KR100497319B1 - Conductive polymer composition containing fluorine-treated carbon black and ptc device prepared therefrom - Google Patents

Abstract

The present invention relates to a conductive polymer composition for overcurrent blocking having a PTC characteristic and a PTC device using the same, wherein the conductive polymer composition is melt-mixed with an olefinic polymer resin matrix after treating carbon black by a direct fluorine treatment according to the present invention. The present invention can provide a PTC device having excellent PTC characteristics while eliminating the NTC phenomenon. The conductive polymer composition according to the present invention can be manufactured at room temperature by a simple method and device without a separate material and energy, and there is no penetration of moisture into the composition, thereby improving performance as well as economy.

Description

CONDUCTIVE POLYMER COMPOSITION CONTAINING FLUORINE-TREATED CARBON BLACK AND PTC DEVICE PREPARED THEREFROM}

The present invention relates to a conductive polymer composition for overcurrent blocking having a PTC characteristic and a PTC device using the same, and more particularly, by treating carbon black, which is a conductive filler, by direct fluorine treatment, followed by melt mixing with an olefin-based polymer resin matrix. A conductive polymer composition made and a PTC device fabricated therefrom.

The positive temperature coefficient (PTC) behavior exhibited by conductive polymer compositions is already known in the electronics industry and is used in many applications, including devices in constant temperature heaters, thermal sensors, overcurrent regulators and low power circuit protection devices.

The PTC characteristic refers to a characteristic in which electrical resistance increases rapidly in a relatively narrow temperature range as the temperature increases, although the resistance is low at low temperatures such as room temperature. The cause of the PTC phenomenon is that the change in the crystalline and amorphous states in the polymer, that is, when the temperature rises near the melting point of the used resin, increases the spacing between the conductive filler particles and the spacing between the agglomerates, thereby destroying the conductive network formed by the electrons. It has been described as occurring because it interferes with the tunneling phenomenon.

In contrast, when the melting point lasts longer or rises to a higher temperature, the flow of conductive particles freely rearranges, causing aggregation between the particles and forming a new conductive network, thereby increasing the flow path of electrons. NTC phenomenon occurs with low resistance. This phenomenon is fatal in circuit protection devices that cut off the overcurrent by maintaining a high resistance while the overcurrent is applied. Therefore, various crosslinking processes are used to remove the NTC characteristics, and chemical crosslinking methods and irradiation crosslinking methods are generally used as the crosslinking method.

Chemical crosslinking methods include silane treatment between the conductive filler and the polymer resin matrix, and resin crosslinking methods for increasing the degree of crosslinking of the resins used. Such chemical crosslinking methods have the advantage of obtaining a uniform and efficient crosslinking structure. Since the crosslinking may proceed in the process of mixing the conductive polymer and the crosslinking aid, there is a disadvantage in that the degree of crosslinking is limited because the crystallinity depends on the crosslinking because crystallization by cooling occurs after crosslinking.

The irradiation crosslinking method is the most commonly used method of inducing intermolecular crosslinking of a crystalline polymer to form a network structure by irradiating a finally formed conductive polymer material with an irradiation beam such as an electron beam. However, this type of irradiation crosslinking method requires more energy and requires more energy than other process facilities. Therefore, the manufacturing cost increases during the crosslinking process, which incurs high costs in process processing, and a certain portion of the conductive molding is fixed for a certain time. The amount of radiation absorbed during the time depends on the distance from the molding surface, the intensity of the irradiation, the energy form, and the like, and thus, it is difficult to maintain the degree of crosslinking uniformly.

Therefore, in the present invention, in consideration of the problems of the chemical crosslinking method and the irradiation crosslinking method, the surface of the carbon black used in the production of the conductive polymer composition using the conductive carbon black and polyolefin-based polymer material directly surface treatment using fluorine gas It is an object of the present invention to provide a PTC polymer having excellent PTC strength and a conductive polymer composition in which the NTC phenomenon is removed by reducing the surface free energy of carbon black according to the pressure of fluorine treatment.

Accordingly, the present invention provides a conductive polymer composition for a PTC device, comprising carbon black powder surface-treated with fluorine gas as a conductive filler.

The present invention also provides a PTC device fabricated from the conductive polymer composition of the present invention.

Hereinafter, the present invention will be described in detail.

The present invention is characterized by the use of fluorine-surfaced carbon black powder in conductive polymer compositions for PTC devices. The composition according to the present invention comprises a resin matrix and fluorinated carbon black powder, and the fluorinated carbon black used in the present invention is used in an amount of 20 to 50 parts by weight based on 100 parts by weight of the polymer resin matrix. If too small amount of carbon black is added to the polymer matrix, the resistance value is increased and the value as PTC element is lost. On the other hand, when too much carbon black is used, the resistance value at room temperature or at the melting point of the polymer is too small. Loss of value as an element.

The resin matrix used in the conductive polymer composition for PTC devices of the present invention is crystalline polyethylene (PE), high density polyethylene (HDPE), low density polyethylene (LDPE), ethylene vinyl acetate (EVA) copolymer, ethylene methyl acrylate ( Polyolefin resins such as EMA) copolymers, ethylene ethyl acrylate (EEA) copolymers, polypropylenes are usually used, and polyethylene derivatives in the form of copolymers which improve the filling properties of polymer particles are more suitable. These resins well exhibit PTC properties that increase the resistance of the composition in response to an increase in temperature in a relatively small temperature range, and are desirable for preventing loss of physical properties by heat due to their low melting point.

According to the present invention, the resin matrix may also optionally include nickel powders, gold powders, copper powders, metal alloy powders, carbon powders, graphite powders, carbon blacks and the like which are conventional conductive fillers.

The carbon black used in the present invention preferably has an average particle size of 10 to 100 nm and a DBP value of 60 to 160 cc / 100 g.

The fluorinated carbon black may be obtained by treating carbon black commonly used in a conductive polymer composition for PTC with fluorine (F ₂ ) gas, and the fluorine gas for fluorine treatment may have impurities (eg, , It is preferable to remove nitrogen gas and HF). In the fluorine treatment, it is preferable to use an injection pressure of fluorine gas at 0.1 to 0.4 MPa, and a treatment time of 10 to 30 minutes is preferable because it can prevent structural changes of carbon black itself due to excessive fluorination. The reason for limiting the injection pressure or processing time of fluorine gas is that if the injection pressure is too small or the processing time is too short, that is, if the conditions for fluorine gas and carbon black cannot be sufficiently combined, the surface of the carbon black may be fluorine. This is because the introduction of groups is not easy, and thus the purpose of fluorination of carbon black cannot be achieved. In addition, if the injection pressure of fluorine gas is increased or the processing time is excessively lengthened, excessive fluorine groups are introduced to the surface of the carbon black, which affects the conductivity of the carbon black, a conductive filler, thereby greatly increasing the initial resistance value. This results in no value as a PTC device.

The reactor used for the fluorine treatment is preferably using a stainless steel material having corrosion resistance at room temperature with respect to fluorine gas, purging the reaction line to move the fluorine gas after the fluorine treatment and the reactor treated carbon black with nitrogen gas. Purging is desirable in view of reactor life, accuracy of the reaction process and safe working environment.

According to the present invention, the conductive carbon black is directly fluorinated, and then charged into the crystalline olefin resin matrix to be melt mixed together to prepare a conductive polymer composition. According to the present invention, the method of using carbon black, which is a conductive filler added to the conductive polymer composition in advance, in advance by using fluorine-surface treatment may also prevent process temperature setting constraints that may occur during mixing with the polymer. In the conductive polymer produced, the fluorine gas directly treated reduces the surface free energy of the carbon black to prevent aggregation between the carbon black at the melting point of the resin, thereby reducing the NTC phenomenon and bonding strength between the carbon black and the resin. This can be lowered to show excellent PTC strength.

Melt mixing of the resin matrix and the conductive filler may be performed at a melting point (T _m ) of the crystalline polyolefin-based polymer in the resin matrix to a temperature range of 20 ° C. or more. When the melt mixing temperature is lower than T _m , the mixing between the conductive filler and the polymer resin is not completely performed, and when the temperature is too high, the mechanical properties and the structure change are caused by the physical property change due to the thermal decomposition of the used polymer resin. There are disadvantages.

In addition, the temperature increase rate during the melt mixing is preferably 5 to 10 ° C / min. If the temperature increase rate is less than 5 ℃ / min, the productivity is not preferable, and if the temperature is above 5 ℃ / min is due to the change in the electrical properties due to the difference in the thermal expansion coefficient between the polymer resin and the conductive filler.

The melt mixing is preferably performed for a time of about 10 to 20 minutes in order to obtain a good conductive polymer composition having a relatively low crystallinity. If the mixture is cooled after mixing more than that, there is no physical property enhancing effect and economicality.

In the mixing of the conductive filler and the matrix resin, the agglomeration phenomenon between the carbon black powder particles and the interfacial bonding force between the carbon black and the resin can be appropriately controlled by controlling the pressure and the treatment time of the processing gas during the fluorine gas treatment of the carbon black. have.

It is desirable for the conductive polymer composition for PTC devices to have as high PTC strength and reduced NTC as possible. Fluorine according to the present invention is the conducting polymer compositions containing the treated carbon black has a specific resistance value at room temperature (ρ _RT) is 10~20 ohm · cm, ³ the PTC intensity variation of from room temperature to T _m + 5 ℃ 10 It may be in the range ~ 10 ⁶ .

The general structure of the PTC device is shown in FIG. 1 as a plan view and a side view. The PTC device is usually manufactured in the form of a thin circular sheet of about 0.5 to 1 mm, the metal thin film (2) bonded to both sides of the conductive polymer composition (1) in the production using a low-resistance metal electrolyte thin film, both sides thereof The two copper electrodes 3 can be produced by bonding a low-resistance conductive adhesive and a hot-presser to each other.

According to the present invention, a PTC device fabricated from a conductive polymer composition including fluorine-treated carbon black by injecting fluorine gas directly into the carbon black powder as a filler has an NTC at the melting point of the resin due to a reduction in free energy of the fluorinated carbon black. The phenomenon is eliminated, and the interfacial bonding force between the carbon black and the resin is lowered, thereby showing excellent PTC strength.

The PTC device manufactured according to the present invention has a specific resistance of 10 to 30 ohm · cm at room temperature and no NTC phenomenon at a temperature of T _m +5 to 20 ° C. or more, and a maximum peak resistance of 10 ³ to 10 ⁶ ohm · cm. , Has excellent reproducibility.

Fluorine treatment of carbon black according to the present invention is relatively simple since the device is operated under low vacuum at room temperature or less, and is economical since it does not require an initiator, a catalyst or energy for initiating the surface treatment reaction, There is no water penetration, so processing time and device fabrication time are short, which can greatly contribute to reducing PTC device fabrication cost and performance.

The invention is described in more detail in the following examples, although the scope of the invention is not limited to the examples. In the present invention, each characteristic value was measured by the following method.

1. Resistance and PTC strength measurement

After connecting the produced PTC device (diameter 1 ~ 1.5 cm) to the digital multimeter, measure the change of the temperature-resistance curve at the temperature increase rate of 2 ℃ / min in the temperature control oven, and use it. PTC strength, which is the ratio of the specific resistance value ρ _RT at room temperature to the maximum specific resistance value ρ _max , was calculated.

2. Carbon Black Surface Analysis

FT-IR spectroscopy (Hartmann & Brawn Model Bomen MB 102) and XPS (ESCA LAB MKII, VG Scientific Co.) were used to confirm the change spectrum of surface functional groups of fluorinated carbon black. FT-IR mixed carbon black with KBr powder to make KBr pellets under pressure and measured them at the scanning range of 4000 ~ 400 cm ^-1 . The X-ray light source used for XPS measurement showed that Mg K _α was measured at 45 ° angle. The pressure in the chamber was adjusted to 1 × 10 ^-9 Torr.

In addition, the change in surface free energy of the surface of the carbon black according to the fluorine surface treatment was confirmed by measuring the contact angle at a temperature of 20 ± 1 ℃. At this time, distilled water and diiodomethane were used as the wetting liquid used for measuring the contact angle.

Example 1

Carbon black (HI-BLACK 420B, particle size 24 nm, DBP 153 cc / 100 g, specific surface area 88 m ² / g) is placed in a nickel boat (Aldrich, 99.99%), and SUS is corrosion resistant to fluorine gas. The mixture was placed in a -316 reactor and surface treated directly at room temperature for 10 minutes at a pressure of 0.1 MPa for fluorine gas.

30 parts by weight of the fluorinated carbon black was mixed with 100 parts by weight of pure high density polyethylene (Honam Chem Co., T _m : 135 ° C, density: 0.954 g / cm ³ ) to prepare a conductive polymer composition according to the present invention. Prepared.

Examples 2-4

A conductive polymer composition according to the present invention was prepared in the same manner as in Example 1 except that the pressure of fluorine gas was 0.2, 0.3, and 0.4 MPa, respectively.

FT-IR and XPS analyzes were performed to confirm the introduction of fluorine groups on the surface of the carbon black for the fluorinated carbon black according to Examples 1 to 4, and the results are shown in FIGS. 2 and 3, respectively.

In addition, in each of the compositions using the conductive polymer compositions prepared in Examples 1 to 4 and the non-fluorinated carbon black as a comparative example, as shown in FIG. Product, containing copper-nickel component) A copper electrode is fused by a hot press using a conductive adhesive to fabricate a circular PTC device having a thickness of about 1.0 mm, and then, as described above, at room temperature and peak resistance. The measured values are shown in FIG. 4, and the surface free energy of fluorinated carbon black and untreated carbon black and the PTC strength of the device fabricated using the same are shown in Table 1, and the log PTC strength is shown in FIG. 5. Shown in

Surface free energy (mJ / m ² ) PTC Century Comparative example 16.34 1.7 × 10 ² Example 1 14.94 1.2 × 10 ³ Example 2 13.85 1.4 × 10 ³ Example 3 13.78 1.7 × 10 ⁴ Example 4 13.64 3.6 × 10 ⁵

As can be seen from Table 1 and the results of FIGS. 4 and 5, the PTC device manufactured using the fluorinated carbon black according to the present invention has a high peak resistance (10 ⁶ Ω · cm or more) in the melting temperature range of the resin. It showed excellent PTC strength according to the removal of NTC phenomenon at the melting point of resin due to the reduction of free energy of fluorinated carbon black and the decrease of interfacial bond between carbon black and resin.

In the fluorine treatment of carbon black according to the present invention, the fluorine content of the carbon black can be controlled by adjusting the pressure and treatment time of the fluorine gas for treatment, and the limitation of the mixing process temperature and the degree of crosslinking, which are problems of the conventional chemical crosslinking method, are limited. There is no problem in that the manufacturing cost increases during the crosslinking process, which is a limitation of the irradiation crosslinking method, and it is difficult to maintain the crosslinking degree uniformly, and it is difficult to maintain the crosslinking degree uniformly. Operation is relatively simple, and the surface treatment device is relatively simple. It is economical because it does not require initiator, catalyst or energy for initiating the surface treatment reaction, and there is no penetration of moisture into the composition. And can greatly contribute to performance improvement.

According to the present invention, a conductive polymer composition comprising carbon black fluorinated by injecting fluorine gas directly into the carbon black powder as a filler is produced at the melting point of the resin due to the reduction of free energy of the fluorinated carbon black when the PTC device is manufactured. It is possible to exhibit excellent PTC strength due to the elimination of the NTC phenomenon and the reduction of the interfacial bond between carbon black and resin.

1 is a plan view and a side view of a PTC device;

2 and 3 are FT-IR spectra and XPS spectra for confirming whether fluorine groups are generated on the surface of fluorinated carbon black according to the present invention, respectively.

4 is a graph showing temperature-resistance curves of the PTC compositions of Comparative Examples and Examples 1 to 4,

5 is a graph showing the PTC strength according to the fluorine pressure change of the PTC composition of Comparative Examples and Examples 1 to 4.

* Brief description of the symbols in the drawing

(1) conductive polymers (2) thin metal films (3) copper electrodes

Claims (9)

A conductive polymer composition for a PTC (positive temperature coefficient) device, comprising fluorinated carbon black powder as a conductive filler. The method of claim 1, The fluorinated carbon black is a composition characterized in that the carbon black powder is produced by a process of directly surface-treated with fluorine (F ₂ ) gas. The method of claim 2, The fluorine treatment process comprises treatment with fluorine for 10-30 minutes under pressure 0.1-0.4 MPa at room temperature. The method of claim 1, A composition comprising 100 parts by weight of a polymer resin matrix and 20-50 parts by weight of fluorinated conductive carbon black. The method of claim 4, wherein A composition, wherein the resin matrix comprises at least one crystalline polyolefin resin. The method of claim 1, The specific resistance at room temperature (ρ _RT) value and 10~20 ohm · cm, the composition characterized in that the PTC intensity change to ^{_{T m + 5 ℃ 10 3 ~10}} 6 at room temperature. A PTC device comprising a pair of electrodes fused on both sides of a circular sheet molded from the conductive polymer composition according to any one of claims 1 to 6, and bonded on both sides by a conductive adhesive. . The method of claim 7, wherein PTC device, characterized in that the total thickness is 0.5 to 1 mm. The method of claim 7, wherein A PTC device having a specific resistance of 10 to 30 ohm · cm at room temperature and no NTC phenomenon at a temperature of T _m +5 to 20 ° C. or higher, and having a maximum peak resistance of 10 ³ to 10 ⁶ ohm · cm.