JP2002338861A - Water-base ink for ink jet recording - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water-base ink for ink jet recording which has viscosity little dependent on temperature, can be stably delivered without being affected by the environmental temperature, and enables an excellent record quality to be obtained. SOLUTION: This water-base ink contains at least one water-soluble organic solvent selected from the group consisting of glycerin, (poly) alkylene glycols, diols, and amides, a hydrophilic polymer, a colorant, and water and has a viscosity (at 5-50 deg.C) of 10-1 mPaS and a viscosity/temperature change rate of -0.3-0 mPaS/ deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an aqueous ink for ink-jet recording. More specifically, the present invention is excellent in ejection stability, print quality, print stability, and the like, characterized in that the temperature dependence of viscosity is small and the ink viscosity is not affected by a remarkable change in environmental temperature. The present invention relates to an aqueous ink for inkjet recording.

[0002]

2. Description of the Related Art The ink jet recording system is a printing system in which small droplets of an ink composition are made to fly and adhere to a recording medium to perform printing. This method has a feature that a high-resolution and high-quality image can be printed at a high speed with a relatively inexpensive device. Usually, as the ink used in the ink jet recording method, an aqueous ink occupies the mainstream in terms of odor, safety, etc., and is composed of a solution in which various dyes or pigments are mixed with water and a water-soluble organic solvent as a dye. Ink is used. Properties required for ink jet recording inks include high print quality, quick drying, water resistance, abrasion resistance, storage stability, ejection stability, and the ability not to damage members such as a head. The composition and physical properties of the ink satisfying the above conditions have been intensively studied.

[0003] By the way, viscosity, which is the basic physical property of ink,
The values of the surface tension and the specific gravity change depending on the environmental temperature. In particular, the viscosity has a large temperature dependence, and generally the viscosity is significantly higher at low temperatures than at high temperatures, the ratio of the viscosities at low temperatures to high temperatures is several times, and the lower the temperature, the greater the rate of viscosity increase. For example, ink at a low temperature has high viscous resistance, so that the amount and speed of the ejected ink are reduced.
As a result, unstable ejections such as a decrease in the recording density and variations in the dot shape increase, and the recording quality deteriorates. Conversely, ink at high temperatures tends to have low viscosity resistance, increase the amount of ejected ink, and increase the recording density.
As described above, as the temperature dependency of the ink viscosity increases, the ejection characteristics such as the ejection amount and the ejection speed are affected by the environmental temperature, and it is difficult to obtain a constant recording quality.

On the other hand, a mechanism capable of discharging ink in accordance with the viscosity of the ink, such as a heating mechanism, is attached to the recording head for the purpose of preventing the recording quality from deteriorating even if the viscosity of the ink changes due to the environmental temperature. There is a way.
However, this method is not appropriate because the attachment of the mechanism increases the cost and size of the printer. On the other hand, an ink in which the temperature dependency of the ink viscosity is limited has been proposed by improving the ink composition, for example, by using a solvent having a small temperature dependency of the viscosity. As an example,
In JP-A-10-53737, the viscosity of the ink at 5 ° C. and the temperature of 40 ° C.
By setting the viscosity ratio in the range of 1.0 or more to 3.5 or less, it is possible to reduce the temperature dependence of the ink and to keep the recording quality constant.As an ink component, diethylene glycol is an organic solvent having a small temperature dependence of the viscosity. Monobutyl ether acetate, n-decane, dimethyl sulfoxide and the like are said to be effective.

However, the types of organic solvents having a small temperature dependence of viscosity are very limited, and as a result, the composition thereof is restricted. Further, inks containing these organic solvents have high permeability to a recording medium, and may affect recording quality. Furthermore, even if the ink has reduced temperature dependence of viscosity as described above, it can be used for continuous printing with a thermal jet type inkjet printer that applies thermal energy to the thin film resistor and generates and ejects ink droplets. ,
Thermal energy is accumulated in the ink ejection head, and the temperature of the ink locally rises so that ejection stability is impaired. Therefore, in order to stabilize ink ejection and obtain constant recording quality, it is necessary to not only reduce the temperature dependence of the ink viscosity itself, but also to prevent the ink viscosity from being affected by a remarkable change in environmental temperature. It has been found that there is.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and in particular, has an excellent ink jet stability with excellent ejection stability against a change in environmental temperature and good print quality and print stability. An object of the present invention is to provide an aqueous recording ink.

[0007]

Thus, according to the present invention, there is provided one or more water-soluble organic solvents selected from the group consisting of glycerin, (poly) alkylene glycols, diols and amides. , A hydrophilic polymer, a dye, and water, a viscosity at 5 to 50 ° C is 10 to 1 mPa · S, and a viscosity / temperature change rate is −0.3 to 0 mPa · S / ° C. A water based ink is provided.

[0008]

DETAILED DESCRIPTION OF THE INVENTION The water-soluble organic solvent used in the present invention is selected from the group consisting of glycerin, (poly) alkylene glycols, diols, and amides. Specifically, as (poly) alkylene glycols, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol (PEG) having a molecular weight of 200 to 600,
1,3-diols such as polypropylene glycol
Amides such as propanediol, 1,4-butanediol, 1,5-pentanediol, and 1,3-pentanediol include dimethylformamide, acetamide, dimethylacetamide, 2-pyrrolidinone, and N-methyl-2-pyrrolidinone. Can be These can be used alone or in combination of two or more. In particular, glycerin, ethylene glycol, polyethylene glycol having a molecular weight of 400, 1,5-pentanediol, 2-pyrrolidinone, and dimethylacetamide are preferably used.

[0009] These solvents are based on the total weight of the ink.
It is preferably contained in the range of 10 to 40% by weight. The solvent has properties such as high boiling point, low volatility, high hygroscopicity, and high moisturizing property suitable for inkjet recording inks, as well as high solubility in dyes and dispersibility in pigments described below. However, from the viewpoint of ejection stability, the ink according to the present invention contains 5
The viscosity (η) in the range of ℃ 50 ° C. is 10 to 1 mPas, specifically 5.0 to 9.5 mPas as η _max , 1.5 to 3.5 mPas as η _min
S is preferable, and η _max / η _min is an approximate value of 3.0.

The viscosity / temperature change rate (Δη / Δt), that is, a scale representing the linearity of the viscosity / temperature change (a measure of the stability of the viscosity change at a point where the temperature rises or falls rapidly) is −0.3. It is preferably from 0 to 0 mPa · S / ° C. Examples of the viscosity measuring device include a rotary type, a vibration type viscoelasticity measuring device, and the like, and a rotary viscometer or a viscous viscometer such as a B-type viscometer or a Rotosco and Visco tester (Haake Co.) is preferably used. . The viscosity / temperature change rate is calculated from the slope by creating a η-t curve by measuring the viscosity η when the temperature is changed in one minute intervals in the range of 5 to 50 ° C.

The ink of the present invention has a total weight of 0.5 to 5%.
% By weight, preferably in the range of 1 to 4% by weight, further comprises a hydrophilic polymer having a high affinity for the organic solvent, whereby the viscosity / temperature change rate of the ink can be satisfactorily adjusted and the ink can be applied to a recording medium. The print quality can be improved by adjusting the permeability of the ink, and the fastness of the recorded matter can be increased. As such a hydrophilic polymer, from the viewpoint of re-dissolvability after solidification of the ink, quick drying of printed matter, fastness and dispersibility of the pigment, the glass transition temperature Tg is 50 to 100.
° C., for example, preferably those in the range of 60 to 90 ° C., further GPC a weight average molecular weight Mw measured by (Gel filtration chromatography) or the like is 3,000 to 15,000, and a weight-average molecular mass M _w to number average molecular weight M _N ratio (dispersion degree M _w / M _N ) is 1
Those having a value of .about.2.5, especially 1-1.5 are preferred.

Accordingly, the constituents of the hydrophilic polymer of the present invention are monomer units having one or two carboxyl groups in the molecule, for example, acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, maleic anhydride. It is selected from the group consisting of acids, fumaric acid and their monoesters. These monomers may be used as a single homopolymer or a copolymer composed of a plurality of the above monomers. Further, in addition to the above monomers, a hydrophobic monomer having a high affinity for the pigment, for example, styrene, α
-Using methylstyrene, naphthalene, vinyltoluene, vinylnaphthalene (derivative), alkyl (meth) acrylate, aryl (meth) acrylate, alkyl crotonate, dialkyl itaconate, dialkyl maleate, etc. The above-mentioned monomers can be used as a copolymer in any form such as a block copolymer, a graft copolymer or a random copolymer.

The polymerization ratio and the polymerization form of the copolymer are determined within an appropriate range without deteriorating the required physical properties of the ink, generally, the water solubility of the copolymer, and the physical properties such as viscosity and dispersity. Acrylic acid: butyl acrylate: methyl methacrylate in a weight ratio of 15:75:10, or 30: 4
It may consist of styrene: acrylic acid: methyl acrylate in a weight ratio of 0:30. These copolymers can be more fully neutralized by a method known in the art using a base such as a hydroxide of an alkali metal such as lithium, potassium or sodium, ammonia, an aliphatic amine, morpholine or an alcohol amine. High hydrophilicity can be obtained.

The dye used in the present invention can be selected from known water-soluble dyes and known water-dispersible pigments.
It is desirable that it be contained in the range of weight%. Examples of the dye include a direct dye, an acid dye, a reactive dye, a disperse dye, a construction dye, a soluble construction dye, a reactive disperse dye, and an oil dye, and any of them can be used. The content of these dyes depends on the type of the liquid medium component, the characteristics required for the ink, and the like.

As the pigments, inorganic pigments and organic pigments can be used. As the inorganic pigments, yellow pigments (cadmium yellow, chrome yellow, strontium yellow, yellow iron oxide, etc.), and red pigments (Komeitan, Zhu, Bengala, Cuprous oxide), purple pigment (cobalt violet, etc.), blue pigment (prussian blue, etc.), green pigment (emerald green, cobalt green, chromium oxide, etc.), white pigment (titanium oxide, zinc white, lead white, lithobon) Black pigments (self-dispersible carbon black such as carbon black, graphite, or modified carbon black whose surface has been oxidized, or graft carbon whose pigment surface has been treated with a resin, etc.)
Etc. can be used. As the organic pigment, azo, acridine, phthalocyanine, quinacridone, anthraquinone, indanthrene, dioxazine, indigo, thioindigo, perylene, perinone, isoindolenine and the like can be used.

The pigment may be generally used as a pigment dispersion by subjecting it to a dispersion treatment with a commercially available or synthesized polymer dispersant such as polyvinyl alcohol, polyvinylpyrrolidone, styrene-acrylic acid copolymer salt or the like. 25
It is preferable to use a pigment composed of particles having a particle size of not more than μm, more preferably not more than 0.5 μm from the viewpoint of printing density, storage stability of ink, ejection stability and the like.

In addition, if necessary, inorganic salts such as potassium hydrogen phosphate and sodium hydrogen phosphate as pH adjusters;
Benzoic acid, dichlorophen, hexachlorophen, sorbic acid, p-hydroxybenzoic acid ester, ethylenediaminetetraacetic acid (EDTA), and the like can be added to the ink for the purpose of preventing mold, preserving, and preventing rust. Further, urea, thiourea, ethylene urea and the like can be added for the purpose of preventing nozzle drying. Further, various nonionic or anionic surfactants and dispersants can be added for the purpose of adjusting the surface tension, improving the fixing property, and improving the dispersibility of the pigment. Preferred surfactants include non-ionic surfactants such as alkylphenyl ether ethylene oxide adducts, polyethylene oxide-polypropylene oxide copolymers, and acetylene glycol ethylene oxide adducts, and sulfate and sulfonate type anionic surfactants. And the amount of addition is
0.01 to 10% by weight is preferred.

In the present invention, the ink can be produced by mixing and stirring the above components. Mixing and stirring can be performed using a normal stirrer, and if necessary,
Sand mills, homogenizers, ball mills, ultrasonic dispersers, high-speed dispersers, emulsifiers and the like can be used. The mixed ink is preferably sufficiently filtered by a centrifugal separator using a centrifugal separator and a membrane filter having a pore size of 5 μm or less, if necessary.

As a recording apparatus suitable for performing recording using the ink of the present invention, an on-demand type or continuous type ink jet apparatus which ejects ink to perform printing on a recording medium can be cited. As a method of ink ejection, thermal energy corresponding to a recording signal is given to ink in a recording head chamber, and a droplet is generated by the energy.
Either a thermal jet method of ejecting ink or a piezoelectric element method of ejecting ink by pressurizing ink in a print head chamber by a piezoelectric element corresponding to a recording signal may be used. The recording medium to which the ink of the present invention is attached is not particularly limited, and examples thereof include a paper dedicated to inkjet printing and a PPC paper that are well known in the art.

[0020]

EXAMPLES Examples and comparative examples of the present invention will be described below in more detail, but the present invention is not limited to these examples. Hydrophilic polymer: A: Styrene-maleate copolymer (molecular weight 1,500, trade name: SMA resin 1440H, manufactured by Alcochemical Chemical) B: Acrylic acid-butyl acrylate-methyl methacrylate copolymer (monomer composition 15:75) C: Styrene-acrylic acid-methyl acrylate copolymer (monomer composition 30:40:30, molecular weight 12,700) D: Polyvinylpyrrolidone (molecular weight 7,500)

Dyes: Black: 5% by weight of Cabojet 300 (carbon black, manufactured by Cabot Corporation) Yellow: C.I. Acid Yellow 172 2% by weight Magenta: C.I. Acid Red 52 2.5% by weight Cyan: C.I. Direct Blue 199 2.5% by weight

According to a known method for synthesizing an acrylic polymer ("Synthesis and Reaction of Polymer (1) (2)", see Kyoritsu Shuppan), a hydrophilic polymer having the above composition (% by weight) was synthesized. After sufficiently stirring the four-color compositions shown in the Examples and Comparative Examples, the resulting mixture was subjected to pressure filtration with a membrane filter having a pore size of 0.80 μm to obtain an ink of the present invention. The viscosity was measured using a viscometer manufactured by Haake. The viscosity (η) in the table is a measured value of the black ink, and the viscosity / temperature change rate (Δη /
Δt) was obtained from the slope of the η-t curve.

[0023]

[Table 1]

Comparative Example 1 has a viscosity / temperature change rate of -0.3 mPa
Comparative Example 2 is an ink composition example having a viscosity / temperature change rate of less than -0.3 mPa · S / ° C. and a viscosity exceeding 10 mPa · S; Comparative Example 3 is glycerin; (Poly) an ink composition example containing no water-soluble organic solvent belonging to the group consisting of alkylene glycols, diols and amides; Comparative Example 4 has a viscosity exceeding 10 mPa · S, and the water-soluble organic solvent Comparative Example 5 has a viscosity / temperature change rate of less than -0.3 mPa · S / ° C, and contains (meth) acrylic acid, crotonic acid, itaconic acid,
(Anhydride) An ink composition example in which a monomer unit selected from the group consisting of maleic acid, fumaric acid and their monoesters is not a constituent element; Comparative Example 6 has a viscosity exceeding 10 mPa · S, and the hydrophilic polymer has a total weight of ink. This is an example of an ink composition in which the content is more than 5% by weight.

These inks were evaluated for ejection characteristics, print quality and print stability using a commercially available ink jet printer BJ-870 (manufactured by Canon Inc.). (1) Ejection characteristics: Ink is ejected for a unit time in an environment of 0 ° C, 25 ° C, and 50 ° C, and the ejected ink weight per ejection is calculated from “total weight of ejected ink / number of ink ejections”. Then, the change rates of the ejected ink weights at 0 ° C. and 50 ° C. with respect to the ejected ink weight at 25 ° C. were determined and evaluated according to the following standards. ◎: Change rate of ejected ink weight is less than ± 5% ○: Change rate of ejected ink weight is less than ± 10% △: Change rate of ejected ink weight is ± 10% or more

(2) Print quality: English characters and lines were printed on PPC paper (Xerox Corporation registered trademark PPC paper), and the print quality was evaluated by observation at a magnification of 100 times with a microscope and visual observation. ◎: Bleeding, whiskers, and line burrs are not observed with the naked eye.…: Bleeding, whiskers, and line burrs are slightly observed. △: Many bleeding, whiskers, and line burrs are seen, but characters are recognizable. (3) Printing stability: Continuous printing was performed, and the time during which stable printing was possible was measured. …: 24 hours or more Δ: 10 hours to less than 24 hours ×: less than 10 hours The results are shown in Table 2.

[0027]

[Table 2]

[0028]

According to the present invention, one or more water-soluble organic solvents, hydrophilic polymers and dyes selected from the group consisting of glycerin, (poly) alkylene glycols, diols and amides are provided. And water, the viscosity at 5 to 50 ° C is 10 to 1 mPas, and the viscosity / temperature change rate is -0.
Since it is 3 to 0 mPa · S / ° C., it is possible to provide a water-based ink for inkjet recording that can obtain excellent recording quality that can be stably ejected regardless of the environmental temperature. Further, as the hydrophilic polymer, (meth) acrylic acid, crotonic acid, itaconic acid, (anhydride) maleic acid, one or more of monomer units selected from the group consisting of fumaric acid and their monoester constituents By using the polymer, the viscosity / temperature change rate is adjusted favorably, and the print quality is improved by adjusting the permeability of the ink into the recording medium, and the robustness of the recorded matter is increased. be able to.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroaki Nakaya 22-22, Nagaikecho, Abeno-ku, Osaka City, Osaka Inside (72) Inventor Ichiro Fujii 22-22, Nagaikecho, Abeno-ku, Osaka City, Osaka Inside Sharp Corporation (72) Inventor Hiromi Nakatsu 22-22 Nagaikecho, Abeno-ku, Osaka City, Osaka Prefecture Inside Sharp Corporation (72) Inventor Masaru Nakamura 22-22 Nagaikecho, Abeno-ku, Osaka City, Osaka Sharp Corporation F-term (reference) 2C056 FC02 2H086 BA52 BA53 BA55 BA59 BA61 BA62 4J039 AD09 AD10 AD13 AD14 AE07 BC07 BC09 BC10 BC11 BC36 BC50 BE01 BE02 BE03 BE04 BE07 BE08 BE12 BE22 CA03 CA06 EA42 EA44 EA48 GA24

Claims (7)

[Claims] 1. A water-soluble organic solvent which is one or more selected from the group consisting of (a) glycerin, (poly) alkylene glycols, diols and amides, (b)
Comprising a hydrophilic polymer, (c) a dye, and (d) water, 5 to 5
A water-based ink for ink-jet recording characterized by having a viscosity at 0 ° C. of 10 to 1 mPa · S and a viscosity / temperature change rate of −0.3 to 0 mPa · S / ° C. 2. The ink according to claim 1, wherein the water-soluble organic solvent (a) is contained in an amount of 10 to 40% by weight based on the total weight of the ink. 3. The (b) hydrophilic polymer is (meth) acrylic acid, crotonic acid, itaconic acid, (anhydride) maleic acid,
3. The ink according to claim 1, wherein one or more monomer units selected from the group consisting of fumaric acid and their monoesters are used as constituent elements. 4. The ink according to claim 1, wherein the hydrophilic polymer (b) is contained in an amount of 0.5 to 5% by weight based on the total weight of the ink. 5. The ink according to claim 1, wherein the dye (c) is a dye or a pigment. 6. The ink according to claim 5, wherein the dye (c) is a pigment dispersion that has been subjected to a dispersion treatment with a polymer dispersant. 7. An ink jetting apparatus for jetting the ink according to claim 1 to perform printing on a recording medium.