JPS63197643A - Composite polyester film - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a composite polyester film, and more specifically, the present invention relates to a composite polyester film, which has a small amount of oligomer precipitation, and has improved bed touch when used as a disk-shaped magnetic recording medium. The present invention relates to a composite polyester film that is particularly useful as a base film.

Conventionally, biaxially oriented films made of polyethylene terephthalate have good surface flatness and mechanical properties (such as strength), and have good wear resistance when used as magnetic recording media.
Due to its excellent running properties and fatigue resistance, it is often used as a base film for magnetic recording media. However, magnetic recording media based on biaxially oriented films have the disadvantage of being susceptible to dropouts. For this reason, various attempts have been made to reduce dropouts by improving the magnetic layer, such as by selecting the binder used to improve the surface smoothness of the magnetic layer, but these efforts are still insufficient. No satisfactory results have been obtained.

In view of the current situation, the present inventors have conducted various studies focusing on polyester base films, and have found that the occurrence of dropouts is greatly influenced by the polyester oligomers present in polyester base films.
For example, oligomers that adhere to the surface of the film or exist very close to the surface of the film may migrate into the applied magnetic layer by contact with a solvent or heating, or the oligomers that are present on the surface of the magnetic layer during storage as a magnetic recording medium. In addition, when trying to apply a thin metal film to a polyester film by vapor deposition or sputtering, It has become clear that oligomer crystals precipitate on the film surface, creating abnormally high protrusions, which cause poor contact with a magnetic head and dropout when used as a perpendicular magnetic medium.

Conventionally, as a method for reducing the amount of oligomers precipitated on the surface of a polyethylene terephthalate film, there is a method of preventing the @aim of the film by making the @aim structure of the film difficult for oligomers to precipitate.

■A method of adding substances that easily dissolve oligomers to the polymer to prevent precipitation on the film surface.

■A method of preventing precipitation by applying an oligomer precipitation inhibitor to the film surface online or offline;
■Methods such as removing oligomers from the base film by solvent extraction have been proposed.

These methods can suppress the precipitation of oligomers to a certain extent, but in order to completely suppress the precipitation, there is a constraint that other properties of the film, such as mechanical properties and surface properties, have to be changed. Fully satisfactory results have not been obtained. For example, methods such as (1) adding a substance that dissolves oligomers to polyester and (2) applying an oligomer sealant create constraints in designing the surface of the base film, which is an important characteristic for magnetic tape applications. There are many problems in implementation.

In addition, since the solvent extraction method uses solvents with relatively high boiling points such as xylene and dimethylformamide, oligomers can be removed to the extent that almost no oligomers remain in the film, but the solvent remains and processing into magnetic recording media is difficult. For example, the process of vapor deposition and sputtering is very difficult to perform and has the problem of contaminating the vacuum chamber. Also, solvent extraction and dry fermentation.

There is a problem in that it is very difficult to apply to magnetic tape films due to the complexity of operations. Furthermore, (2) A biaxially oriented polyester film made of polyethylene-2,6-naphthalene dicarboxylate is known as a polyester film in which the amount of oligomer precipitated is small. This polyester film has higher mechanical properties and heat resistance than polyethylene terephthalate film, but when used as a magnetic recording flexible disk, the molten rate is too high, so when it comes into contact with a magnetic head, the magnetic head However, it has the disadvantage that it is prone to wear due to poor contact or uneven contact.

11 SUMMARY OF THE INVENTION An object of the present invention is to provide a composite polyester film which has a small amount of oligomer precipitated, has improved helad touch when used as a disk-shaped magnetic recording medium, and is particularly useful as a base film for a magnetic recording medium. be.

According to the present invention, the object of the present invention is to provide a three-layer structure in which the core layer is a biaxially oriented polyethylene terephthalate film and both outer layers are biaxially oriented polyethylene-2,6-naphthalene dicarboxylate films. This is achieved by a composite polyester film characterized in that the thickness of both outer layers is 1/40 to 115 of the total thickness of the film.

Polyethylene terethalate (hereinafter referred to as P) in the present invention
(sometimes abbreviated as E'f') are copolymers containing 70% by weight or more of ethylene terephthalate repeating units, including myopolyethylene terephthalate homopolymer, and mixtures of these and various polymers (however, if the PET component is 7
It includes polyester compositions that do not essentially lose the properties of PET, such as those containing 0% by weight or more. This PET
is a polymer with film-forming ability.

In addition, polyethylene-2,6-naphthalene dicarboxylate (hereinafter sometimes abbreviated as PEN) in the present invention includes polyethylene-2,6-naphthalene dicarboxylate homopolymer, ethylene-2,6-
Polyesters that do not lose their woody PEN properties, such as copolymers containing 70 or more naphthalene dicarboxylate repeating units, and mixtures of these and various polymers (however, the PEN component accounts for 70i1% or more) It includes compositions, etc. This PEN is a polymer with film-forming ability.

The composite polyester film of the present invention can be produced, for example, by biaxially orienting an unstretched composite film having a three-layer structure of PEN/PET/PEN by a known method. This unstretched composite film can be manufactured by a known composite method6.For example, it is common to melt PET and PEN in separate extruders and combine them in an extrusion die. Dai.

It is also possible to combine using a stack plate die or the like. The biaxial orientation method may be a sequential biaxial stretching method or a simultaneous biaxial stretching method, but the former is preferred.

For example, in the sequential biaxial stretching method, biaxial orientation is performed at a temperature higher than the glass turning temperature (Tg) of PEN, preferably (7 g
+3) to (7g+10)'C, the first stage of stretching is carried out, and then the second stage of stretching is carried out at a temperature ranging from the same as the first stage stretching temperature to 10 ° C higher, and the stretching ratio is at least uniaxial. It is preferable that the area magnification is 2 times or more, more preferably 2.5 times or more, and the area magnification is 6 times or more, and even 8 times or more. The upper limit of the heat treatment temperature depends on the treatment time, but it goes without saying that it is a temperature at which the film can take a stable shape. 308- is preferable.

The composite polyester film of the present invention has a thickness structure after biaxial orientation, and the ratio of the thicknesses of both outer layers is 1/40 to 115 of the total thickness of the film. If the ratio is smaller than 1/40, oligomer precipitation cannot be prevented, and if the ratio of the thicknesses of both outer layers is larger than 115, the influence of the mechanical properties of the PEN film becomes excessive, and the resulting composite film cannot be used for magnetic recording media, especially flexible disks. This is not preferable because the contact with the magnetic head decreases when the magnetic head is used.

In the present invention, in order to improve the slipperiness of the composite polyester film, the polyester, especially PEN, can contain a lubricant such as inorganic or organic inert fine particles or organic polymer inert fine particles.

Examples of inorganic inert fine particles include MgO.

ZnO, MgC0,, CaCO3, Ca5O,.

BaSO4, Af20. ．． 5i02, TiO2.

Typical examples include silica, titanium oxide, and alumina. Examples of the organic inert fine particles include sorbitan, thyroid, and cataloid, and examples of the organic polymer inert fine particles include tetrafluoroethylene and polyethylene fine particles.

By adding and containing these lubricants, the surface shape of the composite polyester film can be controlled. For example, when used in a coating type magnetic recording medium, the center line average surface roughness can be reduced to 0.
．． 0.007 μm to 0.03 μm, and preferably 0.007 μm or less when used in a metal thin film type magnetic recording medium, especially a perpendicular magnetic recording medium.

The composite polyester film of the present invention is particularly useful as a base film for magnetic recording media, but the magnetic paint applied to the base film may be any known one.For example, ferromagnetic powder such as γ-Fe2O3, cellulose Acetate butyrate, epoxy resin, lecithin,
A silicone oil or the like dissolved and dispersed in molten oil such as methyl isobutyl ketone or toluene can be used. Further, in this case, the known means 10 conditions can be applied to dry the magnetic paint. Furthermore, known means and known treatment conditions can be applied to the calender treatment to smooth the magnetic layer. For winding up the magnetic recording medium on which the Wi magnetic layer is formed, known winding equipment can be used as is.

In addition, Co-Cr alloy is most commonly used as the ferromagnetic metal that can be used as a magnetic recording medium by providing a ferromagnetic metal thin film layer on the composite polyester film, but for example, Co-Re, Co-V, Co-Ru,
Ba ferrite.

Co-0, Co-Ni-Mn-P, etc. can also be used. These films are formed using, for example, a vapor deposition method, an ion blating method, a sputtering method, or an electrolytic plating method.

It can be formed by electroless plating method etc.
In particular, the sputtering method is preferable because it provides a high film strength and is difficult to form pinballs in the film.

If the metal thin film is a perpendicular magnetization film, a permalloy film made of a Ni-Fe alloy film may be provided as a soft magnetic film alongside the perpendicular magnetization film, but from an industrial perspective, it is preferable to provide only a perpendicular magnetization film. However, it is advantageous from an economic point of view. Also, on the perpendicularly magnetized film, the i! As the film, a vapor deposited film of carbon, a metal film such as AI, and/or a coating film made of an organic polymer can also be formed.

The biaxially oriented composite polyester film of the present invention hardly precipitates oligomer crystals on the film surface when it comes into contact with a solvent and is heated or heated under reduced pressure.
When a magnetic recording medium is created by applying a magnetic layer using such a base film, which has the characteristic that even if precipitation occurs, it is less prone to oligomer precipitation, reduces dropouts, and prevents dirt from adhering to the magnetic head. etc. can be reduced. Furthermore, when a thin metal film is applied by vapor deposition or sputtering to form, for example, a perpendicular magnetic recording medium, precipitation of oligomers on the film surface can be suppressed, thereby improving the performance of the resulting magnetic recording medium.

EXAMPLES The present invention will be further explained with reference to Examples. In addition, the film properties in the examples are evaluated by the following method.

Example 1 and Comparative Examples 1 and 2 0.50% by weight of titanium oxide with an average particle size of 0.30 μm
The pellet containing PEN (homopolymer) with an intrinsic viscosity of 0.63 was dried at 170° C. for 3 hours. This PEN
The pellets were melted at 295°C in a melt extruder.

On the other hand, a pellet of PET (homopolymer) having an intrinsic viscosity of 0.65 was dried in a separate melt extruder under the same conditions as the PEN, and then melted at 295°C.

The above molten PEN and PET are introduced into a multi-manifold die consisting of three layers, the core layer is PET, and both outer layers are PF and N, which are laminated in the die, and extruded through slits onto a rotating cooling drum. A composite unstretched film is obtained by cooling, and the stretching temperature is set to 113 by a method of preheating the composite unstretched film with a roll and heating it with an infrared heater.
℃, stretched 3.6 times in the machine direction, then stretched 3.7 times in the transverse direction using a stenter method at a stretching temperature of 125 degrees Celsius, and further stretched 2 times in the transverse direction.
Heat setting was performed at 15° C. for 30 seconds to obtain a biaxially oriented composite polyester film having a thickness of 75 μm.

On the other hand, for comparison, biaxially oriented P consisting of a single layer containing 0.5% by weight of titanium oxide with an average particle diameter of 0.30 μm
An EN film (thickness 75μ) was obtained. This was designated as Comparative Example 1. Further, a biaxially oriented film (thickness 75 μm) consisting of a single layer of PET was obtained by a known method, and this was designated as Example 2.

The amount of oligomer extracted from the biaxially oriented film thus obtained was evaluated by the following method.

A 38 m+ square sample is placed in a 100 m1 Erlenmeyer flask, 20 m1 of chloroform is pipetted into the flask, and the sample is immersed in a constant temperature bath at 25±0.5°C for 60 minutes. After 60 minutes, remove the film sample while pouring chloroform into the flask, measure the ultraviolet absorption spectrum of the above solution, and measure the absorbance at a wavelength of 248 mμ. The amount of oligomer extracted is determined from the relationship between the absorbance and the amount of oligomer. A calibration curve for the relationship between absorbance and oligomer amount is created in advance.

The results are shown in Table 1.

Table 1 Amount of oligomer extracted from the film From the above table, it can be seen that the amount of oligomer extracted from the composite film is extremely small.

These biaxially stretched films were used as a base film, and a magnetic paint having the following composition was coated at a solid content of 3 g/cd, dried at 120°C, and then heated at 80°C.

Calendar treatment was performed at 300 kg/am (linear pressure).

Composition of magnetic paint Fe-Co metal magnetic powder 100 parts by weight Chloride vinyl-vinyl acetate copolymer 1Q 77 (VAGH manufactured by Union Carbide) Urethane resin (1711 Nistin 5701 manufactured by Guttrich) Hardening agent (lQ tr Dismodule L manufactured by Bayer) -75> Butyl acetate 140 n Methyl ethyl ketone 200 II The obtained coated web (RJ & air recording medium) was placed on a disc (5
, 25 inches), and the surface of the magnetic layer was finished by polishing. After the disk was left in a temperature and humidity condition of 60° C. x 80% RH for 72 hours, dropout was measured using a floppy disk tester.

The floppy disk made of the composite film of Example 1 was excellent with no dropouts.

On the other hand, in the floppy disk of Comparative Example 1 using a base film made of PEN alone, output fluctuations occurred due to non-uniformity per magnetic head. Furthermore, the floppy disk using the base film made of PET alone in Comparative Example 2 had more dropouts than the floppy disk using the base film in Example 1.

The floppy disk tester is a drop-in, out-counter 5K-44 made by Tokyo Engineering.
4B was used.

Example 2 and Comparative Example 3.4 0.10% by weight of cataloid with an average particle size of 0.05 μm
The pellet containing PF,N (homopolymer) having an intrinsic viscosity of 0.65 was dried at 170° C. for 4 hours. This pellet was melted at a temperature of 300° C. according to a conventional method.

On the other hand, a PET (homopolymer) pellet having an intrinsic viscosity of 0.65 was dried at 170° C. for 4 hours. This pellet was melted at a temperature of 300° C. according to a conventional method.

The above molten polyesters were merged and composited in a three-layer multi-manifold die so that the core layer was PET and both outer layers were PEN, extruded through a slit and quenched to obtain a composite unstretched film. This composite unstretched film was stretched 3.4 times in the machine direction by a known roll stretching method at a stretching temperature of 115°C, and then by a known stenter method at a stretching temperature of 12°C.
After stretching 3.7 times in the transverse direction at 5°C, it was stretched 3.7 times at 235°C.
Heat setting was performed for 0 seconds to obtain a biaxially oriented composite film with a thickness of 50 μm. The surface roughness of this composite film was measured and found to be 0.004 μm.

In the same way, a PEN14C film (thickness 50 μm) and a PET single film (thickness 50 μm) were created.
Comparative Example 3. This was the film of Comparative Example 4.

Example 2. The small pieces of the film of Comparative Example 3.4 were each placed between slide glasses and left in an air oven controlled at a predetermined temperature for 10 minutes.The surfaces of these film pieces were observed under a microscope, and it was found that Comparative Example 4
In the film, precipitation of oligomer crystals was observed at a temperature of 120° C., and it was observed that the size of the precipitated crystals increased as the temperature increased. On the other hand, in the films of Example 2 and Comparative Example 3, precipitation of oligomers is observed at a temperature of 160°C, but the crystal size is smaller than that of the film of Comparative Example 4, and the crystal size remains large even at higher temperatures. The tendency was small.

Thus, it can be seen that in the composite film of Example 2, precipitation of oligomers due to heating is less likely to occur.

A soft magnetic film made of permalloy with a thickness of 0.45 μm per side is placed on both the front and back sides of these films, and a perpendicularly magnetized film made of Co-Cr alloy with a thickness of 0.4 μm per side is further applied on the soft magnetic film. A protective film made of carbon with a thickness of 0.1 μm was formed to produce a perpendicular magnetic recording medium.

The film was formed using a continuous sputtering device with two rotating cans, and while the sheet was continuously fed along the rotation of the cans, a target made of a Ni-Fe alloy and a target made of a Co-Cr alloy adjacent to the cans were formed. Sputtering with a target was performed. After reaching a vacuum level of 5 x 10-r Torr, sputtering was performed under the conditions of applying an argon gas pressure of 5 x 10-3 Torr and an average deposition rate of 0.3 μm/min.

Furthermore, a protective film was separately formed using another sputtering device.

5. The perpendicular magnetic recording medium thus obtained.
A 25-inch floppy disk is installed in a floppy disk driver equipped with a known vertical head,
We did a performance test.

The floppy disk obtained from the composite film of Example 2 had no dropouts and exhibited satisfactory properties.

On the other hand, the floppy disk obtained from the film of Comparative Example 4 had many dropouts. The cause of this dropout is that the metal thin film locally becomes protrusive due to oligomer crystal precipitation. Further, although the floppy disk obtained from the film of Comparative Example 3 had almost no oligomer crystal precipitation, the output decreased due to poor head contact.

Claims (1)

[Claims] The core layer is a biaxially oriented polyethylene terephthalate film,
A three-layer composite film in which both outer layers are made of biaxially oriented polyethylene-2,6-naphthalene dicarboxylate films, and the thickness of both outer layers is 1/40 to 1/40 of the total thickness of the film.
A composite polyester film characterized in that: /5.