JPH04247601A - Ceramic resistor and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a ceramic resistor with high breakdown voltage, especially a ceramic resistor for suppressing electron gun discharge and a method for fabricating the same. CONSTITUTION:A ceramic resistor comprises a mixture containing insulating inorganic material powder as an aggregate, carbon powder as a conductive material and clay as a binder, which is molded and baked with an insulating layer not containing carbon formed on a surface, wherein apparent porosity is 15% or less. The ceramic resistor can be fabricated by molding and baking a mixture containing 55 to 56wt. part of insulating inorganic material powder whose average particle diameter is 1mum or less, 5 to 10wt. part of carbon powder and 35 to 45wt. part of clay.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic resistor and a method for manufacturing the same.

0002

2. Description of the Related Art Conventionally, abnormal discharge between the grids of an electron gun installed in a cathode ray tube has caused serious problems, such as adversely affecting images and causing destruction or malfunction of various semiconductors. One way to suppress this abnormal discharge current is to replace the lead wire between the grids of the electron gun in the cathode ray tube with a resistor, and have this resistor absorb surge energy (energy generated by overvoltage). The use of a ceramic resistor as a resistor for suppressing discharge in this electron gun is being considered.

Ceramic resistors are manufactured by mixing, molding, and firing a powder of an insulating inorganic material as an aggregate, carbon powder as a conductive material, and clay as a binding material. By firing in an atmosphere containing an oxidizing gas, such as the air, carbon near the surface of the resistor is oxidized and disappears, forming an insulating layer near the surface, and a double layer consisting of this insulating layer and an internal resistance layer containing carbon. It becomes the resistor of the structure. This resistor has an insulating layer and a resistance layer integrally formed, and has excellent insulation resistance and heat resistance. However, because the conventional ceramic resistor for suppressing electron gun discharge is manufactured using aggregate with large particle size, it is a porous body with an apparent porosity of about 20% in the insulating layer, resulting in dielectric breakdown. There is a problem with low voltage. Therefore, especially in the knocking treatment performed in the final step of the cathode ray tube manufacturing process, cracks occur due to dielectric breakdown of the insulating layer, which causes defects due to dust inside the cathode ray tube.

0004

SUMMARY OF THE INVENTION An object of the present invention is to provide a ceramic resistor having a high dielectric breakdown voltage, particularly a ceramic resistor for suppressing electron gun discharge. Another object of the present invention is to provide a method for manufacturing the ceramic resistor having a high dielectric breakdown voltage.

[0005]

[Means for Solving the Problems] The object of the present invention is to form and fire a mixture containing insulating inorganic material powder as an aggregate, carbon powder as a conductive material, and clay as a binding material, and to provide an insulating material that does not contain carbon on the surface. This is achieved by a layered ceramic resistor characterized by a porosity of 15% or less.

The ceramic resistor of the present invention can be manufactured, for example, by using an insulating inorganic material powder having an average particle size of 1 μm or less. Examples of insulating inorganic materials used in the present invention include alumina, silica, mullite, steatite, forsterite, cordierite, zircon, beryllia, boron nitride, aluminum nitride, and the like. The insulating inorganic material powder used in the present invention has an average particle size (particle size at 50% by weight of cumulative distribution) of 1 μm.
m or less. Preferably, the cumulative distribution is 90% by weight
The particle size is 3 μm or less, more preferably 2 μm.
The following are suitable.

The ceramic resistor of the present invention is made of aggregate having an average particle diameter of 1 μm or less, such as alumina or mullite 55-55.
Carbon powder, preferably 5 to 10 parts by weight, is mixed with 100 parts by weight of a mixture of 65 parts by weight and 35 to 45 parts by weight of clay as a binder (preferably a mixture of calcined clay and ultra-refined clay), and For example, it is extruded into a rod shape with a diameter of about 2 to 5 mm, and fired in a tunnel furnace or the like at a high temperature of 1000°C or higher, preferably about 1200°C, for about 10 minutes to remove the carbon near the surface. It can be manufactured by oxidizing the material, cutting it into a predetermined length, and attaching an electrode. The resistance value of the ceramic resistor can be set to a desired value by appropriately adjusting the amount of carbon powder, the shape of the resistor, firing time, firing temperature, etc.

The ceramic resistor of the present invention is particularly advantageously used for suppressing discharge of an electron gun in a cathode ray tube.

[0009]

[Examples] The present invention will be explained in more detail with reference to Examples below. Example 1 60 parts by weight of alumina (average particle size 0.2 μm), 40 parts by weight of clay raw material (a mixture of calcined clay and ultra-refined clay), and 6.5 parts by weight of carbon black were extruded into a rod shape with a diameter of 2.5 mm. Shaped, in tunnel furnace, under atmospheric atmosphere, 1
After firing at 200° C. for about 10 minutes, it was cut into a length of 20.0 mm to produce a ceramic resistor with an insulating layer thickness of about 0.5 mm. Example 2 A ceramic resistor was produced in the same manner as in Example 1 except that alumina having an average particle size of 0.3 μm was used. Example 3 A ceramic resistor was produced in the same manner as in Example 1 except that alumina having an average particle size of 0.4 μm was used. Example 4 A ceramic resistor was produced in the same manner as in Example 1 except that alumina having an average particle size of 1.0 μm was used. Example 5 In Example 1, 55 parts by weight of alumina and 4 parts by weight of clay raw material
A ceramic resistor was produced in the same manner except that 5 parts by weight was used. Example 6 In Example 1, 65 parts by weight of alumina and 3 parts of clay raw material
A ceramic resistor was produced in the same manner except that 5 parts by weight was used. Comparative Example 60 parts by weight of alumina (average particle size 4.6 μm), 40 parts by weight of clay raw material (a mixture of calcined clay and ultra-refined clay) and 3.3 parts by weight of carbon black were thoroughly mixed and kneaded to give a diameter of 2.5 mm. extruded into a rod shape, placed in a tunnel furnace,
After baking at 1200℃ for about 10 minutes in an air atmosphere, 2
Cut into a length of 0.0 mm, and the thickness of the insulating layer is approximately 0.5 mm.
A ceramic resistor was fabricated.

The specific resistance, apparent porosity, and dielectric breakdown voltage of the ceramic resistors produced in Examples and Comparative Examples were measured. The method for measuring dielectric breakdown voltage is as follows. Equipment: Diode curve tracer Model
5830, Max 30KV (manufactured by Kikusui Electronics Co., Ltd.), Power supply: Half-wave rectification (50Hz), Surrounding medium: Fluorinert liquid (inert liquid, FC-77: Sumitomo 3M)
Also, the apparent porosity AP was measured by the Archimedes method.

[0011] AP (%) = (W3 - W1)/ (W
3-W2) × 100W1: Dry weight W2: Weight in water (boiled in clean water for 3 hours, cooled to room temperature, hung in water and weighed) W3: Saturated weight (after measuring the weight in water, remove the sample from the water) Excess water on the surface was wiped off and weighed.) The specific resistance value was calculated from the cross-sectional area of the conductive layer.

The results are shown in the following table. The dielectric breakdown voltage is 10
This is the average value of multiple measurements. ──────────────────────────
────────── Example Example Example Example Example Example Example Comparative example 1
2 3 4
5 6 ──────
──────────────────────────
──── Average particle size of alumina 0.2 0.3
0.4 1.0 0.2
0.2 4.6 (μm) ──────────────────────────
────────── Insulating layer thickness 0.49 0.5
0 0.49 0.49 0.49
0.51 0.48 (mm) ──────────────────────────
────────── Specific resistance value (Ωcm) 42.0 18.0
9.9 2.5 24.9
235.1 110.5 ──────────
──────────────────────────
Apparent porosity 1.6 4.4
6.3 12.0 1.5
1.8 21.9 (%) ──────────────────────────
────────── Dielectric breakdown voltage 24.8 20.5
19.2 18.8 23.7
25.5 18.7 (KV) ──────────────────────────
────────── Figure 1 shows the relationship between the average particle diameter and dielectric breakdown voltage of alumina used in Examples 1 to 4 and comparative examples.
FIG. 2 shows the relationship between the apparent porosity and dielectric breakdown voltage of the obtained ceramic resistor. From the table and FIG. 1, in order to obtain a higher dielectric breakdown voltage than conventional products, the average particle diameter of alumina must be 1.0 μm or less, preferably 0.5 μm or less.
It can be seen that it is necessary that the thickness be less than μm. Also,
It can be seen from the table and FIG. 2 that the apparent porosity of the ceramic resistor of the present invention is 15% or less, preferably 12% or less, and more preferably 8% or less.

[0013]

The ceramic resistor of the present invention has a high dielectric breakdown voltage and is particularly useful as a ceramic resistor for suppressing electron gun discharge.

[Brief explanation of the drawing]

FIG. 1 is a drawing showing the relationship between the average particle diameter of alumina and dielectric breakdown voltage.

FIG. 2 is a drawing showing the relationship between the apparent porosity and dielectric breakdown voltage of a ceramic resistor.

Claims (2)

[Claims] 1. A ceramic resistor in which a mixture containing insulating inorganic material powder as an aggregate, carbon powder as a conductive material, and clay as a binder is molded and fired to form an insulating layer that does not contain carbon on the surface, A ceramic resistor characterized by an apparent porosity of 15% or less. [Claim 2] Insulating inorganic material powder 55~ as aggregate
Molding a mixture containing 65 parts by weight, 5 to 10 parts by weight of carbon powder as a conductive material, and 35 to 45 parts by weight of clay as a binder.
2. A method for producing a ceramic resistor by firing to form an insulating layer that does not contain carbon on the surface, wherein the ceramic according to claim 1, wherein the insulating inorganic material powder has an average particle size of 1 μm or less. Method of manufacturing a resistor.