Magnetic recording medium

A magnetic recording medium having a metamorphosed layer on the surface of the magnetic layer of conventional magnetic recording media, said metamorphosed layer being derived from some of a binder component included in the magnetic layer, can prevent the sticking trouble taking place between the magnetic recording medium and the magnetic head. Said metamorphosed layer can be formed by irradiation with ultraviolet rays in the course of the production of magnetic recording media at the step of coating a dispersion of magnetic particles on a flexible support or after the coating step. Said metamorphosed layer can also be formed on the surface of once produced magnetic recording media irrespective of having caused the sticking trouble by irradiation with ultraviolet rays. Suitable apparatuses for producing such improved magnetic recording media are also provided.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a magnetic recording medium having a 
metamorphosed layer on the magnetic layer to prevent emergence of sticky 
material from the magnetic layer, a process for producing the same, a 
method for treating the surface of a magnetic recording medium so as to 
prevent sticking trouble between a magnetic head and the magnetic 
recording medium, and an apparatus for conducting such a treatment. 
2. Description of the Prior Art 
Magnetic tapes used as magnetic recording medium in magnetic tape recording 
equipments, magnetic tape recoders, and the like have structure as shown 
in the attached FIG. 1 wherein a magnetic layer 2 obtained by dispersing 
magnetic particles in a binder is adhered to a base film 1 such as 
polyethylene terephthalate film. These magnetic tapes are usually produced 
by the steps as shown in FIG. 2. That is, magnetic particles are mixed 
with a binder, a solvent and other additives for dispersion and the 
resulting coating dispersion is filtered before coating with, for example, 
a roll coater. On the other hand, a base film previously washed is led to 
the roll coater and the coating dispersion is coated on the base film at a 
speed of, for example, about 6 m/min. After the coating step, a magnetic 
field is applied to the resulting coating, if necessary to the coating 
direction, to impart magnetic orientation (orientation step). 
Subsequently, the solvent is evaporated in a high-temperature drying step, 
e.g. at about 120.degree. C. for 2 minutes. If it is necessary to smooth 
the surface of the resulting magnetic layer, the magnetic layer is 
subjected to a surface treatment step by using a calender roll 
conventionally used to smooth the surface. The resulting tape is slitted 
to a prescribed size and then subjected to testing and packaging steps not 
shown in FIG. 2 to give commercially available magnetic tapes. 
When these conventional magnetic tapes thus produced are used practically 
in magnetic tape recording equipments, magnetic tape recorders, and the 
like, there often occurs sticking phenomenon of the magnetic tape on a 
magnetic head which reads on signals depending on travel and stoppage of 
the magnetic tape. That is, when the magnetic tape is stopped after travel 
of a certain distance and starts travel again after some intervals, there 
occasionally occurs a trouble of not moving the magnetic tape due to 
sticking of the magnetic tape to the magnetic head. Hereinafter such a 
trouble is referred to as sticking trouble. 
Heretofore, there has been almost no systematic report on the sticking 
trouble except for an article "A Sudy of Frictional and Stick-Slip 
Behavior of Magnetic Recording Tapes " by S. H. Kalfayer, R. H. Silver and 
J. K. Hoffman--NASA Technical Report 32-1548 (published Apr. 1, 1972). But 
there is no description as to fundamental countermeasure for preventing 
the sticking trouble in said article and there is disclosed only an idea 
of keeping magnetic tapes at low temperatures for preventing the sticking 
trouble with some effect. 
Contrary to such a poor countermeasure for preventing the sticking trouble, 
there is a great need for urgent development of a technique for preventing 
the sticking trouble taking the output and using amount of magnetic tapes 
into consideration. Magnetic tapes conventionally used have many chances 
of suffering the sticking trouble except for special kinds of magnetic 
tapes. 
The present inventors extensively studied to remove such a defect of 
magnetic tapes and found that no remarkable effects were obtained by a 
heating treatment wherein the temperature of the tape is raised, a 
treatment under high humidity, a radiation treatment, washing with 
chemicals, a treatment by irradiating light or infrared rays. When an 
isocyanate which is known as an urethane curing accelerator was used, 
considerable effect was obtained but there was also produced an 
undesirable side effect of extension of one-side of the magnetic tape; 
such a treatment cannot be used practically. Only a treatment with 
ultraviolet rays was effective and the present invention was accomplished. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide a magnetic recording medium 
which can prevent the sticking trouble. It is another object of this 
invention to provide a process for producing such a magnetic recording 
medium. It is a further object of this invention to provide a method for 
treating the surface of a magnetic recording medium so as to prevent the 
sticking trouble. It is a still further object of this invention to 
provide an apparatus for conducting such a treatment. 
This invention provides a magnetic recording medium comprising a flexible 
support, a magnetic layer containing magnetic particles bonded by a binder 
and being adhered to the flexible support, and a metamorphosed layer which 
is derived from some of said binder and is formed on the surface of the 
magnetic layer. 
This invention also provides a process for producing such a magnetic 
recording medium characterized by employing the step of irradiation of the 
magnetic layer with ultraviolet rays at the time of coating a dispersion 
of magnetic particles on a flexible support or any time after the coating 
in the conventional process for producing magnetic tapes. 
This invention provides a method for treating the surface of a magnetic 
layer of a magnetic recording medium produced by the conventional process 
with irradiating the surface of the magnetic layer with ultraviolet rays 
so as to form the metamorphosed layer thereon. 
Further, this invention provides an apparatus for forming the metamorphosed 
layer on the surface of the magnetic layer of a magnetic recording medium 
by irradiating ultraviolet rays through an ultraviolet transmitting filter 
.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
This invention is based on the finding of a cause and mechanism of the 
sticking trouble of magnetic recording media. When a deposit on the 
magnetic head at which the sticking trouble had been occurred was analyzed 
by conventional gel permeation chromatography (hereinafter referred to as 
"GPC method"), there was found a substance having a molecular weight of 
10,000 to 100,000 converted to the styrene molecular weight. On the other 
hand, when a magnetic tape was treated with Fleon TMC (a trade name, 
manufactured by Mitsui Fluorochemical Co.) which can well extract the 
above-mentioned substance having a molecular weight of 10,000 to 100,000 
converted to the styrene molecular weight and the extracted substance was 
analyzed by the GPC method, there was found that the above-mentioned 
substance was included in the magnetic tape in a large amount. These 
results can be explained that a fundamental cause of the sticking trouble 
is based on some portions of a binder component by which magnetic 
particles are adhered to a base film or flexible support retained 
unreacted while maintaining the molecular weight from 10,000 to 100,000 
due to insufficient reaction. Particularly when urethane type binders are 
used for producing magnetic tapes, this tendency is remarkably observed. 
On the other hand, it seems very difficult to proceed the reaction so as 
not to retain the unreacted binder at all, or to proceed the reaction to 
at least a degree causing no sticking trouble. Further, there is another 
problem of solving the sticking trouble of a gigantic amount of magnetic 
tapes widely used. In order to solve such problems, it is necessary to 
make clear the mechanism of the sticking trouble caused by the 
above-mentioned substance. After extensive study, it has been found that 
the presence of the substance which causes the sticking trouble in a 
magnetic tape does not lead to the sticking trouble immediately and that 
such a substance oozes out by the actions of outer factors such as 
pressure, tension, temperature rise, and the like under the normal use 
conditions of magnetic tapes and when the substance oozes out has a 
sticking activity, there takes place the sticking trouble. 
This can be tested by a very simple method named as "press binding test" 
devised by the present inventors. The press binding test can be carried 
out as follows: two magnetic tapes are piled by contacting each magnetic 
layer and a pressure (e.g. 100 atm.) and a temperature (e.g. 50.degree. 
C.) are applied thereto by using, e.g. a press and allowed to stand for a 
certain period of time (e.g. 5 hours) so as to make the two magnetic tapes 
adhere to each other. Sticking activity of the substance which causes the 
sticking trouble is judged by measuring strength required for peeling off 
the two magnetic tapes. After evaluating peeling strength of magnetic 
tapes which caused the sticking trouble and of those which did not cause 
the sticking trouble by the press binding test, it is revealed by 
experience that there is a fear of causing the sticking trouble if peeling 
strength is 2 kg or more, whereas there is almost no fear of causing the 
sticking trouble if peeling strength is 1 kg or less. 
A further detailed study as to the deposit on the magnetic head after the 
sticking trouble caused by carrying out forward operating, stoppage, and 
reverse operating of a magnetic step revealed that the deposit was a 
polyurethane type polymer having a molecular weight of 10,000 to 100,000, 
molecular weight calibrated by styrene. Such a substance was not found on 
the magnetic head at which no sticking trouble was caused by a magnetic 
tape. 
In the next place, various treatments were applied to polyurethane type 
materials having a molecular weight of the above-mentioned range so as not 
to cause the sticking trouble and found that irradiation with ultraviolet 
rays gave remarkably excellent effects. 
In order to know effects of ultraviolet-rays irradiation, a sheet made of 
the same polyurethane type polymer, Paraprene 22S (a trade name, 
manufactured by Japan Polyurethane Ltd.), as deposited on the magnetic 
head having a molecular weight of 10,000 to 100,000, molecular weight 
colibrated by styrene was irradiated by ultraviolet rays and analyzed by 
using the GPC method. The results are as shown in FIG. 3. As the 
ultraviolet-rays source, a 1 kW mercury lamp was used at a distance of 
about 25 cm. In FIG. 3, the term "relative strength" means the output 
voltage of detector in G.P.C. device. As is clear from FIG. 3, the amount 
of the polymer having a molecular weight of 10,000 to 100,000 decreases 
with an increase of irradiation time of ultraviolet rays. These results 
show good agreement with the results obtained by the press binding test as 
shown in Table 1 below. 
TABLE 1 
______________________________________ 
Irradiation time of UV rays 
Peeling strength 
______________________________________ 
0 min 2.1 kg 
2 0.8 
7 0.3 
15 0.0 
______________________________________ 
Note 
Press binding conditions: 100 atm., 50.degree. C., 5 hours, sectional are 
3 cm.sup.2 ; 
Irradiation conditions: 1 kW mercury lamp, distance 25 cm. 
The same excellent effects of ultraviolet-rays irradiation are also 
obtained in the case of using magnetic tapes commercially available and 
causing the sticking trouble. This invention is based on the 
above-mentioned technical principle. 
The magnetic recording medium according to this invention comprises a 
flexible support (or base film), a magnetic layer adhered to the base 
film, and a metamorphosed layer. FIG. 4 is a cross-sectional view of the 
magnetic recording medium of this invention in which the numeral 1 denotes 
the magnetic recording medium (or the magnetic tape), the numeral 1 
denotes the flexible support, the numeral 2 denotes the magnetic layer 
containing magnetic particles bonded by a binder, and the numeral 3 
denotes the metamorphosed layer which is derived from some of the binder 
component. 
As the flexible support, there can be used conventional ones such as paper, 
aluminum, copper and other thin metallic strips, cellophane, cellulose 
acetate, polyvinyl chloride, polyethylene terephthalate, polyimides, 
polyesters, etc. 
The magnetic layer is made from a magnetic coating formulation comprising a 
magnetic pigment dispersed in a suitable polymer binder system such as a 
polyurethane type binder dissolved in organic solvents. As the magnetic 
pigment, there can be used generally acicular .gamma.-ferric oxide and the 
like. The magnetic coating formulation may contain one or more conductive 
agents, dispersants, stabilizers, lubricants, and the like conventionally 
used. 
The term "metamorphosed layer" means a layer which is derived from some of 
the binder component and becomes insoluble in organic solvents after the 
methamorphosis such as irradiation with ultraviolet rays. 
According to this invention, since the methamorphosed layer is formed on 
the surface of the magnetic layer, there is no oozing out of the binder 
component from the magnetic layer during the use of the magnetic tape in 
magnetic tape recorders and the like equipments and therefore no sticking 
trouble takes place during the use. For example, conventional magnetic 
tapes bring about the sticking trouble at a running distance of about 70 m 
under the normal use conditions of pressure 10 g, tape speed 3 m/sec 
(usually from 1 m/sec to 5 m/sec), while the magnetic tapes of this 
invention do not bring about the sticking trouble over a running distance 
of 700 m (about 2400 feet). 
The process for producing the magnetic recording medium of this invention 
is characterized by employing the step of irradiation of the magnetic 
layer with ultraviolet rays at the time of coating a dispersion of 
magnetic particles on the flexible support or at any time after the 
coating in the conventional process as shown in FIG. 2 which comprises the 
steps of mixing and 
dispersion-filtration-coating-orientation-high-temperature drying-surface 
treatment-slitting, and testing and packaging (not shown in the drawing). 
FIG. 5 is one example of the process of this invention wherein the step of 
irradiation with ultraviolet rays is inserted between the steps of coating 
and orientation. In FIG. 5, the magnetic particle dispersion obtained by 
the step of mixing and dispersion of magnetic particles and a binder is 
passed to the step of filtration in order to remove dust particles mixed 
therein. In parallel, the base film which has been washed is passed to the 
step of undercoating so that the surface of the base film is easily wetted 
by the dispersion of magnetic particles and the binder. Then the step of 
coating is conducted by a conventional method. Thereafter, the magnetic 
particles dispersion is irradiated with ultraviolet rays. 
Relationship between the magnetic recording medium and the apparatus 
factors for conducting ultraviolet-rays irradiation under such conditions 
is as follows. Since the amount of ultraviolet-rays irradiation energy K 
necessary for the unit area of the magnetic recording medium is not 
dependent on the moving speed of the magnetic recording medium in 
practical procedure and seems to be only dependent on the irradiation time 
(T), K can be represented by the following equation: 
##EQU1## 
When luminous intensity of the ultraviolet-rays source (e.g. input of a 
mercury lamp, kW) is expressed as W, distance between the light source and 
the magnetic recording medium L, and length of the light source 
practically used l', the intensity of irradiation can approximately be 
represented as follows: 
(a) in the case of L&lt;l', W/L 
(b) in the case of L&gt;l', W/L.sup.2 
Summarizing the above, ultraviolet-rays irradiation conditions can be 
determined by the following equations: 
(i) in the case of the irradiation at a sufficiently smaller distance than 
the length of the light source (e.g. a mercury lamp) (L&lt;l'), 
EQU K.ltoreq.(W.multidot.T)/(L.multidot.l') 
wherein 
W=input of the light source (kW) 
T=irradiation time (sec) 
L=distance between the light source and the magnetic recording medium (cm) 
l'=length of the light source (cm), 
(ii) in the case of the irradiation at a sufficiently longer distance than 
the length of the light source (L&gt;l'), 
EQU K&gt;(W.multidot.T)/L.sup.2 
wherein W, T and L are as defined above. Preferable effects can be obtained 
when K=0.05-50 W.multidot.sec/cm.sup.2. In these cases, when the magnetic 
recording medium is moved in parallel to the direction of the length of 
the light source, the speed of the magnetic recording medium (v) can be 
represented as follows: 
EQU v=l'/T 
wherein l' and T are as defined above. 
More concretely, as the light source, a 1 kW mercury lamp having a central 
wavelength of 2500 A can be used at a distance of 30 cm. The irradiation 
time is about 10 minutes. As the source of ultraviolet rays, there can be 
used conventionally used sources such as a mercury lamp, high pressure arc 
lamp, etc. 
The thus treated base film is subjected to the conventional steps of 
orientation wherein, magnetic anisotropy is imparted to the coating of 
magnetic particles, high-temperature drying, surface treatment and 
slitting. 
FIG. 6 is another example of the process of this invention wherein the step 
of irradiation with ultraviolet rays is inserted between the steps of 
orientation and high-temperature drying. 
FIG. 7 is a still another example of the process of this invention wherein 
the step of irradiation with ultraviolet rays is inserted between the 
steps of high-temperature drying and surface treatment. 
FIG. 8 is a further example of the process of this invention wherein the 
step of irradiation with ultraviolet rays is inserted between the steps of 
surface treatment and slitting. 
FIG. 9 is a still further example of the process of this invention wherein 
the step of irradiation with ultraviolet rays is effected after the step 
of slitting. The process of FIG. 9 is very useful and most important since 
this process can be applied to not only magnetic tapes newly produced but 
also those widely practically used. Further this process can also be 
applied to not only magnetic tapes which have caused the sticking trouble 
but also those to be the cause of the sticking trouble. Therefore, the 
process of FIG. 9 makes it possible to provide a method for recovering 
magnetic tapes which have caused the sticking trouble. 
Thus, this invention also provides a method for treating the surface of a 
magnetic layer of a magnetic recording medium characterized by irradiating 
the surface of the magnetic layer with ultraviolet rays so as to form a 
metamorphosed layer on the magnetic layer, said metamorphosed layer being 
derived from some of the binder component included in the magnetic layer. 
Principle of the treatment of the surface of magnetic tapes according to 
this invention is illustrated diagrammatically in FIG. 10, wherein either 
magnetic tapes newly produced or magnetic tapes in use or having caused 
the sticking trouble may be used effectively. In FIG. 10, the numeral 1 
denotes a magnetic tape, the numeral 4 denotes a magnetic tape reel for 
feeding (hereinafter referred to as "feed reel"), the numeral 4' denotes a 
magnetic tape reel for take-up (hereinafter referred to as "take-up 
reel"), the numeral 5 denotes a mercury lamp, the symbol l means a 
distance between the mercury lamp and the magnetic tape, and an arrow mark 
indicates the direction of tape travel. As the feed reel 4 and the take-up 
reel 4', there may be used so-called jumbo rolls as they are. In such a 
case, the apparatus as shown in FIG. 10 can be applied to the process of 
FIG. 8. 
Suitable ultraviolet-rays irradiation conditions are K=0.05 to 50 
W.multidot.sec/cm.sup.2, wherein K is defined in the equation (1). More 
concretely, when a 1 kW mercury lamp 5 having a central wavelength of 2500 
A is used, irradiation for a period of about 10 minutes at a distance (l) 
of 20 to 30 cm is sufficient for preventing the sticking trouble. 
In order to increase efficiency of the ultraviolet-rays irradiation, an 
apparatus shown diagrammatically in FIG. 11 can practically be used. In 
FIG. 11, the numeral 6 denotes a water bath, the numeral 7 denotes water 
used as a water filter, the numerals 8, 8', 8", and 8''' are guide rolls 
used for immersing the magnetic tape in water 7. Numerals 1, 4, 4' and 5 
are as denoted in FIG. 10. 
In order to increase efficiency of ultraviolet-rays irradiation, it is 
necessary to shorten the distance between the mercury lamp and the tape to 
be irradiated. But in such a case, it is also necessary to remove 
undesirable effects of rays simultaneously irradiated from the lamp 
belonging to the infrared region. This is because irradiation with the 
rays belonging to the infrared region generates heat in the magnetic tape, 
which results in causing mechanical strain in the magnetic tape and said 
mechanical strain will be retained in the tape as permanent strain after 
the treatment. The apparatus as shown in FIG. 11 is designed so as to 
solve such problems. That is, as shown in FIG. 11. the magnetic tape 1 
from the feed reel 4 is immersed in water 7 in the water bath 6 at a 
suitable position via guide rolls 8 and 8'. The water 7 functions as a 
water filter so as to remove unnecessary heat rays belonging to the 
infrared wavelength components and to increase efficiency of the 
ultraviolet-rays irradiation. The magnetic tape 1 irradiated with 
ultraviolet rays (h.nu.) via the water filter is passed through guide 
rolls 8" and 8''' which are placed suitably in the water bath and is wound 
up by the take-up reel 4' to complete the step of ultraviolet-rays 
irradiation. In such a case, when a 1 kW mercury lamp 5 is used at a 
distance (l as a total) of 8.5 cm (a distance between the lamp and the 
water surface being 7 cm and a distance between the water surface and the 
tape being 1.5 cm), irradiation for a period of about 5 or 6 seconds gives 
sufficient effects for preventing the sticking trouble. 
In practical irradiation of magnetic tapes with ultraviolet rays for 
preventing them from the sticking trouble, it is advisable to use more 
improved apparatuses as shown in FIGS. 12, 13 and 14, since the 
ultraviolet-rays irradiation step requires a long period of time. Such 
apparatuses for producing magnetic racording media having the 
metamorphosed layer on the surface of the magnetic layer as mentioned 
above comprise an ultraviolet generating means, e.g. a mercury lamp, etc., 
an ultraviolet transmitting filter means disposed between the ultraviolet 
generating means and a magnetic recording medium to be irradiated, and 
magnetic recording medium holding means comprising a feed reel and a 
take-up reel, the magnetic recording medium being passed between the two 
reels over no or a plurality of guide rolls therebetween. 
A simplified example of such apparatuses is shown in FIG. 11, wherein the 
ultraviolet transmitting filter means is the water between the magnetic 
recording medium which is immersed in water and the surface of the water 
in the water bath and under the ultraviolet generating means. 
Another example of such improved apparatuses is shown in FIGS. 12 (a) and 
(b), wherein the ultraviolet transmitting filter is a double walled 
cylinder between which walls is disposed in liquid which functions as 
filter, e.g. water, and the ultraviolet generating means is disposed 
axially lengthwise in the cylinder and around the cylinder is passed a 
magnetic recording medium separately fed and taken up by two reels. 
FIG. 12 (a) is a side view of the apparatus wherein the numeral 1 denotes a 
magnetic tape, the numeral 4 denotes a feed reel, the numeral 4' denotes a 
take-up reel, the numeral 9 denotes water filter means in the form of a 
double walled cylinder between which walls 9 and 9', said walls being made 
of transparent quartz which can transmit ultraviolet rays, is disposed 
water 7 and said water filter means 9 is revolved around the ultraviolet 
generating means 5, i.e. a mercury lamp, by means of motor means not shown 
in the drawing. Necessary tension can be applied to the feed reel 4 and 
the take-up reel 4' by driving servo motors not shown in the drawing. 
FIG. 12 (b) is a top view of the apparatus, wherein the magnetic tape is 
wound helically on the outer surface 9 of the water filter means 9 (inner 
diameter of the cylinder being 150 mm). 
A further improved example of such apparatuses is shown in FIG. 13, wherein 
the ultraviolet generating equipment comprising an ultraviolet generating 
lamp and a concave mirror covering said lamp and reflecting ultraviolet 
rays generated is placed in front of a water filter means and a reflecting 
mirror is placed in parallel with the water filter means, and a magnetic 
recording medium is passed in an elongated loop over a plurality of guide 
rolls between the water filter means and the reflecting mirror, so that 
the magnetic layer on the magnetic recording medium is able to be 
irradiated with ultraviolet rays through the water filter means and 
reflected by the mirror. 
In FIG. 13, ultraviolet rays generated by the ultraviolet generating means 
5 (e.g. a mercury lamp) disposed at the focus of a concave mirror 10 
having a parabolic plane are reflected by the concave mirror to give 
parallel beams which pass through a water filter means 9'. Ultraviolet 
rays (h.nu.) transmitted through the water filter means 9' are irradiated 
on the magnetic layer 1 on a magnetic tape 1 fed from a feed reel 4 to 
form a metamorphosed layer on the magnetic layer. Ultraviolet rays (h.nu.) 
not directly irradiating the magnetic tape 1 are reflected by the 
reflecting surface 11 of the reflecting mirror 11 to irradiate the surface 
1' of the magnetic tape so as to accomplish the desired object. By making 
the space surrounding the magnetic tape 1 to be irradiated with 
ultraviolet rays h.nu. an enclosed structure within the limits of 
possibility, the internal space becomes an ultraviolet-rays bath and 
efficiency of the irradiation increases. The magnetic tape 1 irradiated 
with ultraviolet rays h.nu. is taken up by the take-up reel 4' to complete 
the irradiation procedure. 
FIG. 14 shows an apparatus improved in efficiency of irradiation of 
ultraviolet rays compared with that shown in FIG. 13. The improvement of 
the apparatus of FIG. 14 can be accomplished by replacing the reflecting 
mirror 11 shown in FIG. 13 by the ultraviolet generating equipment 
comprising an ultraviolet generating means 5" and a concave mirror 10" as 
shown in FIG. 14, so that the magnetic tape can be irradiated with 
ultraviolet rays directly immediately before being taken up by the take-up 
reel 4'. The rest of the structure of the apparatus of FIG. 14 is the same 
as that of FIG. 13. 
The apparatuses shown in FIGS. 13 and 14 may further contain a plurality of 
pairs of rolls 12 and 12' so that the magnetic recording medium can be 
retained in the ultraviolet-rays bath for a long period of time for 
further exposure in order to attain the object of this invention. Needless 
to say, such structure can be included in the scope of this invention. 
These apparatuses mentioned above can be used not only for newly producing 
improved magnetic tapes but also for re-producing magnetic tapes which 
have caused the sticking trouble during use. 
The above-mentioned explanations are given mainly to magnetic tapes, but 
the technical idea of this invention can also be applied to various 
magnetic recording media such as magnetic disk. In the case of the 
magnetic disk, there often takes place a trouble of damaging the surface 
of magnetic disk by the contact of the magnetic disk and the magnetic head 
or by contact resistance which is generated by such a contact and is 
strengthened to sticky force (so-called sliding trouble). In such a case, 
since the cause of the trouble is stickness of magnetic recording media, 
the technique of this invention can also be applied thereto with the same 
effects. 
The effects of this invention are particularly shown in the case of 
magnetic recording media in which a polyurethane type binder is contained 
as binder in the magnetic layer. Such polyurethane type binders are 
commercially available and have as a major component as ester type 
polyurethane produced by reacting, for example, adipic acid, butanediol 
and 4,4'-diphenylmethane diisocyanate. 
As mentioned above, the magnetic recording media having the structure of 
this invention cause no sticking trouble. According to the process for 
producing magnetic recording media of this invention, magnetic recording 
media causing no sticking trouble can be produced easily and it is 
possible to prevent the sticking trouble from occurring. Further, 
according to the method of this invention for treating the surface of the 
magnetic layer of conventional magnetic recording media, not only newly 
produced magnetic recording media but also those used once or in use and 
causing the sticking trouble can be prevented from the sticking trouble. 
Still further, when the apparatuses according to this invention are used, 
there can be produced easily new magnetic recording media causing no 
sticking trouble and there can also be re-produced magnetic recordingg 
media, which have caused the sticking trouble, so as not to cause the 
sticking trouble. Therefore, the contribution of this invention to the 
technique of this field is very great.