Method for the fusion cutting of thermoplastic sheets and textile webs

Fusion cutting of thermoplastic sheets and textile webs involving bonding of the cut edges is achieved with excellent quality without the accumulation of dirt particles, if the material to be cut is subjected, in the area of the intended cut, to pre-stamping and cutting in immediate succession, under heat and with precise guidance of the separator device in relation to the pre-stamping device, said pre-stamping and cutting being effected in such a way that the plane of symmetry through the pre-stamping device, which plane of symmetry extends perpendicularly to and in the same direction as the material web, is identical to the plane of symmetry extending through the separator device.

The invention relates to a method and a device for the fusion cutting of 
thermo-plastic sheets and textile webs based on the use of two separator 
members and a heat source. 
135 system photographic films (miniature films) are used in cartridges 
which are inserted into the camera and in which the film is wound onto a 
rotatable spool and is wound off the spool in the camera, frame by frame, 
through the cartridge mouth. No light can reach the inside of the 
cartridge through the mouth thereof. For this reason, the upper and lower 
lips of the cartridge mouth are lined with narrow velvet strips, which are 
cut from wide velvet webs. 
The invention relates on the one hand to a method for the fusion cutting of 
wide velvet strips into narrow velvet strips, but may also be applied to 
the cutting of other textile webs and to the cutting of thermoplastic 
sheets. The method is distinguished, in particular, by the fact that the 
cut edges are bonded by fusion of the material, thereby preventing the 
formation of dirt while cutting which could settle on the photographic 
film, for example, and there lead to defects. 
Previously known methods of fusion cutting are not suited to the 
satisfactory achievement of these objects. 
On the one hand, it is known to guide the textile web between a heat source 
and a separator wheel, which is pressed with a certain compressive force 
against the textile web. The heat source, for example an ultrasonic 
sonotrode, causes partial fusion of the material, which is then separated 
by the stationary separator wheel. 
A narrow separator wheel cuts easily through the material, but does not 
bond the cut edges to the required extent, such that fluffing and fuzzing 
occur, which contaminate the photographic material. A wide separator wheel 
does bond the cut edges satisfactorily but its cutting quality is 
inadequate. 
On the other hand, it is known to precede the cutting process proper by 
pre-stamping, which is carried out under heat, compressing the material to 
a smaller thickness than before and causing momentary fusion thereof 
(without cutting being effected), cutting being carried out thereafter by 
means of a separator wheel pressed against a counter roll, wherein the 
material is guided between separator wheel and counter roll. The 
pre-stamped path is considerably wider than the separating path, to ensure 
that the separating path remains on the pre-stamped path in the case of 
slight sideways wandering of the material web between pre-stamping and 
cutting, since otherwise too much dirt would again arise and the 
application of the pre-stamped path would not have achieved its purpose. 
However, too wide a pre-stamped path reduces the overall cutting 
performance and bonds the material in areas where such bonding is really 
unnecessary and indeed undesirable, because the ability of the velvet to 
seal a film cartridge against the incidence of light is then impaired. 
The object was therefore to avoid these disadvantages. 
It was found that this object may be achieved if the material to be cut is 
subjected, in the area of the intended cut, to pre-stamping and cutting in 
immediate succession, under heat and with precise guidance of the 
separator device in relation to the pre-stamping device, said pre-stamping 
and cutting being effected in such a way that the plane of symmetry 
through the pre-stamping device, which plane of symmetry extends 
perpendicularly to and in the same direction as the material web, is 
identical to the plane of symmetry extending through the separator device. 
The pre-stamping device and separator device are thus arranged in tandem 
closely one behind the other. 
The invention also provides a device for the fusion cutting of 
thermoplastic sheets and textile webs, comprising a pre-stamping device 
and a separator device as well as at least one heat source on which the 
pre-stamping device and separator device are so mounted that the sheet or 
web to be cut may be guided between them and the at least one heat source, 
characterised in that the separator device is arranged in tandem closely 
behind the pre-stamping device in such a way that the plane of symmetry 
extending perpendicularly to the axis of the pre-stamping device is 
identical with the plane of symmetry perpendicular to the axis of the 
separator device. 
The pre-stamping device and separator device may each be arranged on a heat 
source, for example an ultrasonic sonotrode. Preferably, however, the 
distance between them is so small that they are arranged together on one 
heat source. 
The pre-stamping device is preferably in the form of a pre-stamping rocker, 
i.e. in the form of a segment of a circle when viewed in cross section. 
The circle has, in particular, a diameter of from 10 to 50 mm. The width 
is such that a stamped path arises which is at least as wide as the 
subsequent separating path, preferably 0.1 to 
1.0 mm, especially 0.1 to 0.6 mm. The separator device is preferably in the 
form of a rotating or preferably stationary separator wheel, whose 
diameter is especially from 10 to 30 mm and whose separating face (width 
of circumferential surface of the wheel) is especially from 0.05 to 0.3 
mm. 
The points of contact of the pre-stamping device and the separator device 
on the web to be separated are, in particular, from 0.3 to 2 cm apart. 
As the Figures, discussed below, illustrate, the distance between the 
pre-stamping rocker and the heat source is defined by a finely adjustable 
limit stop, i.e. the pre-stamping rocker does not come into contact with 
the heat source. In this way, the remaining material thickness to be 
separated by the subsequent separator wheel may be precisely determined, 
since the pre-stamping depth is precisely defined down to very thin 
residual material thicknesses, even in the case of high compressive 
forces. The material cannot be crushed without check. The subsequent 
separator wheel has to separate only very thin layers of material, which 
is in addition substantially constant and plastic owing to the effect of 
prior pre-stamping up to the limit stop. In this way, a high cutting 
output is obtained without wear to the pre-stamping rocker and with 
minimal wear to the separator wheel. 
In combination with the ultrasonic sonotrode acting as the heat source, 
heat generation occurs only when the material is pressed against the 
sonotrode. When, during this contact pressure, the limit stop is reached, 
the compressive force against the sonotrode and thus the generation of 
heat are virtually cancelled. Thus, the limit stop has the effect of 
making the cutting performance self-regulating, or of making the cutting 
quality substantially independent of cutting speed and material quality. 
The distance between the pre-stamping curve and the heat source depends on 
the type and thickness of the material to be cut and is therefore 
basically greater than nil and smaller than the material thickness. 
Likewise, the temperature to which the material is heated by the heat 
source is dependent on the material. It is preferably between 100 and 
200.degree. C.

The web 1 to be separated is guided between a pre-stamping rocker 2 and a 
separator wheel 3 on one side and a heat source 4, e.g. an ultrasonic 
sonotrode. 5 designates the distance between the pre-stamping point and 
the separating point. 6 and 7 designate the lever arms for the 
pre-stamping rocker and the separator wheel, 8 the corresponding lever 
pivot points. A limit stop 9 determining the stamping depth is provided 
for the lever arm 6 of the pre-stamping rocker 2. 
The means of guiding the separator wheel is designated 10. The pre-stamping 
width 11 and the separating width 12 are obtained. 13 is the common plane 
of symmetry through the pre-stamping rocker 2 and the separator wheel 3. 
Stamping results in the reduced web thickness 14 in the stamping area. 
The arrangement relationships are such that the forces do not affect each 
other. Other lever arrangements than those shown, for example one-armed 
levers, are also possible. 
The compressive forces for stamping rocker and separator wheel may be 
exerted by springs or pneumatic cylinders, for example. Both force systems 
have a certain spring action which is necessary for operation, so that the 
separator members may be raised, in the case of thicker portions of 
material or foreign bodies for example. 
EXAMPLE 
A velvet ribbon 1.6 mm thick with a backing of polyethylene terephthalate 
and a fleece of polyamide is cut with a device according to FIGS. 1 and 2, 
wherein the device has the following dimensions: 
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Separator wheel diameter: 16 mm 
Diameter of the circle, a segment of which 
25 mm 
constitutes the pre-stamping rocker: 
Distance between contact points of separator 
7 mm 
wheel and pre-stamping rocker: 
Separating width: 0.1 mm 
Pre-stamping width: 0.3 mm 
Ribbon temperature on cutting: ca. 
150.degree. C. 
Ribbon speed: 20 m/min 
Distance between pre-stamping rocker and 
0.1 mm 
ultrasonic sonotrode: 
Result: problem-free cutting, no dirt particles. 
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