Water developable diazo printing plate composition with quaternary nitrogen stabilizer

A water developable printing plate is provided with a photopolymerizable system as a latex comprising a water soluble diazopolymer reaction product of a diazoaryl amine and an aldehyde and an aqueous cationic or nonionic dispersion of a water insoluble polymer. The inclusion of a water miscible organic solvent improves the shelf-life of the photopolymerizable system and the printing plate especially under high humidity conditions.

BACKGROUND OF THE INVENTION 
This invention relates to photopolymerizable systems which include 
photopolymerizable compositions that are light-sensitive latices which 
form water developable printing plates when coated on suitable backing 
members. Selected image areas can be insolubilized and crosslinked by 
exposure to actinic radiation and the composition in the non-radiated 
non-image areas can be washed away with water to provide the desired 
planographic image. 
Emulsion photopolymerizable systems are taught in U.S. Pat. Nos. 4,186,069; 
4,224,398; and 4,288,520. In these systems, the photopolymerizable coating 
is an emulsion mixture of a polymer component having water insoluble 
polymer particulates within an aqueous suspension medium, together with a 
water soluble or water dispersible light-sensitive component including a 
polymer having at least two moieties per molecule. Such polymers are 
sensitive to actinic radiation, and by generating a free radical or other 
crosslinking species form a matrix of crosslinked polymer which 
encapsulate or entrap therein and disperse therethrough the water 
insoluble polymer. Prior to curing this system is a three-phase emulsion 
including the water insoluble polymer particulates within the aqueous 
suspension medium with which is also mixed the light-sensitive polymer. 
When the coating composition is applied to a suitable backing member, the 
aqueous suspension is substantially removed to realize a two-phase mixture 
of the polymer particulates and light-sensitive polymer. 
It has long been known to use water insoluble polymers in producing 
light-sensitive coatings for use on substrates such as planographic 
printing plates in which the polymers are incorporated as part of a 
solvent system layer which uses organic materials and which must be driven 
off from the plate, a requirement which is time and energy consuming, 
wasteful of solvents and possibly hazardous to the operator and the 
environment. 
Use of water soluble systems generally avoids the disadvantages of the 
organic base systems, but they are not particularly long lasting because 
the polymers are water soluble and are therefore subject to erosion of the 
image area when in use and/or through the action of atmospheric moisture. 
The emulsion systems of the aforementioned patents provide an improved 
stability with respect to other water based systems, but they are still 
characteried by a shelf-life which is less than optimum, especially under 
high humidity conditions. Additionally, the images provided by such 
emulsion systems often include spots which are commercially unacceptable. 
It is therefore the object of the present invention to provide a 
photopolymerizable system and a water developable printing plate based on 
such a system which exhibits improved properties, particularly with 
respect to shelf-life under high humidity conditions. This and other 
objects of the invention will become apparent to those skilled in this art 
from the following detailed description. 
SUMMARY OF THE INVENTION 
This invention relates to photopolymerizable compositions and printing 
plates therefrom, and more particularly to light-sensitive latex coating 
compositions which comprise a water soluble diazo polymer reaction product 
of a diazoarylamine and an aldehyde and an aqueous cationic or nonionic 
dispersion of water insoluble polymer. This system preferably contains a 
water miscible organic solvent which improves the shelf-life of the 
composition, especially under high humidity conditions. 
DESCRIPTION OF THE INVENTION 
The light-sensitive coating composition of the present invention is an 
emulsion mixture of a cationic or nonionic polar emulsion component having 
water insoluble polymer particulates within an aqueous suspension medium 
together with a water soluble or water dispersible component which is a 
diazo polymer reaction product of a diazoarylamine and an aldehyde. The 
water insoluble polymer emulsion component and the light-sensitive 
component are generally present in quantities of the same order of 
magnitude but can vary from a weight percent ratio of about 25:1 to 1:25, 
preferably about 5:1 to 1:5. 
The water soluble diazo polymer used in the present invention are prepared 
by the well known condensation reaction of a diazoaryl amine such a 
p-diazodiphenylamine and an aldehyde such as formaldehyde or 
paraformaldehyde which results in the formation of an oligomer or low 
molecular weight polymer. Many such diazo polymers are commercially 
available and typical examples include Diazo-8000 sold by Polychrome 
Corporation of Yonkers, N.Y., which is a zinc chloride salt of the 
reaction product of para-diazodiphenylamine with paraformaldehyde, and 
Diazo Resin No. 4 of Fairmount Chemicals, which is a reaction product of 
para-diphenylamine diazonium chloride with formaldehyde. Salts of the 
reaction product of p-diazodiphenylamine with paraformaldehyde are 
especially preferred. Zinc chloride, phosphate, sulfate salts and the like 
can be utilized; the zinc chloride salts being preferred. 
The aqueous dispersion of the water insoluble polymer of the present 
invention is cationic or nonionic either as a result of the use of an 
emulsifier or by having the cationic or nonionic group linked to the 
polymer. The water insoluble polymer is preferably a solid particulate 
having a size in the range of about 100 Angstroms to 10 microns in 
diameter. In general, any polymer which carries a cationic or nonionic 
group or which can be formulated into an emulsion using a cationic or 
nonionic emulsifier can be employed in the present invention. Suitable 
polymers include the homopolymers and copolymers of styrene, ethyl 
acrylate, butyl acrylate, ethyl methacrylate, butyl methacrylate, vinyl 
acetate, vinyl chloride, vinylidene chloride, butadiene, methylstyrene, 
vinyl toluene, dimethylaminoethyl acrylate, acrylic acid, methacrylic 
acid, isoprene, chloroprene, maleic anhydride, ethylene glycol acrylates 
such as polyethylene glycol acrylate, halogenated vinyl aromatics such as 
chlorostyrene and bromostyrene, methylvinyl ether, vinyl pyrrolidone, 
polyurethane and the like. 
Among the cationic and nonionic emulsifiers which can be used in the 
present invention are: ammonium salts of substituted amines containing 
alkyl and/or aryl groups attached to the nitrogen, alkyl or aryl sulfonium 
salts, alkyl and alkyl-aryl polyethers, cationic or nonionic 
fluorosurfactants and polyoles. 
Various cationic and nonionic emulsions are commercially available and can 
be used in the practice of the present invention. For example, Witcobond 
W-212, a cationomeric polyurethane emulsion sold by Witco can be used in 
the present invention. Such emulsions are carried by U.S. Pat. Nos. 
3,873,484 and 4,160,065; the disclosures of which are incoporated herein 
by reference. A typical nonionic emulsion is Vondic 1310F sold by 
Dainippon Inc., which is available as a polyurethane emulsion. 
When it is desired to enhance the sensitivity of the light-sensitive diazo 
polymer, known sensitizers can be included in the composition. For 
example, the composition can contain Michler's ketone, benzoin, benzoin 
methyl ether and other well known sensitizers which may be water 
solubilized as required by the use of amines, amine salts, quaternary 
amines, or polyalkoxy groups. 
The light-sensitive composition of the present invention generally contains 
stabilizers which are derivatives of pyridine-N-oxide or other quaternized 
ammonium compounds. Typical examples include nicotinamide-N-oxide, 
pyridine-N-oxide, quinoline-N-oxide, 4-nitroquinoline-N-oxide, tetramethyl 
ammonium chloride, dimethyldiallyl ammonium chloride. These stabilizers 
are present at a weight percent ratio range of from about 1:50 to 2:1, 
preferably 1:10 to 1:1, relative to said light-sensitive diazo polymers. 
The compositions of the present invention can also include antihalation 
agents, dyes, pigments, fillers, plasticizers, extenders, crosslinked 
particles and other materials for aiding in maintaining or modifying the 
viscosity, plasticity and/or stability of the compositions. It will be 
appreciated that any dyes should be water soluble cationic or nonionic 
dyes although anionic dyes having at most one anionic group can also be 
used. 
It has been found that the inclusion of a water miscible organic solvent in 
the aqueous dispersion of the water insoluble polymer improves the 
shelf-life of the composition especially under high humidity conditions. 
Typical organic solvents which can be used include methanol, ethanol, 
acetone, dimethylformamide, methylcellosolve, acetonitrile, dioxane, 
propanol, etc. The water miscible organic solvent will generally be about 
0.1-75 weight percent, preferably about 1 to 40 weight percent, based on 
the weight of the total solvent system. 
The photosensitive compositions of the present invention can be applied to 
any conventional substrate such as aluminum, copper, zinc, magnesium, 
steel or plastic, in any convenient fashion such as spray, roll or dip 
methods. After coating, the aqueous phase is evaporated or dried to remove 
the water or water and miscible organic solvent at low or elevated 
temperatures with or without imposition of a vacuum to leave the water 
insoluble emulsion and light-sensitive polymer together with a small 
amount of residual water or water and miscible organic solvent on the 
substrate. Areas of the composition which are exposed to actinic radiation 
harden and become hydrophobic, while the portions which are not so exposed 
remain water receptive and can be removed by simple water development.

In order to further illustrate the invention, various examples are set 
forth below. Throughout these examples, as well as throughout this 
specification and claims, all parts and percentages are by weight and all 
temperatures in degrees Centrigrade unless otherwise specified. 
EXAMPLE I 
A photopolymerizable composition was prepared by mixing 5.37 percent of a 
cationomeric polyurethane emulsion (Witcobond W-212) and 0.64 percent of a 
water soluble diazopolymer which was the zinc chloride salt of a reaction 
product of para-diazodiphenylamine and paraformaldehyde. The composition 
additionally contained 0.16 percent zinc chloride, 0.48 percent 
tris(2-chloroethyl)phosphate, 0.16 percent nicotinamide-N-oxide, 0.032 
percent methyl green, 76.6 percent water and 16.5 percent 
dimethylformamide. The photosensitive composition was coated on a grained 
anodized and silicated sheet of aluminum and allowed to dry. The plate was 
thereafter exposed to ultraviolet radiation, developed with tap water and 
gummed in the conventional fashion. The resulting lithographic plate was 
found to produce 30,000 good quality copies. A sample of the thusly 
produced plate with a coating weight of 0.75 g/m.sup.2 was subjected to 
accelerated shelf-life testing under high humidity conditions by exposure 
to 90 percent humidity at 38.degree. C. for 120 h. The plate showed quite 
satisfactory properties in exposure speed, adhesion and development. 
Another sample subjected to accelerated shelf-life testing at 60.degree. 
C. and low humidity for 120 h. also performed satisfactorily. 
EXAMPLE II 
The substrate used in the previous example was coated with an emulsion 
containing 4.09 percent of a nonionic polyurethane emulsion (Vondic 1310F, 
Dainippon Inc.) and 0.66 percent of the same diazopolymer used in Example 
I. The composition additionally contained 0.16 percent zinc chloride, 
0.49% tris(2-chloroethyl)-phosphate, 0.16 percent nicotinamide-N-oxide, 
0.25% Surfynol SE (Air Products Inc.), 0.04 percent Zonyl FSC (du Pont), 
77.8 percent water and 16.4 percent 2-methoxyethanol(methylcellosolve). 
The composition was subjected to the same accelerated shelf life as in 
Example I without any negative effects. 
Various changes and modifications can be made in the process and products 
of this invention without departing from the spirit and scope thereof. The 
various embodiments which have been disclosed herein were for the purpose 
of further illustrating the invention, but were not intended to limit it.