Durable glass articles for use as writable erasable marker boards

Abstract

The invention relates to glass articles suitable for use as writeable erasable marker boards. More particularly, disclosed is a strengthened glass article suitable for use as a writeable erasable marker boards, wherein the glass sheet exhibits an ion exchanged glass having a front surface and a back surface and exhibiting a thickness of less than 2.0 mm and having a depth of layer (DOL) greater than 20 microns and a surface compressive strength of at least 300 MPa. The strengthened glass article exhibits certain optical properties which render it particularly suitable for use as a writeable erasable marker boards electronic including: (1) shadow parallax of less than 1.73/n measured at 60 degree incident light angle and for an index of refraction n; and, (2) a haze of less than 50%. Further disclosed is a markerboard with improved magnetic force attributes; sufficient to hold weak magnets in place.

We claim: 
     
         1 . A writeable erasable marker boards comprising a strengthened glass sheet having a front surface and a back surface wherein the glass sheet exhibits a thickness of less than 2.0 mm, shadow parallax of less than or equal to 1.73/n when measured at a 60 degree incident light angle and for an index of refraction of n, and a transmitted haze of less than 50%. 
     
     
         2 . The writeable eraseable marker board of  claim 1  which further includes a magnetic or ferrous steel backing plate positioned on at least one side of the glass sheet such that when the marker board is vertical, a permanent magnet with maximum energy product of less than 10 MGOe will remain attached to the glass sheet through magnetic force only. 
     
     
         3 . The writeable erasable marker board of  claim 1  which further includes a magnetic or ferrous steel backing plate positioned on at least one side of the glass sheet such that when the marker board is vertical, a permanent magnet with maximum energy product of less than 5 MGOe will remain attached to the glass sheet through magnetic force only. 
     
     
         4 . The writeable erasable marker board of  claim 1  which further includes a magnetic or ferrous steel backing plate positioned on at least one side of the glass sheet such that when the marker board is vertical, a permanent magnet with maximum energy product of less than 1 MGOe will remain attached to the glass sheet through magnetic force only. 
     
     
         5 . A writeable eraseable marker board of  claim 1  wherein the marker board further includes an organic film structure which is laminated to at least one side of the glass sheet which provides anti-splinter functionality. 
     
     
         6 . A writeable eraseable marker board of  claim 1  wherein the marker board further includes a decorative layer is attached to at least one side of the glass sheet. 
     
     
         7 . The writeable erasable marker board of  claim 1  wherein the strengthened glass article further exhibits a fracture toughness of greater than 0.75 MPa·m½, an abraded MOR of greater than 350 MPa, a Vickers hardness of at least 600 kgf/mm2, a Young's Modulus of greater than 60 GPa, and a surface compressive stress of greater than 300 MPa 
     
     
         8 . The writeable erasable marker board of  claim 1 , wherein the strengthened glass sheet has a thickness less than 2.0 mm and a surface compressive strength of at least 300 MPa. 
     
     
         9 . The writeable erasable marker board of  claim 1 , wherein the strengthened glass sheet has at least one compressively-stressed region near the front surface or the back surface, and wherein the compressively-stressed region has a layer depth of at least 20 microns. 
     
     
         10 . The writeable erasable marker board of  claim 1 , wherein the strengthened glass sheet has a thickness that is selected from the group consisting of less than 2.0 mm, less than 1.0 mm, and less than 0.7 mm. 
     
     
         11 . The writeable erasable marker board of  claim 1 , wherein the strengthened glass has an distinctness-of-reflected image (DOI) of less than 95. 
     
     
         12 . The writeable erasable marker board of  claim 1 , wherein the strengthened glass has an RMS roughness in a range from about 50 nm up to about 500 nm, a distinctness of image (DOI) of less than about 85 and a transmission haze of less than 40%. 
     
     
         13 . The writeable erasable marker board of  claim 1 , wherein the strengthened glass article exhibits an MOR of greater than 475 MPa. 
     
     
         14 . The writeable erasable marker board of  claim 1  further comprising a mounting means, wherein the mounting means is selected from the group consisting of (i) a magnetic layer on the back surface of the strengthened glass sheet, (ii) an adhesive layer on the back surface of the strengthened glass sheet, and (iii) a static cling layer on the back surface of the strengthened glass sheet. 
     
     
         15 . The writeable erasable marker board of  claim 1  further comprising a mounting means, wherein the mounting means is selected from the group consisting of (i) one or more mounting holes formed in the strengthened glass sheet, (ii) one or more glass sheet hanging elements attached to the strengthened glass sheet, and (iii) one or more glass sheet framing elements attached to the strengthened glass sheet. 
     
     
         16 . The writeable erasable marker board of  claim 1  wherein the glass is an ion-exchanged alkali-aluminosilicate glass comprising, in weight percent as oxides on a batched basis, 40-80% SiO 2 , 0-28% Al 2 O 3 , 0-8% B 2 O 3 , 0-18% Li 2 O, 0-10% Na 2 O, 0-11% K 2 O, 0-16% MgO, 0-18% CaO, 0-15% CaF 2 , 0-20% SrO, 0-12% BaO, 0-8% ZnO, 0-20% P 2 O 5 , 0-8% TiO 2 , 0-5% ZrO 2 , 0-1% SnO 2  and 0-1 Sb 2 O 3 , 0-1% As 2 O 3  . 
     
     
         17 . The writeable erasable marker board of  claim 1 , wherein the glass is an ion-exchanged alkali-aluminosilicate glass comprising : 60-70 mol % SiO 2 ; 6-14 mol % Al 2 O 3 ; 0-15 mol % B 2 O 3 ; 0-15 mol % Li 2 O; 0-20 mol % Na 2 O; 0-10 mol % K 2 O; 0-8 mol % MgO; 0-10 mol % CaO; 0-5 mol % ZrO 2 ; 0-1 mol % SnO 2 ; 0-1 mol % CeO 2 ; less than 50 ppm As 2 O 3 ; wherein 12 mol %≦Li 2 O+Na 2 O+K 2 O≦20 mol % and 0 mol %≦MgO+CaO≦10 mol %. 
     
     
         18 . The writeable erasable marker board of  claim 1  wherein the glass is an ion-exchanged alkali-aluminosilicate glass comprising at least 50 mol % SiO 2 , less than 10 mol % B 2 O 3 , and at least 8 mol % Na 2 O, wherein the aluminoborosilicate glass is ion exchangeable, wherein a ratio 
       
         
           
             
               
                 
                   
                     
                       
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       wherein Al 2 O 3 (mol %)>B 2 O 3 (mol %) and the modifiers are Na 2 O and, optionally, at least one oxide selected from the group consisting of alkali metal oxides R 2 O other than Na 2 O and alkaline earth oxides RO, wherein the aluminoborosilicate glass has a Young's modulus of less than about 69 GPa, and wherein −6 mol %<Σmodifiers−Al 2 O 3 <3 mol %.