JPH0742433B2 - Recording liquid manufacturing method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a recording liquid used for on-demand type ink jet recording, in which the recording liquid is ejected from an ejection orifice of a recording head to fly as droplets for recording. For more details,
The present invention relates to a method for producing a recording liquid in which a pigment is dispersed with a polymer dispersant.

[0002]

2. Description of the Related Art Among various recording methods known at present, it is a non-impact recording method that generates almost no noise during recording, is capable of high-speed recording, and requires a special fixing process on plain paper. The so-called inkjet recording method, which enables recording without recording, is recognized as an extremely useful recording method. Regarding the inkjet recording method,
Various methods have been proposed so far, some of which have been improved and commercialized, and some of which are still being put into practical use.

In this ink jet recording method, small droplets of a recording liquid called ink are ejected according to various principles of operation, and the droplets are adhered to a recording member such as paper for recording. is there.

The ink applied to this is basically composed of a dye and its solvent, and the physical properties of the ink are largely influenced by the properties peculiar to the dye. Therefore, conventionally, when ink jet recording is mainly performed using an ink containing a water-soluble dye, the obtained ink image is affected by the physical properties of the water-soluble dye, and its water resistance,
There was a drawback that it was inferior in light resistance. Further, the storage stability of the ink itself containing such a water-soluble dye is not so high. Therefore, in recent years, attempts have been made to apply a pigment-based ink to an inkjet recording system instead of such a dye-based ink. This pigment-based ink has the advantage that the light resistance and water resistance of the obtained ink image are extremely good as compared with the image formed by the dye-based ink. However, since the pigment is insoluble in the ink medium, it requires a high technique to finely disperse the pigment in the ink, and it is very difficult to increase the dispersion stability.

Nevertheless, in the ink jet recording method, the ejection conditions (the driving voltage of the piezoelectric element, the driving frequency, the shape and material of the ejection orifice,
Liquid physical properties (viscosity,
Surface tension, electrical conductivity, etc.), stable for long-term storage, does not cause clogging of inkjet devices, and fast and reliable for fixing to recording materials (paper, film, etc.) In addition, the surroundings of the dots are smooth and the bleeding is small, the color tone of the formed ink image is clear and the density is high, and the formed ink image is excellent in water resistance and light resistance. It is required to have various properties such as not invading (container, connecting tube, sealing material), having little odor and toxicity, and having excellent safety such as flammability. However, it is quite difficult to satisfy the above various characteristics at the same time. In this respect, the above-mentioned prior art is still unsatisfactory.

[0006]

The present invention, except for the above-mentioned drawbacks of the prior art, simultaneously satisfies ejection stability, long-term storage stability, fixability, image density, sharpness, water resistance, and light resistance. Furthermore, it is an object of the present invention to provide a method for producing a recording liquid used for an on-demand type inkjet recording method which has no odor and toxicity and is highly safe such as flammability and is highly practical. Furthermore, it is an object of the present invention to provide a method for producing a recording liquid which is excellent in driving frequency response and is suitable for high-speed recording and used in an on-demand type inkjet recording method.

[0007]

Therefore, the present invention is suitable for an on-demand type ink jet recording method and is a method for producing a recording liquid containing a pigment and a dispersant for dispersing the pigment. (A) As the dispersant, a polymer having both a hydrophilic structure portion and a hydrophobic structure portion and having an average molecular weight of 1200 to 10,000 is used,
(B) selecting a pigment / polymer combination in which the ratio of the molecular weight of the pigment to the average molecular weight of the polymer is in the range of 1: 2.7 to 1:22, and (c) containing the polymer. 100 pigments
The pigment and the dispersant are mixed in an aqueous liquid medium containing a water-soluble organic solvent in an amount of 5 to 300 parts by weight per part by weight, and the pigment is dispersed in the aqueous medium. This is a method for producing a recording liquid.

Here, the pigment-based ink used in the present invention will be described in detail.

Since the pigment particles are not dissolved in a solvent such as water, even if they are simply mixed and dispersed in the ink solvent, they immediately aggregate and precipitate and separate from the solvent, so that a practical ink composition is obtained. You cannot do it. Therefore, when forming such a pigment-based ink, a good dispersion medium for the pigment particles is required.

Therefore, as the first component of the dispersion medium,
There is a method in which a polymer having both a hydrophilic structure portion and a hydrophobic structure portion (... Dispersant) is used and an aqueous liquid is used as the second component. This dispersion medium can very stably disperse the pigment particles in the viscosity range of about 1 to 20 cps.

The polymer used as the first component of the dispersion medium is a polymer dispersant having a molecular weight of 1200 to 10,000. One example of a preferable polymer dispersant is polyacrylic acid, polymethacrylic acid,
Condensed naphthalene sulfonic acid, styrene-maleic acid copolymer, diisobutylene-maleic acid copolymer, styrene- (meth) acrylic acid, (meth) acrylic acid ester-
(Meth) acrylic acid copolymer, styrene-itaconic acid copolymer, itaconic acid ester-itaconic acid copolymer, vinylnaphthalene-maleic acid copolymer, vinylnaphthalene- (meth) acrylic acid copolymer, vinylnaphthalene −
Itaconic acid copolymers and their derivatives.

In addition to the above polymers, monomers such as acrylonitrile, vinyl acetate, (meth) acrylamide, N-methylol (meth) acrylamide, vinyl chloride, vinylidene chloride, ethylene, hydroxyethyl acrylate, glycidyl methacrylate, hydroxypropyl methacrylate, etc. May be copolymerized. Some of these polymeric dispersants are commercially available and can be easily synthesized by known polymerization methods. By the way, it is necessary to form a salt of the polymer for the purpose of solubilizing this polymer in an aqueous liquid which is the second component or dispersing it in a colloidal form. As a partner for forming a salt with the above polymer, in addition to alkali metals Na and K, aliphatic amines such as mono-, di- or tri- (methylaluminum), mono-, di-, or tri- (ethylaluminum) , Mono-, di-, or tree (ethanolamine), mono-, di-, or tree (propanolamine), alcoholamines such as methylethanolamine and dimethylethanolamine, morpholine, N-methylmorpholine and the like.

In the above polymer, the ratio of the monomer units forming the hydrophilic structural part is particularly important. That is, if the weight ratio of the monomer units forming the hydrophilic structural portion such as the carboxyl group, the sulfonic acid group, or the sulfuric acid ester group exceeds about 40% by weight, the adsorptivity of the polymer to the pigment particles decreases. It deteriorates the dispersion stability of the pigment particles. On the other hand, when the amount is 2% by weight or less, the solubility of the polymer itself in the aqueous liquid decreases, and the polymer coagulates or precipitates in the aqueous liquid together with the pigment particles. Therefore, the more preferable ratio of the hydrophilic structural portion in the polymer is about 25 to 40% by weight. If the molecular weight of the polymer is too low, it does not contribute to the dispersion stability of the pigment particles, and conversely, if it is too high, the viscosity of the ink itself tends to increase too much (for example, 20 cps or more). Therefore, the molecular weight range of this polymer is about 12
00 to 10000 is desirable.

Here, as a result of various experiments, the present inventor
Ratio W ₁ of the molecular weight W _{1 of the} pigment and the average molecular weight W ₂ of the polymer
It was found that there is a close relationship between / W ₂ and the dispersion stability and drive frequency response. That is, when various dispersions in which the molecular weights of the pigment and the polymer were changed were prepared and investigated, the ratio W ₁ / W ₂ was found to be about ₁ / W.
In the range of 2.7 to 1/22, the stability of the dispersion liquid and the high driving frequency response in ejection are good, and it is clarified that the driving frequency response tends to decrease as the dispersion deviates from this range. The present invention has been completed.

In the ink used in the present invention, the amount of the above polymer used is approximately 5 to 300 per 100 parts by weight of the pigment.
Parts by weight, more preferably approximately 10 to 150 parts by weight. If the upper limit of the range is exceeded, there are disadvantages that the color density of the ink is lowered and the viscosity of the ink cannot be maintained at an appropriate value. Further, when the value is below the lower limit below, the dispersion stability of the pigment particles becomes poor.

Examples of the aqueous liquid component that constitutes the recording liquid of the present invention include water and a water-soluble organic solvent. Examples of the water-soluble organic solvent include methyl alcohol, ethyl alcohol, n-propyl alcohol, iso-propyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, iso-butyl alcohol, furfuryl alcohol, tetrahydrofuran. Alcohols such as furyl alcohol; ketones or keto alcohols such as acetone, methyl ethyl ketone, diacetone alcohol; alkanolamines such as monoethanolamine, diethanolamine, triethanolamine; amides such as dimethylformamide, dimethylacetamide; tetrahydrofuran, dioxane Ethers such as, ethyl acetate, methyl benzoate, ethyl lactate, ethylene carbonate, esters such as propylene carbonate, Polyhydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, etraethylene glycol, polyethylene glycol, glycerin, 1,2,6-hexanetriol and thiodiglycol; ethylene glycol monomethyl (or ethyl) ether; Lower alkyl mono- or di-alkylene glycols such as diethylene glycol monomethyl (or ethyl) ether, propylene glycol monomethyl (or ethyl) ether, triethylene glycol monomethyl (or ethyl) ether, diethylene glycol dimethyl (or ethyl) ether Is a diether; a nitrogen-containing cyclic compound such as pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, and morpholine It can be mentioned.

Among these many solvents, in order to improve various properties required for the recording liquid, preferably polyhydric alcohols or alkyl ethers of polyhydric alcohols, more preferably diethylene glycol. And other polyhydric alcohols. The content of these components is
Percentage by weight, based on the total weight of the recording liquid, generally 1
0 to 70%, and preferably 20 to 50% in order to reduce the temperature dependence of the physical properties.

The water content at this time is in the range of 5 to 90%, more preferably 10 to 70%, and further preferably 20 to 70% in weight percent with respect to the total weight of the recording liquid. It is desirable to be done.

By the way, as the pigment for forming the recording liquid of the present invention, various organic pigments including conventionally known ones can all be used. Examples thereof include azo-based, phthalocyanine-based, quinacridone-based, anthraquinone-based, dioxazine-based, indigo-based, thioindigo-based, perinone-based, isoindolenone-based, and perylene-based pigments. These pigments are in the form of fine particles having a particle size of about several hundred millimicrons to several microns in the recording liquid, and preferably an aqueous paste immediately after production is suitable for use. The suitable concentration of the pigment in the recording liquid is approximately 3 to 30% in weight% with respect to the total weight of the recording liquid, considering its coloring power and the influence on the viscosity of the recording liquid.

In addition to the above-mentioned essential components, the recording liquid used in the present invention may also contain various conventionally known additives such as surfactants, salts, synthetic and natural resins, and various dyes. .

The recording liquid used in the present invention is composed mainly of the above components, and various methods can be adopted for its preparation. For example, the above components are blended, and a pole mill, roll mill, speed line mill, homomixer,
A method of mixing and grinding using a sand grinder or the like is adopted.

The pigment dispersion step is carried out in a state where the pigment concentration is as high as possible. After the dispersion treatment, the pigment is diluted with an aqueous liquid so that the viscosity of the ink finally becomes about 1 to 15.
cps, preferably adjusted to about 2-10 cps.

In the recording liquid thus prepared, the pigment particles do not aggregate or settle in the low viscosity region even when stored for a long period of time.

The recording liquid is (1) a wide range of recording liquid ejection conditions (piezoelectric element drive voltage,
Liquid physical properties (viscosity, surface tension, etc.) that match drive frequency, shape and material of discharge orifice, discharge orifice diameter, etc.
It has electrical conductivity, etc.) and has excellent responsiveness to a particularly high driving frequency. (2) It is stable for long-term storage and does not cause clogging of the inkjet device. (3) The fixing to the recording material (paper, film, etc.) is fast and reliable, and the periphery of the dots is smooth and has no bleeding. (4) The color tone of the formed image is clear and the density is high. (5) The formed image is excellent in water resistance and light resistance. (6) Do not attack materials around the recording liquid (container, connecting tube, sealant, etc.). (7) It has various characteristics such as low odor and toxicity and excellent safety such as flammability.

[0025]

EXAMPLES The present invention will now be described in more detail with reference to examples.

Example 1 Styrene-maleate copolymer (molecular weight about 1500,
Product name SMA resin 1440H, made by Alkomi Chemical)
6 parts, triethanolamine 2 parts, water 60 parts, ethylene glycol 25 parts, phthalocyanine blue (molecular weight 56
0) 7 parts were added and dispersed by a ball mill for 48 hours to obtain a pigment dispersion (ratio of the molecular weight of the pigment to the average molecular weight of the polymer W).
₁ / W ₂ = 1 / 2.7). The coarse particles that could not be dispersed were removed by an ultracentrifuge to obtain an inkjet recording liquid.

Printing Example 1 The recording liquid obtained in Example 1 is used to have an on-demand type recording head (discharge orifice diameter 50 μ, piezo oscillator driving voltage 60 V, frequency 20 kHz) for ejecting the recording liquid by a piezo oscillator. The printing characteristics were examined by the recording device.

Further, an on-demand type multi-head (a discharge orifice diameter 35 μ, a heating resistor resistance value 150 Ω, an oscillating voltage 30 V, a frequency 5 kHz) is used for recording by applying heat energy to the recording liquid in the recording head to generate droplets. )
The same examination as above was carried out using a recording apparatus having a.

In any of the cases, the recorded images obtained were excellent in light resistance and water resistance, had a clear color tone and high density, had smooth dots around the edges and had no blurring or blurring, and had good fixability. . Further, the recording liquid did not cause aggregation or sedimentation of pigment particles even after long-term storage, and stable ejection was performed.

Example 2 Diisobutylene-maleate copolymer (molecular weight about 10
000) 6 parts, morpholine 10 parts, diethylene glycol 17 parts, water 60 parts, and antoanthrone orange (molecular weight 456) 7 parts were added and dispersed by a ball mill for 48 hours to obtain a dispersion liquid (W ₁ / W ₂ = 1/22). ). After that, coarse particles were removed to obtain an inkjet recording liquid.

Example 3 5 parts of condensed naphthalene sulfonate (molecular weight: about 1200, trade name: Demol N, manufactured by Kao Atlas Co., Ltd.), 1 part of ethanolamine, 20 parts of glycerin, 74 parts of water, rose red (molecular weight of 265) 5 parts were added and dispersed by a ball mill for 48 hours to obtain a dispersion liquid (W ₁ / W ₂ = 1 / 4.5). Then, the coarse particles were removed to obtain an inkjet recording liquid.

Example 4 Ammonium polyacrylate (molecular weight about 2000) 10
20 parts of diethylene glycol monoethyl ether,
Add 64 parts of water and 6 parts of Bordeaux 5B (molecular weight 270),
Disperse with a ball mill for 48 hours to obtain a dispersion (W ₁ / W ₂
= 1 / 7.4). Then, the coarse particles were removed to obtain an inkjet recording liquid.

Example 5 Ethyl acrylate-acrylic acid copolymer (molecular weight about 5
000) 5 parts to 40 parts water, 45 parts ethylene glycol,
Pyrazolone Red B (molecular weight 738) (10 parts) was added and dispersed by a ball mill for 48 hours to obtain a dispersion liquid (W ₁ / W ₂ =
1 / 6.8). Then, the coarse particles were removed to obtain an inkjet recording liquid.

Example 6 5 parts of a styrene-octyl acrylate-itaconic acid monoethyl ester copolymer (molecular weight of about 8000), 1 part of triethanolamine, 59 parts of water, 25 parts of diethylene glycol monoethyl ether, benzidine yellow G (molecular weight of 720) ) 10 parts were added and dispersed by a ball mill for 48 hours to obtain a dispersion (W ₁ / W ₂ = 1/11). Then, the coarse particles were removed to obtain an inkjet recording liquid.

Printing Examples 2-6 When the recording liquids obtained in Examples 2-6 were examined in the same manner as in Printing Example 1, the same excellent results as in Printing Example 1 were obtained.

Front page continued (72) Inventor Tokuya Ota 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Masahiro Haruta 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) References JP-A-54-10023 (JP, A) JP-A-50-49003 (JP, A) JP-A-55-18412 (JP, A)

Claims (1)

[Claims] 1. A method for producing a recording liquid, which is suitable for an on-demand type ink jet recording method and contains a pigment and a dispersant for dispersing the pigment, wherein (a) the dispersant is a hydrophilic structural portion and a hydrophobic structure. Having an organic structure part and having an average molecular weight of 1200 to 10,000
(B) selecting a combination of pigment and polymer having a ratio of the molecular weight of the pigment to the average molecular weight of the polymer in the range of 1: 2.7 to 1:22. (C) The content of the polymer is 5 to 3 per 100 parts by weight of the pigment.
A method for producing a recording liquid, comprising mixing the pigment and a dispersant in an aqueous liquid medium containing a water-soluble organic solvent so that the amount of the pigment is 100 parts by weight, and dispersing the pigment in the aqueous medium. .