JP2763404B2 - Thermal head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head having excellent corrosion resistance.

[0002]

2. Description of the Related Art In recent years, thermal heads have been widely used as thermal printers mounted on word processors, facsimile machines and the like.

[0003] As shown in FIG.
Reference numeral 1 denotes a heat storage layer 3 made of glass on a substrate 2 made of an electrically insulating material such as alumina, a resistance layer 4 made of tantalum nitride or the like, and a conductive layer 5a made of Cu, Al or the like. And 5b are sequentially laminated, and a protective layer 6 made of, for example, silicon nitride is further laminated by a thin film forming technique such as sputtering or vacuum deposition.

[0004]

However, in the protective layer 6 of such a thermal head 11, a large number of defective portions 9 including voids such as pinholes and cracks are generated. And contaminants such as moisture, chlorine ions, and sodium ions generated from the thermal paper 7 penetrate and come into contact with the conductive layers 5a and 5b to corrode them.

In order to prevent the above-described corrosion, a conventional thermal head 12 in which a resin layer 18 is laminated on a protective layer 6 as shown in FIG. 5 has been proposed (hereinafter, the same portions are denoted by the same reference numerals). ), As an example of such a thermal head 12, a fluorine-based coating agent (viscosity 19 cp)
s, a surface tension of 12 dyn · s / cm) is applied onto the protective layer 6 of the thermal head 11, and the solvent of the coating agent is evaporated to be cured, thereby producing a thermal head 12 having a resin layer 18 formed thereon. The following experiment was conducted to compare the durability with the thermal head 11.

Each of the thermal heads 11 and 12 is left in an environment of a temperature of 35 ° C. and a humidity of 85%, and is in a printing standby state (when the thermal paper 7 is brought into contact with the protective layer 6 and the driver IC driving voltage 5 V and the printing voltage 24 V are applied). Applied to each other, and print signal OF
F state), the initial destruction time (the time required until the ratio of the number of defective heating elements to the total number of heating elements reaches 0.1%) is about 20 hours by the thermal head 11. On the other hand, the life of the thermal head 12 was only slightly extended to about 30 hours.

Subsequently, a running test (continuous printing) of thermal heads 11 and 12 using a thermal paper having a high ion content (Na ⁺ 2000 ppm or more) (applied power: 0.2 W, applied cycle: 10.0 msec, applied time: 2. 0 msec), both showed corrosion failure after traveling about 10 km.

Therefore, when the thermal head 12 was examined in more detail, it was found that the coating agent was defective 9
It is confirmed that a large number of spaces 9a are formed in the protective layer 6 as a space 9a in which the opening is simply sealed without sufficiently filling the space 9a, and the space 9a has a fine diameter of 0.1 μm or less. Turned out to be something.

When such a thermal head 12 is mounted on a printer for printing, the resin layer 18 on the space 9a is printed.
The above-mentioned contaminants penetrate, reach the conductive layers 5a and 5b, and corrode them, resulting in a problem that white streak-like image defects occur in the obtained printed image.

The present invention has been developed to solve the above-mentioned problems, and an object of the present invention is to provide a thermal head which suppresses corrosion of a conductive layer by contaminants and has improved reliability.

[0011]

A thermal head according to the present invention is a thermal head in which a resistive layer is formed on an electrically insulating substrate, and a conductive layer and a protective layer are sequentially laminated on the resistive layer. Is less than 5 cps and surface tension is 20 dyn · s
/ Cm or less and the properties after curing are as follows: softening temperature 100 ° C or higher, thermal decomposition temperature 150 ° C or higher, temperature 25
A resin layer having a withstand voltage of 10 kv / mm or more in an environment of 35 ° C. and a humidity of 35% is provided on the protective layer.

[0012]

According to the present invention, the above conditions a) and
By applying a coating agent comprising b), the coating agent is filled to a depth that can prevent the transmission of the contaminant to a fine defect having a diameter of 0.1 μm or less, and the coating agent is subjected to the above conditions. By forming the resin layer by curing as described in c) to e), softening, thermal decomposition, and dielectric breakdown of the resin layer due to heat generated during traveling are prevented, and corrosion of the conductive layer due to contact with contaminants is prevented. Suppression improves the reliability of the thermal head.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below (the same reference numerals are used for the same parts as in the conventional example). As shown in FIG. 1, in the thermal head manufactured by the manufacturing method of the present invention, a heat storage layer 3 made of glass is formed on a substrate 2 made of an electrically insulating material such as alumina, and the heat storage layer 3 is made of tantalum nitride or the like. A resistive layer 4, a conductive layer 5a and 5b made of Cu, Al or the like, and a protective layer 6 made of silicon nitride or the like are sequentially laminated by a thin film forming technique such as sputtering and vacuum evaporation.
Further, a coating agent made of, for example, a fluorine-based resin is applied on the protective layer 6 to form a resin layer 8.
In addition, 1,1,2-trichloro-1,2,2,
FC-721 (trade name: 0.9 cps, trade name of Sumitomo 3M) containing 2-trifluoroethane as a solvent.
Surface tension of 12 dyn · s / cm) was used.

Subsequently, the coating agent is allowed to stand for about 2 minutes, and is allowed to penetrate into the defective portion 9 by capillary action.
To heat the coating agent for about 30 minutes,
The resin layer 8 is formed.

The resin layer 8 of the thermal head 1 manufactured as described above penetrates into a defect 9 having a diameter of about 0.1 μm and a depth of about 3 μm to a depth of about 70%, and has a softening temperature of 12%.
0 ℃, pyrolysis temperature 300 ℃, temperature 25 ℃, humidity 35%
Has a physical property value of 59 kv / mm under the above conditions.

Next, FIG. 2 shows the relationship between the permeability at the defect 9 and the viscosity at the time of application, two minutes after the application of the coating agent. This figure is a semilogarithmic graph, in which the vertical axis shows the permeability and the horizontal axis shows the viscosity. The penetration rate is about 0.1μ in diameter
m and a depth of about 3 μm. The resin material of the coating agent is FC-721 (trade name of Sumitomo 3M Limited) and the solvent is 1,1,2-trichloro-1,2,2.
-Each coating agent was adjusted to a predetermined viscosity using trifluoroethane. In addition, the surface tension of the coating agent was set to be approximately 12 dyn · s / cm.

As is apparent from FIG. 1, the permeability of the coating agent gradually increases from around 5.0 cps according to the decrease in viscosity, about 30% at around 1.4 cps, and 1.0 cps.
In the vicinity of ps, it is about 70%. Therefore, it is necessary to adjust the viscosity of the coating agent to 5 cps or less, and preferably to 1.4 cps.

Further, it has been found that the penetrating power of the coating agent increases as the surface tension decreases.
In order to allow the above-mentioned coating agent to penetrate the defect 9 having a diameter of 1 μm or less to a depth sufficient to prevent the permeation of contaminants, the surface tension of the coating agent is set to 20 dyn ·
s / cm or less, preferably 15 dyn · s / cm or less.

FIGS. 3A and 3B show the results of a study on the surface temperature of the conventional thermal head 11 when it is driven. 3A and 3B are partial cross-sectional views showing the surface temperature distribution diagram of the thermal head and the corresponding temperature measurement position of the thermal head. In FIG. 3A, the vertical axis represents the surface temperature, and the horizontal axis represents the measurement position. Indicated. The above surface temperature was applied to a heating element of 150 μm × 100 μm with an applied power of 0.2 W, an application cycle of 10.0 msec, and an application time of 2.0 m.
The thermal head was driven for msec, and the measurement was performed when the 10th pulse was emitted.

According to the figure, the surface temperature is about 145 ° C. at the point C where the surface temperature is the highest, and the surface temperature is about 70 ° C. at the points A and E located near the boundary between the conductive layer and the resistive layer. Has a pyrolysis temperature of 1 as solids.
Applying a coating agent having a temperature higher than 50 ° C. on the protective layer 6 prevents generation of harmful gas due to thermal decomposition, and applying a coating agent having a softening temperature of 80 ° C. or higher as a solid content allows the thermal paper 7 It is possible to prevent the defective portion from being opened due to adhesion to heat or thermal decomposition.

Also, for example, the protective layer 6 of the thermal head 1
When the thermal head 1 is driven, an electric field of 6 kv / mm is generated between the conductive layer and the upper portion of the protective layer when a drive voltage of 24 V is applied. The dielectric breakdown strength of the resin layer filled into the substrate is 59 kv / mm in an environment of a temperature of 25 ° C. and a humidity of 35%.
The resin layer is not broken and opened by the external electric field at the time of driving.

Accordingly, the physical properties of the coating agent require the following conditions a) and b), and the physical properties of the resin layer obtained by curing the coating agent require the following conditions c), d) and e). Resin materials satisfying such conditions include acrylic resin, silicone resin,
Examples thereof include a polyimide-based resin or a mixture of any combination thereof. a) Viscosity of 5 cps or less, preferably 1.4 cps or less, b) Surface tension of 20 dyn · s / cm or less, preferably 15 dyn · s / cm or less c) Softening temperature of 100 ° C or more d) Thermal decomposition temperature of 150 ° C or more e) Dielectric strength is 10 in an environment of 25 ° C and 35% humidity.
kv / mm or more

Using the above resin material, a)
A coating agent is prepared so as to satisfy the condition of b),
The resin layer 8 was formed by applying the coating agent on the protective layer 6 and curing to form the thermal head 1a. The thermal head 1a had a permeability of about 0.1 μm in diameter and about 3 μm in depth for a pinhole. In each case, it was 20% or more, and it was confirmed that the permeation of the contaminant was sufficiently suppressed. When the thermal heads 1 and 1a as described above are
Leave in an environment of 5 ° C. and a humidity of 85% to set a printing standby state (a state in which the thermal paper 7 is brought into contact with the protective layer 6, a driver IC driving voltage of 5 V and a printing voltage of 24 V are applied, and the printing signal is OFF). As a result, their initial destruction time (here, the ratio of the number of defective heating elements to the total number of heating elements was 0.
The time required to reach 1% is about 100 hours, which is about 5 times longer than that of the conventional thermal head 11. The thermal heads 1 and 1a were subjected to a running test (applied power: 0.2 W, applied cycle: 10.0 msec, applied time: 2.0 msec) by continuous printing using thermal paper having a high ion content (Na ⁺ 2000 ppm or more). As a result, the running life was about 30 km, which was about three times longer than that of the conventional thermal head 11. The Y region of the resin layer 8 laminated on the heat generating portion of the resistance layer 4 with the protective layer 6 interposed therebetween can be easily removed by initial running, lapping, or the like. Image quality degradation can be prevented.

[0024]

According to the thermal head of the present invention, opening of a defective portion due to dielectric breakdown, permeation of a contaminant into a resin layer, thermal decomposition of a resin layer due to heat generation of a resistance layer, opening of a defective portion due to softening, and the like are caused. Corrosion of the conductive layer is suppressed, and as a result, the reliability of the thermal head is improved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a thermal head according to the present invention.

FIG. 2 is a graph showing the relationship between the viscosity and the permeability of a coating agent.

FIGS. 3A and 3B are a partial sectional view showing a surface temperature distribution diagram of the thermal head and a corresponding temperature measurement position of the thermal head.

FIG. 4 is a sectional view of a conventional thermal head.

FIG. 5 is a sectional view of a conventional thermal head having a resin layer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Thermal head of this invention 2 Substrate 3 Thermal storage layer 4 Resistance layer 5a, 5b Conductive layer 6 Protective layer 7 Thermal paper 8 Resin layer 9 Defective part 9a Space part 11 Conventional thermal head 12 Conventional thermal head provided with resin layer 18 Resin layer

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B41J 2/335

Claims (1)

(57) [Claims] A resistive layer formed on an electrically insulating substrate;
A thermal head in which a conductive layer and a protective layer are sequentially laminated on the resistance layer, wherein the viscosity is 5 cps or less and the surface tension is 20
The properties after application and curing under the condition of dyn · s / cm or less have a softening temperature of 100 ° C. or more, a thermal decomposition temperature of 150 ° C. or more, a temperature of 25 ° C., and a dielectric strength of 10% in an environment of 35% humidity.
A thermal head comprising a resin layer of kv / mm or more on the protective layer.