Photographic glass plates having antihalation underlayer

Photographic glass plates can be prepared by directly coating the appropriate layer formations onto a glass support. One element comprises a thin subbing layer (less than 2 .mu.m), an antihalation layer, a silver halide emulsion layer, and a protective overcoat layer that can also include a matting agent or lubricant. Another embodiment has the antihalation layer coated directly onto the support.

FIELD OF THE INVENTION 
This invention relates in general to photography, and in particular to 
photographic glass plates having an antihalation underlayer. 
BACKGROUND OF THE INVENTION 
Photographic elements are coated on a wide variety of support materials, 
such as plastic resins, paper and glass. Plastics are used as the support 
when a combination of transparency, strength, dimensional stability and 
light weight is needed. Paper is used when the physical properties are not 
too demanding, cost is a major factor or an opaque base is needed. Glass 
has the advantages of excellent dimensional stability and extreme 
flatness, but is disadvantageous in that it is expensive, heavy and 
brittle. Photographic glass supports typically range in thickness from 
about 1 to 10 millimeters and are graded by flatness. Those with the 
lowest degree of flatness are used in such applications as 
photomicrography and graphic arts, those with an intermediate degree of 
flatness are used in such applications as photofabrication, stereoplotters 
and aerial photography, and those with the highest degree of flatness are 
used in such applications as high-precision stereoplotters, ballistic and 
aerotriangulation camera systems and special scientific investigations. 
The coating of glass plates with photographic layers is a very demanding 
art since the layers must be extremely thin, highly uniform in thickness, 
and completely free from defects. One technique for coating such layers 
based on wicking action using an arcuate surface is described in U.S. Pat. 
No. 4,033,290 (Dude). There are many difficulties in coating glass 
substrates, including the likelihood of "skips" that result in uncoated 
areas, the difficulty in coating extremely thin layers, and the presence 
of streaks and contaminants such as dust. There is a continuing need to 
reduce or eliminate these problems. 
One attempt at this is described in U.S. Pat. No. 5,254,447 (Meyer et al) 
in which various layers are applied to glass plates by lamination 
techniques. Such techniques solve certain problems such as protection of 
the photosensitive layers, and other features described in the noted 
patent. Moreover, these techniques allow for the production of multilayer 
plates that were difficult to prepare using previously known coating 
techniques. 
However, lamination of various layers to provide photographic glass plates 
has a number of disadvantages. Dirt entrapped between laminated layers can 
become prominent in the resulting element causing undesirable 
non-uniformities, sometimes called "tentpoles". In certain elements, 
protective overcoats are desired, but when matting agents are included in 
such overcoat layers, they cannot protrude because this layer rests on a 
film support prior to the lamination process. This renders the matting 
agent ineffective. In order to be effective, it is necessary that the 
matting agent protrude from the overcoat surface to provide excellent 
vacuum drawdown and reduced tackiness. Moreover, lubricants cannot readily 
be put into the protective overcoat layers using the prior art process 
because the lubricants decrease adhesion of the layers to the polymer 
films required in lamination procedures. 
It would be desirable to provide photographic glass plates that contain 
antihalation layers beneath the photographic layer, over which is a 
protective overcoat that can contain a matting agent or lubricant. Such 
elements cannot be readily prepared by lamination techniques. 
SUMMARY OF THE INVENTION 
The problems described above are overcome with photographic element 
comprising a glass support having hereon, in order: 
a subbing layer having a dry thickness of less than 2 .mu.m, 
an antihalation layer, 
a silver halide emulsion layer, and 
a protective overcoat layer. 
This invention also provides a photographic element comprising a glass 
support having thereon, in order, only the following layers: 
an antihalation layer, 
a silver halide emulsion layer, and 
a protective overcoat layer comprising a matting agent or lubricant. 
The photographic elements of this invention are advantageously prepared 
using coating techniques rather than lamination techniques. Thus, the 
problems noted above with lamination, such as entrapped dirt causing 
non-uniformities, ineffectiveness of matting agent and the inability to 
use lubricants in the protective overcoat layers are avoided with this 
invention. The elements of this invention have an antihalation layer 
between the glass support and photographic layer to reduce light 
backscatter, light "piping" from edges of the glass support, and unwanted 
image distortion from manufacturing non-uniformities within the glass 
supports. Moreover, the application of antihalation layers on the backside 
of the glass support can be avoided. Such backside layers are generally 
coated out of objectionable organic solvents and render the resulting 
plates difficult to process. The backside layers are also subject to 
abrasion during the manufacturing process. This invention avoids these 
problems. 
In preferred embodiments, the elements of this invention also have a very 
thin subbing layer to adhere the antihalation layer to the glass support. 
The subbing layers are not conventional pressure-sensitive or heat-curable 
adhesive layers that are required to prepare elements using lamination 
techniques. Alternatively, the antihalation layers can be coated directly 
on the glass supports, with additives to promote adhesion to the supports. 
In all embodiments, the protective overcoat layer can contain either a 
lubricant or matting agent, and preferably both.

DETAILED DESCRIPTION OF THE INVENTION 
Common to all embodiments of the present invention is a glass plate that 
provides a rigid and highly dimensionally stable support upon which all of 
the element layers are disposed. Any suitable glass plate can be used 
having the desired degree of flatness and clarity. Preferably, the glass 
plate has a high degree of flatness. Generally, the glass support has a 
thickness of at least about 0.5 mm, and preferably it has a thickness of 
from about 1 to about 10 mm. The resulting elements can have any suitable 
dimensions, and include the large format photographic plates that have a 
major dimension greater than about 75 cm. 
In a preferred embodiment of this invention, a subbing layer is disposed on 
the glass support to adhere the other layers of the element. Generally, 
such subbing layers are film-forming hydrophilic colloidal materials or 
hydrophilic polymer binders that are well known in the photographic art, 
but which are not used specifically for antistatic or antihalation 
purposes. Such materials must adequately adhere the upper layers to the 
glass support, and be essentially transparent to radiation of the 
wavelength used in exposing the photographic element. Moreover, it should 
be resistant to any processing solutions that would penetrate the 
overlying layers or contact the subbing layer at its edges. Typical 
subbing layer materials include, but are not limited to, gelatin and other 
film-forming colloidal materials, vinylidene chloride polymers such as 
poly(vinylidene chloride-co-methyl acrylate-co-itaconic acid), and 
poly(acrylonitrile-co-vinylidene chloride-co-acrylic acid)! and other 
materials readily apparent to one skilled in the art. Various subbing 
materials are described, for example, in U.S. Pat. No. 4,415,626 
(Hasenauer et al) and the Alles et al, Nadeau et al and Khanna et al 
patents mentioned therein. More than one subbing layer can be used as long 
as the total dry thickness of the one or more subbing layers is less than 
2 .mu.m, preferably from about 0.02 to about 1 .mu.m, and most preferably, 
from about 0.02 to about 0.2 .mu.m. 
The subbing layers used in the invention are not considered adhesives as 
described in U.S. Pat. No. 5,254,447 (noted above). Thus, the subbing 
layers of this invention are not considered to be the conventional 
heat-curable or pressure-sensitive adhesives that are required for the 
lamination of various layers to form multilayer photographic glass plates. 
Moreover, they are much thinner than the adhesive layers described in the 
noted patent. 
Photographic glass plates of the art typically have an antihalation layer 
on the side of the glass support opposite that on which the silver halide 
emulsion layer is coated (that is, on the backside of the glass support). 
The plates of this invention, however, differ in that the antihalation 
layer is on the same side as the silver halide emulsion layer. Of course, 
U.S. Pat. No. 5,254,447 (noted above) shows the antihalation layer and 
silver halide emulsion layer on the same side in the elements, but there 
is no thin subbing layer used in those elements. 
The antihalation layers used in the invention generally comprise one or 
more dyes or pigments dispersed in one or more film-forming binders, such 
as gelatin and other materials known in the photographic art for that 
purpose. These layers function to prevent light from being reflected into 
the overlying silver halide emulsion layer(s) thereby avoiding an 
undesired spreading of the image that is known in the art as "halation". 
The layers also may comprise one or more surfactants that are useful as 
coating aids. 
Suitable binder materials useful in such layers include, but are not 
limited to, naturally occurring hydrophilic colloids such as gelatin or 
gelatin derivatives, cellulose derivatives, polysaccharides such as 
dextran, zein, casein, pectin, collagen derivatives and other materials 
known in the art for this purpose, including synthetic polymeric binder 
materials. 
Dyes that are useful in the antihalation layer can be essentially any dye 
that is useful as a photographic filter dye, including, but not limited 
to, oxonols, cyanines, merocyanines, arylidenes and others known in the 
art for this purpose. The filter dyes may be diffusible or non-diffusible, 
but are preferably solublizable during photographic processing. Various 
classes of useful dyes are described in U.S. Pat. No. 5,254,447 (noted 
above), and the references cited therein. Basically one or more filter 
dyes are selected to cover a suitable range of spectral sensitivity for 
the photographic plate, whether that sensitivity be in the visible, 
infrared or ultraviolet regions (or combinations thereof) of the 
electromagnetic spectrum. 
Alternatively and preferably, the filter dyes are solid particle dispersion 
filter dyes, as described in Cols. 14 and 15 of U.S. Pat. No. 5,254,447 
(noted above) and the references cited therein. 
A mixture of filter dyes can be used in the antihalation layer. Moreover, 
more than one antihalation layer can be used with the same or different 
dyes, as long as the total dry thickness of the one or more antihalation 
layers is from about 0.5 to about 5 .mu.m, and preferably, from about 1 to 
about 3 .mu.m. 
The photographic elements of this invention can be black-and-white elements 
(of various spectral sensitivities), color elements adapted for use in a 
negative-positive process, or color elements adapted for use in a reversal 
process. They can include one or more photographic silver halide emulsion 
layers over the antihalation layer(s), each of which can include any of 
the photographically useful silver halides, binders or vehicles, and other 
addenda commonly used in such emulsions. Thus, useful silver halides 
include, but are not limited to silver chloride, silver bromide, silver 
iodobromide, silver iodochloride, silver iodobromochloride, silver 
bromochloride, silver chlorobromide and the like (the halides being named 
in ascending order of molar amount based on total halides). Other details 
of useful photographic silver halide emulsions are provided in Research 
Disclosure, publication 36544, pages 501-541 (September 1994). Research 
Disclosure is a publication of Kenneth Mason Publications Ltd., Dudley 
House, 12 North Street, Emsworth, Hampshire PO10 7DQ England (also 
available from Emsworth Design Inc., 121 West 19th Street, New York, N.Y. 
10011). The binder materials described above for the antihalation layer 
can also be used in the silver halide emulsion layer. 
As noted above, one or more silver halide emulsion layers can be used, 
although preferred embodiments include only a single emulsion layer. The 
dry thickness of the emulsion layer(s) used in the elements is generally 
from about 1 to about 10 .mu.m, and preferably from about 2 to about 5 
.mu.m. 
As indicated above, the photographic element also comprises a protective 
overcoat layer. The function of this layer is to provide protection 
against abrasion, scratching, fingerprints and the like. The protective 
overcoat layer is generally comprised of gelatin or another suitable 
hydrophilic colloid or polymeric material and typically contains other 
components such as one or more surfactants and/or filter dyes (as 
described above for the antihalation layer). 
Preferably, the protective overcoat layer also includes a matting agent 
that can be of either an organic or inorganic material. Examples of 
organic matting agents are polymeric particles or beads. Examples of 
inorganic matting agents include, but are not limited to, particles of 
silicon dioxide, titanium dioxide, magnesium oxide, aluminum oxide, barium 
sulfate, calcium carbonate and others known in the art. The desired 
dimensions of such matting agents can vary, and generally they are present 
in an amount of at least about 0.005 g/m.sup.2 and preferably at from 
about 0.01 to about 0.1 g/m.sup.2. The level of matting agent is chosen to 
assure that a sufficient number of matting agent particles protrude from 
the outer surface of the protective overcoat layer, giving it a roughened 
surface. This provides desired vacuum drawdown and reduced surface 
tackiness. A preferred matting agent is silicon dioxide. 
Alternatively or in addition to the matting agent, it is preferred that the 
protective overcoat layer includes one or more lubricants. Such materials 
provide ease of handling and protection from abrasion and fingerprints. 
Useful lubricants include those that are low in haze and typically used in 
the manufacture and finishing of photographic films, plates and papers. 
Useful lubricants that can be used singly or in combination include, but 
are not limited to, silicone oils or waxes (including silicone oil, 
silicones having polar groups, fatty acid-modified silicones, and 
fluorine-containing silicones), fluorine-containing alcohols, 
fluorine-containing esters or ethers, fluorinated polyalkanes, 
polyolefins, polyglycol alkyl phosphates or alkali metal salts thereof, 
polyphenyl ethers, fluorine-containing alkylsulfates or alkali metal salts 
thereof, monobasic fatty acids having 10 to 24 carbon atoms (branched or 
linear, saturated or unsaturated) or metal (alkali metals or copper) salts 
thereof, mono- or polyvalent alcohols having 12 to 22 carbon atoms 
(branched or linear, saturated or unsaturated), alkoxy alcohols having 12 
to 22 carbon atoms, mono-, di or triesters of monobasic fatty acids having 
10 to 24 carbon atoms (branched or linear, saturated or unsaturated), 
fatty acid esters of monoalkyl ethers of alkylene oxide polymers, fatty 
acid amides having 8 to 22 carbon atoms (branched or linear, unsaturated 
or saturated) or aliphatic amines having 8 to 22 carbon atoms (branched or 
linear, unsaturated or saturated, and optionally interrupted by one or 
more carbonyl, oxy, amino, thio, carbonyoxy, oxycarbonyl or carbonamide 
groups). Mixtures of compounds within any group noted above, or mixtures 
of compounds from two or more groups are also useful. Mixtures are likely 
since many of these materials are commercially available as such. 
Specific examples of useful lubricants include, but are not limited to, 
lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, 
butyl stearate, oleic acid, linolic acid, linolenic acid, elaidic acid, 
octyl stearate, amyl stearate, isooctyl stearate, octyl myristate, 
butoxyethyl stearate, anhydrosorbitan monostearate, anhydrosorbitan 
distearate, anhydrosorbitan tistearate, pentaerythrityl tetrastearate, 
oleyl alcohol and lauryl alcohol, and mixtures thereof. 
A more preferred lubricant comprises alcohol esters of methyl myristate, 
methyl palmitate or methyl stearate, or mixtures thereof. 
The protective overcoat layer of the elements generally has a dry thickness 
of at least about 0.5 .mu.m, and more particularly a dry thickness of from 
about 1 to about 4 .mu.m, and more preferably a dry thickness of from 
about 2 to about 3 .mu.m. 
The layers of the elements can be coated on the glass support using any 
suitable conventional coating technique and coating equipment, including 
wick application, gravure, slide hopper, X-hopper and other techniques 
known in the art. The coating conditions and solvents for each layer would 
be readily apparent to one skilled in the photographic art. Thus, the 
various embodiments of this invention can be prepared by coating the 
appropriate layer formulations, in order, onto the glass support. 
Preferably, those layers are coated using the same multilayer coating 
machine in one pass. 
The elements of this invention can include other layers not specifically 
defined herein, such as conventional interlayers or filter layers. Layers 
can be on the backside of the glass support if desired, but preferably the 
glass support is free of layers on the backside. 
Referring to FIG. 1, a preferred embodiment of this invention includes 
glass support 10 on which is disposed thin subbing layer 12, antihalation 
layer 14, silver halide emulsion layer 16, and protective overcoat layer 
18. 
A second embodiment, illustrated in FIG. 2, includes glass support 10 on 
which is directly coated antihalation layer 14, silver halide emulsion 
layer 16 and protective overcoat layer 18. 
The following example is intended to illustrate the invention but not to 
limit it in any way. The coating coverages are in g/m.sup.2 unless 
otherwise indicated. 
EXAMPLE 
Preferred Photographic Glass Plate 
A preferred element of this invention was prepared by coating the following 
layer formulations, in order, on a conventional glass plate support using 
a conventional multilayer coating machine: 
(a) a subbing layer formulation comprising gelatin binder material in 
water/alcohol mixture to provide a dry thickness of 0.05 .mu.m; 
(b) an antihalation layer formulation comprising a conventional UV and 
blue-light absorbing filter dyes (0.03), in gelatin to provide a dry 
thickness of 1 .mu.m; 
(c) a silver halide emulsion layer formulation comprising a black and white 
silver chloride emulsion to provide a dry thickness of 5 .mu.m; and 
(d) a protective layer overcoat formulation comprising silicon dioxide 
matting agent (0.03 g/m.sup.2) in gelatin binder material to provide a dry 
thickness of 3 .mu.m. 
The glass plate support was 4.7 mm thick. 
The invention has been described in detail with particular reference to 
preferred embodiments thereof, but it will be understood that variations 
and modifications can be effected within the spirit and scope of the 
invention.