JPH05217802A - Polymer electret and its molded body - Google Patents

Abstract

PURPOSE:To facilitate molding by a method wherein a molded body is formed by using a polymer electret which is formed by electrifying poly-alpha-olefin composed mainly of a syndiotactic structure. CONSTITUTION:The title electret is a polymer electret which is formed by electrifying poly-alpha-olefin composed mainly of a syndiotactic structure. The title molded body is a polymer electret molded body whose structure is composed of a thin filmlike structure, a fiberlike structure, a sheetlike structure or other arbitrary shapes. Polyolefin having the syndiotactic structure may be used as the syndiotactic polyolefin; not only the single polymer of an olefin but also a random copolymer with two or more kinds of other olefins or a block copolymer is included. Thereby, it is possible to obtain the polymer electret whose charged characteristic is good and whose physical-property balance is excellent.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to polymeric electrets. Specifically, it relates to a polymer electret composed of a poly-α-olefin having a specific three-dimensional structure.

[0002]

2. Description of the Related Art It is known that when a polymer material having a very low electric conductivity is charged by various polarization treatments, the life of the charge extends for a very long time. A substance having these properties is known as an electret, and as a material thereof, polyolefin, polyester, polyvinylidene fluoride, silicon resin, epoxy resin, polystyrene, etc. have excellent electrical insulation properties, are flexible, and have heat resistance. , Hydrophobic polymeric materials have been used.

[0003]

Polyolefins, especially polypropylenes, are very often used because they are easy to process and can be obtained at low cost. However, it cannot be said that the charging characteristics of the polypropylene alone are very excellent, and in order to improve it, various additives are usually added to the polypropylene alone to improve the charging characteristics. Therefore, there are problems that the moldability becomes poor and the cost becomes high.

[0004]

[Means for Solving the Problems] The inventors of the present invention solved the above problems and conducted various studies on polyolefins which can be provided at low cost without impairing moldability. Polyolefins having a syndiotactic structure have hitherto been known only for polypropylene, but it was difficult to say that they have a low syndiotacticity and exhibit the characteristics of syndiotactic polypropylene. However, it has recently been discovered that by using a special metallocene catalyst, polypropylene with good tacticity can be obtained with a syndiotactic pentad fraction exceeding 0.7. This syndiotactic polypropylene is expected to be used as a polypropylene having a relatively excellent balance of physical properties such as rigidity and impact resistance, at a level at which it can be sufficiently used for conventional isotactic polypropylene. In order to solve the above-mentioned problems, the present inventors have made earnest studies on the physical properties of syndiotactic polyolefin, and have found that the syndiotactic polyolefin has good electret properties and an excellent physical property balance, and completed the present invention.

That is, the present invention is a polymer electret obtained by charging a poly-α-olefin mainly having a syndiotactic structure. Further, the present invention is a polymer electret molded product having a thin film-like structure, a fibrous structure, a plate-like structure or any other shape.

In the present invention, the syndiotactic polyolefin may be any polyolefin having a syndiotactic structure, and may be not only an olefin homopolymer but also a random copolymer with two or more kinds of other olefins, or a block copolymer. Polymers are also included. For example, poly-α-olefins such as polypropylene, polybutene, polypentene, polyhexene, polyheptene, and polyoctene having a syndiotactic structure and cyclic polyolefins such as polycyclopentene and polynorbornene, or these olefins and α-olefins having 2 to 20 carbon atoms And a copolymer is used, and in the case of copolymerization, the proportion of the copolymerization monomer used is less than 10 wt% in random copolymerization,
In the block copolymerization, it is preferable that the polymerization of the olefin alone is 50% or more of the whole.

The catalyst used to produce syndiotactic polyolefins is described by JAEWEN et al. In J. Am. Che.
The compounds described in m.Soc., 1988, 110, 6255-6256 can be exemplified, but even if the catalyst has a different structure, the polyolefin obtained when homopolymerization of olefin is a polyolefin having a syndiotactic structure. Can be used as long as it can be manufactured.

[0008] Specifically, the catalyst composed of isopropyl (cyclopentadienyl-1-fluorenyl) hafnium dichloride or isopropyl (cyclopentadienyl-1-fluorenyl) zirconium dichloride and aluminoxane described in the above literature is exemplified. It As the aluminoxane, two types of structures represented by the following general formulas 1 and 2 (in the formula, R is a hydrocarbon residue having 1 to 3 carbon atoms and n is an integer of 1 to 50) are known. Any of these can be used, and in particular, a methylaluminoxane in which R is a methyl group and n is 5 or more, preferably 10 or more is used.

[0009]

[Chemical 1]

[0010]

[Chemical 2]

In order to use the thus obtained polyolefin having a syndiotactic structure as a polymer electret, it is necessary to form polarization of charges in the polymer. A known method can be used as a method of forming polarization to generate an electret. That is,
(1) A method in which a polymer compound is heated to a melting temperature and then cooled while applying a high DC voltage thereto. (2) A method of injecting charges into a polymer compound by using corona discharge. (3)
Examples include a method of irradiating a high molecular compound with a low energy electron beam in a vacuum. Here, the shape of the polymer compound is not particularly limited, and an amorphous shape, a thin film shape, a fibrous shape, a plate shape, or a combination thereof can be used.

For example, the electret fiber is obtained by forming a film-like syndiotactic polypropylene into an electret by corona discharge while stretching, and then splitting the fiber into a fiber, or by treating with a high voltage during spinning to an electret fiber. It is created by etc. The fibers thus produced can be used for air filters, masks, wipers, hair caps and the like. In addition, since it has good moldability, it can be used as an electret molded product having various shapes as an electric device or a medical material.

In the present invention, the polymer compound was evaluated by applying a voltage close to the dielectric breakdown voltage at room temperature into an electret. That is, a polymer film is sandwiched between a SUS disc having a diameter of 95 mm and a SUS flat plate larger than that, and a DC high electric field is slowly raised to a voltage just before the breakdown voltage, and the state is maintained for 30 seconds as it is. An electro electret was prepared by reducing the applied voltage to 0 V without turning it off.

[0014]

EXAMPLES The present invention will be further described with reference to the following examples.

Example 1 0.2 g of isopropyl (cyclopentadienyl-1-fluorenyl) zirconium dichloride and 30 g of methylaluminoxane (polymerization degree: 16.1) manufactured by Tosoh Akzo Co., Ltd. were used, and an internal volume of 100 liters containing 100 liters of toluene was used. After adding propylene to the autoclave at 20 ° C and adding propylene to a polymerization pressure of 3 kg / cm ² -G, polymerization was carried out at 20 ° C for 2 hours, and then deashing treatment was performed with methanol and methyl acetoacetate. It was washed with a hydrochloric acid aqueous solution, then filtered, and dried under reduced pressure at 80 ° C. to obtain 5.6 kg of syndiotactic polypropylene.

This polypropylene has a syndiotactic pentad fraction of 0.935 according to ¹³ C-NMR,
C. Tetralin solution has an intrinsic viscosity (η) of 1.45, 1,
The ratio of the weight average molecular weight to the number average molecular weight (MW / MN) measured with 2,4-trichlorobenzene was 2.2.

(Preparation of electret) A film having a thickness of 50 μ was prepared using the syndiotactic polypropylene obtained above, and a voltage (2-3 MV / cm) close to the dielectric breakdown voltage was applied to this film at room temperature. After holding for 30 seconds, the voltage was rapidly lowered to 0 V without interrupting the circuit to prepare an electret, and the surface charge density was measured. Further, as a comparison, the same measurement was performed using a commercially available isotactic polypropylene (Comparative Example 1).

The surface charge density was measured using a JIS-K6911 compliant product having a main electrode of 50 mmφ and a guard ring inner / outer diameter of 70/80 mmφ at room temperature and a pressure of 2.5 kg. In addition, the measurement is shown as an average value of a total of 9 points in the central portion and 8 points in the peripheral portion, and an average value of 5 samples electretized under the same conditions. FIG. 1 shows the changes over time in the surface charge density ratio (σ ratio immediately after measurement and immediately after charging) of each sample when left at room temperature and 50% humidity. The surface charge of isotactic polypropylene decreased sharply within a few hours after charging, whereas the syndiotactic polypropylene retained 70% of the initial surface charge even after 2 weeks.

Example 2 The time course of the surface charge density was measured when the measurement conditions were changed and the temperature was kept at room temperature and humidity of 100%. As a result, the surface charge of isotactic polypropylene decreased sharply within several hours after charging. However, the syndiotactic polypropylene retained 80% of the initial surface charge even after 2 weeks. FIG. 1 shows the change over time in the surface charge density ratio.

[0020]

INDUSTRIAL APPLICABILITY The polymer electret of the present invention has good charge characteristics and an excellent balance of physical properties, and is industrially extremely valuable.

[Brief description of drawings]

FIG. 1 shows a time-dependent change in the surface charge density ratio (ratio of σ during measurement and σ ₀ immediately after charging) of an electret when left at room temperature.

Claims (2)

[Claims] 1. A polymer electret obtained by charging a poly-α-olefin mainly composed of a syndiotactic structure. 2. A molded product composed of a polymer electret obtained by charging a poly-α-olefin mainly composed of a syndiotactic structure.