Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-02-17
2001-06-12
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...
C524S548000, C524S556000
Reexamination Certificate
active
06245832
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an ink for ink jet recording which can be used in the ink jet recording system, a process for producing the ink and an ink jet recording method using the ink.
BACKGROUND OF THE INVENTION
The principle of ink jet recording system is to eject a liquid or fused solid ink from nozzle, slit, porous film or the like to make recording on a recording material such as paper, cloth or film. For ejecting an ink, various methods have been proposed, such as a method of ejecting an ink using an electrostatic induction, namely, so-called charge control system; a method of ejecting an ink using a piezoelectric element and an oscillation pressure; and a method of ejecting an ink using a pressure generated as a result of forming and growing bubbles by heat, so-called thermal ink jet system. Using these methods, a high precision image can be obtained.
The ink for ink jet recording is required to have the following properties:
(1) that a high-resolution and high-density uniform image can be obtained without causing blotting or fogging on paper;
(2) that clogging due to drying of the ink does not occur at a nozzle tip and ejection responsibility and ejection stability are always kept in good condition;
(3) that the ink on paper exhibits good drying property;
(4) that the image has good fastness; and
(5) that high stability is ensured in the long-term storage.
As the ink for ink jet recording, an ink comprising a dye as a coloring material is predominantly used. However, the dye is disadvantageous in that the image is inferior in the water resistance and light fastness. To cope with this, development of an ink using a pigment as a coloring material is proceeding. Since the pigment is substantially insoluble in water, studies are being made on the method using a dispersant for stably dispersing the pigment in ink. However, if a surfactant is used as the dispersant, the surface tension excessively decreases and troubles are readily caused, such as deterioration in the quality of the printed image and printing drop out due to bubbles. Accordingly, use of a dispersant comprising a polymer compound is being studied.
As the polymer dispersant, various copolymers having both a hydrophobic moiety highly affinitive for a pigment and a hydrophilic moiety highly affinitive for an aqueous medium have been proposed. For example, an ink containing a polymer dispersant and a specific solvent (JP-A-56-147859 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)), an ink containing acidic carbon black and a water-soluble resin having a specific molecular weight in a specific content ratio (JP-A-3-210373) and an ink containing acidic carbon black and a water-soluble resin having a specific acid value (JP-A-4-18461) are disclosed.
With respect to the form of the copolymer for the polymer dispersant, inks using a random copolymer (JP-A-56-147859), a block copolymer (U.S. Pat. No. 5,085,698) or a graft copolymer (JP-A-6-100810) are disclosed. Block copolymers and graft copolymers controlled in the orientation of monomers are considered to have an ideal structure as the dispersant, however, these are disadvantageously complicated in the synthesis process and in turn expensive. Conventional random copolymers are relatively easy to produce, however, properties of this polymer such as the kind of monomer selected, molecular weight and acid value, have not yet been thoroughly studied and copolymers satisfying all of the above-described properties required have not yet obtained.
SUMMARY OF THE INVENTION
Accordingly, the object of the present invention is to solve the problems in related techniques and provide an ink for ink jet recording, capable of forming a high-resolution, high-density uniform image on a paper without undergoing blotting or fogging, prevented from generation of clogging at the nozzle tip due to drying of the ink, always exhibiting good ejection responsibility and good ejection stability, assuring good fastness of the image and having good long-term storage stability.
As a result of extensive investigations on the polymer dispersant, the present inventors have found that the above-described object can be attained by an ink for ink jet recording comprising water, a water-soluble organic solvent, a pigment and a dispersant, wherein the dispersant consists of a hydrophilic moiety and a hydrophobic moiety and comprises a copolymer obtained by copolymerizing from 40 to 80 mol % of a monomer having an &agr;,&bgr;-ethylenically unsaturated group constituting the hydrophilic moiety and from 20 to 60 mol % of a monomer having an &agr;,&bgr;-ethylenically unsaturated group constituting the hydrophobic moiety and assuming that the weight average molecular weight is Mw and the number average molecular weight is Mn, the copolymer has a specific Mw/Mn. That is, an ink for ink jet recording in which the change in viscosity of the ink after storage at 60° C. for 100 hours is 0.3 mPa·s or less at a shear rate of 1,400 s
−1
can be provided. The present invention has been accomplished based on this finding.
More specifically, the present invention provides:
an ink for ink jet recording comprising water, a water-soluble organic solvent, a pigment and a dispersant, wherein the change in viscosity of the ink after storage at 60° C. for 100 hours is 0.3 mPa·s or less at a shear rate of 1400 s
−1
;
an ink for ink jet recording comprising water, a water-soluble organic solvent, a pigment and a dispersant, wherein the dispersant has a hydrophilic moiety and a hydrophobic moiety and comprises a copolymer obtained by copolymerizing from 40 to 80 mol % of a monomer having an &agr;,&bgr;-ethylenically unsaturated group constituting the hydrophilic moiety and from 20 to 60 mol % of a monomer having an &agr;,&bgr;-ethylenically unsaturated group constituting the hydrophobic moiety, the copolymer has a weight average molecular weight Mw of from 3,000 to 15,000 and assuming that the number average molecular weight is Mn, the Mw/Mn is from 1 to 2.5;
a process for producing an ink for ink jet recording, comprising previously mixing a pigment with the above-described dispersant, dispersing the pigment in water and then mixing the dispersion solution with water and a water-soluble organic solvent; and
an ink jet recording method comprising ejecting the above-described ink for ink jet recording from an orifice according to a recording signal to effect recording on a recording material.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below.
The ink for ink jet recording of the present invention comprises water, a water-soluble organic solvent, a pigment and a dispersant. The dispersant has a hydrophilic moiety and a hydrophobic moiety and comprises a copolymer obtained by copolymerizing a monomer having an &agr;,&bgr;-ethylenically unsaturated group constituting the hydrophilic moiety and a monomer having an &agr;,&bgr;-ethylenically unsaturated group constituting the hydrophobic moiety.
The constitutional ratio of the monomer having an &agr;,&bgr;-ethylenically unsaturated group constituting the hydrophilic moiety is from 40 to 80 mol %, preferably from 50 to 80 mol %, more preferably from 60 to 80 mol %. The constitutional ratio of the monomer having an &agr;,&bgr;-ethylenically unsaturated group constituting the hydrophobic moiety is from 20 to 60 mol %, preferably from 20 to 50 mol %, more preferably from 20 to 40 mol %. If the constitutional ratio of each monomer in the copolymer departs from this range and the hydrophobic moiety occupies the major part, the solubility in an aqueous medium decreases and the stability is deteriorated, whereas if the hydrophilic moiety occupies the major part, the water solubility becomes excessively high and the water resistance is deteriorated or the image density decreases.
The monomer having an &agr;,&bgr;-ethylenically unsaturated group constituting the hydrophilic moiety is not particularly limited, however, monomers having a carboxyl group, a sulfonic acid grou
Doi Takatsugu
Hashimoto Ken
Ichizawa Nobuyuki
Suzuki Atsushi
Yamashita Kunichi
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Fuji Xerox Co. LTD
Jagannathan Vasu
Shosho Callie E.
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