Tape cartridge and method for producing same

A tape cartridge is provided with a cartridge case constituted by installing a cover on an upper surface of a base plate, a magnetic tape runningly installed in the cartridge case, and a drive belt for running the magnetic tape. The base plate includes a hard protective coat layer at its upper and lower surface or either of upper and lower surfaces. The base plate is formed by punching a base plate material sheet covered with the protective coat layer into a predetermined shape.

TECHNICAL FIELD 
The present invention relates to a tape cartridge, such as a data cartridge 
which is widely used as an external memory medium of a computer, and a 
method for producing the same. 
BACKGROUND OF TECHNOLOGY 
As shown in FIG. 15, a data cartridge, namely a tape cartridge 101 
functioning as an external memory medium of a computer, comprises a 
cartridge case 104 constituted by installing a cover 103 at an upper 
surface of a base plate 102, a magnetic tape runningly installed in the 
cartridge case 104 and a drive belt 106 for running the magnetic tape 105. 
As shown in FIG. 16, the base plate 102 is formed by installing a hard 
protective coat layer 112 on upper, lower and side surfaces of an aluminum 
plate 111. 
The hard protective coat layer 112 is formed by treating an 
alumite-treatment on the aluminum plate 111. 
As shown in FIG. 15, the cover 103 is made of a transparent synthetic 
resin. Grooves 103c and 103d for opening right and left side peripheral 
portions 102a and 102b of the base plate 102 are formed at right and left 
side surfaces 103a and 103b of the cover 103 with a predetermined length 
directing from a front surface 103e to a rear surface 103f. 
A head inserted hole 103g is formed at one side portion of the front 
surface 103e of the cover 103, and a cutout window 103h for opening a 
first belt roller functioning as a drive roller mentioned hereinafter is 
formed at a center portion thereof. 
As shown in FIG. 17, an end side of the magnetic tape 105 is wound around a 
first tape reel 121 and the other end side thereof is wound around a 
second reel tape 122. 
The magnetic tape 105 is hooked on first and second tape guides 123 and 124 
so as to run into the head inserted hole 103g formed at the front surface 
of the cover 103. 
The drive belt 106 is hooked on a first roller 125 as a drive roller which 
is disposed to a front end 102a side of the base plate 102 so as to be 
directed to the cutout window 103h formed at the center portion of the 
front surface 103e of the cover 103, and second and third belt roller 126 
and 127 functioning as corner rollers which are disposed at both side 
portions of the rear end 102b of the base plate 102, so as to generally 
form a triangle shape as flatly viewed. 
The drive belt 106 between the first belt roller 125 and the second belt 
roller 126 is pressfitted on an outer surface of the magnetic tape 105 
wound around the first tape reel 121, and the drive belt 106 between the 
first belt roller 125 and the third belt roller 127 is pressfitted on an 
outer surface of the magnetic tape 105 wound around the second tape reel 
122. 
The conventional tape cartridge 101 constituted as mentioned above is used 
in a recording and reproducing apparatus upon installed therein. 
As shown in FIG. 15, a recording and reproducing apparatus 201 includes 
cartridge-insert guiding portions 203 and 204 of a U-shaped groove at 
right and left side portions of a cartridge inserting port 202. 
Inserting the conventional tape cartridge 101 to the recording and 
reproducing apparatus 201, the right and left side peripheral portions 
102a and 102b of the base plate 102 of the tape cartridge 101 are engaged 
with the cartridge insert guiding portions 203 and 204 of the recording 
and reproducing apparatus 201, and the tape cartridge 101 is inserted to a 
predetermined position of the recording and reproducing apparatus 201 
while being guided by the cartridge insert guiding portions 203 and 204. 
Inserting the tape cartridge 101 to the predetermined position (a loading 
position) of the recording and reproducing apparatus 201, as shown in FIG. 
18, the loading of the tape cartridge 101 is detected by a cartridge 
detecting sensor 211 installed in the recording and reproducing apparatus 
201, and a magnetic head 212 of the recording and reproducing apparatus 
201 is contacted with the magnetic tape 105 upon entering in the head 
inserted hole 103g of the tape cartridge 101. Also, a drive capstan roller 
213 is contacted with the first belt roller 125 functioning as a drive 
roller of the tape cartridge 101. 
By rotating the drive capstan roller 213, the first belt roller 125 is 
rotated, and the drive belt 106 and the magnetic tape 105 are run by the 
rotation of the first belt roller 125, so that the recording and 
reproducing to the magnetic tape 105 is executed by the magnetic head 212. 
Next, the producing method of the conventional tape cartridge 101 will be 
explained. 
First, an original base plate is formed by punching an aluminum-alloy 
material roll into a predetermined shape. 
Next, the alumite-treatment is applied to the original base plate by 
dipping it in sulfuric acid or oxalic acid solution. 
The alumite-treated original base plate obtained by dipping in sulfuric 
acid or oxalic acid solution forms a hard protective coat layer (oxide 
layer) on its all surface and thereby becomes a base plate. 
The first and second tape reels and tape guides and first to third belt 
rollers are assembled on an upper surface of the base plated to which the 
hard protective coat layer is coated. The drive belt is hooked on the 
first to third belt rollers, and the magnetic tape is wound around the 
first and second tape reels. 
As mentioned above, the conventional tape cartridge is produced by 
assembling a cover on the base plate so as to cover the magnetic tape and 
the drive belt after the magnetic tape and the drive belt are assembled to 
the base plate. 
By the way, the conventional tape cartridge and its producing method have 
the following problems. 
(1) In the producing method of the conventional tape cartridge, the 
original base plate is formed by punching an aluminum-alloy base plate 
material-sheet into a predetermined shape, and an oxide layer functioning 
as a protective coat layer is coated by the alumite treatment by dipping 
the original base plate in sulfuric acid or oxalic acid solution. 
Therefore, it is necessary to execute the alumite treatment to every 
original base plate. This complicates the alumite treatment process and 
raises a cost of the base plate. 
(2) Due to the high cost of the base plate, the tape cartridge produced by 
the above-mentioned method necessarily raises its total cost. 
Also, in the conventional tape cartridge, the hard protective coat layer 
112 is formed on side surfaces of the base plate 102 in addition to the 
upper and lower surfaces of the base plate 102. 
Accordingly, as shown in FIG. 18, there is a problem that the hard 
protective coat layer 112 formed on the side peripheral portions 102a and 
102b are in contact with the inner side surfaces of the cartridge insert 
guiding portions 203 and 204, and the inner side surfaces are injured when 
the right and left side peripheral portions 102a and 102b of the base 
plate 102 are engaged with and slid along the cartridge insert guiding 
portions 203 and 204 of the recording and reproducing apparatus 201. 
The present invention aims to solve the above-mentioned conventional 
problems. 
DISCLOSURE OF INVENTION 
A producing method of the tape cartridge which executes a driving of tape 
by a drive belt, the producing method of a tape cartridge according to the 
present invention comprising the steps of: 
a step for forming a hard protective coat layer on a surface of a base 
plate material sheet; 
a step for punching the hard protective coat layer formed base plate 
material sheet into a predetermined shape of a base plate and forming a 
hole at a predetermined position on the base plate; 
a step for embedding a plurality of tape guides, roller shafts rotatably 
supporting a plurality of belt rollers, and reel shafts rotatably 
supporting a pair of tape reels on the base plate; 
a step for installing belt rollers to the roller shafts, the pair of tape 
reels to the reel shafts, a tape to the tape reels and a drive belt to the 
belt rollers; and 
a step for installing a cover to the base plate and screwing down the cover 
on the base plate through the holes. 
Also, the tape cartridge according to the present invention being arranged 
so that a tape wound around a pair of tape reels is frictionally run by a 
drive belt, the tape cartridge comprising: 
a base plate punched in to a predetermined shape from a plate 
aluminum-alloy material whose surface is coated by a hard protective coat 
layer; 
a pair of tape reels rotatably supported to a pair of reel shafts embedded 
on the base plate, a magnetic tape being wound around the pair of tape 
reels and being run between the pair of tape reels upon being runningly 
guided by a plurality of tape guides embedded on the base plate; 
a drive belt runningly guided by a plurality of belt rollers rotatably 
supported to a plurality of roller shafts embedded on the base plate and 
frictionally driving the magnetic tape wound around the pair of tape 
reels; 
a cover installed to the base plate so as to cover the magnetic tape on the 
base plate; and 
a cap portion disposed at the cover to open and close a head inserted hole 
so that the magnetic head is contactable with the magnetic tape runningly 
guided by the tape guide. 
In the producing method of the tape cartridge and the tape cartridge 
according to the present invention, as mentioned above, since the base 
plate is formed by punching the base plate material sheet into a 
predetermined shape after the base plate material sheet is coated by the 
hard protective coat layer, the base plate is in a condition that the hard 
protective coat layer is already formed at a time that the base plate 
material sheet is punched. Accordingly, it is possible to eliminate a 
complicated step that a hard protective coat layer is formed to each base 
plate after punching the base plate material sheet. This improves a 
produtivity of the base plate and the tape cartridge. 
Also, since the tape cartridge according to the present invention is 
arranged so that a hard protective coat layer is not formed on side 
surfaces of the base plate, it is possible to prevent side surfaces of a 
cartridge inserting portion of a drive system from being injured by the 
hard protective coat layer of the side surfaces of the base plate when it 
is inserted into the drive system as the conventional tape cartridge is 
done.

PREFERRED EMBODIMENT FOR EXECUTING INVENTION 
Next, the present invention will be explained with reference to FIG. 1 to 
FIG. 14. 
FIG. 1 and FIG. 2 are a perspective view and an exploded perspective view 
of a tape cartridge in which a magnetic tape wound around a pair of tape 
reels is frictionally run by a drive belt. 
The tape cartridge 1 comprises a base plate 3 which is punched into a 
predetermined shape from a plate-shape aluminum-alloy material sheet whose 
surface is coated by a hard protective coat layer 2; a pair of tape reels 
6 and 7 which are rotatably supported by a pair of reel shafts 4 and 5 
embedded on the base plate 3; a magnetic tape 11 which is wound around the 
pair of tape reels 6 and 7 and which is runningly guided by a plurality of 
tape guides 8, 9 and 10 embedded on the base plate 3 and runs between the 
pair of tape reels; a drive belt 18 which is runningly guided by first, 
second and third belt rollers 15, 16 and 17 which are rotatably supported 
by first, second and third roller shafts 12, 13 and 14 embedded on the 
base plate 3 and which frictionally drives the magnetic tape 11 wound 
around the pair of tape reels 6 and 7; a cover 21 which is installed to 
the base plate 3 so as to cover the magnetic tape 11 on the base plate 3; 
and a cap portion 23 which is disposed to open and close the head inserted 
hole 22 disposed at the cover 21 so that a magnetic head is connectable 
with the magnetic tape 11 runningly guided by the tape guides 8, 9 and 10. 
As shown in FIG. 3, the base plate 3 includes the hard protective coat 
layer 2 at its upper and lower surfaces, and a cut surface 3a generated 
when the aluminum-alloy material sheet is punched out is bared at side 
surfaces. 
The hard protective coat layer 2 is formed by executing the alumite 
treatment (anodic treatment) or coating synthetic resin. 
The reel shafts 4 and 5, the tape guides 8, 9 and 10 and roller shafts 12, 
13 and 14 are embedded in the plurality of imbedding holes formed in the 
base plate 3. 
As shown in FIG. 2, first to fourth tack-pin receiving holes 31 to 34 for 
installing the cover 21 are formed in the vicinity of the four corners of 
the base plate 3. A first screw receiving hole 35 is formed between the 
first and second tack-pin receiving holes 31 and 32, and a second screw 
receiving hole 36 is formed between the third and fourth tack-pin 
receiving holes 33 and 34. 
The plurality of embedding holes are formed in circular, so that the end 
portions of the reel shafts 4 and 5, the tape guides 8, 9 and 10 and the 
roller shafts 12, 13 and 14 are embedded into the holes by being 
pressfitted therein. 
As shown in FIG. 4, the first to fourth tack-pin receiving hole 31 to 34 
are constituted by a small hole portion 41 which is open toward the upper 
surface 3a of the base plate 3, a large hole portion 42 which is 
communicated with the small hole portion 41 and open toward the lower 
surface 3b of the base plate 3. 
The large hole portion 42 is formed into a truncated cone shape and is 
arranged to be communicated with the small hole portion 41 through a 
ring-shaped loose-proofing surface (pin connection surface) 43. 
The first and second screw receiving holes 35 and 36 are formed into a 
truncated cone shape where the upper surface 3a side of the base plate 3 
is formed small and the lower surface 3b side is formed large. 
As shown in FIG. 2, the cover 21 is formed into a shape corresponding to 
the base plate 3 by plastic. The first to fourth tack pins 51 to 54 are 
formed at positions corresponding to the first to fourth tack-pin 
receiving holes 31 to 34, and boss portions 55 to 56 for screwing the 
first and second screws are formed at positions corresponding to the first 
and second screw receiving holes 35 to 36. 
As shown in FIG. 5, each of the first to fourth tack pins 51 to 54 is 
constituted by a large-size shaft portion 61 whose diameter is larger than 
that of the small hole portion 41 of the first to fourth tack-pin 
receiving holes 31 to 34, a small-size shaft portion which is connected to 
a tip end of the large-size shaft portion 61 and whose diameter is smaller 
than that of the small-size hole portion 41, and a flange portion 63 for a 
loose-proof which is connected with a tip end of the large-size shaft 
portion 62 and whose diameter is larger than that of the small-size hole 
portion 41. The flange portion 63, the small-size shaft portion and a part 
of the large-size shaft portion 61 are respectively divided into two part 
along the axial direction by means of a slit 64 and are formed into a 
so-called cotter pin shape. 
The boss portions 55 and 56 for screwing the first and second screws are 
formed into a large-size shaft shape whose diameter is larger than that of 
the first and second screw receiving holes 35 and 36, and a screw 
connected hole 65 is formed at its center portion. 
By fixing the cover 21 on the base plate 3, adjusting the first to fourth 
tack pins 51 to 54 with the position of the first to fourth tack-pin 
receiving holes 31 to 34, and pressfitting the cover 21 toward the base 
plate 3 side, the first to fourth tack pins 51 to 54 decrease their 
diameters due to the existence of the slit 64. Then, as shown in FIG. 6, 
the small-size shaft portion 62 is inserted into the small-size hole 
portion 21 of the first to fourth tack-pin receiving portion 31 to 34, and 
the flange portion 63 is inserted into the large hole portion 42. 
The flange portion 63 inserted into the large hole portion 42 is expanded 
in diameter by the recovery force of the cotter pin and is connected to 
the loose-proofing surface 43 so that the loosening from the tack-pin 
receiving holes 31 to 34 is prevented, and the base plate 3 is clamped 
between the flange portion 63 and a tape end surface of the large-size 
shaft portion 61 to tack the cover 21 on the base plate 3. 
Then, as shown in FIG. 7, by screwing a screw 71 to the screw hole of the 
boss portions 55 and 56 for inserting the screw through the first and 
second screw receiving holes 35 and 36, the cover 21 is fixingly installed 
on the base plate 3. 
Next, a producing method of the cartridge tape which executes a driving of 
a magnetic tape by the drive belt will be explained. 
The producing method according to the present invention comprises a step 
for forming a hard protective coat layer on a surface of the base plate 
material sheet; a step for punching the hard protective coat layer from 
the base plate material sheet into a predetermined shape of the base plate 
and forming a hole at a predetermined position on the base plate; a step 
for embedding a plurality of tape guides, roller shafts rotatably 
supporting a plurality of belt rollers, and reel shafts rotatably 
supporting a pair of tape reels on the base plate; a step for installing 
belt rollers to the roller shafts, the pair of tape reels to the reel 
shafts, a tape to the tape reels and a drive belt to the belt rollers; and 
a step for installing a cover on the base plate and screwing down the 
cover on the base plate through the holes. 
Next, each step will be explained. 
The step for forming the hard protective coat layer on the surface of the 
base plate material sheet is executed by applying the alumite-treatment on 
the surface of the base plate material sheet or by coating synthetic resin 
thereon. 
The alumite treatment is executed by flowing electric current to the 
aluminum-alloy base plate material sheet as an anode in sulfuric acid or 
oxalic acid solution. 
For example, by cleaning the aluminum-alloy base plate material sheet, 
dipping it in sulfuric acid or oxalic acid solution and applying electric 
current of 2 to 3 A/cm.sup.2 and direct current voltage 70 V for about 40 
to 50 minutes, an oxide layer of about 15 to 20 .mu.m thickness is 
obtained. This oxide layer is used as a hard protective coat layer. 
The coating treatment is executed by coating synthetic-resin coating 
material on the surface of the base plate material sheet. 
For example, epoxy resin coating material of 10 .mu.m thickness is coated 
on the base-plate material 301 through a 280 mesh screen plate in a manner 
of silk screen printing method. Then, the coated material is baked at 
150.degree. C. for 30 minutes. As a result, the surface hardness of the 
protective covering layer became larger than 2H. Also, coating material 
including silicone compound is coated to 5 .mu.m thickness on the 
base-plate material 301 by a roll coat method. Then, the coated material 
is baked at 240.degree. C. for 5 minutes. As a result, the surface 
hardness of the protective covering layer became larger than 3H. 
Next, steps for punching and opening holes to the base plate material sheet 
coated by the hard protective coat layer will be explained. 
As shown in A of FIG. 8, a base plate outline punched portion 303 is 
continuously punched while a non-punched portion 302 is remained in the 
base plate material sheet 301 whose surface is formed by the hard 
protective coat layer, and a window portion 304 for mirror is punched. 
Next, as shown in B of FIG. 8, prepared holes 401, 401 for forming the 
tack-pin receiving holes, prepared holes 501, 501 for forming screw 
receiving holes, embedding holes 305, 305 for embedding the reel shafts 4 
and 5, the tape guides 8, 9 and 10 and the roller shafts 12, 13 and 14 are 
punched. 
Next, as shown in C of FIG. 8, by applying a press-working or drilling for 
forming tack-pin receiving holes, which working will be mentioned later, 
the first to fourth tack-pin receiving holes 31 to 34 are formed. 
On the other hand, the first and second screw receiving holes 35 and 36 are 
formed by applying a press-working or drilling for forming screw receiving 
hole as mentioned later to the prepared holes 501, 501. 
After the tack-pin receiving holes 31 to 34 and the receiving holes 35 and 
36 are formed as mentioned above, the base plate 3 is formed by cuttingly 
removing the non-punched portions 302 and by separating an inner side of 
the outline punched portion 303 from the base plate material sheet 301 as 
shown in D and E of FIG. 8. 
Next, assembly steps of the magnetic tape and the drive belt to the base 
plate 3, which is punched into a predetermined shape and forms holes as 
mentioned above, are executed as follows. 
As shown in FIG. 9, by utilizing the embedded holes 305, 305 formed in the 
base plate 3, the reel shafts 4 and 5, the tape guides 8, 9 and 10, the 
roller shafts 12, 13 and 14, and a cap support shaft 19 are embedded to 
the base plate 3. 
Next, as shown in FIG. 10, the pair of tape reels 6 and 7 are assembled to 
the reel shafts 4 and 5, the first to third belt roller 15, 16 and 17 are 
assembled to the first, second and third roller shafts 12, 13 and 14, and 
a mirror 20 for detecting a tape end is assembled so as to confront to the 
window portion 304. 
Next, as shown in FIG. 11, the drive belt 18 is hooked on the first to 
third belt rollers 15, 16 and 17. 
The drive belt 18 located between the first belt roller (drive roller) 15 
and the second belt roller 16 is pressfitted on the outer surface of the 
tape reel 6, and the drive belt 18 located between the first belt roller 
15 and the third belt roller 17 are pressfitted on the outer surface of 
the other tape reel 7. 
The magnetic tape 11 is wound around the tape reels 6 and 7 by driving the 
drive belt 18. 
Next, as shown in FIG. 12, the tape cartridge 1 is formed by assembling the 
cap portion 23 and a spring 24 for setting so as to close the cap portion 
23 are assembled to the cap support shaft 19 and by assembling the cover 
21 on the base plate 3. 
The assembly of the cover 21 to the base plate 3 is executed by inserting 
the first to fourth tack pins 51 to 54 formed with the cover 21 into the 
first to fourth tack-pin receiving holes 31 to 34 for temporarily fixing 
the cover 21 on the base plate 3, and by screwing screws 71 through the 
first and second screw receiving holes 35 and 36 into the boss portions 55 
and 56 which are for screwing and are disposed in the cover 21. 
The forming of the tack-pin receiving holes 31 to 34 and the screw 
receiving holes 35 and 36 are executed by a press-working or drilling 
discussed hereinafter. 
As to the tack-pin receiving holes 31 to 34, as shown in A of FIG. 13, a 
forming of the prepared holes 401, 401 on the base plate material sheet 
301, to which the hard protective coat layer is applied, is first 
executed. 
The prepared hole 401 is formed by using a punch 611 and a die 612 shown in 
the above-mentioned figure. 
Next, as shown in B of FIG. 13, the truncated-cone shaped large hole 
portion 42, which is gradually compressed in diameter from an end to the 
other end, is formed by expanding an one end side (the lower surface 301b 
side of the base plate material sheet 301) of the prepared hole 401 in 
diameter and by compressing the other end side (the upper surface 301a 
side of the base plate materiel sheet 301) in diameter. 
The large hole portion 42 of the truncated cone shape is formed by using a 
punch 621 and a die 622 shown in the above-mentioned figure. 
The punch 621 is provided with a ring-shaped flange portion 623 which is in 
contact with the lower surface 301b of the base plate material sheet 301, 
a cone-shaped oblique surface portion 624 which is integrally formed at 
the inner side of the flange portion 623 and forms a round surface for the 
truncated-cone shaped large hole portion 42, and a circular plane portion 
625 which is disposed at a tip end portion of the oblique surface portion 
624 and forms a bottom surface of the large hole portion 42. 
The diameter of the circular plane portion 625 is formed so as to be 
slightly smaller than that of the prepared hole 401. 
By pressing the punch 621 into the prepared hole 401, an end portion of the 
prepared hole 401 is expanded in diameter, the other end portion is 
compressed in diameter, and the prepared hole 401 is deformed along the 
oblique surface portion 624 and the plane surface portion 625. 
By pressing the punch 621 until the flange portion 623 is contacted with 
the lower surface 301b of the base plate material sheet 301, the large 
hole portion 42, which is of a truncated cone shape and whose depth D is 
the same as the height H from the flange portion 623 to the plane portion 
625, is formed. 
The oblique angle .theta. of the large hole portion 42 is within the range 
from 3.degree. to 70.degree.. 
Next, as shown in C of FIG. 13, the small hole portion 41 is punched at the 
center portion of the bottom portion of the truncated-cone shaped large 
hole portion 42. 
The small hole portion 41 is formed by using a punch 631 and the die 632 
shown in the above-mentioned figure. 
The diameter of the punch 631 is formed so as to be smaller than that of 
the bottom portion of the large hole portion 42. 
By punching the center portion of the bottom portion of the large hole 
portion 42 by means of the punch 631, a peripheral portion of the bottom 
surface portion is remained as a ring-shaped loose-proofing surface 43. 
Next, as shown in D of FIG. 13, a chamfering of an open end side of the 
small hole portion 41 is executed. 
The chamfering is executed by using a punch 641 and a die 642 as shown in 
the above-mentioned figure. 
When the small hole portion 41 is punched, burr 41a (refer to C of FIG. 13) 
unavoidably generated at the open end side of the small hole portion 41 is 
removed by the above-mentioned chamfer-working. 
Next, as shown in E of FIG. 13, strain in the vicinity of the tack-pin 
receiving holes 31 to 34 of the upper and lower surface 301a and 301b of 
the base plate material sheet 301 is removed. 
The removing operation of the above-mention strain is executed by using a 
punch 651 and a die 652 shown in the above-mentioned Figure. 
By executing the above-mentioned series of works, the tack-pin receiving 
holes 31 to 34 are formed in the base plate material sheet 301. 
Next, a case for forming the screw receiving holes 35 and 36 will be 
explained. 
A forming of the screw receiving holes 35 and 36 are generally similar to 
that of the tack-pin receiving holes 31 to 34. 
That is, a prepared hole 501 is first formed in the base plate material 
sheet 301 as shown in A of FIG. 14. 
The prepared hole 501 is formed by using a punch 711 and a die 712 shown in 
the above mentioned figure. 
Next, as shown in B of FIG. 14, the cone shaped large hole portion 42, 
which is gradually compressed in diameter from an end side to the other 
end side, is formed by expanding the end side (the lower surface 301b side 
of the base plate material sheet 301) of the prepared hole 501 in diameter 
and by compressing the other end side (the upper surface 301a side of the 
base plate material sheet 301) in diameter. 
The large hole portion 42 of a cone shape is formed by using a punch 721 
and a die 722. 
Since a tip end of the punch 721 is formed into a cone shape, by pressing 
it into the prepared hole 501, the one end side of the prepared hole 501 
is expanded in diameter and the other end side is compressed in diameter. 
Therefore, the prepared hole 501 is deformed into a cone shape along the 
tip end of the punch 721. 
Next, as shown in C of FIG. 14, the small hole portion 41 is punched at a 
center portion of a bottom portion of a cone shape. 
The small hole portion 41 is formed by using a punch 731 and a die 732. 
Next, as shown in D of FIG. 14, a chamfering of the open end side of the 
small hole portion 41 is executed. 
The above chamfering is executed by using a punch 741 and a die 742 shown 
in the above-mentioned figure. 
Next, as shown in E of FIG. 14, strain in the vicinity of the screw 
receiving holes 35 and 36 of the upper and lower surfaces 301a and 301b of 
the base plate material sheet 301. 
The removing operation of the above-mentioned strain is executed by using a 
punch 751 and a die 752 shown in the above-mentioned figure. 
By executing the above-mentioned series of workings, the screw receiving 
holes 35 and 36 are formed on the base plate material sheet 301. 
Although the embodiment has been shown as to a case that the tack-pin 
receiving holes 31 to 34 and the screw receiving holes 35 and 36 are 
formed by a press working, these tack-pin receiving holes 31 to 34 and the 
screw receiving holes 35 and 36 may be formed by a drilling. 
While the embodiment has been explained as to the tape cartridge, the 
present invention may be applied to a tape cartridge in which a magnetic 
tape is run without using a drive belt. 
As explained above, in the tape cartridge producing method of the present 
invention, since the hard protective coat layer is formed on the base 
plate material sheet, a base plate, which has been already covered by the 
hard protective coat layer, is formed by punching the base plate material 
sheet. 
Accordingly, it is possible to eliminate a complicated step that the hard 
protective coat layer is formed on each base plate after it is 
conventionally punched from the base plate material sheet, and therefore 
an improvement in the productivity is promoted. 
Since the tape cartridge of the present invention uses a base plate which 
is punched into a predetermined shape from the sheet shape aluminum-alloy 
materiel sheet which is covered by the hard protective coat layer, the 
cost of the base plate is decreased as compared with a case that the 
sheet-shape aluminum alloy sheet is conventionally punched into a 
predetermined shape, and the hard protective coat layer is covered on its 
surface. Therefore, it becomes possible to decrease the cost of the tape 
cartridge. 
Since the side surfaces of the base plate are not covered with the hard 
protective coat layer, when the tape cartridge is inserted into the 
recording and reproducing apparatus, no hard protective coat layer is in 
contact with the recording and reproducing apparatus. Accordingly, there 
is a merit that the injury of the recording and reproducing apparatus by 
the base plate is suppressed as compared with the case that the hard 
protective coat layer is formed at side surfaces of the conventional base 
plate.