Radiation imagery chemistry: process – composition – or product th – Diazo reproduction – process – composition – or product – Composition or product which contains radiation sensitive...
Reexamination Certificate
2002-04-05
2004-08-31
Chu, John S. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Diazo reproduction, process, composition, or product
Composition or product which contains radiation sensitive...
C430S176000, C430S270100, C430S326000, C525S056000, C525S061000
Reexamination Certificate
active
06783913
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to lithographic printing. More particularly, this invention relates to imageable elements useful as lithographic printing plate precursors.
BACKGROUND OF THE INVENTION
In lithographic printing, ink receptive regions, known as image areas, are generated on a hydrophilic surface. When the surface is moistened with water and ink is applied, the hydrophilic regions retain the water and repel the ink, and the ink receptive regions accept the ink and repel the water. The ink is transferred to the surface of a material upon which the image is to be reproduced. Typically, the ink is first transferred to an intermediate blanket, which in turn transfers the ink to the surface of the material upon which the image is to be reproduced.
A class of imageable elements useful as lithographic printing plates, also called printing plate precursors, comprises a photosensitive layer over the surface of a hydrophilic substrate. The photosensitive layer comprises one or more radiation-sensitive components, which may be dispersed in a suitable binder. Alternatively, the radiation-sensitive component can also be the binder material.
If after exposure to radiation, the exposed regions of the photosensitive layer are removed in the developing process, revealing the underlying hydrophilic surface of the substrate, the element is positive working. Conversely, if the unexposed regions are removed by the developing process, the element is negative working. In each instance, the regions of the radiation-sensitive layer (i.e., the image areas) that remain are ink-receptive and the regions of the hydrophilic surface revealed by the developing process accept water, typically a fountain solution, and repel ink.
Of particular value in lithographic photosensitive compositions are binders based on a polymeric acetal backbone. Photosensitive compositions which contain polyvinyl acetals, for example, polyvinyl formal or polyvinyl butyral, as binders and diazonium salt polycondensation products as photosensitive compounds are disclosed in Baumann, U.S. Pat. No. 5,700,619, incorporated herein by reference; Pawlowski, U.S. Pat. No. 4,631,245; and WO 9303068. Although these binders produce lithographic printing plates having high print run performance, the photosensitive compositions and the lithographic printing plate precursors derived therefrom, have limited shelf life. Thus, a need exists for lithographic printing plate precursors that have a high print run performance and good shelf life.
SUMMARY OF THE INVENTION
In one aspect, the invention is a polymeric acetal resin comprising units (A), (B), (C), (D), and (E), in which:
unit (A) has the structure:
unit (B) has the structure:
unit (C) has the structure:
unit (D) is selected from the group consisting of (D
1
), (D
2
), and combinations thereof,
in which unit (D
1
) has the structure:
and unit (D
2
) has the structure
unit (E) is selected from the group consisting of (E
1
), (E
2
), and combinations thereof in which
unit (E
1
) has the structure:
and unit (E
2
) has the structure
in which the polymeric acetal resin comprises about 10 to about 60 mol % of unit (A), about 5 to about 60 mol % of unit (B), about 0.3 to about 30 mol % of unit (C), about 1 to about 40 mol % of unit (D), and about 0.01 to about 2 mol % of unit (E);
in which:
R and R
2
are each independently hydrogen, an aliphatic group, an aromatic group, or an arylaliphatic group;
Ac
1
and Ac
2
are each independently a group comprising a carboxylic acid group, a sulfonic acid group, a sulfonamido group, a phosphonic acid group, a proton-bearing phosphoric ester group, a phenolic group, or an alkali metal salt or an ammonium salt thereof;
R
1
is H, C
1
-C
10
alkyl, or carboxyl-substituted C
1
-C
10
alkyl; and
In
1
and In
2
are each independently a group that inhibits free radical polymerization.
In another aspect, the invention is a photosensitive composition comprising a polymeric diazo resin and the polymeric acetal resin.
In another aspect, the invention is a lithographic printing plate precursor comprising a layer of the photosensitive composition over a hydrophilic surface of a substrate having the hydrophilic surface.
In a further aspect, the invention is a method for preparing a lithographic printing plate comprising imagewise exposing and developing the lithographic printing plate precursor to remove the unexposed regions. In yet a further aspect, the invention is a printing plate produced by this method.
Incorporation of the radical inhibiting groups In
1
and In
2
into the polymeric acetal resins produces significant and useful improvements in the shelf life of the photosensitive compositions and imageable elements, even though unbound inhibitors in equivalent amount produce no noticeable improvement in shelf life.
DETAILED DESCRIPTION OF THE INVENTION
Photosensitive Composition
The photosensitive composition comprises a polymeric acetal resin and a polymeric diazo resin. Other ingredients that are conventional components of photosensitive compositions may also be present.
Polymeric Acetal Resin
The photosensitive composition comprises a binder based on either polyvinyl alcohol or on a copolymer comprising units of (1) vinyl alcohol and (2) acrylic acid and/or a substituted acrylic acid. Although acrylic acids substituted with a C
1
-C
10
alkyl group that is optionally carboxyl-substituted can be used, preferred acids are acrylic acid, methacrylic acid, and crotonic acid. The hydroxyl groups of the polymer or copolymer are acetalized or esterified with the appropriate groups to form the polymeric acetal resin.
Preferred polyvinyl alcohols or copolymers for the synthesis have a residual content of esterified groups in the range of about 0.3 to about 30 mol %. More preferred are polyvinyl alcohols prepared starting from polyvinyl acetate, i.e. R
2
=—CH
3
with a residual acetate content of about 1.5 to about 22 mol %. The behavior in alkaline developers and the photosensitivity of photosensitive compositions employing the polymeric resin as binder can be influenced by the molecular weight of the polyvinyl alcohols used in the synthesis. Preferred polyvinyl alcohols exhibit viscosities of between about 2 and about 26 mPa·s as 4% aqueous solution in water at 20° C.
The acetalization of the polyvinyl alcohols may be carried out by conventional techniques, such as are described; for example, in EP-B-216 083 and DE-A-28 38 025. The acetal moieties can be introduced starting with aldehydes or acetals of these aldehydes with a lower alcohol, i.e., an alcohol comprising up to about six carbon atoms such as methanol, ethanol, n-propanol, n-butanol, n-pentanol, n-hexanol, iso-propyl alcohol, iso-butyl alcohol, tert-butyl alcohol, iso-pentyl alcohol, and cyclohexanol. This reaction generally requires the addition of a strong inorganic or organic catalyst acid, such as hydrochloric acid, sulfuric acid, phosphoric acid and p-toluene sulfonic acid. A particularly preferred catalyst acid is hydrochloric acid. The amount of acid added should preferably be about 1 to about 25 wt % based on the amount of polyvinyl alcohol used. The reaction temperature of the acetalization depends on the aldehyde as well as the desired extent of reaction. It is typically between about 0° C. and, if applicable, about the boiling point of the solvent used. Preferably the temperatures are between about 5° C. and about 100° C.
Organic solvents as well as mixtures of water with organic solvents are used as acetalization agents. Particularly suitable organic solvents are alcohols (such as methanol, ethanol, propanol, butanol and glycol ether), cyclic ethers (such as tetrahydrofuran, 1,4-dioxane, and 1,3-dioxolane) and dipolar aprotic solvents (such as dimethyl sulfoxide, formamide, N,N-dimethyl formamide, hexamethyl phosphoric acid triamide and N-methylpyrrolidone). If the acetalization is carried out in organic solvents or mixtures of organic solvents with water, the reaction product often remains in solution even if the starting polyvinyl alcohol was not completely
Baumann Harald
Dwars Udo
Glatt Hans-Horst
Glatt Ingrid
Chu John S.
Kodak Polychrome Graphics LLC
RatnerPrestia
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