JPH0747652B2 - Polyester film and capacitor using the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polyester film and a capacitor using the same as a dielectric.

[Conventional technology]

Conventionally, various polyester films and capacitors using the same have been known (for example, JP-A-63-182351 and JP-A-63-194318).

[Problems to be Solved by the Invention]

However, such a conventional polyester film has a larger dielectric absorption than polypropylene or polycarbonate, so when a capacitor using it as a dielectric is used, the power consumed in the dielectric is large and the cause of lowering the insulation resistance value is It was one.

It is an object of the present invention to improve the drawbacks of the conventional polyester film, and to provide a capacitor having a high insulation resistance value even at high temperature and excellent characteristics, and a film serving as a dielectric thereof.

[Means for Solving the Problems]

The polyester film of the present invention is a plastic film containing polyethylene terephthalate as a main component, and the melt specific resistance value of the plastic film is 1.0 × 10 ⁹
Ω · cm or more, and crystal size Xc (Å) by X-ray method
And the plane orientation index Xi satisfies the relational expression (Xc−22.0) × (Xi × 10 ³ −20.0) × 10 ⁻³ ≧ 1.20, and when the film is measured with a differential scanning calorimeter, it is 80 to 120 ° C. It is characterized by having an endothermic peak in the range.

Further, the capacitor of the present invention is characterized by using the above polyester film as a dielectric.

In the present invention, a polyester containing polyethylene terephthalate (hereinafter abbreviated as "PET") as a main component is used, and it is preferable that PET is contained in an amount of 75% by weight or more, preferably 80% by weight or more. If the PET component is less than the above range, the dimensional stability and mechanical properties that are characteristic of the film may not be sufficiently exhibited. Further, a polymer other than PET may be contained in the range of 25% by weight or less, preferably 20% by weight or less. Such polymers include polyarylate, polyethylene naphthalate, polyethylene α, β
-Bis (phenoxy) ethane 4,4 'dicarboxylate, polycarbonate and the like. In addition, antioxidants,
Inorganic or organic additives such as a heat stabilizer, a lubricant, an ultraviolet absorber, a nucleating agent and a surface protrusion forming agent may be appropriately added.

The polyester film of the present invention is a film in which the polymer containing PET as a main component is biaxially oriented, and the melt specific resistance value (hereinafter, simply referred to as “ρ”) at 280 ° C. of the film is 1.0 × 10 ⁹ Ω · cm or more, preferably 1.5 × 10 ⁹ Ω
・ It is more than cm. If ρ is less than the above value, the effect of improving the insulation resistance (hereinafter abbreviated as “IR”) of the present invention is small, which is not preferable. The upper limit of ρ is not particularly limited, but 1.0 × 10 ¹⁰ Ω ・ c
It is preferably m or less from the viewpoint of maintaining the moldability of the film.

The crystal size Xc (Å) and plane orientation index Xi by the X-ray method of the polyester film of the present invention need to satisfy the relational expression (Xc−22.0) × (Xi × 10 ³ −20.0) × 10 ⁻³ ≧ 1.20. And preferably satisfies the relational expression (Xc−22.0) × (Xi × 10 ³ −20.0) × 10 ⁻³ ≧ 1.25. If the above relational expression is not satisfied,
The IR improving effect, which is the object of the present invention, is small. The upper limit of the crystal size Xc is not particularly limited, but the crystal size Xc is preferably 80.0 Å or less, more preferably 75.0.
Å It is less than or equal to. If the crystal size Xc is too large, mechanical properties may deteriorate. The upper limit of Xi is not particularly limited, but it is preferably 9.0 × 10 ⁻² or less from the viewpoint of film forming stability.

The melt viscosity of the polyester film of the present invention is 1000 to 6000.
Poise (temperature 280 ° C., shear rate 200 sec ⁻¹ ) is preferable from the viewpoint of film formability.

The polyester film of the present invention shows an endothermic peak in the range of 80 to 120 ° C. when measured with a differential scanning calorimeter (hereinafter abbreviated as “DSC”). The temperature at which this endothermic peak appears is preferably 95 to 115 ° C. When the temperature where the endothermic peak appears is less than 80 ° C and when the endothermic peak does not appear at 120 ° C or less, the IR improving effect is not sufficient. When the endothermic peak exceeds 120 ° C., the flatness of the film is impaired and the commercial value is remarkably reduced, which is not preferable.

In addition, the polyester film of the present invention JIS-B-0601
Surface roughness Ra (cutoff: 0.25 mm) due to is 0.01 to 0.2 μ
It is preferably in the range of m.

The thickness of the polyester film of the present invention is not particularly limited, but it is preferably in the range of 0.5 to 30 μm.

The heat shrinkage rate of the polyester film of the present invention is not particularly limited, but it is preferable that the length direction of the film is in the range of 0.1 to 5% and the width direction is in the range of -1 to 5% at 150 ° C. for 30 minutes. .

The capacitor of the present invention can be manufactured by a known method such as a winding method or a lamination method. The electrodes may be either metal foil or a metal thin film formed by forming a metal on a dielectric film by a known method such as vacuum deposition or sputtering. Aluminum as a metal forming the electrodes,
Examples include, but are not limited to, zinc, tin, titanium, nickel and alloys thereof.

The capacitor of the present invention may have any shape, but may be of a type having a normal lead wire or a type having no lead wire and being directly soldered to the substrate surface (so-called chip capacitor). In addition, the capacitor of the present invention,
It can be used for both AC and DC applications.

Next, a method for producing the polyester film of the present invention will be described.

First, carboxylic acid having terephthalic acid as a main component or its alkyl ester and glycol having ethylene glycol as a main component are added in the presence of a catalytic metal compound such as calcium, magnesium, lithium or manganese element.
Perform esterification or transesterification at ~ 260 ℃.
After that, a catalyst compound and a phosphorus compound composed of antimony, germanium, titanium elements, etc. are added, and under high vacuum,
A polycondensation reaction is carried out at a temperature of 220 to 300 ° C. Examples of the phosphorus compound include phosphorous acid, phosphoric acid, phosphoric acid triester, phosphonic acid, and phosphonate, but are not particularly limited, and two or more of these phosphorus compounds may be used in combination. The amount of the additive of the above-mentioned catalyst compound is not particularly limited, but the ratio of the catalyst metal compound such as calcium, magnesium, lithium and manganese to the phosphorus compound is 0.5 ≦ (M / P) ≦ 1.5 (where M is The total number of moles of calcium, magnesium, lithium and manganese elements in the film, and P is the number of moles of phosphorus element in the film.) Are included so that ρ of the film is 1.0 × 10 ⁹
Desirable to be more than Ω · cm. The ρ of the film has the same value as the ρ measured in advance at the stage of the extruded polymer.

Further, at any stage from esterification or transesterification to polycondensation, if necessary, an antioxidant, a heat stabilizer, a lubricant,
An ultraviolet absorber, a nucleating agent, a surface protrusion forming agent, etc. are added.

The polycondensation polymer thus obtained is supplied to an extruder, melt-extruded from a slit-shaped die, and cooled and solidified to prepare an unstretched film.

Next, this unstretched film is biaxially stretched and oriented. As a stretching method, a sequential biaxial stretching method or a simultaneous biaxial stretching method can be used, but the sequential biaxial stretching method is particularly preferable for obtaining a polyester film satisfying the relational expression of the present invention.

The conditions for sequential biaxial stretching are not particularly limited, but after stretching 2.5 to 4.5 times in one direction, 3.
The range of 0 to 5.0 times is suitable for obtaining a polyester film satisfying the relational expression of the present invention.

The stretching temperature may be in the range of 70 to 130 ° C. Usually, the stretching speed is preferably in the range of 10 ^{3 to} 5 × 10 ⁴ % / min.

Next, this stretched film is heat-treated. The heat treatment conditions are a temperature of 190 to 250 ° C, preferably 210 to 240 ° C, and a time of 1
It is effective to obtain a polyester film satisfying the relational expression of the present invention by setting the time to 60 seconds.

Furthermore, winding this film on a roll and subjecting it to a reheat treatment at a temperature of 40 to 90 ° C for 12 hours to 4 weeks is effective for causing an endothermic peak to appear in the range of 80 to 120 ° C by DSC measurement. .

Next, a method for manufacturing the capacitor of the present invention will be described.

The film obtained as described above is used as a dielectric, and a metal foil or a metal thin film is used as a conductor to form a capacitor element by laminating or winding, but using a metal thin film as a conductor improves IR of the present invention. Great effect. As a method for forming the metal thin film in this case, a well-known vapor deposition method, sputtering method, or the like can be used. In particular, the thickness of the dielectric film is 1.0 to 5
The most preferable method for obtaining the effects of the present invention is to use a vapor-deposited film having a thickness of 100 μm and a vapor-deposited film thickness of 100 to 5000Å to obtain the effect of the present invention.

Next, this capacitor element is pressed by a conventional method,
Heat treatment, end face sealing and lead wire mounting are performed to make a capacitor.

Although the present invention is characterized by the above capacitor, the film may be subjected to a known corona discharge treatment, and also for the purpose of imparting adhesiveness, heat sealability, moisture resistance, lubricity, surface smoothness, and the like. Multi-layered polymer, organic and / or
Alternatively, it may be used in a form coated with an inorganic composition. Also,
The capacitor of the present invention may be impregnated with insulating oil or the like to be used as a so-called oil-immersed capacitor.

Next, a method of measuring characteristics and a method of evaluating effects used in the present invention will be described.

(1) Crystal size Xc and plane orientation index Xi by X-ray method Wide-angle X-ray diffraction measurement was performed on a film sample by an X-ray diffractometer (manufactured by Rigaku Denki Co., Ltd.) by a reflection method using CuKα rays as an X-ray source. It was The crystal size Xc was calculated from the following formula from the measurement result of the (100) plane. Where k is a constant, k = 1.0,
λ is the X-ray wavelength, θ is the diffraction peak angle of the (100) plane, and β is the half width (radian) of the peak.

Xc = kλ / β cos θ The plane orientation index Xi was determined by the ratio of the intensity of the (10) plane to the intensity of the (100) plane, I (10) / I (100).

(2) Melt specific resistance ρ Opposite electrode (electrode area:
25 cm ² each, empty insulation resistance between the electrodes: 10 ¹² Ω or more), and the sample is extruded at 280 ° C. Next, a direct current of 5 kV is applied between the electrodes, and the current I (mA) flowing at that time is obtained. 280 ° C
Ρ of is calculated from the following equation.

ρ (Ω · cm) = 1.25 × 10 ⁸ / I (3) Measurement of endothermic peak by differential scanning calorimeter Heat flux differential scanning calorimeter (“DSC-50” manufactured by Shimadzu Corporation) was charged with 10 mg of sample, and the temperature was 10 ° C / The endothermic peak was measured while the temperature was raised from 25 ° C to 300 ° C in minutes. Compared with the height of the endothermic peak of Tm that appears in the range of 220 ℃ to 280 ℃, 80 ℃ to 120 ℃
The temperature of an endothermic peak having a height of 0.3% or more in the range of ℃ was read. When it was less than 0.3%, no endothermic peak was defined.

(4) Insulation resistance (IR) characteristics of the capacitor Put the capacitor (capacity 1.5μF) in an oven at a temperature of 85 ° C and measure the resistance value after 100 minutes of voltage application at 100V with a super insulation meter (made by HP).
Was used for measurement. In addition, the measurement was carried out for each of 100 pieces, and the average value was obtained.

(5) Intrinsic viscosity This is a value measured at 25 ° C using o-chlorophenol as a solvent.

(6) Metal analysis in film Quantification of elements such as calcium, magnesium, lithium and manganese in the film was measured by an atomic absorption method,
The phosphorus element was measured by a colorimetric method.

〔Example〕

Example 1 (1) Preparation of Film of the Present Invention 100 parts by weight of dimethyl terephthalate, ethylene glycol 7
0 parts by weight, using 0.09 parts by weight of calcium acetate as a catalyst, a transesterification reaction is carried out by a conventional method. 0.1 part by weight of a particle diameter of 1.2 μm) was added and polycondensed by a conventional method to obtain a polymer pellet having an intrinsic viscosity of 0.64.

Then, the pellets were vacuum dried at 180 ° C. for 4 hours, fed to an extruder, melt-extruded at 280 ° C., and wound on a cooling drum at 60 ° C. to prepare an unstretched sheet.

With strength, this unstretched sheet was stretched 3.8 times in the longitudinal direction at 95 ° C. This stretching was carried out with a peripheral speed difference between the two sets of rolls, and the stretching speed was 10,000% / min. Using a stenter, this uniaxially stretched film was stretched at 105 ° C in the width direction at a stretching speed of 2
It was stretched 4 times at 500% / min, and heat-treated at 230 ° C. for 10 seconds under a constant length to obtain a biaxially oriented film having a thickness of 1.5 μm.

Next, this film was wound into a roll and subjected to reheat treatment for 10 days in an oven kept at 70 ° C.

Ρ measured at the time of melt extrusion of this film is 1.60 × 10
It was ⁹ Ω · cm. The crystal size Xc was 65.3Å and the plane orientation index Xi was 0.065. Further, in DSC, an endotherm having a peak at 104 ° C. was measured (film A).

(2) Preparation of Capacitor Set the film obtained in (1) above in a vacuum evaporation system,
Aluminum was continuously vapor-deposited to form a vapor-deposited film having a film resistance of 3Ω / □ on the film. The vapor-deposited film was slit, and a capacitor element was produced by applying it to an element winding machine, and further, end faces were sealed and lead wires were attached by a conventional method to produce a capacitor (capacitor A) (capacitor A).

(3) Evaluation 85 ℃ for 1000 capacitors created in (2) above
IR was measured. This average value was 8.3 × 10 ² MΩ, which was good (Table 1).

Examples 2 to 4, Comparative Examples 1 to 4 A capacitor (Example 2) and a roll-shaped film produced in exactly the same manner as in Example 1 except that the heat treatment temperature after stretching was changed to 210 ° C. A capacitor (Example 3) prepared in exactly the same manner as in Example 2 except that reheat treatment was carried out at 0 ° C. for 3 weeks, and trimethyl phosphate was added to 0.3
The capacitor (Example 4) produced in exactly the same manner except that the weight part was used was good in the IR characteristics as shown in Table 1.

However, in Example 1, a film (Comparative Examples 1 to 3) in which the film production conditions such as the heat treatment temperature after stretching, the heat treatment time, the reheat treatment temperature of the roll-shaped film, and the time were changed,
A capacitor made by using a film having a different melting specific resistance by changing the metal / phosphorus ratio in the film (Comparative Example 4) has a characteristic that the film that is a dielectric is one of the claims of the present invention. Since the requirements were not met, a capacitor with improved IR characteristics could not be obtained.

[Effect of the invention] The polyester film of the present invention contains PET as a main component,
Moreover, since the melting specific resistance, crystal size, plane orientation state, and DSC characteristics are optimized, the IR characteristics are improved.

The fact that this IR characteristic is good means that the dielectric has a high insulating property, and is particularly suitable for a capacitor used in a high voltage circuit. Further, the film can be used not only for capacitors but also for cables, motors, transformers, and other electrical insulation applications.

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Claims (2)

[Claims] 1. A plastic film containing polyethylene terephthalate as a main component, which has a melting specific resistance of 1.0 × 10 ⁹ Ω · cm or more and a crystal size Xc (Å) by an X-ray method. And the plane orientation index Xi satisfies the relational expression (Xc−22.0) × (Xi × 10 ³ −20.0) × 10 ⁻³ ≧ 1.20, and when the film is measured with a differential scanning calorimeter, it is 80 to 120 ° C. A polyester film having an endothermic peak in the range. 2. A capacitor using the polyester film according to claim 1 as a dielectric.