JPH081973A - Thermal head - Google Patents

Abstract

PURPOSE:To provide a thermal head capable of forming a good printing image free from a white stripe on thermal recording paper without increasing the power applied to a heating resistor. CONSTITUTION:A plurality of heating resistors 2 and a pair of the conductive layers 5 connected to the heating resistors 2 are provided on an electric insulating substrate 1 and each of the heating resistors 2 is formed by laminating a first heating resistor layer 3 and a second heating resistor layer 4 having sheet resistance smaller than that of the first heating resistor layer 3 and an aperture part 4a is formed to the central part of the second heating resistor layer 4 between a pair of the conductive layers 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a thermal head incorporated as a printer mechanism for a word processor, a facsimile or the like.

[0002]

2. Description of the Related Art Conventionally, a thermal head incorporated as a printer mechanism for a word processor or the like is made of tantalum nitride or the like on an electrically insulating substrate 11 made of alumina ceramics on which a heat storage layer 11a is adhered, as shown in FIG. The heating resistor 12 and a pair of conductive layers 13 made of aluminum or the like and connected to both ends of the heating resistor 12 are sequentially deposited, and the heating resistor 12 and the pair of conductive layers 13 are further deposited.
Is covered with a protective layer 14, a predetermined electric power is applied between the pair of conductive layers 13 to cause the heating resistor 12 to generate Joule heat at a predetermined temperature, and the generated heat is subjected to thermosensitive recording. It functions as a thermal head by forming a predetermined print image on the heat-sensitive recording paper by making the heat-sensitive recording paper develop color by being conducted to the paper.

The heat storage layer 11a is composed of a heating resistor 12
This is for accumulating a part of the heat generated by the thermal head to improve the thermal response characteristics of the thermal head, and is formed of a low thermal conductive material such as glass or polyimide resin.

Further, the protective layer 14 protects the heating resistor 12 and the pair of conductive layers 13 from oxidative corrosion due to contact of moisture contained in the atmosphere and abrasion due to sliding contact of the thermal recording paper. And is made of silicon nitride, sialon, or the like.

[0005]

However, in this conventional thermal head, for example, when a predetermined electric power (0.2 mJ) is applied between the pair of conductive layers 13 to cause the heating resistor 12 to generate Joule heat, As shown in FIG. 5, the surface temperature of the heating resistor 12 is greatly different between the central portion and the peripheral portion of the heating resistor 12, and is the lowest temperature at the central portion (surface temperature: about 150 ° C.) where the temperature is highest. Both ends (surface temperature:
(About 90 ° C), a large temperature difference of about 60 ° C occurs. A predetermined heat-sensitive recording paper (for example, TSP-F50US manufactured by Fuji Photo Film Co., Ltd.) that develops color when the surface temperature of the heat generating resistor 12 reaches a temperature of about 120 ° C. or more is used as the heat generating resistor 12 of the thermal head. When printing is performed by sliding contact, the thermosensitive recording paper develops color in the vicinity of the central portion of the heating resistor 12, but does not develop color in the peripheral portion, and the size of the printing dot formed on the thermosensitive recording paper is the resistance to heat generation. The size of the body 12 is extremely small as compared with the size of the body 12, and there is a defect that white lines are formed between adjacent print dots.

In order to solve the above-mentioned drawbacks, it is conceivable that the electric power applied to the heating resistor 12 is increased so that the heat-sensitive recording paper also develops color in the peripheral portion of the heating resistor 12.

However, when printing is performed with a large electric power applied to the heating resistor 12, the central portion of the heating resistor 12 becomes excessively hot, and there is a risk that the heating resistor 12 will be thermally damaged in a short time. Have

Further, when printing is performed with a large electric power applied to the heat generating resistor 12, the amount of electric power required for printing increases, so that the thermal efficiency of the thermal head decreases.

[0009]

SUMMARY OF THE INVENTION The present invention has been devised in view of the above-mentioned drawbacks, and an object of the present invention is to produce a good printed image on a thermosensitive recording paper without white streaks without increasing the electric power applied to the heating resistor. It is to provide a thermal head that can be formed.

[0010]

A thermal head according to the present invention comprises a plurality of heating resistors and a pair of conductive layers connected to the heating resistors, which are adhered on an electrically insulating substrate. The heating resistor is formed by stacking at least a first heating resistor layer and a second heating resistor layer having a sheet resistance smaller than that of the first heating resistor layer on an electrically insulating substrate, and An opening is formed in the center of the second heating resistance layer located between the conductive layers.

[0011]

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

FIG. 1 is a plan view showing an embodiment of the thermal head of the present invention, FIG. 2 (a) is an enlarged view of the R portion of FIG. 1, and FIG.
2B is a sectional view taken along line XX of FIG. 2A, in which 1 is an electrically insulating substrate, 1 a is a heat storage layer, 2 is a heating resistor, and 3 is a first
The heating resistance layer, 4 is a second heating resistance layer, 4a is an opening, 5 is a pair of conductive layers, and 6 is a protective layer.

The electrically insulative substrate 1 is made of electrically insulative material such as alumina ceramics. It is formed by adding and mixing an appropriate organic solvent and solvent to ceramic raw material powder such as alumina, silica, magnesia, etc. A ceramic green sheet is formed by adopting a conventionally known doctor blade method, calender roll method or the like, and thereafter, the ceramic green sheet is punched into a predetermined shape and at a high temperature (about 1600).
It is manufactured by firing at (° C).

A heat storage layer 1a made of a low heat conductive material such as glass or polyimide resin is deposited on the upper surface of the electrically insulating substrate 1 to a thickness of 25 to 60 μm, and the heat storage layer 1a is formed on the upper surface thereof. It accumulates a part of the heat generated by the heat generating resistor 2 to be deposited, and makes the temperature of the thermal head the temperature necessary for forming a printed image on the thermal recording paper in a short time.

When the heat storage layer 1a is made of glass, a glass paste obtained by adding and mixing a suitable organic solvent to glass powder is formed on a predetermined area of the upper surface of the electrically insulating substrate 1 by a conventionally known screen printing method or the like. Is applied by printing, and then is baked at a high temperature, for example, a temperature of about 600 ° C. to be applied on the upper surface of the electrically insulating substrate 1.

A plurality of heating resistors 2 (width W: 115 μm, length L: 175 μ) are formed on the upper surface of the heat storage layer 1a.
m) and a pair of conductive layers 5 connected to the heating resistor 2 are sequentially deposited.

The heat generating resistor 2 is made of TaSiO ₂ and has a predetermined sheet resistance (4000 μΩ · cm), and the first heat generating resistor layer 3 is made of Cr—Si—O and is smaller than the first heat generating resistor layer 3. Sheet resistance (1000μΩ ・ c
m) and a second heating resistor layer 4 having a rectangular opening 4a (width w: 75 μm, long length) at the center of the second heating resistor layer 4 located between the pair of conductive layers 5. L: 13
5 μm) is formed.

Since the first heating resistance layer 3 and the second heating resistance layer 4 themselves have a predetermined electric resistivity, when a predetermined electric power is applied via the pair of conductive layers 5, the pair of heat generation resistance layers 3 and 4 are paired. Joule heat is generated in each region between the conductive layers 5.

The opening 4a of the second heating resistance layer 4 is also provided.
Has a function of causing most of the current flowing between the pair of conductive layers 5 to flow in the peripheral portion of the heating resistor 2, and therefore, a predetermined electric power (0.
2 mJ), a predetermined current flows through the first heating resistance layer 3 and the second heating resistance layer 4, respectively, and the first heating resistance layer 3
Near the center of the heating resistor 2, that is, near the center of the heating resistor 2 and the second
The surface temperature of the heating resistor 2 becomes substantially constant from the central portion to the peripheral portion by simultaneously generating heat with the peripheral portion of the heating resistor 2 on which the heating resistor layer 4 is arranged.

FIG. 3 is a line A-B in FIG. 2A when Joule heat is generated in the heating resistor 2 by applying an electric power of 0.2 mJ between the pair of conductive layers 5 of the thermal head of FIG. 2 is a graph showing the results of measuring the surface temperature of the heating resistor 2 using an infrared radiation thermometer, and as is clear from the measurement results, the surface temperature of the heating resistor 2 ranges from the central portion to the peripheral portion. The temperature becomes almost constant over time, and most of the heating resistor 2 is raised to a temperature close to the center.

In the heating resistor 2 of the thermal head,
When printing is performed by sliding a predetermined thermosensitive recording paper (TSP-F50US manufactured by Fuji Photo Film Co., Ltd.) that develops color when the surface temperature of the heating resistor 2 reaches a temperature of about 120 ° C. or higher,
The size of the print dot is almost the same as the size of the heating resistor 2, and white lines or the like are effectively prevented from being formed on the thermal recording paper. This makes it possible to form a good printed image on the thermosensitive recording paper without increasing the electric power applied to the heating resistor 2.

If the sheet resistance of the second heating resistance layer 4 is equal to or larger than the sheet resistance of the first heating resistance layer 3, the current flowing through the second heating resistance layer 4 is reduced, and Since most of the heat will flow through the first heating resistor layer 3, it becomes impossible to effectively heat the peripheral portion of the heating resistor 2. Therefore, the sheet resistance of the second heating resistance layer 4 needs to be smaller than the sheet resistance of the first heating resistance layer 3.

The first heating resistance layer 3 and the second heating resistance layer 4 are made of TaSiO ₂ , Cr-Si-O having a predetermined thickness (TaSiO ₂ thickness: 100) on the heat storage layer 1a by a conventionally known sputtering method or the like. ~ 1000Å, Cr-S
i-O thickness: 100-500 Å) is applied in sequence, then TaSiO ₂ and Cr-Si-O are processed into a predetermined pattern by using a photolithography technique, and a rectangular shape is formed on Cr-Si-O. By forming the opening, it is deposited on the heat storage layer 1a.

On the other hand, the pair of conductive layers 5 connected to both ends of the heating resistor 2 are made of aluminum or the like, and the conductive layer 5 applies a predetermined electric power required for causing the heating resistor 2 to generate Joule heat. Make the action.

The pair of conductive layers 5 are deposited in a predetermined pattern and a predetermined thickness (0.5 μm to 2.0 μm thickness) on the heating resistor 2 by adopting the conventionally known sputtering method and photolithography technique. It

The heating resistor 2 and the pair of conductive layers 5 are covered with a protective layer 6, and the protective layer 6 contacts the heating resistor 2 and the pair of conductive layers 5 with moisture contained in the atmosphere. It protects against oxidative corrosion due to abrasion and abrasion due to sliding contact of thermal recording paper.

The protective layer 6 is made of silicon nitride, sialon, or the like, and is deposited on the upper surfaces of the heating resistor 2 and the pair of conductive layers 5 to a thickness of 3 to 6 μm by a conventionally known sputtering method or the like.

Thus, in the thermal head of the present invention, a predetermined electric power is applied between the pair of conductive layers 5 to cause the heating resistor 2 to selectively generate Joule heat and to conduct the generated heat to the thermal recording paper. The thermal recording paper functions as a thermal head by forming a color on the thermal recording paper to form a predetermined print image on the thermal recording paper.

The present invention is not limited to the above-mentioned embodiments, and various modifications and improvements can be made without departing from the gist of the present invention. For example, in the above-mentioned embodiments, the first heating resistance layer is provided. Although the second heating resistance layer is formed on the upper side, instead of this, the first heating resistance layer may be formed on the second heating resistance layer. In this case, the same effect as that of the above-described embodiment can be obtained. it can.

Further, in the above-mentioned embodiment, the heating resistor is formed of the two layers of the first heating resistor layer and the second heating resistor layer. However, the heating resistor is formed on the second heating resistor layer further than the second heating resistor layer. A third resistance layer having a small sheet resistance and an opening larger than the opening of the second heating resistance layer may be applied, and in this case, the temperature difference on the surface of the heating resistor is smaller. Therefore, it becomes possible to form a very good printed image on the thermal recording paper. Therefore, a third resistance layer having a sheet resistance smaller than that of the second heating resistance layer and having an opening larger than the opening of the second heating resistance layer is deposited on the second heating resistance layer. It is preferable to leave it.

[0031]

According to the thermal head of the present invention, a plurality of heat generating resistors and a pair of conductive layers connected to the heat generating resistors are adhered on an electrically insulating substrate, and the heat generating resistors are provided. Is composed of at least a first heating resistance layer and a second heating resistance layer having a sheet resistance smaller than that of the first heating resistance layer, and has an opening at the center of the second heating resistance layer located between the pair of conductive layers. Therefore, when a predetermined electric power is applied between the pair of conductive layers during printing, the vicinity of the central portion of the first heating resistance layer and the second heating resistance layer simultaneously generate heat,
The surface temperature of the heating resistor becomes almost constant from the central part to the peripheral part. As a result, when printing is performed by sliding a predetermined heat-sensitive recording paper on the heat-generating resistor, the size of the print dot becomes almost equal to the size of the heat-generating resistor, and white lines are formed on the heat-sensitive recording paper. Is effectively prevented. As a result, a good printed image can be formed on the thermal recording paper without increasing the power applied to the heating resistor.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of a thermal head of the present invention.

2A is an enlarged view of an R portion of FIG. 1, and FIG. 2B is a sectional view taken along line XX of FIG.

FIG. 3 is a graph showing the results of measuring the surface temperature of the heating resistor 2 shown in FIG. 2A along the line AB.

FIG. 4A is a partially enlarged view of a conventional thermal head,
(B) is a YY line sectional view of (a).

FIG. 5 is a graph showing the results of measuring the surface temperature of the heating resistor 12 shown in FIG. 4A along the line A′-B ′.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Electrically insulating substrate 1a ... Heat storage layer 2 ... Heating resistor 3 ... 1st heating resistor layer 4 ... 2nd heating resistor layer 4a ... Opening 5 .... A pair of conductive layers 6 ... Protective layers

Claims (1)

[Claims] 1. A thermal head comprising a plurality of heating resistors and a pair of conductive layers connected to the heating resistors deposited on an electrically insulating substrate, wherein the heating resistors are electrically insulating. At least first on the substrate
The heating resistor layer and a second heating resistor layer having a sheet resistance smaller than that of the first heating resistor layer are laminated, and an opening is formed in the center of the second heating resistor layer located between the pair of conductive layers. The thermal head is characterized by being.