JPH0770420B2 - Biaxially stretched polyester film for capacitors - Google Patents

Description

TECHNICAL FIELD The present invention relates to a film for capacitors having excellent electric characteristics and sliding properties, and more particularly to an ultrathin film for capacitors having excellent electric capacity and withstand voltage when used as a capacitor. .

[Problems to be solved by conventional technology and invention]

Polyester film is widely used in industry due to its excellent physical and chemical properties. In particular, biaxially stretched polyethylene terephthalate film is widely used as a film for capacitors because it is superior to other films in terms of elastic modulus, flatness, electrical characteristics and chemical resistance.

On the other hand, in recent years, the capacitor element has been in the direction of becoming thinner, lighter, shorter and smaller. Specifically, by thinning the dielectric layer, the surface area per unit volume is increased, the distance between the electrodes is reduced, and the electric capacity is increased. Indispensable for making the capacitor element lighter, thinner, shorter, and smaller is to make the film thinner. Conventionally, those having a thickness of 2 μm to 6 μm have been mainly used for capacitors, but for the above purpose,
The demand for films below 2 μm is currently increasing.

As the film becomes thinner, various problems arise in the film manufacturing process and the capacitor manufacturing process. Also, in terms of physical properties, new problems will arise.

First of all, the problem of film slippage is raised. Generally, for the purpose of improving the handling workability of the film in the film manufacturing process and processing process, inactive inorganic or organic fine particles are usually present in the film to impart appropriate irregularities to the film surface. . This unevenness is affected not only by the vicinity of the film surface but also by the particles inside the film, depending on the particle size of the fine particles, so as the film thickness decreases, the film roughness decreases,
The slipperiness deteriorates. For this reason, workability is lowered, and especially winding property is deteriorated, so that film formation becomes impossible in some cases.

Another problem is that irregularities on the film surface cause gaps between the films, which reduces the electric capacity. There is a difference Δd between the film thickness of the 10-sheet micrometer method film and the weight method film as an index for knowing the amount of decrease in the electric capacity. The large Δd means that the gap between the films is large and the decrease in the electric capacity is large. In order to make a capacitor with good characteristics, it is desirable that this Δd be small.

The solutions to the above two problems are in conflict. That is, in order to improve the slipperiness for improving the workability, it is sufficient to increase the surface irregularities and increase the roughness, but if the roughness is increased, Δd is increased and the electrical characteristics are deteriorated. In addition, if Δd is reduced and the roughness is reduced for the purpose of improving the electrical characteristics, the workability is deteriorated.

Therefore, ultra-thin films could not be obtained in the past without sacrificing either slipperiness or electrical properties.

By the way, the method of making particles exist in the film can be roughly divided into two. One of the methods is a method called addition method, which is to add kaolin, silica, talc, calcium carbonate, calcium phosphate, etc. as they are or after making them into fine particles, and then adding them to the polyester reaction system, molding and the like. The method of adding inactive inorganic particles to these polyesters can control the particle size and amount of fine particles, so that the results are reproducible, but unnecessary coarse particles are often mixed. In order to remove the coarse particles, a classification operation and a crushing operation as a pretreatment thereof are required if necessary, which makes the operation complicated.

Moreover, even if such an operation is performed, it is inevitable that coarse particles are mixed. The presence of coarse particles or secondary particles due to agglomeration is particularly fatal for a film for capacitors and adversely affects withstand voltage characteristics and other electrical characteristics.

Another method compared with the addition method is a method called a precipitation method, in which a catalyst such as a calcium or lithium compound used in a transesterification reaction is finely inert to a polyester production reaction system in the presence or absence of a phosphorus compound. The particles are deposited as fine particles.

When it is attempted to improve the slidability by using the precipitated inactive fine particles, generally, the deposited particle diameter and the amount of the particles are easily changed, and it becomes difficult to control the slidability. In addition, there is a drawback that the slipperiness is generally poorer than that of the addition method and that the original slipperiness is not given when recycled.

As described above, if an attempt is made to make a film for an ultra-thin capacitor using the above-mentioned inert fine particles, there is a problem regardless of whether the film is an addition system or a precipitation system, and a satisfactory film cannot be obtained.

[Means for solving problems]

In view of the above circumstances, the present inventors have conducted intensive studies on a biaxially stretched film for capacitors having both excellent electrical properties and sliding properties, and as a result, contain a specific amount of silica particles having specific properties by a specific production method. The present inventors have found that a biaxially stretched film in which the number of protrusions and Δd of the film formed from the polyester are in a specific range have excellent properties for use as a capacitor, leading to the present invention.

That is, the gist of the present invention is to obtain an average particle size of 0.01 to 3.0 μm obtained by a hydrolysis reaction and a condensation reaction of an alkoxysilane.
Containing substantially amorphous and spherical silica particles of 0.001 to 5% by weight, and the number of projections on the film surface is 1.0 × 10 ³ / mm ²
The biaxially stretched polyester film for capacitors is characterized in that the difference Δd [μm] between the film thickness of the 10-layer micrometer method film and the weight method film satisfies the following expression (1).

0.1 ≦ Δd ≦ 0.4 (1) The present invention will be described in more detail below.

The polyester referred to in the present invention means an aromatic dicarboxylic acid such as terephthalic acid, isophthalic acid, naphthalene-2,6-dicarboxylic acid, or an ester thereof, and ethylene glycol, diethylene guaycol, tetramethylene glycol, neopentyl glycol, etc. It is a polyester that can be obtained by polycondensing such a glycol component.

This polyester can be obtained by directly polycondensing an aromatic dicarboxylic acid and glycol, or by subjecting an aromatic dicarboxylic acid dialkyl ester and a glycol to transesterification and then polycondensing, or by polycondensing an aromatic dicarboxylic acid diester. Can also be obtained by the method.

Typical examples of such a polymer include polyethylene terephthalate and polyethylene-2,6-naphthalate. This polymer may be a homopolymer or may be a copolymer of a third component. In any case, in the present invention, a polymer having 80 mol% or more of ethylene terephthalate units and / or ethylene-2,6-naphthalate units is preferable.

The spherical silica fine particles used in the present invention are obtained by a hydrolysis reaction and a condensation reaction using an alkoxysilane as a starting material and an amine catalyst.

The alkoxysilane compound is a compound represented by (CnH _{2n + 1} O) ₄ Si ... (n = 1 to 8), and specific compounds include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane and the like. Compounds are preferably used. As the hydrolysis reaction and condensation reaction catalyst, an aqueous ammonia solution, trimethylamine, tetraethylammonium aqueous solution, urea or the like can be used, but an aqueous ammonia solution is preferable.

In the present invention, the spherical silica fine particles obtained by the hydrolysis and condensation method of alkoxysilane are characterized in that they are spherical in shape and have very uniform particle diameters. That is, the particle size distribution of the particles is determined by an electron micrograph, and the number and volume of the respective particle sizes are integrated from the larger one, and the respective particle sizes showing 10% and 90% of the integrated volume are d ₁₀ and d ₉₀ , respectively. d
The value of ₁₀ / d ₉₀ ] is preferably in the range of 1.1 to 2.7.

More preferably, the value of [d ₁₀ / d ₉₀ ] is in the range of 1.0 to 1.6.

When the value of [d ₁₀ / d ₉₀ ] exceeds 2.7, it means that the particle size distribution is broad, which is not preferable because it becomes difficult to control the surface roughness of the film and the number of coarse particles increases.

It is understood that the film for capacitors, which has a good sliding property and a small Δd and an excellent electric property, can be obtained due to the sharpness of the particle size distribution.

The average particle size of the spherical silica fine particles used as fine particles in the present invention is required to be 0.01 to 3.0 μm, preferably 0.05 to 3.0 μm, and more preferably 0.1 to 2.0 μm. If it is less than 0.01 μm, the effect of improving the slipperiness of the film is not sufficient. If it exceeds 3.0 μm,
The surface roughness of the film becomes too large, and Δd becomes large, so that the electrical characteristics are deteriorated, which is not preferable.

The content of spherical silica fine particles in the polyester film needs to be 0.001 to 5% by weight, preferably 0.01 to 3.0% by weight, and more preferably 0.05 to 2.0% by weight. When the content of the spherical silica fine particles in the polyester film is less than 0.001% by weight, the effect of improving the slipperiness of the obtained film is insufficient, and when it exceeds 5% by weight, the surface roughness of the film becomes too large. However, the capacity is reduced, and the probability that unnecessary coarse particles contained in a very small amount are present in the film is increased, which shortens the life of the capacitor, which is not preferable.

The spherical silica fine particles used in the present invention have an extremely sharp particle size distribution and are excellent in dispersibility in ethylene glycol, and thus do not require a special dispersion treatment or classification treatment, and moreover, pass through a filter at the time of slurry overtreatment. The property is also extremely excellent.

The spherical silica fine particles used in the present invention can be added to the polyester at any stage in the polyester production process, but it is preferable to add them after the transesterification or esterification reaction and before the polycondensation. . or,
It is also possible to prepare a masterbatch containing spherical silica in a high concentration in advance and appropriately dilute it during extrusion. A publicly known method can be adopted for the polycondensation of the polyester. For example, one or more antimony compounds, germanium compounds, titanium compounds and the like are used as a catalyst for the polycondensation reaction, heated to about 230 to 300 ° C., and ethylene glycol is distilled off under reduced pressure to proceed the reaction. Further, for the purpose of slightly improving the surface shape and film characteristics, particles other than spherical silica, for example, inorganic particles such as silicon dioxide, titanium dioxide, calcium carbonate, kaolin, talc, clay, amorphous zeolite, calcium phosphate, crosslinked polymer particles and Fine particles or the like deposited by the reaction of the catalyst residue and the phosphorus compound in the polyester polymerization reaction size can also be used together within the range not impairing the characteristics of the present invention. Of course, it is also possible to use two or more types of spherical silica.

In the film obtained in the present invention, the number of projections on the film surface needs to be 1.0 × 10 ³ pieces / mm ² or more, and the particle diameter and the particle concentration may be selected so as to satisfy this. More preferably, it is 5.0 × 10 ³ pieces / mm ² or more. The number of protrusions is 1.0 x 1
When it is less than 0 ³ pieces / mm ² , film slipperiness is poor and workability is significantly deteriorated, which is not preferable.

In addition, the film is simultaneously formed by a difference between the thickness of the 10-layer micrometer method film and the weight method film, Δd [μm]
Must satisfy 0.1 ≦ Δd ≦ 0.4. When Δd exceeds 0.4, the distance between the electrodes becomes large when a capacitor is used, which causes a decrease in electric capacity, which is not preferable. When Δd is less than 0.1, sufficient slipperiness is not obtained and workability is deteriorated, which is not preferable.

The polyester film satisfying the requirements of the invention described in detail above is excellent in handleability during production and processing, and at the same time a high electric capacity is obtained, and at the same time, the spherical silica obtained in the present invention is excellent in affinity with polyester. When formed into a film, there are few voids (voids) between the particles and the polyester, the withstand voltage is excellent, and since the particle size distribution of the particles is very sharp, the number of coarse particles is also small, so the life when used as a capacitor is long. It is long and has excellent withstand voltage characteristics, and is useful as a very excellent film for ultra-thin capacitors.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples as long as the gist thereof is not exceeded.

Various physical properties and characteristics in the examples are measured and defined as follows. In addition, "parts" and "%" in the examples are "parts by weight" unless otherwise specified.
And "% by weight".

(1) Average particle size and particle size distribution of silica particles The particles are photographed with an electron microscope and measured by a photographic method. The particle size of about 1000 particles is measured, each particle size is converted into volume, and the larger one is converted. The average particle size is defined as the cumulative volume fraction of 50%, and the particle size distribution is expressed as the particle size ratio at 10% and 90% of the total volume by integrating the volume from the large particle side.

(2) Film slidability measurement The film slidability is represented by the coefficient of kinetic friction, which is measured by AS.
According to TM D-1894, the method was modified so that measurement could be performed on a tape sample. Measurement temperature 23 ℃ ± 1 ℃, humidity
The sample was used in an atmosphere of 50 ± 5% Rh, the size of the sample was 15 mm in width and 150 mm in length, and the pulling rate was 20 mm / min.

(3) Measurement of Δd 10-ply micrometer method Film thickness (d ₁₀ ) JIS
According to B-7502. Measuring force is 700 ± 100gf, measuring length is 0
-25 mm, 1/1000 micrometer, 10 film
The value measured by stacking the sheets is divided by 10 to obtain d ₁₀ (μm).

Gravimetric film thickness (d _W ) The film was cut into a 10 cm square, and it was calculated from the weight W measured by a METTLER electronic balance by the following formula.

Δd is defined by the following equation.

Δd = d ₁₀ −d _W [μm] (4) Number of surface protrusions The number of protrusions per 0.1 mm ² was counted from the optical micrograph of the film surface and converted into the number per 1 mm ² .

(5) Aluminum is vapor-deposited on the condenser capacity film by a vacuum vapor deposition device,
Slit the vapor deposition part to a width of 10 mm, and wrap two 2 m long slit tapes with different left and right non-deposited ends.
After that, end face sealing and lead wire attachment were performed to obtain a capacitor element. The capacitance of the capacitor element is 23
The measurement was performed under the condition of 1 KHz.0.3 Vrms using "RLC Digibridge" manufactured by General Radio Co., Ltd. in an atmosphere of 50 ° C. and 50% Rh.

(6) Measurement of withstanding voltage Using a 100KV DC withstanding voltage tester, connect the capacitor element electrode end obtained in (5) to the voltage application electrode and the earth electrode of the tester with clips, and set the tester voltage to 100V / sec. The voltage was read when the capacitor was broken and short-circuited by increasing the voltage at the step-up speed.

(7) Life characteristics Apply a DC voltage of 300 V across the electrodes of the capacitor obtained in (5), and use 1000 V in an atmosphere of 85 ° C as an accelerated test.
It was represented by the residual rate of the element having a function as a capacitor without being short-circuited in 100 capacitor elements after the passage of time.

Example 1 (Synthesis Method of Spherical Silica Particles) Tetramethylsilane (30.4 g) was dissolved in 400 g of methanol.
The temperature was maintained at 0 ° C (solution A). On the other hand, 900 g of methanol and 110 g of water
Was added and 243 g of 2.8% aqueous ammonia solution was added and mixed at 20 ° C.
I resigned (B liquid). Then, a stirring device was attached to the liquid B, and the liquid A was added while stirring. Immediately after the addition, a hydrolysis reaction and a condensation reaction occurred and the inside of the reaction system became cloudy. Ethylene glycol 103
g was added, and the mixture was heated under reduced pressure to distill off excess water, methanol, and ammonia to obtain an ethylene glycol slurry containing 10% concentration of spherical silica fine particles.

The slurry was overtreated using a filter having an overprecision of 3 μ cut, but the filter passability was very good.

(Production of polyester film) 100 parts of dimethyl terephthalate and 60 of ethylene glycol
Parts and 0.03 parts of manganese acetate tetrahydrate are heated in a reactor and heated, and methanol is distilled off to carry out a transesterification reaction, which takes 4 hours from the start of the reaction and is heated to 230 ° C. to practically produce an ester. The exchange reaction was completed.

Then, an ethylene glycol slurry containing 10% of spherical silica having an average particle diameter of 0.27 μm was added, and then 0.021 part of ethyl acid phosphate and 0.00 of antimony trioxide were added.
35 parts were added and polycondensation was carried out for 4 hours to obtain a polyethylene terephthalate resin having an intrinsic viscosity of 0.66. The amount of particles added is 0.
It was set to 5%.

The resulting polyester resin was heated and dried at 180 ° C. in a nitrogen atmosphere for 6 hours, and then extruded into a sheet by an extruder to prepare an amorphous sheet of 24 μm by electrostatic contact cooling. Next, this amorphous sheet was stretched 4 times in the machine direction and 4 times in the transverse direction to obtain a biaxially stretched film having a thickness of 1.5 μm.

Table 1 shows the characteristics of the polyester film obtained as described above and the electric characteristics when it is used as a capacitor. Both the film characteristics and the electrical characteristics of the capacitor were excellent, and satisfactory results were obtained.

[Examples 2 and 3] In Example 1, the production method of silica particles was slightly changed to
Table 1 shows the characteristics of the film and the electric characteristics of the capacitor obtained by the same method as in Example 1 except that silica particles having the average particle diameters listed in the table were prepared and used. Both the film characteristics and the electrical characteristics of the capacitor were excellent, and a sufficiently satisfactory product was obtained.

[Comparative Example 1] Table 1 shows the characteristics of the film obtained in the same manner as in Example 1 and the electric characteristics of the capacitor, except that the spherical silica particle diameter was 3.7 μm. The slipperiness was good, but the capacity was small, the withstand voltage and the life were poor, and a satisfactory film could not be obtained.

Comparative Example 2 Example 3 is the same as Example 3 except that the amount of particles added is 0.002%.
The characteristics of the film obtained in the same manner as in Table 1 are shown in Table 1. Since the flat surface is flat, the electrical characteristics of the capacitor are good, but the dynamic friction coefficient is high and it is difficult to wind, so only a film with poor yield was obtained.

[Comparative Examples 3 and 4] The characteristics of the film obtained in the same manner as in Example 1 except that CaCO ₂ and dry process silica having the particle sizes listed in Table 1 were used instead of the spherical silica Shown in the table. In both cases, since the particle size distribution was broad, there were many coarse particles and Δd was also large, resulting in poor electrical characteristics of the capacitor.

[Effects of the Invention] According to the present invention described above, a polyester film for a capacitor for an ultrathin product, which is excellent in electric characteristics and slip characteristics, particularly electric capacity and withstand voltage, is provided.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location B29L 7:00 (56) Reference JP-A-58-65744 (JP, A) JP-A-62- 72514 (JP, A) Japanese Patent Sho 51-36779 (JP, B2)

Claims (1)

[Claims] 1. A substantially amorphous spherical silica particle having an average particle diameter of 0.01 to 3.0 μm, which is obtained by a hydrolysis reaction and a condensation reaction of an alkoxysilane, is contained in an amount of 0.001 to 5% by weight, The number of protrusions is 1.0 × 10 ³ pieces / mm ² or more, and the difference Δd [μm] between the film thickness of the 10-layer micrometer method film and the weight method film satisfies the following expression (1). Biaxially stretched polyester film for capacitors. 0.1 ≦ △ d ≦ 0.4 (1)