JPS63110716A - Manufacture of electrette film - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a method for producing an electret film used for producing electret filters and the like that are widely used as high-performance filters.

``Prior art'' Electret filters efficiently collect fine particles such as cigarette smoke with a size of about 0.1 to 0.5 μm using Coulomb force and induced electromotive force, so they are used in special rooms in hospitals and in cleanliness in the electronics industry. It is widely used as a dust removal filter for air conditioning systems in rooms, etc., a dust mask for work, a filter incorporated in vacuum cleaners, etc., or a pre-treatment filter for ultra-high performance HEPA filters.

Conventionally, the manufacturing method for the above-mentioned electret filters includes: (1) corona charging after molding a non-polar polymer substance into a filter;
Alternatively, a method using corona-charged electret fill 12 during or after heating the film (Japanese Patent Publication No. 56-47299); Method using Rin-treated film (JP-A-60-1
96921) and the like are known.

[Problems to be Solved by the Invention] To make a filter using an electret film, the film is usually defibrated into small pieces and then processed into a filter by non-woven fabric processing or the like.

In this case, attenuation of the amount of charge over time is an unavoidable problem, but it is extremely important that the filter has a residual charge as close as possible to the initial charge.

By the way, in the method (2) above, even if the film is charged at the maximum voltage at which pinholes do not occur due to corona discharge, there is a limit to the amount of initial charge, and its attenuation over time is relatively large. On the other hand, in the method (■) above, the load 1ffi is small,
Further, due to frictional charging, only a negative Fi charge was generated, and a more stable load 711m could not be obtained, resulting in unevenness in the product.

The present inventors have conducted intensive research to obtain an electret film with a large initial charge amount and a small attenuation of the trapped charge amount, and have found that the charge riffi and decay rate of the electret film are due to polymer structural defects, impurities, etc. Does it differ depending on the chemical structure, and is the corona charge a stable and large charge? It was found that 11tffi could be obtained.

The present invention was developed based on the above findings, and an object of the present invention is to provide a method for producing an electret film that has a large charge amount and a low decay rate.

``Means for Solving the Problems'' The present invention has achieved the above-mentioned objects, so the gist of the present invention is to add water to an insulating polymer material (1 ri = 4 wt%).
Production of an electret film characterized by mixing the following fatty acid magnesylano, salt or oxyfatty acid magnesium salt to form a film, and then heating and stretching the film and corona charging it at the same time, or heating and stretching and then corona charging the film. It's in the law.

"Specific structure and operation of the invention" The present invention will be explained in detail below.

The insulating polymer material used in the present invention has a volume resistivity of 1□tsΩ・cm or more, preferably 1015Ω.
・Any film can be used as long as it is larger than cm and the film can be defibrated, such as polypropylene, polyethylene,
Examples include polyester, vinyl chloride resin, and fluororesin.

Furthermore, magnesium salts of fatty acids or oxyfatty acids blended into insulating polymeric substances have a water content of 4w.
It is necessary that it is L% or less.

Magnesium salts of fatty acids or oxyfatty acids include:
Examples include magnesium enanthate, magnesium laurate, magnesium palmitate, magnesium stearate, magnesium ricinoleate, magnesium oxystearate, magnesium lappalmitate, and the like.

The water content here refers to the water content of magnesium salts of fatty acids or oxyfatty acids measured using Karl Fissi and Yar reagents, and films using materials with this value exceeding 4 wt% will have charge decay without exception. The speed is too high and inappropriate.

The amount of the magnesium salt of fatty acid or oxyfatty acid having a water content of 4 wt% or less based on the insulating polymer material is 0.1 to 2.0 wt%, particularly 0.5 to 2.0 wt%.
% is preferred. If the amount is less than 0.1 wt%, there is no effect, and if it exceeds 2.0 wt%, the effect will not change and it will be uneconomical.

An excellent electret film can be obtained by mixing a magnesium salt of a fatty acid or oxyfatty acid with the above insulating polymeric substance and forming a film, and then heating and stretching and corona charging at the same time, or heating and stretching and then corona charging. .

The film may be stretched using any stretching method such as a hot roll or a hot plate. The stretching temperature and stretching ratio are not particularly limited and may be set to optimal conditions depending on the type, shape, etc. of the film.

To give a preferable example of the stretching temperature and stretching ratio, for example, when a polypropylene film is stretched with a hot roll, the stretching temperature is preferably 110 to 140°C, and the stretching ratio is preferably within the range of 4 to 10 times.

For the above-mentioned corona charging, it is preferable to use a high voltage within a range that does not generate pins on the film in order to increase the amount of charge, and it is usually 5 to 20 KV, although it varies depending on the type of insulating polymer material used. It is done.

"Example" Next, the present invention will be explained in detail by showing Examples and Comparative Examples.

Example 1 0.5 wt % of magnesium stearate having a water content of 3.4 wt % was added to polybropyrene having a volume resistivity of 1QI5 Ω·cm to form a film with a thickness of 40 μm. This film was stretched with a heated roll at 120°C to a stretching ratio of 5 times and corona charged at 10 KV to create an electret film with a thickness of 20 μm. was measured.

Example 2 Measurements were carried out in the same manner as in Example 1, except that magnesium oxystearate having a water content of 3.6 wt% was used instead of magnesium stearate having a water content of 3.4 wt%.

Example 3 Moisture content is 3wt instead of magnesium stearate
The measurements were carried out in the same manner as in Example 1 except that % magnesium enanthate was used.

Comparative Example 1 Measurements were carried out in the same manner as in Example 1, except that magnesium stearate with a water content of 4.7 wt% was used.

Comparative Example 2 Example 1 except that magnesium stearate was not used
Measurements were carried out in the same manner.

Comparative Example 3 Example 1 except that Marin charging was performed instead of corona charging.
Measurements were carried out in the same manner.

Comparative Example 4 Measurement was carried out in the same manner as in Example 1 except that zinc stearate having a water content of 3.2 wt% was used.

The measurement results of Examples 1 to 3 and Comparative Examples 1 to 4 are shown in Table 1.

As is clear from Table 1, the electret film produced by the method of the present invention has a large initial charge mound and a small attenuation 1.

After converting the electret film produced by the method of the present invention into strip fibers, the filter is processed into a nonwoven fabric.
It was extremely effective in removing dust.

"Effects of the Invention" As mentioned above, the method of the present invention is an excellent method for obtaining an electret film with a large initial charge 1 and a small attenuation of the amount of charge.

Claims (1)

[Claims] After forming a film by mixing a fatty acid magnesium salt or an oxyfatty acid magnesium salt with a water content of 4 wt% or less into an insulating polymeric substance, the film is heated and stretched and corona charged at the same time, or after the film is heated and stretched. A method for producing an electret film characterized by corona charging.