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Патент USA US2256390

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Patented Sept. 16, 1941
' 2,256,390‘
UNITED STATES PA'E'EN'E' OFFIQE
2,256,390
METHOD OF PREVENTING PRECIPITATION.
0F ALKALBNE-EARTH METAL SALTS IN
GELATW
‘ Edward Hewitson, Rochester, N. Y2, assignor, by
mesne assignments, to Eastman Kodak Com
pany, Rochester, N. Y., a. corporation of New
Jersey
_
No Drawing. Application August 19, 1936,
Serial No. 96,855
2 Claims. (Cl. 95-7)
action involved may be explained in the follow
This invention relates to photographic gelatin
ing way: When sodium metaphosphate is heated
and emulsions and particularly to a method for
to a temperature of about 620° C., it passes into
preventing precipitation of insoluble salts in gel
the hexametaphosphate according to the follow
atin solutions and emulsions.
ing reaction:
Di?iculties have often been encountered when
certain solutions, emulsions, or suspensions are
added to gelatin solutions or photographic emul
When the sodium hexametaphosphate is added
sions used for coating light sensitive plates, ?lms,
to a solution containing a calcium or other al
and papers, by reason of the separation of insol
uble calcium, magnesium, or other alkaline-earth 10 kaline-earth metal compound, a double salt of
sodium and calcium or other alkaline-earth
metal salts which are formed by the interaction
metal is formed according to the following re
of soluble salts of these metals contained in the
gelatin solution or photographic emulsion with
. action:
some constituent of the solution, emulsion, or
suspension added. This effect is undesirable for 15
a number of reasons. The coatings, produced by
This double salt of sodium and calcium ionizes in
the gelatin or photographic emulsion in which
solution to sodium ions and calcium hexameta
a soluble salt has been precipitated, are cloudy
phosphate ions both of which are soluble. The
or hazy and not fully transparent as desired for
calcium ions are bound up in the hexameta
photographic uses, and another objection is that 20 phosphate radical and are not produced as free
the active ingredients of the solution added to
calcium ions in the solution. This ionization
the gelatin or photographic emulsion may be
may be represented as follows:
wholly or partially precipitated and thereby pre
vented from having the desired effect on the
25» In addition to sodium hexametaphosphate,
gelatin solution or photographic emulsion. It is, therefore, an object of the present inven
other alkali-metal salts of hexametaphosphoric
tion to provide a method for preventing precipi
acid may be employed such as the lithium and
tation‘of insoluble salts of alkaline-earth metals
potassium salts.
'
in gelatin solutions and emulsions. A further
This property of the alkali-metal salts of hexa
object is to provide a method for the clari?cation 30 metaphosphoric acid may be taken advantage of
of gelatin solutions and emulsions. A still fur
in a number of ' ways in connection with photo
ther object is an improved photographic emul
graphic. gelatin and emulsions. One use is the
sion free from haze. Other objects will appear
clari?cation ‘ of gelatin solutions. Many solu
from the following description of my invention.
-tions of gelatin are cloudy or hazy due to the
These objects are accomplished by adding an 35 presence of ?nely suspended matter, which in
alkali-metal salt of hexametaphosphoric acid to
many cases consists largely of insoluble calcium
the gelatin solution or photographic emulsion or
salts. The addition of sodium hexametaphos
to the solution or emulsion to be added to the
phate to a gelatin’ solution containing a. haze of
such material lowers the concentration of cal
The alkali-metal salts of hexametaphosphoric 40 cium ions in the‘ solution to such an extent that
acid have the property of forming soluble com
a greater amount of calcium salt dissolves. This
gelatin solution or photographic emulsion.
plex ions with ions of calcium, magnesium and
other alkaline earth metals and this results in
process is repeated until ?nally all of the calcium
salt passes into solution and the gelatin becomes
lowering the concentration of these metallic~ions - clear. The amount of sodium hexametaphos
to such a value that they are no longer precipi 45 phate necessary to achieve this result will vary
tated by acidic ions or radicals such as carbonate,
with the condition of the gelatin and the amount
sulphate, oxalate, oleate, and other fatty acid
of calcium saltpre'sent. In general, about 8.0%
radicals etc. Other heavy metal ions such as
of sodium hexametaphosphate as reckoned on
' iron and aluminum also form complex ions with
the amount of gelatin, will be su?icient. This
hexametaphosphates which are soluble in solu 50 amount may vary, however, from %% to about
tion, but these complex ions are formed to a
20.0%, depending on the quantity of calcium, or
lesser degree.
1'
‘ I other alkaline earth metals, present.
Although I do not wish to commit myself to
Another important use of this property of the
the following explanation of the reason for this
alkali-‘metal hexametaphosphate is in connec-v
effect; I believe that the mechanism of the re- 55 tion with the addition of wax ‘emulsions to photo
2
2,256,390‘
graphic emulsions for the manufacture of self
p.
make solution A. To this is added the wax emul
lubricating ?lms. The addition of wax emul
sions to photographic emulsions for this pur
pose is described in the patent of E. J. Ward,
sion B slowly with stirring. The mixture of A
and B is then added slowly with stirring to the
photographic emulsion C.
In- the above examples, I have referred to mix
ing the wax emulsion with sensitive photographic
emulsions. It should be understood, however,
No. 2,059,829, granted November 3, 1936. Wax
emulsions are readily ?occulated and coagulated
by small amounts of ions of calcium, magnesium,
and other alkaline-earth metals and in fact,
that the wax emulsion may be mixed with gelatin
most heavy metals. Photographic emulsions and
solutions for use as backings, undercoats, or over
gelatin solutions, however, rarely contain more 10 coating layers for photographic ?lms.
than slight traces of metallic ions other than
Another use of alkali-metal hexametaphos
those of magnesium and the other alkaline-earth
phates according to my invention, is in the manu
group; and it is in connection with this group
facture of the suspension of ?nely divided man
that the hexametaphosphates are most effective.
ganese dioxide by the reduction of potassium per
I have found that the ?occulation of wax 15 manganate. When manganese dioxide is manu
emulsions upon addition to photographic emul
factured in this way, carbon dioxide is frequently
sions or gelatin solutions may be prevented by
liberated and if the suspension is mixed with
adding sodium hexametaphosphate to the wax
gelatin, the carbon dioxide thus produced pre
emulsion or to the photographic emulsion or
cipitates insoluble carbonates from the gelatin
gelatin solution before the mixture is. made. 20 solution since the gelatin frequently contains
The sodium hexametaphosphate must be added
alkaline-earth metal compounds. The precipita
in su?icient amount to react with all of the metal
tion of these insoluble salts may be prevented
ions which tend to ?occulate the wax emulsion.
by the addition of the hexametaphosphate to the
The following formulas have been found satis
gelatin solution before the reduction of the
factory.
25
Three solutions or emulsions are made up as
follows:
A.
B.
potassium permanganate takes place.
A further use for the compounds according to
my invention is in the incorporation of certain
dyes in gelatin solutions or emulsions. Dyes such
Emample I
as sulfonated aryl amino ethyl alcohols of the '
Grams 30 Ionamine type are precipitated by calcium and
Sodium hexametaphosphate _________ __
9
similar ions. This property has heretofore
Water ______________________________ __
81 I
limited the use of these dyes in photographic
gelatin. With the aid of sodium hexametaphos
Photographic emulsion ______________ __ 5000
phate, such precipitation can be readily prevented
C. Wax emulsion (20% wax) ___________ __
100
either by adding the hexametaphosphate to the
Water _____________________________ __
210
dye solution or to the emulsion or solution of
In making up the ?nished photographic emulsion
containing wax, the solution A, which is made
is added to the photographic emulsion B. The
gelatin to which the dye solution is to be added.
It is to be understood that my invention may be
used in other ways and that the compounds may
be employed in other proportions than those
wax emulsion is added to water to form the emul
speci?cally mentioned in the preceding descrip
sion C,-which is then added slowly to the mixture
of A and B with stirring. Any suitable natural
tion of my invention. I intend my invention to
be limited only by the scope of the appended
claims.
by dissolving the hexametaphosphate in water,
or synthetic wax such as that disclosed in the
Ward Patent No.‘ 2,059,829 may be used. A pre
45
I claim:
I
- 1. The method of incorporating wax in a gela
ferred wax is carnauba wax.
tin photographic emulsion, which comprises add
Example II
ing an alkali metal salt of hexametaphosphoric
acid to the gelatin emulsion, and mixing the wax
Solutions or emulsions are made up as follows:
Grams 50 emulsion with the gelatin emulsion.
2. The method of incorporating wax in a gela
A. Sodium hexametaphosphate _________ __
9
Water _____________________________ __
291
B. Wax emulsion (20% wax) ___________ __
100
. Photographic emulsion ______________ __ 5000
The hexametaphosphate is dissolved in water to
tin photographic emulsion, which comprises add
ing sodium hexametaphosphate to the gelatin
emulsion, and mixing the wax emulsion with the
55
gelatin emulsion.
EDWARD HEWITSON.
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