JPS6329579B2 - - Google Patents

Description

[Detailed description of the invention]

Sintered bodies such as ceramics, cermets, and cemented carbide need to have as few internal pinholes as possible and be as fine as possible, which greatly affect their properties. It is necessary to increase the roundness of the granules made of the inorganic raw material powder (hereinafter simply referred to as raw material powder) and thereby increase the packing density. Granulation by spray drying is generally used to produce granules with the above-mentioned high roundness, but when turning the raw material powder into a slurry for spray drying, the raw material powder is combined with water. It is necessary to add a water-soluble or uniformly dispersible polymeric material (hereinafter simply referred to as a polymeric binder) that is granulated with water, and this polymeric binder is sprayed into the high-temperature drying chamber during the spray drying process. It covers the periphery of the slurry droplets, preventing the passage of water vapor inside them, increasing the internal pressure, causing abnormal expansion of the slurry droplets, or destroying them before they become granules, resulting in dissatisfaction in terms of yield. . The abnormal swelling and destruction of the granules mentioned above can be somewhat improved by reducing the drying rate of the slurry droplets, but no substantial solution could be expected. In the present invention, when adding an emulsion-type polymeric binder that is water-soluble or uniformly dispersible with water to raw material powder to form a slurry, it is compatible with water,
In addition, by adding a solvent that is difficult to dissolve in the polymeric binder, the above-mentioned dissatisfaction is resolved, and the yield of granules with uniform particle size and high roundness is improved,
By densifying the sintered body, we succeeded in significantly improving the mechanical properties represented by transverse rupture strength as well as other properties. In the present invention, the reason for adding a solvent that is compatible with water and difficult to dissolve in the polymeric binder when turning the raw material powder into a slurry is that the raw material powder sprayed from the nozzle in the spray drying process, In the process in which slurry droplets consisting of a molecular binder, water, and solvent are dried by the surrounding hot air, vapor that is higher in moisture than the liquid phase of water and the solvent is first evaporated, and as the temperature rises, the solvent in the liquid phase is evaporated. This method aims to suppress the harmful increase in internal pressure when the slurry droplets dry by increasing the concentration and rapidly lowering the solubility of the polymer binder in the slurry droplets, causing them to precipitate inward. This will be explained using a curve. The drawing shows the case where 3-methyl-3-methoxybutanol is dissolved in water as a solvent. For example, when water is 70% by weight and solvent is 30% by weight, the boiling point at point P is approximately 101°C.
At that time, the water in the steam is about 92% of the point P′
As a result, the solvent component evaporates from the slurry droplets, but only a small amount of about 8% of the solvent component evaporates at the same time. Subsequently, as the temperature of the slurry droplet rises above the liquidus line, the amount of solvent components evaporated increases, but even if the temperature rises to 120°C, the water content in the vapor is approximately 77%, as shown by the P'' point. The solvent component remains at about 23%, and it easily evaporates from the slurry droplets, increasing the concentration of the solvent inside.The polymeric binder present together precipitates inward, enveloping the raw material powder, and completing drying. Examples Alumina (Showa Light Metal A-13) 960g Silicic anhydride (Hayashi Junyaku 1st grade) 18g Calcium carbonate (Katayama Chemical 1st grade) 36g Magnesium oxide (Yoneyama Pharmaceutical 1st grade) 20g as raw material powder, and plasticizer polyethylene Oxide (Steel Chemical PEO-1) 5g, anti-settling agent methylcellulose (Dow Chemical A-4M) 2g,
Additionally, 10 g of polymer binder polyvinyl alcohol (Denka B-05), 630 c.c. of water, and 70 c.c. of 3-methyl-3-methoxybutanol (Kuraray, Solfit) were added, and the mixture was heated in a ball mill with an internal volume of 3. The slurry was then mixed and crushed for 18 hours to form a slurry.The slurry was then mixed at a gas temperature of 180℃ and a disc diameter of 120mm.
φ, 4800 R.PM, 10 c.c. per second. Table 1 shows the results of comparison with granules of a comparative product made by a conventional method.

[Table] However, the yield is within the target of 60 to 325 in all dry powder.
The content within the mesh range is expressed in weight %, and the packing density was determined by naturally filling a stainless steel container with an inner diameter of 50 mm and a depth of 51 mm, and measuring the filling weight. The above table reveals that the granules obtained by the present invention exhibit higher values in both yield and packing density than conventional products. Next, using the above two types of granules, a square plate element of 12 x 60 mm and 6 mm thick was produced by pressing, and this was fired in an oxidizing atmosphere of an electric furnace at 1560°C for 1 hour. Table 2 shows the results of comparing the obtained sintered bodies.

[Table] From Table 2, the products of the present invention are molded at molding pressures of 500, 1000,
In both cases of 1500Kg/ ^cm2 , both the element body and the sintered product showed clearly higher density than the comparative product, and the transverse rupture strength was significantly higher than the comparative product, demonstrating the excellent effects of the present invention. I was able to confirm that. As explained in the drawings, the above-mentioned effects of the present invention are obtained by significantly increasing the water content of the vapor that evaporates during drying of the slurry particles compared to the solvent component. An aqueous solution of a solvent exhibiting a vapor-liquid equilibrium curve that increases the concentration of water is preferable, and a solvent with a high boiling point is also preferable.For these reasons, in addition to 3-methyl-3-methoxybutanol shown in the example, ethylene glycol was used. Although n-butanol, acetic acid and the like can produce similar effects and be satisfactory, the former 3-methyl-3-methoxybutanol and ethylene glycol are preferred from the viewpoint of toxicity and bad odor. However, the mixing ratio of these solvents and water is within the range of 30 to 90% by weight of water and 70 to 10% by weight of solvent, and when the solvent is less than the lower limit of 10% by weight, the organic binder becomes a slurry. 70% of the upper limit seeps around the outer periphery of the drop
If the amount exceeds 100%, the water content in the slurry will naturally decrease and the solubility of the polymeric binder will decrease, making it impossible to completely dissolve the required amount of polymeric binder.To compensate for this, increase the amount of water. It is necessary to limit the concentration within the above range because the concentration of the slurry becomes thinner, making spray drying difficult.

[Brief explanation of the drawing]

The drawing is a vapor-liquid equilibrium curve diagram of an aqueous solution of a solvent to explain the present invention.

Claims (1)

[Scope of Claims] 1. When granulating an inorganic raw material powder made into a slurry using a water-soluble or water-uniformly dispersible polymeric material as a particle binder by spray drying, A method for granulating an inorganic raw material powder, characterized in that a solvent in which the polymeric material is difficult to dissolve is added to water to turn the inorganic raw material powder and the polymer binding material into a slurry. 2. The solvent that is compatible with water and difficult to dissolve the polymeric material according to claim 1 is 3-methyl-3-methoxybutanol, ethylene glycol, n
- A method for granulating inorganic powder, characterized in that the solvent is butanol or acetic acid, and the mixing ratio of the solvent and water is 30 to 90% water and 70 to 10% solvent.