JP6797279B2 - Method for manufacturing thermoplastic resin film and thermoplastic resin film - Google Patents

Description

The present disclosure relates to a thermoplastic resin film and a method for producing a thermoplastic resin film.

The thermoplastic resin film is produced by melt-extruding the thermoplastic resin to form a film, and then undergoing steps such as stretching and heat treatment such as heat relaxation. Further, in recent years, a thermoplastic resin film is imparted with various functions by applying or affixing a functional material on the film, and is widely used as a functional film.

On the other hand, in the case of a thin-film thermoplastic resin film, if heat treatment is applied in the process of imparting functionality to the film, streaky wrinkles (wrinkles) extending in the film transport direction are formed in the film width direction during the heat treatment. It may occur so that multiple lines are lined up. Since the shape of these wrinkles is fixed by cooling after the heat treatment, the appearance may be hindered as a failure such as film quality or coating unevenness.

As a technique related to the above, for example, in Japanese Patent Application Laid-Open No. 2014-238612, a base film having a tensile elastic modulus of 140 MPa or more with the film transport direction as the tensile direction is used to prevent wrinkles of the base film. Techniques for suppressing defects are disclosed.
Further, for example, Japanese Patent Application Laid-Open No. 2014-210433 discloses a polyester resin molded film having an elastic modulus at 30 ° C. and 100 ° C. in a specific range from the viewpoint of shape stability and flexibility of the film. ..

As described above, various studies have been made on techniques for improving the wrinkles or flatness of the film, for example, reducing the transport tension in each step. However, wrinkles that tend to appear wrinkled in the width direction of the film are easy to twist when the film is heat-shrinked due to heat treatment of the film, or easy to move when the film is thermally expanded (for example, the surface of a transport roll). It appears due to the slipperiness of the film, etc.).
Although the above-mentioned Patent Documents 1 and 2 disclose a technique for improving the occurrence of wrinkles and the like by adjusting the elastic modulus in one direction of the film, for example, simply adjusting the elastic modulus in the film transport direction is sufficient. A sufficient improvement effect cannot be expected in a film having a property that creates a barrier when trying to alleviate a dimensional change in one direction due to thermal shrinkage or thermal expansion in the other direction.
The frequency of wrinkles generated on the film becomes more remarkable as the thickness of the film becomes thinner, and the size of the wrinkles also increases.

The present disclosure has been made in view of the above.
An object to be solved by one embodiment of the present disclosure is to provide a thermoplastic resin film in which wrinkles are less likely to occur.
A problem to be solved by another embodiment of the present disclosure is a thermoplastic resin film in which wrinkles are less likely to occur even when a thin (preferably having a thickness of 200 μm or less) thermoplastic resin film is heated and conveyed. Is to provide a manufacturing method for.

Specific means for achieving the above tasks include the following aspects.
<1> film transport direction of the elastic modulus ^{E MD,} the elastic modulus ^{E TD} in the film width direction perpendicular to the film conveying direction, the ratio ^{Er 30} at 30 ° C., is 1.1 to 1.8, and, elastic modulus ^{E TD} for elastic modulus ^{E MD,} the ratio of the ratio ^Er 30, the ratio at 90 ° C. ^Er 90, the ratio ^Er 120 at 120 ° C., the ratio ^{Er 0.99} at 0.99 ° C., and 180 ° C. at the 30 ° C. A thermoplastic resin film having a difference between a maximum value Er _max and a minimum value Er _min selected from Er ¹⁸⁰ of 0.7 or less.
<2> The thermoplastic resin film according to <1>, wherein the surface roughness Ra of at least one surface is 0.5 nm to 50 nm.
<3> The thermoplastic resin film according to <1> or <2>, which has a thickness of 200 μm or less.
<4> The thermoplastic resin film according to any one of <1> to <3>, which is a polyester film or a cyclic polyolefin film.

<5> The method for producing a thermoplastic resin film according to any one of <1> to <4>.
The process of melt-extruding the raw material resin and cooling it to form a thermoplastic resin sheet,
A step of first stretching the molded thermoplastic resin sheet in the longitudinal direction to obtain a thermoplastic resin film, and
A preheating part for preheating the thermoplastic resin film, a stretched part for stretching the preheated thermoplastic resin film by applying tension in the film width direction orthogonal to the longitudinal direction of the thermoplastic resin film, and a tensioned thermoplastic resin. The thermoplastic resin film is sequentially conveyed to a heat-fixing part that heats and fixes the film, a heat-relaxing part that heat-relaxes tension, and a cooling part that cools the heat-relaxed thermoplastic resin film. And the process of stretching
Including
The area magnification, which is the product of the stretching ratio in the first stretching and the stretching ratio in the second stretching, is 12.8 times to 15.5 times.
In the second stretching step, in the cooling section, the heat-relaxed thermoplastic resin film is further strained in the film width direction, and the film width at the end of the heat relaxation in the heat-relaxing section is -1. A method for producing a thermoplastic resin film, which expands or contracts the thermoplastic resin film in the range of 5.5% to 3%.

<6> The second stretching step is the method for producing a thermoplastic resin film according to <5>, wherein the thermoplastic resin film is stretched at a stretching rate of 8% / sec to 45% / sec in the stretched portion. is there.
<7> The thermoplastic resin film according to <5> or <6>, wherein in the second stretching step, the thermoplastic resin film is stretched at a stretching rate of 15% / sec to 40% / sec in the stretched portion. It is a manufacturing method of.
<8> The thermoplastic resin according to any one of <5> to <7>, wherein the second stretching step is to stretch the thermoplastic resin film at a stretching temperature of 100 ° C. to 150 ° C. in the stretched portion. This is a film manufacturing method.
<9> The thermoplastic resin according to any one of <5> to <8>, wherein in the second stretching step, the thermoplastic resin film is stretched at a stretching temperature of 110 ° C. to 140 ° C. in the stretched portion. This is a film manufacturing method.

<10> Any one of <5> to <9> in which the area magnification, which is the product of the stretching ratio in the first stretching and the stretching ratio in the second stretching, is 13.5 times to 15.2 times. The method for producing a thermoplastic resin film according to the above.
<11> In the step of performing the second stretching, the thermoplastic resin film is expanded in the range of 0.0% to 2.0% with respect to the film width at the end of the heat relaxation in the heat relaxation part in the cooling part. The method for producing a thermoplastic resin film according to any one of <5> to <10>.
<12> The heat according to any one of <5> to <11>, in which the first stretching step is performed by performing the first stretching with a draw ratio of 2 to 5 times the thermoplastic resin sheet. This is a method for producing a plastic resin film.

According to one embodiment of the present disclosure, there is provided a thermoplastic resin film in which wrinkles are less likely to occur.
According to another embodiment of the present disclosure, there is a method for producing a thermoplastic resin film in which wrinkles are less likely to occur even when a thin (preferably having a thickness of 200 μm or less) thermoplastic resin film is heated and conveyed. Provided.

It is a top view which shows an example of the biaxial stretching machine. It is a conceptual diagram for demonstrating the mechanism which a twist occurs by the anisotropy of the elastic modulus of a film. It is a front view for demonstrating the mechanism which a film is twisted on a transport roll. It is a front view which shows the state which the film was twisted and buckled on the transport roll.

Hereinafter, the thermoplastic resin film of the present disclosure and a method for producing the same will be described in detail.
In the present specification, the numerical range represented by using "~" means a range including the numerical values before and after "~" as the lower limit value and the upper limit value. In the numerical range described stepwise in the present disclosure, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the upper limit value or the lower limit value of another numerical range described stepwise. Further, in the numerical range described in the present disclosure, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the value shown in the examples.

Further, in the present specification, the term "process" is not limited to an independent process, and even if it cannot be clearly distinguished from other processes, the term "process" is used as long as the intended purpose of the process is achieved. include.

<Thermoplastic resin film>
The thermoplastic resin film of the present disclosure, for the elastic modulus of the film conveyance direction ^{E MD,} in the film width direction perpendicular to the film conveying direction of the elastic modulus ^{E TD,} the ratio ^{Er 30} at 30 ° C., 1.1 to 1. 8 and the maximum selected from a ratio of Er ³⁰ at 30 ° C, a ratio of Er ⁹⁰ at 90 ° C, a ratio of Er ¹²⁰ at 120 ° C, a ratio of Er ¹⁵⁰ at 150 ° C, and a ratio of Er ¹⁸⁰ at 180 ° C. The difference between the value Er _max and the minimum value Er _min is 0.7 or less.
In addition, Er ³⁰ , Er ⁹⁰ , Er ¹²⁰ , Er ¹⁵⁰ and Er ¹⁸⁰ are as follows.
Er ³⁰ represents the ratio of the elastic modulus ^{ETD in} the film width direction to the elastic modulus ^{EMD in} the film transport direction when the film temperature is 30 ° C.
Er ⁹⁰ represents the ratio of the elastic modulus ^{ETD in} the film width direction to the elastic modulus ^{EMD in} the film transport direction when the film temperature is 90 ° C.
Er ¹²⁰ represents the ratio of the elastic modulus ^{ETD in} the film width direction to the elastic modulus ^{EMD in} the film transport direction when the film temperature is 120 ° C.
Er ¹⁵⁰ represents the ratio of the elastic modulus ^{ETD in} the film width direction to the elastic modulus ^{EMD in} the film transport direction when the film temperature is 150 ° C.
Er ¹⁸⁰ represents the ratio of the elastic modulus ^{ETD in} the film width direction to the elastic modulus ^{EMD in} the film transport direction when the film temperature is 180 ° C.

The "difference between the maximum value _{Er max} and the minimum value _{Er ^min",} select ^{Er 30, Er 90, Er 120} , up from ^{Er 0.99} and ^{Er 180} value _{Er max} and the minimum value _{Er min,} the minimum from the maximum value _{Er max} It refers to the value obtained by subtracting the value Er _min .

In the present disclosure, the thermoplastic resin film is also simply referred to as a "film", and a film having a thickness of 200 μm or less is also referred to as a “thin film”. From the viewpoint that the effect of the embodiment of the present invention is more exerted, the thickness of the thin film is preferably 100 μm or less, more preferably 50 μm or less.

The method for producing the thermoplastic resin film will be described in detail later, but a thin film is usually obtained by transporting and stretching the film using a roll or the like. Here, the transport direction of the film is also referred to as an MD (Machine Direction) direction. The MD direction of the film is also referred to as the longitudinal direction of the film. The width direction of the film is a direction orthogonal to the longitudinal direction of the film. The width direction of the film is also referred to as the TD (Transverse Direction) direction in the film produced while transporting the film.
In the present specification, the transport direction of the film is referred to as "MD" or "MD direction", and the width direction of the film orthogonal to the transport direction of the film is referred to as "TD" or "TD direction".

The thermoplastic resin film may be made highly functional or composite by laminating a plurality of thermoplastic resin films or laminating a functional layer on the thermoplastic resin film. In processing such a thermoplastic resin film, the film is usually stretched, heated, or the like while being conveyed by a roll or the like.
When a thin thermoplastic resin film is heat-conveyed, it tends to have wrinkles (wrinkles) arranged in an uneven shape so as to undulate in the TD direction of the thermoplastic resin film.
The following factors can be considered for this phenomenon.
(1) The elastic modulus in the TD direction is smaller than the elastic modulus in the MD direction.
As described above, the thermoplastic film is conveyed by a roll or the like. Due to the stress acting in the MD direction such as the transport tension at this time, the compressive stress acts in the TD direction due to the Poisson effect. When the elastic modulus in the TD direction is smaller than the elastic modulus in the MD direction, the generated compressive stress in the TD direction disturbs the shape of the film in the TD direction, and it is considered that twisting occurs in the TD direction of the film. That is, as shown in FIG. 2, when the polymer main chains (solid lines in FIG. 2) exist side by side in the MD direction and the molecular orientation in the MD direction is strong, the side chains between the main chains (FIG. 2). The TD direction of the film simply connected by the broken line in 2) has a weaker shape-retaining force than the MD direction, and the anisotropy of the film strength becomes stronger. Therefore, it is presumed that the film is likely to be wrinkled in the TD direction as shown in FIG. On the other hand, when the molecular orientation in the TD direction is strong (the polymer main chains are lined up in the TD direction), the molecular chains become deformation resistance and the film is wrinkled in the TD direction. It will be difficult.
That is, it is presumed that the ratio of the elastic modulus of the film in the MD direction and the TD direction can contribute to the generation of wrinkles.
(2) The holding force of the film by the transport roll at the end in the TD direction is strong.
During the heating step, the film tends to expand with a width of z ¹ and z ² at the edges in the TD direction, as shown in FIG. At this time, if the holding force of the film 3 at both ends of the TD on the surface of the transport roll 4 is strong, the expanded film 3 cannot move in the TD direction, and the stress σ _{x of the} expanded portion escapes in the film thickness direction. Therefore, it is considered that the film 3 is twisted in the TD direction and buckles as shown in FIG. As a result, it is estimated that wrinkles appear in the TD direction of the film.
Since the roughness of the surface of the film also affects the holding power, it is presumed that it may contribute to the generation of wrinkles.

As described above, when the film is cooled and solidified while wrinkles are generated in the TD direction of the film, the unevenness caused by the wrinkles remaining on the film is treated as streaky in the present specification. It is called burr).
If the thermoplastic resin film has streaky burrs, some adverse effects are likely to occur. As adverse effects, for example, when the coating liquid is applied on the film, it becomes difficult to apply the coating solution uniformly, winding failure during film winding (winding deviation, winding wrinkles, etc.), and functional layers such as a laminate layer are placed on the film. When affixed, air bubbles may enter between the film and the functional layer.

The thin thermoplastic resin film has been conventionally used for, for example, a magnetic tape. Conventionally, a coating liquid using an organic solvent as a solvent is generally applied to the film, and the heating temperature of the film required to volatilize and remove the solvent is low (for example, 100 ° C. or lower). However, in recent years, there has been a tendency to use an aqueous solvent (solvent containing water) for environmental protection, and the film may be heated at a high temperature of about 150 ° C. to volatilize and remove the aqueous solvent. In addition, a material that is cured by heating (so-called dural agent) may be laminated on the film. Further, when the film contains a dural agent, the film may be heated to 170 ° C. to 180 ° C.
When the film is heated as described above, wrinkles are more likely to occur on the film, and streaky burrs are more likely to occur as compared with the conventional case.

Under the above circumstances, the occurrence of streak burrs was examined.
It is considered that streaky burrs are generated when the film is deformed into a wrinkle shape due to thermal expansion due to heating of the film and tension during film transportation, and the film is fixed in the deformed state. The generation of streaky burrs is a phenomenon that can occur anywhere in the heating process. Specifically, in the film forming process, immediately after the molten resin is discharged onto the cooling roll, it is stretched in the MD direction, and then in the TD direction. This is a phenomenon that can occur after stretching, after annealing treatment for removing residual stress of the film, and after drying treatment after applying the coating liquid on the film. Further, even if streaky burrs are not observed in the film after film formation, streak burrs may appear by undergoing the subsequent annealing treatment or drying treatment.
Conventionally, it has been known to suppress wrinkle-like deformation by suppressing the transport tension during film transport in each step in the manufacturing process. However, suppressing the transport tension has a trade-off relationship with maintaining good coatability or take-up property, and it is not always possible to expect a sufficient improvement effect only by controlling the tension.
Further, for example, as described in JP-A-2014-238612 and JP-A-2014-210433, attempts have been made to improve failures such as wrinkles by focusing on the elastic modulus in one direction of the film surface. , The effect of suppressing the occurrence of streak burrs is not sufficient.

The thermoplastic resin film of the present disclosure and the method for producing the same are in view of the above circumstances.
The streak burrs generated due to heating are caused by the film being deformed and fixed in a wavy manner in the TD direction due to the thermal expansion due to the heating of the film and the tension applied to the film during transportation. Therefore, in the thermoplastic resin film of the present disclosure, the TD direction of the elastic modulus E ^TD, and higher than the MD direction of the elastic modulus E ^MD, and suppress the temperature dependence of the elastic modulus E ^TD.
Specifically, the ratio Er ³⁰ of the elastic modulus ^ETD to the elastic modulus ^EMD at 30 ° C. is 1.1 to 1.8, and the ratio Er ³⁰ at 30 ° C. and the ratio Er ⁹⁰ at 90 ° C. , The difference between the maximum value Er _max and the minimum value Er _min selected from the ratio Er ¹²⁰ at 120 ° C., the ratio Er ¹⁵⁰ at 150 ° C., and the ratio Er ¹⁸⁰ at 180 ° C. is 0.7 or less.
That is, when the polymer chains are lined up in the MD direction and the molecular orientation in the MD direction is strong, the anisotropy becomes stronger and twisting occurs in the TD direction, and the film buckles and is easily deformed. By arranging the chains in the TD direction and strengthening the molecular orientation in the TD direction, the molecular chains become resistance to deformation, and buckling of the film in the TD direction is less likely to occur. In the production of the thermoplastic resin film, various heating temperatures are considered during the heat treatment, and the anisotropy of the elastic modulus occurs in a wide temperature range of 30 ° C., 90 ° C., 120 ° C., 150 ° C. and 180 ° C. Due to its small size, buckling of the film in the TD direction is effectively suppressed.
As a result, the generation of wrinkled wrinkles (streak burrs) of the thermoplastic resin film is suppressed.

The thermoplastic resin film of the present disclosure, the ratio ^{Er 30} at 30 ° C. modulus ^{E TD} for elastic modulus ^{E MD} is 1.1 to 1.8.
When Er ³⁰ is 1.1 or more, the molecular chain acts as a resistance to deformation and suppresses buckling of the film, so that streak burrs are suppressed. The larger the value of Er ³⁰ , the higher the inhibitory effect on streak burrs can be expected. Further, by setting Er ³⁰ to 1.8 or less, the molecular orientation in the TD direction does not become too large, and tearing of the film can be suppressed.
The Er ³⁰ is preferably 1.1 to 1.6, more preferably 1.2 to 1.4, for the same reason as described above.

Modulus E ^TD elastic modulus E ^MD and the width direction of the film in the film conveying direction, each of the stretching ratio of the MD stretch and TD stretching, the stretching speed, and can be adjusted by the balance between MD and TD. Further, in the cooling portion of the second stretching step, the adjustment can be made by adjusting the ratio of expanding the film stretched by the stretching portion by further applying tension in the width direction.

In the thermoplastic resin films of the present disclosure, from the ratio Er ³⁰ at 30 ° C., the ratio Er ⁹⁰ at 90 ° C., the ratio Er ¹²⁰ at 120 ° C., the ratio Er ¹⁵⁰ at 150 ° C., and the ratio Er ¹⁸⁰ at 180 ° C. The difference between the maximum value Er _max and the minimum value Er _min selected is 0.7 or less.
The difference between the maximum value Er _max and the minimum value Er _min indicates that the variation in the elastic modulus ratio at each temperature is suppressed. Since the difference between the maximum value Er _max and the minimum value Er _min is 0.7 or less, the molecular orientation is preferentially made in the TD direction regardless of the film temperature, and the heating temperature during the heat treatment is wide. The buckling of the film in the TD direction is effectively suppressed even in such a manufacturing process.
The difference between the maximum value Er _max and the minimum value Er _min is preferably smaller, more preferably 0.6 or less, more preferably 0.5 or less, and more preferably 0.4 or less.
The lower limit of the difference between the maximum value Er _max and the minimum value Er _min is, for example, 0.1.

The following ranges are preferable for Er ³⁰ , Er ⁹⁰ , Er ¹²⁰ , Er ¹⁵⁰ , and Er ¹⁸⁰ from the viewpoint of keeping the difference between the maximum value Er _max and the minimum value Er _min .
The Er ⁹⁰ is preferably 1.1 to 1.8, more preferably 1.2 to 1.6, and even more preferably 1.2 to 1.4.
The Er ¹²⁰ is preferably 1.1 to 1.8, more preferably 1.2 to 1.6, and even more preferably 1.2 to 1.5.
The Er ¹⁵⁰ is preferably 0.8 to 1.5, more preferably 0.9 to 1.3, and even more preferably 1.0 to 1.2.
The Er ¹⁸⁰ is preferably 0.8 to 1.5, more preferably 0.9 to 1.3, and even more preferably 1.0 to 1.2.

The elastic modulus ratio at each temperature is adjusted by adjusting the stretching ratio in the MD direction and the stretching ratio in the TD direction, or stretching in the step of stretching in the TD direction (second stretching step described later) during film production. This can be done by adjusting the speed (stretching ratio / sec) or the like.

30 ℃, 90 ℃, 120 ℃ , 150 ℃ and at each temperature of 180 ° C., for elastic modulus ^{E MD} in the film conveying direction, the ratio of the elastic modulus of the film width direction perpendicular to the film conveying direction ^{E TD} (Er; = elasticity The modulus ^ETD / elastic modulus ^EMD ) is a value obtained by the following method.
First, a sample piece is punched out from the film to be measured (width 6 x length 115 mm (JIS K 6251, dumbbell-shaped No. 5 type)). The obtained sample piece is pulled by Tencilon (manufactured by Toyo Seiki Co., Ltd., Strograph VE50) under the conditions of a chuck distance of 50 mm and a tensile speed of 100 mm / min, and the elongation of the film with respect to a load is measured. From the measured values, create a graph with the load on the horizontal axis and the elongation on the vertical axis, and calculate the elastic modulus from the tangent to the rising part of the load-elongation curve. This operation is performed 5 times, and the average value of 3 points excluding the maximum value and the minimum value is defined as the elastic modulus. Then, each temperature is carried out for each of the case of pulling in the film transport direction and the case of pulling in the film width direction.
Here, the elastic modulus in the case of pulling the film conveying direction and E ^MD, denoted the elastic modulus when stretched in the film width direction E ^TD.
<Measurement conditions>
・ Measurement site: Hot air heating furnace ・ Measurement temperature: 30 ℃, 90 ℃, 120 ℃, 150 ℃, 180 ℃
(The set temperature of the furnace rises to the desired temperature in 1.5 minutes, and the temperature is set and the air volume is adjusted so that the temperature rise is within 2 ° C. even after 1 minute has passed from the desired temperature.)
-Temperature control: A test piece of the same type and size for temperature measurement is installed near the test piece, and a thermocouple is attached to the test piece for temperature measurement to monitor the temperature at the time of measurement.
(The above "when the film temperature is 30 ° C." refers to the case where the temperature of the test piece for temperature measurement is 30 ° C., and the same applies to other temperatures.)
-Test start timing: Pulling is started after the desired temperature is reached.

The surface roughness (Ra) of at least one surface of the thermoplastic resin film of the present disclosure is preferably 0.5 nm to 50 nm.
When Ra is 0.5 nm or more, for example, the slipperiness on the surface of the transport roll can be enhanced, and the effect of improving streak burrs is excellent. Further, when Ra is 50 nm or less, the appearance is not damaged and the device is suitable for optical applications.
Generally, the thermoplastic resin film expands in the TD direction during the heating process, but the holding force on the surface of the transport roll at the end of the film in the TD direction is strong, and the expanded film cannot move in the TD direction. The stress tries to escape in the thickness direction. As a result, wrinkles are generated so as to undulate in the TD direction, resulting in streaky burrs. In the thermoplastic resin film of the present disclosure, the occurrence of streaky burrs on the film can be suppressed by adjusting the surface roughness (Ra) of the film within the above range.
The larger the value of Ra (that is, the rougher the surface), the more the effect of reducing streak burrs can be expected. Above all, from the viewpoint of effectively reducing streaky burrs while suppressing the influence on other properties, Ra is preferably 0.8 nm to 30 nm, more preferably 1 nm to 20 nm.

Ra is adjusted to a desired Ra value by adjusting the stretching speed (stretching ratio / sec) or the stretching temperature in the step of stretching in the TD direction (second stretching step described later) during film production. Can be done. Specifically, for example, the Ra value can be increased (the surface is roughened) by a method of increasing the stretching speed when stretching in the TD direction or a method of lowering the stretching temperature when stretching in the TD direction. it can.

Ra is a value measured by the following method. That is,
Using a contact shape measuring machine (Mitutoyo FORMTRACER EXTREME CS-5000 CNC), in accordance with JIS B 0601: 2001, measure 12 times each in the MD direction and TD direction at arbitrary positions under the following conditions, and Ra The average of 10 points in the MD direction and 10 points in the TD direction from which the minimum and maximum values of the above are removed is obtained, and the average value of 20 points is defined as Ra.
<Conditions>
・ Measuring needle tip diameter: 0.5 μm
・ Needle load: 0.75mN
・ Measurement length: 0.8 mm
・ Cutoff value: 0.08 mm

The thickness of the thermoplastic resin film of the present disclosure is preferably in the range of 200 μm or less.
When the film has a thickness of 200 μm or less, wrinkles in the TD direction due to heat treatment are particularly likely to occur. Therefore, when the thickness is 200 μm or less, the effect of the thermoplastic resin film of the present disclosure is more exhibited.
The thickness of the thermoplastic resin film is more preferably 100 μm or less, further preferably 80 μm or less, and further preferably 50 μm or less.
The lower limit of the thickness of the thermoplastic resin film is, for example, 1 μm.

The thickness of the thermoplastic resin film is measured using a tactile film thickness measuring machine (Mitutoyo ID-C112X) over the entire width of the film in the TD direction at intervals of 50 mm. This operation is performed for 5 sets at 1 m intervals in the MD direction, and the average value of the measured values is taken as the thickness.

Examples of the raw material resin for forming the thermoplastic resin film of the present disclosure include polyester and cyclic olefin resin.
As the polyester, polyethylene terephthalate (PET) and polyethylene-2,6-naphthalate (PEN) are preferable, and PET is more preferable.
The cyclic olefin resin is a polymer resin having a cyclic olefin structure, and examples of the polymer resin having a cyclic olefin structure include (1) a norbornene-based polymer, and (2) a polymer of a monocyclic cyclic olefin. Examples thereof include a polymer of a cyclic conjugated diene, (4) a vinyl alicyclic hydrocarbon polymer, and hydrides of (1) to (4).

-Polyester-
Polyester is synthesized by copolymerizing a dicarboxylic acid component and a diol component. Polyester can be obtained, for example, by subjecting (A) a dicarboxylic acid component and (B) a diol component to an esterification reaction and / or a transesterification reaction by a well-known method, and polycondensing the reaction product. At this time, a trifunctional or higher functional monomer may be further copolymerized. Further, the polyester may contain an end-capping agent such as an oxazoline compound, a carbodiimide compound, and an epoxy compound.
For examples and preferred embodiments of the terminal encapsulant, reaction catalyst, etc., and details of polycondensation and the like, see paragraphs 0051 to 0064, paragraphs 0121 to 0124, and paragraphs 0087 to 0111 of JP2014-189002. Can be referred to.

Examples of the (A) dicarboxylic acid component include malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecandioic acid, dimer acid, eikosandioic acid, pimeric acid, azelaic acid, and methylmalonic acid. , Alicyclic dicarboxylic acids such as ethylmalonic acid, adamantandicarboxylic acid, norbornenedicarboxylic acid, isosorbide, cyclohexanedicarboxylic acid, decalindicarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid, 1,4- Naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 5-sodium sulfo Examples thereof include dicarboxylic acids such as isophthalic acid, phenylindandicarboxylic acid, anthracendicarboxylic acid, phenanthrangecarboxylic acid, and aromatic dicarboxylic acids such as 9,9'-bis (4-carboxyphenyl) fluoric acid, or ester derivatives thereof.
(B) Examples of the diol component include fats such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, and 1,3-butanediol. Group diols, alicyclic diols such as cyclohexanedimethanol, spiroglycol, isosorbide, bisphenol A, 1,3-benzenedimethanol, 1,4-benzenedimethanol, 9,9'-bis (4-hydroxyphenyl) ) Diol compounds such as aromatic diols such as fluorene can be mentioned.

As the (A) dicarboxylic acid component, it is preferable that at least one aromatic dicarboxylic acid is used. More preferably, among the dicarboxylic acid components, an aromatic dicarboxylic acid is contained as a main component. It may contain a dicarboxylic acid component other than the aromatic dicarboxylic acid. Examples of such a dicarboxylic acid component include an ester derivative such as an aromatic dicarboxylic acid.
The "main component" means that the ratio of the aromatic dicarboxylic acid to the dicarboxylic acid component is 80% by mass or more.
As the diol component (B), it is preferable that at least one aliphatic diol is used. Ethylene glycol can be contained as the aliphatic diol, and ethylene glycol is preferably contained as a main component.
The main component means that the ratio of ethylene glycol to the diol component is 80% by mass or more.

The amount of the diol component is preferably in the range of 1.015 mol to 1.50 mol, more preferably 1.02 mol to 1.30 mol, based on 1 mol of the dicarboxylic acid component and, if necessary, the ester derivative thereof. Yes, more preferably 1.025 mol to 1.10 mol. When the amount of the diol component is 1.015 or more, the esterification reaction proceeds well. When the amount of the diol component is 1.50 mol or less, for example, by-production of diethylene glycol due to dimerization of ethylene glycol is suppressed, and melting point, glass transition temperature, crystallinity, heat resistance, hydrolysis resistance, and weather resistance are suppressed. Properties such as sex can be kept good.

The raw material resin preferably contains a polyfunctional monomer in which the total number (a + b) of the number of carboxylic acid groups (a) and the number of hydroxyl groups (b) is 3 or more as a copolymerization component. "The raw material resin contains a polyfunctional monomer as a copolymerization component" means that the raw material resin contains a structural unit derived from the polyfunctional monomer.

Examples of the structural unit derived from the polyfunctional monomer in which the total (a + b) of the number of carboxylic acid groups (a) and the number of hydroxyl groups (b) is 3 or more include the structural units derived from carboxylic acid shown below. ..
As an example of a carboxylic acid having 3 or more carboxylic acid groups (a) (that is, a polyfunctional monomer), examples of the trifunctional aromatic carboxylic acid include trimesic acid, trimellitic acid, pyromellitic acid, and naphthalene tricarboxylic acid. , Anthracentricarboxylic acid and the like, examples of the trifunctional aliphatic carboxylic acid include methanetricarboxylic acid, ethanetricarboxylic acid, propanetricarboxylic acid, butanetricarboxylic acid and the like, and examples of the tetrafunctional aromatic carboxylic acid include For example, benzenetetracarboxylic acid, benzophenonetetracarboxylic acid, naphthalenetetracarboxylic acid, anthracenetetracarboxylic acid, perylenetetracarboxylic acid and the like can be mentioned, and examples of the tetrafunctional aliphatic carboxylic acid include ethanetetracarboxylic acid and ethylenetetra. Carboxylic acid, butanetetracarboxylic acid, cyclopentanetetracarboxylic acid, cyclohexanetetracarboxylic acid, adamantantetracarboxylic acid and the like can be mentioned, and examples of the pentafunctional or higher functional aromatic carboxylic acid include benzenepentacarboxylic acid and benzenehexacarboxylic acid. Naphthalene pentacarboxylic acid, naphthalene hexacarboxylic acid, naphthalene heptacarboxylic acid, naphthalene octacarboxylic acid, anthracene pentacarboxylic acid, anthracene hexacarboxylic acid, anthracene heptacarboxylic acid, anthracene octacarboxylic acid, etc. Examples of the carboxylic acid include ethanepentacarboxylic acid, ethaneheptacarboxylic acid, butanepentacarboxylic acid, butaneheptacarboxylic acid, cyclopentanepentacarboxylic acid, cyclohexanepentacarboxylic acid, cyclohexanehexacarboxylic acid, adamantanpentacarboxylic acid, and adamantanhexacarboxylic acid. Examples include acids.
These ester derivatives, acid anhydrides and the like are examples of carboxylic acids (that is, polyfunctional monomers) having 3 or more carboxylic acid groups (a), but are not limited thereto.

Further, as the carboxylic acid having 3 or more carboxylic acid groups (a) (that is, a polyfunctional monomer), oxyacids such as l-lactide, d-lactide, and hydroxybenzoic acid are added to the carboxy terminal of the above-mentioned carboxylic acid. Those to which the derivative, a plurality of oxyacids in a row, or the like are added are also preferably used.

As an example of a polyfunctional monomer having 3 or more hydroxyl groups (b), examples of the trifunctional aromatic compound include trihydroxybenzene, trihydroxynaphthalene, trihydroxyanthracene, trihydroxychalcone, trihydroxyflavon, and trihydroxycoumarin. Examples of the trifunctional aliphatic alcohol include glycerin, trimethylolpropane, and propanetriol, and examples of the tetrafunctional aliphatic alcohol include pentaerythritol and the like. Further, as the polyfunctional monomer having 3 or more hydroxyl groups (b), a compound in which diols are added to the hydroxyl group ends of the above-mentioned compound is also preferably used.
These may be used alone or in combination of two or more, if necessary.

Further, as other polyfunctional monomers other than the above, one molecule has both a hydroxyl group and a carboxylic acid group, and the total (a + b) of the number of carboxylic acid groups (a) and the number of hydroxyl groups (b) is 3. The above-mentioned oxyacids can also be mentioned. Examples of oxyacids include hydroxyisophthalic acid, hydroxyterephthalic acid, dihydroxyterephthalic acid, trihydroxyterephthalic acid and the like. Further, as another polyfunctional monomer, oxyacids such as l-lactide, d-lactide, and hydroxybenzoic acid and their derivatives, and a plurality of oxyacids in a row thereof are added to the carboxy terminal of the polyfunctional monomer. Is also preferably used.

The content ratio of the constituent units derived from the polyfunctional monomer in the raw material resin is preferably 0.005 mol% to 2.5 mol% with respect to all the constituent units in the raw material resin. The content ratio of the structural unit derived from the polyfunctional monomer is more preferably 0.020 mol% to 1 mol%, still more preferably 0.05 mol% to 0.5 mol%.

A coating layer in which functional groups not used for polycondensation are applied and formed on the polyester film when a polyester film is formed due to the presence of a structural unit derived from a trifunctional or higher functional monomer in the raw material resin. By hydrogen-bonding or covalently bonding with the components inside, the adhesion between the coating layer and the polyester film can be better maintained, and the occurrence of peeling can be effectively prevented. In addition, a structure in which polyester molecular chains are branched from a structural unit derived from a trifunctional or higher functional monomer can be obtained, and entanglement between polyester molecules can be promoted.

Conventionally known reaction catalysts can be used for the esterification reaction and / or the transesterification reaction. Examples of the reaction catalyst include alkali metal compounds, alkaline earth metal compounds, zinc compounds, lead compounds, manganese compounds, cobalt compounds, aluminum compounds, antimony compounds, titanium compounds, phosphorus compounds and the like. Usually, it is preferable to add an antimony compound, a germanium compound, or a titanium compound as a polymerization catalyst at any stage before the polyester production method is completed. As such a method, for example, taking a germanium compound as an example, it is preferable to add the germanium compound powder as it is.

When the thermoplastic resin film is a polyester film, the intrinsic viscosity (IV; Intrinsic Viscosity) of the polyester film is 0.55 dL / g or more and 0.90 dL from the viewpoint of enhancing the hydrolysis resistance of the polyester film and improving the weather resistance. It is preferably / g or less, more preferably 0.60 dL / g or more and 0.80 dL / g or less, and further preferably 0.62 dL / g or more and 0.78 dL / g or less.
The intrinsic viscosity (IV) is the specific viscosity (η _sp = η _r -1) obtained by subtracting 1 from the ratio η _r (= η / η ₀ ; relative viscosity) of the solution viscosity η and the solvent viscosity η ₀ divided by the concentration. It is the value extrapolated to the state where the density is zero. IV is determined from the solution viscosity at 25 ° C. by dissolving polyester in a 1,1,2,2-tetrachloroethane / phenol (= 2/3 [mass ratio]) mixed solvent using an Ubbelohde viscometer.

When the thermoplastic resin film is a polyester film, the amount of terminal carboxy groups [terminal COOH amount (also referred to as acid value), AV; Acid Value] of the polyester film is preferably 5 eq / ton or more and 35 eq / ton or less. The amount of terminal COOH is more preferably 6 eq / ton or more and 30 eq / ton or less, and further preferably 7 eq / ton or more and 28 eq / ton or less.
In addition, in this specification, "eq / ton" represents a molar equivalent per ton.
For AV, polyester is completely dissolved in a mixed solution of benzyl alcohol / chloroform (= 2/3; volume ratio), using phenol red as an indicator, and titrated with a reference solution (0.025N KOH-methanol mixed solution). It is a value calculated from an appropriate fixed amount.

-Cyclic olefin resin-
Examples of the cyclic olefin resin include an addition (co) polymer cyclic polyolefin containing at least one repeating unit represented by the following general formula (II) and, if necessary, a repeating unit represented by the following general formula (I). Examples thereof include additional (co) polymer cyclic polyolefins further containing at least one of the units. Further, as an example of the cyclic olefin resin, a ring-opening (co) polymer containing at least one cyclic repeating unit represented by the following general formula (III) is also preferably mentioned.

In the general formulas (I), (II), and (III), m represents an integer of 0 to 4, and R ^{1 to} R ⁶ independently represent a hydrogen atom or a hydrocarbon group having 1 to 10 carbon atoms. X ^{1 to} X ³ and Y ^{1 to} Y ³ are independent hydrogen atoms, hydrocarbon groups having 1 to 10 carbon atoms, halogen atoms, and hydrocarbon groups having 1 to 10 carbon atoms substituted with halogen atoms,-(CH). ₂ ) _n COOR ¹¹ ,-(CH ₂ ) _n OCOR ¹² ,-(CH ₂ ) _n NCO,-(CH ₂ ) _n NO ₂ ,-(CH ₂ ) _n CN,-(CH ₂ ) _n CONR ¹³ R ¹⁴ , -(CH ₂ ) _n NR ¹³ R ¹⁴ ,-(CH ₂ ) _n OZ, or-(CH ₂ ) _n W. Note that X ¹ and Y ¹ , X ² and Y ² , or X ³ and Y ³ may be combined with each other to form (-CO) ₂ O or (-CO) ₂ NR ¹⁵ . Here, R ¹¹ , R ¹² , R ¹³ , R ¹⁴ and R ¹⁵ represent a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms, and Z represents a hydrocarbon group or a hydrocarbon group substituted with a halogen. , W is represents _{^{SiR 16 p D 3-p,}} n represents an integer of 0. Further, D represents a halogen atom, −OCOR ¹⁶ or −OR ¹⁶ , R ¹⁶ represents a hydrocarbon group having 1 to 10 carbon atoms, and p represents an integer of 0 to 3.

By introducing a highly polar functional group into all or part of the substituents of X ^{1 to} X ³ and Y ^{1 to} Y ³ , the thickness direction retardation (Rth) of the optical film is increased, and the in-plane letter is increased. The expression of the substrate (Re) can be increased. A film having a large Re-expressing property can have a large Re value by stretching in the film forming process.

Norbornene-based addition (co) polymers are disclosed in JP-A No. 10-7732, JP-A-2002-504184, US Patent Publication No. 2004/229157A1, International Publication No. 2004/070463A1 and the like. The norbornene-based addition (co) polymer is obtained by addition polymerization of norbornene-based polycyclic unsaturated compounds. Further, the norbornene-based addition (co) polymer may be, if necessary, a norbornene-based polycyclic unsaturated compound and a conjugated diene such as ethylene, propylene, butene; butadiene, isoprene; a non-conjugated diene such as etylidene norbornene; It may be obtained by addition-polymerizing with a linear diene compound such as acrylonitrile, acrylic acid, methacrylic acid, maleic anhydride, acrylic acid ester, methacrylic acid ester, maleimide, vinyl acetate and vinyl chloride.
Examples of the norbornene-based addition (co) polymer on the market include APL8008T (Tg: 70 ° C.) and APL6013T (Tg:) having different glass transition temperatures (Tg) from Mitsui Chemicals, Inc. 125 ° C.), or APL6015T (Tg: 145 ° C.), etc.), pellets of TOPAS 8007, 6013, 6015, etc. of Polyplastics Co., Ltd., and Appear 3000 of Ferrania, etc.

The norbornene-based polymer hydride is JP-A No. 1-240517, JP-A-7-196736, JP-A-60-26024, JP-A-62-19801, JP-A-2003-159767, or JP-A-2004. As disclosed in each publication such as No. 309979, it can be produced by addition polymerization or metathesis ring-opening polymerization of a polycyclic unsaturated compound and then hydrogenation.
In the norbornene-based polymer, in the general formula (III), R ^{5 to} R ⁶ are preferably hydrogen atoms or -CH ₃ , X ³ and Y ³ are preferably hydrogen atoms, Cl, or -COOCH ₃ , and other groups are preferable. It is selected as appropriate.
Examples of norbornene-based resins on the market are Arton G or Arton F (trade name) of JSR Corporation, Zeonor ZF14, ZF16, Zeonex 250, or Zeonex of Nippon Zeon Corporation. 280 (trade name) and the like can be mentioned.

<Manufacturing method of thermoplastic resin film>
The thermoplastic resin film of the present disclosure may be produced by any method as long as the difference between the ratio Er ³⁰ and the maximum value Er _max and the minimum value Er _{min described} above satisfies a predetermined range. The thermoplastic resin film of the present disclosure is most preferably produced by the method for producing a thermoplastic resin film of the present disclosure shown below.
Hereinafter, the method for producing the thermoplastic resin film of the present disclosure will be described in detail.

The method for producing a thermoplastic resin film of the present disclosure includes a step of melt-extruding a raw material resin and cooling it to form a thermoplastic resin sheet (hereinafter, also referred to as a “molding step”), and a method of forming a thermoplastic resin sheet. A step of obtaining a thermoplastic resin film by performing the first stretching in the direction (MD) (hereinafter, also referred to as a "first stretching step"), a preheating part for preheating the thermoplastic resin film, and preheated thermoplasticity. A stretched portion that stretches the resin film by applying tension in the film width direction orthogonal to the longitudinal direction of the thermoplastic resin film, a heat fixing portion that heats and fixes the tensioned thermoplastic resin film, and the above. A step of sequentially transporting the above-mentioned thermoplastic resin film to a heat-relaxing section for heat-relaxing tension and a cooling section for cooling the heat-relaxed thermoplastic resin film to perform a second stretching (hereinafter, "second Also referred to as "stretching process"), including
The stretching ratio in the second stretching is larger than the stretching ratio in the first stretching, and the area ratio, which is the product of the stretching ratio in the first stretching and the stretching ratio in the second stretching, is 12. It is 0.8 times to 15.5 times,
In the second stretching step, tension is further applied in the film width direction in the cooling section, and the film width is expanded in the range of −1.5% to 3% with respect to the film width at the end of heat relaxation in the heat relaxation section. Or shrink. For example, "-1.5%" means "reduction of 1.5%".

In the method for producing a thermoplastic resin film of the present disclosure, in producing a biaxially stretched film, the thermoplastic resin sheet is first stretched in the MD direction and then further stretched in the TD direction to produce a biaxially stretched film. The stretch ratio in the second stretch is increased with respect to the stretch ratio in the first stretch, and the area ratio, which is the product of the stretch ratio in the first stretch and the stretch ratio in the second stretch, is set to 12. In addition to increasing the thickness from 8 times to 15.5 times, in the second stretching step, tension is already applied in the film width direction at the stretched portion, and tension is further applied in the film width direction at the cooling portion after stretching. The film is expanded or contracted in the range of −1.5% to 3% with respect to the film width at the end of heat relaxation at the heat-relaxed portion. Similar to the above, for example, "-1.5%" means "1.5% reduction".
As a result, a thermoplastic resin film in which the generation of wrinkled wrinkles (streak burrs) is suppressed can be obtained.

As described above, the method for producing a thermoplastic resin film of the present disclosure includes at least a molding step, a first stretching step, and a second stretching step, and may further include other steps. The first stretching means stretching the film in the longitudinal direction (MD direction), and the second stretching means stretching the film in the width direction (TD direction).
In the method for producing a thermoplastic resin film of the present disclosure, in the second stretching step, the thermoplastic resin film is sequentially conveyed to a preheating section, a stretching section, a heat fixing section, a heat relaxation section, and a cooling section. It is done by doing.
Hereinafter, each step in the method for producing a thermoplastic resin film of the present disclosure will be described in detail.

-Molding process-
In the molding process in the manufacturing method of the present disclosure, the raw material resin is melt-extruded and cooled to form a thermoplastic resin sheet.
The molding of the thermoplastic resin sheet is performed by charging the raw material resin and cooling the thermoplastic resin melt-extruded into a sheet on a casting roll.
The method for melt-extruding the raw material resin and the raw material resin are not particularly limited, but the intrinsic viscosity can be set to a desired intrinsic viscosity by a catalyst used for synthesizing the raw material resin, a polymerization method, or the like.
The details of the raw material resin are as described above.

(Melting extrusion)
In the molding process, the raw material resin is melt-extruded and then subjected to cooling to form a thermoplastic resin sheet.
The melt extrusion of the raw material resin is performed, for example, by using an extruder equipped with one or two or more screws, heating the raw material resin to a temperature equal to or higher than the melting point of the raw material resin, rotating the screws, and melt-kneading. The raw material resin is melted in the extruder by heating and kneading with a screw to become a molten resin (also referred to as melt). Further, from the viewpoint of suppressing thermal decomposition (for example, hydrolysis of polyester) in the extruder, it is preferable to perform melt extrusion of the raw material resin by substituting nitrogen in the extruder. The extruder is preferably a twin-screw extruder because the kneading temperature can be kept low.
The molten resin (melt) is extruded from an extrusion die through a gear pump, a filter, or the like. The extrusion die is also simply referred to as a "die" [see JIS B 8650: 2006, a) Extruder, No. 134].
The melt may be extruded in a single layer or in multiple layers.

When polyester is used as the raw material resin and a terminal sealant is included in the raw material resin, the polyester raw material resin to which the terminal sealant is added is melt-kneaded in the molding step, and the polyester that reacts with the terminal sealant during melt-kneading. The raw material resin is melt-extruded.

When the raw material resin is melt-extruded and cooled, the molten resin (melt) may be extruded from a die onto a casting roll to form a sheet (that is, cast).
When extruding melt from the die, the casting roll and the melt-extruded sheet are adhered by applying methods such as electrostatic application method, air knife method, air chamber method, vacuum nozzle method, and touch roll method on the casting roll. It is preferable to raise it. Above all, for example, when a polymer resin having a cyclic olefin structure is used as a raw material resin, it is preferable to improve the adhesion between the casting roll and the sheet by the touch roll method. The touch roll method is a method in which a touch roll is placed on a casting roll to shape the surface of the sheet. As the touch roll, a roll having elasticity is preferable to a normal roll having high rigidity.

As the temperature of the touch roll, when the glass transition temperature of the melt-extruded sheet is Tg, it is preferably more than (Tg-10 ° C) and less than (Tg + 30 ° C), and more preferably (Tg-7 ° C) to (Tg + 20 ° C). Preferably, (Tg-5 ° C.) to (Tg + 10 ° C.) are even more preferable. The temperature of the casting roll is preferably in the same temperature range.
Examples of the touch roll include the touch roll described in JP-A-11-314263 or JP-A-11-235747.

The thickness of the sheet-shaped molded product (thermoplastic resin sheet) obtained by the casting treatment is preferably 0.1 mm to 3 mm, more preferably 0.2 mm to 2 mm, still more preferably 0.3 mm to 1.5 mm.
When the thickness of the thermoplastic resin sheet is 3 mm or less, the cooling delay due to the heat storage of the melt can be avoided. When the thickness of the thermoplastic resin sheet is 0.1 mm or more, the hydroxyl groups and carboxy groups in the thermoplastic resin sheet (preferably polyester sheet) are the thermoplastic resin (preferably polyester) during the period from extrusion to cooling. The hydroxyl groups and carboxy groups that are diffused inside and cause hydrolysis to occur are suppressed from being exposed on the resin surface.

The means for cooling the melt extruded from the extrusion die is not particularly limited, and the melt may be exposed to cold air, brought into contact with a casting roll, sprayed with water, or the like. As the means for cooling the melt, only one of the means may be carried out, or two or more means may be carried out in combination.
As a means for cooling the melt, at least one of cooling with cold air and cooling with a casting roll is preferable from the viewpoint of preventing oligomers from adhering to the film surface during continuous operation. Further, it is particularly preferable to cool the melt extruded from the extruder with cold air and bring the melt into contact with the casting roll to cool it.

Further, the thermoplastic resin sheet cooled by using a casting roll or the like is stripped from the cooling member such as a casting roll by using a stripping member such as a stripping roll.

-First stretching step-
In the first stretching step in the manufacturing method of the present disclosure, the thermoplastic resin sheet molded in the above molding step is first stretched in the longitudinal direction (MD direction) (hereinafter, also appropriately referred to as "longitudinal stretching"). ) Is performed to obtain a thermoplastic resin film.

In the first stretching, for example, the thermoplastic resin sheet is passed through a pair of nip rolls sandwiching the thermoplastic resin sheet, and the thermoplastic resin sheet is conveyed in the longitudinal direction of the thermoplastic resin sheet while being conveyed in the conveying direction of the thermoplastic resin sheet. This can be done by applying tension between two or more pairs of side-by-side nip rolls. Specifically, for example, when a pair of nip rolls A are installed on the upstream side in the transport direction of the thermoplastic resin sheet and a pair of nip rolls B are installed on the downstream side, the nip roll B on the downstream side is installed when the thermoplastic resin sheet is transported. By making the rotation speed of the nip roll A faster than the rotation speed of the nip roll A on the upstream side, the thermoplastic resin sheet is stretched in the transport direction (MD direction). Two or more pairs of nip rolls may be independently installed on the upstream side and the downstream side, respectively. Further, the first stretching of the thermoplastic resin sheet may be performed by using a stretching device provided with a nip roll.

It is preferable that the draw ratio of the thermoplastic resin sheet in the first stretching step during the first stretching is adjusted to be smaller than the stretching ratio in the second stretching in the second stretching step described later. The larger the draw ratio by the first stretching, the higher the elastic modulus at room temperature, but it is easy to relax by heating, and the elastic modulus tends to decrease when reheated by heat treatment or the like. Therefore, the stretching ratio by the first stretching should be smaller than the stretching ratio by the second stretching in the TD direction, in other words, the stretching ratio by the second stretching should be larger than the stretching ratio by the first stretching. As a result, it is easy to obtain a thermoplastic resin film in which the generation of streaky burrs derived from wrinkled wrinkles is suppressed.
The draw ratio of the thermoplastic resin sheet in the first stretching step is preferably 2 to 5 times, more preferably 2.5 times to 4.0 times, still more preferably 2.8 to 3.5 times.

The area magnification represented by the product of the draw ratio of the first stretch and the draw ratio of the second stretch is the area of the thermoplastic resin sheet before the first stretch and the second stretch are applied. It is set to 12.8 to 15.5 times.
The larger the area magnification, the higher the elastic modulus at room temperature, but the elastic modulus in this case tends to be relaxed by heating, and the elastic modulus tends to decrease when reheated by heat treatment or the like. In the present disclosure, when the area magnification is 12.8 times or more, the molecular orientation in the film width direction becomes good, so that the generation of streaky burrs is effectively suppressed. Further, when the area magnification is 15.5 times or less, it is easy to maintain a state in which the molecular orientation is difficult to be relaxed when subjected to the heat treatment.
For the same reason as described above, the area magnification is preferably 13.5 times to 15.2 times, more preferably 14.0 times to 15.0 times.

The temperature at the time of the first stretching of the thermoplastic resin film is preferably (Tg-20 ° C.) to (Tg + 50 ° C.), more preferably (Tg-10 ° C.), where Tg is the glass transition temperature of the thermoplastic resin film. ~ (Tg + 40 ° C.), more preferably (Tg ° C.) to (Tg + 30 ° C.).

As a means for heating the thermoplastic resin film, when stretching using a roll such as a nip roll, the thermoplastic resin film in contact with the roll is provided by providing a heater or a pipe through which a hot solvent can flow inside the roll. Can be heated. Further, even when the roll is not used, the thermoplastic resin film can be heated by blowing warm air on the thermoplastic resin film, contacting the thermoplastic resin film with a heat source such as a heater, or passing the film in the vicinity of the heat source.

The method for producing a thermoplastic resin film of the present disclosure includes a second stretching step of stretching the film in the TD direction after the first stretching step. As a result, in the method for producing a thermoplastic resin film of the present disclosure, the thermoplastic resin film is arranged in the longitudinal direction (MD) of the thermoplastic resin film and the film width direction (TD) orthogonal to the longitudinal direction of the thermoplastic resin film. , Will be stretched in at least two axes. Stretching in the MD direction and the TD direction may be performed at least once each.
The "film width direction (TD) orthogonal to the longitudinal direction (MD) of the thermoplastic resin film" is intended to be a direction perpendicular to (90 °) the longitudinal direction (MD) of the thermoplastic resin film. However, there is a direction in which the angle with respect to the longitudinal direction (MD) can be regarded as 90 ° due to mechanical error or the like (for example, a direction of 90 ° ± 5 ° with respect to the MD direction).

In the present disclosure, as the biaxial stretching method, in addition to the sequential biaxial stretching method in which the first stretching (longitudinal stretching) and the second stretching (transverse stretching) described later are separated, the first stretching (longitudinal stretching) Any of the simultaneous biaxial stretching methods in which the longitudinal stretching (longitudinal stretching) and the second stretching (transverse stretching) are performed at the same time may be used. The first stretching and the second stretching may be independently performed twice or more. Regardless of which of the longitudinal stretching and the transverse stretching is performed first, the generation of wrinkles can be suppressed, and as the mode of the biaxial stretching, for example, longitudinal stretching → transverse stretching, longitudinal stretching → transverse stretching → longitudinal stretching , Longitudinal stretching → longitudinal stretching → transverse stretching, transverse stretching → longitudinal stretching and the like. Among them, as a mode of biaxial stretching, longitudinal stretching → transverse stretching is preferable as in the manufacturing method of the present disclosure from the viewpoint of ease of production, that is, production suitability and the like.

-Second stretching step-
In the second stretching step in the manufacturing method of the present disclosure, the thermoplastic resin film subjected to the first stretching in the first stretching step described above is preheated by a preheating section for preheating the stretched thermoplastic resin film. A stretched part that stretches the thermoplastic resin film by applying tension in the film width direction orthogonal to the longitudinal direction of the thermoplastic resin film, a heat-fixing part that heats and fixes the tensioned thermoplastic resin film, Further, the tension is sequentially conveyed to the heat-relaxing section for heat-relaxing the tension and the cooling section for cooling the heat-relaxed thermoplastic resin film, and the cooling section further applies tension in the film width direction to relax the heat. It expands or contracts in the range of −1.5% to 3% with respect to the film width at the end of thermal relaxation in the section. As a result, the second stretching (hereinafter, also appropriately referred to as “transverse stretching”) is performed. Here, for example, "-1.5%" means "reduction of 1.5%".

The second stretching step is a step of performing a second stretching (transverse stretching) of the thermoplastic resin film after the first stretching (longitudinal stretching) in the film width direction orthogonal to the longitudinal direction. The second stretching (transverse stretching) can be carried out by sequentially transporting the thermoplastic resin film to the following (a) to (e).
(A) A preheating unit that preheats the thermoplastic resin film after longitudinal stretching to a temperature at which it can be stretched.
(B) A stretched portion for stretching a preheated thermoplastic resin film by applying tension in the film width direction orthogonal to the longitudinal direction.
(C) A heat-fixing portion that crystallizes and heat-fixes a thermoplastic resin film after performing longitudinal stretching and transverse stretching by heating.
(D) A heat-relaxing portion that heats a heat-fixed thermoplastic resin film to heat-relax the tension of the thermoplastic resin film and remove residual strain of the film, and
(E) The thermoplastic resin film after heat relaxation is cooled, and at the same time, tension is applied in the film width direction, and the film width at the end of heat relaxation at the heat relaxation portion is −1.5% to 3%. Cooling unit that expands or contracts within the range of

In the (e) cooling section in the second stretching step of the manufacturing method of the present disclosure, after stretching in the film width direction (TD) at the (b) stretched section, tension is further applied in the film width direction, and the heat relaxation section is used. The thermoplastic resin film is expanded or contracted in the range of −1.5% to 3% with respect to the film width at the end of thermal relaxation.
When the expansion ratio or reduction ratio of the thermoplastic resin film in the TD direction in the cooling section is −1.5% or more with respect to the film width at the end of heat relaxation in the heat relaxation section, the elastic modulus in TD. It is easy to obtain the effect of increasing. Further, when the expansion ratio or the reduction ratio of the thermoplastic resin film in the TD direction is 3% or less with respect to the film width at the end of the heat relaxation in the heat relaxation portion, it is effective in suppressing the breakage of the film.
The larger the area magnification and the stretching ratio at the time of the second stretching, the higher the elastic modulus at room temperature, but it is easily relaxed by heat, and the elastic modulus tends to decrease due to the heat treatment. Therefore, in the production method of the present disclosure, relaxation is suppressed by forcibly re-stretching the film that has undergone thermal fixation and crystallized while suppressing an increase in the area magnification due to the first stretching and the second stretching. However, it is possible to improve the elastic modulus.
Of the above, the expansion ratio or reduction ratio of the thermoplastic resin film in the TD direction in the cooling section is 0 with respect to the film width at the end of heat relaxation in the heat relaxation section for the same reason as described above. It is more preferably 0.0% to 2.0%, and even more preferably 1.5% to 1.8%.

In the present disclosure, "the end time of heat relaxation in the heat relaxation part" is the time when the thermoplastic resin film invades the cooling part, that is, the speed at which the thermoplastic resin film shrinks in the width direction when the residual stress is relaxed. Refers to the time when is changed.

In the second stretching step, the specific means is not limited as long as the thermoplastic resin film is transversely stretched in the above configuration, but a transverse stretching device or a biaxial structure capable of processing each step forming the above configuration is possible. It is preferable to use a stretching machine.

-2-axis stretcher-
As shown in FIG. 1, the biaxial stretching machine 100 includes a pair of annular rails 60a and 60b, and gripping members 2a to 2l attached to each annular rail and movable along the rails. The annular rails 60a and 60b are symmetrically arranged with the thermoplastic resin film 200 in between, and the thermoplastic resin film 200 is gripped by the gripping members 2a to 2l and stretched in the film width direction by moving along the rail. It has become possible.

In the biaxial stretching machine 100, the preheating portion 10 for preheating the thermoplastic resin film 200 and the preheated thermoplastic resin film 200 are arranged in a direction orthogonal to the direction (longitudinal direction) of the arrow MD of the thermoplastic resin film. A stretched portion 20 that stretches by applying tension in the direction of TD (film width direction), a heat fixing portion 30 that heats and fixes the tensioned thermoplastic resin film while applying tension, and heat fixing. A heat relaxation unit 40 that heats and fixes the tension of the thermoplastic resin film that has been heat-fixed, and a cooling unit 50 that cools the heat-relaxed thermoplastic resin film through the heat relaxation unit. It is composed of the including area.

Gripping members 2a, 2b, 2e, 2f, 2i, and 2j that can move along the annular rail 60a are attached to the annular rail 60a, and the annular rail 60b can move along the annular rail 60b. 2c, 2d, 2g, 2h, 2k, and 2l gripping members are attached. The gripping members 2a, 2b, 2e, 2f, 2i, and 2j grip one end of the thermoplastic resin film 200 in the TD direction, and the gripping members 2c, 2d, 2g, 2h, 2k, and 2l are heat. The other end of the plastic resin film 200 in the TD direction is gripped. The gripping members 2a to 2l are generally referred to as chucks, clips, and the like.
The gripping members 2a, 2b, 2e, 2f, 2i, and 2j move counterclockwise along the annular rail 60a, and the gripping members 2c, 2d, 2g, 2h, 2k, and 2l are along the annular rail 60b. And move clockwise.

The gripping members 2a to 2d grip the end portion of the thermoplastic resin film 200 in the preheating portion 10 and move along the annular rail 60a or 60b while being gripped, and the stretching portion 20 and the gripping members 2e to 2h are located. It proceeds through the heat relaxation unit 40 to the cooling unit 50 where the gripping members 2i to 2l are located. After that, the gripping members 2a and 2b and the gripping members 2c and 2d are separated from the ends of the thermoplastic resin film 200 at the downstream ends of the cooling unit 50 in the MD direction in the order of transport direction, and then the annular rail 60a is further separated. Alternatively, it moves along 60b and returns to the preheating section 10. At this time, the thermoplastic resin film 200 moves in the direction of the arrow MD, and sequentially preheats in the preheating section 10, stretches in the stretching section 20, heat-fixing in the heat-fixing section 30, and heat-relaxation in the heat-relaxing section 40. , The cooling unit 50 is cooled and stretched laterally. The moving speed of the gripping members 2a to 2l in each region such as the preheating portion is the transport speed of the thermoplastic resin film 200.

The moving speeds of the gripping members 2a to 2l can be changed independently.
The biaxial stretching machine 100 enables lateral stretching in which the thermoplastic resin film 200 is stretched in the TD direction in the stretching portion 20, but the thermoplastic resin film 200 is made thermoplastic by changing the moving speeds of the gripping members 2a to 2l. The resin film 200 can also be stretched in the MD direction. That is, it is also possible to perform simultaneous biaxial stretching using the biaxial stretching machine 100.

Only 2a to 2l of the gripping member for gripping the end portion of the thermoplastic resin film 200 in the TD direction are shown in FIG. 1. However, in order to support the thermoplastic resin film 200, the biaxial stretching machine 100 has 2a to 2l. In addition, a gripping member (not shown) is attached. In the following, the gripping members 2a to 2l may be collectively referred to as "grasping member 2".

(A. Preheating section)
In the preheating section, the thermoplastic resin film after being longitudinally stretched in the first stretching (longitudinal stretching) step is preheated to a temperature at which it can be stretched.
As shown in FIG. 1, the thermoplastic resin film 200 is preheated in the preheating section 10. In the preheating section 10, the thermoplastic resin film 200 is preheated before being stretched so that the thermoplastic resin film 200 can be easily stretched laterally.

The film surface temperature (hereinafter, also referred to as “preheating temperature”) at the end point of the preheating portion shall be (Tg-10 ° C.) to (Tg + 60 ° C.) when the glass transition temperature of the thermoplastic resin film 200 is Tg. Is preferable, and is more preferably (Tg ° C.) to (Tg + 50 ° C.).
The end point of the preheating portion refers to the time when the preheating of the thermoplastic resin film 200 is completed, that is, the position where the thermoplastic resin film 200 is separated from the region of the preheating portion 10.

(B. Stretched part)
In the stretched portion, the thermoplastic resin film preheated in the preheated portion is stretched (transversely stretched) by applying tension in the width direction (TD direction) orthogonal to the longitudinal direction (MD direction).
Specifically, for example, in the stretched portion 20 shown in FIG. 1, the preheated thermoplastic resin film 200 is tensioned at least in the direction of the arrow TD orthogonal to the longitudinal direction of the thermoplastic resin film 200, and the thermoplastic resin film is applied. 200 is stretched laterally. For example, as shown in FIG. 1, the width length of the thermoplastic resin film is stretched from the width L0 to the width L1 to make it wider.
Stretching (transverse stretching) in the direction (TD) orthogonal to the longitudinal direction (MD) of the thermoplastic resin film 200 is stretched in a direction at an angle perpendicular to (90 °) the longitudinal direction (MD) of the thermoplastic resin film 200. However, in consideration of mechanical error, the film is not limited to 90 °, but also includes stretching in a direction (90 ° ± 5 °) that can be regarded as perpendicular to the MD direction of the film.

In the stretched portion 20, the area magnification of the thermoplastic resin film 200 (the product of the stretch ratio of the first stretch and the stretch ratio of the second stretch) is 12.8 times the area of the thermoplastic resin film 200 before stretching. It is ~ 15.5 times. The details are as described above.

The film surface temperature of the thermoplastic resin film 200 during lateral stretching (hereinafter, also referred to as “second stretching temperature”) is preferably 100 ° C. to 150 ° C., more preferably 110 ° C. to 140 ° C., 120 ° C. ° C to 130 ° C is more preferable.
When the second stretching temperature is 100 ° C. or higher, the risk of breakage due to the yield stress becoming too large is reduced. Further, by adjusting the second stretching temperature (film surface temperature), the surface roughness Ra can be adjusted within the above-mentioned range, the film is less likely to buckle on the TD, and the thin thermoplastic resin film is heated. Wavy wrinkles are less likely to occur even when transported.
Further, when the second stretching temperature is 150 ° C. or lower, crystallization of the film itself is suppressed, so that the film is less likely to break.

The stretching speed of the thermoplastic resin film 200 during lateral stretching is, for example, 5% / sec or more, preferably 8% / sec or more, more preferably 10% / sec or more, still more preferably 15% / sec or more. ..
The upper limit of the stretching speed of the thermoplastic resin film 200 during lateral stretching is, for example, 50% / sec or less, preferably 45% / sec or less, more preferably 40% / sec or less, still more preferably 30% or more. , 20% / sec or less is particularly preferable.
Here, the range of the stretching speed at the time of lateral stretching of the thermoplastic resin film 200 can be appropriately set by arbitrarily combining each of the above upper limit value and lower limit value. The range of the stretching speed of the thermoplastic resin film 200 during lateral stretching is, for example, 8% / sec to 45% / sec, 15% / sec to 40% / sec, and 10% / sec to 30%. There is / sec, and there are 10% / sec to 20% / sec.
The stretching rate is the time when the length Δd obtained by stretching the thermoplastic resin film from the state of the length d ⁰ before stretching to 1 second is the length of the thermoplastic resin film before stretching (that is, after passing through the preheating portion). Length) The value divided by d ⁰ is expressed as a percentage.
When the stretching speed is within the above range, the film is stretched at a relatively slow speed, so that stretching unevenness can be suppressed and the roughness of the film surface can be suppressed to an appropriately low level.
Further, when the stretching speed is 8% / sec or more, the stretching step does not become too long, and the crystallization of the film due to the long residence time is suppressed, so that the film is less likely to break. Further, when the stretching speed is 45% / sec or less, it is effective in suppressing the breakage of the film, and Ra can be suppressed so as not to become too large.

As described above, the gripping members 2a to 2l can independently change the moving speed. Therefore, for example, the thermoplastic resin film 200 is made by increasing the moving speed of the gripping member 2 on the downstream side in the stretching portion 20MD direction of the stretching portion 20, the heat fixing portion 30, etc., rather than the moving speed of the gripping member 2 in the preheating portion 10. It is also possible to perform longitudinal stretching in which the above is stretched in the transport direction (MD direction).
The longitudinal stretching of the thermoplastic resin film 200 in the second stretching step may be performed only by the stretching section 20, or may be performed by the heat fixing section 30, the heat relaxing section 40, or the cooling section 50, which will be described later. Further, the longitudinal stretching of the thermoplastic resin film 200 in the second stretching step may be performed at a plurality of positions among the stretching section 20, the heat fixing section 30, the heat relaxing section 40, and the cooling section 50.

(C. Heat fixing part)
In the heat-fixing portion, the thermoplastic resin film that has already been subjected to longitudinal stretching and lateral stretching is heated and crystallized to be thermally fixed.
The heat fixing means that the thermoplastic resin film 200 is heated in the stretched portion 20 while applying tension to crystallize the thermoplastic resin (for example, polyester).

In the heat-fixing portion 30 shown in FIG. 1, the maximum reachable film surface temperature on the surface of the thermoplastic resin film 200 with respect to the tensioned thermoplastic resin film 200 (in the present specification, the “heat-fixing temperature”, “heat-fixing temperature”, “ It is preferable to heat the film by controlling "T _{heat fixation} ") in the range of 160 ° C. to 240 ° C.
When the heat-fixing temperature is 160 ° C. or higher, the thermoplastic resin (for example, polyester) is easily crystallized, and the molecules of the thermoplastic resin (for example, polyester) can be fixed in a stretched state, and the resistance of the thermoplastic resin film can be reduced. Hydrolyticity is enhanced. Further, when the heat fixing temperature is 240 ° C. or lower, slippage does not easily occur at the portion where the molecules of the thermoplastic resin (for example, polyester) are entangled with each other, and the molecules do not easily shrink, so that the hydrolysis resistance of the thermoplastic resin film is lowered. Is suppressed. In other words, by heating so that the heat fixing temperature is 160 ° C. to 240 ° C., the molecular crystals of the thermoplastic resin (for example, polyester) are oriented to enhance the hydrolysis resistance of the thermoplastic resin film. Can be done.
For the same reason as described above, the heat fixing temperature is preferably in the range of 170 ° C. to 230 ° C., more preferably in the range of 175 ° C. to 225 ° C.
The maximum ultimate film surface temperature (heat fixing temperature) is a value measured by bringing a thermocouple into contact with the surface of the thermoplastic resin film.

Further, when the heat fixing temperature is controlled to 160 ° C. to 240 ° C., the variation of the maximum film surface temperature in the film width direction is preferably 0.5 ° C. or higher and 10.0 ° C. or lower. In the film width direction, the variation in the maximum film surface temperature of the film is 0.5 ° C or higher, which is advantageous in terms of wrinkles during transportation in the subsequent process, and the variation is 10.0 ° C or less. By suppressing it, the variation in crystallinity in the width direction is suppressed. As a result, the difference in slack in the film width direction is reduced, the occurrence of scratches on the film surface during the manufacturing process is prevented, and the hydrolysis resistance is enhanced.
Among the above, the variation in the maximum reaching film surface temperature is more preferably 0.5 ° C. or higher and 7.0 ° C. or lower, further preferably 0.5 ° C. or higher and 5.0 ° C. or lower, and 0. Particularly preferably, it is 5.5 ° C. or higher and 4.0 ° C. or lower.

Further, the heating of the film at the time of heat fixing may be performed only from one side of the film, or may be performed from both sides. For example, when cooled on a casting roll after melt extrusion in a film molding process, the molded thermoplastic resin film is cooled differently on one side and the other side, causing the film to curl. It's getting easier. Therefore, it is preferable that the heating in the main heat fixing portion is performed on the surface in contact with the casting roll in the film forming step. Curling can be eliminated by making the heating surface of the heat fixing portion a surface in contact with the casting roll, that is, a cooling surface.
In this case, in the heating, the surface temperature of the heated surface at the heat fixing portion immediately after heating is higher in the range of 0.5 ° C. or higher and 5.0 ° C. or lower than the surface temperature of the non-heated surface on the opposite side of the heated surface. It is preferable that the temperature is increased. When the temperature of the heated surface at the time of heat fixing is higher than that of the surface on the opposite side and the temperature difference between the front and back surfaces is 0.5 to 5.0 ° C., the curl of the film is more effectively eliminated. From the viewpoint of curl elimination effect, the temperature difference between the heated surface and the non-heated surface on the opposite side is more preferably in the range of 0.7 to 3.0 ° C, and is 0.8 ° C or higher and 2.0 ° C. The following is more preferable.

Further, the method for heating the thermoplastic resin film in at least one of the heat fixing portion 30 and the heat relaxing portion 40 may be a method of blowing hot air or a method of selectively radiant heating with a heater. By selectively radiating heating the thermoplastic resin film, the film surface temperature distribution in the TD direction can be uniformly controlled, and the quality (for example, heat shrinkage rate) of the produced thermoplastic resin film is uniform. Can be something like that.
When the film is selectively radiantly heated in the heat relaxation unit 40, the radiant heating in the heat fixing unit 30 may be omitted, or the radiant heating in the heat fixing unit 30 may be performed in parallel.
Examples of the heater capable of radiant heating include an infrared heater, and a ceramic heater (ceramic heater) is particularly preferable.

When the film is heated in the heat-fixing portion, the residence time in the heat-fixing portion is preferably 5 seconds or more and 50 seconds or less. The residence time is the time during which the film is continuously heated in the heat fixing portion. When the residence time is 5 seconds or more, the change in crystallinity with respect to the heating time becomes small, which is advantageous in that uneven crystallinity in the width direction is relatively unlikely to occur. It is advantageous in terms of productivity because it is not necessary to make the line speed extremely low.
Among them, the residence time is preferably 8 seconds or more and 40 seconds or less, and more preferably 10 seconds or more and 30 seconds or less for the same reason as described above.

(D. Heat relaxation unit)
In the heat relaxation section, the heat-fixed thermoplastic resin film is heated to heat-relax the tension of the thermoplastic resin film and remove the residual strain of the film. This heat relaxation causes the film to shrink at least one in the longitudinal and lateral directions.

The heat relaxation heats the heat-fixed thermoplastic resin film and heat-relaxes the tension of the thermoplastic resin film. The heating of the thermoplastic resin film in the heat-relaxing portion is performed as follows. Is preferable.
In the heat relaxation section 40 shown in FIG. 1, the maximum reachable film surface temperature of the surface of the thermoplastic resin film 200 is 5 ° C. higher than the maximum reachable film surface temperature (T _{heat fixation} ) of the thermoplastic resin film 200 in the heat fixing section 30. It is preferable to heat the thermoplastic resin film 200 so that the temperature becomes as low as possible.
Hereinafter, the maximum temperature of the film surface reached on the surface of the thermoplastic resin film 200 at the time of _{heat relaxation} is also referred to as “heat relaxation temperature (T _{heat relaxation} )”.

In the heat relaxation unit 40, the heat relaxation temperature (T _{heat relaxation} ) is heated at a temperature 5 ° C. or more lower than the heat fixation temperature (T _{heat fixation} ) (T _{heat relaxation} ≤ T _{heat fixation} -5 ° C) to release the tension. By (reducing the stretching tension), the dimensional stability of the thermoplastic resin film can be further improved.
When the T _{heat relaxation} is "T _{heat fixation-} 5 ° C." or less, the hydrolysis resistance of the thermoplastic resin film is excellent. Further, the T _{heat relaxation} is preferably 100 ° C. or higher in terms of improving dimensional stability.
Further, the T _{heat relaxation} is preferably in a temperature region (100 ° C. ≤ T _{heat relaxation} ≤ T _{heat fixing} -15 ° C.) which is 100 ° C. or higher and 15 ° C. or higher lower than the T _{heat fixing} , and is 110 ° C. or higher. In addition, it is more preferable that the temperature region is 25 ° C. or more lower than T _{heat fixing} (110 ° C. ≤ T _{heat relaxation} ≤ T _{heat fixing} -25 ° C.), 120 ° C. or more, and 30 ° C. or more lower than T _{heat fixing.} It is particularly preferable that the temperature range is (120 ° C. ≦ T _{heat relaxation} ≦ T _{heat fixing} −30 ° C.).
The T _{thermal relaxation} is a value measured by bringing a thermocouple into contact with the surface of the thermoplastic resin film 200.

(E. Cooling unit)
In the cooling section, the thermoplastic resin film after heat relaxation in the heat relaxation section is cooled. Further, when the thermoplastic resin film is cooled, tension is applied in the film width direction, and the film width is expanded or contracted in the range of −1.5% to 3% with respect to the film width at the end of heat relaxation at the heat relaxation portion.
As shown in FIG. 1, in the cooling unit 50, the thermoplastic resin film 200 that has passed through the heat relaxation unit 40 is cooled. By cooling the thermoplastic resin film 200 heated by the heat fixing portion 30 and the heat relaxing portion 40, the shape of the thermoplastic resin film 200 is fixed. FIG. 1 shows a biaxially stretched thermoplastic resin film having a width of L2.
Here, in order to expand the film width in the cooling unit 50, the same method as in the stretching in the stretching unit 20 described above may be used.
Further, in order to reduce the film width in the cooling unit 50, the same method as in the heat relaxation of the film tension in the heat relaxation unit 40 described above may be used.

When the gripping member that grips the thermoplastic resin film is separated from the thermoplastic resin film, the thermoplastic resin film is separated from the region of the cooling portion. For example, when the gripping member 2j shown in FIG. 1 is at point P and the gripping member 2l is at point Q, the end portion (end portion in the MD direction) of the cooling portion 50 when the thermoplastic resin film 200 is released is at point P. It is represented by a straight line connecting the point Q and the point Q.

The temperature (hereinafter, also referred to as “cooling temperature”) of the surface (film surface) of the thermoplastic resin film at the outlet of the cooling section of the thermoplastic resin film 200 in the cooling section 50 is the glass transition temperature Tg of the thermoplastic resin film 200. When it is, it is preferably lower than Tg + 50 ° C. Specifically, the cooling temperature is preferably 25 ° C. to 110 ° C., more preferably 25 ° C. to 95 ° C., and even more preferably 25 ° C. to 80 ° C. When the cooling temperature is in the above range, it is possible to prevent the film from shrinking unevenly after releasing the clip grip.
Here, the cooling unit outlet means the end portion of the cooling unit 50 when the thermoplastic resin film 200 separates from the cooling unit 50, and the gripping member 2 that grips the thermoplastic resin film 200 (in FIG. 1, the gripping member 2j). And 2l) refer to the position when the thermoplastic resin film 200 is separated, that is, the straight portion connecting the points P and Q.

Further, in the cooling unit 50, the average cooling rate when the temperature of the surface (film surface) of the thermoplastic resin film is cooled from 150 ° C. to 70 ° C. may be set in the range of 2 ° C./sec to 100 ° C./sec. preferable.
Here, the average cooling rate is obtained by actually measuring the film temperature of the film in the cooling zone with a radiation thermometer. That is, the cooling time (Z ÷ S) seconds from 150 to 70 ° C. is obtained from the distance Zm between the point where the film temperature becomes 150 ° C. and the point where the film temperature becomes 70 ° C. and the film transport speed Sm / sec. By further calculating (150-70) ÷ (Z ÷ S) from that, the average cooling rate can be obtained.

By setting the average cooling rate to 2 ° C./sec or more, insufficient cooling of the thermoplastic resin film in the stretching apparatus is suppressed, and the adhesiveness of the thermoplastic resin film is lowered. Therefore, in the process after the thermoplastic resin film is separated from the outlet of the cooling unit, a failure such as the thermoplastic resin film sticking to the roll for transporting the film is less likely to occur. Further, by setting the average cooling rate to 100 ° C./sec or less, rapid cooling of the thermoplastic resin film is prevented, residual stress unevenness is less likely to occur in the film surface, unevenness of the heat shrinkage rate is suppressed, and streaky burrs are formed. It becomes difficult to occur.
The average cooling rate is more preferably 4 ° C./sec to 80 ° C./sec, even more preferably 5 ° C./sec to 50 ° C./sec.

In the preheating, stretching, heat fixing, heat relaxation, and cooling in the second stretching step, as a temperature control means for heating or cooling the thermoplastic resin film 200, hot air or cold air is blown onto the thermoplastic resin film 200. Alternatively, the thermoplastic resin film 200 may be brought into contact with the surface of a temperature-controllable metal plate or passed in the vicinity of the metal plate.

(Recovery of film)
The thermoplastic resin film 200 cooled in the cooling step is wound into a roll by cutting the gripped portions gripped by the clips at both ends in the TD direction.

In the second stretching step, in order to further improve the hydrolysis resistance and dimensional stability of the produced thermoplastic resin film, it is preferable to relax the stretched thermoplastic resin film by the following method.

In the present disclosure, it is preferable that the cooling unit 50 relaxes in the MD direction after performing the second stretching step after the first stretching (longitudinal stretching) step. That is,
In the preheating section 10, both ends of the thermoplastic resin film 200 in the width direction (TD) are gripped at one end using at least two gripping members. For example, one end of the thermoplastic resin film 200 in the width direction (TD) is gripped by the gripping members 2a and 2b, and the other is gripped by the gripping members 2c and 2d. Next, the thermoplastic resin film 200 is conveyed from the preheating section 10 to the cooling section 50 by moving the gripping members 2a to 2d.

In such transportation, the gripping member 2a (2c) that grips one end of the thermoplastic resin film 200 in the width direction (TD direction) of the preheating portion 10 and the other gripping member 2b (2d) adjacent to the gripping member 2a (2c). ) Rather than the distance between the grip member 2a (2c) that grips one end of the thermoplastic resin film 200 in the cooling section 50 in the width direction, and the other grip member 2b (2d) adjacent to the grip member 2a (2c). By narrowing the distance between the film and the film 200, the transport speed of the thermoplastic resin film 200 is reduced. By such a method, the cooling unit 50 can relax in the MD direction.

The relaxation of the thermoplastic resin film 200 in the MD direction may be performed at least a part of the heat fixing portion 30, the heat relaxing portion 40, and the cooling portion 50.
As described above, the distance between the gripping members 2a-2b and the distance between the gripping members 2c-2d are narrowed on the downstream side of the upstream side in the MD direction to relax the thermoplastic resin film 200 in the MD direction. be able to. Therefore, when the heat relaxation in the MD direction is performed by the heat fixing portion 30 or the heat relaxation portion 40, the grip members 2a to 2d move when the grip members 2a to 2d reach the heat fixing portion 30 or the heat relaxation portion 40. The speed may be slowed down to reduce the transport speed of the thermoplastic resin film 200, and the spacing between the gripping members 2a-2b and the spacing between the gripping members 2c-2d may be narrower than the spacing in the preheating section 10.

Hereinafter, embodiments of the present invention will be described in more detail with reference to Examples. However, the embodiments of the present invention are not limited to the following examples as long as the gist of the present invention is not exceeded.

<Synthesis of polyester raw material resin 1>
As shown below, polyester (Ti catalyst) is subjected to a continuous polymerization apparatus using a direct esterification method in which terephthalic acid and ethylene glycol are directly reacted to distill off water, esterified, and then polycondensed under reduced pressure. System PET) was obtained.

(1) Esterification reaction 4.7 tons of high-purity terephthalic acid and 1.8 tons of ethylene glycol were mixed over 90 minutes to form a slurry in the first esterification reaction tank, and continuously at a flow rate of 3800 kg / h. It was supplied to the first esterification reaction tank. Further, an ethylene glycol solution of a citrate chelated titanium complex (VERTEC AC-420, manufactured by Johnson Massey) in which citric acid is coordinated to a Ti metal is continuously supplied, and the temperature in the reaction vessel is 250 ° C., and the average retention under stirring is performed. The reaction was carried out in about 4.3 hours. At this time, the citrate chelated titanium complex was continuously added so that the amount of Ti added was 9 ppm in terms of element. At this time, the acid value of the obtained oligomer was 600 equivalents / ton. In addition, in this specification, "equivalent / t" represents the molar equivalent per ton.
This reaction product was transferred to a second esterification reaction vessel and reacted under stirring at a temperature in the reaction vessel at 250 ° C. with an average residence time of 1.2 hours to obtain an oligomer having an acid value of 200 equivalents / ton. The inside of the second esterification reaction tank is divided into three zones, and an ethylene glycol solution of magnesium acetate is continuously supplied from the second zone so that the amount of Mg added is 75 ppm in terms of element, and then. From the third zone, an ethylene glycol solution of trimethyl phosphate was continuously supplied so that the amount of P added was 65 ppm in terms of element.

(2) Polycondensation reaction The esterification reaction product obtained above is continuously supplied to the first polycondensation reaction tank, and under stirring, the reaction temperature is 270 ° C., and the pressure inside the reaction tank is 20 torr (2.67 × 10 ^−). Polycondensation was carried out at ³ MPa) with an average residence time of about 1.8 hours.
Further, it was transferred to the second double condensation reaction tank, and under stirring in this reaction tank, the temperature inside the reaction tank was 276 ° C., the pressure inside the reaction tank was 5 torr (6.67 × 10 ^-4 MPa), and the residence time was about 1.2 hours. The reaction (polycondensation) was carried out under the conditions.
Then, it is further transferred to the third triple condensation reaction vessel, in which the reaction vessel temperature is 278 ° C., the reaction vessel pressure is 1.5 torr (2.0 × 10 ^-4 MPa), and the residence time is 1.5 hours. The reaction (polycondensation) was carried out under the above conditions to obtain a reaction product (polyethylene terephthalate (PET)).

Next, the obtained reaction product was discharged into cold water in a strand shape and immediately cut to prepare polyester pellets <cross section: major axis of about 4 mm, minor axis of about 2 mm, length: about 3 mm>.

The obtained polyester was measured as shown below using high-resolution high-frequency inductively coupled plasma-mass spectrometry (HR-ICP-MS; AttoM manufactured by SII Nanotechnology). As a result, Ti = 9 ppm, Mg = 75 ppm, P = 60 ppm. Although P is slightly reduced with respect to the initial addition amount, it is presumed that P was volatilized during the polymerization process.
The obtained polymer had IV = 0.67, terminal carboxy group amount (AV) = 23 equivalents / ton, melting point = 257 ° C., and solution haze = 0.3%. The IV and AV measurements were performed by the methods shown below.

~ Measurement of IV and AV ~
The intrinsic viscosity (IV) of the polyester raw material resin is such that the polyester raw material resin is dissolved in a 1,1,2,2-tetrachloroethane / phenol (= 2/3 [mass ratio]) mixed solvent in the mixed solvent. It was determined from the viscosity of the solution at 25 ° C.
For the terminal COOH amount (AV) of the polyester raw material resin, unstretched polyester films 1 to 4 are completely dissolved in a mixed solution of benzyl alcohol / chloroform (= 2/3; volume ratio), and phenol red is used as an indicator, and a reference solution is used. It was titrated with (0.025N KOH-methanol mixed solution) and calculated from the appropriate amount.
As described above, the polyester raw material resin 1 was synthesized.

(Examples 1 to 15 and Comparative Examples 1 to 4)
In addition, Examples 3, 8 to 11, 14, and 15 are reference examples.
<Making unstretched polyester film>
The polyester raw material resin 1 was dried to a water content of 20 ppm or less, and then charged into a hopper of a uniaxial kneading extruder having a diameter of 50 mm. The polyester raw material resin 1 was melted at 300 ° C. and extruded from a die via a gear pump and a filter (pore diameter 20 μm) under the following extrusion conditions. The size of the slit of the die was adjusted so that the thickness of the polyester sheet was 0.4 mm. The thickness of the polyester sheet was measured by an automatic thickness gauge installed at the outlet of the casting roll.

At this time, the extrusion of the molten resin was carried out under the conditions that the pressure fluctuation was 1% and the temperature distribution of the molten resin was 2%. Specifically, the back pressure in the barrel of the extruder is set to 1% higher than the average pressure in the barrel of the extruder, and the piping temperature of the extruder is set to be 2% higher than the average temperature in the barrel of the extruder. Heated as temperature. Upon extruding from the die, the molten resin was extruded onto a casting roll for cooling and brought into close contact with the casting roll using an electrostatic application method. To cool the molten resin, the temperature of the casting roll was set to 25 ° C., and cold air of 25 ° C. was blown out from a cold air generator installed facing the casting roll to apply the molten resin to the molten resin. An unstretched polyester film (unstretched polyester film 1) having a thickness of 0.4 mm and a film width of 0.9 m was peeled from the casting roll by a stripping roll arranged to face the casting roll.

Further, in the same manner as described above, the unstretched polyester film 2 having a thickness of 2.8 mm (used in Example 12 below) and the thickness of 1. were obtained, except that the size of the slit of the die and the discharge amount of the molten resin were adjusted. The 2 mm unstretched polyester film 3 (used in Example 13 below) and the 0.9 mm thick unstretched polyester film 4 (used in Example 14 below) were peeled off.
The film width is 0.9 m in each case.

The obtained unstretched polyester films 1 to 4 had an intrinsic viscosity IV = 0.64 dL / g, an amount of terminal carboxy groups (AV) = 25 equivalents / ton, and a glass transition temperature (Tg) = 72 ° C. ..
The IV and AV measurements were performed in the same manner as described above.

<Making a biaxially stretched polyester film>
The obtained unstretched polyester films 1 to 4 were sequentially biaxially stretched through the following steps to prepare a biaxially stretched polyester film having a thickness of 31 μm and a film width (total length of TD) of 2.5 m. ..

-First stretching step-
The unstretched polyester films 1 to 4 were passed between two pairs of nip rolls having different peripheral speeds, and the first stretching (longitudinal stretching) was performed in the MD direction (conveying direction) under the following conditions.
<Conditions>
Preheating temperature: 80 ° C
Stretching temperature: 90 ° C
Stretching ratio: Magnification (times) shown in Table 1 below
Stretch stress: 12 MPa

-Second stretching step-
The vertically stretched polyester film (uniaxially stretched polyester film) was subjected to the second stretching (transverse stretching) under the following method and conditions using a tenter (biaxial stretching machine) having the structure shown in FIG.

(Preheating part)
The preheating temperature was set to 110 ° C., and the mixture was heated so that it could be stretched.

(Stretched part)
The preheated uniaxially stretched polyester film was stretched (transversely stretched) by applying tension in the film width direction (TD direction) orthogonal to the MD direction under the following conditions.
<Conditions>
Stretching temperature: Temperature (° C) shown in Table 1 below
Stretching ratio: Magnification (times) shown in Table 1 below
Stretch stress: 18 MPa
Stretching rate: Stretching rate (% / sec) shown in Table 1 below.

The stretching ratios for the first stretching and the second stretching were adjusted, and the area ratios after the first stretching and the second stretching were adjusted to the magnifications shown in Table 1 below.
The area magnification is the product of the stretching ratio at the time of the first stretching and the stretching ratio at the time of the second stretching.

(Heat fixing part)
Next, the maximum reachable film surface temperature (heat fixing temperature) of the polyester film was controlled within the following range and heated to crystallize.
-Maximum reach film surface temperature (heat fixing temperature T _{heat fixing} ): 220 [° C]

(Heat relaxation section)
The heat-fixed polyester film was heated to the following temperature to relieve the tension of the film.
<Conditions>
-Heat relaxation temperature (T _{heat relaxation} ): 190 ° C
-Heat relaxation rate: TD direction (TD heat relaxation rate; ΔL) = 5%

(Cooling part)
Next, the heat-relaxed polyester film was cooled at a cooling temperature of 65 ° C. At the same time, the polyester film was tensioned in the film width direction (TD direction) under the following conditions, and slightly expanded or reduced.
<Conditions>
Expansion or reduction magnification: Values shown in Table 1 below (%)
Expansion or reduction rate: 0.1% / sec The magnification indicates the expansion ratio or reduction ratio with respect to the film width at the end of heat relaxation in the heat relaxation unit. Negative values in Table 1 represent "reduction".

-Recovery of film-
After the cooling was completed, both ends of the polyester film were trimmed by 20 cm. Then, both ends were extruded (knurled) with a width of 10 mm, and then wound up at a tension of 25 kg / m.

As described above, a biaxially stretched polyester (PET) film having a thickness of 31 μm was produced.

<Preparation of biaxially stretched cyclic polyolefin film>
In the preparation of the above PET film, except that the polyester raw material resin 1 was replaced with ARTON (registered trademark; specific gravity ρ: 1.08 g / cm ³ , glass transition temperature (Tg): 138 ° C., manufactured by JSR Corporation). , A biaxially stretched cyclic polyolefin film (COP) was produced in the same manner as the above-mentioned production of the biaxially stretched polyester (PET) film.
The first stretching and the second stretching were performed as follows.
That is, the first stretching (longitudinal stretching) is performed at a preheating temperature: 120 ° C., a stretching temperature: 140 ° C., and a stretching ratio of 3.5 times, and the second stretching (transverse stretching) is performed at the preheating temperature of the preheating portion: Of the above PET film, except that the stretching temperature of the stretched portion was 120 ° C., the stretching ratio was 4.2 times, the stretching speed was 18% / sec, and the expansion ratio of the cooling portion was 1.5%. The conditions were the same as those for production.

<Measurement and evaluation>
The biaxially stretched polyester film and the biaxially stretched cyclic polyolefin film obtained as described above were subjected to the following measurements and evaluations. The results of measurement and evaluation are shown in Table 1 below.

-1. Modulus ratios E ^30, E ^90, E ^120, E ¹⁵⁰ and E ^180-
From the biaxially stretched polyester film or the biaxially stretched cyclic polyolefin film, a sample piece having a width of 6 mm and a total length of 115 mm (JIS K 6251, dumbbell-shaped No. 5 type) was punched out. The obtained sample piece was pulled by Tencilon (manufactured by Toyo Seiki Co., Ltd., Strograph VE50) under the conditions of 50 mm between chucks and 100 mm / min in tensile speed, and the elongation of the film with respect to the load was measured. Next, a graph was created from the measured values with the load on the horizontal axis and the elongation on the vertical axis, and the elastic modulus was calculated from the tangent line of the rising portion of the load-elongation curve. This operation was performed 5 times, and the average value of 3 points excluding the maximum value and the minimum value was taken as the elastic modulus.
For each temperature, carried out for each case pulling when the film width direction to pull the film conveying direction, the elastic modulus in the case of pulling the film conveying direction and E ^TD, the elastic modulus in the case of pulling the film width direction E ^{It was designated as TD} .
<Measurement conditions>
・ Measurement site: Hot air heating furnace ・ Measurement temperature: 30 ℃, 90 ℃, 120 ℃, 150 ℃, 180 ℃
(The temperature was set and the air volume was adjusted so that the set temperature of the furnace rose to the desired temperature in 1.5 minutes and the temperature rise was within 2 ° C. even after 1 minute had passed from the desired temperature.)
-Temperature control: A test piece of the same type and size for temperature measurement was installed near the test piece, and a thermocouple was attached to the test piece for temperature measurement to monitor the temperature at the time of measurement.
-Test start timing: Pulling was started after reaching the desired temperature.

-2. Surface Roughness Ra-
Using a contact shape measuring machine (Mitutoyo FORMTRACER EXTREME CS-5000 CNC), measure 12 times each at arbitrary positions in the MD direction and TD direction of the biaxially stretched polyester film or biaxially stretched cyclic polyolefin film under the following conditions. , The average of 10 points in the MD direction and 10 points in the TD direction from which the minimum and maximum values of Ra were removed was obtained, and the average value of 20 points was defined as Ra.
<Conditions>
・ Measuring needle tip diameter: 0.5 μm
・ Needle load: 0.75mN
・ Measurement length: 0.8 mm
・ Cutoff value: 0.08 mm

-3. Film thickness-
Using a tactile film thickness measuring machine (Mitutoyo ID-C112X), measurements were taken at intervals of 50 mm over the entire width of the biaxially stretched polyester film or biaxially stretched cyclic polyolefin film in the TD direction. This operation was performed for 5 sets at 1 m intervals in the MD direction, and the average value of the measured values was taken as the thickness.

-4. Streaky burr
A biaxially stretched polyester film or a biaxially stretched cyclic polyolefin film was passed through a heat transfer device, and the maximum temperature of the film was set to 90 ° C., 120 ° C., 150 ° C. or 180 ° C. for 1 minute, and the heat transfer process was performed at a transfer tension of 1 MPa. .. After that, the biaxially stretched polyester film or the biaxially stretched cyclic polyolefin film which has been heat-conveyed is placed on a flat surface, and the biaxially stretched polyester film or the cyclic polyolefin film is so as to reflect the light of the fluorescent lamp installed on the ceiling of the room. The film was observed from an angle, and the degree of undulation of the reflected image of the fluorescent lamp reflected on the biaxially stretched polyester film or the biaxially stretched cyclic polyolefin film by reflecting light was evaluated according to the following evaluation criteria.
<Evaluation criteria>
AA: There is no swell in the reflected image, and no streaky burrs are observed.
A: There were slight streaky burrs in some parts, but the swell of the reflected image was weak and there was no problem in practical use.
B: The reflected image appears to be slightly wavy on the entire surface, but it does not hinder practical use.
C: Streaky burrs are remarkably generated, and the swell of the reflected image is strong on the whole, which hinders practical use.

As shown in Table 1, in the examples in which the elastic modulus ratio Er ³⁰ at 30 ° C. and the elastic modulus ratio Er in the temperature range of 30 ° C. to 180 ° C. were appropriately adjusted, even a film having a thickness of 200 μm or less was streaked. The generation of burrs was suppressed, and the effect of suppressing streaks was remarkably exhibited even in a thin film having a thickness of less than 100 μm.
On the other hand, in Comparative Examples 1 to 4 in which the variation of the elastic modulus ratio or the elastic modulus ratio (difference between the maximum value Er _max and the minimum value Er _min ) was out of the desired range, the occurrence of wrinkles in the TD direction was suppressed. However, the occurrence of streaky burrs was remarkable.

2a to 2l Gripping member 3 Film 4 Conveying roll 10 Preheating part 20 Stretching part 30 Heat fixing part 40 Heat relaxation part 50 Cooling part 60a, 60b Amplified rail 100 Biaxial stretching machine 200 Polyester film P, Q The gripping member is a thermoplastic resin film. MD film transport direction (longitudinal direction)
TD film width direction L0, L1, L2 width length ^Z 1 of a thermoplastic resin film, ^{Z 2} expansion width sigma _x Stress

The disclosure of Japanese Patent Application 2017-037662, filed February 28, 2017, is incorporated herein by reference in its entirety.
All documents, patents, patent applications, and technical standards described herein are those specifically and individually stated that the individual documents, patents, patent applications, and technical standards are incorporated by reference. To the same extent, it is incorporated by reference herein.

Claims (11)

Film transport direction with respect to the elastic modulus ^{E MD,} in the film width direction perpendicular to the film conveying direction of the elastic modulus ^{E TD,} the ratio ^{Er 30} at 30 ° C., and 1.2 to 1.6, and,
Of the elastic modulus ^{E TD} with respect to the elastic modulus ^{E MD,} a ratio ^Er 30, the ratio at 90 ° C. ^Er 90, the ratio ^Er 120 at 120 ° C., the ratio ^{Er 0.99} at 0.99 ° C., and 180 ° C. at the 30 ° C. A thermoplastic resin film in which the difference between the maximum value Er _max and the minimum value Er _min selected from the ratio Er ¹⁸⁰ is 0.7 or less, and the film is wound in a long roll shape . The thermoplastic resin film according to claim 1, wherein the surface roughness Ra of at least one surface is 0.5 nm to 50 nm. The thermoplastic resin film according to claim 1 or 2, wherein the thickness is 200 μm or less. The thermoplastic resin film according to any one of claims 1 to 3, which is a polyester film or a cyclic polyolefin film. The method for producing a thermoplastic resin film according to any one of claims 1 to 4.
The process of melt-extruding the raw material resin and cooling it to form a thermoplastic resin sheet,
A step of first stretching the thermoplastic resin sheet in the longitudinal direction to obtain a thermoplastic resin film, and
A preheated portion for preheating the thermoplastic resin film, a stretched portion for stretching the preheated thermoplastic resin film by applying tension in the film width direction orthogonal to the longitudinal direction of the thermoplastic resin film, and a tensioned thermoplastic. The thermoplastic resin film is sequentially conveyed to a heat fixing part that heats and fixes the resin film, a heat relaxation part that heat-relaxes the tension, and a cooling part that cools the heat-relaxed thermoplastic resin film. Then, the process of performing the second stretching and
Including
The area magnification, which is the product of the stretching ratio in the first stretching and the stretching ratio in the second stretching, is 12.8 times to 15.5 times.
In the step of performing the second stretching, the heat-relaxed thermoplastic resin film is further tensioned in the film width direction in the cooling portion, and the film width at the end of the heat relaxation in the heat-relaxing portion is relative to the film width. A method for producing a thermoplastic resin film, wherein the expansion ratio in the width direction is 0.0% to 2.0%. The method for producing a thermoplastic resin film according to claim 5, wherein the step of performing the second stretching is to stretch the thermoplastic resin film at a stretching speed of 8% / sec to 45% / sec in the stretched portion. The thermoplastic resin film according to claim 5 or 6, wherein in the step of performing the second stretching, the thermoplastic resin film is stretched at a stretching rate of 15% / sec to 40% / sec. Manufacturing method. The thermoplastic resin according to any one of claims 5 to 7, wherein in the step of performing the second stretching, the thermoplastic resin film is stretched at a stretching temperature of 100 ° C. to 150 ° C. How to make a film. The thermoplastic resin according to any one of claims 5 to 8, wherein in the step of performing the second stretching, the thermoplastic resin film is stretched at a stretching temperature of 110 ° C. to 140 ° C. How to make a film. Any one of claims 5 to 9, wherein the area magnification, which is the product of the stretching ratio in the first stretching and the stretching ratio in the second stretching, is 13.5 times to 15.2 times. The method for producing a thermoplastic resin film according to. The thermoplasticity according to any one of claims 5 to 10, wherein the step of performing the first stretching is to perform the first stretching having a draw ratio of 2 to 5 times with respect to the thermoplastic resin sheet. A method for manufacturing a resin film.