U.S. patent application number 10/607858 was filed with the patent office on 2004-12-30 for gypsum board faced with non-woven glass fiber mat.
Invention is credited to Jaffee, Alan Michael.
Application Number | 20040266303 10/607858 |
Document ID | / |
Family ID | 33540403 |
Filed Date | 2004-12-30 |
United States Patent
Application |
20040266303 |
Kind Code |
A1 |
Jaffee, Alan Michael |
December 30, 2004 |
Gypsum board faced with non-woven glass fiber mat
Abstract
A gypsum board comprises a set gypsum layer having a first face
and a second face. A fibrous mat is affixed to at least one of the
faces. The mat comprises a non-woven web bonded together with a
resinous binder. The web is composed of chopped continuous glass
fibers having an average fiber diameter ranging from about 9.5 to
12.5 .mu.m. The board is exceedingly durable. It has a smooth
surface that is readily finished in an aesthetically pleasing way,
using paint or other wall covering systems.
Inventors: |
Jaffee, Alan Michael;
(Bowling Green, OH) |
Correspondence
Address: |
JOHNS MANVILLE
Legal Department
10100 West Ute Avenue
Littleton
CO
80127
US
|
Family ID: |
33540403 |
Appl. No.: |
10/607858 |
Filed: |
June 27, 2003 |
Current U.S.
Class: |
442/386 ;
442/331 |
Current CPC
Class: |
B32B 38/164 20130101;
B32B 38/18 20130101; B32B 2317/122 20130101; H01F 41/0226 20130101;
B32B 5/24 20130101; B32B 7/12 20130101; Y10T 442/604 20150401; B32B
2260/023 20130101; H02K 1/02 20130101; E04C 2/043 20130101; B32B
2607/02 20130101; B32B 3/04 20130101; B32B 13/14 20130101; H01F
3/04 20130101; H02K 15/02 20130101; B32B 2262/101 20130101; Y10T
442/665 20150401 |
Class at
Publication: |
442/386 ;
442/331 |
International
Class: |
B32B 013/14; B32B
013/02 |
Claims
What is claimed is:
1. A gypsum board, comprising: a. a gypsum layer having a first
face and a second face and comprising set gypsum; and b. first and
second facers affixed to said first and second faces, said first
facer being a fibrous mat comprising a non-woven web bonded
together with a resinous binder, and said web being composed of
chopped continuous glass fibers having an average fiber diameter
ranging from about 9.5 to 12.5 .mu.m.
2. A gypsum board as recited by claim 1, wherein said chopped
continuous glass fibers are composed of at least one member
selected from the group consisting of E glass, C glass, T glass,
sodium borosilicate glass, and mixtures thereof.
3. A gypsum board as recited by claim 1, wherein said chopped
continuous glass fibers are composed of E glass.
4. A gypsum board as recited by claim 1, wherein at least about 90%
by weight of said chopped continuous glass fibers have a diameter
ranging between about 9.5 and 12.5 .mu.m.
5. A gypsum board as recited by claim 1, wherein at least about 95%
by weight of said chopped continuous glass fibers have a diameter
ranging between about 9.5 and 12.5 .mu.m.
6. A gypsum board as recited by claim 1, wherein at least about 97%
by weight of said chopped continuous glass fibers have a diameter
ranging between about 9.5 and 12.5 .mu.m.
7. A gypsum board as recited by claim 1, wherein said chopped
continuous glass fibers have an average fiber length ranging from
about 6 to 12 mm.
8. A gypsum board as recited by claim 1, wherein at least a
majority of said chopped continuous glass fibers have a fiber
length ranging from about 6 to 18 mm.
9. A gypsum board as recited by claim 1, wherein said resinous
binder is composed of at least one member selected from the group
consisting of urea formaldehyde; conventional modified urea
formaldehyde; acrylic resin; melamine resin; high nitrogen melamine
resin; homopolymer and copolymer of polyacrylic acid having a
molecular weight of less than 10,000; crosslinking acrylic
copolymer; crosslinked vinyl chloride acrylate copolymer; and
modified acrylic latex binder.
10. A gypsum board as recited by claim 1, wherein said resinous
binder is composed of a modified acrylic latex binder.
11. A gypsum board as recited by claim 9, wherein said resinous
binder further comprises a cross-linker in an amount ranging up to
about 10 weight percent.
12. A gypsum board as recited by claim 11, wherein said cross
linker is present in an amount ranging from about 2 to 5 weight
percent.
13. A gypsum board as recited by claim 11, wherein said resinous
binder comprises melamine formaldehyde.
14. A gypsum board as recited by claim 1, wherein said resinous
binder has a glass transition temperature ranging from about 15 to
45.degree. C.
15. A gypsum board as recited by claim 1, wherein said resinous
binder further comprises at least one water repellant agent.
16. A gypsum board as recited by claim 1, wherein said fibrous mat
further comprises effective amounts of fine particles of limestone,
glass, clay, coloring pigments, biocide, fungicide, intumescent
material, or mixtures thereof.
17. A gypsum board as recited by claim 1, wherein said fibrous mat
has a basis weight ranging from about 0.6 to 2.2 pounds per 100
square feet.
18. A gypsum board as recited by claim 17, wherein said fibrous mat
has a basis weight ranging from about 0.9 to 2.2 pounds per 100
square feet.
19. A gypsum board as recited by claim 18, wherein said fibrous mat
has a basis weight of about 1.25.+-.0.2 pounds per 100 square
feet.
20. A gypsum board as recited by claim 1, said second facer
comprising kraft paper.
21. A gypsum board as recited by claim 1, said second facer
comprising a fibrous mat.
22. A gypsum board as recited by claim 1, said second facer being a
fibrous mat comprising a non-woven web bonded together with a
resinous binder, and said web being composed of chopped continuous
glass fibers having an average fiber diameter ranging from about
9.5 to 12.5 .mu.m.
23. A gypsum board as recited by claim 1, wherein said gypsum core
further comprises at least one water repellant agent.
24. A gypsum board as recited by claim 1, wherein said gypsum core
further comprises reinforcing fiber.
25. A gypsum board as recited by claim 1, wherein said gypsum core
further comprises a biocide.
26. A gypsum board as recited by claim 1, said board having flame
resistance sufficient to pass the test of ASTM Method E84, Class
1.
27. In a gypsum board having a first face and a second face and a
non-woven fibrous mat affixed to at least one of said faces, the
improvement wherein said mat comprises a web bonded together with a
resinous binder and comprising chopped continuous glass fibers
having an average fiber diameter ranging from about 9.5 to 12.5
.mu.m.
28. A process for manufacturing an article comprising a hydraulic
set material layer having first and second faces, and first and
second facers affixed thereto, at least said first facer comprising
a non-woven, fibrous mat, the process comprising: a. providing said
non-woven, fibrous mat having a fibrous web composed of chopped
continuous glass fibers having an average fiber diameter ranging
from about 9.5 to 12.5 .mu.m bound together with a resinous binder;
b. forming an aqueous slurry comprising at least one member
selected from the group consisting of anhydrous calcium sulfate,
calcium sulfate hemi-hydrate, and hydraulic setting cement; c.
distributing the slurry to form a layer on said first facer; d.
applying said second facer onto the top of said layer; e.
separating the resultant laminate into individual articles; and f.
drying the articles.
29. A fibrous mat comprising a non-woven web bonded together with a
resinous binder, said web being composed of chopped continuous
glass fibers having an average fiber diameter ranging from about
9.5 to 12.5 .mu.m.
30. A fibrous mat as recited by claim 29, wherein at least about
90% by weight of said chopped continuous glass fibers have a
diameter ranging between about 9.5 and 12.5 .mu.m.
31. A fibrous mat as recited by claim 29, said mat having a
permeability of at least about 300 cfm/ft.sup.2 measured by the
Frazier test.
32. A hydraulic set board, comprising: a. a hydraulic set material
layer having a first and a second face; and b. first and second
facers affixed to said first and second faces, at least of said
first facer being a fibrous mat comprising a non-woven web bonded
together with a resinous binder, and said web being composed of
chopped continuous glass fibers having an average fiber diameter
ranging from about 9.5 to 12.5 .mu.m.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a gypsum board used in
building construction and to a process for its manufacture; and
more particularly, to a non-woven glass fiber mat comprising a
blend of glass fibers having a narrow range of diameters and
various lengths bonded together with a resinous latex binder, a
gypsum board or similar product in panel form faced on at least one
side with such a mat, and processes for the manufacture
thereof.
[0003] 2. Description of the Prior Art
[0004] Wallboard formed of a gypsum core sandwiched between facing
layers is used in the construction of virtually every modern
building. In its various forms, the material is employed as a
surface for walls and ceilings and the like, both interior and
exterior. It is relatively easy and inexpensive to install, finish,
and maintain, and in suitable forms, is relatively fire
resistant.
[0005] Although paper-faced wallboard is most commonly used for
finishing interior walls and ceilings, other forms with different
kinds of facings have superior properties that are essential for
other uses. One known facing material is non-woven fiberglass
mat.
[0006] Gypsum wallboard and gypsum panels are traditionally
manufactured by a continuous process. In this process, a gypsum
slurry is first generated in a mechanical mixer by mixing at least
one of anhydrous calcium sulfate (CaSO.sub.4) and calcium sulfate
hemihydrate (CaSO.sub.4.1/2H.sub.2O, also known as calcined
gypsum), water, and other substances, which may include set
accelerants, waterproofing agents, reinforcing mineral, glass
fibers, and the like. The gypsum slurry is normally deposited on a
continuously advancing, lower facing sheet, such as kraft paper.
Various additives, e.g. cellulose and glass fibers, are often added
to the slurry to strengthen the gypsum core once it is dry or set.
Starch is frequently added to the slurry in order to improve the
adhesion between the gypsum core and the facing. A continuously
advancing upper facing sheet is laid over the gypsum and the edges
of the upper and lower facing sheets are pasted to each other with
a suitable adhesive. The facing 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 sheets. Such a flat strip of unset gypsum is
known as a facing or liner. The strip is conveyed over a series of
continuous moving belts and rollers for a period of several
minutes, during which time the core begins to hydrate back to
gypsum (CaSO.sub.4.2H.sub.2O). The process is conventionally termed
"setting," since the rehydrated gypsum is relatively hard. During
each transfer between belts and/or rolls, the strip is stressed in
a way that can cause the facing to delaminate from the gypsum core
if its adhesion 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.
[0007] After the cutting step, the gypsum boards are fed into
drying ovens or kilns so as to evaporate excess water. Inside the
drying ovens, the boards are blown with hot drying air. 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. The
boards are commonly sold to the building industry in the form of
sheets nominally 4 feet wide and 8 to 12 feet or more long and in
thicknesses from nominally about 1/4 to 1 inches, the width and
length dimensions defining the two faces of the board.
[0008] While paper is widely used as a facing material for gypsum
board products because of its low cost, many applications demand
water resistance that paper facing cannot provide. Upon exposure to
water either directly in liquid form or indirectly through exposure
to high humidity, paper is highly prone to degradation, such as by
delamination, that substantially compromises its mechanical
strength. Gypsum products typically rely on the integrity of the
facing as a major contributor to their structural strength.
Consequently, paper-faced products are generally not suited for
exterior or other building uses in which exposure to moisture
conditions is presumed.
[0009] In addition, there is growing attention being given to the
issue of mold and mildew growth in building interiors and the
potential adverse health impact such activity might have on
building occupants. The paper facing of conventional gypsum board
contains wood pulp and other organic materials that may act in the
presence of moisture or high humidity as nutrients for such
microbial growth. A satisfactory alternative facing material less
susceptible to growth is highly sought.
[0010] A further drawback of paper-faced gypsum board is flame
resistance. In a building fire, the exposed paper facing quickly
burns away. Although the gypsum itself is not flammable, once the
facing is gone the board's mechanical strength is greatly impaired.
At some stage thereafter the board is highly likely to collapse,
permitting fire to spread to the underlying framing members and
adjacent areas of a building, with obvious and serious
consequences. A board having a facing less susceptible to burning
would at least survive longer in a fire and thus be highly
desirable in protecting both people and property.
[0011] To overcome these and other problems, a number of
alternatives to paper facing have been proposed. U.S. Pat. No.
4,647,496 discloses an exterior insulation system including a
fibrous mat-faced gypsum board having a set gypsum core that is
water-resistant. The fibrous mat is preferably sufficiently porous
for the water in the gypsum slurry to evaporate during the
production drying operation as the gypsum sets. The mat comprises
fibrous material that can be either mineral-type or a synthetic
resin. One preferred mat comprises non-woven fiberglass fibers,
randomly oriented and secured together with a modified or
plasticized urea formaldehyde resin binder, and sold as
DURA-GLASS.RTM. 7502 by the Manville Building Materials
Corporation.
[0012] However, gypsum board products incorporating such
conventional fibrous mats have proven to have certain drawbacks.
While fibrous mats are undesirably more costly than the
traditionally used kraft paper, there are other, more troublesome
issues as well. Some persons are found to be quite sensitive to the
fiberglass mat, and develop skin irritations and abrasions when
exposed to the mat at various stages, including the initial
production of the mat, the manufacture of composite gypsum board
with the mat facing, and during the cutting, handling, and
fastening operations (e.g., with nails or screws) that attend
installation of the end product during building construction.
Handling of the mat, and especially cutting, is believed to release
glass fibers responsible for the irritation. The fibers may either
become airborne or be transferred by direct contact. As a result,
workers are generally forced to wear long-sleeved shirts and long
pants and to use protective equipment such as dust masks. Such
measures are especially unpleasant in the sweaty, hot and humid
conditions often encountered either in manufacturing facilities or
on a construction jobsite.
[0013] There have been suggestions that a small portion of the
glass fiber in such mats be replaced by polymer fiber materials and
that an acrylic binder be used instead of urea formaldehyde resin.
While gypsum boards incorporating such mats have somewhat improved
strength and handling characteristics, they are undesirably more
expensive to make and stiffer and less fire resistant. Moreover,
the problems of irritation from dust released, e.g. during cutting,
remain.
[0014] In addition, many of the available non-paper faced gypsum
boards have further features that make them undesirable for many of
the wall facing applications for which they are intended. For
example, the surface roughness of current fiber-faced boards makes
them difficult to finish satisfactorily by normal painting, because
the texture of the mat remains perceptible through the paint. The
fibers in the mat themselves give rise to various asperities, and
to additional, larger sized irregularities often termed in the
industry with descriptives such as "orange peel", "cockle", or
similarly evocative terms describing surface non-planarity. The
perceived smoothness of a board surface is the result of a complex
interplay between various topographic features of the board,
including the size, depth, spacing, and regularity of the features.
Although some of these attributes may be quantified somewhat using
image analysis techniques, visual comparison, especially under
obliquely incident light, is more than sufficient for comparing the
relative smoothness of different surfaces.
[0015] Many of the aforementioned surface defects arise during the
drying or curing of the mat or gypsum board. Even after painting,
these defects and the underlying fibrous texture remain perceptible
and aesthetically unappealing. As a result, a uniform, smooth
finish can be achieved only in conjunction with a prior
ameliorative treatment. Typically it is necessary to skim coat the
surface with drywall joint compound or the like and then sand to a
requisite smoothness to achieve a surface that will accept paint
satisfactorily. This treatment must be accomplished at the
construction site, resulting in added labor and materials cost. The
additional steps entail inconvenience and delay, the consequences
of the time needed for applying and drying the coating and the
generation of further nuisance dust. These difficulties are not
encountered with paper-faced gypsum board, whose as-produced
surface is smooth enough to accept paint readily with a minimum of
surface preparation. Accordingly, current fiber-faced gypsum board
is seldom if ever used for interior finished walls.
[0016] Another form of mat-faced gypsum board is known from U.S.
Pat. No. 4,879,173, which discloses a mat of non-woven fibers
having a reinforcing resinous binder that can comprise a single
resin or a mixture of resins, either thermoplastic or
thermosetting. Exemplary resins disclosed include a styrene-acrylic
copolymer and a self-crosslinking vinyl acetate-acrylic copolymer.
A small amount of the binder is applied to the surface of the mat
and penetrates but part of the way therethrough. The board is said
to be useful as a support member in a built-up roof. The highly
textured surface of the mat binder provides many interstices into
which can flow an adhesive used to adhere an overlying component.
However, considerable care is required in using a mat containing
substantial numbers of voids as a facer for gypsum board.
Conventional processing that incorporates deposition of a
relatively wet slurry is generally found to result in considerable
intrusion of the slurry through the mat and onto the faced surface,
which is frequently undesirable. Prevention of this excess
intrusion typically requires very careful control of the slurry
viscosity, which, in turn, frequently leads to other production
problems. Alternative mats, which inherently limit intrusion, yet
still have sufficient permeability to permit water to escape during
the formation and heat drying of the gypsum board are thus eagerly
sought as a simpler alternative.
[0017] A fibrous mat facer with improved strike-through resistance
and useful as a facer substrate or carrier for receiving a curable
substance in a fluid state is disclosed by U.S. Pat. No. 4,637,951.
The porous, non-woven mat comprises a blend of microfibers
intermixed and dispersed with base fibers and bound with a binder
comprising a water miscible combination of a heat settable polymer.
The mat is said to be useful in forming composite materials
employing a curable thermoset, preferably foamable material such as
a polyurethane or polyisocyanurate rigid foam board and as a
carrier web in the vinyl flooring industry where the settable
polymer comprises a vinyl plastisol.
[0018] Notwithstanding the advances in the field of gypsum boards
and related articles, there remains a need for a readily and
inexpensively produced mat-faced gypsum board having one or more of
a smoother surface, a stronger internal bond to prevent
delamination of the facer when subjected to prolonged wetness after
installation, a surface requiring less paint to produce an
aesthetically acceptable finished wall, etc., and better flame and
mold resistance.
SUMMARY OF THE INVENTION
[0019] The present invention provides a gypsum board and a process
for the manufacture thereof. The board comprises a layer of set
gypsum having a first face and a second face and a non-woven,
fibrous mat affixed to at least one of the faces. The gypsum board
of the invention typically is used for a number of purposes in
building construction, such as a surface material for walls and
ceilings and as an underlayment for floors, roofs, and the like.
The board finds application in both interior and exterior
environments. As a result of the selection of fibers in the facing,
the board has a smooth, uniform surface that readily accepts paint
or other surface treatments to provide a pleasing aesthetic
appearance.
[0020] Various embodiments of the invention have further desirable
attributes, including resistance to flame, moisture, and growth of
mold and mildew. In addition, the inadvertent release of fibers
from the mat used in the present gypsum board is minimized,
limiting the incidence of skin irritation among workers involved in
either production or installation of the board.
BRIEF DESCRIPTION OF THE DRAWING
[0021] The invention will be more fully understood and further
advantages will become apparent when reference is had to the
following detailed description of the preferred embodiments of the
invention and the accompanying drawing, in which:
[0022] FIG. 1 is a cross-sectional view of a mat-faced gypsum board
of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0023] The present invention provides gypsum board and other
hydraulic set and cementitious boards having front and back large
surfaces, at least one of which is faced with a non-woven, fibrous
mat. By hydraulic set is meant a material capable of hardening to
form a cementitious compound in the presence of water. Typical
hydraulic set materials include gypsum, Portland cement, pozzolanic
materials, and the like.
[0024] Referring now to FIG. 1, there is shown generally at 30 a
sectional view across the width direction of one embodiment of a
mat-faced gypsum board in accordance with the invention. The board
comprises a layer of set gypsum 28 which is sandwiched between
first and second fibrous mats 14, 20, and bonded thereto. Two
right-angled folds are formed in each lateral edge of first mat 14,
a first upward fold and a second inward fold. The two folds are
separated by a small distance, whereby the thickness of board is
generally determined. The second folds define longitudinally
extending strips 16 and 18 that are substantially parallel to the
main part of the mat. A second fibrous mat 20 covers the other side
of the set gypsum core 28. The respective lateral edges of second
mat 20 are affixed to strips 16 and 18, preferably with adhesive
22, 23. Ordinarily board 30 is installed with the side bearing mat
14 facing a finished space. The board is advantageously ready for
painting, but other finishing forms such as plaster, wallpaper or
other known wall coverings may also be applied with a minimum of
surface preparation.
[0025] The mats used in the present invention for one or both of
the large faces of the gypsum board comprise a non-woven web bonded
together with a resinous binder. The web comprises chopped
continuous glass fibers, of which preferably at least about 90
percent, more preferably at least about 95 percent, and most
preferably at least about 97 percent have a fiber diameter within a
narrow range of about 11.+-.1.5 .mu.m. Although mixtures of
different lengths of chopped strand fibers are contemplated and
included within the scope of the invention, it is most preferred
that a majority of the fibers have lengths of 12.+-.6 mm. The
present web also includes a small fraction of fibers that are
broken into two or more pieces and a very small fraction of small
glass fibers and chips. The presence of such broken and chipped
fibers in a chopped fiber product is well known in the fiber
industry. However, it is surprising and unexpected that gypsum
board produced using mat formed with fibers having a diameter
within a narrow range centered at about 11 .mu.m is considerably
smoother than board faced with mats wherein the fibers have a
narrow range of diameters centered about 16, 15, 13, 8, and 5
.mu.m, and smoother than other fiber-faced gypsum boards known in
the art.
[0026] Chopped strand fibers are readily distinguishable from
staple fibers by those skilled in the art. Staple fibers are
usually made by processes such as rotary fiberization or flame
attenuation of molten glass known in the fiber industry. They
typically have a wider range of lengths and fiber diameters than
chopped strand fibers. By way of contrast, it would have been
anticipated that the smoothest mats would be obtained with a
preponderance of fine fibers.
[0027] Even more importantly, the surface of boards made in
accordance with the present invention has an improved "hand," i.e.,
an improved subjective feel, and better accepts surface treatments
because of its greater smoothness. Even after prior art boards are
coated with substantial amounts of paint in multiple coats, the
texture of the facing mat in many instances remains visible, making
the surface aesthetically unpleasing for many applications. By way
of contrast, the present boards may be finished to provide an
aesthetic and functional surface with far less paint and the
associated labor to prepare the surface and apply the paint or
other desired finish, wallpaper or other coating, or the like.
[0028] A preferred continuous glass fiber for fibrous web is at
least one member selected from the group consisting of E, C, and T
type and sodium borosilicate glasses, and mixtures thereof. As is
known in the glass art, C glass typically has a
soda-lime-borosilicate composition that provides it with enhanced
chemical stability in corrosive environments, and T glass usually
has a magnesium aluminosilicate composition and especially high
tensile strength in filament form. The present mat is preferably
composed of E glass, which is also known as electrical glass and
typically has a calcium aluminoborosilicate composition and a
maximum alkali content of 2.0%. E glass fiber is commonly used to
reinforce various articles. The chopped fibers of the major portion
can have varying lengths, but more commonly are substantially of
similar length. E glass fiber has sufficiently high strength and
other mechanical properties to produce acceptable mats and is
relatively low in cost and widely available. Most preferred is E
glass having an average fiber diameter of about 11.+-.1.5 .mu.m and
a length ranging from about 6 to 12 mm.
[0029] The aforementioned glass fibers are bound together with any
known water resistant resinous binder. Suitable binders include
urea formaldehyde; conventional modified urea formaldehyde; acrylic
resins; melamine resins, preferably having a high nitrogen resins
such as those disclosed by U.S. Pat. No. 5,840,413; homopolymers or
copolymers of polyacrylic acid having a molecular weight of less
than 10,000, preferably less than 3,000; crosslinking acrylic
copolymer having a glass transition temperature (GTT) of at least
about 25.degree. C., crosslinked vinyl chloride acrylate copolymers
having a GTT preferably no higher than about 113.degree. C.; and
other known flame and water resistant conventional mat binders. It
is typically found that a lower GTT promotes better softness and
smoothness of the mat surface, but tensile strength is improved
with a higher GTT. Binder systems having a GTT ranging from about
15 to 45.degree. C. are thus preferred. Aqueous modified and
plasticized urea formaldehyde resin binders may be used and have
low cost and acceptably high performance.
[0030] It is further preferred that the binder used for the present
mats comprise an effective amount of a water repellant to limit the
intrusion of gypsum slurry during board production. For example,
vinyl acrylate latex copolymers may further incorporate stearylated
melamine for improvement in water repellency, preferably at a level
ranging from about 3 to 10 wt. %, and more preferably at about 6
wt. %. A suitable aqueous stearylated melamine emulsion is
available from the Sequa Chemical Corporation, Chester, S.C., under
the tradename SEQUAPEL.TM. 409. The stearylated melamine is in
liquid form having a solids content of about 40 wt. percent and is
mixed with a suitable copolymer latex and water to prepare binders
for the mats. This material mixture has a pH of about 9, a
viscosity of about 45 centipoises and is anionic. In addition,
gypsum board incorporating mat with the preferred binder is more
resistant to abrasion than conventional either fiber-faced or
paper-faced boards.
[0031] A preferred binder for the present mat comprises an acrylate
copolymer binder latex with a GTT of about 25.degree. C. available
from Noveon, Inc. of Cleveland, Ohio, under the tradename Hycar.TM.
26138. As delivered, this acrylate copolymer latex has a solids
content of about 50 weight percent solids, but it is preferred to
dilute the concentration with water to about 25 wt. percent solids
before using it. Preferably up to about 10 weight percent of a
crosslinker such as melamine formaldehyde is added to the acrylate;
and more preferably about 2-5 weight percent crosslinker is added.
Advantageously, mat bound with the acrylate copolymer latex is
smoother and the mat thinner for equivalent weight and properties
than with other known binders. In addition, expensive
fluorochemical emulsions needed in certain prior art binders are
not required.
[0032] The amount of acrylate copolymer latex binder (and any
optional cross-linker) left in the wet mat during manufacture can
be determined by a loss on ignition (LOI) test, the result thereof
being specified as a percentage of the dry weight of the finished
mat. Preferably, the amount of binder in the final mat, based on
its dry weight, ranges from about 15 to 35 wt. percent, with about
20-30 wt. percent being more preferred, and 25.+-.2.5 wt. percent
being most preferred. The upper limit is dictated by process
constraints and cost, while the minimum is required for adequate
tensile strength.
[0033] Optionally the fibrous mats of the present invention further
contain fillers, pigments, or other inert or active ingredients
either throughout the mat or concentrated on a surface. For
example, the mat can contain effective amounts of fine particles of
limestone, glass, clay, coloring pigments, biocide, fungicide,
intumescent material, or mixtures thereof. Such additives may be
added for known structural, functional, or aesthetic qualities
imparted thereby. These qualities include coloration, modification
of the structure or texture of the surface, resistance to mold or
fungus formation, and fire resistance. Preferably, flame retardants
sufficient to provide flame resistance, e.g. according to NFPA
Method 701 of the National Fire Protection Association or ASTM
Standard E84, Class 1, by the American Society for the Testing of
Materials, are added. Biocide is preferably added to the mat and/or
gypsum slurry to resist fungal growth, its effectiveness being
measurable in accordance with ASTM Standard D3273. The mats and
gypsum layer of the present invention preferably have a very low
cellulosic fiber content from which microbes could derive
nutrition. More preferably any cellulosic fiber present in the mats
or gypsum is only an impurity of other ingredients.
[0034] Gypsum board in accordance with the present invention
preferably is faced with a mat having a basis weight ranging from
about 0.6 to 2.2 pounds per 100 square feet, more preferably
ranging from about 0.9 to 2.2 lbs./100 sq. ft., and most preferably
about 1.25.+-.0.2 lbs./100 sq. ft. (about 29-110, 45-110, and
60.+-.10 g/m.sup.2, respectively). Preferably the binder content of
the dried and cured mats ranges from about 10 to 35 wt. percent,
more preferably from about 15 to 30 wt. percent, and most
preferably from about 25.+-.3 wt. percent, based on the weight of
the finished mat. The basis weight must be large enough to provide
the mat with sufficient tensile strength for producing quality
gypsum board. At the same time, the binder content must be limited
for the mat to remain sufficiently flexible to permit it to be bent
to form the corners of the board, as shown in FIG. 1. Furthermore,
too thick a mat renders the board difficult to cut during
installation. Such cuts are needed both for overall size and to fit
the board around protrusions such as plumbing and electrical
hardware.
[0035] It is conventional in the wallboard industry to characterize
mat using mechanical testing machines with samples about 7.5 cm (3
inches) wide. Tests are conducted with tension applied either in
the machine direction (i.e., along the mat's elongated dimension)
or in the cross-machine direction (i.e., along its width). Mats
having adequate strength in both the machine and cross-machine
directions are required for producing gypsum board that will
withstand the stresses invariably encountered in manufacturing,
handling, shipping, and installing the board. It is also preferred
that the combined strengths in the two directions be high for the
same reason.
[0036] The utility of the present mat is further enhanced by its
relatively high air permeability. During the gypsum board formation
process, far more water is present in the gypsum slurry than is
stochiometrically needed to drive the gypsum rehydration reaction.
The excess is removed during a drying operation, and preferably
escapes through the facings. Hence, facers must have sufficient
permeability to allow the drying to be accomplished within an
acceptable time period and without bubbling, delamination, or other
degradation of the facer. The air permeability of a mat is
conventionally measured by the air flow between reservoirs
separated by the mat. One such test is called the Frazier test and
is further described by ASTM Standard Method D737, with the results
ordinarily being given in units of cubic feet per minute per square
foot (cfm/ft.sup.2). The test is usually carried out at a
differential pressure of about 0.5 inches of water. In preferred
embodiments, the permeability of the present mat, as measured by
the Frazier method, is at least about 250, and more preferably, at
least about 300 cfm/ft.sup.2.
[0037] Any suitable method may be used to form the present mats.
One such method, known from U.S. Pat. No. 4,129,674, employs a
wet-laid, inclined wire screen mat-forming machine. Generally
stated, the method comprises forming a slurry, preferably a water
slurry, containing the requisite fibers. The solids content of such
a slurry may be very low, such as approximately 0.2%. The slurry is
intensely mechanically agitated to disperse the fibers uniformly
therein and then dispensed onto a moving screen. A vacuum is
applied to remove a substantial part of the water, which is
preferably recycled, and thereby form a web of the fibers. After
application of a binder, the web is heated to evaporate any
remaining water and cure the binder, thus forming the bonded mat.
Preferably, the mat-forming process is carried out in a continuous
operation. The moving screen is provided as a continuous
conveyor-like loop and is slightly upwardly inclined during the
portion of its travel in which the fiber slurry is deposited
thereon. Subsequently, a binder is applied and the mat heated to
effect final drying and curing. After the vacuum step is completed,
the web is optionally transferred to one or more additional
downstream conveyor systems for binder application and passage
through a heated oven for the final drying and curing operation.
Machines suitable for carrying out such a web-forming process are
available commercially and include devices manufactured under the
tradenames Hydroformer.TM. by Voith-Sulzer of Appleton, WS, and
Deltaformer.TM. by Valmet/Sandy Hill of Glenns Falls, N.Y.
[0038] The aqueous binder solution is preferably applied using a
curtain coater or a dip and squeeze applicator. Normally, the mat
is subjected to temperatures of about 120-330.degree. C. for
periods usually not exceeding 1 or 2 minutes, and frequently less
than 40 seconds, for the drying and curing operations. Alternative
mat forming methods useful in forming mat for the present invention
include the use of well-known cylinder forming and "dry
laying."
[0039] The invention further provides a method for making gypsum
board and other hydraulic set and cementitious board products for
interior and/or exterior use, i.e. products appointed for
installation on either interior or exterior surfaces of building
structures. By exterior surface is meant any surface of a completed
structure expected to be exposed to weather; by interior surface is
meant a surface within the confines of an enclosed, completed
structure and not intended to be exposed to weather. The
above-described non-woven, fibrous mat is present on at least one
of the large faces of the gypsum board.
[0040] The present improved gypsum board production method
comprises the steps of: forming an aqueous slurry comprising at
least one of anhydrous calcium sulfate, calcium sulfate
hemi-hydrate, or cement; distributing the slurry to form a layer on
a first facing; applying a second facing onto the top of the layer;
separating the resultant board into individual articles; and drying
the articles. The process is characterized in that at least one of
the facings comprises a non-woven, fibrous mat comprising chopped
continuous glass fibers having an average fiber diameter ranging
from about 9.5 to 12.5 .mu.m. Preferably, at least about 90% by
weight of the chopped continuous glass fibers have a diameter
ranging between about 9.5 and 12.5 .mu.m. The fibers in the web are
bound together with a polymeric binder. Alternatively, the slurry
may be distributed to form a layer between two facings. The slurry
optionally includes reinforcing fibers or other known additives
used as process control agents or to impart desired functional
properties to the board, including one or more of agents such as
biocides, flame retardants, and water repellents. The product of
the invention is ordinarily of a form known in the building trades
as board, i.e. a product having a width and a length substantially
greater than its thickness. Gypsum and other hydraulic set and
cementitious board products are typically furnished commercially in
nominal widths of at least 2 feet, and more commonly 4 feet.
Lengths are generally at least 2 feet, but more commonly are 8-12
feet.
[0041] Gypsum and other hydraulic set boards made in accordance
with the present invention exhibit a number of desirable qualities.
The fibrous mat used results in a surface that is smoother and more
amenable to painting or other surface finishing processes than
prior art boards. The mat is also more flexible, facilitating the
bending operations needed to fold the facer around the core during
production, as illustrated for mat 14 in FIG. 1. Moreover, board
incorporating the fibrous mat of the invention has a reduced
tendency to generate irritating dust during cutting and handling
than prior art boards faced with other facing materials.
[0042] The following examples are presented to provide a more
complete understanding of the invention. The specific techniques,
conditions, materials, proportions and reported data set forth to
illustrate the principles and practice of the invention are
exemplary and should not be construed as limiting the scope of the
invention.
COMPARATIVE EXAMPLE 1
Preparation and Testing of a Conventional Non-Woven Glass Fiber
Mat
[0043] A non-woven glass fiber mat of types typically used as a
facer for conventional gypsum board is prepared using a wet laid
mat machine in the manner disclosed in U.S. Pat. No. 4,129,674,
which is hereby incorporated in the entirety by reference thereto.
The mat, designated as comparative example 1, contains chopped
glass fibers and is bonded together with a polymer binder. The
specific materials used are set forth in Table I. The M137 and K137
glass fibers are commercially available from the Johns Manville
Corporation of Denver, Colo. A conventional modified urea
formaldehyde binder is applied with a curtain coating/saturation
technique.
1TABLE I Constituents of Conventional Non-Woven Glass Fiber Mats
Comparative Property Example 1 Fiber type K137 avg. length (mm) 18
avg. fiber diam. (.mu.m) 13 amount (wt. %. of mat) 79 Binder type
modified urea formaldehyde amount (wt. %. of mat) 21
[0044] Standard tests for characterizing the physical and
mechanical properties are carried out on the comparative example
mat, including basis weight per unit area, loss of weight on
ignition, and thickness. Strengths are measured both along the web
direction and across the web, using a conventional mechanical
testing machine to determine the peak tensile strength of a sample
about 7.5 cm wide. The stiffness is determined using the standard
Taber stiffness test, wherein a 38 mm wide strip is deflected by
applying force at a point 50 mm from a clamping point. The torque
(in g-cm) required to achieve a 15.degree. deflection is
conventionally termed the Taber stiffness. Air permeability is
measured using the Frazier test at a differential pressure of 0.5
inches of water in accordance with ASTM Method D737.
2TABLE II Physical and Mechanical Properties of A Conventional
Non-Woven Glass Fiber Mat Comparative Example Physical/Mechanical
Property 1 Basis weight (lbs./100 sq. ft.) 2.1 LOI (%) 21 Thickness
(mils) 36.5 Machine Direction (Tensile Strength lbs./3 in. width)
124 Cross Machine (" " " " ") 84 Taber Stiffness 45 Frazier
Permeability (cfm/ft.sup.2) 625
EXAMPLES 2-4
Preparation and Testing of Non-Woven Glass Fiber Mats of the
Invention
[0045] Four non-woven fiberglass mats designated as Examples 2-4
are formed using a wet-laid, inclined wire screen mat forming
machine in the manner disclosed in U.S. Pat. No. 4,129,674. Each
mat contains E glass fibers having an average fiber diameter of
about 11.+-.1.5 .mu.m bound with a binder composed of 97.5 wt.
percent, dry basis, of Hycar.TM. 26138 acrylic latex having a glass
transition temperature of 25.degree. C. and available from Noveon,
Inc. with about 2.5 wt. percent of melamine formaldehyde latex. A
curtain coating/saturation technique is used to apply the
binder.
[0046] The physical and mechanical properties of the mats of
Examples 2-4 are characterized using the techniques delineated for
Comparative Example 1. The results are set forth in Table III.
3TABLE III Physical and Mechanical Properties of Non-Woven Glass
Fiber Mats of the Invention Example Physical/Mechanical Property 2
3 4 Basis Weight (lbs./100 sq. ft.) 0.72 1.25 1.5 LOI (%) 26 28 28
Thickness (mils) 23 16 21 Machine Direction 102 91 101 (Tensile
Strength lbs./3 in. width) Cross Machine (" " " " ") 127 108 116
Taber Stiffness 4.9 33 32 Frazier Permeability (cfm/ft.sup.2) 800
603 527
[0047] All of the mats of Examples 2-4 exhibit acceptable values
for the sum of machine direction and cross machine direction
strengths.
EXAMPLE 5
Preparation and Testing of Gypsum Board Having Non-Woven Glass
Fiber Facer Mat
[0048] The mats of the above examples are used as facers for the
manufacture of gypsum board in a manner as disclosed in U.S. Pat.
No. 4,647,496. Smoothness is determined by relative ranking of
samples observed for shadows cast by surface irregularities when
viewed under low incident light angle. Samples with deeper surface
or non-uniform irregularities are ranked lower than shallow or
uniform irregularity. Samples are ranked on a scale of 1-10 with 10
being completely smooth. All the mats of Examples 2-4 produce
gypsum board having smoothnesses rated at about 8 and are therefore
smoother than board made with the mat of Comparative Example 1,
which has a smoothness rating of 4. It is unexpected and surprising
that the smoothness of the dry cured mat is not indicative of the
smoothness of that same surface after the mat passes through the
gypsum board manufacturing process, since it is presumed in the
prior art that In practicing the method of the invention, any known
process for making mat faced gypsum board can be used along with
the mats described for facing at least one major face of the gypsum
boards of the present invention. For example, those processes
described in U.S. Pat. Nos. 4,647,496, 5,220,762, 6,524,679, all
herein incorporated by reference, are typical, but the method of
the present invention is not limited to only these known processes
of making fibrous mat faced gypsum board.
[0049] Having thus described the invention in rather full detail,
it will be understood that such detail need not be strictly adhered
to, but that additional changes and modifications may suggest
themselves to one skilled in the art, all falling within the scope
of the invention as defined by the subjoined claims.
* * * * *