JP2015102655A - Polarizer protective film, polarizing plate, and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizer protective film that has less optical drawbacks and is excellent in transparency and visibility.SOLUTION: There is provided a polarizer protective film that has an adhesive modified resin layer at least on one side of a polyester film, where the number of scratches with a depth of 0.5 μm or more is 10 to 10000/1000 m, and the number of foreign substances with a major axis of 50 μm or more is 3 to 2000/1000 m.

Description

The present invention relates to a polarizer protective film made of a polyester film.

A liquid crystal display uses a polarizing plate for image display. Along with the improvement of the quality of the liquid crystal display, an improvement in the quality of the polarizing plate is required, and at the same time, a polarizer protective film which is a protective film for the polarizing plate is also required to have a higher quality.

Polyester films are widely used as various optical films because of their excellent transparency, dimensional stability, and chemical resistance. When this polyester film is used as a polarizer protective film, it is desired that optical defects are as small as possible.

As a main cause of the optical defects of the film, there are scratches and foreign matters generated on the film. For example, as a technique for suppressing the generation of scratches, Japanese Patent Application Laid-Open No. 9-183201 discloses that there are 10 scratches having a length of 20 mm or more and a maximum depth of 0.5 μm or more by having a surfactant on the film surface. A polyester-based optical film that is m ² or less is disclosed. However, with this technique, it is difficult to suppress the generation of finer scratches, and the level required for the polarizer protective film is not satisfied.

Moreover, when the foreign material is mixed in the polarizer protective film, the transparency of the film and the flatness of the surface are lowered, and the quality as the polarizer protective film tends to be impaired. In a polarizer protective film used for protecting a polarizing plate or a liquid crystal display element, the polarizing function can function sufficiently if foreign matter is present even when the transmitted light is blocked by sandwiching the film between two polarizing plates. However, a problem arises in that so-called light passes through only that portion to form a bright spot. The presence of such a bright spot results in a decrease in the polarizing function of the polarizing plate. When the polarizing function is lowered more than a certain level, it causes a decrease in image recognition in a liquid crystal display device using the polarizing plate.

JP-A-9-183201

This invention is made | formed in view of the said situation, and there are few optical faults and it is providing the polarizer protective film excellent in transparency and visibility. A further preferred embodiment is to provide a polarizer protective film that suppresses the generation of rainbow spots and is excellent in the visibility of a liquid crystal display device.

The representative present invention is as follows.
Item 1.
A polarizer protective film having an adhesive modified resin layer on at least one side of a polyester film,
The number of depth 0.5μm or more flaws are 10 to 10,000 pieces / 1000 m ^2, the number of long diameter 50μm or more foreign matter is 3-2000 cells / 1000 m ^2, a polarizer protective film.
Item 2.
Item 2. The polarizer protective film according to Item 1, wherein the polyester film has a retardation of 3000 to 30000 nm.
Item 3.
A polarizing plate in which a polarizer protective film is laminated on both sides of a polarizer,
The polarizing plate whose polarizer protective film of at least one side is the polarizer protective film of claim | item 1 or 2.
Item 4.
A liquid crystal display device having a backlight light source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates,
4. A liquid crystal display device, wherein at least one polarizing plate is the polarizing plate according to item 3.
Item 5.
Item 5. The liquid crystal display device according to item 4, wherein the backlight source is a white light source having a continuous emission spectrum.

According to the present invention, optical defects due to scratches and foreign matters are reduced by controlling the generation of scratches having a specific depth or more on the film surface and the generation of foreign matters having a specific major axis or more within a certain range. A polarizer protective film having excellent visibility can be provided. The polarizer protective film of this invention can be used for a polarizing plate and a liquid crystal display device using it from the outstanding characteristic.

The polarizer protective film of the present invention is obtained by forming an adhesive modified resin layer on at least one surface of a polyester film.

In the polarizer protective film of the present invention, the number of scratches having a depth of 0.5 μm or more present on the film surface is in the range of 10 to 10,000 / 1000 m ² . If the number of scratches is less than or equal to the above upper limit, there is no problem due to optical defects as a polarizer protective film. The number of scratches having a depth of 0.5 μm or more is preferably 10 to 5000/1000 m ² , more preferably 10 to 2000/1000 m ² , and even more preferably 10 to 200/1000 m ² . . In addition, the flaw which exists in the surface of a polarizer protective film includes any surface of the surface which provided the adhesive property modification resin layer, and the surface which is not provided.

In addition, a crack means the fine recessed part and / or convex part of the surface of a polarizer protective film, and includes a protrusion-like state. In addition, when the surface of the polarizer protective film is observed from the vertical direction, the unevenness of the scratches that are close to each other within 50 μm is considered as the same scratch. The depth of the scratch means the maximum depth in the thickness direction from the surface of the optical laminated film, and when the surface of the film is raised due to the scratch, the maximum depth from the top to the bottom of the raised portion Means.

  Shallow scratches with a depth of less than 0.5 μm can be obtained by laminating an adhesive or a functional layer on the polarizer protective film so that the resin is embedded in the recesses and finally incorporated into a polarizing plate or a liquid crystal display device. Is often inconspicuous. However, a scratch having a depth of 0.5 μm or more remains as a scratch even when it is finally incorporated into a polarizing plate or a liquid crystal display device, and the visibility of the liquid crystal display device may be deteriorated. Therefore, it is preferable to control the number of scratches having a depth of 0.5 μm or more within a specific range.

In the polarizer protective film of the present invention, the number of foreign matters having a major axis of 50 μm or more present in the film is in the range of 3 to 2000/1000 m ² . The major axis means the distance between the two points that is the maximum when the distance between any two points on the outer periphery of the cross section of the foreign matter is measured. If the number of foreign matters is less than or equal to the above upper limit, there is no problem due to optical defects as a polarizer protective film. The number of foreign matters having a major axis of 50 μm or more is preferably 3 to 1000/1000 m ² , more preferably ³ to 500/1000 m ² , and even more preferably 3 to 50/1000 m ² .

  The polarizer protective film of the present invention preferably has a small amount of foreign matter existing inside the polyester film. In order to reduce the foreign matter in the film, for example, a method of precisely filtering the polyester resin in a molten state can be employed when forming the polyester film. If foreign matter is present in the polyester film, the crystallization of the polyester is likely to proceed around the foreign matter in the cooling process during film production. Such crystallization causes non-uniform stretching in the subsequent stretching step, so that a slight difference in thickness occurs in the polyester film, and the vicinity of that portion tends to be in a lens state. Since light is refracted or scattered in the above-described lens state of the polyester film, it is observed larger than the actual foreign matter when visually observed. Therefore, when a polarizer protective film using such a polyester film is used as a polarizer protective film of a polarizing plate in a liquid crystal display device, image spots tend to occur in the above-described lens state. In addition, the above-described minute difference in thickness of the polyester film may cause rainbow spots and polarized spots in the liquid crystal display device.

  The structure and manufacturing method of the polarizer protective film of this invention are explained in full detail.

1. Polyester film The polarizer protective film of the present invention is obtained by forming an adhesive modified resin layer on at least one surface of a polyester film. Although the thickness of a polyester film is not specifically limited, Usually, it is 15-300 micrometers, Preferably it is 25-150 micrometers. If the thickness of the polyester film is less than 15 μm, tearing, tearing or the like may occur. On the other hand, if the upper limit of the thickness of the polyester film exceeds 300 μm, the thickness of the polarizing plate becomes too thick. From the viewpoint of practicality as a polarizer protective film, the thickness of the polyester film is particularly preferably 50 to 100 μm.

The polyester film used in the present invention can be obtained from any polyester resin. The type of polyester resin is not particularly limited, and any polyester resin obtained by condensing dicarboxylic acid and diol using a known antimony, titanium, germanium-based catalyst, or the like can be used. In particular, the germanium catalyst is preferable from the viewpoint of obtaining transparency of the film because the aggregate derived from the catalyst can be reduced. Polyester polymerized using a polycondensation catalyst containing aluminum and / or a compound thereof disclosed in JP2010-21227A and a phosphorus compound having an aromatic group in the molecule also has film transparency. This is preferable because it can be kept high.

  The polyester resin used in the polyester film is excellent in transparency, dimensional stability, and chemical resistance. For example, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene-2,6-naphthalate (PEN), Or the polyester-type copolymer which has as a main component the component which comprises these resin is mentioned. Particularly preferred polyester resins are polyethylene terephthalate (PET) and polyethylene-2,6-naphthalate (PEN). In addition, the “main component” in the polyester-based copolymer is a component (ester component formed from a polyvalent carboxylic acid component and a polyhydric alcohol component) constituting the above exemplified polyester (PET, PBT and PEN). It means that it is 50 mol% or more in 100 mol% of the ester component formed from the polyvalent carboxylic acid component and the polyhydric alcohol component constituting the polyester copolymer.

  These polyesters may be used singly or in combination of two or more as long as the effects of the present invention, in particular, transparency can be ensured. Among these, a polyester resin mainly composed of PET and / or PEN is preferable. The “main component” as used herein means that PET and / or PEN is 50% by mass or more in 100% by mass of the polyester resin.

  In the above polyester copolymer, when the component constituting the above exemplified polyester is a main component, the polyvalent carboxylic acid used for the other copolymer component (subcomponent) is adipic acid, sebacic acid or the like. Aliphatic dicarboxylic acid; terephthalic acid (except when the main component is PET or PBT), isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid (except when the main component is PEN) Aromatic dicarboxylic acids such as); and polyvalent carboxylic acids such as trimellitic acid and pyromellitic acid. In addition, as the polyhydric alcohol component, ethylene glycol (except when the main component is a component of PET or PEN), diethylene glycol, propylene glycol, or 1,4-butanediol (when the main component is a component of PBT) ), Aliphatic glycols such as neopentyl glycol; aromatic glycols such as p-xylene glycol; alicyclic glycols such as 1,4-cyclohexanedimethanol; polyethylene glycol having an average molecular weight of 150 to 20000 .

  In addition, when using the polyester illustrated above as a main component as a constituent material of the polyester film and using the polyester resin mixed with the above polyester-based copolymer, the ratio of the copolymer in the total polyester resin is less than 20% by mass. It is preferable. When the ratio of the polyester-based copolymer is 20% by mass or more, the strength, transparency, and heat resistance of the polyester film tend to decrease.

  The intrinsic viscosity of the polyester resin pellets used for the polyester film is preferably 0.45 dl / g or more and 0.85 dl / g or less. If the intrinsic viscosity is less than 0.45 dl / g, the tear resistance of the polyester film tends to be insufficient, and breakage tends to occur frequently during film production. On the other hand, when the intrinsic viscosity exceeds 0.85 dl / g, in the microfiltration performed when the base film is produced from the pellets, the increase in the filtration pressure is increased, which may make it difficult to perform the filtration. In particular, when the thickness of the polyester film is reduced, it is desirable from the viewpoint of tear resistance to increase the intrinsic viscosity.

The polyester film is usually melt-extruded into a film and cast into a film by a metal roll. In this casting, it is recommended to make electrostatic contact in order to improve the adhesion between the molten film and the metal roll. Therefore, it is desirable that the polyester resin constituting the polyester film has a low melting specific resistance value. Specifically, the melt specific resistance value at 275 ° C. of the polyester resin is preferably 0.45 × 10 ⁸ Ω · cm or less, and more preferably 0.30 × 10 ⁸ Ω · cm or less. . On the other hand, if the melt specific resistance value of the polyester resin is too low, the polyester film tends to be affected by static electricity and the handling property tends to be lowered. Therefore, the melt specific resistance value at 275 ° C. of the polyester resin is preferably 0.10 × 10 ⁸ Ω · cm or more, and more preferably 0.12 × 10 ⁸ Ω · cm or more.

The melt specific resistance value of the polyester resin is determined by the following method.
(Melting specific resistance value of polyester resin)
Place two electrodes (stainless steel wire) in polyester melted at 275 ° C, measure the current (i _o ) when a voltage of 120 V is applied, and calculate the specific resistance value Si (Ω · cm) by the following formula. Ask.
Si (Ω · cm) = (A / L) × (V / i _o )
Here, A is the area between electrodes (cm ² ), L is the distance between electrodes (cm), and V is the voltage (V).

The melt specific resistance value of the polyester resin can be ensured by including a magnesium compound and a phosphorus compound in the polyester resin.

  Magnesium in the magnesium compound has an action of lowering the melt specific resistance value of the polyester resin. From the viewpoint of effectively exhibiting such an action and suppressing the generation of foreign matters due to the magnesium compound and the coloration of the polyester resin, the amount of the magnesium compound in the polyester resin is 40 ppm in terms of magnesium atom (mass basis, the same applies hereinafter). Above, preferably 45 ppm or more and 70 ppm or less, preferably 65 ppm or less is recommended.

  Specific examples of preferred magnesium compounds include magnesium hydroxide, aliphatic dicarboxylate (acetate, butyrate, etc., preferably acetate), aromatic dicarboxylate, salt with a compound having a phenolic hydroxyl group ( Salt with phenol).

  The phosphorus compound itself does not have an action of lowering the melt specific resistance value of the polyester resin, but it can contribute to the reduction of the melt specific resistance value when combined with the magnesium compound. The reason for this is not clear, but it is thought that the inclusion of a phosphorus compound can suppress the generation of foreign substances and increase the amount of charge carriers. Therefore, the amount of the phosphorus compound in the polyester resin is 10 ppm (mass basis, the same shall apply hereinafter) or more, preferably in terms of phosphorus atom, from the viewpoint of effectively exhibiting the above-described action and suppressing the generation of foreign matters due to the phosphorus compound. It is recommended that it be 15 ppm or more and 55 ppm or less, preferably 50 ppm or less.

Examples of the phosphorus compounds include phosphoric acids (phosphoric acid, phosphorous acid, hypophosphorous acid, etc.) and esters thereof (alkyl esters, aryl esters, etc.), as well as alkylphosphonic acids, arylphosphonic acids, and esters thereof (alkyls). Ester, aryl ester, etc.). Preferred phosphorus compounds, such as phosphoric acid, aliphatic esters (alkyl esters of phosphoric acid of phosphoric acid; for example, phosphoric acid monomethyl ester, phosphoric acid monoethyl ester, phosphoric acid such as phosphoric acid monobutyl ester mono C _1-6 Phosphoric acid tri-C ₁ alkyl ester, phosphoric acid dimethyl ester, phosphoric acid diethyl ester, phosphoric acid dibutyl ester, etc. phosphoric acid diC _1-6 alkyl ester, phosphoric acid trimethyl ester, phosphoric acid triethyl ester, phosphoric acid tributyl ester, etc. _-6 alkyl esters), aromatic esters of phosphoric acid (such as mono-, di-, or tri-C _6-9 aryl esters of phosphoric acid such as triphenyl phosphate, tricresyl phosphate), aliphatic esters of phosphorous acid ( Alkyl esters of phosphorous acid and the like; for example, trimethyl phosphite, Mono-, di-, or tri-C _1-6 alkyl esters of phosphorous acid such as tributyl phosphite), alkyl phosphonic acids (C _1-6 alkyl phosphonic acids such as methyl phosphonic acid, ethyl phosphonic acid), alkyl phosphonic acids Esters (such as mono- or di-C _1-6 alkyl esters of C _1-6 alkylphosphonic acids such as dimethyl methylphosphonate and dimethyl ethylphosphonate), arylphosphonic acid alkyl esters (such as dimethyl phenylphosphonate, diethyl phenylphosphonate C) Mono- or di-C _1-6 alkyl esters of _6-9 aryl phosphonic acids), aryl phosphonic acid aryl esters (such as mono- or di-C _6-9 aryl esters of C _6-9 aryl phosphonic acids such as diphenyl phenylphosphonic acid) Etc. are examples That. Particularly preferred phosphorus compounds include phosphoric acid and trialkyl phosphate (such as trimethyl phosphate). These phosphorus compounds can be used alone or in combination of two or more.

  In the polyester resin which comprises a polyester film, various additives may be contained in the range which does not inhibit the effect | action of this invention as needed. As said additive, an antistatic agent, UV absorber, a stabilizer, etc. are mentioned, for example.

  The polyester film may contain particles for the purpose of imparting slipperiness, but from the viewpoint of improving transparency, it is preferable that the content of such particles is smaller, and that the particles are substantially absent. preferable. Note that “substantially no particles” means that the amount of particles present in the polyester film on which the adhesive modified resin layer is not laminated is below the detection limit of the fluorescent X-ray analysis method. In order to improve the transparency while maintaining the handling properties and scratch resistance of the polyester film, for example, the polyester film is substantially free of particles, and the particles are applied only to the adhesive modified resin layer. The method of making it contain etc. is mention | raise | lifted.

  It is preferable that the polyester film used for the polarizer protective film of the present invention has a retardation of 3000 to 30000 nm. This is because when the retardation is less than 3000 nm, an interference color is exhibited when the liquid crystal display device is observed from an oblique direction, and thus good visibility cannot always be ensured. The preferred retardation of the polyester film is 4500 nm or more, then preferably 5000 nm or more, more preferably 6000 nm or more, still more preferably 8000 nm or more, and even more preferably 10,000 nm or more.

The upper limit of the retardation of the polyester film is 30000 nm. Even if a polyester film having a retardation higher than that is used, the effect of improving the visibility is not substantially obtained, and as the retardation increases, the thickness of the film is considerably increased, and the handling property as an industrial material is lowered. It is to do.

  The polyester film has a ratio (Re / Rth) of retardation (Re) to thickness direction retardation (Rth) of preferably 0.2 or more, more preferably 0.5 or more, still more preferably 0.6 or more, particularly Preferably it is 0.89 or more. This is because 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 rainbow-like 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 will be described later, the mechanical strength in the direction orthogonal to the orientation direction is significantly lowered as the film approaches a complete uniaxial (uniaxial symmetry) film.

  Therefore, the upper limit of the ratio of 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. Even if the ratio is 1.0 or less, it is possible to satisfy the viewing angle characteristics (180 degrees left and right, 120 degrees up and down) required for the liquid crystal display device.

2. Adhesive modified resin layer The resin constituting the adhesive modified resin layer of the polarizer protective film of the present invention ensures adhesion to functional layers and polarizers such as a hard coat layer, an antiglare layer and an antireflective layer. In view of this, it is preferable to use one or more selected from the group consisting of copolyester resins, polyurethane resins, acrylic resins and polyvinyl alcohol resins as a main component. In particular, from the viewpoint of adhesiveness with a polarizer, it is preferable to use a copolyester resin and a polyvinyl alcohol resin, a polyurethane resin and a polyvinyl alcohol resin, or an acrylic resin and a polyvinyl alcohol resin. is there. The “main component” in the adhesive modified resin layer means that at least one of the resins listed above is 50% by mass or more in 100% by mass of the resin constituting the layer. Further, conventionally known crosslinking agents may be added.

  The copolymer polyester resin that can be used for the adhesive property-modified resin layer is not particularly limited, and conventionally known polyester resins can be used.

  Examples of the dicarboxylic acid component constituting the copolymer polyester resin include terephthalic acid, isophthalic acid, phthalic acid, 2,5-dimethylterephthalic acid, 1,4-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,2 -Bisphenoxyethane-p, p'-dicarboxylic acid, adipic acid, sebacic acid, dodecanedioic acid and the like, and ester-forming derivatives thereof. Examples of the glycol component include ethylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, diethylene glycol, 1,4-cyclohexanedimethanol, trimethylolpropane, and the like.

  When forming an adhesive modified resin layer on a polyester film, a so-called in-line coating in which an aqueous coating solution in which an adhesive modified resin is dissolved or dispersed in water is applied to a substrate and dried at the time of production of the film. The method is preferably employed. With this in-line coating method, a wide and thin polarizer protective film can be obtained with high productivity. Therefore, the copolymer polyester resin is preferably excellent in water solubility or water dispersibility. For example, “a compound having a carboxyl group and a salt thereof” and / or “a compound having a sulfonic acid group and a salt thereof” are copolymerized. It is recommended that it be used as an ingredient. Hereinafter, the carboxyl group and its salt are referred to as “carboxylic acid (salt) group”, and the sulfonic acid group and its salt are referred to as “sulfonic acid (salt) group”.

Examples of the compound having a carboxylic acid (salt) group include trimellitic acid, trimellitic anhydride, pyromellitic acid, pyromellitic anhydride, 4-methylcyclohexene-1,2,3-tricarboxylic acid, trimesic acid, 1 , 2,3,4-butanetetracarboxylic acid, 1,2,3,4-pentanetetracarboxylic acid, 3,3 ′, 4,4′-benzophenonetetracarboxylic acid, 5- (2,5-dioxotetrahydro Furfuryl) -3-methyl-3-cyclohexene-1,2-dicarboxylic acid, 5- (2,5-oxotetrahydrofurfuryl) -3-cyclohexene-1,2-dicarboxylic acid, cyclopentanetetracarboxylic acid, 2 , 3,6,7-naphthalenetetracarboxylic acid, 1,2,5,6, -naphthalenetetracarboxylic acid, ethylene glycol bistrimelli 2,2 ′, 3,3′-diphenyltetracarboxylic acid, thiophene-2,3,4,5-tetracarboxylic acid, ethylenetetracarboxylic acid, or the like, or alkali metal salts or alkaline earth metal salts thereof , Ammonium salts and the like, but are not limited thereto.

  Examples of the compound having a sulfonic acid (salt) group include sulfoterephthalic acid, 5-sulfoisophthalic acid, 4-sulfoisophthalic acid, 4-sulfonaphthalene-2,7-dicarboxylic acid, sulfo-p-xylylene glycol, Examples include alkali metal salts such as 2-sulfo-1,4-bis (hydroxyethoxy) benzene, alkaline earth metal salts, and ammonium salts, but are not limited thereto.

Two or more of the dicarboxylic acid component and the glycol component constituting the copolymerized polyester resin or the compound for copolymerization may be used in combination.

  In addition, examples of the copolymer polyester resin include modified polyester copolymers such as block copolymers modified with (meth) acrylic acid, compounds having a urethane bond, compounds having an epoxy group, and graft copolymers. It is also possible to use a resin or the like.

  Among them, a self-crosslinking polyester-based graft copolymer obtained by grafting an acid anhydride having at least one double bond to a hydrophobic copolymerized polyester resin is particularly suitable for an acrylic resin that is a main component of a hard coat layer. Excellent adhesiveness and water-resistant adhesion. For this reason, the polarizer protective film using the self-crosslinkable polyester-based graft copolymer for the adhesive modified resin layer can be used even in a high humidity environment.

  The polyurethane-based resin that can be used for the adhesive modified resin layer may be any of solvent solubility, water solubility, and water dispersibility, and can be appropriately selected according to the characteristics and manufacturing method required for the adhesive modified resin layer. . When forming an adhesive modified resin layer by the in-line coating method preferably employed in the production of the polarizer protective film of the present invention, it is recommended to use an aqueous polyurethane resin having excellent water solubility or water dispersibility. Is done. Examples of such an aqueous polyurethane-based resin include polyurethane-based resins whose affinity for water is enhanced by a carboxylic acid (salt) group, a sulfonic acid (salt) group, a sulfuric acid half ester group, and a salt thereof.

  Examples of the polyhydroxy compound used for the synthesis of the polyurethane resin include polyethylene glycol, polypropylene glycol, polyethylene / polypropylene glycol, polytetrapropylene glycol, hexamethylene glycol, tetramethylene glycol, 1,5-pentanediol, diethylene glycol, Examples include triethylene glycol, polycaprolactone, polyhexamethylene adipate, polyhexamethylene sebacate, polytetramethylene adipate, polytetramethylene sebacate, trimethylolpropane, trimethylolethane, pentaerythritol, and glycerin.

  Examples of the polyisocyanate compound used for the synthesis of the polyurethane resin include hexamethylene diisocyanate, diphenylmethane diisocyanate, tolylene diisocyanate, isophorone diisocyanate, and an adduct of tolylene diisocyanate and trimethylolethane.

  Examples of the carboxyl group-containing polyol used for the synthesis of the polyurethane resin include dimethylolpropionic acid, dimethylolbutyric acid, dimethylolvaleric acid, trimellitic acid bis (ethylene glycol) ester, and the like.

  Examples of the amino group-containing carboxylic acid used for the synthesis of the polyurethane resin include β-aminopropionic acid, γ-aminobutyric acid, p-aminobenzoic acid, and the like.

  Examples of the hydroxyl group-containing carboxylic acid used for the synthesis of the polyurethane resin include 3-hydroxypropionic acid, γ-hydroxybutyric acid, p- (2-hydroxyethyl) benzoic acid, malic acid and the like.

  Examples of the compound having an amino group or a hydroxyl group and a sulfonic acid group used for the synthesis of the polyurethane resin include aminomethanesulfonic acid, 2-aminoethanesulfonic acid, 2-amino-5-methylbenzene-2- Examples thereof include sulfonic acid, sodium β-hydroxyethanesulfonate, propane sultone and butane sultone addition product of an aliphatic diprimary amine compound. Of these, a propane sultone adduct of an aliphatic diprimary amine compound is preferred.

  Examples of the compound having an amino group or hydroxyl group and a sulfuric acid half ester group used for the synthesis of the polyurethane resin include aminoethanol sulfate, aminobutanol sulfate, hydroxyethanol sulfate, α-hydroxybutanol sulfate and the like.

  Two or more kinds of compounds used for the synthesis of the polyurethane resin can be used in combination.

  Further, as the above polyurethane-based resin, JP-B-42-24194, JP-B-46-7720, JP-B-46-10193, JP-B-49-37839, JP-A-50-123197, JP-A-53-126058, JP-A-54-138098 and the like can include polyurethane resins having a known anionic group or polyurethane resins based thereon.

The main constituent components of the polyurethane resin are polyisocyanate, polyol, chain extender, cross-linking agent and the like. Further, a resin composed of a polyol having a molecular weight of 300 to 20,000, a polyisocyanate, a chain extender having a reactive hydrogen atom, a group that reacts with an isocyanate group, and a compound having at least one anionic group is desirable. The anionic group in the polyurethane resin is preferably —SO ₃ H, —OSO ₂ H, —COOH, and ammonium salts, lithium salts, sodium salts, potassium salts, or magnesium salts thereof.

  It does not specifically limit as acrylic resin used for an adhesive property modification resin layer, A conventionally well-known thing is employable. That is, as a monomer component constituting the acrylic resin, a known component, specifically, an alkyl (meth) acrylate (the alkyl group includes a methyl group, an ethyl group, an n-propyl group, a t-butyl group, 2- Ethyl hexyl group, lauryl group, stearyl group, cyclohexyl group, phenyl group, benzyl group, phenylethyl group, etc.); hydroxyl group-containing monomers such as 2-hydroxylethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate; acrylamide, Amide group-containing monomers such as N-methylacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, N, N-dimethylolacrylamide, N-methoxymethylacrylamide, N-phenylacrylamide; -Amino group-containing monomers such as diethylaminoethyl acrylate and N, N-diethylaminoethyl methacrylate; Epoxy group-containing monomers such as glycidyl acrylate and glycidyl methacrylate; Acrylic acid, methacrylic acid and salts thereof (lithium salt, sodium salt, potassium salt, etc.) Monomers containing a carboxyl group such as) or a salt thereof; and the like, and can be copolymerized using one or more of these. Furthermore, these can be used in combination with other monomers.

  Examples of the other monomers include epoxy group-containing monomers such as allyl glycidyl ether; sulfonic acid groups such as styrene sulfonic acid, vinyl sulfonic acid and salts thereof (lithium salt, sodium salt, potassium salt, ammonium salt, etc.) Monomers containing salts thereof; monomers containing carboxyl groups or salts thereof such as crotonic acid, itaconic acid, maleic acid, fumaric acid and salts thereof (lithium salt, sodium salt, potassium salt, ammonium salt, etc.); maleic anhydride Monomers containing acid anhydrides such as acid and itaconic anhydride; vinyl isocyanate, allyl isocyanate, styrene, vinyl methyl ether, vinyl ethyl ether, vinyl trisalkoxysilane, alkyl maleic acid monoester, alkyl fumaric acid mono Ester, acrylonitrile, methacrylonitrile, alkyl itaconic acid monoester, vinylidene chloride, vinyl acetate, and vinyl chloride.

  In addition, as the acrylic resin, for example, a modified acrylic resin such as a block copolymer modified with a compound having a urethane bond, a compound having an epoxy group, or a graft copolymer can be used. is there.

  The number average molecular weight of the acrylic resin is 100,000 or more, preferably 300,000 or more, and adhesion with functional layers such as an antireflection layer, a hard coat layer and an antiglare layer formed on the polyester film. It is preferable at the point which ensures property.

  The copolymer polyester resin, polyurethane resin, acrylic resin, and polyvinyl alcohol resin can be used alone or in combination of two or more. In particular, when a copolyester resin and a polyurethane-based resin are used in combination, there are combinations that can achieve good adhesiveness, water resistance, and solvent resistance, and are recommended. In addition, from the viewpoint of adhesiveness between the polyester film and the polarizer, the co-polyester resin and the polyvinyl alcohol resin are used together, the polyurethane resin and the polyvinyl alcohol resin are used together, or the acrylic resin and the polyvinyl alcohol resin. Is preferred. You may add a crosslinking agent to these further.

  In the present invention, the adhesion-modified resin layer is formed, for example, by applying a coating solution containing the above-described components constituting the adhesion-modified resin layer onto a base material polyester film. In this case, in the production of the coating solution, the adhesive modified resin layer constituents may be dissolved or dispersed in a solvent.

  Furthermore, a catalyst may be added to the coating solution in order to accelerate the thermal crosslinking reaction of the constituent resins. As the catalyst, for example, among various chemical substances known as catalysts, such as inorganic substances, salts, organic substances, alkaline substances, acidic substances and metal-containing organic compounds, depending on the resin constituting the adhesive modified resin layer. May be selected as appropriate.

  Moreover, when making the said coating liquid into aqueous solution, in order to adjust pH according to resin which comprises the adhesive property modification resin layer, you may add an alkaline substance and / or an acidic substance.

  An appropriate amount of a surfactant can be added to the coating solution in order to improve the wettability to the polyester film surface and uniformly apply the coating solution when applied to the polyester film. As the surfactant, a known anionic surfactant or nonionic surfactant can be used.

  The solvent used in the coating solution is preferably water, but alcohols such as ethanol, isopropyl alcohol, and benzyl alcohol may be blended in addition to water. When alcohols are used, the proportion of alcohols in the total coating solution is preferably less than 50% by mass.

  Furthermore, you may mix in the range which can dissolve organic solvents other than alcohol. When using an organic solvent other than alcohols, the ratio of the other organic solvent to the total amount of the coating solution is preferably less than 10% by mass, and the total of the alcohol and the other organic solvent is the total amount of the coating solution. However, it may be less than 50% by mass. If the blending ratio of the organic solvent containing the alcohol is less than 50% by mass with respect to the total amount of the coating solution, the drying property at the time of drying the coating solution is improved and the adhesive property-modified resin is compared with the case where the solvent is only water. This has the effect of improving the appearance of the layer. If it is 50% by mass or more, the evaporation rate of the solvent is high, the concentration changes during the coating of the coating liquid, the viscosity increases, and the coating property deteriorates. .

  As described above, in the present invention, from the viewpoint of ensuring transparency, it is preferable to adopt a configuration in which particles that impart slipperiness are not substantially present in the polyester film as the base material. Therefore, in order to secure the slipperiness of the polarizer protective film, particles should be included in the adhesive modified resin layer, and appropriate protrusions should be formed on the surface of the adhesive modified resin layer (that is, the surface of the polarizer protective film). Is preferred. Examples of the method of incorporating particles into the adhesive modified resin layer include adding particles to the coating liquid for forming the adhesive modified resin layer.

  Particles added for such purpose include inorganic particles such as calcium carbonate, calcium phosphate, silica, kaolin, talc, titanium dioxide, alumina, barium sulfate, calcium fluoride, lithium fluoride, zeolite, molybdenum sulfide; Particles: Organic particles such as calcium oxalate. Silica is particularly preferable when the adhesive modified resin layer is formed mainly of the above-mentioned copolymerized polyester resin. Since silica has a relatively close refractive index to that of polyester, it is most preferable in that it can secure an optical laminated film with better transparency.

  The average particle size of the particles to be contained in the adhesive modified resin layer is preferably 0.005 to 1.0 μm from the viewpoint of ensuring transparency, handling properties, and scratch resistance of the polarizer protective film. The upper limit of the average particle size of the particles is more preferably 0.5 μm, particularly preferably 0.2 μm, from the viewpoint of transparency. Further, the lower limit of the average particle diameter of the particles is more preferably 0.03 μm, particularly preferably 0.01 μm, from the viewpoint of handling properties and scratch resistance.

  The content of the particles in the adhesive modified resin layer is 0.1 to 60% by mass with respect to the total amount of the constituent components of the adhesive modified resin layer. From the viewpoint of securing handling properties and scratch resistance. The upper limit of the content of the particles is more preferably 50% by mass, particularly preferably 40% by mass, from the viewpoints of transparency and adhesiveness. Further, the lower limit of the content of the particles is more preferably 1% by mass, particularly preferably 0.5% by mass from the viewpoints of handling properties and scratch resistance.

  Two or more kinds of the particles may be used in combination, and the same kind of particles having different particle sizes may be blended, but in any case, the average particle size of the whole particles and the total content are within the above range. Is preferably satisfied.

  When applying the coating solution for forming the adhesive modified resin layer to the polyester film as the base material, the coating solution is used to remove coarse aggregates and foreign contaminants in the coating solution. It is preferable that the coating solution is precisely filtered with a filter medium immediately before.

  The filter medium for finely filtering the coating solution preferably has a filtration particle size of 25 μm or less (initial filtration efficiency: 95%). When the filtered particle size exceeds 25 μm, removal of coarse aggregates of particles and foreign contaminants may be insufficient. In such a case, many coarse agglomerates that could not be removed by the filter medium are adhesive-modified resin layers when the film obtained by applying and drying the coating liquid on the substrate is uniaxially or biaxially stretched. Among them, the film spreads in the stretching direction of the film and may be recognized as an aggregate of 50 μm or more, for example. As a result, many optical defects can occur due to such aggregates.

  The type of the filter medium is not particularly limited as long as it has the above performance, and examples thereof include a filament type, a felt type, and a mesh type. The material of the filter medium is not particularly limited as long as it has the filtering performance and does not adversely affect the coating solution, and examples thereof include stainless steel, polyethylene, polypropylene, and nylon.

  Various additives such as an antistatic agent, an ultraviolet absorber, a plasticizer, a light-proofing agent, and a lubricant may be blended in the adhesiveness-modified resin layer as long as the effects of the present invention are not impaired. In addition, when the coating solution for forming the adhesive modified resin layer is aqueous, other water-soluble resins, water-dispersible resins and emulsions are added to the coating solution as long as the effects of the present invention are not impaired. Thus, it is possible to improve the performance.

  As a method for forming the adhesive modified resin layer on the polyester film, when a coating method for applying a coating solution is used, the solid content concentration in the coating solution is preferably 30% by mass or less, more preferably 10% by mass. % Or less.

3. The manufacturing method of a polarizer protective film The polyester film which is a base material of the polarizer protective film of this invention can be manufactured in accordance with the manufacturing method of a general 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 manufacturing method of the polarizer protective film of the present invention will be described mainly using a case where a polyethylene terephthalate film is mainly used as a base material, but the present invention is not limited to this.

PET pellets substantially free of particles are sufficiently dried in vacuum, and then supplied to an extruder, for example, melt-extruded into a sheet at about 280 ° C., preferably solidified on a metal cooling roll while applying static electricity ( Cast) to obtain an unstretched PET film. At this time, microfiltration is performed in an arbitrary melt line in which the molten PET resin is maintained at about 280 ° C. to remove foreign substances contained in the PET resin. The filter medium used for microfiltration of molten PET is not particularly limited, but the filter medium of the stainless steel sintered body is metal Sb in which Sb ₂ O ₃ which is a polymerization catalyst of the polyester resin is reduced and precipitated, or pelletized from polymerization It is suitable because it is excellent in the removal performance of the agglomerates and refractory organic substances mainly composed of Si, Ti, Sb, Ge, Cu and the like mixed from the outside up to the stage.

  The filtration particle size (initial filtration efficiency: 95%) of the filter medium is preferably 15 μm or less. With a filter medium having a filtration particle size exceeding 15 μm, particles having a size that needs to be removed from the viewpoint of reducing optical defects cannot be sufficiently removed. Although productivity may be reduced by performing microfiltration of molten PET resin using a filter medium having the filtration performance as described above, it is indispensable to obtain a film with few optical defects.

Filtration of the molten PET resin may be performed in a single stage, but is preferably performed in multiple stages. For example, the first stage may be a slightly coarser filtration, the second stage may be more precisely filtered than the first stage, and so on. Thus, productivity can be improved more by making it multistage.

It is preferable to clean the filter medium regularly because foreign substances and the like are likely to aggregate and accumulate. A conventionally known method can be used for washing. It is preferable to employ conditions that minimize the cleaning residue. After washing, it is preferable to wash away not only the polishing residue but also the residue remaining on the filter medium, including the abrasive used for washing.

When a film is produced immediately after exchanging the filter, the residue may be mixed into the film as a foreign substance. Therefore, it is preferable to avoid production immediately after filter replacement. It is preferable from the viewpoint of foreign matter reduction to start production of a film after discharging a certain amount of the polyester resin to be used.

  The piping through which the molten resin passes accumulates agglomerates such as foreign matters, which may peel off and enter the film to become foreign matters. Therefore, it is preferable to keep the piping used clean. Further, the discharge amount is preferably performed in a stable state so as to have a fluctuation of ± 60% or less from the viewpoint of reducing foreign matter. This is because it is possible to reduce the probability that the accumulated aggregates peel off.

  The timing of adding the magnesium compound and the phosphorus compound is not particularly limited as long as it is during the polymerization step of the polyester resin. For example, in the case of the direct esterification method, before the esterification reaction, during esterification, It may be any stage from the end of esterification to the start of the polymerization process, during the polymerization, or after the polymerization, but preferably at any stage after the end of the esterification, more preferably from the end of the esterification to the start of the polymerization process. is there. When added after completion of esterification, the amount of foreign matter produced due to the magnesium compound can be reduced as compared with the case where it is added before that.

  The obtained unstretched film is stretched 1.0 to 3.5 times in the longitudinal direction (longitudinal direction: travel direction during production of the polyester film) with a roll heated to 80 to 145 ° C. to obtain a uniaxially oriented film. In addition, the process of performing this uniaxial stretching may be called "longitudinal stretching process".

  In this case, in order to prevent the generation of scratches on the film, (a) the film surface itself or the roll surface, in particular, the roll surface in contact with the film should not generate “defects” that cause scratches, and (b) contact. It is important that the film does not shift in the machine and transverse directions on the surface of the roll to be rolled.

  The above-mentioned “defects” refer to all factors that cause fine scratches on the film by coming into contact with the film, such as scratches, deposits, deposits, and foreign matters formed on the roll surface. Therefore, by eliminating these defects, it is possible to reduce the occurrence of scratches on the film surface. In order to prevent the occurrence of the above defects, for example, the following methods can be employed.

  In order to prevent the surface roughness of the roll used at the time of film production from 0.1 μm or less by Ra, or to prevent the generation of scratches such as deposits, deposits, and foreign matters on the roll surface, a longitudinal stretching step (hereinafter referred to as the And a method of installing a roll cleaner at the preheating inlet and the cooling roll in the “MD process”.

  In addition, there is a method in which the degree of cleanliness in the film production process is class 1000 or less (1000 particles or less of 0.5 μm or more in a volume per cubic foot). It is preferable to use clean air of class 100 or less for the blower cooling device for cooling the roll surface.

  Furthermore, there is a method of cleaning the roll by an operation of scraping off defects on the roll using an abrasive before film production. In addition, in order to prevent the film from adsorbing dust or the like due to the generation of static electricity and causing a defect, there is a method of providing a static eliminator so that the charge amount of the film becomes ± 1500 V or less in all steps. The process from the casting of the base film to the tenter described later is a process in which scratches are mainly likely to occur, and laying out this section in a compact manner and reducing the passage time to 5 minutes or less can also contribute to the suppression of the occurrence of defects. .

  About a roll, it can be set as the structure where the fault of a roll surface does not contact a film directly by forming a water film on the roll surface, or setting it as an air floating type roll. Moreover, the adhesion of the defect to a roll surface can be reduced and the defect of a roll surface can be reduced because the oligomer amount which precipitates from a film shall be 1000 ppm or less.

  Furthermore, in the winding process after stretching described later, the surface on the end side in the width direction of the film (lateral direction: the direction perpendicular to the running direction during the production of the polyester film) is pressed with a roller with a protrusion, and the part And forming the projection on the roller with the projection into a tapered shape, and forming the projection on the roller with the projection. By rounding the top and setting the curvature radius of the top surface to 0.4 mm or less, it is possible to prevent the film and the defect from contacting each other in the film winding apparatus.

  Moreover, as a method for preventing the film from shifting on the roll surface, for example, the following methods can be employed.

  By increasing the adhesion of the film to the roll by reducing the diameter of the roll, using a suction roll, electrostatic adhesion, or using a part nip adhesion device, the occurrence of long scratches can be suppressed. In particular, reducing the diameter of the roll also subdivides the amount of shift of the film and can contribute to the prevention of long scratches. In addition, many of the scratches increase in length and frequency toward the end in the roll width direction, and it is difficult to obtain a scratch-free portion at the end in the roll width direction. By trimming around the center of the direction, a film with few scratches can be obtained.

  As a cause of occurrence of longitudinal scratches or lateral scratches, deformations such as expansion and contraction in the longitudinal direction or the lateral direction of the film can be mentioned, respectively. These film deformations are mainly caused by temperature changes in the film. Therefore, for example, by suppressing the temperature change of the film on the roll surface, the amount of film deformation due to such temperature can be reduced, and the occurrence of vertical scratches and horizontal scratches can be prevented. Specifically, the temperature change of the film per roll is 40 ° C. or less, preferably 30 ° C. or less, more preferably 20 ° C. or less, still more preferably 10 ° C. or less, and particularly preferably 5 ° C. or less. Is recommended.

  Examples of the method for suppressing the temperature change of the film on the roll surface include air cooling between the rolls and water cooling through a water tank. Furthermore, the temperature change of the film on the roll surface per roll can be reduced by increasing the number of rolls. Preferably, the number of rolls in the MD process is 10 or more.

  Further, by setting the relationship between the relative speeds of the plurality of rolls to a speed profile that is closest to the amount of deformation due to the temperature and tension of the film, it is possible to reduce the vertical shift of the film.

  Furthermore, in the coating step of the coating liquid for forming the adhesive property-modified resin layer, which will be described later, the drying condition is completed at the beginning of the dryer section and is cooled to the outlet, whereby the film temperature at the outlet of the dryer is 40 ° C. In the following, film shift due to temperature change can be reduced.

  If the tension during running of the film is too low, the gripping force will be reduced and deviation will occur, and if it is too high, stress deformation will increase and deviation will occur, so the optimum tension range will be 4.9-29.4 MPa. It is preferable to adjust by the driving roll speed and tension adjusting means. Moreover, the shift | offset | difference of the film on a roll surface can be suppressed by making the friction coefficient between the film and roll in the use temperature at the time of manufacture 0.2 or more.

  Furthermore, it is preferable to use a special bearing for the free roll and to set the rotational resistance to 19.6 N or less. For the drive roll, the rotation spots are controlled to 0.01% or less.

  In the film after uniaxial stretching, stress is applied in the longitudinal direction in order to convey the film, and further, deformation stress commensurate with the Poisson's ratio and the elastic modulus is generated in the orthogonal direction. In order to reduce this stress and to reduce the heat shrinkage stress of the film, it is preferable to lower the orientation within a range that does not adversely affect the film properties. Specifically, the refractive index difference in the X-axis direction [(refractive index in the X-axis direction of uniaxially stretched film) − (refractive index in the X-axis direction of unstretched film)] is 0.01 to 0.12. A uniaxially oriented film with orientation is recommended.

In the present invention, the method for forming the adhesive modified resin layer on the substrate is not particularly limited. For example, the adhesive modified resin described above may be formed on at least one surface of the polyester film, for example, at any stage in the above process. What is necessary is just to form the adhesive property modification resin layer by apply | coating the coating liquid for layer formation.

  In order to apply the coating solution on the polyester film, a predetermined amount of a solvent is mixed with the constituent components of the adhesive property-modified resin layer in advance to prepare the coating solution, and any known coating method is used. 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, impregnation coating method and curtain Examples thereof include a coating method, and these methods can be applied singly or in combination.

When using the method of applying a coating liquid as a method for forming an adhesive property-modified resin layer on a polyester film, the coating amount is 0.04 per 1 m ^{2 of the} film at the final time after the production of the polarizer protective film. ˜5 g is preferable from the viewpoints of coating uniformity, blocking resistance, adhesion to a substrate, and transparency. The lower limit of the coating amount, in terms of adhesion and transparency of the substrate, more preferably 0.08 g / ^{m 2,} particularly preferably 0.2 g / ^{m 2.} The upper limit of the coating amount, in terms of coating uniformity and blocking resistance, and more preferably from 4g / m ^2, particularly preferably 2 g / m ^2. If the coating amount is too small, the adhesion between the polyester film and the adhesive modified resin layer tends to be lowered, and the particles in the adhesive modified resin layer easily fall off. When the coating amount is too large, not only the transparency and blocking resistance are deteriorated, but also there is a tendency that uniform coating is difficult due to problems such as physical properties (particularly rheology) of the coating solution and equipment.

  The uniaxially oriented film is guided to a tenter for further stretching and heat setting in the width direction (transverse direction = direction perpendicular to the running direction of the film). In addition, when apply | coating the coating liquid for adhesive property modification resin layer formation as mentioned above, it heats with a tenter and a stable adhesive property modification resin layer is formed by thermal crosslinking reaction. By the stretching step in the width direction, the film is stretched in the width direction by 2.5 to 6.0 times, further subjected to heat setting treatment, subjected to relaxation treatment as necessary, and then slit to an appropriate width and wound. Thus, the polarizer protective film of the present invention is obtained.

When creating a film roll, it is preferable to knurl the end of the film. The knurling process is a process for imparting minute irregularities to the film edge and is also called an embossing process. By performing the knurling process, it is possible to prevent the films from slipping at the time of film winding and to efficiently wind the film, so that a film roll excellent in appearance quality can be obtained. Also, by performing the knurling process, the amount of air entrained between the films can be increased, so that a slight gap is formed between the films, and the occurrence of gauge bands, scratches and foreign matter transfer can be suppressed.

In the knurling process, the concavo-convex portions can be imparted by a conventionally known method. For example, it is preferable to impart the embossing roll and the flat roll by appropriately arranging them. Specifically, the film end is sandwiched between the flat surface of the flat roll and the embossed surface of the embossing roll that face each other, and pressure is applied to the flat roll to form unevenness on the film surface. At this time, although the pressing force of the flat roll varies depending on the film thickness, it is possible to apply a constant height of knurl by enabling fine adjustment of the pressure.
The height of the irregularities is preferably 1 μm to 100 μm, more preferably 1 to 70 μm, still more preferably 1 to 50 μm, particularly preferably 1 to 30 μm, and most preferably 1 to 10 μm. If the height of the knals exceeds 100 μm, unacceptable appearance defects may occur.

  A polyester film having a specific retardation can be obtained by adjusting conditions at the time of film formation (for example, stretching ratio, stretching temperature, film thickness, etc.). For example, the higher the stretching ratio, the lower the stretching temperature, and the thicker the film, the higher the retardation. On the other hand, the lower the stretching ratio, the higher the stretching temperature, and the thinner the film, the lower the retardation.

  As specific film forming conditions, for example, the longitudinal stretching temperature and the transverse stretching temperature are preferably 80 to 145 ° C, and particularly preferably 90 to 140 ° 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 specific range described above, 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. It is also preferable to set the stretching temperature low in order to increase the retardation. The temperature of the subsequent heat treatment is preferably 100 to 250 ° C, particularly preferably 160 to 245 ° C.

  In addition, although an adhesive property modification resin layer may be provided in the surface of the base film after biaxial stretching mentioned later, Preferably in manufacture of a polyester film, film manufacture and formation of an adhesive property modification resin layer It is recommended from the viewpoint of productivity to carry out simultaneously.

  In addition, the step of applying the coating solution for forming the adhesive modified resin layer to the polyester film may be any time after the production of the unstretched film, after the production of the uniaxially stretched film, or after the production of the biaxially stretched film. After applying the coating solution, it is preferable to perform stretching in at least one direction. More preferably, the coating solution is applied at a stage before the crystal orientation is completed with an unstretched film or a longitudinally uniaxially stretched film before stretching in the width direction. More preferably, the coating liquid is applied to the surface of the longitudinally uniaxially stretched film and then stretched in the width direction.

  In addition, the various methods for preventing generation | occurrence | production of the above-mentioned damage | wound can be used combining multiple types of method according to the required quality level of the optical member in which the polarizer protective film of this invention is used.

  The polarizer protective film of the present invention has at least one selected from the group consisting of a hard coat layer, an antireflection layer, a low reflection layer, an antiglare layer and an antistatic layer as long as the effects of the present invention are not impaired. You may do it.

4). The polarizing plate is composed of a polarizer protective film laminated on both sides of the polarizer. It is preferable that at least one of the polarizer protective films is the polarizer protective film of the present invention. The other polarizer protective film may be the polarizer protective film of the present invention. For example, it is preferable to use a film having no birefringence such as a TAC film, an acrylic film, and a norbornene film. . The polarizer and the polarizer protective film can be bonded together via a PVA-based adhesive or a UV curable resin.

5. 2. Liquid Crystal Display Device In general, a liquid crystal display device is composed of a rear module, a liquid crystal cell, and a front module in order from the side facing the backlight light source toward the image display side (viewing side or outgoing 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 side facing the backlight light source in the rear module, and is disposed on the image display side (viewing side or outgoing light side) in the front module.

  The liquid crystal display device of the present invention includes at least a backlight light source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates as constituent members. The liquid crystal display device of the present invention may have other constituent members other than these, for example, a color filter, a lens film, a diffusion sheet, an antireflection film and the like as appropriate.

  The configuration of the backlight may be an edge light method using a light guide plate, a reflection plate, or the like as a constituent member, or a direct type. In the present invention, it is preferable to use a white light source having a continuous broad emission spectrum as a backlight light source of a liquid crystal display device. Here, the continuous 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 the visible light region. As such a white light source having a continuous broad emission spectrum, for example, a white LED can be exemplified, but the present invention is not limited thereto.

  The white LED usable in the present invention includes a phosphor type, that is, an element that emits white light 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 diode). -Emitting diode (OLED). Examples of the phosphor include yttrium / aluminum / garnet yellow phosphor and terbium / aluminum / garnet yellow phosphor. Among white LEDs, white light-emitting diodes, consisting of light-emitting elements that combine blue light-emitting diodes using compound semiconductors with yttrium, aluminum, and garnet-based yellow phosphors, have a continuous and broad emission spectrum and have a luminous efficiency. Therefore, it is suitable as the backlight light source of the present invention. Since the white LED has low power consumption, the liquid crystal display device of the present invention using the white LED contributes to energy saving.

  A fluorescent tube such as a cold cathode tube or a hot cathode tube, which has been widely used as a backlight light source, has a discontinuous emission spectrum whose emission spectrum has a peak at a specific wavelength. It is not preferable.

  In a preferred embodiment, the polarizer protective film of the present invention is used as a polarizer protective film on the incident light side of the polarizing plate on the incident light side, and the polarizer on the outgoing light side of the polarizing plate on the outgoing light side. Used as a protective film. When the polarizer protective film of the present invention is used for only one of the two polarizer protective films constituting the polarizing plate, an arbitrary polarizer protective film (for example, a TAC film) may be used for the other. it can. When the polarizer protective film of the present invention is used as the polarizer protective film on the liquid crystal cell side of the polarizing plate arranged on the incident light side and the polarizer protective film on the liquid crystal cell side of the polarizing plate arranged on the outgoing light side, the liquid crystal Since there is a possibility of changing the polarization characteristics of the cell, the polarizer protective film at these positions should be a film having no birefringence such as a TAC film, an acrylic film and a norbornene film. Is preferred.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples, and can be 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.

The evaluation methods in the examples are as follows.

(1) Polyester is dissolved in a mixed solution of 60% by mass of inherent viscosity phenol of polyester and 40% by mass of 1,1,2,2-tetrachloroethane, and measured at 30 ° C. by a conventional method.

(2) Elemental analysis The amount of each element in polyester is quantified by the following method.

(A) The Mg analysis sample is incinerated and decomposed with a platinum crucible, 6 mol / L hydrochloric acid is added and evaporated to dryness.
This is dissolved in 1.2 mol / L hydrochloric acid, and Mg is quantified by ICP emission analysis (“ICPS-2000” manufactured by Shimadzu Corporation).

(B) Analyzing P by dry ashing in the presence of sodium carbonate, or by wet decomposition in sulfuric acid / nitric acid / perchloric acid system or sulfuric acid / hydrogen peroxide system to convert phosphorus into normal phosphoric acid. Subsequently, molybdate is reacted in a 1 mol / L sulfuric acid solution to form phosphomolybdic acid, and this is reduced with hydrazine sulfate. The absorbance at 830 nm of the heteropoly blue produced is a spectrophotometer (Shimadzu Corporation, UV-150-02). ) To measure colorimetrically.

(C) Wet analysis sample of Sb in sulfuric acid / hydrogen peroxide system, add sodium nitrite to Sb ⁵⁺ , add brilliant green to form a blue complex with Sb, extract with toluene, The absorbance at 625 nm is measured with an absorptiometer (manufactured by Shimadzu Corporation, UV-150-02) and colorimetrically determined.

(3) Melt specific resistance value of polyester resin Two electrodes (stainless steel wire) are placed in polyester melted at 275 ° C., and the current (i _o ) when a voltage of 120 V is applied is measured. The specific resistance value Si (Ω · cm) is obtained.
Si (Ω · cm) = (A / L) × (V / i _o )
Here, A is the area between electrodes (cm ² ), L is the distance between electrodes (cm), and V is the voltage (V).

(4) Color tone of polyester L value and b value are measured using a color difference meter (“Model TC-1500MC-88” manufactured by Tokyo Denshoku Co., Ltd.).

(5) Number Evaluation of Scratches and Foreign Objects First, scratches and internal foreign matters were screened based on black and white judgment using a defect inspection machine (MaxEye.CORE / 160C manufactured by Hughtec).
Sampling is performed from the corresponding place, and the depth is measured with a laser microscope if it is a flaw, and the major axis is measured if it is a foreign object. The number per 1000 m ² was calculated from the area where the number of scratches with a depth of 0.5 μm or more became 20 or more. Similarly, the number per 1000 m ² was calculated from the area where the number of foreign matters having a major axis of 50 μm or more became 20 or more.

(6) Retardation Retardation is defined by the product (ΔNxy × d) of anisotropy of biaxial refractive index (ΔNxy = | nx−ny |) and film thickness d (nm) on the film. Parameter that is a measure of optical isotropy and anisotropy. The biaxial refractive index anisotropy (ΔNxy) was determined by the following method. Using a molecular orientation meter (manufactured by Oji Scientific Instruments Co., Ltd., MOA-6004 type molecular orientation meter), the orientation axis direction of the film is obtained, and a 4 cm × 2 cm rectangle is cut out so that the orientation axis direction becomes the long side, for measurement A sample was used. For this sample, the biaxial refractive index (nx, ny) orthogonal to each other and the refractive index (Nz) in the thickness direction were measured using an Abbe refractometer (NAR-4T manufactured by Atago Co., Ltd., measurement wavelength 589 nm). The absolute value (| nx−ny |) of the difference between the biaxial refractive indexes 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).

(7) A polyethylene terephthalate film prepared by the method described later is attached to one side of a polarizer made of rainbow spot observation PVA and iodine so that the absorption axis of the polarizer and the orientation main axis of the film are perpendicular to each other. A TAC film (manufactured by FUJIFILM Corporation, thickness 80 μm) was attached to create a polarizing plate. The obtained polarizing plate is made of polyethylene on the outgoing light side of a liquid crystal display device using a white LED composed of a light emitting element combining a blue light emitting diode and a yttrium / aluminum / garnet yellow phosphor as a light source (Nichia Chemical, NSPW500CS). The terephthalate film was placed on the viewing side. This liquid crystal display device had 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 and oblique directions of the polarizing plate of the liquid crystal display device, and the presence or absence of rainbow spots was evaluated. In Comparative Example 1, a backlight light source using a cold cathode tube as a light source instead of the white LED was used.

(Production Example 1 Production of polyethylene terephthalate resin)
When the temperature of the esterification reactor was raised to 200 ° C., a slurry consisting of 86.4 parts by mass of terephthalic acid and 64.4 parts by mass of ethylene glycol was charged, and antimony trioxide was added as a catalyst while stirring. 0.017 parts by mass and 0.16 parts by mass of triethylamine were added. Next, the temperature was raised by heating, and a pressure esterification reaction was carried out under conditions of a gauge pressure of 0.34 MPa and 240 ° C.

  Thereafter, the inside of the esterification reaction vessel was returned to normal pressure, and 0.071 part by mass of magnesium acetate tetrahydrate and then 0.014 part by mass of trimethyl phosphate were added. Furthermore, the temperature was raised to 260 ° C. over 15 minutes, and 0.012 part by mass of trimethyl phosphate and then 0.0036 part by mass of sodium acetate were added. The obtained esterification reaction product was transferred to a polycondensation reaction can, gradually heated from 260 ° C. to 280 ° C. under reduced pressure, and subjected to a polycondensation reaction at 285 ° C. After the polycondensation reaction, filtration was performed with a NASRON filter having a pore size of 5 μm (initial filtration efficiency: 95%).

Next, PET, which is the polycondensation reaction product, was pelletized in a sealed chamber in which foreign matter having a diameter of 1 μm or more existing in the air was reduced with a hepa filter. Pelletization was performed by a method of extruding molten PET into a cooling water tank from a nozzle of an extruder and cutting the formed strand-like PET while flowing cooling water that had been previously filtered (pore size: 1 μm or less). The obtained PET pellets have an intrinsic viscosity of 0.62 dl / g, an Sb content of 144 ppm, an Mg content of 58 ppm, a P content of 40 ppm, a color L value of 56.2, and a color b value of 1.6. The melt specific resistance value at 275 ° C. was 0.23 × 10 ⁸ Ω · cm, and inert particles and internally precipitated particles were substantially absent.

(Production Example 2 Production of Coating Solution for Adhesive Modified Resin)
As a coating solution for the adhesive modified resin layer, a copolymerized polyester resin dispersion (“MD-1200” manufactured by Toyobo Co., Ltd.) is mixed with a mixed solvent composed of 60% by weight of water and 40% by weight of isopropyl alcohol. And 4 parts by mass with respect to 100 parts by mass of the total amount of the resin dispersion, 5 parts by mass of colloidal silica (“Snowtex 20L” manufactured by Nissan Chemical Industries, Ltd., average SEM particle size: 45 nm) with respect to 100 parts by mass of the total solid content The mixture was mixed and dispersed and mixed.

Example 1
As the raw material of the base film, PET pellets having an intrinsic viscosity of 0.62 dl / g and containing no particles were used. The pellets were dried under reduced pressure (1 Torr) at 135 ° C. for 6 hours, then supplied to an extruder, melt-extruded into a film at about 280 ° C., and rapidly cooled and solidified on a metal roll maintained at a surface temperature of 20 ° C. A cast film of 500 μm was obtained.

At the time of melting, microfiltration was performed using a stainless steel filter medium having a filtration particle size (initial filtration efficiency of 95%) of 5 μm as a filter medium for removing foreign substances from the molten resin. Regarding the pre-use cleaning of the filter medium, a known cleaning method was used, and conditions under which the cleaning residue was minimized were adopted. As production timing, production was avoided after 2000 kg discharge, avoiding production immediately after filter replacement. In addition, after the filter was replaced, the discharge amount was changed when the brand was changed and the discharge adjustment was stabilized so that the fluctuation would be ± 60% or less.

The adhesive modifying resin coating solution was microfiltered using a felt type polypropylene filter medium having a filtration particle size (initial filtration efficiency: 95%) of 25 μm, and applied to one side of the cast film using a reverse roll method. . The drying conditions in the coating process of the coating solution for the adhesive modified resin layer were such that the drying was completed at the beginning of the dryer section and cooled to the outlet, so that the film temperature at the outlet of the dryer was 29 ° C. Further, the speed of the driving roll and the adjustment with the tension adjusting device were adjusted so that the tension during running of the film was 11.8 MPa.

In addition, the roll which managed the surface roughness of the roll to 0.1 micrometer or less by Ra with respect to all the rolls used at the time of film manufacture was used.

After coating, the film edge is held with a clip and guided to a hot air zone heated to 100 ° C, dried for 15 seconds, and stretched 4.0 times at 95 ° C in the width direction (perpendicular to the running direction). Then, it was heat-set at 170 ° C. and led to a winding process. A roll cleaner was installed at the entrance of the winding process. The film temperature after transverse stretching was cooled to 50 ° C. or lower in the air, and the film was conveyed so that the temperature change on each roll was small.
The diameter of the guide roll was 150 mm, and the film was brought into close contact with the roll using a suction roll, electrostatic contact, and part nip contact apparatus.

Thus, a uniaxially stretched film having an adhesive modified resin layer having a final coating amount of 0.25 g / m ² on one side and a thickness of 100 μm was obtained. A polarizer protective film 1 was obtained by trimming a central portion 1.3 m of the full width of the uniaxially stretched film. Table 1 shows the evaluation results of scratches and foreign matter. The retardation of the polarizer protective film was about 10,000 nm. No erythema was observed, and the erythema observation was good.

(Comparative Example 1)
A polarizer protective film 2 was obtained in the same manner as in the production chart of Example 1 except that it was produced under the following conditions (1) to (4). Table 1 shows the evaluation results of scratches and foreign matter. When an iris was evaluated using a backlight source using a cold-cathode tube as a light source instead of a white LED, an iris was observed when observed from an oblique direction.
(1) As a filter material for removing foreign matters from the molten resin, a filter material made of stainless fiber with a filtration particle size (initial filtration efficiency 95%) of 150 μm was used, and the membrane was formed immediately after filter replacement without performing cleaning before using the filter media. .
(2) About all the rolls used at the time of film manufacture, the roll which controlled the surface roughness of Ra to 0.1 micrometer or less was not used, and the roll cleaner was not installed.
(3) The roll diameter in the longitudinal stretching step was 300 mm, and no contact equipment such as a suction roll, electrostatic contact, or part nip was used.
(4) The film temperature at the outlet in the coating process was 63 ° C., and the speed of the drive roll was set so that the tension during running was 4.9 MPa.

As shown in Table 1, in the polarizer protective film 1 obtained in Example 1, the generation of scratches and foreign matters is suppressed, and a polarizer protective film with reduced optical defects due to scratches and foreign matters is obtained. I was able to.

Since the optical defect is reduced, the polarizer protective film of the present invention can be used as a polarizer protective film used for a polarizing plate in a liquid crystal display device.

Claims (5)

A polarizer protective film having an adhesive modified resin layer on at least one side of a polyester film,
The number of depth 0.5μm or more flaws are 10 to 10,000 pieces / 1000 m ^2, the number of long diameter 50μm or more foreign matter is 3-2000 cells / 1000 m ^2, a polarizer protective film. The polarizer protective film according to claim 1, wherein the polyester film has a retardation of 3000 to 30000 nm. A polarizing plate in which a polarizer protective film is laminated on both sides of a polarizer,
The polarizing plate whose polarizer protective film of at least one side is a polarizer protective film of Claim 1 or 2. A liquid crystal display device having a backlight light source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates,
A liquid crystal display device, wherein at least one polarizing plate is the polarizing plate according to claim 3. The liquid crystal display device according to claim 4, wherein the backlight light source is a white light source having a continuous emission spectrum.