Mesh electrodes

A mesh electrode for a c.r.t. display device consists of a number of coplanar portions of mesh insulated from each other and secured to a support plate by means of a refractory compound incorporating particles larger than the pitch of the mesh. These particles space the mesh away from the support plate and allow the electrode to be easily fabricated.

This invention relates to mesh electrodes, and although of general 
application, it is particularly suitable for use with display tubes which 
are the subject of patent application Nos. 6455/76,, 28792/76 and 
28793/76. In these prior applications a requirement arises to mount a 
segmented mesh electrode so that it can control the passage of electrons 
selectively through the different segments, and to enable this to be done 
it is necessary for the segments to be electrically insulated from each 
other. This requirement poses manufacturing difficulties since the 
segments are thin and fragile and must be accurately positioned in 
relation to each other, and the present invention seeks to provide a mesh 
electrode which can be readily produced. 
According to this invention a mesh electrode having a plurality of 
electrically mutually insulated segments is mounted on a supporting member 
by means of a refractory compound which incorporates particles which are 
larger than the pitch of the mesh so as to hold the mesh electrode away 
from the supporting member. 
Normally the supporting member will be a metal, in which case both the 
refractory compound and the particles are composed of electrically 
insulating materials. 
The refractory compound is applied as a paste or liquid containing the 
solid particles, and preferably the refractory compound is a glass cement. 
Suitable glass cements are those marketed by the Corning Glass Works under 
the name Pyroceram. 
Preferably, the particles are composed of refractory material, such as 
silicon dioxide or aluminium oxide. Alternatively, very small glass balls 
can be used.

Referring to the drawings, the mesh electrode consists of a metallic 
support plate 1 having seven apertures 2 arranged in a figure of eight 
pattern. The plate 1 supports a sheet of mesh material 3 which is attached 
by a thin layer of electrically insulating cement 4. The cement 4 contains 
particles (not separately shown) which are larger than the pitch of the 
mesh material 3, and so serve to space the mesh material 3 away from the 
plate 1. It is not necessary for all particles to be larger than the pitch 
of the mesh. After fixing the mesh material 3 to the plate the mesh 
material 3 is separated into seven electrically isolated portions 31 to 37 
by producing channels 5 which extend into the layer of cement 4. 
A method of making the mesh electrode is as follows. 
The apertures 2 are formed in the rectangular metallic plate 1 by any 
convenient machining process, e.g. punching. The refractory material known 
as Pyroceram (Pyroceram is a trade name of Corning Glass Works) which is 
supplied as a fine powder is mixed in a binder of nitrocellulose dissolved 
in amyl acetate. Particles of a non-reactive insulating refractory 
material, e.g. silicon dioxide, aluminium oxide or microscopic glass balls 
are added to the mixture. The particles have diameters which are greater 
than the size of the holes in the mesh material 3, and the particles 
typically form about 20% of the mixture. The mixture is then thickly 
painted onto the plate 1 and allowed to dry. The mesh 3 is applied, and a 
pressure plate is positioned over the mesh whilst the mixture is fired at 
a temperature of about 450.degree. C. for some hours. The binder 
decomposes, and the Pyroceram becomes initially glassy and then forms a 
ceramic material which cannot subsequently be melted. The particular 
Pyroceram used is selected to have a coefficient of expansion which is 
matched with the plate and mesh material. During the firing step the 
refractory particles hold the mesh away from the plate 1 so that when the 
Pyroceram hardens the mesh is electrically insulated. During the firing 
process some Pyroceram may ooze through the holes in the mesh material as 
shown at 6, and this serves to strengthen the bond between the mesh 
material 3 and the plate 1. 
The individual segments 31 to 37 are then formed from the initially 
continuous mesh material 3 by the use of a high-speed narrow grinding 
wheel which cuts out the channels 5 to leave each segment insulated from 
the others and from the plate 1. 
The use of the invention enables segmented mesh electrodes to be made which 
are tautly held in a plane parallel to and very close to the plane of the 
supporting plate.