JPH01284534A - Biaxially oriented polyester film - Google Patents

Abstract

PURPOSE:To obtain the title film which is flat, excellent in lubricity, chipping resistance, air scape, etc., and suitable for a magnetic tape, etc., by incorporating two specified kinds of spherical silica particles into a polyester and biaxially orienting it. CONSTITUTION:0.01-2.0wt.%, based on the polyester, spherical silica particles of a mean particle diameter of 0.12-0.6mum and an aspect ratio (major diameter/ minor diameter) of 1.0-1.2 as the first component and 0.005-1.8wt.% (smaller than the amount of the first component) of spherical silica particles of a mean particle diameter which is smaller than that of the first component by at least 0.1mum and is in the range of 0.02-0.5mum and an aspect ratio of 1.0-1.2 as the second component are incorporated into a polyester comprising an acid component based on an aromatic dicarboxylic acid (e.g., terephthalic acid) and a glycol component based on an aliphatic glycol (e.g., ethylene glycol) during, for example, the reaction for forming the polyester. The obtained polyester is formed into an unoriented film, and this film is biaxially oriented, heat-set and optionally heat-treated for relaxation to obtain the title film.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a biaxially oriented polynisder film, more specifically, it contains spherical silica particles with different average particle diameters, and is flat, slippery, and crack-resistant. This invention relates to a biaxially oriented polyester film with excellent properties.

[Prior Art] Because of its excellent properties, biaxially stretched polyester films are widely used in many applications such as magnetic tapes, electricity, photography, metallization, and packaging. In particular, because of its properties such as high strength and modulus, magnetic recording media, such as video tapes.

Widely used as a base film for audio tapes, computer tapes, floppy disks, etc.

In recent years, demands for high-density recording and high quality have been increasing in these fields of application, and as a result, there has been an increasingly strong demand for the base polyester film to have a flat surface. However, if the surface becomes flat, the winding appearance of the film during the process of winding it into a roll will deteriorate significantly, making it difficult to obtain a film roll with a good winding appearance.

Defects in the winding appearance of the film roll include: (1) Knot-like protrusions appear on the roll; (2) Wrinkles appear in the longitudinal direction of the film. ■When the edge surface is misaligned, etc., ■ is when the film has poor slipperiness, ■ is when the film is wound with high tension to prevent knot-like protrusions, ■ is when the film is rolled when flat film is wound. Each of these tends to occur when the air space that forms between them becomes difficult to escape.

Therefore, the base polyester film is required to have not only flatness but also excellent slipperiness and air escape properties in order to obtain a good film winding appearance.

Conventionally, methods for improving the slipperiness of films include adding inorganic particles such as silicon oxide or calcium carbonate to polyester, or precipitating fine particles containing calcium 1 lithium or phosphorus in the polymerization system during polyester synthesis. Proposed. In either method, when polyester is formed into a film, projections are formed on the surface of the film due to fine particles, thereby improving the slipperiness of the film.

However, in the above-mentioned method of improving the slipperiness of a film using protrusions made of fine particles, the slipperiness is usually improved by roughening the film surface, but on the other hand, due to the roughening, for example, magnetic recording In media applications, the surface after applying the magnetic paint tends to become rough, and the electromagnetic conversion characteristics tend to deteriorate.

Measures to resolve these contradictory issues of flatness and slipperiness -
・Many methods have been proposed that utilize composite ta-free fine particles in which large-sized particles and small-sized particles coexist. However, these means also have problems, and as they are, it is difficult to meet the demands for higher grades of magnetic recording media, such as higher density and higher quality. The reason for this is that the size of the large particles used in composite inorganic particles is too large for the quality required for high-grade grades, and the larger the particles, the higher the protrusions on the film surface. In addition, the larger the particles become, the higher the protrusions on the film surface and the larger the voids surrounding the particles. In the cleaning process or calendar processing process, high protrusions are scraped off, causing dropouts (missing information that occurs during recording and playback). This will cause dust fabric stains, which will greatly impair the properties of the magnetic recording medium.

[Object of the Invention] The present inventor has solved the above-mentioned problems, and has created a film that has both flatness and good film winding shape applicable to the field of high-quality magnetic recording applications, and also has good crack resistance. As a result of intensive research to develop the film, we have sharpened the shape of the protrusions on the film surface, and created a specific combination of large particles and small particles to improve slipperiness, air escape, and abrasion resistance even if the film surface is flat. In order to sharpen the shape of the protrusions, it is most preferable that the particles present in the film be spherical.There are many particles that are close to spherical, including crow beads, but these Although it is difficult to obtain a film that satisfies the surface properties especially for video tapes, it was discovered that a film that satisfies the above properties can be obtained by using specific spherical silica particles in combination with large particles and small particles. , arrived at the present invention.

Therefore, an object of the present invention is to maintain smoothness that can correspond to higher density recording and higher quality magnetic recording media, while improving slipperiness.
An object of the present invention is to provide a biaxially oriented polyester film having excellent abrasion resistance and the like.

[Configuration and Effects of the Invention] An object of the present invention is to provide polyester with
As the first component, 0.01 to 2.0 weight of spherical silica particles with an average odor diameter of 0.12 to less than 0.6 μm and a particle size ratio (major axis/minor axis) of 1.0 to 1.2 are used. %, and as a second component, the average particle diameter is in the range of 0.02 μm or more and less than 0.5 μm, smaller than the first component by 0.1 μm or more, and the particle size ratio (major axis / short axis) is 1.0 to 1. This is achieved by a biaxially oriented polyester film characterized in that it contains spherical silica particles of 0.005 to 1.8% by weight, which is less than the first component.

The polyester according to the present invention is a polyester containing an aromatic dicarboxylic acid as a main acid component and an aliphatic glycol as a main glycol component.

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, diphenoxyethane dicarboxylic acid.

Examples include diphenyl dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, diphenyl ketone dicarboxylic acid, and anthracene dicarboxylic acid. Examples of aliphatic glycols include alkylene glycols having 2 to 10 carbon atoms, such as ethylene glycol, 1-rimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, decamethylene glycol, or cyclohexane. Examples include alicyclic diols such as dimethanol.

In the present invention, polyesters containing, for example, alkylene terephthalate and/or alkylene naphthalate as main constituents are preferably used. Among the polyesters, examples include polyethylene terephthalate (polyethylene terephthalate) to polyethylene 2,6-naphthalate, and for example, 80 mol% or more of the total dicarboxylic acid component is terephthalic acid and/or 2,6-naphthalene dicarboxylic acid. A copolymer in which 80 mol% or more of the total glycol component is ethylene glycol is preferred. In this case, up to 20 mol% of the dicarboxylic acid 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 fatty acids such as adipic acid, cepatic acid, etc. group dicarboxylic acids; alicyclic dicarboxylic acids such as cyclohexane-1,4-dicarboxylic acid; Further, up to 20 mol% of the total glycol component can be the above glycol other than ethylene glycol, or for example, hydride o-
Aromatic diols such as 4non-2resorcin, 2,2-his(4-human 0xyphenyl)propane; Aliphatic diols containing aromatic rings such as 1,4-dihydroxymethylbenzene; polyethylene glycol, polypropylene glycol , polyalkylene glycol (polyoxyalkylene glycol) such as polytetramethylene glycol and the like.

In addition, in the polyester of the present invention, a component derived from an oxycarboxylic acid such as an aromatic oxyacid such as hydroxybenzoic acid, an aliphatic oxyacid such as ω-hydroxycaproic acid, a dicarboxylic acid component and an oxycarboxylic acid component, Those copolymerized or combined in an amount of 20 mol % or less based on the total amount of acid components are also included.

Furthermore, the polynisdel in the present invention contains a trifunctional or more functional polycarboxylic acid or a polyhydroxy compound, such as trimellitic acid, in an amount in a substantially linear range, for example, an amount of 2 mol% or less based on the total acid components. , pentaerin litol, etc. are also included.

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 measured as a solution in 0-chlorophenol at 35°C.
~0.8 is preferred.

The biaxially oriented 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 produced at any time during the reaction to form the polyester, for example, during the transesterification reaction or polycondensation reaction when using the transesterification method, or at any time during the polycondensation reaction when using the direct polymerization method. It can be prepared by adding spherical silica particles (preferably as a slurry in glycol) into the reaction system at the same time. Preferably, the spherical silica particles are added to the reaction system at the beginning of the polycondensation reaction, for example, until the intrinsic viscosity reaches about 0.3.

In the present invention, the spherical silica particles dispersed and contained in the polyester have a particle diameter ratio (major axis/minor axis) of 1.0 to 1.2, preferably 1.0 to 1.1. More preferably 1.0 to 1.
05. These spherical silica particles have individual shapes extremely similar to pearls, and the silica particles conventionally known as lubricants are ultrafine lump particles of about 10 mm, or aggregates of about 0.5 μm. It is distinctive in that it is significantly different from forming particles (agglomerated particles). If the particle size ratio becomes too large, the void ratio becomes large, which may lead to poor machinability, which is not preferable.

The spherical silica particles as a first component have an average particle diameter of 0.12 to less than 0.6 μm, preferably 0.2 to 0.6 μm.
54 μm, more preferably 0.25 to 0.49 μm, particularly preferably 0.38 to 0.48 μm, and a second component with an average particle size of 0.02 μm or more and less than 0.5 μm,
Preferably 0.06 μm or more and less than 0.4 μm, more preferably 0.08 to 0.3 μm, particularly preferably 0.10 μm
There are two types: one with a diameter of ~0.25 μm. If the average particle diameter of the spherical silica particles as the first component becomes too small, the effect of improving slipperiness will be insufficient, which is not preferable.

Also, the difference in average particle size between the first component and the second component is 0.1μ
m or more, preferably 0.15 μm or more, more preferably 0.20 μm or more, particularly preferably 0.30 μm or more. If the difference in average particle size between the first component and the second component is too small, air escape performance will be poor, end face deviation will easily occur during film winding, and the film winding appearance will be poor, which is not preferable.

Here, the major axis and minor axis of the spherical silica particles are determined using an electron microscope, for example, after depositing metal on the particle surface.
It is determined from an image magnified 30,000 to 30,000 times, and the average particle size/particle size ratio is determined by 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 Also, it is preferable that the spherical silica particles have a sharp particle size distribution. , the relative standard deviation representing the steepness of the distribution is 0.
The relative standard deviation, which is preferably 5 or less, more preferably 0.3 or less, particularly 0.12 or less, is expressed by the following formula.

Relative standard deviation = Here, Dl: Area circle equivalent diameter of each particle (μm) Average value of D2 area equivalent diameter (=(Σ Di)/nl (μm), I=1 Measured number of n2 particles represents.

When spherical silica particles with a relative standard deviation of 0.5 or less are used, the particles are truly spherical and have an extremely steep particle size distribution, so the distribution of protrusions formed on the film surface is extremely uniform, with no protrusions. A polyester film with uniform height and excellent slip properties can be obtained. Also, in this case, the first
The average particle size of the component and the average particle size of the second component are at least 0.
．． Since there is a difference of 1 μrn, the particle size distributions of the first component and the second component do not substantially overlap each other. Spherical silica particles are
As long as the above conditions are met, there are no limitations on the manufacturing method or anything else. For example, spherical silica particles can be obtained by producing hydrated silica LSi (OH) a ] monodisperse spheres by hydrolyzing ethyl orthosilicate [S + (OC2H5) a ], and then dehydrating this hydrated silica monodispersion method. It can be produced by three-dimensionally growing silica bonds [=S i -0-3i =] (Journal of the Chemical Society of Japan' 81
．． No. 9. P, 1503).

S i (OC2Hr, ) a
+4 1-12 0→ S i (OH)
a + 4 C2H50l-1=S i -O
H + HO-3i Mi → = 3i -0-8i 3 = + T-f
20 In the present invention, the amount of spherical silica particles added as the first component is 0.01 to 2.0% by weight, preferably 0.01 to 0.8% by weight, more preferably 1% by weight, based on the polyester. 0.01-0.2% by weight, particularly preferably 0
．． 02-0.10% by weight. Further, the amount of the spherical silica particles added as the second component is 0.00% relative to the polyester.
005-1.8% by weight, preferably 0.005-1.6
1% by weight, more preferably 0.005-0.15% by weight,
Particularly preferably, the amount is within the range of 0.01 to 0.09% by weight and is less than the amount of the first component. The amount of the first component added is less than 0.01% by weight, and the amount of the second component added is 0.0050.
Less than 5% by weight, the effect of improving slipperiness and abrasion resistance is insufficient. In addition, the total amount of the first component and second component added is as follows:
o, ois~3.0 1% by weight, preferably 0°02~2.
0% by weight, more preferably 0.04-0.8% by weight,
Particularly preferably, it is 0.05 to 0.15% by weight.

If the total amount added exceeds 3.0% by weight, the surface flatness will deteriorate, which is not preferable.

In the polyester of the present invention, film-16-
In order to further improve the slipperiness of the polyester, an ester product of a polyol having three or more hydroxyl groups and a fatty acid monocarboxylic acid having eight or more carbon atoms was added to the polyester.
It is preferred that the dispersion content be 5% by weight or less, preferably 0.05 to 2% by weight, particularly preferably 0.1 to 0.9% by weight. In addition, if the amount of this ester product is too large,
Film blocking is likely to occur, so you need to be careful.

The polyol used as a raw material for the above ester product must have three or more hydroxyl groups. hydroxyl group 2
If less than 10% alcohol is used, the slipperiness of the film cannot be improved, even if the resulting ester product is dispersed in the polyester, for reasons that are not clear. In particular, polyols having 3 to 6 hydroxyl groups are preferred from the viewpoint of easy availability. Examples of such polyols having three or more hydroxyl groups include glycerin, erythritol, and triit.

Pentaerythritol, Arabit, Ximerit.

Atonito, Tarit 1~. sorbit, mannit.

examples include, but are not limited to, examples.

Further, as the aliphatic monocarboxylic acid to be reacted with the polyol E, it is necessary to use an aliphatic monocarboxylic acid having 8 or more carbon atoms.

If an aliphatic monocarboxylic acid with fewer than 8 carbon atoms is used, the resulting ester product will have insufficient heat resistance, and will easily decompose under the heating conditions when dispersing into polyester, making it difficult to disperse into polyester. It is unsuitable as a substance.

In particular, aliphatic monocarboxylic acids having 8 to 25 carbon atoms are preferred because they are easily available. Such aliphatic monocarboxylic acids having 8 or more carbon atoms include pelargonic acid and capric acid.

undecylic acid, lauric acid, tridecylic acid, myristic acid, pentadecylic acid, valmitic acid, heptadecylic acid,
stearic acid, nonadecanoic acid, arachidic acid, behenic acid,
Examples include lignoceric acid and cerotic acid.

” When the polyol described in 1. is reacted with an aliphatic monocarboxylic acid, mono-, di-, and triesters are usually produced. All of these ester products are effective in improving slipperiness, but
Triesters are particularly preferred from the viewpoint of heat resistance when dispersed in polyvarnish-18=chill.

Since the effect of the ester product varies depending on the surface properties of the film, the amount added is preferably selected depending on the surface roughness.

Any method can be used to disperse the above ester product in the polyester, such as adding and dispersing it during the polycondensation reaction or kneading it in an extorter. It is also possible to make a polymer and dilute it with unadded polynisder.

The biaxially oriented polyester film of the present invention can be produced according to conventional methods for producing biaxially oriented films, but in particular, in order to obtain the film properties described below, stretching in the lateral direction may be performed by the method described below. is preferred. For example, polyester containing a predetermined amount of spherical silica particles is melt-cast to form an amorphous unstretched film, then the unstretched film is stretched biaxially, heat-set, and if necessary, subjected to relaxation heat treatment. A biaxially oriented film can be produced by 6 At that time, the film surface properties vary depending on the particle size, amount, etc. of the pulverized silica particles, and also depending on the stretching conditions, so it is necessary to select the stretching conditions as appropriate from the following stretching conditions. is preferred.

In addition, the density, heat shrinkage rate, etc. are also determined by the temperature 1x ratio during stretching and heat treatment,
Since it changes depending on the speed, etc., conditions that satisfy these characteristics at the same time are determined. To explain further, for example, the stretching ratio may be selected from a range in which the uniaxial stretching ratio is 2.5 or more, particularly 3 times or more, and the area stretching ratio is 8 times or more, particularly 10 times or more.

In addition, the stretching temperature is the longitudinal stretching temperature: T1 ('rf, -
10) ~, ger g+45) "C range (however, 'T
'g: glass transition temperature of polyester), and the transverse stretching temperature is ('I'g + 20) ~ ('r g -) -
100) It is recommended to select from the range 'C. Furthermore,
Heat setting temperature is 180-250℃, even 200-230℃
It is recommended to select from the range of ℃.

Moreover, it is preferable that the above-mentioned lateral direction stretching is carried out in several stages. In that case, the transverse stretching ratio at each stage is preferably 1.2 times or more, particularly 1.3 times or more -20=. Further, the difference in stretching temperature at each step of the transverse stretching is preferably 10°C or more, particularly preferably 20°C or more.

By using such a multi-stage stretching method, the coefficient of friction can be lowered without significantly changing the centerline average roughness (Ra) of the film surface. The reason for this is not clear, but the multi-stage stretching in the transverse direction essentially causes ``waviness'' on the film surface due to repeated stretching-relaxation-stretching, which lowers the film's coefficient of friction. It is considered that

The biaxially oriented polyester film in the present invention has a center line average roughness (Ra”) of 6.002 to 0.0 on its surface.
It is preferably 12 μm. If this center line average roughness (Ra) is too large, it will be difficult to maintain the electromagnetic conversion characteristics necessary for a magnetic recording medium, especially for high image quality, and if it is too small, the penetrability will deteriorate. Handling of film
The resistance to winding and winding into a roll deteriorates. The center line average roughness (Ra, ) is preferably 0.003 to 0.008.
μm, more preferably 0.003 to 0.005 μm.

Furthermore, the biaxially oriented polynisder film in the present invention has the above-mentioned center line average roughness (Ra) and 10 point average roughness (Rz
'u・) preferably has a relationship that satisfies the following formula % formula %.

If Rz D/Ra becomes too large, there will be too many high protrusions despite the small film surface roughness (Ra), resulting in poor electromagnetic conversion characteristics (especially low frequency region tIA), which is undesirable6. When winding a film into a roll, whether the film is rolled up with accompanying air or not, and if RZ'D7R,a is of an appropriate size, the accompanying air will quickly move between the film and the film layer. Rz D
/ If Ra becomes too small, the escape of the accompanying air will be poor and the air will be caught up in the roll, and as the air gradually escapes, the shape of the roll will change over time after it is wound. However, wrinkles appear, which is not desirable. From this point R7-D/Ra is 10 or more 1
It is more preferably 6 or less, and particularly preferably 12 or more and 16 or less.

Further, in the biaxially oriented polyester film of the present invention, it is preferable that the 10-point average surface (R, ZD) and the film-to-film static friction coefficient (μS) satisfy the following formula %. If the value of RZDXμS is too small, it may be because the air escape between the film layers becomes poor when the film is rolled up, and the film becomes meandering, which tends to cause edge misalignment, and the film becomes larger. From these points, R
, ZD×μs preferably satisfies 0.020 to 0.050, more preferably 0.025 to 0.040. Compared to , the surface is flat, but it has extremely good slipperiness, good air escape, good winding performance when winding into a roll, and even better shape of the roll after winding. It is characterized by little change over time.

The biaxially oriented polyester film of the present invention can be widely used in various applications by taking advantage of such characteristics. For example, it is useful for stamping foils, packaging films, vapor deposition of gold and silver threads, 0T (P), drawing, etc., and is especially useful as a base film for magnetic recording media, especially high-density magnetic recording media.

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

In addition, various physical property values and characteristics included in the present invention were measured as follows.

(1) Particle size of spherical silica particles There are two conditions for measuring particle size:

1) When determining the average particle size, particle size ratio, etc. from powder 2) When determining the average particle size, particle size ratio, etc. of particles in a film.

(+) In the case of powder, the powder is scattered on an electron microscope sample stage so that the individual particles do not overlap as much as possible, and a gold thin film is deposited on the surface using a gold sputtering device to a thickness of 200 to 300 people. Formed and observed with a scanning electron microscope at a magnification of, for example, 10,000 to 30,000 times, using a Luzex 500 manufactured by Gulator ■, at least 100 particles with a long axis (Dli) and a short axis (]) si) and the area circular phase diameter (Di). Then, with the number average value expressed by the following formula, the major axis (DI), minor axis (Ds), and average particle diameter (D) of the silica particles are calculated.
represents.

1) t = (ΣDli)/n.

1・1 D S = (Σ Dsi)/n.

D = (Σ D i ) / n 1 = 1 (II) In the case of particles in a film, a small piece of sample film was fixed on a sample stage for a scanning electron microscope, and a sputter link device manufactured by JEOL (JFC-110) was used.
The surface of the film is subjected to ion etching using a Type 0 ion sputtering device under the following conditions. The conditions were to place the sample in a Pel jar, raise the degree of vacuum to about 10' Torr, and apply a voltage of 0.25 KV and a current of 1.
Ion etching is performed at 2.51A for about 10 minutes. Furthermore, gold sputtering is applied to the film surface using the same device, and the film is observed at a magnification of, for example, 10,000 to 30,000 times using a scanning electron microscope.
The major axis (Dli) and minor axis (Dsi) of at least 100 particles were measured using Ruse° Tusk 500 manufactured by Nippon Regulator @.
) and the area circular phase diameter (Di) are determined. Below, above (+
).

(2) Center line average roughness (Ra) JI of the film surface
This is a value defined in S-BO601, and in this invention,
6 measurement conditions etc. to be measured using ER3E-30C) are as follows.

~26 - (a) Stylus tip radius: 2 μm (b) Measurement pressure = 30 ■ (C) Cutoff: 0.25 nm (d) Measurement length: 1. Om (e) How to summarize the data - Repeat the measurement 5 times for the sample and set the largest value as 1.
The average value of the remaining four data is displayed.

(3) Ten-point average surface roughness of the film surface (Rzo
) In the above (2) measurement, the difference Rz1, Rz2.・Old...

RZD is displayed as the average value of RZ5.

(4) Coefficient of static friction (μS) Place a fixed glass plate under the two stacked films, and roll the film on the bottom side of the stack (the film in contact with the glass plate) with a low speed roll. Adoption (1
5ao/min), a detector was fixed to one end of the upper film (the end opposite to the pulling direction of the lower film), and the tensile force of the film/film was detected. Incidentally, the thread used at that time has a weight of 1 kg and a lower surface area of 70 an.

(5) Windability In the manufacturing process of biaxially oriented polyester film, the film is rolled into a roll with a width of 800 m and a length of 5000 m at a speed of 2
The roll is rolled up at a speed of 50 m/min, and the appearance of the roll is inspected in detail and graded into grades 1 to 5.

The end face misalignment is graded as follows based on the distance of the end face misalignment in the width direction.

Regarding knob-like protrusions, the number of nodular protrusions with a major diameter of 2 mm or more is counted and graded as follows.

= 28- Furthermore, the roll wound up above was heated at 40°C x 80% RH.
After storage for 10 days, the occurrence of vertical and horizontal wrinkles was determined by looking at the surface and inner layer of the roll.

Implementation FJ 1 Dimethyl terephthalate and ethylene glycol were used, manganese acetate was used as a transesterification catalyst, antimony trioxide was used as a polymerization catalyst, hypophosic acid was used as a stabilizer, and the average particle size was 0.48 μm as a lubricant.

Spherical silica with particle size ratio 1.04 and average particle size 0.20 μm1
Using spherical silica with a particle size ratio of 1.04, polymerization was performed by a conventional method, and the intrinsic viscosity (orthochlorophenol, 35°C) was 0.
．． Obtain 62 polyethylene prephthalate.

This polyethylene terephthalate pellet 170
℃, after drying for 3 hours, feed it to the extruder hopper, and melt temperature 2
The molten polymer was melted at 80 to 300°C and extruded through a series of slit ties onto a rotating cooling drum with a surface temperature of 20°C to obtain an unstretched film.

The unstretched film thus obtained was preheated at 76°C, and further rolled between low speed and high speed rolls from 15 degrees above.
3.6 by heating with an IR heater with a surface temperature of 890℃
Stretched twice, quenched, then fed into a stenter, stretched to 2.9 at 98°C as the first stage of transverse stretching, and further stretched at 132°C as a second stage to final transverse direction. The stretching ratio was set to 3.9 times. Subsequently, the obtained biaxially oriented film was heat-set at 208° C. for 4 seconds.

On the other hand, acicular α-FeOOH containing 5% cobalt
was heated and reduced with hydrogen to obtain Fe2o3, which was further heated in air to obtain ferromagnetic iron powder with an average acicular length of 0.2 μm.

100 parts by weight of the above ferromagnetic iron powder (hereinafter simply referred to as "Part 1")
The following composition was mixed and dispersed in a ball mill for 12 hours.

Polyester polyurethane 12 parts Vinyl chloride-vinyl acetate-maleic anhydride copolymer 10 parts α-alumina 5 parts Carbon black
1 part butyl acetate
Part 7 medyl edil ketone
35 part cyclohexanone
After dispersing 100 parts, 1 part of fatty acid, 1 part of oleic acid, 1 part of palmitic acid, 1 part of fatty acid ester (amyl stearate) was added, and after kneading for 15 to 30 minutes, 7 parts of a 25% ethyl acetate solution of the compound of 1 to triisothiamine was added. was added and subjected to high-speed shear dispersion for 1 hour to prepare a magnetic coating solution.

The obtained coating liquid was applied onto the heat-set biaxially oriented film so that the dry film thickness was 3 μm.

Then, after orientation treatment in a DC magnetic field, it was dried at 100'C. After drying, a magnetic tape for video was obtained by applying a calendar link treatment and slitting each portion to a width of 2 inches.

The film obtained in this way has good winding properties, has little edge slippage even when rolled at high speed, and has few bump-like protrusions.
Furthermore, the winding appearance after aging was good, and the electromagnetic conversion characteristics of the tape after being made into a magnetic tape were also good. The properties of this film are shown in Table-1.

Comparative Example 1.2 A film was prepared in the same manner as in Example 1, except that spherical particles with different average particle diameters were used, and the transverse stretching during film formation was carried out at 110°C and by a factor of 3.9 in -steps. Axially oriented films and magnetic tapes were made.

The properties of this biaxially oriented film are shown in Table 1. In Comparative Example 1, when it was rolled up at high speed, the edge misalignment was good, or bump-like protrusions occurred, and in Comparative Example 2, when it was rolled up at high speed, When it is rolled up, end face misalignment tends to occur, and the characteristics are not good.

Example 2 Biaxial orientation was carried out in the same manner as in Example 1 except that spherical silica particles with different average particle sizes were used and 0.3% by weight of pentaerythritol tristearate was added to the polynisder. A polyester film and magnetic tape were made.

This film had good properties, with good wind-up properties and little occurrence of bump-like protuberances. The properties of this film are shown in Table-1.

Table-1

Claims (1)

[Claims] 1. As the first component in polyester, the average particle size is 0.1
Spherical silica particles having a size of 2 μm to less than 0.6 μm and a particle size ratio (major axis/breadth axis) of 1.0 to 1.2 are
2.0% by weight, and as a second component, the average particle size is 0.1 μm or more smaller than the first component and 0.02 μm or more.
Particle size ratio (major axis/minor axis) is within the range of less than 5 μm and is 1
．． 0 to 1.2 spherical silica particles to 0.005 to 1.2.
A biaxially oriented polyester film characterized by containing an amount within the range of 8% by weight and less than the first component. 2. The biaxially oriented polyester film according to claim 1, wherein the spherical silica particles have a relative standard deviation represented by the following formula of 0.5 or less. ▲There are mathematical formulas, chemical formulas, tables, etc.▼ Here, Di: Area circle equivalent diameter of each particle (μm) @D@: Average value of area circle equivalent diameter ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (μm) n : Represents the number of particles. 3. Center line average roughness (Ra) of the film surface is 0.00
2 to 0.012 μm, and the center line average roughness (Ra)
and the 10-point average roughness (R_Z_D) of the film surface satisfy the following formula 10≦R_Z_D/Ra≦20, and the 10-point average roughness (R_Z_D) and the film-film static friction coefficient (μs) satisfy the following formula 0 .015≦
The biaxially oriented polyester film according to claim 1, which satisfies R_Z_D×μs≦0.05.