Abstract:
An acoustic building material and method for manufacture incorporates a homogenously dispersed reactive silicone to improve water repellency and physical properties.

Description:
FIELD OF INVENTION 
       [0001]    The field relates to an acoustic building material or fiber board as well as a method for its manufacture, and more particularly, to fiber board having increased water repellency and improved physical properties. The fiber board includes a reactive silicone homogeneously dispersed within the board construction. 
       BACKGROUND OF INVENTION 
       [0002]    The acoustic building material or fiber board may be in the form of a ceiling tile, a ceiling panel, a wall panel or wall tile as are well known in the building trades. The boards are prepared from a slurry of fibers, fillers, binders and other ingredients. 
         [0003]    The boards are typically prepared using the slurry in a water felting process as is known in the art. A dispersion of fiber, filler, binder and other ingredients flow onto a moving, porous support such as a Fourdrinier forming machine for dewatering. The dispersion is dewatered first by gravity and then by vacuum suction. The wet base mat is dried in heated convection drying ovens and the dried material is cut to the desired dimensions and optionally coated to produce the acoustic panels and tiles. 
         [0004]    For convenience, the invention is described below with particular reference to a wall panel of the type frequently employed as a division wall in a cubical wall or other room divider. A wall covering is typically applied to the division wall using a water-based adhesive. 
         [0005]    It is known to provide wall panels as a fibrous panel structure including a base mat or core manufactured from base fibers, fillers, and binders. The base fibers are usually mineral fibers such as mineral wool or glass fibers. Also, organic fiber may be used. Frequently, the organic fiber is cellulosic fiber in the form of recycled newsprint. The fillers are commonly perlite, clay, calcium carbonate, or stucco (gypsum). The binder is typically starch, latex, or similar materials. These materials or ingredients are combined in aqueous slurry, and processed in a water felting process as described above. Upon drying, the binder forms bonds with the other materials to provide a fibrous network that provides strength and rigidity to the core. 
         [0006]    To be used as a typical division wall, the core should have sufficient strength and rigidity to remain planar in its panel configuration during use. Preferably, the panel density is sufficient to provide the perception of solidarity associated with an interior structural wall. For example, the wall density should be greater than about 16 pounds per ft 3  (pcf). 
         [0007]    In addition to these physical characteristics, the division wall should display water repellency sufficient to withstand liquid contact imposed in subsequent wall finishing and/or wall use applications. However, the described constructions tend to be porous and hydrophilic, susceptible to moisture absorption and to the ingress of liquid applied to the wall surface. It is customary to adhesively apply a wall covering, such as fabric, to division wall surfaces to provide a desired aesthetic appearance. 
         [0008]    Frequently, the fabric or other wall covering is applied using a water-based adhesive. The water absorbency or natural take-up of water by the panel has been found to hinder the achievement of the desired strong adhesive bond between the wall covering and the panel. In many instances of insufficient adhesion, it is believed that the water-based adhesive is prematurely removed from the adhesion interface by absorption or uptake into the panel without forming a strong adhesive bond. 
         [0009]    In order to retard the ingress of water-based adhesive and provide a better bond, sizing agents are used with the panel to act as water repellants. Typical sizing materials include paper sizing materials such as imidazolidone reactive sizing agents. 
         [0010]    The above sizing agents improve the bond between the wall covering and division wall, but they are not entirely satisfactory because relatively large amounts of product are required for effectiveness. Further, the prior agents are characterized by an undesirable level of volatile organic component or VOC during drying or curing. In addition, the MSDS indications of these products respectively include a formaldehyde content of 0.3% and 0.113%. 
         [0011]    Although current products are within applicable standards, it is desirable to reduce VOC and formaldehyde in both processing and final product. For example, the imidazolidone based sizing agents contribute to the VOC and are believed to be responsible for a “blue haze” observed at the production plant exhaust system. It is desirable to reduce or eliminate the haze. In any case, imidazolidone agents may contribute to both process VOC and product formaldehyde. 
         [0012]    U.S. Pat. No. 5,964,934 teaches that the water retention of expanded perlite contained in the composition of acoustic tiles may be reduced by initially spray coating the perlite with a silicone and drying the treated perlite at an elevated temperature to cure the silicone. The composition containing the treated perlite may be formed into an acoustic tile using a water felting process. The water retention of the base mat containing the silicone treated perlite is reduced without affecting the physical properties of the resulting tile. The reduction in water retention is indicated to enable increased manufacturing line speeds. 
         [0013]    U.S. Pat. No. 5,539,028 discloses the incorporation of silicone fluid comprising polymethylhydorgensiloxane (PMHS) into the slurry used to form fiberboard for improving the water resistance without affecting the physical properties of the board. The fiberboard may contain mineral fiber, non-fibrous inorganic filler, organic fiber and a binder such as starch. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0014]    It has been discovered that reactive additives may be incorporated in acoustic building materials or fiber boards to improve water repellency. The reactive additives also improve the physical properties of the material or board. 
         [0015]    The reactive additives may be included in division wall ingredients at relatively low levels to provide water repellency. Further, the level of water repellency achieved is sufficient to provide improved adhesion for subsequently applied wall coverings using water based adhesive. The additive is homogenously dispersed in the aqueous slurry used to form the core or base mat to provide the desired water repellency. 
         [0016]    The reactive additives comprise reactive silicones or silicone fluids, and particularly those having a polydimethylsiloxane backbone with substituted reactive side chains and/or ends. For example, hydrophilic side chains such as polyether side chains. One preferred silicone includes alpha-iso-tridecly-omega-hydroxy polyglycolether side chains. Another preferred silicone has a similar polyether side chain and further includes an amino-functional polydimethylsiloxane. 
         [0017]    It has also been discovered that the homogenous dispersion of the reactive silicone in the slurry composition provides a desired water repellency that is superior to that of the imidazolidone agents. Further, the reactive silicone has been found to reduce the cost of the water repellant treatment in wall panel applications due to lower usage and increased effectiveness. 
         [0018]    The reactive silicone also improves the mechanical properties of the panel. Particularly, improved strength characterized by increased modulus of rupture (MOR) and ball hardness is achieved. This is most unexpected since the prior art use of polymethylhydorgensiloxane (PMHS) silicone does not result in improved panel physical properties. In addition, no deleterious effect on other physical properties has been observed at the required silicone levels for water repellency. 
         [0019]    It has been found that the reactive silicones provide the desired water repellency for the above adhesion purposes at concentrations also providing improved physical properties. Accordingly, the resulting division wall has increased water repellency and improved strength as indicated by increased modulus of rupture. 
         [0020]    Further, the reactive silicones tend to reduce, if not eliminate, the objectionable VOC emissions associated with processing. In fact, preferred silicones are characterized by a water by-product upon curing so as to substantially eliminate all organic emissions. 
         [0021]    In typical compositions, the fiber and filler components comprise the primary ingredients. However, a wide variation of ingredients may be employed. For example, the following chart summarizes typical ceiling and wall compositions. It should be appreciated that the compositions may contain one or more of the illustrative types of fiber, filler, binder or reactive silicone as listed in the following table. The percentages herein are weight percent based on solids unless otherwise indicated by comment or context. 
         [0000]    
       
         
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Ingredient 
                 Range % 
                 Preferred % 
               
               
                   
                   
               
             
             
               
                   
                 Fiber 
                   
                   
               
               
                   
                 Mineral wool 
                 5-80% 
                 30-40% 
               
               
                   
                 fiber 
                 5-80% 
                 30-40% 
               
               
                   
                 Cellulose (recycle paper) 
                 0-25% 
                 15-20% 
               
               
                   
                 Filler 
               
               
                   
                 Perlite 
                 15-70%  
                 25-35% 
               
               
                   
                 Clay 
                 0-25% 
                  0-10% 
               
               
                   
                 Calcium carbonate 
                 0-20% 
                  5-15% 
               
               
                   
                 Binder 
               
               
                   
                 Corn starch 
                 3-18% 
                  5-15% 
               
               
                   
                 Latex 
                 0-8%  
                 0-5% 
               
               
                   
                 Reactive silicone 
               
               
                   
                 PDMS (polyether) 
                 0.02-0.5%  
                  0.1-0.15% 
               
               
                   
                 PDMS (polyether/amino) 
                 0.02-0.5%  
                  0.1-0.15% 
               
               
                   
                   
               
             
          
         
       
     
         [0022]    The fiber, filler and binder components are combined in aqueous slurry at a level of about 3% to 6% solids in a known manner. The reactive silicone is added and homogenously blended into the slurry. Hydrophilic groups present in the silicone enhance the uniform distribution of the silicone and the thorough penetration and wetting of the fiber and filler slurry ingredients. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    The division walls or wall panels of interest herein include base fibers that are usually mineral fibers such as mineral wool or glass fibers. Also, organic fiber such as cellulosic fiber derived from recycled newsprint may be used. The fillers are commonly perlite, clay, calcium carbonate, or stucco. The binder is typically starch, latex, or similar materials. These materials or ingredients are typically combined in aqueous slurry, and processed in a water felting process as described above. 
         [0024]    A number of water repellents or sizing agents were evaluated in order to resolve the adhesion problems encountered during the subsequent application of a wall covering using a water-based adhesive. Also, the contribution of the water repellants or sizing agents to the processing and final use levels of VOC and formaldehyde was determined. The evaluated agents include the following commercially available products. 
         [0025]    Imidazolidone A—an imidazolidone reactive sizing. The sizing is supplied as an emulsion that contains 45% solids and it was evaluated at an addition rate of about 0.75% based on the dry stock weight. 
         [0026]    Imidazolidone B—An imidazolidone reactive sizing. This sizing is supplied as an emulsion that contains 30% solids and it was evaluated at an addition rate of about 1.125% based on the dry stock weight. 
         [0027]    SILRES BS 1042 is a reactive PDMS supplied by Wacker Chemie AG as an emulsion containing 60% solids. The silicone has an alpha-iso-tridecly-omega-hydroxy polyglycolether side chain and the curing by-product is water. 
         [0028]    SILRES BS 1306 is a reactive PDMS also supplied by Wacker Chemie AG as an emulsion containing 55% solids. The silicone has an alpha-iso-tridecly-omega-hydroxy polyglycolether side chain and amino-functional side chains. The curing by-product is methanol. 
         [0029]    PARAFFIN WAX A—a non-curing paraffin wax emulsion. 
         [0030]    PARAFFIN WAX B—a non-curing paraffin wax emulsion. 
       Tappi Board Making Procedure 
       [0031]    Three wall panel Tappi boards were prepared using the following formulation: 35% mineral wool; 30% perlite; 18% recycled newsprint; 13% corn starch and 4% clay. The stock consistency was 4.5% solids, and 0.08% flocculent was added to the slurry. The boards were formed with a 0.5″ thickness and a target density of 17 pounds/ft. 3  (pcf). Different grades of wall panel may be simulated in accordance with product densities ranging from 16 pcf to 24 pcf and thicknesses ranging from about ⅜″ to about ¾″. 
         [0032]    After forming the Tappi boards, the wet boards were dried in an air-circulating oven for 45 minutes at 600° F. Thereafter, the drying was completed at 300° F. for 3 hours. The Tappi boards were cut into 3″×10″ and 4″×4″ samples and tested. 
       Test Procedures 
       [0033]    The MOR and ball hardness measurements were carried out on an APL Instron (Model 1130). The 3″×10″ samples were used for the MOR measurement. In the hardness test, a 2″ diameter steel ball is pressed at a constant rate into the board to a depth of ⅛″ and the maximum force is reported. 
         [0034]    The 4″×4″ square samples were used for the water absorption test. The samples were first weighed individually, and then immersed in 70° F. tap water and held at a depth of approximately 6-8 inches below the water surface for 1 hour. After 1 hour, the samples were taken from the water and re-weighed after excess surface water had been removed by tapping with a dry paper towel. 
         [0035]    Absolute water absorption is expressed as the weight difference before and after immersion for each sample. The percent water absorption is the percent of water of absorbed compared to the original dry weight of the test sample. 
         [0036]    The test results are reported in the following Table 1. 
         [0000]    
       
         
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                   
                   
                   
                 % Water 
                   
                   
               
               
                   
                 Additive 
                 Amount 
                 Density 
                 Abs. water 
                 Uptake 
                 MOR 
                 Hardness 
               
               
                   
                 (solid %) 
                 (wet wt %) 1   
                 (lb/ft{circumflex over ( )}3) 
                 uptake (g) 
                 (%) 
                 (psi) 
                 (lbf) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 none 
                 0.00% 
                 16.79 
                 69.38 
                 184%  
                 248.9 
                 189.1 
               
               
                 2 
                 Imidazolidone A 
                 0.75% 
                 17.06 
                 5.90 
                 16% 
                 248.9 
                 209.0 
               
               
                 3 
                 BS 1306 
                 0.40% 
                 16.93 
                 3.78 
                 10% 
                 248.4 
                 187.8 
               
               
                 4 
                 BS 1306 
                 0.30% 
                 16.50 
                 4.34 
                 11% 
                 270.2 
                 197.8 
               
               
                 5 
                 BS 1306 
                 0.20% 
                 16.93 
                 4.32 
                 12% 
                 262.0 
                 227.2 
               
               
                 6 
                 BS 1306 
                 0.10% 
                 16.42 
                 5.91 
                 16% 
                 268.4 
                 226.3 
               
               
                 7 
                 BS 1042 
                 0.40% 
                 16.44 
                 4.31 
                 11% 
                 259.5 
                 220.4 
               
               
                 8 
                 BS 1042 
                 0.30% 
                 16.61 
                 4.59 
                 12% 
                 240.0 
                 215.1 
               
               
                 9 
                 BS 1042 
                 0.20% 
                 16.70 
                 4.30 
                 12% 
                 254.6 
                 216.1 
               
               
                 10 
                 BS 1042 
                 0.10% 
                 16.79 
                 5.35 
                 14% 
                 258.0 
                 221.3 
               
               
                 11 
                 Paraffin Wax A 
                 3.00% 
                 16.79 
                 7.93 
                 21% 
                 244.8 
                 215.1 
               
               
                 12 
                 Paraffin Wax A 
                 2.00% 
                 16.55 
                 13.41 
                 35% 
                 215.7 
                 203.3 
               
               
                 13 
                 Paraffin Wax A 
                 1.50% 
                 16.58 
                 15.20 
                 39% 
                 255.3 
                 199.5 
               
               
                 14 
                 Paraffin Wax A 
                 1.00% 
                 16.46 
                 14.47 
                 51% 
                 218.2 
                 212.3 
               
               
                 15 
                 Paraffin Wax B 
                 3.00% 
                 17.23 
                 7.73 
                 21% 
                 221.7 
                 206.3 
               
               
                 16 
                 Paraffin Wax B 
                 2.00% 
                 16.82 
                 9.97 
                 27% 
                 227.1 
                 192.3 
               
               
                 17 
                 Paraffin Wax B 
                 1.50% 
                 16.87 
                 21.54 
                 57% 
                 230.4 
                 202.4 
               
               
                 18 
                 Paraffin Wax B 
                 1.00% 
                 16.82 
                 9.97 
                 100%  
                 227.1 
                 192.3 
               
               
                 19 
                 Imidazolidone A 
                 0.50% 
                 16.87 
                 21.54 
                 20% 
                 230.4 
                 202.4 
               
               
                 20 
                 none 
                 0.00% 
                 16.83 
                 30.80 
                  84%0 
                 254.5 
                 216.90 
               
               
                   
               
               
                   1 Based on the solids in the slurry 
               
             
          
         
       
     
         [0037]    Referring to Table 1, the overall test results show the effectiveness of the silicones as water repellants even at the low concentrations employed. Also, there is an increase in the MOR values as compared with the controls and the wax based products. The silicones did not adversely affect the physical properties of the boards. 
         [0038]    Three Tappi boards were prepared as described above to evaluate the VOC processing and final product levels characteristics. The board composition included the following ingredients: 35% mineral wool; 30% perlite; 18% recycled newsprint; 13% corn starch and 4% clay. The stock consistency was 4.5% solids, and approximately 0.08% a flocculent was added. The boards were formed with a thickness of 0.5″ and a target density of 23 pounds/ft. 3  (pcf). This formulation was varied to provide Tappi board Sample 1 containing no water repellant, Tappi board Sample 2 containing 0.45% Imidazolidone A and Tappi board Sample 3 containing 0.12% SILRES BS 1042. 
         [0039]    After forming the wet Tappi board, a 3.625″×5.5″ sample was cut from each board, placed in a sealed plastic container and stored in a refrigerator at about 40 F. prior to the VOC emission measurement. 
         [0040]    For purposes of measuring the VOC contribution of the various agents, an ARCADIS brand oven system was used. The oven system consists of an electrically heated cabinet for receiving and drying small (e.g. 4″×6″) panel samples with the capture of the oven air for analysis. To that end, the oven system also includes an air transport system for delivering the oven air together with sample emissions to an analyzer/detector for measuring total hydrocarbon content (THC). Water is not included in the THC total. 
         [0041]    Each Tappi board sample is placed in the oven at the same location to avoid effects of uneven heating in the comparison. The total hydrocarbon content (THC) concentration is measured throughout the drying process for a total test duration of about 2 hours and 5 minutes for each sample. The THC concentration in ppm was plotted against the drying time in seconds. The overall VOC emission is deemed equal to the area under the THC curve verses the drying time in seconds. In Table 2 below, the overall VOC emission is reported below in ppm-s. 
         [0000]    
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
             
             
               
                   
                   
               
               
                   
                   
                 Wet 
                 Dry 
                   
                 Total 
                   
               
               
                   
                 Water Repellent 
                 Weight 
                 Weight 
                 Percent 
                 THC 
                 Total Change 
               
             
          
           
               
                 Sample 
                 type 
                 amount 1   
                 (g) 
                 (g) 
                 dry (%) 
                 (ppm-s) 
                 (%) 
               
               
                   
               
             
          
           
               
                 1 
                 none 
                 0.00% 
                 145.37 
                 54.40 
                 37.4% 
                 1159104 
                 0.0% 
               
               
                 2 
                 Imidazolidone A 
                 0.75% 
                 142.87 
                 56.44 
                 39.5% 
                 1609186 
                 38.8% 
               
               
                 3 
                 SILRES BS 
                 0.20% 
                 143.96 
                 55.68 
                 38.7% 
                 1267064 
                 9.3% 
               
               
                   
                 1042 
               
               
                   
               
               
                   1 Wet weight % based on the solids in the slurry. 
               
             
          
         
       
     
         [0042]    Compared to the control Sample 1, Sample 2 (containing 0.34% Imidazolidone A) and Sample 3 (containing 0.12% SILRES BS 1042) showed increased VOC. However, the degree of VOC increase was much less for Sample 3 than for Sample 2. Accordingly, although the addition of a silicone water repellent is found to increase the VOC during the drying process, SILRES BS 1042 is preferred since it has only a slight increase. Although not tested, it is expected that Imidazolidone B would have an increase in VOC similar to Imidazolidone A since they are chemically similar and require like addition rates. As shown, the BS 1042 provides a reduced amount of VOC as compared with the Imidazolidone A. 
         [0043]    A trial production plant run confirmed the superior performance of reactive silicone over the production use of imidazolidone reactive Imidazolidone B. In the trial run, slurry was processed on a production water felting line to compare BS 1042 and Imidazolidone B. A slurry composition including typical percentages of mineral wool, perlite, recycled newsprint, corn starch and clay within the above preferred ranges was prepared. The stock consistency was 4.5% solids and identical flocculent was added to the compared slurries. 
         [0044]    A slurry flow rate of 1300 gallons per minute (gpm) was used. In the trial run, the BS 1042 (60% % solids) was added at a rate of 0.15 gpm and the reactive silicone is deemed to be added at a concentration of 1.5 wt % based on the total solids present in the slurry. In the comparative control run, Imidazolidone B (30% solids) was added a rate of 0.40 gpm in place of the BS 1042. In each case, about 75000 ft 2  of wall board was produced with target specifications of a thickness equal to 0.5″ and a density of 23 pcf. (These specifications correspond with one form of commercial product and, as noted above, other commercial products may have different thicknesses and densities.) 
         [0045]    The plant exhaust system was monitored during production for identification of the blue haze heretofore associated with the use of water repellent agents. The blue haze was not detected in the plant exhaust consistent with the low THC observed above in connection with BS 1042. 
         [0046]    A further advantage observed during the plant trial is the reduced foam generation in the slurry during the production of the wall board incorporating the silicone additive. Typically, the slurry processing results in foam accumulation even with the addition of defoamers. The silicone agent aids the defoamers allowing elimination and/or reduction of the amount of defoamer additive required with the use of other water repellant agents such as Imidazolidone B. 
         [0047]    Standard quality control tests were performed in connection with the trial run material and the control material. The test results are reported below in Table 3. 
         [0000]    
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Caliper 
                 Density 
                 MOR 
                   
                 Water 
               
               
                   
                 (inches) 
                 (pcf) 
                 (psi) 
                 % COM. 1   
                 Absorp. 2   
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Trial Sample 1 
                 0.501 
                 24.5 
                 472.9 
                 27.4 
                 13.9 g 
               
               
                 Trial Sample 2 
                 0.505 
                 24.2 
                 476.2 
                 27.5 
                 13.4 g 
               
               
                 Control Sample 1 
                 0.500 
                 25.2 
                 418.9 
                 26.2 
                 10.0 g 
               
               
                 Control Sample 2 
                 0.502 
                 25.3 
                 406.0 
                 26.2 
                 10.5 g 
               
               
                   
               
               
                   1 % Combustibles equal to amount burned-off. 
               
               
                   2 Absolute amount of water absorbed by the 4″ × 4″ sample. 
               
             
          
         
       
     
         [0048]    As indicated, the BS 1042 yields a much higher MOR result as compared with Imidazolidone B. The reactive side chains of the silicones are believed to be associated with the improved strength. The hydrophilic side chains of the silicone may cause improved penetration and wetting of the base mat structure by the aqueous slurry and thereby enhance the connection between the base mat ingredients with each other and the cured silicone. 
         [0049]    It should be evident that this disclosure is by way of example and that various changes may be made by adding, modifying or eliminating details without departing from the fair scope of the teaching contained in this disclosure. The invention is therefore not limited to particular details of this disclosure except to the extent that the following claims are necessarily so limited.