JP2008175940A - Optical film defect marking method - Google Patents

Abstract

A marking for marking a defect in an optical film enables easy identification of the position of the defect, and even when the marking itself is misidentified, the marking itself is not a defect and is marked. An object of the present invention is to provide a defect marking method for an optical film that can prevent the optical film from adversely affecting the quality of the final product.
An optical film defect marking method for marking an optical film defect using an ink that fluoresces with light having a wavelength outside visible light.
[Selection figure] None

Description

  The present invention relates to a method for marking defects in an optical film in which the marking itself does not adversely affect the quality of the optical film.

In recent years, with respect to retardation films used for liquid crystal televisions and the like, the demand for optical defects has been increasing with the increase in the screen size of liquid crystal televisions and the like. In response to this requirement, humans used a microscope or a polarizing plate to examine the number of foreign objects generated within a specific area, or to determine surface defects by visual observation or projection, but these determinations took a long time. In addition, a great deal of labor is required, and skill is required for visual determination, so that it is difficult to ensure sufficient quality.
Therefore, research on detection of optical defects by automatic inspection is also underway, and inspection using a CCD camera and a polarizing plate (for example, see Patent Document 1) has been proposed. In this inspection method, an optical defect can be detected using a CCD camera such as an area sensor or a line sensor and two polarizing plates.
In this way, after the defect is detected, if the position of the defect is always clearly known, the loss of the optical film in the liquid crystal panel that is the final product can be reduced as much as possible. Marking with ink is performed.
Japanese Patent Laid-Open No. 6-148095

However, in the defect inspection method as described above, noise due to the CCD camera cannot be reduced, and the detection sensitivity is still low.
Accordingly, there are many marked defects that were not actually defects. In that case, defects were caused by marking ink in places that were not originally defects, and the optical film Loss increases, resulting in reduced production efficiency.

  The present invention has been made in view of the above problems, and the position of the defect can be easily specified by marking the defect of the optical film, and even when the marking itself is a false detection, the marking is made. It is an object of the present invention to provide a defect marking method for an optical film that does not itself become a defect and that can prevent the marked optical film from adversely affecting the quality of the final product.

The optical film defect marking method of the present invention is characterized in that an optical film defect is marked using an ink that fluoresces with light having a wavelength outside visible light.
In this optical film defect marking method, the optical film defect is preferably an optical defect or detected in a crossed Nicols state.
Moreover, it is preferable to perform marking inline using an inkjet system.
Furthermore, a telecentric laser beam linearly polarized in a predetermined direction is irradiated while scanning the optical film inline,
The laser beam transmitted through the optical film is received after passing through a polarizing plate having an absorption axis in a direction parallel to the polarization direction of the laser beam at the time of irradiation, and a defect is detected.
It is preferable to mark the detected defect.
The optical film is preferably a retardation film or formed of a norbornene-based resin.

  In the optical film defect marking method of the present invention, the optical film containing defects can be eliminated before using the optical film in order to directly mark the defects present in the optical film. Moreover, even when a defect is erroneously detected, it is possible to avoid an adverse effect on the quality due to the marking and prevent the loss of the optical film.

In particular, when the defect of the optical film is an optical defect or is detected in a crossed Nicols state, it is more effective because there is a high possibility of erroneous detection due to a small amount of light.
Further, when marking is performed inline using an inkjet system, for example, even a long optical film can be efficiently inspected over the entire surface.
Furthermore, when a defect is marked by a predetermined method using a telecentric laser beam linearly polarized in a predetermined direction, the optical defect can be detected more effectively, and the defect marking method can be appropriately selected. Can be applied.
Further, when the optical film is a retardation film, it is possible to detect an optical defect with high sensitivity, which is more effective.
Furthermore, when the optical film is formed of a norbornene-based resin, the intrinsic birefringence can be reduced and the photoelastic coefficient can be suppressed, which is advantageous.

The defect marking method of the optical film of the present invention is a marking method using an ink that fluoresces with light having a wavelength outside visible light with respect to a defect of the optical film.
As the ink that fluoresces with light having a wavelength outside visible light, for example, an ink called a known invisible ink is suitable. The invisible ink is not particularly limited. For example, the invisible ink is not visible under visible light or daylight. When irradiated with ultraviolet light (for example, 275 nm to 450 nm, preferably 350 nm to 410 nm), the ground state changes to the excited state. The fluorescent colorant, the fluorescent whitening agent, etc., which emit light from colorless to colored and can be visually recognized.

  Examples of such ink include diaminostilbene, stilbene (for example, 4,4′-bis (triazin-2-ylamino) stilbene-2,2′-disulfonic acid derivative, etc.), imidazole, thiazole, Oxazole-based (for example, 2,2 ′-(2,5-thiophendiyl) -bis (5-t-butylbenzoxazole, etc.), triazole-based, oxadiazole-based, coumarin-based, naphthalimide-based, pyrazoline-based, etc. Commercially available fluorescent whitening dyes, rare earth metal chelates (for example, derivatives of europium acetonate, etc.), etc. Further, for example, JP-A-8-199101, JP-A-11-152436, JP-A-2004-189850 Gazette, JP-T-2001-507052, JP-A-2005-187540 It can be used any of known ones that are described in.

  Optical film defects include defects such as ring-shaped defects, dent dent defects, gel defects, and contamination / adhesion of foreign substances, among which dent defects, gel defects, contamination / adhesion of alien substances, etc. It is preferably an optical defect. The optical defect means a defect having locally birefringence, for example, refers to a defect that passes through in a crossed Nicol state, and is caused by foreign matter or distortion of the film itself.

Such a defect can be detected using a conventionally known method. In particular, it is preferable that it is detected in a crossed Nicol state. For example, visual detection or detection using a magnifying glass may be used, or a method using a CCD camera may be used (see JP-A-6-148095). In particular, it is possible to detect an optical defect by using a method in which a polarizing plate is disposed between the light source and the CCD camera in a crossed Nicol manner so that the film passes between them.
Moreover, the inspection method performed using a laser may be sufficient (for example, refer Unexamined-Japanese-Patent No. 2001-264259 etc.). In particular, linearly polarized laser light is set to be parallel or perpendicular to the transport direction of the optical film, and the polarizing plate is arranged on the front surface of the detector so that the polarization direction of the laser upon irradiation is the absorption axis. It is preferable to perform the detection under the condition that the laser does not pass in the state where the laser is disposed and there is no defect.

  Furthermore, as an inspection method using a laser, for example, as shown in FIG. 1, at least a projector 11 including a laser, a detector 13 capable of receiving laser light, and a polarization disposed on the front surface of the detector 13 The inspection apparatus 10 configured to include the plate 12 may be used.

The projector is provided with a laser as a light source. The laser is preferably a semiconductor laser having a wavelength of about 350 nm to 800 nm, for example. The laser light is preferably linearly polarized, for example, one that is polarized in the width direction or longitudinal direction of the optical film to be irradiated is preferable.
The incident angle of the laser beam on the optical film is preferably 60 ° to 90 ° with respect to the optical film surface. That is, an optical defect can be detected by setting the regular transmission axis (90 °), and by setting the tilt axis (60 ° to less than 90 °), not only the presence or absence of an optical defect but also the shape of the defect. Can also be detected.
The laser beam may be a single mode or a longitudinal multimode. The spot diameter of the laser light is preferably set so that the average value in the vertical and horizontal directions is about 100 μm or less.

  A telecentric method is used as a method of irradiating laser light. Thereby, the laser beam can be incident at the same incident angle over the entire width of the optical film irradiated with the laser beam. In other words, when measurement is performed using a conventional CCD camera, there is a difference in detection sensitivity between the central portion and the peripheral portion of the camera. Since the degree of light omission (light intensity at the time of crossed Nicols) is different, the detection sensitivity is different, and it is difficult to detect with the same sensitivity over the entire width. On the other hand, in this method, such a difference due to detection sensitivity can be avoided, and defects can be detected without a sensitivity difference in the entire width of the optical film. The telecentric method may be realized by any method or means as long as it can obtain a telecentric beam of laser light. For example, Japanese Patent Application Laid-Open No. 2004-138828 and Japanese Patent Application Laid-Open No. 2002-122781. It can be realized by using a conventionally known optical system or a method and means according to these optical systems, such as Japanese Laid-Open Patent Publication No. 11-500834.

  The scanning frequency of the laser beam is not particularly limited, and can be set to an appropriate frequency depending on the line speed of the optical film, for example, and is about 2000 to 5000 Hz. Specifically, if the line speed is 20 m / min and the resolution in the flow direction (for example, the longitudinal direction of the optical film) is 100 μm, for example, the frequency in the width direction is suitably 3333 Hz.

  The polarizing plate needs to be disposed on the front surface of the detector. Moreover, it is necessary to install the polarizing plate so that the polarization direction of the laser beam applied to the optical film is parallel to the absorption axis. By installing the polarizing plate in this way, the laser beam irradiated to the defect of the optical film and whose polarization state is changed by the defect passes through the polarizing plate, and easily passes through the detector described later. The detected laser beam can be detected.

The detector is not particularly limited as long as it can receive and detect laser light, and any detector may be used. For example, a photoelectric sensor, a light detection element, and a photoelectric conversion element can be mentioned, and among them, a photomultiplier tube is suitable. In the case of using a photomultiplier tube, the capture frequency of the photomultiplier tube can be set to an appropriate frequency depending on the resolution in the width direction and the flow direction, for example, about 1 MHz to 80 MHz. Specifically, if the line speed is 20 m / min, the resolution in the flow direction is 100 μm, and the inspection width detected by one detector is 1000 mm, 33.3 MHz is suitable.
When a photoelectric sensor is used in the detector, it is preferable to have a shape or arrangement corresponding to the width of the projector or the optical film so that the telecentric laser beam of the projector can be received as it is. . For example, a plurality of photomultiplier tubes may be arranged in the width direction of the projector or the optical film, or one photomultiplier tube is arranged only at the end, and the acrylic over the width direction of the projector or the optical film. A light guide member such as a rod may be used.

  In addition, when using such an apparatus, although the optical film which irradiates a laser beam may be a stationary state, it is preferable to carry out in the state currently conveyed in the width direction or longitudinal direction of an optical film. For this reason, in the apparatus capable of realizing the optical film inspection method as described above, the conveying means is arranged so that the optical film is conveyed between the projector and the polarizing plate disposed in front of the detector. It is preferable to provide. The conveying means may be a moving stage on which an optical film is placed and moved at a constant speed, or a long optical film is wound from a winding roll to a winding roll. It may be like a hoisting device.

  Using such an apparatus, first, a telecentric laser beam linearly polarized in a predetermined direction is irradiated while scanning the optical film. The scanning in this case may be in any direction, and examples include the width direction and the longitudinal direction of the optical film, but the latter is preferable. By scanning in the longitudinal direction, the optical film can be inspected continuously in the longitudinal direction.

  Next, the laser beam transmitted through the optical film is received after passing through a polarizing plate having an absorption axis in a direction parallel to the polarization direction of the laser beam at the time of irradiation. Light reception can be performed by a light reception sensor or the like as described above. Thereby, the intensity of the received laser beam is compared with a preset threshold value, and it is determined whether it is larger or smaller than the threshold value, thereby detecting the presence or absence of a defect in the optical film.

The method for marking the defect of the optical film thus detected is preferably performed using, for example, an inkjet system. Furthermore, it is preferable to carry out in-line.
As the inkjet system, a known system can be used as it is or according to a known system. In addition, in order to directly mark the defect, the ink jet head uses a mechanism provided with a mechanism for driving in the width direction of the optical film, or a plurality of ink jet heads arranged in the film width direction. There is a method of marking with the head closest to. As an inkjet ejection system, various systems such as a piezoelectric inkjet system, a thermal inkjet system, a continuous inkjet system, and the like can be given.

The optical film may be any known film such as a retardation film, a polarizing plate, a color filter, and a diffusion plate, but is preferably a retardation film.
The material of the optical film is not particularly limited, and any material may be used. For example, a thermoplastic resin is mentioned, and among these, an amorphous thermoplastic resin is preferable. Here, the amorphous thermoplastic resin is a polymer that maintains an amorphous state that hardly takes a crystal structure. By using such a resin, an optical film excellent in transparency can be obtained. In addition, the glass transition point Tg of such a resin is not particularly limited, and generally has a glass transition point of 100 ° C. or higher. This is because sufficient durability can be ensured even in the case of being mounted on an automobile and used in a high temperature environment. Examples of the amorphous thermoplastic resin include polysulfone, polymethyl methacrylate, polystyrene, polycarbonate, polyvinyl chloride, and norbornene resin. These may be used alone or in combination of two or more. Moreover, a single layer structure may be sufficient and the laminated structure of two or more layers may be sufficient.

  Among these amorphous thermoplastic resins, in consideration of optical characteristics, the intrinsic birefringence is low and the photoelastic coefficient is small. Therefore, a norbornene resin is particularly suitable for the retardation film.

  Examples of the norbornene resin include hydrogenated ring-opening polymers of norbornene monomers, addition polymers of norbornene monomers and olefins, addition polymers of norbornene monomers and derivatives thereof. These may be used alone or in combination of two or more.

  Examples of the norbornene-based monomer include bicyclics such as norbornene and norbornadiene; tricyclics such as dicyclopentadiene; tetracyclics such as tetracyclododecene; pentacyclics such as cyclopentadiene trimer; tetracyclopentadiene. Such as methyl, ethyl, propyl, butyl, etc., vinyl, alkenyl, etc., ethylidene, etc. alkylidene, phenyl, tolyl, naphthyl, etc., aryls, etc .; further ester groups, ether groups thereof A group containing elements other than carbon and hydrogen, such as cyano group, halogen atom, alkoxycarbonyl group, pyridyl group, hydroxyl group, carboxylic acid group, amino group, hydroxyl group-free, silyl group, epoxy group, acrylic group, methacryl group, Substituents having a so-called polar group can be mentioned, among others, it is easy to obtain, Excellent refractoriness, since the heat resistance of the molded article obtained is excellent, tricyclic body, norbornene-based monomer tetracyclic body and pentacyclic body is preferably used. These norbornene monomers may be used alone or in combination of two or more.

  As a ring-opening polymer hydrogenated product of a norbornene monomer, a product obtained by hydrogenating a remaining double bond after ring-opening polymerization of a norbornene monomer by a known method is widely used. The ring-opening polymer hydrogenated product may be a norbornene monomer homopolymer or a copolymer of a norbornene monomer and another cyclic olefin monomer.

  Examples of the addition polymer of a norbornene monomer and an olefin include a copolymer of a norbornene monomer and an α-olefin. The α-olefin is not particularly limited, but is an α-olefin having 2 to 20 carbon atoms, preferably 2 to 10 carbon atoms, such as ethylene, propylene, 1-butene, 3-methyl-1-butene, 1-pentene, Examples include 3-methyl-1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene and the like. Especially, since it is excellent in copolymerizability, ethylene is used suitably. Also, when other α-olefin is copolymerized with a norbornene-based monomer, it is preferable that ethylene is present because the copolymerizability can be improved.

  Norbornene resins are known and are commercially available. Examples of known norbornene-based resins include those manufactured by JSR Corporation, trade name “Arton” series, manufactured by Nippon Zeon Co., Ltd., trade name “Zeonor” series, and the like.

Various additives may be optionally added to the optical film of the present invention. Examples of such additives include various additives that prevent deterioration of the thermoplastic resin and improve the heat resistance, ultraviolet resistance, smoothness, and the like of the molded optical film. For example, phenol-based or phosphorus-based antioxidants; lactone-based thermal deterioration inhibitors; benzophenone-based, benzotriazole-based, acrylonitrile-based ultraviolet absorbers, etc .; aliphatic alcohol esters, polyhydric alcohol partial esters Examples thereof include lubricants such as system and partial ethers; and antistatic agents such as amines. These may be used alone or in combination of two or more.
The optical film preferably has a thickness of about 15 to 300 μm, preferably about 15 to 200 μm. This is because the laser beam can be reliably transmitted.
Hereinafter, an embodiment of the defect marking method for an optical film of the present invention will be described in detail with reference to the drawings.

(Optical film)
A film having a thickness of about 60 μm was prepared using a thermoplastic norbornene resin (trade name “Zeonor 1420R” manufactured by Nippon Zeon Co., Ltd.), and then stretched under the following stretching conditions to obtain a retardation film. .
Stretching method: Roll-to-roll stretching method Stretching ratio: 1.8 times Traveling speed before stretching: 9 m / min
Preheating temperature: 80 ° C
Stretching temperature: 142 ° C
Cooling temperature ... 90 ℃

(Example 1)
The optical film produced as described above is arranged on the front surface of the light source (light guide / halogen lamp), and further, two polarizing plates are arranged in a crossed Nicols state before and after the optical film, thereby The light was passed through an optical film and two polarizing plates, and visually inspected visually and with a magnifying glass (10 times) to detect defects.
The detected defect was marked with a transparent ink in a visible light region containing an Eu-chelate compound.

(Example 2)
The optical film 24 obtained above was inspected using the inspection apparatus 20 shown in FIG.
The inspection apparatus 20 includes a CCD camera 21 as a detector, a transmission light 23 using a metal halide as a light source, a polarization filter 25 disposed in a lens portion of the CCD camera 21, and a polarization disposed in front of the transmission light 23. And a plate 22.
In this inspection apparatus 20, the polarizing filter 25 and the polarizing plate 22 are set so as to be in a crossed Nicols state. The incident angle α of the laser beam was set to 75 ° over the entire width of the film.

The optical film 24 is transported in the longitudinal direction between the CCD camera 21 and the polarizing plate 22 using a winding device (not shown) that winds up from the unwinding roll to the winding roll. While inspecting.
The detected defects were marked with an ink jet marker having a moving mechanism in the width direction of the optical film with an ink transparent in the visible light region containing an Eu-chelate compound.

(Example 3)
The optical film 14 obtained above is inspected with a projector 11 provided with the laser shown in FIG. 1, a detector 13 capable of receiving laser light, and a polarizing plate 12 disposed in front of the detector 13. The apparatus 10 was used for inspection.
In this inspection apparatus 10, the projector 11 is provided with a laser diode (wavelength 660 nm) as a light source, and the linear polarization direction is set to be perpendicular to the transport direction A of the optical film 14 to be inspected. The laser power was 1.4 W, and the spot size of the laser beam was 50 μm long and 100 μm wide. The incident angle α of the laser beam was set to 75 ° over the entire width of the film. The polarizing plate 12 was set so as to be in a crossed Nicols state in the linear polarization direction of the laser beam emitted from the light source.

The optical film 14 is placed between the projector 11 and the polarizing plate 12 in the longitudinal direction by using a winding device (not shown) that winds from the unwinding roll to the winding roll. Inspection was performed while transporting.
With respect to the detected defect, it had a head that corresponded to the length in the width direction of the optical film with a transparent ink in a visible light region containing an Eu-chelate compound, and a plurality of nozzles were arranged in the entire length in the width direction. Marking was performed using an inkjet marker.

(Comparative Example 1)
A defect was marked in the same manner as in Example 2 except that marking was performed using black pigment ink.

The presence of the marking could be confirmed by cutting out the sheet film from the films obtained in Examples and Comparative Examples so as to include a portion where defects were detected, and irradiating the sheet film of Examples with ultraviolet rays. This makes it possible to efficiently perform defect inspection with increased accuracy in the reinspection process.
Next, when the visibility of the marking was confirmed by incorporating these single-wafer films into a liquid crystal panel, the marking itself was a new optical defect in the comparative film regardless of the presence or absence of optical defects (for example, bright spot defects). On the other hand, in the film of the example, the marking is not visually recognized, and it is possible to incorporate an optical defect that is erroneously detected in the inspection process or an acceptable degree of optical defect into the product as it is. The problem can be solved.

  The defect marking method of the optical film of the present invention can be used at the time of detecting defects of various optical films, and can also be used at the time of detecting defects of films, thin plate-like members, etc. used for other applications. it can.

It is the schematic of the apparatus which implement | achieves the inspection method of an optical film. It is the schematic of another apparatus which implement | achieves the inspection method of an optical film.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 20 Inspection apparatus 11 Projector 12, 22 Polarizing plate 13 Detector 14, 24 Optical film A Transport direction 21 CCD camera 23 Transmission light 25 Polarizing filter

Claims (7)

  An optical film defect marking method, wherein an optical film defect is marked with an ink that fluoresces with light having a wavelength outside visible light.   The defect marking method according to claim 1, wherein the defect of the optical film is an optical defect.   The defect marking method according to claim 1, wherein the defect of the optical film is detected in a crossed Nicols state.   The defect marking method according to claim 1, wherein the marking is performed inline using an inkjet system. Irradiate a telecentric laser beam linearly polarized in a predetermined direction while scanning the optical film inline,
The laser beam transmitted through the optical film is received after passing through a polarizing plate having an absorption axis in a direction parallel to the polarization direction of the laser beam at the time of irradiation, and a defect is detected.
The defect marking method according to any one of claims 1 to 4, wherein the detected defect is marked.   The defect marking method according to claim 1, wherein the optical film is a retardation film.   The defect marking method according to claim 1, wherein the optical film is formed of a norbornene-based resin.

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