JPH07280523A - Method and device for measuring thickness of film, and manufacture of film - Google Patents

Abstract

PURPOSE:To provide a method and device for measuring a thickness of a film capable of detecting thickness variation in width and longitudinal directions thereof in a processing line without cutting out the film and to provide a manufacturing method for managing a process by the method and device. CONSTITUTION:The thickness measuring device comprises moving means that move a position 6 for measuring a thickness of a film in width and longitudinal directions thereof, respectively. When measuring the thickness, one of the moving means is not operated. Thereby, it is possible to independently measure the thickness in the width direction or longitudinal direction. An reflection optical interference type thickness meter is used as a thickness detection device 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thickness measuring device and a measuring method for measuring the thickness of a film in-line, and a film manufacturing method using the thickness measuring device.

[0002]

2. Description of the Related Art Nonuniformity of thickness of polymer films such as polyester and polypropylene, that is, nonuniformity of film thickness is an important quality of the film, and when unevenness of product thickness is large or local thickness is large. If there is unevenness or periodic thickness unevenness, it causes various troubles such as poor handling, poor transport, poor coating of magnetic material, and poor vapor deposition at the stage when the user uses it.

Therefore, for quality assurance that products with large thickness unevenness or products with local / periodic thickness unevenness are not shipped to the user, and immediately when defects of these thickness unevenness occur. It is important to constantly measure the thickness unevenness of the product in order to manage the process so as to prevent defective products from being manufactured by correcting corresponding parts in the manufacturing process.

From the viewpoint of the final quality assurance of such a film, the parameter representing the thickness unevenness of the film is generally used in the width direction (TD: Transversal Direc) of the film.
unevenness in the longitudinal direction (MD: Machine Directi
Two types of uneven thickness (on) are used.

TD thickness unevenness occurs due to non-uniformity in the width direction of the film manufacturing process. That is, in the film produced by melting and discharging from the die, a local uneven thickness of a convex or concave having a minimum width of 2 to 3 mm is linearly streaked in the longitudinal direction of the film due to the influence of foreign matters attached near the outlet of the die. May occur. Since this streak-like thickness unevenness seriously affects the quality of the film, when the height of the convex portion (the height of the concave portion) is, for example, 0.25 μm or more, this is shipped as a product. It is not possible.

Therefore, in order to prevent subsequent production of products containing such streak-like thickness unevenness,
It is necessary to take measures in the manufacturing process such as immediately cleaning the base part. Therefore, it is important to quickly and quantitatively measure the shape of the striped local uneven thickness in the width direction.

In order to detect such streaky thickness unevenness, it is necessary that the measurement accuracy of the TD thickness unevenness be within ± 0.1 μm, and the measurement interval needs to be about 1 mm. .

On the other hand, the MD thickness unevenness is caused by non-uniformity in the time of the film manufacturing process. That is, in the film produced by stretching in the longitudinal direction, the thickness unevenness may occur periodically in the longitudinal direction due to eccentricity of the roll used for stretching. Since this periodic thickness unevenness also has a significant influence on the quality of the product, it is necessary to quantitatively measure this shape in the longitudinal direction, like the TD thickness unevenness. In order to detect such periodic thickness unevenness, it is necessary to have the same measurement accuracy and measurement interval as the TD thickness unevenness.

As an apparatus for measuring the film thickness unevenness online in the film manufacturing process, for example, a thickness gauge mounted on a scanner, which is described in Japanese Patent Publication No. 5-67881, is used in the width direction of the film. A device for measuring thickness while traveling back and forth is known. This thickness measuring device measures the thickness of the film after molding and feeds back the result to the die to adjust the gap and temperature of the die in order to keep the average thickness of the entire film uniform. The purpose is to control the thickness.

That is, this thickness measuring device measures the thickness of the film while reciprocating it in the width direction of the film in the process of forming and winding the film in the film manufacturing process. In other words, the film thickness measurement position moves in the longitudinal direction as the film is wound, and at the same time reciprocates in the width direction as well. Therefore, the film thickness is measured zigzag to measure the thickness unevenness in the oblique direction. Therefore, the variation in the measured thickness is influenced by the variation in thickness in both the longitudinal direction and the width direction, and represents the variation in the overall thickness of the film. Moreover, since the measurement is performed at the same time as the film formation in the film manufacturing process, the measurement interval in the longitudinal direction is large, for example, about 400 mm.

Therefore, it is difficult to measure local streak-like thickness unevenness (TD thickness unevenness) and periodic thickness unevenness (MD thickness unevenness), which are problems in the quality assurance stage as described above. Met.

For this reason, conventionally, there is no apparatus for measuring the TD thickness unevenness and the MD thickness unevenness online, and a sample is cut out from the surface layer of the film roll after manufacturing, and this is measured offline. That is, as shown in FIG. 2, a TD thickness unevenness, for example, a long tape-shaped sample having a width of 40 mm and a film roll full width (for example, 6 m) is cut out with a cutter knife, and while moving at a constant speed, a contact called an electron micro It was measured with a thickness gauge. Similarly, the MD thickness unevenness was measured by a contact type thickness meter while cutting out a tape-shaped sample having a width of 40 mm and a fixed length (for example, 20 m) in the longitudinal direction of the film roll and moving the sample at a constant speed. . In order to move the sample at a constant speed, for example, a method of winding the sample from one end at a constant speed is used.

However, this method has the following problems. That is, (1) it takes time and labor to cut out a sample, and quick measurement cannot be performed. (2) wrinkles and creases may occur when handling a long tape-shaped sample. When it is measured with, the measurement result is similar to the local thickness unevenness and it cannot be distinguished.
(3) A certain level of skill is required to handle the contact-type thickness gauge, and the measurement accuracy is affected by the skill of the measurer. (4) When cutting out a sample, a cutter knife may cause injury. Is.

In particular, when a product is inspected with this measuring device, the measurement accuracy is poor when the skill of the measurer is low, and even if local thickness unevenness occurs, it is considered as a wrinkle of the film. It may be misjudged and missed. As a result, in reality, a film having uneven thickness outside the standard range or a film having local uneven thickness is shipped as a product. Also, if you miss the occurrence of local thickness unevenness or periodic thickness unevenness,
Corresponding steps cannot be modified either, which leads to continued production of defective films.

[0015]

SUMMARY OF THE INVENTION Therefore, a first object of the present invention is to make it possible to detect the thickness unevenness of the TD and MD of the film in-line and to detect the thickness of the film quickly without cutting the sample. It is to provide a measuring device.

A second object of the present invention is to provide a film thickness measuring device and a measuring method which are less likely to cause a decrease in measurement accuracy due to the influence of transparency and surface roughness of the film.

A third object of the present invention is to provide a film thickness measuring device capable of detecting TD and MD thickness unevenness of a film by a simple operation and without being affected by the skill of a measurer. It is to provide a measuring method.

A fourth object of the present invention is to provide a film production method capable of efficiently detecting the thickness unevenness of TD and MD to minimize the production of defective films and improving the yield. To do.

[0019]

Means for Solving the Problems A film thickness measuring device of the present invention for achieving the above object is a film thickness measuring device and a film thickness measuring position by the film thickness measuring device with respect to the film. And a longitudinal direction measuring position moving means for moving the thickness measuring position relative to the film in the longitudinal direction of the film. Prepare,
And, at least one of the width direction measuring position moving means and the longitudinal direction measuring position moving means moves the thickness measuring position when the thickness measuring means measures the thickness of the film. The feature is that it does not let you.

A preferred embodiment of the film thickness measuring device of the present invention is characterized in that the longitudinal direction measuring position moving means is a film rewinding device.

In a preferred embodiment of the film thickness measuring device of the present invention, the thickness measuring means irradiates white parallel light to the thickness measuring position, and the thickness measuring position. And a thickness calculation means for calculating the thickness of the film on the basis of the spectral intensity of the reflected light. It is characterized by that.

In a preferred embodiment of the film thickness measuring device of the present invention, the spectral reflection intensity measuring means is (a)
A light guide means having a plurality of light guide paths in which an incident light axis is directed to the thickness measurement position and an emission light axis is arranged in parallel; and (a) a specific direction of the light emitted from the light guide means. And (c) spectroscopic measuring means for measuring the intensity of the outgoing light extracted by the outgoing light component extracting means for each wavelength component. It is characterized by being.

Another aspect of the film thickness measuring apparatus of the present invention is a white parallel light source for generating white parallel light,
Incident light converging means for converging the white parallel light to a film thickness measurement position, and reflected light parallel for collimating the reflected light at the thickness measurement position of the white parallel light converged by the incident light converging means A film thickness comprising a light conversion means, a spectral reflection intensity measurement means for measuring the spectral intensity of the reflected light, and a thickness calculation means for calculating the thickness of the film based on the spectral intensity of the reflected light. A measuring device, and the distribution of the optical optical path difference between the component of the reflected light reflected on the surface of the film and the component of the reflected light transmitted on the surface of the film and reflected on the back surface of the film. The range width is 0.2 times or less of the shortest wavelength of the effective spectral range of the spectral reflection intensity measuring means.

A preferred embodiment of the film thickness measuring device of the present invention is characterized in that the incident light converging means also serves as the reflected light collimating means.

Further, a preferred embodiment of the film thickness measuring apparatus of the present invention is characterized by further comprising inclination regulating means for regulating the inclination of the film surface at the thickness measuring position.

A preferred embodiment of the film thickness measuring device of the present invention further comprises width direction measuring position moving means for moving the thickness measuring position relative to the film in the width direction of the film. A longitudinal direction measuring position moving means for moving the thickness measuring position relative to the film in the longitudinal direction of the film, and comprising the width direction measuring position moving means and the longitudinal direction measuring position moving means. At least one of them is characterized in that the thickness measurement position is not moved when the spectral reflection intensity measuring means is measuring the thickness of the film.

Further, in a preferred aspect of the film thickness measuring apparatus of the present invention, the thickness calculating means calculates the film thickness based on a plurality of wavelength positions that give extreme values of the spectral intensity of the reflected light. It is characterized by being calculated.

Further, in the film thickness measuring method of the present invention, white parallel light is generated, the white parallel light is converged on the film thickness measurement position, and the thickness of the converged white parallel light is measured. A method for measuring the thickness of a film, in which the reflected light at a position is collimated, the spectral intensity of the reflected light is measured, and the thickness of the film is calculated based on the spectral intensity of the reflected light, and the film The distribution range of the optical optical path difference between the component of the reflected light that is transmitted on the surface of the film and reflected on the back surface of the film and the component of the reflected light that is reflected on the surface of the film is effective in the spectral reflection intensity measurement. 0.2 of the shortest wavelength in the spectral range
The feature is that the number of times is less than twice.

Another aspect of the film thickness measuring method of the present invention is that the thickness measuring means and the film thickness measuring position by the thickness measuring means are arranged in the width direction of the film with respect to the film. Of the thickness of the film using a width direction measuring position moving means for relatively moving and a longitudinal direction measuring position moving means for relatively moving the thickness measuring position in the longitudinal direction of the film with respect to the film. A measuring method, wherein (A) when measuring the thickness of each position in the width direction of the film, (B) the film while moving the thickness measurement position only by the width direction measurement position moving means. When measuring the thickness of each position in the longitudinal direction, the thickness of the film is measured while moving the thickness measuring position only by the longitudinal direction measuring position moving means. That. .

A preferred embodiment of the film thickness measuring method of the present invention is characterized in that the thickness of each position in the longitudinal direction of the film is measured while the film roll is rewound.

In the method for producing a film of the present invention, the thickness of the film is measured at each position in at least one of the width direction and the longitudinal direction of the film by the film thickness measuring device as described above. The film manufacturing process is controlled based on the result of comparing the thickness with a predetermined threshold value.

[0032]

According to the film thickness measuring apparatus of the present invention, it is possible to detect in-line the thickness unevenness of the film in the longitudinal direction or the width direction.

Further, according to the film thickness measuring apparatus and the measuring method of the present invention, the measurement result does not change even if the film surface is slightly inclined, and a sufficient amount of light can be obtained by the light receiving element.

Further, according to the method for producing a film of the present invention, it is possible to efficiently detect the thickness unevenness of TD and MD and minimize the production of a defective film.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a thickness gauge detecting device 6 (thickness measuring means) and a thickness measuring position by the thickness gauge detecting device 6 by reciprocating the thickness gauge detecting device 6 in the width direction of the film 1. 1 shows a configuration of an embodiment of the present invention in which a scanner 8 (width direction measurement position moving means) for moving the film in the width direction is installed on the unwinding side of a film rewinding device (longitudinal direction measurement position moving means). .

In FIG. 1, a film 1 is unwound from a film roll 2, passes over the rolls 3 and 4 of a rewinding device, then vertically descends from it, passes through a roll 5, and is slit into a predetermined width and then rewound. It is wound around a winding unit (not shown) of the device.

The thickness gauge is composed of a thickness gauge detecting device 6 and a thickness gauge data processing device 7 (thickness calculating means). Of these, only the thickness gauge detection device 6 is mounted on the scanner 8 in the rewinding device, and the thickness gauge data processing device 7 is installed outside the rewinding device and is a pen for recording the thickness unevenness measurement result. It is connected to the recorder 9.

The scanner 8 is connected to the scanner controller 10. The scanner control device 10 controls the operation of the scanner, and the thickness gauge detection device 6 can be moved at a constant speed and can be stopped at an arbitrary position of the entire width of the film. Further, the scanner control device 10 includes the thickness gauge data processing device 7 and the rewinding control device 11 of the rewinding device.
The scanner 8 and the rewinding device do not operate at the same time during the measurement of the thickness gauge. It has become.

In this embodiment, a reflection type optical interference type thickness gauge is used as the thickness gauge detection device 6. This is because white parallel light is made incident on the film at a certain incident angle, and the spectral intensity of the reflected light whose spectral intensity has changed due to the interference phenomenon of the light reflected on the front and back surfaces of the film is measured. Is calculated.

Next, the operation of this device will be described.
In the TD thickness unevenness measurement, the thickness gauge detection device 6 is at the retracted position outside one end of the film before the measurement is started. First, the scanner controller 10 causes the rewind controller 11
A rewind stop signal is output to the film and the film becomes stationary.

On the other hand, the scanner control device 10 outputs a measurement start control signal to the thickness gauge data processing device 7, and the thickness gauge data processing device 7 sends a chart recording start signal to the pen recorder 9 and at the same time. Start measurement. Thereafter, the scanner 8 starts to move at a constant speed under the control of the scanner control device 10, and the thickness gauge data processing device 7 outputs a voltage output according to the thickness at the measurement position to the pen recorder 9.
The TD thickness unevenness is recorded on the chart.

When the thickness gauge detection device 6 reaches the outside of the other end of the film, the scanner control device 10 stops the movement of the scanner 8 and sends a measurement end control signal to the thickness gauge data processing device 7. . In response to this, the thickness gauge data processing device 7 terminates the thickness measurement and sends a chart recording end signal to the pen recorder 9.

Thereafter, the scanner control device 10 moves the scanner 8 in the reverse direction until the thickness gauge detection device 6 reaches the retracted position.

FIG. 3 shows the TD thickness unevenness measurement results of the polyester film thus measured. The moving speed of the scanner during the TD thickness unevenness measurement is 25 mm / sec.

The moving speed V of the thickness gauge detection device 6
_s (mm / sec), the number of times the thickness meter can measure the thickness N _m (times / sec), and the distance D _m (mm) between the thickness measurement points on the film are V _s = D There is a relationship of _m × N _m .
For example, when N _m = 20 to 50 times / second, V _s is 10 to 5
If it is 0 mm / sec, D _m can be 0.5 to 1 mm. As a result, it is possible to reliably detect the local unevenness of the thickness of the protrusion or the recess having a width of 2 to 3 mm due to the foreign matter on the die of the film manufacturing apparatus.

Next, in the MD thickness unevenness measurement, the thickness gauge detection device 6 is at the retracted position outside one end of the film before the measurement is started, as in the case of the TD thickness unevenness measurement. First, the scanner starts to move under the control of the scanner control device 10, and stops when the thickness gauge detection device 6 reaches a preset position in the width direction.

Next, a rewinding start signal is sent from the scanner control device 10 to the rewinding control device 11, and the rewinding device starts winding the film at a constant speed. After that, the scanner control device 10 outputs a measurement start control signal to the thickness gauge data processing device 7, and the thickness gauge data processing device 7 sends a chart recording start signal to the pen recorder 9 and measures the thickness. Start. A voltage output corresponding to the thickness at the measurement position is output from the thickness gauge data processing device 7 by the pen recorder 9.
And the MD thickness unevenness is recorded on the chart.

When a predetermined length of time has passed and the fixed length is rewound, the scanner controller 10 sends a stop signal to the rewind controller 11 and a control signal to the thickness gauge data processor 7 to terminate the measurement. To do. In response to this, the thickness gauge data processing device 7 terminates the thickness measurement and sends a chart recording end signal to the pen recorder 9.

Thereafter, the scanner control device 10 moves the scanner 8 in the reverse direction until the thickness gauge detection device 6 reaches the retracted position.

FIG. 4 shows an example of the MD thickness unevenness measurement results of the polyester film thus measured. The rewinding speed (film moving speed) is 50 mm / sec.

The rewinding speed V of the rewinding device
V _f = D for _f (mm / sec), the number of times the thickness gauge can measure the thickness N _m (times / sec), and the distance D _m (mm) between the thickness measurement points on the film. There is a relationship of _m × N _m . For example, when N _m = 20 to 50 times / second, if V _f is 20 to 200 mm / second, D _m can be 1 to 4 mm. As a result, it is possible to reliably detect the steep unevenness in thickness in the longitudinal direction that appears periodically as shown in FIG.

Next, one embodiment of a method for producing a film using the above film thickness gauge will be described. The TD measured in this way was used in the film manufacturing method.
Using the thickness unevenness and MD thickness unevenness, product inspection and process control are performed as follows.

Regarding the TD thickness unevenness, the change amount (difference between the maximum value and the minimum value) of the thickness is read for each slit width from the chart recording this. Next, this change amount is compared with a threshold value that is predetermined for each type of film. If the thickness unevenness for each slit width is larger than this threshold value, the product of that slit is rejected. The threshold value for the pass / fail judgment of the variation in thickness is, for example, 0.5 in the case of a general video tape film having a thickness of about 14 μm.
It is determined by the thickness of the film itself, the purpose of the film, etc., such as μm.

If there is local thickness unevenness, the height of the protrusion (or the height of the recess) is read. Next, this height (lowness) is compared with a predetermined threshold value that is preset for each type of film, and if it is greater than this threshold value, the product with the slit at the corresponding position is rejected. And Regarding the threshold value for the pass / fail judgment of this local unevenness in thickness, for example, 0.2 μm for a general video tape film having a thickness of about 14 μm and 0.1 μm for an audio tape film having a thickness of 7 μm. As such, it is determined by the thickness of the film itself, the purpose of the film, and the like.

On the other hand, since this local unevenness in thickness is caused by the foreign matter attached to the vicinity of the mouth of the mouthpiece as described above, the corresponding die position is cleaned.

Regarding the MD thickness unevenness, the amount of change in the thickness (difference between the maximum value and the minimum value) is read from the chart recording this for each constant length. Next, this amount of change is compared with a predetermined threshold value that is predetermined for each type of film, and if the amount of change is large, a slit product corresponding to the position where the MD thickness unevenness is measured is selected. Reject.

When there is a periodic thickness unevenness, the height of the convex (or the height of the concave) is read. Next, this height (lowness) is compared with a predetermined threshold value that is predetermined for each film type, and if it is greater than this threshold value, the MD thickness unevenness is measured at the position where it is measured. The product with the slit at the corresponding position is rejected. On the other hand, since the apparatus corresponding to the film forming process can be specified from the cycle of the periodic thickness unevenness, the apparatus is corrected.

Also in the MD thickness unevenness, the amount of change and the threshold value for the pass / fail judgment of the periodic thickness unevenness are determined depending on the thickness of the film itself, the application of the film and the like.

In the present invention, as the thickness measuring means,
Non-contact type thickness gauges such as optical interference type thickness gauges, infrared or radiation absorption type thickness gauges, capacitance type thickness gauges, etc.,
A contact-type thickness gauge such as an electronic micro is preferably used.

When a transmissive type thickness gauge or an infrared ray or radiation absorption type thickness gauge is used among the optical interference type thickness gauges, two units of the thickness gauge detection device are sandwiched between the light emitting section and the light receiving section with the film interposed therebetween. To be installed in each scanner. It is assumed that the two scanners move in synchronization so that the relative positions of the light projecting unit and the light receiving unit do not change.

Similarly, when a capacitance type thickness gauge is used,
Two electrodes are mounted on each of the two scanners with a film sandwiched between them. It is assumed that the two scanners move synchronously so that the relative positions of the two electrodes do not change.

In the case of using the contact type thickness gauge, a reference plate for setting a displacement amount reference is provided on the opposite side of the contact head of the thickness gauge detection device mounted on the scanner with the film interposed therebetween. The measured value is the amount of displacement when the tip of the detection head is in close contact with the film and the reference plate, and the film thickness is the amount of displacement when there is no film measured in advance (when the tip of the detection head and the reference plate are in contact). Calculate from the difference.

Further, the thickness gauge used in the present invention will be described in detail below. As described above, in the present invention, a contact type thickness gauge, an infrared absorption type thickness gauge, a radiation absorption type thickness gauge, a capacitance type thickness gauge or an optical interference type thickness gauge is used as the thickness gauge. You can The advantages and disadvantages of these thickness gauges will be described below.

The contact-type thickness gauge is mainly used for measuring the thickness of a relatively thick film having a high light absorption coefficient. This is because the measurement error is large when the film is thin as described below. In principle, the contact type thickness gauge causes an error in the measured value when the relative position of the thickness gauge detection device and the film in the thickness direction changes. That is, in the measurement of the TD thickness unevenness of the present invention, the measurement is performed while moving the thickness gauge detection device itself in the width direction of the film, and with this movement, the relative position in the thickness direction of the thickness gauge and the film. When changes, there will be an error in the measured value.

This is for the following reason. The amount of change in the relative position in the thickness direction is detected from the locus of movement of the contact head in the thickness direction due to movement of the thickness gauge detection device by the scanner. The amount of this change is measured for the case with the film and the case without the film as described above,
The difference is used as the measured value of the thickness of each part of the film. Therefore, it is not possible to distinguish between the movement of the thickness gauge detection device by the scanner in the thickness direction and the movement of the contact head in the thickness direction due to the film thickness.

Therefore, the measurement accuracy of such a contact type thickness gauge is determined by the reproducibility of the running locus of the scanner. However, it is quite difficult to keep the repeatability accuracy within ± 0.1 μm in a scanner having a width of 6 m, for example. Therefore, in the case of the contact type thickness gauge, the measurement error is likely to be large particularly in the measurement of the TD thickness unevenness when the film width is large.

However, the contact type thickness meter is used when the optical thickness meter such as the optical interference type cannot provide sufficient measurement accuracy, such as when the film is thick and the light absorption rate is extremely high.
It is preferably used. Further, it is preferably used when the measurement of MD thickness unevenness is the center or when the width of the film is narrow.

An energy absorption type thickness gauge such as an infrared absorption type thickness gauge or a radiation absorption type thickness gauge is mainly used for measuring the thickness of a relatively thick film. This is because, when measuring the thickness of a thin film, it is necessary to increase the measurement spot at the thickness measurement position in order to obtain the required measurement accuracy, and especially the width required for measuring TD thickness unevenness This is because it is difficult to obtain the spatial resolution necessary for detecting a narrow local uneven thickness.

This is for the following reason. That is, the energy absorption type thickness meter converts the amount of energy absorbed by the irradiation line by the film into the thickness, and the energy of the irradiation line becomes a direct signal. When the film is thin, the amount of energy absorbed per unit area becomes small and S / N
Deteriorates, and the deterioration of the S / N directly affects the measurement accuracy. Therefore, it is necessary to increase the measurement area in order to obtain a signal (energy absorption amount) necessary for obtaining measurement accuracy. For example, if the film thickness of 30 μm or less is ± 0.1
The diameter of the measurement spot required for measurement with an accuracy of μm is 20 to 30 mm or more, and the measured thickness is the average thickness in this measurement spot. Therefore, in the case of the energy absorption type thickness gauge, it is difficult to measure the shape of the local thickness unevenness with the minimum width of 2 to 3 mm required in the TD thickness unevenness measurement.

However, such an energy absorption type thickness gauge is preferably used because it can obtain sufficient energy absorption when measuring the thickness of a thick film. In particular, since there is no limitation on the width of the film as in the contact type, it is preferably used for the measurement of TD thickness unevenness.

Similarly, a capacitance type thickness gauge is used for measuring the thickness of a relatively thick film. This is because in order to measure the thickness of a thin film with high accuracy, it is necessary to increase the area of the measurement electrode, and the spatial resolution is limited as in the energy absorption type thickness gauge.

On the other hand, the optical interference type thickness gauge is preferably used for measuring the TD and MD thickness unevenness of a transparent (or nearly transparent) film having a thickness of 30 μm or less, for example. This is because the film thickness is measured from the spectral waveform of the interference light, and the absolute amount of energy of the irradiation line does not indicate the thickness. Therefore, the spatial resolution of the thin film, which is found in the energy absorption type thickness gauge and the capacitance type thickness gauge, is relatively loose, and for example, a measurement light spot diameter of 3 mm or less can be obtained. It's easy. Therefore, it is possible to measure the shape of the local uneven thickness having a minimum width of 2 to 3 mm, which is particularly required in the TD uneven thickness measurement. There are a reflection type and a transmission type in the optical interference type thickness gauge. Generally, the rate of change in the spectral intensity of the interference light is more preferable in the reflection type than in the transmission type. However, if the position of the film surface changes extremely,
The transmissive type, in which the light receiving unit is less susceptible to the influence, is more advantageous.

Next, three types of embodiments of the thickness gauge detection device of the reflection type optical interference thickness gauge will be described.

FIG. 5 shows an example of the embodiment of the detecting device of the reflection type optical interference type thickness gauge used in the present invention (hereinafter referred to as "first embodiment").
Say. ) Is shown. This mode has a thickness of 30μ
It is suitable for TD and MD thickness unevenness measurement of a film having a relatively high transparency of about m or less. The light emitted from the white light source 12 passes through the condenser lens 13, the pinhole plate 14, the collimator lens 15, the polarizing plate 16 and is guided to the film 1 through an entrance window 18 provided in a condenser 17 described later. It is like this.

A condenser 17 is arranged on the film 1 so as to face it. The condenser 17 has a center of curvature in the vicinity of the thickness measurement position on the film 1, a hemispherical support 19 having the entrance window 18 perforated therein, and a large number of optical fibers 20. The respective incident ends of (1) are integrally fixed to the holes formed in the support body 19, and the respective emitting ends are bundled and fixed. One ends of all the optical fibers 20 are fixed such that the fiber axis (incident optical axis) faces the thickness measurement position of the film 1, that is, the center of curvature of the support 19. On the other hand, the output ends of the optical fibers 20 are fixed so that the output optical axes are parallel to each other. In this way, the optical fiber 20
Is formed as a light guide path.

Behind the condenser 17, each optical fiber 20 is provided.
The extraction lens 21 is disposed so as to face the emission end surface of the extraction lens 21. Further, the extraction pinhole plate 2 is provided behind the extraction lens 21.
2, collimator lens 23, spectroscope 24, imaging lens 2
5, the image intensifier 26, and the linear image sensor 27 are arranged in this order.

Next, the operation of the above-mentioned device will be described. The white light emitted from the white light source 12 is condensed by the condenser lens 13
After being converged to the pinhole of the pinhole plate 14 by the collimator lens 15 and made parallel by the collimator lens 15, only the linearly polarized light having the oscillation direction of the P-wave component or the S-wave component is generated by the polarizing plate 16, and this is the collector 17 Entrance window 1
It is incident on the film thickness measurement position of the film 1 through 8. At this time, the light beam is focused by the entrance window 18 into a spot having an appropriate size. At this time, the light incident on the film is linearly polarized white parallel light. Since the influence of the birefringence of the film can be reduced by using linearly polarized light, the change in the spectral intensity of the reflected light becomes sharp, which is preferable, but it is not always necessary.

The light incident on the film 1 is reflected by the film 1, and at this time, due to the interference phenomenon, the spectral intensity I can be changed as shown in FIG. The film thickness is d, the incident angle is θ, and the film refractive index is n.
, The light reflected on the surface of the film and the light transmitted through the surface of the film and reflected on the back surface

[Equation 1] This is because a difference in optical optical path length (optical path length converted into a propagation length in vacuum in consideration of the influence of the refractive index) represented by, that is, an optical optical path difference Δ occurs and causes interference. That is,
Since the light reflected on the surface is phase-inverted on the reflection surface, the light whose Δ is an integer multiple of the wavelength is the opposite of the phase of the light reflected on the front surface and the light reflected on the back surface and weakens each other to create a dark area. Become. On the other hand, in the light whose Δ is shifted from the integral multiple of the wavelength by a half wavelength, the light reflected on the front surface and the light reflected on the back surface are mutually strengthened to form a bright portion.

Therefore, by keeping the incident angle θ constant and measuring the refractive index n of the film in advance, the thickness can be obtained from the change of the spectral intensity of the reflected light by the following equation 2.

[0081]

[Equation 2] Here, d is the thickness to be measured, λ _m , λ _{m + 1} (λ _m >
λ _{m + 1} ) represents the wavelength of the adjacent bright or dark portion (peak). In addition, m is an integer.

By the way, the light incident on the film 1 is normally specularly reflected, but when the film surface has wrinkles, vertical movement or inclination, the reflection direction changes or the reflected light diffuses. To do. However, in this embodiment, since a light guide is used in which the incident optical axes of the respective incident ends of the large number of optical fibers 20 are arranged so as to face the measurement points on the film 1, the surface of the film 1 is used. The reflected light in can be reliably captured.

This is due to the following action of this light guide. That is, even if the reflection direction of the white parallel light reflected at the thickness measurement position is changed due to the inclination of the film surface or the like, the incident optical axis of each optical fiber 20 is directed from various directions to the thickness measurement position. It coincides with the incident optical axis of any one of the optical fibers 20. Moreover, since the outgoing optical axes of the optical fibers 20 are fixed in parallel, no matter how the reflection direction changes or diffuses, the reflected light propagates in a certain direction at the stage of being guided to the extraction lens 21. Come to do. Therefore, the influence of the variation of the reflection direction and the diffusion is minimized.

The reflected light whose emission directions are parallel to each other is guided to the extraction lens 21 and further to the pinhole of the extraction pinhole plate 22. The extraction lens 21 extracts, through the extraction pinhole plate 22, only the component in the specific direction in the vicinity of the emission optical axis direction of the emission light from the other end of each optical fiber 20. In this way, of the reflected light emitted from the optical fiber 20, only the component in the vicinity of the emission optical axis direction is extracted. The reflected light thus extracted is collimated by the collimator lens 23, and then,
It is guided to the spectroscope 24 at a constant angle. Since the reflected light is scattered while passing through each optical fiber 20, only the component in the same direction is extracted from the light emitted from the emission end of each optical fiber 20. Is preferably very small.

The light incident on the spectroscope 24 at a constant angle is diffracted at a different angle for each wavelength due to the diffraction phenomenon and is emitted. At this time, the relationship between the incident angle ι and the outgoing angle (that is, the diffraction angle) β is expressed by the following equation (3).

[0086]

[Equation 3] Here, λ represents the wavelength of light, and b represents the grating interval of the diffraction grating. m is called the order of diffraction and is 0, ± 1, ± 2, ...
However, in a normal optical system, diffracted light when m = 1 is used.

The diffracted lights emitted from the spectroscope 24 are incident on the imaging lens 25 at the same wavelengths, which are parallel to each other and at different angles depending on the wavelengths. Since the imaging lens 25 is arranged so as to image the incident parallel light on the light receiving surface of the image intensifier 26, the diffracted light of each wavelength is imaged at a different point on the light receiving surface for each wavelength. It With such a configuration, only the diffracted light of a specific wavelength is incident on each pixel of the image intensifier 26. The image intensifier 26 is a device that amplifies incident light and is used when the amount of light incident on the linear image sensor 27 is small. When a light guide using a bundle of optical fibers or the like as described above is used, less light is available, so it may be preferable to insert the light guide into the optical system as needed.

This light is emitted from the image intensifier 26.
The light is input to the linear image sensor 27, which is in close contact with the light output surface, and is detected as the light intensity for each wavelength, that is, the spectral intensity.

The thickness gauge data processing device 7 described above takes in the detected spectral intensities, finds the wavelength that gives the extreme value of the bright part or the dark part caused by the interference phenomenon, and calculates the film 1 of the film from the formula (2) described above. Calculate the thickness d.

Thus, according to this embodiment, the thickness 30
TD of transparent (or close to transparent) film of less than μm
In the MD thickness unevenness measurement, the thickness unevenness is measured with high accuracy (for example, with a measurement accuracy of ± 0.1 μm), and the height of the convex portion (the height of the concave portion) is 0 with the minimum width of 2 to 3 mm described above. ．
It is possible to measure the shape of a local striped thickness unevenness of 25 μm or more. Further, since the light guide using the bundle of optical fibers is used, the reflected light on the film can be efficiently captured even when the reflection direction changes due to the inclination of the film surface. Therefore, in the MD thickness unevenness measurement, it is possible to move the thickness measurement position by the film rewinding device at a relatively high speed.

Next, another embodiment example of the optical interference type thickness gauge used for the film thickness gauge of the present invention (hereinafter referred to as "second embodiment example") will be described. This mode is suitable for measuring TD and MD thickness unevenness of a film having a thickness of about 30 μm or less, and if the variation range of the light reflection direction on the film surface is small, the birefringence and surface roughness of the film Even when the conditions such as are bad and the change in the spectral intensity of the reflected light at the film thickness measurement position of the white parallel light is gentle,
Highly accurate measurement is possible. The reason for this will be described below.

The optical interference type thickness gauge detects a wavelength giving an extreme value of a bright portion or a dark portion from the change of the spectral intensity of reflected light,
The thickness is obtained from this wavelength, but the difference in the intensity between the bright portion and the dark portion differs depending on the characteristics of the film to be measured.

That is, the spectral intensity I changes due to the interference phenomenon of the film because the optical path difference represented by the formula (1) is due to the light reflected on the front surface of the film and the light reflected on the back surface of the film. This is because Δ occurs and causes interference.
However, when actually measuring the film, the optical optical path difference Δ in the measurement spot at the thickness measurement position is not uniform,
It has a certain fluctuation range.

Factors that determine the magnitude of this fluctuation range include the following film characteristics. That is, (1) nonuniformity of the thickness within the measurement point due to minute irregularities on the film surface called surface roughness, and scattering of reflected light due to the minute irregularities, (2) Scattering, and (3) nonuniformity of the refractive index due to the birefringence of the film. The larger these factors are, that is, the larger the surface roughness is, the larger the amount of internal particles is, and the larger the birefringence is, the larger the fluctuation range of the optical optical path difference in the measurement spot at the thickness measurement position is. The thicker the thickness of, the larger the absolute value of the fluctuation range.

In the above embodiment, linearly polarized incident light is used in order to reduce the influence of birefringence of the film. However, in a film produced by biaxial stretching, the orientation direction is generally different depending on the position in the width direction, and it is not always easy to completely remove the effect of birefringence over the entire TD width.

The wavelengths of the bright and dark portions of the interference are the optical optical path difference Δ.
Therefore, when Δ is not uniform and has a certain fluctuation width, the obtained spectral waveform is a superposition of the light and dark wavelengths that are slightly deviated, and as a result, the light portion,
The dark part is offset and the difference becomes small, and the change in the spectral intensity becomes gentle.

By the way, it is the wavelength of the bright portion or the dark portion that the optical interference type thickness meter uses for the thickness calculation, and the magnitude of the intensity difference between the bright portion and the dark portion is not directly related to the measurement accuracy. However, in a real device, the signal contains a noise component, so
When the difference between the bright part and the dark part becomes small, the accuracy of detecting the wavelength decreases.

That is, in the case of a film having high transparency, small surface roughness, small birefringence, and thin thickness,
Since there is a large difference between the bright portion and the dark portion in the spectral intensity as compared with the noise on the device, there is no problem in measurement. However, in some products, factors such as film transparency, surface roughness, birefringence, and thickness may overlap to reduce the difference between the bright and dark parts in the spectral intensity. In some cases, the influence of is increased and the measurement accuracy is reduced. Therefore, in order to measure the thickness of these films with high accuracy, it is necessary to sufficiently reduce the noise contained in the spectral intensity signal.

By the way, in the structure of the optical interference type thickness gauge in the above-mentioned first embodiment, a light guide using a bundle of optical fibers is used. Therefore, as described above, only a small part of the reflected light from the film thickness measurement position can be used. Therefore, in the first embodiment, the amount of light is amplified by using an image intensifier or the like in order to detect the intensity of the weak diffracted light. However, the noise caused by the optical amplifying device such as the image intensifier may be the largest factor of the noise on the device.

The image intensifier converts weak light into electrons on the light-receiving surface (photoelectric surface), multiplies the number of the electrons by an electron multiplying device called a microchannel plate, and outputs light on the light-emitting surface (fluorescent surface). The electrons are converted back into light and emitted. However, the multiplication factor of electrons in the microchannel plate has a statistical variation in principle, and changes temporally and spatially.
Therefore, the intensity of light emitted from the image intensifier also varies temporally and spatially. This temporal and spatial change becomes noise and is superimposed on the spectral intensity detected by the light receiving element. The same noise is unavoidable even in an optical amplifying device other than the image intensifier or in a configuration in which the amplification degree of the electric signal of the light receiving element is increased.

In order to remove the statistical fluctuation of the multiplication factor of the optical amplifier or the like, a method of averaging the outputs over time is usually used. That is, noise is reduced by detecting the spectral intensity detected at a rate of 40 times / second in the first embodiment, for example, at a lower frequency, for example, 5 times / second.

However, since this method reduces the number of times of thickness measurement per time, in order to measure the thickness on the film at regular intervals, the whole (TD full width) measurement time becomes long. That is, in order to measure the shape of the local striped thickness unevenness with a minimum width of 2 to 3 mm, it is necessary to measure the thickness at least on the film at 1 mm intervals, and therefore the measurement frequency is, for example, 5 times / second. In such a case, it takes 20 minutes to measure the TD thickness unevenness of a film having a width of 6 m. Then, as described above, the film remains stationary during this period, which reduces productivity.

Therefore, if the light interference type thickness gauge is configured without using a light guide using a bundle of optical fibers, and if a sufficient light amount can be given to the light receiving element, it is included in the spectral intensity signal. It is possible to reduce the generated noise.

The light guide using the bundle of optical fibers has an effect when the variation in the reflection direction of the incident white parallel light is large due to the inclination of the film surface at the film thickness measurement position and the scattering of light. Is to be minimized. The inventors of the present invention have devised an optical system having another configuration that can efficiently capture the reflected light within the varied range instead of such a light guide if the variation in the reflection direction of the incident white parallel light is small. did.

FIG. 8 shows the construction of an embodiment of the film thickness measuring apparatus of the present invention using such an optical system.

The light emitted from the white light source 12 is used as the condenser lens 13, the pinhole plate 14, and the collimator lens 1.
5, the polarizing plate 16, the light beam diaphragm 28, and the half mirror 2
9. The light passes through the condenser lens 30 and is guided almost vertically to the film 1 (at an incident angle of about 0 degree).

The film 1 holds a flat surface at the thickness measuring position by its own tension, and the condenser lens 30 has a focal point near the thickness measuring position.

An extraction lens 31 is arranged on the side of the half mirror 29, and further behind the extraction lens 31, an extraction pinhole plate 32, a collimator lens 33, a spectroscope 24, an imaging lens 25, and a light receiving element. Elements such as the linear image sensor 34 are arranged in this order.

Next, the operation of the above-mentioned device will be described. The white light emitted from the white light source 12 is condensed by the condenser lens 13
After being focused on the pinhole of the pinhole plate 14 by the collimator lens 15 and made parallel by the collimator lens 15, only the linearly polarized light is passed through the polarizing plate 16, and the light beam is converged through the light beam diaphragm 28 into a light beam having a constant diameter. A part of this collimated parallel light passes through the half mirror 29, and becomes a convergent light by the condenser lens 30.

Since the condenser lens 30 has a focal point in the vicinity of the thickness measuring position on the film 1 with the film 1 held flat, the converged light is in the vicinity of the thickness measuring position on the film 1. Form an image. The contour of this formed image (measurement spot) is an image of the pinhole of the pinhole plate 14, and therefore the ratio of the diameter of this measurement spot to the pinhole diameter of the pinhole plate 14 is It is equal to the ratio of the focal length of the lens 30 (here, it acts as an incident light converging means) and the focal length of the collimator lens 15.

The light incident on the film 1 is reflected by the film 1, but at that time, the spectral intensity I changes due to the interference phenomenon. As described above, this change occurs if the incident angle θ and the refractive index n of the film are constant.
Since the thickness depends on the thickness of the film 1, the thickness can be calculated according to the equation (2).

The light incident on the film 1 is specularly reflected by the film 1 because the film 1 holds the flat surface by the tension of the film 1 and is received by the condenser lens 30 again. At this time, since the thickness measurement position is near the focal point of the condenser lens 30, the reflected light specularly reflected from the thickness measurement position is the condenser lens 30 (here, it acts as a reflected light collimating means). Is received by and becomes parallel light again. In this way, if the reflected light on the surface of the film 1 is in the range where it is received by the condenser lens 30, this reflected light is collimated by the condenser lens 30. The reflected light that has been collimated is reflected by the half mirror 29.
It is reflected by and is guided to the extraction lens 31 by changing the direction by 90 degrees. This reflected light becomes convergent light at the extraction lens 31, passes through the pinhole of the pinhole plate 32 at the focal position of the extraction lens 31, becomes collimated light again at the collimator lens 33, and enters the spectroscope 24 at a constant angle. Incident.

The light guided to the spectroscope 24 at a constant angle is the first
In the same manner as in the embodiment example described above, the light is diffracted and separated by the spectroscope 24, and the lights having the same wavelength are incident on the imaging lens 25 in parallel with each other and at different angles depending on the wavelength. Imaging lens 25
Is arranged so that the incident parallel light is imaged on the light receiving surface of the linear image sensor 34, so that the diffracted light of each wavelength is imaged at a different point on the light receiving surface for each wavelength. In this way, the white light reflected at the film thickness measurement position is detected by the linear image sensor 34 as the intensity for each wavelength.

The data processing device 7 takes in the detected light intensity, that is, the spectral intensity, obtains the wavelength of the bright portion or the dark portion caused by the interference phenomenon, and calculates the thickness d of the film 1 from the above equation (2). .

Next, the operation of the above optical system in the case where the film surface has a slight inclination α and the reflection direction of the white light incident on the film 1 surface changes or fluctuates will be described below.

FIG. 9 shows the optical path of white light when there is such an inclination α. The white parallel light incident on the condenser lens 30 is converged by the condenser lens 30,
It is converged in the vicinity of the thickness measurement position of the film 1. Here, the spectral intensity changes according to the thickness and the refractive index of the film 1, is reflected, and enters the condenser lens 30 again. here,
Since the surface of the film 1 is inclined by the angle α, the position at which the reflected light is incident on the condenser lens 30 again is different from the position at which it was previously incident, and is a position closer to the left in FIG. 9.
However, since the condenser lens 30 converges the white light that was originally a parallel light, it can be returned to the original parallel light when the divergent light reflected by the surface of the film 1 holding the plane is incident. it can. This is true unless the focal position of the condenser lens 30 is extremely far from the thickness measurement position of the film 1.

In other words, in the range where the reflected light is incident on the condenser lens 30 again, the reflected light is always collimated no matter how the film surface inclination α changes. Means This is because, in the first embodiment, when the reflected light is incident on any one of the optical fibers 20 of FIG. 5, the outgoing optical axes of the optical fibers 20 become parallel to each other. The reflected light is emitted in parallel on the emission side, and it is shown that the same effect as this is obtained by the optical system of the present embodiment example. Here, the reflected light which is collimated is extracted by the extraction lens 31 and the pinhole of the pinhole plate 32 in the same manner as in the first embodiment to extract only the component in the specific direction near the emission optical axis to the spectroscope 24. Incident.

At this time, the incident angle to the spectroscope 24 is also the same as the incident angle when the film 1 holds the flat surface and is not tilted. Therefore, the diffraction angle for each wavelength is also the same according to the equation (3). After all, the relationship between the image formation position on the linear image sensor and the wavelength is also the same. That is, according to this embodiment, even if the reflection direction changes, the change in the spectral intensity for each wavelength can be accurately detected.

As described above, according to the configuration of this embodiment, if the inclination α of the film surface is sufficiently small, the influence of the change or variation of the inclination α is not required without using a light guide using an optical fiber. It becomes possible to measure. Therefore, a sufficient amount of light can be provided to the linear image sensor without using an optical amplifier such as an image intensifier. As a result, it is possible to reduce the influence of noise on the optical amplifier and the electronic circuit.

With such a structure, the noise on the apparatus in this embodiment is mainly due to the linear image sensor and its detection circuit. This is minute compared to noise caused by an optical amplifier such as an image intensifier. Therefore, even when factors such as transparency, surface roughness, birefringence, and thickness of the film are overlapped to reduce the difference between the bright portion and the dark portion in the spectral intensity, the noise on the spectral intensity signal is sufficiently small. It is possible to detect the wavelengths of the bright part and the dark part with high accuracy. Therefore, the accuracy of the thickness measurement value obtained using the wavelengths of these bright and dark parts is high.

Further, according to this structure, it is possible to reduce the influence of light outside the thickness gauge detection device 6 and reflection within the optical system.

That is, a part of the light outside the thickness gauge detection device 6 is the same as the reflected light from the film 1 and the condenser lens 30.
Reach. However, since the pinhole of the extraction pinhole plate 32 is located at a position where only the light reflected at the measurement point passes, most of the outside light is blocked by the extraction pinhole plate 32.

Further, when the cube beam splitter is used as the half mirror, a part of the light that has passed through the beam stop 28 and is incident on the half mirror 29 is reflected by the half mirror, and then reflected by the end face of the cube and again. It passes through the half mirror and reaches the extraction lens 31. Part of the light that has entered the half mirror 29 through the light beam diaphragm 28 passes through the half mirror, is then reflected by the end surface of the cube, is reflected again by the half mirror, and reaches the extraction lens 31. However, a mechanism for adjusting the cube angle while holding the half mirror surface changes the traveling direction of this light from the traveling direction of the light reflected from the thickness measurement position, so that the light is shielded by the extraction pinhole plate 32. You can A mechanism for adjusting the cube angle while holding the half mirror surface can be realized, for example, by fixing the cube to a goniometer having a rotating surface that matches the half mirror surface. Also, the diameter of the pinhole of the extraction pinhole 32 plate needs to be determined by adjusting the cube angle to change how much the traveling direction of the reflected light from the cube end face can be changed. Is preferred.

Next, the conditions of the optical system in this embodiment will be described.

In the present embodiment, the light incident on the film 1 is convergent light, so that the incident angle on the film 1 is not constant. That is, as shown in FIG. 9, the angle α (> 0)
When light is incident on the film inclined at a convergence angle ψ (> 0), the incident angles of the incident light are distributed in the range of α ± ψ. Therefore, the optical path difference Δ between the light reflected on the front surface of the film 1 and the light reflected on the back surface is not constant, and has a distribution range depending on the distribution of incident angles. If the distribution range becomes large, the difference between the bright portion and the dark portion may become small as described above.

In order to prevent the bright portion and the dark portion from canceling each other due to the interference, the distribution range of the optical path difference Δ needs to be sufficiently small with respect to the wavelength of the spectrum. For example,
Λ _b to λ, which is the wavelength range of the spectrum (the range that includes the bright and dark parts of the spectral intensity that is actually used to calculate the film thickness)
_{When e} (λ _b <λ _e ), when the range of the distribution range of the optical path difference Δ is ± λ _b / 2, the bright portion and the dark portion are completely canceled in the vicinity of λ _b . The intensity difference between the bright and dark areas,
The distribution range of the optical optical path difference Δ must be smaller than 0.2 × λ _{b in} order to maintain 90% or more of the optical optical path difference Δ of 0.

By the way, the optical path difference Δ when the convergent light is incident
The range of distribution of changes with the convergence angle of the incident light as well as with the central angle α thereof. Below, this relationship is quantified.

Letting Δ (θ) be the optical path difference of the light reflected on the front and back of the film when the light is incident on the film at an angle θ,

[Equation 4] Becomes Here, d is the thickness of the film, and n is the refractive index of the film. Now, consider Δ ′ (θ) = Δ (θ) −Δ (0) as the amount of change in the optical path difference from the case of θ = 0. That is,

[Equation 5] And FIG. 10 is a plot of Δ ′ (θ) assuming that d = 25 μm and n = 1.65. As shown in FIG. 9, when the light converged at the angle α ± ψ enters the film at the central angle α, the distribution range of the optical optical path difference between the light reflected on the film front surface and the light reflected on the back surface is shown in FIG. ,
This corresponds to the distribution range of the value of Δ ′ (θ) when θ is varied over a range of ± ψ with θ = α as the center.

The distribution range of the value of Δ '(θ) is α> ψ
The case must be considered separately from the case of α <ψ. That is, when α> φ as shown in FIG. 9, the range of the incident angle θ of light does not include 0 ° (that is, the vertical incident component on the film surface). Therefore, the maximum value of Δ ′ (θ) is obtained when θ = α−ψ, and the minimum value is θ = α +
It is obtained when ψ. Therefore, the distribution range width δ of the value of the variation Δ ′ (θ) of the optical path difference is

[Equation 6] Becomes On the other hand, when α <ψ, the range of the incident angle θ of light includes 0 ° (that is, the vertical incident component on the film surface). Therefore, the maximum value of Δ ′ (θ) is obtained when θ = 0 °, and the minimum value is obtained when θ = α + ψ.
Therefore, the distribution range δ of the value of the variation Δ ′ (θ) of the optical path difference is

[Equation 7] Becomes

After all, in order to prevent the bright portion and the dark portion from being canceled by the interference, it is necessary to set the convergence angle ψ of the incident light so as to satisfy the following relationship. That is, the maximum thickness d of the film to be measured, the minimum wavelength λb of the effective spectral range,
When the refractive index n and the maximum angle of inclination of the film surface are α, with respect to δ expressed by the formula (6) or the formula (7),

[Equation 8] It is necessary that the optical path difference ratio a calculated in step 2 is 0.2 or less.

Therefore, for example, λ _b is 600 nm
(0.2λ _b = 120 nm), the maximum film thickness is 2
When the film thickness is 5 μm, the refractive index of the film is 1.65, and the maximum angle α of the film surface is 5 °, Δ ′ (3.6
°) =-65 nm, Δ '(6.4 °) =-185
Since it is nm, the convergence angle ψ needs to be 1.4 ° or less. Further, when α is 2.5 °, Δ ′ (0 °) = 0
Since Δ '(5.0 °) = 120 nm with respect to nm, ψ may be set to 2.5 ° or less. These are values when the maximum thickness of the film is about 25 μm. Generally, in the case of polymer films such as polyester and polypropylene, the practical maximum thickness d is often set to 3 to 30 μm. Therefore, ψ can be further increased when the maximum thickness is smaller than 25 μm.

Next, in the case where the same converging lens realizes the function of converging white parallel light when entering the film and making the reflected light at the thickness measurement position parallel light, all the reflected light is The conditions for the effective diameter φL of the condenser lens to be received by the condenser lens are shown below. The operation of the present invention can be obtained even if all of the reflected light does not enter the condenser lens, but it is preferable to satisfy this condition in order to secure a sufficient amount of light.

That is, as shown in FIG. 9, when convergent light with a convergence angle ψ is incident on a film with an inclination α, the light is 2α ±.
It is reflected at an angle of ψ. Therefore, to receive all this reflected light,

[Equation 9] Must be Further, the convergence angle ψ is first determined by the diameter D _A of the white parallel light received by the condenser lens and the focal length f of the condenser lens,

[Equation 10] It is represented by.

For example, in this embodiment, α = 5 °, D
_{If A} = 5 mm, f = 120 mm, and φL = 50 mm, ψ = 1.2 °, tan (2α + ψ) = 0.20, φ
Since L / 2f = 0.21, the above condition can be satisfied.

In order to determine the maximum inclination angle α of the film in an actual device, it is necessary to confirm how much the film is inclined in the rewinding device. Generally, it is about 5 ° when the film has no apparent wrinkles or slack.
Further, when it is possible to measure in the vicinity of an object such as a roller of a rewinding device that regulates the state of the film, it is possible to set it to 3 °.

Therefore, according to the structure of this embodiment, when the maximum inclination angle of the film surface is sufficiently small, a larger amount of light can be made incident on the light receiving element than that of the first embodiment, and the surface roughness of the film is reduced. Even when the change in the spectral intensity of the reflected light is gentle due to the birefringence, the thickness can be measured with high accuracy.

Next, another embodiment example of the optical interference type thickness gauge used for the film thickness gauge of the present invention (hereinafter referred to as "third embodiment example") will be described.

In order to apply the above-mentioned second embodiment example, it was necessary that the maximum inclination angle α of the film was sufficiently small. Due to the structural restrictions of the film rewinding device, the inclination of the film surface may not be within the practical range by the tension of itself. Therefore, the present inventors have realized that the maximum inclination angle α of the film can be reduced by further adding a means for regulating the inclination of the film.

FIG. 11 shows an embodiment including the above-described film inclination regulating means of the thickness detecting device of the optical interference type thickness gauge used in the present invention. This embodiment example enables the measurement using the optical system of the second embodiment example even when the inclination of the film surface is not within the practical range by the tension of itself.

In FIG. 11, the ring-shaped film guide 35 is attached to the front surface of the detection device, and when the thickness gauge detection device 6 is pressed against the film 1, the film 1 has its own tension. A flat surface is held inside and the inclination of the film surface is regulated. The condenser lens 30 has a focal point in the vicinity of the thickness measurement position on the film 1 while the film 1 holds the flat surface.

Other configurations of the embodiment shown in FIG. 11,
The operation is the same as in FIG. In this case, the maximum inclination angle of the film surface can be set to 1.5 ° at the film thickness measuring position.

Therefore, according to the structure of this embodiment, even if the maximum tilt angle of the film surface cannot be sufficiently reduced only by the tension of the film itself, by adding the film surface tilt regulating means, the second embodiment Similar to the example, even if the change in the spectral intensity of the reflected light is gentle due to the surface roughness of the film or birefringence, the thickness can be measured with high accuracy.

In the present invention, an organic or inorganic polymer film such as polyester or polypropylene is used as the film.

In the present invention, as the width direction measuring position moving means, a scanner for moving all or a part of the thickness measuring means as in the above-described embodiment, or a rotating structure for changing the direction of the optical path of the measuring light is used. A mirror or the like is preferably used.

In the present invention, the longitudinal direction measurement position moving means is a film rewinding device as in the above-described embodiment, a scanner for moving all or a part of the thickness measuring means, and an optical path for measuring light. A mirror having a rotating structure that changes its direction is preferably used. Further, as the film rewinding device, a so-called slitter that slits the film wound during the manufacturing process while rewinding it, or an inspector for visually inspecting the surface state of the film while rewinding is preferably used. When these are used, it is not necessary to provide a dedicated member as the longitudinal direction measurement position moving means, which is preferable.

In the present invention, the light source for generating white collimated light emits light having a wavelength in a range in which at least two wavelengths giving the extreme values of the bright portion or the dark portion are included in the spectral intensity of the reflected light in the film to be measured. It has to be something that can be generated. Therefore, the wavelength range is not limited to the visible range, for example, 400 to
The ranges of 750 nm and 700 to 850 nm are preferably used. As the white light source, an incandescent lamp, a halogen lamp, a xenon lamp or a laser with a variable wavelength is preferably used.

In the present invention, as the spectroscopic measurement means,
Used are a combination of a linear image sensor and a member that propagates light in different directions for each wavelength with a plane diffraction grating or a spectral prism, and a device that measures the wavelength sensitivity of a light receiving element while changing it over time. . Further, when a light source such as a variable wavelength laser whose wavelength changes with time is used as a light source, spectroscopic measurement is realized by a combination of an ordinary light receiving element and a wavelength variable device such as a laser. As a linear image sensor, a CCD
(Charge Coupled Device) element and PCD (Plasma Coupled Device)
ce) element or the like is preferably used. Alternatively, a two-dimensional image sensor may be used.

In the present invention, as the thickness calculating means,
Calculated by calculating the film thickness based on multiple wavelength positions that give the extreme value of the bright or dark part of the spectral intensity of reflected light, or by fitting the profile of the spectral intensity of reflected light by the method of least squares, etc. Those that do are preferably used.

The shortest wavelength of the effective spectral range of the spectral reflection intensity measuring means means the shortest wavelength of the wavelengths of the range used for actual film thickness measurement. For example, when the thickness calculation means that calculates the thickness based on the wavelength position of the bright portion or the dark portion of the spectral intensity of the reflected light is used, the shortest wavelength of the wavelength positions of the bright portion and the dark portion used for the calculation. In the case where the position is for fitting the profile of the spectral intensity of the reflected light to calculate the thickness, the shortest wavelength in the wavelength range used for fitting corresponds to the shortest wavelength in the spectral range.

Further, in the present invention, any means for controlling the inclination of the film may be used as long as it can forcibly apply tension to the vicinity of the film thickness measuring position. For example, those that press an annular frame or rod of metal or plastic against the film surface or those that blow compressed air are preferably used.

[0151]

【Example】

Example 1 A film thickness gauge having the configuration shown in FIG. 1 and using the reflection type optical interference type shown in FIG. 5 as the thickness gauge detection device 6 was manufactured. A 100 W halogen lamp was used as the white light source 12, and 600 optical fibers 20 made of plastic having a diameter of 1 mm were used. As the spectroscope 24, the blaze wavelength is 750 nm and the number of grooves is 1200 / m.
A linear image sensor 27 using a plane diffraction grating of m
An optical fiber plate (a plate material formed by bundling a plurality of optical fibers having a diameter of about 6 μm) and a linear image sensor is used as the unit. As the linear image sensor 27, a 1024 pixel PCD element is used. An image intensifier 26 as a light amplification device is inserted between the spectroscope 24 and the linear image sensor 27. The spot diameter of white light at the film thickness measurement position is 2 mm, and the effective spectral range is 700 to 850.
nm.

FIG. 7 shows the measurement result of the TD thickness unevenness measured by using this film thickness measuring device. The film used for this measurement was thin, transparent, had a smooth surface, and showed a sharp change in the spectral intensity of the reflected light. In this embodiment, the average thickness of the film is about 9 μm, and the moving speed of the thickness gauge is 25 mm / sec.
The number of thickness measurements per second was 40 times / second, and the thickness measurement interval on the film was about 0.6 mm. According to the measurement results shown in FIG. 7, the central portion has a width of 20 mm and a height of 0.4 μ.
The striped thickness unevenness of m can be measured.

Example 2 As a thickness gauge detection device 6 having the configuration shown in FIG.
A film thickness gauge using the reflective optical interference type shown in FIG. The same white light source 12, spectroscope 24, and linear image sensor 27 as in Example 1 were used. A cube beam splitter with a side of 50 mm was used as the half mirror. The effective spectral range was 700 to 850 nm.

In this example, the maximum thickness d of the film to be measured d = 25.0 μm, the shortest wavelength λ _b = 700 nm in the effective spectral range, and the maximum inclination angle α = of the film surface.
The beam diameter of white parallel light was 5 degrees, D _{A was} 5 mm, and the focal length of the condenser lens 30 was f = 120 mm. As a result, the convergence angle ψ of white light is 1.2 °, the optical optical path difference distribution range δ = 60 nm, and the optical path difference ratio a = 0.086.

FIG. 14 shows the results of TD thickness unevenness measurement of the polyester film measured by using this film thickness measuring device. As the film used for this measurement,
We used a relatively thick surface with a slightly rough surface and a gradual change in the spectral intensity of the reflected light. In this measurement example, the average thickness of the film is about 21 μm, and the moving speed of the scanner is 2 μm.
It is 5 mm / sec.

FIG. 3 also shows that the TD of the polyester film measured by using the film thickness measuring device in the same manner.
This is the measurement result of thickness unevenness. In this measurement example, the average thickness of the film is about 14 μm, and the moving speed of the scanner during the TD thickness unevenness measurement is 25 mm / sec.

Also, FIG. 4 shows the MD of the polyester film measured by using the film thickness measuring device in the same manner.
This is the measurement result of thickness unevenness. In this measurement example, the average thickness of the film is about 14 μm, and the rewinding speed is 50 mm / sec.

Next, the effects of noise of the film thickness measuring devices of Example 1 and Example 2 will be compared.

FIG. 12 shows the time variation of the measured values when the thickness at the same point of the polyester film having a thickness of about 21 μm was continuously measured by using the film thickness measuring apparatus shown in Example 1. It is a thing. Since the polyester film used for this measurement contains many internal particles and has a large birefringence, the difference between the bright portion and the dark portion in the spectral intensity detected as described above is small. In the measuring apparatus of Example 1, since the noise due to the image intensifier is superimposed on the detected spectral intensity, the measured value fluctuates within a width of about 1 μm even though the same point on the film is measured. ing. That is, with respect to this polyester film, the apparatus of Example 1 could not obtain the measurement accuracy of ± 0.1 μm necessary for detecting the local unevenness in thickness.

On the other hand, FIG. 13 shows the time variation of the measured values when the thickness at the same point of the same polyester film as in the case of FIG. 12 was continuously measured using the film thickness measuring apparatus of Example 2. Is shown. In this measurement example, similar to the above measurement example, the difference between the bright portion and the dark portion of the spectral intensity is small, but since the image intensifier is not used in the apparatus of Example 2, noise superimposed on the spectral intensity Was small, so that the fluctuation of the measured value could be 0.02 μm or less. That is, with the apparatus of Example 2, the measurement accuracy required for TD thickness unevenness measurement and MD thickness unevenness measurement was obtained.

[0161]

According to the present invention, the TD of a film can be quickly and accurately inline without cutting out a sample.
The thickness unevenness and the MD thickness unevenness can be measured. Further, since the thickness unevenness can be measured by a simple operation, the measured value does not depend on the skill of the measurer. As a result, the number of personnel required for the inspection for quality assurance can be reduced, and the manufacturing cost of the film can be reduced.

Further, since it is not necessary to cut out the sample, there is no accident caused by the cutter, and the working environment is improved.

Further, as compared with the case where a sample is cut out and measured offline, wrinkles and creases are not generated during handling of the sample, so that a highly accurate and highly reliable measurement result can be obtained. As a result, the accuracy of product quality assurance is improved.

Further, in particular, when an optical interference type thickness gauge is used as the thickness measuring means, a local streak-like thickness unevenness occurs in the film or a thickness having periodicity in the longitudinal direction. When unevenness occurs, it can be reliably measured. Therefore, the yield is improved.

Further, when these thickness irregularities occur, the situation can be confirmed quickly, and countermeasures such as cleaning the mouthpiece can be taken. Therefore, since the number of defective products to be manufactured is reduced, the manufacturing cost of the film can be reduced.

Further, according to a preferred embodiment of the film thickness measuring apparatus of the present invention, the thickness can be accurately measured even when the spectral intensity changes slowly due to the influence of the birefringence and surface roughness of the film to be measured. Can be measured.

Further, according to the method for producing a film of the present invention, it is possible to quickly find the TD and MD thickness unevenness of the film and eliminate the cause, thereby improving the production yield.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an example of an embodiment of a film thickness measuring device of the present invention.

FIG. 2 is a schematic diagram showing an example of conventional thickness unevenness measurement.

FIG. 3 is a graph showing an example of measuring TD thickness unevenness of a polyester film having an average thickness of 14 μm according to an embodiment of the film thickness measuring device of the present invention.

FIG. 4 is a graph showing an example of MD unevenness measurement of a polyester film having an average thickness of 14 μm according to an embodiment of the film thickness measuring device of the present invention.

FIG. 5 is a schematic configuration diagram showing the structure of a thickness gauge measuring device used in one embodiment of the film thickness measuring device of the present invention.

FIG. 6 is a schematic diagram showing an interference waveform of spectral intensity due to a thin film.

FIG. 7 is a graph showing an example of measuring TD thickness unevenness of a polyester film having an average thickness of 9 μm according to an embodiment of the film thickness measuring apparatus of the present invention.

FIG. 8 is a schematic configuration diagram showing the structure of a thickness gauge measuring device used in one embodiment of the film thickness measuring device of the present invention.

FIG. 9 is a diagram showing a relationship between parameters of an optical system.

FIG. 10 is a graph showing the relationship between the incident angle and the amount of change in optical optical path difference.

FIG. 11 is a schematic configuration diagram showing the structure of a thickness gauge measuring device used in one embodiment of the film thickness measuring device of the present invention.

FIG. 12 is a graph showing a measurement example in which one point of a 21 μm-thick polyester film is continuously measured by an embodiment of the film thickness measuring apparatus of the present invention.

FIG. 13 is a graph showing a measurement example in which one point of a polyester film having a thickness of 21 μm is continuously measured by an embodiment of the film thickness measuring device of the present invention.

FIG. 14: TD of a polyester film having an average thickness of 21 μm according to an embodiment of the film thickness measuring device of the present invention
It is a graph which shows the thickness unevenness measurement example.

[Explanation of symbols]

 1: Film 2: Film roll 3: Roll 4: Roll 5: Roll 6: Thickness gauge detection device 7: Thickness gauge data processing device 8: Scanner 9: Pen recorder 10: Scanner control device 11: Rewinding control of rewinding device Device 12: White light source 13: Condenser lens 14: Pinhole plate 15: Collimator lens 16: Polarizing plate 17: Concentrator 18: Incident window (hole) 19: Support 20: Optical fiber 21: Extraction lens 22: Pin Hall plate 23: Collimator lens 24: Spectroscope 25: Imaging lens 26: Image intensifier 27: Linear image sensor 28: Light flux diaphragm 29: Half mirror 30: Condensing lens 31: Extraction lens 32: Pinhole plate 33 : Collimator lens 34: Linear image sensor 35: Film guide

Claims (14)

[Claims] 1. A thickness measuring means, a width direction measuring position moving means for moving a film thickness measuring position by the thickness measuring means relative to the film in a width direction of the film, and the thickness. A longitudinal measuring position moving means for moving the measuring position relative to the film in the longitudinal direction of the film, and at least the width measuring position moving means and the longitudinal measuring position moving means. One of the above is a film thickness measuring device, wherein the thickness measuring means does not move the thickness measuring position while the thickness measuring means is measuring the thickness of the film. 2. The film thickness measuring device according to claim 1, wherein the longitudinal direction measuring position moving means is a film rewinding device. 3. The thickness measuring means measures white parallel light irradiating means for irradiating white parallel light to the thickness measuring position and spectral intensity of reflected light of the white parallel light at the thickness measuring position. 3. A spectral reflection intensity measuring means, and a thickness calculating means for calculating the thickness of the film based on the spectral intensity of the reflected light.
Alternatively, the film thickness measuring device according to the item 2. 4. The light guide means having a plurality of light guide paths in which (a) an incident optical axis is directed to the thickness measurement position and an outgoing optical axis is arranged in parallel. When,
(A) Outgoing light component extracting means for extracting a component propagating in a specific direction in the outgoing light of the light guiding means, and (c) intensity of the emitting light extracted by the emitting light component extracting means for each wavelength component. 4. The film thickness measuring device according to claim 3, further comprising a spectroscopic measuring unit for measuring the film thickness. 5. The thickness calculating means calculates the thickness of the film based on a plurality of wavelength positions that give an extreme value of the spectral intensity of the reflected light. 4. The film thickness measuring device according to 4. 6. A white parallel light source for generating white parallel light,
Incident light converging means for converging the white parallel light to a film thickness measurement position, and reflected light parallel for collimating the reflected light at the thickness measurement position of the white parallel light converged by the incident light converging means A film thickness comprising a light conversion means, a spectral reflection intensity measurement means for measuring the spectral intensity of the reflected light, and a thickness calculation means for calculating the thickness of the film based on the spectral intensity of the reflected light. A measuring device, and the distribution of the optical optical path difference between the component of the reflected light reflected on the surface of the film and the component of the reflected light transmitted on the surface of the film and reflected on the back surface of the film. A film thickness measuring device, wherein the range width is 0.2 times or less of the shortest wavelength of the effective spectral range of the spectral reflection intensity measuring means. 7. The film thickness measuring device according to claim 6, wherein the incident light converging means also serves as the reflected light collimating means. 8. The film thickness measuring device according to claim 6, further comprising an inclination restricting means for restricting inclination of the film surface at the thickness measuring position. 9. The thickness calculating means calculates the thickness of the film based on a plurality of wavelength positions that give an extreme value of the spectral intensity of the reflected light. 7. The film thickness measuring device according to 7 or 8. 10. A width direction measurement position moving means for moving the thickness measurement position relative to the film in the width direction of the film, and the thickness measurement position for the film with respect to the film. Of the longitudinal direction measuring position moving means, and at least one of the width direction measuring position moving means and the longitudinal direction measuring position moving means, the spectral reflection intensity measuring means The film thickness measuring device according to claim 6, 7, 8 or 9, wherein the thickness measuring position is not moved when measuring the thickness of the film. 11. White parallel light is generated, the white parallel light is converged to a film thickness measurement position, the reflected light at the converged white parallel light thickness measurement position is converted into parallel light, and the reflection is performed. Measuring the spectral intensity of light, a film thickness measuring method for calculating the thickness of the film based on the spectral intensity of the reflected light, and, with the component of the reflected light reflected on the surface of the film The distribution range width of the optical optical path difference between the reflected light component that is transmitted on the front surface of the film and reflected on the back surface of the film is 0.2 times the shortest wavelength of the effective spectral range in the spectral reflection intensity measurement. A method for measuring the thickness of a film, comprising: 12. A thickness measuring unit, a width direction measuring position moving unit for moving a film thickness measuring position by the thickness measuring unit relative to the film in a width direction of the film, and the thickness measuring unit. A method for measuring the thickness of a film using a longitudinal direction measuring position moving means for moving a measuring position relative to the film in the longitudinal direction of the film, comprising: When measuring the thickness at each position, (B) when measuring the thickness at each position in the longitudinal direction of the film while moving the thickness measurement position only by the width direction measurement position moving means,
A film thickness measuring method, characterized in that the film thickness is measured while moving the thickness measuring position only by the longitudinal direction measuring position moving means. 13. The film thickness measuring method according to claim 12, wherein the film thickness at each position in the longitudinal direction of the film is measured while rewinding the film roll. 14. The film thickness measuring method according to claim 11, 12 or 13 is used to measure the thickness at each position in at least one of the width direction and the longitudinal direction of the film, and the thickness at each position is measured. A method of manufacturing a film, comprising: controlling a film manufacturing process based on a result of comparison with a predetermined threshold value.