JPH05263028A - Production of water-based ink for ink-jet recording - Google Patents

Abstract

PURPOSE:To efficiently filter a water-based pigmented ink having a high surface tension to obtain a water-based ink for ink-jet recording which ink is excellent in pigment dispersion stability and storage stability, by using a metallic filter under pressure to conduct the filtration. CONSTITUTION:This production process for producing an ink-jet containing at least water and a pigment includes step of filtration under pressure in which a metallic filter is used as a filter medium at a pressure of preferably 10kg/cm<2> or lower. The pore diameter of the filter is preferably 0.5-25mum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aqueous recording ink for use in an inkjet printer that records using liquid ink.

[0002]

2. Description of the Related Art Conventional ink jet recording inks are mainly those in which a dye is dissolved in water, an organic solvent, wax or the like as a coloring agent. It was poor in water resistance. In order to solve the problem, an ink using a pigment such as carbon black or aniline black as a colorant has been devised, and is disclosed in JP-A-61-283875, JP-A-64-6074, and JP-A-1-31881. It is shown in the official gazette.

Ink jet recording inks have problems that fine ejection nozzles are not clogged with coarse particles and the like, and that there is no change in the physical properties of the ink during production or storage and no precipitation of solid content. In particular, since an ink using a pigment as a colorant is a dispersion system in which fine pigment particles are dispersed in an aqueous medium, coarse particles contained in the ink are not only fine dust, but also sufficiently fine when dispersed. There are large particles of pigment remaining that cannot be formed, and coarse particles are more likely to be mixed in as compared with dye ink that is a complete solution. Therefore, by performing filtration or centrifugation during the manufacturing process, we are removing the coarse particles in the ink that cause clogging of the nozzle and solid analysis, as one example of the manufacturing method, in the aqueous medium A method of dispersing a pigment and performing an ultrafiltration treatment is described in JP-A-64-48875. Further, JP-A-2-255875 describes a method of separating coarse particles by sedimentation by centrifugation.

[0004]

Generally, as a method for filtering an inkjet ink containing a pigment, since the lower limit of the diameter of particles to be removed is as small as 1 to 5 μm, pressure filtration using a membrane filter is performed. Alternatively to the method of performing vacuum filtration, the method of performing ultrafiltration as described above,
There is a method of centrifuging.

However, these methods have various problems. First, in the case of the vacuum filtration method, volatile components in the ink may evaporate during the filtration to change the composition of the ink. Further, since the centrifugal separation method is a batch process, it is necessary to insert and remove the ink before and after the filtration step, which is not suitable for mass production. The ultrafiltration method is originally a method of filtering colloidal particles having a diameter of several tens of nm, and when many pigment inks having a diameter of 100 nm or more are filtered, clogging occurs and the filtration speed is significantly reduced.

On the other hand, a membrane filter made of nitrocellulose, cellulose acetate, tetrafluoroethylene or the like and having a small pore size is often used as a filtration filter when the pressure filtration method is used. However, the water-based pigment ink has a property that fine particles are dispersed in an aqueous medium, and when a cellulose-based filter is used as a filter medium, the ink composition changes because the particles in the ink are adsorbed in the internal porous structure, Further, there is a drawback that the filter is clogged quickly and the filtration rate is low. On the other hand, since the aqueous pigment ink has a high surface tension, tetrafluoroethylene, which is poor in hydrophilicity, repels the ink, and the aqueous ink cannot be filtered.

The present invention has been made in view of such problems, and an object thereof is to efficiently filter an aqueous pigment ink having a high surface tension, evaporate a solvent or the like, and filter a coloring material particle. There is no change in composition due to adsorption inside,
An object of the present invention is to provide a method for producing an aqueous recording ink which does not contain coarse particles and has excellent pigment dispersion stability and storage stability.

[0008]

The method for producing an aqueous recording ink for ink jet of the present invention is a method for producing an aqueous ink containing at least water and a pigment, wherein pressure filtration using a metal filter as a filter medium during the step is carried out. It is preferable that the pressure in the pressure filtration step is 10
It is characterized in that it is Kg / cm ² or less, and the pore size of the metal filter is 0.5 to 25 μm. More preferably, the pressure applied in the pressure filtration step is 5 Kg / cm ² or less, and the pore size of the metal filter is 0.5 to 10 μm.

(Detailed Description of the Invention) The method for producing a water-based recording ink of the present invention comprises press-filtering an ink containing at least water and a pigment using a metal filter.
Aqueous recording ink is manufactured.

The pigment to be used is not particularly limited, and any pigment having a good affinity with water as a main solvent can be used. For example, for black and white, furnace black, lamp black, acetylene black, channel Carbon blacks such as black, simple metals such as copper and iron, ortho-nitroaniline black and the like can be used. Furthermore, for color, Fast Yellow 10
G, Disazo Yellow AAMX, Disazo Yellow AAO
T, disazo yellow AAOA, yellow iron oxide, disazo yellow HR, orthonitroaniline orange, dinitroaniline orange, vulcan orange, toluidine red, chlorinated para red, brilliant fast scarlet, naphthol red 23, pyrazolone red, barium red 2B, calcium red 2B, Strontium red 2B, manganese red 2B, barium lysosome red, pigment scar red 3B rake, rake bordeaux 10B, anthocin 3B rake, anthocin 5
B rake, Rhodamine 6G rake, Eosin rake, Bengal, Fafthor red FGR, Rhodamine B rake, Methyl violet red rake, Dioxazine violet, Basic blue 5B rake, Basic blue 6G rake, Fast sky blue, Alkali blue R
Toner, Peacock Blue Rake, Navy Blue, Ultramarine, Reflex Blue 2G, Reflex Blue R, Brilliant Green Lake, Diamond Green Thioflavin Lake, Phthalocyanine Green G, Green Gold, Phthalocyanine Green Y, Iron Oxide Powder, Rust, Zinc Flower , Titanium oxide, calcium carbonate, clay, barium sulfate, alumina white, aluminum powder, bronze powder, daylight fluorescent pigment, pearl pigment, naphthol carmine FB, naphthol red M, permanent carmine F
B, Fastero G, Disazo Yellow AAA, Disazo Orange PMP, Lake Red C, Brilliant Carmine 6B, Phthalocyanine Blue, Quinacridone Red,
Dioxane violet, Victoria pure blue, alkali blue G toner, and other processed pigments such as graft carbon whose pigment surface is treated with a resin can be used.
The addition amount is preferably 1 to 30% by weight, more preferably 3 to 12% by weight. A pigment having a particle size of 25 μm or less is used, and it is more preferable to use a pigment composed of particles having a particle size of 1 μm or less.

In order to disperse the pigment better, it is preferable to add a dispersant. As the dispersant, an anionic or nonionic surfactant, a polymer dispersant, or the like may be used, or a soap-free dispersant may be used. For example, acrylic acid, methacrylic acid, maleic acid, etc., and salts thereof, acrylic acid esters, styrene or its derivatives, vinyl ethers, ethylenically unsaturated monomers such as vinyl esters, etc., alone or in combination of two or more. Can be used by mixing and polymerizing.

It is preferable to add a water-soluble resin in order to fix the ink on the paper. As the water-soluble resin, for example, gelatin, protein such as casein, natural rubber such as gum arabic, glucooxide such as savonine, methyl cellulose, carboxymethyl cellulose, cellulose derivative such as hydroxymethyl cellulose, lignin sulfonate, natural polymer such as shellac, Polyacrylic acid salt, styrene-acrylic acid copolymer salt, vinylnaphthalene-acrylic acid copolymer salt, styrene-maleic acid copolymer salt, vinylnaphthalene-maleic acid copolymer salt, β-naphthalenesulfonic acid folimarin condensation Sodium salt of
One kind or a mixture of two or more kinds of anionic polymers such as polyphosphoric acid and nonionic polymers such as polyvinyl alcohol, polyvinylpyrrolidone and polyethylene glycol can be used.

Further, water or water and a water-soluble organic solvent can be added to the ink. Examples of the water-soluble organic solvent include alcohols and glycols. For example, alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, monoethylene glycol, diethylene glycol,
Propylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, glycerin,
Examples thereof include glycols such as polyethylene glycol, but are not limited thereto. In addition, a dispersion liquid in which a water-insoluble polymer is dispersed in a medium containing water as a main component, for example, acrylic acid ester type, methacrylic acid ester type, styrene type, styrene-acrylic copolymer, olefin type and amino group, amide group , Homopolymerization or copolymerization resin monomers, microemulsions of monomers having hydrophilic functional groups such as carboxyl groups and hydroxyl groups,
Internal three-dimensional crosslinked organic fine particles, paraffin wax,
Natural and synthetic wax emulsions such as polyethylene wax, carnauba wax, latex, colloidal solution,
A suspension or the like can be added to the ink.

In addition, if necessary, antifungal agents, rust preventive agents,
Urea, thiourea, ethylene urea and the like can be added as a defoaming agent, a viscosity adjusting agent, a penetrating agent, a pH adjusting agent, and a nozzle drying inhibitor.

The ink prepared from these components must remove coarse particles and dust that cause clogging. This method includes filtration and centrifugation. However, when the vacuum filtration method is used, volatile components in the ink may evaporate during the filtration to change the composition of the ink. In addition, the ultrafiltration method is a method of filtering colloidal particles having a diameter of several tens nm, and the diameter of many particles is 100 nm.
When the above pigment ink is filtered, clogging occurs and the filtration speed is significantly reduced. Since the centrifugal separation method is a batch process, ink must be taken in and out before and after the filtration step, which is not suitable for mass production.

Therefore, in the present invention, pressure filtration treatment is adopted in the step of removing coarse particles. The ink sent into the filtration device is once pressurized by a compressor or the like to increase the filtration flow rate and suppress evaporation of volatile components of the ink. The pressurized ink passes through the filter and the coarse particles are trapped and removed on the filter. Pressurized pressure is 1
When it exceeds 0 Kg / cm ² , air is dissolved in the ink, so that when the pressure is returned to normal pressure, air bubbles are generated in the ink, which causes deterioration of the ink and ejection failure. Needless to say, the pressurizing pressure is set to be equal to or lower than the pressure resistance of the filter used.

The aqueous pigment ink is a dispersion system of fine particles,
Further, since the surface tension is large, it is preferable to use a metal filter which has no particle adsorption and has excellent wettability. Conventionally, a membrane filter made of nitrocellulose, cellulose acetate, tetrafluoroethylene or the like and having a small pore size is often used as a filtration filter when using the pressure filtration method. However, when a cellulosic filter is used as a filter medium, the ink composition is changed because particles in the ink are adsorbed in the internal porous structure, and the filter is clogged quickly and the filtration rate is low. On the other hand, since the aqueous pigment ink has a high surface tension, tetrafluoroethylene, which is poor in hydrophilicity, repels the ink, and the aqueous ink cannot be filtered. However, by using a metal filter, both of these two drawbacks can be avoided.

As the material of the metal filter, a single metal element such as iron, aluminum, copper, zinc, nickel, tin, chromium, titanium, manganese, or an alloy such as stainless steel containing two or more kinds can be used. Can have a plate shape, a wire mesh shape, or the like. The shape of the filter does not necessarily have to be a flat surface, but may be a three-dimensional structure such as a cylindrical shape or a bellows shape. The shape of the pores of the filter may be circular, rectangular, hexagonal or the like.

Since the pore size of the filter has an upper limit for the particle size of the pigment particles in the ink, the physical properties of the ink change depending on the value of the pore size. If the pore size is made extremely small, the particle size of the pigment particles in the ink also becomes small and the pigment particles are stably dispersed, so that the storage stability of the ink is improved, but there is a drawback that the density of the ink is lowered. On the other hand, if the pore size is increased, the number of large-sized particles increases, so that the density of the ink increases, but the fine nozzles of the inkjet head may be clogged. Therefore, the pore size of the filter is 0.5-
The range of 25 μm is preferable.

The particles clogging the metal filter are not adsorbed on or inside the filter by physical or chemical force. Therefore, when the metal filter is clogged and the filtration speed is reduced, the ink is caused to flow backward from the filter outlet to the filter tank, so that the clogged particles can be easily separated from the filter, and the clogging is temporarily eliminated. can do. Further, the clogged filter can be completely removed by washing with water or the like, so that it can be reused again and again.

[0021]

The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited to these examples.

(Example 1) MA-100 used here is carbon black manufactured by Mitsubishi Kasei Co., Ltd., and PVP (K-
30) is polyvinylpyrrolidone having an average molecular weight of about 40,000 manufactured by Tokyo Kasei.

The ink is manufactured by the following procedure, but the invention is not limited to this. First, stir and mix carbon black and a dispersant in water using a paint shaker for 30 minutes or more, and confirm by microscopic observation that the particle size has become about 1 μm or less. Add polyvinylpyrrolidone to it and mix for another 30 minutes. Stir to dissolve completely. Glycerin and ethanol were added to the dispersion and the mixture was stirred for 5 minutes, and filtered with a stainless mesh filter having a pore size of 5 μm and a filter diameter of 47 mm at a pressure of 1 kg / cm ² to remove dust and coarse particles. Average particle size 0.15 μm,
An aqueous recording ink having a pH of 6 was obtained. Further, it is preferable to perform pre-filtration with a filter having a large pore size in order to increase the collection efficiency of coarse particles.

Regarding the ink composition thus obtained,
The weight average particle diameter was measured by a light scattering type particle size distribution meter (DLS-600 Otsuka Electronics registered trademark), and the viscosity at 20 ° C. was measured using a B-type viscometer (Toyo Keiki registered trademark) No. 1 rotor, HL.
The surface tension at 25 ° C. was measured using a V-ST type surface tensiometer (registered trademark of Kyowa Interface Science).

Also, using a prototype 9-nozzle inkjet evaluation machine having a discharge nozzle diameter of 50 μm, a piezoelectric element drive voltage of 120 V, a drive frequency of 2 kHz, and a resolution of 360 dots / inch, solid letters, alphabetical characters, etc. on PPC paper, bond paper, high-quality paper, etc. Print quality evaluation by printing and character print sample, Macbeth TR-927 type (Koll
OMORGAN (registered trademark) optical densitometer was used to evaluate solid print density, and continuous ejection stability was evaluated by investigating the presence or absence of missing dots during continuous printing at room temperature for 12 hours. Further, the solid printed sample was immersed in tap water for 24 hours, and then the change in concentration was measured to evaluate the water resistance.

Further, the storage stability was evaluated by observing a change in particle size of carbon black particles in a glass sample bottle sealed at an environmental temperature of 70 ° C. and a humidity of 85% for 30 days with a 400 × transmission microscope.

Regarding the print quality, the evaluation results were classified as follows.

Bleeding is not observed with the naked eye .... ◎ Bleeding is seen but characters are recognizable. ○ Characters are not recognizable .. The evaluation results are classified as follows.

O. D. Value 1.3 or more ・ ・ ・ ・ ・ ◎ O. D. Value 1.1 or more and less than 1.3 ... O. D. The value is less than 1.1 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ × Regarding the water resistance, the evaluation results are classified as follows.

The concentration change was within 0.1 in the OD value ... ◎ The concentration change was within 0.3 in the OD value ... O The concentration change was greater than 0.3 in the OD value. Regarding dot omission, the evaluation results were classified as follows.

Dot missing 10 times or less within 12 hours. ◎ Dot missing 10 times or less within 6 hours .... ○ Dot missing 10 times or more within 1 hour .. × Furthermore, evaluation results regarding storage stability Were classified as follows.

No change in particle size after 30 days ... ◎ A slight change in particle size was observed after 30 days ... △ The particle size obviously increased after 30 days ... -X The following examples were carried out by a procedure similar to the above.

In Example 2, filtration was performed using a metal filter having a pore diameter of 0.5 μm.

In Example 3, filtration was performed using a metal filter having a pore diameter of 10 μm.

In Example 4, filtration was performed using a metal filter having a pore diameter of 25 μm.

In Example 5, the pressure applied during filtration was 5 Kg /
It is expressed in cm ² .

In Example 6, the pressure applied during filtration was 10 kg.
/ Cm ² .

The evaluation results of Examples 1 to 6 were all ⊚. Although the ink can be produced under any of the conditions of this embodiment, the pore size of the filter is preferably 10 μm or less in order to avoid the inclusion of coarse particles as much as possible.
Further, if the pressurizing pressure is large, the pressurizing device such as a compressor becomes large in size. Therefore, the pressurizing pressure is preferably 5 Kg / cm ² or less.

Comparative Example An ink composition similar to that of Example 1 was prepared as a comparative example. Comparative Example 1 is an ink composition obtained without performing a filtering process.

In Comparative Example 2, vacuum filtration (ultimate vacuum degree 100 mmHg) was carried out instead of pressure filtration in the filtration step.

In Comparative Example 3, a nitrocellulose membrane filter (manufactured by Toyo Roshi Kaisha, Ltd.) having a pore diameter of 5 μm and a filter diameter of 47 mm was used as a filter medium for pressure filtration. Comparative Example 4 has a pore size of 3 μm as a filter medium for pressure filtration,
A membrane filter made of tetrafluoroethylene resin having a filter diameter of 47 mm (made by Toyo Roshi Kaisha, Ltd.) was used.

In Comparative Example 5, pressure filtration was performed using a stainless mesh filter, and then ultrafiltration membrane Ultra Filter Q2000 (registered trademark of Toyo Roshi Kaisha, Ltd.) was used to obtain 1 kg / c.
An ink composition was obtained by pressure filtration at a pressure of m ² .

Further, Comparative Example 6 is an example in which a metal filter was used in the filtration step, but the pressurization pressure exceeded 10 kg / cm ² kg and the filtration was carried out at 15 kg / cm ² .

Further, in Comparative Example 7, the pore size of the filter medium is 0.5 μm.
Example of performing pressure filtration using a metal filter of less than 0.3 μm. Further, Comparative Example 8 is an example in which a metal filter having a pore size of the filter medium of more than 25 μm and 40 μm is used.

When these comparative examples were evaluated in the same manner as in Example 1, the results shown in Table 1 and below were obtained.

[0046]

[Table 1]

Since Comparative Example 1 was not subjected to coarse particle removal treatment such as filtration, in addition to dot omission and poor storage stability, the pigment fixing property on paper was also deteriorated and the water resistance was also deteriorated. In Comparative Example 2, since the ink was exposed to a reduced pressure during filtration, the volatile components in the ink were evaporated and the weight of the ink was reduced by 0.5% before and after filtration.

In Comparative Example 3, the filtration rate dropped sharply after the start of the filtration, and when 230 ml of the ink was filtered, the filter was clogged and the filtrate did not come out.

In Comparative Example 4, since the filter repels the ink, it cannot be filtered at all.

In Comparative Example 5, particles were excessively removed with an ultrafiltration membrane having a very small pore size, but the print density was lowered, and bleeding occurred on the paper, resulting in a slight print quality. Degradation was observed.

Further, in Comparative Example 6, since the pressure inside the filtering device becomes high, gas such as nitrogen melts into the ink,
There was a problem that bubbles of those gases were easily generated under normal pressure.

Comparative Example 7 has a very small pore size of 0.
Since a metal filter of 3 μm was used, excessive removal of particles caused a decrease in the coloring material content, resulting in a decrease in print density, further bleeding on the paper, and a slight deterioration in print quality was observed. The filtration time is 0.5 μm
Three times as large as the filter having the above pore size was required.

Comparative Example 8 has a very large pore size of 40.
Although it was filtered with a metal filter of μm, when printing was performed with an inkjet head having a nozzle diameter of 50 μm, clogging occurred and dot omission occurred. In addition to the poor storage stability due to the large-sized particles remaining, the pigment fixing property on paper was also deteriorated, and the water resistance was also deteriorated.

From the results shown in Table 1, it is possible to efficiently generate the water-based pigment ink having a high surface tension, and to change the ink composition due to the evaporation of the solvent, the adsorption of the coloring material particles into the filter, etc., and the gas dissolution to form the bubbles. In order to obtain an aqueous recording ink containing no coarse particles and having excellent pigment dispersion stability and storage stability, it is necessary to perform pressure filtration using a metal filter in the filtration step. Further, it is preferable that the pressure applied in the pressure filtration step is 10 Kg / cm ² or less, and the pore size of the metal filter used in the filtration step is 0.5 to 25 μm. Further, it is preferable that the pressure applied in the pressure filtration step is 5 Kg / cm ² or less, and the pore size of the metal filter used in the filtration step is 0.5 to 10 μm.

[0055]

As described above, according to the present invention, a pressure filter step is included in the manufacturing process, and a metal filter having no particle adsorbability and excellent water wettability is used as the filter material.
The filtration speed of the water-based recording ink is greatly improved, and the ink can be efficiently manufactured. Further, by applying pressure, evaporation of volatile components such as organic solvent in the ink can be suppressed, so that the composition change of the ink before and after the filtration step can be prevented. Even when the filter is clogged with coarse particles, it can be easily reused by washing. In addition, there is no change in the ink composition due to adsorption of the coloring material in the filter, generation of bubbles due to gas dissolution, it is possible to obtain an aqueous recording ink excellent in dispersion stability and storage stability of pigments without containing coarse particles. it can.

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Claims (5)

[Claims] 1. A method for producing an aqueous inkjet ink containing at least water and a pigment, which comprises a pressure filtration step using a metal filter as a filter medium during the step. .. 2. The pressure applied in the pressure filtration step is 10
^{2. The} method for producing a water-based inkjet recording ink according to claim 1, which has a Kg / cm ² or less. 3. The pressure applied in the pressure filtration step is 5 K.
The method for producing a water-based inkjet recording ink according to claim 2, wherein the method is g / cm ² or less. 4. The pore size of the metal filter used in the filtration step is 0.5 to 25 μm.
A method for producing the water-based inkjet recording ink described above. 5. The metal filter used in the filtration step has a pore size of 0.5 to 10 μm.
A method for producing the water-based inkjet recording ink described above.