Imaging element comprising an electrically-conductive layer containing particles of a metal antimonate

Imaging elements, such as photographic, electrostatographic and thermal imaging elements, are comprised of a support, an image-forming layer and an electrically-conductive layer comprising a dispersion in a film-forming binder of fine particles of an electronically-conductive metal antimonate. Use of metal antimonate particles provides a controlled degree of electrical conductivity and beneficial chemical, physical and optical properties which adapt the electrically-conductive layer for such purposes as providing protection against static or serving as an electrode which takes part in an image-forming process.

FIELD OF THE INVENTION 
This invention relates in general to imaging elements, such as 
photographic, electrostatographic and thermal imaging elements, and in 
particular to imaging elements comprising a support, an image-forming 
layer and an electrically-conductive layer. More specifically, this 
invention relates to electrically-conductive layers containing 
electronically-conductive particles and to the use of such 
electrically-conductive layers in imaging elements for such purposes as 
providing protection against the generation of static electrical charges 
or serving as an electrode which takes part in an image-forming process. 
BACKGROUND OF THE INVENTION 
Problems associated with the formation and discharge of electrostatic 
charge during the manufacture and utilization of photographic film and 
paper have been recognized for many years by the photographic industry. 
The accumulation of charge on film or paper surfaces leads to the 
attraction of dust, which can produce physical defects. The discharge of 
accumulated charge during or after the application of the sensitized 
emulsion layer(s) can produce irregular fog patterns or "static marks" in 
the emulsion. The severity of static problems has been exacerbated greatly 
by increases in the sensitivity of new emulsions, increases in coating 
machine speeds, and increases in post-coating drying efficiency. The 
charge generated during the coating process results primarily from the 
tendency of webs of high dielectric polymeric film base to charge during 
winding and unwinding operations (unwinding static), during transport 
through the coating machines (transport static), and during post-coating 
operations such as slitting and spooling. Static charge can also be 
generated during the use of the finished photographic film product. In an 
automatic camera, the winding of roll film out of and back into the film 
cassette, especially in a low relative humidity environment, can result in 
static charging. Similarly, high-speed automated film processing can 
result in static charge generation. Sheet films are especially subject to 
static charging during removal from light-tight packaging (e.g., x-ray 
films). 
It is generally known that electrostatic charge can be dissipated 
effectively by incorporating one or more electrically-conductive 
"antistatic" layers into the film structure. Antistatic layers can be 
applied to one or to both sides of the film base as subbing layers either 
beneath or on the side opposite to the light-sensitive silver halide 
emulsion layers. An antistatic layer can alternatively be applied as an 
outer coated layer either over the emulsion layers or on the side of the 
film base opposite to the emulsion layers or both. For some applications, 
the antistatic agent can be incorporated into the emulsion layers. 
Alternatively, the antistatic agent can be directly incorporated into the 
film base itself. 
A wide variety of electrically-conductive materials can be incorporated 
into antistatic layers to produce a wide range of conductivities. Most of 
the traditional antistatic systems for photographic applications employ 
ionic conductors. Charge is transferred in ionic conductors by the bulk 
diffusion of charged species through an electrolyte. Antistatic layers 
containing simple inorganic salts, alkali metal salts of surfactants, 
ionic conductive polymers, polymeric electrolytes containing alkali metal 
salts, and colloidal metal oxide sols (stabilized by metal salts) have 
been described previously. The conductivities of these ionic conductors 
are typically strongly dependent on the temperature and relative humidity 
in their environment. At low humidities and temperatures, the diffusional 
mobilities of the ions are greatly reduced and conductivity is 
substantially decreased. At high humidities, antistatic backcoatings often 
absorb water, swell, and soften. In roll film, this results in adhesion of 
the backcoating to the emulsion side of the film. Also, many of the 
inorganic salts, polymeric electrolytes, and low molecular weight 
surfactants used are water-soluble and are leached out of the antistatic 
layers during processing, resulting in a loss of antistatic function. 
Colloidal metal oxide sols which exhibit ionic conductivity when included 
in antistatic layers are often used in imaging elements. Typically, alkali 
metal salts or anionic surfactants are used to stabilize these sols. A 
thin antistatic layer consisting of a gelled network of colloidal metal 
oxide particles (e.g., silica, antimony pentoxide, alumina, titania, 
stannic oxide, zirconia) with an optional polymeric binder to improve 
adhesion to both the support and overlying emulsion layers has been 
disclosed in EP 250,154. An optional ambifunctional silane or titanate 
coupling agent can be added to the gelled network to improve adhesion to 
overlying emulsion layers (e.g., EP 301,827; U.S. Pat. No. 5,204,219) 
along with an optional alkali metal orthosilicate to minimize loss of 
conductivity by the gelled network when it is overcoated with 
gelatin-containing layers (U.S. Pat. No. 5,236,818). Also, it has been 
pointed out that coatings containing colloidal metal oxides (e.g., 
antimony pentoxide, alumina, tin oxide, indium oxide) and colloidal silica 
with an organopolysiloxane binder afford enhanced abrasion resistance as 
well as provide antistatic function (U.S. Pat. Nos. 4,442,168 and 
4,571,365). 
Antistatic systems employing electronic conductors have also been 
described. Because the conductivity depends predominantly on electronic 
mobilities rather than ionic mobilities, the observed electronic 
conductivity is independent of relative humidity and only slightly 
influenced by the ambient temperature. Antistatic layers have been 
described which contain conjugated polymers, conductive carbon particles 
or semiconductive inorganic particles. 
Trevoy (U.S. Pat. No. 3,245,833) has taught the preparation of conductive 
coatings containing semiconductive silver or copper iodide dispersed as 
particles less than 0.1 .mu.m in size in an insulating film-forming 
binder, exhibiting a surface resistivity of 10.sup.2 to 10.sup.11 ohms per 
square. The conductivity of these coatings is substantially independent of 
the relative humidity. Also, the coatings are relatively clear and 
sufficiently transparent to permit their use as antistatic coatings for 
photographic film. However, if a coating containing copper or silver 
iodides was used as a subbing layer on the same side of the film base as 
the emulsion, Trevoy found (U.S. Pat. No. 3,428,451) that it was necessary 
to overcoat the conductive layer with a dielectric, water-impermeable 
barrier layer to prevent migration of semiconductive salt into the silver 
halide emulsion layer during processing. Without the barrier layer, the 
semiconductive salt could interact deleteriously with the silver halide 
layer to form fog and a loss of emulsion sensitivity. Also, without a 
barrier layer, the semiconductive salts are solubilized by processing 
solutions, resulting in a loss of antistatic function. 
Another semiconductive material has been disclosed by Nakagiri and Inayama 
(U.S. Pat. No. 4,078,935) as being useful in antistatic layers for 
photographic applications. Transparent, binderless, electrically 
semiconductive metal oxide thin films were formed by oxidation of thin 
metal films which had been vapor deposited onto film base. Suitable 
transition metals include titanium, zirconium, vanadium, and niobium. The 
microstructure of the thin metal oxide films is revealed to be non-uniform 
and discontinuous, with an "island" structure almost "particulate" in 
nature. The surface resistivity of such semiconductive metal oxide thin 
films is independent of relative humidity and reported to range from 
10.sup.5 to 10.sup.9 ohms per square. However, the metal oxide thin films 
are unsuitable for photographic applications since the overall process 
used to prepare these thin films is complicated and costly, abrasion 
resistance of these thin films is low, and adhesion of these thin films to 
the base is poor. 
A highly effective antistatic layer incorporating an "amorphous" 
semiconductive metal oxide has been disclosed by Guestaux (U.S. Pat. No. 
4,203,769). The antistatic layer is prepared by coating an aqueous 
solution containing a colloidal gel of vanadium pentoxide onto a film 
base. The colloidal vanadium pentoxide gel typically consists of 
entangled, high aspect ratio, flat ribbons 50-100 .ANG. wide, about 10 
.ANG. thick, and 1,000-10,000 .ANG. long. These ribbons stack flat in the 
direction perpendicular to the surface when the gel is coated onto the 
film base. This results in electrical conductivities for thin films of 
vanadium pentoxide gels (about 1 .OMEGA..sup.-1 cm.sup.-1) which are 
typically about three orders of magnitude greater than is observed for 
similar thickness films containing crystalline vanadium pentoxide 
particles. In addition, low surface resistivities can be obtained with 
very low vanadium pentoxide coverages. This results in low optical 
absorption and scattering losses. Also, the thin films are highly adherent 
to appropriately prepared film bases. However, vanadium pentoxide is 
soluble at high pH and must be overcoated with a nonpermeable, hydrophobic 
barrier layer in order to survive processing. When used with a conductive 
subbing layer, the barrier layer must be coated with a hydrophilic layer 
to promote adhesion to emulsion layers above. (See Anderson et at, U.S. 
Pat. No. 5,006,451.) 
Conductive fine particles of crystalline metal oxides dispersed with a 
polymeric binder have been used to prepare optically transparent, humidity 
insensitive, antistatic layers for various imaging applications. Many 
different metal oxides--such as ZnO, TiO.sub.2, ZrO.sub.2, SnO.sub.2, 
Al.sub.2 O.sub.3, In.sub.2 O.sub.3, SiO.sub.2, MgO, BaO, MoO.sub.3 and 
V.sub.2 O.sub.5 --are alleged to be useful as antistatic agents in 
photographic elements or as conductive agents in electrostatographic 
elements in such patents as U.S. Pat. Nos. 4,275,103, 4,394,441, 
4,416,963, 4,418,141, 4,431,764, 4,495,276, 4,571,361, 4,999,276 and 
5,122,445. However, many of these oxides do not provide acceptable 
performance characteristics in these demanding environments. Preferred 
metal oxides are antimony doped tin oxide, aluminum doped zinc oxide, and 
niobium doped titanium oxide. Surface resistivities are reported to range 
from 10.sup.6 -10.sup.9 ohms per square for antistatic layers containing 
the preferred metal oxides. In order to obtain high electrical 
conductivity, a relatively large amount (0.1-10 g/m.sup.2) of metal oxide 
must be included in the antistatic layer. This results in decreased 
optical transparency for thick antistatic coatings. The high values of 
refractive index (&gt;2.0) of the preferred metal oxides necessitates that 
the metal oxides be dispersed in the form of ultrafine (&lt;0.1 .mu.m) 
particles in order to minimize light scattering (haze) by the antistatic 
layer. 
Antistatic layers comprising electro-conductive ceramic particles, such as 
particles of TiN, NbB.sub.2, TiC, LaB.sub.6 or MoB, dispersed in a binder 
such as a water-soluble polymer or solvent-soluble resin are described in 
Japanese Kokai No. 4/55492, published Feb. 24, 1992. 
Fibrous conductive powders comprising antimony-doped tin oxide coated onto 
non-conductive potassium titanate whiskers have been used to prepare 
conductive layers for photographic and electrographic applications. Such 
materials are disclosed, for example, in U.S. Pat. Nos., 4,845,369 and 
5,116,666. Layers containing these conductive whiskers dispersed in a 
binder reportedly provide improved conductivity at lower volumetric 
concentrations than other conductive fine particles as a result of their 
higher aspect ratio. However, the benefits obtained as a result of the 
reduced volume percentage requirements are offset by the fact that these 
materials are relatively large in size such as 10 to 20 micrometers in 
length, and such large size results in increased light scattering and hazy 
coatings. 
Use of a high volume percentage of conductive particles in an 
electro-conductive coating to achieve effective antistatic performance can 
result in reduced transparency due to scattering losses and in the 
formation of brittle layers that are subject to cracking and exhibit poor 
adherence to the support material. It is thus apparent that it is 
extremely difficult to obtain non-brittle, adherent, highly transparent, 
colorless electro-conductive coatings with humidity-independent 
process-surviving antistatic performance. 
The requirements for antistatic layers in silver halide photographic films 
are especially demanding because of the stringent optical requirements. 
Other types of imaging elements such as photographic papers and thermal 
imaging elements also frequently require the use of an antistatic layer 
but, generally speaking, these imaging elements have less stringent 
requirements. 
Electrically-conductive layers are also commonly used in imaging elements 
for purposes other than providing static protection. Thus, for example, in 
electrostatographic imaging it is well known to utilize imaging elements 
comprising a support, an electrically-conductive layer that serves as an 
electrode, and a photoconductive layer that serves as the image-forming 
layer. Electrically-conductive agents utilized as antistatic agents in 
photographic silver halide imaging elements are often also useful in the 
electrode layer of electrostatographic imaging elements. 
As indicated above, the prior art on electrically-conductive layers in 
imaging elements is extensive and a very wide variety of different 
materials have been proposed for use as the electrically-conductive agent. 
There is still, however, a critical need in the art for improved 
electrically-conductive layers which are useful in a wide variety of 
imaging elements, which can be manufactured at reasonable cost, which are 
resistant to the effects of humidity change, which are durable and 
abrasion-resistant, which are effective at low coverage, which are 
adaptable to use with transparent imaging elements, which do not exhibit 
adverse sensitometric or photographic effects, and which are substantially 
insoluble in solutions with which the imaging element typically comes in 
contact, for example, the aqueous alkaline developing solutions used to 
process silver halide photographic films. 
It is toward the objective of providing improved electrically-conductive 
layers that more effectively meet the diverse needs of imaging 
elements--especially of silver halide photographic films but also of a 
wide range of other imaging elements--than those of the prior art that the 
present invention is directed. 
SUMMARY OF THE INVENTION 
In accordance with this invention, an imaging element for use in an 
image-forming process comprises a support, an image-forming layer, and an 
electrically-conductive layer; the electrically-conductive layer 
comprising a dispersion in a film-forming binder of fine particles of an 
electronically-conductive metal antimonate. 
The imaging elements of this invention can contain one or more 
image-forming layers and one or more electrically-conductive layers and 
such layers can be coated on any of a very wide variety of supports. Use 
of an electronically-conductive metal antimonate dispersed in a suitable 
film-forming binder enables the preparation of a thin, highly conductive, 
transparent layer which is strongly adherent to photographic supports as 
well as to overlying layers such as emulsion layers, pelloids, topcoats, 
backcoats, and the like. The electrical conductivity provided by the 
conductive layer of this invention is independent of relative humidity and 
persists even after exposure to aqueous solutions with a wide range of pH 
values (i.e., 2.ltoreq.pH.ltoreq.13) such as are encountered in the 
processing of photographic elements. 
For use in imaging elements, the average particle size of the 
electronically-conductive metal antimonate is preferably less than about 
one micrometer and more preferably less than about 0.5 micrometers. For 
use in imaging elements where a high degree of transparency is important, 
it is preferred to use colloidal particles of an electronically-conductive 
metal antimonate, which typically have an average particle size in the 
range of 0.01 to 0.05 micrometers.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The imaging elements of this invention can be of many different types 
depending on the particular use for which they are intended. Such elements 
include, for example, photographic, electrostatographic, 
photothermographic, migration, electrothermographic, dielectric recording 
and thermal-dye-transfer imaging elements. 
Photographic elements which can be provided with an antistatic layer in 
accordance with this invention can differ widely in structure and 
composition. For example, they can vary greatly in regard to the type of 
support, the number and composition of the image-forming layers, and the 
kinds of auxiliary layers that are included in the elements. In 
particular, the photographic elements can be still films, motion picture 
films, x-ray films, graphic arts films, paper prints or microfiche. They 
can be black-and-white elements, color elements adapted for use in a 
negative-positive process, or color elements adapted for use in a reversal 
process. 
Photographic elements can comprise any of a wide variety of supports. 
Typical supports include cellulose nitrate film, cellulose acetate film, 
poly(vinyl acetal) film, polystyrene film, poly(ethylene terephthalate) 
film, poly(ethylene naphthalate) film, polycarbonate film, glass, metal, 
paper, polymer-coated paper, and the like. The image-forming layer or 
layers of the element typically comprise a radiation-sensitive agent, 
e.g., silver halide, dispersed in a hydrophilic water-permeable colloid. 
Suitable hydrophilic vehicles include both naturally-occurring substances 
such as proteins, for example, gelatin, gelatin derivatives, cellulose 
derivatives, polysaccharides such as dextran, gum arabic, and the like, 
and synthetic polymeric substances such as water-soluble polyvinyl 
compounds like poly(vinylpyrrolidone), acrylamide polymers, and the like. 
A particularly common example of an image-forming layer is a 
gelatin-silver halide emulsion layer. 
In electrostatography an image comprising a pattern of electrostatic 
potential (also referred to as an electrostatic latent image) is formed on 
an insulative surface by any of various methods. For example, the 
electrostatic latent image may be formed electrophotographically (i.e., by 
imagewise radiation-induced discharge of a uniform potential previously 
formed on a surface of an electrophotographic element comprising at least 
a photoconductive layer and an electrically-conductive substrate), or it 
may be formed by dielectric recording (i.e., by direct electrical 
formation of a pattern of electrostatic potential on a surface of a 
dielectric material). Typically, the electrostatic latent image is then 
developed into a toner image by contacting the latent image with an 
electrographic developer (if desired, the latent image can be transferred 
to another surface before development). The resultant toner image can then 
be fixed in place on the surface by application of heat and/or pressure or 
other known methods (depending upon the nature of the surface and of the 
toner image) or can be transferred by known means to another surface, to 
which it then can be similarly fixed. 
In many electrostatographic imaging processes, the surface to which the 
toner image is intended to be ultimately transferred and fixed is the 
surface of a sheet of plain paper or, when it is desired to view the image 
by transmitted light (e.g., by projection in an overhead projector), the 
surface of a transparent film sheet element. 
In electrostatographic elements, the electrically-conductive layer can be a 
separate layer, a part of the support layer or the support layer. There 
are many types of conducting layers known to the electrostatographic art, 
the most common being listed below: 
(a) metallic laminates such as an aluminum-paper laminate, 
(b) metal plates, e.g., aluminum, copper, zinc, brass, etc., 
(c) metal foils such as aluminum foil, zinc foil, etc., 
(d) vapor deposited metal layers such as silver, aluminum, nickel, etc., 
(e) semiconductors dispersed in resins such as poly(ethylene terephthalate) 
as described in U.S. Pat. No. 3,245,833, 
(f) electrically conducting salts such as described in U.S. Pat. Nos. 
3,007,801 and 3,267,807. 
Conductive layers (d), (e) and (f) can be transparent and can be employed 
where transparent elements are required, such as in processes where the 
element is to be exposed from the back rather than the front or where the 
element is to be used as a transparency. 
Thermally processable imaging elements, including films and papers, for 
producing images by thermal processes are well known. These elements 
include thermographic elements in which an image is formed by imagewise 
heating the element. Such elements are described in, for example, Research 
Disclosure, June 1978, Item No. 17029; U.S. Pat. No. 3,457,075; U.S. Pat. 
No. 3,933,508; and U.S. Pat. No. 3,080,254. 
Photothermographic elements typically comprise an oxidation-reduction 
image-forming combination which contains an organic silver salt oxidizing 
agent, preferably a silver salt of a long-chain fatty acid. Such organic 
silver salt oxidizing agents are resistant to darkening upon illumination. 
Preferred organic silver salt oxidizing agents are silver salts of 
long-chain fatty acids containing 10 to 30 carbon atoms. Examples of 
useful organic silver salt oxidizing agents are silver behenate, silver 
stearate, silver oleate, silver laurate, silver hydroxystearate, silver 
caprate, silver myristate and silver palmitate. Combinations of organic 
silver salt oxidizing agents are also useful. Examples of useful silver 
salt oxidizing agents which are not silver salts of long-chain fatty acids 
include, for example, silver benzoate and silver benzotriazole. 
Photothermographic elements also comprise a photosensitive component which 
consists essentially of photographic silver halide. In photothermographic 
materials it is believed that the latent image silver from the silver 
halide acts as a catalyst for the oxidation-reduction image-forming 
combination upon processing. A preferred concentration of photographic 
silver halide is within the range of about 0.01 to about 10 moles of 
photographic silver halide per mole of organic silver salt oxidizing 
agent, such as per mole of silver behenate, in the photothermographic 
material. Other photosensitive silver salts are useful in combination with 
the photographic silver halide if desired. Preferred photographic silver 
halides are silver chloride, silver bromide, silver bromoiodide, silver 
chlorobromoiodide and mixtures of these silver halides. Very fine grain 
photographic silver halide is especially useful. 
Migration imaging processes typically involve the arrangement of particles 
on a softenable medium. Typically, the medium, which is solid and 
impermeable at room temperature, is softened with heat or solvents to 
permit particle migration in an imagewise pattern. 
As disclosed in R. W. Gundlach, "Xeroprinting Master with Improved Contrast 
Potential", Xerox Disclosure Journal, Vol. 14, No. 4, July/August 1984, 
pages 205-06, migration imaging can be used to form a xeroprinting master 
element. In this process, a monolayer of photosensitive particles is 
placed on the surface of a layer of polymeric material which is in contact 
with a conductive layer. After charging, the element is subjected to 
imagewise exposure which softens the polymeric material and causes 
migration of particles where such softening occurs (i.e., image areas). 
When the element is subsequently charged and exposed, the image areas (but 
not the non-image areas) can be charged, developed, and transferred to 
paper. 
Another type of migration imaging technique, disclosed in U.S. Pat. No. 
4,536,457 to Tam, U.S. Pat. No. 4,536,458 to Ng, and U.S. Pat. No. 
4,883,731 to Tam et al, utilizes a solid migration imaging element having 
a substrate and a layer of softenable material with a layer of 
photosensitive marking material deposited at or near the surface of the 
softenable layer. A latent image is formed by electrically charging the 
member and then exposing the element to an imagewise pattern of light to 
discharge selected portions of the marking material layer. The entire 
softenable layer is then made permeable by application of the marking 
material, heat or a solvent, or both. The portions of the marking material 
which retain a differential residual charge due to light exposure will 
then migrate into the softened layer by electrostatic force. 
An imagewise pattern may also be formed with colorant particles in a solid 
imaging element by establishing a density differential (e.g., by particle 
agglomeration or coalescing) between image and non-image areas. 
Specifically, colorant particles are uniformly dispersed and then 
selectively migrated so that they are dispersed to varying extents without 
changing the overall quantity of particles on the element. 
Another migration imaging technique involves heat development, as described 
by R. M. Schaffert, Electrophotography, (Second Edition, Focal Press, 
1980), pp. 44-47 and U.S. Pat. No. 3,254,997. In this procedure, an 
electrostatic image is transferred to a solid imaging element, having 
colloidal pigment particles dispersed in a heat-softenable resin film on a 
transparent conductive substrate. After softening the film with heat, the 
charged colloidal particles migrate to the oppositely charged image. As a 
result, image areas have an increased particle density, while the 
background areas are less dense. 
An imaging process known as "laser toner fusion", which is a dry 
electrothermographic process, is also of significant commercial 
importance. In this process, uniform dry powder toner depositions on 
non-photosensitive films, papers, or lithographic printing plates are 
imagewise exposed with high power (0.2-0.5 W) laser diodes thereby, 
"tacking" the toner particles to the substrate(s). The toner layer is 
made, and the non-imaged toner is removed, using such techniques as 
electrographic "magnetic brush" technology similar to that found in 
copiers. A final blanket fusing stem may also be needed, depending on the 
exposure levels. 
Another example of imaging elements which employ an antistatic layer are 
dye-receiving elements used in thermal dye transfer systems. 
Thermal dye transfer systems are commonly used to obtain prints from 
pictures which have been generated electronically from a color video 
camera. According to one way of obtaining such prints, an electronic 
picture is first subjected to color separation by color filters. The 
respective color-separated images are then converted into electrical 
signals. These signals are then operated on to produce cyan, magenta and 
yellow electrical signals. These signals are then transmitted to a thermal 
printer. To obtain the print, a cyan, magenta or yellow dye-donor element 
is placed face-to-face with a dye-receiving element. The two are then 
inserted between a thermal printing head and a platen roller. A line-type 
thermal printing head is used to apply heat from the back of the dye-donor 
sheet. The thermal printing head has many heating elements and is heated 
up sequentially in response to the cyan, magenta and yellow signals. The 
process is then repeated for the other two colors. A color hard copy is 
thus obtained which corresponds to the original picture viewed on a 
screen. Further details of this process and an apparatus for carrying it 
out are described in U.S. Pat. No. 4,621,271. 
In EPA No. 194,106, antistatic layers are disclosed for coating on the back 
side of a dye-receiving element. Among the materials disclosed for use are 
electrically-conductive inorganic powders such as a "fine powder of 
titanium oxide or zinc oxide." 
Another type of image-forming process in which the imaging element can make 
use of an electrically-conductive layer is a process employing an 
imagewise exposure to electric current of a dye-forming 
electrically-activatable recording element to thereby form a developable 
image followed by formation of a dye image, typically by means of thermal 
development. Dye-forming electrically activatable recording elements and 
processes are well known and are described in such patents as U.S. Pat. 
Nos. 4,343,880 and 4,727,008. 
In the imaging elements of this invention, the image-forming layer can be 
any of the types of image-forming layers described above, as well as any 
other image-forming layer known for use in an imaging element. 
All of the imaging processes described hereinabove, as well as many others, 
have in common the use of an electrically-conductive layer as an electrode 
or as an antistatic layer. The requirements for a useful 
electrically-conductive layer in an imaging environment are extremely 
demanding and thus the art has long sought to develop improved 
electrically-conductive layers exhibiting the necessary combination of 
physical, optical and chemical properties. 
As described hereinabove, the imaging elements of this invention include at 
least one electrically-conductive layer comprising a dispersion in a 
film-forming binder of fine particles of an electronically-conductive 
metal antimonate. 
Metal antimonates which are preferred for use in this invention have rutile 
or rutile-related crystallographic structures and are represented by 
either Formula (I) or Formula (II) below: 
EQU (I) M.sup.+2 Sb.sup.+5.sub.2 O.sub.6 
where M.sup.+2 =Zn.sup.+2, Ni.sup.+2, Mg.sup.+2, Fe.sup.+2, Cu.sup.+2, 
Mn.sup.+2, Co.sup.+2 
EQU (II) M.sup.+3 Sb.sup.+5 O.sub.4 
where M.sup.+3 =In.sup.+3, Al.sup.+3, Sc.sup.+3, Cr.sup.+3, Fe.sup.+3, 
Ga.sup.+3. 
Several colloidal conductive metal antimonates are commercially available 
from Nissan Chemical Company in the form of dispersions in organic 
solvents. Alternatively, U.S. Pat. Nos. 4,169,104 and 4,110,247 teach a 
method for preparing compound I (M.sup.+2 =Zn.sup.+2, Ni.sup.+2, 
Cu.sup.+2, Fe.sup.+2, etc.) by treating an aqueous solution of potassium 
antimonate (i.e., KSb(OH).sub.6) with an aqueous solution of an 
appropriate soluble metal salt (e.g., chloride, nitrate, sulfate, etc.) to 
form a gelatinous precipitate of the corresponding insoluble hydrate of 
compound I. The isolated hydrated gels are then washed with water to 
remove the excess potassium ions and salt anions. The washed gels are 
peptized by treatment with an aqueous solution of organic base (e.g., 
triethanolamine, tripropanolamine, diethanolamine, monoethanolamine, 
quaternary ammonium. hydroxides, etc.) at temperatures of 25.degree. to 
150.degree. C. as taught in U.S. Pat. No. 4,589,997 for the preparation of 
colloidal antimony pentoxide sols. Other methods used to prepare colloidal 
sols of metal antimony oxide compounds have been reported. A sol-gel 
process has been described by Westin and Nygren (J. Mater. Sci., 27, 
1617-25 (1992); J. Mater. Chem., 3, 367-71 (1993) in which precursors of I 
comprising binary alkoxide complexes of antimony and a bivalent metal are 
hydrolyzed to give amorphous gels of agglomerated colloidal particles of 
hydrated I. Heat treatment of such hydrated gels at moderate temperatures 
(&lt;800.degree. C.) is reported to form anhydrous particles of I of the same 
size as the colloidal particles in the gels. Further, a colloidal compound 
I prepared by such methods can be made conductive through appropriate 
thermal treatment in a reducing or inert atmosphere. 
In order to be suitable for use in antistatic coatings for critical 
photographic applications, the conductive metal antimonates must have a 
small average particle size. Small particle size minimizes light 
scattering which would result in reduced optical transparency of the 
coating. The relationship between the size of a particle, the ratio of its 
refractive index to that of the medium in which it is incorporated, the 
wavelength of the incident light, and the light scattering efficiency of 
the particle is described by Mie scattering theory (G. Mie, Ann, Physik., 
25, 377 (1908). A discussion of this topic as it is relevant to 
photographic applications has been presented by T. H. James ("The Theory 
of the Photographic Process", 4th ed., Rochester: EKC, 1977). In the case 
of electroconductive particles of formula I or II coated in a thin layer 
using a typical photographic gelatin binder system, it is necessary to use 
powders with an average particle size less than about 0.2 .mu.m in order 
to limit the scattering of light at a wavelength of 550 nm to less than 
20%. For shorter wavelength light, such as the ultraviolet light used to 
expose some daylight-insensitive graphic arts films, electroconductive 
particles with an average size much less than about 0.1 .mu.m are 
preferred. 
In addition to the optical requirements, a very small average particle size 
is needed to ensure that even in thin coatings there is a multiplicity of 
interconnected chains or networks of conductive particles which afford 
multiple electrically-conductive pathways through the layer and result in 
electrical continuity. The very small average particle size of conductive 
colloidal metal antimonates (typically 0.01-0.05 .mu.m) results in 
multiple conductive pathways in the thin antistatic layers of the present 
invention. 
In the case of other commercially available conductive metal oxide 
pigments, the average particle size (typically 0.5-0.9 .mu.m) can be 
reduced by various mechanical milling processes well known in the art of 
pigment dispersion and paint making. However, most of these metal oxide 
pigments are not sufficiently chemically homogeneous to permit size 
reduction by attrition to the colloidal size required to ensure both 
optical transparency and multiple conductive pathways in thin coatings and 
still retain sufficient interparticle conductivity to be useful in an 
antistatic layer. 
Binders useful in antistatic layers containing conductive metal antimonate 
particles include: water-soluble polymers such as gelatin, gelatin 
derivatives, maleic acid anhydride copolymers; cellulose compounds such as 
carboxymethyl cellulose, hydroxyethyl cellulose, cellulose acetate 
butyrate, diacetyl cellulose or triacetyl cellulose; synthetic hydrophilic 
polymers such as polyvinyl alcohol, poly-N-vinylpyrrolidone, acrylic acid 
copolymers, polyacrylamides, their derivatives and partially hydrolyzed 
products, vinyl polymers and copolymers such as polyvinyl acetate and 
polyacrylate acid esters; derivatives of the above polymers; and other 
synthetic resins. Other suitable binders include aqueous emulsions of 
addition-type polymers and interpolymers prepared from ethylenically 
unsaturated monomers such as acrylates including acrylic acid, 
methacrylates including methacrylic acid, acrylamides and methacrylamides, 
itaconic acid and its half-esters and diesters, styrenes including 
substituted styrenes, acrylonitrile and methacrylonitrile, vinyl acetates, 
vinyl ethers, vinyl and vinylidene halides, olefins, and aqueous 
dispersions of polyurethanes or polyesterionomers. 
Solvents useful for preparing coatings of conductive metal antimonate 
particles include: water, alcohols such as methanol, ethanol, propanol, 
isopropanol; ketones such as acetone, methylethyl ketone, and 
methylisobutyl ketone; esters such as methyl acetate, and ethyl acetate; 
glycol ethers such as methyl cellusolve, ethyl cellusolve; and mixtures 
thereof. 
In addition to binders and solvents, other components that are well known 
in the photographic art may also be present in the electrically-conductive 
layer. These additional components include: surfactants and coating aids, 
thickeners, crosslinking agents or hardeners, soluble and/or solid 
particle dyes, antifoggants, matte beads, lubricants, and others. 
The ratio of the amount of the particles of metal antimonate to the binder 
in the dispersion is one of the important factors which influence the 
ultimate conductivity achieved by the coated layer. If this ratio is 
small, little or no antistatic property is exhibited. If this ratio is 
very large, adhesion between the conductive layer and the support or 
overlying layers can be diminished. The optimum ratio of conductive 
particles to binder varies depending on the particle size, binder type, 
and conductivity requirements. The volume fraction of conductive metal 
antimonate particles is preferably in the range of from about 20 to 80% of 
the volume of the coated layer. The dry coated weight of the conductive 
layer is preferably in the range of from about 0.1 to about 10 g/m.sup.2. 
The concentration of conductive metal antimonate present in the coated 
layer will vary depending on the weight density of the particular compound 
used. 
Dispersions of conductive metal antimonate particles formulated with binder 
and additives can be coated onto a variety of photographic supports. 
Suitable film supports include polyethylene terephthalate, polyethylene 
naphthalate, polycarbonate, polystyrene, cellulose nitrate, cellulose 
acetate, cellulose acetate butyrate, cellulose acetate propionate, and 
laminates thereof. Film supports can be either transparent or opaque 
depending on the application. Transparent film supports can be either 
colorless or colored by the addition of a dye or pigment. Film supports 
can be surface treated by various processes including corona discharge, 
glow discharge, UV exposure, solvent washing or overcoated with polymers 
such as vinylidene chloride containing copolymers, butadiene-based 
copolymers, glycidyl acrylate or methacrylate containing copolymers, or 
maleic anhydride containing copolymers. Suitable paper supports include 
polyethylene-, polypropylene-, and ethylene-butylene copolymer-coated or 
laminated paper and synthetic papers. 
The formulated dispersions can be applied to the aforementioned film or 
paper supports by any of a variety of well-known coating methods. 
Handcoating techniques include using a coating rod or knife or a doctor 
blade. Machine coating methods include skim pan/air knife coating, roller 
coating, gravure coating, curtain coating, bead coating or slide coating. 
The antistatic layer or layers containing the conductive metal antimonate 
particles can be applied to the support in various configurations 
depending upon the requirements of the specific application. In the case 
of photographic elements for graphics arts application, an antistatic 
layer can be applied to a polyester film base during the support 
manufacturing process after orientation of the cast resin on top of a 
polymeric undercoat layer. The antistatic layer can be applied as a 
subbing layer under the sensitized emulsion, on the side of the support 
opposite the emulsion or on both sides of the support. When the antistatic 
layer is applied as a subbing layer under the sensitized emulsion, it is 
not necessary to apply any intermediate layers such as barrier layers or 
adhesion promoting layers between it and the sensitized emulsion, although 
they can optionally be present. Alternatively, the antistatic layer can be 
applied as part of a multi-component curl control layer on the side of the 
support opposite to the sensitized emulsion. The antistatic layer would 
typically be located closest to the support. An intermediate layer, 
containing primarily binder and antihalation dyes functions as an 
antihalation layer. The outermost layer containing binder, matte, and 
surfactants functions as a protective overcoat. Other addenda, such as 
polymer lattices to improve dimensional stability, hardeners or 
crosslinking agents, and various other conventional additives as well as 
conductive metal antimonate particles can be present optionally in any or 
all of the layers. 
In the case of photographic elements for direct or indirect x-ray 
applications, the antistatic layer can be applied as a subbing layer on 
either side or both sides of the film support. In one type of photographic 
element, the antistatic subbing layer is applied to only one side of the 
film support and the sensitized emulsion coated on both sides of the film 
support. Another type of photographic element contains a sensitized 
emulsion on only one side of the support and a pelloid containing gelatin 
on the opposite side of the support. An antistatic layer can be applied 
under the sensitized emulsion or, preferably, the pelloid. Additional 
optional layers can be present. In another photographic element for x-ray 
applications, an antistatic subbing layer can be applied either under or 
over a gelatin subbing layer containing an antihalation dye or pigment. 
Alternatively, both antihalation and antistatic functions can be combined 
in a single layer containing conductive particles, antihalation dye, and a 
binder. This hybrid layer can be coated on one side of a film support 
under the sensitized emulsion. 
The conductive layer of this invention may also be used as the outermost 
layer of an imaging element, for example, as the protective overcoat that 
overlies a photographic emulsion layer. Alternatively, the conductive 
layer can function as an abrasion-resistant backing layer applied on the 
side of the film support opposite to the imaging layer. 
It is also contemplated that the electrically-conductive layer described 
herein can be used in imaging elements in which a relatively transparent 
layer containing magnetic particles dispersed in a binder is included. The 
electrically-conductive layer of this invention functions well in such a 
combination and gives excellent photographic results. Transparent magnetic 
layers are well known and are described, for example, in U.S. Pat. No. 
4,990,276, European Patent 459,349, and Research Disclosure, Item 34390, 
November, 1992, the disclosures of which are incorporated herein by 
reference. As disclosed in these publications, the magnetic particles can 
be of any type available such as ferro- and ferri-magnetic oxides, complex 
oxides with other metals, ferrites, etc. and can assume known particulate 
shapes and sizes, may contain dopants, and may exhibit the pH values known 
in the art. The particles may be shell coated and may be applied over the 
range of typical laydown. 
Imaging elements incorporating conductive layers of this invention that are 
useful for other specific applications such as color negative films, color 
reversal films, black-and-white films, color and black-and-white papers, 
electrophotographic media, thermal dye transfer recording media etc., can 
also be prepared by the procedures described hereinabove. 
The present invention is further illustrated by the following examples of 
its practice. 
EXAMPLE 1 
An antistatic coating formulation comprising colloidal conductive particles 
with average particle size of about 0.01 to 0.05 .mu.m (by TEM) of metal 
antimonate compound I (M.sup.+2 =Zn.sup.+2), gelatin, and various 
additives described below was applied, using a coating hopper, to a moving 
web of 0.1 millimeter thick polyethylene terephthalate film support that 
had been previously undercoated with a terpolymer latex of acrylonitrile, 
vinylidene chloride, and acrylic acid. The weight percent composition of 
the aqueous coating formulation is listed below: 
______________________________________ 
Component Weight % (dry) 
Weight % (wet) 
______________________________________ 
colloidal ZnSb.sub.2 O.sub.6 
88.8 1.8 
binder (gelatin) 
9.9 0.2 
hardener (dihydroxy- 
0.3 0.006 
dioxane 
wetting aid (Olin 10G) 
0.5 0.01 
silica matte 0.5 0.01 
water 0.0 (balance) 
______________________________________ 
The antistatic subbing layer was coated at a dry coverage of 0.3 g/m.sup.2 
(total solids) which corresponds to a wet coating laydown of .about.12 
cm.sup.3 /m.sup.2. The surface resistivity (SER) of the antistatic layer 
was measured at both nominally 50% R.H. and after conditioning for 48 hrs 
at 20% R.H. using a two-point probe method. The SER values measured are 
reported in Table 1 below. Optical and UV densities of the antistatic 
layer were both measured using a X-Rite Model 361T densitometer. These 
measured values are also reported in Table 1. 
The antistatic layer described above is just as conductive at 20% R.H. as 
it is at 50% R.H. The optical and UV densities are nearly identical to 
those of the uncoated support. The antistatic layer of this example is 
strongly adherent to the subbed support. Further, the antistatic property 
of the conductive layer of this example was not diminished at all by 
processing with commercial photographic processing solutions such as KODAK 
ULTRATEC developing solution. The SER value measured after processing is 
given in Table 1. 
EXAMPLE 2 
An antistatic coating formulation comprising colloidal conductive particles 
with an average particle size of about 0.01 to 0.05 .mu.m (by TEM) of 
metal antimonate compound II (M.sup.+3 =In.sup.+3) substituted for metal 
antimonate compound I (M.sup.+2 =Zn.sup.+2), gelatin, and varous other 
additives in the same relative amounts as in Example 1 was prepared. This 
coating formulation was coated in the identical manner as used to prepare 
the antistatic layer of Example 1. 
The surface resistivity (SER) of the resulting antistatic layer was 
measured at nominally 50% R.H. and after conditioning for 48 hours at 20% 
R.H. using a two-point probe as in Example 1. The optical and UV densities 
were measured as in Example 1. The SER values and optical and UV densities 
are reported in Table 1. The antistatic layer was also subjected to 
processing using commercial solutions as in Example 1. The SER value 
measured after processing at 50% R.H. (nominal) is given in Table 1. 
The substitution of colloidal conductive particles of the metal antimonate 
compound II (M.sup.+3 =In.sup.+3) for I (M.sup.+2 =Zn.sup.+2) in the 
coating formulation also results in a transparent, highly conductive, 
adherent, and permanent antistatic layer for use on photographic film 
support. 
EXAMPLES 3-6 
Antistatic coating formulations comprising colloidal conductive particles 
of either metal antimonate compounds I (M=Zn) or II (M=In), 
polyvinylbutyral as binder, isopropanol as solvent, and other additives in 
the same relative amounts as in Example 1 were prepared. The colloidal 
metal antimonate particles were added as nominally 20% (w/w) dispersions 
in methanol. The polyvinylbutyral binder was added as a 10% solution in 
isopropanol. Isopropanol was substituted for water as the primary solvent. 
The two coating solutions each were coated at dry coverages of 0.5 
g/m.sup.2 and 0.25 g/m.sup.2 The surface resistivities of the four 
antistatic layers were measured at both nominally 50% R.H. and after 
conditioning for 48 hours at 20% R.H. as in Example 1. The SER values are 
given in Table 2. Optical and UV densities of the coated layers were also 
measured and are reported in Table 2. 
Examples 3-6 demonstrate that it is possible to prepare transparent 
antistatic layers using a colloidal dispersion of either metal antimonate 
compound I or II in a solvent-based coating formulation with a nonaqueous 
binder system. The antistatic layers of these examples are nearly as 
conductive as those prepared in Examples 1 and 2. Additionally, these 
antistatic layers are suitable for use as abrasion-resistant conductive 
backing layers for photographic imaging elements. 
EXAMPLE 7 
An antistatic coating formulation comprising colloidal conductive particles 
of metal antimonate compound II (M.sup.+3 =In.sup.+3), a vinylidene 
chloride based terpolymer latex as binder, and other additives was 
prepared as in Example 1. The weight percent composition of the aqueous 
coating formulation is listed below: 
______________________________________ 
Component Weight % (dry) 
Weight % (wet) 
______________________________________ 
colloidal InSbO.sub.4 
75 0.78 
binder (terpolymer 
24 0.26 
latex) 
wetting aid (Olin 10G) 
0.5 0.005 
silica matte 0.5 0.005 
water 0 (balance) 
______________________________________ 
The coating formulation of this example was coated at a nominal coverage of 
0.25 g/m.sup.2. The surface resistivity of the coated layer was measured 
at both nominally 50% R.H. and after conditioning for 48 hours at 20% R.H. 
as in Example 1. The SER values are given in Table 2. Optical and UV 
densities of the coated layer were also measured and are reported in Table 
2. Even at a lower conductive metal antimonate II (M=In) content (75%) in 
the coated layer than in Example 6, the antistatic layer of this example 
is just as conductive. This example demonstrates that other aqueous 
polymeric binder systems besides gelatin are suitable for preparing 
transparent, conductive layers on photographic film support. 
TABLE 1 
______________________________________ 
Resistivity 
(log.OMEGA./square) 
Density (D.sub.min) 
Example 50% R.H. 20% R.H. UV Optical 
______________________________________ 
1 7.6 8.1 0.040 0.020 
1 (post- 7.5 -- -- -- 
processing) 
2 8.2 8.1 0.040 0.023 
2 (post- 7.9 -- -- -- 
processing) 
Subbed &gt;13 &gt;13 0.027 0.017 
support 
______________________________________ 
TABLE 2 
__________________________________________________________________________ 
Resistivity 
Example 
Metal Total Dry (log.OMEGA./square) 
Density (D.sub.min) 
No. Antimonate 
Coverage (g/m.sup.2) 
Binder 
50% RH 
20% RH 
UV Optical 
__________________________________________________________________________ 
1 ZnSb.sub.2 O.sub.6 
0.3 B-1 7.6 8.1 0.040 
0.020 
2 InSbO.sub.4 
0.3 B-1 8.2 8.1 0.040 
0.023 
3 ZnSb.sub.2 O.sub.6 
0.5 B-2 8.5 9.2 0.070 
0.027 
4 InSbO.sub.4 
0.5 B-2 8.0 8.2 0.066 
0.030 
5 ZnSb.sub.2 O.sub.6 
0.25 B-2 9.0 9.7 0.059 
0.023 
6 InSbO.sub.4 
0.25 B-2 9.0 9.2 0.052 
0.022 
7 InSbO.sub.4 
0.25 B-3 8.9 8.8 0.063 
0.025 
__________________________________________________________________________ 
Notes 
B-1 = gelatin 
B-2 = polyvinylbutyral 
B-3 = vinylidene chloridebased terpolymer latex 
EXAMPLE 8 
The electrically-conductive antistatic subbing layer of Example 1 was 
overcoated with a hydrophilic curl-control layer comprising gelatin, 
bisvinylmethane sulfone hardener, water-soluble anionic cyan and yellow 
filter dyes, polymeric matte, and Olin 10 G surfactant as a coating aid. 
The hydrophilic curl-control layer was coated at a dry coverage of 4 
g/m.sup.2 (total solids). The resistivity of the overcoated antistatic 
layer was measured by the salt bridge method both before and after 
processing with commercial photographic processing solutions such as KODAK 
ULTRATEC developing solution. These measured values are reported in Table 
3. 
A test sample of the coating of this Example was also evaluated for 
adhesion of the gelatin curl-control layer to the antistatic subbing 
layer. Dry adhesion was evaluated by scribing a small crosshatched region 
into the coating with a razor blade, placing a piece of high tack adhesive 
tape over the scribed area, and then quickly stripping the tape from the 
surface. The relative amount of material removed from the scribed area is 
a qualitative measure of dry adhesion. Wet adhesion was also evaluated. A 
sample of the coating of this Example was placed into developing and 
fixing solutions at 35.degree. C. for 30 seconds each, rinsed in distilled 
water, and while still wet, a one millimeter wide line was scribed into 
the curl-control layer. The scribed line was rubbed vigorously with a 
finger in a direction perpendicular to the line. The relative width of the 
line after rubbing compared to that before rubbing is a qualitative 
measure of wet adhesion. The results of these evaluations are reported in 
Table 3. 
EXAMPLE 9 
The electrically-conductive antistatic subbing layer of Example 2 was 
overcoated with a hydrophilic curl-control layer in a manner identical to 
that described in Example 8. The resistivity of the overcoated antistatic 
layer was measured by the salt bridge method both before and after 
processing in commercial photographic processing solutions. These measured 
resistivity values are reported in Table 3. The wet and dry adhesion of 
the curl control layer to the antistatic layer were evaluated in a manner 
identical to that described in Example 8. The results of these evaluations 
are also reported in Table 3. 
TABLE 3 
______________________________________ 
Example Resistivity (log.OMEGA./square) 
Coating Adhesion 
No. Initial Post-Processing 
Dry Wet 
______________________________________ 
8 7.65 7.15 excellent 
excellent 
9 8.15 7.30 excellent 
excellent 
______________________________________ 
As hereinabove described, the use of fine particles of an 
electronically-conductive metal antimonate to provide 
electrically-conductive layers in imaging elements overcomes many of the 
difficulties that have heretofore been encountered in the art. In 
particular, the use of fine particles of an electronically-conductive 
metal antimonate together with a suitable binder enables the preparation 
of electrically-conductive layers which are useful in a wide variety of 
imaging elements, which can be manufactured at reasonable cost, which are 
resistant to the effects of humidity change, which are durable and 
abrasion-resistant, which are effective at low coverage, which are 
adaptable to use with transparent imaging elements, which do not exhibit 
adverse sensitometric or photographic effects, and which are substantially 
insoluble in solutions with which the imaging element typically comes in 
contact. 
The invention has been described in detail, with particular reference to 
certain preferred embodiments thereof, but it should be understood that 
variations and modifications can be effected within the spirit and scope 
of the invention.