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Патент USA US3041178

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1 715:
Patented “June 26, 19627
using copolymer coatings are sometimes unsatisfactory?
For example, in electrostatic printing processes using‘
liquid developer dispersions such as those described in
Metcalf and Wright, op. cit., uneven and inadequate‘ de
posit of developer particles on the charged areas of the
Henry Wieliclri, Philadelphia, Pa, assignor to Radio Cor
poration of America, a corporation of Delaware ' ‘
No Drawing. Filed Sept. 18, 1959, Ser. No. 840,801
2 Claims.
(Cl. 96-1)
coating results. The ?nished print in such a case is de
?cient in intensity and presents a blotchy appearance,
particularly when large areas are developed.
This invention relates generally to electrostatic print
ing. More particularly, it relates to improved recording
elements, and methods of preparing such recording ele
Accordingly, it is a general object'of this invention to
ments for use in electrostatic printing.
provide improved electrostatic printing’ on ‘a surface of
a photoconductive insulatin‘g'layer which includes a ?lm
forming styrenebutadiene copolymer as a major constitu
‘ In the art of electrostatic printing, electrostatic images
are produced on the surface of a photoconducting insu
ent ‘thereof. ‘
It is another object of this invention to‘ provide im
lating material. This frequently is accomplished by ?rst
producing on the surface a substantially uniform electro 15 proved photoconductive recording elementsand coatings
containing a resinous ?lm-forming styrene-butadiene co
static charge, as for example, by exposure to -a corona
discharge device.‘ Upon exposure to a light image the
electrostatic image is produced comprising areas bearing
electrostatic charges ‘and 'other areas wherein electro
static- charges have been substantially reduced or re
It is a further object of this invention to provide im
proved methods of preparing electrophotographic re—‘
cording elements comprising a :backing member coated
with a ?nely-divided pho-toconductor dispersed in a
moved by the ‘exposureim light. Visible images are pro
duced same charge image surface by ‘the electrostatic
resinous binder at least a major portion of which is a
?lm-forming styrene-butadiene-copolymer.’
' '
attraction of ?nely-divided developer particles to that sur
It is yet another, object of this invention to provide‘
face. Methods of developing electrostatic images are de
scribed in “Electrofax” Direct Electrophotogr'aphic Print 25 improved‘ methods of electrostaticipr-inting on the sur
face of a photoconductive layer which includes a resinous
ing On Paper, by'C. J. Young and, H. G. Greig, 'RCA Re
view,’ December 1954, vol. XV, No. 4.
?lm-forming styrene-butadiene copolymer.
' So called liquid processes for developing electrostatic
images have been proposed inwhich the solid developer
The foregoing objects and other advantages are ac
Wright consists of ?nely-divided developer particles dis
persed in' an insulating‘ liquid. This liquid developer
major portion of ?hn-forming styrene-butadiene copolye
complished ‘in accordance with this invention which is
particles are‘ suspended in an- insulating carrier liquid. 30 based on the ,discovery that pretreatment of photocon
ductive coating compositions containing a resinous ?lm-_
A liquid development process is described. by K. A. Met
forming styrene-butadiene copolymer with a selectivei
calf and R; ‘J. Wright in a paper entitled “Xerography,”
solvent provides unusual and unexpected results. The
published in‘the Journal vof the Oil and Colour Chemist’s
class of coatings or layers which have been found to be
Association, November. 1956, vol. 39, No. 11, London,‘
England and in another paper entitled “Liquid Devel 35 improved by such treatment includes those comprising, a
?nely-divided photoconductoi‘ dispersed in a resinous,
opers for Xerography” published in the Journal of Scien
binder of a ?lm-forming styrene-butadiene copolymer or,‘
ti?c Instruments, February 1955, vol. 32.
wherein the resinous ‘binder comprises a mixture of a
Brie?y, the liquid developer described by Metcalf an
mer and a minor portion of another compatible resinous
can be‘ flowed over ‘a surface bearing an electrostatic
material or wax.
' liquid developer. The liquid developer may also be
sprayed or rolled on to the surface. .Deposition of the '
developer particles on the charge image is an example
of the phenomenon known asrelectrophoresis or cata
' ,
, _
The selective solvent employed is one having a kauri
image, or the surface ‘can be immersed in a tray of
‘ One'type of recording element usable in the fore
butanol number of from about 20 to about 40 and which
preferably is highly volatile to‘ aid in rapid drying._ The
solvent is applied to the surface of the photoconductive
layer on the backing member. Application to the surface
of the photoconductive layer may be accomplished by‘
immersion,'spraying or washing techniques.
Speci?c examples and additional advantages‘are in}v
cluded in the detailed description which follows:
Photoconductive coatings ‘which can be improved in»
going electrostatic printing processes ‘comprises, a back
ing member coated with an electrically-insulating photo 50
conductive layer .such as a particulate photoconductive
accordance with this invention comprise'lOO'to 900 parts,
zinc oxide suspended in a resinous polysiloxane (silicone)
by weight, of a ?nely-divided photoconductor dispersed in
binder. A coating alsolhas been developed which com
about 100 parts, by weight, of binder. The binder corn
prises a particulate photoconductive zinc oxide suspended
in a'binder of a ?lm-forming resinous styrene-butadiene 55 prises a resinous ?lm-forming styrene-butadiene copoly
mer including 60 to 92%, by weight, styrene and _40_ to"
copolymer or in ‘a binder mixture comprising a major
8%, by Weight,’ butadienel Such a coating may be pre_-‘
proportion of the copolymer and a minor proportion of
pared according to the process disclosed in U.S. Patent’
another insulating resinous material or wax which is
2,611,719, issued to Alvin'M. Borders, or the process de
compatible with‘ the copolymer. ‘An important advan
tage of coatings containing a styrene-butadiene copolymer 60 scribed in U.S. Patent’2,537,1l'4, issued to A_.E.‘Y_oi.1ng,v
is one of cost, resins such-as silicone being much more
'Although desirable from ‘the standpoint of cost, it has‘
been found that photoconductive coatings containing
a styrene'butadiene copolymer are not suitable for all elec 65
trostatic printing applications. I 'When charged with a
‘corona discharge device indgarkness (or with a safe light) ‘
et al.
Example 1
A coating‘ mixture is prepared of the following formu;
lation in part by weight.
45 parts photoconductive zinc~oxide ‘(FlorenceGreen‘
Seal 8, marketed by the New Jersey Zinc Sales Co, New;
York, New York).
p ,
it hasbeen found that the top voltage _to which such'a
15 ‘parts, by weight, Pliolite S-SD, a high styrene-_
photoconductive coating can be charged is substantially
butadiene copolymerv marketed by ‘the Goodyear Tire and
less than the top voltage to which a coating containing 70 Rubber Co., Akron,‘ Ohio.
silicone can be charged. Since, in many‘ applications, a
1.5 parts plasticizer.
high top voltage is a prerequisite, the results obtained
100 parts toluene.
may be used to provide a ?nal coating thickness of from
coating which has been pretreated, unevenness of deposi
tion is not noticeable and the density of the image is
substantially increased.
Additional examples of photoconductive coatings which
about 0.0003 to about 0.002 inches.
may be prepared in the same manner as Example I and
The mixture is milled to a smooth uniform consistency '
and is coated on the surface of a backing member such
as, for example, paper. Any conventional coating process
The coating is
air dried or heat may be used to accelerate the drying step.
which may be improved by the application thereto of
Once dried, this coating has applied to it, a volatile solvent
one of the forernentioned solvents include the follow
such as, for example, trichlorotri?uoroethane. Upon
evaporation of the volatile solvent from the surface of
Example 2
the coating, the recording element is ready for use in 10
electrostatic printing.
Florence Green Seal-8 zinc oxide, marketed by the
‘ Any solvent having a kauni-butanol number of from
about 20 to about 40 may be applied to the coating to
provide improved results. In adition to trichlorotri
?uoro'ethane (kauri-butanol Number 31), speci?c exam
New Jersey Zinc Sales Co., New York, NY. ____, 45
Piccopale 100 resin, a methylated para?in resin
marketed by the Pennsylvania Industrial Chemical
ples include the following:
Kauri-butanol No.
Petroleum ether ___________________________ __
__________________________________ __
____ __
Hexane' __
____ __
Rubber Co., Akron, Ohio _________________ __
- 32
New York, NY. _________________________ __ 1.5
20 Toluene
Example 3
Pliolite S-S
for producing improved recording elements or, in the alter
Aroclor 1254, plasticizer marketed by Monsanto
Chemical Co., Organic Chemicals Division, St.
the electrical properties of the photoconductive coating.
native, solvent-treatment may be incorporated in an elec
trostatic printing process. It has also been found that
duration of treatment is not critical. For example, a
recording element prepared as described in Example I
may be given a quick dip in 1a quantity of the solvent or
it may be immersed therein for several hours without any
noticeable difference in results.
The solvent-treated recording element may be used
for electrostatic printing by any of the methods described
25 Piccopale 100 resin __________________________ __
It has been found that solvent-treatment as described
above produces a substantially permanent improvement in
Hence, solvent-treatment may be incorporated in a process
Florence Green Seal-8 zinc oxide _____________ __ 125
_ 35.5
F-2l Plasticizer, marketed by the National Lead Co.,
Isoheptane __
Co., Clairton, Pa. ________________________ __
Pliolite S-SD, marketed by the Goodyear Tire and
Louis 7, Missouri ________________________ __
__________________________________ .._
Example 4
Florence Green Seal-8 zinc oxide _____________ __ 125
Pliolite S-S
35 Piccopale 100 resin _ _______________________ __
Aroclor 5460 (a chlorinated polyphenyl resin solu
ble in toluene) marketed by Monsanto Chemical
____ __
__________________________________ __ 120
‘ in the Young and Greig publications or in the Metcalf 40
Example 5
and Wright publications op. cit. By Way of example, the
recording element may be placed with its pap er backing on
a grounded metal plate and in darkness an electrostatic
Florence Green Seal-8 zinc oxide _____________ __ 125
charging device passed over the photoconductive coating
to provide a substantially uniform electrostatic charge
Pliolite S—5
thereon. The next step in the process is to discharge
selected areas of the charge surface of the recording ele
nrent in order to produce an electrostatic image thereon.
This may be accomplished by placing a photographic
transparency upon the charged surface and exposing it
to light through the transparency. Other exposure
45 Aroclor 5460 ...l ____________________________ __
________________ ______; ______________ _. 140
Florence Green Seal-8 zinc oxide ____________ __
5° Pliolite s-s resin ______ _; ___________________ __
Picoopale 100 resin ________________________ __
processes also may be used such as, for example, projec
tion and re?ection exposure. Wherever light strikes the
F-Zl Plasticizer _________________________ __.__
Toluene __________________________________ __
surface of the photooonductive coating, the electrostatic
Cellosolve acetate __________________________ __
charge thereon is substantially reduced or removed to 55 Rose‘Bengal (Cl. 779) dissolved in methyl ethyl
_____ __
create a pattern of charges corresponding to the non~
illuminated areas.
The electrostatic charge pattern may be converted into
a visible image by any of the dry powder techniques de
scribed in the Young and Greig publication, or by any
60 Florence Green Seal-8 zinc oxide ______________ __ 150
Pliolite S-S resin ____________ __,_____________ __
of the so-called liquid development techniques described
proved performance of the photoconducting coating de-'
marketed by Barrett Division, Allied Chemical
and Dye ‘Corporation, 40 Rector Street, New York
Tricresyl phosphate plasticizer ________________ __
'6, NY. _‘_ ‘
’ particles of development material are attracted to the
surface than when a photoconductive coating is employed
which has been so treated. This e?ect is particularly
evident when the electrostatic image is developed by means
of liquid processes. In the absence of treatment, the
developed image exhibits an insu?ieient density and an
uneveness in the deposition of developer material. On
the other hand, when one employs a’photoconductive
Cumar T-3 a synthetic coumarone indene resin
in the Metcalf and Wright publications op. cit. It is dur
ing development of the electrostatic image that the im
_scribed herein becomes evident. Without treatment of
the photoconducting surface with a volatile solvent, fewer
Example 7
__; _______________ __"___ _____________ __ 200
Example 8
Florence Green Seal-8 oxide _____. ____________ __
Pliolite S—5D _________'_.____.__.__. ____________ __
Piccopale 100 _____________________________ __
F~2l plasticizer ____________________________ __ 0.75
75 Toluene .....'> _
It is not known Why coatings containing styrene-buta
What is claimed is:
diene copolym‘ers are improved as described herein other ‘
1. In a method of electrostatic printing including the
steps of producing a latent electrostatic image on the
is greatly enhanced. In actual tests, one sample was
surface of a photoconductive insulating material compris
found to be capable of being charged to a voltage of 360
ing a ?nely-divided photoconductor suspended in a ?lm
volts in darkness, whereas before it was treated with
forming binder at least a major portion of which con
a solvent it could only be charged up to 160 volts. An
sists of a resinous styrene-butadiene copolymer and ap
other sample evidenced improvement of from 200 up to
plying to said surface a ?nely-divided developer sub
400 volts as a result of solvent treatment. It is known,
stance to produce thereon a visible image; the improve
however, that pretreatment of a resin prior to the formu 10 ment comprising applying to said surface a solvent the
lation of a coating composition does not produce the
active element of which is selected from the class con
than that the charge storage capability of such coatings
same result. Such a test was made by immersing a powder
sisting of trichlorotri?uoroethane, petroleum ether,
of Pliolite S-SD in trichlorotri?uoroethane for a time
pentane, isohexane, hexane, isoheptane, iso-octane, octane, ~
su?ieient for the solvent to thoroughly wet all of the
and mixtures thereof, and drying said coating prior to said
Pliolite resin. The resin was then dried, dissolved in 15 step of producing said latent electrostatic image.
toluene and a photooonductive zinc oxide dispersed there
2. The method of claim 1 wherein said solvent is
in. This mixture was coated on paper following which
prints were made thereon with liquid developer disper
References Cited in the ?le of this patent
sions. It was found that such pretreatment of the resin
provided no enhancement of development. It was fur 20
ther ?ound that subsequent immersion of such a coated
Lion ______ __.____'_____ Oct. 26, 1954
paper in trichlorotri?uoroethane or the other solvents de
Griggs et :al. _-_ _______ __,Feb. 24, 1959
scribed herein did enhance development results. No
Mayer et al ___________ __ June 23, 1959
explanation can be given for this phenomenon other than
Myer ______________ __ June 30, 1959
that the solvent treatment of a coated recording element 25
Moncrei?-Yeates __.______ Sept. 15, 1959
must result in some physical reordering of the photo»
conductive surface which may result in an effect equiva
lent to providing-a substantially greater surface area
Payne: “Organic Coating Technology, vol. 1, page 258.
capable of retaining an electrostatic charge.
30 Wiley ‘and Sons, Inc., New York, 1954.
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