JPH0420369B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Application Fields The present invention is suitable for use as a base film for magnetic recording media, which has excellent smoothness, adhesion with the magnetic layer, multi-time running properties, etc., and generates little white powder even when it comes into contact with the guide part. The present invention relates to particularly useful biaxially oriented polyester films. Conventional technology and problems to be solved Biaxially stretched polyester film has excellent heat resistance, mechanical properties, chemical resistance, etc., and is used for magnetic recording media, especially magnetic tapes for audio and video, and floppies. Demand for magnetic sheets is rapidly increasing. In recent years, these magnetic recording media have been trending toward higher quality and higher density, and there is a demand for better flat base film lubricity, better adhesion with the magnetic layer, and better multi-run performance. There is. Further, magnetic recording media are manufactured by applying a binder containing magnetic powder onto a base film using, for example, a combination of a coating roll and a doctor knife. Also, the friction and abrasion between the polyester film and the roll surface are severe, and the surface of the film itself is scraped and a white powder-like substance is precipitated, resulting in dropouts. Furthermore, recording a tape or sheet coated with the magnetic material,
When used for recording, etc., friction and abrasion at the guide portion may cause scratches on the film, producing white powder, and worsening the slipperiness after running many times. A base film that satisfies all of these characteristics has not yet been perfected, and there has been a strong demand from film manufacturers. Means for Solving the Problems The present inventor has conducted intensive studies to develop a film that maintains the smoothness of the film and its adhesion to the magnetic layer, while also improving its abrasion resistance and multi-running performance. As a result, the inventors have discovered that the problem can be solved by adjusting the physical properties of the polyester film to a certain range and mixing it with a suitable organic lubricant and particles, and have arrived at the present invention. That is, the present invention has a refractive index n in the thickness direction of the film of 1.492 or more, and the number A (number of protrusions and recesses per 1 mm ² of the film surface area) consisting of a protrusion and a depression with a major axis of at least 0.5 μm with the protrusion as the core. /mm ² ) satisfies the formula 0≦A≦5000... and the organic lubricant is 0.005% by weight or more, 0.5
The present invention relates to a polyester film for magnetic recording media, characterized in that the content is less than % by weight. The polyester referred to in the present invention refers to aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, and naphthalene-2,6-dicarboxylic acid or esters thereof, and diols such as ethylene glycol, diethylene glycol, tetramethylene glycol, and neopentyl glycol. It is a crystalline aromatic polyester that can be obtained by polycondensation. The polyester can be obtained by direct polycondensation of aromatic dicarboxylic acid and glycol, or can be obtained by transesterification of aromatic dicarboxylic acid dialkyl ester and glycol, followed by polycondensation, 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., such as polyethylene terephthalate,
Or polyethylene-2,6-naphthalate is
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 glycol.
It may be a copolyester consisting of 2,6-naphthalate units, in which 20 mol% or less of the repeating units are other components, or a mixed polyester obtained by adding and mixing other polymers to these polyesters. In particular, it is preferable to copolymerize a polyalkylene glycol such as polyethylene glycol or polytetramethylene glycol as a diol component in order to improve the adhesiveness with the magnetic layer. When adding or mixing other polymers to polyester, it is necessary to add or mix within a range that does not essentially change the properties of the polyester, and polyolefins, polyamides, polycarbonates, other polyesters, etc. must be added in a proportion of less than 15% by weight. Can be added. 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 it is usually preferable to add 0.005 to 2 wt%. Further, the average particle size of the particles is in the range of 0.005 to 5.0 μm. 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. Therefore, internal precipitated particles formed inside the polymer during polyester production and, for example, MgO, ZnO, MgCO ₃ ,
CaCO ₃ , CaSO ₄ , BaSO ₄ , Al ₂ O ₃ , SiO ₂ , TiO ₂ ,
Examples include clay minerals such as SiC, LiF, talc, and kaolin, celite, mica, and 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,
The mixture may be kneaded during the polymerization reaction, or may be kneaded in an extruder when pelletizing after the polymerization is completed. 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 flat smoothness, the refractive index n〓 in the film thickness direction is 1.492.
As mentioned above, it is necessary that the value is preferably 1.493 or more, and the number A (pieces/mm ² ) per 1 mm ² of the film surface area of a unit of unevenness consisting of a protrusion and a depression with a major axis of at least 0.5 μm with the protrusion as a core. It is necessary that the equation is satisfied. 0≦A≦5000...Although A may be zero, 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, the amount and type of the inert fine particles described above and the film forming conditions described below can be adjusted by changing Δn after longitudinal stretching. In order to produce a film having a refractive index n〓 in the thickness direction of 1.492 or more and satisfying the formula, this can be achieved by lowering the birefringence (△n) after longitudinal stretching to 0.080 or less. △n after longitudinal stretching is 0.080
In order to achieve the following, when longitudinal stretching is performed in one step, it is obtained by stretching at a temperature of 90°C or higher and 3.5 times or less, but in order to improve the thickness unevenness in the longitudinal direction, stretching is performed in two or more stages. It is preferable to do so. 2
When carrying out multi-stage longitudinal stretching, first the temperature is adjusted to 75°C so that △n is 0.015 to 0.055 before the final stage stretching.
Longitudinal stretching 1.2 to 4.0 times at ~150°C in one or multiple stages,
Furthermore, at the final stage, the temperature is increased to 85℃ so that △n is 0.080 or less.
Stretch 1.1 to 2.0 times in the machine direction at 150°C. In this way, a film is obtained in which n〓 is 1.492 or more and has concavo-convex units consisting of concavities and concavities with particles as nuclei. Here, it is not clear why n〓 becomes high by keeping Δn low after longitudinal stretching and uneven units are formed with the particle diameter as the core, but the following is thought to be the reason. By keeping the birefringence (Δn) low after the longitudinal stretching, the plane orientation of the benzene rings in the skeleton of polyethylene terephthalate toward the film surface is reduced, and the refractive index n〓 in the thickness direction is accordingly increased.
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 nucleus. In the film thus obtained, the particles of the film are uniform and dense, and the particles are steep with voids surrounding them, resulting in a film that is extremely flat and has excellent slipperiness. By the way, even with a film that satisfies the above-mentioned characteristics, the mass coefficient when the film is run many times, especially when it is run many times under high temperature and humidity, is still not sufficient. As a means to improve this, in the present invention, 0.005 to 0.5% by weight of an organic lubricant is contained in 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 able to exhibit 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, resulting in poor adhesion with the magnetic layer. or reduce the strength of the film,
This is not preferred because it reduces thermal stability. The organic lubricants used in the present invention are not particularly limited, but examples include fatty acids, fatty acid esters, alkylene bisalkylamides, N,
N'-dialkyl aromatic amides are preferred. Fatty acids and fatty acid esters preferably have 16 or more carbon atoms,
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 fatty acid esters include montanic acid EG ester and the like. Examples of alkylene bis aliphatic and aromatic amides include hexamethylene bis behenamide, hexamethylene bis stearyl amide, N,N'-
Examples include distearyl terephthalamide. In this way, a film can be obtained that is excellent in flat lubricity, adhesion to the magnetic layer, and multi-time 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, inert external particles with an average particle size of 0.9 μm to 10.0 μm are used.
This can be solved by containing 0.001% to 0.7% by weight. The average particle size of the inert externally added particles is 0.9 to 10.0μ
m, more preferably 1.0 to 7.0 μm. Moreover, it is preferable that the average particle size of the inert external particles is larger than that of the other particles used. Further, the content of the inert externally added particles must be 0.001 to 0.7% by weight, preferably 0.003 to 0.5% by weight. If the average particle size of the inert externally added particles exceeds 10.0μ or the content of the inert externally added particles is
If it exceeds 0.7% by weight, it is unsuitable because the number of coarse particles increases and drop-outs occur frequently. On the other hand, the average particle size of the inert externally added particles is 0.9μ
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 a polyester film of the present invention will be specifically explained. A polymer resin containing an appropriate amount of inert fine particles (inner particles and/or inert outer particles), inert outer particles with an average particle size of 0.9 μm to 10.0 μm, and an organic lubricant, or a mixed resin thereof or addition at the time of extrusion. The resin is dried by conventional means, melt extruded through an extruder, 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 has a refractive index △n in the first axis direction, usually in the longitudinal direction.
0.080 or less, then stretched 2.5 to 5.0 times in the direction perpendicular to the first axis direction at a temperature of 90°C to 150°C, and heat set at 200°C to 250°C for 1 second to 10 minutes. In this way, a biaxially stretched polyester film with n≧1.492 and 0≦A≦5000 is obtained. However, n〓≧1.492,
As long as 0≦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, it is necessary that Δn after first axial stretching, usually longitudinal stretching, be 0.080 or less. △n
If it exceeds 0.080, 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 especially improve thickness unevenness, it is preferable to carry out multi-stage stretching in the first axial direction, and when performing multi-stage stretching, the birefringence before the final stage is set to 0.015 to 0.055, and the longitudinal stretching at the final stage is set to 0.080. It is preferable to stretch it so that it becomes as follows. In order to increase the longitudinal stretching ratio, it is also preferable to apply super draw or stretching in the vicinity of super draw. EXAMPLES The present invention will be explained in more detail in Examples below, but it goes without saying that the present invention is not limited thereto. The method for measuring each physical property of the film will be described below. (1) Coefficient of friction (μ) A film is brought into contact with a fixed hard chrome-plated metal roll (diameter 6 mm) at a wrapping angle of 135° (θ), and a load of 53 g (T ₂ ) is applied to one end.
This was run at a speed of m/min, the resistance force [T ₁ (g)] at the other end was measured, and the coefficient of friction during running was determined using the following equation. μ = 1/θln (T ₁ / T ₂ ) = 0.424ln (T ₁ / 53) (2) Multiple running performance, anti-slip property The film was slit into a thin strip, passed through a winder, and placed in the middle. It was rubbed against a metal guide roll and moved back and forth at high speed. at this time
The 50th Masatsu coefficient was measured as μ50.
In addition, the amount of white powder generated at this time was measured, and the powder resistance was ranked as follows. Rank 1st grade Good 2nd grade Fair 3rd grade Bad 4th grade Extremely poor (3) Center line average surface roughness (Ra) Kosaka Laboratory Co., Ltd. surface roughness measuring instrument (SE-3FK)
It was calculated as follows. The tip radius of the stylus is
2μm, load is 30mg. A part of the standard length L (2.5 mm) is extracted from the film cross-sectional curve in the direction of its center line, and with the center line of this extracted part as the X axis and the vertical magnification direction as the Y axis, the roughness curve y is
When expressed as =f(x), the value given by the following formula is expressed in μm. However, the cutoff value is 80μ
It is m. For Ra, the average value of a total of 10 points, 5 points in the vertical direction and 5 points in the horizontal direction, was calculated. 1/L∫ ^L ₀ |f(x)|dx (4) Birefringence Retardation was measured using a polarizing microscope manufactured by Carl Zeiss, and birefringence (△n) was determined using the following formula. △n=R/d where R: Retardation d: Film thickness (5) An uneven unit (propeller) with depressions around the projections
Number of pieces (A) Photograph the surface of the aluminum-deposited film using a Carl Zeiss differential interference microscope at 750x magnification to determine the number of concavo-convex units consisting of depressions with protrusions as cores and depressions with a major diameter of at least 0.5 μm per 1 mm ² of total film surface area. The number A (pieces/mm ² ) was counted. Example 1 (Production method of polyester) 100 parts of dimethyl tereftate, 70 parts of ethylene glycol, 0.10 parts of calcium acetate monohydrate, and 0.17 parts of lithium acetate dihydrate were charged into a reactor, and as the temperature was raised, methanol was distilled off. The transesterification reaction was carried out by allowing the transesterification to occur, and it took about 4 hours after the start of the reaction.
The temperature was reached to 230°C, and the transesterification reaction was substantially completed. This reaction product is then treated with triethyl phosphate.
After adding 0.35 part of antimony trioxide and further adding 0.05 part of antimony trioxide as a polycondensation catalyst, polymerization was carried out according to a conventional method to obtain a polyester. In the polyester, many uniform and fine precipitated particles containing calcium, lithium, and phosphorus elements with a particle size of approximately 0.5 to 1 μm were observed. The polyester A had [η]=0.65. Separately, polyester B ([η]=0.65) containing neither internally precipitated particles nor inert externally added particles was produced. In addition, polyester C contains 0.4% by weight of calcium carbonate with an average particle size of 1.4μ as measured by the Coulter counter method as external particles in polyester B.
([η] = 0.65) and polyester D containing 0.4% by weight of lithium fluoride with a similar average particle size ([η] = 0.65)
was manufactured. On the other hand, polyester E ([η]=0.65) containing 0.2% by weight of hexamethylene bisbehenamide in polyester B was produced. (Film forming method) Example 1 Polyester A, polyester B, polyester C and polyester E were mixed into A:B:C:E=50:
The mixture was blended in a ratio of 35:5:10, dried by a conventional method, extruded at 285°C and rapidly cooled to form an amorphous sheet. The amorphous sheet was stretched 3.4 times at 105℃ to obtain △n.
0.040 and then stretched 1.25 times at 100℃ △n=0.059
And so. The thus obtained longitudinally stretched film was then stretched 3.8 times in the transverse direction at 140°C using a tenter and heat-set at 207°C to obtain a 15μ film. Example 2 A 15 μm film was obtained by polymerizing and forming a film in the same manner as in Example 1 except that A:B:D:E=50:35:5:10. Example 3 Polymerization and film formation were carried out in the same manner as in Example 1, except that the second stage stretching ratio during longitudinal stretching was 1.32 times, and Δn after longitudinal stretching was 0.070, to obtain a 15μ film. Ta. Example 4 The longitudinally and laterally stretched film before heat setting in Example 1 was stretched 1.07 times at 150°C and heat set at 207°C to obtain a 15μ film. 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, then stretched 3.9 times in the transverse direction at 100°C, and heat-set at 210°C. A 15μ film was obtained. The film contains an organic lubricant, but after longitudinal stretching
The film has a high n value, a low n〓 of 1.4887, and has no concavo-convex units having depressions. Comparative Example 2 Polymerization and film formation were carried out in the same manner as in Example 3, except that the second stage stretching ratio was 1.37 times and Δn after longitudinal stretching was 0.085, to obtain a 15 μm film. In this film, a very small amount of uneven units having depressions is present and it also contains an organic lubricant, but the Δn after longitudinal stretching is high.
It is a film with n〓 smaller than 1.492. Comparative Example 3 A 15 μm film was obtained by polymerization and film formation in the same manner as in Example 4, except that the longitudinal stretching ratio was set to 1.20 times. In this film, there are enough uneven units having depressions, and △n after longitudinal stretching and before transverse stretching is low, but because the re-longitudinal stretching ratio is high, n〓 is 1.492.
It is a smaller film. Comparative Example 4 A 15 μm film was obtained in the same manner as in Example 1 except that polyester A, polyester B, and polyester C were blended in a ratio of A:B:C=50:45:5. The film has a sufficient number of concavo-convex units having depressions, has a low Δn after longitudinal stretching, and has a n〓 of 1.492 or more, but does not contain an organic lubricant. Example 5 Polyester A, polyester B, and polyester E were blended in a ratio of A:B:E = 50:45:5 and formed into a film in the same manner as in Example 1 to obtain a 15μ film. Comparative Example 5 Polyester A and Polyester B A:B=
A film of 15μ was obtained by forming a film in the same manner as in Comparative Example 1 with a ratio of 1:1. The film does not contain an organic lubricant, has a high Δn after longitudinal stretching, has a n〓 of less than 1.492, and has no concavo-convex units having depressions. As shown in Table 1, it contains an organic lubricant and
A film that is 1.492 or more and 0≦A≦5000 and further contains inert particles with an average particle size of 0.9 μm or more and 10.0 μm or less has better flat lubricity and multiple running properties than films outside these ranges. , it can be seen that the material is significantly superior in terms of resistance to Japanese porpoise.

[Table] *: Calcium carbonate ☆: Effect of the lithium fluoride invention As described above, the present invention is as described in the claims, where n〓 is 1.429 or more, 0≦A≦
5000 and contains an organic lubricant of 0.005% by weight or more and 0.5% by weight or less, and furthermore, the average particle size is 0.9μ.
0.001% by weight of inert particles with a size of 10.0 μm or more
By containing 0.7% by weight or less, it has good wear resistance, multi-cycle running properties, and does not generate white powder.
An excellent polyester film is obtained and is an excellent polyester film as a base film for magnetic recording media.

Claims (1)

[Claims] 1. The refractive index n〓 in the thickness direction of the film is 1.492 or more, and the length of the protrusion and the major axis of the protrusion are at least
The number A (pieces/mm ² ) of uneven units consisting of 0.5 μm depressions per 1 mm ² of film surface area satisfies the formula,
A polyester film for magnetic recording media, characterized in that it contains an organic lubricant in an amount of 0.005% by weight or more and 0.5% by weight or less. 0≦A≦5000...2 The polyester for magnetic recording media according to claim 1, which contains inert external particles with an average particle size of 0.9 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. film.