U.S. patent application number 09/748989 was filed with the patent office on 2002-10-03 for dual layer acoustical ceiling tile having an improved sound absorption value.
Invention is credited to Baig, Mirza A..
Application Number | 20020139611 09/748989 |
Document ID | / |
Family ID | 25011746 |
Filed Date | 2002-10-03 |
United States Patent
Application |
20020139611 |
Kind Code |
A1 |
Baig, Mirza A. |
October 3, 2002 |
Dual layer acoustical ceiling tile having an improved sound
absorption value
Abstract
An acoustical ceiling tile having an improved sound absorption
value and having a dual layer of acoustical materials. The base mat
layer has either no mineral wool or a low mineral wool content. The
surface layer has a high mineral wool content which provides
improved sound absorption values with or without perforating or
fissuring the tile. The dual layer acoustical ceiling tile has a
noise reduction coefficient (NRC) value of at least about 0.50.
Inventors: |
Baig, Mirza A.;
(Lindenhurst, IL) |
Correspondence
Address: |
John M. Lorenzen
USG Corporation
700 North Highway 45
Libertyville
IL
60048-1296
US
|
Family ID: |
25011746 |
Appl. No.: |
09/748989 |
Filed: |
December 27, 2000 |
Current U.S.
Class: |
181/286 ;
181/294 |
Current CPC
Class: |
B32B 2262/062 20130101;
B32B 5/26 20130101; E04B 9/045 20130101; B32B 2419/00 20130101;
C04B 28/14 20130101; B32B 2317/12 20130101; B32B 2315/14 20130101;
D21J 1/20 20130101; D21H 17/67 20130101; D21H 17/28 20130101; B32B
2307/56 20130101; B32B 2250/20 20130101; C04B 26/06 20130101; C04B
26/285 20130101; C04B 28/28 20130101; D21H 27/34 20130101; G10K
11/162 20130101; B32B 19/06 20130101; C04B 2111/52 20130101; Y02W
30/91 20150501; E04B 9/001 20130101; C04B 2111/00612 20130101; C04B
26/28 20130101; D21H 27/38 20130101; D21H 13/40 20130101; B32B
2250/02 20130101; C04B 26/28 20130101; C04B 14/10 20130101; C04B
14/46 20130101; C04B 22/142 20130101; C04B 24/26 20130101; C04B
28/14 20130101; C04B 14/10 20130101; C04B 14/46 20130101; C04B
24/26 20130101; C04B 24/38 20130101; C04B 26/28 20130101; C04B
14/10 20130101; C04B 14/18 20130101; C04B 18/24 20130101; C04B
24/26 20130101; C04B 26/28 20130101; C04B 14/10 20130101; C04B
14/185 20130101; C04B 18/24 20130101; C04B 24/26 20130101 |
Class at
Publication: |
181/286 ;
181/294 |
International
Class: |
E04B 001/82 |
Claims
What is claimed is:
1. A dual layer acoustical ceiling tile having an improved sound
absorption value (NRC) comprising a low mineral fiber base mat
containing less than about 50% by weight of mineral fiber and
having a thickness ranging from about 0.25 inch to about 0.625 inch
and a mineral wool fiber-rich overlay surface layer containing at
least about 75% by weight of mineral wool fibers and having a
thickness ranging from about 0.125 inch to about 0.5 inch, said
ceiling tile having a noise reduction coefficient (NRC) value of at
least about 0.50.
2. The ceiling tile of claim 1 wherein the low mineral fiber base
mat contains at least about 30% by weight of expanded perlite.
3. The ceiling tile of claim 1 wherein the fiber-rich surface layer
contains both a starch binder and a latex binder.
4. The ceiling tile of claim 1 wherein said mineral fiber-rich
surface layer has a thickness of about 1/4 inch or less.
5. The ceiling tile of claim 1 wherein there is a fiberglass scrim
between the base mat material and the fiber-rich surface layer.
6. The ceiling tile of claim 3 wherein the latex binder in the
fiber-rich surface layer has been deposited on the mineral fibers
by adding a small amount of flocculant to an aqueous slurry
containing the mineral fibers and the latex binder.
7. The ceiling tile of claim 1 wherein both the low mineral fiber
base mat material and the fiber-rich surface layer contain a starch
gel binder which has been pre-cooked before incorporating it into
the base mat material and the fiber-rich surface layer
material.
8. The ceiling tile of claim 1 wherein the ceiling tile has a total
thickness ranging from about 0.375 inch to about 1 inch.
9. The ceiling tile of claim 1 wherein the fiber-rich surface layer
contains cellulose fibers ranging from about 3 to about 7.5 weight
percent.
10. The ceiling tile of claim 1 wherein both layers of the tile
contain a starch gel binder in the form of a pre-gelatinized starch
which is converted to a gel merely by adding it to water.
11. The ceiling tile of claim 1 wherein the ceiling tile has a base
mat material and a fiber-rich surface layer which both contain
paper fibers.
12. The ceiling tile of claim 1 wherein the density of the tile
ranges from about 12 pcf to about 21 pcf.
13. The ceiling tile of claim 1 wherein there is a fiberglass scrim
applied to the surface of the fiber-rich layer.
14. The ceiling tile of claim 1 wherein there is a calcium
carbonate coating on the surface of the fiber-rich layer.
Description
FIELD OF THE INVENTION
[0001] This invention relates to an acoustical ceiling tile having
an improved sound absorption value. More particularly, this
invention relates to a dual layer acoustical ceiling tile having a
low or no mineral wool base mat layer and a high mineral wool
overlay surface layer which provides improved sound absorption
values with or without perforating or fissuring the tile. The
invention also relates to a dual layer acoustical tile which is
manufactured using a high speed, water-felting process. A pattern
can be applied before drying the tile (wet end embossing), or the
pattern can be formed in the tile after the drying.
BACKGROUND OF THE INVENTION
[0002] The water-felting of dilute aqueous dispersions of mineral
wool and lightweight aggregate is a commercial process for
manufacturing acoustical ceiling tile. In this process, a
dispersion of mineral wool, lightweight aggregate, binder and other
ingredients as desired or necessary is flowed onto a moving
foraminous support wire, such as that of a Fourdrinier or Oliver
mat forming machine, for dewatering. The dispersion is first
dewatered by gravity and then vacuum suction is applied. After
vacuum dewatering, the wet mat is dried in heated convection drying
ovens, and the dried mat is cut to the desired panel or tile
dimensions. If desired, the panels or tiles can be top coated with
paint.
[0003] Acoustical ceiling tiles can also be made by a wet pulp
molding or cast process such as described in U.S. Pat. No.
1,769,519. In accordance with this process, a molding composition
comprising granulated mineral wool fibers, fillers, colorants and a
binder (e.g. starch gel), is prepared for molding or casting the
tile. The composition is placed upon suitable trays which have been
covered with paper or a metallic foil and then the composition is
screeded to a desired thickness with a screed bar or roller. A
decorative surface, such as elongated fissures, may be provided by
the screed bar or roller. The trays filled with the mineral wool
composition are then placed in an oven to dry or cure.
[0004] In U.S. Pat. No. 5,250,153, issued Oct. 5, 1993, a process
is disclosed for making mineral wool panels on a foraminous support
wire by forming a dilute aqueous dispersion of mineral wool fibers
and/or aggregate and an anionically stabilized latex binder. The
binder is deposited onto the mineral wool fibers by adding a small
amount of a cationic flocculant. Substantially all of the binder
latex becomes coupled to the mineral wool fibers. The wet mat can
be dried quickly by passing heated air through the mat that is
capable of maintaining its structure.
[0005] In my U.S. Pat. No. 5,558,710, issued Sep. 24, 1996, I
disclose a gypsum/cellulosic fiber composition that can replace all
or a portion of the mineral wool normally present in acoustical
ceiling tiles. The gypsum/cellulosic fiber composition is combined
with a lightweight aggregate material and a binder to form a
composition that is used in a water-felting process to manufacture
acoustical ceiling tiles.
[0006] As disclosed in Example 1 of U.S. Pat. No. 5,558,710, a
water-felting process was used to make the acoustical tiles. The
feed slurry during mat formation was held at 4% solids, and this 4%
solids consistency was also used in making the control tile. The
control tile, using 100% mineral fiber (i.e. no gypsum/wood fiber)
had the following formulation:
1 Weight % Mineral Fiber 37.58 Expanded Perlite 34.83 Newspaper
15.91 CTS-1 Clay 3.54 Starch 8.01 Flocculant 0.06 Surfactant
0.08
[0007] Samples of the control tile were tested for NRC (noise
reduction coefficient) using the Impedance tube method. The samples
were not perforated, fissured or painted. The control tiles had an
average NRC value of only 0.434.
[0008] In general, acoustical tiles made using a water-felting
process have a hard surface that does not have good sound
absorption properties. The sound absorption is substantially
improved by fissuring and/or perforating the surface that increases
the NRC value. However, many purchasers prefer a smooth,
unperforated acoustical ceiling tile for its aesthetic
appearance.
[0009] As disclosed in U.S. Pat. No. 5,250,153, acoustical ceiling
tiles having an average NRC equivalent to commercially available
cast ceiling tiles can be made by using an anionically stabilized
latex binder and a cationic flocculant to couple the latex binder
onto the mineral fiber materials. In the acoustical tiles made by
this process, the mineral fibers constitute about 50% or more of
the total dry solids, preferably from about 60 to about 95 weight %
of the acoustical panel. However the tiles made by this process are
quite soft compared to the water-felted tiles having a starch
binder. In addition, the tiles made with a latex binder have lower
structural strength and are made in thicknesses of at least about
1/2 inch and frequently have a woven scrim applied thereto to
increase strength. These acoustical tiles do have smooth surfaces
and higher NRC values resulting from the higher mineral wool
content.
[0010] Mineral wool acoustical tiles are porous which is necessary
to provide good sound absorption. The prior art (U.S. Pat. Nos.
3,498,404, 5,013,405 and 5,047,120) also discloses that mineral
fillers, such as expanded perlite, may be incorporated into the
composition to improve sound absorbing properties.
[0011] It is an object of this invention to provide an acoustical
tile having a dual layer of acoustical materials both of which
contain mineral fibers or having a base mat with no mineral
fibers.
[0012] It is another object of this invention to provide a
water-felted base mat having a relatively low mineral fiber content
or no mineral fibers and a surface layer having a high mineral
fiber content to form an acoustical tile with improved sound
absorbing properties.
[0013] It is a further object of this invention to provide a dual
layer acoustical ceiling tile having a smooth, unperforated surface
and also good sound absorbing properties.
[0014] It is a still further object of this invention to provide a
dual layer acoustical ceiling tile having a sound absorption value
(NRC) of at least about 0.50.
[0015] These and other objects will be apparent to persons skilled
in the art in view of the description that follows.
SUMMARY OF THE INVENTION
[0016] It has been discovered that a dual layer acoustical ceiling
tile having an improved sound absorption value (NRC) can be made in
a water-felting process wherein a base mat layer has a relatively
low mineral fiber content, and a surface layer having a high
mineral fiber content is overlaid onto the base mat. The base mat
layer is made from a low mineral fiber content or no mineral fiber
material which has relatively low NRC values unless its surface is
perforated and/or fissured. The mineral fiber-rich surface layer
that has a thickness of about 1/4 inch or less also has a
relatively low NRC value at such thickness. It was discovered that
these two low NRC value materials could be combined to provide a
dual layer ceiling tile having a high NRC value.
DETAILED DESCRIPTION OF THE INVENTION
[0017] The acoustical ceiling tiles of this invention are based on
the discovery that two acoustical materials having relatively low
NRC values can be combined to form a dual layer acoustical ceiling
tile having excellent sound absorption values (NRC). These ceiling
tiles are made using a water-felting process to form both the base
mat layer and the fiber-rich surface layer. In carrying out the
process, two head boxes are used to feed the acoustical materials
to the production line.
[0018] One head box feeds the base mat material, having a
relatively low mineral fiber content (less than about 50% by weight
of mineral fiber) or it may contain no mineral fiber, to a moving
foraminous support wire, such as that of a Fourdrinier or Oliver
mat forming machine for dewatering. After water is removed through
the support wire by gravity, additional water can be removed by
applying a vacuum to the wet base mat, but depending upon the
consistency of the base mat material in the head box, the line
speed and other considerations, it may not be necessary to use
vacuum for dewatering purposes prior to depositing the fiber-rich
overlay material onto the base mat. The base mat material consists
essentially of mineral wool fibers, expanded perlite, cellulose
fiber, starch binder and gypsum which can be present, preferably,
in the following amounts, and having at least about 30% by weight
of expanded perlite:
2 Ingredient Weight % Mineral Wool Fibers 5-25 Expanded Perlite
30-60 Cellulose Fiber 10-21 Starch Binder 4-9 Gypsum 3-30
[0019] After the initial dewatering of the base mat material on the
wire support, the still wet base mat may be passed under a press
roller to compress the mat, removing more water and establishing
the thickness of the wet base mat. In general, the thickness of the
wet base mat just prior to depositing the fiber-rich surface layer
may range from about 1 inch to about 2.5 inches. It is preferred
that the completely dried base mat have a thickness ranging from
about 0.25 inch to about 0.625 inch.
[0020] If desired or necessary to strengthen the dual layer ceiling
tile, a fiberglass scrim can be placed on the wet base mat prior to
depositing the fiber-rich surface layer. The fiberglass scrim can
be either woven or non-woven. If a fiberglass scrim is used, it is
generally preferred that it be placed between the base mat material
and the fiber-rich surface layer, however, if desired, the scrim
can be placed on top of the fiber-rich surface layer or in contact
with the back of the base mat material, in which case, the base mat
slurry from the head box would be deposited on the scrim.
[0021] The fiber-rich surface layer consists essentially of mineral
wool fibers, gypsum, clay filler, latex binder, starch binder and
flocculant to deposit the latex binder on the mineral wool fibers
as disclosed in U.S. Pat. No. 5,250,153. These ingredients may be
present, preferably, in the following amounts:
3 Ingredient Weight % Mineral Wool Fibers 70-90 Perlite 0-15
Cellulose Fibers 3-7.5 Gypsum 1-15 Clay Filler 0-12 Latex Binder
3-9 Starch Binder 3-9 Flocculant 0.05-0.1
[0022] The fiber-rich surface material is prepared in accordance
with the method disclosed in U.S. Pat. No. 5,250,153 wherein an
anionically stabilized latex binder is deposited on or coupled to
the mineral fibers by adding a small amount of a flocculant such as
a cationic polyacrylamide to the slurry. In accordance with this
invention, the fiber-rich slurry contains a very large amount of
mineral wool fibers (at least about 75% by weight) and little or no
expanded perlite. The fiber-rich material is deposited on the base
mat from a second headbox to form a dual layer material which is
dewatered by applying a vacuum to the wet dual layer material and
also by passing the wet dual layer material under a press roll. The
press roll helps to remove some of the water. The fiber-rich
surface is textured and the thickness of the dual layer material is
established under the pattern/texture roll. The dual layer material
is subsequently passed to an oven to complete the drying process
and to cure the starch and latex binders.
[0023] When completely dried and cut into ceiling tiles, the dual
layer material has a smooth or textured surface that is rich in
mineral wool fibers and unperforated. In general, it is preferred
that the dried dual layer ceiling tiles have a total thickness
ranging from about 0.5 inch to about 1 inch, with the thickness of
the fiber-rich surface layer ranging from about 0.125 inch to about
0.5 inch. The thickness of the wool-rich surface layer can be
increased from about 0.5 inch to about 0.625 inch to provide higher
NRC values.
[0024] Prior to drying the dual layer material in an oven, it is
preferred to apply a "wet end coating" to the mineral fiber-rich
surface, which is smooth and unperforated. One or more coats of
paint may be spray applied. It has been found that the application
of paint actually increases the NRC value, because the unpainted
surface tends to reflect the sound and therefore has a lower NRC
(noise reduction coefficient).
[0025] Other ingredients may also be present in either the base mat
or the fiber-rich surface layer or both layers. Examples of such
ingredients include dyes, pigments, inorganic fillers,
antioxidants, surfactants, water repellents, fire retardants and
the like.
[0026] As noted above, gypsum (calcium sulfate dihydrate) is
preferably present in both layers. The gypsum is soluble in the
aqueous slurry comprising both the base mat and the fiber-rich
layer feed material. The solubility of the gypsum in the processing
slurry enables the gypsum to function as a flocculant in the slurry
formulation. The flocculating function provides uniform
distribution of fine particles (e.g. clay, gypsum, perlite and
starch) present in the formulation during mixing. This flocculating
function helps to prevent the fine and high density particles from
migrating to the bottom of the mat. In addition, the gypsum helps
to disperse the mineral wool fibers in the aqueous slurry.
[0027] A starch binder is also present in both the base mat and the
fiber-rich surface layer. It is preferred to use the starch in the
form of a gel which is prepared by dispersing starch particles in
water and heating the slurry until the starch is fully cooked and
the slurry thickens to a viscous gel. If the binder is corn starch,
cooking temperatures may range from about 180.degree. F.
(82.degree. C.) to about 195.degree. F. (90.degree. C.). It should
be noted that starch may also be used as a binder without
pre-cooking the starch to form a gel. In addition, the starch can
be used in a pre-gelatinized form which is converted to a gel
merely by adding it to water, without the need to cook it.
[0028] The following specific examples will further illustrate
various specific embodiments of the present invention. Unless
specified to the contrary, all amounts are expressed as parts by
weight on a dry solids total weight basis. Of course, it is to be
understood that these examples are by way of illustration only and
are not to be construed as limitations on the present
invention.
EXAMPLE 1
[0029] Samples of commercially available, mineral fiber-rich,
acoustical ceiling tiles were used to determine sound absorption
properties (NRC values) for thin layer (approximately 1/4 inch
thick) materials. Such materials do not have sufficient structural
strength to be made in a water-felting process in such thin layers,
and therefore, ceiling tiles were made having a thickness of about
0.7 inch and a density of about 16 pcf. The tiles had a back
coating of 35-C clay at coverage of about 24 grams/ft..sup.2 (dry)
which increase the tile density by about 0.85 pcf. The thin layer
samples were cut from the back of the tile. Samples 1-4 had the
following formulation:
4 Samples 1&2 Samples 3&4 Weight % Weight % Mineral Wool
Fibers 88.9 91.8 Gypsum 1.5 1.5 Clay Filler 0 0 Latex Binder 6.6
4.7 Starch Binder 3.0 2.0 Flocculant 0.07 0.07
[0030] Sample 3 did not have the clay back coating. The samples
were cut into 12 inch squares for testing. The following NRC
(impedance tube) values were recorded:
5 Sample Thickness (inch) Actual NRC 1-a 0.225 0.23 1-b 0.225 0.23
2-a 0.25 0.33 2-b 0.25 0.33 3-a 0.25 0.21 3-b 0.25 0.23 4-a 0.25
0.32 4-b 0.25 0.30
[0031] This data demonstrates that the fiber-rich material in
thicknesses of about 1/4 inch had very low NRC values.
EXAMPLE 2
[0032] The purpose of this trial was to determine the effect of
different amounts of latex binder in the fiber-rich overlay
formulation, particularly its effect on the dry mat surface
hardness. The base mat had the following formulation:
6 Weight % Mineral Wool Fibers 36.6 Starch Gel Binder (pre-cooked)
6 Clay (CTS-2) 5 Paper Fibers 14 Perlite 38.4
[0033] A standard water-felting process was used to make the base
mat, with the stock material having a consistency of about 5.8% by
weight of solids. The line speed was about 30 feet/minute. The
dried base mat had a thickness of about 0.5 inch.
[0034] The fiber-rich overlay material had the following
formulation:
7 Weight % A B Mineral Wool Fibers 86.4 86.4 Starch Gel Binder 6 3
(pre-cooked) Latex (Dow 3 6 XU31518.00) Clay (CTS-2) 2.3 2.3 Gypsum
2.3 2.3 Flocculant 0.07 0.07
[0035] The mineral wool, starch, latex binder, clay and gypsum
combined had a total weight of 173.6 lbs. and were added to 500
gallons of water, providing a stock consistency of about 4% by
weight of solids. The flocculant was subsequently added after
thorough mixing of the stock to deposit the latex binder on the
mineral fibers. The stock was fed through a 4 foot wide head box at
a rate of about 125 gallons/minute.
[0036] The NRC values were determined using the Impedance tube
method as follows:
8 Overlay Total Thickness Formulation (inch) Density (pcf) NRC A
0.731 16.3 0.53 B 0.725 16.5 0.51
[0037] The surface of the dried tiles (both formulations) was
hard.
EXAMPLE 3
[0038] In this trial, the use of paper fiber in the fiber-rich
overlay formulation was evaluated. The base mat used the same
formulation as in Example 2 and also the same standard
water-felting process.
[0039] The fiber-rich overlay material had the following
formulation:
9 Weight % A B Mineral Wool Fiber 82.6 85 Starch Gel Binder 2.9 6
(pre-cooked) Latex Binder (Dow, 3.9 0 XU31518.00) Clay (CTS-2) 3.9
2 Gypsum 1.9 2 Paper Fiber 4.8 5 Flocculant 0.07 0
[0040] In trial A, a wet end coating was applied on the production
line before drying. A standard coating (18% solids) was applied,
with coverage on the dry tile amounting to 10 gm/ft..sup.2.
[0041] The NRC values were determined using the Impedance tube
method as follows:
10 Overlay Total Thickness Formulation (inch) Density (pcf) NRC A
0.676 19.6 0.54 B 0.683 17.8 0.52
[0042] The use of paper fiber in the overlay formulation improved
the surface smoothness, the wet end texturability and the wet
strength without adversely affecting the NRC values.
EXAMPLE 4
[0043] This trial evaluated the use of larger amounts of gypsum in
the overlay formulation. The base mat used the same formulation as
in Example 2 and also the same standard water-felting process.
[0044] The fiber-rich overlay material had the following
formulation:
11 Weight % A B Mineral Wool Fiber 83.1 83.1 Starch Gel Binder 2.9
2.9 (pre-cooked) Latex Binder 2.9 2.9 (Dow XU31518.00) Gypsum 11.1
11.1 Flocculant 0.07 0.07
[0045] In both trials, a wet end coating (18% solids) was applied
on the production line. The coating coverage amounted to 10
gm./ft..sup.2 on the dry tile. In Trial B, a spray coating (55%
solids) was applied to the dry tile, with coverage amounting to 8.5
gm./ft..sup.2.
[0046] The NRC values were determined using the Impedance tube
method as follows:
12 Total Thickness Trial (inch) Density (pcf) NRC A 0.690 18.0 0.56
B 0.710 18.2 0.51
[0047] The increased use of gypsum in the overlay formulation
increased the surface hardness and smoothness.
EXAMPLE 5
[0048] Trials were performed to evaluate a variety of tile
finishing procedures. The base mat used the same formulation as in
Example 2 and also the same standard water-felting process.
[0049] The fiber-rich overlay material had the following
formulation:
13 Amount (Weight %) Mineral Wool Fibers 80.9 Starch Gel Binder
(pre-cooked) 2.8 Latex Binder (Dow XU31518.00) 3.9 Clay (CTS-2) 2.7
Gypsum 9.7 Flocculant 0.07
[0050] A pair of samples were evaluated in each test. In test 1,
the samples were spray painted once. In test 2, the samples were
spray painted twice, and in test 3, they were spray painted three
times.
[0051] The NRC values were determined using the Impedance tube
method as follows:
14 Total Thickness Trial (inch) Density (pcf) NRC 1 0.724 15.62
0.55 1 0.729 15.55 0.58 2 0.731 16.24 0.63 2 0.729 16.01 0.60 3
0.737 16.57 0.63 3 0.741 16.46 0.65
[0052] It is believed that the improved NRC values in these tests
resulted from the lower density tiles compared to previous tests.
It is generally preferred that the density of the dual layer
ceiling tiles range from about 12 pcf to about 21 pcf.
EXAMPLE 6
[0053] Trials were performed to compare estimated (Impedance Tube)
NRC values for the dual layer ceiling tiles of this invention with
full-scale NRC tests. The base mat and overlay formulations were as
follows:
15 Ingredients Base Mat (% by wt) Overlay (% by wt) Mineral Wool
36.6 86 Expanded Perlite 39.4 0 Paper Fiber 19 0 Starch Binder 5 3
Latex Binder 0 4 Gypsum 0 7 Flocculant 0 0.07
[0054] Three samples were prepared and tested for NRC values.
16 Overlay Total Tile Total Tile Estimated Caliper Caliper Density
(Imp.Tube) Test (inches) (inches) (pcf) NRC Value 1 0.274 0.693 17
0.58 2 0.262 0.622 17.2 0.62 3 0.250 0.7525 16.1 0.54 Overlay Total
Tile Total Tile Caliper Caliper Density Full-Scale Test (inches)
(inches) (pcf) NRC Value 1 0.274 0.725 15.8 0.61 2 0.262 0.675 16.3
0.56 3 0.250 0.725 15.8 0.61
EXAMPLE 7
[0055] Two different overlay formulations were tested for their
full-scale NRC values. The base mat formulation was the same as
reported in Example 6. The overlay formulations were as
follows:
17 Formulation B Formulation C Ingredients (% by wt) (% by wt)
Mineral Wool 83.1 86.4 Starch Binder 2.9 3 Latex Binder 2.9 6
Gypsum 11.1 2.3 Clay 0 2.3 Flocculant 0.07 0.07
[0056] The full-scale NRC values were as follows:
18 Total Tile Total Tile Full-Scale Formulation Caliper (inches)
Density (pcf) NRC Value B 0.725 16.9 0.50 C 0.725 16.5 0.51
EXAMPLE 8
[0057] Dual layer ceiling tiles were made including the application
of a glass fiber scrim onto the mineral wool rich surface. The base
mat formulation was the same as the formulation used in Example 6.
The mineral wool rich overlay was approximately 0.25 inches in
thickness and contained 86% by weight of mineral wool.
[0058] The mineral wool rich overlay surface was not ground and was
not perforated. However, a standard, non-woven glass fiber scrim
was applied to the mineral wool rich overlay surface using an
adhesive. The adhesive was Super 77 multipurpose spray adhesive
made by 3M Company. The adhesive coverage was approximately 1.5
gm/ft..sup.2.
[0059] The dual layer tiles were spray painted (single application)
on the mineral wool rich surface with a standard acoustical tile
paint. The paint coverage was approximately 27 gm/ft..sup.2. The
tiles were tested for estimated (Impedance Tube) NRC values.
19 Test Thickness (inch) Density (pcf) E-NRC 1-a 0.627 16.5 0.53
1-b 0.627 16.5 0.54 2-a 0.770 15.6 0.68 2-b 0.770 15.6 0.66
EXAMPLE 9
[0060] Dual layer ceiling tiles having a calcium carbonate surface
coating were evaluated for estimated NRC value. The dual layer
tiles were not perforated. The base mat formulation was the same as
the formulation used in Example 6. The mineral wool rich overlay
was approximately 0.25 inches in thickness and contained 86% by
weight of mineral wool.
[0061] The mineral wool rich surface was coated with dry calcium
carbonate particles. The coarse calcium carbonate was spray coated
at a coverage of about 38 gm./ft..sup.2. Prior to applying the
calcium carbonate, the tiles were painted with standard acoustical
tile paint. The paint was applied with a roll coat and then with a
flow coat and dried. After applying the calcium carbonate, the
tiles were spray painted with a standard acoustical tile paint and
were dried.
[0062] This dual layer ceiling tile with the calcium carbonate
coating had an estimated NRC of 0.50.
* * * * *