Defect inspection method and defect inspection apparatus

Abstract

To provide a defect inspection method that can detect unevenness of optical characteristics.SOLUTION: A defect inspection method has: an arrangement step of arranging a first filter, an optical film, and a second filter in this order so as to satisfy following conditions a1 and a2: (a1) an angle θ1 formed by an absorption axis of a first polarizer of the first filter and an absorption axis of a polarizer to be inspected falls within a range of 90° ± 5°; and (a2) an angle θ2 formed by the absorption axis of the polarizer to be inspected and an absorption axis of a second polarizer of the second filter falls within a range of 90° ± 35°; a detection step of detecting light radiated from a light source and transmitting through the first filter, the optical film, and the second filter in this order; and a determination step of determining a defect in the optical film on the basis of, a result of detection in the detection step.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for inspecting defects in an optical film and a defect inspection apparatus.

Background Art

[0002] A polarizing plate used in a display device such as a liquid crystal display device or an organic EL display device is generally configured such that a polarizer is sandwiched between two protective films. In order to bond the polarizing plate to the display device, an adhesive layer is laminated on one of the protective films, and a protective film for preventing scratches or the like from occurring on the surface of the protective film during circulation may be laminated on the other protective film. A release film is usually laminated on the adhesive layer. Specific examples of the polarizer include a PVA-based polarizing film in which dichroic dyes such as iodine or dichroic dyes are adsorbed and oriented on a uniaxially stretched polyvinyl alcohol (PVA)-based resin film, and a polarizer composed 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 polarizer"). The liquid crystal polarizer is usually formed by applying a composition containing a polymerizable liquid crystal compound on a base film and curing it, and has the advantage of being able to manufacture a thin polarizer. Such a PVA-based polarizing film and a liquid crystal polarizer have the function of passing linearly polarized light of a specific vibration plane as described later, and are called "linear polarizers". In addition, those having protective films on one or both sides of the linear polarizer are generally called "linear polarizing plates".

[0003] Defects may occur in the polarizing plate or the polarizer during the manufacturing process. For example, defects such as foreign matter being mixed between the polarizer and the protective film or air bubbles remaining may occur. In addition, in the case of a liquid crystal polarizer, unevenness in the optical characteristics of the polarizing plate may occur due to uneven coating during manufacturing.

[0004] Therefore, before incorporating the polarizing plate into the display device, an inspection is performed to detect defects in the polarizing plate. As shown in Japanese Patent Application Laid-Open No. 9-229817 (Patent Document 1), in this defect inspection, a polarizing filter is provided between the polarizing plate to be inspected and the light source, and then the polarizing plate or the polarizing filter is rotated in the plane direction so that their respective polarization axis directions have a specific relationship. When the polarization axis directions are perpendicular to each other (i.e., in the configuration forming crossed nicols), the linearly polarized light passing through the polarizing filter does not pass through the polarizing plate. However, if there is a defect in the polarizing plate, linearly polarized light will pass through at that location, and the presence of the defect is determined by detecting the light.

[0005] On the other hand, when the polarization axis directions of the polarizing plate and the polarizing filter are parallel, the linearly polarized light passing through the polarizing filter passes through the polarizing plate. However, if there is a defect in the polarizing plate, linearly polarized light will be blocked at that location, and the presence of the defect is determined by the fact that the light is not detected. Whether the inspector visually detects the light passing through the polarizing plate or automatically detects it based on the image analysis processing value obtained by combining a CCD camera and an image processing device, the presence or absence of defects in the polarizing plate can be inspected.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] According to the method described in Patent Document 1, although local defects with a large difference in optical properties from the surroundings, such as the inclusion of foreign matter or air bubbles, can be detected, it is difficult to detect unevenness in optical properties.

[0008] An object of the present invention is to provide a defect inspection method and a defect inspection device capable of detecting unevenness in optical properties.

Means for Solving the Problem

[0009] The present invention provides a defect inspection method and a defect inspection apparatus as described below. 〔1〕A method for inspecting defects of an optical film having a polarizer to be inspected, The defect inspection method uses a first filter having a first polarizer, a second filter having a second polarizer, and a light source. The first filter, the optical film, and the second filter are arranged in this order and under the following conditions a1 and a2: (a1) The angle θ1 formed by the absorption axis of the first polarizer and the absorption axis of the polarizer to be inspected is within the range of 90° ± 5°; (a2) The angle θ2 formed by the absorption axis of the polarizer to be inspected and the absorption axis of the second polarizer is within the range of 90° ± 35°. An arrangement step of arranging them so as to satisfy the above conditions; The following step b1 or step b2: (b1) A step of detecting light irradiated from the light source and transmitted through the first filter, the optical film, and the second filter in this order; or (b2) A step of detecting light irradiated from the light source and transmitted through the second filter, the optical film, and the first filter in this order. A detection step; A defect inspection method having a determination step of determining a defect of the optical film based on the detection result in the detection step.

[0010] 〔2〕The optical film Further has a protective film made of 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 inspected is within the range of 0° ± 30°. In the arrangement step, The optical film is oriented such that the surface on the side opposite to the polarizer to be inspected side of the protective film is located on the second filter side, and The optical film is arranged such that the angle formed between the alignment axis of the protective film and the absorption axis of the second polarizer is within the range of 90° ± 5°. The detection step is the defect inspection method described in [1] according to step b1.

[0011] 〔3〕 The optical film further has a protective film made of a polyethylene terephthalate-based resin, the angle formed between the alignment axis of the protective film and the absorption axis of the polarizer to be inspected is within the range of 90° ± 30°, In the arrangement step, the optical film is oriented such that the surface of the protective film opposite to the side of the polarizer to be inspected faces the second filter side, and the angle formed between the alignment axis of the protective film and the absorption axis of the second polarizer is within the range of 0° ± 5°. The detection step is the defect inspection method described in [1] according to step b1.

[0012] 〔4〕 The polarizer to be inspected contains a cured product of a polymerizable liquid crystal compound, and is the defect inspection method according to any one of [1] to [3].

[0013] 〔5〕 The optical film further has a λ / 4 retardation layer, in the inspection method, the first filter used has a λ / 4 retardation layer, in the arrangement step, the optical film and the first filter are arranged such that their λ / 4 retardation layers face each other without passing through the polarizer to be inspected and the first polarizer, and is the defect inspection method according to any one of [1] to [4].

[0014] 〔6〕 A defect inspection apparatus for an optical film having a polarizer to be inspected, the defect inspection apparatus has a first filter having a first polarizer, a second filter having a second polarizer, and a light source, the first filter, the optical film, and the second filter are arranged in this order and satisfy the following conditions a1 and a2: (a1) The angle θ1 formed between the absorption axis of the first polarizer and the absorption axis of the polarizer under test is within the range of 90° ± 5°; (a2) The angle θ2 formed between the transmission axis of the polarizer under test and the absorption axis of the second polarizer is within the range of 90° ± 35°. It is arranged to satisfy the above conditions, The light source satisfies the following condition b1 or condition b2: (b1) The light irradiated from the light source passes through the first filter, the optical film, and the second filter in this order; (b2) The light irradiated from the light source passes through the second filter, the optical film, and the first filter in this order. A defect inspection apparatus arranged to satisfy the above conditions.

Advantages of the Invention

[0015] According to the defect inspection method and apparatus of the present invention, unevenness in the optical properties of an optical film can be detected.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0017] The present invention relates to a method and apparatus for inspecting defects in an optical film having a polarizer under test. The defect inspection method according to the present invention uses a first filter having a first polarizer, a second filter having a second polarizer, and a light source, arranging the first filter, the optical film, and the second filter in this order and satisfying the following conditions a1 and a2: (a1) The angle θ1 formed by the absorption axis of the first polarizer and the absorption axis of the polarizer to be inspected is within the range of 90° ± 5°; (a2) The angle θ2 formed by the transmission axis of the polarizer to be inspected and the absorption axis of the second polarizer is within the range of 90° ± 35°. An arranging step of arranging them to satisfy the above conditions; The following step b1 or step b2: (b1) A step of detecting light irradiated from the light source and transmitted through the first filter, the optical film, and the second filter in this order; (b2) A step of detecting light irradiated from the light source and transmitted through the second filter, the optical film, and the first filter in this order. A detecting step; And a determining step of determining a defect of the optical film based on the detection result in the detecting step.

[0018] The defect inspection apparatus according to the present invention includes a first filter having a first polarizer, a second filter having a second polarizer, and a light source, The first filter, the optical film, and the second filter are arranged in this order and satisfy the following conditions a1 and a2: (a1) The angle θ1 formed by the absorption axis of the first polarizer and the absorption axis of the polarizer to be inspected is within the range of 90° ± 5°; and (a2) The angle θ2 formed by the transmission axis of the polarizer to be inspected and the absorption axis of the second polarizer is within the range of 90° ± 35°. They are arranged to satisfy the above conditions, The light source satisfies the following condition b1 or condition b2: (b1) The light irradiated from the light source is transmitted through the first filter, the optical film, and the second filter in this order; (b2) The light irradiated from the light source passes through the second filter, the optical film, and the first filter in this order. It is arranged so as to satisfy.

[0019] Hereinafter, embodiments of the defect inspection apparatus and the defect inspection method of the present invention will be described with reference to the drawings. The same elements are denoted by the same reference numerals, and redundant descriptions are omitted. The dimensional ratios in the drawings do not necessarily match those in the description.

[0020] 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 apparatus 3A. The defect inspection of the belt-shaped optical film 100 is performed by the defect inspection apparatus 3A arranged in the transport path while the transport unit 2 transports the optical film 100 in its longitudinal direction. The optical film 100 includes a polarizer to be inspected.

[0021] The transport unit 2 has transport rollers R. The transport unit 2 may include a tension applying device that applies tension to the transported optical film 100 in addition to the transport rollers R. FIG. 1 shows XYZ orthogonal coordinates used for convenience of explanation. The X direction indicates the width direction of the optical film 100, the Y direction indicates the transport direction of the optical film 100, and the Z direction indicates a direction orthogonal to each of the X direction and the Y direction. In the description of other drawings, similar XYZ orthogonal coordinates may be used for explanation.

[0022] As shown in Fig. 1, the defect inspection system 1 may include a marking device 4. The marking device 4 is a device that uses the defect information sent from the defect inspection device 3A to attach a mark M on the optical film 100. The marking device 4 has, for example, an arm extending along the width direction X of the optical film 100 and a marker head having a pen or the like. By moving the marker head on the arm in the width direction X, a mark M is attached on the optical film 100. 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. Further, the marking device 4 may two-dimensionally encode the defect information sent from the defect inspection device 3A and print it on the optical film 100.

[0023] The defect inspection performed by the defect inspection device 3A may include, in addition to the process of detecting defects that may occur during the manufacturing process (including the conveying process) of the optical film 100, the process of creating a defect map indicating the positions of the inspected defects on the optical film 100. Examples of the defects of the optical film 100 that can be detected in this embodiment include unevenness in optical characteristics and local defects such as local disturbances in the polarization axis. In the optical film 100, when the polarizer to be inspected is a liquid crystal polarizer, it may have unevenness in optical characteristics due to coating unevenness in the manufacturing process. Further, in the optical film 100, when bubbles or foreign matters are mixed in or unevenness occurs in the manufacturing process, they become local defects.

[0024] The defect inspection device 3A will be described with reference to Fig. 2. Fig. 2 is a schematic diagram of the defect inspection device 3A.

[0025] In Fig. 2, a polarizing plate 100 is illustrated as the optical film 100 to be inspected by the defect inspection device 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 serves as the polarizer to be inspected.

[0026] The polarizer 101 has linearly polarized light characteristics. In the present embodiment, the absorption axis PA0 of the polarizer 101 is parallel to the Y direction which is the conveyance direction of the optical film 100. Hereinafter, light polarized in the conveyance direction of the optical film 100 (the direction of the absorption axis PA0 of the polarizer 101) is referred to as first polarized light, and light polarized in a direction orthogonal to the first polarized light is referred to as second polarized light.

[0027] The defect inspection device 3A includes a light irradiation unit 10A having a light source 11, a first filter 40 having a first polarizer 41, a second filter 50 having a second polarizer 51, and a detection unit 20A having a camera 21. The defect inspection device 3A may include a control device 30 that controls the detection unit 20A. Hereinafter, unless otherwise specified, a form including the control device 30 will be described. The same applies to other embodiments.

[0028] The first filter 40 and the second filter 50 are arranged so as to sandwich the optical film 100. The first filter 40 is arranged such that the angle θ1 formed by the absorption axis PA1 of the first polarizer 41 and the absorption axis PA0 of the polarizer 101 of the optical film 100 is within the range of 90° ± 5° (so as to satisfy the above condition a1). The second filter 50 is arranged such that the angle θ2 formed by the absorption axis PA2 of the second polarizer 51 and the absorption axis PA0 of the polarizer 101 of the optical film 100 is within the range of 90° ± 35° (so as to satisfy the above condition a2).

[0029] In FIG. 2, the absorption axis PA0 of the polarizer 101 is indicated by a double arrow, and the direction at 90° to the absorption axis PA0 is indicated by a black circle. Further, in FIG. 2, since the case where the angle θ1 is 90° and the angle θ2 is 90° is shown, the absorption axis PA1 and the absorption axis PA2 are indicated by black circles. In the present invention, as described above, the angle θ1 only needs to be within the range of 90° ± 5°, and the angle θ2 only needs to be within the range of 90° ± 35°. Hereinafter, unless otherwise specified, a form in which the angle θ1 is 90° and the angle θ2 is 90° will be described.

[0030] In FIG. 2, the arrangement satisfies the above condition b1. Specifically, the light irradiation unit 10A is arranged via the first filter 40 as viewed from the optical film 100, and the detection unit 20A is arranged via the second filter 50 as viewed from the optical film 100. The 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 first filter 40. The light emitted from the inspection region A enters the detection unit 20A via the second filter 50. That is, the detection process is performed by the above process b1.

[0031] The first filter 40 emits the non-polarized light L1 emitted from the light source 11 as light L2 having a predetermined polarization state.

[0032] The light source 11 is not limited as long as it can output non-polarized light that does not affect the composition and properties of the optical film 100. Examples of the light source 11 are, for example, a metal halide lamp, a halogen transmission light, a fluorescent lamp, etc. As shown in FIG. 1, the light source 11 can extend in the width direction of the optical film 100. Alternatively, the light irradiation unit 10A may include a plurality of light sources 11, and they may be discretely arranged along the width direction of the optical film 100.

[0033] In the present embodiment, the first filter 40 selectively passes the first polarized light among the polarized light contained in the light emitted from the light source 11.

[0034] The detection unit 20A has at least one camera 21 that images the optical film 100. FIG. 1 illustrates a form in which the imaging unit 20A has a plurality of cameras 21 arranged along the width direction of the optical film 100. The camera 21 is an area sensor camera such as a CCD camera. The camera 21 may be a line sensor camera. When the camera 21 is a line sensor camera, the inspection region A of the optical film 100 can be imaged by relatively moving the camera 21 and the optical film 100. The detection unit 20A (specifically, the camera 21) is electrically connected to the control device 30, the imaging timing is controlled, and the obtained imaging data is input to the control device 30.

[0035] FIG. 1 and FIG. 2 show a form in which the detection unit 20A has a camera 21 and defects are detected based on the captured image of the camera 21. However, the detection unit 20A may detect defects by visually inspecting the optical film 100. When the detection unit 20A detects defects visually, a form without the control device 30 is preferable.

[0036] The control device 30 controls the detection unit 20A. The control device 30 has, for example, a computer (arithmetic unit). The control device 30 may have functions such as performing image processing to detect defective portions and highlight the defective portions on the captured data input from the detection unit 20A, and creating a defect map indicating the defect positions on the image of the optical film 100. In a form where the defect inspection system 1 includes the marking device 4 as illustrated in FIG. 1, the control device 30 is also electrically connected to the marking device 4 as shown in FIG. 1, and may control the marking device 4 to apply a mark M based on the detected defect information to the optical film 100.

[0037] Next, an inspection process for inspecting the optical film 100 using the defect inspection device 3A will be described. When performing defect inspection, light L1 from the light source 11 is irradiated as light L2, which is first polarized light, through the first filter 40 onto the inspection area A of the optical film 100. A part of the light L2 passes through the optical film 100. The light L3 that passes through the optical film 100 is emitted as light L4 by the second filter 40 and enters the detection unit 20A, and the detection unit 20A detects the light L4. More specifically, the camera 21 captures an image of the inspection area A, or the inspection area A is visually observed. This is the above detection process. Then, based on the detection result in the detection process, defects in the inspection area A of the optical film are determined (determination process).

[0038] In the above-described defect inspection method, the optical film 100 is irradiated with the light L2, which is the first polarized light transmitted through the first filter 40. The light L2 and the polarizer 101 of the optical film 100 are in a crossed Nicol state, that is, the light L2 enters the optical film 100 in a state where the polarization direction of the light L2 and the absorption axis PA0 direction of the polarizer 101 are substantially parallel, so it is absorbed.

[0039] However, the optical film 100 may have a defect region where the absorption axis of the polarizer 101 does not coincide with the absorption axis PA0. FIG. 3 shows an example of the defect region B in the optical film 100, and the absorption axes in the defect region B are indicated by arrows at both ends. In the defect region B, it has an absorption axis (hereinafter referred to as "absorption axis PA3") that does not coincide with the absorption axis PA0. When the defect in the defect region B is unevenness in optical characteristics, it can be assumed that the angle formed by the absorption axis PA3 and the absorption axis PA0 continuously changes as shown in FIG. 3. In the defective optical film 100, the region having the absorption axis PA0 is defined as the normal region A1.

[0040] In the defect region B having the absorption axis PA3 that does not coincide with the absorption axis PA0, the polarization direction of the light L2 and the direction of the absorption axis PA0 of the polarizer 101 are not parallel, and the light L2 passes through the optical film 100. The light L3 that has passed through the optical film 100 is polarized light in the direction corresponding to the absorption axis of the defect region B of the polarizer 101. When the direction of the absorption axis of the defect region of the polarizer 101 is not in one direction, the light L3 includes polarized light in a plurality of directions. Hereinafter, these are collectively referred to as the third polarized light, and a part of the plurality of polarized lights included in the third polarized light is referred to as the third a polarized light, the third b polarized light, the third c polarized light,... in ascending order of the angle formed with the first polarized light.

[0041] The light L3 is incident on the detection unit 20A as light L4 through the second filter 50. In the second filter 50, since the absorption axis PA2 of the second polarizer 51 is in a cross-Nicol state with respect to the absorption axis PA0 of the polarizer 101, if the light L3 is the first polarized light, it is incident on the second polarizer 51 and absorbed. However, since the light L3 is the third polarized light different from the first polarized light, it passes through the second filter 50. The light L3 is emitted from the second filter 50 with a proportion of light absorbed according to its polarization direction. That is, the proportion of light absorbed by the second filter 50 decreases in the order of the third a-polarized light, the third b-polarized light, the third c-polarized light, and so on.

[0042] The inventors of the present invention focused on the fact that the degree of polarization of the light transmitted through the first filter and the optical film is substantially low. By passing such light through the second filter, it was found that the contrast ratio between the region of the first polarized light and the region of the third polarized light can be increased, and the detection sensitivity can be greatly improved.

[0043] As described above, the transmission characteristics of the light L3 in the optical film 100 are different between the normal region A1 and the defect region B, and the transmission characteristics of the light L4 in the second filter 50 are different according to the absorption axis direction in the defect region B. In the detection unit 20A, in order to detect the light L4 reflecting these transmission characteristics, it is possible to detect the presence or absence of defects in the optical film 100 and the presence or absence of unevenness in the absorption axis direction in the defect region. The unevenness in the absorption axis direction in the optical film 100 corresponds to the unevenness in the optical characteristics.

[0044] In the above description, the case where the angle θ1 is 90° and the angle θ2 is 90° has been explained. However, the amount of light of the light L4 varies depending on the magnitudes of the angle θ1 and the angle θ2. As long as the angle θ1 is within the range of 90° ± 5° and the angle θ2 is within the range of 90° ± 35°, the transmission characteristics of the light L3 in the optical film 100 differ between the normal region A1 and the defective region B, and the transmission characteristics of the light L4 in the second filter 50 differ depending on the absorption axis direction in the defective region B. Therefore, even when the angles θ1 and θ2 are not 90°, the detection unit 20A can detect the presence or absence of defects in the optical film 100 and the presence or absence of unevenness in the absorption axis direction in the defective region by detecting the light L4 that reflects these transmission characteristics.

[0045] The defect inspection device 3A can efficiently detect unevenness in optical characteristics by having the first filter 40 and the second filter 50. Therefore, in the manufacturing method of the optical film 100 including the above defect inspection method, the optical film 100 as a product without defects can be efficiently produced.

[0046] In FIGS. 1 and 2, an arrangement that satisfies the above condition b1 and in which the above step b1 is performed in the detection step is shown. However, an arrangement that satisfies the above condition b2 and in which the arrangement positions of the light irradiation unit 10A and the detection unit 20A are interchanged may also be used. In this case, the light emitted from the light source 11 of the light irradiation unit 10A enters the inspection region A of the optical film 100 to be inspected through the second filter 50. The light emitted from the inspection region A enters the detection unit 20A through the first filter 40. That is, the above step b2 is performed in the detection step. Even with such an arrangement, the same effect as the arrangement that satisfies the condition b1 shown in FIGS. 1 and 2 can be obtained.

[0047] <Manufacturing Method of Optical Film> A manufacturing method of the optical film 100 including the defect inspection method using the defect inspection device 3A shown in FIGS. 1 and 2 will be described. Here, as shown in FIG. 2, the case of manufacturing the optical film 100 which is a laminate of the protective film 102, the film body 101, and the protective film 103 will be described as an example.

[0048] When manufacturing the optical film 100, while transporting the strip-shaped polarizer 101, the strip-shaped protective film 102, and the strip-shaped protective film 103 in the longitudinal direction respectively, the protective film 102 is bonded to one side of the polarizer 101, and the protective film 103 is bonded to the other side (bonding step). The bonding of the polarizer 101 to the protective film 102 and the protective film 103 can be performed using, for example, a pair of bonding rollers. In the bonding step, the protective film 102 and the protective film 103 may be bonded to the polarizer 101 simultaneously, or after bonding one of the protective film 102 and the protective film 103 to the polarizer 101, the other may be bonded.

[0049] After the above bonding step, while transporting the optical film 100 as a laminate of the protective film 103, the polarizer 101, and the protective film 102 between the light irradiation unit 10A and the detection unit 20A in the defect inspection device 3A, the defect inspection of the optical film 100 is performed by the defect inspection device 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 form where the defect inspection system 1 includes the marking device 4, a step of applying the mark M to the optical film 100 with the marking device 4 (marking step) may be performed according to the result of the defect inspection step.

[0050] The polarizer 101 can be an absorption-type polarizer having the property of absorbing linearly polarized light having a vibration plane parallel to its absorption axis and transmitting linearly polarized light having a vibration plane perpendicular to the absorption axis (parallel to the transmission axis). Typical polarizers include liquid crystal polarizers containing cured products of polymerizable liquid crystal compounds, polarizing films in which dichroic dyes are adsorbed and oriented on a uniaxially stretched polyvinyl alcohol-based resin film, and the like.

[0051] A typical manufacturing method of a liquid crystal polarizer will be briefly described. First, a suitable support is prepared. Next, an alignment film is formed on the surface of the support. Subsequently, a liquid composition containing a polymerizable liquid crystal compound and a dichroic dye is coated on the alignment film and dried, thereby forming a coating layer containing the polymerizable liquid crystal compound on the alignment film. Thereafter, the coating layer is polymerized and cured by light irradiation, and a liquid crystal polarizer is obtained on the support. If a transparent resin film is used as such a support, a polarizer using the transparent resin film as a protective film can be manufactured.

[0052] The liquid crystal polarizer may be, for example, those described in JP-A-2016-170368. As the dichroic dye, those having absorption in the wavelength range of 380 to 800 nm can be used, and it is preferable to use an organic dye. Examples of the dichroic dye include azo compounds. The liquid crystal compound is a liquid crystal compound that can be polymerized while being aligned and can have a polymerizable group in the molecule. Also, as described in WO2011 / 024891, a polarizer may be formed from a dichroic dye having liquid crystallinity. Note that after polymerization (after formation of the polarizer composed of the liquid crystal cured layer), the liquid crystal compound does not need to exhibit liquid crystallinity any more.

[0053] The thickness of the liquid crystal polarizer is, for example, 0.2 μm to 10 μm. The liquid crystal polarizer may cause unevenness in optical properties due to uneven coating of the liquid composition in the manufacturing process. In the defect inspection by the defect inspection method and defect inspection apparatus of the present embodiment, such unevenness in optical properties can also be detected.

[0054] Subsequently, the PVA-based polarizing film will be briefly described. The PVA-based polarizing film can be manufactured, for example, by a method including a step of uniaxially stretching a PVA-based resin film; a step of adsorbing a dichroic dye by dyeing the PVA-based resin film with a dichroic dye (dyeing treatment); a step of treating the PVA-based resin film adsorbed with the dichroic dye with a crosslinking solution such as an aqueous boric acid solution (crosslinking treatment); and a step of washing with water after treatment with the crosslinking solution (washing treatment).

[0055] As the PVA-based resin, those obtained by saponifying polyvinyl acetate-based resins can be used. Examples of the polyvinyl acetate-based resin include polyvinyl acetate which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and (meth)acrylamides having an ammonium group, etc.

[0056] In this specification, “(meth)acryl” means at least one selected from acrylic and methacrylic. The same applies to “(meth)acryloyl”, “(meth)acrylate”, etc.

[0057] The saponification degree of the PVA-based resin is usually 85 to 100 mol%, preferably 98 mol% or more. The polyvinyl alcohol-based resin may be modified. For example, polyvinyl formal or polyvinyl acetal modified with aldehydes can also be used. The average degree of polymerization of the PVA-based resin is usually 1000 to 10000, preferably 1500 to 5000. The average degree of polymerization of the PVA-based resin can be determined in accordance with JIS K 6726.

[0058] A film formed from such a PVA-based resin is used as a raw film for producing a polarizer (PVA-based resin film). The method for forming a film from the PVA-based resin is not particularly limited, and a known method is adopted. The thickness of the PVA-based resin film is not particularly limited, but in order to make the thickness of the polarizing film 15 μm or less, it is preferable to use a film having a thickness of 5 to 35 μm. More preferably, it is 20 μm or less. The thickness of such a PVA-based resin film can be selected so that the finally obtained PVA-based polarizing film has a desired thickness.

[0059] The uniaxial stretching of the PVA-based resin film may be performed before, simultaneously with, or after the dyeing treatment with the dichroic dye. When the uniaxial stretching is performed after the dyeing treatment, such uniaxial stretching may be performed before or during the crosslinking treatment. Further, the uniaxial stretching may be performed in multiple steps at these multiple treatment stages.

[0060] In the case of uniaxial stretching, when using a long PVA-based resin film, for example, the PVA-based resin film may be wound around a roll and stretched uniaxially between the rolls by varying the peripheral speed of the roll, or may be stretched uniaxially using a hot roll. Also, the uniaxial stretching may be dry stretching performed in the atmosphere, or wet stretching performed in a state where the PVA-based resin film is swollen using a solvent or water. The stretching ratio is usually 3 to 8 times. When stretching the PVA-based resin film by multiple uniaxial stretchings, the stretching ratio compared to the original length is usually set to be 3 to 8 times. Note that this stretching ratio can also be selected so that the finally obtained PVA-based polarizing film has a desired thickness.

[0061] As a method (dyeing treatment) for dyeing the PVA-based resin film with a dichroic dye, typically, a method of immersing the PVA-based resin film in an aqueous solution containing the dichroic dye is adopted. As the dichroic dye, iodine or a dichroic organic dye is used. Note that it is preferable to subject the PVA-based resin film to an immersion treatment in water before the dyeing treatment.

[0062] As the crosslinking treatment after the dyeing treatment with the dichroic dye, usually, a method of immersing the dyed PVA-based resin film in an aqueous solution containing boric acid is adopted. When iodine is used as the dichroic dye, this aqueous solution containing boric acid preferably contains potassium iodide.

[0063] Thus, a PVA-based polarizing film is obtained. Similar to the liquid crystal polarizer, the thickness of the PVA-based polarizing film is preferably thinner, 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, and preferably 3 μm or more.

[0064] The linear polarizer can be used alone as a polarizing plate (optical film). As described above, generally, it can be made into a polarizing plate (optical film) with a structure in which a protective film is laminated on one or both sides of the linear polarizer. As the protective film, for example, a transparent resin film is used. Examples of the transparent resin constituting such a resin film include acetyl cellulose-based resins typified by triacetyl cellulose and diacetyl cellulose, methacrylic resins typified by polymethyl methacrylate, polyester resins, polyolefin-based resins, polycarbonate resins, polyether ether ketone resins, polysulfone resins, and the like. Among these, a resin film composed of a plurality of types of transparent resins can also be used as the protective film.

[0065] <First Filter, Second Filter> The first filter 40 has a first polarizer 41, and the second filter 50 has a second polarizer 51. Similar to the above-described polarizer 101, the first polarizer 41 and the second polarizer 50 can be absorption-type polarizers having the property of absorbing linearly polarized light having a vibration plane parallel to the absorption axis and transmitting linearly polarized light having a vibration plane orthogonal to the absorption axis (parallel to the transmission axis). As a typical polarizer, a polarizing film in which a dichroic dye is adsorbed and oriented on a uniaxially stretched PVA-based resin film can be mentioned. The detailed description of the polarizing film applies to the description of the polarizing film in the above-described polarizer 101. The first polarizer and the second polarizer are defect-free.

[0066] [First Application Example] In the first application example, a preferred application example of the present embodiment will be described for the case where the optical film to be inspected by the defect inspection apparatus 3A is a polarizing plate with a protective film having a protective film made of a polyethylene terephthalate resin.

[0067] 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 the first application example. 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 laminate of a polarizer 101, a protective film 102, and a protective film 103. Regarding the polarizing plate 100, the above description applies. The protective film 120 is composed of a base film and an adhesive layer laminated thereon, and is laminated and bonded to the polarizing plate 100 via the adhesive layer.

[0068] The protective film 120 is a film for protecting the surface of the polarizing plate 100. For example, after the polarizing plate with a protective film is bonded to an image display element such as a liquid crystal cell or other optical member, it is peeled off and removed together with the adhesive layer it has.

[0069] The base film of the protective film 120 is a film made of a uniaxially stretched polyethylene terephthalate resin. The protective film 120 has an orientation axis that coincides with the uniaxial stretching direction of the base film and exhibits birefringence. Therefore, a phase difference occurs in the light transmitted through the protective film 120. In the detection unit 20A, when the incident light has birefringence, the detection accuracy of defects decreases.

[0070] When the object to be inspected for defect inspection by the defect inspection method and apparatus of the present embodiment shown in FIGS. 1 and 2 is the polarizing plate 110 with a protective film, the inspection is performed such that the protective film 120 side of the polarizing plate 110 with a protective film is located on the second filter 50 side, and the irradiation direction of light from the light source in the detection step is from the first filter 40 side (satisfying the above condition b1), and it is preferable that the detection step is performed in the above step b1. That is, it is preferable to transmit the light from the light source 11 in the direction of the arrow shown in FIG. 4. The second filter 50 is arranged by appropriately adjusting the angle θ2 formed between the absorption axis of the second polarizer 51 and the absorption axis of the polarizer 101 which is the polarizer to be inspected within the range of 90° ± 35°, because the retardation generated by the protective film 120 can be reduced. The retardation generated in the light transmitted through the protective film 120 is reduced by the second filter 50 and enters the detection unit 20A.

[0071] In this application example, even when the inspection object is a polarizing plate with a protective film having a protective film made of a polyethylene terephthalate resin, a decrease in the defect detection accuracy at the detection unit 20A can be suppressed.

[0072] In order to perform defect inspection by the defect inspection method and apparatus of the present embodiment, the polarizing plate with a protective film is preferably manufactured so as to satisfy the following condition c1 or condition c2. By manufacturing so as to satisfy the following condition c1 or condition c2, the retardation generated by the protective film 120 can be effectively reduced by the second filter 50. (c1) The angle θ3 formed between the absorption axis of the polarizer 101 and the alignment axis of the protective film 120 is within the range of 0° ± 30°. (c2) The angle θ3 formed between the absorption axis of the polarizer 101 and the alignment axis of the protective film 120 is within the range of 90° ± 30°.

[0073] For a polarizing plate with a protective film manufactured to satisfy the above condition c1, in the above arrangement step, it is preferable to arrange the polarizing axis of the protective film and the absorption axis of the second polarizer 51 of the second filter 50 so that the angle formed therebetween is 90° ± 5°. With such an arrangement, the retardation generated by the protective film 120 can be effectively reduced by the second filter 50.

[0074] For a polarizing plate with a protective film manufactured to satisfy the above condition c2, in the above arrangement step, it is preferable to arrange the polarizing axis of the protective film and the absorption axis of the second polarizer of the second filter so that the angle formed therebetween is 0° ± 5°. With such an arrangement, the retardation generated by the protective film 120 can be effectively reduced by the second filter 50.

[0075] In order to perform defect inspection with the defect inspection method and defect inspection apparatus of the present embodiment, although it is preferable that the polarizing axis of the protective film of the polarizing plate with a protective film is consistent in the entire region, usually, the polarizing axes do not match in the entire region. The protective film preferably has a maximum value of the angle formed by different polarizing axes of 25° or less. This is because, for a polarizing plate using such a protective film, it is easy to obtain an effect of suppressing a decrease in the detection accuracy of the defect inspection performed in the defect inspection method and defect inspection apparatus of the present embodiment.

[0076] [Second Application Example] In the second application example, a preferred application example of the present embodiment will be described for the case where the optical film to be inspected by the defect inspection apparatus 3A is a polarizing plate having a λ / 4 retardation layer.

[0077] In the second application example, 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 retardation body 140 laminated on the surface of the polarizing plate 100, which is a laminate of a polarizer 101, a protective film 102, and a protective film 103, on the side of the protective film 103. The above description applies to the polarizing plate 100.

[0078] The polarizing plate 130 includes, as the retardation layer 140, a λ / 4 retardation layer that imparts a retardation of 1 / 4 wavelength to transmitted light, and may further include a λ / 2 retardation layer, a positive A plate, and a positive C plate that impart a retardation of 1 / 2 wavelength to transmitted light. The retardation layer 140 of the polarizing plate 130 shown in FIG. 5 includes a first retardation layer 141 and a second retardation layer 142. Examples of the combination of the first retardation layer 141 and the second 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.

[0079] The polarizing plate 130 of the second application example may be configured as a circular polarizing plate having a λ / 4 retardation layer. The circular polarizing plate can be used as an antireflection polarizing plate.

[0080] The retardation layer can be an optical film exhibiting optical anisotropy. Examples of the optical film exhibiting optical anisotropy include stretched films obtained by stretching a polymer film made of, for example, polyvinyl alcohol, polycarbonate, polyester, polyarylate, polyimide, polyolefin, polycycloolefin, polystyrene, polysulfone, polyethersulfone, polyvinylidene fluoride / polymethyl methacrylate, acetyl cellulose, saponified ethylene-vinyl acetate copolymer, polyvinyl chloride, etc. to about 1.01 to 6 times. Among the stretched films, it is preferable that they are polymer films obtained by uniaxially or biaxially stretching acetyl cellulose, polyester, polycarbonate film, or cycloolefin-based resin film. Further, the retardation layer may be a retardation layer made of a cured product of a polymerizable liquid crystal compound in which the polymerizable liquid crystal compound is applied to a substrate and oriented to exhibit optical anisotropy.

[0081] When the object to be inspected for defects by the defect inspection method and the defect inspection apparatus according to the present embodiment shown in FIGS. 1 and 2 is the polarizing plate 130, the inspection is performed with the retardation layer 140 side of the polarizing plate 130 positioned on the first filter 40 side. That is, the light from the light source 11 is transmitted in the direction of the arrow shown in FIG. 5. Further, as the first filter 40, one having a λ / 4 retardation layer is used on the polarizing plate 130 side of the first polarizer 41. The polarizing plate 130 and the first filter 40 are arranged such that their λ / 4 retardation layers face each other without passing through the polarizer 103 and the first polarizer 41. Since the first filter 40 includes a λ / 4 retardation layer, the section where light is transmitted as circularly polarized light is only between the λ / 4 retardation layer of the first filter 40 and the λ / 4 retardation layer of the polarizing plate 130. Even when the inspection object is a polarizing plate having a λ / 4 retardation layer, it is possible to detect defects based on the same principle as that of the present embodiment.

[0082] Note that, only when the inspection object is the polarizing plate 130 (that is, only in the case of a circular polarizing plate), the absorption axis of the first polarizer of the first filter and the absorption axis of the polarizer of the polarizing plate 130, and the slow axis of the λ / 4 retardation layer of the first filter and the slow axis of the λ / 4 retardation layer of the polarizing plate 130 are all arranged to be parallel, and a crossed Nicol state can be obtained.

[0083] In this application example, when performing defect detection for the purpose of detecting defects in the polarizing plate 130, the irradiation of light from the light source in the detection process may be from the first filter 40 side (arrangement of condition b1, detection process by process b1) or from the second filter 50 side (arrangement of condition b2, detection process by process b2). In order to detect unevenness in the optical characteristics of the polarizer 101 of the polarizing plate 130, it is preferable that the irradiation of light from the light source be from the first filter side 40. This is because when it is from the first filter side 40, although the defects of the retardation layer 140 are not reflected in the detection light incident on the detection unit 20A, when it is from the second filter side 50, the defects of the retardation layer 140 are reflected in the detection light incident on the detection unit 20A, and the detection accuracy of the unevenness in the optical characteristics of the polarizer 101 may decrease.

Explanation of Reference Numerals

[0084] 1 Defect inspection system, 2 Conveyor section, 3A Defect inspection device, 4 Marking device, 10A Light irradiation section, 11 Light source, 20A Detection section, 21 Camera, 30 Control device, 40 First filter, 41 First polarizer, 50 Second filter, 51 Second polarizer, 100 Polarizing plate, 101 Polarizer, 102, 103 Protective film, 110 Polarizing plate with protective film, 120 Protective film, 130 Polarizing plate, 140 Retarder, 141 First retardation layer, 142 Second retardation layer.

Claims

1. A method for inspecting defects of an optical film having a test polarizer, comprising: using a first filter having a first polarizer, a second filter having a second polarizer, and a light source; arranging the first filter, the optical film, and the second filter in this order and satisfying the following conditions a1 and a2: (a1) The angle θ1 formed by the absorption axis of the first polarizer and the absorption axis of the test polarizer is within the range of 90° ± 5°; (a2) The angle θ2 formed by the absorption axis of the test polarizer and the absorption axis of the second polarizer is within the range of 90° ± 35°; and arranging them so that the absorption axis of the first polarizer and the absorption axis of the second polarizer are not parallel, an arranging step; the following step b1: (b1) A step of detecting light irradiated from the light source and transmitted through the first filter, the optical film, and the second filter in this order; a detecting step; a determining step of determining a defect of the optical film based on the detection result in the detecting step, and having: the optical film further has a protective film made of a polyethylene terephthalate resin; the angle formed by the alignment axis of the protective film and the absorption axis of the test polarizer is within the range of 0° ± 30°; the alignment axis is a slow axis; in the arranging step, the optical film is arranged such that the surface on the side opposite to the test polarizer side of the protective film is located on the second filter side, and the angle formed by the alignment axis of the protective film and the absorption axis of the second polarizer is within the range of 90° ± 5°; a defect inspection method.

2. A method for inspecting defects of an optical film having a test polarizer, comprising: using a first filter having a first polarizer, a second filter having a second polarizer, and a light source; arranging the first filter, the optical film, and the second filter in this order and satisfying the following conditions a1 and a2: (a1) The angle θ1 formed by the absorption axis of the first polarizer and the absorption axis of the test polarizer is within the range of 90° ± 5°; (a2) The angle θ2 formed by the absorption axis of the test polarizer and the absorption axis of the second polarizer is within the range of 90° ± 35°; and arranging them so that the absorption axis of the first polarizer and the absorption axis of the second polarizer are not parallel, an arranging step; the following step b1: Step (b1) of detecting light that is irradiated from the light source and that has passed through the first filter, the optical film, and the second filter in this order; a detection step as described above; a determination step of determining a defect of the optical film based on the detection result in the detection step, and the optical film further has a protective film made of a polyethylene terephthalate resin, the angle formed between the alignment axis of the protective film and the absorption axis of the polarizer to be inspected is within the range of 90° ± 30°, the alignment axis is a slow axis, in the placement step, the optical film is placed such that the surface on the side opposite to the polarizer to be inspected of the protective film faces the second filter side, and is placed such that the angle formed between the alignment axis of the protective film and the absorption axis of the second polarizer is within the range of 0° ± 5°, a defect inspection method.

3. The defect inspection method according to claim 1 or 2, wherein the polarizer to be inspected contains a cured product of a polymerizable liquid crystal compound.

4. the optical film further has a λ / 4 retardation layer, in the defect inspection method, the first filter having a λ / 4 retardation layer is used, in the placement step, the optical film and the first filter are placed such that their λ / 4 retardation layers face each other without passing through the polarizer to be inspected and the first polarizer, according to any one of claims 1 to 3.

5. A defect inspection apparatus for an optical film having a polarizer to be inspected, the defect inspection apparatus includes a first filter having a first polarizer, a second filter having a second polarizer, and a light source, the first filter, the optical film, and the second filter are arranged in this order and satisfy the following conditions a1 and a2: (a1) The angle θ1 formed between the absorption axis of the first polarizer and the absorption axis of the polarizer to be inspected is within the range of 90° ± 5°; (a2) The angle θ2 formed between the transmission axis of the polarizer to be inspected and the absorption axis of the second polarizer is within the range of 90° ± 35°, and are arranged to satisfy the above conditions, the light source satisfies the following condition b1: (b1) Light irradiated from the light source passes through the first filter, the optical film, and the second filter in this order, and is arranged to satisfy the above condition and such that the absorption axis of the first polarizer and the absorption axis of the second polarizer are not parallel, the optical film further has a protective film made of a polyethylene terephthalate resin, The angle formed between the alignment axis of the protection film and the absorption axis of the polarizer to be inspected is within the range of 0° ± 30°; The alignment axis is the slow axis; In the defect inspection apparatus; The optical film is arranged such that the surface of the protection film opposite to the polarizer to be inspected side is positioned on the second filter side, and The optical film is arranged such that the angle formed between the alignment axis of the protection film and the absorption axis of the second polarizer is within the range of 90° ± 5°; Defect inspection apparatus.

6. A defect inspection apparatus for an optical film having a polarizer to be inspected, The defect inspection apparatus includes a first filter having a first polarizer, a second filter having a second polarizer, and a light source, The first filter, the optical film, and the second filter are arranged in this order and satisfy the following conditions a1 and a2: (a1) The angle θ1 formed between the absorption axis of the first polarizer and the absorption axis of the polarizer to be inspected is within the range of 90° ± 5°; (a2) The angle θ2 formed between the transmission axis of the polarizer to be inspected and the absorption axis of the second polarizer is within the range of 90° ± 35° and are arranged to satisfy; The light source satisfies the following condition b1: (b1) The light irradiated from the light source passes through the first filter, the optical film, and the second filter in this order, and is arranged such that the absorption axis of the first polarizer and the absorption axis of the second polarizer are not parallel, The optical film further has a protection film made of a polyethylene terephthalate resin, The angle formed between the alignment axis of the protection film and the absorption axis of the polarizer to be inspected is within the range of 90° ± 30°, The alignment axis is the slow axis, In the defect inspection apparatus, The optical film is arranged such that the surface of the protection film opposite to the polarizer to be inspected side is positioned on the second filter side, and The optical film is arranged such that the angle formed between the alignment axis of the protection film and the absorption axis of the second polarizer is within the range of 0° ± 5°; Defect inspection apparatus.

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