Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – By casting liquids on a solid supporting or shaping surface
Reexamination Certificate
1998-06-10
2001-07-24
Vargot, Mathieu D. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Forming continuous or indefinite length work
By casting liquids on a solid supporting or shaping surface
C264S204000, C264S236000, C264S331190, C264S347000
Reexamination Certificate
active
06264866
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a method for producing a polyimide film, more particularly, to a method for producing a polyimide film by means of controlling its adhesive property.
2. Disclosure of the Related Art
As is commonly known, a polyimide film has various excellent properties such as heat-resistance, cold resistance, chemical-resistance, insulation and mechanical strength. Therefore, a polyimide film is widely used as such materials as an electric insulating film, a heat insulating film and a base film of flexible printed wiring board. In order to use a polyimide film for various purposes, a copper-clad laminated board is produced by superposing a layer of adhesive agent and copper foil on one or a both sides of a polyimide film, a pre-impregnated film (prepreg) is produced by coating a polyimide film with adhesive agent, or a composite film is produced by laminating fluorocarbon resin on a polyimide film. The adhesive strength is one of the important properties of a film, so that various attempts to improve the adhesive strength of a film have been made.
In order to provide the adhesive strength to a surface of a polymeric film, there are various techniques such as flame treatment for a film surface, corona discharge treatment, ultraviolet treatment, alkaline treatment, primer treatment, sand blast treatment and plasma treatment. For the purpose of providing the adhesive strength to a polyimide film without spoiling its other properties, one or more of the above-mentioned treatments are selected. These treatments are considered to be used for removing a weak boundary layer, which is formed on the film surface in the course of solvent-cast process and lowers the adhesive strength of a film.
All of the above-mentioned treatments are executed after producing a film to improve the adhesive strength of a finished film. The adhesive strength of a finished film is not constant. The above-mentioned after-treatments are also unstable. Therefore, it is difficult to stably provide a film with an improved adhesive strength by a prior art method. There is also an inevitable problem that the cost goes up due to the additional step to improve an adhesive property of a finished film. Same troubles and problems also occur in the course of producing a composite of a polyimide film and fluorocarbon resin. Thus, it has been difficult to constantly provide high adhesive strength to a film by using the conventional methods.
OBJECTS AND SUMMARY OF THE INVENTION
As the result of our researches to remove the above disadvantages and to stably provide a film with a high adhesive strength, we have eventually found the method for producing a film having an excellent adhesive property in which an adhesive property is controlled in course of producing a film. In the conventional method, an adhesive property of a film is improved by way of treating the surface of a finished film, however, in the present invention, an excellent adhesive property is incorporated in course of producing a film.
The method for producing a polyimide film according to the present invention, which overcomes the above-discussed and numerous other disadvantages and deficiencies of the prior art, comprising the steps of i) casting a composition into a film shape, wherein said composition consists substantially of organic solvent solution of polyamide acid; ii) heating the film-shaped composition to obtain a prefilm with an adjusted imidation ratio and/or an adjusted amount of volatile constituent; and iii) further heating said prefilm to obtain a polyimide film.
The adjusted imidation ratio of the prefilm can be 70% or more.
The adjusted amount of volatile constituent of the prefilm can be 40 weight % or less.
The adjusted imidation ratio of the prefilm can be 70% or more and the adjusted amount of volatile constituent of the prefilm can be 40 weight % or less.
The highest temperature of heating a prefilm can be in a range from 450° C. to 630° C.
Thus, the present invention disclosed herein makes possible the objectives of (1) providing an adhesive property directly to a polyimide film; (2) providing an adhesive property extremely stably to a polyimide film for the purpose of overcoming uneven quality of adhesiveness and sudden loss of adhesiveness, which are often the case with conventional methods for providing adhesiveness to a finished film; and (3) maintaining a high value of the adhesive strength of a composite film obtained by laminating fluorocarbon resin on a polyimide film.
REFERENCES:
patent: 4470944 (1984-09-01), Asakura
patent: 4797307 (1989-01-01), Kunimoto et al.
patent: 5324475 (1994-06-01), Okahashi et al.
Egawa Naoki
Fukudome Manabu
Kondo Yuzuru
Maki Haruhiko
Yamada Hirofumi
Kanegafuchi Kagaku Kogyo & Kabushiki Kaisha
Pillsbury & Winthrop LLP
Vargot Mathieu D.
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