Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1998-05-28
2001-01-16
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
06174936
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an oil-based ink for the preparation of a printing plate by an ink jet process, and a method for the preparation of a printing plate by an ink jet process using it. More particularly, the present invention relates to an oil-based ink excellent in dispersion stability, redispersibility, storage stability, image reproducibility and printing durability (press life), and a method for the preparation of 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 small commercial printing, platemaking systems wherein an image is formed on a direct imaging type lithographic printing plate precursor comprising a water-resistant support having provided thereon an image receiving layer having a hydrophilic surface in a various manner to prepare an offset lithographic printing plate have been widely employed.
A conventional lithographic printing plate precursor for direct imaging type comprises a support formed of paper subjected to water-resistant treatment or a plastic film having provided thereon an image accepting layer (or an image receiving layer) containing an inorganic pigment, a water-soluble resin and a water resistance imparting agent. On such a direct imaging type lithographic printing plate precursor, a lipophilic image is formed with a typewriter or by hand writing using a lipophilic ink, or by transferring an image from an ink ribbon by heat melting with a heat transfer printer, thereby preparing a printing plate.
However, the printing plate prepared by such a method are not sufficient in mechanical strength of image areas, so that cutting easily takes place in the image areas during printing.
On the other hand, ink jet recording is a recording method low in noise and printable at a high speed, and has recently been rapidly popularized.
As such ink jet recording methods, there are proposed various systems 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 oscillation pressure of a piezoelectric element, and a so-called bubble (thermal) jet system in which ink is discharged using pressure generated by forming bubbles and allowing them to grow up with heating at high temperature. According to these systems, highly accurate images can be obtained.
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 conventionally employed.
It is also known that plate making is performed using an ink jet printer on a lithographic printing plate precursor for direct imaging type described above. In this case, although aqueous ink in which water is used as a dispersion medium is employed, the aqueous ink has the problems in that blurs appear in images formed on the precursor and in that a picture drawing speed is decreased because of slow drying. In order to overcome such problems, a method using oil-based ink in which a nonaqueous solvent is used as a dispersion medium is proposed as described in JP-A-54-117203 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”).
However, this method is still insufficient, because blurs are observed in images formed by plate making and blurs are developed in prints. Further, the number of prints obtained is limited to several hundred at most. Moreover, such ink has the problem of being liable to clog a nozzle for discharging minute ink droplets which make it possible to obtain images having high resolution by the plate making.
In the ink jet recording systems, ink is usually discharged from a nozzle through a filter, so that abnormal discharge of ink tends to take place by clogging of the nozzle or the filter, change in fluidity of the ink with the lapse of time, or various other factors.
This abnormal discharge of ink occurs with respect to not only an aqueous ink composition, but also an oil-based ink composition. Various proposals for controlling the abnormal discharge of ink have been made. For example, in order to prevent the abnormal discharge of ink in case of using an oil-based ink composition, it is proposed that the viscosity and the specific resistance of the ink composition is controlled as described in JP-A-49-50935, for the ink jet recording method of the electric field controlling system. It is also proposed that the dielectric constant and the specific resistance of the solvent used in the ink composition are controlled as described in JP-A-53-29808.
Furthermore, as attempts to prevent clogging of nozzles caused by ordinary oil-based ink for ink jet printer, 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 incorporated into ink compositions (e.g., JP-A-3-79677, JP-A-3-64377, JP-A-4-202386 and JP-A-7-109431).
However, when these ink compositions are used for the image formation of lithographic printing plate, the images formed are poor in image strength during printing, and a printing plate which has a sufficient press life cannot been obtained.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an oil-based ink for the preparation of a printing plate by an ink jet process which is excellent in redispersibility, storage stability, image reproducibility and press life.
Another object of the present invention is to provide an oil-based ink for the preparation of a printing plate by an ink jet process which does not induce clogging in a nozzle and in the course of ink supply and which makes it possible to conduct stable discharge.
A further object of the present invention is to provide a method for the preparation of a printing plate by an ink jet process in which ink jet recording is carried out stably when repeated and which provides a lithographic printing plate excellent in press life.
A still further object of the present invention is to provide a method for the preparation of a printing plate by an ink jet process which makes it possible to provide many sheets of prints having clear images.
Other objects of the present invention will become apparent from the following description.
It has been found that these objects of the present invention are accomplished by an oil-based ink for the preparation of a printing plate by an ink jet process comprising dropwise supplying from a nozzle an oil-based ink comprising 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 lithographic printing plate precursor comprising a water-resistant support and a lithographically printable hydrophilic surface to form an image, wherein the resin particles dispersed are copolymer resin 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 that is at least miscible with the nonaqueous carrier liquid and becomes insoluble in the nonaqueous solvent by polymerization;
(ii) at least one monomer (C) represented by the formula (I) shown below which is copolymerizable with the monomer (A):
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 (III):
wherein R
21
represents a hydrogen atom or an aliphatic group having from 1 to 18 carbon atoms;
B
1
and B
2
, which may be the same or different, each represents —O—, —S—, —CO—, —CO
2
—, —OCO—, —SO
2
—, —N(R
22
)—, —CON(R
22
)—, —N(R
22
)CO—, —N(R
22
)SO
2
—, —SO
2
N(R
22
)—, —NHCO
2
— or —NHCONH—, in which R
22
has the same meaning as defined
Fuji Photo Film Co. , Ltd.
Jagannathan Vasu
Shosho Callie E.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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