Water developable, negative working overlay or transfer type diazo color proofing system

This invention relates to water developable, negative working photosensitized sheet constructions which, upon exposure to an actinic radiation source through a screened image, can accurately reproduce said image. The construction is useful as a color proofing film which can be employed to predict the image quality from a lithographic printing process. The invention provides both overlay and transfer type proofing sheets which have good fingerprint resistance.

BACKGROUND OF THE INVENTION 
The present invention relates to an improved overlay or transfer type of 
negative working color proofing system which is developable with water 
alone. It has long been desired in the art to produce color proofing 
systems which are water developable. Water developability renders 
developer effluent more ecologically acceptable and provides a less 
hazardous working environment. Water developable color proofing systems 
are known in the art. These typically employ a combination of certain 
water soluble diazonium salts in conjunction with water soluble binder 
resins. While such materials are truly water developable, they are 
disadvantageous because fingerprint resistance is low. This invention 
improves upon such prior systems such as taught in U.S. Pat. No. 4,469,772 
which specifies a combination of the methane sulfonate and mesitylene 
sulfonate salts and a water soluble resin binder. 
In the field of reprographics, it is desirable to produce a color proof to 
assist a printer in correcting a set of photomasks which will be used in 
exposing printing plates. The proof should reproduce the color quality 
that will be obtained during the printing process. The proof must be a 
consistent duplicate of the desired half tone or line image, and should 
neither gain nor lose color. Visual examination of a color proof should 
reveal any defects on the photomask; the best color rendition to be 
expected from press printing of the material; the correct gradation of all 
colors and whether grays are neutral; and the need, if any, for subduing 
any of the colors and/or giving directions for altering the film photomask 
before making the printing plates. 
Color proofing sheets for multicolored printing have heretofore been made 
by using a printing press proof which requires taking all the steps 
necessary for actual multicolor printing. Such a conventional method of 
color proofing has been costly and time consuming. Alternate color 
proofing methods have therefore been developed to simulate the quality of 
press proofs. There are three known types of photographic color proofing 
methods, namely, the surprint type, the overlay type and the transfer 
type. 
In the overlay type of color proofing, an independent transparent plastic 
support is used for producing an image of each color separation film. A 
number of such supports carrying colored images are then superimposed upon 
each other and placed on a white sheet to produce a color proof. 
Advantages are that it is quick and can serve as a progressive proof by 
combining any two or more colors in register. 
In the surprint type of color proofing method, a color proofing sheet is 
prepared by successfully producing images of different colors from 
different color separation films onto a single receptor sheet. This is 
done by utilizing a single opaque support and by applying toners, 
photosensitive PG,4 solutions or coatings of photosensitive materials of 
corresponding colors on the opaque support in succession. An example of 
this approach is described in U.S. Pat. No. 3,671,236. An advantage of the 
surprint type of color proof is that the color saturation is not 
influenced by superimposed plastic supports. This method more closely 
resembles actual printing and eliminates the color distortion inherent in 
overlay systems. 
Various processes for producing copies of an image embodying 
photopolymerization and thermal transfer techniques are known as shown in 
U.S. Pat. Nos. 3,060,023; 3,060,024; 3,060,025; 3,481,736; and 3,607,264. 
In these processes, a photopolymerizable layer coated on a suitable 
support is imagewise exposed to a photographic transparency. The surface 
of the exposed layer is then pressed into contact with the image receptive 
surface of a separate element and at least one of the elements is heated 
to a temperature above the transfer temperature of the unexposed portions 
of the layer. The two elements are then separated, whereby the thermally 
transferrable, unexposed, image areas of the composite transfer to the 
image receptive element. If the element is not precolored, the tacky 
unexposed image may now be selectively colored with a desired toner. The 
colored matter preferentially adheres to the clear unpolymerized material. 
U.S. Pat. No. 3,574,049 provides a transfer process for printing a design 
on a final support which comprises (a) printing a design onto a temporary 
support, (b) superimposing the temporary support and the final support, 
(c) applying heat and/or pressure to the superimposed structure formed in 
(b), and (d) separating the temporary support from the final support which 
retains the printed design. The affinity of the design for the temporary 
support is lower than its affinity for the final support. 
In U.S. Pat. No. 3,721,557, a method of transferring colored images is 
claimed which provides a stripping layer coated between the photosensitive 
element and the support. When the photosensitive layer is exposed to 
actinic light and developed, the more soluble portions are, selectively 
removed to produce a visible image. The image-carrying support is pressed 
against a suitable adhesive coated receptor member and, subsequently, the 
carrier support sheet is stripped to accomplish the transfer of the image. 
A fresh layer of adhesive is applied to the receptor for each subsequent 
transfer. 
This invention employs a polycondensation product of 
3-methoxy-4-diazodiphenylamine sulfate and 4,4'-bis-methoxymethyl 
diphenylether precipitated as the chloride salt formulated with various 
water soluble and certain water insoluble but swellable resins to prepare 
a completely water developable overlay or, when overcoated with adhesive 
and transferred by lamination, a one piece proofing film. Additionally, 
since the preferred formulation utilizes water insoluble resin binders, 
the films have the advantage of excellent fingerprint resistance.

SUMMARY OF THE INVENTION 
The invention provides a color proofing film and method for forming a 
colored image which comprises: 
(A) providing a negative working, photosensitive, overlay color proofing 
film which comprises, in order: 
(i) a transparent, preferably adhesion promoted substrate; and 
(ii) a photosensitive layer on said substrate, which photosensitive layer 
comprises a light sensitive, negative working, polymeric diazonium 
compound which is the polycondensation product of 
3-methoxy-4-diazodiphenylamine sulfate and 4,4'-bis-methoxymethyl diphenyl 
ether precipitated as the chloride salt, which diazonium compound is 
present in sufficient amount to photosensitize said layer; and a water 
insoluble, water swellable binder resin in sufficient amount to bind the 
layer components in a uniform film; and at least one colorant in 
sufficient amount to uniformly color said layer; and then 
(B) imagewise exposing said photosensitive layer to sufficient actinic 
radiation to form a latent image; and then 
(C) developing said film with water. 
The invention also provides a color proofing film and a method for forming 
a colored image which comprises: 
(A) providing a negative working, photosensitive, transfer color proofing 
film which comprises, in order: 
(i) a substrate having a release surface; and 
(ii) a single, colored photosensitive layer on said release surface, which 
photosensitive layer comprises a light sensitive, negative working, 
polymeric diazonium compound which is the polycondensation product of 
3-methoxy-4-diazodiphenylamine sulfate and 4,4'-bis-methoxymethyl diphenyl 
ether precipitated as the chloride salt, which diazonium compound is 
present in sufficient amount to photosensitize said layer; and a water 
insoluble, water swellable binder resin in sufficient amount to bind the 
layer components in a uniform film; and at least one colorant in 
sufficient amount to uniformly color said layer; and 
(iii) an adhesive layer on said photosensitive layer, which adhesive layer 
comprises a major amount of a polymeric material and which adhesive layer 
has a softening point in the range of from about 60.degree. C. to about 
180.degree. C., and thereafter 
(B) either 
(i) laminating said element with heat and pressure via said adhesive layer 
to a developer resistant receiver sheet; and removing said substrate by 
the application of peeling forces; and imagewise exposing said 
photosensitive layer to actinic radiation; or 
(ii) imagewise exposing said photosensitive layer to actinic radiation; and 
laminating said element with heat and pressure via said adhesive layer to 
a developer resistant receiver sheet; and removing said substrate by the 
application of peeling forces; or 
(iii) laminating said element with heat and pressure via said adhesive 
layer to a developer resistant receiver sheet; and imagewise exposing said 
photosensitive layer to actinic radiation; and removing said substrate by 
the application of peeling forces; and 
(C) removing the non-exposed areas of said photosensitive layer with water, 
which removing is conducted at a temperature at which said adhesive layer 
is substantially non-tacky, and preferably 
(D) repeating steps A through C at least once whereby another 
photosensitive element having at least one different colorant is laminated 
onto said receptor sheet over the non-removed portions of the previously 
laminated photosensitive layer or layers. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
In preparing the overlay version of this invention, one prepares a 
photographic element which broadly comprises a transparent substrate and a 
colored photosensitive layer on it. 
In carrying out the transfer version of the invention, one employs a 
photographic element which broadly comprises a substrate having a release 
surface, a colored photosensitive layer on the release surface and an 
adhesive layer on the photosensitive layer. Optional additional layers 
containing anti-halation materials, adhesion promoters or release agents 
may also be used. 
In the preferred embodiment, the substrate is composed of a dimensionally 
and chemically stable base material which does not significantly change 
its size, shape or chemical properties as the result of the heating, 
coating or other treatments which it must undergo. One preferred material 
is polyethylene terephthalate. In the usual case it has a thickness of 
from about 1 to about 10 mils, a more preferred thickness is from about 
2-5 mils and most preferably from about 2-3 mils. Suitable films include 
Hostaphan 3000, available from Hoechst Celanese Corporation, Mylar D, 
available from DuPont and Melinex grades 0; 052; 442; 516 and S, available 
from ICI. The surface of the substrate may be smooth or may be provided 
with a matte texture by various methods known in the art. 
Matte films include Melinex 377 and 470 from ICI. These materials have the 
unique property of giving the final image of the transfer version a 
desired matte finish without any extra steps. One can control the gloss of 
the final image by properly selecting the matte finish of the temporary 
support. This effect works because the top layer of the final image is 
originally in contact with this matte surface. This does not occur with a 
separate release layer between the temporary support and photosensitive 
layer. An additional advantage of coating on a matte surface is that 
subsequent transferred layers generally adhere better to a rough surface 
than to a smooth surface. 
A similar matte finish of the final image can be obtained by embossing the 
shiny, top surface of the image with a matte material, such as described 
above. This is done by laminating together the final image and matte 
material under pressure and temperature. The matte material is then 
generally removed after lamination. The advantage of this method is that 
the finish of the final proof can be varied. Furthermore, the matting 
material can be used repeatedly. 
A third method for producing a matte finish uses a heat transferable layer 
such as Butvar 90 available from Monsanto, coated onto a film with a rough 
surface such as Melinex 329, available from ICI. The adhesive layer is 
laminated to the final image under pressure and temperature. Then the film 
with the rough surface is peeled off. The rough surface imparts a matte 
finish to the final image. The advantage is that all layers appear matte 
and that the extra adhesive layer protects the image. U.S. Pat. Nos. 
4,294,909 and 4,376,159 also suggest various methods for making a matte 
surface. 
In the transfer case, the substrate must have a release surface, that is, 
it must be capable of releasably holding the photosensitive layer thereto. 
This may be accomplished either by the substrate surface being inherently 
releasable, being rendered releasable by a suitable treatment or being 
provided with a release layer over the substrate surface. Such a release 
layer may comprise polyvinyl alcohol. 
Bonded to the substrate or the release surface is the photosensitive layer. 
The photosensitive layer broadly comprises a photosensitizer, a colorant, 
a binding resin, and other optional ingredients such as plasticizers, acid 
stabilizers, surfactants, anti-static compositions, uv absorbers and 
residual coating solvents. 
The photosensitizer is a light sensitive, polymeric diazonium salt which is 
the polycondensation product of 3-methoxy-4-diazo-diphenyl amine sulfate 
and 4,4'-bis-methoxy methyl-diphenyl ether, precipitated as the chloride 
salt as taught in U.S. Pat. No. 3,849,392. 
Suitable binding resins are water insoluble and water swellable. Water 
insoluble resins include those which are less than about 2% by weight 
soluble in water. An important resin selection criterion is that it must 
be a good film former. The most preferred resins are polyvinyl acetate 
polymers such as Mowilith 30 which is available from Hoechst AG and has an 
average molecular weight of about 30,000; a polyvinyl alcohol/polyvinyl 
acetate copolymer available as Gelvatol 20/30 from Monsanto; and a 
polyvinyl acetate/crotonic acid (95:5) copolymer having an average 
molecular weight of about 100,000, available as Mowilith CT-5 from Hoechst 
AG. Carboset (acrylic) resins from B. F. Goodrich are also useful. 
The colorants useful for the present invention include various classes of 
dyes and pigments. In the most preferred embodiment, pigments having an 
average particle size of about 1 micrometer or less are used. 
Optional plasticizers which may be incorporated into the photosensitive 
layer include those of the phthalate and phosphate types. Preferred 
plasticizers include dibutyl phthalate and dimethyl phthalate. Acid 
stabilizers include phosphoric acid and p-toluene sulfonic acid. 
These ingredients may be blended with such compatible solvents as ethanol, 
methyl cellosolve and methyl ethyl ketone, coated on the release surface 
and dried. In the preferred embodiment, the photosensitive layer has a 
coating weight between approximately 0.1 and 5.0 g/m. The most preferred 
weight is from about 0.5 to 2.0 g/m. 
In the preferred embodiment, the photosensitizer is present in the 
photosensitive layer in an amount of from about 10 to about 70 percent by 
weight; or more preferably from about 20 to about 60 percent by weight. 
In the preferred embodiment, the colorant is present in the photosensitive 
layer in an amount of from about 5 to about 30 percent by weight; or more 
preferably from about 10 to about 20 percent by weight. 
In the preferred embodiment, the binding resin is present in the 
photosensitive layer in an amount of from about 5 to about 50 percent by 
weight; or more preferably from about 15 to about 35 percent by weight. 
In the preferred embodiment, the plasticizer, when one is used, is present 
in the photosensitive layer in an amount of up to about 10 percent by 
weight or more preferably at about 5 percent by weight. 
In the preferred embodiment, the acid stabilizer, when one is used, is 
present in the photosensitive layer in an amount of up to about 10 percent 
of the photosensitizer. 
In the transfer version the adhesive layer comprises a polymeric material 
which is preferably polyvinyl acetate and may optionally contain such 
other desired components as uv absorbers, anti-static compositions and 
plasticizers. Useful polyvinyl acetates non-exclusively include Mowilith 
DM-6, 20, DM-22, 25, 30 and mixtures thereof, available from Hoechst AG. 
Other suitable polymers non-exclusively include polyvinyl acetates, 
MOWILITH CT-5, as before described, polyvinyl acetals such as Formvar, 
available from Monsanto and the vinyl acetate/vinyl alcohol/vinyl acetal 
terpolymers described in U.S. Pat. No. 4,670,507 which is incorporated 
herein by reference. These are usually dispersed in water, or dissolved in 
methyl isobutyl ketone or n-butyl acetate or other solvent compositions 
for coating on the photosensitive layer. It is then dried to a coating 
weight of from about 5 to about 30 g/m.sup.2, more preferably from about 
10 to about 20 g/m.sup.2. The layer may optionally contain a uv absorber 
such as Uvinul D-50 from GAF. It may also contain a plasticizer such as 
Resoflex R-296, available from Cambridge Industries. It may also contain 
antistats, such as Gafac and Gafstat from GAF. It may also contain other 
resins, such as Nitrocellulose RS 1/2, available from Hercules. The 
adhesive layer should not be tacky to the touch, during storage or during 
development of the photosensitive element. The layer should have a 
softening point in the range of from about 60.degree. C. to about 
180.degree. C., preferably 60.degree. C. to 120.degree. C., more 
preferably 60.degree. C. to 100.degree. C. In the preferred embodiment, 
the polyvinyl acetate is present in the adhesive layer in an amount of 
greater than about 50 percent by weight. The plasticizer may be present in 
an amount of up to about 30 percent by weight, the uv absorber up to about 
20 percent by weight, and other resins up to about 50 percent by weight. 
______________________________________ 
Typical adhesive formulations include: 
______________________________________ 
I. 
Water 50.00 
Mowilith DM-22 50.00 
II. 
n-butyl acetate 78.00 
Resoflex R-296 1.00 
Mowilith 25 21.00 
III. 
n-butyl acetate 68.70 
Uvinul D-50 1.30 
Mowilith 20 30.00 
______________________________________ 
In operation in the transfer mode, the photosensitive element is laminated 
to a receptor sheet via the adhesive layer. The receiver sheet should be 
resistant to any adverse effects which may be caused by the developer of 
choice. For example, the receiver sheet should be water resistant if 
aqueous developers are used. Plastic or plastic coated receiver sheets are 
useful for this purpose. 
Useful receiver sheets include Melinex 329, 339, 994 and 3020 from ICI. 
Other white and non-white receiver sheets may also be used. Rough textured 
and/or adhesion promoted surfaces are preferred for the receiver, which 
must be able to withstand the laminating and development processes. 
Lamination may be conducted by putting the receiver sheet in contact with 
the adhesive side of the colored composite and then introducing the two 
materials into the nip of a pair of heated laminating rollers under 
suitable pressure. Suitable laminating temperatures usually range from 
about 60.degree. C. to about 90.degree. C., preferably about 75.degree. C. 
to about 85.degree. C. After lamination, the substrate is peeled away, 
usually merely employing manual peeling forces. The adhesive and 
photosensitive layers thus remain on the receiver sheet. 
The photosensitive layer is imagewise exposed by means well known in the 
art either before or after lamination. Such exposure may be conducted by 
exposure to a uv light source through a photomask under vacuum frame 
conditions. Exposure may be performed with actinic light through a 
conventional negative flat. Exposures after lamination and peel apart are 
preferred for emulsion-to-emulsion contact, Mercury vapor discharge lamps 
are preferred over metal halide lamps. Filters may be used to reduce light 
scattering in the material. 
After lamination, peel apart and exposure, the photosensitive layer is 
developed by dissolving the non-exposed area in a water developer and 
dried. The adhesive layer is not removed by this development. 
The process can then be repeated whereby another photosensitive element 
having a different color is laminated to the same receiver sheet over the 
previously formed image. In the usual case, four colored layers are 
employed to produce a full color reproduction of a desired image. These 
are cyan, magenta, yellow and black. 
In the overlay version, the photosensitive layer on the substrate is 
exposed as above and developed with water. A colored image appears on the 
transparent substrate. In the usual case four such films, each bearing a 
different colored image, are produced. They are held over one another in 
register over an opaque background sheet. A full color image may thereby 
be examined. In the overlay version the substrate is preferably adhesion 
promoted by means well known in the art, such as that method taught in 
U.S. Pat. No. 4,157,918 which is incorporated herein by reference. 
To further explain the operation of the overlay version of the invention, 
reference is now made to FIG. 1. A transparent substrate 2 is coated with 
photosensitive layer 4. This composite is exposed to actinic radiation 
through color separation negative 6. This produces exposed area 4' of 
layer 4. Upon development with water, the unexposed portion of layer 4 is 
removed and only image portion 4' remains on substrate 2. 
In the transfer mode, reference is made to FIG. 2 which explains one 
processing sequence. Temporary substrate 10 is coated with colored 
photosensitive layer 4 and adhesive layer 8. This construction is then 
laminated to a receiver sheet 12 via the adhesive 8 and the temporary 
substrate 10 is peeled away. After exposure and development of the 
photosensitive layer with water, exposed image 4' is positioned on the 
adhesive/substrate composite. 
The following non-limiting examples serve to illustrate the invention: 
EXAMPLE 1 (Overlay) 
A resin binder stock solution is prepared by dissolving 30 g. of Gelvatol 
20/30 (Polyvinyl alcohol/polyvinyl acetate copolymer) in 800 ml. of 
H.sub.2 O and adding 200 ml. of ethanol and 0.2 ml. Triton X-100. To 20 g. 
of this stock solution, 20 g. of methanol, 0.45 g. Calcozine yellow and 
1.1 g. of the polycondensation product of 3-methoxy-4-diazo diphenyl amine 
sulfate and 4,4'-bis-methoxymethyl diphenyl ether precipitated as the 
chloride salt, are added and stirred until dissolved. 
An aliquot is coated by Meir rod drawdown onto a Melinex 516 polyester 
sheet. After oven drying at 100.degree. C. for one minute, the coated 
sheet is exposed in a Berkey-Ascor exposure light source through a 
negative mask. The sample could be spray developed with water giving 
excellent resolution including 6 micron lines of an UGRA target. 
EXAMPLE 2 (Transfer) 
To 25 g. of methyl cellosolve and 25 g. of methanol are added 0.3 g. 
Mowilith CT-5 resin (polyvinyl acetate/crotonic acid: 95/5) followed by 
Victoria Cyan at 0.023 g. and Victoria Pure Blue at 0.35 g. After 
dissolving these dyes, 1.0 g. of the diazo of example 1 are dissolved and 
the solution is coated onto Melinex 516 with a Meir rod. After colordrying 
for one minute at 100.degree. C., the color coat is overcoated with 
Mowilith 30 (polyvinylacetate) to a coating weight of 10-12 g/m.sup.2. 
After drying at 100.degree. C. for one minute, the coatings (color coat 
and adhesive) can be transferred by lamination at 165.degree. F. to an 
adhesion promoted (acrylate) white receiver sheet (Melinex 3020). Exposure 
in a Berkey Ascor light source through a negative mask followed by water 
development gives excellent image contrast with good fingerprint 
resistance. 
EXAMPLE 3 
The coating solution of Example 1 is diluted 1:1 with a 50:50 mixture of 
methyl Cellosolve and methanol. An aliquot is coated with a Meir rod onto 
a polyester sheet. After air drying at 100.degree. C. for one minute, the 
coated sheet is exposed in a Berkey-Ascor exposure light source. The 
sample could be spray developed with water, giving excellent resolution 
including 8 microns of a UCRA test target. 
EXAMPLE 4 
The composition of Example 3 is 1:1 diluted with a 50:50 mixture of methyl 
Cellosolve and methanol and the steps are repeated. The sample is still 
imageable with a resolution of at least 12 microns with a UCRA test 
target.