JP2001334571A - Biaxially oriented polyethylene naphthalate film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate a winding nature having a trend bringing about in the case of using a biaxially oriented heat-set polyethylene naphthalate film in a rolled state. SOLUTION: The biaxially oriented polyethylene naphthalate film comprises characteristics of a fraction of a crystal area when measured by an NMR measuring instrument of 35.0% or more and a fraction of the crystal area measured by the NMR instrument when the film is heat treated at 190 deg.C for 4 min of a reduction of 0.3% or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film which can be used for various purposes, and more particularly, to a polyester film required for use in an electric insulating material, a magnetic material, a photographic material, a packaging material, and the like. The present invention relates to an improvement of a biaxially oriented polyethylene naphthalate film which is excellent in transparency and mechanical strength, is hardly rolled when transported and stored in a roll shape, and is easy to handle.

[0002]

2. Description of the Related Art A representative example of a polyester film,
Biaxially oriented, heat-set polyethylene naphthalate film has excellent mechanical strength, thermal properties, and transparency, and is required to have low oligomer properties and heat resistance. It is used as a support for magnetic recording materials, photographic materials, etc., which require high mechanical strength, transparency and heat resistance. This film is often used by taking out a necessary amount from a form wound in a roll. When the film is stored in a roll, if the film is rolled over time, a medium-sized sheet such as a magnetic card, a floppy (registered trademark) disk, an electrical insulating sheet, a radiographic material, etc. It cannot be used in the field where it is required to be non-curled when used in the form of (1). Further, in any field, when the film requires surface treatment and coating work, if the film is wound, there is a problem that the surface treatment and coating work cannot be performed uniformly.

[0003] As described above, the polyester film often used in the form of a roll has been desired to eliminate the curl, and various treatments have been conventionally performed for this purpose. In one conventional technique, in order to eliminate the curl of a thermoplastic resin film, the glass transition temperature of this film is defined as Tg.
Heat treatment for 1 to 1500 hours has been proposed (see, for example, JP-A-51-16358). Further, in another conventional technique, a film is formed from Tg + 25 ° C. to Tg + 5 ° C.
It has been proposed that heat treatment is performed by passing through a heating region in a temperature range of 20 seconds to 300 seconds (Japanese Patent Laid-Open No. 9-2).
No. 81650).

In these prior arts, the film is heat-treated at a temperature lower than the glass transition temperature for a long time, or the film is heat-treated at a temperature higher than the glass transition temperature for a short time to make it difficult to curl. When the film hardly curled in this way is heated again at a temperature higher than the glass transition temperature, there is a disadvantage that the film is easily curled again. As described above, even if this conventional technique is used as it is for processing of a polyethylene naphthalate film, the curling cannot always be eliminated.

[0005]

The problem to be solved by the present invention is that the biaxially oriented polyethylene naphthalate film, which has a particularly high mechanical strength and can be made thin, is hardly curled and has a curl characteristic. It is to provide a biaxially oriented polyethylene naphthalate film excellent in handling and capable of easily estimating the level of polyethylene naphthalate.

[0006]

The basic object of the present invention is to provide a biaxially oriented polyethylene naphthalate film having a crystal domain fraction of 35.0 as measured by an NMR (nuclear magnetic resonance) measuring apparatus. % Or more, and when the film is heat-treated at 190 ° C. for 4 minutes, the fraction of the crystal region measured by an NMR (nuclear magnetic resonance) measuring device is reduced by 0.3% or more. To provide a biaxially oriented polyethylene naphthalate film.

[0007] The object of the present invention is to study whether there is a relationship between the curling improvement effect and the change in the microstructure of the polyethylene naphthalate film, and as a result of intensive studies,
Since the fractions of the crystalline region and the amorphous region measured by an NMR (nuclear magnetic resonance) measuring device change with the heat treatment, the curling improvement effect (the effect of eliminating the curling) can be improved by using a polyethylene Find out that it can be unambiguously explained by the change in physical quantity caused by the structural change of the phthalate film, and specify the fraction of the crystalline region and the amorphous region of the biaxially oriented polyethylene naphthalate film and the thermal change ratio thereof Can be solved.

[0008] The object of the present invention is to provide a biaxially oriented polyethylene naphthalate film which is heat-treated at 190 ° C for 4 minutes, and the decrease in the fraction of crystal regions measured by an NMR (nuclear magnetic resonance) measuring apparatus is 0.3%. % Or more and the greater the decrease, the higher the curling improvement effect can be obtained. However, when a biaxially oriented polyethylene naphthalate film is heat-treated at 190 ° C. for 4 minutes, NMR (nuclear magnetic resonance) measurement is performed. 0.8% fraction of crystal area measured by the instrument
It has been found that it is more preferable that the material has a characteristic of decreasing by at least 1.5% or more.

The biaxially oriented polyethylene naphthalate film of the present invention preferably contains at least 85% by weight of an ethylene-2,6-naphthalenedicarboxylate unit.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The biaxially oriented polyethylene naphthalate film of the present invention has a crystal domain fraction of 35.5 when measured with an NMR (nuclear magnetic resonance) measuring apparatus.
Support having at least 0% and comprising the film,
NMR (nuclear magnetic resonance) when heat treated at 90 ° C for 4 minutes
It has such characteristics that the fraction of the crystal region measured by the measuring device is reduced by 0.3% or more, preferably 0.8% or more, and more preferably 1.5% or more.

A method for achieving the characteristic values of the present invention will be described below.
It is not limited to the method described below.

In order to achieve the characteristic values of the present invention, there are the following three methods. (1) A biaxially oriented polyethylene naphthalate film is heated for a long time at a temperature lower than its glass transition temperature. (2) Heating the biaxially oriented polyethylene naphthalate film at a temperature higher than its glass transition temperature but close to the glass transition temperature for a short time. (3) The biaxially oriented polyethylene naphthalate film is heat-treated while applying a magnetic field in a range from a temperature lower than its glass transition temperature to a temperature lower than its melting point.

In particular, the method (3) is the most preferable method, which will be described in more detail below. Assuming that the melting point of the polyethylene naphthalate film is Tm and its glass transition temperature is Tg, the polyethylene naphthalate film is 30 ° C. lower than its glass transition temperature Tg (Tg−3).
0 ° C) lower than the melting point Tm by 20 ° C (Tm-20 ° C)
Heat treatment in a temperature range up to and applying a magnetic field,
It has been found that the heat treatment time can be greatly reduced and the curl can be largely eliminated, as compared with the degree of curl improvement obtained by simply heat treatment.

Although the reason is not clear, it is considered that application of a strong magnetic field promotes the orientation of the polymer chains of polyethylene naphthalate. It is easily presumed that this phenomenon applies not only to polyethylene naphthalate but also to polyethylene terephthalate and other polymers in general.However, the present invention is directed to a polyethylene naphthalate film. Do not mention.

The strength of the magnetic field applied to the polyethylene naphthalate film is not particularly limited depending on the temperature and time of the heat treatment, but generally depends on the temperature of the heat treatment. Must be long enough. Maximum magnetic field strength is 40T (tesla)
Degree, preferably 0.002 to 30 T (tesla), more preferably 0.02 to 30 T (tesla), and most preferably 0.1 to 20 T (tesla). When the naphthalate film is heat-treated for 30 seconds to 500 hours, curling of the film can be largely eliminated.

When heating the biaxially oriented polyethylene naphthalate film while applying a magnetic field, the direction in which the magnetic field is applied may be such that the lines of magnetic force are perpendicular to the film surface, or may be oblique or horizontal. Here, "the magnetic field lines are horizontal to the film surface" means that the magnetic field may be applied in all directions such as the longitudinal direction and the width direction in the film surface.

A method for treating a film while applying a magnetic field may be to apply heat to a biaxially oriented polyethylene naphthalate film substrate and apply a magnetic field while transporting the film. The magnetic field may be applied while applying heat in the placed state.

The means for generating a magnetic field is not particularly limited.
A permanent magnet or the like may be used in addition to a coil or the like represented by a solenoid coil. Further, a device that generates a magnetic field intermittently (for example, a pulse magnetic field generating device or the like) may be used.

The mechanism by which the curl is eliminated by the above treatment is not clear, but when the treatment is performed with the combination of the heat treatment temperature, the heat treatment time, and the magnetic field as described above, the biaxial orientation and the heat set before the treatment are obtained. It is thought to be caused by the fact that the incomplete structure of the polyethylene naphthalate (PEN) film, in which the crystalline and amorphous structures are mixed, slowly changes to a more completely stable structure. It is presumed that the curl when wound around a core or the like is caused by slipping of a PEN molecular chain in a bulky amorphous region which is oriented to some extent and can easily move with slight heat. At this time, it is thought that if a strong magnetic field is applied, these movements will be promoted and the orientation will be increased. Therefore, the disordered molecular orientation is repaired, the close-packing of the crystal chains and the conversion of the amorphous region to the crystal region occur, and as a result, the slip of the PEN molecular chain when wound around a core or the like is suppressed. , It will be hard to be curled.

As described above, the biaxially oriented and heat-set polyethylene naphthalate film (PEN film) is subjected to a heat treatment at a temperature lower than the glass transition temperature for a long time, or is relatively close to the glass transition temperature which is higher than the glass transition temperature. Heat treatment at a temperature for a short time, or from a temperature lower than the glass transition temperature (Tg−30 ° C.) to a temperature lower than the melting point (Tg).
(m-20 ° C.), a heat treatment while applying a magnetic field changes the microstructure and makes it difficult to wind up. However, the treated polyethylene naphthalate film is again transformed into a glass transition of the polyethylene naphthalate film. If only heat is applied at a temperature equal to or higher than the temperature (Tg = 123 ° C.) without applying a magnetic field, curling is likely to occur and the material returns to its original state. This means that the obtained microstructure is lost by the heat treatment. Therefore, it is essential to apply a magnetic field in order to heat-treat the film at a temperature higher than the glass transition temperature Tg so that the film is hardly curled. Here, “heat setting” means applying heat at a temperature equal to or higher than the vertical and horizontal stretching temperatures (Heat set) in order to obtain dimensional stability after biaxially orienting (biaxially stretching) the polyethylene naphthalate film. The term "heat treatment" means that heat is further applied under the above-mentioned conditions to make the film less curled. `` Heat treatment '' is a process in which the curl is hardly attached by heat treatment, again at a temperature higher than the glass transition temperature of the polyethylene naphthalate film, without applying a magnetic field, and without fixing both ends of the film, that is, the molecular Heating in a free state without restricting the direction means a process for eliminating this effect.

It is considered that the unwinding of the PEN film is caused by the formation and manifestation of the above-mentioned structure by a combination of physical forces such as a heating temperature, time, and an externally applied magnetic field.

Hereinafter, specific examples of the present invention will be described in detail. In the present invention, polyethylene naphthalate is a polyethylene naphthalate containing naphthalenedicarboxylic acid as a main acid component and ethylene glycol as a main glycol component. As the naphthalenedicarboxylic acid, for example, 2,6-naphthalenedicarboxylic acid, 2,7-
Examples thereof include naphthalenedicarboxylic acid and 1,5-naphthalenedicarboxylic acid.
-Naphthalenedicarboxylic acid is preferred. When the content of the ethylene-2,6-naphthalenedicarboxylate unit is 85% by weight or more based on the polyester, transparency,
A film having excellent mechanical strength and dimensional stability can be obtained. If the main acid component is not naphthalenedicarboxylic acid, for example, curling occurs when molded into a film, which is not preferable.

Other acid components include aromatic dicarboxylic acids (for example, terephthalic acid, isophthalic acid, diphenylethanedicarboxylic acid, diphenyldicarboxylic acid, diphenyletherdicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenylketonedicarboxylic acid, anthracenedicarboxylic acid, etc.) ); Aliphatic dicarboxylic acids (eg, adipic acid, sebacic acid, etc.); alicyclic dicarboxylic acids (eg, cyclohexane-1,4-dicarboxylic acid, etc.).

As glycol components other than ethylene glycol constituting the polyethylene naphthalate film, aliphatic glycols (for example, those having 3 to 3 carbon atoms such as trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, decamethylene glycol, etc.) Polymethylene glycol, cyclohexanedimethanol, etc.); aromatic diols (eg, hydroquinone, resorcin, 2,2-bis (4-hydroxyphenyl) propane, etc.); polyalkylene glycols (polyoxyalkylene glycols)
(For example, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, etc.).

The polyethylene naphthalate used in the present invention may be an oxycarboxylic acid such as an aromatic oxyacid such as hydroxybenzoic acid or an aliphatic oxyacid such as ω-hydroxycaproic acid, as long as the effects of the present invention are not impaired. Can be copolymerized or combined.

Further, the polyethylene naphthalate of the present invention contains a tricarboxylic or polyfunctional polycarboxylic acid or a polyhydroxy compound in an amount within a range substantially in a linear form and as long as the effects of the present invention are not impaired. It can also be polymerized.

The polyethylene naphthalate of the present invention may further include, for example, a lubricant, a pigment, a dye, an antioxidant, a light stabilizer, a light-shielding agent (eg, silica) as long as the surface flatness and thermal stability of the film are not impaired. Additives such as cross-linked polystyrene, terazole blue, Irganox, cobalt, etc.).

The polyethylene naphthalate in the present invention can be produced by a conventional polyester production method, but it is preferably produced by transesterification, that is, by reacting a lower alkyl ester of naphthalenedicarboxylic acid with ethylene glycol. Preferably, in this reaction, part of the lower alkyl ester of naphthalenedicarboxylic acid may be substituted with another acid component, and part of the glycol may be substituted with another glycol component.

Examples of such lower alkyl esters of naphthalenedicarboxylic acid include, for example, dimethyl ester, diethyl ester, dipropyl ester and the like, with dimethyl ester being particularly preferred.

The polyethylene naphthalate polymer of the present invention preferably has an intrinsic viscosity of 0.4 to 0.9 (dl / g).
2-tetrachloroethane / p-chlorophenol (1:
3% by weight) Measured at 35 ° C. with a mixed solvent). When a mechanical strength is required for a polyethylene naphthalate polymer, it is necessary to increase the intrinsic viscosity. In such a case, the intrinsic viscosity is 0.4 to 0.6 (dl / g).
Degree of polyethylene naphthalate polymer is melt-polymerized by a known method, and thereafter, the polymer obtained by the melt polymerization method is subjected to solid-state polymerization to have an intrinsic viscosity of 0.7 to 0.9 (dl /
g) to obtain a polyethylene naphthalate polymer.

Next, a method for producing the biaxially oriented polyethylene naphthalate film of the present invention using the polymer thus obtained will be described below.

The method for obtaining the unstretched sheet and the method for uniaxially stretching in the longitudinal direction can be performed by a conventionally known method. For example, polyethylene naphthalate as a raw material is formed into pellets,
C., heated in air for 2 to 4 hours to crystallize at least the surface layer, dehumidified by hot air drying or vacuum drying at 140 to 170 ° C. for 3 to 6 hours, and supplied to the extruder with the water content in the pellets reduced to 50 ppm or less. I do. It is melt-extruded, extruded into a sheet from a T-die, brought into close contact with a cooling drum by an electrostatic application method or the like, and cooled and solidified to obtain an unstretched sheet.

Next, the obtained unstretched sheet is passed through a plurality of roll groups and / or a heating device such as an infrared heater, etc., and the glass transition temperature Tg of polyethylene naphthalate (Tg of homo-PEN varies depending on the copolymerization ratio. About 1
(23 ° C.) to (Tg + 70 ° C.),
This is a method in which one-stage or multi-stage longitudinal stretching is performed. The stretching ratio is usually in the range of 2.5 to 6 times, and it is necessary to make the subsequent transverse stretching possible.

Next, the polyethylene naphthalate film uniaxially stretched in the machine direction obtained as described above was used.
The film is transversely stretched in a temperature range from the glass transition temperature Tg to (Tg + 70 ° C.), and then heat-set. The transverse stretching ratio is usually 3 to 6 times, and the ratio of the longitudinal and transverse stretching ratios is determined by measuring the physical properties of the obtained biaxially oriented film and appropriately adjusting the film to have preferable characteristics.

The heat setting is performed at a temperature higher than the final transverse stretching temperature and at a temperature not higher than (Tm-20 ° C.). PEN
In the case of a film, the film is usually heat-set in a temperature range of 150 ° C to (Tm-20 ° C) for 1 to 300 seconds.

At this time, within a temperature range from the final heat setting temperature or lower to Tg or higher, 0.1 mm is set in the width direction and / or the longitudinal direction.
It is preferable to perform a 1 to 10% relaxation treatment. The heat-fixed film is usually cooled to Tg or less, cut at clip holding portions at both ends of the film, and wound up in a roll.

For the purpose of improving the strength, known stretching such as multi-stage longitudinal stretching, re-longitudinal stretching, and re-longitudinal and transverse stretching can also be performed. The generated film waste may be reused as a raw material for the same kind of film after being pulverized or subjected to a granulation treatment or a depolymerization / repolymerization treatment as required.

The biaxially oriented polyethylene naphthalate film obtained as described above still has a property of being easily rolled, and therefore has a glass transition temperature (Tg) of the film.
= 123 ° C), for example, (Tg-5
C) to (Tg-30C) in a temperature range of 0.1 to 1500.
By performing the heat treatment for a long time, a significant curling improvement effect can be obtained (the processing method (1) above).

Alternatively, a heat setting process for forming a biaxially oriented polyethylene naphthalate film, or after completion of the heat setting of the film formation, in a temperature range of (Tg + 25 ° C.) to (Tg + 5 ° C.) for 20 seconds to 300 seconds. When the heat treatment is performed while cooling so as to pass through, the curling improvement effect can be obtained (the treatment method (2) above).

Alternatively, a heat setting process for forming a biaxially oriented polyethylene naphthalate film, or
After completion of the heat setting of the film formation, the temperature and time of the heat treatment in a temperature range from a temperature lower than the glass transition temperature of the polyethylene naphthalate film (Tg-30 ° C) to a normal heat setting temperature range (Tm-20 ° C). The magnetic flux density is about 40 T (tesla) at the maximum,
Preferably, a magnetic field of 0.002 to 30 T (tesla) is applied, more preferably 0.02 to 30 T (tesla), and most preferably 0.1 to 20 T (tesla).
By performing the heat treatment for 0 second to 500 hours, curling can be largely eliminated (the processing method (3)).

The glass transition temperature (Tg) and melting point (Tm) of the polyethylene naphthalate film used in the methods (2) and (3) can be determined by the following method. (Method of measuring glass transition temperature (Tg)) Glass transition temperature (Tg) of biaxially oriented polyethylene naphthalate film
Is a sample film 1 using a differential scanning calorimeter (DSC).
When 0 mg was heated at a rate of 10 ° C./min in a nitrogen stream, the arithmetic mean of the temperature at which the temperature began to shift from the baseline and the temperature at which the temperature returned to the new baseline, or when an endothermic peak appeared at Tg, The temperature showing the maximum endothermic peak is determined as Tg (° C.). (Measurement method of melting point (Tm)) The melting point (Tm) of the biaxially oriented polyethylene naphthalate film is determined by the glass transition temperature (Tm).
g) using a differential scanning calorimeter (DSC) as in the measurement of
When 10 mg of a sample film is heated at a rate of 10 ° C./min in a nitrogen stream, the temperature at which the maximum endothermic peak of melting is obtained is determined as Tm (° C.).

The film thus treated is cooled to room temperature, wound up, and stored as needed until it is sent to the next step. In the above processing, the case where only the biaxially oriented polyethylene naphthalate film is processed has been described. However, this film is used as a support (support), and the surface thereof is previously subjected to surface treatment, undercoating, emulsion coating, and other processes. It is needless to say that the present invention includes a case where the surface-treated material is subjected to a heat treatment while similarly changing the combination of the temperature and the magnetic field.

The biaxially oriented polyethylene naphthalate film of the present invention has a crystal area fraction of 35.0% or more as measured by an NMR measuring apparatus and is free from restraining both ends of the film at 190 ° C. for 4 minutes. When the heat treatment was performed in a free state, the fraction of the crystal region measured by the NMR measurement apparatus was 0.1%.
Treated in the manner described above to have a property of decreasing by more than 3%. The biaxially oriented polyethylene naphthalate film having such characteristics has a curl degree of about 130 m ^-1 or less after the heat treatment of the film obtained by the following method.
If the degree of curl of the support is too large, transportability, workability,
Coating suitability is poor, which is not preferable.

The biaxially oriented polyethylene naphthalate film of the present invention has a NM
More preferably, the fraction of the crystal region measured by the R measuring device is reduced by 0.8% or more. The biaxially oriented polyethylene naphthalate film having such properties has a curl degree after heat treatment of about 115 m ^-1 or less, as determined by the following method.

When the biaxially oriented polyethylene naphthalate film of the present invention was heat-treated at 190 ° C. for 4 minutes, the NM
Most preferably, the fraction of the crystal region measured by the R measuring device is reduced by 1.5% or more. The biaxially oriented polyethylene naphthalate film having such properties has a curl degree after heat treatment of about 95 m ^-1 or less, as determined by the following method.

When the biaxially oriented polyethylene naphthalate film of the present invention was heat-treated at 190 ° C. for 4 minutes, NMR
The upper limit at which the fraction of the crystal region measured by the measuring device decreases is
Although not particularly limited, it is about 4.0%. In the biaxially oriented polyethylene naphthalate film having such properties, the lower limit of the degree of curl after heat treatment determined by the following method is about 5 m ^-1 .

When the biaxially oriented polyethylene naphthalate film contains 85% by weight or more of ethylene-2,6-naphthalenedicarboxylate units, it is very excellent in transparency, mechanical strength, dimensional stability and the like. A film is obtained.

The method for evaluating the physical properties defining the film in the present invention is described below. <Solid high-resolution ¹³ C NMR (nuclear magnetic resonance) measurement> ¹³ C
The NMR spectrum was measured by JEOL FT-N
The physical properties of the film were measured using an MR EX270 solid-state high-resolution NMR (nuclear magnetic resonance) measuring device (observation frequency: 270 MHz). 90 ° pulse width of ¹³ C; 4.2 μS ¹ H decoupling width; 1.2 mT repetition time; 2 seconds Number of integrations: 5000 times Spectrum width: 27000 Hz Data point: 8200 points The two methods described above were adopted, and information on the state of molecular motion was obtained depending on the method. 1) ¹³ C CP (Cross Polarization)
Method: 63.1 ppm was defined as a peak corresponding to the crystal region by a method effective for measuring the ¹³ C nucleus spectrum of the polymer crystal region in which the molecular motion was restricted. 2) ¹³ C CPST (Pulse Transfer) method: 61.5 ppm was defined as a peak corresponding to the amorphous region by a method effective for measuring the ¹³ C nucleus spectrum of the amorphous region of the polymer in which the molecular motion was released.

(Analysis of Crystalline Region and Amorphous Region Size of Polyethylene Naphthalate Sample) The size of the crystalline region and amorphous region of the polyethylene naphthalate (PEN) sample was determined by measuring ¹³ CCP- Peaks corresponding to the CH ₂ CH ₂ amorphous region of the MAS spectrum (61.
5 ppm) and a peak corresponding to the crystalline region (63.1 p
pm) to computer-fit
Using ting), waveform separation was performed assuming a GAUSS distribution as a function of signal, and the intensity of each peak was expressed as a fraction (%). Therefore, the sum of the fraction (%) of the crystalline region and the fraction (%) of the amorphous region is 100%.

(Curl after Heat Treatment) A film sample having a sample size of 15 cm (vertical direction at the time of manufacture) × 50 mm (horizontal direction at the time of manufacture) was heated at a constant temperature and constant humidity (23 ° C. × 55%).
(RH) after conditioning for one day under the conditions of (RH).
This is wound around a 0 mm core, 60 ° C x 20% R
Heat was applied under H conditions for 3 hours. Then, it is allowed to cool for 1 hour under a constant temperature and constant humidity atmosphere and released from the core,
After a lapse of minutes, the curl degree of the film sample was measured.

The degree of curl is represented by 1 / r (m ^-1 ). This r represents the radius of curvature of the curled film,
The unit is m (meter). The curl degree was evaluated from the average of five pieces in the following four grades. From the viewpoint of handling, a grade of ○ or more is preferable. ◎: Curling degree is 95 m ⁻¹ or less, the curling is very weak, and the handling in the process is very good. ◎: curl degree exceed 95 m ^-1, at 115m ^-1 or less, although somewhat curled than those described above ◎◎, the handling in the process, as no practical problem at all. ：: The curl degree exceeds 115 m ^-1 and is 130 m ^-1
In the following, the curls are slightly curled from those of the above ◎, but have no practical problem in handling in the process. X: Curling degree exceeding 130 m ^-1 , tight curling, practically problematic in handling in the process.

When the film is used for a magnetic recording material such as a floppy disk, the magnetic layer and / or the back layer on both sides coated on the film (support) are peeled off, and the film is exposed to light. When used for materials,
Even when the emulsion layer and / or the back layer on both sides coated on the film (support) are peeled off and the same evaluation as above is performed, almost the same degree of curl can be obtained.
The coating layer may be peeled off from the photographic material, and the curl degree of the film (support) may be measured.

The thickness of the biaxially oriented polyethylene naphthalate film of the present invention is not particularly limited.
The thickness is preferably 0 μm, and may be appropriately set according to the purpose of use.

[0054]

EXAMPLES Examples will be described in detail below along with comparative examples, but it goes without saying that the present invention is not limited to these examples.

Transesterification of 2,6-naphthalenedicarboxylic acid dimethyl ester (100 parts) and ethylene glycol (60 parts) with manganese acetate tetrahydrate (0.03 part (1.23 mol)) as a transesterification catalyst was carried out according to a conventional method. After the reaction, 0.023 parts (1.64 mol) of trimethyl phosphate was added to substantially terminate the transesterification reaction.

Further, 0.024 parts of antimony trioxide (0.
After the addition, a polycondensation reaction was carried out in the usual manner under a high temperature and high vacuum to obtain polyethylene naphthalate having an intrinsic viscosity of 0.60 (dl / g).

The polyethylene naphthalate pellets were dried at 170 ° C. for 4 hours and then supplied to an extruder hopper.
It melted at a melting temperature of 315 ° C. This molten polymer was extruded through a slit die onto a rotating cooling drum at 30 ° C. to obtain an unstretched film having a thickness of 743 μm. The unstretched film obtained in this way is stretched 3.0 times in the machine direction at 130 ° C., and subsequently supplied to a stenter.
The film was stretched 3.3 times in the transverse direction at ℃. The obtained biaxially oriented film was heat-set at 225 ° C. to obtain a polyethylene naphthalate film having a thickness of 75 μm. The intrinsic viscosity of this film was 0.56 (dl / g).

[Examples 1 to 4 and Comparative Examples 1 and 2] The thus obtained polyethylene naphthalate film having a thickness of 75 μm was cut into a size of A4 and placed in an air oven. Is heat treatment at 108 ° C. for 25 hours, Example 2 is heat treatment at 108 ° C. for 35 hours, Example 3 is heat treatment at 108 ° C. for 50 hours, Example 4 is
The heat treatment was performed at 108 ° C. for 1000 hours. In Comparative Example 1, the heat treatment was not performed in an air oven.
In Comparative Example 2, heat treatment was performed at 108 ° C. for 1 hour.
A final product (support) of a biaxially oriented polyethylene naphthalate film was obtained.

The biaxially oriented polyethylene naphthalate film was subjected to the measurement of the crystal area by the NMR measuring apparatus and the curl degree after the heat treatment described above. Was measured. Subsequently, these samples (Examples 1 to 4 and Comparative Example 2) were heat-treated at 190 ° C. for 4 minutes in an air oven for free, and the crystal fraction was determined. Became identical. The crystal fraction, the degree of curl in curl, and the reduction ratio of the crystal fraction were measured, and the results are shown in Table 1.

As can be seen from Table 1, each of the biaxially oriented polyethylene naphthalate films according to Examples 1 to 4 has a crystal domain fraction of 3 as measured by an NMR measuring apparatus.
It was 5.0% or more.

When the biaxially oriented polyethylene naphthalate film according to Example 1 was subjected to free heat treatment at 190 ° C. for 4 minutes, the fraction of the crystal region measured by the NMR measurement apparatus was reduced by 0.3%, and the film was rolled up. Was good.

Next, when the biaxially oriented polyethylene naphthalate film according to Example 2 was heat-treated at 190 ° C. for 4 minutes, the fraction of the crystal region measured by the NMR measurement apparatus was reduced by 0.8%, and The biaxially oriented polyethylene naphthalate films according to Examples 3 and 4 had better elimination of looseness, and when they were heat-treated at 190 ° C. for 4 minutes, the fractions of the crystal regions measured by an NMR measurement apparatus were 1% each. It decreased by 4.5% and 4.5%, and the degree of elimination of curling was the best.

On the other hand, when the biaxially oriented polyethylene naphthalate film of Comparative Example 2 was heat-treated at 190 ° C. for 4 minutes, the fraction of the crystal region measured by the NMR measurement apparatus was reduced by only 0.1%. Only like the biaxially oriented polyethylene naphthalate film of Comparative Example 1 without heat treatment, a large amount of curl remained.

[0064]

[Table 1]

[Examples 5 to 8 and Comparative Examples 1 and 3] A polyethylene naphthalate film having a thickness of 75 µm obtained in the same manner was applied to a polyethylene naphthalate film in an air oven to give a magnetic flux density of 7.0 T (tesla). Examples 5 to 7 and Comparative Example 3 were conducted while applying a magnetic field in the thickness direction to the glass transition temperature (Tg) of the polyethylene naphthalate film.
= 123 ° C). That is, in Example 5, the film was heated at 115 ° C. for 45 seconds, in Example 6, the film was heated at 115 ° C. for 60 seconds, and in Example 7, the film was heated at 115 ° C. for 200 seconds. . On the other hand, in Example 8, the polyethylene naphthalate film was subjected to a heat treatment at 140 ° C., which is higher than the glass transition temperature (Tg = 123 ° C.), for 300 seconds.

On the other hand, in Comparative Example 3, the polyethylene naphthalate film was used for its glass transition temperature (Tg = 123).
C) at a temperature of 115 ° C or less, and a magnetic flux density of 7.0 T
Heat treatment was performed for 30 seconds while applying a magnetic field of (Tesla) in the thickness direction.

Using these biaxially oriented polyethylene naphthalate films in the same manner as in Examples 1 to 4 and Comparative Examples 1 and 2, <Measurement of Crystal Region by NMR Measurement Apparatus> and <Curl Degree After Heat Treatment>> According to the measuring method, the fraction of the crystal region and the degree of curl were measured. Continued
When these samples (Examples 5 to 8 and Comparative Example 3) were heat-treated in an air oven at 190 ° C. for 4 minutes free of charge and the crystal fraction was determined, it was the same as that of Comparative Example 1 (untreated). became. The crystal fraction, the degree of curl in winding, and the rate of decrease in the crystal fraction were measured, and the results are shown in Table 2.

As can be seen from Table 2, each of the biaxially oriented polyethylene naphthalate films according to Examples 5 to 8 has a crystal domain fraction of 3 as measured by an NMR measuring apparatus.
It was 5.0% or more.

In the biaxially oriented polyethylene naphthalate film according to Example 5, when the film was heat-treated at 190 ° C. for 4 minutes free of charge, the fraction of the crystal region measured by the NMR measurement apparatus was reduced by 0.4%. The degree of curling was good.

Next, when the biaxially oriented polyethylene naphthalate film according to Example 6 was heat-treated at 190 ° C. for 4 minutes, the fraction of the crystal region measured by the NMR measurement apparatus was reduced by 0.9%, and The biaxially oriented polyethylene naphthalate films according to Examples 7 and 8 had better elimination of looseness, and when these were heat-treated at 190 ° C. for 4 minutes, the fractions of the crystal regions measured by an NMR measurement apparatus were 1% each. 5.6% and 5.1%, and the degree of elimination of curling was the best.

On the other hand, when the biaxially oriented polyethylene naphthalate film of Comparative Example 3 was heat-treated at 190 ° C. for 4 minutes, the fraction of the crystal region measured by the NMR measurement apparatus was reduced by only 0.1%. Only like the biaxially oriented polyethylene naphthalate film of Comparative Example 1 without heat treatment, a large amount of curl remained.

[0072]

[Table 2]

Considering the results in Table 1 and Table 2, the film obtained by heating the biaxially oriented polyethylene naphthalate film with or without applying a magnetic field was measured by an NMR measuring apparatus. The fraction of the crystalline region at the time is 35.0% or more, and when the film is heat-treated at 190 ° C. for 4 minutes, the fraction of the crystalline region measured by the NMR measurement device is reduced by 0.3% or more. It can be seen that the presence of is good enough to eliminate curling so as not to cause a practical problem.

In particular, when a biaxially oriented polyethylene naphthalate film is heat-treated at 190 ° C. for 4 minutes, the degree of reduction of the curl increases as the decrease in the fraction of crystal regions measured by an NMR measuring device increases. For example, the degree of reduction of the fraction is 0.8% or more, and
It is understood that when the content is 5% or more, curling can be more effectively eliminated.

It should be noted from the results of the above study that when the film is subjected to a heat treatment while applying a magnetic field to eliminate the curl, the processing time is greatly reduced as compared with a case where no magnetic field is applied, and Can be obtained with high efficiency.

[0076]

As described in detail above, the biaxially oriented polyethylene naphthalate film having the characteristics of the present invention is characterized by various excellent properties possessed by the biaxially oriented polyethylene naphthalate film, for example, excellent mechanical properties ( (Mechanical strength), excellent thermal properties (heat resistance), excellent electrical properties, excellent optical properties (transparency), etc. It is excellent, and therefore can be handled in a roll form for various uses such as for electric insulating materials, magnetic materials, photographic materials, and packaging materials.

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Claims (4)

[Claims] The biaxially oriented polyethylene naphthalate film has a fraction of crystal domains of at least 35.0% as measured by an NMR (nuclear magnetic resonance) measuring apparatus, and is heat-treated at 190 ° C. for 4 minutes. A biaxially oriented polyethylene naphthalate film having such a property that the fraction of a crystal region measured by an NMR (nuclear magnetic resonance) measuring device is reduced by 0.3% or more. 2. The biaxially oriented polyethylene naphthalate film according to claim 1, wherein the film is
A biaxially oriented polyethylene naphthalate film, characterized in that, when heat-treated at 4 ° C. for 4 minutes, the fraction of crystal regions measured by an NMR (nuclear magnetic resonance) measuring device is reduced by 0.8% or more. 3. The biaxially oriented polyethylene naphthalate film according to claim 1, wherein said film is a biaxially oriented polyethylene naphthalate film.
A biaxially oriented polyethylene naphthalate film, characterized in that, when heat-treated at 4 ° C. for 4 minutes, the fraction of crystal regions measured by an NMR (nuclear magnetic resonance) measuring device is reduced by 1.5% or more. 4. The biaxially oriented polyethylene naphthalate film according to claim 1, 2 or 3, wherein
85 2,6-naphthalenedicarboxylate units
A biaxially oriented polyethylene naphthalate film, characterized in that the content is at least 10% by weight.