Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1998-01-20
2001-02-06
Jagannathan, Vasu (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C430S049700
Reexamination Certificate
active
06184267
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an oil-based ink for preparing a printing plate by an ink jet process, and a method for preparing a printing plate by an ink jet process using it. More particularly, the present invention relates to an oil-based ink excellent in redispersibility, stability, image reproducibility and printability (press life), and a method for preparing a printing plate by an ink jet process using it.
BACKGROUND OF THE INVENTION
With recent developments in business machines and progress in office automation, in the field of light printing, offset lithographic systems have been widely applied in which printing process is conducted, namely images are formed, on direct imaging lithographic printing plate precursors comprising water-resistant supports having provided thereon image receiving layers having hydrophilic surfaces.
Conventional printing plate precursors for direct imaging lithographic printing comprise supports formed of paper or plastic films which are subjected to water-resistant treatments having provided thereon image accepting layers (or image receiving layers) containing inorganic pigments, water-soluble resins and water resistance imparting agents. Methods are known in which lipophilic images are formed on such direct imaging lithographic printing plate precursor with typewriters or by hand writing using lipophilic ink, or by transferring images from ink ribbons by heat melting with heat transfer printers, thereby preparing printing plates.
However, the printing plates prepared by such methods are not sufficient in mechanical strength of image areas, so that missing easily takes place in the image areas in printing.
On the other hand, ink jet recording is a recording method low in noise and printable at high speed, and has recently been rapidly popularized.
As such ink jet recording systems, there are proposed various ink jet processes such as a so-called electric field controlling system in which ink is discharged using electrostatic attraction, a so-called drop-on-demand system (pressure pulse system) in which ink is discharged using the oscillation pressure of a piezoelectric element, and a so-called bubble (thermal) system in which ink is discharged using pressure developed by forming bubbles and allowing them to grow by heating at high temperature, and very detailed images can be obtained by these systems.
In these ink jet recording systems, aqueous ink using water as a main solvent, and oil-based ink using an organic solvent as a main solvent are generally used.
It is also carried out that the above-mentioned lithographic printing plate precursors are made with typewriters using ink jet recording systems, and in this case, aqueous ink in which water is used as a dispersing medium is also employed. However, the aqueous ink has the problem that blurs appear in images on precursor materials, or that the picture drawing speed is decreased because of slow drying. In order to reduce such a problem, a method using oil-based ink in which a nonaqueous solvent is used as a dispersing medium is disclosed in JP-A-54-117203 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”).
However, this method is also insufficient, because blurs are observed in actual printing process images, furthermore, blurs are developed in printing, and the number of printing sheets is limited to several hundred at the most. Furthermore, such ink has the problem of being liable to clog a nozzle for discharging minute ink droplets which make it possible to obtain printing process images having high resolution.
In the ink jet recording systems, ink is generally discharged from nozzles through filters, so that abnormal discharge of ink is liable to take place by clogging of the nozzles or the filters, changes in fluidity of ink with time, or other various factors.
This abnormal discharge of ink takes place with respect to not only aqueous ink compositions, but also oil-based ink compositions. Various proposals for improving such abnormal discharge of ink have been submitted. For example, in order to prevent the abnormal discharge of ink at the time when oil-based ink compositions are used, it is proposed that the viscosity and the specific resistance of the ink compositions are controlled as described in JP-A-49-50935, for the ink jet recording system of the electric field controlling system. It is further proposed that the dielectric constant and the specific resistance of solvents used in the ink compositions are controlled as described in JP-A-53-29808.
Furthermore, as attempts to prevent clogging of nozzles caused by general oil-based ink for ink jet printers, there are proposed, for example, methods in which the dispersion stability of pigment particles is improved (e.g., JP-A-4-25573, JP-A-5-25413 and JP-A-5-65443) and methods in which specific compounds are contained as ink compositions (e.g., JP-A-3-79677, JP-A-3-64377, JP-A-4-202386 and JP-A-7-109431).
However, when they are used in image formation of lithographic printing plates, all of them are poor in image strength in printing, and printing plates which can satisfy the press life have not been obtained.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an oil-based ink for a printing plate by an ink jet process excellent in redispersibility, storage stability and press life.
Another object of the present invention is to provide an oil-based ink for a printing plate by an ink jet process which makes it possible to print many sheets of printed material having clear images.
A further object of the present invention is to provide an oil-based ink for a printing plate by an ink jet process which does not induce clogging in a nozzle and in the course of ink supply and stabilizes ink discharge.
A still further object of the present invention is to provide a method for preparing a printing plate by an ink jet process using the above-mentioned oil-based ink.
These and other objects of the present invention have been accomplished by the following:
(1) an oil-based ink for a printing plate by an ink jet process comprising spraying an oil-based ink comprising at least resin particles dispersed in a nonaqueous carrier liquid having an electric resistance of 10
9
&OHgr;cm or more and a dielectric constant of 3.5 or less on a water-resistant support having a lithographically printable hydrophilic surface dropwise from a nozzle to form an image,
wherein said resin particles dispersed are polymer particles obtained by polymerization granulation of a solution comprising (i), (ii) and (iii):
(i) at least one monofunctional monomer (A) which is soluble in a nonaqueous solvent which is at least miscible with said nonaqueous carrier liquid and becomes insoluble therein by polymerization;
(ii) (ii-a) at least one monomer (B) represented by the following formula (I-A) which is copolymerizable with said monomer (A), or
(ii-b) at least one monofunctional macromonomer (MA) having a weight average molecular weight of 2×10
4
or less obtained by combining a polymerizable double bond group represented by the following formula (II-B) with only one end of a main chain of a polymer comprising a repeating unit corresponding to a monomer represented by the following formula (I-B); and
(iii) at least one resin for dispersion stabilization (P) which is a polymer comprising a repeating unit represented by the following formula (III), wherein said polymer is crosslinked at a part of its main chain thereof, and said resin (P) is soluble in said nonaqueous solvent:
wherein E
1
represents an aliphatic group having 8 or more carbon atoms or a substituent having a total number of atoms of 8 or more, provided that hydrogen atoms directly attached to a carbon or nitrogen atom are excluded from the number, represented by the following formula (IV-A):
wherein R
21
represents a hydrogen atom or an aliphatic group having 1 to 18 carbon atoms;
B
1
and B
2
are the same or different and each represents —O—, —S—, —CO—, —CO
2
—, —OCO—, —SO
2
—, —N(R
22
)—, —CON(R
22
)—, —N(R
Ishii Kazuo
Kato Eiichi
Osawa Sadao
Fuji Photo Film Co. , Ltd.
Jagannathan Vasu
Shosho Callie E.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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