JP2008304284A - Infrared thickness meter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an infrared thickness meter for accurately measuring a thin film, etc. without being affected by interference on a front or rear surface of the film or by molecular orientation. <P>SOLUTION: In this infrared thickness meter, polarized light is inputted into a film at an oblique angle with its surface to measure the thickness of the film based on the attenuation amount of the light owing to absorption. This thickness meter is characterized by being equipped with a molecular orientation detection part 20 for detecting the scatter distribution of the light applied to the surface of the film, an orientation calculation part 42 for calculating an orientation index based on a detection signal outputted from the detection part 20, and a corrective calculation part 43 for correctively calculating the thickness of the film based on the orientation index. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an infrared thickness meter that measures the thickness of a thin film based on absorption of irradiated light.

As a conventional technique, there is an infrared thickness meter that measures the thickness of a film by measuring the absorption sensitivity of the film.
FIG. 4 is an explanatory view showing the principle of a conventional infrared thickness gauge. The light emitted from the light source 51 passes through the bandpass filter 52 and is split into light having absorption sensitivity and light having no sensitivity in the measurement film. The spectral characteristics of the bandpass filter 52 are switched by the rotation of the motor 53. The light split by the bandpass filter 52 is polarized only in a component parallel to the film surface of the film sheet 55 when passing through the polarizing filter 54, and enters the film 55 in an oblique direction and passes therethrough. A reflection mirror 56 is placed on the opposite side of the light source in the flow direction (also referred to as MD direction) of the film 55, and the light reflected by the mirror 56 passes through the film sheet 55 again and is detected by the detector 57. It is converted into an electrical signal according to Based on the detection signal output from the detector 57, the thickness of the film 55 can be measured by comparing the light with and without the light absorption sensitivity of the film 55 and obtaining the light absorption index. In the above, when light is incident on the film 55 in an oblique direction, an interference phenomenon usually occurs on the front and back of the film 55, resulting in a measurement error, but the light dispersed by the bandpass filter 52 is transmitted through the polarizing filter 24, By polarizing only the component parallel to the film surface and entering the film 55, the interference phenomenon can be avoided.

  Prior art documents related to the infrared thickness gauge include the following.

JP-A-4-212003

  According to the infrared thickness meter of FIG. 4, since the light polarized in a component parallel to the film surface is incident on the film from an oblique direction, the influence of optical interference can be removed, and the thickness of a thin film can be accurately measured. .

However, an infrared thickness meter is a sensor that measures the thickness using infrared absorption between film molecules. In a stretched film, the orientation of the molecular alignment inside the film is oriented at different angles. As a result, measurement errors would occur, so accurate measurement could not be performed.

In addition, a general thin film is produced by applying heat to a film called an original fabric to soften it, and pulling (stretching) it in the flow direction and the width direction to make it thin. The molecular orientation of the film is determined by the distribution of the pulling force at this time, and the distribution occurs in the molecular orientation in the width direction of the film.

Therefore, an infrared thickness meter that vertically enters light is hardly affected by orientation, but has a problem that it is easily affected by orientation when light is incident in an oblique direction.

FIG. 5 is a result of measuring a polyester film of 15 μm with the infrared thickness meter of FIG. 4, and a chart showing a result of recording a relationship between an angle and an absorption index by rotating the measurement film every 10 ° around the measurement point. It is. When the measurement film is rotated around the measurement point, an angle with a large absorption index and a small angle appear. When the thickness of the stretched film is measured online, the orientation difference occurs depending on the strength and direction of stretching, and the infrared absorption index changes even in the same thickness film. It will occur and accurate thickness measurement cannot be performed.

There is a molecular orientation meter that measures the molecular orientation of a film with a sensor different from the film thickness meter. The measurement principle is to measure the molecular orientation of the film by irradiating light perpendicular to the film surface and measuring the distribution of scattered light according to the orientation of the film with a plurality of detectors arranged around the measurement center. . The distribution of scattered light with respect to the measurement center correlates with the distribution of FIG. 5, and the ratio between the maximum value and the minimum value of the received signal level is defined as the orientation index.

Here, the principle of the molecular orientation meter will be described below.
FIG. 6 shows a basic configuration of the detection unit of the molecular orientation meter. The light from the infrared light emitting diode (LED) 61 is converted into parallel light by the lens 62 and irradiated perpendicularly to the surface of the film 65 to be measured. A plurality of photodiodes (PD) 63 for detecting the reflected light intensity distribution are arranged on the circumference of a large angle with respect to the light projection axis toward the measurement surface. At this time, if the positional relationship between the LED 61 and the PD 63 fluctuates, the reflection intensity distribution is affected, so that the positional relationship between the LED 61 and the PD 63 does not fluctuate with an integrated block structure.

Moreover, the direction of each PD is fixed by fixing the attachment position of this block with respect to the flow direction (MD direction) of the film sheet 65. A plurality of PD signals are amplified, A / D converted, and sent to the calculation unit. The calculation unit develops the light intensity distribution detected by the plurality of PDs 63 on the polar coordinates with the center of the projection axis as the origin to create an elliptical distribution. This is shown in FIG. This is approximated by an elliptic function by the method of least squares, the “orientation angle” is determined from the direction of the minor axis 72, and the strength of the orientation (orientation index) is determined from the shape of the ellipse 71 (ratio of major axis b to minor axis a). Obtain (see the following formula).
Orientation angle = θ (1)
Orientation index = (b / a-1) (2)
The polarity of the orientation angle is defined as a positive polarity in the direction of the arrow θ in the figure when FIG. 7 is a film surface viewed from above.

Note that the film orientation meter also has a method of detecting light components reflected in the vertical direction by irradiating light obliquely from a plurality of angles around the measurement point.

FIG. 8 is a characteristic curve diagram showing an error between the result of measuring the thickness of a film having different molecular orientations with an infrared film thickness meter and the actual thickness. When the thickness of a film having a different stretching ratio in the width direction is measured with an infrared film thickness meter, the indicated value of the infrared film thickness meter tends to be lower as the orientation index is larger. This is because, as the orientation index of the film increases, the direction in which the film molecules are bonded increases with respect to the optical axis measured by the infrared thickness meter, so the component that absorbs infrared rays decreases, and the same Even if it is a thickness, a thickness indication value will become low.

  The present invention is intended to solve such a problem, and provides an infrared thickness meter that can accurately measure a thin film or the like without being affected by interference or molecular orientation on the front and back surfaces of the film. With the goal.

In order to achieve such an object, an infrared thickness meter according to the invention of claim 1 is provided.
In an infrared thickness meter that measures the thickness of a film based on the amount of attenuation of light due to absorption when the polarized first light is incident on the film surface at an oblique angle.
A molecular orientation detection unit that detects a scattering distribution of the second light irradiated in the vicinity of the flow direction of the film at a point of incidence of the first light on the film surface;
An orientation calculation unit for calculating an orientation index of the film based on a detection signal output from the molecular orientation detection unit;
A correction calculation unit that corrects the film thickness based on an error characteristic of the film thickness with respect to the orientation index.

The invention according to claim 2
The infrared thickness meter according to claim 1,
The molecular orientation detection unit includes a light source that irradiates a second light perpendicular to the film surface;
And a plurality of detectors arranged around the light source for detecting light scattered by the film.

The invention described in claim 3
The infrared thickness meter according to claim 1,
The molecular orientation detection unit includes a plurality of light sources that irradiate the measurement points on the film surface with second light obliquely from the surroundings,
And a detector that is disposed above the measurement point and detects light scattered on the film surface.

The invention according to claim 4
In the infrared thickness meter according to any one of claims 1 to 3,
The orientation calculation unit calculates an orientation index from a maximum level and a minimum level of a plurality of detection signals output from the molecular orientation detection unit.

  As is apparent from the above description, according to the present invention, the polarized first light is incident on the film surface from an oblique angle, and the film thickness is measured based on the attenuation of light due to absorption. In the infrared thickness meter, the molecular orientation detection unit for detecting the scattering distribution of the second light irradiated on the film surface, and the orientation calculation for calculating the orientation index based on the detection signal output from the molecular orientation detection unit And a correction calculation unit that corrects and calculates the film thickness based on the error characteristic of the film thickness with respect to the orientation index. It is possible to provide an infrared thickness meter that can be accurately measured without being affected by molecular orientation.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

1A and 1B show a sensor unit 30 of an example of an infrared thickness meter according to an embodiment of the present invention. FIG. 1A is a configuration explanatory view viewed from a side surface direction, and FIG. FIG.
The sensor unit 30 of the infrared thickness meter includes an infrared thickness detection unit 10 and a molecular orientation detection unit 20.

In the infrared thickness detector 10, the light source 11 emits infrared light, and the band-pass filter 12 separates the infrared light emitted from the light source 11 into a wavelength band necessary for measurement. 15 is split into light having absorption sensitivity and light having no sensitivity. The motor 13 switches the spectral characteristics of the bandpass filter 12 by rotation. The polarizing filter 14 makes the light split by the bandpass filter 12 incident, polarizes and passes only the component parallel to the film surface of the film sheet 15, and makes it incident on the film 15 from an oblique direction. . The reflection mirror 16 is placed below the flow direction of the film 15, reflects light transmitted through the film 15, and transmits the film sheet 15 again. Usually, the distance between the two transmission points is around 2 cm. The detector 17 transmits the film sheet 15 again, is absorbed according to the thickness of the film 15, detects the attenuated infrared light, and converts it into an electrical signal corresponding to the optical signal level.

In the molecular orientation detection unit 20, the light source 21 is composed of an LED or the like, and irradiates the measured surface of the film 15 vertically. The detector 23 includes a plurality of photodiodes (PD) or the like arranged on the circumference of a large angle with respect to the light projection axis toward the surface to be measured, and detects the reflected light intensity distribution from the surface to be measured. . Although four or more detectors 23 are arranged, FIG. 1 shows a case where twelve detectors are arranged. At this time, if the positional relationship between the light source 21 and the detector 23 fluctuates, the reflection intensity distribution is affected. Therefore, an integrated block structure is adopted so that the mutual positional relationship does not fluctuate.
In addition, although it is ideal that the light irradiation position on the film sheet 15 in the infrared thickness detection part 10 and the light irradiation position (incident point) on the film sheet 15 in the molecular orientation detection part 20 coincide, it is difficult. In this case, it is desirable that the positions in the width direction are matched, and the film sheet 15 is arranged in the vicinity of 15 cm or less along the flow direction of the film sheet 15 (also referred to as MD direction). The mutual arrangement of the infrared thickness detector 10 and the molecular orientation detector 20 is performed in consideration of this point.

FIG. 2 is a configuration block diagram of the entire infrared thickness gauge.
The calculation unit 40 includes a thickness calculation unit 41, an orientation calculation unit 42, and a correction calculation unit 43.
Based on the detection signal output from the infrared thickness detector 10, the thickness calculator 41 compares the light with or without the light absorption sensitivity (such as taking a ratio) on the film 15, and absorbs light by a well-known method. The thickness of the film 15 is calculated by obtaining the index. The orientation calculation unit 42 calculates an orientation index based on the detection signal output from the molecular orientation detection unit 20. The correction calculation unit 43 performs correction calculation using the orientation index obtained by the orientation calculation unit 42 with respect to the film thickness obtained by the thickness calculation unit 41.

Next, the operation of the infrared thickness meter shown in FIGS. 1 and 2 will be described.
In the infrared thickness detector 10 of FIG. 1, the light emitted from the light source 11 passes through the bandpass filter 12 and is split into light having absorption sensitivity and light having no sensitivity in the measurement film 15. The spectral characteristics of the bandpass filter 12 are switched by the rotation of the motor 13. The light dispersed by the bandpass filter 12 passes through the polarizing filter 14 and becomes polarized light having a component parallel to the film surface of the film sheet 15 (first light), and enters the film 15 from an oblique direction. . The light that has passed through the film 15 is reflected by the reflecting mirror 16, passes through the film sheet 15 again, enters the detector 17, and is converted into an electrical signal corresponding to the signal level of the light.

In the molecular orientation detection unit 20 of FIG. 1, the light emitted from the light source 21 is collimated by a lens or the like (not shown) (second light), and then irradiates the measured surface of the film 15 vertically. . The light reflected and scattered by the surface to be measured. The intensity distribution of scattered light is detected by entering the plurality of detectors 23.

In FIG. 2, the detection signal output from the infrared thickness detection unit 10 is sent to the calculation unit 40 and input to the thickness calculation unit 41, and the detection signal when the film 15 has light with or without absorption sensitivity. The light absorption index is calculated by a well-known method of comparing the two, and the thickness of the film 15 is obtained based on the light absorption index.

The detection signal output from the molecular orientation detection unit 20 is amplified, A / D converted, sent to the calculation unit 40, and the orientation index is calculated by the alignment calculation unit 42. In the orientation calculation unit 42, the orientation index is calculated from the level at which the reflected signal is maximized and the level at which the reflected signal is minimized among the plurality of detection signals output from the detector 23, based on the above equation (2). Ask for.

The film thickness obtained by the thickness computing unit 41 and the orientation index obtained by the orientation computing unit 42 are input to the correction computing unit 43, and a correction operation for correcting the film thickness by the orientation index is performed. Here, when the thickness (before correction) of the film calculated by the thickness calculator 41 is T1, the orientation index of the film measured by the orientation calculator 42 is A, and the function of the orientation index is F (A), the orientation The film thickness T2 corrected by the index is given by equation (3).
T2 = T1-F (A) (3)

That is, the actual thickness T2 can be measured by correcting the film thickness T1 calculated by the thickness calculator 41 with the function F (A) of the orientation index. Here, the correction function F (A) is obtained by measuring the characteristic of FIG. 8 showing the error characteristic of the film thickness with respect to the orientation index in advance with respect to the infrared thickness detector 10, and storing the result in a table as a table. Use the same thing. Moreover, you may perform the calculation by an approximate expression.

FIG. 3 is a diagram showing the indication values before and after orientation correction for an example in which the thickness of a polyimide film having a thickness of 48 μm is measured with an infrared thickness meter. Before the alignment correction, the signal intensity of the light that is attenuated by the absorption of infrared rays changes due to the influence of the alignment, resulting in a measurement error, and the correct thickness measurement is not performed. In general, a film with a small orientation index displays a high thickness indication value, but a film with a large orientation index displays a component that absorbs infrared rays and displays a thickness indication value lower than the actual thickness. End up.

On the other hand, by measuring the same measurement location with the molecular orientation detection unit 20 and correcting with the obtained orientation index, the corrected calculation result has a correlation with the actual thickness L1.

According to the infrared thickness meter having the above-described configuration, the film thickness obtained by the thickness computing unit 41 is corrected by the orientation index obtained by the orientation computing unit 42, thereby being affected by the orientation. Accordingly, the film thickness can be accurately calculated and displayed. The effect is particularly great when the film is thin.

In addition, by measuring the film thickness by making polarized light incident at an oblique angle with respect to the film surface, the film thickness can be accurately measured without being affected by light interference.

Moreover, in the production process of a stretched film, the thickness in the width direction of the film and the orientation distribution can be measured simultaneously by the scanning means, so that the quality can be improved.

Moreover, since the orientation index of a film can be measured, it can be used for purposes other than thickness correction. For example, by measuring the orientation index online, it is possible to detect a film breakage due to excessive pulling in the width direction, and it is possible to increase production efficiency by avoiding a production line stop due to film breakage.

In the above embodiment, the orientation calculation unit 42 obtains the orientation index by the ratio of the numerical value at which the detection sensitivity is the maximum value to the minimum value among the plurality of detectors. As shown in FIG. 7, the light intensity distribution detected by the plurality of detectors 23 is approximated by an elliptic function by the least square method, and the orientation angle is determined from the direction of the minor axis 72 to the shape of the ellipse 71 (the major axis b and From the ratio of the minor axis a), the orientation index is obtained by the above equation (2), and the correction calculation unit 43 corrects the film thickness output from the thickness calculation unit 41 using both the orientation angle and the orientation index. May be. In this case, the film thickness can be accurately corrected even when the orientation angle is large.

In addition, in the example of the molecular orientation detection unit 20 shown in the present proposal, scattering of light emitted from one light source is detected by a plurality of surrounding detectors, but from a plurality of light sources arranged around the light source. The light scattering distribution from each light source may be measured with one detector that is irradiated with light and installed in the central portion.

It is composition explanatory drawing of the sensor part 30 of one Example of the infrared thickness meter which concerns on embodiment of this invention. FIG. 2 is a configuration block diagram of the infrared thickness meter of FIG. 1. It is a figure which shows the instruction | indication value before and behind orientation correction | amendment about the example which measured thickness with the infrared thickness meter of FIG. It is explanatory drawing which shows the principle of the conventional infrared thickness meter. It is the chart which showed the relationship between an angle and an absorption index from the measurement result of the infrared thickness meter of FIG. It is a figure which shows the basic composition of the detection part of a molecular orientation meter. It is a polar coordinate chart which shows the elliptical distribution of the reflected light intensity by the apparatus of FIG. It is a characteristic curve figure which shows the difference | error between the result of having measured the thickness of the film which has a different molecular orientation with the infrared film thickness meter of FIG. 4, and actual thickness.

Explanation of symbols

15 Film 20 Molecular Orientation Detection Unit 21 Light Source 23 Detector 42 Orientation Calculation Unit 43 Correction Calculation Circuit

Claims (4)

In an infrared thickness meter that measures the thickness of a film based on the amount of attenuation of light due to absorption when the polarized first light is incident on the film surface at an oblique angle.
A molecular orientation detection unit that detects a scattering distribution of the second light irradiated in the vicinity of the flow direction of the film at a point of incidence of the first light on the film surface;
An orientation calculation unit for calculating an orientation index of the film based on a detection signal output from the molecular orientation detection unit;
An infrared thickness meter, comprising: a correction calculation unit that corrects the film thickness based on an error characteristic of the film thickness with respect to the orientation index. The molecular orientation detection unit includes a light source that irradiates a second light perpendicular to the film surface;
The infrared thickness meter according to claim 1, further comprising: a plurality of detectors that are disposed around the light source and detect light scattered by the film. The molecular orientation detection unit includes a plurality of light sources that irradiate the measurement points on the film surface with second light obliquely from the surroundings,
The infrared thickness meter according to claim 1, further comprising: a detector that is disposed above the measurement point and detects light scattered on the film surface. The infrared ray according to any one of claims 1 to 3, wherein the orientation calculation unit calculates an orientation index from a maximum level and a minimum level of a plurality of detection signals output from the molecular orientation detection unit. Thickness gauge.

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