U.S. patent number 3,647,440 [Application Number 04/796,552] was granted by the patent office on 1972-03-07 for photographic diffusion transfer product and process.
This patent grant is currently assigned to Eastman Kodak Company. Invention is credited to Arthur A. Rasch.
United States Patent |
3,647,440 |
Rasch |
March 7, 1972 |
PHOTOGRAPHIC DIFFUSION TRANSFER PRODUCT AND PROCESS
Abstract
A receiving layer for use in the photographic diffusion transfer
process comprises finely divided nonsilver noble metal nuclei
obtained by reducing a metal salt in the presence of a colloid with
a reducing agent having a standard potential more negative than
-0.30. The nuclei typically have an average particle size in the
range of about 15 A. to about 65 A., at least 80 percent, by
number, of the nuclei having a particle size in the range of about
20 A. to about 50 A. The receiving layers can be on a support such
as paper or film base.
Inventors: |
Rasch; Arthur A. (Webster,
NY) |
Assignee: |
Eastman Kodak Company
(Rochester, NY)
|
Family
ID: |
25168468 |
Appl.
No.: |
04/796,552 |
Filed: |
February 4, 1969 |
Current U.S.
Class: |
430/232;
430/231 |
Current CPC
Class: |
G03C
8/28 (20130101) |
Current International
Class: |
G03C
8/00 (20060101); G03C 8/28 (20060101); G03c
005/54 () |
Field of
Search: |
;96/29,76 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Torchin; Norman G.
Assistant Examiner: Goodrow; John L.
Claims
We claim:
1. A receiving layer for use in a diffusion transfer transfer
process comprising a colloid binder and nonsilver noble metal
nuclei having an average particle size in the range of about 15 A.
to about 65 A., at least about 80 percent, by number, of said
nuclei having a particle size in the range of about 20 A. to about
50 A.
2. A receiving element comprising a support having thereon said
receiving layer of claim 1.
3. A receiving element according to claim 2 in which said support
is paper.
4. A receiving element according to claim 2 in which said nuclei
are coated on said support in an amount of about 1 to about 200
.mu.g./ft..sup.2.
5. A receiving element according to claim 2 in which said colloid
is gelatin.
6. A photographic element comprising a support having thereon said
receiving layer of claim 1 and having over said layer an overcoat
of a photographic silver halide emulsion.
7. A receiving element of claim 2 in which said metal nuclei are
palladium
8. A receiving element according to claim 2 in which said support
is photographic film base.
9. A photographic element comprising a image in a receiving layer
on a support, said silver image obtained by a silver ion diffusion
transfer process, said receiving layer comprising a colloid binder
and nonsilver noble metal nuclei, substantially all nuclei in said
layer having a particle size in the range of about 15 A. to about
65 A. and about 80 percent of the total number of said nuclei
having a particle size in the range of about 20 A. to about 50
A.
10. A receiving layer for use in the diffusion transfer process
comprising a reaction product obtained by forming finely divided
nonsilver noble metal nuclei from a salt of said metal by reducing
said metal salt, in the presence of a colloid, with a reducing
agent having a standard potential more negative than -0.30.
11. A receiving layer of claim 10 in which said reducing agent is a
hypophosphite or a borohydride.
12. A receiving layer of claim 10 in which said metal salt is
palladium chloride.
13. A receiving layer of claim 10 in which said metal salt is
palladium nitrate.
14. A receiving layer of claim 10 in which said metal salt is
ammonium chloroplatinate.
15. A receiving layer of claim 10 which comprises a gelatin
polymeric latex vehicle for said nuclei.
16. A receiving layer of claim 15 in which said vehicle is prepared
from a monomeric mixture containing acrylonitrile, vinylidene
chloride, acrylic acid with gelatin.
17. A receiving layer of claim 10 in which said metal salt is
sodium chloropallidate.
18. A receiving layer of claim 10 in which said nuclei are coated
in an amount in the range of about 1 to about 200
.mu.g./ft..sup.2.
19. A receiving layer of claim 10 which comprises a gelatin vehicle
for said nuclei.
Description
BACKGROUND OF THE INVENTION
This invention relates to the preparation of nonsilver noble metal
nuclei and their use in diffusion transfer products and
processes.
Diffusion transfer processes are well known. For example, Rott,
U.S. Pat. No. 2,352,014 describes such a process wherein
undeveloped silver halide of an exposed photographic emulsion layer
is transferred as a silver complex imagewise by imbibition to a
silver precipitating or nucleating layer, generally to form a
positive image therein. The silver precipitating or nucleating
layer generally comprises a binder containing nuclei such as nickel
sulfide, colloidal metal or the like. It is known that the
particular nuclei play an extremely important role in determining
the nature of the silver image which is formed in the receiving
layer. For instance, depending upon the particular nuclei employed,
the image formed may have inadequate density, may not have a
neutral tone, i.e., may have a brownish or yellow color, may lack
stability, etc.
Many of the nuclei which have been found suitable from the
standpoint of tone and/or density have had to be prepared fresh
prior to coating, since they have often had poor stability on
standing. For instance, when a dispersion of the nuclei is
permitted to stand, the dispersion appears to lose density,
probably due to a bleaching effect so that the nuclei are no longer
of practical use. In addition, with many nuclei it is difficult to
obtain a satisfactory tone even with a conventional toning agent,
particularly when gelatin is used in the binder. Moreover, many
nuclei do not provide a desirable density in the positive
image.
Silver nuclei have long been considered particularly suitable for
use in diffusion transfer processes, except for the detrimental
yellow color generally associated with their use. Since the image
obtained in the receiving sheet is usually composed of silver
deposited on a suitable site, it appeared that use of silver nuclei
would facilitate the deposition of the silver on these nuclei and
result in a particularly good dense image. In addition, evidence
points to the importance of the shape and size of the grains which
are formed by depositing the silver on the nucleating sites, and it
appeared likely that silver nuclei would encourage the formation of
desirable grain sizes and grain shapes.
Carey Lea silver, a colloidal silver, can be used as nuclei in
diffusion transfer processes. According to the Carey Lea method of
preparing colloidal silver, silver nitrate is reduced in a solution
of dextrin and sodium hydroxide at a pH of about 13.3. The average
particle size is about 150 A. However, the average particle size
can be reduced to about 50-70 A. by modifying the Carey Lea process
to adjust the pH to a lower level in order to lower the reduction
rate after which the reaction is quenched with a strong acid
solution. Wiegel, Zeit. Wiss Photo. 24 316ff (1926) describes a
modified Carey Lea process. Unfortunately, the yellow color of
Carey Lea silver results in a yellow minimum density when it is
used as nuclei in a receiving layer. Moreover, colloidal silver has
not been found to provide an entirely satisfactory nuclei for many
reasons other than the yellow color, such as failure to provide an
image which can be suitably toned, an image which does not have
satisfactory density and the like. Accordingly, there has been a
need for nuclei which are more satisfactory for use in the
diffusion transfer process than those that are known in the prior
art.
Some of the aforementioned problems have been recognized in the art
and various attempts have been made to overcome them, as can be
seen by McGuckin, U.S. Pat. No. 3,345,169 which describes the
treatment of silver precipitating nuclei such as colloidal silver
with a noble metal in the ionic form. This treatment permits toning
of the image formed in the diffusion transfer process when Carey
Lea silver has been treated using this method.
Noble metal nuclei of metals such as palladium, platinum, gold,
etc., are also known in the prior art. Particle sizes of the nuclei
often range from at least 300 A. up to 2,500 A., the larger
particle sizes requiring a greater concentration per square foot
when coated on a receiving support. In many instances, there is a
definite lack of uniformity among the particle sizes. Although the
average particle size might be 500 A. for instance, there might be
many of the very large sizes as well as some very small to result
in a particular average size. However, nonsilver noble metal nuclei
known in the art generally have not provided the desired improved
properties over silver nuclei.
It is recognized that nuclei which would provide improved density
of a positive image, which would be easy to tone and which would
also behave satisfactorily when used either in a binder containing
gelatin or in a polymeric binder would be very useful in diffusion
transfer processes. It is also recognized that it would be
desirable to obtain nuclei which can be coated at a relatively low
concentration on a support and which would provide a surface which
is relatively colorless or water white in nonimage areas of a
positive. Such desirable results can be achieved by the practice of
this invention.
SUMMARY OF THE INVENTION
In accordance with this invention, it has been found that nonsilver
noble metal nuclei, as described herein, can be used in diffusion
transfer processes to overcome several of the disadvantages
described hereinbefore. The nonsilver noble metal nuclei of this
invention are characterized by a small and uniform particle size.
Their use in diffusion transfer materials and processes gives
several advantages, including a significant increase in density and
tone of a positive image, in comparison to the use of prior art
nuclei which do not exhibit such particle size characteristics.
Non-silver noble metal nuclei having the desired size and
distribution can be prepared by reducing a nonsilver noble metal
salt, in the presence of a colloid, with a reducing agent having a
standard potential more negative than -0.30, e.g., a borohydride or
hypophosphite, as described herein. Due to the small size of the
nuclei, their particle size and distribution are difficult to
measure. However, careful analysis indicates that the nuclei
employed in the practice of this invention have an average particle
size in the range of about 15 A. to about 65 A., preferably about
30 A. to about 60 A., at least 80 percent, by number, of said
particles having an average particle size in the range of about 20
A., to about 50 A., preferably about 25 A. to about 40 A.
Particularly useful nuclei are those of the noble metals, platinum,
palladium, gold, mercury, rhodium, ruthenium and osmium. Preferred
nuclei are those of palladium and platinum, in that order. These
two metals provide the greatest density in the positive image and
also have a low background density or minimum density (Dmin).
Palladium, in particular, provides a very low minimum density.
Gold, on the other hand, does not provide as high a maximum density
(Dmax) and provides a relatively high minimum density. Mixtures can
be used.
Particularly useful reducing agents which can be used in preparing
nuclei according to this invention include borohydrides, such as
alkali (e.g., sodium, potassium, ammonium, etc.) borohydrides which
have a standard potential of -1.24 measured at 25.degree. C., and
hypophosphites (H.sub.2 PO.sub.2 .sup.-) such as hypophosphorous
acid (H.sub.3 PO.sub. 2) which has a standard potential (E.degree.)
of -0.50 measured at 25.degree. C. See W. M. Latimer, "The
Oxidation States of the Elements and Their Potentials in Aqueous
Solution," 2nd Edition, Prentice Hall, Inc., New York, 1952. The
E.degree. values are in keeping with the IUPAC convention as to
sign. Preferred borohydrides for use in the invention are the
alkali metal borohydrides and more particularly sodium or potassium
borohydride.
Water-soluble amine-boranes having the following structure are also
useful reducing agents:
wherein, within the limitation that the amine-borane is stable in
aqueous solution, the groups R.sub.1 and R.sub.2 separately
represent hydrogen atoms or alkyl, aryl or aralkyl groups and
R.sub.3 represents an alkyl, cycloalkyl, aryl or aralkyl group or
R.sub.1 and R.sub.2 constitute with the nitrogen atom a heterocycle
and R.sub.3 is then a hydrogen atom.
Referring to the foregoing formula, examples of alkyl groups are
methyl, ethyl, propyl and isopropyl, an example of cycloalkyl is
cyclohexyl, examples of aryl are phenyl and naphthyl which can be
optionally substituted, an example of an aralkyl group is benzyl
and examples of nitrogen heterocyclic groups are pyridyl,
morpholino and piperazyl. Specific compounds of the class are
trimethylamine borane, dimethylamine borane, pyridine borane,
cyclohexylamine borane, morpholine borane or piperazine borane.
Methods for the production of such boranes are described in
articles by Burg et al., J.A.C.S. 59, 1937, 785-787 and Taylor et
al., J.A.C.S. 77, 1955, 1506. In general terms, the compounds may
be prepared by reacting sodium borohydride, NaBH.sub.4, with a
hydrochloride salt of an amine of the formula R.sub.1 R.sub.2
R.sub.3 N.
In a modification of the invention, there may be used, instead of
an amine-borane, a precursor for an amine-borane as referred to
above. Generally, it is preferred to carry out the reduction
reaction using gelatin as the colloid, though other protective
colloids, e.g., polyvinyl pyrrolidone, may also be employed.
According to the invention, a receiving layer for use in the
diffusion transfer process can comprise the entire reaction product
obtained by precipitating finely divided nonsilver noble metal
nuclei from a salt of the metal by reducing the metal salt, in the
presence of a colloid, to metal nuclei using a reducing agent
having a standard potential more negative than -0.30. Particularly
useful nuclei are those prepared from noble metal salts such as
palladium, platinum, and gold salts, and especially preferred
nuclei are those of palladium and platinum. The receiving element
is prepared by reducing the metal salt as described above and
coating the reaction product on a suitable support. In a
particularly advantageous embodiment, the nuclei are coated at
about 1 to about 200 .mu.g./ft..sup.2.
The receiving element as described above is used advantageously to
provide a photographic print having an image in the receiving layer
on a support. The image is obtained by the diffusion transfer
process and is formed in the receiving layer which comprises a
colloid binder and the nonsilver noble metal nuclei of our
invention. Particularly good results are obtained using palladium
and platinum nuclei.
DESCRIPTION OF PREFERRED EMBODIMENTS
In one embodiment of this invention, palladium nuclei are prepared
by reducing a palladium salt such as ammonium chloropallidate in an
aqueous solution containing a colloid, such as gelatin, preferably
using a borohydride reducing agent such as potassium borohydride.
Advantageously, the reducing agent is used slightly in excess and
the reaction mixture heated to about 70.degree. C for about 5
minutes. Additional colloid and other addenda can then be added and
the mixture coated on a suitable support such as baryta coated
paper. In a particularly useful embodiment, 14 micrograms of
palladium nuclei in 80 milligrams of gelatin is coated per square
foot of support.
In one example of the utility of this nucleated layer on a support,
the nucleated layer having the nonsilver noble metal nuclei
thereon, is overcoated with a substantially unhardened silver
halide emulsion. Particularly useful emulsions are described in
Yackel et al., U.S. Pat. No. 3,020,155. After exposure, the
emulsion is developed with a silver halide diffusion transfer type
developing solution containing a silver halide developer such as
hydroquinone and also containing a silver halide complexing agent
such as sodium thiosulfate. The undeveloped silver halide,
complexed with the thiosulfate, diffuses to the nucleated
underlayer where an image is formed which is positive with respect
to the negative image formed in the silver halide emulsion. The
unhardened silver halide emulsion is then removed by washing with
warm water.
As indicated above, the nuclei of this invention are prepared in a
suitable colloid suspension. In a particularly useful embodiment, a
hydrophilic colloid is used such as gelatin. However, any suitable
colloid or colloids may be used, including both water-soluble
polymers and water-insoluble polymers. A latex or hydrosol may
advantageously be employed if the polymer is insoluble in the
liquid used to carry out the reduction. The amount of colloid can
be varied depending upon the particular colloid, reducing agent,
ratio of proportions, etc. Typically about 0.5 percent to about 20
percent, by weight, based on the total reaction mixture of colloid
is used, preferably from about 1 percent to about 10 percent.
Usually a water-soluble metal salt is used which is dissolved in
water which either contains a colloid or to which the colloid is
added. The borohydride reducing agent is then added to the
solution, usually at a pH of about 6 until the pH reaches about
8.5, typically at temperatures of 0.degree.-95.degree. C.,
preferably 20.degree.-70.degree. C. The time allowed for the
reaction to be completed depends upon the reducing agent, colloid,
metal salt used, temperature, etc. Usually from 3 minutes to about
2 hours are sufficient, but greater or less time may be adequate.
The reaction mixture can then be coated directly on an appropriate
support for use as a receiving sheet in the diffusion transfer
process or additional colloid can be added to the reaction mixture
before coating.
It will be appreciated that more than one type of colloid can be
incorporated in the coating composition. Any suitable colloid may
be used. Particularly useful colloids are those which are used for
binders in silver halide emulsions. Advantageously, they are coated
in a range of about 5-500 mg./ft..sup.2. Included among the
suitable colloids are gelatin, preferably coated at a level in the
range of about 7-100 mg./ft..sup. 2, polymeric latices such as
copoly(2-chloroethyl methacrylate-acrylic acid) preferably coated
in the range of 15-350 mg./ft..sup.2 and a polymeric vehicle
containing two components (1) polyvinyl alcohol, and (2)
interpolymer of n-butyl acrylate, 3-acryloyloxypropane-1sulfonic
acid, sodium salt and 2-acetoacetoxyethyl methacrylate, in a
preferred range of about 10-300 mg./ft..sup.2.
As pointed out above, various colloids may be used as dispersing
agents or as binders for the nuclei of our invention. The use of
these various colloid materials results in varying the aspects of
the process such as the time of contact between the negative and
the receiver sheet, the speed of transfer, the tone and the like.
Whereas various latex materials are suitable for use as vehicles
for nuclei, it will be appreciated that some latex formulations are
also difficult to successfully coat with consistently good results,
especially without mottle.
Coating solutions containing polymers are also useful. A
particularly useful polymer coating solution which has a viscosity
resembling gelatin solutions and can be hardened with an aldehyde
comprises polyvinyl quaternary salts containing aldehyde hardenable
groups. Also, in addition to various colloids, toners, surfactants,
coating aids, developing agents, stripping agents, silver halide
solvents etc., may be added to improve the image quality in the
receiving sheet.
Due to the unexpectedly high activity of the nuclei of the
invention, the concentration on the receiving sheet can be very
low, suitable concentrations being about 1 to about 200
.mu.g./ft..sup.2, preferably 6 to 100 .mu.g./ft..sup.2. The size of
the particles of the nuclei can be determined using an electron
microscope. In a convenient method of preparing the nuclei for
examination, discrete nuclei are prepared in a suitable colloid,
such as a latex, after which the latex is placed on a suitable
support for viewing using an electron microscope. The size of the
particles can then be measured from a micrograph of the viewed
dispersion.
It will be greatly appreciated from the above, that the coating
composition generally contains not only nuclei but also reaction
products which are obtained from reducing the metal salt.
Accordingly, it is within the scope of the invention to include in
the receiving layer, nuclei having the specified size and specified
size distribution, plus the reaction byproducts which are obtained
during the reducing operation.
The supports which can be used for coating with the receiving layer
are any of those which are suitable and include paper, wood, glass,
plastics, etc. A particularly useful support is baryta coated
paper. However, in a preferred embodiment, a polymeric material
which acts as a moisture barrier, such as polyethylene or the like,
which is pigmented to provide a white surface is used. Other
polymeric materials which may be used as coatings on paper or as
self-supported webs include polyesters, polyamides, polycarbonates,
polyolefins, cellulose esters, polyacetals and the like.
In order to obtain adhesion or to improve adhesion to a receiving
support, treatments of the support, e.g., photographic film base,
may be carried out including subbing the support, electron
bombardment, treating with peroxide and the like.
In one embodiment, the nuclei can be coated in a polyethylene
latex. For instance, polyethylene latex may be used as a dispersing
medium when the nuclei are formed or the polyethylene latex may be
added to the reaction mixture after the nuclei have been formed in
the presence of some other colloid. It will be appreciated that a
polyethylene latex may also be used with other nucleating or silver
precipitating materials, including metal sulfides and the like.
The nuclei may be formed in situ by coating a layer of non-silver
noble metal salt in a colloid on a support and overcoating with a
layer of reducing agent. For instance, a coating containing gelatin
and gold chloride may be coated on a suitable support over which is
then coated a layer containing sodium borohydride. However,
improved results are obtained by carrying out the reduction in a
reaction vessel and then coating on a suitable support.
As pointed out previously, the receiving sheet may also contain
various toning agents or these toning agents may be in the
processing solution or even, in some instances, contained in the
silver halide emulsion. Toning agents which may be included for
improving the image include sulfur compounds such as
2-mercaptothiazoline, 2-amino-5-mercapto-1,3,4-thiadiazole,
2-thionoimidazolidene, 2-mercapto-5-methyloxazoline and
2-thionoimidazolyne. These toners are particularly useful in a
range of 0.01 to 3.0 mg./ft..sup.2 either in the receiving layer or
coated in a layer on top of the nucleated layer. It will be
appreciated that these toners can be used either alone or in
conjunction with other toning agents. Other toning agents which may
be used include the 5-mercaptotetrazoles of Abbott et al., U.S.
Pat. No. 3,295,971 and Weyde, U.S. Pat. No. 2,699,393. Still other
toning agents are disclosed in Tregillus et al., U.S. Pat. No.
3,017,270.
It has been found that the use of a 5-mercaptotetrazole such as
1-phenyl-5-mercaptotetrazole as a toning agent in diffusion
transfer processes results in a restraining effect, prolonging the
transfer time. This can be prevented by the use of an alkali metal
iodide such as, for example, potassium iodide, in the processing
solution, particularly the activator solution, without loss of the
blue-black toning effect obtained by using a
5-mercaptotetrazole.
The nuclei of the invention may also be precipitated in colloidal
dispersions which also have therein particles such as silica,
bentonite, diatomaceous earth such as Kieselguhr, powdered glass
and fuller's earth. In addition, colloids and colloidal particles
of metal oxides such as titanium dioxide, colloidal alumina, coarse
aluminum oxide, zirconium oxide and the like may be used with the
nuclei.
In one method of carrying out the diffusion transfer process, the
exposed silver halide emulsion is contacted against a web in which
has been imbibed some or all of the processing solutions. The
processing solutions and other components of the web and/or the
emulsion can be adjusted so that either a useable negative is
obtained in the emulsion layer or a useable positive in the web, or
both a useable negative and a useable positive.
In any event, the web is nucleated with silver precipitating
nuclei. I have found that the nuclei of the invention are
especially suitable for use in the web processing system. In a
particularly useful embodiment, the web comprises a support
carrying a layer of gelatin which contains nuclei such as those
described in this application. The web is soaked with a desired
processing solution prior to use and then placed in close contact
with an exposed negative for a time which depends upon the
particular components used. The two films are then separated,
revealing a positive image in the web material. If desired, a cover
sheet may be applied over the negative or processing web after they
have been separated for ease of handling or to improve stability of
the images therein. Typical processing webs and processes of using
processing webs are disclosed in U.S. Pat. No. 3,179,517 issued
Apr. 20, 1965 to Tregillus et al.
In carrying out the diffusion transfer process, conventionally the
silver halide emulsion is exposed to a light image after which it
is contacted with a silver halide developing agent containing a
silver halide complexing agent. The exposed emulsion is developed
in the light areas and the unexposed silver halide is complexed
with the silver halide complexing agent after which the emulsion is
contacted against the receiving sheet and the complex silver halide
diffuses imagewise to the receiving sheet containing nuclei.
In some instances it may be desirable to treat the receiving sheet
in order to improve the stability of the sheet, particularly with
regard to the silver image thereon. A simple stabilizing method
merely involves washing the print in order to remove any processing
chemicals which may remain thereon. However, the washing step does
not protect the print from subsequent chemical reactions with
oxygen, hydrogen sulfide, etc., in the atmosphere, which have an
adverse effect on the stability of the silver image.
For these reasons, it has been proposed to coat the print with a
coating composition such as that disclosed in U.S. Pat. No.
2,979,477 comprising a mixture of vinylpyridine polymer and a
hydantoin-formaldehyde condensation polymer.
Suitable print coating compositions may also employ a polymeric
material such as methylmethacrylate-methacrylic acid copolymer or
the combination of an acid group or sulfate group containing
polymer such as copoly(methylmethacrylate-methacrylic acid) and a
hydantoin-formaldehyde condensation polymer, such as that disclosed
in French Pat. No. 1,493,188. A heavy metal salt such as zinc
acetate may also advantageously be incorporated in the print
coating composition. Further improvement is obtained by
incorporating in the coating composition an acid such as acetic
acid, propionic acid or the like.
In some instances, it can be helpful to apply a solution, e.g., an
aqueous solution of a strong reducing agent, such as sodium
borohydride, to the surface of a print made employing a diffusion
transfer process, such as described in U.S. Pat. No. 2,698,237 of
Land issued Dec. 28, 1954. Application of this solution can return
the developed image to a neutral black tone should undesired loss
of black tone or loss of image resulting from affects of hydrogen
sulfide in the atmosphere, highly humid keeping conditions or the
like have occurred. It is desirable to apply the solution without
any protective overcoat having been applied to the print. A 10
percent, by weight, aqueous solution of sodium borohydride is
especially suitable, but other reducing agents are effective, e.g.,
stannous chloride, hydrazine and ascorbic acid.
It can be also useful in some instances after formation of a
developed image in an image receiver by a diffusion transfer
process, such as described in U.S. Pat. No. 2,698,237 of Land
issued Dec. 28, 1954, to stabilize the image by treatment with
various stabilizing agents. This can include, for instance,
treatment of a print prepared by the described process, such as by
swabbing, with a stabilizer solution, e.g., an aqueous solution
containing equal parts, by weight, water and methanol, or a
solution of a cationic stabilizer such as a phosphonium or
quaternary ammonium stabilizer, such as poly 1,2-dimethyl-5-vinyl
pyridinium methyl sulfate, 2-methyl-3-ethyl benzothiazolium para
toluene sulfonate, tetrabutyl phosphonium chloride, or triphenyl
benzyl phosphonium chloride. A concentration of the described
stabilizer of about 0.5 to about 3 milligrams per milliliter of
solution is usually sufficient. This stabilization can provide
desired cold tone and maintain desired speed.
The silver halide emulsions employed in this invention can contain
incorporated addenda, including chemical sensitizing and spectral
sensitizing agents, coating agents, antifoggants and the like. They
can also contain processing agents such as silver halide developing
agents and/or developing agent precursors. Of course, the
processing agents can be incorporated in a layer adjacent to the
silver halide emulsion if desired.
The developing agents and/or developing agent precursors can be
employed in a viscous processing composition containing a thickener
such as carboxymethyl cellulose or hydroxyethyl cellulose. A
typical developer composition is disclosed in U.S. Pat. No.
3,120,795 of Land et al. issued Feb. 11, 1964.
The silver halide developing agents used for initiating development
of the exposed sensitive element can be the conventional types used
for developing films or papers with the exception that a silver
halide solvent such as sodium thiosulfate, sodium thiocyanate,
ammonia or the like, is present in the quantity required to form a
soluble silver complex which diffuses imagewise to the receiving
support. Usually, the concentration of developing agent and/or
developing agent precursor employed is about 3 to about 320
mg./ft..sup.2 of support.
The developing agents and/or developing agent precursor can be
employed alone or in combination with each other, as well as with
auxiliary developing agents. Suitable silver halide developing
agents and developing agent precursors which can be employed
include, for example, polyhydroxybenzenes, such as hydroquinone
developing agents, e.g., hydroquinone, alkyl substituted
hydroquinones, as exemplified by t-butyl hydroquinone, methyl
hydroquinone and 2,5-dimethylhydroquinone, catechol and pyrogallol;
chloro substituted hydroquinones such as chlorohydroquinone or
dichlorohydroquinone; alkoxy substituted hydroquinones such as
methoxy hydroquinone or ethoxy hydroquinone; aminophenol developing
agents such as 2,4-diaminophenols and methylaminophenols; ascorbic
acid, ascorbic acid ketals, such as those described in U.S. Pat.
No. 3,337,342 of Green issued Aug. 22, 1967; hydroxylamines such as
N,N-di(2-ethoxyethyl) hydroxylamine; 3-pyrazolidone developing
agents such as 1-phenyl-3-pyrazolidone, including those described
in Kodak British Pat. No. 930,572 published July 3, 1963; and acyl
derivatives of p-amino-phenol such as described in Kodak British
Pat. No. 1,045,303 published Oct. 12, 1966.
Lactone derivative silver halide developing agents which have the
property of forming a lactone silver halide developing agent
precursor under neutral and acid conditions are particularly
useful. Typical lactone derivatives are described in copending U.S.
application Ser. No. 764,348 filed Oct. 1, 1968 entitled
"Photographic Compositions and Processes" in the name of Oftedahl.
The particularly suitable lactone derivatives provide desired
developing activity and reduction of stain without adversely
affecting desired maximum density, minimum density, photographic
speed and other desired sensitometric properties. Suitable lactone
derivative developing agents include those which under neutral,
slightly alkaline or acid conditions, i.e., when the pH is lowered
to a level of about 9 or lower, i.e., about 2 to about 9, do not
have significant developing activity, if any, due to formation of a
developing agent precursor.
A wide variety of hydroxy cinnamic acid and/or amino cinnamic acid
developing agents can be employed. Suitable hydroxy cinnamic acid
or amino cinnamic acid developing agents include any such compounds
which cause reduction of a photographic silver salt in exposed
areas of a layer containing such photographic silver salt without
adversely affecting the unexposed areas of the photosensitive
silver salt. Especially suitable developing agents are derivatives
of 6-hydroxy coumarins, 6-amino coumarins, mixtures thereof and
their salts, e.g., water-soluble salts.
As pointed out above, combinations of developing agents can be used
in the diffusion transfer process. Particularly useful developers
include combinations of the following:
1-phenyl-3-pyrazolidone
hydroquinone
methyl hydroquinone
2,5-dimethyl hydroquinone
2,6-dimethyl hydroquinone
tertiary butyl hydroquinone
3,6-dihydroxy benzonorbornane
2,4-diamino-6-methyl phenol dihydrochloride
4-phenyl catechol
tertiary butyl pyrocatechol
2,4-diaminophenol dihydrochloride
ascorbic acid
N-methyl-p-aminophenol sulfate
N,N'-ethylene di(oxymethyl)pyridinium perchlorate
2-(3-sulfopropyl)-2-thiopseudo urea
7,14-diazo-6,15-dioxoeicosane-1,21-bis(pyridinium perchlorate)
The receiving layers and receiving elements of this invention can
be employed with a wide range of photographic emulsions. The
photographic emulsions employed can be X-ray or other nonspectrally
sensitized emulsions or they can contain spectral sensitizing dyes
such as described in U.S. Pat. Nos. 2,526,632 of Brooker et al.
issued Oct. 24, 1950 and 2,503,776 of Sprague issued Apr. 11, 1950.
Spectral sensitizers which can be used include cyanines,
merocyanines, styryls and hemicyanines.
The photographic emulsions can contain various photographic
addenda, particularly those known to be beneficial in photographic
compositions. The various addenda and concentrations to be employed
can be determined by those skilled in the art. Suitable
photographic addenda include hardeners, e.g., those set forth in
British Pat. No. 974,317; buffers which maintain the desired
developing activity and/or pH level; coating aids; plasticizers,
speed increasing addenda, such as amines, quaternary ammonium
salts, sulfonium salts and alkylene oxide polymers; and various
stabilizing agents, such as sodium sulfite. The photographic silver
salt emulsions of the invention can be chemically sensitized with
compounds of the sulfur group such as sulfur, selenium and
tellurium sensitizers, noble metal salts such as gold, or reduction
sensitized with reducing agents or combinations of such
materials.
Various photographic silver salts can be used in the practice of
the invention. These include photographic silver halides such as
silver iodide, silver bromide, silver chloride, as well as mixed
halides such as silver bromoiodide, silver chloroiodide, silver
chlorobromide and silver bromochloroiodide. Photographic silver
salts which are not silver halides can also be employed such as
silver salts of certain organic acids such as silver behenate,
silver-dye salts or complexes, etc.
The photographic silver salts are typically contained in an
emulsion layer comprising any of the known binding materials
suitable for photographic purposes. These include natural and
synthetic binding materials generally employed for this purpose,
for example, gelatin, colloidal albumin, water-soluble vinyl
polymers, such as mono and polysaccarides, cellulose derivatives,
proteins, water-soluble polyacrylamides, polyvinyl pyrrolidone and
the like, as well as mixtures of such binding agents. The elements
can also contain stripping layers and/or antistatic layers (i.e.,
conducting layers).
Stripping agents can be used either on the surface of the silver
halide emulsion layer, on the receiving layer containing the
nuclei, or can be contained in the developing or processing
solutions. When added to the processing solution in concentrations
of about 3 percent to about 10 percent, by weight, the stripping
agents prevent the processing solution from sticking to the
receiver. Suitable stripping agents normally are used which have a
composition different from the binder used in the silver halide
emulsion. Typical stripping agents include alkali permeable
polysaccharides such as, for example, carboxymethyl cellulose or
hydroxyethyl cellulose, 4,4'-dihydroxybiphenol, glucose, sucrose,
sorbitol (hexahydric alcohol C.sub.6 H.sub.8 (OH).sub.6), inositol
(hexahydroxy-cyclohexane C.sub.6 H.sub.6 (OH).sub.6.sup. . 2H.sub.2
O), resorcinol, phytic acid sodium salt, thixcin (a castor bean
product), zinc oxide, and finely divided polyethylene. These
coatings are relatively thin having a preferred coverage of about
6.0 mg./ft..sup.2. However, a useful range may be from 1.0 mg. to
1.0 g./ft..sup.2. It will also be understood that a stripping agent
or release agent can be incorporated in the receiving layer along
with the nuclei and/or binder used as a carrier for the nuclei.
In some adaptations, the nuclei can be carried in the developing or
processing solution to form the receiving layer. The use of nuclei
in the processing solution permits use of receiving surfaces which
have not been specifically prepared as receiving layers. If
desired, developing or processing solutions containing nuclei can
be used with receiver sheets having thereon a coating containing
the nuclei of this invention.
The following examples are included for a further understanding of
the invention:
EXAMPLE 1
Palladium Nuclei
Solution A Water 657 ml. 20% Latex-copoly(2-chloroethyl 35 ml.
methacrylate-acrylic acid) 96% 2-chloroethyl methacrylate- 4%
acrylic acid 20% Latex--copoly(butyl acrylate 3.55 ml. acrylic
acid) 90% butyl acrylate- 10% acrylic acid 15% Saponin solution 5.0
ml.
To 100 ml. portions of Solution A are added (1) 2.50 ml. of
palladium chloride solution at 1.25 mg./ml. of solution; (2) 5.0
ml. of reducing agent solution and (3) distilled water to bring the
total volume of each solution to 118 ml.
The samples are held for 30 minutes at 70.degree. C. All of the
solutions are then coated at 0.002 inch on a polyethylene coated
paper support to give a nuclei coverage of about 75
.mu.g./ft..sup.2 and about 80 mg./ft..sup.2 of latex (solids). All
of the coatings are made at 100.degree. F. and cured at 205.degree.
F. for 1 minute. The receiving sheet is used in a photographic
silver salt diffusion transfer process with an exposed silver
chlorobromide emulsion and a developer having the following
composition:
Component g./l.
__________________________________________________________________________
2,4-diamino-6-methylphenol sulfate 5-10 Tertiary butyl hydroquinone
25 Na.sub.2 S.sub.2 O.sub.3.sup. . 5H.sub.2 O 60 NaOH 20 KOH 20 KI
0.6-1.6 Hydroxyethyl cellulose 3-4.5% K.sub.2 SO.sub.3 25-50 Water
to make 1 liter
__________________________________________________________________________
The following results are obtained:
Sensitometry
__________________________________________________________________________
Soln. Average nuclei Reducing Conc. particle size Agent mg./ml.
Dmax E.degree.,25.degree. C. in melt
__________________________________________________________________________
NaBH.sub.4 10 1.64 - 1.24 about 30 A. H.sub.3 PO.sub.2 100 1.52 -
0.50 about 60 A. SnCl.sub.2 100 1.34 + 0.15 about 135 A. HCHO 100
1.14 + 0.056 about 110 A.
__________________________________________________________________________
the above data indicate that the nuclei obtained by reducing a
palladium salt with a reducing agent having a standard potential
more negative than -0.30 result in particularly good transfer
densities. This example also shows that a lower density is obtained
with nuclei having a large average particle size.
EXAMPLE 2
Palladium nuclei prepared according to this invention are
contrasted with other palladium nuclei and with silver nuclei
prepared using borohydride and hypophosphite reducing agents.
Sensitometric data is determined in this example, using the
procedure of Example 1.
a. Palladium Nuclei
Strong reducing agents (e.g., borohydride and hypophosphite) used
to form nuclei by the method of Example 1 yield well defined fine
particle size nuclei which result in high image density after
transfer.
Reducing Agent Dmax
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borohydride 1.30 hypophosphite 1.32 stannous chloride 0.84
formaldehyde 0.99 hydrazine 0.80
__________________________________________________________________________
b. Silver Nuclei
Strong reducing agents (e.g., borohydride) produced nuclei by the
method of Example 1 which result in much lower transfer
density.
Reducing Agent Dmax
__________________________________________________________________________
borohydride 0.98 hypophosphite 0.28
__________________________________________________________________________
EXAMPLE 3
Platinum Nuclei
Strong reducing agents (e.g., borohydride) produce nuclei by the
method of Example 1 which result in high transfer density and fine
particle size.
Reducing Agent Dmax Average particle size of nuclei
__________________________________________________________________________
borohydride 1.22 32 A.
__________________________________________________________________________
EXAMPLE 4
Palladium Nuclei vs. Cadmium Sulfide Nuclei
A coating solution containing colloidal palladium nuclei is
prepared by adding Solution A to Solution B with vigorous stirring
at 25.degree. C.
solution A PdCl.sub.2 0.01 g. 10 N HCl 0.01 ml. Distilled Water 0.8
ml. Solution B Latex containing 7.6% polymeric 54 ml. material
prepared from acrylonitrile, vinylidene chloride, acrylic acid and
gelatin in a ratio of 15:77:08:25 Distilled water 202 ml.
Isopropanol 45 ml. H.sub.3 PO.sub.2 0.5 ml. Polyoxyethylene ether
alcohol nonionic 0.6 ml. wetting agent
After heating the above mixture at 70.degree. C. for one hour, the
resulting solution is coated on a polyethylene-coated paper
support. Reducing agents other than hypophosphorous acid can be
used, such as its sodium salt or the like. Other water-soluble
salts of palladium, such as palladium nitrate or ammonium
chloropallidate can be used.
Cadmium sulfide is prepared in a latex having the same composition
in a manner similar to the above procedure, but without heating. A
coating solution containing colloidal CdS nuclei is prepared by
adding Solution C to Solution D.
solution C 0.02 M Cd(C.sub.2 H.sub.3 O.sub.2).sub.2 4 ml. Solution
D Latex 60 ml. Distilled water 210 ml. Isopropanol 50 ml. Na.sub.2
S.sup.. 9H.sub.2 O 3 ml. Polyoxyethylene ether alcohol 0.4 ml.
nonionic wetting agent
A silver bromoiodide gelatin emulsion coated on a support is
exposed and the above receiving sheets tested with it and a
developer having the following composition:
Water 1,860 g. Sodium carboxymethyl cellulose 117 g. Sodium sulfite
73 g. Sodium hydroxide 74.6 g. Sodium thiosulfate 14.5 g. Citric
acid 38.5 g. Hydroquinone 52 g.
The following results are obtained, showing that palladium nuclei
even at a lower coverage than CdS nuclei produce a good image:
Average Particle Polymer Nuclei size mg./ft..sup.2 .mu.g./ft..sup.2
Nuclei Dmax Dmin
__________________________________________________________________________
30 A. 7.6 11 Pd.degree. 1.58 0.00 35 A. 10.0 30 CdS no image formed
__________________________________________________________________________
EXAMPLE 5
Cellophane, 1.6 mils in thickness, is nucleated by the following
treatment to form a processing web: A sample is first bathed for 3
minutes in a 0.1 percent gold chloride solution and then bathed for
3 minutes in an alkaline 0.2 percent solution of potassium
borohydride. This treatment forms metallic gold nuclei on the
cellophane sheet. After washing for 3 minutes, the nucleated sheet
is contacted for 30 seconds with a developer having the composition
listed below, rolled in contact with a suitably exposed negative,
after which the two are separated. A fully developed negative image
forms on the exposed film.
Tertiary butyl hydroquinone 25 g. Na.sub.2 S.sub.2 O.sub.3.sup. .
5H.sub.2 O 60 g. NaOH 20 g. KOH 20 g. KI 0.6-1.6 g. Hydroxyethyl
cellulose 3-4.5 % K.sub.2 SO.sub.3 25-50 g.
2,4-diamino-6-methylphenol 5-10 g. sulfate Water to make 1
liter
The cellophane sheet shows bronzing and a high minimum density. The
minimum density is 0.5 compared to a maximum density of 1.3, or a
density difference of 0.8. This is a poor density difference and is
not an acceptable image.
This example shows that a reduction using borohydride in the
absence of colloid results in nuclei which are unsatisfactory for
use in the diffusion transfer system.
EXAMPLE 6
In situ Preparation
Part A
Potassium choraurate is dispersed in a physical mixture of 9 parts
latex containing polymeric material prepared from a mixture
consisting of 2-chloroethyl methacrylate and acrylic acid in a
ratio of 98:2 and one part of a polymeric latex consisting of
N-butyl acrylate and acrylic acid in a ratio of 9:1 and coated on a
polyethylene-coated paper support at 0.144 mg./ft..sup.2.
Part B
Prepared like Part A except that palladium chloride is used instead
of potassium chloraurate and coated at 0.125 mg./ft..sup.2.
These coatings are overcoated with an ethanolic solution of
NaBH.sub.4 at 4 mg. NaBH.sub.4 /ft..sup.2, allowed to dry at
100.degree. F. and stand overnight, then cured 2 minutes at
100.degree.-110.degree. C. before being processed. A high-speed
silver bromoiodide gelatin emulsion coated on a paper support is
exposed and the above receivers tested with it and a developer at
20.degree. C. as described in Example 1 to yield the following
results:
Receiver Dmax Dmin Tone
__________________________________________________________________________
A 1.33 0.14 cold B 1.53 0.11 fairly cold
__________________________________________________________________________
A and B are overcoated with solutions of hypophosphorous acid and
processed as above with similar results.
EXAMPLE 7
Palladium Nuclei vs. Cadmium Sulfide, CLS and Silver Sulfide Nuclei
in Latex
A coating solution containing colloidal palladium nuclei is
prepared by adding Solution A to Solution B with vigorous stirring
at 25.degree. C. The mixture is heated to 70.degree. C. for one
hour, then cooled.
Solution A PdCl.sub.2 0.00312 g. 10 N HCl 0.003 ml. Distilled water
0.25 ml. Solution B Latex containing 20% polymeric 10 ml. material
consisting of 2-chloro ethyl methacrylate & acrylic acid in a
ratio 98:2 Distilled water 180 ml. H.sub.3 PO.sub.2 0.1 ml. Anionic
wetting agent 1 ml.
A yellow colloidal dispersion of CdS in latex is prepared: 5 g. of
the latex used above in Solution B is dispersed in 35 ml. distilled
water; to this is added 30 ml. of a 20 percent cadmium acetate
(.sup.. 2 H.sub.2 O) solution and then 30 ml. of 1 percent sodium
sulfide (.sup.. 9 H.sub.2 O), dropwise with good stirring at
72.degree. F.
Carey Lea silver (CLS) is prepared in a latex having the above
composition by mixing 10 ml. of a colloidal Carey Lea silver
dispersion with 40 ml. of a 1 percent latex solution.
Silver sulfide nuclei coated in a latex are prepared as above for
the CdS using a silver sulfide dispersion.
The above nuclei are coated on polyethylene-coated paper and tested
as in Example 1, with the following results showing that palladium
produces an image of higher quality.
Polymer Nuclei mg./ft..sup.2 mg./ft..sup.2 Nuclei Dmax Dmin Tone
__________________________________________________________________________
39 0.035 Pd.degree. 1.34 0.07 Cold 37 65.0 CdS 0.76 0.30 Cold 30
0.03 CLS no ima ge formed 30 0.06 Ag.sub.2 S0.76 0.04 Cold
__________________________________________________________________________
EXAMPLE 8
Palladium Metal Nuclei in a Colloidal Silica Vehicle
A coating solution containing colloidal palladium nuclei is
prepared by adding Solution A to Solution B with vigorous stirring
at 25.degree. C.
solution A PdCl.sub.2 0.0156 g. 10 N HCl 0.0156 ml. Distilled water
1.25 ml. Solution B Colloidal dispersion of SiO.sub.2 80 ml. in
water Distilled water 120 ml. Hypophosphorous acid 0.1 ml. Anionic
wetting agent 1 ml.
The above nuclei are coated on polyethylene-coated paper at 160
mg./ft..sup.2 silica and 0.15 mg./ft..sup.2 palladium metal and
tested as in Example 1 to give a silver image of very good
quality.
EXAMPLE 9
Noble Metals in Latex
Solution A Water 657 ml. Latex containing 20% polymeric 35 ml.
material prepared from a mixture consisting of methyl acrylate, 2-
chloroethyl acrylate, vinyldene chloride and itaconic acid in a
ratio of 25:39:34:02 Latex (19.73% solids) (90% butyl 3.55 ml.
acrylate-10% acrylic acid polymer) 15% Saponin solution 5.0 ml.
To 100 ml. portions of Solution A are added: (1) metal salt
solutions at 2.0 mg. metal salt/ml. solution (except PdCl.sub.2
solution which is at 1.25 mg./ml. solution) in the amounts listed
in Table I below; (2) 5.0 ml. of NaBH.sub.4 solution except for
coatings A and B in which 0.05 ml. of commercial H.sub.3 PO.sub.2
is used as the reducing agent, and (3) distilled water to bring the
total volume of each solution to 118 ml.
The solution for A and B is held for 30-45 minutes at 70.degree.
C.; the remaining solutions are held 1-2 hours at 50.degree. C.;
all are then coated at 0.002 inches on a polyethylene-coated paper
support to give a nuclei coverage of 75 .mu.g./ft..sup.2 and aged
approximately 5 minutes at 100-110.degree. C. These receiving
sheets are tested as in Example 1 except that the following
processing composition is used to process B, D, F, H, K and M.
sodium sulfite 21.85 g./l. Sodium thiosulfate.sup.. 5 H.sub.2
O83.87 g./l. Potassium bromide 31.33 g./l. Potassium iodide 0.08
g./l. Sodium hydroxide 71.39 g./l. Methylhydroquinone 5.5 g./l.
Diaminophenol hydrochloride 31.5 g./l. Hydroxyethyl cellulose 30
g./l. Water to make 1 liter
Results are listed in Table I.
---------------------------------------------------------------------------
TABLE I
Results
__________________________________________________________________________
Metal ml. metal Coating Salt salt soln. Tone Dmax Dmin
__________________________________________________________________________
A PdCl.sub.2 2.50 Black Very good fair B PdCl.sub.2 2.50 Black Very
good fair C PdCl.sub.2 2.50 Brown Very good fair D PdCl.sub.2 2.50
Brown Very good fair E Na.sub.2 PtCl.sub.6.sup.. 6H.sub.2 O 2.70
Brown good good F Na.sub.2 PtCl.sub.6.sup. . 6H.sub.2 O 2.70 Brown
good good G RuCl.sub.3 1.92 Black fair good H RuCl.sub.3 1.92 Black
fair good J RhCl.sub.3.sup. . 4H.sub.2 O 2.56 Black
.times..times..times.Dmax fair fair Brown Dmin K RhCl.sub.3.sup. .
4H.sub.2 O 2.56 Brown Dmin fair good L KAuCl.sub.4 1.80 Brown
excellent good M KAuCl.sub.4 1.80 Brown excellent good
__________________________________________________________________________
EXAMPLE 10
A nuclei processing web dispersion is prepared containing the
following components:
Nuclei Dispersion A. 20%, by weight, gelatin in water 90 g. Water
1,680 cc. Sodium hypophosphite anhydrous 2.16 g. Sulfuric Acid, 2 N
60 cc. B. Ammonium chloropallidate, 1.665 g./l. 90 cc. Water 510
cc. C. 20%, by weight, gelatin in water 2,160 g.
B is poured into A and maintained 5 minutes at 70.degree. C. and C
is added. Water is added to bring the solution to 4,500 cc.
A coating composition having the following components is
prepared:
Nuclei dispersion 600 g. Gelatin 453 g. Water 4,680 g. Mucochloric
acid 250 cc. 15%, by weight, Saponin in water 30 cc.
This composition is coated on cellulose acetate film support to
form a nucleated web and dried. The nucleated web is then immersed
for 3 minutes in a processing solution having the following
composition:
4,4-dimethyl-1-phenyl-3-pyrazolidone 1.0 g. Hydroquinone 10.0 g.
2,2'-iminodiethanol-SO.sub.2 addition product 190.0 g. (20 mole
percent SO.sub.2) 2,2'-iminodiethanol 50.0 g. Sodium thiosulfate,
pentahydrate 8.0 g. Water to make 1 liter
The sheet is then squeegeed to removed excess solution and rolled
in contact with an exposed silver chlorobromide photographic
emulsion. After ten minutes, the two are separated. A developed
negative is obtained in the emulsion layer, as well as a positive
in the processing web.
EXAMPLE 11
A processing web is prepared as in Example 10 except that the
following coating composition is applied to the film support:
Nuclei dispersion 500 g. Gelatin 453 g. Water 4,680 g. 15%, by
weight, Saponin in water 30 cc. Formalin (40%, by weight,
formaldehyde 40 cc. in water)
After imbibing with the processing solution of Example 10, the web
is rolled in contact with an exposed silver positive and negative
images.
EXAMPLE 12
Size Frequency Study
Pictures are obtained as in Example 1 using platinum nuclei formed
by means of borohydride reduction. A size frequency count involving
86 nuclei particles show that about 85 percent of the particles are
less than 40 A. in diameter with the following distribution:
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about 20 A. 13 particles about 25 29 about 35 28 about 45 7 about
50 6 about 62.5 2 about 75 1
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86
__________________________________________________________________________
The invention has been described in detail with particular
reference to preferred embodiments thereof, but it will be
understood that variations and modifications can be effected within
the spirit and scope of the invention.
* * * * *