X-ray sheet film cassette

The X-ray sheet film cassette has a top part hinged to a base part. The bottom of the base part is provided with a frame enclosing a film supporting plate through which the radiation is transmitted. The supporting plate has a laminated structure including two face plates of thermoplastically bonded carbon fibers and a comparatively thicker intermediate plate of a synthetic hard foam rubber sandwiched between the face plates and being glued thereto. The face plates are considerably thinner than the intermediate plate in the laminated supporting plate of the present invention.

BACKGROUND OF THE INVENTION 
The present invention relates to an X-ray sheet film cassette composed of a 
base part positionable adjacent a source of radiation and a top part 
hinged to the base part and lockable with the base part. The bottom of the 
base part is formed with a frame enclosing a plate for supporting a sheet 
film. 
Cassettes of this kind are known, for example from German publications 
DE-GMS 8,014,696 or DE-GMS 8,520,091 or DE-PS 2,729,660. According to 
DE-GMS 8,014,696 the film supporting plate in the base part of the 
cassette is made of a plastic which is, reinforced by carbon fibers. In 
this manner the thickness of the plate can be reduced, because its 
strength is comparable with that of a metal. However a carbon fiber 
reinforced plastic has a greater radiation opacity than a pure plastic. 
Nevertheless due to the reduced thickness of a plate made of carbon fiber 
reinforced plastic a slight advantage is achieved. However, the production 
of carbon fiber reinforced plastic is expensive and costly. 
SUMMARY OF THE INVENTION 
It is therefore an object of the invention to provide a plastic cassette of 
the above described kink, wherein the film supporting plate in its base 
part is simpler and less costly to manufacture while having a comparable 
strength and radiation opacity as the prior art plates. 
In keeping with this object and others which will become apparent 
hereinafter, one feature of the present invention resides in the provision 
of a laminated supporting plate in the base part of the cassette which is 
composed of an intermediate plate of hard foam rubber sandwiched and glued 
between two face plates of thermoplastically bonded carbon fibers. The 
face plates are considerably thinner than the intermediate plate in the 
laminated supporting plate of the present invention. 
In the prior art X-ray sheet film cassettes, the thickness of the above 
described known film supporting plate is about 1.5 mm. The plastics 
component of the prior art plate is the main source of absorption of 
X-rays. In the laminated plate according to the invention, the thickness 
of the plastic component can be reduced by half in comparison with the 
prior art plates, inasmuch as only two comparatively thinner inner and 
outer face plates made of thermoplastically bonded carbon fibers which are 
simple to manufacture are glued to opposite sides of a somewhat thicker 
intermediate plate made of hard foam rubber, which is also easy to 
manufacture and exhibits only a negligible absorption of x-rays. In 
addition, the laminated structure is simpler and cheaper to manufacture 
than the conventional plates using carbon fiber reinforced plastics or 
laminated structures of plastic plates and carbon. 
The novel features which are considered as characteristic for the invention 
are set forth in particular in the appended claims. The invention itself, 
however, both as to its construction and its method of operation, together 
with additional objects and advantages thereof, will be best understood 
from the following description of specific embodiment when read in 
connection with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The X-ray sheet film cassette illustrated in the Figures includes a base 
part 1 which is linked by a hinge 3 to a top part 2. The top part 2 is 
provided with locking elements 4a engageable with a locking mechanism 4 on 
the base part. A top part 2 is formed with reinforcing ribs 2a to which a 
pressure plate 8 of thermoplastic material is welded. A cushion layer 6 is 
glued to the pressure plate 8 and a reinforcing foil 5 is secured to the 
free side of the cushion sheet 6. An X-ray sheet film 7 is supported on 
the base part 1. 
A characteristic feature of the cassette of this invention is the provision 
of a frame 1b in the bottom of the base part in combination with a 
laminated supporting plate 1a which is attached to the frame by welding or 
glueing. In a modification it is also possible to insert the laminated 
plate into a frame which has been either inserted into the base part 
during its production in an injection mold or produced together with the 
base part in the mold by an injection molding process whereupon the plate 
is secured to the frame by a peripheral spraying. The important feature of 
the supporting plate 1a is its laminated construction consisting of two 
face plates 1c made of thermoplastically bonded carbon fibers and a 
somewhat thicker intermediate plate of hard foam rubber 1d, which is 
sandwiched and glued between the two carbon fiber face plates 1c. For 
example, the plate 1d of hard foam rubber can be about 2.5 mm thick, while 
the respective carbon fiber plates 1c have a thickness of about 0.3 mm. 
While the thickness of plastic material in conventional cassettes is about 
1.5 mm, the combined thickness of the thin thermoplastically bonded carbon 
fiber plates 1c has been reduced to 0.6 mm. 
The supporting plate 1a of this invention consisting of the above described 
glued layers is somewhat thicker than the conventional bottom plates or 
cassette bottoms made of carbon fiber reinforced plastics or laminated 
structures composed of carbon fiber material. In spite of this, the 
transmission coefficient of the laminated plate 1a of this invention for 
X-rays is greater than that of the prior art bottom plates, because of 
reduced thickness of components containing the plastic material and due to 
the negligible radiation absorption of the hard foam rubber. The requisite 
strength of the plate of the invention, in spite of the reduced thickness 
of the thermoplastically bonded carbon fiber plates 1c, is obtained by the 
particular laminated arrangement. The manufacturing cost for the laminated 
plate 1a of this invention is substantially lower than the cost of 
cassette base parts of carbon - fiber reinforced plastics or of carbon - 
fiber plates laminated with plastic plates because both the 
thermoplastically bonded carbon - fiber sheets and hard foam rubber sheets 
are mass produced and are commercially available at a low price.