JPH0224823A - Biaxially oriented polyester film for magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve a traveling property, wear resistance and above all, scratching resistance by using polyester as the magnetic recording medium and specifying the average grain sizes and contents of the inert material particles deposited by a reaction system at the time of forming a base film by biaxially orienting the polyester. CONSTITUTION:The polyester is formed from arom. dicarboxylic acid such as terephthalic acid and 2, 6-naphthalene dicarboxylic acid or the ester thereof, ethylene glycol as main starting raw materials and is biaxially oriented to form the base film for magnetic recording. The inert material particles of 0.1-5mum average grain size deposited in the process for production of the polyester are incorporated at 0.01-1wt.% and the inorg. particles which have >=6 Mohs' hardness and are inert to the polyester are incorporated at 0.01-3wt.% into the polyester at this time. The fine deposited compd. formed in the reaction refers to elements such as calcium, lithium, antimony, and phosphorus. The particles having >=6 hardness refers to rutile type titanium dioxide and aluminum oxide.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a polyester film that provides excellent running properties, electromagnetic conversion characteristics, and abrasion resistance when used as a magnetic recording medium. More specifically, the present invention relates to a base film suitable for high-density magnetic recording, which generates extremely few scratches and abrasion particles during tape running, and suppresses the occurrence of dropouts.

[Prior Art and Problems to be Solved] Polyester films have excellent physical and chemical properties and are widely used as industrial base materials.

In particular, biaxially oriented polyethylene tele-7 tarlate film is now indispensable as a base film for magnetic recording media because it is particularly excellent in mechanical strength, dimensional stability, flatness, etc. In recent years, improvements in magnetic recording media have been made at a rapid pace, and as a result, demands on base films have become even more stringent. For example, in products that require high-density recording such as videotapes, the magnetic layer is made thinner, but in this case, the unevenness of the base film itself is reflected on the surface of the magnetic layer, and if the degree of unevenness is large, the electromagnetic conversion characteristics This leads to a decrease in performance and frequent dropouts. Therefore, it is desirable that the surface of the base film be as flat as possible, but as is well known, when the film surface becomes flat, it not only deteriorates the runnability of the film, but also causes problems between the film and the base material, such as guide bins. If the friction and abrasion between the parts is large, scratches may occur on the film and abrasion powder may be generated.

That is, if the abrasion resistance of the polyester film is insufficient, abrasion powder will be generated between the film and various rolls or guide bins during the magnetic layer manufacturing process or after it is made into a product.
Otherwise, it becomes inferior in terms of stain magnetic conversion characteristics and dropout.

Furthermore, if the scratch resistance of the film is insufficient, the film is likely to be scratched before and after coating the magnetic layer, and this will be reflected on the surface of the magnetic layer, resulting in poor electromagnetic properties. Furthermore, the electromagnetic properties are often deteriorated by the presence of white powder-like substances that have been scraped off.

As a means of improving surface properties such as runnability and abrasion resistance of polyester films, conventional methods include the presence of inert fine particles in the film to appropriately roughen the film surface, specifically the so-called precipitated particle method and addition. The particle method is known.

The precipitated particle method is a method in which catalyst residues are precipitated into polyester as fine particles during the polyester manufacturing process.It is easy to operate and can produce polymers at low cost, and it also shortens the life of the filter during film formation. It has the advantage of being long. Furthermore, it generally has excellent affinity with polyester, has little detachment of particles from the film, and has relatively excellent abrasion resistance. However, since the main component of the particles is an organic component, they are inferior in scratch resistance.

On the other hand, the additive particle method, which is contrasted with the precipitated particle method, uses calcium carbonate, kaolin, silica, etc. Another method is to make it into fine particles and then add it during polyester production or molding. However, it generally lacks compatibility with polyester, has insufficient abrasion resistance, and often contains unnecessary large particles, creating a rough surface on the film surface. Thus, attempts have also been made to use the two in combination in order to obtain effects that cannot be achieved by each alone. For example, Tokko Akira! S--〇'ltt publication or special public show S
Publication S-90930 describes the combined use of the precipitated particle method and the additive particle method, but even if these methods are adopted, running properties, abrasion resistance, and scratch resistance cannot be highly satisfied. has not been possible until now.

[Means for solving problems]

In view of the above-mentioned circumstances, the present inventor has conducted intensive studies on polyester films for magnetic recording media, and has found that certain particles obtained by the precipitated particle method and additive particles having a certain particle size and hardness. The inventors have found that the above problems can be easily solved industrially by using a combination of the following, and have thus arrived at the present invention.

That is, the gist of the present invention is that the average particle size precipitated in the polyester manufacturing process is 0. / -5μm inert particles 0.0
1-/wt%, inorganic particles having an average particle diameter of less than 1 μm and inert to polyester having a Mohs hardness of 6 or more.
-3% by weight of a biaxially oriented polyester film for magnetic recording media.

The present invention will be explained in more detail below.

Polyester as used in the present invention refers to terephthalic acid%2.
It refers to a polyester obtained using an aromatic dicarboxylic acid such as 6-f phthalene dicarboxylic acid or its ester and ethylene glycol as the main starting materials, but it may contain other third components. In this case, the dicarboxylic acid component includes, for example, isophthalic acid, phthalic acid, 2.6
-S7tale dicarboxylic acid, terephthalic acid, adipic acid, sebacic acid, and oxycarboxylic acid components, such as p-
One or more types of oxyethoxybenzoic acid can be used.

As the glycol component, one or more of diethylene glycol, propylene glycol, butanediol, Hehiro-cyclohexane dimetatool, neopentyl glycol, etc. can be used. Even if K eventually,
The polyester of the present invention means that 04 or more of the repeating structural units are ethylene terephthalate units or ethylene to 6
- Refers to polyesters with naphthalene units.

Further, the polyester film of the present invention refers to a biaxially oriented polyester film using such a polyester as a starting material, and known methods can be used for its production. For example, it is usually melt-extruded into a sheet at -70 to 10°C, then cooled and solidified at #0 to 10°C to form an amorphous sheet, and then biaxially stretched sequentially in the longitudinal and transverse directions. , a method such as heat treatment at 160 to 100°C (for example, the method described in Japanese Patent Publication No. Sho JO-ZTST can be used. When stretching in the longitudinal and transverse directions, stretching may be carried out in stages respectively. However, if necessary, it is also possible to perform multi-stage stretching and provide a heat treatment section for orientation relaxation between multi-stage stretching.

In addition, after biaxial stretching, 1
It is also possible to stretch again. This re-stretching may be performed in either the longitudinal or transverse directions, or in both directions.

In the present invention, the inert substance particles precipitated in the reaction system are particles precipitated in the reaction system by, for example, polymerizing a system using an alkali metal or alkaline earth metal compound as a transesterification catalyst by a conventional method. It is something to do. Alternatively, terephthalic acid may be added during the transesterification reaction or polycondensation reaction to cause precipitation. In these cases, one or more phosphorus compounds such as phosphoric acid, trimethyl phosphate, triethyl phosphate, tributyl phosphate, acidic ethyl phosphate, phosphorous acid, trimethyl phosphite, triethyl phosphite, and tributyl phosphite are used. It may be left to exist.

Furthermore, even when an esterification step is performed, inert material particles can be precipitated by these methods. For example, an alkali metal or alkaline earth metal compound is made to exist before or after the completion of the esterification reaction, and the polymerization reaction is carried out in the presence or absence of a phosphorus compound.

In any case, the fine precipitated compounds produced during the polyester production reaction in the present invention contain one or more elements such as calcium, lithium, antimony, and phosphorus.

For example, when calcium acetate is used as a transesterification catalyst, a calcium compound estimated to have the following composition consisting of calcium terephthalate and a calcium salt of a polyester oligomer is precipitated during the polymerization reaction.

When n = 0 or an integer of 1 to 3 and a phosphorus compound is used in combination with this system, it is thought that the following compounds will precipitate in addition to formula (1).

n=0. /, co or J In addition, when a phosphorus compound is used together with this system, the above formula ■
In addition, it is thought that a part of a compound estimated to have the following structural formula will precipitate. ・n = = 0 or an integer from 1 to S m = = 0 or) ~ n = 0 or an integer from /-j- n = 0 or l Furthermore, when a calcium compound and a lithium compound are used together, it is thought that complex compounds represented by the above formulas (1), (2), and the following formula will precipitate.

If a lithium compound is used instead of a calcium compound, and a phosphorus compound is used in combination with the base system, the following structure is assumed during polycondensation. It is estimated that complex compounds such as those described above will precipitate.

Tsuru n = 0 or 1 m = o or l In any case, in the present invention, these precipitated particles are Vco, oi ~/, 0% by weight, preferably O, OS ~ o, r weight coefficient in the polyester film. If the precipitated particle content is less than 0.0% by weight, the film will lack lubricity; on the other hand, if this amount exceeds 0.0% by weight, the film will no longer have lubricity. The problem is not improved; on the contrary, coarse protrusions frequently occur due to aggregation of particles.

Further, the average particle size of the precipitated particles is 0. /-3μm. This is because the average particle size is 0. If it is less than /μm, the effect of developing lubricity will be insufficient and the running properties will not be satisfied, and the wear resistance will also deteriorate. On the other hand, the average particle size is 5μ
If the particle size exceeds m, the life of the filter during film formation will be shortened even though it is a precipitated particle, and the electromagnetic properties will deteriorate when used as a magnetic recording medium.

The average particle size of the precipitated particles is particularly preferably 0.3 to 3 μm.

Since there are a wide variety of methods for producing precipitated particles that can be used in the present invention, it is not possible to discuss all of them in detail, but the following examples can be cited as specific examples.

That is, (1) a lithium compound is used as a transesterification reaction catalyst at a rate of 0.0% relative to the total acid components constituting the polyester; /-0,! ;
When the polycondensation reaction is completed using a mortar, the precipitated particles with an average particle size of O,S~λμ are 0.0! -0.3% by weight of polyester can be obtained, and (1) In this case, after the transesterification reaction, phosphoric acid is added to the lithium compound by 0.3% by weight. ! -/, If the same operation is performed with r times the molar addition, precipitated particles with an average particle size of about 0.3 to lμ are o
, os~0.2% by weight is obtained.

■ Also, in ■, trimethyl phosphate is substituted for phosphoric acid.
When triple-kill esters such as triethyl phosphate or tributyl phosphate are used, the amount of precipitated particles ranges from 0.1 to O,S.
% by weight.

■ Calcium compounds are used as transesterification catalysts.
When the polycondensation reaction is completed using r~o,is morti, precipitated particles o, o, t-o with an average particle size of ~3μ
, a polyester containing % by weight can be obtained, and
In addition, if terephthalic acid is added after the transesterification reaction in this operation, the average particle size of the precipitated particles will be O, S-λ.
It will be about μ.

It should be noted that, as a matter of course, the particle size and amount of the precipitated particles also depend on the polymerization conditions, particularly the temperature and pressure, and the examples shown above are only some of the results.

Use in combination with inorganic particles of specific diameter and hardness K
be.

In other words, the use of precipitated particles improves the running properties of the button.
It is also possible to improve wear resistance to a modest degree, but
Scratch resistance remains insufficient. The present inventor was very busy and took this into consideration, and found that in addition to the precipitated particles, inorganic particles 'f! :0.01-3 weight ratio, it was found that scratch resistance could be imparted while taking advantage of the characteristics of the precipitated particles, and the present invention was completed.

Examples of particles with a Mohs hardness of 6 or more used in the present invention include rutile titanium dioxide, crystalline silica, aluminum oxide, titanium carbide, titanium black, silicon carbide, etc. Among these, particles with a Mohs hardness of 5 Aluminum oxide and silicon carbide, especially aluminum oxide, are preferably used because they are industrially easily available.

When these particles with high Mohs hardness are present in the film, the abrasion resistance and scratch resistance, especially the scratch resistance, are significantly improved. However, if the amount of particles is less than 0.01% by weight based on the polyester film, or if the Mohs hardness is less than 6, the effect will sharply decrease. Incidentally, even if particles having a Mohs hardness of 6 or more are present in an amount exceeding 3 weight ts'fr:, the scratch resistance will no longer be improved, and on the contrary, coarse protrusions will occur frequently, which is not preferable. A particularly preferred amount range is 0.1-cowt%.

Incidentally, the average particle size of such particles used in the present invention must be less than 1 μm. If this value exceeds 1 .mu.m, the particles often separate from the film surface, resulting in a worsening of the abrasion resistance.

The preliminarily average particle diameter of the added particles is preferably at most O.S.mu.m, particularly at most 1.mu.m, and at the same time is desirably smaller than that of the precipitated particles.

An example of particles that meet these requirements and can be particularly suitably used in the present invention is aluminum oxide produced by a so-called thermal decomposition method. These particles are usually produced by flame hydrolysis using anhydrous aluminum chloride as a raw material, and have a particle size of about 1 OrrLμ to ioamμ. Further, in the present invention, aluminum oxide particles produced by an alkoxide hydrolysis method can also be suitably used. In this case, usually AI (OQ Hy )
Alternatively, if A 1 (0Cd=4e) is used as a starting material and the hydrolysis conditions are appropriately selected, fine particles with k diameter of 1 μm or less can be obtained. Of course, in this case, a method such as adding an acid to the synthesized slurry to obtain a transparent sol, then gelling the sol, and then heating it to a temperature above SOO°C to form a sintered body may be adopted. You can also do it. Alternatively, aluminum oxide fine powder obtained by another method, namely, adding methyl acetate or ethyl acetate to a sodium aluminate solution and stirring to obtain A100H't-, and then heating this may be used. In any case, in the present invention, the average particle size is 1 μm.
Aluminum oxide less than or equal to 1 F# is preferably used for IF#. In the present invention, as with other additive particles, it is preferable to use such aluminum oxide particles by completely dispersing them to the primary particles. It is okay to behave as such. However, in this case as well, the apparent average particle size must be less than 1 μm. - In this case, a part of the aluminum oxide, for example less than JO weight, is S 1 e
There is no problem even if it is substituted with an oxide such as T i * Fe * Na or .

In any case, in the present invention, if a specific amount of inorganic particles having an average particle size of less than 1 μm and a Mohs hardness of 6 or more are used together with the precipitated particles, the inorganic particles have the characteristics, but the particle size distribution of the inorganic particles is particularly There are no restrictions. However, in the present invention, the ratio of the particle size of weight fraction ys% to 25% is 100 or less, preferably /, j or less when integrated from the smaller particle size. are preferably used.

Further, there are no particular restrictions on the shape of these particles, but those that are generally clumpy or nearly spherical are preferably used. Specifically, it is preferable to use particles having a volume shape of 0.1 to π/6, preferably 0,0 to π/6, as defined in, for example, Japanese Patent Publication No. 33/1983/DaSza No. 3.

Furthermore, there is no particular restriction on the specific surface area of the particles used. For example, a perfectly spherical particle with an average particle diameter of 0.3μ and a density of −f/d has a specific surface area of about 67Fl″/, but!r
Porous materials up to about 00 @ / f can be suitably used.

Note that the surfaces of these particles may be modified with various surface treatment agents. These surface treatment agents, such as so-called silane coupling agents and titanium coupling agents, which are normally used for the purpose of improving the affinity with ethylene glycol and polyester, are generally applied in an amount of 3 weight percent or less to the particles.

These inorganic particles used in the present invention are blended into polyester after operations such as pulverization, classification, and filtration, as required. For the crushing process, for example, a rod mill, ball mill, vibrating rod mill, vibrating hall mill, pan mill, roller mill, impact mill, stirring mill, fluid energy mill, etc. can be used, and for the classification process, for example, a semi-free spiral mill can be used. , forced whirlpool type, hydrocyclone type,
A centrifugation method etc. can be adopted.

The method of blending the particles into the polyester is usually to add the core particles as an ethylene glycol slurry to the reaction system at the initial stage of polyester expansion, which is preferred from the viewpoint of dispersibility, but of course it is preferable to mix the core particles with the polyester directly before film formation. A blending method may also be used.

As described above, the button of the present invention uses one type of particles having different properties, that is, precipitated particles and additive particles, and in order to blend these into the polyester film, for example, the following method is adopted.

■ Polyester containing precipitated particles and polyester containing additive particles are blended and then a film is formed.

(2) Obtain a polyester containing both precipitated particles and additive particles, and use this to form a film.

■ After blending polyester containing precipitated particles and inorganic particles, a film is formed.

In addition, in the present invention, particles other than the two types of particles essential to the present invention or other compounding agents may be included as long as the purpose is not impaired. For example, for the purpose of finely adjusting surface roughness and lubricity, additive particles with a Mohs hardness of less than 6 are used, such as kaolin, talc, calcium carbonate, sulfur fluoride, mordenite, calcium fluoride, zinc oxide, calcium silicate, zeolite, and calcium phosphate. etc. may be used together. Further, the effects of the present invention are fully exhibited even in systems containing weathering agents, light stabilizers, antistatic agents, lubricants, light shielding agents, antioxidants, heat stabilizers, and the like.

As described above, the present invention improves runnability, wear resistance, and scratch resistance by using certain precipitated particles together with inorganic particles having an average particle size of less than 1 μm and a Mohs hardness of 6 or more. This has been achieved to a high degree and easily, and by using the polyester film of the present invention, it is finally possible to obtain a magnetic recording medium with excellent electromagnetic properties.

〔Example〕

The present invention will be explained in more detail below using examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof. In the Examples and Comparative Examples, "parts" indicate "parts by weight."

Furthermore, the measurement method used in the present invention is as follows.

(1) Average particle size In the case of precipitated particles, the polyester containing the particles was sandwiched between slides, melted, cooled, and then measured using a microscope. In the present invention, the average particle size refers to the particle size (diameter) at a point where the volume fraction is jO in terms of an isostatic sphere, regardless of its shape.

In the case of added particles, the particle size is also measured using a microscope, and the average particle size is calculated in the same way as for precipitated particles.

If the precipitated particles and additive particles are present at the same time, it is best to depolymerize and separate only the precipitated particles using the method described in Japanese Patent Publication No. 5S-201794 to reduce the average particle size of each. Calculate.

(2) Measurement of amount of precipitated particles Polyester ioOf K: o-chlorophenol/, After adding O1 and heating at 720°C for 3 hours, centrifugation was performed using a Beckman ultracentrifuge with a 7-kOft jO,000
The resulting particles were centrifuged for 10 min at rpm.
Vacuum dry at 0°C. When the particles are measured using a scanning differential calorimeter, if a melting peak corresponding to the polymer is observed, 0-chlorophenol is added to the particles, and after heating and cooling, centrifugation is performed again. Particles whose melting peak is no longer observed are defined as precipitated particles. Normally centrifugation operation is 2
times is enough.

(3) Surface roughness of film Center line average roughness (Ra) K is expressed as K, and this value was determined using a surface roughness meter (SE-JFK) manufactured by Koita Research Institute as follows. The radius of the tip of the stylus is 1 μm5 The load is JO■
It is.

A reference length L (
Ko,! The roughness curve y=f(x) is given by the following formula: μ
Represented by m.

Ra=ff,” If(xi ldX The cut-off value is o, otrμm.

(4) Abrasion resistance Using the device shown in Figure 2, the film was run for 100 meters, and the amount of white powder adhering to the fixed bottle was visually judged, and the abrasion resistance was ranked A (the amount of adhesion was It was divided into three ranks: extremely small (excellent) to C (poorly practical due to large amount of adhesion).

(5) Running properties The film was evaluated for its lubricity. The lubricity was measured using the apparatus shown in FIG. In other words, the film is wrapped around a fixed hard chrome-plated metal roll (diameter 6 mm).
j', that is, J s t, rad (so contact, and apply a load of s J f (Tt) on one end /
? This was run at a speed of Fl/311 m, the resistance force CT1-t)' at the other end was measured, and the coefficient of friction (μd) during running was determined using the following equation.

/T T μd=-Fl! n = 0. (6) Scratch resistance First, a magnetic tape was manufactured. That is, the following magnetic paint was applied to a polyester film to form a magnetic layer so that the film thickness after drying was 1 μm. That is, 200 parts of magnetic fine powder,
Polyurethane resin JO part% Nitrocellulose IO part, vinyl chloride-vinyl acetate copolymer io part, lecithin S part,
100 parts of cyclohexanone, 7 parts of methyl isobutyl ketone
00 parts and methyl ethyl ketone, 100 parts were mixed and dispersed in a ball mill for several hours, and then polyisocyanate compound j
This was applied to a polyester film, magnetically oriented before the paint was fully dried and solidified, and then dried.

This coated film was surface-treated using a supercalender, and slit into 5-inch widths to make a videotape.

Next, attach the magnetic tape to a hard chrome-plated metal pin (diameter 4
11% surface roughness JS) IfC wrapping is angle/Jl°, tension! It was contacted at fOf and rubbed at a running speed of 97,717 seconds.

Next, aluminum was vapor-deposited on the scratched surface of the magnetic tape, and the degree of scratches was visually judged and divided into the following five ranks.

Rank L: There are many scratches and often deep scratches.

Rank Co. The amount of scratches is relatively large, with some deep scratches here and there.

Rank J: The degree of scratches is relatively small and there are only a few deep scratches.

Ranked: There are some scratches, but the level is satisfactory.

Rank S rarely has 2 wounds.

(7) Electromagnetic characteristics The electromagnetic characteristics of the above magnetic tape were measured using Matsushita Electric's NV-37.
Measurements were made using a 00 type video deck.

The VTR head output was measured using a VTR head output synchroscope at a measurement frequency of 100 MHz, and the relative value was expressed in decibels with the flank set to θ decibels.

A videotape recording a signal of #0 dropout and 1 megahertz was played back, and the number of dropouts was measured for about -0 minutes using a Daikin Industry ■ dropout counter, and was converted to the number of dropouts per minute.

Example 1 100 parts of dimethyl terephthalate, 70 parts of ethylene glycol, calcium acetate hydrate o, i.

1 part and 061j part of acetic acid lytecum dihydrate were heated to boiling point with the reactor button, methanol was distilled off, and a transesterification reaction was carried out. It took about 7 hours after the start of the reaction to reach 230°C, and the ester was substantially converted into ester. The exchange reaction was completed.

Next, 0.37 part of triethyl phosphate was added to the reaction mixture, and 0.1 part tm of antimony trioxide was added thereto, followed by polymerization according to a conventional method to obtain polyethylene terephthalate having an intrinsic viscosity of o and b6 after 3 hours.

(Polyester (A)) A large number of uniform and fine precipitated particles were observed in the polyester, and the particle size was 0.05 μm.

When the amount of precipitated particles was measured according to the method described in the text, it was found to be 0.37 weight relative to polyester.

On the other hand, 100 parts of dimethyl terephthalate, 70 parts of ethylene glycol, and 0.09 parts of magnesium acetate tetrahydrate were placed in a reactor, and the temperature was raised while methanol was distilled off. The temperature was reached to 0°C to complete the transesterification reaction.

Next, i and o parts of aluminum oxide having an average particle diameter of θ and 0λ μm obtained by pyrolysis were added, and then o and oq parts of triethyl phosphate and 0.09 parts of antimony trioxide were added, and the mixture was processed using a conventional method. Performs polycondensation reaction and has an intrinsic viscosity of 0.6
Polyethylene terephthalate No. 6 was obtained. (Polyester (B)) Aluminum oxide was dispersed extremely uniformly in the polyester, and substantially no aggregated particles were observed.

Next, polyester (A) and polyester (B),! :
were mixed at a weight ratio of 70:30, dried, and then kettled.

The mixture was extruded into a sheet using an extruder at ℃ to obtain an amorphous sheet. At this time, we adopted a so-called electrostatic cooling method that applies an electrostatic charge to the sheet. Then, the sheet was stretched 3.3 times in the vertical direction.
3. Laterally. The film was stretched in Hiroshima and then heat-treated at 3° C. to obtain a biaxially stretched film with a thickness of 15 μm.

A magnetic layer was then applied to the polyester film, and scratch resistance and electromagnetic properties were evaluated.

Example λ A polyethylene terephthalate film and the film were used in the same manner as in Example 1, except that the amount of precipitated particles in the polyester film and the average particle size and blending amount of added particles were changed as shown in Table 7. A magnetic tape was obtained.

Example 3 In the production of polyester (A) in Example 1, 0.26 parts of triethyl phosphate was substituted for 0.31 part of triethyl phosphate.
A polyester containing precipitated particles with an average particle diameter of O.S .mu.m was obtained in the same manner as in Example 1, except that 0.03 parts and 0.03 parts of acidic ethyl phosphate were used.

A polyethylene terephthalate film containing particles shown in Table 7 was obtained by mixing the polyester and a polyester containing aluminum oxide particles, and then evaluated as a magnetic tape.

Example 2 A polyethylene terephthalate film containing the particles shown in Table υ was obtained by using the precipitated particles obtained in Example 3 in combination with silicon carbide particles, and then evaluated as a magnetic tape.

Comparative Example/-& As shown in Table 1, a biaxially oriented film with a thickness of 15 μm was obtained by forming a film in the same manner as in Example/, except that the particles contained in the polyethylene terephthalate film were changed, and then it was made into a magnetic tape and its properties were evaluated. evaluated.

The results obtained above are summarized in Table-/.

All of the films of Example 1-da that meet the requirements of the present invention have excellent lubricity and abrasion resistance, and are particularly excellent in scratch resistance, so that their electromagnetic properties are at a highly satisfactory level.

On the other hand, Comparative Example 1 is an example in which only precipitated particles are used without the additive particles specified in the present invention, but the scratch resistance is poor, and as a result, only a product with poor electromagnetic properties can be obtained.

Comparative Example - This is an example in which calcium carbonate particles having a Mohs' hardness of J were used as additive particles, but the scratch resistance was not improved at all and the properties as a magnetic tape were poor. Comparative Example 3 is an example in which the Mohs hardness of the additive particles used together with the precipitated particles is 6 or more, but the average particle size is 1 μm or more, but in this case, the surface roughness of the film is too large and The added particles detach and adversely affect the characteristics of the magnetic tape.

Further, Comparative Example D is an example in which only fine particles of aluminum oxide are used, but in this case, the film has extremely poor lubricity, and a large amount of abrasion powder is produced, deteriorating the electromagnetic properties.

〔Effect of the invention〕

As described in detail above, the present invention uses a combination of specific precipitated particles and additive particles. It has achieved an improvement over the conventional method, and its industrial value is high.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing the running system of the device for evaluating the coefficient of dynamic friction with metal.
aO-JJ fixed bottle, (II) Id Input tension meter (■) indicates the exit tensilon meter, and the winding angle (θ) is 133°. Figure 2 is a schematic diagram showing the running system of the device for evaluating wear resistance.
(V) indicates the tension meter, and the angle (θ) of the winding is /? ! 'is. Applicant Diafoil Co., Ltd.

Claims (1)

[Claims] (1) The average particle size precipitated in the polyester manufacturing process is 0.
Containing 0.01 to 1% by weight of inert material particles of 1 to 5 μm and 0.01 to 3% by weight of inorganic particles having an average particle size of less than 1 μm and inert to polyester having a Mohs hardness of 6 or more. Biaxially oriented polyester film for magnetic recording media.