JP2980209B2 - Noble metal sintered body and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to gold, silver and their gold.
Parts or components made of precious metal materials whose main components are
The present invention relates to a noble metal sintered body such as an accessory and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, a precision casting method is generally used to obtain a precious metal product such as gold, silver , or an alloy thereof. However, the precision casting method requires a large number of molds as many as the product in order to produce a large number of parts of the same shape, and pinholes are likely to occur, so precious metal products that generally require high surface properties are required. If so, it is difficult to obtain a sufficient surface property in terms of specularity.

As an attempt to avoid such disadvantages of the precision casting method, as disclosed in Japanese Patent Publication No. 62-21611, a mixture of fine powder of precious metal powder and plastic particles is heated and molded and cooled. There is a method of manufacturing a pseudo-precious metal product. This method is capable of mass-producing articles having the same shape, and is a method excellent in productivity. However, this method is a technology to make a composition containing plastic by compounding precious metal particles with plastic particles as a binder and molding, and even if it is difficult to distinguish it from the precious metal product with the naked eye, it is different from precious metal products, so to speak, by imitation It is difficult to satisfy the texture required for precious metal products.

In addition, the product shape obtained by forging is limited, and furthermore, work hardening is caused by forging, and a plurality of heat treatments for softening are required, and it is difficult to reduce the manufacturing cost.

[0005]

SUMMARY OF THE INVENTION The present invention avoids the deterioration of surface properties and high manufacturing costs, which are problems of precious metal products by the precision casting method or forging method, and avoids complicated shapes having excellent surface properties such as mirror finish. It is an object of the present invention to provide a technology capable of mass-producing products at low cost.

[0006]

The present invention SUMMARY OF THE INVENTION has been made to solve the above problems, gold, in the sintered body of the noble metal mainly containing Gin及 beauty alloys of these metals, carbon content 0. Provided is a noble metal sintered body characterized in that the sintered body has a relative density of not more than 05% by weight and a relative density of not less than 95%. Also,
Provided is a noble metal sintered body having a carbon content of 0.05% by weight or less, an oxygen content of 0.1% by weight or less, and a relative density of 98% or more. The gold strike the production of sintered bodies of the noble metal mainly containing Gin及 beauty alloys of these metals, adding a binder and mixing and injection molded at the end following the noble metal fine volume average diameter 20 [mu] m, followed by leaving the injection molded body Is heated to degrease and adjust the carbon content to 0.05% by weight or less, and then sintering the degreased body. In addition, a binder is added to and mixed with a noble metal fine powder having a volume average diameter of 20 μm or less, followed by injection molding. Subsequently, the injection molded body is heated and degreased, and the carbon content is adjusted to 0.05% by weight or less. After sintering the degreased body to reduce the oxygen content to 0.1% by weight or less and the relative density to 95% or more, the sintered body is pressed at a pressure of 10 kgf.
/ Cm ² or more in a non-oxidizing gas having a melting point of 75
It is intended to provide a method for producing a noble metal sintered body, characterized in that a relative density is 98% or more by pressurizing in a temperature range of up to 98%.

[0007]

The present inventors have proposed a method for producing precious metal products as follows.
Investigate the production of metal powders used in iron-based products by the injection molding method, conduct research to adapt the production conditions to the physical properties of the resulting sintered precious metal, and mass produce precious metal products with excellent surface properties. We have developed a way to make it possible.

Hereinafter, the present invention will be described in detail. The precious metal sinter of the present invention refers to a sintered body mainly composed of gold, a Gin及 beauty alloys of these metals. In practicing the present invention,
Alloys of these noble metals or powders of pure metals are required. In particular, the particle size is important because it is one of the factors that determine the properties of the subsequent product, and in order to obtain the desired properties of the present invention, the volume average diameter must be 20 μm or less in order to achieve a high sintered density. is there.

That is, in the case of coarse powder having a volume average diameter of more than 20 μm as shown in FIG. 2 as an example later, it is difficult to increase the density of the sintered body to 95% or more even if the subsequent steps are optimized. In addition, the polishing properties are inferior, and the mirror quality of the final product is inferior, so that a noble metal product having excellent surface properties aimed at by the present invention cannot be obtained. Therefore, the metal powder used in the present invention needs to have a volume average diameter of 20 μm or less.

In order to mold this metal powder using an injection molding machine, it is necessary to add a thermoplastic binder so that sufficient fluidity can be obtained at the time of heating and knead the mixture uniformly. That is, if the injection molding of the metal powder is performed only with the metal powder, there is a problem in the injection fluidity and the strength of the molded body as is well known. Therefore, the molding is performed using a compound to which a binder is added and mixed. In the present invention, a binder for injection molding is mainly composed of a resin such as a general thermoplastic resin and / or a wax, and a plasticizer, a lubricant, a degreasing accelerator and the like are added as necessary.

The thermoplastic resin includes acrylic, polyethylene, polypropylene, and polystyrene resins, and the waxes include natural wax such as beeswax, wood wax, montan wax, and low molecular weight polyethylene. There are synthetic waxes represented by, for example, microstalin wax, paraffin wax, etc., and one or more selected from these are used.

The plasticizer is selected depending on the combination with the main resin or wax. Specifically, di-2-ethylhexyl phthalate (DOP), diethyl phthalate (DEP), and di-n-butyl phthalate are used. (DEP) and the like. Examples of the lubricant include higher fatty acids, fatty acid amides, fatty acid esters, and the like. In some cases, waxes are also used as the lubricant.

A sublimable substance such as camphor may be added as a defatting accelerator. The amount of the binder for injection molding is usually about 50% by volume of the compound.
A batch or continuous kneader can be used for mixing and kneading the metal powder and the binder. Among the batch kneaders, a pressure kneader and a Banbury mixer are used, and in a continuous kneader, a twin screw extruder is used. Are each advantageously fitted. Then, after kneading, granulation is performed using a pelletizer or a pulverizer or the like, if necessary, to obtain a compound for injection molding.

In the present invention, these compounds are injection-molded to give a shape. The injection molding can be performed by using an injection molding machine usually used for molding plastics. If the binder is selected within the range of 30 to 60% by volume according to the physical properties of the metal powder, the molding can be performed sufficiently without using any special means. The obtained molded body is heated in an inert, reducing, oxidizing or other atmosphere or in a vacuum to remove the binder.

Particularly important in the present invention is that the sintered body has a carbon content of 0.05% by weight or less. 0.
If the content exceeds 05% by weight, the relative density of the sintered body decreases, and it becomes impossible to obtain surface properties equivalent to those of the ingot. Therefore, carbon remaining from the binder in the degreased body before the sintering step is set to 0.05% by weight or less, preferably 0.01% by weight or less. In the degreasing step of the present invention, it is possible to select a method suitable for a binder necessary for maintaining a shape, such as heat degreasing, vacuum degreasing, and pressure degreasing, which are generally used for degreasing an injection molded body of a metal powder or a ceramic powder. It is.

However, as described above, it is necessary to sufficiently reduce carbon before the sintering step. This is because, as shown in FIG. 1 as an example, when there is a large amount of residual carbon, sintering does not proceed even in a vacuum or reducing atmosphere, and a dense sintered body cannot be obtained. That is, when the amount of degreased carbon in the noble metal powder exceeds 0.05% by weight, sintering is hindered by carbon, and it is difficult to obtain a high quality product. Therefore, the amount of degreased carbon before sintering of the present invention is set to 0.05% by weight or less, preferably 0.01% by weight or less.

The carbon can be reduced by a method such as degreasing in wet hydrogen, heat treatment in an atmosphere containing oxygen, or removal by reacting with oxygen under reduced pressure. Is also possible, for example a maximum temperature of 300
The amount of carbon is reduced to 0.05 by heating in air at a maximum temperature of 300 ° C. or higher in the air after degreasing in air or another atmosphere or under vacuum or the like.
It is easily possible to set the amount to not more than% by weight.

On the other hand, it is difficult to reduce the carbon content to 0.1% by weight or less in the usual degreasing in nitrogen, for example. The sintering of the present invention is performed in a reducing or inert atmosphere or in a vacuum. The sintering conditions in the present invention may be appropriately selected depending on the desired noble metal composition. It is usually carried out within the range of 30 to 300 ° C. below the melting point.

By limiting the volume average diameter of the noble metal fine powder and the content of the degreased carbon before sintering, a relative density of 95% or more can be obtained in the sintering step. This is subjected to post-processing such as polishing to obtain a product. The density after sintering is important because it greatly affects the mechanical properties of the product. When the sintering density is less than 95% relative density, even if it is polished, since many holes exist on the surface, the mirror surface is inferior and the characteristics required for the precious metal product cannot be satisfied.

By setting the relative density to 95% or more,
Sufficient specularity can be obtained by polishing. In addition, when the density is increased, the polishing property is improved, and more efficient production of a precious metal product is possible. In addition, in the present invention, by using injection molding for molding, it is not necessary to use as many molds as the number of products as in the precision casting method, and pinholes do not occur, and the shape of the product as in the forging method is reduced. There are no restrictions or increased manufacturing costs.

By manufacturing a noble metal product by the manufacturing method of the present invention, a noble metal product having a complicated shape and good surface properties, which was impossible in the past, could be mass-produced. In addition, the present invention provides a method in which a binder is added to and mixed with a noble metal fine powder having a volume average diameter of 20 μm or less and injection-molded. Then, after sintering the degreased body to reduce the oxygen content to 0.1% by weight or less and the relative density to 95% or more, the sintered body is sintered in a non-oxidizing gas at a pressure of 10 kgf / cm ² or more. According to a method for producing a noble metal sintered body characterized in that a relative density is 98% or more by applying a pressure treatment in a temperature range of 75 to 98% of the melting point of the sintered body, Content 0.1% by weight or less and relative density 98%
A precious metal sintered body characterized by the above is obtained.

Also in this method, when the volume average diameter of the fine noble metal powder used in the same manner as the above-mentioned method exceeds 20 μm, and when the carbon content of the degreased body exceeds 0.05% by weight, the open communication on the surface is performed. 95% relative density with voids
And the pressure of the pressurized gas in the subsequent pressure treatment does not effectively increase the relative density of the sintered body.

The oxygen content of the sintered body is 0.1% by weight or less. The oxygen content of the sintered body does not change during the pressurization process in a non-oxidizing gas used to prevent oxidation of the sintered body during the pressurization process, and oxygen forms an oxide. Remains.
When oxygen exceeding 0.1% by weight remains, not only does it become difficult to obtain a relative density of 98% or more even when pressure treatment is performed, and it is a part of the noble metal, for example, part of an alloy. It produces oxides of metals such as copper, which leads to deterioration of specularity and poor color tone of products, resulting in poor surface properties.

The oxygen content of the degreased body can be controlled by heat treatment in a reducing atmosphere. In the case of a noble metal or an alloy thereof, reduction can be performed at a relatively low temperature and can be performed simultaneously with degreasing and / or sintering. . The pressing treatment is performed at 75 to the melting point of the sintered body.
This is performed in a 98% temperature range with a non-oxidizing gas having a pressure of 10 kgf / cm ² or more. Melting point 98, which is just below the melting point of the sintered body
%, It takes a long time to increase the relative density to 98% or more at a pressure of less than 10 kgf / cm ² ,
If the temperature is less than 75% of the melting point, 300 kgf / cm ²
Need more pressure and are not both economical.

[0025]

EXAMPLES Example 1 K18 yellow gold water atomized powder of the composition shown in Table 1 was used as the noble metal fine powder, and the particle size was adjusted by classification to obtain a volume average diameter of 10 μm.

[0026]

[Table 1] Metal Au Ag Cu content (% by weight) 75.1 15.2 9.7 に This fine powder A thermoplastic resin and a wax were mixed as a binder and kneaded using a pressure kneader. After cooling the kneaded product, it was pulverized into granules, and a molded body for a watch case was molded using an injection molding machine.

The obtained compact was heated to 600 ° C. at a rate of 5 to 10 ° C./h in a nitrogen atmosphere to remove the binder in the compact. However, since the residual carbon is as high as 0.25% by weight only in this step, 300 to 6%
The remaining carbon was removed by heating at 00 ° C for 1 hour. As a result of this treatment, the residual carbon could be reduced to 0.002 to 0.05% by weight.

The degreased body was placed in a hydrogen atmosphere at 850.
Sintering was performed at 2 ° C. for 2 hours. As a result, as shown in FIG. 1, a sintered body having a carbon content of 0.05% by weight or less and a relative density of 95% or more was obtained, and characteristics excellent in both abrasiveness and mirror finish were obtained. In Comparative Example 1 in which the maximum temperature was less than 300 ° C. even when the heat treatment was performed in the atmosphere, the carbon amount after the treatment was 0.1% by weight.
The relative density exceeded 5% by weight and the relative density of 86%, which is a characteristic of the present invention, was not obtained.

Further, in Comparative Example 2 in which the carbon content after the treatment was 0.20% by weight because the degreasing treatment was in nitrogen, the relative density was even lower at 55%. Example 2 The density of a product obtained by sintering in the same process as in Example 1 using powder having a volume average diameter of 5 μm to 22 μm was the relative density shown in FIG. In addition, the residual carbon amount of each of the degreased bodies was 0.03% by weight. The relative density of Comparative Example 3 having a volume average diameter of 22 μm was 93%, and the polishing property was poor and the mirror surface was poor, so that the product of the present invention could not be obtained. Example 3 A molded body produced in the same manner as in Example 1 and from which the binder was removed,
By heating at 600 ° C. for 1.5 hours in the atmosphere, a degreased body having a carbon content of 0.03% by weight was obtained.

The degreased body is placed at 850 ° C. for 2 hours in a hydrogen atmosphere.
To obtain a sintered body having a relative density of 97% and an oxygen content of 0.09% by weight, and a pressure of 15 kgf / cm
Perform pressure treatment of 850 ° C. 2h in ² of hydrogen atmosphere to obtain a relative density of 99% of the sintered body. The obtained sintered body had few irregularities on the surface, was extremely excellent in polishing properties and specularity, and had surface properties equivalent to those of a molten product.

[0031]

According to the present invention, a noble metal product having a complicated shape and excellent surface properties can be manufactured at low cost.

[Brief description of the drawings]

FIG. 1 is a view showing the relationship between the relative density of a sintered body and the residual carbon content of a degreased body.

FIG. 2 is a view showing a relationship between a relative density of a sintered body and a volume average diameter of a noble metal fine powder.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-63-235404 (JP, A) JP-A-62-283875 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C22C 5/00 B22F 3/10

Claims (4)

(57) [Claims] 1. A gold, in the sintered body of the noble metal mainly containing Gin及 beauty alloys of these metals, carbon content 0.05
A noble metal sintered body characterized by being not more than 95% by weight and having a relative density of not less than 95%. 2. A gold, in the sintered body of the noble metal mainly containing Gin及 beauty alloys of these metals, carbon content 0.05 wt% or less, oxygen content 0.1 wt% or less, and a relative density of 98% A precious metal sintered body characterized by the above. 3. A gold strike the production of sintered bodies of the noble metal mainly containing Gin及 beauty alloys of these metals, the volume average diameter of 20
A binder is added to and mixed with a noble metal fine powder having a particle size of not more than μm, and the mixture is injection-molded. Subsequently, the injection-molded product is heated and degreased, and the carbon content is adjusted to 0.05% by weight or less. A method for producing a precious metal sintered body, comprising sintering. 4. A gold strike the production of sintered bodies of the noble metal mainly containing Gin及 beauty alloys of these metals, the volume average diameter of 20
A binder is added to and mixed with a noble metal fine powder having a particle diameter of not more than μm and injection molding is performed. Subsequently, the injection molded body is degreased by heating, and the carbon content is adjusted to 0.05% by weight or less. After sintering to make the oxygen content 0.1% by weight or less and the relative density 95% or more, the sintered body was subjected to a pressure of 10 kgf / c.
m seventy-five to nine of the melting point of the sintered body ² or more in a non-oxidizing gas
A method for producing a noble metal sintered body, characterized in that a relative density is 98% or more by applying a pressure treatment in a temperature range of 8%.