JPH02296836A - Biaxially oriented polyester film - Google Patents

Abstract

PURPOSE:To obtain a film excellent in electromagnetic transduction properties, travelling properties and abrasion resistance, having a low light transmittance and being useful for a magnetic recording medium by using a polyester in which a specified carbon black and specified inert spherical particles are dispersed so as to give thereto specified physical properties. CONSTITUTION:This film is comprised of a polyester (e.g. polyethylene terephthalate) in which 0.1-5wt.% carbon black of a mean particle diameter of 0.01-0.6mum and 0.01-3wt.% inert spherical particles (e.g. silica particles, silicone particles or crosslinked PS particles) of a mean particle diameter of 0.1-1.2mum and an aspect ratio (major diameter/minor diameter ratio) of 1.0-1.4 are dispersed. It has a thickness of 4-15mum, a transmittance <=70% at a wavelength of 900nm and a Young's modulus >=630kg/mm<2> in the crosswise direction and a surface roughness <=0.025mum.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a biaxially oriented polyester film, and more specifically to a magnetic recording medium that has excellent electromagnetic conversion characteristics, runnability, and abrasion resistance as well as low light transmittance. The present invention relates to a biaxially oriented polyester film for use.

(Prior Art) Biaxially oriented polyester films, typified by polyethylene terephthalate films, are used in a wide range of applications due to their excellent physical and chemical properties, especially for magnetic recording in video, audio, computers, and floppy disks. Widely used as base film for media. recent years,
In these applications, high-density recording has become remarkable, and the magnetic powder used in magnetic tapes has become finer in order to improve electromagnetic conversion characteristics. As the magnetic powder becomes finer, light with longer wavelengths becomes less likely to be scattered by the magnetic powder, resulting in higher light transmittance. For this reason, problems have arisen in magnetic recording media that have conventionally performed edge detection using the difference in light transmittance between the non-magnetic support and the magnetic recording layer, and there is a need to reduce the light transmittance of the base film. .

In the past, many proposals have been made to add carbon black to the base film in order to impart light-shielding properties.
It cannot be said that sufficient performance is maintained in terms of flatness, runnability, wear resistance, etc. required of a magnetic recording medium.

Attempts have also been made to improve the above-mentioned properties by adding two-component additives such as carbon black, calcium carbonate, and titanium oxide, but these efforts are still in progress.

(Objective of the Invention) The object of the present invention is to provide a material with low light transmittance that can compensate for these drawbacks, and with sufficient flatness to be used as a magnetic recording medium.
An object of the present invention is to provide a biaxially oriented polyester film having running properties and abrasion resistance.

(Structure and Effect of the Invention) According to the present invention, an object of the present invention is that the average particle diameter is 0,01
0.1 to 5% by weight of carbon black having a particle diameter of ~0.6 μm, and a particle size ratio of 1.0 to 1.2 μm having an average particle size of 0.1 to 1.2 μm and a particle size ratio defined by major axis/breadth axis. The film is made of polyester containing 0.01 to 3% by weight of inert spherical particles dispersed in No. 4, and has a film thickness of 4 to 15 μm,
The light transmittance of the film at a wavelength of 900 nm is 70%.
or less, and the transverse Young's modulus of the film is 630 Kg
/mm2 or more, and the film surface roughness (Ra) is 0.025 μm or less.

The polyester in the present invention is a polyester containing an aromatic dicarboxylic acid as the main acid component and an aliphatic glycol as the 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, diphenylethanedicarboxylic acid, diphenyldicarboxylic acid, diphenyl ether dicarboxylic acid, diphenylsulfone dicarboxylic acid, diphenylketone dicarboxylic acid, anthracene dicarboxylic acid, and the like. can. Examples of aliphatic glycols include alkylene glycols having 2 to 10 carbon atoms such as ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, and decamethylene glycol, and alicyclic glycols such as cyclohexane dimetatool. Examples include group diols.

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

Among such polyesters, for example, not only polyethylene terephthalate and polyethylene-2,6-naphthalate, but also terephthalic acid and/or 26-naphthalene dicarboxylic acid account for 80 mol% or more of the total dicarboxylic acid component, and A copolymer in which 80 mol% or more is ethylene glycol is preferred. At that time, less than 20 mol% of the total acid component is terephthalic acid and/or 2
．． Can be the above-mentioned aromatic dicarboxylic acids other than 6-naphthalene dicarboxylic acid, and also aliphatic dicarboxylic acids such as adipic acid, cepatic acid, etc.; cyclohexane-
It can be an alicyclic dicarboxylic acid such as 1,4-dicarboxylic acid. In addition, 20 mol% of the total glycol component
The following can be the above glycols other than ethylene glycol, and aromatic diols such as hydroquinone, resorcinol, 2,2-bis(4-hydroxyphenyl)propane, etc.; aromatic diols such as l,4-dihydroxymethylbenzene. Aliphatic diols having a ring; polyalkylene glycols (polyoxyalkylene glycols) such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol, etc. can also be used.

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

Furthermore, the polyester of the present invention may contain a trifunctional or higher functional polycarboxylic acid or a polyhydroxy compound, such as trimellitic acid, penta-functional acid, etc., in a substantially linear amount, for example, 2 mol % or less based on the total acid component. Copolymerized products such as erythritol 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.
~0.9 is preferred.

In the present invention, the average particle size of the polyester is 0.
．． Carbon black of 0.01 to 0.6 μm is contained in an amount of 0.1 to 5% by weight. If the carbon black content is less than 0.1% by weight, the decrease in light transmittance will be insufficient for a film used for magnetic recording media. Furthermore, if the carbon black content exceeds 5% by weight, the flatness of the film surface deteriorates, leading to deterioration of the electromagnetic conversion characteristics required for magnetic recording media. The required amount of carbon black varies depending on the thickness of the film, but it may be set within the above range so that the light transmittance is 70% or less, preferably 50% or less.

In the present invention, inert spherical particles having an average particle size of 0.1 to 1.2μ0 and a particle size ratio defined by major axis/breadth axis of 1.0 to 1.4 are added to the polyester together with carbon black. It is contained in an amount of 0.01 to 3% by weight.

These inert spherical particles have individual shapes that are extremely close to true spheres.

It is necessary that the average particle size of the inert spherical particles is 0.1 to 1.2 μm, preferably 0.2 to 1.0 μm. If the average particle size is less than 0.1 μm, the effect of improving the runnability and abrasion resistance of the film is insufficient, which is not preferable. Moreover, if the average particle diameter exceeds 1.2 μm, the surface of the film becomes too rough, which is not preferable. The particle size ratio (major axis/breadth axis) of the inert spherical particles needs to be 1.0 to 1.4, preferably 1.0 to 1.2.

If this particle size ratio exceeds 1.4, large voids will occur around the spherical particles in the film after biaxial stretching, and the effect of improving runnability and abrasion resistance will decrease. Furthermore, it is desirable that the average particle size of the spherical particles be equal to or larger than the average particle size of the carbon black added at the same time, and furthermore, it is preferable that the particle size distribution of the spherical particles be sharp, for example, if the distribution is steep. The relative standard deviation representing the degree is 0.5 or less,
Furthermore, it is preferably 0.3 or less, particularly 0.15 or less.

This relative standard deviation is expressed by the following formula: Relative standard deviation = where, Di = area circle equivalent diameter of each particle (μm) r5
=Average value of area circle equivalent diameter (=Σ Di/n) (μm1 n: Measured number of particles.

In addition, the major axis, minor axis, and area-equivalent diameter of the inert spherical particles are determined from an image magnified, for example, 10,000 to 30,000 times with an electron microscope after metal is deposited on the particle surface, and the average particle diameter and particle diameter are The ratio is calculated 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 spherical particles / Average minor diameter of the particles By containing spherical particles, compared to a film containing only carbon black Running properties and abrasion resistance are improved, and the effect becomes even greater by making the average particle size of the spherical particles equal to or larger than the average particle size of carbon black. In addition, when the distribution of spherical particles becomes steep, the height of the large protrusions caused by the spherical particles on the film surface becomes uniform, and even if the height of the protrusions caused by carbon black is uneven, it has the effect of improving running performance and wear resistance. becomes larger.

Examples of inert spherical particles include true spherical silica, true spherical titanium oxide, true spherical zirconium, true spherical silicone,
Preferred examples include truly spherical crosslinked polystyrene, with silica particles, silicone particles, and crosslinked polystyrene particles being particularly preferred.

The biaxially oriented polyester film of the present invention has a thickness of 4 to
15 μm, light transmittance (light wavelength 900 nm) is 70% or less, and lateral Young's modulus is 630 Kg/mm.
2 or more, and the film surface roughness (Ra) is 0.0
It needs to be 25 μm or less. It is further preferable that the biaxially oriented polyester film has a thickness of 5 to 13 μm. If the film thickness is less than 4 μm, the tape will be thin;
Durability is poor, and if the diameter exceeds 15 μm, there are few features for long-term recording. Young's modulus in the lateral direction is 630 Kg/
If it is less than mm2, the VTR head touch will be poor and the electromagnetic conversion characteristics will be poor. Furthermore, etch damage (hereinafter referred to as edge damage) during tape running also increases. A preferred transverse Young's modulus is 700 Kg/mm2 or more. When the surface roughness (Ra) of the film is greater than 0.025 μm, the surface of the magnetic layer after coating becomes rough, and the electromagnetic conversion characteristics become poor. The preferred surface roughness (Ra) is 0.
02 μm or less. More preferably, it is 0.016 μm or less.

The biaxially oriented polyester film of the present invention can be produced according to conventional methods for producing biaxially oriented films. For example, polyester containing a predetermined amount of carbon black particles and spherical particles is melt-cast to form an amorphous unstretched film, and then the unstretched film is stretched biaxially, heat-set, and if necessary Manufactured by relaxation heat treatment. At this time, the surface characteristics of the film vary depending on the particle size and content of the carbon black particles and spherical particles, and also depending on the stretching conditions, so they are appropriately selected from conventional stretching conditions. Furthermore, since the density, thermal shrinkage rate, etc. change depending on the temperature, magnification, speed, etc. during stretching and heat treatment, conditions are determined to satisfy these characteristics at the same time. For example, the stretching temperature is such that the first stage stretching temperature (e.g. longitudinal stretching temperature: T1) is (T
g-1o) to (7g+45)°C (however, Tg: glass transition temperature of polyester) to the second-stage stretching temperature (
For example, the lateral stretching temperature 2T2> is (T++15) to (T
It is recommended to select from the range ++40)'C. In addition, the stretching ratio in the longitudinal direction is selected from 2.5 times or more, especially from 3.0 times to 3.8 times, and the stretching ratio in the horizontal direction is selected from 3.5 times to 3.8 times.
It is preferable to select from the range of 4.5 times, particularly 4.0 to 4.5 times. If the stretching ratio in the lateral direction is lower than this range, the surface flatness will deteriorate and the electromagnetic conversion characteristics will deteriorate. Furthermore,
Heat setting temperature is 180-250℃, even 200-230℃
It is recommended to select from the range of ℃.

The biaxially oriented polyester film of the present invention not only has superior light-shielding properties achieved by containing carbon black compared to conventional films, but also has an extremely sharp particle size distribution in addition to the surface protrusions caused by carbon black. It has extremely uniform surface protrusions made of certain inert spherical particles, and has excellent runnability and wear resistance, as well as excellent head touch and edge damage. Therefore, when the biaxially oriented polyester film of the present invention is used as a base film of a magnetic recording medium, it has high electromagnetic conversion characteristics.
It is possible to manufacture a magnetic recording medium that has excellent runnability and wear resistance, and has light-shielding properties that allow end detection without any specific treatment.

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

Note that various physical property values and characteristics in the present invention were measured as follows.

(1) Particle size There are the following conditions for particle size measurement.

1) When calculating the average particle size, particle size ratio, etc. from the powder 2) When calculating the average particle size, particle size ratio, etc. of the particles in the film 1) When using the powder, place the powder on the electron microscope sample stage. The particles are scattered so that the individual particles do not overlap as much as possible, and a thin gold film deposited layer is formed on the surface using a gold sputtering device to a thickness of 200 to 300 mm.
Observe at 00x magnification, and measure the length of at least 100 particles (Dli
1, the minor axis (Dsl), and the area equivalent to a circle (Di).

Then, with the number average value expressed by these following formulas,
Particle length diameter (DI), breadth diameter (Ds), average particle diameter (r5
).

D1 = (Σ　Dli) 7 mouths.

Ds-(Σ　Dgil/rt.

D=(Σ Di)/n 2) In the case of particles in a film, a small piece of the sample film was fixed on a scanning electron microscope sample stage and sputtered using a JEOL sputtering device (JFC-110).
The surface of the film is subjected to ion etching using a Type 0 ion etching apparatus under the following conditions. The conditions were to place the sample in a Pel jar, increase the vacuum to about 10-'Torr, voltage 0.25 kV, and current 12.5
Ion etching is performed at mA for about 10 minutes. Furthermore, using the same equipment, gold sputtering was applied to the film surface, and the film was observed using a scanning electron microscope at a magnification of 10,000 to 30,000 times.
Find the major axis (Dli), minor axis (Dsil), and area circle equivalent diameter (Dl) of at least 100 particles.Hereinafter,
Proceed in the same manner as 1) above.

(2) Film surface roughness (Ra) This is the value defined in JIS-BO601 as the center line average roughness (Ra), and in the present invention, ). The measurement conditions are as follows.

(a) Radius of stylus tip = 2μm (b) Measurement pressure: 30mg (cl cutoff: 0.25mm) (d) Measurement length: 2.5mm (e) How to summarize the data - Repeatedly measure the sample 5 times, The largest value is 1
The average value of the remaining four data is rounded off to the fourth decimal place and displayed to the third decimal place.

(3) 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 172 inches was cut with a fixed rod (with a surface roughness of 0.3 μml and an angle θ-(152/180) yr radian). (152°)
and move (friction) at a speed of 200 cm/min. The outlet tension (Tz) when the tension controller is adjusted so that the inlet tension T1 is 35g
:g) is detected by an exit tension detector after the film has traveled 90 m, and the running friction coefficient μk is calculated using the following formula.

μk = (2j03 /θ) log (T2/T
I>=0.8681og (T2/35) (4) Abrasion resistance The abrasion resistance of the running surface of the film is evaluated using a 5-stage mini super calendar. The calendar is a 5-stage calendar with nylon rolls and steel rolls, and the processing temperature is 8.
0℃, linear pressure on the film is 200 Kg/cm,
The film was run at a speed of 50 m/min. After running the running film for a total length of 2000 m, the abrasion resistance of the base film was evaluated based on the dirt that adhered to the top roller of the calendar.

4-level judgment> ◎ No stains on the nylon roll ○ Almost no stains on the nylon roll × Nylon roll gets dirty ×× Nylon roll gets very dirty (5) Light transmittance Shimadzu multi-purpose self-recording spectrophotometer (MPS-5000)
1 to measure the light transmittance of the film at a wavelength of 900 nm.

(6) Young's modulus film is cut into 150 mm lengths, and stretched using an Instron type universal tensile tester at a tension speed of 10 mm/min, a chart speed of 500 mm, and 7 minutes with a chuck gap of 100 mm. Young's modulus was calculated from the tangent to the rising portion of the obtained load-elongation curve.

(7) Running performance of magnetic tape Set the magnetic tape in a home video tape recorder (helical scan), and repeat the running start and stop.
The vehicle was run for 00 hours, and the running condition was examined and the output was measured. During this run, if all of the following items were satisfied, the running performance was determined to be good, and if not, the running performance was determined to be poor.

■ The edges of the tape will not bend or become seaweed-like.

■ No tape squeal occurs while running.

■ The tape will not tear or break.

(8) Electromagnetic conversion characteristics of magnetic tape The video characteristics of a VH3 system VTR (manufactured by Victor Japan, product name: r
This is a value obtained by measuring the reproduction output of 4M4 (Z) using HR7300J).

The C/N ratio is the C/N ratio when a 4 MHz carrier signal is recorded and the level at 30M) IZ of the reproduced amplitude modulation signal is taken as the noise level.

Examples 1 to 3 and Comparative Example 1 Polyethylene terephthalate containing carbon black with different average particle sizes and spherical silica with an average particle size of 0.5 μm, a particle size ratio of 1.15, and a relative standard deviation of 0.25. Particle-containing polyethylene terephthalate is blended with the additive concentration shown in Table 1, and if necessary, polyethylene terephthalate that does not substantially contain a lubricant is blended in a V-type blender, and then thickened by a conventional method. Sa14
A biaxially oriented polyester film of μm was obtained. Table 1 shows the properties of this film.

On the other hand, acicular α-FeOOH containing 6% cobalt
α-Fe203 obtained by thermally decomposing the α-Fe203 was reduced with hydrogen to obtain ferromagnetic iron powder with an average needle length of 0.23 μm.

100 parts by weight of the above ferromagnetic iron powder (hereinafter simply referred to as "parts")
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
70 parts methyl ethyl ketone
35 parts cyclohexanone 100
After partial dispersion, it was further added and dispersed under high speed shear for 1 hour to prepare a magnetic coating solution.

The obtained coating solution was applied onto the polyethylene terephthalate films of Examples 1 to 3 and Comparative Example 1 to a dry film thickness of 3.5 mm.
It was coated to a thickness of 4 μm. Next, after orientation treatment in a DC magnetic field, it was dried at 100°C. After drying, it was calendered and slit into 172-inch pieces with a thickness of 1
An 8.0 μm video magnetic tape was obtained.

Table 1 shows the results of evaluating the magnetic tape thus obtained.

Add 1 part of fatty acid ester (amyl stearate) and knead for another 15 to 30 minutes. Furthermore, 7 parts of a 25% ethyl acetate solution of a triisocyanate compound was added to polyethylene terephthalate containing carbon black with an average particle size of 0.023 μm in Examples 4 to 7 and Comparative Example 2, and a particle size ratio, A biaxially oriented polyester film having a thickness of 14 μm was obtained in the same manner as in Example 1 using polyethylene terephthalate containing spherical silica particles with a relative standard deviation of 1.2° and 0.25°, respectively.

Examples 8-9 and Comparative Examples 3-4 Polyethylene terephthalate containing carbon black with an average particle size of 0.023 μm and spherical silica with an average particle size of 0.5 μm, a particle size ratio of 1.2, and a relative standard deviation of 0.25. A biaxially oriented polyethylene terephthalate film with a thickness of 14 μm was obtained in the same manner as in Example 1, except that the Young's modulus in the lateral direction was changed by changing the stretching conditions during film formation. . Table 3 shows the results of measuring each characteristic of this film.

Examples 10 to 11 Polyethylene terephthalate containing carbon black with an average particle size of 0.023 μm and spherical silicone with an average particle size of 0.5 μm, a particle size ratio of 1.2, and a relative standard deviation of 0.25.
Polyethylene terephthalate containing spherical cross-linked polystyrene was prepared in the same manner as in Example 8 to a thickness of 14 μm.
A biaxially oriented polyethylene terephthalate film was obtained. Table 4 shows the results of measuring each characteristic of this film.

Comparative Example 5 A biaxially oriented polyester film with a thickness of 14 μm was obtained in the same manner as in Example 1 using only polyethylene terephthalate containing carbon black with an average particle size of 0.3 μm. Table 4 shows the results of measuring each characteristic of this film.

As shown in the Examples and Comparative Examples above, the film of the present invention is a biaxially oriented polyester having low light transmittance, flatness, excellent running properties, excellent abrasion resistance, and excellent electromagnetic conversion properties. It's a film.

Claims (1)

[Claims] 1. 0.1 to 5% by weight of carbon black with an average particle size of 0.01 to 0.6 μm, and an average particle size of 0.1 to 1
．． 2μm and the particle size ratio defined by major axis / minor axis is 1
．． The film is made of polyester containing 0.01 to 3% by weight of inert spherical particles having a molecular weight of 0 to 1.4%, the thickness of the film is 4 to 15 μm, and the light transmittance of the film at a wavelength of 900 nm is 70% or less. A biaxially oriented polyester film, characterized in that the transverse Young's modulus of the film is 630 Kg/mm^2 or more, and the film surface roughness (Ra) is 0.025 μm or less. 2. The biaxially oriented polyester film according to claim 1, wherein the inert spherical particles are silica particles. 3. The biaxially oriented polyester film according to claim 1, wherein the inert spherical particles are silicone particles. 4. The biaxially oriented polyester film according to claim 1, wherein the inert spherical particles are crosslinked polystyrene particles.