JPH04101855A - Thin film, thermal head using that, and forming method of the same thin film - Google Patents

Abstract

PURPOSE:To obtain an appropriate heat reserving layer of a thermal head by a method wherein a thin film consisting of a plasma polymer of pyromellitic dianhydride is used. CONSTITUTION:An alumina substrate 11 as a substrate is established in a reacting container of a plasma polymerization apparatus PD-10s and besides pyromellitic dianhydride (PMDA)is prepared on a board for sublimation by heating inside the reacting container. After making an inside of the reacting container a high vacuum state, ammonia gas in the reacting container is made plasma by high frequency while ammonia gas is being introduced. Then, PMDA is sublimated by heating in the reacting container under a state in which plasma is generated, and a thin film (a polymerized film having polyamic acid structure) is formed on the alumina substrate. When this thin film reaches a specific film thickness, sublimation by heating of PMDA is stopped, and supply of ammonia gas is stopped. Then, when the thin film is heated in the reacting container under a vacuum state, a dehydrating cyclization reaction occurs in the thin film, and this thin film 13 becomes a polymerized film having an imide ring structure.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a thin film suitable for use, for example, as a heat insulating layer of a thermal head, a thermal head using this thin film, and a method for forming this thin film.

(Prior art) Thermal printing involves bringing a thermal head into contact with thermal paper to print on the thermal paper, or bringing a thermal head into contact with an ink ribbon to transfer ink from the ink ribbon onto recording paper to perform printing. A thermal transfer printing device is a typical non-impact printing device, and is used in various fields including the ○A field.

In order to achieve low power consumption and high-speed printing in this type of device, the characteristics of the thermal head are very important.

The thermal heads conventionally used are as follows. FIG. 4(A) is a diagram for explaining an example thereof, and is a sectional view showing the vicinity of one heat generating part of this thermal head taken along the thickness direction of the substrate.

This thermal head includes a substrate 1, a heat insulating layer 3 provided on the substrate 1, a heating resistor 15 provided on the heat insulating layer 13, and a heating resistor 15 that is spaced apart from each other. The power supply bodies 17a and 17b provided with the power supply body 17
a, 17b and a protective layer provided to cover the heating resistor 15] 9. In this structure, a portion of the heat generating resistor 15 between the power supply bodies 17a and 17b becomes a heat generating portion 15a.

In addition, in order to protect the heat insulating layer 13 from various treatments in the manufacturing process of the thermal head that are performed after forming the heat insulating layer 13, an intermediate layer 2 is placed on the heat insulating layer 13, as shown in FIG. 4(B).
1 was also known.

In any type of thermal head, a heat insulating layer] 3 is provided between the substrate 11 and the heating resistor 15.

This heat insulating layer] 3 is connected to a power supply body 17a,
Electric power is applied to the heat generating part 15a through 17b8, and the heat generating part 1
This is provided in order to prevent heat from escaping to the substrate 11 side when heat is generated by 5a, and to efficiently secure the heat necessary for printing.

Therefore, the thermal conductivity of the heat insulating layer 3 is determined by its thermal conductivity or the heat generating resistor 15
The protective layer 19 may be made of a material whose thermal conductivity is lower than that of the protective layer 19 placed on the opposite side.

However, in the past, the protective layer ] 9 was generally made of silicon dioxide (Si
O2) and tantalum pentoxide (Ta205), and their thermal conductivity is 3 to 9 x 1O-3cal/cm-
sec・”C, and since the heat insulating layer 13 was also made of glazed glass, its thermal conductivity was approximately 3 to 9×1O−3.
cal/cm・sec・°C. Therefore, in order to ensure the necessary and sufficient amount of heat during printing (to reduce the amount of heat escaping to the board side), the thickness of the heat insulating layer 13 must be adjusted. It was necessary to make it thicker to increase the heat retention effect. Therefore, as the thickness of the heat insulating layer 13 increases, its heat capacity increases.
When cooling a thermal head, thermal resistance increases. Therefore, the next printing is performed before the thermal head is completely cooled down, so the temperature of the thermal head gradually increases each time printing is repeated, and as a result, the print quality deteriorates.

In order to solve this problem, a thermal head with a heat insulating layer made of a glass layer with many holes was developed, for example in Japanese Patent Laid-Open No. 62-15
This was disclosed in the prior art section of Publication No. 54.

Since this heat insulating layer has a large number of pores inside it, its thermal conductivity is lower than that of a layer without pores. Therefore, in this heat insulating layer, heat from the heat generating portion when voltage is applied is difficult to escape to the substrate side. Furthermore, since the thermal conductivity can be reduced, the film thickness of the heat insulating layer can be made thinner, and therefore the heat capacity of the heat insulating layer can be reduced, so that the heat generating part can be cooled well during cooling. Therefore,
It is expected that a thermal head exhibiting good thermal responsiveness will be obtained.

(Problems to be Solved by the Invention) However, in order to obtain such a heat retaining layer, there are actually problems as described below.

- When forming a glass layer with a large number of pores, there is a method in which a paste-like material containing glass powder is fired under certain conditions to generate a desired amount of bubbles from inside the glass powder. Conceivable. However, in order to apply this method to the formation of a heat insulating layer of a thermal head and to control the diameter and density of the pores within a certain range, the firing temperature of the paste must be, for example, ±2 to 3°C relative to the set temperature. It becomes difficult to control the formation conditions, such as having to control them within the range of .

■・-Also, if the formation conditions of (■) cannot be controlled, the amount of bubbles generated from inside the glass powder will vary, which will cause the amount of pores in the heat insulating layer to vary, resulting in variations in the thermal response of the thermal head. This can cause Furthermore, when air bubbles with an abnormally large diameter are generated, pores with an abnormally large diameter are generated in the heat insulating layer, thereby reducing the mechanical strength of the heat insulating layer. In some cases, the holes may not remain inside the heat insulating layer but may extend to the surface, making the surface of the heat insulating layer uneven. This can make printing difficult and ultimately have a negative impact on print quality.

This invention was made in view of these points,
Therefore, an object of the present invention is to solve the above-mentioned problems and provide a thin film suitable for use as a heat insulating layer of a thermal head, a thermal head using this thin film, and a method for forming this thin film.

(Means for Solving the Problem) In order to achieve this objective, the inventor of this application has conducted various studies. First, they focused on the fact that polymers have a lower thermal conductivity than glass, and conducted extensive research into using a polymer membrane as a heat-insulating layer. Here, the problem was ensuring heat resistance. They concluded that among polymers, those that can withstand the heat generated by the thermal head are limited to heat-resistant polymers such as polyimide.

However, the usual polyimide film formation method is based on the following reaction formula (
As shown in 1), first, the monomer doromellitic dianhydride (hereinafter referred to as P
It is sometimes abbreviated as MDA. ) and 4゜4゛-diaminodiphenyl ether (ODA) are solution-polymerized in a polar solvent (for example, dimethylformamide (DMF)) to obtain a boamic acid solution, and then this solution is lowered by a method such as a spin code method. A polyimide film is obtained by coating on the ground to obtain a thin film, and then heat-treating this thin film to cause dehydration and ring closure. However, with this method, there are the following problems: 1. It is difficult to control the film thickness, 2. There were problems such as insufficient density of the film, and (1) impurities were easily mixed into the thin film during processes such as addition, removal, and recovery of the solvent during thin film formation.

After conducting a rough study, we discovered that each invention of this application can be completed by applying plasma polymerization technology.

Therefore, according to the thin film of the first invention of this application, the thermal head of the second invention of this application is characterized in that it is made of a plasma polymer of pyromellitic dianhydride.
To thermal, which has a heat insulating layer between the board and the heating resistor.
The invention is characterized in that the heat-retaining layer is made of a plasma polymer of pyromellitic dianhydride.

Further, according to the method for forming a thin film of the third invention of this application,
In forming a thin film made of a plasma polymer of dianhydride pyromellitic acid on a substrate, a step of installing the substrate in a reactor of a plasma polymerization apparatus, a step of introducing ammonia gas into the reactor, and the reaction. A step of converting ammonia gas in the vessel into plasma, a step of heating and sublimating pyromellitic anhydride in the reactor where the plasma is already being generated to form a thin film on the aforementioned substrate, and a step of heat-treating the thin film. It is characterized by including.

In addition, in carrying out this third invention, the above-mentioned heat treatment is
The above-mentioned reactor was placed in a vacuum state, and the above-mentioned thin film @200~30
This is preferably carried out by heating to an ambient temperature of 0°C.

(Function) According to each invention of this application, the following functions can be obtained.

Since the thin film made of the plasma polymer of pyromellitic dianhydride of the first invention is a polymer film, it has a lower thermal conductivity than glass, and exhibits properties useful as a heat-retaining layer for thermal conductors from a thermal standpoint. .

Furthermore, a thin film made of a plasma polymer of dianhydride pyromellitic acid can be obtained as an amorphous thin film;
Plasma polymerization provides a flat thin film with few pinholes, ■...excellent chemical resistance due to high crosslinking density, ■...excellent heat resistance, ■...excellent adhesion to the substrate, etc. Since it has various characteristics due to the above properties, it exhibits properties useful as a heat insulating layer of a thermal head from the viewpoint of mechanical strength.

Further, in the thermal head of the second invention of this application, the heat insulating layer is made of a plasma polymer of dianhydride pyromellitic acid which has lower thermal conductivity than the glass layer and has the above-mentioned characteristics (1) to (4). Therefore, since the thermal conductivity is low, it is difficult for the heat from the heat generating part to escape to the substrate, so the input power to the thermal head to obtain the necessary heat can be reduced compared to the conventional method. Furthermore, since the thickness of the heat insulating layer can be made thinner, responsiveness when cooling the heat generating part is improved. Furthermore, since the surface of the heat insulating layer is flat, the surface of the thermal head that comes into contact with the recording paper is also flat, so that printing quality can be improved.

Further, according to the method for forming a thin film of the third invention of this application,
PMDA% in a reactor that turned ammonia gas into plasma
Since it is heated and sublimated, it is thought that a polymer film having an amic acid structure is formed on the substrate. Then, when this film is subjected to heat treatment, a dehydration ring-closing reaction occurs, and the film on the base is thought to change into the thin film of the first invention having an imide ring structure. This reaction seems to occur according to the following equation (2).

, --H-m=, \ / However, in plasma, the energy of electrons is distributed over a wide range, so the types of ions, radicals, and atoms and molecules in excited states that are generated by collisions with these electrons are so-called active species. Since there are many types of polymers, the reaction process of polymerization is also complicated. Therefore, it is thought that various reactions other than the reaction of formula (2) occur, and this polymerization mechanism has not yet been fully elucidated.

(Example) Hereinafter, the first to third inventions will be described in detail using an example in which a thin film made of a plasma polymer of pyromellitic dianhydride is used as a heat insulation layer of a thermal head.

Note that although specific devices, materials, and numerical conditions are mentioned in the following description, these are merely preferred examples of each invention. Therefore, it should be understood that these inventions are not limited only to the following equipment, materials, and numerical conditions.

1st embodiment of thermal insulation according to the present invention: First, on a substrate, a heat insulating layer, a heating resistor,
The thermal head of the first embodiment, which includes a power supply body and a protective film in this order, is manufactured as described below. The structure of the thermal head of this first embodiment is as shown in Fig. 4 (A
) corresponds to the thermal head explained using.

First, the plasma polymerized membrane manufactured by Samco International Laboratories? In the case of this example, the size is 50 x 50 mm and the thickness is 1 m as a base in a 1lPD-10s reactor.
One side of M is polished and an alumina substrate is installed. Furthermore, dianhydride pyromellit 11 (PMDA) is prepared on a heated sublimation boat in this reactor.

Next, the inside of the reactor is kept under a high vacuum condition, for example, 10-'T.

Create a vacuum below rr.

Next, ammonia gas was introduced into the reactor at a flow rate of 10 mβ/min in this example, and the flow rate was 13.56 MHz.
The ammonia gas in the reactor is turned into plasma using high frequency waves.

Next, in the reactor with plasma generated, PMDA
is heated and sublimated to form a thin film (presumed to be a polymeric film having a polyamic acid structure) on an alumina substrate. In this example, the degree of vacuum during thin film formation was 10-2 to 10
-'Torr r level.

When this thin film reaches a predetermined thickness, the heating sublimation of PMDA is stopped, and the supply of ammonia gas is stopped.

The thin film is then placed in the vacuum reactor and heated for 2 hours at a temperature of 300° C. in this example. The degree of vacuum inside the reactor during heating is, for example, 1O-2 Torr.
It is preferable that it be less than or equal to r. It is thought that this heating causes a dehydration ring closure reaction in the thin film, and the thin film becomes a polymer film having an imide ring structure.

By such a procedure, a heat insulating layer having a film thickness of 5 um made of a plasma polymer of dianhydride pyromellitic acid was formed on the alumina substrate.

Note that the heating temperature when heat-treating the thin film is preferably higher, because the reaction that occurs at a temperature lower than this heating temperature can be terminated during the thin film forming process. However, considering the heat resistance of polyimide itself, the upper limit of the heating temperature is about 300"C, so the heating temperature is 200"C.
A value within the range of ~300'C is preferred. Further, in this embodiment, the heat treatment is performed at a constant heating temperature of 300° C., or the heat treatment may be performed by changing the heating temperature.

Next, in this embodiment, a Ti-B-N film is formed as a heating resistor forming material to a predetermined thickness by sputtering on the heat-insulating layer of the alumina substrate on which the heat-insulating layer has been formed.

Next, this Ti--B--N film is patterned into the shape of a heating resistor using well-known photolithography and etching techniques.

Next, in order to obtain a power feeder, the Cr-Au'J film of this example is formed on this sample by vapor deposition, and then this Cr-Au'J film is etched by polylithography and etching.
u Pattern the thin film into the shape of a power supply body.

Next, in this example, Si is applied as a protective film on this sample.
A C2 film is formed by sputtering to obtain the thermal head of the first embodiment.

<Second Embodiment> Next, a thermal head according to a second embodiment, which is provided with a heat insulating layer, an intermediate layer, a heat generating resistor, a power supply body, and a protective film according to the present invention in this order on a substrate, will be described below. to be prepared. Incidentally, this thermal head structurally corresponds to the thermal head described using FIG. 4(B).

First, a heat insulating layer made of a plasma polymer of pyromellitic dianhydride and having a thickness of 5 um is formed on an alumina substrate in the same manner as in the first embodiment.

Next, as an intermediate layer on this heat insulating layer, S
An iC2 film is formed to a thickness of lum by sputtering.

Next, a heating resistor, a power supply body, and a protective film are sequentially formed on this intermediate layer in the same manner and under the same conditions as in the first embodiment to obtain a thermal head of the second embodiment.

<Comparative Example 1> Next, a polyimide film ((1
In order to produce a thermal head of Comparative Example 1 in which the heat insulating layer was formed according to the reaction formula (2), the following process was attempted.

First, an alumina substrate similar to that used in the first embodiment is prepared.

Next, in order to improve the adhesion of the polyimide film obtained by solution polymerization to the alumina substrate, N-β
(Aminoethyl)γ-aminopropyltrimethoxysilane (manufactured by Shin-Etsu Chemical) A solution of 1°5 mβ, 150 mβ of pure water, and 150 mβ of isopropyl alcohol was applied to an alumina substrate at 4000 rpm for 30 seconds. Coating is carried out by the subin coat method under the condition that it can be rotated in both directions.

The sample is then dried for 30 minutes at a temperature of 100°C.

Next, a dimethylformamide solution of polyamic acid is applied onto this sample by a spin cord method under the condition that the alumina substrate is rotated in the same direction for 30 seconds at 1000 revolutions per rotation.

Next, this sample was heated in vacuum at a temperature of 200″C for 1 hour.
Further, heat treatment is performed at a temperature of 300° C. for 3 hours. The thickness of the heat insulating layer in the comparative example was 5 um, the same as in each example.
Met.

Next, a SiO2 film with a thickness of 1 um was formed as an intermediate layer on the heat insulating layer of this comparative example by sputtering.

Next, a Ti-B-N film is formed on this intermediate layer using the same procedure and conditions as in the first embodiment, and then this Ti-B-N film is formed into the shape of a heating resistor using photolithography and etching techniques. Butter it.

However, during etching for patterning the T1-B-N film, the heat insulating layer and Ti-B-N film peeled off from the substrate from the heat insulating layer, and the thermal head of Comparative Example 1 could not be fabricated. .

Comparative Example 2> Next, using commonly used glaze glass, a thickness of 10
A thermal head of Comparative Example 2 is produced in the same manner as in the first embodiment except that a um heat insulating layer is produced.

Erasing 111 Fixation Next, using the thermal heads of the first example, the second example, and the comparative example 2, the power input to them was changed to print on the thermal paper so that all dots were black. The printing test is carried out by measuring the printing density using a Mauhes densitometer.

In Figure 1, the horizontal axis shows the input power (W/dot), and the vertical axis shows the printing density (○D:○ptical density).
) is a characteristic diagram showing the relationship between the input power of each thermal head and print density. In FIG. 1, ■ is a characteristic diagram of the thermal head of the first embodiment, II is a characteristic diagram of the thermal head of the second embodiment, and ■ is a characteristic diagram of the thermal head of Comparative Example 2.

As is clear from FIG. 1, it can be seen that the thermal head of each example requires less power than the comparative example to obtain the same print density. Therefore, it can be understood that according to each invention of this application, a thermal head with low power consumption can be obtained.

By FT-IR In addition, the PMDA plasma polymerized film produced in Example 1 and the polyimide film produced in Comparative Example 2 were analyzed by FT-IR. The device used was FTS-6 manufactured by BIORAD.
It is 0.

FIG. 2 shows the IR spectrum of the PMDA plasma polymerized film produced in Example 1, and FIG. 3 shows the IR spectrum of the polyimide film produced in Comparative Example 1.

As is clear from comparing Figures 2 and 3, P
The plasma polymerized film of MDA is different from the polyimide film of Comparative Example 1 (
It shows absorption at almost the same wave number, especially at wave number 1779.
From the fact that 1724crrr' shows an absorption derived from the stretching vibration of C=O in the imide ring, it can be understood that the imide ring can be formed by the thin film forming method carried out in the example.

The above-mentioned embodiment was an example in which the first and third inventions of this application were applied to a thermal head, but the thin film of the invention can be used in a wide range of applications other than the heat insulation layer of a thermal head (for example, an interlayer insulating film). It is clear that the thin film forming method of the third invention can be used in a wide range of applications other than forming a heat insulating layer of a thermal head.

(Effects of the Invention) As is clear from the above explanation, the thin film made of the plasma polymer of doromellitic dianhydride of this application is heat resistant and has a lower thermal conductivity than glass because it is a polymer film. It has various features such as fewer pinholes and excellent adhesion to the substrate, so it can be used as a heat-retaining layer for thermal heads, for example.

Useful. Therefore, its industrial value is extremely large.

Further, the thermal head of the second invention of this application has a heat-retaining layer made of a plasma polymer of dianhydride pyromellitic acid having the above-mentioned characteristics, and thus exhibits better thermal response than conventional ones. For this reason, it is possible to provide a thermal head that consumes less power than before and has slower printing speeds. Furthermore, since the surface smoothness of the heat insulating layer is superior to that of conventional products, it can be expected that the printing quality will also improve.

Further, according to the method for forming a thin film of the third invention of this application,
Since the polyimide film is obtained by plasma polymerization, the polyimide film can be obtained without using a solvent, so a thin film with less contamination of impurities can be obtained. Furthermore, a polyimide film having better adhesion to the substrate than a film obtained by solution polymerization can be obtained. In general, the film thickness can be easily controlled by controlling the flow rate of ammonia gas, the sublimation rate of PMDA, and the sublimation time. Therefore, it is possible to easily form a thin film made of a plasma polymer of dianhydride pyromellitic acid, which is suitable for use as a heat insulating layer of a thermal head, for example.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the recording characteristics of the thermal heads of each example and comparative example, FIG. 2 is a diagram showing the IR spectrum of the PMDA plasma polymerized film produced in the first example, and FIG. FIGS. 4A and 4B are diagrams showing the IR spectrum of the polyimide film produced in Comparative Example 1, and are diagrams used to explain the conventional method and the present invention. 1]...Substrate, ]3...Heat insulation layer 15...
-Heating resistor, 15a...heating parts 17a, 17b
-... Power feeder 19... Protective film, 21... Intermediate layer.

Claims (4)

[Claims] (1) A thin film comprising a plasma polymer of pyromellitic dianhydride. (2) A thermal head comprising a heat insulating layer between a substrate and a heating resistor, characterized in that the heat insulating layer is made of a plasma polymer of pyromellitic dianhydride. (3) In forming a thin film made of a plasma polymer of dianhydride pyromellitic acid on a substrate, the steps include: installing the substrate in a reactor of a plasma polymerization device; and introducing ammonia gas into the reactor. , a step of turning ammonia gas in the reactor into plasma, a step of heating and sublimating pyromellitic anhydride in the reactor where the plasma is generated to form a thin film on the substrate, and heat-treating the thin film. A method for forming a thin film, comprising the steps of: (4) In the method for forming a thin film according to claim 3, in the heat treatment, the interior of the reactor is kept in a vacuum state, and the thin film is
A method for forming a thin film, characterized in that it is carried out by heating to a temperature within the range of 0 to 300°C.