FIELD OF THE INVENTION
[0001] This invention relates to an imaging element with improved physical properties of
its surface layer, and in particular to an imaging element comprising a support, at
least one image-forming layer, and a surface protective layer. More specifically,
this invention relates to such imaging elements having a surface protective layer
that is applied from an aqueous medium and exhibits superior surface lubricity and
excellent manufacturing characteristics.
BACKGROUND OF THE INVENTION
[0002] During the handling of an imaging material, such as coating, drying, finishing, winding,
rewinding, printing, projecting, and so on, the material surfaces are often damaged
by contact friction with various equipment or as a result of contact between the front
and back side of the imaging material. For example, scratches or abrasions can result
on the emulsion and back side of a photographic material. These scratches or abrasion
marks are visible during printing or projecting processes. This causes serious problems
in the practical use of the films. In addition, when the contact friction is high,
the imaging materials do not transport smoothly during the manufacturing process or
in various exposure, processing, and projection machines. These transport problems
may result in product waste. In recent years, the conditions under which the imaging
materials are manufactured or utilized have become more severe, because their applications
have been extended (for example, in an atmosphere of high humidity and high temperature)
or because the methods for their preparation have been advanced (for example, high
speed coating, high speed finishing and cutting, and fast processing). Under these
conditions, the imaging materials are more easily damaged.
[0003] To lower the contact friction and improve the resistance to damage to surfaces, a
lubricant or slipping agent is often used. Examples of the lubricants used for these
purposes include silicone fluids as described in
U.S. Patent No. 3,489,567, and wax esters of high fatty acids or high fatty alcohols in
U.S. Patent No. 3,121,060. Problems are encountered in the use of these lubricants. For example, waxes such
as Carnauba wax have been used to form the backing lubricant layer. However, they
need to be coated from solvents such as propylene dichloride, which is on the EPA
P/U highly hazardous list. Furthermore, waxes in most cases have to be applied as
a separate layer, which requires an additional coating station and therefore increases
product cost.
[0004] Silicone fluids are frequently used as lubricants, but, they are prone to transferring
from one side of the imaging element to the other side when the element is stored
or supplied in a wound roll form, such as a photographic film for amateur photography.
In addition, since these silicone fluids are insoluble in water they must be dispersed
with mechanical energy and, typically, in the presence of large amounts of surfactant,
into aqueous coating compositions. This process results in coatings containing silicone
fluids dispersed as fairly large droplets which may cause the dried coatings to be
hazy in appearance. The large amounts of surfactant used to disperse the silicone
fluids may be undesirable since they may cause the coating composition to foam and
may compromise the physical properties (for example the barrier properties) of the
dried layer.
[0005] Siloxane-containing polymers have been described for use in backing layers or slipping
layers for imaging materials.
U.S. Patent No. 4,961,997 describes a backing layer for use in a thermal recording medium which comprises a
cured product of a mixture of a silicone-modified polyurethane resin and a heat-resistant
organic powder. The patent discloses that the backing layer may be applied from organic
solvents such as paraffin solvents, aromatic solvents, ketones, alcohols, esters,
and their mixtures. The patent does not teach or disclose backing layers applied from
aqueous medium.
[0006] U.S. Patent Nos. 4,910,087 and
4,942,212 describe heat-resistant layers for heat-sensitive recording elements in which the
heat-resistant layers are made of a polyurethane resin containing a siloxane. These
patents disclose applying such layers from organic solvent medium.
[0007] U.S. Patent No. 5,330,840 describes polysiloxane containing polyurethane coatings for rollers and belts useful
for toner fusing in electrophotography. The coatings were applied from an organic
solvent such as tetrahydrofuran.
[0008] U.S. Patent No. 5,451,495 describes a photographic element comprising a support, at least one light-sensitive
silver halide containing layer and a layer comprising a crosslinked polymer having
tertiary nitrogen atoms that are converted to quaternary amines. The polymer backbone
moieties are polycondensation polymers such as polyurethanes and the crosslinking
moieties are siloxanes. However, polymers containing quaternary amines are undesirable
for photographic applications due to their propensity to interact with anionic filter
dyes leading to possible dye stain after film processing. In addition, the layers
were not described as being applied from aqueous medium.
[0009] Solvent-soluble siloxane-containing polyimides and polyesters for use in slipping
layers for dye-donor elements in thermal dye transfer are described in
U.S. Patent Nos. 5,252,534 and
5,234,889, respectively. These slipping layers were described as being applied from organic
solvent medium.
[0010] A foremost objective of the present invention is to provide an imaging element having
a new surface protective layer composition which can be applied from an aqueous medium.
The coating compositions used to form such a surface lubricant layer are stable with
respect to manufacturing processes and are attractive from an environmental standpoint.
The surface protective layer prepared has excellent lubricity.
SUMMARY OF THE INVENTION
[0011] In accordance with the present invention, an imaging element includes a support,
at least one image-forming layer, and an outermost protective layer. The protective
layer is formed by the coating and subsequent drying of an aqueous coating composition
containing a water dispersible, siloxane-containing polyurethane. The surface protective
layer of the invention exhibits superior lubricity and excellent manufacturing characteristics.
[0012] In accordance with the present invention, a photographic element comprises a support,
at least silver halide light sensitive layer, and an outermost protective layer having
a siloxane-containing polyurethane. The surface protective layer of the invention
exhibits superior lubricity and excellent manufacturing characteristics.
DESCRIPTION OF THE INVENTION
[0013] The coating compositions utilized herein to form the surface protective layer of
an imaging element comprise a continuous aqueous phase containing a water dispersible,
siloxane-containing polyurethane. Such coating compositions are particularly advantageous
because they eliminate the need to utilize undesirable solvents, such as chlorinated
solvents, which are otherwise needed to dissolve conventional lubricants. The coating
compositions are resistant to flocculation, precipitation, or coagulation of the lubricant.
In addition, the coating compositions of the invention form dried layers that provide
excellent frictional characteristics and the siloxane-containing polyurethane lubricant
does not transfer to other surfaces during the manufacture, storage, and use of the
imaging element and is not removed during conventional photographic film processing,
thus providing excellent lubricity to the developed film.
[0014] The imaging elements of this invention can be of many different types depending on
the particular use for which they are intended. Details with respect to the composition
and function of a wide variety of different imaging elements are provided in
U.S. Patent No. 5,300,676, herein incorporated by reference, and references described therein.
[0015] Imaging elements can comprise various polymeric films, papers, glass, and the like,
but both acetate and polyester supports well known in the art are preferred. The thickness
of the support is not critical. Support thickness of 2 to 10 mil (0.002 to 0.010 inches)
can be used. The supports typically employ an undercoat or subbing layer well known
in the art that comprises, for example, for polyester support a vinylidene chloride/methyl
acrylate/itaconic acid terpolymer or vinylidene chloride/acrylonitrile/acrylic acid
terpolymer.
[0016] The coating compositions of the invention contain a water dispersible, siloxane-containing
polyurethane. Water dispersible polyurethanes are well known and are prepared by chain
extending a prepolymer containing terminal isocyanate groups with an active hydrogen
compound, usually a diamine or diol. The prepolymer is formed by reacting a diol or
polyol having terminal hydroxyl groups with excess diisocyanate or polyisocyanate.
To permit dispersion in water, the prepolymer is functionalized with hydrophilic groups.
Anionic, cationic, or nonionically stabilized prepolymers can be prepared. Anionic
dispersions contain usually either carboxylate or sulphonate functional co-monomers,
e.g., suitably hindered dihydroxy carboxylic acids (dimethylol propionic acid) or
dihydroxy sulphonic acids. Cationic systems are prepared by the incorporation of diols
containing tertiary nitrogen atoms, which are converted to the quaternary ammonium
ion by the addition of a suitable alkylating agent or acid. Nonionically stabilized
prepolymers can be prepared by the use of diol or diisocyanate co-monomers bearing
pendant polyethylene oxide chains. These result in polyurethanes with stability over
a wide range of pH. Nonionic and anionic groups may be combined synergistically to
yield "universal" urethane dispersions. Of the above, anionic polyurethanes are by
far the most significant.
[0017] Several different techniques may be used to prepare polyurethane dispersions. For
example, the prepolymer may be formed, neutralized or alkylated if appropriate, then
chain extended in an excess of organic solvent such as acetone or tetrahydrofuran.
The prepolymer solution is then diluted with water and the solvent removed by distillation.
This is known as the "acetone" process. Alternatively, a low molecular weight prepolymer
can be prepared, usually in the presence of a small amount of solvent to reduce viscosity,
and chain extended with a diamine just after the prepolymer is dispersed into water.
The latter is termed the "prepolymer mixing" process and for economic reasons is much
preferred over the former.
[0018] Polyols useful for the preparation of polyurethane dispersions include polyester
polyols prepared from a diol (e.g. ethylene glycol, butylene glycol, neopentyl glycol,
hexane diol or mixtures of any of the above) and a dicarboxylic acid or an anhydride
(succinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid,
isophthalic acid, maleic acid and anhydrides of these acids), polylactones from lactones
such as caprolactone reacted with a diol, polyethers such as polypropylene glycols,
and hydroxyl terminated polyacrylics prepared by addition polymerization of acrylic
esters such as alkyl acrylates or methacrylates with ethylenically unsaturated monomers
containing functional groups such as carboxyl, hydroxyl, cyano groups and/or glycidyl
groups.
[0019] Diisocyanates that can be used are as follows: toluene diisocyanate, tetramethylene
diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, ethylethylene diisocyanate,
2,3-dimethylethylene diisocyanate, 1-methyltrimethylene diisocyanate, 1,3-cycopentylene
diisocyanate, 1,4-cyclohexylene diisocyanate, 1,3-phenylene diisocyanate, 4,4'-biphenylene
diisocyanate, 1,5-naphthalene diisocyanate, bis-(4-isocyanatocyclohexyl)-methane,
4,4'diisocyanatodiphenyl ether, tetramethyl xylene diisocyanate and the like.
[0020] Compounds that are reactive with the isocyanate groups and have a group capable of
forming an anion are as follows: dihydroxypropionic acid, dimethylolpropionic acid,
dihydroxysuccinic acid and dihydroxybenzoic acid. Other suitable compounds are the
polyhydroxy acids which can be prepared by oxidizing monosaccharides, for example
gluconic acid, saccharic acid, mucic acid, glucuronic acid and the like.
[0021] Suitable tertiary amines which are used to neutralize the acid and form an anionic
group for water dispersability are trimethylamine, triethylamine, dimethylaniline,
diethylaniline, triphenylamine and the like.
[0022] Diamines suitable for chain extension of the polyurethane include ethylenediamine,
diaminopropane, hexamethylene diamine, hydrazine, amnioethylethanolamine and the like.
[0023] Solvents which may be employed to aid in formation of the prepolymer and to lower
its viscosity and enhance water dispersibility include methylethylketone, toluene,
tetrahydofuran, acetone, dimethylformamide, N-methylpyrrolidone, and the like. Water-miscible
solvents like N-methylpyrrolidone are much preferred.
[0024] For the purpose of the present invention, the water dispersible polyurethane features
the inclusion of siloxane bonds in its molecule. This may be accomplished either by
utilizing a polysiloxane having a hydroxyl or amine group, preferably the polysiloxane
is a diol or diamine in the preparation of the polyurethane. Such siloxane-containing
diols or diamines are represented by the following general formula:

wherein: X is an amino or hydroxyl group, R
1, R
2, R
3, R
4, R
5, R
6, R
7, R
8, R
9, R
10, R
11 and R
12 are each independently an alkyl, aryl, or arylalkyl group, the alkyl group or alkyl
portion of the arylalkyl group containing 1 to 6 carbon atoms, and n and m are each
from 0 to about 500, such that the value of n + m is from 10 to about 500.
[0025] For the purpose of the present invention the siloxane-containing polyurethane comprises
more than 0.25 weight % and less than 25 weight % of the siloxane component, preferably
more than 1.0 weight % and less than 10 weight %. The proportion of siloxane component
may be controlled within this range by regulating the value of the molecular weight
of the siloxane component (n + m value in the above structures) used in the preparation
of the siloxane-containing polyurethane or by using together with a polysiloxane polyol
or polysiloxane diamine a conventional polyol which does not contain polysiloxane
such as ethylene glycol, propylene glycol, polyether polyol, polyester polyol, polyacrylate
polyol, and the like, or a conventional diamine which does not contain polysiloxane
such as ethylenediamine, diaminopropane, hexamethylene diamine, hydrazine, aminoethylethanolamine
and the like.
[0026] Coating compositions of the present invention may comprise the water dispersible,
siloxane-containing polyurethane in combination with other water soluble or water
dispersible polymers in order to tailor the physical and chemical properties of the
surface protective layer for a specific imaging application. Water soluble polymers
include, for example, gelatin, polyvinyl alcohol, polyvinyl pyrrolidone, cellulosics,
polystyrene sulfonic acid and its alkali metal salts or ammonium salts, acrylic or
methacrylic acid interpolymers, and the like. Water dispersible polymers that may
be used in conjunction with the siloxane-containing polyurethane include latex interpolymers
containing ethylenically unsaturated monomers such as acrylic and methacrylic acid
and their esters, styrene and its derivatives, vinyl chloride, vinylidene chloride,
butadiene, acrylamides and methacrylamides, and the like. Other water dispersible
polymers that may be used include polyurethane and polyester dispersions. Still further
water dispersible polymers that may be used are the base neutralized, carboxylic acid-containing
latex polymers described in the commonly assigned copending application Serial No.
712,006, filed Sept. 11, 1996. Preferably, the surface protective layer contains at least 2 mg/m
2 of the siloxane-containing polyurethane.
[0027] The surface protective layer compositions in accordance with the invention may also
contain suitable crosslinking agents including aldehydes, epoxy compounds, polyfunctional
aziridines, vinyl sulfones, methoxyalkyl melamines, triazines, polyisocyanates, dioxane
derivatives such as dihydroxydioxane, carbodiimides, and the like. The crosslinking
agents may react with the functional groups present on the siloxane-containing polyurethane,
and/or the other water soluble or water dispersible polymer present in the coating
composition.
[0028] Matte particles well known in the art may also be used in the surface protective
layer compositions of the invention, such matting agents have been described in
Research Disclosure No. 308119, published Dec 1989, pages 1008 to 1009. When polymer matte particles are employed, the polymer may contain reactive functional
groups capable of forming covalent bonds with the binder polymer by intermolecular
crosslinking or by reaction with a crosslinking agent in order to promote improved
adhesion of the matte particles to the coated layers. Suitable reactive functional
groups include: hydroxyl, carboxyl, carbodiimide, epoxide, aziridine, vinyl sulfone,
sulfinic acid, active methylene, amino, amide, allyl, and the like.
[0029] The surface protective layer can contain other additives such as magnetic recording
particles, abrasive particles, conductive polymers, conductive metal oxide particles,
coating aids, charge control surfactants, and a secondary lubricant. There are no
particular limits on the secondary lubricants that may be used. They may include,
for example, perfluorinated polymers, natural and synthetic waxes, silicone fluids,
stearamides, oleamides, stearic acid, lauric acid, ethylene glycol distearate, ethylene
glycol monostearate, and the like.
[0030] The coating compositions of the present invention may be applied as aqueous coating
formulations containing up to 20% total solids by coating methods well known in the
art. For example, hopper coating, gravure coating, skim pan/air knife coating, spray
coating, and other methods may be used with very satisfactory results. The coatings
are dried at temperatures up to 150 °C to give dry coating weight of 20 mg /m
2 to 10 g/m
2.
[0031] The surface protective layer of the invention may be present on the side of the support
opposite to the imaging layer and serve as an outermost backing layer, or an outermost
layer coated on the top of an abrasion resistance backing layer, or an outermost layer
coated on the top of an antistatic layer, or an outermost layer coated on a magnetic
recording layer. The surface protective layer may also be used as the outermost layer
on the imaging side of the support, for example as the protective overcoat for a silver
halide emulsion layer.
[0032] In a particularly preferred embodiment, the imaging elements of this invention are
photographic elements, such as photographic films, photographic papers or photographic
glass plates, in which the image-forming layer is a radiation-sensitive silver halide
emulsion layer. Such emulsion layers typically comprise a film-forming hydrophilic
colloid. The most commonly used of these is gelatin and gelatin is a particularly
preferred material for use in this invention. Useful gelatins include alkali-treated
gelatin (cattle bone or hide gelatin), acid-treated gelatin (pigskin gelatin) and
gelatin derivatives such as acetylated gelatin, phthalated gelatin and the like. Other
hydrophilic colloids that can be utilized alone or in combination with gelatin include
dextran, gum arabic, zein, casein, pectin, collagen derivatives, collodion, agar-agar,
arrowroot, albumin, and the like. Still other useful hydrophilic colloids are water-soluble
polyvinyl compounds such as polyvinyl alcohol, polyacrylamide, poly(vinylpyrrolidone),
and the like.
[0033] The photographic elements of the present invention can be simple black-and-white
or monochrome elements comprising a support bearing a layer of light-sensitive silver
halide emulsion or they can be multilayer and/or multicolor elements.
[0034] Color photographic elements of this invention typically contain dye image-forming
units sensitive to each of the three primary regions of the spectrum. Each unit can
be comprised of a single silver halide emulsion layer or of multiple emulsion layers
sensitive to a given region of the spectrum. The layers of the element, including
the layers of the image-forming units, can be arranged in various orders as is well
known in the art.
[0035] A preferred photographic element according to this invention comprises a support
bearing at least one blue-sensitive silver halide emulsion layer having associated
therewith a yellow image dye-providing material, at least one green-sensitive silver
halide emulsion layer having associated therewith a magenta image dye-providing material
and at least one red-sensitive silver halide emulsion layer having associated therewith
a cyan image dye-providing material.
[0036] In addition to emulsion layers, the elements of the present invention can contain
auxiliary layers conventional in photographic elements, such as overcoat layers, spacer
layers, filter layers, interlayers, antihalation layers, pH lowering layers (sometimes
referred to as acid layers and neutralizing layers), timing layers, opaque reflecting
layers, opaque light-absorbing layers and the like. The support can be any suitable
support used with photographic elements. Typical supports include polymeric films,
paper (including polymer-coated paper), glass and the like. Details regarding supports
and other layers of the photographic elements of this invention are contained in
Research Disclosure, Item 36544, September, 1994 and in
Research Disclosure, Item 38957, September, 1996, incorporated by reference herein.
[0037] The light-sensitive silver halide emulsions employed in the photographic elements
of this invention can include coarse, regular or fine grain silver halide crystals
or mixtures thereof and can be comprised of such silver halides as silver chloride,
silver bromide, silver bromoiodide, silver chlorobromide, silver chloroiodide, silver
chorobromoiodide, and mixtures thereof. The emulsions can be, for example, tabular
grain light-sensitive silver halide emulsions. The emulsions can be negative-working
or direct positive emulsions. They can form latent images predominantly on the surface
of the silver halide grains or in the interior of the silver halide grains. They can
be chemically and spectrally sensitized in accordance with usual practices. The emulsions
typically will be gelatin emulsions although other hydrophilic colloids can be used
in accordance with usual practice. Details regarding the silver halide emulsions are
contained in
Research Disclosure, Item 36544, September, 1994,
Research Disclosure, Item 38957, September, 1996, and the references listed therein.
[0038] The photographic silver halide emulsions utilized in this invention can contain other
addenda conventional in the photographic art. Useful addenda are described, for example,
in
Research Disclosure, Item 36544, September, 1994 and
Research Disclosure, Item 38957, September, 1996. Useful addenda include spectral sensitizing dyes, desensitizers, antifoggants, masking
couplers, DIR couplers, DIR compounds, antistain agents, image dye stabilizers, absorbing
materials such as filter dyes and UV absorbers, light-scattering materials, coating
aids, plasticizers and lubricants, and the like.
[0039] Depending upon the dye-image-providing material employed in the photographic element,
it can be incorporated in the silver halide emulsion layer or in a separate layer
associated with the emulsion layer. The dye-image-providing material can be any of
a number known in the art, such as dye-forming couplers, bleachable dyes, dye developers
and redox dye-releasers, and the particular one employed will depend on the nature
of the element, and the type of image desired.
[0040] Dye-image-providing materials employed with conventional color materials designed
for processing with separate solutions are preferably dye-forming couplers; i.e.,
compounds which couple with oxidized developing agent to form a dye. Preferred couplers
which form cyan dye images are phenols and naphthols. Preferred couplers which form
magenta dye images are pyrazolones and pyrazolotriazoles. Preferred couplers which
form yellow dye images are benzoylacetanilides and pivalylacetanilides.
[0041] The following examples are used to illustrate the present invention. However, it
should be understood that the invention is not limited to these illustrative examples.
EXAMPLES
Examples 1 to 3 and Comparative Sample A
[0042] The following examples show that coating compositions of the invention provide stable
coating formulations and yield dried films that are highly transparent and have excellent
frictional characteristics (i.e., low coefficient of friction values). Protective
layer coating compositions comprising a water dispersible polyurethane-polydimethyl
siloxane (Neorez R9649, Zeneca Resins Inc.) containing about 5 weight % polydimethyl
siloxane and a water dispersible polyurethane that does not contain a siloxane (Witcobond
232, Witco Corp.) were applied from an aqueous medium onto a polyethylene terephthalate
imaging support that had been previously subbed with a vinylidene chloride-containing
terpolymer latex. The coatings were dried at 100 °C to give layers with a total dried
coating weight of 1000 mg/m
2. The coefficient of friction (COF) was determined using the methods set forth in
ANSI IT 9.4-1992. The stability of the coating formulations and the appearance of
the dried films were also visually evaluated. The results are listed in Table 1. The
results show that coating compositions of the invention are very stable and form dried
films that are transparent and have excellent lubricity.
TABLE 1
Example |
Wt % Neorez R9649 |
Wt % Witcobond 232 |
Formulation Stability |
Coating Appearance |
COF |
Comparative Sample A |
0 |
100 |
Excellent |
Excellent |
0.43 |
Example 1 |
2 |
98 |
Excellent |
Excellent |
0.21 |
Example 2 |
5 |
95 |
Excellent |
Excellent |
0.18 |
Example 3 |
10 |
90 |
Excellent |
Excellent |
0.14 |
Examples 4 to 6 and Comparative Sample B
[0043] The following examples show that coating compositions of the invention in which a
urethane-siloxane polymer lubricant is used in a gelatin binder provide stable coating
formulations and yield dried films that are highly transparent and have excellent
frictional characteristics (i.e., low coefficient of friction values). Protective
layer coating compositions comprising the water dispersible polyurethane-polydimethyl
siloxane (Neorez R9649, Zeneca Resins Inc.), lime-processed gelatin, and bis(vinyl
sulfone) methane hardener were applied from aqueous medium onto a polyethylene terephthalate
imaging support that had been previously subbed with a vinylidene chloride-containing
terpolymer latex. The coatings were chill-set at 4.5 °C and dried first at 21 °C and
then at 38 °C to give layers with a total dried coating weight of 800 mg/m
2. The coefficient of friction (COF) was determined using the methods set forth in
ANSI IT 9.4-1992. The stability of the coating formulations and the appearance of
the dried films were also visually evaluated. The results are listed in Table 2. The
results show that gelatin-containing coating compositions of the invention are very
stable and form dried films that are transparent and have excellent lubricity.
TABLE 2
Example |
Wt % Neorez R9649 |
Wt % Gelatin |
Formulation Stability |
Coating Appearance |
COF |
Comparative Sample B |
1.25 |
98.75 |
Excellent |
Excellent |
0.46 |
Example 4 |
3.75 |
96.25 |
Excellent |
Excellent |
0.37 |
Example 5 |
6.25 |
93.75 |
Excellent |
Excellent |
0.27 |
Example 6 |
12.50 |
87.5 |
Excellent |
Excellent |
0.24 |
[0044] While it has been shown and described what are at present the preferred embodiments
of the invention, various modifications and alterations will be obvious to those skilled
in the art. All such modifications and alterations are intended to be included in
the following claims.