Defect inspection device

Abstract

The utility model provides a defect inspection device capable of performing inspection with high precision by using an easily obtained light source. A defect inspection device (1) is provided with a transmission window-equipped shutter (5) disposed between a mounting table (3) and a light source (4), the transmission window-equipped shutter (5) having: a first linear polarizing plate (35A) that has an absorption axis in a first direction and is disposed corresponding to the optical axis of white light (L0) from the light source (4) toward the mounting table (3), and a second linear polarizing plate (35B) that has an absorption axis in a second direction and is disposed corresponding to the optical axis of the white light (L0) from the light source (4) toward the mounting table (3); a second linear polarizing plate (35B) that has an absorption axis in a second direction orthogonal to the first direction and is disposed adjacent to the first linear polarizing plate (35A); and a shielding plate (33) which shields the regular reflection light (L1) of the white light (L0) from the polarizing plate (P) and enables at least part of the reflection light other than the regular reflection light (L1) to pass through the second linear polarizing plate (35B).

Description

Technical Field

[0001] The present disclosure relates to a defect inspection device. Background Art

[0002] Polarizing plates have been widely used as one of the optical elements used in devices such as liquid crystal displays. There are various configurations for polarizing plates. A representative example is a polarizing plate in which protective films are laminated on both sides of a polarizing film formed by aligning iodine adsorbed on a polyvinyl alcohol (PVA) resin film. Depending on the manufacturing conditions, such polarizing plates may produce defects (potassium sulfate defects) caused by residual crystalline potassium sulfate used in the manufacturing process. While the defects themselves are difficult to visually detect due to iodine staining, slight deformations and tiny bubbles generated near the defects can cause visually detectable color unevenness (haze unevenness) caused by light scattering.

[0003] As a technique for inspecting polarizing plate defects, for example, there is a method for inspecting optically transparent films described in Patent Document 1. In this method, light is prevented from reaching the outer surface of a release film, and the color of the illumination light is set to a complementary color to the color of the release film. In this state, the optically transparent film is illuminated with illumination light, and the film surface is observed.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2001-108630 Utility Model Content

[0007] Issues to be solved by utility models

[0008] In Patent Document 1, a green lamp is used as a light source for illumination light. In inspections using a green lamp, although sufficient intensity of illumination light can easily achieve inspection accuracy, the green lamp itself for inspection may be difficult to obtain, which is a problem.

[0009] The present disclosure has been made to solve the above-mentioned problems, and an object of the present disclosure is to provide a defect inspection device that can perform inspection with high precision using a readily available light source.

[0010] Means for solving problems

[0011] The gist of the present disclosure is as follows.

[0012] [1] A defect inspection device for inspecting whether a polarizing plate comprising a polyvinyl alcohol-based resin film has defects, wherein the defect inspection device comprises: a stage on which the polarizing plate is mounted; a light source for irradiating white light onto the polarizing plate on the stage; and a baffle with a transmission window, which is arranged between the stage and the light source, the baffle with a transmission window having: a first linear polarizing plate having an absorption axis in a first direction and arranged corresponding to the optical axis of the white light from the light source toward the stage; a second linear polarizing plate having an absorption axis in a second direction orthogonal to the first direction and arranged adjacent to the first linear polarizing plate; and a baffle arranged in such a manner as to block the regular reflection light of the white light from the polarizing plate and allow at least a portion of the reflected light other than the regular reflection light to pass through the second linear polarizing plate.

[0013] In this defect inspection device, a light source that irradiates white light is used to inspect defects of a polarizing plate comprising a polyvinyl alcohol-based resin film. The intensity of white light is lower than that of conventional light based on green lamps, and on the other hand, light sources that irradiate white light are easily available. In addition, in this defect inspection device, a shielding plate with a transmission window is arranged between a mounting table for mounting the polarizing plate and the light source. By using this shielding plate with a transmission window, the first linear polarizing plate and the second linear polarizing plate in an orthogonal Nicol relationship can be used to divide the regular reflection light from the polarizing plate and the diffuse light caused by the defect, and the shielding plate can be used to block the regular reflection light from the polarizing plate. Therefore, even when using white light with a relatively low intensity compared to conventional light based on green lamps, defect inspection can be carried out with high precision.

[0014] [2] The defect inspection device according to [1], wherein the shielding plate with a transmission window is tilted relative to the mounting table. In this case, the optical axis of the regular reflected light from the polarizing plate is easily deviated from the observation axis for visually observing defects, thereby enabling appropriate defect inspection.

[0015] [3] The defect inspection device according to [2], wherein the obstructing plate with a transmission window is tilted at an angle of 25° to 40° relative to the mounting table. In this case, it is easier and more reliable to deviate the optical axis of the regular reflected light from the polarizing plate from the observation axis for visually observing defects, thereby enabling more appropriate defect inspection.

[0016] [4] The defect inspection device according to any one of [1] to [3], wherein the mounting table includes a sliding plate for advancing and retracting the polarizing plate relative to the irradiation area of ​​the white light. The use of such a sliding plate facilitates scanning of the defect inspection position, thereby improving inspection operability.

[0017] [5] The defect inspection device according to [4], wherein the sliding plate is configured to include a circular polarizing plate and an antireflection layer provided on a surface of the circular polarizing plate. In this case, reflection generated at the interface between the polarizing plate and the sliding plate can be suppressed, and defect inspection can be performed with high accuracy even when using the sliding plate.

[0018] [6] The defect inspection device according to any one of [1] to [5], wherein the directional angle of the white light from the light source is 10° to 90°. By setting the directional angle of the white light in this range, insufficient intensity of the white light at the visual position can be prevented, and sufficient defect inspection accuracy can be ensured.

[0019] [7] The defect inspection device according to any one of [1] to [6], wherein the distance between the shielding plate with a transmission window and the mounting platform in the direction of the optical axis of the white light is 40 mm to 70 mm. By setting the distance between the shielding plate with a transmission window and the mounting platform to be below the upper limit of the above range, excessive spread of white light at the visual position can be prevented, and sufficient defect inspection accuracy can be ensured. By setting the distance between the shielding plate with a transmission window and the mounting platform to be above the lower limit of the above range, sufficient space can be ensured between the shielding plate with a transmission window and the mounting platform to allow a hand to enter, thereby ensuring good adjustment and other workability for inspection.

[0020] Utility model effect

[0021] According to the present disclosure, inspection can be performed with high precision using a readily available light source. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic top view of a defect inspection device according to one aspect of the present disclosure.

[0023] Figure 2 yes Figure 1 A schematic side view of a defect inspection apparatus is shown.

[0024] Figure 3 It is a schematic cross-sectional view showing an example of a polarizing plate to be inspected.

[0025] Figure 4 It is a schematic plan view showing a state of a defect generated in a polarizing plate.

[0026] Figure 5 (a) is a schematic plan view showing a main portion of the shielding plate with a transmission window, and (b) is a cross-sectional view taken along line VV of (a).

[0027] Description of reference numerals:

[0028] 1…defect inspection device; 3…carrying table; 4…light source; 5…shielding plate with transmission window; 21…sliding plate; 22…circular polarizing plate; 23…anti-reflection layer; 32…transmission window; 33…shielding plate; 35A…first linear polarizing plate; 35B…second linear polarizing plate; L0…white light; L1…regularly reflected light; L2…diffused light; P…polarizing plate; Ka…defect. DETAILED DESCRIPTION

[0029] Hereinafter, preferred embodiments of a defect inspection device according to one aspect of the present disclosure will be described in detail with reference to the accompanying drawings.

[0030] Figure 1 : is a schematic top view of a defect inspection device according to one aspect of the present disclosure. Figure 2 It is a schematic side view thereof. Figure 1 and Figure 2 The defect inspection device 1 shown is configured to inspect whether a polarizing plate P including a polarizing film made of a polyvinyl alcohol resin film has a defect Ka. The polarizing plate P to be inspected is, for example, a linear polarizing plate or a circular polarizing plate. Figure 3 As shown, the polarizing plate P has a laminated structure in which, for example, polarizing film protective films 102 are laminated on both surfaces of a polarizing film 101. A polarizing plate protective film 103 may be releasably laminated on one or both polarizing film protective films 102 on the surface opposite to the surface in contact with the polarizing film 101.

[0031] The polarizing film 101 is manufactured, for example, through the following steps: a stretching step of uniaxially stretching a polyvinyl alcohol resin film; an adsorption step of dyeing the PVA film with iodine to adsorb iodine; a crosslinking step of treating the iodine-adsorbed PVA film with a boric acid aqueous solution to crosslink it; and a washing step (also called a boric acid treatment step) of washing with a boric acid aqueous solution after the crosslinking treatment. In the polarizing plate P, depending on the manufacturing conditions, for example, Figure 4 As shown, defects (potassium sulfate defects) Ka may occur where potassium sulfate used in the crosslinking process remains in a crystalline state. While the defects Ka themselves are difficult to visually identify due to iodine staining, minute deformations and tiny bubbles generated near the defects Ka can cause visually detectable color unevenness (haze unevenness) Kb due to light scattering.

[0032] The defect inspection device 1 is a device that visually observes whether there is such color unevenness Kb. Figure 1 and Figure 2As shown, the frame 2 includes a mounting platform 3, a light source 4, and a shielding plate with a transmissive window 5. The frame 2 includes, for example, a pair of legs 11, 11, a pair of columns 12, 12, a mounting platform holder 13, a shielding plate holder 14 with a transmissive window, and a light source holder 15. The materials of the components of the frame 2 are not particularly limited; for example, metal or hard plastic materials can be used. To suppress light reflection, the components of the frame 2 can also be colored black, for example.

[0033] A pair of legs 11, 11 is a portion for stably placing the defect inspection device 1 on a workbench or the like. The pair of legs 11, 11 is, for example, in the shape of a rod, and extends parallel to each other at a predetermined interval. It should be noted that the legs of the frame 2 do not necessarily have to be composed of a pair of legs 11, 11, and may be, for example, composed of a flat plate member. A pair of columns 12, 12 is a portion for holding the stage holding portion 13, the shielding plate holding portion with a transmission window 14, and the light source holding portion 15. The columns 12, 12 are, for example, in the shape of a rod, and extend from a position on one end of each of the legs 11, 11 in the height direction (a direction perpendicular to the extension direction of the legs 11, 11).

[0034] The platform holding portion 13 is a portion that holds the platform 3. The platform holding portion 13 is, for example, in the shape of a plate, and is mounted between the column portions 12, 12 near the center of the column portions 12, 12 in the height direction. Threaded holes for screwing screws W are provided at both end portions of the platform holding portion 13, for example, and a plurality of threaded holes corresponding to the threaded holes are provided on the column portions 12, 12 along the height direction. The platform holding portion 13 is fixed to the column portions 12, 12 in a freely attachable and detachable manner while selecting one of the threaded holes of the column portion 12 and screwing the screw W into the threaded hole of the platform holding portion 13, thereby freely adjusting the installation height. By adjusting the inclination of the platform holding portion 13 during screw fixing, the inclination angle of the platform holding portion 13 relative to the extension direction of the leg portions 11, 11 can be freely adjusted.

[0035] The shielding plate holding portion 14 with a transmission window is a portion that holds the shielding plate 5 with a transmission window. The shielding plate holding portion 14 with a transmission window has, for example, a base portion 14A (see Figure 2 ), which is mounted between the columns 12, 12 at a position higher than the platform holding portion 13; a protrusion 14B, which protrudes from a position of the base 14A close to the column 12 on one side and is roughly parallel to the foot 11; and a plate-like portion 14C, which extends from the front end portion of the protrusion 14B toward the column 12 on the other side and is roughly parallel to the base 14A.

[0036] The base end of protrusion 14B is provided with a threaded hole, for example, for screwing a screw W. Base 14A is provided with multiple threaded holes along the height direction corresponding to these threaded holes. Protrusion 14B and plate-shaped portion 14C are integrally formed. By selecting one of the threaded holes in base 14A and tightening the threaded holes of protrusion 14B together with screws W, the mounting height can be freely adjusted. Protrusion 14B and plate-shaped portion 14C are detachably secured to base 14A. Adjusting the inclination of protrusion 14B during screwing allows for flexible adjustment of the angle of inclination of plate-shaped portion 14C relative to the extension direction of legs 11, 11.

[0037] The light source holder 15 is the portion that holds the light source 4. For example, the light source holder 15 includes a base 15A, which is mounted between the columns 12 and 12 at a higher position than the window-mounted shielding plate holder 14; a protrusion 15B, which extends from near the center of the base 15A in the height direction of the column 12 and bends upward from the front end of the column 12 to protrude approximately parallel to the leg 11; and a support portion 15C, which protrudes further from the front end of the protrusion 15B. The portion of the protrusion 15B that extends in the height direction of the column 12 is provided with multiple threaded holes along the extending direction, and the base 15A is provided with threaded holes corresponding to these threaded holes. By selecting one of the multiple threaded holes and screwing a screw W into the threaded hole of the base 15A, the installation height of the light source holder 15 relative to the column 12 can be freely adjusted.

[0038] Furthermore, a threaded hole, for example, for screwing a screw W, is provided at the base end of support portion 15C, and a threaded hole corresponding to the threaded hole is provided at the tip end of protruding portion 15B. By fastening the threaded hole at the base end of support portion 15C and the threaded hole at the tip end of protruding portion 15B together with screw W, support portion 15C is detachably secured to protruding portion 15B. By adjusting the inclination of support portion 15C during screw fastening, the inclination angle of support portion 15C relative to protruding portion 15B can be freely adjusted.

[0039] The loading platform 3 is a platform on which the polarizing plate P to be inspected is placed. The loading platform 3 is formed into a plate shape by, for example, black plastic corrugated paper that has been subjected to a matte treatment. The planar shape of the loading platform 3 is, for example, a rectangular shape with the extension direction of the pair of legs 11, 11 set as the longitudinal direction. One end side of the loading platform 3 is directly supported on, for example, a workbench (not shown) on which the defect inspection device 1 is placed, and the other end side of the loading platform 3 is held by the loading platform holding portion 13. As a result, the loading platform 3 is tilted relative to the extension direction of the pair of legs 11, 11 in a manner such that the other end side of the loading platform 3 is higher than the one end side. The tilt angle θ1 of the loading platform 3 relative to the pair of legs 11, 11 is, for example, 35° to 50°.

[0040] The light source 4 is a device that irradiates the polarizing plate P on the mounting table 3 with white light L0. In the present embodiment, the light source 4 is composed of, for example, a white LED 16 in the form of a handy light. The white LED 16 preferably has a certain directivity. As an indicator of directivity, for example, a directivity angle can be cited. The so-called directivity angle is an angle that is twice the angle of the optical axis relative to the central axis at which the brightness becomes 1 / 2, when the brightness on the central axis of the white light L0 emitted from the light source 4 is set to 1. In the present embodiment, the directivity angle of the white light L0 from the white LED 16 is 10° to 90°, preferably 10° to 60°, and more preferably 10° to 40°.

[0041] exist Figure 1 as well as Figure 2 In the example, light source 4 includes a plurality of white LEDs 16 arranged in a row perpendicular to the direction in which the pair of legs 11 extend. Light source 4 is held above window-blind holder 14 by light source holder 15. Light source 4 is held above window-blind holder 14 by light source holder 15, with the optical axis of white light L0 output from the plurality of white LEDs 16 tilted relative to the direction in which column 12 extends. The tilt angle of the optical axis of white light L0 relative to the direction in which column 12 extends is, for example, 5° to 10°.

[0042] White light L0 emitted from the light source 4 passes through the transmission window 32 (described later) of the transmission window shielding plate holder 14 and is irradiated onto the polarizing plate P on the mounting table 3. On the polarizing plate P irradiated with the white light L0, reflected light including regular reflection light L1 is generated. Regular reflection light L1 is light emitted at the same angle as the incident angle of the white light L0 on the polarizing plate P. There is color unevenness Kb (see [Ka]) caused by a defect Ka on the polarizing plate P. Figure 4 ), in the portion with color unevenness Kb, diffused light L2 is generated due to the incidence of white light L0. By visually observing the presence of diffused light L2, the polarizing plate P can be inspected for defects.

[0043] In this embodiment, the mounting platform 3 includes a sliding plate 21 that moves the polarizing plate P forward and backward relative to the irradiation position R of the white light L0, enabling the polarizing plate P placed on the sliding plate 21 to slide on the mounting platform 3. The tilt angle of the sliding plate 21 relative to the pair of legs 11, 11 is based on the tilt angle θ1 of the mounting platform 3 relative to the pair of legs 11, 11. The sliding plate 21 is formed, for example, from a matte-treated black acrylic plate. In this embodiment, a circular polarizing plate 22 is provided on the surface of the black acrylic plate, and an antireflection layer 23 is further provided on the surface of the circular polarizing plate 22. The circular polarizing plate 22 and the antireflection layer 23 suppress reflections generated at the interface between the polarizing plate P and the sliding plate 21.

[0044] The sliding plate 21 is provided with a protruding grip portion 24. The grip portion 24 is disposed, for example, at one end of the width direction of the sliding plate 21. By configuring the grip portion 24 as a knob, the sliding plate 21 can be manually slid along the longitudinal direction of the mounting table 3. By sliding the sliding plate 21, various portions of the polarizing plate P on the sliding plate 21 can be moved forward or backward relative to the irradiation position R of the white light L0.

[0045] In this embodiment, the mounting platform 3 is provided with a positioning member 3A and a pair of positioning members 3B, 3B for positioning the sliding plate 21 on the mounting platform 3. The positioning member 3A is disposed at one end of the mounting platform 3 and supports the sliding plate 21 when the mounting platform 3 is tilted. The positioning members 3B, 3B are disposed in the width direction of the mounting platform 3 at intervals corresponding to the width of the sliding plate 21, and guide the sliding direction of the sliding plate 21 to prevent displacement in the width direction.

[0046] In this embodiment, the sliding plate 21 is also provided with positioning members 21A and 21B for positioning the polarizing plate P on the sliding plate 21. The positioning member 21A is disposed at one end in the longitudinal direction of the sliding plate 21, and the positioning member 21B is disposed at one side in the width direction of the sliding plate 21. By bringing the polarizing plate P into contact with the positioning members 21A and 21B, respectively, the polarizing plate P can be easily positioned on the sliding plate 21.

[0047] The shielding plate with a transmission window 5 is a portion that separates the regular reflection light L1 from the diffused light L2 when observing the defect Ka. Figure 5 (a) is a schematic top view showing the main part of the shielding plate 5 with a transmission window, and (b) is a cross-sectional view of (a) along the line V-V. Figure 5 (a) and Figure 5 As shown in FIG. 5 ( b ), the shielding plate with a transmission window 5 includes a plate-shaped main body 31 , a transmission window 32 fitted into the main body 31 , and a shielding plate 33 .

[0048] The main body 31 is made of, for example, a matte-treated black acrylic plate. The main body 31 has a planar shape, for example, a rectangular shape that is slightly smaller than the planar shape of the mounting table 3. The main body 31 is held in a cantilevered state by the window-blind plate holder 14, and is fixed to the plate-like portion 14C of the window-blind plate holder 14 (see FIG. 1 ) by, for example, adhesive bonding, so that one end of the main body 31 in the longitudinal direction is tilted downward relative to the other end. Figure 2 ).

[0049] The tilt angle θ2 of the main body 31 (window-blinding plate holder 14) relative to the extension direction of the leg 11 is, for example, 5° to 10°, based on the tilt angle of the optical axis of the white light L0 relative to the vertical axis. The tilt angle θ3 of the main body 31 (window-blinding plate 5) relative to the mounting platform 3 is, for example, 25° to 40°. Furthermore, the distance S between the window-blinding plate 5 and the mounting platform 3 in the direction of the optical axis of the white light L0 is 40 mm to 70 mm. The distance S is, for example, the distance along the optical axis of the white light L0 between the surface of the window-blinding plate 5 facing the mounting platform 3 and the surface of the mounting platform 3 (excluding the sliding plate 21). To facilitate the sliding of the sliding plate 21 relative to the mounting platform 3, the distance S is preferably 50 mm or greater. Furthermore, to prevent excessive spread of the white light L0 and ensure a sufficient angle of illumination of the white light L0 on the polarizing plate P, the distance S is more preferably 60 mm or less.

[0050] The transmission window 32 includes a glass plate 34 serving as a base, a first linear polarizing plate 35A, and a second linear polarizing plate 35B. The planar shape of the transmission window 32 is, for example, a rectangular shape slightly smaller than that of the main body 31. The glass plate 34 is positioned on one side of the transmission window 32 in the thickness direction (on the mounting table 3 side). The first linear polarizing plate 35A and the second linear polarizing plate 35B are bonded to one side of the glass plate 34 and positioned on the other side of the transmission window 32 in the thickness direction (on the light source 4 side).

[0051] The first linear polarizing plate 35A has an absorption axis in a first direction and is positioned to correspond to the optical axis of the white light L0 traveling from the light source 4 toward the mounting table 3. The second linear polarizing plate 35B has an absorption axis in a second direction perpendicular to the first direction and is positioned adjacent to the first linear polarizing plate 35A. In other words, the first linear polarizing plate 35A and the second linear polarizing plate 35B have a crossed Nicol relationship. In this embodiment, when the longitudinal direction of the window-mounted shielding plate 5 is set at 0°, the absorption axis of the first linear polarizing plate 35A is in the +45° direction, and the absorption axis of the second linear polarizing plate 35B is in the -45° direction.

[0052] The first linear polarizing plate 35A forms a rectangular portion on one side of the glass plate 34 at one end of the transmission window 32 in the longitudinal direction. The second linear polarizing plate 35B forms a rectangular portion on one side of the glass plate 34 at the other end of the transmission window 32 in the longitudinal direction. Figure 5 (a) and Figure 5In example (b), the length M2 of the second linear polarizing plate 35B relative to the longitudinal direction of the transmission window 32 is longer than the length M1 of the first linear polarizing plate 35A relative to the longitudinal direction. Consequently, the area S2 of the second linear polarizing plate 35B on the glass plate 34 is larger than the area S1 of the first linear polarizing plate 35A. By making the area S2 of the second linear polarizing plate 35B larger than the area S1 of the first linear polarizing plate 35A, the adjustment range of the observation axis for visual observation can be expanded, thereby improving inspection workability.

[0053] The shielding plate 33 blocks the regularly reflected light L1 from the polarizing plate P. For example, the shielding plate 33 is made of a matte-treated black acrylic plate, similar to the main body 31. For example, the shielding plate 33 has a width approximately equal to that of the transmission window 32 and a generally rectangular planar shape approximately equal in length to that of the first linear polarizing plate 35A. The shielding plate 33 is positioned on the surface of the transmission window 32 facing the light source 4, such that it blocks the regularly reflected light L1 of the white light L0 from the polarizing plate P and allows at least a portion of the reflected light other than the regularly reflected light L1 to pass through the second linear polarizing plate 35B.

[0054] If the polarizing plate P has color unevenness Kb caused by a defect Ka, at least a portion of the reflected light other than the regular reflected light L1 can include the diffused light L2 generated in the area of ​​color unevenness Kb. In this embodiment, the shielding plate 33 is positioned on the transmission window 32 so as to overlap the boundary between the first linear polarizing plate 35A and the second linear polarizing plate 35B. Therefore, when viewing the transmission window 32 from above, the first linear polarizing plate 35A is exposed on one side of the shielding plate 33, and the second linear polarizing plate 35B is exposed on the other side of the shielding plate 33.

[0055] When inspecting the polarizing plate P using the defect inspection apparatus 1 having the above-described structure, the polarizing plate P is first placed on the sliding plate 21 on the stage 3. The light source 4 is turned on, and white light L0 is emitted from each white LED 16. The white light L0 emitted from the white LED 16 passes through the first linear polarizing plate 35A and the glass plate 34 of the transmission window 32 toward the stage 3, forming an irradiation position R on the stage 3. Next, the grip 24 of the sliding plate 21 is gripped and slid on the stage 3, thereby positioning the polarizing plate P in the irradiation position R. The observation axis of the polarizing plate P observed by the naked eye is set at an angle different from the optical axis of the regular reflected light L1, for example, by passing through the second linear polarizing plate 35B located in front of the shielding plate 33 relative to the first linear polarizing plate 35A.

[0056] When the polarizing plate P enters the irradiation position R, the irradiation of the white light L0 generates reflected light including regular reflection light L1 on the surface of the polarizing plate P. Regular reflection light L1 travels from the polarizing plate P toward the transmission window 32 and then to the second linear polarizing plate 35B. The white light L0 that passes through the first linear polarizing plate 35A becomes linearly polarized light in a direction orthogonal to the absorption axis of the first linear polarizing plate 35A. This polarization direction is maintained in the regular reflection light L1. Therefore, regular reflection light L1 is blocked by the second linear polarizing plate 35B, which is in a cross-Nicol relationship with the first linear polarizing plate 35A. Even if some component of the regular reflection light L1 passes through the second linear polarizing plate 35B, this component is blocked by the shielding plate 33.

[0057] If the polarizing plate P has color unevenness Kb caused by a defect Ka, as described above, at least a portion of the reflected light other than the regular reflected light L1 can include diffused light L2 generated in the area of ​​the color unevenness Kb. The diffused light L2 is generated by light scattering caused by microscopic deformation and tiny bubbles near the defect Ka, and a portion of this diffused light passes through the second linear polarizing plate 35B. Therefore, if the color unevenness Kb is observed through the second linear polarizing plate 35B, it can be determined that the polarizing plate P has a defect Ka.

[0058] As described above, in the defect inspection device 1, a light source 4 that irradiates white light L0 is used to inspect defects Ka of a polarizing plate P made of a polyvinyl alcohol-based resin film. The intensity of white light L0 is relatively low compared to conventional light using a green lamp, and on the other hand, a light source 4 that irradiates white light L0 is easily available. In addition, in the defect inspection device 1, a shielding plate 5 with a transmission window is arranged between the mounting table 3 on which the polarizing plate P is mounted and the light source 4. By using the shielding plate 5 with a transmission window, the first linear polarizing plate 35A and the second linear polarizing plate 35B in an orthogonal Nicol relationship can be used to separate the regular reflected light L1 from the polarizing plate P from the diffused light L2 caused by the defect Ka, and the shielding plate 33 can be used to block the regular reflected light L1 from the polarizing plate P. Therefore, even when using white light L0, which has a relatively low intensity compared to conventional light using a green lamp, inspection for defects Ka can be carried out with high precision.

[0059] In this embodiment, the shielding plate 5 with a transmission window is tilted relative to the mounting table 3. Furthermore, its tilt angle θ4 is between 25° and 40°. This configuration facilitates deflection of the optical axis of the regular reflected light L1 from the polarizing plate P from the observation axis for visually observing the defect Ka, enabling appropriate defect inspection.

[0060] In this embodiment, the mounting table 3 includes a slide plate 21 that moves the polarizing plate P forward and backward relative to the irradiation position R of the white light L0. By using such a slide plate 21, the inspection position of the defect Ka can be easily scanned, thereby improving the inspection workability.

[0061] In this embodiment, the sliding plate 21 is configured to include a circularly polarizing plate 22 and an antireflection layer 23 provided on the surface of the circularly polarizing plate 22. In this case, reflection generated at the interface between the polarizing plate P and the sliding plate 21 can be suppressed, and defect inspection can be performed with high precision even when the sliding plate 21 is used.

[0062] In this embodiment, the directional angle of the white light L0 from the light source 4 is 10 to 90 degrees. By setting the directional angle of the white light L0 within this range, insufficient intensity of the white light L0 at the visual position can be prevented, and sufficient inspection accuracy of the defect Ka can be ensured.

[0063] In this embodiment, the distance S between the shielding plate with a window 5 and the mounting platform 3 in the optical axis direction of the white light L0 is 40 mm to 70 mm. By setting the distance S between the shielding plate with a window 5 and the mounting platform 3 to be below the upper limit of the above range, excessive spread of the white light L0 at the visual position can be prevented, thereby ensuring sufficient inspection accuracy for defects Ka. Furthermore, by setting the distance S between the shielding plate with a window 5 and the mounting platform 3 to be above the lower limit of the above range, sufficient space is ensured between the shielding plate with a window 5 and the mounting platform 3 for manual access, ensuring good operability for adjustments and other inspection tasks.

Claims

1. A defect inspection device for inspecting whether a polarizing plate including a polyvinyl alcohol-based resin film has defects, characterized in that: The defect inspection device comprises: a mounting table for mounting the polarizing plate; a light source that irradiates white light toward the polarizing plate on the mounting table; and A shielding plate with a transmission window is arranged between the mounting platform and the light source, The shielding plate with a transmission window has: a first linear polarizing plate having an absorption axis in a first direction and arranged corresponding to an optical axis of the white light directed from the light source toward the mounting table; a second linear polarizing plate having an absorption axis in a second direction orthogonal to the first direction and disposed adjacent to the first linear polarizing plate; as well as The shielding plate is arranged so as to shield the regular reflected light of the white light from the polarizing plate and to allow at least a portion of reflected light other than the regular reflected light to pass through the second linear polarizing plate.

2. The defect inspection device according to claim 1, wherein The shielding plate with a transmission window is inclined relative to the mounting platform.

3. The defect inspection device according to claim 2, characterized in that The tilt angle of the shielding plate with the transmission window relative to the mounting platform is 25° to 40°.

4. The defect inspection device according to claim 1, wherein: The mounting table includes a slide plate that moves the polarizing plate forward and backward relative to an irradiation area of ​​the white light.

5. The defect inspection device according to claim 4, characterized in that The sliding plate is configured to include a circular polarizing plate and an antireflection layer provided on a surface of the circular polarizing plate.

6. The defect inspection device according to claim 1, wherein: The white light from the light source has a directivity angle of 10° to 90°.

7. The defect inspection device according to claim 1, wherein: The distance between the shielding plate with the transmission window and the mounting table in the optical axis direction of the white light is 40 mm to 70 mm.

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