Additive correction fluid for metal printing forms

Details Additive correction fluid for metal printing forms Additive correction fluid for metal printing forms

2000-09-05

2003-02-11

Klemanski, Helene (Department: 1755)

Compositions: coating or plastic

Coating or plastic compositions

Marking

C106S031320, C106S031640

Reexamination Certificate

active

06517622

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a composition for positive correction of lithographic printing plates. In particular, the invention relates to a correction fluid applicable by a pen or a brush. The invention also relates to a correction kit containing the composition and methods for adding image areas to a printing plate.
BACKGROUND OF THE INVENTION
The art of lithographic printing is based upon the immiscibility of oil and water. The oily material or ink is preferentially retained by the image area and the water or fountain solution is preferentially retained by the non-image area. When a suitably prepared surface is moistened with water and an ink is applied, the background or non-image area retains the water and repels the ink, while the image area accepts the ink and repels the water. The ink on the image area is then transferred to the surface of a material upon which the image is to be reproduced, such as paper, cloth, and the like. Typically, the ink is transferred to an intermediate material called the blanket, which in turn transfers the ink to the surface of the material upon which the image is to be reproduced.
Lithographic printing plates typically comprise a radiation-sensitive coating applied over the hydrophilic surface of a support. If after exposure to radiation the exposed regions of the coating become soluble or dispersible in a developer and are removed in the developing process, revealing the underlying hydrophilic surface of the support, the plate is called a positive-working printing plate. Conversely, if the exposed regions of the plate become insoluble in the developer, and the unexposed regions are removed by the developing process, the plate is called a negative-working plate. Independent of the specific type of printing plate (positive working or negative working plate imaged by the use of a mask, plates which are directly imageable by a laser, i.e. without using a mask, organic photoconductive plates, etc.), the image area (i.e. the imagewise remaining parts of the coating after the developing of the plate) is ink-receptive or oleophilic and the non-image area or background is water-receptive or hydrophilic.
If the developed plate shows “errors” in the form of missing image areas, it is time consuming and expensive to prepare a new plate. Therefore, additive correction fluids have been developed that add further image areas and make the printing plate suitable for use. These fluids can be applied to non-image areas of a plate to make corrections or to add signs and marks thereon.
Various methods for the correction of lithographic printing plates have been disclosed. DE-A-3717653 [Pliefke, U.S. Pat. No. 4,834,844] describes a method for the electrolytic deposition of organic compounds on the aluminum oxide layer. In the examples epoxides, acrylics, melanin resins and polymers based on maleic acid are mentioned as suitable organic compounds. DE-B-2418789 [Hamilton, U.S. Pat. No. 4,150,623] describes a method for the deposition of carbon particles on the aluminum oxide layer at high temperatures. However, these methods are cumbersome to use.
In another method, pens are used for additive correction. These pens work by mechanical rubbing on the plate surface. By this, aluminum oxide is removed and the underlying aluminum then functions as ink receptive area.
In yet another method, pens containing a polyvinylphenolic derivative are used. However, these pens suffer from the disadvantage that image areas obtained by them have only a low press life. Furthermore, the solvent used in the pens may attack the coating of the plate making correction within an image area extremely difficult.
Previously known correction fluids suffer from the disadvantage that they do not show good adhesion to all known substrates, i.e. substrates having different interlayers. A particular correction fluid can only be successfully used with a particular type of plate so the printer must have a different type of correction fluid for each type of printing plate.
Usually, the developed printing plates are subjected to a preheat or a baking step at a temperature of about 50 to about 300° C., preferably about 100° C. to about 250° C. in order to improve the print run stability. Correction fluids based on polymers different from novolac resins (which are often used in the coating of plates) often do not withstand such temperatures.
For large size corrections, the correction fluid is preferably applied by a brush instead of a pen; however, most of the known fluids cannot be applied by a brush but only by a pen.
Thus a need exists for a correction fluid for lithographic printing plates that is applicable to all kinds of plates independent of the type of interlayer present, shows good adhesion on all types of interlayers, can be baked, and produces image areas having a high print run stability. Furthermore, the correction fluid should dry quickly, have no dissolving effect on the image areas of the plate and should preferably be applicable by pen and brush.
SUMMARY OF THE INVENTION
In one embodiment, the invention is an additive correction fluid comprising:
(a) a film forming aliphatic and/or aromatic ester of phosphoric acid; and
(b) an organic solvent or solvent mixture that does not dissolve the image areas of a plate to be corrected.
In another embodiment, the invention is a method for adding image areas to a printing plate. In still another embodiment, the invention is a kit comprising the additive correction fluid.
DETAILED DESCRIPTION OF THE INVENTION
The first essential component of the additive correction fluid is a film forming aliphatic and/or aromatic ester of phosphoric acid (hereafter also referred to as the “film forming phosphate” or simply “phosphate”).
The phosphate may have further functional groups selected from the group consisting of epoxy groups, hydroxy groups, C
1
-C
10
alkoxy groups (in which the alkyl moiety may be substituted by a C
6
-C
20
aryl group), aryloxy groups (in which the aryl moiety comprises 6-20 carbon atoms), —SO
3
R (in which R is selected from the group consisting of hydrogen, C
1
-C
10
alkyl and C
6
-C
20
aryl), —O—SO
3
R (in which R is as defined above), halogen, —NO
2
, —O—PO(OR)
2
(in which each R independently is as defined above), —COOR and —CONR
2
(in which each R independently is as defined above), carbonyl groups and mixtures thereof.
Suitable phosphates are commercially available from Lubrizol Corporation, Wickliffe, Ohio, USA, and Lubrizol Coating Additives GmbH, Ritterhude, Germany, under the trade names LUBRIZOL® 2061 (a epoxy-functional phosphate), LUBRIZOL®2062 (an aliphatic/aromatic phosphate) and LUBRIZOL® 2063 (a hydroxy/carboxy functional phosphate). These phosphates are available in the form of highly viscous fluids comprising ethyleneglycol monobutyl ether.
The second essential component is an organic solvent, which does not dissolve the image areas of the plate to be corrected. Organic solvent also refers to solvent mixtures, i.e. mixtures of various organic solvents.
In principle, any organic solvent or solvent mixture conventionally used in lithographic printing inks as well as any organic solvent commonly used for cleaning printing plates may be used. Preferably, the solvent is selected from aliphatic and aromatic hydrocarbons, including terpenes and mixtures thereof. In connection with the drying properties of the correction fluid, it is preferred that the organic solvent or solvent mixture has an evaporation number measured according to DIN 53170 of about 1 to about 200, preferably about 1 to about 160, more preferably about 1 to about 50.
Especially preferred solvents are o-, m- or p-xylene and mixtures thereof, white spirit, toluene, and benzene. White spirit, or solvent naphtha, is a petroleum fraction comprising mainly hydrocarbons that boil in the range of about 135 to about 210° C. White spirit is available in various boiling ranges, for example about 145 to about 160° C., about 150 to about 195° C., about 140 to about 170° C., about 135 to about 180° C., about 180 to ab

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