JPH0525892Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to the structure of a thermal head used in facsimiles, printers, various measurement recorders, and the like.

[Conventional technology]

In facsimiles, printers, various measurement recorders, etc., there is a so-called thermal head as a means for converting information sent as electrical signals onto heat-sensitive recording paper as graphic information such as characters and images and recording and fixing the same.

As shown in FIGS. 5 and 6, the thermal head 10 has heating elements 11 made of thick-film or thin-film resistors formed on the surface of a ceramic substrate 12 in a horizontal line or at appropriate intervals vertically and horizontally. The heat-sensitive recording paper 14 is pressed against the heating element section 11 (the surface of which is usually covered with a wear-resistant layer) via the platen roller 13, and pulses are applied to the heating element at appropriate locations. When a voltage is applied, the coloring layer on the recording paper 14 develops color in dots. By repeating the pulsed heating while moving the recording paper 14 with respect to this thermal head, a predetermined figure such as a character can be obtained by the arrangement of colored points.

Conventionally, the ceramic substrate 12 of this type of thermal head 10 is equipped with a heat sink, as shown in FIG. As shown in FIG. 7, a heat dissipating plate 15 made of metal such as aluminum having a high heat transfer coefficient was attached by adhesive or the like on the back side opposite to the side on which the heating element portion 11 was formed.

[Problem that the invention attempts to solve]

According to this configuration, in a high temperature state during use, the metal heat sink 15 having a large coefficient of thermal expansion extends with respect to the ceramic substrate 12 having a small coefficient of thermal expansion, thereby causing a so-called bimetal phenomenon.

For example, if the ceramic substrate 12 and the heat dissipation plate 15 are bonded together in a straight plane at a low temperature such as room temperature, then at a high temperature the long thermal head 10 will extend along the longitudinal direction of the platen roller 13.
In this case, the thermal expansion of the heat dissipation plate 15 along the longitudinal direction has a large effect, and due to the thermal stress, the gap between the longitudinal center portion A of the platen roller 13 in FIG. 6 and the heating element portion 11 becomes large. As a result, the entire thermal head 10 is warped due to thermal deformation, and the contact pressure between the recording paper 14 pressed via the platen roller 13 and the heating element section 11 is increased along the longitudinal direction of the platen roller 13. Variation occurs, and the clarity of the print along the longitudinal direction of the platen roller 13 is affected, such as the density of the print at the central part A of the platen roller 13 being light, and the density of the print at the left and right ends B and C being thick. Variation occurs.

As a countermeasure, the shape or material of the heat sink 15 may be devised to make it difficult for the heat sink 15 to warp due to the thermal stress caused by the rigidity of the heat sink 15 itself, or as shown in FIG. Deformation in the opposite direction to thermal deformation, that is, deformation in which the heating element 11 approaches the central portion A of the platen roller 13 and moves away from the heating element 11 at the left and right ends B and C of the platen roller 13. It is conceivable to apply this to the heat dissipation plate 15 in advance and attach the ceramic substrate 12 to this.

However, it is difficult to find a metal with a coefficient of thermal expansion approximately equal to that of the ceramic substrate and a high heat transfer rate, and in order to reduce warping due to thermal stress, the thickness of the heat sink 15 must be made extremely thick, and the thermal head There is a problem that the entire 10 is bulky.

Furthermore, even if the heat dissipation plate 15 is previously given a deformation in the opposite direction to the warping deformation at high temperatures, if the optimum shape is guaranteed at high temperatures, the warping at both left and right ends B and C of the platen roller 13 at low temperatures will occur. There was a problem that the contact became weak.

The present invention aims to easily solve such conventional problems.

[Means for solving problems]

For this reason, the present invention uses a heating element consisting of a resistor,
In a thermal head formed on the surface of a ceramic substrate, a heat sink made of a shape memory alloy or a heat sink made of a metal plate with a reinforcing member made of a shape memory alloy is attached to the back surface of the ceramic substrate, The structure is such that the warping deformation of the ceramic substrate and the heat sink due to heat is corrected.

〔Example〕

Next, an embodiment of the present invention will be explained with reference to the drawings. In FIG. On the back side of the ceramic substrate 2 in 1, a heat sink 4 made of a shape memory alloy or a metal heat sink 5 with a reinforcing member 4' made of a shape memory alloy, which will be described later, is fixed or stretched. It is something to be worn.

Code 6 is a cover body, code 7 is a connector, code 8
1 is a mounting screw portion for attaching the thermal head 1 to an external component; the reference numeral 13 indicated by a dashed line in FIGS. .

Then, as shown in FIG.
The heat dissipation plate 4 made of shape memory alloy is fixed to the back surface of the
Memorize the shape as follows.

That is, in the high temperature range when the thermal head 1 is in use, the platen roller 1 shown in FIG.
Assuming that a warp occurs that moves away from the central part A of the platen roller 13 and approaches the left and right end parts B and C of the platen roller 13, a warp shape in the opposite direction to counteract this warp deformation is created in advance. The temperature is stored in the heat sink 4 made of the shape memory alloy in the high temperature range.

Next, in a low temperature range such as room temperature, the shape memory alloy heat sink 4 is processed and deformed into a substantially flat planar shape, and in the low temperature range, the shape memory alloy heat sink 4 is attached to the ceramic substrate. Attach it to the back side of 2 by applying adhesive or fixing it with bolts.

When the heating element 3 of the thermal head 1 configured in this way is pressed against the circumferential surface of the platen roller 13 while holding the recording paper 14 between them, and pulses are applied according to an appropriate external signal, heat is generated at a predetermined position in the heating element 3. The rise in body temperature causes printing on the recording paper 14.

According to the present invention, when the temperature of the entire thermal head 1 immediately after the start of use is relatively low, the ceramic substrate 2 and the heat sink 4 made of a shape memory alloy become flat as described above. Therefore, the heating element part 3 on the surface side of the ceramic substrate is located at the central part A of the platen roller 13 and at both left and right ends B and C.
The contact pressure can be made substantially equal between the two locations, and printing can be performed with substantially the same density over the entire width direction of the recording paper 14 along the circumferential surface of the platen roller 13.

Through continuous use, the thermal head 1
When the temperature reaches a high temperature, due to the difference in thermal expansion between the ceramic substrate 2 and the shape memory alloy heat sink 4, the ceramic substrate 2 and the shape memory alloy heat dissipation plate 4 separate from the central part A of the platen roller 13, and the platen roller 13 moves away from the center part A and the left and right end parts B and C of the platen roller 13. A thermal stress (in the direction of the arrow X1 in FIG. 3) is generated that tends to cause a warp that approaches the shape of the shape memory alloy. Since a shape restoring force (in the direction of arrow Y1 in FIG. 3) is generated that tries to restore the shape, this shape restoring force and the thermal stress are balanced, so that the thermal head 1 as a whole can maintain its shape even in a high temperature range.
The heating element portion 3 is held in a flat planar shape, and printing with uniform density can be performed in the axial direction of the platen roller 13, as in the low temperature range.

In the embodiment shown in FIG. 4, an ordinary metal heat sink 5 is attached to the back surface of the ceramic substrate 2 in the thermal head 1 by pasting it with an adhesive or fastening it with bolts. A reinforcing member 4' made of shape memory alloy is further stretched on the back surface,
The shape memory of this reinforcing member 4' made of shape memory alloy is substantially the same as in the previous embodiment.

In addition to the case where this reinforcing member 4' made of shape memory alloy is stretched over the entire back surface of the heat sink 5,
The reinforcing member 4' made of the shape memory alloy is directly stretched on the back side of the ceramic substrate 2, and a heat sink 5 is placed on the back side.
Needless to say, the reinforcing member 4' may be formed into an appropriate rib protrusion that is fixed to the back surface of the heat sink plate 5.

[Functions and effects of the idea]

As mentioned above, the shape memory imparted to the heat dissipation plate 4 or reinforcing member 4' made of a shape memory alloy prevents the heat dissipation plate 4 or reinforcing member 4' from warping due to thermal stress of the entire thermal head only when the heat dissipation plate 4 or reinforcing member 4' reaches a high temperature range. By balancing the shape restoring force and thermal stress in the high temperature range, it is possible to maintain the shape of the heating element 3 in the thermal head flat in the high temperature range.

In the present invention, since the heat dissipation plate 4 or the reinforcing member 4' made of the shape memory alloy is previously formed into a flat shape in a low temperature range such as room temperature, it can be used in a low temperature range such as room temperature. Compared to the case where the thermal head 1 is given a warp deformation in the opposite direction to the warp deformation that occurs in advance in the room temperature range, the heating element portion 3 in the thermal head 1 of the present invention is flat in almost the entire temperature range of the usage condition from the low temperature range to the high temperature range. It can be held in the same shape, and its warp deformation can be extremely reduced.

Therefore, fluctuations in printing pressure due to warping deformation caused by thermal stress, as well as fluctuations in printing density, can be extremely reduced, and stable printing can be performed from a room temperature range to a high temperature range.

In addition, since the prevention of warpage deformation caused by conventional metal heat sinks relies on the rigidity of the heat sink, it is necessary to increase the moment of inertia around the axis parallel to the thickness of the plate. ,
Although it will inevitably be bulky, if you follow this idea,
Shape memory alloy heat sink 4 or reinforcing member 4'
The thickness of the thermal head can be formed to a thickness sufficient to generate shape recovery stress to counteract the thermal stress that causes warping due to temperature changes, and this has a great effect in contributing to the miniaturization and weight reduction of the thermal head. It is something.

[Brief explanation of the drawing]

1 to 4 show an embodiment of the present invention. FIG. 1 is a side view of the thermal head shown in FIG. 2, FIG. 2 is a plan view, and FIG.
FIG. 4 is a cross-sectional view of another embodiment, and FIGS. 5 to 7 show the prior art. FIG. 5 is a plan view of a thermal head, FIG. 6 is a cross-sectional view of FIG. 5 taken along line A, and FIG. 7 is a cross-sectional view showing the pre-warped state. 1, 10: Thermal head, 2, 12: Ceramic substrate, 3, 11: Heating element, 13:
Platen roller, 14... Recording paper, 5, 15...
Heat sink, 4... Heat sink made of shape memory alloy, 4'...
...Reinforcing member made of shape memory alloy.

Claims (1)

[Scope of utility model registration request] A heat sink made of a shape memory alloy or a heat sink made of a metal plate with a reinforcing member made of a shape memory alloy is attached to the back side of a ceramic substrate with a heating element formed on the front side, and the ceramic substrate and the heat sink are attached. A heat dissipation device for a thermal head, characterized in that it is configured to correct warping deformation due to heat.