Aromatic polyamide resin moldings, production methods thereof, and magnetic recording medium produced therefrom

Abstract

The present invention provides aromatic polyamide resin moldings comprising at least one surface that is 1.0 nm or more in root-mean-square roughness and is 80 nm or less in 10-point average roughness, both of the roughness being as determined by atomic force microscopy, and that is 9.8 GPa or more in tensile Young's modulus at least in one direction. Such aromatic polyamide resin moldings serve effectively as material for film, film for magnetic recording medium in particular, that is highly resistant to scraping and has highly uniform surface protrusions.

Description

TECHNICAL FIELD[0001]The present invention relates to an automatic polyamide resin moldingsmolding having fine protrusions uniformly distributed over theirits surface, particularly aromatic polyamide film that can be suitably used as a magnetic recording medium.BACKGROUND ART[0002]With high heat resistance and good mechanical properties, aromatic polyamides have various potential uses in the form of fiber, film, and aramid paper. Para-oriented aromatic polyamides, in particular, arehave higher in rigidity, strength, and mechanical properties than other polymers, and are widely known as the materialmaterials for high-strength fibers such as “Kevlar”. When used as materialmaterials for filmfilms, they can produce very thin products, with potential onesuses including printer ink ribbon, magnetic tape, and capacitors. Aromatic polyamides withhaving better surface properties including running performance and abrasiveness are now demanded as more rapid processes for aromatic polyamide pr...

AI Technical Summary

Benefits of technology

[0039]With their excel lentexcellent surface properties, aromatic polyamide resin moldings of the present invention will be processed into such products as film and in-mold material, but film is most preferred to produce the intended effect of the invention. Studies by the present inventors have also shown that surface protrusions with very high uniformity are formed in the case of thin film of 1 to 20 μm, preferably 2 to 10μm more preferably 2.5 to 7 μm, in heightthickness.

[0040]Film of the present invention has a tensile Young's modulus Ha of 9.8 GPa or more at least in one direction. This, combined with excel lentexcellent surface properties, makes it possible to provide thin film products that have good processing properties and stability against external force despite their small thickness. In the case of magnetic recording medium, in particular, the output level of magnetic tape increases with the head-tape sliding properties, and therefore it is necessary to develop base film with a high Young's modulus. In particular, a high Young's modulus is required in the longer direction when a fixed head is used for recording, while it is required in the transverse direction when helical scanning is adopted. Base film withhaving a Young's modulus less than 9.8 GPa in any directionall directions is unfavorable because high output is not obtained regardless of the recording mechanism used. For aromatic polyamide film of the present invention, the Young's modulus should preferably be 11.7 GPa or more, more preferably 12.7 GPa, at least in one direction. Needless to say, it is preferred that the Young's modulus is 9.8 GPa or more in all directions.

[0041]Film sFilm's elongation should preferably be 10% or more, more preferably 20% or more, further morepreferablymore preferably 30% or more, at least in one direction to achieve a moderate degree of softness.

[0042]For magnetic recording, the film's moisture absorption coefficient should preferably be 5% or less, more preferably 3% or less, further more preferably 2% or less, to reduce the taperstape's expansion and contraction caused by moisture changes, allowing good output properties to be maintained.

[0043]For magnetic recording, film's heat shrinkage at 200° C. for 10 minutes should preferably be 0.5% or less, more preferably 0.3% or less, to the taperstape's expansion caused by temperature changes, allowing good output properties to be maintained.

[0044]Such film may be of a monolayer or a multilayer structure. To produce two-layered film, a solution of polymerized aromatic polyamide is divided into two parts, and two layers are built up after adding a dissimilar polymer to at least one part. The same process applies when film consisting of three or more layers is to be produced. Known methods to produce such a structure include the building up of layers in a die or in a feed block, and production of one layer followed by laminating it with another layer. In the case of a multilayer film, athe film surface of the present invention should preferably be formed as the outmost layer on at least one side of the film.

Problems solved by technology

However, above-mentioned conventional aromatic polyamide films containing (inorganic or other) particles as major component of the surface protrusions have three serious basic problems as described below.

First, if inorganic or other foreign particles with different properties are added to aromatic polyamide to form surface protrusions, the affinity with the inorganic material may be reduced due to the strong intermolecular force of aromatic polyamide, which will cause removal of protrusions, and the film surface may become liable to scraping or other damage that will decrease the abrasion resistance of the film surface.

However, as the diameter of the particles contained decreases, the repulsion among particles decreases, tending to cause their coagulation, resulting in a decreased uniformity of the distribution of protrusions and an increased number of large protrusions.

This is an essential problemsproblem arising from thenthe mixing of aromatic polyamide with particles of a foreign nature, and this problem cannot be avoided completely when solid particles, organic or inorganic, are used.

Furthermore, aromatic polyamide during the process for preparing the polymer solution is liable to suffer large changes in pH of the solution to accelerate the coagulation of particles.

Thus, the use of aromatic polyamide is disadvantageous regarding this particle coagulation.

Third, during such a processing as stated above or during the use of a final product, aromatic polyamide film may often travelstravel along guide rolls or guide pins, but the protrusions consisting of particles contained are generally so high in hardness that the surface of the guide will be scraped to produce dust which in turn will fall on the film.

This problem will be particularly serious if the guide is made of plasticsa plastic or if the film travels along it rapidly and repeatedly.

Further, no specific methods for preparing the surface of the support are virtually disclosed, and the only description regarding surface preparation is that it is done by adjusting the film formation conditions for surface smoothing and by adjusting the size and density of the particles added, which cannot work effectively enough to solve the above-mentioned problems.

Further, the content of the soluble resin is large compared to aromatic polyamide, reducing the good mechanical properties, the high Young's modulus in particular, characteristic of aromatic polyamide.

However, aromatic polyamides, particularly para-oriented ones, generally are not high in solubility, and if an aromatic polyamide is blended with another which is still lower in solubility, it will be difficult for them to mix completely to form a homogeneous polymer solution, even though complete dissolution seems apparent.

Therefore, it is difficult for the technique disclosed in the Application to produce uniformly-distributed fine protrusions.

Images