(12) United States Patent
`Bruce et al.
`
`USOO68.00361B2
`(10) Patent No.:
`US 6,800,361 B2
`(45) Date of Patent:
`Oct. 5, 2004
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`4,057.443 A 11/1977 Stiling et al.
`4,810,569 A 3/1989 Lehnert et al.
`6,187.409 B1
`2/2001 Mathieu
`6,221,521 B1
`4/2001 Lynn et al.
`
`CA
`DE
`GB
`
`FOREIGN PATENT DOCUMENTS
`1189 434
`6/1985
`4122964 A
`1/1993
`1561. 232 A 3.
`
`Primary Examiner Merrick Dixon
`(57)
`ABSTRACT
`
`The present invention relates to a gypsum board having a
`nonwoven liner and a gypsum core. The gypsum board of
`the present invention has a high work to break, resulting in
`a gypsum board product that has a high resistance to abuse
`in use. The gypsum board of the invention is also more
`flexible and more resistant to water and fire than paper-lined
`gypsum board, and does not contain nutrients that Support
`mold growth.
`48 Claims, 13 Drawing Sheets
`
`--.
`
`- Exomple 22
`-Exomple 23
`-Example 17
`---Exomple 24
`
`(54) GYPSUM BOARD HAVING IMPROVED
`FLEXIBILITY, TOUGHNESS, ABUSE
`RESISTANCE, WATER RESISTANCE AND
`FIRE RESISTANCE
`
`(75) Inventors: Robert B. Bruce, Burlington, CA (US);
`Ashok Harakhlal Shah, Midlothian,
`VA (US)
`
`(73) Assignee: E. I. du Pont de Nemours and
`Company, Wilmington, DE (US)
`
`(*) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21) Appl. No.: 10/172,135
`(22) Filed:
`Jun. 14, 2002
`(65)
`Prior Publication Data
`US 2003/O232182 A1 Dec. 18, 2003
`f
`ec. 18,
`(51) Int. Cl." ................................................ B32B 13/02
`(52) U.S. Cl. ................. 428/294.7; 428/703; 428/319.1;
`428/182; 428/913; 428/309.9
`(58) Field of Search .............................. 428/292.1, 703,
`428/220, 312.4, 319.1, 182, 219,913, 294.7,
`70, 420, 482, 426, 309.9, 71
`
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`
`Louisiana-Pacific Corporation, Exhibit 1024
`IPR of U.S. Pat. No. 8,474,197
`Page 1
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`Louisiana-Pacific Corporation, Exhibit 1024
`IPR of U.S. Pat. No. 8,474,197
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`Louisiana-Pacific Corporation, Exhibit 1024
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`Louisiana-Pacific Corporation, Exhibit 1024
`IPR of U.S. Pat. No. 8,474,197
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`Louisiana-Pacific Corporation, Exhibit 1024
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`US 6,800,361 B2
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`Louisiana-Pacific Corporation, Exhibit 1024
`IPR of U.S. Pat. No. 8,474,197
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`Louisiana-Pacific Corporation, Exhibit 1024
`IPR of U.S. Pat. No. 8,474,197
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`Louisiana-Pacific Corporation, Exhibit 1024
`IPR of U.S. Pat. No. 8,474,197
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`Louisiana-Pacific Corporation, Exhibit 1024
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`US 6,800,361 B2
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`1
`GYPSUM BOARD HAVING IMPROVED
`FLEXIBILITY, TOUGHNESS, ABUSE
`RESISTANCE, WATER RESISTANCE AND
`FIRE RESISTANCE
`
`FIELD OF THE INVENTION
`The present invention relates to an improved gypsum
`based Substrate faced with a polymeric nonwoven sheet
`material, the gypsum-based Substrate Suited for use in con
`Struction materials Such as wall panels, ceiling panels, floor
`underlayment and interior and exterior sheathing.
`
`BACKGROUND OF THE INVENTION
`Gypsum board is traditionally manufactured by a con
`tinuous process. In the process, a gypsum slurry is first
`generated in a mechanical mixer by mixing calcium Sulfate
`hemihydrate (also known as calcined gypsum), water, and
`other agents. These various additives are used in the gypsum
`Slurry as set accelerators (such as ground gypsum, potassium
`Sulphate), Set retarders (such as diethylene triamine tetra
`acetic acid), water reducing agents (Such as condensed
`naphthalene Sulphonates), foaming agents (such as lauryl
`alcohol ether Sulphates), liner bonding agents (Such as
`Starch), anti-burning agents (Such as boric acid), glass fibers
`for improved physical properties and fire resistance, other
`agents to improve reaction to fire properties (Such as clay),
`water proofing agents (such as wax or Silicones), or other
`agents. The gypsum Slurry is deposited on a paper sheet
`which has had each edge Scored or creased to facilitate the
`folding of the edges to make a sidewall of height equal to
`board thickness and a further flap of width about 1 inch wide
`folded back over the board. An upper continuously advanc
`ing paper sheet is then laid over the gypsum Slurry and the
`edges of the upper and lower sheets are pasted to each other
`using glue at the edges of the top and/or bottom sheet. The
`paper sheets and gypsum Slurry are passed between parallel
`upper and lower forming plates or rolls in order to generate
`an integrated and continuous flat Strip of unset gypsum
`Sandwiched between the paper sheets that are known as
`facing or liners. This Strip is conveyed over a Series of
`continuous moving belts and rollers for a period of 2 to 5
`minutes during which time the core begins to hydrate back
`to gypsum and hardens. During each transfer between belts
`and/or rolls, the Strip is stressed in a way that can cause the
`paper facing to delaminate from the gypsum core if the
`adhesion between the gypsum core and the facing is not
`Sufficient. Once the gypsum core has set Sufficiently, the
`continuous Strip is cut into Shorter lengths or even individual
`boards or panels of prescribed length. Once again, it is
`important for there to be good adhesion between the paper
`sheets and the Set, but Still wet, gypsum core or the cutting
`action will pull the edges of the paper facing sheet away
`from the gypsum core. Good adhesion between the top and
`bottom paper sheet at the edges which are pasted with glue
`is also important here.
`After the cutting Step, the gypsum boards are separated
`and grouped through a Series of belts and rollers and then
`flipped over before being fed into drying Ovens or kilns
`where the boards are dried So as to evaporate excess water.
`The hydration from hemihydrate to gypsum must be essen
`tially complete by this point, normally between 7 and 15
`minutes after mixing. When the gypsum boards are
`accelerated, flipped and fed into the drying ovens, the boards
`are Subjected to a variety of Stresses that can cause the facing
`to peel away from the gypsum core of the boards unless
`
`15
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`there is good adhesion between the set (but still wet) gypsum
`core and the facing material. Inside the drying ovens, the
`boards are blown with hot drying air at speeds up to 4000
`feet/minute which can cause further delamination of the
`paper facing if there is not good wet adhesion between the
`gypsum and the paper liners. If portions of the facing sheets
`delaminate from the gypsum core during drying in the oven,
`the liner can become entangled in the rollers and the gypsum
`crumbles as it dries, jamming the oven, which then requires
`the line to be shut down while the loose gypsum and liner is
`cleaned out of the ovens. Poor wet bond between liner and
`the gypsum core can also result in blisters due to delami
`nation during the drying process. The gypsum boards are
`dried in the ovens for anywhere from 30 to 75 minutes. After
`the dried gypsum boards are removed from the Ovens, the
`ends of the boards are trimmed off and the boards are cut to
`desired sizes. Good adhesion between the top and bottom
`paper sheet at the edges which are pasted with glue is also
`important throughout the board forming process as well as
`during use of the board.
`Gypsum board has been the Subject of numerous patents,
`Such as U.S. Pat. No. 4,057,443, Canadian Patent No.
`1,189,434, as well as co-pending U.S. patent application Ser.
`Nos. 09/512,921 and 09/513,097, all of which are incorpo
`rated herein by reference.
`For years it has been recognized that high toughness and
`abuse resistance are desirable properties in gypsum-based
`board for use in buildings. High toughneSS and abuse
`resistance are here defined in terms of high initial modulus,
`high flexural Strength corresponding to high-to-moderate
`initial modulus, high maximum flexural Strength and high
`work-to-break. In addition to high toughness, it is desirable
`for gypsum board to have an abrasion resistant property in
`order to resist abuse. Further, it is desired to have gypsum
`board with some flexibility under load.
`Standard gypsum boards are produced with a cellulosic
`paper liner. Paper has good wet adhesion with the gypsum
`slurry during board formation. It is believed that cellulose
`draws moisture from the slurry and pulls the Slurry into close
`contact with the paper fibers. AS the gypsum Sets, there is
`Some interlocking of the gypsum crystals with the paper
`fibers at the Surface of the liner, as well as Some chemical
`bonding between the wet gypsum matrix and the hydrophilic
`paper fibers. Paper does not allow the gypsum Slurry to Seep
`through during board forming, provides reasonable Strength
`and a paintable Surface to the finished gypsum board.
`However, there are Several disadvantages to the use of
`paper as a liner for gypsum board. Paper acts as a food
`Source for mold and mildew, and it becomes especially weak
`and Subject to delamination either directly from the gypsum
`core or between the layers of the multi-layer sheets when the
`paper becomes damp due to water leaks or high humidity.
`In addition, Standard paper-lined gypsum board has lower
`work-to-break and abrasion resistance than is needed for
`certain applications. Work-to-break (WTB) is defined as the
`force (or stress) required to break the sample times the
`distance (or Strain) that the sample is deformed before
`failure. On a stress-strain curve, WTB is represented by the
`area under this StreSS-Strain or breaking curve.
`In use, paper-faced gypsum boards are generally coated
`with another material, Such as Specialty paint or wall
`coverings, in order to achieve high abrasion resistance. To
`overcome these durability problems, paper-faced board is
`frequently covered with a wall paper of hard sheet or plastic
`film when used in high traffic areas.
`There are international and foreign building materials
`Standards that also classify conventional gypsum boards in
`
`Louisiana-Pacific Corporation, Exhibit 1024
`IPR of U.S. Pat. No. 8,474,197
`Page 15
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`

`

`3
`the combustible category. There have been efforts to make
`panel products from gypsum that can achieve noncombus
`tible status. The weight fraction of 5-6% paper in standard
`paper-lined gypsum would most likely cause this building
`material to fail the test for combustibility as described in
`ASTM E136, were it not for the fact that some building
`materials, Such as gypsum board, have been defined in
`Section X1.2.3b of the standard as noncombustible, based on
`their composition and flame spread properties alone. U.S.
`Pat. No. 6,221,521 concerning gypsum boards made without
`liners describes how even these gypsum/fiber boards that are
`reinforced with internal cellulosic fibers instead of external
`paper liners are deemed combustible as tested by ASTM
`E136 because of the presence of more than 3-4% of organic
`fibers in the core of the board.
`A normal paper liner contains about 170-220 g/m of
`cellulosic content. Similar Standards exist in other countries
`and new European Standards being implemented do not
`classify Standard cellulosic paper-lined gypsum board as
`noncombustible, due to the calorific content of the Surface
`liner.
`AS technology evolves regarding fire protection in
`buildings, consideration is being given to both building
`System fire resistance as well as a products reaction to fire.
`It is desirable to have a gypsum board that contributes as
`little fuel load as possible in a fire Situation to improve the
`overall fire risk in buildings. It is beneficial for the liners
`used to make gypsum board to have a low calorific content
`in order to reduce the fuel load brought about through its use
`in the building.
`Commercially available gypsum board products with lin
`erS other than cellulosic paper have been developed, an
`example being Dens-Glass(E) Gold exterior sheathing
`(available from Georgia-Pacific, Inc., Atlanta, Ga.). Dens
`Glass(E) Gold exterior Sheathing uses a glass mat in place of
`cellulosic paper liner. However, this product has relatively
`low WTB and low deflection and hence, is brittle. In
`addition, the Surface of the Dens-Glass(E) Gold exterior
`sheathing is very different from Standard cellulosic paper
`lined gypsum board for interior use. For use in interior walls,
`it is desired to have a gypsum board with a Surface Similar
`to Standard paper-lined gypsum board So that it can be
`painted and have a similar appearance as Standard paper
`lined board.
`It has been a notorious problem with the Standard paper
`lined gypsum board that the paper liner peels off while
`removing wall paper. The most common technique for
`removing the old wall paper is to perforate the old wall paper
`by Scoring and then wetting the perforated wall paper with
`water to loosen up the glue underneath the wall paper, which
`results in moist paper liner and hence, the paper liner
`becomes very Susceptible to peeling when the wall paper is
`removed.
`There have been attempts to Substitute Stronger and more
`durable Synthetic sheet materials for the paper liners found
`in conventional gypsum board products. Canadian Patent
`No. 1,189,434 discloses gypsum panels made with a facing
`of a moisture vapor permeable Spunbonded nonwoven mate
`rial. Canadian Patent No. 1,189,434 discloses gypsum pan
`els faced with TyvekCR) spunbonded olefin sheet material.
`Tyvek(R) is a registered trademark of E.I. du Pont de Nem
`ours and Company of Wilmington, Del. TyvekCE) sheets are
`made by Solution flash-spinning polyethylene to form fine
`plexifilamentary fibril structures that can be thermally
`bonded to form sheet material. The product of Canadian
`patent number 1,189,434 has several shortcomings. The
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`US 6,800,361 B2
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`product has been found to have poor adhesive bonding
`between the liner material and the gypsum Slurry during the
`board manufacturing process. In addition, although the
`TyvekCR liner is as Strong as paper in the machine direction
`(MD) and almost three times as Strong in the cross direction
`(CD), the board strength is about one-third that of paper
`lined standard gypsum board in the MD of the liner. In
`addition, the Surface of the gypsum board is Shiny and
`almost film-like Smooth, which are characteristics of the
`Tyvek(R) sheet surface. Also, the melting point of TyvekOR
`sheet is quite low at 135 C., and the sheet starts shrinking
`at temperatures close to 100° C. This is a disadvantage
`because the drying Ovens used in conventional gypsum
`board-making processes operate at temperatures well above
`100° C., usually above 150° C.
`It is desired to have gypsum board which would not Sag
`or significantly lose its flexural Strength when wet or in a
`high humidity environment. In addition, it is also desired to
`have abrasion resistant gypsum board. It is also desired to
`have gypsum board with high peel Strength between the liner
`and the core. It would also be desirable to have good release
`properties between the liner and an overlying covering.
`It is also desired to have a gypsum board free of ingre
`dients that would act as nutrients for mold growth. Conven
`tional gypsum board contains organic matter which provides
`food for fungi Such as mold and mildew.
`It is an object of the present invention to provide a
`gypsum board which provides the following product
`attributes: flexibility, high toughness, high Surface Stability
`against abrasion and peeling, resistance to liquid water and
`high humidity, fire resistance, mold resistance and paper-like
`Surface.
`BRIEF SUMMARY OF THE INVENTION
`In one embodiment, the present invention relates to a
`gypsum board comprising a gypsum core held between two
`sheets of porous, fibrous polymeric nonwoven liner, wherein
`the work-to-break of the gypsum board in the MD of the
`nonwoven liner at a strain of 0.75 inch is greater than 30
`lb.-in.
`In another embodiment, the invention also relates to a
`gypsum board having a work-to-break in the MD at a Strain
`of 0.75 inch of greater than 60*X lb-in, where X is the
`thickness of the board in inches.
`In another embodiment, the present invention is directed
`to a gypsum board comprising a gypsum core held between
`two sheets of porous, fibrous polymeric nonwoven liner,
`wherein the nonwoven liner has Strip tensile in the machine
`direction of at least 35 lb./in., percent elongation at 1 lb. in
`the MD of less than 0.7%, percent elongation at 3 lb. in the
`MD of less than 1.5% and percent elongation-at-break in the
`MD of less than 100%, strip tensile in the CD of at least 12
`lb./in., percent elongation at 1 lb. in the CD of less than
`3.0%, percent elongation at 3 lb. in the CD of less than 7.0%
`and percent elongation-at-break in the CD of less than
`300%.
`In another embodiment, the present invention is directed
`to a gypsum board comprising a gypsum core held between
`two sheets of porous, fibrous polymeric nonwoven liner,
`wherein the nonwoven liner has strip tensile in the MD of at
`least 65 lb./in., percent elongation at 1 lb. in the MD of less
`than 0.5%, percent elongation at 3 lb. in the MD of less than
`0.7% and percent elongation-at-break in the MD of less than
`50%, strip tensile in the CD of at least 22 lb./in., percent
`elongation at 1 lb. in the CD of less than 1.5%, percent
`elongation at 3 lb. in the CD of less than 3.0% and percent
`elongation-at-break in the CD of less than 100%.
`
`Louisiana-Pacific Corporation, Exhibit 1024
`IPR of U.S. Pat. No. 8,474,197
`Page 16
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`S
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIGS. 1-13 are stress-strain curves illustrating the defor
`mation of various gypsum board Samples (measured in
`distance units) as an increasing level of force is applied
`(measured in force units).
`DETAILED DESCRIPTION OF THE
`INVENTION
`This invention describes a gypsum board product that is
`made by using Special liners and a core formulated to take
`advantage of these liners. This board product has very
`unique and improved properties when compared to the
`conventional boards sold today: high work to break (WTB);
`good initial modulus, yield Strength and peak load; and good
`resistance to abuse through abrasion, either before or after
`decoration of the Surface, as compared to Standard paper
`lined board. In addition, due to the generally hydrophobic
`nature of the polymeric liners, the board is much more
`resistant to the deleterious effects of liquid water or water
`Vapor when compared to conventional paper-lined gypsum
`boards. The high Strength of the liners per unit weight also
`gives a product with good Strength properties but much leSS
`fuel content and thus has improved fire resistance and
`reaction to fire properties. The enhanced product character
`istics give a more flexible product that allows for easier
`installation in a wider range of building Systems. The
`product can also be manufactured in Such a way that the
`product will not Support mold growth and allows the con
`Struction of mold resistant Structures.
`This invention also describes the process by which this
`product is made, in particular the use of a dense layer of
`gypsum next to the liner Surface to promote good wet
`bonding and the use of additives that will promote good
`bonding of the liner to the gypsum core. It has also been
`found that it is possible to choose proceSS additives that are
`suitable for board production but also will result in a product
`that is mold resistant. The invention can be implemented
`using a conventional gypsum board machine to make a wide
`range of Superior products, with only minor changes to the
`equipment as required to accommodate the high perfor
`mance properties of the novel liner and board. Furthermore,
`the invention uses a liner material that is dimensionally
`Stable when exposed to water, making the manufacturing
`proceSS easier to control.
`Reference will now be made in detail to the presently
`preferred embodiments of the invention, examples of which
`are illustrated below.
`In a first embodiment, the present invention is directed to
`a gypsum board product that has high WTB in addition to
`good initial modulus, yield Strength and peak load. The
`gypsum board products of the present invention exhibit
`WTB in the MD of the nonwoven liners of greater than 30
`lb.-in. at a strain of 0.75 in., and preferably greater than 40
`lb.-in. at a strain of 1.0 in., even when the board has a
`thickness of only about 2 in. More preferably, the WTB in
`the MD of the gypsum board products of the present
`invention can be expressed by the equation:
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`1O
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`wherein X is the thickness of the board in inches.
`The WTB of the gypsum boards of the present invention
`in the CD of the nonwoven liners is greater than 10 lb.-in.
`at a strain of 0.75 in., preferably greater than 10 lb.-in. at a
`strain of 1.0 in.
`The initial modulus of the inventive gypsum boards in the
`MD is at least 500 lb./in., with a peak load of at least 40 lb.
`The WTB at peak load is at least 30 lb.-in.
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`US 6,800,361 B2
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`6
`The gypsum boards of the present invention preferably
`will not break even when subjected to a bending strain of 0.5
`in. at a bending StreSS of greater than 40 lb., or even at 1.0
`in. Strain and 45 lb. StreSS. The gypsum boards of the present
`invention have a loss in MD flexural strength of less than
`75% when flexural strength peak load is measured imme
`diately after holding the board under water for 2 hours as per
`ASTM C36. The gypsum board of the present invention has
`a ratio of the flexural strength peak load in the MD to the
`peak load in the CD less than 3.
`The gypsum board of the invention includes a first non
`woven liner and a Second nonwoven liner which envelope a
`gypsum core. The first and Second nonwoven liners are
`porous, fibrous, polymeric nonwoven sheets which can be
`comprised of thermally and/or chemically bonded meltspun
`Substantially continuous fibers, carded and/or air laid Staple
`fibers webs, needle punched staple fiber webs, hydroen
`tangled fibrous webs or other nonwoven structures. The
`nonwoven liners are made from fiber forming polymers
`derived from condensation- and/or addition-type monomers.
`Such polymers include polyethylene, polypropylene, ali
`phatic or aromatic polyamides or poly (ethylene
`terephthalate) (PET). Preferably, the nonwoven liners com
`prise a polymer having a Softening or melting point of
`greater than 150° C. Such polymers include polypropylene
`which has a softening or melting point of 160° C. and PET
`which has a softening or melting point of 250 C. The reason
`for this is that the drying oven temperature is much higher
`than 100° C., and usually above 150° C. Liners made from
`sheets having a Softening or melting point lower than 150
`C. can melt, buckle or shrink during the drying Step of the
`process.
`The fibers that form the nonwoven liners for use in the
`present invention can contain additives Such as dyes,
`pigments, UV and thermal Stabilizers and antimicrobial
`agents.
`Preferably, the nonwoven liners are a mixture of mono
`component fibers and bicomponent fibers that have been
`carded and/or air laid and hydroentangled into a nonwoven
`sheet and then bonded during drying and hot calendering.
`When sheath-core type bicomponent fibers are used in the
`nonwoven liner, the melting point of the sheath is Suffi
`ciently lower than that of the Strength contributing fiber core
`and any monocomponent fibers to thermally bond the entire
`sheet structure. It is possible that the fibers providing ther
`mal bonding can be low melting monocomponent fibers,
`although bicomponent fibers are preferred. When the non
`woven liners comprise a mixture of monocomponent and
`bicomponent fibers, the amount of bicomponent fiberS is
`between about 10 wt.% and 50 wt.% of the weight of the
`liner fabric, preferably between about 15 wt.% and 35 wt.
`%.
`Additionally, the liner should have the right level and
`right type of Strength properties in order to produce novel
`gypsum board with Specific strength properties. The non
`woven liners for use in the invention preferably have a Strip
`tensile Strength in the machine and croSS directions similar
`to paper. In addition, the liners according to the present
`invention should have a low-to-moderate percent
`elongation-to-break under load.
`The tensile strength of the liners contributes to the
`improved properties of the board of the present invention.
`The strip tensile strength is at least 35 lb./in., preferably
`above 65 lb./in., in the MD and at least 12 lb./in., preferably
`above 22 lb./in in the CD. By “machine direction” is meant
`the direction in which the nonwoven liners are produced
`(parallel to the direction of travel through the sheet-forming
`
`Louisiana-Pacific Corporation, Exhibit 1024
`IPR of U.S. Pat. No. 8,474,197
`Page 17
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`

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`7
`machine), and by “cross direction' is meant the direction
`perpendicular to the machine direction. The elongation-to
`break, that is the percentage of deformation at the breaking
`point, of the nonwoven liners is at least less than 100%,
`preferably less than 50% in the MD and at least less than
`300%, preferably less than 100% in the CD. The percent
`elongation of the liner at 1 lb. of force is at least less than
`0.7%, preferably less than 0.5% in the MD and at least less
`than 3%, preferably less than 1.5% in the CD. The percent
`elongation of the liner at 3 lb. of force is at least less than
`1.5%, preferably less than 0.7%, in the MD and at least less
`than 7.0%, preferably less than 3.0%, in the CD.
`The nonwoven sheet of the liners has a stiffness which is
`high enough to allow the Sheet to be folded and Scored, like
`paper, for ease of replacing paper on existing gypsum board
`manufacturing machines. This is especially desired for the
`bottom liner on which the gypsum Slurry is first deposited
`during the board forming process.
`The liners should have sufficient porosity and bulk
`(defined he rein as the thickness per unit basis
`weight density) to allow Some penetration of the wet gyp
`Sum Slurry through the liners during board formation while
`Still containing the gypsum slurry within its structure. A
`Structure having very densely packed fibers will have very
`poor wet adhesion to the gypsum slurry, while too bulky and
`open liner Structure can not have the desired Strength per unit
`basis weight and can allow complete Seepage of the wet
`gypsum Slurry.
`The nonwoven liners of the present invention are a porous
`sheet material in which the mean flow pore diameter is 5 to
`100 micrometer range, preferably 10-70 micrometers. The
`mean flow pore pressure is at least leSS than 3 psi, preferably
`less than 1 psi. The liner has a specific level of body, that is,
`it comprises at least 20% voids by volume, preferably
`greater than 50% and its bulk is at least 1.25, preferably
`greater than 2.
`According to one preferred embodiment of the invention,
`the first and Second nonwoven liners each have a first Surface
`characterized by pores or spaces formed between fibers,
`which pores are of Sufficient Size for a gypsum slurry to enter
`the pores and become intertwined with the fibers in the
`nonwoven liners So as to form a strong mechanical bond
`between the gypsum core and the liners when the gypsum
`Sets up. The gypsum Slurry which forms the gypsum core is
`deposited on the first porous Surface of the first nonwoven
`liner, and the first porous Surface of the Second nonwoven
`liner is juxtaposed against the gypsum slurry Such that when
`the gypsum Slurry is enclosed between said first and Second
`nonwoven liners, the slurry impregnates the pores or spaces
`between the fibers on the inner Surfaces of the first and
`Second nonwoven liners. The above-described combination
`of pore size, Voids and bulk range allow the wet, Set gypsum
`layer to intertwine with the fibers of the liner, providing
`good wet adhesion, without the gypsum Slurry penetrating
`completely through the nonwoven liner to the other Side.
`The liners for use in the gypsum board of the invention
`must have good wet adhesion with the gypsum core. The wet
`adhesion between the liners and the core is partly deter
`mined by the Structure and composition of the nonwoven
`sheet used as the liner material and partly by the composition
`of the gypsum core. The wet adhesion is particularly impor
`tant for the production of the board Since as a routine part of
`the conventional process for making board, after wet gyp
`Sum Slurry is applied to the first nonwoven liner and the
`Second nonwoven liner is applied to the opposite side of the
`Slurry, the assembly of the liners and gypsum core is flipped.
`Good wet adhesion is critical to keep the assembly intact
`during this Step of the board production process.
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`It is also important to have good dry adhesion between the
`liners and the gypsum core for translating liner Strength to
`the finished gypsum board Strength properties. In addition to
`mechanical interaction due to Slurry penetration inside the
`liner Structure, it is believed that chemical bonding between
`the liner and gypsum core also helps in improving the dry
`adhesion.
`It is desired that the fibers at the Surface of the liners
`coming in contact with the wet gypsum Slurry be chosen to
`have sufficient micro-movement to allow for the Swelling
`and then shrinking of the gypsum core that occurs during the
`Setting and drying Steps.
`In addition, it is advantageous that the gypsum board
`product of the present invention has improved reaction to
`fire characteristics as measured by tests Such as found in
`ASTM E136.
`Depending on the application, the liner can have different
`types of Surface; e.g., liner Surface exposed to the interior of
`a room in an indoor application will have Smoothness
`Similar to paper based gypsum board while the liner Surface
`exposed to gypsum core can be preferentially more rough
`for improving wet and dry adhesion.
`When the gypsum board of the invention is intended for
`interior use, it is preferable for the appearance of the
`exposed Surface of the nonwoven liners, i.e. the “outside
`Surface', to be as Similar as possible to that of paper liners
`commonly used in gypsum board. It is preferable for the
`nonwoven liners of the present invention to resemble the
`Surface of common paper liners in order to provide a Suitable
`appearance upon painting of the Outer Surface. Likewise, the
`outer Surface of the nonwoven liners should be as Similar as
`possible to common paper liners in order to facilitate appli
`cation and removal of wall paper. To these ends, the Surface
`of the nonwoven liners of the present invention should have
`a coefficient of friction of greater than 10 degrees, measured
`as described below.
`In order to impart a similar degree of SmoothneS