Photoimaging process using water removable coatings

Photographic images may be produced on a backing such as paper and polyester sheets, from photographic negatives which encompass line rendering, design comps, copy, complex color separation or the like with water-based varnishes and pigments, the resulting images closely resembling, if not exactly, the same image in its commercially printed form. Thus all aspects of color proofs produced by this invention provide greatly improved predictability as to the appearance of the final printed job, with a further improvement of cost savings over conventional techniques of preparing color proofs. Also, said proofing method can be used to provide a "transfer" so that one may transfer the colored image or images to a more suitable or required backing.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a method of producing colored images on various 
substrates. By first coating the substrate with a sealer and when dried, 
coating with a water based pigmented photo-sensitive coating; after 
drying, exposing this coating to ultraviolet light through a photographic 
negative, and developing this image by removing the unexposed portion with 
water. These colored images using this process are particularly useful in 
preparing direct images, transfer or rub off images, and can also be used 
in preparing pre-press proofs that more closely resemble actual press 
proofs or press runs than similar proofs from the techniques of the prior 
art. 
2. Description of the Prior Art 
The color printing industry is, of course, massively large, with billions 
of dollars going toward the creation of beautiful color reproductions of 
photographs for magazines, art work, sales brochures, and the like. 
As a color print job is laid out, it is often necessary to prepare a color 
proof or composition for careful examination prior to going forward with 
the substantial expense of setting up the press for commercial printing of 
the color reproduction. The original art work might consist of a single 
negative or multi negatives for complex color work, or it might consist of 
accurate four color separations to reproduce process color images. 
A disadvantage of the prior art process is that most direct imaging and 
transfer systems use solvent based ink solutions which contain flammable 
or hazardous materials. In addition, a clear solvent solution or solutions 
which are also flammable or hazardous must be used for these images to be 
developed after exposure to ultraviolet light. 
When using the method which uses a solvent based ink, another disadvantage 
is that the system will not hold fine line detail which is necessary in 
many cases of reproductions of art work and mandatory when required to 
make a detailed four color process image. 
In Lupo, U.S. Pat. No. 2,716,061, a pigmented contact printing emulsion is 
disclosed for use in reproducing multi-colored photographic images on 
flexible supports, and especially vinyl plastic sheets. While having some 
similarity to the invention of this application, the formulations 
disclosed in the Lupo patent exhibit significant disadvantages, and are 
not practically capable for commercial use in the preparation of direct 
imaging, transfer lettering or, pre-press proofs. 
Substantial disadvantages are found in the commercially available 
formulation of the Lupo patent compared with the preferred formulations of 
this invention. First, the formulation of the Lupo patent is less viscous 
and when a substrate is coated by placing it in a conventional whirler it 
dries unevenly and leaves mottled areas having different color densities. 
Furthermore, the exposed coating of the prior art patent tends to wash 
away more easily than the exposed coating in accordance with this 
invention after a comparable amount of exposure to ultraviolet light. 
The photosensitive emulsion or varnish of this invention requires less 
ultraviolet light exposure time to cure. Furthermore, the exposed 
photosensitive coating of this invention may be washed with pure water to 
remove the noncross-linked portions, rather than requiring an ammonium 
hydroxide solution for washing as in the prior art. 
The prior art formulations are applied, in their commercially available 
forms, by hand application to a backing by the whirler process. It is then 
dried by conventional methods after which a photographic negative is laid 
over the coating which is on a substrate and is exposed to ultraviolet 
light. After the desired exposure period, the negative is then removed and 
the portions of the coating underneath the transparent parts of the 
negative are rendered insoluble. When the negative is removed, the 
substrate with a particular color which has just been exposed is washed 
with a dilute ammonia solution to remove the portions of the applied 
coating which were not rendered insoluble by exposure to ultraviolet 
light. 
Prior art processes used commercially in producing pre-press proofs consist 
of expensive mechanical equipment and involve the use of micropulverized 
pigmented material which is applied to a sensitized flexible film by hand 
or some mechanical means. Then the proper negative is placed over the 
flexible film which has the color applied and is exposed to ultraviolet 
light. After exposure the negative is removed and the applied color on the 
sensitized flexible film is developed. Successive sensitized films are 
used, each having its specific color. When the required number of flexible 
films are developed they are laminated after they are placed in register, 
however, the laminations cause a gloss and depth of image which is not 
achieved when the job is actually printed. 
SUMMARY OF THE INVENTION 
The method of this invention comprises the steps of mechanically applying a 
sealer coat onto a flexible or rigid backing (including metal, glass, 
paper, polyester, etc.) surface using a rod. The sealer coat is dried, and 
then a uniform layer of a water-based mixture is applied by means of a 
wire wound rod over the sealer coat, the mixture containing a selected 
pigmented color dispersion and sufficient water solubilized organic resins 
to form a film on drying. The mixture also contains either an alkali 
dichromate salt or aromatic diazo compound commonly used in the printing 
art. The organic resins are selected from the group consisting of 
polyvinyl alcohol, polyvinyl acetate, acrylic polymers, silicone acrylics, 
acrylated urethanes, and proteinbased hydrolysates such as casein. The 
alkali dichromate salt is selected from the group consisting of a sodium 
dichromate, potassium dichromate, and ammonium dichromate. 
A selected photographic negative image is pressed against the dried uniform 
pigmented layer and exposed to ultraviolet radiation for cross-linking the 
applied coating and the dichromate salt. Following exposure, the negative 
is removed and the cured film is washed with potable water to remove the 
noncross-linked portions thereof. The backing and exposed developed 
coating is now dried. The image which has been developed is a reproduction 
of the photograph from which the negative was made. When the seal coat and 
then the pigmented organic resin mixture is applied to a flexible film 
backing on which a silicone release type of coating has been deposited and 
a photographic negative is exposed and the coating exposed and dried in 
the same manner as mentioned above, one has produced the colored image of 
a potential transfer. In order to cleanly transfer this image the seal 
coat should be removed. Then a thin layer of adhesive is applied to the 
entire sheet over the exposed cured image and the flexible backing is then 
placed on the substrate with the image contacting the surface to which one 
wishes to transfer. By rubbing with a burnishing tool the image will leave 
the silicone treated surface and adhere to the pre-selected new surface. 
Transfer imaging has now been accomplished. 
Another advantage of this invention is that the photosensitive coating when 
exposed and developed produces a sharper image with finer lines resulting 
in a more detailed colored image. 
Another advantage of this invention is that several colors can be applied 
in successive steps using different negatives made from the color 
separation process. 
As each color is deposited, developed, and dried and the next color 
deposited progressively in this manner as many times as the entire sets of 
negatives require and using the appropriate color on the negative 
separations the entire original image, or art picture can be reproduced as 
a direct image. These steps are all accomplished by applying colored 
vehicle over the same base coat. This process is known as multi-color 
direct imaging. 
In addition, another unique use of this invention is to color match the 
primary colored coatings prior to using them so that they are the same 
density and hue as the Standard Web Offset Printing (SWOP) standard color 
chips, as circulated to the printing industry as standards; or any other 
conventionally used color standards. Using the precisely controlled color 
coating, it is possible to make repeated identical reproductions of the 
initial process colored photograph and hence the standard for the 
commercial press run of this product. This state of the art is known as 
"pre-press proof". 
Accordingly, it is an object of the present invention to create a 
water-based system which can be cast onto various substrates so as to 
produce a colored image by using a pigmented colored water based 
photosensitive coating and a photographic negative. 
Another object of the present invention is to create a colored image on a 
substrate, from a single negative. This negative being made from the 
entire artwork common to the art design industry. 
Another object of the present invention is to create a colored image on a 
selected substrate, from several negatives, each negative being a 
principal part of a composite photograph that has been recorded on 
photographic film. 
Another object of the present invention is to provide a system which is 
capable of producing a duplicate of the original color photograph, using 
the separation negatives of the original and by using the four primary 
color inks applied and processed in sequence. 
Another object of the present invention is to produce a pre-press proof 
using a water-based system. 
Another object of the present invention is to produce a pre-press proof 
which more closely resembles the image of its commercially printed form, 
by using pigmented coatings which contain the same selection of pigments 
as found in the inks used in printing the picture. 
Another object of the present invention is to be able to transfer the color 
image to any type of material, e.g. paper, vinyl, styrene, wood or metal. 
Another object of the present invention is to produce a photosensitive 
coating or varnish having decreased curing time. 
Another object of the present invention is to produce a color image having 
improved sharpness and overall quality. 
Another object of the present invention is to produce a reproducible film 
thickness by using a number eleven (11 mm diameter of wire wound on a 
suitable rod) rod when coating a substrate. 
In addition, using a larger numbered rod than a number eleven rod when a 
heavier wet film giving a greater density of color is desired, and 
conversely using a smaller numbered rod when a thinner wet film is desired 
giving a less dense color. 
Another object of this invention is to produce a photosensitive colored 
liquid mixture which is stable over extended periods of time and only 
under adverse conditions is a bactericide added in order to prevent 
bacteriological degradation. 
Other objects, features, and advantages of the present invention will 
become apparent from the following description.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now in detail to the steps of the method of the present 
invention, one mechanically applies onto a flexible backing a uniform 
layer of a pigment free sealer coat. The flexible backing may be a 
silicone treated styrene-based stock or any other suitable material of 
appropriate size, including acrylic, mylar, vinyl, acetate or metallic 
substrates such as aluminum foil or on coated, or semi-coated paper 
stocks. 
The sealer coat of this invention comprises the following ingredients, with 
the amount of each ingredient being expressed in percent by weight: 
______________________________________ 
ethyl acetate 51.0 percent 
nitrocellulose solution 
44.0 percent 
dioctyl phthalate 4.8 percent 
citric acid 0.2 percent 
100.0% 
______________________________________ 
The nitrocellulose solution comprises the following ingredients, also being 
expressed in percent by weight: 
______________________________________ 
18-25 cps. RS nitrocellulose 
40.0 percent 
isopropyl alcohol 17.0 percent 
isopropyl acetate 23.0 percent 
n-propyl acetate 20.0 percent 
100.0% 
______________________________________ 
The sealer coat is squirted onto the backing in a straight line along the 
top edge. A coating rod is placed above the applied liquid coating and 
drawn towards the bottom edge of the backing material in a smooth, even 
motion. The coating is dried with a conventional forced warm air dryer or 
other suitable means until completely dry to the touch. 
The selected water-based color pigments are then mechanically applied to 
the backing. In some instances it may be desirable to apply a coating of 
opaque white ink prior to application of the desired pigments to provide a 
background which contrasts with the image. The pigments are dispersed in a 
water-based varnish comprising a sufficiently dispersed organic resin to 
form a film on drying and an alkali dichromate salt, preferably ammonium 
dichromate but also possibly including sodium dichromate, potassium 
dichromate, or a dichromate salt of an amine or quaternary ammonium 
radical. Alternatively, a diazo compound may be substituted for the alkali 
dichromate salt. 
Broadly, it is contemplated to use any organic resin which is susceptible 
to a cross-linking reaction with an alkali dichromate salt under 
ultraviolet light exposure. Typical examples of organic resins which may 
be used are artificial resins such as polyvinyl alcohol, polyvinyl 
acetate, acrylic polymers, silicone acrylics, acrylated urethanes, and 
protein based resins such as casein. The dissolved resin is preferably 
present in the varnish and dispersion mixture 25 to 75 times greater 
quantity by percent weight than the dissolved dry dichromate salt, which 
constitutes a substantial reduction in the amount of dichromate salt 
present when compared with the prior art. As the result of this, the 
pigment-free varnish layer exhibits less color tint (caused by the 
dichromate salt) than that of the prior art, which helps in obtaining the 
pure color value desired when pigment is added to the varnish. 
The uniform layer of water-based varnish containing the color pigments may 
be applied onto the backing by the use of a conventional wire-wound rod, 
preferably with a winding wire having a diameter of about 5 to about 18 
mils. Wirewound rods are commercially available expressly for the purpose 
of placing uniform liquid coatings on a backing. 
The uniform layer is then dried, for example, with a forced warm air dryer 
of conventional design or any other suitable means. The drying step is 
accelerated by using a hot air blower. Following the drying step, the 
uniform colored layer on the backing is pressed against a selected 
transparent negative image such as a photographic screened or lined 
negative or a half-tone negative. The two members are held together 
preferably by vacuum suction or other mechanical means for intimate, 
facing contact. Any pigment area not covered by the film negative should 
be masked. Thereafter, the negative is exposed to actinic radiation, 
particularly ultraviolet radiation, which passes through transparent areas 
of the negative image causing cross-linking of the organic resin, 
typically polyvinyl alcohol, polyvinyl acetate, acrylic polymers, silicone 
acrylics, acrylated urethanes, and casein and the like, and an alkali 
dichromate salt. A one to three minute application of ultraviolet light 
has proven to be quite adequate when emitted from a 2 kilowatt metal 
halide ultraviolet source such as is conventionally used in plate making. 
Following the ultraviolet light radiation step, the backing and cured 
emulsion layer is separated from the negative, unexposed ink is removed by 
gently rubbing the surface of the backing with a water saturated paper 
towel and then washing with water to remove the noncross-linked portions 
of the emulsion. Unlike the preferred formulations, the water does not 
have to be buffered on the alkaline side with ammonia or the like, but 
simple tap water or deionized water may be used for a substantial savings 
in cost. 
When a transfer is desired, the above described process is applied to a 
silicone coated backing sheet and, after the last pigmented coating is 
developed with water, the surface is dried. The seal coat is removed by 
wetting a soft foam strip with acetone and drawing the strip over the 
cured emulsion applying moderate pressure for the entire distance and then 
drying the image area with a warm air dryer. The entire surface of the 
backing sheet is coated with adhesive using the same technique and rod as 
used for applying th seal coat. After the adhesive has dried, the image is 
ready to be transferred onto any desirable substrate. Satisfactory results 
are obtained using a 30% solution of A 673 adhesive diluted with acetone. 
This material is available from Advance Process Supply Company, Chicago, 
Ill. 
The water-based varnish of this invention is generally maintained within a 
pH range of from about 7.0 to about 9.0 by using selected pH controlling 
agents. It is particularly preferred to use a mixture of ammonium 
hydroxide and an organic amine having a boiling point of at least 
100.degree. C. The organic amine should be present in an amount capable of 
imparting a pH of 7.0 to the varnish in the absence of the ammonium 
hydroxide. By way of example, organic amines which may be used in this 
invention include: 2-dimethylamino-2-methyl-1-propanol (which contains 20% 
added water as DMAMP80); 2-amino-2-methyl-1-propanol (which contains 5% 
added water as AMP-95); or the group of amines represented by diethylamino 
ethanol. 
When the water-based pigmented emulsion or varnish mixture is placed on the 
backing and dried, the ammonium hydroxide is removed by evaporation. 
However, because the organic amine is sufficiently less volatile than 
water, it remains to impart latent akaline conditions to the film and to 
facilitate the process of developing after ultraviolet exposure. During 
the washing step, some of the organic amine may remain to facilitate 
dissolving of the resin. Furthermore, as stated above, the rate of cure 
under ultraviolet radiation and the separation of the soluble portions of 
the resin layer from the insoluble portions is greatly facilitated in the 
invention of this application. 
It is generally preferable for the emulsion and pigmented varnish of this 
invention to include from 5 to 20 percent by weight of resin and from 0.1 
to 1.0 percent by weight of ammonium dichromate. It is also generally 
preferable for the weight of dissolved dry resin present to be from 25 to 
75 times greater in quantity than the weight of the dissolved dry ammonium 
dichromate therein. 
It is also preferable for the pigmented emulsion or varnish mixture of this 
invention to have a viscosity range, as measured by a commercially 
available No. 2 Zahn cup, of 30 to 60 seconds at 72.degree. F and more 
particularly of about 40 to 55 seconds at 72.degree. F. 
The acrylic polymer of this invention may be mixed as desired with dry 
pigment or pigment press cake to provide a formulation of 8 to 20 percent 
by weight of any desired dry pigment (and typically 10 percent by weight), 
1 to 5 percent by weight of a defoaming agent (typically a volatile 
organic solvent such as isopropanol) to prevent foaming during the process 
of milling in the dry pigment, with the balance of the material comprising 
the base varnish described above. Alternatively, the dry pigments can be 
mixed with the defoaming agent and water prior to adding to the varnish. 
This mixture can be milled in a steel ball mill or porcelain lined pebble 
mill or any other suitable dispersing equipment, until completely uniform 
to provide an aqueous pigment dispersion ready for mixing with the base 
varnish in desired proportions to accurately match the desired color for 
use in the preparation of color imaging. 
The addition of a small amount of coalescing agent is also desirable, for 
example from 0.5 to 2 percent by weight, and typically about 0.5 percent 
by weight of a polyether solvent such as Cellosolve or Carbitol. This 
helps to impart desirable synergistic properties to the pigment dispersion 
producing a homogeneous state with the emulsion or varnish mixture. 
One specific embodiment of the clear varnish of this invention comprises 
the following ingredients, present in water dispersion, with the amount of 
each ingredient being expressed in percent by weight: 
______________________________________ 
organic resin or casein 10.0 percent 
ammonium hydroxide (concentrated) 
0.2 percent 
amine 0.1 percent 
coalescing agent such as 
0.5 percent 
Cellosolve or Carbitol 
water 89.2 percent 
100.0% 
______________________________________ 
This clear varnish material may then be mixed with a pigment dispersion in 
the acrylic polymer to provide differing colors and color intensities as 
desired, and to serve as the coating for color imaging according to the 
process described above, or for other photoreproduction techniques as may 
be desired. 
By way of example, various aqueous pigment dispersions may be prepared by 
mixing together the ingredients as set forth in Table I. 
TABLE I 
______________________________________ 
Aqueous Pigment Dispersions 
Percent 
by 
Pigment Ingredient Weight 
______________________________________ 
DIARYLIDE AAA diarylide yellow presscake.sup.1 
20.0 
YELLOW (50% solids) 
Joncryl 74F.sup.2 60.0 
Water 15.0 
Isopropyl Alcohol (anydrous) 
5.0 
100.0 
RUBINE RED Lithol Rubine pigment.sup.3 
10.0 
Joncryl 74F 70.0 
Water 20.0 
100.0 
PHTHALO BLUE 
Phthalo blue presscake.sup.4 
45.0 
(40% solids) 
Joncryl 74F 55.0 
100.0 
CARBON BLACK 
Regal 99R carbon black pigment.sup.5 
10.0 
Joncryl 74F 70.0 
Carbitol 0.5 
Water 19.5 
100.0 
______________________________________ 
.sup.1 Available from Hilton Davis, Cincinnati, Ohio as C68-C-102 
.sup.2 Styrenated acrylic copolymer 48% solids, available from S. C. 
Johnson, Racine, Wisconsin 
.sup.3 Available from Hilton Davis as 106C-65F334 
.sup.4 Available from Hilton Davis as 106C-65-F315, Peacoline Blue 
.sup.5 Available from Cabot Corp. 
The red, blue and black aqueous dispersion mixtures were ground in steel 
ball mills for 24 hours. The yellow aqueous dispersion mixture was ground 
in a porcelain jar mill for 24 hours. This method produces uniform 
dispersions by reducing the pigment agglomerates to very fine particles, 
thus yielding optimum gloss, transparency and coating capability. 
The photosensitive inks were prepared by mixing the ingredients as 
indicated in Table II. 
TABLE II 
______________________________________ 
Aqueous Photosensitive Inks 
Viscosity 
Percent (Sec. #2 
by Zahn) 
Color Ingredients Weight (@ 72.degree. F.) 
______________________________________ 
YELLOW Diarylide Yellow Dispersion.sup.1 
15.0 55 
Resin Solution.sup.2 
55.0 
Water 30.0 
100.0 
RED Rubine Red Dispersion.sup.1 
15.0 53 
Resin Solution.sup.2 
55.0 
Water 30.0 
100.0 
BLUE Phthalo Blue Dispersion.sup.1 
13.0 55 
Resin Solution.sup.2 
55.0 
Water 32.0 
100.0 
BLACK Carbon Black Dispersion.sup.1 
15.0 52 
Resin Solution.sup.2 
55.0 
Water 30.0 
100.0 
FLUOR- Fluorsescent Orange 
16.7 50 
ESCENT Pigment.sup.3 
ORANGE Resin Solution.sup.2 
48.0 
Joncryl 74F 8.3 
Water 27.0 
100.00 
______________________________________ 
.sup.1 See Table I 
.sup.2 See page 12 lines through 14 for resin solution 
.sup.3 Available from Magruder Co. Sunset Orange, 319, JS503019 
Typically, to each 100 gm ink solution (See Table II) 0.1 to 5.0 gm of a 
20% by weight solution of ammonium dichromate is added, which has been 
adjusted previously to a pH of 8.5 with concentrated ammonium hydroxide, 
commonly known in the industry as 28 Baume. The ammonium dichromate 
functions as a photosensitizer which reacts with the resin solids in the 
finished dry ink film when exposed to ultraviolet light to form water 
insoluble cross-linkages at the point of exposure. 
The above examples have been offerred for illustrative purposes only, and 
are not intended to limit the invention of this application, which is as 
defined in the claims below.