JPS6015137B2 - Electret - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electret comprising a specific 4-methyl-1-pentene polymer.

Electrets are used in acoustic devices such as microphones, speakers, and cartridges, and attempts are being made to apply them to measurement devices such as vibration meters and strain meters, non-contact switches, dust filters, and other memory devices.

In addition, in recent years, polymer electret films have been used on a trial basis for callus growth, and their use in the medical field is also expanding. Polyethylene and polypropylene have been considered as base materials for electrets, but their polarization attenuates relatively quickly, making them impractical.

As a result of examining substrates suitable for use as electrets, the present inventors discovered that a specific 4-methyl-1-pentene polymer exhibits excellent performance, and thus arrived at the present invention.

That is, the present invention relates to an electret characterized by comprising a copolymer of 4-methyl-1-bentene and a Q-olefin having 6 to 18 carbon atoms. Here, Q-olefins having 6 to 18 carbon atoms include 1-hexene, 3
-Methyl-1-bentene, 1-octene, 1-decene,
Examples include 1-tetradecene and 1-octadecene, and one or more of these may be used.

The average content of Q-olefin having 6 to 18 carbon atoms in the copolymer is 0.3 to 20 mol%, especially about 1
It is desirable that the content be 12 mol%. If the content is less than 0.3 mol%, especially 1 mol%, the resulting copolymer will have poor moldability, and the electret molded product will also have poor impact resistance.

If it exceeds 20 mol%, especially 12 mol%, the electret performance deteriorates seriously.

These 4-methyl-1-pentene copolymers may be blended with at least one monomer selected from unsaturated carboxylic acids and derivatives thereof, or further heated to form 4-methyl-1-pentene copolymers. It is also possible to graft-copolymerize a polymer and modify it, or to blend the grafted material into a base polymer.

For the 4-methyl-1-bentene copolymer, polyamide, polyester, polycarbonate, ionomer resin, polypynylacetate, polystyrene, ABS resin, acrylic resin, vinyl chloride resin, petroleum resin, rosin, natural rubber, fluororesin can be used as necessary. etc. may be included.

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 are magnesium oxide, magnesium hydroxide, talc, barium sulfate, gypsum, calcium carbonate, magnesium carbonate, clay, silicate, hydrotalcite, titania, mica, glass powder, glass fiber, wood flour, vinylon fiber. , synthetic wood fibers, etc. Various conventionally known methods, such as a thermal electret method, an electroelectret method, a radioelectret method, and a mechanical Z-electret method, can be used for the electret formation.

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

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 device pairs 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 20.
A T-die film with a thickness of 50 mm was molded using high-density polyethylene (HDPE) of 954 mm/mm.

This film is interposed between a pair of electrodes, and a DC voltage of 61
After impressing 0KV, heat from room temperature to 120oo,
After 2 minutes, the heating was stopped, and after forced cooling to room temperature, the application of the 3 DC voltage was stopped, and an electret was produced. The surface potential of this electret was -1800 V immediately after production, and after being left in an atmosphere of 2500 V and 60 to 70% RH for 7 days, it became almost zero.

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

Comparative Example 2 Isotactic polypropylene (PP) of M17 and a density of 0.91 polypropylene was molded into a T-die film with a thickness of 50 mm.

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

The results are shown in Table 1. Example 1 A 4-methyl-1-bentene copolymer (4-M-1-P copolymer) containing 2.5 mol% of 1-decene was deposited to a thickness of 50 mol %.
It was molded into a French T-die film and made into an electret using the same machine as Comparative Example 1, and its surface potential was measured.

The results are shown in Table 1. The electrostatic voltage of the TPX electret stabilized at that value after 7 days. Other similar results are shown in Table 1.

Table 1.

Claims (1)

[Scope of Claims] 1. An electret comprising a copolymer of 4-methyl-1-pentene and an α-olefin having 6 to 18 carbon atoms. 2. The electret according to claim 1, wherein the average content of α-olefin having 6 to 18 carbon atoms is 0.3 to 20 mol%.