CA1060174A - Post-press embossing of a consolidated man-made board - Google Patents

Abstract

POST-PRESS EMBOSSING OF A CONSOLIDATED MAN-MADE BOARD
Abstract of the Disclosure A consolidated man-made board, such as hardboard, is wetted on one surface and thereafter embossed with a contoured embossing plate at a pressure of at least about 1000 p.s.i., at a temper-ature in the range of about 400-550°F. and for a period of time sufficient to permanently re-shape the surface of the consolidated board.

Description

0:~4 }~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 ., . :
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 ., ,.. -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 ;:
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, .
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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~0~74 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 i .

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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~6~'74 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 . . . ..

~o~Vl74 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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; -8-0~4 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 ., o '', 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 ; : .
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 .i , . ' ,' .

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'791 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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Claims (11)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

I claim:

1. A method of embossing a decorative man-made board comprising wetting the surface of a consolidated man-made board with an aqueous liquid in an amount sufficient to wet substantially the entire surface to be embossed, embossing the wetted man-made board with a contoured embossing plate at a pressure of at least about 1000 p.s.i., at a temperature in the range of about 400-550°F.
and for a period of time sufficient to permanently reshape at least one surface of the man-made board.

2. A method as defined in claim 1 wherein the wetted board is embossed at a pressure in the range of about 1500-5000 p.s.i. and for a period of time of from about 1 to 60 seconds.

3. A method as defined in claim 1 wherein the liquid comprises water.

4. A method as defined in claim 2 wherein the wetted board is embossed at a pressure in the range of about 3,000 to 5,000 p.s.i. and for a period of time from 1 to 30 seconds.

5. A method as defined in claim 1 wherein the man-made consolidated board is embossed against a compressible cushion.

6. A method as defined in claim 5 wherein the compressible cushion is porous rubber.

7. A method as defined in claim 5 wherein the compressible cushion is a sheet of man-made board.

8. A method as defined in claim 5 wherein the compressible cushion is water-penetrable.

9. A method as defined in claim 1 wherein the man-made consolidated board is embossed in a platen press.

10. A method as defined in claim 1 wherein the man-made board is continuously embossed against a roller.

11. A method as defined in claim 5 wherein an adhesive is disposed between the board and the cushion to adhere the cushion to the board material during hot-pressing.