KR102565518B1 - Fabric film, manufacturing method of stretched optical film, and stretched optical film - Google Patents

Abstract

A raw film from which a stretched optical film that is thin and difficult to tear can be obtained relatively easily, a stretched optical film that is thin and difficult to tear, and a method for producing a stretched optical film that can be obtained with relative ease.
The present invention contains a vinyl alcohol-based polymer having an average thickness of 45 μm or less and a resin particle having a glass transition temperature of 30 ° C. or less as a main component, and the content of the resin particle relative to 100 parts by mass of the vinyl alcohol-based polymer, It is a raw film for stretched optical film manufacture which is 1 mass part or more and 50 mass parts or less.

Description

Fabric film, manufacturing method of stretched optical film, and stretched optical film

The present invention relates to a raw film, a method for producing a stretched optical film, and a stretched optical film.

BACKGROUND OF THE INVENTION A polarizing plate having functions of transmitting and shielding light is a basic component of a liquid crystal display (LCD) together with a liquid crystal that changes the polarization state of light. Many polarizing plates have a structure in which a protective film such as a cellulose triacetate (TAC) film was bonded to the surface of the polarizing film. As a polarizing film constituting the polarizing plate, a vinyl alcohol-based polymer film (hereinafter, “vinyl alcohol-based polymer” may be abbreviated as “PVA” in some cases) is uniaxially stretched to orientate a stretched film with an iodine-based dye (I ₃ ^- I ₅ ^-, etc.) and dichroic dyes such as dichroic organic dyes are adsorbed in the mainstream. Such a polarizing film uniaxially stretches a PVA film containing a dichroic dye in advance, adsorbs a dichroic dye simultaneously with uniaxial stretching of the PVA film, or adsorbs a dichroic dye after uniaxially stretching the PVA film. made or made.

LCDs are used in a wide range of small devices such as electronic desk calculators and wristwatches, smartphones, notebook PCs, LCD monitors, liquid crystal color projectors, LCD televisions, in-vehicle navigation systems, mobile phones, and measuring instruments used indoors and outdoors. It became. In recent years, with development to mobile applications such as small note PCs and mobile phones, the demand for thinning the polarizing plate has become stronger. In addition, since mobile phones are used in a wide range of places, there is a demand for improvement in durability at the same time.

Thinning a polarizing film or a protective film is mentioned as one of the methods of thinning a polarizing plate. For this purpose, it is necessary to thin the raw film (PVA film) used as a raw material of a polarizing film. However, a thin raw film tends to tear in the stretching direction in a drying process at the time of manufacturing a polarizing film, a process of bonding the obtained polarizing film and protective film together, and the like. In addition, when the polarizing film is thin, the polarizing film may tear in the stretching direction or cause fine cracks on the end surface of the polarizing film during handling, such as when punching or cutting the polarizing film or polarizing plate. easy. For this reason, when a thin raw film is used, productivity and yield of a polarizing plate and LCD fall, and it is easy to lead to high cost. Thus, productivity and a yield fall, and thinning of a raw film and a polarizing film tends to lead to high cost. Further, stretched optical films other than polarizing films, such as retardation films, are also expected to be thinner, but similarly have a problem in that tearing and the like tend to occur.

As a technique for producing a thin polarizing film with good yield, a method is known in which a thin PVA film is formed on a plastic film by a coating method, and the laminate is stretched and dried (see Patent Documents 1 and 2). In addition, in order to improve handleability such as punchability of the obtained polarizing film, after manufacturing the polarizing film under specific conditions, a polarizing plate in which a urethane resin layer was laminated on at least one side of the polarizing film (see Patent Document 3), and flexibility A composition capable of forming this excellent cured resin layer (see Patent Literature 4) has also been proposed.

Japanese Patent Publication No. 4804588 Japanese Patent Publication No. 4815544 Japanese Patent Publication No. 3315914 Japanese Unexamined Patent Publication No. 2014-115538

However, the methods described in Patent Documents 1 and 2 have the following problems.

(1) Coating work and subsequent drying work are complicated.

(2) Since heat treatment for insolubilization treatment of the PVA film needs to be performed in the state of a laminate, the plastic film used is limited to one that can be stretched even after heat treatment, resulting in high cost.

(3) In a laminate obtained by forming a PVA film on a plastic film by a coating method, the adhesive strength between the plastic film and the PVA film is relatively high. For this reason, when such a laminate with high adhesive strength is stretched, appropriate neck-in of the PVA film is hindered, and it is difficult to obtain a polarizing film excellent in polarization performance.

In addition, also in the methods described in Patent Literatures 3 and 4, problems such as an increase in cost due to an increase in the number of steps in producing a polarizing plate and a decrease in yield arise.

The present invention has been made based on the above circumstances, and its object is a raw film from which a thin and tear-resistant stretched optical film can be obtained relatively easily, a thin and tear-resistant stretched optical film, and such a stretched optical film. It is to provide a method for producing a stretched optical film in which the film can be obtained relatively easily.

As a result of repeated intensive studies in order to achieve the above object, the inventors of the present invention have found that even when the thickness of the film is reduced, by adding resin particles having a relatively low glass transition temperature to the film, a stretched optical film that is difficult to tear can be obtained. After finding out what could be obtained, further studies were repeated based on these findings, and the present invention was completed.

That is, this invention made in order to solve the said subject is as follows.

[1] It contains a vinyl alcohol-based polymer having an average thickness of 45 μm or less and a main component, and resin particles having a glass transition temperature of 30 ° C. or less, and the content of the resin particles relative to 100 parts by mass of the vinyl alcohol-based polymer is 1 A raw film for producing a stretched optical film that is not less than 50 parts by mass and not more than 50 parts by mass.

[2] The raw film according to [1], wherein the resin particles have an average particle diameter of 1 nm or more and 300 nm or less.

[3] A method for producing a stretched optical film comprising the step of stretching the raw film of [1] or [2].

[4] It contains a vinyl alcohol-based polymer having an average thickness of 20 μm or less and a main component, and resin particles having a glass transition temperature of 30 ° C. or less, and the content of the resin particles relative to 100 parts by mass of the vinyl alcohol-based polymer is 1 A stretched optical film of 50 parts by mass or more and 50 parts by mass or more.

[5] The stretched optical film according to [4], wherein the length of the resin particles in the stretching direction observed in the transmission electron microscope image on the cut plane parallel to the stretching direction is longer than the length in the direction perpendicular to the stretching direction.

According to the present invention, a raw film from which a thin, tear-resistant stretched optical film can be obtained relatively easily, a stretched optical film that is thin and difficult to tear, and a stretched optical film from which such a stretched optical film can be obtained relatively easily. method can be provided.

1 is a schematic view showing a cut plane parallel to the stretching direction in a stretched optical film according to an embodiment of the present invention.

<Fabric film>

A raw film according to an embodiment of the present invention is a film used for production of a stretched optical film. That is, the said raw film is a film used as the material of stretched optical films, such as a polarizing film and retardation film. A stretched optical film is obtained by stretching the raw film.

The raw film concerned may be a single layer film or a multilayer film (laminate). As a form of a multilayer film, the film etc. which have a PVA layer formed on the thermoplastic resin film by the coating method etc. are mentioned, for example. It is preferable that the raw film concerned is a single-layer film from the viewpoints of the effect of the present invention being more remarkably exhibited, the complexity of lamination (coating, etc.) work, and the cost of the thermoplastic resin film.

(average thickness)

The upper limit of the average thickness of the raw film concerned is 45 μm, preferably 40 μm, more preferably 35 μm, still more preferably 30 μm. When the average thickness of the raw film concerned is below the above upper limit, a thin stretched optical film can be obtained. On the other hand, as a lower limit of this average thickness, 1 micrometer is preferable, 3 micrometers are more preferable, 10 micrometers are still more preferable, and 20 micrometers are still more preferable. The tear resistance of the stretched optical film obtained can be further improved because the average thickness of the said raw film is more than the said lower limit.

(PVA)

The raw film concerned contains PVA (vinyl alcohol-based polymer) as a main component. In addition, a main component means the component with the largest content on a mass basis (the same below). PVA is a polymer having a vinyl alcohol unit (-CH ₂ -CH(OH)-) as a structural unit. PVA may have a vinyl ester unit and other units other than a vinyl alcohol unit.

Examples of PVA include one or two or more vinyl esters such as vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate, vinyl benzoate, and isopropenyl acetate. What is obtained by saponifying the polyvinyl ester obtained by polymerizing can be used. Among the above vinyl esters, compounds having a vinyloxycarbonyl group (H ₂ C=CH-O-CO-) in the molecule are preferable from the viewpoints of ease of production, availability, and cost of PVA, and vinyl acetate is more preferred. desirable.

The polyvinyl ester is preferably one obtained by using only one or two or more vinyl esters as monomers, and more preferably obtained by using only one vinyl ester as monomers, but within a range that does not significantly impair the effect of the present invention. If it is an inner surface, the copolymer of 1 type, or 2 or more types of vinyl ester, and the other monomer copolymerizable with this may be sufficient.

Other monomers copolymerizable with the vinyl ester include, for example

C2-C30 alpha-olefins, such as ethylene, propylene, 1-butene, and isobutene;

(meth)acrylic acid or its salt;

Methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, i-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, t- (meth)acrylate (meth)acrylic acid esters such as butyl, 2-ethylhexyl (meth)acrylate, dodecyl (meth)acrylate, and octadecyl (meth)acrylate;

(meth)acrylamide;

N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, diacetone (meth) acrylamide, (meth) acrylamide propanesulfonic acid or a salt thereof, (meth) ) (meth)acrylamide derivatives such as acrylamide propyldimethylamine or salts thereof, N-methylol (meth)acrylamide or derivatives thereof;

N-vinylamides such as N-vinylformamide, N-vinylacetamide, and N-vinylpyrrolidone;

Vinyl such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, and stearyl vinyl ether ether;

Vinyl cyanide, such as (meth)acrylonitrile;

vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride;

maleic acid, or its salt, ester or acid anhydride;

Itaconic acid, or its salt, ester or acid anhydride;

vinylsilyl compounds such as vinyltrimethoxysilane;

An unsaturated sulfonic acid or its salt etc. are mentioned.

The said polyvinyl ester may have a structural unit derived from 1 type, or 2 or more types of the said monomers.

The upper limit of the ratio of structural units derived from the other monomers in the polyvinyl ester is preferably 15 mol%, more preferably 10 mol%, based on the number of moles of all structural units constituting the polyvinyl ester, 5 mol% is more preferable, and 1 mol% is still more preferable.

As PVA, what is not graft-copolymerized can be used preferably. However, as long as the effect of the present invention is not significantly impaired, PVA may be modified by one type or two or more types of graft-copolymerizable monomers. Graft copolymerization can be performed with respect to at least one of polyvinyl ester and PVA obtained by saponifying it. Examples of the monomer capable of graft copolymerization include unsaturated carboxylic acids or derivatives thereof; Unsaturated sulfonic acid or its derivative(s); C2-C30 alpha-olefin etc. are mentioned. It is preferable that the ratio of the structural unit derived from the monomer which can be graft-copolymerized in polyvinyl ester or PVA is 5 mol% or less based on the number of moles of all the structural units which comprise polyvinyl ester or PVA.

As for the said PVA, some of the hydroxyl groups may or may not be crosslinked. In addition, in the PVA, a part of the hydroxy group may react with an aldehyde compound such as acetaldehyde or butyraldehyde to form an acetal structure, or may not form an acetal structure without reacting with these compounds.

As a lower limit of the polymerization degree of the said PVA, 1,000 is preferable, 1,500 is more preferable, and 2,000 is still more preferable. When the polymerization degree of PVA is more than the said lower limit, the optical characteristic of the stretched optical film obtained can be improved. On the other hand, as an upper limit of this degree of polymerization, 10,000 is preferable, 8,000 is more preferable, and 5,000 is still more preferable. By making the polymerization degree of PVA below the said upper limit, the raise of the manufacturing cost of PVA, and the occurrence of defects at the time of film forming can be suppressed. In addition, the degree of polymerization of PVA means the average degree of polymerization measured according to description of JISK6726-1994.

The lower limit of the degree of saponification of PVA is preferably 95 mol%, more preferably 98 mol%, still more preferably 99 mol%, and particularly preferably 99.5 mol%, from the viewpoint of improving the heat-and-moisture resistance of the stretched optical film obtained. do. On the other hand, the upper limit of this degree of saponification may be substantially 100 mol%. In addition, the degree of saponification of PVA refers to the ratio (mol%) of the number of moles of vinyl alcohol units to the total number of moles of structural units (typically vinyl ester units) and vinyl alcohol units that can be converted into vinyl alcohol units by saponification. . The degree of saponification can be measured according to the description of JIS K 6726-1994.

As a lower limit of content of PVA in the said raw film, 60 mass % is preferable, 70 mass % is more preferable, and 75 mass % is still more preferable. By making content of PVA into more than the said minimum, the stretched optical film obtained WHEREIN: Optical characteristics, such as polarization performance, express more favorably. On the other hand, as an upper limit of this content, 95 mass % is preferable, 90 mass % may be more preferable, and 85 mass % may be still more preferable. By making content of PVA below the said upper limit, the stretched optical film obtained becomes more difficult to tear.

(resin particles)

The said raw film contains resin particles whose glass transition temperature is 30 degrees C or less. The raw film concerned can obtain a stretched optical film that is thin and difficult to tear by containing such resin particles. The reason for such an effect is not clear, but as a result of observing the cross section of the place where the stretched optical film produced from the raw film was torn, the cross section was rough, so the resin particles dispersed in the film It is estimated that tearing became difficult by suppressing propagation of tearing. In particular, since the glass transition temperature of the resin particles is 30 ° C. or lower, that is, the general stretching treatment temperature when producing a stretched optical film using a raw film, the resin particles can also be deformed in the stretching direction during the stretching process. Thereby, PVA can fully orientate, maintaining the adhesiveness of PVA and a resin particle. For this reason, it is estimated that the stretched optical film obtained from the raw film is difficult to tear, and optical properties such as polarization performance can be improved by adjusting the content and average particle diameter of the resin particles.

Resin particles are particles whose main component is a polymer (resin). As a lower limit of content of the polymer in a resin particle, it is 50 mass %, for example, 80 mass % is preferable and 95 mass % is more preferable. The resin particles may be substantially formed only of resin.

The upper limit of the glass transition temperature (Tg) of the resin particles (Tg of the polymer as the main component of the resin particles) is 30°C, but is preferably 25°C, more preferably 20°C, still more preferably 15°C, and 10°C. even more desirable When this glass transition temperature is below the said upper limit, the stretched optical film which is hard to tear can be obtained. Moreover, optical characteristics, such as polarization performance, can also be improved by making this glass transition temperature below the said upper limit, and also adjusting content and average particle diameter of a resin particle.

The lower limit of the glass transition temperature of the resin particles is not particularly limited, but is preferably -100°C, more preferably -80°C, and still more preferably -60°C. By making this glass transition temperature more than the said lower limit, aggregation of the resin particle at the time of heating in the film forming process which produces a raw film is suppressed, and cloudiness of the raw film and stretched optical film obtained can be suppressed. Moreover, the optical characteristics of the stretched optical film obtained can be improved.

In addition, the glass transition temperature of the resin particles is taken as a measured value by DSC (differential scanning calorimetry) performed on the resin film obtained by forming a film using the resin particles. When a resin particle contains a plurality of different resins, let the glass transition temperature of the resin which has the lowest glass transition temperature be the glass transition temperature of this resin particle.

The lower limit of the content of the resin particles in the raw film is 1 part by mass with respect to 100 parts by mass of PVA, preferably 3 parts by mass, more preferably 5 parts by mass, and even more preferably 7 parts by mass. By setting the content of the resin particles to be equal to or greater than the above lower limit, the resulting stretched optical film can be made difficult to tear, and handling properties and the like are improved. On the other hand, the upper limit of this content is 50 parts by mass, preferably 30 parts by mass, more preferably 20 parts by mass, and still more preferably 15 parts by mass. By setting the content of the resin particles below the above upper limit, the light transmittance of the resulting stretched optical film can be made good, and optical properties such as polarization performance can be improved.

The lower limit of the average particle diameter of the resin particles in the raw film is preferably 1 nm, more preferably 5 nm, still more preferably 10 nm, still more preferably 20 nm, still more preferably 30 nm. By setting the average particle diameter of the resin particles to the above lower limit or more, the resulting stretched optical film becomes more difficult to tear, and handling properties and the like are improved. On the other hand, as an upper limit of this average particle diameter, although it may be, for example, 500 nm, 300 nm is preferable, 200 nm is more preferable, and 100 nm is still more preferable. By setting the average particle diameter of the resin particles to the above upper limit or less, particularly 300 nm or less, the light transmittance of the resulting stretched optical film can be made good, and optical properties such as polarization performance can be improved.

In addition, the average particle diameter of the resin particle in the said raw film is taken as the measured value based on the TEM (transmission electron microscope) image of the cut surface of a film. By measuring TEM of a cut surface perpendicular to the in-plane direction of the raw film, the presence or absence of resin particles and the dispersed state can be observed as a sea-island structure. In addition, the sea-island structure refers to a structure in which a discontinuous part (island part) is mixed in a continuously visible part (dissection) in a mixture composed of two types of physical properties. Since the dyeability of resin particles and PVA are different, the color of the part that looks continuous and the part that looks discontinuous is light, or the part that looks continuous is light and the part that looks discontinuous is dark. do. In this TEM image, resin particles are observed as an integument. With respect to the TEM image of the cut surface of the film, using image analysis software, resin particles are mechanically extracted, and the average value of the diameters of these resin particles is calculated. This calculated value is taken as the average particle diameter of the resin particles. A specific method for measuring the average particle diameter of the resin particles is the method described in Examples.

A resin particle contains a polymer. The polymer is not particularly limited as long as it has a glass transition temperature of 30°C or lower, and examples thereof include polyolefin, polyurethane, and acrylic resin, but acrylic resin is preferred. An acrylic resin refers to a polymer containing a structural unit derived from (meth)acrylic acid ester.

As (meth)acrylic ester,

Alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, dodecyl (meth)acrylate, and octadecyl (meth)acrylate ester;

(meth)acrylic acid esters having alicyclic groups such as dicyclopentanyl (meth)acrylate and isobornyl (meth)acrylate;

(meth)acrylic acid aryl esters, such as phenyl (meth)acrylate, etc. are mentioned.

It is preferable that the resin particle contains, among acrylic resins, an acrylic resin containing a structural unit ((meth)acrylic acid alkyl ester unit) derived from an alkyl (meth)acrylate ester. The lower limit of the number of carbon atoms in the alkyl group of the (meth)acrylic acid alkyl ester is 1, but is preferably 2, more preferably 3, and still more preferably 4. On the other hand, as an upper limit of carbon number of this alkyl group, it is 10, for example, 8 is preferable, 6 is more preferable, and 4 is still more preferable. Moreover, it is also preferable that it is an acrylic acid alkylester unit. That is, among the (meth)acrylic acid alkyl ester units, a butyl acrylate unit is most preferable. Resin particles using an acrylic resin containing such a (meth)acrylic acid alkyl ester unit have a low glass transition point, and can further enhance tear resistance and optical properties. Although the reason for this is not certain, it is presumed that the flexibility of the resin particles is increased and the resin particles are easily deformed in the stretching direction during the stretching treatment.

Moreover, as an acrylic resin, the acrylic resin containing a (meth)acrylic acid unit ( _-CH2- CHCOOH- and _-CH2 -C( _CH3 )COOH-) can also be used suitably. Resin particles using such a polymer can exhibit good dispersibility and the like in a PVA matrix. In this case, for example, a block copolymer of a (meth)acrylic acid unit and a (meth)acrylic acid alkyl ester unit is preferable. Moreover, when an acrylic resin is a block copolymer, any, such as a diblock copolymer and a triblock copolymer, may be sufficient.

As the resin particle, particles formed from one type of polymer may be used, or particles having a so-called core-shell structure, in which materials of the inner and outer sides are different, may be used. In the case of using core-shell type particles, it is preferable that the material of the core contains an acrylic resin containing an alkyl (meth)acrylic acid ester unit. In the case of using core-shell type particles, the material of the shell is preferably an acrylic resin containing an alicyclic group-containing (meth)acrylic acid ester unit or a (meth)acrylic acid unit.

A resin particle can be manufactured by a well-known method. Moreover, you may use a commercial item for resin particle. Moreover, the method of making the said raw film contain resin particle is not specifically limited, either. For example, resin particles may be added to a PVA chip, or resin particles may be added to a film-forming stock solution used at the time of film formation.

(plasticizer)

The raw film may further contain a plasticizer. When the said raw film contains a plasticizer, the handling property, the improvement of ductility, etc. can be aimed at. A polyhydric alcohol is mentioned as a preferable plasticizer, and ethylene glycol, glycerol, propylene glycol, diethylene glycol, diglycerol, triethylene glycol, tetraethylene glycol, a trimethylol propane etc. are mentioned as a specific example. These plasticizers can use 1 type, or 2 or more types. Among these, glycerol is preferable from the viewpoint of the effect of improving the stretchability.

The lower limit of the content of the plasticizer in the raw film is preferably 2 parts by mass, more preferably 3 parts by mass, still more preferably 4 parts by mass, and still more preferably 6 parts by mass with respect to 100 parts by mass of PVA. By making content of a plasticizer more than the said minimum, ductility improves more. On the other hand, as an upper limit of this content, 20 mass parts is preferable, 17 mass parts is more preferable, and 14 mass parts is still more preferable. By making content of a plasticizer below the said upper limit, it can suppress that a raw film becomes soft too much, a plasticizer bleeds out on the surface, and handling property falls.

(other additives, etc.)

In addition to PVA, resin particles and plasticizers, the fabric film, in addition to fillers, processing stabilizers such as copper compounds, weather resistance stabilizers, colorants, ultraviolet absorbers, light stabilizers, antioxidants, antistatic agents, flame retardants, other thermoplastic resins, lubricants, fragrances , antifoaming agent, deodorant, extender, release agent, release agent, reinforcing agent, crosslinking agent, antimold agent, antiseptic agent, and other additives such as a crystallization rate retardant can be appropriately blended as necessary.

However, as an upper limit of content of additives other than PVA, resin particle, and plasticizer in the said raw film, 1 mass % may be preferable and 0.2 mass % may be more preferable. When the content of other additives exceeds the above upper limit, the tear strength and optical properties of the resulting stretched optical film may be affected.

As a lower limit of the swelling degree of the said raw film, 160 % is preferable, 170 % is more preferable, and 180 % is still more preferable. When the degree of swelling is equal to or greater than the lower limit above, it is possible to suppress extremely progressing crystallization, and it is possible to stably extend the film to a high magnification. On the other hand, as an upper limit of this degree of swelling, 240% is preferable, 230% is more preferable, and 220% is still more preferable. When the degree of swelling is equal to or less than the above upper limit, dissolution during stretching is suppressed, and stretching can be performed even under higher temperature conditions. In addition, the degree of swelling of the raw film is a value obtained by dividing the mass when the raw film is immersed in distilled water at 30 ° C. for 15 minutes by the mass of the raw film dried at 105 ° C. for 16 hours after being immersed in distilled water at 30 ° C. for 15 minutes means a percentage of

Although there is no restriction|limiting in particular in the shape of the said raw film, It is preferable that it is a long film from the point which can manufacture a stretched optical film continuously with good productivity. The length of the elongated raw film is not particularly limited, and can be appropriately set according to the purpose of the stretched optical film to be produced, for example, within the range of 5 m or more and 20,000 m or less. There is no particular restriction on the width of the raw film, for example, the lower limit can be 50 cm, but from the point where a polarizing film of a wide width has recently been requested, the lower limit is preferably 1 m, more preferably 2 m, 4 m is more preferable. Although there is no restriction|limiting in particular in the upper limit of the width|variety of the said raw film, It can be set as 7 m, for example. If the width is too wide, it tends to be difficult to uniformly stretch when producing a stretched optical film with a device that has been put into practical use.

The raw film can be relatively easily produced as a stretched optical film that is difficult to tear at the time of production or handling. Therefore, it can be used suitably as a material of stretched optical films, such as a polarizing film and retardation film. Especially, since the said raw film can manufacture a polarizing film with favorable polarization performance easily, it is especially preferable to use it as a raw film for manufacturing a polarizing film.

(Manufacturing method of raw film)

The manufacturing method of the raw film of this invention is not specifically limited, The manufacturing method in which the thickness and width of the raw film after film formation become more uniform is employable preferably. For example, the PVA and resin particles constituting the raw film, and, if necessary, a plasticizer, other additives, and a film forming stock solution in which one or two or more of the surfactants described later are dissolved in a liquid medium. It can be obtained by using and forming a film. Moreover, it can manufacture also using the film forming stock solution which melted PVA as needed. In the film forming stock solution, it is preferable that the resin particles are uniformly mixed. Further, when the film-forming dope contains at least one of a plasticizer, other additives, and a surfactant, it is preferable that these components are mixed uniformly.

Examples of the liquid medium include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, Trimethylolpropane, ethylenediamine, diethylenetriamine, etc. are mentioned. 1 type or 2 or more types can be used for these liquid media. Among these, water is preferable from the viewpoint of a small load on the environment and recoverability.

The volatile matter content of the film-forming dope (the ratio of content of volatile components such as liquid media removed by volatilization or evaporation during film-forming in the film-forming dope) varies depending on the film-forming method, film-forming conditions, etc., but in general, the lower limit As 50 mass % is preferable, 55 mass % is more preferable, and 60 mass % is still more preferable. When the volatile content of the membrane forming stock solution is equal to or greater than the lower limit, the viscosity of the membrane forming stock solution does not increase too much, filtration and degassing are performed smoothly when preparing the membrane forming stock solution, and production of a raw film with fewer foreign substances or defects is facilitated. On the other hand, as an upper limit of this volatile matter rate, 95 mass % is preferable, 90 mass % is more preferable, and 85 mass % is still more preferable. When the volatile content of the film-forming dope is equal to or less than the above upper limit, the concentration of the film-forming dope does not become too low, and production of an industrial raw film becomes easy.

It is preferable that the membrane forming stock solution contains a surfactant. By including surfactant, while film forming property improves and generation|occurrence|production of thickness nonuniformity of a raw film is suppressed, peeling of the film from the metal roll or belt used for film forming becomes easy. When a raw film is produced from a film-forming stock solution containing a surfactant, the raw film may contain a surfactant. Although the kind of said surfactant is not specifically limited, From a viewpoint of peelability from a metal roll or belt, etc., anionic surfactant and nonionic surfactant are preferable.

Examples of the anionic surfactant include carboxylic acid types such as potassium laurate; sulfuric acid ester types such as polyoxyethylene lauryl ether sulfate and octyl sulfate; Sulfonic acid types, such as dodecylbenzenesulfonate, etc. are preferable.

Examples of nonionic surfactants include alkyl ether types such as polyoxyethylene oleyl ether; Alkyl phenyl ether types, such as polyoxyethylene octyl phenyl ether; Alkyl ester types, such as polyoxyethylene laurate; Alkylamine types, such as polyoxyethylene laurylamino ether; Alkyl amide types, such as polyoxyethylene lauric acid amide; polypropylene glycol ether types such as polyoxyethylene polyoxypropylene ether; alkanolamide types such as lauric acid diethanolamide and oleic acid diethanolamide; Allylphenyl ether types, such as polyoxyalkylene allylphenyl ether, etc. are preferable.

These surfactants can be used individually by 1 type or in combination of 2 or more types.

When the membrane forming stock solution or the obtained raw film contains a surfactant, the lower limit of the content thereof is preferably 0.01 part by mass, and more preferably 0.02 part by mass, based on 100 parts by mass of PVA contained in the membrane forming stock solution or raw film. When content of surfactant is more than the said lower limit, film forming property and peelability improve more. On the other hand, as an upper limit of this content, 0.5 mass part is preferable, 0.3 mass part is more preferable, and 0.1 mass part is still more preferable. When content of surfactant is below the said upper limit, it can suppress that surfactant bleeds out on the surface of a raw film, blocking arises, and handling property falls.

Examples of the film forming method when forming a raw film using the above film forming undiluted solution include a cast film forming method, an extrusion film forming method, a wet film forming method, and a gel film forming method. These film forming methods may be employed singly or in combination of two or more. Among these film forming methods, the cast film forming method and the extrusion film forming method are preferred in terms of obtaining a raw film having uniform thickness and width and good physical properties. Drying or heat treatment can be given to the raw film formed into a film as needed.

The heat treatment temperature is not particularly limited, and may be appropriately adjusted. When the heat treatment temperature is too high, discoloration and deterioration of the raw film are seen. Therefore, the upper limit of the heat treatment temperature is preferably 210°C, more preferably 180°C, and still more preferably 150°C. On the other hand, as a lower limit of heat treatment temperature, it is 60 degreeC, for example, and 90 degreeC is preferable.

There is no restriction|limiting in particular in heat treatment time, and what is necessary is just to adjust suitably, but as an upper limit from a viewpoint of manufacturing a raw film efficiently, 30 minutes are preferable and 15 minutes are more preferable. On the other hand, as this lower limit, 1 minute is preferable, for example, and 3 minutes is more preferable.

<stretched optical film>

A stretched optical film according to an embodiment of the present invention is an optical film containing PVA oriented in a predetermined direction, such as a polarizing film or a retardation film. The stretched optical film may be uniaxially stretched or biaxially stretched, but is preferably uniaxially stretched. The stretched optical film uniaxially stretched can be preferably used as a polarizing film or the like. The stretched optical film may be a single layer film or a multilayer film, but is preferably a single layer film.

(average thickness)

The upper limit of the average thickness of the stretched optical film is 20 μm, preferably 18 μm, more preferably 16 μm, still more preferably 14 μm. Sufficient thickness reduction can be aimed at when the average thickness of the said stretched optical film is below the said upper limit. On the other hand, as a lower limit of this average thickness, 5 micrometers are preferable, 8 micrometers are more preferable, and 10 micrometers are still more preferable. When the average thickness of the stretched optical film is equal to or greater than the lower limit, it is possible to make the stretched optical film more resistant to tearing and to improve handling properties and the like.

(Ingredients, etc.)

The said stretched optical film contains PVA which is a main component, and resin particle.

The upper limit of the glass transition temperature (Tg) of the resin particles contained in the stretched optical film (Tg of the polymer as the main component of the resin particles) is 30°C, preferably 25°C, more preferably 20°C, and preferably 15°C. It is more preferable, and 10 degreeC is still more preferable. When the glass transition temperature is equal to or lower than the above upper limit, the stretched optical film is resistant to tearing and has excellent handling properties and the like. Moreover, optical characteristics, such as polarization performance, can also be improved by making this glass transition temperature below the said upper limit, and also adjusting content and average particle diameter of a resin particle. The lower limit of the glass transition temperature of the resin particles is not particularly limited, but is preferably -100°C, more preferably -80°C, and still more preferably -60°C. By making this glass transition temperature more than the said minimum, aggregation of a resin particle can be suppressed and cloudiness of a stretched optical film can be suppressed. Moreover, the optical characteristics of a stretched optical film can be improved.

In addition, the glass transition temperature of the resin particles contained in the stretched optical film is the same as the resin particles contained in the raw film, formed into a film using resin particles, and DSC (differential scanning calorimetry) performed on the resulting resin film. is taken as a measure of

The lower limit of the content of the resin particles in the stretched optical film is 1 part by mass, preferably 3 parts by mass, more preferably 5 parts by mass, and even more preferably 7 parts by mass with respect to 100 parts by mass of PVA. By making content of a resin particle more than the said lower limit, the stretched optical film can be made hard to tear, and handling property etc. improve. On the other hand, the upper limit of this content is 50 parts by mass, preferably 30 parts by mass, more preferably 20 parts by mass, and still more preferably 15 parts by mass. By setting the content of the resin particles below the above upper limit, the light transmittance of the stretched optical film can be made good, and optical properties such as polarization performance can be improved.

In the stretched optical film, the length of the resin particles observed in the transmission electron microscope (TEM) image on the cut plane parallel to the stretching direction in the stretching direction (diameter in the stretching direction) is in the direction perpendicular to the stretching direction. It is preferably longer than the length (diameter in the direction perpendicular to the stretching direction). That is, it is preferable that the resin particle in the said stretched optical film has an elliptical shape with a long axis along the extending|stretching direction. In such a case, PVA can form sufficient orientation state, with the adhesiveness of PVA and a resin particle maintained. For this reason, it is estimated that the said stretched optical film becomes hard to generate|occur|produce tear, and optical characteristics, such as polarization performance, can also be improved by adjusting content and average particle diameter of a resin particle. In addition, such elliptical resin particles may be formed by stretching a raw film containing resin particles having a glass transition temperature of 30° C. or less, by deforming the resin particles along the stretching direction. In addition, the stretching direction in a stretched optical film is usually the orientation direction of the crystal|crystallization of PVA.

Specifically, as shown in FIG. 1 , in the TEM image in a cut plane parallel to the stretching direction (X) of the stretched optical film 1, the stretching direction (X) of the resin particles 2 (drawing part) It is preferable that the length (A) of is longer than the length (B) in the direction perpendicular to the stretching direction (X). The lower limit of the ratio (A/B) of the length (A) in the stretching direction (X) to the length (B) in the direction perpendicular to the stretching direction (X) in this resin particle 2 is 1.2 is preferred, 1.6 is more preferred, and 2.0 is still more preferred. In addition, as an upper limit of this ratio (A/B), 3 may be sufficient as it, and 2.6 may be sufficient as it, for example.

The lower limit of the length (A) of the resin particles in the stretching direction is preferably 1 nm, more preferably 10 nm, still more preferably 30 nm, still more preferably 50 nm, still more preferably 70 nm. On the other hand, as an upper limit of this length (A), although 800 nm may be sufficient, for example, 300 nm is preferable, 200 nm is more preferable, and 100 nm is still more preferable. The lower limit of the length (B) in the direction perpendicular to the stretching direction of the resin particles is preferably 1 nm, more preferably 10 nm, still more preferably 20 nm, still more preferably 30 nm. On the other hand, as an upper limit of this length (B), although it may be 500 nm, for example, 200 nm is preferable, 100 nm is more preferable, and 50 nm is still more preferable. When the lengths (A) and (B) are within the above ranges, tearing is less likely to occur, and optical properties such as polarization performance can be improved by adjusting the resin particle content and average particle diameter.

The length (A) of the resin particles in the stretching direction and the length (B) in the direction perpendicular to the stretching direction are measured by the following method. Resin particles are mechanically extracted from the TEM image of the cut surface of the film parallel to the stretching direction using image analysis software. The average length of the extracted resin particles in the direction of the major axis is taken as the length (A), and the average length in the direction of the minor axis is taken as the length (B). From these lengths (A) and (B), the ratio of the lengths (A/B) is also obtained. These specific measurement methods are set as the methods described in Examples.

The preferable forms of the PVA and resin particles contained in the stretched optical film are the same as the PVA and resin particles contained in the raw film described above. It is the same as that of the raw film mentioned above also about other components which may be contained in the said stretched optical film. When the stretched optical film is a polarizing film, the stretched optical film has a dichroic dye adsorbed on the front and back surfaces. As the dichroic dye, an iodine-based dye is common.

When the stretched optical film is a polarizing film, the lower limit of the polarization degree at a transmittance of 44.0% may be, for example, 70%, but preferably 99.0%, more preferably 99.8%, It is more preferable that it is 99.9%. When the degree of polarization is less than the lower limit, the contrast of the LCD may decrease when used for a smartphone, a note PC, a liquid crystal television, an in-vehicle navigation system, or the like.

When the stretched optical film is a polarizing film, the polarizing film is usually used as a polarizing plate by attaching a protective film that is optically transparent and has mechanical strength to both surfaces or one surface thereof. As the protective film, a cellulose triacetate (TAC) film, a cellulose acetic acid/butyrate (CAB) film, an acrylic film, a polyester film, or the like is used. Moreover, as an adhesive agent for bonding, a PVA-type adhesive agent, an ultraviolet curable adhesive agent, etc. are mentioned, and a PVA-type adhesive agent is preferable.

The polarizing plate obtained by the above may further bond a retardation film, a viewing angle improvement film, a brightness improvement film, etc. Further, the stretched optical film of the present invention may be used as the retardation film. A polarizing plate can be bonded to a glass substrate after coating adhesives, such as an acrylic type, and can be used as a component of LCD.

<Method for producing a stretched optical film>

The stretched optical film according to one embodiment of the present invention can be obtained by a manufacturing method including a step of stretching the raw film. That is, the said stretched optical film can be manufactured by the same method as the prior art except using the raw film mentioned above. That is, according to the manufacturing method, a thin, tear-resistant stretched optical film can be obtained relatively easily without going through a special process. Hereinafter, the specific manufacturing method in case the said stretched optical film is a polarizing film is demonstrated.

As a specific method for producing the polarizing film, with respect to the raw film, swelling treatment, dyeing treatment, uniaxial stretching treatment, and if necessary, further crosslinking treatment, fixing treatment, washing treatment, drying treatment, heat treatment and the like. In this case, the order of each treatment, such as swelling treatment, dyeing treatment, crosslinking treatment, uniaxial stretching, and fixation treatment, is not particularly limited, and two or more treatments may be performed simultaneously. Moreover, one or two or more of each process may be performed twice or more.

A swelling process can be performed by immersing a raw film in water. As a lower limit of the temperature of the water at the time of being immersed in water, 20 degreeC is preferable, 22 degreeC is more preferable, and 25 degreeC is still more preferable. On the other hand, as an upper limit of this temperature, 40 degreeC is preferable, 38 degreeC is more preferable, and 35 degreeC is still more preferable. Moreover, as a lower limit of time to immerse in water, 0.1 minute is preferable and 0.5 minute is more preferable. On the other hand, as an upper limit of this time, 5 minutes is preferable and 3 minutes is more preferable. In addition, water at the time of immersion in water is not limited to pure water, An aqueous solution in which various components were dissolved may be sufficient, and a mixture of water and an aqueous medium may be sufficient as it.

A dyeing process can be performed by making a dichroic dye contact with respect to a raw film. As the dichroic dye, it is common to use an iodine-based dye. As the timing of the dyeing treatment, any stage before the uniaxial stretching treatment, at the time of the uniaxial stretching treatment, and after the uniaxial stretching treatment may be used. Dyeing treatment is generally performed by immersing a fabric film in a solution (particularly aqueous solution) containing iodine-potassium iodide as a dyeing bath. The concentration of iodine in the dyeing bath is preferably 0.01% by mass or more and 0.5% by mass or less, and the concentration of potassium iodide is preferably 0.01% by mass or more and 10% by mass or less. Moreover, 20 degreeC is preferable and, as for the minimum of the temperature of a dyeing bath, 25 degreeC is more preferable. On the other hand, the upper limit of this temperature is preferably 50°C and more preferably 40°C.

By performing a crosslinking treatment on the raw film, elution of PVA into water can be effectively prevented during wet stretching at a high temperature. From this point of view, it is preferable to perform the crosslinking treatment before the uniaxial stretching treatment. The crosslinking treatment can be performed by immersing the raw film in an aqueous solution containing a crosslinking agent. As said crosslinking agent, 1 type(s) or 2 or more types of boron inorganic compounds, such as borates, such as boric acid and borax, can be used. 1 mass % is preferable, as for the lower limit of the density|concentration of the cross-linking agent in the aqueous solution containing a cross-linking agent, 2 mass % is more preferable, and its 3 mass % is still more preferable. On the other hand, the upper limit of this concentration is preferably 15% by mass, more preferably 7% by mass, and still more preferably 6% by mass. Sufficient stretchability can be maintained when the concentration of the crosslinking agent is within the above range. The aqueous solution containing a crosslinking agent may contain auxiliary agents, such as potassium iodide. 20 degreeC is preferable and, as for the minimum of the temperature of the aqueous solution containing a crosslinking agent, 25 degreeC is more preferable. On the other hand, the upper limit of this temperature is preferably 50°C and more preferably 40°C. Efficient crosslinking can be achieved by setting this temperature within the above range.

The uniaxial stretching treatment may be performed by either a wet stretching method or a dry stretching method. In the case of the wet stretching method, it can also be carried out in a boric acid aqueous solution, in the dyeing bath described above or in a fixing treatment bath described later. In addition, in the case of the dry stretching method, the uniaxial stretching treatment may be performed at room temperature, the uniaxial stretching treatment may be performed while heating, or the uniaxial stretching treatment may be performed in air using a raw film after water absorption. Among these, the wet stretching method is preferable, and it is more preferable to perform a uniaxial stretching process in boric acid aqueous solution. 0.5 mass % is preferable, as for the lower limit of the boric acid concentration of boric acid aqueous solution, 1.0 mass % is more preferable, and 1.5 mass % is still more preferable. On the other hand, as for the upper limit of this boric acid concentration, 6.0 mass % is preferable, 5.0 mass % is more preferable, and 4.0 mass % is still more preferable. Moreover, boric acid aqueous solution may contain potassium iodide, and it is preferable that the concentration shall be 0.01 mass % or more and 10 mass % or less.

The lower limit of the stretching temperature in the uniaxial stretching treatment is preferably 30°C, more preferably 40°C, still more preferably 50°C. By setting the lower limit of the stretching temperature to 30° C. or higher, which is the upper limit of the glass transition temperature of the resin particles, the resin particles are favorably deformed so as to extend in the stretching direction during stretching. In this way, a stretched optical film that is difficult to tear and has excellent handling properties can be obtained relatively easily.

The lower limit of the draw ratio in the uniaxial stretching treatment is preferably 5 times, more preferably 5.5 times, and still more preferably 6 times, from the viewpoint of the polarization performance of the polarizing film obtained. Although the upper limit of the draw ratio is not particularly limited, for example, 10 times is preferable and 8 times is more preferable in some cases.

In manufacture of a polarizing film, it is preferable to perform a fixing process after a uniaxial stretching process in order to strengthen the adsorption|suction of a dichroic dye (iodine type dye etc.) to a raw film. As a fixation treatment bath used for fixation treatment, the aqueous solution containing 1 type(s) or 2 or more types of boron inorganic compounds, such as boric acid and borax, can be used. Moreover, you may add an iodine compound or a metal compound to the fixation treatment bath as needed. 0.5 mass % is preferable and, as for the lower limit of the concentration of the boron inorganic compound in a fixed treatment bath, 1 mass % is more preferable. On the other hand, 15 mass % is preferable and, as for the upper limit of this density|concentration, 10 mass % is more preferable. Adsorption of the dichroic dye can be made more robust by setting this concentration within the above range. The lower limit of the temperature of the fixed treatment bath is preferably 15°C. On the other hand, the upper limit of this temperature is preferably 60°C and more preferably 40°C.

The washing treatment is generally performed by immersing the raw film in water or the like. At this time, from the viewpoint of improving the polarization performance, it is preferable that the water or the like used for the washing treatment contains an adjuvant such as potassium iodide. At this time, the concentration of iodides such as potassium iodide is preferably 0.5% by mass or more and 10% by mass or less. The lower limit of the temperature of water or the like used for the washing treatment is generally 5°C, preferably 10°C, and more preferably 15°C. On the other hand, the upper limit of this temperature is generally 50°C, preferably 45°C, and more preferably 40°C. From an economical point of view, it is undesirable that the temperature of the water or the like is too low. On the other hand, if the temperature of water or the like is too high, the polarization performance may decrease.

The conditions for the drying treatment are not particularly limited, but the lower limit of the drying temperature is preferably 30°C and more preferably 50°C. On the other hand, as an upper limit of drying temperature, 150 degreeC is preferable and 130 degreeC is more preferable. By drying at a temperature within the above range, it is easy to obtain a polarizing film having excellent dimensional stability.

By performing a heat treatment after the drying treatment, a polarizing film further excellent in dimensional stability can be obtained. The heat treatment here refers to a treatment of further heating a polarizing film having a moisture content of 5% or less after the drying treatment to improve the dimensional stability of the polarizing film. The heat treatment conditions are not particularly limited, but it is preferable to heat treatment within the range of 60°C or more and 150°C or less. When heat treatment is performed at a temperature lower than 60°C, the effect of dimensional stabilization by heat treatment is insufficient. On the other hand, if heat treatment is performed at a temperature higher than 150°C, yellowing may occur severely in the polarizing film.

<Other embodiments>

The manufacturing method of the raw film of this invention, a stretched optical film, and a stretched optical film is not limited to the said embodiment. For example, the stretched optical film and its manufacturing method have been mainly described in the case where the stretched optical film is a polarizing film, but the stretched optical film is not limited to the polarizing film. For example, stretched optical films other than polarizing films such as retardation film are also within the scope of the present invention, and can be manufactured by a manufacturing method including a step of stretching the raw film of the present invention. The manufacturing method of the retardation film as one embodiment of the present invention can be carried out using a conventionally known method other than stretching the raw film of the present invention.

Example

The present invention will be specifically described by the following examples, but the present invention is not limited at all by these examples. In addition, each evaluation method employed in the following Examples and Comparative Examples is shown below.

[Glass Transition Temperature of Resin Particles]

After dissolving the raw film obtained in each of the following Examples or Comparative Examples in water, it was filtered with a filter capable of collecting resin particles (Merck's "MF-Millipore Membrane Filter VSWP" pore diameter 0.025 μm), and the collected material (resin particles ) was dried. Thereafter, by heat-treating the resin particles at 100°C, a resin film molded only from the resin particles was sampled. The glass transition temperature of the resin film was determined using DSC ("Q2000" manufactured by TA Instruments). This was made into the glass transition temperature of the resin particle.

[Swelling degree of fabric film]

About 1.5 g of the raw film obtained in each of the following Examples or Comparative Examples was collected. After cutting this into about 2 mm x 10 cm, it was wrapped with 100 mesh ("N-N0110S 115" by NBC Meshtech) and immersed in 30 degreeC distilled water for 15 minutes. After that, centrifugal dehydration was performed at 3,000 rpm for 5 minutes, and the mass (W1) of the raw film swollen after removing the mesh was determined. Then, after drying the raw film with a 105 degreeC drying machine for 16 hours, mass (W2) was calculated|required. The degree of swelling of the raw film was calculated by the following formula.

Degree of swelling (%) = {(W1)/(W2)} × 100

[Average Particle Diameter of Resin Particles in Raw Film]

After cutting out the raw film obtained in each of the following Examples or Comparative Examples with an ultra microtome (“Ultra Cut S/FC-S” by Leica), exposed to osmium tetroxide vapor in an atmosphere of 23° C. for 5 days, and PVA The hydroxy group was dyed. After the staining treatment, frozen sections for observation were further cut out in an atmosphere of -100°C using a diamond knife (DiATOME's "Ultra Cryo Dry" 2 mm 35°). Thereafter, the frozen sections for observation that were stained excessively were washed with distilled water and dried. The cut surface was observed using a transmission electron microscope ("Transmission Electron Microscope HT7000" manufactured by Hitachi High-Technologies), and a TEM image was obtained. The accelerating voltage was set to 100 kV and the emission current was set to 10 ㎂, and a LaB6 filament was used as the electron gun.

The average particle diameter of the resin particle in a raw film was measured by the following method using the TEM image obtained by the said method. First, after opening the TEM image using image analysis software "Image-Pro Plus 7.0J" (manufactured by Media Cybernetics), converting to 8-bit scale in "Conversion", and performing flattening in "Filter processing" did Next, after setting the contrast value to 80 in "Contrast Emphasis" and selecting "Average Particle Diameter" on the measurement item setting page in "Count/Size", light-colored objects are automatically extracted to mechanically extract the resin particles. It extracted and calculated the average particle diameter of the resin particle in a raw film. In addition, those with a particle diameter smaller than 1/10 of the maximum diameter in the TEM image were removed as noise. Moreover, in the TEM image, when the color of the resin particles was darker than that of PVA, the average particle diameter of the resin particles in the raw film was calculated by automatically extracting a dark-colored object.

[Length of Resin Particles in Polarizing Film]

About the polarizing film obtained by each following Example or Comparative Example, it carried out similarly to the method described in the said "average particle diameter of the resin particle in a raw film", and obtained the TEM image of the cut surface. However, about this polarizing film, it observed from the cut plane parallel to the extending|stretching direction.

Using the TEM image obtained by the above method, the length (A) (major axis length) of the resin particles in the polarizing film in the stretching direction and the length (B) (short axis length) in the direction perpendicular to the stretching direction were measured by the following method did First, after opening the TEM image using image analysis software "Image-Pro Plus 7.0J" (manufactured by Media Cybernetics), converting to 8-bit scale in "Conversion", and performing flattening in "Filter processing" did Next, after setting the contrast value to 80 in "Contrast Emphasis" and selecting "Ellipse major axis/short axis ratio" in the measurement item setting page in "Count/Size", a light-colored object is automatically extracted, mechanically resin particles are extracted, and the length of the resin particles in the polarizing film in the major axis direction (A) (length in the stretching direction), the length in the minor axis direction (B) (length in the direction perpendicular to the stretching direction), and the length ratio thereof (A/B) was calculated. In addition, those with a particle diameter smaller than 1/10 of the maximum diameter in the TEM image were removed as noise. Moreover, in the TEM image, when the color of the resin particles was darker than that of PVA, each length of the resin particles in the polarizing film was calculated by automatically extracting a dark object.

[Evaluation of tear resistance: puncture resistance]

The polarizing film obtained in each of the following Examples or Comparative Examples was left still at a temperature of 23°C and a relative humidity of 20% for 24 hours. After that, a 20 mm film piece was cut out from this polarizing film in the longitudinal direction (stretching direction of the polarizing film) in the 40 mm × width direction, sandwiched with a metal frame, and four sides were fixed. After that, this polarizing film was attached to a tensile tester ("Autograph AGS-H" by Shimadzu Corporation), and the stretching direction of this polarizing film and the minus driver (contact area with the polarizing film: 1 mm × 5 mm) A minus driver was attached to the upper chuck so that the long sides were parallel, and the minus driver was pressed against the polarizing film at a speed of 1 mm/min. And the maximum load when a minus driver penetrated a polarizing film was made into piercing intensity|strength, and the piercing property was evaluated according to the following criteria. In addition, A and B were judged to be good because they could be used without problems in practical use, and C was judged to be poor.

A: Break strength of 5 N or more

B: Break strength is 3 N or more and less than 5 N

C: Break strength less than 3 N

[Evaluation of tear resistance: cutting property]

The polarizing film obtained in each of the following Examples or Comparative Examples was left still at a temperature of 23°C and a relative humidity of 50% for 24 hours. After that, this polarizing film was cut using a cutter knife at a speed of 600 mm/min in a direction perpendicular to the stretching direction, and the cut cross section was observed under a stereomicroscope. In addition, the angle formed by the blade of the cutter knife and the stretching direction of the polarizing film was set to 45°. And the number of cracks existing per 1 cm of the cut cross section of the polarizing film was measured, and cutting property was evaluated according to the following criteria. In addition, A and B were judged to be good because they could be used without problems in practical use, and C was judged to be poor.

A: No cracks

B: 1 to 4 pieces/cm

C: 5 or more/cm

[Evaluation of tear resistance: punchability]

The polarizing film obtained in each of the following Examples or Comparative Examples was left still at a temperature of 23°C and a relative humidity of 50% for 24 hours. After that, the polarizing film was placed on a cutting mat ("MA 40N" manufactured by Kokuyo Co., Ltd.), and the polarizing film was punched out using a circular punch having a diameter of 10 mm (belt punch "TPO-100" manufactured by Three Riechi Co., Ltd.), A punched cross section of the polarizing film cut out in a circular shape was observed under a stereomicroscope. Then, the number of cracks present in the polarizing film was measured, and punchability was evaluated based on the following criteria. In addition, A and B were judged to be good because they could be used without problems in practical use, and C was judged to be poor.

A: No cracks

B: 1 to 4 per circumference

C: 5 or more per circumference

[Polarization Performance of Polarizing Film]

(Measurement of transmittance (Ts))

Two samples having a length of 2 cm were taken from the central portion of the polarizing film in the stretching direction of the polarizing film. For one sample, a spectrophotometer with an integrating sphere (“V7100” by Nippon Spectroscopy Co., Ltd.) was used to correct the visibility in the visible light region with a C light source and a 2° field of view in accordance with JIS Z 8722 (method for measuring object color). Then, the transmittance of light when tilted by +45° and the transmittance of light when tilted by -45° with respect to the longitudinal direction were measured, and their average value Ts1 (%) was obtained. In the same manner for another sample, the transmittance of light when tilted by +45° and the transmittance of light when tilted by -45° were measured, and their average value Ts2 (%) was obtained. Using the following formula (1), Ts1 and Ts2 were averaged, and the transmittance (Ts) (%) of the polarizing film was obtained.

Ts = (Ts1 + Ts2)/2 ... (1)

In the following Examples or Comparative Examples, dyeing treatment conditions were adjusted, samples were prepared so that the transmittance (Ts) was 44.0%, and the polarization degree (V) was measured below.

(Measurement of degree of polarization (V))

For the two samples used in the measurement of the transmittance (Ts), the light transmittance T _⊥ (%) when the two samples are overlapped so that their stretching directions are orthogonal to each other and the light transmittance T _/ when they are overlapped so that the stretching directions are parallel _/ (%) was measured. This measurement was performed by using a spectrophotometer with an integrating sphere (“V7100” by Nippon Spectroscopy Co., Ltd.) and correcting the visibility in the visible light region with a C light source and a 2° field of view in accordance with JIS Z 8722 (method for measuring object color). . From the measured T _// (%) and T _⊥ (%), the polarization degree (V) (%) was determined using the following formula (2).

V = {(T _// − T _⊥ )/(T _// + T _⊥ )} ^1/2 × 100 ... (2)

[Production Example 1] Production of Resin Particles A

0.20 g of potassium peroxodisulfate as a polymerization initiator, 36.0 g of a reactive emulsifier "JS-20" manufactured by Sanyo Chemical Industry Co., Ltd., and 300 g of ion-exchanged water were charged into a dried 0.5 L pressure resistant polymerization tank. Deoxygenation treatment was performed by bubbling this with nitrogen gas for 30 minutes to obtain a starting emulsion. Next, after raising the temperature to 60 ° C. while stirring this starting emulsion, a mixture of 45.0 g of n-butyl acrylate, 0.45 g of allyl methacrylate, and 0.23 g of trimethylolpropane trimethacrylate, respectively degassed, was added at 1.0 mL/ml. It was added continuously at a rate of 10 min.

Then, when it was confirmed that the conversion rate of each monomer calculated by the method described later exceeded 95% by mass, 5.6 g of degassed dicyclopentanyl methacrylate was continuously added at a rate of 1.0 ml/min. After the above addition, it was confirmed that the monomer conversion ratio calculated by the above method exceeded 95% by mass, and the temperature of the polymerization tank was raised to 100°C to perform polymerization, and polymerization was carried out until the remaining monomers were below the detection limit of gas chromatography. was carried out. It cooled to 25 degreeC after superposition|polymerization, and obtained the emulsion solution (resin content 17 mass %) containing resin particle A. In addition, the polymerization time required for cooling from polymerization start to 25 degreeC was 8 hours. Further, the obtained resin particles are core-shell type particles in which the core is n-butyl polyacrylate and the shell is dicyclopentanyl polymethacrylate.

(monomer conversion rate)

The emulsion (0.100 g) sampled every hour from the start of the polymerization is added dropwise to a tetrahydrofuran solution (10.0 g, 0.1% by mass of 4-tert-butylcatechol added) to coat the polymer particles or the tetrahydrofuran solution of the polymer particles. was prepared. This solution was analyzed by gas chromatography (GC-14A manufactured by Shimadzu Corporation, column UAWAX-20EX-1.0F), and the monomer conversion rate (%) was calculated from the amount of the detected monomer and the added amount of the monomer at the start of the emulsion polymerization.

[Production Example 2] Production of Resin Particles B

In a twin screw extruder (manufactured by Parker Corporation), a (meth)acrylic block copolymer, methyl methacrylate-n-butyl acrylate-methyl methacrylate triblock copolymer (Kurarity (registered trademark) LA2140, Kura Co., Ltd.) 24% by mass of methyl methacrylate units, manufactured by Leh, was supplied at 0.66 kg/hr, and N-methylcyclohexylamine was added at 72 kg/hr from the middle of the cylinder (with respect to 100 moles of methyl methacrylate units in the (meth)acrylic polymer). 40 mol), and melt-kneaded at a cylinder temperature of 220°C and a screw rotation speed of 100 rpm. Thus, a methacrylic anhydride-n-butyl acrylic acid copolymer 1 was obtained. This was pulverized to 20 mm 3 or less and immersed in hot water at 80° C. for 24 hours to convert the acid anhydride into a carboxy group to obtain a methacrylic acid-n-butyl acrylic acid-methacrylic acid triblock copolymer. Thereafter, this copolymer was taken out by filtration, dried, and dissolved in methanol to a solid content concentration of 10% by mass. After that, methanol and water of the same mass were added dropwise to obtain a dispersion solution, and then the obtained solution was subjected to a reduced pressure treatment at 60°C, methanol was distilled off, and methacrylic acid-n-butyl acrylic acid-methacrylic acid triblock air An emulsion solution (resin content: 10% by mass) containing the composite resin particles B was obtained.

Below, commercially available resin particles used in Examples and Comparative Examples are shown.

Resin particle C: "AE986B" of e-tech company (acrylic resin particle)

Resin particle D: Saiden Chemical Co., Ltd. "UC-143" (acrylic resin particle)

Resin particle E: "QE-1042" manufactured by Seiko PMC

Resin particle F: "KE-1062" manufactured by Seikou PMC

Resin Particle G: "N827(A)-1" (Acrylic Resin Particles) manufactured by E-Tech Co., Ltd.

[Example 1]

(Manufacture of raw film)

PVA (saponified product of homopolymer of vinyl acetate, polymerization degree is 2,400, saponification degree is 99.95 mol%), glycerin (12 parts by mass with respect to 100 parts by mass of PVA) and surfactant (0.03 parts by mass with respect to 100 parts by mass of PVA Part) and water were mixed, and the PVA aqueous solution was obtained by dissolving at 90 degreeC for 4 hours. Then, 10 mass parts of resin particles A were added to this PVA aqueous solution with respect to 100 mass parts of PVA, and it stirred at 85 degreeC for 30 minutes. Then, for degassing of the PVA aqueous solution, the PVA aqueous solution was kept warm at 85°C for 16 hours.

The PVA aqueous solution was dried on a metal roll at 80°C to obtain a PVA film. Then, heat treatment was performed for 10 minutes with a dryer at 110°C to obtain a raw film of Example 1 having an average thickness of 30 µm.

(2) Manufacture of polarizing film

A rectangular test piece of 9 cm in the longitudinal direction x 5 cm in the width direction was sampled from the raw film obtained in the above (1). Both ends in the longitudinal direction of this test piece were fixed to a stretching jig so that the size of the stretched portion was 5 cm in the longitudinal direction x 5 cm in the width direction, and while immersed in water at a temperature of 30 ° C. for 38 seconds, a stretching speed of 24 cm / min. It was uniaxially stretched (first stage stretching) in the longitudinal direction to 2.2 times the original length. Thereafter, while being immersed for 60 seconds in an iodine/potassium iodide aqueous solution at a temperature of 30°C containing iodine at a concentration of 0.03% by mass and potassium iodide at a concentration of 3% by mass, at a stretching rate of 24 cm/min to 3.3 times the original length. It was uniaxially stretched (second stage stretching) in the longitudinal direction. Next, while immersed for about 20 seconds in a boric acid/potassium iodide aqueous solution at a temperature of 30°C containing boric acid at a concentration of 3% by mass and potassium iodide at a concentration of 3% by mass, at a stretching rate of 24 cm/min to 3.6 times the original length. It was uniaxially stretched (stretched in the third stage) in the longitudinal direction. Subsequently, while immersing in a boric acid/potassium iodide aqueous solution at a temperature of 58 ° C. containing boric acid at a concentration of 4% by mass and potassium iodide at a concentration of about 5% by mass, at a stretching rate of 24 cm / min. and uniaxial stretching (fourth stage stretching) was performed in the longitudinal direction up to the limit stretching ratio). Then, it was immersed for 10 seconds in the potassium iodide aqueous solution containing 1.5 mass % of boric acid, and potassium iodide at a density|concentration of 3 mass %, and the fixation process was performed. After that, it was made to dry for 4 minutes with a 60 degreeC drying machine, and the polarizing film (average thickness of 13 micrometers) of Example 1 which is a stretched optical film was obtained.

[Examples 2 to 6, Comparative Examples 1 to 4]

Each raw film and polarizing film of Examples 2-6 and Comparative Examples 1-4 were obtained in the same manner as in Example 1, except that the type and amount of the resin particles added to the PVA aqueous solution were shown in Table 1. . In Comparative Example 1, no resin particles were added.

[Comparative Example 5]

A raw film and a polarizing film of Comparative Example 5 were obtained in the same manner as in Comparative Example 1 except that the average thickness of the raw film was 60 µm. The average thickness of the obtained polarizing film was 26 micrometers.

[evaluation]

Using each obtained raw film, the glass transition temperature of the resin particles, the degree of swelling of the raw film, and the average particle diameter of the resin particles in the raw film were measured by the method described above. Moreover, using the obtained polarizing film, by the method described above, the length (A) (length in the stretching direction) and the length (B) (length in the direction perpendicular to the stretching direction) of the resin particles in the polarizing film, and their length ratio Measurement of (A/B), and evaluation of permeability, cutability, punchability, and polarization performance were performed. A result is shown in Table 1.

As shown in Table 1, it can be seen that the polarizing films obtained in Examples 1 to 6 had an evaluation of A or B in piercing properties, cutting properties, and punching properties, and were thin, difficult to tear, and had excellent handling properties and productivity. there is. Moreover, Examples 1-6 are implemented without passing through a complicated process, and it turns out that a polarizing film can be manufactured comparatively easily. Moreover, in the polarizing films of Examples 1-4, it turns out that polarization performance is also especially good.

On the other hand, the polarizing films obtained in Comparative Examples 1 to 4 have low piercing properties, cutability, and punching properties, and it turns out that they are easily torn. Moreover, in Comparative Example 5, although the obtained polarizing film had tear resistance, a thin polarizing film could not be obtained.

1: stretched optical film
2: resin particles
X: stretching direction
A: Length in the stretching direction
B: Length in the direction perpendicular to the stretching direction
industrial applicability
The raw film of this invention can be used suitably as materials, such as a polarizing film which is a constituent material of LCD. Moreover, the manufacturing method of the stretched optical film and the stretched optical film of this invention can be used suitably as a polarizing film or its manufacturing method.

Claims (5)

an average thickness of 45 μm or less;
Containing a vinyl alcohol-based polymer as a main component and resin particles having a glass transition temperature of 10 ° C. or less,
The raw film for stretched optical film manufacture whose content of the said resin particle with respect to 100 mass parts of said vinyl alcohol-type polymers is 1 mass part or more and 50 mass parts or less. According to claim 1,
The raw film whose average particle diameter of the said resin particle is 1 nm or more and 300 nm or less. The manufacturing method of the stretched optical film provided with the process of extending|stretching the raw film of Claim 1 or 2. The average thickness is 20 μm or less,
Containing a vinyl alcohol-based polymer as a main component and resin particles having a glass transition temperature of 10 ° C. or less,
The stretched optical film in which the content of the resin particles relative to 100 parts by mass of the vinyl alcohol-based polymer is 1 part by mass or more and 50 parts by mass or less. According to claim 4,
A stretched optical film wherein a length in the stretching direction of the resin particles observed in a transmission electron microscope image on a cut plane parallel to the stretching direction is longer than a length in a direction perpendicular to the stretching direction.

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