JPS60219073A - Thermal printing head - Google Patents

Abstract

PURPOSE:To provide the titled head in which electrostatic breakdown of a heating resistor is prevented from occurring due to electrostatic charging and printing quality is enhanced, wherein the surface of the heating resistor is coated with an abrasion-resistant protective film consisting of a conductive glass. CONSTITUTION:In the thermal printing head, a substrate layer 2 is provided on a base board 1 formed of an insulating material such as a ceramic, leads 3 consisting of a conductive material such as gold are provided on the surface of the layer 2 at a predetermined interval, and the heating resistor 4 is provided in a belt form astride the leads 3. In said head, the resistor 4 is coated with the protective film 5 consisting of, e.g., a glass sheet obtained by mixing ruthenium dioxide, lead or the like into silicon dioxide, to obtain the objective thermal printing head. The sheet resistance of the protective film 5 may be 10<6>-10<9> OMEGA/square.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a thermal print head, and particularly to a thermal print head suitable for use in thermal transfer printing.

(Prior Art) As is well known, this type of thermal print head generates heat by energizing a heating resistor, presses it against an ink film, heats the ink, and transfers the ink to an image-receiving paper.

Print. Usually, the surface of the heating resistor is coated with a wear-resistant protective film.

FIG. 1 is a cross-sectional view showing an example of this type of thermal print head, in which 1 is a substrate made of an insulating material such as ceramic;
is a glaze layer formed on the surface. Leads 3 made of a conductive material such as gold are placed on the surface of this glaze layer at predetermined intervals. A heating resistor 4 is formed in a band shape so as to straddle this lead 3. Usually, a resistive paste is printed and fired to form a thick film.6 The heating resistor 4 is defined by a lead 3 that crosses it. A resistor portion 4A between a pair of adjacent leads 3 functions as one dot. A wear-resistant protective film 5 is applied to the surface of the heating resistor 4.
Coat with. Reference numeral 6 denotes an ink film, which is generally composed of a base film 7 made of a resin such as polyester and an ink 8 coated on the surface of the base film 7.
9 is an image receiving paper, and 10 is a platen. When electricity is applied between the pair of REETs 3, the heating element portion 4A located therebetween generates heat, and this heat melts the ink portion of the ink film 6'' and transfers it to the image receiving paper 9. This is as stated earlier.

Conventionally, it has been common practice to use wear-resistant glass, such as silicon oxide (SiO2), as the protective film 5. However, since the protective film 5 and the base film 7 of the ink film 6 come into sliding contact during printing, static electricity is generated and charged in both. According to actual measurements, this static voltage can reach 10KV. In this case, charging of the ink film 6 poses no particular problem, but charging of the protective film 5 causes a serious problem. That is, the electric charge charged on the protective film 5 is discharged to the ground side, but this discharge passes through the heating resistor 4 located directly under the protective film 5, and a part of it passes through the beam part 3, and the other part goes through the glaze layer. 2. Discharge passes through the substrate 1, passes through a heat sink such as an aluminum plate on the underside of the substrate 1, and discharges to the ground side.

In any case, since the discharge occurs through the heating resistor 4, the heating resistor 4 may be damaged by static electricity and its characteristics may deteriorate due to static electricity. Since such deterioration of characteristics promotes a change in resistance value, the heat generation energy of that part becomes different from that of other parts.

As a result, density unevenness occurs in the print on the receiver paper, resulting in a loss of print quality.

(Problems to be Solved by the Invention) An object of the present invention is to avoid deterioration in print quality by preventing electrostatic damage to the heating resistor.

(Means for Solving the Problems) The present invention is characterized in that conductive glass is used as the protective film coating the surface of the heating resistor so that the protective film is prevented from being charged as much as possible.

(Function) If the heating resistor is coated with a protective film made of conductive glass in this way, it will be difficult to be charged even if it comes into sliding contact with the ink film, and even if it is charged, the charging voltage will be the same as before. This is sufficiently lower than when an insulating protective film is used, and as a result, static electricity is less likely to be generated, thereby preventing electrostatic damage to the heating resistor.

The conductive glass used as the protective film used in the present invention has a sheet resistance value of approximately 10 6 to 10 9 Ω/Ω. Incidentally, the sheet resistance value of conventionally used silicon oxide glass is 10 9 Ω/hole or more.

In addition, when the heating resistor 4 is formed of a ruthenium oxide paste, its sheet resistance value is usually about 2×10 3 Ω/hole, so the protective film used in this invention has a resistance value 10 3 to 10'' times that of the resistance heating element. It has a sheet resistance value.

For example, suppose that a protective film whose sheet resistance value is 103 times that of the heating resistor is used. The power required to generate heat in the resistor portion 4A (one dot) between adjacent leads is approximately 0.7 W/h using the above-mentioned resistor material.

When an insulating protective film was used as in the past, 0.7 W/8 was consumed in one resistor part 4A, whereas when a conductive protective film was used according to the present invention, Even if power is consumed due to current flowing through the protective film in addition to 0.7 W/v, h, the power consumption is 0.7X1/103 W/s, so the total power is 0.7 W/v, h. 7007W/1. ,
, h, and the increase is only a very small amount.

Note that if the sheet resistance value of the protective film used in this invention is more than 10 times that of the heating resistor, the static electricity charge in the protective film will become large, and electrostatic damage to the heating resistor will be reliably avoided. It becomes difficult to do so. Further, if it is less than 103 times, the current flowing through the protective film, that is, the leakage current increases, which is undesirable because unnecessary power loss increases.

(Example) An embodiment of the invention will be explained with reference to FIG.

In accordance with the spirit of the present invention, the protective film 5 is made of metal such as ruthenium dioxide (RuO2) or lead with silicon dioxide (
Glass mixed with SiO2) is suitable. The sheet resistance value of this glass is approximately 10 6 to 10 9 Ω/hole, and it can be used as a protective film in the present invention. When the above glass was used as a protective film, the electrostatic voltage of the protective film was approximately 1 to 3 KV. When printing was carried out using conventional silicon oxide glass as a protective film under the same conditions as Pudding 1, the electrostatic voltage was 10 KV.
In addition, when the above-mentioned protective film according to the present invention is used, 100
As a result of continuous printing for 0 hours, no electrostatic damage occurred in the heating resistor. However, when a conventional protective film was used and continuous printing was performed for the same period of time, electrostatic discharge damage occurred in about 30% of the number of dots. Note that the present invention is also applicable to cases where the resistance heating element is a thin film.

(Effects) As detailed above, according to the present invention, since conductive glass is used as the protective film of the heating resistor, electrostatic damage to the heating resistor due to charging of the protective film can be reliably prevented. This has the effect of preventing the temporary density unevenness of the print 1 due to deterioration of the characteristics of the heating resistor, thereby making it possible to sufficiently improve the quality of the print 1 compared to the conventional one.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention, and FIG. 2 is a plan view with the protective film omitted. 1... Board, 4... Heat generating resistor,
5... Protective film procedure amendment export) July 13, 1988 Patent Application No. 75440 of 1988 2 Name of the invention Thermal Print 1-Head 3 Relationship with the person making the amendment Patent Applicant's residence: 21 Saiin Mizosakicho, Ukyo-ku, Kyoto City Name: ROHM Co., Ltd. 4 Detailed explanation of the invention in the agent's specification Column 8 Contents of the amendment (1) Page 3, line 2 of the specification [For example... 5in
2) Delete J. (2) Add the following sentence next to "Electrostatic damage" on page 4, line 3. "In other words, a change in resistance due to the application of a high voltage." (3) On page 5, line 3, "silicon oxide-based" is corrected to "wear resistance." (4) In the fifth line of the same page, add "within the range of use" after "usually". (5) Line 18 of the same page: ``For electric power, add ``about'' next to J. (6) On the 19th line of the same page, add "about" after "electric power". (7) Add "or its oxide" next to "metal" on page 6, line 12. (8) In the 15th line of the same page, ``deari'' is corrected to ``nishiruba''.

Claims (1)

[Claims] Thermal print head is made by coating the surface of the heating resistor for printing on the surface of the substrate with a wear-resistant protective film made of conductive glass.