JPH0227733B2 - JIKEHAIROKUBAITAINOSEIZOHOHO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention suppresses precipitation of polyester oligomers on the surface of a polyester film when forming a ferromagnetic thin film on a polyester film in vacuum. The purpose is to improve wear and, in particular, to stabilize still life.

Stretched polyester films, which are widely used as supports for magnetic recording media, contain about 1% of low polymer components, ie, oligomers, which are produced as by-products during the polymerization of polyester resins. When the polyester film is exposed to high temperatures, this oligomer diffuses onto the film surface and evaporates from the surface, or forms fine crystalline precipitates on the surface. When forming a ferromagnetic thin film mainly composed of Fe, Ni, Co, alloys thereof, or oxides thereof on a polyester film by vacuum evaporation, ion plating, sputtering, etc., the surface of the polyester film serving as a substrate is coated with metal, The temperature rises due to the energy of vapors such as ions, the radiant energy from evaporation sources and other high-temperature parts, and evaporation and precipitation of oligomers occur. When used as a magnetic recording medium, this oligomer precipitated portion is separated from the magnetic head. It has become clear that wear is likely to occur due to friction. JP-A-54-143112 describes dirt on the magnetic head, and the relationship between the film surface roughness y (μm) and the amount of oligomer x (wt%) contained in the film is y0.2x. It has been revealed that staining of the magnetic head can be prevented when a magnetic layer is formed on a polyester film represented by: Magnetic recording media with ferromagnetic thin films as the magnetic layer only show their true potential when applied to high-density recording such as video recording, so it is inevitable that the surface properties of the film that serves as the substrate will be improved. be. In the above relational expression, the surface roughness is
In the case of 0.1 μm or less, the oligomer content is required to be 0.5% or less, but in reality the oligomer content is
When mass-producing polyester films containing less than 0.5%, current technology requires quite complicated processes such as solvent pouring, so it is necessary to solve this problem by some other means.

In addition, substrate surfaces suitable for high-density recording include:
Merely reducing the surface roughness and flattening the surface will increase the frictional resistance of the obtained magnetic recording medium with the magnetic head, which is undesirable, and it is necessary to provide fine irregularities with high density and uniformity. One way to achieve this is to form a thin polymer film with fine irregularities on a smooth polyester film, but it is clear that such a thin polymer film is highly effective in suppressing the precipitation of oligomers from the film. Summer.
Furthermore, as a result of a detailed study of oligomer precipitation when forming ferromagnetic thin films in vacuum, it became clear that increasing the deposition rate of ferromagnetic thin films tends to suppress oligomer precipitation. Ta. The reason for this is that since there is no oligomer precipitation from the polyester surface covered with a ferromagnetic thin film even when heated, the state of oligomer precipitation is determined by the competition between the temperature rise rate of the film surface and the film formation rate in the early stage of film formation. it is conceivable that. It has also become clear that cooling the film itself is effective in suppressing oligomer precipitation, and that it is necessary to control the material, temperature, etc. of the film support. The present invention was obtained based on the above results.

That is, the present invention provides a polyester film surface that has a polymer thin film with a thickness of 0.5 μm or less on the surface and whose minimum temperature at which polyester oligomer microcrystals start to precipitate is at least 140° C. when heated continuously at a constant temperature in the atmosphere for 5 minutes. The present invention relates to a method for manufacturing a magnetic recording medium, comprising forming a ferromagnetic thin film on the back side of the polyester film in vacuum along a metal support at a temperature of 60° C. or less at a deposition rate of 0.05 μm/sec or more. .

To evaluate the ease with which oligomers come out from a polyester film, after continuously heating the film in the air at a constant temperature for 5 minutes, the surface of the film was observed using a differential interference interference optical microscope at a magnification of 500, and fine particles that were not present before heating were evaluated. The temperature at which oligomers were first seen when the heating temperature was increased from 130°C in 5°C increments was determined as the lowest temperature at which oligomer microcrystals began to precipitate.
Hereinafter, this temperature will be expressed as T _MIN (°C).
The T _MIN of various polyester films without a polymer thin film on the surface is 130°C or less. When a thin polymer film is formed on the surface of polyester,
T _MIN increases. The rate of increase varies depending on the material, thickness, fine structure, etc. of the thin polymer film, but those suitable for the present invention have a T _MIN of 140° C. or higher. These candidates include linear polymer compositions with good heat resistance such as polyamide resins and cellulose resins, epoxy resins, urethane resins, Thickness 0.01 to 0.5μ made of a crosslinked polymer composition such as silicone resin, or a resin composition in which fine particles such as silica, titanium oxide, alumina, carbon black, etc. are added.
m thin film exists, and the surface has fine irregularities (for example, the surface roughness is 0.003 to 0.1 μm, and the period of the irregularities is 0.1 μm).
There is a film in which a cross-linked polymer thin film mainly made of modified silicone, epoxy, urethane, etc. is formed on the film surface during the stretching process during polyester film production. It is suitable that a surface having a liquid or granular pattern is formed in the subsequent stretching step. Whether these candidates are suitable for the present invention can be determined by the T _MIN measurement described above. In general, the thicker the polymer thin film, the greater the effect of preventing oligomer precipitation, but it is difficult to obtain anything comparable to stretched polyester film in terms of mechanical strength, especially toughness, and the dimensions of magnetic recording media under various environments. In consideration of stability, it is desirable that the film be formed to a thickness that does not directly affect the mechanical properties, dimensional stability, etc. of the substrate film, that is, 0.5 μm or less.

The drawing shows the results of an example of a magnetic recording medium obtained according to the present invention, which is the relationship between T _MIN and still life. Thickness as a film sample
Made of polyethylene terephthalate with a diameter of 10 μm and free of fine particles caused by polymerization catalyst residue, etc.
A modified silicone emulsion liquid containing a thickener is applied to both sides of the film during stretching, hardening, and re-stretching to form fine wavy irregularities.The film has a surface roughness of approximately 0.03 μm. Five types of films were used in which the ease with which oligomers come out, that is, the T _MIN temperature, was varied by changing the temperature conditions. We prepared four sets of roll samples in which these five types of films were connected and wound.
CoNi (Ni content 20wt%) ferromagnetic thin film (film thickness 0.1μm)
The films were formed in close contact with a metal roll by a continuous oblique evaporation method in the presence of a trace amount of oxygen gas under four conditions in which the film formation rate conditions and the metal roll temperature conditions were changed. These samples were slit and assembled into a cassette half, and the still lifespan was measured using a still lifespan tester having a machine similar to a home video recorder. The T _MIN of the film used was 130℃,
There was one type each of 135°C, 140°C, 150°C, and 160°C. The drawing shows the still life test results.
The relationship between the marks in the figure and the deposition conditions is as follows.

A: Film deposition rate 0.05 μm/sec, metal roll temperature 60°C B: Film deposition rate 0.1 μm/sec, metal roll temperature 60°C C: Film deposition rate 0.01 μm/sec, metal roll temperature 60°C D: Film deposition rate 0.05 μm/sec, metal roll temperature 70°C. As a film substrate, epoxy resin thin films in various states with carbon fine particles dispersed on a smooth polyester film (thickness 0.1 to 0.5 μm, surface roughness 0.05 μm, T _MIN 135 ~170℃)
Even when a ferromagnetic thin film (thickness 0.15 μm) was formed under similar conditions to the above, the results were similar to those of the CoNi thin film described above (T _MIN was 140°C or higher, and the deposition rate was
Good still life was obtained under conditions of 0.05 μm/sec or more and metal roll temperature of 60° C. or less.

In addition, the ferromagnetic thin film of the magnetic recording medium according to the present invention may be multilayered, the surface of the ferromagnetic thin film may be overcoated with an organic or inorganic substance, and the back surface of the polyester film may be back coated with an organic or inorganic substance. Those skilled in the art can arbitrarily select and carry out these steps.

As described above, according to the manufacturing method of the present invention, a magnetic recording medium suitable for high-density recording with stable still life characteristics can be easily obtained, and its industrial efficiency is great.

[Brief explanation of drawings]

The figure shows the relationship between the minimum temperature (T _MIN ) at which oligomer microcrystals begin to precipitate on the surface when a film substrate is continuously heated in the atmosphere for 5 minutes, and the still life of a magnetic recording medium obtained using that substrate. It is.

Claims (1)

[Claims] 1. Has a thin polymer film with a thickness of 0.5 μm or less on the surface 5
The minimum temperature at which polyester oligomer microcrystals begin to precipitate during continuous constant temperature heating in the atmosphere for 1 minute is at least
On the polyester film surface that is 140℃ or higher,
The back side of the polyester film is heated to a temperature of 60℃ in a vacuum.
Film deposition rate 0.05μ along metal support below ℃
A method for manufacturing a magnetic recording medium, characterized by forming a ferromagnetic thin film at a speed of m/sec or more.