JPH0249309A - Biaxially oriented polyester film for capacitor - Google Patents

Abstract

PURPOSE:To raise the max. service temp. and increase the electrostatic capacity by constituting over a certain amount of glycol component from 1.4-cyclohexane dimethanol, and over a certain amount of acid component from terephthalic acid. CONSTITUTION:A biaxially oriented polyester film for capacitor is a one fixed thermally. Over 97mol% glycol component of this polyester is 1.4-cyclohexane dimethanol, and over 90mol% acid components consist of terephthalic acid. Concerning the temp. dependency of dielectric tangential, in particular, the rising temp. at high temp. shifts to the high temp. side compared with that of polyethylene phthalate, so that a capacitor using this film can have a higher set max. service temp. Also the dielectric factor is in the same degree as polyethylene terephthalate, and biaxial stretching makes it thinner to several mums, so that capacitor using this film can have a large electrostatic capacity while remaining small-sized.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a biaxially oriented polyester film for capacitors having excellent electrical properties. , 6. [Prior art and problems to be solved by the present invention] Currently, biaxially oriented polyethylene terephthalate is widely used as an insulating material and dielectric material for capacitors. This is because polyethylene terephthalate can be made as thin as about 1 μm and has a dielectric constant (ε) of about 3. This is due to the fact that it is larger than olefin, and also because it has the advantage of being able to make a capacitor with a relatively large capacity compactly.

However, its operating temperature range is limited by the dielectric loss tangent (tan
Since the temperature dependence of δ) is large, restrictions are particularly severe on the high temperature side. I with polyethylene teletumerate film
d/K) (When an alternating voltage of z is applied, the temperature rises from room temperature to
Tan δ gradually decreases as the temperature rises up to about 0.degree. C., but after exceeding tro'c, tan δ rapidly increases as the temperature rises.

As the dielectric loss factor of a capacitor increases, as tan δ increases, the capacitor dissipates more energy as heat, and the capacitor generates heat, further increasing tan δ.

As a result of this vicious cycle, the capacitor runs out of control, eventually leading to thermal damage. For this reason, the maximum operating temperature of capacitors using polyethylene terephthalate film as an insulating material/dielectric material is set at about 0.degree. Therefore, it is difficult to use a polyethylene terephthalate film capacitor at a temperature higher than this, and a ceramic capacitor or the like must be used. However, it is generally difficult to make ceramic capacitors thin and their capacitance is small, and compared to capacitors with a film-wrapped structure, they require a larger volume to provide the same capacitance. In recent years, as electrical equipment has become smaller, there has been a demand for capacitors that are smaller, have higher capacitance, have a higher tanδ start-up temperature, and have a higher maximum operating temperature. A material that satisfies these requirements was previously unknown.

[Means to solve all problems]

The present inventors have discovered that a certain polyester film is useful as a capacitor film, and have completed the present invention.

That is, the gist of the present invention is that the intrinsic viscosity is 0. A heat-set polyester film having a diameter of 5 or more,
The glycol component of the polyester has a mole ratio of 77 or more/
, F-cyclohexane dimetatool, a biaxially oriented polyester film for a capacitor, characterized in that the mole fraction of the acid component is terephthalic acid.

The present invention will be explained in detail below.

The polyester film of the present invention must be composed of cyclohexane dimetatool with a glycol component of at least 97 mol, preferably at least qg mol, more preferably at least qq mol. If it is less than 100%, the rise temperature of tan δ cannot be shifted to a higher temperature side than that of polyethylene terephthalate film, and the heat shrinkage rate and strength of the film are also adversely affected. In addition, as the remaining glycol component of 3 moles or less, for example, ethylene glycol, propylene glycol, U-butanediol, etc. can be used.

In the present invention, the ratio of the cis isomer to the trans isomer of cucyclohexanedimethanol is not particularly limited, but is preferably in the range of cis isomer/trans isomer=da/6 to 0710.

In addition, it is necessary that at least 90 moles of the acid component of the polyester film of the present invention, preferably at least 93 moles, more preferably at least 7 moles, be composed of terephthalic acid, and less than 90 moles. In some cases, as in the case of glycol components, the rise temperature of tan δ cannot be shifted to a higher temperature side than that of a polyethylene terephthalate film, and the physical properties of the film are also adversely affected. Further, as the remaining acid component having a molar ratio of 10 or less, examples include aromatic dicarboxylic acids such as isophthalic acid, co-, 6- or co-, khu-naphthalene dicarboxylic acid, t14'-biphenyldicarboxylic acid, p-hydroxybenzoic acid, etc. Aromatic hydroxy acids can be used.

For the polymerization of cyclohexane dimethylene terephthalate, a known polyester melt polymerization method can be used, but in order to minimize thermal deterioration, a combination of melt polymerization and solid phase polymerization is used to achieve the desired polymerization. It is also possible to adopt the method of

In particular, when attempting to obtain a polymer having an intrinsic viscosity of o or g o or more, which will be described later, it is preferable to use a method in which solid phase polymerization is used in combination.

The degree of polymerization of the film of the present invention is such that its intrinsic viscosity is 3 in a solution of phenol:tetrachloroemene l:/(weight ratio).
When measured at 0° C., o, tis or more is reed, preferably 0.65 or more. If the intrinsic viscosity is less than O,aS, it is impossible to obtain a biaxially oriented film due to poor stretchability. Be appropriate.

The polyester film of the present invention can contain fine particles inert to polyester, if necessary. For example, inorganic or organic fine particles, specifically kaolin, Merck, silicon dioxide, calcium carbonate, lithium fluoride, titanium dioxide, zeolite, calcium terephthalate, highly crosslinkable It is also possible to contain fine particles such as molecules. In addition, the method of incorporating these fine particles can be the known method conventionally used for polyethylene terephthalate films, and the average particle size and content should be within a range that does not impair the electrical properties of the film for capacitors. Can be selected arbitrarily.

Additionally, known additives such as stabilizers, antioxidants, lubricants, etc. can be blended into the polyester film of the present invention, but these compounds do not significantly reduce the electrical properties as in the case of containing fine particles. , the amount added is required.

Next, film forming conditions will be specifically explained, but the present invention is not limited to the following film forming conditions. Drying of the polymer chips can be carried out at a temperature of /20 to /000 for about 3 to 3 hours.

Polymer chips that have undergone solid phase polymerization and have a high degree of crystallinity can be sufficiently dried in 5 hours at 720°C. The extrusion temperature varies slightly depending on the polymer composition, but the extrusion temperature is
It is best to choose within the range of ~3/, 5'C. In addition, when forming the sheet into a sheet, it is preferable to use a so-called electrostatic adhesion method, in which the sheet is cooled and solidified while being brought into close contact with the casting drum. In particular, this electrostatic adhesion method is often required in the case of a polyester whose composition is close to 100% of zone chlorohexanedimethanol and terephthalic acid.

The unstretched film thus obtained is subjected to the next stretching step. The stretching method may be any known sequential biaxial stretching, simultaneous biaxial stretching, or a combination thereof. The preferred range for the stretching temperature is 90~i3o'G. At a lower temperature, whitening and uneven stretching are not likely to occur; at a higher temperature, orientation does not proceed and the thickness is uneven. It becomes more likely to occur. A more preferable stretching temperature range is 70
0 to 20°C, which makes it suitable for use as a film for capacitors. ;-/5μm
A film having a certain thickness can be stably obtained. The stretching ratio is set to 3.0-t, 0 times, preferably 3.3-g, 3 times in the longitudinal direction, and 3.0-s, o times, preferably 3.3-Lj times in the transverse direction. Good. Moreover, these magnifications can be achieved not only by stretching to the stretching ratio set in the - stage, but also by dividing the stretching ratio into two or more stages and performing multi-stage stretching.

The film thus biaxially stretched is fed into a heat setting zone and heat set. The heat fixing is preferably carried out by a so-called tenter method in which both ends of the film are held with clips and passed through a heating zone. Further, when heat-setting is performed using a tenter, the inside of the tenter may be divided and heat-setting may be performed in multiple stages, or multi-stage heat-setting may be performed using one or more tenters. Further, in order to obtain a film with a heat shrinkage rate suitable for the intended use, relaxation treatment may be performed in the longitudinal and/or transverse directions, or conversely, tentering may be performed.

In the present invention, the heat setting of such a biaxially oriented film is usually carried out at a temperature higher than or equal to iso°C and lower than the film melting point, preferably between /gθ and
By carrying out the heating in the range of -5θ°C for 7 to 720 seconds, a film for capacitors having excellent electrical properties can be obtained.

When the heat setting temperature is lower than iso° C., the heat shrinkage rate of the film increases, which is not preferable. The above heat fixing temperature is
It affects the rise temperature of tan δ and the absolute value of tan δ. Heat fixing temperature is high, for example Yuko 0-25
When the temperature is 0°C, the absolute value of tanδ from room temperature to tanδ rise temperature can be kept low;
The rising temperature of δ is slightly lower. Conversely, if the heat fixation temperature is low, for example /gO-210°C, tan
The rising temperature of δ can be shifted to the high temperature side, but from room temperature to ta
The absolute value of tan δ up to the n δ rise temperature becomes slightly larger. In the present invention, the heat setting temperature can be appropriately selected from the above-mentioned range according to the temperature dependence of electrical characteristics required of the capacitor.

For capacitors that are frequently used and where the tan δ rise temperature is important, we provide a film with a low heat setting temperature, and for capacitors where tan δ near room temperature is important, we set a higher heat set temperature. A film can be provided.

〔Example〕

Hereinafter, the present invention will be explained in more detail using actual winding examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof.

Incidentally, the measured values described in the examples were obtained by the measuring method shown below.

(1) Intrinsic viscosity [η] Polymer or film: 10orr of mixed solvent of phenol/tetrachloroethane = ro/go (weight ratio)
t: Measured at 30°C. At this time,
The Hqggins constant is independent of the polymer composition, and all -
Calculate the intrinsic viscosity by setting it as 0.33.

(2) Thermal shrinkage rate (correspondence) Calculated using the following formula by heat-treating in a 150° C. atmosphere for 5 minutes in a tension-free state and measuring the length of the sample before and after that.

(3) Dielectric loss tangent/tan δ (chi) Aluminum was vacuum-deposited on both sides of a sample film to form a main electrode, a counter electrode, and a guard electrode, thereby preparing a measurement sample. Manufactured by Ando Electric Co., Ltd., thermostat (To-9) and electrode (SE
-70), set all samples for measurement, and
! ! Avtoma 1cCapacj, tance
The tanJ'ff at the Bridge ('IkkoA)/ was measured at a frequency of KHz. In addition, the temperature of the constant temperature bath was raised at a rate of 2° C./2 m, and the temperature at which tan δ rose was measured.

(4) Dielectric constant/ε Using device 2 similar to the dielectric loss tangent measurement, at 3°C! r O%
The dielectric constant at RH was measured.

(5) Evaluation of film breakability during film formation When an amorphous sheet is longitudinally stretched and then laterally stretched, the situation in which the film breaks during stretching or heat setting in a horizontal stretching machine (tentter) is ranked as follows: Judgment and evaluation were made.

Rank ○: Good productivity with almost no film breakage Rank Δ: Occasional film breakage occurs and productivity is poor.

Ranks: Always breaks and has no productivity.

Actual example 1 Using 97 moles of terephthalic acid as the dicarboxylic acid component, 3 moles of isophthalic acid, 100 moles of cucyclohexane dimetatool as the glycol component, and adding 0.06 moles of titanium oxide to the acid component as a catalyst. hand,
Esterification was carried out by heating in a polymerization tank while stirring.

Here, silica with an average particle size of O.S μm was added as a lubricant so that it became 0.3 wt% in the polymer, and then polycondensation was performed to obtain % Cvl = 0. A polycyclohexane dimethylene terephthalate copolymer of A5 was obtained. After this polymer was made into chips, solid phase polymerization was carried out under a nitrogen stream to finally obtain a polyester having [η]=7.05.

After drying this polyester, it was melt-extruded at 305° C. and cooled onto a casting drum maintained at UO° C. using an electrostatic adhesion method to obtain an unstretched film of 100 μm. This unstretched film was brought into contact with a metal roll adjusted to 100° C. and preheated, and then stretched 3.7 times in the longitudinal direction between rolls having different circumferential speeds while being irradiated with an infrared heater. Next, I introduced this film to the tenter and /I! r℃
The film was stretched 3.9 times in the transverse direction. Furthermore, within the same tenter,
Heat setting was performed at 2 J O'C to obtain a biaxially oriented film with a thickness of about 7 μm. (Film melting point, 2g, 9°C) The properties of this film are shown in Table 7.

Example In Example 1, the dicarboxylic acid component was replaced with 1 terephthalic acid.
00%, melt polymerization and solid phase polymerization were carried out in the same manner as in Example. J-7,9L-cyclosan dimethylene terephthalate was obtained. ([W]=0.T O) A biaxially oriented film with a thickness of about 7 μm was obtained in the same manner as in Example 1 except that the extrusion temperature of this polyester was 3 is°C. Various properties of this film are shown in Table 1.

Example 3 A biaxially oriented film with a thickness of about 7 μm was obtained in exactly the same manner as in Example 1, except that the heat setting temperature was 1 tro°C. Table 7 shows the properties of this film.

Comparative Example 1 Polyethylene terephthalate was subjected to melt polymerization and solid phase polymerization according to conventional methods to obtain a polyester with [η]=o, tro. Using this, the same procedure as in Example 1 was carried out except that in Example 1, the extrusion temperature was set to xqo°C, the longitudinal stretching preheating roll fg was set to 2°C, and the transverse stretching temperature was set to 705°C.
A micrometer biaxially oriented film was obtained. Various properties of this film are shown in Table 1.

Comparative Example In Example 1, a poly-barrycyclohexane dimethylene terephthalate copolymer was obtained in the same manner as in Example 1, except that the dicarboxylic acid component was 4 moles of terephthalic acid and 4 moles of isophthalic acid. ([η”l = 7
．． o o) Using this polyester resin, in Example 1, the extrusion temperature was 300°C and the preheating roll for longitudinal stretching was
A biaxially oriented film with a thickness of about 7 μm was obtained in the same manner as in Example except that the temperature was 3° C. and the transverse stretching temperature was 110° C. Various properties of this film are shown in Table 1.

Comparative Example 3 The polyester resin used in Example 1 and polyethylene terephthalate were blended at a weight ratio of 3.6 and then melt-extruded into pellets. ([η]
=o, ql) Using this resin, sheeting, stretching and heat setting were performed under the same conditions as in Comparative Example 3 to obtain a biaxially oriented film with a thickness of 7 μm. When this film was measured by DSC, the peak corresponding to the melting point of polyethylene terephthalate completely disappeared, confirming that the blended λ polyesters were randomized. Various properties of this film are shown in Table 1.

Comparative Example q A polyester resin with [η] = O, S S was obtained by shortening the melt polymerization time in Example/ without performing solid phase polymerization. Using this resin, film formation and heat setting were carried out in the same manner as in Example 1 to obtain a biaxially oriented film with a thickness of about 7 μm. Various properties of this film are shown in Table 1.

〔Effect of the invention〕

Does the biaxially oriented polyester film for capacitors of the present invention have better electrical properties than the biaxially oriented polyethylene terephthalate film that has been widely used as an insulating material and dielectric material for capacitors? have. In particular, regarding the temperature dependence of the dielectric loss tangent, the rise temperature at high temperatures is 0 to 30% higher than that of polyethylene terephthalate.
Since the temperature is shifted to the high temperature side by about .degree. C., the maximum operating temperature of a capacitor using the film of the present invention can be set high. In addition, the dielectric constant is almost the same as that of polyethylene terephthalate, and it can be made as thin as a few μm by biaxial stretching. The industrial value is high.

Procedural amendment 1 Indication of the case 1932 Patent Application No. 1986 = 14 2 Name of the invention Biaxially oriented polyester film for capacitors 3 Person making the amendment

Claims (1)

[Claims] (1) A heat-set polyester film having an intrinsic viscosity of 0.45 or more, in which 97 mol% or more of the glycol component of the polyester is 1,4-cyclohexanedimmenol and 90 mol% of the acid component A biaxially oriented polyester film for capacitors, characterized in that the above is composed of terephthalic acid.