Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
2000-03-24
2002-07-23
Hamilton, Cynthia (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C528S065000, C522S096000, C522S097000
Reexamination Certificate
active
06423472
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to radiation curable polymers and formulations or compositions containing them, as well as photosensitive articles having solid surfaces or layers prepared from such polymers or formulations. The invention also relates to a process for making and using the polymers and making and using the photosensitive articles.
BACKGROUND OF THE INVENTION
Photocurable polymers and compositions are well known in the art for forming printing plates and other photosensitive or radiation sensitive articles. Generally, photocured printing plate comprise a support and a photosensitive surface or layer of photocurable composition. To prepare the printing plate the photosensitive surface is exposed to radiation in an imagewise fashion. The unexposed areas of the surface are then removed in developer baths.
In the past, removal of the unexposed surfaces has required the use of organic solvents which are environmentally unsafe, toxic and highly volatile. Thus, there has been a need to develop photocurable compositions which can be developed in non-organic solvent. In addition to possessing an aqueous photodevelopable photosensitive surface, a flexographic printing plate must be sufficiently flexible to wrap around a printing cylinder, while being strong enough to withstand the rigors of the typical printing process. Furthermore, the printing plate must be soft enough to facilitate ink transfer during printing and must be solvent resistant to inks typically used in printing. U.S. Pat. No. 5,328,805, Huynh-Tran, et al., “Aqueous Developable Photosensitive Polyurethane(METH)-acrylate” (1994) and U.S. Patent No. Huynh-Tran, et al., “Aqueous Developable Photosensitive Polyurethane(METH)-acrylate” (1994) teach photopolymer resins comprised of a urethane prepolymer prepared by reacting polyoxyalkylene diols with polyester diols, or a mixture thereof, with an excess of diisocyanate followed by chain extending the resulting prepolymer mixture with an alkyldialkanolamine, then reacting the chain-extended product with a hydroxyalkyl(meth)acrylate.
However, improved mechanical properties such as resistance to inks including oil, water and alcohol based inks is still desired. Incorporation of butadiene would yield more flexible, softer compositions. However, until now, urethane prepolymers have not incorporated butadiene because butadiene polymers are generally incompatible with typical urethanes resulting in a cloudy product which causes light scattering during the imagewise exposure step. Light scattering results in poor image quality in the resulting printing plate.
The printing plates of the present invention overcome this limitation, incorporating butadiene into urethane prepolymers and resulting in photopolymer products which are more resistant to inks, have improved resilience, improved cold-flow properties and lower surface tension.
SUMMARY OF THE INVENTION
A photopolymer resin composition comprising a polyether-polybutadiene prepolymer is provided by the present invention.
Methods of preparing photopolymer resins of the present invention are also provided comprising reacting to completion hydroxy-terminated butadiene homopolymer with isocyanate to produce isocyanate-terminated polybutadiene polyurethane; reacting isocyanate-terminated polybutadienepolyurethane with polyether diol to produce prepolymer; reacting prepolymer with 0 to 25 parts by weight of a hydroxyalkyl(meth)acrylate; reacting the products with 1-20 parts by weight of alkyldialkanolamine in the presence of solvent; and adding a photoinitiator, stablizers and UV absorber. Printing plates of the present invention may be prepared by casting photopolymers of present invention onto a plate substrate and drying the plate to remove the solvent.
OBJECTS OF THE INVENTION
It is an object of the invention to provide novel solid, water-dispersable polymer which can be cross-linked or cured by exposure to actinic radiation.
It is a further object of the invention to provide aqueous-developable flexographic relief printing plates and methods of making the same.
Another object of the invention is to provide a novel butadiene urethane prepolymer.
DETAILED DESCRIPTION
Photopolymer resins of the present invention comprise polyether-polybutadiene prepolymer and photoinitiator.
As general guidance in preparing compositions of the present invention, the milliequivalents of isocyanate added should be equal to or greater than the total milliequivalents of the remaining components, namely polybutadiene, polyether diol, alkyldialkanolamine, and hydroxyalkyl(meth)acrylate. However, it is generally preferred that the ratio of milliequivalents of isocyanate to non-isocyanate components be approximately equal. Alkyldialkanolamine generally is about 15-60% of the non-isocyanate components (based upon total milliequivalents) and preferably about 55-60%. Hydroxyalkyl(meth)acrylate makes up about 7-40% of the total non-isocyanate components, and preferably is about 8%.
To prepare compositions of the present invention hydroxy-terminated polybutadiene is reacted at about 25-80° C. with a stoichiometric excess of diisocyanate in the presence of a urethane forming catalyst to produce isocyanate terminated polybutadiene polyurethane. Thereafter, the isocyanate terminated polybutadiene polyurethane is mixed with polyether diol to form a prepolymer. The ratio of polybutadiene to polyether diol is from 1:1 to 1:5, and preferably 1:3. The prepolymer is reacted with hydroxyalkyl(meth)acrylate at a temperature of from about 60-80° C. Further reaction with an alkyldialkanolamine is performed in the presence of an organic solvent. Suitable solvents include methyl methyl ketone, methyl isobutyl ketone, toluene, and mixtures thereof. The solvents should have a boiling point in the range of 80-120° C. for easy casting of the films and evaporation of the solvent. Thereafter a curing agent is added.
Hydroxy-terminated Polybutadiene
Hydroxy-terminated polybutadiene has the formula
where x+y+z is 1 and n is from about 25 to about 50. It is preferred that x is 20%, y is 20% and z is 60% of the overall molecule. In preferred embodiments n is 50. Suitable polymers have a number average molecular weight in the range of about 1,000 to 10,000, preferably in the range of about 1,000 to 3,000. As used herein molecular weights are numbered average, M
n
, as determined by Permeation Chromatography, using polystyrene standards. Hydroxylated polybutadiene is available from commercial sources such as Elf Atochem.
Polyether Diol
Polyether diols have the formula OH—(A—O—)
b
H where A is a divalent radical of ethylene, propylene, isopropylene, butylene, isobutylyene; and b is such that the numbered average molecular weight of the group [A—O]
b
or of the polymer diol, is within the range of about 650 to about 7,000, preferably about 1,000-3,500. Ethylene oxide block polyether diol where the amount of ethylene oxide is 1-50 weight percent, preferably 10-30 weight percent and the overall molecular weight, 1,000 to about 7,000, preferably 1,000 to 4,000 are particularly preferred. In the instance where copolymers are used, the structure for A(O)
b
would be —(CH
2
CH
2
0)
x
—(CH
2
CH(CH
3
)—O)
y—(CH
2
CH
2
0)
z
— where x+z and y are such that the ethylene oxide moiety represent about 1-50, preferably 10-30 weight percent of the overall polyol molecular weight. Such copolymers include POLY G55-37 (MW 2952, containing about 30 weight percent of ethylene oxide), and POLY L 228-28(MW 4000, containing about 20 weight percent ethylene oxide), both available from Olin Corporation. The polyether diol reactants may be made by processes well known in the art by reacting an alkylene oxide or mixtures of alkylene oxides with a compound having at least one active hydrogen atom such as water, monohydroxylic alcohols such as ethanol and propanol; and dihydroxylic alcohols such as ethylene glycol and monoethyl ether of glycerine. The poly(oxyalkylene) products of such reactions will have linear oxyalkylene or oxyethylene higher oxyalkylene chains, and suc
Carter Martin Lewis
Kumpfmiller Ronald James
Carmody & Torrance LLP
Hamilton Cynthia
MacDermid Graphic Arts, Inc.
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