JP6761381B2 - Liquid crystal display, polarizing plate and protector protective film - Google Patents

Description

The present invention relates to a liquid crystal display device. More specifically, the present invention relates to a liquid crystal display device in which the occurrence of rainbow spots is improved.

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

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

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

The polyester film is superior in durability to the TAC film, but unlike the TAC film, it has birefringence. Therefore, when this film is used as a polarizer protective film, there is a problem that the image quality is deteriorated due to optical distortion. That is, since a polyester film having birefringence has a predetermined optical anisotropy (polarization), when it is used as a polarizer protective film, iridescent color spots occur when observed from an oblique direction, and the image quality deteriorates. .. Therefore, in Patent Documents 1 to 3, measures are taken to reduce retardation by using a copolymerized polyester as the polyester. However, even in that case, the iridescent color spots could not be completely eliminated.

The present inventors have found that as a means for solving the above problems, a white light source having a continuous emission spectrum is used as a backlight light source, and an oriented polyester film having a certain retardation is used as a polarizer protective film. It was. However, after further studies on a liquid crystal display device having such a configuration, the inventors have made polyester as a polarizer protective film on both of the pair of polarizing plates even in such an improved liquid crystal display device. It was rediscovered that when the film was used, rainbow spots could occur depending on the angle when observed from an oblique direction, and the problem of rainbow spots was not completely solved.

That is, when a liquid crystal display device is industrially produced using a polarizing plate using a polyester film as a polarizer protective film, the directions of the polarizing axis of the polarizer and the orientation spindle of the polyester film are usually perpendicular to each other. Be placed. This is because the polyvinyl alcohol film, which is a polarizer, is produced by longitudinally uniaxially stretching, and the polyester film, which is the protective film thereof, is usually produced by longitudinally stretching and then laterally stretching. This is because the main axis direction of film orientation is the horizontal direction, and when a polarizing plate is manufactured by laminating these long objects, the main axis of orientation of the polyester film and the polarization axis of the polarizer are usually in the vertical direction. In this case, by using an oriented polyester film having a specific retardation as the polyester film and using a white light source having a continuous emission spectrum as the backlight light source, the rainbow spots were significantly improved, but were observed from an oblique direction. Occasionally, it was rediscovered that thin rainbow spots were observed at some angles.

As a result of studying the above problems day and night, the present inventor found that the polarization axis of the polarizer and the orientation main axis of the alignment polyester film (polarizer protection film) were substantially parallel to the two polarizing plates arranged on both sides of the liquid crystal. By doing so, it was found that the iris spots caused by the angle at which the liquid crystal display device is viewed are significantly reduced. The present invention is an invention completed as a result of further research and improvement based on the above findings.

A typical invention is as follows.
Item 1.
A liquid crystal display device having a backlight light source, two polarizing plates, and a liquid crystal cell arranged between the two polarizing plates.
The backlight source is a white light source having a continuous emission spectrum, and is a white light source.
The two polarizing plates are each composed of a polarizer and protective films on both sides thereof.
At least one of the protective films on both sides is an oriented polyester film having a retardation of 3000 to 30000 nm.
The polarization axis of the polarizer and the orientation spindle of the orientation polyester film which is the protective film thereof are substantially parallel.
Liquid crystal display device.
Item 2.
Item 2. The liquid crystal display device according to Item 1, wherein the ratio (Re / Rth) of the retardation of the oriented polyester film to the retardation in the thickness direction is 0.2 or more and 1.2 or less.
Item 3.
Item 2. The liquid crystal display device according to any one of Items 1 or 2, wherein the white light source having a continuous emission spectrum is a white light emitting diode.
Item 4.
The polyester film consists of three or more layers.
UV absorbers are contained in layers other than the outermost layer,
The light transmittance at 380 nm is 20% or less.
Item 4. The liquid crystal display device according to any one of Items 1 to 3.

The liquid crystal display device, the polarizing plate, and the polarizer protective film of the present invention can ensure good visibility in which the occurrence of iridescent color spots is significantly suppressed at any observation angle. Further, in a preferred embodiment, the polarizer protective film of the present invention has mechanical strength suitable for thinning.

Generally, the liquid crystal display device has a rear surface module, a liquid crystal cell, and a front surface module in the order from the backlight light source side to the image display side (visual recognition side). The rear module and the front module are generally composed of a transparent substrate, a transparent conductive film formed on the surface of the liquid crystal cell side thereof, and a polarizing plate arranged on the opposite side thereof. Here, the polarizing plate is arranged on the backlight light source side in the rear module, and is arranged on the image display side (visual recognition side) in the front module.

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

The backlight may be configured by an edge light system having a light guide plate, a reflector, or the like as a constituent member, or a direct system, but in the present invention, it is continuous as a backlight light source of a liquid crystal display device. It is preferable to use a white light source having a target and a wide emission spectrum. Here, the continuous and wide emission spectrum means an emission spectrum in which there is no wavelength at which the light intensity becomes zero in the wavelength region of at least 450 nm to 650 nm, preferably in the visible light region. As a white light source having such a continuous and wide emission spectrum, for example, a white light emitting diode (white LED) can be mentioned. White LEDs include a phosphor method, that is, an element that emits white light by combining a light emitting diode that emits blue light using a compound semiconductor or ultraviolet light and a phosphor, and an organic light-emitting diode (OLED). Etc. are included. Examples of the phosphor include an yttrium / aluminum / garnet-based yellow phosphor and a terbium / aluminum / garnet-based yellow phosphor. Among them, the white light emitting diode, which consists of a light emitting element that combines a blue light emitting diode using a compound semiconductor and an yttrium aluminum garnet yellow phosphor, has a continuous and wide emission spectrum and also has a wide luminous efficiency. Since it is excellent, it is suitable as a backlight light source of the present invention. Further, since the white LED having low power consumption can be widely used by the method of the present invention, it is possible to achieve the effect of energy saving.

Fluorescent tubes such as cold-cathode tubes and hot-cathode tubes, which have been widely used as backlight sources, have only a discontinuous emission spectrum having a peak at a specific wavelength. It is not preferable because it is difficult to obtain the effect of the period.

The polarizing plate has a configuration in which both sides of a polarizing element obtained by dyeing iodine on PVA or the like are sandwiched between two polarizing element protective films, but the present invention has at least one of the polarizing element protective films constituting the polarizing plate. As a result, a polyester film having a specific range of polarization is used.

The mechanism by which the occurrence of iridescent color spots is suppressed by the above aspect is considered as follows.

When an oriented polyester film having birefringence is arranged on one side of the polarizer, the linearly polarized light emitted from the polarizer causes disturbance when passing through the polyester film. The transmitted light exhibits an interference color peculiar to retardation, which is the product of birefringence and thickness of the oriented polyester film. Therefore, if a discontinuous emission spectrum such as a cold-cathode tube or a hot-cathode tube is used as the light source, the transmitted light intensity differs depending on the wavelength, and iridescent color spots occur (see: Proceedings of the 15th Microoptical Conference, No. Pages 30-31).

In contrast, white light emitting diodes typically have a continuous and wide emission spectrum in the wavelength region of at least 450 nm to 650 nm, preferably in the visible light region. Therefore, focusing on the envelope shape of the interference color spectrum due to the transmitted light transmitted through the birefringent, it is possible to obtain a spectrum similar to the emission spectrum of the light source by controlling the retardation of the oriented polyester film. In this way, the emission spectrum of the light source and the envelope shape of the interference color spectrum due to the transmitted light transmitted through the birefringent are similar to each other, so that rainbow-shaped color spots do not occur and the visibility is remarkable. It is thought to improve.

As described above, by using a white light emitting diode having a wide emission spectrum as a light source, it is possible to approximate the envelope shape of the transmitted light spectrum to the emission spectrum of the light source with only a relatively simple configuration.

In order to obtain the above effects, the oriented polyester film used for the polarizer protective film preferably has a retardation of 3000 to 30000 nm. If the retardation is less than 3000 nm, when used as a polarizer protective film, it exhibits a strong interference color when observed from an oblique direction, so the envelope shape is different from the emission spectrum of the light source, and good visibility cannot be ensured. .. The lower limit of the preferred retardation is 4500 nm, the next preferred lower limit is 5000 nm, the more preferred lower limit is 6000 nm, the more preferred lower limit is 8000 nm, and the further preferred lower limit is 10000 nm.

On the other hand, the upper limit of retardation is 30,000 nm. Even if an oriented polyester film having a retardation of more than that is used, not only the effect of further improving the visibility cannot be substantially obtained, but also the thickness of the film becomes considerably thick, and the handleability as an industrial material is lowered. Not preferable.

The retardation of 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.). it can. As used herein, the term retardation means in-plane retardation.

The present invention is characterized in that at least one of the protective films provided on both sides of the polarizer is a polarizer protective film having the above-mentioned specific retardation. The polarizer protective film having the specific retardation is used for both the incident light side (light source side) and the outgoing light side (visual recognition side). In the polarizing plate arranged on the incident light side, the polarizer protective film having the above-mentioned specific retardation is arranged on both sides regardless of whether the polarizing element is arranged on the incident light side or the liquid crystal cell side as a starting point. Although it may be arranged in, it is preferable that it is arranged at least on the incident light side. Regarding the polarizing plate arranged on the emitting light side, the polarizing element protective film having the above-mentioned specific retardation is arranged on both sides regardless of whether it is arranged on the liquid crystal side or the emitting light side starting from the polarizing element. It may be arranged, but it is preferable that it is arranged at least on the emitted light side. From the viewpoint of ensuring good polarization characteristics, the polarizing element protective film on the incident light side of the polarizing plate arranged on the incident light side and the polarizer protective film on the emitted light side of the polarizing plate arranged on the emitted light side are used. , It is preferable to use a polarizer protective film having the above-mentioned specific retardation.

The polarizing plate of the present invention has a structure in which both sides of a known polarizing element such as a film obtained by dyeing iodine with polyvinyl alcohol (PVA) or the like are sandwiched between two polarizing element protective films, and at least one of the polarized light is polarized. The child protective film is a polarizing plate protective film having the above-mentioned specific retardation. On the other hand, as the polarizer protective film, it is preferable to use a film having no birefringence, such as a TAC film, an acrylic film, and a norbornene-based film.

When an oriented polyester film is used as the protective film on both sides of the polarizer, it is preferable that the orientation principal axes of both oriented polyester films are substantially parallel to each other.

In the liquid crystal display device of the present invention, the polarization axis of the polarizer and the orientation spindle of the oriented polyester film (polarizer protective film) are substantially parallel to each other. Here, substantially parallel means that the angle formed by the polarizing axis of the polarizer and the orientation spindle of the polarizer protective film is -15 ° to 15 °, preferably -10 ° to 10 °, and more preferably -5 ° to -5 °. It means that it is 5 °, more preferably -3 ° to 3 °, even more preferably -2 ° to 2 °, and even more preferably -1 ° to 1 °. In one preferred embodiment, substantially parallel is substantially parallel. Here, substantially parallel means that the polarization axis and the orientation main axis are parallel to the extent that the deviation that inevitably occurs when the polarizer and the protective film are bonded to each other is allowed. Although the mechanism has not been elucidated yet, the fact that the polarization axes of the polarizers of the two polarizing plates and the orientation main axis of the orientation polyester film are substantially parallel in this way suppresses the occurrence of rainbow spots on the liquid crystal display screen. be able to. The direction of the main axis of orientation can be determined by measuring with a molecular orientation meter (for example, MOA-6004 type molecular orientation meter manufactured by Oji Measuring Instruments Co., Ltd.).

A polarizing plate in which the polarizer and the polarizer protective film satisfy the above relationship can be obtained, for example, by the following procedure. That is, the polarizing element and the oriented polyester film can be cut into an appropriate size, and the polarizing axis of the polarizing element and the oriented main axis of the oriented polyester film can be bonded so as to be substantially parallel to each other. Further, by continuously laminating a long material of a polarizing element film made of polyvinyl alcohol stretched vertically and uniaxially and a long material of an oriented polyester film stretched substantially vertically uniaxially, the polarizing axis of the polarizer is formed. It is also possible to manufacture a polarizing plate in which the main orientation axes of the polyester film are substantially parallel to each other.

The polarizing plate used in the present invention may be provided with various functional layers, that is, a hard coat layer, an antiglare layer, an antireflection layer, etc. on the surface of the oriented polyester for the purpose of preventing reflection, glare, and scratches. This is a preferred mode. When providing various functional layers, it is preferable that the oriented polyester film has an easily adhesive layer on its surface. At that time, from the viewpoint of suppressing interference due to reflected light, it is preferable to adjust the refractive index of the easy-adhesion layer so as to be close to the synergistic average of the refractive index of the functional layer and the refractive index of the oriented polyester film. A known method can be adopted for adjusting the refractive index of the easy-adhesion layer. For example, it can be easily adjusted by adding titanium, germanium, or other metal species to the binder resin.

As the oriented polyester used in the present invention, polyethylene terephthalate or polyethylene naphthalate can be used, but other copolymerization components may be contained. These resins are excellent in transparency as well as thermal and mechanical properties, and retardation can be easily controlled by stretching. In particular, polyethylene terephthalate is the most suitable material because it has a large intrinsic birefringence and a large retardation can be obtained relatively easily even if the film thickness is thin.

Further, for the purpose of suppressing deterioration of an optically functional dye such as an iodine dye, it is desirable that the protective film of the present invention has a light transmittance of 20% or less at a wavelength of 380 nm. The light transmittance at 380 nm is more preferably 15% or less, further preferably 10% or less, and particularly preferably 5% or less. When the light transmittance is 20% or less, deterioration of the optical functional dye due to ultraviolet rays can be suppressed. The transmittance in the present invention is measured by a method perpendicular to the plane of the film, and can be measured using a spectrophotometer (for example, Hitachi U-3500 type).

In order to reduce the transmittance of the protective film of the present invention at a wavelength of 380 nm to 20% or less, it is achieved by adding an ultraviolet absorber to the film or applying a coating liquid containing an ultraviolet absorber to the film surface. It is desirable to appropriately adjust the type and concentration of the ultraviolet absorber 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 benzotriazole-based, benzophenone-based, cyclic iminoester-based, and combinations thereof, but are not particularly limited as long as they are within the absorbance range specified by the present invention. However, from the viewpoint of durability, benzotoazole-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 benzophenone-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, and acrylonitrile-based ultraviolet absorbers include 2- [2'-hydroxy-5'-(methacryloyloxymethyl) phenyl] -2H-benzotriazole, 2- [2'. -Hydroxy-5'-(methacryloyloxyethyl) phenyl] -2H-benzotriazole, 2- [2'-hydroxy-5'-(methacryloyloxypropyl) phenyl] -2H-benzotriazole, 2,2'-dihydroxy- 4,4'-Dimethoxybenzophenone, 2,2', 4,4'-tetrahydroxybenzophenone, 2,4-di-tert-butyl-6- (5-chlorobenzotriazole-2-yl) phenol, 2- ( 2'-Hydroxy-3'-tert-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2- (5-chloro (2H) -benzotriazole-2-yl) -4-methyl-6- ( Examples thereof include tert-butyl) phenol and 2,2′-methylenebis (4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazole-2-yl) phenol). Cyclic iminoester. Examples of the ultraviolet absorbers include 2,2'-(1,4-phenylene) bis (4H-3,1-benzoxadinone-4-one) and 2-methyl-3,1-benzoxazine-4-one. , 2-Butyl-3,1-benzoxazine-4-one, 2-phenyl-3,1-benzoxazine-4-one and the like, but are not particularly limited thereto.

In addition to the ultraviolet absorber, it is also preferable to contain various additives as long as the effects of the present invention are not impaired. As additives, for example, inorganic particles, heat-resistant polymer particles, alkali metal compounds, alkaline earth metal compounds, phosphorus compounds, antistatic agents, light retardants, flame retardants, heat stabilizers, antioxidants, antigelling agents. , Surfactants and the like. Further, in order to obtain high transparency, it is also preferable that the polyester film contains substantially no particles. "Substantially free of particles" means, for example, in the case of inorganic particles, the content is 50 ppm or less, preferably 10 ppm or less, and particularly preferably the detection limit or less when the inorganic element is quantified by Keiko X-ray analysis. Means quantity.

Further, the oriented polyester film of the present invention can be subjected to a corona treatment, a coating treatment, a flame treatment or the like in order to improve the adhesiveness with the polarizer.

In the present invention, in order to improve the adhesiveness with the polarizer, an easy-adhesion layer containing at least one of polyester resin, polyurethane resin or polyacrylic resin as a main component is provided on at least one side of the film of the present invention. Is preferable. Here, the "main component" refers to a component that is 50% by mass or more of the solid components constituting the easy-adhesion layer. The coating liquid used for forming the easy-adhesion layer of the present invention is preferably an aqueous coating liquid containing at least one of a water-soluble or water-dispersible copolymerized polyester resin, acrylic resin and polyurethane resin. Examples of these coating solutions include water-soluble or water-dispersible copolymers disclosed in Japanese Patent No. 3567927, Japanese Patent No. 3589232, Japanese Patent No. 3589233, Japanese Patent No. 3900191, Japanese Patent No. 4150982, and the like. Examples thereof include a polymerized polyester resin solution, an acrylic resin solution, and a polyurethane resin solution.

The easy-adhesion layer can be obtained by applying the coating liquid to one or both sides of a uniaxially stretched film in the vertical direction, drying at 100 to 150 ° C., and further stretching in the horizontal direction. The final coating amount of the easy-adhesion layer after drying is preferably controlled to 0.05 to 0.20 g / m ² . If the coating amount is less than 0.05 g / m ² , the adhesiveness with the obtained polarizer may be insufficient. On the other hand, if the coating amount exceeds 0.20 g / m ² , the blocking resistance may decrease. When the easy-adhesion layers are provided on both sides of the polyester film, the coating amounts of the easy-adhesion layers on both sides may be the same or different, and can be independently set within the above ranges.

It is preferable to add particles to the easy-adhesion layer in order to impart slipperiness. It is preferable to use particles having an average particle size of 2 μm or less. When the average particle size of the particles exceeds 2 μm, the particles are likely to fall off from the coating layer. Particles contained in the easy-adhesion layer include, for example, titanium oxide, barium sulfate, calcium carbonate, calcium sulfate, silica, alumina, talc, kaolin, clay, calcium phosphate, mica, hectrite, zirconia, tungsten oxide, lithium fluoride, etc. Examples thereof include inorganic particles such as calcium fluoride and organic polymer particles such as styrene-based, acrylic-based, melamine-based, benzoguanamine-based, and silicone-based particles. These may be added to the easy-adhesion layer alone, or may be added in combination of two or more.

Further, as a method of applying the coating liquid, a known method can be used. For example, the reverse roll coating method, the gravure coating method, the kiss coating method, the roll brush method, the spray coating method, the air knife coating method, the wire bar coating method, the pipe doctor method, etc. can be mentioned, and these methods can be used alone. Alternatively, it can be performed in combination.

The average particle size of the above particles is measured by the following method. The particles are photographed with a scanning electron microscope (SEM), and the maximum diameter of 300 to 500 particles (between the two most distant points) is magnified so that the size of one of the smallest particles is 2 to 5 mm. Distance) is measured, and the average value is taken as the average particle size.

The oriented polyester film, which is the protective film of the present invention, can be produced according to a general method for producing a polyester film. For example, a non-oriented polyester 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 by utilizing the speed difference of rolls, and then stretched in the horizontal direction by a tenter. A method of applying heat treatment can be mentioned.

The oriented polyester film of the present invention may be a uniaxially stretched film or a biaxially stretched film, but when the biaxially stretched film is used as a polarizer protective film, it is observed from directly above the film surface. However, it should be noted that rainbow-shaped color spots may be observed when observed from an oblique direction.

The cause of this phenomenon is that the biaxially stretched film is composed of refractive index ellipsoids having different refractive indexes in the traveling direction, the width direction, and the thickness direction, and the retardation becomes zero depending on the light transmitting direction inside the film ( This is because there is a direction (the refractive index ellipsoid 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 rainbow-shaped color spots 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 hard to see.

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

The present inventors have specified the ratio of the retardation (in-plane retardation) of the protective film to the retardation (Rth) in the thickness direction as a means for suppressing the occurrence of rainbow spots while maintaining the mechanical strength of the protective film. We have found that it is controlled so that it falls within the range of. The thickness direction phase difference means the average of the phase differences obtained by multiplying the two birefringences ΔNxz and ΔNyz when the film is viewed from the cross section in the thickness direction by the film thickness d, respectively. The smaller the difference between the in-plane retardation and the thickness direction retardation, the more isotropic the action of birefringence depending on the observation angle, and therefore the smaller the change in retardation depending on the observation angle. Therefore, it is considered that rainbow-shaped color spots are less likely to occur depending on the observation angle.

The ratio (Re / Rth) of the retardation of the polyester film of the present invention to the retardation in the thickness direction is preferably 0.200 or more, more preferably 0.500 or more, and further preferably 0.600 or more. The larger the ratio (Re / Rth) of the above retardation to the thickness direction retardation, the more isotropic the action of birefringence, and the less likely it is that iridescent color spots will occur depending on the observation angle. Then, in a perfect uniaxial (uniaxially symmetric) film, the ratio (Re / Rth) of the retardation to the thickness direction retardation is 2.0. However, as described above, the mechanical strength in the direction orthogonal to the orientation direction significantly decreases as the film approaches a perfect uniaxial (uniaxially symmetric) film.

On the other hand, the ratio (Re / Rth) of the retardation of the polyester film of the present invention to the retardation in the thickness direction is preferably 1.2 or less, more preferably 1.0 or less. In order to completely suppress the occurrence of iridescent color spots depending on the observation angle, the ratio of retardation to the phase difference in the thickness direction (Re / Rth) does not need to be 2.0, and 1.2 or less is sufficient. is there. Further, even if the ratio is 1.0 or less, it is sufficiently possible to satisfy the viewing angle characteristics (about 180 degrees left and right and 120 degrees up and down) required for the liquid crystal display device.

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 to 120 ° C. The longitudinal stretching ratio is preferably 1.0 to 3.5 times, particularly preferably 1.0 to 3.0 times. The transverse stretching ratio is preferably 2.5 to 6.0 times, particularly preferably 3.0 to 5.5 times. In order to control the retardation within the above range, it is preferable to control the ratio of the longitudinal stretching ratio to the transverse stretching ratio. If the difference between the vertical and horizontal stretching ratios is too small, it becomes difficult to increase the retardation, which is not preferable. 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 have a great influence on the thickness unevenness of the film, it is necessary to optimize the film forming conditions from the viewpoint of the thickness unevenness. In particular, when the longitudinal stretching ratio is lowered in order to increase the retardation, the value of the longitudinal thickness spot may increase. Since there is a region where the vertical thickness unevenness becomes very high in a specific range of the draw ratio, it is desirable to set the film forming conditions outside this range.

The thickness unevenness of the film of the present invention is preferably 5.0% or less, further preferably 4.5% or less, further preferably 4.0% or less, and 3.0% or less. It is particularly preferable to have. The thickness unevenness of the film can be measured by any means. For example, a tape-shaped sample (length 3 m) continuous in the flow direction of the film is taken and an electronic micrometer (Millitron) manufactured by Seiko EM Corporation is collected. Using a measuring machine such as 1240), the thickness of 100 points is measured at a pitch of 1 cm, the maximum value (dmax), the minimum value (dmin), and the average value (d) of the thickness are obtained, and the thickness unevenness (d) is calculated by the following formula. %) Can be calculated.
Thickness spot (%) = ((dmax-dmin) / d) × 100

As described above, controlling the retardation of the film within a specific range can be performed by appropriately setting the stretching ratio, the stretching temperature, and the thickness of the film. For example, the higher the difference in stretching ratio between longitudinal stretching and transverse stretching, the lower the stretching temperature, and the thicker the film, the easier it is to obtain high retardation. On the contrary, the lower the difference in stretching ratio between the longitudinal stretching and the transverse stretching, the higher the stretching temperature, and the thinner the film thickness, the easier it is to obtain lower retardation. Further, the higher the stretching temperature and the lower the total stretching ratio, the easier it is to obtain a film having a low ratio (Re / Rth) of retardation and retardation in the thickness direction. On the contrary, the lower the stretching temperature and the higher the total stretching ratio, the easier it is to obtain a film having a high ratio (Re / Rth) of retardation and retardation in the thickness direction. The final film forming conditions need to be set in consideration of the physical properties required for processing in addition to the control of retardation.

The thickness of the oriented 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 15 to 200 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 and the like are likely to occur, and the practicality as an industrial material is remarkably lowered. A particularly preferable lower limit of the thickness is 25 μm. On the other hand, if the upper limit of the thickness of the polarizer protective film exceeds 300 μm, the thickness of the polarizing plate becomes too thick, which is not preferable. From the viewpoint of practicality as a polarizer protective film, the upper limit of the thickness is preferably 200 μm. A particularly preferable upper limit of the thickness is 100 μm, which is equivalent to that of a general TAC film. In order to control the retardation within the range of the present invention even in the above thickness range, polyethylene terephthalate is preferable as the polyester used as the film base material.

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. The weight of the ultraviolet absorber added to the film is preferably 0.3 to 1.5%, more preferably 0.4 to 1.0%.

At this time, the concentration of the 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 the polyester raw material at a temperature equal to or higher than the melting point of the polyester raw material and lower than 290 ° C. for 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 residence time is 1 minute or less, it becomes difficult to uniformly mix the ultraviolet absorber. 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 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 film having a three-layer structure containing an ultraviolet absorber in the intermediate layer can be produced as follows. A polyester pellet alone for the outer layer, and a masterbatch containing an ultraviolet absorber for the intermediate layer and polyester pellets are mixed at a predetermined ratio, dried, and then supplied to a known melt lamination 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, a three-layer manifold or a merging block (for example, a merging block having a square merging portion), a film layer forming both outer layers and a film layer forming an intermediate layer are laminated. A three-layer sheet is extruded from the base and cooled 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 filter particle size (initial filtration efficiency 95%) of the filter medium used for high-precision filtration of the molten resin is preferably 15 μm or less. If the size of the filtered particles of the filter medium exceeds 15 μm, the removal of foreign matter of 20 μm or more tends to be insufficient.

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 carried out with appropriate modifications to the extent that it can be adapted to the gist of the present invention. It is also possible, all of which are within the technical scope of the invention. The method for evaluating physical properties in the following examples is as follows.

(1) Film Orientation Main Axis The orientation main axis direction of the film was determined using a molecular orientation meter (MOA-6004 type molecular orientation meter manufactured by Oji Measuring Instruments Co., Ltd.).

(2) Reference (Re)
The retardation is a parameter defined by the product (ΔNxy × d) of the anisotropy of the refractive indexes of the two orthogonal axes on the film (ΔNxy = | Nx−Ny |) and the film thickness d (nm). Yes, it is a scale showing optical isotropic and anisotropy. The biaxial refractive index anisotropy (ΔNxy) was determined by the following method. Using a molecular orientation meter (MOA-6004 type molecular orientation meter manufactured by Oji Measuring Instruments Co., Ltd.), determine the orientation principal axis direction of the film, and 4 cm x 2 cm so that the orientation principal axis direction is parallel to the long side of the measurement sample. Was cut out and used as a measurement sample. For this sample, the refractive index (Nx, Ny) of two orthogonal axes and the refractive index (Nz) in the thickness direction were determined by an Abbe refractive index meter (manufactured by Atago Co., Ltd., NAR-4T, measurement wavelength 589 nm). The absolute value (| Nx-Ny |) of the difference in refractive index of the shaft was defined as the anisotropy of the refractive index (ΔNxy). The film thickness d (nm) was measured using an electric micrometer (Millitron 1245D, manufactured by Finereuf), and the unit was converted to nm. The retardation (Re) was determined from the product (ΔNxy × d) of the anisotropy of the refractive index (ΔNxy) and the thickness d (nm) of the film.

(3) Thickness direction retardation (Rth)
The thickness direction retardation is obtained by multiplying two birefringences ΔNxz (= | Nx−Nz |) and ΔNyz (= | Ny−Nz |) when viewed from a cross section in the film thickness direction by the film thickness d, respectively. It is a parameter indicating the average of the refraction obtained. Nx, Ny, Nz and the film thickness d (nm) are obtained by the same method as the measurement of retardation, and the average value of (ΔNxz × d) and (ΔNyz × d) is calculated to calculate the thickness direction retardation (Rth). ) Was asked.

(4) Light transmittance at a wavelength of 380 nm Using a spectrophotometer (manufactured by Hitachi, Ltd., U-3500 type), the light transmittance of each film in the wavelength range of 300 to 500 nm is measured using the air layer as a standard, and light rays at a wavelength of 380 nm are measured. The transmittance was calculated.

(5) Observation of rainbow spots One of the polyester films 1 to 10 prepared by the method described later is attached to one side of a polarizing element composed of PVA and iodine so that the polarization axis of the polarizer and the orientation main axis of the film are perpendicular or parallel. A TAC film (manufactured by Fuji Film Co., Ltd., thickness 80 μm) was attached to the opposite surface to prepare a polarizing plate. A liquid crystal display device was produced by arranging the obtained polarizing plates one by one on both sides of the liquid crystal so that each polarizing plate would be under the condition of cross Nicol. At this time, each polarizing plate was arranged so that the polyester film was on the opposite side (distal) to the liquid crystal. As the light source of the liquid crystal display device, a white LED composed of a light emitting element combining a blue light emitting diode and an yttrium aluminum garnet yellow phosphor was used as the light source (Nichia Corporation, NSPW500CS). Visual observation was performed from the front surface of the polarizing plate of such a liquid crystal display device and from an oblique direction, and the presence or absence of rainbow spots was determined as follows.

A: No rainbow spots from any direction.
B: When observed from an oblique direction, a thin rainbow spot can be observed depending on the angle.
C: Rainbow spots can be observed when observed from an oblique direction.
D: Rainbow spots can be observed when observed from the front and diagonal directions.

(6) Tear strength The tear strength of each film was measured according to JIS P-8116 using an Elemendorff tear tester manufactured by Toyo Seiki Seisakusho. The tearing direction was made parallel to the orientation main axis direction of the film, and the determination was made as follows.
◯: Tear strength is 50 mN or more ×: Tear strength is less than 50 mN

(Production Example 1-Polyester A)
When the temperature of the esterification reaction can reached 200 ° C., 86.4 parts by mass of terephthalic acid and 64.6 parts by mass of ethylene glycol were charged, and 0.017 parts by mass of antimony trioxide was used 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. 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, 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 a polycondensation reaction was carried out under reduced pressure at 280 ° C.

After completion of the polycondensation reaction, filtration is performed with a Naslon filter having a 95% cut diameter of 5 μm, extruded into strands from a nozzle, and cooled and solidified using cooling water that has been previously filtered (pore diameter: 1 μm or less). , Cut into pellets. The intrinsic viscosity of the obtained polyethylene terephthalate resin (A) was 0.62 dl / g, and the inert particles and internally precipitated particles were substantially not contained. (Hereafter, it is abbreviated as PET (A).)

(Production Example 2-Polyester B)
10 parts by mass of dried UV absorber (2,2'-(1,4-phenylene) bis (4H-3,1-benzoxadinone-4-one), particle-free PET (A) (intrinsic viscosity) 0.62 dl / g) 90 parts by mass was mixed, and a polyethylene terephthalate resin (B) containing an ultraviolet absorber was obtained using a kneading extruder (hereinafter abbreviated as PET (B)).

(Manufacturing Example 3-Adhesive Modification Coating Liquid Adjustment)
The ester exchange reaction and polycondensation reaction were carried out by a conventional method, and 46 mol% of terephthalic acid, 46 mol% of isophthalic acid and 8 mol% of sodium 5-sulfonatoisophthalate were carried out as dicarboxylic acid components (relative to the entire dicarboxylic acid component). A water-dispersible metal sulfonate metal base-containing copolymer resin having a composition of 50 mol% ethylene glycol and 50 mol% neopentyl glycol as a glycol component was prepared. Next, 51.4 parts by mass of water, 38 parts by mass of isopropyl alcohol, 5 parts by mass of n-butyl cell solution, and 0.06 parts by mass of a nonionic surfactant are mixed, and then heated and stirred. When the temperature reaches 77 ° C., the above Water-dispersible metal sulfonic acid base-containing copolymerized polyester resin 5 parts by mass was added, and stirring was continued until the resin clumps disappeared, and then the resin aqueous dispersion was cooled to room temperature to have a solid content concentration of 5.0% by mass. A uniform water-dispersible copolymerized polyester resin solution was obtained. Further, after 3 parts by mass of aggregate silica particles (Silicia 310 manufactured by Fuji Silysia Chemical Ltd.) were dispersed in 50 parts by mass of water, 99.46 parts by mass of the water-dispersible copolymerized polyester resin liquid was added to Syricia 310. 0.54 parts by mass of an aqueous dispersion was added, and 20 parts by mass of water was added with stirring to obtain an adhesive modification coating liquid.

(Polarizer protective film 1)
After 90 parts by mass of PET (A) resin pellets containing no particles and 10 parts by mass of PET (B) resin pellets 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. , It was supplied to the extruder 2 (for the intermediate layer II layer), and the PET (A) was dried by a conventional method and supplied to the extruder 1 (for the outer layer I layer and the outer layer III), respectively, and melted at 285 ° C. .. Each of these two types of polymers is filtered through a filter medium of a stainless sintered body (nominal filtration accuracy of 10 μm particles 95% cut), laminated in a two-type 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 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 10:80:10.

Next, the adhesive modification coating solution was applied to both sides of the unstretched PET film by the reverse roll method so that the coating amount after drying was 0.08 g / m ² , and then dried at 80 ° C. for 20 seconds. ..

The unstretched film on which the coating layer was formed was guided to a tenter stretching machine, and while gripping the edge 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 50 μm.

(Polarizer protective film 2)
By changing the thickness of the unstretched film, a uniaxially oriented PET film was obtained in the same manner as in the polarizer protective film 1 except that the thickness was about 100 μm.

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

(Polarizer protective film 4)
A biaxially oriented PET film having a film thickness of about 50 μm was obtained by stretching 2.0 times in the traveling direction and 4.0 times in the width direction in the same manner as in the polarizer protective film 3.

(Polarizer protective film 5)
A uniaxially oriented PET film having a film thickness of 50 μm was obtained in the same manner as in the polarizer protective film 1 without using a PET resin (B) containing an ultraviolet absorber in the intermediate layer.

(Polarizer protective film 6)
A uniaxially oriented PET film having a film thickness of about 100 μm was obtained by stretching 4.0 times in the traveling direction and 1.0 times in the width direction in the same manner as in the polarizer protective film 3.

(Polarizer protective film 7)
A uniaxially oriented PET film having a film thickness of about 75 μm was obtained by stretching 1.0 times in the traveling direction and 3.5 times in the width direction in the same manner as in the polarizer protective film 1.

(Polarizer protective film 8)
A uniaxially oriented PET film having a thickness of about 275 μm was obtained by changing the thickness of the unstretched film using the same method as that of the polarizer protective film 1.

(Polarizer protective film 9)
A biaxially oriented PET film having a film thickness of about 38 μm was obtained by stretching 3.6 times in the traveling direction and 4.0 times in the width direction in the same manner as in the polarizer protective film 3.

(Polarizer protective film 10)
A uniaxially oriented PET film having a thickness of about 10 μm was obtained by changing the thickness of the unstretched film using the same method as that of the polarizer protective film 1.

(Polarizer protective film 11)
A uniaxially oriented PET film having a film thickness of 50 μm was obtained in the same manner as the polarizer protective film 5 except that the film was made into a single layer. The rainbow spots were observed using an OLED instead of a white LED composed of a light emitting element in which a blue light emitting diode and an yttrium aluminum garnet yellow phosphor were combined as the light source of the liquid crystal display device.

Table 1 below shows the results of rainbow spot observation and measurement of tear strength of the liquid crystal display device manufactured as described above using the polarizer protective films 1 to 11.

In Table 1, the “relationship between the orientation spindle and the polarization axis” means the relationship between the polarization axis of the polarizing element of the polarizing plate in the liquid crystal display device and the alignment spindle of the alignment polyester film used as the protective film. Polarizer protective film No. Reference numeral 12 is a polarizer protective film No. 12. The case where 1 is attached to the polarizer so that the angle formed by the main axis of orientation and the polarization axis of the polarizer is 8 ° is shown (substantially parallel). Polarizer protective film No. Reference numeral 13 is a polarizer protective film No. 13. The case where 1 is attached to the polarizer so that the angle formed by the main axis of orientation and the polarization axis of the polarizer is 4 ° is shown (substantially parallel).

As shown in Table 1, by using the polarizer protective films 1 to 8 or 11 and arranging the angles formed by the polarization axis of the polarizing element of the polarizing plate and the orientation main axis of the alignment polyester film substantially in parallel, eventually No rainbow spots were observed when the screen of the liquid crystal display device was viewed from the above angle. On the other hand, even if the same polarizer protective films 1 to 8 and 11 are used, if the orientation spindle of the polyester film constituting the polarizing plate and the polarization axis of the polarizer are perpendicular to each other, the angle at which the screen of the liquid crystal display device is viewed. In some cases, rainbow spots may occur. Further, when the polarizer protective film 9 or 10 was used, a clear rainbow spot was observed when the screen of the liquid crystal display device was observed from an angle.

Claims (3)

A liquid crystal display device having a backlight source and two polarizing plates.
Of the two polarizing plates, the polarizing plate arranged on the incident light side is a polarizing plate in which an oriented polyester film having a retardation of 3000 to 30,000 nm is laminated on the incident light side of the polarizing element (however, the incident light of the polarizing element). (Excluding polarizing plates on which an oriented polyester film having a retardation of 10 μm or more is laminated on the side) .
Of the two polarizing plates, the polarizing plate arranged on the emitted light side is a polarizing plate in which an oriented polyester film having a retardation of 3000 to 30,000 nm is laminated on the emitted light side of the polarizing element (however, the emitted light of the polarizing element). (Excluding polarizing plates on which an oriented polyester film having a retardation of 10 μm or more is laminated on the side).
In each of the polarizing plates, the absorption axis of the polarizer and the orientation spindle of the oriented polyester film are substantially parallel, and the ratio (Re / Rth) of the retardation of the oriented polyester film to the retardation in the thickness direction is 0.5 to 5. A liquid crystal display device that is 2.0. A liquid crystal display device having a backlight source and two polarizing plates.
Of the two polarizing plates, the polarizing plate arranged on the incident light side is a polarizing plate in which an oriented polyester film having a retardation of 3000 to 30,000 nm is laminated on the incident light side of the polarizing element (however, the incident light of the polarizing element). (Excluding polarizing plates on which an oriented polyester film having a retardation of 10 μm or more is laminated on the side) .
Of the two polarizing plates, the polarizing plate arranged on the emitted light side is a polarizing plate in which an oriented polyester film having a retardation of 3000 to 30,000 nm is laminated on the emitted light side of the polarizing element (however, the emitted light of the polarizing element). (Excluding polarizing plates on which an oriented polyester film having a retardation of 10 μm or more is laminated on the side).
In each of the polarizing plates, the polarizer is a uniaxially stretched polyvinyl alcohol film, and the stretching direction of the polyvinyl alcohol film and the orientation principal axis of the oriented polyester film are substantially parallel to each other, and the retardation of the oriented polyester film. A liquid crystal display device having a thickness-direction retardation ratio (Re / Rth) of 0.5 to 2.0. The liquid crystal display device according to claim 1 or 2, wherein the thickness of the oriented polyester film is 15 μm or more and 200 μm or less.