JP2002029079A - Method for trimming resistance of thermal head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for trimming the resistance of a thermal head such that a good and clear image can be formed by preventing generation of uneven density effectively. SOLUTION: Resistance of heating resistors arranged on the substrate of a thermal head is trimmed according to following steps 1-4. In the step 1, Joule's heat is generated from the heating resistors of the thermal head while carrying a recording medium onto the heating resistors thus forming an image on the recording medium. In the step 2, density of a print formed in Step 1 is measured. In the step 3, the print density obtained in Step 2 is compared with a target density to determine a correction width of resistance corresponding to the difference of density. In the step 4, resistance of each heating resistor is trimmed based the correction width of resistance obtained in Step 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for adjusting a resistance value of a thermal head incorporated as a printer mechanism of a word processor, a facsimile or the like.

[0002]

2. Description of the Related Art Conventionally, a thermal head has been used as a printer mechanism of a word processor, a facsimile or the like.

Such a conventional thermal head has a structure in which a plurality of heating resistors are attached and arranged on the upper surface of a substrate made of alumina ceramic or the like via a glaze layer, and these are covered with a protective film. While conveying a recording medium such as thermal paper on the heating resistor, a plurality of heating resistors are individually and selectively subjected to Joule heating based on image data from the outside, and the generated heat is applied to the protective film. The recording medium is transmitted through the recording medium to form a predetermined print on the recording medium, thereby functioning as a thermal head.

The glaze layer serves to maintain a good thermal response characteristic of the thermal head by accumulating a part of the heat generated by the heat generating resistor. For example, the glaze layer is made of a low heat conductive material such as glass. Had been formed.

The plurality of heating resistors provided on the glaze layer are, for example, 600 dpi (dot / in).
ch) with a dot density linearly arranged in the main scanning direction,
Conventionally, by adopting a well-known thin-film technique or thick-film technique, a predetermined pattern is formed on the upper surface of the glaze layer.

If the resistance values of the plurality of heating resistors differ greatly from one dot to another, the heating values of the individual heating resistors differ when the heating resistors generate Joule heat.
In order to avoid density unevenness, the heating resistor is trimmed to avoid the unevenness, and the resistance value of the heating resistor is adjusted to be substantially constant.

As such conventional trimming methods, a pulse trimming method and a laser trimming method are known. For example, when the pulse trimming method is adopted,
The resistance value of the heating resistor is adjusted by applying a predetermined trimming pulse to the heating resistor. In this pulse trimming method, when a trimming pulse having a short pulse width (energization time) and a large amplitude (voltage value) is applied to the heating resistor, the heating resistor is heated at a relatively low temperature, crystallization proceeds, and annealing is performed. When a trimming pulse having a long pulse width and a small amplitude is applied to the heating resistor, a part of the heating resistor reacts violently with oxygen in the atmosphere to form an oxide film. This utilizes the characteristic that the resistance value increases.

[0008]

However, the above-described conventional resistance value adjusting method is intended to solve the density unevenness by making the resistance values of all the heat generating resistors uniform, and the method other than the resistance value variation. No consideration is given to factors such as variations in the amount of heat accumulated in the substrate and the glaze layer and differences in the strength of the paper contact when the recording medium is brought into sliding contact with the thermal head. That is, even if the resistance values of the heat generating resistors are uniform, the width and thickness of the glaze layer may vary, or the heat radiation characteristics of a heat radiating plate disposed immediately below the substrate may be uneven. In this case, the amount of heat accumulated in the substrate and the glaze layer may be large, causing concentration unevenness.If the substrate has undulation or the thickness of the protective film varies, the thermal head , The sliding contact pressure of the recording medium on the recording medium becomes uneven, which also causes uneven density. Therefore, it is difficult to effectively prevent density unevenness of a print simply by making the resistance values of the heat generating resistors constant, and an epoch-making method capable of solving the various problems described above at once is required. Was.

The present invention has been devised in view of the above-mentioned problems, and the present invention effectively adjusts the resistance value of a thermal head capable of effectively preventing the occurrence of density unevenness and forming a good and clear print. It provides a method.

[0010]

According to the present invention, there is provided a thermal head having a plurality of heating resistors disposed on a substrate of the thermal head.
The resistance value of the heating resistor is adjusted by the following steps 1 to 4. Step 1: a step of forming a print on the recording medium by causing the heating resistor to generate Joule heat while conveying the recording medium onto the heating resistor of the thermal head. Step 2: a step of measuring the density of the print formed in step 1. Step 3: a step of comparing the print density obtained in Step 2 with the target density and obtaining a resistance value correction width corresponding to the density difference. Step 4: a step of adjusting the resistance value of each heating resistor by trimming the heating resistor based on the resistance value correction width obtained in Step 3.

According to the thermal head resistance adjusting method of the present invention, the resistance of the heating resistor is adjusted based on the actual printing result so that the target density can be obtained for all the printing dots. Considering not only variations in the resistance value of the heating resistor, but also variations in the shape of the substrate, variations in the width and thickness of the glaze layer, and variations in the paper contact when the recording medium is brought into sliding contact with the thermal head, etc. It is possible to obtain a heating resistor having an optimum resistance value for realizing quality printing, thereby effectively preventing the occurrence of density unevenness and forming good and clear printing.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a perspective view of a thermal head to which the resistance value adjusting method of the present invention is applied, FIG. 2 is a cross-sectional view of the thermal head of FIG. 1, 1 is a substrate, 2 is a glaze layer,
3 is a heating resistor, 5 is a protective film, and 6 is a heat sink.

The substrate 1 is formed in a rectangular shape from an electrically insulating material such as alumina ceramics or glass, and has a top surface serving as a supporting base material for supporting a large number of heating resistors 2 and the like. It is.

When the substrate 1 is made of, for example, alumina ceramics, an appropriate organic solvent and a solvent are added to and mixed with a ceramic raw material powder of alumina, silica, magnesia, etc. to form a slurry, and this is formed into a conventionally known doctor. A ceramic green sheet is formed by employing a blade method, a calendar roll method, or the like, and thereafter,
The ceramic green sheet is manufactured by punching a predetermined rectangular shape, firing at a high temperature (about 1600 ° C.), and finally polishing the surface. In this case, the substrate 1
In some cases, "undulation" may occur due to non-uniformity of polishing or the like.

On the upper surface of the substrate 1, a glaze layer 2 having an arc-shaped cross section is applied in a strip shape along the longitudinal direction.

The glaze layer 2 is made of a low thermal conductive material such as glass, and has a function of maintaining a good thermal response characteristic of the thermal head by accumulating a part of the heat generated by the heat generating resistor 3 therein. Do

The glaze layer 2 is formed by printing a predetermined glass paste obtained by adding and mixing an appropriate organic solvent, an organic binder and the like to glass powder on the upper surface of the substrate 1 by a conventionally known screen printing method or the like. By coating and baking at a high temperature, for example, 800 μm to 2000 μm
m and a thickness of 20 μm to 90 μm. In this case, the thickness and width of the obtained glaze layer 2 vary within a range of about ± 5% around the average value.

A plurality of heating resistors 2 are linearly attached and arranged on the top of the glaze layer 2.

The plurality of heating resistors 3 are, for example, 60
It is arranged at a high density with a dot density of 0 dpi, each of which is made of an electric resistance material such as TaSiO, TiSiO, TiCSiO, etc., so that power is supplied through a pair of electrodes 4, 4 connected to both ends thereof. When electric power is supplied, Joule heat is generated, and the temperature reaches a predetermined temperature required for forming an image on a recording medium such as thermal paper.

Further, the heating resistor 3 is adjusted to a predetermined resistance value by trimming each resistance value by an adjustment method described later.

By the trimming, the resistance values of the heat generating resistor 3 are not all made uniform, but the variation in the thickness and width of the glaze layer 2 located immediately below, the undulation of the substrate 1, the variation per paper, and the like are comprehensively measured. It is determined in consideration of the above, and is adjusted so as to have a resistance value specific to each heating resistor 3. Therefore, when an image is formed on the recording medium, the amount of heat of the heating resistor 3 transmitted to the surface of the recording medium can be made equal to make the density of each of the printing dots formed on the recording medium substantially constant. It is possible to form a good print with less density unevenness.

The heating resistor 3 is formed by a conventionally known thin-film method,
Specifically, by applying a sputtering method, a photolithography technique, an etching technique, and the like, a predetermined thickness and a predetermined pattern are adhered to and formed on the upper surface of the glaze layer 2, and the obtained heating resistor 3 has a predetermined resistance value variation. Will have. These heating resistors 3 are individually adjusted to a predetermined resistance value by a resistance value adjustment method described later.

A protective film 5 is provided on the upper surfaces of the heating resistor 3 and the pair of electrodes 4 and the like, and the heating resistor 3 and the like are covered with the protection film 5.

The protective film 5 is made of an inorganic material such as silicon nitride, silicon oxide, silicon carbide or the like, which has excellent wear resistance and corrosion resistance. The heating resistor 3 and the pair of electrodes 4 and 4 serve as a recording medium. It functions to effectively prevent abrasion due to sliding contact and corrosion due to contact with moisture or the like contained in the atmosphere.

The protective film 5 is formed on the upper surface of the heating resistor 3 or the like by, for example, 3 μm by a well-known sputtering method or the like.
It is deposited and formed to a thickness of m to 12 μm. This protective film 5
In some cases, a thickness variation of about ± 20% may occur.

The above-mentioned substrate 1 is supported and fixed on the upper surface of the heat sink 6. The heat radiating plate 6 is formed of a good heat conductive material such as aluminum so as to form a predetermined rectangular shape. The effect of effectively preventing the temperature of 1 from becoming excessively high.

The heat radiating plate 6 is manufactured by processing an ingot (lump) of aluminum or the like into a predetermined shape by a conventionally known metal working method, and a double-sided tape, an adhesive or the like is applied on the upper surface of the obtained heat radiating plate 6. The substrate 1 is fixed by placing the substrate 1 through the intermediary. At this time, the thickness of the double-sided tape and the adhesive interposed between the substrate 1 and the radiator plate 6 may be non-uniform.
This causes variations in the heat transfer characteristics to heat.

The above-described thermal head becomes a thermal head as a product by adjusting the resistance value of the heating resistor 3 by employing a resistance value adjusting method described later, and a platen is placed on the heating resistor 3 of the obtained thermal head. While transporting the recording medium using rollers or the like, a plurality of heating resistors 3
Is selectively and individually heated based on image data from the outside, and the generated heat is transmitted to the recording medium via the protective film 5, whereby a good print with less density unevenness is formed on the recording medium. .

Next, a resistance value adjusting method for adjusting the resistance value of the heating resistor 3 of the thermal head will be described with reference to FIG.

(Step 1) First, while conveying the recording medium onto the heating resistor 3 of the above-described thermal head, the heating resistor 3 is heated for all dots and joules to form a print on the recording medium.

The printing here is carried out under conditions as close as possible to the actual conditions of use of the finished product, and the actual use of the platen roller is limited to the size, material, pressing force, type of recording medium, transport speed, etc. Set the same as the condition.

The same print pulse is applied to all of the heating resistors 3 to form a solid print on the recording medium.

(Step 2) Next, the density of the print dots obtained in the above step 1 is measured. This measurement is performed by reading a print using an image reading device such as a flat scanner or a drum scanner, and irradiating the recording medium with light when using a recording medium such as thermal paper that expresses an image with reflected light. The intensity of the reflected light obtained at the time of reading is converted into a predetermined electric signal, and when a recording medium that expresses an image by transmitted light, such as an X-ray film, is transmitted when the recording medium is irradiated with light. The light intensity is read and converted into a predetermined electric signal.

At this time, the density may be measured for all the printing dots formed on the recording medium,
Alternatively, the printing result may be visually observed first, and the density of the printing dots may be measured only for the high density portion or the low density portion.

The measured print dot density is represented by an optical density (OD), and at the same time, the obtained print density is associated with the heating resistor 3.

(Step 3) Next, the print density obtained in the above-mentioned step 2 is compared with a predetermined target density, and a resistance value correction width (trimming amount) corresponding to the density difference is obtained.

The target density may be set to the lightest density, the darkest density among the printing dots formed in the step 1, or a predetermined density which does not correspond to any of them. The density may be set.

The resistance value correction width is determined based on the graph of FIG. 4 showing the relationship between the print density and the resistance value correction width.

According to this, for example, when the density difference is corrected by 0.05, the resistance value correction width becomes 3%, and the resistance value of the corresponding heating resistor 3 is reduced by 3% in step 4 described later.
Thus, a printing dot having a target density can be obtained by changing only the above.

(Step 4) Finally, the resistance value of each heating resistor 3 is adjusted by trimming the heating resistor 3 based on the resistance value correction width obtained in Step 3.

For this trimming, a conventionally well-known pulse trimming method, laser trimming method, or the like is used. For example, when the pulse trimming method is employed, a predetermined trimming pulse is applied to the heating resistor 3 to generate heat. Adjust the resistance of the body 3.

For example, when a trimming pulse having a short pulse width (energization time) and a large amplitude (voltage value) is applied to the heating resistor 3, the heating resistor 3 is heated at a relatively low temperature, so that crystallization proceeds and annealing is performed. As a result, when a trimming pulse having a long pulse width and a small amplitude is applied to the heating resistor 3, the heating resistor 3
Some of them react with oxygen and the like in the protective film 6 and the glaze layer 2 to form an oxide film, thereby increasing the resistance value. In this case, since the oxidation of the heating resistor 3 has a limit, it is preferable to adjust the resistance value mainly by annealing.

The waveform of the trimming pulse applied to the heating resistor 3 is calculated using a calibration curve as shown in FIG.
It is determined by obtaining the applied energy corresponding to the trimming amount (resistance value correction width).

Using such characteristics, the thermal head as a product can be obtained by trimming the resistance value of all the heating resistors 3 or a part of the heating resistors 3 and adjusting it to a predetermined resistance value. .

According to the method of adjusting the resistance value of the thermal head of the present embodiment as described above, the resistance value of the heating resistor 3 is adjusted based on the actual printing result so that the target density can be obtained for all the printing dots. As a result, not only the variation in the resistance value of the heating resistor 3 but also the substrate 1 and the heat sink 6
The optimal resistance value for realizing high quality printing, taking into account the overall shape, the width and thickness variations of the glaze layer 2, and the variation per sheet when the recording medium is brought into sliding contact with the thermal head. The heating resistor 3 described above can be obtained, whereby the occurrence of density unevenness can be effectively prevented, and a good and clear print can be formed.

Note that the present invention is not limited to the above-described embodiment, and various changes and improvements can be made without departing from the gist of the present invention.

[0047]

According to the thermal head resistance adjusting method of the present invention, the resistance of the heating resistor is adjusted based on the actual printing result so that the target density can be obtained for all the printing dots. Therefore, not only the variation in the resistance value of the heating resistor, but also the variation in the shape of the substrate, the variation in the width and thickness of the glaze layer, and the variation per sheet when the recording medium is brought into sliding contact with the thermal head are comprehensively considered. Thus, it is possible to obtain a heating resistor having an optimum resistance value for realizing high quality printing, thereby effectively preventing the occurrence of density unevenness and forming a good and clear printing.

[Brief description of the drawings]

FIG. 1 is a perspective view of a thermal head to which a resistance value adjusting method of the present invention is applied.

FIG. 2 is a sectional view of the thermal head of FIG.

FIG. 3 is a chart showing steps related to a method for adjusting a resistance value of a thermal head according to the present invention.

FIG. 4 is a diagram illustrating a relationship between a print density and a resistance value correction width.

FIG. 5 is a diagram showing a relationship between a resistance value change rate and an applied energy of a trimming pulse.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Glaze layer, 3 ... Heating resistor, 5 ... Protective film, 6 ... Heat sink

Claims (1)

[Claims] 1. A thermal head comprising a plurality of heating resistors arranged on a substrate of a thermal head, wherein the resistance value of the heating resistors is adjusted by the following steps 1 to 4. The method of adjusting the resistance value of the thermal head. Step 1: a step of forming a print on the recording medium by causing the heating resistor to generate Joule heat while conveying the recording medium onto the heating resistor of the thermal head Step 2: measuring the density of the print formed on the recording medium in step 1 Step 3: a step of comparing the print density obtained in Step 2 with a predetermined target density to obtain a resistance value correction width corresponding to the density difference. Step 4: Obtaining the heating resistor in Step 3 Adjusting the resistance value of each heating resistor by trimming based on the corrected resistance value correction width