JP4748996B2 - Method for producing aqueous pigment dispersion, aqueous pigment dispersion, image recording method, recorded image, and image recording apparatus - Google Patents

Description

  The present invention relates to a method for producing an aqueous pigment dispersion, an aqueous pigment dispersion, an image recording method, an image recording product, and an image recording apparatus, and more specifically, a method for producing an aqueous pigment dispersion in which pigments are ultrafinely dispersed. An image recording method for forming an image exhibiting color development and gloss that could not be achieved conventionally, and exhibiting excellent fine particle dispersion state, ink storage stability and ejection stability when used as an ink for ink jet recording, and the like An object of the present invention is to provide an image recording apparatus such as a water-based ink jet printer equipped with.

  Color materials used in ink jet recording inks are roughly classified into dyes and pigments, but ink jet recording inks using pigments as color materials are more difficult to print than inks using dyes as color materials. It is characterized by excellent fastness such as water resistance and light resistance. The dye ink is used by dissolving a dye as a coloring material in an ink medium, whereas the pigment ink is used as a pigment dispersion in which a pigment as a coloring material is finely dispersed in the ink medium. Therefore, in the method for producing a pigment ink, a dispersion step for finely dispersing the pigment is essential.

  In particular, inkjet recording is a printing method in which ink droplets are ejected from very thin nozzles of several tens of μm to record an image, so that ink does not clog the nozzles, ink ejection stability is excellent, High color development and gloss are required on the recording medium. Furthermore, it is necessary for the ink to maintain these characteristics for a long time, that is, to have high storage stability. Pigmentization of the pigment is essential in order to give the printer satisfactory nozzle clogging resistance and ejection stability, and to give a satisfactory color density and gloss to the printed matter. To satisfy these characteristics, the pigment in the ink Is required to disperse the fine particles as much as possible.

  Pigment dispersion is an operation in which a pigment existing as an aggregate is ground or pulverized to primary particles or a state close to primary particles. A general dispersion method of a pigment is a method in which a pigment and a dispersant are dispersed in a dispersion medium. The mixed pigment dispersion is ground or dispersed by combining a dispersing device such as a ball mill or a sand mill with a dispersion medium. As the dispersion medium, beads having a diameter of about several mm to 1 mm made of a material such as glass, iron, or ceramics are used. By reducing the bead diameter, the number of beads per unit volume increases geometrically, the number of collisions between the pigment and the beads increases dramatically, and the fine particles of the pigment can be dispersed.

  However, if the bead diameter becomes too small, the mass per bead becomes small, and the impact force against the pigment becomes much weaker when colliding with the pigment, and it takes a long time to disperse the pigment, or the fine particles of the pigment. Dispersion is not possible. Furthermore, the beads and the pigment dispersion mixture cannot be separated inside the disperser. For this reason, especially when the fine particles of the pigment are dispersed, beads having a diameter of 0.2 mm to 1.0 mm are used.

  With recent high resolution and high printing speed of ink jet printers, there has been a demand for further ejection stability, high density and high gloss of pigment ink. For this reason, it is necessary to further refine the pigment dispersed particle size in the ink. That is, if the pigment particle diameter in the ink is reduced, the color density of the ink is increased, and the scattering of light by the pigment particles in the ink film can be suppressed, thereby making it possible to increase the gloss of the image. However, in the method using beads having a bead diameter in the range of 0.2 mm to 1.0 mm, it is difficult to make the pigment finer than the current method. In addition, it is possible to further refine the pigment by means such as strengthening the operating conditions of the dispersing device, for example, increasing the residence time of the pigment dispersion mixture in the dispersing device or increasing the peripheral speed of the dispersing device. However, in these methods, there are problems that the storage stability of the obtained dispersion liquid is remarkably lowered and the productivity of the dispersion liquid is lowered.

One aspect of the present invention provides the following.
1. An aqueous pigment dispersion comprising a step of ultrafinely dispersing a pigment dispersion mixed solution obtained by mixing at least a pigment and a dispersant in an aqueous medium using micro beads having a diameter of 0.02 mm or more and less than 0.2 mm. Liquid manufacturing method.
2. 2. The method for producing an aqueous pigment dispersion according to 1 above, which comprises a step of finely dispersing the pigment dispersion mixed solution in advance using beads having a diameter of 0.5 mm to 2 mm.
3. 3. The method for producing an aqueous pigment dispersion according to 2 above, which comprises a step of previously dispersing the pigment dispersion mixture into fine particles having an average particle diameter of 100 to 500 nm.
4). 2. The method for producing an aqueous pigment dispersion as described in 1 above, wherein the pigment dispersion mixture is ultrafinely dispersed with an annular disperser.
5. When the flow rate X (liter) of the pigment dispersion mixed liquid per hour of the disperser is the mill effective volume L (liter) of the disperser, the ultrafine dispersion is performed so as to satisfy the following inequality (1). 5. A method for producing an aqueous pigment dispersion according to 4.
0.005 <L / X <0.01 (1)
6). An aqueous pigment dispersion obtained by the production method described in 1 above.
7). In aqueous pigment dispersions, film-forming polymers, crosslinking agents, film-forming aids, pH adjusters, surfactants, nozzle drying inhibitors, thickeners, antifoaming agents, antiseptics, antibacterial agents and antibacterial agents 7. The aqueous pigment dispersion according to 6 above, which contains at least one additive selected from the group consisting of:
8). 8. The aqueous pigment dispersion as described in 7 above, which is an inkjet recording ink.
9. 7. An image recording method comprising performing image recording using the aqueous pigment dispersion described in 6 above.
10. 10. An image recorded matter obtained by the image recording method described in 9 above.
11. An image recording apparatus comprising the aqueous pigment dispersion described in 6 as an image recording material.
12 12. The image recording apparatus as described in 11 above, which is an aqueous ink jet printer.

More specifically, the present inventors have solved the problems of the water-based pigment ink produced by the above-described disperser, and have improved the discharge stability, concentration, and glossiness of the water-based pigment ink. As a result of diligent research to develop a dispersion method for micronization, microbeads having a diameter of 0.02 mm or more and less than 0.2 mm are used as a dispersion medium, preferably in combination with an annular circulation type disperser, and more preferably Has found that this object is achieved by dispersing the pigment so that the flow rate of the pigment dispersion mixed liquid from the disperser of the pigment dispersion mixed liquid satisfies the following inequality (1), and the present invention has been completed. It was.
0.005 <L / X <0.01 (1)
In the inequality (1), L and X have the same meaning as described above.

  Here, the flow rate of the pigment dispersion liquid mixture will be described below. The dispersing device includes a dispersing machine, a transport pump for feeding the pigment dispersion liquid mixture to the dispersing machine, and a receiving container for the pigment dispersion liquid mixture fed from the dispersing machine. The receiving container is connected to the disperser via a transport pump. The pigment dispersion mixed liquid is sent to a disperser by a transport pump, subjected to dispersion treatment, and discharged. The discharge amount per hour is defined as the flow rate of the pigment dispersion mixed solution, and this is defined as X (liter). L (liter) represents the mill effective volume of the disperser. If L / X is less than 0.005, it is difficult to make the desired pigment fine particles. If L / X is more than 0.01, it is possible to make the pigment fine particles, but the ink made from the obtained dispersion liquid. It has been found that the storage stability of the is reduced.

  An annular circulation type disperser has an annular rotor structure that rotates at high speed. The pigment dispersion mixed liquid introduced from the inlet circulates inward from the outer rotor, and the pigment dispersion mixed liquid that has passed through the mill is discharged from the central rotating screen. On the other hand, the beads circulating together with the pigment dispersion mixture are returned by the centrifugal force generated by the high speed rotation of the beads themselves at the entrance of the pigment dispersion mixture of the outer rotor through the slits or holes provided in the outer rotor. Therefore, the dispersion and the microbead can be separated without substantially contacting the microbead and the screen.

  It has been described above that the pigment dispersion is an operation of grinding or pulverizing the pigment existing as an aggregate into primary particles or a state close to the primary particles. In the initial stage of pigment dispersion, this aggregate is present as coarse particles in the pigment dispersion liquid, but when the pigment dispersion liquid introduced from the entrance of the disperser or the outer screen is discharged through the rotating screen, The problem arises that the coarse particles clog the screen. This is because the opening size of the screen that separates the pigment dispersion mixture and beads is smaller than the bead diameter used, and in the initial stage of pigment dispersion, coarse particles of a size that clogs the screen are included in the pigment dispersion mixture. is there.

As a result of intensive studies on this problem, the pigment dispersion liquid was preferably dispersed in advance into fine particles having an average particle diameter of preferably 100 to 500 nm, preferably using beads having a diameter of 0.5 mm to 2 mm. Later, it was found that the problem can be solved by performing ultrafine dispersion of the pigment by using the microbeads. Furthermore, by using microbeads, the mass per bead is reduced, and the impact force is remarkably weakened when the beads collide with the pigment, and the crystal structure of the pigment particles is not damaged. The storage stability of the pigment dispersion is greatly improved.
The aqueous pigment dispersion according to the present invention is excellent in the fine particle properties of the pigment, has few coarse particles, has a sharp particle size distribution, and can be an ink excellent in color development and storage stability.

  The ink for inkjet recording by the aqueous pigment dispersion by the production method of the present invention exhibits an excellent pigment fine particle dispersion state, storage stability and ejection stability, and forms an image exhibiting color development and gloss that could not be achieved conventionally. be able to.

  Next, the present invention will be described in more detail with reference to the best mode for carrying out the invention. The micro beads having a diameter of 0.02 mm or more and less than 0.2 mm, which are used in the present invention and characterize the present invention, are preferably ceramic micro beads made of a material such as zirconia, silicon nitride, or silicon carbide. Next, as the annular circulation type disperser, either a vertical type or a horizontal type can be used, and the microbeads are preferably filled in the range of 80 to 100% of the mill effective volume, and the particularly preferred filling amount is 85 to 100. % Range.

  Although there is no restriction | limiting in particular as a pigment included in the aqueous pigment dispersion liquid of this invention, A conventionally well-known organic pigment and an inorganic pigment can be used. For example, azo pigments, polymer azo pigments, azomethine azo pigments, phthalocyanine pigments, quinacridone pigments, anthraquinone pigments, dioxazine pigments and other organic pigments, carbon black pigments, titanium oxide pigments, iron oxide pigments, complex oxide pigments and other inorganic pigments Is mentioned.

  The dispersant is preferably an alkali-soluble polymer dispersant generally used for pigment dispersion, and is used after being dissolved in an aqueous medium. More specifically, styrene- (meth) acrylic acid copolymer, (meth) acrylic acid- (meth) acrylic acid alkyl ester copolymer, styrene- (meth) acrylic acid- (meth) acrylic acid alkyl ester copolymer Styrene-α-methylstyrene- (meth) acrylic acid- (meth) acrylic acid alkyl ester copolymer, vinylnaphthalene- (meth) acrylic acid copolymer, styrene-maleic acid copolymer, maleic acid-anhydride Maleic acid copolymer, amine salt of vinyl naphthalene-maleic acid copolymer, alkali metal salt, etc. Furthermore, polyethylene glycol mono (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, etc. are added to the above anionic copolymer. Comonomers and dimethylaminoethyl (meth) having nonionic hydrophilic groups Acrylate may be copolymerized comonomer having a cationic group, such as diethylaminoethyl (meth) acrylate. The above copolymers mean random, graft and block copolymers. Moreover, polyester, polyurethane, etc. which have hydrophilic groups, such as a carboxyl group and a sulfone group, can be used. These dispersants are used alone or in combination of two or more.

  The aqueous medium in which the pigment and the dispersant are mixed is preferably a mixture of water and an organic solvent soluble in water. Specific examples of the organic solvent soluble in water include ethylene glycol, propylene glycol, 1,3-propanediol, butylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, glycerin ethylene oxide adduct, and the above glycol Alkyl ethers (diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, diethylene glycol monopropyl ether, triethylene glycol monopropyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, polyethylene glycol monopropyl ether, polyethylene glycol monobutyl ether , Polyethylene glycol monostearyl ether, etc.) N-methylpyrrolidone, 1,3-dimethylimidazolidinone, thiodiglycol, 2-pyrrolidone, sulfolane, dimethyl sulfoxide, diethanolamine, triethanolamine, methanol, ethanol, isopropanol, neopentyl alcohol, trimethylolpropane, 2,2 -Dimethylpropanol etc. are mentioned.

  The pigment dispersion mixture used in the present invention preferably has a pigment content of 10 to 40% by mass, and the dispersant is preferably used in a ratio of 5 to 100 parts by mass with respect to 100 parts by mass of the pigment.

  For the production of the aqueous pigment dispersion of the present invention, as described above, the pigment particles are obtained by carrying out preliminary dispersion using beads having a slightly larger particle diameter than immediately performing the ultrafine dispersion process using the microbeads. It is preferable to carry out ultrafine dispersion with microbeads after the size of the material is refined to a certain extent. That is, the pigment dispersion mixed liquid composed of the above components is premixed after the pigment and the dispersant are added to the aqueous medium, and beads having a diameter of 0.5 mm to 2 mm are used as the first stage dispersion. Then, the pigment is dispersed in the form of fine particles having an average particle diameter of 100 to 500 nm, and then dispersed for a predetermined time with an annular type disperser filled with the above-mentioned microbeads as the second stage dispersion. Become.

  Water, water-soluble organic solvent, film-forming polymer, crosslinking agent, film-forming aid, pH adjuster, surfactant, nozzle drying inhibitor, thickener, antifoam Ink for inkjet recording, after mixing at least one additive selected from the group consisting of a preservative, preservative, antibacterial agent and antibacterial agent, adjusting the pigment concentration, removing coarse particles by centrifugation An aqueous pigment dispersion such as can be obtained.

  The aqueous pigment dispersion of the present invention is excellent in sharpness such as writing instrument ink, aqueous gravure ink, aqueous flexographic ink, etc. in addition to the above-mentioned ink jet recording ink, and is suitable as a high color density and high definition image forming ink. It is also used as an aqueous pigment dispersion for water-based paints and water-based printing agents.

Next, the present invention will be described more specifically with reference to examples and comparative examples. In the text, “part” or “%” is based on mass unless otherwise specified.
[Example 1]
Polymer dispersant (methacrylic acid / butyl acrylate / styrene / hydroxyethyl acrylate = copolymerized at a mass ratio of 25/50/15/10, weight average molecular weight 12,000) 40 parts 7 parts potassium hydroxide, water 23 parts and 30 parts of triethylene glycol-mono-n-butyl ether are added, and the polymerization reaction is performed by heating and stirring at 80 ° C. to prepare a polymer dispersant varnish.

  To 2.4 kg of this varnish (solid content: 43%), red pigment C.I. I. Pigment Red (hereinafter abbreviated as “PR”) 122 (dimethylquinacridone pigment) 3.0 kg, ethylene glycol 1.5 kg, and water 8.1 kg are mixed and stirred with a mixing stirrer for premixing. The pigment dispersion mixture was dispersed by a multi-pass method in a horizontal bead mill equipped with a multi-disc type impeller having an effective volume of 1.5 liters filled with 85% of 0.5 mm zirconia beads. Specifically, the bead peripheral speed was 8 m / sec, and two passes were performed at a discharge rate of 30 liters per hour to obtain a pigment dispersion mixed liquid having an average particle diameter of 325 nm. Next, circulation dispersion was performed in a horizontal annular bead mill having an effective volume of 1.5 liters filled with 95% of 0.05 mm zirconia beads. A screen of 0.015 mm is used, and a bead peripheral speed is 10 m / sec, a pigment dispersion mixed liquid volume of 10 kg is dispersed for 4 hours at a circulation rate of 300 liters / hour, and an aqueous pigment dispersion liquid with a pigment concentration of 20%. Got. The average particle size of the pigment in this dispersion was 96 nm.

  Add 25 parts of ethylene glycol, 10 parts of glycerin and 50 parts of ion-exchanged water to 25 parts of this dispersion to adjust the pigment concentration to 5%, and after stirring sufficiently, remove coarse particles by centrifugal filtration at 12,000 rpm for 30 minutes. Ink was obtained. The viscosity of the ink was 2.8 mPa · s (25 ° C.), and the average particle size of the pigment was 95 nm.

[Examples 2 and 3]
Instead of the pigment used in Example 1, the pigment of Table 1, ie, blue pigment C.I. I. Pigment Blue (hereinafter abbreviated as PB) 15: 3, yellow pigment C.I. I. Ink was obtained in the same manner as in Example 1 using Pigment Yellow (hereinafter abbreviated as PY) 74.

[Example 4]
The second-stage dispersion process performed in Example 1 was performed at a circulation rate of 200 liters / hour for 4 hours, and ink was obtained in the same manner as in Example 1.

[Reference Example 1]
The second-stage dispersion process performed in Example 1 was performed at a circulation rate of 100 liters / hour for 4 hours, and ink was obtained in the same manner as in Example 1.

[Reference Example 2]
The second-stage dispersion process performed in Example 1 was performed at a circulation rate of 500 liters / hour for 4 hours, and ink was obtained in the same manner as in Example 1.

[Comparative Examples 1-3]
Instead of the horizontal annular type bead mill used in Examples 1 to 3, a horizontal type bead mill equipped with a multi-disc type impeller having an effective volume of 1.5 liters filled with 85% of 0.5 mm zirconia beads, A circulation dispersion treatment was carried out in the same manner as in Examples 1 to 3 with a bead peripheral speed of 10 m / sec, a pigment dispersion mixed liquid amount of 10 kg and a discharge amount of 20 liters / hour, and an aqueous pigment dispersion liquid having a pigment concentration of 20% was obtained. Obtained. An ink was obtained from this aqueous pigment dispersion in the same manner as in Example 1.

[Comparative Example 4]
In place of the horizontal annular bead mill used in Example 1, circulation dispersion was performed by a horizontal bead mill having a multi-disc type impeller having an effective volume of 1.5 liters filled with 85% of 0.5 mm zirconia beads. went. An aqueous pigment dispersion having a pigment concentration of 20% was obtained by carrying out a dispersion treatment for 10 hours with a bead peripheral speed of 14 m / sec and a pigment dispersion of 10 kg at a discharge rate of 10 liter / hour. An ink was obtained from this aqueous pigment dispersion in the same manner as in Example 1.

  The average particle diameter of the pigments in the aqueous pigment dispersions obtained in Examples 1 to 4, Reference Examples 1 and 2, and Comparative Examples 1 to 4 was measured. In addition, the viscosity of the ink obtained from each dispersion and the average particle diameter of the pigment were measured before and after heating the ink at 50 ° C. for 7 days. The measurement results are shown in Table 1.

  Next, each ink was solid-printed on a dedicated glossy paper with a commercially available inkjet printer, the density was measured with a Macbeth optical densitometer, and 20 ° gloss was measured with a gloss meter. The evaluation results are shown in Table 2.

  The measurement result will be described. From Table 1, the dispersion obtained by operating an annular circulation type disperser under the condition of L / X = 0.005 using microbeads having a diameter of 0.05 mm in Examples 1 to 3, It turns out that it is excellent in fine particle dispersibility compared with the dispersion liquid (comparative examples 1-3) obtained from the conventional dispersion processing conditions. Moreover, a difference in storage stability is not recognized between the dispersion liquids of Examples 1 to 3 and the dispersion liquids of Comparative Examples 1 to 3. In Example 4, the same result as in Example 1 was obtained even under the condition of L / X = 0.005. In Reference Example 1 where L / X = 0.015 was set, the dispersion was excellent in fine particle dispersibility, but the storage stability was deteriorated. Ink obtained from such a dispersion easily changes in ink physical properties, and thus cannot guarantee long-term ejection stability. In addition, the difference in the average particle size of the ink before heating and after heating is large, and it is estimated that the dispersion according to Reference Example 1 has a particle size distribution containing many coarse particles. In Reference Example 2 in which the dispersion condition is set to L / X = 0.003, the dispersion has sufficient storage stability but is inferior in fine particle dispersibility. In Comparative Example 4, a conventional dispersion apparatus and dispersion media were used, the bead peripheral speed was increased, and the residence time of the pigment dispersion mixed liquid in the disperser was increased. Although the dispersion liquid and ink obtained in Comparative Example 4 have excellent fine particle dispersibility, the storage stability is remarkably lowered.

  From Table 2, it is apparent that there is a correlation between the pigment dispersed particle diameter of the ink, the ink density, and the gloss. That is, the ink in which the pigment is finely divided is excellent in ink density and image gloss.

  The ink for inkjet recording by the aqueous pigment dispersion by the production method of the present invention exhibits an excellent fine particle dispersion state, storage stability and ejection stability, and can form an image exhibiting color development and gloss that cannot be achieved conventionally.

Claims (8)

A method for producing an aqueous pigment dispersion for use in ink jet recording ink, wherein a pigment dispersion mixture obtained by mixing at least a pigment and a dispersant in an aqueous medium is finely dispersed using beads having a diameter of 0.5 mm to 2 mm. to process, and, by using the microbeads of less 0.2mm or more in diameter 0.02mm with annular type dispersing machine the mixture have a step of super-finely dispersed, in the above-mentioned ultrafine dispersion step, the dispersion machine It is characterized in that ultrafine dispersion is carried out so as to satisfy the following inequality (1), where X (liter) is the flow rate of the pigment dispersion liquid mixture per hour and L (liter) is the effective mill volume of the disperser. A method for producing an aqueous pigment dispersion.
0.005 ≦ L / X ≦ 0.0075 (1) Method of manufacturing a pigment dispersion mixture in a fine dispersion step, an aqueous pigment dispersion according to 請 Motomeko 1 average particle size of the pigment you dispersed particulate 100 to 500 nm.   An aqueous pigment dispersion obtained by the production method according to claim 1. Selected from the group consisting of film-forming polymers, cross-linking agents, film-forming aids, pH adjusters, surfactants, nozzle drying inhibitors, thickeners, antifoaming agents, antiseptics, antibacterial agents and antibacterial agents The aqueous pigment dispersion according to claim 3 , comprising at least one additive. An image recording method comprising performing image recording using the aqueous pigment dispersion according to claim 3 . An image recorded matter obtained by the image recording method according to claim 5 . An image recording apparatus comprising the aqueous pigment dispersion according to claim 3 as an image recording material. The image recording apparatus according to claim 7 , wherein the image recording apparatus is an aqueous inkjet printer.