JP6848327B2 - A method for producing a composition for a positive temperature coefficient resistor, a paste for a positive temperature coefficient resistor, a positive temperature coefficient resistor, and a positive temperature coefficient resistor. - Google Patents

Description

The present invention relates to compositions and resistance pastes used in the manufacture of positive temperature coefficient resistors. Furthermore, the present invention relates to a positive temperature coefficient resistor formed by using this resistance paste.

A positive temperature coefficient resistor is a resistor whose specific resistance increases as the temperature rises. In particular, a device whose resistivity suddenly increases at a certain temperature is called a "PTC thermistor" and is widely applied as a temperature control element, an overcurrent control element, a low temperature heating element and the like.
This "PTC thermistor" uses _{an inorganic material typified by BaTiO 3} ceramics and an organic material in which a conductive filler such as carbon black is dispersed in a thermoplastic polymer. It is roughly divided.

BaTiO ₃ based ceramics, Ba, after mixing the raw materials uniformly or Ti, calcined to must promote crystallization of the composite oxide, a composite oxide was the crystallized was pressure formed Manufactured by firing the molded body.
Therefore, the shape of the element is limited, and it is difficult to reduce the size. Also called switching temperature, the temperature at which the resistivity changes abruptly in BaTiO ₃ based ceramics are typically of the order of 120 ° C. Curie point temperature.

Patent Document 1, or by substituting a part of BaTiO ₃ based ceramic of Ba in alkali metal element, but the thermistor magnetic composition part is replaced with Group 5 element such as Nb of Ti is disclosed, There is no disclosure of Curie points above 250 ° C, and it is very difficult to make them hotter. Further, the range of the resistivity of the adjustable ceramics is small.

On the other hand, the "PTC thermistor" using an organic material has the advantage that there are few restrictions on the element shape, the resistivity can be changed depending on the type and content of the conductive filler, and the range of adjustable resistivity is wide. .. However, there is a limit to the switching temperature that can be obtained from the temperature at which the thermoplastic polymer softens, and it is not possible to manufacture an element whose resistance value changes rapidly at high temperatures. In addition, the polymer, which is a matrix, has a drawback of poor reliability because decomposition proceeds in a long-term use at a high temperature or in an environment where the temperature is repeatedly high.

In addition, a "PTC thermistor" in which conductive particles such as Ag are dispersed in glass is also proposed in Patent Document 2, but it is limited to a low resistivity and the switching temperature is too high to be 400 ° C or lower. However, there are drawbacks such as a high positive temperature coefficient at a temperature lower than the switching temperature.

Therefore, it is desired to develop a resistor capable of switching operation in a temperature range of 250 ° C. or higher and 400 ° C. or lower.

WO2014-141814 International Publication Japanese Unexamined Patent Publication No. 11-97207

Under such circumstances, the present invention is a highly reliable positive temperature coefficient resistor at high temperature, which has few restrictions on the element shape, a wide range of adjustable specific resistance, and switches in the range of 250 ° C to 400 ° C. The present invention provides a composition for use, a resistor paste made from the composition, a resistor formed from the resistor paste, and a method for producing the same.

In the present invention, a composition for a positive temperature coefficient resistor and a resistor paste in which ruthenium-based oxide particles and glass powder having a glass transition point of 250 ° C. to 400 ° C. are mixed as conductive particles are used as means for solving the problem.

The first invention of the present invention is a composition for a positive temperature coefficient resistor characterized by containing metal oxide-based conductive particles and a glass powder having a glass transition point of 400 ° C. or lower . The present invention is a composition for a positive temperature coefficient resistor, wherein the glass powder according to the first invention has a glass transition point of 400 ° C. or lower and a softening point of 50 ° C. or higher higher than the glass transition point. ..

A third invention of the present invention is a composition for a positive temperature coefficient resistor, characterized in that the metal oxide-based conductive particles in the first and second inventions are ruthenium-based oxide particles.

The fourth invention of the present invention is a composition for a positive temperature coefficient resistor, characterized in that the ruthenium-based oxide particles in the third invention are ruthenium oxide particles.

A fifth aspect of the present invention is a paste for a positive temperature coefficient resistor, which comprises an organic vehicle and the composition for a positive temperature coefficient resistor according to any one of the first to fourth inventions. Is.

A sixth aspect of the present invention is a positive temperature coefficient resistor characterized in that metal oxide-based conductive particles are contained in glass having a glass transition point of 400 ° C. or lower.

A seventh invention of the present invention is a positive temperature coefficient resistor characterized in that the metal oxide-based conductive particles in the sixth invention are ruthenium-based oxide particles.

Eighth inventions of the present invention are ruthenium-based oxide particles in the seventh aspect of the invention is a positive temperature coefficient resistor which is a ruthenium oxide particles.

In the ninth invention of the present invention, the positive temperature coefficient resistor paste according to the fifth invention is applied and fired on an insulating substrate to eliminate the organic solvent and the organic resin and soften the glass powder. The metal oxide-based conductive particles contained in the paste for a positive temperature coefficient resistor are taken into a glass matrix formed by the glass powder contained in the paste for a positive temperature coefficient resistor, dried and solidified. It is a method for manufacturing a positive temperature coefficient resistor, which is characterized in that it is manufactured by the above.

According to the present invention, a composition for a highly reliable positive temperature coefficient resistor at high temperature, which has few restrictions on the element shape, has a wide range of adjustable specific resistance, and switches in the range of 250 ° C to 400 ° C. A resistor paste made from the composition and a resistor formed from the resistor paste can be easily obtained.

It is a figure which shows the "temperature dependence of the electric resistance" of the resistor which concerns on Example 1. FIG. It is a figure which shows "the temperature dependence of the electric resistance" of the resistor which concerns on Example 2. FIG. It is a figure which shows "the temperature dependence of the electric resistance" of the resistor which concerns on Example 3. FIG. It is a figure which shows "the temperature dependence of the electric resistance" of the resistor which concerns on Example 4. FIG. It is a figure which shows "the temperature dependence of the electric resistance" of the resistor which concerns on Example 5. It is a figure which shows "the temperature dependence of the electric resistance" of the resistor which concerns on Comparative Example 1. It is a figure which shows "the temperature dependence of the electric resistance" of the resistor which concerns on Comparative Example 2.

The present invention uses a glass powder having a glass transition point of 250 ° C. or higher and 400 ° C. or lower in a composition for a positive temperature coefficient resistor containing metal oxide-based conductive particles such as ruthenium oxide particles and glass powder. As a result of discovering a phenomenon in which the resistance value of the obtained resistor suddenly changes at a set temperature within the temperature range of 250 ° C. or higher and 400 ° C. or lower, and further diligently developing it, such a glass transition point was established. A positive temperature coefficient resistor whose switching temperature can be controlled in the range of 250 ° C to 400 ° C, which is the temperature at which the rate of increase in specific resistance with respect to temperature rise changes depending on the combination of the glass powder and the metal oxide-based conductive particles. It has been completed.

In general, in a thick film resistor in which conductive particles are dispersed in a glass matrix, the contact between the conductive particles becomes weak due to the volume expansion of the glass matrix, which causes an increase in specific resistance.
By the way, the volume expansion coefficient of glass changes greatly with the glass transition point as a boundary, and the glass has a property that the volume expansion coefficient is higher on the high temperature side of the glass transition point than on the low temperature side.
Even in the positive temperature coefficient resistor according to the present invention, since the volume expansion coefficient increases on the high temperature side of the glass transition point, the increase rate of the specific resistance also changes at the glass transition point. That is, it was expected that the rate of increase in the resistance value would be sharply larger at the temperature above the glass transition point than at the temperature below the glass transition point.

However, although a general thick film resistor is fired at around 850 ° C., if glass having a low glass transition point is used, the glass becomes excessively soft and the shape of the thick film resistor cannot be maintained. It is common to use glass that exhibits a glass transition point of 500 ° C. or higher.

By the way, if a glass powder having a glass transition point of 500 ° C. or higher and a metal oxide-based conductive particle are used, it is considered that a positive temperature coefficient resistor having a switching temperature of 500 ° C. or higher is possible, but the switching temperature exceeds 500 ° C. Assuming that a positive temperature coefficient resistor is obtained, the positive temperature coefficient resistor operates at a temperature of 500 ° C. or higher. Therefore, not only the positive temperature coefficient resistor but also peripheral parts such as terminal electrodes incorporated in the thick film resistor are exposed to a temperature of 500 ° C. or higher, which causes problems such as deterioration of the terminal electrodes.
Further, when it is desired to keep the switching temperature lower than 500 ° C., these combinations cannot be used.

From such a problem, when a positive temperature coefficient resistor is formed from a thick film resistor, it cannot be dealt with when a resistor having a switching temperature of 400 ° C. or less is desired, and a corresponding product cannot be provided. It is sought after.

Therefore, as the glass powder used in the present invention, a glass powder having a component composition having a glass transition point in the range of 400 ° C. or lower, preferably 250 ° C. or higher and 400 ° C. or lower is used.
The composition of the glass powder having the glass transition point as described above is not limited, and examples thereof include lead borate-based glass, tin phosphate-based glass, and tellurium vanadium acid.

The lower limit of the glass transition point of the glass powder in the present invention is not limited, but at present, no oxide glass substantially below 240 ° C. has been found, and therefore, the desirable ranges are 250 ° C. or higher and 400 ° C. or lower. The glass transition point and softening point of the glass powder used in the present invention can be adjusted by adjusting the composition of the glass powder. Specifically, the mixing ratio of each element such as silicon, boron, aluminum, zinc, lead, and bismuth constituting the glass may be adjusted.
Here, the glass transition point is measured as a temperature indicating a bending point of a thermal expansion curve by measuring a rod-shaped sample obtained by remelting glass powder or the like in the atmosphere by a thermomechanical analysis method (TMA). To.

Further, it is desirable that the softening point of the glass powder used in the present invention is a temperature higher than the glass transition point by 50 ° C. or more.
The softening point of the glass powder is the lowest temperature at which the glass softens, and the shape of the positive temperature coefficient resistor cannot be maintained at a temperature well exceeding the softening point. The positive temperature coefficient resistor according to the present invention needs to maintain the positive temperature coefficient resistor even at a temperature exceeding the glass transition point. Therefore, the softening point of the glass powder used in the present invention is preferably a temperature higher than the glass transition point by 50 ° C. or more and less than the upper limit of the firing temperature described later.

Here, the softening point is measured by measuring the glass powder in the atmosphere by a differential thermal analysis method (TG-DTA), and the next differential thermal curve on the higher temperature side than the temperature at which the decrease in the differential thermal curve on the lowest temperature side appears is The temperature of the peak that decreases.
The glass transition point and softening point of the glass powder used in the present invention are adjusted according to the component composition of the glass powder.

The particle size of the glass powder is not particularly limited, but considering the variation in resistance value and stability _{, it is desirable that the median value (D 50} ) of the volume distribution diameter of the laser diffraction scattering type particle size distribution meter is 10 μm or less, and more preferably. Is 3 μm or less.

Metal oxide-based conductive particles are used as the conductive particles in the present invention.
Examples of the metal oxide-based conductive particles include ruthenium-based oxide particles, iridium oxide particles, tin oxide-based particles such as tin oxide particles and antimony-added tin oxide particles, and tin-added indium oxide particles.
The method for producing these metal oxide-based conductive particles is, for example, to obtain a precipitate of a hydroxide of a metal element in an aqueous solution, appropriately select a compound of an additive element, an air atmosphere, an inert atmosphere, or the like, and heat roast. It can be obtained by baking.

Among the above metal oxide-based conductive particles, ruthenium-based oxide particles are preferable because of their high conductivity, and the ruthenium-based oxide particles include ruthenium dioxide (hereinafter referred to as ruthenium oxide), lead ruthenium acid, and ruthenium. Pyrochloroa-type crystal structures such as bismuth acid and oxide particles having a perovskite-type crystal structure such as strontium ruthenium and calcium ruthenium are suitable.
Further, the ruthenium oxide can cover a wide resistance value region by changing the compounding ratio with glass, and the temperature coefficient of resistance can be adjusted by adding a small amount of a specific metal oxide or the like.

The mixing ratio of the glass powder and the ruthenium-based oxide particles is 10% by mass to 50% by mass of the conductive particles with respect to the total of the glass powder and the conductive particles. If the conductive particles are less than 10% by mass, the resistance value becomes too high, and if it is more than 50% by mass, the film becomes too brittle.
With such a blending ratio of the glass powder and the ruthenium-based oxide particles, the surface of the temperature coefficient resistor obtained from the composition for the temperature coefficient resistor according to the present invention becomes smooth and the film structure is maintained. The positive temperature coefficient resistor is not damaged by temperature changes.

Further, from the viewpoint of gently adjusting the resistance value according to the compounding ratio with glass, the particle size of the conductive particles is not limited, but is preferably 0.1 μm or less. As a method for measuring the particle size of the conductive particles, the specific surface area may be measured by the BET method and converted into particles to obtain the particle size.

By the way, as the conductive particles of the resistor composition containing the glass powder and the conductive particles, it is known that metal particles such as silver-palladium alloy particles are used in addition to the metal oxide-based particles. When the sex particles are composed of only metal particles, the metal particles may be oxidized or sintered and the desired resistance value may not be obtained, or the positive temperature coefficient resistor may be damaged due to temperature changes or the like. , It is not desirable to use it in the composition for a positive temperature coefficient resistor according to the present invention.

Therefore, an additive may be added to the composition for a positive temperature coefficient resistor of the present invention for the purpose of improving or adjusting the resistance value and the temperature coefficient of resistance, and MnO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , Examples thereof include TiO ₂ , CuO, ZrO ₂ , Al ₂ O ₃ , SiO ₂ , Mg ₂ SiO _{4 , and ZrSiO 4} .
By adding these additives, a positive temperature coefficient resistor having better characteristics can be produced. The amount to be added is adjusted according to the purpose, but is usually 20 parts by weight or less based on 100 parts by weight of the total of the ruthenium oxide conductive particles and the glass powder.
The additive may be in the form of a powder having a median value (D ₅₀ ) of the number average diameter of 3 μm or less, or the organometallic compound is decomposed in the process of firing the paste for a positive temperature coefficient resistor, and these additives are used. Compounds may be produced.

The ruthenium oxide conductive particles and the glass powder are mixed and dispersed in an organic vehicle to form a printing paste together with additives as required.
The organic vehicle used is not particularly limited, and an organic vehicle in which resins such as ethyl cellulose, acrylic acid ester, methacrylic acid ester, rosin, and maleic acid ester are dissolved in a solvent such as tarpineol, butyl carbitol, and butyl carbitol acetate can be used. Used. Further, if necessary, a dispersant, a plasticizer, or the like can be added.
The dispersion method is not particularly limited, but it is common to use a three-roll mill, a bead mill, a planetary mill, or the like that disperses fine particles. The blending ratio of the organic vehicle is appropriately adjusted by the printing or coating method, but is about 20 to 200 parts by weight with respect to 100 parts by weight of the total of the ruthenium oxide conductive particles, the glass powder and the additive.

[Manufacturing method of resistor]
An example of the method for manufacturing a positive temperature coefficient resistor according to the present invention is a printing process in which a positive temperature coefficient resistor paste is applied onto an insulating substrate such as ceramic by a known screen printing method or the like, and a positive temperature coefficient resistor paste. It is produced through each step of a drying step of heating and removing the solvent contained in the above to obtain a dry film and a firing step of firing the obtained dry film.

In the firing process, the resin is debindered by heating to remove it, and then fired at a temperature higher than the softening point of the glass powder used. The glass powder softens and the particles are fused and melted to form a glass film-like glass. It forms a matrix and is fixed to the substrate.
In addition, the conductive particles exist around the glass powder and are fixed in the glass matrix formed by the fusion of the glass powder when the dry film is fired.
As a result, the positive temperature coefficient resistor is obtained as a fired body in which conductive particles are introduced into a glass matrix formed by fusing glass powder.

The firing temperature in the firing step is determined in consideration of the glass transition point and the softening point of the glass powder to be used. If the firing temperature is too high, the fired body cannot be formed into a predetermined shape and is too low. However, the firing is insufficient, a fired body having a predetermined shape cannot be obtained, and the introduction of the conductive particles into the fired body is insufficient.
As the temperature range, the softening point + 50 ° C. to 150 ° C. is preferable, and the softening point + 60 ° C. to 130 ° C. is more preferable.

The drying temperature and drying time of the drying step can be timely selected under conditions sufficient for the solvent in the paste to volatilize.
A ceramic substrate such as alumina is used as the insulating substrate. Further, a terminal electrode is provided on the obtained positive temperature coefficient resistor and connected to an electric circuit. The terminal electrode may be formed on an insulating substrate in advance by using a known thick film silver paste or the like.
Although the present invention has been described so far, the resistor obtained by firing the composition for a positive temperature coefficient resistor according to the present invention is the positive temperature coefficient resistor according to the present invention, and relates to the present invention. it can be a positive temperature coefficient resistor composition by dispersing in an organic vehicle to obtain a positive temperature coefficient resistor-body paste.

Although the present invention will be specifically described, the present invention is not limited to these examples.
Table 1 shows the component composition of the glass powder used in Examples and Comparative Examples of the present invention, the median value (D ₅₀ ) of the number mean diameter, and the glass transition point.
^{For the conductive particles, ruthenium oxide particles having a specific surface area of 20 m 2} / g and a particle size of 40 nm obtained from the specific surface area measurement by the BET method were used, and for the glass powder, the number average diameter of the laser diffraction scattering type particle size distributor was used. Each glass powder shown in Table 1 having a median value (D _{50) of 1.5 μm was used.}
The conductive particles and the glass powder were mixed as shown in Table 2, and the total of 100 parts by weight was added to and mixed with 43 parts by weight of the organic vehicle, and then dispersed with a three-roll mill to prepare the test material. A resistance paste was prepared.

Next, the prepared resistance paste was printed on the Ag electrode formed by firing on an alumina substrate in advance, dried under the conditions of 150 ° C. × 5 minutes, and then adjusted to the degree of softening of each glass powder shown in Table 2. After raising the temperature to the temperature, firing was performed under the condition of holding for 10 minutes, and the temperature was lowered to the room temperature to form a resistor.
The resistor size of the test material was such that the resistor width was 1.0 mm and the resistor length (between electrodes) was 1.0 mm.

Using an oven that can control the temperature of the "temperature dependence of the resistance value" indicated by the produced resistor, the above-mentioned test material used as a 4-terminal method potential resistance measurement sample is placed in the oven, and the oven temperature is adjusted. While changing, the electrical resistance was measured with a digital multimeter by the 4-terminal method.
The measurement results are shown in FIGS. 1 to 5 (Examples 1 to 5), FIG. 6 (Comparative Example 1), and FIG. 7 (Comparative Example 2).

Examples 1 and 2 are resistors made of glass powder having a glass transition point of 240 ° C. and ruthenium oxide particles. From the temperature characteristics of the resistance values shown in FIGS. 1 and 2, it can be seen that the change in resistance value (resistance temperature coefficient) with respect to temperature changes at about 250 ° C. The inflection point of this temperature coefficient of resistance almost coincides with the glass transition point of the glass as a raw material.
Examples 3 and 4 are resistors composed of glass powder having a glass transition point of 270 ° C. and ruthenium oxide particles. From FIGS. 3 and 4, the inflection point of the temperature coefficient of resistance appears at about 280 ° C., which almost coincides with the transition point of the glass.
Example 5 is a resistor composed of glass powder having a glass transition point of 400 ° C. and ruthenium oxide particles. From FIG. 5, the inflection point of the temperature coefficient of resistance appears at about 400 ° C., which almost coincides with the transition point of the glass.

In contrast to the above Examples, Comparative Examples 1 and 2 shown in FIGS. 6 and 7 showed the resistance temperature characteristics of the resistor made of glass and ruthenium oxide having glass transition points of 510 ° C. and 550 ° C. In each case, no inflection point of resistance temperature characteristics appeared in the temperature range of 25 ° C. to 500 ° C.

As can be seen from Examples and Comparative Examples, according to the present invention, it is possible to manufacture a positive temperature coefficient resistor whose resistance temperature coefficient changes in the temperature range of 250 ° C. to 400 ° C., which has been difficult in the past, and the resistance temperature. The temperature coefficient variation point can be selected by adjusting the glass transition point of the raw material glass.

Claims (9)

A composition for a positive temperature coefficient resistor, which comprises metal oxide-based conductive particles and a glass powder having a glass transition point of 400 ° C. or lower. The composition for a positive temperature coefficient resistor according to claim 1, wherein the glass powder has a glass transition point of 400 ° C. or lower and a softening point of 50 ° C. or higher higher than the glass transition point. The composition for a positive temperature coefficient resistor according to claim 1 or 2 , wherein the metal oxide-based conductive particles are ruthenium-based oxide particles. The composition for a positive temperature coefficient resistor according to claim 3 , wherein the ruthenium-based oxide particles are ruthenium oxide particles. A paste for a positive temperature coefficient resistor, which comprises an organic vehicle and the composition for a positive temperature coefficient resistor according to any one of claims 1 to 4. A positive temperature coefficient resistor characterized in that metal oxide-based conductive particles are contained in glass having a glass transition point of 400 ° C. or lower. The positive temperature coefficient resistor according to claim 6 , wherein the metal oxide-based conductive particles are ruthenium-based oxide particles. The positive temperature coefficient resistor according to claim 7 , wherein the ruthenium-based oxide particles are ruthenium oxide particles. By applying and firing the paste for a positive temperature coefficient resistor according to claim 5 on an insulating substrate, the organic solvent and the organic resin are eliminated, and the glass powder is softened to obtain the paste for a positive temperature coefficient resistor. It is characterized in that it is produced by incorporating the contained metal oxide-based conductive particles into a glass matrix formed of glass powder contained in the paste for a positive temperature coefficient resistor, drying and solidifying the mixture. A method for manufacturing a positive temperature coefficient resistor.

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