JP2022028752A - Polyester film and use of the same - Google Patents

Abstract

An object of the present invention is to provide a polyester film suitable for use as a polarizer protective film by reducing the number of whisker-like defects present on the slit end face of the film. A polyester film in which the number of whiskers protruding of 5 μm or more on the end face of the film slit along the machine flow direction during film production is 1 or less per 100 μm of film length. The polyester film for a polarizer protective film having an in-plane retardation of 3000 nm or more and 30000 nm or less. It is also used for polarizing plates and liquid crystal display devices. [Selection figure] None

Description

The present invention relates to a polyester film that is slit along the machine flow direction at the time of film production and has few whiskers-like defects on the slit end face. More specifically, the polyester for a polarizing element protective film having few whiskers defects on the slit end face. The present invention relates to a film, a polarizing plate using the film, and a liquid crystal display device.

The polarizing plate used in a liquid crystal display (LCD) is usually composed of a polarizing element obtained by dyeing polyvinyl alcohol (PVA) or the like with iodine, sandwiched between two polarizing element protective films, and protects the polarizing element. As the film, a triacetyl cellulose (TAC) film is usually used. In recent years, as LCDs have become thinner and costs have been reduced, thinner polarizing plates have been required. However, if the thickness of the TAC film used as the polarizing element protective film is reduced for this reason, sufficient mechanical strength cannot be obtained, and there arises a problem that the moisture permeability is deteriorated. Further, the TAC film is very expensive, and there is a strong demand for an inexpensive alternative material.

The polyester film is superior in durability to the TAC film, but unlike the TAC film, it has birefringence. Therefore, when it is used as a polarizing element 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 (literation), when it is used as a polarizing element protection film, rainbow-shaped color spots occur when observed from an oblique direction, and the image quality deteriorates. do.
Therefore, in Patent Document 1, measures against color spots are taken by controlling the in-plane retardation of the polyester film to a specific range.

Further, in the production of TAC films and polyester films in which molecules are oriented in the stretching direction, both ends in the width direction have a non-uniform film thickness and are cut off by a cutting device (slitter) after production (slit step). However, the misalignment of the molecular chains that make up the film is a disaster, and whiskers and fluff appear at the slit ends of the film, causing problems such as an increase in foreign matter and breakage of the film during cutting. rice field. Therefore, Patent Document 2 proposes a method for solving the above problem by a cutting method.

On the other hand, when producing a polyester film, a waste film is generated. Attempts have been made to reuse or recycle scrap films such as film edges that have been cut and removed from the product. However, when a film having a coating layer such as an easy-adhesive resin or an antistatic resin is recycled and the recycled polyester raw material is used as a main component, the components of the coating layer contained therein are thermally deteriorated and the obtained film is significantly colored. There was a problem that it became turbid. Therefore, Patent Document 3 proposes a method for obtaining a transparent polyester fill containing a self-recovering raw material and having little coloring.

However, in Patent Document 2, there is no knowledge about polyester film, and it is doubtful whether it can be applied. Further, in Patent Document 3, when considering application to optical applications, the hurdle for generating internal foreign substances due to the addition of self-recovery raw materials is high, and in the composition of the coating layer, which has become complicated (diversified) in recent years, crosslinked components and the like are present. It had the disadvantage that contamination hindered recovery and caused internal foreign matter. In addition, after removing the coating layer of the polyester film, which is the self-recovery raw material, by either method, only the base polyester film is used, and then melt extrusion and pelletizing are required to obtain a recycled raw material, which is a complicated separate process. there were.

International Publication No. 2011/162198 JP-A-2017-109262 Japanese Unexamined Patent Publication No. 2013-039764

The present invention has been made in the background of the problems of the prior art. That is, an object of the present invention is to eliminate the above-mentioned defects, and in particular, to provide a polyester film suitably used as a polarizing element protective film by reducing the number of whiskers on the slit end surface of the film. It is in.

The present inventor has arrived at the present invention as a result of diligent studies to achieve such an object.
That is, the present invention has the following configuration.
1. 1. A polyester film in which the number of whisker-like objects protruding by 5 μm or more on the end face of the film slit along the machine flow direction at the time of film production is 1 or less per 100 μm of the film length , constituting the polyester film. The polyester resin to be used is a polyester resin containing at least one selected from polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate as a constituent component, or a third component monomer is copolymerized with the polyester resin. A polyester film that is a copolymerized polyester resin .
2. 2. The polyester film according to the first item, wherein the intrinsic viscosity is 0.55 dl / g or more and 0.65 dl / g or less.
3. 3. The polyester film according to the first or second above, wherein the haze value is 2.0% or less and the b value is −0.5 or more and 3.0 or less.
4. The polyester film according to any one of the above 1 to 3 having a thickness of 15 μm or more and 300 μm or less.
5. The polyester film according to any one of the above 1 to 4, wherein a part of the polyester constituting the polyester film contains a self-recovering polymer produced in the process of producing the polyester film.
The above 6. The polyester film according to any one of the above 1 to 5, which has a coating layer on at least one side.
7. It has a laminated structure of three or more layers having at least a surface layer made of polyester on both sides of the intermediate layer made of polyester, and the intermediate layer contains a self-recovering polymer produced in the process of manufacturing a polyester film. The polyester film according to any one of the above 1st to 6th.
8. It has a laminated structure of three or more layers having at least a surface layer made of polyester on both sides of the intermediate layer made of polyester, and the intrinsic viscosity of the polyester constituting the intermediate layer is that of the polyester constituting both surface layers. The polyester film according to any one of the above 1 to 7, which is smaller than the intrinsic viscosity.
9. The polyester film for a polarizing element protective film according to any one of 1 to 8 above, wherein the in-plane retardation is 3000 nm or more and 30,000 or less.
10. A polarizing plate in which a polyester film for a polarizing element protective film according to the ninth aspect is laminated on at least one surface of a polarizing element.
11. A liquid crystal display device having a backlight, a liquid crystal cell, and polarizing plates arranged on both sides of the liquid crystal cell, wherein the polarizing plate on at least one side is the polarizing plate according to the tenth aspect.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a polyester film roll having a small amount of whiskers on the end face of the slit, and it is possible to reduce a factor which becomes a defect, so that it can be further applied to optical applications, particularly a polarizing element protective film.

Hereinafter, the present invention will be described in detail.

(Polyester film)
The polyester film referred to in the present invention is a film made of a polyester resin, and a polyester film mainly containing at least one selected from polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate is preferable. .. Further, it may be a film made of a copolymerized polyester in which a third component monomer is copolymerized with the polyester as described above. Among these polyester films, polyethylene terephthalate film is most preferable from the viewpoint of the balance between physical properties and cost.

Further, the polyester film may be a single layer or a plurality of layers. Further, as long as the effect of the present invention is exhibited, each of these layers may contain various additives in the polyester resin, if necessary. Examples of the additive include antioxidants, lightfasteners, antigelling agents, organic wetting agents, antistatic agents, ultraviolet absorbers, surfactants and the like.

(Coating layer)
In the polyester film of the present invention, it is preferable that an easily adhesive coating layer is laminated on the polyester base film as described above. The coating layer usually contains a binder resin, lubricant particles, a cross-linking agent, a surfactant and the like.

The lubricant particles in the coating layer include (1) silica, kaolinite, talc, light calcium carbonate, heavy calcium carbonate, zeolite, alumina, barium sulfate, carbon black, zinc oxide, zinc sulfate, zinc carbonate, and dioxide. Inorganic particles such as titanium, satin white, aluminum silicate, silica clay, calcium silicate, aluminum hydroxide, hydrohalosite, magnesium carbonate, magnesium hydroxide, etc., (2) acrylic or methacrylic acid, vinyl chloride, vinyl acetate, etc. Nylon, styrene / acrylic, styrene / butadiene, polystyrene / acrylic, polystyrene / isoprene, methylmethacrylate / butylmethacrylate, melamine, polycarbonate, urea, epoxy, urethane, phenol, diallyl Examples thereof include organic particles such as phthalate and polyester, but silica is particularly preferably used in order to give an appropriate slipperiness to the coating layer.

The average particle size of the lubricant particles is preferably 200 nm or more, more preferably 250 nm or more, still more preferably 300 nm or more, and particularly preferably 350 nm or more. When the average particle size of the lubricant particles is 200 nm or more, it is preferable that the lubricant particles are less likely to aggregate and the slipperiness can be ensured.

The average particle size of the lubricant particles is preferably 2000 nm or less, more preferably 1500 nm, still more preferably 1000 nm, and particularly preferably 700 nm. When the average particle size of the lubricant particles is 2000 nm or less, transparency is maintained and the particles do not fall off, which is preferable.

The lubricant particles may be surface-treated, and the surface treatment methods include physical surface treatment such as plasma discharge treatment and corona discharge treatment and chemical surface treatment using a coupling agent, but the use of a coupling agent is used. Is preferable. As the coupling agent, an organoalkoxy metal compound (eg, titanium coupling agent, silane coupling agent) is preferably used. When the lubricant particles, which are the inorganic ultrafine particle fillers, are silica, the silane coupling agent treatment is particularly effective. The surface treatment may be applied in advance before the preparation of the coating liquid, or it may be added as an additive at the time of preparation of the coating liquid and contained in the coating layer.

The binder resin constituting the coating layer is not particularly limited as long as it is a resin that provides easy adhesion, but specific examples of the polymer include polyester resin, acrylic resin, urethane resin, polyvinyl resin (polyvinyl alcohol, etc.), and poly. Examples thereof include alkylene glycol, polyalkyleneimine, methyl cellulose, hydroxy cellulose, and starches. Among these, it is preferable to use polyester resin, acrylic resin, and urethane resin from the viewpoint of particle retention and adhesion. Further, considering the compatibility with the polyester film, the polyester resin is the most suitable. These binder resins may be used in combination.

The polyester resin may be contained in the coating layer in an amount of 100% by mass, but preferably 10% by mass or more and 90% by mass or less in the total solid component. More preferably, it is 20% by mass or more and 80% by mass or less. When the content of the polyester resin is 90% or less, the adhesion to the hard coat layer under high temperature and high humidity is maintained, which is preferable. On the contrary, when the content is 10% by mass or more, the adhesion with the polyester film at room temperature and high temperature and high humidity is maintained due to the presence of other urethane resins and the like, which is preferable.

In the present invention, the coating layer may be formed by containing a cross-linking agent in order to form a cross-linking structure in the coating layer. By containing a cross-linking agent, it becomes possible to further improve the adhesion under high temperature and high humidity. Specific examples of the cross-linking agent include urea-based, epoxy-based, isocyanate-based, oxazoline-based, and carbodiimide-based. Among these, melamine-based, isocyanate-based, oxazoline-based, and carbodiimide-based cross-linking agents are preferable because of the stability of the coating liquid over time and the effect of improving adhesion under high-temperature and high-humidity treatment. Further, in order to promote the cross-linking reaction, a catalyst or the like can be appropriately used as needed.

The content of the cross-linking agent in the coating layer is preferably 5% by mass or more and 50% by mass or less in the total solid components. More preferably, it is 10% by mass or more and 40% by mass or less. When it is 5% by mass or more, the strength of the resin of the coating layer is maintained, and there is no possibility that the adhesion under high temperature and high humidity is deteriorated, which is preferable. On the other hand, when it is 50% by mass or more, the flexibility of the resin of the coating layer is maintained, and the adhesion at normal temperature and high temperature and high humidity is maintained, which is preferable.

The content of the lubricant particles in the coating layer is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and further preferably 1% by mass or more. When the content of the lubricant particles in the coating layer is 0.1% by mass or more, it is preferable that appropriate slipperiness is maintained.

The content of the lubricant particles in the coating layer is preferably 20% by mass or less, more preferably 15% by mass or less, and further preferably 10% by mass or less. When the content of lubricant particles in the coating layer is 20% by mass or less, haze is kept low and transparency is preferable.

The film thickness of the coating layer is preferably 0.001 μm or more, more preferably 0.01 μm or more, still more preferably 0.02 μm or more, and particularly preferably 0.05 μm or more. When the film thickness of the coating layer is 0.001 μm or more, the adhesiveness is good and it is preferable.

The film thickness of the coating layer is preferably 2 μm or less, more preferably 1 μm or less, still more preferably 0.8 μm or less, and particularly preferably 0.5 μm or less. When the film thickness of the coating layer is 2 μm or less, blocking may not occur, which is preferable.

The coating layer may contain a surfactant for the purpose of improving the leveling property at the time of coating and defoaming the coating liquid. The surfactant may be any of a cationic type, an anionic type, a nonionic type and the like, but a silicone type, an acetylene glycol type or a fluorine type surfactant is preferable. It is preferable that these surfactants are contained in the coating layer to the extent that the effect of suppressing iris-like color and the adhesion are not impaired under fluorescent light.

In order to impart other functionality to the coating layer, various additives may be contained to the extent that the effect of suppressing iris-like color under fluorescent light and the adhesion are not impaired. Examples of the additive include fluorescent dyes, fluorescent whitening agents, plasticizing agents, ultraviolet absorbers, pigment dispersants, defoaming agents, defoaming agents, preservatives and the like.

As the coating method, either a so-called in-line coating method in which the polyester film is applied at the same time as the film is formed and a so-called offline coating method in which the polyester film is applied separately with a coater after the film is formed can be applied, but the in-line coating method is efficient. Is more preferable.

As a method for applying the coating liquid to the polyester film, any known method can be used. For example, reverse roll coat method, gravure coat method, kiss coat method, die coater method, roll brush method, spray coat method, air knife coat method, wire bar coat method, pipe doctor method, impregnation coat method, curtain coat method, etc. Be done. These methods are applied alone or in combination.

In the present invention, as a method of providing a coating layer on the polyester film, a method of applying a coating liquid containing a solvent, particles and a resin to the polyester film and drying it can be mentioned. Examples of the solvent include an organic solvent such as toluene, water, or a mixed system of water and a water-soluble organic solvent, but preferably, from the viewpoint of environmental problems, water alone or a water-soluble organic solvent is mixed with water. The one is preferable.

The solid content concentration of the coating liquid depends on the type of the binder resin, the type of the solvent, and the like, but is preferably 2% by mass or more, and more preferably 4% by mass or more. The solid content concentration of the coating liquid is preferably 35% by mass or less, more preferably 15% by mass or less.

The drying temperature after coating also depends on the type of binder resin, the type of solvent, the presence or absence of a cross-linking agent, the solid content concentration, and the like, but is preferably 80 ° C. or higher, and preferably 250 ° C. or lower.

The surface roughness (Ra) of the coating layer is related to the slipperiness of the surface of the coating layer and is preferably 0.01 nm or more, more preferably 0.1 nm or more, and further preferably 0.2 nm. The above is particularly preferable, and it is 0.5 nm or more. On the other hand, the upper limit of the surface roughness (Ra) of the coating layer is preferably 200 nm or less, more preferably 100 nm or less, further preferably 80 nm or less, and particularly preferably 50 nm or less.

(Manufacturing of polyester film)
The polyester film of the present invention can be produced according to a general method for producing a polyester film. For example, an unoriented polyester sheet or film obtained by melting a polyester resin and extruding it into a sheet is stretched in the vertical direction at a temperature equal to or higher than the glass transition temperature, if necessary, by utilizing the speed difference of the rolls. Alternatively, a method of laterally stretching and heat-treating at a temperature equal to or higher than the glass transition temperature by a tenter without performing the above-mentioned longitudinal stretching can be mentioned.

Although the polyester film of the present invention is considered to be widely applicable, it is suitably applied to optical films, particularly a polarizing element protective film application.

The polyester film for protecting the extruder may be a uniaxially stretched film or a biaxially stretched film, but when the biaxially stretched film is used as the polarizing element protective film, it depends on the in-plane retardation of the film. Although rainbow-shaped color spots are not seen when observed from directly above the film surface, care must be taken because rainbow-shaped color spots may be observed when observed from an oblique direction.

In this phenomenon, the biaxially stretched film consists of a refractive index ellipsoid having different refractive indexes in the traveling direction, the width direction, and the thickness direction, and the retardation becomes zero depending on the light transmission direction inside the film (refractive index ellipsoid). This is because there is a direction (where the body looks like a perfect circle). Therefore, when the liquid crystal display screen is observed from a specific diagonal direction, a point where the retardation becomes zero may occur, and a rainbow-shaped color spot may occur concentrically around the point. If the angle from directly above the film surface (normal direction) to the position where the rainbow-shaped color spots can be seen is θ, this angle θ increases as the birefringence in the film surface increases, and the rainbow-shaped color. The spots are hard to see. Since the angle θ tends to be small in the biaxially stretched film, the uniaxially stretched film is preferable because the iridescent color spots are difficult to see.

However, in a completely uniaxial (uniaxially symmetric) film, the mechanical strength in the direction orthogonal to the orientation direction may be significantly reduced, so that the present invention is in a range that does not substantially generate iridescent color spots. Or, it is also preferable to have biaxiality (biaxial symmetry) in a range that does not cause iridescent color spots in the viewing angle range required for the liquid crystal display screen.

The polyester film used for the stator protective film application preferably has an in-plane retardation of 3000 to 30,000 nm. When the in-plane retardation is 3000 nm or more, when it is used as a polarizing element protective film, it does not exhibit a strong interference color when observed from an oblique direction, and good visibility can be ensured, which is preferable. The lower limit of the preferred in-plane retardation is 4500 nm, the more preferable lower limit is 5000 nm, the more preferable lower limit is 6000 nm, the particularly preferable lower limit is 8000 nm, and the most preferable lower limit is 10000 nm.

On the other hand, the preferred upper limit of in-plane retardation is 30,000 nm. Even if a polyester film having an in-plane retardation of more than 30,000 nm is used, the effect of further improving visibility is substantially saturated. Further, if the film is 30,000 nm or less, the thickness of the film does not become too thick, and the film is easy to handle as an industrial material, which is preferable.

The in-plane retardation in the present invention can be obtained by measuring the refractive index and the thickness in the biaxial direction, or can be obtained by using a commercially available automatic birefringence measuring device such as KOBRA-21ADH (Oji Measuring Instruments Co., Ltd.). You can also do it. The measurement wavelength of the refractive index is 589 nm.

Specifically explaining the film forming conditions of the polyester film of the present invention, the longitudinal stretching temperature and the transverse stretching temperature are preferably 80 to 130 ° C, particularly preferably 90 ° C to 120 ° C. The longitudinal stretching ratio is preferably 1.0 to 3.5 times, and particularly preferably 1.0 to 3.0 times. The lateral stretching ratio is preferably 2.5 to 6.0 times, and particularly preferably 3.0 to 5.5 times. In order to control the in-plane retardation, it is preferable to control the ratio between the longitudinal stretching ratio and the transverse stretching ratio. It is preferable to increase the difference in the vertical and horizontal stretching ratios because the retardation can be increased. Further, setting the stretching temperature low is also a preferable measure for increasing the retardation. In the subsequent heat treatment, the treatment temperature is preferably 100 to 250 ° C, particularly preferably 180 to 245 ° C.

In order to suppress fluctuations in retardation, it is preferable that the thickness unevenness of the film is small. Since the stretching temperature and the stretching ratio affect the film thickness unevenness, it is preferable to optimize the film forming conditions from the viewpoint of the thickness unevenness.

The thickness unevenness of the film of the present invention is preferably 5.0% or less, more preferably 4.5% or less, further preferably 4.0% or less, and more preferably 3.0% or less. It is particularly preferable to have.

As described above, in order to control the in-plane retardation of the film within a specific range, it can be performed by appropriately setting the draw ratio, the draw temperature, and the thickness of the film. For example, the larger the difference in stretching ratio between the vertical and horizontal directions, the lower the stretching temperature, and the thicker the film, the easier it is to obtain high in-plane retardation. On the contrary, the smaller the difference in the stretching ratio between the vertical and horizontal directions, the higher the stretching temperature, and the thinner the film, the easier it is to obtain low retardation. However, when the thickness of the film is increased, the phase difference in the thickness direction tends to increase. Therefore, it is desirable to appropriately set the film thickness within the range described later. Further, in addition to controlling the in-plane retardation, it is preferable to set the final film forming conditions in consideration of the physical characteristics required for processing and the like.

The thickness of the polyester film of the present invention is arbitrary, but is preferably in the range of 15 to 300 μm, more preferably in the range of 20 to 200 μm, and even more preferably in the range of 30 to 150 μm. In principle, it is possible to obtain 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, tearing, tearing, etc. are likely to occur, and the practicality as an industrial material is likely to be lowered, which is not very preferable. A particularly preferable lower limit of the thickness is 35 μm. On the other hand, it is preferable that the upper limit of the thickness of the polarizing element protective film is 300 μm or less because the thickness of the polarizing plate does not become too thick. From the viewpoint of practicality as a polarizing element 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 equivalent to that of a general TAC film. In order to control the in-plane retardation within the range of the present invention even within the above thickness range, polyethylene terephthalate is suitable as the polyester constituting the film.

The polyester film in the present invention preferably has a light transmittance of 20% or less at a wavelength of 380 nm for the purpose of suppressing deterioration of an optically functional dye such as an iodine dye. The light transmittance at 380 nm is more preferably 15% or less, further preferably 10% or less, and particularly preferably 5% or less. When the light transmittance is 20% or less, the alteration of the optical functional dye due to ultraviolet rays can be suppressed. The transmittance in the present invention is measured in the direction perpendicular to the plane of the film, and can be measured using a spectrophotometer.

In order to reduce the transmittance of the polyester film of the present invention at a wavelength of 380 nm to 20% or less, it is desirable to appropriately adjust the type and concentration of the ultraviolet absorber contained in the polyester film and the thickness of the film. The UV 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, but an organic ultraviolet absorber is preferable from the viewpoint of transparency. Examples of the organic ultraviolet absorber include, but are not limited to, benzotriazole-based, benzophenone-based, cyclic iminoester-based, and combinations thereof. However, from the viewpoint of durability, benzotriazole-based and cyclic iminoester-based are particularly preferable. When two or more kinds of ultraviolet absorbers are used in combination, ultraviolet rays having different wavelengths can be absorbed at the same time, so that the ultraviolet absorption effect can be further improved.

Examples of the ultraviolet absorber include a benzophenone-based ultraviolet absorber, a benzotriazole-based ultraviolet absorber, and an acrylonitrile-based ultraviolet absorber, for example, 2- [2'-hydroxy-5'-(methacryloyloxymethyl) phenyl] -2H-benzotriazole. , 2- [2'-Hydroxy-5'-(methacryloxyethyl) phenyl] -2H-benzotriazole, 2- [2'-hydroxy-5'-(methacryloxypropyl) phenyl] -2H-benzotriazole, 2 , 2'-Dihydroxy-4,4'-dimethoxybenzophenone, 2,2', 4,4'-tetrahydroxybenzophenone, 2,4-di-tert-butyl-6- (5-chlorobenzotriazole-2-yl) ) Phenol, 2- (2'-hydroxy-3'-tert-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2- (5-chloro (2H) -benzotriazole-2-yl) -4 -Methyl-6- (tert-butyl) phenol, 2,2'-methylenebis (4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazole-2-yl) phenol, etc. Examples of the cyclic iminoester-based ultraviolet absorber include 2,2'-(1,4-phenylene) bis (4H-3,1-benzoxadinone-4-one), 2-methyl-3,1-. Examples thereof include benzoxazine-4-one, 2-butyl-3,1-benzoxazine-4-one, 2-phenyl-3,1-benzoxazine-4-one, etc., but are not particularly limited thereto. do not have.

Further, as a method of blending the ultraviolet absorber into the polyester film in the present invention, a known method can be used in combination. For example, a kneading extruder is used in advance to blend the dried ultraviolet absorber and the polymer raw material. A masterbatch can be prepared and blended by a method of mixing a predetermined masterbatch with a polymer raw material at the time of film formation.

At this time, the concentration of the ultraviolet absorber in the masterbatch is preferably 5 to 30% by mass in order to uniformly disperse the ultraviolet absorber and to blend it economically. As a condition for producing a masterbatch, it is preferable to use a kneading extruder and extrude at a temperature equal to or higher than the melting point of the polyester raw material and not higher than 290 ° C. in 1 to 15 minutes. At 290 ° C. or higher, the amount of the ultraviolet absorber is greatly reduced, and the viscosity of the masterbatch is significantly reduced. If the extrusion temperature is 1 minute or less, it becomes difficult to uniformly mix the ultraviolet absorbers. At this time, a stabilizer, a color tone adjusting agent, and an antistatic agent may be added as needed.

Further, in the present invention, it is preferable that the polyester film has a multilayer structure of at least three layers or more, and an ultraviolet absorber is added to the intermediate layer of the film. Specifically, a polyester film having a structure of three or more layers containing an ultraviolet absorber in the intermediate layer can be produced as follows. A polyester pellet alone for both surfaces, a masterbatch containing an ultraviolet absorber for the intermediate layer and a polyester pellet are mixed in a predetermined ratio, dried, and then supplied to a known melt laminate extruder to form a slit. It is extruded from a die into a sheet and cooled and solidified on a casting roll to form an unstretched film. That is, using two or more extruders, three or more layers of manifolds or a merging block (for example, a merging block having a square merging portion), both surface layers and a film layer constituting an intermediate layer are included and laminated. Extrude three or more layers of sheets from the base and cool with a casting roll to make an unstretched film. In the present invention, in order to remove foreign substances contained in the raw material polyester, which causes optical defects, it is preferable to perform high-precision filtration at the time of melt extrusion. The filtered 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 filtered particle size of the filter medium is 15 μm or less, it is preferable that foreign matter of 20 μm or more is sufficiently removed.

For the polyester film of the present invention, it is preferable to use a self-recovered polymer raw material.

Here, a method for producing a self-recovery raw material will be described. The scrap film at the end of the film, which was slit in the machine flow direction from the product and cut and removed, was crushed and dried at a glass transition temperature of about 160 ° C. to remove water. The dried crushed film is melted by an extruder, discharged from a die in a strand shape, and rapidly cooled and solidified with cold water. The solidified strand is cut into a pellet shape by a strand cutter, and then the surface is dried to prevent fusion to obtain a self-recovery pellet.

The water content after drying is preferably 10 ppm or less. When it is 10 ppm or less, the hydrolysis of the polymer is difficult to accelerate and there is no possibility of causing a decrease in intrinsic viscosity, which is preferable.

Both ends of the film of the master roll have a non-uniform film thickness, and the film quality is poor due to the influence of clip marks that are caught during transportation in the tenter, and they are usually cut off. Note that, depending on the coating layer laminated on the cut portion, foreign matter may be mixed, colored, or turbid in the polyester film produced using this self-recovery raw material. It takes.

In the present invention, the coating layer at both ends of the master roll that is slit and cut off is a coating layer having characteristics such as easy adhesion required for a polyester film, which is a product suitably used for the above-mentioned polarizing element protective film. Unlike the coating composition for laminating the product polyester film, the product polyester film has a different coating composition that does not easily cause foreign matter to be mixed, colored or turbid even if it is re-injected as a part of the raw material polyester of the product polyester film. It is preferable that the coating layer is separately applied without overlapping with the coating layer laminated on the top, and the portion to which the coating liquid is separately applied located at both ends in the width direction of the master roll is cut off and used as a self-recovery raw material.

The coating liquid to be separately applied, which is located at both ends in the film width direction, is not particularly limited as long as it has a composition capable of producing a self-recovering raw material. However, in consideration of the stability and safety of the composition used, it is preferable that the resin composition is a coating liquid containing water as a main medium.

The water-based coating liquid may contain a small amount of an organic solvent for the purpose of assisting the stability of the coating liquid. Examples of the organic solvent include methyl ethyl ketone, acetone, ethyl acetate, tetrahydrofuran, dioxane, cyclohexanone, n-hexane, toluene, xylene, methanol, ethanol, 1-propanol and 2-propanol. A plurality of types of organic solvents may be contained.

The above-mentioned aqueous coating liquid contains known additives such as heat-resistant stabilizers, oxidation-resistant stabilizers, weather-resistant stabilizers, ultraviolet absorbers, organic lubricants, organic and inorganic fine particles as long as the effects of the present invention are not impaired. Etc. may be added.

As the coating method, any known coating method may be applied. For example, any method such as reverse coat method, gravure coat method, micro gravure coat method, rod coat method, die coat method, roll coat method, roll brush method, spray coat method, air knife coat method, curtain coat method, etc. may be used. Can be done.

In the present invention, the separate coating layers at both ends of the film width direction are applied to at least one side of both ends of the polyester film, but are applied before the crystal orientation of the polyester film is completed, and then stretched in at least one direction. , The method of completing the crystal orientation of the polyester film is preferable because the effect of the present invention can be more remarkably exhibited.

The coating amount is preferably 2 g or more and 15 g or less, more preferably 4 g or more and 13 g or less per 1 m ² . The thickness of the final dry coating film is preferably 0.001 μm or more, more preferably 0.01 μm or more, still more preferably 0.02 μm or more, and particularly preferably 0.05 μm or more. .. When the film thickness of the coating layer is 0.001 μm or more, the slipperiness can be sufficiently ensured, the slipperiness to the film roll is improved, and the film roll having few defects such as scratches can be obtained.

The film thickness of the coating layer is preferably 2 μm or less, more preferably 1 μm or less, still more preferably 0.8 μm or less, and particularly preferably 0.5 μm or less. When the film thickness of the coating layer is 2 μm or less, blocking may not occur, which is preferable.

In the present invention, a water-based coating liquid is applied to the polyester base material, and then a drying and stretching treatment is performed. This drying depends on the type of binder resin, the type of solvent, the presence or absence of a cross-linking agent, the solid content concentration, and the like. , 80 ° C or higher, preferably 250 ° C or lower.
The stretching treatment conforms to the above-mentioned polyester film film forming method, and it is preferable that the conditions are adjusted accordingly.

In addition to the above, the self-recovery raw material can be made into a self-recovery raw material by peeling off the coating layer from the ear roll at the end of the slit roll or the downgraded roll that does not meet the product specifications. be able to.

The method for peeling off the coating layer is not particularly limited as long as it does not cause problems such as contamination of the film after peeling, but only the coating layer chemically and physically such as sandblasting. There is a method of peeling off and leaving only the resin layer, and this method may be applied also in the present invention.

The polyester film for a polarizing element protective film in the present invention preferably has a b value indicating yellowish-blueishness in the vicinity of zero even when a self-recovery raw material is used. When the b value is 3.0 or less, the film does not appear yellowish, and when applied to a polarizing element protective film, there are no problems such as deterioration of image quality and discoloration, which is preferable. Further, when the b value is −0.5 or more, the film does not look blue and does not give a dark impression, which is preferable.

The same applies to the haze of the film, which is preferably 2.0% or less, and when it is 2.0% or less, transparency is maintained and there is no risk of causing display of a liquid crystal display or the like, which is preferable.

The intrinsic viscosity of the polyester film obtained by the present invention is preferably 0.55 dl / g or more, more preferably 0.56 dl / g or more, still more preferably 0.57 dl / g or more. be. When the intrinsic viscosity is 0.55 dl / g or more, the mechanical strength of the film is maintained, and there is no possibility that problems in film formation stability and fracture resistance occur, which is preferable.

The intrinsic viscosity of the polyester film obtained by the present invention is preferably 0.65 dl / g or less, more preferably 0.64 dl / g or less, still more preferably 0.63 dl / g or less. be. When the intrinsic viscosity is 0.65 dl / g or less, the film does not become too hard and it is difficult to cause cutting defects when cutting off both end portions in the film width direction with a slitter, so that the cutting quality and the cutting state are good, which is preferable.

Here, the intrinsic viscosity of the produced polyester film can be obtained by dissolving the polyester film in a specific solvent and evaluating the solution in a viscosity tube.

In the polyester film of the present invention, it is preferable that the number of whiskers (including cutting irregularities such as burrs and fluffy substances) protruding from the slit end face by 5 μm or more is one or less per 100 μm of the film length.

The fact that the number of whiskers (cutting disorder) protruding from the end face of the film by 5 μm or more in the polyester film is within 1 per 100 μm of the film length means that the end face of the film slit by a slitter in the mechanical flow direction is electron-micrographed. Observing with a microscope or an optical microscope, the number of whiskers (cutting disorder) protruding from the end face of the film at a size of 5 μm or more per 100 μm is counted, and the number is one or less. ..

If this whiskers (disordered cutting) is less than 5 μm and protrudes from the end face, it does not have a significant effect on the uptake and adhesion of foreign matter during transportation and handling when applied to the polarizing element protective film. Moreover, since it is easy to remove the adhered foreign matter, no particular problem is required.

In order to obtain a polyester film in which the number of whiskers (cutting disorder) protruding from the slit end face of the polyester film of the present invention is 5 μm or more within one per 100 μm of the film length, the film end face of the present invention is obtained by the slit method. The method is not particularly limited as long as it can be used, but preferably a method of applying a laser beam as a slit means (a laser beam oscillator irradiates the film surface with a beam, and the film is instantly melted or evaporated by the irradiation energy of the laser. A method of slitting along the scanning locus of the beam, in which various oscillators such as carbon dioxide laser, argon laser, and YAG laser are applied to irradiate the laser beam.), Blades (Thomson blades, rotary blades, etc.) ) Slit method and the like.

When a method of slitting with a blade (Thomson blade, rotary blade, etc.) is adopted, it is necessary to replace the blade or update the cutting edge under certain conditions. For example, when slitting a polyester film, the cutting area is large. The polyester film of the present invention can be obtained by replacing the blade or renewing the cutting edge so as not to exceed 200 m ² or more preferably 160 m ² , for example, a 100 μm film is used at 150 m / min for 7 consecutive days. When slitting at the speed of, it becomes 151 m ² , and it is preferable to replace the blade or renew the blade at this point.

The amount of the self-recovery raw material added is not particularly limited as long as it satisfies the above-mentioned film characteristics, but the mass ratio of the layer to which the self-recovery raw material of the film is added is 3 mass. % Or more, more preferably 5% by mass, still more preferably 7% by mass or more, and particularly preferably 8% by mass or more. When it is 3% by mass or more, the intrinsic viscosity of the obtained film can be easily adjusted to 0.65 dl / g or less, the elastic modulus of the film is not too high, and the whiskers protruding from the end face are reduced, which is preferable.

The amount of the self-recovery raw material added is not particularly limited as long as it satisfies the above-mentioned film characteristics, but the mass ratio of the layer to which the self-recovery raw material of the film is added is 30 mass. % Or less, more preferably 28% by mass or less, still more preferably 26% by mass or less, and particularly preferably 25% by mass or less. When it is 30% by mass or less, the intrinsic viscosity of the film tends to be 0.55 dl / g or more, the mechanical strength of the film is maintained, and it is preferable from the viewpoints of film forming stability, fracture resistance and the like.

The polyester film of the present invention reduces the whiskers on the end face of the slit. It was found that the intrinsic viscosity of the resin at the time of film molding is related to the reduction of the number of whiskers, and by controlling the intrinsic viscosity of the resin within a certain range, the whiskers on the end face of the slit can be preferably reduced. ..

In terms of the strength of the obtained polyester film, the intrinsic viscosity of the polyester constituting the film having a certain height is desirable, and in order to realize them, the polyester is composed on both sides of the intermediate layer composed of the polyester. It is preferable to have a laminated structure of three or more layers having at least a surface layer, both surface layers being a polyester layer having a relatively high intrinsic viscosity, and the intermediate layer being a polyester layer having a relatively low intrinsic viscosity. In particular, it is preferable that the intermediate layer contains a self-recovering polymer having a low intrinsic viscosity generated in the process of manufacturing the polyester film.

Here, the intrinsic viscosity of both surface layers of the polyester film having such a laminated structure of three or more layers is preferably 0.63 dl / g or more, more preferably 0.64 dl / g or more, and further. It is preferably 0.65 dl / g. When the intrinsic viscosity is 0.63 dl / g or more, the intrinsic viscosity of the entire film is not too low, and there is no problem such as breakage during film formation, which is preferable.

Further, the intrinsic viscosity of both surface layers of the polyester film having such a laminated structure of three or more layers is preferably 0.67 dl / g or less, more preferably 0.66 dl / g or less, and further preferably. Is 0.65 dl / g. When the intrinsic viscosity is 0.67 dl / g or less, the intrinsic viscosity of the resin is not too high, the pressure applied to the filter or the like at the time of extrusion does not become too large, and there is no problem of ejection failure or thickness unevenness, which is preferable.

Further, the intrinsic viscosity of the intermediate layer of the polyester film having such a laminated structure of three or more layers is preferably 0.56 dl / g or more, more preferably 0.57 dl / g or more, and further preferably 0.57 dl / g or more. , 0.58 dl / g or more. When the intrinsic viscosity is 0.56 dl / g or more, the intrinsic viscosity of the entire film is not too low, and there is no problem such as breakage during film formation, which is preferable.

Here, the intrinsic viscosity of the intermediate layer of the polyester film obtained by the present invention is preferably 0.62 dl / g or less, more preferably 0.61 dl / g or less, and further preferably 0. It is .60 dl / g or less. When the intrinsic viscosity is 0.62 dl / g or less, the intrinsic viscosity of the resin does not become too high, the pressure applied to the filter during extrusion is not high, and the film can be formed without causing ejection failure, so the target thickness is controlled. It is easy to do and the thickness unevenness is small.

Here, the intrinsic viscosity (dl / g) of each layer of the polyester film having a laminated structure of three or more layers is the fluid viscosity obtained from an online viscometer such as a thin tube viscometer provided in the pipe at the time of each melt extrusion. It can be obtained by converting from the measurement temperature (° C.) or the like, and the intrinsic viscosity (dl / l) can be obtained by a conversion formula programmed in advance.

The intrinsic viscosity of the resin can control the intrinsic viscosity of the obtained polyester film and reduce the generation of whiskers, but it is also important in the layer structure of the polyester film, and there is a coating layer. Taking only the three-layer structure of polyester excluding the above as an example, the thickness composition ratio can be controlled between 4: 92: 4 and 13:74:13 (as surface layer: intermediate layer: surface layer). It is preferable to control between 5:90: 5 and 10:80:10. When the thickness ratio of both surface layers is 4% or more, the film haze does not increase due to the bleed-out of the ultraviolet absorber and other additives added to the intermediate layer, which is preferable.

When the ratio of both surface layers is 13% or less, the intrinsic viscosity of the obtained polyester film does not become too high, and the effect of suppressing the generation of whiskers becomes clear, which is preferable.

Generally, the polarizing plate has a structure in which a polarizing element protective film is laminated on both sides of a polarizing element, and it is preferable that at least one of the polarizing element protective films is the polyester film of the present invention. As the polarizing element, a film in which polyvinyl alcohol (PVA) is mainly used and iodine compound molecules are adsorbed and oriented is usually used.

Further, in the present invention, it is also preferable to use a polarizing element protective film in which various hard coat layers are laminated on the surface for the purpose of preventing reflection, suppressing glare, suppressing scratches, etc., as the polarizing plate. It is preferable that the surfaces having the above are laminated so as to be provided on the side not in contact with the polarizing element.

In the liquid crystal display device of the present invention, polarizing plates are arranged on both sides of a liquid crystal cell, and a backlight is used as a light source such as a cold cathode fluorescent tube (CCFL) or a light emitting diode (LED) arranged on one surface. It is a device that displays images and the like. It is preferable that the polarizing plate of the present invention is used for at least one of the two polarizing plates. The liquid crystal display device may appropriately have, for example, a color filter, a lens film, a diffusion sheet, an antireflection film, and the like as other constituent members other than these.

The backlight may be configured by an edge light system in which a light guide plate or a reflector is made of steel, or a direct type system, but a white LED is used as the backlight source of the liquid crystal display device. Is preferable.
The white LED is a phosphor type, that is, an element that emits white light by combining an LED that emits blue light using a compound semiconductor or an ultraviolet light and a phosphor. Examples of the fluorescent material include yttrium / aluminum / garnet-based yellow fluorescent material and terbium / aluminum / garnet-based yellow fluorescent material. Among them, a blue LED using a compound semiconductor and yttrium / aluminum / garnet-based yellow fluorescent material are used. A white LED composed of a light emitting element combined with a body has a continuous and wide emission spectrum and is also excellent in emission efficiency, so that energy saving can be expected.

A method of combining LEDs that emit red, green, and blue colors (three-color LED method) has also been put into practical use, but this method has a narrow and discontinuous emission spectrum, and is used as a conventional backlight source. It should be noted that the widely used fluorescent tube such as CCFL also has a peak at a specific wavelength and has a discontinuous emission spectrum, so that the effect of the present invention may not be sufficiently obtained.

The arrangement of the polarizing element protective film of the present invention in the liquid crystal display device is not particularly limited, but is arranged on the polarizing plate arranged on the incident light side (light source side) and on the liquid crystal cell and the emitted light side (visual recognition side). In the case of a liquid crystal display device having a polarizing plate, it is preferable that the polarizing plate is arranged on the incident light side of the polarizing plate arranged on the incident light side or on the emitted light side of the polarizing plate arranged on the emitted light side. It is more preferable that the polarizing plate is arranged on the emitted light side of the polarizing plate. When the polarizing element protective film of the present invention is placed at a position other than the above, the polarization characteristics of the liquid crystal cell may be changed. On the other hand, it is preferable to use a film having no in-plane retardation as represented by a TAC film, an acrylic film, and a norbornene-based resin film on the surface on which the polarizing element protective film of the present invention is not used.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited by the following examples, and is appropriately modified to the extent that it can be adapted to the gist of the present invention. It is possible to do so, all of which are within the technical scope of the invention.

The evaluation methods in the examples and various physical property evaluation methods described in the text are shown below.

(1) Average particle size [Measurement method using scanning electron microscope]
The average particle size of the particles used for the coating layer or the like can be measured by the following method. The particles are photographed with a scanning electron microscope (SEM), and the maximum diameter of 300 to 500 particles (distance between the two farthest points) is magnified so that the size of one of the smallest particles is 2 to 5 mm. ), And the average value is taken as the average particle size. The average particle size of the particles present in the coating layer in the present invention can be measured by the measuring method.

(2) Intrinsic Viscosity of Resin As the intrinsic viscosity of the resin of each layer in the present invention, the fluid viscosity at the time of melt molding is evaluated, and the online viscosity meter VIS (manufactured by Gneuss) provided in the pipe of the molten fluid is used. Evaluation was performed and the intrinsic viscosity (dl / l) was obtained by a pre-programmed conversion formula.

(3) Film thickness (d)
The thickness d was determined in accordance with JIS K 7130-1999 "Method for measuring thickness of plastic film and sheet (method A)".

(4) Refractive index (Nx, Ny, Nz)
Refractive index in MD direction (Nx), Refractive index in TD direction (Ny), Refractive index in thickness direction (Nz) in accordance with JIS K 7142-2014 "Refractive index measurement method for plastic film (Method A)". Asked. The measurement wavelength was 589 nm.

(5) Birefringence (ΔNxy), in-plane retardation (Re)
The retardation is the refractive index (Nx) in each axial direction of the film in the thickness direction (Z-axis) with respect to the film surface and in two axial directions (x-axis and y-axis) perpendicular to the thickness direction and also orthogonal to each other. , Ny, Nz), which is the phase difference represented by the product of the double refraction and the thickness d of the film. Here, it is incident on the film surface (xy plane) with MD as the x-axis and TD as the y-axis. The in-plane retardation, which is the product of the double refraction Nxy generated by light and the thickness d, was obtained from the following equation. As is customary, the unit of in-plane retardation is nm.
ΔNxy = | Nx-Ny |
Re = Nxy / d

(6) Thickness direction retardation (Rth)
The thickness direction retardation is based on the light incident on the film surface in the thickness direction (z-axis) and in two axial directions (x-axis and y-axis) that are orthogonal to the film surface and also orthogonal to each other. It shows the retardation that occurs, and here, it is obtained from the following equation as the product of the average of the two compound refractions of the x-z plane and the yz plane and the film thickness d. As is customary, the unit is nm.
Rth = (| Nx-Nz | + | Ny-Nz |) / 2xd

(7) Intrinsic viscosity of the entire produced film and raw material pellets JIS K 7376-2002 "Plastic-How to determine the viscosity of the diluted solution using a capillary viscometer-Part 5: Thermoplastic polyester (TP) homopolymer and In accordance with "Copolymer", the value when the mass concentration c = 0 is defined as the intrinsic viscosity (iV) from the relationship of the viscosity number with respect to the mass concentration c of the solution under the following measurement conditions with respect to the obtained viscosity number. did.
Solvent: Phenol / 1, 1, 2, 2-tetrachloroethane = 60/40 (wt%)
Tube: Ubbelohde viscous tube Temperature: 30 ± 0.1 ° C

(8) Observation of rainbow spots In the film of the example and comparative example prepared by the method described later on one side of a commercially available polarizing element, the absorption axis of the polarizing element and the orientation main axis of the film (the higher of Nx and Ny) are perpendicular to each other. A commercially available TAC film was attached to the opposite surface thereof to prepare a polarizing element. This was carried out by removing the polarizing plate on the emission light side of a commercially available liquid crystal display device having a liquid crystal cell sandwiched between polarizing plates having a white LED as a backlight and two TAC films as a polarizing element protection film. The films of the example and the comparative example were installed so as to be on the emission light side, and visual observation was performed from the front of the liquid crystal display device and from an oblique direction, and the occurrence of iris spots was determined as follows.
○: No rainbow spots occur from any direction ×: Rainbow spots can be clearly observed when observed from an oblique direction.

(9) Thickness fluctuation rate in the width direction A continuous tape-shaped sample having a length of 3 m in the width direction and 5 cm in the longitudinal direction is wound up, and the film thickness is measured by a film thickness continuous measuring machine (manufactured by Anritsu Co., Ltd.). Measure and record on the recorder. From the chart, the maximum value (dmax), the minimum value (dmin), and the average value (d) of the thickness were obtained, and the thickness fluctuation rate (%) was calculated by the following formula. The measurement was performed three times, and the average value was obtained. If the length in the width direction is less than 3 m, they are joined together. The connecting part is deleted from the data.
Thickness volatility (%) = ((dmax-dmin) / d) x 100
The average value was obtained as the thickness fluctuation rate (%) in the width direction, and the judgment was made according to the following criteria.
○: Thickness fluctuation rate in the width direction is 3% or less △: Thickness fluctuation rate in the width direction is 5% or less ×: Thickness fluctuation rate in the width direction is more than 5%

(10) Film transparency (haze)
Measurement was performed using a turbidity meter (Nippon Denshoku Co., Ltd., NDH2000) in accordance with JIS K 7136-2000 "Plastic-How to determine haze of transparent material".

(11) Color tone (b value)
Measurement was performed using a colorimetric color difference meter (manufactured by Nippon Denshoku Co., Ltd., ZE2000) in accordance with JIS K 7373-2006 "Plastic-How to determine yellowness and yellowing degree".

(12) Surface roughness (Ra)
At Surfcom (registered trademark) 304B (manufactured by Tokyo Seimitsu Co., Ltd.) in accordance with JIS B 0601-2001 "Geometric characteristics specifications (GPS) of products-Surface texture; Contour curve method-Terms, definitions and surface texture parameters". Ra was measured. The measurement conditions were a cutoff of 0.08 μm, a stylus radius of 2 μm, a measurement length of 0.8 mm, and a measurement speed of 0.03 mm / sec.

(13) Glass transition temperature Measured using a differential scanning calorimeter (DSC6200, manufactured by Seiko Instruments) in accordance with JIS K 7121-2012 “Method for measuring transition temperature of plastic”. 10 mg of the resin sample was heated at 20 ° C./min over a temperature range of 25 ° C. to 300 ° C., and the extra glass transition start temperature obtained from the DSC curve was defined as the glass transition temperature.

(14) Number average molecular weight 0.03 g of resin was dissolved in 10 ml of tetrahydrofuran, and a column temperature was 30 ° C., a flow rate of 1 ml / min, and a column (column (LS-8000 manufactured by Tosoh Corporation) using a GPC-LALLS device low angle light scattering photometer). The number average molecular weight was measured using shodex KF-802, 804, 806) manufactured by Showa Denko KK.

(15) Resin composition The resin is dissolved in deuterated chloroform, 1H-NMR analysis is performed using a nuclear magnetic resonance spectrometer (NMR) Gemini-200 manufactured by Varian, and the mol% ratio of each composition is determined from the integral ratio. did.

(16) Membrane-forming stability (transmembrane property)
The presence or absence of film breakage during the process from the stabilization of the process temperature to the formation of a film having a film length of 5,000 m was investigated.
○: Stable film formation is possible (breakage does not occur)
△: Slightly unstable running (rarely, breakage may occur)
×: Frequently broken and unable to form a stable film

(17) Measurement of whiskers on the end face of the film The slit end face of the polyester film slit with a slitter along the machine flow direction is observed under an optical microscope or a scanning electron microscope at a magnification of 500 to 3000 times, and a photograph is taken. From the images obtained above, the protrusions of beard-like objects of 5 μm or more per 100 μm of different slit end face positions were counted, and the counts at 10 positions were averaged and evaluated as the number of beard-like objects on the end face of the film.

(Manufacturing Example 1: Polyethylene terephthalate resin A)
When the temperature of the esterification reaction can was raised to 200 ° C., 86.4 parts by mass of terephthalic acid and 64.4 parts by mass of ethylene glycol were charged, and 0.017 parts by mass of antimony trioxide was added as a catalyst while stirring. , 0.064 parts by mass of magnesium acetate tetrahydrate and 0.16 parts by mass of triethylamine were charged. Then, the pressure was raised, and the pressure esterification reaction was carried out under the conditions of a gauge pressure of 0.34 MPa and 240 ° C., the esterification reaction can was returned to normal pressure, and 0.014 parts by mass of phosphoric acid was added. did. Further, the temperature was raised to 260 ° C. over 15 minutes, and 0.012 parts by mass of trimethyl phosphate was added. Then, after 15 minutes, the dispersion treatment was carried out with a high-pressure disperser, and after 15 minutes, the obtained esterification reaction product was transferred to a polycondensation reaction can, and the polycondensation reaction was carried out at 280 ° C. under reduced pressure. After completing the polycondensation reaction using the stirring torque as a guide, the cooled and solidified material is cut into pellets in cooling water in a strand state, and further dried under reduced pressure to have an intrinsic viscosity of 0.65 dl / g. Polyethylene terephthalate resin A (hereinafter referred to as resin A) was obtained.

(Manufacturing Example 2: Polyethylene terephthalate resin B)
Prepared in Production Example 1 containing 10 parts by mass of a dried ultraviolet absorber (2,2'-(1,4-phenylene) bis (4H-3,1-benzoxadinone-4-one) and no particles. 90 parts by mass of polyethylene terephthalate resin A was mixed, and a kneading extruder was used to obtain polyethylene terephthalate resin B (hereinafter, resin B) having an intrinsic viscosity of 0.58 dl / g containing an ultraviolet absorber.

(Manufacturing Example 3: Self-recovery polyethylene terephthalate resin C)
The scrap film at the end of the film cut and removed from the product was crushed and dried at 150 ° C. to remove water. The dried crushed film is melted by an extruder, discharged from a die in a strand shape, and rapidly cooled and solidified with cold water. The solidified strand is cut into pellets with a strand cutter, and then the surface is dried to prevent fusion, and a self-recovering polyethylene terephthalate resin C (hereinafter referred to as resin C) having an intrinsic viscosity of 0.50 dl / g is applied. Obtained.

(Manufacturing Example 4: Self-recovery polyethylene terephthalate resin D)
The ear rolls and non-standard products generated in the slit process were externally cleaned and peeled off. The obtained film from which the coating layers on both surfaces were peeled off was pulverized and dried at 150 ° C. to remove water. The dried crushed film is melted by an extruder, discharged from a die in a strand shape, and rapidly cooled and solidified with cold water. The solidified strand is cut into pellets with a strand cutter, and then the surface is dried to prevent fusion, and a self-recovering polyethylene terephthalate resin D (hereinafter referred to as resin D) having an intrinsic viscosity of 0.60 dl / g is applied. Obtained.

(Production Example 5: Coating liquid X1: Preparation of adhesive modification coating liquid)
(Polyester resin polymerization)
194.2 parts by mass of dimethylterephthalate, 184.5 parts by mass of dimethylisophthalate, 14.8 parts by mass of dimethyl-5-sodium sulfoisophthalate in a stainless steel autoclave equipped with a stirrer, a thermometer, and a partial reflux condenser. , 233.5 parts by mass of diethylene glycol, 136.6 parts by mass of ethylene glycol, and 0.2 parts by mass of tetra-n-butyl titanate were charged, and a transesterification reaction was carried out at a temperature of 160 ° C to 220 ° C for 4 hours. Then, the temperature was raised to 255 ° C., the reaction system was gradually reduced in pressure, and then the reaction was carried out under a reduced pressure of 30 Pa for 1 hour and 30 minutes to obtain a copolymerized polyester resin (D-1). The obtained copolymerized polyester resin was pale yellow and transparent. The reduced viscosity of the copolymerized polyester resin was measured and found to be 0.70 dl / g. The glass transition temperature by DSC was 40 ° C.

(Preparation of polyester aqueous dispersion)
30 parts by mass of the polyester resin and 15 parts by mass of ethylene glycol n-butyl ether were placed in a reactor equipped with a stirrer, a thermometer and a reflux device, and heated at 110 ° C. and stirred to dissolve the resin. After the resin was completely dissolved, 55 parts by mass of water was gradually added to the polyester solution with stirring. After the addition, the liquid was cooled to room temperature with stirring to prepare a milky white polyester aqueous dispersion having a solid content of 30% by mass.

(Preparation of aqueous polyvinyl alcohol solution)
90 parts by mass of water was placed in a container equipped with a stirrer and a thermometer, and 10 parts by mass of a polyvinyl alcohol resin (manufactured by Kuraray) having a degree of polymerization of 500 was gradually added while stirring. After the addition, the liquid was heated to 95 ° C. while stirring to dissolve the resin. After dissolution, the mixture was cooled to room temperature with stirring to prepare a polyvinyl alcohol aqueous solution having a solid content of 10% by mass.

(Polymerization of block polyisocyanate cross-linking agent)
100 parts by mass of a polyisocyanate compound (Duranate TPA manufactured by Asahi Kasei Chemicals Co., Ltd.) using hexamethylene diisocyanate as a raw material in a flask equipped with a stirrer, a thermometer, and a reflux cooling tube, 55 parts by mass of propylene glycol monomethyl ether acetate, polyethylene. 30 parts by mass of glycol monomethyl ether (average molecular weight 750) was charged and kept at 70 ° C. for 4 hours under a nitrogen atmosphere. Then, the temperature of the reaction solution was lowered to 50 ° C., and 47 parts by mass of methyl ethyl ketooxime was added dropwise. The infrared spectrum of the reaction solution was measured, and it was confirmed that the absorption of the isocyanate group had disappeared, and a blocked polyisocyanate aqueous dispersion having a solid content of 75% by mass was obtained.

The following coating agents were mixed to prepare a coating liquid X1.
Water 40.75% by mass
Isopropanol 25.00% by mass
Polyester aqueous dispersion 10.32% by mass
Polyvinyl alcohol aqueous solution 20.82% by mass
Block polyisocyanate cross-linking agent 0.50% by mass
Particles 1.24% by mass
(Silica sol with an average particle size of 100 nm, solid content concentration of 40% by mass)
Particle 0.74% by mass
(Silica sol with an average particle size of 450 nm, solid content concentration of 4% by mass)
Catalyst (organic tin compound solid content concentration 14% by mass) 0.48% by mass
Surfactant 0.15% by mass
(Silicone, solid content concentration 10% by mass)

(Production Example 6: Coating liquid Y: Preparation of water-based coating liquid)
The following coating agents were mixed to prepare a coating liquid Y.
Water 70.64% by mass
Isopropanol 9.25% by mass
Polyester aqueous dispersion 15.00% by mass
Particle 3.41% by mass
(Silica sol with an average particle size of 100 nm, solid content concentration of 20% by mass)
Particles 1.70% by mass
(Silica sol with an average particle size of 450 nm, solid content concentration of 4% by mass)

(Production Example 7: Coating liquid X2: Adjustment of adhesive modification coating liquid)
The following coating agents were mixed to prepare a coating liquid X2.

Water 54.89% by mass
Isopropanol 15.00% by mass
Polyester aqueous dispersion 18.19% by mass
Block polyisocyanate cross-linking agent 2.08% by mass
Zinc oxide particles 9.37% by mass
(Ceramese S-8 manufactured by Taki Chemical Co., Ltd., solid content concentration 8% by mass)
Particles 0.17% by mass
(Silica sol with an average particle size of 500 nm, solid content concentration of 15% by mass)
Surfactant 0.30% by mass
(Silicone, solid content concentration 10% by mass)

(Production Example 8: Coating liquid X3: Adjustment of adhesive modification coating liquid)
(Polymerization of carbodiimide-based cross-linking agent)
A flask equipped with a stirrer, a thermometer, and a reflux cooling tube was charged with 168 parts by mass of hexamethylene diisocyanate and 220 parts by mass of polyethylene glycol monomethyl ether (M400, average molecular weight 400), stirred at 120 ° C. for 1 hour, and further 4, Add 26 parts by mass of 4'-dicyclohexylmethane diisocyanate and 3.8 parts by mass of 3-methyl-1-phenyl-2-phosphoren-1-oxide (2% by mass with respect to total isosianate) as a carbodiimidation catalyst, and 185 under a nitrogen stream. The mixture was further stirred at ° C. for 5 hours. The infrared spectrum of the reaction solution was measured, and it was confirmed that the absorption at a wavelength of 2200 to 2300 cm-1 disappeared. After allowing to cool to 60 ° C., 567 parts by mass of ion-exchanged water was added to obtain a carbodiimide-based cross-linking agent having a solid content of 40% by mass.

The following coating agents were mixed to prepare a coating liquid X3.
Water 48.27% by mass
Isopropanol 25.00% by mass
Polyester aqueous dispersion 20.09% by mass
Carbodiimide-based cross-linking agent 2.86% by mass
Zirconium oxide particles 1.88% by mass
(ZR-40BL manufactured by Nissan Chemical Industries, Ltd., solid content concentration 40% by mass)
Particles 1.60% by mass
(Silica sol with an average particle size of 450 nm, solid content concentration of 4% by mass)
Surfactant 0.30% by mass
(Silicone, solid content concentration 10% by mass)

(Example 1)
81 parts by mass of resin A and 9 parts by mass of resin C and 10 parts by mass of resin B containing an ultraviolet absorber were dried under reduced pressure (1 Torr) at 135 ° C. for 6 hours as raw materials for the base film intermediate layer, and then the extruder 2 (1 Torr). It was supplied to the intermediate layer II layer), and the resin A was dried by a conventional method and supplied to the extruder 1 (for the surface layer I layer and the surface layer III), respectively, and melted at 285 ° C. The two layers of polymer are filtered through a stainless steel sintered filter medium (nominal filtration accuracy of 10 μm particles 95% cut), laminated with a two-kind three-layer confluence block, extruded into a sheet from the base, and then extruded. An unstretched film was prepared by winding it around a casting drum having a surface temperature of 30 ° C. and cooling and solidifying it by using an electrostatic application casting method. At this time, the discharge amount of each extruder was adjusted so that the ratio of the thicknesses of the I layer, the II layer, and the III layer was 8:84: 8. Further, from the installed online viscometer, the intrinsic viscosity of the resin forming the I layer and the III layer was 0.65 dl / g, and the intrinsic viscosity of the resin forming the II layer was 0.60 dl / g.

Then, the width range used as a product even after slitting excluding both ends in the film width direction so that the coating amount after drying on both sides of this unstretched film by the reverse roll method is 0.1 g / m ² . After applying the adhesive modification coating liquid X1 at 80 ° C., the film was dried at 80 ° C. for 20 seconds.

After the slits at both ends of the unstretched film on which this coating layer is formed, it does not become a product. The water-based coating liquid Y was applied so that the coating amount after drying was 0.07 g / m ² . At this time, the coating was applied so as not to overlap with the coating layer of the coating liquid X1 as much as possible.

The unstretched film coated with the water-based coating liquid on the end was guided to a tenter stretching machine, and while gripping the end of the film with a clip, it was guided to a hot air zone having a temperature of 125 ° C. and stretched 4.0 times in the width direction. Next, the film was treated at a temperature of 225 ° C. for 30 seconds while maintaining the width stretched in the width direction, and further subjected to a relaxation treatment of 3% in the width direction to obtain a uniaxially oriented PET film having a film thickness of about 100 μm. The intrinsic viscosity of the obtained film was 0.61 dl / g, the number of whiskers on the end face of the slit was small, and the film permeability was good. Other film characteristics are shown in Table 1 below.

(Example 2)
The film thickness is about 100 μm in the same manner as in Example 1 except that the resin composition ratio supplied to the extruder 2 (for the intermediate layer II layer) is 86 parts by mass of resin A, 4 parts by mass of resin C, and 10 parts by mass of resin B. A uniaxially oriented PET film was obtained. The intrinsic viscosity of the obtained film was 0.63 dl / g, the number of whiskers on the end face of the slit was small, and the film permeability was good. Other film characteristics are shown in Table 1 below.

(Example 3)
The film thickness is about 100 μm in the same manner as in Example 1 except that the resin composition ratio supplied to the extruder 2 (for the intermediate layer II layer) is 72 parts by mass of resin A, 18 parts by mass of resin C, and 10 parts by mass of resin B. A uniaxially oriented PET film was obtained. The intrinsic viscosity of the obtained film was 0.58 dl / g, the number of whiskers on the end face of the slit was small, and the film permeability was good. Other film characteristics are shown in Table 1 below.

(Example 4)
A uniaxially oriented PET film having a film thickness of about 100 μm was prepared in the same manner as in Example 1 except that the resin composition ratio supplied to the extruder 2 (for the intermediate layer II layer) was 90 parts by mass of the resin A and 10 parts by mass of the resin C. Obtained. The intrinsic viscosity of the obtained film was 0.62 dl / g, the number of whiskers on the end face of the slit was small, and the film permeability was good. Other film characteristics are shown in Table 1 below.

(Example 5)
A uniaxially oriented PET film was obtained in the same manner as in Example 1 except that the finished film thickness was 60 μm. The intrinsic viscosity of the obtained film was 0.59 dl / g, the number of whiskers on the end face of the slit was small, and the film permeability was good. Other film characteristics are shown in Table 1 below.

(Example 6)
A uniaxially oriented PET film was obtained in the same manner as in Example 1 except that 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 5: 90: 5. .. The intrinsic viscosity of the obtained film was 0.57 dl / g, the number of whiskers on the end face of the slit was small, and the film permeability was good. Other film characteristics are shown in Table 1 below.

(Example 7)
A uniaxially oriented PET film was obtained in the same manner as in Example 1 except that 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. .. The intrinsic viscosity of the obtained film was 0.63 dl / g, the number of whiskers on the end face of the slit was small, and the film permeability was good. Other film characteristics are shown in Table 1 below.

(Example 8)
The uniaxially oriented PET film was prepared in the same manner as in Example 1 except that the resin composition ratio supplied to the extruder 2 (for the intermediate layer II layer) was 76 parts by mass of resin A, 14 parts by mass of resin D, and 10 parts by mass of resin B. Obtained. The intrinsic viscosity of the obtained film was 0.62 dl / g, the number of whiskers on the end face of the slit was small, and the film permeability was good. Other film characteristics are shown in Table 1 below.

(Example 9)
The same as in Example 1 except that the resin composition ratio supplied to the extruder 2 (for the intermediate layer II layer) was 67 parts by mass of resin A, 9 parts by mass of resin C, 14 parts by mass of resin D, and 10 parts by mass of resin B. A uniaxially oriented PET film was obtained. The intrinsic viscosity of the obtained film was 0.63 dl / g, the number of whiskers on the end face of the slit was small, and the film permeability was good. Other film characteristics are shown in Table 1 below.

(Comparative Example 1)
The resin composition ratio supplied to the extruder 2 (for the intermediate layer II layer) was 90 parts by mass of the resin A and 10 parts by mass of the resin B, and a uniaxially oriented PET film having a film thickness of about 100 μm was obtained in the same manner as in Example 1. When the resin was extruded, the intrinsic viscosity of the resin forming the II layer was 0.64 dl / g, and the intrinsic viscosity of the obtained film was 0.67 dl / g, and the film permeability was good. However, the number of whiskers on the end face of the slit was large. Other film characteristics are shown in Table 2 below.

(Example 10)
The resin composition ratio supplied to the extruder 2 (for the intermediate layer II layer) is 63 parts by mass of the resin A, 27 parts by mass of the resin C, and 10 parts by mass of the resin B. I got a film. When the resin was extruded, the intrinsic viscosity of the resin forming the II layer was 0.55 dl / g, and the intrinsic viscosity of the obtained film was 0.54 dl / g. However, there were few whiskers on the end face after the slit. Other film characteristics are shown in Table 2 below.

(Example 11)
The resin composition ratio supplied to the extruder 2 (for the intermediate layer II layer) is 63 parts by mass of the resin A, 27 parts by mass of the resin D, and 10 parts by mass of the resin B. I got a film. The intrinsic viscosity of the obtained film was 0.61 dl / g, and although some dissatisfaction remained in terms of thickness volatility and yellowness, there were few whiskers on the end face after slitting. Other film characteristics are shown in Table 2 below.

(Example 12)
The water-based coating liquid X1 was not applied to both ends of the unstretched film, the coating width of the adhesive modification coating liquid X1 was widened, the coating was applied to the positions of both ends where the water-based coating liquid Y was applied, and the water-based coating liquid Y was not applied. A uniaxially oriented PET film having a film thickness of about 100 μm was obtained in the same manner as in Example 1 except for the above. The intrinsic viscosity of the obtained film was 0.60 dl / g. There was some dissatisfaction with the transmembrane property, but there were few whiskers on the end face after the slit. Other film characteristics are shown in Table 2 below.

(Example 13)
A uniaxially oriented PET film was obtained in the same manner as in Example 1 except that 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 3: 94: 3. .. The intrinsic viscosity of the obtained film was 0.59 dl / g, and the film permeability was also good. I was a little dissatisfied with the haze and yellowness of the film, but there were few whiskers on the end face after the slit. Other film characteristics are shown in Table 2 below.

(Comparative Example 2)
A uniaxially oriented PET film was obtained in the same manner as in Example 1 except that 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 14:72:14. .. The intrinsic viscosity of the obtained film was 0.63 dl / g, and the film permeability was also good. However, the number of whiskers on the end face of the slit was large. Other film characteristics are shown in Table 2 below.

(Example 14)
By the wire bar coating method, in the range of the width used as a product even after slitting excluding both ends in the film width direction so that the coating amount after drying on both sides of the unstretched film is 0.15 g / m ² . A uniaxially oriented PET film was obtained in the same manner as in Example 1 except that the adhesive modification coating liquid X2 was applied instead of the adhesive modification coating liquid X1. The intrinsic viscosity of the obtained film was 0.57 dl / g, the number of whiskers on the end face of the slit was small, and the film permeability was good. Other film characteristics are shown in Table 2 below.

(Example 15)
By the wire bar coating method, the adhesive modification coating liquid X1 was applied to one side of the unstretched film so that the coating amount after drying was 0.10 g / m ² , and the adhesive modification coating liquid X1 was applied to the other surface. Instead, the adhesive modification coating liquid X3 was applied so that the coating amount after drying was 0.08 g / m ² within the width range used as a product even after slitting excluding both ends in the film width direction. A uniaxially oriented PET film was obtained in the same manner as in Example 1 except for the above. The intrinsic viscosity of the obtained film was 0.57 dl / g, the number of whiskers on the end face of the slit was small, and the film permeability was good. Other film characteristics are shown in Table 2 below.

Tables 1 and 2 summarize various film properties of the polyester films of Examples 1 to 15 and Comparative Examples 1 and 2.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a polyester film roll with less whiskers on the end face of the slit, and it is possible to reduce the factors which are disadvantages, so that it can be further applied to optical applications, particularly to a polarizing element protective film. Further, by using the polyester film of the present invention as a polarizing element protective film, it is possible to provide a polarizing plate or a liquid crystal display device that can contribute to thinning and cost reduction of a display device without deteriorating visibility due to iris spots. It was possible.

Claims (11)

A polyester film in which the number of whisker-like objects protruding by 5 μm or more on the end face of the film slit along the machine flow direction at the time of film production is 1 or less per 100 μm of the film length , constituting the polyester film. The polyester resin to be used is a polyester resin containing at least one selected from polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate as a constituent component, or a third component monomer is copolymerized with the polyester resin. A polyester film that is a copolymerized polyester resin . The polyester film according to claim 1, which has an intrinsic viscosity of 0.55 dl / g or more and 0.65 dl / g or less. The polyester film according to claim 1 or 2, wherein the haze value is 2.0% or less and the b value is −0.5 or more and 3.0 or less. The polyester film according to any one of claims 1 to 3, wherein the polyester film has a thickness of 15 μm or more and 300 μm or less. The polyester film according to any one of claims 1 to 4, wherein a part of the polyester constituting the polyester film contains a self-recovering polymer produced in a step of producing the polyester film. The polyester film according to any one of claims 1 to 5, which has a coating layer on at least one side. A claim that has a laminated structure of three or more layers having at least a surface layer made of polyester on both sides of an intermediate layer made of polyester, and the middle layer contains a self-recovering polymer produced in a step of producing a polyester film. The polyester film according to any one of 1 to 6. It has a laminated structure of three or more layers having at least a surface layer made of polyester on both sides of the intermediate layer made of polyester, and the intrinsic viscosity of the polyester constituting the intermediate layer is that of the polyester constituting both surface layers. The polyester film according to any one of claims 1 to 7, which has a viscosity smaller than the intrinsic viscosity. The polyester film for a polarizing element protective film according to any one of claims 1 to 8, wherein the in-plane retardation is 3000 nm or more and 30,000 or less. A polarizing plate in which the polyester film for a polarizing element protective film according to claim 9 is laminated on at least one surface of the polarizing element. A liquid crystal display device having a backlight, a liquid crystal cell, and polarizing plates arranged on both sides of the liquid crystal cell, wherein the polarizing plate on at least one side is the polarizing plate according to claim 10.