JPH08209045A - Method for producing ink jet recording ink - Google Patents

Abstract

PURPOSE: To obtain an ink for ink jet recording by admixing a variety of additives to a dispersion dispersing pigments in a medium, converting them into an ink and dispersing again the pigment particles using a high-pressure homogenizer. CONSTITUTION: (A) Pigments are dispersed in a medium to prepare a pigment dispersion, (B) the pigment dispersion is diluted and combined with a variety of additives for regulating ink characteristics such as a physical properties- regulating agent or a humectant to convert the mixture into ink, and (C) the resultant ink is passed through a plurality of fine orifices under a fluid pressure of at least 1×10<7> kg/m/sec<2> and accelerated. The accelerated ink flows are allowed to collide to each other in a dispersion tank and the particle sizes of the pigment are regulated. Preferably, they are subjected to centrifugal filtration to give the objective ink. It is preferred that this ink comprises at least a pigment, a water-soluble resin dispersion, a resin emulsion, saccharides and an aqueous dispersion medium.

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 an aqueous pigment ink used in an ink jet printer or the like.

[0002]

2. Description of the Related Art The characteristics of ink jet recording inks are that the physical property values do not change during storage, the fine ink ejection nozzles are not clogged, the color density of the printed matter is high, and the printed matter is clear. High storage stability (water resistance, weather resistance), etc. are required.

Conventionally, inks used in ink jet printers basically consist of a dye and an aqueous medium. However, due to the properties of the dye, there is a problem that the water resistance and weather resistance of the printed matter are poor. Therefore, in order to solve these problems, inks using pigments instead of dyes are being developed.

A general method for producing a pigment ink is to grind and disperse pigment particles with a dispersing device such as a ball mill, a sand mill, a roll mill, etc., and add various additives to the obtained pigment dispersion liquid to form an ink. is there. The pigment ink produced in this manner has not only the above-mentioned water resistance and weather resistance, but also the property that it can be applied to a wider range of paper.

However, the above-mentioned pigment ink has problems in reliability such as clogging characteristics and storage stability. In an ink jet recording method in which ink is ejected from fine nozzles, the clogging property is an important issue, and many efforts have been made to solve the problem.

In order to solve the reliability problem, it is necessary to make the dispersion state uniform, that is, to realize a sharp particle size distribution.

Japanese Patent Publication No. 4-501128 proposes a method for producing a pigment ink using a high pressure homogenizer. The high-pressure homogenizer is a device that crushes and disperses pigment particles by allowing a dispersion medium containing a pigment, a dispersant, and the like to pass through a fine orifice at high speed under high pressure. (A)
The shearing force generated when passing through the orifice, (b) cavitation (pressure drop) that occurs when the pressure is released after passing through the orifice, (c) particles colliding with each other, or particles colliding with a wall, etc. It is believed to progress.

In the high-pressure homogenizer, particles having a large mass are accelerated at a high speed due to their characteristics, so that a pigment dispersion having a sharp particle size distribution can be obtained.

[0009]

However, even the pigment ink manufactured by the conventional manufacturing method is insufficient in terms of reliability improvement.

When the time-dependent change of the prior art water-based pigment ink was investigated, it was found that the reliability deteriorates with the passage of time. That is, nozzles were not clogged immediately after the ink was produced, and the ink was ejected stably. When the same evaluation was performed after leaving for several months, some nozzles were clogged, or the physical properties were It has been confirmed that the change in the value causes unstable ejection. Both the deterioration of the clogging property and the change of the physical properties are problems caused by the fact that the pigment particles are not stably dispersed.

Another problem is "print unevenness" which is a problem peculiar to pigment inks. What is uneven printing?
It is the disturbance of the color density of the printed matter due to the deviation of the coloring material (pigment) on the paper. Print unevenness is one of the parameters that determines print quality, like the color density of printed matter or the sharpness of contours (hereinafter referred to as "blurring"), and must be solved to achieve high print quality. This is a task that must be done.

Therefore, an object of the present invention is to provide a method for producing a pigment-based ink for ink jet recording, which can provide a printed matter which is stable even after being left for a long period of time and has no printing unevenness. It is in the place of providing.

[0013]

Detailed analysis of the cause of the above-described problem of ink reliability deterioration has revealed the following.

In the method for producing a pigment ink, usually, pigment particles are dispersed to produce a pigment dispersion, and then various additives are added so as to satisfy various properties required for the ink.
Examples of the additives include physical property adjusting agents for adjusting viscosity and surface tension, moisturizing agents for improving clogging characteristics, and the like. When this additive is added, the stable dispersion state collapses due to the change in the liquidity of the ink. Especially for ink p
The change of H has a great influence on the dispersion system, and the pigment particles may momentarily undergo shock aggregation.

When the dispersed state collapses, the particle size distribution of the pigment particles becomes broad, and the center of the distribution shifts to the large particle size side. Since the ink whose stable dispersion state has collapsed can no longer exist stably, the deterioration of the ink progresses over time. As a result, there is a problem in that ink that has been stably ejected without causing clogging in the initial stage will have its clogging characteristics lowered in level after being left for a long time, and that stable ejection will become difficult due to changes in physical properties. Occurs.

Destruction of the dispersed state depends on selection of the kind of additive,
Although it can be avoided to some extent by optimizing the addition method, it is impossible to completely suppress the decrease in dispersion stability. Therefore, it is necessary to ensure dispersion stability by performing some treatment after adding the additive.

The present invention is a method for producing an ink jet recording ink containing a pigment, which comprises at least the following three steps. (A) A step of producing a pigment dispersion by dispersing a pigment in a dispersion medium. (B) A step of diluting the pigment dispersion liquid and further adding various additives for adjusting ink characteristics to form an ink. (C) The ink is accelerated through a plurality of fine orifices under a liquid pressure of at least 1 × 10 ⁷ kg / m · sec ² , and the inks passing through different orifices in the dispersion chamber are made to collide with each other to form pigment particles. The process of adjusting the particle size.

The method for producing the ink jet recording ink of the present invention will be described below step by step.

(A) First, a water-soluble resin dispersant is dissolved in an amine aqueous solution to prepare an aqueous dispersant solution.

As the water-soluble resin dispersant, any polymer dispersant which is soluble in an amine aqueous solution and has a pigment dispersibility can be used. For example, acrylic resin,
Specifically, styrene-acrylic acid copolymer, acrylic acid-acrylic acid alkyl ester copolymer, styrene-acrylic acid-acrylic acid alkyl ester copolymer, styrene-methacrylic acid copolymer, styrene-methacrylic acid-acrylic Acid alkyl ester copolymer, styrene-α
-Methylstyrene-acrylic acid copolymer, styrene-α
-Methylstyrene-acrylic acid-acrylic acid alkyl ester copolymer, and salts thereof, polyacrylic acid salts,
Polymethacrylate, vinylnaphthalene-acrylic acid copolymer, styrene-maleic acid copolymer, maleic acid-
Examples thereof include maleic anhydride copolymers, vinylnaphthalene-maleic acid copolymers and salts thereof. Further, proteins such as gelatin, albumin and casein, natural polymers such as gum arabic, sodium salts of β-naphthalenesulfonic acid formalin condensate, anionic polymers such as phosphates, further, acrylonitrile, vinyl acetate, Polymers such as vinylidene chloride, ethylene, hydroxyethyl acrylate and glycidyl methacrylate may be copolymerized. These are used alone or in combination of two or more.

The weight average molecular weight of the water-soluble resin is 300.
It is preferably 0 to 50,000, and more preferably 7,000 to 15,000.

The amine used here is preferably an organic amine such as monoethanolamine, diethanolamine, aminomethylpropanol or ammonia.
The amine is added to increase the solubility of the water-soluble resin dispersant in the dispersion medium.

Next, a pigment is added to the aqueous dispersant solution.

The pigment used in the ink of the present invention includes:
Various conventionally known inorganic pigments and organic pigments can be used. Examples thereof include inorganic pigments such as carbon black and titanium oxide, organic pigments such as azo pigments, phthalocyanine pigments, quinacridone pigments, anthraquinone pigments and dioxazine pigments. In addition to the various pigments listed above,
Any pigment that can be dispersed in an aqueous medium can be used, and a processed pigment such as graft carbon whose surface is treated with a resin can also be used.

The concentration ratio of the pigment and the water-soluble resin dispersant may be in the range of 2 to 50% by weight based on the pigment. However, since the dispersant / pigment ratio has a great influence on the quality of printed matter and the reliability of the ink, it is desirable to find the optimum addition ratio for each combination.

After the pigment is added, the pigment and the aqueous dispersant solution are mixed. Usually, the pigments do not mix uniformly when added to the dispersing medium. The mixing method is not particularly limited, and any method may be used as long as the pigment and the dispersion medium are uniformly mixed. For example, stirring with a rotary blade, stirring with ultrasonic waves, shaking, etc. may be mentioned.

Subsequently, the pigment is dispersed. The pigment dispersion can be carried out by various commercially available dispersion devices (for example, ball mill, sand mill, high pressure homogenizer, etc.).

(B) After dispersion of the pigment, the dispersion is diluted to a desired pigment concentration and various additives are added to form an ink.
Examples of additives include resin emulsions, thickeners and surfactants for adjusting physical properties such as ink viscosity and surface tension, humectants such as sugars and glycerin for preventing nozzle clogging, and the like. To be

The resin emulsion used in the present invention includes polyacrylic ester emulsion, polymethacrylic ester emulsion, acrylic emulsion, vinyl acetate emulsion, styrene-butadiene emulsion, vinyl chloride emulsion, and internal three-dimensional emulsion. Examples include crosslinked microemulsions and intermediates thereof, and the content thereof is in the range of 0.1 to 40% by weight, preferably 1 to 25% by weight in terms of solid content. By adding the resin emulsion, bleeding on the paper surface is suppressed and the print density is improved.

As the saccharides, monosaccharides such as pentose, hexose, heptose, and octose, or polysaccharides such as disaccharides, trisaccharides, and tetrasaccharides, or their derivatives such as sugar alcohols and reduced derivatives such as deoxy acids, and aldones. Examples thereof include oxidized derivatives such as acids and uronic acids, dehydrated derivatives such as glycoceene, amino acids and thiosugars. Polysaccharides refers to sugars in a broad sense, and also includes substances widely existing in the natural world such as alginic acid, dextrin, and cellulose. The saccharides mentioned above may be used alone or in combination of two or more to be added to the aqueous pigment ink of the present invention.

The content of these sugars is in the range of 0.1 to 40% by weight, preferably 0.5 to 30% by weight. 0.
If it is less than 1% by weight, the effect of adding saccharides cannot be obtained, and if it exceeds 40% by weight, dissolution in water becomes difficult, so that favorable results cannot be obtained.

If necessary, a water-soluble organic solvent, p
An H regulator, an antiseptic agent, an antifungal agent and the like may be added.

As the water-soluble organic solvent, 2-pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-
Examples thereof include nitrogen-containing compounds such as 2-imidazolidinone and amides such as dimethylformamide and dimethylacetamide.

Examples of the pH adjuster include organic amines such as diethanolamine and triethanolamine, inorganic bases such as sodium hydroxide and potassium hydroxide, organic acids and mineral acids.

(C) Next, various additives are added to form an ink, and then the dispersion treatment is performed again by a high pressure homogenizer to adjust the particle size of the pigment particles. (Hereinafter, "redispersion process")
Called. Even if an additive is added to the pigment dispersion liquid, or even if the dispersion liquid is simply diluted, the stable dispersion state may be destroyed due to that. This is because the liquid properties of the ink (for example, pH, solid content concentration, etc.) change due to addition of additives, etc., and the stable dispersed state up to that point cannot be maintained. As a result, the particle size distribution becomes broad and the center of the distribution also shifts to the large particle size side. In particular, when a resin emulsion is added, different dispersion systems are mixed, so that the dispersion stability is likely to be impaired due to the interaction between the dispersed pigment and the resin emulsion.

Large particles produced by aggregation during the process of making into ink adversely affect the reliability of the ink. Therefore, the particle size of the pigment particles is adjusted by performing a redispersion treatment with a high pressure homogenizer, and the particle size distribution is made sharp.

The high-pressure homogenizer used here includes Microfluidizer (registered trademark of Microfluidizer Co., Ltd.), Nanomizer (Nanomizer Co., Ltd.).
Manufactured, registered trademark) and the like, and good results can be obtained using either device.

The processing pressure of the re-dispersion processing is 2 to 20 × 10 ⁷ k
The range is g / m · sec ² , preferably 5 to 15 × 10 ⁷ kg / m · sec ² . If the treatment pressure is low, the proportion of pigment particles that are not crushed / dispersed increases, while if the treatment pressure is too high, the crushing of the pigment particles is performed effectively, but the temperature of the dispersion medium rises. Will start to aggregate.

After the step of redispersing the pigment particles, centrifugal filtration and filter filtration are carried out if necessary. Centrifugal filtration condition is 1
The conditions are determined according to the particle size distribution of the pigment particles at 000 rpm to 20,000 rpm / 5 to 60 minutes.

The filter filtration and centrifugal filtration play a role of removing large particles that could not be dispersed by the redispersion treatment and improving the stability of the ink.

[0041]

According to the method for producing an ink jet recording ink of the present invention, it is possible to solve at the same time two problems that have been encountered with pigment inks, namely improvement of reliability and suppression of printing unevenness. The reason why such good results are obtained is considered as follows.

(B) Reliability It is considered that the reason why the reliability is improved is a sharp particle size distribution. Larger particles settle out over time,
This causes pigment aggregation. On the other hand, particles having a small particle size also have a large surface energy, so that they easily aggregate due to collision with adjacent particles, and the dispersion system becomes unstable.

In the present invention, a sharp particle size distribution is realized by adding various additives to the pigment dispersion liquid and then carrying out a redispersion treatment with a high pressure homogenizer. As a result, sedimentation and aggregation of pigment particles are effectively prevented and high reliability is obtained.

Further, by carrying out centrifugal filtration, large particles which could not be dispersed by the redispersion treatment by the high pressure homogenizer can be removed, and a highly reliable pigment ink can be produced.

(B) Uneven printing There are several possible causes of uneven printing, and one of them is the particle size distribution of pigment particles contained in the ink. That is, if the particle size distribution is broad, when ink drops adhere to the paper surface, an in-plane distribution occurs depending on the degree of ink penetration, and as a result of this variation in penetrability, printing unevenness occurs. In the present invention, after being made into an ink, it is subjected to a redispersion treatment with a high pressure homogenizer to make the particle size distribution sharp and suppress the occurrence of printing unevenness.

[0046]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples of the present invention.

Example 1 (Preparation of Pigment Dispersion) Styrene-acrylic acid copolymer 4 parts Triethanolamine 7 parts Ion-exchanged water Remaining amount The above components are mixed and heated to about 70 ° C. to remove the resin component. It was completely dissolved. Add carbon black (MA7,
20 parts of Mitsubishi Kasei) was added, and the pigment and the dispersion medium were mixed by ultrasonic stirring.

After mixing, pigment dispersion was performed under the following conditions. Dispersing device: Sand mill (Yasukawa Seisakusho) Grinding media: Glass beads (1.7 m diameter) Media filling rate: 1.5 times (weight ratio) Dispersion time: 2 hours After dispersion, remove glass beads and use 5 μm membrane filter Coarse particles and dust were removed to obtain a pigment dispersion liquid.

[0049] The above components were mixed, stirred at room temperature for 20 minutes, and then redispersed with a high pressure homogenizer to adjust the particle size. Dispersing device: Nanomizer (manufactured by Nanomizer Co., Ltd.) Treatment pressure: 5 × 10 ⁷ kg / m · sec ² Number of treatments: 1 time Subsequently, centrifugal filtration was performed at 12000 rpm for 20 minutes to remove large particles, and further 5 μm An ink was obtained by filtering with a membrane filter.

Example 2 (Preparation of Pigment Dispersion) Styrene-maleic anhydride copolymer 4 parts Triethanolamine 7 parts Ion-exchanged water Remaining amount The above components are mixed and heated to about 70 ° C. to give a resin component. Was completely dissolved. Carbon black (MA10
20 parts (manufactured by Mitsubishi Kasei Co., Ltd.) and the pigment and the aqueous dispersant solution were mixed by ultrasonic stirring. After mixing, pigment dispersion was performed under the same conditions and conditions as in Example 1.

[0051] After adding the above additives, redispersion treatment and centrifugal filtration were performed under the same conditions as in Example 1 to obtain an ink.

(Example 3) After the above components were mixed, they were stirred well. 20 parts of carbon black (FW200, manufactured by Degussa) was added to this aqueous solution, and dispersion treatment was performed under the following conditions. Dispersing device: Nanomizer (manufactured by Nanomizer Co., Ltd.) Treatment pressure: 5 × 10 ⁷ kg / m · sec ² Number of treatments: 3 times After dispersion, coarse particles and dust are removed by a 5 μm membrane filter to obtain a pigment dispersion liquid. Obtained.

[0053] The above components were mixed, stirred at room temperature for 20 minutes, and then redispersed with a high pressure homogenizer to adjust the particle size. Dispersing device: Nanomizer (manufactured by Nanomizer Co., Ltd.) Treatment pressure: 5 × 10 ⁷ kg / m · sec ² Number of treatments: 1 time Subsequently, centrifugal filtration was performed at 8000 rpm for 20 minutes to remove large particles, and further 5 μm An ink was obtained by filtering with a membrane filter.

(Embodiment 4) An ink having the same formulation as in Embodiment 3 but omitting centrifugal filtration.

(Comparative Example 1) An ink having the same formulation as in Example 1 but not subjected to redispersion treatment with a high pressure homogenizer and centrifugal filtration.

(Comparative Example 2) An ink having the same formulation as in Example 2 but not subjected to redispersion treatment with a high pressure homogenizer and centrifugal filtration.

(Evaluation 1) Clogging property The ink cartridge of the ink jet printer MJ-500 (manufactured by Seiko Epson Corp.) is filled with a predetermined ink, and after printing the alphanumeric characters continuously for 10 minutes, the printer is stopped. Then, it was left for 2 weeks in an environment of 40 ° C. and 25% RH without a cap. After leaving it, print alphanumeric characters again,
The number of times of the clogging recovery operation required until a print equivalent to that before leaving was obtained was examined. ◯: The same printing as the initial printing is possible with 0 to 2 times of the returning operation, Δ: The same printing as the initial printing is possible with the returning operation of 3 to 5 times, ×: The same printing as the initial printing is possible even with the returning operation of 6 times or more Is impossible. The evaluation of the clogging property was performed twice for the same ink immediately after the ink was prepared and 6 months after the ink was prepared, and the relationship between the ink history and the clogging property was investigated.

(Evaluation 2) Storage stability 50 cc of ink was sampled in a Labran-Screw tube bottle,
It was left at 50 ° C. for 2 months. The average particle size before and after standing was compared, and the storage stability was evaluated according to the following criteria. ◯: Increase in average particle diameter is 10% or less, Δ: Increase in average particle diameter is 10 to 20%, ×: Increase in average particle diameter exceeds 20%.

(Evaluation 3) Printing Quality (Bleed) The following 10 papers were printed with MJ-500, and the presence or absence of bleed was evaluated according to the following criteria. Evaluation paper 1) Xerox P (Fuji Xerox Co., Ltd.) 2) Riccopy 6200 (Ricoh Co., Ltd.) 3) EPP (Seiko Epson Co., Ltd.) 4) Xerox R (Fuji Xerox Co., Ltd., recycled paper) 5) Yamayuri (Honshu Paper Co., Ltd., recycled paper) 6) Conqueror Laid (European paper) 7) Rapid Copy (European paper) 8) Modo Copy (European paper) 9) Neenah Bond (US paper) 10) Xerox 4024 3R721 (US paper) ) ○: Clear printing without bleeding, Δ: Whisker-like bleeding occurred, ×: Blurring so that the outline of the character was not clear.

(Evaluation 4) The above 10 papers were printed with MJ-500, and the slit width was 200 μm × 20 μm using Sakura Microdensitometer manufactured by Konica Corporation.
1 mm for the filled and printed portion is measured. OD at that time
The difference between the maximum value and the minimum value was evaluated according to the following criteria. ◯: No print unevenness (less than 0.2), Δ: slight print unevenness (0.5 or less), x: print unevenness is noticeable (0.5 or more).

(Evaluation 5) Print Quality (OD Value) Mj-500 was printed on the above 10 papers by Machbe.
The OD value of 10 points of the solid print portion was measured by th PCMII and the average value was calculated.

[0062]

[Table 1]

From Table 1, in Examples 1 and 2 which were subjected to redispersion treatment with a high-pressure homogenizer, deterioration of clogging characteristics with time was not recognized, and inks were compared with Comparative Examples 1 and 2 in which the dispersion treatment was not performed. It can be seen that the dispersion stability of is improved.
This is nothing but the effect of improving the dispersion stability by sharpening the particle size distribution by performing redispersion with a high pressure homogenizer.

Further, comparing Example 1 with Comparative Example 1, it is found that the redispersion treatment with the high-pressure homogenizer is effective for suppressing printing unevenness.

From the comparison of Examples 3 and 4, the effect of centrifugal filtration on the reliability of the ink can be seen. In Example 4 in which centrifugal filtration is not performed, deterioration of the clogging property with time is observed, whereas in Example 3 in which centrifugal filtration is performed, such deterioration is not observed. Therefore, it can be confirmed that the centrifugal filtration greatly contributes to the improvement of the dispersion stability of the ink.

(Comparative Example 3) In the manufacturing process of Example 1,
It is an ink in which no acrylic ester-styrene copolymer / emulsion was added. Other prescriptions and ink manufacturing processes are the same as in Example 1.

Comparative Example 4 In the manufacturing process of Example 2,
It is an ink to which no polymethacrylate ester emulsion was added. Other prescriptions and ink manufacturing processes are the same as those in the second embodiment.

(Comparative Example 5) This is an ink in which sucrose and maltitol (above, sugars) were not added in the process of preparing the ink of Example 1. The other ink composition and manufacturing method are the same as in Example 1.

[0069]

[Table 2]

Comparing Examples 1 and 2 with Comparative Examples 3 and 4, it can be seen that there is no difference in the bleeding of the printed matter depending on the presence or absence of the addition of the resin emulsion, but there is a difference in the color density (OD value). . This is because the resin emulsion suppresses the penetration of ink and leaves pigment particles, which are colorants, on the paper surface. Also, by adding a resin emulsion,
The abrasion resistance of the printed matter is also improved.

The effect of adding saccharides can be seen by comparing Example 1 and Comparative Example 5. The sugar plays a large role in improving the clogging property, and Comparative Example 5 in which the sugar was not added
Has significantly inferior clogging characteristics.

[0072]

According to the method for producing an ink jet recording liquid of the present invention, it is possible to obtain a pigment ink having a sharp particle size distribution, so that an ink jet printing ink which has good reliability and is less likely to cause uneven printing can be obtained. Recording ink can be obtained.

Claims (5)

[Claims] 1. At least a pigment, a water-soluble resin dispersant,
And (a) a step of producing a pigment dispersion liquid by dispersing a pigment in a dispersion medium, and (b) diluting the pigment dispersion liquid, and further producing an ink. A step of adding various additives for adjusting properties to form an ink, and (c) accelerating the ink through a plurality of fine orifices under a liquid pressure of at least 1 × 10 ⁷ kg / m · sec ² to form a dispersion chamber. And adjusting the particle diameters of the pigment particles by causing the inks that have passed through different orifices to collide with each other, the method for producing an ink for inkjet recording. 2. The method for producing an ink jet recording ink according to claim 1, wherein centrifugal filtration is performed after the step (c). 3. The inkjet recording ink according to claim 1, wherein the inkjet recording ink contains at least a pigment, a water-soluble resin dispersant, a resin emulsion, a saccharide, and an aqueous dispersion medium. Production method. 4. The water-soluble resin is a polymer having both a hydrophilic structure part and a hydrophobic structure part in the molecule, and its molecular weight is 3,000 to 50,000, more preferably 500.
The range of 0 to 15000 is set.
4. A method for producing an ink jet recording ink according to any one of 3 to 3. 5. The saccharide is one kind or a mixture of two or more kinds selected from monosaccharides, disaccharides, polysaccharides and derivatives thereof, and the content thereof is in the range of 0.1 to 40% by weight. The method for producing an inkjet recording ink according to claim 1, wherein