JP3545508B2 - Biaxially oriented polyester film for magnetic recording media - Google Patents

Description

【００５３】
【表２】

【００５４】
【発明の効果】
本発明によれば、特に磁気テープ用途に有用な表面性を有し、かつ磁気テープ加工工程の高速化に充分対応しうる滑り性、耐スクラッチ性、スリット性、およびテープとしたときの電磁変換特性の良好な積層ポリエステルフイルムを提供することができる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a biaxially oriented polyester film for a magnetic recording medium, and more particularly to a biaxially oriented polyester film containing at least inert particles and spinel-type oxide MgAl ₂ O ₄ particles. The present invention relates to a biaxially oriented polyester film for a magnetic recording medium, which is excellent in scratch resistance, slitting properties and electromagnetic conversion characteristics when formed into a tape while ensuring abrasion.
[0002]
[Prior art]
BACKGROUND ART Biaxially oriented polyester films represented by biaxially oriented polyethylene terephthalate films are widely used as base films for magnetic tapes because of their excellent physical and chemical properties.
[0003]
In this film, scratch resistance, slitting property, slipperiness, and abrasion resistance are major factors that determine the workability of the film manufacturing process and the working process in each application, and the quality of the product. .
[0004]
Generally, in order to improve the slipperiness of a film, a method of reducing the contact area with a guide roll or the like by providing fine irregularities on the film surface is adopted.
[0005]
Conventionally, as a method for imparting fine irregularities to the film surface, a method of adding inorganic fine particles such as silicon dioxide, titanium dioxide, calcium carbonate, talc, clay, and calcined kaolin to polyester as a film substrate (for example, Japanese Patent Application Laid-Open No. No. 57562) or a method of precipitating fine particles containing calcium, lithium or phosphorus in a polymerization system for producing polyester (Japanese Patent Publication No. 52-32914). These fine particles form fine projections on the film surface when formed into a film, and the projections improve the slipperiness of the film.
[0006]
However, in a polyester film formed by the method of adding the inorganic fine particles, peeling usually occurs at the boundary between the fine particles and the polyester by biaxial stretching, and voids are formed around the fine particles. The voids are larger as the fine particles are larger and the stretching area ratio is larger and the stretching is performed at a lower temperature.
[0007]
The larger the void, the more the shape of the projection becomes gentler and the higher the coefficient of friction. In addition, small scratches (scratches) on the voids of the biaxially oriented polyester film generated during repeated use cause the particles to fall off, lowering the durability and causing shavings. The shavings often cause a loss of a magnetic signal, that is, a dropout when used as a magnetic tape, for example. In addition, light scattering occurs due to the presence of large voids, and the transparency of the film decreases.
[0008]
On the other hand, the method of precipitating fine particles in a polyester polymerization system has the advantage that the affinity between the precipitated fine particles and the polyester is good, but it is difficult to control the size of the particles and the amount of precipitation. There is a disadvantage that the unevenness of the surface of the resulting film tends to vary.
[0009]
[Problems to be solved by the invention]
The present inventor has solved these inconveniences and improved the slipperiness and abrasion resistance of the film by reducing voids around the inactive fine particles and appropriately roughening the film surface. By adding ₂ O ₄ particles, these properties are secured, the scratch resistance, the slitting property and the electromagnetic conversion properties when formed into a tape are also improved, and a biaxially oriented polyester film having a surface suitable for use is obtained. As a result of intensive research for development, the present invention has been achieved.
[0010]
Therefore, an object of the present invention is to reduce voids, uniform the roughness of the film surface, and prepare a uniform surface unevenness, and to improve the slipperiness, abrasion resistance, scratch resistance, slitting properties, and electromagnetic conversion characteristics when formed into a tape. An object of the present invention is to provide an excellent biaxially oriented polyester film for a magnetic recording medium.
[0011]
[Means for Solving the Problems]
The present invention has the following configuration to achieve the above object.
[0012]
A biaxially oriented laminated film in which a polyester film A layer is laminated on at least one side of a polyester film B layer, wherein the polyester film A layer has a thickness of 0.1 to 3.0 μm, and at least an average in the film A layer. It contains 0.05 to 0.5% by weight of inert particles having a particle size of 0.3 to 2.0 μm, has an average primary particle size of 0.002 to 0.2 μm, and has a specific surface area of 50 to 110 m ^2. A biaxially oriented polyester film for a magnetic recording medium, comprising 0.005 to 2.0% by weight of MgAl ₂ O ₄ particles / g.
[0013]
The polyester in the present invention is a polyester containing an aromatic dicarboxylic acid as a main acid component and a fatty acid glycol as a main glycol component. Such polyesters are substantially linear and have film forming properties, especially film forming by melt molding. Examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, diphenoxyethane dicarboxylic acid, diphenyl dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, diphenyl ketone dicarboxylic acid, and anthracene dicarboxylic acid. And the like. Examples of the aliphatic glycol 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 diols such as cyclohexanedimethanol. And the like.
[0014]
In the present invention, polyesters containing alkylene terephthalate and / or alkylene naphthalate as a main component are preferable.
[0015]
Among such polyesters, particularly, polyethylene terephthalate and polyethylene-2,6-naphthalate, for example, 80 mol% or more of all dicarboxylic acid components are terephthalic acid and / or 2,6-naphthalenedicarboxylic acid, and all glycol components are A copolymer in which 80 mol% or more is ethylene glycol is preferred.
[0016]
At that time, not more than 20 mol% of the total acid component can be the above-mentioned aromatic dicarboxylic acids other than terephthalic acid and / or 2,6-naphthalenedicarboxylic acid, and also aliphatic dicarboxylic acids such as adipic acid and sebacic acid. An alicyclic dicarboxylic acid such as cyclohexane-1,4-dicarboxylic acid; Further, 20 mol% or less of the total glycol component can be the above-mentioned aliphatic glycol other than ethylene glycol. For example, aromatic diols such as hydroquinone, resorcinol, and 2,2-bis (4-hydroxyphenyl) propane; polyethylene Polyalkylene glycol (polyoxyalkylene glycol) such as glycol, polypropylene glycol, polytetramethylene glycol and the like can also be used.
[0017]
In the polyester of the present invention, for example, a component derived from an oxycarboxylic acid such as an aromatic oxyacid such as hydroxybenzoic acid or an aliphatic oxyacid such as ω-hydroxycaproic acid, a dicarboxylic acid component and an oxycarboxylic acid component. And those which are copolymerized or bonded at 20 mol% or less based on the total amount of
[0018]
Further, in the polyester of the present invention, a polycarboxylic acid or polyhydroxy compound having a functionality of 3 or more, such as trimellitic acid or pentaerythritol, in a substantially linear range, for example, 2 mol% or less based on the total acid component, is used. And the like are also included.
[0019]
The polyesters are known per se and can be produced in a manner known per se.
[0020]
The biaxially oriented polyester film of the present invention takes the structure of a laminated film obtained by laminating a port re ester film A layer and the polyester film B layer. The laminating form is preferably a two-layer structure of B / A and a three-layer structure of A / B / A. Among them, the three-layer structure reduces the waste film generated in the polyester film production process by the polyester film B. It is further preferable that the layer can be mixed and reused. In the case of the laminated polyester film obtained by the co-extrusion method, the polymer of each layer may be the same or different. Among them, the same is preferable.
[0021]
In the laminated polyester film, the thickness of the polyester film A layer is 0.1 to 3.0 μm, preferably 0.5 to 2.0 μm. If the thickness is greater than 3.0 μm, the characteristics are the same as those of a single-layer polyester film. If the thickness is less than 0.1 μm, the particles in the film tend to fall off and the abrasion resistance deteriorates, which is not preferable.
[0022]
Layer A of the laminated polyester film contains inert particles having an average particle size of 0.3 to 2.0 μm, preferably 0.5 to 1.0 μm. When the inert particles exceed 2.0 μm, the influence of the base film on the surface roughness of the magnetic tape becomes large, and even if the thickness of the layer A of the laminated film is reduced to reduce the surface roughness of the base film. In addition, the flatness of the magnetic tape surface cannot be achieved. On the other hand, if the inert particles are less than 0.3 μm, the slipperiness is poor and winding is not possible, and the running of the tape becomes unstable during VTR, so that the shaving property with the guide deteriorates.
[0023]
The layer A of the laminated polyester film further includes MgAl ₂ O ₄ particles having an average primary particle size of 0.002 to 0.2 μm, preferably 0.01 to 0.04 μm (hereinafter, referred to as spinel-type oxide particles). contains. The addition of the particles can prevent the guide pins from being damaged during loading on the cassette, and improve the slitting property in the film or tape production process. When the particle diameter of the spinel-type oxide particles exceeds 0.2 μm, the surface roughness of the film becomes large, and the influence of the base film on the surface of the magnetic tape becomes large. , The life is shortened and productivity is deteriorated. On the other hand, when the average primary particle diameter of the spinel-type oxide particles is less than 0.002 μm, scratches at the guide pins cannot be controlled, and the scratch resistance decreases.
[0024]
The spinel-type oxide particles are present as secondary particles (aggregated particles) in which particles having a primary particle diameter are aggregated, and the degree of aggregation is preferably 2 to 10 as an average degree of aggregation. Moreover, the specific surface area of the spinel type oxide particles is 50 to 110 m ² / g, whereby the scratch resistance and the slit property can be made more favorable.
[0025]
When the spinel-type oxide particles are contained in an amount of 0.005 to 2.0% by weight, preferably 0.1 to 0.5% by weight, and more preferably 0.2 to 0.4% by weight, scratch resistance and Since the slitting property is in a good state, the addition amount of the spinel-type oxide particles needs to be within this range.
[0026]
In the present invention, the inert particles other than the spinel-type oxide particles contained in the film A layer include, for example, (1) silicon dioxide (including hydrate, silica sand, quartz, etc.); (2) alumina of various crystal forms (3) silicates containing 30% by weight or more of SiO ₂ (for example, amorphous or crystalline clay minerals, aluminosilicates (including calcined products and hydrates), hot asbestos, zircon, fly ash, etc.); (4) oxides of Mg, Zn, Zr, and Ti; (5) sulfates of Ca and Ba; (6) phosphates of Li, Ba, and Ca (including monohydrogen salts and dihydrogen salts) (7) Benzoates of Li, Na, and K; (8) Terephthalates of Ca, Ba, Zn, and Mn; (9) Mg, Ca, Ba, Zn, Cd, Pb, Sr, Mn , Fe, Co, and Ni titanates; (1 0) chromates of Ba and Pb; (11) carbon (eg, carbon black, graphite, etc.); (12) glass (eg, glass powder, glass beads, etc.); (13) carbonates of Ca and Mg; 14) fluorite; (15) ZnS; (16) heat-resistant polymer particles (eg, cross-linked silicone resin particles, cross-linked acrylic resin particles, cross-linked polystyrene particles, cross-linked styrene-acryl resin particles, cross-linked polyester particles, Teflon particles, polyimide particles) , Polyimide-amide particles, melamine resin particles, etc.). More preferably, heat-resistant polymer particles and synthetic inorganic particles (for example, calcium carbonate, silica, etc.) are exemplified. These preferably have a narrow particle size distribution, and have a relative standard deviation of 0.4 or less, more preferably 0.3 or less, and particularly preferably 0.2 or less.
[0027]
The polyester film of the present invention preferably has an overall thickness of 5 to 25 μm.
[0028]
The polyester film of the present invention can be obtained basically by a method conventionally known or accumulated in the art. For example, it can be obtained by first producing a laminated unstretched film and then biaxially orienting the film. More specifically, the unstretched laminated film can be produced by a conventionally accumulated method for producing a laminated film. For example, a method of laminating a film layer (polyester A layer) forming the surface and a film layer (polyester B layer) forming the core layer in a molten state or a state of being cooled and solidified can be used. More specifically, it can be manufactured by a method such as coextrusion or extrusion lamination.
[0029]
The unstretched laminated film produced by the above-mentioned method can be further made into a biaxially oriented film according to a conventionally accumulated method for producing a biaxially oriented film. For example, the laminated unstretched film is uniaxially (longitudinal or transverse) at a temperature of (Tg-10) to (Tg + 70) ° C (Tg: glass transition temperature of polyester) of 2.5 to 7.0 times. The film is stretched at a draw ratio, and then at a temperature of Tg (° C.) to (Tg + 70) ° C. in a direction perpendicular to the stretching direction (when the first-stage stretching is a longitudinal direction, the second-stage stretching is a transverse direction). It can be produced by stretching at a magnification of up to 7.0 times. In this case, the area stretching ratio is preferably 9 to 32 times, more preferably 12 to 32 times. The stretching means may be any of simultaneous biaxial stretching and sequential biaxial stretching. Further, the biaxially oriented film can be heat-set at a temperature of (Tg + 70) ° C. to Tm (° C.) (where Tm is the melting point of the polyester). For example, it is preferable that the laminated polyethylene terephthalate film is heat-set at 190 to 230 ° C. The heat setting time is, for example, 1 to 60 seconds.
[0030]
INDUSTRIAL APPLICABILITY The biaxially oriented polyester film of the present invention shows excellent performance in scratch resistance and slitting property while securing slipperiness and abrasion resistance, and is extremely useful for magnetic recording media.
[0031]
The various physical properties and characteristics in the present invention are measured and defined as follows.
[0032]
(1) Average particle size (DP) of inert particles other than spinel oxide
The measurement is performed using a Shimadzu Corporation CP-50 type centrifugal particle size analyzer (Centrifugal Particle Size Analyzer). The particle size corresponding to 50 mass% is read from the integrated curve of the particles of each particle size calculated based on the obtained centrifugal sedimentation curve and the remaining amount, and this value is defined as the above average particle size. (See Book "Particle Size Measurement Technology", Nikkan Kogyo Shimbun, 1975, pp. 242 to 247).
[0033]
(2) A film containing the spinel oxide particles having an average primary particle diameter of about 100,000 times was obtained by using a transmission electron microscope (for example, JEM-1200EX manufactured by JEOL Ltd.) to form a thin section having a thickness of 100 nm in the cross-sectional direction. When the particles are observed at a magnification of, the smallest particles (primary particles) that cannot be further divided can be observed. Using this photograph, the diameter of each particle equivalent to the area circle was measured for 100 particles using an image analyzer or the like, and the average particle diameter was taken as the average particle diameter of the spinel oxide particles. The identification of the particle type can be performed using SEM-XMA or the like.
[0034]
(3) Average agglomeration degree of spinel oxide particles About 100 particles observed from the photograph obtained in the measurement of the average primary particle diameter, and particularly about agglomerated particles (secondary particles), The average cohesion is determined by counting the number of the primary particles and dividing the total number of the primary particles by the number of the measured particles.
[0035]
(4) Specific surface area of spinel oxide particles The specific surface area (m ² / g) is measured by BET method using Autosorb-1 manufactured by Cantachrome.
[0036]
(5) Film surface roughness (Ra)
It is a value defined by JIS-B0601 as the center line average roughness (Ra). In the present invention, it is measured using a stylus type surface roughness meter (SURFCORDER SE-30C) of Kosaka Laboratory Co., Ltd. The measurement conditions and the like are as follows.
(A) Stylus tip radius: 2 μm
(B) Measurement pressure: 30 mg
(C) Cutoff: 0.25 mm
(D) Measurement length: 2.5 mm
(E) How to summarize the data: The same sample is repeatedly measured six times, one of the largest values is removed, and the average value of the remaining five data is displayed.
[0037]
(6) High-speed pin shaving Under an environment of a temperature of 20 ° C. and a humidity of 60%, a SUS sintered plate is bent into a cylindrical shape from a film cut to a width of 1/2 inch, and the surface finish is insufficient (surface roughness Ra = 0). .15 nm) is brought into contact with a fixed guide pin at an angle θ = (60/180) π radian (60 °), and is run (friction) at a speed of 250 m / min and an entrance tension T ₁ = 50 g. After the film has traveled 200 m, the shavings adhering to the fixed guide pins are evaluated.
<Determination of shavings>
◎: No shaving powder is observed at all. ○: Sharp powder is slightly observed. △: Existence of shaving powder is apparent at a glance. X: Shaving powder is extremely adhered. <Scratch judgment>
：: No scratches are observed. ○: 1 to 5 scratches are observed. Δ: 6 to 15 scratches are observed. X: 16 or more scratches are observed.
(7) In an environment of a blade shaving temperature of 20 ° C. and a humidity of 60%, a film cut to a width of イ ン チ inch is attached to the edge of a blade (a blade for an industrial razor testing machine manufactured by US GKI) at an angle θ = (6/180). Contact (π radian (6 °)) and run (friction) at a speed of 100 m / min and an entrance tension T ₁ = 50 g. After the film has traveled 100 m, the amount of shavings attached to the blade is evaluated.
[0039]
This evaluation relates to the impact strength of the projections formed on the film surface, and corresponds well to the generation of shavings on a calender or a die coater in the magnetic tape manufacturing process. <Judgment>
：: The width of the shaving powder adhering to the blade edge is less than 0.5 mm. ：: The width of the shaving powder adhering to the blade edge is 0.5 mm or more and less than 1.0 mm. Δ: The width of the shaving powder adhering to the blade edge is 1 0.0 mm or more and less than 2.0 mm ×: The width of the shaving powder adhering to the blade edge is 2.0 mm or more.
(8) Slit property A film cut to 1/2 inch width in an environment of a temperature of 20 ° C. and a humidity of 60% is attached to the edge of a blade (a blade for an industrial razor testing machine manufactured by GKI, USA) at an angle θ = (6/180). π radians (6 °) the contacted by min 100m speed, repeated 10 times at an inlet tension _T 1 = 50 g causes travel (friction). After the film has run, the blade edge of the blade is observed with a scanning electron microscope (for example, JSM-T300 manufactured by JEOL Ltd.) to evaluate the wear width of the blade edge.
[0041]
This evaluation well corresponds to the length of the service life of the slit blade when slitting the film or tape in the polyester film forming process or the tape producing process.
<Judgment>
：: Abrasion width of blade tip is less than 1.0 μm ：: Abrasion width of blade tip is 1.0 μm or more and less than 3.0 μm △: Abrasion width of blade tip is 3.0 μm or more and less than 5.0 μm ×: Blade tip Has a wear width of 5.0 μm or more.
(9) Electromagnetic conversion characteristics A VHS system VTR (BR6400 manufactured by Victor Company of Japan, Ltd.) was modified, and a sine wave of 4 MHz was input to a recording / reproducing head through an amplifier, and recorded and reproduced on a magnetic tape manufactured by the following method. , And input the reproduced signal to a spectrum analyzer. Noise generated at a distance of 0.1 MHz from the carrier signal 4 MHz is measured, and the carrier to noise ratio (C / N) is expressed in dB. Using this method, the above-described magnetic tape was measured , and the difference from this magnetic tape was used as the electromagnetic conversion characteristic with the value obtained in Example 5 as a reference (± 0 dB).
[0043]
The magnetic tape is manufactured by the following method.
100 parts by weight of γ-Fe ₂ O ₃ (hereinafter simply referred to as “parts”) and the following composition are kneaded and dispersed in a ball mill for 12 hours.
Polyester polyurethane 12 parts vinyl chloride-vinyl acetate-
Malic anhydride copolymer 10 parts α-alumina 5 parts carbon black 1 part butyl acetate 70 parts methyl ethyl ketone 35 parts cyclohexanone 100 parts After further dispersion, fatty acid: oleic acid 1 part fatty acid: palmitic acid 1 part fatty acid: ester (amyl stearate) Add 1 part and knead for 10 to 30 minutes. Next, 7 parts of a 25% ethyl acetate solution of a triisocyanate compound is added, and the mixture is dispersed at high speed for 1 hour to prepare a magnetic coating solution.
[0044]
The obtained coating solution is applied onto the polyester film so that the dry film thickness becomes 3.5 μm (applied to the polyester A _one layer side).
[0045]
Then, after performing an orientation treatment in a direct current electromagnetic field, it is dried at 100 ° C. After drying, it is subjected to a calendering treatment and slit to a width of 1/2 inch to obtain a magnetic tape.
[0046]
【Example】
Hereinafter, the present invention will be further described with reference to examples.
[0047]
[Examples 1 to 5 , Comparative Examples 1 and 2 ]
Dimethyl terephthalate and ethylene glycol, manganese acetate as a transesterification catalyst, antimony trioxide as a polymerization catalyst, phosphorous acid as a stabilizer, and fine particles shown in the polyester A layer of Tables 1 and 2 as a lubricant were added. Polymerization was performed by a conventional method to obtain polyethylene terephthalate used for the polyester film A layer having an intrinsic viscosity (orthochlorophenol, 35 ° C.) of 0.56.
[0048]
A polyethylene terephthalate having an intrinsic viscosity of 0.62 and a polyethylene terephthalate for the film A layer obtained in the same manner as described above except that fine particles were not added as a lubricant were uniformly mixed at a weight ratio of 1: 1. Thus, polyethylene terephthalate used for the polyester film B layer was obtained.
[0049]
These polyethylene terephthalate pellets were each dried at 170 ° C. for 3 hours, and then supplied to two extruder hoppers and melted at a melting temperature of 280 to 300 ° C., and A and B were applied to both sides of the B layer using a multi-manifold type coextrusion die. The layers were laminated, extruded on a rotating cooling drum having a surface finish of about 0.3 s and a surface temperature of 20 ° C., and quenched to obtain a 200 μm-thick unstretched laminated film. Here the drum surface A ₁ layer, an anti-drum side was A ₂ layers.
[0050]
The unstretched laminated film thus obtained is preheated to 75 ° C., and further heated by three IR heaters having a surface temperature of 800 ° C. from 15 mm above between low-speed and high-speed rolls and stretched 3.2 times. After quenching, it was supplied to a stenter and stretched 4.3 times in the transverse direction at 120 ° C. The obtained biaxially oriented film was heat-set at a temperature of 205 ° C. for 5 seconds to obtain a heat-set biaxially oriented polyester film having a thickness of 14 μm.
[0051]
The thickness of each layer of the co-extrusion film is adjusted by changing the discharge amount of the two extruders. When the thickness of the polyester A ₁ layer side and the polyester A ₂ layer side are different, the flow path on one side is changed. Adjusted by narrowing. The thickness of each layer was determined by the fluorescent X-ray method and a method of cutting a film into thin pieces and searching for a boundary surface by a transmission electron microscope.
[0052]
[Table 1]

[0053]
[Table 2]

[0054]
【The invention's effect】
According to the present invention, slip properties, scratch resistance, slit properties, and electromagnetic conversion when used as a tape have a surface property particularly useful for a magnetic tape and can sufficiently cope with a high-speed magnetic tape processing step. A laminated polyester film having good characteristics can be provided.

Claims (4)

A biaxially oriented laminated film in which a polyester film A layer is laminated on at least one side of a polyester film B layer, wherein the polyester film A layer has a thickness of 0.1 to 3.0 μm, and at least an average in the film A layer. It contains 0.05 to 0.5% by weight of inert particles having a particle size of 0.3 to 2.0 μm, and has an average primary particle size of 0.002 to 0.2 μm and a specific surface area of 50 to 110 m ^2. A biaxially oriented polyester film for a magnetic recording medium, comprising 0.005 to 2.0% by weight of MgAl ₂ O ₄ particles / g. The magnetic recording medium for biaxially oriented polyester film according to claim 1, wherein an average primary particle size of MgAl ₂ O ₄ particles are 0.01 to 0.04 .mu.m. The magnetic recording medium for biaxially oriented polyester film of claim 1 or 2 average degree of aggregation of MgAl ₂ O ₄ particles are 2-10. The biaxially oriented polyester film for a magnetic recording medium according to claim 1, wherein the inert particles are heat-resistant polymer particles or synthetic inorganic particles.