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
2001-05-07
2003-01-14
Baxter, Janet (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
C430S280100, C430S281100, C430S285100, C430S273100, C430S306000, C430S905000, C430S907000, C430S916000
Reexamination Certificate
active
06506541
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to photo-curable polymer compositions. In particular, it relates to photo-curable polymer compositions for use in printing plates, comprising a block copolymer having two or more polymerised monovinyl aromatic monomer blocks and one or more polymerised conjugated diene blocks; a second polymer having one polymerised monovinyl aromatic monomer block and one or more polymerised conjugated diene blocks, a low molecular weight block copolymer comprising one polymerised monovinyl aromatic monomer block and one or more polymerised conjugated diene blocks, and a photo-initiator. The invention further relates to flexographic printing plate precursors containing the photo-curable polymer composition, as well as to flexographic printing plates.
BACKGROUND OF THE INVENTION
Flexographic printing plates are well known in the art and are especially useful for commercial printing on diverse products such as flexible plastic containers, cartons, plastic bags, boxes and envelopes. For the purpose of this specification, uncured plates to be used for preparing (cured) flexographic printing plates are referred to as flexographic printing plate precursors. The flexographic printing plate precursors typically comprise a photo-curable layer prepared from a photo-curable polymer composition, and protective layer(s) to protect the photo-curable layer from daylight. Optionally, the flexographic printing plate precursor further comprises a support. A support is often used to give strength to the flexographic printing plate (precursor).
Alternatively, the side of the flexographic printing plate precursor opposite the image (printing) side of the printing plate is cured to form a support. Typically, in the absence of a support, a flexographic printing plate is prepared by first curing the side of the photo-curable layer of the FPP precursor removed from the printing side. As a result that aide of the photo-curable layer cross-links, becomes a thermoset substantially insoluble layer and acts as a support for the uncured part of the flexographic printing plate precursor. Subsequently, the side to be used for printing is selectively cured by exposing the photo-curable layer image-wise to light, e.g. UV light. The unexposed (uncured) parts of the layer are then removed in developer baths, e.g., with a solvent or water. After drying, the flexographic printing plate is ready far use.
It will be appreciated that the image-wise curing of the FPP precursor must be done in a precise manner. Any unintentional curing may load to an unclear image on the flexographic printing plate, and, hence unclear prints. In order to avoid undesired scattering of light it is important that the flexographic printing plate precursor is as transparent as possible, that is, not hazy. Moreover, there is a need for further improvement of the total combination of physical properties of such photo-curable polymer composition for use in a flexographic printing plate (precursor).
Printing plates must be soft and elastic after curing. Normally, elasticity is obtained by the presence of an elastomer in the photo-curable polymer composition. Often, the elastomer is a block copolymer having two or mare polymerised styrene and one or more polymerised diene blocks.
The FPP precursor must be easy and quick to cure, and the uncured material must be easy to remove, and is preferably not tacky. The flexographic printing plate must be dimensionally stable during storage; must be flexible enough to wrap around a printing cylinder; strong enough to withstand the rigors experienced during a printing process; abrasion resistant; soft enough to facilitate ink transfer during the printing process; and resistant enough to the particular ink solvent to avoid blurring of the image. It will be appreciated that the achievement of an attractive balance of all these physical properties will be difficult.
It would be desirable if a photo-curable polymer composition could be found that has a good abrasion resistance when cured, has a relatively low hardness, allows easy removal of uncured parts and/or is not hazy, thus allowing precise curing without scattering of actinic radiation to unwanted parts. Preferably, the photo-curable polymer composition has an attractive balance of the above and other relevant properties.
SUMMARY OF THE INVENTION
Such photo-curable polymer composition has now surprisingly been found. Accordingly, the present invention relates to a photo-curable polymer composition comprising:
(a) a first block copolymer comprising at least two external blocks A of polymerised mono-vinyl aromatic monomer, at least one internal block B of polymerised conjugated diene monomer, and, optionally, a residue of a di- or multi-functional coupling agent, wherein the total polymerised mono-vinyl aromatic monomer content is in the range from 5 to 25% by weight (% wt) of the block copolymer, and wherein the residue, if present, is derived from a di- or multi-functional coupling agent containing alkoxy or epoxy functional groups;
(b) 0 to 70% by weight, basis the total block copolymer composition (a)+(b)+(c), of a second block copolymer, the second block copolymer having one block A of polymerised mono-vinyl aromatic monomer, at least one block B of polymerised conjugated diene monomer, and, optionally, a residua of a di- or multi-functional coupling agent, wherein the total polymerised mono-vinyl aromatic monomer content is in the rangy from 5 to 50% by weight of the block copolymer, and wherein the residue, if present, is derived from a di- or multi-functional coupling agent containing alkoxy or epoxy functional groups;
(c) at least 5% by weight, basis the total block copolymer composition (a)+(b)+(c), of a low molecular weight block copolymer, wherein the total of (b) and (c) is from 15% by weight to 80% by weight, basis the total block copolymer composition (a)+(b)+(c), the low molecular weight block copolymer having one block A of polymerised mono-vinyl aromatic monomer, and at least one block H of polymerised conjugated diene monomer, and having a weight average molecular weight in the range of from 1,000 to 35,000; and
(d) a photo-initiator.
For the purposes of this specification, the total block copolymer composition is taken to be block copolymers (a), (c), and, if present, (b). Typically, and preferably, the photo-curable polymer composition further comprises an ethylenically unsaturated addition-polymerisable cross-linking agent.
DETAILED DESCRIPTION OF THE INVENTION
The cross-linking agent is typically a component, such as a monomer or a mixture of monomers, that is compatible with the block copolymer(s). Monomers that can be used in the photo-curable polymer composition are well known in the art. Examples of such monomers can be found in U.S. Pat. Nos. 4,323,636; 4,753,865; 4,726,877 and 4,994,315.
The term “compatible” means that the captioned component can be mixed in a molecular-disperse fashion in the photo-curable composition or that the component has the same breaking index, does not substantially cause haze and does not separate from the photo-curable composition in the course of time, that is, does not separate within 14 days, preferably not within one month.
Typically, the ethylenically unsaturated addition-polymerisable cross-linking agent has a boiling point of at feast 100° C. at atmospheric pressure and a molecular weight of up to 3000, preferably up to 2000. Examples of suitable ethylenically unsaturated addition-polymerisable cross-linking agents include esters of acrylic acid or methacrylic acid, styrene and derivatives thereof, esters of maleic acid or fumaric acid, acrylamide or methacrylamide and allyl compounds. Preferably, esters of acrylic acid or methacrylic acid are used: Especially preferred monomers are 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, and hydroxyethyl methacrylate.
Preferably, the first block copolymer is linear, and, if a coupling agent is used, the said coupling agent is di-functional. More preferably, no coupling agent
Kegley Larry McArthur
Muyldermans Xavier
Sugiyama Shingo
Tsukakoshi Nobuyuki
Baxter Janet
Kraton Polymers US LLC
Lee Sin J.
LandOfFree
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