2. INTRODUCTION
They are known as Photoconductive materials, i.e., its
electrical conductivity increases with exposure to light.
Polyvinyl carbazole has good resistance to heat and
chemicals.
Softens at 150°C
4. PREPARATION OF MONOMER
Vinyl carbazole is obtained by reacting carbazole with
acetylene.
Readily available as a by product of coal tar distillation.
Done in the presence of a catalyst and solvent under
pressure.
The reaction would be carried out at 140°c in white spirit with
potassium carbazole as catalyst.
5. POLYMERIZATION
High M.W polymers can be prepared by bulk polymerization
using Di-tert-butyl peroxide & 2,2-azobisdi-isobutyronitrile used
as initiators pressurized with N2 .
Heating to 80-90°C causes an onset of polymerisation and a
rapid increase in temperature.
After the maximum temperature has been reached the mass is
allowed to cool under pressure.
6. PROCESSING
The polymer is not easy to process and in injection moulding
melt temperatures of 300°C are employed.
In order to prevent excess embrittlement by shock cooling of
the melt, mould temperatures as high as 150°C may be used.
The polymer may also be compression moulded at
temperatures of 250-260°C.
7. THE MOST IMPORTANT PROPERTIES OF POLY( VINYL
CARBAZOLE) ARE:
Good photoconductivity
A high softening
High refractive index
High brittleness
Poly vinyl carbazole is insoluble in alcohol, esters,
ethers, ketones, carbon tetra chloride & caster oil
8. APPLICATIONS
Earlier applications as a capacitor dielectric and other
electrical applications such as switch parts, cable connectors
and co-axial cable spacers are now very limited.
The main application today for poly(vinyl carbazole) arises out
of its photoconductivity and is in electrostatic dry copying
machine.
9. XEROGRAPHY
The polymer is applied from solution in thin film layers onto a
conductive substrate.
In order to obtain the desired photoconductive characteristics,
toughness and adherence to the substrate various additives
are used.
It is usual to incorporate additives such as electron acceptors,
plasticisers and primers.
A typical electron acceptor is 2,4,7-trinitrofluoronone.
10. WORKING PRINCIPLE OF XEROGRAPHY
When an electrostatic charge is applied to a coating in the dark
it is observed to discharge to an equilibrium value.
When the light source is switched on, the conductivity is
increased and discharging occurs, leading to a negligible
charge.
Which is then developed by a dry method by transferring the
charge onto a powder known as the toner.
11. OTHER APPLICATIONS
The polymer may be regarded in these applications as a form of
photo resistor.
It has been used in holography and in the manufacture of
printing plates.
However, it has also been suggested for use in solar cells and
for measuring photoelectric resistance.
