Radiation imagery chemistry: process – composition – or product th – Regenerating image processing composition – Developer
Reexamination Certificate
2001-08-01
2003-05-13
Le, Hoa Van (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Regenerating image processing composition
Developer
C430S302000
Reexamination Certificate
active
06562555
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method for developing exposed lithographic printing plate precursors using a developer and replenisher. In particular, this invention relates to a method in which the replenisher comprises a higher concentration of a coating attack-suppressing agent than the developer.
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.
Imageable elements useful as lithographic printing plates, also called printing plate precursors, typically comprise an imageable layer applied over the surface of a hydrophilic substrate. The imageable layer includes 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.
To obtain a printing plate with imagewise distribution of printable regions, it is necessary to remove regions of an imaged precursor. The most common method for removing the undesired regions is to contact the imaged precursor with a developer. If after exposure to radiation the exposed regions of the imageable layer are removed by the developer revealing the underlying hydrophilic surface of the substrate, the precursor is a positive-working printing plate. Conversely, if the unexposed regions are removed, the precursor is negative-working. In each instance, the regions of the imageable layer (i.e., the image areas) that remain after development are ink-receptive, and the regions of the hydrophilic surface revealed by the developing process accept water and aqueous solutions, typically a fountain solution, and repel ink.
Most positive-working and negative-working printing plate precursors comprise materials that are soluble or dispersible in aqueous base, such as phenolic polymers, carboxylic acid polymers, and/or sulfonamide polymers, in the imageable layer. Consequently, alkaline solutions are useful as developers.
The development process is typically carried out in a processor equipped with an immersion type-developing bath, a section for rinsing with water, a gumming section, and a drying section. During the development process, some of the developer is removed from the developing bath with the developed printing plates (drag-out). In addition, some of the base in the developer is consumed as the developer becomes loaded with components of the imageable layer that have been removed during the development process.
To achieve constant activity for the developer, the activity of the developer is monitored, and a replenisher is periodically added to the developer bath so that a balance between developer drag-out and developer feed-in is reached. The replenisher differs from the developer in that it has a higher concentration of the alkaline component or components present in the developer to compensate for the base consumed in the development process.
Batches of developer are typically used for periods of several days to several weeks before they are replaced with fresh developer. Although the conductivity of the developer is maintained at its original value during the developer loading cycle, the developer becomes more aggressive during this period. That is, for precursors that have been exposed with equivalent amounts of radiation, the developer removes more of the imageable layer during the later stages of the developer loading cycle than during the early stages of the developer loading cycle. Thus, a need exists for a method for developing exposed lithographic printing plate precursors using a developer and replenisher in which the developer does not become more aggressive during the later stages of the developer loading cycle.
SUMMARY OF THE INVENTION
The invention is a method for developing an exposed lithographic printing plate precursor using a developer and replenisher in which the developer does not become more aggressive during the later stages of the developer loading cycle. The method comprises the steps of:
developing the exposed printing plate precursor with the developer; and
adding the replenisher to the developer so that the activity of the developer remains relatively constant;
wherein:
the printing plate precursor comprises an imageable layer:
the imageable layer comprises a material that is soluble or dispersible in aqueous alkaline solution;
the developer comprises an alkaline material and a developer-soluble coating attack-suppressing agent;
the replenisher comprises the alkaline material and the coating attack-suppressing agent;
the alkaline material in the replenisher is at a higher concentration than the alkaline material in the developer; and
the coating attack-suppressing agent in the replenisher is at a higher concentration than the coating attack-suppressing agent in the developer.
Typically, the coating attack-suppressing agent is a developer-soluble polyethyoxylated, polypropoxylated, and/or polybutyloxylated compound. Preferably, the coating attack-suppressing agent is a developer-soluble compound selected from the group consisting of:
(1) compounds of the structure:
R
1
O(CH
2
—CHR
2
—O)
n
—R
3
in which n is an integer; R
1
is hydrogen, C
1
-C
18
alkyl, C
1
-C
18
aryl, C
1
-C
18
substituted aryl, or C
1
-C
18
aralkyl; R
2
is hydrogen, methyl, or ethyl; R
3
is hydrogen, C
1
-C
8
alkyl, —CH
2
COOH, or CH
2
COO
−
M
+
, in which M is ammonium, substituted ammonium, sodium or potassium; and
(2) polycondensation products of at least one C
2
-C
4
alkylene oxide and ethylene diamine.
DETAILED DESCRIPTION OF THE INVENTION
Coating Attack-Suppressing Agent
The coating attack-suppressing agent is a developer-soluble compound that suppresses attack on the coating by the developer. “Developer-soluble” means that enough of the agent will dissolve in the developer to suppress attack on the coating by the developer. Throughout the specification and claims, unless the context indicates otherwise, “coating attack-suppressing agent” includes mixtures of such agents.
Typically the coating attack-suppressing agent is a developer-soluble polyethyoxylated, polypropoxylated, and/or polybutyloxylated compound. That is, a compound that comprises recurring units of the —(CH
2
—CHR
2
—O)— structural unit, in which each R
2
is independently hydrogen, methyl, or ethyl. Preferably, the coating attack-suppressing agent is an polyethyoxylated, polypropoxylated, or poly(ethoxylated/propoxylated) compound. That is, a compound that comprises recurring units of the —(CH
2
—CHR
2
—O)— structural unit, in which each R
2
is independently hydrogen or methyl. One group of preferred compounds are those that comprise at least one polyoxyethylene block and at least one polyoxypropylene block.
Preferably, the coating attack-suppressing agent is a developer-soluble compound selected from the group consisting of:
(1) polyglycols of the formula:
R
1
O—(CH
2
—CHR
2
—O)
n
—R
3
in which n is an integer; R
1
is hydrogen, C
1
-C
18
alkyl, C
1
-C
18
aryl, C
1
-C
18
substituted aryl, or C
1
-C
18
aralkyl; R
2
is hydrogen, methyl, or ethyl; R
3
is hydrogen, C
1
-C
8
alkyl, —CH
2
COOH, or CH
2
COO
−
M
+
, in which M is ammonium, substituted ammonium, sodium or potassium; and
(2) polycondensation products of at least one C
2
-C
4
alkylene oxide with ethylene diamine.
The value of n will depend on the nature of R
1
, R
2
, and R
3
. If R
1
and/or R
3
are relatively large alkyl groups, n will typically be larger to provide the required developer solubility. However, n should not be so large that the coating attack-suppressing agent unacceptably increases the viscosit
Fiebag Ulrich
Hauck Gerhard
Savariar-Hauck Celin
Kodak Polychrome Graphics LLC
Le Hoa Van
RatnerPrestia
LandOfFree
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