KR900003210B1 - Film capacitor - Google Patents

Abstract

A film condensor comprises poly (p-phenylenterephthalamide) film as dielecric and metal foil (i.e. Al, Zn, Fe, Ti, Ni, Cr or Cu) as conductor. The film has 1-5 micron thickness and above 1.38g/cm3 density, and shows below 4 wt.% of moisture absorptivity (at 25 deg.C and under 65% of relative humidity), below 3% of heat contractivility (for 60 min at 250 deg.C), and above 700 kg/mm2 of Young's modulus to the one direction.

Description

Film capacitor

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel film capacitor. More specifically, the present invention relates to a film capacitor that is extremely useful as a component for an electronic device because it can be miniaturized, reduced in weight, and has a large capacity, and can be called a chip.

Capacitors include electrolytic capacitors, ceramic capacitors, paper capacitors, and film capacitors. Among them, plastic film capacitors have realized the small size, light weight, high performance, and high reliability required by the market by simplifying the capacitor structure and rationalizing the manufacturing method. .

As an insulator (dielectric) used for a plastic film capacitor, there are a polyethylene terephthalate (PET) film, a polypropylene (PP) film, a polystyrene film, a polyvinylidene fluoride film, and the like. Iii) It is widely used because high quality film is available. Then, these dielectric films are used as electrode thin capacitors in which aluminum foil or tin foil is wound therebetween, or as vapor deposition thin capacitors which are used as electrodes by depositing a metal such as aluminum or zinc on the surface of the dielectric film.

By the way, the market demand for a film capacitor is in further miniaturization, weight reduction, high performance, and what is called chip which can be mounted on an electric circuit (plate) only by soldering without a lead wire. And these requirements cannot respond with the dielectric film conventionally used. For example, the PET film has a low dielectric constant of about 3, which is unsatisfactory in terms of capacity even though it can be miniaturized by an extremely thin film, and furthermore, has a disadvantage in that it is insufficient in heat resistance and cannot withstand soldering. In addition, although poly (p-phenylene sulfide) film has recently attracted attention as a capacitor (for example, Japanese Patent Application Laid-Open No. 61-273877, etc.), heat resistance is not sufficient, resulting in a limited mounting method. It is limited to the use of this low-temperature solder bath, the so-called reflow solder system, and the exterior coating type that can be considered to be miniaturized. In addition, it is difficult to increase the Young's modulus. Therefore, in the ultra-thin film, the strength is weak and the handling is difficult. In addition, poly (p-phenylene sulfide) has a chlorine atom-containing compound remaining in the manufacturing method, which adversely affects the metal part for the conductor, resulting in unstable long-term reliability as a capacitor.

In addition, other heat-resistant polymer films, for example, polyimide films have difficulties in producing ultrathin films, and are not suitable for capacitors in terms of electrical characteristics. Aromatic polyamides (aramids) have also been noted as heat-resistant films. Among these, meta-orientation aramids have a low Young's modulus, which is not only difficult to produce ultra-thin films, but also due to their high hygroscopicity, they are considered to be inadequate as capacitors. Moreover, since para-oriented aramid also has comparatively high hygroscopicity, the application for the capacitor | condenser of the film has been abandoned. However, the film of para compound aramid substituted with chlorine atom has relatively low hygroscopicity and has been attracting attention as a condenser (for example, Japanese Patent Application Laid-Open No. 59-45124), but this polymer has no thermal stability and has difficulty in solder resistance. There existed anxiety of the fault which causes corrosion of a metal electrode, etc.

An object of the present invention is to provide a film capacitor which eliminates the above-mentioned drawbacks and thus achieves both miniaturization (thus lightening) and high performance (large capacity). Still another object of the present invention is to provide a film capacitor which is excellent in workability at the time of manufacture and has low performance deterioration and performance imbalance due to occurrence of "wrinkling" in the capacitor element, despite being a capacitor using an ultrathin film. . Still another object of the present invention is to provide a leadless chip type film capacitor having excellent heat resistance that can be soldered by dipping.

In order to achieve the above object, the present invention has the following constitution using a poly (p-phenylene terephthalate) film as opposed to conventional common sense.

That is, the present invention has a thickness of 1 to 5 μm, a density of 1.38 g / cm 3 or more, a moisture absorption rate (25 ° C., 65% relative humidity) of 4 wt% or less, and a heat shrinkage rate (250 ° C., 60 minutes) of 3 A film characterized by using a metal foil or a metal thin film as a conductor, using as a dielectric a film made of substantially poly (p-phenylenetelephthalamido) having a% or less and a Young's modulus of at least one direction of 700 kg / cm 2 or more. It was made with a capacitor.

Poly (p-phenylene telephthalamide) (hereinafter abbreviated as PPTA) substantially constituting the dielectric of the film capacitor of the present invention,

It is a polymer represented by it, and it is good to manufacture from conventionally well-known paraphenylene diamine and telephthaloyl dichloride by low temperature solution polymerization method. In addition, the meaning of constructing substantially means that the PPTA film used for the dielectric may contain a small amount of components other than PPTA in the form of copolymerization or blend without impairing the effects of the present invention.

In addition, in the PPTA film constituting the dielectric of the present invention, an inorganic agent such as an antioxidant, a heat stabilizer, a lubricant, a colorant, an ultraviolet absorber, a nucleating agent, a surface protruding agent, or the like, within the scope of not impairing the object of the present invention; The amount of the organic additive may be added as much as the amount normally added. If the degree of polymerization of the polymer is too low, a film with good mechanical properties cannot be obtained. Therefore, the logarithm viscosity ηinh of 3.5 or more, more preferably 4.5 or more, is measured at 30 ° C by dissolving 0.5 g of the polymer in 100 ml of sulfuric acid. The thing of polymerization degree giving () is selected.

The film used in the present invention will achieve the object only when the five requirements described below are satisfied.

First, as a film of this invention, the thickness is 1-5 micrometers. Films having a thickness of more than 5 μm do not meet the requirements of small size and light weight when used in a condenser. The lower limit of the thickness of the film is 1 µm, which is too thin for problems in handling of capacitors during manufacture, for example, "wrinkling", easy tearing, elongation, deformation and entanglement with others. Moreover, even if it is in the capacitor | condenser, the performance (capacitance) may fall or become irregular by the partial generation | occurrence | production of "wrinkle", etc. in many cases. In addition, the thickness as used in this invention is defined as the average value of the thickness in the measuring point of five or more (10 points is good) arbitrarily selected from the said film.

Second, in the PPTA film used in the present invention, the Young's modulus in at least one direction is 700 kg / cm 2 or more. This requirement is related to the strength of the film and, in spite of being an ultrathin film, is necessary to ensure that there is little deterioration in performance or fluctuation due to handling or "wrinkling" after installation in the capacitor. Preferably, the Young's modulus of at least one direction is 100 kg / mm <2> or more, More preferably, it is 1300 kg / mm <2> or more. There are two forms of the film used in the present invention, one of which is a balance type having almost the same Young's modulus of 700 kg / mm2 in width and length, and the other one of which has a large Young's modulus of 700 kg / in width and length. It is a tensilized type more than mm <2>.

Such a thin film and a film having a large Young's modulus in at least one direction can be obtained as a ratio when carried out by the specific method described later. And especially regarding a high Young's modulus, it is related with extending | stretching in a wet state, and restricting contraction at the time of drying.

Thirdly, the film used in the present invention should have a density of 1.38 g / cm 3 or more, preferably 1.39 to 1.41 g / cm 2, and the feature is to ensure long-term stability as a condenser, and further low moisture absorption described below. It is also related to characteristics. The PPTA film having such a high density is obtained by making a film of a dense structure and drying or / and heat-treating at a relatively high temperature by a special method described later, that is, by a unique method of optically isotropicizing and solidifying the optical anisotropy of the dope. It is possible. In addition, the value of density is measured at 30 degreeC by the Vildo gradient tube method using carbon tetrachloride-toluene.

Fourth, the film used in the present invention should have a moisture absorption of 25% by weight or less (25 DEG C, 65% relative humidity), more preferably 3% by weight or less. Low moisture absorption can be easily achieved by performing drying or heat treatment at a relatively high temperature of about 240 ° C or higher.

Fifth, the heat shrinkage rate (250 ° C., 60 minutes) of the PPTA film used in the present invention should be 3% or less in any direction, and 1.5% or less is better. Low heat shrinkage ratio is suitable for solder bath dipping and the like. Such a low heat shrink film is prepared by drying or heat-processing a film at the temperature of 240 degreeC or more at the time of film manufacture.

PPTA films used in the present invention usually have a high dielectric constant of 4 to 6.5. For this reason, when used as a dielectric for capacitors, there is a characteristic that the capacity per same size is larger than, for example, PET film. Moreover, since the temperature dependence and the frequency dependence of the dielectric constant are small, there is a feature that the performance of the capacitor is stable.

The film used in the present invention is suitable to have an intensity of at least about 15 kg / mm 2 and an elongation of at least about 9% in any direction, and more suitable is an intensity of at least about 20 kg / mm 2 and an elongation of at least about 15%.

In addition, the PPTA film used in the present invention should have extremely high transparency and flatness. High transparency is, for example, the visible light transmittance of a wavelength of 600 mm is preferably 65% or more, more preferably 75% or more.

In addition, the PPTA film used in the present invention should be free of pinholes or voids, even in form and electrical (insulation). For this reason, it usually has an insulation breakdown voltage of 100 KV / mm or more, more preferably 150 KV / mm or more.

As a PPTA film used for this invention, it is preferable to have surface orientation defined as a crystal orientation angle by X-ray rotation demonstrated below. That is, the crystal orientation angle regarding the peak of 2θ ≒ 23 ° due to X-rays incident at right angles to the film surface is 30 ° or more, and the crystal regarding the peak of 2θ ≒ 18 ° due to X-rays incident in parallel to the film surface It is preferable that an orientation angle is 60 degrees or less.

Incident of X-rays is divided into the case where it enters in a right angle to a film surface (henceforth a TV direction), and the case where it enters in parallel to a surface (henceforth an SV direction).

The film used in the present invention has a large rotation peak at 2θ ≒ 23 ° by X-rays from the TV direction, but the crystal orientation angle at 2θ ≒ 23 ° is preferably 30 ° or more, and further 50 ° or more. It is desirable to be. In addition, although a large diffraction peak of 2θ ≒ 18 ° appears on the equator line due to incidence from the SV direction, the crystal orientation angle at 2θ ≒ 18 ° is preferably 60 ° or less.

When both of these crystal orientation angles are satisfied, it can be said that the film of the present invention has a so-called surface orientation structure, and the mechanical properties (eg, strength) of both the winding direction and the direction perpendicular to the film are high. , Elongation, and Young's modulus), and have great strength against tearing. In this regard, the film is clearly distinguished from the "film" disclosed in Japanese Unexamined Patent Application Publication No. 55-14170.

A well-known method is employ | adopted as a measuring method of a crystal orientation angle, and it performs as an example as follows. The diffraction intensity curve is obtained by raising the water pipe at a predetermined angle of 2θ and rotating the film by 180 °. And in TV, it rotates between 90 degrees back and front centering on highest intensity | strength. Between the lowest intensity points, the arc length in the diffractogram corresponding to the point representing half the intensity of the highest intensity baseline of the curve, i.e. 50% of the highest intensity baseline The angle with respect to the point of) is measured, and this is taken as the crystal orientation angle of the sample. In the measurement, the film may be laminated with several sheets as needed to measure the diffraction intensity.

Next, the method of obtaining such a PPTA film is demonstrated.

That is, the optically barbering dope of PPTA is prepared using a solvent such as sulfuric acid, degassed or filtered as necessary, and then discharged from the die to be flexible on the upper surface of the surface, followed by provision of moisture and necessity. The optically isotropicized doped dope by heating in accordance with, and then solidified the island dope, washed to dry again at about 240 ° while limiting the shrinkage is prepared. And optionally, for example, when a film having high precision and high Young's modulus in one direction is achieved by uniaxially stretching the wet film after washing, and when a film having high strength and high Young's modulus in the front direction is desired, for example Achieved by biaxial stretching of a wet film, and if a film with good dimensional stability is desired, for example, it may be heat treated after drying, and if a film having a lower moisture absorption is desired, for example, a hydrophobic compound may be coated or reacted in addition to the heat treatment. It may be.

The method was surprisingly found to be very good in obtaining a thin PPTA film of 5 μm or less. The reason for this is not yet clear, but the fact that the optically anisotropic phase is not chemically changed by physically converting the optically anisotropic phase to the optical isotropic phase, and since the stock solution is prepared at a high concentration, the film is thin and strong due to the dense and highly face-oriented film. It seems that these etc. contribute. The film thickness can be controlled by setting the polymer concentration in the dope, the thickness of the die, the moving speed ratio of the flexible planar body relative to the dope discharge metal, the wet drawing ratio, and the degree of shrinkage (or stretching) during drying. There is a number.

In the present invention, a capacitor is a passive circuit element of an electric circuit, and means to provide a constant capacitance between both electrodes by providing a pair of electrodes made of a conductor with a dielectric interposed therebetween. It is a thing of agreement.

The capacitor conductor of the present invention may be any of a thin metal foil or a thin metal film formed by a known method such as vacuum deposition, sputtering, ion plating, plating, or the like on a dielectric. The shape and the like are not particularly limited, but the metal thin film is preferable in view of the irregular breakdown voltage of the capacitor and the miniaturization of the capacitor, and the thickness of the metal thin film is 100 to 500 A (in the case of aluminum, 0.5 to 5? /). The range of k) is preferred. As the metal constituting the conductor, there are aluminum, zinc, iron, titanium, nickel, chromium, copper or alloys thereof, but not limited thereto. In addition, a metal foil is a self-supporting metal film, The thickness of 3-15 micrometers is good.

In the case of using a metal thin film as the capacitor electrode of the present invention, the heat shrinkage rate in the state of a so-called metallized film in which a metal thin film is formed on the PPTA film support and is integrated at 250 ° C. for 30 minutes is 0 to 5% ( 0 to 3% is better).

The capacitor of the present invention is characterized by using a PPTA film as a dielectric, but insulators other than the PPTA film are provided so long as the temperature characteristics, frequency characteristics, heat resistance, and the like, which are inherent features and advantages of the capacitor using the PPTA film as a dielectric, are not impaired. (For example, an adhesive agent such as epoxy type) There exists no problem that a thin film exists between electrodes with a PPTA film.

As the condenser shape of the present invention, either a mold having a normal lead wire or a type in which a solder is directly soldered to a board without a lead wire (so-called chip capacitor) may be used. However, the latter shows further condensation characteristics of the present invention.

In the condenser of the present invention, for example, when the conductor is formed of a thin film of aluminum, when it is affected by moisture in the air, it is preferable to cover the surroundings of the condenser. Examples of the material of the outer shell include metals such as aluminum, inorganic materials such as glass, plastics, and the like. In the case of a chip capacitor, a resin composition having a softening point of 200 ° C. or higher (preferably 240 ° C. or higher) is preferable.

Next, the capacitor manufacturing method of this invention is demonstrated.

A PPTA film obtained by the above method is used as a dielectric, and a metal foil or a metal thin film is used as a conductor to be wound around a flat plate or a concentric circle to form a capacitor element. As a metal thin film formation method at this time, a well-known vapor deposition method, sputtering method, plating method, etc. can be used.

Next, the capacitor element is press-formed, heat-treated, cross-section encapsulation, and lead wire attachment or skin formation, if necessary, to form a capacitor.

The present invention is characterized by the above-mentioned capacitor, but the PPTA film constituting the dielectric of the present invention may be subjected to a plasma treatment of a known corona discharge treatment, and the adhesion, height sealing, moisture resistance, activity, surface smoothness, etc. It may be used as a mold in which different kinds of polymers are laminated for the purpose of giving, or as a mold coated with other organic and / or inorganic compositions.

The condenser of the present invention may be impregnated with oil to be used as a so-called oil condenser.

Next, an Example demonstrates this invention.

[Examples 1 and 2]

[Production of PPTA Film]

ηinh dissolved 5.5 PPTA polymer in 99.7% sulfuric acid at a polymer concentration of 11.5% to obtain dope with optical anisotropy at 60 ° C. After degassing under vacuum, a tantalum belt, polished like a mirror from a die with a slit of 0.15 × 300 mm, was maintained at about 70 ° C. with a filter from the tank, through a filter, through a starvation pump, and at about 70 ° C. Example 1 casts 12 m / min, Example 2 moves to 7 m / min) and blows air at about 90 ° C. with a relative temperature of about 85%, optically isotropics the flexible dope to bring the belt together at 5 ° C. Solidified in water. The coagulation film was then peeled off the belt and washed by running in about 40 ° C warm water. The washed film was stretched in the longitudinal direction (MD) as a roll without drying, and then hot-air dried at a constant length while stretching in the width direction (TD) using a tenter. The film obtained had a water absorption of 3.2 wt% (Example 1) and 3.7 wt% (Example 2), and had a dielectric constant of 5.8 (25 ° C. at 1 KHz). Properties of other films are shown in the first table.

[Manufacture of Capacitors]

The two kinds of PPTA films described above were set in an electron beam vacuum deposition apparatus, and aluminum was deposited so as to have a film resistance of 3Ω / *. The evaporated film was slit (6 mm wide) to form a capacitor element using an element winding machine, and a capacitor was formed by sealing the end face and attaching the lead wire according to the conventional method (each 20 pieces each). It was an average of 0.82μF standard electron 0.021μF for the PPTA film, and an average of 1.1μ standard deviation of 0.025μF for the 3.5 μm thick film.

TABLE 1

* 1: The wet drawing conditions of Example 1 are 1.2 times for MD and 1.2 times for TD.

* 2: The wet drawing conditions of Example 2 are 1.2 times for MD and 1.2 times for TD.

Comparative Example 1

Twenty capacitors were made from a 2 탆 thick PET film as in Example 1. The capacitance was 0.49 μF on average and 0.038 μF standard deviation.

And about the capacitor | condenser of Example 1.2 and the comparative example 1, the heat resistance test of the solder was done. This is immersed in a 250 degreeC solder bath for 10 second, and this evaluates as a change rate of the electrostatic capacity by this. As a result, in the case of the capacitor | condenser of Example 1 and Example 2, it did not change substantially, but the capacitor | condenser of the comparative example showed the fall of about 20% of capacitance.

Example 3

The film used in Example 1 was processed to a certain length in the tenter heated at 360 degreeC again, and the capacitor | condenser which made this a dielectric material was created. This film has a thickness of 1.8 μm, has a density of 1.405, a water absorption of 1.3% by weight, a strength of 40 to 45 kg / mm 2, and a Young's modulus of 1500 to 1900 kg / mm 2, a thermal shrinkage of 250 ° C. of 0.2%, and a dielectric constant of 4.5.

The film was placed on a vacuum vapor deposition apparatus and zinc was deposited on one side so as to have a surface resistance of 2.5Ω. At this time, by the tape margin method, it deposited in stripe form so that it might become 8.0 mm in width | variety of a vapor deposition part, and 1.0 mm in width | variety of a non-deposition part. Two types of slit films were obtained by slitting a blade in the center of each of the vapor deposition portion and the non-deposition portion of the vapor deposition film, that is, 4.5 mm and having a margin of 0.5 mm on the left and right sides. This was wound on an element winding machine, and a pair of two kinds of films were rolled up in the same direction, rolled up, preheated in an oven at 240 ° C. for 10 minutes, and pressed to press the hollow portions to treat the both ends of the films according to a conventional method. Then, on the metal silicon of both end faces of the device, as the electrode lead-out member, the nickel plating was capped on both ends of the copper paste separately to obtain the capacitor (capacitance of 0.30 mu F) of the present invention.

The solder heat resistance test of the chip capacitor thus obtained was obtained. That is, the capacitor was immersed in the solder bath at 300 ° C. for 10 seconds and taken out, and the capacitance was examined at 25 5 and 1 KHz. As a result, there was almost no change at 0.29 μF.

And although the temperature dependence of the capacitance of the capacitor | condenser was investigated in the range of 25-150 degreeC, there existed only 7% of fluctuations and was stable.

Comparative Example 2

Using a 2 μm-thick PET film, a capacitor was prepared in the same manner as in Example 3 (electrostatic capacity 0.15 μF).

In addition, there is a problem such as generation of wrinkles due to the weak film strength during the production of the capacitor, particularly during the deposition of zinc, which takes much longer than the production of the capacitor of Example 3.

The capacitor was immersed in a 300 ° C. solder bath for 10 seconds and lifted up to measure the capacity, but was completely conducted.

The film capacitor of the present invention exhibits the following remarkable effects.

(1) Since an ultra-thin film made of PPTA having a high dielectric constant is used, it is possible to provide a compact, lightweight and large capacitance capacitor.

(2) Since PPTA has little temperature or frequency dependence of dielectric constant, it is possible to provide a capacitor with stable performance (for example, performance hardly changes even when temperature changes).

(3) Since PPTA film is excellent in heat resistance, the capacitor can be immersed in the solder bath after being mounted on an electronic component (for example, a circuit board), so that the process rationalization in the manufacture of an electronic device is possible. Moreover, it can use at higher temperature (for example, in an automobile engine room) than a conventional capacitor | condenser.

(4) Since PPTA film with a large Young's modulus is used, despite being a thin film, the handleability is good and workability of the capacitor manufacturing process is improved ("wrinkle", rice-type due to elongation, breakage, entanglement, etc. are less likely to occur). ).

⑤ Since PPTA film with a large Young's modulus is used, it is possible to provide a capacitor having a small unbalance in properties due to the fact that it is a thin film and does not easily cause deformation and breakage due to "wrinkling" or stretching (for example, a product). There is little unbalance of dielectric breakdown voltage or capacitance in the liver).

Claims (1)

It has a thickness of 1 to 5 µm, has a density of 1.38 g / cm 3 or more, a moisture absorption rate (25 ° C., 65% relative humidity) of 4% by weight or less, and a heat shrinkage rate (250 ° C., 60 minutes) of 3% or less. A film capacitor, wherein a film made of substantially poly (p-phenylene terephthalamide) having a Young's modulus of at least one direction of 700 kg / mm 2 or more is used as a dielectric, and a metal foil or a metal thin film is used as a conductor.