KR100242877B1 - Biaxially oriented polyester film for capacitor - Google Patents

Abstract

The present invention is a multi-layered polyester film mainly composed of polyethylene terephthalate, wherein the melt specific resistance of the polyester resin used in one outer layer (first outer layer) of the film is in the range of 5 to 50 M ohm and the other outer portion of the film The melt specific resistance of the polyester resin used in the layer (second outer layer) is 75 M ohm or more, and the ultimate viscosity of the polyester resins of the first outer layer and the second outer layer is in the range of 0.5 to 0.7 dl / g, 1 is a biaxially oriented multilayer polyester film for a capacitor, characterized in that the thickness ratio of the outer layer to the second outer layer is 1/3 or less, and the polyester film according to the present invention has thickness stability, winding property, deposition characteristics, and The slitting properties are good and show excellent dielectric loss properties.

Description

Biaxially Oriented Polyester Film for Capacitor

The present invention relates to a biaxially oriented polyester film for capacitors, specifically, in a multilayer polyester film containing polyethylene terephthalate as a main component, melting of a polyester resin used in one outer layer (first outer layer) of the film The resistivity is in the range of 5 to 50 M ohms and the melt resistivity of the polyester resin used in the other outer layer (second outer layer) of the film is 75 M ohm or more and the polyester resin of the first outer layer and the second outer layer It relates to a biaxially oriented multilayer polyester film for a capacitor, characterized in that the intrinsic viscosity is in the range of 0.5 to 0.7 dl / g and the thickness ratio of the first outer layer to the second outer layer is 1/3 or less.

The polyester film represented by polyethylene terephthalate has excellent mechanical properties, so it has good deposition properties and running characteristics in the deposition or slitting process, and shows stable running characteristics in the condenser manufacturing process. Comparable to the polyolefin film used, the dielectric constant value is larger than that of the polyolefin, and can be thinned down to a thickness of about 1 μm, which makes it possible to manufacture a small capacitor having a relatively large capacity. It is widely used.

However, there is a significant limitation in the temperature range of use, because the polyester film is not stable in temperature dependence of dielectric loss, especially because of its high temperature constraints, so that capacitors made of polyester film are used at high temperatures. This is impossible.

For example, when an AC voltage of 1 kHz is applied to a capacitor made of polyethylene terephthalate film, the dielectric loss value decreases with increasing temperature from room temperature to 80 ° C, but the dielectric loss value increases rapidly with temperature rise above 80 ° C. do. In fact, the temperature of 80 ℃ is somewhat unreasonable as the working temperature of the capacitor using polyethylene terephthalate film as dielectric, but in actual view, the actual capacitor has higher temperature than the surrounding temperature due to the generation of calories due to dielectric loss. This causes a surge in hereditary losses. In other words, as the dielectric loss of the capacitor increases, the amount of heat lost in the capacitor increases and the temperature rises, which in turn leads to a vicious cycle in which the dielectric loss of the capacitor is amplified. They deteriorate sharply.

For this reason, the maximum temperature of capacitors using polyethylene terephthalate films as insulation and dielectric materials is set at 80 ° C. At higher temperatures, the use of polyethylene terephthalate film capacitors is difficult and ceramic capacitors must be used. . However, since the ceramic capacitor is difficult to thin, it is difficult to increase the capacitance and becomes bulky in order to have the capacitance of the film capacitor.

However, in recent years, since electronic devices are required to have a smaller size and a smaller capacitor and a larger capacity, a high dielectric loss increase start temperature and a high maximum operating temperature are required for a polyethylene terephthalate film having a relatively high dielectric constant. .

On the other hand, the core of the polyester film production having excellent temperature characteristics of the dielectric loss is an inorganic compound or metal ions generated from the polymerization of the polyester resin in order to improve the processability including the running and winding properties of the polyester film, and In the transesterification reaction, the amount of the metal organic material used as a catalyst is limited.

The process of making a polyester film involves the step of polymer melt being extruded from a die and cast onto a casting roll, in which an electrostatic charge application wire is placed between the polymer melt and the die to stabilize the casting of the sheet. By increasing the adhesion between the sheet and the casting to thereby obtain a film having a uniform thickness and excellent mechanical properties.

The electrostatic application process draws electrons from the polymer melt by applying a positive voltage to the electrostatic application wire to make the melt sheet charged with positive charge (+). In addition, since the sheet charged with the positive charge (+) is electrically in close contact with the casting to which the negative voltage is applied, it is possible to manufacture a film of uniform thickness and excellent mechanical properties. If the insulation resistance is low in the sheet, the amount of charge becomes large at the time of electrostatic application, and the adhesion between the sheet and the casting is good.However, if the insulation resistance is high, the electrical characteristics including dielectric loss of the film are excellent, but the amount of charge is reduced at the time of electrostatic application This becomes small, resulting in uneven thickness and deteriorated mechanical properties. Therefore, in order to cast well, the insulation resistance of the polymer melt is lower, and the thickness of the film and the mechanical properties of the film are excellent, but the electrical properties including dielectric loss are deteriorated.

In order to solve the above problems, many studies have been conducted. For example, Japanese Patent Laid-Open No. 55-21157 attempts to improve the electrical properties by controlling the input amount of potassium compound and inorganic particles and the degree of crystallinity. Not enough yet. In addition, Japanese Patent Application Laid-Open No. 63-182351 uses polyethylene terephthalate as the main component and copolymerizes other polyethylene naphthalates and polycarbonates to improve the glass transition temperature of the polymer to improve dielectric loss at high temperature. In application, Japanese Patent Application Laid-Open No. 2-49309 has more than 97 mol% of the glycol component of 1,4-cyclohexanedimethanol component and more than 90 mol% of terephthalic acid to increase the dielectric loss surge. It is reported that the copolyester film to be used has a stable dielectric loss at 105 ℃ or more when used as a biaxially oriented film for a capacitor, but the supply of raw materials is not stable and is not practical due to the complexity of the manufacturing method.

Therefore, in the present invention to solve the above problems, the sheet on the application wire side has a low insulation resistance in the manufacture of polyester film has a large amount of electricity charged by the application wire increases the adhesion while the sheet on the casting roll side is high insulation By maintaining the resistance to improve the manufacturing processability of the polyester film, to provide a polyester film that maintains the thickness stabilization and improved the dielectric loss characteristics of the polyester within the range of winding, deposition characteristics, slitting characteristics also good For that purpose.

In order to achieve the above object, in the present invention, in the multilayer polyester film containing polyethylene terephthalate as a main component, the melt specific resistance of the polyester resin used in the first outer layer of the film is in the range of 5 to 50 M ohm, 2 The melt resistance of the polyester resin used in the outer layer is 75 M ohm or more, the intrinsic viscosity of the polyester resin of the first outer layer and the second outer layer is in the range of 0.5 to 0.7 dl / g and the first outer layer It provides a biaxially oriented multilayer polyester film for a capacitor, characterized in that the thickness ratio to the second outer layer is 1/3 or less.

Hereinafter, the present invention will be described in detail.

The polyester resin used for the multilayer film of this invention can be manufactured by polycondensing the acid component which has aromatic dicarboxylic acid as a main component, and the glycol component which has alkylene glycol as a main component. Specific examples of the aromatic dicarboxylic acid include dimethyl terephthalate, terephthalic acid, isophthalic acid, dimethyl-2,5-naphthalenedicarboxylate, naphthalenedicarboxylic acid, cyclohexanedicarboxylic acid, diphenoxyethanedicar Acid, diphenyldicarboxylic acid, diphenyletherdicarboxylic acid, anthracenedicarboxylic acid, α, β-bis (2-chlorophenoxy) ethane-4,4'-dicarboxylic acid, In particular, dimethyl terephthalate is preferable.

Specific examples of the alkylene glycol include ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, hexylene glycol and the like, and ethylene glycol is particularly preferable.

In the polyester of the present invention, 97 mol% or more of the repeating unit is made of ethylene terephthalate, and copolymerization is possible within the remaining mol%. Specific examples of the copolymerizable components include diol components such as diethylene glycol, propylene glycol, butanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, and 5-sodium sulforesorcin, and isophthalic acid and para-betaoxye. Dicarboxylic acid components such as methoxybenzoic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-dicarboxylic dikenyl, 5-sodium sulfoisophthalic acid, and polyfunctional acids such as trimellitic acid and pyromellitic acid Carboxylic acid.

The multilayer polyester film of the present invention has a first outer layer made of a polyester resin having a melt resistivity in the range of 5 to 50 M ohms and an intrinsic viscosity in the range of 0.5 to 0.7 dl / g, and a melt resistivity of at least 75 M ohms and extreme And a second outer layer made of a polyester resin having a viscosity in the range of 0.5 to 0.7 dl / g.

The polyester resin used for the first outer layer may be prepared by a transesterification method or a direct polymerization method, and may be either batch or continuous. When the polyester is produced by the transesterification method, there is no restriction on the transesterification reaction catalyst, and any conventionally known one can be used. For example, it can be suitably selected from alkali metal compounds (eg sodium or potassium compounds), alkaline earth metal compounds (eg calcium or barium compounds), cobalt compounds, zinc compounds, zirconium compounds and manganese compounds. The polymerization catalyst is also not limited, and may be appropriately selected from, for example, antimony, germanium and titanium compounds.

It is preferable to manufacture the polyester resin of the said 2nd outer layer of this invention by the direct polymerization method, and it is preferable not to introduce transesterification reaction catalysts, such as a metal organic substance.

The film for condenser of the present invention is subjected to the winding process of the device when the roll is wound or manufactured in the condenser, in order to ensure that the film has an appropriate friction coefficient and runability, and the capacitor after the winding has the appropriate impregnation characteristics and the stability of the capacitance In order to form irregularities on the surface of the film within the range of maintaining the characteristics of the capacitor, particles are added during polyester resin production.

The addition of particles can be achieved by an internal particle precipitation method in which particles are formed during the polymerization reaction and an external particle addition method in which inorganic or organic particles are introduced from the outside, and any method can be used in the present invention. In case of external input, the particles which can be added include calcium carbonate, silica, titanium dioxide, kaolin, mica, barium sulfate, calcium phosphate, alumina and other organic compounds which are insoluble in polyester. In the range which does not impair the object of the present invention, one or two or more kinds of particles may be appropriately selected and added. In addition, the particles are usually preferably dispersed and added to ethylene glycol, a dispersant may be used to increase the dispersibility of the particles in ethylene glycol.

The inorganic particles introduced to the second outer layer resin are appropriately selected and added within a range not impairing the object of the present invention.

When the melt specific resistance of the polyester resin used in the first outer layer is less than 5 M ohms, the insulation after manufacturing the film is insufficient, which is not preferable. If the melt ratio is larger than 50 M ohms, the electrostatic application is lowered to obtain a uniform film. I can't. In addition, the intrinsic viscosity of the polyester resin must be within the range specified above to exhibit uniform physical properties in the melt extrusion process.

In addition, the melt specific resistance of the polyester resin of the second outer layer should be 75 M ohm or more, more preferably 100 M ohm or more. It will lead to degradation of properties.

The multilayer film of the present invention is prepared by co-extrusion of the polyester resin for the first outer layer and the second outer layer manufactured as described above so that the thickness ratio of the first outer layer to the second outer layer is 1/3 or less. can do. Specifically, the polyester resin for use in each layer is first coextruded using a coextrusion feed block at a temperature in the range of 265 to 305 ° C. and cast by electrostatic application. At this time, the thickness of the produced sheet is to be in the range of 30 to 120 ㎛. The sheet cast by the electrostatic method is first stretched 3 to 6 times in the longitudinal direction of the film at a temperature in the range of 80 to 120 ° C. and then recooled to be 3 to 5 in the transverse direction of the film at a temperature in the range of 100 to 140 ° C. Redraw the boat. The obtained polyester film is heat treated at a temperature in the range of 180 to 240 ° C. for 3 to 15 seconds to obtain a biaxially oriented multilayer polyester film of the present invention having a thickness of the final film in the range of 1 to 15 μm.

The polyester coextrusion film prepared as described above exhibits excellent dielectric loss characteristics, which are preferable for use in a condenser, and has good electrostatic application characteristics in melt extrusion and casting processes, thereby obtaining a uniform thickness film.

The present invention will be described in more detail with reference to the following examples. However, the scope of the present invention is not limited only to the following Examples. The physical property measurement method used in the Example and the comparative example and the various performance evaluation methods of the produced film are as follows.

1) permittivity and dielectric loss

The dielectric constant and dielectric loss at room temperature were measured using a DETA apparatus from Polymer Laboratory (UK). The thickness of the sample film before measurement was calculated by the weight method, and aluminum or gold was coated on the sample to give contact stability between the electrode and the sample.

The rapid onset temperature of the dielectric loss measured the temperature (secondary increase temperature) at which the increase starts above 100 ° C.

2) melt resistivity

The polymer sample was vacuum dried at 150 ° C. for 2 hours to remove moisture in the film, and then melted at 275 ° C. for 2 hours, and 50 V was applied thereto. Two electrodes made of stainless steel of 1 cm 2 were arranged at intervals of 1 cm as the measuring electrodes, and the values after 2 to 3 seconds of electrostatic application were measured.

3) Ultimate viscosity

After melt | dissolving 0.12 g of polyester resins in 10 ml of o-chlorophenol solutions, intrinsic viscosity was measured at 35 degreeC using the Woostwald viscous tube.

4) Fairness of film and sheet

The fairness of the film was visually observed for the generation of longitudinal wrinkles and the state of the winding during the film winding after stretching, and the thickness of the film was measured with a micrometer and evaluated as a uniform degree. The fairness of the sheet was evaluated by visual observation of the uniform state of the melt discharged from the die.

Example 1

1) Preparation of First Polyester Resin

Dimethyl terephthalate and ethylene glycol were mixed in an equivalent ratio of 1: 2, 0.07% by weight of calcium acetate and 0.047% by weight of trimethylphosphate as a stabilizer were added as a transesterification catalyst, 0.25% by weight of calcium carbonate particles having an average particle diameter of 1.2 mu m and an average A polyethylene terephthalate monomer was prepared by adding 0.25 wt% of silica particles having a particle diameter of 1.8 μm. Then, polycondensation reaction was performed by adding 0.04% by weight of antimony trioxide as a polycondensation catalyst to prepare a polyethylene terephthalate resin having an intrinsic viscosity of 0.640 dl / g and a melt resistivity of 20 M ohm.

2) Preparation of Second Polyester Resin

Dimethyl terephthalate and ethylene glycol were mixed in an equivalent ratio of 1: 2, and 0.25 wt% of calcium carbonate particles having an average particle diameter of 1.2 mu m and 0.25 wt% of silica particles having an average particle diameter of 1.8 mu m were added to prepare a polyethylene terephthalate monomer. Then, polycondensation reaction was performed by adding 0.04% by weight of antimony trioxide as a polycondensation catalyst to prepare a polyethylene terephthalate resin having an intrinsic viscosity of 0.650 dl / g and a melt resistivity of 350 M ohm.

The first and second polyethylene terephthalate resins obtained as described above were melt-extruded at 290 ° C. to a thickness ratio of 1: 4 using a coextrusion feed block to form a two-layer sheet having a thickness of 80 μm, and then the film was formed at 90 ° C. After stretching 3.5 times in the longitudinal direction and stretching 4.0 times in the transverse direction of the film at 140 ° C., heat treatment was performed at 230 ° C. for 13 seconds to prepare a biaxially stretched two-layered polyethylene terephthalate film having a thickness of 5 μm.

The performance evaluation results of the resin and the film are shown in Table 1 below.

Comparative Examples 1 to 4

A biaxially oriented polyethylene terephthalate film was prepared by performing the same method as Example 1 but changing the melt ratio resistance, the ultimate viscosity, and the thickness ratio between the two layers of the first layer sheet and the second layer sheet, as shown in Table 1. The evaluation results are shown in Table 1 below.

Melt resistivity of the first layer (M ohm) Melt resistivity of the second layer (M ohm) Intrinsic viscosity of the first layer (㎗ / g) Intrinsic viscosity of the second layer (㎗ / g) Thickness ratio (1st layer / 2nd layer) Dielectric loss surge temperature (℃) Fairness Example 1 20 350 0.640 0.650 1/4 203 ◎ Comparative Example 1 18 - 0.620 - - 175 ◎ Comparative Example 2 23 65 0.620 0.620 1/4 184 ○ Comparative Example 3 18 320 0.630 0.630 1/1 184 ◎ Comparative Example 4 23 270 0.720 0.730 1/4 204 ×

◎: excellent, ○: good, ×: poor

As can be seen in Table 1, the polyester film according to the present invention shows good dielectric loss characteristics while good processability. Thus, the film of the invention is particularly suitable for use for capacitors.

Claims (2)

In a multilayer polyester film containing polyethylene terephthalate as a main component, the melt specific resistance of the polyester resin used in the first outer layer of the film is in the range of 5 to 50 M ohms and the polyester resin used in the second outer layer of the film. The melt resistivity is 75 M ohm or more, the ultimate viscosity of the polyester resin of the first outer layer and the second outer layer is in the range of 0.5 to 0.7 dl / g, and the thickness ratio of the first outer layer to the second outer layer is 1 / A multilayer biaxially oriented polyester film for capacitors, characterized in that 3 or less. The method of claim 1, And the polyester resin used in the second outer layer is produced by a direct polymerization method without the use of a metal catalyst.