CN116648618A - Defect inspection method and defect inspection apparatus - Google Patents

Abstract

The present invention is a defect inspection method for a linear polarizing plate, the method comprising the steps of: the optical film is arranged in the direction in which the surface on the release film side faces the phase difference compensation plate, the 1 st optical filter having the 1 st polarizing plate, the 1 st phase difference compensation plate, the optical film, the 2 nd phase difference compensation plate, and the 2 nd optical filter having the 2 nd polarizing plate are arranged in this order along the optical axis, the 1 st phase difference compensation plate compensates for the birefringence of the release film, and the 2 nd phase difference compensation plate compensates for the birefringence of the protective film.

Description

Defect inspection method and defect inspection apparatus

Technical Field

The present invention relates to a defect inspection method and a defect inspection apparatus for a linear polarizing plate using an optical film as an object to be inspected.

Background

Polarizing plates used in display devices such as liquid crystal display devices and organic EL display devices are generally composed of a polarizing plate sandwiched between 2 protective films. In order to attach the polarizing plate to a display device, an adhesive layer may be laminated on one protective film, and a protective film for preventing damage or the like from occurring on the surface of the protective film during circulation may be laminated on the other protective film. A release film is typically laminated on the adhesive layer. Specific examples of the polarizing plate include a PVA-based polarizing film in which a dichroic dye such as iodine or a dichroic dye is adsorbed and oriented to a uniaxially stretched polyvinyl alcohol-based (PVA-based) resin film, a polarizing plate (hereinafter, also referred to as a "liquid crystal polarizing plate") formed of a liquid crystal cured layer of a polymer containing a polymerizable liquid crystal compound and a dichroic dye, and the like. The liquid crystal polarizing plate is generally formed by coating a composition containing a polymerizable liquid crystal compound on a base film and curing the same, and has an advantage that a thin polarizing plate can be manufactured. Such PVA polarizing films and liquid crystal polarizers are called "linear polarizers" because they pass linearly polarized light having a specific vibration plane, as will be described later. In addition, a member having a protective film on one or both surfaces of the linear polarizer is generally called a "linear polarizing plate".

Polarizing plates and polarizing plates may have defects at the stage of their production. For example, there are cases where a defect such as a foreign matter or a residual bubble is mixed between the polarizing plate and the protective film. In addition, the liquid crystal polarizing plate may have uneven optical characteristics due to uneven coating during manufacturing.

Therefore, at a stage before the polarizing plate is assembled to the display device, inspection for detecting defects of the polarizing plate is performed. As shown in japanese patent application laid-open No. 9-229817 (patent document 1), this defect is inspected by providing a polarizing filter between a polarizing plate as an object to be inspected and a light source, then rotating the polarizing plate or the polarizing filter in a plane direction, and setting the respective polarization axis directions to a specific relationship. In the case where the polarization axis directions are orthogonal to each other (i.e., in the case of the arrangement constituting the crossed nicols), the linearly polarized light passing through the polarizing filter does not transmit the polarizing plate. However, if there is a defect in the polarizing plate, linearly polarized light is transmitted at that location, and thus the presence of the defect is recognized by detecting the light.

On the other hand, in the case where the polarization plate and the polarization filter are parallel to each other in the polarization axis direction, the linearly polarized light passing through the polarization filter transmits the polarization plate. However, if there is a defect in the polarizing plate, the linearly polarized light is blocked at that location, and therefore the presence of the defect is recognized by failing to detect the light.

The inspector can visually detect the light transmitted through the polarizing plate or automatically detect the light transmitted through the polarizing plate by an image analysis processing value obtained by combining a CCD camera with an image processing device, thereby making it possible to inspect whether the polarizing plate is defective.

Prior art literature

Patent literature

Patent document 1: japanese patent laid-open No. 9-229817

Disclosure of Invention

Problems to be solved by the invention

According to the method described in patent document 1, although a local defect having a large difference in optical characteristics from the surrounding area such as the contamination of foreign matter or bubbles can be detected, it is difficult to detect the unevenness of the optical characteristics.

In addition, in a state where the protective film and the release film are laminated, it is difficult to detect defects of the polarizing plate due to the influence of birefringence of the protective film and the release film.

The present invention aims to provide a defect inspection method and a defect inspection apparatus capable of detecting non-uniformity of optical characteristics of a linear polarizing plate when an optical film in which a protective film and a release film are laminated on the linear polarizing plate is used as an inspected object.

Means for solving the problems

The present invention provides a defect inspection method and a defect inspection apparatus shown below.

[ 1 ] A defect inspection method for a linear polarizing plate, comprising using an optical film having the linear polarizing plate as an object to be inspected,

The optical film comprises a release film, the linear polarizing plate and a protective film in this order,

the defect inspection method includes:

a disposing step of disposing a 1 st filter having a 1 st polarizing plate, a 1 st phase difference compensation plate, the optical film, a 2 nd phase difference compensation plate, and a 2 nd filter having a 2 nd polarizing plate in this order along an optical axis, and disposing the optical film in an orientation in which a surface of the release film side faces the 1 st phase difference compensation plate;

a detection step of detecting light incident along the optical axis from either one of the 1 st filter side and the 2 nd filter side and light emitted from the other side; and

a judging step of judging a defect of the optical film based on a detection result in the detecting step,

in the above-described arrangement step, the arrangement is performed so as to satisfy the following conditions a and b:

(a) An angle formed between an absorption axis of the 1 st polarizer and an absorption axis of the linear polarizer is within a range of 90 DEG + -5 DEG;

(b) An angle formed between the absorption axis of the 2 nd polarizer and the absorption axis of the linear polarizer is within a range of 90 DEG + -30 DEG,

in the above-mentioned detection step, the step of detecting,

the 1 st phase difference compensation plate compensates for the birefringence of the release film, and the 2 nd phase difference compensation plate compensates for the birefringence of the protective film.

The method for inspecting defects according to [ 2 ], wherein the release film comprises a polyethylene terephthalate resin.

The method for inspecting defects according to [ 1 ] or [ 2 ], wherein the protective film comprises a polyethylene terephthalate resin.

The method for inspecting defects according to any one of [ 1 ] to [ 3 ], wherein the linear polarizing plate has a polarizing plate comprising a cured product of a polymerizable liquid crystal compound.

The method for inspecting defects according to any one of [ 1 ] to [ 4 ], wherein the optical film further comprises a lambda/4 retardation layer between the linear polarizing plate and the release film,

in the disposing step, a λ/4 phase difference plate is disposed between the 1 st filter and the 1 st phase difference compensation plate.

[ 6 ] A defect inspection apparatus for a linear polarizing plate, comprising an optical film having the linear polarizing plate as an object to be inspected,

the optical film comprises a release film, the linear polarizing plate and a protective film in this order,

the defect inspection apparatus includes, in order along an optical axis: a 1 st filter having a 1 st polarizing plate, a 1 st phase difference compensation plate capable of compensating for birefringence of the release film, a 2 nd phase difference compensation plate capable of compensating for birefringence of the protective film, and a 2 nd filter having a 2 nd polarizing plate, and a light source capable of irradiating light from the 1 st filter side or the 2 nd filter side along the optical axis, wherein defect inspection is performed after an arrangement step of arranging the optical film in an orientation in which a surface of the release film side faces the 1 st phase difference compensation plate,

In the above-described arrangement step, the arrangement is performed so as to satisfy the following conditions a and b:

(a) An angle formed between an absorption axis of the 1 st polarizer and an absorption axis of the linear polarizer is within a range of 90 DEG + -5 DEG;

(b) The absorption axis of the 2 nd polarizer and the absorption axis of the linear polarizer form an angle within a range of 90 DEG + -30 deg.

Effects of the invention

According to the defect inspection method and the defect inspection apparatus of the present invention, when an optical film in which a protective film and a release film are laminated on both surfaces of a linear polarizing plate is used as an inspection object, it is possible to detect unevenness in optical characteristics of the linear polarizing plate.

Drawings

Fig. 1 is a cross-sectional view schematically showing an optical film as an example of an object to be inspected according to the present embodiment.

Fig. 2 is a schematic diagram of the defect inspection apparatus of the present embodiment.

Fig. 3 is a diagram showing an example of a defective region in the optical film.

Fig. 4 is a cross-sectional view schematically showing an optical film as an example of an object to be inspected in application example 1.

Detailed Description

The present invention relates to a defect inspection method and a defect inspection apparatus for a linear polarizing plate, in which an optical film having the linear polarizing plate is used as an object to be inspected. Examples of the object to be inspected in the defect inspection method and the defect inspection apparatus of the present invention include an optical film having a release film, a linear polarizing plate, and a protective film in this order.

The defect inspection method of the present invention using an optical film as an inspected object includes:

a disposing step of disposing a 1 st filter having a 1 st polarizing plate, a 1 st phase difference compensation plate, the optical film, a 2 nd phase difference compensation plate, and a 2 nd filter having a 2 nd polarizing plate in this order along an optical axis, and disposing the optical film in an orientation in which a surface of the release film side faces the 1 st phase difference compensation plate;

a detection step of detecting light incident along the optical axis from either one of the 1 st filter side and the 2 nd filter side and light emitted from the other side; and

a judging step of judging a defect of the optical film based on a detection result in the detecting step,

in the above-described arrangement step, the arrangement is performed so as to satisfy the following conditions a and b:

(a) An angle formed between an absorption axis of the 1 st polarizer and an absorption axis of the linear polarizer is within a range of 90 DEG + -5 DEG;

(b) The absorption axis of the 2 nd polarizer and the absorption axis of the linear polarizer form an angle within a range of 90 DEG + -30 deg.

In the detecting step, the 1 st phase difference compensation plate compensates for the birefringence of the release film, and the 2 nd phase difference compensation plate compensates for the birefringence of the protective film.

The defect inspection apparatus of the present invention can be used in the above defect inspection method,

the defect inspection apparatus of the present invention includes, in order along an optical axis: a 1 st filter having a 1 st polarizing plate, a 1 st phase difference compensation plate capable of compensating for birefringence of the release film, a 2 nd phase difference compensation plate capable of compensating for birefringence of the protective film, and a 2 nd filter having a 2 nd polarizing plate, and a light source capable of irradiating light from the 1 st filter side or the 2 nd filter side along the optical axis, wherein defect inspection is performed after an arrangement step of arranging the optical film in an orientation in which a surface of the release film side faces the 1 st phase difference compensation plate,

in the above-described configuration step, the first step is performed,

configured in such a manner that the following condition a and condition b are satisfied:

(a) An angle formed between an absorption axis of the 1 st polarizer and an absorption axis of the linear polarizer is within a range of 90 DEG + -5 DEG;

(b) The absorption axis of the 2 nd polarizer and the absorption axis of the linear polarizer form an angle within a range of 90 DEG + -30 deg.

Hereinafter, embodiments of a defect inspection apparatus and a defect inspection method according to the present invention will be described with reference to the accompanying drawings. The same elements are denoted by the same reference numerals, and repetitive description thereof will be omitted. The dimensional ratios in the drawings are not necessarily consistent with the dimensional ratios described.

A defect inspection apparatus and a defect inspection method according to an embodiment of the present invention will be described.

[ optical film ]

An optical film as an object to be inspected in this embodiment will be described. Fig. 1 is a cross-sectional view schematically showing an optical film 100 as an example of the optical film. As shown in fig. 1, the layer structure of the optical film 100 is a protective film 141/a linear polarizing plate 110 [ 1 st protective film 111/an adhesive layer 114/a polarizing plate 112/an adhesive layer 114/2 nd protective film 113 ]/an adhesive layer 132/a release film 133.

(polarizing plate)

The polarizing plate 112 may be an absorption type polarizing plate having a property of absorbing linearly polarized light having a vibration plane parallel to an absorption axis thereof and transmitting linearly polarized light having a vibration plane orthogonal to the absorption axis (parallel to a transmission axis). Typical polarizing plates include a liquid crystal polarizing plate including a cured product of a polymerizable liquid crystal compound, a polarizing film obtained by adsorption-orienting a dichroic dye to a uniaxially stretched polyvinyl alcohol resin film, and the like.

A typical manufacturing method of the liquid crystal polarizing plate will be briefly described. First, an appropriate 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 the liquid composition is dried, thereby forming a coating layer containing the polymerizable liquid crystal compound on the alignment film. Then, the coating layer is polymerized and cured by light irradiation, and a liquid crystal polarizing plate is obtained on the support. If a transparent resin film is used as the support, a polarizing plate having the transparent resin film as a protective film can be produced.

The liquid crystal polarizer may be, for example, one described in Japanese patent application laid-open No. 2016-170368. As the dichroic dye, a dichroic dye having absorption in a wavelength range of 380 to 800nm can be used, and an organic dye is preferably used. Examples of the dichroic dye include azo compounds. The liquid crystal compound is a liquid crystal compound capable of polymerizing while maintaining alignment, and may have a polymerizable group in a molecule. Further, as described in WO201I/024891, a polarizing plate may be formed of a dichroic dye having liquid crystallinity. After polymerization (after formation of a polarizing plate including a liquid crystal cured layer), the liquid crystal compound is not required to exhibit liquid crystallinity.

The thickness of the liquid crystal polarizer is, for example, 0.2 μm to 10. Mu.m. The liquid crystal polarizing plate may have uneven optical characteristics due to uneven application of the liquid composition in the manufacturing process. In the defect inspection method and the defect inspection apparatus according to the present embodiment, such unevenness in optical characteristics can be detected.

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

As the PVA-based resin, a PVA-based resin obtained by saponifying a polyvinyl acetate-based resin can be used. Examples of the polyvinyl acetate resin include, in addition to polyvinyl acetate which is a homopolymer of vinyl acetate, copolymers of vinyl acetate and other copolymerizable monomers. 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, and the like.

In the present specification, "(meth) acrylic acid" means at least one selected from acrylic acid and methacrylic acid. The same applies to "(meth) acryl", "(meth) acrylate", and the like.

The saponification degree of the PVA-based resin is usually 85 to 100mol%, preferably 98mol% or more. The PVA-based resin may be modified, and for example, polyvinyl formal or polyvinyl acetal modified with aldehydes may be used. The average polymerization degree of the PVA-based resin is usually 1000 to 10000, preferably 1500 to 5000. The average polymerization degree of the PVA-based resin can be determined in accordance with JIS K6726.

Such a PVA-based resin film can be used as a raw material film (PVA-based resin film) for producing a polarizing plate. The method for forming the PVA-based resin into a film is not particularly limited, and a known method can be used. The thickness of the PVA-based resin film is not particularly limited, and in order to make the thickness of the polarizing film 15 μm or less, a PVA-based resin film of 5 to 35 μm is preferably used. More preferably 20 μm or less. The thickness of the PVA-based resin film may 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, may be performed simultaneously with the dyeing treatment, or may be performed after the dyeing treatment. In the case of uniaxial stretching after the dyeing treatment, the uniaxial stretching may be performed before the crosslinking treatment or may be performed during the crosslinking treatment. In addition, the uniaxial stretching may be performed by dividing the stretching into a plurality of steps in these multiple steps.

In the case of using a long PVA-based resin film in uniaxial stretching, for example, the PVA-based resin film may be stretched uniaxially between rolls by laying the film on rolls to vary the peripheral speed of the rolls, or may be stretched uniaxially using a hot roll. The uniaxial stretching may be a dry stretching in which stretching is performed in the atmosphere, or a 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 stretching, the stretching ratio is usually set to 3 to 8 times as large as the original length. The stretching ratio may be selected so that the PVA-based polarizing film to be finally obtained has a desired thickness.

As a method of dyeing a PVA-based resin film with a dichroic dye (dyeing treatment), a method of immersing the PVA-based resin film in an aqueous solution containing a dichroic dye is typically employed. As the dichroic dye, iodine and a dichroic organic dye can be used. The PVA-based resin film is preferably subjected to a dipping treatment in water prior to the dyeing treatment.

As the crosslinking treatment after the dyeing treatment with the dichroic dye, a method of immersing the dyed PVA-based resin film in an aqueous solution containing boric acid is generally used. In the case of using iodine as the dichroic dye, the aqueous solution containing boric acid preferably contains potassium iodide.

Thus, a PVA-based polarizing film can be obtained. The thickness of the PVA-based polarizing film is preferably a thinner film, preferably 15 μm or less, more preferably 13 μm or less, further preferably 10 μm or less, particularly preferably 8 μm or less, similar to the liquid crystal polarizing plate. The thickness of the polarizing film is usually 2 μm or more, preferably 3 μm or more.

The linear polarizer may be formed as a single linear polarizer, and as described above, the linear polarizer may be generally formed by bonding a protective film to one or both surfaces of the linear polarizer. In this specification, the absorption axis of the linear polarizing plate coincides with the absorption axis of the polarizing plate 112.

(protective film)

As the protective films (for example, the 1 st protective film 111 and the 2 nd protective film 113) laminated on one or both surfaces of the polarizing plate 112, films made of thermoplastic resins are used.

Specific examples of such thermoplastic resins include cellulose resins such as triacetyl cellulose; polyester resins such as polyethylene terephthalate and polyethylene naphthalate; polyether sulfone resin; polysulfone resin; a polycarbonate resin; polyamide resins such as nylon and aromatic polyamide; polyimide resin; polyolefin resins such as polyethylene, polypropylene, and ethylene-propylene copolymers; a cyclic polyolefin resin having a ring system and a norbornene structure (also referred to as a norbornene-based resin); (meth) acrylic resins; a polyarylate resin; a polystyrene resin; polyvinyl alcohol resins, and mixtures thereof. In the case where the protective films are laminated on both surfaces of the polarizing plate, the resin compositions of the two protective films may be the same or different.

The thickness of the protective film is preferably 3 μm or more, more preferably 5 μm or more. The thickness of the protective film is usually 100 μm or less. The thickness of the protective film is preferably a thinner film, and may be, for example, 70 μm or less, more preferably 50 μm or less, and still more preferably 30 μm or less. The upper limit value and the lower limit value may be arbitrarily combined.

Since the protective film is bonded to the display device together with the polarizing plate 112 as a constituent of the linear polarizing plate, strict management of the phase difference value and the like are required. As the protective film, a protective film having an extremely small phase difference value can be typically used.

(adhesive layer)

The adhesive layers (e.g., adhesive layers 114, 124) may be formed by curing curable components in the adhesive. The adhesive used for forming the adhesive layer is an adhesive other than a pressure-sensitive adhesive (adhesive), and examples thereof include an aqueous adhesive such as a polyvinyl alcohol-based adhesive and an active energy ray-curable adhesive such as an ultraviolet-curable adhesive. The thickness of the adhesive layer is selected according to the type of adhesive, and may be, for example, 0.05 μm or more, 0.1 μm or more, 0.5 μm or more, 1 μm or more, 3 μm or more, usually 20 μm or less, 15 μm or less, 10 μm or less, or 8 μm or less.

(protective film)

The protective film 141 is provided to be peelable from the linear polarization plate 110, and is used for coating and protecting the surface of the linear polarization plate. As the protective film, a protective film composed of a base film formed using a resin and an adhesive layer laminated thereon is exemplified.

The protective film is a film that is peeled off together with an adhesive layer that the optical film has after being attached to a display device or other optical member, and the peeled protective film is generally discarded. Therefore, unlike the protective film, strict management of the phase difference value is not required. In the defect inspection method according to the present embodiment, even when an optical film including a protective film that does not require strict management of the retardation value is used as an inspection object, the defect of the linear polarization plate can be detected by eliminating the influence of the retardation of the protective film.

The protective film is usually made of a resin, and the resin forming the protective film is not particularly limited, and examples thereof include polyethylene terephthalate resin (PET resin), polybutylene terephthalate resin, polycarbonate resin, polyacrylate resin, and the like, and among these, PET resin can be preferably used. Films comprising PET-based resins are versatile as protective films and have the advantage of being inexpensive.

On the other hand, as described above, the low-cost PET resin film does not require strict management of the phase difference value. Thus, for example, there is a deviation in the phase difference value in each product lot. In addition, even in the same PET resin film, there are some cases where there are variations in the in-plane phase difference value (in-plane phase difference value) and orientation axis.

In this specification, a method for obtaining the in-plane phase difference value Re (550) at the wavelength of 550nm of the protective film is shown. Pieces of 40mm×40mm in size are separated so that the center of the entire protective film is the center (e.g., separated from the long film using an appropriate cutting tool). Re (550) of the sheet was measured 3 times, and the average value of Re (550) was obtained. Re (550) of the sheet was measured in a measuring temperature chamber (about 25 ℃) using a phase difference measuring apparatus KORBRA-WPR (manufactured by Ware measuring instruments Co., ltd.).

The in-plane phase difference Re (550) of the protective film 141 is, for example, 1000nm to 2500nm. This means that the in-plane retardation Re (550) is 1000nm to 2500nm for any sheet of the protective film 141. In the protective film 141, the in-plane phase difference value Re (550) is generally different depending on the patch at the time of measurement.

(Release film)

The release film 133 is provided so as to be peelable with respect to the adhesive layer 132, and covers and protects the surface of the adhesive layer 132. As the release film, a film obtained by subjecting a base film formed using a resin to a release treatment is exemplified. As a mold release treatment to be performed on the substrate film, a known mold release treatment may be performed, and a method of applying a mold release agent such as a fluorine compound or an organosilicon compound to the substrate film is preferable.

The release film 133 is peeled from the adhesive layer 132 when attached to the display device, and the peeled release film is discarded. Therefore, unlike the protective film, strict management of the phase difference value is not required.

The resin to be the base film is not particularly limited, and examples thereof include polyethylene terephthalate resin (PET resin), polybutylene terephthalate resin, polycarbonate resin, and polyacrylate resin, and among them, PET resin is preferably used. Films comprising PET resins are versatile as release films and have the advantage of being inexpensive. On the other hand, as described above, the low-cost PET resin film does not require strict management of the phase difference value. Thus, for example, there is sometimes a deviation in the phase difference value in each product lot. In addition, even in the same PET resin film, there may be a phase difference value (in-plane phase difference value) or a deviation of the orientation axis in the plane. Even in the optical film formed by bonding such a low-cost PET resin film as a release film, the inspection method of the present embodiment can accurately detect the presence or absence of defects. The deviation of the orientation axis in the release film is not particularly limited, and for example, a release film of 135 ° or less may be used. Since the release film 133 is normally released and discarded in the manufacturing process, strict control of the phase difference value is not required as in the case of the protective film.

In the present specification, the method for obtaining the in-plane phase difference value Re (550) at the wavelength of 550nm of the release film is the same as the method for obtaining the in-plane phase difference value Re (550) at the wavelength of 550nm of the protective film. The in-plane phase difference Re (550) of the release film 133 is, for example, 1000nm to 2500nm.

[ Defect inspection apparatus and defect inspection method ]

Fig. 2 is a schematic diagram of the defect inspection apparatus of the present embodiment. As shown in fig. 2, the defect inspection apparatus 1 detects a defect of the linear polarization plate 110 included in the optical film 100 using the optical film 100 as an inspection object. Examples of defects of the linear polarization plate 110 that can be detected by the defect inspection apparatus 1 include unevenness and local defects of the optical characteristics of the linear polarization plate 110.

In the case where the polarizing plate 112 is a liquid crystal polarizing plate, the linear polarizing plate 110 may have uneven optical characteristics due to uneven coating in the manufacturing process. In addition, if bubbles, foreign substances, or irregularities are mixed in the process of manufacturing the linear polarization plate 110, local defects are generated.

The defect inspection apparatus 1 is provided with a 1 st filter 3 having a 1 st polarizing plate, a 1 st phase difference compensation plate 4, a 2 nd phase difference compensation plate 7, and a 2 nd filter 5 having a 2 nd polarizing plate, in this order along an optical axis 9. The defect inspection apparatus 1 includes a light source 2 capable of irradiating light along an optical axis 9 from the 1 st filter 3 side or the 2 nd filter 5 side. In fig. 2, the light source 2 is disposed at a position where light can be irradiated from the 1 st filter 3 side. Hereinafter, a method of irradiating the light source 2 with light from the 1 st filter 3 side will be described in detail, but a method of irradiating the light source 2 with light from the 2 nd filter 5 side can detect defects in the same manner. The defect inspection apparatus 1 includes a detection unit 6, and the detection unit 6 is disposed at a position where light irradiated from the light source 2 is incident after passing through each member.

The light source 2 is not limited as long as it can output light that does not affect the composition and properties of the optical film 100. The light source 2 is, for example, a metal halide lamp, a halogen transfer lamp, a fluorescent lamp, or the like.

In the detection section 6, the defect may be determined by detecting (observing) the detection light with the naked eye, or the defect may be determined by photographing the detection light and based on the photographed image. The imaging means may be a CCD camera or the like. Hereinafter, unless otherwise indicated, a manner of detecting light with the naked eye is described. The same applies to other embodiments.

In the defect inspection apparatus 1, first, a placement process is performed. In the disposing step, the optical film 100 of the object to be inspected is disposed between the 1 st phase difference compensation plate 4 and the 2 nd phase difference compensation plate 7, and is disposed in an orientation in which the surface on the release film 133 side faces the second phase difference compensation plate 4. In the arrangement step, the arrangement angles of the 1 st filter 3, the optical film 100, and the 2 nd filter 5 are adjusted so as to satisfy the following conditions a and b.

(a) The angle θ1 between the absorption axis of the 1 st polarizer of the 1 st filter 3 and the absorption axis of the linear polarizing plate 110 is in the range of 90+±5°.

(b) The angle θ2 formed by the absorption axis of the 2 nd polarizer of the 2 nd filter 5 and the absorption axis of the linear polarization plate 110 is in the range of 90 ° ± 30 °.

Hereinafter, the absorption axis of the linear polarization plate 110 is also referred to as "absorption axis PA0", the absorption axis of the 1 st polarizing plate of the 1 st filter 3 is also referred to as "absorption axis PA1", and the absorption axis of the 2 nd polarizing plate of the 2 nd filter 5 is also referred to as "absorption axis PA2".

In the above-described arrangement step, the angles θ1 and θ2 are preferably adjusted so that the field of view is darkest within a range satisfying the above-described condition. This adjustment can be performed by appropriately adjusting the arrangement angles of the 1 st filter 3, the 1 st phase difference compensation plate 4, the optical film 100, the 2 nd phase difference compensation plate 7, and the 2 nd filter 5 even after the arrangement step. The defect inspection apparatus 1 may include a movable device (not shown) capable of rotating the 1 st filter 3, the 1 st phase difference compensation plate 4, the optical film 1, the 2 nd phase difference compensation plate 7, and the 2 nd filter 5 in a direction perpendicular to the optical axis 9.

In the defect inspection apparatus 1, the inspection step is performed after the arrangement step. In the detection step, light is emitted from the light source 2, and the light sequentially passes through the 1 st filter 3, the 1 st phase difference compensation plate 4, the optical film 100, the 2 nd phase difference compensation plate 7, and the 2 nd filter 5 along the optical axis 9, and reaches the detection unit 6. In the detection unit 6, a determination step of determining a defect in the linear polarization plate 110 based on the detection result of the light that has arrived is performed.

In the 1 st filter 3, only light in a specific polarization direction (hereinafter, also referred to as "1 st polarized light") is transmitted from among unpolarized light irradiated from the light source 2. Light having a polarization direction orthogonal to that of the 1 st polarized light is also referred to as "2 nd polarized light".

In the 1 st phase difference compensation plate 4, a phase difference is given in advance, which cancels out a phase difference caused by birefringence of the release film 133 transmitted in the rear stage. The light incident on the optical film 100 is incident on the linear polarization plate 110 in a state in which the influence of the phase difference caused by the transmission of the peeling film 133 is canceled. Since the angle θ1 formed by the absorption axis PA1 of the first-transmitted 1 st filter 3 and the absorption axis PA0 of the linear polarization plate 110 satisfies the above condition a, the 1 st polarized light incident on the linear polarization plate 110 is almost absorbed in the region without defect.

However, the linear polarization plate 110 sometimes has a defective region in which the absorption axis does not coincide with the absorption axis PA 0. Fig. 3 shows an example of the defective region B in the linear polarization plate 110, and the absorption axis in the defective region B is indicated by a two-end arrow. In the defective region B, there is an absorption axis (hereinafter, referred to as "absorption axis PA 3") that does not coincide with the absorption axis PA 0. When the defects in the defective region B are uneven in optical characteristics, as shown in fig. 3, a state in which the angle with the absorption axis PA0 continuously changes can be assumed as the absorption axis PA3 in the defective region B. In the linear polarization plate 110, the region having the absorption axis PA0 is set as the normal region a.

In the defective region B having the absorption axis PA3 which is not coincident with the absorption axis PA0, the 1 st polarized light is transmitted. The light of the linear polarization plate 110 and the polarized light in the direction corresponding to the absorption axis of the defective region B of the linear polarization plate 110 are transmitted. In the case where the direction of the absorption axis of the defective region of the linear polarization plate 110 is not one direction, the light transmitted therethrough includes polarized light of a plurality of directions. Hereinafter, these are collectively referred to as 3 rd polarized light, and a part of the plurality of polarized light included in the 3 rd polarized light is referred to as 3a polarized light, 3b polarized light, and 3c polarized light in order from the smaller angle to the 1 st polarized light.

The 3 rd polarized light emitted from the linear polarization plate 110 is incident on the 2 nd filter 5 in a state where the influence of the phase difference due to the birefringence of the protective film 141 is offset by the 2 nd phase difference compensation plate 7. The 2 nd filter 5 has a filter function of absorbing light according to the polarization direction with respect to the 3 rd polarized light and emitting the light. The proportion of light absorbed by the 2 nd filter 5 is according to the 3 rd polarized light 3b polarized light, 3c polarized light the order of the order is smaller.

The present inventors focused attention on the fact that the degree of polarization of light transmitted through the 1 st filter and the optical film is substantially low. It was found that by passing such light through the 2 nd filter, the contrast between the 1 st polarized light region and the 3 rd polarized light region can be improved, and the detection sensitivity can be greatly improved.

As described above, the transmission characteristics of light in the linear polarization plate 110 are different in the normal region a and the defective region B, and in addition, the transmission characteristics of light in the 2 nd filter 5 are different according to the absorption axis direction in the defective region B. Since the light reflecting these transmission characteristics is detected by the detection unit 6, the presence or absence of defects in the orthogonal polarizing plate 110 and the presence or absence of uneven absorption axis direction in the defect region B can be detected. The unevenness in the absorption axis direction in the linear polarization plate 110 corresponds to the unevenness in the optical characteristics.

In the defect inspection apparatus 1, the 1 st filter 3 and the 2 nd filter 5 are provided, so that the unevenness of the optical characteristics of the linear polarization plate 110 can be effectively detected. Therefore, in the manufacturing method of the optical film 100 including the above defect inspection method, the optical film 100 as a defect-free product can be efficiently produced.

< 1 st filter, 2 nd filter >

The 1 st filter 3 has a 1 st polarizing plate, and the 2 nd filter 5 has a 2 nd polarizing plate. The 1 st polarizing plate and the 2 nd polarizing plate may be absorption type polarizing plates having a property of absorbing linearly polarized light having a vibration plane parallel to an absorption axis thereof and transmitting linearly polarized light having a vibration plane orthogonal to the absorption axis (parallel to a transmission axis) like the above-described polarizing plate 112. As a typical polarizing plate, a polarizing film obtained by adsorption-orienting a dichroic dye to a uniaxially stretched polyvinyl alcohol resin film is exemplified. The detailed description of the polarizing film can be applied to the description of the polarizing film in the polarizing plate 112 described above. The 1 st and 2 nd polarizers were defect-free.

< 1 st phase difference Compensation plate, 2 nd phase difference Compensation plate >

The shape of the 1 st phase difference compensation plate 4 and the 2 nd phase difference compensation plate 7 (hereinafter, these will be collectively referred to as "phase difference compensation plates") is not particularly limited as long as the birefringence of light of the release film 133 or the protective film 141 can be compensated, but the release film 133 and the protective film 141 containing PET resin are preferably a shape capable of adjusting the phase difference value at the time of inspection because the phase difference value in the plane and the deviation of the slow axis are large. As a shape thereof, as shown in fig. 2, there is a shape in which the thickness is different and the thickness is continuously changed so as to have a thin portion and a thick portion. Since the thickness is continuously varied, the phase difference value is also continuously varied according to the thickness thereof. The phase difference compensation plate 4 has a thickness that is expanded at a predetermined angle from the thinnest part, and has a shape of a wedge (japanese: ku sa) in a cross-sectional view. Such a wedge-shaped retardation compensation plate can easily compensate for birefringence of light caused by the release film 133 or the protective film 141 by being shifted or rotated in the inspection area of the object to be inspected.

The retardation compensation plate is preferably rectangular or square having a length of one side in a range of 1cm to 30 cm.

As the retardation compensation plate, an inorganic material such as a mineral exhibiting birefringence, e.g., quartz or calcite, or a film containing a cycloolefin resin can be used. Particularly, a material having such a flat wavelength dispersion characteristic is preferably used. In addition, minerals such as quartz are preferably used in view of ease of processing into a wedge shape and handling thereafter.

In the case of using a mineral such as quartz, a retardation film may be further used in order to make the wavelength dispersion characteristic flatter. When the slow axis of the phase difference film is arranged in a direction perpendicular to the slow axis of the phase difference plate containing a mineral such as quartz, a positively dispersible phase difference film is preferably used, and when the slow axis of the phase difference film is arranged in a direction parallel to the slow axis of the phase difference compensation plate containing a mineral such as quartz, a negatively dispersible phase difference film is preferably used. When such a retardation film is used, the retardation film is bonded to the surface of quartz.

Examples of the retardation film having the inverse dispersibility include "PURE-ACE WR-S", "PURE-ACE WR-W", "PURE-ACE WR-M" manufactured by Di 'S corporation and "NRF" manufactured by Nito' S electric company. Examples of the positively dispersible retardation film include a film containing a polycarbonate resin and a film containing a polypropylene resin.

Examples of the cycloolefin resin include a resin obtained by ring-opening metathesis polymerization of norbornene or a derivative thereof obtained by diels alder reaction of cyclopentadiene and olefins as monomers and then hydrogenation; a resin obtained by ring-opening metathesis polymerization of tetracyclododecenes obtained by diels alder reaction of dicyclopentadiene and olefins or methacrylates or derivatives thereof as monomers and subsequent hydrogenation; a resin obtained by ring-opening metathesis copolymerization using 2 or more kinds of norbornene, tetracyclododecene, derivatives thereof, or other cyclic olefin monomers, and then hydrogenation; and resins obtained by addition-copolymerizing an aromatic compound having a vinyl group and the like with the norbornene, tetracyclododecene or a derivative thereof.

Cycloolefin resins can be easily obtained as commercial products. Examples of such commercial products include Topas (Topas Advanced Polymers GmbH), ARTON (JSR), ZEONOR, ZEONEX (made by ZEON corporation) and APEL (made by mitsunobu chemical corporation) each of which is expressed by a trade name.

As the phase difference value of the 1 st phase difference compensation plate 4, a phase difference value having a region (hereinafter, sometimes referred to as "wide compensation region") 500 to 600nm larger than Re (550) of the release film 133 is preferably used. As the phase difference value of the 2 nd phase difference compensation plate 7, a phase difference value having a region (hereinafter, sometimes referred to as "wide compensation region") 500 to 600nm larger than Re (550) of the protective film 141 is preferably used. By using the phase difference compensation plate 4 having the region shifted by about 1 wavelength in this way, the transmission spectrum of visible light can be matched to the PET resin film in a wider wavelength range, and phase difference compensation can be performed.

As for the phase difference compensation plate, two phase difference compensation plates having wedge-shaped cross-sectional views may be prepared, and these plates may be used in a state of being overlapped in a direction in which the phase difference value continuously increases in opposite directions.

In this case, the phase difference value of the phase difference compensation plate is the sum of two sheets, and the "wide compensation area" is also based on the sum of two sheets. By using two wedge-shaped phase difference compensation plates, the birefringence of light of the release film 133 or the protective film 141 can be compensated for in a wide range, and therefore the inspection area can be enlarged, and the inspection can be performed effectively.

More specifically, by shifting at least one of the two phase difference compensation plates in the direction in which the thickness thereof changes, the phase difference of the entire phase difference compensation plate can be changed. In the degree of the change, the directions of the increase in thickness are arranged in opposite directions, so that the thickness is gentle compared with the case where the phase difference compensation plate is one sheet. In this way, in the defect inspection apparatus using two retardation plates, the area capable of canceling the birefringence of the release film 133 or the protective film 141 is further increased as compared with the defect inspection apparatus in which the retardation plates are one sheet. The same inspection can be performed by using three or four retardation compensation plates. In addition, a plurality of retardation compensators may be prepared and used by arranging an optimal retardation compensator on the optical axis 9 for counteracting the birefringence of the release film 133 or the protective film 141.

The defect inspection apparatus 1 may be used for a method of inspecting the vicinity of an optical film 100, which is an object to be inspected, after a region to be inspected has been predetermined, by scanning the light source 2, the 1 st phase difference compensation plate 4, and the 2 nd phase difference compensation plate 7, the optical film 100 can be inspected over a wider range. At this time, the detection unit 6 is also moved as needed.

Further, as a method of further expanding the field of view of inspection, it is also effective to further dispose a λ/2 phase difference layer between the 2 nd phase difference compensation plate and the 2 nd optical filter. In this case, the absorption axis of the polarizer of the optical film 100 is arranged parallel to the absorption axis of the polarizer of the 2 nd filter, and the slow axis of the λ/2 retardation layer and the absorption axis of the polarizer of the 2 nd filter are arranged at an angle of approximately 45 °.

< application example 1 >

Regarding application example 1, a suitable application example of the present embodiment will be described in the case where a defect of a circular polarizing plate composed of a combination of a linear circular polarizing plate and a λ/4 retardation layer is inspected for an optical film as an object to be inspected further having a λ/4 retardation layer.

An optical film as an object to be inspected in this application example will be described. Fig. 4 is a cross-sectional view schematically showing an optical film 200 as an example of the optical film. As shown in fig. 4, the optical film 200 has a layer structure of a protective film 141/a linear polarizing plate 110 [ 1 st protective film 111/an adhesive layer 114/a polarizing plate 112/an adhesive layer 114/a 2 nd protective film 113 ]/an adhesive layer 131/a retardation body 120 [ 1 st retardation layer 121/an adhesive layer 124/a 2 nd retardation layer 122 ]/an adhesive layer 132/a release film 133. The same reference numerals are given to the same components as those in the layer structure of the optical film 100 shown in fig. 1, and the description thereof is omitted.

The adhesive layer 114 is applied to the adhesive layer 124, and the adhesive layer 132 is applied to the adhesive layer 131, so that the description thereof is omitted.

The optical film 200 includes, as the retardation body 120, a λ/4 retardation layer that imparts a retardation of 1/4 wavelength to the transmitted light, and may further include a λ/2 retardation layer that imparts a retardation of 1/2 wavelength to the transmitted light, a positive a plate, and a positive C plate. The retardation body 120 of the optical film 200 shown in fig. 4 includes a 1 st retardation layer 121 and a 2 nd retardation layer 122. Examples of the combination of the 1 st retardation layer 121 and the 2 nd retardation layer 122 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 retardation layer may be an optical film exhibiting optical anisotropy. Examples of the optical film exhibiting optical anisotropy include stretched films obtained by stretching a polymer film containing polyvinyl alcohol, polycarbonate, polyester, polyarylate, polyimide, polyolefin, polycycloolefin, polystyrene, polysulfone, polyethersulfone, polyvinylidene fluoride/polymethyl methacrylate, acetyl cellulose, saponified ethylene-vinyl acetate copolymer, polyvinyl chloride, and the like to about 1.01 to 6 times. Among the stretched films, a polymer film obtained by uniaxially stretching or biaxially stretching an acetylcellulose, polyester, polycarbonate film or cycloolefin resin film is preferable. The retardation layer may be a retardation layer containing a cured product of a polymerizable liquid crystal compound, which exhibits optical anisotropy by applying the polymerizable liquid crystal compound to a substrate and aligning the compound.

Examples of the stretched film include a stretched film obtained by stretching a film made of polyvinyl alcohol, polycarbonate, polyester, polyarylate, polyimide, polyolefin, polycycloolefin, polystyrene, polysulfone, polyethersulfone, polyvinylidene fluoride/polymethyl methacrylate, acetylcellulose, saponified ethylene-vinyl acetate copolymer, polyvinyl chloride, or the like to about 1.01 to 6 times.

As the polymerizable liquid crystal compound used for forming the cured layer of the polymerizable liquid crystal compound, a rod-like liquid crystal compound, a discotic liquid crystal compound, and a mixture thereof can be used. The cured product layer can be formed by applying a composition for forming a retardation layer containing a polymerizable liquid crystal compound and a solvent, and various additives as needed, to an alignment film to form a coating film, and curing (hardening) the coating film. Alternatively, a coating film may be formed by applying a composition for forming a retardation layer to a base layer, and the coating film may be stretched together with the base layer to form a cured layer. The composition for forming a retardation layer may contain a polymerization initiator, a reactive additive, a leveling agent, a polymerization inhibitor, and the like in addition to the polymerizable liquid crystal compound and the solvent. The liquid crystal compound, solvent, polymerization initiator, reactive additive, leveling agent, polymerization inhibitor, etc. may be any known ones.

In the defect inspection apparatus 1 shown in fig. 2, when the object to be inspected is an optical film 200 instead of the optical film 100 and the object to be inspected for defects is a circularly polarizing plate, a λ/4 phase difference plate is arranged between the 1 st optical filter 3 and the 1 st phase difference compensation plate 4 in the arranging step. The λ/4 retardation plate gives a retardation which cancels out the retardation of the λ/4 retardation layer of the optical film 200 transmitted in the subsequent stage. The light incident on the optical film 200 is incident on the linear polarization plate 110 in a state where the influence of the phase difference caused by the transmission of the λ/4 phase difference layer is canceled. As the 1 st filter 3, a filter having a λ/4 retardation plate on the optical film 200 side of the 1 st polarizing plate may be used.

The state of the crossed nicols can be obtained by arranging the absorption axis of the 1 st polarizing plate of the 1 st optical filter, the absorption axis of the polarizing plate of the optical film 200, the slow axis of the λ/4 retardation layer of the 1 st optical filter, and the slow axis of the λ/4 retardation layer of the optical film 200 in parallel, only when the inspection object is the optical film 200 (that is, only when it is limited to a circularly polarizing plate).

As the defect of the circularly polarizing plate that can be detected by the defect inspection apparatus 1 in application example 1, there are unevenness, local defect, and the like of the optical characteristics of the linearly polarizing plate 110, as in the case where the object to be inspected is the optical film 100. In the application example 1, when the light source 2 is arranged to enter from the 2 nd filter 5 side, the defect in the phase difference body 120 can be detected in addition to the defect described above. In the case of detecting only a defect of the linear polarization plate 110, the light source 2 is preferably arranged to be used by being incident from the 1 st filter 3 side. With this arrangement, the defect of the linear polarization plate 110 can be detected with higher accuracy.

Description of the reference numerals

1: defect inspection apparatus, 2: light source, 3: 1 st filter, 4: 1 st phase difference compensation plate, 5: filter 2, 6: detection unit, 7: 2 nd phase difference compensation plate, 100, 200: optical film, 111: 1 st protective film, 112: polarizing plate, 113: 2 nd protective film, 114, 124: adhesive layers, 131, 132: adhesive layer, 133: release film, 141: protective film, 120: phase difference body, 121: 1 st phase difference layer, 122: and a 2 nd phase difference layer.

Claims (6)

1. A defect inspection method for a linear polarizing plate, comprising using an optical film having the linear polarizing plate as an object to be inspected,

the optical film is sequentially provided with a stripping film, the linear polarizing plate and a protective film,

the defect inspection method includes:

an arrangement step of arranging a 1 st filter having a 1 st polarizing plate, a 1 st phase difference compensation plate, the optical film, a 2 nd phase difference compensation plate, and a 2 nd filter having a 2 nd polarizing plate in this order along an optical axis, and arranging the optical film in an orientation in which a surface on the release film side faces the 1 st phase difference compensation plate;

a detection step of detecting light incident along the optical axis from either one of the 1 st filter side and the 2 nd filter side and light emitted from the other side; and

A judging step of judging a defect of the optical film based on a detection result in the detecting step,

in the arrangement step, the arrangement is performed so as to satisfy the following conditions a and b:

(a) An angle formed by the absorption axis of the 1 st polarizer and the absorption axis of the linear polarizer is within a range of 90 DEG + -5 DEG;

(b) The absorption axis of the 2 nd polarizer and the absorption axis of the linear polarizer form an angle within the range of 90 DEG + -30 DEG,

in the above-mentioned detection process, in the detection step,

the 1 st phase difference compensation plate compensates for the birefringence of the release film, and the 2 nd phase difference compensation plate compensates for the birefringence of the protective film.

2. The defect inspection method of claim 1, wherein the release film comprises a polyethylene terephthalate based resin.

3. The defect inspection method according to claim 1 or 2, wherein the protective film comprises a polyethylene terephthalate-based resin.

4. The defect inspection method according to any one of claims 1 to 3, wherein the linear polarizing plate has a polarizing plate comprising a cured product of a polymerizable liquid crystal compound.

5. The defect inspection method according to any one of claims 1 to 4, wherein the optical film further has a λ/4 retardation layer between the linear polarizing plate and the release film,

In the disposing step, a λ/4 phase difference plate is disposed between the 1 st optical filter and the 1 st phase difference compensation plate.

6. A defect inspection apparatus for a linear polarizing plate, comprising an optical film having the linear polarizing plate as an object to be inspected,

the optical film is sequentially provided with a stripping film, the linear polarizing plate and a protective film,

the defect inspection apparatus includes, in order along an optical axis: a 1 st filter having a 1 st polarizing plate, a 1 st phase difference compensation plate capable of compensating for birefringence of the release film, a 2 nd phase difference compensation plate capable of compensating for birefringence of the protective film, a 2 nd filter having a 2 nd polarizing plate, and a light source capable of irradiating light from the 1 st filter side or the 2 nd filter side along the optical axis, wherein defect inspection is performed after an arrangement step of arranging the optical film in an orientation in which a surface of the release film side faces the 1 st phase difference compensation plate,

in the arrangement step, the arrangement is performed so as to satisfy the following conditions a and b:

(a) An angle formed by the absorption axis of the 1 st polarizer and the absorption axis of the linear polarizer is within a range of 90 DEG + -5 DEG;

(b) An angle formed by the absorption axis of the 2 nd polarizer and the absorption axis of the linear polarizer is within a range of 90 DEG + -30 deg.