JPH09255435A - Forming of sintered precursor of powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To product a complex formed body having thick wall by mixing a polymer coagulating agent to a slip consisting of dispersed powder, pouring the mixture into a mold and allowing to coagulate and cure the mixture. SOLUTION: A slip (high density dispersion) is prepared by mixing and dispersing 100wt.% of ceramic powder such as alumina powder, about 12-50wt.% of a dispersing medium such as water and optionally 0.05-2wt.% of a dispersing agent such as an acrylic acid monomer in a ball mill, etc. Subsequently, about 0.15wt.% of an acrylic amide polymer coagulating agent such as a polyacrylic amide is mixed to the obtained slip under stirring, the resultant mixture is poured into a mold, it has been cured within about 5min after pouring, and the formed sintered precursor is taken out from the mold. Subsequently, the sintering precursor is allowed to stand for a time at a normal temperature to dry it, and then further heated at about 300-600 deg.C to degrease. The degreased precursor is burned at about 1300 deg.C in the air to obtain a dense sintered body.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for molding a sintering precursor of ceramics, metals or organic products, which is manufactured through a sintering process after molding a powder.

[0002]

2. Description of the Related Art Conventionally, various molding methods have been used for obtaining the shapes of ceramics, metals, intermetallic compounds, and organic products which are manufactured through a sintering process after molding a powder. For example, there are a dry pressing method, a wet pressing method, a rubber pressing method, an extrusion method, a casting method, a doctor blade method, an injection molding method and a hot pressing method. Of these molding methods, the cast molding method is to prepare a high-concentration suspension (slip) in which powder is dispersed in a dispersion medium such as water, and to prepare a water-absorbing mold (gypsum mold, resin mold). Cast,
This is a method in which the powder is deposited on the surface of the mold by the capillary force of the water-absorbent mold. The feature of this method is that a molded product having a complicated shape can be easily obtained by appropriately designing the shape of the mold. As an example of the molded body by the casting method, there are vases, dolls, plates, tiles, refractories, sanitary ware, bent pipes, turbo rotors, etc. in the ceramics industry. This molding method has the characteristic that complicated shapes can be easily manufactured, but on the other hand, the density of the molded body tends to decrease as the distance from the mold increases, and depending on the mold shape, porosity occurs like casting. To do. Further, there is a defect that it takes a long time to mold a thick product.

As one means for improving the drawbacks of the casting method, Japanese Examined Patent Publication No. 7-22931 discloses self-hardening by mixing a powder with a thermosetting resin, a curing agent for the resin and a vaporizable liquid. Then, a self-hardening cast molding method is described in which a dense molded body is obtained by subjecting the liquid to an air diffusion treatment, and a sintered body having excellent characteristics can be obtained by sintering this.

In the present invention, the particles uniformly dispersed in the liquid and the liquid are cured as they are. The curing mechanism is
It is a three-dimensional curing reaction of the thermosetting resin. By this action, a thick molded article having a complicated shape can be obtained. The thermosetting resin used here is indispensable to use a curing agent together as shown in Examples, and slip viscosity increases and gels as the curing reaction proceeds. Since the curable resin is thermosetting, the level of the slip temperature affects the curing time. That is, it is necessary to control the slip temperature. Further, the curing reaction requires 10 minutes or more, and in the case of powder composed of coarse particles, the coarse particles in the slip easily precipitate during the curing reaction, and uneven density distribution in the casting height direction easily occurs. There remains a problem that it takes time to remove the liquid component remaining in the gelled (cured) molded body. As described above, no molding method has yet been developed which can obtain a uniform shape in a short time in a complicated shape and a thick material.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to easily form a complex, thick-walled and uniform body in a short time. Another object of the present invention is to provide a method for forming a powdery sintering precursor capable of achieving the above.

[0006]

As a result of intensive studies on the above problems, the present invention has found the following new findings. That is, 1. Mix a polymer flocculant into the slip in which the powder is dispersed,
Pour this into a mold and let it cure. 2. It has been found that acrylamide type is preferable among the above polymer flocculants.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION When a slip in which powder is dispersed is prepared, and a polymer flocculant (for example, acrylamide) is mixed and cast into a mold having no water absorption, the fluidity of the slip is caused by the polymer flocculation action. Disappears and the entire cast slip undergoes a kind of hardening phenomenon. When the curing phenomenon occurs, the slip changes to a solidified state, and it becomes possible to easily remove the mold and handle the cured body (molded body).

The greatest feature of the present invention is this aggregation action. When a slip without adding a polymer flocculant was cast into a mold without water absorption, the powder particles in the slip settled on the lower surface of the mold according to the Stokes particle settling rate equation, and the supernatant liquid was on the upper part of the mold. Occurs, and it is impossible to obtain a handleable molded body. When a polymer coagulant is added to the slip, the particles and the dispersion medium are firmly trapped by the entanglement of the polymers that make up the polymer coagulant and the complex action such as adsorption on the particle surface or chemical bonding. It is thought that the whole system solidifies by that.

Any powder can be used as long as it is a material that undergoes a sintering process. As typical examples, in the ceramics field, oxide powders such as alumina, zirconia, mullite, alumina-zirconia, and mullite-zirconia, non-oxide powders such as silicon nitride, boron nitride, and aluminum nitride, and these Powders containing two or more kinds of mixed powders, tableware, porcelain, porcelain stones such as sanitary ware, feldspar, clays, silica stones, etc. In powder metallurgy, stainless powder, pure titanium powder, titanium alloy powder, etc. Examples of the metal powder include cemented carbide powder and cermet powder as the intermetallic compound, and fluorine resin powder as the organic material. Furthermore, according to the molding method of the present invention, it is possible to obtain a sintered body having a composite structure in order to coagulate and harden the slip as it is, even if it is a slip in which short fibers and spherical particles, angular particles, flat particles and the like are mixed. .

To produce a slip in which powder is dispersed,
A dispersion medium for dispersing the powder is used. As the dispersion medium, a material that has excellent wettability and leakability with the powder and does not adversely affect the powder is appropriately used. For example, the most representative dispersion medium is water, and other examples include ethyl alcohol, toluene, hexane, ethylene glycol, etc., for the purpose of improving wettability with powder, leakage, and dryness of molded articles. Two or more kinds can be mixed and used. The addition ratio of the dispersion medium to the powder varies depending on the specific gravity, the specific surface area, the particle size distribution, and the particle shape of the powder, but is generally in the range of 12% by weight to 50% by weight.

When making a slip in which powder is dispersed,
When the dispersibility of the powder is poor, or when it is necessary to reduce the amount of dispersion medium, a dispersant is added. The dispersant can be selected in consideration of the dispersibility of the powder and the effect of reducing the amount of the dispersion medium, as long as it is a material type that does not adversely affect the sintered body after sintering. For example, for oxide ceramics such as alumina, polycarboxylic acid ammonium salt, acrylic acid oligomer, etc. can be used. For non-oxide ceramics, an amine dispersant can be used. The dispersant serves to reduce the amount of dispersion medium in the slip and prevent settling of particles. In addition,
Inorganic dispersants such as water glass may be used in raw material powders such as tableware and insulators. The addition rate of the dispersant varies depending on the type of powder and the amount of dispersion medium, but it can be added in the range of about 0.05 to 2% by weight as the solid content.

It is preferable that the polymer flocculant exerts a strong flocculating action in a small amount as much as possible, and a thickener based on a mere polymer chain, such as polyethylene glycol, methyl cellulose or carboxymethyl cellulose, does not significantly increase the viscosity of the slip system. Even if it is possible, it does not have a strong coagulative hardening action that allows demolding. The polymer coagulant necessary for the present invention refers to a compound that can firmly coagulate and cure the slip itself.

A typical material is an acrylamide type. The acrylamide system referred to in the present invention is a polymer such as polyacrylamide, anion system acrylamide system obtained by hydrolyzing or sulfomethylating it, cationic system acrylamide system obtained by Mannich reaction or Hoffmann reaction, and polyacrylamide partially saponified polymer. It refers to a flocculant having an acrylamide molecular structure in its molecular skeleton. The addition rate of these acrylamide-based flocculants to the powder varies depending on the type of powder, the type of dispersion medium, the presence or absence of the dispersant and the addition rate, the molecular structure of the flocculant, the molecular weight, the pH, etc. It can be added within the range of 5 wt%. If the addition ratio is extremely low, less than 0.1% by weight, the entire slip will be insufficiently hardened by coagulation and hardening in the mold, and handling after demolding will be difficult. On the other hand, if the addition rate exceeds 5% by weight, it takes a long time in the degreasing process before the sintering process of the molded body, and it is not possible to completely degrease the central portion of the thick product, or the mechanical properties after sintering. Problems such as adversely affecting In consideration of these, it is preferable to set the addition rate in the above range according to the powder. The addition of the polymeric coagulant causes the slip to immediately undergo a thickening phenomenon and finally solidify.

In the molding method of the present invention, first, the powder, the dispersion medium, and, if necessary, the dispersant are mixed and dispersed at a predetermined ratio to prepare a slip. As the dispersion method, a wet dispersion mixer such as a ball mill or a fine particle disperser can be used at any time. In this dispersion step, the surface of the powder particles is covered with the dispersion medium, and the electrostatic repulsion between the particles due to the adsorption of the dispersant and the pH value and the steric hindrance effect due to the adsorption of the dispersant can produce a stable slip of high concentration. . If air bubbles are caught during slippage in the dispersion process, defoaming under reduced pressure or addition of a defoaming agent is carried out for products in which the air bubbles affect the mechanical strength after sintering. A small amount of a defoaming agent or a defoaming agent may be added in advance during dispersion and mixing.

The polymeric flocculant is then added to the slip.
The polymer flocculant is added to the container containing the slip while stirring and immediately cast, or a two-liquid mixer having an automatic metering device immediately before the slip is automatically cast into the mold, for example, a line mixer is used. By doing so, the polymer coagulant can be uniformly mixed in the slip, so that smooth casting is possible. When the effect of the polymer flocculant is too quick to cast, a coagulation regulator having a delaying effect can be added.

The mold can be appropriately used as long as it is a material type having no water absorption and excellent dimensional stability. Typical examples of the mold material include a mold, a resin mold, a gypsum mold with a seal, and a collapsible mold. The normal atmospheric pressure casting method is simple, but in the case of highly viscous slip, pressure casting, and when there is an inverse taper in the cavity with respect to the casting port, reduced pressure casting I do.

The cast slip quickly cures the entire slip. When it is cured, it is released from the mold. When the mold release property between the mold and the cured product is poor, a mold release agent such as silicon-based, fluorine-based, petrolatum, or grease may be applied to the surface of the mold for smooth mold release. The cured product (molded product) that has been demolded removes the residual water content at room temperature or by heating and drying. This drying is different from the case of the cured molded body using the thermosetting resin, and the water remaining between the particles can be easily removed to the outside of the molded body. As a result, the drying is completed in a short time without cracking or deformation. Naturally, the smaller the amount of dispersion medium in the slip, the shorter the drying time.

Next, all organic components in the dried product are degreased and removed. This degreasing is performed in the air or a non-oxidizing atmosphere.
A good rule of thumb is to heat it above 350 ° C.

Finally, the degreased body is sintered. The term “sintering” as used herein means both semi-sintering that leaves water absorption and sintering that densifies. In the sintering of powder which is required to have mechanical strength and electrical characteristics, it can be completely sintered at a predetermined sintering temperature. When a porous structure is required, it may be sintered in the semi-sintering temperature range. In any case, the molding method of the present invention is for obtaining a sintering precursor on the premise that this sintering step is performed.

[0020]

【Example】

Example Powder: Alumina (purity 99.99%, average particle size 0.2 micron) 100 wt% Dispersion medium: Distilled water 25 wt% Dispersant: Acrylic acid oligomer 0.6 wt% Polymer flocculant: Acrylamide type 0.5 wt % Mold: Stainless split mold having a cavity of 50 mm diameter x 150 mmL

Alumina, distilled water and a dispersant were weighed in the above proportions, wet mixed and dispersed in an alumina ball mill for 12 hours to obtain a slip. This was transferred to a container, a predetermined amount of a polymer flocculant was added while stirring the slip with a mechanical stirrer, and this was cast into a mold under normal pressure. After casting, the viscosity of the slip increased remarkably, and after about 5 minutes, it was strongly cured. After dividing the mold, the cured product was taken out.
The cured product had sufficient strength to be handled by hand, and no defects such as cracks were observed in the cured product. This was left to dry at room temperature for about half a day, and further dried in a dryer at 80 ° C. for 4 hours. No cracking or deformation due to drying was observed. In addition,
The cast molding made of thermosetting resin using the same powder,
It took twice as long to dry.

This was placed in a box-type electric furnace, heated to 300 ° C. for 12 hours, heated to 350 ° C. for 2 hours, and held for 1 hour.
Further, the temperature was raised to 600 ° C. in 5 hours, the temperature was maintained for 1 hour, and the furnace was cooled. No cracks were observed in this process, and it was confirmed that the organic components were completely removed. Finally in the air 1300
Sintering was performed according to a schedule of holding the temperature for 4 hours and raising the temperature for 8 hours. The relative density of the obtained sintered body with respect to the theoretical density reached 99.9%, the three-point bending strength value based on JISR1601 showed an average of 760 MPa, and it was obtained by sintering a cast molded body of a thermosetting resin. Bending strength value average 7
An excellent mechanical strength value equal to or higher than 30 MPa was exhibited.

Example Powder: Titanium powder (average particle size 5 μm) 100 wt
% Dispersion medium: Water + ethyl alcohol 20 wt% Polymeric flocculant: Acrylamide type 2.0 wt% Mold: Resin split mold having a golf head shape

A slip was prepared in the same manner as in the example. Here, ethyl alcohol was added for the purpose of improving the leakability with the titanium powder, and the ratio of water / ethyl alcohol was 98/2 by weight. A container containing a slip and a container containing a polymer coagulant liquid were separately prepared, and were cast into a mold while automatically mixing both liquids in a two-liquid mixing type line mixer so as to have a predetermined ratio. Immediately after casting, the slip viscosity rapidly increased and solidified in 5 minutes. The mold was divided and the cured product was demolded. The obtained golf head shaped article was dried in the same manner as in the previous example, the organic components were removed in a vacuum degreasing furnace, and the resultant was sintered in a vacuum furnace under conditions of 1300 ° C. for 2 hours and a temperature increase of 5 hours. The relative density value of the sintered body with respect to the theoretical density of titanium was 99.6%, and it was confirmed that the sintered body was completely sintered.

Example Powder: Tungsten Carbide + Cobalt Carbide (Average Particle Size 4
Micron) 100 wt% Dispersion medium: Ethanol 12.5 wt% Dispersant: Phthalic acid type copolymer 1.1 wt% Polymeric flocculant: Acrylamide type 0.3 wt% Mold: Silicone resin having an outer diameter of 15 mm and a drill cavity of 200 L Type

After the slip was prepared in the same manner as in the example,
A polymer flocculant was added and cast into a mold. Since the mold had a spiral shape and the mold had a narrow cavity, the mold was placed in a depressurizer and cast under a reduced pressure of about -700 mHg. The slip caused a thickening phenomenon due to aggregation immediately after casting, and solidified solidly in about 3 minutes after casting. After solidification, the molded body is removed from the mold and dried at room temperature for 5 hours,
It heat-dried at 80 degreeC for 2 hours. After degreasing this in a hydrogen atmosphere, holding at 1260 ° C. for 2 hours, heating for 6 hours,
Sintering was performed under a hydrogen atmosphere. The sintered body was completely densified, and a carbide drill having a spiral shape was obtained.

[0027]

The method for molding the powdery sintering precursor of the present invention comprises:
In the ceramics industry, Japanese and Western food and drink, art porcelain, insulators, refractories, various powders for structural ceramic members, in the powder metallurgy industry, various powders for iron, stainless steel, titanium-based sintered bodies, and intermetallic compound sintering It is extremely useful as a molding method on the premise of sintering using powder, powder for fluorine resin in the organic material industry, etc., and has the following advantages.

(1) A complex shape can be acquired. (2) Thick products can be obtained. (3) Molding is possible in a short time. (4) The manufacturing cost by automation is low. (5) Applicable to most manufacturing industries that involve a sintering process.

Claims (2)

[Claims] 1. A method of molding a powdery sintering precursor, which comprises mixing a polymer coagulant with a slip in which powder is dispersed, injecting it into a mold, and coagulating and curing it. 2. The molding method according to claim 1, wherein the polymer flocculant is an acrylamide type.