JPS63168818A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium which permits high-density recording and withstands repetitive use by using a biaxially oriented polyester film into which spherical silica particle having a specified average grain size and grain size ratio are dispersed and incorporated. CONSTITUTION:The biaxially oriented polyester film into which the spherical silica particles having 0.3-4mum average grain size and 1.0-1.2 grain size ratio (major axis/minor axis) are dispersed and incorporated at 0.01-1wt.% is used. The polyester into which the spherical silica particles are dispersed and incorporated is produced by adding the spherical silica particles (preferably in the form of slurry in glycol) to the polyester at the time of reaction for forming ordinary polyester, for example, at an arbitrary timing during ester exchange reaction or polycondensation reaction in the case by an ester exchange method or at an arbitrary timing in the case by a direct polymn. method. The magnetic recording medium formed by using such biaxially oriented polyester film has an excellent electromagnetic conversion characteristic, slipperiness, running durability, etc.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magnetic recording medium, and more preferably has excellent xi conversion characteristics, contains specific spherical silica fine particles, contributes to stiffness resistance, and furthermore The present invention relates to a magnetic recording medium characterized by having a substrate made of a biaxially oriented polynisnar film with improved sliding properties.

[Prior art]

Examples of magnetic recording media based on polyester films include video tapes, audio tapes, Humbuk tapes, and Huminbee disks, which are widely used.

In recent years, demand for improved quality has increased in these fields of application, and as a result, the base polyester film has to have a flat surface, excellent slipperiness, and durable running properties. .

The *X of being excellent in F511 resistance to scratches is becoming more and more strong.

Conventionally, methods for improving slipperiness include adding calcium-containing inorganic particles to polyester, or precipitating fine particles containing calcium, lithium, or phosphorus in the composite system during the formation of polyester. Proposed.

In both methods, projections are formed on the surface of the film due to fine particles when polyester is formed and stretched into a film, which is problematic in terms of the slipperiness of the film.

However, the projections caused by the queen-like particles reduce the film's slipperiness to rR1! In this method, the slipperiness usually improves as the film surface becomes rougher, but on the other hand, due to the roughening, the surface after applying the magnetic paint tends to become rough and the electromagnetic conversion characteristics tend to deteriorate. be.

As one of the measures to solve these contradictory problems of flatness and slipperiness, many methods have been proposed, including the use of composite inorganic particles in which large-sized particles and small-sized particles coexist. . However, these methods also have problems, and if they are not used as they are, it will be difficult to upgrade the magnetic recording medium to a higher grade, for example, to increase the VB degree.

It is difficult to respond to the demands of Shima Shinako and others. The reason for this is
The size of the large particle diameter scaler used for composite inorganic particles is too large compared to the desired quality of high-grade grades. The voids in the area also become larger, and during the cleaning process with non-a cloth or calendering, the C1% protrusion is cut off at the root, causing dropouts (missing information that occurs during recording and playback), and 11LK addition. This causes calendar stains from the air roots and stains from the dust fabric used for cleaning the base film surface, which greatly impairs its properties as a magnetic recording medium.

[Purpose of the invention]

The present inventor has solved the above-mentioned problems and succeeded in developing a film that has flatness, ease of slipping, and abrasion resistance that can be applied to the field of high-quality magnetic recording, and has developed an i-formed film. The present invention was achieved based on the discovery that a magnetic recording medium of the type described above has distinct characteristics.

An object of the present invention is to provide a magnetic recording medium that is capable of high-density recording, has high quality, and can withstand repeated use, and furthermore, in a d-base film, (1) there are no large protrusions on the base. (Although it is flat, there are some small protrusions that do not cause noise such as dropouts.
2) The coefficient of friction during repeated running is small; (3) there is very little wear and tear on the base film due to contact with the J-processing process of the magnetic recording medium and the magnetic recording/reproducing device; it has good durability during continuous use. The purpose of this invention is to provide a magnetic recording medium.

[JlllhX of the invention, effect]

The object of the invention is that according to the invention, the average particle size is between 0.3 and 0.3.
4 μm and a particle size ratio (major axis/minor axis) of 1.0 to 1.
．． This is achieved by a magnetic recording medium comprising a biaxially oriented polyester film containing 0.01 to 1 j [t%] of spherical silica particles of No. 2 dispersed therein, and a magnetic layer on at least one side of the film.

Here, the long axis of the silica particle is 0 gi, and the equivalent diameter of a 1 ml circle is determined from an image magnified 10,000 to 30,000 times with a scanning area electron microscope after depositing a gold thin film layer on the particle surface, and the average particle size is 1 particle size. Find the ratio using the following formula.

Average particle diameter = Sum of area circle equivalent diameters of measured particles / Number of particle diameter ratio of measured particles = Average major diameter of silica particles / Average minor diameter of core particles The polyester in the present invention is a polyester containing aromatic dicarboxylic acid as the main component. , is a polyester whose main glycol component is aliphatic glycol. Such polyesters are substantially linear and have film forming properties, particularly by melt molding. Examples of aromatic dicarboxylic acids include terephthalic acid, naphthalene dicarboxylic acid, isophthalic acid, diphenylethane dicarboxylic acid, diphenyl dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenylsulfone dicarboxylic acid, diphenylgutone dicarboxylic acid, and anthracene dicarboxylic acid #1 etc. can be mentioned. Examples of aliphatic glycols include evapoethylene glycol, trimekylene glycol, tetramethylene glycol, pentamethylene glycol,
Heshisu methylene glycol.

Examples include polymethylene glycols having 2 to 10 carbon atoms such as decamethylene glycol, and alicyclic diols such as cyclohesane dimetatool.

In the present invention, polyesters containing, for example, alkylene terephthalate and/or alkylene naphthalate as a major constituent are preferably used.

Among such polyesters, preferable examples include polyethylene terephthalate and polyethylene-2,6-su7talate, as well as coelectric polymers in which 80 mol % or more of the total dicarboxylic acid component is tere7 gullene glycol. In this case, up to 20 mol% of the total acid component can be the above-mentioned aromatic dicarboxylic acids other than terephthalic acid and/or 2,6-naphthalene dicarboxylic acid, and also aliphatic dicarboxylic acids such as adipine-related and cepatic acid; It can be an alicyclic dicarboxylic acid such as cyclohexane-1,4-dicarboxylic acid. Also, up to 20 mol% of the total glycol component can be the above-mentioned glycols other than ethylene glycol, or e.g.
Aromatic diols such as 1,4-diol, resorcinol, 2,2-bis(4-hydroxyphenyl)propane,
Aliphatic diols containing aromatic groups such as droxymethylbenzene; polyalkylene glycols (polyoxyfulkylene glycols) such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and the like can also be used.

In addition, the polyester used in the present invention includes, for example, aromatic oxyacids such as human mixybenzoic acid; oxycarboxylic acids such as aliphatic oxyacids such as ω-hydroxycaproic acid;
It also includes those in which components derived from the above are combined or combined in an amount of 20 mol 5 or less with respect to m* of the dicarboxylic acid component and the oxycarboxylic acid component.

Furthermore, the polyester in the present invention also includes polycarboxylic acids at the base of the substantially linear range, such as trifunctional or higher functional polycarboxylic acids having a content of 2 mol % or less based on the total acid component.

The above polyester is known per se, and can be produced by a method known per se.

The above polyester has an intrinsic viscosity of about 0.4 as measured at 35°C as a solution of 0-lyaa mitsuenol.
~0.9 is preferred.

The biaxially stretched polyester film of the present invention has many fine protrusions on its surface. According to the invention, these large numbers of fine protrusions originate from a large number of spherical silica particles dispersed and contained in the polyester.

Polyester containing dispersed spherical silica particles is usually used at any time during the reaction to form polyester, for example, during the transesterification reaction when using the transesterification method or during the 1# synthesis reaction when using the swimming direct electrolysis method. It can be produced by adding spherical silica particles (preferably glycol A slurry C) to the reaction system at any time. Preferably, the spherical silica particles are added to the reaction system at the initial stage of the molarization reaction, for example, until the intrinsic viscosity reaches about 0.3.

In the present invention, the spherical silica particles dispersed and contained in polyester are silica particles having an average particle diameter of 0.3 to 4 μm and a particle diameter ratio (-Ik diameter/breadth diameter) of 1.0 to 1.2. . These spherical silica particles have individual shapes that are extremely close to true spheres, and the silica particles conventionally known as lubricants are ultrafine wing-shaped particles of about 10 sp, or they are aggregated into particles of 0.5 μ8. degree of lik agglomeration (agglomerated particles)
There is a point in time that is markedly different from what is currently being formed.

The average particle diameter of the spherical chestnut is preferably 0.3 to 3 μm.
5, more preferably 0.3 to 2 μm. If the average particle size is less than 0.3 μm, the effect of improving slipperiness and abrasion resistance will be insufficient, which is not preferable.

Moreover, if the average particle diameter is 4 μm, the surface of the film becomes too rough, which is not preferable. The particle size ratio of the spherical silica particles is preferably 1.0 to 1.15, more preferably 1.0 to 1.
．． It is 1.

Further, it is preferable that the spherical silica particles have a sharp particle size distribution, and the relative camphor 4A difference representing the steepness of the distribution is 0.
．． Fio is preferably 5 or less, more preferably 4 or less, particularly 0.3 or less.

This relative standard deviation is expressed by the following formula.

Here, Dl2 The area circle equivalent diameter (μm) of each individual particle D
: 6111 constant 116 of particles! fl t is expressed.

When spherical silica particles with a relative standard deviation of 0.5 or less are used, since the particles are spherical and have an extremely steep particle size distribution, the protrusions on the film surface become extremely uniform. Historically, the individual protrusions on the surface of the film have very sharp protrusions because the voids around the lubricant are small, and therefore, even with the same number of protrusions, the slipperiness is extremely good even at ℃.

As long as the spherical silica particles satisfy the above-mentioned conditions, there are no limitations on the manufacturing method or the like.

For example, spherical silica particles are made of ethyl orthosilicate (5i(
Hydrous silica (St
(Of()4) Monodisperse spheres are made, and the hydrous silica monodisperse spheres are further dehydrated to [Silica bond (!Sk −
0-8t Mi] can be grown three-dimensionally to produce '2-1' (Journal of the Chemical Society of Japan '81./$119゜P, 150
3).

S i (QC, H,), + 48. O→S i (
01()4+ 40. H,0H=Si-OH+HQ-8
tdi→==st-o-styo+H1O In the present invention, the effect of spherical silica particles is to reduce CO40 to polyester.
There is a necessary cost of 1 to t, oat%, preferably riO,
01-0.5 t%, more preferably 0.05-0.3
Weight%. When the festival filter is 0.01J [Sumiyu% Miyu, the improvement effect on slipperiness and shaving property becomes a non-light component, while 1. O
A [If it exceeds 111%, the a-plane flatness will decrease, which is not preferable.

The biaxially oriented polyester film of the present invention can be manufactured using the conventional method of splitting the bi-stretched film. For example, a polyester containing spherical silica particles is melt-formed to form an amorphous σ) unstretched film, then an iron unstretched film is stretched in two directions, heat set, and if necessary subjected to relaxation heat treatment. Manufactured by. that time,
The lateral properties of the film vary depending on the particle size of the spherical silica particles (nine folds) and the stretching conditions, so they are appropriately selected from conventional low stretching conditions. T again! ! degree, heat absorption! ′
4th grade also shows the temperature during stretching and heat treatment.

@Military, fast F! Since it changes depending on L, etc., conditions are set to satisfy these characteristics at the same time. For example, the stretching temperature is 1
The stage stretching temperature (e.g. longitudinal stretching temperature: T) or (Tg
−10) to (Tg+45)°C (where 'rg:
From the glass transition temperature of polyester), the second-stage stretching temperature (for example, inertial direction stretching temperature x: 'r*) is ('r, + 15
) to ('r, +40) °C (1) It is preferable to select from range J. In addition, the stretching ratio in one direction is m.
It is preferable to select from a range of 5 or more, 3Wr or more, and an area magnification of 8 times or more, particularly 10 times or more. Historically, the heat setting temperature is 180-250℃, and the length is 200-23℃.
It is preferable to select from the range of 0°C. Film thickness is 1-1
00μ is preferred.

The biaxially oriented polyester film of the present invention has extremely small voids compared to conventional films.The reason why the voids are small is that the spherical silica particles have good affinity for polyester, and the particles themselves are Because it is extremely close to a true sphere, does it smell like stretching? This is thought to be due to the fact that the stress around the lubricant propagates evenly and the stress is not distributed all over the interface between the polyester and the lubricant.

The biaxially oriented polyester film of the present invention has uniform uneven surface characteristics, excellent slipperiness and abrasion resistance, and is characterized in that it generates significantly less scum, white powder, and the like. In the present invention, these characteristics of the 211tl oriented polyester film are utilized to produce magnetic recording media such as video tapes, audio tapes, computer tapes, floppy disks, etc., so that the magnetic recording media have an excellent *m conversion time. It has properties such as flexibility, slipperiness, and running durability.

In the present invention, the magnetic layer provided on at least one side of the biaxially oriented polyester film, that is, on one side or both sides, may be a coated magnetic layer. A magnetic layer and a method for providing the same can be employed.

For example, when a magnetic layer is provided by coating a magnetic paint on a base film, the ferromagnetic powder used for the magnetic layer is r Fetus *Cn.
Fetus e Fe504 * Co-containing Fe1
Known ferromagnetic materials such as Oa IC, O, and Baritum 7 Elite can be used. The binder used with the magnetic powder is a known thermoplastic 11 resin, thermosetting resin 9 reaction #1 resin, or a mixture thereof.

Examples of these resins include vinyl chloride-reactive vinyl copolymers, polyurethane elastomers, and the like.

Magnetic paint is further polished! Agent II, e.g. α-AltOs→
, conductive agent such as carbon blank, dispersant such as lecithin, lubricant such as n-methyl stearate, lecithic acid, curing agent such as epoxy resin, solvent such as methyl ditylgtone, methyl imptylgtone, toluene, etc. can contain.

When the magnetic layer is provided by a method of forming four metal films on a base film, a well-known true nitrogen/Ik
N method, sputtering method, ion blating method, C,
V, D, (Chemical Vapori) ep
A method such as an electroless plating method or an electroless plating method can be employed. Examples of metals include iron, metal, nickel, and alloys thereof (for example, Co-N1-P alloy, Co-Nt-Fe alloy, Go-Cr alloy or C
An example is o-1'H meeting fee 4.

〔Example〕

The present invention will be further explained below with reference to Examples.

The physical property values and characteristics of the present invention are as follows (measured).

(1) Particle size of particles The #1 constant of particle size has the following conditions.

l) When calculating the average particle size 1 particle size ratio etc. from silica powder 2) When calculating the average particle size 9 particle size ratio etc. of silica particles in the film l) When using silica powder 2 electron microscopy sample Silica powder was scattered on a table so that individual particles would not be scattered as much as possible, and a thin gold film deposited layer with a thickness of 200 to 300 A was formed on the surface using a gold sputtering device. 10,000-3,000 at i-wei-kei
Observe at 0x magnification, Japan Regulator ■Rusetux 5
At 00, the major diameter of at least 100 particles (DJi)
, the short axis (Dsi) and the equivalent diameter of the piled circle (Di) are determined.

Then, with the number average value expressed by these following formulas,
Long axis (1) J) and short axis (Ds) of silica particles.

Determine the average particle size (D).

2) In the case of silica particles in a film: A small piece of sample film was fixed on a sample stage for a scanning FM electron microscope, and sputtered using a JEOL sputtering device it (JFC-
The surface of the film was subjected to ion etching using an ion sputtering device (Model 1100) under the following conditions. The conditions were to place the sample in a Pel jar and set it at approximately 10-” T.
Even the odor-like evil of orr is true! ! [Increase the voltage to 0.25k
Ion etching was carried out for 1 min at 12.5 mA.Furthermore, gold sputtering was performed on the film surface at °C using the same equipment, and the etching was performed at 12.5 mA for 10 min at 12.5 mA.
Observe at 000 to 30000 times magnification and use an 8-magulator ■
The long axis (Dji), short axis (Dsi), and area circle equivalent diameter (D
Find i). The following steps are carried out in the same manner as in 1) above.

(2) Film surface roughness R&) Center line average roughness R&) JIS-BO60
1, and in the present invention ■Stylus type surface roughness needle (SURFCORDER8E-30C) from Kozubo Research Institute
Measure using. #j conditions etc. are as follows.

(&) Needle tip radius: 2 μm (bl) Measurement pressure: 30 m (c) Cutoff: 0.25 m (dl)
Measurement length 'U, 5
tm (el) How to summarize the sample - Measure the sample 5 times and take the largest value as 1.
Round off the average value of the remaining four Daeghus to the fourth decimal place and display it to the third decimal place.

(3) Void ratio According to the method of tll-2) above, expose the area around the lubricant in the film, measure the long axis of 50 solid particles and the long axis of the void, and calculate the void ratio using the following formula. Expressed as the numerical average value.

(4) Film friction coefficient (μk) In an environment with a temperature of 20°C and a humidity of 60%, a film cut to a width of 1/2 inch is placed on a fixed rod (surface roughness 0.3μ) at an angle θ = 152/180. It is brought into contact with radians (152°) and moved at a speed of 200α per minute (mo!11). The exit tension when the tension controller is operated so that the entrance tension T1 is 35/(TJ:
y) After the t-film has traveled 90 m, the output rotation is detected by a run-in machine and the running friction coefficient μkft is calculated using a linear equation.

μ = (2,303/θ) log (Tt/T.

=0.868 log (Tt/35) (5)
Scrapability The scratchability of the base film in terms of running ml was evaluated using a 5-stage mini super calendar.

The calendar is a 5-tier calendar made of nylon rolls and steel cool, and it's amazing! 1! The temperature was 80° C., the linear pressure applied to the film was 200 kII/CIL s, and the film speed was 50 s/min.

The running film was run for a total length of 2,000 m, and the abrasion resistance of the base film was evaluated based on dirt adhering to the top cooler of the calendar.

(4! Pi Judgment Qf No stains on the iron roll O Almost no stains on the nylon roll Household V
Using the TR, record a signal obtained by adding the 100% chroma level signal to the 50% white level signal (the 100% white level signal has a peak voltage of 0.714 volts), and The reproduced signal is measured using a noise meter Type 925R. Chroma S/
The definition of H is as follows according to Sibak's definition.

Here, gs(p-p) is the peak-to-peak voltage run (p-p) of the reproduction signal of the white level signal.

k: 8 (p-p) = 0.714V (p-p) Also, gN
(rmm) is the square root value of the peak voltage of the reproduced signal of the beam σma level signal.

EN (rms) = AM noise median voltage (V) (7)
DropAct Commercially available dropout counters (e.g. Shibatsu VH
A dropout of 5 p & cc x 10 dB was calculated using ulBZBil), and the catant ridge for 1 minute was calculated.

(8) Scratch judgment base film IF: slit in t/2 inch, simultaneously with the **Ken a#J leg of (4) above, shade the film to a fixed rod up to an angle of 152°, and film at a film speed of 20α/bulk. The thickness of the scratch on the surface of the 1/2 inch wide base film after running it for 10 meters and returning it 50 times.
By combining the depth and ↓ numbers, I determined Ku's 5th Dan I¥I.

5-level judgment> ◎ No scratches are observed on the 1/2 inch beaten base film.Q Almost no scratches are observed on the 172 inch wide base film.Δ Scratches are observed on the 1/2 inch wide base film. (Several) X Several thick scratches are observed on the 1/2 inch wide base film.

Many thick and deep scratches are observed on the xxl/2 inch wide base film in all images.

Comparative Example 1 Dimethyl terephthalate and ethylene glycol were transesterified, manganese acetate was used as a transesterification catalyst, antiseptane trioxide was used as a gold-producing catalyst, phosphorous acid was used as a stabilizer, and average a diameter was 0.7 μm as a lubricant. Particle size ratio 10 ．． Polyethylene terephthanate having an intrinsic viscosity (orne chlorophenol, 35° C.) of 0.62 was obtained by carrying out conventional polymerization using kaolin of O.

This polyethylene terephthalate≠≠half-dark≠The present pellets were dried at 170°C for 3 hours, then supplied to the extruder hopper, and bath-melted at a melting temperature of 280-300°C. Through surface finish 0.
The film was formed and extruded on a cooling drum with a surface temperature of about 3 S and 2,000 revolutions to obtain an unstretched film of 200 μm size.

The unstretched film thus obtained was preheated at 80°C, and further stretched 90°C from 15m above between low and high speeds.
Heated with one IR heater at 0°C to 3.5°.
Stretched to double, rapidly cooled, and then fed to a stenter 105
It was stretched 3.7 times in the transverse direction at °C. The obtained biaxially oriented film was heat-fixed at a temperature of 205°C for 5 times to a thickness of 15°C.
A heat-set biaxially oriented film of μm was obtained.

The obtained film had a void ratio of 1.7 and had good calendering properties, but was unsatisfactory with poor scratches. The properties of this film are shown in Table 1.

In addition, on this film, Co-containing TC oxide powder with the following composition: 1001 parts of ESLETSUKU A (Sekisui Chemical Co., Ltd.'s vinyl salt-vinyl rnate co-arashi combination) 10 β
Niboran 2304 (Nippon Polycretan elastomer) lOmu Dobeko a
Nate L (polyinsyanate manufactured by Nippon Polyurethane) 5 #Lecithin 1 #Methyl ethyl gluten 75 〃Methyl emptyl gluten 75
#Toluene 75 #Magnetic powder paint with additives (lubricant, silicone w fat) 0.15 # Apply with Kegravure Cool, smooth the magnetic paint layer with a triter knife, and magnetic ll! While the material was still dry, it was magnetically oriented using a conventional method, and then a 172 inch wide magnetic tape was prepared with an open guiding magnetic layer formed thereon. The characteristics of this magnetic tape are shown in the first panel.

Comparative Example 2 Instead of kaolin, average particle diameter 0.6 μm, 9-grain inverse ratio 1.5
The procedure was the same as in Comparative Example 1 except that calcium carbonate was used at ℃
, pellets of polyethylene terephthalate were obtained.

Using this pellet, the thickness was 15 mm in the same manner as in Comparative Example 1.
A biaxially oriented film of μm was obtained. Although this film had a void ratio of 2.0 and had good runnability, white powder was generated in the first step of the calender.

The characteristics of this film are shown in the first machine.

Furthermore, an ffl air tape was prepared in the same manner as in Comparative Example 1 except for using this film. The characteristics of this magnetic tape are shown in Part 2.

Comparative Example 3 Instead of kaolin, average particle size is 0.6μ, 9 particle size ratio is 1.5
Pellets of polyethylene terephthalate were obtained in the same manner as in Comparative Example 1 except that calcium oxide was used.

After drying this pellet at 170°C for 3 hours, it is supplied to an extruder hopper and melted at a melting temperature of 280°C to 300°C, and this molten polymer is extruded through a 1-hole slit-shaped die, and the next surface finish is o, asa degree. The film was formed and extruded on a rotating cooling drum with a surface temperature of 20° C. to obtain an unstretched film with a thickness of 200 μm. The unstretched film thus obtained was
Preheat to 0.5°C and maintain substantially 1.0°C between the low speed roll and high speed roll.
Stretched 5 times, then cooled to 40°C, again brought into contact with a roll row of 10°C for about 3.0 seconds between the cooling rows, and then cooled the inside with controlled slow cooling to 800°C. The water is circulated between the speed rolls and 3 infrared heaters are installed on the film surface for 15 minutes, and the actual 2.6
Stretched twice. The stretched film was further fed to a stenter and stretched 3.5 times in the transverse direction at 105°C to a thickness of 15
A μ2411 stretched film was obtained. This film does not completely eliminate voids, and its calendar properties are not very good (
is not.

Furthermore, a 6-layer tape was prepared in the same manner as in Comparative Example 1 except for using this film. The characteristics of this magnetic tape are i
It is shown in Table 1.

Comparative Example 4 An unstretched film was obtained in the same manner as Comparative Example 2 and 1er1, but
Furthermore, in order to increase the strength in the KM direction, the unstretched film is preheated with a low speed roll whose surface temperature is controlled at 70°C, and three infrared M (IR) heaters are installed between the high speed roll and the stretched film is stretched. It was stretched 4.5 times, then passed through a stenter, preheated to 105°C, and then stretched and pressed for 3.51 f in the transverse direction. This film had a high void ratio of 2.5, was severely calendered, and was not suitable for use.

Furthermore, a magnetic tape was prepared in the same manner as in Comparative Example 1 except for using this film. The characteristics of this magnetic tape are shown in Table 1.

Comparative Example 5 Instead of kaolin, average particle 40.4 μm 9 particle size ratio 1.7
A 15 μm thick polyethylene delphate biaxially stretched film and a magnetic tape were obtained in the same manner as in Comparative Example 1, except that titanium chloride was used.

The void ratio of this film was 1.7, and although the surface was flat and the film was particularly popular, it had a low Takushima coefficient and suffered from arbitrary calendar scraping (and was not satisfactory as a magnetic recording medium). Ta.

Examples 1 to 3 The process was otherwise carried out in the same manner as in Comparative Example 1 to obtain pellets of polyethylene terephthalate.

A heat-set biaxially oriented polyester film having a thickness of 15 μm was obtained in the same manner as in Comparative Example 1 except for using these pellets. The time characteristics of this film are shown in Table 1.

↓ Furthermore, a magnetic tape was prepared in the same manner as in the comparative example except for using this film. The first characteristic of this magnetic tape is
Shown on the machine.

^ The magnetic tapes obtained in the examples showed excellent slipperiness despite the fact that the base film was flat on the surface, and the electromagnetic conversion characteristics were also extremely improved due to the fact that the surface was flat. Moreover, there is almost no inclination or cracking in the calendar, and therefore, the D/Q caused by scratches on the tape is reduced, making it extremely easy to roll.

Procedural amendment June 7, 1986

Claims (1)

[Scope of Claims] 1. Spherical silica particles having an average particle diameter of 0.3 to 4 μm and a particle size ratio (major axis/breadth axis) of 1.0 to 1.2 are 0.0 μm.
1. A magnetic recording medium comprising a biaxially oriented polyester film containing 0.01 to 1% by weight dispersed therein, and a magnetic layer on at least one side of the film. 2. The magnetic recording medium according to claim 1, wherein the relative standard deviation of the spherical silica particles expressed by the following formula is 0.5 or less. Relative standard deviation = ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ Where, Di: Area circle equivalent diameter of individual particles (μm) @D
@: Average value of area circle equivalent diameter ▲ Numerical formulas, chemical formulas, tables, etc. are available ▼ n: Represents the number of particles.