Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
TIT.~E
Electrostatic Printing Process
Background of the Invention
Field of the Invention
The present invention relates to electrostatic
printin~ rolls, and their preparation, b~ ma~netically
forming an image of non-conductive toner on a conductive
image bearing magnetic roll followe~ by transfer of the
ton~r to a conductive substra~e to form the electrostatic
printing roll. The areas of the electrostatic printing
roll bearing the non--conductive toner are electrically
charged while the charge is dissipated from the con
ductive non-image areas. The charged ~on-conductive
areas are decorated with an oppositely charged toner con-
taining a colorant such as a dye or pi~ment, which toneris then ~ransferred to a substrate and Permanently fixed
thereto.
Description of the Prior Art
~agnetic printing processes, particulaxly useful
20 in overco~ing ~he problem in ~lectrostatic copying
proce-~ses of unsatis~actory copying of ~arge dark areas,
are knDwn in the art. Such pr~ce~ses are described, for
instance, i~ U.S. Pa~e~t ~os. 4,0g9,18~ and 4,117,498.
~he particular processes described in U~SO Patent
25 Nos. 4,099,1B6 and 4,117,498 relate to processes wherein
a dye and/or other c~emical treating agent contain~d in
a e~ro~agn~kic to~er is tr~nserred directly to a
~u~stra~e e.g~, such as a tPxtlle material, or is tra~s r
ferred to a first substrate such as paper or subse~uent
3r trans~er to ~h~ ultimate su~stra e. However, all these
techniques relied on removal of the resin and magnekic
components of the toner rom the substrate after dyeing,
hence, eliminating the US2 of this techni~u~ in the ~ig-
ment printing of textiles.
More recently magnetic prin~ing has been used
OR 5794 to form ~he resist when preparing printed circuits or
printing plates by etching or ~lating, or to produce
lithographic pxinting plates dir~ctly. Such processes
are described in U.S. Patent Mos. ~,292,120 and 4,338,391
issued July 6, 1982.
Summary of The Invention
The pr~cess of the present invention involves
making electrostatic printing rolls by magnetography.
First a latent magnetic image is form~d on a conductive
magnetic imaging memher. The latent magnetic image is
decorated with a non-c~ndu~tlve magnetic toner and the
toner transferred to a conductive roll. ~hen the toner
is fused to the conductive roll. The fused non-conduc-
tivP toner is then electrostatically charged with a
suitable means such as a DC corona while the charge is
removed from ~he conductive areas of the roll which are
grounded. Then the electrostatically charged areas of
the printing roll are decorated with electrostatic toner
which is transferred ~o a subs~rate and permanen~ly
f xed thereto. When a new image is to be printed, the
toner image is removed from the conductive roll by
washing it with a suitable resir~-dissolvirlg solvent
drying and rePeating the above~de6cribed proces s .
~r:Lef Description of the Dra~ings
Figure 1 is a srhematic view of the device used
to form an image of magnetic toner on a. conductlve
printing roll.
Figure 2 is a schema~ic view o~ a printer using
three of the printing rolls prepared irl Figure 1.
Detailed Description o~ The Drawings
Re~erriny now to Figure 1, a roll 11, surfaced
with a conductive layer 12, which in turn is covered
with a magnetic member 13, is rotated past a mag~etic
decorator roll 14 fitted with mag~etic toner hopper lS~
After the magnetic toner has been applied to magnetlc
~ayer 13, by decorator roll 14, AC corona 16 serves to
neutralize any elec~rostatlc charges which may he
.3
attracting magnetic toner particle~ -to ma~netic imayiny
member 13. Magne~ic toner part.icles which are on non
image areas of magnetic imaging member 13 are removed by
vacuum knife 17. The magnetic toner imaye is then
transferred to conductive roll 18 by means of pressure
and heat.supplied by lamp 19.
The conductive roll with the magnetic toner
image is removed from the systemO If desired the
magnetic toner image may be rurther treated such as with
solvent vapors or heat to further coalesce the ~agnetic
toner particles. Referriny now to Figure 2, a plurality
of conductive rolls 18, 18', 18" with a ~on conductive
magnetic toner image are mounted in a multi-stage
printer. The magnetic toner areas of rolls 18, 18', 18"
are electrostatically charged by means o DC coronas
21, 22~ 23. Electrostatic toner is then cascaded over
rolls 18, 18'~ 18" by decorators 24, 25, 26 to decorate
the fused magnetic toner image thereon with electrostatic
toner. A substrate 27 is unwound from roll 28 and
passed onto endless belt 29 supported by rollers 31 and
32. As substrate 27 passes under rolls 18, 18' and 18",
DC coronas 33, 34, 35 cause the tonex on rolls 18, 18',
18" to transfer to sub~trate 27. Toner which did not
transfer to substrate 27 is neutralized hy AC coronas
36, 37, 38 and removed by vacuum brushes 39, 40 and 41.
After substrate 27 passes the la~t printing station the
toner is fused to substrate 27 by heater 36. Finally
sub~trate 27 is taken up on roll 42.
Detailed Description
The magnetic imaging member used in the magnetlc
printing step may be first magnetically structured and
then selectively demagnetized in the background area~
by heating such background areas above the Curie point
of the magnetic material in the magnetic imaging member
to leave a latent magne~ic imàge. Alternatiwely the
latent magnetic image may be formed in the mag~e~ic
imaging me~ber by means of a magnetic write head.
. ~
Preferably the magnetic imaging member .is magnetically
structured to have from about 40 to 1200 magnetic lines
per cm. As used herein, a magn~tic line contains cne
north pole and one south pole. Preferably the magnetic
imaging member is formed o a layer of acicular chromium
dioixde in a binder on an electrically conductiv~
support. The acicular chromium dioxide layer generally
is from 1,3 to 50 micrometers in thickness, and
preferably is ~rom 4 to 13 micrometers in thickness.
1~. The magnetic imaging memb~r can be used either
mounted in the form of an endless b~lt supported by a
plurality of rolls or mounted on a cylindrical pri~tin~
roll. The imaging and toning steps are separate entities
which do not need to be dvne consecutively in predeter-
mined sequential ashion. For insta~ce, it may be
desired to mount a preimaged magnetic imaging member
on a printing roll.
ThP imaging member containiny the latent
magnetic image is then brouyht into superimposed rela-
tionship wi~h the conductive member to which the tonerimage is to be transferxed. At this point a DC corona,
situated on the side of the conductive member away from
the imaging member bearing the toner, causes the toner to
tra~sfer to the conductive member. At this point the
conductive member must be insulated from ground.
After being transerred to the conductive
~ember the toner is temporarily fixed to the conductive
member. Generally this is most readily achieved by the
application o~ heat which causes the toner particles ~o
coalesce and become fused to each other as well as to
the conductive member. Generally the application of
pressure is unnecessary; but ~f pressure is to be
applied the pressure applying means should be covered
with a material to which the toner will not adhere,
such as poly(tetrafluoroethylene).
If desired the magnetic toner can be transferred
~rom the magnetlc imaging member to an inkermediate
~ransfer member and then permanently applied ~o the con-
ductive nember, such as described in U.S. 4,292,120.
The conductive member is then mounted in a
suitable electrostatic printing apparatus. Generally
the conductive member is mounted on a roller which in
turn is part of an electrostatic printing machine.
Then the toner image on the conductive member is
~o electrostatically charged. This is most readily
achieved by exposing ~he toner image to a DC corona,
while electrically grounding the conductive member.
Alternatively the conductive member can be electrically
charged and then discharged leaving the toner image
electrically charged~
The charged toner image is then decorated with
an electrostatic toner. This can be done with a magnetic
brush where the ton~r particles are charged triboelec-
trically or by charging the toner particles ill a cascade
type decorator-
The electrostatic toner is then transferred to a sub~
strate such as cotton, wool, polyester/cotton or their
blends 7 paper or a ilm. This ca~ be done either electro~
statically or by application of pressure or heat and
25 pressure.
The magnetic toner particles fused to ~he con
ductive roll preferabl~ are magnetic pigments encapsul~ted
in a suitable binder. Generally the toner particles
have an average size ranging from 10 to 30 microns with a
30 preferred average si~e ranging from 15 to ?0 microns.
Spherical particles such as prepared by spray drying are
preferred because o~ their superior flow ~roperties which
can be enhanced by the addition of minute amounts of a flow
additive such as fumed silica. A ~her ~ crip~on o~ ~e
preparation of toner par~icles may be found in U.S.
Pat. No. 3,627,682. When using ~he apparatus disclosad
herein the toner particles should have a low electrical
conductivity. If the particles have high conductivity,
they will be passed back and ~orth between the drum and
the paper causing a dif~use image and low transfer
efficiency~ Generally the toner powder electrical con-
ductivity is less than 1 x 10 13 mho/cm. The ferro-
~magnetic component can consist o~ hard magnetic particles
or a binary mixture of hard and sot magnetic particles.
The magnetically soft partisles can be iron or another
high-permeable, low-remanence material, such as certain
ferrites, for example, (Zn, Mn~Fe2O4, or p~rmalloysO
The magnetically hard particles can be an iron oxide,
:l5 preferably ~e3O4, y-Fe2O3, other ferrite~, for example,
BaFel2019, chi-iron carbide, chromium dioxide or alloys
of Fe3O4 and nickel or cobaltO A magnetically hard sub-
stanoe has a high-intrinsic coercivity, ranging generally
from about 40 to about 40,000 oersteds and a high
remanence (20 percenk or more of the satuxation magne-
tization) when removed rom the magnetic field.
Such suhstances are of low permeability and require high
flelds or magnetic saturation. A magnetically ~o~t
substance has low coercivity, for example, one oersted
or less~ high permeability, permittin~ saturation to be
obtained with a small applied field, and exhibits a
remanence of less than 5 percent of the saturation
magnetization~ A particularly preferred toner has an
average particle size of 20 microns and contains 40
weight percent thermoplastic binder 30 weight percent
Fe3O4 (magnetite) and 30 w~ight percent soft iron
(carbonyl iron).
The electrostatic toner particle~ used in decorat-
ing the electrostatic printing roll are a colorant en~
capsulatad in a suitable binder. ~enerally the electro-
static toner will have an a~exage par~icle size of from
15 to 20 microns . Spherical par ticles such as prepared
by spray drying are preferred because of their superior
~L~4~
flow propexties. Generally the electrostatic toner
will contain ~rom 1.0 to 20.0 wt.~ pigment and Erom
80.0 to 99.0 wt.% of a thermoplastic binder. Suitable
pigments include copper phthalocyanine, halogenerated
copper phthalocyanines, quinacridon~, quinacridone~
quinona, etc.
Example
~ A magne~ic imagin~ member formed of a 350~
(8.9~ meters~ thick layer of acicular chromium dioxide
in a binder on an electrically grounded silver coated
rubber roll which is 12 inches (0.3 meter) wide. The
magnetic imaging member is magneticially structured to
460 pole reversals/inch 118 pole reversals/mm) or 230
cycles/inch (9 cycles/mm) or 55 microns per pole
reversal b~ recording a square wave with a magnetic
write head at 35 m Amps and 6 to 8 volts. A fllm
positive of th~ image to be pri~ed i.s placed in contact
with the magnetic roll and stepwise uniformly illuminated
by a Xenon flash at 3.3 KV with a 15 turn per flash
passing through the film positive, corresponding to the
areas to be printed, absorb the energy o the Xenon
flash; whereas the claar areas transmit the light and
heat the aciculax chromium dioxide beyond its Curie
point of about 116C thereby demagnetizing the exposed
magnatiæed-lines of acicular chromium dioxide. A ~on~
conductive toner is fed ~rom a slot in a hopper to
decorate the latent magnetic image by means of a
decorator. The decorator comprises a rotating mag~etic
cylinder inside a non-magnetic sleeve. As the magnetic
imaging member rotates after being deeoxated with toner
it passes an AC corona which serves to neutralize any
electrostatic charges which may cause ~oner to adhere
to the magnetic imaging member. Then a vacuum knife
removes stray toner from the non-image areasO The
tonex is then negatlvely charged with a DC corona. The
toner is ~hen ~ransferred to a positively chaxged copper
sheet having a polyethylene terephthalate ilm backing.
The toner is then Eused to the copper sheet. ~he copper
sheet is grounded and th~ toner ~used there~o is
posi~ively charged with a DC corona. ~n electrostatic
toner is negatively charged and then poured over the
side of ~he copper sheet to which ~he charges fused
toner is adhe~ed. The negatively charged toner adheres
to the charged fused toner and not to the yrounded
background copper areas. ~ sheet of paper is laid over
the toner and positively charged with a DC corona to
effect transfer of the negatively charged toner to the
paper. The toner is then ~used to the paper by heating.
