KR20110010471A - Pb-free ptc thermistor ceramic composition and method for preparign of pb-free ptc thermistor ceramic using the same - Google Patents

Abstract

PURPOSE: A Pb-free ptc thermistor ceramic composition is provided to ensure excellent PTC jump properties and PTCR effects, low specific resistance at a room temperature and a curie temperature(Tc) of 160°C or more by substituting Ba1-x(Bi0.5Na0.5)xTiO3 (0.05<=x<=0.10) for MnO2. CONSTITUTION: A Pb-free ptc thermistor ceramic composition comprises a compound represented by chemical formula (1): Ba1-x(Bi0.5Na0.5)xTiO3 + y mol% MnO2. In chemical formula (1), 0.05<=x<=0.10 and 0.00<y<=0.02. A method for preparing the Pb-free ptc thermistor ceramic composition comprises the steps of: mixing MnO2 to Ba1-x(Bi0.5Na0.5)xTiO3 (0.05<=x<=0.10) in a 1:y (0.00<y<=0.02) ratio, and pulverizing and drying the mixture; and molding and sintering the dried powder.

Description

Pb-free PTC THERMISTOR CERAMIC COMPOSITION AND METHOD FOR PREPARIGN OF Pb-free PTC THERMISTOR CERAMIC USING THE SAME}

The present invention relates to a ceramic composition for a lead-free PTC thermistor and a method for producing a ceramic for a lead-free PTC thermistor using the same. More specifically, Ba _1-x (Bi _0.5 Na _0.5 ) _x TiO ₃ (where 0.05 ≦ _x ≦ 0.10) to MnO ₂ , and a method for producing a ceramic composition for lead-free PTC thermistors prepared by substituting MnO ₂ and a ceramics for lead-free PTC thermistors using the same.

PTCR (positive temperature coefficient resistance) is a phenomenon in which resistance increases rapidly at transition temperature with increasing temperature, and PTC is used for resistance heating elements, color TV degaussing elements, constant current, or constant voltage circuit elements. Thermistors are used. In recent years, due to the high performance of electronic products, the thermistors used in the devices are also required to have high reliability and precision in operation, and in particular, the thermistor's electrical characteristics must be precisely controlled.

The positive temperature coefficient (PTC) thermistor is based on BaTiO ₃ .

BaTiO ₃ (BT) -based semiconducting ceramics are compounds of the typical perovskite crystal structure represented by ABO _3, and are occupied by divalent Ba ions at A-site and tetravalent Ti ions at B-site. It is in the form of a polymorphic characteristic that the crystal structure transitions to rhombohedral, orthorhombic, tetragonal and cubic with increasing temperature. .

The resistance-temperature characteristic is obtained by measuring the electrical resistance of the PTC thermistor at a temperature below 1.5 V _{DC. The} temperature at which the resistance increases rapidly is converted to the resistance sudden temperature (switching temperature) or Curie temperature (Curie). Temperature: T _c ). In general, the Curie temperature is defined as the temperature corresponding to twice the minimum resistance value or the reference temperature (25 ° C.) resistance value, which is an important parameter of the material properties.

BT series In ceramics, the Curie temperature (T _c ) is about 130 ° C., which transitions from the tetragonal phase of ferroelectric phase to the cubic phase of phase dielectric.

Conventionally, in order to raise the operating temperature of PTC thermistor to 130 ° C or higher, P-substituted Pb was used in the A-site of BT ceramics. BaTiO ₃ -PbTiO ₃ ceramics in which small amount of PbTiO ₃ is employed is It is commercially available.

However, the lead (Pb) component is very harmful to the human body, may cause environmental pollution, and also has a problem that the lead component evaporated in the device is a factor that reduces the performance of the device.

In order to solve the problems of the prior art as described above, the present invention has a low resistivity value at room temperature without containing a lead component and has a Curie temperature (T _c ) of 160 ° C. or higher and a ceramic composition for a lead-free PTC thermistor using the same An object of the present invention is to provide a method for producing a ceramic for a lead-free PTC thermistor.

In addition, the present invention is excellent in the PTC jump characteristics, excellent PTCR effect improves the reliability of thermistor operation can be useful as a PTC thermistor ceramic composition for lead-free PTC thermistor and a method for producing a ceramic for lead-free PTC thermistor using the same The purpose is to provide.

In order to achieve the above object, the present invention provides a ceramic composition for a lead-free PTC thermistor comprising a compound represented by the following formula (1).

Ba _1-x (Bi _0.5 Na _0.5 ) _x TiO ₃ + y mol% MnO ₂

In Chemical Formula 1, 0.05 ≦ x ≦ 0.10 and 0.00 <y ≦ 0.02.

In the present invention, Ba _1-x (Bi _0.5 Na _0.5 ) _x TiO ₃ (0.05 ≦ x ≦ 0.10) is mixed with MnO ₂ in a ratio of 1: y (at this time, 0.00 <y ≦ 0.02), and pulverized. After drying; And it provides a method for producing a ceramic for lead-free PTC thermistor comprising the step of molding and sintering the dried powder.

The present invention also provides a ceramic for a lead-free PTC thermistor manufactured by the above method and a lead-free PTC thermistor formed using the same.

The ceramics for lead-free PTC thermistors of the present invention have a low resistivity value at room temperature without containing lead, have a Curie temperature (T _c ) of 160 ° C. or higher, excellent PTC jump characteristics, and excellent PTCR effects. Operational reliability is improved and can be used as a PTC thermistor.

Hereinafter, the present invention will be described in detail.

Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms, and only the embodiments make the disclosure of the present invention complete, and the general knowledge in the technical field to which the present invention belongs. It is provided to fully convey the scope of the invention to those skilled in the art, and the present invention is defined only by the scope of the claims.

The ceramic composition for a lead-free PTC thermistor of the present invention includes a compound represented by the following formula (1).

 [Formula 1]

Ba _1-x (Bi _0.5 Na _0.5 ) _x TiO ₃ + y mol% MnO ₂

In Chemical Formula 1, 0.05 ≦ x ≦ 0.10 and 0.00 <y ≦ 0.02.

When x in Formula 1 is less than 0.05 or more than 0.10, a good sintered compact may not be obtained, and thus it may be difficult to apply to a PTC heater, a PTC limiter, a PTC resistor, or the like.

In addition, when the y in Formula 1 exceeds 0.02, the specific resistance at room temperature is greatly increased, and it may be difficult to apply the PTC heater, the PTC limiter, the PTC resistor, and the like.

Next, by using the ceramic composition for lead-free PTC thermistor of the present invention as described above, it is possible to manufacture a ceramic for lead-free PTC thermistor having a high quality PTCR effect, the manufacturing process is Ba _1-x (Bi _0.5 Na _0.5 ) _x TiO ₃ (in this case 0.05 ≦ x ≦ 0.10), and mixes MnO ₂ in a ratio of 1: y (at this time, 0.00 <y ≦ 0.02), pulverizes, and then dried; And molding and sintering the dried powder.

Specifically, the ceramic composition for the lead-free PTC thermistor is first synthesized by heat treating (Bi _0.5 Na _0.5 ) TiO ₃ at 850 ^° C. for 2 hours. Thereafter, the synthesized (Bi _0.5 Na _0.5 ) TiO ₃ , BaCO ₃ , TiO ₂ were mixed at a Ba _0.05 (Bi _0.5 Na _0.5 ) _0.95 TiO ₃ composition ratio, and synthesized by heat treatment at 1100 ^° C. for 2 hours. The synthesized Ba _0.05 (Bi _0.5 Na _0.5 ) _0.95 TiO ₃ , BaTiO _3, and MnO ₂ were further replaced with Ba _1-x (Bi _0.5 Na _0.5 ) _x TiO ₃ : MnO ₂ , respectively 1: 0.005, 1: 0.01, 1: 0.02. Mixing, pulverizing and drying at a ratio of and forming the dried powder and sintering at a temperature of 1250 ^o C or more and 1350 ^o C or less for 2 hours to 10 hours.

In addition, the MnO ₂ is preferably added at a maximum of 0.02% based on the mole of Ba _1-x (Bi _0.5 Na _0.5 ) _x TiO ₃ , and more preferably 0.005 to 0.02%.

At this time, when the added mole of MnO ₂ exceeds 0.02%, the specific resistance at room temperature is greatly increased, and it may be difficult to apply the PTC heater, the PTC limiter, the PTC resistor, and the like.

Next, the step of sintering is preferably carried out for 2 to 10 hours at 1,250 ~ 1,350 ℃.

At this time, if the sintering temperature is less than 1,250 ℃ sintering is not possible to obtain a high-density specimens, if the sintering temperature exceeds 1,350 ℃ room temperature specific resistance increases due to oversintering and excellent PTCR characteristics cannot be obtained.

The ceramics for lead-free PTC thermistors of the present invention prepared as described above have a low resistivity value of 177 to 664 ㎝ · cm at room temperature, have a curvature degree (T _{c )} of 160 ° C. or higher, and PTC jump characteristics. (ρ _max / ρ _min ) is 8.4 × 10 ³ to 3.0 × 10 ⁵ , which makes it a good choice for PTC thermistors.

Hereinafter, the present invention will be described in more detail with reference to examples. These embodiments are for purposes of illustration only and are not intended to limit the scope of protection of the present invention.

Example 1

First, (Bi _0.5 Na _0.5 ) TiO ₃ was synthesized by heat treatment at 850 ° C. for 2 hours. Then, the synthesized (Bi _0.5 Na _0.5 ) TiO ₃ , BaCO ₃ , TiO ₂ were mixed at a composition ratio of Ba _0.05 (Bi _0.5 Na _0.5 ) _0.95 TiO ₃ , and synthesized by heat treatment at 1,100 ° C. for 2 hours. The synthesized Ba _0.05 (Bi _0.5 Na _0.5 ) _0.95 TiO ₃ , BaTiO ₃ and MnO ₂ were again Ba _1-x (Bi _0.5 Na _0.5 ) _x TiO ₃ : MnO ₂ : 1: y (x = 0.05, 0.06, 0.07 , 0.08, 0.09, 0.10; y = 0.005, 0.01, 0.02), the mixture was pulverized through a ball milling process for 24 hours, and then dried at 120 ° C. for 3 hours. The dried powder at a pressure of 1000 kg · f / cm ² Molded and sintered at 1,250 ~ 1,350 ℃ for 2 to 10 hours to prepare a ceramic for lead-free PTC thermistor.

The specific resistance (ρ) at room temperature according to the change of x and y values of the prepared lead-free PTC thermistor ceramics was measured, and the specific resistance (ρ) according to temperature change was measured, and representative results thereof are shown in FIGS. 1 and 2, respectively. .

In addition, the specific resistance, PTC jump, resistance temperature coefficient and Curie temperature (T _c) at room temperature of the prepared lead-free PTC thermistor ceramics were measured, and the results are shown in Tables 1 to 6 below.

y value
(x = 0.05) Room temperature
(Cm) PTC jump
(ρ _max / ρ _min ) Resistance temperature coefficient (% / ℃) T _c (℃) 0 177 1.05 × 10 ⁴ 42.9 167 0.005 239 8.4 × 10 ³ 33.9 163 0.01 424 2.5 × 10 ⁴ 70.7 161 0.02 247 4.6 × 10 ⁴ 64.3 161

y value
(x = 0.06) Room temperature
(Cm) PTC jump
(ρ _max / ρ _min ) Resistance temperature coefficient (% / ℃) T _c (℃) 0 492 1.4 × 10 ⁴ 56.4 172 0.005 271 4.3 × 10 ⁴ 49.8 164 0.01 198 3.0 × 10 ⁵ 93.9 162 0.02 218 2.4 × 10 ⁵ 81.9 162

y value
(x = 0.07) Room temperature
(Cm) PTC jump
(ρ _max / ρ _min ) Resistance temperature coefficient (% / ℃) T _c (℃) 0 584 1.1 × 10 ⁴ 46.3 175 0.005 321 2.3 × 10 ⁴ 47.2 170 0.01 278 8.3 × 10 ⁴ 73.9 168 0.02 312 1.1 × 10 ⁵ 83.7 167

y value
(x = 0.08) Room temperature
(Cm) PTC jump
(ρ _max / ρ _min ) Resistance temperature coefficient (% / ℃) T _c (℃) 0 632 0.8 × 10 ⁴ 47.4 177 0.005 334 1.2 × 10 ⁴ 69.8 172 0.01 251 5.6 × 10 ⁴ 77.9 169 0.02 298 2.0 × 10 ⁵ 80.5 171

y value
(x = 0.09) Room temperature
(Cm) PTC jump
(ρ _max / ρ _min ) Resistance temperature coefficient (% / ℃) T _c (℃) 0 664 1.3 × 10 ⁴ 44.8 178 0.005 378 2.6 × 10 ⁴ 59.8 174 0.01 301 8.4 × 10 ⁴ 83.9 171 0.02 392 1.4 × 10 ⁵ 71.9 173

y value
(x = 0.10) Room temperature
(Cm) PTC jump
(ρ _max / ρ _min ) Resistance temperature coefficient (% / ℃) T _c (℃) 0 651 0.9 × 10 ⁴ 57.1 179 0.005 357 5.1 × 10 ⁴ 62.3 175 0.01 324 3.8 × 10 ⁴ 90.9 173 0.02 407 9.4 × 10 ⁴ 77.9 173

In conventional ceramics for PTC thermistors containing lead, the room temperature resistivity increases rapidly from tens of Ω · cm to hundreds and thousands of Ω · cm as the amount of Pb added to BaTiO ₃ increases.

However, as shown in Tables 1 to 6 and FIGS. 1 to 4, ceramic compositions for PTC thermistors containing no lead according to one embodiment of the present invention (Ba _1-x (Bi _0.5 Na _0.5 ) _x TiO ₃ and MnO) The mixed ceramic composition of ₂ ) had a specific resistance value of 177 to 664 Ω · cm at room temperature, which was considerably lower than that of conventional ceramics containing lead.

In addition, the ceramic composition for the lead-free PTC thermistor of the present invention was found to have a Curie temperature of 160 ° C. or higher and a PTC jump characteristic of 8.4 × 10 ³ to 3.0 × 10 ⁵ .

Although the embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to the above embodiments and can be manufactured in various forms, and having ordinary skill in the art to which the present invention pertains. It will be understood by those skilled in the art that the present invention may be embodied in other specific forms without changing the technical spirit or essential features of the present invention. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

1 is a specific resistance at room temperature according to the y value change of the ceramic (Ba _0.95 (Bi _0.5 Na _0.5 ) _0.05 TiO ₃ + y mol% MnO ₂ ) for a non-lead PTC thermistor manufactured according to an embodiment of the present invention (ρ) ) Is a graph.

Figure 2 is a graph showing the specific resistance (ρ) according to the temperature change of the ceramic (Ba _0.95 (Bi _0.5 Na _0.5 ) _0.05 TiO ₃ + y mol% MnO ₂ ) for lead-free PTC thermistor manufactured according to an embodiment of the present invention to be.

Figure 3 is a non-lead, for ceramic PTC thermistor manufactured according to one embodiment of the invention according to the change in the y value _{(Ba 0 .94 (Bi 0 .5} Na 0 .5) 0.06 TiO 3 + y mol% MnO 2) It is a graph showing specific resistance (ρ) at room temperature.

Figure 4 is the specific resistance as a function of temperature of a lead-based ceramic for the PTC thermistor ratio _{(Ba 0 .94 (Bi 0 .5} Na 0 .5) 0.06 TiO 3 + y mol% MnO 2) prepared according to one embodiment of the present invention It is a graph showing (ρ).

Claims (8)

A ceramic composition for a lead-free PTC thermistor, comprising a compound represented by the following formula (1). [Formula 1] Ba _1-x (Bi _0.5 Na _0.5 ) _x TiO ₃ + y mol% MnO ₂ In Chemical Formula 1, 0.05 ≦ x ≦ 0.10 and 0.00 <y ≦ 0.02. Ba _1-x (Bi _0.5 Na _0.5 ) _x TiO ₃ (0.05 ≦ x ≦ 0.10) with MnO ₂ in a ratio of 1: y (at this time 0.00 <y ≦ 0.02) Mixing, pulverizing and drying; And molding and sintering the dried powder to produce a ceramics for lead-free PTC thermistor of Chemical Formula 1 below. [Formula 1] Ba _1-x (Bi _0.5 Na _0.5 ) _x TiO ₃ + y mol% MnO ₂ In Chemical Formula 1, 0.05 ≦ x ≦ 0.10 and 0.00 <y ≦ 0.02. The method of claim 2, The sintering temperature is 1,250 ~ 1,350 ℃ ceramic manufacturing method for lead-free PTC thermistor, characterized in that. The ceramics for lead-free PTC thermistors manufactured by the method of Claim 3. The method of claim 4, wherein The specific resistance at room temperature of the said lead-free PTC thermistor ceramics is 177-664 ohm-cm, The ceramic for non-lead-type PTC thermistor characterized by the above-mentioned. The method of claim 4, wherein Curie temperature of the non-lead-type PTC thermistor ceramics is at least 160 ℃ ceramics for non-lead-type PTC thermistor. The method of claim 4, wherein PTC jump characteristics (ρ _max / ρ _min ) of the non-lead-type PTC thermistor ceramics is 8.4 × 10 ³ ~ 3.0 × 10 ⁵ Ceramics for non-lead-type PTC thermistor. A lead-free PTC thermistor formed from the ceramics according to any one of claims 4 to 7.

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