Method for producing a self-dispersing hydrophilic recycled carbon black aqueous dispersion

Abstract

This invention provides a suitable method for producing a hydrophilic recycled carbon black aqueous dispersion with a highly reduced silica concentration and excellent storage stability, as well as self-dispersing properties. [Solution] A method for producing a self-dispersible hydrophilic recycled carbon black aqueous dispersion, comprising the following steps sequentially: a suspension step (i) in which recycled carbon black and synergist obtained by oxidative decomposition of self-dispersing carbon black are brought into contact in an aqueous medium; a crushing step (ii) in which the suspension is crushed; a hydrophilization step (iii) in which the crushed material-containing liquid is oxidized; a desalination step (iv) in which the oxidized material-containing liquid is desalined; a silica dissolution step (v) in which the dechlorinated liquid is heated in the presence of alkali to dissolve silica in the hydrophilic recycled carbon black; and a filtration step (vi) in which the silica-eluted material-containing liquid is filtered while being brought into contact with an alkaline aqueous solution with a pH of 9.5 to 14.0 at a temperature of 25°C to 100°C.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a self-dispersing hydrophilic recycled carbon black aqueous dispersion. [Background technology]

[0002] In recent years, efforts have been actively made to reduce the burden on the global environment, aiming for carbon neutrality and a sustainable society. The carbon black industry is also exploring the use of recycled carbon black (rCB (recovered carbon black)) obtained by thermally decomposing waste tires as part of its sustainable activities.

[0003] As a method for producing recycled carbon black by thermal decomposition of waste tires, for example, Patent Document 1 (Japanese Patent No. 5813985) discloses a method of thermally decomposing waste tires at approximately 500°C while circulating nitrogen gas.

[0004] On the other hand, carbon black having hydrophilic functional groups on its surface, which can maintain a stable dispersion state without the addition of surfactants or polymer compounds when suspended in water to form a dispersion, and whose dispersion has a surface tension almost equivalent to that of water (self-dispersing carbon black), is becoming widely used as an aqueous black pigment for inkjet printer inks and the like (see, for example, Patent Document 2). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 5813985 [Patent Document 2] Japanese Patent Publication No. 2000-319572 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Incidentally, the inventors investigated and found that when the above-mentioned recycled carbon black is oxidized to prepare an aqueous dispersion of hydrophilic recycled carbon black having acidic functional groups on its surface, the hydrophilic recycled carbon black particles tend to aggregate in the resulting aqueous dispersion due to the large amount of impurities present in the recycled carbon black, resulting in poor storage stability.

[0007] Furthermore, since waste tires, which are the raw material for the recycled carbon black mentioned above, contain a large amount of silica (SiO2) to reduce rolling resistance, a large amount of silica remains in the recycled carbon black manufactured using waste tires as a raw material.

[0008] The inventors investigated and found that when the aqueous dispersion of hydrophilic recycled carbon black obtained from the above-mentioned recycled carbon black is used in inkjet printer ink, the silica remaining in the hydrophilic recycled carbon black exhibits a high affinity for the printer nozzle, which is often made of silicon (Si), and therefore easily clogs the printer nozzle.

[0009] Under these circumstances, the present invention aims to provide a suitable method for producing an aqueous dispersion of self-dispersible hydrophilic recycled carbon black, which exhibits excellent storage stability and a significantly reduced silica concentration when hydrophilic recycled carbon black is obtained by oxidizing recycled carbon black. [Means for solving the problem]

[0010] As a result of the intensive studies by the present inventors to solve the above technical problems, a method for producing a water-based dispersion of hydrophilic regenerated carbon black having self-dispersibility, comprising: (A) a suspension step (i) of suspending the regenerated carbon black by bringing the regenerated carbon black and a synergist obtained by oxidative decomposition of self-dispersible carbon black into contact in an aqueous medium; (B) a disintegration step (ii) of subjecting the suspension obtained in the suspension step (i) to disintegration treatment; (C) a hydrophilization step (iii) of subjecting the disintegrated product-containing liquid obtained in the disintegration step (ii) to oxidation treatment to hydrophilize the regenerated carbon black into hydrophilic regenerated carbon black; (D) a desalting step (iv) of subjecting the oxidation-treated product-containing liquid obtained in the hydrophilization step (iii) to desalting treatment; (E) a silica dissolution step (v) of dissolving silica in the hydrophilic regenerated carbon black by heat-treating the desalted treatment liquid obtained in the desalting step (iv) in the presence of an alkali; and (F) a filtration step (vi) of filtering while bringing the silica eluate-containing liquid obtained in the silica dissolution step (v) into contact with an aqueous alkali solution having a pH of 9.5 or more and 14.0 or less at a temperature of 25°C or more and 100°C or less. The inventors have found that the above technical problems can be solved, and based on this finding, the present invention has been completed.

[0011] That is, the present invention provides (1) A method for producing a water-based dispersion of hydrophilic regenerated carbon black having self-dispersibility, comprising: (A) a suspension step (i) of suspending the regenerated carbon black by bringing the regenerated carbon black and a synergist obtained by oxidative decomposition of self-dispersible carbon black into contact in an aqueous medium; (B) a disintegration step (ii) of subjecting the suspension obtained in the suspension step (i) to disintegration treatment; (C) a hydrophilization step (iii) of subjecting the disintegrated product-containing liquid obtained in the disintegration step (ii) to oxidation treatment to hydrophilize the regenerated carbon black into hydrophilic regenerated carbon black; (D) a desalting step (iv) of subjecting the oxidation-treated product-containing liquid obtained in the hydrophilization step (iii) to desalting treatment; (E) A silica dissolution step (v) of dissolving silica in the hydrophilic regenerated carbon black by heat-treating the desalinated treatment liquid obtained in the desalination step (iv) in the presence of an alkali; (F) A filtration step (vi) of filtering while bringing the silica eluate-containing liquid obtained in the silica dissolution step (v) into contact with an aqueous alkali solution having a pH of 9.5 or more and 14.0 or less at a temperature of 25°C or more and 100°C or less; A method for producing an aqueous dispersion of hydrophilic regenerated carbon black having self-dispersibility, which comprises sequentially performing the above steps; (2) The method for producing an aqueous dispersion of hydrophilic regenerated carbon black having self-dispersibility according to (1), wherein the crushing treatment in the crushing step (ii) is performed by a bead mill; (3) The method for producing an aqueous dispersion of hydrophilic regenerated carbon black having self-dispersibility according to (1) or (2), wherein the heat treatment in the silica dissolution step (v) is performed at a heating temperature of 50°C or more and 100°C or less; (4) The method for producing an aqueous dispersion of hydrophilic regenerated carbon black having self-dispersibility according to any one of (1) to (3), wherein the filtration step (vi) is performed by repeatedly passing the silica eluate-containing liquid through a filtration membrane while supplying an aqueous alkali solution having a pH of 9.5 or more and 14.0 or less to the silica eluate-containing liquid; and (5) (G) The method for producing an aqueous dispersion of hydrophilic regenerated carbon black having self-dispersibility according to any one of (1) to (4), further comprising a classification step (vii) of classifying the silica-reduced treatment liquid obtained in the filtration step (vi). It is provided.

Effects of the Invention

[0012] According to the present invention, when hydrophilic regenerated carbon black is obtained by oxidizing regenerated carbon black, a method for suitably producing an aqueous dispersion of hydrophilic regenerated carbon black having self-dispersibility, in which the silica concentration is highly reduced and excellent storage stability can be exhibited, can be provided.

Brief Description of the Drawings

[0013] [Figure 1]This is a schematic diagram showing one embodiment of the filtration step (vi) in the present invention. [Modes for carrying out the invention]

[0014] The method for producing a self-dispersing hydrophilic recycled carbon black aqueous dispersion according to the present invention is: A method for producing a self-dispersing hydrophilic recycled carbon black aqueous dispersion, (A) A suspension step (i) in which recycled carbon black is suspended by contacting recycled carbon black with synergist obtained by oxidative decomposition treatment of self-dispersing carbon black in an aqueous medium, (B) A crushing step (ii) in which the suspension obtained in the suspension step (i) is crushed, (C) Hydrophilization step (iii) in which the liquid containing the pulverized material obtained in the pulverization step (ii) is oxidized to hydrophilize the recycled carbon black into hydrophilic recycled carbon black, (D) A desalination step (iv) in which the oxidized product-containing liquid obtained in the hydrophilization step (iii) is desalined, (E) A silica dissolution step (v) in which the dechlorinated solution obtained in the desalination step (iv) is heated in the presence of alkali to dissolve the silica in the hydrophilic regenerated carbon black, (F) A filtration step (vi) in which the silica eluate-containing liquid obtained in the silica dissolution step (v) is filtered while being brought into contact with an alkaline aqueous solution with a pH of 9.5 or higher and 14.0 or lower at a temperature of 25°C or higher and 100°C or lower. This method is characterized by sequentially applying the following steps.

[0015] <Suspension process> In this invention, first, (A) A suspension step (i) is performed in which recycled carbon black is suspended by contacting it with a synergist (a dispersant consisting of a pigment derivative) obtained by oxidative decomposition treatment of self-dispersing carbon black in an aqueous medium.

[0016] In the suspension step (i) of the present invention, recycled carbon black and synergist obtained by oxidative decomposition of self-dispersing carbon black are brought into contact in an aqueous medium. Due to the affinity between the rubber residues adhering to the surface, recycled carbon black tends to form aggregates, and is difficult to disperse in an aqueous medium as is. However, by bringing the recycled carbon black into contact with synergist, the aggregates of recycled carbon black are suitably dispersed in the aqueous medium, and the aggregates of recycled carbon black can be easily disintegrated in the disintegration step (ii) described later.

[0017] In the suspension step (i) of the present invention, the recycled carbon black used as a raw material is carbon black obtained by thermal decomposition of waste tires, and rubber residue mainly composed of rubber carbides is attached to the surface of the recycled carbon black. Examples of the recycled carbon black mentioned above include one or more selected from products such as PB365 (manufactured by Enrestec), BolderBlack (manufactured by Bolder Industries), DE-Black (manufactured by Delta Energy), and MondoBlack (manufactured by ECOLOMONDO). Such recycled carbon black may be produced by any manufacturing method, and is not particularly limited, but examples include the method described in WO2013 / 095145A1.

[0018] In the suspension step (i) of the present invention, the silica concentration of the recycled carbon black used as a raw material is not particularly limited, but since waste tires used as a raw material for the recycled carbon black contain a large amount of silica, it is, for example, 5.0% by mass or more and 40.0% by mass or less.

[0019] In the suspension step (i) of the present invention, the recycled carbon black is brought into contact with a synergist obtained by oxidative decomposition of self-dispersing carbon black in an aqueous medium.

[0020] In the suspension step (i) of the present invention, the self-dispersing carbon black that serves as the raw material for Synergist means a carbon black that, when suspended in water to form a dispersion, can maintain a stable dispersion state without the addition of surfactants or polymer compounds, and whose surface tension is almost the same as that of water. Because carbon black has an oil-lipid surface, self-dispersing carbon black typically uses hydrophilic carbon black, which is made hydrophilic by adding acidic functional groups to the surface of the carbon black to impart self-dispersibility.

[0021] To obtain the above-mentioned self-dispersing carbon black, the acidic functional group introduced to the surface of the carbon black is not particularly limited, and can be one or more selected from, for example, sulfonic acid groups, phosphoric acid groups, carboxyl groups, hydroxyl groups, etc. Of these, the acidic functional group introduced to the surface of the carbon black to obtain the self-dispersing carbon black is preferably an acidic functional group with an acid dissociation constant (pKa) of 1.90 or more and 10.00 or less, with carboxyl groups and sulfonic acid groups being particularly preferred. The amount of these acidic functional groups introduced can be controlled, for example, by gas-phase oxidation conditions or liquid-phase oxidation conditions described below. The above acid dissociation constant (pKa) refers to the value calculated as the logarithm of the reciprocal of the equilibrium constant Ka obtained when hydrogen ions are released from an acidic functional group in an aqueous solution at 25°C.

[0022] Known methods for introducing acidic functional groups to the surface of carbon black in order to obtain the above-mentioned self-dispersing carbon black include liquid-phase methods, gas-phase methods, and methods combining these.

[0023] When oxidation is performed by the liquid-phase method, various oxidizing agents can be used, such as hydrogen peroxide, nitric acid, sulfuric acid, chlorates, persulfates, perborates, percarbonates, hypochlorites, and chlorites. For example, by adding carbon black to an aqueous solution containing the above oxidizing agent and stirring, carbon black having acidic functional groups on its surface can be obtained. By controlling the amount of oxidizing agent added and the reaction temperature, acidic functional groups can be uniformly introduced to the surface of the carbon black.

[0024] Furthermore, when performing oxidation treatment using a gas-phase method, one method is to use ozone or air as an oxidizing agent and bring it into contact with carbon black for oxidation. According to the above gas-phase method, there are no drying costs and oxidation treatment can be performed more easily compared to the liquid-phase method.

[0025] Furthermore, methods for introducing acidic functional groups such as sulfonic acid groups, phosphate groups, and carboxyl groups to the surface of carbon black include introducing acidic functional groups to the surface of carbon black by a coupling reaction with a diazonium salt, introducing acidic functional groups to the surface of carbon black by contacting carbon black with free oxygen at high temperatures, and introducing acidic functional groups to the surface of carbon black by treating the surface of carbon black with bromine and water under normal or pressurized pressure.

[0026] Examples of self-dispersing carbon blacks in which acidic functional groups are imparted to the surface of carbon black by oxidation methods such as the liquid-phase method or gas-phase method described above include Aqua-Black® 162, Aqua-Black® 204 (both manufactured by Tokai Carbon Co., Ltd.), BONJET® BLACK CW-2, and BONJET® BLACK CW-3 (both manufactured by Orient Chemical Industry Co., Ltd.).

[0027] In the suspension step (i) of the present invention, recycled carbon black is brought into contact with a synergist obtained by oxidative decomposition of the self-dispersing carbon black. One method for oxidative decomposition of self-dispersing carbon black is to apply an oxidation treatment to the self-dispersing carbon black that is similar to the method used to introduce acidic functional groups to the surface of carbon black as described above. Specifically, one method involves adding the various oxidizing agents described above to an aqueous dispersion of self-dispersing carbon black and oxidizing it. In the suspension step (i) of the present invention, as a method for oxidative decomposition of self-dispersing carbon black, a method of adding various oxidizing agents to self-dispersing carbon black in a liquid phase is preferred from the viewpoint of obtaining synergists more easily.

[0028] Self-dispersing carbon black is decomposed by the above oxidative decomposition treatment, and the decomposition products containing acidic functional groups formed on the surface are generated as humic acid.

[0029] The synergist used in the suspension step (i) of the present invention may be the humic acid itself, but from the viewpoint of improving the dispersibility of recycled carbon black, it is preferable to use a humic acid salt obtained by neutralizing the humic acid.

[0030] In the suspension step (i) of the present invention, the humic acid or humic acid salt used as a synergist is derived from self-dispersing carbon black, and because the humic acid or humic acid salt is derived from self-dispersing carbon black, its affinity with the recycled carbon black to be adsorbed can be easily improved.

[0031] In the suspension step (i) of the present invention, the amount of synergist to be brought into contact with the recycled carbon black is preferably 0.5 parts by mass or more and 5.0 parts by mass or less per 100.0 parts by mass of recycled carbon black, from the viewpoint of suitably adsorbing the synergist onto the recycled carbon black. Furthermore, in the suspension step (i) of the present invention, when synergist is brought into contact with recycled carbon black in the form of a synergist-containing liquid, the concentration of synergist in the synergist-containing liquid is not particularly limited, but is preferably 0.1% by mass or more and 0.5% by mass or less.

[0032] In addition, in the suspension step (i) of the present invention, the concentration of synergist in the synergist-containing solution, that is, the concentration of humic acid or humic acid salt in the synergist-containing solution, can be calculated, for example, by drying the synergist-containing solution and measuring the mass before and after drying.

[0033] In the suspension step (i) of the present invention, recycled carbon black and synergist obtained by oxidative decomposition of self-dispersing carbon black are brought into contact in an aqueous medium. The aqueous medium is not particularly limited and can include water or a mixture of water and a water-soluble organic solvent. However, water is preferred from the standpoint of economy and safety, and deionized water is particularly preferred.

[0034] In the suspension step (i) of the present invention, the synergist obtained by oxidative decomposition of self-dispersing carbon black can be specifically, as described above, obtained by adding various oxidizing agents to an aqueous dispersion of self-dispersing carbon black, in which case it will be obtained as synergist-containing water. Therefore, in the suspension step (i) of the present invention, methods for contacting the recycled carbon black with synergist obtained by oxidative decomposition of self-dispersing carbon black in an aqueous medium include adding the recycled carbon black to synergist-containing water obtained by the above method, or adding the synergist-containing water obtained by the above method to the recycled carbon black. The contact between the recycled carbon black and synergist may be promoted by stirring after either of the above additions.

[0035] The synergist used in the suspension step (i) of the present invention is obtained by oxidative decomposition of self-dispersing carbon black, and since it is derived from self-dispersing carbon black, it is compatible with recycled carbon black and can therefore be suitably used as a synergist.

[0036] In the suspension step (i) of the present invention, by bringing recycled carbon black into contact with synergist obtained by oxidative decomposition treatment of self-dispersing carbon black, the synergist is adsorbed onto the surface of aggregates of recycled carbon black, thereby ensuring a certain degree of dispersibility in an aqueous medium.

[0037] In other words, as described above, recycled carbon black tends to form aggregates and is difficult to disperse in an aqueous medium as is. However, in the present invention, in the suspension step (i), the recycled carbon black is brought into contact with and adsorbed with the above-mentioned specific synergist, and the aggregates of recycled carbon black are dispersed in an aqueous medium to form a suspension. This allows the aggregates of recycled carbon black to be suitably broken down in the crushing step (ii) described in detail below, and also allows the recycled carbon black to be subjected to a smooth oxidation treatment in the hydrophilization step (iii).

[0038] <Crushing process> In the present invention, (B) the suspension obtained in the suspension step (i) is subjected to a crushing step (ii).

[0039] In the present invention, the suspension disintegration treatment refers to a wet treatment in which mechanical energy is applied to the suspension (liquid containing aggregates of recycled carbon black) obtained in suspension step (i) to break down the aggregates of recycled carbon black into individual recycled carbon black pieces.

[0040] In the present invention, although a certain degree of dispersibility in an aqueous medium can be ensured by contacting the recycled carbon black with synergist in the suspension step (i), the recycled carbon black remains in an aggregated state. In the present invention, by further subjecting the suspension obtained in the suspension step (i) to a crushing step (ii), aggregates of recycled carbon black can be broken down into individual recycled carbon black pieces.

[0041] In the present invention, the crushing process in the crushing step (ii) can be any of the following methods (a) to (d). (a) A method using a bead mill that utilizes the shear force of high-speed stirring with media such as beads (bead mill method). (b) A method of causing pressurized suspensions to collide with each other (liquid-liquid collision method). (c) A method that utilizes cavitation and shear force, in which a pressurized suspension is passed through a fine channel, and the cavity generated by the rapid pressure drop at this time is eliminated by passing it through a wider channel, and the impact force generated when it is eliminated destroys the particles and aggregates (a method using a homogenizer). (d) A method of impacting a pressurized suspension onto a hard body (hard body impact method).

[0042] In the present invention, the bead milling method using the bead mill described above (a) is preferred as the crushing process method in the crushing step (ii). In the present invention, if the bead mill method described above (a) is adopted as the crushing method in the crushing step (ii), the processing conditions can be appropriately selected from known conditions according to the required application.

[0043] In the present invention, by performing a crushing step (ii) together with a suspension step (i), the individual recycled carbon black particles are separated from the aggregated mass of recycled carbon black, and the synergist added in the suspension step (i) is further adsorbed onto the surface of the individual recycled carbon black particles, thereby further improving the dispersibility of recycled carbon black in an aqueous medium. In this invention, the crushing step (ii) is performed after the suspension step (i). However, if the suspension step (i) and the crushing step (ii) can be performed simultaneously, they may be performed simultaneously.

[0044] <Hydrophilization process> In the present invention, (C) the liquid containing the pulverized material obtained in the pulverization step (ii) is subjected to an oxidation treatment to hydrophilize the recycled carbon black into hydrophilic recycled carbon black in a hydrophilicization step (iii).

[0045] In the present invention, the hydrophilization step (iii) means a step of oxidizing the liquid containing the pulverized material obtained in the pulverization step (ii) to impart acidic functional groups to the surface of the recycled carbon black contained in the liquid containing the pulverized material, thereby hydrophilizing it and obtaining an oxidized liquid containing hydrophilic recycled carbon black.

[0046] In this invention, hydrophilic recycled carbon black refers to recycled carbon black having acidic functional groups on its surface. While hydrophilic recycled carbon black exhibits hydrophilicity, this hydrophilicity simply means a high affinity for water. It is distinct from self-dispersing hydrophilic recycled carbon black obtained by the manufacturing method according to the present invention, which can maintain a stable dispersion state without the addition of surfactants or polymer compounds when suspended in water to form a dispersion, and whose dispersion exhibits a surface tension almost equivalent to that of water.

[0047] In the hydrophilization step (iii), the acidic functional groups introduced to the surface of the recycled carbon black are not particularly limited, and can include, for example, one or more selected from sulfonic acid groups, phosphate groups, carboxyl groups, hydroxyl groups, etc. The amount of these introduced can be controlled, for example, by the liquid-phase oxidation conditions described below.

[0048] In the hydrophilization step (iii) of the present invention, as a method for hydrophilizing the recycled carbon black by imparting acidic functional groups to the surface of the recycled carbon black, a method of adding an oxidizing agent to the liquid containing the pulverized material obtained in the pulverization step (ii) and subjecting the recycled carbon black to wet oxidation, i.e., oxidation treatment by a liquid phase method, is preferred from the viewpoint of uniformly introducing acidic functional groups to the surface of the recycled carbon black.

[0049] When oxidation is performed by the liquid phase method, one or more oxidizing agents selected from hydrogen peroxide, nitric acid, sulfuric acid, chlorates, persulfates, perborates, percarbonates, hypochlorites, chlorites, etc., can be used as the oxidizing agent. For example, by adding an oxidizing agent to the liquid containing the pulverized material obtained in the pulverization step (ii) and stirring it, an oxidized product-containing liquid containing hydrophilic recycled carbon black having acidic functional groups on its surface can be obtained. At this time, by controlling the amount of oxidizing agent added and the reaction temperature, acidic functional groups can be uniformly introduced to the surface of the recycled carbon black contained in the liquid containing the pulverized material.

[0050] In these oxidation treatments, the concentration of the oxidizing agent used, the amount of recycled carbon black to be oxidized, the reaction temperature, the reaction time, etc., should be appropriately selected according to the characteristics of each oxidizing agent. In this invention, the hydrophilization step (iii) is performed after the crushing step (ii). However, if the hydrophilization step (iii) can be performed simultaneously with the suspension step (i) and the crushing step (ii), the suspension step (i), the crushing step (ii), and the hydrophilization step (iii) may be performed simultaneously.

[0051] <Desalination process> In the present invention, (D) a desalination step (iv) is performed to desalinate the oxidized product-containing liquid obtained in the hydrophilization step (iii). The oxidized product-containing liquid obtained in the hydrophilization process (iii) contains hydrophilic recycled carbon black, salts reduced by the oxidizing agent, and an aqueous medium. The concentration of salts in this oxidized product-containing liquid is usually very high, so the ionization of protons of acidic functional groups formed on the surface of the hydrophilic recycled carbon black is suppressed by salting out, and the dispersibility of the hydrophilic recycled carbon black in water is significantly reduced.

[0052] Therefore, in the present invention, the oxidized product-containing liquid obtained in the hydrophilization step (iii) is subjected to a desalination step (iv) in order to reduce the salt concentration in the solution. Methods for reducing the salt concentration in the oxidized product-containing liquid obtained in the hydrophilization process (iii), namely the desalination treatment performed in the desalination process (iv), include decantation using coagulation by salting out of hydrophilic recycled carbon black, and membrane separation using a membrane to separate the aqueous medium and hydrophilic recycled carbon black. Examples of filtration membranes used in the membrane separation method include ultrafiltration membranes, microfiltration membranes, and reverse osmosis membranes. While any of these treatment methods are acceptable, membrane separation using an ultrafiltration membrane is suitable considering efficiency.

[0053] The salt concentration in the above solution is expressed by the electrical conductivity (mS / cm) when protons of acidic functional groups formed by oxidation treatment or other processes, or when salts are ionized. Higher salt concentrations result in higher electrical conductivity.

[0054] In the desalination step (iv) of the present invention, the electrical conductivity of the desalination-treated oxidized product-containing liquid, i.e., the dechlorinated liquid, is preferably 0.5 mS / cm or less, more preferably 0.4 mS / cm or less, and even more preferably 0.3 mS / cm or less. While a lower electrical conductivity of the dechlorinated liquid is preferable, it is usually 0.0005 mS / cm or higher.

[0055] In this application, the above electrical conductivity (mS / cm) refers to the value measured in accordance with JIS K 0130:2008.

[0056] In the present invention, after performing the suspension step (i) and crushing step (ii), the hydrophilization step (iii) and desalination step (iv) are performed to reduce the salt concentration of the reducing salt of the oxidizing agent contained in the oxidized product-containing liquid, thereby improving the dispersibility of the hydrophilic recycled carbon black in an aqueous medium.

[0057] <Silica Dissolution Process> In the present invention, (E) a silica dissolution step (v) is performed, in which the dechlorinated solution obtained in the desalination step (iv) is heated in the presence of alkali to dissolve the silica in the hydrophilic regenerated carbon black.

[0058] The alkali used in the silica dissolution step (v) of the present invention refers to a compound that exhibits basicity in water. Examples of the alkalis mentioned above include organic alkaline compounds such as tertiary amines and phosphines, inorganic alkaline compounds such as potassium hydroxide, sodium hydroxide, calcium hydroxide, calcium carbonate, potassium bicarbonate, sodium carbonate, sodium bicarbonate, lithium bicarbonate, sodium dithionite (sodium hydrosulfite), and organometallic salt alkaline compounds such as sodium methoxide and t-butoxypotassium. Among these alkalis, inorganic alkaline compounds are preferred because they are inexpensive and relatively safe. Specifically, the alkalis are preferably one or more compounds selected from potassium hydroxide, sodium hydroxide, calcium hydroxide, calcium carbonate, potassium bicarbonate, and sodium bicarbonate, more preferably one or more compounds selected from alkali metal hydroxides such as potassium hydroxide and sodium hydroxide, and even more preferably sodium hydroxide.

[0059] In the silica dissolution step (v) of the present invention, when the dechlorinated liquid obtained in the desalination step (iv) is heat-treated in the presence of alkali, it is preferable to control the alkali concentration in the mixture obtained by mixing alkali with the dechlorinated liquid so that it is 1.0% by mass or more and 20.0% by mass or less. From the viewpoint of increasing the solubility of silica, the alkali concentration in the mixed solution obtained by mixing alkali with the dechlorination treatment solution is preferably 1.0% by mass or more, more preferably 2.0% by mass or more, and even more preferably 2.5% by mass or more. Furthermore, from the viewpoint of suppressing the aggregation of recycled carbon black contained in the dechlorination treatment solution, the alkali concentration is preferably 20.0% by mass or less, more preferably 10.0% by mass or less, even more preferably 7.5% by mass or less, and particularly preferably 5.0% by mass or less.

[0060] In the silica dissolution step (v) of the present invention, by controlling the alkali concentration in the mixture obtained by mixing alkali with the dechlorination treatment solution within the above range, the hydrophilic regenerated carbon black contained in the dechlorination treatment solution can be suitably neutralized, and the elution of silica from the hydrophilic regenerated carbon black can be promoted and the eluted silica product can be suitably dissolved in the solution.

[0061] The heat treatment in the silica dissolution step (v) of the present invention is preferably carried out at a heating temperature of 50°C to 100°C, more preferably at a temperature of 70°C to 100°C from the viewpoint of efficiently dissolving silica, and even more preferably at a temperature of 80°C to 100°C.

[0062] By having the heat treatment temperature in the silica dissolution step (v) of the present invention fall within the above range, the elution of silica from recycled carbon black, such as the hydrolysis of silica (SiO2) described below, can be suitably promoted.

[0063] Generally, silica is known to be poorly soluble in aqueous media such as water, and furthermore, there has been no known method for dissolving silica from hydrophilic recycled carbon black into an aqueous medium. However, the inventors have found that by heating the dechlorinated solution obtained in the above desalination step (iv) in the presence of alkali, silica in the hydrophilic regenerated carbon black contained in the dechlorinated solution can be suitably dissolved into an aqueous medium such as water. In this case, for example, if the aqueous medium is water (H2O), it is thought that the silica (SiO2) undergoes hydrolysis to produce monosilicic acid (Si(OH)4) and the like in the solution, as shown in the reaction equation below. [ka]

[0064] In the present invention, by controlling the alkali concentration or heating temperature in the mixture obtained by mixing alkali with the dechlorination treatment solution, silica can be suitably eluted from hydrophilic regenerated carbon black and dissolved in the above mixture.

[0065] In the present invention, a specific embodiment of the silica dissolution step (v) is, for example, an embodiment in which the dechlorinated liquid obtained in the desalination step (iv) is brought into contact with a solid alkali or an alkaline aqueous solution under heating and stirred as appropriate, thereby thermally neutralizing the hydrophilic recycled carbon black contained in the dechlorinated liquid and dissolving the silica in the recycled carbon black into an aqueous medium.

[0066] In the present invention, following the suspension step (i), crushing step (ii), hydrophilization step (iii), and desalination step (iv), a silica dissolution step (v) is further performed to thermally neutralize the hydrophilic recycled carbon black contained in the dechlorination treatment liquid and to suitably dissolve the silica in the recycled carbon black into an aqueous medium.

[0067] <Filtration process> In the present invention, (F) the silica eluate-containing liquid obtained in the silica dissolution step (v) is subjected to a filtration step (vi) in which it is filtered while in contact with an alkaline aqueous solution with a pH of 9.5 to 14.0 at a temperature of 25°C to 100°C.

[0068] The silica eluate-containing liquid obtained in the silica dissolution process (v) is thought to contain hydrophilic recycled carbon black obtained by oxidizing recycled carbon black, silica eluates such as metasilicic acid and monosilicic acid (Si(OH)4), and an aqueous medium. As described above, the silica elute is likely to clog printer nozzles when the self-dispersible hydrophilic recycled carbon black aqueous dispersion obtained by the manufacturing method according to the present invention is used in inkjet printer ink. Therefore, in the present invention, the silica elute is filtered in filtration step (vi).

[0069] The filtration method in step (vi) of the present invention is not particularly limited, but examples include reverse osmosis, ultrafiltration, microfiltration, and coarse filtration, and ultrafiltration is particularly preferred when considering efficiency.

[0070] In the filtration step (vi) of the present invention, the silica eluate-containing liquid obtained in the silica dissolution step (v) is brought into contact with an alkaline aqueous solution with a pH of 9.5 to 14.0.

[0071] In the present invention, the alkaline aqueous solution used in the filtration step (vi) means an aqueous solution of a compound (alkali) that exhibits basicity in water. Examples of the alkalis mentioned above include organic alkaline compounds such as tertiary amines and phosphines, inorganic alkaline compounds such as potassium hydroxide, sodium hydroxide, calcium hydroxide, calcium carbonate, potassium bicarbonate, sodium carbonate, sodium bicarbonate, lithium bicarbonate, sodium dithionite (sodium hydrosulfite), and organometallic salt alkaline compounds such as sodium methoxide and t-butoxypotassium. Among these, inorganic alkaline compounds are preferred because they are inexpensive and relatively safe. Specifically, the alkalis are preferably one or more compounds selected from potassium hydroxide, sodium hydroxide, calcium hydroxide, calcium carbonate, potassium bicarbonate, and sodium bicarbonate, more preferably one or more compounds selected from alkali metal hydroxides such as potassium hydroxide and sodium hydroxide, and even more preferably sodium hydroxide.

[0072] In the present invention, the pH of the alkaline aqueous solution that comes into contact with the silica eluate-containing liquid in the filtration step (vi) is 9.5 or higher and 14.0 or lower. The pH of the alkaline aqueous solution that comes into contact with the silica eluate-containing liquid is preferably higher from the viewpoint of efficiently removing silica, but from the viewpoint of reducing the load on the filtration membrane used in the filtration step (vi), it is preferably 9.5 to 12.0, and more preferably 9.5 to 10.5. In this invention, pH refers to the value obtained at 25°C by the method specified in JIS Z 8802. By having the pH of the alkaline aqueous solution in the filtration step (vi) of the present invention be within the above predetermined range, the elution of silica from hydrophilic recycled carbon black is promoted, and the filtration process can be performed with the silica eluate sufficiently dissolved in the silica eluate-containing liquid. In this case, it is thought that the reaction in which monosilicic acid (Si(OH)4) etc. is produced from silica (SiO2) and water (H2O) in the equilibrium reaction in the example described above is accelerated.

[0073] In the present invention, in the filtration step (vi), the silica eluate-containing liquid obtained in the silica dissolution step (v) is filtered while being in contact with an alkaline aqueous solution with a pH of 9.5 to 14.0 at a temperature of 25°C to 100°C. In the filtration step (vi), the holding temperature when the silica eluate-containing liquid obtained in the silica dissolution step (v) is brought into contact with the alkaline aqueous solution is between 25°C and 100°C. The holding temperature when the silica eluate-containing liquid is brought into contact with the alkaline aqueous solution is preferably 30°C or higher, and more preferably 40°C or higher, from the viewpoint of efficiently removing silica. Furthermore, the holding temperature when the silica eluate-containing liquid is brought into contact with the alkaline aqueous solution is preferably 90°C or lower, more preferably 80°C or lower, even more preferably 70°C or lower, and particularly preferably 60°C or lower, from the viewpoint of balancing the efficiency and economic vi of the filtration step (vi).

[0074] In the present invention, by bringing the silica eluate-containing liquid into contact with the alkaline aqueous solution in the filtration step (vi) and holding it at a temperature of 25°C to 100°C, the elution of silica from hydrophilic recycled carbon black can be promoted, and the filtration process can be performed with the silica eluate sufficiently dissolved in the silica eluate-containing liquid. In this case, it is thought that the reaction in which monosilicic acid (Si(OH)4) etc. is produced from silica (SiO2) and water (H2O) in the equilibrium reaction in the example described above is accelerated.

[0075] In the present invention, in the filtration step (vi), the silica eluate in the silica eluate-containing liquid obtained in the silica dissolution step (v) is separated by filtration, i.e., by membrane separation using a filtration membrane.

[0076] In the present invention, filtration in the filtration step (vi) may be performed by passing the silica eluate-containing solution obtained in the silica dissolution step (v) through the filtration membrane only once while contacting it with an alkaline aqueous solution with a pH of 9.5 to 14.0, or by repeatedly passing the silica eluate-containing solution through the filtration membrane while supplying an alkaline aqueous solution with a pH of 9.5 to 14.0. In the filtration step (vi) of the present invention, filtration is performed by repeatedly passing the silica eluate-containing liquid obtained in the silica dissolution step (v) through a filtration membrane while supplying an alkaline aqueous solution with a pH of 9.5 to 14.0, thereby sufficiently removing the silica eluate from the silica eluate-containing liquid.

[0077] As an example of a method for performing filtration in the filtration step (vi) of the present invention by repeatedly passing an alkaline aqueous solution with a pH of 9.5 to 14.0 over a filtration membrane while supplying the silica eluate-containing liquid obtained in the silica dissolution step (v), the following method can be given.

[0078] In other words, a purification apparatus having a stock solution tank for storing a liquid to be treated containing silica eluate, an alkaline aqueous solution storage tank for storing an alkaline aqueous solution, and a filtration device housing a filtration membrane, and also having an alkaline aqueous solution supply pipe for supplying the alkaline aqueous solution from the alkaline aqueous solution storage tank to the stock solution tank, and a circulation pipe for passing the liquid to be treated from the stock solution tank to the filtration device and then returning the liquid to be treated to the stock solution tank, One possible method is to supply the alkaline aqueous solution from the alkaline aqueous solution storage tank to the stock solution tank, pass the liquid to be treated from the stock solution tank to the filtration device, and then return the liquid to be treated to the stock solution tank, while circulating the liquid to be treated.

[0079] More specifically, the following forms can be cited. Figure 1 is a schematic diagram showing one embodiment of the filtration step (vi) of the present invention. In the configuration shown in Figure 1, the purification apparatus R comprises a stock solution tank 1 for storing the liquid to be treated containing silica eluate, an alkaline aqueous solution storage tank 2 for storing an alkaline aqueous solution with a pH of 9.5 to 14.0, and an ultrafiltration device 3 containing an ultrafiltration membrane. It also includes an alkaline aqueous solution supply pipe t1 for supplying the alkaline aqueous solution from the alkaline aqueous solution storage tank 2 to the stock solution tank 1, and a circulation pipe t for returning the liquid to be treated from the stock solution tank 1 to the ultrafiltration device 3 and then back to the stock solution tank 1. 21 and t 22 It has. In the above purification apparatus R, (1) the required amount of alkaline aqueous solution with a pH of 9.5 to 14.0 is supplied from the alkaline aqueous solution storage tank 2 to the raw material tank 1 by pump P1 via the alkaline aqueous solution supply pipe t1, and (2) the circulation liquid supply pipe t is supplied from the raw material tank 1 by pump P2. 21 (3) The liquid to be treated is passed through the ultrafiltration device 3 via the ultrafiltration membrane, the silica-containing waste liquid 4 that has been treated and membrane-separated by the ultrafiltration membrane is discharged from the ultrafiltration device 3, and (4) the liquid to be treated from which the silica-containing waste liquid 4 has been removed is passed through the circulation pipe t 22 The liquid is returned to the stock solution tank 1 via the above-mentioned method, while the liquid to be treated is being circulated (the operations (1) to (4) above are repeated).

[0080] In the present invention, in the filtration step (vi) performed by repeatedly passing the silica-containing liquid obtained in the silica dissolution step (v) through a filtration membrane while supplying an alkaline aqueous solution with a pH of 9.5 to 14.0, it is preferable that the purification ratio (the volume ratio calculated by "total amount of alkaline aqueous solution passed through for purification / amount of liquid to be treated") is high. The higher the purification ratio, the more the silica concentration in the self-dispersing hydrophilic recycled carbon black aqueous dispersion obtained in the present invention can be reduced. In the filtration step (vi) of the present invention, the purification ratio is preferably higher, more preferably 10 times or more, more preferably 30 times or more, and particularly preferably 50 times or more, from the viewpoint of further reducing the silica concentration. Furthermore, in the filtration step (vi) of the present invention, from the viewpoint of balancing the reduction in silica concentration and the economic efficiency of the filtration step (vi), the purification ratio is preferably 120 times or less, more preferably 100 times or less, and particularly preferably 80 times or less.

[0081] In the filtration step (vi) of the present invention, by repeatedly passing the silica eluate-containing liquid obtained in the silica dissolution step (v) through a filtration membrane while supplying an alkaline aqueous solution with a pH of 9.5 to 14.0, the silica eluate in the silica eluate-containing liquid can be removed more easily and sufficiently.

[0082] In the present invention, by performing a filtration step (vi) after the silica dissolution step (v), the silica eluate in the silica eluate-containing liquid obtained in the silica dissolution step (v) can be effectively removed. In this invention, the silica reduction treatment liquid obtained by the filtration step (vi) is in a state in which the acidic functional groups formed on the surface of the hydrophilic recycled carbon black are neutralized, and the concentration of salts and other substances that cause the electrical double layer of the hydrophilic recycled carbon black to thin is sufficiently reduced. Therefore, the hydrophilic recycled carbon black contained in the silica reduction treatment liquid obtained by the filtration step (vi) exhibits self-dispersion properties. In the present invention, the silica concentration of the silica-reduced treatment liquid obtained by the filtration step (vi) is preferably 0.010% by mass or more and 3.300% by mass or less, more preferably 0.030% by mass or more and 1.000% by mass or less, and even more preferably 0.050% by mass or more and 0.100% by mass or less.

[0083] In the present invention, it is preferable to further perform a classification step (vii) in which the silica-reduced liquid obtained in the filtration step (vi) is subjected to classification.

[0084] In the present invention, by further performing a classification step (vii), undispersed clumps and coarse particles remaining in the silica reduction treatment liquid obtained in the filtration step (vi) can be suitably removed.

[0085] In the present invention, the classification process in the classification step (vii) is preferably carried out by methods such as centrifugal separation or filtration. When performing classification by centrifugal separation, methods such as using a horizontal decanter, a rotor-type high-speed centrifuge, a vertical centrifuge, or a separation plate type separator can be used. When classifying materials by filtration, methods such as using depth filters, pleated filters, membrane filters, etc., or using multiple filters in stages, can be used to effectively classify the materials. Furthermore, performing filtration after centrifugation allows for more precise classification.

[0086] In the present invention, by further subjecting the silica-reduced treated liquid obtained in the filtration step (vi) to a classification step (vii), the resulting self-dispersing hydrophilic recycled carbon black aqueous dispersion can be used in an aqueous inkjet printer ink composition to easily suppress nozzle clogging of the printer.

[0087] <Self-dispersing hydrophilic recycled carbon black> The self-dispersing hydrophilic recycled carbon black obtained by the manufacturing method of the present invention is formed in which acidic functional groups are directly bonded to the surface of recycled carbon black particles, and examples of acidic functional groups include carboxyl groups, hydroxyl groups, lactone groups, and the like.

[0088] The amount of hydroxyl groups on the surface of the self-dispersing hydrophilic recycled carbon black obtained by the production method of the present invention is preferably 50 μmol / g or more and 300 μmol / g or less per unit mass of the self-dispersing hydrophilic recycled carbon black, more preferably 50 μmol / g or more and 250 μmol / g or less, and even more preferably 50 μmol / g or more and 200 μmol / g or less.

[0089] In this application, the amount of hydroxyl groups on the surface of self-dispersing hydrophilic recycled carbon black particles refers to the value calculated by the following method: 1.0 g of self-dispersing hydrophilic recycled carbon black, obtained by drying an aqueous dispersion of self-dispersing hydrophilic recycled carbon black, is added to 100 ml of 3.0 N hydrochloric acid, shaken for 3 hours, and then filtered using an ultrafiltration membrane at a concentration of 4% by mass of self-dispersing hydrophilic recycled carbon black until the electrical conductivity is 0.2 mS / cm or less. This process is repeated three times and then dried again. 2,2'-diphenyl-1-picrylhydrazyl is dissolved in carbon tetrachloride, and 5 × 10⁻⁶ of the solution is added. -4 Prepare a mol / L solution. Add 0.1 to 0.6 g of the washed, self-dispersing hydrophilic recycled carbon black to the solution, stir in a 60°C constant temperature bath for 6 hours, filter the solution, measure the absorbance of the filtrate with an ultraviolet spectrophotometer to determine the amount of hydroxyl groups, and divide the obtained amount of hydroxyl groups by the mass of the self-dispersing hydrophilic recycled carbon black to calculate the amount of hydroxyl groups per unit mass of the self-dispersing hydrophilic recycled carbon black.

[0090] The amount of carboxyl groups on the surface of the self-dispersing hydrophilic recycled carbon black obtained by the production method of the present invention is preferably 150 μmol / g or more and 1200 μmol / g or less per unit mass of the self-dispersing hydrophilic recycled carbon black, more preferably 300 μmol / g or more and 1200 μmol / g or less, and even more preferably 400 μmol / g or more and 1200 μmol / g or less.

[0091] In this application, the amount of carboxyl groups on the self-dispersing hydrophilic recycled carbon black surface refers to the value calculated by the following method. Specifically, 10.0 g of self-dispersible hydrophilic regenerated carbon black, obtained by drying a self-dispersible hydrophilic regenerated carbon black aqueous dispersion, is added to 1 L of 3.0 N hydrochloric acid and shaken for 3 hours. Then, using an ultrafiltration membrane, the mixture is treated with a concentration of 4% by mass of self-dispersible hydrophilic regenerated carbon black until the electrical conductivity is 0.2 mS / cm or less. This process is repeated three times and the mixture is dried again. Approximately 2 to 5 g of the washed self-dispersible hydrophilic regenerated carbon black is added to a 0.976 N sodium bicarbonate aqueous solution and shaken for about 6 hours. After filtering, a 0.05 N hydrochloric acid aqueous solution is added to the filtrate, and a neutralization titration test is performed with a 0.05 N sodium hydroxide aqueous solution until the pH becomes 7.0 to determine the amount of carboxyl groups. The amount of carboxyl groups obtained is then divided by the mass of self-dispersible hydrophilic regenerated carbon black to calculate the amount of carboxyl groups per unit mass of self-dispersible hydrophilic regenerated carbon black.

[0092] Because the amount of hydroxyl groups and carboxyl groups on the surface of the self-dispersing hydrophilic recycled carbon black obtained by the production method of the present invention are within the above range, it can easily exhibit good dispersibility in an aqueous medium.

[0093] The total amount of acidic functional groups on the surface of the self-dispersing hydrophilic recycled carbon black obtained by the production method of the present invention is preferably 200 μmol / g or more and 1500 μmol / g or less per unit mass of the self-dispersing hydrophilic recycled carbon black, more preferably 350 μmol / g or more and 1450 μmol / g or less, and even more preferably 450 μmol / g or more and 1400 μmol / g or less. The total amount of acidic functional groups on the self-dispersing hydrophilic recycled carbon black surface obtained by the manufacturing method of the present invention can be determined from the sum of the amounts of each acidic functional group formed on the surface of the recycled carbon black particles.

[0094] The self-dispersing hydrophilic recycled carbon black obtained by the manufacturing method of the present invention preferably has a silica concentration of 0.010% by mass or more and 3.300% by mass or less in the self-dispersing hydrophilic recycled carbon black. When the self-dispersing hydrophilic recycled carbon black aqueous dispersion obtained by the manufacturing method of the present invention is used in an aqueous inkjet printer ink composition, from the viewpoint of suppressing nozzle clogging of the printer, the silica concentration of the self-dispersing hydrophilic recycled carbon black is preferably as low as possible, preferably 3.300% by mass or less, more preferably 1.000% by mass or less, and even more preferably 0.100% by mass or less. Furthermore, from the viewpoint of balancing the reduction in silica concentration with the economic efficiency of the filtration step (vi), the silica concentration of the self-dispersing hydrophilic recycled carbon black is preferably 0.010% by mass or more, more preferably 0.030% by mass or more, and even more preferably 0.050% by mass or more.

[0095] In this application, the silica concentration in self-dispersing hydrophilic recycled carbon black refers to the value calculated by the following method. (Method for measuring silica concentration) A hydrophilic recycled carbon black aqueous dispersion with self-dispersing properties is dried to obtain hydrophilic recycled carbon black with self-dispersing properties. A predetermined amount of the self-dispersing hydrophilic recycled carbon black described above is collected, and silica is eluted from the self-dispersing hydrophilic recycled carbon black by adding hydrofluoric acid to obtain a silica solution. The obtained silica solution is measured using an ICP emission spectrometer (Shimadzu Corporation: ICPE-9820) to obtain a spectral spectrum. Based on the spectral intensity at a wavelength of 212.412 nm, the silica concentration is calculated by converting it to a concentration using a pre-prepared calibration curve.

[0096] The self-dispersing hydrophilic recycled carbon black obtained by the manufacturing method of the present invention can have a highly reduced silica concentration, despite being made from recycled carbon black.

[0097] The self-dispersing hydrophilic recycled carbon black aqueous dispersion obtained by the production method of the present invention preferably contains 1.0% to 20.0% by mass of the above-mentioned self-dispersing hydrophilic recycled carbon black as solid content, more preferably 5.0% to 20.0% by mass, and even more preferably 10.0% to 20.0% by mass. The above concentration adjustment can be achieved by concentrating the solution to a predetermined concentration using a separation membrane such as an ultrafiltration membrane, reverse osmosis membrane, or electrodialysis membrane. From the viewpoint of efficiency, it is more preferable to adjust the concentration using an ultrafiltration membrane.

[0098] In the self-dispersing hydrophilic recycled carbon black aqueous dispersion obtained by the manufacturing method of the present invention, the solid content concentration of the self-dispersing hydrophilic recycled carbon black is within the above range, making it possible to easily prepare desired aqueous ink compositions such as aqueous inkjet printer ink compositions. If the above solid content concentration is less than 1.0% by mass, it becomes difficult to prepare an aqueous ink composition containing hydrophilic recycled carbon black with the desired concentration of self-dispersing properties. When the above solid content concentration exceeds 20.0% by mass, the self-dispersing hydrophilic recycled carbon black particles tend to form aggregates, making it difficult to maintain the dispersibility of the aqueous ink composition over a long period of time.

[0099] The self-dispersing hydrophilic recycled carbon black aqueous dispersion obtained by the manufacturing method of the present invention can be used to prepare an aqueous ink composition by adding other components. Examples of aqueous ink compositions include aqueous inkjet printer ink compositions.

[0100] The content of self-dispersing hydrophilic recycled carbon black in the aqueous ink composition, such as the aqueous ink ink composition described above, is not particularly limited, but is preferably 1.0% by mass or more and 10.0% by mass or less, more preferably 2.0% by mass or more and 9.0% by mass or less, and even more preferably 3.0% by mass or more and 8.0% by mass or less.

[0101] Furthermore, the water content in the aqueous ink composition, such as the aqueous ink ink composition described above, is preferably 20.0% by mass or more and 75.0% by mass or less, more preferably 25.0% by mass or more and 65.0% by mass or less, and even more preferably 30.0% by mass or more and 60.0% by mass or less.

[0102] When preparing an aqueous inkjet printer ink composition using a self-dispersing hydrophilic recycled carbon black aqueous dispersion obtained by the manufacturing method of the present invention, other components such as aqueous organic solvents, penetrating agents, preservatives, chelating agents, viscosity modifiers, surfactants, resins, etc., can be added as needed.

[0103] According to the present invention, when obtaining a hydrophilic aqueous dispersion of recycled carbon black having self-dispersing properties by oxidizing recycled carbon black, a method is provided for suitably producing a hydrophilic aqueous dispersion of recycled carbon black having self-dispersing properties and excellent storage stability, with a highly reduced silica concentration. [Examples]

[0104] Next, the present invention will be described in more detail with reference to examples, but these are merely illustrative and not intended to limit the present invention.

[0105] (Examples 1 to 21) Examples 1 to 21 were obtained by performing the following processing steps to obtain hydrophilic recycled carbon black aqueous dispersions with the desired self-dispersing properties.

[0106] (A) Suspension step (i) Aqua-Black® 162 (manufactured by Tokai Carbon Co., Ltd.) was oxidized with sodium persulfate using a liquid-phase method to obtain an aqueous solution (humic acid concentration 0.2% by mass) in which humic acid was eluted. Furthermore, sodium hydroxide was added to the obtained humic acid aqueous solution to adjust the pH to 12.0, and then neutralized by heating and holding at 100°C for 3 hours to obtain an aqueous solution containing humic acid salt. A suspension was obtained by mixing 1.24 kg of recycled carbon black (silica concentration 8.043% by mass) with 6.20 kg of aqueous solution containing the above humic acid salt, then adding 21.3 kg of pure water and stirring, followed by treatment with an ultrasonic homogenizer (US-1200AT, manufactured by Nippon Seiki Seisakusho Co., Ltd.) for 20 minutes.

[0107] (B) Crushing process (ii) The above suspension was subjected to a crushing treatment using a bead mill (Labostar LMZ06, manufactured by Ashizawa Finetech Co., Ltd.) under the following conditions to obtain a liquid containing crushed material. Bead milling device: LMZ06, manufactured by Ashizawa Finetech Co., Ltd. Bead size: 0.3mm Bead material: Zirconia Bead mill peripheral speed: 14 m / sec Rotation speed: 3472 rpm Bead filling rate: 80% Number of passes: 50

[0108] (C) Hydrophilization step (iii) With the above-mentioned pulverized material-containing liquid contained in the reaction vessel, 4.50 kg of sodium peroxo-disulfate was added, and the temperature was raised to 60°C at a heating rate of 60°C / hour. The temperature was maintained at this temperature for 3 hours while stirring at a stirring speed of 200 rpm to perform the oxidation treatment and obtain an oxidized material-containing liquid.

[0109] (D) Desalination step (iv) The oxidized product-containing liquid obtained in the above hydrophilization step (iii) contains salts such as sodium bisulfate (NaHSO4) produced as by-products by the oxidation treatment with sodium peroxo-disulfate. Therefore, the oxidized product-containing liquid obtained in the hydrophilization step (iii) above was passed through an ultrafiltration membrane (Asahi Kasei Corporation, AHP-1013D, molecular weight cutoff 50,000) to desalinate it, thereby obtaining a dechlorinated liquid (a desalinated liquid from which salts such as NaHSO4 have been removed).

[0110] (E) Silica dissolution process (v) To the above dechlorination treatment liquid, granular sodium hydroxide was added to achieve the alkali concentration (mass%) shown in Table 1, and the liquid was heated and held at the heating temperature shown in the same table for the time shown in the same table to neutralize the heat of the dechlorination treatment liquid obtained in the above desalination step (iv) and to dissolve the silica in the hydrophilic recycled carbon black contained in the dechlorination treatment liquid. Note that the alkali concentration in Table 1 refers to the alkali concentration in the mixture obtained by mixing alkali with the dechlorination treatment solution.

[0111] (F) Filtration step (vi) Using the purification apparatus R shown in Figure 1, (1) an alkaline aqueous solution having the pH shown in Table 1 is supplied from the alkaline aqueous solution storage tank 2 to the raw solution tank 1 by pump P1 via the alkaline aqueous solution supply pipe t1, while (2) a circulation liquid supply pipe t is used by pump P2. 21 Through the ultrafiltration membrane (Asahi Kasei Corporation, AHP-1013D, molecular weight cutoff 50,000) housed in the ultrafiltration device 3, the liquid to be treated (a mixture of silica eluate-containing liquid and sodium hydroxide aqueous solution) is passed through the ultrafiltration membrane (Asahi Kasei Corporation, AHP-1013D, molecular weight cutoff 50,000) at the holding temperature shown in Table 1, (3) the silica eluate-containing waste liquid 4 treated and separated by membrane by the ultrafiltration device 3 is discharged from the ultrafiltration device 3, and (4) the liquid to be treated from which the silica eluate-containing waste liquid 4 has been removed is passed through the circulation pipe t 22 By circulating the liquid to be treated while returning the liquid to the stock tank 1 via the above-mentioned method, the liquid was purified to a purification ratio of 65 times, thereby obtaining a hydrophilic recycled carbon black aqueous dispersion with the desired self-dispersing properties.

[0112] (Comparative Example 1) In the silica dissolution step (v), the dechlorinated liquid obtained in the desalination step (iv) was heated and held at the temperature shown in Table 1 for the time shown in the same table without adding sodium hydroxide, and in the filtration step (vi), the silica eluate-containing liquid was purified at a temperature of 20°C using an ultrafiltration membrane (Asahi Kasei Corporation, AHP-1013D, molecular weight cutoff 50,000) while adding an aqueous sodium hydroxide solution with a pH of 9.0 as shown in Table 1, until the purification ratio was 65 times. Otherwise, a self-dispersing hydrophilic recycled carbon black aqueous dispersion was obtained in the same manner as in Example 1.

[0113] (Comparative Example 2) In the filtration step (vi), a self-dispersible hydrophilic recycled carbon black aqueous dispersion was obtained in the same manner as in Example 1, except that, as shown in Table 1, an aqueous sodium hydroxide solution with a pH of 9.0 was added to the silica eluate-containing liquid, and the solution was purified at a temperature of 20°C using an ultrafiltration membrane (Asahi Kasei Corporation, AHP-1013D, molecular weight cutoff of 50,000) to a purification ratio of 65 times.

[0114] (Comparative Example 3) In the filtration step (vi), a self-dispersible hydrophilic recycled carbon black aqueous dispersion was obtained in the same manner as in Example 1, except that, as shown in Table 1, an aqueous sodium hydroxide solution with a pH of 10.0 was added to the silica eluate-containing liquid, and the solution was purified at a temperature of 20°C using an ultrafiltration membrane (Asahi Kasei Corporation, AHP-1013D, molecular weight cutoff of 50,000) to a purification ratio of 65 times.

[0115] (Comparative Example 4) In the suspension step (i), instead of contacting the regenerated carbon black (silica concentration 8.043 mass%) with a synergist obtained by oxidative decomposition of Aqua-Black® 162 (manufactured by Tokai Carbon Co., Ltd.), which is a self-dispersing carbon black, we attempted to obtain a self-dispersing hydrophilic regenerated carbon black aqueous dispersion in the same manner as in Example 1, except that we contacted Aqua-Black® 162 (manufactured by Tokai Carbon Co., Ltd.), which is a self-dispersing carbon black, with Aqua-Black® 162 (manufactured by Tokai Carbon Co., Ltd.). However, in the crushing step (ii), the bead mill filter section became under high pressure, and we were unable to produce the desired self-dispersing hydrophilic regenerated carbon black aqueous dispersion.

[0116] (Comparative Example 5) In the suspension step (i), a hydrophilic recycled carbon black aqueous dispersion with self-dispersing properties was obtained in the same manner as in Example 1, except that instead of the synergist obtained by oxidative decomposition of Aqua-Black® 162 (manufactured by Tokai Carbon Co., Ltd.), a self-dispersing carbon black, 1.0 part by mass of alkylbenzenesulfonate (manufactured by Kao Corporation) was added to recycled carbon black (silica concentration 8.043% by mass) in the same manner as in Example 1.

[0117] (Comparative Example 6) In the suspension step (i), a self-dispersing hydrophilic recycled carbon black aqueous dispersion was obtained in the same manner as in Example 1, except that a polycarboxylic acid-type polymer surfactant (Poise 520, manufactured by Kao Corporation) was added in 1.0 part by mass per 100.0 parts by mass of recycled carbon black, instead of the synergist obtained by oxidative decomposition of Aqua-Black® 162 (manufactured by Tokai Carbon Co., Ltd.), a self-dispersing carbon black, to recycled carbon black (silica concentration 8.043% by mass).

[0118] [Table 1]

[0119] In Examples 1 to 21 and Comparative Examples 1 to 3, the silica concentration in the recycled carbon black used in the suspension step (i) (silica concentration in the raw material), the silica concentration in the hydrophilic recycled carbon black in the silica eluate-containing liquid obtained after the silica dissolution step (v) (silica concentration in the silica eluate-containing liquid), and the silica concentration in the self-dispersive hydrophilic recycled carbon black obtained after the filtration step (vi) (silica concentration in the final product) were measured by the following methods. The results are shown in Table 2.

[0120] (Method for measuring silica concentration in raw materials) A predetermined amount of recycled carbon black is collected, and silica is eluted from the recycled carbon black by adding hydrofluoric acid to obtain a silica solution. The obtained silica solution is measured using an ICP emission spectrometer (Shimadzu Corporation: ICPE-9820) to obtain a spectral spectrum. Based on the spectral intensity at a wavelength of 212.412 nm, the silica concentration is calculated by converting it to a concentration using a pre-prepared calibration curve.

[0121] (Silica concentration in silica-containing liquid) The silica-dissolving step (v) is performed, and the resulting silica-containing liquid is dried to obtain a mixture of hydrophilic recycled carbon black and silica-dissolved material. A predetermined amount of the above-mentioned mixture of hydrophilic recycled carbon black and silica eluate is collected, and by adding hydrofluoric acid, silica is eluted from the mixture of hydrophilic recycled carbon black and silica eluate to obtain a silica solution. The obtained silica solution is measured using an ICP emission spectrometer (Shimadzu Corporation: ICPE-9820) to obtain a spectral spectrum. Based on the spectral intensity at a wavelength of 212.412 nm, the silica concentration is calculated by converting it to a concentration using a pre-prepared calibration curve.

[0122] (Method for measuring silica concentration in the final product) The obtained self-dispersing hydrophilic recycled carbon black aqueous dispersion is dried to obtain self-dispersing hydrophilic recycled carbon black. A predetermined amount of the self-dispersing hydrophilic recycled carbon black described above is collected, and silica is eluted from the self-dispersing hydrophilic recycled carbon black by adding hydrofluoric acid to obtain a silica solution. The obtained silica solution is measured using an ICP emission spectrometer (Shimadzu Corporation: ICPE-9820) to obtain a spectral spectrum. Based on the spectral intensity at a wavelength of 212.412 nm, the silica concentration is calculated by converting it to a concentration using a pre-prepared calibration curve.

[0123] (Evaluation of nozzle blockage in inkjet printers (printing test without exposure)) Aqueous inkjet printer ink compositions were prepared using the self-dispersing hydrophilic recycled carbon black aqueous dispersions obtained in Examples 1 to 21 and Comparative Examples 1 to 3, respectively, and their nozzle clogging properties in inkjet printers were evaluated by the following method. (1) Using the self-dispersing hydrophilic recycled carbon black aqueous dispersion obtained in any of Examples 1 to 21 or Comparative Examples 1 to 3 immediately after preparation, an aqueous inkjet printer ink composition is prepared using the following ink formulation. (Ink formulation) Self-dispersing hydrophilic recycled carbon black (solids): 6.00% by mass Pure water: 73.15% by mass Diethylene glycol monobutyl ether: 5.00% by mass Acetylene glycol: 1.00% by mass Benzotriazole: 0.02% by mass Proxel XL-2: 0.03% by mass Triethanolamine: 0.80% by mass Glycerin: 14.00% by mass Total: 100.00% by mass (2) Prepare an inkjet printer (Seiko Epson Corporation: PX-S160T) equipped with an ink spray nozzle and fill it with the aqueous inkjet printer ink composition obtained in (1). (3) Using high-quality plain paper of A4 size (manufactured by Seiko Epson Corporation) as the recording medium, a pattern of 1 cm in length × 1 cm in width with an ink adhesion amount of 1 mg / cm 2 is continuously recorded vertically and horizontally with a 1 cm gap between each pattern. (4) An inkjet printer filled with the aqueous inkjet printer ink composition in (2) is left standing for one month in an environment with a temperature of 23°C and a relative humidity of 50%RH, and then the same pattern is recorded again in the same manner as in (3). (5) The 1 cm 3 pattern density of the recorded matter immediately after preparing the ink composition obtained in (3) is D ini and the 1 cm 3 pattern density of the recorded matter after leaving the ink composition prepared in (4) standing for one month is D 1M . Each pattern density is measured with a densitometer (X-Rite model: 528). (6) The ratio D ini of the density D 1M to the density D R { (D 1M / D ini ) × 100} (%) is determined as the one-month density retention rate. Then, those with the one-month density retention rate D R ≧ 85.0 (%) are judged to have a good clogging suppression effect on the nozzles of the inkjet printer and are given an "〇" evaluation, and those with the one-month density retention rate D R < 85.0 (%) are judged to have a poor clogging suppression effect on the nozzles of the inkjet printer and are given an "×" evaluation. The density D ini , the density D 1M , the one-month density retention rate D R and the evaluation results ("〇" evaluation and "×" evaluation) are shown in Table 2.

[0124]

Table 2

[0125] (Storage Stability Evaluation) The storage stability of the self-dispersing hydrophilic recycled carbon black aqueous dispersions obtained in Example 1 and Comparative Examples 4 to 6 was evaluated by the following method. In Comparative Example 4, it was not possible to prepare a hydrophilic recycled carbon black aqueous dispersion with self-dispersing properties, and therefore the storage stability described below could not be evaluated. Furthermore, in Comparative Example 6, the aqueous dispersion gelled after 4 weeks of storage in the incubator described below, resulting in poor viscosity and average particle size D. 50 It could not be measured. (1) 70-80 mL of the self-dispersing hydrophilic recycled carbon black aqueous dispersion prepared in each example and comparative example was taken, and the lidded glass bottles containing the dispersions were stored for 4 weeks in a 70°C incubator (Yamato Scientific Co., Ltd., IS400). (2) Viscosity and average particle size D of the self-dispersing hydrophilic recycled carbon black aqueous dispersion before and after storage in the above incubator 50 The following method was used to measure it. <Viscosity> The viscosity was measured at a temperature of 25°C using an E-type viscometer (TV-22, manufactured by Toki Sangyo Co., Ltd.). <Average particle diameter D 50 > The particle size (nm) corresponding to a cumulative volume fraction of 50% in the particle size distribution, as measured by a dynamic light scattering particle size distribution analyzer (UPA150, manufactured by Nikkiso Co., Ltd.), is defined as the average particle size D. 50 This was the request. (3) The rate of change in viscosity and average particle size D of the self-dispersing hydrophilic recycled carbon black aqueous dispersion before and after storage in the above incubator. 50 The rate of change was calculated using the following formula. Viscosity change rate (%) = {(Viscosity after 4 weeks of storage in an incubator - Viscosity before storage in an incubator) / Viscosity before storage in an incubator} × 100 Average particle diameter D 50 Rate of change (%) = {(Average particle size D after 4 weeks of storage in an incubator) 50 -Average particle size D before storage in incubator 50) / Average particle size D before storage in the incubator 50}×100

[0126] Viscosity of each self-dispersing hydrophilic recycled carbon black aqueous dispersion before and after storage in the above incubator, and average particle size D of each self-dispersing hydrophilic recycled carbon black aqueous dispersion before and after storage in the above incubator. 50 , the rate of change in viscosity and average particle size D of each self-dispersing hydrophilic recycled carbon black aqueous dispersion before and after storage in the above incubator. 50 The rate of change is shown in Table 3.

[0127] [Table 3]

[0128] Tables 1 and 2 show that the self-dispersing hydrophilic recycled carbon black aqueous dispersions obtained in Examples 1 to 21 were manufactured by the specific method specified in the present invention. Therefore, despite using recycled carbon black as a raw material, the silica concentration is significantly reduced, and when used in an aqueous inkjet printer ink composition, the 1-month concentration retention rate D R The fact that it has a success rate of over 85.0% indicates that it is highly effective in suppressing nozzle clogging in inkjet printers. Furthermore, as can be seen from Tables 1 and 3, the self-dispersing hydrophilic recycled carbon black aqueous dispersion obtained in Example 1 was manufactured by the specific method specified in the present invention. Therefore, despite using recycled carbon black as a raw material, the rate of change in viscosity and average particle size D of the self-dispersing hydrophilic recycled carbon black aqueous dispersion before and after storage in an incubator are significantly improved. 50 The low rate of change in all of these indicates excellent storage stability.

[0129] On the other hand, as shown in Table 1, the self-dispersing hydrophilic recycled carbon black aqueous dispersions obtained in Comparative Examples 1 to 3 were prepared by heat treatment without adding alkali in the silica dissolution step (v) (Comparative Example 1), by having the pH of the alkaline aqueous solution less than 10 when contacted with the alkaline aqueous solution in the filtration step (vi) (Comparative Examples 1 to 2), or by holding the material at a temperature of less than 25°C when contacted with the alkaline aqueous solution in the filtration step (vi) (Comparative Examples 1 to 3). Therefore, as shown in Table 2, the self-dispersing hydrophilic recycled carbon black aqueous dispersions obtained in Comparative Examples 1 to 3 had high silica concentrations (Comparative Example 1), or when used in an aqueous inkjet printer ink composition, they had a 1-month concentration retention rate D R The results show that the effectiveness in preventing nozzle clogging in inkjet printers is inferior, with less than 85.0% (rated "×"). (Comparative Examples 1-3) Furthermore, in Comparative Example 4, since the regenerated carbon black was not brought into contact with the synergist obtained by oxidative decomposition of self-dispersing carbon black in the suspension step (i), it was difficult to disperse the aggregates of regenerated carbon black, and the bead mill filter section became under high pressure in the crushing step (ii), making it impossible to produce a hydrophilic regenerated carbon black aqueous dispersion with the desired self-dispersing properties. Furthermore, the self-dispersing hydrophilic recycled carbon black aqueous dispersions obtained in Comparative Examples 5 to 6 were prepared by contacting the recycled carbon black with a commercially available surfactant in the suspension step (i) instead of the synergist obtained by oxidative decomposition of self-dispersing carbon black. Therefore, as shown in Table 3, the self-dispersing hydrophilic recycled carbon black aqueous dispersions obtained in Comparative Examples 5 to 6 show the rate of change in viscosity and average particle size D of the self-dispersing hydrophilic recycled carbon black aqueous dispersion before and after storage in an incubator. 50 The rate of change was large, resulting in poor storage stability (Comparative Example 5), and after storage in an incubator, the self-dispersing hydrophilic recycled carbon black aggregated, causing the aqueous dispersion to gel, and the viscosity and average particle size D50 It can be seen that it is not possible to measure this (Comparative Example 6). [Industrial applicability]

[0130] According to the present invention, when hydrophilic recycled carbon black is obtained by oxidizing recycled carbon black, a self-dispersing hydrophilic recycled carbon black aqueous dispersion can be suitably produced, which has a highly reduced silica concentration and exhibits excellent storage stability. [Explanation of symbols]

[0131] 1. Concentrate tank 2. Alkaline aqueous solution storage tank 3 Ultrafiltration device 4. Waste liquid containing silica elutes R purification equipment t1 Alkaline aqueous solution supply pipe t 21 , t 22 Circulation pipe

Claims

1. A method for producing a self-dispersing hydrophilic recycled carbon black aqueous dispersion, (A) A suspension step (i) in which recycled carbon black is suspended by contacting recycled carbon black with synergist obtained by oxidative decomposition treatment of self-dispersing carbon black in an aqueous medium, (B) A crushing step (ii) in which the suspension obtained in the suspension step (i) is crushed, (C) A hydrophilization step (iii) in which the liquid containing the pulverized material obtained in the pulverization step (ii) is oxidized to hydrophilize the recycled carbon black into hydrophilic recycled carbon black, (D) A desalination step (iv) in which the oxidized product-containing liquid obtained in the hydrophilization step (iii) is desalted, (E) A silica dissolution step (v) in which the silica in the hydrophilic regenerated carbon black is dissolved by heating the dechlorinated liquid obtained in the desalination step (iv) in the presence of alkali, (F) A filtration step (vi) in which the silica eluate-containing liquid obtained in the silica dissolution step (v) is filtered while being in contact with an alkaline aqueous solution with a pH of 9.5 or higher and 14.0 or lower at a temperature of 25°C or higher and 100°C or lower. A method for producing a self-dispersing hydrophilic recycled carbon black aqueous dispersion, characterized by sequentially applying the following steps.

2. A method for producing a self-dispersible hydrophilic recycled carbon black aqueous dispersion according to claim 1, wherein the crushing process in the crushing step (ii) is carried out by a bead mill.

3. A method for producing a self-dispersible hydrophilic recycled carbon black aqueous dispersion according to claim 1, wherein the heat treatment in the silica dissolution step (v) is performed at a heating temperature of 50°C or more and 100°C or less.

4. A method for producing a self-dispersible hydrophilic recycled carbon black aqueous dispersion according to claim 1, wherein the filtration step (vi) is performed by repeatedly passing the silica eluate-containing liquid through a filtration membrane while supplying an alkaline aqueous solution with a pH of 9.5 to 14.

0.

5. (G) A method for producing a self-dispersible hydrophilic recycled carbon black aqueous dispersion according to claim 1, further comprising a classification step (vii) in which the silica reduction treatment liquid obtained in the filtration step (vi) is subjected to classification treatment.

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