JPH0374692B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a biaxially oriented polyester film for magnetic recording media, and more particularly to a biaxially oriented polyester film for magnetic recording media that provides excellent electromagnetic conversion characteristics and has excellent light shielding properties. BACKGROUND OF THE INVENTION Polyester films are used in various applications such as magnetic tape applications and electrical applications. In recent years, in magnetic tape applications, especially video tape applications,
Suitable for high-density recording, a flat film surface is required to improve electromagnetic conversion characteristics, and a low coefficient of friction is required to improve tape runnability, abrasion resistance, and durability on decks. ing. At the same time, the ferromagnetic powder used in these magnetic tapes is becoming increasingly finer. When the magnetic powder is pulverized, light with a long wavelength is less likely to be scattered by the magnetic powder, resulting in higher light transmittance.
For this reason, in a magnetic recording medium in which termination is detected using the difference in light transmittance between the nonmagnetic support and the magnetic recording layer, it is necessary to lower the light transmittance. Conventionally, colored inorganic fine powders such as antistatic agents and abrasives were included in the magnetic recording layer to reduce light transmittance, but this method had limitations in terms of electromagnetic conversion characteristics, head wear, etc. It was hot. Therefore, it has been difficult to simultaneously maintain the contradictory electromagnetic conversion characteristics and light transmittance of a videotape at a suitable level by simply changing the structure of the magnetic layer. Therefore, a method can be considered in which the disadvantage of increased light transmittance of the magnetic layer with improved electromagnetic conversion characteristics is compensated for by increasing the light-shielding properties of the base film.
The present inventor considered a method of adding non-magnetic black inorganic fine powder such as carbon black and other inert powder to the base film as one of the methods, but with this method, the magnetic layer does not work as designed. Although it is possible to fill the base film with finely divided ferromagnetic material to a high degree, it is necessary to add a considerable amount of non-magnetic black inorganic fine powder such as carbon black to the base film that serves as the support to lower the light transmittance. As a result, the surface roughness (Ra) of the base film becomes high and it is difficult to obtain a flat surface.Therefore, even with this method, it is necessary to improve the electromagnetic conversion characteristics of the videotape and reduce the light transmittance. It has become clear that it is difficult to achieve both. OBJECTS OF THE INVENTION It is an object of the present invention to provide a biaxially oriented polyester film that can compensate for these drawbacks and is extremely useful for producing magnetic recording media that have good light-shielding properties and excellent electromagnetic conversion characteristics. Structure/Effects of the Invention According to the present invention, inert particles with an average particle size of 0.01 to 2.0 μm are contained in polyester.
A biaxially oriented polyester film containing dispersed 3% by weight and a light absorbent whose light absorption rate is maximum in the wavelength range of 700 to 1100 nm, the film having a surface roughness (Ra) of 0.025 μm or less. This is achieved by using a polyester film that has a light transmittance of 50% or less at a wavelength of 900 nm. The polyester used in the present invention refers to an aromatic dicarboxylic acid component such as terephthalic acid, isophthalic acid, naphthalene-2,6-dicarboxylic acid, etc. and a glycol component such as ethylene glycol, diethylene glycol, tetramethylene glycol, neopentylene glycol, etc. It is a polymer that can be obtained by polycondensing. The polyester can be obtained by direct polycondensation of aromatic dicarboxylic acid and glycol, or by polycondensation after transesterification of aromatic dicarboxylic acid dialkyl ester and glycol, or by polycondensation of aromatic dicarboxylic acid dialkyl ester and glycol. It can also be obtained by methods such as polycondensation. Typical examples of such polyesters include polyethylene terephthalate and polyethylene-2,6-naphthalene dicarboxylate. The polyester may be a non-copolymerized homopolymer and may have up to 15 mole percent of the dicarboxylic acid component being a non-aromatic dicarboxylic acid component and/or a diol component.
It may be a copolymerized polyester in which 15 mol% or less is a diol component other than aliphatic glycol. Alternatively, a polymer friend may be used in which polyester accounts for 85% by weight or more (preferably 90% by weight or more) and other polymers account for 15% by weight or less (preferably 10% by weight or less). Examples of other polymers that can be blended include polyamides, polyolefins, and other types of polyesters (including polycarbonate). Further, the polyester may contain additives such as stabilizers, colorants, and antioxidants, if necessary. In the present invention, 0.03 to 3% by weight of inert particles with an average particle size of 0.01 to 2.0 μm are added to the polyester.
A light absorbent having a maximum light absorption rate in the wavelength range of 700 to 1100 nm is dispersed and contained. Inert particles are inert to polyester and remain solid during melt molding of polyester, and include, for example, metal salts of organic acids, inorganic substances, and the like. Preferred inert particles include silicon dioxide (including hydrates, diatomaceous earth, silica sand, quartz, etc.);
Alumina, silicates containing 30% by weight or more of _SiO2 (e.g. amorphous clay minerals, aluminosilicate compounds (including calcined products and hydrates), hot asbestos, zircon, fly ash, etc.), Mg, Zn ,
Zr and Ti oxides, Ca and Ba sulfates,
Li, Na and Ca phosphates (including monohydrogen salts and dihydrogen salts), Li, Na and K benzoates, Ca,
Ba, Zn and Mn terephthalates, Mg, Ca,
Titanates of Ba, Zn, Cd, Pd, Sr, Mn, Fe, Co and Ni, chromates of Ba and Pb, carbonates of Ca and Mg, glass (e.g. glass powder, glass beads, etc.), MgCO ₃ , fluorspar, and
ZnS is exemplified. Particularly preferably used are anhydrous silicic acid, hydrated silicic acid, aluminum oxide, aluminum silicate (including calcined products, hydrates, etc.), monolithium phosphate, trilithium phosphate, sodium phosphate, calcium phosphate, barium sulfate, Examples include titanium oxide, lithium benzoate, double salts (including hydrates) of these compounds, glass powder, clay (including kaolin, pentonite, clay, etc.), talc, diatomaceous earth, and the like. These are not limited to one type,
Two or more types can be used with respect to each average particle size and addition amount. The average particle size of the inert particles is 0.01 to 2.0 μm,
Its dispersion content is 0.03-3% by weight. If the particle size is too large or the content is too large, the film surface will become too rough, which is not preferable. On the other hand, if the particle size is too small or the content is too low, the film properties, especially running properties, will deteriorate, which is not preferable. In the present invention, the light absorbent used in combination with the above-mentioned inert particles is not particularly limited as long as it is an organic compound that exhibits maximum light absorption in the wavelength range of 700 to 1100 nm.
Normally, the light absorber melts under polyester molding conditions or is extremely small in shape compared to the above-mentioned inert particles, so there is no concern that the amount added will affect the surface roughness (Ra) of the base film. do not have. Therefore, the surface roughness of the polyester film can be freely adjusted by adjusting the type, average particle size, and amount of the inert particles added depending on the purpose. There are many light absorbers commercially available, and these are usually used in optical lenses, sunglasses,
It is used in optical applications such as welding glasses; agricultural applications such as plant growth suppression and heat ray shielding, and the light absorbing agent in the present invention can be selected from these. Examples of such light absorbers include IRG-003 manufactured by Nippon Kayaku Co., Ltd., and bis(cis-1,2-diphenylethylene-1,2-
dithiolate) palladium, bis(cis-1,2
-diphenylethylene-1,2-dithiolate)
Platinum; bis(1-methylcaprate-2-naphthorate)nickel()tetrabutylammonium, bis(1-thio-2-phenolate)nickeltetrabutylammonium, bis(1-thio-
Examples include nickel complexes such as nickel tetrabutylammonium (2-naphthlate) and infrared absorbers equivalent to these. These are 1
A species or two or more species can be used. Also 2
Wavelength 700-1100nm with a combination of more than one species
It is also possible to use materials that exhibit excellent absorption characteristics. The selection criteria for the light absorber is that the maximum sensitivity wavelength is approximately 900 nm, and this maximum sensitivity is further increased to 100 nm.
When expressed as %, the wavelength range showing sensitivity of 50% or more is 700.
~1100nm should be adopted. Inclusion of the inert particles and the light absorbing agent can be carried out by a method conventionally known as a method of dispersing and containing fine particles. For example, inert particles and a light absorber can be dispersed and contained in the reaction system of polyester production, for example, by adding them before, during, or after the reaction. The polyester film of the present invention can be obtained by melt-extruding a polyester containing a predetermined amount of inert particles and a light absorbing agent uniformly dispersed therein in a conventional manner, followed by biaxial stretching and heat setting. Conventionally known methods and conditions for stretching and heat setting can be used. For example, the stretching can be carried out by a sequential or simultaneous biaxial stretching method, a method of longitudinal multi-stage stretching followed by transverse stretching, a method of longitudinal stretching followed by transverse stretching, and then longitudinal stretching again, or a combination thereof. The thickness of the film is preferably 3 to 100 .mu.m, more preferably 4 to 75 .mu.m, most preferably 6 to 25 .mu.m. This biaxially oriented polyester film needs to have a surface roughness (Ra) of 0.025 μm or less, preferably 0.004 to 0.023 μm. In a magnetic tape, it is desirable that the surface of the magnetic layer be flat in order to improve the electromagnetic conversion characteristics targeted by the present invention, and for this purpose, the surface of the biaxially oriented polyester film that is the support must be flat. is preferred. On the other hand, running durability is one of the characteristics required for magnetic tape, but surface roughness (Ra)
If it becomes too flat, this running durability will be poor, which is not preferable. In general, in video tapes, if the surface roughness (Ra) of the base film is less than 0.008 μm, the running durability will be poor, and the base film may be damaged and its abrasions may become a major cause of dropouts in actual equipment. There is. Therefore, from the viewpoint of normal running durability, the surface roughness (Ra) of the base film is preferably 0.008 μm or more.
In applications where a lower surface roughness (Ra) than this is required from the viewpoint of electromagnetic characteristics, it is preferable to take measures such as providing a back coat layer on the running surface in order to enhance running durability. It is not preferable for the surface roughness (Ra) to exceed 0.025 μm from the viewpoint of electromagnetic conversion characteristics. Furthermore, when dispersing inert particles and other additives into polyester,
If these additives are not uniformly dispersed and cause some agglomeration, high protrusions may occur on the film surface. This type of protrusion is formed from the film surface.
If the height exceeds 0.87 μm, abnormal protrusions will remain on the surface of the magnetic layer even after it is coated, and when molded into a video tape, the head contact of the actual device will be abnormal and the recording of the signal will be lost. However, the presence of this type of high protrusion is undesirable because it causes so-called dropout. The polyester film of the present invention has excellent flatness and light transmittance at a wavelength of 900 nm.
It has a light blocking property of 50% or less, preferably 30% or less, and more preferably 15% or less. Therefore, the magnetic recording medium made of the polyester film of the present invention has excellent light shielding properties and electromagnetic conversion properties, is also excellent in resistance to running abrasion, and has optical properties that allow endpoint detection without special treatment. This magnetic recording medium is particularly useful as a magnetic recording medium for video. EXAMPLES The present invention will be described in detail with reference to Examples below. Note that each characteristic value was measured according to the following method. 1 Average particle size Stokes equation ν=1/18(ρ _p −ρ _p )g/ηD ² _p [where, ρ _p : Density of sample particle ρ _p : Density of medium η : Viscosity of medium g : Gravitational acceleration ν: sedimentation velocity of sample particles D _p average diameter of sample particles] It is expressed by the value of the particle diameter D _p calculated by measuring the sedimentation velocity of the particles. 2 Film surface roughness (Ra) Measured according to JIS B 0601. Tokyo Precision Co., Ltd.
Stylus type surface roughness meter (SURFCOM 3B) manufactured by Co., Ltd.
A chart (film surface roughness curve) was drawn using a needle with a radius of 2μ and a load of 0.07g. A portion of measurement length L is extracted from the film surface roughness curve in the direction of its center line, the center line of this extracted portion is the X axis, and the direction of vertical magnification is Y.
When the roughness curve is expressed as Y=f(x) as the axis, the value (Ra: μm) given by the following equation is defined as the film surface roughness. Ra=1/L∫ ^L _p |f(x)|dx In the present invention, eight measurements are performed using a reference length of 0.25 nm, and Ra is expressed as the average value of five measurements, excluding three from the largest values. 3. Number of surface projections Aluminum is uniformly vacuum-deposited on the surface of the film to a thickness of 400 to 500 mm or less, and collodion is applied to the opposite non-vapor-deposited surface (film surface) and attached, followed by drying. Tl monochromatic light multiple interference reflection microscope (for example, manufactured by Carl Zeiss JENA)
An arbitrary 100 cm ² of the aluminum-deposited surface was observed at a magnification of 100 times. Three or more rings (0.87 μ
Count the number of protrusions H ₃ (pieces) having interference fringes of m or more. 4 Scratch Resistance Measured as follows using the apparatus shown in Figure 1. In FIG. 1, 1 is an unwinding reel, 2 is a tension controller, 3, 5, 6, 8, 9, and 11
is a free roller, 4 is a tension detector (inlet), 7 is a fixed rod made of stainless steel SUS304 (outer diameter 5 mmφ), 10 is a tension detector (outlet), 12 is a guide roller, and 13 is a take-up reel. . In an environment with a temperature of 20℃ and a humidity of 60%, cut the film into 1/2 inch width with a fixing rod (7) (with surface roughness)
Scratches on the surface of a 1/2 inch wide base film after making contact with a 0.3 μm film at an angle θ = 152/180π radians (152°) and running it for 10 m at a film speed of 20 cm/sec, and repeating this 50 times. Judgment is made in the following five stages based on the thickness, depth, and number of <5-level judgment> ◎ No scratches were observed on the 1/2 inch wide base film. ○ There are almost no scratches on the 1/2 inch wide base film. △ Scratches are observed on the 1/2 inch wide base film (several scratches). × Several thick scratches can be seen on the 1/2 inch wide base film. ×× Many thick and deep scratches can be seen all over the 1/2 inch wide base film. 5 Signal troubles Polyester film is used as a base, magnetic tape is made using conventional methods, and signals and detection troubles occur using a commercially available VHS video recorder (○).
Evaluate with no (x). 6 Light transmittance Using a self-recording spectrophotometer made by Hitachi (model U-3400), insert a mesh on the reference side and adjust the full scale, measure the wavelength range from 600 nm to 1500 nm, and measure at the wavelength of 900 nm. Evaluate the light transmittance of Examples 1 to 6 Dimethyl terephthalate and ethylene glycol are used as raw materials, manganese acetate is used as a transesterification catalyst,
Polyethylene terephthalate was produced by a conventional method using antimony trioxide as a polymerization catalyst and phosphorous acid as a stabilizer. At that time, as shown in Table 1, calcium carbonate, titanium dioxide, silica, and their two components were added as inert particles in ethylene glycol, with the average particle size and amount added as light absorbers made by Nippon Kayaku Co., Ltd. IRG-003 manufactured by ) was incorporated into the polymer by dispersing it in the amounts shown in Table 1. The obtained polymer was melt-extruded to form a film using a conventional method, and sequentially biaxially stretched at a stretching temperature of 90°C, a longitudinal magnification of 3.5 times, and a transverse magnification of 3.7 times, and heat-set at 220°C to determine the film thickness.
A 14μ biaxially oriented film was obtained. Table 1 shows the measurement results of each characteristic using these biaxially oriented films as the base film. In each example, results of a good level were obtained and were sufficiently satisfactory as base films.

[Table] * Overall evaluation ◎...particularly good, ○...good, △...slightly poor, ×...poor Comparative Examples 1 to 6 In the production of polyethylene terephthalate, calcium carbonate, titanium dioxide, titanium dioxide, The average particle size and amount of inert particles such as silica and their two components are measured using carbon black (the average particle size and amount of addition are shown in the table below).
A biaxially oriented film having a thickness of 14 μm was obtained in the same manner as in Examples 1 to 6, except that the film was dispersed with the following materials (as shown in Section 2). The results of measuring each characteristic using these films as base films are as shown in Table 2, and all of them had unsatisfactory performance as base films.

[Table] * Overall evaluation ◎...particularly good, ○...good, △...slightly poor, ×...poor

[Brief explanation of drawings]

FIG. 1 shows the film flow of the apparatus used to measure the scratch resistance of the film.

Claims (1)

[Claims] 1. 0.03 to 3% by weight of inert particles with an average particle size of 0.01 to 2.0 μm in polyester and a light absorption rate of 700 to 700 μm.
A biaxially oriented polyester film containing a dispersed light absorbent having a maximum wavelength between 1100 nm and a surface roughness (Ra) of 0.025 μm or less and a light transmittance of 50 nm at a wavelength of 900 nm. % or less. 2. The polyester film according to claim 1, characterized in that the film surface does not contain any protrusions with a height of 0.87 μm or more.