Process of making a photographic elements comprising protective layers containing antistats

Photographic elements comprising at least one protective hydrophilic colloid layer comprising at least one urethane of polyethylene oxide compounds as antistatic agent in the form of dispersed droplets having an average diameter ranging from 1500 to 12000 nm and method of covering such photographic elements with at least one such protective hydrophilic colloid layer obtained by the steps of dissolving such urethane in a water-immiscible solvent medium, emulsifying the resulting solution in aqueous hydrophilic colloid, removing said water-immiscible solvent medium by evaporation to form the dispersed droplets in the aqueous hydrophilic colloid, and coating the latter as such or after having been mixed with additional hydrophilic colloid to form the protective hydrophilic colloid layer.

The present invention relates to a method of covering photographic elements 
with protective hydrophilic colloid layers comprising antistatic agents as 
well as to photographic elements comprising a support, at least one 
photosensitive silver halide emulsion layer, and at least one such 
protective hydrophilic colloid layer. 
It is known that the accumulation of electric charges during both the 
production and use of photographic elements may give rise to great 
difficulties. These static electric charges may be caused by friction 
between the photographic element and other contacting surfaces such as 
rollers and guiding members of the apparatus, through which the element 
runs. The static charges present in the photographic elements before 
development may cause spark exposure of the photosensitive silver halide 
emulsion, these spark-exposed areas being visualized during development in 
the form of irregular stripes or lines, or of dark spots. Such stripes, 
lines, or spots may lead to misinterpretation of the reproduced image, 
which is particularly harmful in the case of X-ray diagnosis. Whereas 
achieving an adequate antistatic behaviour in surface or outermost layers 
that do not essentially consist of a hydrophilic colloid, as is sometimes 
the case in e.g. backing layers of cinematographic materials, is not very 
difficult since the incorporation of electroconductive substances therein 
has no adverse effect, achieving a satisfactory antistatic effect in 
surface layers that essentially consist of a hydrophilic colloid e.g. 
gelatin is often very difficult to realize. As a matter of fact, not all 
kinds of known conductivity-increasing substances can be used in gelatin 
surface layers. In spite of having a satisfactory antistatic effect many 
of these known conductivity-increasing substances are of limited utility 
since they cause coating difficulties or impair the photographic and/or 
physical characteristics of the photographic elements, to which they had 
been added. 
For instance, quaternary salts cannot be used in photographic elements 
because of their fogging influence. High concentrations of hygroscopic 
materials such as glycerol, potassium acetate and lithium chloride cause 
the surface layers of contacting photographic elements to adhere to each 
other. Moreover, these compounds are ineffective at low relative humidity. 
High molecular weight carboxylic or sulphonic acids such as sodium salts 
of polystyrene sulphonic acid and polyvinyl sulphonic acid have a 
favourable antistatic effect when applied directly to a hydrophobic 
support, but this positive effect is almost completely annihilated when 
these substances are used in hydrophilic colloid layers e.g. gelatin 
layers or light-sensitive gelatin silver halide emulsion layers. Chromium 
complexes may enter into reaction with hydrophilic colloids and can 
therefore be used only in limited conditions. 
From U.S. Pat. No. 3,552,972 it is known that the urethanes or esters of 
hydroxyalkylated fatty alcohols or hydroxyalkylated alkylphenols are 
interesting antistatic agents. However, when added to aqueous hydrophilic 
colloid coating compositions, these compounds adversely affect the coating 
properties of the latter and as a consequence lead to irreproducible and 
thus less effective antistatic results. Indeed, when added as such to 
aqueous hydrophilic colloid coating compositions, they generally form a 
floating smeary film at the surface of these coating compositions, thus 
impeding normal coating thereof and leading to unpredictable results. When 
added in the form of an alcoholic solution they tend to leave the 
dissolved state at least partially and also form the above described 
floating smeary film at the surface of the coating compositions. The 
dissolved phase, whenever still present, is in the form of large and 
irregular drops. Such drops disturb the hydrophilicity of the hydrophilic 
colloid coating compositions so that the latter can hardly be coated on a 
support because of repellency spots or comets forming in the layer. 
Moreover, the addition of these solutions to aqueous hydrophilic colloid 
coating compositions often results in the formation of pinholes during the 
drying of the coated layer. These pinholes manifest themselves in the form 
of craterlike spots that are already visible before development of the 
photographic element and, of course, also after development thereof. 
Probably they are formed when the antistatic urethanes or esters locally 
abandon the dissolved state within some of the drops. 
While in recent years the trend towards automation with enhanced and high 
speed transport of photographic elements has even increased the chances of 
accumulation of static charges therein, great emphasis is laid nowadays on 
the importance of using adequate antistatic agents, which satisfy the high 
demands imposed on photographic elements that have to be manipulated very 
much and treated at high speed in sizing and processing devices. An 
example of intensive manipulation can be found for instance in the 
automatic loading and unloading of X-ray film elements in cassettes, these 
X-ray film elements being e.g. double-coated film elements having on both 
sides one or more silver halide emulsion layers covered with protective 
gelatin layers. 
It is an object of the present invention to provide photographic elements 
comprising a support, at least one photosensitive silver halide emulsion 
layer, and at least one protective hydrophilic colloid layer comprising 
urethanes of polyethylene oxide compounds as antistatic agents, such 
protective hydrophilic colloid layers presenting no problems during their 
coating and demonstrating a reproducible and satisfactory antistatic 
effect even when the photographic elements undergo extensive manipulation 
and/or high speed processing. 
It is another object of the present invention to provide a method of 
covering photographic elements comprising a support and at least one 
photosensitive silver halide emulsion layer, with at least one protective 
hydrophilic colloid layer comprising such urethane antistatic agent. 
Other objects of the present invention will become apparent from the 
disclosure herein. 
The above objects have been accomplished according to the present invention 
by the use of urethanes as defined hereinafter, which have been dispersed 
in droplet form in a protective hydrophilic colloid layer of a 
photographic element comprising a support, at least one photosensitive 
silver halide emulsion layer, and at least one such protective hydrophilic 
colloid layer by the steps of dissolving at least one such urethane in a 
water-immiscible solvent medium, emulsifying the resulting solution in 
aqueous hydrophilic colloid e.g. aqueous gelatin by stirring, removing the 
water-immiscible solvent medium by evaporation to form dispersed droplets 
having an average diameter ranging from 1500 to 12000 nm in the aqueous 
hydrophilic colloid, and coating the aqueous hydrophilic colloid as such 
or after having been mixed with additional hydrophilic colloid to form 
such protective hydrophilic colloid layer on the photographic element. 
The urethanes used in dispersed form in accordance with the present 
invention correspond to the following general formula: 
##STR1## 
wherein: R represents 
a C.sub.6 -C.sub.18 alkyl group e.g. dodecyl, tetradecyl, hexadecyl, 
octadecyl, 
an aryl group, preferably phenyl, 
an alkaryl group e.g. nonylphenyl, 
an aralkyl group e.g. benzyl or phenylethyl, or 
a cycloalkyl group e.g. cyclohexyl, 
which groups, particularly the phenyl group, may be further substituted 
e.g. with nitro; 
y is 1 or 2; 
R.sup.l is an aryl group e.g. phenyl or naphthyl when y=1 or an arylene 
group e.g. phenylene or naphthylene when y=2; 
m is 0 or 1; 
n.sub.1 is an integer from 4 to 8; 
n.sub.2 is 0 or an integer from 4 to 8, n.sub.2 being 0 when m=0. 
When m=1, the resulting copolymers are block polymers and not compounds 
that contain ethylene oxide and propylene oxide units in statistical 
distribution. 
Preferred urethanes are the simple compounds corresponding to the above 
general formula wherein m=0 and consequently n.sub.2 =0, y=1, and R is a 
C.sub.6 -C.sub.18 alkyl group or an alkaryl group. 
Representatives of the urethanes corresponding to the above general formula 
are the following: 
##STR2## 
The urethanes used in accordance with the present invention can be prepared 
as described in U.S. Pat. No. 3,552,972. 
The urethanes used in accordance with the present invention are poorly 
soluble in water and photographically inert. Indeed, although comprising 
ethylene oxide units they have no development-influencing effect. 
Generally, they are highly viscous, syrupy substances. In accordance with 
the present invention they are dispersed by first dissolving them 
temporarily in a water-immiscible solvent medium, then emulsifying the 
resulting solution in aqueous hydrophilic colloid, usually 2 to 20% by 
weight aqueous gelatin, preferably 5% by weight aqueous gelatin, by 
homogenizing e.g. stirring the solution, preferably in the presence of an 
anionic, cationic, or non-ionic surface-active agent, into the aqueous 
hydrophilic colloid, and finally removing the water-immiscible solvent 
medium by evaporation so that dispersed droplets of antistatic agent 
having an average diameter ranging from 1500 to 12000 nm remain in the 
aqueous hydrophilic colloid. It is assumed that some of the small droplets 
of antistatic agent formed during the homogenizing step grow at the 
expense of the other small droplets due to conglomeration taking place 
during the evaporation of the solvent medium. 
The resulting dispersion of droplets in aqueous hydrophilic colloid, called 
antistatic dispersion herein, can be added as such to aqueous hydrophilic 
colloid coating compositions for forming antistatic protective layers of a 
photographic element. The antistatic dispersion can be added to the 
aqueous hydrophilic colloid coating compositions for forming antistatic 
protective layers, alone or together with other additives such as matting 
agents e.g.polymethyl methacrylate and polytetrafluoroethylene. 
The antistatic dispersion can be prepared in bulk and stored for a long 
time without loosing its antistatic effect. A batch can be taken at any 
moment from this bulk and added to an aqueous hydrophilic colloid coating 
composition for forming an antistatic protective layer of a photographic 
element, to realize the desired antistatic effect in said photographic 
element. 
The amount of water-immiscible solvent medium used in the preparation of 
the dispersion depends on the solubility of the particular antistatic 
agent therein. It may vary between very wide limits but is preferably 
limited to a minimum value, which minimum value can easily be established 
by making a few comparative tests. 
The dispersing of the solution into aqueous hydrophilic colloid can be 
assisted by means of high speed stirrers, homogenizers (single or double 
stage homogenizers), colloid mills or ultrasonic wave generators. 
The solvent or mixture of solvents constituting said water-immiscible 
solvent medium, from which the urethanes are dispersed in aqueous 
hydrophilic colloid, have a solubility in water of at most 25% by weight 
at room temperature (20.degree. C.). Solvents having a solubility in water 
comprised between 2 and 10% by weight at room temperature are preferred. 
Moreover, such solvents or mixture of solvents preferably are low-boiling 
solvents, in other words solvents having a boiling point of at most 
130.degree. C. and they have a sufficiently high vapour pressure so that 
they can be removed from the aqueous dispersion by applying a vacuum of 
500 to 10 mm Hg at a temperature of 25.degree. to 80.degree. C. 
The removal of the water-immiscible solvent medium is effected by 
evaporation and, whenever desired, this removal can be accelerated by 
applying reduced pressure and/or moderate heating. 
The water-immiscible solvent medium consists of a water-immiscible solvent 
or of a mixture of water-immiscible solvents preferably chosen from the 
group consisting of methylene chloride, ethyl formate, n-butyl formate, 
ethyl acetate, n-propyl acetate, isopropyl acetate, butyl acetate, methyl 
propionate, ethyl propionate, diethyl carbonate, carbon tetrachloride, 
sym.-dichloroethane, 1,1,2-trichloroethane, 1,2-dichloropropane, 
chloroform, n-butyl alcohol, amyl chloride, diethyl ketone, methyl 
n-propyl ketone, diisopropyl ether, cyclohexane, methylcyclohexane, 
ligroin (boiling range: 60.degree.-110.degree. C.), benzene, toluene, and 
nitromethane. Very good results are obtained with a water-immiscible 
solvent medium consisting of ethyl acetate. 
At least one so-called oil-former may be added to the water-immiscible 
solvent medium referred to above. Suitable oil-formers for that purpose 
are tricresyl phospate, tributyl phthalate, dibutyl phthalate, diisooctyl 
phthalate, tributyl citrate, dibutyl sebacate, N,N-dimethyl palmitamide 
and those described in U.S. Pat. Nos. 4,430,421 and 4,430,422. 
During the preparation of the antistatic dispersions of the present 
invention at least one anionic, cationic, or non-ionic surface-active 
agent must be present in the aqueous hydrophilic colloid, into which the 
solution of the urethane is to be dispersed. The surface-active agent is 
added preferably at the very stage of dispersing said solution in the 
aqueous hydrophilic colloid. 
The amount of anionic, cationic, or non-ionic surface-active agent used in 
preparing the antistatic dispersion of the present invention may vary 
within wide limits. Generally, it is comprised between 0.5 and 20% by 
weight relative to the weight of the urethane to be dispersed. 
Suitable surface-active agents that can be used during the preparation of 
the antistatic dispersion of the invention have been described in U.K. 
Pat. Nos. 1,293,189 and 1,460,894, in BE Pat. No. 742,680, and in U.S. 
Pat. No. 4,292,402. A survey of surface-active agents that can be used 
during the preparation of the antistatic dispersion of the invention can 
be found in Gerhard Gawalek's "Wasch- und Netzmittel" Akademieverlag, 
Berlin (1962). Examples of suitable surface-active agents are the sodium 
salt of N-methyl-oleyltauride, sodium stearate, heptadecenylbenzimidazole 
sulphonic acid sodium salt, sodium sulphonates of higher aliphatic 
alcohols e.g. 2-methyl-hexanol sodium sulphonate, sodium 
diiso-octyl-sulphosuccinnate, sodium dodecyl sulphate, tetradecyl benzene 
sulphonic acid sodium salt. It is advisable to use fluorinated 
surface-active agents e.g. perfluorocaprylic acid ammonium salt as they 
have an antistatic effect of their own and demonstrate an even more 
prominent antistatic effect when used together with a matting agent in a 
protective hydrophilic colloid layer of a photographic element as 
described in U.K. Pat. No 1,293,189. 
The urethanes used in accordance with the present invention are employed in 
quantities of 10 to 200 mg per square meter of the resulting coated 
antistatic protective layer, preferably of 50 to 100 mg per square meter 
of antistatic protective layer. 
Although gelatin is used customarily as aqueous hydrophilic colloid in the 
preparation of the antistatic dispersion of the invention, other 
hydrophilic and water-permeable film-forming substances, e.g. proteins 
other than gelatin, cellulose derivatives such as alkyl cellulose for 
instance hydroxyethyl cellulose or carboxymethyl cellulose, alginic acid 
and derivatives thereof, gum arabic, polyvinyl alcohols, polyvinyl 
pyrrolidone and even mixtures thereof can be employed as well. 
Likewise gelatin is currently used as hydrophilic colloid in the 
hydrophilic colloid coating composition, to which the antistatic 
dispersion of the present invention is to be added before this hydrophilic 
colloid coating composition is coated to form an antistatic protective 
layer of a photographic element. Of course, the other hydrophilic and 
water-permeable film-forming substances mentioned above can also be 
employed instead of or combined with gelatin. 
The antistatic dispersion of the invention can be used normally in 
antistatic protective layers such as antistress layers but it can also be 
employed in photosensitive silver halide emulsion layers, antihalation 
layers and NC-layers for black-and-white or colour photographic films. 
They are particularly interesting for use in protective layers of X-ray 
materials. They do not cause fogging, do not accelerate development, do 
not migrate from the layers, and do not cause sticking of the layers. 
If desired matting agents can be added together with the antistatic 
dispersion to the hydrophilic colloid coating compositions for forming 
antistatic protective layers, so that heterogeneously distributed 
particles having a size of 1-3 microns are formed in these antistatic 
protective layers. Smooth layers that have an excellent antistatic effect 
are obtained thereby. 
Other additives such as i.a. plasticizers, filling agents, hardening 
accelerators, antifriction agents, anti-Newton additives can also be added 
to the hydrophilic colloid coating compositions for forming the antistatic 
protective layers. 
The silver halide used in the preparation of the photosensitive silver 
halide emulsion layers of the photographic elements according to the 
present invention can be silver bromide, silver iodide, silver chloride, 
or mixed silver halides e.g. silver chlorobromide and silver bromoiodide. 
The photosensitive silver halide emulsion layers of the photographic 
elements according to the present invention may contain the usual 
additives such as e.g. stabilizers, fog-inhibitors, speed-increasing 
compounds, colloid hardeners, plasticizers etc. The silver halide 
emulsions may be spectrally sensitized or non-spectrally sensitized.

The following example illustrates the present invention. 
EXAMPLE 
A gelatin silver bromoiodide (2 mol % of iodide) X-ray emulsion comprising 
per kg 80 g of gelatin and an amount of silver halide corresponding to 190 
g of silver nitrate was coated on both sides of a subbed polyethylene 
terephthalate support at a ratio of 1 kg covering 27 sq. m per side of 
the support. 
Five Batches A to E of hydrophilic colloid coating composition for forming 
antistatic protective layers were prepared. 
Batch A was a coating composition comprising per liter 30 g of gelatin and 
7.5 ml of a 5% aqueous solution of the ammonium salt of perfluorocaprylic 
acid as surface-active agent; 
Batch B was a same coating composition as Batch A, into which, however, per 
liter of coating composition 1.5 ml of the above-mentioned compound IX had 
been stirred; 
Batch C was a same coating composition as Batch A, into which, however, per 
liter of coating composition 15 ml of a 10% methanolic solution of the 
above-mentioned compound IX had been stirred; 
Batch D was a same coating composition as Batch A, into which, however, per 
liter of coating composition 30 g of a 5% antistatic dispersion had been 
stirred, which had been prepared by emulsifying a temporary sqlution of 
compound IX in ethyl acetate into 5% by weight aqueous gelatin with 
stirring and subsequently removing the ethyl acetate by evaporation, the 
stirring having been such that the resulting disperse drops of compound IX 
had a diameter averaging about 1300 nm; 
Batch E was a same coating composition as Batch D with the difference that 
the stirring had been such that the resulting disperse drops of compound 
IX had a diameter averaging about 8000 nm. 
The resulting five Batches A to E were examined twice for comparison; a 
first time immediately after their preparation and a second time after 
having been left standing for two days. 
Batch A appeared to be unaltered during the second examination, whereas in 
Batch B the antistatic compound IX appeared to have formed an oily film at 
the surface of the coating composition. 
During the first examination Batch C appeared to comprise disperse droplets 
consisting of antistatic compound IX dissolved in methanol but during the 
second examination the antistatic compound IX appeared to have left the 
dissolved state at least partially and formed an oily film at the surface 
of the coating composition. The dissolved phase that was still present had 
taken the form of large and irregular drops in the coating composition. 
During the first examination Batches D and E appeared to consist of aqueous 
gelatin comprising disperse drops of antistatic compound IX; during the 
second examination Batches D and E, unlike Batches B and C, appeared to 
show no change whatsoever. 
Five strips of the above emulsion-coated support were coated on both sides 
while still wet with Batches A, B, C, D, and E respectively that had been 
left standing for two days after their preparation. Both antistatic 
protective layers were coated at a ratio of 27 sq. m. per liter of coating 
composition, which means that per sq. m. and on each side of the support 
about 1.1 g of gelatin was present. The concentration of compound IX in 
each of the antistatic protective layers coated from the Batches B, C, D, 
and E was approximately 75 mg per sq. m. 
Coating of the Batches B and C was very difficult and if the coating 
succeeded at all the reproducibility of the coating results was extremely 
poor. Coating of the Batches A, D, and E was easy and reproducible. 
The five strips were stored for 3 days at 57.degree. C. and a relative 
humidity of 34%. Each of them was cut into four samples. 
A first series of samples consisting of a sample of each of the five strips 
coated with Batches A, B, C, D, and E respectively was rubbed against a 
brass surface, a second series against a rubber surface, a third against a 
polyvinyl chloride surface, and a fourth against an intensifying calcium 
tungstate screen, the rubbing being performed in the dark. 
All twenty samples were then developed identically to make visible the 
discharge images produced in the emulsion layers by the sparks formed 
during the rubbing. The discharge images were then evaluated. An 
appreciation of these evaluations is given in the following Table 1 ; the 
values listed therein should be interpreted as follows: 0 stands for 
excellent, 1 stands for very good, 2 stands for good, 3 stands for 
unsatisfactory, 4 stands for poor antistatic behaviour, and 5 for no 
antistatic effect at all. Intermediate values between the above integers 
up to one decimal can be found in the Table. Table 1 also gives the sum of 
the values of the four samples cut from a same strip and rubbed against 
the different surfaces. 
TABLE 1 
______________________________________ 
Antistatic protective 
Discharge evaluations after 
layer coated from 
having been rubbed against 
Sum of 
Batch Brass Rubber PVC Screen 
evaluations 
______________________________________ 
A 0.1 1.0 4.5 5.0 10.6 
B 0.0 0.1 1.0 1.0 2.1 
C 0.1 0.1 1.5 1.0 2.7 
D 0.1 1.0 4.5 4.5 10.1 
E 0.0 0.1 1.2 0.1 1.4 
______________________________________ 
These results learn that the antistatic effect obtained with the antistatic 
dispersion of the present invention, which comprises compound IX in the 
form of dispersed droplets having an average diameter of 8000 nm is 
excellent and exceeds that of the comparison materials. In contrast, the 
antistatic effect obtained with the antistatic dispersion comprising 
compound IX in the form of dispersed droplets having an average diameter 
of 1300 nm is very poor. 
Summarizingly, it can be said that the coating of the antistatic protective 
layer from Batch E was easy and reproducible and that the resulting 
antistatic protective layer showed a highly satisfactory antistatic 
effect, which makes it extremely apt for application in photographic 
elements undergoing extensive manipulation and/or high speed processing.