Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PAPERBEAD FOR PROTECTING DRYWALL CORNERS
FIELD OF THE INVENTION
[0001] The present invention relates to the use of drywall paperbead for
protecting
exposed edges of drywall, particularly for use in protecting drywall edges
where the
drywall surface adjacent the edges has a non-planar contour.
BACKGROUND OF THE INVENTION
[0002] Current building construction techniques frequently call for the use of
drywall
sheets, otherwise called wallboard, to form the surfaces of interior walls.
Sheets of
drywall are made by encasing sheets of plaster with heavy construction paper.
The
paper provides extra strength and resistance to tearing and prevents crumbling
of the
enclosed plaster. The sheets of drywall are typically produced in sizes of
four feet by
eight feet to four feet by twelve feet. These sheets can be installed intact
or can be cut to
custom fit specific interior wall sizes. When cut, the inner plaster is
exposed and is
particularly vulnerable to crumbling or other damage unless the severed edges
can be
protected. An exposed corner, exterior or interior, formed by two interfacing
drywall
sheets not in the same plane is also susceptible to damage. Damage can be
particularly
severe when these corners involve cut or exposed edges. To overcome this
vulnerability
to damage and further reinforce exposed edges, particularly the exposed corner
formed
by two interfacing drywall sheets, a drywall trim such as a drywall corner
bead will
generally be installed at that corner. The corner being reinforced can be
either an
interior or exterior corner.
[0003] Two types of drywall trim are typically used in protecting exposed
edges and
reinforcing drywall corners ¨ a paper-faced bead type (also known as a
paperbead), and
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a solid all-metal or all plastic drywall trim type. Both the paperbead and the
solid
drywall trim typically include a strip of metal or plastic formed or extruded
into a
desired shape. One common example involves forming the metal or plastic strip
into a
core shape having two flanges and a center rib positioned between them. This
form of
drywall trim is called a rib-shape corner bead. Another common shape of
drywall trim
has two flanges and a larger curved portion or bullnose positioned between
them. This
shape of corner bead is called a bullnose corner bead. A third shape of
drywall trim
features an L-shape having one flange longer than the other and an offset rib
between
the flanges. Other common shapes of drywall trim include a J-shape, a splay-
bead, and
a shadow-mold.
[0004] Solid drywall trims such as a rib-shape corner bead are attached to
drywall by
driving nails, screws, staples or other fasteners through the flanges,
securing the
drywall trim with the heads of the fasteners to the underlying framing. A
joint
compound is then applied to cover the flanges and fastener heads. The compound
is
sanded and feathered to provide a smooth and continuous surface from the
drywall
surface to the center rib of the formed metal strip.
[0005] Paperbeads provide several advantages over solid drywall trims. For
instance,
both joint compound and paint adhere significantly better to the surface of a
paperbead
than to the exposed metal or plastic surface of a typical solid drywall trim.
Moreover,
paint applied directly to a metal or plastic surface is easily chipped after
drying.
Drywall corners covered with solid drywall trims are also more susceptible to
cracking
along the edges of the flanges. Thus, a paperbead provides a better surface
for joint
compound and paint adhesion and helps reduce plaster cracking.
[0006] Paperbeads differ from solid drywall trims in several respects. First,
the
paperbead has a paper strip attached to an outer surface of the formed metal
or plastic
core as previously discussed. Generally, portions of the paper strip extend
beyond the
edges of the metal or plastic core forming wings. The paperbead is attached to
drywall
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by applying a joint compound to the drywall surface and embedding the formed
metal
strip and the paper wings in the compound. A second, exterior layer of joint
compound
is subsequently applied on top of the paperbead and allowed to dry. This
exterior layer
of joint compound is then sanded and feathered to form a smooth and continuous
surface between the drywall and the corner bead. The steps of applying,
sanding and
feathering the exterior layer of joint compound can be repeated until a smooth
surface is
created. Throughout this process, the portion of the paper strip covering the
core of the
drywall trim, i.e. the center rib, the bullnose, or the offset rib, is left
exposed or
uncovered by joint compound.
[0007] The paper surface left exposed on a typical paperbead may be scuffed,
or
completely removed during the sanding and feathering process, thus exposing
the
metal surface of the core beneath. Scuffing makes it more difficult to later
obtain a
smooth painted surface at the paperbead because the paper becomes frayed or
fuzzy.
Also, as stated previously, paint does not adhere as easily to the exposed
metal surfaces.
Therefore, paint applied to any exposed metal surface will be more easily
chipped after
it dries. Moreover, a scuff in the paper surface produces a break in the line
of the
paperbead and reduces the aesthetic benefits of having such a bead.
[0008] To overcome the problems of scuffing, some paperbeads provide a surface
coating at the exposed center portion of the paperbead to improve the paper's
resistance
to abrasion and avoid the problems caused by scuffing. This type of surface
coated
paperbead is disclosed in U.S. Pat. No. 5,131,198. A surface coating, however,
only
provides extra resistance to abrasion at the outer surface of the paper strip.
If this
coating is penetrated or removed by the sanding process, the underlying paper
is
exposed and is again made susceptible to scuffing. Consequently, the problems
of paint
adhesion, unsmooth surface finishes and paint chipping are not avoided.
Moreover, the
application of a surface coating at a particular location involves an
additional
installation step thereby increasing the cost of installing the product.
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[0009] To resolve the problem of surface coated paper, U.S. Pat. Nos.
5,836,122 and
5,613,335, both to Rennich et al., propose a paperbead for protecting drywall
corners
containing a paper strip bonded to a metal or plastic core. This paper strip
is made of
stock paper which is uniformly impregnated with latex throughout its thickness
which
imparts scuffing and abrasion resistance to the paper. However, such paperbead
had
problems with adhesiveness of the joint compound because of the latex coating
on both
surfaces of the paperbead.
[00101 Rennich et al, as described in U.S. Pat. No. 7,214,434, developed a
paperbead with
paper where one side of the paper had a strengthening compound penetrating
into only
a portion of the thickness of the paper, and the other side of the paper was
roughened.
This provided a paperbead which was resistant to abrasion and had excellent
adhesiveness to joint compounds. The latex impregnated side of the paper
maintained
increased strength making the paper resistant to scuffing, while at the same
time, the
roughened side of the paper improved its adhesiveness to joint compounds.
[0011] It is not uncommon that the surface of drywall adjacent to its edge may
have a
significant non-planar contour, being rough, uneven, undulating or otherwise
warped.
These conditions may arise for example as a result of damage in handling or
installing
the drywall. For example, one or more drywall nails or screws attaching the
drywall to
the underlying framing may have been angled or recessed too far into the
drywall or
too close to the drywall edge, causing depressions and unevenness. There may
be
deformations due to drywall knife cuts, hammer strikes or other causes
resulting in a
non-planar contour of the surface of the drywall in a region adjacent or along
the edge
of the drywall. In conditions where the drywall surface has such non-planar
contours, it
has been found that there is a possibility of the prior art paperbeads not
being able to
properly follow and adhere to the non-planar surface of the drywall. This can
give rise
to the formation of bubbles or edge lifting of the paperbead.
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[0012] While the above prior art arrangements have been successful in certain
environments where the surface of the drywall panels have not been deformed,
there is
always a push to improve installed fit and finish, so there remains a need for
a
paperbead which can better follow non-planar contours of the drywall surface.
SUMMARY OF THE INVENTION
[0013] In accordance with the present invention, the improved paperbead for
use in
protecting exposed drywall surfaces having a non-planar surface contour in an
edge
region adjacent the drywall edges comprises an elongated core having an inner
surface
and an outer surface, an elongated paper strip having an inner surface and an
outer
surface, a thickness of between 6 and 7 mils, a weight of between 110 and 125
grams/square meter (gsm) and a porosity of 30 to 130 Gurley sec., the inner
surface of
the paper strip being roughened to improve adhesiveness to joint compounds and
bonded to the outer surface of the core. The width of the paper strip is
greater than the
width of the core such that at least one edge of the paper strip extends
laterally beyond
the edge of the core to form a wing on at least one edge of the paperbead. The
outer
portion of the thickness of the paper strip is impregnated with a
strengthening
compound, preferably a polymer strengthening compound, more preferably a latex
strengthening compound in an amount between 3.5% and 13% of the total weight
of the
paper strip.
[0014] Another aspect of the invention provides a method for protecting
exposed
drywall edges where the drywall surface has a non-planar surface contour in an
edge
region adjacent the drywall edges. The method comprises:
a) providing a paperbead having an elongated core with an inner surface and an
outer
surface, and an elongated paper strip having an inner surface and an outer
surface, a
thickness of between 6 and 7 mils, a weight of between 110 and 125
grams/square meter
(gsm) and a porosity of 30 to 130 Gurley sec., the inner surface of the paper
strip being
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roughened to improve adhesiveness to joint compounds and bonded to the outer
surface of the core. The width of the paper strip is greater than the width of
the core
such that at least one edge of the paper strip extends laterally beyond the
edge of the
core to form a wing on at least one edge of the paperbead. The outer portion
of the
thickness of the paper strip is impregnated with a strengthening compound in
an
amount between 3.5% and 13% of the total weight of the paper strip
b) applying a bonding layer of a joint compound to the edge region of the
drywall
surface,
c) embedding the paperbead into the bonding layer of the joint compound, such
that the
wing of the paperbead follows the non-planar surface contour in the edge
region,
d) applying an exterior layer of joint compound to the outer surface of the
paperbead
extending beyond the wing and the bonding layer, and
e) allowing the exterior layer of joint compound to dry followed by sanding
and
feathering to produce a smooth surface between the drywall and the paperbead.
[0015] In a further aspect of the invention, the polymer strengthening
compound
penetrates only up to about half the thickness of the paper strip.
[0016] In another aspect of the invention, the polymer strengthening compound
is a
latex strengthening compound.
[0017] In yet another aspect of the invention, the latex strengthening
compound is cross-
linked.
[0018] In a further aspect of the invention, the inner surface of the paper
strip is
roughened by mechanical means.
[0019] In another aspect of the invention the outer surface of the paper strip
in a border
region of the wing is lightly roughened or buffed.
[0020] In yet another aspect of the invention, the border region extends about
0.5 to
about 1 inch from the edge of the paper strip.
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[0021] In a further aspect of the invention, the paper strip is about 6.5 mils
in thickness,
having a weight of about 117 grams/square meter (gsm) and a porosity of about
80
Gurley sec., and the outer portion of the thickness of the paper strip is
impregnated
with about 8.3% of the total weight of the paper strip of a polymer
strengthening
compound.
[0022] In yet another aspect of the invention, the core has a pair of flanges,
the paper
strip extending beyond the flanges to form a pair of wings to provide a border
region,
the border region being roughened.
[0023] In a further aspect of the invention, the core is selected from the
group consisting
of:
a) a center rib and two shoulders interposed between said flanges, said
shoulders
connecting said center rib and said flanges;
b) a bullnose and a pair of shoulders interposed between said flanges, said
shoulders
connecting said bullnose to said flanges;
c) a shoulder and an offset rib, said flanges comprising a long flange and a
short flange,
said short flange having an inner surface, said shoulder connecting said long
flange and
said offset rib, said wing extending beyond said short flange bonded to said
inner
surface of said short flange;
d) a center portion, an offset rib, a first flange and a second flange, said
center portion
positioned between said offset rib and said second flange, said second flange
extending
from said center portion, said first flange extending from said offset rib in
a direction
opposite said second flange;
e) a center portion, a short flange and a long flange, said center portion
positioned
between said long flange and said short flange to form a J-shape;
f) two strips, said strips positioned so as to form a space between them; or
g) two strips, said strips being joined by a living hinge.
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[0024] In another aspect of the invention, a formulated synthetic emulsion
adhesive
bonds the paper strip to the core.
BRIEF DESCRIPTION OF DRAWINGS
[0025] Preferred embodiments of the present invention are illustrated in the
attached
drawings in which:
FIG. 1 is a perspective view of an exterior drywall corner with a preferred
embodiment
of the paperbead for use in the present invention applied thereto and with
portions
broken away and in section.
FIG. 2 is a preferred embodiment of the invention showing a horizontal cross
section
through an exterior corner of Figure 1.
FIG 3 is a preferred embodiment of the invention showing a vertical cross
section
through an exterior corner along the line 3-3 of Figure 1.
FIG. 4 is a preferred embodiment of the invention showing a cross section
through an
exterior corner with a bullnose shape of paperbead applied thereto.
FIG. 5 is a preferred embodiment of the invention showing a cross section
through a
corner with a L-shape paperbead applied thereto.
FIG. 6 is a preferred embodiment of the invention showing a cross section
through an
interior corner with a bullnose shape of corner bead applied thereto.
FIG. 7 is a perspective of a preferred embodiment of the invention showing a J-
shape
type of paperbead.
FIG. 8 is a perspective of a preferred embodiment of the invention showing a
splay-
bead shape of paperbead.
FIG. 9 is a perspective of a preferred embodiment of the invention showing a
shadow-
mold shape of paperbead.
FIG. 10 is cut away view of the paper strip utilized in the paperbead of the
present
invention.
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FIG. 11 is a plan view of the latex impregnated side of the paperbead of the
invention.
DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS
[0026] The present invention is directed to the use of an improved paperbead
for
protecting exposed drywall surfaces having a non-planar contour in an edge
region
adjacent the drywall edges. The improved paperbead is able to follow the non-
planar
contours of the drywall surface in the edge region to result in an improved
installed fit
and finish. The paperbead includes an elongated core having an inner surface
and an
outer surface. The paperbead also includes an elongated paper strip having an
inner
surface and an outer surface, a thickness of between 6 and 7 mils, having a
weight of
between 110 and 125 grams/square meter (gsm) and a porosity of 30 to 130
Gurley sec.
The inner surface of the paper strip is bonded to the outer surface of the
core. The inner
surface of the paper strip is also roughened to improve adhesiveness to joint
compounds. The paper strip has a width greater than the width of the core such
that at
least one edge of the paper strip extends laterally beyond an edge of the core
to form at
least one wing along the edge of the paperbead. The outer portion of the
thickness of
the paper strip is impregnated with between 3.5% and 13% of the total weight
of the
paper strip of a strengthening agent, preferably a polymer strengthening
agent, more
preferably a latex strengthening agent. Preferably a border region of the
outer surface of
the paper strip along the wing of the paper strip is also roughened. The
combination of
paper strip properties as described herein results in a paperbead which
maintains
sufficient strength to keep the paper strip resistant to scuffing, while at
the same time,
achieving good bonding to joint compounds and allowing the paper strip to
follow non-
planar contours of the surface of the drywall adjacent the edges. The
particular
advantages of the use of this paperbead will be set out herein below.
Preferred
embodiments of the paperbead according to the present invention will now be
described.
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[0027] Referring now to the drawings in detail, preferred embodiments of the
paperbead of the present invention are illustrated. In particular, referring
to FIGS. 1, 2
and 3, a rib-shape embodiment of the paperbead for use in the invention is
illustrated
generally indicated by the number 10. A paperbead 10 is shown covering an
exposed
drywall corner 12 formed by two sheets of drywall 14. The sheets of drywall 14
are
attached to underlying framing member 16 by the use of suitable fasteners such
as
screws 18. While the embodiments illustrated in the drawing show metal studs
as the
framing member 16, it will be appreciated by those skilled in the art that
other types of
framing members including channels or members constructed of other materials
including wood may take the place of the metal stud. Typically, screws 18 are
driven
through the drywall 14 and into the framing member 16 so that the head 18a is
below
the surface of the drywall 14 to form a depression 21. In some instances, the
screws 18
may be installed too deep to result in a deeper depression 21 or may be
installed at an
angle. During installation of the drywall 14, there may also be other defects
which may
result in the drywall surface having a non-planar contour in the edge region
14a. These
defects can include knife cuts 20 or other deformations 22.
[00281 The paperbead 10 has an elongated core 24 and an elongated paper strip
26
bonded to the core as shown in FIGS. 1 and 2. The core 24 is preferably made
out of
metal, such as galvanized steel which meets or exceeds ASTNI-C1047 zinc
coating
specifications. However, other metals or materials such as plastic can
function as the
core element. In an exemplary embodiment, the core 24 is made of galvanized
steel
having a thickness of about 0.009 to 0.0150 inches, more preferably 0.0120 to
0.0150
inches. In the rib-shape embodiment of the paperbead, the core 24 is formed
into a rib
shape having flanges 24a, a center rib 24c and a pair of shoulders 24b
connecting the
center rib 24c and the flanges 24a. The core 24 also has an outer surface 24d
and an
inner surface 24e. The flanges 24a are commonly positioned at an angle of no
greater
than about 89 degrees relative to each other, but other angular variations may
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utilized to accommodate the relative positioning of the drywall sheets 14
and/or the
desired shape of the corner. In the rib-shape embodiment shown in FIGS. 1, 2
and 3, the
flanges 24a are about 1 inch wide. The center rib 24c is generally about
0.0625 inches
high and 0.125 inches wide.
[0029] The paperbead can be used to protect exterior corners, as shown in the
embodiments of FIGS. 1 to 5, or to protect interior corners as shown in the
FIG. 6
embodiment. For example, FIGS. 4 and 6 illustrate the use of a bullnose shape
embodiment paperbead for protecting, respectively, an exterior and interior
corner.
[0030] A bullnose paperbead 28 has a core 30 having a pair of flanges 30a, a
bullnose
30c, a pair of shoulders 30b, an outer surface 30d and an inner surface 30e.
The outer
surface 30d is defined as that surface facing away from the corner 12,
independent of
whether that outer surface forms a concave or a convex surface as shown in
FIGS. 4 and
6. The flanges 30d are generally about 1 inch wide and are positioned, in this
embodiment, at an angle of about ninety degrees relative to one another. Other
angular
variations can be implemented. The radius of the bullnose 30c is typically in
the range
of about 0.5 inches to 1.5 inches. In the preferred embodiment shown, each of
the
shoulders 30b is about 0.125 inches wide and has a drop of 0.0625 from the
surface of
the bullnose 30c to the surface of the flange 30a.
[0031] A third embodiment of the paperbead for use in the present invention is
the L-
shaped paperbead 32 shown in FIG. 5. In this embodiment, the core 34 has a
long flange
34a, a short flange 34b, an offset rib 34c, a shoulder 34d positioned between
the offset
rib 34c and the long flange 34a, an inner surface 34e and an outer surface
34f. In this
embodiment, the long flange 34a is about 1.5 inches to 2 inches long, while
the short
flange 34h is about 0.75 inches long. The long flange 34a is positioned in
this
embodiment at no greater than about 89 degrees (per ASTM-C1047) to the short
flange
34b forming an L-shape. In an exemplary embodiment, the offset rib 34c is
about 0.0625
inches high and about 0.125 inches wide.
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[0032] A fourth embodiment of the paperbead for use in the present invention
is the I-
shaped paperbead 36 shown in FIG. 7. In this embodiment, the core 38 has a
long flange
38a, a short flange 38b, and a center portion 38c positioned between the
flanges. The
core 38 also has an outer surface 38d and an inner surface 38e. The long
flange 38a is
typically about 1 inch long. The short flange 38b is typically about 1/2
inches long. The
center portion 38c is typically about 3/8 inches to 5/8 inches wide. An offset
rib 38f is
also shown in this embodiment as positioned between the center portion 38c and
the
long flange 38a. However, the offset rib 38f can also be positioned between
the center
portion 38c and the short flange 38b. Two offset ribs 38f can be provided, one
positioned between the center portion 38c, and the short flange 38h, the other
between
the centre portion 38c and long flange 38a. Alternatively, the ribs 38f may be
excluded
all together. In an exemplary embodiment, the offset rib 38f is about 0.0625
inches high
and about 0.125 inches wide.
[0033] A fifth embodiment of the paperbead for use in the present invention is
the
shadow-mold paperbead 40 shown in FIG. 9. In this embodiment, the core 42 has
a first
flange 42a, a second flange 42d, a center portion 42b, and an offset rib 42c.
The core 42
also has an outer surface 42e and an inner surface 42f. The first flange 42a
extends from
the offset rib 42c forming an angle of about 90 degrees to the center portion
42b. The
center portion 42b is positioned between the offset rib 42c and the second
flange 42d.
The second flange 42d extends from the center portion 42b at an angle of about
90
degrees in a direction opposite from the first flange 42a. In an exemplary
embodiment,
the flanges 42a and 42d are generally about 3/8 inches to 1 inch in width, but
are not
necessarily of equal width. The center portion 42b is about 3/8 inches to 1
inch in width.
[0034] A sixth embodiment of the paperbead for use in the present invention is
the
splay-bead paperbead 44 shown in FIG. 8. In this embodiment, the core 46 has
two
strips 46a each of which has an outer surface 46b and an inner surface 46c. In
an
exemplary embodiment, the strips 46a are about 1/2 inches to 3/4 inches in
width.
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[0035] Referring again to Figures 1 and 2, an inner surface 26a of the paper
strip 26 is
bonded to the outer surface 24d of the core 24. In the rib-shape embodiment,
the paper
strip 26 extends laterally beyond the edge of each of the core flanges 24a
about 1 inch to
form a pair of wings 26c. In a preferred embodiment, a border region 26d (see
Figures 1
and 11) of the outer surface 26b along the edge of the paper strip 26 may
receive
additional processing as described below.
[0036] Now referring again to Figure 5, in making the L-shaped paperbead 32,
the wing
26c extending beyond the short flange 34b is wrapped around the flange and its
inner
surface 26a is bonded to the inner surface 34e of the short flange 34b.
[0037] As shown in Figure 8, in the splay-bead paperbead 44 embodiment of the
invention, the outer surfaces 46b of the two core strips 46a are bonded to the
inner
surface 26a of the paper strip 26 leaving a space 48 between them. The space
48 may be,
for example, 0.050 inches. This spacing allows the strips 46a to rotate
relative to each
other. The strips 46a, therefore, can be positioned at different angles
relative to each
other. Accordingly, the splay-bead paperbead 44 can accommodate a variety of
wall
angle combinations. In an exemplary embodiment, the paper strip 26 extends
beyond
the metal strips 46a about N inches to 11/4 inches. In another embodiment of
the
invention, the strips 46a are polymer or plastic strips connected one to the
other by a
living hinge rather than being spaced apart.
[0038] In making the I-shaped paperbead 36, the inner surface 26a of the paper
strip 26
can be bonded to the outer surface 38d of the core 38 in a number of ways. For
instance,
in the embodiment shown in FIG. 7, one wing 26c extends beyond the long flange
38a
about 3/4 inches and a second wing 26c wraps around the short flange 38h about
0.125
inches. In other I-shaped paperbead 36 embodiments, the wings 26c may extend
beyond
or wrap around the long flange 38a and short flange 38c in any number of
combinations.
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[0039] In the shadow-mold paperbead 40 embodiment, one wing 26c extends beyond
the first flange 42a about 1/2 inches to 1 inch. The second wing 26c wraps
around the
second flange 42d about 0.125 inches as shown in FIG. 9.
[0040] FIG. 10 shows the paper strip 26 as used in the present invention. The
paper strip
26 is made from a stock paper, preferably a softwood and/or hardwood fiber
Kraft stock
paper. However, synthetic fiber products can also be used. The paper strip is
between 6
and 7 mils in thickness, has a weight of between 110 and 125 grams/square
meter (gsm),
a porosity of between 30 and 130 Gurley sec. and has two surfaces, an outer
surface 26b
and an inner surface 26a. The outer portion 26e of the thickness of the paper
strip 26 is
impregnated with between 3.5% and 13% of a strengthening compound 54 based on
the
weight of the paper strip. Outer portion 26e is preferably impregnated about
half the
thickness t of the paper strip. To obtain high wet and dry strength
properties, the
strengthening compound is preferably a polymer, more preferably a latex.
Generally, a
latex consists of a stable colloidal dispersion of a polymeric substance in an
aqueous
medium. There are a large number of commercial latexes. For example, rubber
latexes,
including a styrene-butadiene rubber, and resin latexes, including acrylic
resins, may be
used to impregnate the stock paper strip. The inner surface 26a of the paper
strip 26 is
roughened resulting in a rough and irregular surface pattern.
[0041] In a preferred embodiment, the latex is cross-linked. As a result, the
paper strip
has a good internal bond and exhibits excellent Z-direction tensile strength
properties.
Cross-linking can be accelerated by heating or superheating the latex
impregnated
paper strip. The process of impregnating the paper strip and cross-linking the
latex does
not increase the thickness of the paper strip yet increases its strength
properties and its
ability to resist abrasion. The paper strip also provides an excellent outer
surface 26b for
paint adhesion.
[0042] In a preferred embodiment, paper strip 26 is composed of 100% soft wood
pulp
formed on a Fourdrinier paper machine. A polyamide wet strength resin is
preferably
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added prior to forming to impart wet strength properties to the sheet. After
forming,
the sheet is pressed and the dried on conventional dryer cans.
[0043] The paper strip 26 is then impregnated with latex in its outer portion
26e such
that the latex only penetrates about half way through the thickness t of the
paper strip.
The inner surface 26a of paper strip 26 is roughened to obtain a felt-like
texture.
[0044] Most types of metal paperbeads, exterior and interior, are produced by
feeding a
roll of paper and a flat metal strip into a paperbead roll former. Preferably,
as the paper
is being fed into the roll former, the non-impregnated inner surface 26a of
the paper
strip is roughened by an abrasive, granular, or metal wire surface. The metal
strip is roll
formed into its respective core shape, whether it be a bullnose type, a center
rib type, an
L-shaped type or any other type of corner bead. Metal cores can also be made
by
extrusion. As noted previously, plastic cores can also be utilized. In an
exemplary
embodiment, the paper strip 26 is covered with a hot melt glue on the non-
impregnated
inner surface 26a. For example, several suitable fast-setting hot melt glues
are
commercially available. This type of glue is typically a formulated synthetic
emulsion
adhesive. The paper strip is then bonded to the outer surface of the core by
applying
pressure to the core and the paper strip with a series of pressure rolls to
ensure an even
bond. The paperbead is then cut to the desired length.
[0045] Referring to FIG. 11, in a preferred embodiment, outer surface 26b of
the
paperbead has a border region 26d on the outer edges of the paper strip 26.
The edges
24f of the underlying core 24 are shown in dashed lines. The border region 26d
is
provided with a means for improved bonding with joint compound as is common in
the
art. This means may include slitting of the paper strip or skiving where the
surface is
slightly roughened or buffed by an abrasive, granular or metal wire surface.
The width
z of the border region 26d may cover a part or all of the entire wing 26c,
preferably
about 0.5 to about 1 inch, more preferably about 0.6 to about 0.7 inch, and
most
preferably about 0.625 inch. The purpose of the border region 26d is to
improve
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bonding of the paperbead with the exterior layer compound or joint cement to
prevent
edge curl when the paperbead is applied to walls as described below. Although
FIG. 11
shows a generic paperbead similar to that shown in FIG. 1, the border region
26d is also
applicable to other configurations, such as the bullnose paperbead 28 (FIG. 4
and 6), L-
shaped paperbead 32 (FIG. 5), J-shaped paperbead 36 (FIG. 7), shadow-mold
paperbead
40 (FIG. 9), and splay-bead paperbead 44 (FIG. 8).
[0046] As shown in FIGS. 1 to 4, a paperbead 10 or 28 is installed by first
applying a thin
bonding layer 60 of joint compound or joint cement of about 4 inches to 4-1/2
inches
wide to the leading edges of two interfacing drywall sheets 14. The corner
beads 10 or
28, including the core 24 or 30 and the paper strip wings 26c are then firmly
embedded
in the bonding layer 60. Excess joint compound is removed by wiping the paper
strip
surface with a finishing knife. As the bonding layer 60 of the joint compound
dries, the
paperbead 10 or 28 follows the contour of the surface of the drywall 14,
particularly the
non-planar contours from screw heads 18a, knife cuts 20 or other deformations
22. This
is best illustrated in Figure 1, where the paper strip 26 is shown following
the non-
planar contour 21 from an underlying screw head 18a forming a shallow
depression 19,
and in Figure 3.
[0047] An exterior layer 62 of joint compound is then applied to the top of
the
paperbead 10 or 28 extending about 8 inches inward on the drywall sheet 14,
leaving
only a paper covered center rib 24c or a paper covered bullnose 30c exposed.
The
exterior layer 62 of joint compound is allowed to dry and is then sanded and
feathered
to produce a smooth surface between the drywall sheet 14 and the paper covered
center
rib 24c or the paper covered bullnose 30c. J-shaped paperbeads 36, shadow-mold
paperbeads 40 and splay-bead paperbeads 42 are installed in a similar fashion.
[0048] As shown in FIG. 6, an interior paperbead is also installed by
embedding a
paperbead 28 and paper strip wings 26c in a bonding layer 60 of joint
compound. After
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drying, an exterior layer 62 of joint compound is applied, sanded and
feathered. Interior
bullnose paperbeads 28 will have an exposed paper covered bullnose 30c.
[0049] FIG. 5 shows an L-shaped paperbead 32 installed by applying a thin
bonding
layer 60 of joint compound to a drywall sheet 14 and the exposed end 14b of
the sheet.
The L-shaped paperbead 32 is embedded in the bonding layer 60. An exterior
layer 62
of joint compound is then applied to cover a paper covered long flange 34a and
wing
26c. This layer is sanded and feathered to provide a smooth and continuous
surface
between a paper covered offset rib 34c and the drywall sheet 14.
[0050] In preliminary testing, a paperbead for use in accordance with the
present
invention was compared with the preferred embodiment of a paperbead produced
in
accordance with Rennich et al as described in U.S. Pat. No. 7,214,434. The
paperbead
for use in the present invention utilized a paper strip of about 6.5 mils in
thickness,
having a weight of about 117 grams/square meter (gsm) and a porosity of about
80
Gurley sec., the outer portion of the thickness of the paper strip being
impregnated with
about 8.3% of the total weight of the paper strip of a polymer strengthening
compound.
Both paperbeads were produced to include top side skiving of the border region
and
met QC specifications. Each of the paperbeads was installed on a test wall
with 90 deg
corners and tested using ASTM C474 standards and test methods and both
paperbeads
met the ASTM C475 standard specifications for Joint Compound and Joint Tape
for
finishing Gypsum Board. However, in this testing, it was readily but
surprisingly
observed that the described paperbead of the present application was following
and
adhering to non-planar contours of the drywall surface noticeably better than
the prior
art paperbead. For example, as is illustrated in Figure 1, when applied over
screw head
depressions 21, the wings 26c of the paperbead 10 adhered very closely to the
underlying depressions 21, whereby a significant visible depression 19 was
seen in the
outer surface of the wings 26c. In contrast, no such significant visible
depressions could
be seen when the prior art paperbead was used. Unexpected improvements noted
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included more rapid adhesion to the drywall, improved ability of the paperbead
to
follow the contours and indentations of the drywall, and reduced edge lifting
of the
paperbead, resulting in a faster, more efficient installation and superior
bond to the
joint compound.
[0051] Similar results were confirmed in blind field tests on job sites
conducted with
professional drywall trim applicators.
[0052] Although the present invention has been described in detail by way of
illustration and example, various changes and modifications may be made
without
departing in any way from the appended claims. In addition, many of the
features and
dimensions portrayed in the drawings have been exaggerated for the sake of
illustration
and clarity.
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