CN115015280A

CN115015280A - Defect inspection method and defect inspection apparatus

Info

Publication number: CN115015280A
Application number: CN202210196953.4A
Authority: CN
Inventors: 小林信次; 松田俊介
Original assignee: Sumitomo Chemical Co Ltd
Current assignee: Sumitomo Chemical Co Ltd
Priority date: 2021-03-04
Filing date: 2022-03-01
Publication date: 2022-09-06
Also published as: JP2022134936A

Abstract

The invention provides a defect inspection method capable of detecting optical characteristic unevenness. The defect inspection method includes: a disposing step of disposing the 1 st optical filter, the optical film, and the 2 nd optical filter in this order while satisfying the following conditions a1 and a 2: (a1) an angle θ 1 formed by an absorption axis of a1 st polarizing plate of the 1 st filter and an absorption axis of the polarizing plate to be inspected is in a range of 90 ° ± 5 °, (a2) an angle θ 2 formed by an absorption axis of the polarizing plate to be inspected and an absorption axis of a2 nd polarizing plate of the 2 nd filter is in a range of 90 ° ± 35 °; a detection step of detecting light irradiated from a light source and sequentially transmitted through the 1 st optical filter, the optical film, and the 2 nd optical filter; and a judging step of judging a defect of the optical film based on a detection result in the detecting step.

Description

Defect inspection method and defect inspection apparatus

Technical Field

The present invention relates to a defect inspection method and a defect inspection apparatus for an optical film.

Background

Polarizing plates used in display devices such as liquid crystal display devices and organic EL display devices are generally formed by sandwiching a polarizing plate with 2 protective films. In order to bond the polarizing plate to a display device, an adhesive layer may be laminated on one protective film, and a protective film for preventing scratches or the like from being generated on the surface of the protective film during distribution may be laminated on the other protective film. A release film is generally laminated on the pressure-sensitive adhesive layer. Specific examples of the polarizing plate include a PVA-based polarizing film in which a dichroic dye such as iodine or a dichroic dye is adsorbed onto a uniaxially stretched polyvinyl alcohol-based (PVA-based) resin film and the dichroic dye is aligned, and a polarizing plate formed of a liquid crystal cured layer containing a polymer of a polymerizable liquid crystal compound and a dichroic dye (hereinafter, also referred to as a "liquid crystal polarizing plate"). A liquid crystal polarizing plate is generally formed by applying a composition containing a polymerizable liquid crystal compound onto a base film and curing the composition, and thus has an advantage that a thin polarizing plate can be manufactured. Such a PVA-based polarizing film and a liquid crystal polarizing plate have a function of passing linearly polarized light of a specific vibration plane as described later, and are referred to as "linear polarizing plates". In addition, a polarizing plate having a protective film on one or both surfaces of the linear polarizer is generally called a "linear polarizing plate".

In polarizing plates and polarizing plates, defects may occur in the production stages thereof. For example, a defect such as mixing of foreign matter or remaining of air bubbles between the polarizing plate and the protective film may occur. In addition, the liquid crystal polarizer may have unevenness in optical characteristics of the polarizing plate due to coating unevenness during production.

Therefore, in a stage before the polarizing plate is incorporated into the display device, an inspection for detecting defects of the polarizing plate is performed. As shown in japanese patent application laid-open No. 9-229817 (patent document 1), in the inspection of the defect, a polarizing filter is provided between a polarizing plate as a test object and a light source, and then the polarizing plate or the polarizing filter is rotated in the plane direction to set the respective polarization axis directions in a specific relationship. When the directions of the polarization axes are orthogonal to each other (that is, when the crossed nicols are arranged), the linearly polarized light passing through the polarization filter does not transmit the polarization plate. However, if a defect exists in the polarizing plate, the linearly polarized light is transmitted through the defect, and the light is detected, whereby the presence of the defect is recognized.

On the other hand, in the case where the polarizing plate and the polarizing filter are parallel to each other in the polarization axis direction, the linearly polarized light passing through the polarizing filter is transmitted through the polarizing plate. However, if a defect exists in the polarizing plate, the linearly polarized light is blocked at the position, and therefore the light cannot be detected, and the existence of the defect is found. The inspector can inspect the presence or absence of defects of the polarizing plate by visually inspecting the light transmitted through the polarizing plate or automatically inspecting the light transmitted through the polarizing plate using an image analysis processing value obtained by combining a CCD camera and an image processing device.

Disclosure of Invention

Problems to be solved by the invention

According to the method described in patent document 1, although a local defect having a large difference from the surroundings in optical characteristics, such as mixing of foreign matter or air bubbles, can be detected, it is difficult to detect unevenness in optical characteristics.

The invention aims to provide a defect inspection method and a defect inspection device capable of detecting optical characteristic unevenness.

The present invention provides a defect inspection method and a defect inspection apparatus described below.

[ 1 ] A defect inspection method for an optical film having a polarizing plate to be inspected,

the defect inspection method uses a1 st filter having a1 st polarizing plate, a2 nd filter having a2 nd polarizing plate, and a light source, and has:

a disposing step of disposing the 1 st filter, the optical film, and the 2 nd filter in this order while satisfying the following condition a1 and condition a2,

(a1) an angle theta 1 formed by the absorption axis of the 1 st polarizing plate and the absorption axis of the detected polarizing plate is in a range of 90 DEG +/-5 DEG,

(a2) an angle theta 2 formed by the absorption axis of the detected polaroid and the absorption axis of the 2 nd polaroid is in a range of 90 degrees +/-35 degrees;

a detection step of the following step b1 or step b2,

(b1) a step of detecting light irradiated from the light source and sequentially transmitted through the 1 st filter, the optical film, and the 2 nd filter, or

(b2) Detecting light irradiated from the light source and sequentially transmitted through the 2 nd filter, the optical film, and the 1 st filter; and

and a judging step of judging a defect of the optical film based on a detection result in the detecting step.

[ 2 ] the defect inspection method according to [ 1 ], wherein,

the optical film also has a protective film comprising a polyethylene terephthalate-based resin,

the angle formed by the orientation axis of the protective film and the absorption axis of the polarizer to be detected is in the range of 0 DEG +/-30 DEG,

in the process of the disposition,

the optical film is disposed so that a surface of the seed film on a side opposite to the side of the object polarizer is positioned in a direction of the 2 nd filter and an angle formed by an orientation axis of the seed film and an absorption axis of the 2 nd polarizer is in a range of 90 ° ± 5 °,

the detection step is performed in the step b 1.

[ 3 ] the defect inspection method according to [ 1 ], wherein,

the angle formed by the orientation axis of the protective film and the absorption axis of the polarizer to be detected is in the range of 90 DEG +/-30 DEG,

in the process of the disposition,

the optical film is disposed so that a surface of the seed film on a side opposite to the side of the object polarizer is positioned in a direction of the 2 nd filter and an angle formed by an orientation axis of the seed film and an absorption axis of the 2 nd polarizer is in a range of 0 ° ± 5 °,

the detection step is performed in the step b 1.

The method according to any one of [ 1 ] to [ 3 ], wherein the polarizing plate to be inspected contains a cured product of a polymerizable liquid crystal compound.

[ 5 ] the defect inspection method according to any one of [ 1 ] to [ 4 ], wherein,

the optical film also has a lambda/4 phase difference layer,

in the inspection method, the 1 st filter uses a filter having a λ/4 phase difference layer,

in the disposing step, the optical film and the 1 st optical filter are disposed in a direction in which the λ/4 retardation layer faces each other without interposing the polarizing plate to be tested and the 1 st polarizing plate therebetween.

[ 6 ] A defect inspection apparatus for an optical film having a polarizing plate to be inspected,

the defect inspection apparatus comprises a1 st filter having a1 st polarizing plate, a2 nd filter having a2 nd polarizing plate, and a light source,

the 1 st filter, the optical film, and the 2 nd filter are sequentially arranged to satisfy a condition a1 and a condition a 2:

(a1) an angle theta 1 formed by the absorption axis of the 1 st polarizing plate and the absorption axis of the polarizing plate to be detected is in a range of 90 DEG + -5 DEG,

(a2) an angle theta 2 formed by the transmission axis of the tested polaroid and the absorption axis of the 2 nd polaroid is in a range of 90 DEG +/-35 DEG,

the light source is configured to satisfy a condition b1 or a condition b 2:

(b1) the light irradiated from the light source sequentially passes through the 1 st optical filter, the optical film, and the 2 nd optical filter,

(b2) the light irradiated from the light source sequentially passes through the 2 nd filter, the optical film, and the 1 st filter.

Effects of the invention

According to the defect inspection method and the defect inspection apparatus of the present invention, unevenness in optical characteristics of the optical film can be detected.

Drawings

Fig. 1 is a diagram showing a defect inspection system according to the present embodiment.

Fig. 2 is a schematic diagram of the defect inspection apparatus of the present embodiment.

Fig. 3 is a diagram showing an example of a defective region of the optical film.

Fig. 4 is a cross-sectional view showing an example of the layer structure of the polarizing plate with a protective film as an inspection target in application 1.

Fig. 5 is a cross-sectional view showing an example of the layer structure of the polarizing plate to be inspected in application example 2.

Description of the reference numerals

The optical film includes a defect inspection system 1, a defect inspection system 2, a defect inspection system 3A, a marking system 4, a light irradiation system 10A, a light source 11, a detection system 20A, a camera 21, a control system 30, a1 st optical filter 40, a1 st optical filter 41, a2 nd optical filter 50, a2 nd optical filter 51, a 100 th optical plate, a 101 optical plate,

protective films

102 and 103, a protective film 110 with a protective film, a protective film 120, a polarizing plate 130, a phase difference body 140, a phase difference layer 1 141, and a phase difference layer 2 142.

Detailed Description

The present invention relates to a defect inspection method and a defect inspection apparatus for an optical film having a polarizing plate to be inspected.

The defect inspection method of the present invention uses a1 st optical filter having a1 st polarizing plate, a2 nd optical filter having a2 nd polarizing plate, and a light source, and has:

a disposing step of disposing the 1 st filter, the optical film, and the 2 nd filter in this order while satisfying the following conditions a1 and a 2:

(a2) an angle theta 2 formed by the transmission axis of the tested polaroid and the absorption axis of the 2 nd polaroid is in a range of 90 degrees +/-35 degrees;

a detection step in which the following step b1 or step b2 is performed:

(b1) a step of detecting light irradiated from the light source and sequentially transmitted through the 1 st optical filter, the optical film, and the 2 nd optical filter,

The defect inspection device of the present invention comprises a1 st optical filter having a1 st polarizing plate, a2 nd optical filter having a2 nd polarizing plate, and a light source,

(a1) an angle theta 1 formed by an absorption axis of the 1 st polarizer and an absorption axis of the detected polarizer is within a range of 90 degrees +/-5 degrees; and

(a2) an angle θ 2 formed by the transmission axis of the polarizing plate to be inspected and the absorption axis of the 2 nd polarizing plate is in a range of 90 ° ± 35 °.

The light source is configured to satisfy a condition b1 or a condition b 2:

(b1) the light irradiated from the light source sequentially passes through the 1 st optical filter, the optical film, and the 2 nd optical filter;

Hereinafter, embodiments of a defect inspection apparatus and a defect inspection method according to the present invention will be described with reference to the drawings. The same elements are denoted by the same reference numerals, and redundant description thereof is omitted. The dimensional ratios in the drawings do not necessarily correspond to the dimensional ratios illustrated.

Fig. 1 is a schematic diagram of a defect inspection system including a defect inspection apparatus according to an embodiment. The defect inspection system 1 includes a transport unit 2 and a defect inspection device 3A, and inspects defects of the optical film 100 by the defect inspection device 3A disposed on a transport path while transporting the optical film 100 in a strip shape in a longitudinal direction thereof by the transport unit 2. The optical film 100 includes a test polarizing plate.

The conveying section 2 includes a conveying roller R. The conveying section 2 may further include a tension applying device for applying tension to the conveyed optical film 100, in addition to the conveying roller R. In fig. 1, XYZ orthogonal coordinates used for convenience of explanation are shown. The X direction indicates the width direction of the optical film 100, and the Y direction indicates the conveyance direction of the optical film 100. The Z direction indicates a direction orthogonal to each of the X direction and the Y direction. In the description of the other drawings, the same XYZ rectangular coordinates will be used.

The defect inspection system 1 may include a marking device 4 as shown in fig. 1. The marking device 4 is a device for applying a mark M to the optical film 100 by using the defect information sent from the defect inspection device 3A. The marking device 4 has, for example, an arm extending in the width direction X of the optical film 100 and a marking head having a pen or the like. The mark M is added to the optical film 100 by moving the marking head on the arm in the width direction X. The marking device 4 may be configured to be controlled by the defect inspection device 3A, or the marking device 4 itself may have a control unit such as a computer. The marking device 4 may print the defect information sent from the defect inspection device 3A on the optical film 100 as a two-dimensional code.

The so-called defect inspection performed by the defect inspection apparatus 3A may include a process of detecting a defect that may occur in a manufacturing process (including a transport process) of the optical film 100, and a process of creating a defect map that displays the position of the detected defect on the optical film 100. Examples of the defects of the optical film 100 that can be detected in the present embodiment include local defects such as unevenness in optical characteristics and local disturbance of the polarization axis. In the optical film 100, when the polarizing plate to be tested is a liquid crystal polarizing plate, there may be variations in optical characteristics due to coating unevenness in the production process. In addition, in the optical film 100, if bubbles or foreign matter are mixed in or unevenness occurs in the manufacturing process, it becomes a local defect.

The defect inspection apparatus 3A will be described with reference to fig. 2. Fig. 2 is a schematic diagram of the defect inspection apparatus 3A.

In fig. 2, a polarizing plate 100 is illustrated as an example of the optical film 100 inspected by the defect inspection apparatus 3A. The polarizing plate 100 is a laminate of a polarizer 101, a protective film 102, and a protective film 103. The polarizer 101 of the polarizing plate 100 is a polarizer to be tested.

The polarizing plate 101 has a linear polarization characteristic. In this embodiment, the absorption axis PA0 of the polarizing plate 101 is parallel to the Y direction which is the conveyance direction of the optical film 100. Hereinafter, light polarized in the transport direction of the optical film 100 (the direction of the absorption axis PA0 of the polarizing plate 101) is referred to as 1 st polarized light, and light polarized in the direction orthogonal to the 1 st polarized light is referred to as 2 nd polarized light.

The defect inspection apparatus 3A includes a light irradiation section 10A having a light source 11, a1 st filter 40 having a1 st polarizing plate 41, a2 nd filter 50 having a2 nd polarizing plate 51, and a detection section 20A having a camera 21. The defect inspection apparatus 3A may include a control device 30 for controlling the detection unit 20A. Hereinafter, the embodiment including the control device 30 will be described unless otherwise specified. The same applies to other embodiments.

The 1 st filter 40 and the 2 nd filter 50 are disposed so as to sandwich the optical film 100. The 1 st optical filter 40 is disposed so that the angle θ 1 between the absorption axis PA1 of the 1 st polarizing plate 41 and the absorption axis PA0 of the polarizing plate 101 of the optical film 100 is in the range of 90 ° ± 5 ° (so as to satisfy the condition a 1). The 2 nd filter 50 is disposed so that the angle θ 2 between the absorption axis PA2 of the 2 nd polarizing plate 51 and the absorption axis PA0 of the polarizing plate 101 of the optical film 100 is in the range of 90 ° ± 35 ° (so as to satisfy the condition a 2).

In fig. 2, the absorption axis PA0 of the polarizing plate 101 is indicated by a double-headed arrow, and the direction at 90 ° to the absorption axis PA0 is indicated by a black dot. In fig. 2, since the angle θ 1 is 90 ° and the angle θ 2 is 90 °, the absorption axes PA1 and PA2 are indicated by black dots. In the present invention, as described above, the angle θ 1 may be in the range of 90 ° ± 5 °, and the angle θ 2 may be in the range of 90 ° ± 35 °, and hereinafter, unless otherwise specified, the description will be made of the mode in which the angle θ 1 is 90 ° and the angle θ 2 is 90 °.

In fig. 2, a configuration is formed that satisfies the above condition b 1. Specifically, the light irradiation section 10A is disposed with the 1 st filter 40 interposed therebetween when viewed from the optical film 100, and the detection section 20A is disposed with the 2 nd filter 50 interposed therebetween when viewed from the optical film 100. Light emitted from the light source 11 of the light irradiation unit 10A enters the inspection region a (see fig. 1) of the optical film 100 to be inspected via the 1 st filter 40. The light emitted from the inspection region a enters the detection unit 20A via the 2 nd filter 50. That is, the detection step is performed in the step b 1.

The 1 st filter 40 emits unpolarized light L1 emitted from the light source 11 as light L2 having a predetermined polarization state.

The light source 11 is not limited as long as it can output unpolarized light without affecting the composition and properties of the optical film 100. Examples of the light source 11 are a metal halide lamp, a halogen transmitting lamp (japanese: ハロゲン yung ライト), a fluorescent lamp, and the like. The light source 11 may extend along the width direction of the optical film 100, as shown in fig. 1. Alternatively, the light irradiation section 10A may include a plurality of light sources 11 that are discretely arranged along the width direction of the optical film 100.

In the present embodiment, the 1 st filter 40 selectively passes the 1 st polarized light among the polarized lights included in the light emitted from the light source 11.

The detection unit 20A includes at least one camera 21 for imaging the optical film 100. Fig. 1 illustrates an embodiment in which the imaging unit 20A includes a plurality of cameras 21 arranged along the width direction of the optical film 100. The camera 21 is a surface scanning camera called a CCD camera. The camera 21 may also be a line scan camera. When the camera 21 is a line scan camera, the inspection area a of the optical film 100 can be imaged by moving the camera 21 and the optical film 100 relative to each other. The detection unit 20A (specifically, the camera 21) is electrically connected to the control device 30, and the control device 30 inputs the obtained imaging data while controlling the imaging timing.

Although fig. 1 and 2 show a system in which the camera 21 is provided as the detection unit 20A and the defect is detected based on the image captured by the camera 21, the detection unit 20A may detect the defect by visually observing the optical film 100. When the detection unit 20A is a system for detecting a defect by visual observation, the system is preferably a system without the control device 30.

Control device 30 controls detection unit 20A. The control device 30 includes, for example, a computer (arithmetic unit). The control device 30 may detect a defective portion from the captured data input from the detection unit 20A, and may have a function of performing image processing for emphasizing and displaying the defective portion, a function of creating a defect map showing a defective position with respect to the image of the optical film 100, and the like. As illustrated in fig. 1, in the defect inspection system 1, in the embodiment including the marking device 4, the control device 30 may be electrically connected to the marking device 4 as illustrated in fig. 1, control the marking device 4, and give the mark M based on the detected defect information to the optical film 100.

Next, an inspection process of inspecting the optical film 100 by the defect inspection apparatus 3A will be described. When defect inspection is performed, light L1 from the light source 11 passes through the 1 st filter 40 and is irradiated to the inspection area a of the optical film 100 as light L2 which is light of the 1 st polarization. A portion of light L2 is transmitted through optical film 100. The light L3 transmitted through the optical film 100 is emitted from the 2 nd filter 40 as light L4, enters the detector 20A, and detects light L4 in the detector 20A. More specifically, the inspection area a is photographed by the camera 21 or visually observed. The above steps are detection steps. Thereafter, based on the detection result in the detection step, a defect in the inspection area a of the optical film is determined (determination step).

In the defect inspection method, the light L2 of the 1 st polarized light transmitted through the 1 st filter 40 is irradiated to the optical film 100. In a state where the light L2 and the polarizing plate 101 of the optical film 100 are crossed nicols, that is, in a state where the polarization direction of the light L2 is substantially parallel to the absorption axis PA0 direction of the polarizing plate 101, the light L2 enters the optical film 100 and is absorbed.

However, the optical film 100 sometimes has a defective region where the absorption axis of the polarizing plate 101 does not coincide with the absorption axis PA 0. Fig. 3 shows an example of a defective region B in the optical film 100, and the absorption axis in the defective region B is indicated by a double-headed arrow. The defect region B has an absorption axis (hereinafter referred to as "absorption axis PA 3") that does not coincide with the absorption axis PA 0. When the defect in the defect region B has uneven optical characteristics, a state in which the angle formed by the absorption axis PA0 is continuously changed can be assumed as the absorption axis PA3 in the defect region B as shown in fig. 3. In the defective optical film 100, a region having the absorption axis PA0 is set as a normal region a 1.

In defect region B having absorption axis PA3 that does not coincide with absorption axis PA0, the polarization direction of light L2 is not parallel to the direction of absorption axis PA0 of polarizer 101, and light L2 transmits through optical film 100. The light L3 transmitted through the optical film 100 is polarized in a direction corresponding to the absorption axis of the defect region B of the polarizing plate 101. When the direction of the absorption axis of the defect region of the polarizing plate 101 is not one direction, the light L3 includes polarized light in a plurality of directions. Hereinafter, these are combined to be the 3 rd polarized light, and a part of the plural polarized lights included in the 3 rd polarized light is referred to as the 3a polarized light, the 3b polarized light, and the 3c polarized light, ·, in order of increasing angle with respect to the 1 st polarized light.

The light L3 passes through the 2 nd filter 50 and enters the detection unit 20A as light L4. In the 2 nd filter 50, the absorption axis PA2 of the 2 nd polarizing plate 51 and the absorption axis PA0 of the polarizing plate 101 are in a cross nicol state, and therefore, if the light L3 is the 1 st polarized light, the light enters the 2 nd polarizing plate 51 and is absorbed, whereas the light L3 is the 3 rd polarized light different from the 1 st polarized light, and therefore, the light passes through the 2 nd filter 50. The light L3 is absorbed by the 2 nd filter 50 at a ratio corresponding to the polarization direction thereof, and is emitted. That is, the ratio of light absorbed by the 2 nd filter 50 becomes smaller in the order of the 3 rd polarized light, and the 3c polarized light, ·.

The present inventors have paid attention to the fact that the degree of polarization of light transmitted through the 1 st filter and the optical film is substantially low. It was found that by passing such light through the 2 nd filter again, the contrast between the 1 st polarized light region and the 3 rd polarized light region can be improved, and the detection sensitivity can be greatly improved.

As described above, the transmission characteristics of the light L3 in the optical film 100 are different in the normal region a1 and the defect region B, and in addition, the transmission characteristics of the light L4 in the 2 nd filter 50 are different according to the absorption axis direction of the defect region B. Since the light L4 reflecting these transmission characteristics is detected in the detection unit 20A, the presence or absence of a defect in the optical film 100 and the presence or absence of unevenness in the absorption axis direction in the defect region can be detected. The unevenness in the absorption axis direction in the optical film 100 corresponds to the unevenness in the optical characteristics.

In the above, the case where the angle θ 1 is 90 ° and the angle θ 2 is 90 ° was explained, however, the light amount of the light L4 differs depending on the magnitude of the angle θ 1 and the angle θ 2. As long as the angle θ 1 is 90 ° ± 5 ° and the angle θ 2 is 90 ° ± 35 °, the transmission characteristics of light L3 in optical film 100 differ between normal region a1 and defect region B, and the transmission characteristics of light L4 in second filter 2 50 differ depending on the absorption axis direction of defect region B. Therefore, even when the angles θ 1 and θ 2 are not 90 °, the detection unit 20A detects the light L4 reflecting these transmission characteristics, and thus can detect the presence or absence of a defect in the optical film 100 and the presence or absence of unevenness in the absorption axis direction in the defect region.

The defect inspection apparatus 3A includes the 1 st filter 40 and the 2 nd filter 50, and thus can efficiently detect unevenness in optical characteristics. Thus, in the method for manufacturing the optical film 100 including the defect inspection method described above, the optical film 100 as a product not including a defect can be efficiently produced.

Fig. 1 and 2 show the case where the step b1 is performed in the detection step while the arrangement satisfying the condition b1 is performed, but the arrangement satisfying the condition b2 may be performed by replacing the arrangement positions of the light irradiation unit 10A and the detection unit 20A. In this case, light emitted from the light source 11 of the light irradiation section 10A passes through the 2 nd filter 50 and enters the inspection region a of the optical film 100 to be inspected. The light emitted from the inspection area a passes through the 1 st filter 40 and enters the detection unit 20A. That is, the detection step is performed in step b 2. Even with this arrangement, the same effects as those of the arrangement satisfying the condition b1 shown in fig. 1 and 2 can be obtained.

< method for producing optical film >

A method for manufacturing the optical film 100 including a defect inspection method using the defect inspection apparatus 3A shown in fig. 1 and 2 will be described. Here, as shown in fig. 2, a case of manufacturing an optical film 100 as a laminate of a protective film 102, a film main body 101, and a protective film 103 will be described as an example.

In the production of the optical film 100, while the belt-shaped polarizing plate 101, the belt-shaped protective film 102, and the belt-shaped protective film 103 are conveyed in the longitudinal direction, the protective film 102 is bonded to one surface of the polarizing plate 101, and the protective film 103 is bonded to the other surface (bonding step). The polarizing plate 101, the protective film 102, and the protective film 103 can be bonded to each other by using a pair of bonding rollers, for example. In the bonding step, the protective film 102 and the protective film 103 may be bonded to the polarizing plate 101 at the same time, or one of the protective film 102 and the protective film 103 may be bonded to the polarizing plate 101 and then the other may be bonded thereto.

After the bonding step, the defect inspection of the optical film 100 is performed by the defect inspection apparatus 3A while conveying the optical film 100, which is a laminate of the protective film 103, the polarizing plate 101, and the protective film 102, between the light irradiation section 10A and the detection section 20A of the defect inspection apparatus 3A (defect inspection step). In the defect inspection step, the defect inspection of the optical film 100 is performed by the defect inspection method described above. In the aspect in which the defect inspection system 1 includes the marking device 4, a step (marking step) of giving the mark M to the optical film 100 by the marking device 4 may be performed based on the result of the defect inspection step.

The polarizing plate 101 may be an absorption-type polarizing plate having a property of absorbing linearly polarized light having a vibration plane parallel to the absorption axis thereof and transmitting linearly polarized light having a vibration plane orthogonal to the absorption axis (parallel to the transmission axis). Typical examples of the polarizing plate include a liquid crystal polarizing plate containing a cured product of a polymerizable liquid crystal compound, a polarizing film in which a uniaxially stretched polyvinyl alcohol resin film is allowed to adsorb a dichroic dye and the dichroic dye is aligned, and the like.

A typical manufacturing method of the liquid crystal polarizing plate will be briefly described. First, an appropriate support is prepared. Then, an alignment film is formed on the surface of the support. Next, a liquid composition containing a polymerizable liquid crystal compound and a dichroic dye is applied to the alignment film and dried, thereby forming a coating layer containing a polymerizable liquid crystal compound on the alignment film. Thereafter, the coating layer is polymerized and cured by light irradiation, and a liquid crystal polarizing plate is obtained on the support. When a transparent resin film is used as the support, a polarizing plate having the transparent resin film as a protective film can be produced.

The liquid crystal polarizing plate may be, for example, one described in Japanese patent laid-open publication No. 2016-170368. As the dichroic dye, a dichroic dye having absorption in a wavelength range of 380 to 800nm can be used, and an organic dye is preferably used. Examples of the dichroic dye include azo compounds. The liquid crystal compound is a liquid crystal compound which can be polymerized in a state where the alignment is maintained, and may have a polymerizable group in the molecule. Further, as described in WO2011/024891, the polarizing plate may be formed of a dichroic dye having liquid crystallinity. Note that after polymerization (after formation of a polarizing plate including a cured layer of liquid crystal), the liquid crystal compound does not need to exhibit liquid crystallinity.

The thickness of the liquid crystal polarizing plate is, for example, 0.2 to 10 μm. The liquid crystal polarizing plate may have uneven optical characteristics due to uneven application of the liquid composition in the production process. Such unevenness in optical characteristics can be detected even in defect inspection by the defect inspection method and the defect inspection apparatus of the present embodiment.

Next, the PVA-based polarizing film will be briefly explained. The PVA-based polarizing film is produced, for example, by a method including a step of uniaxially stretching a PVA-based resin film; a step (dyeing treatment) of dyeing the PVA-based resin film with a dichroic dye to adsorb the dichroic dye; a step (crosslinking treatment) of treating the PVA-based resin film having the dichroic dye adsorbed thereon with a crosslinking liquid such as an aqueous boric acid solution; and a step (cleaning treatment) of performing water washing after the treatment with the crosslinking liquid.

As the PVA-based resin, a resin obtained by saponifying a polyvinyl acetate-based resin can be used. Examples of the polyvinyl acetate resin include polyvinyl acetate which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other copolymerizable monomers. Examples of the other monomer copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and (meth) acrylamides having an ammonium group, and the like.

In the present specification, "(meth) acrylic" means at least one member selected from the group consisting of acrylic and methacrylic. The same applies to "(meth) acryloyl group", "(meth) acrylate", and the like.

The saponification degree of the PVA resin is usually 85 to 100 mol%, preferably 98 mol% or more. The polyvinyl alcohol resin may be modified, and for example, polyvinyl formal, polyvinyl acetal, or the like modified with aldehydes may be used. The PVA-based resin has an average polymerization degree of usually 1000 to 10000, preferably 1500 to 5000. The average polymerization degree of the PVA resin can be determined in accordance with JIS K6726.

A film obtained by forming such a PVA-based resin film is used as a raw material film (PVA-based resin film) for producing a polarizing plate. The method for forming the PVA-based resin film is not particularly limited, and a known method can be used. The thickness of the PVA based resin film is not particularly limited, but in order to set the thickness of the polarizing film to 15 μm or less, it is preferable to use a PVA based resin film of 5 to 35 μm. More preferably 20 μm or less. The thickness of the PVA-based resin film may be selected so that the finally obtained PVA-based polarizing film has a desired thickness.

The uniaxial stretching of the PVA-based resin film may be performed before the dyeing treatment with the dichroic dye, simultaneously with the dyeing treatment, or after the dyeing treatment. In the case of performing uniaxial stretching after the dyeing treatment, the uniaxial stretching may be performed before the crosslinking treatment or may be performed during the crosslinking treatment. In addition, the uniaxial stretching may be performed in a plurality of stages of these plural treatments.

In the case of using a long PVA-based resin film in the uniaxial stretching, for example, the PVA-based resin film may be stretched uniaxially between rolls by being stretched over rolls at different peripheral speeds, or uniaxially by using a heat roll. The uniaxial stretching may be dry stretching in which stretching is performed in the air, or wet stretching in which stretching is performed in a state where the PVA-based resin film is swollen with a solvent or water. The draw ratio is usually 3 to 8 times. When the PVA-based resin film is stretched by a plurality of uniaxial stretches, the stretching ratio is usually 3 to 8 times as large as the original length. The stretching ratio may be selected so that the finally obtained PVA-based polarizing film has a desired thickness.

As a method for dyeing a PVA-based resin film with a dichroic dye (dyeing treatment), typically, a method of immersing the PVA-based resin film in an aqueous solution containing a dichroic dye is employed. Iodine or a dichroic organic dye is used as the dichroic dye. The PVA-based resin film is preferably subjected to an immersion treatment in water before the dyeing treatment.

As the crosslinking treatment after the dyeing treatment with the dichroic dye, a method of immersing the dyed PVA-based resin film in an aqueous solution containing boric acid, or the like is generally employed. In the case of using iodine as the dichroic dye, the aqueous solution containing boric acid preferably contains potassium iodide.

Thus, a PVA polarizing film was obtained. The thickness of the PVA-based polarizing film is preferably smaller, as in the liquid crystal polarizing plate, preferably 15 μm or less, more preferably 13 μm or less, still more preferably 10 μm or less, and particularly preferably 8 μm or less. The thickness of the polarizing film is usually 2 μm or more, preferably 3 μm or more.

The linear polarizer may be used alone as a polarizing plate (optical film), or as a polarizing plate (optical film), a polarizing plate (optical film) having a structure in which a protective film is generally bonded to one or both surfaces of the linear polarizer as described above may be used. For example, a transparent resin film is used as the protective film, and examples of the transparent resin forming the resin film include acetyl cellulose resins represented by triacetyl cellulose and diacetyl cellulose, methacrylic resins represented by polymethyl methacrylate, polyester resins, polyolefin resins, polycarbonate resins, polyether ether ketone resins, and polysulfone resins. Among them, a resin film containing a plurality of kinds of transparent resins may be used as the protective film.

< 1 st optical filter, 2 nd optical filter >

The 1 st filter 40 has a1 st polarizing plate 41, and the 2 nd filter 50 has a2 nd polarizing plate 51. Similarly to the polarizing plate 101, the 1 st polarizing plate 41 and the 2 nd polarizing plate 50 may be absorption-type polarizing plates having a property of absorbing linear polarization having a vibration plane parallel to the absorption axis thereof and transmitting linear polarization having a vibration plane orthogonal to the absorption axis (parallel to the transmission axis). A typical polarizing plate includes a polarizing film in which a uniaxially stretched PVA-based resin film is allowed to adsorb a dichroic dye and the dichroic dye is oriented. Detailed description of the polarizing film the description of the polarizing film in the polarizing plate 101 described above can be applied. The 1 st and 2 nd polarizing plates are defect-free polarizing plates.

[ 1 st application example ]

In application example 1, a suitable application example of the present embodiment will be described with respect to a case where the optical film inspected by the defect inspection apparatus 3A is a polarizing plate with a protective film having a protective film containing a polyethylene terephthalate resin.

Fig. 4 is a cross-sectional view showing an example of the layer structure of the polarizing plate with a protective film to be inspected in application example 1. As shown in fig. 4, the polarizing plate with a protective film 110 includes a protective film 120 laminated on the surface of the polarizing plate 100 on the side of the protective film 102, which is a laminated body of the polarizer 101, the protective film 102, and the protective film 103. For the polarizing plate 100, the above description is applied. The protective film 120 is formed of a base film and an adhesive layer laminated thereon, and is laminated to the polarizing plate 100 via the adhesive layer.

The protective film 120 is a film for protecting the surface of the polarizing plate 100, and is peeled off together with the pressure-sensitive adhesive layer of the protective film after the polarizing plate with the protective film is attached to an image display element such as a liquid crystal cell or another optical member, for example.

The base film of the seed film 120 is a uniaxially stretched film containing a polyethylene terephthalate-based resin. The pellicle film 120 has an orientation axis that coincides with the uniaxial stretching direction of the substrate film, and exhibits birefringence. Thus, a phase difference is generated in the light transmitted through the seed film 120. In the detection unit 20A, when the incident light has birefringence, the detection accuracy of the defect is lowered.

When the polarizing plate with a protective film 110 is used as the object of defect inspection by the defect inspection method and the defect inspection apparatus of the present embodiment shown in fig. 1 and 2, it is preferable that the inspection is performed such that the protective film 120 side of the polarizing plate with a protective film 110 is positioned on the 2 nd filter 50 side, and the light source is disposed such that the irradiation direction of the light from the light source in the inspection step is directed toward the 1 st filter 40 side (the above-mentioned condition b1 is satisfied), and the inspection step is performed by the above-mentioned step b 1. That is, it is preferable to transmit light from the light source 11 in the direction of the arrow shown in fig. 4. This is because the 2 nd filter 50 can be disposed by appropriately adjusting the angle θ 2 between the absorption axis of the 2 nd polarizing plate 51 and the absorption axis of the polarizing plate 101 as the polarizing plate to be inspected to be 90 ° ± 35 °, and the retardation due to the seed film 120 can be reduced. The phase difference generated in the light transmitted through the pellicle 120 is reduced by the 2 nd filter 50 and enters the detection unit 20A.

In the present application example, even if the inspection target is a polarizing plate with a protective film having a protective film containing a polyethylene terephthalate resin, it is possible to suppress a decrease in the detection accuracy of the defect by the detection section 20A.

In order to inspect a defect by the defect inspection method and the defect inspection apparatus of the present embodiment, it is preferable to manufacture a polarizing plate with a protective film so as to satisfy the following condition c1 or condition c 2. By manufacturing so as to satisfy the condition c1 or the condition c2 described below, the phase difference due to the seed film 120 can be effectively reduced by the 2 nd filter 50.

(c1) An angle θ 3 formed by the absorption axis of the polarizing plate 101 and the alignment axis of the pellicle film 120 is in the range of 0 ° ± 30 °.

(c2) The angle θ 3 formed by the absorption axis of the polarizing plate 101 and the alignment axis of the protective film 120 is in the range of 90 ° ± 30 °.

In the polarizing plate with a protective film manufactured so as to satisfy the condition c1, it is preferable that the polarizing plate with a protective film is disposed so that the angle formed by the orientation axis of the protective film and the absorption axis of the 2 nd polarizer 51 of the 2 nd filter 50 is 90 ° ± 5 ° in the disposing step. With this configuration, the phase difference due to the seed film 120 can be effectively reduced with the 2 nd filter 50.

In the polarizing plate with a protective film manufactured so as to satisfy the condition c2, in the disposing step, the polarizing plate with a protective film is preferably disposed so that the angle formed by the orientation axis of the protective film and the absorption axis of the 2 nd polarizer of the 2 nd filter is 0 ° ± 5 °. With this configuration, the phase difference due to the seed film 120 can be effectively reduced with the 2 nd filter 50.

In order to perform defect inspection using the defect inspection method and the defect inspection apparatus of the present embodiment, the orientation axes of the protective films of the polarizing plates with protective films are preferably uniform in all regions, but are usually not uniform in all regions. The maximum value of the angle formed by the different orientation axes is preferably 25 ° or less. This is because the polarizing plate using such a protective film is likely to have an effect of suppressing a decrease in detection accuracy of defect inspection performed in the defect inspection method and the defect inspection apparatus of the present embodiment.

[ 2 nd application example ]

In application example 2, a suitable application example of the present embodiment will be described with respect to a case where the optical film inspected by the defect inspection apparatus 3A is a polarizing plate having a λ/4 retardation layer.

In application example 2, an example of the layer structure of the polarizing plate to be inspected will be described with reference to fig. 5. As shown in fig. 5, the polarizing plate 130 includes a phase difference body 140 laminated on the surface of the polarizing plate 100 on the side of the protective film 103, which is a laminated body of the polarizer 101, the protective film 102, and the protective film 103. For the polarizing plate 100, the above description is applied.

The polarizing plate 130 may include a λ/4 retardation layer as the retardation body 140, which imparts a retardation of 1/4 wavelengths to the transmitted light, and may further include a λ/2 retardation layer, a positive a plate, and a positive C plate as the retardation body 140, which impart a retardation of 1/2 wavelengths to the transmitted light. The retardation body 140 of the polarizing plate 130 shown in fig. 5 includes a1 st retardation layer 141 and a2 nd retardation layer 142. Examples of the combination of the 1 st retardation layer 141 and the 2 nd retardation layer 142 include a combination of a λ/2 retardation layer and a λ/4 retardation layer, a combination of a λ/4 retardation layer and a positive C layer, and the like.

The polarizing plate 130 of application example 2 may be formed as a circular polarizing plate having a λ/4 phase difference layer. The circularly polarizing plate can be used as a polarizing plate for antireflection.

The phase difference layer may be an optical film exhibiting optical anisotropy. Examples of the optical film exhibiting optical anisotropy include stretched films obtained by stretching a polymer film containing polyvinyl alcohol, polycarbonate, polyester, polyarylate, polyimide, polyolefin, polycycloolefin, polystyrene, polysulfone, polyethersulfone, polyvinylidene fluoride/polymethyl methacrylate, acetyl cellulose, a saponified ethylene-vinyl acetate copolymer, polyvinyl chloride, or the like by about 1.01 to 6 times. Among the stretched films, preferred are polymer films obtained by uniaxially or biaxially stretching an acetylcellulose film, a polyester film, a polycarbonate film, or a cycloolefin resin film. The retardation layer may be a retardation layer comprising a cured product of a polymerizable liquid crystal compound, which exhibits optical anisotropy by applying and aligning the polymerizable liquid crystal compound to a substrate.

When the polarizing plate 130 is used as the object of defect inspection by the defect inspection method and the defect inspection apparatus of the present embodiment shown in fig. 1 and 2, the polarizing plate 130 is disposed so that the phase difference body 140 side is positioned on the 1 st optical filter 40 side for inspection. That is, light from the light source 11 is transmitted in the direction of the arrow shown in fig. 5. In addition, a filter having a λ/4 retardation layer on the polarizing plate 130 side of the 1 st polarizer 41 is used as the 1 st filter 40. The polarizing plate 130 and the 1 st filter 40 are arranged in such a direction that the λ/4 phase difference layers thereof face each other without interposing the polarizing plate 103 and the 1 st polarizing plate 41 therebetween. By providing the 1 st filter 40 with the λ/4 retardation layer, and allowing light to pass as circularly polarized light only between the λ/4 retardation layer of the 1 st filter 40 and the λ/4 retardation layer of the polarizing plate 130, even if the inspection target is a polarizing plate provided with the λ/4 retardation layer, defects can be detected by the same principle as that of the present embodiment.

Note that, if and only if the inspection target is the polarizing plate 130 (that is, if and only if it is a circularly polarizing plate), the state of the cross nicol can be obtained even if the absorption axis of the 1 st polarizer included in the 1 st filter and the absorption axis of the polarizing plate included in the polarizing plate 130, and the slow axis of the λ/4 retardation layer included in the 1 st filter and the slow axis of the λ/4 retardation layer included in the polarizing plate 130 are all arranged in parallel.

In the present application example, when defect detection is performed for the purpose of detecting defects in the polarizing plate 130, the irradiation of light from the light source in the detection step may be from the 1 st optical filter 40 side (the arrangement of condition b1, the detection step performed in step b1), or may be from the 2 nd optical filter 50 side (the arrangement of condition b2, the detection step performed in step b 2). In order to detect the unevenness of the optical characteristics of the polarizer 101 of the polarizing plate 130, it is preferable that the light from the light source is irradiated from the 1 st filter side 40. This is because, in the case of the light from the 1 st filter side 40, the defect of the phase difference body 140 is not reflected in the detection light entering the detection unit 20A, whereas in the case of the light from the 2 nd filter side 50, the defect of the phase difference body 140 is reflected in the detection light entering the detection unit 20A, and the detection accuracy of the unevenness of the optical characteristics of the polarizing plate 101 may be lowered.

Claims

1. A defect inspection method for an optical film having a polarizing plate to be inspected,

(a2) an angle theta 2 formed by the absorption axis of the detected polaroid and the absorption axis of the 2 nd polaroid is within the range of 90 +/-35 degrees;

a detection step in which the following step b1 or step b2 is performed:

2. The defect inspection method according to claim 1,

in the process of the disposition,

the detection step is performed in the step b 1.

3. The defect inspection method according to claim 1,

in the process of the disposition,

the detection step is performed in the step b 1.

4. The defect inspection method according to any one of claims 1 to 3,

the polarizing plate to be tested contains a cured product of a polymerizable liquid crystal compound.

5. The defect inspection method according to any one of claims 1 to 4,

the optical film also has a lambda/4 phase difference layer,

in the disposing step, the optical film and the 1 st filter are disposed in a direction in which the λ/4 retardation layer faces each other without interposing the polarizing plate to be tested and the 1 st polarizing plate therebetween.

6. A defect inspection apparatus for an optical film having a polarizing plate to be inspected,

the defect inspection apparatus comprises a1 st optical filter having a1 st polarizing plate, a2 nd optical filter having a2 nd polarizing plate, and a light source,

the 1 st filter, the optical film, and the 2 nd filter are sequentially configured to satisfy the following conditions a1 and a 2:

(a1) an angle theta 1 formed by the absorption axis of the 1 st polarizing plate and the absorption axis of the detected polarizing plate is within a range of 90 DEG +/-5 DEG;

the light source is configured to satisfy a condition b1 or a condition b 2:

(b2) light irradiated from the light source sequentially passes through the 2 nd optical filter, the optical film, and the 1 st optical filter.