U.S. patent number RE28,459 [Application Number 05/313,158] was granted by the patent office on 1975-07-01 for transpiration drying and embossing of wet paper webs.
This patent grant is currently assigned to Scott Paper Company. Invention is credited to Richard I. Cole, Samuel Greenhalgh, Donald E. Holcroft, Edward A. Milligan.
United States Patent |
RE28,459 |
Cole , et al. |
July 1, 1975 |
Transpiration drying and embossing of wet paper webs
Abstract
A method and apparatus are disclosed for drying a wet paper web
by passing gaseous fluid such as air which may be at an elevated
temperature, up to about 1500.degree. F., through the web while it
is supported upon a foraminous surface. The arrangement of the
apparatus whereby the heated air passes through the web prior to
passing through the foraminous surface enables the use of higher
temperatures than heretofore possible. A method and apparatus for
embossing the wet paper webs during drying are also disclosed along
with the new products formed by the method and apparatus. The
embossing is accomplished in one of several different ways, which
involve rearranging the fibers in the web before the web is dried
and interfiber bonds are formed. The rearranging may be done by a
fluid pressure differential through the web while it is supported
on a contoured foraminous surface such as a woven wire, by fluid
flow at high speeds through the web, or by mechanical pressure
against the web. In some embodiments, holes may be formed in the
web during embossing by subjecting the web to sufficient fiber
rearrangement in spaced localized areas to form breaks or create
apertures. Paper web products are formed which have raised
contoured portions in which substantially all of the bonds between
fibers are intact so that the raised contoured portions passes
substantial stiffness and permanency.
Inventors: |
Cole; Richard I. (Springfield,
PA), Holcroft; Donald E. (Claymont, DE), Milligan; Edward
A. (Wilmington, DE), Greenhalgh; Samuel (Philadelphia,
PA) |
Assignee: |
Scott Paper Company
(Philadelphia, PA)
|
Family
ID: |
27405651 |
Appl.
No.: |
05/313,158 |
Filed: |
December 7, 1972 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
555748 |
Jun 7, 1966 |
|
|
|
Reissue of: |
649776 |
May 31, 1967 |
03432936 |
Mar 18, 1969 |
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Current U.S.
Class: |
34/306;
162/115 |
Current CPC
Class: |
F26B
13/101 (20130101); D21F 5/18 (20130101); F26B
13/16 (20130101); D21F 5/182 (20130101) |
Current International
Class: |
F26B
13/16 (20060101); D21F 5/00 (20060101); D21F
5/18 (20060101); F26B 13/10 (20060101); F26b
003/06 () |
Field of
Search: |
;34/6,16,18,41,92
;162/113,114,115 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Camby; John J.
Attorney, Agent or Firm: Vickrey; R. Duke Foley; W. J.
Parent Case Text
This application is a continuation-in-part of our previous
application, Ser. No. 555,748, filed June 7, 1966, now abandoned,
entitled Transpiration Drying and Embossing of Wet Paper Webs.
Claims
What we claim is:
1. A method for drying a substantially continuous wet web of paper
fibers issuing at high speed from a papermaking machine, including
the steps of pressing the web into contact with a foraminous
surface, advancing said web into a drying zone while supporting it
on said foraminous surface, contacting the surface of said
supported web most remote from said foraminous surface with a
gaseous fluid under a pressure greater than atmospheric pressure,
creating a pressure drop and a flow of gaseous fluid through the
web from the surface most remote from said foraminous surface to
the surface adjacent said foraminous surface, advancing said web
out of said drying zone, and withdrawing said web from said
foraminous supporting surface.
2. A method according to claim 1, wherein said gaseous fluis is air
at a temperature of up to about 1,500.degree. F.
3. A method according to claim 1, wherein said gaseous fluid is air
at a temperature of from about 300.degree. F. to about 800.degree.
F.
4. A method according to claim 1, including the step of reducing
the pressure of the surrounding gaseous fluid at the surface of
said web adjacent said foraminous surface to a value lower than
atmospheric pressure.
5. A method according to claim 1, wherein said foraminous surface
contains a plurality of openings arranged in a predetermined
pattern, and including the step of forcing the cellulosic fibers in
portions of wet web covering said openings in said foraminous
surface to shift their positions relative to one another and to the
remainder of said web so that said web portions are forced
generally toward and into said openings at least partially out of
the plane of said web and into the plane of said foraminous
surface.
6. A method according to claim 5, wherein a web is momentarily
subjected within said drying zone to a stream of fluid across at
least a portion of its width which causes said fibers to shift
their positions.
7. A method according to claim 5, wherein said cellulosic fibers
are re-arranged to form apertures of a larger size than the
interstices between the cellulosic fibers of the wet paper web,
said apertures being located generally at the outermost extremities
of said seb portions which are forced generally toward and into
said openings.
8. A method according to claim 5, wherein said forcing step is at
least partially performed prior to the advance of said supported
web into said drying zone.
9. An embossed cellulosic fiber web .Iadd.having a basis weight in
the tissue or towel product range, .Iaddend.comprising a generally
flat sheet defined by randomly interwoven cellulosic fibers between
two parallel planes, said fibers being bonded together at randomly
spaced points throughout the paper matrix where they contact one
another by the bonding process associated with papermaking, said
sheet having regularly spaced portions thereof extending beyond at
least one of said planes from the space between said planes, said
portions representing raised contoured portions of said sheet,
.Iadd.and being spaced to have a concentration of from 36 to 760
per square inch of sheet, .Iaddend.substantially all of the bonds
between the fibers in said raised contoured portions being intact,
whereby said raised contoured portions of said sheet possess
substantial stiffness and permanency.
10. An embossed cellulosic fiber web according to claim 9, wherein
said raised contoured portions of said sheet terminate at their
outermost extremities in an annular edge defining an opening
through said web.
11. A drying unit for a papermaking machine, comprising a moveable
endless foraminous surface upon which a paper web to be dried is
fed so as to leave one surface of said web exposed, hood means
disposed adjacent at least a portion of said surface contacted by
said paper web and adapted to substantially enclose said portion so
as to form a drying zone, supply means for introducing gaseous
fluid under pressure into said hood means, and vacuum bias means
disposed adjacent said foraminous surface opposite the portion
thereof contacted by said web and enclosed by said hood means, said
vacuum bias means being adapted to draw gaseous fluid through said
web while it is in contact with and supported by said surface in
order to effect drying of said web.
12. A drying unit according to claim 11, including first means
contacting the exposed surface of said web and adapted to press the
web into contacting engagement with said surface along an initial
line of contact between said web and said surface, and second means
contacting the exposed surface of said web and adapted to press the
web into contacting engagement with said surface along a second
line of contact adjacent the removal point of said web, said second
line being separated from said initial line by said drying zone in
which the pressure hood and the vacuum bias means cooperate to
create a pressure drop through the web so as to cause removal of
moisture therefrom.
13. A drying unit according to claim 11, wherein said supply means
include means for heating said gaseous fluid prior to its
introduction into said hood means.
14. A drying unit according to claim 11, wherein said moveable
endless foraminous surface is a foraminous cylindrical shell
mounted for rotation about its central axis and said vacuum bias
means are disposed on the interior of said shell.
15. A drying unit according to claim 14, wherein said moveable
endless foraminous surface is a foraminous cylindrical shell
mounted for rotation about its central axis and said vacuum bias
means are disposed on the exterior of said shell adjacent the
surface thereof, and arranged to operate through the openings in
successive transverse segments of said shell during rotation
thereof, which successive transverse segments have previously
supported the web in the drying zone and have passed, during
rotation, out of contact with said web.
16. A drying unit according to claim 14, including an endless
flexible foraminous belt entrained over said cylindrical shell in
at least partial wrapping engagement therewith.
17. A drying unit according to claim 15, including an endless
flexible foraminous belt entrained over said cylindrical shell in
at least partial wrapping engagement therewith.
18. A drying unit according to claim 11, wherein said moveable
endless foraminous surface is an endless flexible foraminous belt
entrained about a foraminous cylindrical shell mounted for rotation
about its central axis, said vacuum bias means are disposed on the
exterior of said shell adjacent the surface thereof, said supply
means include means for heating said gaseous fluid prior to its
introduction into said hood means, and including a plurality of
cylindrical rolls rotatably mounted and disposed in spaced apart
relation adjacent said shell, said endless flexible foraminous belt
being entrained about said cylindrical shell and said cylindrical
rolls in at least partial wrapping engagement therewith, means
operably connected to said belt for moving it through an endless
path over said rolls and said shell.
19. A drying unit according to claim 11, wherein said foraminous
surface has openings therein arranged in a predetermined pattern
and said unit includes means to force the cellulosic fibers in
portions of said web covering said openings to shift their
positions relative to one another prior to movement of said web
through said drying zone so that said web portions are forced
generally toward and into said openings at least partially out of
the plane of said web and into the plane of said foraminous surface
so as to form raised contoured portions in said web portions having
substantial stiffness and permanency.
20. A drying unit according to claim 19, wherein said means include
means to exert fluid pressure momentarily upon said web to cause
the fibers thereof to shift their positions.
21. A drying unit according to claim 19, wherein said means are
arranged to operate upon said web prior to movement of said web
into said drying zone.
22. A drying unit according to claim 19, wherein said foraminous
surface has a plurality of upstanding, projections in the portions
thereof between said openings, and said fiber forcing means are
adapted to force the fibers in portions of said web covering said
projections to shift their positions relative to one another so
that said web portions are forced upwardly out of the plane of said
web and above the plane of said foraminous surface.
23. In a drying unit for a papermaking machine, having a movable
endless foraminous carrying member having an undulating upper
surface which is adapted to carry a wet paper web through a drying
region, and drying means for passing a gaseous fluid through said
web within said drying region for removing moisture from said web,
the improvement comprising embossing means for initially
simultaneously directing gaseous fluid at high velocity toward the
side of said web spaced from said carrying member and applying a
high vacuum to the side of said carrying member and spaced from
said web, whereby said web is pressed into conformity with said
undulating upper surface and retains its resulting shape when
dried.
24. The improvement in a drying unit for a papermaking machine
according to claim 23, wherein said embossing means include a
nozzle disposed adjacent to but spaced from the side of said
carrying member, said nozzle being adapted to direct a gaseous
fluid at high velocity against successive transverse segments of
said web as it is carried on said foraminous carrying member toward
said drying region, a vacuum box disposed adjacent the opposite
side of said carrying member and opposite said nozzle, said vacuum
box being adapted to receive and remove substantially all of the
gaseous fluid emitted by said nozzle which passes through said
web.
25. The improvement in a drying unit for a papermaking machine
according to claim 24, wherein siad gaseous fluid is air at an
elevated temperature.
26. The improvement in a drying unit for a papermaking machine
according to claim 24, wherein said gaseous fluid is steam.
27. The improvement in a drying unit for a papermaking machine
according to claim 24, wherein said moveable endless foraminous
carrying member comprises a woven wire cloth.
28. In a method for drying a wet paper web, in which the wet paper
web is carried through a drying region upon a movable endless
foraminous carrying member having an undulating upper surface while
a gaseous fluid is passed through said web to remove moisture
therefrom, the improvement comprising simultaneously directing
gaseous fluid at high velocity against the side of said web spaced
from said carrying member and creating a high vacuum adjacent the
side of said carrying member spaced from said web, wherein said web
is pressed into conformity with said undulting upper surface and
retains its resulting shape when dried.
29. The improvement in a method for drying a wet paper web
according to claim 28, wherein said high vacuum is created adjacent
the side of said carrying member spaced from said web in a position
substantially opposite the position toward which the gaseous fluid
is directed, so that substantially all of the gaseous fluid
directed against successive transverse segments of said web and
passing through said web is received and withdrawn by said
vacuum.
30. A drying unit for a papermaking machine, comprising:
a movable endless foraminous carrying member,
means for pressing into contacting engagement with a portion of the
surface of said carrying member a wet paper to be dried while
leaving one surface of said web exposed,
hood means disposed adjacent at least a portion of the surface of
said carrying member contacted by said paper web, said hood means
being adapted to substantially enclose said portion so as to form a
drying zone,
supply means for introducing gaseous fluid into said hood means,
and
vacuum bias means adapted to draw said gaseous fluid successively
through said paper web and said foraminous carrying member while
said paper web is in contact with and supported by said surface so
as to dry said web.
31. A drying unit according to claim 30, wherein said carrying
member is a foraminous cylindrical shell.
32. A drying unit according to claim 30, wherein said carrying
member is a foraminous woven wire belt.
33. A drying unit according to claim 30, wherein said carrying
member is a foraminous woven wire belt entrained over a foraminous
cylindrical shell.
34. A drying unit according to claim 30, wherein said vacuum bias
means are disposed adjacent the portion of said carrying member
supporting said web, and opposite the surface of said carrying
member contacted by said web.
35. A drying unit according to claim 31, wherein said vacuum bias
means are adapted to act through portions of said foraminous shell
which have passed out of contact with said web.
36. A drying unit according to claim 33, wherein said vacuum bias
means are adapted to act through portions of said cylindrical shell
which have passed out of contact with portions of the wire
supporting said web.
37. A drying unit according to claim 11, wherein said movable
endless foraminous surface is an endless flexible foraminous belt
entrained over a foraminous cylindrical shell.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the treatment of wet paper webs and, more
particularly, to a new and improved method and apparatus for drying
wet paper webs, which drying is alternatively accompanied by
embossing or by another related fiber rearranging treatment, and to
the products formed thereby.
2. Description of the Prior Art
Wet paper webs are normally dried by mechanically pressing them and
by placing them in contact with a heated surface. On a conventional
papermaking machine such drying occurs in a drying section
comprising one or more rotatably mounted drum dryers over which the
web is entrained. In many instances, the web is creped from one of
the rotatable drum dryers as opposed to leaving it as a flat sheet.
The web is then removed from a large drum dryer called a Yankee
dryer, at a point angularly displaced from the point where it is
pressed onto the dryer, normally by creping it with a creping
doctor blade. In some instances, after leaving the Yankee dryer,
the paper web is then fed into an afterdrying section which
comprises a plurality of rotatably mounted, steam-heated, drum
dryers over which the paper web is entrained in partial wrapping
engagement therewith. Commercial paper machines normally utilize
one or more of the above-described drying systems.
It is well-known that such apparatus is extremely complicated and
expensive, requiring exceptionally high capital investment.
Furthermore, maintenance costs of Yankee type drum dryers are quite
high. The cost of supplying steam to these multiple drum dryers for
heating the dryers is quite high and the means for distributing the
steam to each drum dryer is quite complex and expensive. In
addition, the foregoing apparatus does not inherently maintain
cross-machine drying uniformity as it is difficult to maintain
uniform drum surface temperatures and humidity throughout the
apparatus.
More efficient and less costly schemes for the drying of wet paper
webs have been investigated in the past but have largely proved
unacceptable and uneconomical. It has long been recognized that a
system of drying wet paper webs uniformly at high drying rates
would be desirable so that the drying function could be performed
on relatively inexpensive equipment occupying a relatively small
floor space.
It is well-known that the drying rate of a wet fibrous web is
partly a function of the amount of moisture carried in the web,
normally expressed in terms of percent by weight of the web, and
the amount of heat transferred to the moisture in a given time in
order to cause it to vaporize. A well-known principle of
thermodynamics is that the heat transfer from a moving fluid such
as a gas to a surface increases with the velocity of the fluid over
the surface. Conventional drying equipment has been designed with
the intention that the above principles would be applied to
advantage, but it has been discovered that the new methods of the
invention, for drying wet paper webs, more advantageously apply
such principles.
For example, dryer hoods are presently commonly employed in
connection with Yankee dryers and other types of rotary drum dryers
mentioned above. These hoods are provided with means for
introducing drying air under pressure and at certain velocities and
with means for removing the air at various points about the hood.
The air is caused to sweep one exposed surface of the wet web as it
progresses around the dryer. Vapors having a high moisture content
are exhausted from the hook and low humidity drying air introduced
into the hood and directed toward the surface. In other instances,
methods of drying paper webs by fluidized beds have been attempted
and have been largely unsuccessful.
In each of the above instances, contact of the drying air with the
web occurs only at the surface and very little movement or contact
results between the drying gas and the moisture. Furthermore, heat
transfer depends upon the thermal conductivity of the moisture, the
fibers in the web, and, in the case of a Yankee dryer, the thermal
conductivity of the dryer shell.
It is a principal object of the present invention to provide a new
and improved method and apparatus for drying wet paper webs.
It is an additional object of the invention to provide a new method
and apparatus for drying wet paper webs by transpiration of gaseous
fluids through the webs.
BRIEF SUMMARY OF THE INVENTION
The method of the invention involves the use of a moving gaseous
fluid, generally air at an elevated temperature, flowing
transversely through the web, directly in contact initially with
the moisture carried in the interstices and pores of the web and,
finally, in contact with substantially all of the fibers in the
web. In accordance with the invention, movement of the gaseous
fluid is primarily through the web from one facing surface to the
other resulting in contact by the moving gaseous fluid of
substantially all of the fibers forming the web. It has been found
that the above process of drying webs by transpiration of a gaseous
fluid through a web results in a very rapid rate of heat transfer
from the gaseous fluid to the moisture on the web causing it to
quickly attain its heat of vaporization. The gaseous fluid also
provides a means for removing the vaporized moisture from the web
to a remote point where it can be exhausted, condensed for reuse,
or otherwise disposed of.
As further distinguished from previously employed drying processes,
the method of the invention makes possible the removal of moisture
from a wet by mechanical separation. It will readily be appreciated
that this could not be accomplished by prior art drying methods
where gaseous fluid was not passed through the web. In accordance
with the invention, large amounts of moisture are rapidly removed
from a wet paper web by the gaseous fluid passing through the web
and generally between and around the fibers thereof.
The following example clearly illustrates the increase in drying
rate which is achieved by the method and apparatus of the
invention. A conventional afterdryer section comprising five steam
heated drying cans will dry a creped wet paper web having a basis
weight of 13.4 pounds per 2,880 ft..sup.2 and a water content of
35% by weight while the web is traveling at 2,000 feet per minute.
The web is dried to the point where it contains 5% water by weight.
In that case, drying occurs over a length of web travel of about 58
feet. At any given time, 47 feet of the web are actually in contact
with the surface of the drying cans and 11 feet of the web are in
the draws between the drying cans.
Apparatus capable of performing the method of the invention,
wherein a pressure drop of 10 inches of water is created through
the web and air at a temperature of 600.degree. F. is introduced to
one surface of the web, accomplishes drying of the same web at the
same speed described above in a length of web travel of
approximately 11.5 feet. If a pressure drop of 30 inches of water
through the web is employed with air at 600.degree. F., the same
degree of drying can be achieved in a length of web travel of about
7.25 feet.
The overall efficiency of the above-described process has been
found to be dependent in part upon the velocity of the gaseous
fluid through the web. In the case of wet paper webs which have
been recently formed, substantially no firm interfiber bonds have
been established. Therefore, these transpiration velocities and the
corresponding pressure drops through the web must be carefully
controlled to avoid web breakage where this is undesirable.
In the course of establishing feasibility of the above process, new
and improved web handling and drying apparatus was contrived which
enables the recently formed web to withstand the pressure drops
involved and which makes it possible to dry the paper webs by
transpiration of a gaseous fluid through the webs. The apparatus of
the invention comprises, as a drying unit for a papermaking
machine, a movable endless foraminous surface upon which a paper
web to be dried is fed into engagement therewith. Hood means are
disposed adjacent at least a portion of the foraminous surface
contacted by the paper web and adapted to substantially enclose
this portion. Supply means are provided for introducing gaseous
fluid under pressure into the hood means and vacuum bias means are
disposed adjacent the foraminous surface opposite the portion of
the web enclosed by the hood means. The vacuum bias means are
adapted to draw gaseous fluid through the web while it is in
contact with and supported by the foraminous surface in order to
effect drying of the web.
By passing gaseous fluid through the wet paper web prior to passing
it through the foraminous surface in contact with the web, it has
been found possible to utilize gaseous fluid at an elevated
temperature without deleteriously affecting the web. For example,
air up to 1500.degree. F. can be utilized for drying the wet paper
webs without destroying the physical properties of the web.
To anyone familiar with conventional web drying equipment and
techniques employed in papermaking, the following comparative
examples will more clearly illustrate the outstanding advance which
the present invention has made possible. In a typical arrangement
in a conventional papermaking machine, a sheet of tissue grade
paper having a basis weight of approximately 13 pounds per 2,880
square feet, the paper is partially dried on a Yankee dryer and is
creped by removing it from a Yankee dryer with a doctor blade. The
creped tissue paper is then fed into an afterdrying section. At the
point of introduction in the afterdryer section, the web consists
of approximately 65% pulp and 35% water by weight. In the
afterdryer section, the web is entrained in partial wrapping
engagement over five or more steam heated drying cans on which the
average evaporation rate typically ranges from about 2 to about 5
pounds of water per hour per square foot of circumferential area.
The sheet issuing from the afterdryer normally comprises 95% pulp
and 5% water by weight. The above-described afterdryer section,
including the drying cans, typically comprises 25 feet or more of
the total length of the paper machine. Furthermore, the capital
investment for such afterdrying equipment is quite substantial.
The same web can be removed from the Yankee dryer and dried on a
single transpiration dryer of the invention in accordance with the
method of the invention to the point where it comprises 95% pulp
and 5% water by weight. In a typical situation, the transpiration
dryer required to perform this task costs substantially less than
the afterdrying equipment as described above and occupies only
about 8 feet of the total length of the paper machine. Rates of
drying or water removed of up to about 60 pounds of water per hour
per square foot of circumferential area are possible depending upon
the nature of the web being dried and the parameters of the drying
process.
As will become apparent from subsequent description, the
transpiration drying apparatus of the present invention may be
employed at other positions in a paper machine and to treat a web
having vastly different moisture characteristics. Another very
important advantage of the transpiration drying process and
apparatus of the invention is the elimination of the elaborate
procedures and apparatus previously employed to insure that an even
moisture profile is present in the finally dried web. This even
moisture profile was difficult to achieve with the steam heated
drying cans and Yankee dryers previously employed.
A further discovery made in conjunction with the above-described
method and apparatus of the invention is that by embossing or
otherwise performing a related texturizing treatment on the paper
web prior to drying, a new and improved paper web product is formed
having properties distinguishing it from webs so formed or treated
by conventional processes. Thus, it was quite suprising to discover
that the pressure differentials created in the transpiration drying
apparatus and utilized advantageously for the transpiration drying
process can be employed in combination and cooperation with certain
modifications or provisions in the web supporting apparatus to
emboss or otherwise texturize the recently formed wet paper sheet.
Alternatively, slight additions or modifications to the apparatus
have been discovered which make possible the accomplishment of this
new process and the formation of these new products. These
modifications involve means to apply pressure to portions of the
wet web to cause the fibers to locally shift their relative
positions in the desired manner.
The most advantageous form of apparatus for causing fiber
rearrangement or a shift in the relative positions of fibers in the
web to emboss or texturize it includes means for creating a higher
pressure differential through the wet web carried on the foraminous
surface initially prior to movement of the web through the final
drying zone. In a specific embodiment, the apparatus includes means
for directing a gaseous fluid such as air or steam at high velocity
toward the wet paper web while it is supported on a foraminous
surface backed by a high vacuum box adapted to receive the gaseous
fluid passing through the web and to enhance its flow through the
web.
For reasons that will be presented subsequently, it has been
discovered that by embossing, texturizing or otherwise altering the
relationship of the fibers comprising the sheet to one another
while the web is wet and causing the fibers to retain their new
positions until drying of the web has occurred, new products are
formed which have substantially different properties attributed to
them by this particular embossing or texturizing treatment. That
is, these webs have properties which are different in many respects
from the properties which would be found in a paper sheet or web
which was dried by normal techniques and subsequently embossed or
mechanically treated.
It has been discovered that many different types of embossing or
texturizing may be performed. In one typical situation where a
plurality of projections are formed in the sheet by pressure from
the opposite side, the projections formed in the sheet of the
present invention demonstrate a greatly increased stiffness and
permanency in the sheet than is the case with normal mechanical
embossings. These properties are desirable in certain types of
paper products, such as wipers, into which such paper may
advantageously be converted after formation. In addition, it is
possible by means of the invention to form a foraminous sheet in
which holes are present at predetermined and desired positions.
Obviously, there are many applications for a product of this
configuration with these properties. Thus, it is a further object
and advantage of the present invention to provide a new and
improved method and apparatus for embossing a paper web.
It is a still further object and advantage of the invention to
provide a method and apparatus for forming a new and improved paper
product, distinguished by novel physical properties caused by
embossing or texturizing immediately subsequent to sheet formation
and immediately prior to or during sheet drying.
Additional objects and advantages of the present invention will
become apparent from the following detailed description thereof,
when read in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic elevation view of a paper machine
incorporating a transpiration dryer of the invention and capable of
performing the method of the invention,
FIG. 2 is an elevation view of a preferred embodiment of a
transpiration dryer of the invention,
FIG. 3 is a sectional view taken along line 3-- 3 of FIG. 2,
FIG. 4 is a greatly enlarged view of a portion of FIG. 3,
FIG. 5 is a greatly enlarged perspective view of a portion of the
foraminous dryer shell and the foraminous layer arranged in contact
therewith,
FIG. 6 is a sectional plan view of an alternative embodiment of the
invention,
FIG. 7 is a sectional elevation view of an additional alternative
embodiment of the invention,
FIG. 8 is a sectional end view of a still further alternative
embodiment of the invention,
FIG. 9 is a sectional side elevation view of a still further
alternative embodiment of the invention,
FIG. 10 is a sectional side elevation view of a still further
alternative embodiment of the invention,
FIG. 11 is a sectional side elevation view of the transpiration
drying apparatus of the invention including means for
embossing,
FIG. 12 is a sectional elevation view of a transpiration drying
apparatus of the invention illustrating alternative means for
embossing,
FIG. 13 is a partial sectional elevation view of apparatus
according to the invention illustrating an alternative method and
apparatus for embossing,
FIG. 14 is a perspective view of a typical product formed in
accordance with the invention,
FIG. 15 is a perspective view of an alternative embodiment of a
product formed in accordance with the invention, and
FIG. 16 is a sectional elevation view of transpiration drying
apparatus of the invention illustrating alternative means for
embossing.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the method of the invention, a wet web of paper fibers is fed
into contact with a foraminous supporting surface and advanced in
the supported condition on the foraminous supporting surface into a
drying zone. The feature of supporting the web during drying is
extremely important since a wet paper web, unlike many other webs,
has very little bonding between the fibers thereof and generally
comprises only randomly interwoven paper fibers held together by
mechanical entanglement. It is well-known to those skilled in the
art that bonds are created in a paper web primarily during the
drying thereof, although the exact physical and chemical mechanism
causing bonding is not clearly understood. In fact, one of the
reasons transpiration drying of wet paper webs has not been
employed in the past is believed to be due to the fact that it was
not considered possible to adequately support a wet paper web while
passing the required amounts of gaseous fluids through it to remove
moisture therein in a thorough drying operation.
Within the drying zone, the supported web is contacted on its
exposed surface with a gaseous fluid such as air under pressure so
that a pressure drop is created through the web. In this manner,
flow of air through the web and between the fibers comprising the
web is effected. This air flow is preferably of sufficient velocity
to physically sweep entrained moisture out of the web and through
the foraminous supporting surface while also serving to evaporate
moisture on and within the fibers. After the desired amount of
moisture is removed from the web the web is advanced out of the
drying zone and withdrawn from the foraminous supporting surface.
In accordance with the method of the invention, a vacuum bias is
preferably applied to the side of the foraminous supporting surface
opposite the side contacting the web to increase the pressure drop
and air flow through the web and to assist drying and moisture
removal. It is also a preferred feature of the method of the
invention to initially heat the gaseous fluid in order to assist
the evaporative drying and to cause the moisture in the web to
attain its heat of evaporization. In this regard, it has been found
preferable to employ air at a temperature of from about 300.degree.
F. to about 850.degree. F. although it is possible to use air
having a temperature varying from ambient to as high as about
1500.degree. F., without damaging the paper web.
One feature of the method and, correspondingly, of the apparatus of
the invention is the ability to utilize air for drying which is at
a temperature higher than that normally thought to be tolerable
without deleteriously affecting the physical properties of the
resulting paper web. It is believed to be due to the direction of
movement of the gaseous fluid through the web and the foraminous
supporting surface. By passing the heated air through the web
initially, heat is transferred to the moisture in the web which
vaporizes. Very little heat is transferred to the actual fibers
themselves because of the short period during which they are
subjected to hot air. Also, the heated air is cooled considerably
before contacting the foraminous carrying surface and does not,
therefore, raise the temperature of that surface anywhere near the
initial temperature of the heated gaseous fluid or air. Since the
foraminous carrying surface intimately contacts the web, the above
fact is important because the web could be damaged by a carrying
surface at too high a temperature.
Another benefit derived from the preferred direction of movement of
the gaseous fluid is that, by initially passing through the web, it
is evenly distributed in rate of flow, through the web. Were it to
first pass through an adjacent foraminous surface, the air flow
would be greater through some spaced localized areas of the web
adjacent open areas of the foraminous surface than it would be
through other areas of the web adjacent closed areas of the
foraminous surface, causing an uneven moisture profile in the web
resulting from uneven drying rates. This makes the proportion of
open area in the foraminous carrying surface less critical in
apparatus of the invention than would otherwise be the case.
The method of the present invention is a drying process operable on
a wet web which, in some instances, is creped on a Yankee dryer or
other apparatus and, in other instances, is uncrepted and dried by
the method of the invention while it is supported on the carrying
web used during formation. In still other instances, the web is
formed on a first carrying member and transferred to a second
foraminous carrying member upon which it is supported and dried
according to the invention. The method of the invention also is
significantly different from prior art processes described above
since it involves the passage of a gaseous fluid under pressure
through the supported web. This causes large amounts of gaseous
fluid to pass between the fibers forming the web thereby both
physically removing entrained moisture as well as causing
evaporative action to occur.
It has been found that the physical parameters of the method of the
invention may be varied quite widely to achieve good results with a
wide variety of paper webs. The most rapid rates of drying by the
method of the invention are experienced with tissue and towel
grades having a basis weight of from about 6 pounds per 2,880 feet
to about 30 pounds per 2,880 feet and higher. These grades are more
porous and allow the free passage of heated air through them.
The pressures and air flow rates which should be employed to
achieve the desired results depend to a large extent on the nature
of the supporting surface and on the type and condition of the
fibers employed in the web. Papers made of long fibers or short
fibers or mixtures thereof can be dried successfully according to
this method. The parameters may very slightly for each type,
however. Other factors affecting these parameters are the degree of
freeness of the pulp determined by the beating or defibering
operation and the refining operation. Wet webs having a moisture
content of up to about 90% by weight and even higher can be dried
successfully to remove substantially all of the moisture
therein.
The gaseous fluid contemplated for the method can be of many
different types. However, because of economy, air is by far the
preferred gaseous fluid. It is preferably heated to more readily
cause evaporization and to transfer more heat of vaporization. Wet
paper webs will withstand surprisingly high temperatures without
bad effects. This may be due to the cooling of the fibers by the
removal of the heat to the moisture in its vaporization.
The following relationship has been found to exist between various
parameters involved in the method of the invention. ##EQU1##
t= Drying time in seconds L= Weight of liquid in web being dried S=
Weight of solid in web being dried W= Basis weight of web being
dried in pounds per 2880 square feet h.sub.fg = Heat of
vaporization A.sub.x = Area of web being dried = Dimensionless
parameter relating to drying process efficiency (approximately
equal to 0.45) m= Mass flow rate of drying gas C.sub.p = Specific
heat of drying gas T.sub.i = Temperature of incoming gas T.sub.b =
Boiling temperature of liquid in web
______________________________________
The above expression indicates that the drying rate is strongly
dependent on the mass flow rate and the temperature of the gaseous
fluid. This is also illustrated by the following Table I presenting
data taken during the drying of paper webs, having a basis weight
of 12 pounds per 2,880 square feet, in accordance with the method
of the invention.
TABLE I
__________________________________________________________________________
m/A.sub.x Moisture content Drying Pressure drop Run T.sub.i,
(lbs/sec. (lbs. water/lbs.paper) time through paper, No.
(.degree.F.) ft..sup.2) (seconds) inches water Wet web Dry web
(p.s.i.)
__________________________________________________________________________
1 585 .0815 1.33 0.03 1.36 6.0(.216) 2 578 .0946 1.31 0.00 1.20
6.9(.249) 3 305 .1015 1.45 0.07 2.66 6.4(.231) 4 840 .340 1.52 0.57
.174 18.64(.67)
__________________________________________________________________________
In the above drying operation, the paper was supported during its
passage through the drying zone upon a fiberglas screen, 18 by 18
mesh, weighing 9 ounces per square yard. Surprisingly, in run
number 2, an evaporative rate of 10 pounds of water per square foot
per hour was achieved with a pressure drop of only 7 inches of
water through the web. From this it can be seen that evaporative
rates up to 60 pounds of water per square foot per hour and even
higher can be achieved with only relatively slight increases in the
mass flow rate and/or the temperature of the drying air. It has
been determined that the advantages of the invention can be
achieved and realized, when drying tissue and towelling grades of
paper, by maintaining the mass flow rate within a range which
creates a pressure drop of between about 5 and about 30 inches of
water, and by maintaining the initial temperature of the drying air
between about 300 and about 800.degree. F.
An alternative method of the invention involves the method
described above and, in addition, the step of forcing the fibers in
portions of the wet web covering openings in the foraminous
supporting surface to shift their positions relative to one
another. As a result, these web portions are forced generally
toward and into the openings. Thus, the web portions are moved at
least partially out of the plane of the web and into the plane of
the foraminous surface. Thus, one method of the invention includes
an embossing operation in which the fluid pressure employed for
transpiration drying is also employed to perform a type of
embossing or related texturing treatment. In some instances, this
step is performed prior to the introduction of the supported web
into a normal drying zone and, in that instance, a generally higher
fluid pressure is applied to the web to cause the fibers to
initially shift their position relative to one another.
Alternatively, a generally higher vacuum bias is momentarily
employed to cause a similar deformation prior to drying.
The most preferred method of deforming or embossing the web
comprises simultaneously directing a stream of gaseous fluid at
high velocity against successive transverse segments of the web as
it is carried on the foraminous supporting surface while applying a
high vacuum to the opposite side of the web to receive and remove
substantially all of the high velocity gaseous fluid directed
against the web which passes through the web either prior to or at
the start of the drying operation. Preferably, the web is supported
on an undulating surface such as that of a foraminous woven wire
cloth. This method of embossing enables the web to be positively
shaped into the desired configuration while deformable and wet
during only a very short distance of web travel.
The additional pressure or vacuum bias impressed on the web depends
largely upon the nature of the supporting surface, the size of the
openings therein, and the length and condition of the fibers
comprising the web. For a web having longer fibers, more force must
be exerted. Similarly, if supported on a surface with smaller
openings, more force must be exerted.
It is preferable, for reasons which will subsequently be pointed
out, for web deformation to occur and to be substantially completed
prior to substantial drying of the web. When drying occurs, firm,
strong bonds are created between the fibers in the paper web which
will prevent subsequent web deformation or movement of the fibers
by fluid pressure as contemplated by the invention.
Although one embodiment of the invention contemplates the use of
fluid pressure to accomplish embossing and, primarily, by pressure
of the same fluids which are used in drying, it is also possible to
mechanically emboss the wet web into the openings or apertures in
the supporting surface prior to the introduction of the wet web
into the drying zones, or within the drying zone. In this instance,
the fibers in portions of the wet web covering openings in the
foraminous surface are forced to shift their positions relative to
one another by pressure of a resilient member which has a yieldable
surface allowing the application of pressure over the entire
surface of the web. The nature of various surfaces and materials
useful for this purpose and their construction will be
described.
The above-described methods of the invention enable the production
of an embossed paper product which has characteristics
distinguishing it from dry embossed paper products formed from
prior art methods. As was pointed out above, by embossing or
deforming the web prior to drying, substantially no bonds are
created between the fiber until the desired shaft has been
attained. Upon subsequent drying, the embossed sheet exhibits a
much greater resilience and ability to retain its embossed
configuration and the embossed portions have a resistance to
deformation not found in dry embossed paper products which are
embossed after creation of the bonds. This increase in resilience
and resistance to compressive deformation is due to the fact that
substantially all of the bonds formed between fibers remain intact
even in the deformed areas. This is different than in the case of
mechanical dry embossing where many of the bonds previously formed
between fibers are broken during embossing.
With the above-described processes it is possible to form new paper
products, that is, embossed paper products having regularly spaced
portions thereof extending beyond at least one of two planes
defining the space occupied by generally the flat sheet or web,
these portions representing raised contoured portions of the sheet
having substantially improved stiffness and permanency. By
increasing the fluid pressure exerted on the web during embossing
in accordance with the method of the invention, an even more
distinctive product can be formed wherein the raised contoured
portions of the sheet have openings at their outermost end and,
therefore, terminate at their outermost extremities in an annular
edge. These are shown in FIGS. 14 and 15.
Products such as those described above have many new uses. For
example, rough abrasive wiping materials may be created by these
types of paper webs. The holes or apertures in the web provide a
greater porosity in the web while allowing web strength and basis
weight to be sufficiently high to avoid deterioration and
distintegration of the wiper during use.
Although, as indicated above, the specific form of the apparatus
will vary depending upon many factors, Tables II and III present
some data on various combinations of foraminous carrying members,
wet paper webs and ranges of pressure drops which have been
employed in practicing the method of the invention.
TABLE II
__________________________________________________________________________
Number Diameter Number Diameter Screen Type of weave/material of
warp of warp of shute of shute No. wires wires wires wires per inch
(in.) per inch (in.)
__________________________________________________________________________
1 Plain Dutch twill stainless 24 .014 56 .010 steel. 2
Twill/stainless steel 38 .011 60 .009 3 Plain or double crimped/ 14
.030 11 .015 phosphor bronze 4 Plain or double crimped/ 10 .032 10
.031 stainless steel. 5 do. 6 .065 6 .065
__________________________________________________________________________
TABLE III
__________________________________________________________________________
Screen Open area Basis weight Minimum Maximum used of screen
(pounds per pressure pressure during (percent) ream) drop (p.s.i.)
drop (p.s.i.) run
__________________________________________________________________________
1 29.2 12.6 uncreped 3.5 10.0 12.8 creped 3.5 10.0 -- -- -- 2 26.8
12.6 uncreped 2.0 10.0 12.8 creped 3.5 10.0 30.2 creped 5.0 10.0 3
48.5 -- -- -- 12.8 creped 0.5 6.5 -- -- -- 4 47 -- -- -- 12.8
creped 0.5 4.0 30.2 creped 2.0 10.0 5 37 -- -- -- 12.8 creped 0.5
2.0 30.2 creped 0.5 10.0
__________________________________________________________________________
It is believed that a brief description of the equipment typically
associated with the dryer in performing the method of the invention
will facilitate a better understanding of both the method of the
invention and the advantages and features of the transpiration
dryer apparatus. With that view in mind, the following description
of FIG. 1 is presented.
Referring now to FIG. 1 of the drawings, there is shown one type of
conventional Fourdrinier papermaking machine of the double-felt
type in which paper furnish 10 is fed from a head box 11 through a
slice 12 onto the substantially horizontal surface of a Fourdrinier
wire 13 through which water is withdrawn and upon which web
formation takes place. Wire 13 is entrained around a breast roll 14
and over a plurality of table rolls 15 to a wire turning roll 16.
It is then fed around a lower couch roll 17 and around to other
guide rolls 18 back to breast roll 14. One or more of the
above-described rolls is driven and propels the Fourdrinier wire 13
through the desired path so that the upper surface or flight moves
from the breast roll 14 to the lower couch roll 17 and returns
along the bottom. In addition, one or more vacuum boxes,
deflectors, and hydrofoils (not shown) may be employed between
table rolls 15 to assist in the removal of water from the web
during its formation.
The wet web formed on the upper surface of Fourdrinier wire 13 is
transferred to a pickup felt 20, pressed into engagement with the
web on wire 13 by means of an upper couch roll 21. The pickup felt
20 meeting wire 13 moves in the same direction as the wire 13, as
indicated in FIG. 1, and at substantially the same speed. Pickup
felt 20 carrying the newly formed web is advanced through the nip
of a press assembly, indicated generally by reference numeral 22.
Felt 20 is then moved around a pressure roll 23 which may be of the
suction type, and, hence, is entrained around a plurality of guide
rolls 24 back to upper couch roll 21. A guard board 25 and showers
(not shown) are employed adjacent the surface of felt 20 in front
of the point where it contacts the newly formed sheet and
accomplishes pickup. Guard board 25 and the showers clean and
condition the felt to receive the wet web.
Press assembly 22 comprises an upper press roll 26 and a lower
press roll 27, one of which is a suction press roll. A wet felt 28
is entrained over a plurality of guide rolls 30 and over lower
press roll 27. One or more of the rolls contacting wet felt 28 and
pickup felt 20 is driven to insure movement thereof at the proper
speed. Moisture is removed from the newly formed web in the nip of
press assembly 22 and transferred into wet felt 28. It is normally
removed from wet felt 28 by a wringer roll 29.
The formed and pressed web on felt 20 issuing from the nip of press
assembly 22 is then pressed into engagement with the surface of the
rotating drying cylinder 31 of a conventional Yankee dryer. The
Yankee dryer includes a hood 32 surrounding a portion of the
surface of cylinder 31 contacted by the web. Hood 32 includes
therein a plurality of air input nozzles 33 and an exhaust means 34
for removing air from the chamber enclosed by hood 32. This flow of
air within hood 32 over the surface of the web carried on the
drying cylinder 31 assists in removing moisture from the web and
accomplishing drying. The paper web 35 shown issuing from the
opposite side of drying cylinder 31 is removed from the surface of
drying cylinder 31 by a conventional doctor blade 36 which
accomplishes creping of the web. In other embodiments where no
creping is desired, the web might be pulled from the surface of
cylinder 31 without the use of a doctor blade 36.
Web 35 is then fed into a transpiration dryer, one embodiment of
which is shown and indicated generally by reference numeral 37.
Transpiration dryer 37 includes a rotatably mounted foraminous
cylindrical shell 38 over the surface of which a foraminous
flexible carrying member or web 40 is arranged in partial wrapping
engagement therewith. Carrying member 40 is then fed over a guide
roll 41 and around a stretch roll 42 and into the nip between the
pressure roll 43 and a pressure roll 44. Cylinder 38 is rotatably
driven by means of a motor 45 which is operably connected to
cylinder 38 by means of a drive chain 46. Suitable variable speed
mechanisms (not shown) may be employed in a well-known manner to
control the speed of the dryer.
A pressure hood 47 is positioned over a portion of cylinder 38
contacted by web 35. A blower 48 is arranged to move a gaseous
fluid such as air into a heater 50 and, hence, into either one of
two ducts 51 and 52 which lead into hood 47 at different points. An
exhaust hood 53 is positioned at the bottom of cylinder 38 to
withdraw air through the portion of cylinder 38 which momentarily
is not covered by foraminous carrying member 40. A duct 54 is
connected to a vacuum source 55, which comprises a vacuum blower or
a vacuum pump.
With this arrangement heated air is introduced under pressure into
hood 47 and is caused to flow through the web 35 and through
foraminous carrying member 40 into the foraminous cylinder 38 and
then out through the bottom of foraminous cylinder 38 and into
exhaust hood 53 after which it is withdrawn through duct 54.
Moisture entrained in web 35 is removed by a combination of
physical force as well as by evaporative action. Web 35 is removed
from member 40 on the opposite side of cylinder 31 by a pickup roll
56 and fed between two calender rolls 57 and 58 as is well-known in
the art. The web is then fed over a reel drum 60 and wound into a
parent roll 61.
At this point it should be clearly understood that FIG. 1 is
intended to illustrate merely one embodiment of apparatus in which
one embodiment of a transpiration dryer of the invention is
employed as an element thereof. It will be apparent that a
transpiration dryer could be employed with a different type of
papermaking machine or with a combination of different pieces of
equipment or in different arrangements in a papermaking machine.
For example, in some instances, it may be desirable to dry a paper
web which has not been creped and, in that instance, the
transpiration dryer 37 would receive a sheet drawn from press roll
23 which might be substituted for press roll 44 shown in FIG. 1.
Obviously, in that instance, various modifications to the design
and operating parameters of transpiration dryer 37 would be
required to allow it to operate on a web having a greater amount of
moisture so as to produce an uncreped but dry web which can then be
calendered and wound in the manner shown. In other embodiments or
arrangements, the apparatus of FIG. 1 might include, in addition to
the elements shown or as substitutes for the elements shown, one or
more dryer sections or afterdryer sections operating in cooperation
with or in addition to the transpiration dryer 37.
FIG. 2 is a more detailed sectional elevation view of the
transpiration dryer 37 shown in FIG. 1 and illustrates more clearly
the construction thereof. The apparatus of FIG. 2 includes a
movable baffle 62 extending into hood 47 and transversely across
the dryer along the length of foraminous cylinder 38. Baffle 62 is
arranged for movement into and out of hood 47 and when inserted,
serves to divide the space enclosed by hood 47 into two sections to
allow a different pressure to be applied to each section of the
hood through ducts 51 and 52 so as to permit drying adjustments for
a variety of webs. Ducts 51 and 52 include flow control elements or
dampers (not shown) which may be used to control the flow and
pressure fed into portions of hood 47.
FIG. 2 also shows more clearly the nature of the foraminous
carrying member which in the embodiment shown is a woven wire cloth
of a type similar to that employed for Fourdrinier wires commonly
used in papermaking. It generally has a more porous weave, however,
there are many types of flexible web materials which may be
employed for the carrying member 40. For example, these could be
some of the woven fiber glass mats or fabrics which demonstrate
great strength at higher temperatures, a typical Fourdrinier wire,
or a suitable plastic screen. In some instances, the porous
supporting member 40 may be constructed of several different layers
of foraminous members having differing structure and/or pore
size.
In operation, a web 35 is fed into engagement with the wire 40
through the nip of the support roll 43 and a pressure roll 44 and
remains in contact with the surface of the wire 40 during the
passage of the wire 40 around a portion of the dryer cylinder 38.
The web 35 is then withdrawn from the wire 40 onto a suction roll
56 and wound onto a roll for subsequent processing or converting.
With the above arrangement, during rotation of the dryer cylinder
38, the wire 40 and the web 35 are moved into a position adjacent
the surface of the dryer cylinder 38 and there is substantially no
relative movement between these various layers 40 and 35 and the
surface of the dryer cylinder 38.
In accordance with the invention, a heated gaseous fluid such as
air is fed into the pressure hood 47 wherein it distributes itself
substantially uniformly and exerts a pressure bias against the
exposed surface of the web 35. The web 35 is supported upon the
wire 40 which is correspondingly supported during a portion of its
travel upon a portion of the surface of the foraminous cylinder 38.
The gaseous fluid is forced through the web 35 and between the
fibers thereof causing some of the moisture contained in the web to
attain its heat of vaporization and to vaporize. Where the wet web
has a high moisture content, much of the moisture will initially be
mechanically removed. That is, the air moving through the web will
sweep the water off of the fibers thereof and out of the web. In
this manner, the kinetic energy of the air is utilized to remove
most of the water on the exterior of the fibers and in the pores of
the paper. The moisture in the fibers is largely removed by
vaporization.
If a heated gaseous fluid is employed, the amount and rate of heat
transfer occurring from the gaseous fluid to the moisture is
extremely high due to the high velocity of the gaseous fluid as it
passes over the fibers. In any event, the rapid movement of the
gaseous fluid past the moisture on the web 38 causes some of the
moisture to vaporize and it is carried away into the interior of
the dryer shell 38. Thus, the gaseous fluid on the interior of the
dryer cylinder 38 has an increased humidity over the gaseous fluid
fed into the pressure hood 47 due to the moisture picked up from
the web 35.
Gaseous fluid is continuously exhausted from the interior of the
foraminous cylinder 38 through the openings in that portion of the
cylinder 38 enclosed by the exhaust hood 53. The location of the
exhaust hood 53 at the lowermost portion of the drying cylinder 38
insures that any moisture in the form of a liquid which passes
through the wire 40 and through and into the cylinder 38 will
settle to the bottom and will be removed from the cylinder 38.
Depending upon the type of embossing or texturizing treatment
applied, portions of the above-described apparatus may be designed
so as to accomplish this process during drying of the paper web 35.
Thus, in some instances, it may be desired to merely emboss the
paper web 35 or create small projections extending outwardly from
one surface of the web 35. This is accomplished in accordance with
the invention by employing a wire 40 over a foraminous cylinder 38
which is woven so as to provide a plurality of depressions or holes
therethrough in a predetermined pattern. During the performance of
the process of drying, the air pressure will force the deformable
wet paper web 35 to conform to the contour of the supporting wire
surface 40 and upon drying, the paper web 35 will retain that form.
It is well-known that a web of paper fibers generally follows the
normal rules of plastic deformation when wet and has only slight
memory characteristics. This is believed to be due to the fact that
prior to the inital drying operation, relatively few bonds have
been formed between the fibers forming the web, allowing it,
therefore, to deform quite readily. However, when once deformed
into the desired contoured shape, and then dried, the resulting
embossed portions or texturizing effects will tend to have an
increased permanency and increased "spring back" over that normally
experienced in dry embossing.
It has also been found possible to create perforations or holes in
the web during the texturizing and drying processes. Thus, the
variations in the process which determine whether mere drying will
occur or embossing and drying together with the creation of
perforations will occur are quite numerous but with some methods
may be a matter of applying the proper pressures. For example, with
a given wire and a given initial wet web having a specified basis
weight, by controlling the pressure drop between the hood and the
exhaust, the above features can be caused or prevented as described
above.
FIG. 3 is a sectional view taken along line 3--3 of FIG. 2. It
illustrates in greater detail the construction of the hood 47 in
the areas adjacent the surface of the foraminous cylinder 38 and,
particularly, the manner in which a seal is provided between
cylinder 38 and the edge of hood 47. A seal is necessary to insure
uniform pressure within the area enclosed by the hood 47 across the
width of the drying cylinder 38. Similarly constructed seals are
employed at the entrance and exit ends of the hood 47 but modified
slightly to allow a web to pass freely beneath them. The seal is
not so important in these latter areas since they have little or no
effect on the moisture profile of the resulting dried paper web.
FIG. 3 also illustrates the manner in which the foraminous cylinder
38 is attached to the head 63 containing the bearings upon which
the drying cylinder is rotatably mounted.
A section of the dryer cylindrical shell 38 extends beyond heads 63
at each end of the dryers serving to support shell 38. Shell 38 is
adjacent and parallel to an outwardly depending flange 64 welded to
the outermost edge of header 63. A bolt 65 passes through a hole 66
in cylinder 38 and through a hole in flange 64. Hole 66 has a
diameter larger than the diameter of bolt 65 which allows movement
of cylinder 38 in a direction parallel to the longitudinal axis of
cylinder 38 caused by expansion of cylinder 38 due to heat. It will
be appreciated that where air at relatively high temperatures is
employed with a dryer of the invention and in instances where
momentarily no wet web is entrained over the dryer cylinder 38, the
large amount of heat transferred to cylinder 38 will cause
substantial expansion thereof which must necessarily be relieved as
by enlarged hole 66.
Similarly, expansion of cylinder 38 must be allowed away from
flange 64 and outwardly from header 63 to insure roundness of the
rotating cylinder 38 and to prevent buckling of the foraminous
shell in the event of thermal expansion. To provide for this
feature, the through-extending portion of bolt 65 passes
successively through a washer 67, a coil spring 68, and a washer 70
and is secured snugly thereto by a pair of nuts 71 and 72. Cylinder
or shell 38 may be formed in a plurality of separate sections
around the periphery of the dryer shell. Spring 68 must have
sufficient compressive force to firmly retain cylinder 38 in
contact with the outer surface of flange 64 during normal operation
of the transpiration dryer. It will be appreciated that when the
dryer is operated at the contemplated speeds of up to 4,000 feet
per minute and higher, the centrifugal forces exerted on the plates
and hence on each of the springs 68 will be quite substantial.
However, it is also well-known that the forces exerted by metals
during thermal expansion are quite sufficient to overcome these
stresses caused by the spring 68 and will cause cylinder 38 to move
outwardly from the outer surface of flange 64.
The above-described construction allows the substitution of
different foraminous cylinder members 38 into the dryer or for the
replacement of worn cylinders 38. This feature is important where
an embossing operation is performed and it is desired to change the
pattern of embossing.
The manner in which the hood 47 is sealed at its side edges
adjacent the surface of cylinder 38 at the longitudinal ends
thereof, will now be described. As shown in FIG. 3 and in greater
detail in FIG. 4, cylindrical shell 38 has a raised portion or
strip 73 extending around its outside surface and welded thereto
along a line inwardly spaced from the shell 38. The side wall 74 of
hood 47 extends vertically downward toward the surface of shell 38.
A top wall 75 is attached to side wall 74 at each side of hood
assembly 47. The end of duct 51 is secured to the top wall 75 by
bolts 76 and is adapted to insert air under pressure into the
chamber enclosed by a wall member 77 and top wall 75 through an
opening in top wall 75.
Wall member 77 extends upwardly from the bottom of side wall 74 to
the top wall 75 enclosing chamber 78 in which is disposed
insulation. This feature is important where the air is heated to
relatively high temperatures prior to passage through the web to
minimize heat losses.
On the opposite side of side wall 74 a duct 80 is provided leading
to a source (not shown) of seal air under pressure substantially
equal to the pressure of the air on the interior of hood 47. Duct
80 leads to an arcuate chamber formed by a second side wall member
81 outwardly spaced from the open side wall 74. Member 81 is
secured to side wall 74 by means of a bolt 82 holding it against a
spacer member 83. Member 81 has an extension 84 stretching toward
the surface of cylinder 38 and bolted to member 81 by bolts 85.
Seal strip 86 made of a resilient material, such as rubber or
plastic, bolted by means of a bolt 87 to the lower end of extension
84 is arranged to ride in sealing contact with strip 73 on the
surface of cylinder 38 to substantially prevent the passage of seal
air through that joint.
Side wall 74 has an angle 88 adjustably secured along its bottom
edge adjacent its cylindrical surface 38 by means of a bolt 90. A
slight clearance or space 91 is provided between bottom surface 88
and the outermost surface of shell 38 so that the pressure of the
seal air entering through duct 80 causes it to pass through the
chamber defined by side walls 81 and 84, and, hence, through the
space 91 between member 88 and shell 38 to balance the pressure in
hood 47.
It should be understood that in operation, the above-described seal
mechanism prevents flow of heated air from the interior of hood 47
outwardly through space 91. This flow would cause an increase in
heated air flow near the edges of the paper web being dried and
would cause overdrying of these edges. It is similarly not intended
that substantial flow of the seal air occur into the chamber
defined by hood 47 through the space 91 since the addition of this
cooler seal air into the heated drying air passing through the
edges of the paper web would cause them to be insufficiently dried.
In accordance with the invention, suitable control mechanisms (not
shown) are employed in connection with the supply of air to duct 80
to insure that the pressure of the seal air passing through duct 80
is substantially equal at all times to the pressure of the gaseous
fluid on the interior of hood 47. In this manner, a seal is
provided while flow through space 91 in either direction is
minimized.
In practice, resilient seal strip 86 rides in contact with or
immediately adjacent to the surface of strip member 73 and provides
a mechanical type seal on this side of the hood, preventing or
minimizing leakage of the seal air. As the strip 86 wears during
operation of the dryer, it may be periodically placed or adjusted
to reduce the clearance involved. Since flow of the seal air into
the chamber is minimized and controlled, the seal air is normally
at ambient temperature.
FIG. 5 is a greatly enlarged perspective view of a portion of the
dryer shell illustrating the relationship between the foraminous
shell or cylinder 38 and a typical flexible foraminous layer of
woven wire or other material superimposed thereon. As will become
apparent from subsequent description, the size and shape of the
openings in shell 38 may vary depending upon the process involved
and the type of product desired. Similarly, the type of flexible
web material superimposed over the cylinder 38 can vary
considerably in construction and in size and shape
relationships.
The example shown in FIG. 5 comprises a section of cylindrical
shell 38 having openings 92 passing therethrough. These openings
may typically have a size of about 3/8 inch diameter where a
flexible web is employed over them as shown to support the paper
web. The flexible web indicated generally by reference numeral 93
is comprised of a plurality of parallel warp strands 94 oriented
perpendicular to the axis of the cylinder 38 and interwoven with a
plurality of parallel shute strands 95 arranged perpendicular to
the warp strands. A wide variety of weaves and materials can be
employed for flexible web 93. It will be apparent from the above
description that the openings between the strands may be varied to
advantage to perform alternative methods of the invention.
Cylinder 38 comprises a shell of metal such as steel having a
thickness of about 1/8 inch. The cylinder 38 could be formed of
many types of porous materials such as sintered metal, perforated
plate, expanded metal, or honeycomb structures provided that these
structures have sufficient porosity to allow the free passage of
gaseous fluids therethrough at high speeds. The thickness of these
materials is not critical to the process although strength is an
important factor in the apparatus. The main consideration in the
construction of the layers shown in FIG. 5 is to provide a means
for supporting a wet web of loosely attached and bonded paper
fibers while the paper fibers are subjected to a drying action by a
gaseous fluid under high pressure.
It is also desirable in accordance with the method and apparatus of
the invention to minimize the pressure drop created by the
supporting surface. That, in the case of FIG. 5, is the composite
structure formed by layer 38 and layer 93. It is preferable to have
the major portion of the pressure drop created by the paper web
being dried in order to carry out the process of the invention in
the most efficient manner. Therefore, any pattern of openings or
apertures employed in cylinder 38 should be sufficiently
concentrated so that areas of cylinder 38 comprising the
interconnecting web materials between the apertures or openings do
not seriously impede the substantially uniform passage of gaseous
fluids through the supporting structure. This enables uniform
drying of the wet paper web.
The following examples illustrate the application of the method and
apparatus of the invention in the drying of wet paper webs of
differing basis weights. The paper web in Example 1 is a tissue
weight paper which might be used in a number of sanitary paper
products while the paper web in Example 2 is a towel weight paper
of the type used as disposable paper toweling. Throughout the
examples, reference numerals utilized in describing FIGS. 2 and 3
will be referred to for purposes of clarity.
EXAMPLE 1
A paper stock slurry of 3.32% consistency comprising a mixture of
40% soft wood sulphite pulp, 13% pine kraft pulp, 39% hardwood
kraft gum pulp and 8% mechanical fiber pulp was defined to a 482
cc. Canadian Standard freeness. The stock was pulped through a
typical stock system with the necessary piping, pumps, overflow
chests, controls, cleaners, etc. to a diffusion chamber and slice.
A paper sheet was formed, pressed, partially dried, and creped on
apparatus similar to that described in U.S. Pat. No. 3,252,853. The
wet web 35 was fed in an unsupported condition from the creping
doctor 36 at 40.6% moisture to the pressure roll 44. It was lightly
nipped by pressure roll 44 against pressure roll 43 causing the wet
web to be applied to the plain weave double crimped carrying wire
40 made of Phosphor bronze with 14 shute wires per inch of 0.019
inch diameter and 16 cable warps per inch of 0.25 inch diameter.
The wire 40 carrying the wet web 35 contacted the hollow cylinder
38 made of two 6 foot diameter 1/4 inch thick steel heads 63 as
shown in FIG. 3, suitably braced and covered with an 11 gauge steel
perforated blade 38 having a plurality of 21/32 inch diameter
(0.328 inch) holes staggered on 7/16 inch centers, resulting in a
50% plate open area. The plate 38 was suitably attached to allow
for expansion as shown in FIG. 3. The wet web 35, the wire 40 and
the perforated plate 38 were advanced together through a hood 47 at
a speed of 1635 feed per minute. This was 368 feet per minute
slower than the surface speed of the Yankee dryer 31 resulting in a
web 35 having a weight of 13.9 pounds per 2880 square feet on wire
40. The dry end of hood 47 wrapped the plate 38 for 82.degree. of
angular motion and was supplied with air at 610.degree. F. through
duct 52 in a manner such that the air pressure immediately above
web 35 was at atmospheric pressure (0 inches of water). The wet end
of hood 47 supplied by duct 51 was not operating and the dampers
were closed. The air at 610.degree. F. was forced through the web
35 at a velocity of 3.7 feet per second thereby transferring heat
to the water in web 35 causing the water to evaporate and the
resulting vapor to pass through the web 35, the wire 40, the
perforated plate 38, and into the interior chamber which was under
a vacuum of 2.0 inches of water. The air temperature in passing
through the web 35 was found to have dropped from 610.degree. F. in
the hood 47 to 170.degree. F. in the interior chamber. The air was
then removed from the interior chamber through the roll 38 across
the bottom, through perforated plate 38, wire 40 into exhaust hood
53 and out duct 54 by means of an exhaust blower. A web 35 was
removed from wire 40 by means of an air blow-off shower positioned
between pickup roll 56, guide roll 41, wire 40 and exhaust hood 53.
The web 35 as removed from wire 40 had 6.4% moisture. The web 35
was conveyed to calender 57 and 58 and reeled up in a parent roll
61 by a reel 60. There was no evidence of non-uniform drying,
marking, or deterioration of sheet quality when the web was dried
in this manner. The quality of this web, dried by the passage of
air at a temperature of 610.degree. F. through it, was within
accepted standards for this type of paper web. The results of the
physical tests of this web are shown in Table IV below.
TABLE IV ______________________________________ Physical Tests:
Results ______________________________________ Tensile, oz. per
inch, Instron tester: Machine direction 17.7 Cross machine
direction 9.3 Stretch, percent (Instron tester): Machine direction
6.1 Cross machine direction 4.2 Bulk (24 sheets), inches 0.081
Brightness (G.E. tester) 83.5 Absorbency (cured), seconds 12.3
______________________________________
EXAMPLE 2
A paper stock slurry of 3.15% consistency comprising a mixture of
55% Soundview soft wood sulfite pulp, 37% pine kraft pulp and 8%
mechanical fibers was refined to a 456 cc. Canadian Standard
freeness. The sheet was formed, pressed, partially dried, and
creped, on apparatus similar to that described in U.S. Pat. No.
3,252,853. The wet web 35 was fed to the wire 40 in the manner and
under the condition described in Example 1. The wet web 35, the
wire 40, and the perforated plate 38 were advanced together through
a hood 47 at a speed of 802 feet per minute, 202 feet per minute
slower than the Yankee 31 surface speed, resulting in a web 35
having a weight of 31.3 pounds per 2880 square feet on wire 40.
Hood 47 wrapped a portion of the plate 38 and was supplied with
582.degree. F. air at 5.0 inches of water pressure by wet end duct
51 and 632.degree. F. and 4.2 inches of water by dry end duct 52.
The seal air which surrounds hood 47 was typically supplied by duct
80 shown in FIG. 3 at a pressure of 4.5 inches of water to minimize
the hot air leakage from the wet end hood and at a pressure of 4.6
inches of water to minimize the leakage of hot air from the dry end
of hood 47. The seal air pressure was adjusted so that it balanced
the hot air pressure typically found at location 91 for hot air
leakage control.
The 582.degree. F. air was forced through the wet web 35 at a
velocity of 6.10 feet per second as it was carried through the
first portion of hood 47 which wrapped roll 38 for 138.degree.. The
632.degree. air was forced through the partially dried web 35 at a
velocity of 5.53 feet per second as it was carried through the last
portion of hood 47 which wrapped roll 38 for 82.degree.. The vapors
were conveyed from the web 35 through wire 40, perforated plate 38
to the interior of the roll which was under a vacuum of 6.4 inches
of water generated by the exhaust blower attached to exhaust duct
54 and exhaust hood 53. The air (now at 200.degree. F.) passed
through the perforated plate 38, wire 40 and into exhaust hood 53,
out duct 54, and into the atmosphere. The web 35 was removed from
wire 40 by means of an air blow off shower positioned between
pickup roll 56, guide roll 41, wire 40 and exhaust hood 53. Web 35
as removed from wire 40 contained 3.1% moisture. The web's creped
basis weight was 31.3 pounds per 2,880 feet. Web 35 was conveyed to
calender 57, 58 which was operating at a speed of 813 feet per
minute where it was reeled up into parent roll 61.
The paper web, dried in this manner, showed no signs of nonuniform
drying, marking or deterioration of sheet quality. The web 35 was
exposed to the high temperature air for 0.86 seconds. The drying
rate under hood 47 was 27.7 pounds of water removed per hour per
square foot. The quality of this web, dried by the passage of air
at a temperature of up to 632.degree. F. through it, was within
typical standards for this type of paper. The results of the
physical tests run on this web are shown on Table V.
TABLE V ______________________________________ Physical tests:
Results ______________________________________ Tensile, ounces per
inch, Instron tester: Machine direction 79.9 Cross machine
direction 58.0 Stretch, percent (Instron) Machine direction 16.2
Cross machine direction 3.3 Bulk (24 sheets), inches 0.144
Brightness (G.E. tester) 80.0 Absorbency, (cured) seconds 12
______________________________________
Although a specific embodiment of apparatus has been described
above illustrating a preferred method and apparatus of the
invention, it will be apparent that a number of variations in the
basic equipment and method of the invention may be made without
departing from the spirit and scope of the invention. FIGS. 6
through 10 illustrate some of these alternative embodiments.
Thus, FIG. 6 is a partial plan view of an alternative embodiment of
the transpiration dryer shown in FIG. 2 and illustrates a rotably
mounted foraminous cylindrical shell 96 carried by a pair of spaced
headers 97 and 98. Journals 100 and 101 extend axially outwardly
from headers 97 and 98 and are carried by a pair of journal
bearings 102 and 103, respectively. Journal 101 has a portion 104
extending beyond bearing 103 and carries a seal bearing 105 on its
outermost end. Journal 101 and extending portion 104 thereof are
hollow and allow the passage of fluids from the interior of the
cylindrical shell 96 therethrough. A duct member 106 is attached to
the seal bearing 105 and is connected to a vacuum source (not
shown). In this manner, air passing through the web 107 carried on
the surface of shell 96 is withdrawn from the interior of shell 96
through the passage in journal 101 and out through duct 106. This
arrangement enables the elimination of the exhaust hood 53 shown in
FIGS. 1 and 2 but will require the addition of a shield member (not
shown) along the portions covered by exhaust hood 53 to prevent the
passage of air through the cylinder over that area. This shield
member may be stationarily mounted with a slight clearance between
it and the outside surface of the rotating dryer cylinder 38.
FIG. 7 shows a still further alternative embodiment of the dryer
shown in FIG. 2 having a foraminous cylindrical shell 96 carried by
spaced headers 97 and 98 on journals 100 and 101 carried in
bearings 102 and 103, respectively. In this embodiment, a plurality
of openings 110 are provided in header 98 which, during rotation of
cylinder 96, pass adjacent to the opening in a duct 108 which is
connected to a vacuum source (not shown). When openings 110 are not
adjacent the opening in duct 108, they are passing closely to but
just out of contact with a shield plate 111 stationarily mounted by
a bracket 112 on a dryer frame and extending around the entire end
or outer surface of header 98. By this arrangement, air passing
through web 107 carried on shell 96 is withdrawn from the interior
of shell 96 through one of the openings 110 which is adjacent the
open end of duct 108 and, hence, withdrawn by the vacuum
source.
FIG. 8 illustrates a still further embodiment of the invention
wherein the flexible carrying member 40 shown in FIGS. 1 and 2 is
eliminated and the paper web 113 is fed by a pressure roll 114 into
engagement with the surface of a foraminous cylinder shell 155
mounted for rotation. A pressure hood 116 receives air from ducts
117 and 118 in a manner similar to that shown in FIGS. 1 and 2.
Similarly, an exhaust hood 120 is connected by a duct 121 to a
vacuum source (not shown). The web is withdrawn from cylinder 115
by means of a suction pickup roll 122. In this instance, the
surface of cylinder 115 has a plurality of relatively fine openings
so that it adequately supports the web. This is especially true
where no embossing of the paper web is desired. A wire type sleeve
generally used on cylinder rolls may be used around shell 38.
Generally, these openings are much smaller than 3/8 inch openings
typically employed in the shell 38 as shown in FIGS. 1 and 2 and
may range from extremely fine openings such as those contained in a
sintered metal shell to openings up to about 1/8 inch. If embossing
is desired as described above, these openings may be even
larger.
FIG. 9 illustrates a still further alternative embodiment of the
dryer of the invention where a flexible carrying member 123 is fed
over a first support roll 124 and over the surface of a vacuum box
125 connected by a duct 126 to a vacuum source 127 and, hence,
passes over a second supporting blow roll 128 and over a guide or
tension roll 130 back to support roll 124. A web 131 is fed into
engagement with foraminous carrying member 123 and is pressed into
contact with the upper surface of 123 by a pressure roll 132
carried by the forward lip of a hood 133 which also serves to seal
the forward edge of the hood to prevent the leakage of gaseous
fluid therefrom. Air is provided under pressure by a pressure
blower 134 and the air is heated by passing over a heating coil 135
connected to a suitable electrical source (not shown) and is
directed under pressure toward the web carried on member 135 over a
vacuum box 125. Alternatively, gas or oil fired heating units or
high pressure steam may be used to heat the air. The exit end of
hood 133 is sealed by a second pressure roll 136 and the web 131 is
withdrawn from carrying member 123 and calendered and wound as
shown in FIG. 1. The side portions of hood 123 are arranged to ride
in a position of slight clearance above the surface of the web 131
so as to form a mechanical seal.
FIG. 10 illustrates a modified embodiment of the dryer shown in
FIG. 9 where a greater amount of dryer contact time is provided in
a reduced horizontal space. In this embodiment, a third support
roll 137 is positioned above and between support rolls 124 and 128
and the vacuum box 125 is divided into two vacuum boxes 125a and
125b, each being connected by a duct 126 to a vacuum source 127. In
this embodiment, the web 131 is pressed into engagement with
formanious carrying member 123 at the forward end of the hood 133.
Pressure roll 136 forms a seal between hood 133 and the paper web
on the carrying member 123.
To attain even higher drying efficiency from transpiration dryers
as described above, it is advantageous to employ radiant heaters
within the hood adapted to heat the wet web by radiation as an
assist to the amount of heat transferred by the moving air. These
may be any well-known type, using as, oil, or electricity as a
power source.
To accomplish an alternative embodiment of the invention wherein
the wet paper web is treated with pressure so that portions of it
are forced into openings in the foraminous supporting surface, the
invention involves a number of different forms of apparatus. From
the above description of this method of embossing a wet paper web
and of forming various novel paper products, it will be apparent
that many different types of apparatus could be employed.
Therefore, the following specifically described embodiments of
apparatus are intended to disclose only preferred forms of
apparatus and alternative embodiments thereof.
FIG. 11 is a partial sectional side elevation view of apparatus
constructed generally according to FIG. 2 but including additional
provision enabling the accomplishment of the embossing process in
conjunction with the transpiration drying process. To avoid undue
confusion and repetition in the following description, the same
reference numerals employed in FIG. 2 will be employed to the
extent possible in the description of FIGS. 11, 12 and 13. A wet
paper web 35 is fed into engagement with a foraminous carrying
member 40 and between the nip of pressure rolls 43 and 44. It then
is carried on carrying member 40 around a portion of the
circumference of foraminous cylinder 38. Web 35 is removed from
carrying member 40 after passing through the drying zone under hood
47 by a vacuum pickup roll 56 and, hence, transferred to subsequent
equipment.
An air knife 140 connected by a conduit 141 to a source (not shown)
of high pressure air is disposed in a position normal to the
surface of web 35 and carrying member 40 immediately prior to the
entrance into hood 47. By directing high pressure air through an
orifice 142 toward the web, the fibers thereof will be aligned into
new positions by the fluid force so that portions of web 35
overlying holes in foraminous carrying member 40 will be forced out
of the plane of web 35 and into the plane of carrying member 40.
These portions will be shaped and arranged substantially in the
image of the openings in foraminous carrying member 40. It has been
found that by supplying air to air knife 140 at a sufficiently high
pressure, holes or apertures can be created in wet paper web 35 by
additional reorienting and movement of fibers in the impressed
portions of the web. Thus, the web is ruptured at the points most
remote from the plane of the paper web in the portions overlying
the openings in the supporting member 40 as shown in FIG. 15. Where
treated on a woven wire surface having upwardly projecting
knuckles, holes may be formed in the web in portions overlying the
knuckles.
Suitable controls can be employed to control the air pressure
issuing from air knife 140 to obtain the desired products described
above. Once fibers in portions of the web have been oriented while
the web 35 has a relatively high percentage of moisture, the web is
dried and the normal bonds created during papermaking are formed
between the fibers thereof so that the embossed areas or deformed
portions of the web have substantial resiliency and permanency.
FIG. 12 represents an alternative embodiment of apparatus for
accomplishing the embossing step in which at least two vacuum
chambers are employed in the interior of the foraminous shell 38.
In this instance, a vacuum chamber 143 is arranged to act upon the
paper web 35 immediately after its entrance into hood 47. The
vacuum in chamber 144 should be quite high to accomplish embossing
or deformation of the web while the web and the fibers comprising
it are in a relatively plastic state. A second vacuum chamber 145
is employed for the drying region, for which a relatively lower
vacuum is required for drying. A duct 146 is arranged to draw a
relatively high vacuum from chamber 144 through the axis of
cylinder 38 and a duct 147 is arranged to draw a relatively low
vacuum from chamber 145 through the axis of cylinder 38 in a manner
well-known in the art.
FIG. 16 illustrates the most preferred form of drying and embossing
apparatus of the invention in which, in general, the features of
the embossing apparatus shown in FIGS. 11 and 12 are combined with
each other along with the dryer configuration of FIG. 2. For
purposes of clarity, reference numbers relating to FIG. 11 have
been used wherever they refer to corresponding parts in FIG.
16.
In FIG. 16, the air knife or nozzle 140 is directed toward the web
35 upon member 40 between roll 44 and the point where the web 35
passes into hood 47. Nozzle 140 is connected to a source of high
velocity air (not shown) and is adapted to direct it against
successive transverse segments of web 35 as it is carried past
nozzle 140. Nozzle 140 is adjacent but spaced from web 35 and
member 40 so as not to contact or damage web 35 by rubbing against
it. It is disposed quite close to web 35 to promote the action of
the high velocity air against the web 35.
A two compartment vacuum box having a leading compartment 152 and a
trailing compartment 153 is disposed adjacent the opposite side of
carrying member 40 in a position generally opposite nozzle 140. It
is preferred that leading compartment 152 be directly opposite
nozzle 140 so as to receive substantially all of the air issuing
from nozzle 140 which passes through the web 35. In this manner, it
makes the force from air issuing from nozzle 140 more effective in
embossing web 35. Leading compartment 152 is connected to a source
of high vacuum (not shown) while trailing compartment 153 is
connected to a source of relatively high vacuum (not shown) which
is generally less than the vacuum of compartment 152. The function
of trailing compartment is to receive and remove any air which
becomes trapped between web 35 and member 40 which would otherwise
tend to lift web 35 off of member 40. It also picks up any air from
the surface of web 35 which has been deflected from nozzle 140, and
draws this air through web 35 and member 40, tending to hold them
together.
The apparatus shown in FIG. 16 accomplishes fiber rearranging and
forces the web 35 into conformity with the undulating surface of
member 40 before it enters the principal drying region beneath hood
47. Thus, the high velocity air and high vacuum simultaneously
cooperate on successive transverse segments of moving web 35 to
emboss the web into the desired configuration as determined by the
the carrying surface, after which it is dried to form bonds which
cause it to retain this embossed shape.
FIG. 13 illustrates a method and apparatus for impressing web 35 on
carrying member 40 and employs a resilient embossing roll 150 in
place of roll 44 shown in FIG. 2 and forming a pressure nip with
pressure roll 43. Roll 150 has a plurality of bristles 151
extending radially outward from its cylindrical surface. Bristles
151 serve to press the paper in the portions of the web 35 covering
the holes in foraminous carrying member 40 into the holes so as to
emboss the web. Although bristles 151 are shown in FIG. 13, a
number of different constructions may be employed for roll 150 and
in some instances may comprise a resilient foam-like material or a
combination of foam and fibers. A roll formed from compressed discs
of felt, fabric or paper may also be employed for this embossing
function.
In each instance where apparatus of the type shown in FIGS. 11, 12
and 13 is employed, the apparatus cooperates with the transpiration
drying equipment to form a new and improved paper product by a new
and improved process. Thus, in each of the above-described
instances, the fibers are rearranged and the web is deformed while
it has a relatively high precentage of moisture and is in a
generally plastic state. The web is then dried in the deformed
condition by the transpiration drying process so that the bonds are
formed between the fibers thereof and the embossed regions exhibit
superior strength and permanency.
* * * * *