JPH0588850B2 - - Google Patents

Description

[Detailed description of the invention]

"Field of Industrial Application" The present invention relates to a heat-resistant polyimide film and a method for producing the same, and more specifically to a polyimide film with improved adhesive properties by greatly reducing the amount of residual volatile matter in the film compared to conventional polyimide films. It relates to films and their manufacturing methods. "Prior Art and Problems" Polyimide films are known to have excellent properties such as heat resistance, cold resistance, chemical resistance, electrical insulation, and mechanical strength, and are used as electrical insulating films, heat insulating films, and flexible films. Widely used for base films of printed wiring boards, etc. In the main applications of polyimide films, such as flexible printed circuit boards and electrical insulation films, polyimide films can be bonded to copper foil through adhesives, made into prepregs by coating with adhesives, or combined with fluororesins. There are many cases, and therefore the adhesive ability of the film has become an important characteristic. Conventional adhesion techniques for polymer films include flame treatment, corona treatment, ultraviolet treatment, alkali treatment, primer treatment, sandblasting, and the like. Among these general techniques, polyimide films also utilize methods that can satisfy the purpose of producing heat-resistant films, such as sandblasting and alkali treatments. However, all of these methods attempt to improve the adhesion ability by subjecting the manufactured film to further post-treatment. Therefore, these methods do not produce films with excellent adhesion ability already in the film forming process, so there may be problems in terms of fluctuations in the adhesion ability of the product film before post-processing, stability, homogeneity, etc. of the post-processing method. Problems may arise, and it is basically difficult to stably supply a film with improved adhesive ability. Furthermore, from a practical standpoint, a new process is required, which inevitably leads to an increase in cost. The same applies to composite films with fluororesin, and it has been difficult to stably achieve high peel strength using conventional techniques. "Means for Solving the Problems" In view of the above circumstances, the inventors of the present invention have conducted intensive research to solve these technical problems, and have found that the amount of residual volatile matter in the film is lower than that of conventional polyimide films. The inventors discovered that a film with high adhesive ability could be provided by reducing the amount of adhesive, and completed the present invention. That is, the first aspect of the present invention is a polyimide film characterized in that the amount of residual volatile matter in the film is 0.45% by weight or less per 100 parts by weight of the film, and the second aspect of the present invention is a polyimide film characterized in that the amount of residual volatile matter in the film is 0.45% by weight or less per 100 parts by weight of the film. Each content is a method for producing a polyimide film characterized in that the amount of residual volatile matter in the film is 0.45% by weight or less per 100 parts by weight of the film. The present inventors considered that because conventional polyimide films are manufactured using the solvent cast method, a mechanically fragile layer is formed on the surface of the film, which impairs adhesion, and considered various improvement methods. I've been doing it. The sandblasting and alkali treatments that are actually carried out can be interpreted as removing these fragile layers. However, as a result of not only focusing on the surface layer, but also conducting intensive research on modifying the film as a whole, we discovered that the amount of residual volatile matter exhibited by the film as a whole affects its adhesion ability. . Usually, in order to evaluate adhesive ability, various solvent-based adhesives are used, which are coated onto a film, dried, and then heated and laminated. Since various solvents are used at this time, it is a surprising finding that the amount of residual volatile matter in the film used influences the adhesive ability. In other words, it is a method that does not necessarily remove the surface layer, and it does not depend on the amount of product produced by the adhesive system.
They discovered that the adhesive ability can be improved by controlling the amount of adhesive present in the film. In the present invention, the amount of volatile matter remaining in the film is the amount of volatile matter remaining in the film excluding moisture, and is defined by the following formula. Amount of residual volatile matter (%) = (W ₀ - W) / W ₀ × 100 W ₀ : Weight after drying at 150°C for 10 minutes W : Weight after heat treatment at 450°C for 20 minutes The polyimide film of the present invention has no residual volatile matter. The amount is 0.45% by weight or less per 100 parts by weight of the film.
If it exceeds this value, it is difficult to obtain a film with sufficient adhesion ability. Preferably the amount is 0.15~
It is in the range of 0.4% by weight. If it is less than 0.15% by weight, mechanical properties etc. may deteriorate, which may be undesirable. The polyimide film of the present invention can be obtained from various known raw materials, and there are no special restrictions. However, in view of the balance of various properties, a polyimide film made of poly-[N, N'-P, P' oxydiphenylene)-pyromellit]-imide is preferred. In addition, the method for producing polyimide film does not depend on whether it uses an imidizing agent (chemical cure method) or only by heating (dry-up method), but the chemical cure method is more effective. This is preferable because it is noticeable. The thickness of the polyimide film of the present invention is not particularly limited, but preferably 10 to 125 μm,
More preferably, it is 50 to 125 μm. The effects of the present invention are particularly noticeable for films of 50 μm or more. In other words, conventional polyimide films had weaknesses such as requiring a large amount of post-treatment to improve their adhesion ability and that it was difficult to improve them on both sides, but the method of the present invention can easily do so. It is possible to improve both aspects. A specific method for reducing the amount of residual volatile matter to 0.45% by weight or less in the present invention includes, for example, a method of applying heat treatment. That is, necessary and sufficient heat treatment is performed at a high temperature of 300° C. or higher, and the time and temperature at this time can be easily set within a range that achieves the purpose of the present invention. As a guideline, the shaded area shown in FIG. 1 is effective. Although the heat treatment of the present invention is based on the conditions under the highest temperature in the production process, it is not necessarily limited to the case where it is carried out in the production process, and it is also possible to provide a separate process and carry out the heat treatment. The method of the present invention improves the adhesion ability by controlling the amount of volatile matter remaining in the film.
It is not necessarily limited to the case where this method is carried out alone, and other known post-processing methods can be further applied as necessary. "Action/Effect" There have been no reports in the past that discuss the relationship between the adhesion ability of polyimide film and the amount of volatile matter remaining in the film. The present inventors have discovered for the first time that the adhesive ability of a polyimide film can be improved by controlling the amount of volatile matter remaining in the film. Although the mechanism is not necessarily clear, it is presumed that it is due to the effect of removing volatile substances that inhibit adhesive ability during the process of reducing the amount of volatile substances remaining in the film to 0.45% by weight or less. By using the present invention, it is possible to directly impart adhesive ability, which has been considered difficult in the past. In addition, conventionally, a polyimide film with excellent adhesion ability on both sides has not been provided, but according to the present invention, it is possible to easily improve the adhesion ability on both sides. Furthermore, since it is not a post-processing method, it is not only advantageous in terms of equipment costs as it does not require a separate process, but it is also extremely advantageous in that it can overcome the instability such as variations in adhesive ability and deactivation of adhesive ability that tend to occur with post-processing methods. Moreover, it is an inexpensive method. Further, according to the present invention, it is possible to stably achieve a high peel strength of a composite film with a fluororesin. "Examples" The present invention will be specifically described below with reference to Examples, but the present invention is not limited in any way by these. Examples 1 to 4 Polyimide films with a thickness of 50 μm consisting of pyromellitic dianhydride and 4,4'-diaminodiphenyl ether were produced. This film was further subjected to heat treatment to produce films with different amounts of residual volatile matter, and their adhesive strength etc. were measured. The results are shown in Table 1. Comparative Example 1 A polyimide film with a thickness of 50 μm was produced in the same manner as in Examples 1 to 4, except that no heat treatment was performed.
Adhesive strength etc. were investigated. The results are shown in Table 1. Examples 5 and 6 By the same method as Examples 1 to 4, 75 μm and
Polyimide films each having a thickness of 125 μm were produced. This film was heat treated at 450° C. for 1 minute, and its adhesive strength etc. were measured. The results are shown in Table 1. Comparative Examples 2 and 3 Polyimide films with a thickness of 75 μm and 125 μm were prepared in the same manner as in Examples 5 and 6, except that no heat treatment was performed, and adhesive strength and other properties were measured. The results are shown in Table 1.

[Table] Examples 7 to 9 Various polyimide films shown in Table 2 were produced with a thickness of 50 μm using the same method as Examples 1 to 4.
Table 2 shows the results of examining the amount of residual volatile matter and adhesive strength.

[Table] Example 10 On one side of the 50μm polyimide film of Example 3,
A composite film was prepared by thermally laminating a surface-treated FEP film with a thickness of 12.5 μm with a fluororesin, and the sheets were sealed so that the FEP layers overlapped.
A T-peel test was performed at a test speed of 300 mm/min, and the peel strength was determined to be 300 g/min.
An excellent value of 0.5 inch width was obtained. Comparative Example 4 Using the polyimide film of Comparative Example 1, the peel strength was determined in the same manner as in Example 10. The results are as follows:
It was 150g/0.5 inch wide.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between heat treatment temperature and heat treatment time.

Claims (1)

[Scope of Claims] 1. A polyimide film characterized in that the amount of residual volatile matter in the film is 0.45% by weight or less per 100 parts by weight of the film. 2. A method for producing a polyimide film, which comprises heat-treating the polyimide film so that the amount of residual volatile matter in the film is 0.45% by weight or less per 100 parts by weight of the film.