Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
2001-02-07
2002-08-13
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S213000, C428S215000, C428S216000, C428S328000, C428S330000, C428S331000, C428S336000, C428S457000, C428S458000, C428S480000, C428S690000, C428S690000, C427S079000, C427S080000, C427S099300, C427S123000
Reexamination Certificate
active
06432509
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
1. Filed of the Invention
The present invention relates to a composite film for a condenser, a method for the production thereof and a base film for use therefor. More specifically, it relates to a composite film for a condenser which film comprises, as a base film, a biaxially oriented film containing polyethylene-2,6-naphthalenedicarboxylate as a main polymer component and an electrically conductive metal thin film layer formed thereon, a method for the production of the composite film and a base film for use in the composite film.
2. Prior Art
Having excellent mechanical properties, thermal properties and heat resistance, a biaxially oriented film containing polyethylene-2,6-naphthalenedicarboxylate as a main polymer component is used as a base film (dielectric) for a condenser, and the production thereof is increasing.
Meanwhile, as it is required to decrease electric or electronic circuits in size in recent years, it is also required to decrease the condenser in size and increase the capacitance thereof. It is therefore required to decrease the thickness of a film made of a dielectric as a base. In a film condenser, the thickness of the film as a dielectric is decreased for a reason that the electrostatic capacity of the condenser is (a) in proportion to the dielectric constant and the electrode area of the dielectric and (b) in inverse proportion to the thickness of the film. In other words, the electrostatic capacity of a dielectric per unit volume is in inverse proportion to a square of a film thickness and in proportion to a dielectric constant. If it is attempted to decrease a condenser in size or increase the capacitance thereof while using dielectrics having one dielectric constant, it is inevitable to decrease the film thickness.
It is clear that decreasing the film thickness has the above effect. However, simply decreasing conventional biaxially oriented films in thickness causes new problems. For example, decreasing the film thickness involves poor workability during deposition of electrodes on a film or in the step of slit or winding elements.
The above workability is mainly concerned with the slipperiness of a film. For improving the slipperiness, there is known a method of imparting the film surface with microscopic hills and valleys, and the method is employed. As this method, there is known a method in which inert inorganic fine particles are added to a polyester as a film material during or after polymerization for the polyester (external particle addition method), or part or the whole of a catalyst, etc., used for the polymerization for the polyester is precipitated in a polymer in a reaction step (internal particle precipitation method).
However, when the method for producing a very thin film uses a polymer containing inert inorganic particles having the same concentration as that of inert inorganic particles used for producing a film having an intermediate thickness, the number of the inert inorganic fine particles per unit area of the very thin film decreases, and one fine particle is more widely spaced from another fine particle in the film surface, so that the film surface is flattened and shows a decrease in slipperiness. Further, a very thin film has low stiffness and films adhere easily each other, thereby causing the slipperiness to decrease. For offsetting a decrease in slipperiness caused by a decrease in thickness of the film, therefore, it is required to increase the concentration of the inert inorganic fine particles added to a polymer or increase the size thereof with a decrease in the thickness of the film.
When a polymer containing inert inorganic fine particles is melt-extruded, voids are liable to be formed around the inert inorganic fine particles in the film due to poor affinity between the inert inorganic fine particles and the polymer if a high draft ratio is employed or if the film is further stretched, and the frequency of such formation also increases. Therefore, not only the obtained film is poor in mechanical properties (such as breaking strength or breaking elongation) and electrical properties (such as electrical insulation defect), but also breaking is liable to take place during the production of the film, which causes problems such as a decrease in productivity and an absence of stability of production conditions.
As a film for making it possible to decrease the occurrence of voids, JP-A-1-266145 (JP-B-7-47645) discloses a thin thermoplastic film which is excellent in workability (handling properties) and improved in film formability (non-breaking properties) and has a thickness of 4 &mgr;m or less, and which comprises 0.01 to 3% by weight of porous inert inorganic particles having a porosity of 50 to 95% and having an average particle diameter of 0.05 to 5 &mgr;m and 0.005 to 1% by weight of spherical silica particles having an average particle diameter of 0.2 to 4 &mgr;m which is greater than the thickness of the film in a thermoplastic polymer constituting a film.
Studies made by the present inventors have showed that, when a polyethylene-2,6-naphthalenedicarboxylate film is used as the above film, the film has advantages that it shows no decrease in the mechanical properties, that its heat resistance and electric insulating properties are excellent and that voids do not occur much. However, it has been shown that the film still has a problem that it suffers breaking during the formation thereof and therefore impairs productivity of the film.
A polyethylene-2,6-naphthalenedicarboxylate film generally has a characteristic feature that it has poor tear resistance properties as compared with a polyethylene terephthalate film, and this feature causes the trouble of breaking to take place frequently during the formation of the film. The factor which has not caused any problem during the formation of the polyethylene terephthalate film causes the breaking in the production of the polyethylene-2,6-naphthalenedicarboxylate film in some cases.
JP-A-7-57964 discloses a polyethylene-2,6-naphthalenedicarboxylate film containing two types of porous silica particles having different average particle diameters in a specific mixing ratio. However, this film involves a problem that it has poor productivity since it also breaks frequently during its formation.
It has been also made clear that each of the above polyethylene-2,6-naphthalenedicarboxylate films has a thick air layer due to surface protrusions when stacked one sheet thereof is stacked on another, whereby they are not sufficient in insulating properties and space factor, so that there is still a problem to be solved that excellent workability is not compatible with the space factor and insulating properties.
In the production of a film condenser, further, for avoiding poor productivity caused by decreasing the thickness of a film as a dielectric and poor workability (deposition of a metal for electrodes on a film, slitting and winding of an element) in the step of processing a thin film to a condenser, JP-A-10-294237 proposes that two different types of inert fine particles as a lubricant be added to a polyethylene-2,6-naphthalate film.
The above film is improved in workability in the steps of forming a thin film and processing the film into a condenser. Since, however, an insulating failure is caused due to additives (the lubricants in particular) contained in the film, the above film is not yet satisfactory as a film for a condenser.
Problems to Be Solved by the Invention
It is a first object of the present invention to provide a very thin biaxially oriented film made of polyethylene-2,6-naphthalenedicarboxylate which is for use as a dielectric in a high-quality film condenser having excellent physical and electrical properties.
It is a second object of the present invention to provide a biaxially oriented film having advanced surface properties so that it is suitable for exhibiting processability for a film condenser and electric properties of a film condenser even if it is a very thin biaxially oriented film.
It is a third object of t
Furuya Koji
Kameoka Akira
Kusume Hiroshi
Watanabe Shinya
Chen Vivian
Teijin Limited
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