Display panel having reduced tensile stress

Abstract

The invention relates to a method for press-forming a cathode ray tube panel, in which, before the panel is removed from the press, a heat radiation controlling means is provided at a small distance from the panel, parallel to the panel surface. Said means comprises an area with a high reflectivity for heat radiation, which first area is near the center of the panel. The result of this measure during the cooling of a panel is a more even temperature distribution over the surface of the panel. In particular, the temperature gradient between center and edges of the panel is reduced. Because of the glass wedge of (Real) Flat panels the center of the panel is thinner than the edge of the panel. The thinner part will normally cool down faster because of the lower heat capacity. Local temperature differences over the surface of the panel during cooling down will lead to so-called ‘membrane’ stresses. The method of the invention will minimize these stresses.

1 . A method for manufacturing a glass panel comprising a viewing window and peripheral side walls for a display tube, comprising a first stage of press-forming molten glass put in a mold using a plunger and a second stage of cooling the formed glass after it has been taken out from the mold, characterized in that during a part of the first stage after pull back of the plunger the heat radiation of the inner face portion of the central panel portion is reduced to reduce a temperature gradient to the edge portions of the panel.  
   
   
       2 . A method as claimed in  claim 1 , characterized in that for reducing the heat radiation of the central panel portion before removing the panel from the mold, a heat reflection means is arranged in a position facing the inner face portion of the central panel portion.  
   
   
       3 . A method as claimed in  claim 2 , characterized in that a heat reflection means is used which comprises at least one plate made of a material selected from the group comprising Ni, Al, Au, Al-oxide, or a plate coated with such a material.  
   
   
       4  A method as claimed in  claim 2 , characterized in that simultaneously with the heat reflection means an edge cooling means is arranged adjacent at least one of the edge portions of the glass panel.  
   
   
       5 . A display panel having a central portion which is substantially thinner than the edge portions which presents substantially no tensile stress in the central area of at least one of the long and short side portions of the panel.  
   
   
       6 . A method as claimed in  claim 1 , characterized in that after removal from the mold the panel is transported to a next processing stage while a stream of cooling fluid is directed to a selected area, or selected areas, of the panel for correcting the contour of the inner face of the panel.