JPH01252575A - Dielectric porcelain material - Google Patents

Abstract

PURPOSE:To provide fine and homogeneous crystal grains and contrive both improvement in cutting properties and reduction in frictional coefficient, by adding MgO and Al2O3 to a CaBiO-TiO2 based dielectric porcelain material containing ZnO added thereto to provide a specific composition. CONSTITUTION:A dielectric porcelain material obtained by adding 0.5-7.0 pts.wt. ZnO, 0.5-5 pts.wt. MgO an/or 0.5-15 pts.wt. Al2O3 to 100 pts.wt. basic composition expressed by the formula (x is 40<=x<=85 by composition mol% and y is 0.005<=y<=0.6 by composition molar ratio) and calcining the resultant mixture. In this case, fine and uniform crystal grains are contrived by the adding the MgO. If the amount of the added MgO is 40.5 pt.wt., such effects are insufficient. If the amount exceeds 5 pts.wt., pores are conversely increased to deteriorate processability. If the Al2O3 is added, protruding parts are formed on the surface of the dielectric porcelain material to provide point contact, resulting in reduction in friction. Accordingly, the amount of the added Al2O3 is preferably >=0.5 pt.wt. If the amount is too large, the material is excessively hardened to deteriorate workability. As a result, the amount is preferably <=15 pts.wt. for practical use.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a dielectric ceramic material used as a guard material or a substrate material for a magnetic head installed in, for example, a video tape recorder, a micro-floppy disk drive device, or the like.

[Conventional technology]

Generally, a magnetic head installed in a magnetic recording medium drive device such as a video tape recorder or a micro-floppy disk drive has a non-magnetic core sandwiching the magnetic core portion, which forms part of the facing surface of the magnetic recording medium. guard material is arranged.

As such a guard material, conventional Ca0-Tie is used.

Aj2. type dielectric ceramic materials are often used, and Aj2. Si, Ca, Mg.

Oxides such as Sn, Zr, Ba, and Sr are added.

However, in order to create dielectric ceramic materials to which these oxides are added, high firing temperatures are required, and the pores cannot be made sufficiently small. In order to make the pores finer, special treatment such as so-called HIP treatment (hot isostatic pressing) is required, which increases manufacturing costs.

As a technique to solve these drawbacks, the applicant has
Previously, in JP-A No. 60-231463, Ca
We have proposed a dielectric ceramic material in which a part of Ca in a TiOz-based dielectric ceramic material is replaced with Bi and ZnO is added.

According to this system, a dielectric ceramic material with few pores can be obtained by a normal firing method without special treatment such as HIP, and the coefficient of thermal expansion can be selected from a wide range depending on the Bi content.

[Problems to be Solved by the Invention] However, the above-mentioned dielectric porcelain materials have poor grinding properties, causing chipping during the grinding process, and causing considerable wear and tear on the grinding wheel. There is. This is thought to be because some of the crystal grains in the dielectric ceramic material become large and the fibers are non-uniform.

Alternatively, the friction is insufficient, and the large friction causes problems such as damage to the medium and conversely damage to the head.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide a dielectric ceramic material in which crystal grains are made finer and more uniform, and which has excellent grindability.

A further object of the present invention is to provide a dielectric ceramic material that has a small coefficient of friction and does not damage magnetic recording media, magnetic heads, etc.

[Means to solve the problem]

As a result of intensive studies to achieve the above objectives, the present inventors found that addition of MgO is effective in making crystal grains finer and more uniform, and addition of A1.03 is effective in reducing the coefficient of friction. We have come to the conclusion that this is the case.

The dielectric ceramic material according to the present invention has been completed based on the above-mentioned knowledge, and has the general formula % (% formula %) (where X represents the composition in mol%, 40≦x≦85, and y represents the composition as a molar ratio and satisfies 0.005≦y≦0.6.
．． 5 to 760 parts by weight of ZnO is added, and an additional 0.5
~5 parts by weight of MgO and/or 0.5 to 15 parts by weight of 1
! ,0. is added and fired.

Here, the composition of the basic composition and the amount of ZnO added are determined from the same viewpoint as the dielectric ceramic material described in JP-A-60-231463.

That is, the dielectric ceramic material serving as the basic composition is Ca-
Bi is added to a TiCh-based dielectric ceramic material. The thermal expansion coefficient α of this dielectric ceramic material basically changes depending on the molar ratio of Ca and Ti, but it also changes with the molar ratio of Ca and Ti.
It is also controlled by the amount of addition. Therefore, Ti and B
If the content of i is appropriately selected within the above range, the thermal expansion coefficient α can be varied over a wide range of 80×10-'/"C-120X10-'/'C. It is also effective in lowering the temperature.

The amount of ZnO added is determined for the purpose of reducing the size of pores in the dielectric ceramic material. If the amount added is less than 0.5 parts by weight, the pores cannot be made sufficiently fine. If the amount exceeds 7.0 parts by weight, it will lead to a decrease in flexural strength and the like.

On the other hand, MgO and A f , 0. is an additive unique to the present invention, and by adding MgO in particular, crystal grains can be made finer and more uniform. In this case, if the amount of MgO added is less than 0.5 parts by weight, the effect of making crystal grains finer and more uniform will be insufficient. On the other hand, if the amount added exceeds 5 parts by weight, the number of pores will increase and the processability will deteriorate.

Also, Al! Os is added to lower the effective coefficient of friction, and A j! By adding zO3, convex portions are formed on the surface of the dielectric ceramic material, resulting in point contact, which reduces friction. The amount of Altos added is preferably 0.5 parts by weight or more based on 100 parts by weight of the basic composition from the viewpoint of friction reduction effect, but if it is too large, it will become too hard (too much, resulting in poor workability). (Therefore, it is practically desirable that the amount be 15 parts by weight or less.

Of course, these MgO and A1.03 may be added at the same time, and in this case, both the refinement and uniformity of crystal grains and the reduction of the coefficient of friction are achieved.

In order to create the dielectric ceramic material as described above, Ca
, Bi, Ti, Zn, Mg, Al oxides, carbonates, etc. are mixed at a predetermined molar ratio or parts by weight, and 750 to 90
After calcination at 0°C, the temperature is 1200~1350 after the molding process.
Main firing may be performed at °C.

[Function] By adding both ZnO and MgO to the CaB10-Ti0□-based dielectric ceramic material, it is possible to do so without causing a change in the thermal expansion coefficient α or an increase in pores compared to when only ZnO is added. The crystal grains become finer and the fibers become uniform.

On the other hand, AI! When 20z is added, as schematically shown in Fig. 1, a precipitated phase (1) containing CaTiO3 as the main component and a precipitated phase (2) containing Tie as the main component form in the parent phase. to Al□0. There is a precipitated phase (3) containing as the main component. Here, Al2O. Since the precipitated phase (3) whose main component is harder than the parent phase, it is finished in a more convex state than the parent phase due to the difference in polishing method. When considering contact with a magnetic recording medium, it can be said that if the guard material has a convex part, there will be point contact rather than if it is flat, and the friction will be lower than if it is in full contact. The convex state was confirmed by scanning electron microscopy (SEM), and each phase was identified by EPMA.

〔Example〕

The present invention will be explained below using specific examples.

1 to 0 First, the raw materials T i OH, Ca COs, B
i 2oz.

Predetermined amounts of ZnO and MgO were weighed and wet mixed in a ball mill. Each mixture thus obtained was dried, then ground, and calcined at 750 to 900°C. After calcination, each mixture was pulverized again and press-molded at a pressure of 1.0 to 2.0 tons/cm, and then main calcination was performed at 1200 to 1350°C in an oxygen atmosphere to form each dielectric material. Created porcelain material.

The thermal expansion coefficient, crystal grain size, and workability of each dielectric M1 material obtained were evaluated. Thermal expansion coefficient is 50-4
Measurements were made in a temperature range of 00°C. Regarding the crystal grain size, each dielectric ceramic material was polished and etched and observed under a microscope to determine the maximum and minimum grain sizes.
The average particle size was also calculated.

Regarding workability, we visually observed the occurrence of chipping when cutting each dielectric ceramic material with a grinding machine, and determined that the state of the dielectric ceramic material without MgO added was "normal". Dielectric ceramic materials with less chipping were rated as "good."

The composition and evaluation results of the dielectric ceramic materials in each example are summarized in Table 1. In addition, in the composition of the dielectric ceramic material,
The amounts of ZnO and MgO added were determined based on the basic composition [X mol% of Tie and (100-x) mol% of (Cal-1,5
yBf y) This is the amount (parts by weight) added to 3100 parts by weight of the mixture with O.

As a comparison with the above-mentioned examples, a dielectric ceramic material to which no MgO was added was prepared, and various evaluations were conducted in the same manner. The composition of the dielectric ceramic material and the evaluation results are also shown in Table 1.

Comparison 1 As a comparison with the above example, the amount of MgO added was 6
A dielectric ceramic material whose weight part was larger than the range defined by the present invention was prepared, and each evaluation was conducted in the same manner. dielectric porcelain material,
The evaluation results are also shown in Table 1.

(Left below) First, a comparison example! , and each of the dielectric ceramic materials created in Examples 1 to 6, it is found that as the amount of MgO added increases, the distribution width of the crystal grain size becomes narrower.
There is also a tendency for the average particle size to become smaller. Processability is Mg
All cases where O is added are better. Furthermore, the coefficient of thermal expansion α remains unchanged.

The change in the coefficient of thermal expansion α is not caused by the addition of MgO, but by Ti
dominated by O, t It X or Bi substitution 1y. This means that the amount of MgO added should be 3 parts by weight lB1
Example 4 corresponding to the case where the molar ratio of 1y converted to 1y was fixed at 0.05. Mutual comparison of Example 8 and Example 9, or the amount of MgO added was 3 parts by weight.

This is clear from a mutual comparison of Example 4 and Example 7, which correspond to the case where the amount added was fixed at 55 mol%. As the TiO□ amount X or the Bi substitution 1y increases, the thermal expansion coefficient α decreases.

Furthermore, from a comparison between Example 4 and Example 10, as long as the amount of ZnO added varies within the range limited in the present invention,
It can be seen that this does not affect the physical properties of the dielectric ceramic material obtained.

Furthermore, in Comparative Example 2 in which MgO was added in an amount greater than the range defined in the present invention, the thermal expansion coefficient α did not change and the crystal grain size was sufficiently small, but it was found that the workability was not improved.

Note that similar results were obtained even when MgC (h) was added instead of MgO.

Actual difference number → 0 sugars First, the raw materials Ti0t, CaCO5, BizO:
+.

Predetermined amounts of ZnO and A j2203 were weighed and wet mixed in a ball mill. Each mixture thus obtained was dried, then ground, and calcined at 750 to 900°C. Each mixture after calcination is ground again and the powder is 1.0~
2. After press forming at a pressure of 0 tons/cm'', main firing was performed at 1200 to 1350°C in an oxygen atmosphere to create each dielectric ceramic material.

Each of the obtained dielectric ceramic materials was evaluated for thermal expansion coefficient and friction.

・Furthermore, friction is due to contact start-stop characteristics (
C3S characteristics). That is, after grinding and mirror-finishing the prepared dielectric porcelain material, it was cut into square blocks of 3 sl x 3 m and 2 mm thick, as shown in Fig. 2.
This block (11) was placed at a constant distance from the center of the magnetic disk (12). Then, the magnetic disk (12) was rotationally driven by the rotation drive system (13) in the pattern shown in FIG. 3, and the maximum friction coefficient at this time was determined by the friction coefficient detection system (14). Repeat this 1000 times,
A comparison was made using the 1000th friction coefficient. The magnetic disk used was a 3.5-inch disk on which a magnetic layer was formed by sputtering and a liquid lubricant was applied.
The coefficient of friction of a dielectric ceramic material to which tOx is not added (Comparative Example 3 described later) is assumed to be 1, and is expressed as a relative value.

The composition and evaluation results of the dielectric ceramic materials in each example are summarized in Table 2. In addition, in the composition of the dielectric ceramic material,
The amounts of ZnO, MgO and Al z Ox added are again determined based on the basic composition [X mol % of T i O2 and (IOQ-
x) The amount (parts by weight) added to 3100 parts by weight of a mixture with mol% (Ca +-+, syB i y)0.

Comparison H Main As a comparison with the above-mentioned example, a dielectric ceramic material without the addition of Affi,o was prepared, and each evaluation was conducted in the same manner. The composition of the dielectric ceramic material and the evaluation results are also shown in Table 2.

Comparative Coal Soil As a comparison with the above-mentioned examples, a dielectric ceramic material was prepared in which the amount of Alzos added was 20 parts by weight, which was larger than the range defined by the present invention, and the evaluations were conducted in the same manner. The dielectric ceramic materials and evaluation results are also shown in Table 2.

(Left below) As is clear from Table 2, A j! zOs
Friction tends to decrease when is added.

In addition, Aj2□0. Comparative Example 4, in which 20 parts by weight of was added, showed good results in terms of friction, but was very hard and had poor workability.

〔Effect of the invention〕

As is clear from the above explanation, in the dielectric ceramic material according to the present invention, MgO is added in addition to ZnO to the CaBtO-TiO It becomes possible to improve the processability by making it uniform and uniform. Such dielectric porcelain materials are
Since chipping during grinding and falling off of crystal grains during lapping are unlikely to occur, it is possible to manufacture magnetic heads with high yield.

Furthermore, in the dielectric ceramic material according to the present invention, A
Since a predetermined amount of l z Os is added, it is possible to provide a dielectric ceramic material having an appropriate coefficient of thermal expansion and coefficient of friction as desired. Therefore, if the dielectric ceramic material of the present invention is used, for example, as a guard material for a magnetic head, the torque can be kept low and damage to the magnetic recording medium and the magnetic head can be prevented.

Of course, if both MgO and A It z Os are added, both workability and friction can be improved, and the utility value thereof is extremely high.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing the crystal phase when AffijO is added, Fig. 2 is a schematic diagram showing the schematic configuration of an evaluation device for evaluating friction, and Fig. 3 is a schematic diagram showing the structure of an evaluation device for evaluating friction. It is a characteristic diagram showing a C3S cycle. Patent applicant Sony Corporation representative Patent attorney Akira Koike (and 2 others)

Claims (1)

[Claims] General formula {(Ca_1_-_1_._5_yBi_y)O
}_1_0_0_-_x(TiO_2)_x (however,
x represents the composition in mol% and satisfies 40≦x≦85, and y represents the composition in molar ratio and satisfies 0.005≦y≦0.6. ) 0.5-7.
0 parts by weight of ZnO is added, furthermore 0.5-5 parts by weight of MgO and/or 0.5-15 parts by weight of Al_2O_
3 is added and fired.