JPH11302406A - Biaxially oriented polyester film and its preparation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare a biaxially oriented polyester film suitable for a magnetic recording medium, a printing ribbon, a capacitor, a packaging, or the like, with an excellent film manufacturing stability as well as a high strength to deal with a trend towards a thinner film. SOLUTION: This biaxially oriented polyester film is composed of a polyethylene terephthalate and a copolyester having a methogen group in its main chain, T1ρ value of the carbon atoms of the ethylene glycol component in the polyester film being >=90 msec and <=135 msec. According to the manufacturing method, the film is stretched at an overall drawing ratio in the film longitudinal and transverse directions in the range of 40-100 times.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film obtained by greatly improving the physical properties and quality of a conventional biaxially oriented polyester film, and more specifically, to a magnetic recording film having a high elastic modulus and excellent film forming stability. The present invention relates to a biaxially oriented polyester film suitable for a medium, a printer ribbon, a capacitor, a packaging, and the like, and a method for producing the same.

[0002]

2. Description of the Related Art Biaxially stretched polyester films have been used for various applications because of their excellent thermal stability, dimensional stability and mechanical properties, but their usefulness is particularly well known as a base film for magnetic tapes and the like. is there. In recent years, further thinning of the base film has been demanded in order to reduce the weight, size, and long-term recording of equipment. In recent years, there has been a very strong tendency for thin films for thermal transfer ribbons and capacitors. However, as the film becomes thinner, the mechanical strength becomes insufficient and the stiffness of the film becomes weaker and the film becomes easier to expand. The characteristics deteriorate. Further, in the thermal transfer ribbon application, the flatness of the ribbon at the time of printing is not maintained, causing printing unevenness and overtransfer, and in the capacitor application, there is a problem that the dielectric breakdown voltage is lowered.

[0003] For this reason, various methods have heretofore been studied for strengthening a base film. Representative examples include a method of performing vertical / re-horizontal stretching represented by JP-A-3-190719 and a vertical / horizontal stretching method represented by JP-A-54-56674 and JP-A-49-99169. There is a method of performing multi-stage stretching of two or more stages.

[0004] As one method of increasing the elastic modulus, a method of increasing the degree of molecular orientation by improving stretching or the like is generally used. However, if the intrinsic viscosity of the film is low,
If the molecular orientation is excessively attempted to increase the elastic modulus, the film is inevitably broken during stretching, and there is a limit in improving the elastic modulus.

[0005]

SUMMARY OF THE INVENTION The present invention has been achieved as a result of studying to solve the problems in the prior art described above. That is, an object of the present invention is to highly plane-orientate, not only one of the film longitudinal direction and the width direction, but also have a balanced strength in the two directions, to be thin, and to have a stable film formation. An object of the present invention is to provide an excellent biaxially oriented polyester film and a method for producing the same.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, added a specific copolymerized polyester (B) to polyethylene terephthalate (A) and added ethylene glycol to a polyester film. The T1ρ value of the carbon atom of the component is 90 ms or more and 135 ms.
It has been found that a high elastic modulus can be obtained when controlled to be less than ec, and the present invention has been completed. That is, the biaxially oriented polyester film of the present invention comprises polyethylene terephthalate (A) and a copolymerized polyester (B) containing a mesogen group in the main chain, and has a T1ρ value of carbon atom of an ethylene glycol component of the polyester film. 90m
The main feature is a biaxially oriented polyester film characterized by being not less than sec and not more than 135 msec and a method for producing the same.

[0007]

Embodiments of the present invention will be described below.

The polyethylene terephthalate (A) constituting the biaxially oriented polyester film of the present invention is a polymer containing at least 80 mol% of terephthalic acid as an acid component. As for the acid component, a small amount of another dicarboxylic acid component may be copolymerized, and ethylene glycol is used as a main diol component, but another diol component may be added as a copolymer component.

The dicarboxylic acid components other than terephthalic acid include aromatic dicarboxylic acid components such as isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid,
1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 4,4′-diphenyldicarboxylic acid,
4,4′-diphenyletherdicarboxylic acid, 4,4 ′
-Diphenylsulfone dicarboxylic acid and the like can be used. As the alicyclic dicarboxylic acid component, for example, cyclohexanedicarboxylic acid or the like can be used. As the aliphatic dicarboxylic acid component, for example, adipic acid, suberic acid, sebacic acid, dodecanedioic acid and the like can be used. One of these acid components may be used alone, or two or more thereof may be used in combination. Further, an oxyacid such as hydroxyethoxybenzoic acid may be partially copolymerized. Also,
Examples of the diol component other than ethylene glycol include 1,2-propanediol, 1,3-propanediol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, , 6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol, polyalkylene glycol, 2,2′-bis (4′- (β-hydroxyethoxyphenyl) propane and the like can be used. These diol components may be used alone or in combination of two or more.

The copolymer polyester (B) may be added to the polyethylene terephthalate (A) before the polymerization of the polyethylene terephthalate (A), for example, before the esterification reaction, or after the polymerization and before the melt extrusion. It may be added. Before the melt extrusion, the polyethylene terephthalate (A) and the copolymerized polyester (B) may be pelletized.

Copolyester (B) having a mesogen group in the main chain of the biaxially oriented polyester film of the present invention
Is a melt-moldable polyester having a mesogen group in the main chain. For example, an aromatic oxycarbonyl unit,
Polyesters forming an anisotropic molten phase composed of structural units selected from aromatic dioxy units, aromatic dicarbonyl units, alkylenedioxy units and the like.

Preferred examples of the copolymerized polyester (B) having a mesogen group in the main chain used in the present invention include a main chain composed of the following structural units (I), (II), (III) and (IV). Copolymerized polyester having a mesogen group,
A copolymerized polyester having a mesogen group in the main chain consisting of the structural units of (I), (III) and (IV), (I),
One or more selected from copolymerized polyesters having a mesogen group in the main chain composed of the structural units of (II) and (IV).

[0013]

Embedded image (However, R1 in the formula is

Embedded image And R2 is

Embedded image R3 represents one or more groups selected from

Embedded image Represents one or more groups selected from In the formula, X represents a hydrogen atom or a chlorine atom, and the structural unit [((II) + (II
I)] and the structural unit (IV) are substantially equimolar. )
The structural unit (I) is p-hydroxybenzoic acid and / or
Or a structural unit of a polyester formed from 6-hydroxy-2-naphthoic acid, wherein the structural unit (II) is 4, 4 ′
-Dihydroxybiphenyl, 3,3 ', 5,5'-tetramethyl-4,4'-dihydroxybiphenyl, hydroquinone, t-butylhydroquinone, phenylhydroquinone, 2,6-dihydroxynaphthalene, 2,7-dihydro The structural unit formed from an aromatic dihydroxy compound selected from xinaphthalene, 2,2'-bis (4-hydroxyphenyl) propane and 4,4'-dihydroxydiphenyl ether, and the structural unit (III) was formed from ethylene glycol Structural unit, structural unit (IV)
Is terephthalic acid, isophthalic acid, 4,4′-diphenyldicarboxylic acid, 2,6-naphthalenedicarboxylic acid,
Selected from 1,2-bis (phenoxy) ethane-4,4'-dicarboxylic acid, 1,2-bis (2-chlorophenoxy) ethane-4,4'-dicarboxylic acid and 4,4'-diphenyletherdicarboxylic acid The structural units formed from the aromatic dicarboxylic acids are shown below.

In the case of a copolymerized polyester comprising the above structural units (I), (II) and (IV), R1 is

Embedded image And R2 is

Embedded image R3 is at least one member selected from

Embedded image Those which are at least one kind selected from

In the case of a copolymerized polyester having a mesogen group in the main chain consisting of the structural units (I), (III) and (IV), R1 is

Embedded image And R3 is

Embedded image Is particularly preferred.

The structural units (I), (II) and (II)
In the case of the copolymerized polyester having a mesogen group in the main chain consisting of I) and (IV), R1 is

Embedded image And R2 is

Embedded image And R3 is

Embedded image Is particularly preferred.

The copolymerization amount of the above structural units (I), (II), (III) and (IV) is optional, but the following copolymerization is preferred in view of fluidity and compatibility with polyethylene terephthalate (A). Preferably, it is an amount.

In the case of a copolymerized polyester comprising the above structural units (I), (II), (III) and (IV), [(I) to the above structural unit [(I) + (II) + (III)] ) + (II)] is 5 to 95 mol%, preferably 20 to 80%, and most preferably 40 to 75 mol%. In addition, the structural unit [(I) + (II) + (II
The mole fraction of (III) with respect to (I)) is 95 to 5 mol%, preferably 80 to 20 mol%, and most preferably 60 to 25 mol%. The molar ratio of the structural units (I) / (II) is preferably 75/25 to 95 from the viewpoint of fluidity.
/ 5, more preferably 78/22 to 93/7. The number of moles of the structural unit (IV) is the same as that of the structural unit [(II)
+ (III)].

In the case of a copolymerized polyester comprising the structural units (I), (III) and (IV), the structural unit (I) is 5 to 95 mol% of [(I) + (III)].
Is preferably 20 to 80 mol%, more preferably 40 to 80 mol%.
75 mol% is most preferred. The structural unit (IV) is substantially equimolar to the structural unit (III).

Further, in the case of the copolymerized polyester comprising the above structural units (I), (II) and (IV), the copolymer is not alone, but may be the structural units (I), (II), (III) and (IV)
And / or a blend polymer of a copolymerized polyester composed of the structural units (I), (III) and (IV).
Also in the case of this blend polymer, as described above,
The molar ratio of [(I) + (II)] to the structural unit [(I) + (II) + (III)] is preferably 5 to 95 mol%, more preferably 20 to 80%, and more preferably 40 to 75 mol. %
Is most preferred.

The term “substantially” in the above description means that the number of the terminal groups of the polyester can be increased to either the carboxyl group terminal or the hydroxyl terminal group, if necessary. This is because the number of moles of the unit (IV) is not completely equal to the total number of moles of the structural unit [(II) + (III)].

When the above-mentioned copolymerized polyester (B) having a mesogen group in the main chain is subjected to polycondensation, in addition to the components constituting the structural units (I) to (IV), 3,3'-
Aromatic dicarboxylic acids such as diphenyldicarboxylic acid, 2,2′-diphenyldicarboxylic acid, aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid and dodecanedioic acid; alicyclic dicarboxylic acids such as hexahydroterephthalic acid; Chlorohydroquinone, methylhydroquinone, 4,4'-dihydroxydiphenylsulfone,
4,4'-dihydroxydiphenyl sulfide, 4,4
Aromatic diols such as' -dihydroxybenzophenone, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, 1,4-cyclohexanediol, aliphatic and alicyclic such as 1,4-cyclohexanedimethanol Diols and m-hydroxybenzoic acid,
Aromatic hydroxycarboxylic acids such as 2,6-hydroxynaphthoic acid, p-aminophenol, p-aminobenzoic acid, and the like can be further copolymerized in a small proportion that does not impair the object of the present invention.

The method for producing the copolymerized polyester (B) having a mesogen group in the main chain in the present invention is not particularly limited, and it can be produced according to a known polyester polycondensation method.

For example, in the above-mentioned method for producing a copolymerized polyester preferably having a mesogen group in the main chain, when the structural unit (III) is not contained, the following (1)
And (2) when the structural unit (III) is contained, the following production method (3) is preferred.

(1) p-acetoxybenzoic acid and 4,
A method of producing from a diacylated aromatic dihydroxy compound such as 4'-diacetoxybiphenyl, 4,4'-diacetoxybenzene and an aromatic dicarboxylic acid such as terephthalic acid by a deacetic acid polycondensation reaction.

(2) The phenolic hydroxyl group is acylated by reacting acetic anhydride with p-hydroxybenzoic acid, an aromatic dihydroxy compound such as 4,4'-dihydroxybiphenyl or hydroquinone, or an aromatic dicarboxylic acid such as terephthalic acid. And then subjecting it to a production process by a deacetic acid polycondensation reaction.

(3) Polyester polymers such as polyethylene terephthalate, oligomers or bis (β-
(Hydroxyethyl) terephthalate or the like, in the presence of bis (β-hydroxyethyl) ester of an aromatic dicarboxylic acid, by the method of (1) or (2).

Although these polycondensation reactions proceed without a catalyst, it is sometimes preferable to add a metal compound such as stannous acetate, tetrabutyl titanate, potassium acetate and sodium acetate, antimony trioxide, and metallic magnesium. .

In the present invention, the melt viscosity ratio of the low-viscosity copolymerized polyester, ie, polyethylene terephthalate (A) (melt viscosity (polyethylene terephthalate) /
A copolymerized polyester which increases the melt viscosity (copolymerized polyester) is preferred. This is because, when a low-viscosity copolymerized polyester is added, the dispersibility in the polyester film is improved, and an increase in the draw ratio and an improvement in the film-forming stability can be more effectively achieved. The melt viscosity ratio is preferably at least 5 or more and 3000 or less, more preferably 50 or more and 3000 or less, and particularly preferably 100 or more and 3000 or less. Therefore, although the melt viscosity of the copolymerized polyester (B) depends on the melt viscosity of the polyethylene terephthalate (A) used, it is 280.
° C and a shear rate of 200 sec ^-1.
Seconds, preferably 0.3 to 10 Pa
Second, more preferably 0.5 to 3 Pa second. On the other hand, the melt viscosity ratio is preferably 5 or more and 3000 or less from the viewpoint of a practical melt viscosity of the polyester film.
Further, by adding an appropriate amount of such an ultra-low-viscosity copolymerized polyester to polyethylene terephthalate (A), the copolymerized polyester is finely dispersed in polyethylene terephthalate and a highly transparent, highly elastic film. Is obtained.

The copolymerized polyester (B) having such a low melt viscosity and which can be particularly preferably used to achieve the object of the present invention is the above-mentioned structural units (I) and (I).
It is a copolymerized polyester consisting of (I), (III) and (IV). This copolymerized polyester is finely dispersed uniformly in polyethylene terephthalate (A).

The polyethylene terephthalate (A) and the copolymerized polyester (B) having a mesogen group in the main chain used in the present invention may be, if necessary, a flame retardant, a heat stabilizer, an antioxidant, an ultraviolet absorber, An organic lubricant such as an inhibitor, a pigment, a dye, a fatty acid ester, or a wax, or an antifoaming agent can be added. In addition, clay, mica, titanium oxide, calcium carbonate, carion, talc, wet or dry silica, colloidal silica, calcium phosphate, barium sulfate, alumina, zirconia, etc., for imparting lubricity, abrasion resistance and scratch resistance Inorganic particles, acrylic acid, or blending organic particles and the like as a constituent of styrene or the like, or include so-called internal particles precipitated by a catalyst or the like added during the polyester polymerization reaction,
Surfactants can be added.

The T1ρ value of the carbon atom of the ethylene glycol component of the biaxially oriented polyester film of the present invention is 90.
It is necessary to be not less than msec and not more than 135 msec. The T1ρ value is an index indicating the local mobility of molecules determined by nuclear magnetic resonance (NMR), and the larger the value, the more strongly the molecule is constrained. Therefore, there is a tendency that the elastic modulus increases as the T1ρ value increases. The T1ρ value is preferably 95 msec or more, more preferably 100 msec.
That is all. When the T1ρ value is less than 90 msec,
The orientation of the molecules in the polyester film becomes weak, and a polyester film having a high elastic modulus cannot be obtained. Although a larger T1ρ value is more preferable,
The upper limit value is 135 msec or less from the practical viewpoint of the current film forming technology of the polyester film.

The T1 value of the carbon atom of the ethylene glycol component of the biaxially oriented polyester film is 40 seconds.
It is preferable that it is not less than c and not more than 60 sec. This T1
The value is an index obtained in the same manner as the above T1ρ value, but is an index representing a molecular motion in a wider range than the molecular motion indicated by the T1ρ value. The T1 value is more preferably 4
It is at least 5 sec, most preferably at least 50 sec.
Similar to the T1ρ value, the larger the value, the more difficult it is for the molecule to move, indicating that the molecule is constrained. Therefore, from the viewpoint of high elastic modulus, the T1 value is preferably 40 seconds or more. The T1 value is also preferably as large as the T1ρ value, but the upper limit of the T1 value is 60 sec or less from the practical viewpoint of the current film forming technology of the polyester film.

The intrinsic viscosity of the biaxially oriented polyester film of the present invention is preferably 0.7 to 3 dl / g. It is preferably from 0.75 to 2.5 dl / g, more preferably from 0.8 to 2 dl / g. As a means for obtaining such a polyester having a high intrinsic viscosity, a method of solid-phase polymerization of a polyester chip is most preferably used. From the viewpoint of mechanical strength and film forming stability, the intrinsic viscosity of the biaxially oriented polyester film is 0.7 dl / g or more, and 3 dl / g from a practical viewpoint such as a driving current value during extrusion and a filtration pressure.
It is as follows.

In the biaxially oriented polyester film of the present invention, the copolymerized polyester (B) having a mesogen group in the main chain is contained in the polyester film in an amount of 0.01 to 10%.
%, More preferably 0.2 to 7% by weight, particularly preferably 0.5 to 5% by weight. From the viewpoints of the temperature rise crystallization temperature, the surface characteristics, the film winding characteristics, and the like, the amount of the copolymerized polyester (B) is preferably 0.01% by weight or more. % By weight or less is preferred.

Further, the biaxially oriented polyester film of the present invention has a sum of elastic modulus in the longitudinal direction and the width direction of 14 GPa to 18 GPa, preferably 15 GPa to 18 GPa.
When used for a long-time recording magnetic tape, the following is the suppression of the elongation of the magnetic tape caused by the tension received from the magnetic head and the guide pins during running,
It is preferable for use as a film for a magnetic recording medium requiring good electromagnetic conversion characteristics.

Although the biaxially oriented polyester film of the present invention may be a single film, another polymer layer, for example, polyester, polyolefin, polyamide, polyvinylidene chloride, acrylic polymer or the like may be laminated thereon. In particular, when the polyester layer is thinly laminated on the surface layer, the thickness (M) of the laminated portion is set to be smaller than the average diameter (N) of the particles contained in the laminated portion (M <N).
1/1000 to 1/2 of M, more preferably 1/1
By setting the ratio to 00/10, it is possible to obtain a film having excellent running properties, slipperiness, and smoothness, and is particularly preferable as a base film for magnetic recording, which emphasizes surface characteristics. Further, in the case of a laminated film of three or more layers made of polyester, productivity and quality can be improved by mixing a recovered material and the like in the central layer. Examples of such particles include, but are not limited to, silicon oxide, magnesium oxide, calcium carbonate, titanium oxide, aluminum oxide, crosslinked polyester, crosslinked polystyrene, mica, talc, kaolin, and the like.

Next, the method for producing the polyester film of the present invention will be specifically described.

Although an example using polyethylene terephthalate having a high intrinsic viscosity is shown here, the production conditions differ depending on the polyethylene terephthalate used.

First, according to a conventional method, bis-β-hydroxyethyl terephthalate (BH) is esterified from terephthalic acid and ethylene glycol, or transesterified between dimethyl terephthalate and ethylene glycol.
T). Next, while transferring this BHT to the polymerization tank,
Heat to 280 ° C. under vacuum to advance the polymerization reaction. Here, a polyester having an intrinsic viscosity of about 0.5 is obtained. At this time, a predetermined amount of the copolymerized polyester (B) may be added. The obtained polyester is subjected to solid-state polymerization in a pellet form under reduced pressure. In the case of solid phase polymerization, after preliminarily crystallizing at a temperature of 180 ° C. or less,
Solid-state polymerization is carried out at ~ 250 ° C under a reduced pressure of about 1 mmHg for 10-50 hours to increase the intrinsic viscosity.

Next, polyethylene terephthalate (A)
And chips of the copolyester (B)
After vacuum drying at ℃ for 3 hours or more, it is supplied to an extruder heated to 280 ° C, filtered by a filter, and extruded into a sheet by a T-die. The polyethylene terephthalate (A) and the copolyester (B) may be mixed together as chips, but in order to enhance dispersibility, a high-concentration copolyester (B) is first used using a twin-screw kneader or the like. )
It is also preferable to prepare a polyethylene terephthalate master chip containing the above and dilute the chip with a polyethylene terephthalate chip. At this time, if necessary, a laminated film of two or more layers may be formed by using two or more extruders, a pinol divided into two or more layers, or a die. It is preferable to use a known filter, such as a sintered metal, a porous ceramic, a sand, or a wire mesh, for removing foreign matter. The sheet extruded from the T-die is adhered and solidified by electrostatic force on a drum cooled to a surface temperature of 25 ° C. to obtain a substantially amorphous cast film. Draft ratio when extruding from a die is preferably 2 to 200, more preferably 5 to 15
0, and most preferably 10 to 100. Alternatively, the undried pellets are supplied to a vented extruder to obtain a non-oriented film in the same manner. Further, a film having a ratio (C / D) of the maximum thickness (C) at the edge portion of the non-oriented film to the thickness (D) at the center in the width direction of the non-oriented film is preferably 2 to 6.

In the present invention, it is necessary to stretch the non-oriented film in a total stretching ratio of 40 to 100 times in the longitudinal direction and the width direction. Preferably, the total stretching ratio is 45 to 95 times, more preferably 50 to 8 times.
The range is five times. The film forming method is not particularly limited, but the following (1) and (2) are preferable.

(1) Polyethylene terephthalate (A)
And copolymerized polyester (B) having a mesogen group in the main chain
When a polyester film having an intrinsic viscosity of 0.7 to 3 dl / g is stretched in the longitudinal (longitudinal) direction and the width (horizontal) direction, the stretching temperature is set to the glass transition temperature of polyethylene terephthalate (A) ( Tg) + 30 ° C.
A method for producing a biaxially oriented polyester film, which is performed at a temperature of Tg + 70 ° C.

(2) Polyethylene terephthalate (A)
And copolymerized polyester (B) having a mesogen group in the main chain
Is stretched biaxially in the vertical and horizontal directions or in the horizontal and vertical directions so that the birefringence (Δn) of the film is 0 to 0.02 and the crystallinity is 10% or less, and then the stretching temperature at the time of the previous transverse stretching A method for producing a biaxially oriented polyester film, wherein the film is stretched in the transverse direction again at a lower temperature, stretched again in the machine direction, and then stretched again in the transverse direction.

When the total stretching ratio is less than 40 times, the orientation of the molecules is weak, the T1ρ value becomes small, and the elastic modulus does not become high. On the other hand, when the total stretching ratio exceeds 100 times, there arises a problem that the film-forming stability is deteriorated.

As a more specific explanation of (1), after a non-oriented polyester film is sufficiently heated by passing it over several rolls which are sufficiently heated, the longitudinal direction is determined by utilizing the peripheral speed difference between the rolls. Stretch in the direction. The stretching temperature is the glass transition temperature (Tg) of polyester + 30 ° C. to (Tg) +70.
° C, more preferably the stretching temperature is (Tg) +3
Stretching at 5 ° C. to (Tg) + 65 ° C. From the viewpoint of performing high-magnification stretching, the stretching temperature is preferably equal to or higher than the glass transition temperature (Tg) of the polyester + 30 ° C. From the viewpoint of effectively orienting the molecules to obtain a high elastic film, the glass transition temperature (Tg) ) A stretching temperature of + 70 ° C or less is preferred.

Next, the obtained film after longitudinal stretching is subsequently stretched in the transverse direction. The stretching in the transverse direction is performed using a known stenter. The stretching temperature is the glass transition temperature of the polyester (Tg) +3 as in the longitudinal stretching temperature.
It is preferably stretched at 0 ° C. to (Tg) + 70 ° C.,
More preferably, the stretching temperature is (Tg) + 35 ° C. to (Tg)
It is in the range of + 65 ° C. Thereafter, re-longitudinal and / or re-horizontal stretching may be further performed, and in the heat setting step, stretching may be performed at least in one or more zones by 1-2 times. Similarly to the longitudinal stretching conditions, the stretching temperature is set at the glass transition temperature (T) of the polyester from the viewpoint of high-magnification stretching.
g) It is preferably + 30 ° C. or lower, and from the viewpoint of effectively aligning molecules, the glass transition temperature (Tg) +70
A stretching temperature of less than or equal to ° C is preferred.

As a more specific explanation of (2), a non-oriented polyester film is first stretched in the longitudinal direction. After passing the polyester film over several heated rolls and sufficiently heating, the polyester film is stretched in the longitudinal direction by utilizing the peripheral speed difference of the rolls. The stretching temperature is preferably the glass transition temperature (Tg) to (Tg) + 60 ° C. of the polyester, and the stretching ratio is preferably 1.2 to 3 times. More preferably, the stretching temperature is (Tg) + 15 ° C. (Tg) +
The stretching ratio is in the range of 1.5 to 2.5 times at 45 ° C.

The obtained film after longitudinal stretching is subsequently stretched in the transverse direction. The stretching in the transverse direction is performed using a known stenter. The transverse stretching temperature (T1) is the glass transition temperature (Tg) of the polyester similarly to the longitudinal stretching temperature.
To (Tg) + 60 ° C., and the stretching ratio is preferably 1.2 to 3 times. More preferably, the stretching temperature is (Tg) + 15 ° C. to (Tg) + 45 ° C., and the stretching ratio is 1. The range is 5 to 2.5 times.

The birefringence (Δn) of the thus-obtained biaxially stretched film is preferably in the range of 0 to 0.02, more preferably in the range of 0 to 0.01. When the birefringence is within the above range, it is possible to obtain a film having a balanced mechanical strength in the longitudinal and lateral directions and excellent heat shrinkage characteristics. When the birefringence exceeds 0.02, the stretchability is deteriorated, and a film having the above-mentioned balanced mechanical strength and excellent heat shrinkage characteristics cannot be obtained.

The crystallinity of the film after longitudinal stretching is as follows:
From the viewpoint of stretchability in the stretching step after longitudinal stretching and film breakage, it is at most 10%, preferably at most 8%, more preferably at most 6%. By forming a biaxially stretched film that satisfies the above ranges of birefringence and crystallinity at the same time, higher mechanical strength can be developed in the subsequent stretching step.

The longitudinally and transversely biaxially stretched film obtained as described above is horizontally and transversely stretched again in the same stenter. The re-stretching temperature (T2) is from the above-mentioned transverse stretching temperature (T1) -10 ° C.
(T1) By performing the stretching at a temperature of -50 ° C and a stretching ratio of 1.2 to 4 times, the film can be stretched without difficulty in the transverse direction, the mechanical strength in the transverse direction can be improved, and the longitudinal stretching is performed again after the transverse stretching. This is preferable because the stretchability when performing transverse re-stretching again becomes good. More preferably, the stretching temperature is equal to the previous transverse stretching temperature (T
1) -20 ° C to (T1) -40 ° C, stretching ratio is in the range of 2 to 3 times. Further, after the transverse stretching, heat treatment can be performed if necessary.

Further, the film obtained as described above is stretched again in the longitudinal direction. Stretching temperature is the previous transverse stretching temperature (T2)
(T2) + 60 ° C. and a draw ratio in the range of 1.2 to 6 times are preferable because a suitable orientation is imparted in the longitudinal direction and the film becomes balanced in the longitudinal and lateral directions. More preferably, the stretching temperature is the re-transverse stretching temperature (T2) + 5 ° C.
(T2) + 55 ° C., the stretching ratio is in the range of 2 to 5 times.
When performing the re-longitudinal stretching, one-stage stretching or multi-stage stretching with a temperature gradient of two or more stages may be performed as long as the stretching temperature and the magnification are within the above-mentioned ranges.

In the present invention, after the longitudinal stretching, the transverse stretching can be performed again. In the re-transverse stretching, the stretching temperature is from the previous longitudinal stretching temperature to the polyester melting temperature (Tm) -20.
It is preferable that the stretching is performed at a temperature in the range of 1.05 to 3 times.

The biaxially stretched film thus obtained is subjected to a heat treatment under tension or relaxation in order to impart flatness and thermal dimensional stability. Taken.

The total thickness of the polyester film in the present invention may be determined depending on the application, as described below as an example.
It can be determined appropriately according to the purpose and the like. Usually, it is preferably 1 μm or more and 20 μm or less for magnetic materials, 1 μm or more and 6 μm or less for thermal transfer ribbons, and 0.1 μm or more and 15 μm or less for capacitors.

Further, in the present invention, a film whose surface is modified by attaching a resin coat layer represented by urethane, acryl, ester, silicon, wax or the like to the surface of the film may be used. In this case, it is preferable to perform the surface modification in the middle of the film forming line from the viewpoint of reducing the production cost.

[0058]

EXAMPLES Examples and comparative examples will be described below to further clarify the effects of the present invention.

The methods for measuring physical properties and the methods for evaluating the effects used here are as follows.

[0060]

[Method for measuring physical properties and method for evaluating effects] (1) T1
ρ value, T1 value—relaxation time (NMR measurement) The T1ρ value and T1 value, which are the relaxation times of the carbon atoms (around 62 ppm) of the ethylene glycol component of the polyester film, were determined as follows.

A spectrometer JNM manufactured by JEOL Ltd.
-GX270, amplifier manufactured by JEOL Ltd., MAS controller NM-GSH27MU, probe manufactured by JEOL Ltd. NM-GSH27T VT. W), the T of ¹³ C nucleus
1 and T1ρ (longitudinal relaxation in rotational coordinates) measurements were performed.

The measurement conditions were as follows: temperature 24.5 ° C., humidity 50R.
H%, static magnetic field strength 6.34 T (tesla), resonance frequencies of ¹ H and ¹³ C are 270.2 MHz and 67.9 MH, respectively.
z. In order to eliminate the influence of the anisotropy of the chemical shift, a MAS (magic angle rotation) method was adopted. The rotation speed was 3.5 to 3.7 kHz. The condition of the pulse sequence is
90 ° to ¹ H, pulse width 4.2μ (micro)
Second, the locking magnetic field strength was set to 62.5 kHz. The contact time of CP (cross-polarization) for transferring the polarization of ¹ H to ¹³ C is 1.5 msec (msec = × 10 ⁻³ sec). The holding time τ of the T1ρ measurement is 0.00
1, 0.5, 0.7, 1, 3, 7, 10, 20, 30,
40 and 50 msec were used. The free induction decay (FID) of the ¹³ C magnetization vector after the retention time τ was measured (FI
High power decoupling was performed during the D measurement to remove the effect of dipole interaction due to ¹ H. Note that 256 integrations were performed to improve the S / N ratio.) The pulse repetition time was between 5 seconds and 15 seconds.

Measurement Conditions Reference Material TMS Measurement Core 67.94 MHz Pulse Repetition Time ACQTM 0.076 sec PD = 12.0 sec Data Point POINT 8K SAMPO 4K Spectral Width 27027 kHz The T1ρ value is usually expressed by Equation 1.

[0064] (Ai: ratio of component to T1ρi) Then, the peak intensity observed for each retention time can be obtained from the slope by semilogarithmic plotting. Here, a two-component system (T1ρ1: an amorphous component, T
(1ρ2: crystal component), and the value was obtained by least squares fitting using the following equation.

I (t) = fa1 · exp (−t / T1ρ1) + fa2 · exp (−t / T1ρ2) fa1: Ratio of component to T1ρ1 fa2: Ratio of component to T1ρ2 fa1 + fa2 = 1 T1ρ = T1ρ1 × fa1 + T1ρ2 × a The T1 value was measured using the Torcia pulse method.
This pulse sequence consists of two parts, the first of which is C
The ¹³ C magnetization obtained in P is tilted in the + z direction, and the subsequent relaxation is measured. In the second series, the magnetization is tilted in the −z direction, and the same observation is performed thereafter, and the difference obtained in both series is integrated. Then, the time change of the ¹³ C magnetization of the first series and the second series is M1 (t) = Mcp exp (−t / T1) + M (∞) ｛1−exp (−t
/ T1)｝ M ₂ (t) = − Mcp exp (−t / T1) + M (∞) ｛1−exp (−
t / T1)｝, and the difference between the two is given by the following equation 2.

Mc (t) = 2Mcp exp (−t / T1) Formula 2 Here, Mcp is ¹³ C magnetization obtained immediately after CP. It should be noted that the ¹ H magnetization is set to 0 in order to satisfy Equation 2. To do so, a 90 pulse of ¹ H is applied at regular intervals τ ¹ during time t. This interval is usually set to 10-20 msec when T2H <τ1 <T1H. From Equation 2, lnMc
(T) was plotted against t to obtain a straight line, and T1 was determined from the slope.

When one resonance line includes a plurality of components having different T1s, it is assumed that Equation 2 holds for each component. That is, a normal multi-component analysis is performed according to Mc (t) = 2ΣMcp, iexp (−t / T1, T), and each T1 value is obtained.
The T1 value was determined in the same manner as the 1ρ value.

(2) Intrinsic viscosity 0.1 g / ml in orthochlorophenol at 25 ° C.
It is a value measured at 25 ° C. in terms of concentration. The unit is represented by dl / g.

(3) Melt viscosity Under the condition of melting point (Tm) + 15 ° C., shear rate 1000 (1/1)
Second) nozzle diameter 0.5mmφ, nozzle length 10
It is a value measured by a height type flow tester using a nozzle of mm. The unit is expressed in Pa · sec. The melting point (T
m) means the endothermic peak temperature (Tm1) observed when the polymerized polymer is measured from room temperature under a heating condition of 40 ° C./min in the differential scanning calorimetry.
After holding at a temperature of + 20 ° C. for 5 minutes, once cooling to room temperature at a temperature lowering condition of 20 ° C./min, and then measuring again at a temperature rising condition of 20 ° C./min, an endothermic peak temperature (Tm) observed
It refers to peak 2).

(4) Birefringence (Δn) The retardation of the film was measured using a Berek compensator under a polarizing microscope, and the birefringence (Δ
n) was determined.

Δn = R / d R: retardation d: film thickness (5) Elastic modulus According to a method specified in JIS-Z1702, using an Instron type tensile tester at 25 ° C., 65
It was measured under an atmosphere of% RH.

(6) Crystallization temperature, melting temperature, glass transition temperature (Tg) A robot DSC “RDC220” manufactured by Seiko Denshi Kogyo Co., Ltd. was used as a differential scanning calorimeter (DSC). Station "SS
5 mg in an aluminum saucer using “C / 5200”
And the temperature was raised from room temperature at a temperature rising rate of 20 ° C./min to obtain a temperature rising DSC curve. From the chart, an exothermic peak due to crystallization is obtained and defined as a crystallization temperature (Tcc). An endothermic peak is obtained along with melting to obtain a melting temperature (Tcc).
m).

The glass transition temperature was measured according to JIS K7121. (7) Break Frequency In the process of producing a biaxially stretched polyester film, the break frequency was determined according to the following criteria.

◎: When tearing from the edge does not occur for 48 hours or more: When tearing from the edge does not occur for 24 hours or more ×: When film formation cannot be continued for 6 hours or more due to tearing from the edge, For reasons such as film stability and yield, a film with a judgment result of ◎ or ○ was judged to be acceptable.

Example 1 (Tables 1, 2, and 3) Pellets of polyethylene terephthalate (intrinsic viscosity 0.75) obtained by a known method and copolymerized polyester pellets having a mesogen group in the main chain shown below were mixed in a ratio of 99/1. The mixture was blended at a ratio of weight%, vacuum dried at 180 ° C. for 3 hours, supplied to an extruder heated to 280 ° C., melt-extruded, and discharged from a T-die into a sheet.

[Copolymer Polyester (B)] As the copolymer polyester having a mesogen group in the main chain, copolymer polyester (B1, melting point 22)
5 ° C., liquid crystal onset temperature 205 ° C., melt viscosity 2 Pa · s)
Was used.

[Copolymerized polyester raw material (B1) having a mesogen group in the main chain] Copolymerization molar ratio Hydroxybenzoic acid 42.5 4,4'-dihydroxybiphenyl 7.5 Ethylene glycol 50.0 Terephthalic acid 57.5 The sheet was brought into close contact with a cooling drum having a surface temperature of 25 ° C. by electrostatic force to be cooled and solidified to obtain a substantially non-oriented film. This film was stretched under the conditions shown in Table 2. First, using a longitudinal stretching machine in which several rolls are arranged, stretching in the longitudinal direction using the peripheral speed difference of the rolls, subsequently performing transverse stretching with a stenter, and further longitudinal stretching with a roll longitudinal stretching machine After heat treatment with a stenter and cooling to room temperature, the film edge was removed to a thickness of 9.5 μm,
A biaxially oriented polyester film having a T1ρ value of 92 msec was obtained.

Table 3 shows the properties of the obtained biaxially oriented polyester film. It was possible to obtain a film having a large T1ρ value, high strength, and excellent film formation stability.

Examples 2 to 4 and Comparative Examples 1 to 2 In Examples 2 to 4, the types and amounts of the copolyesters (B) were the same, and the intrinsic viscosities and stretching conditions of polyethylene terephthalate (A) were as shown in Table 1. This is an example manufactured by changing as shown in FIG. Table 3 shows the properties of the obtained biaxially oriented polyester film. It was possible to obtain a film having a large T1ρ value, high strength, and excellent film formation stability. on the other hand,
Comparative Examples 1 and 2 are examples manufactured under conditions deviating from the stretching conditions of the present invention. As shown in Table 3, the T1ρ value was small, the elastic modulus was small, the film was frequently broken, and the film formation stability was deteriorated.

Tables 1 to 3 summarize the above.

[0081]

[Table 1]

[Table 2]

[Table 3] Example 5 (Tables 4, 5, and 6) In the same manner as in Example 1, a sheet was discharged.

The sheet was brought into close contact with a cooling drum having a surface temperature of 25 ° C. by electrostatic force to be cooled and solidified to obtain a substantially non-oriented film. This film was stretched under the conditions shown in Table 5. First, using a longitudinal stretching machine in which several rolls are arranged, stretching is performed in the longitudinal direction using the peripheral speed difference between the rolls. Subsequently, transverse stretching is performed by a stenter, and further transverse stretching is performed by using the same stenter. After that, after re-longitudinal stretching with a roll longitudinal stretching machine, horizontal stretching again with a stenter,
After heat treatment and cooling to room temperature, the film edge was removed to obtain a biaxially oriented polyester film having a thickness of 10.5 μm.

Table 6 shows the properties of the obtained biaxially oriented polyester film. The T1ρ value was as large as 95 msec, and a film having high strength and excellent film formation stability could be obtained.

Examples 6 to 10 and Comparative Examples 3 to 6 (Table 4,
5, 6) Examples 6 to 8 are examples in which the type and the amount of the copolymerized polyester (B) are the same, and the intrinsic viscosity and stretching conditions of polyethylene terephthalate are changed as shown in Tables 4 and 5. Table 6 shows the properties of the obtained biaxially oriented polyester film. It was possible to obtain a film having a large T1ρ value, high strength, and excellent film formation stability.

In Example 9, a copolymerized polyester (B2) having the following composition was used.

[Copolyester (B)] As the copolyester having a mesogen group in the main chain, a copolyester polycondensed from the following materials (melting point: 235 ° C.,
A liquid crystal onset temperature of 215 ° C. and a melt viscosity of 5 Pa · s) were used.

[Copolymerized polyester raw material (B2) having a mesogen group in the main chain] Copolymerization molar ratio Hydroxybenzoic acid 32.5 4,4'-dihydroxybiphenyl 7.5 Ethylene glycol 60.0 Terephthalic acid 67.5 In Example 10, a copolymerized polyester (B2) having a melt viscosity of 1 Pa · sec was used. Table 6 shows the properties of the biaxially oriented polyester film obtained in Example 10.
It was possible to obtain a film having a large T1ρ value, high strength, and excellent film formation stability.

Comparative Examples 3 and 4 are examples in which the copolyester (B) was not used and the stretching conditions were out of the stretching conditions of the present invention as shown in Table 5. As shown in Table 6, the T1ρ value was small, the elastic modulus was small, the film was frequently broken, and the film formation stability was deteriorated.

Comparative Examples 5 and 6, as shown in Table 5, are examples produced under conditions other than the stretching conditions of the present invention. As shown in Table 6, the T1ρ value was small, the elastic modulus was small, the film was frequently broken, and the film formation stability was deteriorated.

Tables 4 to 6 summarize the above.

[0091]

[Table 4]

[Table 5]

[Table 6] As described above, the biaxially oriented polyester film within the scope of the present invention has high elasticity and excellent film formation stability, but the biaxially oriented polyester film outside the range does not have high elasticity,
The film formation stability also deteriorates.

[0092]

The biaxially oriented polyester film of the present invention comprises polyethylene terephthalate (A) and a copolymerized polyester (B) having a mesogen group in the main chain, and increases the elastic modulus of the biaxially oriented polyester film.
It is intended for film formation stability and can be widely used for various film applications such as magnetic recording, printer ribbon, condenser, and packaging.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI B29L 7:00

Claims (10)

[Claims] 1. A polyethylene terephthalate (A),
It is composed of a copolymer polyester (B) having a mesogen group in the main chain, and the T1ρ value of the carbon atom of the ethylene glycol component of the polyester film is 90 msec or more and 135 m
A biaxially oriented polyester film, which is not more than sec. 2. The T1 value of the carbon atom of the ethylene glycol component of the polyester film is 40 seconds or more and 60 seconds or more.
2. The biaxially oriented polyester film according to claim 1, wherein the ec is equal to or less than ec. 3. The biaxially oriented polyester film according to claim 1, wherein the copolymerization amount of the mesogen group in the main chain of the copolymerized polyester (B) is 5 to 95 mol%. . 4. The copolymerized polyester (B) comprises a copolymerized polyester comprising the following structural units (I), (III) and (IV), and a structural unit comprising (I), (II) and (IV) Copolyester, (I), (II), (II
The biaxially oriented polyester film according to any one of claims 1 to 3, wherein the biaxially oriented polyester film is at least one selected from copolymerized polyesters comprising the structural units (I) and (IV). Embedded image (However, R1 in the formula is R2 represents one or more groups selected from Represents one or more groups selected from In the formula, X represents a hydrogen atom or a chlorine atom, and the structural unit [((II) + (II
I)] and the structural unit (IV) are substantially equimolar. ) 5. The method according to claim 1, wherein the polyethylene terephthalate (A) and the copolymerized polyester (B) have a melt viscosity ratio (ηA / ηB) of from 5 to 3,000. Biaxially oriented polyester film. 6. The biaxially oriented polyester film according to claim 1, wherein the copolyester (B) is contained in the polyester film in an amount of 0.01 to 10% by weight. 7. The biaxially oriented polyester film according to claim 1, wherein the sum of the elastic modulus in the longitudinal direction and the width direction of the polyester film is 14 to 18 GPa. 8. A polyethylene terephthalate (A),
A biaxially oriented polyester film comprising a copolymerized polyester (B) having a mesogen group in the main chain, and stretched in a total stretch ratio of 40 to 100 times in the longitudinal direction and width direction of the film. Production method. 9. When stretching a polyester film having an intrinsic viscosity in the range of 0.7 to 3 dl / g in the longitudinal (longitudinal) direction and the width (horizontal) direction of the film, the stretching temperature is set to polyethylene terephthalate (A). The method for producing a biaxially oriented polyester film according to claim 8, wherein the heat treatment is performed in a range of glass transition temperature (Tg) + 30 ° C. to Tg + 70 ° C. 10. A polyester film is stretched biaxially in the vertical and horizontal directions or in the horizontal and vertical directions so that the birefringence (Δn) of the film is 0 to 0.02 and the crystallinity is 10% or less. 9. The method for producing a biaxially oriented polyester film according to claim 8, wherein the film is further re-transversely stretched in the transverse direction at a temperature lower than the stretching temperature, further longitudinally re-stretched, and then re-transversely stretched.