JPH0629146A - Film capacitor - Google Patents

Abstract

PURPOSE:To achieve a film capacitor which is inexpensive and has a high heat resistance and stability and improved electrical characteristics using a two-axis extension film consisting of a styrene polymer having a syndiotactic structure or its composition for a main dielectric. CONSTITUTION:A biaxial oriented film 1 which consists of a styrene polymer having a syndiotactic structure or its compound and has a weight average molecular weight of 100000-500000, a heat shrinkage rate of 7% or less at 30 deg.C and for ten minutes, and a friction coefficient of 0.6 or less is used for a main dielectric. After the film 1 is slit to a specific width, it is wound for a required number of times alternately with an aluminum foil 2, is flattened by hot press, and a lead wire is welded to both end faces. After that, a particle sheathing is performed for manufacturing a coil-type film capacitor, thus obtaining an improved heat resistance and electrical performance and its stability with time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film capacitor used in electronic equipment and the like.

[0002]

2. Description of the Related Art Conventionally, polyethylene terephthalate (PET) and polypropylene (PP) have been widely used as a material for a main dielectric film of a film capacitor, and recently, polyphenylene sulfide (PPS) has been used mainly for the purpose of improving heat resistance. Film capacitors have been developed.

[0003]

However, the film capacitor using the above-mentioned conventional dielectric material has various problems in use due to the restriction of its basic performance.

That is, a film capacitor using a PET film has a large capacity change due to moisture absorption over time, and a large change in capacity change rate and dielectric loss tangent with respect to changes in temperature and the like, and is suitable for use in electronic circuits requiring high precision. Have difficulty.

Further, a film capacitor using a PP film is very stable with respect to electrical performance and aging, but it is difficult to miniaturize it because of its small dielectric constant, and the biggest problem is Since is low in heat resistance, it is difficult to use in a high temperature environment.

Although a film capacitor using a PPS film as a dielectric material to overcome these problems has been put into practical use, the cost is high and the temperature is high, especially 10
In the temperature range exceeding 0 ° C, the capacitance change rate and the dielectric loss tangent change with respect to 20 ° C have non-linearity, which is not suitable for temperature compensation in a wide temperature range. Was there.

The present invention solves the above conventional problems and has excellent electrical performance, high stability and high heat resistance,
Moreover, it is an object of the present invention to provide a low cost film capacitor.

[0008]

In order to achieve the above object, the film capacitor of the present invention comprises a styrene polymer having a syndiotactic structure as a main dielectric or a composition thereof, and has a weight average molecular weight of 100. 1,000
It was composed of a biaxially stretched film having a heat shrinkage of 7% or less and a coefficient of friction of 0.6 or less at ˜500,000, 230 ° C.-10 minutes.

The styrene polymer having a syndiotactic structure in the present invention is a syndiotactic structure having a stereochemical structure, that is, a phenyl group or a substituted phenyl group which is a side chain with respect to the main chain formed from carbon-carbon bonds. The groups have a steric structure in which the groups are alternately located in opposite directions, and the tacticity thereof is quantified by a nuclear magnetic resonance method using isotope carbon. The tacticity measured by the nuclear magnetic resonance method is the proportion of a plurality of continuous constitutional units, for example, diad in the case of 2 units, triad in the case of 3 units,
The case of 5 can be indicated by a pentad,
The styrene-based polymer having a syndiotactic structure referred to in the present invention is usually a racemic dyad of 75% or more,
Preferably 85% or more, or 3 for racemic pentad
Polystyrene, poly (alkylstyrene), poly (halogenated styrene), poly (alkoxystyrene), poly (vinyl benzoate), and hydrogenated products thereof having a syndiotacticity of 0% or more, preferably 50% or more. Polymers and their mixtures, or copolymers containing these structural units are collectively referred to. Here, as poly (alkylstyrene), poly (methylstyrene), poly (ethylstyrene), poly (propylstyrene), poly (butylstyrene), poly (phenylstyrene), poly (vinylnaphthalene), poly ( Vinyl styrene), poly (acena styrene), etc., and as poly (halogenated styrene), poly (chlorostyrene),
Examples include poly (promostyrene) and poly (fluorostyrene). Examples of poly (alkoxystyrene) include poly (methoxystyrene) and poly (ethoxystyrene). Among these, particularly preferable styrene polymers include polystyrene, poly (p-methylstyrene), poly (m-methylstyrene), poly (p-tertiarybutylstyrene), poly (p-chlorostyrene), and poly (p-chlorostyrene). Examples thereof include (m-chlorostyrene), poly (p-fluorostyrene), and a copolymer of styrene and p-methylstyrene.

The weight average molecular weight of the styrene polymer in the present invention is preferably 100,000 or more and 500,000 or less.

Here, if the molecular weight is less than 100,000, the heat resistance of the film is insufficient and 500,000 is obtained.
If it exceeds, it is difficult to stretch at a high magnification and it is difficult to form a thin stretched film.

In the present invention, fine particles are added so that the friction coefficient of the film is 0.6 or less. The type and amount of the fine particles to be added are selected according to the thickness of the film and the purpose of use, but the fine particles of 0.01 to 3 μm should be added so as to be contained in the styrene polymer in an amount of 0.01 to 1 wt%. Good.

Here, the inorganic fine particles are group IA and IIA.
Group, IVA, VIA, VIIA, VIII, IB, IIB
Group III, Group IIIB, Group IVB element oxides, hydroxides, sulfides, nitrides, halides, carbonates, sulfates, acetates, phosphates, phosphites, organic carboxylates, silicates, titanium Salts, borates and hydrous compounds thereof, complex compounds centered on them, and natural mineral particles are shown.

Specifically, lithium fluoride, borax (sodium borate hydrous salt) and other group IA element compounds, magnesium carbonate, magnesium phosphate, magnesium oxide (magnesia), magnesium chloride, magnesium acetate, magnesium fluoride, titanic acid. Magnesium, magnesium silicate,
Magnesium silicate hydrous salt (talc), calcium carbonate,
Calcium phosphate, calcium phosphite, calcium sulfate (gypsum), calcium acetate, calcium terephthalate,
Calcium hydroxide, calcium silicate, calcium fluoride,
Group IIA element compounds such as calcium titanate, strontium titanate, barium carbonate, barium phosphate, barium sulfate, barium phosphite, titanium dioxide (titania), titanium monoxide, titanium nitride, zirconium dioxide (zirconia), zirconium monoxide, etc. Group IVA element compounds, molybdenum dioxide, molybdenum trioxide, molybdenum sulfide and other VIA group element compounds, manganese chloride, manganese acetate, etc.
V of group VIIA element compounds, cobalt chloride, cobalt acetate, etc.
Group III element compounds, Group IB element compounds such as cuprous iodide,
Group IIB element compounds such as zinc oxide and zinc acetate, aluminum oxide (alumina), aluminum hydroxide, aluminum fluoride, group IIIB element compounds such as aluminosilicate (alumina silicate, kaolin, kaolinite), silicon oxide (silica, silica gel) ), Graphite, carbon, graphite, glass, and other IVB group element compounds, and particles of natural minerals such as carnal stone, kainite, mica (mica, quinnemo), and birose ore.

Although the inorganic fine particles are contained in the final molded article, the method of containing them is not limited. For example, a method of adding or precipitating in an arbitrary process during polymerization and a method of adding in an arbitrary process of melt extrusion can be mentioned.

The film capacitor of the present invention is used as a film (hereinafter referred to as SPS) formed mainly from the styrene polymer having the syndiotactic structure as described above.
Film), and the method for producing this film is not particularly limited, but it can be obtained by heating and melting these materials, forming a preform, heating and stretching, and further heat treating.

The operation from heating and melting to heat setting will be specifically described as follows. First, the styrene-based polymer obtained as described above is used as a molding material and is usually extrusion-molded to obtain a stretching preform (film, sheet or tube). In this molding, it is common to mold the above-mentioned molding material heated and melted into a predetermined shape by an extruder, but without heating and melting the molding material,
It may be molded in a softened state. The extruder used here may be either a single-screw extruder or a twin-screw extruder, and may or may not have a vent,
A uniaxial tandem type is preferred. If a suitable mesh is used for the extruder, foreign matters can be removed. Further, the shape of the mesh can be appropriately selected and used such as a flat plate shape or a cylindrical shape.

The extrusion conditions are not particularly limited and may be appropriately selected according to various situations, but the temperature is preferably selected within the range of the melting point of the molding material to about 50 ° C. higher than the decomposition temperature. The shear stress is 5 × 10 ⁶ dyn.
e / cm ² or less. Examples of the die used include a T-die and a ring die.

After the above extrusion molding, the obtained preform for stretching is cooled and solidified. At this time, various kinds of refrigerant such as gas, liquid and metal roll can be used. When a metal roll or the like is used, methods such as an air knife, an air chamber, a touch roll, and electrostatic loading are effective in preventing uneven thickness and waviness.

The temperature for cooling and solidification is usually in the range of 0 ° C. to 30 ° C. higher than the glass transition temperature of the preform for stretching,
The temperature is preferably about 70 ° C. lower than the glass transition temperature to the glass transition temperature. The cooling rate is 200-3
It is appropriately selected within the range of ° C / sec.

The stretched film used in the present invention is preferably a uniaxially or biaxially stretched cooled and solidified preform. In the case of biaxial stretching, it may be simultaneously stretched in the machine direction and the transverse direction, but may be sequentially stretched in any order. The stretching may be performed in one stage or in multiple stages. The draw ratio is 2 times or more, preferably 3 times or more in terms of area ratio. When the stretching ratio is within this range, the crystallinity of the film is 25% or more, and favorable physical properties can be obtained.

There are various stretching methods, such as a tenter method, a method of stretching between rolls, a bubbling method using gas pressure, and a rolling method.
These may be appropriately selected or combined and applied. The stretching temperature may be generally set between the glass transition temperature and the melting point of the preform. The stretching speed is usually 1 × 10 to 1 × 10 ⁵ % / min, preferably 1 × 10 ³ to 1
× 10 ⁵ % / min.

Further, at 230 ° C. according to the present invention
In order to obtain a film having a heat shrinkage ratio of 7% or less in 10 minutes, heat treatment is performed after stretching. The heat treatment is carried out at 230 ° C. or higher and a melting point of the film or lower, preferably 240 ° C. or higher and a melting point or lower for 0.5 sec to 60 sec, preferably 1 sec to 40 sec under a fixed width and limited shrinkage.

Here, if the heat treatment temperature is low, the heat shrinkage rate is large, and if the heat treatment temperature is high, the heat treatment is difficult because it melts. Further, when the heat treatment time is short, the effect of the heat treatment is not sufficient and the heat shrinkage rate becomes large, and when the heat treatment time is long, heat deterioration of the film is apt to occur and the heat resistance of the completed film capacitor becomes insufficient.

[0025]

With the above-mentioned structure, the present invention has stable electrical performance with linearity up to a high temperature range without much cost increase as compared with PET and PP, and has high heat resistance that hardly changes with time due to moisture absorption. The film capacitor of can be realized.

[0026]

EXAMPLES A film capacitor according to an example of the present invention will be specifically described below based on examples.

(Embodiment 1) FIG. 1 is a schematic sectional view of a film capacitor of the present embodiment, in which 1 is a 6 μm thick SPS film which is a dielectric and 2 is a 6 μm thick aluminum which serves as an internal electrode. It is a foil.

A specific method for producing the SPS film used in the present invention will be described below. In a glass container with an internal volume of 500 ml that was replaced with argon, copper sulfate pentahydrate (CuSO
_{4 · 5H 2 O) 17.8g (} 71mmol), toluene 2
00 ml and trimethylaluminum 24 ml (250
(mmol) was added and reacted at 40 ° C. for 8 hours. Then, from the solution obtained by removing the solid portion, toluene was further distilled off under reduced pressure at room temperature to obtain 6.7 g of a contact product. The molecular weight of this product was 610 as measured by the freezing point depression method.

In a reaction vessel having an internal volume of 2 liters, the above-obtained contact product as an aluminum atom was 5 mmol, triisobutylaluminum was 5 mmol, and pentamethylcyclopentadienyl titanium trimethoxide was 0.025 m.
Mol and 1 liter of styrene monomer were added, and a polymerization reaction was carried out at 90 ° C. for 5 hours.

Then, methanol was injected to terminate the polymerization and the polymer was dried to obtain 300 g of a polymer. Next, this polymer was extracted with methyl ethyl ketone using a Soxhlet extractor, and an extraction residue (MIP) of 98.0% was obtained.
The weight average molecular weight of the obtained polymer was 390,000, and the weight average molecular weight / number average molecular weight was 2.6. Again 3
Melt viscosity at 00 ° C and shear rate of 10 / sec is 2 × 10 ⁴
It was a poise. It was confirmed that the polymer obtained by the melting point and nuclear magnetic resonance measurements was polystyrene having a syndiotactic structure. Further, this polymer composition was decalcified with a methanol solution of sodium hydroxide and then repeatedly washed with methanol. The styrene-based polymer powder thus obtained was vacuum dried while stirring at 150 ° C. for 2 hours. 0.3 wt% of spherical amorphous silica fine particles (1.0 μm in diameter) were powder-blended with this powder. After melt-extruding this mixed powder with a device equipped with a die containing a plurality of capillaries at the tip of a twin-screw extruder with a vent,
It was cooled and cut to prepare a molding material (pellets) for extrusion. At this time, the melting temperature was 300 ° C., the screw diameter of the extruder was 50 mm, a full flight type was used, the extrusion rate was 30 kg / hour, and the vent pressure was 10 mmHg. Then, the pellets were crystallized and dried with stirring in hot air. The amount of residual styrene monomer in the obtained pellets was 1100 ppm, and the crystallinity was 35%. The pellets were extruded by a device equipped with a T-die at the tip of a single screw extruder. The extrusion temperature at this time is 320 ° C.
The shear stress was 3 × 10 ⁵ dyne / cm ² .

The melt-extruded sheet was brought into close contact with a metal cooling roll and cooled by electrostatic loading to prepare a raw material for stretching. At this time, the metal cooling roll was adjusted to 70 ° C. The cooling rate was 50 ° C / sec. Further, the thickness of the prepared original fabric was 50 μm, and the crystallinity was 15%. The raw fabric was sequentially biaxially stretched at 110 ° C. and 3000% / min in the extrusion direction and in the direction perpendicular thereto by 3 times in order. Then, this stretched film was heat-treated at 260 ° C. for 20 seconds under the limited shrinkage. The obtained film had a thickness of 6 μm and a crystallinity of 55.
%Met.

After slitting the film thus formed into a predetermined width, the film is alternately wound with aluminum foil a required number of times, flattened by a heating press, and lead wires are welded to both end faces, and then the powder coating is applied. Then, a foil type film capacitor was manufactured. The capacitance value at this time is about 0.047.
It was μF.

Example 2 Using the same contact product as in Example 1, 2 l of toluene as a solvent and cyclopentadienyl titanium trichloryl 1 as a catalyst component were placed in a reaction vessel.
0.6 mole of aluminum and methylaluminoxane as an aluminum atom were added, and 3.6 l of a styrene monomer was added thereto at 20 ° C. to carry out a polymerization reaction for 1 hour.

After completion of the reaction, the product was washed with a hydrochloric acid-methanol mixed solution to decompose and remove the catalyst component. Then, it was dried to obtain 330 g of a styrene polymer (polystyrene).

Next, this polymer was subjected to Soxhlet extraction using methyl ethyl ketone as a solvent to obtain an extraction residue of 95 wt%. The weight average molecular weight of this extraction residue was 29,000.
0, number average molecular weight 158,000, melting point 27 ℃
Met. In addition, this polymer was confirmed to be polystyrene having a syndiotactic structure by analysis by nuclear magnetic resonance.

A film was prepared in the same manner as in Example 1 except that the styrene polymer thus obtained was used to prepare a foil type film capacitor.

(Comparative Example 1) A film was prepared in the same manner as in Example 2 except that the heat treatment temperature was set to 200 ° C, and a foil type film capacitor was manufactured.

(Comparative Example 2) A film was prepared in the same manner as in Example 2 except that fine particles were not added to prepare a foil type film capacitor.

Comparative Example 3 A foil type film capacitor having a capacitance value of about 0.047 μF was manufactured by using a polypropylene film having a thickness of 6 μm.

(Comparative Example 4) Using a polyethylene terephthalate film having a thickness of 6 μm, the capacitance value was about 0.04.
A 7 μF foil type film capacitor was manufactured.

(Comparative Example 5) Using a polyphenylene sulfide film having a thickness of 6 μm, the capacitance value was about 0.047.
A μF foil type film capacitor was manufactured.

The results of evaluation of various physical properties of the films prepared in Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Table 1 below.
The foil yield of the produced film capacitor is shown in Fig. 10 and the lead wire root is placed in a molten solder bath at 260 ° C.
The rate of change in electrostatic capacity after immersion for 2 seconds is shown in (Table 2).

[0043]

[Table 1]

[0044]

[Table 2]

In addition, the foil type film capacitors manufactured in Example 1, Comparative Example 3, Comparative Example 4, and Comparative Example 1 were
(Table 3) shows the transition of the short-circuit defect occurrence rate when a direct current voltage of 140 V is applied for 1000 hours in an atmosphere of 50 ° C.
With the transition of the rate of change of capacitance when 100 V is applied at a DC voltage of 100 V in an atmosphere of 60 ° C. and 95% relative humidity for 500 hours, the ambient temperature is changed in the range of −40 ° C. to 150 ° C. The changes in the rate of change in capacitance and changes in the dielectric loss tangent with respect to 20 ° C. are shown in Table 5.

[0046]

[Table 3]

[0047]

[Table 4]

[0048]

[Table 5]

As can be seen from the above results, the film capacitor according to this example has excellent heat resistance and electrical performance without deteriorating the workability of manufacture and its change with time is small.

Although the foil type film capacitor is used in this embodiment, it is obvious that the same effect can be obtained also in the vapor deposition type film capacitor.

[0051]

As is apparent from the above examples, the film capacitor of the present invention can be significantly improved by using a film made of a styrene polymer having a syndiotactic structure or its composition as a main dielectric. It has excellent heat resistance, electrical performance, and stability over time, which can sufficiently compensate the drawbacks of conventional film capacitors without increasing costs.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a film capacitor according to an embodiment of the present invention.

[Explanation of symbols]

 1 Dielectric film (SPS film) 2 Internal electrode (aluminum foil)

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Claims (1)

[Claims] 1. A main dielectric material is a styrene polymer having a syndiotactic structure or a composition thereof,
Weight average molecular weight 100,000-500,000, 23
A film capacitor comprising a biaxially stretched film having a heat shrinkage ratio of 7% or less at 0 ° C. for 10 minutes and a friction coefficient of 0.6 or less.