JP2020173463A - Biaxially stretched polyethylene terephthalate film for optical film inspection - Google Patents

Abstract

To provide a biaxially stretched polyethylene terephthalate film for optical film inspection which enables accurate and quick inspection of optical films for large-screen displays.SOLUTION: Provided is a biaxially stretched polyethylene terephthalate film for optical film inspection, which satisfies the following conditions (1)-(3) and (8)-(10): (1) total light transmittance is 85% or more, (2) film haze is 15% or less, (3) transmission polarization degree is 7.0% or more, (8) the film is a laminated film consisting of a central layer and surface layers abutting the central layer, (9) the surface layers contain 0.10-0.20 mass% of fine particles with an average particle diameter of 1.5-4.0 μm, (10) the central layer contains 0.00-0.10 mass% of fine particles with an average particle diameter of 1.5-4.0 μm.SELECTED DRAWING: None

Description

The present invention relates to a biaxially stretched polyethylene terephthalate film for optical film inspection. More specifically, the present invention relates to a biaxially stretched polyethylene terephthalate film for optical film inspection, which has excellent polarization inspectability and processing characteristics.

A polarizing plate, a retardation polarizing plate, or a retardation plate, which is a component of a liquid crystal display device, is an indispensable component for adding light and darkness to the transmitted light of the liquid crystal display device and changing the hue, and is stable in quality. Maintenance is an important issue. These optical films are inspected in the state of a laminated body in which an adhesive layer is provided on one surface thereof and a film for protecting the optical film (film for optical film inspection) is laminated on the adhesive layer. It is rolled and transported or stored. A biaxially stretched polyethylene terephthalate film is widely used as a base material for such an optical film inspection film from the viewpoint of strength function and cost. A biaxially stretched polyethylene terephthalate film having a structure in which a linear polymer is oriented is a birefringent that optically exhibits birefringence. Therefore, the biaxially stretched polyethylene terephthalate film has two optical axes that are perpendicular to the direction parallel to the orientation direction of the molecule and perpendicular to the direction. Therefore, if the optical axis of the base material of the inspection film is laminated in a state of being tilted with respect to the optical axis of the optical film, it exhibits transmitted light or interference color when placed under the conditions of cross Nicol, and defects are inspected. It becomes a factor that hinders. Therefore, an excellent optical axis accuracy is required for a biaxially stretched polyethylene terephthalate film for optical film inspection (Patent Document 1).

The biaxially stretched polyethylene terephthalate resin film for optical film inspection is stretched in the longitudinal direction between rolls having different rotation speeds, and then stretched in the width direction while the end portion of the film is gripped in the tenter. Manufactured by being heat-fixed. In this case, due to the Boeing phenomenon, the distortion of the optic axis, that is, the distortion of the orientation spindle is larger at the edge than at the center of the film, so that only a very limited product at the center can be used for this purpose.

As a method of reducing the boeing of the film, a method of temporarily cooling the polyethylene terephthalate below the glass transition temperature after stretching in the width direction and then heat-treating, a method of providing a nip roll after stretching in the width direction, and a method of dividing the heat treatment chamber into a plurality of zones in stages A method of raising the temperature in the width direction, a method of providing a temperature distribution in the width direction to lead to a heat treatment zone, a method of increasing the stretching ratio in the width direction, and the like have been proposed. (Patent Documents 2 to 5)

In the optical film inspection process, a release film for optical film inspection and a protective film are produced by applying adhesive processing to a film whose distortion of the optical axis is reduced by the above method, and the film is laminated on the optical film. , Visually check the quality of the optical film under the conditions of Cross Nicol.

JP-A-2002-40249 Japanese Unexamined Patent Publication No. 2008-2466885 JP-A-2008-163263 Japanese Unexamined Patent Publication No. 2005-14545 Japanese Unexamined Patent Publication No. 2004-18588 Japanese Patent No. 4531117

Currently, the film proposed in the above patent document is used for optical film inspection. However, the increase in the screen size of displays has been dramatically advanced, and large screen displays of 42 inches or more have penetrated the market. In order to satisfy the demands for the progress of large-screen displays and the improvement of inspection accuracy, it has become necessary to reduce the distortion of the optical axis over a longer width. Furthermore, due to the demand for higher definition, it has become necessary to reliably recognize foreign substances and defects at a level that has not been a problem in the past, and it has become difficult to deal with the films that have been proposed conventionally.

An object of the present invention is to provide a biaxially stretched polyethylene terephthalate film for optical film inspection capable of inspecting such an optical film for a large screen display with high accuracy and high speed. That is, it is an object of the present invention to provide a biaxially stretched polyethylene terephthalate film for optical film inspection which has high polarization inspection property and excellent contrast under cross Nicol with respect to an optical film for large screen display.

Typical inventions are as follows.
Item 1.
A biaxially stretched polyethylene terephthalate film for optical film inspection that satisfies the following requirements (1) to (3) and (8) to (10) .
(1) Total light transmittance is 85% or more (2) Film haze is 15% or less (3) Transmission polarization degree is 7.0% or more
(8) A laminated film composed of a central layer and both surface layers in contact with the central layer.
(9) Both surface layers contain 0.10 to 0.20% by mass of fine particles having an average particle size of 1.5 to 4.0 μm.
(10) Item 2. The central layer contains 0.00 to 0.10% by mass of fine particles having an average particle size of 1.5 to 4.0 μm .
Item 2. The biaxially stretched polyethylene terephthalate film for optical film inspection according to Item 1, which further satisfies the following requirements (4) to (6).
(4) The heat shrinkage rate when heated at 150 ° C. for 30 minutes is 2.0% or less in both the longitudinal direction and the width direction. (5) The difference between the maximum and minimum omnidirectional heat shrinkage rates when heated at 150 ° C. for 30 minutes. Is 0.5% or less (6) The maximum amount of change in the omnidirectional heat shrinkage rate per 5 ° when heated at 150 ° C. for 30 minutes is 500 ppm or less.
Item 2. The biaxially stretched polyethylene terephthalate film for optical film inspection according to Item 1 or 2, which further satisfies the following requirement (7 ) .
(7) The maximum orientation angle of 18 ° or less under

The biaxially stretched polyethylene terephthalate film for optical film inspection of the present invention has excellent polarization inspection properties, and is therefore suitable for high-precision inspection of optical films for large screen applications. Further, according to a more preferable embodiment, it is possible to provide a biaxially stretched polyethylene terephthalate film for optical film inspection, which is excellent in post-processing at a high temperature.

The biaxially stretched polyethylene terephthalate film for optical film inspection of the present invention is made of a polyethylene terephthalate resin. Here, the polyethylene terephthalate resin contains ethylene glycol and terephthalic acid as main constituents. Other dicarboxylic acid components and glycol components may be copolymerized as long as the object of the present invention is not impaired. Other dicarboxylic acid components mentioned above include isophthalic acid, p-β-oxyethoxybenzoic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-dicarboxybenzophenone, bis- (4-carboxyphenyl ethane), and adipic acid. Acids, sebacic acid, 5-sodium sulfoisophthalic acid, cyclohexane-1,4-dicarboxylic acid and the like can be mentioned. Examples of the above-mentioned other glycol components include ethylene oxide adducts such as propylene glycol, butanediol, neopentyl glycol, diethylene glycol and bisphenol A, polyethylene glycol, polypropylene glycol, polytetramethylene glycol and the like. In addition, an oxycarboxylic acid component such as p-oxybenzoic acid can also be used.

Examples of the polymerization method for such a polyethylene terephthalate resin (hereinafter, simply referred to as PET) include a direct polymerization method in which terephthalic acid and ethylene glycol, and if necessary, other dicarboxylic acid components and diol components are directly reacted, and terephthalic acid. Any production method such as a transesterification method in which dimethyl ester (including a methyl ester of another dicarboxylic acid if necessary) and ethylene glycol (including another diol component if necessary) are subjected to a transesterification reaction is used. Can be done.

The intrinsic viscosity of the polyethylene terephthalate resin is preferably in the range of 0.45 dl / g to 0.70 dl / g. If the intrinsic viscosity is lower than 0.45 dl / g, the film is likely to tear, and if it is higher than 0.70 dl / g, the increase in filtration pressure becomes large and high-precision filtration becomes difficult.

It is preferable to add fine particles to the polyethylene terephthalate resin in the present invention to improve the workability (slipperiness) of the film. Any fine particles can be selected, and examples thereof include inorganic particles such as silica, calcium carbonate, barium sulfate, calcium sulfate, alumina, kaolinite, and talc, and other organic particles. In particular, from the viewpoint of transparency, silica particles having a refractive index relatively close to those of the resin component are preferable, and amorphous silica is particularly preferable.

As a preferred embodiment of the present invention, in order to obtain good transparency and stable workability (particularly surface friction characteristics), a polyethylene terephthalate layer which is a film having a multilayer structure and contains fine particles only on the surface layer is used. You can also. As such a base film, a polyethylene terephthalate film having a multilayer structure (a / b / a) in which a surface layer (a layer) containing fine particles is laminated on both sides of a central layer (b layer) by a coextrusion method. It is preferable to use. The layers constituting the front and back surface layers may be of the same type or different types, but in order to maintain the flatness of the base film, the polyethylene terephthalate resin on the front and back surface layers should have the same structure. Is desirable.

The average particle size of the fine particles contained in the surface layer is preferably 1.0 to 5.0 μm, more preferably 1.5 to 4.0 μm, and further preferably 2.0 to 3.0 μm. .. When the average particle size of the fine particles is 1.0 μm or more, it is preferable that the surface can be provided with an uneven structure suitable for imparting slipperiness. On the other hand, when the average particle size of the fine particles is 5.0 μm or less, high transparency is maintained, which is preferable. The content of the fine particles in the surface layer is preferably 0.10 to 0.20% by mass, preferably 0.10 to 0.15% by mass. When the content of the fine particles in the surface layer is 0.10% by mass or more, it is possible to impart an uneven structure suitable for imparting slipperiness to the surface layer surface, which is preferable. On the other hand, when the content of the fine particles in the surface layer is 0.20% by mass or less, high transparency is maintained, which is preferable.

The average particle size of the fine particles contained in the central layer is preferably 1.0 to 5.0 μm, more preferably 1.5 to 4.0 μm, and even more preferably 2.0 to 3.0 μm. .. When the average particle size of the fine particles is 1.0 μm or more, the film haze can be easily adjusted, which is preferable. On the other hand, when the average particle size of the fine particles is 5.0 μm or less, high transparency is maintained, which is preferable. The content of the fine particles contained in the central layer is preferably 0.10% by mass or less, more preferably 0.08% by mass or less, and further preferably 0.05% by mass or less. The lower limit is 0.00% by mass.

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

The biaxially stretched polyethylene terephthalate film for optical film inspection of the present invention preferably has a total light transmittance of 85% or more. The inspection accuracy of the optical film is improved in response to higher definition. In order to improve the detection of foreign matter, it is desirable that the film for optical film inspection has high transparency. Therefore, the total light transmittance of the biaxially stretched polyethylene terephthalate film for optical film inspection of the present invention is preferably 85% or more, more preferably 87% or more, still more preferably 89% or more. In order to improve visibility in the optical film inspection process, the higher the total light transmittance, the better, but for polyethylene terephthalate film containing particles for slipperiness, 100% total light transmittance is a technique. It is difficult to achieve, and the practical upper limit is 91%.

Further, the biaxially stretched polyethylene terephthalate film for optical film inspection of the present invention preferably has a haze of 15% or less. It is desirable to obtain high contrast in order to emphasize the presence of foreign matter and obtain higher inspection accuracy. Therefore, the haze in the biaxially stretched polyethylene terephthalate film for optical film inspection of the present invention is preferably 15% or less, more preferably 7% or less, further preferably 3% or less, and 2.8. % Or less is particularly preferable. In order to obtain high contrast, it is preferable that the haze is low, but it seems that 1% is the lower limit in the polyethylene terephthalate film containing particles due to the slipperiness. The haze and total light transmittance can be measured by using a turbidity meter according to JIS-K7105.

The biaxially stretched polyethylene terephthalate film for optical film inspection of the present invention preferably has a transmitted polarization degree of 7.0% or more. This makes it possible to realize high inspection accuracy. More preferably, it is 8.0% or more. In order to obtain high inspection accuracy, a higher transmission polarization degree is preferable, but a practical upper limit is 10%. In order to achieve a degree of polarization of 10% or more, it is necessary to add a polarizing additive or a crystal nucleating agent, which may increase the haze and decrease the total light transmittance. Is.

One example of an index showing the polarization selectivity of a biaxially stretched polyethylene terephthalate film for optical film inspection is the transmission polarization degree. The transmitted polarization degree of a film is an index showing a property of selectively transmitting either polarized light V or polarized light P orthogonal to the polarized light V. In the case of the present invention, the biaxially stretched polyethylene terephthalate film has a property of selectively transmitting polarized light P parallel to the orientation spindle direction rather than polarized light V perpendicular to the alignment spindle direction. The high degree of transmitted polarization improves the contrast during inspection and enables highly accurate inspection.

The transmitted polarization degree is represented by the following formula. In the following formula, "Tv" indicates the total light transmittance (%) of the film with respect to the polarized light V perpendicular to the main axis of orientation. On the other hand, "Tp" indicates the total light transmittance (%) of the film with respect to the polarized light P parallel to the orientation principal axis.

The biaxially stretched polyethylene terephthalate film for optical film inspection of the present invention preferably has a heat shrinkage rate of 2.0% or less in both the longitudinal direction and the width direction when heated at 150 ° C. for 30 minutes. The heat shrinkage rate is more preferably 1.5% or less. When the heat shrinkage rate is 2.0% or less, high dimensional stability can be obtained even in a high-temperature heat treatment process at 150 ° C. or higher, which can significantly contribute to the improvement of productivity. The heat shrinkage rate is preferably low, but the lower limit is considered to be about 0.5% from the viewpoint of manufacturing.

Further, in order to cope with the increase in heat treatment temperature in post-processing such as adhesive processing, not only the thermal dimensional stability at high temperature is excellent, but also the difference in heat shrinkage rate is small in all directions in the film surface. Is desirable. Therefore, the difference between the maximum and minimum omnidirectional heat shrinkage when heated at 150 ° C. for 30 minutes in the biaxially stretched polyethylene terephthalate film for optical film inspection of the present invention is preferably 0.5% or less. It is more preferably 3% or less, and further preferably 0.1% or less. As described above, the film of the present invention is excellent in thermal dimensional stability, and preferably has a well-balanced heat shrinkage ratio that is substantially the same in the longitudinal direction and the width direction, and wrinkles and thickness unevenness are less likely to occur even by heat treatment. , Very suitable for defect inspection of large screens using polarized light on large screens. The smaller the difference between the maximum and minimum omnidirectional heat shrinkage, the better, and the preferable lower limit is 0%.

Further, in order to cope with the increase in heat treatment temperature in post-processing such as adhesive processing, it is desirable that the amount of change in the heat shrinkage rate is small in all directions in the film surface. Therefore, the maximum amount of change in the omnidirectional heat shrinkage rate per 5 ° when heated at 150 ° C. for 30 minutes in the biaxially stretched polyethylene terephthalate film for optical film inspection of the present invention is preferably 500 ppm or less, preferably 400 ppm or less. Is more preferable, and 300 ppm or less is further preferable. If the maximum amount of change in the omnidirectional heat shrinkage rate per 5 ° exceeds 500 ppm, local deformation occurs during heat load processing in post-processing, causing defects in the coating process such as adhesive processing and wrinkles. As a result, it may be difficult to perform a high-precision inspection when inspecting an optical film. The smaller the maximum amount of change in the omnidirectional heat shrinkage is, the better, and the preferable lower limit is 0 ppm.

The biaxially stretched polyethylene terephthalate film for optical film inspection of the present invention preferably has a maximum orientation angle of 18 ° or less. This makes it possible to obtain even higher contrast. The maximum orientation angle is more preferably 15 ° or less, and even more preferably 11 ° or less. If the maximum orientation angle is larger than 18 °, even if it has a high transmittance to increase the transmittance under cross Nicol, light leakage will increase and the visual inspection will be hindered, so high-precision visual inspection will be performed. May not be available for.

In the biaxially stretched polyethylene terephthalate film for optical film inspection of the present invention, the amount of change in the orientation angle in the film width direction is preferably in the range of 0.2 ° to 0.8 ° per 100 mm. As described above, the film is distorted in orientation from the center to the edges due to the Boeing phenomenon in the film forming process. Therefore, the optical axis is tilted along the film width direction. The amount of change in the orientation angle is preferably small, but when high thermal stability suitable for high-precision inspection of optical films for large screens is required, the lower limit is substantially 0.2 ° per 100 mm. 0.8
If the above is the case, uniform optical axis accuracy cannot be obtained, which may make high-precision inspection difficult.

The thickness of the biaxially stretched polyethylene terephthalate film for optical film inspection of the present invention is not particularly limited and is arbitrary, but is preferably 9 to 300 μm, more preferably 12 to 100 μm. , 14-50 μm is even more preferred. If the thickness exceeds 300 μm, there is a problem in terms of cost, the retardation becomes large, and the visibility in cross-nicolation tends to decrease. If the thickness is less than 9 μm, the mechanical properties may deteriorate and the function as a protective film may not be fulfilled.

Further, in the case of a two-kind three-layer structure (a / b / a) in which a surface layer (a layer) containing fine particles is laminated on both sides of the central layer (b layer) by a coextrusion method, one side thereof is used. The thickness of the surface layer is preferably 0.5 to 10 μm, more preferably 1 to 5 μm. If the thickness of the surface layer exceeds the above range, the haze of the film may decrease.

The three-dimensional center plane average surface roughness (SRa) of the biaxially stretched polyethylene terephthalate film for optical film inspection of the present invention is preferably 0.020 μm or more and 0.035 μm or less. When the SRa is less than 0.020 μm, the surface unevenness of the film is low, so that the slipperiness is poor, and minute scratches are generated during film handling during the film forming process and the processing process, and the film is used for optical film inspection. Then, the inspectability may decrease. Further, when the SRa exceeds 0.035 μm, the slipperiness is good, but light is diffused on the film surface due to the surface unevenness, and there is a possibility that sufficient contrast cannot be obtained in the optical film inspection step.

The "optical film" in the "biaxially stretched polyethylene terephthalate film for optical film inspection" of the present invention includes, for example, a polarizing plate, a retardation polarizing plate, a retardation plate, and the like. The biaxially stretched polyethylene terephthalate film of the present invention is laminated on at least one surface of these optical films (polarizing plate, retardation polarizing plate, retardation plate, etc.) and inspected in a laminated state (under the conditions of cross Nicol). (Inspection of defects of optical film, etc.) The optical film may be used in such a manner that an optical film having a film shape is laminated on the biaxially stretched polyethylene terephthalate film, or on at least one surface of the biaxially stretched polyethylene terephthalate film. , The polymer solution may be applied and dried to form a layer, and this layer may be used as an optical film.

The method for producing the biaxially stretched polyethylene terephthalate film for optical film inspection of the present invention will be described. A typical example using polyethylene terephthalate pellets will be described in detail, but of course, the present invention is not limited to this.

First, the film raw material is dried or hot air dried so that the moisture content is less than 100 ppm. Next, each raw material is weighed, mixed, supplied to an extruder, and melt-extruded into a sheet. Further, the molten sheet is brought into close contact with a rotating metal roll (casting roll) by an electrostatic application method and cooled and solidified to obtain an unstretched PET sheet.

Further, high-precision filtration is performed in order to remove foreign substances contained in the resin at an arbitrary place where the molten resin is maintained at 280 ° C. The filter medium used for high-precision filtration of molten resin is not particularly limited, but in the case of a stainless sintered filter medium, the ability to remove aggregates and refractory organic substances containing Si, Ti, Sb, Ge, and Cu as main components. Excellent and suitable.

When the surface layer (a layer) and the intermediate layer (b layer) are co-extruded and laminated, the raw materials of each layer are extruded using two or more extruders, and a multi-layer feed block (for example, a merging block having a square merging portion) is used. ) Are used to join the two layers, extrude them into a sheet from a slit-shaped die, and cool and solidify them on a casting roll to form an unstretched film. Alternatively, a multi-manifold die may be used instead of the multi-layer feed block.

Next, the unstretched film obtained by the above method is sequentially biaxially stretched, and then heat-treated.

In the stretching step, the polyethylene terephthalate film of the present invention is stretched at least 1.1 to 7.0 times in the uniaxial direction at a temperature equal to or higher than the glass transition temperature of polyethylene terephthalate and lower than the crystallization temperature by using a known method. Obtainable.

For example, in the case of producing a biaxially oriented polyethylene terephthalate film, a sequential biaxial stretching method in which uniaxial stretching is performed in the longitudinal direction (longitudinal direction) or width direction (horizontal direction) and then stretching in the orthogonal direction, longitudinal direction (longitudinal direction). A method of simultaneously biaxially stretching in the width direction (lateral direction) and a method of using a linear motor as a driving method for simultaneous biaxial stretching can be adopted.

Patent Document 6 discloses a method for producing a polarizing diffusion film having a high degree of transmission polarization by heat-crystallizing an amorphous sheet made of a crystalline resin and then performing uniaxial stretching. However, although the method disclosed above can achieve a high degree of transmitted polarization, it is difficult to use it for optical film inspection because of its high optical haze and diffusing function. Therefore, as a result of diligent studies, the inventor of the present application has achieved a high degree of compatibility between the antinomy characteristics by performing the following stretching methods (1) and (2).

(1) Control of stretch ratio in the film width direction In order to obtain the biaxially stretched polyethylene terephthalate film for optical film inspection in the present invention, it is desirable to stretch in the width direction in the range of 4.8 to 7.0 times. When the stretching ratio in the width direction is 4.8 times or more, the degree of transmitted polarization is high, which is preferable. When it is 7.0 times or less, the frequency of breakage is reduced, which is preferable.

(2) Control of stretch ratio in the longitudinal direction of the film In order to obtain the biaxially stretched polyethylene terephthalate film for optical film inspection in the present invention, it is desirable to stretch the film in the longitudinal direction within a range of 3.0 times or less. When the stretching ratio in the longitudinal direction is 3.0 times or less, the transmission polarization degree is high, which is preferable. The lower limit of the draw ratio in the longitudinal direction is not particularly limited except that the film is stretched in the longitudinal direction, but 2.6 times or more is preferable from the viewpoint of suppressing the thickness fluctuation in the film flow direction to be small.

In order to obtain a film having a small maximum orientation angle and excellent heat shrinkage characteristics, it is preferable to carry out the following (3) to (5) in addition to the above (1) and (2).

(3) Control of heat fixing temperature So far, heat fixing treatment at a relatively low temperature has been recommended in order to maintain optical axis accuracy, but in the present invention, the temperature of the heat fixing treatment step is 220 ° C. It is preferably 230 ° C. or higher and 230 ° C. or lower. When the temperature of the heat fixing treatment is 220 ° C. or higher, the absolute value of the heat shrinkage rate becomes small, which is preferable. Further, when the temperature of the heat fixing treatment is 230 ° C. or lower, the film is less likely to become opaque and the frequency of breakage is reduced, which is preferable.

(4) Control of relaxation rate in the film width direction In order to obtain the biaxially stretched polyethylene terephthalate film for optical film inspection in the present invention, the relaxation rate in the width direction must be in the range of 2.0 to 4.5%. desirable. This is desirable because the difference in omnidirectional contraction rate can be reduced.

(5) Control of relaxation rate in the film width direction In order to obtain the biaxially stretched polyethylene terephthalate film for optical film inspection in the present invention, relaxation treatment in the width direction is performed at a relaxation rate of 0.005 to 6.0% / sec or less. It is desirable to do. When the relaxation speed in the width direction is 6.0% / sec or less, local flatness defects do not occur, which is preferable. More preferably, it is 0.1 to 5.0% / sec, and particularly preferably 0.5 to 4.0% / sec. The lower limit of the widthwise relaxation rate is not limited, but if a specific widthwise relaxation rate that can reduce the omnidirectional contraction rate difference at a widthwise relaxation rate of less than 0.005% / sec is implemented, the time required for the relaxation process becomes longer. The surface of the film becomes white and the transparency is impaired.

The film of the present invention is produced by the above method, but is not limited to the above specifically disclosed method within the scope of the above technical idea. What is important in producing the film of the present invention is to control the above-mentioned production conditions with high accuracy in an extremely narrow range based on the above technical idea.

Next, the effects of the present invention will be described with reference to Examples and Comparative Examples. First, the evaluation method of the characteristic value used in the present invention is shown below.

(1) Three-dimensional center surface average surface roughness (SRa)
Using a stylus type three-dimensional surface roughness meter (SE-3AK, manufactured by Kosaka Laboratory Co., Ltd.) on the surface of the film, the needle radius is 2 μm, the load is 30 mg, and the needle speed is 0.1 mm / sec. , Measured over a measurement length of 1 mm with a cutoff value of 0.25 mm in the longitudinal direction of the film, divided into 500 points at a pitch of 2 μm, and the height of each point was measured by a three-dimensional roughness analyzer (manufactured by Kosaka Laboratory Co., Ltd.). , TDA-21). The same operation was continuously performed 150 times in the width direction of the film at intervals of 2 μm, that is, over 0.3 mm in the width direction of the film, and the data was taken into the analyzer. Next, the three-dimensional average surface roughness SRa was determined using the analysis device. The unit of SRa is μm. The measurement was performed three times, and the average value thereof was adopted.

(2) Total light transmittance, haze JIS K 7105 "Optical property test method for plastics" Haze (cloud value) was measured. An NDH-300A turbidity meter manufactured by Nippon Denshoku Kogyo Co., Ltd. was used as the measuring instrument.

(3) Heat shrinkage rate (heat shrinkage rate in the longitudinal direction and the width direction)
The measurement was performed in accordance with JIS C 2318-1997 5.3.4 (dimension change). The film was cut into a width of 10 mm and a length of 250 mm in the direction to be measured, marked at intervals of 200 mm, and the interval (A) of the marks was measured under a constant tension of 5 gf. Next, the film was placed in an oven at 150 ° C. and heat-treated at 150 ± 3 ° C. for 30 minutes under no load, and then the mark interval (B) was measured under a constant tension of 5 gf. The heat shrinkage rate was calculated from the following formula.
Heat shrinkage rate (%) = (AB) / A × 100

(4) Omnidirectional heat shrinkage The film was cut to a width of 300 mm and marked in a circle with a diameter of 250 mm. The heat shrinkage rate in the film surface was determined according to the above heat shrinkage rate measurement method at a pitch of 5 ° with 0 ° in the longitudinal direction and 90 ° in the lateral direction. The difference between the maximum value and the minimum value is taken as the maximum and minimum difference of the omnidirectional heat shrinkage rate, the difference in the heat shrinkage rate at adjacent positions is calculated, and the maximum value is the maximum change amount of the omnidirectional heat shrinkage rate per 5 °. And said.

(5) Maximum Orientation Angle In the biaxially stretched polyethylene terephthalate film width for optical film inspection obtained in each example, the edge is set to 0% and the other edge is set to 100%. N 100 mm square film samples were continuously cut out at a pitch of 100 mm in the width direction from a region corresponding to 10% of the film width to a region corresponding to 90%. The square film sample was cut out at a right angle with respect to either the longitudinal direction or the width direction. For each film sample, using a MOA-6004 type molecular orientation meter manufactured by Oji Measuring Instruments Co., Ltd., the orientation angle of the molecular chain spindle with respect to the longitudinal direction of the film (θi, -90 ° ≤ θi ≤ 90 °), and the following formula The tilt angle (ξi) of the optical spindle with respect to the defined mechanical axis direction (either the longitudinal direction or the width direction) was measured. Three locations were sampled in the longitudinal direction, and the average value was calculated. Note that n is an integer obtained by multiplying the total width of the film by 0.8, dividing by 10 mm, and rounding up to the nearest whole number. Further, i represents a sample number, and i = 1 to n. Of these, the one with the largest value of the tilt angle (ξi) of the optical spindle was defined as the maximum orientation angle.
When | θ | ≤ 45 degrees ξ = | θ |
When | θ |> 45 degrees ξ = | 90 degrees − | θ ||

(6) An NDH-5000 type turbidity meter manufactured by Nippon Denshoku Kogyo Co., Ltd. was used as the transmission polarization degree measuring device. A polarizing plate was set in front of the turbidity meter test piece installation part. The film was set in close contact with the polarizing plate, and the main orientation axis of the film was set parallel to the polarization direction of the incident linearly polarized light, and the measurement was performed. The measured value was divided by the total light transmittance of the polarizing plate to obtain the total light transmittance Tp of polarized light parallel to the main orientation axis. Next, the film was rotated 90 degrees in a plane including the film surface so that the main orientation axis of the film was perpendicular to the polarization direction of the incident linearly polarized light. The measurement was carried out in the same manner as described above, and the measured value was divided by the total light transmittance of the polarizing plate to obtain the total light transmittance Tv of polarized light perpendicular to the main orientation axis. The transmission polarization degree was determined according to Equation 1.

(7) Heat Wrinkle Judgment Method Silicone was applied on a biaxially stretched polyethylene terephthalate film for optical film inspection by a die coat method with a processing tension of 10 kg / m applied, and dried in an oven at 120 ° C. Cut the sample after the above-mentioned silicone application from the roll, spread the length of 5 m on a flat table, and reflect the light of the fluorescent lamp on the application surface to check for heat wrinkles. confirmed.
◯: Good with no heat wrinkles.
X: Heat wrinkles were confirmed.

Example 1
(1) Production of PET Resin (A) When the temperature of the esterification reaction can was raised and reached 200 ° C., a slurry consisting of 86.4 parts by mass of terephthalic acid and 64.4 parts by mass of ethylene glycol was charged. While stirring, 0.017 parts by mass of antimony trioxide and 0.16 parts by mass of triethylamine were added as catalysts. Next, the pressure was raised and the pressure esterification reaction was carried out under the conditions of a gauge pressure of 3.5 kgf / cm2 and 240 ° C. Then, the inside of the esterification reaction can was returned to normal pressure, and 0.071 parts by mass of magnesium acetate tetrahydrate and then 0.014 parts by mass of trimethyl phosphate were added. Further, the temperature was raised to 260 ° C. over 15 minutes, and 0.012 parts by mass of trimethyl phosphate and then 0.0036 parts by mass of sodium acetate were added. After 15 minutes, the obtained esterification reaction product was transferred to a polycondensation reaction can, the temperature was gradually raised from 260 ° C. to 280 ° C. under reduced pressure, and the polycondensation reaction was carried out at 285 ° C.

After completion of the polycondensation reaction, filtration is performed with a Naslon filter having a 95% cut diameter of 5 μm, extruded into a strand shape 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 obtained PET resin (A) had a melting point of 257 ° C., an intrinsic viscosity of 0.616 dl / g, and substantially contained no inert particles and internally precipitated particles.

(2) Production of PET resin (B) Polyethylene terephthalate containing 2000 ppm of silica particles (Fuji Silysia Chemical Ltd., Cyricia 310, average particle size 2.7 μm) as an additive is produced by the same production method as PET (A) resin. Created.

(3) Production of Biaxially Stretched Polyethylene Terephthalate Film for Optical Film Inspection As a raw material for the surface layer (a), 40 parts by mass of PET resin (A) and 60 parts by mass of PET resin (B) are pellet-mixed and at 135 ° C. After drying under reduced pressure (1 Torr) for 6 hours, the mixture was supplied to the extruder 1. Further, 82 parts by mass of PET resin (A) and 18 parts by mass of PET resin (B) were pellet-mixed as raw materials for the intermediate layer (b), dried under reduced pressure (1 Torr) at 135 ° C. for 6 hours, and then extruded. Supplied to 2. The resin temperature of each raw material supplied to the extruder 2 and the extruder 1 to the melted portion, the kneaded portion, the polymer tube, the gear pump, and the filter of the extruder was set to 280 ° C, and then to 275 ° C for the polymer tube. It was laminated so as to be a / b / a using a layer merging block, and melted and extruded into a sheet from the base. The thickness ratio between the a layer and the b layer was controlled by using a gear pump of each layer so that a / b / a = 8/84/8. In addition, a stainless sintered filter medium (nominal filtration accuracy: 10 μm particles cut by 95%) was used for all of the above filters. The temperature of the base was controlled so that the extruded resin temperature was 275 ° C.

Then, the extruded resin was cast on a cooling drum having a surface temperature of 30 ° C. and brought into close contact with the surface of the cooling drum by an electrostatic application method to be cooled and solidified to prepare an unstretched film having a thickness of 480 μm.

The obtained unstretched sheet is heated to 105 ° C. with an infrared heater after raising the film temperature to 75 ° C. in a roll group heated to 78 ° C., and then heated to 105 ° C. in a roll group heated to a peripheral speed difference of 2 in the longitudinal direction. It was stretched 9 times.

Next, the obtained uniaxially stretched film was gripped with a clip and stretched in the film width direction. The stretching temperature in the width direction was 120 ° C., and the stretching ratio was 4.9 times. Then, a heat treatment was performed at 225 ° C. for 15 seconds, and a relaxation treatment of 3.8% was performed at 185 ° C. In the obtained biaxially stretched polyethylene terephthalate film width, the edge is 0% and the other edge is 100%. A slit was made in the region corresponding to 55% from the region corresponding to 50% of the film width to obtain a biaxially stretched polyethylene terephthalate film for optical film inspection having a thickness of 38 μm. Table 2 shows the physical properties of the obtained film.

Example 2
The film was prepared in the same manner as described in Example 1 except that the taking position was changed from the region corresponding to 80% of the film width to the region corresponding to 90%. Table 2 shows the physical properties of the obtained film.

Examples 3 to 6
It was prepared in the same manner as described in Example 1 except that the film forming conditions were changed to the conditions shown in Table 1. Table 2 shows the physical properties of the obtained film.

Comparative Example 1
The film was prepared in the same manner as described in Example 1 except that the layer structure and film forming conditions were changed to the conditions shown in Table 1, and the region corresponding to 50% to 55% of the film width was prepared. Slitting was performed to obtain a biaxially stretched polyethylene terephthalate film for optical film inspection. Table 2 shows the physical properties of the obtained film.

Comparative Example 2
The film was prepared in the same manner as described in Comparative Example 1 except that a slit was formed in a region corresponding to 90% from a region corresponding to 80% of the film width. Table 2 shows the physical properties of the obtained film.

Comparative Example 3
It was prepared by the same method as described in Example 1 except that the layer structure and film forming conditions were changed to the conditions shown in Table 1. Table 2 shows the physical properties of the obtained film.

Comparative Example 4
It was prepared in the same manner as described in Example 1 except that the film forming conditions were changed to the conditions shown in Table 1. Table 2 shows the physical properties of the obtained film.

The biaxially stretched polyethylene terephthalate films obtained in Examples 1 to 6 have high contrast and excellent optical film inspection properties, and are suitable for high-precision inspection in the optical film manufacturing process for large screen applications. It was a usable film. Further, the biaxially stretched polyethylene terephthalate films obtained in Examples 1 to 5 were excellent in thermal dimensional stability and excellent processing characteristics. On the other hand, since the films obtained in Comparative Examples 1 to 3 have low transmission polarization, they have low contrast and are inferior in easy inspection, and it is difficult to use them for high-precision inspection. In addition, it was inferior in processing characteristics.

The biaxially stretched polyethylene terephthalate film for optical film inspection of the present invention has excellent polarization inspection properties, and is therefore suitable for high-precision inspection of optical films for large screen applications. Further, according to a more preferable embodiment, it is possible to provide a biaxially stretched polyethylene terephthalate film for optical film inspection, which is excellent in post-processing at a high temperature.

Claims (3)

A biaxially stretched polyethylene terephthalate film for optical film inspection that satisfies the following requirements (1) to (3) and (8) to (10) .
(1) Total light transmittance is 85% or more (2) Film haze is 15% or less (3) Transmission polarization degree is 7.0% or more
(8) A laminated film composed of a central layer and both surface layers in contact with the central layer.
(9) Both surface layers contain 0.10 to 0.20% by mass of fine particles having an average particle size of 1.5 to 4.0 μm.
(10) The central layer contains 0.00 to 0.10% by mass of fine particles having an average particle size of 1.5 to 4.0 μm. The biaxially stretched polyethylene terephthalate film for optical film inspection according to claim 1, further satisfying the following requirements (4) to (6).
(4) The heat shrinkage rate when heated at 150 ° C. for 30 minutes is 2.0% or less in both the longitudinal direction and the width direction. (5) The difference between the maximum and minimum omnidirectional heat shrinkage rates when heated at 150 ° C. for 30 minutes. Is 0.5% or less (6) The maximum amount of change in the omnidirectional heat shrinkage rate per 5 ° when heated at 150 ° C for 30 minutes is 500 ppm or less. The biaxially stretched polyethylene terephthalate film for optical film inspection according to claim 1 or 2, which further satisfies the following requirement (7 ) .
(7) The maximum orientation angle of 18 ° or less under