JPH07114724A - Polyester film for magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide a polyester film excellent in running performance, running durability against repeated use, winding characteristics like a pancake and slitting characteristics and useful as a base film for a magnetic recording medium satisfying even the requirement of high image quality. CONSTITUTION:This polyester film contains spherical silica particles having 0.1-2.0mum volume average particle diameter and a relative standard deviation of >0.5 in polyester and simultaneously satisfies inequalities DELTAN(1,413-8,327XF, 20<DELTAN<80 and F<0.1800, wherein DELTAN=(NMD-NTD)X1,000 and F=(NMD+ NTD)/2-nz (where NMD is the refractive index of the film in the longitudinal direction, NTD is the refractive rndex of the film in the width direction and nz is the refractive index of the film in the thickness direction).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film for a magnetic recording medium, and more particularly to a polyester film suitable for a video tape having excellent running durability and slitting property.

[0002]

2. Description of the Related Art A magnetic recording medium using a polyester film has a drawback that the surface of the polyester film is scratched by a roll or the like which is in contact with the magnetic material coating / calendering process in the magnetic medium manufacturing process due to an increase in process speed. Has become a problem recently. Furthermore, with regard to video tapes, video recorders (V
(TR) Repeated reproduction and recording are often repeated, and the film surface is scratched due to contact friction with guide pins in the tape cassette, or powdery substances generated from the film due to contact friction. Problems such as deterioration of images due to dropouts are occurring. Further, at the time of slitting, which is the final step in the manufacturing process of magnetic recording media, particularly video tapes and the like, chips are generated from the cross section of the film, which causes an increase in dropout during magnetic recording. To solve these problems,
It is necessary to improve the runnability of the film by roughening the film surface and reducing the friction coefficient while making it difficult to scratch the film surface, but on the other hand, high image quality,
Due to the demand for recording for a long time, there is an increasing demand for a film that is smoother on the surface of the film to improve electromagnetic conversion characteristics and is thinner and has excellent dimensional stability. Furthermore, it is also necessary to impart the sharpness at the time of slitting to the film characteristics. Many studies have been made on the dilemma of these film surface characteristics and various characteristics, and for example, JP-A-59-171623 and JP-A-63-234038 contain spherical silica particles. In Japanese Patent Laid-Open No. 61-5431, it is disclosed in Japanese Patent Laid-Open No. 62-198439 that inert inorganic particles such as colloidal silica are contained.
A polyester film has been proposed in which the refractive index in the thickness direction of the film, the average refractive index, and the strength in the longitudinal direction are specified.

However, in reality, it is difficult to satisfy all the above problems even with such a known method.

[0004]

DISCLOSURE OF THE INVENTION The present invention solves these problems, the surface is less likely to be scratched (hereinafter referred to as scratch resistance), is excellent in running durability by repeated use, and has a slit in a magnetic recording medium manufacturing process. It is an object of the present invention to provide a polyester film for a magnetic recording medium which meets the demands for improved characteristics and higher image quality.

[0005]

The above object of the present invention is to provide a polyester having a volume average particle diameter of 0.1 to 2.0 μm and a relative standard deviation defined by the following formula (1) of 0.
0.005 to 5.0% by weight of spherical silica particles exceeding 5
It is achieved by a polyester film for a magnetic recording medium, which contains and simultaneously satisfies the following expressions (2) to (4).

[0006]

[Equation 2] ΔN <1413-8327 × F ‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ (2) 20 <ΔN <80 ‥‥‥‥‥‥‥‥‥ (3) F <0.1800 ‥‥‥‥‥‥‥‥‥‥ (4) [here , ΔN = (NMD-NTD) × 1000, F = (N
MD + NTD) / 2-nz, where NMD is the refractive index in the film longitudinal direction, NTD is the refractive index in the film width direction, and nz is the refractive index in the film thickness direction.] The polyester applied in the present invention is an aromatic dicarboxylic acid. Alternatively, it is produced by a polycondensation reaction as a bifunctional component such as its alkyl ester and a glycol component. Of these, those containing polyethylene terephthalate as a main component are preferable.

Further, a small amount of copolyester which does not impair the basic properties of the polyester film of the present invention may be mixed. Examples of the copolymerization component of the copolyester include dicarboxylic acid components such as 2,6-naphthalenedicarboxylic acid and isophthalic acid, oxycarboxylic acid components such as P-oxyethoxybenzoic acid, and tetramethylene glycol, propylene glycol, neopentyl. Examples include diol components such as glycol, polyoxyalkylene glycol, P-xylylene glycol, 1,4-cyclohexanedimethanol, polyethylene glycol, and 5-sodium sulforesorzine. Of these, a copolyester obtained by copolymerizing a diol component such as polyethylene glycol is preferable in order to improve the adhesiveness of the film to the magnetic binder and to keep the chargeability due to static electricity low.

Further, the polyester film of the present invention may contain recovered polyester mainly composed of non-product parts generated in the production stage. Furthermore, these polyesters preferably have an intrinsic viscosity of 0.5 or more, more preferably 0.55 or more.

The spherical silica particles in the present invention are synthetic silica produced by an alkoxide method, a water glass method or the like, for example, an ion exchange method using water glass (sodium silicate aqueous solution) as a starting material or an alkoxy silicate as a starting material. Can be synthesized by a hydrolysis method or the like. In particular, in order to improve the slitting property, which is one of the objects of the present invention, synthetic silica starting from water glass is more preferable, and further, 25% by weight of a 20 wt% ethylene glycol slurry of the spherical silica particles. The refractive index at
When it is 1.430 or more, preferably 1.435 or more, not only the occurrence of voids around the particles in the polyester is reduced, but also the effect of improving the slit property becomes remarkable, which is more desirable.

The term "spherical" as used in the present invention means the particle size ratio of the maximum diameter and the minimum diameter on the projection plane of the particles (maximum diameter / minimum diameter).
Is preferably 1.0 to 1.3, more preferably 1.
It is preferably 0 to 1.1. Here, it is shown that the particle diameter ratio of 1.0 is a true sphere. When the particle size is out of the range, friction between the metal guide and the film becomes large, and the running property is apt to deteriorate when the video tape is repeatedly used in the VTR, causing tape squeaking and running in the VTR. It may stop.
Therefore, it is preferable that the particles are in the above range particularly for a video tape application requiring durability during running, for example, a base film for recorded commercial tapes for movies and the like.

The relative standard deviation, which is a measure of the spread of the particle size distribution of the spherical silica particles, needs to exceed 0.5, preferably exceeds 0.6, and further exceeds 0.7. It is preferable. Further, the upper limit is not particularly defined, but it is preferably 3 or less in order to keep the waviness of the film surface well.

The relative standard deviation referred to here is represented by the following equation (1) as the ratio of the standard deviation obtained in number unit from the area-equivalent diameter of particles and the number average diameter.

[0013]

[Equation 3] When spherical silica particles with a relative standard deviation of more than 0.5 are used, the slitting property, especially the continuous slitting property is improved, and the slit blade is changed for a long time at the time of the final step of the magnetic tape manufacturing process such as video tape. At least, the amount of cutting chips or shavings generated from the film cut edge is extremely small, and the swelling of the end cross section of the film cut edge is also reduced. It is considered that the manifestation of this effect is brought about by the extremely small wear of the slit blade in the step.

In the present invention, the volume average particle diameter of the spherical silica particles is required to be 0.1 to 2.0 μm, preferably 0.1 to 1.0 μm. When the volume average particle diameter of the particles is smaller than 0.1 μm, friction increases, and running characteristics when a video tape is used deteriorates.
On the other hand, if it is larger than 2.0 μm, the electromagnetic conversion characteristics of the magnetic recording medium represented by the video tape will be poor. Also,
The content of the spherical silica particles is required to be 0.005 to 5.0% by weight, preferably 0.01 to 2.0% by weight, and more preferably 0.1 to 5.0% by weight based on the polyester.
It is preferably from 05 to 1.0% by weight. If the content of the particles is less than 0.005% by weight, friction increases and the running characteristics of a video tape deteriorate. On the other hand, if it is more than 5.0% by weight, the electromagnetic conversion characteristics of the magnetic recording medium represented by the video tape will be poor.

In the present invention, the method of incorporating the spherical silica particles into polyester is not particularly limited,
Generally, it is preferable to add a slurry of spherical silica particles during the production of polyester. How and when to add
Conventionally known methods and times are used, but as the addition method, a method of adding as a slurry of glycol, which is a raw material for synthesizing the polyester, is particularly preferable. The slurry concentration at this time is 0.5 to 40 as SiO ₂ weight%.
It is preferably in the range of 1 to 20% by weight, and more preferably in the range of 1 to 20% by weight because the particle dispersibility in polyester is improved. The water content in the glycol of the slurry at the time of addition is 1% by weight or less, further 0.5% by weight.
The following is preferable because the particle dispersibility in polyester is improved. The addition time may be arbitrary, and it may be added at the time of charging the monomer, at the time of transesterification reaction, or before and after it. In addition, the slurry of the particles may be added and dispersed by using a uniaxial or biaxial vent type extruder after the production of the polymer.

In addition to the spherical silica particles of the present invention, fine agglomerated fine particles may be contained in combination for the purpose of imparting scratch resistance to the film surface, that is, scratch resistance. Such aggregated fine particles are aggregates composed of a large number of particles having a primary particle diameter of 5 to 50 nm, and examples thereof include those containing zirconium oxide, aluminum oxide, etc. as a component, and have a specific surface area of 10 m ² by the BET method.
/ G or more is preferable, and 40 m ² / g or more is more preferable.

In addition, the aggregate fine particles made of aluminum oxide are known to have various types of crystal structures such as alpha type, gamma type, delta type and theta type.
Particularly excellent scratch resistance can be obtained by containing aluminum oxide having a delta type crystal structure. Although the reason for this is unknown, it is considered that the aluminum oxide particles having a theta-type or delta-type crystal structure have a high affinity with polyester and have a function of increasing the abrasion resistance of the film surface. Aluminum oxide having a theta-type crystal structure can be produced, for example, by a method in which alum is neutralized with carbonate after thermal decomposition, a thermal decomposition method from an aluminum alkoxide method, and the like.
It can be obtained by controlling conditions such as temperature. Aluminum oxide having a delta-type crystal structure can be produced by, for example, a method of hydrolyzing aluminum chloride.

When the fine particles of the aggregate are used in combination, the secondary particle diameter of the aggregate is 0.5 so as not to impair the effects of the present invention.
It is desirable to add 0.5% by weight or less, preferably 0.3% by weight or less, more preferably 0.2% by weight or less of aggregate fine particles having a size of less than or equal to μm, preferably less than or equal to 0.3 μm.

The agglomerate fine particles are, for example, 1 to 20.
It can be obtained by using, if necessary, a dispersion treatment by a sand grinder or the like, a classification treatment by a centrifugal classification treatment, a filtration treatment, etc., after making a wt% ethylene glycol slurry. Further, a dispersant such as a surfactant may be used together.

Further, other inert particles such as calcium carbonate, titanium dioxide, titanium monoxide, titanium nitride, kaolin, talc and other inorganic particles, and cross-linked polystyrene and other organic particles may be used as long as the effects of the present invention are not impaired. Particles, internally precipitated particles, additives such as antioxidants, heat stabilizers, and ultraviolet absorbers may be contained to the extent that they are usually added.

Examples of the internally deposited particles include particles produced by binding at least one compound selected from the group consisting of a calcium compound, a magnesium compound, a manganese compound, and a lithium compound added at the time of polyester synthesis with a polyester constituent component. . Further, the internally precipitated particles may contain elemental phosphorus and a trace amount of other metal components such as zinc, cobalt, antimony, germanium and titanium within a range that does not impair the effects of the present invention.

In order to achieve the object of the present invention, it is necessary that the plane orientation index F and ΔN are within the ranges which simultaneously satisfy the following expressions (2) to (4). Within such a range, not only the wear characteristics during repeated running become good, but also the film cut surface becomes smooth at the time of the slit and the edge corner becomes sharp, so that the contact with the guide pin in the VTR becomes uniform during running. Damage to the edges of the videotape is extremely low. Particularly when used as a video tape of a long-time recording type, peeling of the magnetic recording binder layer in the vicinity of the edge portion on the film surface is reduced, and the dropout characteristic upon repeated use becomes extremely good. ΔN <1413-8327 × F ‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ (2) 20 <ΔN <80 ‥‥‥‥‥‥‥‥‥ (3) F <0.1800 ‥‥‥‥‥‥‥‥‥‥ (4) [here , ΔN = (NMD-NTD) × 1000, F = (N
MD + NTD) / 2-nz, where NMD is the refractive index in the longitudinal direction of the film, NTD is the refractive index in the width direction of the film, and nz is the refractive index in the thickness direction of the film] Further, in the polyester film of the present invention, the plane orientation index F When the refractive index nz in the thickness direction is within the range that simultaneously satisfies the following formulas (5) and (6), not only the slit property becomes good, but also the abrasion property in the calendering process becomes good, and It is preferable because the adhesion between the magnetic recording binder layer and the film is also improved. nz ≦ 1.603-0.6407 × F (5) nz ≧ 1.595-0.6407 × F (6) where ΔN is increased by lowering NMD. It can be lowered by raising it. NMD can be raised by increasing the stretching ratio in the longitudinal direction, and can be lowered by lowering it. NTD can be raised by increasing the draw ratio in the width direction, and can be lowered by lowering it. The NMD can be raised by lowering the stretching temperature in the longitudinal direction, and conversely, can be lowered by raising it. NTD can be raised by lowering the stretching temperature in the width direction, and conversely, it can be lowered.

The plane orientation degree F can be raised by increasing the area ratio (stretching ratio in the longitudinal direction × stretching ratio in the width direction) during stretching, and conversely can be lowered by lowering it. it can. When the area ratio is the same, it can be raised by lowering the stretching temperature in the longitudinal direction or the width direction, and conversely, it can be lowered by raising the temperature.

The refractive index nz in the thickness direction can be increased by increasing the area ratio (stretch ratio in the longitudinal direction × stretch ratio in the width direction) during stretching, and conversely, can be decreased by lowering it. be able to. When the area ratio is the same, it can be increased by decreasing the stretching temperature in the longitudinal direction or the width direction, and conversely, it can be decreased by increasing the temperature. Further, it can be increased by increasing the heat treatment temperature, and conversely can be decreased by decreasing the heat treatment temperature.

The polyester film of the present invention is produced by appropriately adjusting the stretching ratio in the longitudinal and width directions, the stretching temperature and the heat treatment temperature. In particular, (2)-
In order to satisfy all the formulas (4), it is effective to stretch the unstretched film in the longitudinal and transverse directions or in the transverse and longitudinal directions and then stretch it again in the longitudinal direction. In this case, the re-stretching temperature is 90 to 150 ° C., and the stretching ratio is 1.05 to 1.
Six times is preferable in order to satisfy the above range.

The scraping index K in the present invention means a thickness of 10
Film 1 after being slit to 1/2 inch at a slit speed of 50 m / min with a shear cutter type slitter, and then slit to 1/2 inch
m was placed in a container containing 50 cc of pure water so that only one cut surface was immersed, and after ultrasonic treatment, the film sample was removed, and the immersion liquid was measured with a particle counter. It is defined as the number of particles having a particle size of ˜20 μm. In the present invention, it is preferable that the scraping index K is 60 or less, preferably 40 or less, because the audio characteristics during reproduction of the video tape are particularly good.

The polyester film for a magnetic recording medium in the present invention is biaxially oriented by a conventional method,
The thickness is preferably 3 to 50 μm, and further 5
It is applied in the range of -14 μm, more preferably 5-12 μm.

At least one surface of the polyester film of the present invention has a center line average surface roughness (Ra) of 8 to 30 n.
m, and the three-dimensional average surface roughness (SRa) is 13 to 50 n
m is preferable, and Ra is 12 to 25 n.
m, SRa is preferably from 17 to 40 nm. When the surface roughness is in the above range, the coefficient of friction is small, the abrasion resistance is good, and the image quality characteristics are good, which is preferable.
Furthermore, the number of protrusions having a height of 200 to 400 nm is 0.1 m.
More than 1200 pieces per m ² , and even more than 1350 pieces,
Particularly, the number is 1500 or more and the height is 400 nm to 80
The number of protrusions of 0 nm is 400 or less per 0.1 mm ² ,
Further, it is preferably 300 or less, and particularly preferably 200 or less. When the number of protrusions having a height of 200 to 400 nm and the number of protrusions having a height of 400 nm to 800 nm are within the above ranges, the use durability is particularly good and the image quality characteristics are good.

The polyester film of the present invention comprises a single layer,
Although it can be applied to both laminated films, from the viewpoint of surface flatness and the like, it is preferable to use a laminated film in which at least one layer of the polyester film of the present invention is arranged. The following combinations are desirable as the specific constitution when the laminated polyester film is formed. B / A / B B / A / C B / A where A: base layer polyester film B, C; laminated polyester film B / A is one side of the base layer polyester film A, B
/ A / B indicates that the polyester B is laminated on both sides of the polyester film A of the base layer.

Further, although A to C may contain the above-mentioned polyester and spherical silica particles, it is possible to utilize the above-mentioned recovered polyester in at least the A layer, and as the recovered polyester, , The terminal carbonyl group is 30 to 50 equivalents / ton, and further 30 to 4
It is preferably 0 equivalent / ton.

Here, the polyester film A of the base layer portion
May be a polyester film containing substantially no particles, or may contain particles. The type of particles is not particularly limited, for example, calcium carbonate as an inorganic particle, silica, kaolin, alumina, barium sulfate, may be fine particles unnecessary for polyester such as titanium oxide, also, organic particles such as cross-linked polystyrene. May be included.

The polyester films B and C of the laminated portion form a surface, and in order to realize the effects of the present invention, the polyester film containing the particles of the present invention is used for at least one laminated polyester film. It is preferable to laminate films. When laminated on both sides, the opposite surface is not limited to the polyester film containing the particles of the present invention, may be substantially free of particles, particles outside the present invention May be included. further,
A coating layer such as an antistatic agent may be provided in order to improve the adhesiveness with the magnetic agent and prevent static electricity.

The thickness ratio of the polyester film of the laminated portion containing the spherical silica particles of the present invention to the polyester film A of the base layer portion is preferably 40% or less, and the volume average diameter of the spherical silica particles is preferably 40% or less. However, it is more effective when the laminated thickness is 0.2 to 5 times.

Next, the method for producing the polyester film of the present invention will be described. First, as a method of incorporating spherical silica particles into a predetermined polyester, it may be added before polymerization, during polymerization, or after polymerization, but it is mixed and dispersed as a slurry in ethylene glycol which is a diol component of polyester. Is effective for obtaining the volume average diameter and relative standard deviation in the present invention.
Further, as a method for adjusting the content of particles, high concentration,
Preferably, a method of diluting a master pellet having a particle content of 1.0 to 5.0% by weight at the time of film formation is effective in obtaining the relative standard deviation, the volume average and the desired height distribution of surface protrusions in the present invention. It is valid.

Also, 1 part of ethylene glycol slurry is used.
The method of heat treatment at a temperature of 40 to 200 ° C., particularly 180 to 200 ° C. for 30 minutes to 5 hours, especially 1 to 3 hours is effective for obtaining the desired range of the relative standard deviation and the scraping index K in the present invention.

Thus, the pellets containing a predetermined amount of spherical silica particles are sufficiently dried, then supplied to a known melt extruder, extruded into a sheet form from a slit die at 270 to 330 ° C., and cooled on a casting roll. An unstretched film is made by solidifying. At this time, it is effective to install a high-precision two-stage filtration filter in the polymer channel in order to reduce coarse protrusions when the film is formed. The high-precision two-stage filtration filter referred to here is a filter in which the first stage has a 95% cutoff particle size of 4 to 10 μm and the second stage has a 95% cutoff particle size of 1.5 to 5 μm. The 95% cut-off particle size is the first stage> the second stage.

Here, in the laminated polyester film, at least one of polyesters B and C in the laminated portion is laminated by coextrusion on at least one surface of the polyester A in the base layer portion to form an unstretched film.

The laminated film in the present invention can be obtained by extruding the polyesters A, B and C by different extruders and coextruding them before discharging the laminated sheet from the die. This lamination may be performed in a die for forming and discharging into a sheet (for example, a manifold), but since the lamination thickness is thin as described above, it is preferable to perform it in the polymer pipe before being introduced into the die. . In particular, it is particularly preferable that the laminated portion in the polymer tube is formed in a rectangular shape because the laminated portion can be uniformly laminated in the width direction. The molten polymer laminated at the rectangular laminated portion in the polymer tube is widened to a predetermined width in the sheet width direction by the manifold in the die to obtain a sheet-shaped unstretched film from the die.

Therefore, even if the laminated polyester film after biaxial orientation is extremely thin, the polymer in the rectangular laminated portion in the polymer tube is laminated with a considerable thickness, so that it is easy and accurate. Can be stacked. By using two or three melt extruders, a confluent block or a die for two, three or five layers, B / A /
B, B / A / C, B / A, B / A / B / A / B, B / A
A laminated sheet of / C / A / B can be obtained. When the confluence block is used, it is effective to make the laminated portion rectangular as described above in order to stably produce the laminated polyester film of the present invention industrially without unevenness in the width direction.

Further, in the production of the polyesters B and C, a biaxial extruder is used to melt the particle slurry and the particle-free polyester while kneading, and the mixture is melted under a vacuum through a vent hole arranged in the extruder. A polyester containing the particles of the present invention may be produced by dispersing the solvent in the slurry while distilling it off.

Next, this unstretched film is biaxially stretched to be biaxially oriented. As a stretching method, a sequential biaxial stretching method or a simultaneous biaxial stretching method can be used. However, the sequential biaxial stretching method of first stretching in the longitudinal direction and then in the width direction is used, and the stretching in the longitudinal direction is divided into two stages, particularly three or more stages (polymer glass transition point + 20 ° C.) to In the range of (glass transition point of polymer + 60 ° C.), after stretching 3 to 5 times, the stretching temperature in the width direction is 100 to 160 ° C., the stretching ratio is 3 to
After stretching 5 times, the stretching temperature is 90 to 15 again in the longitudinal direction.
It is stretched at 0 ° C. and a stretch ratio of 1.05 to 2 times. Next, this stretched film is heat-treated. In this case, the heat treatment condition is preferably 150 to 230 ° C., preferably 180 to 210 ° C. for 0.5 to 60 seconds. In this heat treatment step, the stretching can be performed in the running direction and the width direction in any state of relaxation, fine stretching, and under constant length.

The characteristic values in the present invention are measured by the following measuring method,
According to evaluation criteria. (1) Particle content The film was thoroughly washed with methanol to remove surface deposits, washed with water and dried to add 300 kg of a sample to which 2.7 kg of o-chlorophenol was added, and the temperature was raised to 100 ° C with stirring to raise the temperature. After warming, it is left as it is for 1 hour to dissolve the polyester part. However, in the case where the polyester portion is not dissolved due to a high degree of crystallization, the above melting operation is performed after once melting and quenching. Then, coarse insoluble matters such as dust contained in the polyester are filtered off with a G-1 glass filter and removed, and the weight of the above-mentioned substance is subtracted from the weight of the sample.

Hitachi's separation ultracentrifuge 40p type was equipped with a rotor RP30, and after injecting 30 cc of the glass filter-filtered solution into each cell, the rotor was rotated to 45
After rotating at 00 rpm and confirming that there is no abnormal rotation, the inside of the rotor is evacuated, the rotation speed is increased to 30,000 rpm, and the particles are centrifuged at this rotation speed. Although the completion of the separation is about 40 minutes later, this confirmation is performed if necessary by the light transmittance at 375 mμ of the liquid after the separation becoming a constant value higher than that before the separation. After separation, the supernatant is removed by a gradient method to obtain separated particles.

Since polyester particles may be mixed in the separated particles due to insufficient separation, normal temperature o-chlorophenol is added to the collected particles, and the particles are almost uniformly suspended, and then the ultracentrifuge is again used. Perform processing. In this operation, after the particles described below are dried, the particles are subjected to a differential scanning calorimetric analysis,
It must be repeated until no melting peak corresponding to the polymer can be detected. Finally, the separated particles thus obtained are vacuum dried at 120 ° C. for 16 hours and weighed.

When the separated particles A obtained by the above operation contain silica particles and internally precipitated particles,
It is necessary to separately determine the amount of internal particles and the amount of spherical silica particles. First, the separated particles A are quantitatively analyzed for the metal content, and the Ca and Li contents and the metal contents other than Ca and Li are obtained. Then, the separated particles A are heated under reflux in a 3-fold molar amount of ethylene glycol for 6 hours or more, and then ethylene glycol is distilled off at 200 ° C. or more to depolymerize, whereby only the internally precipitated particles are dissolved. Separated particles B obtained by centrifuging the remaining particles are dried and weighed to determine the amount of spherical silica particles. Further, the remaining weight obtained by subtracting the spherical silica particle amount from the initial total separated particle amount is defined as the internally precipitated particle amount.

When the separated particles B contain calcium carbonate in addition to the spherical silica particles, the separated particles B are 1N.
When the solution is stirred in the nitric acid solution for 6 hours or longer, only calcium carbonate particles are dissolved. Separated particles C obtained by centrifuging the remaining particles are dried and weighed to obtain the content of spherical silica particles. Further, the weight of the separated particles C is subtracted from the weight of the separated particles B to obtain the content of calcium carbonate particles.

When the separated particles C contain other inert particles such as aluminum oxide in addition to the spherical silica particles, the separated particles C are heated under reflux in a 20% aqueous solution of sodium hydroxide for 6 hours or more to obtain spherical silica. Only the particles dissolve. Separated particles D obtained by centrifuging the remaining particles are dried and weighed to obtain the content of other inert particles (for example, aluminum oxide). Further, the weight of the separated particles D is subtracted from the weight of the separated particles C to obtain the content of the spherical silica particles.

In order to confirm whether the separation operation of the particles has been completely performed, quantitative analysis of the metal content is performed on the separated particles after each of the above separation operations, and the accuracy of particle amount measurement is improved by repeating these operations. You can

(2) Particle Size Ratio of Spherical Silica Particles Polyester is removed from the film by a plasma low temperature ashing method to expose the particles. The processing conditions are selected such that polyester is incinerated but particles are not damaged.
Scanning electron microscope (ESM32 manufactured by Elionix Co., Ltd.)
00) and the image of the particles is processed with an image analyzer (IBAS2000 manufactured by Carl Zeiss).

In this measurement, the major axis / minor axis ratio of each particle shown in the following formula is obtained, and the particle diameter ratio "average value of major axis / minor axis" is calculated from these values. However, only the particle diameter ratio of individual particles of 1.3 or less was counted as spherical silica and subjected to numerical processing. Ratio of major axis to minor axis of individual particles = D1 / D2 where D1 is major axis (maximum diameter) and D2 is minor axis (shortest diameter). Particle size ratio = Σ (D1i / D2i) / N D1i, D2i is the long diameter (maximum diameter) of each individual particle,
Minor diameter (shortest diameter), N is the number of counted particles.

(3) Relative Standard Deviation of Spherical Silica Particles For each particle counted in the measurement in (2) above, the area equivalent circle diameter is determined, and the number of particles is changed to 5,000 or more, and the following numerical processing is performed. What to do Here, Di is the equivalent circle diameter of the particles, and N is the number of counted particles. And

(4) Volume average diameter of spherical silica particles The volume average diameter V of the particles counted in the measurement of the above (3) is calculated from the following formula. V = (ΣDi ³ / N) ^1/3 Here, Di is the equivalent circle diameter of the particles, and N is the number of counted particles.

(5) Volume average diameter of inert particles other than spherical silica particles The inert particles separated in the above (1) are dispersed in methanol, and a centrifugal sedimentation type particle size distribution measuring device (manufactured by Horiba Ltd. The median cumulative value (50% by volume) in the cumulative distribution curve of the Stokes diameter obtained by measurement with CAPA500) was defined as the volume average diameter.

(6) Scraping index K A film sample having a thickness of 11 μm was slit into 1/2 inch with a shear cutter manufactured by Nishimura Seisakusho at a slit speed of 50 m / min, and then slit into 1/2 inch to obtain a film sample 1 m. Was placed in a container containing 50 cc of pure water so that only one cut surface of the film sample was immersed, and after ultrasonic treatment, the film sample was removed and the immersion liquid was removed by a particle counter (HIAC / ROYCO). CL-
The number of particles having a size of 3 to 20 μm measured in 5) was defined as the abrasion index K.

(7) Refractive index nz in the thickness direction The refractive index nz in the thickness direction of the biaxially oriented film is set by using an Abbe refractometer as a light source of sodium D line (wavelength 589 nm). Methylene iodide is used for the mount solution,
It was measured at 25 ° C. and 65% RH.

(8) The refractive index nz in the thickness direction of the biaxially oriented film and the refractive index NMD in the longitudinal direction of the biaxially oriented film using an Atsube refractometer with the plane orientation index F and ΔN sodium D line (wavelength 589 nm) as the light source. From the refractive index NTD in the film width direction, ΔN = (NMD-NTD) ×
1000, F = (NMD + NTD) / 2-nz.
Methylene iodide is used as the mount solution at 25 ° C, 65%
It was measured by RH.

(9) Number of projections on film surface and three-dimensional surface roughness (SRa) Kosaka Laboratory's non-contact surface roughness meter HIPSS (Model ET
-30HK) and three-dimensional roughness analyzer (model SPA-
11) was used to measure the three-dimensional roughness. The conditions are as follows, and the average value of 20 measurements was taken as the value.・ Vertical magnification: 20,000 times ・ Horizontal magnification: 500 times ・ Cutoff: 0.08 mm ・ Feed pitch: 0.5 μm ・ Measuring length: 500 μm ・ Measuring area: 0.0194 mm ²・ Measuring speed: 100 μm / sec ・ HYST: ± 6.25 nm-COUNT MODE: SIMPLE-Z standard: UPPER The protrusion height was calculated with reference to the cut surface at which the area ratio of the cut surface was 70%. The number of protrusions having a height of 200 to 400 nm and 400 nm or more measured under the above conditions was converted into each number / 0.1 mm ² . S
Ra is the three-dimensional surface roughness (center plane average roughness).

(10) Center Line Average Surface Roughness (Ra) Using a stylus type surface roughness meter BE-3E manufactured by Kosaka Laboratory according to JIS-B-0601, the center line was measured at a cutoff of 0.25 mm and a measurement length of 4 mm. The average surface roughness (Ra) was measured.

(11) Image Quality, Scratch Resistance, Use Durability The film is coated with a magnetic coating composition having the following composition by a gravure roll, magnetically oriented, and dried. Furthermore, after calendering at a temperature of 70 ° C and a linear pressure of 200 kg / cm with a small calendar device (styrene roll, nylon roll, 5 stages),
Cure at 70 ° C. for 48 hours. 1/2 of this material
Slit into inches to make a pancake. This pancake was incorporated into a VTR cassette to obtain a VTR cassette tape. (Composition of magnetic paint) Co-containing iron oxide (BET value 50 m ² / g): 100
Parts by weight ・ S-REC A (Sekisui Chemical vinyl chloride / vinyl acetate copolymer): 10 parts by weight ・ Nopollan 2304 (Nippon urethane polyurethane elastomer): 10 parts by weight ・ Contonate L (Nippon urethane polyisocyanate): 5 parts by weight Lecithin: 1 part by weight Methyl ethyl ketone: 75 parts by weight Methyl isobutyl ketone: 75 parts by weight Toluene: 75 parts by weight Carbon black: 2 parts by weight Lauric acid: 1.5 parts by weight Use this tape for household use A 100% chroma signal is recorded by a TV test waveform generator (TG7 / U706) made by Shibasoku using a VTR, and the chroma S / N is measured from the reproduced signal by a color noise measuring instrument made by Shibasoku (925D / 1). Was judged.

Furthermore, this VTR cassette is used for home VT
It was incorporated into R and repeated running (reproduction / high-speed rewinding) was repeated 100 times, and similarly, the chroma S / N was measured from the reproduced signal with a Shiba Soku color noise measuring machine (925D / 1) to determine the image quality. V after repeated running
The scratch resistance was judged by the amount of white powder scraped on the TR cassette guide pin and the amount of scraped film. The criteria for these judgments are as follows, and if the rank is 4 or higher, there is no problem in practical use. Judgment rank S / N (image quality) Film scraping (scratch resistance) 5 Excellent, image quality is extremely good Guide pin stains almost none 4 Good, almost no problem 3 Slight white powder stains 3 Disturbance in image quality Scraped object stains 2 Image quality Distortion is large. There is a lot of dirt on shavings. 1 Poor image quality.

(12) Evaluation of Slitting Property A magnetic coating solution having the following composition is coated on one surface of a polyester film having a thickness of 11 μm so that the film thickness after drying is 3 μm. After coating, it is oriented in a DC magnetic field, dried, and then calendered. This sheet is slit into 1/2 inch width with a shear cutter to make a video tape. The degree of occurrence of whiskers and powder is visually classified and evaluated by visually observing the slit portion by the shear cutter. Slitting property A: generation of whiskers and powder is extremely small. 〃 B: 〃 Little. 〃 C: 〃 Normal level. 〃 D: 〃 Somewhat large. 〃 E: There are many. (Note) Most of the biaxially oriented polyester films for video tapes currently on the market have a slit property level of C or D.

(13) Evaluation of Film Edge Damage The 1/2 inch wide video tape obtained in (12) above was placed in a VTR cassette by a loader, and replayed on the VTR for 30 minutes-rewinding was repeated 300 times. After that, the edge of the video tape is visually observed, and the degree of flatness such as bending and wakame-like elongation is divided into the following four ranks and evaluated. There is no wrinkle-like elongation on the edge of the film.
‥ ◎◎ Slightly wakame-like stretch is seen ‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥
‥ ○ A slight wakame-like stretch is seen, and breakage has also occurred.
… △ Seaweed-like expansion and breakage are large ‥‥‥‥‥
‥‥ ×

[0063]

EXAMPLES The present invention will be described based on examples. Reference Example Preparation of Polyester 100 parts by weight of terephthalic acid and 43 parts by weight of ethylene glycol were kneaded to prepare a slurry. The slurry is continuously added at a constant rate to a reaction product of 50 parts by weight of terephthalic acid and 21.5 parts by weight of ethylene glycol stored in a reactor at 245 ° C., and transesterification reaction is performed at 245 ° C. under normal pressure to produce a product. Water was continuously distilled out of the system from the rectification tower.
The slurry supply time was 3 hours and 30 minutes, and the transesterification reaction was 4 hours. An esterification reaction product corresponding to 100 parts by weight of terephthalic acid was transferred from the obtained reaction product to a polymerization apparatus, and 0.045 parts by weight of phosphoric acid, 0.023 part by weight of antimony trioxide, and a volume average particle size of 0.19 μ
2.4 parts by weight of spherical silica synthesized by the water glass method having m, a particle size ratio of 1.1 and a relative standard deviation of 0.76 was added as an ethylene glycol slurry, and a polycondensation reaction was performed according to a conventional method. At this time, the ethylene glycol slurry containing the spherical silica particles was heat-treated at the boiling point of ethylene glycol for 10 minutes. The polymer thus obtained had an intrinsic viscosity of 0.615 and contained 2 parts by weight of spherical silica. The refractive index of the spherical silica in the ethylene glycol slurry was 1.439. (Polyester A) Further, a particle-free polymer was obtained in the same manner as in the above polyester A without adding spherical silica. The intrinsic viscosity of the obtained polymer was 0.620. (Polyester B) Example 1 Pellets C prepared by mixing the polyesters A and B thus obtained in a predetermined amount so that the spherical silica content in the final polyester film is 0.60% by weight are 180 ° C. Then, it was dried under reduced pressure (3 Torr) for 3 hours to obtain a raw material for the laminated portion. Further, separately prepare a polyethylene terephthalate raw material having an intrinsic viscosity of 0.63 as a base layer raw material,
It was dried under reduced pressure (3 Torr) at 180 ° C. for 3 hours in the same manner as the material for the laminated portion.

The base layer portion was fed to the extruder 1 at 310 ° C., and the laminating portion raw material was fed to the extruder 2 to melt at 280 ° C.
These polymers are combined and laminated in a confluent block having a rectangular laminated part before entering the mouthpiece, and are wound around a casting drum having a surface temperature of 45 ° C. by an electrostatic applied casting method to be cooled and solidified, and both sides of the base layer polyester A An unstretched film having a three-layer structure was produced by laminating polyester B on the above. At this time, the discharge amount of each extruder was adjusted, and the total thickness and the laminated thickness were adjusted.

This unstretched film was subjected to the roll temperature of FIG. 1 at 75 ° C. for rolls 1 and 2, 115 ° C. for rolls 3 and 4, 115 ° C. for roll 5, and 11 for roll 6.
9 ° C., roll 7 at 113 ° C., 1.2 times between rolls 5 and 6, 1.3 times between rolls 6 and 7, 2.5 times between rolls 7 and 8 The peripheral speed difference of the roll was adjusted and the roll was stretched in the vertical direction.

This uniaxial film is heated at 120 ° C. in a stenter.
3.5 times in the horizontal direction under hot air, and then re-stretched in the vertical direction at a drawing temperature of 130 ° C and a draw ratio of 1.50 times, and then under a slight drawing of 1.03 times, into hot air at 205 ° C. For 5 seconds to obtain a biaxially oriented film having a thickness of 9 μm. The final running speed of the biaxially oriented film at this time is 140 m /
It was a minute.

Measurement of characteristics of the obtained biaxially oriented film
The evaluation results are shown in Tables 1 and 2. Δ in Tables 1 and 2
N is 50, plane orientation index F is 0.1738, and refractive index nz in the thickness direction is 1.487 MD direction (longitudinal direction of film).
Had an F-5 value of 18.6 kg / mm ² , an abrasion index K of 39, and an average surface roughness Ra of 20 nm, both of which were within the range of the present invention. Further, as is clear from the results of Tables 1 and 2, it is found that the S / N ratio (image quality) characteristics, film scraping, slitting property, and film edge damage are all excellent.

Examples 2 to 3 The content of spherical silica in the polyester film was 0.8.
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that 0% by weight (Example 2) and 1.5% by weight (Example 3) were used. The measurement and evaluation results of the properties of the obtained biaxially oriented film are shown in Tables 1 and 2. As is clear from the results of Table 1 and Table 2, each of the films of Examples 2 to 3 was
It can be seen that S / N ratio (image quality) characteristics, film scraping, slitting property, and film edge damage are all excellent.

Examples 4 to 5 Spherical silica having a volume average particle diameter of 0.55 μm, a particle diameter ratio of 1.05, and a relative standard deviation of 0.76, which is spherical silica synthesized by a water glass method, has a content of 0.30 in a polyester film. Wt% (Example 4), 0.60 wt% (Example 5) except that
A biaxially oriented polyester film was obtained in the same manner as in Example 1. The measurement and evaluation results of the properties of the obtained biaxially oriented film are shown in Tables 1 and 2. As is clear from the results in Tables 1 and 2, each of the films of Examples 4 to 5 is excellent in all of S / N ratio (image quality) characteristics, film scraping, slitting property, and film edge damage. .

Example 6 Spherical silica synthesized by the water glass method having a volume average particle size of 0.89 μm, a particle size ratio of 1.1 and a relative standard deviation of 0.78 was used.
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the content in the polyester film was 0.14% by weight. The measurement and evaluation results of the properties of the obtained biaxially oriented film are shown in Tables 1 and 2. As is clear from the results of Table 1 and Table 2, the film of Example 6 had an S / N ratio.
It can be seen that it has excellent ratio (image quality) characteristics, film scraping, slitting property, and film edge damage.

Example 7 A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the re-stretching ratio was adjusted to 1.4 times. The measurement and evaluation results of the properties of the obtained biaxially oriented film are shown in Tables 1 and 2. As is clear from the results shown in Tables 1 and 2, the film of Example 7 is excellent in all of S / N ratio (image quality) characteristics, film scraping, slitting property, and film edge damage.

Example 8 The re-stretching ratio was 1.3 times, and the lateral stretching ratio was 4.
A biaxially oriented polyester film was obtained in the same manner as in Example 1, except that the stretching temperature was adjusted to 0 times and the stretching temperature in the horizontal direction was 115 ° C. The measurement and evaluation results of the properties of the obtained biaxially oriented film are shown in Tables 1 and 2. Table 1, Table 2
As is clear from the results of the above, the film of Example 8 had S /
It can be seen that it is excellent in N ratio (image quality) characteristics, film scraping, slitting property, and film edge damage.

Example 9 In the same manner as in Example 1 except that spherical silica synthesized by the water glass method having a volume average particle diameter of 0.19 μm, a particle diameter ratio of 1.05 and a relative standard deviation of 0.56 is used. A biaxially oriented polyester film was obtained. The refractive index of the spherical silica in the ethylene glycol slurry was 1.442.

Measurement of characteristics of the obtained biaxially oriented film
The evaluation results are shown in Tables 1 and 2. As is clear from the results shown in Tables 1 and 2, the film of Example 9 is excellent in all of S / N ratio (image quality) characteristics, film scraping, slitting property, and film edge damage.

Example 10 A biaxially oriented polyester film was obtained in the same manner as in Example 1, except that calcium carbonate particles having a volume average particle diameter of 0.8 μm were also used in combination. The measurement and evaluation results of the properties of the obtained biaxially oriented film are shown in Tables 1 and 2. As is clear from the results in Tables 1 and 2, the film of Example 10 is excellent in all of S / N ratio (image quality) characteristics, film scraping, slitting property, and film edge damage.

Comparative Example 1 The procedure of Example 1 was repeated except that spherical silica synthesized by the alkoxide method having a volume average particle size of 0.18 μm, a particle size ratio of 1.03 and a relative standard deviation of 0.17 was used. An axially oriented polyester film was obtained. The refractive index of the spherical silica in the ethylene glycol slurry was 1.423. The measurement and evaluation results of the properties of the obtained biaxially oriented film are shown in Tables 3 and 4. As is clear from the results of Tables 3 and 4, the film of Comparative Example 1 is inferior in slit property.

Comparative Example 2 The procedure of Example 1 was repeated except that spherical silica synthesized by the alkoxide method having a volume average particle size of 0.55 μm, a particle size ratio of 1.1 and a relative standard deviation of 0.19 was used. An axially oriented polyester film was obtained. The refractive index of the spherical silica in the ethylene glycol slurry was 1.425. The measurement and evaluation results of the properties of the obtained biaxially oriented film are shown in Tables 3 and 4. As is clear from the results of Tables 3 and 4, the film of Comparative Example 2 is inferior in slit property.

Comparative Example 3 The same procedure as in Example 1 was carried out except that spherical silica synthesized by the water glass method having a volume average particle diameter of 2.2 μm, a particle diameter ratio of 1.05 and a relative standard deviation of 0.69 was used. A biaxially oriented polyester film was obtained. The measurement and evaluation results of the properties of the obtained biaxially oriented film are shown in Tables 3 and 4. As is clear from the results of Tables 3 and 4, the film of Comparative Example 3 is inferior in all of the electromagnetic conversion characteristics (S / N ratio), film scraping (scratch resistance), and slit property.

Comparative Example 4 Using spherical silica synthesized by the water glass method having a volume average particle diameter of 0.08 μm, a particle diameter ratio of 1.1 and a relative standard deviation of 0.58,
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the content in the polyester film was 0.60% by weight. The measurement and evaluation results of the properties of the obtained biaxially oriented film are shown in Tables 3 and 4. As is clear from the results of Tables 3 and 4, the film of Comparative Example 4 is inferior in film abrasion (scratch resistance).

Comparative Example 5 Spherical silica synthesized by the water glass method having a volume average particle size of 0.55 μm, a particle size ratio of 1.1 and a relative standard deviation of 0.68 was used.
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the content in the polyester film was 5.2% by weight. However, the amount of spherical silica particles added in the reference example was 6.0 parts by weight. The measurement and evaluation results of the properties of the obtained biaxially oriented film are shown in Tables 3 and 4. As is clear from the results of Tables 3 and 4, the film of Comparative Example 5 is inferior in all of the electromagnetic conversion characteristics (S / N ratio), film scraping (scratch resistance), and slit property.

Comparative Example 6 Spherical silica synthesized by the water glass method having a volume average particle size of 0.55 μm, a particle size ratio of 1.1 and a relative standard deviation of 0.68 was used.
A biaxially oriented polyester film was obtained in the same manner as in Example 1, except that the content in the polyester film was 0.004% by weight.

Measurement of characteristics of the obtained biaxially oriented film
The evaluation results are shown in Tables 3 and 4. As is clear from the results of Tables 3 and 4, the film of Comparative Example 6 is inferior in both film abrasion (scratch resistance) and film edge damage.

Comparative Example 7 The temperature of roll 5 and roll 6 in FIG.
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the stretching ratio in the horizontal direction was 4.6 and the stretching ratio during re-stretching was 1.03. The measurement and evaluation results of the properties of the obtained biaxially oriented film are shown in Tables 3 and 4. As is clear from the results in Tables 3 and 4, it is understood that the film of Example 7 is inferior in both film abrasion (scratch resistance) and film edge damage.

Comparative Example 8 Calcium carbonate particles having a volume average particle diameter of 0.8 μm were used in place of the spherical silica particles. A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the content in the polyester film was 0.40% by weight. The measurement and evaluation results of the properties of the obtained biaxially oriented film are shown in Table 3,
The results are shown in Table 4. As is clear from the results of Tables 3 and 4, the film of Comparative Example 8 had film scraping (scratch resistance),
It can be seen that the film edge damage is inferior.

[0085]

[Table 1]

[Table 2]

[Table 3]

[Table 4]

[0086]

INDUSTRIAL APPLICABILITY The present invention uses spherical silica particles in a specific range and has surface orientation indices F and ΔN in specific ranges to provide both excellent scratch resistance and slit resistance, and dropout during repeated running. It is possible to obtain a polyester film in which the increase in the film thickness is extremely small, and the film is less likely to be scratched even when running at a high speed, so that the film processing speed in each application can be increased. Also,
When used as a video tape, a film was obtained in which the S / N, that is, the image quality was not easily deteriorated even after repeated use. The use of the polyester film for a magnetic recording medium of the present invention is not particularly limited, but scratches on the film surface in the processing step are particularly problematic in terms of product performance. It is especially useful as a base film for long-time recording pancakes with the spread of software.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an outline of a vertical stretching device.

[Explanation of symbols]

 1: Hard chrome-plated metal roll 2 to 6: Silicone rubber-coated metal roll 7: Mirror-finished ceramic roll 8 and 9: Hard chrome-plated metal roll 11 and 14: Rubber roll 12 and 13: Silicone rubber-coated metal roll 10: the film

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location C08L 67/02 KJS // B29K 67:00 105: 16

Claims (4)

[Claims] 1. A polyester having a volume average particle diameter of 0.1 to 0.1.
A spherical silica particle having a diameter of 2.0 μm and a relative standard deviation defined by the following formula (1) exceeding 0.5 is 0.005
A polyester film for a magnetic recording medium, characterized in that the polyester film contains 0.1 to 5.0% by weight and simultaneously satisfies the following expressions (2) to (4). [Equation 1] ΔN <1413-8327 × F ‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ (2) 20 <ΔN <80 ‥‥‥‥‥‥‥‥‥ (3) F <0.1800 ‥‥‥‥‥‥‥‥‥‥ (4) [here , ΔN = (NMD-NTD) × 1000, F = (N
MD + NTD) / 2-nz, where NMD is the refractive index in the film longitudinal direction, NTD is the refractive index in the film width direction, and nz is the refractive index in the film thickness direction. 2. The polyester film for a magnetic recording medium according to claim 1, wherein the refractive index nz in the thickness direction and the plane orientation index F satisfy the following expressions (5) and (6). nz ≤ 1.603-0.6407xF ... (5) nz ≥ 1.595-0.6407xF ... (6) 3. The polyester film for a magnetic recording medium according to claim 1, which has a scraping index K of 60 or less. 4. A laminated polyester film for a magnetic recording medium, comprising at least one layer of the polyester film according to any one of claims 1 to 3.