JPH01204761A - Thermal head substrate - Google Patents

Abstract

PURPOSE:To enable high precision high speed printing to be performed with small electric power, by a method wherein a glaze layer on an insulating substrate is formed by a polyimide resin layer and a porous silica layer formed thereon. CONSTITUTION:A glaze layer 12 formed on an alumina substrate 11 as an insulating substrate is composed of a polyimide resin layer 13 and a porous silica layer 14 formed thereon. Polyimide resin is comparatively efficient in heat resistance and has extremely small heat resistivity (by about one place lower than glass) and a characteristic of efficient heat insulation. Further, porous silica has a characteristic of efficient heat resistance. Then, when a heating element is formed directly on the glaze layer 12, heat generated instantaneously and locally in the heating element is transmitted not directly to the polyimide resin layer 13, but via the porous silica layer 14. Therefore, the polyimide resin layer 13 does not locally become high in temperature, and a phenomenon in which a heating resistor film and a thin film of a protective film or the like provided thereon are destroyed by gas produced from heat decomposition of the polyimide resin layer 13 can be eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a substrate for a thermal head used in, for example, facsimiles and printers.

[Conventional technology]

As a conventional thermal head substrate, for example, as shown in the cross-sectional view of FIG. 2, a glaze layer 2 as a heat insulating layer is directly provided on an alumina ceramic substrate 1.
There is one in which the glaze layer 2 is made of glass.

[Problem that the invention seeks to solve]

However, in recent years, there has been a strong demand for reliability, immediacy, labor-saving, etc., which are the basic requirements for communication systems. Performance that is possible is required. In order to achieve this kind of performance, it is necessary to have a thermal head structure that allows sufficient heat to be stored in the board when electricity is applied to the heat generating part, and then absorbs the heat sufficiently quickly into the board when the electricity is turned off. .

In conventional thermal head substrates, the thickness of the glaze layer is made sufficiently large to provide sufficient heat retention, and once heat is stored on the substrate, printing can be performed using a small amount of electric power. Something has been proposed to do so.

However, in this case, the temperature of the substrate does not decrease sufficiently quickly after the power to the heat generating part is turned off, so that the heat of the heat generating part is not absorbed quickly. This results in poor thermal separation,
There was a problem in terms of constant height 'M# fine printing and high speed printing where bleeding occurs between each pixel and tailing occurs during high speed printing. On the other hand, if an attempt was made to make the glaze layer thinner to improve its thermal response and enable high-definition and high-speed printing, a problem arose in that a large amount of electric power was required for printing.

That is, there are mutually contradictory demands that the glaze layer is preferably thicker from the viewpoint of improving thermal efficiency, and preferably thinner from the viewpoint of improving thermal response.

Therefore, measures were taken to solve the above problems.
This method is proposed in Japanese Patent No. 1-148640. This proposal involves attaching a porous glass body to a substrate, and provides a thermal head with excellent heat retention and thermal isolation properties, but manufacturing requires a thin porous glass body. Another problem was that the above difficulties increased manufacturing costs.

Therefore, the present invention has been made to solve the above-mentioned problems, and its purpose is to provide a substrate for a thermal head that can perform high-definition and high-speed printing with low power and at low cost. There is a particular thing.

[Means to solve the problem]

The thermal head substrate according to the present invention includes an insulating substrate and a glaze layer formed on the insulating substrate, and the glaze layer includes a polyimide resin layer and a porous resin layer formed on the polyimide resin layer. It is characterized by having a silica layer.

[For production]

In the present invention, the glaze layer on the insulating substrate is formed of a polyimide resin layer and a porous silica layer formed thereon.

The reason for using a polyimide resin layer for the glaze layer is that polyimide resin has relatively high heat resistance, and also has extremely low thermal conductivity (about an order of magnitude lower than glass), which has excellent heat retention properties. This is to have.

Further, the reason for forming the porous silica layer on the polyimide resin layer is to prevent the polyimide resin layer from thermally decomposing when the heating element is formed directly on the polyimide resin layer. In other words, the porous silica layer, which has excellent heat resistance, spreads the heat instantaneously generated by the heating element in a plane, disperses it over time, and transmits it to the polyimide resin layer, so that the polyimide resin layer can locally and instantaneously transmit the heat. functions to prevent high temperatures.

〔Example〕

The present invention will be explained below based on illustrated embodiments.

FIG. 1 is a sectional view showing an embodiment of a thermal head substrate according to the present invention. In the figure, 11 is an alumina substrate as an insulating substrate, 12 is a glaze layer formed on the alumina substrate 11, and this glaze layer 12 is composed of a polyimide resin layer 13 and a porous silica layer 14 formed thereon.
It is made up of. Polyimide resin has relatively excellent heat resistance, has extremely low thermal conductivity (about one order of magnitude lower than glass), and has excellent heat retention properties. On the other hand, porous silica has excellent heat resistance.

Therefore, in this embodiment, the heat-insulating function of the glaze layer 12 is performed by the polyimide resin layer 13, which has low thermal conductivity and excellent heat-retaining properties, and the heat-resistant function of the glaze layer 12 is supplemented by the porous silica layer 14, which has excellent heat resistance. It is configured as follows. That is, when the heating element is directly formed on the glaze layer 12, the heat generated instantaneously and locally by the heating element is transferred to the polyimide resin layer 13.
It is not directly transmitted to the silica layer 14, but is transmitted through the porous silica layer 14. While the heat that is instantaneously and locally generated is transmitted through the porous silica layer 14, it is spread in a plane and is transmitted in a temporally dispersed manner. Therefore, the polyimide resin layer 13 does not reach a high temperature locally, and the gas generated by thermally decomposing the polyimide resin layer 13 does not destroy the thin film layers such as the heating resistor film and the protective film provided thereon. This can be prevented from occurring.

Furthermore, since the glaze layer 12 of this embodiment has lower thermal conductivity than conventional glaze layers made of glass, it is possible to maintain the same heat retention even if the thickness is made thinner than that of conventional glaze layers. It is. Furthermore, since this thermal head substrate allows the glaze layer to be made thinner, the substrate 1
1, it becomes possible to quickly absorb heat and hasten the decrease in temperature of the heating element, and as a result, the thermal separation performance can be improved.

The thermal head substrate described above can be manufactured as follows. First, polyimide varnish is coated on the alumina substrate 11 by a spin coating method,
This is dried and fired to form a 10 μm thick polyimide resin layer 1.
form 3.

Next, a solution prepared by adding ammonia water to silicone arelecoxide is coated on the polyimide resin layer 13 by a day-lag coating method, and this is dried at 120° C. to form a porous silica layer 13 with a thickness of 0.8 μm. form. This process is one of the thin film forming methods called the sol-gel method, in which a solution containing silicon ethoxide and silicon nidramexide as main components, a catalyst such as HCJI or NH3, and an appropriate amount of water is used. A silica layer is formed by coating and drying. According to this method, very small pores on the order of several +A can be formed in the silica layer, resulting in a porous silica layer.

Incidentally, in the above embodiment, only the case where the alumina substrate 11 is used as the insulating substrate is explained, but the present invention is not limited thereto, and materials that maintain strength and heat resistance, such as A, llN, SiC, etc. A ceramic substrate such as the above, a metal substrate whose surface is insulated, a quartz substrate, or the like may be used.

Next, the performance of the thermal head substrate of this example will be explained. Here, the thermal head substrate of this example and a conventional glazed alumina substrate with a glass glaze layer (manufactured by Nippon Spark Plug Co., Ltd.) are used to construct a thermal head for each, and the power supply and print density (0 ,D,'
) was measured. Here, the substrate of this example has a glaze layer thickness of 20 μm, and the conventional glazed alumina substrate has a glass glaze layer thickness of 10 μm.
Tests were conducted on samples with a diameter of 0 μm. Also, the heating element size of the thermal head is 50x60μ
m rectangle, and the heating element is driven with a repetition period of 2n+se
c, 0.31115 (performed with a 3C width pulse, printed on thermal paper, and measured the density.

FIG. 3 is a characteristic curve diagram of applied power versus print density, but does not show the results of the above measurements. From the figure, it can be seen that the thermal head using the substrate of this example can print with higher density with lower power than the conventional one with a glaze layer thickness of 40 μm. This is considered to be because the glaze layer 12 of this example is made of a material that has better heat retention than a conventional glass glaze layer. Furthermore, by making the glaze layer of a material with excellent heat retention properties, it is possible to make the glaze layer thinner than conventional glaze layers and still have the same heat retention properties. By making the glaze layer 12 thinner, the heat absorption performance from the heating element to the substrate 11 can be improved, and the thermal isolation performance can be improved, so that good printing with less thermal compression is possible.

〔Effect of the invention〕

As explained above, the thermal head substrate of the present invention has excellent heat retention properties, so if a thermal head is constructed using this substrate, printing can be performed using less power than when using a conventional substrate. can do. In addition, since the glaze layer is made of a material with excellent heat retention, it is possible to make the glaze layer thinner, which improves heat absorption performance to the substrate, which improves thermal isolation. , thermal tailing can be reduced. Therefore, high-speed and high-definition printing is possible.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of the thermal head substrate according to the present invention, FIG. 2 is a sectional view of a conventional thermal head substrate, and FIG. 3 is a sectional view of the thermal head substrate of this embodiment and the conventional thermal head substrate. FIG. 3 is a characteristic curve diagram showing the relationship between power supply and print density of a thermal head configured using the thermal head substrate of FIG. 11... Alumina substrate (insulating substrate), 12... Glaze layer 13... Polyimide resin layer, 14... Porous silica layer. Patent Applicant: Oki Electric Industry Co., Ltd. Agent Patent Attorney 1) Iku 1-cho 1i-ko of “U?Sai Iku・” Figure 1 Example of Kasuri surface diagram Figure 2

Claims (1)

[Scope of Claims] An insulating substrate, and a glaze layer formed on the insulating substrate, wherein the glaze layer includes a polyimide resin layer and a porous silica layer formed on the polyimide resin layer. A thermal head substrate comprising: