Method for making film cassettes

In an improved embodiment, film cassettes comprising a substantially cylindrical casing, a film mouth of an upper lip and lower lip extending over the width of the casing, a film spool and end caps, the upper lip and lower lip of the film mouth being provided with sealing strips, contain the sealing strips for the lower lip bonded to the metal in such a way that the edge zones of the sealing strip on the narrow sides and the edge zones of the sealing strip on the longitudinal side are completely bonded to the metal on the lower lip while the edge zone of the sealing strip on the longitudinal side is completely or partly bonded to the metal inside the cassette and all or part of the inner region of the surface of the sealing strip is not bonded to the metal, so that 10 to 60% of the total surface area of the sealing strip is not bonded to the metal strip.

This invention relates to a method for making film cassettes comprising a 
substantially cylindrical casing, a film mouth of an upper lip and lower 
lip extending over the width of the casing, a film spool and end caps, the 
film mouth being provided with a sealing material, for example with a 
strip of velvet, on the upper lip and lower lip. 
The cassettes according to the invention are intended in particular for 
microfilms. 
Whereas the upper lip of the film mouth is formed simply by tangential 
termination of the last piece of the metal strip of the casing, the lower 
lip is formed by bending of the casing metal through more than 90.degree. 
(see FIG. 1). The film cassettes are produced by bending of a 
corresponding flat piece of metal which may be bonded to the sealing 
strips before or after bending. The sealing strip for the upper lip and 
lower lip of a cassette has a rectangular shape substantially 
corresponding in length to the height of the cassette. The width, which 
may be different at the upper and lower lip, is at least so great that the 
sealing strip extends over the bend of more than 90.degree. into the 
interior of the cassette. The surface of the sealing strip for the lower 
lip is divided into two edge zones on the narrow sides, one edge zone on 
the longitudinal side in the interior of the cassette and one edge zone at 
the longitudinal side on the lower lip. The edge zones enclose an inner 
region of the strip surface which makes up 10 to 60% of the total bonding 
surface of a sealing strip. 
After bending, the film spool is introduced into the curved casing and the 
cassette is closed by application of the end caps. Because the already 
bent casing is difficult to bond to the velvet, it is best for economic 
reasons initially to bond the still flat metal strip to the velvet and 
then to bend it into the shape of the cylindrical casing with the upper 
lip and lower lip. 
However, it has been found that this approach results in a certain 
percentage of faulty cassettes in which the velvet is torn or unacceptably 
deformed at the edge of the lower lip. 
The problem addressed by the present invention is to provide the flat metal 
strip with the velvet in such a way that the velvet does not tear during 
bending, particularly at the sharp bend of the lower lip, and unacceptable 
deformation of the velvet is avoided. 
This problem is solved in accordance with the claim 1. Further embodiments 
of the invention are covered by the subsidiary claims. 
More particularly, the sealing strip is applied in such a way that a strip 
of metal, of which the width corresponds to the circumference of a 
ready-shaped casing for a cassette and of which the length is several 
times the width of the casing for a cassette, is initially introduced and 
then provided along the edges forming the film mouth with the sealing 
material which is delivered in the form of continuous ribbon-like sealing 
strips that are joined to the metal strip of the casing on passing through 
a bonding station. 
According to the invention, the stamps with which the sealing strip is 
pressed on are designed in such a way that, for the metal strip of each 
cassette, only the edge of the sealing strip is pressed on, spot-like or 
strip-like regions optionally being pressed on in the middle part of the 
sealing strip surface. The other parts of the sealing material, which are 
not to be bonded to the metal surface, may be adhesive-free or may also be 
coated with adhesive. Preferably, the entire surface of one side of the 
sealing material contains adhesive. 
After application, the sealing material is cut between the individual 
lengths of metal, the length of metal required for one cassette is cut 
from the strip of sheet metal and shaped into the cassette casing as 
described above. 
The cap notches have already been punched out from the metal strips to be 
bonded, as shown in FIG. 2. 
The invention enables film cassettes to be produced in largely automated 
steps. Despite the increase in output, the method according to the 
invention guarantees consistently high quality of production. 
At the same time, the manufacture of cassettes by the method according to 
the invention is very inexpensive.

The metal strip 4 is drawn intermittently between the pressure block 5 and 
the heating block 6 and pressed against it by the pressure block 5. 
The sealing strips 7, 8 hug the underneath of the metal strip 4 at its 
edges and, in doing so, pass through the groove-like recesses 9 of the 
pressure block 5. The sealing strips 7, 8 are delivered to the underneath 
of the metal strip 4 at its edges in such a way that they project slightly 
laterally beyond the edges of metal strip 4. 
The sealing strips 7, 8, typically of velvet, are coated on the side facing 
the metal strip with a layer of a typical hot-sealing adhesive. For 
bonding, the heating block 6 is equipped with an electrical heating 
element known per se (not shown) which heats the edges of the metal strip 
4 inductively from above. By contact with the heated edge of the metal 
strip 4, the hot-sealing adhesive is melted, so that the sealing strips 7, 
8 are bonded to the underneath of the metal strip 4 and remain permanently 
bonded thereto, even after cooling. 
Since the sealing strips 7, 8 are initially endless, they also span the 
marginal cap notches 10 on the underneath of the metal strip 4, as can 
clearly be seen. 
In the interests of clarity, the guide rails 11, 12, the pressure block 5 
and the heating block 6 are shown drawn apart from one another in relation 
to the metal strip 4. In reality, however, the metal strip 4 travels on 
the guide rails 11, 12. 
The bonding station further comprises two storage magazines 13, 14 for the 
ribbon-like sealing strips 7, 8 which are run off in the form of "endless" 
ribbons from supply reels 15, 16 serving as storage packs and are 
delivered over fixed curved guides 17, 18 into the path of the metal strip 
4 at its edges substantially tangentially from below. 
After leaving the bonding station, the metal strip 4 travels in the 
direction of the arrow 19 over the guide rail 12 to the other processing 
stations (cutting of the sealing strips, separation of the individual 
sections from the metal strip, bending of the individual sections to form 
the cassette casing, insertion of the film spool, fitting of the end 
caps). 
According to the invention, the sealing strip is applied by corresponding 
design of the pressure block 6. 
FIGS. 3a to 3f show different possibilities for bonding the sealing strips 
to each individual metal section. The adhesive-coated region is denoted by 
the reference 20 and the adhesive-free region by the reference 21. Within 
the adhesive-free region, spot- or strip-form bonding 22 can be carried 
out. In the embodiments 3e and 3f, the adhesive-coated longitudinal side 
is bonded to the lower lip while the only partly adhesive-coated 
longitudinal side is bonded inside the cassette. 
The special type of bonding is characteristic of the lower lip. The sealing 
material for the upper lip is preferably stuck on its entire bonding 
surface area. 
The end caps are axially symmetrical, flanged at their outer edges and, 
with the end edges of the cassette casing, form a force fit and a 
light-proof labyrinth seal when the caps are fitted onto the cassette 
casing. The axially symmetrical design of the caps is possible because the 
end edges of the final cassette casing are offset slightly in the region 
of the film mouth on account of the cap notches, the offset parts 
receiving the flanged edge of the caps in the region of the film mouth. 
Despite these offset parts, the cassette remains light-proof in this 
region because the sealing strips project beyond the offset parts, as can 
be seen from FIG. 2.