JP7687686B2 - Resistor paste, fired body and electrical products - Google Patents

Description

The present invention relates to a resistor paste for use in forming resistors such as resistive heating elements. The present invention also relates to a sintered body obtained by sintering the resistor paste, and an electrical product including the sintered body.

Conventionally, resistor paste has been used as a material for forming resistive heating elements (resistors) used in ceramic heaters, etc. Metals contained in resistor paste include, for example, ruthenium oxide and its compounds, silver, and palladium.

As an example of a ceramic heater, Patent Document 1 describes a ceramic heater that includes a substrate made of ceramic, a conductive pattern formed on the substrate, a resistive heating element formed on the substrate so as to be electrically connected to the conductive pattern, and an overcoat layer formed to cover at least the resistive heating element. Patent Document 1 also describes that the resistive heating element contains an alloy made of silver and palladium, and graphite, and that the graphite content of the total of the alloy and the graphite is 16 to 47%.

Patent Document 2 describes a heater for a thermal print head or a heater for fixing toner in a printer. Patent Document 2 describes a ceramic substrate heater manufactured by forming a heater circuit on a ceramic substrate using a resistor paste. Patent Document 2 further describes a resistor paste for a ceramic substrate heater, which contains (A) silver powder (A-1) and (A-2) palladium powder as conductive powders, (B) glass frit, and (C) inorganic metal oxide powder. Patent Document 2 also describes that the softening point of the (B) glass frit of the resistor paste is 750° C. or higher and its particle size is within the range of 1 to 3 μm, that the (C) inorganic metal oxide powder is a powder of at least one inorganic metal oxide selected from the group consisting of alumina, zirconia, titania, and yttria, its particle size is within the range of 0.1 to 1 μm, and that the resistance value fluctuation rate of the resistor after firing is 10% or less.

JP 2013-200945 A JP 2013-161770 A

Ruthenium oxide and its compounds, silver and palladium are used as the materials for the metal powder contained in the resistor paste. By adding glass frit and various additives to the silver and palladium, it is possible to control the change in resistance value due to temperature of the resistor formed using the resistor paste, and to control the sheet resistance. The temperature coefficient of resistance (TCR) is used as a coefficient that indicates the change in resistance value due to temperature of the resistor.

Resistors used as resistive heating elements are heated by passing electricity through them, and their temperature repeatedly changes between room temperature and the operating temperature. In order to stably obtain highly reliable operation of a resistive heating element, it is necessary for the resistor to have a small temperature coefficient of resistance (TCR).

In order to reduce the temperature coefficient of resistance (TCR) of resistors, palladium (Pd) is added as a material for the metal powder contained in resistor paste. However, the high price of palladium raises the problem of high costs for resistor paste and resistors manufactured using it. For this reason, there is a demand to reduce the palladium content of resistor paste.

Therefore, the present invention aims to provide a resistor paste for manufacturing a resistor having a reduced palladium content and suppressed change in resistance value due to temperature.

In order to solve the above problems, the present invention has the following configuration.

(Configuration 1)
The present invention provides a first aspect comprising: (A) a metal powder containing silver and tin and substantially no rhodium or palladium;
(B) a rhodium component; and
(C) a glass frit,
(A) When the total weight of the silver and tin in the metal powder is 100% by weight, the weight ratio of silver in the metal powder is 75% by weight or more;
This resistor paste has a rhodium content of 0.1 to 10 parts by weight in the rhodium component (B) relative to 100 parts by weight of the metal powder (A).

(Configuration 2)
A second aspect of the present invention is the resistor paste of the first aspect, wherein (A) the metal powder is an alloy powder of silver and tin.

(Configuration 3)
Configuration 3 of the present invention is the resistor paste of configurations 1 or 2, further comprising (D) palladium.

(Configuration 4)
A fourth aspect of the present invention is the resistor paste of any one of the first to third aspects, in which the rhodium component (B) is a rhodium resinate.

(Configuration 5)
A fifth aspect of the present invention is the resistor paste of any one of the first to fourth aspects, wherein the glass frit (C) has a softening point of 700°C to 850°C.

(Configuration 6)
A sixth aspect of the present invention is the resistor paste of any one of the first to fifth aspects, wherein the resistor paste is a resistor paste for a heating element.

(Configuration 7)
A seventh aspect of the present invention is a sintered body obtained by sintering the resistor paste of any one of the first to sixth aspects.

(Configuration 8)
The eighth aspect of the present invention is an electrical product using the sintered body according to the seventh aspect.

According to the present invention, it is possible to provide a resistor paste for manufacturing a resistor having a reduced palladium content and suppressed change in resistance value due to temperature.

FIG. 2 is a schematic diagram showing an example of a heating element having a resistor.

The following describes in detail the embodiments of the present invention. Note that the following embodiments are forms for embodying the present invention and do not limit the scope of the present invention.

This embodiment is a resistor paste for use in forming resistors such as resistive heating elements. The temperature coefficient of resistance (TCR) is used as a coefficient indicating the change in resistance value of a resistor depending on the temperature. The temperature coefficient of resistance (TCR) can be expressed by the following formula 1.
TCR (ppm/°C) = [(Rb-Ra)/Ra]/(Tb-Ta)×10 ⁶ (Formula 1)

In formula 1, Ta is the reference temperature (°C), Ra is the resistance value at the reference temperature, Tb is a predetermined temperature (temperature to be compared (°C)), and Rb is the resistance value at the predetermined temperature (temperature to be compared). In this specification, the temperature coefficient of resistance (TCR) is evaluated with Ta (reference temperature) set to 25°C and Tb (temperature to be compared) set to 125°C. This is because the room temperature is about 25°C and the temperature of the resistor when it is heated (operating) is about 125°C, so the temperature coefficient of resistance (TCR) can be evaluated in the range of the operating temperature of the resistor. When Ta (reference temperature) is 25°C and Tb (temperature to be compared) is 125°C, the temperature coefficient of resistance (TCR) of the resistor must be 1000 ppm or less, and preferably 800 ppm or less. If the TCR exceeds 1000 ppm, it may not be possible to use it as a reliable resistor.

Next, we will explain the resistor paste of this embodiment.

The resistor paste of this embodiment contains (A) metal powder, (B) rhodium component, and (C) glass frit. Each component is described below.

(A) Metal Powder The resistor paste of this embodiment contains (A) metal powder. The (A) metal powder contains silver (Ag) and tin (Sn), and does not substantially contain rhodium (Rh) and palladium (Pd). By containing a predetermined (A) metal powder in the resistor paste of this embodiment, a resistor paste for manufacturing a resistor having a reduced palladium content and suppressed resistance value change due to temperature can be obtained. In addition, by controlling the compounding ratio of silver and tin, the resistance value (e.g., sheet resistance) of the obtained resistor can be controlled.

(A) The metal powder contains silver and tin. The metal powder in conventional resistor pastes usually contains palladium along with silver. The price of tin is significantly lower than that of palladium, a precious metal. Therefore, by using the (A) metal powder of this embodiment, a resistor paste can be obtained at a significantly lower cost.

In the resistor paste of this embodiment, the metal powder (A) is substantially free of rhodium and palladium. In this specification, "substantially free of" means that rhodium and palladium are not intentionally added to the metal powder (A), and does not exclude the inclusion of rhodium and palladium that are inevitably mixed in as impurities. Rhodium is added separately to the resistor paste as the rhodium component (B) described later.

(A) The metal powder can be a mixed powder containing silver powder and tin powder. The mixed powder can contain metal powders other than silver and tin as long as the effect of this embodiment is not impaired. However, in order to reliably achieve a low temperature coefficient of resistance (TCR), it is more preferable that the metal powder consists of only silver and tin metal powders.

In addition, it is preferable that the (A) metal powder is an alloy powder of an alloy containing silver and tin. By using the (A) metal powder as an alloy powder containing silver and tin, a lower temperature coefficient of resistance (TCR) can be achieved compared to a mixed powder containing silver powder and tin powder. The alloy powder can also contain metals other than silver and tin as long as the effect of this embodiment is not impaired. However, in order to achieve an even lower temperature coefficient of resistance (TCR), it is more preferable that the alloy powder is an alloy powder consisting essentially of silver and tin only.

In the resistor paste of this embodiment, when the total weight of the silver and tin in the (A) metal powder is taken as 100% by weight, the weight percentage of silver in the metal powder is 75% by weight or more, preferably 80% by weight or more, and more preferably 90% by weight or more. By having the weight percentage of silver be a predetermined percentage or more, a resistor paste with low resistance can be obtained.

It is preferable that the weight percentage of tin in the (A) metal powder is less than 10% by weight. In that case, the resistance value of the resistor obtained by firing the resistor paste can be lowered, and the temperature coefficient of resistance (TCR) can be lowered. If the weight percentage of tin in the (A) metal powder is 10% by weight or more, the resistance value of the resistor cannot be lowered. Also, if the weight percentage of tin in the (A) metal powder is less than 2% by weight, the temperature coefficient of resistance (TCR) becomes high. Therefore, it is preferable that the weight percentage of tin in the (A) metal powder is 2% by weight or more, and more preferably 7% by weight or more.

(A) Examples of elements other than silver and tin that can be contained in the metal powder include copper, nickel, molybdenum, carbon, silicon, tungsten, and iron. Elements other than silver and tin can be added to the metal powder (A) to the extent that they do not interfere with the effects of the embodiment.

From the viewpoint of performing printing such as screen printing well, the average particle size of the metal powder (A) is preferably 0.1 to 5 μm, and more preferably 1 to 3 μm. Here, the average particle size of the metal powder refers to the average particle size (D50) measured by a laser diffraction scattering method. The shape of the metal powder is not particularly limited, and examples include spherical and scale-like shapes, with spherical being preferred. In this specification, the average particle size of the other components is also the average particle size (D50) measured by a laser diffraction scattering method, just like the metal powder.

(B) Rhodium (Rh) Component The resistor paste of the present embodiment contains a rhodium (Rh) component (B). By containing the rhodium component (B) in the resistor paste, the temperature coefficient of resistance (TCR) of the resistor obtained by firing the resistor paste can be made lower.

In the resistor paste of this embodiment, the rhodium content in the (B) rhodium component per 100 parts by weight of the (A) metal powder is 0.10 to 10 parts by weight, and preferably 0.10 to 6 parts by weight. If the rhodium content in the (B) rhodium component of the resistor paste is low, it becomes difficult to reduce the temperature coefficient of resistance (TCR) of the resistor obtained by firing the resistor paste. In addition, if the rhodium content in the (B) rhodium component of the resistor paste is too high, problems arise such as poor printability of the resistor paste and increased costs of the resistor paste.

In the resistor paste of this embodiment, the rhodium component (B) is preferably rhodium resinate. By using the rhodium component (B) as rhodium resinate, the rhodium component (B) can be blended more uniformly into the resistor paste than when rhodium metal powder is added directly, and as a result, the amount of rhodium component added can be reduced compared to when rhodium metal powder is added, while still achieving the same effect.

The resistor paste of this embodiment contains (C) glass frit.

By including glass frit (C) in the resistor paste, the resistor is given adhesion to the ceramic substrate after firing the resistor paste, and cracks during firing of the resistor can be prevented. In addition, by adjusting the glass frit content, the electrical resistance (e.g., sheet resistance) of the fired body obtained by firing can be controlled, and the temperature coefficient of resistance (TCR) can be reduced.

The content of (C) glass frit in the resistor paste is preferably 0.1 to 30 parts by weight, and more preferably 0.5 to 15 parts by weight, per 100 parts by weight of (A) metal powder. If the glass frit content is less than 0.1 parts by weight, the adhesive strength of the resistor to the ceramic substrate decreases. Also, if the glass frit content is more than 30 parts by weight, the resistance value of the resistor becomes higher than the allowable range.

In the resistor paste of this embodiment, the glass frit (C) preferably has a softening point of 700°C to 850°C. By using a glass frit of high heat-resistant glass with a relatively high softening point, it is possible to reduce the change in resistance value due to repeated firing when manufacturing a resistor device, and also to reduce the temperature coefficient of resistance (TCR). The softening point is a value measured by a differential thermal analyzer. In addition, when Ta (reference temperature) is 25°C and Tb (comparison temperature) is 125°C, the temperature coefficient of resistance (TCR) of the resistor must be 1000 ppm or less, and is preferably 800 ppm or less. If the TCR exceeds 1000 ppm, it may not be possible to use it as a reliable resistor.

In order to improve printing such as screen printing, and adhesion to the substrate, the average particle size of the glass frit (C) is preferably 0.1 to 10 μm, and more preferably 1 to 5 μm.

The resistor paste of this embodiment preferably further contains (D) palladium (Pd). By further containing (D) palladium, the resistor paste of this embodiment can further reduce the electrical resistance of the resistor obtained by firing, and can further reduce the temperature coefficient of resistance (TCR).

The content of (D) palladium in the resistor paste is preferably 0.1 to 5 parts by weight, and more preferably 0.1 to 3 parts by weight, per 100 parts by weight of (A) metal powder. In the resistor paste of this embodiment, palladium is not an essential component, but if the content of palladium is less than 0.1 parts by weight, the effect of reducing the temperature coefficient of resistance (TCR) is small. Also, if the content of palladium is more than 5 parts by weight, the cost of the resistor paste becomes high.

In order to facilitate printing such as screen printing, and to reduce the electrical resistance of the resistor, the average particle size of the (D) palladium particles is preferably 0.01 to 5 μm, and more preferably 0.05 to 3 μm.

The resistor paste of this embodiment may contain (E) a thermoplastic resin such as cellulose resin and cellulose resin.

(E) Thermoplastic resins impart printability, thixotropy, and a lower binder removal temperature to the resistor paste. Examples of cellulose resins include ethyl cellulose and nitrocellulose. Examples of acrylic resins include polymers of methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, and butyl methacrylate, or copolymers thereof. (E) Thermoplastic resins may be used alone or in combination of two or more types.

The resistor paste of this embodiment may contain (F) a solvent.

Solvents for the resistor paste include terpene, ester alcohol, aromatic hydrocarbon, and ester solvents. Examples of terpene solvents include limonene, paramenthane, pinane, terpineol, and dihydroterpineol. Examples of ester alcohols include 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate. Examples of aromatic hydrocarbons include xylene, isopropylbenzene, and toluene. Examples of ester solvents include ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether acetate, and diethylene glycol monobutyl ether acetate. These solvents may be used alone or in combination.

The resistor paste of this embodiment may contain optional components such as viscosity adjusters, defoamers, flame retardants, and antioxidants, provided that the effects of this embodiment are not impaired.

The resistor paste of this embodiment can be produced by mixing the above-mentioned materials, i.e., (A) metal powder, (B) rhodium component, and (C) glass frit, with optional materials such as (D) palladium, (E) thermoplastic resin, and/or (F) solvent, which are blended as necessary, using, for example, a mortar and pestle mixer, a pot mill, a triple roll mill, a rotary mixer, a twin-shaft mixer, or the like.

In this embodiment, it is preferable that the resistor paste is a resistor paste for a heating element.

Figure 1 shows a schematic diagram of an example of a heating element 10. In the heating element 10 shown in Figure 1, a resistor 2 is formed on the surface of a substrate 1. The resistor 2 is electrically connected to a set of electrodes 3, and a current from an external power source (not shown) can be passed through the resistor 2 via a set of lead wires 4. The resistor 2 generates heat due to the applied current, and is thereby able to release heat to the outside. The resistor paste of this embodiment can be preferably used to form the resistor 2 of the heating element 10.

The resistor 2 of the heating element 10 shown in FIG. 1 is a sintered body obtained by sintering the resistor paste of this embodiment. That is, the resistor paste of this embodiment is applied to the surface of the substrate 1 in a predetermined pattern by screen printing or the like. By sintering the resistor paste pattern in an air atmosphere, a resistor 2 (sintered body) having a predetermined pattern shape can be obtained. If the resistor paste of this embodiment is used, a resistor 2 (sintered body) with low resistance and a low temperature coefficient of resistance (TCR) can be obtained by sintering in air as the sintering atmosphere.

The method for applying the resistor paste of this embodiment is arbitrary. Examples of application methods include known methods such as dispensing, jet dispensing, stencil printing, screen printing, pin transfer, and stamping. It is preferable to use screen printing as the method for applying the resistor paste, since it is possible to form a predetermined pattern shape with a desired film thickness with good reproducibility.

By firing the applied resistor paste, a fired body like resistor 2 in FIG. 1 can be obtained. The resistor paste of this embodiment can be fired in an air atmosphere. The firing temperature is preferably 500 to 900°C, more preferably 600 to 900°C, even more preferably 700 to 900°C, and particularly preferably 800 to 900°C. By firing at such a firing temperature, the metal powders contained in the resistor paste are sintered together, and the organic binder and other components contained in the resistor paste can be burned off.

The sheet resistance of the sintered body (resistor 2) must be 50 to 500 mΩ/□ (mΩ/square). If the sheet resistance of the resistor at 25°C (room temperature) is 50 mΩ/□ or less, or 500 mΩ/□ or more, it may not be usable as a resistor.

The thickness of the fired body is preferably 5 to 30 μm, and more preferably 10 to 20 μm. The thickness of the fired body can be adjusted so that the sheet resistance of the fired body falls within the above-mentioned range. When using a screen printing method, for example, the thickness of the fired body can be controlled by selecting the screen and adjusting the printing conditions.

This embodiment is an electrical product that uses a sintered body obtained by sintering the resistor paste described above. Examples of electrical products include thermal print heads, printers, and hot plates.

The sintered body obtained by sintering the resistor paste of this embodiment can be used as a resistor for a ceramic substrate heater (heating element) used in a heater for a thermal print head, a toner fixing heater for a printer, a heater for a hot plate, etc. By printing the resistor paste of this embodiment in a predetermined pattern on the surface of a ceramic substrate and sintering it, a ceramic substrate heater having a predetermined heater circuit can be manufactured.

The resistor paste of this embodiment is low-cost because it can reduce the palladium content. In addition, a resistor (sintered body) obtained by sintering the resistor paste of this embodiment can suppress changes in resistance value due to temperature. Therefore, by using the resistor paste of this embodiment, a resistor can be obtained that is low-cost and can suppress changes in resistance value due to temperature. Therefore, electrical products using resistors using the resistor paste of this embodiment can be made relatively low-cost and can have high reliability during operation accompanied by temperature changes when the resistor is used as a heating element.

The present invention will be explained in detail below with reference to examples, but the present invention is not limited to these.

The resistor pastes of the examples and comparative examples were prepared by mixing the components according to the ratios shown in Tables 1 and 2. The materials used as (A) metal powders A1 to A6, (B) rhodium component, (C) glass frits C1 and C2, (D) palladium component, (E) thermoplastic resins E1 and E2, and (F) solvents F1 and F2 are explained below. Note that the average particle size in the following explanation is the average particle size (D50) measured by the laser diffraction scattering method.

(A) Metal Powder As the (A) metal powder, the following metal powders A1 to A6 were used. The Ag/Sn values below are weight ratios.
Metal powder A1 (alloy powder): Ag/Sn=93/7, spherical, average particle size 2.5 μm
Metal powder A2 (alloy powder): Ag/Sn=98/2, spherical, average particle size 2.5 μm
Metal powder A3 (alloy powder): Ag/Sn=95/5, spherical, average particle size 2.5 μm
Metal powder A4 (alloy powder): Ag/Sn=70/30, spherical, average particle size 2.5 μm
Metal powder A5: Ag powder, spherical, average particle size 2.5 μm
Metal powder A6: Sn powder, spherical, average particle size 2.5 μm

(B) Rhodium Component The following was used as the (B) rhodium (Rh) component: Table 1 shows the weight percentage of Rh in the resinate when the (A) metal powder is taken as 100 parts by weight.
Rh resinate: Rh content 10% (manufactured by Daiken Chemical Co., Ltd.)

(C) Glass Frit As the (C) glass frit, the following glass frits C1 and C2 were used. The softening point was a value measured by a differential thermal analyzer. The average particle size of the glass frit was 2 μm.
Glass frit C1: _SiO2 type, softening point 820°C (manufactured by Okuno Chemical Industries Co., Ltd.)
Glass frit C2: SiO2 _type , softening point 740°C (manufactured by Okuno Chemical Industries Co., Ltd.)

(D) Palladium Component As the (D) palladium (Pd) component, palladium particles having an average particle size of 0.1 μm were used.

(E) Thermoplastic Resin As the thermoplastic resin, the following thermoplastic resins E1 and E2 were used.
Thermoplastic resin E1: Ethyl cellulose resin (STD-14, manufactured by Dow Chemical Company)
Thermoplastic resin E2: Ethyl cellulose resin (STD-200, manufactured by Dow Chemical Company)

(F) Solvent As the solvent, the following solvents F1 and F2 were used.
Solvent F1: Butyl carbitol (manufactured by Taishin Chemical Co., Ltd.)
Solvent F2: Texanol (manufactured by Eastman Chemical Co.)

The materials mentioned above were mixed in the specified preparation ratios in a planetary mixer, then dispersed in a three-roll mill and made into a paste to prepare a resistor paste.

Next, the following tests were performed on the resistor pastes of the examples and comparative examples.

(Sheet resistance at 25° C.)
The sheet resistance (unit: mΩ/□) at 25° C. (room temperature) was measured by producing resistors using the resistor pastes of the examples and comparative examples and measuring the sheet resistance of the resistors.

First, the resistor paste of the examples and comparative examples was printed on the surface of an alumina substrate using a screen printing method to form a rectangular test pattern 71 mm long and 1 mm wide, with a film thickness of 10 μm.

The substrate with the resistor paste test pattern printed on its surface as described above was dried at 150°C for 10 minutes. The substrate with the test pattern was then fired in a belt furnace in an air atmosphere at a maximum temperature of 850°C for 10 minutes with an in-out time of 60 minutes, to produce resistors in the shape of the test patterns of the examples and comparative examples.

Next, the samples were left to stand for 30 minutes in a constant temperature and humidity atmosphere at a temperature of 25°C and a relative humidity of 65%, and then the sheet resistance (Ra) (mΩ/□) of the resistors in the examples and comparative examples at room temperature (Ta = 25°C) was measured using a tester with a four-terminal method.

The sheet resistance of the manufactured resistor at 25°C (room temperature) must be in the range of 50 to 500 mΩ/□. If the sheet resistance of the manufactured thin film at 25°C (room temperature) is 50 mΩ/□ or less, or 500 mΩ/□ or more, it is considered difficult to use it as a resistor.

The sheet resistance of the examples and comparative examples obtained as described above is shown in the "Sheet resistance at 25°C (mΩ/□)" column in Tables 1 and 2.

(Temperature Coefficient of Resistance)
The temperature coefficient of resistance (TCR) was measured as follows.

As described above, the sheet resistance (Ra) of the resistors of the examples and comparative examples at room temperature (Ta = 25°C) was measured, and then the resistors were heated to a temperature Tb = 125°C, and the sheet resistance (Rb) was measured at a temperature of 125°C (Tb). From the temperatures Ta and Tb, and the measured sheet resistances Ra and Rb, the temperature coefficient of resistance (TCR) was calculated using the following formula.
TCR (ppm/°C) = [(Rb-Ra)/Ra]/(Tb-Ta) x ¹⁰⁶

The temperature coefficient of resistance (TCR) of the resistor must be 1000 ppm or less, and preferably 800 ppm or less. If the TCR exceeds 1000 ppm, it is considered difficult to use it as a reliable resistor.

The temperature coefficient of resistance (TCR) of the examples and comparative examples obtained as described above are shown in the "Temperature coefficient of resistance (TCR) (ppm/°C)" column of Tables 1 and 2.

(Evaluation of Printability)
The printability of the resistor pastes of the Examples and Comparative Examples was evaluated by printing a test pattern similar to that described above in "Sheet resistance at 25°C" and evaluating the image of the test pattern photographed using a confocal microscope.

That is, first, the resistor pastes of the examples and comparative examples were printed on the surface of an alumina substrate by screen printing to form a rectangular test pattern with a length of 1 mm and a width of 71 mm to a film thickness of 10 μm. Next, the test pattern was photographed using a confocal microscope. The printability was evaluated based on the photographed image and judged as follows. Table 1 shows the results of the printability evaluation.
○: No unevenness on the surface, no bleeding. △: Some unevenness on the surface, some bleeding. ×: Some unevenness on the surface, some bleeding.

(Reliability assessment)
The reliability was measured as follows. First, resistors of the examples and comparative examples were manufactured in the same manner as described above in "Sheet resistance at 25°C". Next, the sheet resistance (R ₀ ) at 25°C was measured before the test. Next, the sample was heated and held at 600°C for one hour, and then cooled to room temperature. This heating, holding at 600°C, and cooling constitute one cycle, and 10 cycles of heat treatment were performed. After the 10 cycles of heat treatment, the sheet resistance (R ₁ ) was measured at room temperature (25°C). The reliability was evaluated by judging whether the rate of change ((R _{1 -R 0} )/R ₀ ) of the sheet resistance after the test relative to the sheet resistance before the test (R 0 ) was within a predetermined range. Table 1 shows the results of the reliability judgment. The symbols in Table 1 indicate the ranges of the rate of change of the sheet resistance as follows.
○: The rate of change in sheet resistance is within 5%. △: The rate of change in sheet resistance is 5-10%.
×: The rate of change in sheet resistance is 10% or more

(Evaluation Results)
From the results shown in Tables 1 and 2, it is clear that Examples 1 to 13 of the present invention satisfy the requirements for a resistor in all evaluation items including sheet resistance at 25° C., temperature coefficient of resistance, printability, and reliability.

On the other hand, from the results shown in Table 2, the sheet resistance of Comparative Example 3 at 25°C is 50 mΩ or less, making it difficult to use as a resistor. The sheet resistance of Comparative Example 5 at 25°C was too high to measure. The temperature coefficient of resistance (TCR) of Comparative Examples 1, 3, and 4 exceeds 1000 ppm, making it difficult to use as a reliable resistor. In addition, the image of Comparative Example 2 obtained by the evaluation of the printability of Comparative Example 2 with a confocal microscope showed surface irregularities and bleeding. Therefore, it is clear that it is difficult to print a pattern of the desired shape when the resistor paste of Comparative Example 2 is used.

Reference Signs List 1 Substrate 2 Resistor 3 Electrode 4 Lead wire 10 Heating element

Claims (7)

(A) a metal powder containing silver and tin and substantially free of rhodium and palladium;
(B) a rhodium component; and
(C) a glass frit,
(A) When the total weight of the silver and tin in the metal powder is 100% by weight, the weight ratio of silver in the metal powder is 75% by weight or more;
A resistor paste comprising: (B) a rhodium component having a rhodium content of 0.1 to 10 parts by weight per 100 parts by weight of (A) metal powder;
(B) the rhodium component is a rhodium resinate;
The resistor paste contains 0 to 5 parts by weight of (D) palladium per 100 parts by weight of (A) metal powder,
The content of the glass frit (C) relative to 100 parts by weight of the metal powder (A) is 0.1 to 30 parts by weight,
A resistor paste, the components of which are not burned away when the resistor paste is fired at a firing temperature of 500 to 900°C, are comprised of (A) metal powder, (B) rhodium in the rhodium component, and (C) glass frit, or comprised of (A) metal powder, (B) rhodium in the rhodium component, (C) glass frit, and (D) palladium . The resistor paste according to claim 1, wherein the metal powder (A) is an alloy powder of silver and tin. The resistor paste according to claim 1 or 2, further comprising (D) palladium. The resistor paste according to any one of claims 1 to 3 , wherein the glass frit (C) has a softening point of 700°C to 850°C. The resistor paste according to any one of claims 1 to 4 , which is a resistor paste for a heating element. A fired body obtained by firing the resistor paste according to any one of claims 1 to 5 . An electrical product using the fired body according to claim 6 .

Images