JPS5923098B2 - Electret - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electret with improved long-term charge retention.

Electrets are used in acoustic devices such as microphones, speakers, and cartridges, and are also being used in measurement devices such as vibration meters and strain meters, non-contact switches, dust filters, and memory devices.

In addition, in recent years, polymer electret films have been used for temporary propagation, and applications in the medical field are also expanding.

'Polyolefin resins such as polyethylene, polypropylene, and poly-4-methyl-1-pentene have been considered as base materials for electrets, but their polarization decays relatively quickly, making them impractical. .

The present invention was arrived at as a result of studies aimed at improving the long-term charge retention of electrets. Regarding electrets that are made into electrets.

The modified polyolefin used as the base material of the electret of the present invention is prepared by blending at least one monomer selected from unsaturated carboxylic acids and derivatives thereof into the raw polyolefin, or by further heating, etc., a part or all of the raw polyolefin. It can be obtained by graft copolymerization with.

, raw material polyolefins include ethylene, propylene, butene, isobutyne, pentene, impentene, 4-
There are homopolymers and copolymers of two or more of α-olefins with methyl-1-pentenna, such as polyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-pentene, and ethylene/propylene. copolymer,
Ethylene-butene copolymer, ethylene-4-methyl-1
-pentene copolymers, propylene-1-butene copolymers, 4-methyl-1-pentene-1-decene copolymers, etc., as well as α-olefins and other polymerizable monomers, such as vinyl acetate, Unsaturated esters of carboxylic acids such as vinyl propionate or saponified products thereof, unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid or their anhydrides, monomers such as esters, amides, imides, chlorides, phthalene, dicyclo pentagen,
There are copolymers with conjugated or non-conjugated diene monomers such as ethylidenenorbornene, and a mixture of two or more of these may be used.

Unsaturated carboxylic acids used to modify raw material polyolefins include acrylic acid, methacrylic acid, maleic acid, fumaric acid, and itaconic acid, and derivatives of unsaturated carboxylic acids include acid anhydrides, esters, amides, imides, There are metal salts, such as maleic anhydride, citraconic anhydride, itaconic anhydride, himic anhydride (5-norbornene-2,3-dicarboxylic anhydride), tetrahydrophthalic anhydride, methyl acrylate, ethyl acrylate, Methyl methacrylate, butyl acrylate, glycidyl acrylate, glycidyl methacrylate, maleic acid monoethyl ester, maleic acid diethyl ester, acrylamide, maleic acid monoamide, maleic acid diamide, maleic acid-N-monoethylamide, maleic acid-N , N
-diethylamide, maleic acid-N-monobutylamide, maleic acid-N,N-dibutylamide, fumaric acid monoamide, fumaric acid diamide, fumaric acid-N-monoethylamide, fumaric acid-N,N-diethylamide, fumaric acid Examples include -N-monobutylamide, N-fumaric acid, N-dibutylamide, maleimide, N-butylmaleimide, and N-phenylmaleimide, and these may be used alone or in combination of two or more.

Various known methods can be used to modify the raw polyolefin with the above monomer.

For example, by mixing the raw polyolefin and monomer in the presence or absence of a solvent or under heating, or by heating with or without the addition of a radical initiator, some or all of the raw polyolefin can be There is a method of graft copolymerizing monomers, and other vinyl monomers such as styrene may be present in the reaction.

Although the monomer concentration in the modified polyolefin can take various values, it is particularly preferably 10-4 to 100% by weight, most preferably 10-2 to 10% by weight.

From the viewpoint of industrial production, the monomer concentration is set in advance from 10 to 50.
Although it is preferable to produce a modified polyolefin by weight and then mix this modified polyolefin with an unmodified polyolefin to obtain a modified polyolefin, it is also possible to blend a predetermined monomer into the polyolefin from the beginning.

It is also preferable to blend modified polyolefins with different types of raw material polyolefins.

In other words, modified polyethylene wax, modified polypropylene wax, modified low-density polyethylene, modified polypropylene, etc., each having a relatively high monomer concentration, are used as polyethylene waxes.
It can also be blended with 4-methyl-1-pentene, high-density polyethylene, and the like.

Here, wax refers to a viscosity average molecular weight of 400 to 15
000, hardness (IS-2530 needle strength) 0
to 50 polymers.

Modified polyolefins include polyamide, polyester, polycarbonate, ionomer resin, polyvinyl acetate, polystyrene, ABS resin, acrylic resin, vinyl chloride resin, petroleum resin, rosin, natural rubber, fluororesin, etc. as necessary. Good too.

In addition, other additives may be added as necessary, such as process oils, plasticizers, organic or inorganic fillers, dyes, pigments, nucleating agents, mold release agents, flame retardants, voltage stabilizers, as long as they do not impair the properties of the modified polyolefin. , antioxidants, ultraviolet absorbers, etc.

Examples of these include magnesium oxide, magnesium hydroxide, talc, barium sulfate, gypsum, calcium carbonate, magnesium carbonate, clay, silica, hydrotalcite, titania, mica, glass powder, glass fiber, wood powder,
Examples include vinylon fiber and synthetic wood fiber.

These additives are added before or after modification of the polyolefin.

The modified polyolefin is electretized by various conventionally known methods, such as a thermoelectret method, an electroelectret method, a radioelectret method, a mechanoelectret method, and the like.

The electret of the present invention can be formed into a fibrous, film, tube, or capillary shape, or can be further used as a woven fabric or nonwoven fabric, or laminated with other resins or as a coating layer.

Electretization is performed simultaneously with each of these molding steps, or before or after each step depending on the purpose.

Since the electret of the present invention has improved long-term charge storage, it can be used in a wide range of applications, including acoustic devices such as microphones, measurement devices, various filters, memory devices, and the medical field.

Examples are shown below.

Comparative example 1 Melt flow index (MI) 0.9, density 0
．． 954 g/i high density polyethylene (HDP E
) was used to mold a T-die film with a thickness of 50 μm.

This film is interposed between a pair of electrodes, and a DC voltage e1
After applying 0 KV, it was heated from room temperature to 120° C. After 2 minutes, heating was stopped, and after forced cooling to room temperature, the application of DC voltage was stopped, and an electret was produced.

The surface potential of this electret is -1800V immediately after manufacture.
After leaving this in an atmosphere of 250\60 to 70% RH for 7 days, the atmosphere was almost the same.

However, the surface potential was measured with a rotating sector type surface voltmeter.

Comparative Example 2 Isotactic polypropylene (PP) with MI7 and density of 0.91 g/i was molded into a T-die film with a thickness of 50 μm.

This film was made into an electret in the same manner as in Comparative Example 1, and its surface potential was measured.

The results are shown in Table 1.

Example 1 5 parts by weight of acrylic acid grafted PP obtained by graft copolymerizing 7 parts by weight of acrylic acid with the PP used in Comparative Example 2 and 95 parts by weight of unmodified polypropylene (PP) were mixed, and after granulation at 220 ° C., the thickness It was molded into a 50μ T-die film.

This film was converted into an electret and its surface potential was measured in the same manner as in Comparative Example 1.

The results are shown in Table 1.

Examples 2 to 20 Table 1 shows the results of carrying out the same procedure as in Example 1 using the unmodified polyolefins (unmodified PO) and modified polyolefins (modified PO) shown in Table 1.

Claims (1)

[Claims] 1. An electret obtained by converting a polyolefin modified with at least one kind selected from unsaturated carboxylic acids or derivatives thereof into an electret.