JP2001349839A - Inspection method for polarizing film defect - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily inspect micro defects inside a polarizing film. SOLUTION: Light from a light source 21 below is made incident on the polarizing film 20 to observe light transmitted through the polarizing film 20 via a polarizer 22 or polarizer 23. The polarizers 22 and 23 intersect the axis of polarization 24a of a polarizing layer 24 in the polarizing film 20 substantially at right angles. When defects present inside the polarizing film 20 of a laminated structure are observed, upper foreign matter 26 appears to be lighter and lower foreign matter 25 appears to be darker than the overall dark field of view.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting defects of a polarizing film used for a liquid crystal display device or a polarizing filter.

[0002]

2. Description of the Related Art Conventionally, a polarizing film manufactured by stretching a synthetic resin film has been used for a liquid crystal display device or an optical polarizing filter. FIG. 5 shows the principle of a liquid crystal display, and FIG. 6 shows the principle of a polarizing filter.

FIG. 5A shows a state in which light is transmitted in FIG.
(B) shows a state in which light is blocked. Two polarizing plates 1 and 2
Are arranged at intervals so that the polarization axis directions a and b for selectively transmitting the polarization component of the incident light are orthogonal to each other. Between the polarizing plates 1 and 2, two transparent electrodes 3 and 4
Are spaced apart. A liquid crystal layer 5 is filled between the transparent electrodes 3 and 4. Alignment films 6 and 7 are formed on the surfaces of the transparent electrodes 3 and 4 that face each other and are in contact with the liquid crystal layer 5, respectively. The alignment films 6 and 7 are provided with an orientation in a direction orthogonal to the direction.

[0004] In the state shown in FIG.
No voltage is applied between the liquid crystal layers 4, and the liquid crystal molecules 8 in the liquid crystal layer 5 are arranged in the direction in which the alignment is provided on the surfaces of the alignment films 6 and 7, respectively. Since the directions in which the liquid crystal molecules 8 are arranged on both sides of the liquid crystal layer 5 are orthogonal to each other, the direction of the liquid crystal molecules 8 continuously changes in the entire thickness direction of the liquid layer 5. For this reason,
Even if a polarization component whose polarization direction coincides with the polarization axis direction a is selected in the polarization plate 1, the polarization direction changes by 90 ° while passing through the liquid crystal layer 5 and coincides with the polarization axis direction b of the polarization plate 2. , Through the polarizing plate 2.

[0005] In the state shown in FIG.
A voltage is applied between the transparent electrodes 4 and the liquid crystal molecules 8 in the liquid crystal layer 5 are arranged in the direction of the electric field formed between the transparent electrodes 3 and 4. Even if light passes through the liquid crystal layer 5, the polarization direction does not change. Therefore, when a polarization component whose polarization direction coincides with the polarization axis direction a is selected in the polarizing plate 1, the polarization direction does not change even after passing through the liquid crystal layer 5, and is orthogonal to the polarization axis direction b of the polarizing plate 2. Therefore, the light cannot pass through the polarizing plate 2.

The liquid crystal display as described above is called a TN type from a twisted nematic type and is called a normally white mode, and is one of the most typical types of liquid crystal displays. Even in other types of liquid crystal displays, polarized light is often used, and the polarizing plates 1 and 2 are indispensable constituent materials for a liquid crystal display using a liquid crystal display element abbreviated as LCD from Liquid Crystal Device. Today, LCDs
It is widely used in OA equipment, in-vehicle instruments, liquid crystal televisions, liquid crystal projectors, and the like.

FIG. 6 shows that two polarizing filters 9a and 9b are used to transmit light as shown in FIG.
The state in which light is blocked as shown in FIG. In (a), the polarization axis directions a and b of the two polarizing filters 9a and 9b are parallel, and in (b) two polarizing filters 9a and 9b.
Are perpendicular to each other. The state where the polarization axis directions a and b are orthogonal to each other as shown in (b) is called crossed Nicols. The polarizing filters 9a and 9b are used alone or in combination in a field where optical characteristics as shown in FIG. 6 can be used.

FIG. 7 shows an example of a schematic configuration of a polarizing film 10 used as the polarizing plates 1 and 2 in the liquid crystal display shown in FIG. Optical polarization characteristics are given to a PVA (PolyVinyl Alcohol) layer 11. On both sides of the PVA layer 11, TAC (Triallyl Cyanurate) layers 12, 1 for reinforcement are used.
3 are joined to form a polarizer (PL: polarizer) as a whole. As the PL, not only such a three-layer structure but also a five-layer structure is used. The polarization filters 9a and 9b shown in FIG. 6 are used in the state of PL. A protection film 14 for protection is bonded to one surface of the PL. An adhesive 15 is attached to the other surface of the PL,
It is covered with a separate film 16. The separate film 16 can be peeled off from the surfaces of the transparent electrodes 3 and 4 in FIG.

The polarizing plates 1 and 2 are arranged on a liquid crystal display as shown in FIG.
It is necessary that the polarizing film 10 to be used as above does not have a defect such as adhesion of a foreign substance that inhibits light transmission. If there is a defect, even if the liquid crystal molecules 8 of the liquid crystal layer 5 are controlled by an electric field, the state of the light cannot be changed as a whole, and a part of the image display will be lost and the display quality will be reduced. This is because it deteriorates. For this reason, in the manufacturing process of the polarizing film 10, inspection for defects is strictly performed.

[0010]

The inspection of the polarizing film 10 as shown in FIG. 7 is performed by observing the surface enlarged. However, the polarizing film 10
It is formed by laminating a plurality of layers, and a minute foreign matter may enter between the layers. Even if the surface is magnified and observed,
It is very difficult to detect defects such as minute foreign matter inside. A minute foreign substance may change the polarization direction by diffracting light rather than blocking it. A case in which minute luminescent spots or white points are displayed in an originally dark image due to diffraction by minute foreign objects, rather than a case where minute black points are displayed in an originally bright image due to shading by a minute foreign object. Is noticeable. Therefore, there is a strong demand for establishing an inspection method that can easily detect minute defects inside the polarizing film 10.

An object of the present invention is to provide a method for inspecting a polarizing film, which can easily detect minute internal defects.

[0012]

According to the present invention, a light from a light source is transmitted through a polarizing film which selectively transmits only a polarized light component in a predetermined polarization axis direction among incident light,
The light transmitted through the polarizing film is guided to a polarizing plate disposed so as to have a polarizing axis in a direction substantially orthogonal to the polarizing axis. When there is a different portion, if it is brighter than the visual field, it is a defect present on the observation side than the part showing the polarization characteristics of the polarizing film, and if it is darker than the visual field, it shows the polarizing characteristics of the polarizing film. A defect inspection method for a polarizing film, characterized in that it is determined that the defect is located closer to the light source than the portion.

According to the present invention, the polarization component in the direction of the polarization axis of the polarizing film is selected by transmitting the light from the light source through the polarizing film. The selected polarization component is
Since the light passes through a polarizing plate whose polarization axis directions are substantially orthogonal to each other, most of the light is blocked, and the observation results in a dark field as a whole.
If there is a defect on the observation side relative to the portion of the polarizing film exhibiting the polarization characteristics, the polarization direction changes at the defect portion, and the ratio of passing through the polarizing plate increases, so that the overall visual field becomes brighter. If there is a defect on the light source side than the part showing the polarization characteristics of the polarizing film, the amount of light decreases at the defect part, the ratio of passing through the polarizing plate further decreases, so that it looks darker than the entire field of view. Become. Therefore, in the polarizing film having the laminated structure, minute defects existing on the observation side or the light source side of the layer exhibiting the internal polarization characteristics can be easily detected.

Further, according to the present invention, a polarizing film which selectively transmits only a polarized light component in a predetermined polarization axis direction of incident light has a polarization axis in a direction substantially orthogonal to the polarization axis. Through the light from the light source
Observing the light transmitted through the polarizing film, when there is a part having a different overall brightness from the visual field, if it is darker than the visual field, it is present on the observation side than the part showing the polarizing characteristics of the polarizing film. A defect inspection method for a polarizing film, wherein the defect is determined to be a defect that is present on the light source side of a portion showing the polarization characteristics of the polarizing film if the defect is brighter than the visual field.

According to the present invention, the polarizing film for selectively transmitting only the polarized light component in the direction of the predetermined polarization axis of the incident light has a polarization axis in a direction substantially orthogonal to the polarization axis. Even if light from a light source is transmitted, most of the light is blocked, and when the transmitted light is observed, an overall dark field is obtained. If there is a defect on the light source side relative to the portion showing the polarization characteristics of the polarizing film, the polarization direction changes at the defect portion, the ratio of passing through the polarizing film increases, and the entire field of view looks brighter. If there is a defect on the observation side rather than the part showing the polarization characteristics of the polarizing film, the amount of light decreases at the defect part, the rate of passing through the polarizing film further decreases, so that it looks darker than the overall field of view. Become. Therefore, in the polarizing film having the laminated structure, a minute defect existing on the light source side or the observation side of the layer exhibiting the internal polarization characteristics can be easily detected.

In the present invention, the polarizing film is formed by laminating a transparent protective layer on both surfaces of a layer having a polarizing optical characteristic, and the defect exists in the laminating part. It is characterized in that it contains a foreign substance that does.

According to the present invention, a polarizing film formed by laminating a transparent protective layer on both surfaces of a layer having a polarizing optical characteristic can easily detect a foreign substance present in a lamination portion. can do. Such a foreign substance is present inside the polarizing film and is difficult to understand by inspection of the appearance, but can be easily detected in the present invention, including the direction in which it exists.

[0018]

FIG. 1 schematically shows a polarizing film defect inspection method as one embodiment of the present invention. The polarizing film 20 to be subjected to the defect inspection transmits light from the lower light source 21 in a substantially horizontal state. The light transmitted through the polarizing film 20 is reflected by the polarizing plate 22 or the polarizing plate 2.
Observe through 3. The polarizing film 20 has basically the same configuration as the polarizing film 10 shown in FIG. 7, and the inside polarizing layer 24 has optical polarization characteristics. The polarization characteristics of the polarization layer 24 are formed so as to selectively transmit the polarization component in the direction of the polarization axis 24a. Therefore, the light source 21
Is transmitted through the polarizing film 20 even when the light from the polarizing film 20 is isotropic.
The polarization component of the direction is selected.

Above the polarizing film 20, a polarizing plate 22 or 8 whose polarizing axis direction differs from that of the polarizing film 20 by 90 °.
Polarizing plates 23 different by 0 ° are arranged. Polarizing film 20
Since the polarized light component selected in (1) passes through the polarizing plates 22 and 23 whose polarization axis directions are substantially orthogonal to each other, most of the polarized light component is blocked, and a dark field is observed when observed. If there is a lower foreign matter 25 which is a defect on the light source 21 side of the polarizing layer 24 which is a part showing the polarization characteristics of the polarizing film 20, the amount of light is reduced at the lower foreign matter 25 part, and the polarizing plates 22 and 23 are removed. The passing rate is further reduced so that it appears dark. If there is a foreign matter 26 which is a defect on the observation side of the polarizing layer 24 which is a part showing the polarization characteristics of the polarizing film 20, the polarization direction changes at the foreign matter 26 above and passes through the polarizing plates 22 and 23. The rate at which they do so increases, making them appear brighter.

FIG. 2 shows an image of the lower foreign substance 25 and the upper foreign substance 26 viewed through the polarizing plates 22 and 23 of FIG. FIG.
2A shows an image that has passed through the polarizing plate 22, and FIG. 2B shows an image that has passed through the polarizing plate 23. The upper foreign matter 26 looks brighter than the overall visual field 27, and the lower foreign matter 25 looks darker than the overall visual field 27. However, in FIG. 2A, since the visual field 27 is quite dark, the bright foreign matter 26 can be detected very clearly, but the lower foreign matter 25 may not be detected very clearly. . In FIG. 2B, since the field of view 27 is slightly brighter, the portion darkened by the foreign matter 25 below can be more clearly detected.

The brightness of the visual field 27 in FIG.
The polarizing axis of the polarizing plate 23 is the polarizing axis 24a of the polarizing film 20.
It changes according to the angle formed. Therefore, an angle of 80
° is merely an example, and adjustment may be made so that both the lower foreign substance 25 and the upper foreign substance 26 have a detectable brightness within a range close to 90 °.

FIG. 3 schematically shows a defect inspection method for a polarizing film as another embodiment of the present invention. In the present embodiment, portions corresponding to the embodiment of FIG. 1 are denoted by the same reference numerals, and redundant description will be omitted. Light passing through a polarizing plate 22 from a lower light source 21 is incident on the polarizing film 20 to be inspected in a substantially horizontal state. Light source 2
Although 1 is isotropic, as for the light transmitted through the polarizing plate 22, a polarization component in the direction of the polarization axis of the polarizing plate 22 is selected, and light from a substantially polarizing light source is incident. . The direction of the polarization axis of the polarizing plate 22 and the polarization axis 24 of the polarizing film 20
The direction of a is set so as to be substantially orthogonal.

Since light having a polarization component whose polarization axis direction is substantially orthogonal to the polarizing film 20 is incident on the lower part of the polarizing film 20, most of the light is blocked. If the lower foreign matter 25 which is a defect is present on the side of the polarizing plate 22 which is a polarizing light source than the polarizing layer 24 which is a part showing the polarization characteristics of the polarizing film 20, the lower foreign matter 2
At part 5, the direction of the polarization axis of the polarization component changes, and the ratio of passing through the polarizing film 20 increases, so that the image looks bright. If there is a foreign matter 26 which is a defect on the observation side of the polarizing layer 24, which is a part showing the polarization characteristics of the polarizing film 20, the amount of light is further reduced at the foreign matter 26 above and the part looks dark.

FIG. 4 shows an image of the lower foreign substance 25 and the upper foreign substance 26 viewed through the polarizing film 20 of FIG. The lower foreign matter 25 looks brighter than the overall visual field 27, and the upper foreign matter 26 looks darker than the overall visual field 27. The angle of the polarization axis between the polarizing plate 22 and the polarizing film 20 is set to 90.
In this case, since the visual field 27 becomes considerably darker, the bright lower foreign matter 25 can be detected very clearly, but the upper foreign matter 26 may not be detected very clearly. If the angle of the polarization axis is shifted from 90 °, the field of view 27 becomes slightly brighter, so that the portion darkened by the foreign matter 26 above can be more clearly detected. That is, also in the present embodiment, the brightness of the visual field 27 in FIG. 4 changes according to the angle between the polarization axis of the polarizing plate 22 and the polarization axis 24 a of the polarizing film 20. Therefore, by adjusting the angle between the polarization axes, the polarizing film 20 having a laminated structure can be obtained.
Thus, a minute defect existing on the observation side or the light source side of the polarizing layer 24 exhibiting the internal polarization characteristics can be easily detected.

In the embodiment shown in FIGS. 1 and 3, light is transmitted upward from the bottom while the polarizing film 20 is in a substantially horizontal state, but the direction of light at the time of inspection is from the bottom to the top. Of course, it is not limited to. Also,
Observation can not only be performed by the naked eye but also automatically detected by image processing based on an image signal captured by a camera or the like.

Further, in the embodiment of FIG. 1, if the polarizing plate 22 is moved to the light source 21 side, it corresponds to the embodiment of FIG.
Therefore, a defect that is dark and difficult to see in one arrangement is bright and easy to see in the other arrangement. Also,
When the light becomes bright, it depends on the change in the direction of the polarization axis at the defect portion. Therefore, even a transparent foreign substance or defect having no light shielding property can be easily detected.

Further, as an application of the polarizing filter 20,
If it is used for a liquid crystal display element and the front side or the back side on which an image is to be displayed as a liquid crystal display element is known, the inspection can be performed in an arrangement in which a defect on the side conspicuous in use state makes the display brighter.

[0028]

As described above, according to the present invention, light from a light source is transmitted through a polarizing film and a polarizing plate whose polarization axis direction is substantially perpendicular to the polarizing film, so that bright spots or white spots in a dark visual field can be obtained. As a point, it is possible to easily detect a defect present on the observation side with respect to the portion showing the polarization characteristics of the polarizing film. Defects that exist on the light source side of the polarizing film on the light source side with respect to the portion exhibiting the polarizing characteristics cause the ratio of light passing through the polarizing plate to be further reduced and appear dark. Therefore, in the polarizing film having the laminated structure, minute defects existing on the observation side or the light source side of the layer exhibiting the internal polarization characteristics can be easily detected.

According to the present invention, the polarizing film further comprises
Transmits light from a light source configured to have a polarization axis in a direction substantially perpendicular to the polarization axis, and as a bright point or a white point in a dark visual field, closer to the light source than a portion showing the polarization characteristics of the polarizing film. Can be easily detected. Defects that are present on the viewing side of the polarizing film with respect to the portion exhibiting the polarizing characteristics cause the proportion of light passing through the polarizing plate to be further reduced and appear dark. Therefore, in the polarizing film having the laminated structure, minute defects existing on the observation side or the light source side of the layer exhibiting the internal polarization characteristics can be easily detected.

Further, according to the present invention, there is a polarizing film formed by laminating a transparent protective layer on a layer having a polarizing optical property, and a foreign substance present in a laminating portion inside the polarizing film is present. It can be easily detected, including the direction.

[Brief description of the drawings]

FIG. 1 is a view schematically showing a polarizing film defect inspection method as one embodiment of the present invention.

FIG. 2 is a diagram showing how a foreign substance looks in the embodiment of FIG. 1;

FIG. 3 is a view schematically showing a defect inspection method for a polarizing film as another embodiment of the present invention.

FIG. 4 is a diagram showing how a foreign matter looks in the embodiment of FIG. 3;

FIG. 5 is a diagram illustrating the principle of liquid crystal display.

FIG. 6 is a diagram showing how to use a polarizing filter.

FIG. 7 is a diagram illustrating a configuration of a polarizing film.

[Explanation of symbols]

 Reference Signs List 20 polarizing filter 21 light source 22, 23 polarizing plate 24 polarizing layer 24a polarizing axis 25 foreign matter below 26 foreign matter above 27

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2G051 AA90 AB06 AB20 AC21 CA04 CA11 CB02 CC07 EA16 EB01 2H049 BA02 BA26 BB03 BB33 BB43 BC01 BC03 BC22 2H088 FA13 FA18 FA24 FA30 HA18 MA16 2H091 FA08X FA08Z FC30 FC07 FC07 FC07 FC07 FC07 FC07 GA17 HA07 LA11 LA12

Claims (3)

[Claims] 1. A polarizing film that selectively transmits only a polarization component in a predetermined polarization axis direction of incident light, transmits light from a light source, and transmits the light transmitted through the polarizing film to the polarization axis. To a polarizing plate arranged so as to have a polarization axis in a direction substantially orthogonal to, observing the light transmitted through the polarizing plate, when there is a portion different in brightness from the entire visual field, from the visual field If it is too bright, it is a defect present on the observation side than the part showing the polarization characteristics of the polarizing film, and if it is darker than the field of view, it is a defect present on the light source side than the part showing the polarization characteristics of the polarizing film. A defect inspection method for a polarizing film, characterized by making a judgment. 2. A light source configured to have a polarization axis in a direction substantially orthogonal to the polarization axis on a polarizing film that selectively transmits only a polarization component in a predetermined polarization axis direction of incident light. The light transmitted through the polarizing film is observed, and when there is a part having a different brightness from the entire visual field, if the part is darker than the visual field, the part showing the polarization characteristics of the polarizing film is displayed. A defect inspection method for a polarizing film, characterized in that the defect is present on the observation side, and if the light is brighter than the field of view, it is determined that the defect is present on the light source side rather than a portion showing the polarization characteristics of the polarizing film. 3. The polarizing film is formed by laminating a transparent protective layer on both surfaces of a layer having a polarizing optical characteristic, and the defect removes a foreign substance present in the laminating part. The method for inspecting defects of a polarizing film according to claim 1, wherein the method comprises: