|Title of Invention||
|Abstract||A fibrous mat faced gypsum panel having on at least one of the facing sheets a moisture resistant, cured coating of a radiation curable, e.g., UV curable, polymer.|
|Full Text||FIELD OF THE INVENTION
The present invention relates to gypsum panels and, more particularly, to gypsum
panels having at least one surface faced with a fibrous mat adhered to a set gypsum
core, wherein the surface of the fibrous mat has a coating of a moisture resistant,
radiation-cured, e.g., UV-cured, polymer coating. The present invention also relates
to the method of making such a gypsum panel structure.
BACKGROUND OF THE INVENTION
Panels of gypsum wallboard having a core of set gypsum sandwiched between two
sheets of facing paper have long been used as structural members in the fabrication of
buildings. Such panels are typically used to form the partitions or walls of rooms,
elevator shafts, stairwells, ceilings and the like. Paper facing provides a smooth
surface that is especially desirable for painting or wall papering interior walls.
Although paper is a relatively inexpensive facing material and is easily used in the
process of manufacturing wallboard, it has certain disadvantages, particularly with
regard to durability and moisture-resistance.
As an alternative to paper facing, other fibrous mats (such as glass fiber mats) also
have been used as facing materials for gypsum wallboard. One example of such a
wallboard is described in U.S. Patent 3,993,822. Fibrous glass matting provides
improved water resistance and often provides significant improvements in strength
and other structural attributes. More recently, fibrous glass mats having various types
of coatings also have found acceptance for use in applications requiring moisture
One specialty application for the use of panels of gypsum wallboard of this
construction is in bathrooms-typically a place of high humidity and residual water
because of the flow of water from the use of showers, bathtubs, and sinks. Gypsum
wallboards suitable for use in these applications share a common requirement; that is
a resistance or tolerance to high humidity and high moisture environments, often for
A usual construction of bathroom walls includes a multi-ply structure of ceramic tile
adhered to an underlying base member, for example, a panel of wallboard comprising
gypsum or other material. Such a panel is referred to in the industry as a "tile backing
board," which for convenience is referred to herein as "tile backer". In usual fashion,
sheets of tile backer (for example, 4' x 8' x 1/2") are fastened by rust-resistant nails or
screws to studs. Blocks of ceramic tiles (for example, 4" x 4") are adhered to the
sheets of tile backer using a water-resistant adhesive which is referred to in the
industry as "mastic" or by a Portland cement-based adhesive which is referred to
commonly as "thin set mortar". Thereafter, spaces between the tiles and between the
tiles and other adjoining surfaces, for example, the lip of a bathtub or sink, are filled
with a water-resistant material which is referred to in the industry as "grouting".
It should be appreciated that a primary goal in constructing a bathroom that includes
one or more of a bathtub, shower and sink is to make the contiguous and adjacent
walls water-tight utilizing materials that resist being degraded by water, including hot
water. Tiles made from ceramics are such materials and are basically inert to both the
hot and cold water with which the tiles come into direct contact.
It is important also that the tile backer to which the tiles are adhered be waterresistant.
Theoretically, it would seem that the water-resistant properties of the tile
backer should be inconsequential because the backer is shielded from shower, bath
and sink water by water-resistant tiles, grouting and mastic. However, experience has
shown this is not the case and that moisture can and does in fact seep, in various
ways, through the plies of material which overlie the tile backer.
One way has to do with the fact that grouting is not water-impervious and over time
permits the seepage of moisture, a situation which is aggravated upon the formation of
cracks, including hairline cracks, in the grouting. Eventually, the moisture which
penetrates through the grouting finds its way through the mastic and comes into
contact with the facing of the wallboard. Such facing is generally paper, typically a
multi-ply paper, which upon contact with moisture tends to degrade by delaminating
or otherwise deteriorating. For example, the paper facing may be subject to biological
degradation from mold and mildew. The paper can actually rot away. Furthermore,
as the moisture comes into contact with the underlying set gypsum core, it tends to
dissolve the set gypsum and also the core adhesive, which bonds the core and paper
facing together. Such adhesive is typically a starch material. The development of
these conditions can lead to tiles coming loose from the underlying deteriorated
paper-faced gypsum wallboard. This undesirable situation is exacerbated when hot
water comes into contact with the paper-faced wallboard.
Another type of moisture condition which leads to the loosening or falling off of tiles
from their underlying support substrate is associated with those segments of the multiply
wall structure which include a joint formed from an edge portion of the wallboard.
An example is the joint formed by the edge of a wallboard panel and the lip of a
bathtub. Another example is the joint formed by two contiguous wallboard panels.
As moisture penetrates through the multi-ply structure and reaches such a joint, it
tends to wet significant portions of the paper facing and core by virtue of its spreading
through capillary action. This can lead to delamination of the paper facing and/or
dissolution of the core and/or the paper/core adhesive. As this occurs, tiles can come
loose and fall off.
One water-resistant gypsum panel suitable for use in such moisture-prone conditions
is described in U.S. Patents 5,397,631 and 5,552,187. According to these patents,
following the manufacture of a fibrous glass mat-faced gypsum panel, a surface of the
panel faced with a glass mat is coated with a substantially humidity- and waterresistant
resinous coating of a cured (dried) latex polymer. The coating acts as both a
liquid and vapor barrier and is formed from an aqueous coating composition
comprising from about 15 to about 35 wt. % of resin solids, about 20 to about 65 wt.
% of filler, and about 15 to about 45 wt. % of water, applied to obtain a solids loading
of about 110 Ibs. per 1000 sq. ft. A preferred resin for use according to this patent is
a latex polymer that has been sold by Unocal Chemicals Division of Unocal
Corporation under the mark 76 RES 1018. The resin is a styrene-acrylic copolymer
that has a relatively low film-forming temperature. Aqueous coatings formed from
the resin are dried effectively at temperatures within the range of about 300° to 400° F.
If desired, a coalescing agent can be used to lower the film-forming temperature of
While this approach produces a gypsum panel that satisfactorily solves many of the
previous-mentioned problems encountered when using paper-faced gypsum panels in
severe moisture environments, the added cost, due both to the cost of the resinous
coating itself and the cost associated with how the coating is applied, has been an
impediment to wider use of such panels.
One important embodiment of the present invention thus relates to an improved
gypsum-based structural panel having a water impervious coating, such that the panel
can be used effectively as a tile backer. Still other embodiments of the improved
gypsum panel may have use in other applications such as in the return air
installations, shaft walls and area separator walls in commercial buildings where
water and humid conditions are commonly encountered. Other applications where
moisture and humid conditions are likely to present difficulties either during the
installation or the use of the board also will be apparent to those skilled in the art.
These and other embodiments of the invention, which relies on the provision of a
radiation cured, e.g., ultraviolet (UV) cured, coating on a fibrous mat faced gypsum
panel, will be apparent from the following description.
SUMMARY OF THE INVENTION
One aspect of the present invention is directed to a fibrous mat faced gypsum panel
having on at least one of the facing sheets a moisture resistant, cured coating of a
radiation curable, e.g., UV curable, polymer.
Another aspect of the present invention is directed to a method of preparing a fibrous
mat-faced gypsum panel having the cured coating of a radiation curable, e.g., UV
curable, polymer on at least one of the fibrous facing sheets.
Still another aspect of the present invention is directed to a fibrous mat faced gypsum
panel having on at least one of the facing sheets a moisture resistant cured coating of a
radiation curable, e.g., UV curable, polymer and an aggregate material sufficient to
facilitate the bonding of tiles or other decorative surface treatments to the gypsum
The cured coating provides excellent water resistance and vapor barrier properties. It
also improves the durability of the surface conferring excellent abuse resistance and
abrasion/scratch resistance to the coated surface. In roofing applications, the coating
significantly reduces frothing often encountered when using gypsum panels in hotmop
roofing installations. Coatings containing the aggregate additive also show excellent
adhesion for tile setting materials such as mortars, mastics and epoxies, yet also having
exceptional resistance to blocking.
The present invention is particularly advantageous for use in applications in which the
gypsum panel is expected to be exposed to a high humidity or high moisture environment
during installation or use, such as in shaft walls, stairwells, area separation walls, return
air installations and especially as a tile backer in bathroom applications. Still other
applications and uses will become apparent from the detailed description of the invention,
which appears hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
The objects, features, and advantages of the invention will be apparent from the following
more detailed description of certain embodiments of the invention and as illustrated in the
accompanying drawings in which reference characters refer to the same parts throughout
the various views. The drawings are not necessarily to scale, emphasis instead being
placed upon illustrating the features of the invention.
FIG. 1 is an isometric view of a gypsum panel or gypsum board having fibrous facing
sheets and a coating of a cured radiation curable formulation in accordance with one
embodiment of the present invention.
Figure 2 is a cross-sectional view of the moisture resistant panel of Figure 1.
Figure 3 is a partial schematic illustration of a portion of a wallboard production line
illustrating a process for making a gypsum panel.
DETAILED DESCRIPTION OF THE INVENTION
Accordingly, the present invention provides a gypsum panel comprising:
(a) a gypsum core having a planar first face and a planar second face;
(b) a fibrous facing material adhered at least to the first face by gypsum in the gypsum
core obtained from step (a) at least partially penetrating into the said fibrous
(c) a high energy radiation cured coating of a radiation curable formulation on the
fibrous facing material obtained from step (b), wherein the radiation curable
formulation comprises at least one high energy radiation curable polymer having
ethylenically unsaturated double bonds, and at least one high energy radiation
curable reactive diluents; and
(d) an aggregate material on and /or in the high energy radiation cured coating of step
As shown in Figure 1, one embodiment of a moisture-resistant gypsum panel or gypsum
board of the present invention 10, having a radiation (UV) cured polymer coating 15
comprises a gypsum board core 12 faced with two fibrous facing sheets or mats, 14 and
16. Both of the fibrous facing sheets or mats may be glass fiber mats, both may be mats
of paper fibers, or one may be a paper mat and the other a glass mat. Other fibrous mats
suitable for use in the present invention will be apparent from the following description.
For example, pre-coated glass fiber mats, such as described in U.S. Pat. Pub.
20030203191 and U.S. Pat. Pub. 20020134079 can advantageously be used as well. The
surface of at least one of the mats, preferably a fibrous glass mat in the case where the
panel is designed for use in a high moisture environment, is coated with a radiation-cured,
e.g., UV-cured, polymer coating (indicated by the numeral 15 in Figures 1 and 2).
The radiation cured coating is applied using a formulation that preferably is essentially
free of any unreactive components. The coating is typically applied following the initial
preparation of the panel and the coated panel then is exposed to a radiation (UV) source to
cure the coating on the fibrous facing sheet.
In one preferred embodiment, the gypsum panel is initially prepared using, as at least one
of the facing sheets, a pre-coated glass mat having a dried (heat cured) aqueous coating
composition containing a combination (e.g., a mixture) of a mineral pigment (filler); a first
binder of a polymer latex adhesive and, optionally a second binder of an inorganic
adhesive. Such a construction is described, for example, in co-pending U.S. application
Serial No. 09/837,226 filed April 19, 2001, the entirety of which is incorporated herein by
Following initial preparation of the gypsum panel, the radiation curable formulation (e.g.,
UV curable formulation) then is applied as a coating onto the pre-coated mat side of the
gypsum panel and exposed to a radiation (UV) source to effect cure of the radiation (UV)
There are numerous advantages associated with the use of the present invention. Of
primary importance is that the radiation cured polymer-coated fibrous mat-faced panel has
superior weathering characteristics, and accordingly, can be used effectively for indefinite
periods of time as a stable substrate in applications involving water contact and high
humidity exposure, either in the initial installation of the panel or during its use. A
radiation-cured polymer-coated glass mat-faced panel of the present invention is moldresistant
The cured coating provides excellent water resistance and vapor barrier properties. It also
improves the durability of the surface conferring excellent abuse resistance and
abrasion/scratch resistance to the coated surface. In roofing applications, the coating
significantly reduces frothing often encountered when using gypsum panels in hotmop
roofing installations. Coatings containing an aggregate additive also show
excellent adhesion for tile setting materials such as mortars, mastics and epoxies, yet
also exhibit exceptional resistance to blocking.
Gypsum board is typically manufactured by a method that includes dispersing a
gypsum slurry onto a moving sheet of fibrous facer. The fibrous facer typically is
supported by equipment such as forming tables, support belts, carrier rolls and/or the
like. Usually a second sheet of fibrous facer is then fed from a roll onto the top of the
slurry, thereby sandwiching the slurry between two moving fibrous facer sheets.
Forming or shaping equipment is utilized to compress the slurry to the desired
thickness. The gypsum slurry is allowed to at least partially set and then sequential
lengths of board are cut and further processed by exposure to heat, which accelerates
the drying of the board by increasing the rate of evaporation of excess water from the
Figure 3 is a schematic drawing of a portion of a manufacturing line for producing
gypsum panels. The specific details of such a configuration are conventional and thus
are provided only by a schematic representation. In conventional fashion, dry
ingredients from which the gypsum core is formed are pre-mixed and then fed to a
mixer of the type commonly referred to as a pin mixer (not shown). Water and other
liquid constituents, such as soap, used in making the core are metered into the pin
mixer where they are combined with the desired dry ingredients to form an aqueous
gypsum slurry 41, which emerges from a discharge conduit 40 of the pin mixer.
Foam (soap) is generally added to the slurry to control the density of the resulting
core. The slurry is deposited through one or more outlets of the discharge conduit 40
onto a horizontally moving continuous web of fibrous facing material 24 (such as
multi-ply papers or a pre-coated fibrous glass mat). The amount deposited can be
controlled in manners known in the art.
Fibrous facing material 24 is fed from a roll (not shown), and if pre-coated, with the
coated side down. Prior to receiving the gypsum slurry 41, the web of fibrous facing
material 24 is flattened by rollers (not shown) and usually is scored by one or more
scoring devices (not shown). Scoring allows the sides of fibrous facing material 24 to
be folded upward and around the edges of the gypsum panel. Fibrous facing material
24 and the deposited gypsum slurry 41 move in the direction of arrow B. The moving
web of fibrous facing material 24 will form the second facing sheet of the panel being
fabricated, and the slurry at least partially (and preferably, only partially) penetrates
into the thickness of the fibrous facing material and sets. On setting, a strong
adherent bond is formed between the set gypsum and the fibrous facing sheet. The
partial penetration of the slurry into the fibrous facing sheet can be controlled
according to methods known in the art such as, for example, controlling the viscosity
of the slurry and by applying various coatings to the fibrous facing.
The gypsum core of the panel of the present invention is basically of the type used in
gypsum structural products commonly known as gypsum wallboard, dry wall, gypsum
board, gypsum lath and gypsum sheathing. The core of such a product is formed by
mixing water with powdered anhydrous calcium sulfate or calcium sulfate hemihydrate
(CaSCVl/l t^O), also known as calcined gypsum, to form an aqueous
gypsum slurry, and thereafter allowing the slurry mixture to hydrate or set into
calcium sulfate dihydrate (CaSCV2 H20), a relatively hard material. The core of the
product will in general comprise at least about 75-85wt% of set gypsum, though the
invention is not limited to any particular content of gypsum in the core.
After the gypsum slurry 41 is deposited upon the web of fibrous facing mat material
24, the edges of that web are progressively folded (using equipment well-known to
those skilled in the art) around the edges of the forming panel or wallboard, and
terminate on the upper surface of the slurry along the sides. Another web of fibrous
facing material, e.g., paper 22, fed in the direction of arrow C from a roll (not shown),
usually is applied to the upper surface of the gypsum slurry 41, and usually only
slightly overlaps the folded-around edges of the (bottom) web of fibrous facing
material 24. Of course, any facing sheet suitable for use a facing sheet 24 can also be
used for facing sheet 22. Prior to applying the (top) web of fibrous facing material,
such as paper 22, to the upper surface of the gypsum slurry, glue is applied to the web
along portions of the web that will overlap and be in contact with the folded-over
edges of the bottom fibrous facing sheet (glue application is not shown). Preferably
non-starch-based glues are used. One suitable glue is a poly(vinyl alcohol) latex glue.
Glues based on vinyl acetate polymers, especially vinyl acetate that has been
hydrolyzed to form a polyvinyl alcohol, are widely available commercially as white
glues. Various configurations may be used for feeding and joining the webs.
After the (top) web of facing material, such as paper 22, is applied, the "sandwich" of
fibrous facing material web, gypsum slurry and second fibrous facing material web
are pressed to the desired wallboard thickness between plates 50 and 52.
Alternatively, the webs and slurry can be pressed to the desired thickness with rollers
or in another manner. The continuous sandwich of slurry and applied facing materials
then is carried by conveyor(s) 54 in the direction of arrow D. Slurry 41 sets as it is
As noted above, the gypsum panel of the present invention is faced with at least one
and preferably a second facer sheet of a fibrous mat. A suitable fibrous mat
comprises a mat of fibrous material that is capable of forming a strong bond with the
set gypsum comprising the core of the gypsum wallboard. Non-limiting examples of
such fibrous mats are mats made from (1) paper (cellulose) fibers (2) mineral-type
materials such as glass fibers, (3) synthetic resin fibers, such as polyolefm fibers and
(4) blends of fibers, such as blends of mineral fibers and synthetic resin fibers. Glass
fiber mats are normally preferred for panels that are slated to be used in severe
moisture environments. Fibrous mats based on paper fibers generally consist of
multi-ply constructions, while glass fiber mats are often of a single-ply construction.
As noted above, either or both of the facer sheets can be a paper facer sheet, a fibrous
glass mat facer sheet, a fibrous synthetic resin mat facer sheet, or a facer sheet made
from a blend of fibers, such as a blend of glass and synthetic resin fibers. Preferably,
for high moisture applications, at least one of the facer sheets is a fibrous glass mat
facer sheet and more preferably a pre-coated fibrous glass mat, such as the pre-coated
mat disclosed in co-pending application Serial No. 837,226. Thus, in some of the
contemplated embodiments of the present invention the gypsum panel can have, by
way of example, a set gypsum core covered by two paper facers, two fibrous glass
mat facers, or one paper facer and one fibrous glass mat facer. The terms "first facer"
and "second facer" are arbitrary in that each term can refer either to a top layer or a
backing layer of the gypsum panel.
Suitable facer sheets made from paper fibers include those commonly used for the
face sheet of conventional wallboard products. Such paper products are well known
to those skilled in the art. One example of a suitable paper facer sheet is an ivory
paper (multi-ply) having hard internal sizing (100% through) of 1000 to 3500; a basis
weight of about 54 to 56 pounds per 1000 square feet; an overall caliper of about .013
inches; a tensile strength of about 70 Ibs/inch (machine direction) and about 23 Ibs/
inch (cross direction); a top liner Cobb surface wetting of about 1.00 to about 1.50
grams and bottom liner Cobb surface wetting of about 0.50 to about 1.50 grams; and a
porosity of about 15 sec. to about 150 sec. Other suitable papers for making gypsum
wallboard are well known to those skilled in the art.
Suitable fibrous mats, made in part from mineral fibers and/or synthetic resin fibers,
can comprise continuous or discrete strands or fibers and can be woven or nonwoven
in form. Such constructions are commercially available.
Nonwoven glass mats such as made from chopped strands and continuous strands can
be used satisfactorily and are less costly than woven materials. The strands of such
glass mats typically are bonded together to form a unitary structure by a suitable
adhesive. A glass fiber mat can range in thickness, for example, from about 10 to
about 40 mils, with a mat thickness of about 15 to about 35 mils generally being
suitable. The aforementioned fibrous glass mats are known and are commercially
available in many forms. While nonwoven fibrous mats will often be preferred
because of their lower cost, woven fibrous mats may be desirable in certain
specialized instances and thus also are contemplated for use in connection with the
One suitable fibrous glass mat is a fiberglass mat comprising chopped, nonwoven,
fiberglass filaments oriented in a random pattern and bound together with a resin
binder, typically a urea-formaldehyde-based resin adhesive. Fiber glass mats of this
type are commercially available, for example, such as those which have been sold
under the trademark DURA-GLASS by Manville Building Materials Corporation and
those which have been sold by Elk Corporation as BUR or shingle mat. An example
of such a mat is nominally 33 mils thick and incorporates glass fibers about 13 to 16
microns in diameter. Although certain structural applications may utilize a thicker
mat and thicker fibers, a glass fiber mat nominally 20 mils thick, which includes glass
fibers about 10 microns in diameter, is also suitable for use in the present invention.
Glass mats suitable for use in the present invention have a basis weight that is usually
between about 10 and 30 Ibs. per thousand square feet of mat surface area.
Typically, but not exclusively, glass fiber mats are wet-formed into a continuous nonwoven
web of any workable width on a Fourdrinier-type machine. Preferably, an
upwardly inclining wire having several linear feet of very dilute stock lay-down,
followed by several linear feet of high vacuum water removal, is used. This is
followed by a "curtain coater," which applies the glass fiber binder and an oven that
removes excess water and cures the adhesive to form a coherent mat structure.
After being formed and sufficiently set, the wallboard is typically cut to desired
lengths and dried. The drying follows the initial hydration and is ultimately aided by
heating, which causes excess water to evaporate through the fibrous facing sheets or
mats as the calcined gypsum hydrates and sets. Thus, the fibrous facing sheets or
mats must be sufficiently porous to permit the passage of water vapor at this stage
required for adequate drying. Drying conditions typically used in conventional
continuous gypsum board manufacture include temperatures of about 200° to about
600° F., with drying times of about 30 to about 60 minutes, at line speeds of about 70
to about 600 linear feet per minute. Of course, any combination of drying time and
drying temperature for obtaining a suitable gypsum board product can be used and the
above parameters are simply exemplary.
After this initial preparation of the wallboard, the water-resistant coating is applied to
at least one, or alternatively both of the faces of the wallboard.
The resulting gypsum board is schematically illustrated in Figures 1 and 2. The board
has a set gypsum core 12 with the first 16 and second 14 fibrous facer sheets adhered
thereto by the partially penetrating gypsum core. Generally, the core will have voids
(shown as individual dots) distributed there through as a consequence of the foam
added to the gypsum slurry during board manufacture to reduce its density.
The composition from which the set gypsum core of the structural panel is made can
include a variety of additives, such as set accelerators, set retardants, foaming agents,
reinforcing fibers, and dispersing agents. In addition, a viscosity control agent may be
added to adjust the viscosity of the slurry. Examples of viscosity control agents are
described in U.S. Patent 4,647,496. Other typical additives include water-resistant
additives and fire-resistant additives. A variety of additives for improving waterresistant
properties of a gypsum core are described, for example, in U.S. Patent
5,342,680, including a mixture of polyvinyl alcohol and a wax-asphalt emulsion. In
one embodiment, described in more detail below, the water-resistance of the
wallboard is such that it absorbs less than about 10%, preferably less than about 7.5%,
and most preferably less than about 5% water when tested in accordance with the
immersion test of ASTM method C-473.
To reduce the weight (density) of the core, it also has been common practice to
introduce small bubbles into the gypsum to produce a foamed gypsum core. Foaming
agents or soaps, typically long-chained alkyl sulfonates, are conventionally added for
this purpose. One adverse consequence of the normal addition of soaps into gypsum
slurry is a reduction in the strength of the bond between the cured gypsum core and
the paper facers. To counteract this effect, a starch binder normally is added to the
More recently, improved gypsum wallboard constructions have been developed. In
one approach, the gypsum board is prepared with a pre-coated glass fiber mat,
wherein the coating comprises a dried aqueous mixture of a mineral pigment (filler); a
first binder comprised of a polymer latex adhesive; and, optionally a second binder
comprised of an inorganic adhesive. A wallboard of this type is described in pending
U.S. Application Serial No. 09/837,226 filed on April 19, 2001, the entire disclosure
of which is hereby incorporated by reference. In another construction, the gypsum
core is covered with a glass fiber mat (preferably a pre-coated glass mat, such as
described in the just-referenced application) on one face, and with a paper sheet on
the opposite face. This wallboard is described in pending U.S. Application Serial No.
107 245,505 filed on September 18, 2002, the entire disclosure of which also is hereby
incorporated by reference.
Wallboards may contain wax or a wax emulsion as an additive to improve the water
resistance of the gypsum core. The invention is not limited thereby, however, and
examples of other materials which have been reported as being effective for
improving the water-resistant properties of gypsum products include metallic
resinates; wax or asphalt or mixtures thereof, usually supplied as an emulsion; a
mixture of wax and/or asphalt and also cornflower and potassium permanganate;
water insoluble thermoplastic organic materials such as petroleum and natural asphalt,
coal tar, and thermoplastic synthetic resins such as poly(vinyl acetate), poly(vinyl
chloride) and a copolymer of vinyl acetate and vinyl chloride and acrylic resins; a
mixture of metal rosin soap, a water soluble alkaline earth metal salt, and residual fuel
oil; a mixture of petroleum wax in the form of an emulsion and either residual fuel oil,
pine tar or coal tar; a mixture comprising residual fuel oil and rosin; aromatic
isocyanates and diisocyanates; organohydrogen-polysiloxanes; siliconates, such as
available from Dow Corning as Dow Corning 772; a wax emulsion and a wax-asphalt
emulsion each with or without such materials as potassium sulfate, alkali and alkaline
earth aluminates, and Portland cement; a wax-asphalt emulsion prepared by adding to
a blend of molten wax and asphalt an oil-soluble, water-dispersing emulsifying agent,
and admixing the aforementioned with a solution of casein which contains, as a
dispersing agent, an alkali sulfonate of a polyarylmethylene condensation product.
The siliconates are normally used in an amount of from about 0.05% to about 0.4%,
more usually in an amount of about 0.1%. Mixtures of these additives can also be
Species of wax emulsions and wax-asphalt emulsions used to improve wallboard
water resistance are commercially available. The wax portion of these emulsions is
preferably a paraffin or microcrystalline wax, but other waxes also can be used. If
asphalt is used, it in general should have a softening point of about 115° F, as
determined by the ring and ball method. The total amount of wax and wax-asphalt in
the aqueous emulsions will generally comprise about 50 to about 60 wt% of the
aqueous emulsion. In the case of wax-asphalt emulsions, the weight ratio of asphalt
to wax usually varies from about 1 to 1 to about 10 to 1. Various methods are known
for preparing wax-asphalt emulsions, as reported in U.S. Pat. No. 3,935,021.
Commercially available wax emulsions and wax-asphalt emulsions that can be used in
the gypsum composition described herein have been sold by United States Gypsum
Co. (Wax Emulsion), by Monsey Products (No. 52 Emulsion), by Douglas Oil Co.
(Docal No. 1034), by Conoco (No. 7131 and Gypseal II) and by Monsey-Bakor
(Aqualite 70). The amount of wax emulsion or wax-asphalt emulsion used to provide
water resistant characteristics to the gypsum core often can be within the range of
about 3 to about 10 wt%, preferably about 5 to about 7 wt%, based on the total weight
of the ingredients of the composition from which the set gypsum core is made.
Another water-resistant additive for use in the core of the gypsum-based core is an
organopolysiloxane, for example, of the type referred to in U.S. Pat. Nos. 3,455,710;
3,623,895; 4,136,687; 4,447,498; and 4,643,771. One example of this type of
additive is poly(methyl-hydrogen-siloxane). When used, the amount of the
organopolysiloxane usually is at least about 0.2 wt% and often falls within the range
of about 0.3 to about 0.6 wt%.
Unless stated otherwise, the term "wt%" as used herein in connection with the
gypsum core means weight percent based on the total weight of the ingredients of the
composition from which the set gypsum core is made, including any water of the wax
or wax-asphalt emulsion, but not including additional amounts of water that are added
to the gypsum composition for forming an aqueous slurry thereof.
In accordance with another embodiment, polyvmyl alcohol may used as a binder in an
effective amount to promote adhesion between the set gypsum core and the adjacent
facer sheet(s), avoiding the need to use in the gypsum core, starch or other
conventional binders. This is described in co-pending U.S. application Serial No.
10/224,591 filed on August 21, 2002, the disclosure of which is incorporated herein
Typically, the core of the gypsum board has a density of about 35 to about 55 lbs./ft3,
more usually about 40 to about 50 lbs./ft3. Of course, cores having both higher and
lower densities can be used in particular applications if desired. The manufacture of
cores of predetermined densities can be accomplished by using known techniques, for
example, by introducing an appropriate amount of foam (soap) into the aqueous
gypsum slurry from which the core is formed or by molding.
Radiation (e.g., UV) curable formulations suitable for forming a liquid and vapor
impervious coating of the present invention typically comprise at least one polymer
which has ethylenically unsaturated double bonds. This polymer is generally
supplied in an amount between about 20 and 99 wt.% of the total formulation weight.
In addition, the formulation preferably is essentially free of any non-reactive (volatile)
diluents or non-reactive solvents. In this way, there is no need to apply heat to the
panel to remove non-reactive constituents from the coating during the curing step and
essentially all of the radiation curable formulation becomes the radiation cured
coating. As used in this specification and in the claims, the term "essentially free"
means an amount of non-reactive components that constitutes such a small proportion
of the radiation curable formulation that special provisions do not have to be provided
for its removal (e.g., added heat to dry the coating) and by remaining in the coating,
the desired properties of the coating are not adversely impacted.
Productivity of a modern industrial process is very important. The almost
instantaneous curing obtained by using a formulation that is essentially 100% nonvolatile
also minimizes the time between application of the coating formulation and
obtaining a coated gypsum panel that can be handled for inventory or distribution.
This allows the gypsum panel to be coated on-line, shortly after exiting the
conventional drying ovens.
In accordance with the present invention, the formulation is applied to at least one of
the fibrous facing sheets or mats of the gypsum panel and then is cured by exposure to
high-energy radiation, for example by irradiating with UV light of wavelength in the
range from 250 to 400 nm or possibly in the alternative by irradiating with highenergy
electrons (electron beams; from 100 to 350 keV). In some applications, heat
may be sufficient to cause effective crosslinking of the reactive components of the
formulation, or may be used in conjunction with the above-noted high-energy
Polymers suitable for the radiation-curable formulation of the invention are, in
principle, any polymer which has ethylenically unsaturated double bonds which can
undergo free-radical polymerization on exposure to electromagnetic radiation, such as
UV radiation or electron beams. As understood by those skilled in the art, the content
of ethylenically unsaturated double bonds in the polymer must be sufficient to ensure
effective crosslinking of the polymer. Generally, a content of ethylenically
unsaturated double bonds in the range from 0.01 to 1.0 mol/100 g of polymer, usually
from 0.05 to 0.8 mol/100 g of polymer and most often from 0.1 to 0.6 mol/100 g of
polymer will be sufficient.
As used throughout the specification and claims, the term "polymer" is intended to
encompass materials containing ethylenically unsaturated double bonds commonly
referred to in the art as polycondensates, polyaddition products, chemically modified
polymers, oligomers and prepolymers. Suitable polymers often are obtained by
reacting polyfunctional compounds having at least three reactive groups with other
monofunctional or polyfunctional compounds, which can react with the
polyfunctional compounds having at least three reactive groups, with one or more of
the compounds having ethylenically unsaturated double bonds that remain after the
Suitable polymers generally have acryloxy, methacryloxy, acrylamido or
methacrylamido groups, which may be bonded to the backbone of the polymer
directly or through an alkylene groups. Such polymers generally include silicones,
polyurethanes, polyesters, polyethers, epoxy resins, melamine resins and
(meth)acrylate-based polymers and copolymers, having in each case ethylenically
unsaturated groups. Polymers having acryloxy and/or methacryloxy groups are most
common. Such polymers often are called silicone acrylates, polyurethane acrylates,
acrylate-modified polyesters or polyester acrylates, epoxy acrylates, polyether
acrylates, melamine acrylates and acrylate-modified copolymers based on
(meth)acrylates. It also is possible to use ethylenically unsaturated polyesters as the
radiation curable polymer.
The silicones having ethylenically unsaturated double bonds are generally linear or
cyclic polydimethylsiloxanes that have allyl, methallyl, acryloyl or methacryloyl
groups. The ethylenically unsaturated groups are bonded to the silicon atoms of the
main backbone of the polydimethylsiloxane directly, via an oxygen atom, or via an
alkylene group which is linear or branched and may be interrupted by one or more
non-adjacent oxygen atoms. Acrylate and/or methacrylate groups are introduced into
such silicones, for example, by esterifying Si-OH groups in the polydimethylsiloxanes
with an appropriate acid chloride or an alkyl ester of the acid, for example the ethyl
esters and methyl esters. Another method is to hydrosilylate the propynyl esters of
ethylenically unsaturated carboxylic acids with dimethylchlorosilane and then react
the chloroorganosilicon compound obtained in this fashion with a
polydimethylsiloxane containing hydroxyl groups. Another functionalization method
starts from polydimethylsiloxanes which have an oo-chloroalkyl group on a silicon
atom, for example 3-chloropropyl or 2-methyl-3-chloropropyl. Such compounds may
be modified with ethylenically unsaturated compounds containing hydroxyl groups in
the presence of suitable bases, for example tertiary amines, such as triethylamine, to
give ethylenically unsaturated polysiloxanes. Examples of ethylenically unsaturated
compounds containing hydroxyl groups are the esters of ethylenically unsaturated
carboxylic acids with polyhydroxy compounds, eg. hydroxyalkyl acrylates and
hydroxyalkyl methacrylates, such as hydroxyethyl (meth)acrylate, hydroxypropyl
(meth)acrylate, 3-hydroxy-2,2-dimethylpropyl (meth)acrylate, trimethylolpropane
di(meth)acrylate and pentaerythritol di- or tri(meth)acrylate.
The ethylenically unsaturated silicones mentioned are well known to the person
skilled in the art and are generally commercially available.
Ethylenically unsaturated epoxy resin derivatives suitable for use in the radiation
curable formulations encompass in particular the reaction products of epoxy-groupcontaining
compounds or oligomers with ethylenically unsaturated monocarboxylic
acids, such as acrylic acid, methacrylic acid, crotonic acid and cinnamic acid. Instead
of, or together with the monocarboxylic acids, it is also possible to use the monoesters
of ethylenically unsaturated dicarboxylic acids with monoalcohols, such as methanol,
ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, n-hexanol and 2-
ethylhexanol. Suitable epoxy-group-containing substrates encompass in particular the
polyglycidyl ethers of polyhydric alcohols. These include the diglycidyl ethers of
bisphenol A and of its derivatives, and moreover the diglycidyl ethers of oligomers of
bisphenol A, obtained by reacting bisphenol A with the diglycidyl ether of bisphenol
A, and furthermore the polyglycidyl ethers of novolacs. The reaction products of the
ethylenically unsaturated carboxylic acids with the glycidyl ethers under
consideration may be modified with primary or secondary amines. It is moreover
possible to introduce further ethylenically unsaturated groups into the epoxy resin by
reaction of hydroxyl groups in epoxy resins with suitable derivatives of ethylenically
unsaturated carboxylic acids, eg. acid chlorides. Ethylenically unsaturated epoxy
resins are well known to the person skilled in the art and are commercially available.
Examples of ethylenically unsaturated melamine resins suitable as the radiation
curable polymer are the reaction products of melamine-formaldehyde condensation
products with compounds containing hydroxyl groups, with ethylenically unsaturated
dicarboxylic anhydrides, or with the amides of ethylenically unsaturated
monocarboxylic acids. Suitable melamine-formaldehyde condensation products are
in particular hexamethylolmelamine (HMM) and hexamethoxymethylolmelamine
(HMMM). Suitable hydroxyl-group-containing compounds encompass, for example,
the hydroxyalkyl esters of ethylenically unsaturated carboxylic acids, in particular of
acrylic acid and methacrylic acid. Other possible compounds for the reaction with
HMM are ethylenically unsaturated alcohols, such as allyl alcohol and crotyl alcohol.
Other suitable compounds for such reactions are ethylenically unsaturated
dicarboxylic anhydrides, such as maleic anhydride. It also is possible to modify either
HMM or HMMM with the amides of ethylenically unsaturated carboxylic acids, eg.
acrylamide or methacrylamide, to give ethylenically unsaturated melamine resins.
Such melamine resins also are well known.
Ethylenically unsaturated polymers suitable for preparing a radiation curable
formulation for use in this invention may also include polyesters that contain
ethylenically unsaturated double bonds. A distinction can be made here between,
materials identified as ethylenically unsaturated polyesters which are obtained by
copolycondensation of conventional dicarboxylic acids together with ethylenically
unsaturated dicarboxylic acids and/or with anhydrides of these acids and with lowmolecular-
weight diols, and on the other hand ethylenically modified polyesters
obtained by derivatizing free hydroxyl groups in conventional polyesters. The
hydroxyl groups may be derivatized separately or during the preparation of the
hydroxyl group-containing polyester.
Ethylenically unsaturated polyesters encompass in particular the copolycondensates of
maleic anhydride with at least one other dicarboxylic acid and/or their anhydride(s)
and a low-molecular-weight diol. In this case, the dicarboxylic acids and/or their
anhydrides are preferably selected from the class consisting of succinic acid, succinic
anhydride, glutaric acid, glutaric anhydride, adipic acid, phthalic acid, terephthalic
acid, isophthalic acid and in particular phthalic anhydride. Suitable diols can be
selected from the class consisting of ethylene glycol, 1,2-propylene glycol, 1,4-
butanediol, 1,5-pentanediol, neopentyl glycol and 1,6-hexanediol, in particular 1,2-
Suitable hydroxyl-group-containing polyesters for derivatization giving ethylenically
modified polyesters may be prepared in a usual manner by polycondensation of di- or
polybasic carboxylic acids with dihydric alcohols and/or at least one other polyhydric
alcohol component. Possible di- or polybasic carboxylic acids in this case are
aliphatic and aromatic carboxylic acids and their esters and anhydrides. These
include succinic acid, succinic anhydride, glutaric acid, glutaric anhydride, adipic
acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, phthalic
anhydride, isophthalic acid, terephthalic acid, tetrahydrophthalic acid,
tetrahydrophthalic anhydride, trimellitic acid, trimellitic anhydride, pyromellitic acid
and pyromellitic anhydride. Examples of possible dihydric alcohols are ethylene
glycol, propylene glycol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6-
hexanediol, 2-methyl-1,5-pentanediol, 2-ethyl-1,4-butanediol, dimethylolcyclohexane,
diethylene glycol, triethylene glycol, mixtures of these, and also
polyaddition polymers of cyclic ethers, such as polytetrahydrofuran, polyethylene
glycol and polypropylene glycol. Possible polyhydric alcohols include tri- to
hexahydric alcohols, such as glycerol, trimethylolethane, trimethylolpropane,
trimethylolbutane, pentaerythritol, ditrimethylolpropane, sorbitol, erythritol and 1,3,5-
trihydroxybenzene. If the total number of hydroxyl groups in the alcohol component
molecule is larger than the total number of carboxyl groups in the acid component
molecule, a hydroxyl-group-containing polyester is obtained. These hydroxyl groups
may be esterified in a known manner by usual processes with the abovementioned
ethylenically unsaturated carboxylic acids, in particular acrylic and methacrylic acids.
The water formed during the esterification reaction may be removed, for example, by
dehydrating agents, by extraction or by azeotropic distillation. The esterification
usually takes place in the presence of a catalyst, eg. a strong acid, such as sulfuric
acid, anhydrous hydrogen chloride, toluenesulfonic acid and/or acid ion exchangers.
It also is possible to etherify the hydroxyl groups in the polyester with reactive,
ethylenically unsaturated compounds, eg. with allyl chloride or methallyl chloride.
Still another embodiment relates to polyesters made from diols, dicarboxylic acids
and at least one carboxylic acid of higher basicity. In this case, the hydroxyl groups
are introduced into the polyester subsequently by reacting the carboxylic acids groups
with alkylene oxides, such as ethylene oxide or propylene oxide. These alcohol
moieties may then be esterified or etherified in the same manner. These products are
well known to the person skilled in the art and are commercially available. Their
number-average molecular weight is generally in the range from 500 to 10,000 and
more usually from 800 to 3,000.
Other ethylenically modified polyesters that can be used to make the radiation curable
formulation of the present invention are polyesters obtained by co-condensing
conventional di- or polycarboxylic acids with conventional alcohol components along
with ethylenically unsaturated monocarboxylic acids, preferably acrylic and/or
methacrylic acid. Such polymers are known, for example, from European Patent 279
303, to which reference is hereby made for further details. In this case, the
ethylenically unsaturated groups are introduced into the polyester during the
construction of the polyester from its low-molecular-weight components.
As noted above, the radiation curable polymer may also be selected from
ethylenically unsaturated polyethers. Ethylenically unsaturated polyethers are
prepared from a main structure of polyether to have terminal unsaturated groups. The
main structure of a polyether is obtained, for example, by reacting a di- or polyhydric
alcohol, for example an alcohol mentioned above as a di- or polyol component for
preparing polyesters, with an epoxide, usually with ethylene oxide and/or propylene
oxide. This main structure of polyether contains free hydroxyl groups, which may
then be converted in the manner described above into allyl, methallyl, crotyl or
phenylallyl groups or may be esterified with ethylenically unsaturated carboxylic
acids, in particular acrylic and/or methacrylic acid, or with suitable derivatives, such
as acid chlorides, Ci -€4 -alkyl esters or anhydrides.
The radiation curable polymer also may be an ethylenically unsaturated copolymer
based on (meth)acrylates. Such ethylenically unsaturated copolymers are generally
obtained by reacting a functionalized polymer, i.e. a polymer that has a free hydroxyl,
carbonyl, carboxyl, isocyanate, amino and/or epoxy group. The ethylenic double
bonds are generally introduced into the structure by reacting the polymer with a
suitable, low-molecular-weight, ethylenically unsaturated compound which has a
functional group which can react with the reactive group in the polymer, developing a
The functionalized polymers used as a starting material for such polymers are
generally obtained by free-radical polymerization of at least one ethylenically
unsaturated monomer having a functional group of the type mentioned above and, if
desired, other ethylenically unsaturated comonomers. The ethylenically unsaturated
monomer with a functional group generally makes up from 5 to 50 mol %, more
usually from 15 to 40 mol % and most often from 20 to 35 mol %, of the total
monomers to be polymerized. Examples of monomers with a functional group are
hydroxyalkyl acrylates and hydroxyalkyl methacrylates, such as 2-hydroxyethyl
(meth)acrylate, hydroxypropyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate,
aminoalkyl acrylates and aminoalkyl methacrylates, such as 2-aminoethyl
(meth)acrylate, carbonyl compounds, such as acrolein, methacrolein, vinyl ethyl
ketone, N-diacetonacrylamide and -methacrylamide, vinyl isocyanate, dimethyl-3-
isopropenylbenzyl isocyanate, 4-isocyanatostyrene, and isocyanates of ethylenically
unsaturated carboxylic acids, eg. methacryloyl isocyanate, co-isocyanatoalkyl
(meth)acrylatee, glycidyl compounds, such as glycidyl allyl and glycidyl methallyl
ethers, the glycidyl esters of ethylenically unsaturated carboxylic acids, such as
glycidyl (meth)acrylate, ethylenically unsaturated anhydrides, such as maleic
anhydride and methacrylic anhydride and the amides of ethylenically unsaturated
carboxylic acids, such as acrylamide and methacrylamide. Suitable comonomers are
generally selected from the class consisting of esters of acrylic and of methacrylic
acid and, if desired, vinylaromatic compounds. Examples of suitable comonomers are
the Ci-C4 esters of acrylic and methacrylic acids, such as methyl (meth)acrylate, ethyl
(meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl
(meth)acrylate, isobutyl (meth)acrylate and tert-butyl (meth)acrylate. Other suitable
comonomers are styrene, 1-methylstyrene, 4-tert-butylstyrene and 2-chlorostyrene.
To a lesser extent, it is also possible to use monomers such as vinyl acetate, vinyl
propionate, vinyl chloride, vinylidene chloride, conjugated dienes, such as butadiene
and isoprene, vinyl ethers of Ci-C2o alkanols, eg. vinyl isobutyl ether, acrylonitrile,
methacrylonitrile and heterocyclic vinyl compounds, such as 2-vinylpyridine and Nvinylpyrrolidone.
A well-known embodiment encompasses, as comonomers, at least
one monomer selected from the class consisting of the esters of methacrylic acid, in
particular methyl methacrylate, and at least one further comonomer, selected from the
class consisting of the alkyl esters of acrylic acid, and/or styrene.
The ethylenically unsaturated compounds that have a functional group and are
suitable for the above-described reaction are often selected from the abovementioned
ethylenically unsaturated monomers with a functional group. A precondition is that
the functionality of the ethylenically unsaturated compound be able to react with the
functionalities on the polymer, with bond formation with the polymer. Suitable
reactions are condensation and addition reactions. Examples of suitable functional
interactions are isocyanate-hydroxyl, isocyanate-amino, anhydride-hydroxyl,
anhydride-amino, carbonyl-amino, carboxylic acid chloride-hydroxyl, glycidylhydroxyl,
glycidyl-amino or amide and glycidyl-carboxyl. In another well known
embodiment, the ethylenically unsaturated polymer is obtained by reacting a
functionalized polymer having glycidyl groups with ethylenically unsaturated
compounds having hydroxyl groups, in particular the hydroxyalkyl esters of the
abovementioned ethylenically unsaturated carboxylic acids, eg. 2-hydroxyethyl
acrylate. Examples of such ethylenically unsaturated polymers are found in European
Patent 650 979, the disclosure of which is incorporated herein by reference.
Another suitable type of polymer for use in the radiation curable formulation of the
present invention are polyurethane derivatives having ethylenically unsaturated
double bonds. Such polyurethanes can be obtained, for example, by reacting
isocyanate-containing polyurethanes with ethylenically unsaturated compounds which
themselves have at least one functional group reactive with the isocyanate moiety, for
example primary or secondary amino or a hydroxyl. Examples of suitable
ethylenically unsaturated compounds having an amino or hydroxyl group are, in
particular, the abovementioned esterification products of ethylenically unsaturated
carboxylic acids with di- or polyols where at least one hydroxyl group remains
unesterified. Examples of such compounds include, in particular hydroxyalkyl
(meth)acrylates, such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate,
butanediol mono(meth)acrylate, partial esterification products of polyhydric alcohols
with acrylic and/or methacrylic acid, eg. trimethylolpropane mono- and
di(meth)acrylate, pentaerythritol di- and tri(meth)acrylate, and also the corresponding
aminoalkyl esters and hydroxyalkylamides, such as Nhydroxyalkyl(
meth)acrylamides and 3-aminoalkyl (meth)acrylates.
Polyurethanes containing isocyanate groups can be obtained in the well-known
manner by reacting aliphatic and/or aromatic di- or polyisocyanates as one (first)
component with compounds having hydroxyl groups as the other (second)
component. The concomitant use of polyamines and aminoalcohols as the second
component is also possible to a lesser extent. As those skilled in the art understand, if
amines and/or aminoalcohols are used, the resultant polyurethanes have urea groups.
The number of isocyanate groups in the polyurethane is controlled, in a known
manner, via the ratio of molar amounts of the starting materials.
Ethylenically unsaturated moieties may be introduced subsequently into the
polyurethane containing isocyanate groups in a known manner by the functional interreactions
previously described. It is also possible to use ethylenically unsaturated
compounds with functionalities reactive with isocyanate groups directly as a third
component in preparing the polyurethanes.
Examples of the di- or polyisocyanates are straight-chain or branched alkylene
diisocyanates of 4-12 carbon atoms, cycloaliphatic diisocyanates with from 6 to 12
carbon atoms, aromatic diisocyanates with from 8 to 14 carbon atoms,
polyisocyanates having isocyanurate groups, uretdione diisocyanates, polyisocyanates
having biuret groups, polyisocyanates having urethane groups and/or allophanate
groups, polyisocyanates containing oxadiazinetrione groups, uretoneimine-modified
polyisocyanates or mixtures of these.
Examples of diisocyanates are tetramethylene diisocyanate, hexamethylene
diisocyanate(l,6-diisocyanatohexane), octamethylene diisocyanate, decamethylene
diisocyanate, dodecamethylene diisocyanate, tetradecamethylene diisocyanate,
trimethylhexane diisocyanate and tetramethylhexane diisocyanate, and cycloaliphatic
diisocyanates, such as 1,4-, 1,3- and 1,2-diisocyanatocyclohexane, 4,4'-
di(isocyanatocyclohexyl)-methane, 1 -isocyanato-3,3,5-trimethyl-5-
(isocyanatomethyl)-cyclohexane (isophorone diisocyanate), and 2,4- and 2,6-
diisocyanato-1-methylcyclohexane, and aromatic diisocyanates, such as 2,4-
diisocyanatotoluene, 2,6-diisocyanatotoluene, tetra-methylxylylene diisocyanate, 1,4-
diisocyanatobenzene, 4,4'- and 2,4-diisocyanatodiphenylmethane, p-xylylene
diisocyanate, and also isopropenyldimethyltolylene diisocyanate.
The polyisocyanates having isocyanurate groups are in particular simple
triisocyanatoisocyanurates, which are cyclic trimers of the diisocyanates, or mixtures
with their higher homologs having more than one isocyanurate ring.
Uretdione diisocyanates are usually cyclic dimerization products of diisocyanates.
The uretdione diisocyanates may, for example, be used as sole component or in a
mixture with other polyisocyanates, in particular the polyisocyanates containing
isocyanurate groups. Suitable polyisocyanates having biuret groups preferably have
an NCO content of from 18 to 22% by weight and an average NCO functionality of
from 3 to 4.5.
Polyisocyanates having urethane and/or allophanate groups may, for example, be
obtained by reacting excess amounts of diisocyanates with simple, polyhydric
alcohols, for example trimethylolpropane, glycerol, 1,2-dihydroxypropane or mixtures
of these. These poiyisocyanates having urethane and/or allophanate groups generally
have an NCO content of from 12 to 20% by weight and an average NCO functionality
of from 2.5 to 3.
Polyisocyanates containing oxadiazinetrione groups can be prepared from
diisocyanate and carbon dioxide.
Suitable compounds having a reactive hydrogen, such as a hydroxyl, are the lowmolecular-
weight diols and polyols mentioned in connection with the preparation of
polyesters, and also the polyesterpolyols, in particular polyesterdiols. Examples of
polyesterpolyols are reaction products from the abovementioned di- or polybasic,
preferably dibasic, carboxylic acids with polyhydric, preferably dihydric and, if
desired, additionally trihydric alcohols. Examples of suitable starting components are
the abovementioned polybasic carboxylic acids and polyhydric alcohols. The
polyesterdiols may also be oligomers of lactones, such as |3-propiolactone, y.-
butyrolactone and e-caprolactone, obtained by oligomerization of the lactones in the
presence of starters based on the abovementioned low-molecular-weight diols. The
abovementioned polyesterdiols or polyols generally have number-average molecular
weights in the range from 500 to 5,000, preferably from 750 to 3,000.
In the broad practice of the invention, the radiation-curable formulation also may
contain small amounts of additional polymer additives that do not cure by radiation,
i.e., polymers with no ethylenically unsaturated, radiation-curable double bonds.
Such polymers usually may be present in an amount of less than 10 wt.% of the
formulation and should preferably have a relatively low glass transition temperature
of below about 50° C., generally below about 40° C. Suitable polymers include those
prepared by free-radical polymerization of ethylenically unsaturated monomers
selected from vinylaromatic compounds, vinyl esters of aliphatic carboxylic acids
having from 1 to 12 carbon atoms, Ci -Cio -alkyl acrylates and Ci -Cio -alkyl
methacrylates. Vinylaromatic monomers encompass in particular styrene,
particular vinyl acetate, such as vinyl propionate. The acrylates and methacrylates
respectively encompass the esters of acrylic and methacrylic acids with methanol,
ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tert-butanol, n-pentanol, nhexanol,
2-ethylhexanol, n-octanol and cyclohexanol. The monomers to be
polymerized also may encompass, as a co-monomer, up to 35% by weight, often only
up to 20% by weight and in many cases only about from 0.1 to 10% by weight of
acrylonitrile, methacrylonitrile, a-olefins, such as ethylene, propene and isobutene,
dienes, such as butadiene and isoprene, vinyl chloride, vinylidene chloride, acrylic
acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, the amides of these
acids, the N-alkylolamides of these acids, in particular N-methylol(meth) acrylamide,
hydroxyalkyl esters of these acids, in particular 2-hydroxyethyl (meth)acrylate and
hydroxypropyl (meth)acrylate, and also ethylenically unsaturated sulfonic acids, eg.
vinylsulfonic acid, styrenesulfonic acid and acrylamido-2-methylpropanesulfonic
acid. These co-monomers are usually selected from acrylic acid, methacrylic acid, the
amides of these, acrylamido-2-methylpropanesulfonic acid, acrylonitrile and
The preparation of such polymers is well known and generally takes place by freeradical,
aqueous emulsion polymerization of the abovementioned monomers in the
presence of at least one free-radical polymerization initiator and, if desired, a
surfactant selected from the class consisting of emulsifiers, and/or protective colloids.
In some cases, the physical properties of the radiation curable polymer makes it
inconvenient and sometimes difficult to form a thin, uniform coating of the radiation
curable formulation on the fibrous facing sheet of the gypsum panel. In this case, in
addition to the radiation curable polymer component, the radiation curable
formulation also may include a low-molecular-weight diluent or solvent, which itself
preferably is capable of polymerization by cationic or free-radical pathways. The use
of such an ingredient thus is especially useful in those circumstances where the
viscosity of a particular radiation curable polymer does not readily allow the
formation of a thin, uniform coating on the fibrous facing sheet. These additives are
generally compounds that have at least one ethylenically unsaturated double bond
and/or one epoxy group and have a molecular weight of less than about 800. As
noted, such compounds are generally used to adjust to the desired working
consistency of the radiation-curable formulation. This is particularly important in the
present invention, as the formulation preferably should be essentially free of any nonreactive
(volatile) diluents, such as water and/or inert organic solvents, (i.e., the
formulation preferably contains such components only to such a small extent that it is
not necessary to treat the coating formulation (e.g., by heat drying) to remove them).
Such compounds are therefore also called reactive diluents. The proportion of any
reactive diluents in the radiation curable formulation, based on the total amount of
radiation curable polymer and reactive diluent in the radiation-curable formulation, is
normally in the range from 0 to 60% by weight.
Examples of suitable reactive diluents are vinyl-group-containing monomers, in
particular N-vinyl compounds, such as N-vinylpyrrolidone, N-vinyl-caprolactam and
N-vinylformamide, also vinyl ethers, such as ethyl vinyl ether, propyl vinyl ether,
isopropyl vinyl ether, butyl vinyl ether, isobutyl vinyl ether, tert-butyl vinyl ether,
amyl vinyl ether, 2-ethylhexyl vinyl ether, dodecyl vinyl ether, octadecyl vinyl ether
and cyclohexyl vinyl ether, ethylene glycol mono- and divinyl ethers, di-, tri- and
tetraethylene glycol mono- and divinyl ethers, polyethyl ene glycol divinyl ether,
ethylene glycol butyl vinyl ether, triethylene glycol methyl vinyl ether, polyethylene
glycol methyl vinyl ether, cyclohexanedimethanol mono- and divinyl ethers,
trimethylolpropane trivinyl ether, aminopropyl vinyl ether, diethylaminoethyl vinyl
ether and polytetrahydrofuran divinyl ether, vinyl esters, such as vinyl acetate,
propionate, stearate and laurate, and vinylaromatics, such as vinyltoluene, styrene , 2-
and 4-butylstyrene and 4-decylstyrene, and also acrylic monomers, eg. phenoxyethyl
acrylate, tert-butylcyclohexyl acrylate and tetrahydrofurfuryl (meth)acrylate.
Compounds containing vinyl groups may also be used directly as cationically
polymerizable reactive diluents. Further suitable compounds are compounds
containing epoxy groups, such as cyclopentene oxide, cyclohexene oxide, epoxidized
polybutadiene, epoxidized soybean oil, 3',4'-epoxycyclohexyl-methyl 3,4-
expoxycyclohexanecarboxylate and glydidyl ethers, eg. butanediol diglycidyl ether,
hexanediol diglycidyl ether, bisphenol A diglycidyl ether and pentaerythritol
diglycidyl ether, and the concomitant use of cationically polymerizable monomers
such as unsaturated aldehydes and ketones, dienes, such as butadiene, vinylaromatics,
such as styrene, N-substituted vinylamines, such as vinylcarbazole, and cyclic ethers,
such as tetrahydrofuran, also is possible.
The reactive diluents also may include the esters of ethylenically unsaturated
carboxylic acids with low-molecular-weight di- or polyhydric alcohols, preferably the
acrylic and methacrylic esters and in particular the acrylic esters, the alcohols
preferably having no further functional groups or, or at most ether groups, besides the
Examples of such alcohols are ethylene glycol, propylene glycol and more highly
condensed representatives of the class, e.g., diethylene glycol, triethylene glycol,
dipropylene glycol and tripropylene glycol, butanediol, pentanediol, hexanediol,
neopentyl glycol, alkoxylated phenolic compounds, such as ethoxylated and
propoxylated bisphenols, cyclohexanedimethanol, alcohols having three or more
hydroxyl groups, such as glycerol, trimethylolpropane, butanetriol, trimethylolethane,
pentaerythritol, ditrimethylolpropane, dipentaerythritol, sorbitol, mannitol and the
corresponding alkoxylated, in particular ethoxylated and propoxylated, alcohols.
Well-known reactive diluents include the esterification products of the
abovementioned di- or polyhydric alcohols with acrylic and/or methacrylic acid.
Such compounds are generally termed polyacrylates or polyether acrylates.
Hexanediol diacrylate, tripropylene glycol diacrylate and trimethylolpropane
triacrylate are particularly suitable.
In one embodiment, such polyacrylates or polyether acrylates can be modified with
primary and/or secondary amines. Suitable amines encompass both primary and
secondary aliphatic amines, such as n-butylamine, n-hexylamine, 2-ethylhexylamine,
dodecylamine, octadecylamine, di-n-butylamine, cycloaliphatic amines, such as
cyclohexylamine, heterocyclic amines, such as piperidine, piperazine, 1-
ethylpiperazine and morpholine, primary amines containing heterocyclic groups, for
example N-(aminoethyl)imidazole, N-(aminoethyl)morpholine,
tetrahydrofurfurylamine and 2-aminoethylthiophene. Other suitable compounds
include alkanolamines, such as ethanolamine, 3-aminopropanol and
monoisopropanolamine, and also alkoxyalkylamines, such as methoxypropylamine
and aminoethoxyethanol. The molar ratio of amine groups to acrylate and/or
methacrylate groups in the amine-modified polyacrylates or polyether acrylates is
normally in the range from 0.01:1 to 0.3:1.
The radiation-curable formulation used according to the present invention, in
principle, encompass any liquid or flowable (e.g. powder) preparation of a radiation
curable polymer. Thus, pulverulent curable formulations also are encompassed, as
known, for example, for powder-coating metallic surfaces. Hot-melt preparations,
though less preferred, are also possible, these becoming flowable only at an elevated
temperature. The radiation-curable formulation also may include the usual
complement of auxiliaries, such as thickeners, flattening agents, flow control agents,
surfactants, defoamers, UV stabilizers, emulsifiers and/or protective colloids and
fillers. Suitable auxiliaries are well known to the person skilled in the art from
coatings technology and in the aggregate are generally included in the formulation
from about 0 to about 15 wt.%. Suitable fillers may include silicates, which are
obtainable by hydrolyzing silicon tetrachloride, siliceous earth, talc, aluminum
silicates, magnesium silicates, calcium carbonates, alumina, inorganic and organic
pigments, etc. Suitable stabilizers encompass typical UV absorbers, such as
oxanilides, triazines, benzotriazoles and benzophenones. These may be used in
combination with usual free-radical scavengers, for example sterically hindered
amines, eg. 2,2,6,6-tetramethylpiperidine and 2,6-di-tert-butyl-piperidine (HALS
compounds). Stabilizers may optionally be used in amounts of from 0.1 to 5.0% by
weight and preferably from 0.5 to 2.5% by weight, based on the polymerizable
components present in the formulation.
When the formulation is slated to be cured by UV radiation, the formulation also
includes at least one photoinitiator. A distinction needs to be made here between
photoinitiators for free-radical curing mechanisms (polymerization of ethylenically
unsaturated double bonds) and photoinitiators for cationic curing mechanisms
(cationic polymerization of ethylenically unsaturated double bonds or polymerization
of compounds containing epoxy groups). For curing by means of high-energy
electrons (electron-beam curing), the use of photoinitiators may be dispensed with.
Suitable photoinitiators for free-radical photopolymerization, i.e., polymerization of
ethylenically unsaturated double bonds, are benzophenone and benzophenone
derivatives, such as 4-phenyl-benzophenone and 4-chlorobenzophenone, Michler's
ketone, anthrone, acetophenone derivatives, such as 1-benzoylcyclohexan-l-ol, 2-
hydroxy-2,2-dimethylacetophenone and 2,2-dimethoxy-2-phenylacetophenone,
benzoin and benzoin ethers, such as methyl benzoin ether, ethyl benzoin ether and
butyl benzoin ether, benzil ketals, such as benzil dimethyl ketal, 2-methyl-l-[4-
(methylthio)phenyl]-2-morpholinopropan-l-one, anthraquinone and its derivatives,
such as p-methylanthraquinone and tert-butylanthraquinone, acylphosphine oxides,
such as 2,4,6-trimethylbenzoyldiphenylphosphine oxide, ethyl-2,4,6-trimethylbenzoylphenylphosphinate
and bisacylphosphine oxides.
Suitable photoinitiators for cationic photopolymerization, i.e,. the polymerization of
vinyl compounds or compounds containing epoxy groups, are aryl diazonium salts,
such as 4-methoxybenzenediazonium hexafluoro-phosphate, benzenediazonium
tetrafluoroborate and toluenediazonium tetra-fluoroarsenate, aryliodonium salts, such
as diphenyliodonium hexafluoroarsenate, arylsulfonium salts, such as
triphenylsulfonium hexafluorophosphate, benzene- and toluenesulfonium
hexafluorophosphate and bis[4-diphenylsulfoniophenyl] sulfide
bishexafluorophosphate, disulfones, such as diphenyl disulfone and phenyl-4-tolyl
disulfone, diazodisulfones, imidotriflates, benzoin tosylates, isoquinolinium salts,
such as N-ethoxyisoquinolinium hexafluorophosphate, phenylpyridinium salts, such
as N-ethoxy-4-phenylpyridinium hexafluorophosphate, picolinium salts, such as Nethoxy-
2-picolinium hexafluorophosphate, ferrocenium salts, titanocenes and
These photoinitiators are used, if required, in amounts of from 0.05 to 20% by weight,
more usually from 0.1 to 10% by weight and most often from 1.0 to 5% by weight,
based on the polymerizable components of the radiation curable formulation.
The radiation-curable formulation may also include polymers that have cationically
polymerizable groups, in particular epoxy groups. These include copolymers of
ethylenically unsaturated monomers, the copolymers containing, as comonomers,
ethylenically unsaturated glycidyl ethers and/or glycidyl esters of ethylenically
unsaturated carboxylic acids.
They also include the glycidyl ethers of hydroxyl-group-containing polymers, such as
hydroxyl-group-containing polyethers, polyesters, polyurethanes and novolacs. They
include moreover the glycidyl esters of polymers containing carboxylic acid groups.
If it is desired to have a cationically polymerizable component, the radiation curable
formulation may include, instead of or together with the cationically polymerizable
polymer, a low-molecular-weight, cationically polymerizable compound, for example
a di- or polyglycidyl ether of a low-molecular-weight di- or polyol or the di- or
polyester of a low-molecular-weight di- or polycarboxylic acid, for example the
cationically polymerizable reactive diluents specified above.
In the broad practice of the invention, formulation may alternatively include a thermal
initiator, i.e., a compound responsive to heat radiation, in an amount equivalent to
what has been suggested for photointiators.
Most radiation curable formulations suitable for use in accordance with the present
invention will contain a photoinitiator, or thermal initiator in an amount of 1-5% by
weight, an ethylenically unsaturated polymer, such as a urethane, epoxy, polyester or
acrylate, in an amount of 20 to 99% by weight, a multifunctional acrylate in an
amount of 0-60% by weight and other additives in an amount of 5-10% by weight. Of
course, combinations of both photoinitiators and thermal initiators also can be used.
In such a case, for example, the heat generated in a formulation due to the activity of a
photoinitiator can cause activation of the thermal initiator.
According to the invention, the radiation-curable formulation is used to provide a
coating on at least one fibrous facing sheet of a gypsum panel. For this, the radiationcurable
formulation is applied in a known manner, eg. by spraying, trowelling, knife
application, brushing, rolling or pouring onto the fibrous facing sheet of the gypsum
panel. It is also possible that the formulation may be applied to the fibrous facing
sheet of the gypsum panel by a hot-melt process or by a powder-coating process.
The amount of coating applied to the surface of the fibrous mat preferably should be
sufficient to embed the surface of the mat completely in the coating, preferably to the
extent that substantially no fibers protrude through the coating and preferably so that
the coating is impervious to the passage of moisture (in either the liquid or vapor
state). The amount of coating used may be dependent upon the nature of the fibrous
mat. In some case it may be difficult to measure thickness of the coating, such as
where the fibrous mat substrate on which the coating is applied is uneven.
The coating weight is usually in the range from 1 to 50 pounds per 1000 sq. ft. of
gypsum panel, more often in the range from 2 to 25 pounds per 1000 sq. ft. of gypsum
panel, based on the polymerizable components present in the formulation. The
application may take place either at room temperature or at an elevated temperature,
but preferably not at a temperature above 100° C., so as to avoid conditions that could
contribute to undesired calcination of the gypsum core. Although higher or lower
amounts of the radiation curable formulation can be used in any specific case, it is
believed that, for most applications, the amount of powder coating will fall within the
range of about 2 to about 25 Ibs per 1000 sq. ft. of gypsum panel.
In rough terms, the thickness of the coating should be at least about 0.5 mils and is
usually less than about 5 mils, but when the glass mat is relatively thin and the coating
is efficiently dried, a coating as thin as 0.25 mils may suffice. In general, the
thickness of the coating need not exceed about 5 mils and for most applications, a
coating thickness of about 2 mils should usually prove to be sufficient.
Following application of a thin coating of the curable formulation to the fibrous
facing sheet of the gypsum panel, the composition then is cured by passing the coated
gypsum panel under a radiation source, e.g., a UV source, to form the radiation-cured,
e.g., UV-cured polymer coated gypsum panel. The coated gypsum panel made in
accordance with these teachings provides both a liquid and vapor barrier to water.
The coating can be cured by exposure to high-energy radiation, preferably by UV
radiation of wavelength from 250 to 400 nm or by irradiation with high-energy
electrons (electron beams; from 150 to 300 kev). Examples of UV sources include
high-pressure mercury vapor lamps. The radiation dose usually sufficient for
crosslinking is in the range from 80 to 3,000 mJ/cm2.
In another embodiment, especially suitable when the panel is intended to be used as a
tile backer, an aggregate material is included in the radiation curable formulation, or
is applied to the curable formulation that has been coated on a fibrous facing sheet.
The purpose of the added aggregate is to provide the cured coating with sufficient
surface roughness or other surface characteristics to promote or enhance the ability to
adhere tiles or other surface treatments to the radiation cured coating. The nature of
the aggregate can vary widely and this embodiment of the invention is not limited to
any particular type or size of aggregate material. Embraced broadly within the terms
"aggregate" are ceramic microspheres, glass microspheres, calcium carbonate, sand,
aluminum oxide (alumina), crushed stone, glass fibers, gypsum, perlite, and other
inorganic and organic aggregate materials readily recognized by those skilled in the
While the aggregate can be added to the curable coating formulation before it is
coated onto the fibrous facing sheet, in the interest of limiting the amount used and
concentrating it where it is most effective, it is preferred to add the aggregate material
onto the curable coating formulation after it has been coated onto the fibrous facing
sheet but before curing the coating. In this way, the aggregate material remains near
the surface of the coating where it is needed to create a surface morphology conducive
to bonding anyone of a number of surface treatments, such as ceramic tiles, to the
gypsum panel. The amount of aggregate added to the coating can vary within wide
limits and it is preferred to use only that amount needed to provide a suitable surface
onto which an adequate bond can be made. For any particular aggregate material, a
suitable level can be arrived at using only routine experimentation. As will be
understood by skilled workers, the amount of aggregate to apply will be a function of
the density of the aggregate used since the objective is to provide a surface coating of
the aggregate on the coating, it not usually being necessary to complete permeate the
depth of the coating with the aggregate. For low density material such as
microspheres, generally, an amount of aggregate of about 1.25 pounds per 1000 sq. ft.
should be suitable. For higher density materials, such as calcium carbonate, an
amount of aggregate of about 15-40 Ibs per 1000 sq. ft. should be suitable, with 20-35
Ibs per 1000 sq. ft. being more preferred.
The following table illustrates several examples of radiation curable formulations
suitable for coating a fibrous facing sheet of a gypsum panel.
Each formulation includes a photoinitiator and a radiation curable polymer.
The following table illustrates additional preferred examples of radiation curable
formulations suitable for coating a fibrous facing sheet of a gypsum panel.
It will be understood that while the invention has been described in conjunction with
specific embodiments thereof, the foregoing description and examples are intended to
illustrate, but not limit the scope of the invention. Other aspects, advantages and
modifications will be apparent to those skilled in the art to which the invention
pertains, and these aspects and modifications are within the scope of the invention,
which is limited only by the appended claims.. Unless otherwise specifically
indicated, all percentages are based on UF resin solids. Throughout the specification
and in the claims the term "about" is intended to encompass + or - 5%.
1. A gypsum panel(lO) comprising:
(a) a gypsum core(12) having a planar first face (16) and a planar second face(14);
(b) a fibrous facing material(24) adhered at least to the first face by gypsum in the
gypsum core (12) obtained from step (a) at least partially penetrating into the said
(c) a high energy radiation cured coating (15) of a radiation curable formulation on
the fibrous facing material obtained from step (b), wherein the radiation curable
formulation is essentially free of water, which comprises
at least one high energy radiation curable polymer having ethylenically unsaturated double bonds, and
at least one high energy radiation curable reactive diluents; and
(d) an aggregate material on and /or in the high energy radiation cured coating of step
2. A gypsum panel (10) as claimed in claim 1, wherein the fibrous facing material is a
multi- ply paper facing material (1).
3. A gypsum panel (10) as claimed in claim 1, wherein the fibrous facing material is a
non- woven mat of mineral fibers (2).
4. A gypsum panel (10) as claimed in claim 3, wherein the fibrous facing material is a
single- ply glass fiber mat facing material (3).
5. A gypsum panel (10) as claimed in claim 1, wherein the fibrous facing material is a
woven or non-woven mat of synthetic fibers (4).
6. A gypsum panel (10) as claimed in claim 1, wherein the fibrous facing material is a
blend of mineral fibers and synthetic fibers.
7. A gypsum panel (10) as claimed in claim 3-6, wherein the said fibrous facing material
has a dried coating of an aqueous mixture of filler and a binder.
8. A gypsum panel (10) as claimed in claim 1, wherein the gypsum core used is a
water- resistant additive selected from the group comprising of a wax emulsion, an
organopolysiloxane and a siliconate, in an amount sufficient to improve the water-
resistant properties of the core.
9. A gypsum panel (10) as claimed in claim 7, wherein the gypsum core is essentially
void of starch.
10. A gypsum panel (10) as claimed in claim 1, wherein the aggregate material used is
selected from from the group comprising of a ceramic microspheres, glass microspheres,
calcium carbonate, sand, aluminum oxide, crushed stone, glass fibers, gypsum and
11. A gypsum panel (10) substantially as herein described with reference to the examples
and figures accompanying this specification.
|Indian Patent Application Number||2164/DELNP/2005|
|PG Journal Number||26/2008|
|Date of Filing||24-May-2005|
|Name of Patentee||G-P GYPSUM CORPORATION|
|PCT International Classification Number||E04C|
|PCT International Application Number||PCT/US2003/039504|
|PCT International Filing date||2003-12-12|