Stock material or miscellaneous articles – Composite – Of polyamide
Reexamination Certificate
1998-10-27
2001-01-30
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Composite
Of polyamide
C428S690000, C428S690000, C428S690000, C428S900000, C528S183000, C528S348000
Reexamination Certificate
active
06180254
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a biaxially oriented film made from a wholly aromatic polyamide and to a magnetic recording medium comprising the same as a base film. More specifically, it relates to a biaxially oriented film made from a wholly aromatic polyamide, which is excellent in handling properties such as strength, slipperiness and winding property and has excellent abrasion resistance, and to a magnetic recording medium comprising the same as a base film.
In recent years, remarkable progress has been made in high-density magnetic recording, as exemplified by the development and practical implementation of a thin layer coated magnetic recording medium in which a needle-like magnetic powder material such as metal powders or iron oxide powders is coated on a coated magnetic recording medium to a thickness of 2 &mgr;m or less. For example, an extremely thin layer coated magnetic recording medium for high-density magnetic recording is known (refer to technical report MR 94-78 issued by the Institute of Electronics, Information and Communication Engineers (1995-02)).
Since a coated magnetic recording medium of the prior art (a magnetic recording medium in which a mixture of magnetic powders and an organic polymer binder is coated on a non-magnetic base film) has a low recording density and a long recording wavelength, it has a large thickness of about 2 &mgr;m or more. On the other hand, in the case of an extremely thin layer coated magnetic recording medium, there is proposed a magnetic layer as extremely thin as 0.13 &mgr;m, though it has a non-magnetic under-layer.
Along with a reduction in the size of a recording medium itself, it is desired to reduce the thickness of a base film itself in order to increase recording capacity.
An aromatic polyamide film is a material which is excellent in strength, heat resistance and the like due to high Young's moduli as a thin film and suitable for use in a high-density magnetic recording medium.
JP-A 51-129201 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) discloses a magnetic recording medium which comprises a magnetic layer and an aromatic polyamide film in which 70% or more of all the bonds are para bonds and at least 15% of phenyl nuclei have at least one substituent of halogen and nitro groups at the ortho-positions of an amide bond.
In the high-density magnetic recording medium, the surface condition of a non-magnetic base film greatly influences the surface properties of a magnetic layer, and surface irregularities cause noise in recording and reproduction signals. Therefore, it is desirable that the surface of the non-magnetic base film be as smooth as possible.
On the other hand, from a viewpoint of the formation of a non-magnetic base film and handling properties such as transportation, damaging, wind-up and wind-off in the process of film formation, when the surface of the film is too smooth, slipperiness between films deteriorates, a blocking phenomenon occurs, roll formation becomes difficult, and the yield of products lowers, thereby inducing an increase in production costs. Therefore, from a viewpoint of production costs, it is desirable that the surface of the non-magnetic base film be as rough as possible.
As means for satisfying the above antinomic requirements, there is proposed a method for forming protrusions which are appropriate in terms of height and density and derived from particles having optimal particle diameters on the surface of the base film.
As a method for forming protrusions on the surface of an aromatic polyamide film, there have been proposed a) one in which a predetermined amount of inorganic particles are added and b) one in which organic polymer particles or inorganic particles whose surface is treated with an organic polymer are added.
JP-A 61-246919 discloses a film which is essentially composed of an aromatic polyamide or aromatic polyimide containing 0.01 to 10 wt % of inorganic particles as a film produced by a method a). The film has protrusions derived from the inorganic particles and specified as follows. The heights R
m
of fine protrusions range from 30 to 500 Å, the area average diameter D
A
of the fine protrusions ranges from 0.01 &mgr;m or more to less than 0.3 &mgr;m, the average flatness D
A
/R
m
of the protrusions is 15 or less, the number N
A
of fine protrusions having a maximum diameter of 0.01 &mgr;m or more is 10
4
to 10
9
/mm
2
, the number of fine protrusions having a long diameter/short diameter ratio a/b (a: maximum diameter of fine protrusion, b: diameter intersecting the maximum diameter at a right angle) of 2 or more is 0.2×N
A
or less, and the number of fine protrusions having a circularity &pgr;D
N
/C
N
(D
N
: area diameter of fine protrusion, C
N
: circumference of fine protrusion, &pgr;: ratio of the circumference of a circle to its diameter) of 0.7 or less is 0.2×N
A
or less.
JP-A 8-203064 discloses a film made from an aromatic polyamide or an aromatic polyimide, which contains organic polymer particles having an average particle diameter of 10 to 500 nm or inorganic particles surface-treated with an organic polymer, has a center line surface roughness Ra of one surface of 0.5 to 50 nm and an Ra of the other surface of 10 nm or less.
However, the above methods using externally added particles involve such a defect that the particles fall off from the protrusion on the film surface by friction between the guide pin and the surface of the film in the calendering step after the coating of a magnetic layer or during actual use and contaminate the step because the externally added particles easily agglomerate in the added slurry.
Particularly, in the calendering step after the application of a magnetic coating, extremely high shearing force is applied to the base film. Therefore, large voids formed around the agglomeration of the particles produce a great amount of abrasion dust due to the fall-off of the particles, thereby contaminating the calender roll with the result of a great reduction in productivity.
It is an object of the present invention to provide a novel biaxially oriented wholly aromatic polyamide film.
It is another object of the present invention to provide a biaxially oriented wholly aromatic polyamide film for a magnetic recording medium, which is excellent in handling properties such as strength, slipperiness and winding property and has high abrasion resistance.
It is still another object of the present invention to provide a magnetic recording medium which comprises the biaxially oriented wholly aromatic polyamide film of the present invention as a base film, has excellent electromagnetic conversion characteristics and is suitable for high-density recording.
Other objects and advantages of the present invention will become apparent from the following description.
According to the present invention, firstly, the above objects and advantages of the present invention can be attained by a biaxially oriented film made from a wholly aromatic polyamide produced by an acid chloride process, which contains at least one member of inorganic particles having an average particle diameter of 5 to 2,000 nm and selected from the group consisting of hydroxides, carbonates and bicarbonates of metals of groups Ia and IIa of the periodic table, the inorganic particles being derived from inorganic particles which are added as a neutralizing agent to a reaction system to neutralize hydrogen chloride by-produced by the acid chloride reaction and its content corresponding to an excess portion added to the reaction system over the amount required for neutralizing the hydrogen chloride stoichiometrically.
The wholly aromatic polyamide constituting the biaxially oriented film of the present invention is not particularly limited as far as its main chain comprises an aromatic nucleus and an amide bonding group as main constituents.
Preferred examples of the recurring unit forming the wholly aromatic polyamide of the present invention include units represented b
Asai Takeo
Handa Makoto
Ono Mitsumasa
Suzuki Kenji
Tomita Hiroshi
Kiliman Leszek
Sughrue Mion Zinn Macpeak & Seas, PLLC
Teijin Limited
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