Stock material or miscellaneous articles – Composite – Of polyamide
Reexamination Certificate
2001-10-30
2003-07-08
Hightower, P. Hampton (Department: 1711)
Stock material or miscellaneous articles
Composite
Of polyamide
C428S141000, C428S221000, C428S332000, C264S212000, C264S298000, C264S299000, C264S309000, C264S331160, C264S331190
Reexamination Certificate
active
06589663
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an aromatic polyamide film having excellent adhesivity and productivity and to a method for producing the aromatic polyamide film. In more detail, the present invention relates to the aromatic polyamide film having excellent dimensional stability, or excellent strength and surface smoothness and to the method for producing the aromatic polyamide film.
BACKGROUND ART
Aromatic polyamide films have excellent strengths and excellent heat resistance. Therefore, the aromatic polyamide films have been noted in the uses of magnetic recording media, heat transfer recording media, dielectric materials for capacitors, and printed circuit boards. And the consumption quantity of the aromatic polyamide films has been expanded. The application of the aromatic polyamide films to the magnetic recording media is proposed in, for example, Japanese Unexamined Patent Publication 51-129201 (1976).
Then, the polar groups on the surface of an aromatic polyamide film, produced by a conventional technique, participate in intermolecular bonds at a high rate. And the reactivity of the polar groups is extremely poor. Further, when a functional layer is laminated to the film, the adhesivity of the film to the functional layer is inferior. When the aromatic polyamide film is used, for example, for magnetic recording media or printed circuit boards, the adhesivity of the aromatic polyamide film to an adhesive for fixing magnetic coatings and copper foils is poor. For the problem, the application of an easily adhesive coating or the like was proposed, but the effect was insufficient.
Further, the aromatic polyamide film is produced by a solution film production method. In the method, a film-producing dope comprising an aromatic polyamide solution is first cast on a support from a nozzle in a thin film state, and the film is formed by coagulating the aromatic polyamide with removing the solvent component of the film-producing dope from the thin filmy product cast on the support. But, the production cost of the aromatic polyamide film produced by the solution film production method is higher than that of a thermoplastic polymer film, such as a polyester film, produced by a melt film production method. The problem is mostly caused from needing a long time for extracting the solvent from the thin filmy product cast on the support and further from requiring a high cost for recovering the solvent.
Methods for extracting the solvent from the thin film-like aromatic polyamide solution cast on the support are largely classified into a dry method and a wet method. In the dry method among the methods, an aromatic polyamide solution is cast from a nozzle on a support such as a drum or an endless belt to form the thin filmy product. A solvent is then evaporated from said thin filmy product with hot air or the like, thus drying the thin filmy product until to have a self-supporting property. This method has a problem that a long time is needed for diffusing the solvent to the surface of the thin filmy product and further evaporating the solvent from said surface. For shortening the time, it is effective to enhance the temperature and speed of the hot air used for the drying. But the rapid thermal drying treatment causes the boiling of the solvent, and hence roughens the surface of the obtained film. It is difficult to apply the film having the rough surface to the use of magnetic recording media which require good surface flatness. There is further a problem that, when the solvent has a flammable, explosive or corrosive property, an infinite sum of installation cost is necessary for recovering the solvent and for avoiding the adverse effects of the solvent to environments.
On the other hand, the wet methods are classified into a method for directly extruding the aromatic polyamide solution from a nozzle into a coagulation bath in a thin film-like shape, and a method for casting the aromatic polyamide solution on a support similarly to the above-mentioned dry method and then guiding the cast solution together with the support into a coagulation bath. The method for directly guiding the aromatic polyamide solution into the coagulation bath has an advantage that the efficiency for extracting the solvent is high, because there is not a support. However, the form of the thin filmy product extruded from the nozzle as the planar product is remarkably easily deformed, and it is therefore extremely difficult to obtain a satisfactory film. While, the method for casting the aromatic polyamide solution on the support and then guiding the cast solution together with the support into the coagulation bath has a defect that the extraction of the solvent needs a long time, because the solvent can substantially not be extracted from the side on the support, and a defect that wrinkles are liable to be generated on the film due to the transverse-direction contraction of the film on the extraction. Consequently, the surface flatness of the film is deteriorated. In particular, it was difficult to obtain a flat surface which could be applied as the base of a magnetic recording medium.
DISCLOSURE OF THE INVENTION
Accordingly, the object of the present invention is to solve the problems of prior art to obtain in good productivity the aromatic polyamide film which utilizes the excellent heat resistance and high stiffness of the aromatic polyamide and simultaneously has easy adhesivity enabling the application of the polyamide film to printed circuit boards. Another object of the present invention is to obtain the aromatic polyamide film which can be applied to magnetic recording media and has easy adhesivity and good surface flatness. The objects are achieved by the present invention mentioned below.
The aromatic polyamide film of the present invention is the film comprising the aromatic polyamide, characterized by having microdomain structures having sizes of not less than 5 nm and not more than 600 nm. If the sizes of the microdomain structures are less than 5 nm, the adhesivity of the aromatic polyamide film to adhesives is remarkably deteriorated.
On the other hand, if the sizes exceed 600 nm, the breaking elongation of the film is deteriorated to make it difficult to handle the film in processing processes.
The method for producing the aromatic polyamide film in the present invention is a method for producing the aromatic polyamide film via a casting process of a film-producing dope, a coagulation process, a water-washing process, and a drying process. In the casting process of a film-producing dope, the film-producing dope comprising an aromatic polyamide solution is cast from a nozzle on a support in a thin film-like shape. In the subsequent coagulation process, a film is formed by coagulating the aromatic polyamide with at least adopting a wet bath system comprising the aqueous solution of a good solvent for the aromatic polyamide and with removing the solvent component of the film-producing dope from the thin filmy product cast on the support. In the water-washing process, the coagulated film is washed with water and simultaneously peeled from the support. Therein, the peeling process may be carried out at any stage during the water-washing process in response to the state of the produced film. And, in the subsequent drying process, the coagulated film is dried.
Further, in the method for producing the aromatic polyamide film of the present invention, the relation of a time T (minute) and the thickness t (mm) satisfies the following expression (1); (wherein, a time T means the time from the start of the coagulation process to the peeling of the coagulated film from the support and the thickness t means the thickness of the thin filmy product on the support just after cast). Thereby, the aromatic polyamide film which ensures flatness and in which the microdomain structures having proper sizes are formed can be obtained in good productivity.
1.2t (t+1)≦T (1)
BEST MODE FOR CARRYING OUT THE INVENTION
The sizes of the microdomain structures in the present invention are prefe
Handa Makoto
Oya Taro
Hampton Hightower P.
Sughrue & Mion, PLLC
Teijin Limited
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