Abstract:
A corner bead for drywall construction has a galvanized steel core strip which is formed with a central portion, side flanges, and shoulders joining the central portion and side flanges. The front face of the core strip is covered with a paper layer having an outer protective coating thereon overlying the central portion adjoining said shoulders. A paper reinforcing layer covers the back of the core strip in one embodiment to minimize the thickness of the core strip.

Description:
DESCRIPTION 
     This application is a continuation-in-part of copending application Ser. No. 07/541,894, filed Jun. 21, 1990. 
    
    
     TECHNICAL FIELD 
     The present invention relates to corner beads for drywall construction, and particularly to those having an outer paper layer. 
     BACKGROUND OF THE INVENTION 
     In the corner bead for drywall construction art two types of beads have been commonly used, the &#34;nail-on&#34; type and the &#34;tape-on&#34; type. Nail-on beads commonly take the form of an angle strip of metal with side flanges meeting at a center corner rib providing shoulders against which spackle or joint cement can be dressed when feathered from the adjoining wall surfaces to cover the edges and outer faces of the side flanges and the heads of the nails securing these flanges to the wall structure. These nails are usually driven through the bead flanges at intervals of no more than eight inches. 
     Another form of nail-on bead has a rounded nose section between side flanges and presents step-down shoulders at the junctures of the rounded nose and the side flanges. The nails are driven through the side flanges and the spackle or joint cement covering the flanges is dressed to the shoulders, leaving the rounded nose section exposed to be painted later. For purposes of later discussion, corner beads with an abrupt corner will be referred to as the &#34;hard-line&#34; type, and the corner beads with a rounded nose will be referred to as the &#34;soft-line&#34; type. 
     Tape-on corner beads utilize paper wings to secure a metal corner angle in position rather than using nails. These wings are lateral extensions of a paper cover strip which is bonded by a hot melt glue or other suitable adhesive to the metal corner angle, usually on the outer faces of the side flanges. The metal corner angle can be shaped as the hard-line type or soft-line type. Spackle or joint cement and wall paint for dressing and finishing the corner, normally adhere significantly better to the paper cover strip of tape-on beads than to the exposed metal of nail-on beads. Also, normally drywall corners covered with nail-on heads are more susceptible to developing crack lines along the outer edges of the side flanges than when tape-on beads are used. On the other hand, nail-on beads have the advantage of requiring less skill to apply. 
     Preparatory to painting the wall board adjoining a corner covered by a corner bead, the spackle or joint cement spread from the wall surface onto the corner bead is sanded to provide a smooth continuous surface from the wall board to the corner bead. In the case of tape-on beads the exposed portion of the outer paper layer is commonly scuffed during the sanding operation, thereby making it more difficult to later obtain a smooth painted surface at the corner. This scuffing is usually most pronounced at the corner rib of a hard-lien bead, and at the two shoulders adjoining the rounded nose of a soft-line bead. 
     SUMMARY OF THE INVENTION 
     The present invention provides an improved nail-on corner bead having advantages of tape-on beads and which can be produced economically. The invention also provides a solution to the scuffing problem of tape-on beads. 
     In accordance with the present invention, a metal corner element (hard-line or soft-line) is covered on the outside with a paper layer which is folded around the outer edges of the corner element and is bonded to the corner element. The back side of the metal corner element is preferably provided with a reinforcing layer of paper between the folded-around portions of the front paper layer. This permits the metal corner element to be of thinner material. The overall cost of the thinner metal and reinforcing backing paper provides a structure currently more economical to produce than when metal alone is used of a thickness normally currently found (0.012-0.013 inches) on all-metal nail-on corner beads. The corner element has a pair of shoulders as currently provided on hard-line and soft-line types, respectively, of nail-on beads. The portion of the paper layer covering and adjoining each shoulder is provided with a protective coating making it far more resistant to scuffing during the sanding operation in preparation for painting. The protective coating has a composition to which paint will readily adhere. As part of the invention this protective coating is also applied to the pater cover layer of tape-on corner beads. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a transverse cross-sectional view of a hard-line corner bead made in accordance with the present invention, and with the thickness of the elements being exaggerated for illustrative purposes; 
     FIG. 2 is a detail sectional view to an enlarged scale of the circled portion indicated in FIG. 1; 
     FIG. 3 is a transverse cross-sectional view of a soft-line corner bead made in accordance with the present invention, and with the thickness of the elements being exaggerated for illustrative purposes; 
     FIG. 4 is a detail sectional view to an enlarged scale of the circled portion indicated in FIG. 3; and 
     FIGS. 5 and 6 are fragmentary transverse cross-sectional views of a hard-line corner bead and soft-line corner bead, respectively, of the tape-on type provided with the protective coating in accordance with this invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawings, it is seen that finished hard-line and soft-line nail-on corner beads 8, 9 made in accordance with the present invention have a respective core strip 10, 11 and a respective paper cover strip 12 or 13. The core strip is preferably a galvanized steel strip which has been roll-formed to the hard-line shape 10 having a corner rib 10a and side flanges 10b, or to the soft-line shape 11 having a rounded nose 11a, a pair of step-down sloped shoulders 11b, and side flanges 11c. A typical hard-line core strip 10 will have its side flanges 10b at ninety degrees to one another and about one inch wide, and a typical soft-line core strip 11 will have its rounded nose 11a shaped with a radius in the range of about 3/4 to 11/2 inches, and its side flanges 11c at a right angle relative to one another and about one inch wide. The corner rib 10a on the hard-line unit will typically be about 0.0625 inches high and about 0.125 inches wide. Each of the shoulders 11b on the soft-line unit will typically be about 0.125 inches wide and have a drop of about 0.0625 inches from the corresponding outer edge of the rounded nose section 11a and the adjoining side flange 11c. 
     The cover strips 12, 13 have their outer edge portions 12a and 13a folded back over the outer edges of the respective core strips 10, 11 a distance of about 0.25 inches. For economy of construction, respective reinforcing backing strips 14, 15 of paper may be applied to the core strips 10, 11 between the folded-back edge portions 12a, 13a of the respective cover strips 12, 13. The cover strips 12, 13 may be 80 to 90 pound bleached kraft paper like that commonly used for wallboard joint tape, and the backing strips 14, 15 may be kraft paper about 0.016 to 0.017 inches thick like that commonly used for backing paper on wallboard. When the backing strips 14, 15 are not used, the core strips 10, 11 will normally be about 0.012 to 0.013 inches thick, whereas the core strips need only be about 0.007 to 0.009 inches thick when the backing strips are included. Hot melt glue or other suitable adhesive (not shown) is used to bond the entire back surface of the cover strips 12, 13 and backing strips 14, 15 to the core strips 10, 11. 
     In accordance with the present invention a center band 16 of a protective coating is applied to the outer face of the cover strip 12, and a pair of bands 17 of a protective coating is applied to the portions of the outer face of the cover strip 13 which cover the pair of shoulders 11b and are adjacent thereto. The protective bands 16, 17 preferably extend about 0.125 inches beyond both side edges of the corner rib 10b and the shoulders 11b. Although for production economy it is preferred to have relatively narrow protective bands, it will be appreciated that in the case of the soft-line bead 9 a protective band may extend over the entire width of the nose 11a between the pair of shoulders 11b. 
     FIGS. 5 and 6 show the protective bands 16 and 17 applied to standard tape-on beads 8&#39; and 9&#39; with hard-line and soft-line configurations in which the paper cover layers are numbered 12&#39; and 13&#39;, and the metal core strips are identified by 10&#39; and 11&#39;, respectively. The portions of the core strips are identified in the same manner as in FIGS. 2 and 3, except that a prime has been added. 
     The bands 16, 17 of protective coating preferably result from treatment of the outer paper layers 12, 13 (12&#39;, 13&#39;) with a material which penetrates the fibers of the paper to reinforce the paper and provide surface protection against abrasion. For example, the coating material for the bands 14 15 may comprise a fine particle size, acrylic, water-based emulsion such, for example, as Synthemul® synthetic resin emulsion 40-423, produced by Reichhold Chemicals, Inc., Dover, Del., diluted 50% with water. This material may be applied by a brush, roller or spraying apparatus. When the coating has dried, the surface of the paper area to which the coating material has been applied will normally have an acrylic film or layer about 0.001 inches in thickness. This surface film or layer can be increased in thickness to about 0.005 inches by using a suitable primer sealer for the protective coating. For example, the same acrylic resin can be utilized with the following additional ingredients: 
     
         ______________________________________INGREDIENT        % (BY WEIGHT)______________________________________Water             8.00Ethylene Glycol   1.00Cellulosic thickness solution             16.00Potassium Tripolyphosphate             0.10Defoamer          0.40Surfactant        0.40Aluminum Silicate 12.00Titanium Dioxide  7.50Calcium Carbonate 15.00Microbial Agent   0.10Acrylic Resin     39.50______________________________________ 
    
     A typical cellulosic thickener is Natrosol 250 HR solution (11/2%). 
     In applying the hard-liner and soft-line embodiments of the nail-on beads 8-9, nails are driven at regular intervals through the outer cover strips 12, 13 underlying flanges 10b, 11c of the core strips, and backing strips 14, 15, and then spackle or joint cement is feathered from the outer face of the underlying wallboard to the rib 10a and shoulders 11b so as to cover the outer edges of the corner beads and the nails, as indicated in phantom in FIGS. 2 and 4. Since the outer edges of each core strip 10, 11 and the outer faces thereof are covered with paper there is good adherence of the spackle or joint cement to the corner beads. When the spackle or joint cement is later sanded the protective bands 16, 17 prevent adverse scuffing of the paper 12 covering the corner rib 10a and the paper 13 covering the rounded nose 11a adjacent the shoulders 11b. Covering of the relatively sharp outer edges of the metal core strips 10, 11 with the paper covering 12, 13 has the added advantage of protecting workers from hand cuts while handles the corner beads. 
     The hard-line and soft-line corner beads 8&#39;-9&#39; of the tape-on type are applied in the conventional manner for tape-on beads. When the joint cement covering the outer paper layer 12&#39; from the corner rib 10&#39;a to the outer edge of the paper 12&#39; on the hard-line tape-on bead 8&#39;, and covering the outer paper layer 13&#39; from the rounded nose 11&#39;a to the outer edge of the paper 13&#39; on the soft-line tape-on bead 9&#39;, is sanded to dress the joint cement to the rib 10&#39;a and nose 11&#39;a, the protective bands 16&#39;, 17&#39; prevent adverse scuffing of the outer paper layers 12&#39;, 13&#39;. 
     It will be appreciated that the thickness of the protective coatings 16, 17 have been somewhat exaggerated in the drawings for illustrative purposes. The portions of the outer paper layer in FIGS. 2, 4, 5 and 6 adjoining the protective coatings 16, 17 have been dotted to indicate impregnation of the paper by the coating material.