JP2006183041A - Preparation process of azo pigment dispersion - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a preparation process by which an azo pigment dispersion having uniform small particle diameters is prepared by using a simple process. <P>SOLUTION: The process for preparing the azo pigment dispersion comprises the step of causing a solution containing a diazonium compound to react with a solution containing a coupling agent to prepare an azo pigment dispersion in which an azo pigment is dispersed, wherein the reaction is carried out in the presence of a dispersing agent for dispersing the azo pigment in a solvent and a pH buffering agent having a buffering action under alkaline conditions. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing an azo pigment dispersion useful as an ink in image recording or the like using an inkjet method.

  In recent years, properties required for inks used for image recording using an ink jet method are shifting to pigments rather than dyes from the viewpoint of light resistance and water resistance. When a pigment is used, a more uniform and fine nanopigment dispersion having high dispersibility is desired.

  However, the production of inks used in the current ink jet method has many processes and at the same time has problems due to the production method itself. One is that commercially available pigments cannot provide nano-sized uniform powder due to the characteristics of pigments. For this reason, the purchased pigment is pulverized using a dispersing machine such as a ball mill, a roll mill, a sand mill, etc., and then a process such as classification using a filter or a centrifugal separator is required. However, in reality, it is extremely difficult to obtain a uniform pigment of several tens of nanometers even if such grinding is performed.

  Patent Document 1 discloses a method for producing a pigment dispersion in which a wetting agent is added to improve the dispersion efficiency of a pigment in a step of dispersing a self-dispersing pigment that has undergone surface treatment on the pigment in an aqueous medium. .

On the other hand, Patent Document 2 discloses a method for producing a pigment composition using an azo pigment coupling reaction. An object of the invention described in the publication is to provide a method for producing a pigment composition having good water separability when dehydrating an aqueous suspension of the obtained pigment to reduce the water content. In this publication, a pigment composition is prepared by adding a water-insoluble resin that is solid at room temperature before or during the coupling reaction, and mixing the pigment particles and the resin simultaneously with the generation of the pigment particles by the coupling reaction. A manufacturing method is disclosed. In the examples, it is disclosed that a resin is added to an acidic pH buffer solution and a pigment composition is obtained by adding a tetrazo solution and a coupler solution to the pH buffer solution. In this embodiment, ink is obtained through steps such as dehydration, oil varnish addition, and decantation.
USAA2002075369 JP 2002-80743 A

  According to the method disclosed in Patent Document 1, a pigment dispersion excellent in storage stability can be provided. However, in this method, a pigment that has been pulverized in advance is used, and the pigment further has a surface treatment step and a surface treatment pigment dispersion step, and it is necessary to add a wetting agent in the dispersion step. It is said. The dispersion degree of the ink obtained by the technique described in Patent Document 2 is 5 μm, and a dispersion having a finer particle size on the nanometer order has not been obtained. That is, the method disclosed in Patent Document 2 does not disclose a method for producing a pigment dispersion having a nanometer-order fine particle size by a simple process.

  The present invention provides a production method capable of producing an azo pigment dispersion having a small particle size and a uniform particle size by omitting the production steps as much as possible and using a simple process.

  The method for producing an azo pigment dispersion provided by the present invention is a method for producing an azo pigment dispersion in which an azo pigment is dispersed by reacting a solution containing a diazonium compound with a solution containing a coupling agent. The reaction is carried out in the presence of a dispersing agent for dispersing the azo pigment in a solvent and a pH buffering agent having a buffering action under alkalinity.

  Since the method of the present invention is performed all at once, from the synthesis of the azo pigment to the formation of the dispersion, it is a simple production method with few steps. In addition, a pigment dispersion having a relatively small particle size from several hundred to several tens of nanometers is provided by performing the coupling reaction in the presence of a pH buffer having a buffering action under alkaline conditions. Can do.

The azo pigment obtained in the present invention has a structure represented by the following formula (1).
A−N = N−B (1)
Here, A represents an atomic group on the aromatic amine side (diazonium compound side), and B represents an atomic group on the coupling agent side. A may be a disazo compound or a trisazo compound having the structure (1).

  The azo pigment represented by the formula (1) occurs between a general diazotized aromatic amine and a β naphthol, β oxynaphthoic acid anilide, acetoacetate anilide, or pyrazolone compound. Obtained by a coupling reaction. Thus, when A is a plurality of azo compounds, it is desirable that (1) is a water-insoluble or insoluble azo pigment as a whole.

  In the present invention, the coupling reaction between the diazonium compound and the coupling component is performed in the presence of a pH buffer having a buffering action under alkaline conditions.

  In the present invention, a buffering agent having a pH buffering ability and a dispersing agent can be present together with a strong alkali necessary for the coupling reaction in the reaction solution on the coupling agent side.

  The buffering agent needs to be a pH buffering agent that has a buffering action under alkaline conditions. Examples thereof include a quaternary ammonium salt such as a primary amine having a saturated or unsaturated alkyl chain, a secondary amine, a tertiary amine, and tetramethylammonium hydroxide.

  In addition, as seen in some Good buffers, an aliphatic or alicyclic amine sulfonic acid derivative having a buffering ability on the alkaline side can be used. Similarly, carboxylic acid derivatives such as amino acids having a buffering capacity on the alkaline side can also be used.

  In general, an aromatic amine is hardly soluble in water, but the amine that can be used in the present invention may be water-soluble and can be added to a solution containing a coupling agent. At this time, even if the buffer has an acidic functional group in the molecule, it is buffered under the alkalinity of the present invention if the isoelectric point due to the remaining amino group is on the alkaline side after neutralization with alkali. It can be used as an active pH buffer.

  Furthermore, phosphoric acid and carbonic acid which are buffer components of a phosphate buffer and a carbonated bicarbonate buffer which are general buffers subjected to alkalinity can be used.

Hereinafter, specific examples of pH buffering agents having a buffering action under alkaline conditions will be given.
For example, trishydroxymethylaminomethane (hereinafter also referred to as “TRIS”)-hydrochloric acid buffer can be used in a pH range of 7.2 to 9.0. In this case, the TRIS-hydrochloric acid buffer can also be configured by adding hydrochloric acid to the solution containing the diazonium compound, adding TRIS to the solution containing the coupling agent, and mixing the two solutions. Further, a TRIS-hydrochloric acid buffer solution may be prepared separately from the two solutions, and the buffer solution may be added during the coupling reaction.

  A glycine-sodium hydroxide buffer can also be used in the range of pH 8.6 to 10.6. Carbonate-bicarbonate buffer can also be used in the range of pH 9.2 to 10.6. Furthermore, a phosphate buffer can also be used in the range of pH 7.0-8.0. In addition, a so-called Good buffer solution can be used, which will be described later.

It is useful to use a pH buffer that has a buffering action under alkalinity to obtain a transparent dispersion having a very small particle diameter. State.
Study-1: When tert-butylamine obtained by removing alcoholic OH groups from trishydroxymethylaminomethane is used, a transparent dispersion can be obtained. On the other hand, when methanol or ethanol is used, an appropriate dispersion cannot be obtained. From this, it is considered that the functional group contributing to the dispersion is not due to the alcoholic OH group present in the TRIS molecule, but due to the remaining amino group, that is, the property of TRIS as an amine (see Example 3).
Study-2: When sodium hydroxide having no buffering capacity is used instead of TRIS, an appropriate dispersion cannot be obtained even if it is added excessively. That is, the action of TRIS as an amine does not simply act as an alkali (see Example 3).
Study-3: When the simplest ammonia is used instead of TRIS, an appropriate dispersion cannot be obtained. Here, paying attention to the basicity of the amine, the pH after mixing is reduced by the excess strong acid (hydrochloric acid) on the solution side containing the diazonium salt and the weak base (ammonia) on the solution side containing the coupling agent. It is expected to be slightly acidic (see Example 3).
Study-4: When Good's buffer that can produce a buffer solution in the range of weakly acidic to neutral and alkaline is used instead of TRIS, a more suitable dispersion is obtained when the buffering region is acidic. This can be confirmed (see Example 4).

  That is, after mixing the solution containing the diazonium salt and the solution containing the coupling agent, an excess of alkali simply exists, and even if the mixed solution is alkaline, a transparent dispersion is not formed. Rather, upon mixing (coupling reaction), the presence of an alkaline pH buffering agent that is buffered is essential to obtain a transparent dispersion.

  When the pH is about to change drastically due to the coupling reaction, the buffering action is suppressed by a buffer that has a buffering effect under alkaline conditions, and the growth of the pigment particles is suppressed, giving the opportunity for the dispersant polymer to stick to the particle surface. It is considered a thing.

  Examples of the dispersant that can be used in the present invention include, in the case of polymers, styrene, styrene derivatives, vinyl naphthalene derivatives, aliphatic alcohol esters of α, β-ethylenically unsaturated carboxylic acid, etc. that are soluble in alkali, acrylic acid, acrylic Block copolymer consisting of at least two monomers selected from acid derivatives, maleic acid, maleic acid derivatives, itaconic acid, itaconic acid derivatives, fumaric acid, fumaric acid derivatives, etc., or random copolymers, or These salts and the like, and mainly anionic polymers and nonionic polymers of the above monomers can be mentioned.

  In the case of surfactants, higher fatty acid salts, alkyl sulfates, alkyl ether sulfates, alkyl ester sulfates, alkyl aryl ether sulfates, alkyl sulfonates, sulfosuccinates, alkyl allyls and alkyl naphthalene sulfonates. , Alkyl phosphate, polyoxyethylene alkyl ether phosphate ester, alkyl allyl ether phosphate, dimethyl alkyl lauryl betaine, alkyl glycine, alkyl di (aminoethyl) glycine, imidazolinium betaine, polyoxyethylene alkyl ether, poly Oxyethylene alkyl allyl ether, polyoxyethylene polyoxypropylene glycol, glycerin ester, sorbitan ester, sucrose ester, glycerin ester polyoxyethylene ether Ether, polyoxyethylene ether of sorbitan ester, polyoxyethylene ether of sorbitol ester, fatty acid alkanolamide, polyoxyethylene fatty acid amide, amine oxide, can be exemplified polyoxyethylene alkyl amines. Further, a surfactant and a dispersion polymer may be used in combination.

  In the present invention, an azo pigment dispersion can be produced by mixing a solution containing a coupling agent, such as an alkaline solution, and a solution containing a diazonium compound, such as an acidic solution, in an arbitrary ratio. The amount of the dispersant may be equal to or less than the weight of the produced pigment, and larger particles can be obtained as the amount of the dispersant is decreased.

  The amount of the buffering agent should be sufficient to neutralize the excess hydrochloric acid in the solution containing at least the diazonium compound and to provide a buffering composition necessary for exhibiting a buffering action on the alkaline side. . Moreover, the amount corresponding to the acid value of the dispersant polymer and the amount of the buffer smaller than the sum of all of the pigment molecules produced and the excess hydrochloric acid molecules may be sufficient.

  In addition, a diazonium salt and a coupling agent may mix a some diazonium salt or a coupling agent in each solution, when it is thought that the same kind of reaction occurs from the difference in some functional groups.

  In order to use the dispersion of the present invention as an ink used in an ink jet printer, additives such as preservatives, pH adjusters, viscosity adjusters, and surfactants may be blended as necessary. The pH adjuster can be replaced with the buffer of the present invention and does not necessarily need to be added.

  The surfactant is an important element from the viewpoint of adjusting the surface tension and viscosity of the ink and facilitating the ejection from the ink jet head and at the same time improving the permeability to paper, and further defoaming. In order to satisfy these requirements, it is generally known to add a polyhydric alcohol having an ether bond in the molecule such as acetylenol.

  Trishydroxymethylaminomethane, which is a buffer of the present invention, is a polyhydric alcohol having an amino group, and has both a role as a pH adjusting agent by an amino group and a role as a surfactant. The body can be used as ink as it is.

Example 1
(Adjustment of liquid A)
2.45 g (0.021 mol) of 2-methoxy-4-nitroaniline was added to 75 g of ultrapure water and 5.45 g (0.052 mol) of 35% hydrochloric acid aqueous solution, and stirred in an ice bath to which methanol was added. Cool to 0 ° C. Thereafter, 1.45 g (0.021 mol) of sodium nitrite was dissolved in 2 ml of water and added. After stirring for 60 minutes, 0.2 g (0.0021 mol) of sulfamic acid was added to eliminate nitrous acid, and the diazonium salt Make a solution.

(Adjustment of B liquid)
4.45 g (0.0214 mol) of o-acetoacetanisidide is dissolved together with 75 g of ultrapure water and 1.244 g (0.0311 mol) of sodium hydroxide to obtain a coupler solution.

(Synthesis of Pigment Yellow (PY) 74 Dispersion)
0.03 g of styrene-acrylic copolymer (molecular weight / 4479, composition / acrylic acid: styrene = 3: 7, acid value / 198.6) was dissolved in 1 ml of solution B. Then, a 1M solution of trishydroxymethylaminomethane prepared in advance so as to have a concentration of 10 mM is added to prepare a solution (C).
(Dispersion Production (1)) 10 μl of the liquid (C) and 990 μl of ultrapure water are mixed to prepare 1 ml of a 100-fold diluted solution. Similarly, 1 ml of a 100-fold diluted solution (A) is prepared, and both are mixed 1: 1.
(Dispersion Production (2)) 1 ml of the 50-fold diluted solution of the above (C) solution is prepared, 1 ml of the 50-fold diluted solution of the (A) solution is prepared, and both are mixed 1: 1.

(Particle size distribution measurement with DLS7000)
After the dispersion obtained in (1) and (2) is diluted with ultrapure water so that the concentration becomes 1/1000 based on the liquid (A), the light scattering measurement device DLS7000 (Otsuka Electronics) is used. The particle size distribution of the dispersion particles was measured. The result of (1) is shown in FIG. 1, and the result of (2) is shown in FIG. 1 and 2, the horizontal axis of the graph represents the particle size (nm) and the vertical axis represents the measured number.

  In FIG. 1, the average value of the particle size distribution of the obtained dispersion was 57.9 nm, and the standard deviation was 27.8.

  In FIG. 2, the average value of the particle size distribution of the dispersion was 110.0 nm, and the standard deviation was 46.9.

  From these facts, it is understood that it is possible to obtain a dispersion having a desired particle size with a uniform particle size by changing the concentration of the B solution (coupling component and buffer) to be reacted with the A solution. .

(Example 2)
Ink for inkjet printers usually has a pigment concentration of 2 to 5%. In order to respond to such needs, an attempt is made to create a dispersion having a high pigment concentration.

(Adjustment of liquid A)
The same as in Example 1.

(Adjustment of B liquid)
4.45 g (0.0214 mol) of o-acetoacetanisidide was dissolved together with 75 g of ultrapure water and 2.23 g of sodium hydroxide, and 7.88 g of styrene-acrylic copolymer (equal weight with respect to pigment weight) Melt. Further, add 3.96 g of trishydroxymethylaminomethane to make a coupler solution.

(Synthesis of Pigment Yellow (PY) 74 Dispersion)
The total amount of B liquid is mixed with the total amount of A liquid.

(Particle size distribution measurement with DLS7000)
After the obtained dispersion was diluted 1/3000 times with ultrapure water, the particle size distribution of the dispersion particles was measured using a light scattering measurement device DLS7000 (Otsuka Electronics). The results are shown in FIG.

  From FIG. 3, the average value of the particle size distribution of the obtained dispersion was 36.8 nm.

(Example 3)
Here, examples in which various buffering agents are changed in the dispersion synthesis of Pigment Yellow (PY) 74 are shown. The adjustment of liquid A is the same as in Example 2. Moreover, adjustment of the B liquid which does not contain a buffering agent is performed as follows.

(Preparation of solution B without buffer)
Dissolve 0.593 g of o-acetoacetanisidide in 1N sodium hydroxide solution to 7.19 ml, and then dissolve 1.05 g of styrene-acrylic copolymer polymer. Add 2.81 ml of pure water.

(Adjustment of buffering agent and synthesis confirmation experiment of pigment yellow (PY) 74 dispersion)
50 μl of the B solution not containing the above buffer was taken, and after adding a buffer so that various buffers were contained in 43.6 μmol, the whole was made 100 μl. On the other hand, A liquid is diluted 2 times, A liquid, B liquid, and 100 microliters of each are mixed 1: 1, and transparency is confirmed with the naked eye. The results are summarized in Table 1. When buffer (1) to buffer (7) were used, a transparent suitable dispersion was obtained (indicated by ◯). When buffer materials (8) to (11) were used, an appropriate dispersion could not be obtained (indicated by x). About buffer material (8)-(11) (x), even when the quantity was changed into 2 times and 3 times, it did not reach suitable dispersion | distribution.

(Example 4 and Comparative Example 1)
Table 2 shows the pH range in which the buffer capacity of the Good buffer can be exhibited. Based on this, the relationship between the dispersibility of the buffer and the pH was confirmed. The procedure for producing the dispersion followed Example 3. However, when a sulfonic acid group was introduced, an equimolar amount of sodium hydroxide was added to the functional group.

  As a result, no dispersion was obtained for compounds having a pKa lower than MOPS (BES, MOPSO, ACES, PIPEP, ADA, Bis-Tris and MES). Further, MOPS, TES, HEPES, and DIPSO were opaque although a dispersion was obtained. When a material having a pKa higher than TAPSO, that is, TAPSO to CAPS was used, a transparent dispersion was obtained. From this, it was confirmed that the use of a buffer having a buffering action under an alkaline condition is effective for producing a transparent dispersion.

(Example 5)
A dispersion was produced in the same manner as in Examples 1 and 2 using glycine in order to confirm dispersibility in the case of using an amine in which a carboxylic acid group found in an amino acid was introduced. As a result, a transparent dispersion was obtained.

(Example 6)
Instead of the styrene-acrylic copolymer, Igepal CO-990 (trade name, manufactured by Sigma-Aldrich Japan KK) (Mn: about 4626), which is a nonionic polymer, is added with an equal weight to the pigment weight, A dispersion was produced in the same manner as in Examples 1 and 2.

  As a result, the obtained dispersion was transparent.

(Example 7)
(Adjustment of liquid A)
Disperse 5 g (0.021 mol) of 3-amino-4-methoxybenzanilide in 75 g of ultrapure water, and cool to 0 ° C. with stirring in an ice bath to which methanol has been added. Further, 6 g (0.058 mol) of 35% hydrochloric acid aqueous solution is added and stirred for 10 minutes. Then, 1.45 g (0.021 mol) of sodium nitrite was dissolved in 2 ml of ultrapure water and added. After stirring for 60 minutes, 0.2 g (0.002 mol) of sulfamic acid was added to eliminate nitrous acid and diazonium salt Make a solution.

(Adjustment of B liquid)
N- (5-chloro-2-methoxyphenyl) -3-hydroxy-2-naphthalenecarboxamide 6.95 g (0.021 mol) together with 75 g of water and 2.5 g (0.0625 mol) of sodium hydroxide at 90 ° C. After dissolution, return to room temperature to make a coupler solution.

(Synthesis of Pigment Red (PR) 269 Dispersion)
0.03 g of styrene-acrylic copolymer is dissolved in 1 ml of solution B, and a 1M solution of trishydroxymethylaminomethane prepared in advance so as to have a concentration of 10 mM is obtained as solution (C). .

  (Dispersion Production (3)) 10 μl of the liquid (C) and 990 μl of ultrapure water are mixed to prepare 1 ml of a 100-fold diluted solution. Similarly, 1 ml of a 100-fold diluted solution (A) is prepared, and both are mixed 1: 1.

  (Dispersion Production (4)) 1 ml of the 50-fold diluted solution of the above (C) solution is prepared, 1 ml of the 50-fold diluted solution of the (A) solution is prepared, and both are mixed 1: 1.

  When the dispersion obtained in (3) and (4) is measured with DLS7000 in the same manner as in (1) and (2), a pigment dispersion having an average particle size of about 40 nm and about 80 nm is obtained.

(Example 8)
The yellow pigment dispersion prepared in Example 2 was refilled into an ink tank BCI-7Y of a Canon inkjet printer PIXUS iP4100 (trade name), and printing was evaluated.
1. Fixability: After solid printing, the same paper was placed on the printing surface, and the evaluation was made by the number of seconds at which no smearing occurred. As a result, no stain was generated in less than 20 seconds, and the fixability was good.
2. Character quality: Half-width alphanumeric characters were printed, and bleeding and feathering conditions were visually observed. As a result, bleeding and feathering were both inconspicuous and good.
3. Water resistance: Half-width alphanumeric characters were printed on two sheets of paper, and then one paper was immersed in a tapper containing water overnight, taken out and air-dried to visually evaluate. As a result, the appearance of ink flowing out was not seen compared to the case where it was not immersed in water.

It is a graph which shows the particle size distribution of the dispersion obtained by this invention. It is a graph which shows the particle size distribution of the dispersion obtained by this invention. It is a graph which shows the particle size distribution of the dispersion obtained by this invention.

Claims (11)

  A method for producing an azo pigment dispersion in which a solution containing a diazonium compound and a solution containing a coupling agent are reacted to disperse an azo pigment, wherein the reaction is performed to disperse the azo pigment in a solvent. A process for producing an azo pigment dispersion, which is carried out in the presence of an agent and a pH buffer having a buffering action under alkaline conditions.   The method for producing an azo pigment dispersion according to claim 1, wherein the dispersant and the pH buffer are dissolved in a solution containing the coupling agent.   The method for producing an azo pigment dispersion according to claim 1, wherein the solution containing the diazonium compound is an acidic solution, and the solution containing the coupling agent is an alkaline solution.   The method for producing an azo pigment dispersion according to claim 3, wherein the acidic solution contains hydrochloric acid.   The azo pigment dispersion according to claim 4, wherein the pH buffering agent is present in an amount that neutralizes the excess hydrochloric acid after the neutralization reaction between the acidic solution and the alkaline solution, and further becomes alkaline. Manufacturing method.   The method for producing an azo pigment dispersion according to claim 1, wherein the pH buffering agent contains any of amines, amino acids, phosphoric acid, and carbonic acid.   The method for producing an azo pigment dispersion according to claim 6, wherein the amine contains trishydroxymethylmethane.   The method for producing an azo pigment dispersion according to claim 1, wherein the dispersant is selected from an anionic polymer or a nonionic polymer.   The method for producing an azo pigment dispersion according to claim 8, wherein the anionic polymer contains a styrene-acrylic copolymer.   The azo pigment dispersion according to claim 1, wherein pigment yellow 74 is obtained by using 2-methoxy-4-nitroaniline as a material of the diazonium compound and o-acetoacetaniside as the coupling agent. Production method. Pigment Red 269 was prepared using 3-amino-4-methoxybenzanilide as the material of the diazonium compound and N- (5-chloro-2-methoxyphenyl) -3-hydroxy-2-naphthalenecarboxamide as the coupling agent. The method for producing an azo pigment dispersion according to claim 1, wherein the azo pigment dispersion is obtained.

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