JPH04238048A - Thick film type 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 and an abrasion- resistant layer on a ceramic substrate having specific surface roughness and containing specific wt.% of aluminum nitride. CONSTITUTION:A thermal head used in various printers is constituted by forming an aluminum oxide layer 7 with thickness of 0.2-20mum to the surface of a ceramic substrate 1a with surface roughness of 1mum or less containing 90wt.% or more of aluminum nitride if necessary and laminating a heating resistor 2 and an abrasion-resistor layer 5 to said layer 7. Electric conductors (electrodes) 3 formed by transferring and baking conductive paste of Au, Ag, Pd-Ag or Pt-Au are bonded to both end parts of the heating resistor 2. The heating resistor 2 is formed so that the end part connected to an electrode 4 thereof is formed into a strip shape and the width of the central part thereof is set so as to become smaller than that of the end part thereof. The abrasion- resistant layer 5 is formed from a composition based on SiO2-Ta2O3 or SiO2.

Description

[Detailed description of the invention]

[Object of the invention]

0002

[Industrial Application Field] The present invention is a thermal pen type in which a heating resistor and a wear-resistant layer are provided on a ceramic substrate, and the heating resistor is moved in a direction perpendicular to the direction of movement of thermal recording paper to print characters, etc. The present invention relates to a thick-film thermal head used in thermal heads, etc., and particularly relates to a thick-film 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 thermal head, which is the recording section of a conventional thick-film thermal printer, is generally as shown in FIG. The heat-generating resistor 2 and the heat-generating resistor 2 generate heat when a voltage is applied, the electric conductor (electrode) 3 connected to the end of the heat-generating resistor 2 facing each other, and the heat-sensitive recording paper 4 contact wear. It is composed of a wear-resistant layer 5 for protecting the electrical conductor 3.

[0005] A feed roller 6 is attached to this thick film type thermal head.
When the thermal recording paper 4 is pressure-bonded through the heating resistor 2 and a pulse voltage is applied to the heating resistor 2 in this state, the coloring agent coated on the thermal recording paper 4 causes a chemical reaction and the heating resistor 2 is heated. The coloring layer in contact develops color in the form of dots. By repeating pulsed heating while sequentially moving the recording paper 4 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. The heat dissipation time required for the head to cool down to a temperature below that temperature is longer, and as a result, it is more likely to cause stains on the recording paper and trailing of print, making it unsuitable as a head for high-speed recording printers in many cases. . In recent years, there has been a demand for higher printing speeds, and there is a need for thermal heads that can sufficiently support higher printing speeds and have high reliability.

On the other hand, the inventor of the present application has also confirmed that the resistance value of a thin film circuit arranged on a conventional ceramic substrate and the characteristic reliability of a capacitive element are greatly affected by the surface roughness of the ceramic substrate. . In other words, when the surface roughness of the substrate is large, the chemical bonding strength between the substrate surface and the heating resistor or the electric conductor is reduced, resulting in a problem that the reliability and durability of the head are low. .

[0008] For this reason, it has been considered to increase the bonding strength by using an alumina substrate with a purity of 99.5% or more, which would enable the surface roughness to be set to a small level. The disadvantage was that the cost of raw materials increased due to the use of

The present invention has been made to solve the above-mentioned problems, and it improves the thermal response characteristics, enables higher-speed printing, and increases the bonding strength with each layer on the substrate. The purpose is to provide a highly reliable thermal head. [Structure of the invention]

0010

[Means for Solving the Problems] In order to achieve the above object, a thick film type thermal head according to the present invention has a surface roughness of Ra
is 1 μm or less, and a heating resistor and a wear-resistant layer are laminated on the surface of a ceramic substrate containing 90% by weight or more of aluminum nitride.

[0011] Also, on the surface of the ceramic substrate, 0.2 to 20
It is preferable to form an aluminum oxide layer having a thickness of about μm.

0012

[Function] According to the thick-film thermal head having the above structure, a ceramic substrate made of aluminum nitride (AlN), which has thermal conductivity 3 to 10 times better than conventional alumina, is used. Therefore, the time taken to cool down the resistor, which has been heated to the printing 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.

Furthermore, by forming an aluminum oxide layer on the surface of the ceramic substrate, the wettability between aluminum nitride, which is the substrate material, and the heating resistor is improved, and the bonding strength between the two is increased, resulting in excellent durability and high reliability. It is possible to obtain a thermal head with properties.

[0014]

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 thick film thermal head according to the present invention. Note that the same elements as those in the conventional example shown in FIG. 5 are given the same reference numerals, and redundant explanation thereof will be omitted.

That is, the thick-film thermal head according to this embodiment has a heating resistor 2 and a wear-resistant layer 5 on the surface of a ceramic substrate 1a having a surface roughness Ra of 1 μm or less and containing 90% by weight or more of aluminum nitride. It is made up of layers. In addition, Au, Ag, Pd are provided at both ends of the heating resistor 2.
An electric conductor (electrode) 3 formed by transferring and baking a conductor paste such as -Ag or Pt-Au is connected.

[0016] 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 obtained by sintering a mixture of aluminum nitride raw material powder and several weight percent of Y2 O3 as a sintering aid at a predetermined high temperature. In order to maintain the thermal conductivity of the ceramic substrate 1a at a good value, the content of AlN is set to 90% by weight or more. 90
This is because if it is less than % by weight, the good thermal conductivity inherent to AlN will be impaired.

The surface roughness Ra (center line average roughness defined in JIS B0601) of the ceramic substrate 1a made of aluminum nitride depends on the adhesion between the substrate 1a and the heating resistor 2 disposed on the substrate. This has a large effect on the chemical bonding strength, and is set to 1 μm or less in this example. When the surface roughness Ra exceeds 1 μm, the substrate 1
This is because the adhesion and bonding strength between a and the heating resistor 2 and the electric conductor 3 are reduced, resulting in a reduction in the reliability and durability of the thermal head.

The ceramic substrate 1a having a surface roughness Ra of 1 μm or less can be prepared, for example, by subjecting the surface of a sintered body of AlN ceramics to ordinary mirror polishing. Furthermore, by setting the surface roughness Ra to 1 μm or less, the aluminum oxide layer described later is
Even when the oxide layer is formed by oxidizing IN, it is easy to form the oxide layer with a uniform thickness and surface roughness.

The heating resistor 2 also has an electrical conductor (electrode) 3
, 3, which generates heat in response to a pulse voltage applied to the thermosensitive recording paper to color the coloring agent in dots. For example, Ta2N, NiCr, Nesa film, SiO2-Ta,S
After making a raw material such as i-Ta into a paste, it is formed using a manufacturing technique such as screen printing.

The wear-resistant layer 5 is provided to protect the heating resistor 2 from contact wear of the thermal recording paper, and is made of, for example, Si.
O2-Ta2O3,SiC,Al2O3,S
It is composed of materials such as iO2.

When a pulse voltage is applied to the heating resistor 2 via the electrodes 3, 3, the resistor 2 of the thermal head generates heat, and the color forming agent applied to the thermal recording paper pressed against the resistor 2 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 2 is released to the outside of the system through the AlN ceramic substrate 1a, and the heating resistor 2 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.
A printing test was conducted by installing the thick film thermal head of the example using the ceramic substrate 1a and the conventional thick film thermal head using the Al2O3 ceramic substrate 1 as shown in FIG. 5 in a printer. 3 is a graph showing changes in temperature of each heating resistor over time in the case of FIG.

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.

[0025] 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, another embodiment of the present invention will be described with reference to FIG. In the thick film type thermal head according to this embodiment, the surface of the ceramic substrate 1a has a thickness of 0.2 to 20%
An aluminum oxide layer 7 having a thickness of μm is formed.

This aluminum oxide layer 7 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 2 or the electric conductor 3 have poor adhesion due to poor wettability, and it has been difficult to set a large bonding strength between the two. .

However, by partially oxidizing the surface of the aluminum nitride substrate to form an aluminum oxide film, the bonding strength between the two can be greatly increased, resulting in a thick-film thermal head with excellent durability. can be obtained.

[0029] The thickness of the aluminum oxide layer 7 is 0.2 μm.
If the thickness is less than 20 μm, the effect of improving the bonding strength will be small, while if the thickness exceeds 20 μm, the bonding strength will decrease and the proportion of the Al2O3 film as a heat resistance layer will increase, reducing the inherent good thermal properties of the AlN substrate. Since the conductivity is impaired, the thickness of the aluminum oxide layer 7 is set in the range of 0.2 to 20 μm, more preferably 0.5 to 5 μm.

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 2a of the thermal head connected to the electrodes 3, 3 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 2a has the highest resistance value. When a voltage is applied to the heating resistor 2a through the electrodes 3 and a current is passed through the heating resistor 2a, only the central portion generates heat and the 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 2a 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 2a 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.

[0032]

As explained above, the thick-film thermal head according to the present invention uses ceramics mainly made of aluminum nitride (AlN), which has thermal conductivity 3 to 10 times better than conventional alumina. Since a substrate is used, the time needed to raise the temperature up to the printing temperature and then cool down the heated resistor 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.

Furthermore, by forming an aluminum oxide layer on the surface of the ceramic substrate, the bonding strength between the aluminum nitride substrate material and the heating resistor and electrodes is increased, resulting in a thick film type thermal conductor with excellent durability and high reliability. You can get the head.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of a thick film 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 thick film 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 thick-film thermal head.

[Explanation of symbols]

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

Claims (4)

[Claims] 1. A thick film thermal head characterized in that a heating resistor and a wear-resistant layer are laminated on the surface of a ceramic substrate having a surface roughness Ra of 1 μm or less and containing 90% by weight or more of aluminum nitride. 2. The thick film thermal head according to claim 1, further comprising an aluminum oxide layer formed on the surface of the ceramic substrate. [Claim 3] The thickness of the aluminum oxide layer is 0.2~
The thick film type thermal head according to claim 1, characterized in that the thickness is 20 μm. 4. The thick-film 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.