Note: Descriptions are shown in the official language in which they were submitted.
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Background of~the Invention
~ Th;s~invention~relates to~dry developer particles;~or
: developing~an electros~ati~c~charge 1ma~ge:ln~electrophotography and
also:~to a method for developing such an image by the particles.
~; ; Dry~developer particles which are magnetically attrac~ive ;~
- ~ and electrically~conduct:ive has~been developed:for devel.oping~an
; ~ electrostatic image formed on a photosensitive element or an
: el~ectrostatlc record;ng~pàper ln electrophotography. Such de~
veloper particles are used ;n a developlng~process compris;ng steps~ :
of~magnetically~attracting the part;~cles onto a surface of an ~ :~
electrically conduc.t;ve sl~eeve wh;ch ;s earthed, and contact;ng the
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particles attracted to the sleeve with the surface of the photo-
sensitive element on which the electrostat1c image is held, thereby
forming an electrically conductive path through the particles be-
tween the sleeve and the photosensitive element. In this case,
the developer particles positioned adjacent to the surface of the
photosensitive element are affected by two forces, i.e. coulomb
force of an intensity corresponding to the amount of charges de-
posited on the surface portion of the element with which said de- ;
veloper particles are contacting, and magnetically attracting `~
force caused by a magnet mounted within the sleeve. When the
intensity of said coulomb force is larger than that of said mag-
netically attracting force, the developer particles are applied to
the surface portion of the photosensitive element, whereas when the
intensity of the coulomb force is smaller than that of the mag-
netically attracting force the developer particles are not applied
to the surface portion of the element. In this manner, the de-
veloper particles are applied to the surface of the element ln
accordance with the distribution of the electrostatic charges on ~ -
the element thereby developing the electrostatic image.
In such a developing process, there is formed a plurality
of rows of the developer particles extending radially from the
ele trically conductive sleeve, and the developing mechanism will
be described below in reference to one row of the developer parti- ~;
cles formed on the sleeve.
(l) When the row of the developer particles is not contacted with
the surface of the photosensitive element, no electrically con-
ductive path is formed through the row of the developer particles ;
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between the sleeve and the element, but an induced charge or charges
of a polarity opposite to the polarity of the electrostatic charges
deposited on the element are electrostatically induced on the sleeve
and the induced charges are moved through the row of the developer
particles towards an outer or free end thereof.
(2) When the element and the sleeve are moved relative to each other
and the free end of the row of the developer particles is contacted
with the surface of the element, the induced charges have reached
the free end of the row, and since the induced charges have the oppo-
site polarity to that of the charges on the element the coulomb
force is caused between those charges to contact the free end of
the particle row with the element.
(3) Under this condition, the charges on the element are moved to -~
the developer particle row because of the developer particles being
electrically conduct;ve, thereby neutralizing the induced charges,
and thus the coulomb force attracting the developer particles to
the photosens;tive element is lowered. However, when the sleeve
is moved far away from the element during the time when the coulomb
force is larger than the magnetically attracting force affecting the
developer particle row, some of the developer particles at or ad-
jacent the free end of the developer particle row remain attracted
to the surface of the element. While the above-described steps
are continuously repeated, the electrostatic charge image formed on
the element is developed by the developer particles in rows.
Such conventional developer particles are disadvantageous
in that in order to achieve a good developing operation a precise
control has to be provided for the developing time, i.e. the time
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during which the developer particle row ~s contacted with the surface
of the element. In case of the developing time being too short,
there will not exist on the free end portion of the developer parti-
cle row an amount of the induced charges for generating an intensity
of the coulomb force sufficient ~o apply Isome of the developer
particles at the free end portion of the row to the surface of the
element so that any developer particle can not be applied to the
latter and thus the electrostatic charge image on the element can
not be developed. In case of the developing time being too long,
the electrostatic charges on the element will move to the developer
particle row to neutralize the induced charges held on the free end
portion of the developer row, thereby lowering the intensity of the
coulomb force and thus the electrostatic charge image on the element
can not be developed. Furthermore, the above-described developer
particles are disadvantageous in that when they are applied to an
electrophotographic process in which a developer image is formed
on the photosensitive element and the developer image is then
transferred to a receptor sheet, such as a plain paper, the developer
image transferred to the receptor sheet is blurred and thus a de-
s1red quality of p~cture can not be obta~ned.
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Summary of the Invention
It is an object of the present invention to provide new
and improved dry developer particles for use in electrophotography
and whi h have not the disadvantages described heretofore and~si~ply
and conveniently form a good qual1ty of picture.
It lS another object of the present invention to provide
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dry developer particles for use in electrophotography and
which do not require any carriex therefor in use.
It is a further object of the present invention to
provide a new and improved method for developing by such new
dry developer particles an electrostatic image formed in
electrophotography and which method has not the disadvantages
described heretofore and simply and conveniently forms a good
quality of picture.
Brie Explanation of the Drawing
The accompanying drawing is a schematic illustration
in part section of an example of a developing-device to which
the developer particles and method accordinq to the present
invention are applied.
Description o the Preferred Embodiment
The developer particles according to the present in-
vention are, for example, made hy a process in which magnetite ~ -
fine particles having a mean particle size of about OO5 micron
meters, thermoplastic synthetic resin, such as epoxy or styrene,
and solvent, such as dichloroethylene or trichloroèthy-lene, are
mixed in a weight ratio of about 1.5-3-: about 1 : about 8-12,
and these are agitated to dissolve the resin by the solvent. The
mixture is then injected by compressed air into a spray dryer
from its upper portion to be formed into a plurality of fine
droplets. At the same time, hot air heated at a temperature of
about 120C- 170C is also blown into the dryer so that the solvent
is evaporated from the droplets
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to dry the latter, thereby producing developer particles of about
2 micron - 35 micron diameters. The developer particles so pro-
duced contain about 25-40 weight % of the synthetic resin and
about 75-60 weight % of the magnetite particles. Fùrthermore,
the developer particles are colored in black by the magnetite
component and are magnetically attractive and have electric re-
sistance higher than 1014Jlcm when measured by the method de-
scribed later.
The developer particles made as described above are
schematically illustrated by reference numeral 1 in the drawing,
and the particles 1 are attracted by the magnetic force generated
from a cylindrical permanent magnet 2, to an outer peripheral
surface of an electrically conductive carrying member or rotary
sleeve 3. In this example, the magnet 2 has an intensi~y of the
magnetic force to produce 700 Gauss of the flux density, and the -
sleeve 3 ;s earthed through suitable means. As the sleeve 3 ro- ~;
tates in a clockwise direction as seen ~n the drawing, the amount of
deposition of the particles 1 on the sleeve3 is controlled by a
doctor blade 4 to a predetermined thickness to move to a photo~
sensitive element 5.
The photosensitive element 5 in this example comprises
an electrically conductive base layer 6 earthed through suitable
means, a photoconductive layer 7, an Insulating layer 8 and these
layers being integrally bonded in the order mentioned above.
The element 5 is subjected to a suitable image forming process to
form an electrostatic charge image on the surface of the insulaing
layer 8 in accordance with the original image. While the element
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s moves in a direction indicated by an arrow with 1ts insulating
layer 8 contacted with the developer particles 1, the electro-
static charge image on the insulating 'layer is developed in such
a manner as will be described below.
For simplicity, the developing process according to the
present invention will next be expla1ned in reference to the case
in which developer particles 9, 10, 11, 12 and 13 participate in
deveiopment of the electrostatic image on the insulating layer 8
of the element 5.
The developer particle 9 is attracted to the electri-
y
cally conductive sleeve 3 under the action of the magnetic force
of the magnet 2 affecting the magnetic fine particles contained
in the developer particle, and in turn, the developer particle 10
to the particle 9 under the similar action, ~he developer part~cle
11 to the particle 10,the developer particle 12 to the particle 11
and the developer particle 13 to the particle 12~ thereby forming
a developer particle row 14. Further developer particles are
attracted 'to the particle 13 in a developer container 15, but these
excess developer particles are.removed by the blade 4 from the
particle 13.
As the sleeve 3 rotates and when the particle 13 of the
row'l4 contacts with the surface of the insulating layer B of the
photosensitive element 5, dielectric polarization is caused in the
particle 13 by means of the electric field generated by the electro-
static charges on the insulating layer 8, so that an attracting
force is generated to attract the particle 13 to the insulating
layer 8. Furthermore, the particle 13 is subject~d to a gradient
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force caused by the non-uniform eLectric field Erom the electro-
static charges on the layer 8, thereby generatlng a further at-
tracting force to attract the part~cle 13 to the layer 8, and there
is also generated a still further attracting force by the electrlc
double layer between the charges on the l~yer 8 and the charges on
the particle 13 to attract the particle to the layer 8. Accordingly,
the intensity of the resultant force of these attractive forces de-
pends upon the amount of the electrostatic charges deposited on the
portion of the insulating layer with which the developer particle ?
13 is contacting. .
In case that an amount of the charges is desposited on
the portion of the insulating layer 8 in contact with the particle
13 to generate a larger resultant force than the magnetically at-
tracting force affecting the particle 13, as the sleeve 3 and the
element 5 move relative to each other the particle 13 is separated
from the particle 12 to remain attracted to that portion of the
layer 8, but the particles 9, 10, 11 and 12 are moved together with
the sleeve 3. On the contrary, when the particle 13 contacts with
a portion of the insulating layer 8 which is provided with an
amount of the electrostatic charges generàting a smaller resultant
force than the magnetic force affecting the particle 13 from the
magnet 2, the particle i3 is not separated from the particle 12 to
move together therewith and thus the particle 13 can not be applied ~.
to that portion of the layer 8.
Practically, a plurality of developer particle rows simi-
lar to the row 14 is provided over the substantial portion of the
peripheral surface of the sleeve 3 so that as the sleeve 3 and the
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element 5 move relative to each other the electrostatic charge
image on the layer 8 of the element 5 successively developed in
such a manner as described above.
The following experiments were made to confirm the
differences and effects of the present invention over the prior
'I art.
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Experiment l
A photosens1tive element was used in which an aluminium
base plate, a cadmium sulphide photoconductive layer and a polyester
insulating thin layer were integrally bonded in turn. An electro-
static charge image was formed on the insulating layer by the method
described in U.S. Patent Spe~ification No. 3,536,4839 and the initial
i surface potentials at the dark and llght portions of the image were
!j 700 Volts and O Volt, respectively.~ By using the magnetlcally at~
¦ tractive and electrically conductlve developer particles described
in U.S. Patent Specification No. 3,639,245, and the developing
device shown in ~he drawing of the present application, the electro-
static charge image was developed wlth the element moved~at a~speed
of l25 mm/sec. Immediately after the completion of developmPnt,
measurement was made to obtain the result that the surface potential
j of th~ dark portlon of thelcharge image on the insulating layer was
oo Volts. Compressed air was then blown to the developer parti-
cles desposited on the insulating layer of the photosensitive element
so that all the particl~es were removed therefrom, and khen measure-
ment was also made to obtain the result that the surface potential
of the dark portlon of the charge image on the insulating layer was
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310 Volts.
Further experiment was malie sim~lar to the above ex
periment. In this experiment, the init;al surface potentials at
the dark and light portions of the electrostatic char~e image form-
ed on the insulating layer of the element were the same as thosemeasured in the above-described experiment. The image was de-
veloped under the same condition as in the above experiment and
thereafter a result was obtained that the surface potential at the
dark portion of the image was 100 Volts, and after the removal of
the developer particles from the insulating layer the surface po-
tential at the dark portion of the image was 380 Volts.
From these experiments, it will be understood that when
the electrostatic charge image on the element is developed by the ;~
conventional electrically conductive developer particles the
surface potential on the element after the~developing step is
decreased to about one half of that before development, and this
proves the fact that some of the cha~rges on the insulating layèr ;
of thé element are moved through the rows o~ d.eveloper partlcles
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during the developing process.
- ~ A vislble image was formed by the conventional developer
particles on~the insulating layer or the element in such a manner
as descrlbed above, and then a plain paper was overlapped thereon
and corona discharge was applied by a 6000 Volts corona discharger
to the paper during the time of 0.12 seconds to transPer the de~
velper image~from the element to the paper and then the latter was
removed from the element. As a result, the developer image
trdns ferred~to the paper was blurred and i~s~resolving power was
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relatively low. This results from the fact that since the con-
ventional developer particles are electrically conductive the
charges of the particles once adherlng to the paper under the
action of the voltage applied to the latter are neutralized by
the applied voltage during the transfer step and then the parti-
cles are charged with the same polarity as that of the paper
thereby generating a force in a direction of separating them from
the paper and thus the particles are 3umped or moved away from the
paper.
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Experiment 2 ~`
By using the magnetically attractive and electr~cally
insulating developer particles of the present invention, an ex-
periment was made similar to Experiment 1. The pa~ticles were
, made by the method-described and had a mean particle size of 13
I micron meters. Each of the particles was composed of 30 weight
- % of polystyrene, 66 weight % of magnetite having a particle size
of from 0.05 micron meters to 0.1 micron meters and 4 weight % of
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stear;c acid, and the particles had black color by the magnetite.
The electric resistance of the developer particles was about 2 x
1014 ncm. This electric resistance was measured by the method
described in U.S. Patent Specification No. 3,639,245 in which a
circular through hole having a cross-sectional area of 0.073 cm2
was vertically formed in a polytetrafluoroethylene insulating
sleeve, the lower end of the hole being closed by an electrode
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~ hole, an electrically conductive piston being placed on the sample
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to give a pressure of 1,370 g/cm2 to provide a spacin~ of about
0.05 - 0.1 cm between the electrode plate and the piston, a voltage
being applied across them and varied such that the electric field
affecting the sample was varied froln 0 V/cm ~o about S,000 V/cm
during the period of 10 milli-seconds, and dur;ng this period the
electric current flowing between the electrode plate and the piston
being measured to determine the electric resistance of the developer
particles.
In the same manner as in Experiment 1, an electrostatic
charge image was formed on the insulating layer of the photosensi-
tiv~ element used in Experiment 1 and the initial surfaoe potentials
at the dark and light portions of the image were 700 volts and 0
Yolt, respectively. Th2 image was then developed by the developer ;~
part~cles of the present invention described above under the same ~1
condition as in Experiment 1, and the surface potential at the dark
portion of the image measured immediately after the completion of
development was 640 volts. After removal of the developer parti~
cles from the lnsulating layer ln such d manner as in Experiment 1, ~ `
measurement was made that the surface potential at the dark portion ~ `~
of the image~was 700 volts.
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`~ Further experiment was made similarly and the results ~ ; ;
.~ ~ were obtained that the initial surface poten~ials at the dark and
! light portions of ~he charge image formed on the insulating layer
1 were 700 volts and 0 volt~ respectively, and the potential at the
;i dark portion of the image after developm~nt by the developer par~
cles of the present invention was 625 volts, and the potential at
i the dark portion after removal of the particles from the element was
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690 volts.
From these experiments, it is proved that when the
electrically insulating developer particles of the present invention
are u~ed to develop the electrostatlc charge lmage on the photo-
sensitive element the surface potential on the element after
development is ma;ntained at a substantially same level as the
potential thereon before development and no substantial flow of the
electrostatic charges on the element is caused through the rows of
developer particles.
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Practical Example
The same photosensitive element as used in Experiment 1
was used and an electrostatic charge image was formed on the insu- ~ ~
1ating layer of the element by the same developing process as in ~:
Experiment 1 under the condition that the rate of project~on of
the original light image to the-element was 3.8 Lux-second.~ ~ The
surface potentia!s at the dark and light portions of the electro-
static charge image were 700 volts and 50 volts, respectively.
The charge image was then developed by the same developer part~l-
cles as used in Experiment 2 under the same condition as in Ex~
periment l to form a developer image on the insulating layer of the ;:
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element, and then a plain paper was overlapped on the insulating
; layer of the element and the developer image w~s transferred to the P
paper under the action of corona discharge from a corona discharger
to which 6jOOO votlage were applied, and~then the paper was sepa-
rated from the element. As a result, the developer image trans-
ferred to the paper had a high resolving power and there was found
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no substantial blur in the developer image.
~ Though the present invention has been described above,
: ; the invention will be practicable if any substance or substances
other than the components described are contained in the developer
particles with the condition that the partic1es are made to be
magnetically attractive and have an electric resistance higher than
1014 Qcm. It should be appreciated that the invention can be
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: applied to development of an electrostatic charge t?mage formed on
a photoconductive layer of a photosensitive element which is not
provided with an insulating cover layer.
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