DESCRIPTION TITLE OF THE INVENTION: FILM DEFECT INSPECTION DEVICE, DEFECT INSPECTION METHOD, AND RELEASE FILM

TECHNICAL FIELD

[0001]

The present invention relates to the technical field of a defect inspection device and a defect inspection method with which optical defect inspection of an inspection target film is performed simply and at ease, and particularly, with which defect inspection is continuously performed prior to polarizer work processing of a polarizer release film, which is used in a polarizer manufacturing process.

BACKGROUND ART

[0002]

In recent years, there is rapid and increasing demand for liquid crystal displays (LCDs) , which are advantageous in being thin and light-weight, consuming small power, and possessing high light quality as compared to the conventional displays, i.e., CRTs. In particular, demand for LCDs for large-screen monitors and large-screen TVs, e.g., 32 inches or more, is rapidly increasing. Addressing an increase in the screen area of the LCDs, adequate brightness of large screen LCDs is secured often by increasing the brightness of backlight or installing a functional film which improves brightness. With such an LCD of high brightness type, because of its high brightness, small defective spots existing in the display often cause a trouble. The constituents such as polarizers and phase difference plates which possess optical characteristics suffer from defective spots of the size being negligible for conventional LCDs. Therefore, while avoiding occurrence of defective spots in the manufacturing process of the optical members, what is becoming important is an improvement in inspection performance with which defective spots can surely be recognized even if the defective spots occur.

[0003]

The defective spot inspection of a polarizer is generally performed by visual inspection in accordance with the crossed Nicol method. However, with the polarizer used for a large-screen TV of 32 inches or more, various inspection scheme performed by automatic inspection devices using crossed Nicol method are considered.

[0004]

The crossed Nicol method is performed by: arranging two polarizers such that their respective orientation principal axes become perpendicular to each other to thereby form a dark field; and interposing a measurement target object such as a film therebetween to observe the state by transmitted light. Arranging in the crossed Nicol state, in the case where no defect is present, an image being entirely black is input from an imaging unit. In the case where a defect is present, that part does not appear in black. That is, when a foreign object or a defective spot is present in the polarizer, it appears as a bright dot, and thus defective spot inspection can be realized. Here, an oriented polyethylene terephthalate film, which is uniaxially or biaxially oriented, is bonded via an adhesive layer as a release film to each polarizer. Therefore, when any optical defective spot of the release film is added, together with the bright dot of the release film, it hinders the defective spot inspection. It has been known that a foreign object in the release film or a scratch on the surface thereof becomes a bright dot when the defective spot inspection is performed.

[0005]

However, though application of the oriented film is advantageous also from the viewpoint of reducing the thickness, since it involves birefringence (phase difference) attributed to the orientation by stretching, the incoming linearly polarized light becomes elliptically polarized light by transmission, and the crossed Nicol state is not substantially achieved. That is, when the two polarizers are simply arranged to be perpendicular to each other, the light amount of the visible light received by the imaging unit is influenced by the birefringence of the film.

In connection with a film formed by stretching, as disclosed in Patent Document 1, a phenomenon referred to as bowing occurs, due to the central part being delayed in stretching relative to the stretching ends. This is the phenomenon attributed to the film during the process structuring alysoid (catenary) . This is caused by the central part of the manufactured film being pulled and hanging down relative to the gravity direction or the progress direction of manufacturing process by its own weight or by the heat-shrink stress, in the heated stretching process in the state where the ends are gripped. Accordingly, the birefringence of the oriented film differs in the film width direction, similarly to the dichroism disclosed in Patent Document 1. As a result, there has been the problem that, depending on the position of the film in the width direction during manufacture, the defect inspection cannot precisely be performed as to the defect in the film at the central part of the film and at the ends of the film.

[0006]

As a film defect detection device solving the foregoing problem, an inspection device disclosed in Patent Document 2 noted below is known. The defect inspection device includes an inspection-use polarizer between a light source and on the optical path of an imaging unit. In order to cancel the birefringence (phase difference) of the film, the relative angular position of the inspection-use polarizer is adjusted such that the light amount of the visible light received by the imaging unit becomes the minimum value, and the film equipped with the polarizer is inspected for any defect in the crossed Nicol state.

[0007]

However, according to Patent Document 2, in the case where a film in which birefringence varies in the width direction is inspected, a plurality of imaging units and polarizers must be provided in the width direction. The inventors of the present invention have found that, it is difficult to obtain a uniform received light amount over the imaging unit positions, that is, in the width direction, just by adjusting the polarizer angles such that the light amount of the visible light received by the imaging units to be the minimum value. For example, the received light amount level varies between the film ends and
the central part in the film width direction. Accordingly, when the film whose birefringence varies in the width direction is inspected, the defect inspection cannot simultaneously and precisely be performed.

[0008]

Patent Document 1: JP 39-029214 B
Patent Document 2: JP 2007-213016 A

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0010]

An object of the present invention is to provide a defect inspection device with which defect inspection can precisely defect part and the normal part can be increased such that precise inspection is performed.

SOLUTIONS TO THE PROBLEMS

[0011]

In order to achieve the object stated above, the present invention provides a film defect inspection device detecting a defect in a long-length film having a certain width, including: illumination means provided on one face side of the film for illuminating the film; a first polarizer provided between the illumination means and the film; a second polarizer provided on other face side of the film; light receiving means provided on the other face side of the film for receiving transmitted light having been emitted from the illumination means and having transmitted through the first polarizer, the film, and the second polarizer; and angle adjustment means for adjusting an angle of the first polarizer within a plane of the first polarizer and adjusting an angle of the second polarizer within a plane of the second polarizer independently of each other.

[0012]

A preferred mode of the present invention provides the film defect inspection device in which a plurality of the second polarizers and a plurality of the light receiving means are arranged in a width direction of the film, and the second angle adjustment means is provided to each of the plurality of second polarizers.

[0013]

Further, a preferred mode of the present invention provides the film defect inspection device in which the angle adjustment means for adjusting the angle of the first polarizer within the first plane has a shaft that serves as a fulcrum in rotating the first polarizer and a linear motion mechanism that pushes and pulls an end of the first polarizer as a point of effort substantially in a rotary direction.

[0014]

Further, a preferred mode of the present invention provides the film defect inspection device in which the angle of each of the first and second polarizers is adjusted within a range of at least - 8° to + 8° at a rotary precision of 1° or less.

[0015]

Further, another mode of the present invention provides a film defect inspection method for detecting a defect in a long-length film having a certain width, including: illuminating the film by illumination means provided on one face side of the film; providing a first polarizer between the illumination means and the film; providing a second polarizer on other face side of the film; receiving, by light receiving means provided on the other face side of the film, transmitted light having been emitted from the illumination means and having transmitted through the first polarizer, the film, and the second polarizer; and adjusting an angle of the first polarizer within a plane of the first polarizer and adjusting an angle of the second polarizer within a plane of the second polarizer independently of each other.

[0016]

Further, a preferred mode of the present invention provides the film defect inspection method, in which a plurality of the second polarizers and a plurality of the light receiving means are arranged in a width direction of the film, and the angle of each of the second polarizers is independently adjusted in accordance with an arrangement position.

[0017]

Further, a preferred mode of the present invention provides the film defect inspection method, in which, in the step of adjusting the angle of the first polarizer within the
first plane, a shaft that serves as a fulcrum in rotating the first polarizer and a linear motion mechanism that pushes and pulls an end of the first polarizer as a point of effort substantially in a rotary direction finely adjust the angle of the polarizer at a rotary precision of 1° or less.

[0018]

Further, a preferred mode of the present invention provides the film defect inspection method, in which, in a region where the film is inspected, the inspection is performed with the angle of each of the first and second polarizers being displaced such that the received light amount at the light receiving means falls within a range of 10 to 30 in 256-gray scale

[0019]
Further, a preferred mode of the present invention provides the film defect inspection method, in which, in a region where the film is inspected, the inspection is performed with the angle of each of the first and second polarizers being displaced such that the received light amount at the light receiving means falls within a range of 30 to 50 in 256-gray scale.

[0020]

Further, a preferred mode of the present invention provides the film defect inspection method, in which, in a region where the film is inspected, the inspection is started from a state where the angle of each of the first and second polarizers is displaced by a range of 1 to 2° from a state where the received light amount of the light receiving means assumes a minimum value.

[0021]

Further, a preferred mode of the present invention provides the film defect inspection method, in which, in the film to be inspected, the defect inspection is applied in a state of a release film before other optical film or an optical member is bonded thereto.

[0022]

Further, another preferred mode of the present invention provides a release film subjected to defect inspection by a film defect inspection method with a film defect inspection device detecting a defect in a long-length film having a certain width, including.- illumination means provided on one face side of the film for illuminating the film; a first polarizer provided between the illumination means and the film; a second polarizer provided on other face side of the film; light receiving means provided on the other face side of the film for receiving transmitted light having been emitted from the illumination
means and having transmitted through the first polarizer, the film, and the second polarizer; and angle adjustment means for adjusting an angle of the first polarizer within a plane of the first polarizer and adjusting an angle of the second polarizer within a plane of the second polarizer independently of each other.

[0023]

As used herein, the polarizer is a plate-like or film-like element having a characteristic of allowing solely the light oscillating in a particular direction. [0024]
As used herein, the release film is a film which is bonded for the purpose of protecting the optical characteristic of an optical member such as a polarizer or a phase difference plate during manufacture, inspection, and shipping, and of being peeled off in use. To this end, an adhesive layer required for bonding may be provided on the surface, or a release layer may be provided on the surface so that it can be peeled off in use. [0025]
As used herein, the state of the release film before other optical film or the optical member is bonded is the state where a substance having a polarization characteristic, i.e., a substance that changes the incidental polarization light and allows the light to transmit and output, is not bonded.

EFFECTS OF THE INVENTION

[0026]

According to the present invention, what is provided is a defect inspection device with which a defect inspection can precisely be performed even with a film whose birefringence varies in the film width direction, and with which the contrast between the defect part and the normal part can be enhanced and precise inspection can be performed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027]

Fig. 1 is a schematic perspective view showing one mode of a defect detection device of the present invention.

Fig. 2 is a schematic perspective view showing one mode of the defect detection device of the present invention.

Fig. 3 is a schematic cross-sectional view showing one mode of the defect detection device of the present invention.

Fig. 4 is a schematic view showing the polarizer angle in the film width direction and the distribution of the received light amount at the angle.

Fig. 5 is another schematic view showing the polarizer angle in the film width direction and the distribution of the received light amount at the angle.

Fig. 6 is a schematic view showing the distribution of the received light amount over a plurality of light receiving means in the film width direction.

Fig. 7 is another schematic view showing the polarizer angle in the film width direction and the distribution of the received light amount at the angle.
Fig. 8 is another schematic view showing the distribution of the received light amount over a plurality of light receiving means in the film width direction.

Fig. 9 is a schematic view of the comparison between (a) the relationship between the background noise and the received light amount in the defective spot part in the defective spot detection according to the conventional technique, and (b) the relationship between the background noise and the received light amount of the defective spot part in the defective spot detection according to the technique of the present invention.

Fig. 10 is a schematic view showing one mode of arrangement of the fulcrum and the point of effort when a first polarizer is rotated in the defect detection device of the present invention.

Fig. 11 is a schematic view showing one mode of a linear motion mechanism that pushes and pulls the first polarizer substantially in a rotary direction in the defect detection device of the present invention.

Fig. 12 is a schematic view showing one mode of arrangement of the fulcrum and the point of effort when a second polarizer is rotated in the defect detection device of the present invention.

Fig. 13 is (a) a schematic view showing one mode of a mechanism that rotates the second polarizer in the defect detection device in the present invention, and (b) a schematic view showing one mode of the rotation of the second polarizer caused thereby.

Fig. 14 is (a) an image of the surface defect occurred during the film working at room temperature, the image being taken with the light amount received by the light receiving means of the present invention within the range of 10 to 3 0 in the 256-gray scale; (a1 ) an image taken within the range of 30 to 50 in the 256-gray scale; (b) an image of the surface defect occurred during the film manufacturing or heating, the image being taken with the light amount received by the light receiving means of the present invention within the range of 10 to 30 in the 256-gray scale; (b1) an image taken within the range of 3 0 to 50 in the 256-gray scale.

MODE FOR CARRYING OUT THE INVENTION

[0028]

In the following, a detailed description will be given with reference to the drawings. As shown in Fig. 1, a defect inspection device of the present invention, in which a first polarizer is arranged on one face side of a film and a second polarizer is arranged on the other face side each in parallel to the film in the to-be-inspected region of the film surface, includes illumination means for illuminating the film from the outer side of the first polarizer while having the first polarizer interposed therebetween, and light receiving means for receiving, on the other face side of the film, the transmitted light transmitted through the first polarizer, the film, and the second polarizer

[0029]

The film to which the defect inspection device of the present invention is employed may be a film used as a release film of the optical member such as a polarizer, a phase difference plate or the like. Specifically, it may be a plastic film such as a polyethylene terephthalate (PET) film.

[0030]

Further, as to the first polarizer, the polarizer that can be employed is not particularly limited so long as it is large enough to fully polarize the light from the illumination means that illuminates the film, and a commercially available polarizer can be applied. However, in order to fully polarize the light from the illumination means that illuminates the film, it must be large enough to fully cover the illumination range of the illumination means. It is preferable to use a polarizer whose size in the plane being parallel to the film is greater than that of the illumination means. Further preferably, when a plurality of illumination means is used as being aligned in the width direction of the film, use of the polarizers as many as the number of the illumination means makes it possible to adjust the crossed Nicol optical system more precisely.

[0031]

Further, as to the second polarizer also, it is not particularly limited and a commercially available polarizer can be employed so long as it can transmit the film and is large enough to fully polarize the illumination light entering the light receiving means. It is preferable to use the polarizers as many as the light receiving means, and to arrange the polarizers on the front side of the light receiving part of the light receiving means. This makes it possible to adjust the angle of the polarizer for each light receiving means.
Therefore, adjustment of the crossed Nicol optical system can more precisely be performed.

[0032]

Further, as to the light receiving means, though it is not particularly limited so long as the light from the illumination means being scattered or reflected at the defective spot can be received through the polarizers, it is preferable to use a commercially available CCD camera or CMOS camera for advantages of their cost-effectiveness, ease in signal processing and the like. It is more preferable to use a line sensor camera in which CCDs or CMOSs being light receiving elements are linearly aligned for advantages in the installation space, the imaging field of view per camera and the like. Further, taking into consideration of the cost, the light receiving precision, and the inspection range, it is preferable to arrange and use a plurality of light receiving means in the width direction as necessary, as shown in Fig. 2.

[0033]
Further, the illumination means is preferably capable of uniformly illuminating the inspection range of the film. For example, what can be employed is an illumination method of guiding light from a light source, e.g., a linear LED illumination in which light emitting elements are aligned linearly, a rod-like fluorescent lamp, a metal halide lamp or the like, to a rod-like light guide using optical fibers. In particular, because the amount of illumination light is great, the method of illuminating by guiding the light from the metal halide lamp light source to the rod-like light guide using the optical fibers is preferable. In this case, particularly when the width of the film is great and the inspection range is wide, because the cost is increased with one long light guide, it is also possible to use a plurality of illumination means being aligned in the width direction of the film, taking into consideration of the cost, the inspection range, and the number of the light receiving means.

[0034]

Further, as to the positional relationship between the film and each of the first polarizer, the second polarizer, the illumination means, and the light receiving means, they are preferably arranged linearly as shown in Fig. 3, so that the light from the illumination means scattered or reflected at the defective spot can be received at the strongest possible intensity. Further preferably, the plane of the film to be inspected and such a line are perpendicular to each other, in view of easier installation and maintainability.

[0035]

Further, as to the relationship between the first polarizer and the second polarizer, by arranging in the crossed Nicol state according to the crossed Nicol method, the defect inspection can be performed by the method similar to the crossed Nicol method. In this case, in the case where no defect is present, an image being entirely black is input from an imaging unit. In the case where a defect is present, that part does not appear in black. That is, when a foreign object or a defective spot is present in the polarizer, it appears as a bright dot. The signal acquired by the light receiving means is processed by signal processing means, and processing such as determination as to presence/absence of the defective spot is performed.

[0036]

Further, it is preferable that the first and second polarizer angles are adjusted independently of each other. That is, in the case of the film whose birefringence varies in the width direction, since the angles of the first and second polarizers forming the crossed Nicol are different in the width direction of the film, as shown in Fig. 4, birefringence (phase difference) differs at the part around the center of the film and at the part around the edges of the film. Therefore, provided that the first polarizer angle and the second polarizer

#
angle are set to be identical in the width direction, the optimum crossed Nicol condition is not achieved in the width direction, and hence the received light amount at the light receiving means varies in the width direction. It is to be noted that, in Fig. 4 , L • C • R denote the left, the center and the right with reference to the progress direction of the film.

[0037]

Hence, as shown in Fig. 5, it is further preferable to achieve the state which is close to the optically optimum crossed Nicol condition in the width direction, by adjusting each of the first and the second polarizer angles in the width direction of the film to be the angles at which the light amount received by every light receiving means becomes the minimum. Here, to adjust the polarizer angles means to rotate both the first and second polarizers in parallel to the plane of the film and to the inner side or to the outer side relative to the running direction of the film. Further, though the direction and magnitude of the adjusted angles differ depending on the polarization characteristic of the film in the width direction, for example, as shown in Fig. 4, in the case where the polarization characteristic of the film in the width direction becomes U-shape, conforming to the U-shape, in each of the first and second polarizers, the left side relative to the film and
the right side relative to the film with reference to the center become opposite to each other in the rotary direction. Further, as compared to the center of the film, the optimum angle tends to be greater at the ends.

[0038]

Further preferably, angle adjustment means for adjusting the angle of the first polarizer in the first plane has a shaft serving as the fulcrum when rotating the first polarizer, and a linear motion mechanism that pushes and pulls the end of the first polarizer as the point of effort substantially in rotary-direction. Since the first polarizer is required to cover the entire width of the inspected film, the first polarizer must be wider than the optical film which measures over 2 m, e.g. , for a large LCD TV use. In order to tilt the wide and large first polarizer 2 such as shown in Fig. 10 at the rotary precision of 1° or less, a simple rotary mechanism such as a stepping motor or a servo motor is poor in positioning the rotation angle or reproducibility. Therefore, in view of rotary precision, it is preferable to cause a linear motion mechanism 15 as shown in Fig. 11 to move the point of effort 13 as shown in Fig. 10, to thereby push and pull the end of the first polarizer 2 substantially in the rotary direction about the fulcrum 14. Further, it is preferable that the servo motor drives the linear motion mechanism 15, in view of not only the stop precision but also in checking the completion of the driving operation by feedback, or in securing the stability of torque even under a great load.

[0039]

It is further preferable that, by monitoring the light amount received by the light receiving means, automatic adjustment using actuation means such as a motor is performed so as to achieve the optimum angle. At this time, since the polarizer angle must address a change in variations in the birefringence in the width direction of the film, and since the higher adjustment precision of the polarizer further approximates the perfect crossed Nicol state and consequently higher detection precision can be obtained, it is preferable that the first and second polarizer angles are adjusted within the range of - 8° to + 8° at the rotary precision of 1° or less. As the adjustment mechanism of the second polarizer angle, as shown in Figs. 12 and 13, it is preferable that the end of the second polarizer 3 is driven by a lever-like mechanism pivoting about the fulcrum 18 at the point of effort 17 closer the fulcrum 18. This is because, as compared to the case where the end of the second polarizer 3 is simply directly driven by the rotary mechanism such as a stepping motor or a servo motor, or the linear motion mechanism using the same, by the point of effort 17 being driven nearer to the fulcrum 18, the principle of levers makes it possible for a smaller force, i.e., the small torque of the driving device 19 of the mechanism rotating the second polarizer shown in Fig. 13, to greatly rotate the second polarizer. It is to be noted that, though the part serving as the lever can be rod-like as shown in Fig. 13 to achieve the very fine angle adjustment of - 8° to + 8°, similarly on the driving side, a disc can achieve the similar effect.

[0040]

Further preferably, in the inspected region of the film, the inspection is carried out with the angles of the first and second polarizers being displaced such that the light amount received by the light receiving means falls within the range of 10 to 3 0 in 256-gray scale. Thus, as shown in Fig. 14 (a) and (a') , the surface defect occurring during the film working at the room temperature can clearly be captured at higher peak intensity.

[0041]
Further preferably, in the inspected region of the film, the inspection is carried out with the angles of the first and second polarizers being displaced such that the light amount received by the light receiving means falls within the range of 30 to 50 in 256-gray scale. Thus, as shown in Fig. 14 (b) and (b1), the surface defect occurring during the film manufacturing or during the heating can be captured as an image of greater width.

[0042]

Further preferably, the angles of the polarizers are set as being displaced in the range of 1 to 2° from the crossed Nicol state. Even in the case where the state approximating the optimum crossed Nicol condition in the width direction is achieved by adjusting and achieving the optimum first and second polarizer angles according to the method described above, the crossed Nicol state is different among a plurality of light receiving means. Thus, for example, when the light receiving means is provided five in number, as shown in Fig. 6, what is obtained is the received light amount distribution in which the base line of the received light amount is different at around the center of the film and at the ends of the film. However, since the light receiving means is adjusted to the optimum polarizer angles, it is difficult to lower the base line of the received light amount around the edges of the film to match with the part around the center, for example. Accordingly, by displacing the angles of the second polarizers arranged on the front side of the plurality of light receiving means shown in

Fig. 7 within the range of 1 to 2°, to perform adjustment in the direction to raise the base line of the received light amount, the received light amount of the plurality of light receiving means shown in Fig. 8 can be uniformized in the width direction and linearity is obtained, even with the film in which distribution of the birefringence is curved by bowing.

[0043]

Thus, it becomes possible to uniformize the detection sensitivity in the width direction of the film. As compared to the conventional technique as shown in Fig. 9 (a), thanks to the technique of the present invention, as shown in Fig. 9 (b), the base line of the received light amount where no defective spot is present is adjusted in the brighter direction, and the background noise produced by light scattering components by the air layer is covered. Thus, noise N can be reduced to N' , and the S/N ratio is increased. Thus, it becomes possible to approximate the threshold value for sensing the defective spot for the base line of the received light amount where no defective spot is present, as compared to the conventional technique. Thus, since width h for sensing the received light amount exceeding the threshold value because of the defective spot can be secured to wider h' , the inspection of higher precision and with less erroneous detection can Be realized.

EXAMPLES

[0044]

[Example 1]
As the inspection target sample, "Lumirror" [38R64] available from Toray Industries, Inc. was prepared.

[0045]

With the defect inspection device of the present invention, a 250 W-metal halide (BMH-250A, available from Mejiro Precision, Inc.) was used as the illumination means,- and
a combination of a CCD camera having the resolution of 25 am (P3-80-8K-40, available from DALSA) and the second polarizer is arranged at a plurality of places as the light receiving means . Thus, an image was picked up for the inspection width 1255 mm of the inspection target sample, and the base received light amount was checked. [0046]
The evaluation of the base received light amount was performed as follows: both the angles of the first and second polarizers were adjusted, and in the state where the average value obtained when evaluated in 256-gray scale of the received light amount over the entire inspection width is minimum, the

difference between the maximum value and the minimum value of the received light amount was checked. The difference was evaluated as the received light amount variation. It was verified that the received light amount variation in Example was 20 or less.

[0047]
Further, it was verified that, by adjusting both the angles of the first and second polarizers, the base received light amount can be adjusted to fall within the ranges of 10 to 30 and 30 to 50 in 256-gray scale. From the foregoing, it was verified that, under the condition of Example 1, even with the film whose birefringence varies in the film width direction, the detection precision is uniform and inspection can precisely be performed.

[0048]
Fig. 14 shows an image of a surface defect specifically imaged under the condition of Example 1. Comparing (a) an image of the surface defect occurring during the PET film working at room temperature imaged by the light receiving means of the present invention in which the received light amount falls within the range of 10 to 30 in 256-gray scale, and (a1) an image in which the range is 3 0 to 50 in 2 56-gray scale, the peak intensity from the base line is 40 in (a) , and 17 in (a1) . That is, in detecting the defect occurring on the film surface at the room temperature, an improvement in the S/N ratio is realized by imaging by the light receiving means of the present invention in which the received light amount falls within the range of 10 to 30 in 256-gray scale.

[0049]
Further, comparing (b) an image of the surface defect occurring during the heated stretching in PET film manufacture imaged by the light receiving means of the present invention in which the received light amount falls within the range of 10 to 30 in 256-gray scale, and (b') an image in which the range is 3 0 to 50 in 2 56-gray scale, the peak intensity from the base line is 80 in (b) and 70 in (b1) . However, the detection width is 760 in (b) and 940 in (b1), showing the great difference. That is, in detecting the defect occurring on the film surface in the heating process, an improvement in width h with which the received light amount exceeding the threshold value is sensed is realized by imaging by the light receiving means of the present invention in which the received light amount falls within the range of 3 0 to 50 in 2 56-gray scale. [Comparative Example 1]
Using the identical device and film as in Example 1, the base received light amount was checked in the same manner as Example except that the angles of the second polarizers arranged on the camera side are uniformly fixed, and solely the angle of the first polarizer provided on the light source side was adjusted so as to adjust the relative angle of the polarizers as disclosed in Patent Document 2.

[0050]

Under the condition of Comparative Example 1, the received light amount variation became greater than 30, and the base received light amount could not be adjusted to fall within the ranges of 10 to 30 and 30 to 50 in 256-gray scale. From the foregoing, it was verified that, under the condition of Comparative Example, with the film whose birefringence varies in the film width direction, detection precision becomes non-uniform and precise inspection cannot be performed.

INDUSTRIAL APPLICABILITY

[0051]

The application of the present invention is not limited to a defect detection device of a film. Though the present invention can also be applied to a defect detection device of transparent paper or a sheet-like object, the application range of the present invention is not limited thereto.

«
DESCRIPTION OF REFERENCE SIGNS
[0052]

1: Inspection target film

2: First polarizer

3: Second polarizer

4: Illumination means

5: Light receiving means

6: Signal processing means

7.- Film obtained from left side part in manufacturing

8: Film obtained from central part in manufacturing

9: Film obtained from right side part in manufacturing

10: Distribution of received light amount in film

obtained from left side part in manufacturing

11: Distribution of received light amount in film obtained from central part in manufacturing

12: Distribution of the received light amount in film obtained from right side part in manufacturing

13: Point of effort in rotating first polarizer

14: Fulcrum in rotating first polarizer

15: Linear motion mechanism pushing and pulling first
polarizer substantially in rotary direction

16: Driving device of linear motion mechanism 17: Point of effort in rotating second polarizer

18: Fulcrum in rotating second polarizer

19 : Driving device of mechanism rotating second polarizer

CLAIMS

1. A film defect inspection device detecting a defect in a
long-length film, comprising:

illumination means provided on one face side of the film for illuminating the film;

a first polarizer provided between the illumination means and the film;

a second polarizer provided on other face side of the film;

light receiving means provided on the other face side of the film for receiving transmitted light having been emitted from the illumination means and having transmitted through the first polarizer, the film, and the second polarizer;

and angle adjustment means for adjusting an angle of the first polarizer within a plane of the first polarizer and adjusting an angle of the second polarizer within a plane of the second polarizer independently of each other.

2. ' The film defect inspection device according to claim 1,
Wherein a plurality of the second polarizers and a plurality of the light receiving means are arranged in a width direction of the film, and the second angle adjustment means is provided to each of the plurality of second polarizers.

3. The film defect inspection device according to one of
claims 1 and 2, wherein the angle adjustment means for adjusting the angle of the first polarizer within the first plane has a shaft that serves as a fulcrum in rotating the first polarizer and a linear motion mechanism that pushes and pulls an end of the first polarizer as a point of effort substantially in a rotary direction.

4. The film defect inspection device according to one of
claims 1 to 3, wherein the angle of each of the first and second polarizers is adjusted within a range of at least - 8° to + 8° at a rotary precision of 1° or less.

5. A film defect inspection method for detecting a defect
in a long-length film, comprising:

illuminating the film by illumination means provided on one face side of the film;

providing a first polarizer between the illumination means and the film;

providing a second polarizer on other face side of the film;

receiving, by light receiving means provided on the other face side of the film, transmitted light having been emitted from the illumination means and having transmitted through the first polarizer, the film, and the second polarizer;

and adjusting an angle of the first polarizer within a plane of the first polarizer and adjusting an angle of the second polarizer within a plane of the second polarizer independently of each other.

6. The film defect inspection method according to claim 5,
Wherein a plurality of the second polarizers and a plurality of the light receiving means are arranged in a width direction of the film, and the angle of each of the second polarizers is independently adjusted in accordance with an arrangement position.

7. The film defect inspection method according to one of
claims 5 and 6, wherein
in the step of adjusting the angle of the first polarizer within the first plane, a shaft that serves as a fulcrum in rotating the first polarizer and a linear motion mechanism that pushes and pulls an end of the first polarizer as a point of effort substantially in a rotary direction finely adjust the angle of the polarizer at a rotary precision of 1° or less.

8. The film defect inspection method according to one of
claims 5 to 7, wherein the inspection is performed with the angle of each of the first and second polarizers being displaced such that the received light amount at the light receiving means falls within a range of 10 to 3 0 in 256-gray scale.

9. The film defect inspection method according to one of
claims 5 to 7, wherein the inspection is performed with the angle of each of the first and second polarizers being displaced such that the received light amount at the light receiving means falls within a range of 30 to 50 in 256-gray scale.

10. The film defect inspection method according to one of
claims 5 to 9, wherein
the inspection is started from a state where the angle of each of the first and second polarizers is displaced by a range of 1 to 2° from a state where the received light amount of the light receiving means assumes a minimum value.

11. The film defect inspection method according to one of
claims 5 to 10, wherein the defect inspection is applied in a state of a release film before other optical film or an optical member is bonded thereto.

12. A release film, subjected to defect inspection in accordance with the defect inspection method according to one of claims 5 to 11.