JP3099504B2 - Method for producing aqueous recording ink for inkjet - Google Patents

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 used for an ink jet printer that performs recording using a liquid ink.

[0002]

2. Description of the Related Art Conventional ink jet recording inks are mainly those obtained by dissolving a dye as a colorant in water, an organic solvent, wax, or the like. It was poor in water resistance. In order to solve this problem, inks using pigments such as carbon black and aniline black as colorants have been devised, and are disclosed in JP-A-61-283875, JP-A-64-6074, and JP-A-1-31881. It is shown in gazettes and the like.

[0003] Ink-jet recording inks have problems such as the fact that fine discharge nozzles are not clogged by coarse particles and the like, that there is no change in the physical properties of the ink during production or storage, and there is no precipitation of solids. In particular, an ink using a pigment as a colorant is a dispersion system in which fine pigment particles are dispersed in an aqueous medium, so that the coarse particles contained in the ink, besides fine dust, etc., are sufficiently finely divided when dispersing the pigment. There are large pigment particles remaining without being formed, and coarse particles are more likely to be mixed in as compared with the dye ink which is a complete solution. For this reason, by performing filtration and centrifugation during the manufacturing process, coarse particles in the ink that cause nozzle clogging and solid analysis are removed, and as one example of the manufacturing method, an aqueous medium is used. A method of dispersing a pigment and performing an ultrafiltration treatment is described in JP-A-64-48875. Also, a method of sedimenting and separating coarse particles by centrifugation is described in JP-A-2-255875.

[0004]

Generally, as a method for filtering an ink jet ink containing a pigment, the lower limit of the diameter of the particles to be removed is as very small as 1 to 5 μm. Alternatively, in addition to the method of performing vacuum filtration, the method of performing ultrafiltration as described above,
There is a method of performing centrifugation.

However, these methods have various problems. First, in the case of the vacuum filtration method, the volatile components in the ink may evaporate during the filtration and the composition of the ink may be changed. In addition, 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. The ultrafiltration method is a method of filtering colloid particles having a diameter of several tens of nm, and if a pigment ink having many particles having a diameter of 100 nm or more is filtered, clogging occurs and the filtration speed is significantly reduced.

On the other hand, a filter having a small pore size made of nitrocellulose, cellulose acetate, ethylene tetrafluoride or the like is often used as a filter for filtration 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.When a cellulose-based filter is used as a filter medium, the ink composition changes because the particles in the ink are adsorbed into the porous structure inside, There is also a disadvantage that the filter is clogged quickly and the filtration speed is low. On the other hand, since the aqueous pigment ink has a high surface tension, ethylene tetrafluoride having poor hydrophilicity repels the ink, and the aqueous ink cannot be filtered.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to efficiently filter an aqueous pigment ink having a high surface tension, evaporate a solvent or the like, and filter a color material particle. There is no composition change due to adsorption into the 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]

According to the present invention, there is provided a method for producing an aqueous recording ink for ink-jet recording, comprising a method of producing a water-based ink containing at least water and a pigment. A pressure step in the pressure filtration step is preferably 10
Kg / cm ² or less, and the metal filter has a pore size of 0.5 to 25 μm. More preferably, the pressure 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.

(Specific description of the invention) In the method for producing an aqueous recording ink of the present invention, an ink containing at least water and a pigment is subjected to pressure filtration using a metal filter.
Produce an aqueous recording ink.

The pigment to be used is not particularly limited, and any pigment having a good affinity for water as a main solvent can be used. For example, furnace black, lamp black, acetylene black, channel Carbon blacks such as black, simple metals such as copper and iron, and orthonitroaniline black can be used. For color, use Fast Yellow 10
G, Disazo Yellow AAMX, Disazo Yellow AAO
T, disazo yellow AOAA, 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 Lysome Red, Pigment Scar Red 3B Lake, Lake Bordeaux 10B, Ansosine 3B Lake, Ansosine 5
B Lake, Rhodamine 6G Lake, Eosin Lake, Bengala, Phthol Red FGR, Rhodamine B Lake, Methyl Bio Red Lake, Dioxazine Bio Red, Basic Blue 5B Lake, Basic Blue 6G Lake, Fast Sky Blue, Alkaline Blue R
Toner, Peacock Blue Lake, Navy Blue, Ultramarine Blue, Reflex Blue 2G, Reflex Blue R, Brilliant Green Lake, Diamond Green Thioflavin Lake, Phthalocyanine Green G, Green Gold, Phthalocyanine Green Y, Iron Oxide Powder, Sabiko, 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,
Processed pigments such as dioxane bio red, Victoria Pure Blue, and alkali blue G toner, and other pigments such as graft carbon whose pigment surface is treated with a resin or the like can be used.
The addition amount is preferably from 1 to 30% by weight, and more preferably from 3 to 12% by weight. Although a pigment having a particle size of 25 μm or less is used, it is preferable to use a pigment composed of particles having a particle size of 1 μm or less.

For better dispersion of the pigment, it is preferable to add a dispersant. As the dispersant, an anionic, 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 and the like, and salts thereof, acrylates, styrene or derivatives thereof, vinyl ethers, ethylenically unsaturated monomers such as vinyl esters, etc., alone or in combination of two or more Can be used after being mixed and polymerized.

It is preferable to add a water-soluble resin to fix the ink on paper. Examples of the water-soluble resin include gelatin, proteins such as casein, natural gums such as gum arabic, glucoxides such as savonin, methylcellulose, carboxymethylcellulose, cellulose derivatives such as hydroxymethylcellulose, lignin sulfonates, natural polymers such as shellac, Polyacrylate, 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 Product sodium salt,
One or more of anionic polymers such as polyphosphoric acid and the like and nonionic polymers such as polyvinyl alcohol, polyvinylpyrrolidone and polyethylene glycol can be used in combination.

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, methyl alcohol, ethyl alcohol, n-propyl alcohol, alcohols such as isopropyl alcohol, monoethylene glycol, diethylene glycol,
Propylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, glycerin,
Glycols such as polyethylene glycol are exemplified, but are not limited thereto. Further, a dispersion obtained by dispersing a water-insoluble polymer in a medium containing water as a main component, such as an acrylate ester, a methacrylate ester, a styrene, a styrene-acryl copolymer, an olefin and an amino group, an amide group , Carboxyl group, homopolymerization or copolymer resin emulsion such as a monomer having a hydrophilic functional group such as a hydroxyl group, microemulsion,
3D internal crosslinked organic fine particles, paraffin wax,
Natural and synthetic wax emulsions such as polyethylene wax and carnauba wax, latex, colloid solution,
A suspension or the like can be added to the ink.

In addition, if necessary, a fungicide, a rust preventive,
Urea, thiourea, ethylene urea and the like can be added as an antifoaming 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, if the reduced pressure filtration method is used, the volatile components in the ink may evaporate during the filtration and the composition of the ink may change. Ultrafiltration is a method of filtering colloid particles having a diameter of several tens of nm, and the diameter of many particles is 100 nm.
When the pigment ink is filtered as described above, 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 a filtration step, which is not suitable for mass production.

Therefore, in the present invention, pressure filtration is employed 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 coarse particles are trapped on the filter and removed. Pressurizing pressure is 1
If the pressure exceeds 0 Kg / cm ² , air dissolves in the ink, and if the pressure is returned to normal pressure, bubbles will be generated in the ink, which may cause deterioration of the ink or defective ejection. Needless to say, the pressurizing pressure is lower than the pressure resistance of the filter used.

The aqueous pigment ink is a dispersion of fine particles,
Further, since the surface tension is large, it is preferable to use a metal filter having no particle adsorption property and excellent in wettability. Conventionally, a membrane filter having a small pore size made of nitrocellulose, cellulose acetate, ethylene tetrafluoride, or the like has been often used as a filter for filtration when the pressure filtration method is used. However, 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 porous structure inside, and the filter is clogged quickly and the filtration speed is low. On the other hand, since the aqueous pigment ink has a high surface tension, ethylene tetrafluoride having poor hydrophilicity repels the ink, and the aqueous ink cannot be filtered. However, both of these two disadvantages can be avoided by using a metal filter.

As the material of the metal filter, a metal element such as iron, aluminum, copper, zinc, nickel, tin, chromium, titanium, and manganese, or an alloy such as stainless steel containing two or more kinds of metal elements can be used. Can have a plate shape or a wire mesh shape. The shape of the filter does not necessarily have to be flat, 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 upper limit of the particle size of the pigment particles in the ink is the pore size of the filter, the physical properties of the ink vary depending on the value of the pore size. If the pore size is 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. However, there is a disadvantage that the concentration of the ink is reduced. Conversely, if the pore size is increased, the density of the ink increases because the number of particles having a large particle size increases, but fine nozzles of the inkjet head may be clogged. Therefore, the pore size of the filter is 0.5 to
A range of 25 μm is preferred.

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 made to flow backward from the filter outlet to the filtration tank, so that the clogged particles can be easily removed from the filter and the clogging is temporarily eliminated. can do. In addition, the clogged filter can be completely removed by washing with water or the like, so that the filter can be reused repeatedly.

[0021]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

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

The production of the ink was carried out according to the following procedure, but is not limited thereto. First, carbon black and a dispersant are stirred and mixed in water using a paint shaker for 30 minutes or more, and it is confirmed by microscopic observation that the particle size has become about 1 μm or less, and polyvinylpyrrolidone is added thereto and mixed 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 subjected to pressure filtration at a pressure of 1 kg / cm ² with a stainless steel mesh filter having a pore diameter of 5 μm and a filter diameter of 47 mm to remove dust and coarse particles. Average particle size 0.15 μm,
A pH 6 aqueous recording ink was obtained. Pre-filtration with a filter having a large pore size is preferable in order to increase the collection efficiency of coarse particles.

With respect to the ink composition thus obtained,
The weight average particle diameter was measured using a light scattering 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 (Kyowa Interface Science).

Further, using a prototype 9-nozzle ink jet evaluator having a discharge nozzle diameter of 50 μm, a piezoelectric element driving voltage of 120 V, a driving frequency of 2 kHz, and a resolution of 360 dots / inch, alphabet letters and the like on PPC paper, bond paper, and high-quality paper were used. Print and evaluate the print quality by visually observing the character print sample, Macbeth TR-927 type (Koll
The solid print density was evaluated using an optical densitometer (Omorgan Co., Ltd.), and the continuous ejection stability was evaluated to check for dot missing during continuous printing at room temperature for 12 hours. After the solid print sample was immersed in tap water for 24 hours, the water resistance was evaluated by measuring the change in density.

Further, the storage stability was evaluated by observing the change in the particle size of the 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.

With respect to print quality, the evaluation results were classified as follows.

Bleeding is not observed with the naked eye ..... ◎ Bleeding is seen but characters can be recognized. ・ ・ ・ Characters cannot be recognized. The evaluation results were classified as follows.

O. D. Value: 1.3 or more D. Value 1.1 or more and less than 1.3 ... D. Value: less than 1.1... × Regarding water resistance, the evaluation results were classified as follows.

The change in density was within 0.1 in the OD value. ◎ The change in density was within 0.3 in the OD value. ○ The change in density was larger than 0.3 in the OD value. Regarding missing dots, the evaluation results were classified as follows.

Occurrence of dot omission within 10 times within 12 hours. ◎ Occurrence of dot occlusion within 6 hours within 10 times. O O. Occurrence of dot omission over 10 times within 1 hour. Were classified as follows.

No change in particle size in 30 days ・ ・ ・ ・ ・ ・ ◎ A slight change in particle size was observed in 30 days ・ ・ ・ △ The particle size was clearly increased in 30 days ・ ・× × The following examples were performed in substantially the same procedure as above.

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

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

In Example 4, the filtration was performed using a metal filter having a pore diameter of φ25 μm.

In Example 5, the pressure during filtration was 5 kg / g.
cm ² .

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

The evaluation results of Examples 1 to 6 were all ◎. Although ink can be produced under any of the conditions of this embodiment, it is preferable that the filter has a pore diameter of 10 μm or less in order to avoid mixing of coarse particles as much as possible.
Further, if the pressurizing pressure is large, the pressurizing device such as a compressor becomes large, so that the pressurizing pressure is desirably 5 kg / cm ² or less.

Comparative Example As a comparative example, the same ink composition as in Example 1 was prepared. Comparative Example 1 is an ink composition obtained without performing a filtration treatment.

In Comparative Example 2, filtration was performed under reduced pressure (final vacuum degree: 100 mmHg) instead of pressure filtration in the filtration step.

In Comparative Example 3, a nitrocellulose membrane filter (manufactured by Toyo Filter Paper) having a pore diameter of 5 μm and a filter diameter of 47 mm was used as a filter medium during pressure filtration. Comparative Example 4 had a pore size of 3 μm as a filter medium during pressure filtration.
This is a filter using a 47 mm diameter filter made of tetrafluoroethylene resin (made by Toyo Filter Paper).

In Comparative Example 5, 1 Kg / c was filtered using an ultrafiltration membrane ultrafilter Q2000 (registered trademark of Toyo Roshi Kaisha) after pressure filtration with a stainless steel mesh filter.
Filtration under pressure at a pressure of m ² gave an ink composition.

Comparative Example 6 is an example in which a metal filter was used in the filtration step, but filtration was performed at a pressure of more than 10 kg / cm ² kg and 15 kg / cm ² .

Further, in Comparative Example 7, the pore size of the filter medium was 0.5 μm.
Example in which pressure filtration was performed using a metal filter of less than 0.3 μm. Comparative Example 8 is an example in which the pore size of the filter medium exceeds 25 μm and a metal filter of 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 described below were obtained.

[0046]

[Table 1]

In Comparative Example 1, since the treatment for removing coarse particles such as filtration was not carried out, in addition to missing dots and poor storage stability, the pigment fixability on paper and the water resistance were also deteriorated. In Comparative Example 2, since the ink was exposed to the reduced pressure during filtration, the volatile components in the ink were evaporated, and the weight of the ink before and after filtration was reduced by 0.5%.

In Comparative Example 3, the filtration speed was sharply reduced after the start of the filtration, and the filter was clogged at the time when 230 ml of the ink was filtered, so that no filtrate was produced.

In Comparative Example 4, since the filter repelled the ink, no filtration could be performed.

In Comparative Example 5, the particles were excessively removed with an ultrafiltration membrane having a very small pore size. However, the print density was lowered, and bleeding occurred on the paper. Deterioration was observed.

In Comparative Example 6, since the pressure inside the filtration device was high, a gas such as nitrogen dissolved in the ink.
Under normal pressure, there is a problem that bubbles of these gases are easily generated.

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

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

From the results in Table 1, it is found that the aqueous pigment ink having a high surface tension can be efficiently used, the ink composition does not change due to the evaporation of the solvent, the adsorption of the coloring material particles into the filter, etc., and the generation of bubbles due to the dissolution of gas. 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 desirable that the pressure applied in the pressure filtration step be 10 kg / cm ² or less, and the pore size of the metal filter used in the filtration step be 0.5 to 25 μm. Further, it is desirable that the pressure applied in the pressure filtration step be 5 kg / cm ² or less, and the pore size of the metal filter used in the filtration step be 0.5 μm to 10 μm.

[0055]

As described above, according to the present invention, a pressure filtration step is included in the production process, and a metal filter having no particle adsorption property and excellent water wettability is used as the filter medium.
The filtration rate of the aqueous recording ink is greatly improved, and the ink can be manufactured efficiently. In addition, since the evaporation of volatile components such as an organic solvent in the ink can be suppressed by applying pressure, a change in the composition 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. Further, there is no change in the ink composition due to adsorption of the coloring material into the filter, etc., generation of bubbles due to dissolution of the gas, and an aqueous recording ink which does not contain coarse particles and has excellent pigment dispersion stability and storage stability can be obtained. it can.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C09D 11/00 B01D 29/01 B01D 35/02 B01D 39/10 B41J 2/01-2/21 B41M 5 / 00

Claims (5)

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