Note: Descriptions are shown in the official language in which they were submitted.
~VO90/096~1 ~ PCT/Csso/00191
DRYING
The present invention relates to the drying
of materials, particularly, but not exclusively, sheet
or web materials such as photographic paper ~nd film.
A number of methods are Xnown for drying
photographic paper, for example that shown in Britlsh
Patent Specificstion GB-A-l56l8g7. This method
involves directing r~diant hest only on to the
non-image-bearing side of the photographic paper as it
travels through a drying chamber ~nd slmult~neously
csusing ~ stream of air to flow over the image-bearing
side oE the paper.
When drying photographic paper, it is as
important to ensure that the paper is not over-dried
as it ls that is not under-dried. The disclosure of
GB-A-l56l897 does not in ~act indicate tha~ this is 8
factor to be taken into consideration.
It is therefore ~n object of the present
invention to provide a method and apparatus for
ensuring that the materisl being dried is not over- or
under-dried.
According to one aspect of the present
invention, there is provided a method of dryin~ a
material comprising the steps of applying heat to at
least one side of the material; and sensin~ the amount
of moisture remaining in the material ~fter it hss
been heated so as to determine whether any further
drying is required.
According to a ~econd aspect of the present
invention, there is also provided ~pparatus for drying
a ma~erial comprising heater mean-~ for applying heat
to at least one s~de of the material, characterised in
th~t at least one sensor is provided for measuring the
amount of moisture remaining in the materisl after it
has received heat from the heater means so as to
determine whether hny further drying is required.
Advantageously,~the he~ter means comprises at
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W~90/Og6?1 PCT/GB90/00191
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least two heating stages, at le~st one sensor being
positioned between adjacent st~ges.
Each sensor m~y be connected to control means
which controls power supplied to the heater means.
The app~ratu-~ m~y further comprise blower
means for blowin~ ~ir on to ~t least one side o~ the
ma~erial, and e~ch sen~or msy be slso connectèd to the
control me~ns in order to control the power 3upplied
to the blowèr mesns.
Measurement o~ the moisture remsining in the
material can be schieYed by any convenient method. In
one method, at least one of the ~en~ors m~y be R
capacitance sensor. Alternatively, contac~ conductive
resistance sensors may be used.
For a better understanding of the present
invention, reference will now be made, by way of
example only, to the accompanying drawin~s in which:-
Figure l is a s~de elevation of drying
~pparatus according to the present invention; snd
Figure 2 is a schematic block diagram of a
circuit which may be used in controlling the apparstus
of Figure l.
Although the following description is
directed to the drying of photographic psper it is
emphasised that it is equally applicable to the drying
of any material, partlcularly in sheet or web form.
Figure l illustrates drying apparatus in
which a sheet or web of photogrsphic paper 2 is being
dried. The paper 2 passes through the ~pparatus with
its emulsion ~ide uppermost.
ln~ra-red heaters 4, 4' are po~itioned below
~he path of tr~vel of the photographic paper 2, and
are arranged in two stages. These heaters 4, 4l ~re
used to heat the wet emulsion layer of the paper, by
conduction, through the base on to which the emulsion
layer is coated. A reflector 18 is positioned around
each heater 4, 4' so that most of the heat ~enerated
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W0~0/0~6_1 PCT/GB9n/00191
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by the heater is directed upwards vn to the base of
the photographic p~per 2.
At the same time as heat is applied to the
paper 2 throu~h its base, unheated Air iS blown on to
the emulsion side of the paper 2 by f~ns 6. This
~ enables water vapour rele~sed from the sur~ace of the
paper 2 to be carried ~way. - -
Squeegee roller~ 8 sre provided-at the entry
to the apparatus, the paper 2 enter~ng the ~pparatu~
between these rollers. The rollers 8 remove surf~ce
water which then p~sses out through a drain outlet 10.
Tr~nsport roll~rs 12 are pro~ided at the exit
from ~he apparatus. These rollers 12 direct the dried
paper 2 on to further processin~ stages, for example,
to cutting apparatus whlch cuts the p~per ~nto
individual prints.
The squeegee rollers 8 and transport rollers
12 are driven (by means not shown) so as to direct the
paper 2 into and out of the drying apparatus.
A sensor 14 is positioned halfway along the
path which the paper 2 takes through the drying
apparstus, that is between heater stages 4 and 4'.
The sensor 14 senses the amount sf moisture left in
~he paper 2 as ~t passes that sensor (~fter p~Qsing
through heaters 4). The sensor 14 uses a propor~ional
capacitance technique to determlne the amount of
moisture remaining in the paper.
From the measurements made by the sensor 14,
the power ~upplied to the hesters 4' which follow
sensor 14 (in the d~rection of travel of the psper) is
controlled so as to, in turn, control the amount of
further drying thst takes place.
Although only one ~ensor 14 is -~hown after
the first two heaters 4, further sensors could be
provided at that position if desired.
A fan 16 circul~tes air in the space 40 to
provide a small quantity of cooling air for the sensor
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W~0/0962t PCT/GB90/001~1
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14 and the backs of reflectors 18.
Wire guides ~0 are provided to ensure that
the paper 2 is transported across the hesters 4, 4' to
the transport-rollers 12. - -
A sensor 22 is positioned after the tran-~port
rollers 12 so ~s to provide ~ finQl checX on the
amount o~ moisture in the paper 2 as it leRves the
apparatus. ~ T ~
A circu~t which may be u~ed to control the
apparatus o~ Figure l i~ shown in Figure 2. The
circuit comprl~es a centrfll logic controller ~4 which
has inputs 26 And 28 from the ~ensors 14 and 22 (not
shown), and outputs 30, 3~, 34 ~nd 36 which are
connected to the fAns 6, fan 16, transport rollers l~
and heaters 4, 4' respectively (also not shown).
The pre~ent invention has the advantage that
the power consumption is minimised and the danger of
overheating the paper is avoided. Also, the amount of
drying is controlled independently of the temperature
or humidity of the eir being used to dry the material.
When the present invention is used in a dryer
which operates with infra-red radiation And unheated
air, it is very fast. In particular, A high level of
power can be applied at the initial stage and then the
need for any further drying determined as described
above.
The present invention c~n be uRed ~n
processing machines to dry coated exposed and
proces~ed material. It can also be u~ed in dryin~ ~ny
web or material, for exsmple in coating operations, or
in drylng chemical solid-Q out of solutions or other
materials.
Although in the ~bove described arrangement,
use is made of non-contacting heaters, cont~ct heatin~
using a hot surface can also be employed where
appropriate. For exsmple, the wire guides 20 in
contact with the-base of the paper could be heated
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WO9~0~621 PCT/GB90/00191
_5~
directly. Furthermore, recycled hot air can also be
employed.
Capacitance sensing is the preferred
srrangement, although contact conductive resistsnce
sensing can ~lso be used.
Other heating arrangements could al~o be
employed, for example tho~e using in~ra-red or
microwave radlation.
Although as described above the arrangement
utilises heating the material from one side and
blowin~ air from the other side, it i~ emphasised that
any other suitable arrangement could be used as long
as the material is heated from ~t least one side. For
example, both the heating and the blowing of air could
be on the same side of the material. The material
could be he~ted from more than one side. Similarly,
the air could be blown from more than one side.
Although ~s descrlbed above, the psper can
pass through two heating stages, it is emphasised that
any suitable number of heating stages can be employed
as desired.
Furthermore, as an alternative to the heating
stages being provided by physically successive
heaters, they could be provided by the paper being
exposed to the same heaters more than once by
recycling the paper through the same heaters.
The arrangement described above has the added
advantage th~t it can be usPd under any climatic
conditions without requiring ~urther ad~ustment.
Naturally, adjustment will need to be made to
accommodate materisls having different physical
characteris~icsO
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