Tape pad for a magnetic tape cassette

A tape pad for a magnetic tape cassette is placed in the running path of a magnetic tape held in a casing so as to be in press-contact with said magnetic tape. The tape pad has a one piece structure of a tape contacting part and an elastic part for supporting the tape contacting part by molding carbon-containing polyethylene terephthalate.

BACKGROUND OF THE INVENTION 
The present invention relates to a tape pad for a magnetic tape cassette 
such as a video cassette. 
DISCUSSION OF THE RELATED ART 
A magnetic tape cassette of this kind is generally constituted, as shown in 
FIG. 1, by a casing formed by an upper casing 1 and a lower casing 2; 
reels 4, 5 for winding and running a magnetic tape 3 in the casing; a tape 
pad 6 in the running path of the magnetic tape 3 between the reels 4, 5 so 
as to push the magnetic tape 3 by spring pressure of a spring member 6b 
between a guide 7 and a tape contacting part 6a of the tape pad 6, whereby 
the stable running of the magnetic tape 3 is maintained. In FIG. 1, the 
reference numeral 8 designates a guide pole. 
FIG. 2 is an enlarged view of a structure of the conventional tape pad 6 
wherein the tape contacting part 6a having low static property is bonded 
at one end of the spring member 6b formed of an elastic plate and a two 
sided adhesive tape 6c is bonded along the other end of the spring member 
6b. The tape pad 6 is installed in the casings 1, 2 by bonding one surface 
of the two sided adhesive tape 6c to a support 9 connected to the lower 
casing 2. 
There is another proposal for a tape pad having a molded one piece 
structure consisting of a tape contacting part 6a and a spring member 6b 
for supporting the tape contacting part 6a, which is made of 
carbon-blended high pressure process polyethylene. 
A two piece structure of a tape pad in which the tape contacting part 6a 
and the spring member 6b are separate has disadvantages as follows. 
(1) The spring member and the tape contacting part must be separately 
prepared and then, combined. Accordingly, the assembling operation is 
complicated and expensive. 
(2) The spring member 6b is bonded to the tape contacting part 6a with the 
two sided adhesive tape 6d whereby the tacky adhesive of the two sided 
adhesive tape 6d is squeezed from the bonded part and is adhered on the 
surface of the magnetic tape 3 to cause a trouble for magnetic recording 
and a trouble of the running of the magnetic tape etc. 
The tape pad of one piece structure made of the carbon-blended high 
pressure process polyethylene has drawbacks that elasticity of the tape 
pad itself becomes inferior due to aging even though manufacturing steps 
are simplified and it has low thermal deformation temperature and so is 
easily affected by a change in temperature. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to eliminate the disadvantages of 
the conventional magnetic tape cassette and to provide a magnetic tape 
cassette provided with a tape pad which is of a low manufacturing cost and 
is stable in aging as well as for a change in temperature. 
The foregoing and the other objects of the present invention have been 
attained by providing a tape pad for a magnetic tape cassette placed in 
the running path of a magnetic tape held in a casing so as to be in 
press-contact with the magnetic tape, characterized in that the tape pad 
has a one piece structure of a tape contacting part and an elastic part 
for supporting the tape contacting part by molding carbon-containing 
polyethylene terephthalate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An embodiment of the presnet invention will be described with reference to 
drawing. 
FIG. 3 is a perspective view of an embodiment of the tape pad according to 
the present invention. In the present invention, a tape contacting part 6a 
and an elastic part 6b, which were conventionally separate parts, are made 
in one piece by molding them in one piece. A reference numeral 6c 
designates a two sided adhesive tape. 
With such a construction, it is unnecessary to form the tape contacting 
part 6a and the elastic part 6b separately and assemble them, on account 
of which the manufacturing process is shortened and cost of manufacturing 
and assembling is reduced. Further, it is unnecessary to use an adhesive 
tape to bond the tape contacting part 6a and the elastic part 6b whereby 
troubles caused by leakage of the adhesive from the bonded part can be 
completely eliminated. 
For material used for molding the tape contacting part 6a and the elastic 
part 6b in one piece, polyethylene terephthalate including carbon as an 
antistatic material is used. 
The one piece structure of the tape pad having the tape contacting part and 
the elastic part has been already known in a publication such as Japanese 
Unexamined utility Model Publication No. 140978/1981. In the present 
invention, however, provides further improved tape pad by changing 
material from carbon-containing high pressure process polyethylene to 
carbon-containing polyethylene terephthalate (referred to as PET 
hereinbelow). 
A tape pad for a magnetic tape cassette should have a suitably high modulus 
of elasticity for bending, small change in properties caused by lapse of 
time and stability to thermal conditions. The inventors of the present 
invention have been found that the tape pad made of carbon-containing PET 
is superior to that of carbon-containing high pressure process 
polyethylene with respect to these properties. Namely, (1) the tape pad of 
carbon-containing PET assures pad pressures equal to or more than that of 
carbon-containing high pressure process polyethylene even though the 
thickness is small and (2) the thermal deformation temperature of the tape 
pad of carbon-containing PET is 20.degree. C. higher than the conventional 
tape pad and therefore it is thermally stable. 
EXAMPLE 
Two kinds of resin blends were prepared by blending an amount ranging from 
2% wt. to 10% wt. of carbon black to PET and high pressure process 
polyethylene (PE) respectively. The resin blends were molded to form the 
tape contacting part and the elastic part in one piece having a thickness 
of 180 .mu.m and 200 .mu.m respectively, as shown in FIG. 3. The tape 
contacting part of PET was finished to have 8 .mu.m of surface roughness. 
Physical properties of two samples were studied to obtain a result shown 
in Table 1. As apparent from the Table 1, the tape pad according to the 
present invention provides remarkable function and effect with respect to 
above-mentioned points 1 and 2. Further, since the tape contacting part is 
finished to have a high surface roughness, friction to the magnetic tape 
is reduced (friction factor in Table 1 is determined with reference to the 
friction factor of PET without containing carbon black). 
FIG. 4 shows change in the lapse of time of pad pressure between the tape 
pad having a thickness of 180 .mu.m of carbon-containing PET and the tape 
pad having a thickness of 200 .mu.m of carbon-containing high pressure 
process polyethylene shown in the Table 1. It is revealed that the pad of 
PET exhibits small change in aging and stableness even though the pad of 
PET is relatively thin. It is understood from this that the pad of the 
carbon-containing PET has characteristics superior to the conventional 
pad. In FIG. 4, properties of a tape pad made of carbon-containing 
polybutylene terephthalate (PBT) is also shown. Change in aging of the 
tape pad of the present invention is smaller than that of PBT. 
Carbon is incorporated in PET for exhibiting antistatic effect. Preferable 
range of incorporation is from 2% by weight to 10% by weight of PET. 
The tape pad is always in contact with the back surface of the magnetic 
tape during running of it and the running of the magnetic tape is 
influenced by the roughness of the contacting surface of the tape pad. 
When the tape pad has a smooth surface having a roughness of 2 .mu.m or 
less, the area of contact becomes large to increase friction resistance 
which renders the running of the magnetic tape to be unstable. When the 
surface is rough to have a roughness of 15 .mu.m or more, wearing of a 
part of the pad brought into point-contact with the magnetic tape develops 
to produce shaved powder to thereby cause dropout. Accordingly, the 
surface roughness of the pressure-contacting part of the tape pad made of 
carbon-containing PET is preferably in the range of from 2 .mu.m to 15 
.mu.m. 
The tape pad formed by molding carbon-containing PET provides the effect as 
follows. 
(1) Change in elasticity caused by lapse of time of the tape pad of the 
present invention is smaller than the conventional tape pad of 
carbon-containing high pressure process polyethylene. Accordingly, there 
is obtainable a stable running of the magnetic tape. 
(2) The tape pad of the present invention has elasticity the same as or 
stronger than that of the conventional tape pad of carbon-containing high 
pressure process polyethylene even though the thickness of the pad is 
relatively thin and therefore, is economical. 
(3) The tape pad of the present invention has a high thermal deformation 
temperature characteristic in comparison with the conventional pad and 
accordingly, it is thermally stable. 
TABLE 1 
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Comparison of carbon-containing PET with PE 
Item PET PE 
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Thickness (.mu.m) 180 200 
Pad pressure (gr) 1.8 1.0 
Inherent resistance of surface (.OMEGA.) 
5 .times. 10.sup.6 
2 .times. 10.sup.5 
Roughness of surface (.mu.m) 
8 3 
Friction factor of surface (for PET) 
0.12 0.17 
Thermal deformation temperature (.degree.C.) 
80 60 
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Obviously, numerous modifications and variations of the present invention 
are possible in light of the above teachings. It is therefore to be 
understood that within the scope of the appended claims, the invention may 
be practiced otherwise than as specifically described herein.