Sheet film package

A sheet film package contains a sheet film unit in a light-shielding envelope with an open end through which the sheet film unit is movable into and out of the light-shielding envelope. The light-shielding envelope is formed by folding a sheet of light-tight material in half to provide a folded side, and securely sealing joints of the folded sheet along a side opposite side to the folded side as well as an end opposite to the open end, wherein a middle portion of the folded side has a larger folding angle compared with end portions thereof.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a sheet film package wherein a sheet of 
photo film is removably packed in a light-shielding envelope. 
2. Background Art 
A sheet film package contains a relatively large sheet film, e.g. a 
12.5.times.10 cm format sheet film, which is mainly directed to 
professional photography. The light-shielding envelope of the sheet film 
package has an open end for entrance and exit of the sheet film. The open 
end is sealed with a clip in a light-tight fashion to prevent ambient 
light from entering the interior of the light-shielding envelope. 
To expose the sheet film, the sheet film package is loaded in a film holder 
attached to the rear side of a camera. When loading the sheet film 
package, a lock lever of the film holder is set in a releasing position. 
Thereafter, the sheet film package is inserted in the film holder with the 
clip located in the innermost position of the film holder. Then, the lock 
lever is set in a locking position, thereby holding the clip in the 
innermost position and, simultaneously, allowing the light-shielding 
envelope to separate from the clip. Most portion of the light-shielding 
envelope is then withdrawn from the film holder to leave the sheet film in 
an exposure position behind an exposure frame of the camera. 
After exposure of the sheet film, the light-shielding envelope is moved 
back into the film holder so as to insert the exposed sheet film therein. 
Where the sheet film is fully inserted in the light-shielding envelope, 
the open end is sealed with the clip again by resetting the lock lever to 
the releasing position. Thus, the sheet film and the light-shielding 
envelope may be removed together from the film holder by pulling out the 
light-shielding envelope. 
As the sheet film package is a single-use article, the manufacturing cost 
must be low. Japanese Laid-Open Patent Application No. 4-356039 discloses 
a sheet film package whose light-shielding envelope is made of paper of 
about 240 .mu.m thick blackened with carbon. To manufacture the 
light-shielding envelope of the known sheet film package, two identical 
paper sheets are mated together and sealed along longitudinal edges with 
side-sealing tapes, whereas one end is sealed with an adhesive agent. 
Although the black paper is cheap, this known configuration requires a 
large amount of side-sealing tape, two taping machines and accurate 
positioning of the paper sheets, so the material cost and the equipment 
cost cannot be sufficiently lowered, and the production speed is 
relatively low. 
To solve this problem, it is possible to form a light-shielding envelope by 
folding a single sheet of paper along a center line and close the opposite 
side to the folded side with a sealing tape. However, as the side-sealing 
tapes also serve as reinforcing tapes for preventing the light-shielding 
envelope from bending, providing the side-sealing tape only along one side 
can make the light-shielding envelope easy to bend while being inserted 
into the film holder, especially while being moved back into the film 
holder after the exposure. 
OBJECT OF THE INVENTION 
In view of the foregoing, a prime object of the present invention is to 
provide a sheet film package whose light-shielding envelope is 
inexpensive, easy to manufacture, and has a high stiffness in flexure. 
SUMMARY OF THE INVENTION 
To achieve the above object in a sheet film package containing a sheet film 
unit in a light-shielding envelope with an open end through which the 
sheet film unit is movable into and out of the light-shielding envelope, 
the present invention forms the light-shielding envelope by folding a 
sheet of light-tight material in half to provide a folded side, and 
securely sealing joints of the folded sheet along a side opposite to the 
folded side as well as in an end opposite to the open end, such that a 
middle portion of the folded side has a larger folding angle compared with 
end portions of the folded side. 
Due to the large folding angle of the middle portion, the cross-sectional 
area increases in the middle of the light-shielding envelope compared with 
the opposite ends, so the bending stiffness of the middle portion is 
improved. Since the end portions have smaller folding angels and thus the 
envelope has correspondingly small cross-sectional areas in the ends, the 
envelope can be smoothly moved into and out of the film holder, and it is 
easy to seal the open end of the light-shielding envelope with the clip in 
a light-tight fashion. Also, the light-shielding envelope will not apply 
any extraneous load to the sheet film unit, so that the sheet film unit is 
stably contained in the light-shielding envelope, and can be smoothly 
moved into and out of the light-shielding envelope.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows a sheet film package 2 according to a preferred embodiment of 
the invention, in a position where a sheet film unit 4 is pulled out from 
a light-shielding envelope 3. The light-shielding envelope 3 has an open 
end 5 for allowing the sheet film unit 4 to move into and out of the 
light-shielding envelope 3. A light-shielding clip 20 is provided along an 
end of the sheet film unit 4, for sealing the open end 5 of the 
light-shielding envelope 3 when the sheet film unit 4 is fully inserted in 
the light-shielding envelope 3. 
A stop plate 6 of hard cardboard is cemented to an outer surface 3a of the 
light-shielding envelope 3 proximate the open end 5. The outer surface 3a 
with the stop plate 6 is directed toward a taking lens of a camera when 
the sheet film package 2 is properly loaded in a film holder which is 
attached to the camera. Hereinafter, the outer surface 3a of the 
light-shielding envelope 3 will be referred to as the front surface 3a. 
The stop plate 6 is provided for engagement with a latching member of the 
film holder to stop the light-shielding envelope 3 from being farther 
withdrawn from the film holder. Thus, the light-shielding envelope 3 is 
prevented from slipping away from the film holder. The front surface 3a of 
the light-shielding envelope 3 has a printing area 7 as shown in FIG. 2, 
wherein an indicia 7a indicating that this side is to be directed toward 
the taking lens, and an indicia 7b indicating the film manufacturer, the 
film type and other film information are printed. The printing area 7 is 
omitted for clarity from FIG. 1. 
As shown by dashed line in FIG. 1, a grip plate 8 of hard cardboard is 
cemented to a back surface 3b of the light-shielding envelope 3 in an end 
3c opposite to the open end 5. The opposite end 3c is disposed outside the 
film holder when the sheet film package 2 is loaded therein, so that the 
photographer can handle the sheet film package 2 while pinching at the 
grip plate 8. A cut-out out 8a is formed in a middle of the grip plate 8 
so as to pinch the light-shielding envelope 3 directly. Hereinafter, the 
end 3c having the grip plate 8 will be referred to as a handling end. 
Referring to FIG. 3, the light-shielding envelope 3 is made of a sheet of 
light-tight material 10 folded in half. The folded side 11 forms a 
longitudinal edge of the light-shielding envelope 3, while the joint of 
the opposite side is secured with a side-sealing tape 12. The handling end 
3c is sealed with an adhesive agent 13 such as a hot-setting adhesive 
agent. 
The folded side 11 is pressed by a hot-press so as to have partly different 
folding angles. Specifically, a smaller pressure is applied to a middle 
portion A2 compared with end portions A1 and A3 which are indicated by 
hatching, so that the middle portion A2 has a larger folding angle than 
the end portions A1 and A3. Due to the large folding angle of the middle 
portion A2, the cross-sectional area increases in the middle of the 
light-shielding envelope 3 compared with the opposite ends, as shown in 
FIGS. 4 and 5, so the bending stiffness of the middle portion A2 is 
improved. Since the end portions A1 and A3 have smaller folding angles and 
thus the envelope 3 has correspondingly small cross-sectional areas in the 
ends 5 and 3c, it is easy to seal the open end 5 of the light-shielding 
envelope 3 with the clip 20 in a light-tight fashion, and the 
light-shielding envelope 3 can be smoothly moved into and out of the film 
holder. Also, the light-shielding envelope 3 will not apply any extraneous 
load to the sheet film unit, so that the sheet film unit is stably 
contained in the light-shielding envelope 3, and can be smoothly moved 
into and out of the light-shielding envelope 3. 
Referring again to FIG. 1, a first base plate 21 is secured to the clip 20 
by caulking. The first base plate 21 is removably connected to a first end 
of a photographic sheet film 22 through a hot-melt adhesive applied on a 
rear surface of the photographic sheet film 22. A second end of the 
photographic sheet film 22, which is opposite to the first end, is 
removably connected to a second base plate 23 through a hot-melt adhesive 
applied on the rear surface of the photographic sheet film 22. Side edges 
of the second base plate 23 are cut diagonally so as to taper off to a 
free end, so that the sheet film unit 4 can smoothly thrust into the 
light-shielding envelope 3. A plate 24 is securely put on the second base 
plate 23 so as to offset the step between the photographic sheet film 22 
and the second base plate 23. 
A lateral slot 25 and three round holes 26a, 26b and 26c are formed through 
the second base plate 23. The slot 25 allows the opposite walls of the 
light-shielding envelope 3 to come into contact with each other when the 
light-shielding envelope 3 is pinched in the cut-out 8a of the grip plate 
8. Accordingly, it is possible to draw out the sheet film unit 4 along 
with the light-shielding envelope 3 from the film holder, while keeping 
the sheet film unit 4 in the same position relative to the light-shielding 
envelope 3. The round holes 26a to 26c are aligned in a lateral direction 
of the sheet film unit 4, but are spaced differently from one another. The 
round holes 26a to 26c are provided for discrimination between the back 
surface and the photosensitive surface of the sheet film unit 4. In the 
factory, the spacings between the round holes 26a to 26c are checked for 
prevention of reverse insertion of the sheet film unit 4 into the 
light-shielding envelope 3. 
FIG. 6 shows a sequence of manufacturing the light-shielding envelope 3. 
First, a continuous web 10 of a light-fight sheet material is withdrawn 
from a roll, and is flattened. Next, the stop plate 6 is attached to one 
surface of the continuous web 10 at each assigned position. Also wiper 
members such as felt ribbons are cemented to the opposite surface of the 
continuous web 10 at given positions, though the wiper members are not 
shown in the drawings. The wiper members are provided for wiping the dust 
off the photographic sheet film 22. Thereafter, a longitudinal center line 
of the continuous web 10 is aligned with a predetermined line to crease 
the continuous web 10 along the center line. The continuous web 10 is cut 
halfway along transversal lines, i.e. from one side edge to the center 
line, at regular intervals, and then folded according to the crease of the 
center line. 
Next, the continuous web 10 is hot-pressed along the folded side so as to 
adjust the folding angle to the above-described configuration of the 
individual light-shielding envelope 3. The folded continuous web 10 is 
then hot-sealed in those areas which are to be shaped into the handling 
ends 3c of the light-shielding envelopes 3. Thereafter, the side-sealing 
tape 12 is put on aligned longitudinal edges of the folded continuous web 
10 to securely join the edges to each other. After the grip plate 8 is 
secured to a designated position of the folded continuous web 10, the 
continuous web 10 is cut at designated positions into predetermined 
lengths. Each cut piece is then trimmed into the shape of the 
light-shielding envelope 3. Finally, the handling end 3b of the 
light-shielding envelope 3 is hot-pressed again to ensure the sealing. The 
complete light-shielding envelope 3 is stored in a stack. 
The light-tight sheet 10 is a laminated sheet consisting of four layers, as 
shown in FIG. 7. That is, a polyolefin-group thermoplastic resin sheet, 
e.g., a polyethylene sheet 15 is sandwiched between carbon-black mixed 
paper sheets 10a and 10b by extrusion laminating. This construction 
improves the stiffness of the light-shielding envelope 3 and restrains the 
light-shielding envelope 3 from curling, in comparison with the 
conventional envelope made of light-shielding paper which is coated with 
resin merely on one surface. The longitudinal strain of the paper sheets 
10a and 10b responsive to the temperature variation and the humidity 
variation should be approximately equal to each other, so as to prevent a 
curl or crook of the laminated sheet material 10 and thus the 
light-shielding envelope 3. The outer surface of the paper sheet 10a is 
coated with wax of 1 g/m.sup.2 thick as a lubricant layer 16. The 
light-tight sheet 10 should be folded with the lubricant layer 16 inside, 
so that the sheet film unit 4 may be smoothly moved into and out of the 
light-shielding envelope 3 and may not be scratched by the light-shielding 
envelope 3. 
The light-tight sheet 10 can also be formed by dry laminating or wet 
laminating. As the thermoplastic resin, various kinds of polyolefin resin 
including monopolymer-resin, copolymer-resin and mixture of different 
resins may be applicable. 
The weight of the paper sheets 10a and 10b is preferably in a range from 60 
g/m.sup.2 to 120 g/m.sup.2. Below this range, the stiffness in flexure of 
the light-shielding envelope 3 is insufficient so that the sheet film 
package 2 is apt to bend. Above this range, it is hard to achieve smooth 
movement of the light-shielding envelope 3 into and out of the film 
holder. According to the present invention, the paper sheets 10a and 10b 
are 90 g/m.sup.2 in weight. Carbon black is loaded in the paper sheets 10a 
and 10b so as to restrain reflection on the outer surface of the 
light-shielding envelope 3 and shield light from the interior of the 
light-shielding envelope 3. The density of the carbon black in the paper 
sheets 10a and 10b is preferably 2 wt % to 15 wt % (1.2 g/m.sup.2 to 18 
g/m.sup.2). Mixing black dye such as cationic dye in addition to the 
carbon black will improve the light-shielding properties of the 
light-shielding envelope 3. 
Although the paper sheets 10a and 10b must be colored for anti-reflection 
on the outer surfaces of the light-shielding envelope 3, the paper sheets 
10a and 10b need not sufficiently absorb or reduce light by themselves. 
That is, the polyethylene sheet 15 may contain carbon black so as to have 
light-shielding properties. Thus, ambient light is completely shielded 
from the light-shielding envelope 3 interior by the combination of the 
respective layers having light-shielding properties. In this case, the 
polyethylene sheet 15 preferably contains the carbon black at a density 
from 0.5 wt % to 10 wt %. According to this configuration, the interior of 
the light-shielding envelope 3 is shielded from light even if it is left 
under 100,000 lux light for ten minutes. 
The thickness of the polyethylene sheet 15 is preferably in a range from 10 
.mu.m, to 70 .mu.m, that corresponds a weight range from 10 g/m.sup.2 to 
70 g/m.sup.2. Below this range, it is difficult to reliably form the 
polyethylene sheet 15 by laminating, so the laminated layers tend to be 
separated from each other. Above this range, the light-tight sheet 10 is 
not suitable to form by laminating, but rising material cost. The 
polyethylene sheet 15 of the above mentioned thickness range provides the 
light-shielding envelope 3 with a satisfactory moisture-proofness. To 
improve the moisture-proofness of the light-shielding envelope 3, it is 
possible to use waterproof paper as the paper sheets 10a and 10b. 
Impregnating the paper sheets 10a and 10b with a resin may be preferable 
for improving stiffness in flexure and waterproof properties of the 
light-shielding envelope 3. 
The above described sheet film package 2 operates as follows: 
Before use, the open end 5 of the light-shielding envelope 3 of the sheet 
film package 2 is closed by the light-shielding clip 20 in a light-tight 
fashion, as shown in FIG. 1. For exposure, the sheet film package 2 is 
loaded in a film holder attached to a rear side of a camera. When loading 
the sheet film package 2, a lock lever of the film holder is set in a 
releasing position, and then the sheet film package 2 is inserted in the 
film holder with the clip 20 located in the innermost position of the film 
holder thereafter when the lock leer is set in a locking position, the 
clip 20 is arrested in the innermost position, and the light-shielding 
envelope 3 is allowed to separate from the clip 20. Most portion of the 
light-shielding envelope 3 is then withdrawn from the film holder to leave 
the sheet film in an exposure position behind an exposure frame of the 
camera. 
As the light-shielding envelope 3 is coated with wax on its inner surface, 
separation of the light-shielding envelope 3 from the sheet film unit 4 
can be done smoothly without the photographic sheet film 22 being 
scratched by the light-shielding envelope 3. 
After the exposure of the photographic sheet film 22, the light-shielding 
envelope 3 is moved back into the film holder so as to insert the exposed 
sheet film unit 4 therein. Because of the relatively large folding angle 
of the middle area A2 of the folded side 11, the light-shielding envelope 
3 has an improved stiffness in flexure, so the light-shielding envelope 3 
is hardly bent while being pushed back into the film holder. On the other 
hand, because of the relatively small folding angle of the end area A3, 
the margins of the open end 5 is smoothly guided into the clip 20. 
By resetting the lock lever to the releasing position, the clip 20 clamps 
the margins of the open end 5 to seal the light-shielding envelope 3 
again. Since the slot 25 of the sheet film unit 4 is located under the 
cut-out 8a in this position, the sheet film unit 4 and the light-shielding 
envelope 3 are together removed from the film holder by pulled out the 
light-shielding envelope 3 while tightly pinching at the cut-out 8a. After 
the sheet film package 2 is removed from the film holder, the 
light-shielding envelope 3 is folded along a border 8b of the grip 8, so 
as to fix the position of the sheet film unit 4 in the light-shielding 
envelope 3 and thus secure the clip 20 to the light-shielding envelope 3. 
FIG. 8 shows a lamination structure of another light-tight sheet or web 30 
as a material of the light-shielding envelope 3. According to this 
embodiment, an ink layer 31 is formed by printing on a paper layer 10b, 
and two layers of curing agent lacquer 32a and 32b are formed on the ink 
layer 31 by coating with a curing lacquer twice. Furthermore, a lubricant 
layer 33 is formed on the outer curing agent layer 32b. The lubricant 
layer 33 is to be disposed in the outermost position of the 
light-shielding envelope 3. The same laminations as the light-tight sheet 
10 has are designated by the same reference numbers as used in FIG. 7. The 
major components of the curing agent lacquer of the layers 32a and 32b may 
be shown in Table 1, and a curing agent consisting of 100% 
xylene-di-isocyanate (XDI) is loaded in a ratio of 5% to the major 
components. The lubricant layer 33 may have a composition as shown in 
Table 2. 
TABLE 1 
______________________________________ 
COMPOSITION RATIO 
______________________________________ 
aklyl-polyol 36.8% 
vinyl-chloride-acetate 
36.8% 
cellulose-acetyl-butylate (CAB) 
4.2% 
polyethylene wax 7.4% 
silica 14.8% 
______________________________________ 
TABLE 2 
______________________________________ 
COMPOSITION RATIO 
______________________________________ 
polyamide 8.2% 
nitro-cellulose 73.8% 
erucic-acid-amide 
16.4% 
silica 1.6% 
______________________________________ 
Table 3 shows results of experiments on bending stiffness and appearance 
change of light-shielding envelopes made of different kinds of light-tight 
sheets. Each light-shielding envelope was formed by folding a sheet at a 
uniform folding angle, i.e., under a uniform pressure. 
TABLE 3 
__________________________________________________________________________ 
EXAMPLE 
5 
BASIC 
1 2 3 4 MATERIAL + 
BASIC BASIC BASIC BASIC CURING 
MATERIAL + 
MATERIAL + 
MATERIAL + 
MATERIAL + 
LAYER .times. 2 + 
LUBRICANT 
LUBICANT CURING CURING LUBRICANT 
LAMINATIONS 
LAYER .times. 1 
LAYER .times. 2 
LAYER .times. 1 
LAYER .times. 2 
LAYER .times. 1 
__________________________________________________________________________ 
BENDING E D D B B 
STIFFNESS 
APPEARACE 
E A A E A 
CHANGE 
CONCLUSION 
E E E E B 
__________________________________________________________________________ 
In Table 3, "basic material" has the laminated structure as shown in FIG. 
7, wherein a polyolefin-group thermoplastic resin sheet, e.g., a 
polyethylene sheet is sandwiched between carbon-black mixed paper sheets; 
and "A", "B", "D" and "E" respectively represent the grades "excellent", 
"good", "unsatisfactory" and "ineffective in practice". It is to be noted 
that the respective layers were 0.5 to 3 .mu.m thick per coat. As shown in 
Table 3, example-1 with a single layer of conventional lubricant wax lacks 
bending stiffness, and paper-fiber tore along the folded side. Both 
example-2 with two layers of the conventional lubricant wax, and example-3 
with a single layer of curing lacquer which contains 5 parts of 
xylene-di-isocyanate to 100 parts of the major components as shown in 
Table 1, did not suffer any paper-fiber tear, but they were insufficient 
in bending stiffness. Example-4 with two layers of the curing lacquer was 
sufficient in bending stiffness, but the curing lacquer layers tore along 
the folded side. Example-5, as having the lamination structure according 
the embodiment shown in FIG. 8, was sufficient in bending stiffness, and 
no tear was found in the paper fiber and the curing lacquer layers. 
Table 4 shows test results on light-shielding properties and working 
properties (i.e. frequency of bending in this instance) of those 
light-shielding envelopes which have the same configuration as the 
light-shielding envelope 3, but differ from one another in length ratio 
between the middle portion A2 and the end portions A1 and A3 of the folded 
side 11, wherein the end portions A1 and A3 have an equal length in each 
example. The examples were made of both the light-tight sheet 10 and the 
light-tight sheet 30 for each length ratio. 
TABLE 4 
______________________________________ 
LENGTH RATIO WORKING 
(%) LIGHT-SHIELDING 
PROPERTIES 
A1: A2: A3 PROPERTIES WEB 10 WEB 30 
______________________________________ 
0 100 0 E A A 
5 90 5 D A A 
7 86 7 C A A 
10 80 10 B B A 
15 70 15 B B A 
20 60 20 B B A 
25 50 25 B C A 
30 40 30 A C-D C 
40 20 40 A D C-D 
50 0 50 A E D-E 
______________________________________ 
In Table 4, "A" represents excellent light-shielding properties or 
indicates that the light-shielding envelope can be rapidly and smoothly 
moved into the film holder; "B" represents good light-shielding properties 
or indicates that the light-shielding envelope can be smoothly moved into 
the film holder; "C" represents adequate light-shielding properties or 
indicates that the light-shielding envelope can be slowly moved into the 
film holder; "D" represents unsatisfactory light-shielding properties or 
indicates that the light-shielding envelope was not smoothly moved into 
the film holder or sometimes loaded in an improper position; and "E" 
indicates that the light-shielding properties were ineffective in practice 
or that the light-shielding envelope was difficult to insert into the film 
holder and often loaded in an improper position. 
As shown in Table 4, reasonable light-shielding properties and working 
properties were obtained where the length ratio of the middle portion A2 
to the entire length of the folded side 11 was 40% to 86%. With increasing 
length ratio of the middle portion A2, the working properties were 
improved or the frequency of bending of the light-shielding envelope 3 was 
reduced. But too large length ratios of the middle portion A2 lowered the 
light-shielding properties. The improved light-tight sheet or web 30 as 
having the curing lacquer layers 32a and 32b made it possible to improve 
the working properties in a range of the length ratio A2:A1 or A3 wherein 
satisfactory light-shielding properties can be achieved. In any length 
ratio, production cost of the light-shielding envelope 3 formed by folding 
a sheet in half was remarkable reduced compared with the conventional 
light-shielding envelopes made by joining two sheets together with 
side-sealing tapes on both sides of the sheets. 
Although controlled hot-pressing for changing the folding angles of the 
portions A1, A2 and A3 is executed in the last stage of the folding 
process in FIG. 6, it is alternatively possible to execute the controlled 
hot-pressing in the last step of manufacturing the light-shielding 
envelope 3, or provide a separate process for adjusting the folding angle. 
To control the pressure on the folded side 11, a pressure mold having a 
corresponding contour or a series of press rollers applying different 
pressures may be applicable. 
Although the same pressure is applied to within the same portion A1, A2 or 
A3 in the above-described embodiment, it is possible to gradually change 
the pressure around the borders between the portions A1, A2 and A3. In 
that case, a pressure mold for the folded side 11 should have 
correspondingly gradually changed contour. This embodiment effectively 
prevents integration of bending stress in the borders between the 
differently pressed portions A1, A2 and A3, and thus still more improves 
the bending stiffness of the light-shielding envelope 3. 
The sequence of manufacturing of the light-shielding envelope 3 may not be 
limited to the embodiment shown in FIG. 6. The layers of curing agent 
embodiment shown in FIG. 6. The layers of curing agenct lacquer 32a and 
32b and the lubricant layer 33 may be formed on inside of the envelope 3. 
Meanwhile, in the photographic film package as above, if the open end of 
the light-shielding envelope is not properly fitted into the clip when the 
envelope is moved back into the sheet holder of the camera after the 
exposure of the photographic sheet film, a gap is provided between the 
open end and the clip. As a result, the exposed sheet film could be 
unexpectedly exposed to ambient light. To solve this problem, the present 
Applicant has suggested forming light-shielding ridges or waves in 
proximity to the open end of the envelope in U.S. patent application Ser. 
No. 08/014,680, now abandoned. Although the ridges improve light-shielding 
properties of the envelope in a closed position with the clip, inside 
surfaces of the ridges protruding inwardly of the envelope give a certain 
contact pressure to the photographic sheet film, and may scratch the sheet 
film. 
Another problem would arise when such light-shielding ridges are to be 
formed on such an envelope that is formed by folding a sheet in half, as 
is shown in FIG. 3. Because the thickness of that envelope is different 
between the folded side and the sealed side due to the thickness of a 
sealing device such as a side-sealing tape, the amount of projection of a 
ridge disposed on the sealed side would be more than that of a ridge 
disposed on the folded side, and the inside surface of the ridge on the 
sealed side would rub against the film sheet, so that the film sheet is 
more likely to be scratched by that ridge. 
According to a second preferred embodiment of the invention, as shown in 
FIG. 9, a light-shielding envelope 3 of a sheet film package 2 is provided 
with a pair of ridges or waves 41 and 42 in proximity to an open end 5 
thereof. It is to be noted that the sheet film package 2 according to the 
embodiment shown in FIG. 9 has fundamentally the same configuration as the 
first embodiment. Therefore, equivalent elements are designated by the 
same reference numerals, so that the following description will be related 
merely to essential elements for the second embodiment. 
The ridges 41 and 42 extend in a direction traversing the path of a sheet 
film unit 4 movable into or out of the light-shielding envelope 3 through 
an open end 5. In the embodiment shown in FIG. 10, the ridges 41 and 42 
extend substantially in parallel to the open end 5 of the light-shielding 
envelope 3. As set forth in detail below, the ridges 41 and 42 are 
semi-cylindrical or arc-shaped in traverse sections thereof, i.e., in the 
sections along the moving path of the sheet film unit 4. In this way, a 
photographic sheet film 22 of the sheet film unit 4 is prevented from 
being scratched by the ridges 41 and 42 while the sheet film unit 4 is 
being moved relative to the light-shielding envelope 3. 
Also in the second embodiment, the light-shielding envelope 3 is formed by 
folding a sheet of light-tight material 10 in half, in the same way as 
shown in FIG. 3, and a folded side 11 is hot-pressed so as to have partly 
different folding angles. Specifically, a smaller pressure is applied to a 
middle portion A2 compared with end portions A1 and A3 which are indicated 
by hatching, so that the middle portion A2 has a larger folding angle than 
the end portions A1 and A3. The light-tight material 10 may have the same 
lamination structure as described above with reference to FIG. 7 or 8. 
A hole 44 formed through a first base plate 21 is biased toward one side of 
the sheet film unit 4, so as to permit discriminating between obverse and 
reverse surfaces of the photographic sheet film 22. Furthermore, an 
adhesive tape 47 is removably attached to a handing end 3c of the 
light-shielding envelope 3 besides a grip plate 8. The adhesive tape 47 is 
used for securing the light-shielding envelope 3 to a clip 20 after the 
exposure of a photographic sheet film 22 of the sheet film unit 4. A 
cut-out 48 for facilitating removal of the adhesive tape 47 is formed 
through the handing end 3c of the light-shielding envelope 3 and the grip 
plate 8, such that an edge of the adhesive tape 47 overlaps with the 
cut-out 48. 
The ridges 41 and 42 may be formed simultaneously with the trimming step or 
the final heat-sealing step in the manufacturing process of the 
light-shielding envelope 3 such as shown in FIG. 6. Of course, it is 
possible to form the ridges 41 and 42 in another stage of the 
manufacturing process, and separately from the other steps. 
As shown in FIG. 11, the ridges 41 and 42 may be formed by embossing the 
light-shielding envelope 3 by use of two pairs of embossing dies 50 and 
51. The embossing dies 50 and 51 may be formed separately or as a unit. 
Each of the embossing dies 50 and 51 is constituted of a male die 50a or 
51a and a female die 50b or 51b. The male dies 50a and 51a have 
protrusions 53 and 54, respectively. The female dies 50b and 51b have 
cavities 55 and 56 as counterparts of the protrusions 53 and 54, 
respectively. 
The protrusions 53 and 54 have substantially the same shapes as the ridges 
41 and 42, respectively, and are thus semi-circular in transverse sections 
thereof, as shown respectively in FIGS. 12 and 13. Also, internal 
terminals 53a and 54a of the protrusions 53 and 54, which are oriented 
toward a longitudinal center line of the light-shielding envelope 3, are 
rounded with a radius of curvature Rx, as shown with respect to the 
protrusion 53 in FIG. 14. 
The protrusion 53, which is used for forming the ridge 41 on the folded 
side 11 of the light-shielding envelope 3, has a height Hi slightly 
greater than the height H2 of the protrusion 54 which is used for forming 
the ridge 42 on the opposite side that is sealed with a side-sealing tape 
12. The different D1 between the heights H1 and H2 is determined 
considering the thickness of the side-sealing tape 12, as set forth in 
detail below. If the protrusions 53 and 54 have the same height, an inside 
convex surface 42a of the ridge 42 on the sealed side would protrude more 
than an inside convex surface 41a of the ridge 41 on the folded side 11 
due to the thickness of the side-sealing tape 12 that remains after the 
embossing. 
Assuming that the side-sealing tape 12 is 90 .mu.m thick, the side-sealing 
tape 12 as being put on both surfaces of the envelope 3 increases the 
thickness of the envelope 3 on the sealed side by 90.times.2=180 .mu.m 
compared with the folded side 11. As a result of embossing, the thickness 
is reduced by 80 .mu.m. Accordingly, 180-80=100 .mu.m should be determined 
as the difference D1, so that the maximum heights or maximum mounts of 
projection H3 and H4 of the inside convex surfaces 41a and 42a of the 
ridges 41 and 42, i.e., may have the same value. In this way, contact 
pressures applied from the ridges 41 and 42 onto the photographic sheet 
film 22 are equalized and dispersed through the whole inside convex 
surfaces 41a and 42a, so that scratching of the photographic sheet film 22 
is effectively prevented. 
When the light-shielding envelope 3 is 110.8 mm.times.240 mm in size, the 
ridges 41 and 42 preferably have a length of 8-15 mm, and a height of 0.2 
mm to 1.0 mm. To form the ridges 41 and 42 with the length of 12 mm and 
the heights H3 and H4 of 0.4 mm, it is preferable to determine that the 
height H1 of the embossing protrusion 53 is 0.7 mm, and the radius of 
curvature R1 of its section is 0.5 mm, whereas the height H2 of the 
embossing protrusion 54 is 0.6 mm, and the radius of curvature R2 of its 
section is 0.5 mm. 
Also the radius of curvature Rx of the internal terminals 53a and 54a of 
the protrusions 53 and 54 is an important element for the contact pressure 
of the ridges 41 and 42 to the photographic sheet film 22. If the value Rx 
is too small, the consequent ridges 41 and 42 could not uniformly contact 
the photographic sheet film 22, so that the contact pressure would be 
partly increased, and the occurrence of scratches on the photographic 
sheet film 22 could be increased. However, as the ridges 41 and 42 have a 
small length of 8-15 mm, too large radius of curvature Rx would lower the 
light-shielding effect of the ridges 41 and 42. Therefore, the radius of 
curvature Rx should be determined so that the contact pressure of the 
ridges 41 and 42 onto the photographic sheet film 22 may be sufficiently 
small and uniform enough to prevent scratching the photographic sheet film 
22, while maintaining a sufficient light-shielding effect of the ridges 41 
and 42. 
Table 5 shows test results of an experiment on occurrence of scratches on 
the photographic sheet film 22 and the light-shielding effect of the 
ridges 41 and 42, while changing radius of curvature Rx of the internal 
terminals 53a and 54a of the protrusions 53 and 54 of the male dies 50a 
and 51a. The length of the ridges 41 and 42 was set at 12 mm, and the 
radii of curvature R1 and R2 of the protrusions 53 and 54 were 0.5 mm. 
TABLE 5 
______________________________________ 
Radius of 
Curvature Occurrence Light-Shielding 
Total 
Rx (mm) of Scratch Effect Evaluation 
______________________________________ 
0.7 E A E 
18.0 E A E 
20.0 D A D 
22.0 C A B 
24.0 B B B 
26.0 B B B 
28.0 B B B 
30.0 A C B 
32.0 A D D 
34.0 A E E 
______________________________________ 
In Table 5, "A" represents very good; "B" represents good; "C" represents 
satisfactory for practice; "D" represents unsatisfactory and that an 
improvement is needed; and "E" represents that it is impossible to use in 
practice. 
According to the results shown in Table 5, the radius of curvature Rx is 
preferably set in a range from 22 mm to 30 mm, and more preferably from 24 
mm to 28 mm, when the length of the ridges 41 and 42 is 8-15 mm, and the 
radii of curvature R1 and R2 of the protrusions 51 and 52 are both 0.5 mm. 
Although the ridges 41 and 42 extend substantially in parallel with the 
open end 5 of the light-shielding envelope 3 in the above embodiment, it 
is possible to arrange the ridges diagonally to the open end 5. This 
arrangement is effective to disperse resistance of the ridges against the 
clip 20, and thus facilitates fitting of the clip 20 to the 
light-shielding envelope 3. It is also possible to form more than two 
ridges on the light-shielding envelope 3. 
The ridges 41 and 42 may be formed by use of pressing rollers or the like 
instead of the embossing dies 50 and 51. At that time, depressing amount 
of the pressing roller is gradually reduced in proximity to the internal 
terminal of the ridge so as to form a gently curved surface of the 
internal terminal. 
The ridges 41 and 42 according to the present invention are effective for 
improving light shielding properties of a light-shielding envelope that is 
formed by mating a pair of sheets and joining both sides with side-sealing 
tapes. In this case, the protrusions of the male dies of the embossing 
dies may have the same height. 
Thus, the present invention should not be limited by the above-described 
embodiments but, on the contrary, various changes and modifications of the 
present invention can be effected by those skilled in the art without 
departing from the scope and spirit of the appended claims.