JP2000127227A - Film extrusion device and manufacture of film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve quickly a target average thickness and its distribution of respective layers of a laminated film by controlling the flow rate in respective branched flow paths formed from a branched point through a manifold and adjusting the width distribution in the die width direction of respective layers corresponding to respective flow paths. SOLUTION: Valves 8a and 8b of a flow rate control means for changing the flow rate are provided respectively on branched flow paths 7a and 7b after being branched in an adapter 5, and respective valves 8a and 8b are connected with a valve connecting means 9 so that the respective valves can be driven independently. Also thickness control means for changing the thickness distribution in the film width direction of respective layers are provided in respective flow paths between manifolds 10a-10c of a multi-manifold die 11 and a junction. Also a thickness control means formed of a bolt driving means 15 for pushing and drawing a flexible lip 13 by a differential bolt 14 is provided on a flow path of the manifold 10b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for extruding a film, and more particularly, to quickly attain a target average thickness of each layer and its distribution when the number of extruders is smaller than the number of laminated films. The present invention relates to a film extrusion apparatus and a manufacturing method.

[0002]

2. Description of the Related Art As a method for producing a laminated film in which a plurality of layers of a molten resin are laminated, a co-extrusion method in which a plurality of extruders are simultaneously extruded to form a laminated film has become a quite common method. I have. In this method, the resin extruded from a plurality of extruders is guided to a die via a filter for filtering foreign substances and unmelted resin, etc., as necessary, and a gear pump for increasing pressure and improving quantitativeness. .

[0003] This coextrusion manufacturing method can be classified into several types depending on where the resin is laminated for multilayering. Basically, there are a feed block method in which the layers are laminated before the film is widened to the film width, a multi-manifold method in which a plurality of manifolds are provided and laminated after the width is widened, and a method in which both are combined.

In the case of laminating resins having greatly different resin flow characteristics such as viscosity, it is difficult to finely control the thickness distribution of each layer by a feed block method in which lamination is performed before widening. Therefore, a multi-manifold method of laminating after widening is advantageous. With the multi-manifold method, it is relatively easy to optimize the design aiming at uniform flow rates for each layer, and it is also possible to provide a mechanism for adjusting the thickness distribution in the flow path until the layers are stacked. . As a thickness adjusting mechanism, a method using a choker bar is quite common. A method for controlling the temperature of the wall surface, which is generally used as a mechanism for adjusting the thickness of a single-layer die, is disclosed in JP-A-63-1.
It can be applied as disclosed in Japanese Patent No. 20629,
As disclosed in Japanese Patent Application No. 15320, there is a method using a thin flexible lip.

On the other hand, the thickness ratio of each laminated layer is generally determined by the respective extrusion systems, that is, the discharge rate ratio of an extruder or a gear pump. However, the film stack does not necessarily have to be extruded from different extruders for the number of layers. For example, in a three-layer film, the two surface layers are 1
It is advantageous in terms of capital investment that the extruder is extruded from one extruder and the central core layer is extruded from another extruder. In this case, an adapter for branching the surface flow into two flow paths before the extruder reaches the die manifold is required. In order to control each of the branched layers to the target thickness, the branch flow path after branching should be designed with a pressure loss balance in advance so that the desired thickness ratio is achieved, or the gap between the flow path from the manifold to the junction is made. It is conceivable to use means for changing. In addition, Japanese Unexamined Patent Publication
As disclosed in Japanese Patent Publication No. 286217, there has been proposed a method of incorporating an adjustment bar in a portion of the die introduction portion called an adapter.

[0006]

In recent years, there has been an increasing need to increase the added value of a film by forming multiple layers of resins having different properties. Further, in this case, it is required to control not only the total thickness of the multilayer film but also the thickness in the width direction of the layer having a predetermined function.

In order to control the thickness distribution in the width direction of each layer in a multilayer film, it is necessary to provide a mechanism for changing the flow rate distribution for each layer by the multi-manifold method. Further, the film production process cannot be uniform in the width direction, and the target value of the flow rate distribution of the molten resin extruded from the die is not always the uniform flow rate over the entire width.
In addition, it can be changed depending on film forming conditions and aging. Therefore, it must be possible to change the thickness distribution during operation to the target thickness.

On the other hand, for the purpose of reducing capital investment, if there are layers of the same resin in the laminate, it is desirable to use a common extrusion system such as an extruder and a gear pump. Therefore, the flow path is branched from one extrusion system and connected to each manifold. However, since the average thickness of each layer changes due to the pressure balance, as disclosed in the above-mentioned JP-A-2-286217. It is conceivable to provide a throttle valve. However, the operation of changing the thickness distribution of each layer itself changes the thickness balance between the layers, and there is a problem that the average thickness ratio adjusted at the angle changes during operation.

Further, the throttle valve is required to be simple and small from the viewpoint of maintenance, and is required to have no stagnation portion from the viewpoint of film quality. Furthermore, the average thickness of each layer also
It is required to be assured with the same accuracy as a single-layer film. These adjustments increase the complexity due to the required accuracy and the number of layers, and therefore need to be reduced. The present invention has been made in view of such circumstances, and has as its object to provide a film extrusion apparatus and a manufacturing method capable of quickly achieving a target average thickness and distribution of each layer of a laminated film.

[0010]

The above objects are achieved by the present invention described below. That is, the present invention includes an adapter means for branching the molten resin from the extrusion system into a plurality of branch flow paths, and a plurality of manifolds for receiving the molten resin from the branch flow paths, and forms the molten resin supplied to the manifold into a layer. In a film extruder comprising a multilayer die that is joined and extruded as a laminated film, while providing flow rate adjusting means for adjusting the flow rate in each branch flow path from the branch point to the manifold, and from the manifold to the junction point A film extruder, wherein each channel is provided with a thickness adjusting means for adjusting a thickness distribution in a die width direction of a layer corresponding to the channel, and a film is manufactured using the extruder. A method for producing a film.

In the above-mentioned present invention, the flow rate adjusting means includes:
It is preferable that the valve for adjusting the flow rate by changing the flow path cross-sectional area has no stagnation portion and can be easily adjusted even during operation. From this point, the valve having the following configuration, which is used in Examples described later, is preferably used. That is, it is composed of a channel having a rectangular cross section and a column having a radius substantially equal to the width of the rectangular cross section,
A flow path area adjusting member cut down from the circumference to a chord at a predetermined distance by a length substantially equal to the height of the rectangular cross section, and the flow path area adjusting member is flown so that the removed portion is positioned in the flow path. The valve is provided rotatably on the side wall of the road such that the position of the side wall becomes the center of rotation.

Further, the thickness adjusting means of the center layer is a flexible lip type in which the side wall of the flow path has a thin-walled portion, and the thickness adjusting means of the surface layer is a temperature adjusting method of changing the wall surface temperature of the flow path. Is preferable from the viewpoint of the configuration of the die.

On the other hand, in the production method of the present invention, the average thickness and the thickness distribution of each layer of the laminated film in the width direction are measured, and the measured values of the average thickness are fed back to the flow rate adjusting means of each layer to obtain the thickness distribution. It is preferable to control the thickness of each layer by feeding back each measured value of the above to the thickness adjusting means from the viewpoint of quality, stable production and productivity improvement. In addition, the method of measuring the thickness of each single-layer film after separating the laminated film into each layer is preferable from the viewpoint of measurement reliability. Hereinafter, details of the present invention will be described with reference to examples.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the above-mentioned present invention, in forming a laminated film, the same molten resin layer is extruded from the same extruder, the flow path is branched, and each of the layers is connected to each manifold of the die. Guiding and forming each layer into an extruded laminated film as a laminated sheet,
While being introduced into the manifold after the passage branch,
Provide a flow rate adjusting means such as a valve that can change the flow rate by changing the flow path cross-sectional area, and a thickness adjusting means that can change the discharge distribution in the die width direction from the manifold to the junction for lamination. The present invention is characterized in that a die having the same is used, and any adjustment can be performed during operation.

The thickness adjusting means only needs to be capable of adjusting the flow rate distribution for each layer by a multi-manifold in order to adjust the thickness distribution of each layer to a target distribution. As a specific example, there are many achievements in controlling the thickness of a single-layer film,
A flexible lip system that combines a flexible lip that changes the cross-sectional area of the flow path with a driving means such as a heat bolt that utilizes the thermal expansion of a bolt, a temperature adjustment system such as a temperature lip that changes the temperature of the wall surface, or a choker bar. A choker bar method in which a structure that is easy to bend in the film width direction is devised and then combined with a driving means such as a heat bolt is used. As the driving means, a means driven by a motor or the like using a simple bolt or a differential bolt combining bolts having a pitch difference instead of the heat bolt can be applied.

In order to adjust the average thickness of each of the branched layers to the target value, it is necessary to adjust the total extrusion amount. However, the flow rate of the branched branch flow path connected from the same extruder by a flow rate adjusting means such as a valve is required. By adjusting
Change the ratio. This flow rate adjusting means may be of a type in which a balance valve is provided at a branch portion. Further, the flow rate adjusting means may be provided in all of the branched flow paths after branching, but the structure becomes simpler if it is provided only in the layer to be controlled or is not provided in the other one.

As described above, according to the present invention, when the thickness distribution is changed, particularly the pressure balance between the layers of the branched flow path is changed, and the average thickness ratio of each layer is changed. A feature is that both means are provided and can be adjusted during the film forming operation.

Hereinafter, the present invention will be described in detail with reference to embodiments. FIG. 1 is an explanatory diagram of a film manufacturing process for producing a peelable three-layer film according to one embodiment of the present invention. As shown in the figure, the resin of the central layer, which is the core of the three layers, is melt-extruded by the extruder 2, the foreign matter and the like are removed by the filter 4, and the multi-manifold die 11 passes through the flow path 6 in the adapter 5.
To the manifold 10b. The resin of the surface layer is melt-extruded by the extruder 1, passes through the filter 3, and is divided by the adapter 5 from one flow path 7 to two branch flow paths 7 a and 7 b. It is led to 10c.

The branch flow path 7 after branching is provided in the adapter 5.
a, a valve 8 with variable flow rate on 7b
a and 8b are provided respectively. The valves 8a and 8b can change the flow rate by rotation, and are connected to valve driving means 9 such as a motor (driving means for the valve 8a is not shown).
Each can be driven independently.

Each flow path between the manifolds 10a, 10b, 10c and the junction P of the multi-manifold die 11 is provided with a thickness adjusting means for changing the thickness distribution of each layer in the film width direction. In the present embodiment, the surface flow path, that is, the flow path from the manifolds 10a and 10c, is provided with a temperature adjusting type thickness adjusting means including electric heaters 12a and 12b for adjusting the thickness by changing the amount of heat applied to the resin. Layer flow path or manifold 10
The flow path b is a flexible lip type thickness adjusting means comprising a thin flexible lip 13 provided on the flow path, a differential bolt 14 for pushing and pulling the flexible lip 13 and a bolt driving means 15 such as a motor for driving the flexible lip 13. Is provided. With this combination, the configuration of the multi-manifold die 11 can be made compact as shown in the figure.

The molten resin is extruded from the multi-hold die 11 as a three-layer laminated sheet. Then, the sheet-like body extruded from the multi-manifold die 11 becomes a flat unstretched laminated film 19 a by the casting device 16. And this laminated film 19a
Is subjected to necessary processing in the subsequent steps to produce a desired product film.

This embodiment is an example of a processing step suitable for a laminated film in which a combination of incompatible resins such as polyester and polypropylene are used for the surface layer and the core layer. That is, the laminated film 19a from the casting device 16 is successively biaxially stretched in three layers by the longitudinal stretching machine 17 and the transverse stretching machine 18,
A biaxially stretched laminated film 19b is obtained. The surface layer and the core layer of the laminated film 19b can be mechanically peeled off.
The film is separated into axially stretched single-layer films 21a to 21c, and continuously wound by winders 25 to 27, respectively. Thus 3
Two films can be manufactured simultaneously.

In the present embodiment, the thickness of each of the single-layer films 21a to 21c, that is, each layer of the laminated film 19 is individually measured by the thickness gauges 22 to 24 between the separation device 20 and the winders 25 to 27 to control the thickness. The thickness of each of the following layers is controlled by feeding back to the device 28. This thickness control means is similar to known film thickness control, and scans in the width direction of each layer with a thickness gauge 22 to 24 to measure the thickness at each predetermined measurement point in the width direction of each layer, and measures each measured value. Is fed back to the thickness control unit of each layer of the thickness control device 28, and the respective electric heaters 12a arranged in parallel in the width direction of the thickness adjustment means of each layer described above in order to reduce thickness unevenness in the film width direction from each thickness control unit. 12b, a command is given to the bolt driving means 15 to control the thickness distribution in the width direction.

In this embodiment, the thickness control device 28 further includes the following flow control means. In other words, in order to obtain the average thickness from the measured values in the width direction for the surface layers on both sides of each of the above layers and feed it back to the respective flow rate control units to control the average value, the valves 8a and 8 of the flow rate adjusting means are required.
The control is performed by giving a command to the driving means 9 of b, whereby the average thickness of both surface layers is balanced.

As described above, according to this embodiment, three single-layer films can be simultaneously produced on one series of production lines, and a production method with extremely high productivity is realized.

The adapter 5 and the valve 8 of this embodiment
a and 8b have the configuration shown in FIGS. As shown in FIG.
The cross-sectional shapes of a and 7b are gradually changed from a circular cross-section to a rectangular cross-section in section A so that there is no stagnation portion, and sections B and C remain rectangular in cross-section and gradually change to circular cross-section in section D again. I'm back. The rectangular section has a width of W and a height of H.

In sections B and C, valves 8a and 8b as shown in FIG. 3 are provided. That is, as shown in FIG. 2, a cylindrical pin 35 serving as a valve body having the same radius as the width W of the flow path cross section at the installation location forms a branch flow path 7 a, 7 b having a rectangular cross section in sections B and C at its semicircular portion. It is provided so as to block. As shown in FIG. 3, one end of this pin 35
And a donut-shaped stopper 35a is provided at an appropriate position. On the other end, a jack bolt 4 having a button-shaped support member 41a provided at an appropriate position.
1 and screwed into the center hole of the support member 41a.
With this, the other end of the pin 35 is supported, and its mounting position can be adjusted.

As shown in FIG. 3, the pin 35 is inserted into a mounting hole provided in the main body 36, sealed with upper and lower ring-shaped packings 37, and centered on the position of the side wall S of the branch flow paths 7a, 7b. It is rotatable. Reference numeral 38 in the drawing denotes an upper packing presser for pressing the upper packing 37 together with the stopper 35a, and 39 in the drawing denotes a lower packing 3 in the drawing.
7 is a packing retainer at the lower part that presses 7 through a dish-shaped collar 42.

The pin 35 is used to cut off a quarter arc of the circumference by the flow path height Hp at the portion located in the flow path, that is, the valve body portion, as shown by a white background in FIG. Thus, a notch 35b is formed. Therefore, as shown in FIG. 2, this valve has the maximum opening when the cut surface of the cut portion 35b is parallel to the side walls of the branch flow paths 7a and 7b opposed thereto, and closes when rotated by 90 degrees. .

As described above, the valves 8a and 8b of this embodiment
By connecting the valve driving means 9 to the connecting portion at the end protruding from the adapter 5 and rotating the valve driving means 9 from 0 to 90 degrees as described above, it is possible to reduce the flow rate to almost fully closed. The resin flows along a pin having a sufficiently large curvature at any opening degree, so that there is almost no stagnation portion. In addition, this structure is extremely simple, and has good workability and maintainability.

Furthermore, in order to reduce the staying portion as much as possible, the heights Hb and Hc and the widths Wb and Hb of the sections B and C of the branch passages 7a and 7b are reduced.
During Wc, the branch flow path 7 is set so that the following equation is satisfied.
It is better to reduce a and 7b little by little toward the downstream. In addition, Hp and Wp are the height and width of the branch flow paths 7a and 7b at the valve installation location. Hb>Hp> Hc, Wb>Wp> Wc

If the valves 8a and 8b have no stagnation portion and have no adverse effect on the film quality, the flow rate changes greatly due to the operation of the valves in order to perform precise control, and the valve 8a is hardly affected by disturbance such as temperature. Should be. Therefore, ideally, it is better to be as close as possible to the manifold. In other words, it is easy to think that it is sufficient to adjust each unit arranged in the width direction of the thickness adjusting means for adjusting the thickness distribution at the same time in the entire width, but since it is generally difficult for the thickness adjusting means to give a large flow rate change over the entire width uniformly, It is not more advantageous than using the valve of this example. Therefore, it is preferable that the adapter incorporating the valve of the present example is directly connected to or integrated with the die introduction portion.

Further, the above-described manufacturing method of the present example is preferably applied to a case where the control of the thickness distribution in the width direction is also required to be fine. As such a case, for example, in order to produce a film for general use such as a film for thermal transfer ribbon or a film for magnetic recording with high productivity, co-extruding mutually incompatible polymers into an unstretched laminated film, and After at least uniaxial stretching, the laminated film is peeled off, and two or more monolayer films of the product are formed at a time (Japanese Patent Application Laid-Open Nos. Sho 51-30862, 56-113427, and 58-5226). Etc.) and a carrier film of a material incompatible with a thin film for capacitors, etc., which is apt to be cut in the processing process, is reinforced and processed, and after processing is completed, the processed laminated film is peeled off from the carrier film A method of reducing cutting by winding (Japanese Patent Laid-Open No. 04-7198) can be cited.

The thickness may be measured not only after the peeling in this example but also in a laminated state, that is, a laminated film. An online thickness gauge is used for this measurement. The thickness gauge may be a β-ray thickness gauge, an optical interference thickness gauge, an infrared thickness gauge, etc.
When the measurement is performed with the laminated film as it is, an optical interference method that can be measured by reflection can be applied.

The thermoplastic resin in the present invention is not particularly limited as long as it has a film forming property.
Preferred examples include polyester, polyamide, polycarbonate, and polyolefin. Among them, polyester and polyolefin are particularly preferable.

The polyester is preferably an aromatic polyester, particularly preferably polyethylene terephthalate or polyethylene-2,6-naphthalate. As the polyolefin, polyethylene and polypropylene are preferable, and polyolefin is particularly preferable.

As the polymer, either a homopolymer or a copolymer can be used depending on the purpose of the film.

Hereinafter, examples of the film production of the present invention carried out by the above-described apparatus and comparative examples for comparison will be described.

[0039]

EXAMPLES AND COMPARATIVE EXAMPLES Polyethylene terephthalate pellets having an intrinsic viscosity of 0.60 obtained by adding potassium acetate to the dicarboxylic acid component in an amount of 12 mmol% and kaolin having an average particle diameter of 0.9 μm in an amount of 0.3 wt% were used as polyester raw materials. After drying at 170 ° C. for 3 hours, the mixture was supplied to the extruder 1 and melt-extruded at 280 ° C.

On the other hand, 1.0 wt% of anatase type titanium and 0.1% of tetra-n-butylphosphonium 3,5-dicarboxybenzenesulfonate were used as polyolefin raw materials.
Polypropylene (Tm: 152)
C., melt flow rate: 5 g / 10 min, ethylene copolymerized polypropylene, ethylene content ratio: 3 mol%), dried at 100.degree. C. for 1 hour, supplied to the extruder 2, and heated to the same temperature as polyethylene terephthalate.
It was melt extruded at 0 ° C.

Each of the molten polymers merges inside the die 11, and three layers of polyethylene terephthalate / polypropylene / polyethylene terephthalate are laminated.
It was discharged in a sheet form from a die having a width of 760 mm of the die 11. Next, the sheet was wound around a cooling drum 16 maintained at 20 ° C. while applying an electrostatic charge with an electrostatic wire 16a, and cooled and solidified to form a three-layer unstretched laminated film.

The unstretched laminated film is subjected to a longitudinal stretching machine 1
After contacting with a heating roll at 7 and heating to 80 ° C, the film was stretched 3.6 times in the longitudinal direction and immediately cooled to 20 ° C. Subsequently, the film was stretched 3.9 times in the transverse direction at 90 ° C. in a transverse stretching machine 18, specifically, a tenter-type transverse stretching device, and then heat-treated at 120 ° C. and cooled to room temperature. Next, the separation device 2
At 0, each single layer film was separated and wound up as shown.

In the above-mentioned production, for comparison, the flow rate was not adjusted at all as a comparative example, and only the thickness distribution of each layer was adjusted by manually checking the thickness measurement results of each single-layer film after separation. This was carried out by a thickness adjusting means. As a result, although the flow path of the surface layer of the die 11 is made completely symmetrical in the drawing, the average thickness and the thickness distribution of each surface layer on both sides are different. When the thickness unevenness of the surface layer is corrected, the thickness distribution of the other surface layer changes, and the average thickness of both surface layers is set to ± 1 of the target.
% And thickness unevenness could not be adjusted to R4% or less.

Next, as an embodiment of the present invention, when the adjustment by the flow rate adjusting means provided on the adapter 5 was performed in combination with the thickness adjustment, the above target could be satisfied in several hours despite the manual adjustment. Was. The adjustment of the flow rate adjusting means has a characteristic that the tendency of the thickness distribution of each layer does not change even if operated, and the adjustment was completed in a short time.

[0045]

According to the present invention, when a molten resin to be extruded is branched before a die, and is again expanded and extruded with another molten resin by a multi-manifold die, an interlayer generated during correction of thickness unevenness of each layer. And a method for producing a multilayer film having good thickness quality by realizing quick adjustment of each layer to a desired thickness.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a film manufacturing process according to one embodiment of the present invention.

FIG. 2 is a partial cross-sectional view of the adapter used in the embodiment of FIG.

FIG. 3 is a side sectional view showing the configuration of the valve of FIG. 2;

[Explanation of symbols]

 1, 2 Extruder 3, 4 Filter 5 Adapter 6 Flow path 7a, 7b Branch flow path 8a, 8b Valve 9 Valve driving means 10a, 10b, 10c Manifold 11 Multi-manifold die 12a, 12b Electric heater 13 Thin and flexible lip 14 Differential bolt 15 Bolt driving means 16 Casting device 17 Vertical stretching machine 18 Horizontal stretching machine 19a, 19b Laminated film 20 Separator 21a, 21b, 21c Single-layer film 22, 23, 24 Thickness gauge 25, 26, 27 Winder 28 Thickness control device

Claims (8)

[Claims] 1. An apparatus comprising: an adapter for branching a molten resin from an extrusion system into a plurality of branch flow paths; and a plurality of manifolds for receiving the molten resin from the branch flow path. The molten resin supplied to the manifold is merged in a layered manner. In a film extruder comprising a multilayer die extruded as a laminated film, while providing a flow rate adjusting means for adjusting the flow rate in each branch flow path from the branch point to the manifold, each from the manifold to the junction A film extruder, wherein a thickness adjusting means for adjusting a thickness distribution in a die width direction of a layer corresponding to the channel is provided in the channel. 2. An extruder comprising two extruders, a die having three manifolds, and an adapter means for branching a flow path of one extruder into two and a flow path of the other extruder. With a single flow path that does not branch the path, the branch flow path of one extruder is connected to the manifold that becomes the outer layer, and the single flow path of the other extruder is connected to the center layer manifold, 2. The film extruder according to claim 1, wherein a three-layer laminated film having the same resin on both sides is extruded. 3. The film extruder according to claim 1, wherein the flow rate adjusting means is a valve that adjusts a flow rate by changing a flow path cross-sectional area. 4. The valve has a rectangular cross section and a column having a radius substantially equal to the width of the rectangular cross section, and is cut down from the circumference to a chord of a predetermined distance by a length substantially equal to the height of the rectangular cross section. A flow path area adjusting member, wherein the flow path area adjusting member is rotatably provided on a side wall of the flow path such that the removed portion is located in the flow path such that the side wall position is the center of rotation. An apparatus for extruding a film according to claim 3. 5. The thickness adjusting means of the central layer is a flexible lip method in which the side wall of the flow path has a thin wall portion, and the thickness adjusting means of the surface layer is a temperature adjusting method of changing the wall surface temperature of the flow path. Item 5. A film extruder according to any one of Items 1 to 4. 6. A method for producing a film, wherein the film is extruded as a laminated film by a film extruder according to any one of claims 1 to 5. 7. The average thickness and thickness distribution of each layer of the multilayer film in the width direction are measured, and the measured values of the average thickness are fed back to the flow rate adjusting means of each layer, and the measured values of the thickness distribution are measured by the thickness adjusting means. 7. The method for producing a film according to claim 6, wherein the thickness of each layer is controlled by feedback to the film. 8. The method for producing a film according to claim 7, wherein the measurement is performed on each single-layer film after separating the laminated film into each layer.