JP2712300B2 - Polyolefin microporous film for electrolytic separator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a polyolefin microporous film used as a separator for a battery, an electrolytic capacitor, an electric double layer capacitor and the like.

[Prior Art] In batteries, electrolytic capacitors, electric double-layer capacitors, and the like, polyolefin microporous films having fine pores and excellent uniformity of pores have been used. (JP-A-51-18851, JP-A-61-13614, and JP-A-59-1404)
[Problem to be Solved by the Invention] When such a microporous film is used as a separator, it is possible to realize an electrolytic capacitor having a low impedance value that cannot be achieved by a conventional electrolytic capacitor paper. In doing so, there are the following problems.

(1) With the miniaturization of electrolytic capacitors, separators
Element winding characteristics in a narrow width of about 4 mm are required, but in the case of microporous film based on polyolefin, it is inferior in rigidity compared to electrolytic capacitor paper, so it is easy to cause stray winding, Further, the element may not be wound due to extension of the separator.

(2) When mounting elements such as electrolytic capacitors and electric double layer capacitors on a board, the separator may partially shrink due to the amount of heat applied when it comes into contact with the solder bath, and the characteristics may not be sufficiently exhibited or severe. May be damaged.

It is an object of the present invention to provide a polyolefin microporous film for an electrolytic capacitor having a high porosity, a high tensile strength when winding the element, and an excellent solder resistance.

[Means for Solving the Problems] The present invention provides a surface pore size of 0.05 to 3 μm and a porosity of 30 to 90%.
10g of polyolefin which constitutes a microporous film
The present invention relates to a polyolefin microporous film having a coating layer mainly composed of a siloxane polymer in an amount of 0.1 to 6 g per unit and an electrolytic separator using the same.

In the present invention, polyolefin is polyethylene,
It is a homopolymer or copolymer of α-olefin, such as polypropylene, poly (4-methylpentene 1), or polybutene, or a blend thereof. Among these, high-density polyethylene and polypropylene having excellent solvent resistance and mechanical properties are preferable.

Particularly, in the case of polypropylene, the intrinsic viscosity ([η]) is 1.8 to 4.5 dl / g, preferably 2.1 to 4.0 dl / g, more preferably 2.7 to 3.7 dl / g, and the isotactic index (II) is particularly preferable. 93% or more, more preferably 96% or more is preferable because of excellent mechanical properties and solvent resistance.

Next, in the present invention, the surface pore diameter needs to be 0.05 to 3 μm, and preferably 0.1 to 2 μm. If the pore diameter is less than 0.05 μm, the temperature dependence of the resistance value when impregnated with the electrolytic solution increases, which may cause a problem. On the other hand, if the pore diameter exceeds 3 μm, the passage of conductive particles and the like cannot be blocked, and the short-circuit rate increases.

The porosity of the microporous film of the present invention needs to be 30 to 90%, preferably 50 to 80%. If the porosity is smaller than 30%, the amount of retained electrolyte decreases, causing problems such as dry-up. On the other hand, if the porosity is larger than 90%, the mechanical strength is insufficient, and problems such as short circuit occur.

Further, the microporous film needs to be coated with 0.1 to 6 g of a siloxane polymer per 10 g, and preferably 0.2 to 4 g. The coating amount of the siloxane is 0.1 g
If it is less than 3, the element is liable to elongate at the time of winding the element, and stable element winding cannot be performed. Also, the solder resistance is often unsatisfactory. On the other hand, when the coating amount exceeds 6 g, a problem occurs in electrical characteristics.

The siloxane polymer referred to in the present invention may be a 「Si-O as described in“ Latest Coating Technology ”(published by R & D Center) and“ Inorganic Coating ”(published by Kyodai Kyoikusha). -Si≡ (1) is a polymer based on (Si) and only Si and O, ie, (Si
O ₂ ) means a polysiloxane composed of n, or an organopolysiloxane in which an alkyl group or an aminoalkyl group is partially introduced, and those in which a group such as a silanol group (≡SiOH) is introduced. In addition, monovalent and / or
It may contain divalent metal ions (sodium, zinc, potassium, etc.). However, if it contains other metal ions when it is used as a separator, for example, when it is used as an electrolytic capacitor, corrosion of the anodic oxide film may occur. There is a problem in that metal ions other than Si are less, and better characteristics can be obtained.

Further, it is preferable that the layer contains a resin component other than the siloxane polymer, for example, a resin binder component such as a melamine-based resin, an acrylic-based resin, or a urethane-based resin, in terms of affinity with the electrolyte and stability to the electrolyte. However, it is preferred that it is essentially composed of the siloxane polymer described above.

From such a viewpoint, it is preferable that the content of the alkyl group or the like in the siloxane polymer is as small as possible.

Further, the coating according to the present invention refers to a state in which the above-mentioned siloxane layer covers the surface of the micropores in a microporous film having micropores penetrating at least front and back. As a result, the siloxane layer does not block the micropores.

The micropore shape of the film of the present invention is preferably a structure in which voids having an apparent elliptical shape are randomly distributed in the cross-sectional structure. Particularly, the cross-sectional hole shape ratio (Ca / Cb) described later is 1.5. To 7 is preferable. When Ca / Cb is in this range, the effect of improving the winding property of the element by applying the siloxane coat is excellent and the electric properties are excellent.

In the present invention, the heat shrinkage in hot air at 120 ° C. is preferably 6% or less, more preferably 4% or less.
% Or less is preferable because the change with time when the element is formed is small.

The water permeability of the film of the present invention is 5 to 100 g / (mmHg ·
Min · m ^2), preferably preferably less change in resistance characteristics due to temperature changes when in the range of 10 to 60 g / (mmHg · min · m ^2).

The thickness of the film of the present invention is less than 50 μm, especially 10 to 45 μm.
A range of m is preferred because both electrical and mechanical properties are improved.

Further, the film of the present invention is used as a separator by laminating or laminating it with a microporous film or a nonwoven fabric having the same or another structure.

In addition, various known additives such as a heat stabilizer, an antioxidant, a slipping agent, and a surfactant may be added to the film of the present invention, if necessary, in a range not adversely affecting the purpose. .

Among them, it is preferable to add a cation, a nonion, or an anionic surfactant because affinity for an electrolytic solution is improved, and thus polyoxyethylene alkyl ether, polyoxyethylene nonyl phenyl ether,
Nonionic surfactants exemplified by fatty acid alkylolamide and the like are preferable because they have a low possibility of inhibiting an electrode reaction.

As a method of producing the film of the present invention, a polyolefin and a polar room-temperature organic solid having compatibility when melted and capable of phase separation upon cooling are melt-extruded, and the organic solid is extracted and then stretched as necessary. 30-90% porosity obtained by
The most preferred method is to apply a coating agent capable of forming a siloxane film to a microporous film having continuous fine pores, and to dry it.

In the present invention, the polyolefin and the organic solid having compatibility at the time of melting, and phase-separable at the time of cooling, the blendability with olefin, in terms of extractability, the melting point is 35 ~ 100 ℃,
It is preferable that the molecular weight is 200 to 1000, and it is preferable that the molecular structure of the organic solid contains polarizable and polar groups. Here, the polarizable group refers to an aromatic ring, and the polar group is a group containing a polar molecule as shown in the Dictionary of Science and Technology (Iwanami Shoten), such as a carbonyl group and an amino group. , Hydroxyl group and the like. Among the organic solids having the above characteristics, phthalic acid esters and phosphoric acid esters used as plasticizers such as vinyl chloride are excellent. Particularly, dicyclohexyl phthalate (DCH
P), and at least one selected from triphenylphosphate (TPP).

The addition amount of the organic solid is, with respect to 100 parts by weight of the polyolefin resin, 80 to 250 parts by weight, preferably 90 to 200 parts by weight to improve the film-forming properties, uniformity, fine pores excellent in continuity. It is preferable because it is formed.

The polyolefin and the organic solid are melt-blended using, for example, a twin-screw extruder and pelletized. At this time, a known stabilizer is preferably added in order to prevent oxidation or thermal decomposition of the polyolefin.

The pellets thus obtained are formed into a sheet or tube using a T-die or a circular die using an extruder. Here, the T-die method and the circular die method are preferable because the T-die method is excellent in terms of uneven thickness of a film to be produced. In this case, it is preferable to increase the draft ratio as much as possible in order to form uniform fine holes, and the draft ratio is preferably 6 or more, and more preferably 10 or more.

It is preferable to cool the molten sheet uniformly in the thickness direction in terms of uniformity of the formed fine holes and electrical characteristics.
In the case of using the die method, as a casting method, a method of guiding the sheet to a water tank or a method of solidifying the sheet while pressing the sheet against the drum surface by an electrostatic application method on a cooling drum is preferable.

The polyolefin sheet containing the organic solid obtained as described above is used at least 95% of the added amount of the organic solid.
It is obtained by extracting the above.

Here, it is preferable to stretch the film at least uniaxially by less than 10 times because the uniformity of the microporous film is excellent, and it is preferable that the total stretching ratio is 2 to 15 times. Further, the stretching temperature is preferably in the range of the melting point (Tm) of the unstretched sheet −60 ° C. to Tm−10 ° C.

The microporous film obtained as described above is impregnated with a coating agent capable of forming a siloxane film, dried with a solvent such as water or alcohol, and then cured in a temperature range of 60 to 130 ° C. (Referred to as solution method).

Examples of the coating agent component capable of forming such a siloxane film include colloidal silica (“colcoat”, “cataloid”, etc.), a partial hydrolyzate of aminosilane + epoxysilane, and a silane coupling agent + alkyltrialkoxysilane + tetraalkoxysilane. Examples thereof include a partial hydrolyzate, a partial hydrolyzate of alkyl trialkoxysilane + tetraalkoxysilane, and a hydrolyzate of colloidal silica + alkyltrialkoxysilane. However,
Among those exemplified above, those containing halogen such as chlorine,
It is not preferable because electrical characteristics and the like are deteriorated.

Japanese Patent Application Laid-Open No. 61-204007 discloses a method of forming an organosiloxane compound film by plasma polymerization.However, as described in the text, a siloxane film is formed in a portion having extremely small pores. It is hard to be formed. Usually, the microporous film has a pore distribution although it depends on the manufacturing method. For example, even if the average pore diameter is 0.5 μm, the number of pores of 0.1 μm or less is not negligible. Therefore, even if a microporous film having a relatively wide pore distribution, for example, a microporous film obtained by the extraction method is treated by the plasma polymerization method, the siloxane film may be deposited unevenly, which is not desirable. In this regard, according to the process of treating and curing the film with the above-mentioned coating agent capable of forming a sirocysan film, the uniformity of the coating layer is improved and good results are obtained in terms of electrical characteristics. In particular, an alcohol solvent system having a small surface tension is preferable because a hydrophobic polyolefin-based microporous film can be well impregnated and uniform treatment can be performed.

In the present invention, if necessary, a surfactant may be mixed with the coating agent, or a surfactant may be applied before or after application of the coating agent. In this case, the surface tension of the film surface is increased, and the impregnation with water or the electrolytic solution is improved, which is preferable.

Here, it is preferable to apply a method in which a surfactant is mixed with the coating agent and then applied, since the treatment effect is excellent in persistence,
At least 1-50wt of nonionic surfactant in coating agent
% Is preferred because the hydrophilic treatment effect is exhibited without inhibiting the siloxane coating effect.

[Effects of the Invention] The effects of the present invention are listed below.

(1) The siloxane coat layer formed on the surface of the fibril constituting the microporous film reduces the amount of deformation due to the applied tension and improves the winding property of the element.

(2) The amount of deformation during heating is reduced, and the solder resistance of the element is improved.

(3) If the siloxane coat layer is impregnated with a surfactant, the hydrophilizing effect is excellent and the long-term reliability is high.

As described above, the present invention has suitable characteristics as an electrolytic separator, and particularly exhibits excellent characteristics as separators for electrolytic capacitors, electric double layer capacitors, and the like.

[Method for Evaluating Characteristics and Method for Evaluating Effects] Next, methods for measuring characteristics and methods for evaluating effects according to the present invention will be summarized.

(1) Siloxane coat amount Using a Soxhlet extractor, add 2
After the time extraction, vacuum drying is performed at 60 ° C. for 2 hours, and the weight of the campul is measured (W). The sample was immersed in a 20% aqueous solution of sodium hydroxide (or potassium hydroxide) in ethyl alcohol (50 ° C.) for 24 hours, washed thoroughly with water, extracted again with ethyl alcohol, and vacuum-dried at 60 ° C. for 2 hours. The weight (W ') was measured and determined by the following equation. The concentration of ethyl alcohol in the siloxane-extracted alkaline solution may be appropriately changed so that the solution can be uniformly impregnated into the microporous film.

Wsi = 10 × (W−W ′) / W ′ (g) (2) Intrinsic viscosity ([η]) According to ASTM-D-1601, 0.1 g of sample is completely dissolved in 100 ml of tetralin at 135 ° C. Is measured in a thermostat at 135 ° C. with a viscometer, and determined from the specific viscosity S according to the following equation.

[Η] = S / {0.1 x (1 + 0.22 x S)} (2) Isotactic index (II) After washing the sample with ethyl alcohol, remove the coating layer with an alkaline solution or the like, and then wash with ethyl alcohol Then, the sample is vacuum dried at 130 ° C. for 2 hours. From this a sample of weight W (mg) is taken, placed in a Soxhlet extractor and extracted with boiling n-heptane for 12 hours.

Next, this sample is taken out, sufficiently washed with acetone, vacuum-dried at 130 ° C. for 6 hours, and thereafter, the weight W ′ (mg) is measured, and the weight W ′ (mg) is determined by the following equation.

II (%) = (W '/ W) x 100 (3) Surface pore diameter (a) Observe the surface of the sample with a scanning electron microscope (SEM) and adjust so that 200 ± 50 micropores enter the observation field of view. And
The major axis (ax) and minor axis (az) of the pore diameter are measured by approximating the micropores recognized as existing on the surface as an ellipse, the average of each is determined, and the geometric mean expressed by the following equation is calculated as the surface pore diameter. I do. In addition, when there was a fibril-like substance (single or plural) inside the pores, the fibril-like substance was excluded from the measurement, and the structure (fibril or the like) of 0.01 μm or less was similarly excluded.

(4) Cross-sectional hole shape The sample is frozen with liquid nitrogen, a cross section is cut out with a microtome along the direction of maximum intensity, and the sample is scanned with a scanning electron microscope (SE).
M) Observe and approximate to an ellipse according to the method of measuring the surface pore diameter, and calculate the average value of the axial length (Ca) in the sectioning direction (= maximum strength direction) and the average value of the axial length in the thickness direction ( Cb) was measured, and the ratio (Ca / Cb) was determined.

(5) Porosity (P) Sample (10 × 10cm) Weight after immersing in liquid paraffin for 24 hours and thoroughly wiping the surface liquid paraffin (W2)
Is determined by the following equation from the weight (W1) of the sample before immersion and the density (ρ) of the liquid paraffin.

P = (W2−W1) / (V × ρ) Here, V is the apparent volume (value calculated from the thickness and dimensions) of the sample.

(6) Permeability After all pores of the sample were replaced with water, a measuring cell (manufactured by Sartorius, filter holder SM16508B type, with an effective permeation area of 1.3 × 10 ^-3 m ² , and a static pressure of 125 mmHg) Water was supplied at a water pressure, and a time T (minute) until 50 g of water permeated was measured, and the amount of water permeation was determined by the following equation (temperature 25).
℃) Water permeability [g / m ² · mmHg · min] = 50 / 11.3 × 10 ^-3 × 125 × T) (6) ESR (permeation series resistance) As electrolyte, γ-butyrolactone 80wt% + 0-phthalic acid 12.43wt % + Triethylamine 7.57 wt%, sampled into a microporous film of 33 (± 3) mm square, impregnated with electrolyte, sandwiched between five electrodes, sandwiched between electrodes, 250 g The impedance at 25 ° C. and 1 kHz under load was measured, and the ESR component per one separator was determined.

 The conditions are as follows.

Electrode: Platinum black-treated platinum electrode 25mm □ Impedance characteristic measuring device LCR meter AG-4431 manufactured by Ando Electric Co., Ltd. (7) Element winding test method A sample film (separator) was slit into a 4 mm width. Next, anodized aluminum foil and cathode aluminum foil were prepared, and alternately stacked with the sample film, and a child winding test of the electrolytic capacitor was performed. At this time, the winding property was classified according to the following criteria.

-The element could not be wound: ×-The element could be wound but the winding was disturbed and it could not be used as a capacitor: △-There was no element winding problem: ○ (8) Young's modulus The longitudinal Young's modulus was ASTM. It was measured according to D882-64T. The thickness was measured using a dial gauge type thickness gauge (probe 5 mm in diameter flat type).

[Examples] Next, examples of the present invention and comparative examples will be shown, and the effects of the present invention will be described more specifically.

Examples 1-2 and Comparative Examples 1-2 As a polyolefin resin, polypropylene (PP) powder (Mitsui Toatsu Noblen EB type: [η] = 2.95 dl)
/ g), dicyclohexyl phthalate (DCHP; manufactured by Osaka Organic Chemical Co., Ltd.) and a PP stabilizer were melt-blended with a twin screw extruder at the following composition ratio and pelletized.

PP: 100 parts by weight DCHP: 150 parts by weight BHT: 0.8 parts by weight Irganox 1010: 0.3 parts by weight (BHT: manufactured by Sumitomo Chemical, Irganox 1010: manufactured by Ciba Geigy)
It was melt-extruded at 0 ° C. and cooled and solidified into a sheet while being adhered onto a cooling drum at 75 ° C. using an electrostatic application method.

The thickness of the sheet is 85 μm,
-1 to the trichloroethane extraction tank,
More than 99% were extracted.

The extraction sheet obtained as described above is guided to a stretching device, stretched 3 times in the longitudinal direction by a roll stretching method, then guided to a stenter, stretched 1.4 times at 130 ° C., and 5 times in the width direction at 140 ° C. It was heat-fixed and wound up, allowing for a% relaxation.

The film thus obtained was coated with a siloxane coating agent (“Colcoat” N-103X) and cured at 120 ° C.

Here, the relationship between the mechanical properties and the element winding properties when the coating amount is changed as shown in Table 1 is shown.

As can be seen from Table 1, in Examples 1 and 2 where the optimum coating amount was applied, the Young's modulus was high, the element winding property was excellent, and the ESR was high.
It is also found to be small and excellent as a separator for electrolytic capacitors.

Example 3 1 g of "Colcoat" N-103X per 10 g of PP and polyoxyethylene nonylphenyl ether ("Nonipol" 95, manufactured by Sanyo Chemical Industries, Ltd.) as a surfactant were added to the untreated film obtained as described above. ) Was applied in an amount of 0.5 g.

The microporous film thus obtained was slit to a width of 4 mm to prepare 50 electrolytic capacitors of 220 μF. There was no element winding problem.

This device was subjected to a printed circuit board mounting test (solder bath
260 ° C x 10 seconds).

As a result, there were no damaged elements, and the rate of change * of tan δ was small.

* Tan δ change rate (%) = (tan δ after mounting test-tan δ before test) / tan δ before test × 100 Comparative Example 3 PP pellet (WF900 type, manufactured by Sumitomo Chemical Co., Ltd.) as a polyolefin resin at 230 ° C At a draft ratio of 50 and cooled and solidified in a water bath at 65 ° C. The cast film thus obtained was heat-treated at 150 ° C. for 2 minutes. As a result, a film having an elastic recovery rate of 92% described in Japanese Patent Publication No. 50-2176 was obtained. Next, the heat-treated film was heated at 60 ° C. at a stretching speed of 10 ° C.
The film was stretched twice at 0% / min, further stretched 1.5 times at 130 ° C., and then heat-treated at 150 ° C. for 5 minutes. 25 film thickness
μm. The microporous membrane thus obtained was hydrophilized using "Nonipol 95" (polyoxyethylene nonyl phenyl ether, manufactured by Sanyo Kasei Co., Ltd.) as a surfactant. Tested.

The results are shown in Table 2 in comparison with Example 3. As shown in Table 2, the solder resistance was inferior to that of Example 3, a small amount of element damage was confirmed, the tan δ increase rate was large, and the reliability was inferior. I understand.

As can be seen from the above comparative examples, it can be seen that the present invention has excellent characteristics for a separator.

Claims (1)

(57) [Claims] 1. A surface vacancy diameter of 0.05 to 3 μm and a porosity of 30 to 90%.
10g of polyolefin which constitutes a microporous film
A polyolefin microporous film for an electrolytic separator, comprising a coating layer mainly composed of 0.1 to 6 g of a siloxane polymer per unit.