JP7689838B2 - Defect inspection method and defect inspection device - Google Patents

Description

The present invention relates to a defect inspection method and defect inspection device for optical films.

A polarizing plate used in a display device such as a liquid crystal display device or an organic EL display device is generally constructed by sandwiching a polarizer between two protective films. In order to attach the polarizing plate to a display device, an adhesive layer is laminated on one protective film, and a protective film may be laminated on the other protective film to prevent scratches on the surface of the protective film during distribution. A release film is usually laminated on the adhesive layer. Specific examples of polarizers include a PVA-based polarizing film in which a dichroic dye such as iodine or a dichroic dye is adsorbed and oriented on a uniaxially stretched polyvinyl alcohol (PVA-based) resin film, and a polarizer (hereinafter also referred to as a "liquid crystal polarizer") made of a liquid crystal cured layer containing a polymer of a polymerizable liquid crystal compound and a dichroic dye. A liquid crystal polarizer is usually formed by applying a composition containing a polymerizable liquid crystal compound on a substrate film and curing it, and has the advantage of being able to produce a thin polarizer. As described below, such a PVA-based polarizing film and liquid crystal polarizer have the effect of passing linearly polarized light of a specific vibration plane, and are called "linear polarizers". Furthermore, linear polarizers that have protective films on one or both sides are generally called "linear polarizing plates."

Defects can occur in polarizing plates and polarizers during the manufacturing process. For example, defects can occur such as foreign matter being mixed in between the polarizer and the protective film, or air bubbles remaining. Furthermore, uneven coating during manufacturing can cause unevenness in the optical properties of liquid crystal polarizers.

Therefore, before the polarizing plate is incorporated into the display device, an inspection is performed to detect defects in the polarizing plate. As shown in JP-A-9-229817 (Patent Document 1), this defect inspection involves placing a polarizing filter between the polarizing plate to be inspected and a light source, and then rotating the polarizing plate or polarizing filter in a planar direction to set the polarization axis directions of each of these in a specific relationship. When the polarization axis directions are perpendicular to each other (i.e., when they are arranged to form a crossed Nicol), linearly polarized light that passes through the polarizing filter does not pass through the polarizing plate. However, if there is a defect in the polarizing plate, linearly polarized light passes through that location, and the presence of the defect is revealed by detecting that light.

On the other hand, when the polarization axes of the polarizing plate and the polarizing filter are parallel, the linearly polarized light that passes 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, and the presence of the defect becomes apparent because 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 that has passed through the polarizing plate, or by automatically detecting it using image analysis processing values that combine a CCD camera and image processing device.

Japanese Patent Application Publication No. 9-229817

The method described in Patent Document 1 can detect localized defects with optical properties that differ greatly from the surrounding area, such as foreign matter or air bubbles, but it is difficult to detect unevenness in optical properties.

The present invention aims to provide a defect inspection method and defect inspection device that can detect 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 steps of:
The defect inspection method includes using a first filter having a first polarizer, a second filter having a second polarizer, and a light source;
The first filter, the optical film, and the second filter are arranged in this order, and the following conditions a1 and a2 are satisfied:
(a1) an angle θ1 between the absorption axis of the first polarizer and the absorption axis of the polarizer to be inspected is within a range of 90°±5°;
(a2) the angle θ2 between the absorption axis of the test polarizer and the absorption axis of the second polarizer is within the range of 90°±35°;
An arrangement step of arranging the
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; or (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,
and a determination step of determining a defect in the optical film based on a result of the detection step.

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

[3] The optical film is
Further comprising a protective film made of a polyethylene terephthalate resin,
the angle between the orientation axis of the protective film and the absorption axis of the polarizer to be inspected is within a range of 90°±30°;
In the placing step,
The optical film is oriented such that the surface of the protective film opposite to the polarizer to be inspected faces the second filter, and
The protective film is disposed so that an angle between the orientation axis of the protective film and the absorption axis of the second polarizer is within a 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 has a λ/4 phase difference layer,
The defect inspection method according to any one of [1] to [4], wherein in the positioning step, the optical film and the first filter are positioned such that their λ/4 retardation layers face each other without being sandwiched between the inspected polarizer and the first polarizer.

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

The defect inspection method and defect inspection device of the present invention can detect unevenness in the optical properties of optical films.

FIG. 1 is a diagram showing a defect inspection system according to an embodiment of the present invention. 1 is a schematic diagram of a defect inspection apparatus according to an embodiment of the present invention. FIG. 2 is a diagram showing an example of a defective area in an optical film. 1 is a cross-sectional view showing an example of a layer structure of a polarizing plate with a protection film to be inspected in a first application example. FIG. 13 is a cross-sectional view showing an example of a layer structure of a polarizing plate to be inspected in a second application example. FIG.

The present invention relates to a method and apparatus for inspecting defects in an optical film having a polarizer to be inspected.
The defect inspection method according to the present invention includes using a first filter having a first polarizer, a second filter having a second polarizer, and a light source,
The first filter, the optical film, and the second filter are arranged in this order, and the following conditions a1 and a2 are satisfied:
(a1) an angle θ1 between the absorption axis of the first polarizer and the absorption axis of the polarizer to be inspected is within a range of 90°±5°;
(a2) the angle θ2 between the transmission axis of the inspected polarizer and the absorption axis of the second polarizer is within the range of 90°±35°;
An arrangement step of arranging the
Step b1 or step b2 below:
(b1) detecting light that is irradiated from the light source and that is transmitted through the first filter, the optical film, and the second filter in this order;
(b2) detecting light that is irradiated from the light source and that is transmitted through the second filter, the optical film, and the first filter in this order;
a detection step,
and a determination step of determining whether or not the optical film has a defect based on the result of the detection step.

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

Embodiments of the defect inspection device and defect inspection method of the present invention will be described below with reference to the drawings. Identical elements are given the same reference numerals, and duplicate explanations will be omitted. The dimensional ratios in the drawings do not necessarily match those in the description.

Figure 1 is a schematic diagram of a defect inspection system including a defect inspection device according to one embodiment. The defect inspection system 1 includes a transport section 2 and a defect inspection device 3A, and inspects the optical film 100 for defects using the defect inspection device 3A arranged on the transport path while transporting a strip-shaped optical film 100 in its longitudinal direction using the transport section 2. The optical film 100 includes a polarizer to be inspected.

The transport unit 2 has transport rollers R. In addition to the transport rollers R, the transport unit 2 may also be equipped with a tensioning device that applies tension to the transported optical film 100. 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. The Z direction indicates a direction perpendicular to both the X direction and the Y direction. Similar XYZ orthogonal coordinates may also be used in explanations of other drawings.

As shown in FIG. 1, the defect inspection system 1 may include a marking device 4. The marking device 4 is a device that uses defect information sent from the defect inspection device 3A to mark the optical film 100 with a mark M. The marking device 4 has, for example, an arm that extends along the width direction X of the optical film 100 and a marker head having a pen or the like. The mark M is marked on the optical film 100 by the marker head moving on the arm in the width direction X. The marking device 4 may be configured to be controlled by the defect inspection device 3A, or the marking device 4 itself may have a control unit such as a computer. The marking device 4 may also 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 device 3A may include a process of detecting defects that may occur during the manufacturing process (including the conveying process) of the optical film 100, as well as a process of creating a defect map showing the positions of the inspected defects in the optical film 100. Defects of the optical film 100 that can be detected in this embodiment include unevenness in optical characteristics, local defects such as localized disturbance of the polarization axis, etc. In the optical film 100, when the polarizer to be inspected is a liquid crystal polarizer, the optical film 100 may have unevenness in optical characteristics due to uneven coating during the manufacturing process. In addition, if air bubbles or foreign matter are mixed in the optical film 100 during the manufacturing process, or if unevenness occurs, this will result in a local defect.

The defect inspection device 3A will be described using Figure 2. Figure 2 is a schematic diagram of the defect inspection device 3A.

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

The polarizer 101 has linear polarization characteristics. 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, light polarized in the transport direction of the optical film 100 (the absorption axis PA0 direction of the polarizer 101) is referred to as the first polarized light, and light polarized in a direction perpendicular to the first polarized light is referred to as the second polarized light.

The defect inspection device 3A includes a light irradiation unit 10A having a light source 11, a first filter 40 having a first polarizer 41, a second filter 50 having a second polarizer 51, and a detection unit 20A having a camera 21. The defect inspection device 3A may include a control device 30 that controls the detection unit 20A. In the following, unless otherwise specified, a form 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 to sandwich the optical film 100. 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° (satisfying the above condition a1). 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° (satisfying the above condition a2).

In FIG. 2, the absorption axis PA0 of the polarizer 101 is indicated by a double-headed arrow, and the direction at 90° to the absorption axis PA0 is indicated by a black circle. In addition, since FIG. 2 shows a 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. As described above, in the present invention, the angle θ1 may be within the range of 90°±5°, and the angle θ2 may be within the range of 90°±35°, but hereinafter, unless otherwise specified, a form in which the angle 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 unit 10A is arranged via a first filter 40 when viewed from the optical film 100, and the detection unit 20A is arranged via a second filter 50 when viewed from the optical film 100. Light emitted from the light source 11 of the light irradiation unit 10A is incident on the inspection area A (see FIG. 1) of the optical film 100 to be inspected via the first filter 40. Light emitted from the inspection area A is incident on the detection unit 20A via the second filter 50. That is, the detection process is performed by the above process b1.

The first filter 40 converts the unpolarized light L1 emitted from the light source 11 into light L2 having a predetermined polarization state.

The light source 11 is not limited as long as it is unpolarized and can output light that does not affect the composition and properties of the optical film 100. Examples of the light source 11 include a metal halide lamp, a halogen transmission light, and a fluorescent lamp. The light source 11 may extend in the width direction of the optical film 100 as shown in FIG. 1. Alternatively, the light irradiation unit 10A may include multiple 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 light contained in the light emitted from the light source 11.

The detection unit 20A has at least one camera 21 that captures an image of the optical film 100. FIG. 1 illustrates an example in which the imaging unit 20A has multiple cameras 21 arranged along the width direction of the optical film 100. The camera 21 is an area sensor camera such as a CCD camera. The camera 21 may be a line sensor camera. When the camera 21 is a line sensor camera, the inspection area A of the optical film 100 can be captured by moving the camera 21 and the optical film 100 relative to each other. The detection unit 20A (specifically, the camera 21) is electrically connected to the control device 30, which controls the imaging timing and inputs the obtained imaging data to the control device 30.

FIGS. 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, but the detection unit 20A may also detect defects by visually inspecting the optical film 100. When the detection unit 20A detects defects visually, a configuration that does not include a control device 30 is preferable.

The control device 30 controls the detection unit 20A. The control device 30 has, for example, a computer (calculation unit). The control device 30 may have a function of performing image processing on the imaging data input from the detection unit 20A to detect defective parts and highlight the defective parts, and a function of creating a defect map showing the defect positions in the image of the optical film 100. In a form in which the defect inspection system 1 includes a marking device 4 as illustrated in FIG. 1, the control device 30 may also be electrically connected to the marking device 4 as illustrated in FIG. 1, and may control the marking device 4 to apply a mark M based on the detected defect information to the optical film 100.

Next, the inspection process for inspecting the optical film 100 using the defect inspection device 3A will be described. When performing defect inspection, light L1 from the light source 11 is irradiated onto the inspection area A of the optical film 100 as light L2, which is the first polarized light, via the first filter 40. A 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 unit 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 observed visually. This is the detection process. After that, based on the detection results from the detection process, defects in the inspection area A of the optical film are judged (judgment process).

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

However, the optical film 100 may have a defective region in which the absorption axis of the polarizer 101 does not coincide with the absorption axis PA0. FIG. 3 shows an example of a defective region B in the optical film 100, and the absorption axis in the defective region B is indicated by a double-headed arrow. The defective region B has an absorption axis (hereinafter referred to as "absorption axis PA3") that does not coincide with the absorption axis PA0. When the defect in the defective region B is an unevenness in the optical properties, it can be assumed that the angle between the absorption axis PA3 in the defective region B and the absorption axis PA0 changes continuously as shown in FIG. 3. In the defective optical film 100, the region having the absorption axis PA0 is called the normal region A1.

In defect region B having absorption axis PA3 that does not coincide with absorption axis PA0, the polarization direction of light L2 is not parallel to the direction of absorption axis PA0 of polarizer 101, and light L2 passes through optical film 100. Light L3 that passes through optical film 100 is polarized light in a direction corresponding to the absorption axis of defect region B of polarizer 101. When the absorption axis of the defect region of polarizer 101 does not have one direction, light L3 contains polarized light in multiple directions. Hereinafter, these are collectively referred to as third polarized light, and some of the multiple polarized light contained in the third polarized light are referred to as 3a polarized light, 3b polarized light, 3c polarized light, ... in order of the angle they make with the first polarized light.

Light L3 is incident on the detection unit 20A as light L4 via the second filter 50. In the second filter 50, the absorption axis PA2 of the second polarizer 51 is in a cross-Nicol state with the absorption axis PA0 of the polarizer 101, so if the light L3 is the first polarized light, it will be incident on the second polarizer 51 and absorbed, but since the light L3 is the third polarized light different from the first polarized light, it will be transmitted through the second filter 50. The light L3 is absorbed in the second filter 50 at a ratio according to its polarization direction and then emitted. 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, ....

The inventors noticed that the degree of polarization of the light that passed through the first filter and the optical film was substantially low. They discovered that by passing such light through a second filter, the contrast ratio between the first polarized light region and the third polarized light region can be increased, and the detection sensitivity can be greatly improved.

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

In the above, the case where the angle θ1 is 90° and the angle θ2 is 90° has been described, but the amount of light L4 differs depending on the magnitude of the angles θ1 and θ2. As long as the angle θ1 is within the range of 90°±5° and the angle θ2 is within the range of 90°±35°, the transmission characteristics of the light L3 in the optical film 100 differ between the normal area A1 and the defective area B, and the transmission characteristics of the light L4 in the second filter 50 differ depending on the absorption axis direction in the defective area B. Therefore, even if the angles θ1 and θ2 are not 90°, the detection unit 20A detects the light L4 reflecting these transmission characteristics, so that 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 defective area.

The defect inspection device 3A has the first filter 40 and the second filter 50, so that unevenness in the optical characteristics can be efficiently detected. Therefore, the manufacturing method of the optical film 100 including the above-mentioned defect inspection method can efficiently produce the optical film 100 as a product that does not contain defects.

1 and 2 show an arrangement that satisfies the above condition b1 and in which the above step b1 is performed in the detection step, but the arrangement may also be one in which the positions of the light irradiation unit 10A and the detection unit 20A are swapped and the above step b2 is satisfied. In this case, the light emitted from the light source 11 of the light irradiation unit 10A is incident on the inspection area A of the optical film 100 to be inspected via the second filter 50. The light emitted from the inspection area A is incident on the detection unit 20A via the first filter 40. That is, the above 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 the condition b1 as shown in FIG. 1 and FIG. 2.

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

When manufacturing the optical film 100, the band-shaped polarizer 101, the band-shaped protective film 102, and the band-shaped protective film 103 are transported in the longitudinal direction, while the protective film 102 is laminated to one side of the polarizer 101 and the protective film 103 is laminated to the other side (lamination process). The lamination of the polarizer 101, the protective film 102, and the protective film 103 can be performed, for example, using a pair of lamination rollers. In the lamination process, the protective film 102 and the protective film 103 may be laminated to the polarizer 101 at the same time, or one of the protective film 102 and the protective film 103 may be laminated to the polarizer 101 and then the other may be laminated.

After the lamination process, 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 while being inspected for defects by the defect inspection device 3A (defect inspection process). In the defect inspection process, the optical film 100 is inspected for defects by the defect inspection method described above. In a form in which the defect inspection system 1 includes the marking device 4, a process of applying a mark M to the optical film 100 by the marking device 4 (marking process) may be performed depending on the results of the defect inspection process.

The polarizer 101 can be an absorption-type polarizer that has the property of absorbing linearly polarized light with a vibration plane parallel to its absorption axis and transmitting linearly polarized light with a vibration plane perpendicular to the absorption axis (parallel to the transmission axis). Representative 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 aligned on a uniaxially stretched polyvinyl alcohol-based resin film, etc.

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

The liquid crystal polarizer may be, for example, one described in JP 2016-170368 A. The dichroic dye may have absorption in the wavelength range of 380 to 800 nm, and it is preferable to use an organic dye. The dichroic dye may be, for example, an azo compound. The liquid crystal compound is a liquid crystal compound that can be polymerized while remaining oriented, and may have a polymerizable group in the molecule. In addition, as described in WO 2011/024891, a polarizer may be formed from a dichroic dye having liquid crystallinity. Note that after polymerization (after the formation of a polarizer made of a liquid crystal cured 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. Liquid crystal polarizers can have uneven optical properties due to uneven application of the liquid composition during the manufacturing process. The defect inspection method and defect inspection device of this embodiment can detect such uneven optical properties.

Next, a brief description of PVA-based polarizing films will be given. PVA-based polarizing films can be produced, for example, by a method including a step of uniaxially stretching a PVA-based resin film; a step of dyeing the PVA-based resin film with a dichroic dye to adsorb the dichroic dye (dyeing process); a step of treating the PVA-based resin film with the adsorbed dichroic dye with a crosslinking liquid such as an aqueous boric acid solution (crosslinking process); and a step of washing with water after the treatment with the crosslinking liquid (washing process).

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, as well as copolymers of vinyl acetate with other monomers that can be copolymerized with vinyl acetate. Examples of other monomers that can be copolymerized with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and (meth)acrylamides having an ammonium group.

In this specification, "(meth)acrylic" means at least one selected from acrylic and methacrylic. The same applies to "(meth)acryloyl" and "(meth)acrylate", etc.

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

A film made from such a PVA-based resin is used as the raw film (PVA-based resin film) for manufacturing a polarizer. The method for making the PVA-based resin film is not particularly limited, and any known method can be used. The thickness of the PVA-based resin film is not particularly limited, but in order to make the thickness of the polarizing film 15 μm or less, it is preferable to use one having a thickness of 5 to 35 μm. More preferably, it is 20 μm or less. The thickness of such a PVA-based resin film can be selected so that the final PVA-based polarizing film has the desired thickness.

The uniaxial stretching of the PVA-based resin film may be performed before, simultaneously with, or after the dyeing process with a dichroic dye. When the uniaxial stretching is performed after the dyeing process, the uniaxial stretching may be performed before or during the crosslinking process. Moreover, the uniaxial stretching may be performed multiple times at these multiple processing stages.

In the case of uniaxial stretching, when a long PVA-based resin film is used, for example, the PVA-based resin film may be stretched uniaxially between rolls by varying the peripheral speed of the rolls, or may be stretched uniaxially using a heated roll. The uniaxial stretching may be dry stretching in which stretching is performed in the atmosphere, or wet stretching in which stretching is performed in a state in which the PVA-based resin film is swollen with a solvent or water. The stretching ratio is usually 3 to 8 times. When the PVA-based resin film is stretched by multiple uniaxial stretchings, the stretching ratio is usually set to 3 to 8 times the original length. This stretching ratio can also be selected so that the final PVA-based polarizing film has the desired thickness.

A typical method for dyeing a PVA-based resin film with a dichroic dye (dyeing process) is to immerse the PVA-based resin film in an aqueous solution containing the dichroic dye. Iodine or a dichroic organic dye is used as the dichroic dye. It is preferable to immerse the PVA-based resin film in water before the dyeing process.

As a crosslinking treatment after dyeing with a dichroic dye, a method such as immersing the dyed PVA-based resin film in an aqueous solution containing boric acid is usually adopted. When iodine is used as the dichroic dye, it is preferable that the aqueous solution containing boric acid contains potassium iodide.

Thus, a PVA-based polarizing film is obtained. As with the liquid crystal polarizer, the thickness of the PVA-based polarizing film is preferably thinner, preferably 15 μm or less, more preferably 13 μm or less, even more preferably 10 μm or less, and particularly preferably 8 μm or less. The thickness of the polarizing film is usually 2 μm or more, and preferably 3 μm or more.

A linear polarizer can be used as a polarizing plate (optical film) by itself, or as described above, a linear polarizer can generally be used as a polarizing plate (optical film) by laminating a protective film on one or both sides thereof. For example, a transparent resin film is used as the protective film, and examples of transparent resins constituting such a resin film include acetylcellulose-based resins such as triacetylcellulose and diacetylcellulose, methacrylic resins such as polymethyl methacrylate, polyester resins, polyolefin-based resins, polycarbonate resins, polyether ether ketone resins, polysulfone resins, and the like. Of these, a resin film made of multiple types 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. The first polarizer 41 and the second polarizer 50 can be absorption-type polarizers that absorb linearly polarized light having a vibration plane parallel to the absorption axis and transmit linearly polarized light having a vibration plane perpendicular to the absorption axis (parallel to the transmission axis) like the above-mentioned polarizer 101. A representative polarizer is a polarizing film in which a dichroic dye is adsorbed and aligned on a uniaxially stretched PVA-based resin film. The detailed description of the polarizing film is the same as that of the polarizing film in the above-mentioned polarizer 101. The first polarizer and the second polarizer are defect-free.

[First Application Example]
In the first application example, a suitable application example of this embodiment will be described in which the optical film inspected by the defect inspection device 3A is a polarizing plate with a protective film having a protective film made of a polyethylene terephthalate resin.

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

The protective film 120 is a film for protecting the surface of the polarizing plate 100, and is peeled off and removed together with its adhesive layer after the polarizing plate with protective film is attached to an image display element such as a liquid crystal cell or other optical components.

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 coincides with the uniaxial stretching direction of the base film and exhibits birefringence. Therefore, a phase difference occurs in the light that passes through the protection film 120. In the detection unit 20A, if the incident light has birefringence, the detection accuracy of defects decreases.

When the target of defect inspection using the defect inspection method and defect inspection device of the present embodiment shown in Figures 1 and 2 is a polarizing plate with a protect film 110, the inspection is performed so that the protect film 120 side of the polarizing plate with a protect film 110 is located on the second filter 50 side, and the light source is arranged so that the direction of irradiation of light from the light source in the detection process is from the first filter 40 side (satisfying the above condition b1), and the detection process is preferably performed in the above step b1. That is, it is preferable to transmit light from the light source 11 in the direction of the arrow shown in Figure 4. This is because the second filter 50 can be arranged by appropriately adjusting the angle θ2 between the absorption axis of the second polarizer 51 and the absorption axis of the polarizer 101, which is the polarizer to be inspected, within the range of 90°±35°, thereby reducing the phase difference caused by the protect film 120. The phase difference generated in the light transmitted through the protect film 120 is reduced by the second filter 50 and enters the detection unit 20A.

In this application example, even if the object to be inspected is a polarizing plate with a protective film having a protective film made of polyethylene terephthalate resin, it is possible to suppress a decrease in the accuracy of defect detection by the detection unit 20A.

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

For a polarizing plate with a protective film manufactured to satisfy the above condition c1, it is preferable to arrange the protective film in the above arrangement step so that the angle between the orientation axis of the protective film and the absorption axis of the second polarizer 51 of the second filter 50 is 90°±5°. With this arrangement, the second filter 50 can effectively reduce the phase difference caused by the protective film 120.

For a polarizing plate with a protective film manufactured to satisfy the above condition c2, it is preferable to arrange the protective film in the above arrangement step so that the angle between the orientation axis of the protective film and the absorption axis of the second polarizer of the second filter is 0°±5°. With this arrangement, the second filter 50 can effectively reduce the phase difference caused by the protective film 120.

To perform defect inspection using the defect inspection method and defect inspection device of this embodiment, it is preferable that the orientation axis of the protect film of the polarizing plate with protect film is consistent throughout the entire region, but usually the orientation axes do not coincide throughout the entire region. It is preferable that the protect film has a maximum angle between the different orientation axes of 25° or less. This is because polarizing plates using such a protect film are more likely to suppress a decrease in the detection accuracy of the defect inspection performed using the defect inspection method and defect inspection device of this embodiment.

[Second Application Example]
In the second application example, a suitable application example of this 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.

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

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

The polarizing plate 130 of the second application example may be configured as a circular polarizing plate having a λ/4 retardation layer. The circular polarizing plate can be used as an anti-reflection polarizing plate.

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

When the object to be inspected for defects using the defect inspection method and defect inspection device of this embodiment shown in Figures 1 and 2 is a polarizing plate 130, the polarizing plate 130 is arranged so that the retarder 140 side is located on the first filter 40 side and inspection is performed. That is, light from the light source 11 is transmitted in the direction of the arrow shown in Figure 5. In addition, as the first filter 40, one having 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 so that their λ/4 retardation layers face each other without the polarizer 103 and the first polarizer 41. Since the first filter 40 has a λ/4 retardation layer, the section through which light transmits as circularly polarized light is only between the λ/4 retardation layer of the first filter 40 and the λ/4 retardation layer of the polarizing plate 130, and even if the object to be inspected is a polarizing plate having a λ/4 retardation layer, it is possible to detect defects using the same principle as the principle of this embodiment.

In addition, only when the object to be inspected is the polarizing plate 130 (i.e., only when it is a circular polarizing plate), the crossed Nicol state can be obtained even if the absorption axis of the first polarizer of the first filter and the absorption axis of the polarizer of the polarizing plate 130, and the slow axis of the λ/4 retardation layer of the first filter and the slow axis of the λ/4 retardation layer of the polarizing plate 130 are all arranged parallel to each other.

In this application example, when defect detection is performed to detect defects in the polarizing plate 130, the light source may be irradiated from the first filter 40 side (arrangement of condition b1, detection process by process b1) or from the second filter 50 side (arrangement of condition b2, detection process by process b2). In order to detect unevenness in the optical properties of the polarizer 101 of the polarizing plate 130, it is preferable to irradiate light from the light source from the first filter side 40. When irradiated from the first filter side 40, defects in the retarder 140 are not reflected in the detection light incident on the detection unit 20A, but when irradiated from the second filter side 50, defects in the retarder 140 are reflected in the detection light incident on the detection unit 20A, which may reduce the detection accuracy of unevenness in the optical properties of the polarizer 101.

1 Defect inspection system, 2 Conveyor section, 3A Defect inspection device, 4 Marking device, 10A Light irradiation section, 11 Light source, 20A Detection section, 21 Camera, 30 Control device, 40 First filter, 41 First polarizer, 50 Second filter, 51 Second polarizer, 100 Polarizing plate, 101 Polarizer, 102, 103 Protective film, 110 Polarizing plate with protective film, 120 Protective film, 130 Polarizing plate, 140 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 steps of:
The defect inspection method includes using a first filter having a first polarizer, a second filter having a second polarizer, and a light source;
The first filter, the optical film, and the second filter are arranged in this order, and the following conditions a1 and a2 are satisfied:
(a1) an angle θ1 between the absorption axis of the first polarizer and the absorption axis of the polarizer to be inspected is within a range of 90°±5°;
(a2) the angle θ2 between the absorption axis of the test polarizer and the absorption axis of the second polarizer is within the range of 90°±35°;
and arranging the first polarizer and the second polarizer so that the absorption axis of the first polarizer and the absorption axis of the second polarizer are not parallel to each other;
Step b1 below:
(b1) detecting light that is irradiated from the light source and that is transmitted through the first filter, the optical film, and the second filter in this order;
a detection step,
a determination step of determining a defect in the optical film based on a detection result in the detection step,
The optical film is
Further comprising a protective film made of a polyethylene terephthalate resin,
the angle between the orientation axis of the protective film and the absorption axis of the polarizer to be inspected is within the range of 0°±30°;
The alignment axis is a slow axis,
In the placing step,
The optical film is oriented such that the surface of the protective film opposite to the polarizer to be inspected faces the second filter, and
The protective film is disposed so that an angle between the orientation axis of the protective film and the absorption axis of the second polarizer is within a range of 90°±5°.
Defect inspection methods. A defect inspection method for an optical film having a polarizer to be inspected, comprising the steps of:
The defect inspection method includes using a first filter having a first polarizer, a second filter having a second polarizer, and a light source;
The first filter, the optical film, and the second filter are arranged in this order, and the following conditions a1 and a2 are satisfied:
(a1) an angle θ1 between the absorption axis of the first polarizer and the absorption axis of the polarizer to be inspected is within a range of 90°±5°;
(a2) the angle θ2 between the absorption axis of the test polarizer and the absorption axis of the second polarizer is within the range of 90°±35°;
and arranging the first polarizer and the second polarizer so that the absorption axis of the first polarizer and the absorption axis of the second polarizer are not parallel to each other;
Step b1 below:
(b1) detecting light that is irradiated from the light source and that is transmitted through the first filter, the optical film, and the second filter in this order;
a detection step,
a determination step of determining a defect in the optical film based on a detection result in the detection step,
The optical film is
Further comprising a protective film made of a polyethylene terephthalate resin,
the angle between the orientation axis of the protective film and the absorption axis of the polarizer to be inspected is within a range of 90°±30°;
The alignment axis is a slow axis,
In the placing step,
The optical film is oriented such that the surface of the protective film opposite to the polarizer to be inspected faces the second filter, and
The protective film is disposed so that an angle between the orientation axis of the protective film and the absorption axis of the second polarizer is within a range of 0°±5°.
Defect inspection methods. The defect inspection method according to claim 1 or 2, wherein the polarizer to be inspected includes a cured product of a polymerizable liquid crystal compound. The optical film further comprises a λ/4 retardation layer,
In the defect inspection method, the first filter has a λ/4 phase difference layer,
4. The defect inspection method according to claim 1, wherein in the positioning step, the optical film and the first filter are positioned such that their λ/4 retardation layers face each other without being sandwiched between the inspected polarizer and the first polarizer. An apparatus for inspecting defects in an optical film having a polarizer to be inspected, comprising:
the defect inspection apparatus includes a first filter having a first polarizer, a second filter having a second polarizer, and a light source;
The first filter, the optical film, and the second filter are arranged in this order and satisfy the following conditions a1 and a2:
(a1) an angle θ1 between the absorption axis of the first polarizer and the absorption axis of the polarizer to be inspected is within a range of 90°±5°;
(a2) the angle θ2 between the transmission axis of the inspected polarizer and the absorption axis of the second polarizer is within the range of 90°±35°;
are arranged so as to satisfy
The light source satisfies the following condition b1:
(b1) light emitted from the light source is transmitted through the first filter, the optical film, and the second filter in this order;
and the absorption axis of the first polarizer and the absorption axis of the second polarizer are not parallel to each other.
The optical film is
Further comprising a protective film made of a polyethylene terephthalate resin,
the angle between the orientation axis of the protective film and the absorption axis of the polarizer to be inspected is within the range of 0°±30°;
The alignment axis is a slow axis,
In the defect inspection apparatus,
The optical film is oriented such that the surface of the protective film opposite to the polarizer to be inspected faces the second filter, and
The protective film is disposed so that the angle between the orientation axis of the protective film and the absorption axis of the second polarizer is within a range of 90°±5°.
Defect inspection equipment. An apparatus for inspecting defects in an optical film having a polarizer to be inspected, comprising:
the defect inspection apparatus includes a first filter having a first polarizer, a second filter having a second polarizer, and a light source;
The first filter, the optical film, and the second filter are arranged in this order and satisfy the following conditions a1 and a2:
(a1) an angle θ1 between the absorption axis of the first polarizer and the absorption axis of the polarizer to be inspected is within a range of 90°±5°;
(a2) the angle θ2 between the transmission axis of the inspected polarizer and the absorption axis of the second polarizer is within the range of 90°±35°;
are arranged so as to satisfy
The light source satisfies the following condition b1:
(b1) light emitted from the light source is transmitted through the first filter, the optical film, and the second filter in this order;
and the absorption axis of the first polarizer and the absorption axis of the second polarizer are not parallel to each other.
The optical film is
Further comprising a protective film made of a polyethylene terephthalate resin,
the angle between the orientation axis of the protective film and the absorption axis of the polarizer to be inspected is within a range of 90°±30°;
The alignment axis is a slow axis,
In the defect inspection apparatus,
The optical film is oriented such that the surface of the protective film opposite to the polarizer to be inspected faces the second filter, and
The protective film is disposed so that the angle between the orientation axis of the protective film and the absorption axis of the second polarizer is within a range of 0°±5°.
Defect inspection equipment.

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