JPH0647655B2 - High-performance electret - Google Patents

Description

The present invention relates to an electret capable of stably holding a high electric charge for a long period of time.

[Conventional technology]

Many proposals have already been made for polymer electrets. Most of these are electrets having only a non-polar polymer, or electrets having only a polar polymer or two-component electrets having a non-polar polymer / polar polymer. To describe the characteristics of these already known polymer electrets, the electrets of non-polar polymers represented by polyethylene and polypropylene have low conductivity, so the trapped charge is hard to disappear, and Since it is hydrophobic, it is said that it is difficult to lose the electric charge even when it comes into contact with water. However, on the other hand, since it has no polarity, there is a problem that the amount of charges trapped in the electret is small and the performance as the electret is low. Polyethylene
Unlike a non-polar polymer, polar polymer electrets such as terephthalate and polycarbonate have polar groups inside the molecule, so the amount of charge trapped when electretized increases. It has the characteristic of high electret ability, but on the other hand, it has high electrical conductivity, so the electric charge tends to disappear over time, its long-term electret ability is poor, and it is hydrophilic when it comes into contact with water. Has a problem that the electric charge is easily lost. Two-component blend type electrets have also been proposed in order to obtain an electret having excellent properties by utilizing the respective characteristics of the non-polar polymer electret and polar polymer electret. In this case, a blend system with a matrix of a non-polar polymer and a domain of a polar polymer is more electic than a blend system of the opposite structure, that is, a matrix of a polar polymer and a domain of a non-polar polymer. It is also known to have excellent performance as a let. That is, the polymer collection Vo
l.38 No.9 (1981), p587-591, published by The Society of Polymer Science, Japan, regarding electretization of a two-component blend using polystyrene as the inorganic polymer and chlorinated polyethylene as the polar polymer. It has been reported. In the same report, in the case of multiphase blends, the charge is easily trapped in the boundary region between the components, and in the microphase dispersion structure of polystyrene domain and chlorinated polyethylene matrix, the polystyrene-chlorinated polyethylene interface is The electric charge trapped in the matrix is easily detrapped and migrates and disappears in the continuous matrix of chlorinated polyethylene with low electrical resistance, whereas polystyrene has a matrix and chlorinated polyethylene in the microphase dispersion structure of the domain. , It is disclosed that the charge trapped at the interface is suppressed in movement by the polystyrene matrix of the insulating phase, so that the charge decay is delayed. However, the non-polar polymer and the polar polymer are originally poor in compatibility, and the domain diameter is several μm in the usual melt blending method.
Not up to. This is irreversible and it is difficult to obtain a film-shaped electret having a wall thickness of several μm order by an ordinary melt blending method, and it can be obtained only by a special method such as a solvent method. is there.
However, the solvent method has a non-negligible effect on the electrical characteristics due to the residual solvent, and further requires complicated steps such as evaporation and recovery of the solvent. Therefore, it is an industrially preferred blending method. Therefore, the present inventors have conducted diligent research as to whether a polymer electret capable of forming a thin film with a usual melt blending method and capable of stably retaining a high charge density for a long period of time can be obtained. It has been found that the object can be achieved by making the polymer composition comprising three components of a polymer, a polar polymer and a non-polar polymer modified with a monomer having a polar group electret.

By the way, in order to form these polymer compositions into desired shapes, that is, films and fibers, various antioxidants are usually added. The present inventors, while continuing research into making compositions containing various antioxidants into an electret, found that there is a difference in the ability to hold the charge density of the electret depending on the kind of the antioxidant and the like.

[Problems to be solved by the invention]

That is, an object of the present invention is to provide an electret having a high initial charge density and capable of holding the charge density for a long period of time, and further to provide an electret suitable for a filter material.

[Means for solving problems]

That is, the present invention provides a non-polar polymer: 60 to 99% by weight, a polar polymer: 0.5 to 39.5% by weight, an unsaturated carboxylic acid or its derivative (a), an unsaturated epoxy monomer (b) and an olefinic non-polymer. A non-polar polymer modified with a monomer selected from the group consisting of silane monomers having a saturated bond (c): 0.5 to 20 wt%, a compound represented by the following formula in a polymer composition consisting of, (In the formula, R is an alkyl group, and n is a positive number.) Further, the electret is characterized in that, if necessary, a higher fatty acid alkali and / or alkaline earth metal salt is added.

[Work]

The polymer electret according to the present invention is not the two-component system of the non-polar polymer and the polar polymer described above, but the third component
It is a three-component system containing the above-mentioned modified non-polar polymer as a component. Due to the addition of this third component, the domain size of the polar polymer dispersed in the matrix of the non-polar polymer is reduced to 1 m even with the usual melt blending method.
A domain particle size of μ or less is possible. Further, the amount of trapped charges is larger than that of the two-component system, and an electret having a high surface charge density can be obtained. This makes it possible to easily manufacture a film-shaped electret having a thin wall and also to manufacture a high-performance air filter.

The non-polar polymer which is a constituent of the polymer electret of the present invention may be of any type as long as it is usually referred to as a non-polymer, most of which are dielectric loss (dielectric loss tangent;
tan δ) 0.0005 or less (ASTM D150, 60Hz), volume resistivity (ASTM D257, 23 ° C, relative humidity 50%) 10 ¹⁶ 〜 10 ²⁰
It is in the range of Ωcm. Specific examples of non-polar polymers include polyolefins such as polyethylene and polypropylene, polystyrene, polytetrafluoroethylene, and tetratetrafluoroethylene / hexafluoropropylene copolymers.

The polar polymer that is another constituent of the present invention may be any thermoplastic polymer that is usually called a polar polymer, most of which have a dielectric loss of more than 0.0005 and a large volume resistivity. Is in the range of 10 ¹² to 10 ¹⁶ Ωcm. Specific examples of such a polar polymer include at least one kind of polar group such as a carboxylic acid group, an ester group, an amide group, a hydroxyl group, an ether group, a nitrile group, a carbonyl group or a chlorine atom which is melt-moldable. Including thermoplastic resin, especially polyester such as polyethylene terephthalate and polytetramethylene terephthalate, polyamide such as nylon 6, nylon 66 and nylon 12, polycarbonate, acrylic resin such as polymethylmethacrylate and polyethylacrylate, acrylic-styrene series Examples thereof include resins (AS resins), acrylic-butadiene-styrene resins (ABS resins), polyvinyl chloride, polyvinylidene chloride, polychlorotrifluoroethylene, polyacetals, polyacrylonitrile, but not limited to these.

The component used as the third component is a mixture of nonpolar polymers modified with any one of the monomers (a) to (c). Here, the term "modification" means that the modifier is bound to the nonpolar polymer.

An apolar polymer modified with an unsaturated carboxylic acid or a derivative thereof is a random copolymer or block copolymer of an unsaturated carboxylic acid monomer with respect to a monomer constituting the nonpolar polymer, or an apolar polymer. And unsaturated carboxylic acids are graft-copolymerized.

As unsaturated carboxylic acid or its derivative component unit (a)
Is, for example, acrylic acid, methacrylic acid, α-ethyl
Acrylic acid, maleic acid, fumaric acid, itaconic acid,
Traconic acid, tetrahydrophthalic acid, methyltetrahydr
Lophthalic acid, endocis-bicyclo [2.2.1] hep
To-5-ene-2,3-dicarboxylic acid (Nadic
acid ), Methyl-endocis-bicyclo [2.2.1]
Hept-5-ene-2,3-dicarboxylic acid (methylnadi
Tuctric acid ) Such as unsaturated dicarboxylic acids, said unsaturated dicarboxylic acids
Boric acid acid halides, amides, imides, acid anhydrides, S
Derivatives of unsaturated dicarboxylic acids such as tell
Physically, maleenyl chloride, maleimide, maleic anhydride
Acid, citraconic anhydride, monomethyl maleate, male
Examples thereof include dimethyl acid salt. Among these, tired
Preferred are dicarboxylic acids or acid anhydrides thereof, and
Maleic acid, nadic acid or their anhydrides are preferred.
It is suitable.

Similarly, a non-polar polymer modified with an unsaturated epoxy monomer is one obtained by random copolymerization, block copolymerization, or graft copolymerization of the monomer, and the unsaturated epoxy monomer has one molecule. It represents a monomer having at least one polymerizable unsaturated bond and at least one epoxy group therein. Such unsaturated epoxy monomer (b), for example, a general formula, (Wherein, R is a hydrocarbon group having a polymerizable ethylenically unsaturated bond) and an unsaturated glycidyl ester represented by the general formula, (Here, R is the same as that of the formula [I], x is -CH _2-
O- or Is a divalent group represented by) and an unsaturated glycidyl ether represented by (Here, R is the same as that of the formula [I], R ¹ is hydrogen or a methyl group) and the like, and epoxyalkenes.

Specifically, glycidyl acrylate, glycidyl meta
Crylate, mono- and diglycidyl es of itaconic acid
Ter, butene tricarboxylic acid mono, di and triglycerides
Sidyl ester, mono and diglycidic citraconic acid
Ruester, endo-cis-bicyclo [2.2.1]
Pto-5-ene-2,3-dicarboxylic acid [Nadikku
acid ) Mono- and diglycidyl esters, endo-si
Sub-bicyclo [2.2.1] hept-5-en-2-me
Chill 2,3-dicarboxylic acid (methyl nadic acid) )
Mono- and diglycidyl ester, allyl succinic acid mono
And diglycidyl ester, p-styrenecarboxylic acid
Glycidyl ester, allyl glycidyl ether, 2
-Methylallyl glycidyl ether, styrene-p-g
Lysidyl ether, 3,4-epoxy-1-butene,
3,4-epoxy-3-methyl-1-butene, 3,4-
Epoxy-1-pentene, 3,4-Evoxy-3-methyl
Ru-1-pentene, 5,6-epoxy-1-hexene,
To exemplify vinyl cyclohexene monoxide, etc.
You can Among these, glycidyl acrylate,
Lysidyl methacrylate is preferred.

Similarly, a non-polar polymer modified with a silane monomer having an olefinic unsaturated bond is a random copolymer, a block copolymer, or a graft copolymer of the monomer. Silane monomer having olefinic unsaturated bond (c)
The silane monomer having an organic group capable of being hydrolyzed together with an olefinic unsaturated bond is particularly preferable, and has a general formula R ¹ R ² SiY ¹ Y ² , R ¹ XSiY ¹ Y ² or R ¹ SiY
^{The one represented by 1} Y ² Y ³ can be exemplified. In the formula, R ¹ and R ² are monovalent groups having an olefinic unsaturated bond and consisting of carbon, hydrogen and optionally oxygen, and they may be the same or different.

Examples of such groups are vinyl, allyl, butenyl, cyclohexenyl, cyclopentadienyl,
A terminal olefinic unsaturated group is particularly preferable. Other preferred examples are CH ₂ ═C (CH ₃ ) COO (CH ₂ ) _3- , CH ₂ ═C (CH ₃ ) COO (CH ₂ ) ₂ ) -O- (having an ester bond of a terminal unsaturated acid. Examples include groups such as CH ₂ ) ₃ —, CH ₂ ═C (CH ₃ ) COOCH ₂ OCH ₂ CH ₂ (OH) CH ₂ O (CH ₂ ) ₃ —. Of these, the vinyl group is most suitable. X is an organic group having no olefinic unsaturated bond, and examples thereof include divalent hydrocarbon groups such as methyl, ethyl, propyl, tetradecyl, octadecyl, phenyl, benzyl, and tolyl. Alternatively, a halogen-substituted hydrocarbon group may be used. The groups Y ¹ , Y ² and Y ³ are the same or different hydrolyzable groups, and examples thereof include alkoxy groups such as methoxy, ethoxy, butoxy and methoxyethoxy, alkoxyalkoxy groups, formyloxy,
Acetoxy, acyloxy group, oximes such as propionoxy, for example, _{-ON = C (CH 3) 2} , -ON = CHCH 2 C 2 H 5 and -O
N = C (C ₆ H ₅ ) ₂ or a substituted amino group and an arylamino group such as —NHCH ₃ , —NHC ₂ H ₅ and —NH (C ₆ H ₅ ), and any other hydrolyzable organic group. It is a base.

The organosilicon compound preferably used in the present invention is a compound represented by the general formula R ¹ SiY ¹ Y ² Y ³ , and an organosilicon compound having the same groups Y ¹ , Y ² and Y ³ is particularly suitable. Among these, vinyltrisalkoxysilane is preferable, and examples thereof include vinyltrimethoxysilane and vinyltris (methoxyethoxy) silane. However, vinylmethyldiethoxysilane, vinylphenyldimethoxysilane and the like can be used as well.

Among the modified non-polar polymers described above, those grafted with a modified monomer are particularly preferable. Various known methods can be adopted for producing a graft copolymer, for example, a method of melting a non-polar polymer and adding a modifying monomer to graft-copolymerizing or dissolving it in a solvent and adding a modifying monomer. Then, there is a method of copolymerization. In either case, it is preferable to carry out the reaction in the presence of a radical initiator for efficient graft copolymerization. Examples of radical initiators include organic peroxides, organic peresters, and azo compounds, but ionizing radiation, ultraviolet rays, and the like can also be used for radical generation. The graft ratio is preferably 1 to 15 parts by weight of the modified monomer with respect to 100 parts by weight of the nonpolar polymer.

In the case of the three components constituting the polymer electret of the present invention (the modified non-polar polymer, which is one of the three components, one or more of the above three types are collectively considered as one component), Non-polar polymer 60-99% by weight, especially 80-95% by weight,
0.5 to 39.5% by weight of polar polymer, especially 1 to 10% by weight and 0.5 to 20% by weight, especially 4 to 10% by weight of at least one modified non-polar polymer selected from the above (A) to (C). Is. If the amount of the nonpolar polymer is less than 60% by weight, the nonpolar polymer may not become a matrix in the three-component composite system, and trapped charges may easily escape and only poor charge stability may be obtained. In many cases. The polar polymer must be present in at least 0.5% by weight,
If it is less than 0.5% by weight, the trapped charge amount is not so much increased, and only an electret having a low charge density can be obtained. Also, the upper limit is 3
The reason why the content is up to 9.5% by weight is that the charge density obtained even if it is blended beyond that amount does not change so much, and it becomes difficult to disperse it as a domain well in the matrix of the nonpolar polymer. The modified nonpolar polymer is preferably present in an amount of at least 0.5% by weight in order to microdisperse the domain of the polar polymer in the matrix of the nonpolar polymer, and even if it is blended in excess of 20% by weight, the remarkable effect is obtained. Can't expect. In addition, it is desirable to use a modified product whose main chain is a nonpolar polymer used as a matrix.

The antioxidant (radical scavenger) blended in the above polymer composition is one represented by the above formula. There are various known antioxidants, but it is expected that only those represented by the above formula can significantly prevent the decay of the surface charge density of the electretized polymer over time. Outside.

In the above formula, R represents an alkyl group, and more specifically, lower chain alkyl such as methyl, ethyl, propyl, isopropyl, and butyl, higher chain alkyl such as hexadecyl, heptadecyl, octadecyl, nonadecyl, and cyclic such as cyclohexyl. Examples thereof include alkyl. Of these, higher chain alkyl having 12 to 20 carbon atoms is preferable.

Examples of more specific compounds of the above formula are as follows.

Among these, n- which is commercially available and easily available
Octadecyl-3- (4'-hydroxy-3 ', 5'-
Di-tert-butylphenol) propionate is preferred.

By the way, when a resin polymerized with a halogen-containing catalyst such as a Ziegler catalyst is used as a polymer which is a raw material of the electret of the present invention, deterioration of the resin due to halogen, corrosion of a molding machine, and corrosion of a mold are prevented. Therefore, it is common to add a halogen scavenger. According to the studies by the present inventors, it has been found that the charge retention rate of the electret varies depending on the kind of the halogen scavenger. That is,
Usually, the most commonly used halogen scavenger is a metal salt of a fatty acid, but according to the studies by the present inventors, in the case of the same fatty acid metal salt, in the case of an alkali metal salt or an alkaline earth metal salt, the charge with time While the damping rate is small,
It was found that other metal salts had large attenuation rates. It was also found that the other well-known halogen scavengers, calcium oxide and hydrotalcite, have a large attenuation rate. In other words, only the alkali metal salt or alkaline earth metal salt of fatty acid has no inhibitory effect on the electret.

Examples of such alkali or alkaline earth metal salts of fatty acids include lithium stearate, sodium stearate, calcium stearate, and the like, of which calcium stearate is preferred.

The compounding ratio of the compound represented by the above formula to the polymer is 0.01
The range of 1 to 1% by weight, particularly 0.05 to 0.5% by weight is preferable, and when a halogen scavenger is used in combination, it is added in the range of 0.01 to 1% by weight, particularly 0.05 to 0.5% by weight.

In order to produce the electret of the present invention, the compound of the above formula or the halogen scavenger is known to the above nonpolar polymer, polar polymer and modified nonpolar polymer either sequentially or during simultaneous blending of these three. Mixing in various ways.
That is, after mixing or mixing with a ribbon blender, tumbler blender, Henschel mixer, etc., melt mixing with an extruder, Banbury mixer, two rolls, etc. or dissolve in hydrocarbon or aromatic solvent and mix with the polymer solution, then Single-screw extruder, vented extruder, two-screw extruder, three-screw extruder, conical two-screw extruder, co-kneader, platey equator, mixer, twin-screw conical screw extruder, planetary screw Using an extruder, a gear type extruder, a screwless extruder, or the like, it is formed into a desired shape by granulation or various forming methods. Then, the polymer having the above composition is heated to a melting or softening temperature, and a thermal electret obtained by cooling while applying a high DC voltage thereto, and after being formed into a film, a corona discharge or a pulsed high voltage is applied to the surface, Hold both sides of the film with other derivatives and apply electro-high voltage to both sides of the film, radio electret obtained by irradiating γ-rays or electron beams, melt and apply a strong static magnetic field An electret is obtained by a magnet electret obtained by cooling, a mechano electret obtained by plastic deformation under pressure, an auto electret obtained by applying a voltage while irradiating light. A particularly preferable method is a method in which the polymer is formed into a film and then corona discharge is intermittently performed while heat is applied with or without uniaxial or biaxial stretching, or a needle electrode pair on both surfaces of the film. There is a method of bringing corona discharge closer to and performing corona discharge.

The polymer electret of the present invention obtained as described above, the domain of the polar polymer is micro-dispersed in the matrix of the non-polar polymer with the modified non-polar polymer as an intermediary (ie 10 μm even in the usual melt blending method). Because of the following domain particle size), the amount of trapped charges is remarkably increased as the interfacial area between the nonpolar polymer and the polar polymer is increased, resulting in an electret having a large charge density. In addition, since the matrix is a non-polar polymer, the trapped charge cannot easily escape, and the additive does not interfere with the electretization, so the electret can hold the charge stably for a long period of time. Become. Further, since the domain particle size is 10 μm or less as described above, it becomes possible to manufacture a thin film-shaped electret or the like.

The electret according to the invention has a coulomb of 5 × 10 ^{−9 to} 100 × 10 ⁻⁹ coulombs / cm ² , especially 10 × when measured in film form.
10 ^-9 to have a surface charge density of 50 × 10 ^-9 coulombs / cm ^2. Furthermore, this electret has a temperature of 60 ° C and a humidity of 80
% Surface charge density retention rate when left in 1% environment for 1 hour
It has the surprising feature of being over 60%. That is, as shown in the examples described below, in both cases of the electret consisting of the nonpolar polymer alone and the electret of the dispersion structure in which the polar polymer is dispersed in the nonpolar polymer, under the high temperature and high humidity conditions described above. Then, the expressed charge density is greatly reduced. This is because in the former electret, the places where the charges are trapped are unstable with respect to temperature and humidity, such as the interface with impurities and the interface between the final part and the amorphous part. In the latter electret, it is considered that the polar polymer is not sufficiently surrounded by the non-polar polymer having a high electric insulation property, so that the charge disappears under the above conditions.

On the other hand, in the present invention, by adding the modified nonpolar polymer, this compound shows affinity with both the nonpolar polymer and the organic polymer, and the nonpolar polymer of the organic polymer is present. Since it facilitates atomization and dispersion in the matrix and the fine domain particles of the polar polymer are completely encapsulated by the nonpolar polymer, and there is no inhibitory effect of the additive added to the polymer, It is recognized that a high surface charge density can be obtained and a high surface charge retention can be obtained even under high temperature and high humidity conditions.

It should be noted that the above-mentioned surface charge density is for a film in which the surface on which the charges are placed is in a fixed direction. That is, when the electret is in the form of fibers, the surface on which the electric charge is placed is randomly located, and the surface area thereof is also difficult to measure, so that it is impossible to measure the surface charge density.

The electret of the present invention can be used in any known form, for example, various forms such as a film, a sheet and a fiber. In particular, the electret of the present invention has a thickness of 5 to 15 μm because the domain particles are miniaturized.
In the case of the film No. 2, a particularly remarkable effect is exhibited in terms of charge retention.

Further, the film having the above-described resin composition is easily fibrillated by stretching, and therefore, after being stretched, a defibration treatment is performed, and if necessary, cuttable, filament, yarn, string, film yarn, A fibrous electret in the form of defibrated yarn or the like can be formed. Of course, this fibrous electret can be made into a fiber-processed product by performing known treatments such as fiberizing, knitting, tufting, and non-woven fabric formation.

A preferred field of application of the polymeric electrets of the present invention is in air filter applications. That is, in order to improve the dust collection efficiency as an air filter, it can be achieved by maintaining a stable high charge density for a long period of time, and by making the fibers as fine as possible, the polymer electret of the present invention. Since has both performances, it shows excellent performance when used as an air filter.

〔Example〕

Hereinafter, the contents of the present invention will be shown with suitable examples, but the present invention is not limited to these examples unless otherwise specified.

Comparative Example 1 Melt index [ASTM D 1238L unit g / 10 minutes, below
MI]] 0.1% by weight of n-octadecyl-3- (4'-hydroxy-3 ', 5'-di-tert-butylphenol) propionate to homopolypropylene (PP) with a density of 0.91 g / cm ³ Then, the film was formed into a film having a thickness of 30 μm by the inflation film forming method. The molding temperature at that time was 200 ° C.

This film was cut into a size of 5 cm × 5 cm, and electretized by corona discharge under the following conditions using the apparatus shown in FIG.

Electretization condition Sample temperature 23 ° C Voltage 7KV DC application time 7 seconds Electrode distance 8mm The obtained electret film was aged for 48 hours at 60 ° C × 80% RH and then aged at room temperature. The surface charge density on the negative electrode side was measured for each of the front and rear samples.

The surface charge density was measured using the measuring circuit shown in FIG. 2 as follows. First, the switch S is once short-circuited from the state shown in the figure, and then opened, and the movable electrode E ₁ is lifted up.
At this time, the electric charge induced in the electrode E ₁ is transferred to the capacitor C, and a potential difference V is generated between the terminals of C. By measuring this potential difference V with an electrometer M, the surface charge density σ is [Wherein C is the electrostatic capacity (F) of the capacitor, and A is the surface area (cm ² ) of the electret].

The results obtained are shown in Table 1.

Comparative Example 2 95% by weight of polypropylene of Comparative Example 1 and 5% by weight of polycarbonate (softening point 150 ° C., PC) and 0.1% by weight of n-octadecyl-3- (4 ′) based on these polymer compositions.
-Hydroxy-3 ', 5'-di-tert-butylphenol) propionate was kneaded at 260 ° C in an extruder to form an inflatable film having a thickness of 30 µm.

An electret film was prepared in the same manner as in Comparative Example 1, and the surface charge density was measured. The results are shown in Table 1.

Example 1 90% by weight of the polypropylene of Comparative Example 1, 5% by weight of the polycarbonate of Comparative Example 4, 5% by weight of maleic anhydride-grafted polypropylene (maleization rate 3% by weight) and n-octadecyl-3- (4'-hydroxy-). 3 ', 5'-di-
(tert-Butylphenol) propionate was kneaded with 0.1% by weight of the above polymer composition at 260 ° C. by an extruder at the same time to form an inflation film having a thickness of 30 μm.

An electret film was prepared in the same manner as in Comparative Example 1, and the surface charge density was measured. The results are shown in Table 1.

Example 2 The same procedure as in Example 1 was repeated except that 0.1% by weight of calcium stearate was added. The results are shown in Table 1.

Examples 3 to 8 The procedure of Example 2 was repeated except that the type of polar polymer or the type of modified inorganic polymer was changed. The results are shown in Table 1.

Comparative Examples 3 to 6 The procedure of Example 1 was repeated except that the type of additive was changed.
The results are shown in Table 1.

Comparative Examples 7 to 8 The same procedure as in Example 5 or 7 was performed except that the kind of the additive was changed. The results are shown in Table 1.

[Effect] The electret of the present invention has a high initial charge density and
It also has a good long-term charge retention rate, and thus can be used in various applications as a film, sheet or fibrous material.

[Brief description of drawings]

FIG. 1 is a schematic layout diagram of an apparatus used for electretization, and FIG. 2 is a measurement circuit diagram of surface charge density. Reference numeral 1 is a negative needle electrode, 2 is a positive needle electrode, 3 is a sample film, and 4 is a DC power source. Reference numeral E ₁ is a movable electrode, E ₂ is a fixed electrode, D is an electret, S is a short-circuit switch, C is a capacitor, and M is an electrometer.

Claims (1)

[Claims] 1. Non-polar polymer: 60 to 99% by weight, polar polymer: 0.5 to 39.5% by weight, unsaturated carboxylic acid or its derivative (a), unsaturated epoxy monomer (b) and olefinic non-polymer. A non-polar polymer modified with a monomer selected from the group consisting of silane monomers having a saturated bond (c): 0.5 to 20 wt%, a compound represented by the following formula in a polymer composition consisting of, (In the formula, R is an alkyl group, and n is a positive number.) An electret characterized in that a higher fatty acid alkali and / or alkaline earth metal salt is further compounded if necessary.