JP2592288B2 - Method for densifying powder compacts on the premise of sintering - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for densifying a powder compact on the premise of sintering a powder of ceramic, metal, or the like.

<Conventional technology> Powder molding on the premise of sintering includes pressure molding (dry pressing, rubber pressing), casting (slurry casting, doctor blade), and plastic molding (extrusion, injection). It is commonly used,
Each of these has drawbacks.

(Pressure molding) In dry pressure molding, the density tends to be uneven and the dimensional accuracy of large products is poor, and the size and thickness are limited.

In rubber press molding, since a rubber mold is used as a mold, dimensional accuracy is poor, post-processing such as cutting is required, and the apparatus is expensive.

(Casting) In the slip casting, a relatively uniform molded product can be obtained with a thin material, but a density difference is easily generated with a thick material, and the material is easily cracked.

Doctor blade molding can usually form only a thin plate of 2 mm or less.

(Plastic molding) In extrusion molding, a difference in density tends to occur in the vertical direction with respect to the extrusion direction, and the orientation of particles tends to occur.

 Also, products with complicated shapes are difficult.

Injection molding is possible with complicated shapes and good dimensional accuracy, but it takes a long time for volatile decomposition of organic binders and is easily broken.

Therefore, it is extremely difficult to remove the resin after molding if it becomes thick.

The present invention has been made in view of such a problem, and an object of the present invention is to provide a novel compaction of a powder compact on the premise of sintering capable of uniformly compacting even a thick complex shape body. There is a way to provide.

<Means for Solving the Problems> As a result of intensive studies on the above problems, the present inventors have obtained the following new findings.

To the powder for molding, 1 to 5 parts by weight of a curable resin, 15 to 60 parts by weight of a liquid compatible with the resin, and a curing agent for the resin are mixed with 100 parts by weight of the powder, After molding, when a self-hardening reaction is caused, the compatible liquid is discharged from the molded body, the cured body self-shrinks and densifies, and when this is sintered, an extremely dense sintered body is obtained. Be done.

As the curable resin, it has been found that polyvinyl alcohol, phenolic resin, urea resin, melanin resin, epoxy resin, and urethane resin are preferable.

 The present invention has been made based on the above findings.

<Operation> When a curable resin, a curing agent for the resin, and a compatible liquid (for example, water) are mixed with the powder, a self-hardening reaction occurs, and self-shrinkage starts along with the curing.

 During this curing reaction, the compatible liquid is discharged outside.

As the liquid is discharged, the molded body undergoes self-shrinkage and becomes denser.

 When a drying operation is further performed, self-shrinkage is accelerated.

 The greatest feature of the present invention is this densification mechanism.

When this compatible liquid is not mixed when the resin is cured, self-shrinkage hardly occurs in the cured body, and densification does not occur.

When the compatible liquid is mixed with the curable resin, it is unknown what form it is with the resin, but it is certain that it will be easily separated and discharged outside during the curing reaction .

The compatible liquid of the present invention means a liquid capable of dispersing or dissolving a curable resin.

For example, if the curable resin is water-soluble, a typical compatible liquid is water.

In addition, ethyl alcohol, propyl alcohol, etc.
A water-soluble liquid can be used.

When the curable resin is insoluble in water, organic solvents such as toluene, benzenexylene, ethyl acetate, and cyclohexane can be used.

These liquids can be used alone or in combination of two or more such as water + ethyl alcohol.

As the curable resin in the present invention, a phenolic resin, a urea resin, a melanin resin, an epoxy resin, a urethane resin, and the like are typical, but the molding strength is high, and the resin Considering that a small amount of resin is required for smooth removal, an epoxy resin is most suitable among the above resins.

These curable resins may be mixed with each other, or a mixture of other resins may be used.

The mixing ratio of the curable resin to the molding powder is 1 to 15 parts by weight and the compatible liquid is 15 to 60 parts by weight based on 100 parts by weight of the powder. When the amount of the curable resin is less than the lower limit, when the slip is injected into the mold, curing failure occurs depending on the powder characteristics, and it is difficult to secure the shape. Or, even if cured, the molded body strength is insufficient and demolding becomes difficult.However, if the upper limit is exceeded, the curability is significantly increased by the increase of the curable resin, and the obtained molded body has high strength, but the curable resin Since the amount increases, a degreasing operation before sintering, particularly in the case of a thick molded body, is liable to crack during degreasing. In addition, excessive curable resin causes a reduction in mechanical strength after sintering. If the compatible liquid is less than the lower limit, the casting operation becomes difficult because the fluidized component of the powder decreases. In addition, since the slip viscosity increases, bubbles tend to remain in the slip and the mechanical properties of the sintered body after sintering tend to decrease,
If the ratio exceeds the upper limit, the ratio of powder in the slip is too low, the shrinkage ratio during molding is increased, and warpage occurs during drying, and cracks are likely to occur. Further, when this is sintered, it is difficult to obtain a dense body because the density of the formed body is too low.

The cured product of the present invention self-shrinks by about 5% or more in volume, and densifies, though it varies depending on the amount of the compatible liquid added.

Further, when the forced drying is performed, the compatible liquid remaining in the molded body is shrunk by 2% or more due to the outside thereof, and the molded body is further densified.

The obtained molded body has a bending strength of about 100 kg / cm ² or more, and after densification, can be machined freely and can be processed into any shape and dimensions.

The concept of "molding" in the present invention is to use a precision mold to form the target shape in a single
It also includes that the material once hardened and densified is formed into a target shape by so-called removal processing such as machining.

<Examples> Example 1 Molding powder: partially stabilized zirconia powder (particle size: 0.5 µm, containing 3.0 mol% yttrium oxide) Curable resin: water-soluble epoxy resin Compatible liquid: water Casting mold: 100 mm x 100 mm Aluminum mold with a cavity of × 50 ^t mm Mixing ratio Partially stabilized zirconia powder 100 parts Water soluble epoxy resin 4.3 Water 30 Dispersant (ammonium polycarboxylate) 1.0 Hardener (triethylenetetramine) 0.57 Hardener above The composition except for was wet-mixed for 12 hours in an alumina ball mill (alumina balls were twice as large as the raw material powder) to form a slurry.

A hardener was added to the slurry, stirred for about 15 minutes, and then poured into an aluminum mold for casting.

The inner surface of the casting aluminum mold was sprayed with a fluorine-based release agent by spraying two to three times immediately before the injection.

After the injection, it was left at room temperature (about 22 ° C.), and after 12 hours, it was released from the mold.

Water, which was a compatible liquid discharged, adhered to the surface of the obtained cured product, and when the self-shrinkage ratio was calculated using a caliper, the volume was shrunk by 6.2%, resulting in densification.

In the above slurry composition, water was not used as the compatible liquid, and the amount of the water-soluble epoxy resin was increased and cured, and the cured product did not shrink and did not become dense.

The cured product using the compatible liquid was placed in a 50 ° C. hot air drier and forcibly dried for 5 hours.

The cured product further contracted by about 2% in volume, and became a firm dense body.

The molded body was in a good state without cracking or warpage.

In order to measure the strength of the molded body, a 10 mm × 10 mm × 40 mmL square bar was cut out, and the three-point bending strength was measured.

The flexural strength of the molded body was 102 Kgf / cm ^{2 on} average, and it was expected that it could withstand mechanical processing sufficiently. The grooves and cutting tests were performed with an NC milling machine, and raw processing could be performed without any problem.

Using an electric furnace, the resin content in the molded body was removed in the air under the conditions of a temperature rising time of 12 hours, a temperature of 600 ° C., and a holding time of 1 hour.

The degreased body was not cracked or warped, and no resin residue was observed inside.

The degreased body was sintered using an electric furnace under the conditions of a temperature rise of 8 hours, a temperature of 1500 ° C., and a holding time of 1 hour.

The obtained sintered body had a density of 6.04 g / cm ³ and a water absorption of 0% (Archimedes method).
When the bending strength was measured by cutting out a square bar of
It was 1.5 kg / mm ² , which was equivalent to or higher than the properties of commercially available partially stabilized zirconia.

 The sintered body did not show any cracks in appearance.

Example 2 Molding powder: aluminum nitride (0.8 μm) Curable resin: water-based epoxy resin Compatible liquid: toluene Compounding ratio Aluminum nitride 100 parts Sintering aid (Y2O3) 3.0 Non-aqueous epoxy resin 7.5 Toluene 45 Dispersant (Polyester type) 1.4 Hardener (xylene diamine) 1.55 As in Example 1, a slurry was prepared with the composition excluding the hardener, the hardener was added, and the mixture was sufficiently stirred and a brass mold coated with a fluorine release agent was used. After about 5 hours, the cured product was taken out of the mold.

The volume shrinkage was 7.0% due to the caliper, and it was densified by self-shrinkage.

 Further, it was dried with hot air at 50 ° C. for 24 hours to obtain a molded body.

 The molded product was good without cracking or warpage.

 The molded body was degreased in an electric furnace under the same conditions as in Example 1.

Thereafter, sintering was performed in a resistance heating atmosphere furnace under the condition of 1850 ° C. (holding 4 hours) under N 2.

The obtained aluminum nitride sintered body showed good physical properties with a density of 3.27 and an average bending strength of 48.0 kgf / mm ² .

Example 3 Molding powder: silicon nitride (particle diameter: 0.3 μm) Curable resin: water-based emulsion epoxy resin Compatible liquid: water + alcohol Casting mold: 100 mm outer diameter (13 blades) split aluminum alloy for turbo rotor Type Compounding ratio Silicon nitride powder 90.9 Auxiliary agent (Al2O3) 4.55 Auxiliary agent (Y2O3) 4.55 Total 100 parts Water-based emulsion epoxy resin 7.0 (solid content conversion) Water + ethyl alcohol (water: ethyl alcohol = 2: 1) 4
5 Hardener (isophoronediamine) 1.0 Dispersant (ammonium polycarboxylate) 1.0 The composition excluding the above hardener was charged into an alumina pot mill and wet-mixed for 6 hours to form a slurry.

After adding the curing agent to the slurry and stirring for about 15 minutes, the mixture was gently injected into an aluminum mold (split with blades) having a turbo rotor-shaped cavity sufficiently coated with a fluorine-based release agent.

When about 1.5 hours had passed, the cured product was ready to be handled, so the aluminum mold was divided and the cured product was taken out.

The cured product was left tightly closed in a plastic bag, and after 5 hours, the shrinkage ratio was calculated using a take-out caliper, the volume shrunk by 7.4%, and the product was densified.

 Further, it was forcibly dried at 50 ° C. for 24 hours to obtain a molded body.

The obtained molded body was divided vertically at the center, the inside was observed, and the density of the molded body between the outside and the inside was measured, but no difference was found to be 1.52 g / cm ³ .

 The molded body was good without cracking or warping.

Removal of the resin was carried out at a temperature rise of 36 hours, a temperature of 600 ° C. and a holding time of 1 hour, and sintering under N 2 at 1800 ° C. and 9 atm.

The resulting silicon nitride turbo rotor did not crack, the blades were not deformed, etc., and the density was 3.21 and the density was completely dense.

Example 4 Molding powder: Silicon carbide (particle diameter: 0.6 μm) Curable resin: Polyvinyl alcohol Compatible liquid: Water Casting mold: Resin mold having 25φ × 200 cavity Mixing ratio 100 parts of silicon carbide powder Auxiliary agent (boron carbide) 1.0 Auxiliary agent (carbon black) 2.0 Polyvinyl alcohol 10 Distilled water 60 Hardener (formaldehyde) 2.0 Dispersant (ammonium polycarboxylate) 0.4 Except for the above hardener, injection of SiC pot mill, 12
The mixture was wet-mixed for a time to form a slurry.

After adding the curing agent, the mixture was stirred for 20 minutes, and the obtained self-hardening slurry was poured into a resin mold.

Note that a fluorine-based release agent was applied several times to the inner surface of the resin mold.

After a lapse of about 5 hours, the cured product was taken out, placed in a plastic bag, and allowed to stand at room temperature for 48 hours.

As the curing reaction progressed further, the compatible liquid (water) was discharged, and contracted by 6.0% in volume and became dense.

The obtained molded body is placed in a furnace in an argon gas atmosphere for 550 minutes.
Removal of the resin was carried out at ℃.

Next, at about 2100 ° C in an atmosphere of argon gas at 1 atm.
Bake for 30 minutes.

The obtained sintered body had the same appearance as that obtained by another molding method and was excellent.

The sintered body density was 3.13 g / cm ³ and the bending strength was 62 kg / mm ²
Compared with other molding methods, it was no inferior.

Example 5 In Example 4, one of the sintering aids for silicon carbide, C
Although the source was added as carbon black, in this example, the C source was used as a sintering aid using the carbon generated by thermal decomposition of the epoxy resin as the curable resin.

Compounding ratio Silicon carbide powder 100 parts Sintering aid (amorphous boron) 0.5 Water-soluble epoxy resin 12 Curing agent (triethylenetetramine) 2.4 Distilled water 60 Dispersant (polycarboxylate ammonium salt) 0.8 Above, water-soluble epoxy resin The amount of residual carbon due to thermal decomposition of the resin is calculated to be equivalent to 2.5 parts.

 A molded article was obtained through the same steps as in Example 4.

Despite the increase in the amount of the water-soluble epoxy resin, no crack, warpage, deformation, or the like was observed.

The obtained molded body was heated to 550 ° C. in an argon gas atmosphere to carbonize the epoxy resin.

Next, it was baked at 2100 ° C. for 1 hour in a 1 atm argon gas atmosphere.

The obtained sintered body had the same appearance as that obtained by another molding method and was excellent.

The sintered body density was 3.14 g / cm ³ and the bending strength was 65 kg / mm
There was no problem compared with ² and other molding methods.

Example 6 Molding powder: Metal powder (SUS powder) Curable resin: Non-aqueous epoxy resin Compatible liquid: Toluene-benzene (1: 1) Casting mold: Aluminum gold with 100 × 200 × 1 mm ^t cavity Mold Mixing ratio SUS304 powder 100 parts Non-aqueous epoxy resin 3.5 Hardener (xylene diamine) 0.5 Dispersant (polyester) 1.0 xylene 25.0 The above composition excluding the hardener is wet-mixed in a monomalon-based resin pot mill for 6 hours, and mixed with slurry. did.

 After adding the curing agent, the mixture was stirred and gently poured into a casting mold.

When handling became possible, it was taken out of the mold and left tightly closed.

As the curing reaction progressed, xylene appeared on the surface of the cured product, and the molded product shrank by about 5.7% in volume and became dense.

In the case of the densified one, no warpage or deformation was recognized despite its thin thickness.

After forced drying, 1.0φ, 2.0φ, 5.0φ on desktop pole
Drilled easily.

After the molded body was degreased at 600 ° C., it was baked at 1260 ° C. for 2 hours in an aqueous atmosphere.

The baked one has no warpage or deformation and a density of 6.65Kg / cm ³
Met.

<Effects of the Invention> (1) Even a thick complex shaped body can be uniformly densified.

(2) No warping or deformation after firing.

(3) Removal processing such as cutting and drilling is also possible.

(4) Even when thick, cracking during firing is unlikely to occur.

Continuation of the front page (56) References JP-A-62-227448 (JP, A) JP-A-59-190255 (JP, A) JP-A-60-71570 (JP, A) JP-A-60-137865 (JP, A) JP-A-63-219501 (JP, A) JP-A-56-146737 (JP, U) JP-B-61-57641 (JP, B2) JP-B-50-23416 (JP, B2)

Claims (2)

(57) [Claims] 1. A mixture of a powder, 100 parts by weight of a powder, 1 to 5 parts by weight of a curable resin, 15 to 60 parts by weight of a liquid compatible with the resin, and a curing agent for the resin. A method of densifying a powder molded body on the premise of sintering, characterized by causing a self-hardening reaction after molding to discharge the compatible liquid from the molded body. 2. The method according to claim 1, wherein the curable resin is polyvinyl alcohol,
The densification method according to claim 1, wherein the method is a phenolic resin, a urea resin, a melanin resin, an epoxy resin, or a urethane resin.