JPH1052900A - Biaxially oriented laminated polyester film for magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biaxially oriented laminated polyester film for a magnetic recording medium having excellent output and feeding durability, further extremely small rough protrusion due to aggregated particles for causing dropout or head irregular wear and further excellent winding characteristics and slitting properties. SOLUTION: In the biaxially oriented laminated polyester film comprising at least three layers A, B, C, the layer A for constituting a side provided with a magnetic layer is formed of high crystallinity polyester film having a crystallinity parameter ΔTcg of less than 60 deg.C, the number of protrusions each having a height of a protrusion existing on a surface of the layer A from its flat surface exceeding 0.27μm is 2% or less of the entire number of the protrusions. Further, the layer C for constituting an opposite surface side is formed of polyester having crystallinity parameter ΔTc of 60C, contains 0.05 to 2.0wt.% of inert particles each having a mean particle size of 0.1 to 1.0μm, and further has a thickness of a laminated layer of 0.2 to 2.0μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a biaxially oriented laminated polyester film for a magnetic recording medium,
Particularly, the present invention relates to a laminated polyester film suitable as a base film for a high-density magnetic recording medium such as a digital recording system requiring high output.

[0002]

2. Description of the Related Art A typical example of a high-density magnetic recording medium is a coating type magnetic recording medium obtained by dispersing a ferromagnetic metal in a binder and coating the base film surface with a thin film or multilayer coating, and vacuum deposition or sputtering. There is a metal thin-film type magnetic recording medium obtained by the above method. As a metal thin-film type magnetic recording medium, a magnetic recording medium in which a metal thin-film type magnetic layer made of Co-Ni, Co-Cr or the like is provided on a polyester film is known (for example, JP-A-58-68225). ). With higher performance of magnetic recording hardware and software, higher output is required for magnetic material of magnetic tape,
High-performance magnetic recording media as described above are being developed as small digital VTR tapes for home use and business use, and as tapes for storing large-capacity data. like this,
Various improvements have been made to the base film of the magnetic recording medium in accordance with changes in the magnetic recording system, and a laminated type film having different surface properties on the front and back sides from a conventional single-layer film is becoming mainstream. Smoothness on one side of conventional biaxially oriented biaxially oriented polyester film (C / N (carrier / noise ratio) when magnetic tape is used)
(For example, Japanese Patent Application Laid-Open No. 2-77431). Further, in order to remarkably enhance the smoothness on the magnetic surface side and to improve the output of the magnetic tape, there is also known a three-layer structure in which the front and back surfaces have a different roughness (for example, Japanese Patent Application Laid-Open No. H5-2127).
No. 88). In addition, in order to control the surface characteristics of these laminated polyester films, it is necessary to add inert particles derived from inorganic or organic substances (such as cross-linkable polymers) having a specific particle size to the polyester, or to use a catalyst during polymerization. In general, a method using internally precipitated particles resulting from the above-mentioned method is used.

[0003]

However, the above-mentioned conventional laminated polyester film cannot sufficiently satisfy the high smoothness and running property on the magnetic surface side, and in particular, the high density recording tape of the recent digital recording system. In use, a high running durability is required because the relative speed between the magnetic head and the tape surface is increased. Therefore, if the surface is too smooth, friction with the head is increased and a problem is apt to occur. To avoid these problems,
It is necessary to form fine protrusions at high density on the magnetic surface side of the base film, and for that purpose, means for adding a high concentration of inert particles having a very small particle size for forming protrusions in polyester have been taken. I have. However, when such fine particles are added at a high concentration in polyester, agglomeration of particles cannot be avoided in the pellet extrusion or in the melt extrusion step in the film production step, and coarse particles due to the aggregated particles are formed on the film surface. There has been a problem that projections are generated and output is reduced due to dropout and uneven wear of the magnetic head when a metal thin film type magnetic tape is used. Further, there is also a problem that shavings are generated by dropping of particles in the tape manufacturing process, and the dropout is deteriorated.

The present invention solves the above problems, and has excellent output and running durability even when used for a digital recording type VTR tape or a large-capacity data storage tape which requires particularly high performance. Further, it is an object of the present invention to provide a biaxially oriented laminated polyester film for a magnetic recording medium which has very few coarse protrusions due to aggregated particles which cause dropout or head uneven wear, and also has excellent winding characteristics and slitting properties. I do.

[0005]

According to the present invention, there is provided a laminated polyester film having at least three layers of A / B / C, wherein the layer A constituting the side on which the magnetic layer is provided has a crystallization parameter ΔTcg of 60 ° C. Less than 2% of the total number of protrusions, the height of which exceeds 0.2 μm from the flat surface, and the number of protrusions existing on the surface of layer A is less than 2%. The layer is made of polyester having a crystallization parameter ΔTcg of 60 ° C. or more, contains 0.05 to 2.0% by weight of inert particles having an average particle size of 0.1 to 1.0 μm, and has a lamination thickness of 0%. .
A biaxially oriented laminated polyester film for a magnetic recording medium having a thickness of 2 to 2.0 μm, and a tape using this film.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The polymer constituting the film of the present invention is not particularly limited as long as it is a polyester. In particular, at least one structural unit selected from ethylene terephthalate and ethylene-2,6-naphthalate units is mainly used. Preferably, it is a component. Use of a crystalline polyester is desirable because mechanical properties and running durability of the surface are further improved. Although the film of the present invention contains polyester as a main component, other types of polymers may be blended as long as the object of the present invention is not impaired, or an antioxidant, a heat stabilizer, a lubricant, and an ultraviolet absorber And an inorganic or organic additive such as a crystal nucleating agent.

The film of the present invention is a laminated film having at least three layers of A / B / C. The layer A constituting the side on which the magnetic layer is provided has a crystallization parameter ΔTcg of 60.
It is composed of a highly crystalline polyester having a temperature of less than ℃. The crystallization parameter described here represents the easiness of crystallization in the process of heating the polyester from room temperature, and the glass transition point (T
g) and the cold crystallization temperature (Tcc), that is, Tcc−
It is defined as Tg (° C.). Here, △ Tcg
The smaller the value is, the more easily the polyester is crystallized. By using a highly crystalline polyester, surface protrusions utilizing crystallization can be formed in the layer A.
When ΔTcg is 60 ° C. or higher, the crystallization rate is reduced, so that surface projections cannot be formed by crystallization during the film production process, and the surface is too smooth, resulting in a film having poor running durability.

The formation of the surface projections utilizing the crystallization of the polyester constituting the layer A is performed as follows. That is, heat treatment is performed on the surface on the layer A side of the unstretched film, and then the unstretched film is biaxially stretched, whereby desired surface projections are formed. By subjecting the unstretched film to heat treatment first, crystallization of the unstretched film, particularly the layer A portion, is advanced, and many fine crystals are generated in the layer A. This unstretched film is biaxially stretched,
The film is biaxially oriented to achieve the target strength of the film itself, and uniform fine surface projections due to the fine crystals are formed due to the difference in hardness between the crystal and the non-crystal. Here, whether or not the surface projections are made of fine crystals of polyester is determined by etching the appropriate projections under the target projections in the thickness direction of the film with an appropriate solvent. If it remains as a substance, the particles are added externally or particles precipitated internally (P). When there is substantially no insoluble matter remaining, it can be assumed that the cause of formation of the protrusion is a fine crystal (Q). Examples of the solvent include phenol / carbon tetrachloride (weight ratio: 6/4)
Are preferably used. The frequency of P and Q when the visual field is set to 1 mm ² is obtained by this method, and Q / (P +
It is preferable that the value of Q) is 70% or more. However, the method for determining whether or not the surface projections are made of fine crystals of polyester is not limited to the above method, and an appropriate method can be selected.

The height of the projections formed on the surface of the layer A by the above means is desirably as low and uniform as possible from the viewpoint of spacing loss. We have:
In order to keep the contact between the head and the tape uniform and to provide good slipperiness, the height of the projections was changed variously, and as a result, the height from the flat surface was 0%. .
It was confirmed that when the number of particles exceeding 2 μm was 2.0% or less, a high output was obtained stably and the running durability was good. Preferably, it is 1.5% or less, more preferably 1.0% or less, because it is more stable in output. 0.2μ height from flat surface
If the number of protrusions exceeding m exceeds 2.0% of the total number of protrusions, not only does the average spacing increase and a high output cannot be obtained, but the output also tends to decrease due to uneven wear of the head. Become.

Further, when the film of the present invention is used for a magnetic recording medium of a metal thin film type, a high output can be stably obtained when the number exceeding 0.035 μm is 3.0% or less. It was also confirmed that the running durability was good. Preferably, the content is 2.5% or less, more preferably 2.0% or less, and most preferably 1.5% or less, so that the output as a metal thin film type magnetic recording medium is more stable.

If the number of protrusions formed on the surface of the layer A of the film of the present invention is less than 1,000,000 / mm ² , the running friction of the magnetic surface becomes large, which causes troubles such as sticking of the tape to the magnetic head. Is not preferred. When the number of surface projections is preferably 2,000,000 / mm ² or more, more preferably 3,000,000 / mm ² or more, the repetitive running durability of the magnetic surface becomes good. Although the running durability becomes better as the number of projections increases, the upper limit that can be achieved by the projection forming method of the present invention is about 20 million / mm ² .

It is preferable that the layer A contains substantially no inert particles, but a small amount of fine inert particles may be contained within a range that does not affect the present invention. As the content, the number of protrusions (X) existing on the surface of the layer A and A
It is preferable that the ratio X / Y to the number (Y) of the inert particles contained in the layer is in a range satisfying 5 or more. If the content is larger than this range, the number of protrusions due to the inactive particles increases, which is not preferable because problems such as agglomeration and falling off due to the particles occur.

When the inert particles are contained in the layer A, the type thereof is not particularly limited, but colloidal silica or organic particles, especially crosslinked organic particles, particularly divinylbenzene particles, are preferred from the viewpoint of output characteristics and running durability. As other particles, alumina, zirconia, silica, aggregated particles such as titanium oxide, or monodispersed calcium carbonate,
Titanium oxide, silicate alumina and the like can also be used by dispersing particles in a suitable polymer. A plurality of these particles may be used in combination.

The average particle size of the inert particles contained is 0.0
The range is preferably from 0.5 to 0.20 μm, and more preferably from 0.01 to 0.06 μm. If the average particle size is smaller than the above range, the protrusion height becomes too low, so that the slipperiness and running durability deteriorate. If the average particle size is larger than this range, the height of the protrusion formed on the magnetic surface becomes too large. As a result, the spacing loss increases and the output decreases, which is not preferable. Particles in the thermoplastic resin A of the present invention have a particle size ratio (particle major axis / minor axis) of 1.0 to 1.3, and particularly, in the case of spherical particles, more slipperiness and running durability. It is desirable because it becomes even better.

In the film of the present invention, it is desirable to use a magnetic layer provided on the surface side of the layer A in order to achieve the object of the present invention.

Further, in order to suppress coarse projections on the surface of the layer A and to achieve the above-described projection height range, the layer adjacent to the layer A (hereinafter referred to as layer B) contains substantially inert particles. It is desirable that they are not contained or contained in a very small amount.

Further, it is desirable that the polyester constituting the layer B has as few particles as possible which are insoluble in the polymer due to catalyst residue during the polymerization. Therefore, it is particularly desirable to use a germanium compound that hardly generates insoluble particles as a polycondensation reaction catalyst.

In the present invention, a layer C is provided on the side opposite to the layer A side of the layer B to form a laminated film having at least a three-layer structure of A / B / C. With such a configuration having three or more layers, handling properties and running durability are further improved. Here, when the thickness of the C layer is 0.2 to 2 μm, more preferably 0.4 to 1.5 μm, it is desirable because the running durability is further improved.

For the layer C, a polyester having a ΔTcg of 60 ° C. or higher and a relatively low crystallization rate is used instead of the highly crystalline polyester as in the layer A. The C layer is different from the A layer described above, and is provided with a back coat layer to be on the diamagnetic surface side of the magnetic recording medium. There is a problem that the durability when the vehicle is repeatedly driven in the deck is reduced.

Further, the C layer has an average particle size of 0.1 to 1.0.
Contains μm inert particles. Content is 0.05 ~
2.0% by weight, preferably 0.2 to 1.5% by weight is desirable for improving running durability. As the kind of the inert particles, it is preferable to contain the above-mentioned crosslinked organic particles or particles selected from silica, calcium carbonate, alumina silicate, alumina, titania and the like. These particles may be used alone or in combination of two or more. Furthermore, the surface on the C layer side has 500 projections / mm ² or more with a height of 0.3 μm or more from the flat surface, which enhances the handleability of the film of the present invention, and enhances the winding property during production and the like. It is extremely desirable for enhancing slitting properties.

The film of the present invention is a film in which the above composition is biaxially oriented. Uniaxial or non-oriented films are not preferred because mechanical strength is insufficient. The laminated film of the present invention is particularly preferably used as a film having a total thickness of 3 μm to 9 μm. More preferably, 4.5 to 7 μm
m is desirable.

In the present invention, a laminated film is preferably formed by a coextrusion method. Although an in-line or off-line coating method can be used, a co-extrusion method is preferable in order to keep the total reflection Raman crystallization index of the film surface within the range of the present invention. Furthermore, a co-extrusion method is desirable in order to enhance the abrasion resistance of the film surface and further enhance the storage characteristics (in particular, stability under high humidity).

In the film of the present invention, a part of the film in the thickness direction, for example, the orientation of the polymer molecules in the vicinity of the surface layer is not non-oriented or uniaxial, that is, the entire part of the film in the thickness direction. When the molecular orientation is biaxial orientation, the output characteristics are better. In particular, when the molecular orientation measured by an Abbe refractometer, a refractometer using a laser, a total reflection laser Raman method or the like is biaxial orientation on both the front surface and the back surface, it is preferable because the output characteristics are further improved.

The film of the present invention is used for a magnetic recording medium, and in particular, a digital recording system V for a consumer, business, or broadcasting station which requires a high output and a low error rate.
It is preferably used as a base film of a magnetic recording medium for TR. Further, it is preferably used as a large-capacity data storage tape, and is particularly preferably used for a linear storage type data storage tape (for example, a digital linear tape).

Next, a preferred method for producing the film of the present invention will be described, but the present invention is not limited thereto. The polymerization of the polyester constituting the layer A of the film of the present invention,
It is preferable to use antimony trioxide or germanium dioxide as a polymerization catalyst, and an acetate as a metal compound as a transesterification catalyst in order to reduce ΔTcg and enhance a nucleating agent effect. The acetate is not particularly limited, but it is particularly preferable to use a magnesium compound in order to achieve the object of the present invention. Further, it is preferable to use a phosphonate as the phosphorus compound added at the time of polymerization. However, the method for producing the polyester constituting the layer A is not limited to the above.

The polymerization of the polyester constituting the layers other than the layer A can be carried out by a known method. As a method for incorporating particles into the polyester constituting the layer other than the layer A, it is preferable to disperse in the form of a slurry of ethylene glycol, which is a diol component, and to polymerize the ethylene glycol with a predetermined dicarboxylic acid component. Also, a slurry of particles of ethylene glycol was
30 minutes at a temperature of 0 to 200 ° C, especially 180 to 200 ° C
The heat treatment for 5 hours, especially 1 to 3 hours, is effective for further enhancing the effects of the present invention. Another object of the present invention is to provide a method in which the particles are heat-treated in ethylene glycol, then mixed with the polyester in the form of a slurry in which the solvent is replaced with water, and kneaded using a vented twin-screw extruder to knead the polyester. Is extremely effective in achieving

As a method of adjusting the content of particles, a method of preparing a high-concentration master by the above method and diluting it with a polymer substantially free of particles during film formation to adjust the content of particles. Is valid.

Thus, polyester A containing substantially no particles and having high crystallinity (for layer A), polyester B containing no particles and having lower crystallinity than polyester A (for layer B), and particles having a predetermined amount are used. The pellets of the polyester C (for the C layer) which further contains the same crystallinity as the polyester B are dried if necessary. Next, the following method is effective as a method for laminating a film (layer A) made of polyester A and a film (layer C) made of polyester C on both sides of a film (layer B) made of polyester B.

The polyesters A, B, and C are supplied to three extruders, and are laminated using a three-layer manifold or a merging block. The thickness of each layer is adjusted by controlling the number of rotations of an extruder or a gear pump provided in the polymer flow path to control the amount of polymer extruded. The sheet thus laminated is extruded from a die and cooled by a casting roll to produce an unstretched film. In this case, it is preferable to cast such that the surface on the C layer side is in contact with the casting roll in terms of output characteristics and dropout.

In the present invention, at least one surface of the unstretched film is subjected to a heat treatment, and then biaxially stretched. Examples of the heat treatment method include a method of performing heat treatment by winding around a heating roll, a method of performing hot air treatment from a surface opposite to a surface in contact with the roll while being wound around the roll, a method of performing heat treatment between rolls / rolls with an infrared heater, and a stenter. There is a method of heating using such methods, but it is not particularly limited to these methods.

As a preferable method for heat-treating the cooled and solidified unstretched film, the surface temperature on the layer A side is at least 20 ° C. lower than the cold crystallization temperature Tcc of polyester A (Tcc−20 ° C.), 0.5 to 3 at a temperature 40 ° C. higher than the formation temperature Tmc (Tmc + 40 ° C.) or less
The heat treatment is preferably performed so as to be maintained for 0 second.

Next, the unstretched film is biaxially stretched and biaxially oriented. As the stretching method, a sequential biaxial stretching method or a simultaneous biaxial stretching method can be used, but a sequential biaxial stretching method in which stretching in the longitudinal direction and then in the width direction is preferred, and stretching in the longitudinal direction is preferably 3 A method in which the total longitudinal stretching ratio is 3.0 to 6.5 times divided into stages or more is preferable. The longitudinal stretching temperature varies depending on the type of the thermoplastic resin and cannot be unconditionally determined.
It is effective to increase the height after the first stage to achieve the purpose of the film of the present invention. The longitudinal stretching speed is preferably in the range of 5,000 to 50,000% / min. As a stretching method in the width direction, a method using a stenter is generally used, and an appropriate stretching ratio is in the range of 3.0 to 7.0 times. Stretching speed is 1,000-20,000% / m
In, the temperature is preferably in the range of 80 to 160 ° C. Next, this stretched film is heat-treated. In this case, the heat treatment temperature is preferably 150 to 240 ° C, particularly 170 to 210 ° C, and the time is preferably 0.5 to 60 seconds.

[0033]

[Method for measuring physical properties and method for evaluating effects] The method for measuring characteristic values and the method for evaluating effects according to the present invention are as follows.

(1) Average particle size of particles The film was cut into ultrathin sections of about 1000 to 8000 angstroms in the thickness direction, and was subjected to a transmission electron microscope (JEM-1200EX manufactured by JEOL Ltd.) to about 30,000 to 200,000 times. The particles were observed at different magnifications and observed by the following formula. The number average diameter D was defined as the average particle diameter.

D = ΣDi / N where Di is the equivalent circle diameter of the particles and N is the number.

(2) Content of particles The solvent which dissolves the thermoplastic resin and does not dissolve the particles is selected, the particles are centrifuged from the thermoplastic resin, and the particle content is determined by the ratio (% by weight) to the total weight of the particles. And
In some cases, a combination of infrared spectroscopy is also possible.

(3) Lamination Thickness Using a secondary ion mass spectrometer (SIMS), an element originating from the particles having the highest concentration and carbon of the polyester among particles in the film having a depth of 3000 nm from the surface layer. The concentration ratio of the elements (M ⁺ / C ⁺ ) is defined as the particle concentration, and the analysis in the thickness direction is performed from the surface to a depth of 3000 nm. In the surface layer, the particle concentration is low due to the interface of the surface, and the particle concentration increases as the distance from the surface increases. In the case of the film of the present invention, the particle concentration which has once reached a maximum value starts to decrease again.
Based on this concentration distribution curve, the surface particle concentration is 1/1 of the maximum value.
A depth of 2 (this depth is deeper than the depth of the maximum value) was determined, and this was defined as the lamination thickness. The conditions were as follows.

1) Measurement device Secondary ion mass spectrometer (SIMS) A-DIDA3000 manufactured by ATOMIKA, West Germany 2) Measurement conditions Primary ion species: O ₂ ⁺ Primary ion acceleration voltage: 12 kV Primary ion current: 200 nA raster Area: 400 μm □ Analysis area: Gate 30% Measurement vacuum degree: 5.0 × 10 ⁻⁹ Torr E-GUN: 0.5 kV-3.0 A Note that particles most contained in a range from the surface layer to a depth of 3000 nm are the largest. In the case of organic polymer particles, measurement by SIMS is difficult, so XPS (X
Depth profile similar to the above may be measured by X-ray photoelectron spectroscopy, IR (infrared spectroscopy), etc. to determine the lamination thickness, or the particle concentration change state and polymer The interface can be recognized from the difference in contrast due to the difference, and the thickness of the laminate can be determined. Further, after the laminated polymer is peeled off, the laminated thickness can be obtained by using a thin film step measuring device.

(4) Number and Height of Surface Protrusions The height of the flat surface of the film surface was set to 0 using a field emission electron beam three-dimensional roughness analyzer (ERA-8000FE manufactured by Elionix Inc.) of a 4-detection type. The projection height at that time was measured. Here, the magnification of the scanning electron microscope is 50
A range from 00 to 30,000 times was selected, the measurement was performed for 100 visual fields, the number of protrusions having a height of 0.005 μm or more was determined, and converted to the total number of protrusions per 1 mm ² . Of these, the number of projections having a height of 0.035 μm or more was determined, and the ratio to the total number of projections was determined. In some cases, an atomic force microscope (Digital Instrument)
Information obtained by scanning a visual field of 5 μm square at a scanning speed of 0.69 Hz using a Nanoscope IIIa manufactured by ments Co., Ltd. may be obtained for 100 visual fields and may be replaced with the value of the roughness analyzer.

(5) Surface molecular orientation (refractive index), surface total reflection Raman crystallization index Measured with an Abbe refractometer using sodium D line (589 nm) as a light source. The measurement was performed at 25 ° C. and 65% RH using methylene iodide as the mounting solution. The biaxial orientation of the polymer is such that the refractive index in the longitudinal direction, the width direction, and the thickness direction is N1,
When N2 and N3 are used, one criterion may be that the absolute value of (N1-N2) is 0.07 or less and N3 / [(N1 + N2) / 2] is 0.95 or less. Further, the refractive index may be measured using a laser refractometer. Further, when measurement is difficult by this method, a total reflection laser Raman method can be used. Laser total reflection Raman measurement
By Jobin-Yvon Ramanor U-1000 Raman system,
The total reflection Raman spectrum was measured. In the case of PET, for example, 1615 cm ^-1 (skeleton vibration of benzene ring) and 1730 cm
^-1 (stretching vibration of the carbonyl group), the polarization measurement ratio (YY / XX ratio, etc.) of the band intensity ratio, where YY: Raman light detection parallel to Y with the polarization direction of the laser being Y, XX:
It is possible to utilize that the polarization direction of the laser is X and Raman light detection parallel to X) corresponds to the molecular orientation. The biaxial orientation of the polymer can be determined by converting the parameters obtained from the Raman measurement into the refractive index in the longitudinal direction and the width direction, and from the absolute value, difference, and the like. The total reflection Raman crystallization index of the surface was defined as the half value width of 1730 cm ⁻¹ , which is the stretching vibration of the carbonyl group. The measurement conditions in this case are as follows. Light source Argon ion laser (5145 angstroms) Sample setting The film surface is pressed against a total reflection prism, and the angle of incidence of the laser on the prism (the angle with the film thickness direction) is 6
0 degrees.

Detector PM: RCA31034 / Photon Counting System (Hamamatsu C1
230) (supply 1600V) Measurement conditions SLIT 1000μm LASER 100mW GATE TIME 1.0sec SCAN SPEED 12cm ^-1 / min SAMPLING INTERVAL 0.2cm ^-1 REPEAT TIME 6 (6) Number of particles contained in A layer (Y) 300 by electron microscope (TEM)
Observation is performed at 0 to 100000 times, and the number of particles present in the A layer is counted. The A layer is made of polyester having higher crystallinity than the adjacent B layer.
It could be confirmed by EM, and only the layer A portion was observed in 100 fields of view, and the number was converted to the number per 1 mm ² .

(7) Crystallization parameter ΔTcg Measured using a DSC (differential scanning calorimeter) type II manufactured by PerkinElmer. The measurement conditions of DSC are as follows. That is, 10 mg of a sample is set in a DSC device,
After melting at a temperature of 300 ° C. for 5 minutes, it is quenched in liquid nitrogen. The quenched sample is heated at a rate of 10 ° C./min, and the glass transition point Tg is detected. The temperature is further increased, and the crystallization exothermic peak temperature from the glass state is defined as the cold crystallization temperature Tcc,
The endothermic peak temperature based on crystal melting is the melting temperature Tm, and similarly, the crystallization exothermic peak temperature at the time of cooling is the cooling crystallization temperature Tm.
c. The difference between Tcc and Tg (Tcc−Tg) is defined as a crystallization parameter ΔTcg.

(8) Output characteristics

[0044]

[Metal-coated tape] The following composition was mixed and dispersed on the surface of layer A of the film of the present invention by a ball mill for 48 hours, and a kneaded product obtained by adding 6 parts of a curing agent was filtered through a filter to obtain a magnetic material. Paint was obtained. The magnetic paint was applied by a gravure roll, magnetically oriented, and dried at 110 ° C. Further, calendering was performed by a small test calender, and curing was performed at a temperature of 70 ° C. for 48 hours. The raw tape was slit into 1/2 inch to obtain a pancake. Next, a 200 m length of this pancake was assembled into a cassette to form a cassette tape.

(Composition of magnetic coating) Fe: 100 parts Average particle size Length: 0.3 μm Needle ratio: 10/1 Coercive force: 2000 Oe Polyurethane resin: 15 parts Vinyl chloride / vinyl acetate copolymer: 5 parts ・ Nitrocellulose resin: 5 parts ・ Aluminum oxide powder: 3 parts ・ Carbon black: 1 part ・ Lecithin: 2 parts ・ Methyl ethyl ketone: 100 parts ・ Methyl isobutyl ketone: 100 parts ・ Toluene: 100 parts ・ Stearic acid: 2 parts The output level of this tape at a recording density of 100 kBPI was measured using a drum tester. This output level was compared with a commercially available video tape for Hi8 (metal-coated type), and determined to be +3 dB or more: excellent +1 to +3 dB: good and less than +1 dB: bad.

[0046]

[In the case of a metal thin film type magnetic tape] A of the film of the present invention
The thickness of the cobalt-nickel alloy (Ni 20% by weight) on the layer surface in the presence of a trace amount of oxygen using a continuous vacuum evaporation system
A 200 nm deposition layer was provided. Next, a carbon protective film was formed on the surface of the vapor-deposited layer, and a back coat layer was formed on the opposite surface by a known means, and slit to a width of 8 mm to prepare a pancake. Next, a 200 m length of this pancake was assembled into a cassette to form a cassette tape.

The output level of this tape at a recording density of 100 kBPI was measured using a drum tester. This output level was compared with a commercially available video tape for Hi8 (metal thin film type) and determined to be +3 dB or more: excellent +1 to +3 dB: good and less than +1 dB: bad.

(9) Running Durability on Magnetic Surface The above-mentioned tape was treated at 20 ° C. and 5 ° C. by using a tape running tester.
Under a 0% RH condition, the magnetic surface was brought into contact with a metal guide pin (material: SUS, surface roughness: 0.1 S) (running speed: 3.3 cm / sec, running tension: 20 g, winding angle: 60 °) ). The coefficient of friction after 100 times of running was measured, and the rise from the initial coefficient of friction was determined to be less than 0.03: excellent 0.03 or more and less than 0.08: good 0.08 or more: bad.

(10) Adhesiveness to Back Coat A back coat layer (40 parts by weight of polyurethane resin, nitrocellulose 5
A composition consisting of 0 parts by weight, 20 parts by weight of polyisocyanate, and 50 parts by weight of carbon black was subjected to a dispersion treatment for 24 hours by a ball mill) using a gravure coater and dried at 100 ° C. A commercially available cellophane tape was adhered to the coated surface, pressed at a pressure of 20 Pa, then peeled off at a stretch, and the adhesiveness was determined based on the area ratio of the peeled portion. That is, the ratio of the area of the peeled portion to the area to which the cellophane tape was attached was determined to be 0% or more and less than 5%: excellent 5% or more and less than 15%: good 15% or more: bad.

(11) Drop-out The above-mentioned tape was transferred to a Hi8 VTR (SONY EV-
BS3000). A 4.4 MHz signal was supplied from a TV test signal generator, and the number of dropouts having a reproduction signal attenuation of -16 dB or more and a length of 15 μsec or more was determined using a dropout counter. The number of dropouts after repeating reproduction / rewind 100 times at 25 ° C. and 65% RH for 3 minutes was converted into the number per minute, and judged as follows.

0-15 pieces / min: excellent 16-30 pieces / min: good 31-piece / min: bad (12) Film winding property A film having a width of 300 mm was wound at a winding speed of 200 m / min.
It was wound up at a constant tension to form a roll having a length of 6000 m. The appearance of the roll after 24 hours (left standing at room temperature) is visually observed, and two or more wrinkles or 1 mm or more of the end face deviation is recognized as poor, wrinkles are less than 2 places, or the end face deviation is less than 1 mm. Were judged as good, and those without any wrinkles or edge displacement were judged as excellent.

[0052]

EXAMPLES The present invention will be described based on examples and comparative examples.

Example 1 First, the raw material (polyester A) used for the layer A was polymerized by a known method using the following catalyst composition (magnesium acetate: 0.20% by weight, antimony trioxide: 0.03).
Wt%, dimethylphenylphosphonate: 0.35 wt%). Next, polyethylene terephthalate containing no particles as polyester B was prepared using a polymerization catalyst containing only 0.012% by weight of germanium dioxide and 0.013% by weight of trimethyl phosphate.
Further, as a raw material used for the C layer, an average particle diameter of 0.3 μm
Divinylbenzene particles (divinylbenzene component 81)
%) (Polymerization catalyst: 0.60% by weight of magnesium acetate, 0.05% by weight of antimony trioxide, 0.25% by weight of trimethyl phosphate).

These raw materials (polyesters A, B, C)
Was dried under reduced pressure (3 Torr) at 180 ° C. for 6 hours, and then supplied to extruder 1, extruder 2 and extruder 3, respectively, and melted at 280 ° C. After filtering these polymers by a known method, a three-layer laminate of A / B / C was formed by a rectangular merging block (feed block) for three layers. The ratio of the cross-sectional area of the polymer channel in the merging block is A: B:
C = 1: 45: 35 was used. The thickness of each layer was adjusted by adjusting the number of rotations of a gear pump installed on each line and controlling the amount of extrusion.

This was wound around a casting drum having a surface temperature of 25 ° C. by using an electrostatic application casting method such that the surface in contact with the drum was on the C layer side, and was cooled and solidified to produce an unstretched film.

The unstretched film was brought into contact with the surface layer heated to 180 ° C. for 5 seconds while being wound around a roll of silicone rubber (thickness: 3 mm) to allow crystallization of the layer A to proceed. The film was stretched 3.6 times in the longitudinal direction at a temperature of 96 ° C. Stretching was performed in four stages with a peripheral speed difference between two sets of rolls. 2. Using a stenter to stretch the obtained uniaxially stretched film at 95 ° C. in the width direction at a stretching speed of 2000% / min.
Stretched 7 times, heat-treated at 220 ° C for 3 seconds under constant length,
A laminated polyester film having a total thickness of 7 μm was obtained.

A magnetic layer was provided on the surface on the layer A side of this film by the above-mentioned method to obtain a metal-coated magnetic recording medium.

The characteristics of the films and tapes are as shown in Tables 1 and 2. Both the output characteristics and the running durability were excellent, and the dropout due to coarse projections due to agglomerated particles and the like was extremely small, and the film had excellent performance as a base film for a high-density magnetic recording medium.

Examples 2 to 5 The same procedures as in Example 1 were carried out except that the lamination structure, the polyester and the particle formulation of the layer A, the polyester and the particle formulation of the layers B and C, and the crystallization conditions were changed as shown in Tables 1 and 2. A biaxially oriented laminated film was obtained by a stretching process. The layer A used colloidal silica, and the layers B and C used crosslinked polystyrene as particles (the layer B contained only Example 3, and the average particle size was 0.1 μm). Examples 2 and 3 were evaluated as metal-coated magnetic recording media, and Examples 4 and 5 were evaluated as metal thin-film magnetic recording media.

COMPARATIVE EXAMPLE 1 A biaxial structure was prepared under the same production conditions as in Example 1 with the A / B two-layer structure and the laminated structure, the polyester and particle formulation of the A layer, and the polyester and particle formulation of the B layer as shown in Table 3. An oriented laminated film was obtained (particles of layer B were obtained in Example 3
the same as). A magnetic layer was provided on the surface on the layer A side of the film by the above-mentioned method to obtain a metal-coated magnetic recording medium. Since the polymer of layer A was not a highly crystalline polyester, projections due to crystallization were not sufficiently formed, and the durability of the magnetic surface was particularly poor.

Comparative Examples 2 to 5 A laminated film having a three-layer structure of A / B / C was prepared. The biaxially oriented laminated film was obtained by the same stretching process as in Example 1 except that the polyester and the particle formulation of the layer A, the polyester and the particle formulation of the B and C layers, and the crystallization conditions were changed as shown in Table 2. The layer A was made of colloidal silica, and the layers B and C were made of crosslinked polystyrene. In Comparative Examples 3 to 5, no particles were contained in the A layer, and particles were contained in the B layer and / or the C layer. As shown in Tables 3 and 4, only those having inferior characteristics were not obtained because they did not satisfy the range of the present invention.

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[Table 1]

[Table 2]

[Table 3]

[Table 4]

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The film of the present invention has a laminated structure of at least three layers of A / B / C, and the polyester used for the layer A constituting the layer on the magnetic surface side and the layer C constituting the layer on the diamagnetic surface side. The crystallinity is specified, the height and number of protrusions on the surface of layer A are specified, and the amount and average particle size of particles contained in layer C are specified. In a digital recording type magnetic recording medium application, excellent output characteristics and running durability on the magnetic surface side can be achieved at the same time, and it is also effective in suppressing dropout caused by agglomerated particles and shavings caused by falling particles.

Claims (9)

[Claims] 1. A laminated polyester film having at least three layers of A / B / C, wherein the layer A constituting the side on which the magnetic layer is provided is made of a highly crystalline polyester having a crystallization parameter ΔTcg of less than 60 ° C. , The number of protrusions whose height from the flat surface exceeds 0.2 μm is less than 2% of the total number of protrusions on the surface of the layer A, and the crystallization parameter ΔTcg for the layer C constituting the opposite surface side. Is made of polyester having a temperature of 60 ° C. or more, and has an average particle size of 0.1 to 1.
Containing 0.05 to 2.0% by weight of 0 μm inert particles;
A biaxially oriented laminated polyester film for a magnetic recording medium, wherein the laminated thickness is 0.2 to 2.0 μm. 2. The ratio X / Y of the number of projections (X) present on the surface of the A layer to the number of inert particles (Y) contained in the A layer is 5
The biaxially oriented laminated polyester film for a magnetic recording medium according to claim 1, wherein: 3. The method according to claim 1, wherein the number of protrusions on the surface of the layer A whose height from the flat surface exceeds 0.035 μm is 3% or less of the total number of protrusions. The biaxially oriented laminated polyester film for a magnetic recording medium according to any one of the above. 4. The height from a flat surface of the C layer surface is 0.3 μm.
The biaxially oriented laminated polyester film for magnetic recording medium according to any one of claims 1 to 3, characterized in that more protrusions is 500 / mm ² or more. 5. The biaxially oriented laminated polyester film for a magnetic recording medium according to claim 1, wherein the inner layer portion contains substantially no inert particles. 6. The biaxially oriented laminated polyester film for a magnetic recording medium according to claim 1, wherein the magnetic recording medium is a metal-coated magnetic recording medium. 7. A digital recording type VTR tape using the biaxially oriented laminated polyester film for a magnetic recording medium according to claim 1. 8. A linear recording type data storage tape comprising the biaxially oriented laminated polyester film for a magnetic recording medium according to claim 1. 9. The tape according to claim 7, wherein the magnetic recording medium is a metal-coated magnetic recording medium.