Patent Publication Number: US-7214434-B2

Title: Paper and paperbead for protecting drywall corners

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to drywall corner beads, particularly drywall corner beads having an outer paper layer, and paper therefor. 
     Current building construction techniques frequently call for the use of drywall sheets, otherwise called wallboard, to form the surfaces of interior walls. Sheets of drywall are made by encasing sheets of plaster with heavy construction paper. The paper provides extra strength and resistance to tearing and prevents crumbling of the enclosed plaster. The sheets of drywall are typically produced in sizes of four feet by eight feet to four feet by twelve feet. These sheets can be installed intact or can be cut to custom fit specific interior wall sizes. When cut, the inner plaster is exposed and is particularly vulnerable to crumbling or other damage unless the severed edges can be protected. An exposed corner, exterior or interior, formed by two interfacing drywall sheets not in the same plane is also susceptible to damage. Damage can be particularly severe when these corners involve cut or exposed edges. To overcome this vulnerability to injury and further reinforce the exposed corner formed by two interfacing drywall sheets, a drywall corner bead will generally be installed at that corner. The corner being reinforced can be either an interior or exterior corner. 
     Two types of drywall corner beads are typically used in reinforcing drywall corners, a paper faced bead or paperbead type, and a non-paper faced bead or all-metal drywall trims. Both the paperbead type and the all-metal drywall trims typically include a strip of metal formed or extruded into a desired shape, although molded plastic can also be used. One common example involves forming the metal strip into a core shape having two flanges and a center rib positioned between them. This form of corner bead is called a rib-type of corner bead. Another common type of corner bead has two flanges and a larger curved portion or bullnose positioned between them. This type of corner bead is called a bullnose corner bead. A third type of corner bead is an L-shaped type having one flange longer than the other and an offset rib between the flanges. Other types of corner beads include a J-shaped type, a splay-bead type, and a shadow-mold type. 
     All-metal drywall trims are attached to drywall by driving nails, screws, staples or other fasteners through the flanges, securing the drywall trim with the heads of the fasteners. A joint compound is then applied to cover the flanges and fastener heads. The compound is sanded and feathered to provide a smooth and continuous surface from the drywall surface to the center rib of the formed metal strip. 
     Paperbeads provide several advantages over all-metal drywall trims. For instance, both paint and joint compound adhere significantly better to the surface of a paperbead than to the exposed metal surface of a typical nail-on corner bead. Moreover, paint applied directly to a metal surface is easily chipped after drying. Drywall corners covered with nail-on corner beads are also more susceptible to cracking along the edges of the flanges. Thus, a paperbead provides a better surface for paint adhesion and helps reduce plaster cracking. 
     Paperbeads differ from all-metal drywall trims in several respects. First, the paperbead has a paper strip attached to an outer surface of the formed metal or plastic core previously discussed. Generally, portions of the paper strip extend beyond the edges of the metal or plastic core forming wings. The paperbead is attached to drywall corners by applying a joint compound to the drywall surface and embedding the formed metal strip and the paper wings in the compound; or it can be nailed on and then compound is applied. A second, exterior layer of joint compound is subsequently applied on top of the paperbead and allowed to dry. This exterior layer of joint compound is then sanded and feathered to form a smooth and continuous surface between the drywall and the corner bead. The steps of applying, sanding and feathering the exterior layer of joint compound can be repeated until a smooth surface is created. Throughout this process, the portion of the paper strip covering the corner bead, i.e. the center rib, the bullnose, or the offset rib, is left exposed or uncovered by joint compound. 
     The paper surface left exposed on a typical paperbead may be scuffed, or completely removed during the sanding and feathering process, thus exposing the metal surface beneath. Scuffing makes it more difficult to later obtain a smooth painted surface at the corner bead because the paper becomes frayed or fuzzy. Also, as stated previously, paint does not adhere as easily to the exposed metal surfaces. Therefore, paint applied to any exposed metal surface will be more easily chipped after it dries. Moreover, a scuff in the paper surface produces a break in the line of the corner bead and reduces the aesthetic benefits of having such a bead. 
     Joint tape made from paper strips is also used to cover the joint between two abutting sheets of drywall. The joint tape is applied to a thin layer of joint compound covering the joint, covered with an exterior layer of joint compound and sanded and feathered to form a smooth and continuous surface. As with corner beads, the joint tape can be subjected to abrasive contact that can scuff and tear the joint tape, making it difficult to obtain a smooth surface for painting. 
     To overcome the problems of scuffing, some paperbeads provide a surface coating at the exposed center portion of the corner bead to improve the paper&#39;s resistance to abrasion and avoid the problems caused by scuffing. This type of surface coated paperbead is disclosed in U.S. Pat. No. 5,131,198. A surface coating, however, only provides extra resistance to abrasion at the outer surface of the paper strip. If this coating is penetrated or removed by the sanding process, the underlying paper is exposed and is again made susceptible to scuffing. Consequently, the problems of paint adhesion, unsmooth surface finishes and paint chipping are not avoided. Moreover, the application of a surface coating at a particular location involves an additional manufacturing step thereby increasing the cost of making the product. 
     To resolve the problem of surface coated paper, U.S. Pat. Nos. 5,836,122 and 5,613,335, both to Rennich et al., propose a paperbead for protecting drywall corners containing a paper strip bonded to a metal or plastic core throughout its thickness. This paper strip is made of stack paper which is uniformly impregnated with latex which imparts scuffing and abrasion resistance to the paper. 
     SUMMARY OF THE INVENTION 
     Therefore, in view of the above, it is an object of the present invention to provide an arrangement wherein the paperbead is resistant to abrasion and has excellent adhesiveness to joint compounds. 
     In accordance with present invention, the improved paperbead includes an elongated core having an outer surface. A paper is bonded to the outer surface of the core. The paper is impregnated on one side with a polymer, preferably latex, that penetrates into a portion of the thickness of the paper, preferably only about half the thickness of the paper. The other side of the paper is roughened to improve adhesiveness to joint compounds. The latex impregnated side of the paper maintains increased strength making the paper resistant to scuffing, while at the same time, the roughened side of the paper improves its adhesiveness to joint compounds. 
     In a preferred embodiment, the paper includes a stock paper impregnated with a polymer that is cross-linked. The resulting paper is substantially stronger than papers currently used in drywall corner beads. Furthermore, the increased resistance to abrasion is a property of the paper itself, rather than just a localized shield as provided by surface coatings. Therefore, even if the surface of the paper strip is sanded away, the inner layers that are impregnated with the polymer continue to resist abrasion. A smooth surface is thus maintained as the paper strip resists scuffing. The paper strip also provides an excellent surface for paint adhesion. 
     The present invention also provides methods for making the paper and the paper beads. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective of an exterior corner with a preferred embodiment of the invention applied thereto and with portions broken away and in section. 
         FIG. 2  is a preferred embodiment of the invention showing a cross section through an exterior corner with a rib type of paperbead applied thereto. 
         FIG. 3  is a preferred embodiment of the invention showing a cross section through an exterior corner with a bullnose type of paperbead applied thereto. 
         FIG. 4  is a preferred embodiment of the invention showing a cross section through a corner with a L-shaped type of paperbead applied thereto. 
         FIG. 5  is a preferred embodiment of the invention showing a cross section through an interior corner with a bullnose type of corner bead applied thereto. 
         FIG. 6  is a preferred embodiment of the invention showing a cross section of two abutting sheets of drywall and a paper strip applied thereto. 
         FIG. 7  is a perspective of a preferred embodiment of the invention showing a J-shaped type of paperbead. 
         FIG. 8  is a perspective of a preferred embodiment of the invention showing a splay-bead type of paperbead. 
         FIG. 9  is a perspective of a preferred embodiment of the invention showing a shadow-mold type of paperbead. 
         FIG. 10  is cut away view of the paper of the invention. 
         FIG. 11  is a plan view of the latex impregnated side of the paperbead of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS 
     Referring now to the drawings in detail, and more particularly to  FIGS. 1 and 2 , a rib-type embodiment of the invention is illustrated. A paperbead  1  is shown covering an exposed drywall corner  24  formed by two sheets of drywall  8 . The paperbead  1  has an elongated core  3  and a paper strip  4  bonded to the core as shown in  FIGS. 1 and 2 . The core  3  is preferably made out of galvanized steel which meets or exceeds ASTM-C1047 zinc coating specifications. However, other materials such as plastic can function as the core element. In an exemplary embodiment, the core  3  has a thickness of about 0.0125 to 0.0150 inches thickness. In the rib-type embodiment, the core  3  is roll formed into a rib shape having flanges  3   a,  a center rib  3   c  and a pair of shoulders  3   b  connecting the center rib  3   c  and the flanges  3   a.  The core  3  also has an outer surface  3   d.  The flanges  3   a  are commonly positioned at an angle of no greater than 89 degrees relative to each other, but other angular variations may be utilized to accommodate the relative positioning of the drywall sheets  8  and/or the desired shape of the corner. In the rib-type embodiment shown in  FIGS. 1 and 2 , the flanges  3   a  are about 1 inch wide. The center rib  3   c  is generally about 0.0625 inches high and 0.125 inches wide. 
     The paperbead can be used to protect exterior corners, as shown in the embodiments of  FIGS. 1 ,  2 ,  3  and  4 , or to protect interior corners as shown in the  FIG. 5  embodiment. For example,  FIGS. 3 and 5  illustrate, respectively, an exterior and interior bullnose embodiment of the invention. 
     A bullnose paperbead  2  has a pair of flanges  5   a,  a bullnose  5   c,  a pair of shoulders  5   b  and an outer surface  5   d.  The outer surface  5   d  is defined as that surface facing away from the corner  14 , independent of whether that outer surface forms a concave or a convex surface as shown in  FIGS. 3 and 5 . The flanges  5   a  are generally about 1 inch wide and are positioned, in this embodiment, at an angle of ninety degrees relative to one another. Other angular variations can be implemented. The radius of the bullnose  5   c  is typically in the range of about 0.5 inches to 1.5 inches. In the preferred embodiment shown, each of the shoulders  5   b  is about 0.125 inches wide and has a drop of 0.0625 from the surface of the bullnose  5   c  to the surface of the flange  5   a.    
     A third embodiment of the paperbead is the L-shaped paperbead shown in  FIG. 4 . In this embodiment, the core  7  has a long flange  7   a,  a short flange  7   b,  an offset rib  7   c,  a shoulder  7   d  positioned between the offset rib  7   c  and the long flange  7   a,  and an outer surface  7   f.  In this embodiment, the long flange  7   a  is about 1.5 inches to 2 inches long, while the short flange  7   b  is about 0.75 inches long. The long flange  7   a  is positioned in this embodiment at no greater than 89 degrees (per ASTM-C1047) to the short flange  7   b  forming an L-shape. In an exemplary embodiment, the offset rib  7   c  is about 0.0625 inches high and about 0.125 inches wide. 
     A fourth embodiment of the paperbead is the J-shaped paperbead  21  shown in  FIG. 7 . In this embodiment, the core  18  has a long flange  18   a,  a short flange  18   b,  and/a center portion  18   c  positioned between the flanges. The core  18  also has an outer surface  18   d.  The long flange  18   a  is typically about 1 inch long. The short flange  18   b  is typically about ½ inches long. The center portion  18   c  is typically about ⅜ inches to ⅝ inches wide. An offset rib  18   d  is also shown in this embodiment as positioned between the center portion  18   c  and the long flange  18   a.  However, the offset rib can also be positioned between the center portion  18   c  and the short flange  18   b,  positioned between the center portion  18   c  and the short flange  18   b  and the long flange  18   a,  or excluded all together. In an exemplary embodiment, the center rib  18   d  is about 0.0625 inches high and about 0.125 inches wide. 
     A fifth embodiment of the paperbead is the shadow-mold paperbead  22  shown in  FIG. 9 . In this embodiment, the core  19  has a first flange  19   a,  a second flange  19   d,  a center portion  19   b,  and an offset rib  19   c.  The core  19  also has an outer surface  19   e.  The first flange  19   a  extends from the offset rib  19   c  forming an angle of about 90.degree. The center portion  19   b  is positioned between the offset rib  19   c  and the second flange  19   d.  The second flange  19   d  extends from the center portion  19   b  at an angle of about 90.degree. in a direction opposite from the first flange  19   a.  In an exemplary embodiment, the flanges  19   a  and  19   d  are generally about ⅜ inches to 1 inch in length, but are not necessarily of equal length. The center portion  19   b  is about ⅜ inches to 1 inch in width. 
     A sixth embodiment is the splay-bead paperbead  23  shown in  FIG. 8 . In this embodiment, the core  20  has two strips  20   a  and an outer surface  20   b.  In an exemplary embodiment, the strips  20   a  are about ½ inches to ¾ inches in width. 
     Drywall paperbeads typically include the process of bonding a paper strip  4  to the outer surface  3   d  of the core element as shown in  FIG. 2 . In the rib-type embodiment, the paper strip  4  typically extends beyond the edge of each of the core flanges  3   a  about 1 inch to form a pair of wings  4   a.  In making the L-shaped paperbead  6 , the wing  4   a  extending beyond the short flange  7   b  is wrapped around the flange and bonded to an inner surface  7   e  of the short flange  7   b.  In the splay-bead paperbead  23  embodiment of the invention, the two metal strips  20   a  are bonded to the paper strip leaving a space between them. The space may be, for example, 0.050 inches. This spacing allows the strips  20   a  to rotate relative to each other. The strips  20   a,  therefore, can be positioned at different angles relative to each other. Accordingly, the splay-bead paperbead  23  can accommodate a variety of wall angle combinations. In an exemplary embodiment, the paper strip  4  extends beyond the metal strips  20   a  about ¾ inches to 11/4 inches. 
     In making the J-shaped paperbead  21 , the paper strip  4  can be bonded to the outer surface  18   d  of the core  18  in a number of ways. For instance, in the embodiment shown in  FIG. 7 , one wing  4   a  extends beyond the long flange  18   a  about ¾ inches and a second wing  4   a  wraps around the short flange  18   b  about 0.125 inches. In other J-shaped paperbead  21  embodiments, the wings  4   a  may extend beyond or wrap around the long flange  18   a  and short flange  18   c  in any number of combinations. In yet another J-shaped paperbead  21  embodiment, the paper strip  4  ends at the edge of the flanges  18   a  and  18   b.  In the shadow-mold paperbead  22  embodiment, one wing  4   a  extends beyond the first flange  19   a  about ½ inches to 1 inch. The second wing  4   a  wraps around the second flange  19   d  about 0.125 inches as shown in  FIG. 9 . 
       FIG. 10  shows the paper  4  of the present invention. The paper has two sides, a first side  100  and a second side  102 . The first side  100 , is impregnated with latex or other strengthening compound  104  that penetrates only about half the thickness t of the paper. The second side  102  of the paper is roughened resulting in a rough and irregular surface pattern. The paper  4  is made from a stock paper, preferably a softwood and hardwood fiber Kraft stock paper commonly used in the wall covering industry. However, synthetic fiber products can also be used. To obtain high wet and dry strength properties, the stock paper is impregnated with a polymer, preferably latex. However, other strengthening compounds may also be used to impregnate and strengthen the paper. Generally, a latex consists of a stable colloidal dispersion of a polymeric substance in an aqueous medium. There are a large number of commercial latices. For example, rubber latices, including a styrene-butadiene rubber, and resin latices, including acrylic resins, may be used to impregnate the stock paper. In a preferred embodiment, the stock paper is impregnated about 5% to 15% of strengthening compound based on the weight of the paper. The latex, however, preferably penetrates up to only about half the thickness of the paper, resulting in a paper having two different sides and surfaces. 
     In a preferred embodiment, the latex is cross-linked. As a result, the paper has a good internal bond and exhibits excellent Z-direction tensile strength properties. Cross-linking can be accelerated by heating or superheating the latex impregnated paper. The process of impregnating the paper and cross-linking the latex does not increase the thickness of the paper yet increases its strength properties and its ability to resist abrasion. The paper also provides an excellent surface for paint adhesion. The thickness t of the paper may be generally about 0.004 to 0.010 inches. In a preferred embodiment, the paper is about 0.005 inches in thickness. 
     In a preferred embodiment, the paper is composed of 100% soft wood pulp formed on a Fourdrinier paper machine. A polyamide wet strength resin is preferably added prior to forming to impart wet strength properties to the sheet. After forming, the sheet is pressed and the dried on conventional dryer cans. The paper is then impregnated with latex on the first side  100  of the paper such that the latex only penetrates half way through the thickness t of the paper. The second side  102  of the paper is roughen to obtain a felt-like texture. 
     Most types of metal paperbeads, exterior and interior, are produced by feeding a roll of paper and a flat metal strip into a paperbead roll former. Preferably, as the paper is being fed into the roll former, the non-impregnated surface (second side) ( 102 ) of the paper is roughened by an abrasive, granular, or metal wire surface. The metal strip is roll formed into its respective core shape, whether it be a bullnose type, a center rib type, an L-shaped type or any other type of corner bead. Metal cores can also be made by extrusion. As noted previously, plastic cores can also be utilized. In an exemplary embodiment, the paper is covered with a hot melt glue on the non-impregnated side (second side)  102 . For example, several suitable fast-setting hot melt glues are commercially available. This type of glue is typically a formulated synthetic emulsion adhesive. The paper is then bonded to the outer surface of the core by applying pressure to the core and the paper with a series of pressure rolls to ensure an even bond. The paperbead is then cut to the desired length. 
     Referring to  FIG. 11 , in a preferred embodiment, the latex impregnated side  100  of the paperbead has a border region  106  on the outer edges of the paper  4 . The border region  106  is slightly roughened or buffed to create an uneven and irregular surface for improved bonding with compound or joint cement. The thickness z of the border region  106  is preferably about 0.5 to about 1 inch, more preferably about 0.6 to about 0.7 inch, and most preferably about 0.625 inch. The purpose of the border region  106  is to improve bonding of the paperbead with compound or joint cement to prevent edge curl when the paperbead is applied to walls. Although  FIG. 11  shows a generic paperbead similar to that shown in  FIG. 1 , the border region  106  is also applicable to other configurations, such as the bullnose paperbead  2  ( FIG. 3 ), L-shaped paperbead  6  ( FIG. 4 ), J-shaped paperbead  21  ( FIG. 7 ), shadow-mold paperbead  22  ( FIG. 9 ), and slay-bead paperbead  23  ( FIG. 8 ). The border region  106  is also applicable to using the paper strip  4  as a joint tape ( FIG. 6 ). 
     As shown in  FIGS. 1 ,  2 , and  3 , a paperbead  1 ,  2  is installed by first applying a thin bonding layer  10  of joint compound or joint cement of about 4 inches to 41/2 inches wide to the leading edges of two interfacing drywall sheets  8 . The corner beads  1 , including the core  3 ,  5  and the paper wings  4   a  are then firmly embedded in the bonding layer  10 . Excess joint compound is removed by wiping the paper strip surface with a finishing knife. An exterior layer  12  of joint compound is applied to the top of the paperbead extending about 8 inches inward on the drywall sheet  8 , leaving only a paper covered center rib  15  or a paper covered bullnose  16  exposed. The exterior layer  12  of joint compound is allowed to dry and is then sanded and feathered to produce a smooth surface between the drywall sheet  8  and the paper covered center rib  15  or the paper covered bullnose  16 . J-shaped paperbeads  21 , shadow-mold paperbeads  22  and splay-bead paperbeads  23  are installed in a similar fashion. 
     The paper is well suited to prevent scuffing and other damage during this sanding and feathering process. The strength of the latex impregnated side (first side)  100  if the paper provides protection against scuffing or tearing even when the surface of the paper is penetrated or damaged. This provides improved protection over surface coated papers while avoiding the extra manufacturing step required by coating the paper. The process of adding and sanding the exterior layer  12  of joint compound can be repeated as needed to produce a smooth surface. After sanding and feathering, the paper covered center rib  15  and the paper-covered bullnose  16  remain exposed or uncovered by joint compound. The exterior layer  12  of joint compound and the exposed paper covered center rib  15  and paper-covered bullnose  16  provide an excellent surface for paint adhesion. 
     As shown in  FIG. 5 , an interior paperbead is also installed by embedding a paperbead  2  and paper wings  4   a  in a bonding layer  10  of joint compound. After drying, an exterior layer  12  of joint compound is applied, sanded and feathered. Interior bullnose paperbeads  2  will have an exposed paper covered bullnose  16 . As with exterior corner beads, the paper&#39;s added strength helps resist adverse scuffing of the paper. 
       FIG. 4  shows a L-shaped paperbead  6  installed by applying a thin bonding layer  10  of joint compound to a drywall sheet  8  and the exposed end  8   a  of the sheet. The L-shaped paperbead  6  is embedded in the bonding layer  10 . An exterior layer  12  of joint compound is then applied to cover a paper covered long flange  7   a  and wing  4   a.  This layer is sanded and feathered to provide a smooth and continuous surface between a paper covered offset rib  17  and the drywall sheet  8 . 
     As shown in  FIG. 6 , a paper strip  4 , made as described above, can also be used as a joint tape to cover a joint  13  formed between a pair of abutting drywall sheets  8 . To cover and strengthen the joint  13 , a thin bonding layer  10  of joint compound, such as joint cement or spackle, is spread about 2 inches wide on each drywall sheet  8 . A paper strip  4  is applied to the bonding layer  10 . An exterior layer  12  of joint compound is then applied on top of the paper strip  4 . After drying, the exterior layer  12  of joint compound is sanded and feathered to provide a smooth and continuous surface between the sheets of drywall  8 . This method of joining abutting sheets of drywall provides added resistance to abrasion during the sanding and feathering process, thereby avoiding a scuffed surface. In a preferred embodiment, the paper&#39;s thickness is about 0.005 inches. As other papers currently used for this application are about 0.008 inches, less joint compound is required to finish the joint. Because a thinner exterior layer  12  of joint compound is applied, the joint compound dries faster and the installation is expedited. Furthermore, less sanding and feathering is required to finish the joint. 
     Although the present invention has been described in detail by way of illustration and example, various changes and modifications may be made without departing in any way from the spirit of the invention and scope of the appended claims. In addition, many of the features and dimensions portrayed in the drawings have been exaggerated for the sake of illustration and clarity.