Defect inspection method and defect inspection apparatus

Abstract

Provided is a defect inspection method capable of detecting unevenness in optical characteristics. The defect inspection method includes: a configuration step of sequentially and in accordance with conditions a1 and a2 described below, configuring a first optical filter, an optical film, and a second optical filter: (a1) an angle θ1 formed between an absorption axis of a first polarizer of the first optical filter and an absorption axis of an inspection polarizer is within a range of 90° ± 5°, and (a2) an angle θ2 formed between the absorption axis of the inspection polarizer and an absorption axis of a second polarizer of the second optical filter is within a range of 90° ± 35°; a detection step of detecting light that is emitted from a light source and sequentially passes through the first optical filter, the optical film, and the second optical filter; and a determination step of determining a defect of the optical film based on a result of the detection in the detection step.

Description

Technical Field

[0001] This invention relates to a method and apparatus for inspecting defects in optical films. Background Technology

[0002] Polarizing plates used in display devices such as liquid crystal displays (LCDs) and organic EL displays are generally formed by sandwiching polarizing films between two protective films. To ensure adhesion to the display device, the polarizing plate sometimes has an adhesive layer laminated on one protective film and a protective film laminated on the other to prevent scratches on the surface of the protective film during flow. A release film is usually laminated on the adhesive layer. Specific examples of polarizing films include PVA-based polarizing films in which iodine, dichroic dyes, or other dichroic pigments are adsorbed onto a uniaxially stretched polyvinyl alcohol (PVA) resin film and these pigments are oriented; and polarizing films formed from a liquid crystal cured layer containing a polymer containing a polymeric liquid crystal compound and dichroic pigments (hereinafter also referred to as "liquid crystal polarizing films"). Liquid crystal polarizing films are typically formed by coating a composition containing a polymeric liquid crystal compound onto a substrate film and curing it, offering the advantage of being able to manufacture thin polarizing films. These PVA-based polarizing films and liquid crystal polarizing films, as described below, have the function of allowing linearly polarized light with a specific plane of vibration to pass through, and are called "linear polarizing films." In addition, a polarizing plate with a protective film on one or both sides of the linear polarizer is generally called a "linear polarizing plate".

[0003] Defects sometimes occur during the manufacturing process of polarizing plates and polarizers. For example, foreign matter or residual air bubbles may sometimes be introduced between the polarizer and the protective film. In addition, uneven coating during manufacturing can sometimes result in uneven optical properties in liquid crystal polarizers.

[0004] Therefore, before the polarizing plate is installed in the display device, an inspection is performed to detect defects in the polarizing plate. This defect inspection is illustrated in Japanese Patent Application Publication No. 9-229817 (Patent Document 1). After placing a polarizing filter between the polarizing plate (the object under inspection) and the light source, the polarizing plate or polarizing filter is rotated along a plane, setting their respective polarization axes in a specific relationship. When the polarization axes are orthogonal (i.e., when an orthogonal Nicol prism configuration is formed), linearly polarized light passing through the polarizing filter does not pass through the polarizing plate. However, if a defect exists in the polarizing plate, linearly polarized light will pass through that location, thus detecting the light and determining the presence of the defect.

[0005] On the other hand, when the polarization axes of the polarizing plate and the polarizing filter are parallel, linearly polarized light passing through the polarizing filter travels through the polarizing plate. However, if a defect exists in the polarizing plate, the linearly polarized light is blocked at that location, making it undetectable and thus indicating the presence of a defect. Inspectors can visually inspect the light passing through the polarizing plate or automatically detect the light using image analysis processing values ​​combined with a CCD camera and image processing device, thereby checking for the presence or absence of defects in the polarizing plate. Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] While the method described in Patent Document 1 can detect local defects that differ greatly from the surroundings in terms of optical properties, such as the incorporation of foreign matter or bubbles, it is difficult to detect unevenness in optical properties.

[0008] The purpose of this invention is to provide a method and apparatus for inspecting defects that are inhomogeneous in optical properties.

[0009] The present invention provides a defect inspection method and a defect inspection device as shown below.

[0010] [1] A defect inspection method is a method for inspecting defects in an optical film having a polarizer under inspection.

[0011] The defect inspection method uses a first filter with a first polarizer, a second filter with a second polarizer, and a light source, and has the following characteristics:

[0012] The configuration process involves sequentially configuring the first filter, the optical film, and the second filter while satisfying the following conditions a1 and a2.

[0013] (a1) The angle θ1 between the absorption axis of the first polarizer and the absorption axis of the polarizer under test is within the range of 90°±5°.

[0014] (a2) The angle θ2 formed by the absorption axis of the polarizer under test and the absorption axis of the second polarizer is within the range of 90°±35°;

[0015] The inspection process is either process b1 or process b2 as described below.

[0016] (b1) A process of detecting light irradiated from the light source and sequentially passing through the first filter, the optical film, and the second filter, or

[0017] (b2) A process of detecting light irradiated from the light source and sequentially passing through the second filter, the optical film, and the first filter; and

[0018] The judgment process involves determining the defects of the optical film based on the detection results from the detection process.

[0019] [2] According to the defect inspection method described in [1], wherein,

[0020] The optical film also has a protective film comprising a polyethylene terephthalate resin.

[0021] The angle between the orientation axis of the protective film and the absorption axis of the polarizer under test is within the range of 0°±30°.

[0022] In the configuration process,

[0023] The optical film is configured such that the surface of the protective film opposite to the side of the polarizer under test is located on the side of the second filter, and the angle between the orientation axis of the protective film and the absorption axis of the second polarizer is within the range of 90° ± 5°.

[0024] The testing process is performed using process b1.

[0025] [3] According to the defect inspection method described in [1], wherein,

[0026] The optical film also has a protective film comprising a polyethylene terephthalate resin.

[0027] The angle between the orientation axis of the protective film and the absorption axis of the polarizer under test is within the range of 90°±30°.

[0028] In the configuration process,

[0029] The optical film is configured such that the surface of the protective film opposite to the side of the polarizer under test is located in the direction of the second filter side, and the angle between the orientation axis of the protective film and the absorption axis of the second polarizer is within the range of 0°±5°.

[0030] The testing process is performed using process b1.

[0031] [4] A defect inspection method according to any one of [1] to [3], wherein the polarizer under inspection comprises a cured polymeric liquid crystal compound.

[0032] [5] According to any one of the defect inspection methods described in [1] to [4], wherein,

[0033] The optical film also has a λ / 4 phase retardation layer.

[0034] In the inspection method, the first filter is a filter with a λ / 4 phase retardation layer.

[0035] In the configuration process, the optical film and the first filter are arranged facing each other so that their λ / 4 phase difference layers do not separate the polarizer under test and the first polarizer.

[0036] [6] A defect inspection device, which is a defect inspection device for an optical film having a polarizer to be inspected.

[0037] The defect inspection device includes a first filter with a first polarizer, a second filter with a second polarizer, and a light source.

[0038] The first filter, the optical film, and the second filter are sequentially configured to satisfy the following conditions a1 and a2:

[0039] (a1) The angle θ1 between the absorption axis of the first polarizer and the absorption axis of the polarizer under test is within the range of 90°±5°.

[0040] (a2) The angle θ2 formed by the transmission axis of the polarizer under test and the absorption axis of the second polarizer is within the range of 90°±35°.

[0041] The light source is configured to satisfy either condition b1 or condition b2:

[0042] (b1) Light irradiated from the light source passes sequentially through the first filter, the optical film, and the second filter.

[0043] (b2) The light irradiated from the light source passes sequentially through the second filter, the optical film and the first filter.

[0044] Invention Effects

[0045] According to the defect inspection method and defect inspection apparatus of the present invention, the non-uniformity of the optical properties of optical films can be detected. Attached Figure Description

[0046] Figure 1 This is a diagram illustrating the defect inspection system of this embodiment.

[0047] Figure 2 This is a schematic diagram of the defect inspection device according to this embodiment.

[0048] Figure 3 This is a diagram showing an example of a defect region in an optical film.

[0049] Figure 4 This is a cross-sectional view showing an example of the layer structure of a polarizing plate with a protective film, which is the object of inspection in the first application example.

[0050] Figure 5 This is a cross-sectional view showing an example of the layer structure of the polarizing plate, which is the object of inspection, in the second application example.

[0051] Explanation of reference numerals in the attached figures

[0052] 1 Defect inspection system, 2 Transport unit, 3A Defect inspection device, 4 Marking device, 10A Light irradiation unit, 11 Light source, 20A Detection unit, 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 Phase retardation body, 141 First phase retardation layer, 142 Second phase retardation layer. Detailed Implementation

[0053] This invention relates to a method and apparatus for defect inspection of optical films having polarizers to be inspected.

[0054] The defect inspection method of the present invention uses a first filter having a first polarizer, a second filter having a second polarizer, and a light source, and has the following characteristics:

[0055] The configuration process involves sequentially configuring the first filter, the optical film, and the second filter while satisfying the following conditions a1 and a2:

[0056] (a1) The angle θ1 between the absorption axis of the first polarizer and the absorption axis of the polarizer under test is within the range of 90°±5°.

[0057] (a2) The angle θ2 formed by the transmission axis of the polarizer under test and the absorption axis of the second polarizer is within the range of 90°±35°;

[0058] The inspection process is either process b1 or process b2 as follows:

[0059] (b1) A process of detecting light irradiated from the light source and sequentially passing through the first filter, the optical film, and the second filter.

[0060] (b2) A process of detecting light irradiated from the light source and sequentially transmitted through the second filter, the optical film, and the first filter; and

[0061] The judgment process involves determining the defects of the optical film based on the detection results from the detection process.

[0062] The defect inspection apparatus of the present invention includes a first filter having a first polarizer, a second filter having a second polarizer, and a light source.

[0063] The first filter, the optical film, and the second filter are sequentially configured to satisfy the following conditions a1 and a2:

[0064] (a1) The angle θ1 formed by the absorption axis of the first polarizer and the absorption axis of the polarizer under test is within the range of 90°±5°; and

[0065] (a2) The angle θ2 between the transmission axis of the polarizer under test and the absorption axis of the second polarizer is within the range of 90°±35°.

[0066] The light source is configured to satisfy either condition b1 or condition b2:

[0067] (b1) Light irradiated from the light source passes sequentially through the first filter, the optical film, and the second filter;

[0068] (b2) The light irradiated from the light source passes sequentially through the second filter, the optical film and the first filter.

[0069] Hereinafter, embodiments of the defect inspection apparatus and defect inspection method of the present invention will be described with reference to the accompanying drawings. The same reference numerals are used for the same elements, and repeated descriptions are omitted. The scale of the drawings may not necessarily be the same as that in the description.

[0070] Figure 1 This is a schematic diagram of a defect inspection system including a defect inspection device according to one embodiment. The defect inspection system 1 includes a transport unit 2 and a defect inspection device 3A. While transporting a strip-shaped optical film 100 along its length direction using the transport unit 2, the defect inspection device 3A disposed along the transport path performs defect inspection on the optical film 100. The optical film 100 includes a polarizer to be inspected.

[0071] The transport unit 2 has a transport roller R. In addition to the transport roller R, the transport unit 2 may also have a tension applying device for applying tension to the transported optical film 100. Figure 1 The diagram shows the XYZ orthogonal coordinates used for ease of explanation. The X direction represents the width direction of the optical film 100, and the Y direction represents the transport direction of the optical film 100. The Z direction represents the direction orthogonal to both the X and Y directions. The same XYZ orthogonal coordinates are sometimes used in the descriptions of other figures as well.

[0072] Defect inspection system 1 can, as Figure 1As shown, a marking device 4 is included. The marking device 4 is a device that affixes a mark M to the optical film 100 using defect information sent from the defect inspection device 3A. The marking device 4 has, for example, an arm extending along the width direction X of the optical film 100 and a marking head having a pen or the like. By moving the marking head along the width direction X on the arm, the mark M is affixed to the optical film 100. The marking device 4 can be configured under the control of the defect inspection device 3A, or the marking device 4 itself may have a control unit such as a computer. In addition, the marking device 4 can convert the defect information sent from the defect inspection device 3A into a QR code and print it on the optical film 100.

[0073] The so-called defect inspection performed using the defect inspection apparatus 3A can include, in addition to processing the detection of defects that may occur during the manufacturing process (including the transport process) of the optical film 100, also processing the creation of a defect map showing the location of the detected defects on the optical film 100. Examples of defects in the optical film 100 that can be detected in this embodiment include uneven optical properties and localized defects such as localized polarization axis disturbances. In the case of a liquid crystal polarizer being inspected in the optical film 100, uneven optical properties may sometimes be caused by uneven coating during the manufacturing process. Furthermore, if air bubbles, foreign matter, or unevenness are introduced into the optical film 100 during the manufacturing process, these become localized defects.

[0074] use Figure 2 The defect inspection device 3A is described. Figure 2 This is a schematic diagram of the defect inspection device 3A.

[0075] Figure 2 In this example, a polarizing plate 100 is shown as an optical film 100 inspected using 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 the polarizer to be inspected.

[0076] Polarizer 101 has linear polarization characteristics. In this embodiment, the absorption axis PA0 of polarizer 101 is parallel to the Y direction, which is the transport direction of optical film 100. Hereinafter, light polarized along the transport direction of optical film 100 (the direction of absorption axis PA0 of polarizer 101) is referred to as first polarized light, and light polarized along a direction orthogonal to first polarized light is referred to as second polarized light.

[0077] The defect inspection device 3A includes a light irradiation unit 10A with a light source 11, a first filter 40 with a first polarizer 41, a second filter 50 with a second polarizer 51, and a detection unit 20A with a camera 21. The defect inspection device 3A may also include a control device 30 for controlling the detection unit 20A. Hereinafter, unless otherwise specified, the description will focus on the inclusion of the control device 30. The same applies to other embodiments.

[0078] A first filter 40 and a second filter 50 are disposed to hold the optical film 100. The first filter 40 is disposed such that the angle θ1 between 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° (satisfying condition a1 above). The second filter 50 is disposed such that the angle θ2 between 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° (satisfying condition a2 above).

[0079] Figure 2 In the diagram, a double-headed arrow indicates the absorption axis PA0 of polarizer 101, and a black dot indicates a direction at 90° to the absorption axis PA0. Additionally, Figure 2 In this diagram, since the case where angle θ1 is 90° and angle θ2 is 90° is represented, absorption axes PA1 and PA2 are indicated by black dots. In this invention, as described above, angle θ1 can be within the range of 90° ± 5°, and angle θ2 can be within the range of 90° ± 35°. Unless otherwise specified, the following description will focus on angle θ1 being 90° and angle θ2 being 90°.

[0080] Figure 2 In this configuration, a setup satisfying condition b1 is formed. Specifically, the light irradiation unit 10A is positioned with the first filter 40 between it and the optical film 100, and the detection unit 20A is positioned with the second filter 50 between it and the optical film 100. Light emitted from the light source 11 of the light irradiation unit 10A passes through the first filter 40 and enters the inspection area A (refer to) of the optical film 100, which is the object of inspection. Figure 1 Light emitted from inspection area A passes through the second filter 50 and enters the detection unit 20A. That is, the detection process is performed using the above-described process b1.

[0081] The first filter 40 emits unpolarized light L1 emitted from the light source 11 in the form of light L2 with a specified polarization state.

[0082] There are no limitations on the light source 11, as long as it can output unpolarized light that does not affect the composition and properties of the optical film 100. Examples of light source 11 include metal halide lamps, halogen transmission lamps, and fluorescent lamps. Figure 1 As shown, it can extend along the width direction of the optical film 100. Alternatively, the light irradiation section 10A can have a plurality of light sources 11, which are discretely arranged along the width direction of the optical film 100.

[0083] In this embodiment, the first filter 40 allows the first polarized light contained in the polarized light emitted from the light source 11 to selectively pass through.

[0084] The detection unit 20A has at least one camera 21 for capturing the optical film 100. Figure 1 The example illustrates an imaging unit 20A having a plurality of cameras 21 arranged along the width direction of the optical film 100. The cameras 21 are area scanning cameras, also known as CCD cameras. The cameras 21 can also be line scanning cameras. When the cameras 21 are line scanning cameras, by moving the cameras 21 relative to the optical film 100, the inspection area A of the optical film 100 can be captured. The detection unit 20A (specifically, the cameras 21) is electrically connected to the control device 30, the timing of the image capture is controlled, and the obtained image data is input into the control device 30.

[0085] exist Figure 1 and Figure 2 The diagram illustrates a method where a camera 21 is used as the detection unit 20A, and defects are detected based on images captured by the camera 21. However, the detection unit 20A can also detect defects using a visual optical film 100. In the case where the detection unit 20A detects defects visually, it is suitable to omit the control device 30.

[0086] The control device 30 controls the detection unit 20A. The control device 30 may include, for example, a computer (arithmetic unit). The control device 30 detects defects in the image data input from the detection unit 20A, and may have functions such as performing image processing to emphasize the defective parts, and generating a defect map showing the defect location from the image of the optical film 100. The defect inspection system 1 is as follows: Figure 1 As illustrated in the example, in the configuration with marking device 4, control device 30 can be as follows: Figure 1 It is also electrically connected to the marking device 4, which controls the marking device 4 to assign a mark M to the optical film 100 based on the detected defect information.

[0087] The inspection process for inspecting the optical film 100 using the defect inspection device 3A will now be described. During defect inspection, light L1 from the light source 11 passes through the first filter 40 and, as light L2 belonging to the first polarization, illuminates the inspection area A of the optical film 100. A portion of light L2 passes through the optical film 100. Light L3 that has passed through the optical film 100 exits as light L4 through the second filter 40 and enters the detection unit 20A, where light L4 is detected. More specifically, the inspection area A is photographed using the camera 21, or the inspection area A is observed visually. This is the inspection process. Subsequently, based on the inspection results from the inspection process, defects in the inspection area A of the optical film are determined (determination process).

[0088] In the above defect inspection method, light L2, which is of the first polarization, passing through the first filter 40, is irradiated onto the optical film 100. When light L2 and the polarizer 101 of the optical film 100 are in the state of being orthogonal Nicol prisms, that is, when the polarization direction of light L2 is substantially parallel to the absorption axis PA0 direction of the polarizer 101, light L2 enters the optical film 100 and is therefore absorbed.

[0089] However, the optical film 100 sometimes has a defective region where the absorption axis of the polarizer 101 does not coincide with the absorption axis PA0. Figure 3 An example of a defect region B in the optical film 100 is shown, with a double-headed arrow indicating the absorption axis in defect region B. Defect region B has an absorption axis that does not coincide with absorption axis PA0 (hereinafter referred to as "absorption axis PA3"). When the defect in defect region B is an inhomogeneity of optical properties, absorption axis PA3 in defect region B can be like... Figure 3 As shown, it is envisioned as a state where the angle with the absorption axis PA0 changes continuously. In the defective optical film 100, the region having the absorption axis PA0 is designated as the normal region A1.

[0090] In defect region B, which has an absorption axis PA3 that is not aligned with the absorption axis PA0, the polarization direction of light L2 is not parallel to the direction of the absorption axis PA0 of polarizer 101, and light L2 passes through optical film 100. Light L3 that passes through optical film 100 is polarized light in a direction corresponding to the absorption axis of defect region B of polarizer 101. When the direction of the absorption axis of the defect region of polarizer 101 is not uniform, light L3 contains polarized light in multiple directions. Hereinafter, these are collectively referred to as the third polarized light, and a portion of the multiple polarized lights contained in the third polarized light are named, in ascending order of the angles formed with the first polarized light, the third a polarized light, the third b polarized light, the third c polarized light, and so on.

[0091] Light L3 passes through the second filter 50 and is emitted as light L4 into the detection unit 20A. In the second filter 50, the absorption axis PA2 of the second polarizer 51 and the absorption axis PA0 of the polarizer 101 are in an orthogonal Nicol prism state. Therefore, if light L3 is first-polarized light, it will be absorbed after entering the second polarizer 51. However, since light L3 is third-polarized light, different from first-polarized light, it passes through the second filter 50. Light L3 is emitted after being absorbed in the second filter 50 in proportion corresponding to its polarization direction. That is, the proportion of light absorbed by the second filter 50 decreases in the order of third-polarized light, third-polarized light, third-polarized light, ...

[0092] The inventors focused on the situation where the polarization degree of light transmitted through the first filter and the optical film is substantially reduced. They discovered that by allowing this light to pass through the second filter again, the contrast between the region of the first polarized light and the region of the third polarized light can be improved, thereby significantly enhancing the detection sensitivity.

[0093] As described above, the transmittance characteristics of light L3 in the optical film 100 differ between the normal region A1 and the defective region B. Furthermore, the transmittance characteristics of light L4 in the second filter 50 differ depending on the absorption axis direction of the defective region B. Since light L4 reflecting these transmittance characteristics is detected in the detection unit 20A, the presence or absence of defects in the optical film 100, and the presence or absence of non-uniformity in the absorption axis direction within the defective region, can be detected. Non-uniformity in the absorption axis direction of the optical film 100 corresponds to non-uniformity in optical properties.

[0094] The above explanation focused on the case where angle θ1 is 90° and angle θ2 is 90°. However, the amount of light L4 varies depending on the magnitudes of angles θ1 and θ2. Within the range of 90°±5° for angle θ1 and 90°±35° for angle θ2, the transmission characteristics of light L3 in the optical film 100 differ between the normal region A1 and the defect region B. Furthermore, the transmission characteristics of light L4 in the second filter 50 vary depending on the absorption axis direction of the defect region B. Therefore, even when angles θ1 and θ2 are not 90°, light L4 reflecting these transmission characteristics will be detected in the detection unit 20A. Thus, the presence or absence of defects in the optical film 100, and the presence or absence of uneven absorption axis direction in the defect region, can be detected.

[0095] The defect inspection apparatus 3A includes a first filter 40 and a second filter 50, thereby enabling efficient detection of non-uniformity in optical properties. Consequently, in the manufacturing method of the optical film 100 incorporating the aforementioned defect inspection method, an optical film 100 free of defects can be produced efficiently.

[0096] Figure 1 and Figure 2The diagram shows a configuration that satisfies condition b1 and performs step b1 in the inspection process. However, it could also be a configuration that satisfies condition b2 by swapping the 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 unit 10A passes through the second filter 50 and enters the inspection area A of the optical film 100, which is the object of inspection. Light emitted from the inspection area A passes through the first filter 40 and enters the detection unit 20A. That is, step b2 is performed in the inspection process. Even with this configuration, it is possible to obtain the same results as... Figure 1 and Figure 2 The configuration shown that satisfies condition b1 has the same effect.

[0097] <Methods for Manufacturing Optical Films>

[0098] It includes the use of Figure 1 and Figure 2 The manufacturing method of the optical film 100 in the defect inspection method of the defect inspection device 3A shown will be described. Here, as Figure 2 As shown, the example described is an optical film 100 that is manufactured as a laminate of a protective film 102, a film body 101, and a protective film 103.

[0099] During the manufacturing of the optical film 100, a strip-shaped polarizer 101, a strip-shaped protective film 102, and a strip-shaped protective film 103 are conveyed along their length directions, while 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 process). The bonding of the polarizer 101 with the protective films 102 and 103 can be performed, for example, using a pair of bonding rollers. In the bonding process, the protective films 102 and 103 can be bonded to the polarizer 101 simultaneously, or one side of the protective films 102 and 103 can be bonded to the polarizer 101 before the other side is bonded.

[0100] Following the aforementioned bonding process, while the optical film 100, which is a laminate of the protective film 103, polarizer 101, and protective film 102, is being transported between the light irradiation unit 10A and the detection unit 20A of the defect inspection apparatus 3A, defect inspection of the optical film 100 is performed using the defect inspection apparatus 3A (defect inspection process). In the defect inspection process, the defect inspection of the optical film 100 is performed using the defect inspection method described above. In a defect inspection system 1 equipped with a marking device 4, a process of assigning a mark M to the optical film 100 using the marking device 4 can be performed based on the results of the defect inspection process (marking process).

[0101] Polarizer 101 can be an absorption-type polarizer that absorbs linearly polarized light having a vibration plane parallel to its absorption axis and transmits linearly polarized light having a vibration plane orthogonal to the absorption axis (parallel to the transmission axis). Representative polarizers include liquid crystal polarizers containing a cured polymeric liquid crystal compound and polarizing films in which a polyvinyl alcohol-based resin film subjected to uniaxial stretching adsorbs dichroic pigments and orients the dichroic pigments.

[0102] A typical manufacturing method for a liquid crystal polarizer is briefly described. First, a suitable 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 pigment is coated onto the alignment film and dried, thereby forming a coating layer containing the polymerizable liquid crystal compound on the alignment film. Subsequently, the coating layer is polymerized and cured by light irradiation, resulting in a liquid crystal polarizer on the support. If a transparent resin film is used as the support, a polarizer with the transparent resin film as a protective film can be manufactured.

[0103] As a liquid crystal polarizer, for example, the liquid crystal polarizer described in Japanese Patent Application Publication No. 2016-170368 can be used. As a dichroic pigment, a dichroic pigment having absorption in the wavelength range of 380 to 800 nm can be used, preferably an organic dye. For example, an azo compound can be used as a dichroic pigment. The liquid crystal compound is a liquid crystal compound capable of polymerization while maintaining its orientation, and can have polymerizable groups within its molecule. Alternatively, as described in WO2011 / 024891, a polarizer can be formed from a dichroic pigment possessing liquid crystal properties. It should be noted that after polymerization (after forming a polarizer containing a liquid crystal cured layer), the liquid crystal compound no longer needs to exhibit liquid crystal properties.

[0104] The thickness of the liquid crystal polarizer is, for example, 0.2 μm to 10 μm. Sometimes, uneven coating of the liquid composition during the manufacturing process can cause uneven optical properties in the liquid crystal polarizer. This unevenness in optical properties can also be detected during defect inspection using the defect inspection method and apparatus of this embodiment.

[0105] Next, a brief explanation of PVA-based polarizing films will be given. PVA-based polarizing films are manufactured, for example, by a method including the following steps: a step of uniaxially stretching a PVA-based resin film; a step of adsorbing dichroic pigments by dyeing the PVA-based resin film with dichroic pigments (dyeing treatment); a step of treating the PVA-based resin film with adsorbed dichroic pigments with a crosslinking solution such as boric acid aqueous solution (crosslinking treatment); and a step of washing with water after the treatment with the crosslinking solution (washing treatment).

[0106] Resins obtained by saponifying polyvinyl acetate-based resins can be used as PVA-based resins. In addition to polyvinyl acetate homopolymers, copolymers of vinyl acetate with other monomers that can be copolymerized can also be cited as polyvinyl acetate-based resins. Examples of other monomers that can be copolymerized with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and (meth)acrylamides containing ammonium groups.

[0107] In this specification, the term "(meth)acrylic acid" refers to at least one selected from acrylic acid and methacrylic acid. The same applies to "(meth)acryloyl" and "(meth)acrylate".

[0108] The degree of saponification of PVA-based resins is typically 85–100 mol%, preferably 98 mol% or higher. Polyvinyl alcohol-based resins can be modified; for example, aldehyde-modified polyvinyl formal or polyvinyl acetal can be used. The average degree of polymerization of PVA-based resins is typically 1000–10000, preferably 1500–5000. The average degree of polymerization of PVA-based resins can be determined according to JIS K6726.

[0109] The film obtained by forming this PVA-based resin film is used as a raw material film (PVA-based resin film) for manufacturing polarizers. The method for forming the PVA-based resin film is not particularly limited, and known methods can be used. The thickness of the PVA-based resin film is not particularly limited; however, to achieve a polarizer film thickness of 15 μm or less, a PVA-based resin film of 5 to 35 μm is preferred. More preferably, it is 20 μm or less. The thickness of the PVA-based resin film can be selected in a way that results in a PVA-based polarizer film of the desired thickness.

[0110] Uniaxial stretching of PVA-based resin films can be performed before, simultaneously with, or after dyeing with dichroic pigments. When uniaxial stretching is performed after dyeing, it can be done before or during crosslinking. Alternatively, uniaxial stretching can be performed multiple times within these various treatment stages.

[0111] In uniaxial stretching, when using a long strip of PVA-based resin film, the film can be mounted on rollers with varying circumferential speeds, allowing for uniaxial stretching between the rollers. Alternatively, a heated roller can be used for uniaxial stretching. Uniaxial stretching can be dry stretching performed in air or wet stretching performed while the PVA-based resin film is swollen using solvents or water. The stretching ratio is typically 3 to 8 times. When stretching the PVA-based resin film using multiple uniaxial stretching operations, the stretching ratio compared to the original length is typically 3 to 8 times. It should be noted that this stretching ratio can also be selected to achieve the desired thickness of the final PVA-based polarizing film.

[0112] As a method for dyeing PVA-based resin membranes with dichroic dyes (dyeing treatment), typically, the PVA-based resin membrane is immersed in an aqueous solution containing a dichroic dye. Iodine and dichroic organic dyes are used as dichroic dyes. It should be noted that the PVA-based resin membrane is preferably immersed in water before the dyeing treatment.

[0113] As a crosslinking treatment following dyeing with dichroic pigments, a common method is to immerse the dyed PVA-based resin film in an aqueous solution containing boric acid. When iodine is used as the dichroic pigment, the aqueous solution containing boric acid preferably contains potassium iodide.

[0114] By operating as described above, a PVA-based polarizing film is obtained. The thickness of the PVA-based polarizing film is also preferably thinner than that of the liquid crystal polarizer, preferably 15 μm or less, more preferably 13 μm or less, even more preferably 10 μm or less, and particularly preferably 8 μm or less. The thickness of the polarizing film is typically 2 μm or more, preferably 3 μm or more.

[0115] Linear polarizers can be used alone as polarizing plates (optical films), or, as mentioned above, they can generally be configured with a protective film laminated to one or both sides of the linear polarizer. For example, a transparent resin film can be used as the protective film. Examples of transparent resins forming this film include acetylcellulose-based resins such as triacetylcellulose and diacetylcellulose, methacrylic resins such as polymethyl methacrylate, polyester resins, polyolefin resins, polycarbonate resins, polyetheretherketone resins, and polysulfone resins. Furthermore, a resin film containing multiple transparent resins can also be used as the protective film.

[0116] <Filter 1, Filter 2>

[0117] The first filter 40 has a first polarizer 41, and the second filter 50 has a second polarizer 51. The first polarizer 41 and the second polarizer 50, like the polarizer 101 described above, can be absorption-type polarizers that absorb linearly polarized light with a vibration plane parallel to its absorption axis and transmit linearly polarized light with a vibration plane orthogonal to the absorption axis (parallel to the transmission axis). A representative example of a polarizer is a polarizing film that adsorbs dichroic pigments onto a uniaxially stretched PVA-based resin film and orients the dichroic pigments. A detailed description of the polarizing film can be obtained by referring to the description of the polarizing film in polarizer 101 described above. The first and second polarizers are defect-free polarizers.

[0118] [Application Example 1]

[0119] In the first application example, a suitable application example of this embodiment will be described for the case where the optical film inspected by the defect inspection device 3A is a polarizing plate with a protective film containing a polyethylene terephthalate resin.

[0120] Figure 4 This is a cross-sectional view showing an example of the layered structure of a polarizing plate with a protective film, which is the object of inspection in the first application example. (Example:) Figure 4 As shown, the polarizing plate 110 with a protective film 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 the polarizer 101, the protective film 102, and the protective film 103. The above description applies to the polarizing plate 100. The protective film 120 is formed of a substrate film and an adhesive layer laminated thereon, and is laminated to the polarizing plate 100 via the adhesive layer.

[0121] The protective film 120 is a film used to protect the surface of the polarizing plate 100. For example, it is peeled off together with the adhesive layer of the protective film after the polarizing plate with the protective film is attached to the image display element such as the liquid crystal cell or other optical components.

[0122] The substrate film of the protective film 120 is a film containing polyethylene terephthalate resin that has undergone uniaxial stretching. The protective film 120 has an orientation axis aligned with the uniaxial stretching direction of the substrate film, exhibiting birefringence. Therefore, a phase difference is generated in the light transmitted through the protective film 120. In the detection unit 20A, when the incident light exhibits birefringence, the detection accuracy of defects decreases.

[0123] In use Figure 1 and Figure 2When the defect inspection object of the defect inspection method and defect inspection apparatus of this embodiment is a polarizing plate 110 with a protective film, it is preferable to inspect it with the protective film 120 side of the polarizing plate 110 located on the side of the second filter 50. Furthermore, the light source is arranged such that the irradiation direction of the light from the light source in the inspection process is from the side of the first filter 40 (satisfying the above-mentioned condition b1), and the inspection process is performed using the above-mentioned process b1. That is, it is preferable to... Figure 4 The arrows indicate that light from the light source 11 passes through. This is because the second filter 50 can be appropriately configured such that the angle θ2 between the absorption axis of the second polarizer 51 and the absorption axis of the polarizer 101 (which is the polarizer under test) is within a range of 90° ± 35°, thereby reducing the phase difference caused by the protective film 120. The phase difference generated in the light passing through the protective film 120 is reduced by the second filter 50 before it enters the detection unit 20A.

[0124] In this application example, even if the object to be inspected is a polarizing plate with a protective film containing a polyethylene terephthalate resin, the reduction in the detection accuracy of defects using the detection unit 20A can be suppressed.

[0125] In order to perform defect inspection using the defect inspection method and defect inspection apparatus of this embodiment, it is preferable to manufacture the polarizing plate with the protective film in a manner that satisfies either condition c1 or condition c2 below. By manufacturing in a manner that satisfies either condition c1 or condition c2 below, the phase difference caused by the protective film 120 can be effectively reduced using the second filter 50.

[0126] (c1) The angle θ3 formed by the absorption axis of the polarizer 101 and the orientation axis of the protective film 120 is within the range of 0°±30°.

[0127] (c2) The angle θ3 formed by the absorption axis of the polarizer 101 and the orientation axis of the protective film 120 is within the range of 90°±30°.

[0128] For a polarizing plate with a protective film manufactured in a manner that satisfies condition c1 above, in the above configuration process, it is preferable to configure it such that the angle between the orientation axis of the protective film and the absorption axis of the second polarizer 51 of the second filter 50 is 90°±5°. With this configuration, the phase difference caused by the protective film 120 can be effectively reduced using the second filter 50.

[0129] For a polarizing plate with a protective film manufactured in a manner that satisfies condition c2 above, in the above configuration process, it is preferable to configure it such that the angle between the orientation axis of the protective film and the absorption axis of the second polarizer of the second filter is 0°±5°. Using this configuration, the phase difference caused by the protective film 120 can be effectively reduced by the second filter 50.

[0130] In order to perform defect inspection using the defect inspection method and apparatus of this embodiment, the orientation axis of the protective film of the polarizing plate with the protective film is preferably consistent throughout the entire region; however, it is usually inconsistent throughout the entire region. The protective film is preferably a protective film in which the maximum angle between the different orientation axes is 25° or less. This is because, for polarizing plates using this type of protective film, it is easy to obtain an effect that suppresses the reduction in detection accuracy during defect inspection performed using the defect inspection method and apparatus of this embodiment.

[0131] [Application Example 2]

[0132] In the second application example, a suitable application example of this embodiment is explained for the case where the optical film inspected by the defect inspection device 3A is a polarizing plate with a λ / 4 phase difference layer.

[0133] In the second application example, using Figure 5 An example of the layer composition of the polarizing plate that is the object of inspection will be explained. For example... Figure 5 As shown, the polarizer 130 includes a phase difference body 140 laminated on the surface of the polarizer 100, which is a laminate of polarizer 101, protective film 102, and protective film 103, on the side of the protective film 103. The above description applies to the polarizer 100.

[0134] The polarizer 130 may include a λ / 4 phase difference layer that imparts a 1 / 4 wavelength phase difference to the transmitted light as a phase difference body 140, and may also include a λ / 2 phase difference layer that imparts a 1 / 2 wavelength phase difference to the transmitted light, a positive A plate, and a positive C plate as phase difference bodies 140. Figure 5 The phase difference body 140 of the polarizer 130 shown includes a first phase difference layer 141 and a second phase difference layer 142. Examples of combinations of the first phase difference layer 141 and the second phase difference layer 142 include combinations of λ / 2 phase difference layer and λ / 4 phase difference layer, and combinations of λ / 4 phase difference layer and positive C layer.

[0135] The polarizer 130 in the second application example can be formed as a circular polarizer with a λ / 4 phase difference layer. The circular polarizer can be used as an anti-reflective polarizer.

[0136] The retardation layer can be an optical film that displays optical anisotropy. Examples of optical films that display optical anisotropy include stretched films obtained by stretching a polymer film containing polyvinyl alcohol, polycarbonate, polyester, polyarylate, polyimide, polyolefin, polycyclic olefin, polystyrene, polysulfone, polyethersulfone, polyvinylidene fluoride / polymethyl methacrylate, acetyl cellulose, ethylene-vinyl acetate copolymer saponification, polyvinyl chloride, etc., to approximately 1.01 to 6 times its original size. Among stretched films, polymer films obtained by uniaxially or biaxially stretching acetyl cellulose, polyester, polycarbonate films, or cyclic olefin resin films are preferred. Alternatively, the retardation layer can also be a cured product containing a polymeric liquid crystal compound that exhibits optical anisotropy by coating a polymeric liquid crystal compound onto a substrate and oriented it.

[0137] In use Figure 1 and Figure 2 When the defect inspection method and apparatus of this embodiment are used to inspect the polarizer 130, the inspection is performed by arranging the polarizer 130 with the phase difference body 140 side of the polarizer 130 located on the first filter 40 side. That is, the light from the light source 11 is directed along... Figure 5 The direction of the arrow shown is through. Furthermore, a filter having a λ / 4 phase retardation layer on the polarizing plate 130 side of the first polarizer 41 is used as the first filter 40. The polarizing plate 130 and the first filter 40 are arranged facing each other so that their λ / 4 phase retardation layers do not separate the polarizer 103 and the first polarizer 41. By having the first filter 40 have a λ / 4 phase retardation layer, the range in which light passes through in the form of circularly polarized light is only between the λ / 4 phase retardation layer of the first filter 40 and the λ / 4 phase retardation layer of the polarizing plate 130. Even if the object to be inspected is a polarizing plate having a λ / 4 phase retardation layer, defects can be detected using the same principle as in this embodiment.

[0138] It should be noted that the state of the orthogonal Nicol prism can be obtained if and only when the object being inspected is polarizer 130 (i.e., if and only when it is a circular polarizer). Even if the absorption axis of the first polarizer of the first filter and the absorption axis of the polarizer of polarizer 130, and the slow axis of the λ / 4 phase difference layer of the first filter and the slow axis of the λ / 4 phase difference layer of polarizer 130 are all arranged in parallel, the state of the orthogonal Nicol prism can be obtained.

[0139] In this application example, when defect detection is performed for the purpose of detecting defects in the polarizer 130, the illumination from the light source in the detection process can come from the first filter 40 side (condition b1 configuration, detection process performed using process b1) or from the second filter 50 side (condition b2 configuration, detection process performed using process b2). To detect the unevenness of the optical characteristics of the polarizer 101 of the polarizer 130, it is preferable to set the illumination from the light source to come from the first filter side 40. This is because, when the illumination comes from the first filter side 40, the defect of the phase difference element 140 is not reflected in the detection light incident on the detection unit 20A; however, when the illumination comes from the second filter side 50, the defect of the phase difference element 140 is reflected in the detection light incident on the detection unit 20A, thus reducing the detection accuracy of the unevenness of the optical characteristics of the polarizer 101.

Claims

1. A defect inspection method, which is a defect inspection method for an optical film having a polarizer under inspection. The defect inspection method uses a first filter with a first polarizer, a second filter with a second polarizer, and a light source, and has the following characteristics: The configuration process involves sequentially configuring the first filter, the optical film, and the second filter while 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 under test is within the range of 90°±5°. (a2) The angle θ2 formed by the absorption axis of the polarizer under test and the absorption axis of the second polarizer is within the range of 90°±35°. Furthermore, angles θ1 and θ2 are not 90°; The inspection process is either process b1 or process b2 as follows: (b1) A process of detecting light irradiated from the light source and sequentially transmitted through the first filter, the optical film, and the second filter, or (b2) A process of detecting light irradiated from the light source and sequentially transmitted through the second filter, the optical film, and the first filter; and The judgment process involves determining the defects of the optical film based on the detection results from the detection process.

2. The defect inspection method according to claim 1, wherein, The optical film also has a protective film comprising a polyethylene terephthalate resin. The angle between the orientation axis of the protective film and the absorption axis of the polarizer under test is within the range of 0°±30°. In the configuration process, The optical film is configured such that the surface of the protective film opposite to the polarizer being tested is located on the side of the second filter, and the angle between the orientation axis of the protective film and the absorption axis of the second polarizer is within the range of 90°±5°. The testing process is performed using process b1.

3. The defect inspection method according to claim 1, wherein, The optical film also has a protective film comprising a polyethylene terephthalate resin. The angle between the orientation axis of the protective film and the absorption axis of the polarizer under test is within the range of 90°±30°. In the configuration process, The optical film is configured such that the surface of the protective film opposite to the polarizer side is located on the side of the second filter, and the angle between the orientation axis of the protective film and the absorption axis of the second polarizer is within the range of 0°±5°. The testing process is performed using process b1.

4. The defect inspection method according to any one of claims 1 to 3, wherein, The polarizer under test contains a cured polymeric liquid crystal compound.

5. The defect inspection method according to any one of claims 1 to 3, wherein, The optical film also has a λ / 4 phase retardation layer. In the inspection method, the first filter is a filter with a λ / 4 phase retardation layer. In the configuration process, the optical film and the first filter are arranged facing each other so that their λ / 4 phase difference layers do not separate the polarizer under test and the first polarizer.

6. A defect inspection device, comprising an optical film having a polarizer to be inspected. The defect inspection device includes a first filter with a first polarizer, a second filter with a second polarizer, and a light source. The first filter, the optical film, and the second filter are sequentially configured to satisfy the following conditions a1 and a2: (a1) The angle θ1 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 by the transmission axis of the polarizer under test and the absorption axis of the second polarizer is within the range of 90°±35°. Furthermore, angles θ1 and θ2 are not 90°. The light source is configured to satisfy either condition b1 or condition b2: (b1) Light irradiated from the light source passes sequentially through the first filter, the optical film, and the second filter; (b2) The light irradiated from the light source passes sequentially through the second filter, the optical film and the first filter.

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