JP2001301218A - Thermal head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal head in which sticking is suppressed and recording sound or white skip of image caused thereby can be reduced significantly. SOLUTION: The thermal head comprises a glaze layer, a heater layer, a conductive layer constituting an electrode, and at least one protective layer in which the surface of the uppermost layer of the protective layer has a positive gradient from the carry-in side toward the discharge side of a thermal material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to various printers,
The present invention belongs to the technical field of a thermal head for performing thermal recording used as a recording means in a plotter, a facsimile, a recorder, and the like, and particularly relates to an improvement in recording quality of a thermal head that performs high-quality and high-gradation image recording on a thermal film.

[0002]

2. Description of the Related Art Thermal recording is used as recording means in various printers, plotters, fax machines, recorders and the like. In addition, thermal recording does not require a wet development process and has advantages such as easy handling. Therefore, in recent years, large and high-quality images such as CT diagnosis, MRI diagnosis, and X-ray diagnosis have been demanded. In applications where this is used, use for image recording for medical diagnosis is also being studied.

[0003] As is well known, thermal recording uses a thermal head in which heating elements are arranged in one direction (main scanning direction), and a heating section of the thermal head is slightly pressed against a heat-sensitive material. While relatively moving in the sub-scanning direction orthogonal to the scanning direction, according to the recorded image, energy is applied to the heating element of each pixel to generate heat, thereby heating the heat-sensitive recording layer of the heat-sensitive material to record an image. I do.

[0004] A protective layer is formed on the surface of the heat generating portion of the thermal head to protect the heat generating element and the like.
The protective layer is usually formed of a ceramic such as silicon nitride, but the surface of the protective layer is heated during thermal recording and comes into sliding contact with the thermal material. The recording medium is damaged, and eventually, a state in which image recording cannot be performed (head breakage) occurs. As a method of preventing abrasion of the protective layer of such a thermal head and improving durability, it is known to form a carbon protective layer mainly composed of carbon on an insulating protective layer of ceramic or the like. (Japanese Patent Publication No. 61-53955, JP-A-7-13)
2628). The carbon protective layer has characteristics very similar to diamond, has extremely high hardness, and is chemically stable. Therefore, it exhibits extremely excellent wear resistance and corrosion resistance against sliding contact with the heat-sensitive material.

[0005]

One of the problems in thermal recording using a thermal head is noise or blurring of the image due to so-called sticking (stick-slip). No. As described above, in thermal recording, image recording is performed by heating the thermal material while pressing and moving the thermal head and the thermal material relatively. Therefore, the surface of the heat-sensitive material is melted or softened by heat, and when these components are cooled, the surface of the thermal head and the heat-sensitive material are in a bonded state. Sticking occurs because the adhesion prevents smooth transport of the thermal material.

In particular, in applications requiring high-quality and high-quality multi-tone images, such as the above-mentioned medical applications, a high-rigidity heat-sensitive film is used accordingly, and further, a recording temperature, Set the pressing force of the thermal head on the thermal material high. As a result, the heat-sensitive material is easily melted and softened, and the adhesion between the thermal head and the heat-sensitive material is improved.
Therefore, the surface of the thermal head and the heat-sensitive material are easily adhered to each other at the time of thermal recording, and sticking is liable to occur against the purpose of improving the image quality. Also, the thermal head having the carbon protective layer described above tends to cause sticking as compared with a thermal head having a normal protective layer.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a thermal head for performing thermal recording, which has little sticking and greatly reduces recording noise and image overexposure due to this. It is to provide a thermal head which can be reduced.

[0008]

In order to achieve the above object, the present invention provides a thermal head having a glaze layer, a heating resistor layer, a conductive layer forming an electrode, and at least one protective layer. In addition, a thermal head is provided, wherein the surface of the uppermost layer of the protective layer has a positive gradient from the carry-in side to the discharge side of the heat-sensitive material.

Preferably, the surface of the uppermost layer of the protective layer does not have a step caused by the conductive layer, and the gradient is formed by polishing at least one layer of the protective layer. Preferably, furthermore,
The protective layer preferably has a protective layer containing carbon as a main component.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a thermal head according to the present invention will be described in detail based on a preferred embodiment shown in the accompanying drawings.

FIG. 1 conceptually shows a cross section of an example of a thermal head (its heat generating portion). Thermal head 1 in the illustrated example
0 is for performing thermal recording at a recording (pixel) density of about 300 dpi, for example, capable of recording an image up to a maximum B4 size, and excluding the characteristic of the surface shape of the uppermost layer of the protective layer. Heating elements for performing thermal recording are arranged in one direction (the main scanning direction in FIG. 1 and perpendicular to the paper surface) and have a known configuration.

As shown in FIG. 1, a thermal head 1
0 is a glaze layer (heat storage layer) formed on the substrate 12
14, a heat generating (resistance) body layer 16 formed thereon,
It is configured to include a conductor layer 18 to be an electrode formed thereon and a protective layer formed thereon to protect a heating element and the like. The heating element basically includes a heating element layer 16 and a conductor layer 18. The illustrated thermal head 10
In a preferred embodiment, the heating element layer 16 and the conductor layer 1
8 and a lower protective layer 2 formed to cover
0 (hereinafter, referred to as an intermediate layer 22).
) And a carbon protective layer 24, which is a carbon film containing carbon as a main component, formed on the intermediate layer 22.
It has a protective layer.

The protective layer of the thermal head according to the present invention is not limited to the configuration shown in the drawing, and may have only one protective layer. It may have a protective layer.

As described above, the thermal head 1 of the present invention
0 has basically the same configuration as that of a known thermal head except that the surface shape of the uppermost layer of the protective layer has a feature, and the layer configuration and the material of each layer are known. Specifically, the substrate 12 is made of a heat-resistant glass or an electrically insulating material such as ceramics such as alumina, silica, or magnesia. The glaze layer 14 is made of a heat-resistant glass or a heat-resistant resin such as a polyimide resin. As the conductor layer 18, various conductive materials such as aluminum and copper can be used as the heating resistor, such as nichrome (Ni—Cr), tantalum, and tantalum nitride. These are vacuum deposition,
Even thin film type heating elements formed by using a so-called thin film forming technique such as CVD (Chemical Vapor Deposition) and sputtering and a photo-etching method, are formed by using a so-called thick film forming technique by printing and firing such as screen printing. It may be a film type heating element.

The lower protective layer 20 is formed of a material having heat resistance, corrosion resistance and abrasion resistance which is insulative and can be a protective layer of a thermal head, and is preferably made of various ceramic materials. Is done. Specifically, silicon nitride (Si ₃ N ₄ ), silicon carbide (SiC), tantalum oxide
(Ta ₂ O ₅ ), aluminum oxide (Al ₂ O ₃ ), sialon (SiA
lON), silicon oxide (SiO ₂ ), aluminum nitride (AlN), boron nitride (BN), selenium oxide (SeO), titanium nitride (TiN), titanium carbide (TiC), titanium carbonitride (TiCN), chromium nitride ( Cr
N), and mixtures thereof. Above all, nitrides and carbides are preferable in terms of easiness of film formation, production cost, wear resistance against mechanical wear and chemical wear, and silicon nitride, silicon carbide, sialon, and the like are suitably used. Further, the lower protective layer 20 may contain a small amount of an additive such as a metal for adjusting physical properties.

The method of forming the lower protective layer 20 is not particularly limited, and may be formed by using the above-described thick film forming technology, thin film forming technology, or the like.
Sputtering, especially magnetron sputtering,
It may be formed by a known method of forming a ceramic film (layer) such as CVD, particularly plasma CVD.
Is preferably used. As is well known, CVD adds energy such as heat or light to a gaseous raw material introduced into a reaction chamber,
This is a technique in which various chemical reactions are induced to deposit and coat a substance on a substrate to form a film. However, by forming the film by CVD, the lower protective layer 20 is very dense and has no cracks or other defects. Can be formed, and as a result, a thermal head which is more excellent in durability and advantageous in image quality can be produced.

In the illustrated example of the thermal head 10,
When the lower protective layer 20 has a gradient, the uppermost layer of the protective layer (the carbon protective layer 24 in the illustrated example) is formed.
Has a positive slope from the carry-in side to the discharge side of the heat-sensitive material. This will be described in detail later.

The illustrated thermal head 10 has a three-layered protective layer having an intermediate layer 22 formed on such a lower protective layer 20 and a carbon protective layer 24 thereon. Since the carbon protective layer 24 is chemically very stable and has high mechanical strength, a long-life thermal head can be obtained by providing the carbon protective layer 24 on the lower protective layer 20. In addition, the intermediate layer 2
By having 2, the adhesion between the lower protective layer 20 and the carbon protective layer 24, the shock absorption, and the like are improved, and a longer-life thermal head having more excellent durability and long-term reliability can be realized.

The intermediate layer 22 is made of a metal of Group 4A of the periodic table (Group 4 = titanium group) or a group 5A of the periodic table (Group 5 = vanadium group).
The main component is at least one selected from the group consisting of a metal of group 6A, a metal of group 6A (group 6 = chromium group), Si (silicon) and Ge (germanium). This is preferable from the viewpoint of the adhesion to the lower protective layer 20 as a lower layer and the durability of the carbon protective layer 24. Specifically, Si, Ge, Ti (titanium),
Suitable examples include Ta (tantalum), Mo (molybdenum), and mixtures thereof. Among them, particularly, Si and Mo are preferable, and most preferably, Si is preferable in terms of bonding with carbon.

The method for forming the intermediate layer 22 is not particularly limited. The intermediate layer 22 may be formed by a known film forming method according to the material for forming the intermediate layer 22 by using a thin film forming technique or the like. And plasma CVD can also be used.

In the illustrated example of the thermal head 10,
On this intermediate layer 22, a carbon film containing carbon as a main component, that is, a carbon protective layer 24 is formed. In addition,
In the present invention, “having carbon as a main component” means 50a
A carbon film containing more than tm% of carbon, preferably a carbon film composed of carbon and unavoidable impurities. In the thermal head of the present invention, as the additional component other than carbon forming the carbon protective layer 24, hydrogen, nitrogen, fluorine, Si, Ti and the like are preferably exemplified.
When the additional components are hydrogen, nitrogen and fluorine, their contents in the carbon protective layer 24 are preferably less than 50 atm%, and when the additional components are Si and Ti, the carbon protective layer 24 It is preferable that the content of these is 20 atm% or less.

The method for forming the carbon protective layer 24 is not particularly limited, and any known film forming method can be used according to the desired composition. Particularly, magnetron sputtering is preferably exemplified, and CVD (particularly, plasma CVD) can also be suitably used.

The hardness of the carbon protective layer 24 is not particularly limited, as long as it has sufficient hardness as a protective layer of the thermal head. For example, the Vickers hardness is 3000 kg / mm ^2.
A preferred example is about 5000 kg / mm ² . The hardness may be constant or different with respect to the thickness direction of the carbon protective layer 24. When the hardness differs in the thickness direction, the hardness may be changed continuously or stepwise. .

In the thermal head 10 of the present invention, as shown in FIG. 1, the surface of the uppermost layer of the protective layer (hereinafter referred to as the protective layer surface), that is, in the illustrated example, the surface of the carbon protective layer 24 is heat-sensitive. It has a positive gradient from the material loading side to the material discharging side (the side from which the heat-sensitive material enters between the platen roll and the thermal head and exits). In other words, the surface of the protective layer is inclined in a direction approaching the heat-sensitive material toward the direction of conveyance of the heat-sensitive material indicated by an arrow x in the drawing (hereinafter, this slope is referred to as “positive in the conveyance direction” for convenience). Gradient).

One of the problems of the thermal head is as follows.
As described above, this problem becomes remarkable when there is recording sound or overexposure due to sticking, and when the pressing force is improved for the purpose of improving the image quality or when the carbon protective layer 24 is provided. . On the other hand, in the thermal head 10 of the present invention, by providing the above-mentioned gradient (gradient region 26) on the surface of the protective layer, sticking is greatly reduced, and a high-quality thermosensitive recording image without overexposure. Can be silently recorded.

It is not clear why sticking can be reduced when the surface of the protective layer has a positive gradient in the transport direction. However, by having the gradient, the pressing force by the thermal head is reduced in the downstream direction in the transport direction. It gets higher gradually toward. Therefore, it is considered that the lubricant contained in the heat-sensitive material spreads widely and thinly toward the downstream side, so that the lubricating effect can be more appropriately exhibited.

In the present invention, the magnitude of this gradient is not particularly limited, but preferably, the difference in height per 100 μm in the transport direction is 1 μm to 10 μm (on average 0.57 μm).
Degrees to 5.7 degrees), in particular, 1 μm to 2 μm (same as above).
(A gradient of 57 degrees to 1.15 degrees). By setting the magnitude of the gradient within the above range, the stabilization of the heat-sensitive material conveyance characteristics at the time of heat-sensitive recording, such as the effect of reducing sticking and uneven load fluctuation, can be achieved more appropriately. Note that the gradient (gradient region 26) does not need to be perfectly straight, and may have undulation or curvature due to a processing error, or may have a curvature. The magnitude of the gradient may vary partially.

In the thermal head 10 of the present invention in which the surface of the protective layer has such a gradient, it is preferable that the step (so-called electrode step) caused by the conductor layer 18 does not exist as shown in FIG. . Since the thermal head 10 of the present invention has this gradient, as described above, the pressing force of the heat-sensitive material increases toward the downstream side as described above. As a result, if there is an electrode step, dust and the like easily accumulate in this portion, and the durability may be reduced. On the other hand, by having no electrode step, the above problem can be completely avoided, and a better effect can be obtained also in terms of sticking reduction.

The electrode step may be eliminated by filling the step between the conductive layer 18 and the heating element layer 16 by a known means after the conductive layer 18 is formed. Of the electrode at the same time when the protective layer is processed.

In the thermal head of the present invention, there is no particular limitation on the method of forming a positive gradient on the surface of the protective layer in the transport direction (the method of forming the gradient region 26). As a preferable method, a method of forming a gradient on the surface of the protective layer by processing the protective layer after forming any protective layer, thereby giving a gradient on the surface of the protective layer is exemplified. In the illustrated example, after the lower protective layer 20 is formed, the lower protective film 20 is processed to make a positive gradient in the transport direction, and then the intermediate layer 22 and the carbon protective layer 24 are formed.
To form a protective layer surface (carbon protective layer 2).
4 surface).

As a preferable processing method, a polishing treatment is exemplified. The method of the polishing treatment is not particularly limited, and a method of mechanically or manually polishing using a wrapping film (sheet) is preferably exemplified. As an example of a method for mechanically polishing, a method in which a thermal head is attached to a printer and a wrapping film is passed through like a heat-sensitive material is exemplified. The gradient can be adjusted by adjusting the angle at which the wrapping film is applied to the protective layer.Therefore, in the mechanical method, a desired gradient can be provided by adjusting the mounting angle of the thermal head. it can. The wrapping film may be appropriately selected according to the material of the protective layer to be processed. For example, when processing the lower protective film 20 described above, a wrapping film of # 1000 to # 20000 may be used.

The protective layer may be polished by sandblasting using an induction sandblasting machine.

In the present invention, as a method of forming a gradient on the surface of the protective layer, a method of forming a protective layer so as to have the above-mentioned gradient from the beginning can be used in addition to the processing of the above-mentioned protective layer. Specifically, there are a method of designing the gradient of the glaze layer 14 and the position of the heating element (heating unit) in a desired range, a method of using a pre-graded substrate or substrate for the thermal head, and the like. It is preferably exemplified.

In the illustrated example, the lower protective layer 20 is processed (adjusted in shape) to form a positive gradient in the transport direction on the protective layer surface (that is, the surface of the carbon protective film 24). In addition to this, if a desired gradient can be provided after securing a thickness having good performance as the protective layer, the intermediate layer 22 and the carbon protective layer 24 are processed to form a protective layer on the surface of the protective layer in the transport direction. May have a positive slope. Also, by processing two or three layers,
The surface of the protective layer may be graded. That is, in the present invention, the gradient can be applied to the surface of the protective layer by various methods according to the thickness of each layer, workability, and the like.

In the illustrated example of the thermal head 10, the thickness of each layer is not particularly limited, but the thickness of the lower protective layer 22 is preferably 0.2 μm to 20 μm, particularly preferably 2 μm to 15 μm, and the thickness of the intermediate layer 24. Is preferably 0.05 μm to 1 μm, particularly 0.1 μm to 1 μm, and the thickness of the carbon protective layer 26 is preferably 0.5 μm to 5 μm, particularly preferably 1 μm to 3 μm. By setting the thicknesses of the intermediate layer 24 and the carbon protective layer 26 within the above ranges, the functions of the intermediate layer 24 such as adhesion to the lower layer, shock absorption, and durability of the carbon protective layer 26 can be stabilized. And can be realized in a good balance. Also, in the case of a two-layer structure having no intermediate layer, there is no particular limitation, but in terms of a good balance between abrasion resistance and thermal conductivity (that is, recording sensitivity), etc.
The thickness of the lower protective layer 22 is 0.5 μm to 50 μm, in particular,
The thickness is preferably 2 μm to 20 μm, and the thickness of the carbon protective layer 24 is preferably 0.1 μm to 5 μm, particularly preferably 1 μm to 3 μm. Further, when the protective layer is a single layer, usually,
Only the lower protective layer 22 is provided. Also in this case, the thickness is not particularly limited, but is preferably 1 μm to 20 μm, particularly 2 μm to reduce the abrasion resistance and the thermal conductivity (that is, the recording sensitivity). 10 μm is preferred. Each of the above ranges covers the entire protective layer including the gradient region 26.

Although the thermal head of the present invention has been described in detail above, the present invention is not limited to the above-described example, and various improvements and modifications may be made without departing from the gist of the present invention. Of course.

[0037]

Hereinafter, the present invention will be described in more detail with reference to specific examples of the present invention.

Example 1 A heat storage layer 14 was formed on a substrate 12 in the same manner as in a known method of manufacturing a thermal head.
The heating element layer 16 and the conductor layer 18 were formed thereon by sputtering, and a pattern was formed by photolithography and etching. Thus, a base thermal head having no protective layer was manufactured.

Masking was performed on a region other than the region where the protective layer of the formed thermal head was to be formed, and the thermal head was mounted at a predetermined position of a sputtering apparatus. Then, as a target material,
Attach SiN sintering agent at a predetermined position and set R of 2kW to 5kW.
At F power, 100 [sccm] of Ar as a carrier gas,
As a reaction gas, nitrogen gas is 20 [sccm] and oxygen gas is 5 [sccm].
Total gas pressure (pressure in chamber) using [sccm]
Was formed by magnetron sputtering under a condition of 5 mTorr, and a silicon nitride film having a thickness of 11 μm was formed as the lower protective layer 20. The film thickness of the silicon nitride film was determined in advance by calculating the film forming speed, calculating the film forming time to obtain a predetermined film thickness, and controlling the film forming time.

Next, the lower protective layer 20 thus prepared is replaced with # 20.
000 lapping sheet in the transport direction (Fig. 1
A positive gradient was applied in the direction of arrow x). Note that the magnitude of the gradient was 1 μm in height difference per 100 μm in the transport direction. Further, as shown in FIG. 1, the electrode step was completely eliminated by processing for imparting a gradient.

After the lower protective layer 20 is provided with a gradient, masking is performed in areas other than the film formation area, a thermal head is mounted at a predetermined position of the sputtering apparatus, and argon gas is introduced while evacuating the chamber. The pressure in the system was adjusted to 5.0 × 10 ⁻³ Torr. Next, a high-frequency voltage is applied to the substrate, and a self-bias voltage of −300 V is applied.
, The lower protective layer 20 (silicon nitride film) was etched for 10 minutes.

After completion of the etching, S
i The single crystal is set in place, and then the pressure inside the chamber is
Power is 5 × 10^-6Evacuate to Torr, pressure 5 ×
10 ^-3Introduce argon gas to Torr and shut
0.5kW high-frequency power to the target material in the closed state
Was applied for 5 minutes. Then, while maintaining the pressure in the system,
Open the shutter with the supplied power as 2kW high frequency power
Sputtering and intermediate 0.2μm thick Si film
Formed as layer 22. The thickness of the Si film
Calculate the film speed and calculate the film formation time to achieve the specified film thickness
Then, the film formation time was controlled.

After the formation of the intermediate layer 22, the inside of the film forming system was cleaned, and a sintered graphite material was mounted at a predetermined position as a target material. Next, while evacuating the system,
Argon gas was introduced so that the pressure became 2.5 × 10 ⁻³ Torr, and DC power of 0.5 kW was applied to the target material for 5 minutes with the shutter closed. Next, while maintaining the pressure in the chamber, the shutter was opened with a DC power of 5 kW to perform sputtering, and a carbon protective layer 24 having a thickness of 2 μm was formed. The thickness of the carbon protective layer 24 is
The film-forming speed was determined in advance, the film-forming time to obtain a predetermined film thickness was calculated, and the film-forming time was controlled.

Thus, the protective layer having the three-layer structure of the lower protective layer 20, the intermediate layer 22, and the carbon protective layer 24 is provided, and the surface of the protective layer (the surface of the carbon protective layer 24) has a gradient (gradient region). 26) The thermal head 10 having
Was prepared. The obtained thermal head was mounted on a printer, and a solid image (image of uniform density on the entire surface) was recorded on the entire surface of the heat-sensitive film. As a result, no overexposure due to sticking was observed.

Example 2 A thermal head 10 was manufactured in exactly the same manner as in Example 1 except that the gradient applied to the lower protective layer 20 was 2 μm per 100 μm in the transport direction. When a solid image was recorded using the thermal head 10 under the same conditions as in Example 1, no overexposure due to sticking was observed.

Comparative Example 1 A thermal head was manufactured in exactly the same manner as in Example 1 except that the gradient applied to the lower protective layer 20 was reversed. In other words, the surface of the protective layer of this thermal head is minus 1 μm per 100 μm in the transport direction.
has a gradient of m. When a solid image was recorded using this thermal head under the same conditions as in Example 1, overexposure due to sticking was observed in the image.

Comparative Example 2 A thermal head was manufactured in exactly the same manner as in Example 1 except that the lower protective film 20 was not polished. That is, the surface of the protective layer of this thermal head is the same as a normal thermal head having an electrode step or the like. When a solid image was recorded using this thermal head under the same conditions as in Example 1, overexposure due to sticking was observed in the image. From the above results, the effect of the present invention is clear.

[0048]

As described above in detail, according to the present invention, it is possible to realize a thermal head in which sticking is small and recording sound and image overexposure caused by sticking can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is a view conceptually showing an example of a thermal head of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Thermal head 12 Substrate 14 Glaze layer 16 Heat generation (resistance) body layer 18 Conductive layer 20 Lower protective layer 22 Intermediate layer 24 Carbon protective layer 26 area

Claims (4)

[Claims] 1. A thermal head having a glaze layer, a heating resistor layer, a conductive layer constituting an electrode, and at least one protective layer, wherein a surface of an uppermost layer of the protective layer is a heat-sensitive material. A thermal head having a positive gradient from the loading side to the discharging side. 2. The thermal head according to claim 1, wherein the surface of the uppermost layer of the protective layer has no step due to the conductive layer. 3. The thermal head according to claim 1, wherein the gradient is formed by polishing at least one layer of the protective layer. 4. The thermal head according to claim 1, further comprising a protective layer containing carbon as a main component as said protective layer.