JPH01312726A - Polyester film for magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve flat smoothness and light shieldability by using a specific polyester film contg. carbon black for a magnetic material consisting of barium ferrite. CONSTITUTION:The barium ferrite which simultaneously satisfies the equations I-III and contains 0.05-2wt.% carbon black as the magnetic material is used for the polyester film for the magnetic recording medium. The equation I denotes light transmittance at 900nm wavelength converted to 9mum thickness. In the equation II, Ra denotes the center line average height. In the equation III, N<0.81mum> denotes the number of surface projections of >=0.81mum. The light shieldability is insufficient if the amt. of the carbon black to be added into the film is smaller than 0.05wt.% and the flatness is poor if the amt. exceeds 2wt.%. The film having the excellent light shieldability and surface flatness is obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a polyester film for magnetic recording media using barium ferrite as a magnetic material. Specifically, the present invention relates to a polyester film suitable for high-density magnetic recording media that has excellent light-shielding properties and surface flatness.

[Prior art and problems to be solved by the invention] Polyester film has excellent heat resistance, mechanical properties, and chemical resistance, so it is suitable for magnetic recording for magnetic tapes such as audio and video, and for floppies. Used as a base film for media.

In recent years, with the dramatic increase in recording density, perpendicular magnetic recording methods suitable for high-density recording are being adopted. Barium ferrite is attracting attention as a magnetic material for perpendicular magnetic recording systems because of its high-density recording properties as well as its excellent stability and productivity. For example, barium ferrite is being considered for use as a magnetic material for digital signal recording media such as DAT (digital audio tape).

However, magnetic recording media using barium ferrite as a magnetic material have a drawback in that they have lower light-shielding properties than those using r-ferrite, metal, or the like as a magnetic material.

Normally, most floppy disks and magnetic tapes optically sense the index hole or leading tape and mechanically position the disk or tape, so magnetic recording media that use barium ferrite as the magnetic material have light-shielding properties. To this end, various efforts have been made.

For example, - there is a method of applying a bank coat to the diamagnetic layer surface and mixing carbon black, pigment, etc. into the back coat layer to improve light shielding properties.

However, especially when using magnetic materials with low light-shielding properties such as barium ferrite, it is necessary to increase the light-shielding properties even further than before, so the thickness of the back coat layer must be increased or the concentration of the light shielding agent contained in the back coat layer must be increased. However, this results in a considerable increase in cost, and there is a problem with the dispersibility of carbon black, leading to a decline in quality.

[Means for solving problems]

The present inventors have worked hard to develop a film that maintains smooth smoothness suitable for magnetic recording media using barium ferrite as a magnetic material, reduces coarse protrusions, and has light-shielding properties and durability. As a result of investigation, it was discovered that a certain polyester film containing carbon black was most suitable for this purpose, and the present invention was completed.

That is, the gist of the present invention is to satisfy the following formulas (1) to (iii) at the same time, and to set carbon black to 0, Oj -2
The present invention relates to a polyester film for a magnetic recording medium, which uses barium ferrite as a magnetic material in an amount by weight of barium ferrite.

00nm T ≦0% ・・・・・・・・・・・・・・・・・・
...(i) P# Ra≦0.021μm ......
・(11) NO, II pg≦zaO pieces/2jcd ・・
......-(iii) (where T::n" is the thickness μm conversion value of the light transmittance at 00 nm wavelength, Ra is the center line average roughness, NO, 1/am is 0.lr/μm
Represents the number of surface protrusions with a height of or above. ) Hereinafter, the present invention will be explained in detail.

The polyester referred to in the present invention refers to polyesters containing aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, and naphthalene-2,6-dicarboxylic acid, or diols thereof such as nistert, ethylene glycol, diethylene glycol, tetramethylene glycol, and neopentyl glycol. It is a crystalline aromatic polyester that can be obtained by condensation. Typical examples of such polymers include polyethylene terephthalate, polyethylene-λ, 6-naphthalate, polytetramethylene terephthalate, and polytetramethylene-2,6-67 tallate, which are mainly dibasic acids. Not only polyesters in which a component and a glycol component are combined, but also copolyesters in which 10 moles or more of the repeating units consist of the polyester component and 20 moles or less of the repeating units consist of other components, or these polyesters with other polymers. It may also be a mixed polyester in which . In particular, it is also preferable to copolymerize a polyalkylene glycol such as polyethylene glycol or polytetramethylene glycol as a glycol component in order to improve the adhesion with the magnetic layer.

When adding or mixing other polymers to polyester, it is necessary to do so within a range that does not essentially change the properties of the polyester.
Polycarbonate, other polymers, etc. may be added in a proportion of less than 11% by weight.

The carbon black used in the present invention is preferably lamp black, thermal black, furnace black, acetylene black, etc., and its particle size is not particularly limited, but it should have a particle size of 2 μm or less, preferably 1 μm or less. is preferred.

In addition, in order to improve the light-shielding property, not only carbon blank may be used, but also light-shielding agents other than carbon plaque, such as dyes, organic pigments, and inorganic pigments, may be used in combination.
They must not affect the film properties as a magnetic recording medium. Naturally, in order to improve the dispersibility of these light-shielding agents, it is preferable to use a dispersant in combination.

Further, inert fine particles other than a light shielding agent such as carbon black may be added to the polyester as necessary.

The amount of inert fine particles other than light shielding agents such as carbon black added is not particularly limited, but is usually o, o o r-2% by weight.
It is preferable to contain. Further, the average particle diameter of the inert fine particles is preferably in the range of o, o ot -s, o μm. Such inert fine particles are not particularly limited, but include, for example, high melting point organic compounds that are insoluble during melt film formation of polyester resin, crosslinked polymers, and metal compounds such as alkali metal compounds and alkaline earth metal compounds used during polyester synthesis. So-called internal precipitate particles, which are formed inside the polymer during polyester production by catalysts, and inert external additive particles, such as MgO, ZnO1MgCO
3. CaCO3, CaSO4, BaSO4, At203
, SiOz, TiO2, SiC%LiF, talc, clay minerals such as kaolin, celite, mica, etc., Ca, B
Examples include inert externally added particles such as metal terephthalate salts such as a, Zn%Mn. Further, inert organic compounds such as metal soap, starch, and carboxymethyl cellulose can also be used as the inert particulate compound.

Furthermore, in addition to these particles, dyes, pigments,
Compounds such as colorants, stabilizers, antistatic agents, conductive substances, antioxidants, and antifoaming agents may be added.

Inert fine particles containing a light shielding agent such as Carbo/Black may be added at any time during the polyester manufacturing process or before melt extruding the polyester into a sheet.

The polyester film of the present invention contains 0.0! -2% by weight, and the content is preferably from o,i to 0.7% by weight. The amount of carbon black added in the film is 0.0! If the amount is less than % by weight, coarse protrusions will be formed on the surface for the purpose of the present invention, making it impossible to obtain a film with excellent flatness.

The light transmittance of the polyester film of the present invention at a wavelength of OOnm is a μm conversion value (T5'0 (7 nm)) of 2μ
Sea bream J'l must be 17% or less, preferably 70 or less, more preferably 6! % or less. If the thickness is greater than go% in terms of thickness of 7 μm, the light-shielding property will be insufficient and it will be inappropriate. In addition, for a film whose thickness is less than 00 nm than μm, T is calculated by 2 μm using the following formula (2).

X: Film thickness (μm) Tz: Light transmittance (%) at film thickness 2 μm 00
11m.

T, light transmittance (%) in film thickness μm Average surface roughness (Ra) of the polyester film of the present invention
must be 0.023 μm or less, preferably 0.
．． 072 μm or less, more preferably θ, OO μm or less. If the Ra of the film is larger than 0.023 μm, it is not suitable for use as a magnetic recording medium because good electromagnetic conversion characteristics cannot be obtained.

Further, the film of the present invention has a number of surface protrusions with a height of 0.1/μrn or more <NO,I//”) of 10/2
j Cj or less, preferably 5
0 pieces 723- or less. NO, IIpm is to pieces/2
! If the number is larger than -, it is not suitable for use as a magnetic recording medium because the number of dropouts will be too large.

Further, in the present invention, the longitudinal Fs value of the polyester film used for the magnetic tape coated with barium ferrite as the magnetic material, particularly the DAT tape, is preferably 1rH7- or more, more preferably /7 to 9/- or more. The reason for this is that as the base film becomes thinner, its mechanical strength becomes insufficient, and when barium ferrite is used as a magnetic material, the magnetic material obtained is greater than when γ-ferrite or metal is used as a magnetic material. This is because the strength of the recording medium decreases.

That is, the value of F in the vertical direction is /! When barium ferrite is used as a magnetic material in a base film smaller than rkg/- to form a magnetic recording medium, the strength is low and the durability may be poor.

Next, the film forming method of the present invention will be specifically explained, but the present invention is not limited to this example as long as the above requirements are satisfied. The polyester resin containing carbon black and optionally other light-shielding agents and inert fine particles is dried by conventional means and filtered using an extruder at a temperature usually in the range of 260 to 320°C/through a filter of 300 mesh or more. The mixture is extruded into a sheet while cooling to a temperature below tO°C to form a substantially amorphous sheet. At this time, it is preferable to use a conventional electrostatic application cooling method. The sheet-like material obtained in this manner is stretched in the longitudinal and transverse directions so that the area magnification is at least twice or more to obtain a biaxially oriented film, and if necessary, the film is further stretched in the longitudinal and/or transverse directions. After re-stretching, the film is iro~2~0
A film can be easily formed by heat treatment at a temperature in the range of °C.

In addition, in the process, zero in the width direction and lengthwise direction at the highest temperature zone of the heat treatment and/or the cooling seam at the heat treatment outlet. / -20% may be relaxed. Further, two-stage heat treatment may be performed.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof. Note that the characteristics of the film and magnetic recording medium were evaluated by the following method.

(1) Light transmittance (T; 0 ('nln)) The light transmittance at a near-infrared wavelength of 0 nm was measured using a self-recording spectrophotometer (3ψθ type) manufactured by Hitachi, Ltd.

(2) Center line average surface roughness (Ra) It was determined as follows using a surface roughness measuring instrument (SE-JFK) manufactured by Koita Research Institute. The tip radius of the stylus was 2 μm, and the load was 30 μm. 2. A standard length from the film cross-sectional curve in the direction of its center line. jmig) is extracted, and the center line of this extracted portion is the X axis, and the vertical magnification direction is the Y axis, and the roughness curve ν = fCZ) is expressed as the value given by the following formula in μm. . However, the cutoff value is l0
It is μm. Ra is 5 points in the vertical direction and 5 points in the horizontal direction, a total of 1
The average value of 0 points was calculated.

'/L/Ll f (x) l dz (3) Number of coarse protrusions <N', I/-) Aluminum was deposited on the film surface and measured using a two-beam interference microscope. When the measurement wavelength is 0 and j≠μm, the number of interference fringes of third or higher order is converted to per 2j-, and is 0. The number of coarse protrusions with a height of 7 μm or more was taken as the number.

(4) Fs value A sample film with a width of 1/2 inches and a length of jOtn between chucks was pulled at jOmx/1nix at 20°C and 6 degrees RH using a Tensilon (UTM-III) manufactured by Toyo Bold Co., Ltd., and the load at j% elongation was divided by the initial cross-sectional area and expressed in kg/-.

(5) Optical signal detection characteristics The magnetic tape obtained by coating, drying and slitting a magnetic paint containing barium ferrite was applied to an actual machine and used continuously for a long period of time to measure the frequency of false detections such as leading chives. O1Δ in order of good characteristics with few false positives.

It was judged as ×.

(6) Electromagnetic conversion characteristics The magnetic tape was applied to an actual machine and the initial head output was measured. A tape equivalent to the reference tape was marked O, a tape slightly inferior was marked Δ, and a tape clearly inferior was marked ×.

The dropout magnetic tape was placed on a dropout counter and the number of dropouts was measured. The samples were evaluated as ○, Δ, and × in order of good characteristics with fewer dropouts.

Example/λ (Method for manufacturing polyester chips) 100 parts of dimethyl terephthalate, 70 parts of ethylene glycol, and 0.07 parts of calcium acetate hydrate were placed in a reactor and heated to raise the temperature, and methanol was distilled off to perform a transesterification reaction. It took about 1.5 hours from the start of the reaction to reach 230°C, and the transesterification reaction was substantially completed.

Next, phosphoric acid o, o y part and antimony trioxide 0.03
1 part was added, and polymerization was carried out according to a conventional method.

That is, the reaction temperature was gradually raised to 210°C,
Meanwhile, the pressure was gradually reduced to 03 mmHf.

After q hours, the reaction was completed and chipped according to a conventional method to obtain polyester (A) having an intrinsic viscosity of 0.6 ta.

Obtained polyester (A) and average particle size/! Carbon black particles of 100 nm were kneaded using a twin-screw kneader.
After passing through a filter equivalent to 0 mesh, it is made into chips and the carbon black concentration is i.

A masterbatch with wt% and intrinsic viscosity of 0.1.0 was obtained.

This was designated as polyester (B).

In addition, 700 parts of dimethyl terephthalate, 60 parts of ethylene glycol, and 0.2 parts of magnesium acetate tetrahydrate were placed in a reactor, and while the temperature was raised, methanol was distilled off to perform a transesterification reaction, which took μ hours from the start of the reaction. The transesterification reaction was substantially completed. Next, 0.3% by weight of silica particles having an average particle diameter of j Onm previously dispersed in ethylene glycol, classified and filtered was added, and then 0.0 part of ethylene acid phosphate and 0.033 part of antimony trioxide were added. 1, and polycondensation was carried out to obtain a polyester (C) having an intrinsic viscosity of 0.12.

(Film forming method) After blending the above polyesters (A), (B), and (C) with the composition shown in Table 1, drying by a conventional method,
It was extruded and rapidly cooled to form an amorphous sheet.

In addition, a filter equivalent to 3000 mesh was used during extrusion. The amorphous sheet was heated in the longitudinal direction at rt°C at 3.1
Stretched twice, further stretched 6 times in the machine direction at 76°C, then stretched 3.7 times in the transverse direction at 110°C, and then stretched in the machine direction 1≠
After stretching at 0.degree. C./1 times, heat setting was performed at 210.degree. C. to obtain a biaxially oriented polyester film having a thickness of .mu.m.

A magnetic layer having a thickness of II 11 m was formed on the obtained film using barium ferrite as a magnetic material. In addition, a urethane-based resin binder containing 20% by weight of carbon black was used on the diamagnetic layer side, and the thickness was 0.05 μm.
By providing a puncture coat layer of , the thickness / j,!
A magnetic recording medium of rμm was obtained. Table 7 shows the properties of the obtained film and magnetic recording medium.

Comparative Example /, 2 After blending the polyesters (A), (B) and (C) of Example / with the composition shown in Table 1, film formation and processing were carried out in exactly the same manner as in Example /, and a base film was formed. Thickness is 7μ
A magnetic recording medium with a thickness of m/3.6 μm was obtained. Table 7 shows the characteristics of the obtained base film and magnetic recording medium.
Shown below.

Example 3 After blending the polyesters (A), (B) and (c) of Example 1 with the composition shown in Table 7, an amorphous sheet was obtained in exactly the same manner as in Example 1. The amorphous sheet was stretched 3.1 times in the longitudinal direction at rr°C, and further stretched in the same direction at 76°C/2 times.
The film was stretched twice, then stretched 3.7 times in the transverse direction at IIO°C, and then heat-set at 210°C to obtain a biaxially oriented film having a thickness of μm. The obtained film was processed in exactly the same manner as in Example/1 to obtain a magnetic recording medium. Table 7 shows the characteristics of the base film and tape.

Comparative Example 3 After blending the polyesters (A), (B) and (C) of Example 1 with the composition shown in Table 7, drying was carried out by a conventional method.
It was extruded at 213° C. using a filter equivalent to 000 mesh, and rapidly cooled to form an amorphous sheet. The amorphous sheet was formed and processed in exactly the same manner as in Example to obtain a magnetic recording medium. Table 7 shows the properties of the base film and tape obtained.

〔Effect of the invention〕

The film of the present invention has excellent light-shielding properties and surface flatness, and is useful as a base film for magnetic recording media using barium ferrite as a magnetic material.

Sender: Diafoil Co., Ltd. Representative for Hase - Others/names

Claims (1)

[Claims] (1) A polyester film for magnetic recording media using barium ferrite as a magnetic material, which simultaneously satisfies the following formulas (i) to (iii) and contains 0.05 to 2% by weight of carbon black. T^9^0^0^n^m_9_μ_m≦80%...
・(i) Ra≦0.025μm...(ii) N^0^. ^8^1^μ^m≦80 pieces/25cm^2・
・・・・・・・・・(iii) (In the formula, T^9^0^0^n^m_9_μ_m is the wavelength 9
The light transmittance at a thickness of 00 nm is converted to a thickness of 9 μm, Ra is the center line average roughness, and N^0^. ^8^1^μ^m is 0.81
Represents the number of surface projections with a height of μm or more. )