JP2002338336A - Alumina ceramics product for sliding part and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To determine optimum alumina ceramics texture for obtaining favorable surface roughness and to establish manufacturing technique for embodying the texture in an alumina ceramics product for a sliding part. SOLUTION: The alumina ceramics product for the sliding part is characterized by that the product has >=99.9% purity, relative density of >=99%, maximum of maximum circumscribed circle diameter of alumina particles is <=5 μm and an average grain size thereof is <=1.4 μm in an observation visual field 20 of 20 μm×15 μm of a sintered compact when observed by using a scanning type electron microscope of 5,000 magnifications. The alumina ceramics product is manufactured by using alumina particles of single crystal as a raw material, adding MgO by <1000 ppm (0 ppm is not included) as a sintering assistant and sintering at 1250 to 1590 deg.C otherwise by using alumina particles of single crystal or polycrystal as the raw material, sintering at 1250 to 1590 deg.C and then subjecting to hot hydrostatic pressing sintering at 1200 to 1550 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a uniform and fine alumina ceramic product for a sliding portion, and more particularly to an alumina ceramic product for a sliding portion used for implant materials such as artificial joints.

[0002]

2. Description of the Related Art Alumina ceramics is a biologically inert material and is excellent in mechanical strength and abrasion resistance, so that it has been applied to medical materials such as artificial joints and artificial tooth roots. For example, in a hip prosthesis, the alumina-ultrahigh molecular weight polyethylene combination is considered to be less likely to wear and less likely to cause defects. High molecular weight polyethylene is employed.

However, even with such an artificial hip joint composed of "alumina ceramics head / ultrahigh molecular weight polyethylene acetabular socket", the polyethylene acetabular socket actually slides on the alumina ceramics head every time walking. This will reduce wear. And, abrasion powder of polyethylene generated by abrasion accumulates in the tissue in the vicinity of the artificial hip joint, causing bone resorption to cause loosening between the artificial hip joint and the bone.

In order to solve this problem, it is effective to make the surface of the head of the alumina ceramic mirror-mirror. In recent years, there has been a movement to apply alumina ceramic to the acetabular socket side, but also in this case, in order to reduce abrasion of the alumina ceramic bone head and the acetabular socket inside the body, the sliding portion of the head / acetabular socket slides. It is important to minimize the surface roughness. At the current technology level, the surface roughness of the alumina ceramic bone head surface and the inner surface of the alumina ceramic acetabular socket is 0.01
It has reached near μmRa.

[0005]

SUMMARY OF THE INVENTION The inventors of the present invention have made intensive studies on the mirror surface finishing technology of the surface of the head of the alumina ceramic and the inner surface of the acetabular socket of the alumina ceramic. It has been found that dropout prevention is also an important factor in improving the surface roughness. That is, in the conventional medical alumina ceramics, 2
Among the alumina particles observed in a visual field of about 20 μm × 15 μm, those having an average particle diameter of about 1 μm and a maximum circumscribed circle diameter of 5 μm or more are included. However, no matter how much the mirror polishing is performed, particles fall off starting from large particles, and the surface roughness is not improved.

The present invention has been made in view of the above circumstances, and has as its object to determine an optimal alumina ceramic structure for obtaining good surface roughness and to establish a manufacturing technique for realizing the structure. I do.

[0007]

The alumina ceramic product for a sliding portion according to the present invention which has solved the above-mentioned problems has a purity of 99.9% or more, a relative density of 99% or more, and a scanning type electronic device. The maximum value of the maximum circumscribed circle diameter of the alumina particles in the 20 visual field of 20 μm × 15 μm of the sintered body observed at 5,000 times using a microscope is 5 μm or less, and the average particle diameter is 1.4 μm or less. It has.

The alumina ceramic product for a sliding portion of the present invention is preferably used for a sliding portion which receives a load, specifically, an artificial joint head and an acetabular socket, particularly a hip joint and an acetabular socket of an artificial hip joint. is there.

The alumina ceramic product for a sliding portion of the present invention is prepared by using single crystal alumina particles as a raw material, adding less than 1000 ppm (not including 0 ppm) of MgO as a sintering aid, and firing at 1250-1590 ° C. By sintering, or using single crystal or polycrystalline alumina particles as a raw material and sintering at 1250 to 1590 ° C.
It can be manufactured by hot isostatic pressing (HIP sintering) at 200 to 1550 ° C. When the alumina ceramic product for a sliding portion of the present invention is used for an artificial joint or a hip joint or an acetabular socket of an artificial hip joint, HIP is used.
In the case of manufacturing without sintering, it is preferable to use single crystal alumina particles as a raw material regardless of the case of manufacturing by HIP sintering.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Conventionally, it has been considered that the detachment of alumina particles during mirror polishing is related only to processing conditions. However, the present inventors studied the relationship between the alumina particles falling off and the alumina ceramic structure, and as a result, controlled the maximum value and the average particle diameter of the maximum circumscribed circle diameter of the alumina particles in the sintered body to a specific range. In such a case, it was found that falling off of alumina particles was extremely unlikely to occur, and the present invention was completed.

Alumina ceramic product for a sliding portion of the present invention (hereinafter simply referred to as "alumina ceramic product")
The maximum value of the maximum circumscribed circle diameter of the alumina particles in 20 visual fields of 20 μm × 15 μm of the sintered body observed at 5000 times using a scanning electron microscope is 5 μm or less,
Preferably it is 3 μm or less, and the average particle size is 1.4 μm or less, preferably 1.3 μm or less, more preferably 1.2 μm or less.
μm or less. If the maximum value of the maximum circumscribed circle diameter or the average particle diameter exceeds the above range, particles are frequently dropped, and good surface roughness cannot be achieved.

The alumina ceramic product of the present invention must have a relative density of at least 99%.
Although the theoretical density of alumina is 3.98 g / cm ³ , the one having a relative density of less than 99% does not improve the surface roughness because voids are originally present in the structure.

Since the alumina ceramic product of the present invention has an extremely good surface roughness, the sliding portion which receives a load, specifically, a head of an artificial joint, an acetabular socket,
In particular, even when used for a head of an artificial hip joint or an acetabular socket, it is a good product with very little generation of abrasion powder due to sliding.

Next, a method for producing the alumina ceramic product of the present invention will be described. The alumina ceramic product of the present invention can be manufactured by the following two methods.

First, it is produced by sintering under normal pressure using single crystal alumina particles as a raw material and MgO as a sintering aid.

In the first production method, the reason why the single crystal alumina particles are used as the raw material is that the desired fine structure and the relative density of 99% or more cannot be obtained simultaneously with the polycrystalline alumina particles as the raw material. is there. Further, the particle size is preferably from 0.1 to 0.2 μm. Note that single-crystal alumina particles can be obtained by a chemical vapor deposition method (CVD method) or the like.

In the first manufacturing method, it is necessary to add less than 1000 ppm (not including 0 ppm) of MgO as a sintering aid in order to simultaneously achieve a desired microstructure and a relative density of 99% or more. . The addition amount of MgO is 3p
At pm or more, preferably 5 ppm or more, the effect of the addition becomes remarkable. On the other hand, if the added amount of MgO exceeds 1000 ppm, it is not suitable as alumina ceramics for medical materials. More preferably, it is 500 ppm or less.

In the first production method, first, the above-mentioned single-crystal alumina powder and MgO are mixed, and a binder is added to the mixture at 0.1 to 2% by mass. As the binder, an organic solvent such as hydroxypropylcellulose, polyvinyl alcohol, and acrylic can be used. Further, water is added as a solvent. If necessary, 0.1 to 0.5% by mass of a polycarboxylic acid ammonium or the like is added as a dispersant.

The slurry is prepared by mixing the above-mentioned alumina powder, MgO, binder and the like, and the concentration of the slurry at this time is preferably 40 to 80% by mass. The method for mixing them is not particularly limited, and a usual method is adopted. If the slurry is foaming, it is recommended to add a small amount of an antifoaming agent.

The above slurry is granulated and dried with a spray drier to obtain secondary particles containing a sintering aid. As for the conditions of the spray dryer at the time of granulation drying, it is recommended that the hot air temperature be set to about 80 to 150 ° C., which is slightly higher than the boiling point of the solvent, because the binder is concentrated on the surface when the granules are rapidly dried.

Next, the alumina secondary particles containing the sintering aid are formed into a desired shape. The molding method at this time is not particularly limited, but an isostatic pressing method, an injection molding method, a uniaxial molding method, or the like can be applied. After such forming, it may be further formed by machining, or may be formed into a simple floc shape and then formed into a desired shape by machining.

Next, the above compact is sintered. The lower limit of the sintering temperature is preferably 1250 ° C or higher, more preferably 1350 ° C or higher, and particularly preferably 1450 ° C or higher. Further, the upper limit is preferably 1590 ° C. or less, and 1550 ° C.
C. or lower is more preferable. When the sintering temperature is lower than the above range, the density of the sintered body does not sufficiently increase, and when the sintering temperature is higher than the above range, the growth of crystal grains remarkably proceeds and the strength decreases. The sintering time depends on the amount and shape, but in most cases, about 0.5 to 4 hours is sufficient. Even if this time is extended, the growth of crystal grains will rather proceed. The atmosphere during sintering may be air.

In the second manufacturing method, the normal pressure sintered body obtained by sintering in the same procedure as in the first manufacturing method is HIP-sintered. In this case, the raw material alumina may be a single crystal or a polycrystal. Even in the case of polycrystalline alumina, the desired microstructure and 9
This is because a relative density of 9% or more can be achieved. The particle size is 0.1 in both cases of single crystal and polycrystal.
1 to 0.2 μm is preferred. In addition, Mg as a sintering aid
It is not necessary to add O, but it can be added.
When adding, the same addition amount as in the first production method is recommended.

At the time of HIP sintering, the normal pressure sintered body is embedded in a refractory powder such as alumina, zirconia, titania and the like, and is sintered in a pressurized atmosphere of an inert gas such as argon or nitrogen. However, as long as the above atmosphere is achieved, it is not always necessary to embed the normal pressure sintered body in the refractory powder.

The lower limit of the sintering temperature of HIP sintering is 1200 ° C.
Or higher, more preferably 1300 ° C. or higher, and 14
A temperature of at least 00 ° C. is particularly preferred. The upper limit is 1550
C. or lower, and more preferably 1500 C. or lower. If the sintering temperature is lower than the above range, the densification of the sintered body cannot be sufficiently achieved. If the sintering temperature exceeds the above range, the densification proceeds but the crystal becomes coarse and a desired fine structure cannot be obtained. The pressure during HIP sintering is 50.7 to 203 MPa (500 to 200 MPa).
0 atm) is preferred. If the pressure is lower than the above range, the pressurizing effect for densification is insufficient, and if the pressure exceeds the above range, the effect of pressurization is not so much obtained, and the cost of the apparatus is rather increased. The sintering time depends on the size of the sample, but usually 1 to 2 hours is sufficient if it is about the size of the artificial joint.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on embodiments. However, the following embodiments do not limit the present invention, and all changes and implementations without departing from the spirit of the preceding and following embodiments are included in the technical scope of the present invention.

Using alumina particles shown in Tables 1 to 3 as raw materials,
To this, MgO in the amounts shown in Tables 1 to 3, 1% by mass of an acrylic binder for molding, and 0.3% by mass of a dispersant ammonium stearate were added, and water was used as a solvent.
The solute concentration was 60% by mass. These materials were wet-mixed with a ball mill for 20 hours to form a slurry.

The slurry was dried using a spray drier to obtain alumina secondary particles having an average particle size of about 100 μm.

The obtained alumina secondary particles are cold isostatically pressed.
147MPa at pressure (1.5t / cm ^Two) Pressure
And sintering them at the temperature shown in Table 1 under normal pressure for 2 hours.
A ceramic product was obtained. The obtained alumina ceramic
The purity of all the box products was 99.9%.

In the case of HIP sintering, the above-mentioned alumina secondary particle compact was sintered under normal pressure at the temperatures shown in Tables 2 and 3 for 2 hours.
The alumina ceramics product was obtained by performing HIP sintering for 2 hours in an Ar atmosphere at a pressure of 152 MPa (1500 atm). The purity of each of the obtained alumina ceramic products was 99.9%.

These alumina ceramic products are mirror-polished and thermally etched, and are then subjected to a scanning electron microscope (SE).
M) A photograph of the surface was taken at a magnification of 5000 times using "S-4000 manufactured by Hitachi, Ltd." From this SEM photograph, image analysis software "MEDIACYBERNETICS,
20 μm × 1 using “Image-Pro PLUS”
The maximum circumscribed circle diameter and the average particle diameter of each alumina particle in the sintered body in the 20 visual fields of 5 μm were determined. From these, the maximum value of the alumina particles in the above observation field was determined for the maximum circumscribed circle diameter. With respect to the diameter, the average value of the alumina particles in the observation visual field was similarly obtained. Also,
The density of the obtained alumina ceramics product was determined by the Archimedes method.

Table 1 shows the results of the alumina ceramics product obtained only by normal pressure sintering.

[0033]

[Table 1]

First, No. 6-8, 11-13, 16-
The alumina ceramic product of No. 18 is an example satisfying the requirements of the present invention.

On the other hand, no. 1-5,9,10,1
4, 15, 19 to 40 alumina ceramic products are comparative examples that do not satisfy the requirements of the present invention, and have the problems shown in Table 1.

No. 1 to 3 have 0 ppm of MgO added
And the relative density is reduced.

No. 4 and 5 have 0 ppm of MgO added.
In addition, the sintering temperature exceeds the upper limit of the present invention, and the maximum circumscribed circle diameter and the average particle diameter of the alumina particles in the sintered body are increased.

No. 9,10,14,15,19,20
Are examples in which the sintering temperature exceeds the upper limit of the present invention, and the maximum circumscribed circle diameter and the average particle diameter of the alumina particles in the sintered body are increased.

No. Nos. 21 to 23 are examples in which polycrystalline alumina particles are used as a raw material and the amount of MgO added is 0 ppm.
In No. 23, the maximum circumscribed circle diameter and the average particle diameter of the alumina particles in the sintered body are increased.

No. Examples 24 and 25 are examples in which polycrystalline alumina particles are used as a raw material, the amount of MgO added is 0 ppm, and the sintering temperature exceeds the upper limit of the present invention. The diameter and average particle size are increasing.

No. Nos. 26 to 28 are examples in which polycrystalline alumina particles were used as raw materials, and the relative densities of all were low. In No. 27, the maximum circumscribed circle diameter of the alumina particles in the sintered body was no. In No. 28, the maximum circumscribed circle diameter and the average particle diameter are increased.

No. Nos. 29 and 30 are examples in which polycrystalline alumina particles are used as the raw material and the sintering temperature exceeds the upper limit of the present invention, and the maximum circumscribed circle diameter and average particle diameter of the alumina particles in the sintered body are increased. I have.

No. Nos. 31 to 33 are examples using polycrystalline alumina particles as a raw material. In No. 31, the relative density decreased. In No. 32, the maximum circumscribed circle diameter of the alumina particles in the sintered body was no. In No. 33, the maximum circumscribed circle diameter and the average particle diameter are increased.

No. 34 and 35 are examples in which polycrystalline alumina particles are used as a raw material and the sintering temperature exceeds the upper limit of the present invention, and the maximum circumscribed circle diameter and average particle diameter of the alumina particles in the sintered body increase. I have.

No. Nos. 36 to 38 are examples using polycrystalline alumina particles as raw materials. In No. 36, the relative density decreased. In No. 37, the maximum circumscribed circle diameter of the alumina particles in the sintered body was No. In No. 38, the maximum circumscribed circle diameter and the average particle diameter are increased.

No. 39 and 40 are examples in which polycrystalline alumina particles are used as a raw material and the sintering temperature exceeds the upper limit of the present invention, and the maximum circumscribed circle diameter and average particle diameter of the alumina particles in the sintered body are increased. I have.

Next, the results of the alumina ceramics product obtained by the HIP sintering are shown in Tables 2 and 3.

[0048]

[Table 2]

[0049]

[Table 3]

In Table 2, No. 41-49, 53-61, 6
Nos. 5 to 73, 77 to 85, and No. 5 in Table 3. 89-9
The alumina ceramic products of 1,93-95,97-99,101-103 are examples satisfying the requirements of the present invention.

On the other hand, in Table 2, 50-52,6
2 to 64, 74 to 76, 86 to 88, and N in Table 3
o. The alumina ceramic products of 92, 96, 100 and 104 are all comparative examples in which the HIP sintering temperature exceeds the upper limit of the present invention, and the maximum circumscribed circle diameter and average particle diameter of alumina particles in the sintered body are increased. ing.

Alumina ceramic products having the relative density, maximum circumscribed circle diameter and average particle diameter shown in Table 4 were ground with a # 2000-8000 grindstone,
The surface roughness Ra after lapping with a μm diamond slurry was measured. 0.01 μmRa or less was regarded as acceptable. Table 4 shows the results.

[0053]

[Table 4]

In Table 4, No. The alumina ceramic products of Nos. 105 to 109 are examples satisfying the requirements of the present invention and have good surface roughness.

On the other hand, in Table 4, No. No. 110 is a comparative example in which the relative density is lower than the lower limit of the invention. The alumina ceramic products 111 and 112 are comparative examples in which the maximum circumscribed circle diameter of alumina particles on the surface exceeds the upper limit of the present invention, but none of them has improved surface roughness.

[0056]

The alumina ceramic for a sliding portion and the method for producing the same according to the present invention are configured as described above, and specify the relative density of the product, the maximum circumscribed circle diameter and the average particle size of the alumina particles on the product surface. As a result, it has become possible to provide uniformly fine and dense alumina ceramic products for sliding parts. According to the present invention, in an alumina ceramic product for a sliding portion, an extremely good surface roughness of 0.01 μm Ra or less is achieved. Even when used for sockets, especially for head caps and acetabular sockets of artificial hip joints, it is possible to provide a good product with very little generation of wear powder due to sliding.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Katsuhiko Maehara, 1-3-1 Wakihamacho, Chuo-ku, Kobe Kobe Steel, Ltd. Kobe Head Office (72) Inventor Tomiharu Matsushita 1-chome, Wakihamacho, Chuo-ku, Kobe No. 3-18 Kobe Steel Ltd. Kobe Head Office F-term (reference) 4C097 AA03 AA05 AA06 BB01 CC01 DD06 MM04 SC03 SC05 4G030 AA07 AA36 BA18 BA35 CA04 GA01 GA11 GA15 GA27 GA29

Claims (9)

[Claims] (1) a purity of 99.9% or more and a relative density of 99%;
% Or more and 5,000 using a scanning electron microscope.
Observation field 2 of 20 μm × 15 μm of the sintered body observed at × 2
An alumina ceramic product for a sliding part, wherein the maximum value of the maximum circumscribed circle diameter of the alumina particles in 0 field of view is 5 μm or less, and the average particle diameter is 1.4 μm or less. 2. The alumina ceramic product for a sliding portion according to claim 1, wherein the alumina ceramic product is used for a sliding portion receiving a load. 3. The alumina ceramic product for a sliding part according to claim 1, which is used for a head of an artificial joint. 4. The alumina ceramic product for a sliding part according to claim 1, which is used for a head of an artificial hip joint. 5. The alumina ceramic product for a sliding portion according to claim 1, which is used for a sliding portion of an acetabular socket of an artificial joint. 6. The alumina ceramic product for a sliding part according to claim 1, which is used for a sliding part of an acetabular socket of an artificial hip joint. 7. The method according to claim 1, wherein the single-crystal alumina particles are used as a raw material, MgO is added as a sintering aid in an amount of less than 1000 ppm (not including 0 ppm), and sintering is performed at 1250 to 1590 ° C. The method for producing an alumina ceramic product for a sliding portion according to any one of the above. 8. The alumina for a sliding portion according to claim 1, wherein the alumina is sintered at 1250 to 1590 ° C. and then hot isostatically pressed at 1200 to 1550 ° C. Manufacturing method of ceramic products. 9. A method for producing an alumina ceramic product for a sliding portion according to any one of claims 3 to 6, wherein
The method according to claim 7, wherein a single-crystal alumina particle is used as a raw material.