Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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}~CKGROUND OF THE II~VENTION
A. Field of the Invention
This invention relates to a process for embossing a
man-made board, and more particularly to a process ~or embossing
or debossing a man-made cellulosic board at a high temperature
and pressure after consolidation of the board. More specifically,
the process of the present invention relates to embos~ing a man-
made cellulosic board in a post-press embossing step.
Man-made consolidated boaras include hardboard, chip
board, particle board, panel board, acoustical board, insulation
board and the like. The uses of such boards depend upon the
physical characteristics such as the density of the board and
the exterior embossing or decorative effect applied thereto. The
qualities and physical characteristics of a board depend upon
- 15 the conditions under which the board is manufactured, and the
raw materials used to form the board.
There are two principal processes for the manufacture
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of man-made boards - the wet process and the dry process. In
the wet process, the raw material is uniformly blended in a head
box with copious quantities of water to form a slurry. The
slurry is deposited onto a water-pervious support member, generally
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a Fourdrinier wire, whexe much of the water is removed leaving
a wet mat of cellulosic material. The wet mat is transferred
from the pervious support member and consolidated under heat
and pressure to form the board. Typically, pressures of from
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400 to S00 p.s.i. and temperatures up to about 400 F. are en-
countered in conso~idation of a man~made board manufa~ured by
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the wet process.
The dry process is similar to the wet process except
that the cellulosic fibers are first coated with a thermosetting
resin binder, such as a phenol-formaldehyde resin~ and are then
randomly distributed into a mat by air blowing the resin-coated
fibers onto a support member. In the dry process3 the mat is
pressed at tempera~ures up to about 45G F. and pressures less
th~n about 1000 p.s.i. to cure the thermosetting resin and to
compress the mat into an integral consolidated structure.
The process of embossing a wet mat in a platen press
with a heated embossing plate is well known~ especially in the
manufacture of hardboard. An embossing plate is made with a
¦ surface contour of a desired design, such as wood graining. The
¦ heated embossing plate is pressed against the surface of the
wet mat under sufficient pressure to impress the plate design
into the surface of the panel and thereby consolidate the wet
mat into a decorative man-made board.
Boards made in accordance with the dry process are
; also typically decorated or surface-designed by hot-pressing in
a platen press with a heated embossing plate. In embossing mats
made by either ~he wet or dry process, however, the man-made mat
~ i~ embossed concurrently with being compressed into a consolidated,
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integral product so that the bonds between fibers are initially
made in accordance with the final surf~ce design of the product.
Much of the bonding necessary ~or cohesion and strength
in a man-made board occurs during the consolidation of the board.
Prior to drying a board made by the wet processgthe board is weak~
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but the bonding forces created during the final consolidation
are generally quite powerful. Generally the same bonding effect
occurs in the final consolidation of ~he board made by the dry
process. Prior to hot-pressing, the loosely disassociated
cellulosic fibrous product is quite weak, but a~ter hot-pressing
the mat into its final configuration, it is very power~ully
held together ~y the bonding which occurs durlng hot-pressing.
Hot-pressing during consolidation causes a welding or coalescing
of the cellulose fibers at the surface of the product so that
the surface portion consists of wood re-made in modified form.
It is very difficult to re-shape the surface of the consolidated
product without again destroying these fiber-to-fiber surface
welds.
As set forth above, the process of embossing a man-
made board prior to consolidation to establish a surface design
in a product is well known. However, because of the strong inter-
fiber bonding which occurs during consolidation, no effective
~ process has been developed by which a previously consolidated
; product can be post-press embossed to create a surface design
or to re-design the surface of a consolidated product. To be
e~fective~ such a process cannot destroy the inter-fiber bonding
established at the surface of/the board during consolidation -
; yet the process must permanently re-shape the surface of the
product.
One of the most difficult problems found by applicant
in re-shapin~ the surface of a consolidated product is in main-
. . taining "deQig~ fidelity" in the board. "Design fidelity" or.
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8imply "fidelity" as used herein is a measure of the accuracy
of reproduction of the design of the embossing plate onto the
surface of the consolidated board. Because o the strong inter-
fiber bonding referred to above exi~ting in a consolidated board,
the re-shaped surface has a tendency to "spring-back" to its
original surface design. "Spring ba~k" as used herein is the
tendency of a re-shaped board to return to its original surface
shape or contour.
~o existing process is able to maintain a high degree
of fidelity over extended periods of time by embossing a consolidated
product because of the strong inter-fiber ~onding occuring during
i~itial consolidation.
The.present invention relates to a process o~ embossing
a consolidated man-made cellulosic board in such a manner that
the strong inter-fiber bonding established during consolidation
~ and densification is maintained, but the cellulosic material is
; apparently caused to "flow" to new locations to impart a different
contour to the surface of the consolidated product. A process
whereby a consolidated product can be embossed under heat and
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2~ pressure, after already having undergone a fir~t hot-press
consolidation step, so that the inter-fiber bonds established
l~ during the first hot-press step are maintained, but re-oriented
with ~he fibrous material in the new shape, is guite surprising
in the art of man-made cellulosic board manufacture.
i In accordance with the process set forth harein, a
consolidated product is post-press embossed to estahlish new
surface contours. The inter-fiber bonds established in initial
consolidation are realigned to set the surface of ~he product
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permanently into a new design. The re-shaping is very effective
so tha~ very little spring-back occurs.
B. Prior Art
M~ny patents disclose hot-pressing as a step for
consolidating-a composite board into its final shape. Some of
the hot-pressing consolidation procedures are disclo~ed in the
40110wing United States patents: ~ewton 3,113,065, Linzell
2,388,487 and 3,002,878; Stewart 2,888,376, Higyins 3,428,727;
Akerson 3,75B,357; ~uttunen 3,788,929; Loughborough 2,2g8,017;
Duvall 2,803,188; Maher 3,681,115; Willey et al. 2,495,043i
Oshima et al. 3,699,203; and Downs 3,718,536. Some of the above
patents also disclose the chemical treatment of the fibrous
product prior to hot-pressing to enhance one or more properties
o~ the final product. ~he following patents relate to the
chemical treatment of a ~ibrous product: Kenaga 2~811,470;
~rown 2,724,64~; Ericks 2,692,183; Woodhouse 2,395,311; and
Pratt 1,948,314. Of the above patents, the Akerson et al.
3,758,357; Huttunen 3,788,929 and Loughborough ~,298~017 patents
; disclose ~ot-pressing a wood product for the purpose o~ bending
the product. However, none of these three patents discloses
post-press embossing with a contoured embossing plate and therefore
do not encounter the fidelity problems encountered in xe-shaping
a previously consolidated pxoduct. The above-listed Downs 3,718,536
.
. and Oshima 3,699,203 patents relate to a second hot-press step,
but each pa~ent discloses bonding the product into its final shape
by providing a thermosettable plastic which sets on hot-pressing.
The Duvall 2,803,188 patent relates to a hot-press ~ossing step
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after consolidation of an insulation board, but provides a harden-
able coating composition so that spring-back over extended periods
of time is not a significant factor.
~V~ o- a ~ IDV~ION
In brie~, the process of the present invention comprises
the steps of wetting the surface of a consolidated man-made board
and then hot-pressing the wetted board wit~ a heated em~ossing
plate at a high temperature and pressure and for a period of time
suf~icient to permanently re-shape the surface of the board.
Accordingly, an object of the present invention is to
provide a new and improvéd method o~ embossing a consolidated
man-made board to permanently re-shape the surface of the board.
Another object of the present invention is to post-
press emboss a consolidated man-made board to pro~ide a new
and improved method of re-shaping damaged or rejected consolidated
¦ man-made boards.
Another object of the present invention is to provide
a new and improved method of embossing a consolidated man-made
board by embossing under pressure suf~icient to cause the fibrous
~O material at and near the embossed sur~ace of the board to laterally fl~w to a different location.
~hese and other objects and advantages of the present
invention will be better understood with reerence to the
~ollowing detailed description of the invention. `~
DET~ILED DESCRIPTION
For effective post-press embossing of a consolidated
~an-made cellulosic board it has been found that it: is necessary
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to wet the surface o the board with an aqueous liquid prior to
hot-pressing. Any aqueous liquid will function for effective
embossing so long as the aqueous liquid is used in an amount
sufficient to wet the surface of the ~oard. Water is an effective
liquid for wetting the surface of the board. Generally, an amount
of at leas~ about 5 grams of liquid per square foot of surface
to be embossed will sufficiently wet the surface to be embossedA
It ~s preferred to add a wetting agent to the liquid in an amount
of about 0.1-0.5% by weight to achieve hetter and faster wetting
of the surface prior to hot-pressing. m e liquid can be applied
to the surface of the consolidated board in any convenient manner
such as by roller, spray or brush application.
A~ter the surface of the board has been wetted, the
wetted board is subjected to a hot-press step at a temperature
in the range of 400 -550 F., and at a pressure and for a period
of time sufficient to establish and maintain accurate transference
of detail from the embossing plate to the surface of the board ~or
an extended period of time~ Pressure is the most important variable
in the pressure-temperature-time embossing conditions. By the
appropriate selection of combina~ions of temperature, pressure~
~ and time, a wetted consolidated man-made board can be embossed
i to re-shape the surface with excellent design fidelity and very
:1 little spring-back.
PR~SSURE--TEMPERA TURE--TIME U~ R~ BLES
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¦ 25 With each pressure used there is a specific temperature
range and time of embossing necessary to effectively re-shape a
consolidated man-made product. An increase in any variable
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(temperature, time or pressure) enables a decrease in one or
more of the remaining variables necessary for effective post-
press embossing. Many of the pressure-temperatu~e-time inter-
actions will be specifically set forth, and others can be
extrapolated from the data set forth herein. The times indicated
are times of embossing under full pressure and do not include the
loading and unloading or the buildup and decrease of pressure in
the press.
PRESSURE
I 10 A pressure of about 4000 p.s.i. is preferred, but a
¦ wide range of pressures above 1000 p.s.i. are use~ul in the
;~ post-press embossing of a consolidated man-made board.
~' 1000 p.s.i.: Pressure as low as about 1000 p.s.i. requires anembossing temperature of about 525-550F. for a period of time
of at least 15 seconds. At a pressure of about 1000 p.s.i. and
a temperature of 550 ~., most man-made boards begin to char
after a period of time of about 30 seconds. It is important
when using a press temperature o~ about 550 F. that the board
be removed from the press before charring occurs.
2000 e ~ At a pressure of about 2000 p.s.i. e~fective post-
- press embossing can be achieved with temperatures of about 400F.
i f~r a period of time of about 40-60 seoonds. At 2000 p.s.i., a
temperature of at least 400 F. is necessary. Higher temperatures
up to 550F. can be employed with a corresponding decrease in
- 25 tLme necessary ~or the required fidelity in the post-press embossed
product. It is preferred to employ a temperature o~ at least
450 F. so that the press time can be redueed.
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3000 p.s.i._ At a pressure of 3000 p.s.i. it i9 necessary to
employ a temperature of at least about 400 F. for a period of
time of about 1S-30 seconds. With higher temperatures up to
about 550 F., the time period can be reduced accordingly.
4000 p.s.i.: At pressures above 3000 p.s.i. and temperatures
of 400-550F. the time necessary for effective post-prPss
embossing is reduced to 1 to 15 seronds. Pressures higher than
; 4000 p.s.i. can be used with a corresponding decrease in press
time, but higher capability presses do not provide any noticeable
improvement.
a TEMPER~TU~E
' To achieve the necessary fidelity when post-press
embossing a consolidated man made board, it is always necessary
to employ a temperature of at least about ~00F. and not greater
than about 550F. It has been found that temperatures below
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'', about 400 F. are insufficient to effectively re-design the surface
of a consolidated board while achieving suficient sustained
design fidelity. Many of the products embossed in accordance
wi~h the pxocess set forth herein may be subject,ed to the stress of
outside weather conditions and must show sharp, crisp embossing
contours over sustained periods of time. It is an important
fqature of the present invention to always provide a temperature
of at least about 400 F. in embossing. Temperatures above 550F. '
,; , cause charring and are therefore unsuitable. The most suitable
~,, 25 embossing temperature is in the range of about 400-500 F. when
using a pressure in excess of 1500 p,s~
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TIME
~he period of time necessary for sufficient fidelity
and permanence in re-shaping the sur~ace of a consolidated board is
dependent upon the temperature and pressure employed. For example,
a~ a pressure of 4000 p.s.i. ahd a temperature of 500~. only
about one second is required. At lower temperatures and/or
pressures the tLme is increased a~cordingly~ For example, at a
;
temperature of 400F. and pressure of 2000 p.s.i., the board
must be hot-pressed at full pressure for a period of at least
about 40 seconds. Other examples of embossing times required at
various temperature and pressure conditions are set ~orth above
~nder the headings PRESSURE and TEMPER~TURE, and in the examples
to ~ollow.
An important feature of the present invention is the
provision of a compre sible cushion or backing mem~er disposed
to overlie a flat surface of the embossing press. The compressible
backing member provides a yieldable support for cushioning the
non-embossed side of the man-made board during embossing. In
~' this manner a consolidated man-made board can be embossed to
exceptionally surprising depths without fracturing.
A compressible backlng member overlyinq one side of a
piaten press enables embossing of consolidated products at depths
; heretofore unknown in post press embossing. By employing a compress-
ible backing, the composike board can actually be molded - that is,
contoured on both faces. Deep grooves can be imparted to the
~urface to actually cause a deformakion of the non-embossed side
of the board. The cushion permits the deformation o~ the non-embossed
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side of the board. Molding wlth a compressible cushion is
most advantageous when hot-pressing thinner boards where a
~; deep pattern is desired. It is desirable to provide heat to
both sides of the board during embossing to prevent warpage on
removal from the press.
For use as a compressible cushion~ many different
materials are available, for example, a silicone rubber sheet,
a porols or sponge rubber sheet, canvas, neoprene-coated asbestos
cloth of four to six plies, or simply another piece of hardboard
or other man-made board. It is preferred to use a permanently
distortable compressible mat such as another piece o~ hardboard.
A re~ilient cushion having a thickness of about 1/8 to 1/2 inch
~8 generally sufficient for embossing any man-made board to
any desired degree of contour. Por example, when a series of
products are manufactured from the same embossing plate, a
;~ consolidated board can be used as the cushion. After post-press
embossing of one board, the cushion from that press step can be
re-located to be embossed in the next pressing operation. This~
operakion can be repeated using the cushion from one pre~sin~
operation as the product material to be embossed in t~ next
successive embossing step.
Another important feature of the present invention
is in the provision of a water-penetrable compressible bacXing
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member so that the liquid vaporized in the hot-press can escape
through the man-made board and into the backing member. In this
manner, a "breathing" step during embossiny is unnecessary since
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it will be unnecessary to vent vapors to the atmosphere during
pressing. Ihe water-penetrable cushion ~an be used until it
can absorb no more water. Advantageously,t~e backing member
can be of the same material and dimensions as the board being
embossed~ After embossing, the backing member can be repositioned
to be embossed with a new backing member so that a new and water
absorkant backing member is supplied for each embossing operation.
In this manner, breathing is never necessary. Examples of
typical breathing steps, made unnecessary in accordance with
the present invention are set forth in the Egerstrand Patent
No. 3~112,243 at column 4, lines 42 and 51; and in the Grissom
.. . .
et al. Patent No. 3,056,718 at column 3, lines 2-5.
}f desired, a binder can be provided between the
backing member and the man-made board so that after embossing,
the backing member is laminated to the man-made cellulosiz board
as an integral part of the product. In cases where the composite
board is molded in the press, the laminated backing member can
provide a flat sur~ace for ease in attachment of the molded
product to an existing structure.
EX~MPLE5:
The following examples will more fully and completely
disclose minimum conditions under which a consolidated board
~- must be pressed to achieve excellent design fidelity and to
:
;; permanently re-shape the surface of a consolidated board~ In
; 25 bach case, the tLme set forth is the minimum time necessary to
achieve permanent sharp~ crisp reproduction of the design of the
.,,
embossing plate under the specified conditions of pressure and
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temperature. At 550F., the board should be removed before charr-
ing. It should be noted that aqueous solutions containing chemicals
in addition ~o water require less pressing time than when water
alone is used. The most effective chemical solution found is
sodium xylene sulfonate.
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