JPH0873622A - Millipore polyester film - Google Patents

Abstract

PURPOSE: To obtain the subject film consisting of a polyester with specific chemical structure, excellent in thin film formability and durability at high humidity because of its low humidity expansion coefficient and hygroscopicity and excellent mechanical properties, thus useful for e.g. electrolytic capacitor separators, microfilters. CONSTITUTION: This film has structure of the formula (R1 , R2 and R3 are each a divalent hydrocarbon-based group such as 1,4-phenylene or ethylene; X, Y and Z are such as to satisfy the relationship: 0.01<=X<=0.9 in terms of molar fraction, assuming that Y=Z and (X+Y)=1), pref. having the following characteristics: porosity: >=20%; having fine pores communicating with both the surfaces; and humidity expansion coefficient: 50×10<-6> cm/cm/%RH uniaxially and/or biaxially.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has microporosity, strength,
The present invention relates to a microporous polyester film having excellent dimensional stability and chemical resistance.

[0002]

2. Description of the Related Art In recent years, miniaturization in the field of electric and electronic equipment,
With the progress of weight reduction, not only downsizing of materials to be used but also simplification, shortening of process and speeding up have been demanded for heat resistance and high strength. There is a similar demand for microporous films used as separators of electrolytic capacitors, and polyolefin-based films such as polypropylene have been often used. However, they are poor in heat resistance and chemical resistance, and are required to have dimensional stability at higher temperatures year after year, and these films have problems such as lack of long-term reliability due to film deterioration due to aging. Came. An aromatic polyamide film is known as a film having excellent heat resistance and chemical resistance, and a method for producing a porous aromatic polyamide film is also disclosed in JP-B-59-14494 and JP-B-59-36.
It is described in Japanese Patent No. 939.

[0003]

However, electrolytic capacitors and the like tend to have higher operating temperatures, and even films produced by this method have insufficient chemical resistance at the operating temperatures. However, for example, when it is used as a separator of an electrolytic capacitor, it has poor long-term stability such as winding wrapping or slackening and electrical continuity. Further, it has become clear that it cannot be used for applications using an aqueous electrolytic solution because it has a large coefficient of humidity expansion and a high hygroscopicity and lacks dimensional stability. Further, there is a problem that the manufacturing method is complicated and requires a long process, resulting in an extremely high cost.

An object of the present invention is to solve the above problems and to provide a microporous polyester film having microporosity and excellent in strength, dimensional stability, chemical resistance under high temperature and the like. .

[0005]

The present invention is a microporous polyester film comprising a polyester represented by the following formula (I).

[0006]

Embedded image (In the formula, R ₁ , R ₂ , and R ₃ each independently represent a divalent hydrocarbon group, X, Y, and Z represent mole fractions, and Y and Z are substantially equimolar fractions. Rate, and if X + Y = 1, then 0.
01 ≦ X ≦ 0.9) R of the above formula (I) constituting the polyester composition of the present invention
₁ , R ₂ and R ₃ each independently represent a divalent hydrocarbon group, which may be aromatic, aliphatic or aromatic / aliphatic, and contain elements other than hydrocarbons. You may. Preferred R ₁ , R ₂ and R ₃ are each independently an aromatic group having 6 to 30 carbon atoms or an aromatic / aliphatic group,
Alternatively, it is a linear, branched, or cyclic divalent aliphatic hydrocarbon group having 2 to 10 carbon atoms. In particular, as the aromatic type or aromatic / aliphatic type, those having a structure represented by the following formula are preferable,

[Chemical 3] (In the formula, F ₁ and F ₂ are each independently a linear, branched, or cyclic divalent aliphatic group having 1 to 10 carbon atoms, G is —O—,
-S -, - CO -, - SO 2 -, containing 1-5 straight, branched, divalent aliphatic group (some or all of the hydrogen annular halogens such as fluorine, chlorine, etc., Which may be substituted with)) represents one of the following formulas.

[0007]

[Chemical 4] The aromatic ring is a halogen, a nitro group, a sulfonyl group,
It may be substituted with a phosphonium group, an alkyl group, a cyano group or the like. The number of substituents is not particularly limited, and when there are a plurality of substituents, they may be the same or different. In addition,
Two or more kinds of R ₁ and R ₂ may be mixed independently.

On the other hand, a preferred straight chain having 2 to 10 carbon atoms,
As the branched or cyclic divalent aliphatic hydrocarbon group,

[Chemical 5] And the like. Particularly, those having 2 to 10 carbon atoms are preferably used, and above all,

[Chemical 6] Is more preferable. Two or more kinds of R ₁ , R ₂ and R ₃ may be mixed, and for example, a combination of a divalent aliphatic hydrocarbon group and an aromatic group or an aromatic / aliphatic group is preferable.

Further, X, Y, which are the respective mole fractions of the structures constituting the polyester of the formula (I) of the present invention,
Z is Y and Z is a substantially equimolar fraction, preferably 0.9Z ≦ Y ≦ 1.1Z, and when X + Y = 1, 0.01 ≦ X ≦ 0.9. Outside this range, the porosity becomes less than 5%, and the effect of the present invention may not be obtained, or the film may not be formed. Preferably, 0.01 ≦ X ≦ 0.8, and more preferably 0.05 ≦ X ≦ 0.7. More preferably,
0.10 ≦ X ≦ 0.7.

The above polyester is produced by a known method. Monomers corresponding to R ₁ include 1,4-hydroxybenzoic acid, 1,3-hydroxybenzoic acid, 2,6-hydroxynaphthoic acid, 1,5-hydroxynaphthoic acid,
1,4-Hydroxynaphthoic acid, 4,4′-hydroxybiphenylcarboxylic acid and the like, or those in which hydrogen on these aromatic rings is substituted with halogen, an alkyl group or the like are preferably used. Further, as a monomer corresponding to R ₂ , terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid,
1,5-naphthalenedicarboxylic acid, 4,4'-biphenylenedicarboxylic acid, 3,4'-biphenylenedicarboxylic acid, 3,3'-biphenylenedicarboxylic acid, 4,4'-
Biphenyl ether dicarboxylic acid, 3,4'-biphenyl ether dicarboxylic acid, 3,3'-biphenyl ether dicarboxylic acid, 4,4'-biphenyl sulfone dicarboxylic acid, 3,4'-biphenyl sulfone dicarboxylic acid,
Aromatic dicarboxylic acids such as 3,3′-biphenyl sulfone dicarboxylic acid, or those in which hydrogen on these aromatic rings is substituted with halogen, an alkyl group, etc., oxalic acid, succinic acid, adipic acid, sebacic acid, dimer Aliphatic dicarboxylic acids such as acids, maleic acid and fumaric acid, or alicyclic dicarboxylic acids such as 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid and decalindicarboxylic acid , Or their alkyl ester derivatives are preferably used. Further, as monomers corresponding to R ₃ , ethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, 1,4-butanediol, neopentyl glycol, diethylene glycol, 1,5-pentanediol, 1,6 -Aliphatic diol such as hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, 1,2-cyclohexanediol, 1,3-cyclohexanediol, 1, 4-cyclohexanediol, alicyclic diol such as hydrogenated bisphenol A, hydroquinone, resorcinol, 2,6-naphthalene diol,
2,7-naphthalene diol, 2,5-naphthalene diol, 1,4-naphthalene diol, 1,3-naphthalene diol, 1,5-naphthalene diol, 4,4′-
Biphenylene diol, 3,4'-biphenylene diol, 3,3'-biphenylene diol, 4,4'-biphenyl ether diol, 3,4'-biphenyl ether diol, 3,3'-biphenyl ether diol,
4,4'-biphenyl sulfone diol (bisphenol S), 3,4'-biphenyl sulfone diol, 3,
3'-biphenyl sulfone diol, bisphenol A
And aromatic diols, or those in which hydrogen on these aromatic rings is replaced with halogen, an alkyl group, or the like. Known methods of these monomers in a predetermined ratio,
For example, a polyester can be obtained by polymerizing using a solution polycondensation method, a melt polycondensation method, or a solid phase polymerization method.

Further, two or more kinds of polyesters obtained by the above method may be blended or reactively extruded by a known method. For example, a polyester of the following formula (II)

[Chemical 7] (In the formula, R ₂ and R ₃ each independently represent a divalent hydrocarbon group, Y and Z represent mole fractions, and Y and Z are substantially equimolar fractions.) The polyester of the following formula (III)

Embedded image (In the formula, R ₁ , R ₂ , and R ₃ each independently represent a divalent hydrocarbon group, X, Y, and Z represent mole fractions, and Y and Z are substantially equimolar fractions. Rate, and if X + Y = 1, then 0.
1 ≦ X ≦ 0.9) Blending and reactive extrusion are preferred. Formula (III)
Polyester has an intrinsic viscosity (o-chlorophenol,
(Measured at 25 ° C.) is preferably 0.2 to 2.0 dl / g, and particularly preferably 0.2 to 1.0 dl / g.

The microporous polyester film of the present invention can be produced by molding the above polyester into a film. In that case, a conventionally known production method can be applied. For example, after drying the polyester in the form of pellets, if necessary, it is supplied to a known melt extruder, extruded into a sheet form from a slit die at a melting point of the polymer or higher and a decomposition point or lower, and cooled on a casting roll. To make an unstretched film. The ratio (L / D) between the linear velocity of the casting roll and the extrusion speed of the die at this time is preferably 1 to 100, and more preferably 5 to 70 from the viewpoint of providing fine holes as in the present invention. Next, this unstretched film is uniaxially stretched to be uniaxially oriented or biaxially stretched to be biaxially oriented. As the biaxial stretching method, a sequential biaxial stretching method or a simultaneous biaxial stretching method can be used. Stretching area ratio (multiplying the stretching ratio in the machine direction and the stretching ratio in the transverse direction) is 3.
It is preferably from 0 to 30.0 times in order to obtain the microporous film of the present invention, and the stretching temperature varies depending on the type of polymer and cannot be generally stated. However, it is preferably 50 to 200 ° C., and the glass of polyester to be stretched. 5 to 50 ℃ of transition point
It is preferable to stretch at a high temperature. In particular, in the case of sequentially biaxially stretching, the first axis should be 5 to the glass transition point of polyester.
It is preferable to stretch the biaxially at a temperature higher by 50 ° C. at a temperature 5 to 50 ° C. higher than the glass transition point of the uniaxially stretched film. It is also a preferable method to perform stretching in the machine direction in three or more stages. In order to obtain the microporous film of the present invention, it is preferable to perform biaxial stretching and then re-stretch in the longitudinal direction or further in the transverse direction so that the total stretching ratio in the longitudinal direction falls within the above range. Further, this stretched film may be heat treated, and the heat treatment temperature is preferably 150 to 250 ° C. and the heat treatment time is preferably 0.5 to 120 seconds.

The microporous polyester film of the present invention obtained as described above has a pore size of 0.1 nm to 10 nm.
0 μm, preferably 1 nm to 10 μm with a porosity of 5%
Or more, preferably 10 to 90%, more preferably 20 to
90%.

In the microporous polyester film of the present invention, it is preferable that the micropores are continuous on both sides of the film when it is used for a separator of an electrolytic capacitor.
The continuous micropores on both sides of this film mean that they penetrate the front and back of the film, and the liquid paraffin permeation time (JIS K9003) is 0.1 to 10 seconds, preferably 0.5 to 5 seconds. I mean one.

The coefficient of humidity expansion defined by the following formula in at least one direction of the microporous film of the present invention is 50 × 1.
0 ^-6 cm / cm /% RH or less is preferable, 40 × 10 ^-6 cm / cm /% R
H or less is more preferable. If it is larger than this, for example, when the film is wound and used, a change in humidity may cause wrinkles or the like in the film and cause deterioration of electrical characteristics. Furthermore, the moisture absorption rate defined by the following formula of the film is preferably 5% or less, more preferably 4% or less. If it is larger than this, the electric characteristics may deteriorate due to the influence of moisture.

Further, the strength of the microporous film of the present invention is preferably 3 kg / mm ² or more, more preferably 5 kg / mm ² or more in at least one direction. Further, the strength retention rate when immersed in a 10 wt% NaOH aqueous solution at 25 ° C. for 5 days is preferably 80% or more, more preferably 85% or more. If the strength and the strength retention ratio deviate from the above ranges, they may not be used when used as a separator for capacitors and the like.

The microporous polyester film of the present invention has an average particle size of 5n within a range not impairing the effects of the present invention.
Inorganic or organic fine particles of m to 10 μm or another polymer different from the polymer forming the film may be added in an amount of 0.01 to 5% based on the weight of the film. For example, the inorganic fine particles include metal oxides such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, iron oxide, and chromium oxide, and ultrafine metal particles such as gold, silver and platinum, and the organic fine particles include polyimide, Examples thereof include silicone and cross-linked polymers such as cross-linked polyester, cross-linked polystyrene, and cross-linked polymethylmethacrylate. The particle shape is not particularly limited and is spherical, acicular, amorphous, or porous, but spherical is preferable. Further, the polymer different from the polymer constituting the film is not particularly limited, regardless of compatibility or incompatibility, but polyester, polyamide, polyolefin, polystyrene and the like are preferable.

When a film is obtained from the copolyester of the present invention, it can be used as a single film, but can also be used as a composite film laminated with another thermoplastic polymer. The other thermoplastic polymer to be laminated is not particularly limited, but a crystalline polymer is preferable, and examples thereof include polyester, polyamide, polyphenylene sulfide, and polyolefin. In particular, polyesters of the same type as in the present invention are more preferable because of good adhesiveness at the interface. The laminated structure may be any number of layers, but normally, two layers or three layers are preferably used. In the case of three layers, the film of the present invention can be used as an inner layer or an outer layer. From the viewpoint of abrasion resistance, it is particularly preferable that the film composed of the polyester composition obtained from the present invention is arranged in the outermost layer, and the relationship between the film layer thickness t and the average particle diameter D of the organic particles or the inorganic particles. , 0.2D ≦ t ≦ 10D, preferably 0.5D ≦
In the case of t ≦ 5D, particularly preferably 0.5D ≦ t ≦ 3D, the outermost layer preferably has a thickness of 0.005 to 1 μm, more preferably 0.01 to 0.5 μm.
m, especially 0.02 to 0.3 μm is preferable.

[0019]

EXAMPLES Next, the embodiments of the present invention will be explained based on examples, but the present invention is not limited to these. In addition, the measuring method of the characteristic in an Example is as follows.

(1) Strength Set in a Tensilon type tensile tester according to ASTM-D-882 so as to have a trial width of 10 mm and a trial length of 50 mm, and the strength and elongation when the film is broken by pulling at a pulling speed of 300 mm / min. The degree was measured. Atmosphere is 25 ° C, 55
% RH.

(2) Intrinsic viscosity O-chlorophenol was measured as a solvent at 25 ° C.

(3) Humidity expansion coefficient Set in a thermo-hygrostat to have a test width of 1 cm and a test length of 15 cm, dehumidify to a constant humidity (about 30% RH), and keep the film length constant, and then humidify. When (about 80% RH), it begins to grow due to moisture absorption. After about 24 hours, the moisture absorption reaches the equilibrium and the film elongation also reaches the equilibrium. It was calculated from the elongation amount at this time by the following formula. Humidity expansion coefficient (cm / cm /% RH) = elongation / (test length x humidity difference)

(4) Moisture absorption rate The film is cut out into about 100 mm x 100 mm, and the film is cut at 150 ° C
After dehumidifying by heating in an oven for 1 hour, the temperature is lowered in a desiccator and the weight at dehumidification is measured. This film is 75% RH
After leaving it for 48 hours, the product is taken out, the weight after saturation is measured, and the weight is calculated by the following formula. Moisture absorption rate (%) = (weight when absorbing moisture-weight when removing moisture) / weight when removing moisture x 100

(5) Porosity In the case of independent pores, it was determined by the small-angle X-ray scattering method, and in the case of continuous pores, the following was followed. That is, the sample (10 × 10
(cm) was immersed in liquid paraffin for 24 hours, and was determined by the following formula from the weight after the surface liquid paraffin was sufficiently wiped off and the weight before immersion. Porosity (%) = (weight difference before and after immersion) / (apparent volume x
Liquid paraffin density) x 100

(6) Pore diameter In the case of independent pores, it was determined by the small-angle X-ray scattering method, and in the case of continuous pores, the following was followed. That is, a mercury porosimeter (PORESIZER manufactured by MICROMERITICS)
9300), the distribution of pore diameters was measured, and the number average was taken as the pore diameter.

(7) Liquid paraffin permeation time Liquid paraffin having a viscosity of 77 ± 1 centistokes at 37.8 ° C. defined by JIS K 9003 is used, and the liquid paraffin and the sample are kept at an ambient temperature of 25.
After the sample was kept at ℃ for 24 hours, the sample was placed on a horizontal surface, and liquid paraffin 0.03 from the height of 5-20 mm above the sample.
Allow 0.06 g to fall naturally. At this time, the time from when the liquid paraffin comes into contact with the sample surface to when the liquid paraffin permeates the sample surface and wets the opposite surface is measured as the liquid paraffin transmission time.

(8) Chemical resistance (strength retention rate) After soaking in a 10 wt% NaOH aqueous solution at 25 ° C. for 5 days, the strength is measured by the above method (1) and calculated by the following formula. Strength retention rate (%) = strength after immersion / strength before immersion × 100

Example 1 Polyethylene terephthalate (PE having an intrinsic viscosity of 0.63)
T) 30 mol%, acetoxybenzoic acid 60 mol%, terephthalic acid 10 mol%, and diacetylated product of bisphenol A 10 mol% are melted at 250 ° C. in a nitrogen stream at 290 ° C.
Up to 4 hours and the reaction is carried out. Then, the pressure is reduced to 0.5 mmHg in 0.5 hours, and further 290
After polymerizing at 0.5 ° C. and 0.5 mmHg for 3 hours, the polymer was taken out (X = 0.6 in the formula (I), Y = Z = 0.
4, R1: para-phenylene residue, R2: para-phenylene residue, R3: polymer corresponding to ethylene glycol residue / bisphenol A residue = 3/1). The intrinsic viscosity of the obtained polymer was 1.0 g / dl. After this blended polymer was dried, it was extruded at 290 ° C. from a T die onto a casting drum having a surface temperature of 30 ° C. by L / D55 using an extruder to prepare an unstretched film. This unstretched film was stretched 3.0 times in the machine direction at 95 ° C. This stretching is 2
The difference in peripheral speed of the rolls for each set was performed in three stages. This uniaxially stretched film was stretched 3.5 times in the transverse direction at 95 ° C. using a stenter and then wound into a roll. The obtained film having a thickness of 10 μm is a microporous film having a liquid paraffin permeation time of 1.2 seconds, a porosity of 35% and a pore diameter of 0.8 μm, and has a longitudinal strength of 24 kg / mm ² and a temperature of 1 ° C. of 25 ° C.
Longitudinal strength retention 93% when soaked in 0 wt% NaOH aqueous solution for 5 days, longitudinal humidity expansion coefficient 25 × 10
^It had excellent characteristics of ^-6 cm / cm /% RH and moisture absorption rate of 1.2%.

Example 2 The raw material obtained in Example 1 has an average particle size of 0.4 μm and a specific surface area of 225.
Polyethylene naphthalate containing 0.8% by weight of m ² / g of α-aluminum oxide (intrinsic viscosity 0.67) 25
Mol%, hydroxybenzoic acid 67.5 mol%, 4,4 ′
Polymerization was carried out in the same manner as in Example 1 except that the amount of biphenyldicarboxylic acid was changed to 7.5 mol% and the amount of bisphenol S was changed to 7.5 mol%, and a film was prepared in the same manner as in Example 1 except that L / D was changed to 40. . The obtained film having a thickness of 12 μm is
Liquid paraffin permeation time of 1.1 seconds, porosity 42%, pore size 1.1 μm, a microporous film with a longitudinal strength of 1
5 kg in 10 wt% NaOH aqueous solution at 9 kg / mm ² , 25 ° C
Longitudinal strength retention rate 95%, longitudinal humidity expansion coefficient 22 × 10 ^-6 cm / cm /% RH, moisture absorption rate 1.0%
And had excellent characteristics.

Example 3 The starting material used in Example 1 was 35 mol% PET having an intrinsic viscosity of 0.75, 52.5 mol% acetoxynaphthoic acid, 12.5 mol% 1,4-cyclohexanedicarboxylic acid, and 4,4'-.
Polymerization was carried out in the same manner as in Example 1 except that the amount of biphenol was changed to 12.5 mol%, L / D was adjusted to 65, and after transverse stretching, the film was stretched 1.5 times in the longitudinal direction again to form a film. The obtained film having a thickness of 9 μm has a liquid paraffin permeation time of 0.9.
It is a microporous film with a porosity of 38% and a porosity of 1.3 μm, and has a longitudinal strength of 26 kg / mm ² and a longitudinal strength when immersed in a 10 wt% NaOH aqueous solution at 25 ° C. for 5 days. Retention rate 91%, vertical humidity expansion coefficient 19 × 10 ^-6 cm / c
It had excellent characteristics of m /% RH and moisture absorption rate of 0.7%.

Comparative Example 1 A film was prepared in the same manner as in Example 1 using only PET corresponding to X = 0 in the above formula (I). % Film was obtained, and a film having desired micropores was not obtained.

[0032]

The microporous film obtained by the present invention has a small coefficient of humidity expansion and a low coefficient of moisture absorption. Therefore, when it is used as a separator for batteries, electrolytic capacitors, electric double-layer capacitors, etc., the dimensional change does not occur even in a humid atmosphere. Since small wrinkles do not occur, the performance does not deteriorate, and a good winding shape can be maintained even when the film is stored in a roll for a long period of time. In particular, it is effective when an aqueous electrolyte such as a nickel-cadmium battery is used. In addition, it has excellent mechanical properties such as strength and can be made into a thin film. In the case of the above-mentioned applications, there is an effect that a more compact one can be obtained. In addition, it exhibits excellent properties for micro filters, moisture-permeable waterproofing applications, etc.

Claims (4)

[Claims] 1. A microporous polyester film comprising a polyester represented by the following formula (I). Embedded image (In the formula, R ₁ , R ₂ , and R ₃ each independently represent a divalent hydrocarbon group, X, Y, and Z represent mole fractions, and Y and Z are substantially equimolar fractions. Rate, and if X + Y = 1, then 0.
01 ≦ X ≦ 0.9) 2. The microporous polyester film according to claim 1, which has a porosity of 20% or more. 3. The microporous polyester film according to claim 1, wherein the micropores are continuous on both sides of the film. 4. The film has a coefficient of humidity expansion in at least one direction of 50 × 10 ⁻⁶ cm / cm /% RH or less.
The microporous polyester film according to any one of 1.