JPH0371740B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Application Field The present invention relates to the preparation of nickel slurry for sintered battery substrates, and its purpose is to improve the adhesion between the slurry and a porous core material and to ensure the porosity of the sintered substrate. It is in. Conventional technology Conventionally, this type of sintered substrate is made by passing a porous metal core material such as a perforated nickel plate through a slurry of a mixture of carbonyl nickel powder and an aqueous solution of an organic binder such as methyl cellulose or carboxymethyl cellulose. After applying the slurry to both sides of the substrate, the applied slurry is slitted to a desired thickness using a slitter, and then dried and then sintered in an atmosphere of a reducing gas such as hydrogen. Problems to be Solved by the Invention In this case, when methyl cellulose is used as an organic binder in the nickel slurry used for coating, if the amount of binder is large compared to the carbonyl nickel powder, the slurry will become porous core material at the stage of drying. It had the disadvantage that the dried slurry layer peeled off. In addition, when carboxymethylcellulose is used as an organic binder, the above-mentioned peeling is small, but it does not have the so-called thermal gelation effect that rapidly increases viscosity and turns into a gel at a certain temperature, and the slurry does not peel off at the stage of drying. There were problems in that the shrinkage of the slurry was uneven or the degree of shrinkage was large, making it unusable when trying to secure a porosity of 80% or more in a sintered substrate. Means for Solving the Problems The present invention aims to eliminate the above-mentioned drawbacks, and its gist lies in the use of a mixture of methylcellulose and hydroxypropylmethylcellulose as the organic binder of the nickel slurry. Effect: Improves adhesion between slurry and porous core material. Example First, slurries with various amounts of water and methylcellulose were prepared using carbonyl nickel, water, and methylcellulose, and the presence or absence of peeling between the dried slurry layer and the porous core material (perforated nickel board) during the drying stage was determined. I looked into it. The results are shown in the drawings, and it was found that the higher the concentration of the methylcellulose aqueous solution, the more it peeled off, and the lower the concentration, the less it peeled off.
However, in areas where no peeling occurs, the viscosity of the slurry is low and the formability of the dried substrate is poor.In other words, the thickness of the dried substrate becomes extremely uneven due to slurry dripping during drying. It cannot be lowered unnecessarily. From these facts, it is considered that the presence or absence of peeling is closely related to the properties of methylcellulose itself. As mentioned above, methylcellulose has a thermal gelation effect, and the slurry rarely shrinks due to evaporation of water during drying, which is a desirable property for ensuring the porosity of the sintered substrate. Considering the adhesion between the core material and the gelling slurry, it is considered that physical force acts on the interface between the core material and the gelling slurry, which is not preferable. Particularly in areas where the methylcellulose concentration is high, the thermally gelled slurry becomes quite hard, which may promote peeling.
Therefore, there is a problem that thermal gelation occurs all at once at a specific temperature, and we thought that it would be better to cause thermal gelation to occur gradually over a certain temperature range. As a result of various studies based on this idea, it was discovered that peeling can be eliminated by using a mixture of materials with different thermal gelation temperatures. Methyl cellulose (commercially available products are SM type from Shin-Etsu Chemical Co., Ltd. and M type from Matsumoto Yushi Pharmaceutical Co., Ltd.)
has a thermal gelation temperature of approximately 52°C, but hydroxypropyl methylcellulose, which is obtained by replacing the methoxy group of methylcellulose with a hydroxypropoxy group (commercially available products include SH type from Shin-Etsu Chemical Co., Ltd. and MP from Matsumoto Yushi Pharmaceutical Co., Ltd.) type) has a thermal gelation temperature of about 60°C to 85°C. Therefore, it is preferable to use a mixture of methylcellulose and hydroxypropylmethylcellulose as the organic binder. Table 1 shows the presence or absence of peeling of the dried substrate at various mixing ratios. In addition,
Anything that peels off on a dry substrate also peels off on a sintered substrate, so the judgments made on dry substrates also apply to sintered substrates. In addition, there are two methods for producing slurry: the general method of adding and mixing carbonyl nickel powder to an aqueous organic binder solution, and the stable slurry production method of mixing organic binder powder and carbonyl nickel powder, then adding water and mixing. However, in Table 1, the latter method was adopted. After a predetermined amount of organic binder and carbonyl nickel were mixed for 10 minutes, a predetermined amount of water was added and mixed for 30 minutes. After applying slurry to perforated nickel board 120
It was dried at ℃ for about 1 hour to obtain a dry substrate. As can be seen from Table 1, the mixture of methyl cellulose and hydroxypropyl methyl cellulose reduces peeling, and the best part is that when the ratio of hydroxypropyl methyl cellulose in the organic binder is about 50% or more, peeling does not occur, and clearly The effect is recognized. Further, the porosity of the substrates of Experiments No. 1 to 5 was 83 to 84%, which is considerably higher than the porosity that can be achieved with carboxymethyl cellulose. Note that methylcellulose and hydroxypropylmethylcellulose are available in various viscosities, but it is possible to combine them depending on the desired slurry viscosity or to use several types of hydroxypropylmethylcellulose with different thermal gelation temperatures. There is no problem.

[Table] Effects of the Invention As described above, the present invention improves the adhesion between the porous core material and the dried nickel slurry layer, improves the yield of the sintered substrate, and improves the current collecting ability of the sintered substrate itself. It has great industrial value, such as for smoothing.

[Brief explanation of drawings]

The figure is a correlation diagram showing the relationship between slurry composition and peeling in the drying stage.

Claims (1)

[Claims] 1 Nickel slurry for battery sintered substrates, which is made by mixing an organic binder made of a mixture of methyl cellulose and hydroxypropyl methyl cellulose, water, and carbonyl nickel powder.