JPS6297863A - Thermal transfer printer - Google Patents

Abstract

PURPOSE:To obtain the same quality of printing with that of ordinary-paper printing, by specifying the width and the radius of curvature of a partial glaze layer of a thermal head corresponding to printing of paper of low smoothness so that a contact surface pressure to deform elastically the ridged portion of the surface of the paper of low smoothness be given by a pressing force of the head for the ordinary-paper printing. CONSTITUTION:The highest contact surface pressure is obtained when the contact width of a partial glaze layer 3 in the case when it is pressed on the surface of paper of low smoothness is larger slightly than the width (d) of a heating resistor 4, on the condition that a pressing force of a head is identical. Therefore, the width (w) of the glaze layer 13 is set to be 1-4 times larger approximately than the projected width (d) of the heating resistor 4 or to be 450mum or less approximately in consideration of the easiness for manufacture as well. In addition, the height (h) of the glaze layer 3 is set generally to be 30-50mum. Accordingly, a radius of curvature obtained when the cross section of the glaze layer 3 is formed in the shape of a circular-arc is 1,200mum or less when it is calculated by the Hertz's theoretical formula of contact. The same effect can be obtained also when a partial glaze layer having a large radius of curvature is formed to be triangular substantially by etching.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a thermal transfer printer, and particularly to a thermal head that can obtain good print quality even when low smoothness paper is used as the transfer paper. .

[Background of the invention]

A thermal transfer printer is characterized by its ability to transfer onto plain paper due to its transfer principle. But conventionally.

When low smoothness paper (paper with a rough surface) is used as the transfer paper, there is a drawback that the print quality is significantly inferior. In other words, with low smoothness paper, the surface of the paper is rough, so the ink melted by the thermal head cannot penetrate into the valleys of the paper surface, and the ink sticks only to the peaks, resulting in voids and transfer omissions in the transfer dots. This has resulted in a decrease in print quality, print breakage, etc.

However, with the completion of thermal transfer printers and the spread of thermal transfer printers.

City 41 of liberalizing the transfer paper and responding to smooth or low smoothness paper! Demand is becoming extremely strong. In addition.

The structure of the thermal head to obtain striped printing quality is as follows:
As described in JP-A-59-76272, an example is known in which a heating resistor is provided at the top of a circular arc of glass glaze to improve the efficiency of transmitting thermal energy to the transfer paper. However, experiments have confirmed that simply improving the thermal energy transfer efficiency is not enough to support printing on low-smooth paper.

[Purpose of the invention]

An object of the present invention is to provide a thermal head most suitable for obtaining high print quality even when using low smoothness paper as the transfer paper.

[Summary of the invention]

FIG. 2 shows an external view of a basic thermal head used in a thermal transfer printer. As shown in this figure, the thermal head is constructed by providing a partial glaze layer 3 on a head substrate 2 made of an insulator such as ceramic, and disposing a heating resistor 4 on the upper layer.

FIG. 3 shows the thermal head 1 and the ink ribbon 5 when low smoothness paper is used as the transfer paper. Contact shape of low smoothness paper 6! It is a sectional view showing PR't-. A heating resistor 4 disposed on a partial glaze layer 3 made of glass material ρ is connected to an electrode 7.
90 parts generate heat by being energized through them. This heat is transferred to the ink ribbon 5 via the protective layer 8. Therefore, the solid ink 11 applied to the base film 10 of the ink ribbon 5 is melted and transfer is performed. However, the surface condition of low-smoothness paper is very poor and the ridges 6
The difference between a and the valley portion 6b is as much as 10 to 28 μm.

Therefore, the molten ink cannot penetrate into the troughs 6b and adheres only to the peaks.

The present invention was devised based on the following ideas for the purpose of solving this problem.

After conducting various experiments and examining the conditions for making low-smoothness paper printing possible, we discovered an important fact. This increases the pressing force of the thermal head against low-smooth paper, that is, the contact surface pressure between the partial brace layer on the thermal head and the transfer paper (4 to 5 times the head pressing force when printing on plain paper). ), which means that it has very good transfer ability even on low smoothness paper. This will be explained in detail using FIGS. 4 and 5. FIG. 4 shows how the transfer rate changes by changing the contact pressure between the partial glaze layer on the thermal head and the transfer paper by changing the pressing force of the thermal head. The transfer rate will now be explained with reference to FIG. In this figure, the dashed-dotted line represents the ideal shape to be transferred, and the shaded area represents the ink actually transferred onto the surface of the low-smoothness paper. The ratio of the total area of the actually transferred diagonally shaded portion to the total area of the ideal shape (dotted chain line) is defined as the transfer rate. With this definition, it can be said that the higher the transfer rate, the higher the printing quality. As shown in FIG. 4, it can be seen that by increasing the head pressing force, the transfer rate increases as the contact pressure between the partial glaze layer on the thermal head and the low smoothness paper increases. That is, a transfer rate of 85% was obtained by applying a contact surface pressure of 0.1 kf/m'', which is approximately 10 times the contact surface pressure of 0.01 Kf/m'' that can be written on plain paper.

It is possible to perform transfer on low smoothness paper as well as on plain paper. This means the following: That is, the sixth
As shown in the figure, by increasing the contact surface pressure, the contact area of the low-smooth paper with the glaze layer is elastically deformed, which temporarily crushes the peaks of the low-smooth paper during transfer, making the surface smooth. . Therefore.

If the contact surface pressure can be secured at 0.1 Kg/w" or more, transfer to low smoothness paper is possible, but in order to obtain the above surface pressure while maintaining the conventional Helad glaze shape, the head pressing force must be the same as the conventional standard. This requires 4 to 5 times the pressing force required for paper printing.This requires the printer itself to be extremely large and strong.

Furthermore, since the running resistance of the carriage on which the head is mounted also increases in proportion, the capacity of the drive source for driving the carriage must also be increased, which poses too many problems for actual product application.

Next, the reason why it is not possible to obtain the contact surface pressure necessary for printing on low smoothness paper with the conventional head glaze shape will be explained. Generally, partial glazes are formed by printing molten glass material onto a ceramic substrate. Therefore, the shape of the glaze is determined by the surface tension of the glass material.

As shown in FIG. 7, the width W of the bottom of the first part glaze layer is about 700 to 1200 μm, whereas the height of the first part glaze layer is very small, about 30 to 40 μm. Therefore, the radius of curvature γ of this partial brace layer is also very large, reaching 4000 to 5000 μm. Here, if we assume that the partial glaze layer is a cylinder with radius r and the low smoothness paper is a homogeneous object as shown in Figure 8, then the contact area between the first partial glaze layer and the low smoothness paper is roughly as follows. It can be calculated using Hertz's contact theory formula. -where b During contact between the two-part glaze layer and the low-smoothness paper W: Linear load acting on unit length of the part-glaze r: Radius of curve 4 of the glaze El: Longitudinal elastic modulus of the glaze E2: Low-smoothness paper Modulus of longitudinal elasticity ν1: Poisson's ratio of the glaze ν2: Poisson's ratio of the low smoothness paper As is clear from this method, even when the same load is applied.

The contact radius formed at the contact portion between the partial glaze layer and the low smoothness paper is greatly influenced by the radius of curvature r of the partial glaze layer, and the larger the radius of curvature r, the larger the contact radius becomes.

Contact surface pressure is the head pressing force divided by the contact area, so in order to obtain high contact surface pressure with a small head pressing force, the key is how to reduce the contact area, that is, the contact area. This is the point. As explained above, the present invention has a partial glaze layer on the head as described below so that a contact surface pressure that enables printing on low smoothness paper can be obtained even with a head pressing force that is almost the same as the conventional head pressing force for plain paper. The shape is set.

(1) The glaze width dimension W and the radius of curvature γ are defined in accordance with printing on low smoothness paper.

(2) The 'fIr surface shape of the partial glaze layer is approximately triangular,
Alternatively, the low smoothness paper and the partial glaze layer are configured to be in contact with each other in a contact area slightly larger than the area of one heating resistor by forming it into a substantially regular shape.

(3) By configuring the partial glaze layer in multiple stages, making the glaze size of the upper layer smaller and the glaze shape of the lower layer thicker, the contact area between the partial gray layer and the low-smoothness paper is slightly larger than the area of the heating resistor. By increasing the height h of the glaze, the contact of the low smoothness paper with the head substrate is eliminated, and the head contact surface pressure is prevented from being reduced.

[Embodiments of the invention]

Examples of the present invention will be described below.

FIG. 9 is an external view showing the structure of a thermal transfer printer embodying the present invention. Its configuration and operation will be explained. First, a shaft 38 and a stay 34 are fixed between the side plate 24 and the side plate 4o. Further, a carriage 32 is arranged to be slidable on a shaft 38 and a stay 34, and a ribbon cassette 30 and a thermal head 1 are mounted on the carriage 32.

An ink ribbon 5 is stored in the ribbon cassette 30. The carriage 32 is driven by a carriage motor 26 via a timing belt 44.

It is configured to be movable in the left and right directions in the figure. The line feed motor 20 transmits driving force to the gear 18 fastened to the paper feed roller shaft 53 to feed the transfer paper 13. Paper can also be fed in the same way by turning the paper feed knob 22 by hand. 42 is a paper guide. By moving the release lever 16 in the front-back direction, the paper pressing roller 14 slidably disposed on the shaft 15 is released from the paper surface 91 pressed against the paper surface. 36 is a home position sensor, and 28 is a flat cable for supplying electricity to the thermal head 1. This printer uses a unidirectional printing method in which printing is performed only when the carriage 32 moves to the right; when moving to the right, the ink ribbon 5 is wound up; when moving to the left, the ink ribbon 5 is wound. This is a printer that does not require Also, carriage motor 2
6° line feed motor 20. The thermal head IS home position sensor 36 and the like are controlled by a controller 80.

Next, the shape of a partial glaze layer of a thermal head compatible with printing on low-smoothness paper, which is the subject of the present invention, will be explained with reference to FIG. The ideal shape of the partial glaze layer is best if the projected width of one heating resistor 40 is d, and the total medium dimension W of the first partial glaze layer is slightly larger than d. That is, during contact when the partial glaze layer is pressed against the low smoothness paper surface, the contact is only slightly larger than the minimum required heating resistor medium d, so no other unnecessary contact is performed.

Therefore, if the head pressing force is the same, the highest contact surface pressure can be obtained compared to other glaze shapes. Therefore, taking into account the ease of manufacturing the partial glaze layer, the etching W of the first partial glaze layer 3 is approximately 1 of the projected width d of the heating resistor 4.
It is preferable to set the thickness to ~4 times, or approximately 450 μm or less. Further, the height h of the glaze layer should be equal to or greater than the amount of elastic deformation of the surface of the low smoothness paper, but it is generally set to h=30 to 50 μm. Therefore, if we consider w/h, approximately w
/ If set to h≦15, the glaze shape becomes very effective for printing on low smoothness paper. (9) When the cross-sectional shape of the glaze layer is an arc shape, the radius of curvature r is calculated according to the above conditions and becomes r≦1200 μm. 10th
The figure and FIG. 11 are modified examples of FIG. 1. 10th
As shown in the figure, the conventional partial glaze layer having a large radius of curvature is etched to form a substantially triangular shape (substantially trapezoidal shape), thereby preventing unnecessary portions other than the 4 parts of the 1 heating resistor from coming into contact with each other. FIG. 11 shows an example in which another partial glaze layer 51 is provided on top of the conventional partial glaze layer 3, and its cross-sectional shape is approximately triangular. Even with this configuration, not only the same effect as shown in FIG. 10 can be obtained, but also the height of the glaze can be made larger than before, so it is possible to prevent low smoothness paper from hitting the head substrate 2. , head contact pressure is not reduced.

〔Effect of the invention〕

According to the present invention, even with a head pressing force that is almost the same as the head pressing force for conventional plain paper printing, it is possible to provide the contact surface pressure necessary to elastically deform the peaks on the surface of low smoothness paper. Even when low-smoothness paper is used as the transfer paper, by simply adopting one head of the present invention, high print quality equivalent to that of conventional plain paper printing can be obtained even if the printer itself remains conventional.

[Brief explanation of drawings]

Figure 1 shows the partial glaze WR of the thermal head of the present invention.
The top view and Figure 2 are external views of the thermal head. Figure 3 is a cross-sectional view showing the contact state of low smoothness paper, ink ribbon, and thermal head. Figure 4 is an explanatory diagram showing the relationship between head contact surface pressure and transfer rate. Figure 5 is the definition of transfer rate. FIG. 6 is a sectional view illustrating elastic deformation of the surface of low smoothness paper, FIG. 7 is a sectional view of a conventional partial glaze layer, and FIG.
The figure is an explanatory diagram of Hertz's contact theory, FIG. 9 is a perspective view showing the structure of a thermal transfer printer, and FIGS. 10 and 11 are cross-sectional views of a partial glaze layer showing an applied variation of the present invention. 1...Thermal head, 2...-Head board, 3...
- Partial glaze layer, 4... Heat generating resistor, 5... Ink ribbon. 6...Low smoothness paper, 7...'IIc pole, 8...Protective layer, 5a...Mountains on the surface of low smoothness paper, 6b...
Low smoothness paper surface +7) Valley 11S, IO...Base film, 11...Ink. 12...Platen, 51...Upper partial glaze layer. r = (1~4-) Kai 4-≦4CsOμto nail≦15 and ≦qoα! J-Sword 1, Tsumugi 2, Izumi 3, and 6)

Claims (1)

[Scope of Claims] 1. A platen against which the thermal head is pressed through the transfer paper, a ribbon cassette containing a loop-wound transfer film, and supporting the ribbon cassette and the thermal head for traverse movement. In a thermal transfer printer consisting of a carriage etc. and capable of printing on low smoothness paper, the total width of the partial glaze layer that supports the heating resistor of the thermal head is approximately 1 to 4 times the projected width of the heating resistor. Or approximately 450μm or less or the radius of curvature is 12
A thermal transfer printer characterized in that the thickness is set to 00 μm or less. 2. A thermal transfer printer according to claim 1, characterized in that the surface pressure applied to the transfer paper by the partial gray layer of the thermal head is set to approximately 0.1 kg/mm^2 or more. 3. A thermal transfer printer according to claim 1, wherein the partial glaze layer supporting the heating resistor of the thermal head has a cross-sectional shape of approximately triangular or trapezoidal. 4. The device according to claim 1, characterized in that w/h is set to approximately 15 or less, where w is the total width of the partial gray layer of the thermal head and h is the height. Thermal transfer printer. 5. A thermal transfer printer according to claim 1, characterized in that the partial gray layer of the thermal head is constructed in multiple stages, and its cross-sectional shape is approximately triangular.