JP2001059795A - Defect inspection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a defect inspection device capable of accurately measuring only the luminance value of a luminescent spot due to a schlieren-defect defective part without including the luminance value of a normal part of a film to be inspected which changes according to a visual angle as background lightness at the time of inspecting a film to be inspected for optical defects from the luminance value of transmission light transmitted through the film to be inspected, which is an object of optical defect inspection. SOLUTION: This defect inspection device with an optical compensating filter is provided with a pair of polarizers 12a and 12b arranged in parallel with a film to be inspected, an illuminating means to project light to the film to be inspected via one polarizers among the pair of polarizer 12a and 12b via the outside of the polarizer, a light receiving means arranged outside the other polarizer to receive the transmission light transmitted through the film to be inspected via the polarizer, and an optical compensating filter 14 made of a liquid crystal cell to sandwich a nematic liquid crystal arranged in parallel with the film to be inspected between the film to be inspected and pair of polarizers 12a and 12b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a defect inspection apparatus capable of performing an optical defect inspection of a film to be inspected and accurately quantifying a change in only a luminance value with respect to a viewing angle caused by a defective portion, and particularly to a liquid crystal display. The present invention belongs to the technical field of a viewing angle widening film defect inspection apparatus capable of accurately measuring a change in only a luminance value with respect to a viewing angle caused by a defective portion of a viewing angle improvement film used for a display device or the like.

[0002]

2. Description of the Related Art Today, TFT liquid crystal display devices and DSTN liquid crystal display devices are widely used as liquid crystal display devices. However, in these liquid crystal display devices, the viewable area has a viewing angle dependency, so that it is difficult to see the display screen if the area deviates from the viewable area. For example, when the viewing angle is tilted upward, the color of the display screen becomes lighter overall and the contrast is reduced. In addition, when the viewing angle is inclined downward, gradation inversion occurs in the black display portion, making it difficult to view. Further, in the screen of a large-sized liquid crystal display device, the viewing angle is widened with the enlargement of the display screen, so that the above-mentioned decrease in contrast and grayscale inversion are likely to occur. Therefore, a liquid crystal display device having a wide visible area is desired.

Under these circumstances, in order to improve the viewing angle of the liquid crystal display device, a method of dividing the orientation of the liquid crystal of the liquid crystal display device, a method of forming a retardation film using an optical compensation film having a negative birefringence, and the like. Are variously studied. For example, Japanese Patent Application Laid-Open No. 6-2114116 disclosed by the present applicant proposes an optically anisotropic element and a method for manufacturing the same. According to this, the liquid crystal molecules of the liquid crystal cell of the liquid crystal display device are slightly inclined from the normal direction of the substrate of the liquid crystal display device when a voltage is applied.
The liquid crystal display device can be regarded as a positive uniaxial optically anisotropic element having an optical axis in a direction slightly inclined from the normal direction.
Therefore, the optical axis of the negative uniaxial optically anisotropic element is slightly tilted in accordance with the tilt, and the phase difference due to the liquid crystal cell is compensated for by the phase difference of the optically anisotropic element, so that a good liquid crystal display device having no viewing angle dependence is provided. Can be obtained. Then, a viewing angle improving film for liquid crystal is marketed by the present applicant.

The viewing angle characteristics of a liquid crystal display device having such a retardation film are measured by using a commercially available viewing angle measuring device (eg, EZContrast manufactured by Nagase Sangyo Co., Ltd. or CV-1000 manufactured by Minolta Co., Ltd.). 0% of the whole or LCD screen.
The lightness (brightness) of the liquid crystal display screen is measured by changing the viewing angle in a square area of 2 mm square to obtain viewing angle dependent data.

A retardation film composed of a low-molecular liquid crystal, which is an optically anisotropic element, is required to have strict homogeneity in order to maintain an optimized compensation state of a liquid crystal cell uniformly on a screen. For example, the above-mentioned viewing angle improving film for liquid crystal is manufactured through various complicated steps of coating liquid crystal on a liquid crystal flexible support, drying, further aligning, and curing the film. In some cases, defects may be caused by adhesion, or defective portions having no desired negative birefringence may occur. Among such defective portions, the defect due to the incorporation of foreign matter and the defect due to adhesion have a bright point on the liquid crystal screen, but have a small viewing angle dependency even when the viewing angle is changed, and the detection of the defect is difficult. It can be done easily. However, a defect having no desired negative birefringence, that is, a defect portion of a schlieren defect is, for example, a bright spot of 0.1 mm or less, or a bright spot of 0.05 mm or less on a liquid crystal screen. Like the defect caused by the inclusion of foreign matter and the defect caused by adhesion, the luminance value of the luminescent spot at the defective part greatly changes depending on the viewing angle, unlike the defect caused by inclusion of foreign matter and the defect caused by adhesion. For example, it has a considerably large viewing angle dependency in a direction perpendicular to the transport direction of the flexible support when applying liquid crystal. In other words, depending on the viewing angle, it may or may not shine as a bright spot, and the viewing angle is strongly dependent. Moreover, the tendency of the viewing angle dependence also differs depending on the content of the schlieren defect.

In a production line for improving the viewing angle of a liquid crystal obtained through a complicated manufacturing process, the luminance is measured from a specific viewing angle direction in accordance with the content of a Schlieren defect having a strong viewing angle dependency and a different viewing angle dependency tendency. It is desirable to inspect specific schlieren defects, but to perform this inspection, it is necessary to correspond in advance the content of schlieren defects that occur in the manufacturing process and the viewing angle dependency of the brightness value of the bright spot caused by the defect part of the schlieren defect. It is necessary to attach.

[0007]

However, in the viewing angle measuring device for measuring the viewing angle characteristics of the liquid crystal screen, a defect due to the incorporation of foreign matter, a defect due to adhesion or a schlieren in a region of 0.2 mm or more on the liquid crystal screen. It is only possible to confirm the presence of a luminescent spot in a defective portion of a defect, and it is not possible to measure a change in luminance due to the viewing angle of the luminescent spot in the defective portion and to make the viewing angle dependency of this luminance value correspond to the content of the defect. .

On the other hand, a polarizer is sandwiched on both sides of a viewing angle improving film for a liquid crystal, and projection light for defect inspection is incident from one of the outside of the polarizer, and transmitted light transmitted from the opposite side is received by a CCD camera or the like to detect a defect. It is considered that the luminance signal of the portion can be obtained, and the viewing angle dependence of the luminance value of the bright spot of the defect inspection portion can be measured using the luminance signal. However, at this time, since the viewing angle improving film for a liquid crystal to be inspected itself is a negative uniaxial optical anisotropic element having a birefringence, the luminance value of a normal portion also changes depending on the viewing angle. As a result, it is not possible to obtain only a change in the brightness value of the luminescent spot of the defective portion due to the influence of the change in the brightness of the normal portion. By subtracting the viewing angle dependency of the luminance value of the normal portion from the viewing angle dependency of the brightness value of the bright point of the defective portion, it is also possible to estimate the viewing angle dependency of only the brightness value of the bright point of the true defective portion. However, the difference between the luminance value of the luminescent spot caused by the defective portion of the schlieren defect and the luminance value of the normal portion cannot be accurately measured because the luminance value of the normal portion has a large viewing angle dependency. Such a problem is common to not only the liquid crystal viewing angle improving film but also the entire retardation film using the refractive index.

Therefore, the present invention solves the above problems,
A defect inspection apparatus for inspecting an optical defect of a film to be inspected from a luminance value of transmitted light transmitted through a film to be inspected as an object of an optical defect inspection, wherein the luminance of a normal portion of the film to be inspected varies with a viewing angle. It is an object of the present invention to provide a defect inspection apparatus capable of accurately measuring only a luminance value of a luminescent spot caused by a defect part of a Schlieren defect without including the luminance as a background lightness (luminance).

[0010]

In order to achieve the above object, the present invention provides a pair of polarizers arranged on both sides of a film surface of a film to be inspected for optical defects in parallel with the film to be inspected. Arranged outside between the pair of polarizers, an illuminating means for projecting the film to be inspected through one of the pair of polarizers, and an outer portion between the pair of polarizers,
Arranged on the opposite side of the arranging position of the illuminating unit, between the light receiving unit that receives the transmitted light emitted from the illuminating unit and transmitted from the film to be inspected through the other polarizer, and between the two electrode substrates A liquid crystal filter composed of a liquid crystal cell sandwiching a nematic liquid crystal that is a rod-shaped liquid crystal compound, comprising a film to be inspected and an optical compensation filter arranged in parallel with the film to be inspected between one of the pair of polarizers,
An object of the present invention is to provide a defect inspection apparatus for inspecting an optical defect of a film to be inspected by obtaining a luminance signal of transmitted light including a defect portion of the film to be inspected transmitted from the film to be inspected by the light receiving means.

At this time, in the optical compensation filter, the direction of the apparent optical axis based on the birefringence index substantially coincides with the direction of the apparent optical axis of the film to be inspected having the birefringence index. By making the total value of the retardation value in the apparent optical axis direction of the optical compensation filter and the retardation value in the apparent optical axis direction of the film to be inspected substantially zero, the optics based on the birefringence of the film to be inspected. It preferably has a birefringence which cancels anisotropy and a thickness of the liquid crystal cell. When the film to be inspected is made of a discotic compound and the orientation is tilt orientation or hybrid orientation, the nematic liquid crystal of the optical compensation filter is preferably tilted or hybrid orientation. Further, it is preferable to provide an incident angle adjusting means for adjusting an incident angle of the projection light incident on the film to be inspected.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a defect inspection apparatus according to the present invention will be described in detail based on a preferred embodiment shown in the accompanying drawings. Note that the defect used hereinafter refers to the above-described Schlieren defect.

FIGS. 1A and 1B show the defects of the present invention.
Defects in viewing angle improving film for liquid crystal, which is an example of inspection equipment
Of the defect inspection apparatus 10 with an optical compensation filter for performing inspection
A front view and a side view are shown, respectively. Figure 2 shows the optical compensation
FIG. 3 is an explanatory diagram showing a main part of the defect inspection apparatus 10 with a filter.
is there. In addition, the defect inspection of the defect inspection apparatus of the present invention uses a liquid crystal.
Birefringence not limited to defect inspection of viewing angle improving film
It can be applied to defect inspection of retardation film using
You. The defect inspection device 10 with the optical compensation filter
The viewing angle improving film for liquid crystal to be inspected
Films to be inspected on both sides of the film surface of F
F, a pair of polarizers 12a and
And 12b, between the polarizer 12b and the film F to be inspected
Optical compensating filter 14 arranged in parallel to
2b, and placed under the polarizer 12b to be inspected.
A light source 16 for projecting the film F and an outer side of the polarizer 12a
Arranged above, the transmitted light transmitted from the film to be inspected F
A CCD camera 18 that receives light through the polarizer 12a;
Photon 12b, optical compensation filter 14, filter to be inspected
-F and a light source 16 sequentially incident on the polarizer 12a.
By adjusting the incident angle of the projection light, the defect portion of the film F to be inspected
Angle for measuring the viewing angle dependence of the luminance value of the bright spot
(Viewing angle) θ which is an adjustment mechanism ₁Mainly with stage 28
It is composed.

Defect inspection apparatus 10 with optical compensation filter
In general, as shown in FIG. 2, the polarizers 12a are arranged in parallel on both sides of the film F to be inspected for optical defects.
And 12b, and an optical compensation filter 14 is arranged between the polarizer 12b and the film F to be inspected in parallel with the film F to be inspected. Light source 16 on inspection film F
, Incident light is incident at an incident angle of a predetermined viewing angle θ ₁ , and transmitted light of the film F to be inspected coming out of the polarizer 12 a is transmitted by the CCD camera 18 disposed above and outside the polarizer 12 a. This is a device that receives light and measures the luminance value of the defective portion from a signal obtained by receiving the light.

The polarizer 12a is a part that linearly or substantially linearly deflects the projection light emitted from the light source 16 and causes the light to enter the optical compensation filter 14, and a known deflector is used. The polarizer 12b is disposed in parallel with the polarizer 12a, and transmits through the optical compensation filter 14 and the film F to be inspected, and is linearly deflected in one predetermined direction;
Alternatively, it is a part that transmits a part of the transmitted light of the elliptically-deflected defect part, and a known polarizer similar to the polarizer 12a is used. Note that the polarizers 12a and 12b are arranged in a crossed Nicols system with a deflecting direction, and when the transmitted light has no deflecting component in the deflecting direction of the polarizer 12b,
The transmitted light does not pass through the light.

The light source 16 is a light source for irradiating projection light for projecting a defective portion of the film F to be inspected, and is not limited as long as it is a light source of projection light having a spectrum in a visible region, and a white light source is particularly preferable. The CCD camera 18 receives light from the light source 16
It receives light transmitted at a predetermined angle and transmitted through the polarizer 12b, the optical compensation filter 14, the film F to be inspected, and the polarizer 12a, and obtains a luminance signal of the transmitted light. On the other hand, it is arranged on a Z stage 22 whose position in the height direction can be adjusted. The height of the Z stage 22 can be adjusted with the manual knob 24. When the transmitted light is received by the CCD camera 18, the objective lens 26 is arranged and adjusted below the CCD camera 18 so that the transmitted light appropriately forms an image on the light receiving surface where the CCD elements are arranged. .

The defect inspection apparatus 10 with an optical compensation filter comprises a film F to be inspected and an optical compensation filter 14.
From the outside and the film F to be inspected and the optical compensation filter 1
4 After holding together the measurement layer L composed of polarizers 12a and 12b to sandwich is placed on the theta ₂ stage 34 to be described later, the angle of incidence of the projected light entering the object to be inspected film F (viewing angle) theta _In order to adjust _1, as shown by a two-dot chain line in FIG. 1B, a θ ₁ stage 28 capable of tilting the measurement layer L by a predetermined angle is provided. This θ ₁ stage 2
Angle adjustment of 8 is carried out manually knob 30, the incident angle (visual angle) theta ₁ can be adjusted in the range of +60 degrees -60 degrees. Incident angle (viewing angle) adjusted with manual knob 30
theta ₁ of reading is performed by being converted to a rotation angle from mechanically connected pulse signal transmitted to the data processing unit 38 obtained by the rotary encoder 32 which is the rotation shaft of the theta ₁ stage. Further, the defect inspecting apparatus 10 with the optical compensation filter includes a θ ₂ stage 3 that can rotate the measurement layer L in a predetermined azimuth direction (azimuth angle θ ₂ ).
4 is provided. The rotation adjustment of the azimuth angle θ ₂ by the θ ₂ stage 34 can be adjusted by the manual knob 36 in the entire range of 0 to 360 degrees. The theta ₂ stage 34 is provided, perform adjustment of the azimuth direction, the luminance value of the bright point of the defect portion, in addition to greatly varies depending on the incident angle (visual angle) theta ₁ of the projection light,
Since also vary azimuthally theta _2.

The optical compensation filter 14 has a nematic liquid crystal 14a as shown in FIG. The nematic liquid crystal 14a is a glass substrate 1 having rubbed alignment films 14c, 14c having transparent electrodes 14b, 14b.
4d, 14d, and further, the transparent electrodes 14b, 1
4b, the rod-shaped liquid crystal compound of the nematic liquid crystal 14a is applied to the glass substrates 14d and 14d by applying a predetermined voltage.
It is configured to perform tilt alignment or hybrid alignment in a predetermined direction from the substrate surface of d.

The optical characteristics of the optical compensation filter 14 are shown.
Orientation direction of rod-shaped liquid crystal compound defining birefringence and
The retardation value is determined as follows. Inspected
Approximate the optical refractive index characteristics of film F as a refractive index ellipsoid
And its triaxial refractive index is given by n₁, N_TwoAnd n_ThreeToss
You. Here, the refractive index n_TwoAnd the refractive index n_ThreeAre almost equivalent
And the refractive index n₁Direction is the optical axis direction (apparent optical axis
Direction). At this time, ｛n₁− (N_Two+ N_Three) /
2 x (thickness of film F to be inspected)
Retardation value R_thIs defined. In addition, optical compensation
The optical refractive index characteristics of the filter 14 are
Similarly, it is approximately treated as a refractive index ellipsoid,
N₁, N_TwoAnd N_Three(Refractive index N₁Who have
Direction is the apparent optical axis direction), ΔN₁− (N_Two+
N _Three) / 2｝ × (thickness of liquid crystal cell of liquid crystal filter 14)
B) Apparent optical axis direction retardation value R_THAnd definition
I do. At this time, the film F to be inspected has a refractive index n₁Look with
The optical axis direction and the optical compensation filter 14 have a refractive index N₁To
The direction of the apparent optical axis substantially matches the retardation value
R_thSo that the sum of
That is, the total value is adjusted to be 0 to 50 nm. Like
Specifically, the adjustment is performed so that the total value is 0 to 20 nm.

Here, the retardation value means that when light travels in a liquid crystal having a birefringence, the refractive index varies depending on the direction of the vibration plane of the light, for example, in two directions perpendicular to the traveling direction. Are different from each other, the transmitted light transmitted from the liquid crystal has a phase difference depending on the directions of the two orthogonal directions, but this is an amount relating to the phase shift at that time. Therefore, the amount of phase shift also changes according to the distance that light travels through the liquid crystal, that is, the thickness of the liquid crystal. Therefore, the retardation value can be set to a desired value by adjusting the thickness of the liquid crystal cell of the optical compensation filter 14 so that the phase shift amount is eliminated.

For example, when the film F to be inspected is a negative uniaxial optical anisotropic element, the optical compensation filter 14 is a positive uniaxial optical anisotropic element, and the apparent optical axis of the optical compensation filter 14 is the apparent optical axis of the film F to be inspected. The optical compensation filter 14 is designed such that the sum of the apparent retardation value of the optical compensation filter 14 in the optical axis direction and the apparent retardation value of the film F to be inspected is substantially zero. . That is, the film F to be inspected and the optical compensation filter 14 are formed so as to be an optical element having an optically isotropic refractive index by overlapping.

FIG. 4 shows the optical compensation filter 14 and the optical compensation element 14 when the optical anisotropic element of the filter F to be inspected is a negative refractive index ellipsoid and the liquid crystal of the optical compensation filter 14 is approximated by a positive refractive index ellipsoid. The state of the transmitted light transmitted through the inspection film F and these optical elements is described. As shown in FIG. 4, is projected by the light source 16 from the lower side in the figure, the projection light deflected in one direction through the polarizer 12b is incident on the optical compensation filter 14 at an angle of incidence angle (visual angle) theta ₁ I do.
The optical compensating filter 14 is represented by a positive refractive index ellipsoid 40 as shown in the figure, and the birefringence becomes an elliptically polarized transmitted light 42 having a phase difference in advance.
2 is incident on the film F to be inspected. Inspection film F
Is represented by a negative refractive index ellipsoid 44, and the direction of the apparent optical axis is the same as that of the optical compensation filter 14, so that the film F to be inspected cancels the phase difference previously set by the optical compensation filter 14. And optical compensation filter 1
Since the retardation value of 4 is set, the transmitted light transmitted through the normal portion of the film F to be inspected returns to substantially linearly deflected light, and transmitted light having a component deflected in the deflection direction of the deflector 12a. For example, the light other than the light transmitted through the defective portion of the film F to be inspected is not transmitted, and does not reach the CCD camera 18. Similarly, when the film F to be inspected is a positive uniaxial optical anisotropic element, the optical anisotropy of the inspected filter 14 can be compensated by using the optical compensation filter 14 as a negative uniaxial optical anisotropic element.

In the defect inspection apparatus 10 with an optical compensation filter according to the present embodiment, as shown in FIG. 2, the optical compensation filter 14 is disposed closer to the light source 16 than the film F to be inspected. After the projection light is given a phase difference according to the ratio, it is made incident on the film F to be inspected. The projection light is first made incident on the film F to be inspected, and the transmitted light having the phase difference is passed through the optical compensation filter 14. In order to compensate, the film F to be inspected is
4 may be arranged on the light source 16 side.

As described above, in the present invention, the apparent optical axis is aligned with the apparent optical axis of the film F to be inspected, and the transmitted light generated due to the difference between the apparent optical axis of the film F to be inspected and the refractive index in the direction orthogonal thereto. By compensating the phase shift amount due to the direction of the vibration surface by the optical compensation filter 14, it is possible to obtain transmitted light having no phase shift and no elliptical deflection, and the viewing angle dependence of the luminance value of the normal portion of the film F to be inspected. Properties can be suppressed.

The nematic liquid crystal 14a of the optical compensation filter 14 having such optical characteristics is configured as follows. For example, the material of the film to be inspected F is
In the case of a tilt alignment in which the alignment angle is constant, or a hybrid alignment in which the alignment angle is gradually changed in the thickness direction of the liquid crystal, the optical compensation filter 14 is formed of a disc-shaped compound composed of a triphenyl derivative. It is preferable that the nematic liquid crystal 14a is tilt-aligned or hybrid-aligned in accordance with the alignment direction of the discotic compound. The nematic liquid crystal 14a may be any known liquid crystal. For example, as shown below, two 1,4-phenyl groups are directly connected as cores, and a cyan group and an alkyl group are used as terminal groups. And a structure in which the two cores are arranged to extend on both sides of the two cores.
A typical example is a structure in which a -COO- group is disposed as a bonding group between two cores.

Embedded image

Embedded image

When the optical compensation filter 14 is not provided, a retardation film having a birefringence for expanding a viewing angle, when combined with a polarizer, causes a large change in the amount of transmitted light depending on the viewing angle. The brightness change of the bright spot in the normal part is large, which affects the brightness change of the bright spot in the defective part, and it is not possible to obtain only the brightness change of the bright spot caused by the defective part. However, the optical compensation filter 14
The transmitted light from the normal part is
Since the light does not reach the camera 18 and the brightness value is small and does not change with the viewing angle, only the change in the brightness value of the bright spot of the defective portion is measured, and the change of only the brightness value of the bright spot caused by the defective portion can be easily performed. Obtainable.

The defect inspection apparatus 10 with an optical compensation filter is connected to a data processing apparatus 38 comprising a computer which converts the luminance signal obtained by the CCD camera 18 into digital data and converts it into image data to produce image data. The data processing device 38 specifies the position of one pixel or the range of a plurality of pixels having the highest bright spot of the defective portion from the image obtained by the data processing unit 38, and sets the predetermined viewing angle (incident angle) θ ₁ and the predetermined The luminance value at the azimuth angle θ ₂ can be obtained. When specifying a range of a plurality of pixels, an average value of luminance values is obtained.
Further, a luminance signal value in a specified position or a specified range may be obtained by the above method. Also, the θ ₁ stage 28
Is adjusted to change the visual angle (incident angle) θ _1, and the change in the luminance value of the luminescent spot of the defective portion is measured. As shown in FIG. Only the viewing angle dependency can be obtained.

Defect inspection apparatus 10 with optical compensation filter
Is configured as described above. Next, a method for obtaining the viewing angle dependency of the luminance value of the luminescent spot of the defect portion of the film to be inspected F using the defect inspection device 10 with the optical compensation filter will be described.

First, the film F to be inspected is inserted between the polarizer 12a and the optical compensation filter 14, and the polarizer 12a,
Inspected film F, to form a measurement layer L arranged in parallel to the optical compensation filter 14 and the polarizer 12b, it is placed and fixed on the theta ₂ stage 34. Further, a metal plate (not shown) having a hole with a diameter of 1 mm is stacked on the outside of the polarizer 12a,
The defect portion of interest is visually adjusted in advance to match the hole having a diameter of 1 mm. While maintaining this arrangement,
The Z stage 22 adjusts the position in the height direction with respect to the base 20 so that an image is appropriately formed on the light receiving surface on which the CCD elements are arranged. Further, the azimuth angle θ ₂ is adjusted to a desired value by the θ ₂ stage 34. In the case of a retardation film, for example, a viewing angle improving film for liquid crystal, defects such as uneven coating of liquid crystal when coating liquid crystal on a flexible support and disorder of alignment during rubbing treatment are caused by azimuth angle θ. _This is because the viewing angle dependency may not be properly obtained in some cases. The adjustment method of the azimuth angle θ ₂ is the CCD camera 1
8 to display the captured image to the image display device (not shown) included the images captured to the data processing unit 38 by, locating the azimuth angle theta ₂ which the highest luminance value of the bright points of the defective portion.

Next, the pulse signal of the rotation angle sent from the rotary encoder 32 is read in the range of the viewing angle (incident angle) θ ₁ from −60 degrees to +60 degrees while maintaining the fixed azimuth angle θ _2. Then, a visual angle θ ₁ is set, and an image including a bright spot of a defective portion is photographed by the CCD camera 18 while being visually aligned with a hole having a diameter of 1 mm of the metal plate. The luminance signal of the photographed image is sent to the data processing unit 38, and is subjected to AD conversion, LOG conversion, and the like to obtain image data.
The image is displayed on an image display device (not shown). The operator
From the displayed image, a bright point of the defective portion is designated in a pixel unit or a plurality of pixels by an input system such as a mouse or a keyboard, and the luminance value of the bright point of the defective portion is measured.

As described above, the optical compensation filter 14 is provided with an optical compensation filter 14 for compensating the optical anisotropy of the film F to be inspected, and is optically isotropic by overlapping the optical compensation filter 14. Since it is configured to have a natural refractive index, the luminance value of a normal portion of the film F to be inspected has no viewing angle dependency, and a constant luminance value independent of the viewing angle θ ₁ can be obtained. Therefore, the luminance value of the luminescent spot of the defective portion is not affected by the luminance value of the normal portion. As a result, by changing the viewing angle θ ₁ using the θ ₁ stage 28 and measuring the brightness value of the bright spot of the defective portion, it is possible to obtain only the change of the brightness value of the bright spot caused by the defective portion. In addition, it is possible to obtain the viewing angle dependency of only the brightness value of the bright spot caused by the defective portion.

An embodiment using such a defect inspection apparatus 10 with an optical compensation filter will be described. Inspection film F
Is a viewing angle improving film for liquid crystal, and was a WV film manufactured by Fuji Photo Film Co., Ltd. used for a TFT liquid crystal display device. The WV film is a retardation film in which a discotic liquid crystal composed of a triphenylene derivative is oriented in a predetermined direction. The discotic liquid crystal is a liquid crystal having a known structure having a disk-shaped core and a structure in which side chains extend radially from the core.

The birefringence, which is an optical characteristic of the WV film, is measured by using an automatic birefringence measuring device ABR-10 manufactured by Uniopt.
When measured using A, it can be approximated by a refractive index ellipsoid having an optically negative uniaxial characteristic, and the viewing angle direction having the minimum value of the retardation value, that is, the apparent optical axis direction is the WV film surface. The direction was inclined 23 degrees from the normal line. Further, the apparent retardation value R _th in the direction of the optical axis was obtained, and a value of −100 nm was obtained.

Accordingly, an optical compensating filter for compensating for the birefringence having a negative uniaxial characteristic of the WV film was prepared. The WV film has an apparent optical axis in a direction inclined by 23 degrees from the normal to the surface of the WV film, and the apparent optical axis is oriented in the direction of 23 degrees from the direction normal to the substrate surface of the glass substrate 14d. A birefringent optical compensation filter 14 having a positive uniaxial characteristic was prepared. As the nematic liquid crystal, a cyclohexane-based liquid crystal blend that forms a nematic phase at 15 ° C. or higher and within 40 ° C. is adopted, and the polyimide-based alignment films 14 c and 14 c rubbed by a known method are used as glass substrates 14.
d, placed and sealed on the transparent electrode layers 14b, 14b disposed on the 14d, and after the nematic liquid crystal is once made homogeneously oriented, the apparent optical axis is directed at 23 degrees from the normal direction of the glass substrate surface. As described above, the transparent electrode layers 14b, 14
A predetermined voltage was applied to b. As a result, the glass substrate 14
The liquid crystal of tilt alignment in which the liquid crystal molecules were inclined by 67 degrees from the substrate surface of d could be obtained. Incidentally, to compensate for the retardation values of WV filter, in order to obtain the optically isotropic refractive index, so that the retardation value R _TH apparent optical axis of the optical compensation filter 14 is + 110 nm,
The thickness of the liquid crystal was adjusted. Even after the tilt alignment, the apparent retardation value R _TH of the optical compensation filter 14 in the optical axis direction was +110 nm.

First, it was examined how the transmittance of a normal portion of the WV film changes depending on the presence or absence of the optical compensation filter 14. First, assuming that the optical compensation filter 14 is not provided, the optical compensation filter 14 is extracted from the defect inspection apparatus 10 with the optical compensation filter, and the viewing angle (incident angle) θ ₁ with respect to the measurement layer including the polarizer and the WV film is −80. The ratio of the transmitted light to the projected light, that is, the transmittance, was measured in the range of + 80 ° to + 80 °, and FIG.
The result shown in (A) was obtained. According to this, the viewing angle θ ₁ is 0
Every i.e., projection light incident from the normal direction of the film surface of the WV film can transmittance hardly transmitted close to zero, the viewing angle theta ₁ is separated from 0 °, + - large transmittance exceeds 15 degrees It was found that light was easily transmitted. On the other hand, as the case where the optical compensation filter 14 is provided, the defect inspection apparatus 10 having the optical compensation filter 14 having the optical compensation filter 14 is used.
The transmittance was measured in the same manner as in the case where No. 4 was not provided. As a result, as shown in FIG. 5B, it was found that the viewing angle dependence of the transmittance was extremely small, and the transmittance was almost zero. As described above, when the optical compensation filter 14 is not provided, the brightness of the normal portion around the defective portion sharply increases, which affects the measurement of the brightness value of the luminescent spot of the defective portion, and corrects the brightness caused by the defective portion. It is not possible to obtain only luminance values.

Then, the defect portion of the WV film is visually observed, and first, assuming that there is no optical compensation filter, the optical compensation filter 14 is extracted from the defect inspection apparatus 10 with the optical compensation filter, and the measurement layer composed of the polarizer and the WV film is obtained. Was used to measure the change in the brightness value of the luminescent spot at the defective portion. Measurements incident angle (visual angle) theta ₁ a -
Shaking was performed in the range of 45 degrees to +50 degrees. As a result, a graph of the viewing angle dependence of the brightness value of the luminescent spot at the defective portion shown in FIG. 6A was obtained. Further, the change in the luminance value of the luminescent spot of the same defect portion was measured in the range of −60 ° to + 60 ° using the defect inspection device 10 with an optical compensation filter which is the defect inspection device of the present invention. As a result, a graph of the viewing angle dependency of the luminance value of the luminescent spot at the defective portion shown in FIG. 6B was obtained. FIG. 6 (A)
6B, the optical compensation filter 1
Without the 4, when the viewing angle theta ₁ is greater than +20 degrees or visual angle theta ₁ is the luminance value of the smaller becomes the luminescent spot than -40 degrees, in correspondence with the viewing angle dependence shown in Figure 6 (A) 6B, it is not possible to accurately obtain only the brightness value of the bright spot caused by the defective portion. However, when the optical compensation filter 14 is used, the viewing angle dependency is small as shown in FIG. Therefore, unlike FIG. 6A, the viewing angle θ ₁ is +
Even in the range range and viewing angle theta ₁ is greater than 20 degrees is smaller than -40 degrees, could be obtained only the luminance value of the bright spot caused by defective portion accurately. As described above, it is apparent that the defect inspection apparatus of the present invention can accurately obtain only the brightness value of a bright spot caused by a defective portion.

According to the present invention, since only the brightness value of the bright spot caused by the defective portion can be accurately obtained, the visual angle dependency of only the brightness value of the bright spot caused by the defective portion is obtained. Can be associated in advance with the viewing angle dependence of only the brightness value of the luminescent spot of the defect part of the schlieren defect generated by the schlieren defect, and the brightness measurement by the viewing angle from a specific direction is manufactured to inspect a specific schlieren defect It can be done on line. Further, the defect inspection with the optical compensation filter of the present invention is applied only when the angle of incidence of the projection light on the film F is changed to measure the viewing angle dependency of the luminance value of the luminescent spot of the defect portion. Instead, when the transmitted light transmitted through the phase difference film or the like is received by a CCD camera or the like for photographing, the background lightness (luminance) at both ends of the photographing where the viewing angle of the camera becomes large is suppressed. Defect detection can be performed stably.
In particular, when photographing for defect inspection with a wide field of view, the brightness (luminance) of the background can be kept constant not only at both ends of the photographing area but also in a relatively central part of the photographing area. As a result, the defect can be detected more stably without erroneous detection.

Although the defect inspection apparatus of the present invention has been described in detail above, the present invention is not limited to the above embodiment, and various improvements and modifications may be made without departing from the gist of the present invention. Of course.

[0039]

As described above in detail, according to the present invention, when inspecting an optically defective portion of a film to be inspected, an optical compensation filter is used in accordance with the birefringence of the film to be inspected. Since the birefringence of the film to be inspected can be compensated for, the luminance of the normal portion of the film to be inspected, which varies with the viewing angle, is not included as background brightness (luminance).
Only the brightness value of the luminescent spot caused by the defective portion can be accurately measured. In addition, since an incident angle adjusting means for adjusting the incident angle of the projection light is provided, it is possible to accurately measure a change in only the luminance value with respect to the viewing angle caused by the Schlieren defect, and to determine the content of the Schlieren defect and the viewing angle of the luminance value of the bright spot of the defect Dependencies can be associated in advance. Further, when the transmitted light transmitted through the phase difference film or the like is received and photographed by a CCD camera or the like, the brightness (brightness) of the background at both ends of the photographed portion where the camera viewing angle becomes large is suppressed, and defects at both ends are reduced. Detection can be performed stably.

[Brief description of the drawings]

FIG. 1A is a front view showing an embodiment of a defect inspection apparatus of the present invention, and FIG. 1B is a right side view of the embodiment shown in FIG. 1A.

FIG. 2 is an explanatory view schematically illustrating a main part of an embodiment of the defect inspection apparatus of the present invention.

FIG. 3 is a sectional view showing an embodiment of an optical compensation filter of the defect inspection apparatus of the present invention.

FIG. 4 is an explanatory diagram illustrating the operation of an optical compensation filter and a film to be inspected in the defect inspection device of the present invention.

FIGS. 5A and 5B are explanatory diagrams illustrating the difference in the viewing angle dependence of the transmittance of the normal portion of the film to be inspected depending on the presence or absence of an optical compensation filter.

FIGS. 6A and 6B are explanatory diagrams illustrating the difference in the viewing angle dependence of the luminance value of a defective portion of a film to be inspected depending on the presence or absence of an optical compensation filter.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Defect inspection apparatus with an optical compensation filter 12a, 12b Polarizer 14 Optical compensation filter 16 Light source 18 CCD camera 20 Base 22 Z stage 24, 30, 36 Manual knob 26 Objective lens 28 θ ₁ stage 32 Rotary encoder 34 θ ₂ stage 38 Data processing unit 40, 44 Index ellipsoid 42 Transmitted light

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G02F 1/13 505 G02F 1/13 505 3F048 F-term (Reference) 2F065 AA49 BB01 BB22 CC02 DD09 EE00 FF02 FF49 FF65 GG24 HH10 HH12 HH13 HH14 JJ03 JJ08 JJ09 JJ26 LL04 LL21 LL33 PP02 PP13 QQ00 QQ03 QQ28 SS02 SS13 2G051 AA41 AA90 AB06 AB20 BA11 CA04 CB02 CC20 EA25 2G086 EE05 EE10 2H049 BA02 GA06A03 BA02 GA06A03

Claims (2)

[Claims] 1. A pair of polarizers arranged in parallel with the film to be inspected on both sides of a film surface of the film to be inspected for inspecting an optical defect, and a pair of polarizers arranged outside between the pair of polarizers. Illuminating means for projecting the film to be inspected via one of the polarizers, and an outer side between the pair of polarizers, disposed on a side opposite to the arranging position of the illuminating means, and projected by the illuminating means. And a liquid crystal filter comprising a liquid crystal cell in which a nematic liquid crystal as a rod-shaped liquid crystal compound is sandwiched between two electrode substrates, An optical compensation filter disposed between the film to be inspected and one of the pair of polarizers in parallel with the film to be inspected; A defect inspection apparatus for inspecting an optical defect of a film to be inspected by obtaining a luminance signal of transmitted light including a depressed portion. 2. The optical compensation filter according to claim 1, wherein the direction of the apparent optical axis based on the birefringence index substantially coincides with the direction of the apparent optical axis of the film to be inspected having the birefringence index. By making the sum of the retardation value in the optical axis direction of the optical compensation filter and the retardation value in the apparent optical axis direction of the film to be inspected substantially zero, the optical difference due to the birefringence of the film to be inspected. The defect inspection apparatus according to claim 1, wherein the defect inspection apparatus has a birefringence that cancels anisotropy and a thickness of the liquid crystal cell.