Radiation imagery chemistry: process – composition – or product th – Microcapsule – process – composition – or product
Reexamination Certificate
1993-08-27
2001-04-03
Dote, Janis L. (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Microcapsule, process, composition, or product
C430S273100, C430S286100, C430S306000, C522S110000
Reexamination Certificate
active
06210854
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to solid photosensitive elements which can be used to make flexographic printing plates. More particularly, it relates to aqueous developable photosensitive elements and to a process for preparing such elements.
BACKGROUND OF THE INVENTION
Photosensitive compositions useful in preparing flexographic printing plates are well known in the art. These compositions generally comprise (1) an addition polymerizable, non-gaseous, ethylenically unsaturated monomer or oligomer, (2) a photoinitiator or photoinitiating system activated by actinic radiation and (3) a thermoplastic elastomeric polymeric binder comprising polymerized conjugated diene monomers. Flexographic printing elements can be made from these photosensitive compositions by solvent casting, by extruding and calendering, or by pressing the compositions at an elevated temperature into the form of a layer or self-supporting sheet on a suitable casting wheel, belt or platen. The photosensitive sheet can be permanently affixed to a suitable permanent substrate. A removable coversheet is usually placed on top to protect the surface of the photosensitive sheet from contamination by dirt and dust particles during storage prior to use.
Photopolymerizable elements and processes for their use in preparing flexographic printing plates are well known in the art. See, for example, U.S. Pat. Nos. 4,323,636; 4,460,675; 4,970,037; and many others.
Flexographic printing plates can be made from the photosensitive elements described above, by exposing to actinic radiation selected portions of the photosensitive layer, usually through an image-bearing transparency. Upon exposure to actinic radiation, the ethylenically unsaturated monomer or oligomer is polymerized or crosslinked in those areas of the photosensitive layer exposed to actinic radiation, resulting in reduced solubility or swellability in developer solvents. No significant polymerization or crosslinking occurs in the unexposed areas of the photosensitive layer. Consequently, upon application of suitable developer solvent, the exposed areas remain, and the unexposed areas are removed.
The developer solvents most commonly used are organic solvents including aromatic or aliphatic hydrocarbon or halohydrocarbon solvents. Recently, it has become less desirable to use such organic solvents due to toxicity and environmental concerns. Thus, photosensitive compositions which are aqueous developable, i.e., can be washed out with aqueous solutions or plain water, have been proposed for use in preparing flexographic printing plates. Some examples include U.S. Pat. Nos. 4,177,074; 4,361,640; and 4,960,073.
Developability in aqueous alkali solutions can be achieved by using acid-containing copolymers. Developability in plain water can be achieved by using acid-containing copolymers that have been neutralized by the addition of organic or inorganic bases. For example, Mirle et al., U.S. Pat. No. 5,143,819, disclose a method of making an aqueous developable photocurable composition by reacting an acid-modified polybutadiene copolymer with a nitrogen-containing compound having a polymerizable ethylenically unsaturated group. The composition is then used to make an aqueous developable flexographic printing plate.
Aqueous developability can also be achieved using a photosensitive composition in which the binder is a core shell microgel as described by Fryd et al. in U.S. Pat. No. 5,075,192. The core shell microgel binder described by Fryd et al. is prepared in a two-step process whereby an elastomeric core is first formed and then grafted to an acid-modified copolymer. However, such microgel binders sometimes have excessive crosslinking of the elastomeric core which can degrade the elastomeric properties and/or cause processing difficulties.
Accordingly, there is a need for an improved aqueous developable photosensitive element which can be used to prepare a flexographic printing plate.
SUMMARY OF THE INVENTION
The present invention describes an aqueous developable photosensitive element suitable for the production of a flexographic printing plate. The element comprises a support, a layer of a solid photosensitive composition, and an optional coversheet. The photosensitive composition comprises:
(a) an elastomeric microgel binder having a core comprising a homopolymer or copolymer of an elastomeric monomer and a shell comprising a copolymer of the elastomeric monomer and a monomer having acidic functionality;
(b) at least one ethylenically unsaturated monomer or oligomer; and
(c) a photoinitiator system.
The invention further describes a process for preparing an aqueous developable photosensitive element, said process comprising:
(a) polymerizing an elastomeric monomer as a latex dispersion to form an elastomeric core, wherein at least 10% of the elastomeric monomer is unpolymerized;
(b) copolymerizing the unpolymerized elastomeric monomer with an ethylenically unsaturated monomer or oligomer having acidic functionality to form a shell over the elastomeric core;
(c) substantially removing the water;
(d) mixing the binder with (i) at least one ethylenically unsaturated monomer or oligomer, and (ii) a photoinitiator system; and
(e) applying the mixture from step (d) to a support to form a layer.
Optionally, a basic compound can be added after step (b) or step (c) or during step (d). In a preferred embodiment, the optional basic compound is present and is a nitrogen-containing compound having at least one ethylenically unsaturated group.
Optionally, the water can be removed in step (c) by a dewatering extruder as described in Kafka et al., U.S. Pat. No. 4,970,037. If a dewatering extruder is used, it is preferred that step (d) is carried out after step (b) and step (c) is carried out after step (d).
DETAILED DESCRIPTION OF THE INVENTION
This invention relates to a photosensitive element comprising (a) a photosensitive layer which is aqueous developable; (b) a support; and (c) an optional coversheet. By the term, “aqueous developable” it is meant that the elastomeric microgel binder alone is soluble, swellable or dispersible in a water-based developer solution. The developer solution can be a basic water solution, detergent solution, or, preferably, water alone.
The photosensitive layer comprises (a) an elastomeric microgel binder having a core comprising a homopolymer or copolymer of an elastomeric monomer and a shell comprising a copolymer of the elastomeric monomer and a monomer having acidic functionality; (b) at least one ethylenically unsaturated monomer or oligomer;(c) a photoinitiator system; and (d) optionally, a basic compound wherein said basic compound is present in an amount sufficient to neutralize a substantial portion of the acidic functionality of the microgel binder.
I. Photosensitive Element
1. Photosensitive Layer
A. Binder
The binder in the photosensitive layer imparts the bulk properties to the final flexographic printing plate. Thus it should be elastomeric and result in plates with sufficient resilience, flexibility or limpness, toughness, ink solvent resistance, and with good ink transfer. Such desirable properties are well known in the flexographic art area.
Binders suitable for practicing the present invention are core shell microgels having a thermoplastic elastomeric core, which can be crosslinked, and a thermoplastic noncrosslinked shell. The core provides the elastic properties of the binder while the shell confers aqueous developability.
The core comprises a homopolymer or copolymer of an elastomeric monomer and the shell comprises a copolymer of the elastomeric monomer and an ethylenically unsaturated monomer or oligomer having acidic functionality.
As used herein, the term “elastomeric monomer” means an ethylenically unsaturated monomer which forms a homopolymer having a glass transition temperature of 10° C. or less. Suitable elastomeric monomers include butadiene, isoprene, neoprene, urethanes, and mixtures thereof. The elastomeric microgel binder core can comprise an elastomer selected from the group consisting of poly(b
Briones Jose Antonio
Grossman Jan
Quinn John Anthony
Shea Paul Thomas
Swatton David William
Dote Janis L.
E. I. Du Pont de Nemours and Company
Magee Thomas H.
LandOfFree
Aqueous developable flexographic printing plate does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Aqueous developable flexographic printing plate, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Aqueous developable flexographic printing plate will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2522040