JP2002277217A - Web thickness measuring device and web manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thickness measuring device in which accuracy in the measurement of web thickness is improved and a web manufacturing method in which variations in the thickness of a web is substantially reduced. SOLUTION: A measuring part 7 of a light-interference thickness gauge is made to scan the traveling web W in the widthwise direction of the web to detect wavelengths which indicate a maximum value and a minimum value in a wavelength intensity distribution by the interference between two types of reflected lights I and II at the surface and back surface of the web. The thickness of the web is computed from the wavelengths and the refractive index of the web in the device. The refractive index distribution of the widthwise direction of the web is stored in an operation part 8 of the light- interference thickness gauge, a refractive index corresponding to the scanning location of the measuring part 7 in the widthwise direction of the web is specified from the refractive index distribution, and the thickness of the web is computed through the use of the refractive index.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring the thickness of a web and a method for manufacturing the web, and more particularly, to an apparatus for measuring the thickness of a web such as a resin film with improved accuracy, and a method for measuring the thickness of the web. The present invention relates to a method for manufacturing a web which uses a measuring device to significantly reduce unevenness in the thickness of the web.

[0002]

2. Description of the Related Art Conventionally, in a method for producing a resin film, thickness gauges used for controlling film thickness unevenness are disclosed in JP-A-56-115905 and JP-A-6-115905.
An optical interference type thickness gauge described in, for example, JP-A-3-163105 is widely used. This light interference type thickness gauge is designed to measure the reflected light reflected on the front surface of the film and the reflected light reflected on the back surface when the white light parallel to the running resin film is irradiated at a certain incident angle. When the light and the interference show a maximum intensity at a specific wavelength due to interference and a minimum at another specific wavelength, a wavelength intensity distribution is generated. This is based on the fact that it depends on the thickness n and the refractive index λ. That is, the refractive index n is measured in advance, and the thickness d is calculated by measuring the wavelength indicating the maximum intensity and the wavelength indicating the minimum intensity.

[0003] This optical interference type thickness gauge is more accurate than a film thickness gauge utilizing absorption of β-rays and infrared rays.
There is an advantage that even a very thin film of 5 μm or less can be measured. However, in recent years, there has been an increasing demand for improved accuracy with respect to thickness unevenness from users, and in the case where the thickness unevenness of film production was managed with a conventional optical interference type thickness gauge, the thickness corresponding to the above demand was It is becoming difficult to achieve uneven accuracy. In particular, it is difficult to reduce thickness unevenness in the film width direction, and when a manufactured film is divided into a plurality of narrow width films and shipped, there is a problem that products having different thickness unevenness can be produced. Was.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a thickness measuring apparatus having improved accuracy in measuring the thickness of a web such as the above-mentioned resin film, and to provide a web which further reduces unevenness in the thickness of the web. It is to provide a manufacturing method of.

[0005]

According to the present invention, there is provided a web thickness measuring apparatus for scanning a running web with a measuring section of an optical interference type thickness gauge in a width direction of the web.
In a thickness measuring device for calculating the thickness of a web from the output of reflected light or transmitted light on the web detected by the measuring unit and the refractive index of the web, the calculating unit of the optical interference type thickness meter includes a web width direction. Storing the refractive index distribution of, the refractive index corresponding to the scanning position in the web width direction of the measuring unit from the refractive index distribution is specified, and the thickness of the web is calculated using the refractive index. Is what you do.

Further, another web thickness measuring apparatus causes a running web to scan a measuring section of an optical interference type thickness gauge in the width direction of the web, and detects reflected light on the web detected by the measuring section. In a thickness measuring device that calculates the thickness of the web from the output of the transmitted light and the refractive index of the web, the calculating unit of the light interference type thickness meter has a refractive index previously set to a constant value, and The outer diameter distribution in the web width direction of the winding roll is stored, the outer diameter corresponding to the scanning position in the web width direction of the measuring unit is specified from the outer diameter distribution, and the refractive index is corrected using the refractive index from the outer diameter. The thickness of the web is calculated.

In a method of manufacturing a web according to the present invention, the web may be formed by a forming means and then wound into a roll. The thickness is measured by an apparatus, the measured thickness is compared with a preset reference thickness, and the web is controlled to a reference thickness based on a difference between the two thicknesses.

The present inventors have conducted various investigations on the reason why the thickness unevenness of the resin film cannot be reduced to a certain level or more when the thickness unevenness is controlled and controlled by the optical interference type thickness meter in the resin film manufacturing process. As a result, it was found that the cause was the refractive index used for calculating the thickness.
That is, the molten resin is discharged in the form of a sheet from a slit-shaped die and is stretched in the longitudinal and lateral directions.The refractive index of the film is not constant in the width direction of the film, but is small in the central region and high in both end regions. It was found that the distribution was constant, and the thickness of the film was calculated on the assumption that the distribution was constant. Therefore, the thickness unevenness in the width direction could not be reduced to a certain level or more.

According to the first web thickness measuring device, the arithmetic section of the optical interference type thickness gauge stores the refractive index distribution in the web width direction in advance, and calculates the respective refractive index distributions in the web width direction from the refractive index distribution. Since the index of refraction corresponding to the location is determined and the index of the web is used to calculate the thickness of the web, the true thickness can be measured.

According to the second apparatus for measuring the thickness of a web, the outer diameter distribution in the web width direction of a web winding roll manufactured in advance with a constant refractive index is stored, and the web width is calculated from the outer diameter distribution. Since the outer diameter corresponding to each position in the direction is specified, and the thickness of the web is calculated using the refractive index corrected from the outer diameter, the true thickness can be measured as in the first invention. it can.

Therefore, in the method for producing a web according to the present invention, since any one of the above thickness measuring devices is used for thickness control, the thickness is controlled based on the true thickness to obtain the thickness unevenness. Can be significantly reduced.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The principle of measuring the thickness of a film using an optical interference type thickness gauge is as described in JP-A-56-115905, JP-A-63-163105 and the like. Here, a brief description will be given. In the following, a case where the interference phenomenon of reflected light on the front and back surfaces of a single-layer web is used will be described. is there.

As shown in FIG. 1, when a measuring light (parallel white light beam) is irradiated onto the resin film W from the light source of the measuring section at a fixed incident angle θ, a part of the measuring light is directly reflected from the surface of the film W. (Reflected light I), and the rest refractively enters the film W, is reflected at the interface with the air on the back surface, and becomes reflected light II refracted and emitted from the front surface again. The two types of reflected light I and II have a certain optical path difference and interfere with each other to generate a wavelength intensity distribution as shown in FIG.

Light of a specific wavelength λm exhibits a minimum intensity;
Light of another specific wavelength λm + 1/2 has a maximum intensity, and light of another specific wavelength λm + 1 has a minimum intensity.
Such a change in the wavelength intensity distribution depends on the film thickness d and the refractive index n if the incident angle θ of the measurement light is constant. Therefore, the film thickness d is the wavelength of the two types of reflected light. From the wavelengths λm, λm + 1 obtained from the intensity distribution and the refractive index n, it can be calculated by the following equation (1).

[0015]

(Equation 1)

In the conventional light interference type thickness gauge, when calculating the film thickness d from the equation (1), the refractive index n of the film
Has been calculated with a constant value. However, in the first aspect of the present invention, the thickness measuring device according to the first invention uses a refractive index distribution corresponding to the position in the width direction from the refractive index distribution changed in the film width direction as shown in FIG. Select to use.

The molten resin is discharged from a die in a sheet form, cooled and solidified, and then stretched in a longitudinal direction and a transverse direction. Parallel to the traveling direction), but is inclined obliquely at both end regions. Therefore, the refractive index of the film has different values in the width direction as shown in FIG. 3, and the refractive index in both end regions is larger than the refractive index in the central region.

The refractive index distribution in the film width direction can be obtained by measuring a film manufactured in advance, and the obtained refractive index distribution may be stored in an arithmetic unit. From this refractive index distribution, the refractive index is determined in accordance with the position of the measuring unit that scans in the film width direction,
By using the refractive index as the refractive index n in the above equation (1), the true thickness d can be calculated.

As shown in FIG. 3, the refractive index distribution in the film width direction is such that the refractive index in both end regions is larger than that in the center region. When the thickness is controlled in the film manufacturing process by using the above, the wound roll has an outer diameter distribution in which the outer diameter at both ends is smaller than the outer diameter at the center. The second thickness measuring device of the present invention utilizes the outer diameter distribution in the film width direction.

That is, an outer diameter distribution in a web width direction of a winding roll of a web (film) manufactured by setting a refractive index to a constant value in advance is stored in a storage unit of the interference type thickness meter.
The outer diameter corresponding to the scanning position in the web width direction of the measuring unit is specified from the outer diameter distribution, and the thickness of the web is calculated using the refractive index corrected from the outer diameter. This thickness measuring device can also calculate the true thickness d.

FIG. 4 shows a process for producing a resin film using the thickness measuring apparatus of the present invention.

Reference numeral 1 denotes a base having a slit-shaped discharge port on its lower surface, and the slit width of the discharge port is automatically adjusted by adjusting means (not shown) provided at several places in the longitudinal direction of the slit. . The molten resin is discharged from the die 1 onto the sheet-like film W, cooled and solidified by the cooling roll 2, and then stretched in the stretching step 3. In the stretching step 3, a longitudinal stretching step 3a is provided in a preceding stage, and a transverse stretching step 3b is provided in a subsequent stage.
Is provided so that longitudinal stretching and transverse stretching are performed. The longitudinally and horizontally stretched film W is
Next, after passing through the optical interference type thickness measuring device 4 of the present invention,
It is wound up on a winding shaft 5 in a roll shape.

In the thickness measuring device 4, a scanning device 6 is disposed so as to cross the running direction of the film W, and the scanning device 6 causes the measuring unit 7 to scan back and forth in the width direction of the film W. . The measurement unit 7 detects a light source that emits measurement light (parallel white light) and a wavelength intensity distribution that interferes with the above-described two types of reflected light I and II formed by reflection of the measurement light on the film. And a part. From the measurement unit 7, a signal indicating a position in the film width direction by the scan and a signal of a wavelength intensity distribution where reflected light at the position in the width direction interfered are sent to the calculation unit 8. The arithmetic section 8 is preliminarily input to the storage section with the refractive index distribution in the film width direction measured from the film W manufactured in advance and the reference thickness do set for the film W. I have.

The calculation section 8 inputs each measurement position in the film width direction output from the measurement section 7 to determine the refractive index n corresponding to the position from the above-described refractive index distribution.
Similarly, the wavelengths λm and λm + 1 indicating the maximum value and the minimum value are specified from the wavelength intensity distribution of the reflected light input from the measuring unit 7. The thickness d of the film is calculated by substituting the refractive index n and the wavelengths λm and λm + 1 into the above equation (1).

The thickness d thus obtained is compared with a reference thickness do. If there is a difference between the two thicknesses, a difference signal is sent to a slit width adjusting means (not shown) of the base 1. Sent,
Control is performed so that the slit width is adjusted and corrected to the reference thickness do.

As a matter of course, the same effect can be obtained when the second invention is used as the thickness measuring device 4.

According to the above-described film manufacturing method, since the thickness measuring device 4 calculates the film thickness based on the true refractive index at each position in the film width direction, the thickness d of the film can be determined with high precision. Can be shown. In addition, since the film thickness unevenness is controlled based on the high-accuracy thickness d, a high-accuracy film with significantly reduced thickness unevenness can be manufactured.

[0028]

As described above, according to the web thickness measuring apparatus of the present invention, in the case of the first invention, the refractive index distribution in the web width direction is stored in the calculation unit of the optical interference type thickness meter. It is stored in advance, the refractive index corresponding to each position in the web width direction is determined from the refractive index distribution, and the thickness of the web is calculated using the refractive index, so that the true thickness can be measured. .
According to the second aspect of the present invention, the outer diameter distribution in the web width direction of the web winding roll manufactured in advance with a constant refractive index is stored, and the outer diameter distribution corresponding to each position in the web width direction is stored from the outer diameter distribution. Since the diameter is specified and the thickness of the web is calculated using the refractive index corrected from the outer diameter, the true thickness can be measured as in the first invention.

Therefore, in the method for producing a web according to the present invention, since this thickness measuring apparatus is used for controlling the thickness, the thickness is controlled on the basis of the true thickness, whereby the thickness unevenness is significantly reduced. can do.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing the principle of an optical interference type thickness measurement of a web thickness measurement device of the present invention.

FIG. 2 is a spectrum diagram showing a wavelength intensity distribution obtained by the optical interference type thickness measurement principle.

FIG. 3 is a diagram showing a refractive index distribution in a width direction of a resin film.

FIG. 4 is an explanatory view showing a process of manufacturing a resin film using the thickness measuring device of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cap 2 Cooling roll 3 Stretching process 4 Thickness measuring device 5 Winding shaft 6 Scanning device 7 Measuring unit 8 Operation unit

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Jun Torikai 1-1-1, Sonoyama, Otsu-shi, Shiga F-term in the Shiga Plant of Toray Industries, Inc. (reference) 2F065 AA30 BB13 CC02 DD00 FF51 GG02 GG24 HH03 HH12 JJ03 JJ26 MM07 PP15 PP22 UU05 4F207 AG01 AP11 AQ01 AR12 KA01 KA17 KM06

Claims (5)

[Claims] 1. A running web is scanned by a measuring section of an optical interference type thickness gauge in the width direction of the web, and the output of reflected light or transmitted light on the web detected by the measuring section and the refractive index of the web are used. In the thickness measuring device for calculating the thickness of the web, the calculating unit of the optical interference type thickness meter stores the refractive index distribution in the web width direction, and the scanning of the measuring unit in the web width direction is performed based on the refractive index distribution. A web thickness measuring device that specifies a refractive index corresponding to a position and calculates a thickness of the web using the refractive index. 2. A running web is scanned with a measuring section of an optical interference type thickness gauge in the width direction of the web, and the output of reflected light or transmitted light on the web detected by the measuring section and the refractive index of the web are used. In the thickness measuring device for calculating the thickness of the web, in the calculation unit of the optical interference type thickness meter, the outer diameter distribution in the web width direction of the web winding roll manufactured by setting the refractive index in advance to a constant value. Is stored, and the outer diameter corresponding to the scanning position in the web width direction of the measuring section is specified from the outer diameter distribution, and the thickness of the web is calculated using the refractive index corrected from the outer diameter. Measuring device. 3. The web thickness measuring apparatus according to claim 1, wherein the web is a resin film. 4. A method for manufacturing a web, wherein the web is formed by a forming means and then wound into a roll, wherein the thickness of the web before winding is measured by the thickness measuring apparatus according to claim 1, 2, or 3. A method for manufacturing a web, wherein the measured thickness is compared with a preset reference thickness, and the web is controlled to a reference thickness based on a difference between the two thicknesses. 5. The method for producing a web according to claim 4, wherein the web is a resin film which discharges a molten resin in a sheet form from a die, is cooled and solidified by a cooling roll, and is then stretched.