Appeal No. 1998-1735 Page 5
Application No. 08/339,980
die it is cooled by a blower as it enters the forming chamber where it is formed into a tube,
which gives rise to the establishment of a phase transition point
(frost line), that is, the point where the plastic changes from liquid to solid state.
According to the appellant, the thickness of the plastic can become non-uniform and its
state unstable if the phase transition point moves from its optimal position, such as might
be caused by variations in temperature between day and night and summer and winter
(specification, page 4). The appellant’s invention solves this problem by providing infrared
sensors that directly monitor the position of the frost line in the forming chamber. If the frost
line strays from the desired position, an adjustment is then made in one of the operating
parameters of the apparatus to cause it to move back to the desired position. As
manifested in independent claim 4, the invention comprises, inter alia,
means for monitoring phase transition of said molten
plastic into solidified plastic film and adjusting operation
of said apparatus to maintain plastic material phase
transition occurrence at a preselected position downstream
of said die (emphasis added).
According to the examiner, the admitted prior art meets all of the terms of claim
4 except for the means for monitoring the phase transition of the plastic, however, this
would have been obvious to one of ordinary skill in the art in view of the teachings of
Lenius. We do not agree.
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