Color filter inspection apparatus

In a color filter inspection apparatus (1), an image pickup part (13) for performing an image pickup of a color filter (9) which travels along guide rails (23) from above with a line sensor (130) and a fluorescence lamp (14) for irradiating the color filter (9) with an illumination light from below are provided and an optical filter (131) which transmits a light in a predetermined wavelength band is attached to the image pickup part (13). A transmission wavelength band of the optical filter (131) is a wavelength band in which the transmittance of one color component filter of the color filter (9) is high and transmittances of other color component filters are low. It is thereby possible to inspect unevenness in color of the color filter (9) with respect to one color component filter with high precision.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a color filter inspection apparatus for inspecting unevenness in color of a color filter for a display.

2. Description of the Background Art

When a color filter for a display such as a flat panel display typified by a liquid crystal display is inspected singly, usually, the color filter is irradiated with an orange-colored light of a sodium-vapor lamp or a green light from a lamp called a green lamp. Then, unevenness (mura) in color of the color filter is inspected by visual check of transmission and reflection of the light.

It is very hard, however, to inspect the unevenness in color of the patterned color filter by visual check, and in some cases, the unevenness is not detected until a lighting check is performed after actually manufacturing a display panel.

SUMMARY OF THE INVENTION

The present invention is directed to a color filter inspection apparatus for inspecting unevenness in color of a color filter for a display, and it is an object of the present invention to inspect the unevenness in color of the color filter by transillumination with high precision.

According to the present invention, the color filter inspection apparatus comprises a supporter for supporting a color filter in which a transmittance of one color component filter in a specific wavelength band is higher than a sum of transmittances of other color component filters in the specific wavelength band, a light source for emitting a light to one main surface of the color filter, and an image pickup part located opposite to another main surface of said color filter, for acquiring a two-dimensional image of the color filter by receiving a light in the specific wavelength band from the color filter.

Using a specific wavelength band, the present invention makes it possible to inspect unevenness in color of the color filter with high precision.

Preferably, the transmittance of the one color component filter in the specific wavelength band is as high as or higher than the quadruple of the sum of transmittances of the other color component filters in the specific wavelength band.

According to a preferred embodiment of the present invention, the color filter inspection apparatus further comprises an optical filter provided between the light source and the image pickup part, for substantially removing lights in wavelength bands other than the specific wavelength band, and the light source is a discharge lamp. This allows an easy inspection with high precision.

According to another preferred embodiment of the present invention, the light source has a plurality of LEDs and it is therefore possible to simplify the apparatus and extend the lifetime of the light source.

More preferably, an image pickup direction of the image pickup part is inclined with respect to a normal of a main surface of the color filter supported by the supporter.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1is an elevation showing a constitution of a color filter inspection apparatus1in accordance with the first preferred embodiment of the present invention whileFIG. 2is a plan view thereof. InFIG. 1, for clear illustration, part of the constitution is indicated by phantom lines. The color filter inspection apparatus1serves to inspect unevenness in color of a color filter9used in a display such as a liquid crystal display, which is caused by variation in the amount of applied color resist or abnormality of some nozzles in a manufacturing process.

In the color filter inspection apparatus1, a stage12having an opening121is provided on a base11, being movable in the X direction, and the color filter9is supported on the opening121of the stage12. An image pickup part13having a line sensor130is disposed above the stage12(i.e., located opposite to the upper surface of the color filter9), and a fluorescence lamp14is disposed below the stage12(i.e., located opposite to the lower surface of the color filter9). The image pickup part13performs an image pickup of a long area along the Y direction (a direction perpendicular to the paper) through an inside optical system. The fluorescence lamp14is disposed, facing towards the Y direction, correspondingly to an image pickup area, to emit an illumination light towards a lower main surface of the color filter9.

On the base11, as shown inFIG. 2, a ball screw mechanism22connected to a motor21and guide rails23for guiding the travel of the stage12are disposed, and the stage12is transferred along the guide rail23in the X direction by driving the motor21. The color filter9is thereby transferred along the main surface. At a tip of the image pickup part13, as shown inFIG. 1, an optical filter131which is a wavelength selection filter is provided.

The image pickup part13and the motor21are connected to a control part31(shown in FIG.1). The control part31synchronizes the image pickup of the image pickup part13and the travel of the stage12, to control acquisition of a two-dimensional image of the color filter to be performed by the image pickup part13. An output of the image pickup part13is transmitted to an calculation part32, where an inspection is performed on whether or not there is unevenness in color.

The image pickup and the calculation are performed on each of the three color component filters of R (Red), G (Green) and B (Blue) (i.e., color resists) of the color filter9, and at this time, the optical filters131corresponding to these colors are sequentially attached to the image pickup part13.

As shown inFIG. 1, the image pickup direction of the image pickup part13(the direction of an optical axis of the optical system) is inclined with respect to a normal of the main surface of the color filter9supported by the stage12. The angle of inclination is, e.g., about 10 degrees. This prevents the image pickup part13(especially, the tip of the optical system) from being reflected in the color filter9and imaged, to allow acquisition of a proper image.

Next, the characteristics of the optical filter131will be discussed. A curve81ofFIG. 3indicates the spectral transmittance of the color component filter of R (i.e., the color resist of R) and curves82and83indicate the spectral transmittances of the color component filters of G and B, respectively. As shown inFIG. 3, the spectral transmittances of R, G and B are not fully separated with respect to the wavelength. Therefore, a high-precision inspection can not be achieved when a light having a wide wavelength band is used.

FIG. 4is a graph showing spectral intensity (indicated by a curve85) of a light emitted from the fluorescence lamp14having the same spectral characteristics as the light source of the liquid crystal display has, and the three curves81to83ofFIG. 3are also shown in this figure regardless of the scale on the vertical axis for convenience of explanation. As shown inFIG. 4, the light emitted from the discharge lamp such as the fluorescence lamp14has an emission line spectrum and wavelength bands having high intensity are limited. Then, in the color filter inspection apparatus1, when an inspection is performed on the R component (the color component filter of R) of the color filter9, a filter which transmits a light having a wavelength of 600 nm or more is used as the optical filter131and only the light in a wavelength band with a peak851inFIG. 4is used for the inspection. It is thereby possible to properly inspect unevenness of the R component without effects of the transmittances of the G component and the B component of the color filter.

When an inspection is performed on the G component, only the light in a wavelength band near a peak852is used for the inspection. Specifically, a filter which transmits a light in the wavelength band ranging from 500-530 nm to 550-570 nm is used as the optical filter131. When an inspection is performed on the B component, only the light in a wavelength band near a peak853is used for the inspection, and specifically a filter which transmits a light in the wavelength band of 440-480 nm or less is used as the optical filter131.

As discussed above, in the color filter inspection apparatus1, the image pickup part13receives the light in the wavelength band in which the transmittance of one color component filter is high and the transmittance of any other color component filter is low, to acquire a two-dimensional image which corresponds to the transmittance distribution of a specific color component filter of the color filter9. As a result, it is possible to inspect unevenness of each color filter with high precision and obtain a useful information for the manufacturing process.

Further, using the discharge lamp such as the fluorescence lamp14(among other examples are a xenon arc lamp and a metal halide lamp) as the light source, the color filter inspection apparatus1allows an easy high-precision inspection with the emission line spectrum of the light from the discharge lamp even if the optical filter131does not precisely transmit only the light in the specific wavelength band. When an inspection is performed on the filters of R component or B component, particularly, a high-precision inspection can be achieved only by providing the optical filter131(e.g., colored glass filter) which transmits only a light having a wavelength longer or shorter than a predetermined wavelength in consideration of the wavelength band of the emission line spectrum.

With the image pickup part13having the line sensor130, it is possible to suppress bloating of the optical system in the image pickup part13and achieve an easy inspection even if the large-sized color filter9is inspected.

As shown inFIG. 3, there is no case, generally, where the spectral transmittances of two color component filters are both zero. Therefore, even if a light in any wavelength band is used for the inspection of a filter of one color component (hereinafter, referred to as “specific color component”), it is impossible to completely avoid the effect of unevenness of other color component filters. When the transmittance of the specific color component filter is higher than the sum of transmittances of other color component filters, the effect of the specific color component filter becomes predominant in the acquired image and therefore the inspection can be properly performed.

For higher-precision inspection, it is preferable that the transmittance of the specific color component filter should be as high as or higher than the quadruple of the sum of transmittances of other color component filters.

FIG. 5is an elevation showing a color filter inspection apparatus1in accordance with the second preferred embodiment whileFIG. 6is a left side view thereof. In the color filter inspection apparatus1of the second preferred embodiment, a light box41is provided in the base11and a photodiffusion panel42is attached on the light box41. On the photodiffusion panel42, two supporting guides12aare disposed and the color filter9is placed on the supporting guides12a.

An image pickup part13ahas a two-dimensional image pickup device130aand acquires a two-dimensional image of the color filter9without transferring the color filter9. Between the color filter9and the image pickup part13a, a switching mechanism43is disposed to switch the optical filter131to one for each color component. The switching mechanism43rotates a disk432to which the optical filters131are attached with a motor431(see FIG.5), to sequentially position the optical filters131ahead of the image pickup part13a. Like in the first preferred embodiment, the image pickup direction of the image pickup part13ais inclined with respect to the direction of a normal of the color filter9to prevent unnecessary reflection.

As the light source in the light box41, a fluorescence lamp may be used like in the first preferred embodiment or a light source having a filament may be used. When a light having no emission line spectrum is emitted, the optical filters131in consideration of the characteristics of the color components shown inFIG. 3are prepared. For example, three optical filters131which have wavelength ranges centering on 620 nm, 545 nm and 440 nm, respectively, and a half band width of about 10 nm are attached to the disk432for the R component, the G component and the B component.

It is natural that the characteristics of the optical filter131may be changed as appropriate in accordance with the sensitivity characteristics of the image pickup part13a, the spectral transmittance of each color component filter, the spectral intensity of the light source or the like, and if it is possible to substantially remove lights other than the light in the specific wavelength band in accordance with these characteristics, the optical filter131does not strictly have to transmit only the light in the specific wavelength band.

As discussed above, the color filter inspection apparatus1can also use the two-dimensional image pickup device130a, and in this case, there is no need of the mechanism for transferring the color filter9.

FIG. 7is a view showing part of a constitution of another color filter inspection apparatus. The color filter inspection apparatus ofFIG. 7has the same constitution as that of the first preferred embodiment except that an optical filter131ais disposed between the fluorescence lamp14and the color filter9. Thus, the optical filter may be arbitrarily disposed between the image pickup part and the light source.

FIG. 8is a view showing part of a constitution of still another color filter inspection apparatus. The color filter inspection apparatus ofFIG. 8uses an LED array14aconsisting of a plurality of LEDs (light emitting diodes) arranged in a direction perpendicular to the paper as a light source and no optical filter131is provided, unlike in the first preferred embodiment. Between the LED array14aand the color filter9provided is a photodiffusion panel141for giving uniform linear illumination to the color filter9.

When the LEDs are used as the light source, since the illumination light has a single emission line spectrum, there is no need of the optical filter131and the apparatus constitution is thereby simplified. Further, the lifetime of the light source can be extended. Three kinds of LED arrays14aare prepared for emitting lights in accordance with the respective characteristics of the color component filters and sequentially changed.

Though the preferred embodiments of the present invention have been discussed above, the present invention is not limited to the above-discussed preferred embodiments, but allows various variations.

For example, as a light source for emitting linear illumination perpendicular to a scanning direction of the line sensor130(the X direction of FIGS.1and2), combination of an optical fiber array or a quartz rod and a light source may be used.

If the color filter9is large and hard to support only at its limb, a beam for supporting the center portion of the color filter9may be provided in the opening121of the stage12shown inFIG. 2or between the two supporting guides12ashown in FIG.6.

When the image pickup part13having the line sensor130is used, though the inspection of unevenness in color is repeated for the three color components while an operator changes the optical filters131in the above preferred embodiment, three sets of the image pickup part13having the line sensor130, the fluorescence lamp14(light source) and the optical filter131(or three combinations of the image pickup part13and the LED arrays14a) may be provided for the three color components, respectively. It is thereby possible to inspect three color component filters with only one scan of the color filter9.

Only if the travel of the color filter9is achieved relatively to the image pickup part13having the line sensor130, the image pickup part13may be transferred relatively to the color filter9.