TW202305032A - Polyester film for protection of polarizer, and polarizing plate using same - Google Patents

Abstract

The present invention addresses the problem of providing: a polyester film for the protection of a polarizer, the polyester film being free from the occurrence of iridescent unevenness if applied to an image display device, while being capable of contributing to improvement in the durability of a polarizing plate under environmental changes; and a polarizing plate which uses this polyester film for the protection of a polarizer. A means for solving the problem is a polyester film for the protection of a polarizer, the polyester film being composed of a dicarboxylic acid component containing 75% by mole or more of terephthalic acid and a diol component containing 75% by mole or more of ethylene glycol, wherein: the linear thermal expansion coefficient in the in-plane direction of the film in the temperature range from 30 DEG C to 70 DEG C is 70 ppm/DEG C or less; the difference between the lowest refractive index in the in-plane direction and the refractive index in the thickness direction is 0.09 or less; and the thickness is 40 [mu]m or less.

Description

Polyester film for polarizer protection, and polarizing plate using it

The present invention relates to a polyester film for polarizer protection and a polarizing plate using the polyester film for polarizer protection.

In image display devices (for example, liquid crystal display devices, organic EL display devices), due to the method of image formation, in many cases, a polarizer is disposed on at least one side of the display unit. In recent years, the functions and uses of image display devices tend to be further diversified, and they are required to withstand use in harsher environments.

A polarizing plate generally has a structure in which a polarizer is sandwiched between two protective films. For the protective film, triacetyl cellulose, acrylic resin, cycloolefin, polyester resin, etc. are widely used. In particular, polyester-based resins such as polyethylene terephthalate (PET) are generally known to be excellent in durability, mechanical properties, chemical resistance, and moisture barrier properties. This film is excellent in mechanical properties as described above, but has problems such as birefringence, occurrence of iridescent spots, and deterioration of visibility.

As a solution to this, it is used in a liquid crystal display device by uniaxially stretching it to make it strongly oriented, and to obtain a high phase difference at a thickness of 50 μm or more (for example, Patent Document 1).

However, there is a problem that it is difficult to make a thin film because of high retardation, and because of its thick thickness and its anisotropy, it will cause warping, cracks, etc. to affect the polarizer under environmental changes. In order to solve these problems, for example, a polyethylene naphthalate (PEN) film having a higher birefringence than polyethylene terephthalate has been proposed (for example, Patent Document 2). This film is thinned by uniaxial stretching and achieves a high retardation, but it has practical problems due to the low tear resistance derived from the molecular skeleton.

On the other hand, as a solution to iridescence caused by low retardation, a polyester film with a retardation of 100 nm or less and a thickness of 50 μm or less has been proposed (for example, Patent Documents 3 and 4). This proposal can adjust the retardation below 100nm due to the slow film forming speed and high precision batch film stretching machine, but there is a phenomenon called bowing in the continuous film film manufacturing equipment. The physical properties in the width direction are not uniform, so it is difficult to solve the large-area iridescent spot in the polyester film with large birefringence. The film design with a phase difference of less than 100nm has a great effect on the uniformity of the orientation angle that affects the iridescent spot. topic. In particular, in the case of simultaneous biaxial stretching, since the control of stretching temperature and speed is also limited vertically and horizontally, there is still a limit in the control of the coefficient of thermal expansion.

Other protective films made of triacetyl cellulose, acrylic resin, or cycloolefin resin, which are commonly used in the past, have little inherent birefringence derived from the molecular skeleton, so there is almost no phase difference and no rainbow spots. However, the polarizer is made of amorphous resin, so the size is easy to change due to changes in temperature and humidity, and there is a problem of cracks in the polarizer. In recent years, along with the reduction in thickness of image display devices, thinner polarizers are required, and on the other hand, the number of image display devices expected to be used at high temperatures is increasing. Therefore, there is a strong demand for a highly durable polarizing plate that does not cause cracks in the polarizer. [Prior Art Literature] [Patent Document]

[Patent Document 1] International Publication No. 2011/162198 [Patent Document 2] Japanese Patent Laid-Open No. 2014-224894 [Patent Document 3] Japanese Patent Laid-Open No. 2020-126217 [Patent Document 4] International Publication No. 2020/158112

[Problem to be solved by the invention]

Therefore, the object of the present invention is to provide a polyester film for polarizer protection that does not cause iridescent spots when applied to an image display device, and contributes to the improvement of the durability of the polarizer in environmental changes, and a polarizer using the same. . [Means to solve the problem]

In order to solve the above-mentioned problems, the present invention employs the following configurations. (1) A polyester film for polarizer protection, which is a polyester film comprising terephthalic acid with a dicarboxylic acid component of more than 75 mol%, and a diol component of ethylene glycol with a mol% of more than 75 mol%, 30 The thermal linear expansion coefficient in the plane direction of the film in the temperature range from °C to 70 °C is 70 ppm/°C or less, the difference between the minimum refractive index in the plane direction and the refractive index in the thickness direction is 0.09 or less, and the thickness is 40 μm or less. (2) The polyester film for polarizer protection as described in (1), wherein the plane retardation is 400 nm to 3000 nm. (3) The polyester film for polarizer protection according to (1), wherein the thickness variation in the width direction of the film is 10% or less. (4) The polyester film for polarizer protection described in (1), wherein the intrinsic viscosity of the film is above 0.80 dl/g, and the melting point is 245°C to 210°C. (5) The polyester film for polarizer protection as described in (1), wherein the copolymerization component is not less than 3 mol% and not more than 25 mol%, and at least contains adipic acid, isophthalic acid, and cyclohexanedimethanol ingredients. (6) The polyester film for polarizer protection according to (1), wherein the angle formed by the absorption axis of the polarizer and the slow axis of the polyester film is 5° or less. (7) The polyester film for polarizer protection according to (1), which is a three-layer laminate of A layer/B layer/A layer, and the thickness of the A layer is 1 μm or less. (8) A polarizing plate comprising a polarizer, and the polyester film according to any one of (1) to (7) disposed on one side of the polarizer. (9) The polarizing plate according to (8), wherein the polarizer has a thickness of 20 μm or less. (10) The polarizing plate according to (8), further comprising an easy-adhesive layer disposed on the polarizer side of the polyester film. (11) The polarizing plate according to (10), wherein the easily-adhesive layer contains fine particles. (12) The polarizing plate according to (10), wherein the thickness of the easily-adhesive layer is 0.35 μm or less. (13) The polarizing plate according to (10), wherein the refractive index of the easily-adhesive layer is 1.6 or less. [Effect of Invention]

When the polarizing plate using the polyester film for polarizer protection of the present invention is applied to an image display device, no rainbow spots will occur even if it is a large screen, and the durability of the polarizing plate is improved under environmental changes, that is, it helps to suppress The cracks in the polarizer provide sharp images. In particular, it is suitable for foldable and rollable displays because of its thin film thickness, good curve conformability and bending resistance.

[Mode for Carrying Out the Invention]

Hereinafter, preferred embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

A. Polyester film The polyester in the present invention is composed of polyethylene terephthalate as the main skeleton. The polyethylene terephthalate is composed of terephthalic acid as the main dicarboxylic acid component and terephthalic acid as the main diol The component ethylene glycol is obtained by polymerization reaction.

The polyester in the present invention requires terephthalic acid having a dicarboxylic acid component of 75 mol% or more, and diol component of ethylene glycol having 75 mol% or more. By making the dicarboxylic acid component into terephthalic acid of an aromatic dicarboxylic acid, high heat resistance and crystallization can be achieved, so high thermal dimensional stability can be imparted. Specifically, the coefficient of thermal expansion under environmental changes can be reduced. When the terephthalic acid which is a dicarboxylic acid component is less than 75 mol %, the amount of an amorphous component will increase and thermal dimensional stability by crystallization will fall. From the viewpoint of high thermal dimensional stability, it is preferably at least 80 mol%, more preferably at least 90 mol%. It is most preferably 100 mole%, but in this case, from the viewpoint of easily reducing the difference between the minimum refractive index in the plane direction and the refractive index in the thickness direction, and the iris suppression effect for polarizer protection, it is preferable to include 3 Copolymerization components other than ethylene glycol of diol components described later in mole % to 25 mole %. On the other hand, the diol component is also the same as the dicarboxylic acid component, if the ethylene glycol is less than 75 mol%, the amorphous component increases, and the high thermal dimensional stability due to crystallization decreases. More preferably, it is 80 mol% or more, Still more preferably, it is 90 mol% or more. It is most preferably 100 mole%, but in this case, from the viewpoint of easily reducing the difference between the minimum refractive index in the plane direction and the refractive index in the thickness direction, and the iris suppression effect for polarizer protection, it is preferable to include 3 Copolymerization components other than terephthalic acid from mole % to 25 mole %.

Regarding the dicarboxylic acid component of the copolymerization component, examples of the aromatic dicarboxylic acid include isophthalic acid and phthalic acid, and examples of the aliphatic dicarboxylic acid include adipic acid, octane dicarboxylic acid, and acid, sebacic acid, dimer acid, dodecanedioic acid, cyclohexanedicarboxylic acid and their ester derivatives, etc. Among these, adipic acid and isophthalic acid are preferred from the viewpoint of high refractive index and ease of uniaxial orientation. These acid components may be used alone or in combination of two or more. Furthermore, oxyacids such as hydroxybenzoic acid may be partly copolymerized.

Moreover, the diol component of the copolymerization component other than ethylene glycol can mention, for example: neopentyl glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1 ,6-Hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol, polyalkylene Diol, 2,2-bis(4-hydroxyethoxyphenyl)propane, glycerin, trimethylolpropane, trimethylolethane, ethylene oxide, propylene oxide, etc. Among them, 1,4-cyclohexanedimethanol is preferable from the viewpoint of uniaxial anisotropy and a high glass transition point. In particular, these diol components may be used alone or in combination of two or more.

The polyester film of the present invention requires a temperature range of 30°C to 70°C from the viewpoint of suppressing warpage and wrinkles of polarizers in long-term reliability tests and cracks in polarizers in environmental change tests. The thermal linear expansion coefficient in the planar direction is 70 ppm/°C or less (7×10 ^-5 /°C). The thermal linear expansion coefficient in the plane direction of the film means the maximum value of the thermal linear expansion coefficient in the film plane, and when the orientation angle of the film is aligned with the longitudinal direction or the width direction, the film longitudinal direction or the width direction becomes the maximum value. In this case, the average value of the thermal linear expansion coefficients in the longitudinal direction and the width direction is preferably 40 ppm/°C or less, more preferably at least one of the longitudinal direction or the width direction is 30 ppm/°C. If either one is 30ppm/°C or less, the expansion and contraction behavior of the polarizer due to environmental changes can be maintained by aligning its orientation with the absorption axis of the polarizer, thereby suppressing cracks in the polarizer. More preferably, it is 10 ppm/°C or less. Or, preferably, the average value of the longitudinal direction and the width direction is preferably 30 ppm/°C or less. More preferably, it is 20 ppm/°C or less. As means for achieving a small thermal expansion coefficient, directional crystallization by stretching the film at a temperature of 85° C. or higher is preferably applied. The magnification ratio is preferably at least 2 times, more preferably at least 3 times. Alternatively, from the viewpoint of thermal crystallization and orientation relaxation, it is preferable to perform heat treatment at a temperature of 80°C or more and less than 200°C. A uniaxially stretched film is more preferably a biaxially stretched film because the coefficient of thermal linear expansion in the non-stretched direction becomes higher. In addition, the coefficient of thermal expansion can be determined by TMA measurement based on JIS K 7197.

The polyester film of the present invention requires that the difference ΔN(min-ZD) between the minimum refractive index N(min) in the planar direction and the refractive index N(ZD) in the thickness direction be 0.09 or less. The refractive index of the plane orientation of the film can be rotated once every 10 degrees on the circumference to 180 degrees, and the samples are cut out. For the samples of each angle, the refraction of each angle is measured by Abbe refractometer, 稜鏡 coupler, ellipsometer, etc. Rate. Let the minimum value of the refractive index obtained at a wavelength of 590 nm be N(min), and let the refractive index in the thickness direction be N(ZD). When the value of ΔN(min-ZD) of such a difference exceeds 0.09, the birefringence in the thickness direction of the polyester film becomes large, and rainbow spots in oblique viewing angles tend to be seen. On the other hand, if it is 0.09 or less, since the birefringence in the thickness direction is suppressed, it becomes difficult to generate|occur|produce rainbow spots. More preferably, it is 0.07 or less. More preferably, it is 0.05 or less. The means for achieving it is preferably uniaxial stretching, and in particular, in order not to lower the refractive index in the thickness direction, it is preferably glass transition point + 20°C or higher and a stretching ratio of 4 times or less. When low-temperature stretching and high-magnification stretching are used, the planar orientation of the benzene rings of terephthalic acid advances, resulting in a decrease in the refractive index N(ZD) in the thickness direction. The draw ratio is preferably 3 times to 3.5 times.

The polyester film of the present invention is a polyester film for polarizer protection for the purpose of protecting a polarizer. Also, the in-plane retardation is preferably 400 nm to 3000 nm. In-plane retardation is the birefringence in the plane of the film multiplied by the thickness. In addition, the polarization of the incident light perpendicular to the plane is divided into the direction with the largest polarizability and the direction with the smallest polarizability perpendicular to it. The difference in refractive index in these directions is the double refraction of light. When the planar retardation becomes 3000 nm or more, it will become difficult to reduce the thickness. On the other hand, 400 nm or less can be achieved by making the orientation states of longitudinal stretching and transverse stretching equal, but it becomes difficult to make the orientation angle (slow axis) uniform due to the influence of meandering. From the perspective of the relationship with interference color, the higher the planar retardation is, the closer it is to achromatic color, so it is preferably 1500 nm to 3000 nm. More preferably, it is 2000-3000 nm. The method of adjusting the planar retardation can be achieved by making the film thickness between 5 μm and 40 μm, the ratio of vertical and horizontal stretching ratios from 1 to 4, the stretching temperature from 80°C to 120°C, and adjusting the heat treatment below 190°C. In addition, the relationship between birefringence and interference color is widely known as Michel-Levy's interference color chart.

The polyester film of the present invention preferably has a retardation of incident light inclined at 50° from the vertical axis of the film surface of 2000 nm or more and 6000 nm or less from the viewpoint of suppressing oblique iridescent spots. When the thickness exceeds 6000 nm, the plane orientation of the benzene rings proceeds, and rainbow spots tend to occur. More preferably, it is not less than 2500 nm and not more than 5000 nm. More preferably, it is not less than 3000 nm and not more than 4000 nm. In addition, the film tilt axis is the slow axis. As for the means of achievement, it can be achieved by, for example, adjusting the copolymerization component to 3 mol% to 25 mol%, or adjusting the thickness to 10-40 μm, the draw ratio and the temperature of heat treatment described later. In particular, the surface magnification is preferably from 2 to 12 times, more preferably from 3 to 10 times, from the viewpoint of suppressing surface orientation.

The polyester film of the present invention needs to have a thickness of 40 μm or less. If the film thickness is thicker, the stress and strain on the polarizer due to environmental changes will increase, so the polarizer will easily warp and crack. More preferably, it is 30 μm or less. More preferably, it is 20 μm or less. Thickness adjustment can be easily achieved by changing the discharge rate of the extruder and the travel speed of the casting drum.

The thickness variation in the width direction of the polyester film of the present invention is preferably 10% or less. When the thickness unevenness exceeds 10%, the phase difference changes and the color of the interference color changes, so that rainbow spots are easily recognized visually. That is, when the thickness unevenness is large, the shading of the interference color becomes clear. More preferably, it is 8% or less, Still more preferably, it is 5% or less. The method of reducing the thickness unevenness in the width direction of the film is achieved by adjusting the gap between the die openings with die bolts and applying more than twice the transverse stretch in the width direction. The thickness unevenness in the width direction of the polyester film of the present invention is preferably small within the image display size, preferably small within 20 cm.

The intrinsic viscosity of the polyester film of the present invention is preferably 0.80 dl/g or more from the viewpoint of suppressing rainbow spots. The so-called intrinsic viscosity (Intrinsic Viscosity), also known as the limit viscosity or IV value, is the viscosity coefficient of a thin solution. If the IV value is less than 0.80dl/g, the refractive index N(ZD) in the thickness direction is likely to decrease after stretching and heat treatment steps, so the minimum refractive index N(min) in the plane direction and the refractive index N(ZD) in the thickness direction The difference ΔN(min-ZD) becomes larger, and rainbow spots tend to occur. It is preferably at least 0.83dl/g, more preferably at least 0.85dl/g. The IV value can be adjusted to a desired value by adjusting the polycondensation time during solution polymerization and the time during solid phase polymerization.

The melting point of the polyester film of the present invention is preferably 245°C to 210°C. The so-called melting point here refers to the crystal melting peak in the differential scanning calorimetry chart of the first RUN obtained by differential scanning calorimetry (DSC) at a heating rate of 20°C/min from 25°C to 300°C, and there are multiple In the case of a peak, ΔH (crystal melting enthalpy) obtained from the peak area is the peak top temperature of the largest peak. If the melting point is lower than 210° C., the crystal structure of the polymer has poor heat resistance and thermal dimensional stability deteriorates. Therefore, the coefficient of thermal expansion becomes high, and cracks are likely to occur in the polarizer when it is made into a polarizing plate. In addition, when the melting point exceeds 245° C., the heat resistance becomes high, but thermal crystallization tends to proceed and ΔN (min-ZD) becomes large, so rainbow spots tend to occur. The melting point is related to the amount of copolymerization described next, and can be adjusted according to the amount.

The main skeleton of the polyester film of the present invention is polyethylene terephthalate, and its copolymerization component is preferably not less than 3 mol% and not more than 25 mol%. If the amount of copolymerization exceeds 25 mol%, the thermal dimensional stability such as thermal expansion coefficient and thermal contraction rate will decrease due to the approach of an amorphous resin, so that it becomes difficult to produce the effect of preventing cracks of the polarizer when making a polarizing plate. In addition, the problem of warping and curling of the polarizing plate occurs due to poor thermal dimensional stability. On the other hand, if the amount of copolymerization is less than 3 mol%, the crystal structure of polyethylene terephthalate becomes dominant, and ΔN(min-ZD) after the production steps of stretching and heat treatment becomes large, so it becomes Rainbow spots are prone to occur. From the viewpoint of thermal dimensional stability and suppression of rainbow spots, it is preferably from 4 mol% to 18 mol%. More preferably, it is 5 mol% or more and 14 mol% or less.

Among the copolymerization components of the polyester film of the present invention, it is preferable to contain at least a component selected from adipic acid, isophthalic acid, and cyclohexanedimethanol. By copolymerizing these components, there is an effect of reducing ΔN(min-ZD), making rainbow spots less likely to occur. In addition, these components may be used in combination of plural, or may be used individually as a copolymerization component. From the viewpoint of polymerization reactivity as a resin and thermal dimensional stability, it may be a terpolymer or a tetrapolymer. Also, from the viewpoint of heat resistance, either one of isophthalic acid and cyclohexanedimethanol is preferably a copolymerization component.

In the polyester film of the present invention, the angle formed by the absorption axis of the polarizer and the slow axis of the polyester film is preferably 5° or less from the viewpoint of suppressing iridescent spots. More preferably, it is 3° or less. The best aspect will be described using FIG. 1( b ). The orientation of the maximum refractive index of the polyester film 1 is the slow axis 5, which is the plane orientation of the strongest orientation (arrangement) of the molecular chains inside the polyester film. The angle formed by the slow axis 5 of the polyester film and the absorption axis 6 of the polarizer 4 is 0° (coincidence), which is optimal from the viewpoint of preventing iridescent spots. By adopting such a configuration, if the polarizer and the polyester film are bonded together to form a polarizing plate, the linearly polarized light (polarized light rotated by 90° relative to the absorption axis) that passes through the polarizer is also affected by the polyester film in oblique incidence. Since birefringence becomes difficult, it is not necessary to increase the phase difference to 3000 nm or more. In terms of means of realization, the absorption axis of the polarizer film is usually the stretching (orientation) direction after impregnating iodine, so it has an absorption axis in the winding direction, and is bonded to the polarizer protective film in a roll-to-roll manner. Therefore, the slow axis of the polyester film is preferably the film winding direction, that is, the traveling direction of the manufacturing steps (generally the long side direction of the film roll). In addition, since the polyester film has zigzag phenomenon in the film width direction during the production process, the physical property unevenness including the change of the inclination angle (orientation angle) of the slow axis is included from the center portion to the end portion in the film width direction. From the viewpoint of suppressing the buckling phenomenon, the heat treatment temperature is preferably 200°C or lower, more preferably 180°C or lower. Moreover, from the viewpoint of aligning the slow axis with the traveling direction, it is necessary to set the longitudinal stretch ratio to be equal to or higher than the lateral stretch ratio. The so-called zigzag phenomenon refers to the unevenness of the physical properties in the width direction of the film, which is derived from the film deformation behavior of the straight line drawn in the width direction of the film before the tenter in the film manufacturing step, and deformed into a bow shape after transverse stretching and heat treatment. On the other hand, the angle formed by the slow axis 5 of the polyester film and the absorption axis 6 of the polarizer 4 is 90° (orthogonal), which means that the polarization of the oblique light passing through the polarizer is prone to birefringence and rainbow spots .

The polyester film of the present invention is preferably a three-layer laminate of A layer/B layer/A layer, and the thickness of the A layer is 1 μm or less. By having such a three-layer structure, the functions of the surface layer A and the inner layer B can be separated, which is preferable. For example, by adding particles for imparting slipperiness to layer A and making layer B particle-free, a highly transparent and slippery polyester film for polarizer protection can be obtained. Also, by making the amount of copolymerization of the surface layer A layer smaller than that of the B layer, it becomes possible to impart heat resistance to the surface layer side. In addition, if the thickness of the surface A layer exceeds 1 μm, the light scattering distance of the particles inside the A layer will become longer. Therefore, if the polyester film is irradiated with a three-wavelength fluorescent lamp and the reflected light is observed, strong interference fringes and particles will appear. The resulting light scattering becomes easy to generate turbidity, resulting in a decrease in optical performance as a polarizing plate, which is not preferable. More preferably, it is 0.8 to 0.1 μm. In addition, the interference fringes here are a phenomenon caused by bright lines of fluorescent lamps, and are different phenomena from interference unevenness due to phase difference.

The thermal shrinkage rate of the polyester film of the present invention in an environment of 85° C. for 6 hours is preferably 0.5% or less in the longitudinal direction and the width direction. The polarizing plate is exposed to a temperature of 85°C in the manufacturing process and the actual use environment. Therefore, if the polarizing plate protective film shrinks at 85°C, image unevenness due to warping of the polarizing plate will occur. Preferably it is 0.3% or less, More preferably, it is 0.2% or less. The means of achieving this is that the temperature above 100°C is relaxed in the longitudinal direction and the width direction, and the enthalpy is relaxed, and the crystallization of the polyester film is carried out. At the same time, there is no strain in the amorphous part, thus imparting thermal dimensional stability.

(Manufacturing method of polarizing plate) The polarizing plate of the present invention is a polarizing plate comprising a polarizer, and the aforementioned polyester film for polarizer protection arranged on one side of the polarizer. As the polarizer, any suitable polarizer can be used. For example, the resin film forming the polarizer may be a single-layer resin film, or may be a laminate of two or more layers. Specific examples of polarizers made of single-layer resin films include: polyvinyl alcohol (PVA)-based films, partially formaldehyde-based PVA-based films, vinyl. Vinyl acetate copolymers are partially saponified films and other hydrophilic polymer films that are dyed and stretched by adding dichroic substances such as iodine and dichroic dyes, PVA dehydration products, polychlorinated films, etc. Polyene-based oriented films such as ethylene dehydrochlorination acid-treated products, etc. Preferably, a polarizer obtained by dyeing a PVA-based film with iodine and uniaxially stretching it is used because of its excellent optical properties.

The above-mentioned dyeing by iodine is performed, for example, by immersing a PVA-based film in an iodine aqueous solution. The draw ratio of the uniaxial stretching is preferably from 3 to 7 times. Stretching may be performed after dyeing or while dyeing. In addition, dyeing may be performed after stretching. Swelling treatment, crosslinking treatment, cleaning treatment, drying treatment, etc. are applied to the PVA-based film as needed. For example, by immersing the PVA-based film in water for washing before dyeing, not only can the stains and anti-blocking agents on the surface of the PVA-based film be cleaned, but also the PVA-based film can be swollen to prevent uneven dyeing. Specific examples of polarizers obtained by using a laminate include a laminate of a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or a laminate formed using a resin substrate and coating. A polarizer obtained from a laminate of PVA-based resin layers of the resin substrate. A polarizer obtained by using a laminate of a resin base material and a PVA-based resin layer coated and formed on the resin base material. For example, a PVA-based resin solution is applied to a resin base material and dried to form a PVA-based The resin layer is obtained by obtaining a laminate of a resin substrate and a PVA-based resin layer; it can be obtained by stretching and dyeing the laminate to make the PVA-based resin layer into a polarizer. In this embodiment, stretching usually includes stretching by immersing the laminate in an aqueous solution of boric acid. If necessary, the stretching may further include stretching the laminate in air at a high temperature (for example, 95° C. or higher) before stretching in an aqueous boric acid solution. The obtained resin substrate/polarizer laminate can be used as it is (that is, the resin substrate can be used as a protective layer for the polarizer), or the resin substrate can be peeled off from the resin substrate/polarizer laminate , any appropriate protective layer according to the purpose is layered on the peeled area. The details of such a method of manufacturing a polarizer are described in, for example, JP-A-2012-73580. The entire description of this publication is incorporated by reference in this specification.

The polarizer of the polarizing plate of the present invention preferably has a thickness of 20 μm or less. More preferably, it is 3 μm to 15 μm. If the polyester film of the present invention is used, cracks in the polarizer can be effectively prevented, and thus a thin polarizer can be used even in severe environments such as high temperature and large temperature changes. Polarizer and polarizer protective film (polyester film) can be laminated through any appropriate adhesive layer. Preferably, the adhesive layer is formed of an adhesive composition containing a polyvinyl alcohol-based resin.

The polarizing plate of the present invention preferably further includes an easy-adhesive layer disposed on the polarizer side of the polarizer protective polyester film.

唑啉系交聯劑。易接著層的詳細內容記載於例如日本特開2010-55062號公報。該公報其整體的記載被引用於本說明書中作為參考。在一個實施形態中，上述易接著層包含任意的適當微粒子。藉由形成包含微粒子之易接著層，能夠有效地抑制捲取時發生之黏連。上述微粒子可為無機系微粒子，亦可為有機系微粒子。就無機系微粒子而言，可列舉例如：二氧化矽、二氧化鈦、氧化鋁、氧化鋯等無機氧化物、碳酸鈣、滑石、黏土、燒成高嶺土、燒成矽酸鈣、水合矽酸鈣、矽酸鋁、矽酸鎂、磷酸鈣等。就有機系微粒子而言，可列舉例如：聚矽氧系樹脂、氟系樹脂、(甲基)丙烯酸系樹脂等。此等之中，較佳為二氧化矽。上述微粒子的粒徑(數量平均一次粒徑)較佳為10～200nm，進一步較佳為20～60nm。In one embodiment, a polyester film with an adhesive layer is provided. Easy-adhesive layers include, for example, water-based polyurethane and

Azoline-based crosslinking agent. The details of the easily-adhesive layer are described in, for example, JP-A-2010-55062. The entire description of this publication is incorporated by reference in this specification. In one embodiment, the above-mentioned easily-adhesive layer contains arbitrary appropriate fine particles. By forming an easy-adhesive layer containing fine particles, it is possible to effectively suppress the blocking that occurs during winding. The above-mentioned fine particles may be inorganic fine particles or organic fine particles. Inorganic microparticles include, for example, inorganic oxides such as silica, titania, alumina, and zirconia, calcium carbonate, talc, clay, fired kaolin, fired calcium silicate, hydrated calcium silicate, silicon Aluminum oxide, magnesium silicate, calcium phosphate, etc. Examples of organic microparticles include silicone-based resins, fluorine-based resins, (meth)acrylic-based resins, and the like. Among these, silicon dioxide is preferable. The particle diameter (number average primary particle diameter) of the fine particles is preferably from 10 to 200 nm, more preferably from 20 to 60 nm.

The thickness of the above-mentioned easily-adhesive layer is preferably 0.35 μm or less. If it is such a range, when it applies to an image display apparatus, the polyester film with an easy-adhesive layer which does not hinder the optical characteristic of another member easily can be obtained. More preferably, it is 0.2 μm or less and 0.05 μm. In one embodiment, the refractive index of the above-mentioned easily bonding layer is preferably 1.45-1.60. If it is such a range, when it applies to an image display apparatus, the polyester film with an easy-adhesive layer which does not hinder the optical characteristic of another member easily can be obtained. In one embodiment, the polyester film may be provided with a release layer on at least one side thereof. The composition of the release layer can adopt the composition of the easy-adhesive layer described above. Preferably, the release layer contains the aforementioned fine particles.

(Manufacturing method of polyester film) The above-mentioned polyester film is obtained through a forming step of forming a film-forming material (resin composition) containing the above-mentioned polyester-based resin into a film, and a stretching step of stretching the formed film. Preferably, the stretching step includes preheating the film before stretching the film, and heat treatment after stretching the film. In one embodiment, the polyester film is provided in a strip shape (or a shape cut out from a rectangular parallelepiped). The so-called strip shape is also called roll shape.

The film-forming material may contain additives in addition to the polyester-based resin described above, and may also contain a solvent. As additives, arbitrary appropriate additives can be used according to the purpose. Specific examples of additives include reactive diluents, plasticizers, surfactants, fillers, antioxidants, antiaging agents, ultraviolet absorbers, leveling agents, thixotropic agents, antistatic agents, Conductive materials, flame retardants. The number, type, combination, and addition amount of additives can be appropriately set according to the purpose.

The polyester film of the present invention can be formed into a film by using a melt extrusion method. For example, a polyester-based thermoplastic resin can be supplied to an extruder, melted and extruded into a sheet using a T-die or the like, and then cooled and solidified on a casting drum to form an unstretched film. At the glass transition point of the resin composition ( It can be obtained by stretching this unstretched film at a temperature above Tg). The stretching method at this time may be the well-known method of stretching in the width direction after stretching in the longitudinal direction, or a method of stretching in the longitudinal direction after stretching in the width direction, or a combination of multiple times in the longitudinal direction. Stretching and stretching in the width direction are performed. In addition, stretching in an oblique direction is also possible.

The stretching method of the film includes the aforementioned sequential biaxial stretching, simultaneous biaxial stretching of stretching in the longitudinal direction and stretching in the width direction, and uniaxial stretching of only uniaxial stretching. The polyester film of the present invention is uniaxially stretched or sequentially biaxially stretched from the viewpoint of aligning the slow axis with the longitudinal direction. If the film is stretched by sequential biaxial stretching, the plane phase difference can be easily adjusted to 400-3000 nm by the ratio of stretching temperature and stretching ratio, and the coefficient of thermal expansion can be well-balanced to obtain rainbow spots and polarization The polyester film that there are few outbreaks of the crack of the mirror in particular. In particular, from the viewpoint of reducing the thermal linear expansion coefficient in the longitudinal direction while aligning the slow axis with the longitudinal direction to suppress cracks, uniaxial stretching in which only the longitudinal direction is stretched, and stretching in the width direction are most preferable. A method of stretching in the longitudinal direction after stretching, and a method of stretching in the longitudinal direction, then stretching in the width direction, and finally stretching in the longitudinal direction.

Sequential biaxial stretching or simultaneous biaxial stretching is usually performed using a roll stretching machine and a tenter stretching machine. Therefore, the stretching direction of the film is usually the longitudinal direction (MD) and the width direction (TD) of the film. In addition, the MD direction is the advancing direction of a film.

The stretching temperature is preferably Tg+5°C to Tg+50°C relative to the glass transition temperature (Tg) of the film, more preferably Tg+5°C to Tg+30°C, further preferably Tg+5°C to Tg+10°C. By stretching at such a temperature, a polyester film having well-balanced control of the planar retardation Re (measurement wavelength: 590 nm) and the linear expansion coefficient can be obtained. Also, a polyester film excellent in transparency can be obtained.

The draw ratio in MD is preferably from 1.1 times to 5 times, more preferably from 1.1 times to 4 times, further preferably from 1.5 times to 3.5 times, and particularly preferably from more than 2 times to 3.2 times. If it is such a range, the polyester film which has favorable crystallinity can be obtained, for example while converging in-plane retardation in the desired range of 3000-400 nm.

The draw ratio of TD is preferably 1 to 4 times, more preferably 1.1 to 3 times, further preferably 1.1 to 2.5 times. If it is such a range, it is easy to align the slow axis of the polyester film with the longitudinal direction, and it is easy to make the difference ΔN(min- ZD) is 0.09 or less, and a polyester film with little occurrence of iridescent spots can be obtained.

The ratio of the stretch ratio in MD to the stretch ratio in TD (TD stretch ratio/MD stretch ratio), in the case of uniaxial stretching, is preferably 1 or more or 0.35 or less, more preferably 3 to 5, Or 0.15 to 0.3. In the case of biaxial stretching, it is preferable that it is 1.3-3 from a viewpoint of aligning an orientation angle with a width direction, or it is preferable that it is 0.5-1 from a viewpoint of aligning a longitudinal direction. On the production side, the latter is preferable from the viewpoint of being applicable to a roll-to-roll process by aligning the slow axis of the strong orientation of the polyester film with the absorption axis of the PVA polarizer, and more preferably 0.6 to 0.9. If it is such a range, the polyester film which generate|occur|produces especially little rainbow spots can be obtained.

The stretching speed of MD is preferably 5%/sec～400%/sec, more preferably 5%/sec～150%/sec, further preferably 8%/sec～150%/sec, and further preferably 8%/sec～150%/sec. %/sec～100%/sec, especially 8%/sec～80%/sec, best 8%/sec～60%/sec. If it is such a range, it will be excellent in optical characteristics, and the polyester film which has favorable crystallinity can be obtained.

The stretching speed of TD is preferably 5%/sec～150%/sec, more preferably 5%/sec～100%/sec, further preferably 8%/sec～100%/sec, especially preferably 8% /sec～80%/sec, the best is 8%/sec～60%/sec. If it is such a range, it will be excellent in optical characteristics, and the polyester film which has favorable crystallinity can be obtained.

The temperature of the preheating treatment is preferably from 80°C to 150°C, more preferably from 90°C to 130°C. Also, the time for the preheating treatment is preferably from 1 second to 100 seconds, more preferably from 1 second to 100 seconds, and still more preferably from 5 seconds to 80 seconds. If it is such a range, it will be excellent in optical characteristics, and the polyester film which has favorable crystallinity can be obtained.

The temperature of the heat treatment is preferably from 100°C to 250°C, more preferably from 120°C to 200°C, further preferably from 130°C to 180°C. When it is such a range, it is excellent in transparency and the polyester film which has favorable crystallinity can be obtained. The heat treatment time is preferably 1 second to 50 seconds, more preferably 2 seconds to 50 seconds, further preferably 2 seconds to 40 seconds, particularly preferably 5 seconds to 40 seconds, most preferably 8 seconds to 30 seconds. When it is such a range, it is excellent in transparency and the polyester film which has favorable crystallinity can be obtained.

B. Polarizer Fig. 1(a) is a schematic cross-sectional view of a polarizing plate according to an embodiment of the present invention. The polarizer 100 includes a polarizer 4 and a polyester film 1 disposed on one side of the polarizer 4 . As the polyester film 1, the polyester film of this invention demonstrated above was used. The other side of the polarizer can be configured with any other suitable polarizer protective film, or no polarizer protective film can be configured. In one embodiment, the polarizer 4 and the polyester film 1 (or another polarizer protective film) are laminated via the adhesive layer 3 . Moreover, the easy-adhesive layer 2 is laminated|stacked on the polyester film 1 in order to make the adhesive agent layer 3 adhere to the polyester film 1.

In one embodiment, the polarizing plate may be applied to an image display device such that the side on which the polyester film is arranged becomes the viewing side. Moreover, when applying the above-mentioned polarizing plate to a liquid crystal display device, the polarizing plate provided with a polyester film may be arranged on the viewing side of the liquid crystal cell, or may be arranged on the back side. FIG. 2 is an example of an embodiment in which the present invention is applied to a video display device. FIG. 2( a ) is an example of a liquid crystal display device including a polarizer 200 , a liquid crystal cell 10 , a polarizer 300 , a polarizing reflective film 11 , and a backlight 12 according to the present invention. Each polarizer is composed of the polyester film 7 of the present invention, a polarizer 8 , and another polarizer protective film 9 described above. Here, the adhesive layer and the easy-adhesive layer are omitted. FIG. 2( b ) is an example of an organic EL display device including a circular polarizer 400 and an organic electroluminescent (EL) unit 14 according to the present invention. The circular polarizing plate 400 of the present invention is composed of the polyester film 7 of the present invention, a polarizer 8 , and a λ/4 phase difference plate 13 .

(Specific measurement method and evaluation method of effect) The measurement method of the characteristic in this invention, and the evaluation method of an effect are as follows. (1) Composition of polyester The composition of the copolymerized polyethylene terephthalate of the present invention is to adjust the monomer amount of the copolymerized component during polymerization with the blending amount of the diol component and the dicarboxylic acid component, and it can be determined by 1H-NMR and TMAH addition type Simultaneously, derivatization thermal decomposition GC/MS measurement, identification of copolymerized monomers and calculation of composition ratio. Take about 30 mg of polyester film and its wafer, dissolve it in a mixture of deuterated chloroform (CDCl3) and deuterated hexafluoroisopropanol (HFIP-d2), and perform 1H-NMR measurement at a temperature of 40°C. In addition, the ratio of the mixed solution was set to CDCl3:HFIP-d2=2:1. On the occasion of identification, the identification is based on the existing data of the individual spectra of the known individual monomers of terephthalic acid, adipic acid, isophthalic acid, cyclohexanedimethanol, ethylene glycol, the composition of which is given by The ratio of the peak areas of the spectra was used to calculate the copolymerization ratio.

(2) Intrinsic viscosity of polyester The intrinsic viscosity of polyester resin and film is to dissolve 0.1g of polyester resin or film in 10ml of o-chlorophenol at 160°C for 20 minutes, and measure the solution viscosity at 25°C with an Ostwald viscometer.

(3) Film thickness, layer thickness The thickness of the film was measured using a dial gauge thickness gauge (Mitutoyo Co., Ltd. No. 2109-10) having a flat tip and a diameter of 4 mm. The platform for placing the film is the special platform (Code 7002) attached by the manufacturer. In addition, the measurement was performed 5 times at different positions, and the average value was used as the thickness (μm) of the film. A section of the film was cut out using a rotary microtome RMS type (manufactured by Nippon Microtome Research Institute). Sections in the thickness direction and the longitudinal direction, and sections in the thickness direction and width direction of the film were cut out. After vapor-depositing platinum-palladium on the cross-section with an Ion Coater (1B-3 type of Eiko Corporation), a cross-sectional photograph of 100 to 5000 magnifications was taken with a JEOL Electric Field Emission Scanning Electron Microscope (FE-SEM) JSM-6700F. The overall thickness of the film is based on a dial gauge thickness gauge, and the constituent thicknesses such as the thickness of the surface layer containing particles are obtained. In the case where the thickness of the structure cannot be observed, the film is embedded in epoxy resin, and a section of the film is cut out with a microtome. The cross-section was observed with a transmission electron microscope (JEM-1400 Plus manufactured by JEOL Ltd.) at a magnification (any magnification from 100 to 5000 times) at which the overall image of the cross-section of the film can be grasped, and the thickness of the surface layer constituted by the laminate was obtained.

(4) Coefficient of thermal expansion (CTE): The thermal expansion coefficient of the film during the heating process from 30°C to 70°C uses a thermomechanical measuring device TMA/SS6000 (manufactured by Seiko Instruments Co., Ltd.), and the sample width is 4 mm. For the sample length (between chucks) distance) of 20mm, the tension in the constant load mode is 19.6mN. The temperature was raised from 15° C. to 220° C. at a temperature increase rate of 10° C./min, and the values of the dimensions of the samples at each temperature (° C.) were obtained. Then, from the dimension L (30°C) (mm) of the sample at 30°C and the dimension L (70°C) (mm) at 70°C, it was calculated by the following formula (1). In addition, in measuring length, the value of the thermal linear expansion coefficient in the longitudinal direction is CTE-MD, and the value of the thermal linear expansion coefficient in the width direction is CTE-TD. Coefficient of thermal expansion (ppm/℃)=X/distance between chucks/(70-30)×10 ⁶ . ． ． Formula (1) X(mm): film displacement corresponding to film temperature 30℃～70℃=L(70℃)(mm)-L(30℃)(mm)

(5) Refractive index A sample was cut out from the central part of the obtained polyester film in the width direction at 4 cm in the longitudinal direction (MD) × 3.5 cm in the width direction (TD), and a sodium D line (wavelength 589 nm (about 590 nm)) was used as a light source, using diiodine Methane was used as a mounting solution, and the refractive index N (MD) in the longitudinal direction and the refractive index in the width direction of the film were measured in accordance with JIS K7142 (2014) A at 25°C using an Abbe refractometer 4T (manufactured by Atago Co., Ltd.) N(TD), the refractive index N(ZD) in the thickness direction. The refractive index of the test piece is 1.74.

In the central part of the film width direction, the minimum refractive index in the plane direction is the refractive index N(MD) in the longitudinal direction or the refractive index N(TD) in the width direction, so the minimum value is N(min), and the following formula is used (2) Calculate ΔN(min-ZD). In addition, when the cutting position is unknown, measure all the samples cut out every 10° rotation, and adopt the minimum value. ΔN(min-ZD) = Minimum refractive index N (min) in the plane direction - refractive index N (ZD) in the thickness direction. ． ． (2) If it cannot be specified by the above method, the orientation of the fast axis of the phase difference measuring device in the next item is used.

(6) The phase difference and slow axis of the incidence angles of 0° and 50° of the polyester film A phase difference measurement device (KOBRA-21ADH) manufactured by Oji Scientific Instruments Co., Ltd. was used. A sample is cut out from the central part of the film width direction at 4 cm in the width direction x 3 cm in the long side direction, and placed in the device so that the film width direction becomes the angle 0° defined by this measurement device, and the plane phase at an incident angle of 0° at a wavelength of 590 nm is measured The difference and the phase difference at an incident angle of 50° become the orientation angle of the slow axis of the polyester film.

(7) Melting point Tm The differential scanning calorimetry device Robot DSC-RDC6220 manufactured by SII Nanotechnology (formerly SEIKO Electronics Industry; now Hitachi High-Tech Science) is used. The data analysis system uses Muse standard analysis "Standard Analysis Ver.9", according to JIS K7121 (1999 edition), JIS K-7122 (1987 edition) measures the melting point Tm. 5 mg of the polyester film of the present invention was used as a sample, and the temperature at the apex of the endothermic peak obtained from the DSC curve when the temperature was raised from 25°C to 300°C at 20°C/min was defined as the melting point Tm. When there are a plurality of endothermic peaks, the temperature at the apex of the endothermic peak on the highest temperature side is defined as the melting point Tm.

(8) Thickness unevenness in film width direction (TD) For evaluation of thickness unevenness, a 5-cm-wide sample was cut out from the center portion of the entire width of the polyester film so as to be parallel to the film width direction and have a measurement length of 20 cm or more. Next, using this sample, the film was run at a running speed of 0.15 m/min using FILM THICKNESS TESTER KG601A manufactured by ANRITSU Corporation. The wide-range electronic micrometer K306C made by ANRITSU company is used to detect the thickness change, and the high-precision temperature and voltage measurement unit NT-TH08 made by Keynes company is used to store the thickness change relative to time. Sampling frequency at this time: 100ms, AD integration time: 2ms. The thickness data was read out with the analysis software wave logger manufactured by Keynes Corporation. Thickness unevenness was calculated by the following formula (3). The measurement length was set to 20 cm. Uneven thickness (%)=(maximum thickness-minimum thickness)/average thickness×100. ． ． Formula (3)

(9) Heat shrinkage rate at 85°C From the central part of the film width direction, the sample was cut out in the longitudinal direction and the width direction. The sample size: width 10 mm×measurement direction 200 mm. Next, write the marking lines on the sample at intervals of 100 mm in the initial length of the measurement direction, and use a universal projector (Model V-16A, 20×DP lens) manufactured by Nikon Corporation to accurately measure the distance To (mm) between the marking lines ) to the third decimal place. Then, it was placed in a hot-air oven (GPHH-202 manufactured by ESPEC Corporation) heated to 85° C. under a load of 3 g for 6 hours, and heat-treated. The distance T (mm) between the marked lines after the heat treatment was measured, and the thermal contraction rate was calculated by the following formula (4) from the change in the distance between the marked lines before and after heating. Heat shrinkage rate (%)=((To-T)/To)×100. ． ． Formula (4)

(10) rainbow spots Take out the liquid crystal unit from the liquid crystal TV "45UH7500" manufactured by LGD, and peel off the polarizing plate on the backlight side. The polarizing plates obtained in Examples and Comparative Examples were bonded to the surface where the polarizing plate of the liquid crystal TV was peeled off so that the absorption axis of the polarizer became the short side of the liquid crystal TV through an adhesive. The liquid crystal cell to which the polarizing plate obtained in the Example and the Comparative Example was bonded was installed again, and the TV was turned on with a white display. Visually check in all directions with a polar angle of 60° on the lit liquid crystal TV, and observe whether there is a rainbow spot or not. Evaluation was performed by the following criteria. ◎: No rainbow spot was observed at all ○: No rainbow spots observed △: Rainbow spots are slightly observed ×: Rainbow spots are clearly observed

(11) Crack test (thermal shock acceleration test) The polarizing plates obtained in Examples and Comparative Examples were evaluated using a thermal shock tester (manufactured by ESPEC). The polarizing plates obtained in Examples and Comparative Examples were cut into a width of 50 mm x a length of 150 mm. At this time, prepare a sample in which the absorption axis direction of the polarizer is parallel to the transverse direction (short side) of the cut polarizer, and the transmission axis direction of the polarizer is parallel to the transverse direction (short side) of the cut polarizer. Parallel samples. The surface of the protective film (polyester film) on which the polarizing plate was not laminated was bonded to 0.5 mm thick non-alkali glass with an acrylic adhesive to prepare a sample. Put the obtained sample into the test area of the thermal shock tester, and spend 30 minutes to cool the test area from room temperature to -40°C. Next, after raising the temperature in the test area to 85°C over 30 minutes, it took another 30 minutes to lower the temperature to -40°C. The process of raising the temperature from -40°C to 85°C and then lowering the temperature to -40°C is regarded as a cycle. After repeating 100 cycles and 200 cycles, the laminate is taken out, and the presence or absence of cracks is visually observed, and the following criteria are used for evaluation . ⊚: No cracks were observed even after repeating 250 cycles. ○: Cracks were not observed after repeating 200 cycles, but cracks occurred after repeating 250 cycles. Δ: After repeating 100 cycles, no cracks were observed, but after repeating 200 cycles, cracks occurred. X: Cracks occurred after repeating 100 cycles.

(thermoplastic resin) As resin A, the following were prepared. (Resin A) In a mixture of 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol, 0.09 parts by weight of magnesium acetate, 0.03 parts by weight of Parts of antimony trioxide are heated by common method to carry out transesterification reaction. Next, after adding 0.020 weight part of phosphoric acid 85% aqueous solutions to this transesterification reaction product with respect to the quantity of the dimethyl terephthalate, it transferred to the polycondensation reaction layer. Next, while heating and raising the temperature, the reaction system is slowly decompressed, and under a reduced pressure of 1mmHg, a polycondensation reaction is carried out at 290°C by a common method to obtain polyethylene terephthalate with IV=0.64dl/g . The glass transition point is 78°C.

As the resin B, the following were prepared. In addition, IV adjustment was performed by carrying out solid-phase polymerization under reduced pressure at 230° C. after preliminary crystallization of the granular polyester composition obtained by polycondensation reaction at 150° C. for 4 hours.

(Resin B-1) Copolymerize polyethylene terephthalate with IV=0.85dl/g isophthalic acid (IPA 5 mol%). The glass transition point is 78°C.

(Resin B-2) Copolymerize polyethylene terephthalate with IV=0.72dl/g isophthalic acid (IPA 10 mol%). The glass transition point is 78°C.

(Resin B-3) Copolymerize polyethylene terephthalate with IV=0.80dl/g isophthalic acid (IPA 5 mol%). The glass transition point is 78°C.

(Resin B-4) Copolymerize polyethylene terephthalate with IV=0.89dl/g isophthalic acid (IPA 10 mol%). The glass transition point is 78°C.

The following were prepared as resin C. (Resin C) Copolymerize polyethylene terephthalate with IV=0.75dl/g cyclohexanedimethanol (CHDM 10 mole%). The glass transition point is 80°C.

The following were prepared as resin D. (Resin D) Copolymerize polyethylene terephthalate with IV=0.72dl/g adipic acid (10 mol%). The glass transition point is 63°C. [Example]

Hereinafter, the polyester film and the polarizing plate of the present invention will be described in further detail through examples, but the present invention is not limited thereto.

[Example 1 of polyester film] Using a biaxial kneader, particles of Resin B-1 containing 2% by weight of agglomerated silica particles with an average particle diameter of 1.2 μm as an external additive were used as main particles 1 . Next, the particles of resin B-1 to which particles were not added were used as main particles 2 .

Pellet 1 was diluted with Pellet 2 of Resin B-1 to which no particles were added so that the particle concentration of Pellet 1 was 0.04% by weight, dried at 150°C for 5 hours, supplied to single-screw extruder 1, and melted at 280°C . The pellet 2 of resin B-1 dried similarly was supplied to the single-screw extruder 2, and melted at 280 degreeC. For each polymer, layer A, which is the surface layer containing particles, is metered by a gear pump and introduced into a feed block consisting of A/B/A to be divided into two parts, and layer B, which is the inner layer without particles Layers are also introduced into the feed block, whereby these converging flows become a composite laminar flow of A/B/A, which is extruded into sheets by a T-die. Next, it was wound on a casting drum at 25° C. and solidified by cooling to obtain an unstretched film by an electrostatic application casting method.

After that, the film is heated by a roller heated to 110°C and a radiation heater, stretched 1.1 times in the longitudinal direction in the first longitudinal stretching step, and then stretched at 100 in the width direction by a tenter in the first transverse stretching step. Stretch at ~110°C by 2.8 times, and further apply 110°C treatment in the subsequent first heat treatment step of the tenter. Next, stretch 3.2 times in the longitudinal direction at a temperature of 95°C in the second longitudinal stretching step with rollers and radiant heaters, and perform heat fixing at 180°C and 2% relaxation in the width direction in the second heat treatment step , thereby obtaining a successively biaxially stretched polyester film with a thickness of 28 μm. The thickness of the layer A of the obtained thin film was 0.8 μm. In addition, physical properties are described in Table 1.

[Examples 2 to 4 and Comparative Examples 1 to 3 of polyester films] Various polyester compositions are shown in Table 1 and Table 3, and unstretched films were obtained with the same equipment configuration, drying of polyester raw materials, and extrusion conditions as in Example 1. Next, various polyester films that were biaxially stretched sequentially were obtained by using the film-forming conditions of the first longitudinal and transverse stretching, heat treatment, second longitudinal stretching, and heat setting shown in Table 1 and Table 3. The films obtained in the examples achieved a low thermal expansion coefficient effective for preventing cracks in the polarizer of a polarizing plate and low birefringence for suppressing rainbow spots. In particular, it was confirmed that Example 3 is excellent in thickness unevenness and thermal dimensional stability, and is most suitable for polarizer protection. On the other hand, in the comparative example, the coefficient of thermal expansion is excellent in both the longitudinal direction and the width direction of the film, but the birefringence is so large that iridescent spots occur, and the polyester film for polarizer protection used as a polarizing plate has insufficient performance.

[Examples 5-10, 15-17, Comparative Examples 5 and 6 of polyester films] Various polyester compositions are shown in Table 1, Table 2, and Table 3. Unstretched films were obtained with the same device configuration, drying of polyester raw materials, and extrusion conditions as in Example 1. Next, various monoaxially stretched polyester films were obtained under the film forming conditions of longitudinal stretch ratio, temperature, and heat treatment temperature shown in Table 1, Table 2, and Table 3. It was confirmed that the film obtained in the examples realized a low thermal expansion coefficient effective for preventing cracks in the polarizer of a polarizing plate and low birefringence for suppressing rainbow spots. On the other hand, in the comparative example, the thermal linear expansion coefficient in the width direction of the film was large, and the thermal shrinkage rate at 85° C. was also large, and the polyester film for polarizer protection used as a polarizing plate had insufficient performance.

[Examples 11 to 14 and Comparative Example 4 of polyester film] Various polyester compositions are shown in Table 2 and Table 3, and unstretched films were obtained with the same equipment configuration, drying of polyester raw materials, and extrusion conditions as in Example 1. Next, as shown in Table 2 and Table 3, various polyester films were obtained that were uniaxially stretched only in the width (transverse) direction without longitudinal stretching, and were subjected to lateral stretching with a tenter and heat treatment temperature. It was confirmed that the film obtained in the examples achieved a low thermal expansion coefficient effective for preventing cracks in the polarizing plate and low birefringence to suppress rainbow spots. On the other hand, in the comparative example, the thermal linear expansion coefficient in the width direction of the film was large, and the film thickness was also thick, and the polyester film for polarizer protection used as a polarizing plate had insufficient performance.

[Example 1 of Polarizer] As the substrate, a long amorphous isophthalic acid copolymerized polyethylene terephthalate (IPA copolymerized PET) film (thickness: 100 μm) with a water absorption rate of 0.75% and a Tg of 75° C. was used. Corona treatment is applied to one side of the substrate, and on the corona-treated surface, it is coated and dried at 25°C and contains polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mole%) and acetylene in a ratio of 9:1. Aqueous solution of acetyl-modified PVA (polymerization degree 1200, acetyl acetyl modification degree 4.6%, saponification degree 99.0 mol% or more, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFIMER (registered trademark) Z200") , a PVA-based resin layer with a thickness of 11 μm was formed to produce a laminate.

The obtained laminate was uniaxially stretched 2.0 times at the free end in the longitudinal direction (longitudinal direction) between rollers having different peripheral speeds in an oven at 120° C. (auxiliary stretching in the air).

Next, the laminate was immersed in an infusible bath (a boric acid aqueous solution obtained by mixing 4 parts by weight of boric acid with respect to 100 parts by weight of water) at a liquid temperature of 30° C. for 30 seconds (infusion treatment).

Next, in a dyeing bath having a liquid temperature of 30° C., the polarizing plate was immersed while adjusting the iodine concentration and the immersion time so that the polarizing plate had a predetermined transmittance. In this example, it was immersed for 60 seconds in an iodine aqueous solution obtained by mixing 0.2 parts by weight of iodine and 1.5 parts by weight of potassium iodide with respect to 100 parts by weight of water (dyeing treatment).

Next, immerse in a crosslinking bath at a liquid temperature of 30° C. (a boric acid aqueous solution obtained by mixing 3 parts by weight of potassium iodide and 3 parts by weight of boric acid with respect to 100 parts by weight of water) for 30 seconds (crosslinking treatment) .

Afterwards, while the laminate was immersed in an aqueous solution of boric acid at a liquid temperature of 70° C. (an aqueous solution obtained by mixing 4 parts by weight of boric acid and 5 parts by weight of potassium iodide with respect to 100 parts by weight of water), the total draw ratio was adjusted. The 5.5-fold method was uniaxially stretched (stretched in water) in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds.

Thereafter, the laminate was immersed in a cleaning bath (an aqueous solution obtained by mixing 4 parts by weight of potassium iodide with respect to 100 parts by weight of water) at a liquid temperature of 30° C. (washing treatment).

In addition, corona treatment was performed on the polyester film of Example 1, and 15.2 wt% of the product name "SUPERFLEX 210R" manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd. and 2.7 wt% of Japanese The aqueous solution of the product name "WS-700" manufactured by Catalyst Co., Ltd. was dried at 80° C. for 1 minute to obtain a polyester film with an easy-adhesive layer.

On the surface of the PVA-based resin layer of the above-mentioned laminate, a PVA-based resin aqueous solution (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., product name "GOHSEFIMER (registered trademark) Z-200", resin concentration: 3% by weight) used as an adhesive layer was coated, Paste the above polyester film with easy-adhesive layer. The resulting laminate was heated for 5 minutes in an oven maintained at 60°C. Thereafter, the substrate was peeled off from the PVA-based resin layer to obtain a polarizing plate (the polarizer of Example 1 (transmittance: 42.3%, thickness 5 μm)/the polyester film of Example 1). In addition, the polyester film and the polarizer were laminated so that the MD direction of the polyester film was substantially parallel to the absorption axis direction of the polarizer. Table 1 shows the evaluation results of the obtained polarizing plate.

[Examples 2-17, Comparative Examples 1-6] Except having used the polyester film obtained in Examples 2-17 and Comparative Examples 1-6 instead of the polyester film of Example 1, it carried out similarly to Example 1, and obtained various polarizing plates. Table 1, Table 2, and Table 3 show the evaluation results of various obtained polarizing plates. In addition, the polyester films and polarizers of Examples 11 to 14 and Comparative Example 4 were laminated so that the TD direction was substantially parallel to the absorption axis direction of the polarizer because the polyester film was stretched horizontally and uniaxially.

[Table 1] Polyester Film Manufacturing Conditions Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Stretch pattern Way vertical and horizontal vertical and horizontal vertical and horizontal vertical and horizontal longitudinal uniaxial longitudinal uniaxial longitudinal uniaxial longitudinal uniaxial Polyester raw material Resin B-1 Resin B-3 Resin B-1 Resin B-3 Resin A Resin A Resin B-2 Resin B-2 Copolymerization amount Mole % 5 5 5 5 - - 10 10 1st longitudinal stretch magnification 1.1 1.1 1.1 1.1 3.1 3.7 3.7 3.1 Stretch temperature ℃ 110 110 110 110 90 90 90 90 1st horizontal stretch magnification 2.8 2.9 2.5 3.1 1 1 1 1 Stretch temperature ℃ 100～110 100～110 100～110 100～110 - - - - 1st heat treatment temperature ℃ 110 170 110 120 170 170 90 150 2nd longitudinal stretch magnification 3.2 3.2 3.3 3 - - - - Stretch temperature ℃ 95 95 95 90 - - - - 2nd heat treatment temperature ℃ 180 180 180 200 - - - - Polyester Film Properties thickness μm 28 16 28 11 32 30 twenty three twenty four Coefficient of Thermal Expansion CTE-MD ppm/°C 15 13 10 8 1 0 0 11 Coefficient of Thermal Expansion CTE-TD ppm/°C 69 46 55 57 44 36 70 54 CTE average ppm/°C 42 30 33 33 twenty three 18 35 33 ΔN(min-ZD) - 0.06 0.07 0.05 0.07 0.07 0.09 0.04 0.05 Melting point (Tm) ℃ 242 242 242 242 254 254 231 231 plane phase difference nm 2592 1490 2950 1330 3430 3423 1925 2030 50° phase difference nm 3417 2017 4032 1721 4648 4836 2541 2600 slow axis angle ° 90 90 90 89 90 90 90 90 uneven thickness % 8.3 9.9 4.2 22.7 9.7 5.2 8.8 16.3 85℃ heat shrinkage rate MD % 0.2 0.1 0.2 0.1 0.3 0.3 1.9 0.4 85℃ thermal shrinkage rate TD % 0.3 0.2 0.2 -0.1 0.2 0.1 0.1 0.2 polarizer Interference color of polarizer - ○ △ ◎ △ ○ ○ △ △ polarizer crack - △ ◎ ○ ○ ◎ ◎ △ ○

[Table 2] Polyester Film Manufacturing Conditions Example 9 Example 10 Example 11 Example 12 Example 13 Example 14 Example 15 Example 16 Example 17 Stretch pattern Way longitudinal uniaxial longitudinal uniaxial horizontal uniaxial horizontal uniaxial horizontal uniaxial horizontal uniaxial longitudinal uniaxial longitudinal uniaxial longitudinal uniaxial Polyester raw material Resin B-2 Resin B-2 Resin B-1 Resin B-1 Resin B-1 Resin B-1 Resin C Resin D Resin B-4 Copolymerization amount Mole% 10 10 5 5 5 5 10 10 10 1st longitudinal stretch magnification 3.7 3.1 1 1 1 1 3.7 3.5 3.1 Stretch temperature ℃ 90 90 - - - - 90 75 100 1st horizontal stretch magnification 1 1 3.3 3.3 3.3 3.3 1 1 1 Stretch temperature ℃ - - 90 90 90 90 - - - 1st heat treatment temperature ℃ 190 190 90 90 150 150 150 150 150 2nd longitudinal stretch magnification - - - - - - - - - Stretch temperature ℃ - - - - - - - - - 2nd heat treatment temperature ℃ - - - - - - - - - Polyester Film Properties thickness μm twenty three twenty three 18 39 29 40 35 36 39 Coefficient of Thermal Expansion CTE-MD ppm/°C 2 16 66 66 53 64 9 18 17 Coefficient of Thermal Expansion CTE-TD ppm/°C 52 66 16 25 1 5 28 67 59 CTE average ppm/°C 27 41 41 46 27 35 19 43 38 ΔN(min-ZD) - 0.07 0.06 0.05 0.04 0.07 0.07 0.06 0.05 0.04 Melting point (Tm) ℃ 231 231 242 242 242 242 241 210 230 plane phase difference nm 2421 2156 1532 2860 2747 3875 2490 2420 2998 50° phase difference nm 3339 2854 1993 3756 3749 5119 3371 3339 3962 slow axis angle ° 90 90 1 1 1 1 90 90 90 uneven thickness % 8.6 14.6 4 3 2.6 3.3 5.3 7.1 6.4 85℃ heat shrinkage rate MD % 0.2 0.25 4.3 4.4 0.2 0.2 0.5 1.8 0.5 85℃ thermal shrinkage rate TD % 0.1 0.1 3.1 3 0.1 0.2 0.4 1 0.4 polarizer Interference color of polarizer - ○ △ △ ◎ ○ ○ ○ ○ ◎ polarizer crack - ○ △ ○ ○ ○ ○ ◎ △ ○

[table 3] Polyester Film Manufacturing Conditions Comparative example 1 Comparative example 2 Comparative example 3 Comparative example 4 Comparative Example 5 Comparative Example 6 Stretch pattern Way vertical and horizontal vertical and horizontal vertical and horizontal horizontal uniaxial longitudinal uniaxial longitudinal uniaxial Polyester raw material Resin A Resin A Resin B-3 Resin A Resin A Resin A Copolymerization amount Mole% - - 5 - - - 1st longitudinal stretch magnification 4 3.2 3.2 1 3.1 3.7 Stretch temperature ℃ 85 95 92 - 90 90 1st horizontal stretch magnification 2 3.8 4 4.5 1 1 Stretch temperature ℃ 85 100 100 85 - - 1st heat treatment temperature ℃ 180 180 140 190 - - 2nd longitudinal stretch magnification - - 1.4 - - - Stretch temperature ℃ - - 110 - - - 2nd heat treatment temperature ℃ - - 210 - - - Polyester Film Properties thickness μm 25 30 25 80 30 30 Coefficient of Thermal Expansion CTE-MD ppm/°C 0 0 0 78 0 0 Coefficient of Thermal Expansion CTE-TD ppm/°C 28 4 10 16 129 131 CTE average ppm/°C 14 2 5 47 65 66 ΔN(min-ZD) - 0.12 0.15 0.15 0.07 0.02 0.04 Melting point (Tm) ℃ 254 254 242 255 254 254 plane phase difference nm 2549 578 570 8032 3380 3921 50° phase difference nm 4220 1874 1827 10713 4048 4815 slow axis angle ° 89 79 77 4 90 90 uneven thickness % twenty two 3.2 2.5 3 7 5.1 85℃ heat shrinkage rate MD % 0.35 0.44 0.9 0.1 21.6 23.5 85℃ thermal shrinkage rate TD % 0.4 0.63 0.5 0.1 10.4 9.5 polarizer Interference color of polarizer - x x x ○ ◎ ◎ polarizer crack - ◎ ◎ ◎ x x x [Possibility of industrial use]

The polyester film and polarizing plate of the present invention are thin films when they are applied to image display devices, and at the same time solve the iridescent spots unique to polyester films, and still have high durability in environmental changes, so they can be used as thin and flexible displays. The polarizer material of the panel.

1: polyester film 2: Easy bonding layer 3: Adhesive layer 4: Polarizer 5: slow axis 6: Absorption axis 7: polyester film 8: Polarizer 9: Polarizer protective film 10: LCD unit 11: Polarized reflective film 12: Backlight 13:λ/4 phase difference plate 14: Organic EL unit 100: polarizer 200: polarizer 300: polarizer 400: circular polarizer

Fig. 1 is a schematic diagram showing a preferred aspect of the present invention. FIG. 2 is a schematic diagram of an embodiment when the present invention is applied to an image display device.

none.

Claims (13)

A polyester film for polarizer protection, which is a polyester film containing terephthalic acid with a dicarboxylic acid component of more than 75 mol% and ethylene glycol with a diol component of 75 mol% or more, at 30°C to 70 The thermal linear expansion coefficient in the plane direction of the film in the temperature range of °C is 70 ppm/°C or less, the difference between the minimum refractive index in the plane direction and the refractive index in the thickness direction is 0.09 or less, and the thickness is 40 μm or less. The polyester film for polarizer protection as claimed in item 1, wherein the plane retardation is 400nm-3000nm. The polyester film for polarizer protection as claimed in claim 1, wherein the thickness variation in the width direction of the film is less than 10%. For example, the polyester film for polarizer protection in claim 1, wherein the intrinsic viscosity of the film is above 0.80dl/g, and the melting point is 245°C to 210°C. For example, the polyester film for polarizer protection according to claim 1, wherein the copolymerization component is not less than 3 mol% and not more than 25 mol%, and at least contains components selected from adipic acid, isophthalic acid, and cyclohexanedimethanol. The polyester film for polarizer protection as claimed in claim 1, wherein the angle formed by the absorption axis of the polarizer and the slow axis of the polyester film is 5° or less. For example, the polyester film for polarizer protection in Claim 1 is a three-layer laminate of A layer/B layer/A layer, and the thickness of A layer is 1 μm or less. A polarizing plate comprising a polarizer and the polyester film according to any one of Claims 1 to 7 arranged on one side of the polarizer. The polarizing plate according to claim 8, wherein the thickness of the polarizer is 20 μm or less. The polarizing plate according to claim 8, further comprising an easy-adhesive layer disposed on the polarizer side of the polyester film. The polarizing plate according to claim 10, wherein the easily-adhesive layer contains fine particles. The polarizing plate according to claim 10, wherein the thickness of the easy-adhesive layer is 0.35 μm or less. The polarizing plate according to claim 10, wherein the refractive index of the easy-adhesive layer is 1.6 or less.

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