Process of making photographic silver halide element with backing layers with improved coating properties

An improved process for the preparation of backing layers with improved coating qualities is described. These layers are designed to transmit antistatic properties from antistatic layers coated under the backing layers and provide antihalation or anticurl effects in addition thereto. The process of this invention includes in-line addition of a pre-stabilized crosslinking solution to a gelatino-conductive polymer solution just prior to the coating thereof. Smooth, skip-free coatings are obtained and the solutions are stable and can be maintained for long periods of time.

BACKGROUND OF THE INVENTION 
Cross-Reference to Related Applications 
This application is related to Cho, U.S. Pat. No. 4,585,730, "Antistatic 
Backing Layer with Auxiliary Layer for a Silver Halide Element", granted 
Apr. 29, 1986. This application is also related to Miller, U.S. Pat. No. 
4,701,403 granted Oct. 20, 1987, which is directed to a process for 
applying a thin, clear antistatic layer to a photographic film over which 
the layer of this invention may be applied. This invention is also related 
to Cho, U.S. Pat. No. 4,891,308, filed Apr. 14 1989, and entitled 
"Photographic Film Antistatic Backing Layer with Auxiliary Layer Having 
Improved Properties" and is an improvement thereover. 
FIELD OF THE INVENTION 
This invention relates to a photographic film. More particularly this 
invention relates to a photographic film having an improved auxiliary 
backing layer for said film, one that can conduct antistatic properties 
from an antistatic underlayer to the surface thereof and which can be 
applied thereto without premature cross-linking and without producing 
slugs and other deleterious material during the manufacture thereof. 
BACKGROUND OF THE INVENTION 
Polymeric film supports for photographic film are known for their 
propensity to accumulate static charges. This is a particular problem 
where the film is designed to be handled by machine and to be processed 
rapidly over unlike surfaces. Static charges which may be generated at 
this time cannot be readily tolerated because discharging these may expose 
the photographic layer, or layers, coated thereon. The use of so-called 
antistatic layers to prevent the build-up of these static charges is well 
known in the art. Schadt, U.S. Pat. No. 4,225,665, describes one such 
composition comprising a mixture of (1) a water-soluble copolymer of the 
sodium salt of styrene sulfonic acid and a carboxyl-containing monomer, 
(2) a hydrophobic polymer containing carboxyl groups, and (3) a 
water-soluble polyfunctional aziridine. When this mixture is applied as a 
single layer to resin-subbed (resin-subcoated)poly(ethylene 
terephthalate), for example, it provides excellent protection from the 
build-up of static charges (e.g. surface resistivity). 
Miller, U.S. Pat. No. 4,701,403 describes an improvement over the 
aforementioned Schadt patent wherein a polymer such as component (1), for 
example, is applied to the support in a first coating, optionally a 
composition containing component (2), and, after drying, aziridine 
component (3) is applied as a second coating contiguous thereto. This 
improved process permits the application of thinner antistatic layers 
without premature reaction of the aziridine with the other ingredients. 
Products from such premature reaction can sometimes plug and foul coating 
equipment, which is not commercially tolerable. 
Cho, U.S. Pat. No. 4,585,730 describes an auxiliary layer consisting 
essentially of gelatin binder containing various conductive polymers as 
described. This layer is satisfactory in transporting antistatic 
properties from underlayers to the surface thereof. However, occasionally 
the layer described in this patent suffers from certain disadvantages such 
as problems with anchorage and poor processability in the fluids in which 
the photographic layer is processed. 
Cho, U.S. Ser. No. 07/344,974, filed Apr. 14, 1989, describes an even more 
preferred auxiliary layer in which the ingredients of said layer, which 
include a crosslinkable conductive polymer having functionally attached 
carboxylic acid groups and a crosslinking agent for said conductive 
polymer all dispersed in a gelatin binder and coated at a pH of 3 to 12. 
Although this is a functional element, the process of applying this 
mixture can be fraught with problems during coating since premature 
reactions occur between the crosslinking agent, the polymer and gelatin 
prior to the coating thereof. These reactions cause the formation of 
so-called "gel slugs" which tend to plug the coating devices and cause 
streaks and other unwanted defects. These defects cannot be tolerated 
during commercial operation thereof. 
Thus, it is desired to provide a process which will permit the application 
of auxiliary layers over conventional antistatic layers which will 
maintain all the requisite antistatic properties and which can be applied 
with the aforementioned problems. 
SUMMARY OF THE INVENTION 
In accordance with this invention there is provided a process for preparing 
a photographic film comprising a support, at least one silver halide 
emulsion coated on one side of said support, and on the opposite side of 
said support, in order, are (a) a layer containing an antistatic agent and 
(b) an auxiliary layer consisting essentially of at least one 
crosslinkable, conductive polymer having functionally attached carboxylic 
acid groups selected from the group consisting of poly(sodium styrene 
sulfonate-maleic anhydride), hexadecyl betaine, alkyldimethyl betaines, 
carboxylated imidazolines, coco amido betaines, and mixtures thereof, and 
a polyfunctional aziridine crosslinking agent therefor, dispersed in 
gelatin, the process comprising maintaining separate said crosslinking 
agent from said at least one conductive polymer and said gelatin and 
stabilizing said crosslinking agent at a pH of 9.0 to 11.5 and then 
combining said separated components just prior to the coating thereof on 
the antistatic layer whereby a smooth, defect free coating is obtained.

DETAILED DESCRIPTION OF THE INVENTION 
Consisting essentially of, as used herein, means that unspecified 
constituents or conditions are not excluded, provided that they do not 
affect the advantages of this invention from being realized. 
The crosslinkable, conductive polymer may be present alone or in 
combination with at least one other crosslinkable, conductive polymer. A 
particularly preferred crosslinkable, conductive polymer is poly(sodium 
styrene sulfonate-maleic anhydride). Other crosslinkable, conductive 
polymers include: hexadecyl betaine; alkydimethyl betaines wherein the 
alkyl is from 1 to 12 carbon atoms; carboxylated imidazolines; cocoamido 
betaines; etc. These conductive polymers, which also contain functionally 
attached carboxylic acid groups, may be added to the auxiliary layer of 
this invention in a range of 0.5 to 30% by weight of the gelatin binder, 
and preferably at 2 to 5% by weight. The term "gelatin binder" denotes a 
binder wherein the major component is gelatin. Gelatin substitutes, e.g., 
polyvinyl alcohol; dextran; cellulose derivatives; modified gelatins; 
water-soluble acrylic latex; etc., may be present in minor amounts, e.g., 
less than 17% by weight. 
The crosslinking agents which provide the ultimate in crosslinking effects 
between the conductive polymer, the gelatin present and the antistatic 
layer over which the auxiliary layer of this invention is to be applied, 
are the polyfunctional aziridines, such as those described in Schadt, U.S. 
Pat. No. 4,225,665 and Miller, U.S. Pat. No. 4,701,403, the disclosures of 
which are incorporated herein by reference. These agents may be present in 
an amount of 0.5 to 5.0% by weight of the gelatin binder and preferably in 
an amount of 1.0 to 3.0% by weight. 
A mixture of the gelatin binder in water, and the crosslinkable conductive 
polymer, is made up prior to coating. Other additives (e.g. antihalation 
dyes, surfactants, wetting agents, and hardeners or crosslinking agents 
for gelatin) may also be present. At this point, just prior to coating, 
the pH is adjusted to 5.0 to 8.0 and preferably a pH of 6.0 to 7.5. 
The crosslinking aziridine agent is made up in a separate vessel and is 
preferably dissolved in a mixture of alcohol and water and the pH adjusted 
to 9.0 to 11.5, preferably a pH of 9.0 to 10.0. It is important to adjust 
the pH within this critical range since the aziridine must be stable and 
below pH of about 8.9, the aziridine ring begins to degrade by ring 
opening. 
The solution containing the aziridine crosslinking agent is then added to 
the gelatin containing the conductive, crosslinkable polymer just prior to 
coating. This step may easily be accomplished using the so-called "in-line 
injection" method. By preventing the early mixing of ingredients, and by 
using the aforesaid stabilization process for maintaining the integrity of 
the crosslinking agent, a smooth, skip or defective-free coating is 
obtained. 
The aqueous coating composition made as described above may be applied with 
good results to any of the conventional photographic film supports but the 
preferred support is poly(ethylene terephthalate) subcoated with a layer 
or layers of conventional resins and containing the antistatic coatings of 
Miller, U.S. Pat. No. 4,701,403, etc. The invention is not limited to any 
particular antistatic coating; however, the antistatic coatings of the 
aforesaid Miller patent are preferred (see particularly Column 3, line 56 
to Column 4, line 56, the disclosure of which is incorporated herein by 
reference). The backing layer of this invention is then coated over the 
antistatic layer at a coating weight of about 30 to 90 mg/dm.sup.2, 
preferably about 40 to 60 mg/dm.sup.2. 
Thus, in a particularly preferred mode, this invention is represented by an 
element which comprises a support, which is preferably dimensionally 
stable polyethylene terephthalate suitably subbed on both sides with a 
thin, anchoring substratum of a conventional resin sub over which may be 
applied a gelatin sublayer. On one side of this support a standard silver 
halide emulsion layer may be applied and this layer then overcoated with a 
protective overcoat layer, e.g., a conventional hardened gelatin, abrasion 
layer. On the side opposite to the side containing this emulsion layer, 
the antistatic layer of the aforementioned Miller patent is preferably 
applied followed by a layer represented by this invention. As stated 
previously, the layer of this invention may also be an antihalation layer 
or may be coated simply a gelatin anti-curl layer, as is well-known to 
those of normal skill in the art. 
When the layer of this invention is made as taught herein, many advantages 
are obtained. First, this layer will provide transmission of antistatic 
properties from the antistatic layer to the surface of the film as is 
desired. Next, the layer of this invention is stable and will survive the 
rigors of photographic processing without disintegration. This is a very 
desirable trait since prior art layers tended to flake off during the 
processing steps. This loss of layer integrity is a defect that cannot be 
tolerated since particles of the layer tend to foul the processing fluids 
and, more importantly, cause loss of antistatic transmission properties. 
Additionally, the adhesion between previously coated or subsequently 
coated layers is enhanced by the layer of this invention over those of the 
prior art. Finally, as made by the process taught herein, coating speeds 
and quality are vastly improved over the prior art references and 
processes disclosed herein. By stabilizing the aziridine crosslinking 
agent and maintaining a separation between this agent and the conductive 
polymer and gelatin, and mixing the two just prior to coating, the layers 
are stable and free from coating defects and there is no need to filter 
solutions prior to coating. It is also possible to hold and maintain the 
solutions containing their separate ingredients for a longer period of 
time thus improving the entire coating operation and savings in time and 
investment. This is surprising since it was not well-known that the 
stabilization of the aziridine crosslinking agent would react so 
prematurely with the other ingredients. It was also not known that the 
stability of the aziridine agents were so dependent on pH. By following 
the teachings of this invention, the viscosity of the solutions involved 
is closely controlled and the stability vastly improved. These 
improvements aid greatly in the commercial operations involved in the 
coating of this type of solution. 
A host of conventional photosensitive materials may be present as the 
emulsion layer described above. These include photopolymer, diazo, 
vesicular image-forming materials, etc. The films described may be used in 
any of the well-known imaging fields such as graphic arts, printing, 
medical and information systems, among others. The photographic film of 
this invention is particularly useful in processes where rapid transport 
and handling by machines are practiced such as phototypesetting 
applications, for example. Particularly useful elements include the 
so-called "bright-light" films which can be handled in relatively bright 
safelights, for example. This invention will now be illustrated by the 
following examples of which Example 1, Sample 3 is considered to be a 
preferred mode. 
EXAMPLE 1 
A backing layer solution was prepared by mixing the following ingredients: 
______________________________________ 
Solution A: (gelatino-conductive polymer solution) 
Ingredient Amount (g) 
______________________________________ 
distilled water 12,060 
Conductive Polymer (sodium-[poly- 
168 
styrene sulfonate]-maleic anhydride) 
25% solution in water, No. average MW 
ca. 3,000, determined by known 
osometry techniques. 
gelatin 1,200 
silica matte (12 m.mu., 
6.6 
Davidson Chem. Co.) Mix together 
distilled water 300.0 
______________________________________ 
These ingredients were digested together for 15 minutes at room temperature 
and then for 25 minutes at 130.degree. F. (.about.55.degree.). 
______________________________________ 
Solution B: (other ingredients for backing) 
Ingredients Amount (g) 
______________________________________ 
ethyl alcohol 580 
distilled water 580 
5% aqueous solution of perfluoroalky 
270 
carboxylate (FC-127 .RTM., 3M Co.) 
benzenesulfonic acid, 4-[4,5-dihydro- 
138 
4-[[5-hydroxy-3-methyl-1-(4-sulfophen- 
yl)-1H-pyrazol-4-yl]methylene]-3-methyl- 
5-oxo-1H-pyrazol-1-yl]-, dipotassium 
salt Yellow Dye (1) (16% soln) 
Acid Violet Dye (2) (12% soln) 
150 
3N sodium hydroxide 32 
4.2% aqueous solution of sodium octyl 
600 
phenoxy diether sulfonate wetting agent 
(Triton .RTM. X200, Rohm & Haas Co.) 
6% aqueous solution of sodium myristyl 
300 
triether sulfate wetting agent 
(Standapol .RTM. ES40, Henkel, Inc., USA) 
polyethyl acrylate latex (32.5% 
1,320 
solution in water) 
chromium potassium sulfate (12.5% 
60 
solution in water) 
gelatin 1,200 
distilled water 13,240 
______________________________________ 
These ingredients were also mixed thoroughly and then Solution A added to 
Solution B at 100.degree. F. (.about.38.degree. C.) while stirring to mix. 
The pH of the final mixture was 6.52. 
An additional dye solution of 2% benzenesulfonic acid, 
4-[4,5-dihydro-4-[5-hydroxy-3-methyl-1-(4-sulfophenyl)-1H-pyrazol-4-yl]-2, 
4-pentadienylidene]-3-methyl-5-oxo-1H-pyrazol-1-yl]-, Blue Dye (3) was 
made up and kept separate. 
A separate solution containing the aziridine crosslinking agent was made up 
as follows: 
______________________________________ 
Ingredient Amount (g) 
______________________________________ 
distilled water 670 
premixed 
ethyl alcohol 380 
3N sodium hydroxide 30 
1-aziridinepropanoic acid, 2-methyl- 
50 
2-ethyl-2-[3-(2-methyl-1-aziridinyl)- 
1-oxopropoxy]-1,3-propandiyl 
ester CAS #64-265-57-2, formula 
C.sub.24 H.sub.41 N.sub.3 O.sub.6) MW 
467.61-hereinafter 
referred to as "PFAZ322" 
______________________________________ 
These ingredients were thoroughly mixed and the pH was 10-11.5. 
##STR1## 
The three solutions (gelatino-conductive polymer containing two of the 
requisite antihalation dyes; a solution containing the third of the dyes; 
and the crosslinking agent) were held in separate vessels. A sample of 
dimensionally stable and resin/gel subbed polyethylene terephthalate film 
on which an antistatic layer similar to that previously described in 
Miller U.S. Pat. No. 4,701,403 had been applied, was used as the support 
for this coating. The solution containing the gelatino-conductive polymer 
was passed first through a line to the coating station. Just prior to that 
coating station, the solution of the third dye and the crosslinking agent 
were in-line injected so that mixing of all three solutions occurred just 
at said coating station. Coating was continued under varying levels of the 
rate of in-line injection for the crosslinking agent only, as shown below. 
Samples were taken of the coated stock at each point and an assessment 
made of the coating quality, the strength of layer adhesion and the 
surface resistivity, as measured by Cho, U.S. Pat. No. 4,585,730, the 
disclosure of which is incorporated herein by reference, also determined. 
In addition, a conventional, gelatino-silver halide emulsion layer was 
applied on the side opposite to that containing the antistatic and 
auxiliary, antihalation layer and a determination of sensitometry and 
suitability also determined. For control purposes, another experiment 
utilizing the same ingredients, but wherein all ingredients were premixed 
prior to coating, was also made. Samples were obtained at the following 
points: 
______________________________________ 
Amt. PFAZ322 
Sample Injected (g/200 g gel) 
______________________________________ 
Control None--all premixed 
1 0.5 
2 1.0 
3 2.5 
4 4.0 
5 5.0 
6 6.0 
______________________________________ 
In the case of the Control, the coating was hard to manage since over a 
period of time, gel slugs clogged the coating bar and caused coating 
streaks to appear. The coating had to be shut down from time to time to 
clear the coating bar. Additionally, although the coating had good static 
resistance, there was loss of product due to poor coating performance. 
Finally, in the Control, the coating was less efficient since this 
material required higher drying times. 
In the samples representing this invention, there were no slugs or coating 
skips and the drying was much faster than that of the control, resulting 
in an increase of 12.5% thereover. The static protection was excellent and 
the adhesion superb. All the sensitometric results from photographic 
coatings were within specifications. All samples processed well with no 
delamination of layers. Thus, the crosslinking effect was the same over a 
wide range of crosslinking agent. 
EXAMPLE 2 
In this experiment, a purified form of the conductive polymer described in 
Example 1 was used. This purified sample was made by National Starch Co. 
purified to remove excess sodium sulfonate. The solutions were prepared 
similar to those described in Example 1 and equivalent and excellent 
results were achieved. 
EXAMPLE 3 
To test the effect of yet another conductive polymer, coco amido betaine 
was substituted for the sodium(polystyrene sulfonate) maleic anhydride of 
Example 1. Additionally, a mixture of both conductive polymers was also 
made. All other ingredients were identical. The crosslinking agent was 
again added by in-line injection. Equivalent and excellent results to that 
of Example 1 were achieved. 
EXAMPLE 4 
In this example, the aziridine crosslinking agent was replaced with 
pentaerythritol-tri-beta-(2-methyl aziridine). All other ingredients and 
conditions were the same. The crosslinking agent solution was added by 
in-line injection. Equivalent and excellent results to that of Example 1 
were obtained.