JP2015028578A - Polarizer protective film, and polarizing plate and liquid crystal display device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizer protective film that can ensure good visibility without rainbow unevenness (color unevenness) even when observed from an oblique direction relative to the vertical direction on a display screen of a liquid crystal display device, and has a dynamic strength suitable for a reduction in thickness.SOLUTION: There is provided a polarizer protective film composed of a polyester film having a retardation of 3000 to 30000 nm and an impact absorption energy of 0.5 J or more.

Description

  The present invention relates to a polarizer protective film having good visibility and suitable for thinning, a polarizing plate using the same, and a liquid crystal display device.

  A liquid crystal display device has polarizing plates on both sides of a liquid crystal cell, and has a light source such as a cold cathode fluorescent lamp (hereinafter referred to as CCFL) or a light emitting diode (hereinafter referred to as LED) disposed on one surface. It is a device that displays an image or the like by a backlight.

  The polarizing plate is composed of a film called a polarizer mainly composed of polyvinyl alcohol (PVA) and adsorbed and oriented with iodine compound molecules, and a polarizer protective film disposed on both sides thereof. In general, the polarizer protective film is composed of a triacetyl cellulose (hereinafter referred to as TAC) film.

  In recent years, with the thinning of liquid crystal display devices, there has been a demand for thinner polarizing plates. Furthermore, thinning of the polarizer protective film, which is one of the polarizing plate constituent members, has been desired. However, when the polarizer protective film is a TAC film, sufficient mechanical strength cannot be obtained, There were problems such as easy. Further, since the TAC film is expensive, an inexpensive alternative material has been strongly desired.

  In response to the above problems, it has been proposed to use a polyester film as an alternative material (Patent Documents 1 to 4).

  Polyester film is promising as an alternative material because of its high mechanical strength and low moisture permeability compared to TAC film. However, the effect of optical anisotropy is likely to be manifested by thinning, and in a liquid crystal display device. When observed from an oblique direction with respect to the vertical direction of the display surface, there is a problem that rainbow unevenness (color unevenness) or the like is easily recognized.

  In order to solve the above problem, Patent Documents 1 to 3 take measures to reduce optical anisotropy by using a copolyester as the polyester, but to eliminate rainbow unevenness (color unevenness). Not reached.

  Patent Document 4 focuses on the birefringence of the polyester film and the emission spectrum of the backlight, and uses a combination of a specific backlight light source and a polyester film having a specific retardation, whereby the above-mentioned rainbow unevenness (color unevenness). It is disclosed that the problem can be solved.

JP 2002-116320 A JP 2004-219620 A JP 2004-205773 A Japanese Patent No. 4926661

  However, even with the polarizer protective film disclosed in Patent Document 4, there is a problem that the film is easily broken during post-processing in response to the demand for further thinning of the polyester film. There was a case that I could not finish.

  As a result of intensive studies, the present inventor has found that a polyester film having the following configuration can solve the above-described problems, and a film suitable for further thinning the polarizer protective film can be obtained.

Item 1.
A polarizer protective film comprising a polyester film having a retardation of 3000 to 30000 nm and an impact absorption energy of 0.5 J or more.
Item 2.
Item 2. The polarizer protective film according to Item 1, wherein the polyester film has a thickness of 100 µm or less.
Item 3.
Item 3. The polarizer protective film according to Item 1 or 2, wherein a ratio (Re / Rth) of retardation (Re) and thickness direction retardation (Rth) of the polyester film is 0.2 or more and 1.2 or less.
Item 4.
A polarizing plate having a polarizer protective film on both sides of a polarizer,
The polarizing plate whose at least one polarizer protective film is a polarizer protective film in any one of claim | item 1-3.
Item 5.
5. A liquid crystal display device having a backlight, a liquid crystal cell, and polarizing plates disposed on both sides of the liquid crystal cell, wherein at least one polarizing plate is the polarizing plate according to item 4.

  If the polarizer protective film of the present invention, even when observed from an oblique direction to the vertical direction on the display surface of the liquid crystal display device, it is possible to ensure good visibility without rainbow unevenness (color unevenness), It has mechanical strength suitable for thinning. Moreover, according to this invention, it is excellent in visibility and can provide a thinner polarizing plate and a liquid crystal display device.

The polarizer protective film of the present invention comprises a polyester film having a retardation of 3000 to 30000 nm and an impact absorption energy of 0.5 J or more.

1. Polyester resin As the polyester resin constituting the polyester film, for example, known polyester resins such as polyethylene terephthalate and polyethylene naphthalate can be used. The polyester may be a homopolymer, a copolyester, or a blend polymer composed of two or more kinds of polyesters. A polyester film made of polyethylene terephthalate or polyethylene naphthalate is preferable. In particular, in order to keep the retardation high, a resin in which a cyclic monomer that can be expected to have a high refractive index is arranged in the main chain and / or side difference can be considered, but the intrinsic birefringence is large from the viewpoints of handleability and price. Polyethylene naphthalate having a naphthalene ring capable of obtaining a large retardation even when the film is thin as the acid component of the polyester is preferable.

  The polyester resin constituting the polyester film may be a copolyester. The copolymerized polyester alone or a blend of the copolymerized polyester and homopolymer may be used. For example, a blend of polyethylene terephthalate and isophthalic acid copolymerized polyethylene terephthalate, a blend of polyethylene terephthalate and diethylene glycol copolymerized polyethylene terephthalate, or the like. When a copolymer polyester is used, film stretching can be easily performed. Further, when a non-oriented sheet-like material is obtained by extruding the molten resin, the load on the extrusion apparatus can be reduced. In addition, a polyester resin to which a polyester resin monomer is added may be used for the purpose of easily stretching the film.

  Copolyester is a resin composed of a general dicarboxylic acid structural unit and a diol structural unit, and examples of the monomer applicable to the dicarboxylic acid structural unit include terephthalic acid, isophthalic acid, phthalic acid, 2-methylterephthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, biphenyldicarboxylic acid, aromatic dicarboxylic acid such as tetralindicarboxylic acid, and these Ester-forming derivatives, succinic acid, glutaric acid, adipic acid, pimelic acid, corkic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, dodecanedicarboxylic acid, cyclohexanedicarboxylic acid, norbornanedicarboxylic acid, tricyclodecanedicarboxylic acid, pentacyclodode Saturated alicyclic dicarboxylic acids such as Njikarubon acid, and the like ester-forming derivatives.

  Examples of the monomer applicable to the diol constituent unit include ethylene glycol, trimethylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol, propylene glycol, and neopentyl glycol. Aliphatic diols such as polyethylene glycol, polypropylene glycol, polybutylene glycol, and other polyether compounds, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, 1,2-decahydronaphthalenediethanol 1,3-decahydronaphthalene diethanol, 1,4-decahydronaphthalene diethanol, 1,5-decahydronaphthalene diethanol, 1,6-decahydronaphthalene diethanol, 2,7- Alicyclic diols such as cahydronaphthalene diethanol, tetralin dimethanol, norbornene dimethanol, tricyclodecane dimethanol, pentacyclododecane dimethanol, 4,4 '-(1-methylethylidene) bisphenol, methylene bisphenol Examples thereof include bisphenols such as (bisphenol F), 4,4′-cyclohexylidene bisphenol (bisphenol Z), and 4,4′-sulfonyl bisphenol (bisphenol S), and alkylene oxide adducts of the bisphenols. In addition, aromatic dihydroxy compounds such as hydroquinone, resorcin, 4,4′-dihydroxybiphenyl, 4,4′-dihydroxydiphenyl ether, 4,4′-dihydroxydiphenylbenzophenone, and alkylene oxide adducts of the aromatic dihydroxy compounds And diols having a cyclic acetal skeleton.

  Examples of the copolyester include those in which an ethylene terephthalate unit is a main component and a copolymerization component is copolymerized. From the viewpoint of versatility, the dicarboxylic acid structural unit applied as a copolymerization component of the copolyester is preferably isophthalic acid as the aromatic dicarboxylic acid, and succinic acid, glutaric acid, adipic acid, as the saturated alicyclic dicarboxylic acid, Pimelic acid, corkic acid, azelaic acid and sebacic acid are preferred. Further, from the viewpoint of versatility, the diol structural unit is preferably branched aliphatic glycol neopentyl glycol and alicyclic glycol 1,4-cyclohexanedimethanol, and aliphatic diols diethylene glycol and trimethylene. Glycol, 1,4-butanediol, and propylene glycol are preferable, and polyethylene glycol is more preferable.

The copolymerization component of the copolymerized polyester is preferably 0.2 mol% or more, more preferably 0.5 mol% or more, still more preferably 1.0 mol% or more with respect to the total dicarboxylic acid component, with respect to the dicarboxylic acid structural unit. is there. Similarly, the diol structural unit is preferably 0.5 mol% or more, more preferably 1.0 mol or more, and further preferably 2.0 mol% or more with respect to the total diol component. When the ratio of the copolymerization component is smaller than the above lower limit, it tends to be difficult to realize sufficient melt viscosity reduction.
On the other hand, the copolymerization component of the copolymerized polyester is preferably 50 mol% or less, more preferably 20 mol% or less, and still more preferably 10 mol% or less with respect to the total dicarboxylic acid component, with respect to the dicarboxylic acid structural unit. Similarly, the diol constitutional unit is preferably 35 mol% or less, more preferably 30 mol or less, still more preferably 15 mol% or less, based on the total diol component. When the ratio of the copolymerization component is larger than the above upper limit, the ejection stability and the dimensional stability after stretching may be impaired.

  As the polyester resin used in the present invention, a conventionally known catalyst can be used as long as no problem occurs in the properties, processability and color quality of the resin. For example, alkaline earth metal compounds, manganese compounds, cobalt compounds, aluminum compounds, antimony compounds, titanium compounds, titanium / silicon composite oxides, germanium compounds and the like can be used as the catalyst. The polyester film used as the polarizer protective film of the present invention preferably has a small amount of fine foreign matters that cause optical defects, and is preferably an aluminum compound, a titanium compound, a titanium / silicon composite oxide, or a germanium compound with a small amount of addition. More preferably, it is an aluminum compound from the viewpoint of versatility and color tone.

In particular, a polymerization catalyst composed of basic aluminum acetate and a phosphorus compound having a phenol moiety in the molecule as disclosed in JP-A 2010-212272 is preferred. By using this catalyst, it is possible to reduce minute foreign matters that become optical defects in the film. It is preferable that the phosphorus compound which has a phenol part in the same molecule is 1 type, or 2 or more types chosen from the group which consists of a compound represented by the following general formula (1)-(2). As a phosphorus compound which has a phenol part in the same molecule, More preferably, it is 1 type, or 2 or more types chosen from the group which consists of a compound represented by General formula (3).

(In the formulas (1) to (2), R ¹ is a carbon group having 1 to 50 carbon atoms including a phenol part, a hydrocarbon group having 1 to 50 carbon atoms, a hydroxyl group, a halogen group, an alkoxyl group, an amino group, and a phenol part. R ⁴ represents each independently hydrogen, a hydrocarbon group having 1 to 50 carbon atoms, a hydroxyl group, a halogen group, an alkoxyl group, or an amino group, and a hydrocarbon group having 1 to 50 carbon atoms, R ² , R ³ each independently represents hydrogen, a hydrocarbon group having 1 to 50 carbon atoms, a hydrocarbon group having 1 to 50 carbon atoms including a hydroxyl group or an alkoxyl group, provided that the hydrocarbon group represents a branched structure, alicyclic structure or aromatic group. (It may contain a ring structure. The ends of R ² and R ⁴ may be bonded to each other.)

(In the above formula (3), R ¹ and R ² each independently represent hydrogen and a hydrocarbon group having 1 to 30 carbon atoms. R ³ and R ⁴ are each independently hydrogen and hydrocarbon having 1 to 50 carbon atoms. Represents a hydrocarbon group having 1 to 50 carbon atoms including a group, a hydroxyl group or an alkoxyl group, n represents an integer of 1 or more, and the hydrocarbon group represents an alicyclic structure such as cyclohexyl, a branched structure, or an aromatic ring such as phenyl or naphthyl. May contain structure.)

  As described above, it is possible to reduce the load on the extrusion apparatus when a non-oriented sheet-like material is obtained by extruding a molten resin by using a copolyester, but the same effect is obtained by using two polyester resins having different intrinsic viscosities. It can also be obtained by mixing the above. The mixing of the polyester resins having different intrinsic viscosities may be mixing of the same polyester resin or different types of polyester resins as long as the intrinsic viscosities are different. Preferably, the same kind of polyester resin is mixed.

In this case, the intrinsic viscosity of two or more polyester resins having different intrinsic viscosities is preferably in the range of 0.45 to 1.5 dl / g. This is because if the intrinsic viscosity is higher than the upper limit, there may be a problem in extrudability and the like, and if the intrinsic viscosity is lower than the lower limit, bubbles may be generated. Intrinsic viscosities of two or more polyester resins are more effective as the difference is greater. Therefore, the intrinsic viscosity difference is preferably 0.1 dl / g or more, more preferably 0.3 dl / g or more, Preferably, it is 0.5 dl / g or more.

2. Polyester film The polyester film used as the polarizer protective film of the present invention preferably has a retardation of 3000 to 30000 nm. When the retardation is less than 3000 nm, when used as a polarizer protective film, strong rainbow unevenness (color unevenness) occurs when observed from an oblique direction, and good visibility cannot be ensured. The lower limit of retardation is preferably 4500 nm, more preferably 5000 nm, still more preferably 6000 nm, particularly preferably 8000 nm, and most preferably 10,000 nm.

  On the other hand, the upper limit of retardation is preferably 30000 nm. Even if a film having a higher retardation is used, not only a further improvement effect of visibility can be obtained, but also the thickness of the film becomes considerably thick, and the handleability as an industrial material is lowered. is there.

  The retardation described above can be obtained by measuring the refractive index and thickness in the biaxial direction, or can be obtained using a commercially available automatic birefringence measuring device such as KOBRA-21ADH (Oji Scientific Instruments). .

  The polyester film used as the polarizer protective film of the present invention preferably has an impact absorption energy of 0.5 J or more. The impact absorption energy can be determined in accordance with JIS K 7124 “Plastic Film and Sheet—Shock Test Method by Free Dart Method (A Method)”. The value of impact absorption energy is more preferably 0.8 J or more, and still more preferably 1.4 J or more. By making the impact absorption energy of the polyester film 0.5J or more, even if it is a thin polyester film, the bonding process with a protective film to prevent scratches, dirt, etc. during post-processing, a hard coat layer, Sufficient mechanical strength can be obtained during post-processing such as a step of forming an antiglare layer, an antireflection layer, an antistatic layer, and the like. The higher the value of shock absorption energy, the better. However, 7.0 J is sufficient.

  The polyester film can be obtained in accordance with a general method for producing a polymer film. For example, after a polyester is melted and a non-oriented sheet is obtained by extrusion, MD stretching using a difference in roll speed and TD stretching by a tenter are used alone or in combination at a temperature equal to or higher than the glass transition temperature of the polyester. An example is a method of performing a heat treatment after the above.

  The production method of the polyester film is not limited to the above-described method, but in the case of a biaxially stretched film, when observed obliquely with respect to a direction perpendicular to the surface of the polarizer protective film, rainbow unevenness (color unevenness) ) Tends to be recognized, and from the viewpoint of eliminating rainbow unevenness (color unevenness), simple uniaxial TD stretching is preferable, and MD relaxation is more preferable simultaneously with TD stretching. Although simple uniaxial MD stretching is possible, there are problems such as easy stretching unevenness, and attention is required.

  The retardation of the polyester film used in the present invention can be controlled by adjusting the stretching conditions during film production. Specifically, it is preferable to adjust the molecular weight of the resin, the added stretching aid, and the monomer, but the stretching temperature is in the range of −10 ° C. to + 50 ° C. with the glass transition temperature (Tg) as a guide. It is preferable to perform the setting and increase the stretching temperature as the stretching proceeds. When the stretching temperature is low, breakage frequently occurs, and when the stretching temperature is high, uneven thickness or whitening may occur.

  The total stretch ratio of the film (= MD stretch ratio × TD stretch ratio) is set in the range of 3.0 times to 10.0 times, and when stretching in multiple stages, the stretch ratio is increased at the initial stage. In order to break easily, it is preferable to make the latter draw ratio higher than the initial draw ratio.

  In the case of carrying out MD stretching, when the MD stretching magnification is carried out alone, the vicinity of 3.5 times is preferable. When TD stretching is used in combination, the MD stretching ratio is preferably 1.0 to 2.5 times.

  The TD stretching ratio in TD stretching is preferably 3.0 to 6.0 times, and more preferably 3.5 to 5.0 times. In addition, it is possible to relax in the MD direction simultaneously with TD stretching, and although depending on the TD stretching ratio, the relaxation ratio is preferably 0.5 to 0.9 times, more preferably 0.65 to 0.8 times. . It is preferable to control by these methods so that the ratio of retardation to retardation in the thickness direction is within a specific range. In addition, by performing a relaxation process in the MD direction, when heat processing is performed in a post-processing step such as during the manufacture of a polarizing plate, or when a display is used at a high temperature for a long time, the heat shrinkage of the film occurs. It becomes possible to more effectively suppress distortion of optical characteristics, deterioration of flatness, wrinkles, curls, and the like.

  It can also be produced by simultaneous biaxial stretching. Specifically, in general, a facility called a simultaneous biaxial stretching machine is used, and a method of performing heat treatment after simultaneously performing TD stretching and MD stretching, or relaxing in the MD direction simultaneously with TD stretching. In the latter case, pay attention to the thickness unevenness, etc., and make the relaxation magnification in the MD direction 0.5 to 0.9 times, further 0.65 to 0.8 times. Is preferred. When the relaxation magnification in the MD direction is set in this way, heat treatment occurs in post-processing steps such as when manufacturing polarizing plates, or when the display is used at high temperatures for long periods of time, which occurs due to heat shrinkage of the film. It is possible to more effectively suppress distortion of optical characteristics, deterioration of flatness, wrinkles, curls, and the like.

  If uniaxial symmetry is increased from the viewpoint of eliminating rainbow unevenness (color unevenness), the mechanical strength in the direction perpendicular to the axis may be reduced, so care must be taken.

  As shown in Patent Document 4, color unevenness occurs while maintaining the mechanical strength of the protective film by controlling the ratio of the retardation of the polarizer protective film and the retardation in the thickness direction to be within a specific range. Can be suppressed. The retardation in the thickness direction is an average retardation (Rth) obtained by multiplying the two birefringences ΔNxz and ΔNyz by the film thickness d when the film is viewed from the cross section in the thickness direction. In addition, the retardation described so far is a retardation when viewed from the surface direction of the film, and is a retardation (Re) obtained by multiplying the birefringence ΔNxy by the film thickness d.

  From the optical viewpoint, the ratio (Re / Rth) of retardation (Re) and thickness direction retardation (Rth) of the polyester film is preferably 0.2 or more, more preferably 0.5 or more, and still more preferably 0.8. 6 or more. The larger the ratio (Re / Rth), the more the birefringence becomes isotropic, and the occurrence of color unevenness due to observation from an oblique direction is less likely to occur.

  On the other hand, the ratio of the retardation of the polyester film to the retardation in the thickness direction (Re / Rth) is preferably 1.2 or less, more preferably 1.0 or less, from the viewpoint of mechanical strength. In a film having perfect uniaxial symmetry, the ratio of the retardation to the retardation in the thickness direction (Re / Rth) is 2.0. The larger the uniaxial symmetry, the stronger the uniaxial symmetry, and the direction perpendicular to the axis. The mechanical strength (tear strength) of the steel decreases.

  However, by adjusting the optical characteristics as described above, even if the mechanical strength (tear strength) is ensured, the bonding process with the protective film and the hard coat layer to prevent scratches and dirt during post-processing In the post-processing such as a step of forming an antiglare layer, an antireflection layer, an antistatic layer or the like, a problem of breakage may occur.

  As a result of intensive studies on such an event, the present inventors have found that sufficient mechanical strength can be obtained even in post-processing by adjusting the intrinsic viscosity of the polyester.

  The intrinsic viscosity of the polyester used in the present invention is preferably 0.65 dl / g or more, and more preferably 0.70 dl / g or more. This is because if the intrinsic viscosity is low, problems may occur in terms of film-forming stability, fracture resistance, and the like. On the other hand, the upper limit of the intrinsic viscosity is preferably 1.0 dl / g or less, more preferably 0.90 dl / g or less. This is because if the intrinsic viscosity is too high, problems tend to occur from the viewpoint of extrudability.

  The heat treatment is preferably adjusted by the molecular weight of the resin, the added stretching aid, the monomer, and the stretching ratio, and the processing temperature is based on the glass transition temperature (Tg) and the melting point (Tm). It is preferable to set the temperature in the range of Tg + 50 ° C. or higher to Tm−30 ° C., and particularly control so that the heat shrinkage rate does not increase. Specifically, in any direction of MD and TD, the thermal shrinkage rate is preferably -2% to 2%, more preferably -1.5% to 1.5%, and still more preferably -1. 0.0% to 1.0%, more preferably -0.8% to 0.8%, and particularly preferably -0.5% to 0.5%. By performing relaxation in the MD direction during the heat treatment, it is possible to further reduce the thermal contraction rate efficiently.

  The thickness of the polyester film is preferably 25 to 100 μm, and more preferably 30 to 80 μm. Especially preferably, it is 35 micrometers or more. It is preferable that it is 100 micrometers or less from a viewpoint of thickness reduction of a liquid crystal display device. Moreover, it exists in the tendency which is easy to ensure the value of the impact strength energy of a polyester film as film thickness is 25 micrometers or more.

  The thickness unevenness of the film affects the retardation and retardation in the thickness direction, so it is preferably 5.0% or less, more preferably 4.5% or less, and even more preferably 4.0% or less. . Thickness unevenness can be controlled by adjusting the above stretching conditions and heat treatment conditions.

  As for a polarizer protective film, it is desirable for the light transmittance of wavelength 380nm to be 20% or less. The light transmittance at 380 nm is more preferably 15% or less, further preferably 10% or less, and particularly preferably 5% or less. For example, the light transmittance at a wavelength of 380 nm can be reduced to 20% or less by adding an ultraviolet absorber to polyester.

In addition to ultraviolet absorbers, for example, inorganic particles, heat resistant polymer particles, alkali metal compounds, alkaline earth metal compounds, phosphorus compounds, antistatic agents, light proofing agents, flame retardants, thermal stabilizers, antioxidants Further, an antigelling agent and / or a surfactant can be added to the polyester as long as the effects of the present invention are not hindered and the transparency is not impaired.

  The polyester film used in the present invention is a known method such as a combining adapter method, a multi-slot method, a multi-manifold method, and the like, in which polyester and other additives and particles are mixed as long as the performance is not impaired. It is also possible to have a laminated structure such as a two-type two-layer configuration, a two-type three-layer configuration of B / A / B configuration, and a three-type three-layer configuration of C / A / B.

3. Easy-Adhesive Layer The polarizer protective film has an easy-adhesive layer containing at least one of a polyester resin, a polyurethane resin, or a polyacrylic resin as a main component on at least one surface in order to improve the adhesion to the polarizer. It is preferable. Here, the “main component” refers to a component that is 50% by mass or more of the solid components constituting the easy-adhesion layer.

  The coating liquid for the easy-adhesion layer formed on the polarizer protective film is preferably an aqueous coating liquid containing at least one of water-soluble or water-dispersible copolymer polyester resin, acrylic resin, and polyurethane resin. As these coating liquids, water-soluble or water-dispersible properties disclosed in Japanese Patent No. 3567927, Japanese Patent No. 3589232, Japanese Patent No. 3589233, Japanese Patent No. 3900191 and Japanese Patent No. 4150982 are disclosed. Examples thereof include a copolymerized polyester resin solution, an acrylic resin solution, and a polyurethane resin solution.

  The easy adhesion layer formed on the polarizer protective film is a reverse roll coating method, a gravure coating method, a kiss coating method, a roll brush method, a spray coating method, an air knife coating method, a wire bar coating method, a pipe doctor method, The known methods such as these can be applied alone or in combination.

4). Functional Layer For the polarizing plate of the present invention, it is also preferable to use a polarizer protective film having various functional layers coated on its surface for the purpose of preventing reflection, suppressing glare, and suppressing scratches.

  Examples of the functional layer laminated at an arbitrary position on the viewing side of the polarizer protective film include, for example, an antiglare layer, an antireflection layer, a low reflection layer, a low reflection antiglare layer, an antireflection antiglare layer, an antistatic layer, and silicone. One or more selected from the group consisting of a layer, an adhesive layer, an antifouling layer, a water repellent layer, a blue cut layer, and the like can be used.

  When providing various functional layers, it is preferable to have an easy-adhesion layer on the surface of the polarizer protective film. At that time, from the viewpoint of suppressing interference due to reflected light, it is preferable to adjust the refractive index of the easy-adhesion layer so that it is close to the geometric mean of the refractive index of the functional layer and the refractive index of the polyester film. The refractive index of the easy-adhesion layer can be adjusted by a known method. For example, the refractive index of the easy-adhesion layer can be easily adjusted by adding titanium, zirconium, or other metal species to the binder resin.

(Hard coat layer)
The hard coat layer only needs to be a layer having hardness and transparency. Usually, various curable properties such as an ionizing radiation curable resin typically cured by ultraviolet rays or an electron beam, and a thermosetting resin cured by heat. What was formed as a cured resin layer of resin is used. In order to appropriately add flexibility and other physical properties to these curable resins, thermoplastic resins and the like may be added as appropriate. Among the curable resins, ionizing radiation curable resins are preferable because they are representative and an excellent hard coating film can be obtained.

  As the ionizing radiation curable resin, a conventionally known resin may be appropriately employed. As the ionizing radiation curable resin, a radical polymerizable compound having an ethylenic double bond, a cationic polymerizable compound such as an epoxy compound, and the like are typically used. These compounds include monomers, oligomers, prepolymers, and the like. These can be used alone or in appropriate combination of two or more. Typical compounds are various (meth) acrylate compounds that are radical polymerizable compounds. Among the (meth) acrylate compounds, compounds used at a relatively low molecular weight include, for example, polyester (meth) acrylate, polyether (meth) acrylate, acrylic (meth) acrylate, epoxy (meth) acrylate, urethane (meth) ) Acrylate, etc.

  Examples of the monomer include monofunctional monomers such as ethyl (meth) acrylate, ethylhexyl (meth) acrylate, styrene, methylstyrene, N-vinylpyrrolidone; or, for example, trimethylolpropane tri (meth) acrylate, tripropylene glycol di (Meth) acrylate, diethylene glycol di (meth) acrylate, pentaerythritol tri (meth) acrylate, dipentaerythritol hexa (meth) acrylate, 1,6-hexanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, etc. These polyfunctional monomers are also used as appropriate. (Meth) acrylate means acrylate or methacrylate.

  When the ionizing radiation curable resin is cured with an electron beam, a photopolymerization initiator is unnecessary, but when it is cured with ultraviolet rays, a known photopolymerization initiator is used. For example, in the case of a radical polymerization system, acetophenones, benzophenones, thioxanthones, benzoin, benzoin methyl ether, or the like can be used alone or in combination as a photopolymerization initiator. In the case of a cationic polymerization system, an aromatic diazonium salt, aromatic sulfonium salt, aromatic iodonium salt, metatheron compound, benzoin sulfonate, or the like can be used alone or in combination as a photopolymerization initiator.

  The thickness of the hard coat layer may be an appropriate thickness, for example, 0.1 to 100 μm, but usually 1 to 30 μm. The hard coat layer can be formed by appropriately adopting various known coating methods.

  A thermoplastic resin, a thermosetting resin, or the like can be appropriately added to the ionizing radiation curable resin for the purpose of adjusting the physical properties as appropriate. Examples of the thermoplastic resin or thermosetting resin include an acrylic resin, a urethane resin, and a polyester resin, respectively.

  In order to impart light resistance to the hard coat layer and prevent discoloration, strength deterioration, cracking, and the like due to ultraviolet rays contained in sunlight, it is also preferable to add an ultraviolet absorber in the ionizing radiation curable resin. When an ultraviolet absorber is added, the ionizing radiation curable resin is preferably cured with an electron beam in order to reliably prevent the ultraviolet coater from inhibiting the curing of the hard coat layer. Examples of the ultraviolet absorber include organic ultraviolet absorbers such as benzotriazole compounds and benzophenone compounds, or inorganic ultraviolet absorbers such as fine particles of zinc oxide, titanium oxide, and cerium oxide having a particle size of 0.2 μm or less, What is necessary is just to select and use from well-known things. The addition amount of the ultraviolet absorber is about 0.01 to 5% by mass in the ionizing radiation curable resin composition. In order to further improve the light resistance, it is preferable to add a radical scavenger such as a hindered amine radical scavenger in combination with an ultraviolet absorber. In addition, the electron beam irradiation has an acceleration voltage of 70 kV to 1 MV and an irradiation dose of about 5 to 100 kGy (0.5 to 10 Mrad).

(Anti-glare layer)
It is one of the preferred embodiments that an antiglare layer is provided on the most visible side of the image display device. As the antiglare layer, a conventionally known layer may be appropriately employed, and it is generally formed as a layer in which an antiglare agent is dispersed in a resin. As the antiglare agent, inorganic or organic fine particles are used. These fine particles have a spherical shape, an elliptical shape, or the like. The fine particles are preferably transparent. Examples of such fine particles include silica beads as inorganic fine particles and resin beads as organic fine particles. Examples of the resin beads include styrene beads, melamine beads, acrylic beads, acrylic-styrene beads, polycarbonate beads, polyethylene beads, and benzoguanamine-formaldehyde beads. The fine particles are usually added in an amount of 2 to 30 parts by mass, preferably about 10 to 25 parts by mass with respect to 100 parts by mass of the resin.

  The above resin for dispersing and holding the antiglare agent is preferably as hard as possible as in the hard coat layer. Therefore, as the resin, for example, a curable resin such as an ionizing radiation curable resin or a thermosetting resin described in the hard coat layer can be used.

  The thickness of the antiglare layer may be an appropriate thickness, and is usually about 1 to 20 μm. The antiglare layer can be formed by appropriately adopting various known coating methods. In addition, it is preferable to add well-known anti-settling agents such as silica to the coating liquid for forming the anti-glare layer in order to prevent precipitation of the anti-glare agent.

(Antireflection layer)
It is also one of preferable modes that an antireflection layer is provided on the outermost surface side of the image display device and the interface of each film with air.
As the antireflection layer, a conventionally known layer may be appropriately employed. In general, the antireflection layer is composed of at least a low refractive index layer, and a low refractive index layer and a high refractive index layer (having a higher refractive index than the low refractive index layer) are alternately stacked adjacent to each other and the surface side has a low refractive index. It consists of multiple layers as the rate layer. Each thickness of the low-refractive index layer and the high-refractive index layer may be an appropriate thickness according to the application, and is about 0.1 μm when adjacent layers are stacked, and about 0.1 to 1 μm when the low-refractive index layer alone is used. It is preferable.

  As a low refractive index layer, a layer containing a low refractive index material such as silica or magnesium fluoride in a resin, a layer of a low refractive index resin such as a fluorine-based resin, or a low refractive index material in a low refractive index resin A thin film formed by a thin film forming method (for example, physical or chemical vapor deposition such as vapor deposition, sputtering, CVD, or the like), an oxidation layer, or a layer made of a low refractive index material such as silica or magnesium fluoride. Examples thereof include a film formed by a sol-gel method in which a silicon oxide gel film is formed from a silicon sol solution, or a layer in which void-containing fine particles are contained in a resin as a low refractive index substance.

  The void-containing fine particles are fine particles containing gas inside, fine particles having a porous structure containing gas, etc., and with respect to the original refractive index of the fine particle solid portion, It means fine particles whose refractive index is apparently lowered. Examples of such void-containing fine particles include silica fine particles disclosed in JP-A No. 2001-233611. Examples of the void-containing fine particles include hollow polymer fine particles disclosed in JP-A No. 2002-805031, in addition to inorganic substances such as silica. The particle diameter of the void-containing fine particles is, for example, about 5 to 300 nm.

  As the high refractive index layer, a layer containing a high refractive index material such as titanium oxide, zirconium oxide or zinc oxide in a resin, a layer of a high refractive index resin such as a fluorine-free resin, or a high refractive index material is highly refracted. A layer formed of a high-refractive-index material such as titanium oxide, zirconium oxide, or zinc oxide in a thin film forming method (for example, vapor deposition, sputtering, CVD, etc., physical or chemical vapor deposition) Method).

(Anti-fouling layer)
As the antifouling layer, a conventionally known layer may be appropriately employed. Generally, in the resin, a silicon compound such as silicone oil or silicone resin; a fluorine compound such as fluorine surfactant or fluorine resin. It can be formed by a known coating method using a paint containing a stain-proofing agent such as wax. The thickness of the antifouling layer may be set appropriately, and can usually be about 1 to 10 μm.

(Antistatic layer)
As the antistatic layer, a conventionally known layer may be employed as appropriate, and it is generally formed as a layer containing an antistatic layer in a resin. As the antistatic layer, an organic or inorganic compound is used. For example, examples of the antistatic layer of an organic compound include a cationic antistatic agent, an anionic antistatic agent, an amphoteric antistatic agent, a nonionic antistatic agent, and an organometallic antistatic agent. The inhibitor is used not only as a low molecular compound but also as a high molecular compound. As the antistatic agent, conductive polymers such as polythiophene and polyaniline are also used. Further, as the antistatic agent, for example, conductive fine particles made of a metal oxide are used. The particle diameter of the conductive fine particles is, for example, about 0.1 nm to 0.1 μm in average particle diameter in terms of transparency. Examples of the metal oxide include ZnO, CeO ₂ , Sb ₂ O ₂ , SnO ₂ , ITO (indium doped tin oxide), In ₂ O ₃ , Al ₂ O ₃ , ATO (antimony doped tin oxide), AZO (aluminum doped zinc oxide) etc. are mentioned.

  Examples of the resin containing the antistatic layer include curable resins such as ionizing radiation curable resins and thermosetting resins as described in the hard coat layer. When the layer is formed as a layer and the surface strength of the antistatic layer itself is unnecessary, a thermoplastic resin or the like is also used. The thickness of the antistatic layer may be set appropriately, and is usually about 0.01 to 5 μm. The antistatic layer can be formed by appropriately adopting various known coating methods.

5. Liquid crystal display device and polarizing plate The liquid crystal display device of the present invention has a backlight, a liquid crystal cell, and a polarizing plate disposed on both sides of the liquid crystal cell. In the liquid crystal display device, an image or the like is displayed by a backlight using a CCFL, an LED, or the like disposed on one surface as a light source. The polarizing plate is composed of a film called a polarizer mainly composed of polyvinyl alcohol (PVA) and adsorbed and oriented with iodine compound molecules, and a polarizer protective film disposed on both sides thereof. The liquid crystal display device may appropriately include, for example, a color filter, a lens film, a diffusion sheet, an antireflection film, and the like as other constituent members.

  The configuration of the backlight may be an edge light method using a light guide plate or a reflection plate as a constituent member, or may be a direct type, but in the present invention, it is a continuous light source for a liquid crystal display device. It is preferable to use a white light source having a broad emission spectrum.

  “Continuous and broad emission spectrum” means an emission spectrum in which there is no wavelength region where the light intensity becomes zero in the wavelength region of at least 450 to 650 nm, preferably in the visible light region. The visible light region is, for example, a wavelength region of 400 to 760 nm, and may be 360 to 760 nm, 400 to 830 nm, or 360 to 830 nm.

  As a white light source having a continuous and broad emission spectrum, for example, a white light emitting diode (white LED) can be exemplified. A white LED is a phosphor type, that is, an element that emits white light by combining an LED emitting blue light or ultraviolet light using a compound semiconductor and a phosphor, an organic light-emitting diode (OLED), and the like. Can be mentioned. The phosphors include yttrium / aluminum / garnet yellow phosphors and terbium / aluminum / garnet yellow phosphors, among others, blue LEDs using compound semiconductors and yttrium / aluminum / garnet yellow phosphors. A white LED composed of a light-emitting element combined with a body has a continuous and broad emission spectrum and is excellent in luminous efficiency, and thus energy saving can be expected.

  The polarizing plate of the present invention comprises a polarizer mainly composed of polyvinyl alcohol (PVA) and adsorbed and oriented with iodine compound molecules, and a polarizer protective film disposed on both sides thereof. At least one of the polarizer protective films is preferably a polarizer protective film made of a polyester film having the specific retardation of the present invention.

  The polyester film having the specific retardation of the present invention can be used as an arbitrary polarizer protective film in a liquid crystal display device. Preferably, the polyester film is disposed on the light source side of the polarizer protective film disposed on the light source side of the liquid crystal (hereinafter also referred to as “light source side polarizing plate”) or on the viewing side of the liquid crystal cell. It is preferably used as a viewing-side polarizer protective film for a polarizing plate (hereinafter also referred to as “viewing-side polarizing plate”). More preferably, the said polyester film is a polarizer protective film arrange | positioned at the visual recognition side of the visual recognition side polarizing plate. When the polyester film is disposed at a position other than the above, the polarization characteristics of the liquid crystal cell may be changed.

  On the other hand, it is preferable to use a film having no retardation such as a TAC film, an acrylic film, or a norbornene resin film as the polarizer protective film that does not use the polyester film having the specific retardation. For example, a film having no such retardation can be used as a viewing-side polarizer protective film constituting the light source-side polarizing plate and / or a light source-side polarizer protecting film constituting the viewing-side polarizing plate.

  The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited by the following examples, and may be implemented with appropriate modifications within a scope that can meet the gist of the present invention. These are all included in the technical scope of the present invention.

  Evaluation in Examples was performed according to the following method.

(1) Thickness (d)
The thickness (d) was determined in accordance with JIS K 7130 “Method for measuring thickness of plastic film and sheet (Method A)”.

(2) Retardation (Re)
Retardation refers to the refractive index (Nx) in each axial direction of the film with respect to the thickness direction (z-axis) and the two axial directions (x-axis and y-axis) that are orthogonal to and perpendicular to the film surface. , Ny, Nz) is a phase difference represented by the product of birefringence and film thickness d.
Here, the in-plane retardation that is the product of the birefringence index Nxy and the thickness d caused by light incident on the film surface (xy plane) with MD as the x axis and TD as the y axis is referred to as retardation (Re). , In accordance with JIS K 7142 “Plastic Refractive Index Measurement Method (Method A)”, the longitudinal direction (MD) refractive index (Nx), the lateral direction (TD) refractive index (Ny), and the thickness direction refraction. It calculated | required from following Formula using the value which calculated | required the rate (Nz). In general, the unit of retardation is nm.
ΔNxy = | Nx−Ny |
Re = ΔNxy × d

(3) Re / Rth
First, thickness direction retardation (Rth) is calculated | required. Thickness direction retardation refers to the thickness direction (z axis) and two axial directions (x axis and y axis) that are orthogonal to the film surface and perpendicular to each other. The retardation produced is shown here, where the product of the average of the two birefringences in the xz plane and the yz plane and the film thickness d, as in retardation (Re), is JIS K 7142 “Plastic Based on “Refractive Index Measurement Method (Method A)”, the longitudinal direction (MD) refractive index (Nx), the lateral direction (TD) refractive index (Ny), and the thickness direction refractive index (Nz) were determined. Using the value, it was calculated from the following equation. In general, the unit of retardation is nm.
Rth = (| Nx−Nz | + | Ny−Nz |) / 2 × d
Re / Rth was obtained from Rth and the Re value obtained in (2).

(4) Intrinsic viscosity (IV)
For the viscosity number obtained according to JIS K 7367-5 “Plastics—Determination of viscosity of dilute solution using capillary viscometer—Part 5: Thermoplastic polyester (TP) homopolymer and copolymer” Under the following measurement conditions, the value when the mass concentration (c) = 0 was set as the intrinsic viscosity (IV) from the relationship of the viscosity number to the mass concentration (c) of the solution.
Solvent: phenol / 1,1,2,2-tetrachloroethane = 60/40 (wt%)
Tube: Ubbelohde viscosity tube Temperature: 30 ± 0.1 (° C)

(5) Glass transition temperature (Tg), melting point (Tm)
The midpoint glass transition temperature obtained from the DSC curve of differential scanning calorimetry (DSC) in accordance with JIS K 7121 “Plastic transition temperature measurement method” is the glass transition temperature (Tg), and the melting peak temperature is the melting point (Tm). did.

(6) Observation of rainbow unevenness (color unevenness) An example of a film produced by a method described later on one side of a commercially available polarizer and a film of a comparative example were compared with the absorption axis of the polarizer and the orientation axis of the film (the higher of Nx and Ny). ) Were attached so as to be vertical, and a commercially available TAC film was attached to the opposite surface to prepare polarizing plate A.
A commercially available liquid crystal display device having a liquid crystal cell sandwiched between polarizing plates having a white LED as a backlight light source and two TAC films as a polarizer protective film was prepared. The polarizing plate on the viewing side of the liquid crystal display device was replaced with the polarizing plate A, and the viewing side was installed so as to be the film of the example or the comparative example. Visual observation was performed from the front and oblique directions of the liquid crystal display device thus obtained, and the occurrence of rainbow unevenness (color unevenness) was determined as follows.
◎: Rainbow unevenness (color unevenness) is not observed when observed from any direction ○: When observed from an oblique direction, a partly extremely thin rainbow unevenness (color unevenness) can be observed ×: Observed from an oblique direction Rainbow unevenness (color unevenness) can be clearly observed when

(7) Tear Strength Based on JIS K 7128 “Plastic Film and Sheet Tear Test Method (Method B)”, the lower value of the Elmendorf tear strength, which is a value converted into 16 sheets for MD and TD. Was determined as follows.
○: Tear strength is 50 mN or more
×: Tear strength less than 50 mN (8) Impact absorption energy (IFE)
It was determined in accordance with JIS K 7124 “Plastic film and sheet—impact test method by dart method of free fall (A method)”.

(9) Film processability Using a general coating machine, a hard coat (thermosetting resin dissolved with MEK solvent) is applied to a dry thickness of 100 nm, and then a hot air method (80 to 90). In the step of drying at (° C.), the following criteria were ranked. In addition, (double-circle), (circle), and (triangle | delta) were set as the pass, and x was set as the disqualification.
A: Good without breaking. There was no need to adjust conditions such as tension and temperature, and good processability was obtained.
○: No breakage was observed. Stable process passability was obtained even if the conditions such as tension and temperature were slightly changed.
Δ: Good without breaking. When conditions such as tension and temperature were slightly changed, breakage sometimes occurred.
X: It broke.

(10) Thermal contraction rate (SH)
In accordance with JIS C 2318 “Electric polyethylene terephthalate film (dimensional change)”, the dimensional change rate before and after heating at 150 ° C. for 30 minutes was determined as the thermal shrinkage rate for MD and TD.

(Production Example 1-Polyethylene terephthalate A)
Terephthalic acid (TPA) and ethylene glycol (EG) are charged into an esterification reaction kettle and subjected to esterification for 120 minutes under conditions of a pressure of 0.25 MPa and a temperature of 220 to 240 ° C., and then the inside of the reaction kettle is brought to normal pressure. Then, titanium tetrabutoxide or the like is added as a polymerization catalyst, and the reaction system is gradually depressurized while stirring to 0.5 hPa in 75 minutes, and the temperature is raised to 280 ° C. and melt viscosity at 280 ° C. Stirring was continued until the value reached a predetermined value, and the polymerization reaction was carried out. Thereafter, the mixture was discharged into water, cooled and dried to obtain polyethylene terephthalate A. The physical properties were as follows.
IV: 0.62 dl / g
Tm: 258 ° C
Tg: 74 ° C

(Production Example 2-Polyethylene terephthalate B)
The above-mentioned crystallized polyethylene terephthalate A was subjected to a solid phase polymerization treatment in which the pressure was reduced at a temperature lower by about 10 to 15 ° C. than the melting point to obtain polyethylene terephthalate B. The physical properties were as follows.
IV: 0.73 dl / g
Tm: 258 ° C
Tg: 76 ° C

(Production Example 3-Adhesiveness modifying liquid)
With respect to all components of dicarboxylic acid, 46 mol% of terephthalic acid, 46 mol% of isophthalic acid, and 8 mol% of sodium 5-sulfonatoisophthalate and 50 mol% of neopentyl glycol with respect to all components of glycol A water-dispersible sulfonic acid metal base-containing copolymer polyester resin was obtained by a transesterification reaction and a polycondensation reaction by a conventional method. Next, an adhesive property modification liquid was obtained in which this and the agglomerated silica particles were dispersed in a solution in which water, isopropyl alcohol, n-butyl cellosolve, and nonionic surfactant were mixed.

<Comparative Example 1>
Using an extruder, polyethylene terephthalate A was melted at about 280 ° C. and melt extruded from the slit. An unstretched sheet cooled and solidified by electrostatic application on a chill roll having a surface temperature of about 25 ° C. is 0.08 g / m ² after the adhesive reforming liquid is dried on both sides by reverse roll coating. After applying TD stretching with a tenter having a set temperature of 100 ° C. and a stretching ratio of 4.0 times, heat treatment at 180 ° C. was performed to obtain a film having a thickness of about 30 μm.

<Comparative example 2>
In the same manner as in Comparative Example 1, TD stretching was performed at a preset temperature of 110 ° C. to obtain a film having a thickness of 50 μm.

<Comparative Example 3>
A film having a thickness of 25 μm was obtained in the same manner as in Comparative Example 1.

<Comparative Example 4>
In the same manner as in Comparative Example 1, TD stretching was performed at a set temperature of 110 ° C. to obtain a film having a thickness of 30 μm.

<Examples 1-3>
Similarly to Comparative Example 1, using an extruder, polyethylene terephthalate B was melted at about 280 ° C. and melt-extruded from the slit. An unstretched sheet cooled and solidified by electrostatic application on a chill roll having a surface temperature of about 25 ° C. is 0.08 g / m ² after the adhesive reforming liquid is dried on both sides by reverse roll coating. After applying TD stretching with a tenter having a set temperature of 100 ° C. to 115 ° C. and a draw ratio of 4.0, heat treatment at 180 ° C. was performed to obtain a film having a thickness of about 30 μm. In addition, no breakage occurred during the process, and no abnormality such as whitening was observed in the film.

<Examples 4 to 6>
Similarly to Comparative Example 1, using an extruder, polyethylene terephthalate B was melted at about 280 ° C. and melt-extruded from the slit. An unstretched sheet cooled and solidified by electrostatic application on a chill roll having a surface temperature of about 25 ° C. is 0.08 g / m ² after the adhesive reforming liquid is dried on both sides by reverse roll coating. After applying TD stretching with a tenter with a set temperature of 110 ° C. and a draw ratio of 4.0 times, heat treatment at 180 ° C. is performed to obtain films with thicknesses of about 50 μm, about 80 μm, and about 100 μm. It was. In addition, no breakage occurred during the process, and no abnormality such as whitening was observed in the film.

  The results of the above Comparative Examples 1 to 4 and Examples 1 to 6 are shown in Table 1. As shown in Table 1, when a polyester having a low intrinsic viscosity was used, it was not easy to keep the shock absorption energy high, resulting in poor fracture resistance. On the other hand, polyesters with high intrinsic viscosity were used in the examples, and the impact absorption energy could be 0.5 J or more, resulting in excellent fracture resistance and process passability. Further, as the film thickness increases, a rainbow unevenness does not occur, and a film that is less likely to break even in post-processing can be obtained.

  By using the liquid crystal display device, the polarizing plate, and the polarizer protective film of the present invention, it is possible to contribute to the thinning and cost reduction of the display device without reducing the visibility due to color unevenness, Industrial applicability is extremely high.

Claims (5)

  A polarizer protective film comprising a polyester film having a retardation of 3000 to 30000 nm and an impact absorption energy of 0.5 J or more.   The polarizer protective film of Claim 1 whose thickness of the said polyester film is 100 micrometers or less.   The polarizer protective film of Claim 1 or 2 whose ratio (Re / Rth) of the retardation (Re) and thickness direction retardation (Rth) of the said polyester film is 0.2 or more and 1.2 or less. A polarizing plate having a polarizer protective film on both sides of a polarizer,
The polarizing plate whose at least one polarizer protective film is a polarizer protective film in any one of Claims 1-3.   A liquid crystal display device comprising a backlight, a liquid crystal cell, and a polarizing plate disposed on both sides of the liquid crystal cell, wherein at least one polarizing plate is the polarizing plate according to claim 4.