Sliding contact part for recording medium

A wear resistance layer is formed on a surface of a portion of a sliding contact part adapted to contact with a recording medium and slide relative thereto. The wear resistance layer is formed of a material mainly composed of chromium oxide and at least one of conductive nitride and conductive carbide. Accordingly, the wear resistance of the sliding contact part can be greatly improved to thereby extend the service life.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a sliding contact part for a recording 
medium, and more particularly to a sliding contact part such as a thermal 
head or a magnetic head adapted to contact with a recording medium in the 
form of a tape, disk or sheet and slide relative thereto. 
2. Description of the Prior Art 
Now commercially available are various devices for performing recording or 
reproduction with use of a recording medium such as a magnetic layer 
carrying sheet or film or a sheet of paper. Such recording/reproducing 
devices employ many parts adapted to always or temporarily slide on the 
recording medium relative thereto. This kind of parts includes a head 
slider for a flexible disk, a flying slider for a hard disk, a thermal 
head of a thermal printer, or a magnetic head. These parts are required 
not to damage the recording medium and to have a superior durability such 
that no wearing occurs even in long-term use. 
Such a sliding contact part has a portion adapted to contact with the 
recording medium and slide :relative thereto. The sliding contact portion 
is covered with a wear resistance layer for suppressing wear of the 
sliding contact portion. The wear resistance layer is formed of a material 
such as Ta.sub.2 O.sub.5 or SiO.sub.2, but the wear resistance is 
insufficient. 
Now, a conventional thermal head as an example of such a sliding contact 
part will be described in detail. 
In general, a thermal head has the advantages of low noise, low cost, 
maintenance saving, power saving and high print quality. Then, in recent 
years, a thermal head has widely been applied to various recording 
equipments such as facsimiles and printers for word processors. On the 
other hand, these equipments have been increasingly demanded to have the 
performances of compact size, low cost, power saving, high print quality 
and long service life. Accordingly, the thermal head is also demanded to 
enhance its performances of compact size, low cost, high efficiency, high 
print speed, high print quality and long service life. 
In particular, the performances of high print speed, high print quality and 
long service life are strongly demanded in the thermal head for the 
thermal printer. The high print speed and the high print quality are 
realized by designing the shape of the thermal head so as to project 
heating elements for effecting printing on the recording medium and by 
using means for increasing the contact pressure of the heating elements 
against the recording medium. 
In the thermal head thus improved in print speed and print quality, 
however, the heating elements projected are remarkably worn by the 
increased contact pressure against the recording medium, causing the 
service life of the thermal head to become very short. To cope with this 
problem, it is essential to provide a protective layer superior in wear 
resistance on the thermal head. 
Conventionally, such a protective layer used for a thermal head is formed 
of Ta.sub.2 O.sub.5, SiC, Si-O-N, SiAlON, etc. However, these materials 
are inferior in wear resistance against a thermal recording paper in 
particular. Thus, the conventional thermal head has a serious problem that 
the even balance between print quality and service life cannot be 
obtained. The inferiority in wear resistance of the protective layer in 
the conventional thermal head is considered to be due to the fact that the 
material (e.g., Ta.sub.2 O.sub.5) of the protective layer is apt to be 
broken by the friction to the material (e.g., CaCO.sub.3 or SiO.sub.2) 
contained in the thermal recording paper. 
In order to extend the service life of the thermal head at the sacrifice of 
the print quality, it has been tried to reduce an amount of projection of 
the heating elements to thereby increase a contact area of portions other 
than the heating element adapted to contact with the recording medium, or 
reduce the contact pressure against the recording medium, or increase the 
film thickness of the protective layer, thus suppressing the wear of the 
protective layer. However, as especially in a thermal transfer printer 
using an ink ribbon for a word processor, it is demanded to realize high 
print quality on a post card, a so-called rough paper having a low surface 
smoothness, etc., but the high print quality cannot be expected because of 
the occurrence of blur or the like. Thus, the compatibility between high 
print quality and long service life cannot be attainable even by employing 
the above-mentioned means for extending the service life. 
As mentioned above, the wear of the protective layer against a thermal 
recording paper is large in the conventional thermal head, and so the 
print quality in using an ink ribbon is necessarily reduced. Further, the 
demand for high-speed printing in the thermal printer has recently been 
increased to limit the shape of the thermal head and develop a reduction 
in print efficiency. Thus, the even balance between print quality and 
service life becomes further difficult to obtained. 
While the above description has been directed to the conventional thermal 
head, other sliding contact parts in the prior art have similar defects 
such that the wear resistance is insufficient to shorten the service life. 
SUMMARY OF THE INVENTION 
It is accordingly an object of the present invention to provide a sliding 
contact part for a recording medium which can greatly improve the wear 
resistance and the durability of a sliding contact portion adapted to 
slldingly contact with the recording medium. 
It is another object of the present invention to provide a thermal head 
which can effect good printing to a plain paper with use of an ink ribbon 
and ensure a superior wear resistance of the protective layer even in the 
case of using a thermal recording paper. 
It is still another object of the present invention to provide a sliding 
contact part adapted to contact with a recording medium and slide relative 
thereto, wherein a wear resistance layer is formed on a surface of a 
portion of the sliding contact part adapted to contact with the recording 
medium, the wear resistance layer being formed of a material mainly 
composed of chromium oxide and at least one of conductive nitride and 
conductive carbide. 
It is a further object of the present invention to provide a thermal head 
comprising a substrate, a heat retaining layer formed on a surface of the 
substrate, a plurality of heating elements formed on an upper surface of 
the heat retaining layer, a plurality of individual electrodes formed on 
the upper surface of the heat retaining layer so as to be individually 
connected to the heating elements, a common electrode formed on the upper 
surface of the heat retaining layer so as to commonly connected to the 
heating elements, and a protective layer formed so as to cover at least 
:the heating elements, the protective layer being formed of a material 
mainly composed of chromium oxide and at least one of conductive nitride 
and conductive carbide. 
It is a still further object of the present invention to provide a thermal 
printer having a thermal head comprising a substrate, a heat retaining 
layer formed on a surface of the substrate, a plurality of heating 
elements formed on an upper surface of the heat retaining layer, a 
plurality of individual electrodes formed on the upper surface of the heat 
retaining layer so as to be individually connected to the heating 
elements, a common electrode formed on the upper surface of the heat 
retaining layer so as to commonly connected to the heating elements, and a 
protective layer formed so as to cover at least the heating elements, the 
protective layer being formed of a material mainly composed of chromium 
oxide and at least one of conductive nitride and conductive carbide. 
Other objects and features of the invention will be more fully understood 
from the following detailed description and appended claims when taken 
with tile accompanying drawings.

DETAILED DESCRIPTION OF THE=PREFERRED EMBODIMENTS 
A preferred embodiment of the present invention will now be described with 
reference to the drawings. 
Referring to FIG. 1 which shows a preferred embodiment of the present 
invention applied to a thermal head, reference numeral 1 designates an 
insulating substrate formed of ceramics such as alumina. A glazed layer 2 
functioning as a heat retaining layer is formed on the insulating 
substrate 1. The glazed layer 2 is formed of glass or the like. The glazed 
layer 2 has a double-stepped convex shape as viewed in vertical section. 
That is, the glazed layer 2 consists of a lower convex portion 2b formed 
on the insulating substrate 1 and an upper projecting portion 2a formed at 
the top of the lower convex portion 2b. The lower convex portion 2b has an 
arcuate upper surface, and the upper projecting portion 2a has a 
substantially trapezoidal cross section. A plurality of heating elements 3 
are formed on the upper surface of the upper projecting portion 2a of the 
glazed layer 2 according to the number of dots so as to be arranged in 
line. The heating elements 3 are formed by depositing a resistance heating 
material such as Ta.sub.2 N on the upper surface of the glazed layer 2 by 
vapor deposition, sputtering, etc. and then etching the film of the 
resistance heating material. A common electrode 4 is formed on the upper 
surface of the glazed layer 2 so as to be commonly electrically connected 
to all the heating elements 3 on one side thereof. A plurality of 
individual electrodes 5 are also formed on the upper surface of the glazed 
layer 2 so as to be individually electrically connected to all the heating 
elements 3 on the other side thereof. The common electrode 4 and the 
individual electrodes 5 are formed by depositing a conductive material 
such as aluminum or copper by vapor deposition, sputtering, etc. and then 
etching the film of the conductive material to form a pattern having a 
desired shape. 
Furthermore, a protective layer 6 having a thickness of about 7 to 10 .mu.m 
for protecting the heating elements 3 and the electrodes 4 and 5 is formed 
on the surfaces of the heating elements 3 and the electrodes 4 and 5 and 
the surfaces of exposed portions of the insulating substrate 1 and the 
glazed layer 2. That is, the protective layer 6 is so formed as to cover 
the surfaces of all the portions except terminal portions of the 
electrodes 4 and 5. 
The protective layer 6 consists of an oxidation resistance layer 7 having a 
thickness of 2 to 5 .mu.m as a lower layer and a wear resistance layer 8 
having a thickness of 2 to 8 .mu.m as an upper layer formed on the upper 
surface of the oxidation resistance layer 7. The oxidation resistance 
layer 7 is formed of SiO.sub.2, for example. The wear resistance layer 8 
is formed of a material mainly composed of chromium oxide and at least one 
of conductive nitride such as chromium nitride (CrN, Cr.sub.2 N) or 
titanium nitride (TiN) and conductive carbide such as chromium carbide 
(CrC) or titanium carbide (TiC). The protective layer 6 may consist of the 
wear resistance layer 8 only, but is more preferably formed as a 
dual-layer structure consisting of the oxidation resistance layer 7 and 
the wear resistance layer 8. 
It is to be noted that the conductive nitride or the conductive carbide to 
be used as a component of the material of the wear resistance layer in the 
present invention is not limited to the nitride of Ti or Cr or the carbide 
of Ti or Cr. Other examples of the conductive nitride or the conductive 
carbide may include nitrides or carbides of high-melting point metals such 
as Zr, Ta, V, Hf, Nb, W and Mo. 
It has been found from a wear resistance test that the conductive nitride 
such as chromium nitride or titanium nitride or the conductive carbide 
such as chromium carbide or titanium carbide is superior in wear 
resistance to a thermal recording paper to the extent three to five times 
as that of the conventional materials. However, most of the conductive 
nitride and the conductive carbide have a large electrical conductivity, 
that is, a low resistivity (e.g., CrN: 600 .mu..OMEGA..multidot.cm; 
Cr.sub.2 N: 80 .mu..OMEGA..multidot.cm; TiN: 60 .mu..OMEGA..multidot.cm; 
and TiC: 60 .mu..OMEGA..multidot.cm). Therefore, if the conductive nitride 
or carbide is solely used as the material of the protective layer, there 
occurs short-circuit between the electrodes to cause no serviceability as 
a thermal head. In view of this problem, according to the present 
invention, chromium oxide is used as an optimum material capable of 
increasing an electrical resistance of the conductive nitride or carbide 
without reducing the superior wear resistance thereof. That is, chromium 
oxide and conductive nitride or carbide are used as a primary component of 
the material of the wear resistance layer. The thickness of the wear 
resistance layer in the present invention is set to preferably 7 to 10 
.mu.m more preferably 2 to 8 .mu.m as depending upon kinds and materials 
of the thermal head to be used. 
It is to be noted that the above discussion holds good also in the case 
where the materials of tile wear resistance layer is applied to other 
sliding contact parts. 
The wear resistance layer is preferably formed from a sputtering target 
composed of about 20 to 50 mol % of the conductive nitride or the 
conductive carbide, about 0 to 5 mol % of a sintering assistant such as 
Y.sub.2 O.sub.3 or CeO.sub.2, and a remaining proportion of the chromium 
oxide. By setting the composition of the sputtering target to the above 
ratio, both the wear resistance and the electrical resistance of the wear 
resistance layer can be made fall within a utility range as in use for a 
thermal head. This is considered]to be due to the fact that a fine 
structure and a crystal grain size of the film mainly composed of the 
chromium oxide and the conductive nitride or the conductive carbide are 
maintained so as to provide suitable values of the wear resistance and the 
electrical resistance. 
The present invention will be more clearly understood with reference to the 
following examples. 
EXAMPLE 1 
First, a sputtering target for forming the wear resistance layer 8 was 
prepared in the following manner. That is, 55 mol % of Cr.sub.2 O.sub.3 
powder (average particle size of 0.5 .mu.m), 40 mol % of CrN powder 
(average particle size of 5 .mu.m) and 5 mol % of Y.sub.2 O.sub.3 (average 
particle size of 4 .mu.m) were mixed together. The mixture thus obtained 
was homogenized in ethanol for 12 hours by using a ball mill, and then 
dried. Then, the mixture was molded at about 1500.degree. C. for 2 hours 
in an atmosphere of Ar gas by using a hot press, and the molded part thus 
obtained was ground by a diamond dresser. Thus, the sputtering target of 
.phi.203.times.6.sup.t was prepared. 
Then, a thermal head was prepared in the following manner. That is, the 
lower convex portion 2b of the glazed layer 2 was formed on a part of the 
upper surface of the insulating substrate 1 having a good heat 
conductivity, such as alumina, and the upper projecting portion 2a of the 
glazed layer 2 was formed to have a height of about 10 .mu.m at the top of 
the lower convex portion 2b by a print burning process. Then, a film of a 
resistance heating material was formed on the glazed layer 2 by 
sputtering, and a film of an electrically conductive material was formed 
on the film of the resistance heating material by sputtering, Then, the 
laminated films of the resistance heating material and the electrically 
conductive material were patterned by photolithography to form the heating 
elements 3 and the electrodes 4 and 5. Then, the oxidation resistance 
layer 7 of SiO.sub.2 or the like was formed by sputtering to have a 
thickness of about 3 .mu.m on the heating elements 3 and the electrodes 4 
and 5, and the wear resistance layer 8 was formed to have a thickness of 
about 3 .mu.m on the oxidation resistance layer 7 by sputtering in an 
atmosphere of Ar gas with use of the sputtering target composed of Cr-O-N 
prepared above, thus forming the protective layer 6. Thus, the thermal 
head was prepared. 
Then, the thermal head was mounted to a thermal printer as shown in FIG. 2 
to carry out an actual print test. 
The thermal printer shown in FIG. 2 includes a frame 9 as a base, a 
carriage 11 supported to the frame 9 so as to be reciprocatable along a 
shaft 12 extending in a longitudinal direction of the frame 9, a thermal 
head 10 mounted on the carriage 11, a platen 13 extending in the 
longitudinal direction of the frame 9 so as to face the thermal head 10, 
and a timing belt 14 for driving the carriage 11. An ink ribbon or a 
recording paper is adapted to be interposed between the thermal head 10 
and the platen 13, and the thermal head 10 is adapted to come into 
pressure contact with the platen 13 through the ink ribbon or the 
recording paper. When the timing belt 14 is driven under the condition 
where the thermal head 10 is in pressure contact with the platen 13, the 
carriage 11 is reciprocated along the shaft 12 to thereby effect desired 
printing. 
The recording paper is adapted to be introduced from a paper guide 15 into 
the thermal printer and be sequentially fed by paper feed rollers 16 and 
small rollers 17 to a desired print position. 
Using the thermal printer mentioned above and a thermal recording paper 
(trade number: TP50KH-FS) manufactured by Jujo Seishi K.K., the actual 
print test was carried out under the conditions that a printing speed was 
set to 50 cps (characters per second) and a pressure contact force of the 
thermal head to the platen was set to 450 g. Then, tile test result shown 
in FIG. 3 was obtained. In FIG. 3, there is also shown for comparison the 
test result obtained by using the conventional protective layer formed of 
Ta.sub.2 O.sub.5. As apparent from FIG. 3, a wear rate of the conventional 
protective layer decreases from a point corresponding to a travel distance 
of about 5 km. This is due to the fact that wearing of a projecting 
portion of a thermal head was proceeded to cause a rapid increase in 
contact area of the thermal head itself and decreases the wear rate as a 
whole. To the contrary, it is :appreciated that the protective layer in 
tile present invention has a superior wear resistance about five times 
that of the conventional protective layer. Further, a Vickers hardness Hv 
of the protective layer in the present invention was 1500, and 
crystallization of the protective layer in tile present invention was 
confirmed from X-ray diffraction data. Accordingly, it is considered that 
a fine structure of the protective layer in the present invention has 
become anisotropic. 
The component, CrN of the sputtering target for forming the wear resistance 
layer in Example 1 has an important role. If the proportion of CrN is less 
than about 20 mol %, no crystallization occurs in the sputtered film to be 
formed as the wear resistance layer, causing a reduction in internal 
stress. Accordingly, a tensile stress acts on a base under the sputtered 
film to reduce the power resistance of the thermal head. This is 
considered to be due to the fact that the coefficient of thermal expansion 
of Cr.sub.2 O.sub.2 (about 9.times.10.sup.-6 /.degree. C.) is larger than 
tile coefficients of thermal expansion of the insulating substrate 1 and 
the glazed layer 2 (6-7.times.10.sup.-6 /.degree. C.) and that the 
internal stress of the sputtered film is small. 
When the proportion of CrN is increased up to 20 mol %, the tensile stress 
is eliminated and a compressive stress to the base is increased to 
remarkably improve the power resistance of the thermal head. This is 
considered to be due to the fact that the coefficient of thermal expansion 
of CrN (2.3.times.10.sup.-6 /.degree. C.) and that crystallization occurs 
in the sputtered film to increase the internal compressive stress. 
However, if the proportion of CrN exceeds about 50 mol %, the electrical 
conductivity of the sputtered film becomes high, and the sputtered film in 
this case becomes unsuitable as the protective layer 6 of the thermal 
head. This is due to the fact that CrN is an electrically conductive 
material having a resistivity of 600 .mu..OMEGA..multidot.cm. 
Consequently, it is preferable that the proportion of CrN for practical 
application to the thermal head is to be set to about 20 to 50 mol %. 
As to the wear resistance, both Cr.sub.2 O.sub.3 and CrN have a good wear 
resistance. However, it is necessary to maintain a film thickness of the 
protective layer 6 and prevent the generation of cracks in heat cycle in 
the case of application to the thermal head. Therefore, it is important to 
always apply a compressive stress to the protective layer 6. In this 
regard, CrN has an important role. Further, when the sum of the 
proportions of Cr.sub.2 O.sub.3 and CrN is set to about 90 mol % or more, 
the wear resistance and the crack resistance become best. The larger the 
proportion of the sintering assistant such as Y.sub.2 O.sub.3, SiO.sub.2 
or CeO.sub.2 in the sputtering target, the lower the wear resistance. 
EXAMPLES 2 TO 8 
In the same manner as that in Example 1 with the exception that the 
composition of the sputtering target for forming the wear resistance layer 
is changed, thermal heads having different compositions were prepared, and 
the characteristics of the thermal heads were evaluated. 
More specifically, 35 to 95 mol % of Cr.sub.2 O.sub.3 powder (average 
particle size of 0.5 .mu.m), 0 to 60 mol % of CrN powder (average particle 
size of 5 .mu.m) and 5 mol % of Y.sub.2 O.sub.3 (average particle size of 
4 .mu.m) were mixed together in different compositions such that the 
proportions of Cr.sub.2 O.sub.3 and CrN were changed by steps of 10 mol %, 
thus preparing the thermal heads having different compositions. 
Using these thermal heads, various tests concerning wear resistance, crack 
resistance and insulation were carried out to obtain the results shown in 
Table 1. 
In Table 1, it is understood that the sum of the proportions of Cr.sub.2 
O.sub.3 and CrN is set to 95 mol % and the proportion of CrN is increased 
by steps of 10 mol % in the range of 0 to 60 mol %. Further, in Table 1, 
.largecircle., .DELTA. and .times. represent good, fair and poor 
conditions, respectively. 
TABLE 1 
______________________________________ 
Composition Characteristics 
(mol %) Wear Crack Insula- 
Example 
CR.sub.2 O.sub.3 :CrN:Y.sub.2 O.sub.3 
Resistance 
Resistance 
tion 
______________________________________ 
2 95:0:5 .DELTA. X .largecircle. 
3 85:10:5 .DELTA. X .largecircle. 
4 75:20:5 .largecircle. 
.largecircle. 
.largecircle. 
5 65:30:5 .largecircle. 
.largecircle. 
.largecircle. 
6 55:40:5 .largecircle. 
.largecircle. 
.largecircle. 
7 45:50:5 .largecircle. 
.largecircle. 
.largecircle. 
8 35:60:5 .largecircle. 
.largecircle. 
X 
______________________________________ 
In Example 2 where the ratio of Cr.sub.2 O.sub.3, CrN and Y.sub.2 O.sub.3 
was set to 95:0:5 (mol %), no crystallization was confirmed in the 
sputtered film to reduce the wear resistance, and the compressive stress 
in the sputtered film was small to render the crack resistance 
insufficient. Thus, the thermal head in Example 2 is not applicable. 
In Example 3 where the ratio of Cr.sub.2 O.sub.3, CrN and Y.sub.2 O.sub.3 
was set to 85:10:5 (mol %), both the wear resistance and the crack 
resistance were insufficient as similar to Example 2. Thus, the thermal 
head in Example 3 is not applicable. 
In Examples 4, 5, 6 and 7 where the proportions of CrN were set to 20, 30, 
40 and 50 (mol %), respectively, crystallization was confirmed in each 
sputtered film to provide a good wear resistance, and the compressive 
stress in each sputtered film was large to render the crack resistance 
sufficient. Thus, the thermal heads in Examples 4 to 7 are applicable. 
In Example 8 where the ratio of Cr.sub.2 O.sub.3, CrN and Y.sub.2 O.sub.3 
was set to 35:60:5 (mol %), the insulation was insufficient. Thus, the 
thermal head in Example 8 is not applicable. 
The sputtering target composed of Cr-O-N used in each example according to 
the present invention has a good sinterability. Accordingly, it is 
sufficient that the proportion of the sintering assistant is to be set to 
several mol % or less, thereby maintaining a sufficiently high wear 
resistance of the Cr-O-N sputtered film and a sufficiently high mechanical 
strength of the sputtering target. 
As apparent from the above results, the thermal head in each example 
according to the present invention obviated all the problems in the 
conventional protective layer to greatly improve a service life in 
high-speed and high-quality printing. 
EXAMPLE 9 
First, a sputtering target for forming the wear resistance layer 8 was 
prepared in the following manner. That is, 70 mol % of Cr.sub.2 O.sub.3 
powder (average particle size of 0.5 .mu.m) and 30 mol % of TiN powder 
(average particle size of 5 .mu.m) were mixed together. The mixture thus 
obtained was homogenized in ethanol for 12 hours by using a ball mill, and 
then dried. Then, the mixture was molded at about 1500.degree. C. for 2 
hours in an atmosphere of Ar gas by using a hot press, and the molded part 
thus obtained was ground by a diamond dresser. Thus, the sputtering target 
of .phi.203.times.6.sup.t was prepared. 
Then, a thermal head was prepared in the same manner as that in Example 1. 
Using the thermal head prepared above, the actual print test was carried: 
out under the same conditions as those in Example 1 to obtain the result 
shown in FIG. 4. In FIG. 4, there is also shown for comparison the test 
result obtained by using the conventional protective layer formed of 
Ta.sub.2 O.sub.5. As apparent from FIG. 4, it is appreciated that the 
protective layer in the present invention has a superior wear resistance 
about five times that of the conventional protective layer. Further, a 
Vickers hardness Hv of the protective layer in the present invention was 
1500, and crystallization of the protective layer in the present invention 
was confirmed from X-ray diffraction data. Accordingly, it is considered 
that a fine structure of the protective layer in the present invention has 
become anisotropic. 
The component, TiN of the sputtering target for forming the wear resistance 
layer in Example 9 has an important role. If the proportion of TiN is less 
than about 20 mol %, no crystallization occurs in the sputtered film to be 
formed as the wear resistance layer, causing a reduction in internal 
stress. Accordingly, a tensile stress acts on a base under the sputtered 
film to reduce the power resistance of the thermal head. This is 
considered to be due to the fact that the coefficient of thermal expansion 
of Cr.sub.2 O.sub.2 (about 9.times.10.sup.-6 /.degree. C.) is larger than 
the coefficients of thermal expansion of the insulating substrate 1 and 
the glazed layer 2 (6-7.times.10.sup.-6 /.degree. C.) and that the 
internal stress of the sputtered film is small. 
When the proportion of TiN is increased up to 20 mol % the tensile stress 
is eliminated and a compressive stress to the base is increased to 
remarkably improve the power resistance of the thermal head. This is 
considered to be due to the fact that crystallization occurs in the 
sputtered film to increase the internal compressive stress. However, if 
the proportion of TiN exceeds about 40 mol %, the electrical conductivity 
of the sputtered film becomes high, and the sputtered film in this case 
becomes unsuitable as the protective layer 6 of the thermal head. This is 
due to the fact that TiN is an electrically conductive material having a 
resistivity of 100 .mu..OMEGA..multidot.cm. Consequently, it is preferable 
that the proportion of TiN for practical application to the thermal head 
is to be set to about 20 to 40 mol %. 
As to the wear resistance, both Cr.sub.2 O.sub.3 and TiN have a good wear 
resistance. However, it is necessary to maintain a film thickness of the 
protective layer 6 and prevent the generation of cracks in heat cycle in 
the case of application to the thermal head. Therefore, it is important to 
always apply a compressive stress to the protective layer 6. In this 
regard, TiN has an important role. Further, when the sum of the 
proportions of Cr.sub.2 O.sub.3 and TiN is set to about 100 mol %, the 
wear resistance and the crack resistance become best. The larger the 
proportion of the sintering assistant such as Y.sub.2 O.sub.3, SiO.sub.2 
or CeO.sub.2 in the sputtering target, the lower the wear resistance. 
Further, in this example, since Cr.sub.2 O.sub.3 has a good sinterability, 
a good sintered body as the sputtering target can be formed without using 
a sintering assistant, thereby sufficiently increasing the wear resistance 
of the sputtered film and the mechanical strength of the sputtering 
target. 
EXAMPLES 10 TO 16 
In the same manner as that in Example 9 with the exception that the 
composition of the sputtering target for forming the wear resistance layer 
is changed, thermal heads having different compositions were prepared, and 
the characteristics of the thermal heads were evaluated. 
More specifically, 40 to 100 mol % of Cr.sub.2 O.sub.3 powder (average 
particle size of 0.5 .mu.m) and 0 to 60 mol % of TiN powder (average 
particle size of 5 .mu.m) were mixed together in different compositions 
such that the proportions of Cr.sub.2 O.sub.3 and TiN were changed by 
steps of 10 mol %, thus preparing the thermal heads having different 
compositions. 
Using these thermal heads, various tests concerning wear resistance, crack 
resistance and insulation were carried out to obtain the results shown in 
Table 2. 
In Table 2, it is understood that the sum of the proportions of Cr.sub.2 
O.sub.3 and TiN is set to 100 mol % and the proportion of TiN is increased 
by steps of 10 mol % in the range of 0 to 60 mol %. Further, in Table 2, 
.largecircle., .DELTA. and .times. represent good, fair and poor 
conditions, respectively. 
TABLE 2 
______________________________________ 
Characteristics 
Composition (mol %) 
Wear Crack Insula- 
Example 
Cr.sub.2 O.sub.3 :TiN 
Resistance 
Resistance 
tion 
______________________________________ 
10 100:0 .DELTA. X .largecircle. 
11 90:10 .DELTA. X .largecircle. 
12 80:20 .largecircle. 
.largecircle. 
.largecircle. 
13 70:30 .largecircle. 
.largecircle. 
.largecircle. 
14 60:40 .largecircle. 
.largecircle. 
.DELTA. 
15 50:50 .largecircle. 
.largecircle. 
X 
16 40:60 .largecircle. 
.largecircle. 
X 
______________________________________ 
In Example 10 where the ratio of Cr.sub.2 O.sub.3 and TiN was set to 100:0 
(mol %), no crystallization was confirmed in the sputtered film to reduce 
the wear resistance, and the compressive stress in the sputtered film was 
small to render the crack resistance insufficient. Thus, the thermal head 
in Example 10 is not applicable. 
In Example 11 where the ratio of Cr.sub.2 O.sub.3 and TiN was set to 90:10 
(mol %), both the wear resistance and the crack resistance were 
insufficient as similar to Example 10. Thus, the thermal head in Example 
11 is not applicable. 
In Examples 12 and 13 where the proportions of TiN were set to 20 and 30 
(mol %), respectively, crystallization was confirmed in each sputtered 
film to provide a good wear resistance, and the compressive stress in each 
sputtered film was large to render tile crack resistance sufficient. Thus, 
the thermal heads in Examples 12 and 13 are applicable. In Example 14 
where the proportion of TiN was set to 40 mol %, the insulation was 
somewhat reduced, but the wear resistance and the crack resistance were 
good. Thus, the thermal head in Example 14 is usable. 
In Example 15 where the ratio of Cr.sub.2 O.sub.3 and TiN was set to 50:50 
(mol %), the insulation was insufficient. Thus, the thermal head in 
Example 15 is not applicable. Also, in Example 16 where the ratio of 
Cr.sub.2 O.sub.3 and TiN was set to 40:60 (mol %), the insulation was 
insufficient as similar to Example 15. Thus, the thermal head in Example 
16 is not applicable. 
Also in the case of substituting Cr.sub.2 N for TiN as the conductive 
nitride, the test results similar to those shown in Table 2 were obtained. 
Further, using a thermal head having a protective layer formed from a 
sputtering target composed of 70 mol % of Cr.sub.2 O.sub.3 powder and 30 
mol % of TiC powder as the conductive carbide, the actual print test 
similar to that in Example 9 was carried out to obtain the test result 
similar to that shown in FIG. 4. That is, it was confirmed that the 
protective layer in this case also has a good wear resistance about five 
times that of the conventional protective layer formed of Ta.sub.2 
O.sub.5. Further, in the case of changing the ratio of Cr.sub.2 O.sub.3 
and TiC in the same manner as in Examples 10 to 16, the test results 
similar to those shown in Table 2 were obtained. Accordingly, it is 
appreciated that TiN shown in Table 2 may be replaced by TiC. Further, 
although either the conductive nitride or the conductive carbide is used 
in the above preferred embodiment, both the conductive nitride and the 
conductive carbide may be used according to the present invention. 
EXAMPLE 17 
A wear resistance layer formed of a material mainly composed of chromium 
oxide and chromium nitride in the ratio similar to that in Example 1 was 
formed on the surface of a sliding contact portion of a head slider 
adapted to contact with a flexible disk. 
Using this head slider, an endurance test was carried out. As the test 
result, it was confirmed that normal recording and reproduction could be 
effected without any trouble even after continuous operation for 200 
hours. 
Further, a wear resistance layer similar to the above was formed on the 
surface of a sliding contact portion of a flying slider adapted to contact 
with a hard disk, and an endurance test was carried out. As the test 
result, it was confirmed that normal recording and reproduction could be 
effected without any trouble even after continuous operation for 200 
hours. 
Further, a wear resistance layer similar to the above was formed on the 
surface of a sliding contact portion of a magnetic head adapted to contact 
with a magnetic tape, and an endurance test was carried out. As the test 
result, it was confirmed that a service life about twice that of a 
conventional magnetic head could be obtained. 
As described above, according to the present invention, in a sliding 
contact part adapted to contact with a recording medium and slide relative 
thereto, a protective layer formed of a material mainly composed of 
chromium oxide and at least one of conductive nitride and conductive 
carbide is formed on a surface of a portion of the sliding contact part 
adapted to contact with the recording medium. Accordingly, the wear 
resistance of the sliding contact part can be greatly improved to thereby 
extend the service life. 
While the invention has been described with reference to specific 
embodiments, the description is illustrative and is not to be construed as 
limiting the scope of the invention. Various modifications and changes may 
occur to those skilled in the art without departing from the spirit and 
scope of the invention as defined by the appended claims.