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Description  |
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TECHNICAL FIELD
This invention relates to the co-precipitation of coupler dispersions with
polymers that have base ionizable or negatively charged groups. The
coupler is dissolved in base and a water miscible solvent. A polymer latex
with surfactant is ionized by base. These two solutions are then mixed in
a stream and co-precipitated to form fine particle dispersions by
immediate neutralizing using an acid in a mixing device. In such a
precipitated dispersion the coupler precipitates inside the latex to form
the dispersion particles, that have high photographic activity.
BACKGROUND ART
R-1 Townsley et al., U.K. Patent 1,193,349.
R-2 W. J. Priest, Research Disclosure, December, 1977, "Process for
Preparing Stable Aqueous Dispersion of Certain Hydrophobic Materials," pp.
75-80.
R-3 T. J. Chen et al. (Kodak), U.S. Pat. Nos. 4,199,363; 4,214,047;
4,133,687; 4,127,499; 4,203,716; 4,247,627; and 4,127,499.
R-4 L. K. J. Tong (Kodak), U.S. Pat. Nos. 2,852,386 and 2,772,163.
R-5 0. Takahashi, (Fuji), European Patent Application 0,256,531.
R-6 R. Matcjeck (Gaevert), German Patent 3,520,845.
R-7 T. C. Webb et al. (Ciba-Geigy), U.S. Pat. No. 4,490,461.
R-8 K. Nakazyo et al., (Fuji), U.S. Pat. No. 4,120,725.
R-9 M. Yoneyama et al., (Fuji), U.S. Pat. No. 4,198,478.
R-10 J. Minamizono et al., (Fuji), U.S. Pat. No. 4,291,113
R-11 Y. Mukunoki et al., (Fuji), U.S. Pat. No. 4,569,905.
R-12 R. G. Mowrey et al., "Color Dispersions in Synthetic Polymer
Vehicles," Research Disclosure, 15131, p. 42-43 (1976).
R-13 K. Tokitou et al., (Konishiroku), U.S. Pat. No. 4,358,533.
R-14 N. Fujiwhara et al., (Konishiroku), U.S. Pat. No. 4,368,258.
R-15 L. K. J. Tong, (Kodak), Canada 542,135.
R-16 Mitsubishi Paper Mill, Great Britain 1,456,278
R-17 P. Bagchi et al., "Preparation of Low Viscosity Small-Portable
Photographic Disperions in Gelatin," U.S. patent application Ser. No.
366,397.
R-18 B. Chu, "Laser Light-Scattering," Academic Press, 1974, New York.
R-19 Anonymous, "Photographic Silver Halide Emulsions, Preparations,
Addenda, Processing and Systems," Research Disclosure, 308, p. 933-1015
(1989).
R-20 T. H. James, "Theory of Photographic Processes," 4th Ed., McMillan
(1977).
R-21 T. Brandrup et al., "Polymer Handbook," John Wiley, New York (1974).
R-22 P. Bagchi et al., "Methods of Forming Stable Dispersions of
Photographic Materials," U.S. patent application Ser. No. 297,005.
It has been known in the photographic arts to precipitate photographic
materials, such as couplers, from solvent solution. The precipitation of
such materials can generally be accomplished by a shift in the content of
a water miscible solvent and/or a shift in pH. The precipitation by a
shift in the content of water miscible solvent is normally accomplished by
the addition of an excess of water to a solvent solution. The excess of
water, in which the photographic component is insoluble, will cause
precipitation of the photographic component as small particles. In
precipitation by pH shift, a photographic component is dissolved in a
solvent that is either acidic or basic. The pH is then shifted such that
acidic solutions are made basic or basic solutions are made acidic in
order to precipitate particles of the photographic component which is
insoluble at that pH. United Kingdom Patent 1,193,349-Townsley et al.
(R-1) discloses a process wherein an organic solvent, aqueous alkali
solution of a color coupler is mixed with an aqueous acid medium to
precipitate the color coupler. It is set forth that the materials can
either be utilized immediately, or gelatin can be added to the dispersion
and chilled and remelted for use at a later date. In an article in
Research Disclosure, December, 1977, entitled "Process for Preparing
Stable Aqueous Dispersions of Certain Hydrophobic Materials", pages 75-80,
by William J. Priest (R-2), it is disclosed that color couplers can be
formed by precipitation of small particles from solutions of the couplers
in organic auxiliary solvents. However, many coupler dispersions prepared
in this manner are photographically very inactive compared to conventional
dispersions prepared by milling procedures that contain coupler solvents.
It has been shown that when coupler molecules are imbibed into latex
particles by dissolving the coupler in a water-miscible solvent, adding
this to the latex and removing the solvent, the resultant dispersion
produces adequate photographic activity (R-3 and R-4) for photographic
utility. It seems that the polymer latex acts as a coupler solvent;
however, such loading procedure requires very large quantities of solvent,
which makes this procedure very expensive and hazardous for industrial
production. In general such procedure is limited to a load of 3 part
coupler and 1 part latex polymer. Prior art (R-5) indicates that
polymerization or incorporation of a polymer into mechanically ground
dispersions with no permanent solvent produces coupler dispersions that
give very stable dye images. Also, incorporation of polymer into the
photographic layer produces images of high dye stability as indicated in
(R-6). Therefore, it is not clear as to whether the polymer needs to
remain in the coupler particle or just in the photographic layer to
produce the observed dye stability.
In (R-7), Webb et al. describes a process of dispersion preparation by
homogenization of a solid solution of a photographic component and a
polymer into aqueous gelatin solution by milling procedures. In the
process of this invention, a photographic agent and a polymer is dissolved
in a solvent. The solvent is then evaporated off to obtain a solid
solution. The solid solution is then dispersed in aqueous gelatin by
conventional milling procedures. In a specific embodiment this
photographic compound is cross-linked to this polymer. This, in some cases
is done by a cross-linking agent. The cross-linking may be done via a
carboxyl group pendent on the polymer molecule. It is also known that
conventional dispersion of photographic couplers can be prepared with some
photographic advantages that contain both coupler solvent and a synthetic
polyacrylamide polymer (R-8). In an alternate embodiment of this invention
some water soluble acrylamide polymers can be added in aqueous phase along
with gelatin for achieving added stability. Surfactant like polymers
containing --SO.sub.3 H groups in phenol formaldehyde resins (R-9, R-11)
and in acrylate polymers (R-10) have been used to stabilize milled
conventional dispersions. Other polymeric vehicles have also been
incorporated in photographic layers as gelatin replacement material
(R-12).
Other solvent loading techniques like Chen's (R-3) have been described
Tokitou et al. (R-13) and (R-14). (R-13) describes a process and
composition where a photographic material is loaded into a polymer
particle by using a large volume of water miscible solvent comprising a
polymerized oligomeric material. In a special embodiment, the oligomeric
material is polymerized in the presence of the photographic component to
form a latex loaded composition. The process of latex loading in (R-14) is
quite similar to Chen et al. (R-3). Tong (R-15) describes a very
inefficient method of loading of couplers into latex dispersion by
stirring the coupler for long periods of time with the latex and filtering
off the excess coupler. This procedure led to less than 1 g of coupler per
20 g of the latex polymer in many cases. (R-16)-describes loading of
ultraviolet radiation absorbing compounds into polymer resin by the use of
both permanent and auxiliary solvents in the presence of gelatin.
There are drastic differences between this invention and that of Chen
(R-3). In this invention, the coupler is solubilized and the latex is
swollen by base and a water miscible solvent, in contrast with Chen's
(R-3) process where coupler solubilization and latex swelling are done by
a water miscible solvent alone. In the present invention, the impregnation
of this latex by the coupler is achieved by the neutralization by acid,
whereas in the case of Chen, it is achieved by evaporative removal of the
solvent. As Chen's method is a solvent shift method, it requires a large
amount of water miscible (auxiliary) solvent. By Chen's (R-3) process the
amount of solvent needed is between 15 to 20 times the weight of the
coupler to be imbibed. This is a major drawback of Chen's procedure. In
Chen's process the maximum loading is 3 parts coupler to 1 part polymer,
whereas higher loading would be desirable. Chen's method requires at least
2% by weight of the monomers to be of the type that forms a water soluble
polymer. A process that does not have any such requirement would be
desirable.
DISCLOSURE OF THE INVENTION
An object of this invention is to provide more highly reactive dispersions
of photographic dye-form couplers.
Another object is to provide improved photographic flims.
These and other objectives of this invention are generally accomplished by
providing dispersion of photographic dye-forming coupler (or other
photographic agent) wherein the coupler is imbibed inside a polymer
particle that is ionizable or ionized and swellable by base.
Generally the invention is performed by providing a first flow of water,
base, a base swellable polymer latex dispersion, a surfactant and a second
flow comprising a water miscible auxiliary solvent, base and the
photographic coupler material, bringing together and mixing the said first
and the said second flows and then immediately following mixing,
neutralizing the said streams to form the dispersion particles. The
dispersion particles contain the latex polymer, the photographic material
(dye-forming coupler) and the water miscible solvent. The solvent is
subsequently washed off by diafiltrations providing particles that only
contain essentially the latex polymers and the dye-forming coupler. The
size of the dispersion particles are of the same order of magnitude as the
particles in the latex dispersion. Such dispersion particles are generally
considerably more active than the conventional milled dispersion of the
same coupler containing permanent coupler solvent. The latex particles of
this invention may have any diameter between 10 nm (0.01 .mu.m) to 800 nm
(0.80 .mu.m). The preferred diameters of the latex particles of this
invention are below 200 nm or (0.2 .mu.m). The range and the preferred
range of diameters of the coupler loaded polymer particles are same as
these of the polymer particles themselves.
A BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1. Equipment for the precipitation of the dispersions of this
invention in small scale.
FIG. 2. Equipment for the precipitation of the dispersions of this
invention in large scale.
FIG. 3. Base induced swelling of the carboxylated latexes of
poly(butylacrylate-co-methacrylic acid).
FIG. 4. Glass transition temperatures of poly(butylacrylate-co-methacrylic
acid) as a function of the weight % of methacrylic acid.
FIG. 5. Glass transition temperatures of the dried coupler (C-6)
dispersions of this invention as a function of the amount of coupler
incorporation in the dispersion particle as determined by differential
thermal analysis.
FIG. 6. Enhancement of the dye density yields of the inventive dispersions
of coupler (C-6) (Table-IV) over the prior art dispersion of Example 2.
FIG. 7. Thermal properties of the inventive dispersions of coupler (C-1).
FIG. 8. Thermal properties of the inventive dispersions of coupler (C-6).
MODES OF CARRYING OUT THE INVENTION
This invention provides numerous advantages over prior art processes.
Inventive dispersions of many couplers produce images with much higher dye
density compared to conventional milled coupler dispersions containing
high boiling coupler solvents. Precipitated dispersions of the invention
with a particle diameter larger than 100 nm produce no high viscosity
problems when mixed with gelatin.
The invention dispersions are room temperature keepable for very long
periods of time compared to conventional gel containing coupler
dispersions that need to be refrigerated. The co-precipitation technique
of the invention lends itself to loading ratios of coupler to polymer to
any ratio desired. In the examples we have shown up to 4 parts coupler 1
part polymer. In contrast the prior art method of Chen (R-3) ratios of 1
part polymer and 3 part coupler is about the maximum loading ratio that
can be achieved. Compared to the latex loading method of Chen (R-3), the
PCP (polymer co-precipitated dispersions of this invention) dispersions
require a fractional quantity of water-miscible solvent, as solubilization
is assisted by ionization with base. This not only is a cost saving
advantage compared to the method of Chen, but much less hazardous as no
solvent stripping is involved. Another advantage is that images produced
by the dye-forming coupler dispersions of this invention often have high
light stability and better fade resistance. Another advantage is that the
couplers can be precipitated in large scale (15 kg) at 10% coupler which
is in the range of concentration needs for the formulation of standard
photographic products. This is a manufacturing advantage.
It is an advantage that no high boiling coupler solvents are needed for the
activation of the coupler as long as the invention coupler and latex
particle has a glass transition temperature lower than about 50.degree. C.
This reduces tackiness and mushiness of the coated film and creates an
environmentally safer product.
It is an advantage that the inventive dispersion particles are uniform and
have a diameter around 100 nm, a contrast with the milled dispersions
which have a broad size distribution and the larger particles may be as
large as 1000 nm, which sometimes can contribute to the graininess of this
image. The particle size of such narrow distribution particles are easy
and swift to characterize by technique such as photon correlation
spectroscopy, which lends to less expense in quality assurance metrology.
Further, the inventive process is amenable to a continuous process control
(less product variability) manufacturing procedure, which can produce
large cost savings in high volume products such as color paper.
The invention is practiced in the small scale semicontinuous mode by
bringing in a first flow of water, latex polymer, surfactant and base to
fill the reaction vessel. Then a second flow of a solution of coupler,
base and auxiliary solvent is added to the reaction vessel, which is being
continuously stirred by a mixer. Precipitation of the coupler inside the
polymer particle is achieved by a controlled third flow of propionic or
acetic acid solution using a pump controlled by a processor, which senses
the pH of the reactor and stops delivery of the acid at a pH of 6.+-.0.2.
The dispersion is then disfiltered to remove this auxiliary solvent.
In preferred methods, for large scale preparation, the first stream of
coupler and base is dissolved in water and the second stream of the
aqueous surfactant base and latex particles may be brought together
immediately prior to a centrifugal mixer with addition of acid directly
into the mixer. The streams will have a residence time of about 1 to about
30 seconds in the mixer. When leaving the mixer, they may be disfiltered
on line to remove the auxiliary solvent and immediately be processed for
utilization in photographic materials. When the process is stopped, the
mixer may be shut off with minimum waste of material, as it is only
necessary to discard the material in the mixer and pipelines immediately
adjacent to it when the process is reactivated after a lengthy shutdown.
The process of the invention produces particles of coupler that are present
in water without gelatin. The gelatin free suspensions of the invention
are stable in storage and may be stored at room temperature rather than
chilled as are gelatin suspensions.
FIG. 1 illustrates the semicontinuous equipment to prepare such dispersions
as those of this invention for small laboratory size preparation. This
equipment is used for the preparation of the invention dispersion in
volumes up to 700 mL, in semicontinuous mode for a total coupler weight of
20 g. Container 104 is provided with an aqueous surfactant solution with
the latex polymer and some alkali 124. Container 96 is provided with an
acid solution 98. Container 100 combines a basic solution 102 of coupler
in solvent. Container 104 provides high shear mixing and is the reaction
chamber where dispersion formation takes place. The size of the acid
kettle 96, the coupler kettle 100, and the reaction kettle are all of
about 800 mL in capacity. In the system of FIG. 1, the reactor 104 is
initially provided with an aqueous solution of the surfactant, the
carboxylated latex, and some alkali to ionize the latexes. The coupler is
dissolved in base and a water-miscible solvent generally at an elevated
temperature in a separate vessel and then cooled down to room temperature
and placed in kettle 100. The dispersion preparation process is started by
starting the coupler pump 112, which pumps in basic coupler solution into
the reaction chamber 104 under continuous agitation provided by the
stirrer 116. The pH is monitored during any stage of the precipitation
process using pH meter 120 which is connected to the ph-electrode system
122 and a thermostat probe 140 for temperature sensing. The pH is recorded
in the strip chart recorder 130. After the coupler solution has been
pumped into the reaction chamber 104, pump 112 is stopped and pump 118 is
started to pump acid solution into the reaction chamber 104 via tube 121
for the neutralization and precipitation of the coupler, under vigorous
stirring. The acid solution is pumped until the pH of the reaction chamber
reaches a pH of 6.0.+-.0.2, at which time this acid pump 118 is shut off.
The constant temperature bath 136 is provided to keep the temperature of
the three kettles identical. It is usually kept at about room temperature.
Dispersions prepared in this manner are worked by continuous dialysis
against distilled water for 24 h to remove all the salts and solvent from
the formed dispersion.
In a large scale (between 1000 and 3000 g of coupler) the apparatus 100 of
FIG. 2 is utilized to perform the precipitation process for this
invention. The apparatus is provided with high purity water delivery lines
12. Tank 14 contains a suspension 11 of base, surfactant, latex, and high
purity water. Jacket 15 on tank 14 regulates the temperature of the tank.
Surfactant enters the tank through line 16. Tank 18 contains a
photographic component solution 19. Jacket 17 controls the temperature of
materials in tank 18. The tank 18 contains a coupler entering through
manhole 20, a base material such as aqueous sodium hydroxide solution
entering through line 22, and solvent such as n-propanol entering through
line 24. The solution is maintained under agitation by the mixer 26. Tank
81 contains acid solution 25 such as propionic acid entering through line
30. The tank 81 is provided with a heat jacket 28 to control the
temperature, although with the acids normally used, it is not necessary.
In operation, the acid is fed from tank 81 through line 32 to mixer 34 via
the metering pump 86 and flow meter 88. A pH sensor 40 senses the acidity
of the dispersion as it leaves mixer 34 and allows the operator to adjust
the acid pump 86 to maintain the proper pH in the dispersion exiting the
mixer 34. The photographic component 19 passes through line 42, metering
pump 36, flow meter 38, and joins the basic surfactant/polymer suspension
in line 44 at the "T"-fitting 46. The coupler precipitates into the
polymer particles in mixer 34 and exit through pipe 48 into the
ultrafiltration tank 82. In tank 82 the dispersion 51 is held while it is
washed by ultrafiltration membrane 54 to remove the solvent and salt from
solution and adjust the material to the proper water content for makeup as
a photographic component. The source of high purity water is purifier 56.
Agitator 13 agitates the surfactant solution in tank 14. Agitator 27
agitates the acid solution in tank 81. The impurities are removed during
the ultrafiltration process through permeate (filtrate) stream 58. With
some precipitations, materials that undergo crystallization after
formation of the PCP dispersion require additional colloidal stabilizer
after the dispersion particles are formed. In such special cases solution
of the polymer in high purity water is made in tank 8, which has a
temperature control jacket 1 and a mixing stirrer 2. High purity water is
fed in through the line 3, and the polymer is fed in through the manhole
4. The polymer solution passes through the flow meter 6 and pump 5 and is
mixed in at "T", 7, at a metered rate with the formed final dispersion.
The colloidal stabilizing polymers that are useful for this purpose are
polyvinyl pyrrolidone, and other water soluble polymers.
The auxiliary solvent for dissolving the photographic component may be any
suitable solvent that may be utilized in the system in which precipitation
takes place by solvent shift and/or acid shift. Typical of such materials
are the solvents acetone, methyl alcohol, ethyl alcohol, isopropyl
alcohol, tetrahydrofuran, dimethylformamide, dioxane,
N-methyl-2-pyrrolidone, acetonitrile, ethylene glycol, ethylene glycol
monobutyl ethe | | |
