KR101035259B1 - Fluororesin polymer electret and process for producing the same - Google Patents

Abstract

The present invention relates to a fluorine-based polymer resin electret and a method for manufacturing the same, and more particularly, to a fluorine-based polymer having a single-layer thin film comprising a heat resistant fluorine-based polymer resin and a dielectric particle having a perovskite crystal structure. Forming a thin film by spin coating a metal plate with a heat-resistant fluorine-based polymer resin mixture solution containing a polymer resin electret and a dielectric particle having a perovskite crystal structure, and forming the thin plate by drilling the metal plate coated thereon And it relates to a method for producing a fluorine-based polymer resin electret comprising the step of applying a voltage individually to the molded metal plate.

According to the present invention, it is excellent in thermal stability and charge storage characteristics, and can be expected to provide an effect of providing a fluorine-based polymer resin electret capable of implementing stable performance under external environmental conditions such as heat, humidity, impact.

Electret, Piezoelectric element, Corona discharge, Radon sensor

Description

Fluorine-based polymer resin electret and its manufacturing method {FLUORORESIN POLYMER ELECTRET AND PROCESS FOR PRODUCING THE SAME}

The present invention relates to a fluorine-based polymer resin electret and a method for manufacturing the same, and provides an effective fluorine-based polymer resin electret as a core probe in a sensor for measuring radioactive material.

Electret bonds a polymer thin film (eg FEP, PTFE, PFA, etc.) onto a metal substrate to form a semi-permanent polarity through high-temperature corona discharge, and is one of the key components whose performance is determined by the amount of negative charge accumulated. Since electrets have excellent charge storage characteristics, they are used in a wide range of industries such as microphones, touchpads, various sensing devices, and radiation dosimeters.

Conventional electret manufacturing technology is a high temperature bonding of the FEP film on the metal plate, and charge the negative charge by high voltage corona discharge on the formed polymer film to form a semi-permanent residual polarization dielectric. A dielectric substance is a substance that generates electric polarization but no direct current when an electrostatic field is applied, and an electret corresponds to a dielectric.

In general, polymer resin electrets have excellent charge retention properties. For this reason, they are applied to a wide range of fields such as small acoustic sensors such as ECM (Electret condenser microphone), telephone dials, noise detectors such as impact detectors and mechanical motors, radon detectors and air purifier filters.

However, the polymer resin electret can operate normally in a normal environment, but under a poor environment such as a sudden change in temperature or humidity, it loses a charged charge and has a disadvantage in that it cannot work properly.

That is, the existing electrets have a problem in that the reliability of the measured value is lowered and the electrets need to be changed frequently because the charge storage characteristics of heat, humidity, shock, etc. are inferior. Moreover, unused electrets are difficult to secure reliability of performance implementation depending on preservation conditions.

In particular, sensor sensors using a group of electrets are likely to be exposed to abnormal environments in the industrial field or during their manufacturing process, and their purpose of use is related to the safety of workers and equipment, so they may not function as electrets even in harsh environments. In order to improve the charge retention characteristics, it is required.

On the other hand, radon is a colorless, tasteless, and odorless inert gas that emits an alpha ray with a half-life of 3.8 days, and is contained in trace amounts of clay, sand, rocks, minerals, and building materials containing them. Is the sixth decay product of uranium. Radon contained in soil and building materials is released into the ground or indoor environment by diffusion. Radon can come from the soil through cracks or sewers in the bottom of the floor, or enter the room when radon-containing groundwater or natural gas is used. It is also released from high building materials such as cement, sand and gravel concrete and phosphate gypsum board. Therefore, if a house is built on a high radon concentration site or a building material with a high radon emission rate is used, the radon concentration in the room may increase.

The probability of death of lung cancer from radon is the second highest after that of tobacco, and in the United States, it has been reported that between 5,000 and 20,000 people die each year of lung cancer from radon exposure.

Although radon is a natural radioactive substance, it is possible to reduce the concentration sufficiently by a reduction method including ventilation, so developed countries have already established and managed the management standard value. The management standards are not the same in each country and show a slight difference based on the average radon concentration in each country. In Korea, the 4pCi / is based on the “Air Quality Control Act for Multi-use Facilities” established in April 2003. ℓ (148Bq / ㎥) corresponds to the management standard value.

[Table 1] Harmfulness of Radon

Radon concentration Smoker Non-smoker (pCi / ℓ ^* ) % Mortality from lung cancer Comparison with mortality from other accidents Mortality rate due to lung cancer (%) Comparison with mortality from other accidents 20 13.6 100 times as drowned 0.8 Death probability by robbery 10 7.1 100 times of fire death 0.4 - 8 5.7 - 0.3 10 times more than a plane crash 4 2.9 100 times more than a plane crash 0.2 Drowning probability 2 1.5 Twice the number of car crash deaths 0.1 Probability of fire death 1.3 0.9 Indoor average concentration <0.1 Indoor average concentration 0.4 0.3 Outdoor average concentration <0.1 Outdoor average concentration  *: 1pCi / ℓ = 37.037Bq / ㎥, recommended indoor radon concentration 200 ~ 600Bq / ㎥

The radon measurement technique uses alpha, beta, and gamma rays emitted from radon and radon progeny. The most common detectors are pulse ionizers, packed ionizers, ZnS (Ag) scintillation detectors, alpha particle spectrometers using silicon diodes and surface barriers or diffusion junction detectors, NaI (Tl) or Ge (Li). Gamma-ray spectrometer and a solid-state detector for detecting the droplets of alpha particles using.

Electet ion chambers are typical of radon sensors using electrets. Filled membrane ionizers are called E-Perm (electretpassive environment radon monitors), and the concentration of radon can be determined by measuring the ions and electrons generated by the collapse of radon in the ionizer.

E-Perm can operate normally in a normal environment, but under poor conditions such as sudden changes in temperature or humidity, the E-Perm loses its charged charge and is difficult to function, and the potential of the charge film can be discharged by the accidental frictional charge. have.

In addition, the sensors using other types of electrets are likely to be exposed to abnormal environments in the industrial field or in the manufacturing process, and their purpose is related to the safety of workers and equipment, so they can function as electrets even in harsh environments. In order to improve the charge retention characteristics, it is required.

The inventors of the present invention have made efforts to solve the above problems, and found that, when strongly charged on dielectric particles having a perovskite crystal structure, a large amount of charge can be charged into the internal space of the crystal structure. The present invention was completed.

Accordingly, an object of the present invention is to provide an electret excellent in charge retention characteristics and a sensor for measuring radon to which the electret is applied.

Another object of the present invention is to provide a method for producing the electret, which is excellent in charge storage characteristics.

As an example for achieving the above object, the present invention provides a fluorine-based polymer resin, characterized in that it comprises a thin film of a single layer structure comprising a heat resistant fluorine-based polymer resin and a dielectric particle having a perovskite crystal structure Provide a let.

It is more preferable that the heat resistant fluorine-based polymer resin further includes a ceramic dielectric.

As another example for achieving the above object, the present invention provides a sensor for measuring radon provided with the electret.

As another example for achieving the above object, the present invention, the thin film by spin coating a metal plate with a heat-resistant fluorine-based polymer resin mixture solution containing 1 to 5% by weight of dielectric particles having a perovskite crystal structure It provides a method for producing a fluorine-based polymer resin electret comprising the step of forming, forming the perforated metal plate coated with the thin film, and applying a voltage to the molded metal plate individually. .

EMBODIMENT OF THE INVENTION Hereinafter, the fluorine-type polymer resin electret of this invention and its manufacturing method are demonstrated concretely.

The fluorine-based polymer resin electret of the present invention includes a thin film including a heat resistant fluorine-based polymer resin and a dielectric particle having a perovskite crystal structure.

When the heat-resistant fluorine-based polymer resin is used as the basic electret resin for charging, excellent charge storage characteristics can be maintained even in high temperature and wet environments. The heat resistant fluorine-based polymer resin is not limited, but may be at least one selected from PTFE (Polytetrafluoroethylene), Poly (perfluoroalkyl acrylate) (PFA), Fluorinated ethylenepropylene (FEP), Polyvinylidenefluoroide (PVDF), and the like. It is preferable to use one selected from PFA and FEP. Most preferably, PFA or FEP is used in terms of processability and physical properties.

The fluorine-based polymer resin electret of the present invention contains dielectric particles. The dielectric particles are used to form a polymer thin film inducing high-efficiency charge polarization of an electret, and are characterized by including dielectric particles having a perovskite crystal structure.

The dielectric particles having the perovskite crystal structure are ABO ₃ type ferroelectrics. The ABO ₃ type ferroelectric particles have various interesting electrical, mechanical, and optical properties, but have spontaneous polarization and polarization inversion by an external electric field while spontaneous polarization exists among these properties. In addition, it has piezoelectricity or pyroelectricity of single crystal or ceramic ferroelectric, and thus may have dielectric, insulation, ferroelectricity, pyroelectricity, piezoelectricity, optical and mechanical properties of the crystalline state even in the ferroelectric thin film state. Among them, the piezoelectric property may serve to form a pore in the thin film under high charge conditions after the formation of the electret thin film so that the polarized charge is uniformly formed.

When a high voltage is applied to the dielectric particles having the perovskite crystal structure, internal charges and applied charges between the crystal structures are repelled, thereby forming internal spaces of the fluorine-based polymer due to compression and relaxation effects between the crystal structures. In addition, a large amount of charge may be filled into the internal space. In the present invention, by using the dielectric particles having a perovskite crystal structure, the charges of 700 V or more are uniformly filled in the internal space, thereby improving the formation and retention performance of the surface charges of the electret.

The crystal structure of ABO ₃ is a perovskite structure in which anion O (oxygen) is arranged in a cubic close enough structure, and cation A is coordinated to 12 O, and cation B is 1/4 of octahedral gap of O. It appears to occupy structure. 1 shows a perovskite structure of CaTiO ₃ .

As shown in FIG. 1, Ti atoms having a relatively small atomic radius have a space to move within octahedral sites formed by oxygen atoms. This creates a polarity as the Ti ⁴⁺ ions move up and down from the electrically neutral center position, which is called an electric dipole. Applying voltage to the perovskite crystal structure causes the crystal to deform, also known as the Leafman effect. Applying a + (plus pole) to the top of the perovskite crystal structure from the outside and a-(minus pole) to the bottom, respectively, the internal charge and the transferred voltage between the crystal structures repel each other to compress the crystal structures. In addition, when-(minus pole) is applied to the upper part and + (plus pole) is applied to the lower part, internal charges and applied voltages between the crystal structures are attracted to each other, thereby increasing between the crystal structures.

Among such as the perovskite (perovskite) a dielectric particle having a crystal structure is limited, but _{specifically, CaCO 3, BaTiO 3, SrTiO} 3, PbZrTiO 3, KNbO 3, LiNbO 3, LiTaO 3, BiFeO 3 and CaTiO ₃ At least one selected may be used.

The dielectric particles having the perovskite crystal structure may be included in the heat resistant fluorine-based polymer resin in the range of 1 to 5% by weight, preferably 1 to 3% by weight. When the content of the dielectric particles is less than the above range, the internal space relaxation effect is not sufficiently formed in the charging of high voltage, and the effect of maintaining the surface potential of 700 V tends to be lowered. There is a tendency to lower the uniform surface formation at the time of formation.

When the dielectric particles having the perovskite crystal structure are used in combination with the ceramic dielectric, the ceramic dielectric may improve the charging effect and thermal stability as an electrophilic nucleating agent, and may improve the perovskite crystal structural properties. have

Although not limited to the ceramic dielectric material, specifically, PbZrTiO, PbNbO, Al ₂ O ₃ , SiO ₂ , Si ₃ N ₄ , B ₂ O ₃ / ZnO / SiO ₂ , SiO ₂ / Si ₃ N ₄ , TiO ₂ , and At least one selected from carbon black and the like may be used. In the case of using a ceramic dielectric, the content is more than 0% by weight and may be used in the range of 3% by weight or less.

The thin film is preferably made in the range of 50 to 150 ㎛. That is, when the electret of the present invention is to be used as a radon measuring sensor, the surface potential should be formed at a voltage of 700V or more, so that the thickness of the thin film is preferably maintained in the above range.

The fluorine-based polymer resin electret of the present invention prepared by the above method has excellent charge storage characteristics and heat resistance characteristics.

The present invention is used as a sensing element in various industrial and home sensors

The fluorine-based polymer resin electret can be applied to various fields, such as various industrial and home sensors, and of course, it is particularly effective when used in radon measuring sensors.

In other words, the fluorine-based polymer resin electret of the present invention is a core component of electret ion chambers, and has a characteristic of determining radon concentration by measuring ions and electrons generated by the collapse of radon in the ionizer. It has a form of charge preservation characteristic suitable for a measuring probe.

Hereinafter, the manufacturing method of the fluorine-type polymer resin electret of this invention is demonstrated concretely.

First, a thin film is formed by spin coating a metal plate with a heat-resistant fluorine-based polymer resin mixed solution containing 1 to 5 wt% of dielectric particles having a perovskite crystal structure.

In the present invention, a spin coating method is adopted to form a thin film. Spin-coating theory has been used in various fields for several decades and is being researched and developed in recent years as a thin film process using organic materials. In the spin coating method, a thin film is generally grown by applying a solution material to the center of a sample, and rotating it at a high speed (about 3000 rpm or more). The centrifugal force is used to spread the solution evenly throughout the sample and to remove more than necessary solution from the sample for thin film production. The thickness and other properties of the thin film depend on the intrinsic propensity of the solution or other variables such as the speed of rotation, acceleration, drying time and temperature related to the spin process.

In the present invention, a thin film having a thickness in the range of 50 to 150 μm by spin coating and having an even surface is obtained.

That is, the thin film formation method such as the spraying method is not preferable in the implementation of the surface potential 700V and the uniform performance for the radon measuring electret because the thin film surface is rougher and porous than the spin coating.

The heat resistant fluorine-based polymer resin mixed solution may further include a ceramic dielectric in an amount of more than 0 wt% and 3 wt% or less.

The second step is to form a metal plate coated with the thin film.

In the conventional case, in order to form an electret, power was applied to a thin film and then formed by perforation. In these cases, the charged charges were often lost. Accordingly, the present invention solves the problem that the charged charge is lost after the power is applied by forming a thin plate coated metal plate in advance.

The third step is to apply voltage separately to the molded metal plate.

The application of the charge causes the charge to be charged. The application causes the corona discharge to be performed under atmospheric pressure.

In the present invention, the negative charge charging method by the corona discharge was improved, unlike the conventional method, the tip of the counter electrode was improved by processing the round ball type. Such corona discharges may be preferably performed under conditions in which a plurality of electrets each individually charge negatively charge.

In addition, in the present invention, unlike the prior art, a high voltage is applied to a plurality of metal plates after perforating the metal plate coated with the thin film. That is, a circular electret made by drilling a metal plate coated with a thin film (circular processing) is applied to a counter electrode capable of applying a high voltage individually, and simultaneously charging ten or more electrets individually and uniformly. It can increase the production rate and reduce the defective rate.

That is, the fluorine-based polymer resin electret of the present invention uses a mixture of heat-resistant fluorine-based polymer resin and dielectric particles, spin-coats a metal plate to form a thin film, and then perforates and applies it to change the perovskite structure of the dielectric particles during high voltage charging. By inducing the thin film surface and the internal space to relax the electret having the characteristic of forming internal pores,

After placing the perforated metal plate in a charging device for applying a high voltage, a high voltage is applied by adjusting the voltage, the electret and the charging part gap according to the type of polymer resin constituting the thin film coated on the metal plate, and applying the high voltage to the electret substrates. By forming the electrostatic field of the negative field, the molecular dipole momentum in the polymer resin constituting the electret is effectively arranged in one direction, and the discharged charges penetrate deep into the polymer resin, thereby allowing the polymer resin to secure more space charge. The charge retention characteristics of the electret can be improved semi-permanently.

In particular, when a group of fluorine resins are used as an electret resin based on the present invention, when charged according to the embodiment of the present invention, excellent charge storage characteristics can be maintained even in a high temperature and a wet environment.

According to the present invention described above, in the present invention, a ferroelectric material having a heat resistant fluorine-based polymer resin and an ABO ₃ structure is used, and by improving the negative charge charging method by individual corona discharge in each electret, excellent thermal stability and negative charge accumulation capacity are achieved. It is possible to manufacture an electret having improved.

According to the present invention, it is possible to obtain an electret capable of realizing stable performance under external environmental conditions such as heat, humidity, and impact through the development of an electret having excellent charge retention and heat resistance characteristics, which may occur accidentally when using detection equipment. By solving the problem of discharging the potential of the filling film due to the frictional charge and the problem of the accuracy of the electrometer being deteriorated in an excessively high humidity environment, the effect of improving the probe replacement cycle and analysis reliability can be expected.

According to the present invention, since it is possible to provide a fluorine-based polymer resin electret capable of implementing stable performance even in a thermal environment change, it is possible to expect the effect of localizing the core electret of the radioactive material detection equipment depending on the total amount imported.

Hereinafter, the present invention will be described in detail with reference to the following Examples, which should not be construed as limiting the invention thereto.

Example 1 and Comparative Examples 1 to 2. Comparison according to thin film formation method

(1) Spin coating method

Prepare a mixed solution of 1% by weight, 3% by weight, and 5% by weight of dielectric particles (BaTiO ₃ ) in liquid fluorine resins (PFA, FEP, PTFE), and spin-coating them on an STS metal substrate (0.15mm thickness). Coating in a manner. In addition, after spin-coating with a liquid fluorine resin alone, a mixed solution including dielectric particles was spin-coated and laminated to form a secondary thin film. The laminated thin film layer was produced to a total thickness of 75 ± 10.

The result of confirming the shape of each thin film manufactured by the electron microscope is shown in FIG.

In FIG. 2, a single layer and spin coating (a) showed a relatively uniform surface of the specimen, but in the case of the specimen manufactured by forming a secondary thin film as shown in (b), cracks on the surface of the thin film during high temperature firing The occurrence phenomenon can be confirmed.

That is, the multilayer liquid coating specimens had a problem of penetration of surrounding contaminants on the thin film formation surface when the second thin film was formed after the formation of the first thin film and the nonuniform thickness. Adhesion test (cross cutting) was conducted to confirm the thin film formation performance of the fabricated specimen, and all specimens showed good polymer coating adhesion.

(2) liquid electrostatic coating method

Prepare a mixed solution of 1% by weight, 3% by weight, and 5% by weight of dielectric particles (BaTiO3) in liquid fluorine resins (PFA, FEP, PTFE), and the PFA, FEP solution on a 0.15 mm thick STS metal substrate. A primary thin film was formed by the method of electrostatic coating, and a PTFE solution containing a dielectric was laminated on the formed primary thin film. 3 wt% of dielectric particles (BaTiO3) and 5 wt% of a mixed solution were mixed with a fluorine-based polymer solution to form a primary thin film by liquid electrostatic coating, and a secondary thin film was formed by liquid coating. A thin film was formed. The result of confirming the shape of each thin film manufactured by the electron microscope is shown in FIG.

As shown in Figure 3, it can be seen that the relatively good surface state is maintained compared to the liquid spray coating. However, the coating method using the liquid electrostatic coating has been found to form a thin film using only a limited fluorine resin solution and the formation of surface fine bubbles. It was judged that the surface charge storage space of the electret thin film was not suitable for manufacturing the electret.

As a result of confirming the cross-cutting performance of the thin film, it was found that the adhesive strength was slightly weaker than that of the liquid coating method.

(3) Doctor Blade coating method

A mixed solution of 1 wt%, 3 wt%, and 5 wt% of dielectric particles (BaTiO3) was prepared in liquid fluorine resin (PFA, FEP, PTFE), and an electret specimen was manufactured by a doctor blade coating method. The STS metal substrate was placed on a high temperature heating plate and coated with a uniform thickness to prepare a thin film having a porous structure through a continuous heat treatment process. The result of confirming the shape of each thin film prepared by the electron microscope is shown in FIG.

As shown in FIG. 4, the doctor blade coating method has a relatively non-uniform thin film surface compared with the liquid coating method and the liquid electrostatic method, and ensures uniformity of charge storage space by forming an irregular space inside the thin film formation. It was judged to be not suitable in terms of aspects. In addition, it has the disadvantage of using a large amount of raw materials, which leads to an increase in manufacturing cost, which is considered to be an inappropriate method for commercialization.

Reference example. Device for electret charging

In the following example, unlike electrification electrodes which have been used in the past for uniform electret charging and increased production efficiency, each electret is uniformly charged at the same time with a round ball type discharge electrode that can individually charge an electret. This possible device was used. 5 shows a schematic diagram of a device used in charging by corona discharge.

Individual electret charging through the ball-type discharge electrode is very advantageous for checking the surface potential uniformity of each electret and is suitable for improving productivity. A hood was fabricated on top of the corona discharge generator to enable ozone removal and vacuum conditions generated during corona discharge. In corona discharge device, voltage generator is designed and manufactured to control discharge current in order to check the effect of uniform current on the generated surface potential. In order to check the surface potential charging efficiency according to the distance between the discharge electrode and the electret at the time of electret charging with a circular ball type discharge electrode, a manufacturing process was performed to control the distance between the discharge electrode and the electret of the ball type.

Example 2. Electret Fabrication

In the spin coating process, a circular aluminum specimen (1.5T, Ø 40mm) was placed on the chuck and the vacuum was extracted and fixed. A fluorine-based polymer Teflon PTFE, FEP, PFA solution containing 3% by weight of BaTiO 3 was applied onto the fixed specimen, and the specimen was rotated at high speed to form a constant thin film liquid layer. After forming the thin film layer, the solvent was evaporated to prepare a metal plate on which the fluorine-based polymer thin film was formed [Table 2]. 6 shows a photograph of the prepared electret prototype.

TABLE 2 Electret Prototyping

Sample No. Raw material name Coating thickness Sheet MFW-01 PTFE 75 ± 10 1.5T
Aluminum sheet
(Ø40mm round) MFW-02 FEP 75 ± 10 MFW-03 PFA 75 ± 10

In Table 2 above, the surface electron micrograph of the electret prototype MFW-01 is shown in FIG. 7. According to FIG. 7, it can be seen that the formation of the fluorine-based polymer thin film on the surface of the electret is formed in a skeletal form. ABO3 type dielectric particles are included between the skeleton and the skeleton to form a space for electrons to move, and through the space. When the + (plus pole) and the-(minus pole) powers are applied to the perovskite crystal structure from the outside to the top, and to the (negative pole), respectively, the internal charge and the transferred voltage between the crystal structures are repulsed to compress the space between the crystal structures. In addition, when-(minus pole) is applied to the upper part and + (plus pole) is applied to the lower part, internal charges and applied voltages between the crystal structures are attracted to each other, thereby increasing the space between the crystal structures. Changes in the crystal structure of relaxation and contraction can lead to the formation of interskeletal space formation on the surface of the thin film, which can be expected to maximize the effect of surface dislocation formation through corona charging.

Experimental Example 1. Thermal stability and charge preservation characteristics of MFW-01 prototype

Electrets used for measuring radon concentrations are generally measured at room temperature and are under 100 ° C, even in high temperature environments in summer. Thermal stability analysis at high temperature was conducted to investigate how the electret thin film applied with fluorine resin affects the physical and chemical properties of the initial fluorine resin after corona charging.

BaTiO ₃ , CaCO ₃ , BaTiO ₃ , PbZrTiO _3, and CaTiO ₃ in the fluorine-based polymer resin were used to induce the formation of pores that can be charged in the fluorine-based polymer thin film by using a change in the perovskite crystal structure during corona charging. Each was added to confirm the dispersion stability.

Dispersion of the dielectric particles having a perovskite crystal structure and the fluorine resin was carried out by stirring at 20,000 rpm for 10 minutes using an IKA Ultra-terrax T25 device. The dielectric particles were 1.0 wt%, 3.0 wt%, 5.0 wt%, 7.0 wt%, and 9.0 wt% were applied.

The dispersion stability of dielectric particles having a perovskite crystal structure was measured for 24 hours using Light Scattering. When 7.0 wt% and 9.0 wt% were added to the fluororesin, the dielectric particle dispersion stability was increased with time. We could see that it decreased. When the dielectric particles were added to the fluororesin at 9.0 wt% and mixed, it was confirmed that aggregation and precipitation occurred through change of light scattered through the sample suspension after 24 hours.

Based on the above results, thermal stability and charge preservation characteristics were examined by applying MFW-01 prototype coated with fluorinated polymer Teflon PTFE resin containing 3 wt% of BaTiO ₃ on an aluminum plate in a sample having excellent dispersion stability. . Since Teflon is dispersed in the liquid phase at room temperature, it is possible to form a thin film with a thickness of about 75 using spin coating, and has strong adhesive force and high thermal stability. Teflon is also known for its excellent charge storage properties. The thermal stability test was conducted with the electret MFW-01 charged to 790V at the Korea Polymer Testing Institute. The test conditions were heat treated at 275 ℃ for 5 seconds.

The test showed no damage to the Teflon thin film at high temperatures. Through this, it was confirmed that corona charging did not affect the unique physical and chemical properties of Teflon.

In addition, the surface potential charged to the initial 790V was reduced to 2% surface potential to 750V after the heat treatment. Existing research data show that the surface potential decreases by the so-called chargespreading in which surface charge penetrates into the specimen when heat treated at high temperature. In addition, the effect of the charge diffusion reported that the charge trapped inside the specimen having a higher energy level than the surface of the specimen may result in improved thermal stability of the specimen. The results of the above experiments indicate that the state of the specimen is changed by the heat treatment after charging to capture the charge at a deeper energy level, and the surface potential change of about 2% results in thermal stability of the electret of the fluorine-based polymer thin film. This means that it is big.

Experimental Example 2 Measurement of Surface Roughness of MFW-01 Prototype

Thin film formation on the electret surface is very important for achieving uniform surface charging performance of the electret. In order to confirm the surface roughness of the electret prototype MFW-01, a surface roughness measurement test was conducted at the Korea Polymer Testing Institute. The results are shown in Table 3 below.

1) Measuring method: According to KS M ISO 2808 method 4

2) Sample size: Φ40mm

3) Measuring device: Surface profiler (Dektak150)

4) Stylus force: 5.0mg

5) Scan duration: 60sec

TABLE 3 Surface roughness measurement result of MFW-01 prototype

 Sample Name Number of measurements Surface roughness measurement MFW-01 One 13960.2 1.396 2 13074.9 1.307 3 12786.5 1.278 medium 13273.9 1.327

As shown in Table 3, the surface roughness measurement test for the MFW-01 prototype was conducted to obtain a very uniform thin film formation result with an average surface roughness of 13,273.9 (1.3).

Experimental Example 3 Measurement of Coating Film Thermal Conductivity of MFW-01 Prototype

The coating film thermal conductivity test for the electret prototype MFW-01 was made by requesting a prototype to the Korea Institute of Ceramic Technology according to the KS L 1604 standard. The KS L 1604 standard is a method for testing high performance ceramic materials by laser flash method at room temperature diffusion rate from room temperature to 1,700K, specific heat capacity from room temperature to 1,000K, and thermal conductivity test method, at room temperature for electret prototype MFW-01. Thermal conductivity test was performed. The electret prototype MFW-01 was fabricated in a circular 12.5 mm size and repeated three times to obtain an average coating film thermal conductivity of 2.76 w / mk. It was confirmed that the electret prototype MFW-01 had the ability to stably perform the role of radon detection under the conditions of heat as well as thermal stability.

Experimental Example 6. Measurement of Coating Film Adhesion of MFW-01 Prototype

In order to confirm the adhesion stability of the fluorine-based polymer thin film to the radon detecting electret prototype MFW-01, the polymer thin film adhesion through the pencil scraping test was conducted at the Korea Polymer Testing Institute. Scratch hardness (pencil method) measurement of the electret prototype MFW-01 was performed with Mitsubishi: Uni pencil. The result of the scratch hardness (pencil method) is determined by 9B-8B-7B-6B-5b-4B-3B-2B-B-HB-FH-2H-3H-4H-5H-6H-7H-8H- It is classified as 9H, 9B ~ HB is regarded as soft surface, and F ~ 9H is regarded as rigid surface. The electret prototype MFW-01 was tested with a pencil tip of 750 ± 10 g / cm 2 applied to the surface of the paint, resulting in H (750 g). As a result, it was confirmed that the surface of the fluorine-based polymer thin film of the electret prototype MFW-01 had excellent adhesion.

Experimental Example 7. Confirmation of surface potential stability for MFW-01

In order to maintain the surface potential important for the performance of radon sensing electrets and to verify the stability in the measurement environment, the electret prototype MFW-01 was charged with a charging device to charge the surface potential above 700V, and at least 30% wet conditions and impact. A test was conducted to confirm the surface potential retention performance and the surface potential loss with time. Corona charging of the MFW-01 prototype was performed using counter electrodes in the form of bars and balls, and both types showed surface potentials of 700 V or more through the corona charging, resulting in more than 75% of the initial development target. It was confirmed that it has an excellent surface potential.

Experimental Example 8. Confirmation of surface potential retention performance in wet and impact conditions

Surface potential over time at room temperature with the electret prototypes MFW-01, MFW-02, and MFW-03 to verify the surface potential stability of charged electret prototypes under moisture and impact conditions that may occur in radon measurements. The test was performed to measure the change in surface potential change when the Electret prototype was dropped to the floor at 1m height and the 50% humidity condition. The initial charged surface potential was set to 700V or more, and the test was conducted. The results are shown in Table 4 below.

TABLE 4 Verify prototype surface potential retention performance at room temperature, wet conditions and impact conditions

Sample Name Room Temperature Surface Potential (V) Impact Conditions Surface Potential (V) 50% Wetting Condition Surface Potential (V) Early 24 hours later 48 hours later Early 3rd time 5 times Early 24 hours later 48 hours later MFW-01 1 time 792 776 775 794 786 771 787 754 722 Episode 2 795 779 778 797 789 774 790 757 725 3rd time 782 766 765 784 776 761 777 744 713 MFW-02 1 time 785 767 765 787 778 763 779 738 708 Episode 2 791 775 774 793 785 770 786 753 721 3rd time 792 776 775 794 786 771 787 754 722 MFW-03 1 time 785 762 761 787 769 754 769 734 703 Episode 2 793 777 776 795 787 772 788 755 723 3rd time 748 733 732 750 742 728 743 712 682 Max (V) 795 779 778 797 789 774 790 757 725 Min (V) 748 733 732 750 742 728 743 712 682 Avg (V) 785 768 766 787 778 763 778 745 713 Average surface potential reduction% 97.86% 98.84% 95.66%

As described above, the Applicant has transferred the electret manufacturing technology with excellent charge retention properties, verified the previous technology, and carried out a study to adjust the charge retention properties in a form suitable for a radon measurement probe, and investigated the radon measurement environment. In order to provide analytical reliability in the harsh conditions of the field, the test and optimization of the fluorine resin mixture composition and thin film formation conditions of the prior art were performed.

The fluorine-based polymer resin electret according to the present invention was found to have excellent charge retention characteristics and heat resistance characteristics. It confirmed that stable performance was implemented even under external environmental conditions such as heat, humidity, shock, and it was possible to bring uniform charging effect to electret polymer thin film by designing and manufacturing corona charging device for manufacturing electret capable of stable performance.

1 is a schematic diagram of a perovskite structure of CaTiO ₃ .

2 is an electron micrograph of an electret thin film surface according to the spin coating method.

3 is an electron micrograph of an electret thin film surface according to a liquid electrostatic coating method.

4 is an electron micrograph of the electret thin film surface according to the doctor blade coating method.

5 is a schematic diagram of a charging device using corona discharge used in Example 2. FIG.

6 is a photograph of a thin film-forming electret specimen prepared in Example 2. FIG.

7 is a thin film electron micrograph of an electret prototype MFW-01.

FIG. 8 is a photograph showing corona charging using a ball-type counter electrode. FIG.

Claims (13)

A thin film is formed by spin coating a metal plate with a heat-resistant fluorine-based polymer resin mixed solution containing dielectric particles having a perovskite crystal structure, and forming the thin film coated with the perforated metal plate. It is manufactured by applying voltage individually. A fluorine-based polymer resin electret comprising a thin film of a single layer structure comprising a heat resistant fluorine-based polymer resin and a dielectric particle having a perovskite crystal structure. The method according to claim 1, The heat resistant fluorine-based polymer resin fluorine-based polymer resin electret, characterized in that it comprises at least one selected from PTFE (Polytetrafluoroethylene), poly (perfluoroalkyl acrylate) (PFA), Fluorinated ethylenepropylene resin (FEP) and Polyvinylidenefluoroide (PVDF). The method according to claim 1, The dielectric particles having a perovskite crystal structure is in the range of 1 to 5% by weight fluorine-based polymer resin electret. The method according to claim 1, The dielectric particles having the perovskite (perovskite) The crystal structure is characterized in that the _{CaCO 3, BaTiO 3, SrTiO 3} , PbZrTiO 3, KNbO 3, LiNbO 3, LiTaO 3, BiFeO 3 and CaTiO _3, at least any one selected from Fluorine-based polymer resin electret. The method according to claim 1, The thin film is a fluorine-based polymer resin electret, characterized in that in the range of 50 to 150 ㎛. The method according to claim 1, A fluorine-based polymer resin electret, characterized in that further comprising a ceramic dielectric. The method according to claim 6, The ceramic dielectric is greater than 0% by weight and fluorine-based polymer resin electret characterized in that it is included in the range of 3% by weight or less. The method according to claim 6, The ceramic dielectric material is selected from PbZrTiO, PbNbO, Al ₂ O ₃ , SiO ₂ , Si ₃ N ₄ , B ₂ O ₃ / ZnO / SiO ₂ , SiO ₂ / Si ₃ N ₄ , TiO ₂ , and Carbonblack A fluorine-based polymer resin electret comprising at least one. Forming a thin film by spin coating a metal plate with a heat-resistant fluorine-based polymer resin mixed solution containing 1 to 5 wt% of dielectric particles having a perovskite crystal structure, Forming the metal plate coated with the thin film, and Individually applying a voltage to the molded metal plate Method for producing a fluorine-based polymer resin electret comprising a. The method according to claim 9, The application is a method for producing a fluorine-based polymer resin electret, characterized in that to perform a corona discharge at atmospheric pressure conditions. The method according to claim 10, The corona discharge is a method of manufacturing a fluorine-based polymer resin electret, characterized in that the plurality of electrets are carried out under the conditions of individually charging a negative charge. The method according to claim 9, The heat-resistant fluorine-based polymer resin mixed solution is a method for producing a fluorine-based polymer resin electret, characterized in that it further comprises a ceramic dielectric in the range of more than 0% by weight and 3% by weight or less. Radon measuring sensor provided with any one of the electret selected from claim 1 to claim 8.

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