US3513009A - Method of forming fissured acoustical panel - Google Patents

Description

May 19, 1970 G. E. SAUER ETAL v3,513,009

METHOD OF FORMING FISSURED ACOUSTIGAL PANEL Filed Dec. 27, 1965 INVENTORS Arthur C. Austin Gale E.Souer 77, ATTORNEY United States Patent US. Cl. 117-10 6 Claims ABSTRACT OF THE DISCLOSURE A building panel is formed by combining a face layer of a relatively low density mineral fiber and binder composition with a relatively dense gypsum board back layer.

The present invention relates to a method of forming an improved acoustical panel. More particularly, it relates to a method of forming a fissured acoustical panel adapted for mechanical suspension as sound absorbing and attenuation media spaced below a main ceiling structure.

The formation of acoustical products, such as tiles and panels, requires a balance between physical properties. Sound absorption is a critical requirement and depends upon the porosity of the material, so that incident sound waves impinging on the material can enter into the material and be dissipated therein. In order to increase the porosity of the acoustical product, the surface of the body is usually opened, as by forming fissures or drilling holes therein, to expose the fibrous structure in the interior of the product, thereby greatly increasing the sound absorbing efficiency of the product. Therefore, as the porosity of the body increases and the density decreases, sound absorption increases. However, as the porosity increases, the strength of the product decreases; and as the density decreases, sound transmision increases. Since prefabricated acoustical tiles and panels must reduce the transmission of sound and serve as a ceiling as well as absorbing sound, the material must have sufficient strength to withstand handling and to be applied on mechanical suspension systems. In addition, the material must have sufiicient density so that unabsorbed sound is not transmitted through the material into adjoining areas. This is of particular importance when the acoustical material is installed on a mechanical suspension system where the chamber above the suspended ceiling acts as a duct to spread unabsorbed sound waves transmitted through the acoustical material into areas where the sound waves are objectionable. Furthermore, the acoustical material must have an attractive surface so that the ceiling formed will not be aesthetically objectionable.

One of the chief disadvantages of presently available porous acoustical bodies, such as those formed of mineral wool, wood fibers, and the like, is that acoustical panels formed of such materials have a tendency to sag excessively when mounted in mechanical suspension systems, such as exposed grid systems. This is especially true when the panels are exposed to conditions of high humidity. Conventional porous, low density acoustical panels also generally lack sufiicient density to prevent the continued upward movement of sound waves traveling through the material so that an objectionable amount of sound passes through the panel. While it has been suggested to increase the density of the product to thereby increase the sound attenuation, such an increase in density considerably reduces the sound absorption, which is the principal function of the product.

It is therefore an object of the present invention to provide an acoustical panel having the combined properties of high sound absorption, high sound attenuation, and ade- 3,513,009 Patented May 19, 1970 quate strength for mounting in a mechanical suspension system.

Another object of the persent invention is to provide an acoustical panel adapted for mechanical suspension and which adequately prevents the transmission of sound waves while retaining excellent properties of sound absorption.

Another object is to provide laminated acoustical panels having a sound-absorbing facing layer bonded to a soundattenuating backing layer.

A further object of the invention is to provide a method of forming fissures in a sound-absorbing facing layer disposed on a sound-attenuating backing layer.

A further object is to provide a screed bar for opening fissures in the surface of a porous, sound-absorbing material.

Various other objects and advantages will appear from the following description of the invention, and the novel features will be particularly pointed out hereinafter in the appended claims.

In the drawing:

FIG. 1 is a perspective view of the improved acoustical panel of the present invention.

FIG. 2 is a fragmentary cross-sectional view taken along the line 22 of FIG. 1.

FIG. 3 is a fragmentary cross-sectional view of another embodiment of the present invention.

FIG. 4 is a sectional view of the oscillating screed bar of the present invention.

According to the present invention, the properties of high sound absorption, high sound attenuation, and sufficient strength to permit mounting panels in a mechanical suspension system without objectionable sag are combined in a single acoustical product by providing a laminated panel having a surface layer of a material which has excellent sound-absorption properties, bonded to a relatively dense backing layer which serves to prevent the transmission of sound through the panel and has sufficient strength so that the panel may be mounted in an exposed grid system without an objectionable amount of sag. In the embodiment shown in the drawing, the acoustical panel 10 includes a sound-absorbent surface layer 11 of bonded mineral fibers bonded to a backing layer 12 of gypsum board, the gypsum board being constructed of a set gypsum core 13 enclosed in paper cover sheets 14. Fissures 15, of irregular shape and size, are formed in the surface layer, the fissures extending from the surface of the layer 12 into the interior thereof to expose the fibrous structure in the interior of the surface layer, thereby increasing the sound-absorption capacity of the panel. In addition, the fissures are also decorative in that they provide a surface resembling natural travertine stone.

More particularly, the surface layer 11 consist of granulated mineral wool in a starch binder which is cast on the backing layer. Since the mineral wool surface layer is cast rather than being felted, it is highly capable of giving a natural fissured structure when subjected to a screeding operation. The surface layer 11 provides the acoustical panel with sound-absorption properties and is relatively uniform in thickness, having a thickness sufficient to permit the required penetration of the fissures produced by the screeding operation. The thickness of this surface layer directly affects the sound-absorption values of the acoustical panel, for the noise reduction coefficient of acoustical panels of this invention increases as the thickness of the surface layer increases. Generally, the surface layer may have a thickness in the range of about 7 inch to V2 inch or more. However, it is preferred that the surface layer be no more than about /2 inch thick, for the use of a thicker layer requires extended drying periods and increases the cost of the product. Preferably, the surface layer has a thickness of about inch to inch, for acoustical panels having a surface layer of such thickness have excellent sound-absorption properties, are relatively inexpensive, have good sag resistance, and may be dried within short periods of time.

As noted hereinabove, this surface layer preferably consists of granulated mineral wool in a starch binder,

the surface layer preferably having a composition, by weight on a dry basis, within the range set forth in Table I.

In such surface layer compositions, the starch and mineral wool components provide the body of the layer. The boric acid functions as a flame inhibitor and a fungicide. The clay provides body, fire resistance and high temperature dimensional stability. The mineral wool used in forming the surface layer preferably has a size such that essentially none of the wool is retained on a A-inch screen and from to is retained on a /z-inch screen, the mineral wool fibers having a diameter of about 3 to microns. Conventional thickeners, such as, for example, hydroxypropylmethyl cellulose, ethyleneoxide polymers, guar gum derivatives, and the like, are used in forming the surface layer. In addition to the components listed above, the surface layer may, if desired, also contain about 3% to 4% stucco to increase the whiteness of the layer and about 1.4% to 1.5% of a wax emulsion which acts as a sizing to prevent water penetration.

The backing layer 12 is formed of a conventional gypsum board containing a set gypsum core 13, providing structural solidarity and density, and paper cover sheets 14, enveloping the gypsum core and providing tensile and fiexural strength. This backing layer may have a thickness of between about A inch and inch, with thicknesses of about -"/s inch and /2 inch being preferred. The backing layer provides the acoustical panel with sufficient strength to resist sagging when mounted in exposed grid systems and suflicient density to reduce sound transmission so that the panel has a good sound attenuation rating.

Instead of using conventional glysum board, which has cream-faced paper as the upper covering sheet, it has been found to be advantageous to use as the backing layer a gypsum board in which the top plies of the paper cover sheet are unsized. It has been found that the surface layer is bonded more securely to the backing layer when the cover sheets of the backing layer are unsized. In addition, it has also been found to be desirable to use as the backing layer, a gypsum board containing no paper cover sheet on the surface on which the binder-mineral wool layer is deposited, as shown in FIG. 3. It has been found that acoustical panels produced according to this embodiment of the invention have outstanding sag resistance.

In accordance with the present invention, the acoustical panels are made by forming a wet mix of the ingredients set forth in the table above and depositing a layer of this wet mix on a previously formed gypsum board. The wet layer is then screeded to provide a surface layer of relatively uniform thickness, and to open fissures in the wet layer. The slabs are then dried, whereupon the binder in the surface layer functions as an adhesive to bond the two layers into an integral panel which is then cut to size. As will be described more fully hereinafter, particular care must be taken in the screeding operation, in order to prevent scraping the wet mix off the gypsum board backing layer, and in the drying step, in order to prevent calcination of the gypsum core and/or overdrying of the thin surface layer. Usually, the surface layer, as applied, isv slightly greater in thickness than the desired finished thickness so that the dried material may be planed to a uniform thickness.

In the preparation of the surface layer, the binder, containing all of the components listed above in Table I, except the mineral wool, is made up by dispersing the thickener, such as ethyleneoxide polymers, thoroughly in cold water and subsequently adding the remainder of the ingredients in the order listed in the table. Thereafter, the temperature of the batch is brought up to about 195 F. and maintained at this temperature for a sufficient time to properly cook the starch, usually not less than about five minutes. Additional water is then added to provide the binder with a water content of between about and The binder and mineral wool are then fed simultaneously and continuously into a twin-screw-type mixer, such as that manufactured by the Sprout Waldron Company, in which the mineral wool and binder are thoroughly mixed, the mixture having a deformable but selfsupporting consistency so as to be capable of having fissures formed therein while still in the wet state. Preferably, the mineral wool is mixed with the binder solution in the ratio of about 3 to 4 parts of binder solution to 1 part of mineral wool. This binder-mineral wool mixture is then cast directly on the surface of a conventional gypsum board. Preferably, the gypsum board is carried on a moving conveyor, such as an endless belt, and is continuously moved below a container means, holding the wet binder-mineral wool mix, from which the wet bindermineral wool mix is deposited on the gypsum board.

The binder-mineral 'wool mixture deposited on the gypsum board backing layer is then subjected to a wet screeding operation to level the mix, thereby forming a surface layer of a desired thickness, and to open fissures in the surface layer. This screeding operation consists of moving the wet mix under a screed bar which extends across and is in contact with the wet mix. As the screed bar oscillates across the surface of the mix, it levels the mix and opens fissures therein. While this screeding opertion may be performed using only a single screed bar, it is generally preferred to use a pair of spaced oscillating screed bars, the first screed bar leveling the mix to a thickness slightly greater than the desired thickness of the surface layer, and the second screed bar further leveling the wet binder-mineral wool layer to provide a surface layer having a uniform desired thickness, the second bar also opening fissures in the surface layer as it oscillates thereover. The first screed bar, which first levels the wet deposited mix, is positioned substantially perpendicular to the surface of the wet mix. It is mounted so that it extends across the wet mix with the edge of the bar in contact with the wet mix. The second screed bar, which further levels and fissures the surface layer, is positioned at a fixed inclined angle to the plane in which the mix is moving in order to prevent scraping the wet binder-mineral wool surface layer off the gypsum board backing layer. Thus, it has been found that if this second screed bar is perpendicular to the surface layer, it scrapes the wet mix off the backing layer instead of leveling and fissuring the surface layer. This, it is believed, is due to the fact that the binder-mineral wool mix wets the paper cover sheet of the gypsum board, causing it to become slippery so that the wet surface layer is scraped off by the second oscillating screed bar. This problem has been overcome, according to the present invention, by providing a second oscillating screed bar which is held at a fixed angle of between 15 and 60, and preferably between 30 and 45, to the surface of the wet mineral wool layer. When the second oscillating screed bar is held at such an angle, it appears to exert a slight downward pressure on the surface layer to somewhat extrude the wet mix, with the result that the wet layer is not scraped off the backing layer but is leveled to a substantially uniform thickness and fissures are opened in the surface layer. In addition, the use of such an inclined screed bar enables the screeding operation to be controlled to produce varied degrees of fissuring.

Such an inclined oscillating screed bar is illustrated in FIG. 4, in which numeral 16 indicates the gypsum board backing layer carried on conveyor belt 17 in the direction indicated by the arrow. In the embodiment illustrated in FIG. 4, the Wet binder-mineral wool mix deposited on the paper cover sheet 18 of the gypsum board has been screeded by a first oscillating screed bar (not shown) to form a surface layer 19 having a thickness slightly greater than the desired finished thickness. The second or finish screed bar 20 is positioned at a fixed angle of between about 15 and 60 to the surface layer 19 and extends across the wet mix, with the edge of the screed bar in contact with the surface of the wet layer. In the illustrated embodiment, this second screed bar consists of a horizontal bar extending across and substantially parallel to the surface of the wet mix, the bar having an inclined edge which is in contact with the wet fibrous mix, with the edge being inclined downwardly in the direction in which the wet mix is moving, Means (not shown) are provided to support the screed bar and maintain it in such a position that the edge is held a predetermined distance above the conveyor belt. Conventional motor means (not shown) are also provided for imparting oscillation to the screed bar in a direction perpendicular to the direction in which the wet mix is moving. This second screed bar removes a slight amount of the surface layer 19 to form a surface layer 21 having a uniform desired thickness. The oscillation of this second screed bar also opens fissures 22 in the surface layer 21. A curved plate 23 is preferably secured to the back portion of the screed bar to retain the material removed from the layer 18 by the screed bar. If the screeding operation is performed with only a single screed bar, it should be of the type described and illustrated hereinabove; namely, positioned at a fixed inclined angle to the surface of the wet mix.

After the surface layer has been cast onto the backing layer and screeded, the resulting slabs are oven dried to remove moisture from the wet surface layer, whereupon the binder in the surface layer functions as an adhesive to securely bond the surface layer to the backing layer. The temperature and time of this drying step must be carefully controlled in order to prevent calcination of the set gypsum core of the backing layer and/or overdrying of the surface layer. Calcination of the gypsum reduces the core hardness of the gypsum board, thereby reducing the sag resistance of the panel. Overdrying of the surface layer discolors the surface layer, thereby detracting from the appearance of the panel. Therefore, these conditions must be avoided. Generally, it is preferred to dry the wet laminated slabs at a temperature and time sufiicient to maintain the core hardness of the gypsum board above about 20. If the slabs are dried under conditions such that the core hardness is appreci ably reduced below about 20, the resulting panels will have an objectionable amount of sag when mounted in an exposed grid system. It has been found that drying the wet laminates at temperatures within the range of about 250 to 280 F. for up to about four hours will provide a panel in which the core hardness of the backing layer is above about 20. Slightly higher temperatures, i.e. about 300 F. may be used if the drying time is correspondingly shortened. Although lower temperatures, i.e. about 180 to 250 F., may, of course, be used, such lowered temperatures are usually not preferred since their use requires a substantially longer drying time. After drying, the slabs may be cut into panels of any desired size. The panels may also be planed, if desired, so that the upper surface has a. uniform thickness.

The invention will now be described with reference to a specific example which is intended to be illustrative only. All percentages and parts are expressed on a Weight basis unless otherwise designated.

EXAMPLE A number of laminated acoustical panels consisting of a porous sound-absorbing surface layer bonded to a sound-attenuating backing layer were prepared and tested to determined the sound reduction coefiicient, the sound attenuation value, the core hardness, and the sag resistance of the panels. Each of the panels was made according to the procedure described hereinabove, the panels having a surface layer of granulated mineral wool is a starch binder bonded to a gypsum board backing layer. In order to determine the effect of the thickness of the backing layer, both /z-inch and %-inch gypsum board were used. Similarly, in order to determine the effect of the surface layer thickness, the surface layer on some of the panels was A-inch thick and %-inch thick on other panels prepared in the same manner. After fissuring and drying, the panels were tested to determine their noise reduction coeflicient and sound attenuation value, the noise reduction coefficient being determined by mechanically mounting the panels on metal supports. The results of these tests are reported below in Table II.

In order to demonstrate the effect of oven drying conditions on the core hardness of the gypsum board backing layer and the relationship of core hardness to the sag resistance of the acoustical panels, a number of panels were made according to the procedure described above and dried under different conditions. The core hardness of each panel and the sag of the panels were then determined. The core hardness value is the number of pounds required to force a standard punch, having a 0.093-inch diameter, /2 inch into the gypsum core. Sag of the panels was determined when the panels were continuously exposed to conditions of F. and 90% relative humidity for controlled periods of time.

Three groups of panels were prepared for testing, all of the panels having a Aa-inch thick surface layer having the composition set forth above and a /2-inch thick gypsum board backing layer. Group A consisted of three sets of panels, one set having a %-inCh surface layer over a /z-inch gypsum board backing layer; a second set having a %-inch surface layer over a /z-inch gypsum board backing layer from which the upper paper cover sheets had been removed; and the third set having a %-inch surface layer over a /2-inch gypsum board backing layer from the the top plies of paper had been removed. Group B consisted of two sets of panels which were the same as sets (1) and (2) in Group A. The panels of Group A were dried at 230 F. for 2 hours and then at 280 F. for 2% hours. The panels of Group B were dried at 280 F. for 5 hours. Group C consisted of panels having a %-inch surface layer on a /2-inch backing layer, these panels being dried at temperatures between 280 and 430 F. for 13 hours. The core hardness and sag of each of the panels were determined and the results tabulated in Table III.

The results of these tests clearly indicate that as core hardness of the gypsum board backing layer decreases,

TABLE III Core Sag at 90 F., 90% RH. hard- Panels ness 24 hrs. 48 hrs. 72 hrs. 96 hrs.

Grou A:

(1 surface layer, backing layer 24 387 531 585 (2) surface layer, backing layer (paper removed from surface of backing layer) 29 140 149 149 (3) surface layer, backing layer (top plies of paper removed from baeking layer) 19 202 400 520 Group B:

(4) surafce layer, backing layer 523 740 780 (5) surface layer, 56 backing layer (paper removed from surface of baeking layer) .455 .630 130 Group C:

(6) surface layer 8 1.125 (Mag. on sag rack) Control:

(7) backing layer no surface layer--- 23 313 4.02 .510

the sag of the panels increases, and that the gypsum board should not have a core hardness much below in order to avoid an objectionable amount of sag in the acoustical panels. Since calcination of the gypsum core produced by overdrying appreciably lowers the core hardness, it will be apparent that the drying conditions must be carefully controlled.

While the acoustical panels of this invention have been described hereinabove as having a surface layer of granulated mineral fibers in a starch binder cast on and bonded to a backing layer, it is to be understood that other porous, sound-absorbent materials may also be used as the surface layer. Thus, for example, the surface layer may be formed of felted mineral wool in a starch binder. An acoustical panel may be formed using such a material by laminating a dry sheet of the felted material to the backing layer with a suitable adhesive, such as the binder solution. Alternatively, a wet layer of the felted mineral wool may be pressed on the backing layer and dried, whereupon the binder in the surface layer will function as an adhesive to bond the layers together.

It will be understood that various changes in details, materials, steps and arrangement of parts which have herein been described and illustrated in order to explain the nature of the invention may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, although the invention has been described in connection with a surface layer of a wet mix of starch and mineral wool, any conventional porous acoustical material capable of being fissured may be used in forming the surface layer.

We claim:

1. A method of forming a liminated fissured acoustical panel having a porous surface layer bonded to a dense backing layer which comprises mixing granulated mineral wool with a starch binder solution to form a Wet, deformable, self-sustaining castable mix, depositing said mix on the surface of a gypsum board backing layer, leveling and opening fissures in said wet mix by moving the wet mix under at least one oscillating screed bar which extends across and is in contact with the wet mix and oscillates in the direction of its extent thereacross, said screed bar being positioned perpendicular to the surface of the wet mix, thereby forming a fissured Wet laminated panel, and drying said wet laminated panel at a temperature and time sufiieient to maintain the core hardness of the gypsum board backing layer above about 20 pounds requirement to force a .093 inch diameter punch to a /2 inch depth, whereby the binder in the surface layer securely bonds the surface layer to the backing layer.

2. The method as defined in claim 1 in which said deposited wet mix is leveled and has fissures formed therein by contacting said wet mix with said one and at least one additional oscillating screed bar means, said screed bar means being mounted and adapted to oscillate in the direction of their extent across said wet mix, said first screed bar means being perpendicular to the surface of the backing layer and leveling said wet mix to form a Wet layer having a thickness slightly greater than the desired finished thickness of the surface layer, said one additional screed bar means being positioned on and oscillating across the surface of said wet layer to level said mix to a uniform desired thickness and being positioned at a fixed inclined angle to the surface of said surface layer.

3. The method as defined in claim 2 in which said gypsum board backing layer is carried on a moving conveyor and is continuously moved below a container means holding the wet binder-mineral wool mix, said bindermineral wool mix being deposited on the surface of said gypsum board in sufficient amounts to provide, after screeding, a fissured surface layer of from about inch to /2 inch in thickness.

4. The method as defined in claim 2 in which said second screed bar is positioned at a fixed angle of between about 30 and 45 to the surface of said wet layer, said second screen bar being mounted so that the edge thereof extends across and is in contact with said wet layer and oscillates in a direction perpendicular to the direction in which the wet layer is moving, whereby the oscillation of said second screed bar across said wet layer further levels said layer and opens fissures therein.

5. The method as defined in claim 2, wherein said wet mix comprises, by weight, about 75% binder solution and about 25% mineral Wool, said binder solution comprises about by weight water and about 10% solids and said binder solution solids comprises about 30% to 60% starch, about 40% to 70% clay and a minor amount of boric acid, said wet mix being leveled to form a surface layer of a thickness of about 7 inch to /2, and said drying of said wet laminated panel being at temperatures of from about to 300 F. for time periods of about four hours.

6. The method as defined in claim 2 in which said wet laminated panel is dried, said drying being at tempera tures below about 280 F. and being completed in less than about 4 hours.

References Cited UNITED STATES PATENTS 1,983,180 12/1934 McCarthy 118-120 2,910,040 10/ 1959 Agahd.

3,391,013 7/1968 Videen 117-10 1,587,699 6/1926 Daniels 162-116 2,340,535 2/1944 Jenkins 52-144 X 2,717,538 9/1955 Alexander 162-116 2,747,470 5/1956 Jones 162-116 3,061,056 10/1962 Kodaras 52-145 3,077,945 2/ 1963 Thomas et al 117-8 X 3,149,005 9/1964 Brundige 118-120 X DAVID KLEIN, Primary Examiner US. Cl. X.R.

Patent No. 3! 009 Dated May 19, 1970 Inventor(s) Gale E. Sauer and Arthur C. Austin It is certified .that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, line 41, "opertion" should be 0peration--.

Column 6, line 8, "determined" should be ---determine---;

same column, line 13, "is" should be in--' same column, line 71, "430 should be ---340---.

TABLE III, under the heading 48 Hours in the last line,

"4.02" should be --.402--.

Claim 1, line 1, "liminated" should be ---laminated--.-.

Claim 5, line 8, after "1/2" insert ---inch---.

SIGNED AND SEALED szPmgm (SEAL) Attest:

Auesfing Officer mm 1:. sum. as.

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