Patent Publication Number: US-2007111001-A1

Title: Fiber mat and process of making same

Description:
CROSS-REFERENCE TO RELATED U.S. PATENT APPLICATION  
      This application claims priority to provisional application Ser. No. 60/737,173, filed Nov. 16, 2005. 
    
    
     FIELD OF THE INVENTION  
      Embodiments of the present invention relate to a fiber mat and process of making same.  
     BACKGROUND OF THE INVENTION  
      High strength fiber mats have become increasingly popular in the building materials industry. Most commonly used in roofing shingles, fiber mats have numerous other material applications, including use in roofing, siding and floor underlayment; insulation facers; floor and ceiling tile; and vehicle parts.  
      Various fiber mats and methods of making same have been described. For example, U.S. Pat. No. 4,135,029 describes a glass fiber mat made by a wet-laid process. Glass fiber mats made by the wet-laid process are formed from glass fibers held together by a binder material. Typically, in wet process glass fiber mats, the binder is applied in a liquid form and dispersed onto the glass fibers by a curtain type applicator. Conventional wet processes strive to produce a uniform coating of binder on the glass fibers. After the binder and glass fibers have been dried and cured, the glass fiber mat is then cut as desired.  
      A major problem in the manufacture and use of some known fiber mats is inadequate tensile strength. Inadequate tensile strength can cause interruption in roofing manufacture, and may reduce the ability of the finished roofing product to resist stresses during service on the roof. Because building materials, generally, and roofing shingles, in particular, are often subjected to a variety of weather conditions, the fiber mats must also maintain their strength characteristics under a wide range of conditions.  
      For example, the tensile strength of a shingle at low temperature may have a significant impact on the performance of the shingle in cold weather. Similarly, high temperatures can affect shingle performance. The tensile strength over these temperature ranges may depend on the adhesion of the fibers to the fiber binder system, the mechanical properties of the binder system, and the interaction of the fiber mats with asphalt.  
      Various embodiments of the present invention may be suitable for use as a component of building materials, and other applications. Various embodiments may provide a material having improved tensile strength under a variety of conditions. In addition, the process of making fiber mats in accordance with some embodiments of the present invention may provide a fiber mat having improved tensile strength. Additional advantages of embodiments of the invention are set forth, in part, in the description which follows and, in part, will be apparent to one of ordinary skill in the art from the description and/or from the practice of the invention.  
     SUMMARY OF THE INVENTION  
      Responsive to the foregoing challenges, we have developed an innovative fiber mat for use in a building material, the mat comprising: a plurality of fibers; a resinous fiber binder coating the fibers; and a binder modifier comprising from about 0.05 wt. % to about 20 wt. %, based on the weight of the binder, the binder modifier comprising a carboxylic acid.  
      We have further developed an innovative fiber mat for use in a building material, comprising: a plurality of glass fibers; and a fixative composition comprising a fiber binder and between about 0.05 wt. % and about 20 wt. %, based on the weight of the binder, and a binder modifier comprising a carboxylic acid.  
      We have developed an innovative process of making a fiber mat for use in a building material, the process comprising the steps of: (a) forming an aqueous fiber slurry; (b) removing water from the fiber slurry to form a wet fiber mat; (c) saturating the wet fiber mat with an aqueous solution of a fiber binder; (d) spraying the wet fiber mat with a binder modifier comprising a carboxylic acid, and (d) drying and curing the wet fiber mat to form a fiber mat product. In one embodiment, the fiber binder and the binder modifier may be mixed together and applied in a single step.  
      It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a SEM image of Sample 1 and Sample 2. 
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION  
      The fiber mat of the present invention may comprise a plurality of fibers coated or impregnated with a fixative composition. The fixative composition may comprise a resinous fiber binder, and a binder modifier comprising between about 0.05 wt. % and about 20.0 wt. % of a carboxylic acid, based on the fiber binder weight.  
      In one embodiment, an example of the carboxylic acid that can be used is maleic acid. In addition to the other ranges mentioned previously, the maleic acid may also comprise a concentration of between about 1 wt. % and about 3 wt. %, based on the weight of the binder. The maleic acid may be a commercially available acid supplied by, for example, Hunstman. As will be apparent to those of ordinary skill in the art, other commercially or non-commercially available carboxylic acids may be used without departing from the scope and spirit of the present invention. For example, carboxylic acids that may be used include, but are not limited to, formic acid, acetic acid, propionic acid, benzoic acid, butyric acid, acrylic acid, lactic acid, glycolic acid malic acid, all amino acids, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, and salicylic acid.  
      The binder modifier may comprise a substantially pure carboxylic acid. Alternatively, in one embodiment, the modifier may further comprise a secondary binder modifier. The secondary binder modifier may comprise, for example, polyurethane, styrenebutadiene, and/or acrylic. The secondary binder modifier may be incorporated with the binder modifier as a composition, or may be added separately. In one embodiment of the present invention, the secondary binder modifier may comprise less than about 15 wt. %, based on the total weight of the binder solids.  
      The fiber binder may comprise between about 5 wt. % and about 30 wt. %, based on the fiber mat product weight. In one embodiment of the present invention, the fiber binder may comprise a formaldehyde type resin. The fiber binder may include, but is not limited to, a urea/formaldehyde resin, a phenol/formaldehyde resin, a melamine/formaldehyde resin, and/or a mixture thereof. It is contemplated, however, that other binders, such as, for example, ethylene vinyl acetate, and other known resins adapted for binding mat fibers may be used without departing from the scope and spirit of the present invention.  
      In one embodiment of the present invention, the urea-formaldehyde resin is a commercially available material, such as, for example, GP2997 supplied by Georgia Pacific Resins, Inc.; Dynea 246 from Dynea Co.; and Borden FG 486D from Borden Chemical Inc. Other commercial formaldehyde resins may include PR-913-23, supplied by Borden Chemical, Inc. As will be apparent to those of ordinary skill in the art, other commercially or non-commercially available binders may be used without departing from the scope and spirit of the present invention.  
      The resinous fiber binder may contain methylol groups which, upon curing, form methylene or ether linkages. These methylols may include, for example, N,N′-dimethylol; dihydroxymethylolethylene; N,N′-bis(methoxymethyl), N,N′-dimethylol-propylene; 5,5-dimethyl-N,N′-dimethylolpropylene; N,N′-dimethylolethylene; N,N′-dimethylolethylene and the like.  
      The fiber binder and the binder modifier are adapted to be compatible. The components may be intimately admixed in an aqueous medium to form a stable emulsion which may not become overly gummy, or gel, even after storage for periods of 24 hours or longer. This may be advantageous in practical commercial use of the composition. It is contemplated that individual aqueous mixtures for binder and modifier may be used in embodiments of the present invention.  
      In one embodiment of the present invention, the fibers comprise glass fibers. The glass fibers may comprise individual fiber filaments having an average length in the range of, but not limited to, from about ¼ inch to about 3 inches, and an average diameter in the range of, but not limited to, from about 5 to about 50 micrometers (μm). It is contemplated, however, that the glass fibers may be in another form, such as, for example, a continuous strand or strands. In an alternative embodiment of the present invention, the fibers may comprise other fibers, including, but not limited to, wood, polyethylene, polyester, nylon, polyacrylonitrile, and/or a mixture of glass and one or more other fibers. In one embodiment, the fiber mat may further comprise a small amount of filler, e.g. less than about 0.5%, based on the fiber weight. A fiber mixture may be optional for construction material application, such as, for example, roofing and siding, because excessive amounts of filler may reduce porosity and vapor ventability of the fiber mat.  
      In the finished cured mat product, the fiber content may be in the range of from about 55 wt. % to about 98 wt. %. In one embodiment of the present invention, the fiber content is more particularly in the range of from about 66 wt. % and about 88 wt. %. The binder modifier content may be in the range of from about 0.05 wt. % to about 45 wt. %. In one embodiment of the present invention, the binder modifier content is more particularly in the range of from about 15 wt. % to about 30 wt. %.  
      In one embodiment of the present invention, the fibers may be formed into a mat with the aid of a dispersing agent. The fiber dispersing agent may comprise, for example, tertiary amine oxides (e.g. N-hexadecyl-N,N-dimethyl amine oxide), bis(2-hydroxyethyl) tallow amine oxide, dimethyl hydrogenated tallow amine oxide, dimethylstearyl amine oxide and the like, and/or mixtures thereof. As will be apparent to those of ordinary skill in the art, other known dispersing agents may be used without departing from the scope and spirit of the present invention. The dispersing agent may comprise a concentration in the range of from about 10 ppm to about 8,000 ppm, based on the amount of fiber. The dispersing agent may further comprise a concentration in the range of from about 200 ppm to about 1,000 ppm, based on the amount of fiber.  
      In one embodiment, the fibers may be formed into a mat with the aid of one or more viscosity modifiers. The viscosity modifier may be adapted to increase the viscosity of the composition such that the settling time of the fibers is reduced and the fibers may be adequately dispersed. The viscosity modifier may include, but is not limited to, hydroxyl ethyl cellulose (HEC), polyacrylamide (PAA), and the like. As will be apparent to those of ordinary skill in the art, other viscosity modifiers may be used without departing from the scope and spirit of the present invention.  
      The process of making a fiber mat in accordance with one embodiment of the present invention will now be described. The process will be described with particular reference to a wet-laid process. It is contemplated, however, that other processes known in the art, such as, for example, a dry-laid process, may be used without departing from the scope and spirit of the present invention. Furthermore, the process is described using chopped bundles of glass fibers. As discussed above, however, other types of fiber content are considered well within the scope of the present invention.  
      The process of forming glass fiber mats according to one embodiment of the present invention comprises adding chopped bundles of glass fibers of suitable length and diameter to an aqueous medium to form an aqueous fiber slurry. As discussed above, the aqueous medium may include a suitable dispersing agent. A viscosity modifier or other process aid may also be added to the water/dispersing agent medium. From about 0.05 to about 0.5 wt. % viscosity modifier in white water may be suitably added to the dispersant to form the slurry.  
      The glass fibers may be sized or unsized, and may be wet or dry, as long as they are capable of being suitably dispersed in the water/dispersing agent medium. The fiber slurry, containing from about 0.03 wt. % to about 8 wt. % solids, is then agitated to form a workable dispersion at a suitable and uniform consistency. The fiber slurry may be additionally diluted with water to a lower fiber concentration to between about 0.02 wt. % and about 0.08 wt. %. In one embodiment, the fiber concentration may be more particularly diluted to about 0.04 wt. % fiber. The fiber slurry is then passed to a mat-forming machine such as a wire screen or fabric for drainage of excess water. The excess water may be removed with the assistance of vacuum.  
      The fibers of the slurry are deposited on the wire screen and drained to form a fiber mat. The fiber mat may then be saturated with an aqueous solution of binder. The aqueous binder solution may comprise, for example, from about 10 wt. % to about 40 wt. % solids. The fiber mat may be soaked for a period of time sufficient to provide the desired fixative for the fibers. Excess aqueous binder solution may then be removed, preferably under vacuum.  
      The formed fiber mat may then be sprayed with the binder modifier, such as maleic acid, to achieve the desired concentration. An aqueous solution of maleic acid may be used to obtain a uniform distribution over the binder treated fibers. In one embodiment of the present invention, either before or after applying the binder modifier, the fiber mat may be compressed, for example by passing it between rollers or another compressing device, to reduce mat thickness for curing. In addition to spraying, this invention also contemplates neutralizing the acid with a base such as ammonia and adding it into binder solution to avoid gelling. It is believed that the ammonia will volatize at high curing temperature and the acid form will return.  
      After treatment with binder or binder/modifier composition, if desired, the mat is then dried and the fixative composition may be cured in an oven at an elevated temperature. A temperature in the range of about 160° C. to about 400° C., for at least about 2 seconds, may be used for curing. In one embodiment, a cure temperature in the range of about 225° C. to about 350° C. may be used. It is contemplated that in an alternative embodiment of the present invention, catalytic curing may be provided with an acid catalyst, such as, for example, ammonium chloride, p-toluene sulfonic acid, or any other suitable catalyst.  
      The combination of the maleic acid and binder used in various embodiments of the present invention may provide several advantages over current binder compositions. For example, the tensile strength of the mat may be increased. In addition, the tensile strength of the mat may be increased at lower temperatures to minimize cracking and failure. Other advantages will be apparent to one of ordinary skill in the art from the above detailed description and/or from the practice of the invention.  
      Having generally described various embodiments of the present invention, reference is now made to the following examples which illustrate embodiments of the present invention and comparisons to a control sample. The following examples serve to illustrate, but are not to be construed as limiting to, the scope of the invention as set forth in the appended claims.  
     EXAMPLE 1  
      Part A. In a vessel at room temperature, under constant agitation, 5.16 g of chopped bundles of glass fibers, each having an average 30-40 mm length and 8-16 micrometer diameter, were dispersed in 12 liters of water containing 800 ppm of N-hexadecyl-N,N-dimethylamine oxide to produce a uniform aqueous slurry of 0.04 wt. % fibers. The fiber slurry was then passed onto a wire mesh support with dewatering fabric, and vacuum was applied to remove excess water and to obtain a wet mat containing about 60% fibers.  
      Part B. A binder composition was prepared by diluting urea/formaldehyde resin binder (UF) with water to a 24 wt. % solids solution. The wet glass mat, suspended on the wire mesh, then was soaked in the binder composition, and excess binder was removed by reapplying vacuum. The resultant wet glass mat weight, with binder applied, was around 10.5 grams. One wet glass mat containing fibers and binder was sprayed with an aqueous solution of maleic acid to provide a maleic acid concentration of 2% with respect to binder. For comparison purposes, another sample was prepared as described in Parts A and B, however the UF binder was used alone without maleic acid modification.  
      Part C. All samples were dried and cured at 300° C. to obtain dry glass mats weighing about 92 g/m 2 , and containing about 24 wt. % binder. It took 9 seconds to cure plain UF, but it took only 5 seconds to cure the acid modified samples. The tensile strengths of the mats were tested on an Instron® Tensile Machine at room temperature. The results of these tests are recorded in the Tables 1.  
                                                   TABLE 1                                       Cure                               Binder           Time @   Mat   Mat   Break   Tensile   Tensile       Sample   Weight       Maleic   300° C.   Caliper   Caliper   Load   Strength   Strength       No.   (g/m 2 )   Binder   Acid   (Sec)   (mm)   Reduction %   (N/50 mm)   (MPa)   Increase                  1   92.4   GP2997   None   9   1.07       258   4.82           2   92.6   GP2997   2%   5   0.94   12%   252   5.36   11%                  
 
     EXAMPLE 2  
      Part A. In a vessel at room temperature, under constant agitation, 5.16 g of chopped bundles of glass fibers, each having an average 30-40 mm length and 8-16 micrometer diameter, were dispersed in 12 liters of water containing 800 ppm of N-hexadecyl-N,N-dimethylamine oxide to produce a uniform aqueous slurry of 0.04 wt. % fibers. The fiber slurry was then passed onto a wire mesh support with dewatering fabric, and vacuum was applied to remove excess water and to obtain a wet mat containing about 60% fibers.  
      Part B. 11% aqueous solutions of maleic acid and of citric acid were neutralized with ammonia to pH 8. Then the neutralized maleic acid-ammonium salt or citric acid-ammonium salt was added into a UF resin solution in a 99.5/0.5 dry ratio of UF to the acid-ammonium salt. A binder composition was prepared by diluting the maleic or citric treated urea/formaldehyde resin binder (UF) with water to a 24 wt. % solids solution; The wet glass mat, suspended on the wire mesh, then was soaked in the binder composition, and excess binder was removed by reapplying vacuum. The resultant wet glass mat weight, with binder applied, was around 10.5 grams. A sample was prepared following the same procedure with no acid modification for comparison.  
      Part C. All samples were dried and cured at 300° C. to obtain dry glass mats weighing about 92 g/m 2 , and containing about 24 wt. % binder. It took 9 seconds to cure plain UF, but it took only 5 seconds to cure the acid modified samples. The tensile strengths of the mats were tested on an Instron® Tensile Machine at room temperature. The results of these tests are recorded in Table 2.  
                                                   TABLE 2                                   Organic   Cure                               Binder       Acid-   Time @   Mat   Mat   Break   Tensile   Tensile       Sample   Weight       Ammonium   300° C.   Caliper   Caliper   Load   Strength   Strength       No.   (g/m 2 )   Binder   Salt   (Sec)   (mm)   Reduction %   (N/50 mm)   (MPa)   Increase                  1   93.9   GP2997   None   9   1.02       284   5.58           2   92.0   GP2997   0.5%   5   0.92   9%   271   5.88    5%                   Maleic                   Acid-                   Ammonium                   Salt       3   92.9   GP2997   0.5% Citric   5   0.98   4%   311   6.37   14%                   Acid-                   Ammonium                   Salt                  
 
      From SEM images shown in  FIG. 1 , we can tell the thicker mat is mainly contributed by bubbles which are likely caused by the volatile side products generated during the condensation reactions of UF resin. It is believed that carboxylic acids act as both catalysts and reactants to drive the equilibrium condensation reaction to right side for completion and also capture the volatile species to avoid the bubbles forming in the mat. Therefore, the mat caliper is reduced.  
      It will be apparent to those skilled in the art that various other modifications and variations can be made in the construction, configuration, and/or operation of the present invention without departing from the scope or spirit of the invention. Embodiments of the fiber mat may be used in a building material including, but not limited to, shingles, underlayment, insulation facers, floor and ceiling tile, vehicle parts, and/or any other suitable building material. Thus, it is intended that the present invention cover all such modifications and variations of the invention, provided they come within the scope of the appended claims and their equivalents.