JPH04238043A - Thermal head - Google Patents

Abstract

PURPOSE:To improve thermal response characteristics and to perform printing recording at a high speed by laminating a heating resistor, an electric conductor and an abrasion-resistant layer on a ceramic substrate containing specific wt.% of aluminum nitride. CONSTITUTION:A thermal head used in various printers is prepared by forming an aluminum oxide layer with thickness of 0.2-5mum to the surface of a ceramic substrate 1a containing 90wt.% or more of aluminum nitride and arranging a glaze layer 2a to said layer 9. Further, a heating resistor 3, a resistor protecting layer 5 and an abrasion-resistant layer 7 are laminated on the surface of the glaze layer 2a. Electric conductors (electrodes) 4 formed by transferring and baking conductor paste such as Au, Cu, Ag, Pd-Ag or Pt-Au are bonded to both end parts of each heating resistor 3. The heating resistor 3 is formed from a composition based on Ta2N or TiOx (0<x<2) and the abrasion-resistant layer 7 is formed from a composition based on Ta2O3 or SiO2.

Description

[Detailed description of the invention]

[Object of the invention]

0002

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head in which a heating resistor is provided on a ceramic substrate, and more particularly to a thermal head that improves thermal response characteristics and enables high-speed recording.

0003

2. Description of the Related Art Various thermal heads are used to convert information transmitted as electrical signals to measurement recorders, various printers, facsimile machines, etc. into characters, symbols, or graphic images on thermal recording paper. The thermal head has a heating resistor that is heated with an electric current to form characters and images on a heat-sensitive recording paper coated with a chemical material that develops color when heated.

That is, the basic structure of a thin-film thermal head, which is the recording section of a conventional thermal printer, generally consists of a ceramic substrate 1 made of alumina (Al2O3) and a ceramic substrate 1 formed on this substrate 1, as shown in FIG. , a glaze layer 2 with a smooth surface made of a metal oxide or the like, a heating resistor 3 disposed on the surface of the glaze layer 2 and generating heat when a voltage is applied, and facing the end of each heating resistor 3. Protects the heat generating resistor 3 and the resistor protective layer 5 from contact abrasion between the connected electrical conductors (electrodes) 4, the resistor protective layer 5 for preventing oxidation of the heat generating resistor 3, and the thermal recording paper 6. It is composed of a wear-resistant layer 7 for

The thermal recording paper 6 is pressed onto this thermal head via the feed roller 8, and when a pulse voltage is applied to the heating resistor 3 in this state, the coloring agent applied to the thermal recording paper 6 is chemically A reaction occurs, and the coloring layer that is in contact with the 3 parts of the heating resistor develops color in the form of dots. By repeating pulsed heating while sequentially moving the recording paper 6 in the direction of the arrow by a feed roller, a large number of colored dots are obtained, and depending on the arrangement of these colored dots, characters, symbols, or images are recorded. Ru.

[0006]

[Problems to be Solved by the Invention] However, since the ceramic substrate of the conventional thermal head is mainly made of alumina (Al2O3), which has a low thermal conductivity, once the head is heated, the coloring of the thermal paper is difficult. High-speed recording was difficult because it took a long time for heat to dissipate until the temperature was below that temperature. In addition, when high-speed recording is forced, a new pulse voltage is applied before the print temperature generated by the applied pulse voltage drops to the predetermined lower limit of the print temperature, resulting in background smudges on the recording paper and print tails. Pulling was likely to occur, and the performance as a head for high-speed recording printers was significantly reduced. Particularly in recent years, there has been a demand for higher printing speeds, and there has been a demand for thermal heads that can adequately support higher speed printing and have higher reliability.

The present invention has been made to solve the above problems, and aims to provide a highly reliable thermal head that improves thermal response characteristics and enables higher speed printing. shall be. [Structure of the invention]

[0008]

[Means for Solving the Problems] In order to achieve the above object, a thermal head according to the present invention has a heating resistor, an electric conductor, and a wear-resistant layer laminated on a ceramic substrate containing 90% by weight or more of aluminum nitride. It is characterized by

Here, the thermal conductivity of aluminum nitride is Y
If a large amount of sintering aid components such as 2 O3 and AlO2 are contained, the content decreases, so it is desirable that the content be 90% by weight or more, preferably 95% by weight or more.

[0010] Furthermore, in order to improve the smoothness of this ceramic substrate mainly made of aluminum nitride and to form a heat insulating layer of a constant thickness, it is preferable to form a glaze layer on the ceramic substrate. In particular, when forming a heating resistor thinly by a thin film method, smoothness of the ceramic substrate is strictly required, so this is more preferable. In this case, in order to improve the compatibility and paintability between the ceramic substrate mainly composed of aluminum nitride and the glaze layer, the surface of the ceramic substrate is oxidized to a thickness of 0.2 to 20 μm, preferably 0.
．． It is desirable to form a glaze layer after forming a 5-5 μm aluminum oxide layer. If the thickness of this aluminum oxide layer is less than 0.2 μm, there is almost no effect of improving wettability, and even if it exceeds 20 μm, the effect decreases. The thickness is preferably 0.5 to 5 μm. This glaze layer has a heat retaining effect, but since it is a thin layer with a thickness of 1 to 20 μm, the heat retaining effect is limited to a very short period after the heating resistor heats up, and the heat dissipation time by the AlN substrate after the heat generation is shortened. There is very little interference with this.

However, the formation of a glaze layer is not always necessary, especially when forming a heating resistor by a thick film method, and it is also possible to form a heating resistor directly on a ceramic substrate without forming a glaze layer. be. However, in this case as well, in order to improve the compatibility and wettability between the ceramic substrate mainly composed of aluminum nitride and the heating resistor, the surface of the ceramic substrate is oxidized to
It is desirable to form the heating resistor after forming an aluminum oxide layer of 20 μm, preferably 0.5 to 5 μm. In this case, the aluminum oxide layer also functions as a layer having a heat retaining effect.

0012

[Function] The thermal head with the above configuration uses a ceramic substrate mainly made of aluminum nitride (AlN), which has thermal conductivity 3 to 10 times better than conventional alumina. The time taken to cool down the resistor, which has been raised to temperature and generated heat, to a predetermined temperature is significantly shortened. Therefore, the repetition time of printing, which is the sum of the temperature rise time and fall time of the heating resistor, becomes extremely short, which greatly improves the thermal response of the thermal head, making it possible to significantly increase the recording speed. becomes.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a sectional view showing an embodiment of a thermal head according to the present invention. Note that the same elements as those in the conventional example shown in FIG. 5 are denoted by the same reference numerals, and redundant explanation thereof will be omitted.

That is, in the thermal head according to this embodiment, after forming an aluminum oxide (Al2O3) layer 9 of 0.2 to 5 μm on the surface of a ceramic substrate 1a containing 90% by weight or more of aluminum nitride, a glaze layer 2a is formed. In addition, a heating resistor 3, a resistor protection layer 5, and an abrasion resistant layer 7 are laminated on the surface of the glaze layer 2a. In addition, Au, Cu, Ag, and Pd are provided at both ends of each heating resistor 3.
- Electric conductive wires (electrodes) 4 formed by transferring and baking a conductive paste such as -Ag, Pt-Au, etc. are joined.

[0015] The thermal head according to this embodiment uses a ceramic substrate, which is 3 to 1 times smaller than a conventional alumina substrate.
Aluminum nitride (AlN) has a thermal conductivity of 0 times
) A major feature is the use of a substrate 1a. This ceramic substrate 1a is usually obtained by sintering a uniform mixture of aluminum nitride raw material powder and several weight percent of Y2O3 as a sintering aid at a predetermined high temperature.

The glaze layer 2a is formed for the purpose of smoothing the surface of the ceramic substrate 1a, and is formed between a thin film (heating resistor) formed by vapor deposition, sputtering, etc. and the ceramic substrate 1a. Bonding strength and wettability can be significantly improved. This glaze layer 2a
The materials constituting include SiO2, PbO, Al2
O3, B2 O3, CaO, ZnO, MgO, N
There are metal oxides such as a2O and K2O, and these can be formed singly or in a mixture of two or more.

Here, the thermal conductivity of the glaze layer 2a is 1
．． It is preferable that the temperature is 5×10 −3 cal/cms·° C. or more. Thermal conductivity is 1.5 x 10-3 cal/cms・
If it is below ℃, it will act strongly as a thermal resistance layer on the AlN substrate or Al2O3 layer,
This will impair the heat dissipation characteristics of the AlN substrate.

Further, in order to ensure the reliability of the operation of the thermal head, it is desirable that the temperature (softening point) at which the glaze layer 2a softens and deforms under its own weight is 700° C. or higher.

As compositions for forming a glaze layer that satisfies the above characteristic values, for example, those shown in Table 1 below are used. R shown in Table 1 represents an alkali metal such as K, Na, or Li.

[0020]

[Table 1]

Further, the heating resistor 3 is connected to an electric conductor (electrode) 4
, 4, which generates heat in response to a pulse voltage applied to the thermosensitive recording paper, and causes the coloring agent of the thermosensitive recording paper to develop color in dots. It is formed using a thin film manufacturing technique such as a method of vapor depositing a raw material such as Si-Ta.

Furthermore, the resistor protection layer 5 is provided to prevent the heating resistor 3 from deteriorating due to oxidation, and is made of, for example, a SiO2 thin film. However, the resistor protective layer 5 is not necessarily necessary depending on the composition of the wear-resistant layer 7.

The wear-resistant layer 7 is provided to protect the heat-generating resistor from contact wear of the heat-sensitive recording paper.
O3, SiO2-Ta2 O3, SiO2,
It is composed of materials such as Al2O3.

When a pulse voltage is applied to the heating resistor 3 via the electrodes 4, 4, the resistor 3 of the thermal head generates heat, and the color forming agent applied to the thermal recording paper pressed against the resistor 3 is heated. Color appears in dots. The application time of the pulse voltage is usually about 1 to 10 ms.

As the pulse voltage disappears, the heat of the resistor 3 is released to the outside of the system through the AlN ceramic substrate 1a, and the heating resistor 3 is cooled to a predetermined lower limit temperature for printing. Then, by applying the next pulse voltage, heat generation and cooling are repeated in the same way, and a large number of dots are colored on the moving thermosensitive recording paper, and a predetermined character, symbol, image, etc. is recorded by the arrangement of each dot.

Next, the advantages of the thermal head according to this embodiment will be described in comparison with the conventional example. Figure 3 shows the AlN shown in Figure 1.
Each heating resistor when a printing test was conducted by installing the thermal head of the embodiment using the ceramic substrate 1a and the conventional thermal head using the Al2O3 ceramic substrate 1 as shown in FIG. 5 in a printer. It is a graph showing a change in temperature over time.

As shown by the solid line in FIG. 3, in this embodiment, the ceramic substrate 1 is made of AlN, which has a high thermal conductivity.
Since it is made of the constituent material Al2, it has excellent heat dissipation characteristics after the pulse voltage disappears, and the heat dissipation time t1 until the heating resistor is cooled to the predetermined lower limit printing temperature is longer than that of Al2.
It has become possible to significantly shorten the heat dissipation time t0 required in the case of the conventional example configured with the ceramic substrate 1 made of O3.

[0028] This means that the repetition time of printing, which is represented by the total time of heating temperature rise time and heat dissipation time, is reduced, and it is possible to increase the speed of recording equipment such as printers.

Next, as another embodiment of the present invention, a thick film type thermal head will be described with reference to FIG. In the thermal head according to this embodiment, an aluminum oxide layer 9 having a thickness of 0.2 to 5 μm is formed between the ceramic substrate 1a and the heating resistor 3.

This aluminum oxide layer 9 is obtained by heating a sintered aluminum nitride body to a high temperature in an oxidizing atmosphere. By the way, aluminum nitride, which is a non-oxide ceramic material, and the heating resistor 9 have poor wettability, resulting in low adhesion, and it has been difficult to set a large bonding strength between the two.

However, by oxidizing the surface of the aluminum nitride substrate to form an aluminum oxide film, the wettability and bonding strength between the two can be greatly increased, and a thermal head with excellent durability can be obtained. I can do it.

Next, an example of the shape of the heating resistor of the thermal head according to the present invention will be explained. Conventionally, a heating resistor disposed between a pair of electric conductors has been formed in a band shape so that the cross section at each axial position is equal.

However, as shown in FIG. 4, while the part of the heating resistor 3a of the thermal head connected to the electrodes 4, 4 is formed into a band shape, the width W of the central part is set smaller than that of the end part, and the central part is It may be formed into a constricted shape. In this case, the central portion of the heating resistor 3a has the highest resistance value. When a voltage is applied to this heating resistor 3a via the electrodes 4, 4 and a current is passed through it, only the central portion generates heat and its temperature rises, reaching a temperature that dissolves the ink applied to the thermal recording paper. Small dots are transferred onto the paper. If voltage is continued to be applied to the heating resistor 3a in this state, the area where the ink melting temperature is reached gradually expands. In this way, by variably adjusting the energy applied to each heating resistor 3a by the voltage application pulse width, the size of each dot to be transferred can be made variable in accordance with the density of the image. In other words, each dot has a gradation, and printing with excellent gradation is possible without deteriorating resolution. In this embodiment, the shape of the heating resistor 3a is described as being applied to a thick film type thermal head, but it goes without saying that it can also be applied to a thin film type thermal head.

[0034]

[Effects of the Invention] As explained above, according to the thermal head according to the present invention, the thermal conductivity is 33% higher than that of conventional alumina.
Because we use a ceramic substrate made from ~10 times better aluminum nitride (AlN) as the main raw material, the time it takes to heat up to printing temperature and then cool down the heated resistor to the specified temperature is significantly shortened. be done. Therefore, the repetition time of printing, which is the sum of the temperature rise time and fall time of the heating resistor, becomes extremely short, which greatly improves the thermal response of the thermal head, making it possible to significantly increase the recording speed. becomes.

[Brief explanation of the drawing]

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

FIG. 2 is a sectional view showing another embodiment of the present invention.

FIG. 3 is a graph showing the thermal response characteristics of the thermal head according to the present invention in comparison with a conventional example.

FIG. 4 is a plan view showing an example of the shape of a heating resistor.

FIG. 5 is a sectional view showing the basic structure of a conventional thermal head.

[Explanation of symbols]

1, 1a Ceramic substrate 2, 2a Glaze layer 3, 3a　Heating resistor 4 Electrical conductor (electrode) 5 Resistor protective layer 6 Thermal recording paper 7. Wear-resistant layer 8 Feed roller 9 Aluminum oxide layer

Claims (7)

[Claims] 1. A thermal head characterized in that a heating resistor, an electric conductor, and a wear-resistant layer are laminated on a ceramic substrate containing 90% by weight or more of aluminum nitride. [Claim 2] The heating resistor is made of Ta2N or Ti.
A thermal head characterized by having a composition mainly composed of Ox (0<x<2). 3. The thermal head according to claim 1, further comprising a glaze layer formed between the ceramic substrate and the heating resistor. 4. The thermal head according to claim 1, wherein an aluminum oxide layer with a thickness of 0.2 to 20 μm is formed between the ceramic substrate and the heating resistor. [Claim 5] The wear-resistant layer is made of Ta2O3, SiO2
, SiO2 --Ta2 O3. 6. The thermal head according to claim 1, further comprising a resistor protection layer formed between the electrical conductor and the wear-resistant layer. 7. The thermal head according to claim 1, wherein the heating resistor has an end portion connected to the electrode formed in a band shape, and a width of the central portion is set smaller than that of the end portion.