JP2022134936A - Defect inspection method and defect inspection device - Google Patents

Abstract

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

Description

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

A polarizing plate used in a display device such as a liquid crystal display device or an organic EL display device is generally composed of a polarizer sandwiched between two protective films. The polarizing plate has an adhesive layer laminated on one protective film in order to be attached to the display device, and a protective film on the other protective film to prevent the surface of the protective film from being scratched during distribution. protective film may be laminated. A release film is usually laminated on the pressure-sensitive adhesive layer. Specific examples of polarizers include PVA-based polarizing films in which dichroic dyes such as iodine and dichroic dyes are adsorbed and oriented on uniaxially stretched polyvinyl alcohol-based (PVA-based) resin films, and polymerized liquid crystal compounds. A polarizer composed of a liquid crystal cured layer containing a combination and a dichroic dye (hereinafter also referred to as a “liquid crystal polarizer”) and the like can be mentioned. A liquid crystal polarizer is usually formed by applying a composition containing a polymerizable liquid crystal compound onto a substrate film and curing the composition, and has the advantage of being able to produce a thin polarizer. Such PVA-based polarizing films and liquid crystal polarizers have the function of passing linearly polarized light in a specific plane of vibration, as will be described later, and are called "linear polarizers". A linear polarizer having a protective film on one or both sides thereof is generally called a "linear polarizer".

Defects may occur in polarizing plates and polarizers during the manufacturing process. For example, defects such as foreign matter being mixed in between the polarizer and the protective film and air bubbles being left may occur. In addition, the liquid crystal polarizer may have uneven optical characteristics of the polarizing plate due to coating unevenness during manufacturing.

Therefore, before the polarizing plate is incorporated into the display device, an inspection for detecting defects in the polarizing plate is performed. As disclosed in Japanese Patent Laid-Open No. 9-229817 (Patent Document 1), this defect inspection is performed by providing a polarizing filter between the polarizing plate, which is the object to be inspected, and the light source, and then the polarizing plate. Alternatively, the polarizing filters are rotated in a plane direction, and their respective polarization axis directions are in a specific relationship. When the directions of the polarization axes are orthogonal to each other (that is, in the case of an arrangement forming crossed Nicols), the linearly polarized light that has passed through the polarizing filter does not pass through the polarizing plate. However, if there is a defect in the polarizing plate, the linearly polarized light is transmitted through that portion, and the presence of the defect can be found by detecting the light.

On the other hand, when the polarization axis directions of the polarizing plate and the polarizing filter are parallel to each other, the linearly polarized light that has passed through the polarizing filter is transmitted through the polarizing plate. However, if there is a defect in the polarizing plate, the linearly polarized light is blocked at that location, so the existence of the defect becomes clear when the light is not detected. The presence or absence of defects in the polarizing plate can be inspected by an inspector visually detecting the light transmitted through the polarizing plate, or by automatically detecting the value of image analysis processing using a combination of a CCD camera and an image processing device. It can be carried out.

JP-A-9-229817

According to the method described in Patent Literature 1, although it is possible to detect local defects such as foreign substances and air bubbles that have large differences in optical characteristics from the surroundings, it is difficult to detect unevenness in optical characteristics.

An object of the present invention is to provide a defect inspection method and a defect inspection apparatus capable of detecting unevenness in optical characteristics.

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

[2] The optical film is
further comprising a protective film made of polyethylene terephthalate-based resin,
The angle formed by the orientation axis of the protection film and the absorption axis of the polarizer to be inspected is within the range of 0°±30°,
In the arranging step,
The optical film is oriented so that the surface of the protective film opposite to the polarizer to be inspected faces the second filter, and
Arranged so that the angle between the orientation axis of the protection film and the absorption axis of the second polarizer is within the range of 90° ± 5°,
The defect inspection method according to [1], wherein the detection step is the step b1.

[3] The optical film is
further comprising a protective film made of polyethylene terephthalate-based resin,
the angle between the orientation axis of the protection film and the absorption axis of the polarizer to be inspected is within the range of 90°±30°;
In the arranging step,
The optical film is oriented so that the surface of the protective film opposite to the polarizer to be inspected faces the second filter, and
Arranged so that the angle between the orientation axis of the protection film and the absorption axis of the second polarizer is within the range of 0° ± 5°,
The defect inspection method according to [1], wherein the detection step is performed by the step b1.

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

[5] The optical film further has a λ/4 retardation layer,
In the inspection method, the first filter uses one having a λ / 4 retardation layer,
In the arranging step, the optical film and the first filter are arranged such that their λ/4 retardation layers face each other without interposing the polarizer to be inspected and the first polarizer, [1] The defect inspection method according to any one of [4].

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

According to the defect inspection method and the defect inspection apparatus of the present invention, it is possible to detect the unevenness of the optical characteristics of the optical film.

It is a figure which shows the defect inspection system of this embodiment. It is a schematic diagram of the defect inspection apparatus of this embodiment. It is a figure which shows an example of the defect area|region in an optical film. FIG. 4 is a cross-sectional view showing an example of the layer structure of a polarizing plate with a protective film to be inspected in the first application example. FIG. 10 is a cross-sectional view showing an example of the layer structure of a polarizing plate to be inspected in the second application example;

The present invention relates to a defect inspection method and defect inspection apparatus for an optical film having a polarizer to be inspected.
A defect inspection method according to the present invention uses a first filter having a first polarizer, a second filter having a second polarizer, and a light source,
The first filter, the optical film, and the second filter, in this order, under the following conditions a1 and a2:
(a1) an angle θ1 between the absorption axis of the first polarizer and the absorption axis of the polarizer to be inspected is within the range of 90°±5°;
(a2) an angle θ2 between the transmission axis of the polarizer to be inspected and the absorption axis of the second polarizer is within the range of 90°±35°;
an arrangement step of arranging so as to satisfy
Step b1 or step b2 below:
(b1) detecting light emitted from the light source and transmitted through the first filter, the optical film, and the second filter in this order;
(b2) detecting light emitted from the light source and transmitted through the second filter, the optical film, and the first filter in this order;
a detection step of
and a determination step of determining a defect of the optical film based on the detection result of the detection step.

A defect inspection apparatus according to the present invention has a first filter having a first polarizer, a second filter having a second polarizer, and a light source,
The first filter, the optical film, and the second filter satisfy the following conditions a1 and a2 in this order:
(a1) an angle θ1 between the absorption axis of the first polarizer and the absorption axis of the polarizer to be inspected is within the range of 90°±5°; and (a2) the transmission axis of the polarizer to be inspected. The angle θ2 formed with the absorption axis of the second polarizer is within the range of 90° ± 35°.
are arranged to satisfy
The light source satisfies the following condition b1 or condition b2:
(b1) the light emitted from the light source is transmitted through the first filter, the optical film, and the second filter in this order;
(b2) the light emitted from the light source passes through the second filter, the optical film, and the first filter in this order;
are arranged to meet

DETAILED DESCRIPTION OF THE INVENTION Embodiments of a defect inspection apparatus and a defect inspection method of the present invention will be described below with reference to the drawings. The same elements are denoted by the same reference numerals, and overlapping descriptions are omitted. The dimensional proportions of the drawings do not necessarily match those of the description.

FIG. 1 is a schematic diagram of a defect inspection system including a defect inspection apparatus according to one embodiment. The defect inspection system 1 includes a transport unit 2 and a defect inspection device 3A. The defect inspection device 3A is arranged on the transport path while transporting the strip-shaped optical film 100 in the longitudinal direction of the transport unit 2. , the optical film 100 is inspected for defects. Optical film 100 includes a polarizer under test.

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

The defect inspection system 1 may comprise a marking device 4 as shown in FIG. The marking device 4 is a device that puts a mark M on the optical film 100 using the 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 marker head having a pen or the like. A mark M is attached on the optical film 100 by moving the marker head in the width direction X on the arm. The marking device 4 may be configured to be controlled by the defect inspection device 3A, or the marking device 4 itself may have a controller such as a computer. Also, the marking device 4 may convert the defect information sent from the defect inspection device 3A into a two-dimensional code and print it on the optical film 100 .

The defect inspection performed by the defect inspection apparatus 3A includes processing for detecting defects that may occur during the manufacturing process (including the transport process) of the optical film 100, and a defect map indicating the positions of the inspected defects on the optical film 100. may include processing to create Defects of the optical film 100 that can be detected in the present embodiment include unevenness in optical properties, local defects such as local disturbance of the polarization axis, and the like. In the optical film 100, when the polarizer to be inspected is a liquid crystal polarizer, it may have uneven optical properties due to uneven coating in the manufacturing process. Also, in the optical film 100, if air bubbles or foreign substances are mixed in during the manufacturing process, or unevenness is generated, local defects occur.

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

FIG. 2 illustrates a polarizing plate 100 as the optical film 100 to be inspected by the defect inspection apparatus 3A. Polarizing plate 100 is a laminate of polarizer 101 , protective film 102 , and protective film 103 . The polarizer 101 of the polarizing plate 100 is the polarizer to be inspected.

The polarizer 101 has linear polarization properties. In this embodiment, the absorption axis PA0 of the polarizer 101 is parallel to the Y direction, which is the transport direction of the optical film 100 . Hereinafter, the light polarized in the transport direction of the optical film 100 (the direction of the absorption axis PA0 of the polarizer 101) is referred to as first polarized light, and the light polarized in the direction orthogonal to the first polarized light is referred to as second polarized light. .

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

The first filter 40 and the second filter 50 are arranged with the optical film 100 sandwiched therebetween. The first filter 40 is arranged so 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° (the above condition a1 is are arranged so as to satisfy The second filter 50 is arranged so 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° (the above condition a2 is are arranged so as to satisfy

In FIG. 2, the absorption axis PA0 of the polarizer 101 is indicated by a double arrow, and the direction at 90° to the absorption axis PA0 is indicated by a black circle. Also, since FIG. 2 shows the case where the angle θ1 is 90° and the angle θ2 is 90°, the absorption axis PA1 and the absorption axis PA2 are indicated by black circles. In the present invention, as described above, the angle θ1 may be within the range of 90°±5°, and the angle θ2 may be within the range of 90°±35°. A mode in which θ1 is 90° and the angle θ2 is 90° will be described.

In FIG. 2, the arrangement satisfies the above condition b1. Specifically, the light irradiation section 10A is arranged via the first filter 40 when viewed from the optical film 100 , and the detection section 20A is disposed via the second filter 50 when viewed from the optical film 100 . The light emitted from the light source 11 of the light irradiation section 10A passes through the first filter 40 and enters the inspection area A (see FIG. 1) of the optical film 100 to be inspected. The light emitted from the inspection area A passes through the second filter 50 and enters the detection section 20A. That is, the detection step is performed by the above step b1.

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

The light source 11 is not limited as long as it can output light that is non-polarized and does not affect the composition and properties of the optical film 100 . Examples of light source 11 are, for example, metal halide lamps, halogen transmission lights, fluorescent lamps, and the like. The light source 11 can extend in the width direction of the optical film 100 as shown in FIG. Alternatively, the light irradiation section 10A may include a plurality of light sources 11 that are discretely arranged along the width direction of the optical film 100 .

In this embodiment, the first filter 40 selectively passes the first polarized light among the polarized lights contained in the light emitted from the light source 11 .

The detector 20A has at least one camera 21 that captures an image of the optical film 100 . FIG. 1 illustrates a configuration in which the imaging section 20A has a plurality of cameras 21 arranged along the width direction of the optical film 100 . The camera 21 is an area sensor camera such as a CCD camera. Camera 21 may be a line sensor camera. When the camera 21 is a line sensor camera, the inspection area A of the optical film 100 can be imaged by relatively moving the camera 21 and the optical film 100 . The detection unit 20</b>A (specifically, the camera 21 ) is electrically connected to the control device 30 , controls imaging timing, and inputs obtained imaging data to the control device 30 .

1 and 2 show a configuration in which a camera 21 is provided as the detection unit 20A and defects are detected based on an image captured by the camera 21. The detection unit 20A detects defects by visually observing the optical film 100. may be detected. If the detection unit 20A detects defects visually, it is preferable that the control unit 30 is not provided.

The control device 30 controls the detection section 20A. The control device 30 has, for example, a computer (computing section). The control device 30 has a function of detecting a defective portion in the imaging data input from the detection section 20A, performing image processing such as emphasizing the defective portion, and detecting a defective position in the image of the optical film 100. It may also have a function of creating a defect map to show. When the defect inspection system 1 includes the marking device 4 as illustrated in FIG. 1, the control device 30 is also electrically connected to the marking device 4 as illustrated in FIG. Then, a mark M based on the detected defect information may be given to the optical film 100 .

Next, an inspection process for inspecting the optical film 100 using the defect inspection apparatus 3A will be described. When carrying out the defect inspection, the inspection area A of the optical film 100 is irradiated with the light L1 from the light source 11 through the first filter 40 as the light L2 which is the first polarized light. Part of the light L2 is transmitted through the optical film 100 . Light L3 transmitted through the optical film 100 is emitted as light L4 by the second filter 40 and enters the detection section 20A, where the light L4 is detected. More specifically, the inspection area A is imaged by the camera 21, or the inspection area A is visually observed. The detection process is as described above. Thereafter, defects in the inspection area A of the optical film are judged based on the detection result in the detection step (judgment step).

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

However, the optical film 100 may have defect areas where the absorption axis of the polarizer 101 does not match the absorption axis PA0. FIG. 3 shows an example of the defect area B in the optical film 100, and the absorption axis in the defect area B is indicated by a double-headed arrow. The defect region B has an absorption axis (hereinafter referred to as "absorption axis PA3") that does not coincide with the absorption axis PA0. If the defect in the defect area B is unevenness in optical characteristics, it is possible to assume a state in which the angle between the absorption axis PA3 in the defect area B and the absorption axis PA0 is continuously changing as shown in FIG. can. In the defective optical film 100, the area having the absorption axis PA0 is defined as a normal area A1.

In the defect area B having the absorption axis PA3 that does not match the absorption axis PA0, the polarization direction of the light L2 and the direction of the absorption axis PA0 of the polarizer 101 are not parallel, and the light L2 is transmitted through the optical film 100. FIG. The light L3 transmitted through the optical film 100 is polarized light in a direction corresponding to the absorption axis of the defect region B of the polarizer 101. FIG. If the direction of the absorption axis of the defect region of the polarizer 101 is not unidirectional, the light L3 includes polarized light in multiple directions. Hereinafter, these are collectively referred to as third polarized light, and some of the plurality of polarized lights included in the third polarized light are arranged in order of decreasing angle with the first polarized light, 3a polarized light, 3b polarized light, The 3c-polarized light is referred to as . . .

The light L3 passes through the second filter 50 and enters the detector 20A as light L4. 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 a crossed Nicols state. However, since the light L3 is the third polarized light different from the first polarized light, it is transmitted through the second filter 50 . The light L3 is emitted after being absorbed by the second filter 50 at a rate corresponding to its polarization direction. That is, the ratio of light absorbed by the second filter 50 decreases in the order of 3a-polarized light, 3b-polarized light, 3c-polarized light, and so on.

The inventors have noted that the degree of polarization of the light transmitted through the first filter and the optical film is substantially low. It has been found that by passing such light through a second filter, the contrast ratio between the region of the first polarized light and the region of the third polarized light can be increased, and the detection sensitivity can be greatly increased.

As described above, the transmission characteristics of the light L3 in the optical film 100 differ between the normal region A1 and the defect region B, and the transmission characteristics of the light L4 in the second filter 50 vary depending on the absorption axis direction in the defect region B. different. Since the detection unit 20A detects the light L4 reflecting these transmission characteristics, it is possible to detect the presence or absence of defects in the optical film 100 and the presence or absence of unevenness in the absorption axis direction in the defect region. The unevenness in the absorption axis direction in the optical film 100 corresponds to the unevenness in optical properties.

Although the case where the angle θ1 is 90° and the angle θ2 is 90° has been described above, the light amount of the light L4 differs depending on the magnitudes of the angles θ1 and θ2. As long as the angle θ1 is 90°±5° and the angle θ2 is 90°±35°, the transmission characteristics of the light L3 in the optical film 100 are different between the normal area A1 and the defective area B, and The transmission characteristics of the light L4 in the second filter 50 differ according to the absorption axis direction in the defect area B. FIG. Therefore, even if the angles θ1 and θ2 are not 90°, the detection unit 20A detects the light L4 reflecting these transmission characteristics. The presence or absence of unevenness can be detected.

Since the defect inspection apparatus 3A includes the first filter 40 and the second filter 50, it is possible to efficiently detect unevenness in optical characteristics. Therefore, in the method for manufacturing the optical film 100 including the above-described defect inspection method, the optical film 100 as a product containing no defects can be efficiently manufactured.

FIGS. 1 and 2 show a case where the arrangement satisfies the condition b1 and the step b1 is performed in the detection step. An arrangement that satisfies the above condition b2 may also be used. In this case, the light emitted from the light source 11 of the light irradiation section 10A enters the inspection area A of the optical film 100 to be inspected through the second filter 50 . The light emitted from the inspection area A passes through the first filter 40 and enters the detection section 20A. That is, the step b2 is performed in the detection step. Even with such an arrangement, it is possible to obtain the same effect as the arrangement that satisfies condition b1 as shown in FIGS.

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

When manufacturing the optical film 100, while conveying the belt-shaped polarizer 101, the belt-shaped protective film 102, and the belt-shaped protective film 103 in the longitudinal direction, the protective film 102 is attached to one side of the polarizer 101, A protective film 103 is pasted on the other one surface (pasting step). The bonding of the polarizer 101 and the protective films 102 and 103 can be performed using, for example, a pair of bonding rollers. In the bonding process, the protective film 102 and the protective film 103 may be simultaneously bonded to the polarizer 101, or one of the protective film 102 and the protective film 103 may be bonded to the polarizer 101, and then the other is bonded. You may

After the bonding step, the optical film 100 as a laminate of the protective film 103, the polarizer 101 and the protective film 102 is transported between the light irradiation unit 10A and the detection unit 20A in the defect inspection device 3A. In 3A, the optical film 100 is inspected for defects (defect inspection step). In the defect inspection process, the optical film 100 is inspected for defects by the defect inspection method described above. In a mode in which the defect inspection system 1 includes the marking device 4, a step (marking step) of applying the mark M to the optical film 100 by the marking device 4 may be performed according to the result of the defect inspection process.

The polarizer 101 is an absorptive polarizer having a property of absorbing linearly polarized light having a vibration plane parallel to its absorption axis and transmitting linearly polarized light having a vibration plane orthogonal to the absorption axis (parallel to the transmission axis). can be Typical polarizers include a liquid crystal polarizer containing a cured product of a polymerizable liquid crystal compound, a polarizing film in which a dichroic dye is adsorbed and oriented on a uniaxially stretched polyvinyl alcohol resin film, and the like.

A typical manufacturing method for a liquid crystal polarizer will be briefly described. First, a suitable support is prepared. Next, an alignment film is formed on the surface of the support. Subsequently, on the alignment film, a liquid composition containing a liquid composition containing a polymerizable liquid crystal compound and a dichroic dye is applied and dried to obtain a coating layer containing a polymerizable liquid crystal compound on the alignment film. to form Thereafter, the coating layer is polymerized and cured by light irradiation to obtain a liquid crystal polarizer on the support. If a transparent resin film is used as such a support, a polarizer can be produced using the transparent resin film as a protective film.

The liquid crystal polarizer may be, for example, one described in JP-A-2016-170368. As the dichroic dye, those having absorption in the wavelength range of 380 to 800 nm can be used, and organic dyes are preferably used. Dichroic dyes include, for example, azo compounds. A liquid crystal compound is a liquid crystal compound that can be polymerized in an aligned state, and can have a polymerizable group in its molecule. Also, as described in WO2011/024891, a polarizer may be formed from a dichroic dye having liquid crystallinity. After polymerization (after formation of a polarizer composed of a cured liquid crystal layer), the liquid crystal compound no longer needs to exhibit liquid crystallinity.

The thickness of the liquid crystal polarizer is, for example, 0.2 μm to 10 μm. A liquid crystal polarizer may have uneven optical properties due to uneven application of a liquid composition in the manufacturing process. In the defect inspection by the defect inspection method and the defect inspection apparatus of this embodiment, such unevenness in optical characteristics can also be detected.

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

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

As used herein, "(meth)acryl" means at least one selected from acryl and methacryl. The same applies to "(meth)acryloyl", "(meth)acrylate" and the like.

The saponification degree of the PVA-based resin is usually 85 to 100 mol %, preferably 98 mol % or more. The polyvinyl alcohol-based resin may be modified, and for example, polyvinyl formal or polyvinyl acetal modified with aldehydes may be used. The average degree of polymerization of the PVA-based resin is usually 1,000 to 10,000, preferably 1,500 to 5,000. The average degree of polymerization of the PVA-based resin can be determined according to JIS K6726.

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

The uniaxial stretching of the PVA-based resin film may be performed before the dyeing treatment with the dichroic dye, simultaneously with the dyeing treatment, or after the dyeing treatment. When the uniaxial stretching is performed after the dyeing treatment, the uniaxial stretching may be performed before the cross-linking treatment or during the cross-linking treatment. In addition, the uniaxial stretching may be divided into a plurality of stages in these plurality of treatment stages.

In the uniaxial stretching, when a long PVA-based resin film is used, for example, the PVA-based resin film is stretched over rolls and the circumferential speed of the rolls is varied to uniaxially stretch between the rolls. Alternatively, the film may be uniaxially stretched using hot rolls. The uniaxial stretching may be dry stretching in which the film is stretched in the atmosphere, or wet stretching in which the PVA-based resin film is stretched in a swollen state using a solvent or water. The draw ratio is usually 3 to 8 times. When the PVA-based resin film is stretched by uniaxial stretching a plurality of times, the stretching ratio is usually 3 to 8 times the original length. This draw ratio can also be selected so that the finally obtained PVA-based polarizing film has a desired thickness.

As a method of dyeing a PVA-based resin film with a dichroic dye (dyeing treatment), a method of immersing such a PVA-based resin film in an aqueous solution containing a dichroic dye is typically employed. Iodine and dichroic organic dyes are used as dichroic dyes. The PVA-based resin film is preferably immersed in water before being dyed.

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

Thus, a PVA-based polarizing film is obtained. The thickness of the PVA-based polarizing film is preferably as thin as 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. be. The thickness of the polarizing film is usually 2 μm or more, preferably 3 μm or more.

The linear polarizer can be used alone as a polarizing plate (optical film), and as described above, in general, a polarizing plate (optical film ). As the protective film, for example, a transparent resin film is used, and the transparent resin constituting such a resin film includes acetylcellulose resins such as triacetyl cellulose and diacetyl cellulose, and methacrylic resins such as polymethyl methacrylate. , polyester resins, polyolefin resins, polycarbonate resins, polyetheretherketone resins, polysulfone resins, and the like. Among these, a resin film made of a plurality of kinds of transparent resins can also be used as the protective film.

<First Filter, Second Filter>
The first filter 40 has a first polarizer 41 and the second filter 50 has a second polarizer 51 . Similar to the polarizer 101 described above, the first polarizer 41 and the second polarizer 50 absorb linearly polarized light having a plane of vibration parallel to the absorption axis and are orthogonal to the absorption axis (parallel to the transmission axis). It may be an absorbing polarizer having a property of transmitting linearly polarized light having a plane of oscillation. A representative polarizer is a polarizing film in which a dichroic dye is adsorbed and oriented on a uniaxially stretched PVA-based resin film. For the detailed description of the polarizing film, the description of the polarizing film in the polarizer 101 described above is applied. The first polarizer and the second polarizer are defect-free.

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

FIG. 4 is a cross-sectional view showing an example of the layer structure of a polarizing plate with a protective film to be inspected in the first application example. As shown in FIG. 4, polarizing plate 110 with a protective film is a laminate of polarizer 101, protective film 102, and protective film 103, which is a protective layer laminated on the surface of polarizing plate 100 on the protective film 102 side. A film 120 is provided. The above description applies to the polarizing plate 100 . The protection film 120 is composed of a base film and an adhesive layer laminated thereon, and is laminated on the polarizing plate 100 via the adhesive layer.

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

The base film of the protection film 120 is a film made of uniaxially stretched polyethylene terephthalate resin. The protection film 120 has an orientation axis that matches the uniaxial stretching direction of the base film and exhibits birefringence. Therefore, a phase difference occurs in the light passing through the protection film 120 . In the detection section 20A, if the incident light has birefringence, the defect detection accuracy is lowered.

When the object to be inspected for defects by the defect inspection method and the defect inspection apparatus of the present embodiment shown in FIGS. 50 side, and the light source is arranged so that the irradiation direction of the light from the light source in the detection step is from the first filter 40 side (the above condition b1 is satisfied), and the above step b1 is performed. Preferably, the detection step is performed at the That is, it is preferable to transmit the light from the light source 11 in the direction of the arrow shown in FIG. The second filter 50 is arranged so that the angle θ2 formed between the absorption axis of the second polarizer 51 and the absorption axis of the polarizer 101, which is the polarizer to be inspected, is appropriately adjusted within the range of 90°±35°, and is protected. This is because the phase difference caused by the film 120 can be reduced. The phase difference generated in the light transmitted through the protection film 120 is reduced by the second filter 50 and enters the detection section 20A.

In this application example, even if the inspection target is a polarizing plate with a protective film having a protective film made of polyethylene-terephthalate-based resin, it is possible to suppress deterioration in the detection accuracy of defects in the detection unit 20A.

In order to perform defect inspection by the defect inspection method and defect inspection apparatus of the present embodiment, the polarizing plate with a protective film is preferably manufactured so as to satisfy the following condition c1 or condition c2. The phase difference caused by the protection film 120 can be effectively reduced by the second filter 50 by being manufactured so as to satisfy the following condition c1 or condition c2.
(c1) The angle θ3 between the absorption axis of the polarizer 101 and the orientation axis of the protection film 120 is within the range of 0°±30°.
(c2) The angle θ3 between the absorption axis of the polarizer 101 and the orientation axis of the protection film 120 is within the range of 90°±30°.

For the polarizing plate with a protective film manufactured so as to satisfy the condition c1, in the arrangement step, the angle formed by the orientation axis of the protective film and the absorption axis of the second polarizer 51 of the second filter 50 is 90°± It is preferable to arrange it so that it may become 5 degrees. With such an arrangement, the phase difference caused by the protection film 120 can be effectively reduced by the second filter 50 .

For the polarizing plate with a protective film manufactured so as to satisfy the above condition c2, in the arrangement step, the angle formed by the orientation axis of the protective film and the absorption axis of the second polarizer of the second filter is 0°±5°. It is preferable to arrange so as to be With such an arrangement, the phase difference caused by the protection film 120 can be effectively reduced by the second filter 50 .

In order to perform defect inspection with the defect inspection method and defect inspection apparatus of the present embodiment, the orientation axis of the protection film of the polarizing plate with the protection film is preferably the same in the entire area, but usually in the entire area The orientation axes do not coincide. The protective film preferably has a maximum angle of 25° or less between different orientation axes. This is because the polarizing plate in which such a protection film is used easily obtains the effect of suppressing deterioration in the detection accuracy of the defect inspection performed by the defect inspection method and the defect inspection apparatus of the present embodiment.

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

An example of the layer structure of the polarizing plate to be inspected in the second application will be described with reference to FIG. As shown in FIG. 5, polarizing plate 130 is a laminate of polarizer 101, protective film 102, and protective film 103. Retardation film 140 is laminated on the surface of polarizing plate 100 on the protective film 103 side. Prepare. The above description applies to the polarizing plate 100 .

The polarizing plate 130 includes a λ/4 retardation layer that imparts a 1/4 wavelength phase difference to the transmitted light as the retardation film 140, and further imparts a 1/2 wavelength phase difference to the transmitted light. A λ/2 retardation layer, a positive A plate, and a positive C plate may be included. The retarder 140 of the polarizing plate 130 shown in FIG. 5 includes a first retardation layer 141 and a second retardation layer 142 . Examples of the combination of the first retardation layer 141 and the second retardation layer 142 include a combination of a λ/2 retardation layer and a λ/4 retardation layer, a combination of a λ/4 retardation layer and a positive C layer, and the like. .

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

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

When the polarizing plate 130 is inspected for defects by the defect inspection method and the defect inspection apparatus of the present embodiment shown in FIGS. Place it so that it does and inspect it. That is, the light from the light source 11 is transmitted in the direction of the arrow shown in FIG. Further, as the first filter 40, one provided with a λ/4 retardation layer on the polarizing plate 130 side of the first polarizer 41 is used. The polarizing plate 130 and the first filter 40 are arranged such that their λ/4 retardation layers face each other without the polarizer 103 and the first polarizer 41 interposed therebetween. Since the first filter 40 includes a λ/4 retardation layer, the section through which light is transmitted as circularly polarized light is the λ/4 retardation layer of the first filter 40 and the λ/4 retardation layer of the polarizing plate 130. Even if the inspection target is a polarizing plate having a λ/4 retardation layer, it is possible to detect defects based on the same principle as that of the present embodiment.

Note that only when the inspection target is the polarizing plate 130 (that is, only when it is a circularly polarizing plate), the absorption axis of the first polarizer of the first filter and the absorption axis of the polarizer of the polarizing plate 130 are 1 filter and the slow axis of the λ / 4 retardation layer of the polarizing plate 130 are arranged so that both are parallel to obtain a crossed Nicols state. can be done.

In this application example, when performing defect detection for the purpose of detecting defects in the polarizing plate 130, light irradiation from the light source in the detection step is performed from the first filter 40 side (arrangement of condition b1, detection by step b1 step) or from the second filter 50 side (placement of condition b2, detection step by step b2). In order to detect unevenness in the optical characteristics of the polarizer 101 of the polarizing plate 130, it is preferable to irradiate the light from the light source from the first filter side 40. FIG. In the case 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 section 20A. This is because the defect of 140 may be reflected and the detection accuracy of the unevenness of the optical characteristics of the polarizer 101 may be lowered.

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 2 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 retardation body, 141 first retardation layer, 142 second retardation layer;

Claims (6)

A defect inspection method for an optical film having a polarizer to be inspected, comprising:
The defect inspection method uses a first filter having a first polarizer, a second filter having a second polarizer, and a light source,
The first filter, the optical film, and the second filter, in this order, under the following conditions a1 and a2:
(a1) an angle θ1 between the absorption axis of the first polarizer and the absorption axis of the polarizer to be inspected is within the range of 90°±5°;
(a2) an angle θ2 between the absorption axis of the polarizer to be inspected and the absorption axis of the second polarizer is within the range of 90°±35°;
an arrangement step of arranging so as to satisfy
Step b1 or step b2 below:
(b1) detecting the light emitted from the light source and transmitted through the first filter, the optical film, and the second filter in this order; or (b2) the light emitted from the light source and passing through the second filter , detecting light transmitted through the optical film and the first filter in this order;
a detection step of
and a determination step of determining a defect of the optical film based on the detection result of the detection step. The optical film is
further comprising a protective film made of polyethylene terephthalate-based resin,
The angle formed by the orientation axis of the protection film and the absorption axis of the polarizer to be inspected is within the range of 0°±30°,
In the arranging step,
The optical film is oriented so that the surface of the protective film opposite to the polarizer to be inspected faces the second filter, and
Arranged so that the angle between the orientation axis of the protection film and the absorption axis of the second polarizer is within the range of 90° ± 5°,
2. The defect inspection method according to claim 1, wherein said detecting step is based on said step b1. The optical film is
further comprising a protective film made of polyethylene terephthalate-based resin,
the angle between the orientation axis of the protection film and the absorption axis of the polarizer to be inspected is within the range of 90°±30°;
In the arranging step,
The optical film is oriented so that the surface of the protective film opposite to the polarizer to be inspected faces the second filter, and
Arranged so that the angle between the orientation axis of the protection film and the absorption axis of the second polarizer is within the range of 0° ± 5°,
2. The defect inspection method according to claim 1, wherein said detecting step is performed by said step b1. The defect inspection method according to any one of claims 1 to 3, wherein the polarizer to be inspected includes a cured product of a polymerizable liquid crystal compound. The optical film further has a λ/4 retardation layer,
In the inspection method, the first filter uses one having a λ / 4 retardation layer,
2. In the arranging step, the optical film and the first filter are arranged such that their λ/4 retardation layers face each other without interposing the polarizer to be inspected and the first polarizer. 5. The defect inspection method according to any one of -4. A defect inspection apparatus for an optical film having a polarizer to be inspected,
The defect inspection apparatus has a first filter having a first polarizer, a second filter having a second polarizer, and a light source,
The first filter, the optical film, and the second filter satisfy the following conditions a1 and a2 in this order:
(a1) an angle θ1 between the absorption axis of the first polarizer and the absorption axis of the polarizer to be inspected is within the range of 90°±5°;
(a2) an angle θ2 between the transmission axis of the polarizer to be inspected and the absorption axis of the second polarizer is within the range of 90°±35°;
are arranged to satisfy
The light source satisfies the following condition b1 or condition b2:
(b1) the light emitted from the light source is transmitted through the first filter, the optical film, and the second filter in this order;
(b2) the light emitted from the light source passes through the second filter, the optical film, and the first filter in this order;
Defect inspection equipment arranged to satisfy

Images