JP2008225286A - Optical film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical film having excellent optical characteristics, especially, optical isotropy and excellent mechanical characteristics, in combination. <P>SOLUTION: The optical film doesn't contain a plasticizer and/or a rubber component practically but contains a thermoplastic resin and is manufactured by a melt-extrusion method, wherein absolute value of retardation Rth in a perpendicular direction is ≤30 nm when a film thickness is 80 μm and the number of folding times measured by a MIT tester in accordance with JIS P8115 is ≥300. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical film excellent in three-dimensional optical isotropy, particularly having a small absolute value of retardation Rth in the thickness direction and excellent in mechanical properties. The optical film of the present invention is particularly preferable as an optical film used in a liquid crystal driving system called IPS (In-Plane Switching) in which the liquid crystal driving system moves in a plane, and is also excellent as a protective film for a polarizer or the like. Further, the present invention provides a film suitable for optical use as an optical member.

  Triacetyl cellulose (TAC) film has been used for conventional polarizer cover films and optical retardation, but recently, polycarbonate (PC) film and Arton (trade name: cyclic olefin polymer) JSR Co., Ltd.) film, ZEONOR (registered trademark: Nippon Zeon Co., Ltd.) film, and a special acrylic film whose glass transition temperature is raised to about 140 ° C. or higher are also used.

  A typical polycarbonate PC film as an optical film has a relatively high mechanical strength of 1,000 times or more of folding resistance measured by an MIT testing machine, but its optical isotropy is not necessarily excellent. is not. Cyclic olefin polymers and acrylic polymer films exhibit excellent optical properties, but have very poor mechanical properties, and the folding resistance is as small as 250 times or less, and an impact force is applied to these films. If the film is bent many times repeatedly, it will be relatively easy to crack and crack the film, and it will be inferior in handleability, and if cracked, it will be inferior in optical properties. There were problems such as.

  In order to improve the mechanical properties of a normal film, (a) a method for increasing the molecular weight (for example, see Patent Document 1), (b) a method for blending rubber components into a sea-island structure (for example, Patent Document 2, Patent Document 3), (c) Method of blending plasticizer (for example, see Patent Document 4), (d) Method of setting glass transition temperature Tg to less than 120 ° C., (e) Method of laminating tough polymer layer , (F) There are methods such as uniaxial or sequential biaxial stretching, but none of these can be used as an optical film because the essential optical properties are greatly deteriorated, although some mechanical properties can be improved. It is a method that cannot solve the problem completely. That is, in (a), a large melt orientation occurs during extrusion film formation, and not only the absolute value of the retardation is increased, but also the extrudability is extremely deteriorated, and gelation and thermal decomposition occur during melting, resulting in an internal defect. There is a possibility that the characteristics are greatly deteriorated, and usually a film must be produced by a solution casting method which is problematic in terms of cost and working environment. In (b), the optical properties may be deteriorated due to a decrease in transparency or a change or increase in the absolute value of the retardation. In (c), there is a fear of a decrease in heat resistance and a haze deterioration due to bleeding out, which is not preferable. In (c) and (d), the effect of improving the mechanical properties is small, and the number of folding times is not sufficiently large in relation to the purpose, which is not an effective method. In (d) and (e), the refractive index anisotropy of the adhesive interface and the film to be laminated is large, the absolute value of the retardation is large, and the light is diffracted, scattered, and reflected, so that the optical characteristics are high. There are many problems. In (e) and (f), uniaxial stretching is not preferable because the anisotropy is large and the absolute value of retardation is large, and even in successive biaxial stretching, the absolute value of the retardation Rth in the thickness direction is large. Is not necessarily appropriate. As described above, the conventional method cannot obtain an optical film satisfying the optical characteristics and the mechanical characteristics.

  In the case of a liquid crystal drive system such as the recently developed IPS (In-Plane Switching) system, the liquid crystal molecules do not move in the thickness direction, but move only in the plane, so the TN (Twisted Nematic) system or VA Unlike the (Vertical Alignment) method, the viewing angle is difficult to depend on. However, the polarizing plate itself used for this has a viewing angle dependency, which is regarded as a problem. This is because a triacetylcellulose TAC film widely used for protecting polyvinyl alcohol (PVA) polarizers has a large absolute value of retardation Rth in the thickness direction. Therefore, development of such an optically isotropic film that does not depend on the viewing angle, that is, a film having a small absolute value of retardation Rth in the thickness direction is desired. It has been demanded to obtain a screen that does not depend on the viewing angle, which is a characteristic of a liquid crystal television.

As a film close to a zero retardation film having a small absolute value of Rth, there are a cyclic olefin and an acrylic film. When the film thickness is fixed at 80 μm, the absolute value of Rth is as small as about 20 nm and excellent in optical characteristics, but as described above, it is inferior in mechanical characteristics and very fragile, not only handling property but also optical due to cracks. Since defects also occur, it has been difficult to adopt as a liquid crystal display member film in reality.
JP-A-11-142645 JP 2005-132972 A JP 2006-328369 A JP 2000-17087 A

An object of the present invention is to solve the above-mentioned problems and to provide an optical film having excellent optical properties, particularly optical isotropy, and excellent mechanical properties.

  As a result of intensive studies, the inventors have realized a film having an absolute value of retardation Rth in a specific thickness direction and a specific number of folding times, and found that this solves the above problems, leading to the present invention. It was.

That is, the present invention
(1) An optical film substantially free from a plasticizer and / or a rubber component and containing a thermoplastic resin, and the absolute value of the retardation Rth in the thickness direction when the film thickness is 80 μm An optical film having a thickness of 30 nm or less, preferably 15 nm or less, and a melt extrusion method in which the number of folding times measured by a MIT tester according to JIS P8115 is 300 times or more, preferably 600 times or more, more preferably 1000 times or more It relates to the produced optical film. If such a film is used, it can be a film having excellent handleability and excellent optical properties. Here, the retardation Rth in the thickness direction of the film is the X axis in the direction in which the refractive index is maximum in the film plane, the Y axis in the direction perpendicular to the X axis in the plane, Rth = {(nx + ny) / 2−nz, where Z is the thickness direction, nx, ny, nz are the refractive indices for the sodium D line (wavelength 589 nm) in the respective axial directions, and d is the film thickness of the film. } · D is the retardation specified by d.

Hereinafter, (2) to (5) are each one of preferred embodiments of the present invention.
(2) The optical film as described in (1) above, wherein the glass transition temperature of the film is 125 ° C.

When the optical film has a glass transition temperature of 125 ° C. or higher, preferably 145 ° C. or higher, an optical film having excellent temperature and humidity dimensional stability can be obtained. Here, the glass transition temperature of the film is measured by the method described in detail in Examples / Comparative Examples.
(3) The optical film according to (1) or (2), which is used for a member for a liquid crystal display element.
When a film having a small retardation Rth in the thickness direction of the present invention is used as a protective film for a PVA polarizer used for a polarizing plate in a liquid crystal display member, for example, an IPS liquid crystal driving method, color, contrast, and brightness It is preferable because it is possible to obtain a member for a liquid crystal display element having no viewing angle dependency.
(4) The above (1) to (3), wherein the thermoplastic resin is at least one resin selected from the group consisting of a cyclic olefin polymer, a methylpentene polymer, an acrylic polymer, a polycarbonate, and triacetyl cellulose. The optical film according to any one of the above.
(5) The optical film according to any one of (1) to (4), which has been subjected to simultaneous biaxial stretching.

According to the film of the present invention,
1. An optical film having excellent bending resistance and mechanical properties can be provided.
2. An absolute value of retardation value Rth in the thickness direction and retardation value Re in the planar direction are very small, and a film having excellent optically three-dimensional isotropic property with small wavelength dependency can be provided. .
3. Such an optical film, as a member for a liquid crystal display, exhibits excellent image characteristics without color misregistration and color unevenness on the screen. The film of the present invention having the above excellent characteristics is used for liquid crystals. It is suitably used as a member, for example, a protective film such as a polarizing film, a retardation film, a compact disk, a video disk, an optical card, and the like.

In the case of the optical film of the present invention, when the film thickness is 80 μm, the absolute value of the retardation Rth in the thickness direction is preferably 30 nm or less, preferably 15 nm or less, more preferably 5 nm or less, and as small as possible, In other words, it should be close to 0. Moreover, the absolute value of Rth is as small as 30 nm or less in the entire wavelength range from 400 nm to 800 nm, which is an optical wavelength corresponding to visible light that is important in the display element, and the wavelength dependency is small, and Rth is almost constant. It is preferable. When the absolute value of this Rth exceeds 30 nm, depending on the viewing angle, color shift, resolution reduction, contrast reduction, brightness reduction, etc. occur depending on the viewing angle, and the image on the screen depends on the viewing direction. There are concerns about the occurrence of problems such as changes in the appearance of Of course, these become worse as the absolute value of Rth deviates greatly from 30 nm. Further, the retardation value Re in the plane of the film is 5 nm or less, preferably 3 nm or less. Of course, it is preferable that Re ≦ 5 nm in the entire wavelength region from 400 nm to 800 nm.

In the optical film of the present invention, the absolute value of Rth when the film thickness is 80 μm is preferably as small as possible, and there is no lower limit of the absolute value of Rth. That is, the absolute value of Rth is 0 nm or more.
Further, the folding resistance of the film of the present invention measured by an MIT testing machine is 300 or more when the film thickness is 80 μm. The higher the folding endurance is, preferably 600 or more, more preferably 1000 or more, the more excellent mechanical properties are exhibited. When the MIT value is less than 300, the film is inferior in handleability. For example, the film is used during film transport, during cutting processes such as slitting / cutting, during superposition, surface treatment, and bending. However, it is not suitable for use as an optical film because it may be cut, broken, or cracked, causing a problem in optical properties and inferior in handleability.

In the optical film of the present invention, the larger the folding endurance when the film thickness is 80 μm, the more preferable, and there is no upper limit. For reference, a biaxially stretched polyethylene terephthalate PET film that is commercially available often has a folding resistance of about 20,000 times.
Furthermore, the glass transition temperature Tg of the film of the present invention is 125 ° C. or higher, preferably 145 ° C. or higher. When the Tg is less than 125 ° C, it is used as a liquid crystal display member for use in high-temperature environments, such as TVs and car navigation CNs in automobiles used in summer or in the country or region near the equator. In some cases, the characteristics of the optical film change due to an increase in the interior temperature, and as a result, there is a concern that defects such as a change in the color and contrast of the image and a dependency on the viewing angle may occur. The glass transition temperature of the film of the present invention is preferably 200 ° C. or less from the viewpoint of product productivity.

  The film according to the present invention has a light transmittance of 88% or more, preferably 90% or more, and more preferably 91% or more. Transmission of as much light as possible has less transmission loss and a bright liquid crystal screen. A film having a high light transmittance is preferred.

  Furthermore, the thickness unevenness of the film of the present invention is preferably 5% or less, preferably 3% or less in the longitudinal direction, since retardation unevenness does not occur. The thickness unevenness is also required to be small in the width direction, and is preferably 5% or less in the width direction. The thickness unevenness of the film of the present invention can be measured by the following method. Using an electronic micrometer, the measurement length is 20 m in the longitudinal direction MD and the maximum width in the width direction. Assuming that the maximum thickness d1, the minimum thickness d2, and the average thickness da are the measurement results, the film thickness unevenness (%) = [(d1-d2) / da] × 100.

  The thickness of the film of the present invention is usually 200 to 20 μm, preferably 100 to 40 μm, but there is no particular limitation on the thickness, and desired properties such as retardation and mechanical strength. The required film thickness is determined by the relationship.

  Such a film having excellent mechanical properties and optical properties can be used for any member as an optical film, particularly a liquid crystal display member. That is, it can be used as a polarizing plate protective film for a polyvinyl alcohol-based polarizer or as a highly functional optical film such as a zero retardation film.

  The water absorption of the optical film of the present invention is 0.2% or less, preferably 0.1% or less from the viewpoint of dimensional stability. The water absorption rate can be evaluated by measuring the weight increase when immersed in water at a temperature of 23 ° C. for 24 hours in accordance with ASTM D570.

  The film centerline average surface roughness Ra of the present invention is 100 nm or less, preferably 50 nm or less, more preferably 20 nm or less. Further, the haze value of the film is 1.5% or less, preferably 1.0% or less at a thickness of 80 μm.

Further, if necessary, the film of the present invention is subjected to surface treatment such as coating or electric discharge treatment, and the surface wetting tension measured by the wetting tension measuring method of JIS C2151 (2006) is 45 mN / m or more, preferably 50 mN / m or more. It is also possible to enlarge it. Furthermore, the surface specific resistance can be 10 ¹² Ω / □ or less, preferably 10 ¹⁰ Ω / □ or less, by coating or the like.

  The polymer used in the film of the present invention is a thermoplastic resin excellent in transparency that does not substantially contain a plasticizer and / or a rubber component. “Substantially” means that it is not contained at all, or even if it is contained, the total content is less than 8% by weight, preferably less than 3% by weight. Here, the plasticizer is an additive that improves the mobility of the resin when added to the resin, and is an additive that changes the glass transition temperature Tg or the viscoelastic properties. The rubber component is a polymer whose glass transition temperature Tg is 50 ° C. or more lower than that of the matrix polymer, and is excellent in compatibility and adhesion with the matrix polymer, and is finely dispersed in the island state in the matrix polymer. An additive that can improve the mechanical properties of the matrix polymer.

  Thermoplastic is a polymer that exhibits fluidity when heated. Specifically, cyclic olefins COP, COC, methylpentene polymer PMP, acrylic polymer, polycarbonate PC, triacetyl cellulose TAC film, etc. Although it is preferable as a raw material used for, it is not limited to these.

  Examples of the cyclic olefin polymer include COP represented by hydride 2 of ring-opening polymer of dicyclopentadiene, a copolymer of dicyclopentadiene and ethylene, COC represented by hydride 2 thereof, and norbornene polymer. One or more selected ones having a glass transition point of 100 ° C. or higher, preferably 130 ° C. or higher are preferable. A hydride of a ring-opening polymer of dicyclopentadiene is well known in Japanese Patent Publication No. 58-43412 and Japanese Patent Laid-Open No. 63-218727. Further, a copolymer of dicyclopentadiene and ethylene is also known in JP-A-63-331420 and the like, and norbornene-based polymers are described in US Pat. No. 2,883,372, JP-B-46-14910, As disclosed in, for example, Kaihei 1-149738, a polymer obtained by obtaining a polycyclic norbornene-based compound having four or more rings from a mixture of dicyclopentadiene and dienophile is known. Of course, the dicyclopentadiene may also include alkyl substituents such as methyl and ethyl substituents, endo isomers, taxo isomers, and mixtures thereof. The molecular weight of the cyclic polyolefin is 30000 or more and less than 70,000, preferably 35000 or more and less than 60000 in terms of number average molecular weight, from the viewpoint of the mechanical strength of the film, particularly impact properties and extrusion molding.

  The methylpentene polymer PMP is a copolymerized methylpentene polymer obtained by copolymerizing 4 methylpentene-1 homopolymer or a comonomer having an arbitrary length such as 8, 10, 12, or 20 carbon atoms with about 2 to 20 mol%. The main ones are commercially available as TPX (registered trademark) from Mitsui Chemicals, Inc.

  As the acrylic polymer, polymers typified by polymethyl methacrylate PMMA, polymethacrylate and the like are typical, and an optically transparent polymer having a high light transmittance including these copolymers can be used. Further, as disclosed in JP-A-2006-265543, a glutaric anhydride unit-containing copolymer obtained by subjecting a carboxyl group-containing acrylic copolymer to a cyclization reaction has a high glass transition temperature Tg. In addition, it has high heat resistance, colorless transparency, excellent heat processing stability and molding properties, and also reduces foreign matter, and has high colorless transparency and low foreign matter acrylic required for optical materials. Since it becomes a polymer, it can be used effectively for the film of the present invention. Of course, a polymer in which acrylic rubber is dispersed to impart toughness, for example, an acrylic resin having a glutaric anhydride unit as shown in Japanese Patent Application Laid-Open No. 2006-283013, is refracted with the acrylic resin. A polymer containing acrylic elastic particles having a rate difference of 0.05 or less and a particle size of 1 μm or less is also effective.

  Polycarbonate PC is a polyester of carbonic acid and glycol or dihydric phenol, and is a polymer having a carbonate bond of -O-CO-O-, and a polymer of bisphenol and carbonate is most practically used. Teijin Limited (brand names Panlite (registered trademark), Pure Ace (registered trademark)), Kaneka Corporation (brand name Elmec (registered trademark)), Mitsubishi Engineering Plastics Corporation (brand name Iupilon (registered trademark)), etc. Commercially available.

  Triacetyl cellulose TAC is a cellulose compound obtained by acetylating three hydroxyl groups OH of cellulose. In particular, as shown in JP-A-2005-272585 and JP-A-2007-44880, a cellulose body composition containing a benzoic acid anilide compound or the like is also preferred in order to control the refractive index in the thickness direction. May be used.

  In the film of the present invention, any known additive such as anti-coloring agent, antioxidant, antistatic agent, heat stabilizer, crystal nucleating agent, adhesion improver, slip agent, anti-blocking agent, anti-foaming agent, antifoaming agent An agent, a clarifying agent, a viscosity modifier and the like may be contained. As antistatic, known dodecylbenzenesulfonate, bis (octylpolyoxyethylene) phosphate soda, phosphonium dodecylbenzenesulfonate, alkylsulfonate, phosphonium alkylsulfonate, styrenesulfonic acid, polyethylene glycol, etc. Although there are antistatic agents and the like, it is preferable to use a moisture-permeable antistatic agent as an additive because it is excellent in antistatic stability during drying and over time. Here, the antistatic agent having moisture permeability refers to an ionomer polymer having an ionic group selected from alkali metals such as potassium K, rubidium Rb, cesium Ce, lithium Li, and sodium Na. In particular, the inclusion of a polymer containing potassium K ions is preferable in terms of moisture permeability, compatibility and transparency of the film. Typical examples of moisture permeable ionomers include polystyrene sulfonate PSS ionomers, ethylene sulfonate ionomers, and ethylene / unsaturated carboxylic acid ionomers. Entila (trade name) is particularly excellent. Of course, a compatibilizer may be used at the same time. The addition amount of these antistatic agents is 20% or less in terms of weight, preferably 10%, more preferably 5% or less in terms of transparency and bleed-out properties.

  Next, although a preferable example of the manufacturing method of this invention film is described, it is not limited to this.

  Raw material pellets obtained by drying and heating known optical raw materials by a conventional method are supplied to a sheet extruder under a nitrogen atmosphere and melted in a cylinder of the extruder. After passing through a large number of fine leaf disc filters that do not pass, the molten sheet is discharged from the die and is solidified closely to the cooling drum to obtain a cast sheet. It is also possible to laminate with other polymers as a laminated sheet.

In addition, the cast adhesion method includes an adhesion cast method that obtains adhesion while adhering to a cast roll, a method that adheres with electrostatic force while applying an electrostatic charge, etc., but in the case of the present invention, the electrostatic adhesion method is It is particularly preferable in terms of high-speed film formation, defect-free film formation, handling properties, and the like. In order to be able to apply such an electrostatic contact method, it is preferable that the volume resistance value of the polymer at the time of melting is in a range of about 10 ^{8 to 10} Ω · cm if possible. A polymer having such a volume resistance value can be obtained by including a specific compatible polymer having a small resistance value, for example, ENTILA (trade name, manufactured by Mitsui DuPont Polychemical Co., Ltd.) as an antistatic polymer. It can be achieved. Needless to say, a nip-roll (soft nip & hard nip) system, a belt system, a calendar system, an air-knife system, an air-chamber system, etc. can be used. The material of the drum is preferably a surface drum made of chrome plating, stainless steel or ceramic and having a maximum surface roughness Ry of 0.1 μm or less. The drum surface temperature is preferably close to the glass transition temperature of the polymer, although it depends on the type of polymer. In the case of COP and COC, those of 105 to 165 ° C. are often used. A draft ratio of 10 or less, preferably 5 or less, is preferable because an optically isotropic film is obtained.

In order to obtain the optical film of the present invention, it is highly preferable that the film thus extruded is subjected to a specific stretching treatment, that is, simultaneous biaxial stretching. Further, if necessary, an optical film satisfying the optical properties and mechanical properties of the present invention can be obtained by performing a relaxation treatment after stretching.
In the case of the present invention, it is very preferable to perform a specific method of stretching, and specifically, it is preferable to simultaneously biaxially stretch a film obtained by extrusion. Simultaneous stretching is a stretching method in which stretching is performed simultaneously in the machine direction MD and the width direction TD in at least a part of the stretching process. In the present invention, MD and TD are It is particularly preferable that stretching is started at the same time, and it is not always necessary to terminate MD and TD at the end of stretching.

  Like the sequential stretching method used in ordinary biaxial stretching machines, the stretching method in which MD stretching and TD stretching are performed separately in terms of time are optical characteristics like the film of the present invention. From the viewpoint of obtaining a film with improved mechanical properties. That is, with the sequential biaxial stretching method, since the film is stretched individually in each stretching direction, even if a fragile film is stretched uniaxially, the mechanical properties become anisotropic, which further unbalances the optical properties. Therefore, it is often necessary to re-extend again in the direction perpendicular to the initial drawing direction. In this way, there is a concern that once a fragile film once oriented is re-stretched in a direction perpendicular to the orientation direction, the film is broken, stretch unevenness occurs, or only a film having poor thickness uniformity can be obtained. Even if a film with good appearance is obtained, the molecular orientation of the film surface is prioritized and the refractive index in the thickness direction becomes smaller, so the absolute value of the retardation in the thickness direction becomes a relatively large value. Therefore, there is a concern that it is not necessarily suitable for the optical film application of the present invention. That is, to obtain the film of the present invention, it is very preferable to stretch the film by the simultaneous biaxial stretching method. Effective mechanical properties can be expected to be improved by stretching at or near the glass transition temperature Tg of the polymer used.

  By simultaneously biaxially stretching a film having excellent transparency as described above, the brittleness of the film, which is a mechanical property, can be greatly improved. Specifically, as a numerical value representing the brittleness of the film, the number of bending by the bending MIT test may be 2000 times or more by simultaneously biaxially stretching a brittle film of 20 times, for example. The brittleness improvement effect is recognized.

  However, even though the mechanical properties can be improved in this way, molecular orientation is inevitably caused by stretching, so the absolute value of retardation, which is molecular orientation, becomes large, and the absolute value of retardation Rth in the thickness direction May exceed 30 nm. In such a case, a film having an absolute value of Rth of 30 nm or less can be obtained by returning the stretching ratio in the longitudinal direction MD and the width direction TD immediately after simultaneous biaxial stretching, that is, by performing a relaxation treatment. The relaxing direction and temperature may be set as appropriate depending on the degree of initial stretching and the absolute value of the desired retardation Rth.

A film having various surface characteristics can be obtained by subjecting the film thus obtained to surface treatment such as coating treatment, corona discharge treatment, plasma treatment and the like. For example, laminating treatment, antistatic treatment, easy adhesion treatment, easy lubrication treatment, mold release treatment, coloring, abrasion resistance, reflection resistance, roughening treatment and the like can be mentioned. Further, other compounds may be impregnated.
(Example / Comparative Example)
Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. It should be noted that the present invention is not limited to the following examples and the like in any sense.
(Evaluation method of physical properties)
In the following examples and comparative examples, various physical properties of the films were evaluated according to the following measuring methods.
(1) Light transmittance (%)
Measurement was performed using a spectrophotometer U-3410 manufactured by Hitachi, Ltd., and the total light transmittance of visible light from a wavelength of 300 nm to 700 nm was measured, and the value at 550 nm was adopted. The unit is expressed in%.
(2) Retardation Re, Rth (nm)
The film birefringence Δn is multiplied by the film thickness d (nm). The difference obtained by subtracting the refractive index in the width direction TD from the refractive index in the longitudinal direction MD where the refractive index is the maximum is the in-plane birefringence Δnp, and this is multiplied by the film thickness d to obtain the in-plane retardation value Re. To do. On the other hand, the difference obtained by subtracting the refractive index in the thickness direction ZD from the arithmetic average value of the refractive indexes in the longitudinal direction MD and the width direction TD is defined as the thickness direction birefringence Δna, which is multiplied by the film thickness d. The thickness direction retardation Rth value is used.
The refractive index is measured by using an Abbe refractometer and placing the polarizing plate on the eyepiece so that the sodium D line (589 nm) is used as a light source in the horizontal direction so that the contact between the sample film surface and the lens is improved. The measurement was performed by mounting with a methylene iodide solution so that total reflection was uniform. The unit is expressed in nm.
(3) Centerline average surface roughness Ra
According to JIS B0601, the measurement was performed using a high-precision thin film level difference meter ET-10 manufactured by Kosaka Laboratory. Measurement conditions are stylus tip radius 0.5μm, needle pressure 5mg, measurement length 1mm, cut-off 0.08mm. The center line average roughness Ra is obtained by dividing the area of the difference obtained by subtracting the area of the component shifted vertically from the center line of the roughness curve by the measurement length and adding the value to the center line.
(4) Haze (%)
Total haze was determined according to the method of JIS K6782.
(5) Film thickness (μm)
The palpation type contact part was measured with a disc-shaped flat dial gauge.
(6) Film thickness variation (%)
Using an Anritsu electronic micrometer K306C, the measurement length was 20 m in the longitudinal direction MD and the maximum width was measured in the width direction. The maximum thickness of the measurement result is d1, the minimum thickness is d2, and the average thickness is da.
Unevenness of film thickness (%) = [(d1-d2) / da] × 100
(7) Glass transition temperature Tg (° C)
Using a scanning calorimeter DSC3100 manufactured by Mac Science, the sample weight was 5 mg, the temperature was increased to 300 ° C. at a temperature increase rate of 20 ° C./min under a nitrogen stream, held for 3 minutes, the sample was taken out and placed in liquid nitrogen And quickly cooled. The sample was set on the DSC again and heated at a rate of temperature increase of 10 ° C., and the temperature at which the baseline began to shift was defined as Tg, or when the endothermic peak appeared, the peak temperature was defined as Tg.
(8) Fold resistance times (times) by MIT testing machine
This is a bending resistance test using an MIT testing machine, and how many times it breaks is expressed by the number of bendings. Measured with a load of 0.98 N according to JIS P8115 (2006), and obtained an arithmetic average of 5 times. (9) Surface resistivity main electrode (50 mmφ), guard electrode concentric with main electrode (inner diameter 70 mmφ, outer diameter) 80 mmφ) and a counter electrode (80 mmφ), and a resistance is obtained from the current value flowing from the main electrode to the guard electrode when a voltage of 1 kV is applied, and this is multiplied by 60π to obtain the surface resistance and did. The measurement was performed at 23 ° C. and a humidity of 60%. The unit is represented by Ω / □. However, in Tables 1 and 3, logarithmic display was performed.

(Examples 1-4, Comparative Examples 1-2)
Using a raw material obtained by adding 3% by weight of polyethylene glycol PEG having a molecular weight of 4000 as an antistatic agent to 100 parts by weight of a cyclic olefin polymer having a glass transition temperature Tg of 145 ° C. (trade name: APEL6015T, manufactured by Mitsui Chemicals, Inc.) at 105 ° C. After drying for 4 hours, this is supplied to a heated extruder hopper heated to 95 ° C., melted at 285 ° C. using an extruder under a nitrogen atmosphere, filtered out foreign matters of 5 μm or more, and discharged from the die. Apply a static charge at a positive DC voltage of 12,000 V and a current value of 1 mA from a distance of 10 mm on the melt sheet, and adhere and cool the melt on a mirror chrome plating drum at 60 ° C. Then, a stretched original fabric was formed into a film. The film was simultaneously biaxially stretched in the longitudinal direction MD and the width direction TD at the stretching ratio shown in Table 1 at a stretching temperature of 150 ° C. using a simultaneous biaxial stretching machine (Brismner Co., Ltd., LISIM). Relax heat treatment was performed at a relaxation rate described in Table 1 at a temperature of 80 ° C. to obtain a film having a thickness of 80 μm. Table 1 shows the physical properties of the film obtained by subjecting the film surface to atmospheric pressure plasma treatment.

The films of the present invention shown in the examples not only have excellent mechanical properties but also optically almost ideal isotropy, and have an excellent absolute value of retardation Rth in the thickness direction of 30 nm or less. Such a film exhibits excellent characteristics suitable for a liquid crystal display member, particularly a liquid crystal IPS driving type polarizer protective film. Furthermore, it is a film excellent in antistatic property, surface smoothness, and transparency, and it turns out that it is a film suitable also as a new member for optics.
(Reference example)
For reference, the properties of the current commercially available optical films are listed in Table 2.

As shown in Table 2, in the commercially available optical film, the absolute value of retardation Rth in the thickness direction is small, optically excellent, and excellent in mechanical properties expressed by the bending resistance MIT value. There is no thermoplastic optical film.

(Examples 5-8, Comparative Examples 3-4)
Methylpentene polymer (trade name: TPX MX022, manufactured by Mitsui Chemicals, Inc.) was used, and ethylene acrylate-based potassium ionomer (trade name: ENTILA SD1000, manufactured by Mitsui DuPont Polychemical Co., Ltd.) was used as the moisture-permeable polymer. . A homogeneous mixture having a composition in which a moisture-permeable polymer is added in an amount of 20% by weight to 80% by weight of the hydrophobic polymer is dried in a stirred heating tank at 105 ° C. for 4 hours. Supply, melt in an extruder at 285 ° C, filter out foreign matter, discharge from the die, and apply static charge at a positive DC voltage of 12,000 V and a current value of 1 mA from a distance of 10 mm above the melt. Then, the wound melt was brought into close contact with and cooled at a maximum speed on a mirror-finished chromium plating drum at 20 ° C. to obtain a film for stretching. The film was simultaneously biaxially stretched at a stretching ratio described in Table 3 in the longitudinal direction MD and the width direction TD at a stretching temperature of 170 ° C. using a simultaneous biaxial stretching machine (Brookner, product name LISIM). A relaxation heat treatment was performed at 200 ° C. with a relaxation rate shown in Table 2 to obtain a film having a thickness of 40 μm. Table 3 shows the physical properties of the film obtained by subjecting the film surface to atmospheric pressure plasma treatment.

  It can be seen that the optical film of the present invention thus obtained is a novel film which has never existed before, that is, a film having excellent optical properties and mechanical properties. Furthermore, it is a film excellent in antistatic property, surface smoothness, and transparency, and it turns out that it is an optical film suitable as a new member for optics. In order to evaluate as a protective film for the polarizing plate for IPS liquid crystal, an acrylic water-based adhesive is coated on the film of the present invention with a coater, and this is bonded to both sides of the polyvinyl alcohol PVA polarizer. , Dried. About Examples 5-8, the obtained three-layer laminated polarizing film comprising the present invention optical film / PVA polarizer / present invention optical film has not only excellent polarization performance but also occurrence of curls, wrinkles, spots, etc. The performance of the polarizer over time was also stable. When the films of Comparative Examples 3 and 4 were used, even when the comparative film was broken during the production of the three-layer laminating process, or even if a polarizing plate was produced without breaking, a fine polarizing plate was obtained. Cracks are present and cannot be used as an optical polarizing plate.

Claims (5)

An optical film containing substantially no plasticizer and / or rubber component and containing a thermoplastic resin, wherein the absolute value of retardation Rth in the thickness direction when the film thickness is 80 μm is 30 nm or less, An optical film produced by a melt-extrusion method having a folding endurance of 300 or more as measured with an MIT tester in accordance with JIS P8115. The optical film according to claim 1, wherein the film has a glass transition temperature of 125 ° C. or higher. The optical film of Claim 1 or 2 used for the member for liquid crystal display elements. The said thermoplastic resin is at least 1 sort (s) of resin chosen from the group which consists of a cyclic olefin polymer, a methyl pentene polymer, an acryl-type polymer, a polycarbonate, and a triacetyl cellulose, The any one of Claim 1 to 3 Optical film. The optical film according to any one of claims 1 to 4, wherein a simultaneous biaxial stretching process is performed.