Thermal head

A thermal head has one or more slits formed at a portion of a substrate and one or more heat generating resistors arranged between the slits.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a thermal head. 
2. Description of the Prior Art 
In a prior art thermal head, as shown in FIGS. 1A and 1B, a heat insulation 
layer 2 is formed on a ceramic substrate 1, and a heat generating resistor 
3, an electrode layer 4 and a protection layer 5 are stacked thereon. 
With this structure, however, a surface of the thermal head is flat and 
good contact between a heat generating area and a thermal record paper is 
not attained, and hence a high quality of print is not achieved. To avoid 
the above problem, a heat insulation layer 6 is formed only at the heat 
generating area as shown in FIGS. 2A and 2B so that the heat generating 
resistor 3 protrudes from the surface of the thermal head to attain good 
contact between the heat generating area and the thermal record paper. 
However, in the above structure, because a plurality of heat generating 
resistors are fixed on one plane, some of the heat generating resistors 
make good contact to the thermal record paper while others do not, 
depending on the unevenness of the surface of the thermal record paper. As 
a result, print density is not uniform. 
In a thermal transfer printer in which a thermal transfer ribbon is placed 
between the thermal head and a plane paper, non-uniformity in print 
density is a serious problem because of a requirement for a high print 
quality. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a thermal head in which 
each heat generating resistor independently contacts a record paper to 
prevent non-uniformity in the print density due to unevenness of the 
surface of the record paper.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIGS. 3A and 3B, comb shaped slits 3A are formed in a ceramic 
substrate 1. Free ends of the teeth of the comb can make small resilient 
motion thicknesswise of the substrate as shown by an arrow X. A heat 
insulation layer 6, a heat generating resistor 3, an electrode layer 4 and 
a protection layer 5 are stacked at the free end of each tooth of the comb 
to form a heat generating area. 
FIGS. 5A, 5B and 5C show examples of wiring of the electrodes. In FIGS. 5A 
and 5B, a signal line 4b and a common line 4a are arranged on a front 
side, and in FIG. 5C, the common line 4a and the signal line 4b are 
arranged on front and rear sides respectively. 
With this structure, even if the surface of the record paper is not even, 
each heat generating area can move in a resilient motion independently in 
accordance with the unevenness of the surface of the record paper so that 
all heat generating areas can fully contact to the record paper and the 
ununiformity in the print density is avoided. 
In FIGS. 4A and 4B, the slits 3a are of slot shape instead of the comb 
shape. Like the embodiment of FIG. 3, the heat generating areas can move 
in a resilient motion thicknesswise as shown by an arrow X. 
In FIGS. 6A, 6B, 7A and 7B, the ceramic substrate 1 is mounted on a 
resilient substrate 7. Referring to FIGS. 6A and 6B, the resilient 
substrate 7 such as metal has a plurality of slits 3a similar to those of 
the ceramic substrate 1 of FIG. 5. They are of comb shape and the free 
ends thereof can move in a resilient motion. 
The ceramic substrate 1 having the heat generating area is attached to the 
end of the substrate 7 and the electrode layer 4 is connected to a lead 
wire 9. Numeral 8 denotes an insulation layer used when the resilient 
substrate 7 is a conductor. 
In FIGS. 7A and 7B, the slits 3a are of slot shape instead of the comb 
shape. The same effect as that in FIG. 6 is attained. 
In those embodiments, the heat generating members individually follow the 
unevenness of the surface of the record paper and hence non-uniformity in 
print density is avoided. 
In the embodiments of FIGS. 3A, 3B, 4A and 4B, the substrate 1 need not be 
of ceramic material but any insulating material on which the heat 
generating resistor can be formed. A better effect is obtained if it is 
resilient. 
The number of slits formed in the substrate is not restrictive and at least 
one slit may be formed. More than one heat generating resistor may be 
arranged between the slits. 
As described hereinabove, in accordance with the present invention, at 
least one slit is formed at a portion of the substrate and the heat 
generating resistors are arranged between the slits. Accordingly, even if 
the surface of the record paper is uneven, the heat generating resistors 
follow the surface of the record paper by the resilient motion of the heat 
generating resistors, and the ununiformity in the print density is avoided 
and the high quality of print is attained.