KR20140053000A - Biaxially oriented polyester film for mold-releasing film for polarizing plate, laminated body using same, and method for producing polarizing plate - Google Patents

Abstract

(Polarizing plate releasing film) capable of suppressing unevenness of the inclination angle (alignment angle) of the alignment main axis relative to the width direction by setting the width in which the inclination of the alignment main axis relative to the width direction is the same direction, And to provide a biaxially oriented polyester film. In the present invention, the unevenness of the angle of inclination (alignment angle) of the alignment main axis relative to the film width direction is 3.7 degrees or less, and the film width is 1,700 mm or more.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a biaxially oriented polyester film for a polarizing plate release film, a laminate using the same, and a method for producing a polarizer,

The present invention relates to a biaxially oriented polyester film for a polarizing plate release film suitably used for a polarizing plate having excellent optical properties in a member such as a liquid crystal display and a method for producing the same.

In recent years, the demand for a liquid crystal display (LCD) having advantages of thinning, weight saving, low power consumption and high image quality is rapidly expanding as compared with a conventional CRT (cathode ray tube). Particularly, the demand for a large-screen monitor or a large-screen LCD for a 32-inch or larger LCD monitor is rapidly growing. As the LCD becomes a large screen, it has been studied to increase the brightness of the backlight of the LCD and to assemble a functional film for improving brightness on the LCD in order to sufficiently secure the brightness even on a large screen.

In such a high-luminance type LCD, since the luminance is high, a small defect existing in the display frequently becomes a problem. For this reason, in the constituent members of LCDs having optical characteristics such as a polarizing plate and a phase difference plate, drawbacks in size that have not been a problem in use for conventional LCDs have been a problem. Therefore, in each optical member, it is important to prevent the occurrence of defects in the manufacturing process. On the other hand, even if a defect occurs in a constituent member of an LCD having optical characteristics such as a polarizing plate and a phase difference plate, it is also important to improve the inspection property which can be reliably recognized as a defect.

The defect inspection of the polarizing plate is generally carried out by cross-Nicol method. This cross-Nicol method is a method in which two polarizing plates are orthogonalized with their alignment principal axes to make a dark field, and a measurement product is sandwiched therebetween and observed with transmitted light. In the cross-Nicol method, if there are foreign matters or defects in the polarizing plate, they appear as luminescent spots, so that defect inspection can be performed by checking the luminescent spots.

Here, in the production process of the polarizing plate, the biaxially oriented polyester film is often used as a release film in order to give a pressure-sensitive adhesive for bonding a polarizing plate to another member with respect to the polarizing plate. When the release film has optical anisotropy, light leakage occurs from a member in which a polarizing plate, a release film and a pressure-sensitive adhesive are combined. This light leakage causes a defect that the inspection by the Cross Nicol method becomes an obstacle and the mixing of the foreign matter and defects become easy to be missed. In addition, if the release film has optical defects, the bright spots originating from the optical defects of the release film are added, which results in a defect inspection. It is known that foreign matter in the release film or scratches on the surface is a bright spot at the time of defect inspection.

The biaxially oriented polyester film is advantageous when used as a polarizing plate release film because it is easy to form a thin film. However, in the polyester film disclosed in Patent Document 1, when the stretching is performed, a phenomenon referred to as bowing is caused by stretching the middle portion with respect to the stretching end portion. Therefore, the biaxially oriented polyester film has birefringence (phase difference). When linearly polarized light is incident on and transmitted through a biaxially oriented polyester film having birefringence (phase difference), it becomes elliptically polarized light.

Therefore, even if the biaxially oriented polyester film is bonded to the polarizing plate and the polarizing plate is directly passed, the state is not substantially crossed. That is, even if this biaxially oriented polyester film is bonded to the polarizing plate and the defect inspection of the polarizing plate by the Cross-Nicol method is performed, it is affected by the birefringence of the polyester film when linearly polarized light is incident, I can not do it.

With respect to these problems, a method of improving the automatic inspection machine using the Cross-Nicol method as disclosed in Patent Documents 2 to 7 and improving the inclination (hereinafter referred to as the orientation angle) of the alignment main axis of the polarizing plate- Has been conventionally performed.

Japanese Patent Publication No. 39-029214 Japanese Patent Application Laid-Open No. 2007-213016 Japanese Patent Application Laid-Open No. 2004-237451 Japanese Patent Application Laid-Open No. 2001-328159 Japanese Patent Application Laid-Open No. 2004-18588 Japanese Patent Application Laid-Open No. 2004-358742 Japanese Patent Application Laid-Open No. 2008-246685

A defect inspection apparatus disclosed in Patent Document 2 is known as an improvement of an automatic inspection apparatus using the Cross-Nicol method. This defect inspection apparatus has a polarizing filter for inspection between the light source and the optical path of the camera. In this defect inspection apparatus, the birefringence (phase difference) of the film is canceled by appropriately adjusting the relative angular position of the inspection polarizing filter so that the amount of light received in the background portion without defects of the visible light input to the camera is minimized. Therefore, in this defect inspection apparatus, it is possible to inspect defects in the film to which the polarizing plate is attached in the cross-Nicol state.

  However, in the apparatus of Patent Document 2, when inspecting a film having a non-uniform orientation angle in the width direction of the film, it is necessary to have a plurality of cameras and a polarizing filter for inspection in the width direction. According to the knowledge of the present inventors, the angle of the polarizing filter for inspection is adjusted so that the amount of light received at a background portion free of defects of visible light input to the camera is minimized when inspecting a film having a non- It is difficult to obtain the amount of light received at each camera position, that is, in the background portion having no uniform defect in the width direction. For example, there arises a difference in the amount of received light at the film end portion in the film width direction and in the background portion free from defects in the central portion. Therefore, when inspecting a film having unevenness of birefringence in the width direction of the film, defect inspection can not be performed precisely at the same time.

Further, according to the knowledge of the present inventors, it is necessary to arrange the polarizing plate so that the visual field at the time of cross-Nicol inspection becomes dark when inspecting defects that cause only a small amount of light change, regardless of the drawbacks that cause a large light quantity change . In this case, since the contrast difference becomes smaller, the detection becomes more difficult.

Further, in order to improve the inspection property of the polarizing plate releasing film, a cooling step is provided after the transverse stretching, and the cooling temperature in the cooling step is specified, so that Patent Document 7 Has been proposed.

However, according to the study by the present inventors, it has been found that if the orientation angle of the film is set to 5 degrees or less, there is a drawback that only a small amount of light change is caused when the polarizing plate is arranged such that the field of view at the cross- It is difficult to detect defects because there is a difference in the amount of received light in the background portion where there is no light.

Furthermore, when a polarizing plate used for a large-screen television set of 32 inches or more is inspected using a cross-Nicol method, even if the reflected light under cross-Nicol is excessively strong, the difference between the defect portion and the background It is difficult to distinguish between the two, and the inspection property is deteriorated. In addition, when the size of the polarizing plate to be inspected becomes 32 inches or more, the size of the polarizing plate may be inspected by the inspector (person) rather than the automatic inspection apparatus. However, the above- This becomes a big problem. Further, when the reflected light under Cross Nicol is too strong or too weak, it is difficult to discern the difference between the defect part and the background (background part) other than the defect part, even if the automatic inspection device is used, I can not guarantee sex.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a biaxially oriented polyester film for a polarizing plate releasing film which can solve the above problems and improve the productivity, in particular, the polarizing plate used for large-screen TVs is excellent in cross-

In order to solve the above problems, the present inventors have found that the above problems can be solved by having the following characteristics and have reached the present invention.

(1) A biaxially oriented polyester film for polarizing plate release, wherein the nonuniformity of the inclination angle (orientation angle) of the alignment main axis relative to the film width direction is 3.7 degrees or less and the film width is 1700 mm or more.

(2) The polarizing plate for biaxial oriented polyester film according to (1), wherein the film has a haze value of 7 to 13%.

(3) The thermosetting resin composition according to item (1) or (2), which has a heat shrinkage ratio in the longitudinal direction of the film of 5 to 7% and a heat shrinkage ratio in the film width direction of 7 to 9% after heat treatment at 150 DEG C for 30 minutes A biaxially oriented polyester film for polarizing plate release.

(4) The biaxially oriented polyester film for a polarizing plate mold release according to any one of (1) to (3), wherein the main axis of alignment in the film width direction is inclined in the same direction.

(5) The biaxially oriented polyester film according to any one of (1) to (4), wherein the thickness unevenness in the longitudinal direction of the film is less than 2.0 탆.

(6) The biaxially oriented polyester film for polarizing plate releasing according to any one of (1) to (5), wherein the longitudinal direction orientation unevenness (MD orientation angle unevenness) is less than 1.5 degrees.

(7) The polarizing plate molding according to any one of (1) to (6), wherein the angle of inclination (orientation angle) of the main axis of alignment with respect to the film width direction is at least 3.7 degrees over a width of at least 5 m. Axially oriented polyester film.

(8) The biaxially oriented polyester film for polarizing plate release according to any one of (1) to (7), which is obtained by a method having the following steps in this order.

(Step 1) A step of stretching an unoriented polyester film in a longitudinal direction at a draw ratio of 2.5 to 5 to obtain a uniaxially stretched polyester film.

(Step 2) The uniaxially stretched polyester film is stretched in the transverse direction at a draw magnification of 3 to 6 times, and the stretching magnification in the width direction is larger than the stretching magnification in the longitudinal direction to obtain a biaxially stretched polyester film fair.

(Process 3) A step of cooling the biaxially oriented polyester film at a film temperature of 25 to 45 占 폚 and a width shrinkage rate of the film of 0.1 to 20% / min to obtain a cooled polyester film.

(Step 4) The step of heat-treating the cooled polyester film at a heat treatment temperature of 180 to 230 占 폚 to obtain a biaxially oriented polyester film.

(9) A laminate obtained by forming a biaxially oriented polyester film for polarizing plate release according to any one of (1) to (8) on at least one side of a polarizer having a width of 1700 mm or more.

(10) A method for producing a polarizing plate, which comprises peeling the biaxially oriented polyester film for polarizing plate release from the laminate according to (9).

(11) A process for producing a biaxially oriented polyester film for a polarizing plate release film according to any one of (1) to (8), which comprises the following steps in that order.

(Step 1) A step of stretching an unoriented polyester film in a longitudinal direction at a draw ratio of 2.5 to 5 to obtain a uniaxially stretched polyester film.

(Step 2) The uniaxially stretched polyester film is stretched in the transverse direction at a draw magnification of 3 to 6 times, and the stretching magnification in the width direction is larger than the stretching magnification in the longitudinal direction to obtain a biaxially stretched polyester film fair.

(Process 3) A step of cooling the biaxially oriented polyester film at a film temperature of 25 to 45 占 폚 and a width shrinkage rate of the film of 0.1 to 20% / min to obtain a cooled polyester film.

(Step 4) The step of heat-treating the cooled polyester film at a heat treatment temperature of 180 to 230 占 폚 to obtain a biaxially oriented polyester film.

(12) A method for producing a biaxially oriented polyester film in which the unevenness of the angle of inclination (orientation angle) of the oriented main axis with respect to the film width direction is 3.7 degrees or less and the film width is 1700 mm or more, (Method for producing axial oriented polyester film).

(Step 1) A step of stretching an unoriented polyester film in a longitudinal direction at a draw ratio of 2.5 to 5 to obtain a uniaxially stretched polyester film.

(Step 2) The uniaxially stretched polyester film is stretched in the transverse direction at a draw magnification of 3 to 6 times, and the stretching magnification in the width direction is larger than the stretching magnification in the longitudinal direction to obtain a biaxially stretched polyester film fair.

(Process 3) A step of cooling the biaxially oriented polyester film at a film temperature of 25 to 45 占 폚 and a width shrinkage rate of the film of 0.1 to 20% / min to obtain a cooled polyester film.

(Step 4) The step of heat-treating the cooled polyester film at a heat treatment temperature of 180 to 230 占 폚 to obtain a biaxially oriented polyester film.

According to the present invention, it is possible to suppress unevenness of the inclination angles (orientation angles) of the main alignment axis with respect to the width direction even when the width of the main spindle with the inclination of the aligned main spindle in the width direction is set to be the same, It is possible to provide a biaxially oriented polyester film for a polarizing plate release film and a method for producing the same.

1 is an image (image within a film plane) when a detection test is performed by a Cross Nicole tester,
2 is a schematic diagram of a cross-Nicol tester evaluating the inspection property of a film in the present invention.

Hereinafter, the present invention will be described in more detail. The polyester which can be suitably used in the present invention is not particularly limited as long as it is a polyester that becomes a high-strength film by molecular orientation, but it preferably contains polyethylene terephthalate and polyethylene-2,6-naphthalate. Particularly preferably, it is polyethylene terephthalate predominant in price. When polyethylene terephthalate is used, examples of the polyester copolymer component other than ethylene terephthalate include diethylene glycol, propylene glycol, neopentyl glycol, polyethylene glycol, p-xylylene glycol, 1,4-cyclohexane di Diol components such as methanol and the like, dicarboxylic acid components such as adipic acid, sebacic acid, phthalic acid, isophthalic acid and 5-sodium sulfoisophthalic acid, polyfunctional dicarboxylic acid components such as trimellitic acid and pyromellitic acid, p-oxyethoxybenzoic acid and the like can be used within a range that does not impair the intended film properties of the film. Such a polyester can be produced, for example, by the following method. For example, a method of directly esterifying a dicarboxylic acid component and a diol component, followed by polycondensation while removing the excess diol component by heating the product of the reaction under reduced pressure, or a method of producing a dicarboxylic acid component A method in which a dialkyl ester of a dicarboxylic acid is used and subjected to transesterification reaction with a diol component and polycondensation is carried out in the same manner as described above. At this time, for example, alkali metals, alkaline earth metals, manganese, cobalt, zinc, antimony, germanium and titanium compounds may be used as the reaction catalyst, if necessary. The inherent viscosity of the polyester is preferably 0.4 to 0.9, more preferably 0.5 to 0.7, and still more preferably 0.55 to 0.65.

In the biaxially oriented polyester film for a polarizing plate release film of the present invention, the nonuniformity of inclination angle (orientation angle) of the main axis of alignment with respect to the width direction is 3.7 degrees or less and the film width is 1700 mm or more. It is also preferable that the orientation of the alignment main axis relative to the film width direction is the same direction.

The orientation angle referred to in the present invention indicates the inclination angle of the alignment main axis. The orientation angle can be measured by evaluating the orientation by transmitting ultrasonic pulses through the film in all directions and measuring the propagation speed thereof. The orientation angle is defined as 0 degrees when it is parallel to the film width direction, and the inclination of the clockwise rotation with respect to the film width direction is defined as + and the counterclockwise rotation is defined as -. It is to be noted that the inclination of the alignment main axis relative to the film width direction is the same direction, which means that both ends in the film width direction of the width-setting film have the same sign in the above-mentioned inclination measurement of the alignment main axis. In the biaxially oriented polyester film, the inclination of the main alignment axis is caused by the phenomenon of bowing occurring during the stretching process and the heat treatment process. Since the Boeing phenomenon is a phenomenon that the film in the heat treatment process from the stretching process constitutes a suspension line (curtain curve), in the biaxially oriented polyester film, the orientation of the alignment main axis The inclination of the inclined surface tends to increase. In addition, in the two directions from the center in the width direction to the end in the width direction of the biaxially oriented polyester film, they each have an orientation principal axis inclination in the reverse direction.

The term "orientation angle unevenness" used in the present invention is defined as the difference between the maximum and minimum of the orientation angle of an arbitrary position in the film measured as described above. If the unevenness of the orientation angle exceeds 3.7 degrees, light leakage may occur from the polarizing plate in the Cross-Nicol method for inspecting the polarizing plate, which may cause an obstacle to the inspection. The orientation unevenness is more preferably 3.5 degrees or less, and more preferably 3.2 degrees or less.

The biaxially oriented polyester film for polarizing plate of the present invention is preferably obtained from a film having an inclination angle (orientation angle) of the aligned main axis relative to the film width direction of 3.7 degrees or less over a width of at least 5 m because productivity can be enhanced.

The unevenness of the orientation angle is a cause of non-uniformity of the amount of leakage of light in the normal portion free from defects in the film when the film is put into the cross-Nicol state. This unevenness of the light leakage amount can be confirmed as a non-uniformity in the amount of received light in a background portion free from defects in a background portion free from defects in the cross-Nicol tester shown in " (9) Evaluation by Cross Hill Inspection Machine " If ununiformity of the light leakage amount occurs, the inspection property is changed in accordance with the position of the film (depending on the unevenness of the orientation angle), and the defect may be missed. An example is shown below.

Regarding the relationship between the defect detection by the cross Nicole tester and the unevenness of the orientation angle:

[1] Detection test 1

Sample: A polyester film having surface defects that occurred when a polyester film was processed at room temperature. However, the polyester film is a small piece, and there is almost no unevenness of the orientation angle within the film plane.

Measuring device: Cross-Nicol tester shown in "(9) Evaluation by Cross-Nicol tester" described later.

• Baseline: In a Cross Niche tester, it is necessary to establish a baseline for the amount of background light received in the background without defect. Thus, a test in which the baseline (amount of light leakage in the normal part without a defect) of the received light amount in the background part without defect is set in the range of 10 to 30 in 256 gradations is referred to as test 1A, A test in which the baseline was in the range of 30 to 50 with 256 gradations was called test 1B. The adjustment of the base line was performed by adjusting both the angle of the second polarizing filter on the side of the light receiving means and the angle of the first polarizing filter provided on the illumination side.

Test results: When the sample was inspected under the conditions of Test 1A, the surface defects of the film showed the amount of received light at the background portion without defect, which was about 40 times higher than the baseline. On the other hand, when the same sample was inspected under the condition of Test 1B, the amount of light received at the background portion having no defects higher than the base line by 17 was shown at the surface defective portion of the film. In addition, the degree of inspection is high (sensitive) so as to show the amount of received light in the background portion without high defect from the baseline of the amount of received light in the background portion without defect. The test results are shown in Fig. In Fig. 1, the black portion indicates that the amount of received light in the background portion free from defects is small, and the white portion indicates that the amount of received light in the background portion free of defects is large.

Conclusion: From the above test results, it has been found that the inspection property is changed by the baseline of the amount of received light in the background part without defect. If there is a variation in the orientation angle within the plane of the polyester film, the alignment angle varies depending on the position of the film, so that the baseline of the amount of light received in the background without defect is changed. Specifically, even if the base line of the amount of received light in the background portion free from defects is set to be 20 at the position of the orientation angle of 0 degrees, the baseline of the amount of received light in the background portion free from defects Lt; / RTI > When the baseline of the amount of received light in a background part without a defect is changed, the inspection property is changed.

[2] Detection test 2

Sample: A polyester film having surface defects that occurred during the production of a polyester film (particularly during heating and stretching). However, this polyester film is a small piece, and there is almost no unevenness of the orientation angle in the film plane.

Measuring device: Cross-Nicol tester shown in "(9) Evaluation by Cross-Nicol tester" described later.

• Baseline: In a Cross Niche tester, it is necessary to establish a baseline for the amount of background light received in the background without defect. Therefore, a test in which the baseline of the amount of received light in a background part free from defects is set in the range of 10 to 30 in 256 gradations is referred to as test 2A, and the baseline of the amount of received light in the background part without defect is set to 30 to 50 A range of tests was called Test 2B. The adjustment of the base line was performed by adjusting both the angle of the second polarizing filter on the side of the light receiving means and the angle of the first polarizing filter provided on the illumination side.

Test Results: Examination of the sample under the conditions of Test 2A showed that the surface defects of the film received light at a background portion free of defects higher than 80 from the baseline. Further, when the same sample was examined under the conditions of Test 2B, the amount of light received at the background portion of the film with no defects higher than the base line by 70% was found at the surface defective portion of the film. Further, the size of the surface defect was measured under the condition of Test 2A, and the size of about 0.588 mm 2 under the condition of Test 2A. The test results are shown in Fig.

Conclusion: From the above test results, it has been shown that the inspection property (in particular, the magnitude of the defect shown as the measurement value) is changed by the baseline of the amount of received light in the background part without defect. If there is a variation in the orientation angle within the plane of the polyester film, the baseline of the amount of light received at the background portion free from defects changes depending on the position of the film. When the baseline of the amount of received light in a background part without a defect is changed, the inspection property is changed.

As described above, the smaller the unevenness of the amount of received light in the background portion free from defects, the more uniform the inspection property in the film surface. In order to make the inspection property in the film surface uniform, it is important that the unevenness of the orientation angle of the film is 3.7 degrees or less.

It is preferable that the biaxially oriented polyester film of the present invention has an orientation angle unevenness (hereinafter referred to as MD orientation angle unevenness) with respect to the longitudinal direction of the film of 1.5 degrees or less. The MD orientation angle unevenness referred to in the present invention means that the orientation angles at both ends of the film width direction are measured at 10 points every 1000 mm in the longitudinal direction of the film and the absolute value of the difference between the maximum value and the minimum value of the measured value is found at each end of the film, As shown in Fig.

If the non-uniformity of the MD orientation angle is large, the amount of light received at the background portion free from defects in the cross-Nicol tester in the longitudinal direction of the film is undesirable. In the Cross-Nicol tester, when the deviation from the orientation angle when adjusted to the cross-Nicol state is large, the non-uniformity of the received light amount at the background portion free from defects in the Cross Nicol Tester becomes large. Therefore, by suppressing the nonuniformity of the MD alignment angle, it is possible to suppress the ununiformity of the received light amount in the background portion free from defects in the Cross Nicole tester. The MD orientation angle unevenness is preferably 1.5 degrees or less, more preferably 1.2 degrees or less, and further preferably 1.0 degrees or less.

The larger the absolute value of the orientation angle at the film edge position is, the greater the nonuniformity of the MD orientation angle tends to be. Therefore, in the biaxially oriented polyester film of the present invention, it is preferable to form the film so that the absolute value of the orientation angle at the film edge position becomes small.

The biaxially oriented polyester film of the present invention needs to have a film width of at least 1700 mm or more. As described above, since the orientation angle takes an increasing action with respect to the distance from the film center of the formed film, it becomes difficult to suppress the unevenness of the orientation angle and the orientation angle as the film width increases. Therefore, conventionally, it has not been possible to set the unevenness of the orientation angle to 3.7 degrees or less in a biaxially oriented polyester film having a film width of 1700 mm or more. Since the biaxially oriented polyester film of the present invention has a film width of at least 1700 mm and an unevenness of the alignment angle of 3.7 degrees or less, it is preferably used for a polarizing plate for inspection of a polarizing plate of a large screen (specifically, 32 inches or more) Is used. When the film width is 1900 mm or more, it can be more suitably used for a large-screen LCD, and more preferable because productivity is improved. The upper limit of the film width is not particularly limited, but it is preferable that the film width is 10000 mm or less from the viewpoint of manufacturing facility cost.

In the biaxially oriented polyester film of the present invention, it is preferable that the orientation of the main axis of alignment with respect to the film width direction is the same direction. As described above, in the biaxially oriented polyester film, the inclination of the alignment main axis tends to increase as it goes from the center in the width direction to the end portion in the width direction of the film. Further, in the two directions from the center in the width direction to the end in the width direction, the inclination of the alignment main axis is opposite to each other. Therefore, in order to set the minimum unevenness of the orientation angle, the width is set so that the center in the width direction of the film to be set is equal to the center in the width direction of the film after setting the width. However, in this width setting, only the central portion in the width direction of the film can be taken. In order to improve the productivity, it is necessary to set the width so that the orientation of the main axes at both ends in the width direction of the film after the width setting is the same. However, The unevenness of the orientation angle and the unevenness of the MD orientation angle tend to increase. The biaxially oriented polyester film of the present invention can obtain a biaxially oriented polyester having good productivity and good inspection property because the unevenness of the orientation angle is small even if the width setting is performed so that the inclination of the oriented main axis relative to the film width direction is set in the same direction .

The biaxially oriented polyester film of the present invention preferably has heat shrinkage ratios of 5 to 7% and 7 to 9% in the film longitudinal direction and the film width direction after heat treatment at 150 DEG C for 30 minutes. Preferably 5.5 to 6.5% and 7.5 to 8.5%, respectively. If the heat shrinkage ratio exceeds the above-mentioned range, the dimensional stability is deteriorated, which is not preferable. The heat shrinkage ratio can be adjusted at a relaxation rate or a heat treatment temperature in the heat treatment. However, in order to maintain the flatness of the polarizing plate while keeping the unevenness of the orientation angle to 3.7 degrees or less and to keep the heat shrinkage rate lower than the above lower limit range, for example, it is necessary to carry out a separate annealing treatment after the film formation, · It is not desirable because it is inefficient.

The biaxially oriented polyester film for a polarizing plate release film of the present invention preferably has a haze value of 7 to 13%. , Preferably 8 to 12%, and more preferably 9 to 11%. When the haze value is less than 7%, the reflected light is excessively strong when inspecting the polarizing plate. When the haze value is more than 13%, the reflected light is weak, which may cause the inspection. Particularly, even if the reflected light is strong, the reflected light under Cross Nicol becomes difficult to discriminate the difference between the defect part and the background (background part). This effect is particularly noticeable when conducting tests on the eyes. Specifically, when the haze is low, the reflected light is strong, and the unevenness of brightness on the background (background portion) is emphasized. As a result, it is difficult to distinguish between the defect portion and the background (background portion) edge. When the haze is high, And the detectability is lowered. For this reason, in order to improve the inspection property of defect inspection, it is particularly important to set the haze value of the film to the above-mentioned range. By setting the haze value within the above-described range, even when the size of the polarizing plate to be inspected is 32 inches or more, the inspection property can be sufficiently improved.

The film of the present invention may be a single layer or a composite film composed of two or more layers, but it is particularly suitable when the film is composed of a three-layer composite film in order to set the haze value of the film within the above range. When the film of the present invention is used as the three-layer composite film, the polymer composition of the layer (laminate portion) constituting the film surface and the particle species or the content of contained particles may be different from each other in the composition of A / B / A / B / A having the same composition as the particle species or the particle content. The composition of A / B / A having the same composition of the polymer composition of the layer (laminate portion) constituting the film surface and the content of the particle species or the content of the particles is convenient from the viewpoint of productivity. In the case where the three-layer composite film has the composition of A / B / A, it is preferable that the thicknesses of the two layers constituting the film surface side are substantially the same, since the design of quality is easy. The thickness of the layer (laminated portion) constituting the film surface is preferably 0.5 to 2.5 占 퐉, particularly preferably 1.0 to 2.0 占 퐉.

In order to keep the haze value of the film within the above range, a method of containing inert particles in the film is preferably used. When the film of the present invention is a three-layer composite film, if the particles constituting the film surface (lamination portion) and the layer not constituting the film surface (base layer portion) are contained, respectively, the haze value can be set within a desired range Therefore, it is desirable. Examples of the inert particles to be contained include inorganic particles such as spherical silica, aluminum silicate, titanium dioxide, and calcium carbonate, and other organic polymer particles include crosslinked polystyrene resin particles, crosslinked silicone resin particles, crosslinked acrylic resin particles, crosslinked styrene- , Cross-linked polyester particles, polyimide particles, melamine resin particles and the like are preferably used. One or more of these may be selected and used.

Examples of a method for obtaining a film containing inert particles include a method in which inert particles are added in a polyester polymerization process to prepare an inert particle-containing polyester and film formation is performed using the material as a raw material, a method in which a polyester containing no particles is polymerized, And a method of forming the film while blending the polyester and the inert particles in the film forming step. From the viewpoint of suppressing the generation of foreign matter by agglomeration of the particles, a method of adding inert particles in the polymerization step of the polyester is preferable. For example, in the case of polyethylene terephthalate, an inert particle-containing slurry of ethylene glycol as a glycol component is prepared, an inert particle-containing slurry is added after the transesterification before the polycondensation or at the stage of the oligomer after the esterification, To obtain an inert particle-containing polyethylene terephthalate.

The slurry of the inert particles prior to addition may be subjected to dispersion treatment by a sand grinder or the like, separation of coarse particles by centrifugal sedimentation treatment or high-precision filtration if necessary, thereby making it possible to uniformize the particle size distribution and to remove coarse particles, Can be effectively employed for reducing the number of coarse projections.

In order to set the haze value of the film of the present invention within the above range, in the case of the three-layer composite film, inert particles having an average particle diameter of 0.5 to 1.5 mu m, preferably 0.8 to 1.3 mu m, 0.2 to 1.0% by weight, more preferably 0.3 to 0.8% by weight. In addition, if 0.02 to 0.1 wt% of inert particles having an average particle diameter of 0.5 to 1.5 mu m, preferably 0.8 to 1.3 mu m is contained in the layer (base layer portion) which does not constitute the film surface, the haze value can be set within the above range, Do. In addition, it is preferable that the inert particulate paper contained in the layer (laminate portion) constituting the film surface and the layer (base layer portion) not constituting the film surface is the same because the production equipment can be simplified.

The biaxially oriented polyester film for a polarizing plate release film of the present invention preferably has a thickness unevenness in the longitudinal direction of the film of less than 2.0 탆, more preferably 0.5 to 1.5 탆, particularly preferably 0.5 to 1.2 탆. The thickness nonuniformity in the longitudinal direction of the film in the present invention means a value measured in the method described in "(5) thickness nonuniformity in the longitudinal direction of the film" to be described later. If the thickness unevenness exceeds 1.5 탆, unevenness in intensity of light leaked from the polarizing plate becomes strong in the Cross-Nicol method for inspecting the polarizing plate, which may cause an obstacle to the inspection. In particular, when the thickness unevenness exceeds 2.0 占 퐉, stretching unevenness often occurs, and since the base (background portion) is not uniform due to uneven stretching, the cross-Nicol testability is significantly deteriorated, It is not preferable as an oriented polyester film. On the other hand, in order to produce a film having a thickness unevenness of 0.5 탆 or less, production control becomes complicated, which is not preferable.

The thickness of the film of the present invention is preferably 25 to 70 占 퐉, more preferably 30 to 50 占 퐉, and still more preferably 35 to 45 占 퐉. When the thickness of the film is within this range, it is preferable that the haze value of the film is easily adjusted within the above range.

The biaxially oriented polyester film for a polarizing plate release film of the present invention can be obtained, for example, by stretching an unstretched film in a longitudinal direction, then stretching it in a transverse direction, and subjecting it to a heat treatment after passing through a cooling step. In order to keep the unevenness of the orientation angle within 3.7 degrees over the film width of 1700 mm or more, the film temperature is cooled to 25 to 45 占 폚 in the cooling step and the width shrinking speed of the film in the cooling step is set to 0.1 to 20% / min It is important to perform heat treatment after controlling.

As a method for lowering the orientation angle of the film, there is a method in which a cooling step is provided after transverse stretching as described in Patent Document 7, and a cooling temperature in the cooling step is specified to lower the orientation angle. This is achieved by sufficiently cooling the film after the transverse stretching to the glass transition temperature or lower of the film to sufficiently suppress the bowing phenomenon. However, in the above method, it is not possible to sufficiently suppress the unevenness of the orientation angle of a wide film such as a film width of 1700 mm or more. In the present invention, it has been found that by controlling the width shrinkage rate of the film in the cooling step, it is possible to lower the orientation angle to an extent not achievable in the prior art, and to suppress the orientation angle variation after setting the width.

In producing a biaxially oriented polyester film for a polarizing plate release film of the present invention, a mechanism capable of lowering the orientation angle by controlling the width shrinking speed in addition to the temperature in the cooling step after stretching includes a transverse stretching step, The lateral shrinkage relaxation is physically suppressed by controlling the width shrinkage speed in the transient state in which the film temperature is lowered over the entire length of the film, or the width shrinkage in the cooling step is physically suppressed from acting on the film immediately after the stretching process, It is presumed that the Boeing phenomenon can be sufficiently suppressed.

In producing the biaxially oriented polyester film for a polarizing plate release film of the present invention, the width shrinkage rate of the film in the cooling step is preferably 0.1% to 20% / min, more preferably 0.2% to 18% / min More preferable. When the width shrinkage rate is less than 0.1% / min, the film tension due to the suppression of the width shrinkage of the film is affected, which deteriorates the film formability and causes film breakage. If the width shrinkage speed is more than 20% / min, the effect of suppressing the orientation relaxation due to the width shrinkage of the film is small, and the suppression of the bowing phenomenon becomes insufficient.

The width shrinkage rate V1 (% / min) of the film in the cooling step shown here is the film width W1 (mm) just before the transverse stretching step has passed and the film just before entering the cooling step, The width W2 (mm), and the passing time of the cooling process as T1 (min).

V1 = (W1 - W2) / W1 x 1 / T1 (1)

In the production of the biaxially oriented polyester film for a polarizing plate release film of the present invention, it is important that the time for the film to be in a state where the temperature is lowered in the cooling process is elapsed. The reason for this is presumed as follows. As described above, in the cooling step, orientation relaxation is thought to occur at the time of width shrinkage. However, it is presumed that a certain period of time is required to prevent orientation relaxation by cooling the film. Therefore, it is presumed that the effect of suppressing the bowing phenomenon is small because the orientation relaxation can not be suppressed if the passing time of the cooling process is insufficient. In producing the biaxially oriented polyester film for a polarizing plate release film of the present invention, the passage time of the cooling step is preferably 10 seconds or more, more preferably 15 seconds or more. The upper limit of the passage time of the cooling process is not particularly limited, but is preferably 60 seconds or less, because productivity is improved.

The polyester film of the present invention is preferably obtained by a method having the following steps in that order.

(Step 1) A step of stretching an unoriented polyester film in a longitudinal direction at a draw ratio of 2.5 to 5 to obtain a uniaxially stretched polyester film.

(Step 2) The uniaxially stretched polyester film is stretched in the transverse direction at a draw magnification of 3 to 6 times, and the stretching magnification in the width direction is larger than the stretching magnification in the longitudinal direction to obtain a biaxially stretched polyester film fair.

(Process 3) A step of cooling the biaxially oriented polyester film at a film temperature of 25 to 45 占 폚 and a width shrinkage rate of the film of 0.1 to 20% / min to obtain a cooled polyester film.

(Step 4) The step of heat-treating the cooled polyester film at a heat treatment temperature of 180 to 230 占 폚 to obtain a biaxially oriented polyester film.

Each step will be described in detail below.

· Preparation of unstretched film

The polyester obtained by a known method is dried, if necessary, and fed to an extruder and filtered by a filter. Small foreign matters also become film defects. Therefore, it is effective to use, for example, a high-precision filter which collects at least 95% of foreign matter of 5 m or more. Subsequently, the sheet is melt-extruded by using a T-type separator or the like and cooled and solidified on a casting roll to obtain an unstretched film.

(Process 1)

The unstretched film is stretched in the longitudinal direction at a draw ratio of 2.5 to 5 to obtain a uniaxially stretched polyester film. The stretching in the longitudinal direction is preferably conducted at a stretching temperature of 90 to 130 DEG C in one step or in multiple stages. From the standpoint of suppressing the Boeing phenomenon and thickness irregularity in the longitudinal direction of the film, the stretching temperature is preferably 100 to 120 占 폚 and the stretching magnification is preferably 3 to 4 times. In view of prevention of stretching unevenness and scratching, stretching is performed in two or more steps .

(Process 2)

The uniaxially stretched polyester film is stretched in the transverse direction at a stretching magnification of 3 to 6 times in the transverse direction and at a stretching ratio greater than the transverse stretching ratio in the transverse direction to obtain a biaxially stretched polyester film. The stretching in the transverse direction is preferably conducted at a stretching temperature of 90 to 130 캜. When the stretching temperature is lower than 90 占 폚 and the stretching magnification is higher than 6 times, the film tends to break. It is more preferable that the stretching temperature is 100 to 120 占 폚 and the stretching magnification is 4 to 5 times.

Further, in order to reduce the unevenness of the orientation angle, it is preferable that the draw ratio in the width direction is larger than the draw ratio in the length direction. If the stretching magnification in the transverse direction is larger than the longitudinal stretching magnification, the molecular orientation in the film tends to lean toward the longitudinal direction, which makes it difficult to suppress the unevenness of the orientation angle.

In the production of the biaxially oriented polyester film for a polarizing plate release film of the present invention, transverse stretching is performed after longitudinal stretching. When the longitudinal stretching is performed after the transverse stretching, the molecules are oriented strongly in the TD direction mainly after the transverse stretching, but when the longitudinal stretching is performed after that, they are also diverged in the MD direction, and the unevenness of the orientation angle becomes large.

(Process 3)

The biaxially stretched polyester film is cooled at a film temperature of 25 to 45 캜 and a width shrinkage rate of the film of 0.1 to 20% / min to obtain a cooled polyester film.

The film temperature in the cooling step is preferably 25 to 45 占 폚 because it suppresses the lateral orientation relaxation due to the width shrinkage and suppresses the bowing phenomenon. More preferably 30 to 40 占 폚. If the film temperature in the cooling step is higher than 45 캜, the tensile force due to the film width shrinkage affects the film forming property, and the effect of suppressing the lateral orientation may not be sufficiently obtained in some cases. It is not preferable that the film temperature in the cooling step is lowered to less than 20 캜 because the productivity is deteriorated.

Examples of the cooling method of the polyester film include an air cooling method using a tenter for performing a heat treatment, an air cooling method for blocking hot air by a shielding plate such as an aluminum plate above and below a heat treatment region, and a cooling method using a roll. In the air cooling method using a tenter which performs heat treatment, since the zones are all connected in the longitudinal direction, there is a case where the film temperature is not sufficiently cooled due to the occurrence of a temperature difference in the width direction of the film due to the free flow of hot air, have. In this case, it may be coped with by blowing compressed air or the like and actively cooling it.

The number of rolls used and the set temperature are not limited in the roll cooling method, but it is preferable to use a plurality of rolls for cooling. In order to keep the film temperature within the above range in the roll cooling method, the roll temperature is preferably 20 to 45 캜, more preferably 30 to 40 캜. Further, in the cooling method using rolls, it is preferable that the film is stably cooled by applying a load to the cooling roll by the nip roll.

In this cooling step, it is important that the width shrinkage speed of the film is 0.1 to 20% / min. When the width shrinkage rate is less than 0.1% / min, the film tension due to the suppression of the width shrinkage of the film is affected, which deteriorates the film formability and causes film breakage. If the width shrinkage speed is more than 20% / min, the effect of suppressing the orientation relaxation due to the width shrinkage of the film is small and the suppression of the bowing phenomenon may become insufficient in some cases. The width shrinkage speed of the film is more preferably 0.2 to 18% / min.

The passing time of the cooling step is preferably 10 seconds or more, and more preferably 15 seconds or more. The upper limit of the passage time of the cooling process is not particularly limited, but is preferably 60 seconds or less, because productivity is improved.

The method of controlling the width shrinkage direction can be realized by various methods by setting the width shrinkage speed from the cooling step length and the film forming speed. Specifically, in the air cooling method in the tenter, the width shrinkage speed can be set to a desired value by gripping both ends with clips and adjusting the rail width.

(Step 4)

The cooled polyester film is heat-treated at a heat treatment temperature of 180 to 230 캜 to obtain a biaxially oriented polyester film. When the heat treatment temperature is less than 180 캜, the heat treatment becomes insufficient and the heat shrinkage ratios in the film longitudinal direction and the film width direction after heat treatment at 150 캜 for 30 minutes are in the range of 5 to 7% and 7 to 9% It may become difficult. When the heat treatment temperature is higher than 230 占 폚, the orientation by thermal crystallization progresses, which may make it difficult for the nonuniformity of the inclination angle (orientation angle) of the alignment main axis relative to the film width direction to fall within 3.7 degrees.

In the heat treatment step, the temperature difference between the upper and lower portions of the film is preferably 1 to 20 占 폚, more preferably 1 to 10 占 폚, and still more preferably 1 to 5 占 폚. If the temperature difference between the upper and lower portions of the film is larger than 20 캜, the physical properties in the width direction of the film, particularly the mechanical properties or the heat shrinkage ratio, may become uneven. In the heat treatment, a relaxation treatment may be carried out if necessary. The relaxation treatment may be performed either in the lateral direction or in the longitudinal direction, or may be performed in the lateral direction or the longitudinal direction at the same time or separately. The relaxation ratio is preferably 1 to 20%, more preferably 1 to 10%, based on the entire width of the film, and is effective for obtaining a film having good dimensional stability.

The polyester film of the present invention is suitably used as a release film of a polarizing plate of a large size. Specifically, it is preferably used in the following form.

Initially, the polyester film of the present invention is formed on at least one side of a polarizer having a width of 1700 mm or more to obtain a laminate. Here, the laminate is preferably a laminate comprising the polyester film / adhesive layer A / polarizer / adhesive layer B / protective sheet of the invention of the present invention in that order, more preferably a polyester film Film / silicon layer / adhesive layer A / polarizer / adhesive layer B / protective sheet "in that order. As the silicon layer, the adhesive layer, the polarizer, and the protective sheet, known materials can be used.

Next, the laminate is inspected. Since the polyester film of the present invention is used for the laminate, good inspection properties can be obtained. Thereafter, the polyester film of the present invention is peeled from the laminate to obtain a polarizing plate. Here, the polarizing plate refers to a member having at least a polarizer, but may be a polarizing plate such as a polyester film / adhesive layer A / polarizer / adhesive layer B / protective sheet of the present invention or a polyester film / (Removed) the polyester film of the present invention from the adhesive layer A / polarizer / adhesive layer B / protective sheet (laminate), the adhesive layer A / polarizer / adhesive layer B / Thereby obtaining a polarizing plate. Further, the silicon layer is preferably peeled together with the polyester film of the present invention.

Example

The methods of measuring the characteristic values in the examples and comparative examples are as follows.

(1) film width

The film to be measured was spread on a die and the width thereof was measured by a goldsmith (JIS grade 1).

(2) the inclination (alignment angle) of the alignment main axis, the unevenness of the alignment angle

Nomura Shoji Co., Ltd. Measurements are made using the product's orientation meter (SST-4000). (105 mm) of a sample cut into A4 size at both ends with respect to the width of the film to be a sample was measured, and when the alignment main axis was parallel to the film width direction, the alignment angle was 0 degree and the clockwise The inclination is called + and the counterclockwise rotation is -, and the absolute value thereof is determined as the measurement result.

The orientation unevenness was determined as the absolute value of the difference between the maximum dental minimum value and the maximum dental minimum value in the target extraction width setting.

(3) Haze value of the film

Using a haze meter (HGM-2DP (manufactured by Suga Test Instruments Co., Ltd.) (manufactured by Suga Test Instruments Co., Ltd.)) was used as a sample in which the size of the film was 4 cm in the longitudinal direction of the film and 3.5 cm in the film width direction according to JIS K7105 (1981) . Three points were uniformly measured with respect to the film width direction, and the average value was determined as a measurement result.

(4) Heat shrinkage

Two lines are drawn on the surface of the film so that the width is 10 mm and the measurement length is about 100 mm. The distance between the two lines is measured at 23 DEG C and this is referred to as L0. The film sample was allowed to stand in an oven at 150 캜 for 30 minutes under a load of 1.5 g, and then the distance between two lines was measured at 23 캜, and the heat shrinkage rate was obtained by the following equation.

Heat shrinkage percentage (%) = {(L0-L1) / L0} 100

Three measurements were made for each of the film length method and the width direction, and an average value was obtained.

(5) Thickness unevenness in the longitudinal direction of the film

Anritsu Denki Co., Ltd. The film thickness of the product was measured 15 m in the longitudinal direction using a continuous meter, and the difference between the maximum thickness and the minimum thickness was measured from the recorded film thickness chart as the thickness unevenness (mu m). The measurement conditions are as follows.

Composition: K-306C Wide range of electronic micrometer, K-310C recorder, Film delivery device

Detector: 3R ruby terminal, measuring force: 15g ± 5g

Film width: 45 mm, measurement length: 15 m, film delivery speed: 3 m / min.

(6) Film thickness

30 points were measured uniformly in the film width direction using a micrometer (MITSUYO MM-25) according to JIS C2151 (1990), and the average value was determined as a measurement result.

(7) Film temperature

The film temperature was measured using a Handy-type radiation thermometer (IR-TA from CHINO Corporation). Three points were uniformly measured with respect to the film width direction, and the average value was determined as a measurement result.

Height (Z direction) Magnification: 50,000 times.

(8) Inspection by the municipality

Two polarizing plates were placed on a light source (light box), a polyester film was placed therebetween, and two polarizing plates were placed in a state in which the entire film was in a crossed Nicols state. Lt; / RTI > The inspections were carried out by two persons and crosscheck was performed to confirm whether or not the defect was missing, and the evaluation was made based on the following criteria.

◎: Since it was a good background (background part) for the inspection at the time of mosquito inspection, it was possible to perform inspection without missing almost any defect.

?: Since light on the background (background portion) entering the field of view was somewhat strong or somewhat weak, and there was a slight amount of light unevenness in each location, when the test was continuously performed for about two hours, fatigue was felt and some defects were missed.

?: Since light on the background (background part) entering the field of view is somewhat strong or somewhat weak, and there is light quantity variation at each position, if the inspection is continuously performed for about one hour, the user feels fatigue and some defects are omitted.

X: Since light on the background (background portion) entering the field of view was strong or weak, or there was a clear light quantity unevenness in each location, if continuous inspection was performed for about one hour, fatigue was felt strongly, and many defects were missed.

(9) Evaluation by Cross-Nicol tester: Unevenness of received light in a background part without defect

A 250 W metal halide (BMH-250A manufactured by Mejiro Precision Inc.) and a first polarizing plate capable of adjusting the angle were provided as an instrument for evaluating the Cross Nicole inspection property in the present invention. (Manufactured by DALSA Corporation, product name: P3-80-8K-40) was used in combination with a second polarizer capable of adjusting the angle. An outline of the apparatus is shown in Fig.

2, light from the illuminating means 4 is incident and transmitted through the first polarizing plate to the film 1 to be inspected and is picked up by the light receiving means 5 via the second polarizing plate And outputted to the signal processing means 6.

The evaluation of the amount of ununiformity in the amount of light received in the background portion free of base defects was made by setting the angle of the second polarizing plate on the side of the light receiving means as a fixed value and adjusting the angle of the first polarizing plate provided on the illumination side, The difference between the maximum value and the minimum value of the amount of light received at the background without defects is checked in the state that the average value when the amount of light received in the background portion free from defects in the full inspection width is evaluated to 256 gradations , And this car was evaluated as a non-uniformity of the received light amount in the background part without defect.

(10) Inspection by automatic inspection equipment

(9) The inspection apparatus used in the evaluation by the Cross Nicole tester was used, and the film 10 m was inspected with the detection sensitivity of the camera as a fixed value. The testability at this time was confirmed and evaluated according to the following criteria.

○: The inspection could be made without occurrence of the inspection stop due to the bundle of false detectors. Cross-Nicol inspection was carried out on the film after inspection, but almost no defect was found in the inspection machine.

□: The inspection could be performed without occurrence of the inspection stop due to the bundle of false detectors. Cross-Nicole inspection of the film after inspection revealed several defects that could not be detected by the tester.

△: An inspection stop due to a bundle of false detections occurred within 10 m from the start of inspection.

×: An inspection stop due to a bundle of false detections occurred at less than 1 m from the start of inspection.

(11) Unevenness of MD alignment angle

(2) Measurement is performed in the same manner as the tilting of the alignment main axis (alignment angle). 10 points of alignment angle are measured every 1000 mm in the longitudinal direction at both ends of the film. The absolute value of the difference between the maximum dental value and the minimum value of the measurement value is obtained for each end of the film and the value with the largest absolute value is regarded as the measurement result of the MD orientation angle variation.

Hereinafter, the present invention will be described in detail by way of examples.

Example 1:

To 100 parts by mass of dimethyl terephthalate (DMT), 61 parts by mass (1.9 moles relative to 1 mole of DMT) of ethylene glycol, 0.05 part by mass of magnesium acetate quaternary salt and 0.015 part by mass of phosphoric acid were added and thermally transesterified 0.025 part by mass of antimony trioxide was added, and the mixture was heated and heated to be subjected to a polycondensation reaction in vacuo to obtain polyester pellets having an intrinsic viscosity of 0.63, substantially free from particles.

Next, calcium carbonate having a true specific gravity of 2.71 g / cm3 and an average particle diameter of 1.0 占 퐉 was prepared to obtain a 10 weight% ethylene glycol slurry. This slurry was dispersed for 1 hour in a jet agitator and subjected to high-precision filtration with a filter having a collection efficiency of 95% or more of 5 m or more. This slurry was added after the ester exchange and then subjected to a polycondensation reaction as described above to obtain a calcium carbonate-containing master pellet having an intrinsic viscosity of 0.63 containing 1% of calcium carbonate having an average particle diameter of 1.0 탆.

Next, calcium carbonate-containing master pellets and polyester pellets containing no particles were mixed to obtain polyester A containing 0.5% by weight of calcium carbonate and polyester B containing 0.054% by weight of calcium carbonate.

Each of these polyesters A and B was dried under reduced pressure at 160 DEG C for 8 hours and then fed to a separate extruder and melt extruded at 275 DEG C and filtered through a high precision filter having a collection efficiency of 95% And joined together in a confluence block to form a three-layer lamination of polyester A / polyester B / polyester A. Thereafter, the film was cooled and solidified on a casting roll having a surface temperature of 25 DEG C by electrostatic casting through a slit die maintained at 285 DEG C to obtain an unstretched film. This unstretched film was first stretched 3.4 times in the longitudinal direction by a roll heated at 103 DEG C and a radial heater. And then stretched by 4.4 times at 105 DEG C in the transverse direction with a tenter. Thereafter, the film was cooled so that the film temperature was 35 ° C at a width shrinkage rate of 18% / min in the cooling step. In this cooling step, a roll method was employed, the temperature of the roll was set at 30 占 폚, and the passing time of the cooling step was set at 15 seconds. Then, the film was heat-treated at 190 占 폚 to form a three-layer film having a total film thickness of 38 占 퐉, a film thickness of the polyester A / polyester B / polyester A = 1.5 占 퐉 / 35 占 퐉 / And a biaxially oriented polyester film was wound thereon to prepare an intermediate product roll. A sample was taken from the obtained intermediate product roll and the orientation angle was measured at 5 m in the width direction. The maximum value was 3.6 degrees. Then, for the obtained intermediate product roll, an evaluation roll having a width of 2000 mm including the film end was slit to 2000 mm in the evaluation roll take-up width described in Table 1 so as to include the film end. The inclination of the alignment main axis with respect to the prepared evaluation roll was in the same direction. The evaluation rolls were evaluated for film properties, and the results obtained are shown in Table 1.

The obtained results are shown in Table 1.

Examples 2 to 12, Comparative Examples 1 to 4:

A biaxially oriented polyester film composed of three layers was obtained in the same manner as in Example 1 except that the film forming conditions such as the stretching condition, the cooling condition, the heat treatment temperature, the width shrinkage speed of the cooling step, and the picking width were changed. The obtained results are shown in Tables 1-1 and 1-2.

(Table 1-1)

(Table 1-2)

The following items can be confirmed from the above Examples and Comparative Examples.

In other words, by making the shape of the present invention (in particular, the unevenness of the tilt angle (alignment angle) of the alignment main axis relative to the film width direction is set to 3.7 degrees or less, and the haze value of the film is further set to 7 to 13% , It was possible to reduce the unevenness of the received light amount in the background portion free from defects in the cross Niche tester, so that it was less likely to miss or erroneously detect defects even if it was inspected using an automatic inspection apparatus. In addition, even in the case of inspecting with the naked eye, it is confirmed that the light on the background (background portion) is not too strong or too weak, so that the defect is less missed and the inspection property is improved.

(Industrial availability)

Since the film of the present invention has excellent cross-Nicole inspecting property, it can be suitably used as a polarizer release mold.

1: film to be inspected 2: first polarizing filter
3: second polarizing filter 4: illumination means
5: light receiving means 6: signal processing means

Claims (12)

Wherein the unevenness of the angle of inclination (alignment angle) of the alignment main axis with respect to the film width direction is 3.7 degrees or less and the film width is 1700 mm or more. The method according to claim 1,
Wherein the film has a haze value of 7 to 13%. 3. The method according to claim 1 or 2,
Wherein the heat shrinkage ratio in the longitudinal direction of the film after heat treatment at 150 占 폚 for 30 minutes is 5 to 7% and the heat shrinkage ratio in the film width direction is 7 to 9%. 4. The method according to any one of claims 1 to 3,
Wherein the orientation of the main axis of alignment with respect to the film width direction is the same direction. 5. The method according to any one of claims 1 to 4,
Wherein the thickness unevenness in the longitudinal direction of the film is less than 2.0 占 퐉. 6. The method according to any one of claims 1 to 5,
Wherein the uneven orientation angle in the longitudinal direction (MD orientation angle unevenness) is less than 1.5 degrees. 7. The method according to any one of claims 1 to 6,
Wherein the film is taken from a film having an inclination angle (orientation angle) of the alignment main axis with respect to the film width direction of 3.7 degrees or less over at least 5 m width. 8. The method according to any one of claims 1 to 7,
Wherein the biaxially oriented polyester film for polarizing plate release is obtained by a method having the following steps in this order.
(Step 1) A step of stretching an unoriented polyester film in a longitudinal direction at a draw ratio of 2.5 to 5 to obtain a uniaxially stretched polyester film.
(Step 2) The uniaxially stretched polyester film is stretched in the transverse direction at a draw magnification of 3 to 6 times, and the stretching magnification in the width direction is larger than the stretching magnification in the longitudinal direction to obtain a biaxially stretched polyester film fair.
(Process 3) A step of cooling the biaxially oriented polyester film at a film temperature of 25 to 45 占 폚 and a width shrinkage rate of the film of 0.1 to 20% / min to obtain a cooled polyester film.
(Step 4) The step of heat-treating the cooled polyester film at a heat treatment temperature of 180 to 230 占 폚 to obtain a biaxially oriented polyester film. Wherein the biaxially oriented polyester film for polarizing plate releasing according to any one of claims 1 to 8 is formed on at least one side of a polarizer having a width of 1700 mm or more. A method for producing a polarizing plate, which comprises peeling the biaxially oriented polyester film for releasing the polarizing plate from the laminate according to claim 9. 9. A method for producing a biaxially oriented polyester film for a polarizing plate release film according to any one of claims 1 to 8, which comprises the following steps in that order.
(Step 1) A step of stretching an unoriented polyester film in a longitudinal direction at a draw ratio of 2.5 to 5 to obtain a uniaxially stretched polyester film.
(Step 2) The uniaxially stretched polyester film is stretched in the transverse direction at a draw magnification of 3 to 6 times, and the stretching magnification in the width direction is larger than the stretching magnification in the longitudinal direction to obtain a biaxially stretched polyester film fair.
(Process 3) A step of cooling the biaxially oriented polyester film at a film temperature of 25 to 45 占 폚 and a width shrinkage rate of the film of 0.1 to 20% / min to obtain a cooled polyester film.
(Step 4) The step of heat-treating the cooled polyester film at a heat treatment temperature of 180 to 230 占 폚 to obtain a biaxially oriented polyester film. A method for producing a biaxially oriented polyester film having a nonuniformity of an inclination angle (orientation angle) of an alignment main axis relative to a film width direction within 3.7 degrees and a film width of 1700 mm or more, A method for producing a biaxially oriented polyester film.
(Step 1) A step of stretching an unoriented polyester film in a longitudinal direction at a draw ratio of 2.5 to 5 to obtain a uniaxially stretched polyester film.
(Step 2) The uniaxially stretched polyester film is stretched in the transverse direction at a draw magnification of 3 to 6 times, and a stretching magnification in the transverse direction is larger than that in the longitudinal direction to obtain a biaxially stretched polyester film fair.
(Process 3) A step of cooling the biaxially oriented polyester film at a film temperature of 25 to 45 占 폚 and a width shrinkage rate of the film of 0.1 to 20% / min to obtain a cooled polyester film.
(Step 4) The step of heat-treating the cooled polyester film at a heat treatment temperature of 180 to 230 占 폚 to obtain a biaxially oriented polyester film.

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