JP2003132523A - Biaxially oriented polyester film for magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biaxially oriented polyester film for a magnetic recording medium useful as a large capacity digital data storage tape excellent in the durability after the repeated use, in which no error is generated by the deviation of track, and in which the output characteristics are excellent. SOLUTION: The biaxially oriented polyester film for the magnetic recording medium is characterized in that (1) a film is formed by a polyethylene-2,6- naphthalate of which the concentration of the terminal carboxyl group is 10-70 equivalent/10<6> g, (2) the thermal expansion coefficient αt with respect to the width direction of the film is from +15×10<-6> to -10×10<-6> / deg.C, the moisture expansion coefficient αh is from +15×10<-6> to +5×10<-6> /%RH, and the value of (αt+2αh) is equal to or less than 45×10<-6> , (3) the variation of the width between before and after the treatment with the load of 22 MPa in the longitudinal direction of the film for 72 hours at 49 deg.C and 90%RH is equal to or less than 0.35%, and (4) the thickness of the film is 2-7 μm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxially oriented polyester film for a magnetic recording medium, and more specifically, it has excellent durability for long-term use, excellent dimensional stability under high tension, little track deviation, and a particularly large capacity. The present invention relates to a biaxially oriented polyester film for magnetic recording media, which is useful as a digital data storage tape.

[0002]

2. Description of the Related Art As a base film for magnetic recording tape,
Conventionally, biaxially oriented polyethylene terephthalate film has been used. However, in the magnetic recording tape based on this film, the coercive force of magnetic recording is small, and if the tape thickness is made thinner in order to lengthen the length of the tape wound in the cassette and prolong the recording and reproducing time, This causes a problem that running property and durability are deteriorated.

Therefore, in order to solve such problems, it has been proposed to use a biaxially oriented polyethylene-2,6-naphthalate film having a high Young's modulus as a base film.

However, even with a magnetic recording tape using a high Young's modulus biaxially oriented polyethylene-2,6-naphthalate film, it is necessary to further reduce the tape thickness in order to achieve a longer recording / reproducing time. Moreover, it is necessary to further raise the molecular orientation by stretching to improve the Young's modulus of the film, but at that time, some problems become apparent.

That is, as the degree of orientation of the film is increased, the tearability of the film is deteriorated, the number of breaks during film formation is increased, and the productivity is deteriorated. Therefore, there is a strong demand for solving this problem as the recording density of the magnetic recording tape is increased.

On the other hand, in data storage applications that employ a linear track system such as QIC, DLT, super DLT, LTO, etc. having a higher capacity, the track pitch is extremely narrowed in order to realize a high capacity tape. As a result, there is a problem that a track shift is caused by a dimensional change in the tape width direction and an error occurs. These dimensional changes are due to changes in temperature and humidity,
This is due to shrinkage over time in the width direction that occurs when repeatedly running in a high temperature and high humidity state under high tension. If this dimensional change is large, a track shift will occur and an error will occur during electromagnetic conversion. Especially, in the latter case, the tape thickness becomes remarkable as the recording capacity of the tape is increased, and the dimensional change becomes a new issue. This time-dependent shrinkage in the width direction can be improved by increasing the longitudinal Young's modulus of the base film, but on the other hand, from the viewpoint of polymer properties and film-forming properties, the larger the Young's modulus in the longitudinal direction, the more lateral The upper limit of the Young's modulus in the direction becomes small, and as a result, the dimensional change due to the temperature and humidity changes of the former becomes large, and it is difficult to make the both compatible.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to solve such a problem, to ensure the durability of a magnetic recording medium, to have excellent dimensional stability under high tension, and to prevent an error due to track deviation. Another object of the present invention is to provide a biaxially oriented polyester film which is difficult to use and which is particularly useful as a magnetic recording medium having improved output characteristics in a linear track type large capacity digital data storage application.

[0008]

The object of the present invention is, according to the present invention, that (1) the film has a terminal carboxyl group concentration of 10 to 70 equivalents / 10 ⁶ g of polyethylene-
It is formed of 2,6-naphthalate, and (2) the film has a temperature expansion coefficient αt in the width direction of + 15 × 10 ⁻⁶ to −10.
× 10 ^-6 / ℃, humidity expansion coefficient αh +15 × 10 ^-6 ~ +
5 × 10 ⁻⁶ /% RH, and the value of (αt + 2αh) is 45
^{X10 -6} or less, (3) 22M in the longitudinal direction of the film
When a load of Pa is applied and the film is treated at 49 ° C. and 90% RH for 72 hours, the dimensional change in the film width direction before and after the treatment is 0.
35% or less, and (4) the thickness of the film is 2 to 7
and a biaxially oriented polyester film for a magnetic recording medium, characterized in that
The film has a terminal carboxyl group concentration of 1 on at least one side of a polyethylene-2,6-naphthalate film.
0 to 70 equivalents / 10 ⁶ g of polyethylene-2,6-
It is a laminated film in which naphthalate films are laminated,
(2) The temperature expansion coefficient αt in the width direction of the film is + 15 ×
10 ⁻⁶ to −10 × 10 ⁻⁶ / ° C., humidity expansion coefficient αh is +1
5 × 10 ⁻⁶ to + 5 × 10 ⁻⁶ /% RH and (αt + 2
The value of αh) is 45 × 10 ⁻⁶ or less, and (3) a load of 22 MPa is applied in the longitudinal direction of the film, 49 ° C., 90% R
When treated with H for 72 hours, the dimensional change in the film width direction before and after the treatment is 0.35% or less, and (4) the thickness of the film is 2 to 7 μm. Achieved by oriented polyester film.

In a preferred embodiment of the present invention, the Young's modulus in the longitudinal direction is 7 GPa or more and is larger than the Young's modulus in the lateral direction, and the sum of the Young's modulus in the longitudinal direction and the Young's modulus in the lateral direction is 13.
˜18 GPa, the surface roughness (WRa) of the film on which the magnetic layer is provided is 0.2 to 10 nm,
The surface roughness (WRa) on the non-magnetic layer side of the film is 1 to 20.
nm, the coefficient of thermal expansion in the thickness direction of the film is 1.7 × 10 ^{−6 to} 2.2 × 10 ⁻⁶ / ° C., and the Poisson's ratio (ΔTD / ΔMD) of the film is 0.3. ~ 0.6
, A magnetic recording medium of a digital recording system or a magnetic recording medium of a linear recording system, a coating type magnetic recording medium or a ferromagnetic metal thin film type magnetic recording medium.

[Polyester] The polyester forming the biaxially oriented polyester film in the present invention is preferably an aromatic polyester containing an aromatic dicarboxylic acid as a main acid component and an aliphatic glycol as a main glycol component. Here, examples of the aromatic dicarboxylic acid component include terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, diphenylketone dicarboxylic acid,
Anthracene dicarboxylic acid etc. can be mentioned.
The aliphatic glycol component has, for example, 2 carbon atoms such as ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol and decamethylene glycol.
Examples thereof include polymethylene glycol of 10 to 10; aliphatic diols such as cyclohexanedimethanol, and the like.

Among these aromatic polyesters, especially polyethylene-2,6-naphthalate,
For example, a copolymer in which 80 mol% or more of all acid components is 2,6-naphthalenedicarboxylic acid and 80 mol% or more of all glycol components is ethylene glycol is preferable. At that time, 20 mol% or less of the total acid component may be the above aromatic dicarboxylic acid other than 2,6-naphthalenedicarboxylic acid as long as the surface flatness and dry heat deterioration are not impaired. For example, it can be an aliphatic dicarboxylic acid such as adipic acid or sebacic acid; an aliphatic dicarboxylic acid such as cyclohexane-1,4-dicarboxylic acid. Further, 20 mol% or less of the total glycol component may be the above-mentioned glycol other than ethylene glycol, and for example, hydroquino, resorcin, 2,2-
Aromatic diols such as bis (4-hydroxyphenyl) propane; Aliphatic diols having an aromatic ring such as 1,4-dihydroxydimethylbenzene; Polyalkylene glycols such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol (polyoxyalkylene Glycol) or the like.

Further, the polyester of the present invention includes
A component derived from an oxycarboxylic acid such as an aromatic oxyacid such as hydroxybenzoic acid or an aliphatic oxyacid such as ω-hydroxycaproic acid is used as a dicarboxylic acid component and an oxycarboxylic acid component unless the effects of the present invention are impaired. Those which are copolymerized or bonded at 20 mol% or less based on the total amount of

Further, in the polyester of the present invention, an amount in the range of being substantially linear, and within the range of not more than 2 mol% based on the total acid component, unless the effects of the present invention are impaired, A tricarboxylic or higher functional polycarboxylic acid or polyhydroxy compound such as trimellitic acid or pentaerythritol is also included.

In the present invention, as the polyester,
Polyethylene-2,6-naphthalate is particularly preferably used because it has a high Young's modulus when thinned and has high dimensional stability and strength retention when the temperature rises.

The above polyester is known per se and can be produced by a method known per se.
The above polyester has an intrinsic viscosity of 0.4 to 40 measured as a solution in o-chlorophenol at 35 ° C.
0.9, more preferably 0.5-0.7, especially 0.51-0.
65 is preferable.

[Terminal Carboxyl Group Concentration] In the present invention, the terminal carboxyl group concentration of the polymer constituting the biaxially oriented polyester film is 10 to 70 equivalent / 10.
⁶ g, preferably 15 to 50 equivalent / 10 ⁶ g, more preferably 20 to 40 equivalent / 10 ⁶ g. When the terminal carboxyl group concentration exceeds 70 equivalent / 10 ⁶ g, the main chain of the polymer is decomposed, and it becomes difficult to obtain a high Young's modulus of the film. On the other hand, the terminal carboxyl group concentration is 10 equivalents /
A film with a weight of less than 10 ⁶ g is extremely difficult to obtain because it is easily thermally decomposed during melt extrusion of the polymer.

The polyester having a high terminal carboxyl group concentration can be produced by the transesterification method or the esterification method.
It can be produced under the following reaction conditions. For example, metal compounds used in the transesterification reaction or the esterification reaction, such as Mg, Mn, Zn,
A polyester is obtained by using a larger amount of a compound such as Ca, Li, or Ti than usual, and a polymerization reaction is carried out while maintaining a higher temperature and / or a longer time than usual in the latter stage of the polymerization reaction,
Monomers that are relatively susceptible to thermal decomposition, eg, having 4 to 4 carbon atoms
It can be produced by a method such as copolymerizing 12 aliphatic carboxylic acids or aliphatic glycols. Also,
A polyester having the above-mentioned terminal carboxyl group concentration may be obtained by blending a certain amount of a so-called regenerated polymer which is relatively thermally decomposed.

[Inert Fine Particles] The polyester of the present invention may contain a stabilizer, a colorant, an antistatic agent, and
Additives such as lubricants can be included. In particular, in order to make the surface of the film rough and improve the slipperiness of the film, it is preferable to incorporate inert fine particles as a lubricant. Examples of such inert fine particles include (1) silicon dioxide (including hydrate, silica sand, quartz, etc.); (2) alumina;
(3) Silicates containing 30% by weight or more of SiO ₂ (for example, amorphous or crystalline clay minerals, aluminosilicates (including calcined products and hydrates), hot asbestos, zircon, fly ash, etc. ); (4) Mg, Zn, Zr, and Ti oxides; (5) Ca and Ba sulfides;
(6) Li, Na, and Ca phosphates (monohydrogen salts and 2
(Including hydrogen salts); (7) Li, Na, and K benzoates; (8) Ca, Ba, Zn, and Mn terephthalates; (9) Mg, Ca, Ba, Zn, Cd, Pb. , S
Titanate of r, Mn, Fe, Co, and Ni; (1
0) Ba and Pb chromates; (11) Carbon (eg carbon black, graphite etc.); (12) Glass (eg glass powder, glass beads etc.); (13)
Ca and Mg carbonates; (14) fluorspar, and (1
5) ZnS and the like can be preferably exemplified. More preferably,
Silicon dioxide, anhydrous silicic acid, hydrous silicic acid, aluminum oxide, aluminum silicate (including baked products, hydrates, etc.), 1 lithium phosphate, 3 lithium phosphate, sodium phosphate, calcium phosphate, barium sulfate, titanium oxide, benzoin Examples thereof include lithium acid, double salts of these compounds (including hydrates), glass powder, clay (including kaolin, bentonite, clay and the like), talc, calcium carbonate and the like.
Particularly preferred are silicon dioxide, titanium oxide, and calcium carbonate. Two or more of these may be used, and those having different average particle sizes may be used in the same amount or different amounts. The average particle size of such fine particles is 0.
It is preferably from 05 to 0.8 μm, and the addition amount is preferably from 0.01 to 0.5% by weight.

[Expansion Coefficient] The biaxially oriented polyester film of the present invention has a coefficient of thermal expansion α in the width direction of the film.
t is + 15 × 10 ⁻⁶ to −10 × 10 ⁻⁶ / ° C., preferably + 10 × 10 ⁻⁶ to ⁻⁵ × 10 ⁻⁶ / ° C., and more preferably + 5 × 10 ⁻⁶ to ⁻⁵ ×. 10 ^-6 / ° C,
The humidity expansion coefficient αh is + 15 × 10 ⁻⁶ to + 5 × 10 ^−6.
/% RH, preferably + 13 × 10 ⁻⁶ to + 7 × 1
0 ⁻⁶ /% RH, more preferably + 12 × 10 ⁻⁶
˜ + 8 × 10 ⁻⁶ /% RH. And (αt + 2αh)
Value is 45 × 10 ⁻⁶ or less, preferably 35 × 10 ⁻⁶ or less, more preferably 30 × 10 ⁻⁶ or less.

This temperature expansion coefficient αt is + 10 × 10 ^-6 /
If the temperature is higher than 0 ° C, the dimensional change in the film width direction due to the temperature change becomes large, causing a track shift and causing a recording / reproducing error. On the other hand, when the temperature expansion coefficient αt is less than −10 × 10 ⁻⁶ / ° C., it is necessary to considerably increase the Young's modulus in the width direction of the film, and the film frequently breaks during film formation, resulting in a marked deterioration in productivity. To do. Also, the humidity expansion coefficient αh is + 15 × 10 ^-6 /% RH
If it is larger than the above range, the dimensional change in the film width direction due to the change in humidity becomes large, causing a track shift and causing a recording / reproducing error. On the other hand, if the humidity expansion coefficient αh is less than + 5 × 10 ⁻⁶ /% RH, the Young's modulus in the width direction of the film needs to be considerably high, and the film frequently breaks during film formation, resulting in a marked deterioration in productivity. To do. Further, if the value of (αt + 2αh) is larger than 45 × 10 ⁻⁶ , the dimensional change due to the temperature and humidity change becomes large, causing the track shift and causing the recording / reproducing error.

The biaxially oriented polyester film in the present invention
Rum has a coefficient of thermal expansion in the thickness direction of 1.7 × 10.
^-6~ 2.2 x 10^-6/ ° C, and 1.8 × 10^-6
~ 2.1 x 10^-6/ ° C, especially 1.9 x 10^-6~
2.0 x 10^-6It is preferably / ° C. This thickness
Coefficient of thermal expansion is 2.2 × 10^-6If it is higher than / ° C,
When the tape is exposed to high temperature, the expansion in the thickness direction is large
The tape is narrowed and the tape width becomes wider.
There is a problem that the slippage occurs. On the other hand, 1.7 × 10 ^-6/ ° C
If it is smaller, the Young's modulus in the longitudinal and width directions is smaller.
And the durability of the tape becomes problematic.

[Width Dimension Change Due to Temperature and Humidity Treatment Under Load] The biaxially oriented polyester film of the present invention also comprises
When a load of 22 MPa is applied in the longitudinal direction of a film having a width of 12.65 mm and a 72 hour treatment is performed at a temperature of 49 ° C. and a humidity of 90% RH, the dimensional change in the width direction before and after the treatment is 0.35% or less, preferably 0.30. % Or less, particularly preferably 0.2
It is 5% or less. If this dimensional change is larger than 0.35%, when the tape is repeatedly run under high tension and high temperature and high humidity, the dimensional change in the width direction becomes large, causing track deviations, and recording / reproducing errors. Will be generated.

In order to keep the width dimension change due to the temperature and humidity treatment under load within the above range, it is preferable to give a sufficient stretch orientation particularly in the longitudinal direction and perform a sufficient crystallization treatment.

[Film Thickness] The biaxially oriented polyester film of the present invention has a total thickness of 2 to 7 μm, preferably 3 to 6 μm. If this thickness exceeds 7 μm, the tape thickness becomes too thick, for example, the length of the tape to be placed in the cassette becomes short, and a sufficient magnetic recording capacity cannot be obtained. On the other hand, when the thickness is less than 2 μm, the film is thin, so that the film often breaks during film formation, and the film winding property becomes poor, so that a good film roll cannot be obtained.

[Young's modulus] The biaxially oriented polyester film of the present invention has a Young's modulus in the longitudinal direction of 7.0 GPa.
As described above, it is more preferably 8.0 GPa or more, and particularly preferably 9.0 GPa or more. Young's modulus in the vertical direction is 7.0G
If it is less than Pa, the strength of the magnetic tape in the longitudinal direction becomes weak, and if a strong force in the longitudinal direction is applied during recording / reproduction, it may easily be permanently deformed and broken. The Young's modulus in the lateral direction of the film is 6.0 GPa or more, and further 6.5 G
It is preferably Pa or more, particularly 7.0 GPa or more. When the Young's modulus in the lateral direction is less than 6.0 GPa, when the linear track type magnetic tape is used, the dimensional change in the width direction becomes large when the temperature and humidity change, and a recording / reproducing error due to a track deviation easily occurs. .

The biaxially oriented polyester film has a sum of Young's modulus in the longitudinal direction and Young's modulus in the lateral direction of 13 to 13.
18 GPa, further 14-18 GPa, especially 15-1
It is preferably 8 GPa. Further, when used as a linear track type magnetic tape, the Young's modulus in the vertical direction is preferably higher than the Young's modulus in the horizontal direction from the viewpoint of reducing the elongation in the vertical direction. If the sum of the Young's modulus in the longitudinal direction and the Young's modulus in the lateral direction is less than 13 GPa, the strength of the magnetic tape becomes weak, the tape may be easily broken, and the dimensional change when the temperature and humidity change, becomes large. A recording / reproducing error occurs due to track deviation, and a satisfactory high density magnetic medium cannot be obtained. On the other hand, when it exceeds 18 GPa, the stretching ratio becomes high during film formation, the film breaks frequently, and the product yield decreases.

[Surface Roughness] The biaxially oriented polyester film in the present invention may be either a single layer film or a laminated film, but the surface roughness WRa (center surface average roughness) on the side where the magnetic layer is provided is 0.2 to. 10 nm, further 1-8 nm,
It is particularly preferably 1 to 5 nm. Also, WRz
(10-point average roughness) is 2 to 300 nm, further 10
It is preferably 200 nm, particularly preferably 10 to 100 nm. If the surface roughness WRa is greater than 10 nm or WRz is greater than 300 nm, the surface of the magnetic layer becomes rough and satisfactory electromagnetic conversion characteristics cannot be obtained. On the other hand, this surface roughness WRa is less than 0.2 nm, or W
If Rz is less than 2 nm, the surface becomes too flat, slippage on a pass roll or calendar becomes poor, wrinkles occur, and the magnetic layer cannot be evenly coated.
Also, the calendar cannot be applied evenly.

The surface roughness W of the non-magnetic layer side (for example, the back coat layer coating side) of the biaxially oriented polyester film.
Ra (center surface average roughness), WRz (10-point average roughness)
In the case of a single-layer film, is substantially the same as the surface roughness WRa and WRz on the side where the magnetic layer is provided.

In the case of a laminated film, the film surface roughness WRa (center plane average roughness) on the non-magnetic layer side is 1 to 20.
nm, more preferably 2 to 15 nm, and particularly preferably 5 to 10 nm. WRz (10-point average roughness) is 1
0-300 nm, more preferably 100-250 nm, especially 1
It is preferably from 00 to 200 nm. This surface roughness WRa is larger than 20 nm, or WRz is 300.
If it is larger than nm, the protrusion of the protrusion to the surface of the flat layer (magnetic layer) side and the transfer of surface irregularities to the surface of the magnetic layer during winding of the magnetic tape become large, and the surface of the magnetic layer becomes rough, resulting in a satisfactory electromagnetic field. Conversion characteristics cannot be obtained. On the other hand, when the surface roughness WRa is less than 1 nm or WRz is less than 10 nm, the film slips poorly, or the air squeeze property becomes poor, so that the film has slits or has vertical wrinkles. Occurs, and satisfactory windability cannot be obtained.

The above-mentioned surface roughness WRa and WRz can be obtained by adjusting the kind, average particle diameter and addition amount of the above-mentioned inert fine particles.

[Poisson's Ratio] The biaxially oriented polyester film of the present invention has a Poisson's ratio (ΔTD / ΔMD).
Is 0.3 to 0.6, more preferably 0.35 to 0.55, and particularly preferably 0.4 to 0.5. When the Poisson's ratio is larger than 0.6, when a load is applied in the vertical direction, the dimensional change in the width direction becomes large, and track deviation occurs, which is a problem. On the other hand, if the Poisson's ratio is less than 0.3, it cannot be achieved with a homopolymer of polyethylene-2,6-naphthalate, and copolymerization or blending with another polymer is required, which makes recovery of the polymer difficult. ,There's a problem.

[Layer Structure] The biaxially oriented polyester film in the present invention may be either a single layer film or a laminated film, but it is easy to achieve both the electromagnetic conversion characteristics of the tape and the winding property of the film. A laminated film is more preferable. This laminated film has a terminal carboxyl group concentration of 10 to 70 equivalents / 10 ^{6 on} at least one surface of a polyethylene-2,6-naphthalate film.
It is preferably formed by laminating polyethylene 2,6-naphthalate films of g. In this case, the terminal carboxyl group concentration is 10 to 70
The layer of the polyethylene-2,6-naphthalate film having an equivalent weight / 10 ⁶ g may be on the magnetic layer side or the non-magnetic layer side. The thickness distribution of each layer in the laminated film is not particularly limited, but the terminal carboxyl group concentration is 10 to 7
A film (layer) made of polyethylene-2,6-naphthalate of 0 equivalent / 10 ⁶ g is 1/10 to 9 of the total thickness.
/ 10, more preferably 1/7 to 6/7.

[Production of Film] The biaxially oriented polyester film in the present invention is preferably produced by the following method. That is, when the film is a single layer, first, polyethylene-2,6-naphthalate having a terminal carboxyl concentration within a predetermined range is melted with a polymer melting point (T
m: ° C.) to (Tm + 70) ° C. and extruded into a film at a temperature of 10 to 70 ° C. to rapidly solidify to obtain an unstretched film. Thereafter, the unstretched film is uniaxially (longitudinal or transverse) in a conventional manner (Tg-10) to (Tg +).
Magnification of 4.0 to 8.0 times at a temperature of 70 ° C. (however, Tg: glass transition temperature of polymer), preferably 5.
The film is stretched at a draw ratio of 0 to 6.0 times, and then, if necessary, a coating liquid for forming a coating layer is applied to one side or both sides of the film, and then Tg to (Tg + 70) ° C. in the direction perpendicular to the above direction.
Stretching is carried out at the temperature of 4.0 to 8.0 times, preferably 4.5 to 6.0 times. Further, if necessary, it may be stretched again in the machine direction and / or the transverse direction. That is,
It is advisable to perform stretching in two stages, three stages, four stages, or multiple stages. The total draw ratio is preferably 20 to 45 times, more preferably 25 to 35 times as an area draw ratio. Further subsequently, a biaxially oriented film was formed into (Tg + 70) to (Tm-1).
0) ° C temperature, for example 180-250 ° C, preferably 2
Excellent dimensional stability is imparted by heat-fixing crystallization at 00 to 230 ° C. The heat setting time is 1 to 60
Seconds are preferred.

In the case of a laminated film prepared by the coextrusion method, polyethylene-2,6-naphthalate having different terminal carboxyl concentrations are melted by different extruders, and the terminal carboxyl concentration is 10 to 7 on one side or both sides of the film.
A polyethylene-2,6-naphthalate film (layer) of 0 equivalent / g is laminated in a die so as to be laminated and then extruded into a film shape, preferably at a temperature of melting point (Tm: ° C) to (Tm + 70) ° C. Extruded or two or more kinds of molten polyethylene with different terminal carboxyl concentrations-2,6
-After extruding naphthalate from a die, laminate so that a polyethylene-2,6-naphthalate film (layer) having a terminal carboxyl concentration of 10 to 70 equivalents / g comes to one side or both sides of the film, and rapidly solidifies to laminate. An unstretched film is obtained, and then biaxially stretched and heat-treated under the same method and conditions as in the case of a monolayer film to obtain a laminated biaxially oriented film. If necessary, a coating liquid can be applied to one or both surfaces of the film after longitudinal stretching to form a film layer.

[Magnetic Recording Medium] The biaxially oriented polyester film of the present invention has one side (a flat layer in the case of lamination).
On the surface of, iron or fine acicular magnetic powder (metal powder) containing iron as a main component is uniformly dispersed in a binder such as polyvinyl chloride, vinyl chloride / vinyl acetate copolymer, and the magnetic layer has a thickness of 1 μm or less, It is preferably applied so as to have a thickness of 0.1 to 1 μm, and if necessary, by providing a back coat layer on the surface of the other side (B layer in the case of lamination), the output in the short wavelength region, S / It is possible to provide a metal-coated magnetic recording medium for high density recording, which has excellent electromagnetic conversion characteristics such as N and C / N and has a small dropout and error rate. In addition, on the surface of the magnetic layer side (flat layer in the case of lamination),
It is also possible to coat a non-magnetic layer containing fine titanium oxide particles etc. as an underlayer of the magnetic layer containing metal powder. This metal-coated magnetic recording medium is extremely effective for a high-density magnetic recording medium, in particular, a linear recording type magnetic tape such as LTO, DLT, and Super-DLT.

The biaxially oriented polyester film of the present invention has a surface of a coating layer provided on one side (a flat layer surface in the case of lamination), which is coated with iron, cobalt, or the like by a method such as vacuum deposition, sputtering, or ion plating. A ferromagnetic metal thin film layer made of chromium or an alloy or oxide containing these as a main component is formed, and diamond-like carbon (DL)
By providing a protective layer such as C) and a fluorinated carboxylic acid-based lubricating layer in this order, and further providing a known back coat layer on the opposite surface (if necessary, a coating layer is applied), output in the short wavelength region , S / N, C / N, etc. are excellent in electromagnetic conversion characteristics, and a vapor deposition type magnetic recording medium for high density recording with a small dropout and error rate can be obtained.

[0037]

EXAMPLES The present invention will be described in more detail below with reference to examples. The measuring method used in the present invention is as follows. Further, "parts" means parts by weight.

(1) Average Particle Size of Particles CP-50 Model Centrifugal Particle Size Analyzer (Centrifugal Particle S) manufactured by Shimadzu Corporation
ize Analyzer). The particle diameter "equivalent sphere diameter" corresponding to 50 mass% is read from the integrated curve of the particles having respective particle diameters calculated based on the obtained centrifugal sedimentation curve and the abundance thereof, and this value is taken as the above average particle diameter. ("Particle size measurement technology", Nikkan Kogyo Shimbun, 1975, p.242-.
247).

(2) 180 mg of a sample having a terminal carboxyl group concentration was dissolved in a p-xylene / m-cresol mixed solution (volume ratio 2/3) by heating under a nitrogen atmosphere, and the solution was CH ₃ ON using bromophenol blue as an indicator.
Neutralization titration with a (concentration 0.02 mol / l in CH ₃ OH solution). The amount of CH ₃ ONa solution required for neutralization is X
(Ml) and the amount of CH ₃ ONa solution required for neutralization of the mixed solvent which did not contain the sample and which was subjected to the same treatment as B (m).
l), the terminal carboxyl group concentration [COOH] is calculated by the following formula.

[0040]

[Equation 1]

(3) A Young's modulus film was cut into a sample width of 10 mm and a length of 15 cm, and the distance between the chucks was set to 100 mm, and the tensile speed was 10 mm / min and the chart speed was 500 mm / min. Calculate the Young's modulus from the tangent of the rising part of the applied load-elongation curve.

(4) Surface roughness (WRa, WRz) Non-contact type three-dimensional roughness meter (NT-2000) manufactured by WYKO
Measurement magnification of 25 times, measurement area of 246.6 μm × 1
Under the condition of 87.5 μm (0.0462 mm ² ), the number of measurements (n) was measured at 10 or more, and the center plane average roughness (WRa),
And 10-point average roughness (WRz) is calculated. (A) Center surface average roughness (WRa)

[0043]

[Equation 2]

Z _jk is a measurement direction (246.6 μm), and a direction orthogonal to it (187.5 μm) is divided into m,
It is the height on the three-dimensional roughness chart at the j-th and k-th positions in each direction when divided into n. (B) 10-point average roughness (WRz) 5 points are taken from the highest peak (HP) and 5 points from the lowest valley (Hv), and the average roughness is taken as WRz.

[0045]

[Expression 3] WRz = {(H _P1 + H _P2 + H _P3 + H _P4 + H _P5 )
-(H _V1 + H _V2 + H _V3 + H _V4 + H _V5 )} / 5

(5) Thermal expansion coefficient (αt) in the width direction A film sample was cut into a film having a length of 15 mm and a width of 5 mm in the film width direction, set in TMA3000 manufactured by Vacuum Riko Co., Ltd., and pretreated at 60 ° C. for 30 minutes in a nitrogen atmosphere. Then cool to room temperature. After that, from 25 ℃ to 70 ℃, 2 ℃
The temperature is raised at / min, the sample length at each temperature is measured, and the temperature expansion coefficient (αt: / ° C) is calculated from the following equation.

[0047]

## EQU4 ## αt = {(L2-L1) / (L1 × ΔT)} +
0.5 × 10 ⁻⁶ (Note) Here, L1: sample length at 40 ° C. (mm) L2: sample length at 60 ° C. (mm) ΔT: 20 (= 60-40 ° C.) Note: quartz glass It is a coefficient of thermal expansion.

(6) Humidity expansion coefficient (αh) in the width direction A film sample was cut into a film having a length of 15 mm and a width of 5 mm in the film width direction and set on TMA3000 manufactured by Vacuum Riko Co., Ltd., under a nitrogen atmosphere, a humidity of 30% RH, and Humidity 70
% RH is kept constant, the length of the sample at that time is measured, and the humidity expansion coefficient (αh: /% RH) is calculated by the following formula.

[0049]

Αh = {(L2-L1) × / (L1 × ΔH)} Here, L1: sample length (mm) when humidity is 30% RH L2: Sample length (mm) when humidity is 70% RH ΔH: 40 (= 70-30% RH) Is.

(7) Coefficient of thermal expansion in the thickness direction The film sample is set to prevent dust from entering in the thickness direction 1
Zero sheets are stacked, sandwiched between quartz glass, and a linear thermal expansion coefficient in the film thickness direction is measured using a laser thermal dilatometer (LIX-1) manufactured by Vacuum Riko Co., Ltd. Before measurement, the sample was aged at 60 ° C for 30 minutes,
After lowering the temperature, raise the temperature from 5 ° C to 60 ° C at 2 ° C / min, and
The linear expansion coefficient is obtained from the gradient of 0 ° C and 50 ° C. In addition,
The linear expansion of quartz glass is separately measured and corrected without sandwiching the film.

(8) 12.6 in an atmosphere having a shrinking temperature in the width direction of 23 ° C. and a humidity of 50% under a longitudinal load of the film
A film (sample) slit to 5 mm (1/2 inch) is set as shown in FIG. Note that 12.65
For the sample slit to mm, gold is deposited on the surface by sputtering in advance so that the width dimension can be measured by a detector. In this state, a weight is attached to one side (the other side is fixed) of the film (sample) so as to be 22 MPa, and the width (L1) of the film at that time is measured by a Keyence laser outer diameter measuring device (main body LS-: 3100 type, Optical sensor: LS-3060 type).

Thereafter, 49 ° C. (120 ° F.) × 90% R
22MP on one side (the other is fixed) under high temperature and high humidity of H
After applying a weight to a and treating for 72 hours (3 days), remove the weight, adjust the humidity for 24 hours in an atmosphere with a temperature of 23 ° C. and a humidity of 50%, and then again on one side of the film (the other is fixed). Attach a weight to 22MPa,
The width (L2) of the film at that time was measured by Keyence laser outer diameter measuring instrument (main unit: LS-3100 type, optical sensor:
LS-3060 type).

From the dimensions before and after the temperature and humidity treatment measured above, the width dimension change (αW) before and after the temperature and humidity treatment under load is calculated by the following equation.

[0054]

[Equation 6] αW = {(L2-L1) × / L1} × 100 (%)

(9) Track deviation (error rate) The error rate is measured under the following conditions using a ML4500B, QIC system manufactured by Media Logic Co. Current = 15.42 mA Frequency: 0.25 MHz Location = 0 Threshold: 40.0 Bad / Good / MAX: 1: 1: 1 Tracks: 28 The error rate is the number of measured tracks (= 28).
The average value of

The conditions 1 and 2 are measured as follows. Condition 1 4 after recording under temperature and humidity of 10 ° C and 10% RH
Playback is performed at a temperature and humidity of 5 ° C. and 80% RH, and the amount of track deviation due to changes in temperature and humidity is measured. Condition 2: After recording at 23 ° C and 50% RH temperature and humidity, 4
Repeatedly run for 60 hours at a temperature and humidity of 0 ° C and 60% RH, return to a temperature and humidity of 23 ° C and 50% RH, hold for 24 hours, then play back the record and run at a relatively high temperature and high humidity. Measure the amount of track deviation due to width shrinkage.

The evaluation criteria are as follows. ◎: No error rate ○: There is an error rate, but there is no practical problem X: There are many error rates and there is a problem in practical use.

(10) A Poisson's ratio film was tested according to JIS K6771 No. 1 test piece (dumbbell).
Then, the center of the film is marked with 6 mm □, the chuck distance is 70 mm, and an initial load of 200 g is applied to obtain an initial length (initial width). After that, pulling with an Instron type universal tensile testing device at a pulling speed of 0.5 mm / min, measuring the dimensional changes in the vertical and width directions of the marking with a Keyence image sensor, and calculating the Poisson's ratio as Ask more. The outline of this measurement is shown in FIG.

[0059]

Equation 7] Poisson's ratio _{= (△ W / W 0)} / (△ L / L 0) where, △ W: amount of change in the width direction (mm) W _0: a width direction of the initial width (mm) △ L: Amount of change in vertical direction (mm) L ₀ : Initial length in vertical direction (mm).

(11) Film-forming property When the film was formed at a film-forming speed of 150 m / min, the film could be continuously formed without breaking the film for 8 hr or more, the film-forming property was ○, and if it was less than that (the film was broken in less than 8 hr). Film formation ×
And

Example 1 100 parts of 2,6-naphthalenedicarboxylic acid dimethyl ester and ethylene glycol 6
0.025 parts of manganese acetate / tetrahydrate and 0.005 parts of sodium acetate / trihydrate were added to the mixture of 0 parts, and the internal temperature was adjusted to 1
The transesterification reaction was carried out while gradually raising the temperature from 50 ° C. Next, 0.02% by weight of calcium carbonate particles having an average particle size of 0.6 μm and 0.3% by weight of spherical silica particles having an average particle size of 0.1 μm were added as an ethylene glycol slurry, and the transesterification rate was 95%. Trimethyl phosphate 2 as a stabilizer when
0.069 parts of a glycol solution of a phosphorus compound obtained by reacting 5 parts of ethylene glycol with 75 parts of ethylene glycol was added, and after sufficiently stirring, 0.8 parts of trimellitic anhydride and 0.4 parts of tetrabutyl titanate were added in 2.5 parts of ethylene glycol. 0.014 parts of a liquid obtained by reacting 65 parts (titanium content is 11% by weight) was added. Next, the reaction product is transferred to a polymerization reactor, and polycondensation reaction is performed under high temperature vacuum (final internal temperature 295 ° C.),
Polyethylene-2,6-naphthalate having an intrinsic viscosity of 0.57 was obtained.

This polymer was dried at 170 ° C. for 6 hours, then fed into an extruder and melted at 300 ° C. to obtain an unstretched polyester film. Then, the obtained unstretched film was preheated, further stretched 5.8 times at a film temperature of 135 ° C. between low speed and high speed rolls, and rapidly cooled to obtain a longitudinally stretched film. Then, supply to the stenter, 155 ℃
Was stretched in the transverse direction by a factor of 5.2. The resulting biaxially stretched film was heat set with hot air at 205 ° C. for 4 seconds to give a thickness of 6.
A 0 μm biaxially oriented polyester film was obtained.

On the other hand, the composition shown below was put into a ball mill, kneaded and dispersed for 16 hours, then 5 parts of an isocyanate compound (Desmodur L manufactured by Bayer Co.) was added, and high-speed shear dispersion was performed for 1 hour to obtain a magnetic coating material. . Composition of magnetic paint: Needle-like Fe particles 100 parts Vinyl chloride-vinyl acetate copolymer 15 parts (Sekisui Chemical's S-REC 7A) Thermoplastic polyurethane resin 5 parts Chromium oxide 5 parts Carbon black 5 parts Lecithin 2 parts Fatty acid ester 1 part Toluene 50 parts Methyl ethyl ketone 50 parts Cyclohexanone 50 parts This magnetic paint was applied to one side of the above-mentioned polyethylene-2,6-naphthalate film so as to have a coating thickness of 0.5 μm, and then subjected to orientation treatment in a direct current magnetic field of 2500 Gauss. After heating and drying at 100 ° C, super calendering (linear pressure 2000N / cm, temperature 80 ° C)
I wound up. The wound roll was left in an oven at 55 ° C for 3 days.

Further, a back coat layer coating composition having the following composition was applied on the surface opposite to the magnetic layer to a thickness of 1 μm, and after drying,
It was cut to 6.35 mm (= 1 '/ 4) to obtain a magnetic tape. Composition of back coat layer paint: Carbon black 100 parts Thermoplastic polyurethane resin 60 parts Isocyanate compound 18 parts (Coronate L manufactured by Nippon Polyurethane Industry Co., Ltd.) Silicone oil 0.5 parts Methyl ethyl ketone 250 parts Toluene 50 parts Properties of the obtained film and tape Is shown in Table 1. As is clear from this table, the running durability is good and the track deviation is small.

[Example 2, Comparative Examples 1 to 4] Biaxially oriented with a thickness of 6.0 μm according to Example 1 except that the additives, the terminal carboxyl group concentration and the film forming conditions were changed as shown in Table 1. A polyester film was obtained.

A magnetic tape was prepared from the obtained film in the same manner as in Example 1. The characteristics of the obtained film and tape are shown in Table 1.

[Example 3] Polyethylene-2,6-naphthalate containing 0.01% by weight of spherical silica particles having an average particle size of 0.1 µm and having a carboxyl terminal amount shown in Table 1,
Polyethylene-2,6-containing carboxyl-terminal amounts shown in Table 1 containing 0.15% by weight of spherical silica particles having an average particle size of 0.3 μm and 0.13% by weight of spherical silica particles having an average particle size of 0.1 μm. Naphthalate pellets at 170 ℃ 6
After drying for 2 hours, supply each to two extruders, melt at a melting temperature of 300 ° C, and use a multi-manifold type co-extrusion die to make the center a normal polymer and both surface layers become a polymer having a high terminal carboxyl concentration. It was laminated and extruded. A biaxially oriented laminated polyester film having a thickness of 6.0 μm was obtained under the conditions shown in Table 1 below. A magnetic tape was prepared and evaluated in the same manner as in Example 1. The characteristics of the obtained film and tape are shown in Table 1.

[Comparative Examples 5 to 6] A biaxially oriented laminated polyester film having a thickness of 6.0 μm was prepared in the same manner as in Example 3 except that the additives, the amount of carboxyl ends and the film forming conditions were changed as shown in Table 1. Obtained.

A magnetic tape was prepared from the obtained film in the same manner as in Example 1. The characteristics of the obtained film and tape are shown in Table 1.

[0070]

[Table 1]

[0071]

According to the present invention, a biaxially oriented polyester film useful as a large capacity digital data storage tape having excellent running durability after repeated use, no error due to track deviation, and excellent output characteristics is provided. can do.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an apparatus for measuring a dimensional change in a width direction of a film under a longitudinal load.

FIG. 2 is an explanatory diagram of a method for measuring Poisson's ratio.

Continued front page    (72) Inventor Hirofumi Murooka             3-37-19 Oyama, Sagamihara City, Kanagawa Prefecture             People DuPont Films Co., Ltd. Sagamihara Research Center             In the center F-term (reference) 4F071 AA45 AA80 AF43Y AF54Y                       AH14 BB06 BB08 BC01 BC12                       BC16                 5D006 CB01 CB07 CB08

Claims (11)

[Claims] 1. A polyethylene-2,6 film having a terminal carboxyl group concentration of 10 to 70 equivalents / 10 ⁶ g.
-It is made of naphthalate, and (2) the film has a temperature expansion coefficient αt in the width direction of + 15 × 10 ⁻⁶ to −10 × 10.
^-6 / ° C, humidity expansion coefficient αh is + 15 × 10 ^-6 to + 5 × 1
0 ^-6 /% RH and the value of (αt + 2αh) is 45 × 10
^-6 or less, and (3) when a load of 22 MPa is applied in the machine direction of the film and the film is processed at 49 ° C. and 90% RH for 72 hours, the dimensional change in the film width direction before and after the process is 0.35%.
The biaxially oriented polyester film for a magnetic recording medium is as follows, and (4) the thickness of the film is 2 to 7 μm. 2. (1) The film is polyethylene-2,
A laminated film in which a polyethylene-2,6-naphthalate film having a terminal carboxyl group concentration of 10 to 70 equivalents / 10 ⁶ g is laminated on at least one surface of a ⁶ -naphthalate film, and (2) in the width direction of the film. Temperature expansion coefficient αt is + 15 × 10 ⁻⁶ to −10 × 10 ⁻⁶ / ° C., humidity expansion coefficient αh is + 15 × 10 ⁻⁶ to + 5 × 10 ⁻⁶ /% R
H and the value of (αt + 2αh) is 45 × 10 ⁻⁶ or less, and (3) when a load of 22 MPa is applied in the machine direction of the film and the film is treated at 49 ° C. and 90% RH for 72 hours, the film before and after the treatment A biaxially oriented polyester film for a magnetic recording medium, wherein the dimensional change in the width direction is 0.35% or less, and (4) the film has a thickness of 2 to 7 μm. 3. The Young's modulus in the longitudinal direction is 7 GPa or more and is larger than the Young's modulus in the lateral direction, and the sum of the Young's modulus in the longitudinal direction and the Young's modulus in the lateral direction is 13 to 18 GPa.
A biaxially oriented polyester film for a magnetic recording medium according to. 4. The biaxially oriented polyester film for a magnetic recording medium according to claim 1, wherein the surface roughness (WRa) of the film on the side where the magnetic layer is provided is 0.2 to 10 nm. 5. The surface roughness (WR) on the non-magnetic layer side of the film
The biaxially oriented polyester film for a magnetic recording medium according to claim 2, wherein a) is 1 to 20 nm. 6. The coefficient of thermal expansion in the thickness direction is 1.7 × 10.
^The biaxially oriented polyester film for a magnetic recording medium according to claim 1, which has a viscosity of ^{−6 to} 2.2 × 10 ⁻⁶ / ° C. 7. The Poisson's ratio (ΔTD / ΔMD) is 0.3.
The biaxially oriented polyester film for a magnetic recording medium according to claim 1 or 2, wherein 8. The biaxially oriented polyester film for a magnetic recording medium according to claim 1, which is for a magnetic recording medium of a digital recording system. 9. The biaxially oriented polyester film according to claim 1, which is for a magnetic recording medium of a linear recording system. 10. A coating type magnetic recording medium.
Or the biaxially oriented polyester film for magnetic recording media according to 9 above. 11. The biaxially oriented polyester film for a magnetic recording medium according to claim 8, which is for a ferromagnetic metal thin film type magnetic recording medium.