JP2018060230A - Liquid crystal display device, polarizing plate, and polarizer protection film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizer protection film suitable for a liquid crystal display device with excellent visibility.SOLUTION: In a polarizer protection film for a liquid crystal display device having a white light-emitting diode as a backlight light source, on at least one face of a polyester film, a surface layer mainly composed of copolymer polyester resin (A) and resin containing a block type isocyanate group (B) is provided, with retardation of the polyester film being 3000-30000 nm.SELECTED DRAWING: None

Description

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

  A polarizing plate used in a liquid crystal display (LCD) usually has a configuration in which a polarizer in which iodine is dyed on polyvinyl alcohol (PVA) or the like is sandwiched between two polarizer protective films. As the film, a triacetyl cellulose (TAC) film is usually used. In recent years, with the thinning of LCDs, there has been a demand for thinner polarizing plates. However, if the thickness of the TAC film used as the protective film is reduced for this purpose, sufficient mechanical strength cannot be obtained, and the moisture permeability becomes high and the polarizer is likely to deteriorate. Further, TAC films are very expensive, and there is a strong demand for inexpensive alternative materials.

  Therefore, it has been proposed to use a polyester film instead of the TAC film so that the polarizing plate can be made thin so that high durability can be maintained even if the thickness is small as a polarizer protective film (Patent Documents 1 to 3). ).

JP 2002-116320 A JP 2004-219620 A JP 2004-205773 A

  The polyester film is superior to the TAC film in durability, but unlike the TAC film, the polyester film has birefringence. Therefore, when the polyester film is used as a polarizer protective film, there is a problem that the image quality is deteriorated due to optical distortion. That is, since the polyester film having birefringence has a predetermined optical anisotropy (retardation), when used as a polarizer protective film, a rainbow-like color spot is generated when observed from an oblique direction, and the image quality is deteriorated. . Therefore, in patent documents 1-3, the countermeasure which makes retardation small is made by using copolyester as polyester. However, even in that case, the iridescent color spots could not be completely eliminated.

  The present invention is to solve such a problem, and the object thereof is to cope with the thinning of the liquid crystal display device (that is, has sufficient mechanical strength) and is visually recognized by rainbow-like color spots. It is to provide a liquid crystal display device and a polarizer protective film that do not cause deterioration in properties. The present invention also provides a polarizer protective film having the above-mentioned characteristics and excellent adhesion to a functional layer such as a hard coat layer, a polarizing plate using the same, and a liquid crystal display device using them. For further purposes.

As a result of intensive studies to achieve the above-mentioned problems, the present inventors have provided a surface layer mainly composed of a copolymer polyester resin and a resin containing a block type isocyanate group on a polyester film having a specific retardation. The present inventors have found that the above problem can be solved by using the laminated film as a polarizer protective film and combining it with a specific backlight light source, thereby completing the present invention.

That is, the representative present invention is as follows.
Item 1.
At least one surface of the polyester film is provided with a surface layer mainly composed of a copolymer polyester resin (A) and a resin (B) containing a blocked isocyanate group, and the retardation of the polyester film is 3000 to 30000 nm. A polarizer protective film for a liquid crystal display device using a white light source having a continuous emission spectrum as a backlight source.
Item 2.
Item 2. The polarizer protective film according to Item 1, wherein the ratio of the retardation of the polyester film to the retardation in the thickness direction (Re / Rth) is 0.2 or more.
Item 3.
Item 3. The polarizer protective film according to Item 1 or 2, wherein the polyester film comprises three or more layers, and an ultraviolet absorber is contained in a layer other than the outermost layer, and the light transmittance at 380 nm is 20% or less.
Item 4.
One or more layers selected from the group consisting of a hard coat layer, an antiglare layer, an antireflection layer, a low reflection layer, a low reflection antiglare layer, an antireflection antiglare layer, and an antistatic layer are laminated on the surface layer. Item 4. The polarizer protective film according to any one of Items 1 to 3.
Item 5.
The polarizing plate for liquid crystal display devices which makes the backlight light source the white light source which has the continuous emission spectrum by which the polarizer protective film in any one of claim | item 1-4 was laminated | stacked on the at least one side of the polarizer.
Item 6.
Item 6. The polarizing plate for a liquid crystal display device according to Item 5, wherein the polarizer protective film is laminated on the polarizer via an ultraviolet curable, electron beam curable, or thermosetting adhesive.
Item 7.
Item 7. A liquid crystal display device, wherein the backlight source is a white light source having a continuous emission spectrum, and the polarizing plate according to Item 5 or 6.
Item 8.
Item 8. The liquid crystal display device according to item 7, wherein the polarizing plate disposed on the emission light side with respect to the liquid crystal is the polarizing plate according to item 5 or 6.
Item 9.
Item 9. The liquid crystal display device according to item 7 or 8, wherein the white light source having a continuous emission spectrum is a white light emitting diode.

  The liquid crystal display device, the polarizing plate and the polarizer protective film of the present invention have good visibility in which no remarkable rainbow-like color spots are observed at any observation angle. Moreover, the polarizer protective film of this invention has strong adhesiveness with functional layers, such as a hard-coat layer. Furthermore, in a preferred embodiment, the polarizer protective film of the present invention has a mechanical strength suitable for thinning.

In general, the liquid crystal panel includes a rear module, a liquid crystal cell, and a front module in order from the backlight source side toward the image display side (viewing side or emission light side). The rear module and the front module are generally composed of a transparent substrate, a transparent conductive film formed on the liquid crystal cell side surface, and a polarizing plate disposed on the opposite side. Here, the polarizing plate is disposed on the backlight source side in the rear module, and is disposed on the image display side (viewing side or emission light side) in the front module.

  The liquid crystal display device of the present invention comprises at least a backlight source and a liquid crystal cell disposed between two polarizing plates. Moreover, you may have suitably other structures other than these, for example, a color filter, a lens film, a diffusion sheet, an antireflection film etc. suitably.

The configuration of the backlight light source may be an edge light method using a light guide plate or a reflection plate as a constituent member, or a direct type, but a white light source having a continuous and broad emission spectrum is used. It is preferable. Here, the continuous and broad emission spectrum means an emission spectrum in which there is no wavelength at which light intensity becomes zero in a wavelength region of at least 450 nm to 650 nm, preferably in a visible light region. Examples of such a white light source having a continuous and broad emission spectrum include a white light emitting diode (white LED). In the present invention, the white LED includes a phosphor type, that is, an element that emits white by combining a light emitting diode that emits blue light or ultraviolet light using a compound semiconductor and a phosphor, or an organic light emitting diode (Organic light-emitting diode). diode: OLED) and the like. Examples of the phosphor include yttrium / aluminum / garnet yellow phosphor and terbium / aluminum / garnet yellow phosphor. Among white LEDs, white light-emitting diodes that consist of a light-emitting element that combines a blue light-emitting diode using a compound semiconductor and a yttrium / aluminum / garnet-based yellow phosphor have a continuous and broad emission spectrum and light emission efficiency. Therefore, it is suitable as the backlight light source of the present invention. Use of a light source such as a white LED with lower power consumption is also effective for energy saving.

  Fluorescent tubes such as cold cathode tubes and hot cathode tubes that have been widely used as backlight light sources conventionally have only a discontinuous emission spectrum whose emission spectrum has a peak at a specific wavelength. It is difficult to obtain the effects of the present invention.

  The polarizing plate has a configuration in which both sides of a polarizer in which iodine is dyed on PVA or the like are sandwiched between two polarizer protective films. In the present invention, at least one of the polarizer protective films constituting the polarizing plate is used. A polyester film having a specific range of retardation is used.

  The mechanism for suppressing the occurrence of rainbow-like color spots according to the above aspect is considered as follows. When a polyester film having birefringence is disposed on one side of the polarizer, the linearly polarized light emitted from the polarizer is disturbed when passing through the polyester film. The transmitted light shows an interference color peculiar to retardation which is the product of birefringence and thickness of the polyester film. Therefore, if a discontinuous emission spectrum such as a cold cathode tube or a hot cathode tube is used as the light source, the transmitted light intensity varies depending on the wavelength, and a rainbow-like color spot is generated (see: 15th Micro Optical Conference Proceedings, No. 1). 30-31).

  In contrast, white light emitting diodes usually have a continuous and broad emission spectrum in a wavelength region of at least 450 nm to 650 nm, preferably in the visible light region. And since the interference color spectrum by the transmitted light which permeate | transmitted the birefringent body becomes an envelope shape, it becomes possible to obtain the spectrum similar to the light emission spectrum of a light source by controlling the retardation of a polyester film. In this way, by making the emission spectrum of the light source similar to the envelope shape of the interference color spectrum by the transmitted light that has passed through the birefringent body, visibility is not noticeable without rainbow-like color spots. It is thought to improve.

From the above principle, in the present invention, a white light emitting diode having a broad emission spectrum is used as a light source, so that the envelope shape of the spectrum of transmitted light can be approximated to the emission spectrum of the light source with only a relatively simple configuration, and as a result, liquid crystal It is thought that it is possible to suppress rainbow spots on the display.

(Base polyester film)
The polyester film used as the base film of the polarizer protective film of the present invention is preferably an oriented polyester film having a retardation of 3000 to 30000 nm. When the retardation is less than 3000 nm, when used as a polarizer protective film, it exhibits a strong interference color when observed from an oblique direction, so the envelope shape is different from the emission spectrum of the light source, and good visibility cannot be ensured. . The lower limit of the preferable retardation is 4500 nm or more, next preferably 5000 nm or more, more preferably 6000 nm or more, still more preferably 8000 nm or more, and still more preferably 10,000 nm or more.

  On the other hand, the upper limit of retardation is 30000 nm. Even if a polyester film having a retardation of more than that is used, it is not only possible to substantially improve the visibility, but also because the film thickness becomes considerably thick and the handling property as an industrial material is reduced, it is preferable. Absent.

  The retardation of the polyester film can be determined by measuring the biaxial refractive index and thickness, and can also be determined using a commercially available automatic birefringence measuring device such as KOBRA-21ADH (Oji Scientific Instruments). In this document, retardation means in-plane retardation.

  In the present invention, at least one of the polarizer protective films is a polarizer protective film having the specific retardation. The arrangement of the polarizer protective film having the specific retardation is not particularly limited, but the polarizer protective film on the incident light side of the polarizing plate arranged on the incident light side of the liquid crystal display device, or the polarized light arranged on the emission light side It is preferable that the polarizer protective film on the emission light side of the plate is a polarizer protective film made of a polyester film having the specific retardation. A particularly preferred embodiment is an embodiment in which the polarizer protective film on the exit light side of the polarizing plate disposed on the exit light side is a polyester film having the specific retardation. When the polyester film is disposed at a position other than the above, the polarization characteristics of the liquid crystal cell may be changed.

  The polarizing plate of the present invention has a structure in which both sides of a polarizer in which iodine is dyed on polyvinyl alcohol (PVA) or the like are sandwiched between two polarizer protective films, and any one of the polarizer protective films is specified above. It is a polarizing plate protective film which has this retardation. As the other polarizer protective film, it is preferable to use a film having no birefringence such as a TAC film, an acrylic film, and a norbornene-based film.

The polyester film used for the base material layer of the polarizer protective film of the present invention can be obtained by condensing dicarboxylic acid and diol. Examples of the dicarboxylic acid component that can be used for producing the polyester film include terephthalic acid, isophthalic acid, orthophthalic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1 , 5-Naphthalenedicarboxylic acid, diphenylcarboxylic acid, diphenoxyethanedicarboxylic acid, diphenylsulfonecarboxylic acid, anthracenedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid , Hexahydroterephthalic acid, hexahydroisophthalic acid, malonic acid, dimethylmalonic acid, succinic acid, 3,3-diethylsuccinic acid, glutaric acid, 2,2-dimethylglutaric acid, adipic acid, 2-methyladipic acid, trimethyl Horse mackerel Phosphate, pimelic acid, azelaic acid, dimer acid, sebacic acid, suberic acid, dodecamethylene dicarboxylic acid and the like.

  Examples of the diol component that can be used for producing the polyester film include ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, decamethylene glycol, 1 , 3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexadiol, 2,2-bis (4-hydroxyphenyl) propane, bis (4-hydroxyphenyl) sulfone, etc. Can be mentioned.

  Each of the dicarboxylic acid component and the diol component constituting the polyester film may be used alone or in combination of two or more. Specific polyester resins constituting the polyester film include, for example, polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and preferably polyethylene terephthalate and polyethylene naphthalate. These resins are excellent in transparency and excellent in thermal and mechanical properties, and the retardation can be easily controlled by stretching. In particular, polyethylene terephthalate is the most suitable material because it has a large intrinsic birefringence and a large retardation can be obtained relatively easily even if the film is thin.

  In order to suppress deterioration of optical functional dyes such as iodine dyes, it is desirable that the protective film of the present invention has a light transmittance of 20% or less at a wavelength of 380 nm. The light transmittance at 380 nm is more preferably 15% or less, further preferably 10% or less, and particularly preferably 5% or less. If the light transmittance is 20% or less, the optical functional dye can be prevented from being deteriorated by ultraviolet rays. In addition, the transmittance | permeability in this invention is measured by the perpendicular | vertical method with respect to the plane of a film, and can be measured using a spectrophotometer (for example, Hitachi U-3500 type).

  Setting the transmittance at a wavelength of 380 nm of the protective film of the present invention to 20% or less includes adding an ultraviolet absorber in the film, applying a coating solution containing the ultraviolet absorber to the film surface, and an ultraviolet absorber. This can be achieved by appropriately adjusting the type, concentration, and thickness of the film. The ultraviolet absorber used in the present invention is a known substance. Examples of the ultraviolet absorber include an organic ultraviolet absorber and an inorganic ultraviolet absorber, and an organic ultraviolet absorber is preferable from the viewpoint of transparency.

  Examples of the organic ultraviolet absorber include benzotriazole, benzophenone, cyclic imino ester, and combinations thereof, but are not particularly limited as long as the absorbance is within the range defined by the present invention. However, from the viewpoint of durability, benzotoazole and cyclic imino ester are particularly preferable. When two or more kinds of ultraviolet absorbers are used in combination, ultraviolet rays having different wavelengths can be absorbed simultaneously, so that the ultraviolet absorption effect can be further improved. When the ultraviolet absorber is blended with the polyester film, the polyester film is preferably composed of three or more layers, and the ultraviolet absorber is blended with a layer other than the outermost layer (that is, the intermediate layer).

Examples of the benzophenone ultraviolet absorber, benzotriazole ultraviolet absorber, and acrylonitrile ultraviolet absorber include 2- [2′-hydroxy-5 ′-(methacryloyloxymethyl) phenyl] -2H-benzotriazole, 2- [2′-hydroxy-5 ′-(methacryloyloxyethyl) phenyl] -2H-benzotriazole, 2- [2′-hydroxy-5 ′-(methacryloyloxypropyl) phenyl] -2H-benzotriazole, 2,2 ′ -Dihydroxy-4,4'-dimethoxybenzophenone, 2,2 '
, 4,4′-tetrahydroxybenzophenone, 2,4-di-tert-butyl-6- (
5-chlorobenzotriazol-2-yl) phenol, 2- (2′-hydroxy-3′-tert-butyl-5′-methylphenyl) -5-chlorobenzotriazole, 2- (5
-Chloro (2H) -benzotriazol-2-yl) -4-methyl-6- (tert-butyl) phenol, 2,2'-methylenebis (4- (1,1,3,3-tetramethylbutyl)- 6- (2H-benzotriazol-2-yl) phenol, etc. Examples of the cyclic imino ester UV absorber include 2,2 ′-(1,4-phenylene) bis (4H-3,1- Benzoxazinon-4-one), 2-methyl-3,1-benzoxazin-4-one, 2-butyl-3,1-benzoxazin-4-one, 2-phenyl-3,1-benzoxazine- 4-one etc. are mentioned, but it is not particularly limited to these.

  Moreover, it is also a preferable aspect to contain various additives in the range which does not prevent the effect of this invention other than an ultraviolet absorber. Examples of additives include 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, and antigelling agents. And surfactants. Moreover, in order to show high transparency, it is also preferable that a polyester film does not contain a particle | grain substantially. “Substantially free of particles” means, for example, in the case of inorganic particles, when the inorganic element is quantified by fluorescent X-ray analysis, the content is 50 ppm or less, preferably 10 ppm or less, particularly preferably the detection limit or less. Means quantity.

  Further, the polyester film of the present invention can be subjected to corona treatment, coating treatment, flame treatment and the like in order to improve the adhesion to the polarizer.

(Surface layer)
In the polarizing plate obtained by laminating the polarizer protective film of the present invention, it is preferable that functional layers such as various hard coat layers are further laminated for the purpose of preventing reflection, suppressing glare, and suppressing scratches. Therefore, the polarizing plate or the polarizer protective film of the present invention is provided with a surface layer excellent in adhesiveness with various functional layers such as various hard coat layers. The said surface layer has as a main component the copolymer polyester resin (A) and resin (B) containing a block type isocyanate group.

  The copolymerized polyester resin (A) preferably contains ethylene glycol and branched glycol as constituent components as an aromatic dicarboxylic acid component and a glycol component. The branched glycol component is represented by the following general formula (I), for example.

(However, R ¹ and R ² are selected from the group consisting of hydrogen, an alkyl group having 1 to 10 carbon atoms, an alkylene group, an aralkyl group, and a phenyl group, and at least one of them is an alkyl group having 1 to 6 carbon atoms. And n and m are integers from 1 to 6.

Specific examples of the branched glycol component contained in the resin (A) include 2,2-dimethyl-1,3-propanediol, 2-methyl-2-ethyl-1,3-propanediol, and 2-methyl. 2-propyl-1,3-propanediol, 2-methyl-2-isopropyl-1,3-propanediol, 2-methyl-2-butyl-1,3-propanediol, 2-methyl-2-n- Hexyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 2-ethyl-2-n-butyl-1,3-propanediol, 2-ethyl-2-n-hexyl-1 , 3-propanediol, 2,2-di-n-butyl-1,3-propanediol, 2-n-butyl-2-propyl-1,3-propanediol and 2,2-di-n-hexyl- 1, - propane diol.

  The branched glycol component is preferably contained in a proportion of 10 mol% or more, more preferably 20 mol% or more in the total glycol component. As glycol components other than the said compound contained in copolymer polyester resin (A), ethylene glycol is the most preferable. If it is a small amount, diethylene glycol, propylene glycol, butanediol, hexanediol, 1,4-cyclohexanedimethanol or the like may be used.

  As the dicarboxylic acid component contained as a constituent component of the copolymerized polyester resin (A), terephthalic acid and isophthalic acid are most preferable. In small amounts, other dicarboxylic acid components such as fatty acid dicarboxylic acids such as adipic acid, sebacic acid and azelaic acid; aromatic dicarboxylic acids such as diphenyldicarboxylic acid and 2,6-naphthalenedicarboxylic acid are added and copolymerized. May be.

  In addition to the dicarboxylic acid component, 4-sulfoisophthalic acid is preferably used in the range of 1 to 10 mol% in order to impart water dispersibility. For example, sulfoterephthalic acid, 5-sulfoisophthalic acid, 4- Examples thereof include sulfonaphthalene-2,7-dicarboxylic acid and 5- (4-sulfophenoxy) isophthalic acid.

  The resin (B) containing the blocked isocyanate group is a heat-reactive water-soluble urethane in which the terminal isocyanate group is blocked with a hydrophilic group (hereinafter referred to as a block).

  Examples of the isocyanate group blocking agent include phenols, alcohols, lactams, oximes and active methylene compounds containing bisulfites and sulfone groups. The blocked isocyanate group makes the urethane prepolymer hydrophilic or water-soluble. When heat energy is applied to the resin (B) in the course of drying or heat setting during film production, the blocking agent is detached from the isocyanate group, so that the resin (B) is mixed with water dispersed in a self-crosslinked network. While fixing the copolymerizable polyester resin (A), it also reacts with the terminal groups of the resin (A). The resin (B) at the time of preparing the coating solution is poor in water resistance because it is hydrophilic, but the hydrophilic group of the urethane resin (B), that is, the blocking agent is released when the thermal reaction is completed by coating, drying and heat setting. A coating film with good water resistance can be obtained. Of the above blocking agents, bisulfites are most preferred as those having a suitable heat treatment temperature and heat treatment time and widely used industrially.

  The chemical composition of the urethane prepolymer used in the resin (B) includes (1) a compound having two or more active hydrogen atoms in the molecule and a molecular weight of 200 to 20,000, (2) an intramolecular And organic polyisocyanate having two or more isocyanate groups, or (3) a compound having a terminal isocyanate group obtained by reacting a chain extender having at least two active hydrogen atoms in the molecule. it can.

The compound (1) generally known is a compound containing two or more hydroxyl groups, carboxyl groups, amino groups or mercapto groups in the terminal or molecule, and particularly preferred compounds include polyether polyols. , Polyester polyols and polyether ester polyols. Examples of polyether polyols are compounds obtained by polymerizing alkylene oxides such as ethylene oxide and propylene oxide, or compounds obtained by polymerizing styrene oxide and epichlorohydrin, or random copolymerization, block copolymerization, or addition polymerization to polyhydric alcohols. And the like. Examples of the polyester polyol and the polyether ester polyol mainly include linear or branched compounds. Polyvalent saturated and unsaturated carboxylic acids such as succinic acid, adipic acid, phthalic acid and maleic anhydride, or the carboxylic acid anhydride, and the like, ethylene glycol, diethylene glycol, 1,4-butanediol, neopentyl glycol, 1 Condensation with polyvalent saturated and unsaturated alcohols such as 1,6-hexanediol and trimethylolpropane, polyalkylene ether glycols such as relatively low molecular weight polyethylene glycols and polypropylene glycols, or mixtures of these alcohols Can be obtained. Furthermore, polyesters obtained from lactones and hydroxy acids can be used as polyester polyols, and polyether esters obtained by adding ethylene oxide or propylene oxide or the like to polyesters prepared in advance can be used. .

  Examples of the organic polyisocyanate (2) include isomers of toluylene diisocyanate, aromatic diisocyanates such as 4,4′-diphenylmethane diisocyanate, aromatic aliphatic diisocyanates such as xylylene diisocyanate, isophorone diisocyanate, and 4, Alicyclic diisocyanates such as 4'-dicyclohexylmethane diisocyanate, aliphatic diisocyanates such as hexamethylene diisocyanate and 2,2,4-trimethylhexamethylene diisocyanate, or a single or plural of these compounds with trimethylolpropane or the like in advance Examples include added polyisocyanates.

  Examples of the chain extender having at least two active hydrogens in (3) above include glycols such as ethylene glycol, diethylene glycol, 1,4-butanediol and 1,6-hexanediol, glycerin, trimethylolpropane and pentaerythritol. Polyhydric alcohols such as ethylenediamine, hexamethylenediamine and piperazine, aminoalcohols such as monoethanolamine and diethanolamine, thiodiglycols such as thiodiethylene glycol, and water.

  In order to synthesize the urethane polymer of the above (3), it is usually 5 minutes to several times at a temperature of 150 ° C. or less, preferably 70 to 120 ° C., by a single-stage or multi-stage isocyanate polyaddition method using the chain extender. Let react for hours. The ratio of isocyanate groups to active hydrogen atoms can be freely selected as long as it is 1 or more, but it is preferable that free isocyanate groups remain in the obtained urethane prepolymer. Further, the content of free isocyanate groups is preferably 10% by weight or less, and more preferably 7% by weight or less in consideration of the stability of the urethane polymer aqueous solution after being blocked.

  The obtained urethane prepolymer is blocked using bisulfite. Mix with aqueous bisulfite solution and allow reaction to proceed with good agitation for about 5 minutes to 1 hour. The reaction temperature is preferably 60 ° C. or lower. Thereafter, it is diluted with water to an appropriate concentration to obtain a heat-reactive water-soluble urethane composition. The composition is prepared to have an appropriate concentration and viscosity when used. Usually, when heated to about 80 to 200 ° C., the bisulfite of the blocking agent is dissociated and the active isocyanate groups are regenerated. A polyurethane polymer is produced by a polyaddition reaction that occurs within a molecule or between molecules, and it has the property of causing addition to other functional groups.

As an example of resin (B) containing the block type isocyanate group demonstrated above, the brand name Elastron by Dai-ichi Kogyo Seiyaku Co., Ltd. is illustrated typically. Elastolone is an isocyanate group blocked with sodium bisulfite, and is water-soluble because of the presence of a carbamoyl sulfonate group having strong hydrophilicity at the molecular end.

  When the coating liquid is prepared by mixing the copolymer polyester resin (A) and the block type isocyanate group-containing resin (B) used in the present invention, the weight ratio of the resin (A) to the resin (B) is (A) :( B) = 90: 10 to 10:90 is preferable, and (A) :( B) = 80: 20 to 20:80 is more preferable. If the ratio of the resin (A) to the solid content weight is less than 10%, the coating property to the base film is low, and the adhesion between the surface layer and the film may be insufficient. On the other hand, when the ratio of the resin (B) is less than 10%, sufficient adhesion with the hard coat layer may not be obtained.

  A catalyst may be added to the aqueous coating solution for forming the surface layer in order to promote the thermal crosslinking reaction, such as inorganic substances, salts, organic substances, alkaline substances, acidic substances, and metal-containing organic compounds. Various chemical substances are used. Moreover, in order to adjust pH of aqueous solution, you may add an alkaline substance or an acidic substance.

  When an aqueous coating solution for forming a surface layer is applied to the surface of a base film, a known anionic active agent and nonionic agent are used to increase the wettability to the film and coat the coating solution uniformly. A necessary amount of the surfactant can be added and used. As the solvent used in the coating solution, alcohols such as ethanol, isopropyl alcohol and benzyl alcohol may be mixed in addition to water until the ratio of the total coating solution is less than 50% by weight. Furthermore, if it is less than 10 weight%, you may mix in the range which can melt | dissolve organic solvents other than alcohol. However, the total of alcohols and other organic solvents in the coating solution is preferably less than 50% by weight. If the addition amount of the organic solvent is less than 50% by weight, the drying property is improved at the time of coating and drying, and the appearance of the coating film is improved as compared with the case of using only water. If it exceeds 50% by weight, the evaporation rate of the solvent is fast, the coating solution concentration changes during coating, the viscosity rises and the coating property decreases, and there is a risk of causing poor appearance of the coating film, Furthermore, there is a risk of fire.

  Various additions such as an antistatic agent, an ultraviolet absorption inhibitor, a plasticizer, a pigment, an organic filler, an inorganic filler, and a lubricant are added to the composition of the aqueous coating liquid for forming the surface layer as long as the effect is not lost. An agent may be mixed. Furthermore, since the coating solution is aqueous, other water-soluble resins, water-dispersible resins, emulsions, and the like may be added to the coating solution in order to improve performance as long as the contribution effect is not lost.

  Application of the aqueous coating liquid for forming the surface layer can be performed by any known method. Examples include reverse roll coating method, gravure coating method, kiss coating method, roll brush method, spray coating method, air knife coating method, wire barber coating method, pipe doctor method, impregnation / coating method and curtain coating method. These methods can be performed alone or in combination.

The step of applying the aqueous coating solution for forming the surface layer may be a normal application step, that is, a step of applying to a base film that has been biaxially stretched and heat-fixed, but is applied during the manufacturing process of the film. Is preferred. More preferably, it is applied to the base film before the crystal orientation is completed. The solid content concentration in the aqueous solution is usually 30% by weight or less, preferably 10% by weight or less. The aqueous coating solution is applied so that 0.04 to 5 g, preferably 0.2 to 4 g, is attached per 1 m ² of the running film. The film coated with the aqueous coating solution is guided to a tenter for stretching and heat setting, and heated there to form a stable coating film by a thermal crosslinking reaction, thereby forming a polyester-based laminated film. In order to obtain adhesion to the hard coat layer, the coating amount at this time is 0.01 g / m ² or more per 1 m ^{2 of} film, and heat treatment at 100 ° C. for 1 minute or more is preferable.

  As a hard coat layer laminated | stacked on the surface layer provided in the polyester film which is a polarizer protective film as mentioned above, conventionally well-known various hard coat layers can be used. The material used for forming the hard coat layer is not particularly limited, and a resin compound that is polymerized and / or reacted by drying, heat, chemical reaction, or irradiation with electron beam, radiation, or ultraviolet light. Can be used. Examples of such curable resins include melamine-based, acrylic-based, silicon-based, and polyvinyl alcohol-based curable resins. For the purpose of obtaining a high surface hardness or optical design, a photocurable acrylic curable resin is preferred. As such an acrylic curable resin, a polyfunctional (meth) acrylate monomer or an acrylate oligomer can be used. Examples of the acrylate oligomer include polyester acrylate, epoxy acrylate, urethane acrylate, polyether acrylate, polybutadiene acrylate, and silicone acrylate. A coating composition for forming the optical functional layer can be obtained by mixing a reactive diluent, a photopolymerization initiator, a sensitizer and the like with these acrylic curable resins.

  The hard coat layer may have an antiglare function (antiglare function) that scatters external light. The antiglare function (antiglare function) can be obtained by forming irregularities on the surface of the hard coat layer. At this time, the haze of the film is preferably 2 to 50%, more preferably 2 to 40%, and particularly preferably 2 to 30%.

The surface layer used in the present invention (based on the copolymer polyester resin (A) and the resin (B) containing a blocked isocyanate group as a main component) is not only a hard coat layer, but also an antiglare layer, an antireflection layer, It is also excellent in adhesion with a low reflection layer, a low reflection antiglare layer, an antireflection antiglare layer, an antistatic layer or the like. This is because many of these layers are made of a curable resin that is polymerized and / or reacted by drying, heat, chemical reaction, or irradiation with electron beam, radiation, or ultraviolet light. From the viewpoint of preventing reflection from external light such as LCD and touch panel, it consists of a hard coat layer, anti-glare layer, anti-reflection layer, low reflection layer, low reflection anti-glare layer and anti-reflection anti-glare layer on the coating layer. Laminating one or more layers selected from the group is a preferred embodiment of the present invention. In addition, it is also a preferred embodiment of the present invention that an antistatic layer is laminated from the viewpoint of antistatic. Of the hard coat layer, antiglare layer, antireflection layer, low reflection layer, low reflection antiglare layer, antireflection antiglare layer and antistatic layer, only one type may be provided on the polyester film, You may laminate | stack combining 2 or more types as needed. For example, the antiglare layer and the antistatic layer may be laminated in order, or the antiglare layer may be provided with an antistatic function and the antiglare function and the antistatic function may be combined in one layer. . By providing these layers, an effect of reducing iridescent color spots caused by the polarizing plate can be expected. As the antiglare layer, antireflection layer, low reflection layer, low reflection antiglare layer, antireflection antiglare layer and antistatic layer, known ones can be used. The antistatic layer may be a layer containing a known antistatic agent or a layer containing a conductive polymer such as polythiophene, polypyrrole or polyaniline.

(Easily adhesive layer with polarizer)
The oriented polyester film which is the polarizer protective film of the present invention is made of polyester resin, polyurethane resin or polyacrylic resin on the surface opposite to the surface on which the surface layer is provided in order to improve the adhesion to the polarizer. It is preferable to have an easy-adhesion layer containing at least one kind as a main component. 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 solution used for forming the easy-adhesion layer is preferably an aqueous coating solution containing at least one of a water-soluble or water-dispersible copolymerized polyester resin, an acrylic resin, and a polyurethane resin. Examples of these coating solutions include water-soluble or water-dispersible co-polymers disclosed in Japanese Patent No. 3567927, Japanese Patent No. 3589232, Japanese Patent No. 3589233, Japanese Patent No. 3900191, and Japanese Patent No. 4150982. Examples thereof include a polymerized polyester resin solution, an acrylic resin solution, and a polyurethane resin solution.

  In addition to the above embodiment, a polarizer is laminated on the surface of the polarizer protective film of the present invention provided with the surface layer via an ultraviolet curable, electron beam curable, and / or thermosetting adhesive. It is also a preferred embodiment. As described above, the surface layer of the polarizer protective film of the present invention is excellent in adhesiveness with a curable resin, and is excellent in adhesiveness with an adhesive such as an ultraviolet curable type, an electron beam curable type, and a thermosetting type. is there. As the ultraviolet curable adhesive, electron beam curable adhesive, and thermosetting adhesive, a conventionally known adhesive can be used for manufacturing a polarizing plate, and is not particularly limited. For example, curable resins disclosed in JP2011-219548, JP2011-186481, JP2011-175273, JP2011-127003, and the like can be used.

The easy-adhesion layer can be obtained by applying the coating solution on one or both sides of an unstretched or longitudinally uniaxially stretched film, drying at 100 to 150 ° C., and further stretching in the transverse direction. The final coating amount of the easy adhesion layer is preferably controlled to 0.05 to 0.20 g / m ² . If the coating amount is less than 0.05 g / m ² , the adhesion with the resulting polarizer may be insufficient. On the other hand, when the coating amount exceeds 0.20 g / m ² , blocking resistance may be lowered.

  It is preferable to add particles to the easy-adhesion layer in order to impart easy slipperiness. The average particle size of the fine particles is preferably 2 μm or less. When the average particle diameter of the particles exceeds 2 μm, the particles easily fall off from the easy adhesion layer. As particles to be included in the easy adhesion layer, for example, titanium oxide, barium sulfate, calcium carbonate, calcium sulfate, silica, alumina, talc, kaolin, clay, calcium phosphate, mica, hectorite, zirconia, tungsten oxide, lithium fluoride, Examples thereof include inorganic particles such as calcium fluoride, and organic polymer particles such as styrene, acrylic, melamine, benzoguanamine, and silicon. These may be added alone to the easy-adhesion layer, or may be added in combination of two or more.

  In addition, the measurement of the average particle diameter of said particle | grain can be performed with the following method. Take a picture of the particles with a scanning electron microscope (SEM) and at a magnification such that the size of one smallest particle is 2-5 mm, the maximum diameter of 300-500 particles (between the two most distant points) Distance) is measured, and the average value is taken as the average particle diameter.

  Moreover, as a method for applying the coating solution, a known method can be used as in the case of the surface layer. For example, reverse roll coating method, gravure coating method, kiss coating method, roll brush method, spray coating method, air knife coating method, wire bar coating method, pipe doctor method, etc. can be mentioned. Or it can carry out in combination.

  The polyester film which is the polarizer protective film of the present invention can be produced according to a general method for producing a polyester film. For example, the polyester resin is melted and the non-oriented polyester extruded and formed into a sheet shape is stretched in the longitudinal direction by utilizing the speed difference of the roll at a temperature equal to or higher than the glass transition temperature, and then stretched in the transverse direction by a tenter. The method of performing heat processing is mentioned.

The polyester film of the present invention may be a uniaxially stretched film or a biaxially stretched film, but when the biaxially stretched film is used as a polarizer protective film, it may be observed from directly above the film surface. Although rainbow-like color spots are not seen, caution is necessary because rainbow-like color spots may be observed when observed from an oblique direction.

  This phenomenon is that a biaxially stretched film is composed of refractive index ellipsoids having different refractive indexes in the running direction, width direction, and thickness direction, and the retardation becomes zero depending on the light transmission direction inside the film (refractive index ellipse). This is because there is a direction in which the body appears to be a perfect circle. Therefore, when the liquid crystal display screen is observed from a specific oblique direction, a point where the retardation becomes zero may be generated, and a rainbow-like color spot is generated concentrically around that point. When the angle from the position directly above the film surface (normal direction) to the position where the rainbow-like color spots are visible is θ, the angle θ increases as the birefringence in the film increases, and the rainbow-like color increases. Spots are difficult to see. The biaxially stretched film tends to reduce the angle θ, and therefore the uniaxially stretched film is more preferable because rainbow-like color spots are less visible.

  However, a perfect uniaxial (uniaxial symmetry) film is not preferable because the mechanical strength in the direction orthogonal to the orientation direction is significantly reduced. The present invention has biaxiality (biaxial symmetry) in a range that does not substantially cause rainbow-like color spots or a range that does not cause rainbow-like color spots in a viewing angle range required for a liquid crystal display screen. It is preferable.

  The present inventors specify the ratio of the retardation of the protective film (in-plane retardation) and the retardation in the thickness direction (Rth) as a means to suppress the occurrence of rainbow spots while maintaining the mechanical strength of the protective film. It was found that control was performed so as to be within the range. Thickness direction retardation means an average of retardation obtained by multiplying two birefringences ΔNxz and ΔNyz by film thickness d when the film is viewed from the cross section in the thickness direction. The smaller the difference between the in-plane retardation and the thickness direction retardation, the more isotropic the birefringence action due to the observation angle, and the smaller the change in retardation due to the observation angle. Therefore, it is considered that rainbow-like color spots due to the observation angle are less likely to occur.

  The ratio of the retardation of the polyester film of the present invention to the retardation in the thickness direction (Re / Rth) is preferably 0.2 or more, more preferably 0.5 or more, and still more preferably 0.6 or more. As the ratio of the retardation to the retardation in the thickness direction (Re / Rth) is larger, the birefringence action is more isotropic, and the occurrence of iridescent color spots due to the observation angle is less likely to occur. In a complete uniaxial (uniaxial symmetry) film, the ratio of the retardation to the retardation in the thickness direction (Re / Rth) is 2. However, as described above, the mechanical strength in the direction orthogonal to the orientation direction is significantly lowered as the film approaches a complete uniaxial (uniaxial symmetry) film.

  On the other hand, the ratio of the retardation of the polyester film of the present invention to the retardation in the thickness direction (Re / Rth) is preferably 1.2 or less, more preferably 1 or less. In order to completely suppress the occurrence of rainbow-like color spots due to the observation angle, the ratio of retardation to thickness direction retardation (Re / Rth) does not have to be 2, and 1.2 or less is sufficient. Further, even when the ratio is 1 or less, it is possible to satisfy the viewing angle characteristics required for the liquid crystal display device (180 ° left and right, 120 ° up and down).

Describing specifically the film forming conditions of the polyester film of the present invention, the longitudinal stretching temperature and the transverse stretching temperature are preferably from 80 to 130 ° C, particularly preferably from 90 to 120 ° C. The longitudinal draw ratio is preferably 1.0 to 3.5 times, particularly preferably 1.0 to 3.0 times. The transverse draw ratio is preferably 2.5 to 6.0 times, and particularly preferably 3.0 to 5.5 times. In order to control the retardation within the above range, it is preferable to control the ratio of the longitudinal draw ratio and the transverse draw ratio. If the difference between the vertical and horizontal draw ratios is too small, it is difficult to increase the retardation, which is not preferable. Also, setting the stretching temperature low is a preferable measure for increasing the retardation. In the subsequent heat treatment, the treatment temperature is preferably from 100 to 250 ° C, particularly preferably from 180 to 245 ° C.

  In order to suppress retardation fluctuation, it is preferable that the thickness unevenness of the film is small. Since the stretching temperature and the stretching ratio greatly affect the thickness variation of the film, it is necessary to optimize the film forming conditions from the viewpoint of the thickness variation. In particular, when the longitudinal draw ratio is lowered to increase the retardation, the value of the longitudinal thickness unevenness may be increased. Since there is a region in which the value of the vertical thickness unevenness becomes very high in a specific range of the draw ratio, it is desirable to set the film forming conditions outside this range.

The thickness unevenness of the film of the present invention is preferably 5.0% or less, more preferably 4.5% or less, still more preferably 4.0% or less, and 3.0% or less. It is particularly preferred. The thickness unevenness of the film can be measured by any means. For example, a tape-like sample (length 3 m) continuous in the film flow direction is collected, and an electronic micrometer (Millitron) manufactured by Seiko EM Co., Ltd. 1240) or the like is used to measure the thickness at 100 points at a pitch of 1 cm, and the maximum thickness (dmax), minimum value (dmin), and average value (d) are determined. %) Can be calculated.
Thickness unevenness (%) = ((dmax−dmin) / d) × 100

  As described above, the retardation of the film can be controlled within a specific range by appropriately setting the stretching ratio, the stretching temperature, and the film thickness. For example, it becomes easier to obtain a higher retardation as the stretching ratio between the longitudinal stretching and the lateral stretching is higher, the stretching temperature is lower, and the film is thicker. On the contrary, it becomes easier to obtain a lower retardation as the stretching ratio between the longitudinal stretching and the lateral stretching is lower, the stretching temperature is higher, and the film thickness is thinner. Moreover, the higher the stretching temperature and the lower the total stretching ratio, the easier it is to obtain a film having a lower ratio of retardation to thickness direction (Re / Rth). Conversely, the lower the stretching temperature and the higher the total stretching ratio, the easier it is to obtain a film with a higher ratio of retardation to thickness direction retardation (Re / Rth). The final film forming conditions must be set in consideration of the physical properties necessary for processing in addition to the retardation control.

  Although the thickness of the polyester film of this invention is arbitrary, the range of 15-300 micrometers is preferable, More preferably, it is the range of 15-200 micrometers. In principle, it is possible to obtain a retardation of 3000 nm or more even with a film having a thickness of less than 15 μm. However, in that case, the anisotropy of the mechanical properties of the film becomes remarkable, and it becomes easy to cause tearing, tearing, etc., and the practicality as an industrial material is remarkably lowered. A particularly preferable lower limit of the thickness is 25 μm. On the other hand, if the upper limit of the thickness of the polarizer protective film exceeds 300 μm, the thickness of the polarizing plate becomes too thick, which is not preferable. From the viewpoint of practicality as a polarizer protective film, the upper limit of the thickness is preferably 200 μm. A particularly preferable upper limit of the thickness is 100 μm, which is about the same as a general TAC film. Polyethylene terephthalate is preferable as the polyester used as the film substrate in order to control the retardation within the range of the present invention even in the above thickness range.

  In addition, as a method of blending the ultraviolet absorber with the polyester film in the present invention, a known method can be used in combination. For example, a preliminarily kneaded extruder is used to blend the dried ultraviolet absorber and the polymer raw material. A master batch can be prepared and blended by, for example, a method of mixing the predetermined master batch and a polymer raw material during film formation. The added weight of the ultraviolet absorber added to the film is preferably 0.3 to 1.5%, more preferably 0.4 to 1.0%.

At this time, the concentration of the UV absorber in the master batch is preferably 5 to 30% by mass in order to uniformly disperse the UV absorber and economically blend it. As a condition for producing the master batch, it is preferable to use a kneading extruder and to extrude it at a temperature not lower than the melting point of the polyester raw material and not higher than 290 ° C. for 1 to 15 minutes. Above 290 ° C, the weight loss of the UV absorber is large, and the viscosity of the master batch is greatly reduced. When the residence time is 1 minute or less, uniform mixing of the ultraviolet absorber becomes difficult. At this time, if necessary, a stabilizer, a color tone adjusting agent, and an antistatic agent may be added.

  In the present invention, it is preferable that the film has a multilayer structure of at least three layers and an ultraviolet absorber is added to the intermediate layer of the film. A film having a three-layer structure containing an ultraviolet absorber in the intermediate layer can be specifically produced as follows. Polyester pellets alone for the outer layer, master batches containing UV absorbers for the intermediate layer and polyester pellets are mixed at a predetermined ratio, dried, and then supplied to a known melt laminating extruder, which is slit-shaped. Extruded into a sheet form from a die and cooled and solidified on a casting roll to make an unstretched film. That is, using two or more extruders, a three-layer manifold or a merging block (for example, a merging block having a square merging portion), a film layer constituting both outer layers and a film layer constituting an intermediate layer are laminated, An unstretched film is formed by extruding a three-layer sheet from the die and cooling with a casting roll. In the present invention, it is preferable to perform high-precision filtration during melt extrusion in order to remove foreign substances contained in the raw material polyester that cause optical defects. The filter particle size (initial filtration efficiency 95%) of the filter medium used for high-precision filtration of the molten resin is preferably 15 μm or less. When the filter particle size of the filter medium exceeds 15 μm, removal of foreign matters of 20 μm or more tends to be insufficient.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, and is implemented with appropriate modifications within a range that can be adapted to the gist of the present invention. These are all included in the technical scope of the present invention. In addition, the evaluation method of the physical property in the following examples is as follows.

(1) Retardation (Re)
Retardation is a parameter defined by the product (ΔNxy × d) of the biaxial refractive index anisotropy (ΔNxy = | Nx−Ny |) and the film thickness d (nm) on the film. Yes, it is a scale showing optical isotropy and anisotropy. The biaxial refractive index anisotropy (ΔNxy) was determined by the following method. Using two polarizing plates, the orientation axis direction of the film was determined, and a 4 cm × 2 cm rectangle was cut out so that the orientation axis directions were perpendicular to each other, and used as a measurement sample. With respect to this sample, the biaxial refractive index (Nx, Ny) perpendicular to each other and the refractive index (Nz) in the thickness direction were determined by an Abbe refractometer (NAGO-4T, measurement wavelength 589 nm, manufactured by Atago Co., Ltd.). The absolute value (| Nx−Ny |) of the refractive index difference between the axes was defined as the refractive index anisotropy (ΔNxy). The thickness d (nm) of the film was measured using an electric micrometer (manufactured by Fine Reef, Millitron 1245D), and the unit was converted to nm. Retardation (Re) was determined from the product (ΔNxy × d) of refractive index anisotropy (ΔNxy) and film thickness d (nm).

(2) Thickness direction retardation (Rth)
Thickness direction retardation is obtained by multiplying two birefringences ΔNxz (= | Nx−Nz |) and ΔNyz (= | Ny−Nz |) by film thickness d when viewed from the cross section in the film thickness direction. It is a parameter which shows the average of retardation obtained. Thickness direction retardation (Rth) is obtained by calculating Nx, Ny, Nz and film thickness d (nm) in the same manner as the measurement of retardation, and calculating the average value of (ΔNxz × d) and (ΔNyz × d). )

(3) Light transmittance at a wavelength of 380 nm Using a spectrophotometer (manufactured by Hitachi, U-3500 type), the light transmittance in the wavelength region of 300 to 500 nm of each film is measured using the air layer as a standard, and the light beam at a wavelength of 380 nm. The transmittance was determined.

(4) Observation of rainbow spots A polyester film prepared by the method described later is attached to one side of a polarizer made of PVA and iodine so that the absorption axis of the polarizer and the orientation main axis of the film are perpendicular to each other, and TAC is attached to the opposite surface. A polarizing plate was prepared by attaching a film (manufactured by FUJIFILM Corporation, thickness 80 μm). The obtained polarizing plate is made of polyester on the emission light side of a liquid crystal display device using a white LED composed of a light emitting element in which a blue light emitting diode and a yttrium / aluminum / garnet yellow phosphor are combined as a light source (Nichia Chemical, NSPW500CS). The film was installed on the viewing side (outgoing light side). This liquid crystal display device has a polarizing plate having two TAC films as polarizer protective films on the incident light side of the liquid crystal cell. Visual observation was performed from the front side and the oblique direction of the polarizing plate of the liquid crystal display device, and the presence or absence of the occurrence of iridescence was determined as follows. In Comparative Example 3, a backlight light source using a cold cathode tube as a light source instead of the white LED was used.
◎: No rainbow spots from any direction.
○: When observed from an oblique direction, a partly extremely thin rainbow can be observed.
X: When observing from an oblique direction, rainbow spots can be clearly observed.

(5) Tear strength The tear strength of each film was measured in accordance with JIS P-8116 using an Elmendorf tear tester manufactured by Toyo Seiki Seisakusho. The tearing direction was performed so as to be parallel to the orientation main axis direction of the film, and was determined as follows. In addition, the measurement of the orientation axis direction was measured with a molecular orientation meter (manufactured by Oji Scientific Instruments, MOA-6004 type molecular orientation meter).
○: Tear strength is 50 mN or more ×: Tear strength is less than 50 mN

(6) Adhesiveness with hard coat layer On the surface layer of the polyester film, a hard coat layer forming coating solution (E) having the following composition was applied using a # 10 wire bar and dried at 70 ° C for 1 minute. The solvent was removed. Next, the film coated with the hard coat layer was irradiated with 300 mJ / cm ² ultraviolet rays using a high-pressure mercury lamp to obtain a laminated polyester film having a hard coat layer with a thickness of 5 μm. Hard coat layer forming coating solution (E)
Methyl ethyl ketone 65.00% by mass
Dipentaerythritol hexaacrylate 27.20% by mass
(Shin-Nakamura Chemical A-DPH)
Polyethylene glycol diacrylate 6.80 mass%
(Shin-Nakamura Chemical A-400)
Photopolymerization initiator 1.00% by mass
(Irgacure 184 manufactured by Ciba Specialty Chemicals)

As described above, a hard coat layer is provided on the surface layer of the polyester film, and 100 square cuts reaching the base film through the hard coat layer are made using a cutter guide having a gap interval of 2 mm. Next, a cellophane adhesive tape (manufactured by Nichiban Co., Ltd., No. 405; 24 mm width) was attached to the cut surface of the grid and rubbed with an eraser for complete adhesion. Then, after performing the work of peeling the cellophane adhesive tape vertically from the hard coat layer 5 times, visually counting the number of squares of the hard coat layer peeled off from the polyester film, the hard coat layer and the substrate from the following formula The adhesion with the film was determined. In addition, what peeled partially among squares was also counted as the square which peeled, and was ranked according to the following references | standards.
Adhesiveness (%) = (1−number of peeled squares / 100) × 100
A: 100% or material failure of the optical functional layer B: 99-90%
Δ: 89-70%
X: 69 to 0%

(Production Example 1-Polyester A)
When the temperature of the esterification reactor was raised to 200 ° C., 86.4 parts by mass of terephthalic acid and 64.6 parts by mass of ethylene glycol were charged and 0.017 parts by mass of antimony trioxide as a catalyst while stirring. 0.064 parts by mass of magnesium acetate tetrahydrate and 0.16 parts by mass of triethylamine were charged. Subsequently, the pressure was raised and the esterification reaction was performed under the conditions of a gauge pressure of 0.34 MPa and 240 ° C., and then the esterification reaction vessel was returned to normal pressure, and 0.014 parts by mass of phosphoric acid was added. Furthermore, it heated up to 260 degreeC over 15 minutes, and 0.012 mass part of trimethyl phosphate was added. Then, after 15 minutes, dispersion treatment was performed with a high-pressure disperser, and after 15 minutes, the obtained esterification reaction product was transferred to a polycondensation reaction can and subjected to polycondensation reaction at 280 ° C. under reduced pressure.

  After completion of the polycondensation reaction, it is filtered through a NASRON filter with a 95% cut diameter of 5 μm, extruded into a strand from a nozzle, and cooled and solidified using cooling water that has been filtered (pore diameter: 1 μm or less) in advance. And cut into pellets. The obtained polyethylene terephthalate resin (A) had an intrinsic viscosity of 0.62 dl / g and contained substantially no inert particles and internally precipitated particles. (Hereafter, abbreviated as PET (A).)

(Production Example 2-Polyester B)
10 parts by weight of a dried UV absorber (2,2 ′-(1,4-phenylene) bis (4H-3,1-benzoxazinon-4-one), PET (A) containing no particles (inherent viscosity Was 0.62 dl / g) and 90 parts by mass were mixed, and a polyethylene terephthalate resin (B) containing an ultraviolet absorber was obtained using a kneading extruder (hereinafter abbreviated as PET (B)).

(Production Example 3-Preparation of coating solution for easily bonding layer formation with polarizer)
A transesterification reaction and a polycondensation reaction are carried out by a conventional method, and as a dicarboxylic acid component (based on the whole dicarboxylic acid component) 46 mol% terephthalic acid, 46 mol% isophthalic acid and 8 mol% sodium 5-sulfonatoisophthalate, A water-dispersible sulfonic acid metal base-containing copolymer polyester resin having a composition of 50 mol% ethylene glycol and 50 mol% neopentyl glycol as a glycol component (based on the entire glycol component) was prepared. Next, 51.4 parts by mass of water, 38 parts by mass of isopropyl alcohol, 5 parts by mass of n-butyl cellosolve, 0.06 parts by mass of nonionic surfactant were mixed and then heated and stirred. After adding 5 parts by mass of a water-dispersible sulfonic acid metal base-containing copolymer polyester resin and continuing to stir until the resin is no longer agglomerated, the resin water dispersion is cooled to room temperature to obtain a solid content concentration of 5.0% by mass. A uniform water-dispersible copolymerized polyester resin liquid was obtained. Furthermore, after dispersing 3 parts by mass of aggregated silica particles (Silicia 310, manufactured by Fuji Silysia Co., Ltd.) in 50 parts by mass of water, 99.46 parts by mass of the water-dispersible copolyester resin liquid was mixed with 0.54 parts by mass of the aqueous dispersion was added, and 20 parts by mass of water was added with stirring to obtain an adhesive modified coating solution.

(Production Example 4-Preparation of coating solution for forming surface layer)
Preparation of Polyester Resin A1 TPA: IPA: GCM = 49: 48: 3 and EG: NPG = 20: 80; a mixture of weight ratios was prepared according to the following method. The compounds indicated by these abbreviations are as follows.
TPA: terephthalic acid
IPA: Isophthalic acid
GCM: 5-sodium sulfoisophthalic acid
EG: Ethylene glycol
NPG: 2,2′-Neopentyl glycol
DEP: 95 parts of 2,2′-diethyl-1,3-propanediol dimethyl terephthalate, 95 parts of dimethyl isophthalate, 35 parts of ethylene glycol, 145 parts of neopentyl glycol, 0.1 part of zinc acetate and 0.1 part of antimony trioxide The transesterification reaction was carried out at 140 to 220 ° C. for 3 hours. Next, 6.0 parts of 5-sodium isophthalic acid was added and the esterification reaction was performed at 220 to 260 ° C. over 1 hour, and then at 240 to 270 ° C. under reduced pressure (10 to 0.2 mmHg) over 2 hours. A polycondensation reaction was performed to obtain a polyester resin (A1) having a molecular weight of 19,500 and a softening point of 60 ° C.

Preparation of Polyester Resin A2 A polyester resin (A2) mixed at a weight ratio of TPA: IPA: GCM = 50: 45: 5 and EG: DEP = 60: 40 was obtained in the same procedure as above.

Preparation of surface layer forming coating solution (A1) 6.7 parts of 30% aqueous dispersion of polyester resin (A1), 20% of self-crosslinking polyurethane resin (B) containing isocyanate groups blocked with sodium bisulfite 40 parts of an aqueous solution (Daiichi Kogyo Seiyaku: Elastron H-3), 0.5 part of an elastron catalyst (Cat 64), 47.8 parts of water and 5 parts of isopropyl alcohol are mixed, and then an anion 1% by weight of a surfactant was added to obtain a surface layer forming coating solution (A1) having a total solid content of about 10% by weight.

Preparation of Surface Layer Forming Coating Solution (A2) 16.7 parts of 30% aqueous dispersion of polyester resin (A2), 25 parts of 20% aqueous solution of polyurethane resin (B) (Elastrone H-3), catalyst for elastron ( Cat 64), 52.8 parts of water and 5 parts of isopropyl alcohol are mixed, 1% by weight of anionic surfactant is added, and the total solid content is about 10% by weight for forming a surface layer. A coating solution (A2) was obtained.

Preparation of Comparative Surface Layer Forming Coating Solution (A3) Polyester mixed with a weight ratio of TPA: IPA: GCM = 50: 45: 5 and EG: DEP = 50: 50 in the same procedure as polyester resin (A1) Resin (A3) was obtained. Next, without using the polyurethane resin, 16.7 parts of the polyester resin (A3) and 83.3 parts of water were mixed to prepare a coating liquid (A3) having a total solid content of 5% by weight.

Example 1
After drying 90 parts by mass of PET (A) resin pellets containing no particles as a raw material for the base film intermediate layer and 10 parts by mass of PET (B) resin pellets containing an ultraviolet absorber at 135 ° C. for 6 hours under reduced pressure (1 Torr) , And fed to the extruder 2 (for the intermediate layer II layer). Moreover, PET (A) was dried by a conventional method, supplied to the extruder 1 (for the outer layer I layer and outer layer III), and melted at 285 ° C. After filtering these two kinds of polymers with a filter medium made of a sintered stainless steel (nominal filtration accuracy of 10 μm particles 95% cut), laminating them in a two-kind / three-layer confluence block, and extruding them into a sheet form from a die, The film was wound around a casting drum having a surface temperature of 30 ° C. using an electrostatic application casting method, and then cooled and solidified to produce an unstretched film. At this time, the discharge amount of each extruder was adjusted so that the thickness ratio of the I layer, the II layer, and the III layer was 10:80:10.

Next, each coating solution is applied to the unstretched PET film by a reverse roll method so that one side is a coating solution for forming an easily adhesive layer with the polarizer and the other side is a coating solution A1 for forming a surface layer. And dried at 80 ° C. for 20 seconds. In addition, it adjusted so that the application quantity after the last (after extending | stretching) drying might be set to 0.15 g / m < ² >.

  The unstretched film on which this easy-adhesion layer was formed was guided to a tenter stretching machine, guided to a hot air zone at a temperature of 125 ° C. while being gripped by a clip, and stretched 4.0 times in the width direction. Next, a polarizer that is a uniaxially oriented PET film having a film thickness of about 50 μm is processed by maintaining the width stretched in the width direction at a temperature of 225 ° C. for 30 seconds and further performing a relaxation treatment of 3% in the width direction. A protective film was obtained.

(Example 2)
A polarizer protective film, which is a uniaxially oriented PET film, was obtained in the same manner as in Example 1 except that the thickness of the unstretched film was changed to about 100 μm.

(Example 3)
An unstretched film produced by the same method as in Example 1 is heated to 105 ° C. using a heated roll group and an infrared heater, and then stretched 1.5 times in the running direction with a roll group having a difference in peripheral speed. After that, the film was stretched 4.0 times in the width direction in the same manner as in Example 1 to obtain a polarizer protective film which is a biaxially oriented PET film having a film thickness of about 50 μm.

Example 4
In the same manner as in Example 3, the film was stretched 2.0 times in the running direction and 4.0 times in the width direction to obtain a polarizer protective film which is a biaxially oriented PET film having a film thickness of about 50 μm.

(Example 5)
In the same manner as in Example 3, the film was stretched 3.3 times in the running direction and 4.0 times in the width direction to obtain a polarizer protective film which is a biaxially oriented PET film having a film thickness of about 75 μm.

(Example 6)
A polarizer protective film, which is a uniaxially oriented PET film having a film thickness of 50 μm, was obtained in the same manner as in Example 1 without using a PET resin (B) containing an ultraviolet absorber in the intermediate layer. Although the resulting film was free from iridescent color spots, it has a high light transmittance of 380 nm, and there is a concern of deteriorating the optical functional dye.

(Example 7)
In the same manner as in Example 3, the film was stretched 4.0 times in the running direction and 1.0 times in the width direction to obtain a polarizer protective film which is a uniaxially oriented PET film having a film thickness of about 100 μm. The obtained film had Re of 3000 nm or more and good visibility, but the mechanical strength was slightly inferior.

(Example 8)
In the same manner as in Example 3, the film was stretched 3.5 times in the running direction and 3.7 times in the width direction to obtain a polarizer protective film which is a biaxially oriented PET film having a film thickness of about 250 μm. The obtained film had Re of 4500 nm or more, but the Re / Rth ratio was less than 0.2. Therefore, an extremely thin rainbow was observed in an oblique direction.

Example 9
In the same manner as in Example 1, the film was stretched 1.0 times in the running direction and 3.5 times in the width direction to obtain a polarizer protective film which is a uniaxially oriented PET film having a film thickness of about 75 μm.

(Example 10)
A polarizer protective film, which is a uniaxially oriented PET film having a thickness of about 275 μm, was obtained by using the same method as in Example 1 and changing the thickness of the unstretched film.

(Example 11)
The surface layer forming coating solution A1 in Example 1 was changed to the surface layer forming coating solution A2, which was dried at 160 ° C. for 120 seconds and heat-treated, so that the final average coating amount was 0. A polarizer protective film was produced in the same manner as in Example 1 except that the thickness was adjusted to 0.8 g / m ^2, and each test was performed.

(Example 12)
Except that the light source of the liquid crystal display device was an organic light emitting diode (OLED), and rainbow spots were observed, and the evaluation was performed by adding particles to the hard coat layer to make the surface uneven and changing it to an antiglare layer. Was the same as in Example 1.

(Comparative Example 1)
In the same manner as in Example 3, the film was stretched 3.6 times in the running direction and 4.0 times in the width direction to obtain a polarizer protective film which is a biaxially oriented PET film having a film thickness of about 38 μm. The obtained film had low retardation, and rainbow-like color spots were observed when observed from an oblique direction.

(Comparative Example 2)
A polarizer protective film, which is a uniaxially oriented PET film having a thickness of about 10 μm, was obtained by using the same method as in Example 1 and changing the thickness of the unstretched film. Since the obtained film was very easy to tear and there was no stiffness, it could not be used as a polarizer protective film. Moreover, the retardation was low and iridescent colored spots were observed.

(Comparative Example 3)
The same procedure as in Example 1 was performed except that rainbow spots were observed using a cold cathode tube as the light source of the liquid crystal display device.

(Comparative Example 4)
A polarizer protective film was produced in the same manner as in Example 1 except that the surface layer forming coating solution A1 in Example 1 was changed to the surface layer forming coating solution A3, and each test was performed.

(Comparative Example 5)
In Example 11 above, a polarizer protective film was prepared in the same manner as in Example 11 except that the heat treatment conditions after coating the surface layer forming coating solution A2 were changed to 90 ° C. and 120 seconds. Carried out.

The results measured for the above Examples and Comparative Examples are shown in Table 1 below.

Claims (7)

A surface layer mainly comprising a copolymer polyester resin (A) and a resin (B) containing a block type isocyanate group is provided on at least one surface of the polyester film, and the retardation of the polyester film is 3000 to 30000 nm. A liquid crystal display device comprising: a polarizing plate in which a polarizer protective film is laminated on at least one side of the polarizer; and a white light source having a continuous emission spectrum.   The liquid crystal display device according to claim 1, wherein a ratio of the retardation of the polyester film to the retardation in the thickness direction (Re / Rth) is 0.2 or more.   3. The liquid crystal display device according to claim 1, wherein the polyester film comprises three or more layers, and an ultraviolet absorber is contained in a layer other than the outermost layer, and the light transmittance at 380 nm is 20% or less.   One or more layers selected from the group consisting of a hard coat layer, an antiglare layer, an antireflection layer, a low reflection layer, a low reflection antiglare layer, an antireflection antiglare layer, and an antistatic layer are laminated on the surface layer. The liquid crystal display device according to claim 1.   The liquid crystal display device according to claim 1, wherein the polarizer protective film is laminated on the polarizer via an ultraviolet curable, electron beam curable, or thermosetting adhesive.   The liquid crystal display device according to claim 1, wherein the polarizing plate is disposed on an emission light side with respect to the liquid crystal.   The liquid crystal display device according to claim 1, wherein the white light source having a continuous emission spectrum is a white light emitting diode.