Note: Descriptions are shown in the official language in which they were submitted.
10667~9
.
The present invention relates generally to electrophoto-
graphic and electrostatic recording elements and processes for
making the same; and more particularly to an improved technique
for making an electrical ground connection to the intermediate
electrically-conductive layer of such elements.
As used in the present specification, the term "electrostato-
graphic" is intended to mean and cover both electrographic and
` ~' electrophotographic members.
~, Both types of recording elements are employed in reproduc-
1 10 tion processes. Essentially, a latent image is formed in these
~ elements by providing an imagewise surface charge on an insulat-
`, ing surface of the element, and thereafter developing the charg-
`~3
^~ ed latent image by means of an electrically-attractable material,
~ such as a "toner" (i.e., directionally charged colloid carbon
- ~ 15 particles suspended in an insulating liquid or on a dry carrier).
Specifically, an electrophotographic element normally
~; comprises at least a substrate having coated thereon a layer
containing a suitable photoconductor. The support layer i3 ma~`~e
conductive either by the inclusion therein of electrically-con-
ductive materials or by coating its surface ~the surface designed
to receive the photoconductive layer) with an electrically-
conductive material. Images are usually formed on the photo-
conductive layer by first applying a uniform electrostati:c
charge to the photoconductive layer by any suitable method,
i 25 thereafter imaging the charged material by exposing it to light
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10f~6759
through a transparent master or by reflection from an opaque
master which is being reproduced, thereby causing the photocon-
ductive layer to become conductive, resulting in the dissipation
of the charge in those areas of the layer exposed to light. In
5 a subsequent step, the charge pattern or latent image on the
image layer is rendered visible by the application thereto of
a colored or black electroscopic toner.
An electrographic recording element is similar in construc-
tion to the electrophotographic element, with the photoconductive
`` 10 layer being replaced with a high dielectric layer or a "charge
retentive layer", that is, a material having a volume resistivity
of not less than about 1012 ohm-centimeters. During this "print-
; ing" process the electrical charge is applied in the image areas
by a stylus and developed in the same manner as the electrophoto-
` 15 graphic element.
With either type of element, it is often desirable during
one or more of the processing steps (e.g., during charging or
during toning) to establish a ground connection (to a reference
potential) to the conductive layer of the recording element in
.~ ~
`~ 20 order to create a highly conducting reference plane which is
held at or near ground potential. For example, during the
electrostatic charging of the photoconductive layer or during
. ~.
the "printing" of the dielectric layer, the potential of the
conducting layer has a tendency to build-up with respect to
} 25 ground if it is not grounded. If this should occur, then there
'`'t~ iS a less than desirable difference in potential between the areas
truck by light and those not struck in an electrophotographic
' ~J element, and between the areas retaining or not xetaining "print"
charges in an electrographic element, resulting in a latent image
30 which is difficult to develop in the subseque~t toning step,
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1(366759
thereby resulting in copies which exhibit poor image quality,
high background discoloration and/or poor contrast.
The prior art is replete with suggestions as to how to
assure proper electrical grounding of the conductive layer in
such elements. The classical approach is to provide an elec-
trically-conductiv,e substrate which is easy and conventional if
the substrate is a permeable or non-homogeneous substrate such as
paper, since the substxate can be filled during manufacture with
an electrically-conduc~ive pigment such as carbon black, or
saturated with a solution of an ionic, hygroscopic substance, such
as salt of a polyelectrolyte. However, there are disadvantages in
such a technique. For example, the ionic hygroscopic impregnant
is not generally effective in low porosity papers and the conduc-
tivity it imparts is not stable but varies by several orders of
; 15 magnitude with the relative humidity o the environment. The use
of carbon black as a filler insures the stability of the conduc- -
` ~-`tivity, but may be unacceptable for aesthetic reasons, especially
if a white substrate is desired. Moreover, it tends to weaken the
` substrate physically. Finally, it must be formulated into the
` 20 substrate at the time of manufacture and thus, cannot be applied
to separately-made substrates. In addition, the primary dis-
~ , .
advantage of this technique is that it cannot be applied to homo-
geneous, impermeable substrates, such as extruded or cast films
made from, for example, synthetic resins such as polyesters.
A further approach has been to provide a conductive inter-
mediate layer between a non-conducting substrate and the photo-
conductive or dielectric layer~ It has been suggested to con-
; tact this conductive intermediate layer by removing the di- ~-
electric or photoconductive layer from a limited area thereby
exposing the intermediate conductive layer so that an electrode
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can be physically contacted with the conductive layer. Other
approaches have been to cut, punch, scratch or otherwise disrupt
the physlcal integrity of the dielectric or photoconductive
layer with an ele~trode which is forced into contact with the
intermediate conductive layer.
- A further alternative of the prior art has been to provide
a conductive pathway established from the conduative layer to
the outer surface of the member where an electrode can establish
contact with ito Since it is a part of the recording member, it
10 must be inexpensive to apply, inconspicuous, flexible (in flex- -
ible recording elements) and of course both effective and
` reliable.
:;i An example of the prior art's solutions to this problem is
~ shown in U.S. Patent NoO 3,118,789, Wiswell et al. The patent
,,.; ~ ~
~ 15 discloses an electrophotographic recording member comprising a
... .
paper substra~e, a conductive interlayer and a photoconductive
layer overlying the conductive interlayer with, optionally, a
" conductive layer coating the back side of the papèr substrate.
The paper substrate is perforated with fine holes so that the
; .
`~ 20 conductive lacquer of which the conductive interlayer is composed
~ will penetrate through the paper during the coating ope~ation and `~
`j thus enable the establishment of an electrical connection there-
~$ through to the conductive interlayer. A disadvantage with this
3 type o~ electrical connection is that it is not useful with im-
permeable substrates such as polyester films. If the substrate
, ~ iQ a film, and transparency and use as a photographic member is
required, the methods suggestèd in the ~iswell et al Patent can-
-~ not be employèd tO establish contact with the conductive inter-
layer because of the damage such a technique will cause to the
film's optical characteristics~
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66759
Another solution to the problem is disclosed in U.S. Patent
No. 3,639,121, York. The patentee discloses electrophotographic
elements comprising a support, an intèrmediate conducting layer
and an uppermost ~hotoconductive layer wherein electrical contact
to the conducting layer is accomplished by coating the edge of the
lamina~e with a ~onducting lacquer, whiah coating can be connected
to ground to thereby electr~cally ground the intermediate conduct-
ing layerO
` U.SO Patent No. 3,533,692, Blanchette et al, discloses a
` 10 photoconductive medium wherein the photoconductive layer is remov-
ed ~rom an area to expose the conductive interlayer, with which
contact is ~hen made with an elec~rode, or in which a conductive -
metal strap ox rive~ is used to establish an electrical connection
between the inte~layer and a conductive area coated on the back of
~ 15 ~ the laminateO _~
-: U.S. Pa~ent No~ 3,5S2,957, Hodges, discloses the use of
.
i- mechanical devices such as straps, clamps and rivets applied to ~;
c an èxposed area of ~he conductive interlayer of an electrophoto-
? graphic recording member to establish elect~ical connection with
the interlayer~
~t Similarly, U.S~ Patent No. 3,574,615, Morse, discloses a con-
.. ; . .
nection scheme as in Hodges except that an electrically-conductive
elastomeric pad is in~erted between the clamp-electrode and the
, .
exposed surface of the condu~tive interlayer.
Further, U S. Paten~ NoO 3,543,023, ~ellin et al, eliminates
~, the necessity for stLipping the dielectric or photoconductive layer
away to expose the conductive interlayer, and discloses instead
the use of a coLona discharge at the edge o the member to -~
establish the necessary electrical connection. -~
A disclosure relzted to thc ahove discussed York Patent appears ~-;
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~ 106~759
in U.S. Patent No. 3,684,503, Humphriss et al. Humphriss et al
achieves the necessary electrical connection by providing in a non-
recording section of the element, a solid dispersion of a particul-
ate electrically conducting material which extends from an external
surace of the element through à portion of at least one of the
layers overlying ~he conductive layer to electrically contact the
conducting layerO Alternatively, the dispersion can extend into
the element from an edge thereof.
Although the prior ar~ recording members generally function as
intended, there has been a need for a technique of providing the
necessary ele~trical ground connection to the conductive interlayer
in an ~lectrostatographic recording member which is simple to
fabricate and yet is effective in establishing good electrical con-
nection with the conductive interlayer.
.. . . .
lS Ac~ording to the present invention there is provided an electro- `
;~ ~-statographic recording member which includes an electrically-insulat- _~
ing subst~ate, an electrically-condUctiVe layer overlying a first
surfaoe of said subs~ra~e, an electrically-insulating outer layer
` overlying s~id ~onductive layer, said outer layer containing a photo-
conductive material or being composed of a dielectric ma*erial of
high volume resistivity, and means for establishing a ground connec-
tion to said conductive layer; and wherein said ground connection
means comprises a hole in a non-image area of said recording member
;~` extending from a surface thereof at least to said conductive layer
`~ 25 and an electrically-conductive composition in said hole, said elec-
trically-conductive composition comprising an adhesive and a suffi- -`
cient amount of an electrically-conduCtiVe pigment to make said com-
position conductive, said composition being in electrical contact
with said conductive layer and the exposed composition at the sur-
face of said recording medium being covered by a oonductive metallic foil.
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1066759 -
Thus, in the recording member of the present invention,
there is formed at least one hole or aperture disposed through the
entire thickness (or only partially therethrough) of the recording
member in a non-image area thereof, which hole or aperture is sub-
stantially completely filled with an electrically-conductive compo-
sition comprising a plastic adhesive and a sufficient amount of an
electrically-conducting pigment dispersed therein to make the com-
position electrically conductive. A piece of metallic foil is
employed to cover the exposed adhesive composition in the hole or
aperture which has the effect of reducing the contact resistance
between the exterior electrode and the electrically-conductive plas-
tic material in the hole or aperture and further improves the per-
. formance and reliability of the technique of the present invention.
According to the present invention, there is provided a
lS process for establishing ground connection with an intermediate
conductive layer of an electrostatographic recording member, said
recording member comprising at least:
. an electrically-insulating substrate;
an intermediate conductive layer overlying a first
. `:'
. 20 surface of said substrate; and
an electrically-insulating outer layer overlying said
conductive layer, said outer layer containing a photoconductive
~, material or being composed of a dielectric material of high volume
resistivity said process comprising:
(1) forming a hole in a non-image area of said recording
member extending from a surface thereof to at least said intermediate
conductive layer;
(2)inserting in said hole an electrically-conductive
composition comprising an adhesive and a sufficient amount of an
. 30 electrically-conductive pigment to make said composition electric-
~ ally-conductive; and
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1066759
.
(3) bonding said adhesive composition in said hole
to said recording member, said adhesive composition providing the
sole electrically-conductive path between the conductive layer of
the recording medium and a conductive metallic foil covering said
adhesive composition.
Other advantages will be apparent to those skilled in
the art from a consideration of the description of the preferred
embodiments which follows hereinbelow, when taken in conjunction
with the accompanying drawings, in which:
``
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1~6759
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Figu~es 1 and 2 cchematicaily show, in cross-section alterna-
tive embodiments of con~entional electrophotographic recording
members.
Figure 3 schematically illustrates a process for providing the
imprcved electrical ground connection of the present invention.
Figure 4 schematically illustrates an electrophotographic re-
cording member provided with the improved electrical connecting
, means of the present invention.
`~ Figures 5 and 6 show alternative embodiments of the improved
electrical conne~ting means of the present invention.
, As pointed out above, the present invention is applicable
, ' equally to electrophotographic recording memb,ers as well as elec-
trographi~ recording members, Examples of the former are shown
in Figures 1 and 2 of the drawings. ~eferring to Figure 1,
.
support layer 10 is ooated with a conductive layer 11 which' in
, ,' ~turn is coated with a photo~onductive layer 12. The support is ' ~ -
' normally ele~txi~al1y insulating and may comprise any of ~he well~
, ' known materials used fGr such purposes. Any conventional conduc-
., ~ . ....
tive pigment may be employed to render layer 11 electrically con- ~''-
ductive. Similarly, any ~onventional photoconductive material may
' ' be incorporated into layer 12 to render the same photoconductive, -'
: ......................................................................... .
'; and any convent_onal binder can be employed in photoconductive
, ' layer 12 and conducr;ve layer 11. '~
' To assure good adhesion between the conductive layer and the '
; 25 support, if the two mater-als employed are not capable o~ good ad-'
hesion to one another, a bcnding layer or subbiny may be interposed
between conductive layer 11 and support 10, as is conventional in
; the art.
Figure 2 shows an alternative embodiment wherein on the back
side of support 10 is disposed a conductive back layer 13. The
~3
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~' 106675g
latter layer functi^r,s as the grounding layer for the element and
replaces an exterior electrode which is used with the recording
member shown in Figure l.
;: Electrographic re~ording members are similar in structure to
the electrophotographic recording members shown in Figures 1 and 2.
In essence, ~he pho~oconductiYe laye~ 12 of the electrophotographic
recording member is replaced with a dielectric layer having a high
volume resistivity, normally a minimum of 1012 ohm-centimeters.
Any conventional dielectric material can be employed as is obvious
to those skilled in the art.
With either the electrogxaphic or the electrophotographic re-
:: ,
cording members, it is important to electrically connect the con-
ductive layer 11 to gro-~nd during the -harging and development of
`` the uppermost layerc If the conductive layer is not electrically
~- .
, lS grounded, the difference in potential between the upper layer and -~
the conductive layer diminishes as a result of build-up of charge
in the conducti~e layer. The mcre equal charge d..minishes the
quality and clarity of the image since the imaged areas in the
upper layer have les~ or a tendency to selectively attract the
developing materiàl, as compared to the non-imaged areas, due to
` the small di~ference in potential between the upper layer and the
conductive layer. If the conductive layer is properly grounded,
the difference ln potential is signi~icant and therefore the imaged
` :`
areas are easily c~pable of attracting the electrically-directed
;~ 25 developlng material, the ~.oner, thereby producing a clear image.
The improved electrical ground connection of the present inven-
~' tion possesses numerous advanta~es over the priox art. Essentially,
electrical ground connecr.ion to the electri.cally-conduc~ive inter-
mediate layer in the record~ng meI~er is made by first punching or
othexwise cutting a hoie in a non-image area of the xecoxding membex
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~ 1066759
and filling the hole with and bonding thereto an electrically-con-
ductir.g plastic adhesive thereby establishing both a mechanical bond
with the walls defined by the hole and an electrical contact with
the exposed conductive intermediate layer therein. The plastic ad-
hesive ~omposition may or may not contain a solvent for the plasticmaterial, the adhesive without the sol~ent being preferred in order
to eliminate the need for drying the adhesive and to avoid possible
shrinkage problems a~socia~ed with the loss of solvents from the
adhesive composition as the composition dries. Further, any known
adhesive c~mposition can be employed in the practice of the present
invention without limitationO
~n a preferred embodiment, a metallic foil coated with the ad-
.. . .
hesive composition of the present invention can be applied to ~oth ~-
sides ~f the record~ng member over th~ hole ~if the hole extends
thro~gh the entire thi~kne~s) and the adhesive coating may be
~forced into rhe hole fx~m both sides to form the electrical connec- -`-
tion of the present invention.
~` Alternatively, ins~ead of punching or cutting a hole through
the re~ording member, ~he photoc~nductivè or dielectric coating may
be selectively removed from a certain area such as by using a solv-
ent, or by scoring, scl~atching or otherwise destroying the physical ~-
integrity of the coat~ng, to expose the underlying conducting
intermediate layerO The adhesi~e composi~ions of the present in-
vention can then be inserl:ed intc the resulting channel, which
`, 25 extends at leas~ tc the conductive intermediate layer. This embodi-
ment may also he utllized with the adhesive-coated metallic foil.
To be more specific, the first step in the p,rocess for form-
ing the improved electrical connection of the present invention is
to cleanly p~nch or otherwi e cut a hole in the recording member
is not critical as long as it i5 în a non-image area thereof. Pre-
--10--
111 1(~66759
ferably, the hole should be cleanly sheared or punched entering
from the side of the member on which the photoconduc~ive or di-
electric layer is coated. The hole should be punched as neatly as
possible in order ~o preserve the integrity and continuity of the
electrically-conductive intermediate layer around the edge of the
hole.
The adhesive that is used to fill the hole can be any conven-
tional plastic adhesive known to those skilled in the art. The
adhesive is made electrically conductive by mixing therein an
electrically conducting pigment such as carbon black; graphite;
acetylene blac~; metal powders such as nickel, silver, etc.; con-
ductive zinc oxide, pcwdered se~i-conductor material; and the like.
Generally, the pigment employed is not critical as long as it is
- electrically conductive so as to provide the adhesive with a
sufficient conductiYity to prevent build-up of potential in the
conductive layer~ Normally, the adhesive has a maximum resistance
value of about 108 to 1016 ohm~ cm. The resistance of the conduc-
tive adhesive ~hould be less than 1011 ohm cm., and it can be
varied by changes in the formulation. The total resistance of the
entire insert should not be greater than 109 ohms.
Any suitable mixing technique can be employed to disperse the
conductive pigment through the adhesive. As an example, a ball
milling technique can be employed to uniformly disperse the conduc- -
tive pigment through the adhesive composition.
- 25 The adhesive e~ployed ~in the embodiment which requires a
solvent) is not limited and includes any Xnown adhesive composi-
tion which is compatible with the recording members of the inven-
tion, is capable of being made conductive by the inclusion therein
of a conductive pigment and is capable of being applied from a
solvent solution or dispersion.
1066759
Typical solvent-free adhesive formulations include those
adhesives which are known to those skiIled in the art and include
without limitation hot_melt a & esives and pressure-sensitive ad-
hesives. A typical example of the former is as follows, the parts
being parts by weight:
Hot-Melt Adhesive
Component Parts
Kraton 1101 10.00
Shawinigan Black Acetylene2.00
Plastanox 2246 0.05
Plastanox LTDP 0~05
Toluene 55.00
Methyl Ethyl Ketone 32.90
,. 100 00 ''
To obtain a solvent-free, hot_melt adhesive, the formulation
of the example is coated on an all~;num foil and the solvent is removed
in a drying oven. The film thickness of the resulting hot-melt coating
is kept in the neighborhood of 1/2 to l/3 the thickness of the electro-
` photographic or electrographic member to which the coated foil is to be
` 20 applied by heat and/or pressure. The tbickness of the coating may be
~ adjusted to the desirability of the amount of "flash", i.e., the flow
!`. of the hot-melt surrounding the aluminum foil used as a covering
material in such a laminate.
The Kraton I101 is a styrene-butadiene copolymer and is
available from the Shell Chemical Company. The Shawinigan Black
Acetylene is available from the Monsanto Chemical Company, and oom-
prises essentially acetylene black. Both Plastanox components
are av~;lable from American Cyanamid and are anti-oxidants used to
d prevent embrittlement of the resins in which they are employed.
; 30 Plastanox LTDP is dilaurylthiodipropionate and n astanox 2246 is
'' ' '' '`~:
Regi~tered Trademark
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1066759
2,2'-methylenebis-(4-methyl-6-tertiarybutylphenol). The ~urface
resistance of the above hot-melt adhesive is 8.0 x 102 ohm~ per
square centimeter. The relationship between surface resistance
and resistivity is disclosed in columns 2 and 3 of York 3,639,121,
and the curface resistance given herein may be determined by the
method described in said patent.
A typical example of a pressure-sensitive adhesive is as
follows:
` Pressure-Sen~itive Adhesive
- 10 Component Parts
Monsanto RA 1151 23.0
Shawinigan ~lack Acetylene 2.0
Ethyl Acetate 40.0
Toluene 35.0
100.O
The Monsanto RA 1151 is a resin available from the Monsanto
Chemical Company and cQmprises about 35% solids, with the balance
being a solvent comprising ethylacetate (55~) and toluene (45~).
The surface resistance of the pressure-sensitive adhesive described
above i~ 2.0 x 102 ohms per 3quare centimeter.
Suitable hot-melts that are conductivized by pigments dispera-
ed in solvents and coated on the foil and dried may be chosen from
the following:
Solid fatty polyamides, poly(vinyl acetate) - rosin, ethylene -
vinyl acetate copolymer, petroleum wax, laminating grade micro-
crystalline wax, rosin or ester gum, vinyl acetate-crotonic acid,
beta-pinene polymer, polyvinylacetate, polyethylene, paraffin wax,
dimerized rosin, modified rosin or rosin ester, ethyl cellulose,
e~ter wax, paraffin mineral wax, polyterpene, polyterpene urethane,
B-pinene resins, terpene wax - polyethylene covinyl-acetate (Elvax
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66759
260 DuPont), and the like.
If the adhesi~e composition is applied using a solvent, after
the adhesive compcsiticn solution is inserted into the hole in the
recording member, it is then dried to establish a firm mechanical
bond with the ins~de of the hole and also to establish the electrical
contact with the exposed conductive layer on the inner surface of
the hole. The hoi-melt type of solvent-free adhesive is simply
hea~ed ~o mel~ the same and it can be easily flowed into the hole.
It i~ not necessary to heat the pressure-sensitive adhesive since
the application of pxessure alone is sufficient to assure that the
adhesive completely fills the hole in the recording member.
The particle size of the conductive pigment is not at all
critical, and any conventionally-sized conductive pigment can be
employed~ Gener~lly, the particle size of the conductive pigment
will vary depending upon the particular material used and generally
ranges from 5 to 200 millimicrons, although it is not intended to
limit the particle size of the ~onductive pigment used in the pres-
ent invention to th~s range. Those skilled in the art can determine
the optimum parti~le s~ze depending upon the desired surface
resistance, the thick~ess of the adhesive, the amount of pigment
contained in the adhesive, and various other considerations.
~ he amoun~ of the conductive pigment that is present in the
adhesive varies from the minimum amount necessary.to make the ad-
hesive conductiv~ to a maximum amount which is limited only by the -
25 ability of the adhesive to retain the pigment dispersed or mixed ~-
therein. Generally, the amount of conductive pigmen~ will vary
from a minim~m of 0.5 par~s by weight to a maximum of 15 parts by
weight, based on the ~eigh~ of the adhesive composition. A mixture
of conduc~ e pigments may also be employed depending upon the end
30 use. ` -
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1~ 1()66~59
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The solvent-free adhesives are preferred in the practice of
the present in~ention sin~e the need for drying is eliminated and
the shrinkage problems associated with the loss of solvents or
possible solvent retention therein in the event o~ incomplete dxy-
ing, are avcided~ The plasticity necessary for a solvent-free ad-
hesive may be obtained either by melting the adhesives at the
time of application ~in the case of a hot-melt adhesive) or by
formulating i~ with various polymeric materials, tackifying agents,
etc. and applying it as a pressure-sensitive adhesive. Since
these other ingredients are not part of the present invention per
se, and since those skilled in the art can readily prepare such
compositions, they will not be described in aetail here for
purposes of bre~ity.
In a preferred embodiment, an adhesive-coated metallic foil ;-
` lS is employed to fill the hole in the recording member. Rèference
~ `r ~ig made to Figures 3 and 4 which show this preferred emhodiment.
; ~; Figure 3 shows a ~ecording member compri~ing a substrate or
support 14, an intermediate conductive layer lS and an uppermost
.
pho~oconductive layer 16, or dielectric layer. A hole 17 is pro-
vided in a non-image area of the recording member, thereby expos-
ing the intermediate conductive layer 15 on the inner sùrface of
the hole. As shown in Figure 3, two piece~ of adhesive-coated
metallic foils 18 and 21, generally, are disposed on opposite ends
' of the hole. The adhesive-coated metallic foil gene~ally com- -
prises a thin metallic foil 19 having a coating 20 thereon of the
adhesive. The metallic foil can be any conducting metallic foil,
such as aluminum, copper, tin, etc., and the thickness of the
adhesive can be regulated to provide a complete filling of the
hole. The adhesive-coated foil pieces are inserted into the hole
30 such as by the use of pressure as indicated in Figuxe 3. If a hot- -
-15-
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~ melt adhesive is employed, the only pressure necessary is that
¦ sufficient to push the heated adhesive material of the upper and
` lower pieces of adhesive-coated foils into the hole for contact
and fusion. Figure 4 shows the finished product after the ad-
` S hesive-coated foil pieces axe inserted into the hole punched in the
recording member. The advantage of using the adhesive-coated foil
pieces is that the contact resistance between the exterior elec-
trode and the conductive adhesive is reduced thereby providing im-
proved perfo~mance and reliability. It is further possible to
easily extend the conducti-e area from the hole over the surface
of the recording member to whatever contact area and shape is re-
qu-red. Moreover, the metallic foil is more durable and in parti-
cular mcre resistant to abrasion than the exposed conductive ad-
'~ hesive, and in the case of the pressure-sensitive adhesive, it
15 covers and pxotects the tacky surface frcm dirt and prevents its - :
inadvertent a~hesion or blocking to other surfaces. :-
:......................................................................... .:
~` Although ~igures 3 and 4 show the use of two adhesive-coated
foil pieces, ~he ir.vention is equally as applicable to the use of
-~ only a single piece appl~ed from only one side of the recording mem-
ber. The adhesive-coated foil can be conveniently made by pre-coat-
ing one side of the metallic foil with the adhesive composition,
for example, from a sol~ent solation of the same. After drying, the
; coated foil may be heated or slit and wound up to ~he desired size.
.~ ~. .. ~ . .
In the case of the pressu~e-sensitive adhesive, it will usually be
necessary to protect the exposed surface of the adhesive such as
~` by the use of the adhesive-coated metallic foil. The use of the
adhesive-coated foil provides the additional advantage that the pre-
coated foil can be employed to apply a metered amount of the re- --~
~ quired adhesive to the hole in ~he recording member.
-~ 30 The use of two adhesive-coated foil pieces is preferred since
~ -16-
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~066759
not only will a bond be established with the inside of the hole and
with the adjQining surface areas underlying both.pieces of foil,
but the adhesive surfaces will meet in the hole and bond both
pieces of foil flrm`y to each other, which substantially strengthens
the electrical connection. A further advantage o~ using two ad-
hesive-coated foil pieces is evident with electrostatographic re-
cording m~ers ~hich have a conductive back layer as illustrated in
Figure 2. It is func~ionally important to provide electrical con-
nection between the intermediate conductive layer ll ~referring now
~o Figure 2) and the conductive ~ack layer 13~ The use of the
`~ technique shown in Figures 3 and 4 is tery effective for accomplish-
- ing this purpose. The adhesive-coated foil which is applied
simultaneously to the back of the member with the application of
. the adhesive-coated foil to the front of the member simultaneously
establishes contac~ with the interlayer and with the conductive
.~ack layer surrounding ~he punched hole.
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Altern3tive emb~dimen~s of ~he improved electrical connection
technique of ~he present invention are shown in Figures 5 and 6.
Figure 5 shows a recording member ccmprising a support 21, an
intermediate layer 22 which is conductive and an uppermost layer
23 which compr~ses either a photoconductive material or a high di-
electric materialc A "slot" or "hole" 24 can be pxovided through
the uppermost layer 23 and intermediate layer 22 of the recording
member as shown in Figure S. This can be done by any suitable
25 technique, such as by scoring or scratching the surface, or general- -
ly by using any technique which destroys the physical integrity of ;.~.
the uppermost layer 23 down to a point into and through the inter-
mediate conductive 12yer 220 This can be performed for example by
- the use of a solvent which selectively dissolves the upper layer 23
and the conductive layex 22, thereby providing access to the con-
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ductive layer 22~ Whlle a condu~tive adhesive composition by itself
can be filled into this slot or hole, it is preferred to use the ad-
hesive-coated foi~ as shown in Figure 5, the adhesive being designat-
ed 26 and the foil 25o
Figure 6 sho~s a related embodiment wherein the slot or hole 30
is only made in the uppermost layer 29 down to but not into the con-
ductive layer 28, which overlies support 27. The adhesive 32 con-
tacts conductive layer 28 at the bottom of the slot 30, and the ad-
hesive 32 is shown in Figure 6 as being covered by a foil member 31.
The improved technique of the present invention is advantageous
compared to methods and techniques taught in the prior art. For
example, the technique cf the present invention increases the
options one has for making contact with an electrode in the appa-
` ratus emplcyed in imaging the recording member, in that the loca-
tion of the hole is not limited to an edge and any non-image area
can be chosen, and in addition the front or back of the member can
be contacted. Further, the connection of the present invention
provides an effective in~erconnection between the interlayer and
the back coat in recording members having a condu~tive back layer. -
Further, since the connection is made with an adhesive, it is flex-
` ible and durable, especially with the use of the metallic foil. The
present inventicn also makes it unnecessary to remove or render
conductive the upper laysr in order to establish contact with the
intermediate conductive layer.
i 25 If a hot-melt or pressure-sensitivs adhesive is used, the
problems associated with the use of a solvent are avoided as indi-
cated above. If an adhesive-coated foil is employed, this provides
a convenient and effec~ive mannex of metering and applying the con-
ductive adhesive, as well as providing a low contact resistance con-
nection assuring better and more reproducible image quality. Because
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of t~he hi~h conductivity of the foil, it can be used in any desired
size or shape~ The preferred ~ize is one having a surface area of
from about 0.1 cm2 to about 3 cm2, and is easily applied in squares
or discs Lastly, if a pre~sure-sensitive adhesive-coated on foil
is employed, it is easy to apply, no heat being necessary, thereby
avoiding the risk of thermal damage to the recording member.
The present invention relates speci~ically to the improved
technique ~or making ground connection to the electrically-conductive
intermediate layer of the reco~ding members above described. The
` 10 inventicn does no~ per se reside in the composition, basic structure
or other characteristics of the recording member per se~ The pres-
ent invention i~ expressly applicable to any conventional electro-
`~ statographic record ng member having at least three layers, a
support wh~ch is electrically insulati~g, an electrically conduct-
ing layer o~erlying the suppoxt and an uppermost layer which is
either pho~oconducti~e (_n the case of ele~trophotographic members)
or a dielectr~c material ha~ing a high volume resistivity (in the
case of an electrographic recording member). An optional fourth ` ~-
layer is the conductive baek layer on the~opposite side of the
20 support from ~he in~ermedia~e conducting layer and either the pho~o- `
, conductive ¢r dielectric layer~.
One ckilled in the art can select appropriate materials to
form these conventional recording members. Thus, as the support
various materials can be u~ed, such as paper or synthetic resins
~25 such as polyesters (e~g~, polyethylene terephthalate) or cellulose
" esters ~e.g~, cellulose acetate~ and the like. Preferably, the
support is formed of a transparent material such as polyethylene
terephthalate or cellulose acetate when the recording member is to
be used as a maste~ in a photographic reproduction process where
the information imaged thereon is to be exposed from ~he back side
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of the re~ording member. The thickness of the support may vary
depending upon the end use, there being no particular limitation
as to the thickne~s of the support.
The intermediate conducting layer which i9 coated onto the
support, evaporated thereon or formed as a part of the upper ~ur-
face of the support, can comprise literally any conducting compo-
sition. Normally, the conducting layer comprises an electrically-
conducting material dispersed in a binder therefor and coated onto
the support, such as from a ~olvent solution thereof. ~he elec-
trically-conducting material may be the same as that used in appli-
cant's adhesives and the binder may be polymeric in nature, such
as polyolefins, vinyl polymers such as polyvinyl chloride, acryl-
ates, methacrylates, polyesters, styrene-butadiene copolymers,
polyvinyl acetate, polystyrene, polyamides, polycarbonates, copoly-
mers thereof, etc. Illustrative of the electrically-conducting
materials which may be employed in such intermediate conducting
layers are ionizable polyelectrolyte salts, polymeric quaternary
ammonium salts, polystyrene ~ulfonic acid salts, salts of copoly-
mers of vinyl compounds with maleic acid, Calgon 261, vinyl acetate,
and metal coatings deposited by sputtering ox vacuum deposition to
r~nder the component electrically conducting. The thickness of the
conducting layer is not particularly limited, and those skilled in
the art can vary the thickness as desired.
In an electrophotographic element, ~he upper layer is photo-
conductive and normally comprises an organic or inorganic photocon-
ductor dispersed in a binder therefor. Any or~ani¢ or inorganic
`~ photoconductor i8 useful in the electrophotographic elements of the
present invention. Typical organic photoconductors include, for
example, qu~nacridones, carboxamides, carboxanilides, triazines,
anthraquinones, ano compounds, salts and lakes of compounds derived
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from 9-phenylxanth~ne, dioxazines, lakes of fluorescein dyes,
pyrenes, phtha'ocyanines, ~Rtal salts and lakes of azo dyes, poly-
vinyl carbaæole, substit.uted phenylene diamines, and the like.
Several substituted phenylene diamines axe described in detail in
~.S. Patents 3,314,788 issued April 18, 1967 to Mattor and
3,615,404 issued October 26, 1971 to Price et al. The amount of
the photoconductive material in the photoconductive layer is at
least the minimum required to render the layer photoconductive,
with the amount generally varying from 5% to 65% by weight, based
on the weight of the photoconduc~ive layer. The disclosures of
the aforementioned Mattor and Pxice et al Patents are hereby in-
corporated herein by reference for their disclosures of suitable
` photocondu~tive ma~erials.
Also operab'e in ~he photoconductive layer, and preferred,
are sensitizing compounds which further increase the sensitivity
~of the photoconductive ma~erials to light of certain wavelengths.
Any conventional sensitizing compounds may be employed in the
photoconductive layer of the present invention to be used in com-
bination wi~h related photc~onduetive materials to further in-
crease the sensitization of the photoconductive layer. The amountof the sensitizer in the photoconductive layer can vary within
wide ranges, with the optimum concentration in any given case vary-
- ing with the speeific phcto~onducto~ employed and the sensitizing
compound usedO Normally, sensitlzers are employed in amounts of
:1 .
2S from 0.05% to 0O3% by weight, based on the weight of the photocon- -
ductive layer, or about 3 ml. of a 1% solution of the sensitizer ;-
for each 25 grams of photoconductor employed. ~-;
. The photoconductive layer may be coated onto ~he electrically-
; conductive inte~mediate layer such as frsm a solvent solution of
the composition. ~he solvent will o~ course vary depending upon the
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photoccnductor and ser.sirizer, if one is present, and the binder.
Those ~killed in the art can certainly practice the present inven-
tion using ~arious solven~s wlth a m-nimum amount of experimentation.
With the ele~trographic recording elements of the present in-
vention, the supp~rt and intermediate electrically-conductive layers
would be the same and can be formed of any of the above described
materials. The upper layer is formed of a material having a high
volume resistivity, prefexably a minimum of 1012 ohm-centimeters.
Typical materials are as follows: styrenebutadiene copolymers;
silicone resins; styrene-alkyd resins; silicone alkyd resins; soya-
alkyd resins; poly(v~nyl chloride); poly(vinylidene chloride);
vinylidene chloride-acrylonitr * e copolymers; poly~vinyl acetate);
`i vinyl acetate-vinyl chloride~copolymers; poly(vinyl acetals), such
as polytvinyl butyral); polyacrylic and methacrylic esters, such
as polytmethylmetha~rylate), poly(n-butylmethacrylate), poly~iso-
butyl methacrylate), etcO; polystyrene, nitrated polystyrene; poly-
methylstyrene; isobutylene po1ymers; polyesters, such as poly(ethyl-
enealkaryloxyalkylene terephthalate~; phenol-formaldehyde resins;
ketone resins; polyamide; polycarbcnates; polythiocarbonates; poly-
(ethyleneglycol-co-b~shydroxyethoxphenyl-propane terephthalate);
etc. Methods~of making resins o~ this type have been described in
the prior ar~ for example, styrene-alkyd resins can be prepared
according to the method described in U.S. Patents 2,361,019 and
2,250,423. Suitable resins of the type contemplated for use in the
photoconductive layers of the invention are sold under such trade
J' names as Vitel* PE-101, Cymac*, Piccopale* 100, and Saran* F-~20 -
and Lexan* 105~ O~her ~ypes of binders which can be used in the
photoconductive layers of the invention include such materials as
paraffin, mineral waxes, etc. ~-
With regard to the electri~ally-conductive back layer used in
*Registered ~rademark
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certain embodimenrs, this can be formed of materials which are
similar to or the ~ame as the _ntermedia~e electrically-conductive
layer. In addikicn, both of these conductive layers can be formed
of electrically-~onducti~e materials per se instead of conductive
pigments dispersed in a binder. For example, U~S. Patent No.
; 3,011,918 discloses a oonductive resinous polymer, polyvinyl benzyl
trimethyl ammonium chloride, whi~ch is itsel~ conductive. Alterna-
tively, these layers may be made by printing or coatin~ the support
suxface with an elec~rocondu~tive ink, or a metal or a suitable
semi-conductor may be vacuum deposi~ed or sputtered onto the
support. See, for example, U.S. Patent Nos. 3,207,625; 2,756,16i;
3,148,083; 3,245,833; and 3,428,451.
` ` As will be apparent from th& above description, the preferred
compositions are ~hose which provide a flexible recording member,
r ~ 15 particularly thcse matexials are preferred whi~h are flexible and
transparent to prov-de a transparent recording member. In addition,
it is preferred that the suppor~ be substantially electrically
insu~ating in nature.
. . . .
While the inv~ention has been shown and described with reference
20~ to p~eferred embodiments thereof, it is to be expressly understood
` that ~arious changes and modîfi~ations may be made without departing
from the spirit and s~ope of 'the present invention, as defined in
;
~ the appended ~lai~. :
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