JP2011150028A - Optical film, polarizing plate, and image display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical film which has superior low birefringence and aptitude for mass production, and to provide a high-performance polarizing plate and an image display apparatus using the same. <P>SOLUTION: The optical film is configured with a mixed resin composed of (A) a polypropylene formed by polymerization using a metallocene catalyst and (B) polyisobutylene. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical film, a polarizing plate, and an image display device.

  An optical film is a film for industrial materials that requires transparency. For example, a window film such as a scattering prevention film or an ultraviolet ray prevention film, a polarizer protective film, an optical compensation film, an antireflection film, or the like. Films for industrial use such as film for surface protection and surface protection film used for steel plates and design building materials to prevent scratches and dirt. Among these optical films, with the development of liquid crystal displays including liquid crystal cells, organic electroluminescence display devices, or touch panel displays, optical films used in these image display devices have attracted attention.

  The polarizing plate is an optical member having a function of transmitting only light having a specific vibration direction and shielding other light, and is widely used in the image display apparatus as described above. As such a polarizing plate, what has the structure by which the optical film for polarizer protection was provided in the single side | surface or both surfaces of the polarizer is generally used. Among these, the polarizer has a function of transmitting only light having a specific vibration direction, and a uniaxially stretched polyvinyl alcohol (hereinafter referred to as “PVA”) film dyed with iodine or a dichroic dye is used. Recently, a coating type film is also used, but there is a problem that it is generally thin and weak in strength.

  The polarizer protective optical film provided on the polarizer bears functions such as supporting the polarizer, providing practical strength to the entire polarizing plate, and physically protecting the surface of the polarizer. In addition to excellent optical uniformity such as low in-plane retardation, that is, low birefringence, it has practical physical strength and good transparency, etc. More severe performance is required among films that require low birefringence. As such an optical film for protecting a polarizer, a triacetyl cellulose film which is a cellulose film is generally used in many cases. However, the cellulosic film has insufficient moisture resistance, and there are problems such that the dimensions of the film change due to water absorption, and the performance of the polarizer deteriorates due to the transmitted water.

  Therefore, the present inventors have previously found that an optical film for protecting a polarizer using polypropylene polymerized using a metallocene catalyst has good optical properties and moisture resistance (Patent Document 1). reference). However, it is desirable that an optical film, particularly an optical film for protecting a polarizer, originally has no optical influence, and is expected to realize further low birefringence.

Japanese Patent Laid-Open No. 2008-146023

  Incidentally, in recent years, along with the demand for cost reduction of liquid crystal displays, there has been a further demand for thinner and lighter optical members to be used. That is, it is necessary to reduce the thickness of an optical film for protecting a polarizer used in a liquid crystal display device. On the other hand, in order to put it into practical use as an optical film for protecting a polarizer, in addition to the requirements for optical properties such as transparency and low birefringence and basic properties such as moisture resistance, the optical film must be suitable for mass production. Is required.

  For example, in order to stably produce an optical film for protecting a polarizer in a wide width or at a high speed, a resin used for the optical film for protecting a polarizer needs to have sufficient strength. In addition, an optical film for protecting a polarizer used for a polarizing plate of a thin flexible image display device needs to have sufficient rigidity so that it can be molded with a thin film thickness and can withstand bending. Alternatively, for an in-vehicle use image display apparatus that is also used in a cold region, the optical film for protecting a polarizer is required to have durability against cold (cold shock resistance). Of course, by having sufficient strength and rigidity as described above, mass production suitability or durability that enables stable mass production without causing wrinkles or tears has the basic characteristics as described above. It must be satisfied while holding. Furthermore, it is required to provide the optical film for protecting the polarizer with characteristics according to the use of the image display device and the polarizing plate.

  The present invention has been made under such circumstances, and an object of the present invention is to provide an optical film having excellent low birefringence and suitability for mass production. Another object of the present invention is to provide a high-performance polarizing plate and an image display device using the same.

As a result of intensive studies to achieve the above object, the present inventors have found that the problem can be solved by using a mixed resin of polypropylene and polyisobutylene polymerized using a metallocene catalyst. I found it. The present invention has been completed based on such findings.
That is, the gist of the present invention is as follows.

1. An optical film comprising a mixed resin composed of (A) polypropylene polymerized using a metallocene catalyst and (B) polyisobutylene.
2. (B) The optical film as described in 1 above, wherein the polyisobutylene has a number average molecular weight of 17,000 or more.
3. 3. The optical film as described in 1 or 2 above, wherein the content of (B) polyisobutylene in the mixed resin is 1 to 40% by mass.
4). 4. The optical film according to any one of 1 to 3 used for protecting a polarizer.
5. 5. A polarizing plate, wherein the polarizer protective optical film described in 4 above is provided on at least one surface of the polarizer.
6). 6. An image display device using the polarizing plate described in 5 above.
7). The manufacturing method of the optical film which has the process of following (1)-(3).
Step (1) Step of polymerizing polypropylene using a metallocene catalyst Step (2) Step of mixing and melting the polypropylene and isobutylene to obtain a mixed resin Step (3) Step of molding the mixed resin

  According to the present invention, an optical film having excellent low birefringence and mass production suitability can be obtained. In addition, a high-performance polarizing plate and an image display device to which characteristics according to applications are provided can be obtained.

It is a figure which shows the structural example of the optical film of this invention. It is a figure which shows the structural example of the polarizing plate of this invention. It is a figure which shows the structural example of the liquid crystal display containing the liquid crystal cell of this invention.

[Optical film]
The optical film of the present invention comprises a mixed resin composed of (A) polypropylene polymerized using a metallocene catalyst and (B) polyisobutylene, and a typical embodiment thereof is shown in FIG. It has the structure which can be.
The optical film of the present invention is prepared by mixing polypropylene that has been polymerized using a metallocene catalyst and graft-modified polypropylene, heating and melting them, and then molding them by various molding methods such as an unstretched T-die extrusion molding method. Manufactured.
Below, the optical film of this invention and its manufacturing method are demonstrated in detail.

《Polypropylene polymerized using metallocene catalyst》
Polypropylene polymerized using a metallocene catalyst is a propylene polymer synthesized by a polymerization reaction using a metallocene catalyst described later. Polypropylene polymerized using a metallocene catalyst generally has the same molecular weight and crystallinity as compared to polypropylene polymerized using a general-purpose Ziegler-based catalyst, but has a low molecular weight and low crystallinity component. Therefore, an optical film using polypropylene polymerized using a metallocene catalyst has lower transparency and lower birefringence than an optical film using only polypropylene polymerized using a Ziegler-based catalyst. It has a birefringence. For this reason, polypropylene polymerized using a metallocene catalyst is used as one of the essential components of the mixed resin constituting the optical film of the present invention.

  The polypropylene polymerized using the metallocene catalyst is preferably a random copolymer of propylene and an α-olefin. As the α-olefin, ethylene, 1-olefin having 4 to 18 carbon atoms is used. Specifically, ethylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-heptene, 4- Examples thereof include methyl-pentene-1, 4-methyl-hexene-1, 4,4-dimethylpentene-1. The proportion of propylene units in the copolymer is preferably 80 mol% or more, and the comonomer is 20 mol% or less. As the comonomer, the above α-olefin is not limited to one type, and two or more types can be used, and the copolymer can be a multi-component copolymer such as a terpolymer.

(Metallocene catalyst)
As the metallocene catalyst, a known catalyst can be appropriately used. Generally, a group 4-6 transition metal compound such as Zr, Ti, or Hf, particularly a group 4 transition metal compound and an organic transition metal compound having a cyclopentadienyl group or a cyclopentadienyl derivative group is used. be able to.

  As the group of the cyclopentadienyl derivative, an alkyl substituent such as pentamethylcyclopentadienyl, or a group in which two or more substituents are combined to form a saturated or unsaturated cyclic substituent may be used. Typically, an indenyl group, a fluorenyl group, an azulenyl group, or a partial hydrogenated product thereof can be given. Moreover, what combined several cyclopentadienyl group with the alkylene group, the silylene group, the germylene group etc. can be mentioned suitably.

(Cocatalyst)
The cocatalyst was selected from the group consisting of an aluminum oxy compound, an ionic compound capable of reacting with the metallocene compound to convert the metallocene compound component into a cation, or a Lewis acid, a solid acid, or a layered silicate. At least one compound can be used. Moreover, an organoaluminum compound can be added with these compounds as needed.

  The above-mentioned layered silicate refers to a silicate compound having a crystal structure in which structured surfaces are stacked in parallel with each other with a weak binding force by ionic bonds or the like. In the present invention, the layered silicate is preferably ion-exchangeable. Here, ion exchange means that the interlayer cation of the layered silicate can be exchanged. Most layered silicates are naturally produced mainly as the main component of clay minerals, but these layered silicates are not limited to natural ones but may be artificially synthesized products.

Specific examples of the layered silicate are not particularly limited as long as they are known layered silicates, for example, kaolins such as dickite, nacrite, kaolinite, anorxite, metahalloysite, halloysite; chrysotile, lizardite, Serpentine group such as antigolite; Smectite group such as montmorillonite, sauconite, beidellite, nontronite, saponite, teniolite, hectorite, stevensite; vermiculite group such as vermiculite; mica, illite, sericite, sea green stone, etc. Attapulgite; sepiolite; palygorskite; bentonite; pyrophyllite; talc; chlorite group. These may form a mixed layer.
Among these, montmorillonite, sauconite, beidellite, nontronite, saponite, hectorite, stevensite, bentonite, teniolite, and other smectites, vermiculites, and mica are preferred.

  These layered silicates can be chemically treated. Here, as the chemical treatment, any of a surface treatment for removing impurities adhering to the surface and a treatment that affects the crystal structure and chemical composition of the layered silicate can be used. Specific examples include acid treatment, alkali treatment, salt treatment, organic matter treatment, and the like. These treatments have actions such as removing impurities on the surface, exchanging cations between layers, and eluting cations such as Al, Fe, and Mg in the crystal structure. As a result, ion complexes, molecules Complexes, organic derivatives, and the like can be formed to change surface area, interlayer distance, solid acidity, and the like. These processes may be performed independently or two or more processes may be combined.

(Polypropylene polymerization method using metallocene catalyst)
As a method of synthesizing polypropylene using the above metallocene catalyst (polymerization method), in the presence of these catalysts, a slurry method using an inert solvent, a gas phase method using substantially no solvent, a solution method, or a polymerization method. Examples thereof include a bulk polymerization method using a monomer as a solvent.

(Physical properties of polypropylene using metallocene catalyst)
The polypropylene used in the present invention preferably has a flexural modulus of 700 MPa or more, and more preferably 900 MPa or more. When the flexural modulus is in the above range, sufficient strength as an optical film can be obtained, and post-processing can be easily performed. Here, in this invention, a bending elastic modulus shall be measured based on JISK7171.

  The melting point (Tm) of the polypropylene used in the present invention is preferably 130 ° C. or higher. If the melting point (Tm) is 130 ° C. or higher, the unstretched film is preferable because the flexural modulus is increased, the strength of the optical film is increased, and post-processing is not affected. The melting point was evaluated at a temperature at which the peak of the highest intensity appeared in the melting curve measured by a differential scanning calorimeter (DSC). A 10 mg piece of polypropylene resin press film was measured at 230 ° C. under a nitrogen atmosphere. After heat treatment for 10 minutes, the temperature was lowered to 30 ° C. at a temperature drop rate of 10 ° C./min, kept at 30 ° C. for 5 minutes, and further obtained as a melting peak temperature when heated from 30 ° C. to 230 ° C. at a temperature rise rate of 10 ° C./min Value.

  The polypropylene used in the present invention preferably has a tensile strength of 20 MPa or more. When it is 20 MPa or more, when the optical film is bonded to the polarizer via the adhesive layer by the roll-to-roll method, the orientation is not applied, and the optical film has a retardation exceeding the original optical design. Since it does not generate | occur | produce, the performance of a polarizing plate can be maintained. Here, in this invention, tensile strength shall be measured based on ASTMD638 (Type4 conditions).

  The polypropylene used in the present invention preferably has a melt flow rate (hereinafter sometimes referred to as MFR) of 0.5 to 50 g / 10 minutes, more preferably 7 g / 10 minutes or more. Here, MFR is a value measured according to JIS K7210, and the measurement conditions are 230 ° C. and 2.16 kg load. If the MFR of polypropylene is within the above range, it is preferable because distortion can be suppressed when forming an unstretched film, and an optical film having low birefringence can be obtained. Moreover, sufficient intensity | strength as an optical film is obtained and a post-process can be performed easily. Furthermore, since the MFR can be easily stabilized in the production lot, stable molding can be performed, and the amount of additives such as the MFR adjusting agent can be suppressed, so that the physical properties are not adversely affected. The MFR of the polypropylene resin can be adjusted with a general MFR adjuster such as an organic peroxide.

  The width of the molecular weight distribution of the polypropylene used in the present invention can be evaluated by the ratio (dispersion degree) of the weight average molecular weight Mw to the number average molecular weight Mn. 1-20 are preferable as Mw / Mn. Here, the number average molecular weight Mn and the weight average molecular weight Mw are values measured by gel permeation chromatography (GPC) using o-dichlorobenzene at 140 ° C. as a solvent and polystyrene as a standard sample. .

(Method for distinguishing polypropylene using metallocene catalyst)
In polypropylene synthesized using a metallocene catalyst, a residue of a group 4-6 transition metal compound resulting from the metallocene catalyst is mainly present in the polypropylene. On the other hand, polypropylene synthesized using a Ziegler-based catalyst mainly contains residues of Group 1-3 metal hydrides and organometallic compounds resulting from the Ziegler-based catalyst. That is, polypropylene synthesized using a metallocene catalyst and polypropylene synthesized using a Ziegler-based catalyst can be clearly distinguished by analyzing the residual metal compound resulting from the catalyst used in the polypropylene.
The analysis method depends on the amount of residue of the metal compound in the polypropylene, but after increasing the residue concentration of the metal compound by analysis with a fluorescent X-ray analyzer, pretreatment by ashing, etc., an electron beam microanalyzer (EPMA) is used. The qualitative analysis used can be mentioned.

<Polyisobutylene>
The polyisobutylene used in the present invention is a polymer containing isobutylene, and may be a homopolymer of isobutylene or a copolymer with other monomers. Examples of the copolymer include a copolymer of isobutylene and isoprene, a polymer obtained by polymerizing a monomer having a crosslinkable functional group such as a carboxylic acid group or a hydroxyl group based on the copolymer, and a chlorinated one. Can be mentioned. Polyisobutylene can be obtained by polymerizing isobutylene in the presence of an acidic catalyst such as aluminum chloride, silica alumina or a cation exchange resin, particularly a Friedel-Crafts type catalyst, and is a semi-solid polymer. . In addition to isobutylene, for example, a butane-butene fraction obtained by removing butadiene from a C4 fraction obtained during naphtha cracking can also be used as a polymerization raw material.
Polyisobutylene is conventionally known as a rubber component or an additive used for improving resin moldability and adhesiveness (for example, JP-A-9-208907, JP-A-2008-31315). reference). The present invention makes it possible to obtain an unexpected effect that an optical film obtained by combining such polyisobutylene and polypropylene using a metallocene catalyst exhibits excellent low birefringence.

In the present invention, the number average molecular weight Mn as polyisobutylene is preferably 17,000 or more. Although there is no restriction | limiting in particular as an upper limit, From a viewpoint of manufacturability, 400,000 is preferable. Further, it is more preferably in the range of 18,000 to 300,000. Here, the number average molecular weight Mn is a value measured by gel permeation chromatography (GPC), more specifically, a value measured by dissolving in xylene at room temperature and using polystyrene as a standard sample. . Even after mixing with polypropylene polymerized using a metallocene catalyst to form a film, it can be separated from polypropylene by dissolving in the solvent, and the molecular weight of polyisobutylene can be measured.
A number average molecular weight of 17,000 or more is preferable because the mixed resin is not easily stretched, the film is not stretched during molding, and optical properties are not deteriorated. Furthermore, since the strand strength does not decrease, the masterbatch is crushed by its own weight and the pressure from the upper part during storage as a result, and blocking and bleed are not generated, which is preferable. If the number average molecular weight is 400,000 or less, the handling of polyisobutylene is easy and the kneadability of the mixed resin does not deteriorate, so that wrinkles and tears are less likely to occur and a smooth film is obtained. Can do. Moreover, since sufficient intensity | strength and rigidity are obtained, the mass-production suitability of an optical film becomes favorable.

  The polyisobutylene can be used singly or in combination of two or more polyisobutylenes, and even when a plurality of polyisobutylenes are used in combination, the number average molecular weight is preferably within the above range. In the present invention, polybutene can be used in combination as long as the effects of the present invention are not impaired.

  The content of polyisobutylene in the mixed resin is preferably in the range of 1 to 40% by mass, and more preferably in the range of 5 to 35% by mass. If it is 1 mass% or more, excellent low birefringence can be obtained. On the other hand, if it is 40% by mass or less, the optical properties and moisture resistance of polypropylene polymerized using a metallocene catalyst are not impaired, the kneadability of the mixed resin is good, wrinkles and tears can be suppressed, and Since smooth surface properties can be obtained, an excellent optical film can be obtained, and at the same time, the mass production suitability of the film can be improved. In addition, the economy is excellent.

  The shape of polyisobutylene is not particularly limited, but is preferably in the form of powder or pellets. Since the polyisobutylene has such a shape, even when a polyisobutylene having a wider range of number average molecular weight is selected, the mixed resin can be easily kneaded, and as a result, it is more diverse and demanding for optical films. It becomes possible to cope with performance.

《Arbitrary component》
In the present invention, various additives and additive resins can be added as optional components of the mixed resin constituting the optical film as desired.

  For example, a dibenzylidene sorbitol-based additive can be suitably used because it can improve the tensile strength and transparency while minimizing the influence on the phase difference. As dibenzylidene sorbitol-based additives, di-substituted dibenzylidene sorbitol, diglycerin mono-fatty acid ester-added dibenzylidene sorbitol-based nucleating agent containing di-substituted benzylidene sorbitol and diglycerin mono-fatty acid ester can be suitably used. .

It is preferable that content of the said additive is the range of 0.03-0.5 mass part with respect to 100 mass parts of mixed resin. When it is 0.03 parts by mass or more, it is possible to improve transparency and sufficiently improve strength. On the other hand, when the amount is 0.5 parts by mass or less, the effect of improving transparency and strength can be effectively obtained, which is advantageous in terms of cost.
In particular, when di-substituted benzylidene sorbitol added with diglycerin monofatty acid ester is used, 0.01 to 0.3 parts by mass of di-substituted benzylidene sorbitol is mixed with 100 parts by mass of the mixed resin. The diglycerin monofatty acid ester is preferably 0.01 to 0.2 parts by mass.

  In addition, depending on the desired physical properties of the film obtained, various olefin resins other than polypropylene polymerized using a metallocene catalyst and graft-modified polypropylene may be added as an additive resin within a range that does not impair low birefringence and transparency. You can also.

  Furthermore, depending on the desired physical properties, it is within a range that does not affect the low birefringence and transparency, for example, a weather resistance improving agent such as an ultraviolet absorber or a light stabilizer; Abrasion improvers; polymerization inhibitors such as hydroquinone; cross-linking agents such as polyisocyanate compounds, epoxy compounds and metal chelate compounds; infrared absorbers such as dithiol metal complexes and phthalocyanine compounds; barium sulfate, talc, clay, calcium carbonate In addition, an antistatic agent, an adhesion improver, a leveling agent, a thixotropic agent, a coupling agent, a plasticizer, an antifoaming agent, a solvent, and the like can be added.

<Physical properties of optical film>
The thickness of the optical film of the present invention is preferably in the range of 10 to 200 μm, more preferably 30 to 150 μm. When the thickness of the optical film is 10 μm or more, the protective strength of the optical film is sufficiently secured, and when it is 200 μm or less, sufficient flexibility is obtained, and since it is lightweight, handling during work becomes easy. In addition, it is advantageous in terms of cost.

The retardation of the optical film of the present invention is preferably an in-plane retardation measured at an incident angle of 0 degree using a light having a wavelength of R589.5 nm using a retardation measuring device, and is preferably 10 nm or less. Preferably it is 5 nm or less, More preferably, it is 4 nm or less. As described above, since the optical film of the present invention has a small in-plane retardation, that is, excellent low birefringence, it is suitably employed as an optical film used for an image display device, for example, an optical film for protecting a polarizer. can do.
Moreover, the optical film of the present invention is excellent in transparency, and has a haze value of 30% or less required as an optical film. Here, the haze value is a value measured according to JIS K7105.

  The flexural modulus of the optical film is preferably 700 MPa or more. When the flexural modulus is within the above range, sufficient strength when handled in a film state can be obtained, and post-processing can be easily performed. When used as a protective sheet for a polarizing plate, sufficient scratch resistance is obtained. This is because Furthermore, the flexural modulus of the optical film is more preferably 900 MPa or more. This is because if the pressure is 900 MPa or more, the in-plane retardation can be stabilized when manufactured by T-die extrusion. Here, the bending elastic modulus is measured in accordance with JIS K7171 like the above-described polypropylene.

  There is no restriction | limiting in particular as an adjustment method of the bending elastic modulus of the optical film of this invention, It can adjust with the following methods. For example, a method of selecting by the original properties (crystallinity, average molecular weight, etc.) of polypropylene, a method of adding a filler selected from inorganic or organic fillers to a resin, a method of adding a crosslinking agent, etc. Examples thereof include a method of mixing two or more different types of resins, a method of selecting a plasticizer composition of a curable resin, or a method of appropriately combining a plurality of these methods.

  The optical film of the present invention preferably has a tensile strength of 20 MPa or more. When it is 20 MPa or more, when the optical film is bonded to the polarizer via the adhesive layer by the roll-to-roll method, the orientation is not applied, and the optical film has a phase difference exceeding the original optical design. Therefore, the performance of the polarizing plate can be maintained. Here, in this invention, tensile strength shall be measured based on ASTMD638 (Type4 conditions).

  When the optical film of the present invention is used for protecting a polarizer, an easy adhesion treatment can be performed on the surface in contact with the polarizer to improve adhesion. Examples of the easy adhesion treatment include surface treatment such as corona treatment, plasma treatment, low-pressure UV treatment, and saponification treatment, and a method of forming an anchor layer, and these can be used in combination. Among these, a corona treatment, a method of forming an anchor layer, and a method of using these in combination are preferable.

Moreover, when forming an adhesive bond layer in order to raise the adhesiveness of the optical film of this invention, and a polarizer, it carries out by apply | coating an adhesive agent to either the optical film or a polarizer, or both sides.
After bonding the optical film and the polarizer through the surface subjected to the easy adhesion treatment or the surface on which the adhesive layer is formed, a drying step is performed to form an adhesive layer composed of a coating dry layer. This can also be bonded after forming the adhesive layer. Bonding of the polarizer and the optical film can be performed by a roll laminator or the like. The heating and drying temperature and drying time are appropriately determined according to the type of adhesive.
The thickness of the adhesive layer is preferably 0.01 to 10 [mu] m, more preferably 0.03 to 5 [mu] m, since it is not preferable from the viewpoint of adhesiveness of the optical film if the thickness after drying becomes too thick.

  In addition, a functional layer is laminated on the surface of the optical film, and various functions such as a so-called hard coat function, anti-fogging coat function, anti-fouling coating function, and anti-glare coating function having high hardness and scratch resistance. Further, an antireflection coating function, an ultraviolet shielding coating function, an infrared shielding coating function, and the like can be provided.

<< Optical film manufacturing method >>
The optical film of the present invention is preferably a step (1) of polymerizing polypropylene using the above-described metallocene catalyst, a step (2) of mixing the polypropylene and isobutylene and heating and melting to obtain a mixed resin, and the mixed resin. It can be manufactured by a manufacturing method having a step (3) of molding the material.

  More specifically, in the step (2), the polypropylene polymerized using the metallocene catalyst obtained in the step (1), the polyisobutylene described above, and various optional components described above are mixed as desired. Then, it is heated and melted, that is, kneaded to obtain a mixed resin. Here, the polyisobutylene is preferably in the form of powder or pellets, and the size is preferably about 0.1 to 3 mm in diameter as a substantially spherical body, more preferably about 0.1 to 2 mm in diameter.

  The obtained mixed resin becomes the optical film of the present invention through the molding process of step (3). The molding process can be performed by various molding methods such as an extrusion coating molding method, a casting method, a T-die extrusion molding method, an inflation method, and an injection molding method. In the present invention, when the optical film is used for protecting the polarizer, since it is desired that the polarizer protecting optical film produced on the polarizer is not oriented, unstretched T-die extrusion that does not require stretching is performed. desirable.

[Polarizer]
In the polarizing plate of the present invention, the above optical film is provided on at least one surface of a polarizer. As a method for providing an optical film, an optical film for protecting a polarizer may be formed directly on a polarizer, or an optical film for protecting a polarizer is prepared first, and then an adhesive. You may affix on a polarizer through a layer.
FIG. 2 shows an example of the polarizing plate of the present invention. In FIG. 2, reference numeral 2 denotes a polarizer, and an optical film 1 is formed on one surface of the polarizer via an adhesive layer 3, thereby constituting a polarizing plate 4 as a whole.
The polarizing plate of the present invention is a high-performance polarizing plate to which characteristics according to applications are imparted by the optical film.

《Polarizer》
As the polarizer used in the polarizing plate, any polarizer may be used as long as it has a function of transmitting only light having a specific vibration direction. For example, a PVA-based film is stretched, and iodine or a dichroic dye is used. Dyed PVA polarizers; polyene polarizers such as dehydrated PVA and polyvinyl chloride dehydrochlorination; reflective polarizers using cholesteric liquid crystals; thin film crystal film polarizers, etc. Of these, a PVA polarizer is preferably used.
Examples of PVA polarizers include hydrophilic polymers such as PVA films, partially formalized polyvinyl alcohol films, and ethylene / vinyl acetate copolymer partially saponified films, and two colors such as iodine and dichroic dyes. And uniaxially stretched by adsorbing the active substance. Among these, a polarizer composed of a PVA film and a dichroic substance such as iodine is preferably used. The thickness of these polarizers is not particularly limited, and is generally about 1 to 100 μm.

A PVA resin suitably used as a resin constituting the polarizer can be obtained by saponifying a polyvinyl acetate resin. Examples of the polyvinyl acetate resin include, in addition to polyvinyl acetate, which is a homopolymer of vinyl acetate, copolymerization of vinyl acetate and other monomers copolymerizable therewith. Examples of other monomers copolymerized with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids.
The degree of saponification of the PVA-based resin is usually 85 to 100 mol%, preferably 98 to 100 mol%. This PVA-based resin may be further modified, and for example, polyvinyl formal or polyvinyl acetal modified with aldehydes may be used. The degree of polymerization of the PVA resin is usually in the range of 1,000 to 10,000, preferably 1,500 to 10,000.

<< Polarizing plate manufacturing method >>
The polarizing plate includes, for example, a step (I) of uniaxially stretching a PVA film as described above, a step (II) of dyeing a PVA resin film with a dichroic dye, and adsorbing the dichroic dye. Process (III) for treating PVA film adsorbed with chromic dye with boric acid aqueous solution, process for washing with water after boric acid aqueous solution treatment (IV), and dichroic dye adsorbed and oriented by these steps It is manufactured through a step (V) of attaching an optical film for protecting a polarizer to the uniaxially stretched PVA-based film.

(Process (I))
Uniaxial stretching can be performed before, simultaneously with, or after dyeing with a dichroic dye. When uniaxial stretching is performed after dyeing with a dichroic dye, this uniaxial stretching can be performed before boric acid treatment or during boric acid treatment. Moreover, it is also possible to perform uniaxial stretching in these several steps. In order to uniaxially stretch, you may extend | stretch uniaxially between rolls from which peripheral speeds differ, or using a heat roll. Stretching can be performed by dry stretching in which stretching is performed in the air or wet stretching in which stretching is performed in a state swollen by a solvent. The draw ratio is usually about 4 to 8 times.

(Process (II))
In order to dye the PVA film with the dichroic dye, for example, the PVA film may be immersed in an aqueous solution containing the dichroic dye. Specifically, iodine or a dichroic dye is used as the dichroic dye.
When iodine is used as the dichroic dye, a method of dyeing a PVA film in an aqueous solution containing iodine and potassium iodide is usually employed. Moreover, when using a dichroic dye as a dichroic pigment | dye, the method of immersing and dye | staining a PVA-type film in the aqueous solution containing a water-soluble dichroic dye is normally employ | adopted.

(Step (III))
The boric acid treatment after dyeing with the dichroic dye is performed by immersing the dyed PVA film in an aqueous boric acid solution. The boric acid content in the boric acid aqueous solution is usually about 2 to 15 parts by mass, preferably about 5 to 12 parts by mass per 100 parts by mass of water.
When iodine is used as the dichroic dye, the aqueous boric acid solution preferably contains potassium iodide. The content of potassium iodide in the boric acid aqueous solution is usually about 2 to 20 parts by mass, preferably 5 to 15 parts by mass per 100 parts by mass of water. The immersion time in the boric acid aqueous solution is usually about 100 to 1,200 seconds, preferably about 150 to 600 seconds, and more preferably about 200 to 400 seconds. The temperature of the boric acid aqueous solution is usually 50 ° C. or higher, preferably 50 to 85 ° C.

(Process (IV))
The PVA film after the boric acid treatment is usually washed with water. The water washing treatment is performed, for example, by immersing a boric acid-treated PVA film in water. After washing with water, a drying process is performed to obtain a polarizer. The temperature of water in the water washing treatment is usually about 5 to 40 ° C., and the immersion time is usually about 2 to 120 seconds. The drying process performed thereafter is usually performed using a hot air dryer or a far infrared heater. The drying temperature is usually 40 to 100 ° C. The processing time in the drying process is usually about 120 to 600 seconds.
Thus, a polarizer composed of a PVA film on which iodine or dichroic dye is adsorbed and oriented is obtained.

(Process (V))
As a method of laminating the polarizer and the optical film, it can be performed through an adhesive layer. Examples of the adhesive that forms the adhesive layer include a PVA adhesive, an epoxy adhesive, an acrylic adhesive, and a polyolefin adhesive. In addition, it is possible to use an adhesive having transparency, for example, an adhesive such as polyvinyl ether or rubber. Among these, a PVA adhesive is preferable.

The PVA-based adhesive contains a PVA-based resin and a crosslinking agent. Examples of the PVA-based resin include PVA obtained by saponifying polyvinyl acetate and its derivatives, and a non-polymerizable copolymer with vinyl acetate. Saponification products of copolymers with monomers such as saturated carboxylic acids and esters thereof and α-olefins, modified PVA obtained by subjecting PVA to acetalization, urethanization, etherification, grafting or phosphoric esterification, etc. It is done. These PVA resins can be used singly or in combination of two or more.
The degree of polymerization of the PVA resin is not particularly limited, but since the adhesiveness and the like are improved, the average degree of polymerization is about 100 to 3000, preferably 500 to 3000, and the average saponification degree is about 85 to 100 mol%, preferably It is preferable to use about 90-100 mol%.

  In the present invention, the polarizer and the adhesive layer are treated with, for example, an ultraviolet absorber such as a salicylic acid ester compound, a benzophenol compound, a benzotriazole compound, a cyanoacrylate compound, or a nickel complex compound. The ultraviolet absorbing ability may be imparted.

  The adhesive layer is formed by applying an adhesive on either or both sides of the polarizer protecting optical film or the polarizer. The thickness of the adhesive layer is preferably 0.01 to 10 μm, more preferably 0.03 to 5 μm.

  In addition, when the polarizer protecting optical film is bonded to the polarizer, the surface of the polarizer protecting optical film in contact with the polarizer is subjected to corona treatment, plasma treatment, low pressure UV treatment, saponification treatment, etc. in order to improve adhesion. Easy adhesion treatment such as surface treatment or a method of forming an anchor layer can be performed. Of these, a corona treatment, a method of forming an anchor layer, and a method of using these in combination are preferable.

Next, an adhesive layer is formed on the surface subjected to the easy adhesion treatment as described above, and the polarizer and the optical film for protecting the polarizer are bonded through the adhesive layer.
Bonding of the polarizer and the optical film for protecting the polarizer can be performed by a roll laminator or the like. The heating drying temperature and drying time are appropriately determined according to the type of adhesive.

(Other)
For the polarizing plate in which the polarizer protective optical film of the present invention is formed on one surface of the polarizer, the polarizer protective optical film of the present invention is formed on the other surface of the polarizer, if necessary. It is also possible to form a film made of other resin. Examples of films made of other resins include polyethylene terephthalate films, polycarbonate films, cyclic polyolefin films, maleimide resin films, and fluorine resin films. The film made of the other resin may be a retardation film having a specific retardation.

The polarizing plate is preferably a laminate having at least one hard coat layer in order to improve surface properties and scratch resistance. Examples of the hard coat layer include ultraviolet curable resins such as ultraviolet curable acrylic urethane, ultraviolet curable epoxy acrylate, ultraviolet curable (poly) ester acrylate, and ultraviolet curable oxetane, silicone resins, acrylic resins, and urethane resins. Examples thereof include a hard coat layer made of a hard coat agent, and a hard coat layer made of an ultraviolet curable resin is preferable from the viewpoint of transparency, scratch resistance, and chemical resistance. One or more of these hard coat layers can be used.
As for the thickness of a hard-coat layer, 0.1-100 micrometers is preferable, Especially preferably, it is 1-50 micrometers, More preferably, it is 2-20 micrometers. Further, a primer treatment can be performed between the hard coat layers.

  Further, the polarizing plate can be subjected to a known anti-glare treatment such as anti-reflection or low-reflection treatment as necessary.

[Image display device]
The polarizing plate of the present invention can be preferably used for various devices for image display.
Examples of the image display device include a liquid crystal display including a liquid crystal cell, an organic electroluminescence (hereinafter referred to as “organic EL”) display device, a touch panel, and the like. There is no. In the case of a liquid crystal display, an image display device is generally formed by appropriately assembling components such as a liquid crystal cell, an optical film, and an illumination system as necessary, and incorporating a drive circuit. In the invention, the configuration of the image display device is not particularly limited except that the polarizing plate is used. For example, an appropriate image display device such as an image display device in which a polarizing plate is disposed on one side or both sides of a liquid crystal cell, or a backlight or a reflection plate as an illumination system is exemplified. As the liquid crystal cell, any type such as a TN type, an STN type, or a π type can be used. When configuring an image display device, for example, appropriate components such as a diffusion plate, an antiglare layer, an antireflection film, a protective plate, a prism array, a lens array sheet, a light diffusion plate, and a backlight are placed at appropriate positions. A layer or two or more layers can be arranged.

<Liquid crystal display including liquid crystal cell>
The polarizing plate of the present invention is suitably used by being laminated, for example, on a liquid crystal cell.
As an example of the image display device of the present invention, FIG. 3 shows a configuration example of a liquid crystal display including a liquid crystal cell. In FIG. 3, 6 indicates a liquid crystal cell. Examples of the liquid crystal cell 6 include an active matrix drive type typified by a thin film transistor type and a simple matrix drive type typified by a twist nematic type and a super twist nematic type. A phase difference plate (birefringent plate) 5 is laminated on the liquid crystal cell 6 via an adhesive layer (not shown), and a polarizing plate is formed on the liquid crystal cell 6 via an adhesive layer (not shown). The plate 4 is laminated. The polarizing plate 4 has a polarizer 2 at the center, and a polarizer protecting optical film 1 is laminated on both surfaces of the polarizing plate 4 via an adhesive layer 3. When laminating the polarizing plate 4 and the retardation plate 5 and the retardation plate 5 and the liquid crystal cell 6, an adhesive layer may be provided on the polarizing plate 4, the retardation plate 5 and the liquid crystal cell 6 in advance.

The pressure-sensitive adhesive for laminating the polarizing plate and the liquid crystal cell is not particularly limited. For example, an acrylic pressure-sensitive adhesive is excellent in optical transparency, exhibits appropriate wettability, cohesiveness, and adhesive pressure-sensitive adhesive properties, and is weather resistant. It is preferable because it is excellent in properties and heat resistance.
The pressure-sensitive adhesive is required to be excellent in optical transparency, moderate wettability, cohesiveness, adhesive properties such as adhesion, weather resistance, heat resistance and the like. Furthermore, the moisture absorption rate is low in terms of prevention of foaming and peeling phenomena due to moisture absorption, deterioration of optical characteristics due to thermal expansion differences, prevention of warping of liquid crystal cells, and the formation of high-quality and durable image display devices. Therefore, a pressure-sensitive adhesive layer having excellent heat resistance is required.

  Application of the above-mentioned pressure-sensitive adhesive to the polarizing plate is, for example, 10 to 40% by mass in which a base polymer or a composition thereof is dissolved or dispersed in a solvent composed of a single solvent or a mixture of appropriate solvents such as toluene and ethyl acetate. Prepare a pressure-sensitive adhesive solution to the extent, and apply it directly on the polarizing plate by an appropriate development method such as a coating method such as gravure coating, bar coating, roll coating, or casting method, or according to this method. Examples thereof include a method of forming an adhesive layer on a releasable base film and transferring it to a polarizing plate.

  The thickness of the pressure-sensitive adhesive layer can be appropriately determined according to the purpose of use and adhesive force, and is generally 1 μm to 500 μm, preferably 5 μm to 200 μm, particularly preferably 10 μm to 100 μm.

  The exposed surface of the pressure-sensitive adhesive layer is coated with an appropriate thin film such as a plastic film, if necessary, with an appropriate release agent such as a silicone film for the purpose of preventing contamination until it is put to practical use. It is preferable that the released release film is temporarily attached and covered. Thereby, it can prevent contacting an adhesive layer in the usual handling state.

(Organic EL display device)
The polarizing plate of the present invention can be suitably used for an organic EL display device.
Generally, in an organic EL display device, a transparent electrode, an organic light emitting layer, and a metal electrode are sequentially laminated on a transparent substrate to form a light emitter (organic electroluminescent light emitter).

  In the organic EL display device having such a configuration, the organic light emitting layer is formed of a very thin film having a thickness of about 10 nm. For this reason, the organic light emitting layer transmits light almost completely like the transparent electrode. As a result, light that is incident from the surface of the transparent substrate at the time of non-light emission, passes through the transparent electrode and the organic light emitting layer, and is reflected by the metal electrode is again emitted to the surface side of the transparent substrate. The display surface of the organic EL display device looks like a mirror surface.

  In an organic EL display device comprising an organic electroluminescent light emitting device comprising a transparent electrode on the surface side of an organic light emitting layer that emits light upon application of a voltage and a metal electrode on the back side of the organic light emitting layer, the surface of the transparent electrode A polarizing plate may be provided on the side, and a birefringent layer (retardation plate) may be provided between the transparent electrode and the polarizing plate.

  Since the polarizing plate has a function of polarizing light incident from the outside and reflected by the metal electrode, there is an effect that the mirror surface of the metal electrode is not visually recognized by the polarization function. In particular, if the birefringent layer is composed of a λ / 4 plate and the angle between the polarizing direction of the polarizing plate and the birefringent layer is adjusted to π / 4, the mirror surface of the metal electrode can be completely shielded. .

(Touch panel)
The polarizing plate of the present invention can also be suitably used for a touch panel.
There are various types of touch panels, such as a resistive film type, an optical type, a capacitive coupling type (also called an analog capacitive coupling type), an infrared type, an ultrasonic type, and an electromagnetic induction type. Here, an example of a resistive film type touch panel will be described.

  Resistive touch panels include a glass / glass type and a glass / film type. In the glass / glass type, a glass substrate with a transparent conductive layer and a glass substrate with a transparent conductive layer are held via a space, and this is mounted on the display surface. The glass / film type is a type of touch panel in which an upper glass substrate with a transparent conductive layer is replaced with an optical film because a lighter / thinner one is desired in an in-vehicle or portable touch panel.

  If a linearly polarizing plate or a circularly polarizing plate made by combining a polarizing plate with a λ / 4 plate is used on the outermost surface of the touch panel, sufficient strength can be obtained as a touch panel, and visibility can be improved due to the antireflection effect. Will improve. The optical film for protecting a polarizer of the present invention can be suitably used for the polarizing plate of these touch panels.

The optical film of the present invention can be used for any of the upper, lower and lower outer layers (lightweight reduction film provided with ITO) of the polarizing plate. There are two types of anti-reflection for touch panels: linearly polarized and circularly polarized types (linearly polarized light has higher reflectivity than circularly polarized light). Can also be used on plates.
The circularly polarizing plate or linearly polarizing plate using the optical film of the present invention can be used for both transmissive and reflective touch panels.

EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by this example.
(Evaluation methods)
(1) In-plane retardation: Measured at a wavelength of R589.5 nm and an incident angle of 0 degree using a phase difference measuring device (“KOBRA-21ADH” manufactured by Oji Scientific Instruments).
(2) Occurrence of wrinkles and tears The appearance of the wound roll of the formed film was visually confirmed, and the occurrence of wrinkles and tears was evaluated according to the following criteria.
○: Wrinkles were not observed (or were rarely seen)
Δ: Wrinkles were slightly observed, but there was no problem in practical use. ×: Wrinkles were observed.

Example 1
(A) Polypropylene polymerized using a metallocene catalyst (“Wintech WFW4 (trade name)”, manufactured by Nippon Polypro Co., Ltd., melting point: 135 ° C., flexural modulus: 900 MPa, hereinafter referred to as “mPP”) 90 parts by mass and 10 parts by mass of (B) polyisobutylene (“Opanol B100 (trade name)”, manufactured by BASF Corporation, number average molecular weight: 250,000, hereinafter referred to as “polyisobutylene-A”). Were mixed and heated and melted to obtain a mixed resin. The mixed resin was subjected to T-die single layer extrusion molding with a film width of 1000 mm and a film thickness of 100 μm under the conditions of a processing temperature of 200 ° C. and a take-up roll temperature of 30 ° C. to obtain an optical film.

(Example 2)
An optical film was obtained in the same manner as in Example 1, except that mPP was changed to 70 parts by mass and polyisobutylene-A was changed to 30 parts by mass.

(Example 3)
In Example 1, polyisobutylene-A was changed to polyisobutylene-B (“Opanol B13SFN (trade name)”, manufactured by BASF Corp., number average molecular weight: 18,800). To obtain an optical film.

Example 4
In Example 1, polyisobutylene-A was changed to polyisobutylene-C (“Opanol B50SF (trade name)”, manufactured by BASF Corp., number average molecular weight: 120,000). To obtain an optical film.

(Example 5)
In Example 3, an optical film was obtained in the same manner as in Example 3 except that mPP was 70 parts by mass and polyisobutylene-B was 30 parts by mass.

(Comparative Example 1)
In Example 1, an optical film was obtained in the same manner as in Example 1 except that only mPP was used and polyisobutylene-A was not mixed.

(Comparative Example 2)
In Example 1, polypropylene obtained by polymerizing mPP using a Ziegler-Natta catalyst (manufactured by Prime Polymer Co., Ltd., “Novatech EG3FTB (trade name)”, manufactured by Nippon Polypro Co., Ltd., melting point: 140 ° C., flexural modulus : 1,000 MPa, hereinafter referred to as “rPP”), and an optical film was obtained in the same manner as in Example 1.

  Table 1 shows the evaluation results of the optical films obtained in Examples 1 to 5 and Comparative Examples 1 and 2. The optical films obtained in Examples 1 to 5 were compared with the optical film of Comparative Example 1 in which polyisobutylene was not mixed by mixing polyisobutylene with polypropylene polymerized using a metallocene catalyst. The phase difference was changed from 5 nm to 3 nm, and it was confirmed to have excellent low birefringence. In addition, the optical films obtained in Examples 1 to 5 were also excellent in evaluation of wrinkles and tears, and were confirmed to have excellent mass production suitability and excellent quality as an optical film. On the other hand, in Comparative Example 2 using polypropylene obtained by polymerization using a Ziegler catalyst, the phase difference was 25 nm, and sufficient optical properties were not obtained.

  Since the optical film of the present invention has excellent low birefringence and suitability for mass production, an optical film used for protecting an optical member that requires low birefringence such as a polarizing plate and a polarizer constituting the polarizing plate, In particular, it is suitably employed as an optical sheet for protecting a polarizer. The polarizing plate obtained by combining the optical film of the present invention and a polarizer can be effectively used for image display devices such as a liquid crystal display including a liquid crystal cell, an organic electroluminescence display device, and a touch panel. Moreover, it can also be used not only for the use as a display optical film but for other industrial materials. For example, it can be used for an anti-scattering film used for window glass or a protective film for industrial materials.

1: Optical film 2: Polarizer 3: Adhesive layer 4: Polarizing plate 5: Phase difference plate (birefringent plate)
6: Liquid crystal cell

Claims (7)

  An optical film comprising a mixed resin composed of (A) polypropylene polymerized using a metallocene catalyst and (B) polyisobutylene.   (B) The optical film of Claim 1 whose number average molecular weights of polyisobutylene are 17000 or more.   The optical film according to claim 1 or 2, wherein the content of (B) polyisobutylene in the mixed resin is 1 to 40% by mass.   The optical film according to claim 1, which is used for protecting a polarizer.   A polarizing plate, wherein the polarizer protecting optical film according to claim 4 is provided on at least one surface of the polarizer.   An image display device using the polarizing plate according to claim 5. The manufacturing method of the optical film which has the process of following (1)-(3).
Step (1) Step of polymerizing polypropylene using a metallocene catalyst Step (2) Step of mixing and melting the polypropylene and isobutylene to obtain a mixed resin Step (3) Step of molding the mixed resin

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