Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
DOCKET NO. 1955/OA223
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PROCESS AND APPAR~TUS FOR
TREATING A WEB OF PAPER
~IELD OF lH~; INYENTION
The present invention is directed to a process and apparatus for treating a --
web of paper material. More speci~lcally, thepresent invention is directed to a process
and apparatus that includes at least two rollers gaps disposed along the path of a paper
web and a drying device disposed along the path of the paper web between the at least -
two roller gaps.
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BACKGROU~ OF TEIE INVENlION ~-
D~-PS 34 27 967 discloses a web of paper material having a high degree of - -
moisture which runs through a roller gap of a calender. The calender can be, forexample, a compression or a glazing calender. A drying device is used to reduce the
moisture in the paper web after the web has passed through the calender, thereby lowering
25 the moisture content to a desired value. The high moisture content in the paper web in
conjunction with the pressure occuning in the roller gap results in highly compressed
paper, e.g., silicon raw paper or thick vellum paper, which has relatively good properties
in volumetric weight, porosity, transpaTency and smoothness. While the smoothness
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property is reduced by the post drying step, this procedure still provides better results than
30 conventional procedures where paper is dried solely by controlling the temperature of the
calender rollers. Additionally, it should be noted that if the smoothness quality of the
paper is not an important factor, the line pressure in the roller gaps can be reduced and
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thus, a lower compression is achieved.
SUMMARY OF T~IE INVENTION
An object of the present invention is to prepare a paper web having the best
S possible smoothness qua]ity while simultaneously reducing the compression in the roller
gaps.
The present invention achieves this object with an apparatus which process-
es a paper web by passing the paper web through at least one roller gap, then drying the
paper web in a drying device, and then passing the paper web through at least one more
10 roller gap.
Because the drying step is not achieved after passing through all of the
roller gaps, but is disposed intermediate of the roller gaps, the disadvantages norrnally
associated with drying, namely, a resurrection (i.e., an expansion and lifting) of the paper
fibers, which results in a reduction of the lustre and smoothness of the paper, are
15 eliminated by pressing the paper web in at least one more roller gap. While there is less
improvement in the smoothness quality of the paper web in the roller gap treatments
following the drying step than those treatments before the drying step, the final result is
still a paper product which has a high degree of smoothness.
Alternatively, one can produce a paper web having a smoothness quality
- 20 which meets conventional requiremlents by using a lower compression in the roller gap by
reducing the line pressure. An additional advantage of the intermediate drying step of the
present invention is tha~ one can achieve a strong reduction of the moisture and observe a
relatively strong resu~ection of the paper fibers, yet these fibers will flatten out in the
subsequent pressing step(s). The present invention therefore permits working with very
25 high moisture content in the paper web in the roller gaps, which are coMected in series,
without having to keep the rollers themselves at a high temperature. Accord;ngly, elastic
rollers with lower temperature resistant asbestos-substitute coverings can be used instead
of asbestos coverings, the use of which are no longer permitted in most countries.
All of these advantages of the present invention are even more important
30 when the drying device is coupled to only one subsequent roller gap. This one subsequent
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roller gap is sufficient, as a rule, to flatten the fibers which have been raised during the
drying step.
Further features of the present invention permit the drying effect of the
paper web to be changed in a direction transverse to a paper moving direction (i.e., across
5 the width of the paper~, thereby selectively varying the amount of reduction of the
moisture in zones across the paper web.
Additional features of the present invention permit for the measurement of
various properties such as the moisture content, lustre and/or smoothness across the entire
width of the paper. Deviations from a preferred prof~e can be corrected by proper
10 control of a plurality of individually controlled drying elements.
Still further features of the present invention include a suction device being
provided in the drying device, so that the stearn created during drying does not settle as ~
condensate on thepaper web. ~ ;
The d3:ying can be accomplished, for exa nple, by radiation heat transfer, ~;
15 convection heat transfer, or by conduction heat transfer by disposing a heating line in a
plurality of heated rollers which come into contact with the paper web. Regardless of the
drying method used, the drying device is designed to permit an intensive heat transfer :
without exerting pressure on the paper web. -:
An embodiment of the present invention which includes the drying device
20 being disposed in the paper path between the second lowest roller g~p and the lowest
roller gap has the advantage that the highest line pressure can exist in the lowest roller
gap. The reduction of the moisture is achieved by the drying equipment, which isconnected in series to the roller gaps. The drying equipment creates only a small loss in
smoothness in the paper gap due to the use of the lowest roller gap which has the highest
25 line pressure.
An embodiment of the present invention where the drying device is
disposed at the same height as the second lowest roller gap and the paper web is returned
to the lowest roller gap below the drying device per nits the paper web to dry further in
the atmosphere for a predetermined period of time, so that a further evaporation of the
30 heated paper web can take place before the paper web is processed in the last roller gap.
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BRIEF DESCRIPTION OF T~E DRAWINGS
The above and still further objects, features and advantages of the present
invention will become apparent upon consideration of the following detailed description of
a specific embodiment thereof, especially when taken in conjunction with the accompany-
5 ing drawings wherein like reference numerals in the various figures are utilized todesignate like components, and wherein:
Fig. 1 is a schematic view of an apparatus for processing a paper web
according to the present invention; and
Fig. 2 is a schematic top view of a measuring station and a dryer according
10 to the present invention.
` DETAILED DESCRIPl'ION OF T~E PRESENT INVENTION
Referring now to Fig. 1, a web of paper material 1 that is to be processed
is unwound from roll 2. The paper web 1 passes through a glazing calender 3, a drying
15 device 4, a measuring station 10 and is then wound up on a take-up roll 5. The glazing
calender 3 includes a vertical stack of hard rollers 6 and a vertical stack of soft rollers 7.
Hard rollers 6 can be made of, for exarnple, steel. Soft rollers are preferably lined with a
cover that is made from asbestos-substitutes. Roller gaps 8 are formed between adjacent
rollers and the paper web 1 is guided through the roller gaps 8 by lead rollers 9.
As iUustrated in Fig. 1, paper web 1 exits horizontally from the second
lowest roller gap 8a and runs horizontally along path la through drying device 4. The
paper web 1 returns to the lowermost roller gap 8b via a second horizontally disposed
path lb which is disposed below drying device 4. The finished paper web 1 then runs
through measuring station 10. Measuring station 10 includes a sensor 11 which can move
25 back and forth over the entire width of paper web 1 to measure a variety of web proper-
ties such as moisture, lustre and/or smoothness. Sensor 11 transfers a signal representing
hese properties to a regulator 13 through an inlet port 12. The preferred properties are
input to regulator 13 through a second inlet port 14. The proper control signals are then
determined by regulator 13 and forwarded to drying device 4 from exit port 15.
Drying device 4 includes several drying elements 16 which are disposed
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adjacent to one another. The drying action of each element 16 can be controlled indepen-
dently from one another. One could therefore dry some sections of web 1 more so than
others, and change the moisture, lustre and smoothness properties of web 1. Drying
device 4 also has a suction device 17 to remove steam created during the drying process.
5 The drying process can take place, for example, by blowing hot air through an infrared
radiation heater, by disposing a heating line in a plurality of heated rollers or by any other
method that is known in the art.
In operation, a web of paper material 1 having a high degree of moisture
content, e.g., 20%, enters into glazing calender 3 from take-off roll 2. Web 1 runs
10 through several roller gaps 8, except for the lowermost roller gap 8b, and produces a
paper having a relatively good smoothness property. A further improvement in the paper
smoothness can be seen when at least one part of the hard rollers 6 is heated and/or when
the covering of the soft rollers 7 is heated. This improvement in paper smoothness is due
to the change in the elasticity of the paper web 1 as its temperature increases. The drying
15 device 4 reduces the relatively high moisture content in the paper web 1 to substantially
the desired value, e.g., to 5%. However, drying device 4 causes the fibers of the paper
web 1 to rise, at least partially, on their surface. For this reason, the present invention
requires that a further pressure treatment take place in the lowest roller gap 8b. This
pressure treatment occurs with reduced moisture and is suffilcient to produce the desired
20 high smoothness.
Variations from the illustrated design examples are possible in many
respects, without changing the basic concept of the invention. For example, the paper can
be treated in several successive compact calen~ers, and the drying device can be disposed
at the end of the treatment steps, yet still, in any case before the paper web is pressure
25 treated in the last roller gap.
Having described the presently preferred exemplary embodiment of a
process and apparatus for treating a web of paper material in accordance with the present
invention, it is believed that other modifications, variations and changes will be suggested
to those sldlled in the art in view of the teachings set forth herein. It is, therefore, to be
30 understood that all such variations, modifications, and changes are believed to fall within
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the scope of the present invention as defined by the appended claims.
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