JPS61167530A - Polyester film for magnetic recording material - Google Patents

Abstract

PURPOSE:To obtain the titled film which is superior in flat and easily sliding properties and adhesion with a magnetic layer, by a method wherein the titled film is constituted of a matter that the film possesses specific refraction in the direction of a thickness of the same, the number of uneven units composed of protrusions and specific-sized recesses is shown by a specific expression and contains a specific quantity of an organic solvent. CONSTITUTION:An unoriented polyester sheet is formed by a method wherein polymer resin within which inactive exterior particles (example: such as MgO), whose mean particle diameter is about 0.9-10.0mum, and 0.005-0.5wt% organic solvent (such as alkylenebisalkylamide) are made to contain or mixed resin of these resin are dried by a conventional an extruding machine. A target film whose refraction is nd>=1.492 and the number of uneven units A per 1mm<2> of an area of the surface of the film composed of protrusions and recesses whose long diameter having said protrusions for their cores are at least 0.5mum is shown by an expression is obtained by orienting the unoriented polyester sheet in the direction of a first axis and then orienting in the direction meeting at right angles with the first axis.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention has excellent flat smoothness, adhesion with the magnetic layer, multi-time running properties, etc., and does not produce white powder even when it comes into contact with the guide part. The present invention relates to a biaxially oriented polyester film that is particularly useful as a base film for magnetic recording media and has little occurrence of generation.

During its expansion, biaxially oriented polyester film has excellent heat resistance, mechanical properties,
Due to its excellent chemical resistance, demand is rapidly increasing for use in magnetic recording media, especially magnetic tapes for audio and video applications, and magnetic sheets for floppies.

In recent years, these magnetic recording media have become increasingly high in quality and density, and the flatness of the base film is increasing.

There is a demand for a material with better lubricity, adhesion to the magnetic layer, and ability to run multiple times. Also, magnetic v! The production of recording media is carried out by applying a binder containing magnetic powder onto a base film using a combination of a coating roll and a doctor knife. Friction and abrasion between the polyester film and the roll surface are severe, and the surface of the film itself is scraped, precipitating a white powdery substance, which in turn causes dropouts. Furthermore, when a tape or sheet coated with the magnetic material is used for recording, recording, etc., friction and abrasion at the guide portion may cause scratches on the film, producing white powder, and deteriorating the smearability after many runs. A base film that satisfies all of these characteristics has not yet been perfected, and there have been strong demands from film manufacturers.

IS+! In order to achieve this goal, the present inventor conducted extensive research to develop a film that maintains the film's smoothness and adhesion to the magnetic layer, while improving its abrasion resistance and multi-running performance.

We have arrived at the present invention by discovering that this problem can be solved by adjusting the physical properties of the polyester film to a certain range and mixing it with an appropriate organic lubricant and particles.

That is, in the present invention, the refractive index n in the thickness direction of the film is 1.
゜492 or more, and the number A (pieces/mm2) of unevenness units per 1 mm2 of film surface area consisting of a protrusion and a depression with a major axis of at least 0.5 pm centered on the protrusion is 0.
The formula % formula % is satisfied, and the organic lubricant is o, oos weight % or more, 0.
The present invention relates to a polyester film for magnetic recording media, characterized in that it contains 5% by weight or less.

The polyester referred to in the present invention is terephthalic acid.

Crystalline aroma that can be obtained by polycondensing aromatic dicarboxylic acids such as isophthalic acid and naphthalene-2,6-dicarboxylic acid or their esters with diols such as ethylene glycol, diethylene glycol, tetramethylene glycol, and neopentyl glycol. Group polyester. The polyester can be obtained by direct polycondensation of aromatic dicarboxylic acid and glycol, or can be obtained by single polycondensation after transesterification of aromatic dicarboxylic acid dialkyl ester and glycol, or by polycondensation of aromatic dicarboxylic acid dialkyl ester and glycol, or by polycondensation of aromatic dicarboxylic acid dialkyl ester and glycol. It can also be obtained by a method such as polycondensation.

Typical examples of such polymers include polyethylene terephthalate, polyethylene-2,6 naphthalate,
Polytetramethylene terephthalate, polytetramethylene-2,6-naphthalate, etc. 1 For example, polyethylene terephthalate or polyethylene-2,6-naphthalate.

Not only polyesters in which terephthalic acid or naphthalene-2,6-dicarboxylic acid and ethylene glycol are bonded, but also polyesters in which 80 mol% or more of the repeating units are ethylene terephthalate or ethylene-2,6-naphthalate units, and 20% of the repeating units are It may be a copolymerized polyester in which other components account for mol % or less, or a mixed polyester in which other polymers are added and mixed with these polyesters. In particular, it is preferable to copolymerize polyalkylene glycol such as polyethylene glycol, polytetramethylene glycol, etc. as a diol component in order to improve the adhesion with the magnetic layer.When adding or mixing other polymers to polyester, the properties of polyester are essentially the same. Polyolefins, polyamides, polycarbonates, other polyesters, etc. can be added in a proportion of less than 15% by weight.

Furthermore, inert fine particles that act as a lubricant or the like may be added to the polyester, if necessary.

The amount of inert fine particles added is not particularly limited, but is usually 0.
It is preferable to contain 0.005 to 2 wt%.

Also, the average particle diameter of the particles is o, oos~5゜0)bm
is within the range of

Inert fine particles suitable for this purpose include high melting point organic compounds that are insoluble during melt film formation of polyester resin, crosslinked polymers, and metal compound catalysts used during polyester synthesis, such as alkali metal compounds and alkaline earth metal compounds. Internal precipitated particles formed inside the polymer during polyester production, and e.g. M g O+ Z
n O9M g C03HCaCO3, Ca5Oa
l BaSO4HAl2O3,5i02. TiO2,S
in, LiF.

Clay minerals such as talc and kaolin, celite, mica, etc.
Mention may be made of inert externally added particles such as terephthalates such as Ca, Ba, Zn and Mn. In addition, inert organic compounds such as metal soap, starch, and carboxymethyl cellulose can also be cited as examples of inert particulate compounds.

Of course, in addition to these particles, compounds such as dyes, pigments, colorants, stabilizers, antistatic agents, conductive substances, antioxidants, antifoaming agents, etc. may be blended as necessary.

The particles may be added before polyester polymerization, during the polymerization reaction, or may be kneaded in an extruder when pelletizing after polymerization. Furthermore, it may be added during melt extrusion into a sheet, dispersed in an extruder, and extruded.

In the present invention, in order to give the film smoothness and smoothness, the refractive index n in the thickness direction of the film is 1°492 or more,
It is preferably 1.493 or more, and the number A (pieces/mm2) of unevenness units per 1 mm2 of the film surface area consisting of a protrusion and a depression with the protrusion as a core and a diameter of at least 0.5 pm. It is necessary that the expression 0 be satisfied.

0≦A≦5000...■ A may be zero, but it is preferable that at least the uneven unit exists. On the other hand, if it exceeds 5,000, it is unsuitable because it has excellent flatness, but is poor in slipperiness, particularly in runnability during multiple runs.

In order to obtain such a film, among the amount and type of inert fine particles described above and the film forming conditions described later, it is necessary to
It can be adjusted by changing n.

Here, the refractive index in the thickness direction n1. , is 1.492 or more and satisfies the formula 0, this can be achieved by lowering the birefringence (Δn) after longitudinal stretching to 0.080 or less. In order to keep Δn after longitudinal stretching to 0.080 or less, when longitudinal stretching is performed in one step, the temperature is 90°C.
Although it can be obtained by stretching the film by a factor of 3.5 or less, it is preferable to perform the stretching in two or more stages in order to improve thickness unevenness in the longitudinal direction. When performing multistage longitudinal stretching of two or more stages, first, Δn before the final stage stretching is 0.015 to 0.0.
1°2 to 4.0 times 1 at 75℃ to 150℃ so that the temperature becomes 55.
'Longitudinal stretching in stages or multiple stages, and Δn is 0.08 in the final stage.
Stretched in the machine direction by 1.1 to 2.0 times at 85 to 150°C so that the film thickness is 0 or less.

In this way, a film is obtained which has concavo-convex units having n, .

Here, by keeping Δn low after longitudinal stretching, why nC
Although it is not certain whether A becomes high and a concavo-convex unit is formed with the particle diameter as the nucleus, the following can be considered.

By keeping the birefringence (Δn) low after the longitudinal stretching, the plane orientation of the benzene rings in the skeleton of polyethylene terebutarate toward the film surface decreases, and the refractive index n in the thickness direction increases accordingly. It is also believed that if the birefringence after longitudinal stretching is low to some extent, a difference in orientation will occur around the particles, and if this is laterally stretched, a depression will be formed with the particles as a core.

In the film thus obtained, the grains of the film are uniform and dense, and the grains have voids around them and are steep, resulting in a film that is extremely flat and has excellent slipperiness.

By the way, even if the film satisfies the above-mentioned characteristics, it still cannot be said to have a sufficient mass coefficient when it is run many times, especially when it is run many times under high temperature and humidity.

As a means to improve this, the present invention uses an organic lubricant of 0.0
05 to 0.5% by weight of the film. This makes it possible to significantly reduce the mass coefficient after the film has been run many times. If the amount of the organic lubricant is less than 0.005% by weight, it will not be possible to achieve the desired effect of lowering the mass coefficient, and if it exceeds 0.5% by weight, the organic lubricant will bleed out onto the film surface, causing a problem in the magnetic layer. This is not preferable because it lowers the adhesion to the film and the strength and thermal stability of the film.

The organic lubricant used in the present invention is not particularly limited, but fatty acids, fatty acid esters, alkylene bisalkylamides, and N,N'-dialkyl aromatic amides are preferred. Fatty acids and fatty acid esters have 1 carbon number
The number of carbon atoms is preferably 6 or more, and the alkyl group of the amide preferably has 16 or more carbon atoms. Preferred examples of fatty acids include those with a large number of carbon atoms such as montanic acid. Examples of the fatty acid ester include montanic acid EG ester. Examples of alkylene bis aliphatic and aromatic amides include hexamethylene bis behenamide, hexamethylene bis stearyl amide, N,N'-distearyl terephthalamide, and the like.

In this way, a film can be obtained which is excellent in flat lubricity, adhesion to the magnetic layer, and multi-running performance. Furthermore, in order to improve wear resistance, that is, to prevent white powder from being generated due to abrasion with the guide roll during the coating process with the magnetic layer, friction with the guide pin when used as a magnetic tape, and abrasion, it is necessary to In particular, the average particle size is 0°9Pm to 10.0. This can be solved by containing 0.001% to 0.7% by weight of inert external particles of wm.

The average particle size of the inert externally added particles is 0.9 to 10, OP
m, and must be between 1.0 and 7. CIpm is more preferred. Moreover, it is preferable that the average particle size of the inert external particles is larger than that of the other particles used. The content of inert externally added particles is o.

The content should be 0.01 to 0.7% by weight, preferably 0.01 to 0.7% by weight.
0.003 to 0.5% by weight. The average particle size of the inert externally added particles is 10. If the content exceeds OP or if the content of the inert externally added particles exceeds 0.7% by weight, the number of coarse particles will increase and dropout will occur frequently, which is unsuitable. on the other hand.

The average particle size of the inert externally added particles is 0.9. If the content is less than 0.001% by weight, the effect of reducing white powder generation, which is the objective of the present invention, cannot be achieved.

Thus, the present invention has made it possible to provide a polyester film that satisfies various properties required for a magnetic tape.

Next, the method for forming the polyester film of the present invention will be specifically explained.

inert particulates (internal particles and/or inert external particles),
A polymer resin containing an appropriate amount of inert external particles with an average particle size of 0.9 Pm-10,0,0 mm and an organic lubricant, a mixed resin thereof, or a resin added during extrusion is dried by a conventional method and extruded. The polyester is melt extruded through a machine and cooled and solidified on a rotating cooling drum to form an unstretched polyester sheet. At this time, it is preferable to employ a known contact method such as an electrostatic application cooling method.

The unstretched film thus obtained is first stretched in the first axial direction, usually the longitudinal direction, so that its refractive index is 0°080 or less, and then stretched at 90°C in the direction perpendicular to the first axial direction. ~1
Stretched 2.5~5°0 times at a temperature of 50°C, then stretched at 200°C~
Heat set at 250°C for 1 second to 10 minutes. Thus, n1
A biaxially stretched polyester film of ≧1.492.0≦A≦5000 is obtained. However, n4 ≧1.492.0≦
As long as A≦5000 is satisfied, it is also a preferable method to re-stretch longitudinally and/or transversely again before heat setting.

In the present invention, Δn after first axial stretching, usually longitudinal stretching, is 0.
．． It is necessary to set it to 080 or less.

If Δn exceeds o or oso, n will be less than 1.492, and uneven units with protrusions as cores will not be formed, which is not preferable.

In addition, in order to particularly improve thickness unevenness, it is preferable to carry out stretching in the first axial direction in multiple stages, and when performing multi-stage stretching, the birefringence before the final stage is set to 0.015 to 0°055, and the birefringence in the final stage is It is preferable to stretch the film to a length of 0.080 or less in the longitudinal direction. In order to increase the longitudinal stretching ratio, it is also preferable to apply super draw or stretching in the vicinity of super draw.

The present invention will be explained in more detail in Examples below.
It goes without saying that the present invention is not limited to these.

The method for measuring each physical property of the film will be described below.

(1) Coefficient of friction (P) A film is brought into contact with a fixed hard chrome-plated metal roll (diameter 6 mm) at a wrapping angle of 135° (ρ).
A load of g (T2) was applied to one end and the vehicle was run at a speed of 1 m/min, and the resistance force (TI (g)) at the other end was measured, and the coefficient of friction during running was determined using the following equation.

and = 115 I n (TI /T2 ) = 0.
4241n (T+153) (2) Multiple runability,
A strip of slit-resistant film was placed on a winder, rubbed against a metal guide roll placed in the middle, and run back and forth at high speed. The 50th Masatsu coefficient at this time is ps
It was measured as o. In addition, the amount of white powder generated at this time was measured, and the powder resistance was ranked as follows.

Rank 1: Good: 2: Fair: 3: Poor: 4: Extremely poor (3) Center line average surface roughness Ra) It was determined as follows using a surface roughness meter (SE-3FK) manufactured by Koita Research Institute. The tip radius of the stylus is 2, -m, and the load is 30 m g.
It is. A section of standard length L (2.5 mm) is extracted from the film cross-sectional curve in the direction of its center line, and the roughness curve y=f ( x), the value given by the following equation is expressed as wm. However, the cutoff value is 80 parts m. Ra is a total of 5 points in the vertical direction and 5 points in the horizontal direction.
The average value of the points was calculated.

(4) Birefringence Retardation was measured using a polarizing microscope manufactured by Carl Zeiss, and the birefringence (80) was determined using the following formula.

Δn=R However, R: Retardation d: Film thickness 5) Number of uneven units (propellers) with depressions around the protrusions (A) Photograph of the surface of the aluminum-deposited film with a Carl Zeiss differential interference microscope at 750x magnification A total of 1m per shot
The major axis of the protrusion per m2 film surface area is at least 0.5. = Number A (pieces/
m m2) was counted.

Aborted salmon (method for manufacturing polyester) 100 parts of dimethyl terephthalate, 70 parts of ethylene glycol, 0.10 parts of calcium acetate hydrate, and 0.617 parts of lithium acetate dichloride were charged into a reactor, and as the temperature was raised, methanol was distilled off. It took about 4 hours after the start of the reaction to reach 230°C,
The transesterification reaction was substantially completed.

Next, add 0.35% of triethyl phosphate to this reaction product.
of antimony dioxide as a polycondensation catalyst.
．． After adding 05 parts, polymerization was carried out according to a conventional method to obtain a polyester. The polyester contains particles with a particle size of approximately 0.5 to
1) Many uniform and fine precipitated particles containing calcium, lithium, and phosphorus elements were observed. The polyester A had a value of 0.65.

Separately, polyester B ((1)=0.65) containing neither internally precipitated particles nor inert externally added particles was produced.

Further, as external particles in polyester B, the average particle size was measured by Coulter counter method and was 1.04. -Polyester C containing 0.4% by weight of calcium carbonate ((7j)=0.6
5) and 0.4% by weight of lithium fluoride with a similar average particle size
Polyester D containing ((y)=0.65) was produced. on the other hand.

Polyester E containing 0.2% by weight hexamethylene bisbehenamide in polyester B = 0.6
5) was manufactured.

(11 membrane method) Example 1 Polyester A, polyester B, polyester C and polyester E were mixed into A:B:C:E=50:35:5:t
The mixture was blended at a ratio of o, dried by a conventional method, extruded at 285° C., and rapidly cooled to obtain an amorphous sheet.

The amorphous sheet was stretched 3.4 times at 105°C to give Δ.

After n was set to 0.040, it was stretched 1.25 times at 100°C to give Δn=0.059. The longitudinally stretched film thus obtained was then stretched in the transverse direction by 3.8 times at 140°C using a tenter and heat-set at 207°C to obtain a 15P film.

Example 2 A:B:D:E=50:35:5: A 15□ film was obtained by polymerizing and forming a film in the same manner as in Example 1 except for to.

Example 3 In Example 1, the second stage stretching ratio during longitudinal stretching was 1.3.
Polymerization and film formation were carried out in the same manner as in Example 1, except that the film was doubled and Δn after longitudinal stretching was 0°070 to obtain a film of No. 15.

Example 4 The longitudinally and laterally stretched film before heat setting in Example 1 was
Stretched 1.07 times at 0°C and heat hardened at 207°C 15. − film was obtained.

Comparative Example 1 Using an amorphous film prepared in the same manner as in Example 1, the amorphous film was stretched 3°7 times in the longitudinal direction at 85°C, and then 1
The film was stretched 3.9 times in the transverse direction at 00°C and heat-set at 210°C to obtain a 15.1-film.

Although the film contains an organic lubricant, the Δn after longitudinal stretching is high, the n value is as low as 1.4887, and there is no concavo-convex unit having depressions.

Comparative Example 2 In Example 3, the second stage stretching ratio was 1.37 times,
Polymerization and film formation were carried out in the same manner as in Example 3, except that Δn after longitudinal stretching was set to 0.085, to obtain a film 15)-.

In this film, a very small amount of concavo-convex units having depressions is present and it also contains an organic lubricant, but the Δn after longitudinal stretching is high and nd is 1.4.
It is a film smaller than 92.

Comparative Example 3 Polymerization and film formation were carried out in the same manner as in Example 4, except that the re-longitudinal stretching ratio was set to 1.20 times in Example 415)
− film was obtained. The film has a sufficient number of concavo-convex units having depressions, and although the Δn after longitudinal stretching and before transverse stretching is low, the re-longitudinal stretching ratio is high, so n4 is smaller than 1.492.

Comparative Example 4 A film was formed in the same manner as in Example 1 except that polyester A, polyester B, and polyester C were blended at A:B:C=50:45:5. A film of &- was obtained. The film has a sufficient number of concavo-convex units having depressions, and the Δn after longitudinal stretching is low and n(i is also 1.492 or more, but the film does not contain an organic lubricant.

Example 5 Polyester A, polyester B, and polyester E were blended at A:B:E=50:45:5 and a film was formed in the same manner as in Example 1. 15. − film was obtained.

Comparative Example 5 A film of 15P was obtained by forming a film in the same manner as in Comparative Example 1 using polyester A and polyester B with A:B=1:1.

The film does not contain an organic lubricant, has a Δn of less than 1,492 after longitudinal stretching, and has no uneven units having depressions.

As shown in Table 1, it contains an organic lubricant and contains n(((1.
A film containing inert particles with an average particle size of 0.9□m or more and 10.07m or less has an average particle diameter of 0.9□m or more and 10.07m or less, and has a mean particle diameter of 0.9□m or more and 10.07m or less. It can be seen that the material is extremely superior in terms of ease of carrying and slipping, multi-run performance, and anti-slip resistance.

1" mound υ coffee As described above, the present invention is directed to a method in which ng is 1.492 or more and 0≦A≦5000, as described in the claims above.
and organic lubricant o, oos weight% or more, 0.5% by weight
By containing the following, or furthermore, the average particle size O is 9 μm or more, 10.0. By containing 0.001% by weight or more and 0.7% by weight or less of inert particles of -m or less, an excellent polyester film with good abrasion resistance, multi-time running properties, and no white powder generation can be obtained. This polyester film is excellent as a base film for magnetic recording media.

Claims (2)

[Claims] (1) The refractive index n_d in the thickness direction of the film is 1.492
or more, and the major axis of the protrusion and the protrusion as a core is at least 0.
．． Film surface area of uneven unit consisting of 5 μm depressions 1
For magnetic recording material, characterized in that the number A per mm^2 (pieces/mm^2) satisfies the formula [1] and contains an organic lubricant of 0.005% by weight or more and 0.5% by weight or less Polyester film. 0≦A≦5000...[1] (2) The magnetic recording medium according to claim 1, which contains inert external particles with an average particle size O of 9 μm or more and 10.0 μm or less in an amount of 0.001% by weight or more and 0.7% by weight or less. Polyester film.