JPH09193433A - Protective film in heating resistor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the dielectric breakdown caused by static electricity by holding the abrasion resistance and surface smoothness of a protective film by providing heating resistors and the protective film composed of a specific amt. of a mixture of glass and a fine powder of antimony oxide on a heat- resistant insulating substrate. SOLUTION: Heating resistors are formed on the upper surface of a heat- resistant insulating substrate and a protective film coated with a material obtained by mixing a fine powder of antimony oxide with glass in a wt. ratio of 12.5-25% is provided on the heating resistors. As antimony oxide (ATO), a fine powder with specific resistance ρ of 1-10(Ω.cm) and a particle size of 300Åis used and an ATO dispersant with viscosity of 100cps is prepared by adding a thinner being a main component and ethyl cellulose or the like to the fine powder and mixing all of them. A proper amt. of this dispersant is mixed with glass paste containing PbO or the like and a surfactant is added to the resulting mixture to prepare a compsn. with viscosity of 10000cps and this compsn. is applied to the insulating substrate in a film form and baked at about 800 deg.C to form the protective film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating resistor in a thermal head used for printing in a facsimile or the like, or a heating resistor in a heating body used as a heater in a toner fixing portion of a copying machine. The present invention relates to an improvement of a protective film for a heating resistor such as the above.

[0002]

2. Description of the Related Art Generally, as shown in FIGS. 1 and 2, a thermal head 1 has a line-shaped heating resistor 3 for printing on the upper surface of a heat-resistant insulating substrate 2 made of ceramic or the like. The conductor pattern and the conductor pattern are formed in a line shape, and the protective film 4 is formed so as to cover at least the heating resistor 3. Reference numeral 5 is a driving IC for the heating resistor 3, and reference numeral 6 is a protective resin for the driving IC 6.

As shown in FIGS. 3 and 4, the heating element 7 has a heating resistor 9 formed in a strip shape on the upper surface of a heat-resistant insulating substrate 8 made of ceramic or the like, and a protective film 10 is provided on the heating resistor. 9 is formed so as to cover 9.
Reference numeral 11 is a terminal electrode for connection to both ends of the heating resistor 9. In the thermal head 1 and the heating body 7, a protective film 4 covering the heating resistors 3 and 9 thereof.
Since the recording paper or the like is rubbed against the protective films 4 and 10 while being pressed against the protective films 4 and 10, heat resistance and high electrical insulation with respect to the heating resistors 4 and 10 are achieved.
High abrasion resistance for recording paper is required.

Therefore, conventionally, glass is used as the material of the protective films 4 and 10.

[0005]

By the way, in general, the glass has heat resistance and, in addition, its surface is smooth, so that the glass is used as a protective film 4 for the heating resistors 3, 9. When used as No. 10, there is an advantage that scratches on the recording paper and the like can be reduced.

On the other hand, however, the glass has an extremely high electrical insulating property such that the specific resistance ρ is about 10 ¹² (Ω · cm) or more. Therefore, this glass is used as the heating resistor 3, When used as the protective films 4 and 10 for 9, the static electricity generated by rubbing the protective films 4 and 10 made of glass against the protective films 4 and 10 is charged as it is. There is a problem that the protective films 4 and 10 cause dielectric breakdown due to static electricity.

In particular, dielectric breakdown of the protective films 4 and 10 due to static electricity frequently occurs in high-speed printing type thermal heads. According to the present invention, when glass is used as a material of a protective film for a heating resistor, dielectric breakdown due to static electricity occurs, and the abrasion resistance of the protective film and the smoothness of the surface of the protective film are maintained. Under the circumstances, it is a technical issue to ensure that the reduction can be achieved.

[0008]

Means for Solving the Problems Even when glass is used as a material for a protective film, the present inventor mixes glass with conductive antimony oxide (ATO) fine powder to Its specific resistance ρ is 10 ⁹ (Ω
.Cm) or less, the present invention has been completed, paying attention to the fact that static electricity charging can be avoided under the condition that the electrical insulation with respect to the heating resistor is secured.

That is, according to the present invention, "a heat-resistant resistor and a protective film covering the heat-resistant resistor are formed on the upper surface of a heat-resistant insulating substrate, and the protective film is made of glass and is made of antimony oxide (ATO). 12.5 by weight of fine powder
-25% mixed material is used. ".

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In general, antimony oxide (ATO) of the chemical formula SnO ₂ (Sb) is about 1 to 10 (Ω ·
The specific resistance of the glass can be reduced by mixing this fine powder of antimony oxide (ATO) with the glass.

However, this antimony oxide (AT
The surface of the glass becomes rough due to the mixing of the fine powder of (O),
It is expected that the risk of scratching the recording paper will increase. Therefore, the present inventor forms a protective film on the surface of the insulating substrate using glass mixed with the fine powder of antimony oxide (ATO), and the specific resistance of the protective film and the surface roughness of the protective film. (Ra) and the Vickers hardness of the protective film, an experiment was conducted with various mixing ratios of antimony oxide (ATO) to glass, and the results were as shown in FIGS.

The mixing of fine powder of antimony oxide (ATO) with the glass and the formation of the protective film were carried out in the following manner. That is, as antimony oxide (ATO), the specific resistance ρ is 1 to 10 (Ω · c
In step m), a fine powder having a particle size of 300Å is used. To this, an ATO dispersant having a viscosity of 100 cps is obtained by mechanically adding thinner to the main component and adding ethyl cellulose and the like. Appropriate amount of PbO, SiO
₂ and Al ₂ O ₃ etc. are added to the glass paste as a main component and mixed, then a surfactant and a sintering aid, etc. are added, and the viscosity is adjusted to 10,000 cps by adding thinner, and this is added. A protective film was formed by applying a film having a thickness of 10 μm on the surface of the insulating substrate and baking the film at a temperature of about 800 ° C.

As is clear from FIGS. 5 to 7 showing the results of the above experiment, antimony oxide (A
By mixing 12.5% or more by weight of fine powder of (TO), the specific resistance of the protective film can be 10 ⁹ (Ω · cm) or less, and the Vickers hardness of the protective film It was possible to improve even when it was formed only with glass.

However, when the mixing ratio of the fine powder of antimony oxide (ATO) with respect to glass exceeds 30%, the surface roughness of the protective film becomes 0.4 (μm) or more, and the recording paper has a rough surface. The recording paper was scratched when it was rubbed, and the transparency of the protective film was also significantly reduced, resulting in an almost opaque state. Therefore, by setting the mixing ratio of the fine powder of antimony oxide (ATO) to the glass in a weight ratio of 12.5 to 25% (particularly preferably 15 to 20%), the surface roughness of the protective film becomes relatively rough. It was found that the specific resistance in the protection can be made 10 ⁹ (Ω · cm) or less and the Vickers hardness in the protective film can be improved as compared with the conventional case under the condition that no protection occurs.

[0015]

As described above, the glass as the material of the protective film for the heating resistor is mixed with 12.5 to 25% by weight of fine powder of antimony oxide (ATO) to form a protective film. In the condition that the surface roughness in the is not so rough, the specific resistance in protection is set to 1
Since the Vickers hardness of the protective film is less than 0 ⁹ (Ω · cm) and can be improved as compared with the conventional case, the occurrence of dielectric breakdown due to static electricity in the protective film against the heat-generating resistor is prevented. While maintaining the above condition, there is an effect that it can be surely reduced and that the abrasion resistance of the protective film can be improved.

[Brief description of the drawings]

FIG. 1 is a perspective view of a thermal head.

FIG. 2 is an enlarged sectional view taken along line II-II of FIG.

FIG. 3 is a perspective view of a heating body.

FIG. 4 is an enlarged sectional view taken along line IV-IV of FIG. 3;

FIG. 5 is a diagram showing the relationship between the mixing ratio of ATO to glass and the specific resistance of a protective film.

FIG. 6 is a diagram showing the relationship between the mixing ratio of ATO to glass and the surface roughness of a protective film.

FIG. 7 is a diagram showing a relationship between a mixing ratio of ATO to glass and Vickers hardness of a protective film.

[Explanation of symbols]

 1 Thermal Head 2 Insulating Substrate 3 Heating Resistor 4 Protective Film 7 Heating Body 8 Insulating Substrate 9 Heating Resistor 10 Protective Film

Claims (1)

[Claims] 1. A heat-resistant insulating substrate, wherein a heating resistor and a protective film covering the heating resistor are formed on the upper surface of the substrate.
The protective film is formed on glass by using antimony oxide (AT
A protective film in a heating resistor, characterized in that it is formed of a material in which 12.5 to 25% by weight of fine powder of O) is mixed.