JPH0659737B2 - Thermal head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Industrial field of application) The present invention forms a polyimide resin layer as a heat retaining layer on a ceramic support having high thermal conductivity, and deposits the polyimide resin layer on the polyimide resin layer. The present invention relates to a highly efficient thermal head formed by forming a large number of heating resistors.

(Prior Art) In recent years, thermal heads have been widely used in various recording devices such as facsimiles and printers for word processors, taking advantage of low noise, low maintenance, low running cost, and the like. On the other hand, these devices are required to be small in size, low in cost, and low in power consumption. Therefore, a thermal head that is small, inexpensive, and highly efficient is also desired.

Such a thermal head has an Al ₂ O ₃ purity of 90.
% Or more, a glaze glass layer with a thickness of about 50 to 150 μm is formed on a ceramic substrate with a thickness of about 0.5 to 1.0 mm, a large number of heating resistors and a conductive material connected to the heating resistors. The ones that form the body are often used.
Here, the glaze glass layer plays a role as a heat retaining layer that controls heat dissipation and heat storage.

By the way, in the thermal head using the glaze glass layer as a heat insulating layer, there is a limit to the thermal response characteristics as the heat insulating layer. Therefore, in order to increase the efficiency of the thermal head such as high speed printing while satisfying the printing performance. , For example
As described in JP-A-52-100245 and JP-A-56-164876, it is known that a resin having a small thermal conductivity, such as an aromatic polyimide or an epoxy resin, may be used as the heat retaining layer.

However, the method of using such a heat-resistant resin as a heat insulating layer has not yet reached the stage of being sufficiently put into practical use. It has high heat resistance that can withstand the operating conditions of a thermal head that operates instantaneously at 400 ° C to 500 ° C and normal 250 ° C to 350 ° C. It also has excellent adhesiveness to a ceramics support and can be repeatedly heated. This is because there was no heat-resistant resin with excellent reliability that does not cause deterioration of adhesion or peeling.

According to the experiments conducted by the present inventors, for example, JP-A-56-164876
Al ₂ O using a polyimide varnish (polyamic acid) described in Japanese Patent Publication No. TRENEICE # 200 (presumed to be synthesized from pyromellitic dianhydride and o-phenylenediamine) _{When the} thermal decomposition start temperature was measured by thermogravimetric measurement, the polyimide resin layer formed on the ₃ substrate had a considerable heat resistance of about 510 ° C, but sufficient adhesive force was not obtained and immediately at this stage The thermal head was not able to withstand the operation of the thermal head.

(Problems to be Solved by the Invention) As described above, in a thermal head in which a polyimide resin layer is formed on a ceramics support and a large number of heating resistors are formed on the polyimide resin layer, a polyimide head having a low polyimide resin is used. On the other hand, it has the advantage of excellent thermal efficiency due to the thermal diffusivity, but on the other hand, the heat resistance temperature of the polyimide resin itself is not sufficient for the severe operating temperature conditions of the thermal head, and the adhesive strength to the ceramics support is lacking, etc. There was a problem of being low.

The present invention has been made in order to solve such problems, the heat resistance of the polyimide resin layer provided as a heat retaining layer for controlling heat dissipation and heat storage on the ceramic support and the ceramic support It is an object of the present invention to provide a high-performance thermal head having improved adhesive strength, high reliability, and excellent thermal efficiency.

[Structure of the Invention] (Means for Solving the Problems) A thermal head of the present invention comprises a ceramic support having high thermal conductivity, a heat-resistant resin layer formed on the ceramic support, and a heat-resistant resin layer formed on the ceramic support. In a thermal head comprising a plurality of heating resistors formed in, and a conductor connected to each heating resistor, the heat-resistant resin layer,
A biphenyl structure is formed on the main chain formed by applying a polyamic acid varnish obtained by a ring-opening polyaddition reaction of biphenyltetracarboxylic dianhydride and an aromatic diamine onto the ceramic support and then baking it to cause a dehydration cyclization reaction. It is characterized by comprising an aromatic polyimide resin having

That is, the heat-resistant resin layer in the present invention is obtained by subjecting a biphenyltetracarboxylic dianhydride and an aromatic diamine, for example, obtained by subjecting an equimolar mixture to a ring-opening polyaddition reaction, and a suitable polyamic acid serving as a precursor of a polyimide resin. It is composed of an aromatic polyimide resin having a biphenyl structure in the main chain formed by applying a varnish dissolved in an organic solvent to a varnish applied on a ceramic support and then firing it to cause a dehydration cyclization reaction. is there.

Examples of this aromatic diamine include diaminodiphenyl ether, diaminodiphenyl sulfone, p-phenylenediamine, and m-phenylenediamine, but especially p-
When phenylenediamine is used, it is the best in terms of heat, and the difference in the coefficient of thermal expansion, which causes peeling from the ceramic support, becomes small.

In the thermal head of the present invention,
It is preferable to apply any of the above because the adhesion between the heat resistant resin layer and the ceramic support can be further improved.

A Si group is introduced into the molecular structure of a polyimide resin having a biphenyl structure in the main chain. The polyimide resin introduced with the Si group, for example, when synthesizing the above-mentioned polyamic acid, a part of the aromatic diamine in an arbitrary molar ratio, desirably in the range of about 0.05 to 10 mol% of the aromatic diamine component, Si It can be formed by using a polyamic acid obtained by substituting a diamine having a group for ring-opening polyaddition reaction.

Examples of the Si group-containing diamine used for introducing the Si group include those represented by the general formula (In the formula, R represents a divalent organic group, R ′ represents a monovalent organic group,
n shows a positive number. ) And bisaminosiloxane.

At least one of a silane compound having an amino bond and a silane compound having a urea bond is contained as a silane coupling agent component in a polyimide resin having a biphenyl structure in the main chain. This silane coupling agent can be contained by adding and using it in the range of approximately 0.05 to 10% by weight of the solid content of the varnish containing polyamic acid as the main component.

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.

About 500 between the heat resistant resin layer and the ceramic support
An active metal layer made of Cr, Ti or the like having a thickness of Å to 10,000 Å is interposed.

The introduction of Si groups into the molecular structure of the above polyimide resin and the addition of the silane coupling agent into the above polyimide resin further affect the adhesion between the heat resistant resin layer and the thin film formed on the heat resistant resin layer. Can be greatly improved.

Examples of the highly thermal conductive ceramic support used in the present invention include aluminum oxide (Al ₂ O ₃ ), aluminum nitride (AlN), silicon nitride (Si ₃ N ₄ ), silicon carbide (Si
C), sialon (SiAlON), beryllium oxide (BeO), etc. are the main examples of the ceramic sintered body.

(Operation) By using the above means, the aromatic polyimide-based resin having a biphenyl structure in the main chain used as the heat-resistant resin layer in the thermal head of the present invention has a small heat shrinkage rate even by the addition of a cooling / heating cycle. Further, since the difference in the coefficient of thermal expansion with the ceramic support is small, the interfacial stress caused by the difference in the coefficient of thermal expansion, which is considered as one of the factors, can be effectively prevented from peeling. Further, as the aromatic diamine component which is one of the components of the polyamic acid synthesis, an aromatic polyimide resin obtained by using p-phenylenediamine, in particular, has the smallest difference in thermal expansion coefficient from the ceramic support and peels off. Can be prevented more effectively. Furthermore, by using a polyamic acid synthesized by substituting a part of the aromatic diamine with a diamine having a Si group at the time of synthesizing the polyamic acid, or by adding a silane coupling agent component to the polyamic acid and using it, Si The base component further strengthens the adhesive force.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view showing a main part of a thermal head according to an embodiment of the present invention. In FIG. 1, 1 is a ceramic support having high thermal conductivity.
The polyamic acid represented by the following formula (I-1) obtained by the ring-opening polyaddition reaction of an equimolar mixture of biphenyltetracarboxylic dianhydride and p-phenylenediamine was dissolved in an organic solvent. The polyamic acid varnish thus obtained, or the following (III- 1) A polyamic acid varnish obtained by dissolving a polyamic acid having a Si group introduced into the molecular structure represented by the formula in an organic solvent, or a polyamic acid varnish represented by the above-mentioned formula (I-1) is added to By applying and baking a polyamic acid varnish in which γ-ureidopropyltrimethoxysilane represented by the formula is added and dispersed in the range of 0.05 to 10% by weight, the following (I-2 ) Formula or (III-2)
The thickness of the aromatic polyimide resin represented by the formula is approximately 5
A heat-resistant resin layer 2 having a thickness of μm to 50 μm, preferably 10 to 30 μm is formed. And on this heat-resistant resin layer 2, SiO ₂ ,
Underlayer 3 made of β-SiAlON, etc. and Ta-SiO ₂ , Ti-SiO ₂
A heat generating resistor 4 made of, for example, is formed in this order, and A is formed on the heat generating resistor 4 so that an opening serving as a heat generating portion 5 is formed.
l, an individual electrode 6 and a common electrode 7 made of Al-Si-Cu or the like are formed, and at least the heating portion 5 is covered,
An anti-oxidation film / anti-wear film 8 made of a Si-ON type compound or the like is formed.

In the formula, l, m, and n represent positive numbers (the same applies hereinafter).

In this thermal head, by applying a pulse voltage at a predetermined time interval between the individual electrode 6 and the common electrode 7, the heat generating resistor 4 of the heat generating portion 5 generates heat, and print recording is performed.

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

First, a predetermined shape with a thickness of about 0.85 mm, for example, a purity of 96%
After cleaning and drying the ceramic support 1 made of Al ₂ O ₃ sintered body, the above polyamic acid is adjusted to a predetermined viscosity by using a solvent such as N-methyl or 2-pyrrolidone, Coat the ceramic support 1 to a specified thickness with a roll coater, spin-on coater, etc., and use a firing furnace at 50 ° C for 1 hour, 80 ° C for 30 minutes, and then 120 ° C for 30 minutes.
Min., 250 ° C. × 1 hour, 450 ° C. × 1 hour to remove the solvent and to proceed with the dehydration cyclization reaction to form a film,
The heat resistant resin layer 2 is formed. At this time, the silane coupling agent component is not contained, or S in the molecular structure is added.
When using a polyamic acid without introduction of i group,
It is desirable to form a polyimide resin layer after forming an active metal layer such as Cr or Ti having a thickness of about 500Å to 10000Å on the surface of the ceramic support 1 by a method such as vapor deposition.

Next, on the heat-resistant resin layer 2, by sputtering or another method, an underlayer 3 made of SiO ₂ or β-SiAlON or the like having a thickness of 500 Å to 10000 Å and heat generated by Ta-SiO ₂ or Ti-SiO ₂ etc. Resistor 4, individual electrode 6 and common electrode 7
A conductive layer made of Al or Al-Si-Cu is formed. Then, after masking so that an opening to be the heating portion 5 is formed, a predetermined pattern is formed by wet etching, chemical dry etching, or the like. After that, the masking film is removed, and an anti-oxidation film / abrasion resistant film 8 made of a Si-ON based compound or the like is formed by, for example, a sputtering method so as to cover at least the heating portion 5.

Next, in the manufacturing process of this thermal head, characteristics such as adhesion and heat resistance of the polyimide resin were evaluated.

First, with the biphenyltetracarboxylic acid of the above-mentioned example
Using a polyamic acid obtained by the ring-opening polyaddition reaction with p-phenylenediamine, Al ₂ with a Cr vapor deposition film formed
A polyimide resin layer (Example 1) was formed on an O ₃ substrate, and a thermal stress test was repeated in N ₂ gas under the conditions of room temperature × 1 hour and 450 ° C. × 1 hour. The layers were examined for peeling. Further, the thermal decomposition start temperature, the heat shrinkage amount, and the thermal expansion coefficient were also measured by the thermogravimetric method. The results are shown in the table below.

Further, instead of p-phenylenedisamine in the above examples, m-phenylenediamine (Example 2) and diaminogenyl ether (Example 3) were used as aromatic diamine components, respectively, and polyamic acid was similarly added. After the synthesis, a polyimide resin layer was formed under the same conditions. The properties of these materials were evaluated in the same manner, and the results are shown in the following table.

In the comparative examples in the table, p-phenylenediamine used in the examples was used as the aromatic diamine component, and pyromellitic dianhydride (Comparative Example 1) and benzophenonetetracarboxylic acid were used as the tetracarboxylic acid components. (Comparative Example 2) was used to synthesize polyamic acid,
It is a result of forming a polyimide resin layer under the same conditions as in the example and performing the same evaluation as in the example.

As is clear from the previous table, as a tetracarboxylic acid component, a polyimide resin synthesized using biphenyltetracarboxylic dianhydride has less heat shrinkage than polyimide resins using other tetracarboxylic acid components, and Since the coefficient of thermal expansion is small and is close to the coefficient of thermal expansion of the ceramics support, peeling from the ceramics support when heat stress is applied is reduced. In addition, the polyimide resin using p-phenylenediamine as the aromatic diamine component according to Example 1 is particularly excellent in heat resistance and has the smallest difference in the coefficient of thermal expansion from the ceramic support. It can be seen that peeling, which is considered to be caused by the difference, was effectively prevented. In addition, in the polyimide resins according to other examples, by introducing a Si group into the molecular structure or by adding the above-mentioned silane coupling component, the adhesive strength that can be practically used as a thermal head can be obtained.

Next, the adhesive strength and heat resistance of the polyimide resin of Example 1 having Si groups introduced in the molecular structure and the polyimide resin of Example 1 containing the silane coupling agent component were evaluated.

FIG. 2 is a diagram showing the relationship between the ratio of the above-mentioned bisaminosiloxane in the p-phenylenediamine component and the adhesion strength and the thermal decomposition start temperature, and FIG. 3 is the same as the above-mentioned silane coupling agent. FIG. 3 is a diagram showing the relationship between the addition amount (% by weight based on the solid content in the polyamic acid varnish), the adhesion strength, and the thermal decomposition start temperature. In either case,
It can be seen that the adhesion strength is greatly improved.

In addition, the heating resistor of the thermal head is instantaneously 400 ℃ ~ 500
It operates at a temperature of 250 ℃ to 350 ℃, but the substitution ratio of bisaminosiloxane is about 0.05〜.
It is understood that the range of 10 mol% is preferable, and from the result of FIG. 3, the addition amount of the silane coupling agent is preferably 0.05 to 10% by weight. Further, the addition of the silane coupling agent improves the heat resistance, though slightly.

Further, as the silane coupling agent component, the above-mentioned γ-
In addition to ureidopropyltrimethoxysilane, γ-aminopropyltrimethoxysilane represented by the following formula (V) and N-phenyl-γ-aminopropyltrimethoxysilane represented by the formula (VI) are also used. Similar effects were obtained.

Next, the efficiency of the thermal head was evaluated.

First, as a conventional example, a glaze glass layer of SiO ₂ —BaO—CaO—Al ₂ O ₃ —B ₂ O ₃ —ZnO having a thickness of about 70 μm was formed on an Al ₂ O ₃ substrate. Similarly, the underlayer,
A heat generating resistor, an electrode and a protective film were formed to form a thermal head. Then, printing was performed by a thermal head using this glaze glass layer, and the thermal power using the polyimide resin layer (Example 1) in this example was used as a reference, based on the input power at which a certain color density was obtained. The input power for obtaining the color density of was calculated as a ratio. A graph of the relationship between the input power ratio (the ratio of the input power by the thermal head using the glaze glass layer to 1) and the film thickness of the polyimide resin layer
It is shown in FIG.

As is clear from FIG. 4, when the polyimide resin of the present invention is used as the heat insulating layer, a low input power is sufficient to obtain the same color density as in the case of using the glaze glass, that is, thermal efficiency is improved. It turns out to be excellent.
From the result of FIG. 4, the thickness of the polyimide resin layer is
It is also understood that the range of approximately 5 μm to 50 μm is preferable.

Further, FIG. 5 shows the thermal diffusivity in the thickness direction measured by the laser flash method in order to obtain the basic knowledge resulting from the improvement in efficiency. The aromatic polyimide resin having a biphenyl structure in the main chain according to the present invention has a thermal diffusivity as low as about 1/10 of that of conventional glaze glass, which makes it possible to configure a highly efficient thermal head. it is obvious. Further, when Si group is introduced into the molecular structure,
It can be seen that the thermal diffusivity is further lowered, though a little, and further improvement in efficiency can be expected.

In this example, the equimolar mixture was used as the mixture of the biphenyltetracarboxylic dianhydride and the aromatic diamine, but the present invention is not limited to this, and the heat resistance and the viscosity at the time of synthesis are used. The mixing ratio may be changed and used within the allowable range of use. Further, in the present embodiment, the Al ₂ O ₃ substrate was used as the ceramic support, but the present invention is not limited to this, and AlN, Si ₃ N ₄ , S
Similar effects can be obtained when other ceramic sintered bodies having high thermal conductivity such as iC, SiAlON, BeO, etc. are used.

[Effects of the Invention] As is clear from the above examples, according to the thermal head of the present invention, ring-opening polyaddition of biphenyltetracarboxylic dianhydride and aromatic diamine as a heat retaining layer on a ceramic support. Since a heat-resistant resin layer made of an aromatic polyimide resin formed by the dehydration cyclization reaction of polyamic acid by the reaction is used, it has sufficient heat resistance, so it can be heated under severe operating conditions of a thermal head. It does not break or deteriorate, and by using p-phenylenediamine as the aromatic diamine component, the difference in the coefficient of thermal expansion with the ceramic support becomes small, and this is due to the interfacial stress generated by this difference in thermal expansion. Peeling can be effectively prevented. Furthermore, when synthesizing the polyamic acid, part of p-phenylenediamine was replaced with Si.
By using a polyamic acid synthesized by substituting a diamine having a group or by adding a silane coupling agent component to this polyamic acid, the adhesion is further enhanced. Therefore, it is possible to provide an inexpensive and highly efficient thermal head that is excellent in reliability and fully utilizes the characteristics of the polyimide resin.

[Brief description of drawings]

FIG. 1 is a perspective view showing a main part of a thermal head according to an embodiment of the present invention, and FIG. 2 is a graph showing the relationship between the ratio of diaminosiloxane in an aromatic diamine and the adhesion strength and the thermal decomposition starting temperature. FIG. 3 is a graph showing the relationship between the addition amount of the silane coupling agent and the adhesion strength and the thermal decomposition start temperature, and FIG. 4 is a thermal head of one embodiment of the present invention and a conventional heat insulating layer using glaze glass. FIG. 5 is a graph comparing the efficiencies of the thermal heads, and FIG. 5 is a graph comparing the thermal diffusivities of the aromatic polyimide according to the present invention and the glaze glass used in the heat retaining layer of the conventional thermal head. 1 ... Ceramic support 2 ... Heat-resistant resin layer 3 ... Underlayer 4 ... Heating resistor 5 ... Heating part 6 ... Individual electrode 7 ... Common electrode 8 ... Antioxidant and abrasion resistant film

Front Page Continuation (72) Inventor Yoshiaki Ouchi 72 Horikawa-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Higashi-shiba, Higashi-Kawa Plant, Ltd. (72) Teru Okunoyama 9-2 Chidori-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Toshiba Chemical Chidoricho Factory Co., Ltd. (56) References JP-A-60-130190 (JP, A) Actually opened 61-168942 (JP, U)

Claims (14)

[Claims] 1. A ceramic support having high thermal conductivity, a heat-resistant resin layer formed on the ceramic support, a plurality of heat-generating resistors formed on the heat-resistant resin layer, and each of these heat-generating resistors. In a thermal head comprising a connected conductor, the heat-resistant resin layer is formed by applying polyamic acid varnish by ring-opening polyaddition reaction of biphenyltetracarboxylic dianhydride and aromatic diamine onto the ceramic support. A thermal head comprising an aromatic polyimide resin having a biphenyl structure in the main chain formed by baking and then performing a cyclodehydration reaction. 2. The thermal head according to claim 1, wherein the aromatic diamine is p-phenylenediamine. 3. The aromatic polyimide resin having a biphenyl structure in the main chain, wherein Si groups are introduced into the molecular structure thereof.
The thermal head according to the item. 4. An aromatic polyimide resin having a biphenyl structure in the main chain, in which a Si group is introduced into the molecular structure,
It is formed by a dehydration cyclization reaction of a polyamic acid obtained by replacing a part of the aromatic diamine with a diamine having a Si group during a ring-opening polyaddition reaction of biphenyltetracarboxylic dianhydride and an aromatic diamine. The thermal head according to claim 3, characterized in that 5. The diamine having a Si group is represented by the general formula: (In the formula, R represents a divalent organic group, R ′ represents a monovalent organic group,
n shows a positive number. 5. A thermal head according to claim 4, which is a bisaminosiloxane represented by the formula (4). 6. The addition amount of the Si group-containing diamine is
The thermal head according to claim 4 or 5, characterized in that it is in a range of 0.05 to 10 mol% of the aromatic diamine component. 7. 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 or 2. 8. The silane compound having an amino bond is
The thermal head according to claim 7, which is γ-aminopropyltriethoxysilane or N-phenyl-γ-aminopropyltrimethoxysilane. 9. The silane compound having a urea bond is γ
A thermal head according to claim 7, characterized in that it is ureidopropyltrimethoxysilane. 10. The amount of the silane coupling agent added is
The thermal head according to any one of claims 7 to 9, wherein the solid content in the polyamic acid is in the range of 0.05 to 10% by weight. 11. An active metal layer having a thickness of approximately 500Å-10000Å is provided between the high thermal conductive ceramic support and the heat-resistant resin layer. The thermal head according to item 1 or 2. 12. The thermal head according to claim 11, wherein the active metal is made of either Cr or Ti. 13. The heat resistant resin layer has a thickness of 5 μm to 50 μm.
The thermal head according to claim 1, wherein the thermal head has a range of m. 14. The ceramic support having high thermal conductivity,
The thermal head according to claim 1, which is made of a ceramic sintered body containing any of aluminum oxide, aluminum nitride, silicon nitride, sialon, and beryllium oxide as a main component.