Printing – Planographic – Lithographic plate making – and processes of making or using...
Reexamination Certificate
1999-11-16
2002-08-06
Funk, Stephen R. (Department: 2854)
Printing
Planographic
Lithographic plate making, and processes of making or using...
C101S455000, C101S478000, C430S329000
Reexamination Certificate
active
06427596
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to planographic printing, especially lithographic printing. Particularly, although not exclusively, it relates to the correction of mistakes or other imperfections on printing members, for example printing plates, by rendering ink accepting areas non-ink accepting.
BACKGROUND OF THE INVENTION
Our co-pending applications PCT/GB96/02883 (U.S. Pat. No. 6,105,500), PCT/GB98/01500, and PCT/GB98/01496, all three of which are incorporated herein by reference, describe a printing plate that comprises a support provided with a hydrophilic layer comprising a binder based on a material having Si—O bonds in which particulate material is dispersed and an image layer over the hydrophilic layer. Such a hydrophilic layer can advantageously be applied to a wide range of different support materials, for example metals such as aluminum; plastics, such as polyester; and also paper. Printing plates including a hydrophilic layer as described have excellent printing properties. However, a problem has now been noted in relation to the rendering of ink accepting areas non-ink accepting as may be required to correct mistakes or other imperfections on the printing plates.
It is well-known in the printing industry to remove or delete unwanted image material utilizing a deletion fluid, which may be applied to areas to be removed using a brush, a pen or other means. Known deletion fluids for negative plates commonly utilize a hydrogen fluoride solution in combination with an organic solvent and other additives. Hydrogen fluoride based deletion fluids generally remove image material very well. However, it has been noted that, in relation to plastic plates comprising a hydrophilic layer of the type described above, although most or all of an unwanted image area to which a known deletion fluid is applied is rendered non-ink accepting, there is often an area associated with and/or close to the unwanted image area which should be non-ink accepting but is found to be ink accepting. Consequently, such an area accepts ink during printing and leads to imperfections in printed material.
The inadequacies of hydrogen fluoride based deletion fluids in relation to hydrophilic layers of the type described have, to the applicant's knowledge, been unappreciated in the past and, furthermore, the reasons for the apparent inadequate deletion of unwanted image areas using hydrogen fluoride based deletion fluids have not been investigated.
SUMMARY OF THE INVENTION
This invention is based on an appreciation of the existence of a problem with commercially-available hydrogen fluoride based deletion fluids and, additionally, on the discovery of the reasons for the problem. More particularly, it has been discovered that commercially-available hydrogen fluoride deletion fluids attack the aforesaid hydrophilic layer at a greater rate than that at which they attack the image layer and, consequently, the hydrophilic layer is removed in localized regions contacted by the deletion fluid. Such localized regions may be cosmetically undesirable because they imply a defective hydrophilic layer, and they may be undesirable from a performance perspective because they may be less hydrophilic and/or have a different ink-water balance compared to other regions of the plate and/or they may be more prone to wear.
The invention is a method of rendering non-ink accepting a selected ink accepting area of a printing member comprising a support and a hydrophilic layer that comprises a material having Si—O bonds and an image layer. The method comprises contacting the area with a means (hereinafter “the hydrophilizing means”) that renders the area non-ink accepting at a greater rate than that at which it can remove the hydrophilic layer.
DETAILED DESCRIPTION OF THE INVENTION
The hydrophilic layer may be removed by the hydrophilizing means at a rate of less than 0.15 &mgr;m.s
−1
, typically less than 0.1 &mgr;m.s
−1
, preferably less than 0.05 &mgr;m.s
1−1
, more preferably less than 0.02 um.s
−1
.
The ink-accepting area may be rendered non-ink accepting within 3 minutes, typically 2 minutes, preferably 1½ minutes, more preferably within 1 minute, especially within 30 seconds or less of the first contact with the hydrophilizing means.
The rate of rendering of the ink-accepting area non-ink accepting may be at least 5 times, preferably at least 10 times, more preferably at least 20 times, especially at least 30 times the rate of removal of the hydrophilic layer. The relative rates of these processes can be readily compared by visual inspection. A printing member comprising a support, a hydrophilic layer, and a non-ink accepting area is treated with a hydrophilizing means and relative rates visually determined.
In a first embodiment, contact with the hydrophilizing means renders the ink accepting area non-ink accepting by removing the area.
The ink-accepting area may be removed at a rate of greater than 0.005 gm
−2
s
−1
, preferably greater than 0.01 gm
−2
s
−1
, more preferably greater than 0.05 gm
−2
s
−1
.
The thickness of the ink-accepting area may be at least 0.4 &mgr;m, preferably at least 0.8 &mgr;m, more preferably at least about 1 &mgr;m. The thickness of the ink-accepting area may be less than 10 &mgr;m, typically less than 8 &mgr;m, preferably less than 6 &mgr;m, more preferably less than 4 &mgr;m, especially less than 2 &mgr;m or less.
Preferably, in the method, substantially the whole thickness of the ink-accepting area is removed, thereby to reveal an underlying layer which is non-ink accepting and which is typically the hydrophilic layer.
The hydrophilizing means may include one or more of acids and/or alkalis and/or oxidizing formulations.
Preferred acids include strong acids, for example inorganic acids such as sulfuric or nitric; weak inorganic acids, for example phospho-acids such as orthophosphoric; and organic acids for example carboxylic acids such as acetic and acrylic. Solutions comprising greater than 60%, preferably 70%, more preferably 80%, especially 90% of a the acid may be used. An especially preferred acid is sulfuric acid.
Preferred alkalis include sodium hydroxide, potassium hydroxide and silicates such as sodium silicate.
Preferred oxidizing formulations may include nitrites such as sodium nitrite; nitrates such as aluminum or potassium nitrate; halogen-based oxidizers for example peracids such as perchloric acid, perhalates such as periodates and perchlorates; hydrogen peroxide; transition metal oxidizing agents such as potassium permanganate, ferric chloride and chromium VI oxide.
The hydrophilizing means may include means for softening the hydrophilic layer.
The hydrophilizing means may include one or more solvents. Suitable solvents may include one or more of water; acids, typically of the type described above; and organic solvents, especially alcohols such as C
1-3
alcohols and/or alkoxyalcohols such as 2-butoxyethanol, cyclohexanone, N-methylpyrrolidone, gamma-butyrolactone, dimethyl sulfoxide and benzylalcohol.
The hydrophilizing means may include a thickener.
Components of the hydrophilizing means may be applied together or may be applied one after the other.
Especially preferred hydrophilizing means may include one or more of sulfuric acid, hydrogen peroxide, nitrates, transition metal oxidizing agents, potassium hydroxide and a silicate especially sodium silicate.
In a second embodiment, contact with the hydrophilizing means renders the ink-accepting area non-ink accepting by covering the area. In this case, the hydrophilizing means may comprise any material or materials which can be bonded to the image layer and which is/are non-ink accepting. The hydrophilizing means may comprise a first material, which is applied directly to the ink-accepting area, and a second material, which is arranged over the first material. For example, the first material may be provided to aid adhesion of the second material to the ink-accepting area.
The hydrophilizing means of the second embodiment may include one or mo
Bhambra Harjit S.
Dickinson Kelvin
Organ Robert M.
Funk Stephen R.
Kodak Polychrome Graphics LLC
Ratner & Prestia
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