acrylic resin and the residual monomer is obtained. The process includes a step of casting the dope onto a support and then peeling it off to obtain a film-like substance, and a step of drying the film-like substance.

According to the present invention, although it contains a (meth) acrylic resin as a main component, it can be obtained with high manufacturing efficiency due to its high drying property, and has sufficient toughness (mechanical strength). A method for producing a film, a polarizing plate and an optical film can be provided.

The present inventors have high toughness and high toughness by using a relatively high molecular weight (meth) acrylic resin and leaving a certain amount or more of residual monomers derived from the (meth) acrylic resin. It was found to have dryness.

The reason for this is not clear, but it is presumed as follows. When a film is produced by the solution film forming method (casting method), the residual monomer appropriately contained in the film-like material can form an appropriate space in the polymer matrix of the film-like material. As a result, the solvent easily moves along the space, so that the solvent easily volatilizes, and it is considered that the drying property can be improved.

On the other hand, if the content of low molecular weight components such as residual monomers is too large, the toughness of the film tends to be impaired. On the other hand, the optical film of the present invention can suppress a decrease in toughness of the film by adjusting the content of the residual monomer and containing a relatively high molecular weight (meth) acrylic resin.
Further, since the optical film is manufactured by the solution film forming method (cast method), it is not easily exposed to a high temperature such as the melt film forming method (melt method). As a result, even if the film contains an appropriate amount of residual monomer, the color tone of the film is unlikely to deteriorate as in the past. The present invention has been made based on these findings.

1. 1. Optical Film The optical film of the present invention contains a (meth) acrylic resin, a residual monomer, and rubber particles.

In the present invention, the (meth) acrylic resin does not contain residual monomers. Further, (meth) acrylic means acrylic or methacrylic.

1-1. (Meta) Acrylic Resin The glass transition temperature of the (meth) acrylic resin is preferably 115 ° C. or higher. When the Tg of the (meth) acrylic resin is 115 ° C. or higher, not only the heat resistance of the optical film can be increased, but also the drying temperature during production by the solution film forming method can be increased, so that the drying property is improved. Cheap. When the Tg of the (meth) acrylic resin is 160 ° C. or lower, for example, it is not necessary to increase the content of the structural unit derived from the monomer having a large free volume of the molecule, so that the toughness of the optical film is not easily impaired. The Tg of the (meth) acrylic resin is more preferably 120 to 150 ° C.

The glass transition temperature (Tg) of the (meth) acrylic resin can be measured using DSC (Differential Scanning Colorimetry) in accordance with JIS K7121-2012.

The glass transition temperature (Tg) of the (meth) acrylic resin can be adjusted by the type and composition of the monomer. In order to increase the glass transition temperature (Tg) of the (meth) acrylic resin, for example, the content of structural units derived from a monomer having a large free volume of a molecule may be increased.

Further, the weight average molecular weight of the (meth) acrylic resin is preferably 600,000 to 3,000,000. When the weight average molecular weight (Mw) of the (meth) acrylic resin is in the above range, sufficient mechanical strength (toughness) is imparted to the film, and film forming property and drying property are not easily impaired. From the above viewpoint, the weight average molecular weight (Mw) of the (meth) acrylic resin is more preferably 600,000 to 2,000,000.

The weight average molecular weight (Mw) can be measured in polystyrene conversion by gel permeation chromatography (GPC). Specifically, the measurement can be performed using a Tosoh HLC8220GPC) and a column (Tosoh TSK-GEL G6000HXL-G5000HXL-G5000HXL-G4000HXL-G3000HXL series). The measurement conditions may be the same as in the examples described later.

The (meth) acrylic resin is preferably a copolymer having a structural unit derived from methyl methacrylate, as long as the glass transition temperature (Tg) and the weight average molecular weight (Mw) satisfy the above ranges. Alternatively, it may be a copolymer having a structural unit derived from methyl methacrylate and a structural unit derived from a copolymerizable monomer copolymerizable with methyl methacrylate.

Examples of copolymerizable monomers copolymerizable with methyl methacrylate include
Methyl acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, t-butyl (meth) acrylate, hexyl (meth) acrylate, 2--butyl (meth) acrylate Ethylhexyl, octyl (meth) acrylate, phenyl (meth) acrylate, benzyl (meth) acrylate, 2-phenoxyethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, dicyclo (meth) acrylate (Meta) acrylates other than methyl methacrylate, such as pentanyl, isobornyl (meth) acrylate, adamantyl (meth) acrylate, cyclohexyl (meth) acrylate, and 6-membered ring lactone (meth) acrylate. Acrylic acid esters with 1 to 20 carbon atoms in the alkyl group or methacrylic acid esters with 2 to 20 carbon atoms in the alkyl group);
Aromatic vinyls such as styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene;
Alicyclic vinyls such as vinylcyclohexane;
Unsaturated nitriles such as (meth) acrylonitrile and (meth) acrylonitrile-styrene copolymer;
Unsaturated carboxylic acids such as (meth) acrylic acid, crotonic acid, (meth) acrylic acid, itaconic acid, itaconic acid monoester, maleic acid, maleic acid monoester;
Olefins such as vinyl acetate, ethylene and propylene;
Vinyl halides such as vinyl chloride, vinylidene chloride, vinylidene fluoride;
(Meta) acrylamides such as (meth) acrylamide, methyl (meth) acrylamide, ethyl (meth) acrylamide, propyl (meth) acrylamide, butyl (meth) acrylamide, tert-butyl (meth) acrylamide, phenyl (meth) acrylamide;
Unsaturated glycidyls such as (meth) glycidyl acrylate;
Maleimides such as N-phenylmaleimide, N-ethylmaleimide, N-propylmaleimide, N-cyclohexylmaleimide, and NO-chlorophenylmaleimide are included. These may be used alone or in combination of two or more.

Above all, from the viewpoint of making it easier to improve the drying property during solution film formation (making it easier to remove the solvent from the film-like material), the copolymer monomer is preferably a monomer having a large free volume of molecules. A monomer having a large free volume of a molecule tends to form a gap (space) for moving a solvent in a polymer matrix of a film-like substance in a solution film forming step. Thereby, the solvent removability, that is, the drying property can be improved.

An example of a monomer with a large free volume of a molecule is
It has an aliphatic ring such as dicyclopentanyl (meth) acrylate, isobornyl (meth) acrylate, adamantyl (meth) acrylate, cyclohexyl (meth) acrylate, and 6-membered ring lactone (meth) acrylate. ) Acrylic acid ester;
Aromatic vinyls such as styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene;
Alicyclic vinyls such as vinylcyclohexane;
Maleimides such as N-phenylmaleimide, N-ethylmaleimide, N-propylmaleimide, N-cyclohexylmaleimide, and NO-chlorophenylmaleimide are included.

Another example of a monomer with a large free volume of a molecule is
N-butyl (meth) acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, n-hexyl (meth) acrylate, lauryl (meth) acrylate, etc. (Meta) acrylic acid alkyl ester; includes (meth) acrylamides such as n-butyl (meth) acrylamide, pentyl (meth) acrylamide, hexyl (meth) acrylamide, and octyl (meth) acrylamide.

The content of the structural unit derived from the copolymerized monomer is preferably 0 to 50% by mass, preferably 10 to 40% by mass, based on 100% by mass of all the structural units constituting the (meth) acrylic resin. Is more preferable, and 10 to 30% by mass is further preferable. The type and composition of the (meth) acrylic resin monomer can be specified by ^{1 1} H-NMR.

The (meth) acrylic resin is preferably 80% by mass or more, and may be 100% by mass, based on the matrix resin component contained in the optical film.

1-2. Residual monomer The residual monomer is a residual monomer derived from a (meth) acrylic resin.

The content of the residual monomer is preferably 0.1 to 2% by mass with respect to the optical film. When the content of the residual monomer is 0.1% by mass or more, the drying property during solution film formation can be improved, so that the optical film can be obtained with high production efficiency. When the content of the residual monomer is 2% by mass or less, the toughness (mechanical strength) of the optical film does not decrease too much, so that the bendability is not easily impaired. From the above viewpoint, the content of the residual monomer is more preferably more than 0.2% by mass and 1% by mass or less with respect to the optical film.

The content and composition of residual monomers in the optical film can be measured by liquid chromatography. The measurement conditions are as follows.
(Measuring method)
-Column type (adsorbent): Silica gel-Mobile phase: Tetrahydrofuran-Column temperature: 40 ° C
・ Flow velocity: 1 ml / min

As will be described later, the content of the residual monomer can be adjusted by, for example, the content of the residual monomer in the dope when the optical film is produced by the solution film forming method. The content of the residual monomer in the dope can be adjusted by, for example, a drying treatment or purification after the polymerization of the (meth) acrylic resin.

1-3. Rubber particles The rubber particles may have a function of imparting unevenness to the surface of the optical film to impart slipperiness while imparting flexibility and toughness to the optical film.

The rubber particles are graft copolymers containing a rubber-like polymer (crosslinked polymer), that is, core-shell type rubber particles having a core portion made of a rubber-like polymer (crosslinked polymer) and a shell portion covering the core portion. Is preferable.

The glass transition temperature (Tg) of the rubber particles is preferably −10 ° C. or lower. When the glass transition temperature (Tg) of the rubber particles is −10 ° C. or lower, it is easy to impart sufficient toughness to the film. The glass transition temperature (Tg) of the rubber particles is more preferably −15 ° C. or lower, and even more preferably −20 ° C. or lower. The glass transition temperature (Tg) of the rubber particles is measured by the same method as described above.

The glass transition temperature (Tg) of the rubber particles is, for example, the monomer composition constituting the core portion or the shell portion, the mass ratio (graft ratio) between the core portion and the shell portion, and the mass ratio between the soft layer and the hard layer as described later. Can be adjusted by. In order to lower the glass transition temperature (Tg) of the rubber particles, for example, the number of carbon atoms of the alkyl group in the monomer mixture (a') constituting the acrylic rubber-like polymer (a) in the core portion is described later. It is preferable to increase the total mass ratio of the acrylic ester / copolymerizable monomer having a value of 4 or more (for example, 3 or more, preferably 4 or more and 10 or less).

Examples of rubber-like polymers include butadiene-based crosslinked polymers, (meth) acrylic-based crosslinked polymers, and organosiloxane-based crosslinked polymers. Among them, the (meth) acrylic crosslinked polymer is preferable from the viewpoint that the difference in refractive index from the (meth) acrylic resin is small and the transparency of the optical film is not easily impaired, and the acrylic crosslinked polymer (acrylic rubber-like weight) is preferable. Coalescence) is more preferable.

That is, the rubber particles are preferably an acrylic graft copolymer containing the acrylic rubber-like polymer (a). The acrylic graft copolymer containing the acrylic rubber-like polymer (a) may be a core-shell type particle having a core portion containing the acrylic rubber-like polymer (a) and a shell portion covering the core portion. preferable. Such core-shell type particles are a multi-stage polymer obtained by polymerizing at least one stage or more of a monomer mixture (b) containing a methacrylic acid ester as a main component in the presence of an acrylic rubber-like polymer (a). is there. The polymerization can be carried out by an emulsion polymerization method.

(About the core part)
The acrylic rubber-like polymer (a) constituting the core portion is a crosslinked polymer containing an acrylic acid ester as a main component. The acrylic rubber-like polymer (a) is a monomer mixture (a') containing an acrylic acid ester and an arbitrary monomer copolymerizable therewith, and two or more non-conjugated reactive double bonds per molecule. It is a crosslinked polymer obtained by polymerizing a polyfunctional monomer having (radical polymerizable group). The acrylic rubber-like polymer (a) may be obtained by mixing all of these monomers and polymerizing them, or by changing the monomer composition and polymerizing them twice or more.

The acrylic acid ester is preferably an acrylic acid alkyl ester having 1 to 12 carbon atoms of an alkyl group such as methyl acrylate and butyl acrylate. The acrylic ester may be one kind or two or more kinds. From the viewpoint of lowering the glass transition temperature of the rubber particles to −15 ° C. or lower, the acrylic acid ester preferably contains at least an acrylic acid alkyl ester having 4 to 10 carbon atoms.

The content of the acrylic acid ester is preferably 50 to 100% by mass, more preferably 60 to 99% by mass, and 70 to 99% by mass with respect to 100% by mass of the monomer mixture (a'). Is even more preferable. When the content of the acrylic acid ester is 50% by weight or more, it is easy to impart sufficient toughness to the film.

Further, from the viewpoint of facilitating the glass transition temperature of the rubber particles to -10 ° C. or lower, the acrylic acid alkyl ester having an alkyl group having 4 or more carbon atoms in the monomer mixture (a') / other copolymerizable monomer The total mass ratio is preferably 3 or more, and more preferably 4 or more and 10 or less.

Examples of copolymerizable monomers include methacrylic ester such as methyl methacrylate; styrenes such as styrene and methylstyrene; unsaturated nitriles such as acrylonitrile and methacrylnitrile.

Examples of polyfunctional monomers include allyl (meth) acrylate, triallyl cyanurate, triallyl isocyanurate, diallyl phthalate, diallyl malate, divinyl adipate, divinylbenzene, ethylene glycol di (meth) acrylate, and diethylene glycol (meth). Includes acrylates, triethylene glycol di (meth) acrylates, trimethyl roll propanthry (meth) acrylates, tetromethylol methanetetra (meth) acrylates, dipropylene glycol di (meth) acrylates, and polyethylene glycol di (meth) acrylates.

The content of the polyfunctional monomer is preferably 0.05 to 10% by mass, more preferably 0.1 to 5% by mass, based on 100% by mass of the total of the monomer mixture (a'). When the content of the polyfunctional monomer is 0.05% by mass or more, the degree of cross-linking of the obtained acrylic rubber-like polymer (a) is easily increased, so that the hardness and rigidity of the obtained film are not excessively impaired. When it is 10% by mass or less, the toughness of the film is not easily impaired.

(About the shell part)
The polymer of the monomer mixture (b) constituting the shell portion is a graft component for the acrylic rubber-like polymer (a). The monomer mixture (b) contains a methacrylic acid ester as a main component.

The methacrylic acid ester is preferably an alkyl methacrylate ester having 1 to 12 carbon atoms of an alkyl group such as methyl methacrylate. The methacrylic acid ester may be one kind or two or more kinds.

The content of the methacrylic acid ester is preferably 50% by mass or more with respect to 100% by mass of the monomer mixture (b). When the content of the methacrylic acid ester is 50% by mass or more, it is possible to make it difficult to reduce the hardness and rigidity of the obtained film. Further, from the viewpoint of enhancing the affinity with a solvent such as methylene chloride, the content of the methacrylic acid ester is more preferably 70% by mass or more, more preferably 80% by mass or more, based on 100% by mass of the monomer mixture (b). Is more preferable.

The monomer mixture (b) may further contain other monomers, if necessary. Examples of other monomers include acrylic acid esters such as methyl acrylate, ethyl acrylate, n-butyl acrylate; benzyl (meth) acrylate, dicyclopentanyl (meth) acrylate, phenoxy (meth) acrylate. Includes (meth) acrylic monomers having an alicyclic structure such as ethyl, a heterocyclic structure or an aromatic group (ring structure-containing (meth) acrylic monomer).

(About rubber particles (acrylic graft copolymer))
In the example of the acrylic graft copolymer, at least 95 to 25 parts by mass of the monomer mixture containing methacrylic acid ester as a main component (b) in the presence of 5 to 75 parts by mass of the acrylic rubber-like polymer (a). A polymer polymerized in one step is included.

The acrylic graft copolymer may further contain a hard polymer inside the acrylic rubber-like polymer (a), if necessary. Such an acrylic graft copolymer can be obtained through the following polymerization steps (I) to (III).
(I) Monomer mixture (c1) consisting of 40 to 100% by mass of methacrylic acid ester and 60 to 0% by mass of other monomers copolymerizable therewith, and 0.01 to 10 parts by mass of polyfunctional monomer (monomer mixture). Step of polymerizing (with respect to a total of 100 parts by mass of (c1)) to obtain a hard polymer (II) From 60 to 100% by mass of the acrylic acid ester and 0 to 40% by mass of other monomers copolymerizable therewith. Step of polymerizing 0.1 to 5 parts by mass of the monomer mixture (a1) and 0.1 to 5 parts by mass of the polyfunctional monomer (relative to a total of 100 parts by mass of the monomer mixture (a1)) to obtain a soft polymer (III) Methacrylate ester A total of 100 parts by mass of a monomer mixture (b1) consisting of 60 to 100% by mass and 40 to 0% by mass of another monomer copolymerizable therewith, and 0 to 10 parts by mass of a polyfunctional monomer (monomer mixture (b1)). To obtain a hard polymer by polymerizing

Other polymerization steps may be further included between the polymerization steps (I) to (III).

The acrylic graft copolymer may be further obtained through the polymerization step (IV).
(IV) Monomer mixture (b2) consisting of 40 to 100% by mass of methacrylic acid ester, 0 to 60% by mass of acrylic acid ester, and 0 to 5% by mass of other copolymerizable monomers, and 0 to 10 polyfunctional monomers. A hard polymer is obtained by polymerizing parts by mass (relative to 100 parts by mass of the monomer mixture (b2)).

As the methacrylic acid ester, acrylic acid ester, other copolymerizable monomer, and polyfunctional monomer used in each step, the same ones as described above can be used.

The soft layer can impart shock absorption to the optical film. Examples of the soft layer include a layer made of an acrylic rubber-like polymer (a) containing an acrylic acid ester as a main component. The hard layer makes it difficult to impair the toughness of the optical film, and can suppress the coarsening and agglomeration of the particles during the production of the rubber particles. Examples of the hard layer include a layer made of a polymer containing a methacrylic acid ester as a main component.

The graft ratio (mass ratio of the graft component to the acrylic rubber-like polymer (a)) in the acrylic graft copolymer is preferably 10 to 250%, more preferably 25 to 200%, and 40. It is more preferably to 200%, and even more preferably 60 to 150%. When the graft ratio is 10% or more, the ratio of the shell portion is not too small, so that the hardness and rigidity of the film are not easily impaired. When the graft ratio of the acrylic graft copolymer is 250% or less, the proportion of the acrylic rubber-like polymer (a) is not too small, so that the toughness and brittleness improving effect of the film are not easily impaired.

The graft ratio of the acrylic graft copolymer is measured by the following method.
1) Dissolve 2 g of the acrylic graft copolymer in 50 ml of methyl ethyl ketone and centrifuge at a rotation speed of 30,000 rpm and a temperature of 12 ° C. for 1 hour using a centrifuge (Cat. And the soluble component (centrifugal separation work is set 3 times in total).
2) The graft ratio is calculated by applying the weight of the obtained insoluble matter to the following formula.
Graft ratio (%) = [{(weight of methyl ethyl ketone insoluble matter)-(weight of acrylic rubber-like polymer (a))} / (weight of acrylic rubber-like polymer (a))] × 100

The average particle size of the rubber particles is preferably 100 to 400 nm, more preferably 150 to 300 nm. When the average particle size is 100 nm or more, sufficient toughness is easily imparted to the film, and when it is 400 nm or less, the transparency of the film is unlikely to decrease.

The average particle size of the rubber particles is specified as an average value of the equivalent circle diameters of 100 particles obtained by SEM or TEM photography of the film surface and sections. The equivalent circle diameter can be obtained by converting the projected area of the particles obtained by photographing into the diameter of a circle having the same area. At this time, the rubber particles (acrylic graft copolymer) observed by SEM observation and / or TEM observation at a magnification of 5000 times are used for calculating the average particle size. The average particle size of the rubber particles (acrylic graft copolymer) in the dispersion can be measured by a zeta potential / particle size measurement system (ELSZ-2000ZS manufactured by Otsuka Electronics Co., Ltd.).

The content of rubber particles is preferably 5 to 40% by mass with respect to the (meth) acrylic resin. When the content of the rubber particles is 5% by mass or more, not only is it easy to impart sufficient toughness to the film, but also unevenness can be formed on the surface to impart slipperiness. If it is 40% by mass or less, the haze does not rise too much. From the above viewpoint, the content of the rubber particles is more preferably 7 to 30% by mass and further preferably 8 to 25% by mass with respect to the (meth) acrylic resin.

1-4. Other Components The optical film of the present invention may further contain other components as long as the effects of the present invention are not impaired. Examples of other components include fine particles, residual solvents, UV absorbers, antioxidants and the like.

(Fine particles)
The optical film of the present invention may further contain organic fine particles other than inorganic fine particles or rubber particles as a matting agent from the viewpoint of further enhancing slipperiness.

Examples of inorganic materials constituting the inorganic fine particles include silicon dioxide (SiO ₂ ), titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, and hydrated calcium silicate. Includes calcium, aluminum silicate, magnesium silicate, and calcium phosphate. Of these, silicon dioxide is preferred in order to reduce the increase in haze of the resulting film. The organic fine particles may be resin particles having a glass transition temperature (Tg) of preferably 80 ° C. or higher.

(Organic solvent)
Since the optical film of the present invention is produced by the solution casting method as described later, it may contain a residual solvent derived from the doping solvent used in the solution casting method.

The amount of residual solvent is preferably 700 ppm or less, more preferably 30 to 700 ppm with respect to the optical film. The content of the residual solvent can be adjusted by the drying conditions of the dope cast on the support in the process of manufacturing the optical film described later.

The content of the residual solvent in the optical film can be measured by headspace gas chromatography. In the headspace gas chromatography method, a sample is sealed in a container, heated, and the gas in the container is promptly injected into a gas chromatograph with the container filled with volatile components, and mass spectrometry is performed to identify the compound. The volatile components are quantified while doing so. In the headspace method, it is possible to observe all peaks of volatile components by gas chromatography, and by using an analytical method that utilizes electromagnetic interactions, it is possible to quantify volatile substances and monomers with high accuracy. It can be done at the same time.

1-5. Physical properties of optical film (dryness)
As described above, the optical film has high drying property. Specifically, the amount of residual solvent in the optical film after the drying test represented by the following formula is preferably 0.25% or less, and more preferably 0.1% or less.
Residual solvent amount (%) = [(YX) * 100] / Y

The dryness of the optical film can be measured by the following method.
First, the optical film is allowed to stand at room temperature for 2 hours, and then cut into two 10 cm square squares to obtain test pieces. One of the test pieces is dried in an oven at 140 ° C. for 15 minutes, then weighed and the weight is defined as X. The other test piece is dried in an oven at 110 ° C. for 60 minutes, then weighed and the weight is defined as Y. Then, the measured value is applied to the above formula to calculate the residual solvent amount (%).

The dryness of the optical film can be adjusted by adjusting the monomer composition of the (meth) acrylic resin and the content of residual monomers. In order to improve the dryness of the optical film, for example, it is preferable to increase the content of the monomer having a large free volume of the molecule constituting the (meth) acrylic resin or increase the content of the residual monomer.

(Haze)
The optical film of the present invention preferably has high transparency. The haze of the optical film is preferably 4.0% or less, more preferably 2.0% or less, and even more preferably 1.0% or less. Haze can be measured according to JIS K-6714 with a haze meter (HGM-2DP, Suga Test Instruments) at 25 ° C. and 60% RH for a sample of 40 mm × 80 nm.

(Phase difference Ro and Rt)
From the viewpoint of using the optical film of the present invention as a retardation film for IPS mode, for example, the in-plane retardation Ro measured in an environment with a measurement wavelength of 550 nm and 23 ° C. and 55% RH is 0 to 10 nm. It is preferably 0 to 5 nm, and more preferably 0 to 5 nm. The phase difference Rt in the thickness direction of the optical film of the present invention is preferably −20 to 20 nm, and more preferably −10 to 10 nm.

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

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

Ro and Rt can be measured by the following methods.
1) The optical film of the present invention is humidity-controlled for 24 hours in an environment of 23 ° C. and 55% RH. The average refractive index of this film is measured with an Abbe refractometer, and the thickness d is measured with a commercially available micrometer.
2) The retardation Ro and Rt of the film after humidity control at a measurement wavelength of 550 nm were measured at 23 ° C. and 55% RH using an automatic birefringence meter Axoscan (Axo Scan Mueller Matrix Matrix Polarimeter), respectively. Measure in the environment.

The phase difference Ro and Rt of the optical film of the present invention can be adjusted by, for example, the type of (meth) acrylic resin. In order to reduce the phase difference Ro and Rt of the optical film, a (meth) acrylic resin that does not easily generate a phase difference due to stretching is used (for example, a structural unit derived from a monomer having negative birefringence and positive birefringence are used. It is preferable to set the monomer ratio so that the phase difference can be offset with the structural unit derived from the monomer.

(Thickness)
The thickness of the optical film of the present invention can be, for example, 5 to 100 μm, preferably 5 to 40 μm.

2. Manufacturing Method of Optical Film The manufacturing method of the optical film of the present invention is not particularly limited, but the solution casting method (cast method) is used from the viewpoint that there are few restrictions on the materials that can be used, such as the use of a high molecular weight resin. preferable.

That is, the optical film of the present invention has 1) a step of obtaining a dope containing at least a (meth) acrylic resin, a residual monomer, rubber particles, and a solvent, and 2) flowing the obtained dope onto a support. It can be produced through a step of spreading, drying and peeling to obtain a film-like substance, and 3) a step of further drying the obtained film-like substance.

About step 1) In this step, for example, a (meth) acrylic resin, a residual monomer, and rubber particles can be dissolved or dispersed in a solvent to obtain a doping. The (meth) acrylic resin, residual monomer and rubber particles are as described above.

The solvent used for the dope contains at least an organic solvent (good solvent) capable of dissolving the (meth) acrylic resin. Examples of good solvents include chlorine-based organic solvents such as methylene chloride; non-chlorine-based organic solvents such as methyl acetate, ethyl acetate, acetone and tetrahydrofuran. Of these, methylene chloride is preferable.

The solvent used for doping may further contain a poor solvent. Examples of poor solvents include linear or branched aliphatic alcohols having 1 to 4 carbon atoms. When the ratio of alcohol in the dope is high, the film-like material is likely to gel and peel off from the metal support. Examples of the linear or branched aliphatic alcohol having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, and tert-butanol. Of these, ethanol is preferable because of its stability of doping, relatively low boiling point, and good drying property.

The dope may be prepared by directly adding the (meth) acrylic resin, the residual monomer, and the rubber particles to the solvent and mixing them; or using the (meth) acrylic resin as the solvent. A resin solution in which the residual monomer is dissolved and a rubber particle dispersion in which rubber particles are dispersed in a solvent may be prepared and mixed.

The content of the residual monomer in the dope exceeds 0.1% by mass with respect to the total amount of the (meth) acrylic resin and the residual monomer from the viewpoint of improving the drying property of the film-like substance in the step 3) (drying step). It is preferably less than 3% by mass. This is because when the content of the residual monomer in the dope is within the above range, the content of the residual monomer in the obtained optical film can be easily adjusted within the above range. From the above viewpoint, the content of the residual monomer in the dope is more preferably 0.12 to 2.8% by mass with respect to the total amount of the (meth) acrylic resin and the residual monomer, and 0.24 to 1. More preferably, it is 2% by mass. The content of residual monomers in the dope can be measured by liquid chromatography.

The content of the residual monomer in the dope may be adjusted by any method, for example, by performing a drying treatment after the polymerization of the (meth) acrylic resin; the raw material of the (meth) acrylic resin is purified and adjusted. May be good. When the drying treatment is performed, the drying temperature is preferably higher than, for example, the polymerization temperature. The purification method is not particularly limited, and may be, for example, a reprecipitation method.

The reprecipitation method is a method of reducing the amount of monomers remaining in the raw material by dropping a solution of the raw material of the (meth) acrylic resin in a good solvent into a poor solvent. As the poor solvent used in the reprecipitation method, the same ones as those mentioned above as the poor solvent can be used, and alcohols such as methanol and ethanol are preferable. As the good solvent used in the reprecipitation method, the same solvent as those mentioned above as the good solvent can be used, and methyl ethyl ketone or the like is preferable.

The purification conditions by the reprecipitation method (number of purifications, etc.) may be such that the content of the residual monomer remaining in the finally obtained optical film is within the above range; for that purpose, for example, in doping. It is preferable to carry out under the condition that the content of the residual monomer is within the above range.

About step 2) In this step, the obtained dope is cast on the support. Doping can be cast by discharging from a casting die.

Next, after the solvent in the dope cast on the support is appropriately evaporated (after drying), it is peeled off from the support to obtain a film-like substance.

The residual solvent amount of the doping when peeling from the support (the residual solvent amount of the film-like substance at the time of peeling) is preferably, for example, 25% by mass or more, more preferably 30 to 37% by mass, and 30. It is more preferably to 35% by mass. When the amount of the residual solvent at the time of peeling is 25% by mass or more, the solvent is likely to be volatilized at once from the film-like material after peeling. Further, when the amount of the residual solvent at the time of peeling is 37% by mass or less, it is possible to prevent the film-like material from being excessively stretched due to peeling.

The residual solvent amount of the doping at the time of peeling is defined by the following formula. The same applies to the following.
Residual solvent amount of doping (mass%) = (mass before heat treatment of doping-mass after heat treatment of doping) / mass after heat treatment of doping × 100
The heat treatment for measuring the amount of residual solvent means a heat treatment at 140 ° C. for 15 minutes.

The amount of residual solvent at the time of peeling can be adjusted by adjusting the drying temperature and drying time of the doping on the support, the temperature of the support, and the like.

About step 3) In this step, the obtained film-like material is dried.

Drying may be performed in one step or in multiple steps. Further, the drying may be carried out while stretching, if necessary.

For example, the drying of the film-like material includes a step of peeling from the support in the step 2) and then drying before stretching (initial drying step), a stretching step, and a step of drying after stretching (post-drying step). May have.

(Initial drying process)
The drying temperature before stretching (initial drying temperature) can be higher than the stretching temperature. Specifically, when the glass transition temperature of the (meth) acrylic resin is Tg, it is preferably Tg (° C.) or higher, and more preferably (Tg + 10) to (Tg + 50) ° C. When the initial drying temperature is Tg (° C.) or higher, preferably (Tg + 10) ° C. or higher, the solvent is easily volatilized appropriately, so that the transportability (handleability) is easily improved, and when it is (Tg + 50) ° C. or lower, the solvent Is not excessively volatilized, so that the stretchability in the subsequent stretching step is not easily impaired.

The initial drying temperature is (a) when drying with a non-contact heating type while transporting with a tenter stretching machine or roller, the ambient temperature such as the temperature inside the stretching machine or hot air temperature, and (b) drying with a contact heating type such as a hot roller. In the case of making the temperature, it can be measured as either the temperature of the contact heating portion or (c) the surface temperature of the film-like material (surface to be dried). Above all, it is preferable to measure (a) atmospheric temperature such as hot air temperature.

(Stretching process)
Stretching may be performed according to the required optical characteristics, and is preferably stretched in at least one direction, and stretches in two directions orthogonal to each other (for example, the width direction (TD direction) of the film-like object and orthogonal to it. Biaxial stretching in the transport direction (MD direction)) may be performed.

The draw ratio can be 1.01 to 2 times from the viewpoint of using the optical film as a retardation film for IPS, for example. The stretch ratio is defined as (size of the film after stretching in the stretching direction) / (size of the film before stretching in the stretching direction). When biaxial stretching is performed, it is preferable to set the stretching ratio in each of the TD direction and the MD direction.

The in-plane slow-phase axial direction of the optical film (the direction in which the refractive index is maximized in-plane) is usually the direction in which the draw ratio is maximized.

The drying temperature (stretching temperature) at the time of stretching is preferably Tg (° C.) or higher, and is preferably (Tg + 10) to (Tg + 50), when the glass transition temperature of the (meth) acrylic resin is Tg, as described above. More preferably, it is ° C. When the stretching temperature is Tg (° C.) or higher, preferably (Tg + 10) ° C. or higher, the solvent is likely to volatilize appropriately, so that the stretching tension can be easily adjusted to an appropriate range, and when it is (Tg + 50) ° C. or lower, the solvent Does not volatilize too much, so stretchability is not easily impaired. The stretching temperature can be, for example, 115 ° C. or higher. As for the stretching temperature, it is preferable to measure the ambient temperature such as (a) the temperature inside the stretching machine, as described above.

The amount of residual solvent in the film-like material at the start of stretching is preferably about the same as the amount of residual solvent in the film-like material at the time of peeling, for example, preferably 20 to 30% by mass, and 25 to 30% by mass. More preferably.

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

(Post-drying process)
From the viewpoint of further reducing the amount of residual solvent, it is preferable to further dry (post-dry) the film-like substance obtained after stretching. For example, it is preferable that the film-like substance obtained after stretching is further dried while being conveyed by a roll or the like.

The post-drying temperature (drying temperature when not stretched) is preferably (Tg-50) to (Tg-30) ° C., where Tg is the glass transition temperature of the (meth) acrylic resin, and is preferably (Tg-). It is more preferably 40) to (Tg-30). When the post-drying temperature is (Tg-50) ° C. or higher, it is easy to sufficiently volatilize and remove the solvent from the film-like material after stretching, and when it is (Tg-30) ° C. or lower, the film-like material is highly deformed. Can be suppressed. As the post-drying temperature, it is preferable to measure the ambient temperature such as (a) hot air temperature as described above.

In the present invention, the film-like substance contains a predetermined amount of residual monomer. Since such a film-like substance may have a micro space (gap) in which the solvent can move, it is easy to volatilize and remove the solvent from the film-like substance in the drying step, particularly in the initial drying step and the post-drying step. sell. Thereby, the drying speed can be increased as compared with the conventional one, or the drying speed can be equal to or higher than the conventional one even at a low drying temperature.

In this way, the optical film of the present invention can be obtained. The optical film of the present invention is used as an optical film in various display devices such as a liquid crystal display device and an organic EL display device. Examples of the optical film include a polarizing plate protective film (including a retardation film and the like), a transparent substrate, and a light diffusing film, and a polarizing plate protective film is preferable.

3. 3. Polarizing Plate The polarizing plate of the present invention has a polarizing element, an optical film of the present invention, and an adhesive layer arranged between them.

3-1. Polarizer A polarizing element is an element that allows only light on a plane of polarization in a certain direction to pass through, and is a polyvinyl alcohol-based polarizing film. The polyvinyl alcohol-based polarizing film includes a polyvinyl alcohol-based film dyed with iodine and a film obtained by dyeing a dichroic dye.

The polyvinyl alcohol-based polarizing film may be a film obtained by uniaxially stretching a polyvinyl alcohol-based film and then dyeing it with iodine or a bicolor dye (preferably a film further subjected to a durability treatment with a boron compound); polyvinyl. An alcohol-based film may be a film that has been dyed with iodine or a bicolor dye and then uniaxially stretched (preferably a film that has been further subjected to a durability treatment with a boron compound). The absorption axis of the polarizer is usually parallel to the maximum stretching direction.

For example, the ethylene unit content described in JP-A-2003-248123, JP-A-2003-342322, etc. is 1 to 4 mol%, the degree of polymerization is 2000 to 4000, and the saponification degree is 99.0 to 99.99 mol%. Ethylene-modified polyvinyl alcohol is used.

The thickness of the polarizer is preferably 5 to 30 μm, and more preferably 5 to 20 μm in order to reduce the thickness of the polarizing plate.

3-2. Optical film The optical film of the present invention is arranged on at least one surface of the polarizer (at least the surface facing the liquid crystal cell). The optical film can function as a polarizing plate protective film.

When the optical film of the present invention is arranged on only one surface of the polarizer, another optical film may be arranged on the other surface of the polarizer. Examples of other optical films include commercially available cellulose ester films (eg, Konica Minolta Tuck KC8UX, KC5UX, KC4UX, KC8UCR3, KC4SR, KC4BR, KC4CR, KC4DR, KC4FR, KC4KR, KC8UY, KC6UY, KC4UY, KC6UY, KC4UY KC8UY-HA, KC2UA, KC4UA, KC6UA, KC8UA, KC2UAH, KC4UAH, KC6UAH, manufactured by Konica Minolta Co., Ltd. The above includes Fuji Film Co., Ltd.).

The thickness of the other optical film can be, for example, 5 to 100 μm, preferably 40 to 80 μm.

3-3. Adhesive layer The adhesive layer is located between the optical film (or other optical film) and the polarizer. The thickness of the adhesive layer can be, for example, 0.01 to 10 μm, preferably about 0.03 to 5 μm.

3-4. Method for manufacturing a polarizing plate The polarizing plate of the present invention can be obtained by laminating a polarizing element and an optical film of the present invention via an adhesive. The adhesive can be a fully saponified polyvinyl alcohol aqueous solution (water glue) or an active energy ray-curable adhesive. The active energy ray-curable adhesive may be any of a photoradical polymerization type composition utilizing photoradical polymerization, a photocationic polymerization type composition utilizing photocationic polymerization, or a combination thereof.

4. Liquid crystal display device The liquid crystal display device of the present invention includes a liquid crystal cell, a first polarizing plate arranged on one surface of the liquid crystal cell, and a second polarizing plate arranged on the other surface of the liquid crystal cell.

The display modes of the liquid crystal cells are, for example, STN (Super-Twisted Nematic), TN (Twisted Nematic), OCB (Optically Compensated Bend), HAN (Hybridaligned Nematic), VA (Vertical Alignment, MVA (Multi-domain Vertical Alignment), PVA). (Patterned Vertical Alignment)), IPS (In-Plane-Switching), etc. Of these, the VA (MVA, PVA) mode and the IPS mode are preferable.

One or both of the first and second polarizing plates are the polarizing plates of the present invention. The polarizing plate of the present invention is preferably arranged so that the optical film of the present invention is on the liquid crystal cell side.

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

1. 1. Optical film material 1-1. Preparation of resin composition (mixture of (meth) acrylic resin and residual monomer)) <Preparation of resin composition 1>
(polymerization)
Deionized water was put into a SUS polymerization reactor equipped with a stirrer, a dispersion stabilizer and a dispersion stabilizer were added, and the mixture was stirred and dissolved. Further, in a container equipped with another stirrer, methyl methacrylate (MMA) and n-butyl methacrylate (BA) are contained in a monomer mixture containing the mass ratios shown in Table 1 as a polymerization initiator, 2,2'-. Azobisisobutyronitrile, n-octyl mercaptan as a chain transfer agent, and stearyl alcohol as a release agent were added, and the mixture was stirred and dissolved. The monomer mixture in which the polymerization initiator, chain transfer agent and mold release agent thus obtained were dissolved was put into a SUS polymerization reaction apparatus equipped with the above-mentioned stirrer, stirred while replacing nitrogen, and then at 80 ° C. Was heated to polymerize. After completion of the polymerization, heat treatment was performed at 115 ° C. for 10 minutes to complete the polymerization. The obtained beaded polymer was filtered and washed with water, and then dried to obtain a polymerization product (copolymer of methyl methacrylate and n-butyl acrylate).

(Reprecipitation)
The resulting polymerization product was then dissolved in a good solvent, methyl ethyl ketone. The obtained solution was added dropwise to methanol, which is a poor solvent, and reprecipitated. Then, decantation was performed to remove water, and a purified polymerization product (resin composition) was collected.

<Preparation of resin compositions 3 to 8 and 10 to 14>
Resins except that the composition of the monomers used in the polymerization process was changed as shown in Table 1 and the number of reprecipitations was changed so that the amount of residual monomers in the obtained resin composition was the amount shown in Table 1. A resin composition was obtained in the same manner as in Composition 1.

<Preparation of resin composition 9>
Cyclopentene was further added to the resin composition 8 so that the amount of the monomers in the resin composition was as shown in Table 1 to obtain the resin composition 9.

The glass transition temperature (Tg), weight average molecular weight (Mw), and amount of residual monomer (amount with respect to the (meth) acrylic resin) of the (meth) acrylic resin contained in the obtained resin composition are determined by the following method. It was measured.

[Glass transition temperature (Tg)]
The obtained resin composition was repeatedly subjected to the above-mentioned reprecipitation to separate and recover a (meth) acrylic resin containing no monomer.
Then, the glass transition temperature of the (meth) acrylic resin separated and recovered was measured using DSC (Differential Scanning Colorimetry) according to JIS K 7121-2012.

[Weight average molecular weight (Mw)]
The weight average molecular weight (Mw) of the (meth) acrylic resin separated and recovered as described above was measured by gel permeation chromatography (HLC8220GPC manufactured by Tosoh Corporation) and column (TSK-GEL G6000HXL-G5000HXL-G5000HXL-G4000HXL-G3000HXL series manufactured by Tosoh Corporation). Was measured using. 20 mg ± 0.5 mg of the sample was dissolved in 10 ml of tetrahydrofuran and filtered through a 0.45 mm filter. 100 ml of this solution was injected into a column (temperature 40 ° C.), measured at a detector RI temperature of 40 ° C., and a styrene-converted value was used.

[Amount of residual monomer in resin composition]
The amount (amount with respect to the (meth) acrylic resin) and composition of the residual monomer in the obtained resin composition was measured by a liquid chromatography method. The measurement conditions were as follows.
(Measurement condition)
-Column type (adsorbent): Silica gel-Mobile phase: Tetrahydrofuran-Column temperature: 40 ° C
・ Flow velocity: 1 ml / min

Table 1 shows the composition and physical properties of the resin compositions 1 to 14.

The abbreviations in the table are shown below.
MMA: Methyl methacrylate MA: Methyl acrylate LMA: Lauryl methacrylate BA: n-butyl acrylate EHA: 2-ethylhexyl acrylate SMA: Stearyl methacrylate CHMA: Cyclohexyl methacrylate IMA: Isobornyl methacrylate N-EMI: N- Ethylmaleimide N-PMI: N-phenylmaleimide N-CHMI: N-cyclohexylmaleimide

1-2. Rubber particles Rubber particles C1: Acrylic rubber particles M-210 (core part: acrylic rubber-like polymer with a multi-layer structure, shell part: methacrylic acid ester-based polymer containing methyl methacrylate as a main component, core-shell type Rubber particles, Tg: about -10 ° C, average particle size: 220 nm)

The average particle size of the rubber particles C1 was measured by the following method.

(Average particle size)
The dispersed particle size of the rubber particles C1 in the obtained dispersion was measured by a zeta potential / particle size measuring system (ELSZ-2000ZS manufactured by Otsuka Electronics Co., Ltd.). The average particle size of the rubber particles measured using the zeta potential / particle size measurement system (ELSZ-2000ZS manufactured by Otsuka Electronics Co., Ltd.) is the average particle size of the rubber particles C1 measured by TEM observation of the optical film. It is almost the same as.

2. Fabrication and evaluation of optical film <Preparation of optical film 1>
(Preparation of rubber particle dispersion)
20 parts by mass of rubber particles C1 and 380 parts by mass of methylene chloride were stirred and mixed with a dissolver for 50 minutes, and then dispersed under a milder disperser (manufactured by Pacific Machinery & Engineering Co., Ltd.) at 1500 rpm. , A rubber particle dispersion was obtained.

(Preparation of doping)
A dope having the following composition was prepared. First, methylene chloride and ethanol were added to the pressurized dissolution tank. Next, the resin composition 1 (a mixture of a (meth) acrylic resin and a residual monomer) was charged into the pressure dissolution tank with stirring. It was then heated to 60 ° C. and completely dissolved with stirring. The heating temperature was raised from room temperature at 5 ° C./min, melted in 30 minutes, and then lowered at 3 ° C./min. The resulting solution was filtered to give a dope.
Resin composition 1 (mixture of (meth) acrylic resin and residual monomer): 100 parts by mass Methylene chloride: 504 parts by mass Ethanol; 64 parts by mass Rubber particle dispersion: 384 parts by mass

(Film formation)
The dope was then uniformly cast on the stainless steel belt support at a temperature of 31 ° C. and a width of 1800 mm using an endless belt casting device. The temperature of the stainless steel belt was controlled to 28 ° C. The transport speed of the stainless steel belt was 20 m / min.
On the stainless belt support, the solvent was evaporated until the amount of residual solvent in the cast film was 30%. Then, it was peeled from the stainless belt support at a peeling tension of 128 N / m. While transporting the peeled film with a large number of rolls, it was dried (initially dried) at (Tg + 20) ° C. (Tg indicates Tg of (meth) acrylic resin, the same applies hereinafter), and then the obtained film-like film. The product was stretched 1.2 times in the width direction under the condition of (Tg + 10) ° C. in a tenter. Then, the film was further dried (post-dried) at (Tg-30) ° C. while being conveyed by a roll, and the end portion sandwiched between the tenter clips was slit with a laser cutter and wound up to obtain an optical film having a film thickness of 40 μm.

<Optical film 2-14>
An optical film was produced in the same manner as the optical film 1 except that the resin composition 1 was changed to the resin composition shown in Table 2.

The amount of residual monomer, glass transition temperature (Tg), dryness and bendability of the obtained optical films 1 to 14 were evaluated by the following methods, respectively.

[Amount of residual monomer]
The content of residual monomer in the obtained optical film was measured by liquid chromatography. The measurement conditions were the same as described above.

[Glass transition temperature (Tg)]
The glass transition temperature (Tg) of the obtained optical film was measured according to JIS K 7121-2012 in the same manner as described above.

[Dryness]
The obtained optical film was allowed to stand at room temperature for 2 hours, and then cut into two 10 cm square squares to prepare test pieces. One of the test pieces was dried in an oven at 140 ° C. for 15 minutes, then weighed and the weight was defined as X. The other test piece was dried in an oven at 110 ° C. for 60 minutes, then weighed and the weight was defined as Y. Then, the measured value was applied to the following formula to calculate the residual solvent amount (%) after drying at 140 ° C. for 15 minutes.
Residual solvent amount (%) = [(YX) * 100] / Y
Dryness was evaluated based on the amount of residual solvent obtained.
5: Residual solvent amount is 0.1% or less 4: Residual solvent amount is more than 0.1% and 0.2% or less 3: Residual solvent amount is more than 0.2% and 0.3% or less 2: Residual solvent amount is 0 .3% or more and 0.5% or less 1: If the residual solvent amount is more than 0.5% and 3 or more, it is judged to be good.

[Bendability]
The obtained optical film was cut into a width of 15 mm and a length of 150 mm to obtain a test piece. After allowing this test piece to stand at a temperature of 25 ° C. and a relative humidity of 65% RH for 1 hour or more, a MIT bending test is performed in accordance with JIS P8115: 2001 under a load of 500 g until the test piece breaks. The number of times was measured. The MIT bending test was performed using a folding resistance tester (manufactured by Tester Sangyo Co., Ltd., MIT, BE-201 type, bending radius of curvature 0.38 mm). Then, it was evaluated according to the following evaluation criteria.
⊚: 2000 times or more ○: 1500 times or more and less than 2000 times Δ: 500 times or more and less than 1500 times ×: less than 500 times ○ If it is more than that, it was judged to be good.

Table 2 shows the configurations and evaluation results of the optical films 1 to 14. The amount of residual solvent in the obtained optical films 1 to 14 was measured by the above-mentioned headspace gas chromatography, and all of them were in the range of 30 to 600 mass ppm.

As shown in Table 2, the optical films 2, 4, 5, 7, 11, 12 and 14 having a residual monomer content of 0.1 to 2% by mass all have good drying properties and bendability. It can be seen that it has.

In particular, it can be seen that the drying property is particularly enhanced when the content of the residual monomer derived from the (meth) acrylic resin is more than 0.2% by mass (comparison between the optical films 2 and 11).

On the other hand, it can be seen that the optical films 6 and 10 having a residual monomer content of less than 0.1% by mass have low drying properties. It is considered that this is because if the content of the residual monomer is too small, it is difficult to obtain the action of disturbing the orientation of the resin molecules by the residual monomer. Further, it can be seen that the optical films 1 and 13 having a residual monomer content of more than 2% by mass have low bendability. It is considered that this is because the amount of residual monomer is too large and the flexibility is impaired.

This application claims priority based on Japanese Patent Application No. 2019-067499 filed on March 29, 2019. All the contents described in the application specification are incorporated in the application specification.

According to the present invention, it is possible to provide an optical film which can be obtained with high production efficiency by having high drying property and has sufficient toughness even though it contains a (meth) acrylic resin as a main component. Can be done.

Claims

A (meth) acrylic resin having a glass transition temperature of 115 ° C. or higher and a weight average molecular weight of 600,000 to 3 million.
Residual monomer derived from the (meth) acrylic resin and
An optical film containing rubber particles
The content of the residual monomer is 0.1 to 2% by mass with respect to the optical film.
Optical film.
The content of the residual monomer is more than 0.2% by mass and 1% by mass or less with respect to the optical film.
The optical film according to claim 1.
The (meth) acrylic resin is a copolymer containing a structural unit derived from methyl methacrylate and a structural unit derived from a monomer copolymerizable therewith.
The optical film according to claim 1 or 2.
Polarizer and
The optical film according to any one of claims 1 to 3, which is arranged on at least one surface of the polarizer.
Polarizer.
It contains a (meth) acrylic resin having a glass transition temperature of 115 ° C. or higher and a weight average molecular weight of 600,000 to 3 million, a residual monomer derived from the (meth) acrylic resin, and rubber particles.
A step of obtaining a dope in which the content of the residual monomer is more than 0.1% by mass and less than 3% by mass with respect to the total amount of the (meth) acrylic resin and the residual monomer.
A step of casting the dope on a support and then peeling it off to obtain a film-like substance.
Including a step of drying the film-like material.
A method for manufacturing an optical film.
The content of the residual monomer is adjusted by purifying the raw material of the (meth) acrylic resin.
The method for producing an optical film according to claim 5.
The (meth) acrylic resin is a copolymer containing a structural unit derived from methyl methacrylate and a structural unit derived from a monomer copolymerizable therewith.
The method for producing an optical film according to claim 5 or 6.