JP2633578B2 - Thermal head - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head of a thermal printing apparatus used as a printer of a word processor or a typewriter, or used in a facsimile receiver or the like.

Prior Art A typical prior art is shown in FIG. The thermal head 1 basically includes a head substrate 2 and a head cover 3 that covers the head substrate 2.
The head substrate 2 has a large number of heating resistors 4 arranged in one row for forming heating dots, and external terminals 5 for applying an electric signal for causing the heating resistors 4 to selectively generate heat.
Terminals 7 a formed on the wiring conductors 7 of the wiring board 6 are superimposed on the external terminals 5 of the head substrate 2, and both are mounted on the support plate 8. The head substrate 2 and the wiring substrate 6 are sandwiched and pressed by the head cover 3 and the support plate 8. The thermal recording paper 9 is graded in a direction (arrow A direction) perpendicular to the row in which the heating resistors 4 are arranged. When the recording paper 9 is fed, the heating resistor 4 is selectively energized and generates heat, thereby forming dots on the recording paper 9 pressed by the platen 10 and printing.

The heating resistors 4 are grouped into a plurality of groups, and the electrodes 11 connected to the heating resistors 4 are connected to integrated circuit elements 14 for each group provided on the substrate 12. The integrated circuit element 14 is supplied with an electric signal from an external electric circuit via an external terminal 5 formed on the substrate 12. The integrated circuit element 14 is covered with a silicone rubber 15 having excellent water resistance and chemical resistance in order to protect the integrated circuit element 14 and its connection. This wiring conductor 7
Is a terminal 7a.

In the wiring board 6, the wiring element conductors 7 are formed by printing on the surface of the film 16 made of a synthetic resin having an electrical insulating property and facing the head substrate 2. External terminal 5 and terminal
7a is overlaid and pressed by a pressing member 17 fixed to the head cover 3. The pressing member 17 is made of an elastic synthetic resin material, and extends over the entire length of the region where the terminals 5, 7a are arranged.

An insertion hole 18 is formed in the head cover 3, and an insertion hole 19 is formed in the wiring board 6, and a bolt 20 is loosely inserted into these insertion holes 18, 19. A screw hole 21 is formed in the support plate 8, and the bolt 20 is screwed into the screw hole 21. Therefore, when the terminal 7a of the wiring board 6 and the terminal 5 of the head substrate 2 are placed on the support plate 8 so as to overlap with each other, and when the head cover 3 is fixed to the support plate 8 with bolts 20, both terminals 5, 7a Is the head cover 3 and the support plate 8
Are connected by being sandwiched and pressed.

Problems to be Solved by the Invention In a state where the temperature of the head substrate 2 and the temperature of the support plate 8 are increased at the time of printing, particularly, when printing is performed continuously, the head substrate is caused by a difference between the thermal expansion coefficients thereof. 2 may be curved. That is, since the coefficient of thermal expansion of the aluminum support plate 8 is larger than the coefficient of thermal expansion of the base 12 made of a ceramic material, when these temperatures rise, the direction in which the resistance heating elements 4 are aligned is increased. FIG. 8 is a simplified view of a curved surface extending in a plane extending in a direction perpendicular to the plane of FIG.

When the thermal head 1 is used in a facsimile or the like and the head substrate 1 is bent as described above, when the maximum displacement d1 due to the bending of the head substrate 1 becomes 0.1 mm or more, the heat generating resistor 4 is moved to the heat-sensitive recording paper. A portion that does not come into contact with 9 is generated, and heat transfer from the heating resistor 4 is deteriorated, so that printing becomes unclear.

An object of the present invention is to solve the above-described problems, and at the time of printing,
Particularly, it is an object of the present invention to provide a thermal head capable of performing a printing operation in a normal state without bending the head substrate even when the temperature of the head substrate and the support plate is increased when performing continuous printing. .

Means for Solving the Problems The present invention provides a thermal head in which a long head substrate on which a plurality of heating resistors are arranged is bonded and fixed on a support plate, wherein the head substrate and the support plate have the same length. A thermal head characterized in that it is bonded with a soft adhesive having a shear adhesive strength of 25 kg / cm ² or less over the length direction and the central portion in the length direction is fixed by an adhesive having a higher hardness than the soft adhesive. is there.

According to the present invention, the support plate and the head substrate are adhered to each other with a soft adhesive having a shear adhesive strength of 25 kg / cm ² or less over the length thereof, and an adhesive having a higher hardness than the soft adhesive. To fix the central part in the length direction.
By this, at the time of printing, especially in the state where the temperature of the head substrate and the support plate is increased when performing continuous printing,
The head substrate does not curve due to the difference between these coefficients of thermal expansion. For example, even if the thermal expansion of the support plate is greater than the thermal expansion of the head substrate, the plastic deformation of the soft adhesive absorbs the difference due to the thermal expansion of the two components, thereby preventing the head substrate from bending. That is, each displacement during thermal expansion between the head substrate and the support plate is allowed. Therefore, even if the temperature rises, for example, during continuous printing, the head substrate does not bend, so that printing can be continued in a normal state. Experiments of the present invention have confirmed that when the shear adhesive strength of the soft adhesive exceeds 25 kg / cm ² , the amount of bending of the head substrate sharply increases.
Also, by repeatedly using the thermal head, even if the plastic deformation of the soft adhesive is repeated many times,
The position of the head substrate does not change with respect to the support plate, and the center of the head substrate can always be arranged at a predetermined position. Further, since the fixing position by the hard adhesive is substantially at the center in the length direction, the amount of displacement due to thermal expansion of the head substrate itself is small.

Embodiment FIG. 1 is a longitudinal sectional view showing the structure of a thermal head 31 according to an embodiment of the present invention, and FIG.
FIG. 3 is an exploded perspective view of FIG. The thermal head 31 is a heating resistor
A head substrate 34 having an integrated circuit element 32, a wiring substrate 35, a reinforcing plate 36 for reinforcing the wiring substrate 35, and a reinforcing plate 36;
And a support plate 37 on which the head substrate 34 is placed, and a head cover 38 covering these.

In the head substrate 34, a heating resistor 32 is formed on a flat substrate 39 made of an electrically insulating material, for example, an alumina-based ceramic, by vapor deposition as a thin film technique or screen printing as a thick film technique. Conductors 40 and 41 are formed as electrodes on the heating resistor 32, and power is applied to the conductors 40 and 41 to cause the heating resistor 32 to generate Joule heat.

The heating resistors 32 are grouped into a plurality of groups, and the conductors 40 connected to the heating resistors 32 are connected to the integrated circuit elements 33 provided for the respective groups provided on the substrate 39. The integrated circuit element 33 is supplied with an electric signal from an external electric circuit through a conductor 44 formed on the substrate 39. The conductor 44 includes a conductor portion 42 and an external terminal 43, and the integrated circuit element 33 selectively heats the heating resistor 32 via the conductor 40 by an electric signal from the external terminal 43. Then, energizing power is supplied to the selected heating resistor 32.

The wiring substrate 35 includes a substrate 45 made of, for example, a flexible synthetic resin material having an electrical insulation property, and a surface (a lower surface in FIG. 1) of the substrate 45 facing the head substrate 34. And a plurality of wiring conductors 48 formed to individually correspond to the terminals 43. The wiring conductor 48
Terminals individually connected to the conductor portion 46 and the external terminal 43
47.

The terminals 47 are individually connected to the external terminals 43 by solders 49. Therefore, the two terminals 47 and 43 can maintain a strong connection state without being pressed by the pressing member as described in the section of the related art, and the connection state can be shifted by an external impact force. Is prevented.

The reinforcing plate 36 for reinforcing the wiring board 35 is made of a material such as paper phenol or glass epoxy.

The head substrate 34 and the reinforcing plate 36 are bonded to a supporting plate 37 by a soft adhesive 50 described later. The support plate 37 is made of, for example, aluminum, and the head substrate 34
Functions as a heat radiating plate for radiating a part of the heat generated by the resistance heating element 32 to prevent the temperature of the head substrate 34 from becoming abnormally high.

The integrated circuit element 33 is covered with a protective member 51 made of a hard material having a Shore hardness of 60 or more, for example.
The protection member 51 protects the panel from external impact. If the Shore hardness is less than 60, it is too soft, and sufficient protection against the external force of the integrated circuit element 33 and its connection portion cannot be provided. The surface roughness of the protective member 51 is formed smoothly so as to be, for example, 60 μm or less, so that the heat-sensitive recording paper 52
Slides smoothly on the protection member 51,
Is suppressed. When the surface roughness exceeds 60μm,
The surface of the protective member 51 comes into frictional contact with the thermal recording paper 52 to make the thermal recording paper 52 fluff, and the protective member 51 wears faster.

The head cover 38 is made of, for example, a polypropylene-based synthetic resin material, and includes a guide portion 53 for guiding the thermal recording paper 52, a top portion 54, and a support piece for supporting the head cover 38.
55. On the lower surface (lower surface in FIG. 1) of the top portion 54 of the head cover 38, two or three right columnar projections 56 are provided at regular intervals in the longitudinal direction (perpendicular to the paper surface of FIG. 1). It is erected at 57.

Insertion holes 58 and 59 are formed in the wiring board 35 and the reinforcing plate 36 at positions corresponding to the positions where the protrusions 56 are provided. The support plate 37 has a notch on the left side in FIG.
An attachment portion 61 formed by the notch 60 has an attachment hole 62 for attaching the projection 56.
Are formed.

The projection 56 includes a straight cylindrical shaft portion 63 and a head portion 64, and the head portion 64 has a notch 65 that is open toward its free end.
Are formed to extend in the axial direction of the shaft portion 63. head
A guide inclined surface 66 is formed at the free end of the head 64, and a support inclined surface 67 is formed near the shaft 63 of the head 64. The bottom 65a of the notch 65 extends closer to the base end of the shaft 63 than the inclined support surface 67.

The projection 56 having such a configuration is inserted into the insertion holes 58 and 59 formed in the wiring board 35 and the reinforcing plate 36, and is attached to the attachment hole 62 of the attachment portion 61. When the projection 56 is inserted into the insertion holes 58 and 59 and the mounting hole 62, the head 64
The notch 65 is guided and inserted through the guide inclined surface 66 of the head 64 in a state where the end of the notch 65 is slightly closed. In the state where the projection 56 is mounted, the lower end of the mounting hole 62 abuts on the support inclined surface 67 of the head 64, and in this state, the notch 65 attempts to open, and A spring force acts on the side. As a result, the end surface 57a of the mounting base 57 is
To the wiring board 35, the reinforcing plate 36, and the supporting plate.
37 is pressed and held between the end face 57a and the head 64 of the projection 56.

Further, since the wiring board 35 is pressed downward by the elastic force of the projection 56, when printing is continuously performed,
Even when the heat of the heat generating resistor 32 is conducted to the wiring board 35 to cause a bending or the like, the bending state is suppressed by the elastic force of the projection 56.

The notch 60 of the support plate 37 is a free end surface of the protrusion 56 when the head 64 of the protrusion 56 is attached to the support plate 37.
56a is flush with the end face 37a of the support plate 37 or the lower end face 37
The support plate 37 is formed so as to be on the inner side in the thickness direction of the support plate 37 than a.

The guide portion 53 of the head cover 38 has its tip 53a positioned upstream (in the left side of FIG. 1) in the direction of transport of the thermal recording paper 52 with respect to the axis of the integrated circuit element 33. Together, they constitute a guide for guiding the thermal recording paper 52. Further, the tip 53a of the guide portion 53 is located within a section perpendicular to the axis.
It is formed in a circular arc shape having a roundness of about 0.3 to 0.4 mm. This is to prevent the thermal recording paper 52 guided by the guide portion 53 from being damaged. On the other hand, the protection member 51 for protecting the integrated circuit element 33 has a surface roughness as described above.
Guide surface with smooth surface of 60μm or more
When the thermal recording paper 52 conveyed from 53 is connected to the protective member 51, the leading end of the thermal recording paper 52 is prevented from fluffing.

The thermal recording paper 52 guided by the protection member 51 is pressed against the heating resistor 32 by a rubber platen 68 and is conveyed in the direction of arrow P.

As described above, in the present invention, a hard material is used for the protection member 51 for protecting the integrated circuit element 33. Therefore, the integrated circuit element 33 can be protected by only the protection member 51, and the protection member 51 Need not be covered by the head cover 38. Therefore, the guide portion of the head cover 38
53 can be shortened, and can be configured as a guide for the thermal recording paper 52 together with the protective member 51, and the guide 53 of the head cover 38 can be reduced in size.

Further, since the head cover 38 is attached to the support plate 37 by the projection 56, not only the structure is simplified, but also the bending of the wiring board 35 can be prevented by the downward elastic force of the projection 56. Further, since the terminals 47 of the wiring board 35 and the terminals 43 of the conductors 44 are connected by solder 49, it is not necessary to apply an external force separately in order to maintain these connection states. As described above, the thickness of the corresponding portion of the head cover 38 can be made as small as possible, and the related portion, that is, the portion between the connection position of the terminals 43 and 47 and the portion where the projection 56 is formed, is provided. Of the head cover can be made as small as possible. As described above, according to the present invention, the head cover 38 can be downsized, and accordingly, the configuration of the thermal head 31 can be downsized.

As described above, the head substrate 34 and the support plate 37 are bonded by the soft adhesive 50 having a shear bonding strength of 25 kg / cm ² or less. Here, the soft adhesive is used because the difference in thermal expansion coefficient between the head substrate 34 and the support plate 37 is determined by using the soft adhesive 50.
It is for absorbing by. The head substrate 34 is a support plate
Not only is it glued to 37 with a soft adhesive 50,
Only a short interval near the center position in the longitudinal direction of the head substrate 34,
The head substrate 34 and the support plate 37 are fixed with an adhesive having a higher hardness than the soft adhesive 50. As a result, the position of the head substrate 34 does not change with respect to the support plate 37, and the displacement of the head substrate 34 itself is small.

FIG. 3 is a graph showing the results of an experiment for determining the shear adhesive strength in the longitudinal direction of the soft adhesive used in the present invention. Hereinafter, an experimental method performed by the present inventor and a result thereof will be described.

The head substrate 34 provided with the heating resistor 32 may be heated to, for example, about 80 degrees when continuous printing is performed. At this time, the amount of heat of the head substrate 34 is transmitted via the adhesive 50 to the support plate 37 serving as a radiator plate. In such a case, the head substrate 34 and the support plate 37 are curved as shown in FIG. 4 due to the difference in thermal expansion coefficient between the substrate 39 made of alumina ceramic material and the aluminum support plate 37. I do. It is considered that the maximum displacement d2 caused by such bending changes depending on the shearing adhesive strength of the adhesive bonding the head substrate 34 and the support plate 37.

Then, the present inventor used various adhesives to obtain the shear adhesive strength, that is, the adhesive strength when a force was applied to the head substrate 34 and the support plate 37 in the directions of arrows A1 and A2 shown in FIG. Investigating the strength, when using adhesives having various shear bond strengths, the maximum displacement in the curved state
d2 was measured.

The support plate 37 as a heat sink is 19 mm wide and 240 m long
m, having a thickness of 5.0 mm, the alumina-based ceramic substrate 39 has a width of 18.8 mm, a length of 232 mm, and a thickness of 0.62 mm
The size was used. In this experiment, room temperature 25
The head substrate 34 ° C. was heated up to the expected maximum temperature of 80 ° C., that is, the difference from the normal temperature reached 55 ° C., and the maximum displacement d2 in the curved state was measured. This measurement result is the third
This is shown in the graph of the figure.

Referring to FIG. 3, the above-mentioned shear adhesive strength is 25 kg / cm ²
When the following adhesive is used, the maximum displacement d2 is 0.
And at 1mm or less, the shear adhesive strength exceeds 25 kg / cm ^2,
The maximum displacement d2 rises sharply and the shear bond strength is 50
When an adhesive of kg / cm ² or more is used, the maximum displacement d2 is approximately 1.2 mm, and thereafter becomes saturated. on the other hand,
The allowable range of the maximum displacement amount d2 in which a normal printing operation is performed using the curved head substrate 34 is 0.1 mm. Therefore, as is clear from the graph of FIG.
The shear adhesive strength in the longitudinal direction of the soft adhesive 50 used in the present invention is 25 kg / cm ² or less.

The present inventor conducted the following experiment. That is, as shown in FIG.
The strength of peeling 34 in the direction perpendicular to the adhesive surface (the direction of arrow B1 in FIG. 6), that is, the so-called 90 ° peel strength, was measured using various adhesives. As a result, the strength is 25
It has been found desirable to use an adhesive that is at least 200 g per mm. That is, if the strength is less than 200 g per 25 mm length, the adhesive strength between the head substrate and the support plate 37 cannot be said to be sufficient, and the durability of the thermal head 31 will be deteriorated.

The thickness of the soft adhesive 50 is desirably 10 to 200 μm. That is, the thickness of the adhesive 50 is 10 μm
If it is less than this, it cannot be said that the adhesive strength for bonding the head substrate 34 and the support plate 37 is sufficient. On the other hand, when the thickness is 20
If the thickness exceeds 0 μm, the heat of the heated head substrate 34 cannot be sufficiently transmitted to the support plate 37, and the head substrate 34 becomes excessively heated, and the quality of printing deteriorates. That is, if the head substrate 34 does not radiate heat appropriately,
An area other than the desired area of the heating resistor 32 is overheated, the desired printing operation is not performed, and the quality of printing deteriorates. For this reason, it is desirable that the thickness of the adhesive 50 be about 10 to 200 μm. Further, as a material of the adhesive 50, for example, an acrylic adhesive may be used.

As described above, in the present embodiment, the head substrate 34 and the support plate 37 are bonded to each other by the adhesive 50 having the above-described properties. In a state where the temperature of the substrate 34 and the support plate 37 is increased, even if the substrate 34 and the support plate 37 are curved due to a difference in their thermal expansion coefficients,
Soft adhesive having a difference in thermal expansion of 25 kg / cm ² or less in shear adhesive strength
Since it is absorbed by 50 and the maximum displacement d2 due to the bending is suppressed to a desired level or less, printing can be performed continuously without deteriorating the quality of printing.

Effects As described below, according to the present invention, even when the temperature of the head substrate and the temperature of the support plate are increased during printing, particularly when printing is performed continuously, the difference in thermal expansion between the two is limited by the plasticity of the soft adhesive. Since it is absorbed by the deformation, the head substrate does not bend. Further, when the thermal head is used repeatedly, even if the soft adhesive is plastically deformed, the position of the head substrate does not fluctuate or shift with respect to the support plate. Therefore,
Even in continuous printing, printing can be continued in a normal state, and deterioration of printing quality can be prevented.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a configuration of a thermal head 31 according to an embodiment of the present invention, FIG. 2 is an exploded perspective view of the thermal head 31, FIG. 3 is a graph showing experimental results of the present inventor,
4 to 6 are diagrams for explaining the experimental method of the present inventor, FIG. 7 is a longitudinal sectional view of a typical prior art, and FIG. 8 is a diagram for explaining problems of the prior art. It is. 31: Thermal head, 32: Heating resistor, 33: Integrated circuit element, 34: Head substrate, 35: Wiring substrate, 37 ...
Support plate, 38: Head cover, 39: Substrate, 40, 41 ...
Conductor, 43 external terminal, 47 terminal, 49 solder, 50
... Soft adhesive, 51 ... Protective member, 52 ... Heat recording paper, 53
…… Guide member, 56 …… Protrusion, 57 …… Mounting base

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-59-225970 (JP, A) JP-A-61-3575 (JP, A) JP-A-58-63473 (JP, A) JP-A-58-63473 14779 (JP, A) Fully open 60-162042 (JP, U) Fully open 60-191443 (JP, U) Fully open 58-92055 (JP, U)

Claims (1)

(57) [Claims] 1. A thermal head comprising a long head substrate on which a plurality of heating resistors are arrayed and fixed on a support plate, wherein the head substrate and the support plate have a shear bond strength of 25 kg along the length thereof. A thermal head, wherein the thermal head is adhered with a soft adhesive of not more than / cm ^{2 and} the center in the length direction is fixed with an adhesive having a higher hardness than the soft adhesive.