Thermal Printing Head

Abstract

A thermal printing head comprising a plurality of thin insulating layers each being provided on one surface thereof with a plurality of electrically conductive slips arranged in spaced parallel relation to one another. The insulating layers are piled stepwise one upon another so that one end portion of the upper surface of each of the layers with the corresponding end portions of the conductive slips thereon are exposed from beneath the end of the layer immediately above. A slip of an electrically resistive material extends transversely of and in contact with the exposed end portions of the conductive slips on each of said insulating layers, so that between each adjacent two of the conductive slips on all the insulating layers there are defined a plurality of dot-like portions of the resistive slips which are arranged in rows and columns on the printing surface of the head. Upon impression of a voltage between adjacent pairs of the conductive slips those defined portions of the resistive slips which are between the adjacent pairs of conductive slips are heated, and by selecting the pairs of conductive slips between which a voltage is to be applied it is possible to cause the heated defined dot-like portions of the resistive slips to take the shape of a symbol, so that when a sheet of heat-sensitive paper is pressed against the heated portions, the symbol is printed on the paper.

Description

This invention relates to a printing head for use in thermal printing.

Recently there have been in wide use thermal printers which employ a thermal printing head to record information obtained from, say, an electronic computer in the form of various symbols printed on heat-sensitive recording media. The thermal printing head includes those elements which produce heat when electric energy is applied thereto. For printing, the elements are selectively heated to form a required symbol to be pressed onto the heat-sensitive paper so that the symbol is recorded on the paper. It is required of such a printing head that a single head should be capable of selectively printing a plurality of different symbols (including characters, pictures, etc.).

In one known printing head, there are provided many do-like heating elements arranged in rows and columns and spaced equidistantly apart from each other. When a symbol is to be printed by the printing head, those of the elements which correspond to the symbol are selectively energized to be heated, so that the heated elements are combined to form the shape of the symbol. Therefore, when the head is brought into contact with the heat-sensitive paper, those dot-like portions of the paper which are contacted by the heated elements become colored, and the colored dots are combined to appear as the required symbol.

One prior art printing head having such dot-like heating elements comprises a plurality of thin layers of an insulating material laminated into a single block, each layer being provided on one side surface thereof with a plurality of separate thin film heating elements, so that on the side surface of the block there appear a plurality of dot-like heating elements arranged in rows and columns and spaced a predetermined distance apart from each other. For supply of electric energy to each of the elements, on one surface of the insulating layer there is provided a thin layer of an electrically conductive material, through which electric current is supplied to the heating elements.

For manufacture of the printing head of the above-mentioned type, it is necessary to provide dot-like heating elements on one side surface of each insulating layer, and these heating elements are film resistors formed on the surface by vacuum evaporation. The manufacturing process is rather complicated and time-consuming and requires a high degree of skill and precision.

Accordingly, the primary object of the invention is to provide a thermal printing head which is provided with a plurality of dot-like heating resistive elements.

Another object of the invention is to provide such a thermal printing head as aforesaid, in which the heating resistive elements and the electrically conductive elements for supplying electric energy to the resistive elements are composed of a thick film.

Still another object of the invention is to provide such a thermal printing head as aforesaid, wherein the terminals through which electric energy is supplied to the resistive elements are arranged on a substantial plane surface of the head.

The thermal printing head of the invention comprises a base and a plurality of layers of an insulating material piled thereon. Each of the insulating layers is provided on its upper surface with a plurality of slips made of thick film of an electrically conductive material which are arranged in parallel with and equidistantly spaced from each other. A slip made of thick film of an electrically resistive material is provided on the conductive slips at one end thereof and extending transversely thereof in such a manner that the resistive slip bridges the conductive slips in contact therewith. These insulating layers with the conductive slips and the resistive slips thereon are piled stepwise one upon another. The word "stepwise" means that each layer above is a little displaced along the length of the conductive slips from the layer immediately beneath in such a manner that the resistive slip on the end of the upper surface of each insulating layer is exposed while the other area of the upper surface of the slip is covered by the insulating layer immediately above. In other words, the insulating layers are so piled or stacked one upon another that the exposed resistive slips on the layers appear as if they constituted stairs.

When a pulse-like voltage is impressed across any adjacent two of the parallel conductive slips, a current flows through that portion of the resistive slip thereon which is defined between the selected two conductive slips so that the portion is heated. Impression of a voltage between selected pairs of the conductive slips on the insulating layers results in heating of those portions of the resistive slips which are between the selected pairs of the conductive slips. The heated portions individually are dot-like, but their arrangement as a whole forms a symbol or character. Therefore, when the printing head is pressed aganst a sheet of heat-sensitive paper, the symbol or character appears on the paper.

As mentioned above, the resistive slips form stairs. However, since the insulating layers, the conductive slips and the resistive slip are as thin as 0.015 mm, the upper surface of the stairs as a whole practically is flat or plane. If the stepped surface of the printing head causes any impediment to uniform printing, a projection of a heat-conductive material may be provided on those portions of the resistive slip on each insulating layer which are defined between each adjacent two of the conductive slips so that the upper surfaces of the projections are in the same plane. With this arrangement, the heated dot-like portions of the surface of the printing head can contact a sheet of thermally sensitive paper with substantially the same pressure so that a uniform and even printing can be effected.

The insulating layers are piled stepwise one upon another also at the side opposite to that at which the resistive slips are provided, so that the corresponding ends of the conductive slips on the piled insulating layers are exposed at that side, and the exposed ends of the conductive slips can be used as terminals through which electric energy is applied to the slips .

The invention will be described further in detail with reference to the accompanying drawings, wherein:

FIG. 1 is a top plan view of a thermal printing head constructed in accordance with the invention;

FIG. 2 is an enlarged, shematic perspective view of a portion of FIG. 1; and

FIG. 3 is an enlarged side view, in vertical section, of a projection formed on the heated portion of the upper surface of the printing head.

Referring in detail to the drawings, there is shown a printing head comprising a plurality, say, seven layers 1A - 1G made of a suitable insulating material such as alumina or the like ceramic piled on upon another. The layers 1A - 1G are supported by a base 10 preferably made of a similar insulating material. The base and the layers thereon form a unitary structure.

On the upper surface of the lowest layer 1A there are provided a plurality, say, six slips 11A - 16A of an electrically conductive material arranged in parallel with and equidistantly spaced from each other. In a similar manner, there are provided on the surface of each of the other insulating layers 1B - 1G six parallel conductive slips 11B - 16B, 11C - 16C, 11D - 16D, 11E - 16E, 11F - 16F and 11G - 16G. The insulating layers are piled stepwise one upon another so that the end portions of the conductive slips on each of the insulating layers is exposed from beneath the insulating layer above and the exposed areas of the insulating layers appear as if they formed stairs.

A slip 2A of an electrically resistive material is placed on the exposed end portions of the conductive slips so as to extend transversely of or bridge the conductive slips in electrically conductive relation thereto. Similarly, there are provided resistive slips 2B - 2G on the exposed surfaces of the other insulating layers 1B - 1G. The conductive and resistive slips may comprise a thick film formed by the method of screen printing.

The end portions of the insulating layers opposite to those portions where the resistive slips are provided are also arranged stepwise so that the corresponding end portions of the conductive slips are exposed so as to be used as terminals and leads through which electric energy is applied to the slips.

As the material for the insulating layers a ceramic such as alumina is used. On a raw sheet of alumina there are provide a plurality of conductive slips which are formed by the method of screen printing. A plurality of such sheets are piled one upon another stepwise at the opposite end portions thereof and sintered to form a unitary structure. At one end portion of the structure there are formed by the method of screen printing a plurality of resistive slips each of which transversely extends and bridges the sxposed end portions of the conductive slips on the insulating layers.

In one printing head manufactured in the above-mentioned manner, the width of the conductive and resistive slips, and the gap between each adjacent two of the conductive slips are all about 0.2 mm, the thickness of the conductive and resistive slips and the insulating layers are all about 0.015 mm; and the distance between the edge of each insulating layer and the resistive slip thereon is about 0.1 mm. With these dimensions, those portions of the resistive slip which are defined between adjacent two conductive slips (and which are heated) are a square area one side of which is 0.2 mm long, and those defined portions exist as dots equidistantly spaced from one another on the upper surface of the printing head.

Suppose that a pulse-like voltage is impressed between, say, the conductive slips 11A and 12A on the insulating layer 1A. A current flows through that portion of the resistive slip which is between the conductive slips 11A and 12A so that the portion is heated. As will be easily understood, by selecting the conductive slips on the insulating layers between which a voltage is to be applied, it is possible to heat those dot-like portions of the resistive slips which take the shape of a required symbol.

If in FIG. 1 those portions of the resistive slips which are hatched are heated, the heated portions as a whole take the shape of the reversed numeral "3." In order to heat these hatched portions, a voltage is applied between the slips 11A and 12A, 12A and 13A, 13A and 14A, 14A and 15A, 15A and 16A, 15B and 16B, 14C and 15C, 13D and 14D, 14D and 15D, 15E and 16E, 11F and 12F, 15F and 16F, 12G and 13G, 13G and 14G, and 14G and 15G. With those portions of the resistive slips being heated in the above manner, when the printing head is pressed onto a sheet of heat-sensitive paper, the corresponding portions of the paper change its color so that the numeral "3" appears or is printed thereon.

Application of a voltage to the conductive slips is made through those ends of the conductive slips which are opposite to the ends thereof where the resistive slips are provided, that is, through those ends of the conductive slips which are exposed on the stepped end portions of insulating layers. Since the ends of all the conductive slips are exposed, they can be used as terminals through which application of a voltage can be effected with ease.

Strictly speaking, the upper surfaces of the resistive slips on the different insulating layers are not in the same plane but differ in level. In other words, although the insulating layers are very thin, the printing surface of the head is not strictly plane, so that when the head is applied against a sheet of heat-sensitive paper, contacting pressure differs at different areas of the contacting surface of the printing head, with resulting uneveness or obscurity in the print obtained.

To solve the problem, a projection 22 made of a thermally conductive material may be provided on those defined portions of the resistive slips which are between the adjacent conductive slips on each of the insulating layers as shown in FIG. 3, so that the upper surfaces of the projections on different layers are of the same level from the upper surface of the base 10. The projection 22 may comprise one or more layers 21 of a good thermally conductive material applied on the portion of the resistive slip by the method of screen printing. The heat produced by the portion of the resistive slip is transferred to the projection 22. Since the upper surfaces of all the projections 22 are of the same level, when the printing surface of the head is applied onto a sheet of heat-sensitive paper, the contacting pressure between the upper surfaces of the heated projections and the paper becomes substantially the same so that a uniform printing of the symbol can be effected. The thermally conductive layer 21 may be made of a metallic or electrically resistive or insulating material. The projection 22 may comprise a plurality of metallic layers with an insulating layer interposed therebetween.

In the illustrated embodiment, the printing head is designed so as to print a single symbol. In order to be able to print a plurality of symbols (for example, a multi-digit number) at one time, a plurality of matrices each comprising the illustrated arrangement of the conductive and resistive slips may be arranged side by side. In this case it is possible to use the insulating layers and the resistive slips in common with different matrices.

Claims

What I claim is:

1. A thermal printing head comprising: a plurality of layers made of an electrically insulating material and piled one upon another stepwise so that one end portion of one surface of each said layer is exposed from the layer immediately above; a plurality of slips made of a conductive material arranged in spaced parallel relation to each other on said one surface of each said insulating layer; and a slip made of an electrically resistive material arranged so as to extend transversely of and in contact with the end portions of said conductive slips on said exposed end portion of each said insulating layer so that there are defined a plurality of portions of each said resistive slip between each adjacent two of said conductive slips; whereby application of electric energy between an adjacent pair of said conductive slips causes said defined portion of said resistive slip which is between said pair of conductive slips to be heated.

2. The thermal printing head of claim 1, wherein said defined portions of said resistive slips on all said exposed end portions of said insulating layers are spaced equidistantly apart from one another.

3. The thermal printing head of claim 1, wherein those of said defined portions of said resistive slips which are heated are combined to express a symbol.

4. The thermal printing head of claim 1, wherein said conductive slips and said resistive slips are formed on said insulating layers by the method of screen printing.

5. The thermal printing head of claim 1, wherein said insulating layers are raw thin ceramic sheets sintered into a unitary construction.

6. The thermal printing head of claim 1, wherein said insulating layers are made of a raw thin ceramic sheet having said conductive slips formed thereon by the method of screen printing before said layers are sintered.

7. The thermal printing head of claim 1, wherein said insulating layers are arranged stepwise also at the other end portions thereof opposite to said end portions where said resistive slips are provided, so that the corresponding end portions of said conductive slips on each said insulating layer are exposed from beneath the insulating layer immediately above for use as terminals through which electric energy is applied to said conductive slips.

8. The thermal printing head of claim 1, wherein a projection made of a thermally conductive material is formed on each of said defined portions of said resistive slips, the upper surfaces of said projections being arranged at substantially the same level.

9. The thermal printing head of claim 8, wherein said projections are formed by the method of screen printing.

10. The thermal printing head of claim 8, wherein each said projection comprises a plurality of layers of a thermally conductive material.