JPS63302069A - Thermal head - Google Patents

Abstract

PURPOSE:To contrive enhancement of reliability of a thermal head and thermal efficiency, by using an aromatic polyimide resin synthesized from biphenyltetracarboxylic acid dianhydride and an aromatic diamine to provide a heat-resistant resin layer. CONSTITUTION:A thermal head is constructed by providing a heat-resistant resin layer 2 and a substrate layer 3 on a metallic base 1, providing thereon heat generating resistors 4, heat generating parts 5, discrete electrodes 6 and a common electrode 7, and covering them by an oxidation-preventive and abrasion-resistant film 8. The heat-resistant resin layer 2 is provided by using an aromatic polyimide resin synthesized from biphenyltetracarboxylic acid dianhydride and an aromatic diamine. The resin, because of a vinyl structure present in a backbone chain thereof, has a high thermal decomposition starting temperature, is resistant to heat, has a coefficient of thermal expansion little different from that of the metallic base, and can show excellent adhesion. Thus, the reliability of the thermal head is enhanced, and excellent thermal efficiency can be obtained through making the most of the characteristic features of the polyimide resin.

Description

[Detailed description of the invention] [Object of the invention] (Industrial application field) The present invention forms a polyimide resin layer on a metal support,
The present invention relates to a thermal head formed by forming a large number of heating resistors on this polyimide resin layer.

(Prior Art) In recent years, thermal heads have come to be widely used in various recording devices such as facsimiles and word processor printers, taking advantage of advantages such as low commission rates, low maintenance, and low running costs. On the other hand, these devices are required to be smaller, lower in price, and lower in power consumption, and therefore thermal heads are also desired to be small, inexpensive, and highly efficient.

As such a thermal head, Yabu 203 has conventionally been used.
A glazed glass layer is formed on an alumina ceramic substrate with a purity of 90% or more, and a large number of heating resistors are placed on top of the glazed glass layer.
Those formed by forming conductors connected to each of these heating resistors were often used. Here, the glazed glass layer plays the role of a heat-retaining layer that controls heat dissipation and heat accumulation.

However, a thermal head using this glazed glass layer as a heat insulating layer had the following drawbacks.

■ Glazed glass has limited thermal response characteristics as a heat insulating layer, so its efficiency is low.

■ Ceramic substrates require many steps to manufacture, including processing to remove alkaline earth metal components from raw powder, high PA firing, and finishing polishing to remove warping of the substrate that occurs during high-temperature firing. Furthermore, since it is necessary to remove alkali metal components from the raw material powder of glazed glass, the production cost is high.

As methods for solving such problems, for example, Japanese Patent Application Laid-open Nos. 52-100245 and 56-16487
As described in Japanese Patent No. 6, etc., it is known that a heat-resistant resin having a low thermal diffusivity, such as a polyimide resin, may be used as a heat insulating layer of a thermal head.

Recently, a heat insulating layer made of aromatic polyimide resin was formed on a thin metal plate, and a large number of heating resistors were formed on this heat insulating layer to create a flat thermal head, which was then used as a base. A vertical-type thermal head that can be made smaller by bending and gluing the metal member so that the heat generating part is located at the top has also been proposed. 1986), 1-125
and 5-128).

In this way, for example, polyimide resin has a lower thermal diffusivity of 173 to 176 than glaze glass, so it can greatly improve the thermal efficiency of the thermal head, and it can be bent. It is attracting attention as a heat-insulating layer for constructing small, inexpensive, and high-performance thermal heads.

However, thermal heads using such heat-resistant resin as a heat insulating layer have not yet reached the level of practical use, and have problems such as being unable to stably perform printing operations for a long period of time.

This is instantaneous 400°C ~ 500°C, regular use 250°C ~ 3
The metal support and polyimide resin layer have high heat resistance that can stably withstand the operating conditions of a thermal head operating at 50°C over a long period of time, and the adhesive strength does not deteriorate even after repeated application of heat. This is because no heat-resistant resin has been found that simultaneously provides excellent adhesion to the thin film formed thereon. If the heat resistance temperature is low, it will naturally cause thermal deterioration during use, leading to a decrease in performance, and a decrease in adhesive strength will cause the heat-resistant resin layer to peel during use, both of which will reduce the reliability of the thermal head. It reduces condylarity.

For example, a boriamic acid solution called Trenise (trade name), which is described in the examples of JP-A-56-164876, is applied on an aluminum substrate, and
0 minutes, 80℃ x 30 minutes, 120℃ x 30 minutes, 250
When a polyimide resin layer was formed by firing under the conditions of 60 minutes at 450 degrees Celsius and 60 minutes at 450 degrees Celsius, the thermal decomposition initiation temperature of this polyimide resin layer was determined by thermogravimetric measurement to be approximately 510 degrees Celsius, which indicates that it has considerable heat resistance. However, sufficient adhesion strength could not be obtained, and there were many cases of peeling off at this stage, making it impossible to withstand use with a thermal head. Furthermore, Pyre-NL (trade name,
A thermal head was fabricated using an aluminum substrate on which a polyimide resin layer (manufactured by DuPont) was formed, and the applied energy was 0.26 nJ/dot and the pulse width was 1.7 n+s.
, pulse period 5. When a pulse voltage was applied 10 A times under OIs conditions and the surface of the polyimide resin layer was observed using an ultrasonic microscope, unevenness was formed on the surface, which revealed that the quality had changed during the operation. It became.

Further, when the thermal decomposition temperature of this polyimide resin layer was measured by thermogravimetry, it was found to be as low as about 420° C., which could not withstand the operation of a thermal head.

(Problems to be Solved by the Invention) In this way, thermal heads using conventional heat-resistant resins, such as polyimide resins, as a heat insulating layer have excellent thermal efficiency due to the low thermal diffusivity of polyimide resins, and can be bent and miniaturized. While it has the advantage of being easy to use,
There were problems in that long-term reliability could not be obtained, such as the inability to stably obtain heat resistance against severe operating temperature conditions over a long period of time, and the lack of adhesive strength with metal supports.

The present invention has been made to address these conventional problems, and it further improves the heat resistance of a heat-resistant resin layer provided on a metal support as a heat-retaining layer to control heat dissipation and heat accumulation. Thermal has improved adhesion between the layer and the thin film formed on the metal support and heat-resistant resin layer, has excellent thermal efficiency, can be bent, is easy to downsize, is inexpensive, and has excellent reliability over a long period of time. The purpose is to provide the head.

[Structure of the Invention] (Means for Solving the Problems) The thermal bed of the present invention includes a metal support, a heat-resistant resin layer formed on the metal support, and a plurality of heat-resistant resin layers formed on the heat-resistant resin layer. In the thermal head comprising a heating resistor and a conductor connected to each heating resistor, the heat-resistant resin layer is formed by a ring-opening polyaddition reaction between biphenyltetracarboxylic dianhydride and aromatic diamine. It is characterized in that it consists essentially of an aromatic polyimide resin layer having a biphenyl structure in its main chain, which is formed by a dehydration cyclization reaction of the obtained polyamic acid.

Biphenyltetracarboxylic dianhydride, which is one of the starting materials for the polyamic acid that is the precursor of the aromatic polyimide resin in the present invention, is represented by the following general formula.

The biphenyltetracarboxylic dianhydride represented by the above general formula includes, for example, 3.3'', 4.4'-biphenyltetracarboxylic dianhydride, 2,2', 3.3'-biphenyltetracarboxylic dianhydride, Examples include acid dianhydrides.

In addition, as the other starting material, aromatic diamine,
Examples include p-phenylenediamine, m-phenylenediamine, diaminodiphenylsulfone, diaminodiphenylmethane, and diaminodiphenyl ether. It is also possible to use substituted products of these aromatic diamines. Examples of this substituent include lower alkyl groups such as a methyl group and an ethyl group. Specific examples of substituted aromatic diamines include 2,4-dimethyl-p-phenylenediamine, 2,4-dimethyl-m-phenylenediamine, and tetramethyl-p-phenylenediamine.

The aromatic polyimide resin layer having a biphenyl structure in the main chain of the present invention is formed, for example, by the following method.

First, a polyamic acid is produced by subjecting biphenyltetracarboxylic dianhydride and an aromatic diamine to a ring-opening polyaddition reaction, and this polyamic acid is dissolved in a suitable organic solvent to produce a varnish having an arbitrary concentration. The ratio of biphenyltetracarboxylic dianhydride and aromatic diamine used is usually equimolar, but the ratio can be changed within the allowable range of heat resistance and viscosity of the varnish. Also,
As the organic solvent used, polar organic solvents such as N-methyl-2-pyrrolidone, N-N-dimethylacetamide, N-N'-dimethylformamide, etc. are suitable.

Next, the polyamic acid varnish thus obtained is applied onto a metal support, and baked to cause a dehydration and cyclization reaction to form an aromatic polyimide resin layer.

Furthermore, in the heat-resistant resin layer of the thermal head of the present invention, it is preferable to apply any of the following methods (1) to (4), since it is possible to further improve the adhesion between the heat-resistant resin layer and the metal support.

(2) Introducing Si groups into the molecular structure of aromatic polyimide resin. This aromatic polyimide resin into which Si groups have been introduced is prepared by adding a part of the aromatic diamine at an arbitrary molar ratio, preferably approximately 0.05n+o1% to about 0.05n+o1% of the aromatic diamine component, for example, during the synthesis of the above-mentioned polyamine/nic acid. 10101%
It can be formed by using a polyamic acid obtained by substituting a diamine having a Si group and carrying out a ring-opening polyaddition reaction within the range of .

The above-mentioned diamine having a Si group may be, for example, a diamine having the general formula (wherein R is an alkylene group such as an ethylene group or a propylene group; a polymethylene group such as a nitrimethylene group or a tetramethylene group; or a divalent organic group such as a phenylene group). , R'
represents a monovalent organic group such as an alkyl group such as a methyl group or an ethyl group, and n represents a positive number. ) is exemplified by bisaminosiloxane. Typical examples of this bisaminosiloxane are as follows.

CL Cl 3 H2N-(CH2> 3-8i-0-8i = (CH
2>3-NH2CH3Cl(.

CH3CH3 (2) At least one of a silane compound having an amine bond and a silane compound having a urea bond is contained as a silane coupling agent component in an aromatic polyimide resin. This silane coupling agent can be used, for example, in the above-mentioned polyamic acid varnish with a solid content of about 0.05% to 10% by weight.
It can be contained by adding and using it in the range of weight %.

Examples of the silane compound having an amino bond added as the silane coupling agent component include γ-aminopropyltriethoxysilane and N-phenyl-γ-aminopropyltrimethoxysilane. , for example γ-ureidopropyltrimethoxysilane.

■ Between the heat-resistant resin layer and the metal support, there is a gap of 0.05μ.
An active metal layer made of Cr, Ti, etc. and having a thickness of m to 1 μm is interposed.

In addition, the introduction of Si groups into the molecular structure of the aromatic polyimide resin in (1) above and the addition of a silane coupling agent into the aromatic polyimide resin in (2) above are carried out in the thermal head manufacturing process as in (2). Not only is there no need to increase the number of layers, but also the adhesion between the heat-resistant resin layer and the thin film formed on the heat-resistant resin layer can be improved by a factor of 11.

(Function) The aromatic polyimide resin formed using biphenylteracarboxylic dianhydride and aromatic diamine, which is used as the heat-resistant resin layer in the thermal head of the present invention, has a biphenyl structure in the main chain. Due to these factors, the thermal decomposition temperature is high, allowing stable printing operation for a long period of time, and the thermal shrinkage rate is low and the difference in thermal expansion coefficient with the metal support is also small. Peeling caused by generated interfacial stress can be effectively prevented. In addition, this aromatic polyimide resin layer
Since it is formed by coating and baking a polyamic acid varnish and is bonded to the metal support at the same time as imidization, it exhibits excellent adhesion to the metal support.

Furthermore, by incorporating a silane coupling agent component into the aromatic polyimide resin or introducing a Si group into the main chain, it is possible to form a thin film on the metal support and further on the aromatic polyimide resin layer. This further strengthens the adhesive strength and improves reliability.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a partially exploded perspective view showing the main parts of a thermal head according to an embodiment of the present invention.

In the figure, reference numeral 1 indicates a metal substrate made of Fe-Cr alloy or the like and having a thickness of about 0.5 ml.

On this metal substrate 1, the following (I-1> A polyamic acid varnish prepared by dissolving polyamic acid in an organic solvent, or 0.05 m of aromatic diamine component during the synthesis of this polyamic acid.
The following polyamic acid with an SL group introduced into the molecular structure represented by the formula (I [-1> or a polyamic acid varnish using polyamic acid represented by formula (I-1), and γ represented by formula (IV) below.
-Ureidopropyltrimethoxysilane from 0.05% to 10% by weight based on the solid content in the polyamic acid varnish
Apply any of the additives and dispersers within the range of weight %,
By firing, the following formula (I-2) or (II
[-2) Made of an aromatic polyimide resin whose main skeleton is represented by the formula, the thickness is 5μIll to 50μ, preferably 10μ
A heat-resistant resin layer 2 with a thickness of μm to 30 μm is formed.

On this heat-resistant resin layer 2, SiO2, β-8iA
, 9ON, etc., and has a thickness of about 0.05 μm to 1 μm. This base layer 3 serves as a protective layer for the monoaromatic polyimide resin when the four heating resistor layers are formed into a predetermined shape by etching. Furthermore, on this base layer 3, Ta-3i02,
A large number of heating resistors 4 made of Ti-3T02 or the like and having a thickness of about 0.1 μm and having predetermined intervals are formed.
By forming openings to become heat generating parts 5 on each of these heat generating resistors 4, individual electrodes 6 and common electrodes 7 made of AJ2, AJ2-S 1-Cu, etc. and having a thickness of about 0.7 μm to 1 μm are formed. There is. 5i-0-N having a thickness of about 3 μm to 5 μm so as to cover at least the heat generating part 5.
A thermal head is constructed by forming an anti-oxidation film and anti-wear film 8.

t12N -C-NH(CH2) 1-8i(OCH
3) 3-- (IV) In the formula, m, n represent positive numbers; the same applies hereinafter).

According to this thermal head, a pulse voltage is applied between each individual type [16] and the common electrode 7 at predetermined time intervals, the heating resistor 4 corresponding to the heating section 5 generates heat, and printing is performed. be exposed.

This thermal head is manufactured, for example, as follows.

First, for example, the thickness is 0.51 containing 18% by weight of Cr.
After performing a leveling treatment on a metal substrate made of a Fe alloy of about 100 mL, it is cut to a predetermined size and deburred. Next, the metal substrate processed to a predetermined size is degreased in an organic solvent, and then immersed in dilute sulfuric acid at a temperature of about 50° C. to 70° C. to produce the metal substrate 1. This immersion treatment in dilute sulfuric acid is performed for activation treatment, which removes oxides formed on the surface of the metal substrate and roughens the surface microscopically.

Next, the aforementioned polyamic acid varnish, namely (I-
1) Polyamic acid varnish 1 whose main component is represented by the formula
．． Or a polyamic acid varnish whose main component is represented by the formula (ml-1), or a polyamic acid varnish whose main component is represented by the formula (I-1) with a silane coupling agent component added. , N-methyl-2-
The viscosity is adjusted to a predetermined value using an organic solvent such as pyrrolidone, and the film is coated onto the metal substrate 1 to a predetermined thickness using a roller coater or a spion coater. °C x 60 minutes + 80
℃×30 minutes + 120℃×30 minutes + 250℃×60
The heat-resistant resin layer 2 is formed by baking under the conditions of +450°C x 60 minutes to remove the organic solvent and proceed with a dehydration cyclization reaction to imidize the film. When forming this aromatic polyimide resin layer, if a polyamic acid to which no silane coupling agent component is added or a polyamic acid without an SL group introduced into its molecular structure is used, It is desirable to form an active metal layer of Cr, Ti, etc. with a thickness of about 0.05 μm to 1 μm on the surface by vapor deposition, and then form an aromatic polyimide resin layer thereon.

Next, 5i02 and β-8iAJ2ON are deposited on this heat-resistant resin layer 2 by sputtering or other known thin film forming methods.
Underlayer 3 consisting of Ta-8i02, Ti-
Four layers of heating resistors made of 3i02 or the like are sequentially formed.

Further, on top of the four heating resistor layers, A, g and AJ2-
A conductive layer such as 3f-Cu is formed. Next, the four heating resistor layers and the conductor layer are patterned to form a large number of heating resistors 4 and individual electrodes 6 at predetermined intervals.
and a common electrode 7. In this patterning process, first, a masking film is formed on the conductor layer so that heating resistors 4 of a predetermined shape are formed, and unnecessary parts are removed by wet etching or chemical dry etching. 9. Next, form a masking film on the conductor layer except for the part that will become the heat generating part 5, and remove only the conductor layer using the same method. At the same time as forming the heat generating part 5,
Each individual electrode 6 and a common electrode 7 are formed.

Thereafter, an anti-oxidation film and anti-wear film [8] made of 5t-0-N is formed by sputtering or the like so as to cover the heat generating portion 5.

Next, the results of evaluating the properties of the aromatic polyimide resin having a biphenyl structure in its main chain according to the present invention, such as adhesive strength and heat resistance, in the manufacturing process of this thermal head will be described.

First, using a varnish containing polyamic acid as a main component obtained by a ring-opening polyaddition reaction between biphenyltetracarboxylic dianhydride and an aromatic diamine according to this example, Fe-18 on which a Cr vapor deposited film was formed was used. An aromatic polyimide resin layer having a biphenyl structure in the main chain was formed on a wt% Cr alloy substrate, and heated at room temperature for 30 minutes at +450°C in nitrogen gas.
A thermal stress test was conducted by repeating 10 cycles of 1 cycle of 30 minutes at °C, and the presence or absence of peeling of the aromatic polyimide resin layer at that time was examined. In addition, the thermal decomposition initiation temperature, thermal shrinkage rate, and thermal expansion coefficient were measured by thermogravimetry. The results are shown in the table below. The heating shrinkage rate was measured under heating conditions of 400°C x 30 minutes, and the thermal expansion coefficient was measured using a microlinear dilatometer at a heating rate of 5°C.
This value was measured under the condition of /min.

Also, for comparison with the present invention, p
Comparative Example 1) Using phenylene diamine and pyromellitic dianhydride as the tetracarboxylic acid component, respectively.
and benzophenonetetracarboxylic dianhydride (Comparative Example 2), polyamic acids were synthesized, and an aromatic polyimide resin layer was formed under the same conditions as in the example, and then a polyimide resin layer was formed under the same conditions. The characteristics of these were evaluated in the same manner. Furthermore, comparative example 3
uses Trenice (trade name) described in the examples of JP-A No. 56-164876,
Comparative example 4 is Pyre-NL (trade name, manufactured by DuPont)
These aromatic polyimide resin layers were also evaluated in the same manner. These evaluation results are also shown in the table below.

(The following is a blank space) As is clear from the table above, peeling of the polyimide resin layer was observed except for the aromatic polyimide resin having a biphenyl structure in the main chain of this example.

This is thought to be caused by the large thermal shrinkage rate and the difference in thermal expansion coefficient between the metal substrate and the polyimide resin layer. In addition, the aromatic polyimide resin with a biphenyl structure also has the highest thermal decomposition initiation temperature determined by thermogravimetry.
It can be seen that it is suitable as a heat-resistant resin layer for a thermal head.

The aromatic polyimide resin formed using 2.2',3.3-biphenyltetracarboxylic dianhydride as the tetracarboxylic acid component in the same manner as in the above example was
Although the thermal decomposition start temperature was lowered by about 20°C, no difference was observed in other properties, and the layer was similarly effective as a heat-resistant resin layer for a thermal head. Furthermore, in the same way as in the above examples, there is no difference in properties between those using aromatic diamines having substituents such as methyl groups and ethyl groups and those using unsubstituted aromatic diamines. Similarly, it was suitable as a heat-resistant resin layer for a thermal head.

Next, during the formation of molecule rIII represented by the formula (TE-2>), S
Aromatic polyimide resin with t group introduced and (I-2)
Evaluation of adhesion strength and heat resistance of aromatic polyimide resins containing γ-ureidopropyltrimethoxysilane represented by the formula (Iv) as a silane coupling agent component in the aromatic polyimide resin represented by the formula. went.

Figure 2 is a diagram showing the relationship between the substitution ratio of the above-mentioned bisaminodisiloxane in the aromatic diamine component, the adhesion strength and thermal decomposition initiation temperature for the metal substrate (without Cr deposited film) and the 5i02 layer, respectively. be. Figure 3 also shows the amount of the silane coupling agent added (wt% relative to the solid content in the polyamic acid varnish), the adhesion strength and thermal decomposition start temperature to the metal substrate (without Cr vapor deposited film) and the 5i02 layer, respectively. FIG.

The adhesion strength between the aromatic polyimide resin layer and the metal substrate was measured in accordance with JIS standard 06481, 5, 7 r peel strength. On the other hand, the adhesion strength between the aromatic polyimide resin layer and the 5i02 layer was measured as follows. S formed on the aromatic polyimide resin layer
i On the O2 layer, AJ2iμrn, Cr 0.1μ
IIl, 3 μl of Cu, and 1 μl of Au were successively formed by mask sputtering, and then the portions of S i O 2 not covered by these debris were removed by chemical dry etching. After this, a diameter of 0 is placed on Cu.
．． 8In Sn-plated Cu wire was soldered and measured by a tensile test.

In both cases, it can be seen that the adhesion strength is significantly improved by introducing the Si component.

The heating resistor of the thermal head can instantaneously heat up to 400°C to 500°C.
℃, operating at a sustained temperature of 250℃~350℃, but the second
From the results shown in the figure, the substitution ratio by bis-aminosiloxane is
It is clear that a range of 0.051o 1% to 10+1101% is desirable. This is because when the substitution ratio by bis-aminosiloxane is less than approximately 0.05 to 1%, no improvement in adhesive strength is observed;
This is because if it exceeds X, not only the effect of improving adhesion strength will be saturated, but also the heat resistance will deteriorate significantly. Moreover, from the results shown in FIG. 3, it can be seen that the amount of the silane coupling agent added is preferably in the range of approximately 0.05% by weight to 10% by weight. This is because if the amount of the silane coupling agent added is less than approximately 0.05% by weight, the effect of improving bond strength will not be observed, and if it exceeds approximately 10% by weight, the effect of improving bond strength will be saturated. .

In addition to the above-mentioned γ-ureidopropyltrimethoxysilane, silane coupling agent components include γ-aminopropyl I-rimethoxysilane represented by the following formula (V) and N-phenyl represented by the formula (Vf). Similar effects were obtained when -γ-aminopropyltrimethoxysilane was used.

H2N-CsH5-8i (OC2Hs) 3-- (
By introducing an St group or containing a silane coupling agent component in V), the adhesive force with the metal substrate or the inorganic insulating material serving as the underlying layer is further improved. Therefore, a highly reliable thermal conductor can be obtained. In particular, a specific amount of St in the molecule i of aromatic polyimide resin
By introducing the group, the adhesive strength is significantly improved without impairing the heat resistance, making it suitable as a heat-resistant resin layer for a thermal head.

Next, we evaluated the efficiency of the thermal head.

First, as a conventional example, S i O2-B a O-Ca
0-AJ2203'-B203 A glazed glass layer made of ZnO with a thickness of approximately 70 μm was formed on an alumina ceramic substrate, and a base layer, heating resistor, electrode, and protective film were formed in the same manner as in this example. A thermal head was constructed. The aromatic polyimide resin layer represented by the above formula (I-2) in this example is then printed using the thermal head using this glaze glass, and based on the input power at which a certain color density is obtained. , or an aromatic polyimide resin layer represented by the above formula (I [[-2)], or an aromatic polyimide resin represented by the above formula (I-2>) containing a silane coupling agent component. For each thermal head used, the power input to obtain the same color density was determined as a ratio.The results were calculated as the power input ratio (ratio when the power input by the thermal head using glaze glass was set to 1), and Graphed as a relationship with the film thickness of the polyimide resin layer,
It is shown in Figure 4.

As is clear from FIG. 4, when the aromatic polyimide resin having a biphenyl structure in the main chain according to the present invention is used as the heat-resistant resin layer, it is possible to obtain the same color density as when using glaze glass. It can be seen that low input power is sufficient, that is, the thermal efficiency is excellent. Also,
From the results shown in Figure 4, the thickness of the aromatic polyimide resin layer is
It can also be seen that a range of 5 μl to 50 μm is preferable.

When the thickness of the aromatic polyimide resin layer is less than approximately 5 μm,
This is because a sufficient efficiency improvement effect cannot be expected, and this effect will be saturated if the thickness exceeds 50 μm.

Furthermore, in order to obtain basic knowledge related to efficiency improvement, Fig.
Thermal diffusivity in the thickness direction measured using the laser flash method is shown. The aromatic polyimide resin having a biphenyl structure in the main chain according to the present invention has a thermal diffusivity as low as approximately 1/10 of that of conventional glaze glass, making it possible to construct a highly efficient thermal head. it is obvious. Furthermore, when 81 groups are introduced into the molecular structure, the thermal diffusivity is further reduced, albeit slightly, and further improvement in efficiency can be expected.

Furthermore, using the thermal head in this example, the applied energy was 0.26 mJ/dot, and the pulse width was 1.7.
A pulse voltage was applied 106 times under conditions of 1'lls and a pulse period of 5.0 ms, and when the surface of the aromatic polyimide resin layer was observed using an ultrasonic microscope, no deterioration was observed at all.

In this example, the ratio of biphenyltetracarboxylic dianhydride and aromatic diamine used was equimolar, but the present invention is not limited to this, and the use of heat resistance and viscosity during synthesis Within the allowable range, the mixing ratio is ±710
It may be used with a change within a range of about 1%.

Furthermore, in the present invention, since a metal member is used as the support, it is also possible to use this metal support as a common electrode, further reducing production costs.

Further, the anti-oxidation film/wear-resistant film does not necessarily have to be provided on the entire surface, but it can sufficiently exhibit its function if it is formed at least on the heat generating part.

[Effects of the Invention] As explained above, in the thermal head of the present invention,
The aromatic polyimide resin synthesized from biphenyltetracarboxylic dianhydride and aromatic diamine used as the heat-resistant resin layer has a high thermal decomposition temperature due to the biphenyl structure in the main chain, and can withstand harsh usage temperature conditions. It has sufficient heat resistance, has a small difference in coefficient of thermal expansion with the metal support, and has excellent adhesive strength. Therefore, the thermal head of the present invention using such an aromatic polyimide resin as a heat-resistant resin layer has excellent reliability and
It fully takes advantage of the properties of polyimide resin, has excellent thermal efficiency, is inexpensive, and can be miniaturized.

[Brief explanation of the drawing]

FIG. 1 is a partially exploded perspective view showing the main parts of a thermal head according to an embodiment of the present invention, and FIG. 2 is a substitution ratio of aromatic diamine components with diaminodisiloxane in the process of forming an aromatic polyimide resin according to the present invention. A graph showing the relationship between the adhesive strength of this aromatic polyimide resin layer and the base layer formed on the metal substrate and the aromatic polyimide resin layer, and the thermal decomposition initiation temperature of this aromatic polyimide resin. Figure 3 shows the amount of silane coupling agent added during the formation process of the aromatic polyimide resin according to the present invention, and the adhesion strength between this aromatic polyimide resin layer and the base layer formed on the metal substrate and the aromatic polyimide resin layer. , and a graph showing the relationship between the thermal decomposition start temperature of this aromatic polyimide resin, and FIG. A graph showing comparison, FIG. 5, is a graph showing the thermal diffusivity of the aromatic polyimide resin and glaze glass according to the present invention. 1...Metal substrate 2...Heat-resistant resin layer 3...
...Underlayer 4...Heating resistor 5...
・・・・・・Heating part 6・・・・・・・・・Individual electrode 7・・・・・・・・・Both i! Electrode 8...
...Anti-oxidation film and wear-resistant film Applicant: Toshiba Corporation Norishiba Chemical Co., Ltd. Representative patent attorney: Sasuyama - ψ; Figure 1. [- Fig. 2

Claims (3)

[Claims] (1) A metal support, a heat-resistant resin layer formed on this metal support, a large number of heating resistors formed on this heat-resistant resin layer, and a conductor connected to each of these heating resistors. In the thermal head, the heat-resistant resin layer has a main chain formed by a cyclodehydration reaction of a polyamic acid obtained by a ring-opening polyaddition reaction between biphenyltetracarboxylic dianhydride and an aromatic diamine. A thermal head comprising essentially an aromatic polyimide resin layer having a biphenyl structure. (2) The aromatic polyimide resin having a biphenyl structure in the main chain can be produced by replacing a part of the aromatic diamine with a diamine having a Si group during the synthesis of the polyamic acid. The thermal head according to claim 1, wherein a group is introduced. (3) The aromatic polyimide resin having a biphenyl structure in the main chain contains at least one of a silane compound having an amino bond and a silane compound having a urea bond as a silane coupling agent component. The thermal head according to claim 1.