JP4571009B2 - Platinum paste - Google Patents

Description

  The present invention relates to an improvement of platinum paste.

Since platinum is excellent in heat resistance and corrosion resistance, it is used as a conductor component in various applications such as a resistance heating element layer of a ceramic heater, a conductor layer for circuit formation of an electronic component, and via hole filling of a laminated substrate. (For example, refer to Patent Documents 1 to 3). For example, when manufacturing a planar ceramic heater, a platinum paste is applied in a predetermined planar shape on one surface of a substrate made of alumina (Al ₂ O ₃ ) or the like or a green sheet for producing the substrate, and subjected to a firing treatment. To form a resistance heating element layer.

  The platinum paste as described above is prepared, for example, by mixing platinum powder with a solvent together with an organic binder such as ethyl cellulose. At this time, for example, a ceramic material powder or glass powder constituting the substrate to be coated is appropriately added for the purpose of increasing the adhesive force.

  By the way, when forming a conductor or a resistance heating element layer (hereinafter, collectively referred to as “conductor” in this application) from platinum paste, it is fired at a high temperature of, for example, 1500 (° C.) or higher in accordance with the firing temperature of the green sheet. Processing may be performed. When fired at such a high temperature, the conventional platinum paste has problems such as aggregation or evaporation of platinum, and further defects in the conductor or separation from the ceramic substrate or the like.

  On the other hand, the applicant of the present application has proposed a platinum paste in which a platinum powder having a crystallite size in the range of 35 to 60 (nm) is dispersed in a vehicle (see Patent Document 4). According to this platinum paste, since the crystallite size is large, the sinterability is suppressed, so that there is an advantage that aggregation and evaporation of platinum hardly occur even when fired at a high temperature. In the conventional platinum paste, although the particle size of the powder was determined so as to obtain a paste property suitable for printing, the crystallite size was not considered at all, and as a result, the crystallite size was 10 (nm) A platinum powder of high degree and fine sinterability was used. Therefore, problems such as aggregation and evaporation occur when the firing temperature is increased.

The crystallite means a unit that can be regarded as a single crystal in the polycrystalline particle, and the crystallite size t (nm) is, for example, the half width of the intensity peak of a diffraction curve obtained by powder X-ray diffraction. From the following Scherrer equation. Metal powder such as platinum powder is generally polycrystalline and is composed of a large number of fine single crystals.
t = 0.9λ / (Bcosθ _B )
[Where λ is the wavelength of the Kα ray of the tube used (nm), B is the half-width of the strongest peak (radian), θ _B is the diffraction angle of the strongest peak (radian)]
JP 2004-178842 A JP 2004-265607 A JP-A-5-334911 JP-A-7-094012

  However, even when a conductor is formed using the platinum paste described in Patent Document 4, film quality and conductivity change that cannot be ignored when used under conditions of repeated high temperature exposure, that is, high temperature durability Was found to be inadequate. For example, in a heater application, since it is exposed to a high temperature due to its own heat generation during use, the characteristics change during use. It has also been clarified that changes in film quality and conductivity occur when a baking treatment is performed for the purpose of forming another film after the conductor is formed. In the above-mentioned Patent Document 4, only the film quality immediately after the formation is evaluated, and no change is considered when exposed to a high temperature after the formation.

  As a result of repeated research to increase the high temperature durability of the conductor formed from the platinum paste, the present inventors have found that the crystallite size of the platinum powder greatly affects not only the film quality during conductor formation but also the high temperature durability. I found out. In Patent Document 4, the upper limit is set to 60 (nm) due to processing limitations for increasing the crystallite size, but in order to obtain sufficient high-temperature durability, a crystallite size larger than that is required. It has been found that it is necessary to use platinum powder.

  The present invention has been made on the basis of the above knowledge, and an object thereof is to provide a platinum paste capable of forming a conductor that hardly changes in film quality and conductivity due to heating.

In order to achieve such an object, the gist of the platinum paste of the present invention is that the crystallite size is within the range of 70 to 100 (nm) and the average within the range of 0.1 to 10 (μm). A platinum powder having a particle size is dispersed in a predetermined vehicle and used to form a resistance heating element of a ceramic heater .

In this case, since the crystallite size of the platinum powder is sufficiently large to be 70 (nm) or more, the sinterability of the platinum particles is sufficiently suppressed, so even if it is exposed to high temperatures. Aggregation hardly occurs. Further, since the crystallite size is kept at 100 (nm) or less, the conductor has sufficient sinterability to ensure that the conductor is firmly fixed to the formation surface, so that sufficient conductivity can be obtained. Therefore, it is possible to form a conductor that hardly changes in film quality or conductivity due to heating. In addition, since the platinum powder has an average particle size in the range of 0.1 to 10 (μm), a platinum paste having appropriate sinterability and heat resistance can be obtained. Since the sinterability of the platinum powder is affected not only by the crystallite size but also by the average particle diameter, a platinum paste having appropriate sinterability and heat resistance can be obtained. If it is less than 0.1 (μm), the sinterability becomes high and it is necessary to lower the firing temperature. If it exceeds 10 (μm), the sinterability becomes low, so the sinterability is insufficient and sufficient conductivity is obtained. It becomes difficult to form a film having the same. Further, since the platinum paste is used for forming a resistance heating element of a ceramic heater, a resistance heating layer in which film quality change, change in conductivity or resistance value hardly occurs can be obtained.

  In order to increase the crystallite size, it is necessary to subject the platinum powder to heat treatment and grow crystals inside the particles, but the heat treatment temperature increases as the crystallite size to be obtained increases. Therefore, at a heat treatment temperature at which a crystal size exceeding 100 (nm) is obtained, the heat resistance becomes too high and the sintering becomes insufficient. Further, at such a heat treatment temperature, the particles melt, the shape is unstable, and the dispersion of the particle size becomes large, resulting in poor dispersion. As a result, since a dense sintered body cannot be obtained, there is a problem that sufficient conductivity cannot be obtained.

  Preferably, the crystallite size is in the range of 70 to 90 (nm).

  Moreover, as long as the platinum powder which comprises the said platinum paste satisfies the above characteristics, what was manufactured by arbitrary various methods can be used, For example, platinum powder and 3rd group thru | or 15 of a long periodic table A mixing step of mixing a mixture composed of at least one powder of an oxide of a metal element of any of the group, a heat treatment step of subjecting the mixed powder obtained in the mixing step to a heat treatment at a predetermined temperature, and the heat treatment A dissolving step of dissolving the mixed agent by treating the applied mixed powder with an acid or an alkali, and a removing step of removing the mixed agent by subjecting the mixed powder in which the mixed agent is dissolved to a washing treatment , Manufactured by a process including.

Examples of the Group 3 to Group 15 metal element include Zn, Sn, Y, Nd, Sc, Sm, W, Mn, and Nb. As the acid or alkali used in the dissolution step, an appropriate one is used according to the kind of the mixing agent. For example, amphoteric oxides such as ZnO and SnO are hydrochloric acid, nitric acid, sulfuric acid, aqueous ammonia, sodium hydroxide, and the like. Either acid or alkali may be used. For rare earth oxides such as Y ₂ O ₃ , Nd ₂ O ₃ , Sc ₂ O ₃ and Sm ₂ O ₃ , acids such as hydrochloric acid, nitric acid and sulfuric acid are used. For WO ₃ , an alkali such as sodium hydroxide is used. Nb ₂ O ₅ is alkali such as ammonia water or sodium hydroxide. The predetermined temperature is, for example, a temperature within a range of 700 to 1500 (° C.), preferably within a range of 1000 to 1500 (° C.), and more preferably within a range of 1300 to 1400 (° C.). .

  Preferably, the platinum paste is produced by dispersing platinum powder having a predetermined crystallite size produced by the method as described above in a vehicle. For example, a three-roll mill is preferably used for the dispersion treatment. The vehicle is produced by, for example, dissolving an organic binder such as ethyl cellulose or acrylic resin in a solvent such as terpineol, butyl carbitol acetate, or butyl carbitol. In addition to the platinum powder, various subcomponents (for example, ceramic powder and glass powder) such as an inorganic binder, glass frit, and filler may be added. The amount of addition is, for example, in the range of about 1 to 10 (wt%) with respect to platinum powder 100 (wt%). If the amount of ceramic powder added is less than this, the difference in coefficient of thermal expansion when applied to a green sheet cannot be sufficiently mitigated. Sex cannot be obtained. The addition amount is more preferably in the range of 3 to 5 (wt%). The ceramic powder is preferably a constituent material of a ceramic material to which a platinum paste is applied or a main constituent component thereof.

  Further, the amount of platinum powder contained in the platinum paste is appropriately determined according to the application, for example, in the range of 30-95 (wt%), more preferably 35-85 (wt%) ), And more preferably within the range of 45 to 85 (wt%). These lower limit values are determined, for example, so as to obtain the required conductivity, and the upper limit values are determined so as to have a fluidity capable of obtaining appropriate printability and applicability.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the following embodiments, the drawings are appropriately simplified or modified, and the dimensional ratios, shapes, and the like of the respective parts are not necessarily drawn accurately.

FIG. 1 is a process diagram for explaining a method of manufacturing a platinum paste according to an embodiment of the present invention and a method of forming a resistance heating element layer of a heater using the same. In FIG. 1, steps R1 to R7 show a manufacturing process of platinum powder, and steps P1 to P4 show a manufacturing process of a platinum paste and a resistance heating element. In the mixing step R1 of the platinum powder manufacturing process, for example, a platinum powder manufactured by a wet reduction method and an oxide powder of a group 3-15 metal element as a mixture are mixed. The platinum powder used here is not particularly limited. For example, the platinum powder has an average particle size of about 0.2 to 0.8 (μm), but the crystallite size is about 10 (nm), for example. Further, as the mixing agent, for example, may use a powder consisting of _{Y 2 O 3, Nd 2 O} 3, one or a mixture of such ZnO. The average particle diameter of these mixed powders is, for example, in the range of about 0.1 to 10 (μm). The mixing ratio is, for example, 15 to 60 parts by volume of the mixture powder with respect to 1 part by volume of platinum powder, for example, 30 parts by volume.

  Moreover, although the said mixing process R1 can be implemented using a suitable mixer or a stirrer etc., a pot mill type wet mixing, a three roll mill, etc. are suitable, for example. Water or an appropriate solvent can be used as a dispersion medium in the case of wet mixing, and it is preferable to use, for example, zirconia beads as a medium for promoting mixing. Moreover, when mixing with a three roll mill, an organic vehicle is added to the mixed powder of platinum powder and a mixing agent.

  Next, in the drying and loosening step R2, in the case of wet mixing, for example, a drying treatment of about 110 (° C.) × 12 hours is performed, and further, the solid matter after drying is loosened. In addition, this process is unnecessary when it mixes with a three roll mill.

  Next, in the heat treatment step R3, for example, heat treatment is performed within a range of 700 to 1500 (° C.) at a predetermined temperature corresponding to a desired platinum crystallite size, for example, for about one hour. Thereby, the platinum powder particles are crystal-grown, and the crystallite size is increased to, for example, about 30 to 100 (nm), for example, about 80 (nm). The heat treatment temperature is more preferably in the range of 1000 to 1500 (° C.), and more preferably in the range of 1300 to 1400 (° C.).

Next, in the dissolving step R4, the heat-treated mixed powder is processed using an acid or alkali that dissolves the mixed admixture. For example, when Y ₂ O ₃ , Nd ₂ O ₃ , ZnO or the like as described above is used, 3-fold diluted HNO ₃ is used, and about 50 to 80 (° C.) so that dissolution is promoted. And stir for about 12 hours.

  Next, in the water washing step R5, the mixed powder that has undergone the dissolution step R4 is washed with pure water. As a result, the dissolved mixture and the acid used for the dissolution are removed. However, if it cannot be sufficiently removed by a single treatment, the dissolution step P5 and the washing step P6 are performed a plurality of times, for example, 4 Repeat ~ 5 times. However, if the residue does not adversely affect the properties of the platinum powder, it may be dissolved and washed about once or twice.

  Next, in the drying step R6, the platinum powder that has been washed, that is, removed of the mixture, is subjected to a drying process at, for example, 100 (° C.) for about 12 hours. In the sieving step R7, a platinum powder having high dispersibility and high crystallinity is obtained by loosening the agglomerated platinum powder using a sieve having an appropriate opening. Since the obtained platinum powder has a high specific gravity and no adsorbed gas, no distortion occurs during film formation, and a dense fired film (that is, a resistance heating element layer) is obtained. Further, since the particles do not neck each other and are highly dispersible, a denser fired film can be obtained. In addition, since necking does not occur because the above-mentioned mixture is mixed, heat treatment can be performed at a high temperature. Therefore, the crystallite size can be made sufficiently large, that is, a highly crystalline powder can be obtained. In addition, since no alkali metal or alkaline earth metal is used as described in the steps R1 to R7, no migration occurs when using a ceramic substrate on which a resistance heating element layer is formed. There is an advantage that an electronic component can be obtained.

  Next, the manufacturing process of the paste and the resistance heating element layer will be described. First, in the mixing step P1, the above platinum powder, ceramic powder, and vehicle are mixed. This ceramic powder is a powder made of the same kind of material as the ceramic to which the platinum paste is applied, such as alumina, and has an average particle diameter of about 0.2 to 1.0 (μm), for example. The vehicle is composed of an organic binder such as ethyl cellulose and acrylic and an organic solvent such as terpineol. The ratio of the organic binder and the organic solvent is, for example, about 10 to 30:90 to 70. The ratio of platinum powder: ceramic powder: vehicle is, for example, about 60 to 90: 3 to 10: 7 to 37.

  Next, in the dispersion step P2, the platinum powder and the ceramic powder are dispersed in the vehicle by treating the mixture with, for example, a three-roll mill. Thereby, a platinum paste containing platinum powder having a crystallite size of 80 (nm) is obtained. That is, process R1 thru | or process P2 is an example of the manufacturing process for obtaining the platinum paste of a present Example.

  Next, in the printing process P3, for example, the above-described platinum paste is applied in a predetermined pattern to, for example, an alumina substrate using a screen printing method. The printed shape is as shown in FIG. 2, for example. The coating thickness is determined such that the dry thickness is about 10 (μm), for example.

  Next, after performing the drying process, in the firing step P4, for example, the firing process is performed by holding at 1500 (° C.) for about one hour. As a result, the organic component in the paste is burned away, and a resistance heating element layer mainly composed of platinum is formed. The film thickness after firing is, for example, about 5 (μm).

  The resistance heating element layer thus obtained has a high heat resistance because it is formed of platinum powder having a crystal size of 80 (nm) as extremely large as described above. In other words, even when the resistance heating element layer is formed and subjected to baking treatment for the purpose of forming another film or repeatedly used and exposed to a high temperature, the resistance value change rate is remarkably small, and the change remains negligible. .

  FIG. 3 shows a resistance heating element layer formed using platinum powders of various crystallite sizes manufactured according to the steps R1 to R7, and the durability is evaluated by measuring the resistance value change rate when the heat treatment is repeated. The results are summarized. In this evaluation test, repeated heating during production and changes during high temperature use are evaluated by an acceleration test. The heat treatment condition of each time is 1500 (° C.) × 1 hour, the resistance value between both ends of the resistance heating element layer is measured every time, and the ratio to the resistance value immediately after formation is expressed in percentage, and the resistance value change rate It was. The production conditions for each sample were all the same, including the average particle diameter of the platinum powder, the film thickness after firing, etc., except that platinum powder having a different crystallite size was used.

In addition, the difference in the manufacturing conditions of platinum powder of each crystallite size is as follows. All other conditions not described were the same as described above.
10 (nm): 0.8 (μm) particles produced by wet reduction method
30 (nm): Heat treatment of 0.8 (μm) particles for 300 (° C) x 10 minutes
50 (nm): Heat treatment of 0.8 (μm) particles for 500 (° C) x 10 minutes
60 (nm): Heat treatment of 0.8 (μm) particles for 600 (° C) x 10 minutes
80 (nm): 0.2 (μm) particles mixed with a mixture and heat treated for 1300 (° C) x 1 hour
100 (nm): Heat treatment of 1500 (° C) x 10 hours by mixing a mixture with 0.2 (μm) particles

  As shown in the above evaluation results, when the crystallite size is 10 (nm), the resistance value is clearly changed by only two heat treatments, and the resistance value is remarkably increased by four times or more. , It exceeded 60 (%) after 7 heat treatments and was disconnected at 13th time. In the case of 30 (nm), the resistance value increased remarkably after 4 heat treatments, and as much as 40 (%) was observed after 9 heat treatments. Further, in the case of 50 (nm), the resistance value suddenly increased after 12 to 15 heat treatments and was disconnected after 19 heat treatments. Therefore, it is clear that when the crystallite size is in the range of 10 (nm) to 50 (nm), the resistance value change due to repeated heat treatment is large and is not suitable for such manufacturing conditions and applications. That is, it can be seen that it is not suitable as a platinum paste for forming a resistance heating element layer such as a heater.

  On the other hand, when the crystallite size is 60 (nm) and 80 (nm), the increase in the resistance value is only about 20 (%) even if the heat treatment is performed 10 times, and about 20 times. It was confirmed to have high durability without being disconnected even by repeated heating.

  4 to 13 are photographs showing the appearance of the resistance heating element layer after the heat treatment of each sample. In these photographs, the white portion is an alumina substrate, and the black portion is a resistance heating element layer, which corresponds to the left end portion of the pattern shown in FIG.

  FIG. 4 and FIG. 5 show the appearance after repeating the heat treatment 10 times and 15 times using platinum powder having a crystallite size of 10 (nm), respectively. Many white spots in the resistance heating element layer exhibiting black are pinholes in which the alumina substrate is exposed by aggregation and evaporation (or volatilization) of platinum by heating, and conduction of the resistance heating element layer by repeated heating It can be seen that the sectional area in the direction is small. Further, in FIG. 5 in which the heat treatment is performed 15 times, as a result of further progress of aggregation and evaporation, a part of the pattern is cut off (that is, disconnection occurs). Note that the appearance is not particularly shown immediately after firing, that is, when the number of heat treatments is 0, but no pinholes are formed in the pattern.

  FIG. 6 and FIG. 7 show the appearance after repeating the heat treatment 10 times and 15 times, respectively, with a crystallite size of 30 (nm). It can be seen that even with a crystal size of 30 (nm), pinholes are prominently observed in the aggregation of platinum after repeated heat treatment, and the conduction cross-sectional area of the resistance heating element layer is significantly reduced. It can also be seen that as the number of heat treatments increases, the line shape becomes worse and the line width becomes thinner.

  8 and 9 show the appearance after the heat treatment is repeated 10 times and 15 times with a crystallite size of 50 (nm), respectively. It can be seen that even with a crystallite size of 50 nm, numerous pinholes are generated by repeated heat treatment. After 15 heat treatments, the width of the resistance heating element layer is reduced. These changes at 10 (nm), 30 (nm), and 50 (nm) correspond well with the resistance value changes shown in FIG.

  On the other hand, in FIGS. 10 and 11, the heat treatment is repeated 10 times and 15 times at 60 (nm), respectively. Although pinholes are observed, it can be seen that the amount of pinholes is clearly smaller than that of 50 nm or less.

  12 and 13 show the heat treatment repeated at 80 (nm) 10 times and 15 times, respectively. With this crystallite size, it is clear that the occurrence of pinholes is remarkably reduced even when compared with that of 60 (nm). As shown in these figures, the small occurrence of pinholes corresponds well with the small change in resistance value as shown in FIG. That is, it is clear that high temperature durability can be improved by using a platinum powder having a crystallite size of 60 (nm) or more.

  At 100 (nm), the density of the fired film becomes slightly worse due to insufficient sintering. Accordingly, although the conductivity is slightly lowered, the fired film becomes gradually dense by repeatedly performing the heat treatment. In FIG. 3, it can be seen that the electrical conductivity is slightly low in the first baking process because the change in the resistance value tends to decrease in the initial stage (that is, the resistance value becomes low).

  Further, when the particle size distribution of the platinum powder was measured with a laser diffraction particle size distribution measuring device (LA-500 manufactured by Horiba Ltd.), d90 was 2.71 (μm) when the crystallite size was 100 (nm), d50 was about 1.63 (μm) and d10 was about 0.85 (μm). When the crystallite size is 80 (nm), d90 is about 1.03 (μm), d50 is about 0.54 (μm), and d10 is about 0.29 (μm) when measured with the same apparatus. In the case of nm), the particle size is large and the distribution is wide. When preparing a paste with a powder having a large particle size and a wide distribution to this extent, the paste filling rate tends to decrease and the conductivity tends to be low, so the upper limit is about 100 (nm) for the crystallite size, It is desirable to keep below this.

  In short, the platinum paste of this example is sufficiently exposed to a high temperature because the crystallite size of the platinum powder is sufficiently large in the range of 60 to 100 (nm), so that the sinterability is suppressed. However, aggregation hardly occurs, and as a result, it is possible to form a resistance heating element layer in which film quality change, conductivity, or resistance value change due to heating hardly occurs.

  In addition, according to this example, platinum powder having an average particle diameter in the range of 0.1 to 10 (μm) is used, so that a platinum paste having appropriate sinterability and heat resistance can be obtained.

  As mentioned above, although this invention was demonstrated in detail with reference to drawings, this invention can be implemented also in another aspect, A various change can be added in the range which does not deviate from the main point.

It is process drawing for demonstrating the formation method of the resistance heating element layer using the platinum paste of one Example of this invention. It is a top view which shows an example of the resistor pattern of a ceramic heater. It is a figure which shows the relationship between the frequency | count of repeated heating for every crystallite size of platinum powder, and resistance value change rate. It is a figure which shows an example of the state after 10 times heating of the resistance heating element layer using the platinum powder whose crystallite size is 10 (nm). It is a figure which shows the state after 15 times heating of the resistance heating element layer of FIG. It is a figure which shows an example of the state after 10 times heating of the resistance heating element layer using the platinum powder whose crystallite size is 30 (nm). It is a figure which shows the state after 15 times repeated heating of the resistance heating element layer of FIG. It is a figure which shows an example of the state after 10 times repeated heating of the resistance heating element layer using the platinum powder whose crystallite size is 50 (nm). It is a figure which shows the state after 15 times repeated heating of the resistance heating element layer of FIG. It is a figure which shows an example of the state after 10 times heating of the resistance heating element layer using the platinum powder whose crystallite size is 60 (nm). It is a figure which shows the state after 15 times repeated heating of the resistance heating element layer of FIG. It is a figure which shows an example of the state after 10 times repeated heating of the resistance heating element layer using the platinum powder whose crystallite size is 80 (nm). It is a figure which shows the state after the 15 times repeated heating of the resistance heating element layer of FIG.

Explanation of symbols

10: Resistance heating element layer

Claims (1)

Platinum powder having a crystallite size in the range of 70 to 100 (nm) and an average particle size in the range of 0.1 to 10 (μm) is dispersed in a predetermined vehicle, and the resistance heating of the ceramic heater A platinum paste used to form a body .