TWI682957B - Raw material film, method for manufacturing stretched optical film, and stretched optical film - Google Patents

Abstract

Provided is a blank film that can easily obtain a thin and difficult-to-tear stretched optical film; a thin and not easily torn-stretched optical film; and a stretched optical film that can relatively easily obtain such a stretched optical film Of manufacturing methods. The present invention is a raw material film for the production of stretched optical films, which has an average thickness of 45 μm or less, contains a vinyl alcohol polymer as a main component, and resin particles having a glass transition temperature of 30° C. or less, relative to the vinyl alcohol system The content of the resin particles in 100 parts by mass of the polymer is 1 part by mass or more and 50 parts by mass or less.

Description

Raw material film, method for manufacturing stretched optical film, and stretched optical film

The invention relates to a method for manufacturing a raw material film, a stretched optical film, and a stretched optical film.

A polarizing plate with light transmission and shielding functions, and a liquid crystal that changes the polarization state of light are the basic components of a liquid crystal display (LCD). Many polarizing plates have a structure in which a protective film such as cellulose triacetate (TAC) film is bonded to the surface of the polarizing film. As a polarizing film constituting a polarizing plate, a vinyl alcohol polymer film (hereinafter, abbreviated as "vinyl alcohol polymer" abbreviated as "PVA") is uniaxially stretched to adsorb the oriented stretch film. The dichroic pigments such as iodine pigments (I ₃ ^- , I ₅ ^-, etc.) or dichroic organic dyes have become mainstream. Such a polarizing film is obtained by uniaxially stretching a PVA film containing a dichroic dye in advance, or adsorbing the dichroic dye while uniaxially stretching the PVA film, or after uniaxially stretching the PVA film It is produced by adsorbing dichroic pigments and the like.

LCDs are gradually used in small devices such as computers and watches, smart phones, notebook computers, liquid crystal monitors, liquid crystal color projectors, LCD TVs, car navigation systems, mobile phones, and measurement equipment used indoors and outdoors. In scope. In recent years, especially with the progress of portable applications such as small notebook computers and mobile phones, the demand for thinner polarizing plates has gradually increased. In addition, since the use place is spread over a wide range, it is also required to improve durability.

As one method of thinning the polarizing plate, thinning of a polarizing film and a protective film can be mentioned. For this reason, it is necessary to reduce the thickness of the raw material film (PVA film) that is the raw material of the polarizing film. However, a thin raw material film is easily torn in the stretching direction in the drying step when manufacturing the polarizing film, the step of bonding the obtained polarizing film and the protective film, and the like. In addition, when the polarizing film is thin, when the polarizing film or polarizing plate is punched or cut, the polarizing film is easily torn in the stretching direction, or the end face of the polarizing film is likely to be fine. crack. Therefore, when a thin blank film is used, the productivity or yield of the polarizing plate or LCD is reduced, which tends to result in high cost. In this way, the thinning system of the raw material film or the polarizing film has lower productivity and yield, which easily leads to high cost. In addition, stretched optical films other than polarizing films such as retardation films are also expected to be thinner, but there are also such disadvantages that tearing and the like are likely to occur.

As a technique for manufacturing a thin polarizing film with good yield, a method of forming a thin PVA film on a plastic film by a coating method and stretching and drying the laminate is known (see Patent Documents 1 and 2). In addition, in order to improve the workability such as the punching property of the obtained polarizing film, it is also proposed that after manufacturing the polarizing film under specific conditions, the polarizing light of at least a single-area urethane resin layer in the polarizing film A board (refer to Patent Document 3); and a composition capable of forming a cured resin layer having excellent flexibility (refer to Patent Document 4).

Prior technical literature Patent Literature

Patent Literature 1 Japanese Patent No. 4804588

Patent Literature 2 Japanese Patent No. 4815544

Patent Document 3 Japanese Patent No. 3315914

Patent Document 4 Japanese Patent Application Publication No. 2014-115538

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

(1) The coating operation or the subsequent drying operation is complicated.

(2) The heat treatment for the insolubilization of the PVA film needs to be performed in the state of the laminate, so the plastic film used is limited to those that can be stretched after the heat treatment, and the cost becomes high.

(3) In a laminate formed by forming a PVA film on a plastic film by a coating method, the bonding strength between the plastic film and the PVA film is high. Therefore, if such a laminate having high adhesive strength is stretched, proper neck-in of the PVA film is hindered, and it is difficult to obtain a polarizing film excellent in polarizing performance.

In addition, the methods described in Patent Documents 3 and 4 also have disadvantages such as an increase in cost and a decrease in yield due to an increase in steps in the manufacture of polarizing plates.

The present invention is based on the above, and its purpose is to provide: a thin film that can easily obtain a thin and not easily stretched optical film; a thin and not easily torn optical film; and can be compared The method for producing such a stretched optical film is easily obtained.

The inventors have repeatedly conducted a keen review in order to achieve the above object, and found that even in the case of reducing the thickness of the film, it is possible to add resin particles with a lower glass transition temperature to the film. A stretched optical film that is not easily torn is obtained, and the review is further repeated based on the knowledge and knowledge to complete the present invention.

That is, the present invention completed to solve the above-mentioned problems is as follows.

[1] A raw material film for the production of a stretched optical film, the average thickness of which is 45 μm or less, contains a vinyl alcohol polymer as a main component, and resin particles having a glass transition temperature of 30° C. or less, relative to the vinyl alcohol system The content of the resin particles in 100 parts by mass of the polymer is 1 part by mass or more and 50 parts by mass or less.

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

[3] A method for manufacturing a stretched optical film, which includes a step of stretching a raw material film such as [1] or [2].

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

[5] The stretched optical film according to [4], wherein the length of the resin particles in the stretched direction observed by a transmission electron microscope image in a cut plane parallel to the stretched direction is comparable to that of the stretched The length in the direction perpendicular to the direction is long.

According to the present invention, it is possible to provide: a raw film that can relatively easily obtain a thin and difficult-to-tear stretched optical film; a thin and easily-tearable stretched optical film; and can relatively easily obtain such a stretch Manufacturing method of stretched optical film for optical film.

1‧‧‧Stretched optical film

2‧‧‧Resin particles

X‧‧‧Stretch direction

A‧‧‧Length in stretching direction

B‧‧‧Length in the direction perpendicular to the stretching direction

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

Forms for carrying out the invention <raw film>

The raw material film according to one embodiment of the present invention is used to produce a stretched optical film. That is, the raw material film is a film of a stretched optical film such as a polarizing film or a retardation film. By stretching the raw material film, a stretched optical film can be obtained.

The raw material film may be a single-layer film or a multilayer film (laminate). Examples of the form of the multilayer film include a film having a PVA layer formed on a thermoplastic resin film by a coating method or the like. From the viewpoint of further exhibiting the effects of the present invention, the complexity of lamination (coating, etc.) operations, and the cost of the thermoplastic resin film, the raw material film is preferably a single-layer film.

(The average thickness)

The upper limit of the average thickness of the raw material film is 45 μm, preferably 40 μm, more preferably 35 μm, and still more preferably 30 μm. When the average thickness of the raw material film is equal to or less than the above upper limit, a thin stretched optical film can be obtained. On the other hand, the lower limit of the average thickness is preferably 1 μm, more preferably 3 μm, even more preferably 10 μm, and even more preferably 20 μm. When the average thickness of the raw material film is at least the above lower limit, the tear resistance of the obtained stretched optical film can be further improved.

(PVA)

This raw material film contains PVA (vinyl alcohol polymer) as a main component. In addition, the main component refers to the component with the largest content on a mass basis (the same applies hereinafter). The PVA system has a vinyl alcohol unit (-CH ₂ -CH(OH)-) as a structural unit. PVA may have vinyl ester units and other units in addition to vinyl alcohol units.

As the PVA, it is possible to use vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, trimethyl vinyl acetate, vinyl kohterate, vinyl laurate, vinyl stearate , Vinyl benzoate, propylene acetate and other vinyl esters are obtained by polymerizing one or more polyvinyl esters by saponification. Among the above-mentioned vinyl esters, from the viewpoints of ease of production, availability, and cost of PVA, compounds having a vinyloxycarbonyl group (H ₂ C=CH-O-CO-) in the molecule are more preferred. Preferably vinyl acetate.

The above-mentioned polyvinyl ester is preferably obtained by using only one kind or two or more kinds of vinyl esters as monomers, and more preferably obtained by using only one kind of vinyl esters as monomers, as long as it does not significantly damage the present invention. Within the range of effects, it may be a copolymer of one or more vinyl esters and other monomers copolymerizable therewith.

Examples of other monomers copolymerizable with the vinyl esters include α-olefins having 2 to 30 carbon atoms such as ethylene, propylene, 1-butene, and isobutene; (meth)acrylic acid or its salts; Methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate (Meth)acrylates such as esters, tertiary butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, dodecyl (meth)acrylate, octadecyl (meth)acrylate, etc. ; (Meth) acrylamide; N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, diacetone (Meth)acrylamide, (meth)acrylaminopropanesulfonic acid or its salt, (meth)acrylamidepropylpropyl dimethylamine or its salt, N-hydroxymethyl (methyl) (Meth)acrylamide derivatives such as acrylamide or its derivatives; N-vinylamide such as N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone; Methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tertiary butyl vinyl ether, twelve Vinyl ethers such as alkyl vinyl ether and stearyl vinyl ether; vinyl cyanide such as (meth)acrylonitrile; vinyl halide such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride; allyl acetate Allyl compounds such as esters and chloropropene; maleic acid, or its salts, esters, or anhydrides; itaconic acid, or its salts, esters, or anhydrides; vinylsilyl compounds such as vinyltrimethoxysilane; unsaturated sulfonates Acid or its salt.

The polyvinyl ester may have one or more structural units derived from the monomer.

Based on the number of moles of all the structural units constituting the polyvinyl ester, the upper limit of the proportion of the structural units derived from other monomers in the polyvinyl ester is preferably 15 mol%, more preferably 10 mol% , Even better is 5 mol%, Even better is 1 mol%.

As the PVA, a non-grafted copolymer can be preferably used. However, as long as the effect of the present invention is not significantly impaired, PVA may be modified by one or two or more monomers that can be graft copolymerized. The graft copolymerization can be performed on at least one of polyvinyl ester and PVA obtained by saponifying it. Examples of the graft copolymerizable monomer include unsaturated carboxylic acid or its derivative; unsaturated sulfonic acid or its derivative; and α-olefin having 2 to 30 carbon atoms. The ratio of the structural units derived from the monomer which can be graft copolymerized in the polyvinyl ester or PVA is preferably 5 mol% or less based on the number of moles of all the structural units constituting the polyvinyl ester or PVA.

The PVA may have a part of its hydroxyl groups cross-linked or may not be cross-linked. In addition, the PVA may partially react with aldehyde compounds such as acetaldehyde and butyraldehyde to form an acetal structure, or may not form an acetal structure without reacting with these compounds.

The lower limit of the polymerization degree of the PVA is preferably 1,000, more preferably 1,500, and even more preferably 2,000. When the degree of polymerization of PVA is at least the above lower limit, the optical properties of the obtained stretched optical film can be improved. On the other hand, the upper limit of the polymerization degree is preferably 10,000, more preferably 8,000, and even more preferably 5,000. By setting the polymerization degree of PVA to the above upper limit or less, it is possible to suppress an increase in the production cost of PVA and the occurrence of defects during film formation. In addition, the degree of polymerization of PVA means the average degree of polymerization measured in accordance with the description of JIS K6726-1994.

The lower limit of the degree of saponification of PVA becomes better due to the moisture and heat resistance of the obtained stretched optical film, and it is preferably 95 mol%, more preferably 98 mol%, and even more preferably 99 mol%. The best is 99.5 mol%. On the other hand, the upper limit of the degree of saponification may be substantially 100 mol%. In addition, the degree of saponification of PVA refers to the ratio of the number of moles of vinyl alcohol units to the total number of moles of structural units (typically vinyl ester units) that can be converted into vinyl alcohol units by saponification and vinyl alcohol units (Mohr%). The degree of saponification can be measured according to the description of JIS K6726-1994.

The lower limit of the PVA content in the raw material film is preferably 60% by mass, more preferably 70% by mass, and even more preferably 75% by mass. By setting the content of PVA to the above lower limit or more, the obtained stretched optical film exhibits better optical characteristics such as polarization performance. On the other hand, the upper limit of this content is preferably 95% by mass, more preferably 90% by mass, and even more preferably 85% by mass. By setting the content of PVA to the upper limit or less, the obtained stretched optical film becomes more difficult to tear.

(Resin particles)

The raw material film contains resin particles having a glass transition temperature of 30°C or lower. By containing such resin particles, the raw material film can obtain a thin stretched optical film that is not easily torn. The reason for this effect is not clear, but the cross section of the stretched optical film made from this raw material film tearing section is rough, so it is presumed that the resin particles dispersed in the film suppress the tearing Spread, and it becomes difficult to tear. In particular, the glass transition temperature of the resin particles is 30° C. or lower, that is, the general stretching treatment temperature when manufacturing a stretched optical film using a raw material film, and the resin particles can also be Deformation in the direction of stretching. This allows PVA to be sufficiently aligned while maintaining the adhesion between PVA and resin particles. Therefore, it is presumed that the stretched optical film obtained from the raw material film is less likely to tear, and by adjusting the content and average particle diameter of the resin particles, the optical properties such as polarizing performance can also be improved.

Resin particles refer to particles whose main component is a polymer (resin). The lower limit of the content of the polymer in the resin particles is, for example, 50% by mass, preferably 80% by mass, and more preferably 95% by mass. The resin particles may be substantially formed of resin only.

The upper limit of the glass transition temperature (Tg) of the resin particles (Tg of the polymer of the main component of the resin particles) is 30°C, preferably 25°C, more preferably 20°C, even more preferably 15°C, even more preferably 10℃. By this, the glass transition temperature is equal to or lower than the above upper limit, and a stretched optical film that is hard to tear can be obtained. In addition, by setting the glass transition temperature to be equal to or lower than the above upper limit, and adjusting the content and average particle diameter of the resin particles, optical characteristics such as polarizing performance can also be improved.

The lower limit of the glass transition temperature of the resin particles is not particularly limited. For example, it is preferably -100°C, more preferably -80°C, and even more preferably -60°C. By setting the glass transition temperature to the above lower limit or more, the aggregation of resin particles at the time of heating in the film-forming step of producing the raw material film is suppressed, and the resulting raw material film and stretched optical film can be suppressed Cloudy. In addition, the optical properties of the obtained stretched optical film can be improved.

In addition, the glass transition temperature of the resin particle is a measured value by DSC (differential scanning calorimetry) using the resin particle to form a film and the resin film obtained therefrom. In the case where the resin particles contain a plurality of different resins, the glass transition temperature of the resin having the lowest glass transition temperature is set as the glass transition temperature of the resin particles.

The lower limit of the content of the resin particles in the raw material 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 the above lower limit or more, the obtained stretched optical film is less likely to be torn and handling properties and the like can be 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 to the above upper limit or less, the light transmittance of the obtained stretched optical film can be kept in a good state, and the optical characteristics such as polarizing performance can be improved.

The lower limit of the average particle diameter of the resin particles in the raw material film is preferably 1 nm, more preferably 5 nm, still more preferably 10 nm, still more preferably 20 nm, and still more preferably 30 nm. By setting the average particle diameter of the resin particles to the above lower limit or more, the obtained stretched optical film becomes more resistant to tearing and improves workability and the like. On the other hand, the upper limit of the average particle diameter may be, for example, 500 nm, preferably 300 nm, more preferably 200 nm, and even more preferably 100 nm. By setting the average particle diameter of the resin particles to the above upper limit or lower, particularly 300 nm or lower, the optical transmittance of the obtained stretched optical film can be made good, and optical characteristics such as polarization performance can be improved.

In addition, the average particle diameter of the resin particles in this raw material film is the measured value based on the TEM (transmission electron microscope) image of the cut surface of the film. By measuring the TEM of the cut surface perpendicular to the in-plane direction of the raw material film, the presence or absence and dispersion state of the resin particles can be observed in the form of 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 continuous part (sea part) in a mixture containing two physical properties. Since the resin particles and PVA have different dyeing properties, the color of the continuous part becomes darker and the color of the discontinuous part becomes lighter, or the color of the continuous part becomes lighter and the part which looks discontinuous The color becomes darker. In this TEM image, resin particles are observed as islands. For the TEM image of the cut surface of the film, using image analysis software, the resin particles are mechanically selected, and the average diameter of these resin particles is calculated. This calculated value is taken as the average particle diameter of the resin particles. The specific measurement method of the average particle diameter of resin particles is the method described in the Example.

The resin particles contain polymers. The polymer is not particularly limited as long as it has a glass transition temperature of 30° C. or lower, and examples thereof include polyolefins, polyurethanes, acrylic resins, and the like, and acrylic resins are preferred. Acrylic resin refers to a polymer containing structural units derived from (meth)acrylate.

Examples of (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, and hexyl (meth)acrylate. Esters, dodecyl (meth)acrylate, octadecyl (meth)acrylate, and other (meth)acrylic acid alkyl esters; (meth)acrylic acid dicyclopentyl ester, (meth)acrylic acid isobutyl ester, etc. Alicyclic (meth)acrylate; phenyl (meth)acrylate and other (meth)acrylic acid aryl esters.

The resin particles, among the acrylic resins, preferably include an acrylic resin containing a structural unit (alkyl (meth)acrylate unit) derived from alkyl (meth)acrylate. The lower limit of the carbon number of the alkyl group in the alkyl (meth)acrylate is 1, preferably 2, more preferably 3, and even more preferably 4. On the other hand, the upper limit of the carbon number of this alkyl group is, for example, 10, preferably 8, more preferably 6, and even more preferably 4. Moreover, it is also preferably an alkyl acrylate unit. That is, among the alkyl (meth)acrylate units, the butyl acrylate unit is the most preferable. The resin particles using an acrylic resin containing such alkyl (meth)acrylate units have a low glass transition point and can further increase the difficulty of tearing and the optical characteristics. The reason is not clear, but it is presumed that the flexibility of the resin particles is improved, and the resin particles are easily deformed in the stretching direction during the stretching process.

As the acrylic resin, an acrylic resin containing (meth)acrylic units (-CH ₂ -CHCOOH- and -CH ₂ -C(CH ₃ )COOH-) can also be suitably used. Resin particles using such polymers can exhibit good dispersibility in the PVA matrix. In this case, for example, a block copolymer of (meth)acrylic acid units and alkyl (meth)acrylate units is preferable. In addition, when the acrylic resin is a block copolymer, it may be any of a diblock copolymer, a triblock copolymer, and the like.

For the resin particles, particles made of one kind of polymer may be used, or particles having a so-called core-shell structure with different materials on the inside and the outside may be used. When core-shell type particles are used, the core material preferably includes an acrylic resin containing an alkyl (meth)acrylate unit. In addition, when a core-shell type particle is used, the material of the shell is preferably an acrylic resin containing an alicyclic group-containing (meth)acrylate unit or (meth)acrylic unit.

The resin particles can be produced by a well-known method. In addition, commercially available resin particles can be used. In addition, the method of including resin particles in the raw material film is not particularly limited. For example, resin particles may be added to the PVA chip, or resin particles may be added to the film-forming stock solution used during film formation.

(Plasticizer)

The raw material film can further contain a plasticizer. The raw material film can improve the operability and stretchability by including a plasticizer. Preferred plasticizers include polyhydric alcohols, and specific examples include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, and trihydroxy. Methyl propane and so on. One or more of these plasticizers can be used. Among these, from the viewpoint of the effect of improving stretchability, glycerin is preferred.

The lower limit of the content of the plasticizer in the raw material film is preferably 2 parts by mass, more preferably 3 parts by mass, even more preferably 4 parts by mass, and even more preferably 6 parts by mass with respect to 100 parts by mass of PVA. Copies. By setting the content of the plasticizer to the above lower limit or more, the stretchability is further improved. On the other hand, the upper limit of this content is preferably 20 parts by mass, more preferably 17 parts by mass, and still more preferably 14 parts by mass. By setting the content of the plasticizer to be equal to or less than the above upper limit, it is possible to suppress the raw material film from becoming too soft, or the plasticizer oozing out of the surface, and reducing the workability.

(Other additives, etc.)

In addition to PVA, resin particles and plasticizers, this raw material film can be further suitably blended as needed: processing stabilizers such as fillers, copper compounds, weather resistance stabilizers, colorants, ultraviolet absorbers, Light stabilizers, antioxidants, antistatic agents, flame retardants, other thermoplastic resins, lubricants, fragrances, defoamers, deodorants, extenders, stripping agents, mold release agents, reinforcing agents, crosslinking agents , Antifungal agent, preservative, crystallization rate delay agent and other additives.

However, the upper limit of the content of the additives other than PVA, resin particles, and plasticizer in the raw material film is preferably 1% by mass, and more preferably 0.2% by mass. When the content of other additives exceeds the above upper limit, the tear strength or optical characteristics of the obtained stretched optical film may be affected.

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

The shape of the raw material film is not particularly limited, and a stretched optical film can be continuously produced with good productivity, and a long film is preferred. The length of the elongated raw film is not particularly limited, and can be appropriately set according to the use of the stretched optical film to be produced, for example, it can be set within a range of 5 m or more and 20,000 m or less. The width of the raw material film is not particularly limited. For example, the lower limit can be set to 50 cm. In recent years, a wide-width polarizing film has been required. The lower limit is preferably 1 m, more preferably 2 m, and even more preferably 4 m. The upper limit of the width of the raw material film is not particularly limited, and it can be set to 7 m, for example. If the width is too wide, when a stretched optical film is manufactured with a practical device, it tends to become difficult to stretch uniformly.

This raw material film can relatively easily produce a stretched optical film that is not easily torn during manufacturing or during operation. Therefore, it can be suitably used as a material for stretched optical films such as polarizing films and retardation films. Among them, the raw material film can easily produce a polarizing film having good polarizing performance, so it is particularly preferably used as a raw material film for manufacturing a polarizing film.

(Production method of blank film)

The production method of the raw material film of the present invention is not particularly limited, and a production method in which the thickness and width of the raw material film after film formation are made more uniform can be preferably used. For example, it is possible to use one or two or more of the above-mentioned PVA and resin particles constituting a raw material film dissolved in a liquid medium, and further plasticizers, other additives, and surfactants described later, etc. The film-forming stock solution is obtained by film-forming. In addition, if necessary, it can also be produced using a film-forming stock solution in which PVA is melted. In the film-forming stock solution, it is preferable to uniformly mix the resin particles. In addition, when the film-forming stock solution contains at least one of a plasticizer, other additives, and a surfactant, it is preferable to uniformly mix these components.

As the liquid medium, for example, water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol Ethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, diethylenetriamine, etc. One or more of these liquid media can be used. Among these, from the viewpoint of low environmental burden and recyclability, water is preferred.

The volatile fraction of the film-forming stock solution (the content ratio of the volatile components in the liquid medium removed by volatilization or evaporation during film-forming in the film-forming stock solution) varies according to the film-forming method, film-forming conditions, etc. In general, the lower limit is preferably 50% by mass, more preferably 55% by mass, and even more preferably 60% by mass. The volatile content of the film-forming stock solution is above the lower limit, and the viscosity of the film-forming stock solution does not become too high, and the filtration and degassing system at the time of preparation of the film-forming stock solution proceed smoothly, and the raw material film with few foreign materials and defects Manufacturing becomes easy. On the other hand, the upper limit of the volatile fraction is preferably 95% by mass, more preferably 90% by mass, and even more preferably 85% by mass. The volatile fraction of the film-forming stock solution is below the upper limit, and the concentration of the film-forming stock solution does not become too low, and industrial production of the raw material thin film becomes easy.

The film-forming stock solution preferably contains a surfactant. By including a surfactant, the film-forming property is improved to suppress the occurrence of uneven thickness of the raw material film, and the film becomes easy to peel off the metal roll or tape used for the self-made film. When a raw material film is produced from a film-forming stock solution containing a surfactant, the raw material film may contain a surfactant. The type of the above-mentioned surfactant is not particularly limited, and from the viewpoint of releasability from a metal roll or belt, etc., an anionic surfactant and a nonionic surfactant are preferred.

As the anionic surfactant, for example, carboxylic acid types such as potassium laurate; sulfonic acid ester types such as polyoxyethyl lauryl ether sulfate and octyl sulfate; and sulfonic acids such as dodecylbenzenesulfonate are preferred Type and so on.

As the nonionic surfactant, for example, an alkyl ether type such as polyoxyethylene ethyl oleyl ether; an alkyl phenyl ether type such as polyoxyethyl octyl phenyl ether; polyoxyethylene Alkyl ester type such as laurate; alkylamine type such as polyoxyethyl lauryl amino ether; alkyl amide type such as polyoxyethyl lauryl amide; polyoxyethyl ethyl polyoxypropylene Polypropylene glycol ethers such as alkyl ethers; alkanolamides such as lauric acid diethanolamide and oleic acid diethanolamide; allylphenyl ethers such as polyoxyalkylene allylphenyl ether.

These surfactants can be used alone or in combination of two or more.

When the film-forming stock solution or the obtained raw material film contains a surfactant, the lower limit of the content is 100 parts by mass of PVA contained in the film-forming stock solution or the raw material film, preferably 0.01 part by mass, more It is preferably 0.02 parts by mass. When the content of the surfactant is equal to or higher than the above lower limit, the film-forming properties and peelability are further improved. On the other hand, the upper limit of this content is preferably 0.5 parts by mass, more preferably 0.3 parts by mass, and even more preferably 0.1 parts by mass. When the content of the surfactant is equal to or lower than the above upper limit, the surfactant can be suppressed from seeping out of the surface of the raw material film, blocking occurs, and the workability is reduced.

Examples of the film-forming method when manufacturing the raw material thin film using the above-mentioned film-forming stock 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 used alone or in combination of two or more. Among these film-forming methods, the casting film-forming method and the extrusion film-forming method can obtain a raw material film with uniform thickness and width and good physical properties, which is preferable. For the blank film made by the film, it can be dried and heat-treated as required.

The heat treatment temperature is not particularly limited as long as it is appropriately adjusted. If the heat treatment temperature is too high, discoloration or deterioration of the raw material film can be seen. Therefore, the upper limit of the heat treatment temperature is preferably 210°C, more preferably 180°C, and even more preferably 150°C. On the other hand, the lower limit of the heat treatment temperature is, for example, 60°C, preferably 90°C.

The heat treatment time is not particularly limited as long as it is appropriately adjusted. From the viewpoint of efficiently manufacturing the raw material film, the upper limit is preferably 30 minutes, and more preferably 15 minutes. On the other hand, the lower limit is, for example, preferably 1 minute, and more preferably 3 minutes.

<Stretched Optical Film>

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

(The average thickness)

The upper limit of the average thickness of the stretched optical film is 20 μm, preferably 18 μm, more preferably 16 μm, and still more preferably 14 μm. When the average thickness of the stretched optical film is equal to or less than the above upper limit, sufficient thinning can be achieved. On the other hand, the lower limit of the average thickness is preferably 5 μm, more preferably 8 μm, and even more preferably 10 μm. When the average thickness of the stretched optical film is at least the above lower limit, it is less likely to be torn and can improve workability.

(Ingredients, etc.)

The stretched optical film contains PVA and resin particles as main components.

The upper limit of the glass transition temperature (Tg) (Tg of the polymer of the main component of the resin particles) of the resin particles contained in the stretched optical film is 30°C, preferably 25°C, more preferably 20°C, and even more It is preferably 15°C, and even more preferably 10°C. As a result, the glass transition temperature is equal to or lower than the above upper limit, and the stretched optical film is less likely to tear and is excellent in handleability and the like. In addition, by setting the glass transition temperature to be equal to or lower than the above upper limit, and adjusting the content and average particle diameter of the resin particles, optical characteristics such as polarizing performance can also be improved. The lower limit of the glass transition temperature of the resin particles is not particularly limited. For example, it is preferably -100°C, more preferably -80°C, and even more preferably -60°C. By setting the glass transition temperature to the above lower limit or more, the aggregation of the resin particles is suppressed, and the cloudiness of the stretched optical film can be suppressed. In addition, the optical characteristics of the 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 that of the resin particles contained in the raw material film, and it is assumed that the resin film obtained by using the resin particles is formed and the DSC ( Measured value of differential scanning calorimetry).

The lower limit of the content of the resin particles in the stretched optical 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 the above lower limit or more, the stretched optical film is less likely to tear, and the workability and the like can be 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 to the above upper limit or less, the optical transmittance of the stretched optical film can be kept in a good state, and the optical characteristics such as polarizing performance can be improved.

In this stretched optical film, the length of the resin particles in the above-mentioned stretching direction (diameter in the stretching direction), which is observed in a transmission electron microscope (TEM) image in a cut plane parallel to the stretching direction, is preferably It is longer than the length in the direction perpendicular to the stretching direction (diameter in the direction perpendicular to the stretching direction). That is, the resin particles in the stretched optical film preferably have an elliptical shape having a long axis along the stretching direction. In such a case, PVA can form a sufficient alignment state while maintaining the adhesion between PVA and the resin particles. Therefore, it is presumed that the stretched optical film becomes less prone to tearing, and by adjusting the content and average particle diameter of the resin particles, the optical properties such as polarizing performance can also be improved. In addition, such elliptical resin particles can be formed by deforming the resin particles in the stretching direction when the raw material film including the resin particles having a glass transition temperature of 30° C. or lower is subjected to stretching treatment. In addition, the stretching direction in the stretched optical film is usually the alignment direction of the crystals of PVA.

Specifically, as shown in FIG. 1, in the TEM image of the cut surface of the stretched optical film 1 parallel to the stretching direction X, the length A of the resin particles 2 (islands) in the stretching direction X is preferable It is longer than the length B in the direction perpendicular to the stretching direction X. Furthermore, the lower limit of the ratio (A/B) of the length A of the resin particle 2 in the stretching direction X to the length B in the direction perpendicular to the stretching direction X is preferably 1.2, and more preferably 1.6. More preferably, it is 2.0. In addition, the upper limit of this ratio (A/B) may be, for example, 3 or 2.6.

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, and still more preferably 70 nm. On the other hand, the upper limit of the length A may be, for example, 800 nm, preferably 300 nm, more preferably 200 nm, and even more preferably 100 nm. In addition, the lower limit of the length B of the resin particles in the direction perpendicular to the stretching direction is preferably 1 nm, more preferably 10 nm, even more preferably 20 nm, and still more preferably 30 nm. On the other hand, the upper limit of the length B may be, for example, 500 nm, preferably 200 nm, more preferably 100 nm, and even more preferably 50 nm. When the length A and the length B are within the above ranges, tearing is less likely to occur, and by adjusting the content and average particle diameter of the resin particles, optical characteristics such as polarizing performance can also be improved.

The length A of the resin particles in the stretching direction and the length B in the direction perpendicular to the stretching direction were measured by the following methods. For the TEM image of the cut surface of the film parallel to the stretching direction, the resin particles were mechanically selected using image analysis software. The average length of the selected resin particles in the long axis direction is calculated as the length A, and the average length in the short axis direction is calculated as the length B. From this length A and length B, the length ratio (A/B) is also obtained. These specific measurement methods are the methods described in the examples.

The preferred form of the PVA and resin particles contained in the stretched optical film is the same as the PVA and resin particles contained in the raw material film described above. The other components that can be contained in the stretched optical film are also the same as the above-mentioned raw material 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 dye is generally used.

In the case where the stretched optical film is a polarizing film, in terms of its polarizing performance, the lower limit of the degree of polarization at a transmittance of 44.0% may be, for example, 70%, preferably 99.0%, and more preferably 99.8% And even better is 99.9%. In the case where the polarization degree is less than the above lower limit, if it is used in a smartphone, a notebook computer, an LCD TV, an on-board navigation system, etc., the LCD contrast may be lowered.

When the stretched optical film is a polarizing film, the polarizing film is generally used as a polarizing plate by bonding a protective film that is optically transparent and has mechanical strength on both sides or one side. As the protective film, cellulose triacetate (TAC) film, cellulose acetate butyrate (CAB) film, acrylic film, polyester film, etc. can be used. In addition, examples of the adhesive used for bonding include a PVA-based adhesive, an ultraviolet curing adhesive, and the like, and a PVA-based adhesive is preferred.

The polarizing plate obtained as described above can be further laminated with a retardation film, a viewing angle enhancement film, a brightness enhancement film, and the like. In addition, the stretched optical film of the present invention can also be used as the above-mentioned retardation film. The polarizing plate can be used as an LCD component after being coated with an adhesive such as acrylic and then bonded to a glass substrate.

<Manufacturing method of stretched optical film>

The stretched optical film according to an embodiment of the present invention can be obtained by a manufacturing method including the step of stretching the above-mentioned raw material film. That is, this stretched optical film can be produced by the same method as in the prior art except that the above-mentioned raw material film is used. That is, according to this manufacturing method, it is possible to obtain a stretched optical film that is thin and difficult to tear relatively easily without passing through special steps. Hereinafter, a specific manufacturing method in the case where the stretched optical film is a polarizing film will be described.

Specific methods for manufacturing the polarizing film include swelling treatment, dyeing treatment, uniaxial stretching treatment, and further cross-linking treatment, fixing treatment, cleaning treatment, and drying treatment as required. , Heat treatment, etc. In this case, the order of each treatment such as swelling treatment, dyeing treatment, cross-linking treatment, uniaxial stretching, and fixing treatment is not particularly limited, and two or more treatments can be performed simultaneously. In addition, one or two or more of each process may be performed twice or more.

The swelling treatment can be performed by immersing the raw material film in water. The lower limit of the temperature of water when immersed in water is preferably 20°C, more preferably 22°C, and even more preferably 25°C. On the other hand, the upper limit of this temperature is preferably 40°C, more preferably 38°C, and even more preferably 35°C. The lower limit of the time for immersion in water is preferably 0.1 minutes, and more preferably 0.5 minutes. On the other hand, the upper limit of this time is preferably 5 minutes, and more preferably 3 minutes. In addition, the water when immersed in water is not limited to pure water, and may be an aqueous solution in which various components are dissolved, or may be a mixture of water and an aqueous medium.

The dyeing process can be performed by bringing a dichroic dye into contact with the raw material film. As the dichroic pigment, an iodine pigment is generally used. The timing of the dyeing process may be any stage before the uniaxial stretching process, during the uniaxial stretching process, and after the uniaxial stretching process. The dyeing treatment is generally performed by immersing the raw material film in a solution (especially an 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. In addition, the lower limit of the temperature of the dyeing bath is preferably 20°C, more preferably 25°C. On the other hand, the upper limit of this temperature is preferably 50°C, and more preferably 40°C.

By performing a cross-linking treatment on the raw material film, it is possible to effectively prevent the PVA from dissolving into water when wet stretching is performed at a high temperature. From this viewpoint, the cross-linking treatment is preferably performed before the uniaxial stretching treatment. The cross-linking treatment can be performed by immersing the raw material film in an aqueous solution containing a cross-linking agent. As the cross-linking agent, one or more types of boron inorganic compounds such as boric acid such as boric acid and borax can be used. The lower limit of the concentration of the crosslinking agent in the aqueous solution containing the crosslinking agent is preferably 1% by mass, more preferably 2% by mass, and even more preferably 3% by mass. On the other hand, the upper limit of this concentration is preferably 15% by mass, more preferably 7% by mass, and even more preferably 6% by mass. When the concentration of the crosslinking agent is within the above range, sufficient stretchability can be maintained. The aqueous solution containing the cross-linking agent may contain additives such as potassium iodide. The lower limit of the temperature of the aqueous solution containing the crosslinking agent is preferably 20°C, and more preferably 25°C. On the other hand, the upper limit of this temperature is preferably 50°C, and more preferably 40°C. By setting this temperature within the above range, crosslinking can be performed efficiently.

The uniaxial stretching treatment can be performed by any one of a wet stretching method and a dry stretching method. In the case of the wet stretching method, it can be carried out in an aqueous solution of boric acid, and can also be carried out in the above-mentioned dyeing bath or a fixing treatment bath described later. In addition, in the case of the dry stretching method, uniaxial stretching treatment may be performed while maintaining room temperature, or uniaxial stretching treatment may be performed while heating, or the raw material film after water absorption may be used in air Perform uniaxial stretching. Among these, the wet stretching method is preferable, and the uniaxial stretching treatment in a boric acid aqueous solution is more preferable. The lower limit of the boric acid concentration of the aqueous solution of boric acid is preferably 0.5% by mass, more preferably 1.0% by mass, and even more preferably 1.5% by mass. On the other hand, the upper limit of the boric acid concentration is preferably 6.0% by mass, more preferably 5.0% by mass, and even more preferably 4.0% by mass. In addition, the boric acid aqueous solution may contain potassium iodide, and its concentration is preferably 0.01% by mass or more and 10% by mass or less.

The lower limit of the stretching temperature in the uniaxial stretching process is preferably 30°C, more preferably 40°C, and even more preferably 50°C. By setting the lower limit of the stretching temperature to 30° C., which is the upper limit of the glass transition temperature of the resin particles, the resin particles deform well so as to extend in the stretching direction during stretching. This makes it possible to obtain a stretched optical film that is less likely to be torn and is excellent in handleability.

The lower limit of the stretching ratio in the uniaxial stretching process is preferably 5 times, more preferably 5.5 times, and even more preferably 6 times from the viewpoint of the polarization performance of the obtained polarizing film. The upper limit of the stretching magnification is not particularly limited. For example, it is preferably 10 times, and more preferably 8 times.

When manufacturing a polarizing film, in order to stabilize the adsorption of the dichroic dye (iodine-based dye, etc.) to the raw material film, it is preferable to perform a fixing treatment after uniaxial stretching treatment. As the fixing treatment bath used in the fixing treatment, an aqueous solution containing one or more kinds of boron inorganic compounds such as boric acid and borax can be used. In addition, if necessary, an iodine compound or a metal compound may be added to the fixed treatment bath. The lower limit of the concentration of the boron inorganic compound in the fixed treatment bath is preferably 0.5% by mass, more preferably 1% by mass. On the other hand, the upper limit of this concentration is preferably 15% by mass, more preferably 10% by mass. By setting this concentration within the above range, the adsorption of the dichroic pigment can be made more stable. 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, more preferably 40°C.

The cleaning treatment is generally performed by immersing the raw material film in water or the like. At this time, from the viewpoint of improving the polarization performance, it is preferable that the water and the like used in the cleaning treatment contain an auxiliary agent such as potassium iodide. In this case, the concentration of iodide such as potassium iodide is preferably 0.5% by mass or more and 10% by mass or less. In addition, the lower limit of the temperature of water and the like used in 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 economic point of view, the temperature of water or the like is too low to be bad. On the other hand, if the temperature of water or the like is too high, the polarization performance may be reduced.

The conditions of the drying treatment are not particularly limited, and the lower limit of the drying temperature is preferably 30°C, and more preferably 50°C. On the other hand, the upper limit of the drying temperature is preferably 150°C, and more preferably 130°C. By drying at a temperature within the above range, a polarizing film excellent in dimensional stability is easily obtained.

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

<Other embodiments>

The method of manufacturing the raw material film, the stretched optical film, and the stretched optical film of the present invention is not limited to the above-mentioned embodiments. For example, the stretched optical film and its manufacturing method will be described mainly on the case where the stretched optical film is a polarized film, but the stretched optical film is not limited to the polarized film. For example, a stretched optical film other than a polarizing film such as a retardation film is also within the scope of the present invention, and can be manufactured by a manufacturing method including a step of stretching the raw material film of the present invention. As a method of manufacturing a phase difference film according to an embodiment of the present invention, in addition to stretching the raw material film of the present invention, a conventionally known method can be used.

[Example]

The present invention will be described more specifically by the following examples, but the present invention is not limited by these examples. In addition, the evaluation methods used in the following examples and comparative examples are shown below.

[Glass transition temperature of resin particles]

After dissolving the raw material film obtained in each of the following examples or comparative examples in water, it was filtered with a filter that trapped resin particles (Merck's "MF-Millipore Membrane Filter VSWP" pore size 0.025 μm), The collected matter (resin particles) is dried. After that, by heat-treating the resin particles at 100° C., a resin film formed of only the resin particles is taken. Using DSC ("Q2000" of TA Instruments), the glass transition temperature of the resin film was determined. Use this as the glass transition temperature of the resin particles.

[Bulking degree of blank film]

About 1.5 g of the raw material film obtained in each of the following examples or comparative examples was taken. After cutting it to about 2 mm × 10 cm, it was wrapped in a 100 mesh (100 mesh) ("N-N0110S 115" by NBC Meshtech) and immersed in distilled water at 30C for 15 minutes. Then, centrifugal dehydration was carried out at 3,000 rpm for 5 minutes, and the swollen blank film quality was obtained after removing the sieve (W1). Next, after drying the raw material film with a dryer at 105° C. for 16 hours, the mass (W2) was determined. The swelling degree of the raw material film was calculated by the following formula.

Swelling (%)={(W1)/(W2)}×100

[Average particle diameter of resin particles in the raw material film]

After cutting the raw material film obtained in each of the following examples or comparative examples with an ultra-thin slicer ("Ultracut S/FC-S" by Leica), in a vapor of osmium tetroxide, a gas at 23°C After exposure to the environment for 5 days, the hydroxyl group of PVA was dyed. After the dyeing process, a diamond knife (DiATOME's "Ultra Cryo Dry" 2 mm, 35°) was further used to cut out frozen slices for observation under a gas environment of -100°C. After that, the frozen sections that were over-stained for observation were washed with distilled water and dried. The cut surface was observed using a transmission electron microscope ("Transmission Electron Microscope HT7000" by Hitachi High-Technologies) to obtain a TEM image. The acceleration voltage is set to 100 kV, the emission current is set to 10 μA, and the electron gun uses LaB6 filament.

Using the TEM image obtained by the above method, the average particle diameter of the resin particles in the raw material film was measured by the following method. First, use the image analysis software "Image-Pro Plus 7.0J" (manufactured by Media Cybernetics) to open the TEM image, change it to 8-bit level in "Conversion", and perform flattening in "Filtering". Next, set the contrast value to 80 in "Contrast Enhancement" and select "Average Particle Size" in the measurement item setting page in "Count/Size" to automatically select brightly colored objects to mechanically select the resin For particles, calculate the average particle diameter of the resin particles in the raw material film. In addition, a particle size smaller than 1/10 of the maximum diameter in the TEM image is eliminated as noise. In addition, when the color of the resin particles in the TEM image is darker than PVA, it automatically selects a dark object to calculate the average particle diameter of the resin particles in the raw material film.

[Length of resin particles in polarizing film]

The polarizing film obtained in each of the following examples or comparative examples was carried out in the same manner as the method described in "Average particle diameter of resin particles in the raw material film" to obtain a TEM image of a cut surface. However, this polarizing film was observed from a cut plane parallel to the stretching direction.

Using the TEM image obtained by the above method, the length A (long 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 ). First, use the image analysis software "Image-Pro Plus 7.0J" (manufactured by Media Cybernetics) to open the TEM image, change it to 8-bit level in "Conversion", and perform flattening in "Filtering". Next, set the contrast value to 80 in "Contrast Enhancement", and select "Large/Short Axis Ratio of Ellipse" in the measurement item setting page in "Count/Size" to automatically select objects with bright colors. From this, the resin particles are mechanically selected to calculate the length A of the resin particles in the long axis direction (length in the stretching direction), the length B of the short axis direction (length in the direction perpendicular to the stretching direction), and This length ratio (A/B). In addition, a particle size smaller than 1/10 of the maximum diameter in the TEM image is eliminated as noise. In addition, when the color of the resin particles in the TEM image is darker than that of the PVA, the dark objects are automatically selected to calculate the respective lengths of the resin particles in the polarizing film.

[Tear resistance evaluation: stab resistance]

The polarizing film obtained in each of the following Examples or Comparative Examples was allowed to stand at a temperature of 23° C. and a relative humidity of 20% for 24 hours. After that, the polarizing film was cut out into a film piece having a length direction (the stretching direction of the polarizing film) of 40 mm×20 mm in the width direction, and sandwiched with a metal frame to fix the four sides. After that, the polarizing film was installed in a tensile tester ("Autograph AGS-H" by Shimadzu Corporation), and the drawing direction of the polarizing film and a flat-blade screwdriver (contact area with polarizing film: 1 mm × 5 mm) ) So that the long side becomes parallel, install a flat-blade screwdriver on the upper chuck head, and press the flat-blade screwdriver against the polarizing film at a speed of 1 mm/min. Then, the maximum load when the flat-blade screwdriver penetrated the polarizing film was set as the piercing strength, and the piercing property was evaluated by the following criteria. In addition, since the A and B systems can be used practically without problems, they are judged as good and C is judged as bad.

A: The thrust strength is above 5N

B: The thrust strength is more than 3N and less than 5N

C: The thrust strength is less than 3N

[Tear resistance evaluation: cutting property]

The polarizing film obtained in each of the following examples or comparative examples was allowed to stand at a temperature of 23° C. and a relative humidity of 50% for 24 hours. Then, in a direction perpendicular to the stretching direction, the polarizing film was cut at a speed of 600 mm/min using a blade, and the cut cross section was observed with a stereo microscope. In addition, the angle between the blade edge of the blade and the stretching direction of the polarizing film was set to 45°. Then, the number of cracks per 1 cm of the cut section of the polarizing film was measured, and the cutability was evaluated by the following criteria. In addition, since the A and B systems can be used practically without problems, they are judged as good and C is judged as bad.

A: No cracks

B: 1~4 pieces/cm

C: more than 5 pieces/cm

[Tear resistance evaluation: punching property]

The polarizing film obtained in each of the following examples or comparative examples was allowed to stand at a temperature of 23° C. and a relative humidity of 50% for 24 hours. After that, place the polarizing film on a cutting pad ("MA-40N" by Kokuyo), and use a circular punch with a diameter of 10 mm (HHH's "TPO-100" with a punch) to apply the polarizing film. For punching, observe the punched end surface of the polarized film hollowed out into a circle with a stereo microscope. Then, the number of cracks present in the polarizing film was measured, and the punchability was evaluated by the following criteria. In addition, since the A and B systems can be used practically without problems, they are judged to be good, and C is judged to be bad.

A: No cracks

B: 1~4 items/week

C: more than 5 per week

[Polarizing properties of polarizing film] (Measurement of transmittance Ts)

From the center of the polarizing film, two samples with a length of 2 cm were taken in the stretching direction of the polarizing film. For one sample, using a spectrophotometer with an integrating sphere ("V7100" from Japan Spectroscopy Co., Ltd.), in accordance with JIS Z 8722 (method for measuring the color of the object), the visual acuity correction of the C light source and the visible light region of the 2° field of view is performed. The transmittance of light in the case of +45° tilt with respect to the longitudinal direction and the transmittance of light in the case of -45° tilt were measured, and these average values Ts1 (%) were obtained. The other samples were also measured in the same manner, and the transmittance of the light at an inclination of +45° and the transmittance of the light at an inclination of -45° were measured, and these average values Ts2 (%) were obtained. Using the following calculation formula (1), Ts1 and Ts2 are averaged to be the transmittance Ts (%) of the polarizing film.

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

In the following Examples or Comparative Examples, the dyeing treatment conditions were adjusted to prepare a sample so that the transmittance Ts became 44.0%, and the following polarization degree V was measured.

(Measurement of Polarization V)

For the two samples used in the measurement of the transmittance Ts described above, the transmittance of light T _⊥ (%) when the stretching directions overlap each other so as to be parallel to the stretching direction The light transmittance T _// (%) in the case of overlapping. This measurement is carried out by using a spectrophotometer with an integrating sphere ("V7100" from Japan Spectroscopy Co., Ltd.), in accordance with JIS Z 8722 (method for measuring the color of an object), and performing visual sensitivity correction of a C light source and a visible light region of a 2° field of view. Using the following formula (2), the polarization degree V(%) is obtained from the measured T _// (%) and T _⊥ (%).

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

[Production Example 1] Production of resin particles A

To a dried 0.5 L pressure-resistant polymerization tank, 0.20 g of potassium peroxydisulfate as a polymerization initiator, 36.0 g of a reactive emulsifier "JS-20" of Sanyo Chemical Industry Co., and 300 g of ion-exchanged water were charged. This was deoxygenated by bubbling with nitrogen for 30 minutes to obtain a starting emulsion. Next, after stirring this starting emulsion and raising the temperature to 60°C, 45.0 g of n-butyl acrylate, 0.45 g of allyl methacrylate, and trihydroxy were continuously added at a rate of 1.0 ml/min. A mixture of 0.23 g of methyl propane trimethacrylate.

Thereafter, 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 dicyclopentyl methacrylate subjected to degassing treatment was continuously added at a rate of 1.0 ml/minute. After the above addition, it was confirmed that the monomer conversion rate calculated by the above method exceeded 95% by mass, the polymerization tank was heated to 100° C. for polymerization, and the polymerization was carried out until the residual monomer became below the detection limit of the gas chromatography method. After the polymerization, it was cooled to 25° C. to obtain an emulsion solution containing resin particles A (resin component 17% by mass). In addition, the polymerization time required from the start of polymerization to cooling to 25°C was 8 hours. In addition, the obtained resin particle-based core is a core-shell type particle of poly-n-butyl acrylate and the shell is polydicyclopentyl methacrylate.

(Conversion rate of monomer)

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

[Production Example 2] Production of resin particles B

To a twin-screw extruder (manufactured by Parker Corporation), methyl methacrylate-n-butyl acrylate-methyl methacrylate trimethacrylate of (meth)acrylic block copolymer was supplied from the hopper at 0.66 kg/hour. Segment copolymer (Kurarity (registered trademark) LA2140, manufactured by Kuraray Co., Ltd., methyl methacrylate unit 24% by mass), 72 kg/hour (relative to (meth)acrylic polymer) from the middle of the cylinder In the methyl methacrylate unit of 100 moles to 40 moles), N-methylcyclohexylamine was supplied, and melt-kneading was performed at a cylinder temperature of 220°C and a screw rotation speed of 100 rpm. Thus, methacrylic anhydride-n-butyl acrylate copolymer 1 was obtained. This was crushed to 20 mm ³ or less and immersed in hot water at 80° C. for 24 hours, thereby converting the acid anhydride into a carboxyl group to prepare a methacrylic acid-n-butyl acrylate-methacrylic acid triblock copolymer. Thereafter, this copolymer was taken out by filtration, dried, and dissolved in methanol so as to have a solid content concentration of 10% by mass. After that, water of the same mass as methanol was dropped to obtain a dispersion solution, and the resulting solution was subjected to reduced pressure treatment at 60° C., and methanol was distilled off to obtain trimethacrylate containing methacrylic acid-n-butyl acrylate-methacrylic acid. Latex solution (resin component 10% by mass) of the resin particles B of the segment copolymer.

The commercially available resin particles used in Examples and Comparative Examples are shown below.

Resin particles C: "AE986B" by E-tec (acrylic resin particles)

Resin particles D: SAIDEN CHEMICAL INDUSTRY's "UC-143" (acrylic resin particles)

Resin particle E: "QE-1042" of Starlight PMC

Resin particles F: "KE-1062" of Starlight PMC

Resin particles G: E-tec's "N827(A)-1" (acrylic resin particles)

[Example 1] (1) Manufacture of blank film

Mixed PVA (saponification of homopolymer of vinyl acetate, degree of polymerization 2,400, degree of saponification 99.95 mol%), glycerin (12 parts by mass relative to 100 parts by mass of PVA), surfactant (relative to 100 parts by mass of PVA) Parts are 0.03 parts by mass), and water, and dissolved at 90°C for 4 hours to obtain a PVA aqueous solution. Thereafter, to this PVA aqueous solution, 10 parts by mass of resin particles A relative to 100 parts by mass of PVA were added, and stirred at 85° C. for 30 minutes. Thereafter, in order to defoam the PVA aqueous solution, the PVA aqueous solution was kept at 85°C for 16 hours.

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

(2) Manufacture of polarizing film

From the raw material film obtained in the above (1), a rectangular test piece having a length of 9 cm×a width of 5 cm was taken. Fix both ends of the test piece in the longitudinal direction such that the size of the stretched portion is 5 cm in the longitudinal direction and 5 cm in the width direction on the stretching jig, and immerse it in water at a temperature of 30° C. for 38 seconds at 24 cm/ The stretching speed in one minute is uniaxially stretched in the length direction (stretched in the first stage) to 2.2 times the original length. After that, during immersion in an aqueous solution of iodine/potassium iodide 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 for 60 seconds, a stretching speed of 24 cm/min in the longitudinal direction Uniaxial stretching (second stretch) to 3.3 times the original length. Next, while being immersed in a boric acid/potassium iodide aqueous solution containing boric acid at a concentration of 3% by mass and potassium iodide at a concentration of 3% by mass at a temperature of 30° C. for about 20 seconds, at a stretching speed of 24 cm/min in the longitudinal direction Uniaxial stretching (3rd stage stretching) up to 3.6 times the original length. Next, while immersing in a boric acid/potassium iodide aqueous solution containing boric acid at a concentration of 4% by mass and potassium iodide at a concentration of about 5% by mass at a temperature of 58° C., uniaxially pulling at a stretching speed of 24 cm/min in the longitudinal direction Stretching (4th stage stretching) to the ultimate stretching magnification (4 sheets of film are installed, and the stretching magnification of 2 pieces is taken as the ultimate stretching magnification). After that, it was immersed in a potassium iodide aqueous solution containing boric acid at a concentration of 1.5% by mass and potassium iodide at a concentration of 3% by mass for 10 seconds for fixing treatment. After that, it was dried in a dryer at 60° C. for 4 minutes to obtain a polarized film of Example 1 (an average thickness of 13 μm) of a stretched optical film.

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

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

[Comparative Example 5]

Except having made the average thickness of a raw material film into 60 micrometers, it carried out similarly to Comparative example 1, and obtained the raw material film and the polarizing film of Comparative example 5. The average thickness of the obtained polarizing film was 26 μm.

[Evaluation]

Using each of the obtained raw material films, the glass transition temperature of the resin particles, the swelling degree of the raw material film, and the average particle diameter of the resin particles in the raw material film were measured by the method described above. Furthermore, using the obtained polarizing film, the length A (length in the stretching direction), length B (length in the direction perpendicular to the stretching direction) of the resin particles in the polarizing film and the length ratio were performed by the method described above Measurement of (A/B), and evaluation of piercing, cutting, punching, and polarizing properties. The results are shown in Table 1.

As shown in Table 1, it can be seen that the polarizing films obtained in Examples 1 to 6 were evaluated as piercing property, cutting property and punching property as A or B, and were thin and not easy to tear, and were excellent in workability and productivity. In addition, it can be seen that Examples 1 to 6 are carried out without complicated steps, and the polarizing film can be manufactured relatively easily. Furthermore, it can be seen that the polarizing films of Examples 1 to 4 have particularly good polarizing performance.

On the other hand, it can be seen that the polarizing films obtained in Comparative Examples 1 to 4 have low evaluations of piercing property, cutting property, and punching property, and are easily torn. In addition, although the polarizing film obtained in Comparative Example 5 has tear resistance, a thin polarizing film cannot be obtained.

Industrial availability

The blank film of the present invention can be suitably used as a polarizing film or the like as a constituent material of an LCD. In addition, the method for producing the stretched optical film of the present invention and the stretched optical film can be suitably used as a polarizing film or a method for producing the same.

1‧‧‧Stretched optical film

2‧‧‧Resin particles

X‧‧‧Stretch direction

A‧‧‧Length in stretching direction

B‧‧‧Length in the direction perpendicular to the stretching direction

Claims (5)

A raw material film for the production of a stretched optical film, which has an average thickness of 45 μm or less, contains a vinyl alcohol polymer as a main component, and resin particles having a glass transition temperature of 10° C. or less, relative to the vinyl alcohol polymer 100 The content of the resin particles in parts by mass is 1 part by mass or more and 50 parts by mass or less. The raw material film according to claim 1, wherein the average particle diameter of the resin particles is 1 nm or more and 300 nm or less. A method for manufacturing a stretched optical film, which includes a step of stretching a raw material film according to claim 1 or 2. A stretched optical film having an average thickness of 20 μm or less, containing a vinyl alcohol polymer as a main component, resin particles having a glass transition temperature of 10° C. or less, and 100 parts by mass of the resin particles with respect to the vinyl alcohol polymer The content is 1 part by mass or more and 50 parts by mass or less. The stretched optical film according to claim 4, wherein the length of the stretched direction of the resin particles observed in a transmission electron microscope image in a section parallel to the stretched direction is proportional to the length perpendicular to the stretched direction The length of the direction is long.

Images