JP7457572B2 - Method and device for measuring warpage of optical film - Google Patents

Description

The present invention relates to a method and apparatus for measuring warpage of an optical film.

An optical film is incorporated into an image display device as one of its constituent members. Various types of optical films have been developed to meet various required functions, such as polarization properties and hard coat properties.

Optical films may warp (curl). Warpage occurs not only because it is manufactured into a long length and then wound up into a roll for storage, but also, especially when the optical film is a laminated film, due to differences in heat shrinkage rates between the laminated films. Warpage is likely to occur. When a long optical film is cut into a desired size, if there is a large amount of warpage, the workability when assembling it into an image display device decreases, and this also causes a lack of precision in bonding. Conventionally, manufacturing methods for suppressing the occurrence of warpage in optical films have been proposed (for example, Patent Documents 1 and 2).

Japanese Patent Application Publication No. 2015-217654 JP 2015-21034 Publication

Currently, the degree of warpage of optical films is measured manually. Doing it manually takes time and effort, and the accuracy varies depending on the operator, making it difficult to ensure thorough quality control. Therefore, an object of the present invention is to provide a measuring method and a measuring device that can accurately measure the degree of warpage of an optical film without manual work.

The present invention targets an optical film placed on a stage, scans the edge of the optical film with a laser beam from above the optical film, and detects the reflected light of the laser beam from the edge. Provided is a method for measuring warpage of an optical film, which obtains information on the height position of the part.

According to this measurement method, the end position of the optical film can be found by scanning with a laser beam, and information about the height position of the end can be obtained by detecting the reflected light from that position. Therefore, the degree of warpage of the optical film can be measured without manual work.

In this measurement method, the stage may have a hemispherical reflectance of laser light of 2% or less. While scanning from the outside of the optical film toward the edge of the optical film, the laser beam reflected from the stage is reflected on the back side of the optical film, and the position where this reflected light is emitted is located at the edge of the warp. There is a risk that it will be measured as the position of Here, when the hemispherical reflectance of the laser beam of the stage is within the above range, reflection of the laser beam on the stage is suppressed, and a situation in which the back surface of the optical film shines is less likely to occur.

The shape of the optical film to be measured is not particularly limited, and may be polygonal. In this case, scanning with the laser beam and acquisition of the information on the height position are performed at least two of the vertices of the polygon. It may be done at a location. According to this, it is possible to measure the degree of warpage at a plurality of locations, so quality control regarding the amount of warpage can be more thorough.

The laser light may be emitted vertically downward with respect to the scanning direction. Further, it is preferable that the distance between the detection position of the reflected light from the optical film and the center of the optical film is longer than the distance between the center of the optical film and the irradiation position of the laser beam. In this case, the detection position is less susceptible to the effects of halation caused by specular reflection of the laser beam, so detection accuracy is prevented from deteriorating.

The present invention provides a measuring device that includes a stage on which an optical film is placed, an irradiation unit that irradiates the optical film placed on the stage with laser light from above, a detection unit that detects the reflected light of the laser light reflected by the optical film, and a movable mechanism that moves the irradiation unit so that the laser light can be scanned toward the edge of the optical film, the stage having a hemispherical reflectance of the laser light of 2% or less.

In this measuring device, an optical film is the object of measurement, and an irradiation unit that irradiates laser light is moved by a movable mechanism to scan toward the end of the optical film. The detection unit detects the reflected light from the optical film, and the degree of warpage of the optical film can be determined from the information on the height position. In this case, while scanning from the outside of the optical film toward the edge of the optical film, the laser beam reflected by the stage is reflected on the back surface of the optical film, and the position where this reflected light is emitted is determined. There is a possibility that it will be measured as the position of the warped end. However, in the measuring device of the present invention, since the hemispherical reflectance of the laser beam of the stage is within the above range, reflection of the laser beam on the stage is suppressed, and a situation in which the back surface of the optical film shines is less likely to occur.

In the above measuring method and measuring device, the optical film to be measured may be an optical laminated film. A laminated film in which a plurality of films are laminated tends to warp due to differences in heat shrinkage rates between the films. Therefore, optical laminated films are suitable for application of the present invention.

According to the present invention, it is possible to provide a measuring method and a measuring device that can accurately measure the degree of warpage of an optical film without manual work.

FIG. 1 is a front view of the measuring device of this embodiment. FIG. 2 is a plan view of the measuring device shown in FIG. 1 . FIG. 3 is a diagram showing the operation of the SCARA robot during measurement. FIG. 4 is a side view showing the operation of the laser displacement meter during measurement. FIG. 3 is a side view showing the operation of the laser displacement meter during measurement. It is a side view which shows the operation|movement of the laser displacement meter at the time of measurement in other embodiments. 13A and 13B are diagrams for explaining the "warping angle."

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In each figure, the same parts or equivalent parts are given the same reference numerals, and redundant explanations will be omitted.

The measuring device and measuring method of this embodiment are for measuring the degree of warpage of an optical film. Optical films are usually produced in a long form and stored by being wound into rolls. When used, it is unwound from a roll, cut into a desired size and shape, and used for its intended purpose. When incorporating the cut out optical film into an image display device, for example, if the warpage is large, work efficiency will be reduced. Therefore, the degree of warpage is an important quality control item, and it is desirable to control it thoroughly.

The object to be measured in this embodiment is an optical film. The optical film is not particularly limited as long as it exhibits optical properties such as polarization degree and optical compensation, and may be a single layer film or a laminated film. The object to be measured in this embodiment is preferably an optical laminated film among optical films. A laminated film formed by laminating a plurality of films is suitable for application of the present embodiment because it tends to warp due to differences in heat shrinkage rates between the films. Examples of the optical laminated film include films such as polarizing plates, retardation plates, and circularly polarizing plates used in optical products. The polarizing plate may be one in which a protective film is adhered to one or both sides of the polarizing film with an adhesive, and another film such as a release film is further laminated on the protective film via an adhesive layer. It may be something like that.

The shape of the optical film is not particularly limited, and may be circular or polygonal. An optical film with a contoured shape having straight portions, especially a polygonal optical film, is easily applied as a measurement object because it is easily warped.

The optical film may have a transmittance of laser light used for measurement of 20% or more, 40% or more, 60% or more, or 80% or more. The transmittance is not particularly limited, but may be 99% or less, 95% or less, or 90% or less.

<Measuring device>
(composition)
As shown in FIGS. 1 and 2, the measuring device 1 of this embodiment is a device for measuring the degree of warpage of an optical film, and includes a SCARA robot 2, a laser displacement meter 3, and a stage 4. It is equipped with The SCARA robot 2 is placed on a pedestal S that is erected on an arbitrary workbench for height adjustment, and is placed horizontally from the robot main body box part 5 and the upper part of the robot main body box part 5. It has an arm part 6 connected to extend in the direction, and a head part 7 connected to extend in the horizontal direction from the other end of the arm part 6. The arm portion 6 is horizontally rotatable with respect to the robot body box portion 5, and the head portion 7 is horizontally rotatable with respect to the arm portion 6.

The laser displacement meter 3 is supported so as to be suspended from the lower surface of the head section 7. The head section 7 has an electric motor built in the connection section between the robot main body box section 5 and the arm section 6 and the connection section between the arm section 6 and the head section 7 on its lower surface. The laser displacement meter 3 is provided with a mechanism that can move the laser displacement meter 3 in any direction by rotating it (movable mechanism). Further, the laser displacement meter 3 can be rotated in the horizontal direction at the connection part with the head part 7, and has a laser light source (irradiation part) 8 and a CMOS sensor (detection part) 9 on its lower surface. There is.

The measuring device 1 includes a stage 4 below the arm section 6 and the head section 7 on which an optical film to be measured is placed. It is preferable that the stage 4 has a larger area than the optical film to be measured. The stage 4 is preferably a black plate, or a plate of the same color as the laser beam if the laser used is in the visible light range.

In the stage 4, the hemispherical reflectance of the laser light emitted from the laser light source 8 may be, for example, 2% or less, 1.5% or less, preferably 1% or less, and 0. It is more preferably .9% or less, even more preferably 0.8% or less, and particularly preferably 0.7% or less. Specific examples of stage 4 include Metal Velvet (Acktar) and Spectral Black (Acktar).

The wavelength of the laser light emitted from the laser light source 8 is arbitrary, but from the viewpoint of usability and detection sensitivity, it is preferably a wavelength in the near ultraviolet to near infrared region, for example, 300 nm to 700 nm, preferably 350 nm to 450 nm. is more preferable, and even more preferably 380 nm to 430 nm. For example, 405 nm can be selected.

It is preferable that the surface of the stage 4 has a fine uneven structure. The height of each unevenness and the distance between adjacent protrusions are preferably approximately equal to or shorter than the wavelength of the laser light emitted from the laser light source 8. When the surface of the stage 4 has such a fine structure, it is easy to achieve a low hemispherical reflectance. Examples of the fine structure include a moth-eye structure.

The strength of the surface of the stage 4 is such that the number of scratches is preferably 30 or less, more preferably 10 or less when #0000 steel wool is reciprocated 10 times at a load of 250 g/cm ² . If the surface having a fine structure is brittle and easily broken, a transparent protective plate made of a glass plate or resin (acrylic resin, etc.) may be provided above the surface. That is, the stage 4 may have a two-layer structure including, for example, a black plate having a fine structure on its surface and a transparent protection plate provided above the black plate. In the case of this two-layer structure, the fine structure is located under the transparent protective plate, and the fine structure is irradiated with the laser light that has passed through the transparent protective plate.

Furthermore, in the case of this two-layer structure, the optical film to be measured is placed on a transparent protective plate. The surface of the transparent protective plate is preferably subjected to anti-reflection (AR) treatment. When the stage 4 has a two-layer structure, it is preferable that the hemispherical reflectance of the stage 4 as a whole satisfies the above value. Here, the AR process refers to a process in which multiple layers of materials with different reflectances are stacked to shift the phase difference of reflected light in each layer to cancel out the light. In the case of a two-layer structure consisting of a black plate and a transparent protective plate, a gap may be provided between both layers, for example, a gap of 1 mm to 200 mm, preferably 3 mm to 10 mm.

In order to prevent stray light from the laser beam during measurement, it is preferable to construct a dark room environment by surrounding the entire measuring device 1 with a frame and covering the frame with a cloth, resin plate, etc. without any gaps.

The above "hemispheric reflectance" is the reflection of the corresponding wavelength measured by the SCI method (method including specular reflection light) using a spectrophotometer, targeting the wavelength of the light emitted by the laser light source 8 of the laser displacement meter 3. refers to the value of the rate. As the spectrophotometer, for example, "CM-2600d" manufactured by Konica Minolta, Inc. can be used. Here, in addition to measuring the hemispherical reflectance of the wavelength of the laser beam to be measured, if the performance of the spectrophotometer does not correspond to the wavelength of the laser beam that you want to measure, measure the wavelengths before and after that wavelength. The average value of the values may be used as the hemispherical reflectance of the wavelength. For example, when determining the hemispherical reflectance of laser light with a wavelength of 405 nm, measurements may be made at both 400 nm and 410 nm, and the average value may be taken as the hemispherical reflectance at the wavelength of 405 nm.

(motion)
The measuring device 1 drives the electric motors built into each part of the SCARA robot 2 to horizontally rotate the arm part 6, head part 7, and laser displacement meter 3 according to their respective rotation axes. As shown in the figure, the position of the head section 7 can be moved to the four corner positions of the rectangular optical film 10 placed on the stage 4. Here, the laser displacement meter 3 is positioned out of the plane of the optical film 10 in plan view. When performing measurement, the drive mechanism of the SCARA robot 2 causes the laser displacement meter 3 to scan toward the side where the optical film 10 is present. The laser displacement meter 3 can emit a laser beam from its laser light source 8 toward the stage 4 vertically downward (vertically downward in this case). The CMOS sensor 9 has a predetermined angle of view and observes the vicinity of the laser beam emission destination from a direction oblique to the laser beam emission direction. When the CMOS sensor 9 captures the laser beam, the height position from the surface of the stage 4 is determined by image processing based on the shape of the laser beam. Through these series of operations, the measuring device 1 can scan the optical film 10 to be measured with a laser beam and detect the position of the warped end.

<Measurement method and effects>
A method for measuring warpage of an optical film using the measuring device 1 will be explained. A rectangular optical film 10 to be measured is placed on the stage 4. At this time, the optical film 10 that is warped is placed so that it is convex downward, that is, the end that forms the peak of the warp is lifted upward. The SCARA robot 2 and the laser displacement meter 3 are driven to position the laser displacement meter 3 above one of the four corners of the optical film 10 (see FIG. 3). At this time, the laser light source 8 of the laser displacement meter 3 is positioned outside the plane of the optical film 10 in plan view, and the CMOS sensor 9 is positioned further outside the plane.

As shown in FIG. 4, while emitting a laser beam vertically downward (the laser beam is indicated by a solid line arrow), the laser displacement meter 3 is directed inward from a position outside the plane of the optical film 10 as a starting point. to scan. Note that in FIG. 4, the drawing of the SCARA robot 2 is omitted. The CMOS sensor 9 directs its viewing area A so that it can capture the reflected laser light from the optical film 10, if any. In the situation shown in FIG. 4, the laser beam is irradiated onto the stage 4, but the edge of the optical film 10 is not irradiated with the laser beam, so the reflected light from the edge of the optical film 10 is transmitted to the CMOS sensor. Not detected in 9. By further scanning the laser displacement meter 3 from this position, the laser beam is scanned toward the end of the optical film 10.

The end of the warped optical film 10 (in this case, also the apex of the rectangle) is located at the uppermost position and has the highest height from the surface of the stage 4. At this time, as shown in FIG. 5, the laser beam is reflected at the end of the optical film 10, and this reflected light (reflected light is indicated by a broken line arrow) is detected by the CMOS sensor 9. You can measure the height of the end.

After measuring the amount of warping (height of the end from the stage) in this way, the SCARA robot 2 and the laser displacement meter 3 are then moved to another corner of the optical film 10 (see Figure 3). The amount of warping at that end is then measured in the same manner as above. By performing this measurement preferably at two or more of the four corners of the optical film, and more preferably at all four corners of the optical film, the warping condition of the entire optical film 10 can be grasped.

In this measurement method, as shown in FIGS. 4 and 5, the distance between the position of the CMOS sensor 9 (detection position) and the center of the optical film 10 is determined by the distance between the center of the optical film 10 and the position of the laser light source 8. (irradiation position). Therefore, the position of the CMOS sensor 9 is less susceptible to the effects of halation caused by specular reflection of laser light, and therefore detection accuracy is prevented from deteriorating due to halation.

When the optical film 10 has a high transmittance, it is usually preferable to increase the imaging sensitivity in order to increase the detection sensitivity of the CMOS sensor 9. However, although increasing the imaging sensitivity increases the detection sensitivity, it also causes the detection of stray light and the strong influence of halation, which may lead to a decrease in detection accuracy. In this regard, since the measurement method of this embodiment has the above-described configuration, it is possible to perform measurement while keeping the imaging sensitivity relatively low, and it is possible to prevent a decrease in detection accuracy.

In this embodiment, it is advantageous to perform measurements using a stage with a low hemispherical reflectance, especially when measuring an optical film that is highly warped. When measuring an optical film with small warpage, the CMOS sensor will not detect the back reflection shown in Figure 6 due to its reflection angle, so it should be measured correctly regardless of the size of the hemispherical reflectance of the stage. Can be done.

On the other hand, when measuring an optical film with a large degree of warpage (for example, when the angle of warpage is 70 degrees or more), the back reflection shown in Figure 6 may be detected by the CMOS sensor from the reflection angle. There is. Therefore, using a stage with a low hemispherical reflectance is suitable for accurately and continuously measuring a plurality of optical films that may have different amounts of warpage. The above-mentioned "angle of warpage" refers to the angle between the tangent at the warped end and the stage surface when the optical film is placed on the stage when viewed from the side. Of these, the angle α is on the side opposite to the side where the optical film is present.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. For example, in the above embodiment, a mode was shown in which the laser displacement meter scans in-plane from a position outside the plane of the optical film as a starting point; It is also possible to use a mode in which the optical film is scanned using the optical film.

In the above embodiment, a laser displacement meter is used that is equipped with a laser light irradiation unit (laser light source) and a detection unit (CMOS sensor) as an integrated unit, but the irradiation unit and detection unit may be provided in separate locations. For example, the irradiation unit may be slid while the detection unit is attached to an arbitrary position on the SCARA robot and observed from a fixed point without sliding.

Further, in the above embodiment, a mode was shown in which the laser displacement meter 3 is scanned using the SCARA robot 2 (by rotating the arm section 6 and the head section 7), but there is no limit to the scanning mechanism of the laser displacement meter 3. For example, the laser displacement meter may be slid using a linear guide or the like. In this case, it is desirable to use a mechanism for rotating the laser displacement meter 3. Further, a mechanism for moving the laser displacement meter in the height direction may be provided.

Further, in the above embodiment, the shape of the optical film is rectangular, but the shape is not limited, and may be other polygons, circles, ellipses, etc., and some of the sides of these shapes may be used. The shape may have a recess.

(Example 1)
Polyethylene terephthalate film (thickness: 53 μm), triacetyl cellulose film (thickness: 40 μm), polarizing film (stretched, iodine-dyed polyvinyl alcohol resin film; thickness: 25 μm), and cycloolefin polymer film (thickness: 23 μm) were adhered in this order. A 250 mm x 300 mm test piece was cut out from a long optical film laminated with an adhesive or an adhesive so that the transport direction (MD direction) was at 45 degrees with respect to the long side.

The obtained test piece had a curvature angle of 90 degrees at the corner where the amount of curvature was greatest among the four corners. Note that the angle of warpage is a value measured by taking a photograph of the cut-out cross section of the test piece (the side surface of the test piece) and using a protractor. Next, the amount of warpage at the corner (=vertical length from the horizontal stage to the end of the test piece) was measured using a JIS Class 1 metal ruler, and found to be 110 mm.

The obtained test piece was placed in a laser displacement meter (product name: Sensor Head LJ-V7300; Keyence Corporation) equipped with a detection part and an irradiation part, with the curved end facing upward, and a stage (Metal Velvet). (registered trademark, manufactured by Acktar); size: 350 mm x 400 mm; hemispherical reflectance: 0.65%) was placed on the stage of the measuring device shown in FIG. The above "hemispheric reflectance" is a value for laser light with a wavelength of 405 nm, and was measured using a spectrophotometer (product name: CM-2600d, manufactured by Konica Minolta) for laser light with a wavelength of 400 nm and 410 nm. This is the value obtained by measuring the hemispherical reflectance and taking the average value.

By setting the distance between the detection part and the stage in the measuring device to 400 mm, and scanning a laser beam with a wavelength of 405 nm at a scanning speed of 50 mm/sec from the end of the stage toward each end of the test piece, The height of the end of the specimen was measured. While scanning the laser beam, the measuring device is set so that the distance between the detection section and the center of the test piece is longer than the distance between the center of the test piece and the irradiation position of the laser beam. did.

As a result, the amount of curvature at the corner where the amount of curvature is the largest among the four corners was detected to be 110 mm, similar to the value measured using a metal ruler. By adjusting the sensitivity of the laser displacement meter during the measurement, we were able to measure without detecting stray light.

(Example 2)
The test piece described in Example 1 was prepared in the same manner as in Example 1, except that Spectral Black (registered trademark; manufactured by Acktar, size: 350 mm x 400 mm; hemispherical reflectance: 0.83%) was used as the stage. The height and amount of warpage of the ends were measured. As a result, the amount of curvature at the corner where the amount of curvature is the largest among the four corners was detected to be 110 mm, similar to the value measured using a metal ruler. Although some stray light was detected during the measurement, by adjusting the sensitivity, we were able to make accurate measurements at a level that poses no problem for practical use.

INDUSTRIAL APPLICATION This invention can be utilized for measuring the warpage of an optical film.

1... Measuring device, 2... SCARA robot, 3... Laser displacement meter, 4... Stage, 5... Robot body box part, 6... Arm part, 7... Head part, 8... Laser light source (irradiation part), 9... CMOS sensor (Detection part), 10... Optical film, A... Viewing area, S... Pedestal part.

Claims (7)

An optical film placed on a stage is scanned with a laser beam from above the optical film from outside the surface of the optical film toward an edge of the optical film, and the laser beam is reflected from the edge. Obtaining information on the height position of the end by detecting light on the rear side of scanning ,
The stage has a hemispherical reflectance of the laser beam of 2% or less,
How to measure optical film warpage. The optical film is polygonal, and the scanning by the laser beam and the acquisition of the height position information are performed at at least two of the vertices of the polygon.
The measuring method according to claim 1 . The laser light is irradiated vertically downward relative to the scanning direction.
The method for measuring according to claim 1 or 2 . a distance between a detection position of the reflected light from the optical film and a center portion of the optical film is longer than a distance between the center portion of the optical film and an irradiation position of the laser light;
The measurement method according to any one of claims 1 to 3 . The optical film is an optical laminated film,
The measuring method according to any one of claims 1 to 4 . a stage on which an optical film is placed;
an irradiation unit that irradiates the optical film placed on the stage with laser light from above;
a movable mechanism that moves the irradiation unit so that it can scan with the laser beam from outside the plane of the optical film toward the end of the optical film;
a detection unit that detects the reflected light of the laser beam reflected by the optical film on the rear side of the scanning side from the irradiation unit ,
The stage is a measuring device in which a hemispherical reflectance of the laser beam is 2% or less. The measuring device according to claim 6 , wherein the optical film is an optical laminated film.

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