JP2749699B2 - Method for producing compound for powder injection molding - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a compound for powder injection molding, and more particularly to a method for producing a metal, cermet and ceramic product by powder injection molding. The present invention relates to a method for producing a compound for powder injection molding, which can achieve high density, improved dimensional accuracy and prevention of deformation.

[Conventional technology]

As a conventional method of producing a compound for powder injection molding, a method of producing a compound by heating and kneading a raw material powder and a binder component with a kneader is generally employed.

For kneading, a batch or continuous kneader is generally used. Batch type kneaders include a pressure kneader, a disk kneader and a blade type kneader.

In the case of producing a compound using a pressure kneader widely used as a batch type kneader, the following procedure is generally performed.

After the raw material powder is put in the mixing tank and heated to the melting temperature of the binder component, the binder component is added little by little. After kneading the raw materials into a rice cake-like compound, continue kneading for another 30 to 60 minutes. The kneaded compound is removed from the mixing tank, cooled, and then pulverized or pelletized.

There is also a method in which each binder component is melted and mixed in advance, and the raw material powder is put in the mixture.

In the case of a continuous kneader, dry mixing of the raw material powder and the binder component is performed at room temperature in advance.

As a method of uniformly dispersing a ceramic powder in an organic molding aid by heating and kneading for a short time, for example, JP-A-61-22
As disclosed in Japanese Patent No. 2953, there is a method of adding a ceramic dispersant as a composition for the purpose of achieving an affinity between a ceramic powder and an organic molding aid.

[Problems to be solved by the invention]

However, in powder injection molding, since fine powder particles are used, it is difficult to uniformly disperse the raw material powder in a binder, and there is a problem in the quality of the obtained sintered body.

Specifically, the non-uniform compound results in large dimensional variations and large pores in some cases. In addition, the kneading time tends to be long in order to achieve uniform dispersion, and as a result, the quality of the binder component is changed, such as cutting, cross-linking and branching of the polymer chain, resulting in a change in flow characteristics. In order to facilitate kneading and to ensure the fluidity of the compound, the amount of the binder tends to be excessive, which causes deformation in the degreasing step.

[Means for solving the problem]

In order to solve the above-mentioned problem, the present invention performs an operation of dispersing and mixing a part of a polymer binder and a raw material powder in an organic solvent as a pre-process of kneading and resin-coating powder particles, and drying the mixture. A compound for powder injection molding is produced by heating and kneading the compound and the remaining binder components.

As the binder component used when preparing the compound for powder injection molding according to the present invention, those known per se can be used. For example, as the binder, polyethylene, polypropylene, atactic propylene, polystyrene, ethylene-vinyl acetate copolymer, acrylic resin, waxes and the like, as a plasticizer, dibutyl phthalate, dioctyl phthalate, butyl benzyl phthalate and the like Yes, lubricants include metal stearates, mineral oils, natural and synthetic waxes, and the like. Compound fluidity, shape retention, degreasing, dispersibility, thermal stability,
Select the binder component in consideration of mold release properties, etc.
3 to 30 parts are added to 100 parts by weight.

As the polymer binder component that is dissolved in an organic solvent to coat the powder particles, any one or more of the binder components is effective, but a binder component having high affinity with the raw material powder is desirable. Coating with the binder component having the highest melting point among the constituent components is effective for facilitating kneading and enhancing shape retention.
The amount of the polymer binder added in this pretreatment step is
Determined in consideration of the surface area of the raw material powder to be used. If the added amount is small, the effect of this pretreatment step is diminished. Conversely, if the addition amount is too large, the mixture becomes solid during drying, and a pulverizing step is required.

As the organic solvent used for producing the compound for powder injection molding according to the present invention, a known organic solvent can be used. For example, ketones (acetone, methyl ethyl ketone, methyl isoble ketone, etc.), aromatics (benzene, toluene, xylene, etc.), esters (ethyl acetate, n-butyl acetate, isoamyl acetate, etc.), etc. The selection is made in consideration of the solubility of the binder component used.

In the above pre-process, it is desirable to add a dispersant together with the polymer binder component in order to disperse the raw material powder in the organic solvent to the primary particles.

Examples of the dispersing agent to be added include a surfactant, and as is well known, there are an anionic surfactant, a cationic surfactant, a nonionic surfactant, and an amphoteric surfactant.

Examples of the anionic activator include fatty alcohol sulfate, alkyl sulfonate, alkyl naphthalene sulfonate, alkyl benzene sulfonate, phosphate ester salt and the like.

Examples of the cationic activator include primary amine salts, tertiary amines, quaternary ammonium compounds, pyridine derivatives and the like.

Examples of the nonionic activator include partial fatty acid esters of polyhydric alcohols, ethylene oxide adducts of fatty alcohols, ethylene oxide adducts of fatty acids, ethylene oxide adducts of fatty amino or fatty acid amides, and ethylene oxide adducts of alkylphenols. is there.

Examples of the amphoteric activator include a carboxylic acid derivative and an imidazoline derivative.

In selecting a dispersant, it is necessary to consider the adsorptivity with the raw material powder, the heat resistance in the kneading and molding steps, the compatibility with other binder components, and the like. When a metal salt is added, it is necessary to pay attention to the influence of the metal component since the metal component remains in the final product. These are used alone or in combination with various activators.

In addition, these surfactants also have an antistatic effect,
The insulating raw material powder compound can also have conductivity. Thereby, it is possible to prevent the compact from adhering to the mold and pinching, and to prevent powder and dust from adhering to the compact. However, there is no effect unless it is added in a large amount to some extent,
It is necessary to add about 0.5 to 3% by volume in the compound. In general, cationic surfactants and nonionic surfactants are preferred as antistatic agents.

〔Example〕

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples according to the present invention. In addition, all the numbers shown here are based on weight.

<Example 1> Compounds of carbonyl iron powder were prepared by the following procedure with the binder compositions shown in Table 1.

After dispersing the carbonyl iron powder in toluene with a homomixer, 0.2 parts of an ethylene-vinyl acetate copolymer having a good binding property to the powder was added and mixed for 30 minutes. This was vacuum-dried and the remaining binder component was heated and kneaded for 1 hour in a Labo Plastomill. Before kneading, add polystyrene
The mixture was melted at 190 ° C., cooled to 120 ° C., mixed with the remaining binder components, and mixed with the raw material powder coated with the resin.

As a comparative example, a compound was manufactured without performing the resin coating step on the raw material powder in the above manufacturing method.

Table 2 shows the time required to reach an equilibrium state during kneading, the torque at that time, and the state of dispersion of the raw material powder in the compound. From this, it can be seen that the compound subjected to the pretreatment of the present invention has a shorter time to reach an equilibrium state and a better dispersion state than the case where the pretreatment is not performed (conventional method). Further, the torque value at the time of equilibrium is small but small, and it can be seen from this that the dispersion state is also good.

<Example 2> A compound of carbonyl iron powder was prepared in the same procedure as in Example 1, except that 0.2 parts of polystyrene was added instead of the ethylene-vinyl acetate copolymer in the pretreatment step of Example 1.

Also, in this pretreatment step, a case where 0.2 parts of a surfactant (Catanac LSA; manufactured by American Cyanamide) was added for the purpose of improving the dispersibility of the raw material powder and the affinity between the powder particles and the polymer binder was examined. Was done. In order to keep the total number of binders constant at 9 parts,
The wax was 2.3 parts. In the pretreatment, the raw material powder was first dispersed in toluene to which a surfactant was added using a homomixer, and then a polymer binder was added and mixed.

The same evaluation as in Example 1 was performed for the above two compounds, and the results are shown in Table 3.

It can be seen that the effect of the resin coating step on the raw material powder of the present invention is more effective than the case without the pretreatment step in Table 2, but a satisfactory result is not necessarily obtained when the surfactant is not added. I couldn't. Therefore, when coating with a polymer binder having a low affinity for the raw material powder, it is desirable to add a surfactant as in this embodiment.

<Example 3> A zirconia compound was prepared by the following procedure using the binder composition shown in Table 4.

The zirconia raw material powder was dispersed in toluene to which a surfactant (Denone 33 lP; manufactured by Marubishi Yuka Kogyo Co., Ltd.) was added using a homomixer, and 1.0 g of the ethylene-vinyl acetate copolymer was dispersed therein.
Was added and mixed for 30 minutes. This was vacuum-dried and the remaining binder component was heated and kneaded for 1 hour in a Labo Plastomill. Kneading was performed in the same manner as in Example 1.

As a comparative example, a compound was produced without adding a surfactant in the above production method. In order to keep the total number of binders constant at 16 parts, wax was used at 5.0 parts.

Using the above two compounds, small cylindrical parts of φ3 mm × 5 mm were molded. The sample with the added surfactant did not adhere to the mold, whereas the sample without the surfactant adhered to the mold. From this, the antistatic effect by the addition of the surfactant was confirmed.

〔The invention's effect〕

In the present invention, when preparing a compound for powder injection molding, an operation of preliminarily mixing a part of the polymer binder component and the raw material powder in an organic solvent to perform resin coating as a pre-kneading step. Therefore, a uniform compound for powder injection molding can be produced by kneading in a short time with a minimum necessary amount of a binder to be added.

Increasing the concentration of the raw material powder in the compound leads to an improvement in degreasing deformation due to a decrease in the amount of degreasing and an improvement in product dimensional accuracy due to a decrease in sintering shrinkage.

The homogenization of the compound leads to the densification of the sintered body and the improvement of the dimensional accuracy of the product due to the reduction of the large pores.

The shortening of the kneading time can suppress the deterioration of the binder component due to breakage, cross-linking and branching of the polymer chain, and can stabilize the flow characteristics.

The addition of a surfactant when coating with a polymer binder having a low affinity for the raw material powder further promotes the effects of the present invention.

Further, the addition of a surfactant having conductivity has an effect of preventing the compound of the insulating raw material powder from being charged, and can prevent the molded product from adhering to the mold and being pinched.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Kenichi Yoshioka, Inventor Kenichi Yoshioka 840 Takeno, Shimotomi, Tokorozawa-shi, Saitama Citizen Watch Co., Ltd. (72) Inventor Masami Hoshi 6-11-12 Honcho, Tanashi-shi, Tokyo Citizen Watch Co., Ltd. Tanashi Factory (72) Inventor Seiichi Nakamura 1 Shimoyoshida, Fujiyoshida City, Yamanashi Examiner Akihiro Kitamura (56) References JP-A-54-32106 (JP, A) JP-A-1-281707 ( JP, A)

Claims (1)

(57) [Claims] 1. A method for premixing a part of a polymer binder component in a binder constituting a compound for powder injection molding and a raw material powder in an organic solvent to coat the powder particles with a resin, and mixing the mixture with the remaining binder component. A method for producing a compound for powder injection molding, characterized by heating and kneading.