JPH08281794A - Thermoplastic resin film excellent in thickness uniformity and production thereof - Google Patents

Abstract

PURPOSE: To obtain a thermoplastic resin film not having thickness irregularity having a peculiar cycle and extremely high in thickness uniformity by separating the thickness irregularity of the film by the generation cause thereof to eliminate the same. CONSTITUTION: A thermoplastic resin film excellent in thickness uniformity is characterized by that the thickness irregularity in the longitudinal direction of the film is 5% or less and the ratio Pw1/PwT of the spectrum intensity sum Pw1 in a wavenumber of 0.015-0.45 (1/m) when the waveform of the thickness irregularity is subjected to Fourier analysis to the spectrum intensity sum Pw T in a total wavenumber and is 0.2 or less.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a thermoplastic resin film and a method for producing the same. More specifically, the present invention relates to a thermoplastic resin film having extremely high thickness uniformity and a method for producing the same, in which the thickness unevenness of the film is separated and prevented depending on the cause of the occurrence of the thickness unevenness. It is a thing.

[0002]

2. Description of the Related Art Thickness uniformity is one of the important basic qualities in the production of thermoplastic resin films. Taking polyester as an example of the thermoplastic resin, because of its excellent properties, the polyester film is used for electrical insulation applications such as base films for magnetic recording media and capacitors, OA applications for printer ribbons, etc. It is used in various applications such as heat-sensitive stencil paper,
In these applications, high dimensional accuracy of film thickness is being demanded year by year. When the uneven thickness is deteriorated, the physical properties are uneven due to the thickness of the film, which leads to deterioration of product quality. Further, even when the quality of the product is not directly concerned, a trouble in processing the film into a product, a deterioration of the winding shape when wound into a roll, and thus a quality of the processed product may be deteriorated, which is preferable. Absent.

By the way, in a method of forming a thermoplastic resin film, generally, a resin is melted by an extruder, foreign matters are removed through a filter or the like, and then a slit having a shape suitable for the film to be formed is provided. It is discharged from a die (die) and continuously molded on a rotating roll (casting drum) with a cooling medium passing inside. At this time, in order to bring the resin film into close contact with the casting drum, an electrostatic force is often added. Furthermore, in order to increase the strength of the film, it is generally performed to stretch the obtained cast film in the longitudinal direction and the width direction of the film.

The cause of the uneven thickness of the film is the fluctuation of the discharge amount when melt-extruding and extruding into a sheet on the casting drum, and the still molten state between the die and the casting drum (L-D). Vibration of the resin film, uneven rotation of the casting drum, and the like. When the oriented film is used, the temperature unevenness and rotation unevenness of the roll during longitudinal stretching (stretching in the longitudinal direction), and the temperature unevenness and wind speed in the tenter during lateral stretching (stretching in the width direction) are further included. There are spots.

Therefore, various methods have heretofore been proposed for improving the thickness unevenness. For example, a method for suppressing uneven rotation of a casting drum that cools and solidifies the molten resin (Japanese Patent Laid-Open No. 55-93420) or a resin that is easily subjected to electrostatic force when the molten resin is brought into close contact with the casting drum by electrostatic force Method for modifying (see JP-A-59-91)
No. 121) has been proposed, but the effect is still insufficient.

In order to suppress the film vibration between L and D, a method of lowering the extrusion temperature of the thermoplastic resin to increase the melt viscosity of the resin (Japanese Patent Application No. 6-70789) has been proposed. It has not been put to practical use yet. In addition to the purpose of reducing the thickness unevenness, generally, as a method of extruding a thermoplastic resin at a melting point or lower, for example, Japanese Patent Publication No. 53-11980, Japanese Patent Publication No. 53-19625, and Japanese Patent Publication No. 1-550.
No. 87 publication can be mentioned. However, these methods use a circular die, and in the case of a circular die, since it is discharged in a cylindrical shape, there is no edge and it is difficult to disturb the flow even when cooled below the melting point, but when using a flat die However, there is a problem that the edges are more likely to solidify first and disturb the flow more easily. Further, these publications have a configuration in which the resin is cooled to a temperature equal to or lower than the melting point before the land portion of the die, and the cooled resin is supplied to the land portion.
The resin is solidified by cooling it below the melting point inside the die, and then it is supplied to the land portion and extruded while shearing. Therefore, it requires a very high extrusion pressure,
Extrusion is difficult with an ordinary extruder, a special extruder for high pressure is required, and the extrusion stability is poor. Further, a large load is applied to the die body and the die, which causes deformation and deterioration of durability. Further, it is extremely difficult to widen the resin thus solidified in a wide width, and even if the resin can be widened, the unevenness in the flow results in the uneven thickness.

Further, in the longitudinal stretching step, Japanese Patent Laid-Open No. 60-18
Japanese Patent No. 9422 proposes a method of bringing a film into close contact with a drawing roll by an electrostatic force. In addition, JP-A-54
Japanese Patent Laid-Open No. 56674 and Japanese Patent Laid-Open No. 130125/1990 propose a method of performing longitudinal stretching in multiple stages.
However, the current situation is that the solution has not yet been fully resolved.

On the other hand, Japanese Unexamined Patent Publication No. 2-256003 and Japanese Unexamined Patent Publication No. 6-175282 describe films having a peculiar shape and having no thickness unevenness, but the manufacturing method thereof is not clear.

[0009]

As described above, there is a strong demand for improving the unevenness of the thickness of the film, and various improving methods have been proposed for that purpose. However, the effect is still insufficient, and (1) the thickness of the film is large. The trouble caused by the difference in thickness between the thin portion and the thin portion, and (2) the trouble caused by the variation in the thickness having a certain specific period are not extinct.

In order to solve such a problem, the present invention has been completed by reviewing each step of the film manufacturing process and analyzing the cause of the uneven thickness of the film. It is an object of the present invention to provide a thermoplastic resin film having an extremely high thickness uniformity, in which there is no thickness unevenness having a period of, and a method for producing the same.

[0011]

A thermoplastic resin film having excellent thickness uniformity according to the present invention for this purpose has a thickness variation in the longitudinal direction of the film of 5 (%) or less, and the thickness variation waveform is 0.15 (1 /
The ratio Pw1 / PwT of the sum Pw1 of the spectral intensities in the wave number of m) or more and 0.45 (1 / m) or less to the sum PwT of the spectral intensities in the whole wave number band is 0.2 or less.

The thermoplastic resin film having excellent thickness uniformity according to another aspect of the present invention has a thickness unevenness in the longitudinal direction of the film of 5 (%) or less, and the waveform of the thickness unevenness is analyzed by Fourier analysis. 1.00 (1 / m) or more 2.
Spectral intensity sum P for wave numbers below 00 (1 / m)
The ratio Pw2 / PwT of w2 to the sum PwT of spectral intensities in the entire wave number band is 0.15 or less.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. In the present invention, the thickness unevenness in the longitudinal direction of the film is 5
Must be below (%). It is preferably 4 (%) or less, and more preferably 2 (%) or less. When the thickness unevenness exceeds 5 (%), the difference in thickness between the thick portion and the thin portion of the film becomes too large, resulting in a large difference in physical properties and being unusable. For example, in applications such as heat-sensitive stencil sheets and printer ribbons, this uneven thickness causes uneven print density after printing, resulting in unclear finish. In addition, in applications of electrical insulation and capacitors, dielectric breakdown may occur in a thin portion of the film, which may cause a device failure. In recent applications, a particularly high degree of unevenness in thickness is being demanded due to higher performance of hardware.

In the present invention, when the waveform of the thickness unevenness is subjected to Fourier analysis, it is 0.15 (1 / m) or more and 0.4 or more.
Spectral intensity sum Pw at wave numbers of 5 (1 / m) or less
It is necessary that the ratio Pw1 / PwT of 1 to the sum PwT of spectral intensities in all wave number bands is 0.2 or less. It is preferably 0.15 or less, more preferably 0.1 or less. As a result of earnest studies, the inventors of the present invention have found that the troubles that occur correspond to the cycle of uneven thickness. That is, when frequency analysis is performed on the waveform of the thickness unevenness, there is a correspondence relationship that a certain kind of trouble occurs when there are many thickness unevenness components of a certain period.
Here, when the waveform of the thickness unevenness is analyzed by the Fourier transform, the wave number is 0.15 (1 / m) or more and 0.45 (1 / m) or more.
It was found that the following spectral intensities have an effect on meandering and winding disorder when the film is secondarily processed.
That is, 0.15 (1 / m) or more and 0.45 (1 / m)
Ratio Pw1 of spectrum intensity sum Pw1 in the following wave numbers to spectrum intensity sum PwT in all wave number bands
When / PwT exceeds 0.2, problems such as meandering and winding disorder occur when the film is subjected to processing such as coating or secondary processing such as slitting to a certain width.

Further, in the present invention, 1.00 (1 /
It is necessary that the ratio Pw2 / PwT of the sum Pw2 of spectral intensities in the wave number of m) or more and 2.00 (1 / m) or less to the sum PwT of the spectral intensities in all wave number bands is 0.15 or less. It is preferably 0.1 or less. Wave number is 1.00 (1 / m) or more and 2.00 (1 / m)
It was found that the following thickness unevenness contributes to the generation of wrinkles during secondary processing. That is, the sum Pw2 of the spectral intensities Pw2 in the wave number band of 1.00 (1 / m) or more and 2.00 (1 / m) or less in the entire wave number band.
If the ratio Pw2 / PwT with respect to T exceeds 0.15, problems such as wrinkles increase during the secondary processing of the film.

As the thermoplastic resin in the present invention, polyethylene, polypropylene, polyolefin resin such as polymethylpentene, polyamide resin such as nylon 6, nylon 66, polyethylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate, poly A polyester resin such as -1,4-cyclohexanedimethylene terephthalate, a polyacetal resin, a polyphenylene sulfide resin, or the like can be used. In particular, in the present invention, the effect is high when polyester is used, which is preferable. That is, the trouble at the time of secondary processing as described in the present invention is apt to occur when conveyed at high temperature, and is 1 to 2 μm.
It is likely to occur when processing a very thin film such as m, has high heat resistance, and is highly effective in a polyester capable of forming an extremely thin film.
Among them, polyethylene-2,6-naphthalate and polyethylene terephthalate are preferable, and especially polyethylene terephthalate is inexpensive and therefore used in a wide variety of applications and has a high effect. Further, these resins may be homo resins, and may be copolymers or blends. In addition, various known additives such as antioxidants, antistatic agents, crystal nucleating agents, and inorganic particles may be added to these resins.

The biaxially oriented film in the present invention means a film which is stretched in the machine direction and / or the transverse direction to give a molecular orientation in the biaxial direction. Further, in addition, stretching may be carried out in the longitudinal direction and / or the lateral direction again to impart a stronger orientation.

The term "longitudinal stretching" as used in the present invention means stretching for imparting longitudinal molecular orientation to the film, and it is usually carried out by a difference in peripheral speed of rolls. This stretching may be performed in one stage, or may be performed in multiple stages using a plurality of roll pairs. The stretching ratio varies depending on the type of resin, but is usually about 2 to 15 times. Especially when polyethylene terephthalate is used, it is about 2 to 7 times.

The transverse stretching in the present invention means stretching for imparting widthwise orientation to the film, and usually,
A tenter is used to convey the film while holding both ends of the film with clips, and stretch the film in the width direction. The stretching ratio varies depending on the type of resin, but is usually about 2 to 10 times.

After stretching, heat treatment (heat setting) is often performed to remove the strain. As the temperature of the heat treatment, various temperatures from the stretching temperature to the vicinity of the melting point of the resin are adopted. Further, in the present invention, the effect is high when the film thickness is 20 μm or less. More preferably, it is 10 μm or less. Regarding the above-mentioned processing troubles, the thinner the film, the more troubles, and the effect of the present invention becomes more apparent. On the other hand, the film vibration of the resin at the time of extrusion, the unevenness of stretching in the longitudinal stretching, which will be described later, are more likely to occur as the film becomes thinner,
The effect of the present invention becomes more remarkable as the film becomes thinner.

Next, the method for producing the film of the present invention will be explained, but the present invention is not necessarily limited to this. First, a raw material of a thermoplastic resin is prepared in the form of pellets and the like, and if necessary, pre-dried in hot air or under vacuum and supplied to an extruder. In the extruder, the resin melted by heating to a temperature higher than the melting point is used as a filter in a molten state.
Foreign substances are removed through a heated pipe connecting a gear pump and the like. At this time, by connecting the gear pump, the uniformity of the amount of resin extruded is improved, and it is highly effective in reducing unevenness in thickness. However, the thickness unevenness component improved by the gear pump is a long-period component with a wave number of 0.10 (1 / m) or less, and the introduction of the gear pump alone does not reduce the thickness unevenness component as intended by the present invention. I can't achieve it.

The resin sent from the extruder to the die is molded into a desired shape by the die and then discharged. The resin temperature at the time of this discharge is usually the melting end temperature (Tme) or higher. Here, as a result of earnest research, the present inventors have found that the wave number is 0.
The thickness unevenness of the component of 15 (1 / m) or more and 0.45 (1 / m) or less is largely due to the film vibration between the die and the casting drum (L-D) when the resin is extruded into a sheet. I found that. Furthermore, in order to suppress this membrane vibration, it was found that a method of increasing the rigidity by lowering the temperature of the resin between L and D is effective. This cooling for lowering the temperature is preferably performed at the land portion which is the exit of the die. If cooling is done before the resin enters the die, the viscosity will rise, the fluidity will deteriorate, and in some cases it will solidify, resulting in abnormal extrusion, abnormal flow, or inability to extrude. However, it is not preferable because it may cause a load on the extruder, filter and gear pump, causing deformation or shortening of life. Even when cooling in the die, cooling in front of the land (die hopper) is a process in which the resin is molded into the desired shape, which causes uneven temperature and abnormal flow, and worsens uneven thickness. It is not preferable because it causes Especially in the flat die, since the resin flow path length varies in the width direction, the heat history is not uniform due to the difference in cooling time, and temperature unevenness occurs in the width direction, resulting in poor moldability and sufficient thickness unevenness. Not only the improvement effect cannot be obtained, but also the thickness unevenness may worsen, which is not preferable. On the other hand, if the cooling is performed at the land portion of the die, the cooling is performed after the resin is expanded in the width direction and formed into a shape to be extruded, and uniform cooling is possible. The land portion is a portion having the smallest gap in the die, and is suitable for high heat exchange efficiency. Further, since the resin is extruded immediately after cooling, it is possible to minimize an increase in filtration pressure due to an increase in viscosity, an abnormal extrusion, and an abnormal flow due to solidification.

Although the die is not particularly limited, for example, as described in “Plastic extrusion molding and its application” by Keiji Sawada (Seibundo Shinkosha Co., Ltd.), the die has a cylindrical shape. Any of a manifold die having a groove (manifold) (also referred to as a T die), a fish tail die having a shape like a fish tail, and a coat hanger die having an intermediate shape may be used. Flat dies are usually
Consists of a part called the die hopper that spreads the molten resin in the width direction and a part called the land part that is the final part that forms the desired shape after spreading the resin in the width direction and that is a parallel part with a certain slit gap To be done. Immediately after passing through this land portion, the resin is released to the atmosphere and extruded onto the casting drum.

When the resin is crystalline, the temperature of the resin discharged from the die is preferably lower than the melting end temperature (Tme) and higher than the temperature falling crystallization start temperature (Tcb). In the case of the polymer resin, it is possible to maintain a so-called supercooled liquid phase state in which the resin in a molten state is not solidified in a short time even if it is cooled below Tme. Moreover, the resin in this state has a high viscosity, is stable against film vibration and disturbance between the die and the cooling drum after being extruded from the land portion, and a film having a small thickness unevenness can be obtained. The cooling means for the land portion of the die is not particularly limited, but for example,
There is a method in which a hole for cooling is provided in the land portion and a refrigerant is passed through the hole. As the refrigerant, various liquid refrigerants such as air or water can be used, and the desired temperature can be set by controlling the temperature and flow rate of the refrigerant. The use of such a die is advantageous in that the resin and apparatus used in the production of the existing film can be used as they are, and a film having a small thickness unevenness of the components as in the present invention can be obtained. Further, it is preferable to stop the cooling to a temperature exceeding Tcb of the resin. T
When the temperature becomes lower than cb, the resin begins to crystallize, the surface of the extruded film is roughened, the extrusion is abnormal, the flow is uneven, and the resin solidifies over time, which is not preferable because it becomes difficult to extrude with an ordinary extruder. The resin is cooled to the melting point or lower at the land portion of the die, but what is important in this case is that the resin is never solidified. It is important to use the supercooled state of the polymer to extrude it in the liquid phase, although it is below the melting point.

Further, the resin is cooled at the land portion, but at that time, it is preferable to extrude the resin in a cooling transient state. Due to the transitional state, the vicinity of the thick edge is left in a relatively high temperature state, and solidification from the edge portion can be suppressed. On the other hand, the resin cooled in the land portion has a temperature gradient between the temperature of the wall surface of the land portion and the temperature of the central portion in the thickness direction due to the thermal conductivity of the resin. That is, even if the temperature near the wall surface of the land portion decreases, the temperature near the center in the thickness direction may remain high without being cooled. In particular, it tends to occur when the discharge amount is large and when the land has a wide lip interval. In such a case,
The resin is divided into a plurality of parts in the thickness direction inside the die, that is,
Providing multiple lands and manifolds inside the die,
It is possible to adopt a method in which after cooling in each of them, they are joined and discharged. By this method, the temperature gradient in the thickness direction can be greatly reduced. Further, such a die can be realized by making a small modification of a known laminated coextrusion die.

By the way, the melting end temperature (Tme) and the temperature falling crystallization start temperature (Tcb) are measured by a differential scanning calorimeter (DSC).
Can be determined by DSC is a method usually used in thermal analysis and is a method for measuring endothermic and exothermic heat associated with state changes such as melting, crystallization, phase transition, and thermal decomposition of a substance. When measuring the melting temperature of the thermoplastic resin when the temperature is raised and the crystallization temperature when the temperature is lowered by DSC, a known method can be used.

The sheet-shaped molten resin discharged from the die is cooled and solidified on the casting drum to be formed into a film. At this time, a method is preferably used in which static electricity is applied to the sheet-shaped molten resin so that the sheet-shaped molten resin is brought into close contact with the drum and then rapidly solidified.

When stretching is carried out, the unstretched film thus obtained is introduced into a heated roll group and longitudinally stretched. Here, as a result of earnest research, the present inventors have found that the wave number is 1.00 (1 / m) or more and 2.00 (1 / m) or more.
It was found that the thickness unevenness of the following components is largely due to the unevenness of stretching in the longitudinal stretching. Further, it has been found that it is effective to modify the stress-strain curve at the time of longitudinal stretching in order to suppress this stretching unevenness. Here, as a method for modifying the stress-strain curve, one is effective to give a little crystallization before the longitudinal stretching, and as another method, as described above, the resin is excessive. It was found that a method of forming a fine nucleus structure in an unstretched film by discharging from a die in a cooled state and casting is effective. That is, the former method is a crystallization with a crystallinity of 0.5 to 25 (%), more preferably 1 to
10 (%) is crystallized, and the obtained crystallized film is longitudinally stretched in the longitudinal direction in one step or in multiple steps.
In the latter method, the resin is discharged from a die at a temperature lower than the melting end temperature (Tme) of the resin and higher than the temperature falling crystallization start temperature (Tcb), and the take-up ratio (draft ratio) in casting is 5 to 5.
By casting in the range of 50, a film having a fine nuclear structure inside is obtained while it is an unstretched film, and the obtained film is longitudinally stretched in the longitudinal direction in one step or in multiple steps.

Usually, in the stress-strain curve of amorphous unstretched polyethylene terephthalate at the stretching temperature, as shown in FIG. 1, there is a flat section in which the stress does not increase with strain. Figure 1 shows polyethylene terephthalate (P
ET) unstretched film (thickness 200 μm) 90 ° C.
It shows a stress-strain curve at 110 ° C., where 1 is 9
Stress-strain curve of amorphous unstretched PET at 0 ° C.
Stress-strain curve of amorphous unstretched PET at 100 ° C., 3
Shows the stress-strain curves of amorphous unstretched PET at 110 ° C., respectively. However, when stretching is performed in this flat section, strain is not fixed at one point due to stress,
The draw ratio varies from place to place, causing uneven thickness.

However, as a result of earnest studies by the present inventors,
The stress-strain curve of the film which has been slightly crystallized rises as shown in FIG. 2, and the stress and the strain have a one-to-one correspondence. That is, when the film thus slightly crystallized is stretched, it is possible to obtain a film in which unevenness in thickness is not deteriorated. here,
When the crystallinity is small, the effect of rising the stress-strain curve is small, and when the crystallinity is too high, on the contrary, the stretchability is deteriorated and the thickness unevenness is deteriorated. FIG. 2 shows stress-strain curves at 100 ° C. of a film obtained by crystallizing an unstretched film of polyethylene terephthalate (PET) into various crystallinities by heat treatment, and 11 shows PET of 0% crystallinity. Stress-strain curve at 100 ° C, 1
2 is the stress at 100 ° C. of PET having a crystallinity of 3%-
A strain curve 13 indicates a stress-strain curve at 100 ° C. of PET having a crystallinity of 12%.

In order to obtain the crystallinity as described above, the amorphous unstretched film is heat-treated before being longitudinally stretched,
Crystallization is preferably performed. At this time, the temperature of the heat treatment is (Tg + 10 ° C.) or more, (Tm-50) from the glass transition point (Tg) and melting point (Tm) of the resin.
C) or less is preferable. More preferably (Tg + 20
C.) or higher and (Tm-100.degree. C.) or lower. When the heat treatment temperature is (Tg + 10 ° C.) or lower, the effect of crystallization by heat treatment is small, or a large amount of time is required to obtain the desired crystallinity. If it is higher than (Tm-50 ° C), it is difficult to control the crystallinity, and the film is too soft, which causes trouble in handling the film during heat treatment. Further, the above heat treatment is preferably performed using a heating roll. As the heating roll, it is preferable that the surface is treated with Teflon, silicone rubber, or non-adhesive such as metal plating in which Teflon is dispersed. It is also preferable to perform the heat treatment in an oven. The oven may be heated without air, but a type in which hot air is blown onto the film is preferably used in terms of heating efficiency. The means for gripping the film in the oven is not particularly limited, but rolls that pass water through the roll to prevent sticking to the surface, or tenter type gripping both ends of the film can be used. It is preferably used. Further, a heating and levitation treatment apparatus is preferably used, in which hot air is blown from the lower surface of the film to perform heat treatment while floating the film.
In the case of the heating levitation treatment apparatus, there is no problem of film sticking, and since the film is gripped on the surface by air pressure, even a softened film at the time of heating can be heat-treated without problems in running property.

By the way, in the method of heat-treating the amorphous unstretched film, there are problems that a high temperature is required to obtain a desired crystallinity and it is difficult to control the crystallinity.
Here, the present inventors have made it possible to easily control the crystallinity at a relatively low temperature, by preliminarily orienting the film and then heat-treating, and also under the conditions of the pre-orientation and the temperature of the heat treatment. We have found that it can save a lot of time. Here, the preliminary orientation is, for example, in the case of a polyethylene terephthalate film, the film temperature is 80 ° C. or higher and 100 ° C. or lower, more preferably 85 ° C. or higher and lower than 95 ° C., and 1.5 times or more and 2.5 times or less, and more preferably 1.8
It can be applied by stretching at a draw ratio of not less than 2.3 times and not more than 2.3 times. By doing so, the birefringence Δn of the film
It becomes a range of 0.010 to 0.040. here,
If the stretching temperature is lower than 80 ° C., uneven stretching occurs, which is not preferable. If the stretching temperature exceeds 100 ° C., the effect of pre-orientation for controlling crystallization is small. When the draw ratio is less than 1.5 times, the effect of crystallization control by the preliminary orientation is small,
When it exceeds 2.5 times, it is not preferable because unevenness in the thickness of a component having a wave number of 1.00 (1 / m) or more and 2.00 (1 / m) or less occurs in the stretching for preliminary orientation.

By providing such a pre-orientation, the subsequent heat treatment is carried out at a relatively low temperature of 90 to 120 ° C. in the case of polyethylene terephthalate and a short time of 0.5 to 5 seconds. The crystallinity of can be obtained. Moreover, depending on the condition of the preliminary orientation, the crystallinity reaches a predetermined value instantaneously, and the crystallinity hardly changes even when the heat treatment time changes, so that the crystallinity can be controlled very easily. Since the heat treatment after the preliminary orientation is performed at a relatively low temperature in a short time, it is preferable to use a heating roll. Of course, an auxiliary heating means such as an infrared heater may be used.

Thus, the method of stretching for pre-orientation is preferable not only for improving the thickness unevenness but also for increasing the film forming speed by increasing the stretching ratio and improving the productivity. It is a thing.

The crystallized film thus obtained is heated by a heating roll at 80 to 120 ° C. and subjected to pre-orientation, 1.5 to 10 times in the machine direction, and when not pre-orientated. 2 to 15 times, longitudinal stretching in a single step or in multiple steps, the longitudinal stretching ratio becomes 2 to 15 times in total.
Cool with rolls at ~ 50 ° C. Incidentally, this longitudinal stretching,
It may be carried out immediately after the heat treatment for crystallization in the former stage, in this case, heating for stretching can be used in combination with heat treatment,
This is preferable because the equipment can be simplified. Further, when the stretching temperature is lower than the heat treatment temperature, when the stretching is performed while cooling after the heat treatment for crystallization, the thick portion is stretched at a high temperature due to the thickness unevenness before the longitudinal stretching. Easily, and the thickness after longitudinal stretching is corrected to be thin,
The thickness unevenness after the longitudinal stretching can be further reduced, which is preferable.

Further, as a result of further diligent studies by the present inventors, surprisingly, the resin was ejected from the die in a supercooled state without crystallization as described above, and an appropriate take-up ratio ( By casting with a draft ratio), the stress-strain curve rises as shown in FIG.
It was found that stress and strain have a one-to-one correspondence. Although the reason for this is not clear, although it cannot be called a crystal, a nuclear structure close to a very fine crystal is developed in the film, and this nucleus exerts a cross-linking point effect to stand a stress-strain curve. I think I will raise it. Reference numeral 21 in FIG. 2 denotes a stress-strain curve at 100 ° C. of a film obtained by discharging polyethylene terephthalate (PET) from a die at 240 ° C. and casting it at a draw ratio (draft ratio) of 20. Here, when the temperature of the resin discharged from the die is set to the melting end temperature (Tme) or higher, the effect of raising such a stress-strain curve is small, and it is set to the temperature falling crystallization start temperature (Tcb) or lower. In this case, as described above, the resin starts to crystallize, which causes surface roughness of the film, abnormal extrusion, uneven flow, and solidification over time. If the take-up ratio in casting is less than 5, the effect of raising the stress-strain curve is small, probably because a fine nuclear structure is unlikely to occur. On the other hand, when the take-up ratio exceeds 50, the casting is not stable, and on the contrary, the uneven thickness is apt to be deteriorated. The thus-obtained film having a fine nuclear structure is heated by a heating roll at 80 to 120 ° C., longitudinally stretched in the longitudinal direction by 2 to 15 times, in one stage or in multiple stages, and rolled at 20 to 50 ° C. Cool in groups.

When the film is oriented biaxially, subsequently, both ends of the film are guided by a tenter while being held by clips, and Tg
To 2 to 10 times in the transverse direction in a hot air atmosphere heated to ~ Tm. The biaxially stretched film is heat-set in the tenter at a temperature not lower than the stretching temperature and not higher than Tm in order to impart flatness and dimensional stability. The film is gradually cooled to room temperature and then wound up.

[Evaluation Method of Physical Properties] (1) Thermal Characteristics As a differential scanning calorimeter, a robot DSC “RDC220” manufactured by Seiko Denshi Kogyo Co., Ltd. was used, and as a data analysis device, a disk station “SSC / 520” manufactured by the same company.
0 "was used to melt and hold about 10 mg of a sample on an aluminum pan at 300 ° C for 5 minutes, quenching and solidifying with liquid nitrogen, and then raising the temperature from room temperature at a heating rate of 20 ° C / minute. The peak temperature of the glass transition point observed at this time was Tg, the starting temperature of the melting endothermic peak was Tmb, the peak temperature was Tm, and the peak ending temperature was Tme. After that, when the temperature was raised to 300 ° C., it was melted and held at 300 ° C. for 5 minutes as it was, and then the temperature was lowered at a temperature lowering rate of 20 ° C./min. At this time, the starting temperature of the crystallization exothermic peak during temperature falling was Tcb, the peak temperature was Tc, and the peak ending temperature was Tce.

(2) Thickness unevenness in the longitudinal direction of the film Anritsu Corporation film thick tester "KG6"
01A "and an electronic micrometer" K306C "are used to measure the thickness of the film continuously sampled in the lengthwise direction of the film to a width of 30 mm and a length of 10 m. The transport speed of the film was 3 m / min. R = Tmax-Tmin is obtained from the maximum thickness Tmax (μm) and the minimum value Tmin (μm) at a length of 10 m, and the thickness unevenness (%) = R / Tave × from R and the average thickness Tave (μm) of the length of 10 m. It was calculated as 100.

(3) Fourier analysis of film thickness unevenness in the longitudinal direction At the time of measuring the film thickness unevenness described above, the output from the electronic micrometer is digitized through an analog / digital converter (A / D converter). I imported it into a computer. At this time, the output voltage of the electronic micrometer,
To optimize the input voltage of the A / D converter, a preamplifier may be provided between the electronic micrometer and the A / D converter if necessary. In the present invention, the output of the electronic micrometer is supplied to an A / D converter “ADX-98” manufactured by Canopus Electronics Co., Ltd. through a self-made preamplifier.
E "and a dedicated trigger unit" ADT-98E ", and a personal computer" P "manufactured by NEC Corporation
C-9801VM "was loaded. The data acquisition software used the self-made. Data acquisition is 0.195 during thickness unevenness measurement of 10 m length.
1024 points were sampled at an interval of 2 seconds (0.195 seconds x 1024 x 3m /
Min / 60 sec / min = 9.98 m, and captures thickness unevenness data of 9.98 m). Of course, there is no need to be limited to these devices, and there are many known devices having similar functions. The thus-acquired data was subjected to a fast Fourier transform (FFT) process in the above-mentioned computer by using a self-made software. At this time, when the film forming time (second) converted from the film forming speed of the film and the transport speed at the time of measurement is taken as the variable of the flow direction, the intensity distribution with respect to the frequency (Hz) is obtained by the FFT process, and , If the length of the film (m) is taken as the variable of the flow direction, the intensity distribution with respect to the wave number (1 / m) is obtained by the FFT processing. Regarding the FFT processing, for example, the theory of Fourier transform is described in “Engineer's Mathematics 1” first edition (Kyoritsu Publishing Co., Ltd. Kyoritsu Zensho 516), and about the method of FFT processing in “Optical Engineering” first edition (Kyoritsu Publishing Co., Ltd.). This is a known process such as described. Here, the acquired data was subjected to Fourier transform processing as shown in the following formula 1 to obtain the sum of spectrum intensities.

[0041]

[Equation 1]

Here, the real part of Xn is a _n and the imaginary part is b.
_{As n} , the spectrum intensity Pw ⁿ can be expressed by the following equation 2.

[0043]

[Equation 2]

On the other hand, the wave number for n has a measurement length of 10 m.
To n / 10 (1 / m), and the sum of the spectral intensities from the wave numbers α to β is nα, nβ corresponding to α and β.
As shown below,

[0045]

(Equation 3)

The sum of all spectral intensities is 1≤n≤
It becomes the sum in (N / 2-1), and the total spectrum intensity sum is expressed by the following expression 4.

[0047]

[Equation 4]

(4) Birefringence By a polarizing microscope equipped with Berek compensator,
The retardation Rd of the film was determined. Rd was divided by the film thickness to obtain birefringence.

(5) Resin Temperature The resin temperature in the die was measured by forming a hole into which a rod-shaped thermocouple is inserted at a desired measurement point, inserting the thermocouple, and providing a seal for preventing resin leakage. The temperature of the land portion outlet of the die was measured by measuring the temperature of the discharged resin with a thermocouple just below the die.

(6) Film Temperature Using a non-contact radiation thermometer "Thermometer 505" manufactured by Minolta Camera Co., Ltd., the spot was measured at the portion where the film temperature was to be measured. At this time, the emissivity ε is 0.
95 was used.

(7) Crystallinity A density gradient tube made of an aqueous solution of sodium bromide was prepared and
Measure the density of the film at ° C. From this density d, the crystallinity (%) = (d−da) / (dc−da) × 100. Here, da is an amorphous density, dc is a perfect crystal density, and in the case of polyethylene terephthalate, from literature values,
da = 1.335 g / cm ³ , dc = 1.445 g / c
It was m ^3.

(8) Stress-strain curve Using a biaxial stretching device manufactured by Toyo Seiki Seisaku-sho, Ltd., the sample was adjusted to 90 mm × 90 mm, preheated for 20 seconds in a predetermined temperature atmosphere, and then stretched at 2000%. / Min,
The stress was measured by a strain gauge attached to a clip, which was stretched in the longitudinal direction under the restraint in the lateral direction.

(9) Film processing suitability: A film wound into a width of 500 mm was unwound from an unwinder and fed at a conveying speed of 20 m / min to an oven treatment apparatus manufactured by Inoue Metal Industry Co., Ltd. It was heat-treated and wound into a length of 100 m. At that time,
"X" indicates that the end of the rolled-up film protruded beyond 10 mm due to meandering and became uneven, and the end projection was 5 mm or more and 10 mm or less, or less than 5 mm during processing. The case where wrinkles were observed was marked with “Δ”, and the case where the protrusion of the end portion was less than 5 mm and no wrinkles were observed during processing was marked with “◯”.

(10) Casting take-up ratio (draft ratio) The cross-sectional area of the die is S (m ² ), and the amount of resin discharged is Q (kg /
), The take-up speed of the cast is V (m / min), and the density of the resin at the time of extrusion is d (g / cm ³ ), the take-up ratio (draft ratio) = V / {Q / (60000 × d × S) } Was set.
When polyethylene terephthalate is used as the resin, the resin temperature during extrusion is 220 to 290 ° C. and d = 1.2.
0 (g / cm ³ ) was used.

[0055]

【Example】

Example 1 As a thermoplastic resin, polyethylene terephthalate having an intrinsic viscosity of 0.65 was used. When thermal characteristics were measured using DSC, Tg: 69 ° C., Tmb: 240 ° C., Tm:
255 ° C, Tme: 268 ° C, Tcb: 203 ° C, T
c: 188 ° C, Tce: 174 ° C. The pellets of polyethylene terephthalate are vacuum dried at 180 ° C. for 3 hours, supplied to an extruder, and melted at 290 ° C.
It was supplied to the molding die. As the die, a manifold die having a lip gap of 1 mm and a land length of 25 mm was used. The land portion of the die has a structure in which a plurality of holes having a diameter of 7 mm are formed in the width direction and water can be passed through the holes to cool the land. The temperature of the die hopper is 290 ° C, and the temperature of the land is 25
The cooling water at 0 ° C. was cooled by passing a flow rate of 30,000 cm ³ / min. In this state, the resin was extruded, and the film extruded from the die was rapidly cooled and solidified on a casting drum whose surface temperature was kept at 25 ° C. while applying static electricity. The take-up ratio at this time was 4. The temperature of the resin at the die entrance is 290
C., the resin temperature at the land inlet was 286.degree. C., and the resin temperature at the land outlet was 247.degree. This film was subsequently supplied to a longitudinal stretching machine, heated to a film temperature of 93 ° C. by a plurality of heating rolls, and pre-stretched by 2.0 times. The birefringence after the pre-stretching was 0.022. Then, heat treatment was performed for 4 seconds at a film temperature of 115 ° C. with a plurality of heating rolls, and the crystallinity was set to 5.4%. After that, the film was cooled to 100 ° C. and stretched 2.0 times. Then, the obtained film is introduced into a tenter, and
Preheated in a hot air atmosphere of ℃, and transversely stretched 3.6 times in a hot air atmosphere of 100 ℃, heat set in a hot air atmosphere of 220 ℃ for 5 seconds, while gradually cooling the film uniformly, from the tenter The film was drawn out, and both ends of the film were trimmed and wound up to obtain a biaxially oriented film having a thickness of 12 μm.

Table 1 shows the conditions of each step of forming the obtained film, and Table 2 shows the measured physical properties such as thickness unevenness and processability. It was possible to obtain a film having a small thickness unevenness, a small thickness unevenness component in each wave number region, high thickness homogeneity, and no meandering or wrinkling in the secondary processing.

Example 2 In Example 1, the flow rate of the cooling water in the land portion was set to 52,000.
The film was changed to cm ³ / min to obtain a biaxially stretched film. The resin temperatures at the die inlet, the land portion inlet, and the land portion outlet were 290 ° C., 284 ° C., and 226 ° C., respectively. Table 1 shows the conditions of each film forming step of the obtained film, and Table 2 shows measured physical properties such as thickness unevenness and processability. 0.15
It was possible to obtain a film having a smaller thickness unevenness component in the wave number region of up to 0.45 (1 / m), high thickness uniformity, and no meandering or wrinkling in the secondary processing.

Example 3 In Example 1, a biaxially stretched film was obtained without passing cooling water through the land portion. The resin temperatures at the die inlet, the land portion inlet, and the outlet were 290 ° C., 288 ° C., and 278 ° C., respectively. The conditions of each film forming process of the obtained film are shown in Table 1.
Table 2 shows the measured physical properties such as thickness unevenness and processability.
Shown in The thickness unevenness component was large in the wave number region of 0.15 to 0.45 (1 / m), and the thickness unevenness of the entire film was slightly large. Although some meandering was observed in the secondary processing, it was within the practical range because the thickness unevenness component in the wave number range of 1.00 to 2.00 (1 / m) was small.

Example 4 In Example 1, a biaxially stretched film was obtained without passing cooling water through the land portion. The resin temperatures at the die inlet, the land portion inlet, and the outlet were 290 ° C., 288 ° C., and 278 ° C., respectively. Further, the longitudinal stretching is heated to a film temperature of 90 ° C. by a plurality of heating rolls and stretched 2.2 times to obtain a birefringence of 0.2.
032 and immediately set the film temperature to 1 with multiple heating rolls.
It was heated to 05 ° C. and heat-treated for 3 seconds to give a crystallinity of 8.4%. Then, the film temperature was cooled to 100 ° C. and stretched 1.7 times. Other conditions are the same,
A biaxially stretched film was obtained. Table 1 shows the conditions of each film forming step of the obtained film, and Table 2 shows measured physical properties such as thickness unevenness and processability. By improving the thickness unevenness in the longitudinal stretching, the thickness unevenness component in the wave number region of 0.15 to 0.45 (1 / m) is also dragged to be small, and a film free from meandering and wrinkling in the secondary processing can be obtained. It was

Comparative Example 1 In Example 1, the flow rate of the cooling water in the land portion was set to 80,000.
The film was changed to cm ³ / min to obtain a biaxially stretched film. The temperature at the die entrance, land entrance, and exit is 290 ° C,
It was 282 ° C and 195 ° C. The resin started to solidify with the passage of time, and a film could not be obtained.

Example 5 In Example 1, longitudinal stretching was carried out by heating the film to a film temperature of 90 ° C. with a plurality of heating rolls and stretching the film 3.3 times in one step. The other conditions were the same, and a biaxially stretched film was obtained.
Table 1 shows the conditions of each film forming step of the obtained film, and Table 2 shows measured physical properties such as thickness unevenness and processability.
Although the thickness unevenness component in the wave number region of 0.15 to 0.45 (1 / m) is small, the thickness unevenness component in the wave number region of 1.00 to 2.00 (1 / m) is large, which is within the practical range. In the secondary processing, wrinkles were observed.

Example 6 In Example 5, the cast take-up ratio is 20,
The other conditions were the same, and a biaxially oriented film having a thickness of 2.5 μm was obtained. The conditions of each film forming step of the obtained film are shown in Table 1 and the measured physical properties such as thickness unevenness and processability are shown in Table 2.
Shown in Compared to Example 5, 1.00 to 2.00 (1 /
The thickness unevenness component in the wave number region of m) is also small, and the workability is improved.

Comparative Example 2 In Example 1, a biaxially stretched film was obtained without passing cooling water through the land portion. The resin temperatures at the die inlet, the land portion inlet, and the outlet were 290 ° C., 288 ° C., and 278 ° C., respectively. Further, the longitudinal stretching is heated to a film temperature of 95 ° C. with a plurality of heating rolls and stretched 2.0 times to obtain a birefringence of 0.
018 and immediately set the film temperature to 1 with multiple heating rolls.
It was heated to 05 ° C. and stretched 2.5 times. The crystallinity before stretching was almost 0%. The other conditions were the same, and a biaxially stretched film was obtained. Table 1 shows the conditions of each film forming step of the obtained film, and Table 2 shows measured physical properties such as thickness unevenness and processability. Since the resin temperature between L and D is high, 0.
The thickness unevenness component is large in the wave number region of 15 to 0.45 (1 / m), and although multi-stage stretching is performed in the longitudinal stretching, 1.00 to 2.00 (1
/ M) has a large thickness unevenness component, and the overall thickness unevenness is large, and the meandering is large in the secondary processing, and wrinkles are also generated, and the film is not suitable for processing.

Comparative Example 3 In Example 2, a biaxially stretched film was obtained without passing cooling water through the land portion. The resin temperatures at the die inlet, the land portion inlet, and the outlet were 290 ° C., 288 ° C., and 278 ° C., respectively. Further, in the longitudinal stretching, the film was heated to a film temperature of 90 ° C. by a plurality of heating rolls and stretched 3.3 times in one step.
Table 1 shows the conditions of each film forming step of the obtained film, and Table 2 shows measured physical properties such as thickness unevenness and processability.
Since the resin temperature between L and D is high, 0.15 to 0.45 (1
/ M) has a large thickness unevenness component in the wave number range, and
Since the longitudinal stretching is a conventional one-stage stretching,
The thickness unevenness component at 2.00 (1 / m) was also large, and the thickness unevenness of the entire film was large, and meandering was large in the secondary processing, and wrinkles were also observed, resulting in a film having poor processability.

[0065]

[Table 1]

[0066]

[Table 2]

[0067]

As is apparent from the above description, the thermoplastic resin film of the present invention has remarkably improved thickness uniformity, and troubles such as meandering and wrinkling during secondary processing can be avoided. it can. Moreover, the manufacturing method is not necessarily limited to the method described in the present invention, but it is a method that requires only a small modification of the existing equipment and is easy to control the conditions. Further, cooling of the land portion of the die also has an effect that it is difficult for the die streaks and oligomers to be generated.

[Brief description of drawings]

FIG. 1 is a stress-strain curve at 90 ° C. to 110 ° C. of an unstretched film of polyethylene terephthalate (thickness: 200 μm).

FIG. 2 is a stress-strain curve at 100 ° C. of a film obtained by crystallizing an unstretched film of polyethylene terephthalate into various crystallinities by heat treatment and a film discharged and collected in a supercooled state at 100 ° C.

[Explanation of symbols]

1 Stress-strain curve of amorphous unstretched PET at 90 ° C 2 Stress-strain curve of amorphous unstretched PET at 100 ° C 3 Stress-strain curve of amorphous unstretched PET at 110 ° C 11 PET with 0% crystallinity Stress at 100 ℃-
Strain curve 12 Stress at 100 ° C. of PET with 3% crystallinity −
Strain curve 13 Stress-strain curve of PET having a crystallinity of 12% at 100 ° C. 21 Stress-strain curve of PET cast at a resin temperature of 240 ° C. and a draw ratio of 20 at 100 ° C.

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display area C08L 67:02

Claims (7)

[Claims] 1. The thickness unevenness in the longitudinal direction of the film is 5
(%) Or less and 0.15 (1 / m) or more and 0.45 (1 / m) when Fourier analysis of the waveform of the thickness unevenness is performed
Ratio Pw1 of spectrum intensity sum Pw1 in the following wave numbers to spectrum intensity sum PwT in all wave number bands
/ PwT is 0.2 or less, a thermoplastic resin film having excellent thickness uniformity. 2. The thickness unevenness in the longitudinal direction of the film is 5
(%) Or less, and 1.00 (1 / m) or more and 2.00 (1 / m) when Fourier analysis of the waveform of the thickness unevenness is performed
Ratio Pw2 of spectrum intensity sum Pw2 in the following wave numbers to spectrum intensity sum PwT in all wave number bands
/ PwT is 0.15 or less, a thermoplastic resin film having excellent thickness uniformity. 3. The thermoplastic resin film having excellent thickness uniformity according to claim 1 or 2, wherein Pw1 / PwT is 0.2 or less and Pw2 / PwT is 0.15 or less. 4. A thermoplastic resin film having excellent thickness uniformity according to claim 1, wherein the thermoplastic resin is polyester. 5. The method according to claim 1, which is biaxially oriented.
A thermoplastic resin film having excellent thickness uniformity according to any one of 1. 6. The resin according to claim 1, wherein the temperature of the resin discharged from the die is lower than the melting end temperature (Tme) and higher than the temperature falling crystallization start temperature (Tcb). The method for producing a thermoplastic resin film having excellent thickness uniformity according to claim 1. 7. The thickness according to claim 1, further comprising a step of increasing the crystallinity of the film to 0.5% or more and 25% or less by heat treatment in the longitudinal stretching step. A method for producing a thermoplastic resin film having excellent uniformity.