Preparation process of polymer coated self-crosslinking dispersant modified pigment ink

Abstract

The invention relates to the technical field of ink-jet printing ink, in particular to a preparation process of polymer coated self-crosslinking dispersant modified pigment ink, which comprises the following steps: 1, weighing an anchoring monomer, a hydrophilic monomer and a crosslinking monomer according to a mass ratio of 3: 5: 2, and mixing; 2, adding deionized water and the self-crosslinking dispersing agent prepared in the step 1 into a dispersing tank; step 3, coating the polymer by adopting a core-shell miniemulsion polymerization method; 4, adding a water-soluble solvent, a defoaming agent and a sterilizing agent into the polymer coated pigment emulsion prepared in the step 3; the self-crosslinking dispersing agent designed by the invention has anchoring groups, hydrophilic chains and crosslinkable active sites, the anchoring groups can be tightly adsorbed on the surface of a pigment, the hydrophilic chains provide steric hindrance to realize preliminary stabilization, and the active sites participate in a crosslinking reaction in a subsequent polymerization process, so that the dispersing agent and a coated polymer form covalent binding; the interface bonding force between the dispersing agent and the pigment and the coating layer is obviously improved, and the desorption of the dispersing agent and the agglomeration of the pigment are effectively avoided.

Description

Technical Field

[0001] This invention relates to the field of inkjet printing ink technology, specifically to the preparation process of polymer-coated self-crosslinking dispersant modified pigment ink. Background Technology

[0002] Inkjet printing technology, with its advantages of non-contact operation, high precision, and high efficiency, is widely used in packaging printing, textile dyeing, and advertising production. Pigment ink, as the core consumable in inkjet printing, directly determines print quality and application results. Compared to dye ink, pigment ink has advantages such as lightfastness, water resistance, and abrasion resistance. However, pigments are water-insoluble particles that easily aggregate in aqueous systems, leading to poor ink stability and easy nozzle clogging during printing, thus limiting its further applications.

[0003] To address the issue of pigment dispersion stability, existing technologies often employ the addition of dispersants. These dispersants utilize anchoring groups that adsorb onto the pigment surface, while their hydrophilic chains extend into the aqueous phase, creating steric hindrance and thus achieving stable pigment dispersion. However, traditional dispersants suffer from insufficient anchoring force and limited steric hindrance effect. Under long-term storage or harsh environments (such as high or low temperatures), desorption can still occur, leading to pigment aggregation. Furthermore, pigment inks stabilized solely by dispersants exhibit weak adhesion to the substrate after printing, and their resistance to abrasion and migration needs improvement.

[0004] Polymer coating modification technology can significantly improve the dispersion stability and interfacial compatibility of pigments by constructing a polymer coating layer on the pigment surface. However, existing polymer coating processes often suffer from problems such as uneven coating layer, weak bonding force with the pigment surface, and difficulty in accurately controlling the degree of crosslinking. As a result, the long-term stability and post-printing performance of the ink still cannot meet the requirements of high-end applications. Therefore, a preparation process for polymer-coated self-crosslinking dispersant modified pigment ink is proposed to address the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide a preparation process for polymer-coated self-crosslinking dispersant modified pigment inks to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: The preparation process of polymer-coated self-crosslinking dispersant modified pigment ink includes four steps: synthesis of self-crosslinking dispersant, preparation of nano-pigment paste, polymer coating and self-crosslinking, and ink compounding and adjustment. Step 1: The self-crosslinking dispersant: Weigh the anchoring monomer, hydrophilic monomer and crosslinking monomer in a mass ratio of 3:5:2, and mix them to obtain a monomer mixture; Step 2: Preparation of the nano pigment paste: Add deionized water and the self-crosslinking dispersant prepared in step 1 to a dispersion tank, stir and dissolve. The amount of self-crosslinking dispersant is 50%-200% of the mass of the pigment added later. Add pigment and zirconia beads. The mass ratio of pigment, self-crosslinking dispersant, zirconia beads and deionized water is 1:1-2:5-10:10-20. Step 3: The polymer coating is carried out by core-shell microemulsion polymerization. The nano pigment paste, core monomer and shell monomer prepared in step 2 are weighed in a mass ratio of 10:3:2. Step 4: Add water-soluble solvent, defoamer and bactericide to the polymer-coated pigment emulsion prepared in Step 3. The amount of water-soluble solvent is 5%-20% of the mass of the polymer-coated pigment emulsion.

[0007] In step one, the anchoring monomer is a carboxylic acid, sulfonic acid, or carboxylic acid + amide complex group, the hydrophilic monomer is PEGMA or NVP, and the crosslinking monomer is DVB.

[0008] In step two, the particle size of the nano pigment paste is controlled at 70-100nm, PDI<0.2, and absolute value of Zeta potential ≥30mV; the grinding speed is 3000-4500r / min, the grinding time is 4-6h, and ultrasonic treatment and centrifugation are used to remove impurities.

[0009] In step three, the core-shell monomer mass ratio is 3:2, the crosslinking monomer dosage is 5%-15% of the shell monomer mass, the fine emulsion particle size is <200nm, the core polymerization temperature is 60-70℃, the shell polymerization temperature is 75-85℃, and the degree of crosslinking is ≥80%. The core monomer is the soft monomer butyl acrylate (BA), and the shell monomer is the hard monomer methyl methacrylate (MMA).

[0010] In step four, the amounts of defoamer and bactericide used are 0.1%-1% of the mass of the polymer-coated pigment emulsion.

[0011] The water-soluble solvent in the prepared polymer-coated self-crosslinking dispersant modified pigment ink is a mixture of propylene glycol and glycerin in a mass ratio of 2:1, or a mixture of propylene glycol and ethylene glycol in a mass ratio of 1:1.

[0012] Compared with the prior art, the beneficial effects of the present invention are: The self-crosslinking dispersant designed in this invention has anchoring groups, hydrophilic chains, and crosslinkable active sites. The anchoring groups can be tightly adsorbed onto the pigment surface, the hydrophilic chains provide steric hindrance to achieve initial stability, and the active sites participate in the crosslinking reaction during subsequent polymerization, so that the dispersant and the coated polymer form a covalent bond, which significantly improves the interfacial bonding force between the dispersant and the pigment and the coating layer, and effectively avoids dispersant desorption and pigment agglomeration.

[0013] The core-shell microemulsion polymerization method is used to achieve polymer coating and self-crosslinking. Soft monomers are used in the core layer to improve printing adhesion, while hard monomers are used in the shell layer to improve weather resistance. The stepwise addition of crosslinking monomers and precise temperature control enable controllable adjustment of the degree of crosslinking (≥80%), which ensures the density and stability of the coating layer while avoiding the problem of excessive particle size caused by excessive crosslinking. The microemulsion polymerization process ensures the uniformity of the coating layer. After coating, the pigment particle size is controlled at 100-150nm, PDI<0.2, and the ink printing smoothness is improved.

[0014] The pigment ink prepared by this invention has a viscosity controlled at 2-10 mPa·s and a surface tension controlled at 30-40 mPa·s. It is compatible with piezoelectric inkjet printheads and has shown no delamination or emulsion breakage after cyclic testing at 50℃ for 7 days and -5℃ for 7 days, demonstrating excellent long-term stability. After printing, the pattern shows uniform color development and no smudging. It has a water resistance rating of ≥4, abrasion resistance rating of ≥3, and sun resistance rating of ≥6, meeting the application requirements of high-end inkjet printing. Detailed Implementation

[0015] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0016] Example The preparation process of polymer-coated self-crosslinking dispersant modified pigment ink includes four steps: synthesis of self-crosslinking dispersant, preparation of nano-pigment paste, polymer coating and self-crosslinking, and ink compounding and adjustment. Step 1: The self-crosslinking dispersant: Weigh the anchoring monomer, hydrophilic monomer and crosslinking monomer in a mass ratio of 3:5:2, and mix them to obtain a monomer mixture; Add solvent to the reactor, the amount of solvent being 2-3 times the total mass of the monomer mixture. Purge the air in the reactor with nitrogen gas 3-5 times, the nitrogen flow rate being 0.5-1 L / min. Heat the reactor to 70-90℃, add initiator and chain transfer agent, the amount of initiator being 0.5%-2% of the total mass of the monomer mixture, and the amount of chain transfer agent being 0.1%-1% of the total mass of the monomer mixture. After stirring evenly, add the monomer mixture dropwise at a rate of 2-3 g / min. After the dropwise addition is complete, maintain the temperature for 4-8 hours. After the reaction is complete, the temperature is lowered to below 40℃, and the mixture is neutralized to pH 7-8 with ammonia or triethanolamine. Then, the solvent is removed under reduced pressure at a vacuum of -0.08 to -0.1 MPa and a temperature of 50-60℃ to obtain a self-crosslinking dispersant with a solid content of 30%-50%.

[0017] In step one, the anchoring monomer is a carboxylic acid or sulfonic acid monomer, the hydrophilic monomer is polyethylene glycol methacrylate (PEGMA) or N-vinylpyrrolidone (NVP), the crosslinking monomer is divinylbenzene (DVB), the initiator is azobisisobutyronitrile (AIBN) or ammonium persulfate, the chain transfer agent is RAFT reagent or thiol, and the solvent is toluene or methyl ethyl ketone (MEK).

[0018] Step 2: Preparation of the nano pigment paste: Add deionized water and the self-crosslinking dispersant prepared in step 1 to a dispersion tank, stir and dissolve. The amount of self-crosslinking dispersant is 50%-200% of the mass of the pigment added later. Add pigment and zirconia beads. The mass ratio of pigment, self-crosslinking dispersant, zirconia beads and deionized water is 1:1-2:5-10:10-20. The zirconia beads have a diameter of 0.1-0.3 mm. They are first pre-dispersed by high-speed stirring at 2000-3000 r / min for 20-30 min, and then transferred to a sand mill and ground at 3000-4500 r / min for 4-6 h. During the grinding process, the temperature of the grinding chamber is controlled to be ≤45℃. After grinding, the mixture is ultrasonically treated with 200-400W and 20-40kHz for 20-30 minutes, and then centrifuged at 8000-10000r / min for 20-30 minutes to remove coarse particles. The supernatant is then collected to obtain nano pigment paste.

[0019] In step two, the particle size of the nano pigment paste is controlled at 70-100nm, PDI<0.2, and absolute value of Zeta potential ≥30mV; the grinding speed is 3000-4500r / min, the grinding time is 4-6h, and ultrasonic treatment and centrifugation are used to remove impurities.

[0020] Step 3: The polymer coating is carried out by core-shell microemulsion polymerization. The nano pigment paste, core monomer and shell monomer prepared in step 2 are weighed in a mass ratio of 10:3:2. Nano pigment paste, core layer monomer, RAFT reagent and deionized water are added to the reaction vessel. The amount of RAFT reagent is 0.2%-0.8% of the total mass of core layer and shell layer monomers. Deionized water is added to adjust the solid content of the system to 20%. The crude emulsion is obtained by high-speed shearing at 4000-5000 rpm for 15-20 min. During the shearing process, an ice-water bath is used to control the temperature ≤30℃. The crude emulsion was treated with ultrasound at 300-500W and 25kHz for 10-20 minutes to obtain a fine emulsion with a particle size <200nm and PDI <0.15. Nitrogen gas was introduced into the reactor to replace the air 3-5 times at a flow rate of 0.5-1L / min. The temperature was increased to 60-70℃ at a rate of 3℃ / min. An initiator was added, with the amount of initiator being 0.8%-1.5% of the total mass of the core and shell monomers. The reaction was carried out at a constant temperature for 2-4 hours to complete the core-shell polymerization. Then, the mixture of shell monomer and crosslinking monomer is added dropwise at a rate of 1-1.5 g / min. The amount of crosslinking monomer is 5%-15% of the mass of shell monomer. After the addition is completed, the temperature is raised to 75-85℃ and the reaction is kept at a constant temperature for 3-5 hours to achieve shell polymerization and self-crosslinking. After the reaction was completed, the temperature was reduced to room temperature at a rate of 2℃ / min, neutralized with ammonia water to pH 7-9, and filtered under negative pressure through a 0.22μm filter membrane to obtain a polymer-coated pigment emulsion. The particle size of the polymer-coated pigment emulsion was controlled at 100-150nm, PDI<0.2, and crosslinking degree ≥80%.

[0021] In step three, the core-shell monomer mass ratio is 3:2, the amount of crosslinking monomer is 5%-15% of the shell monomer mass, the fine emulsion particle size is <200nm, the core polymerization temperature is 60-70℃, the shell polymerization temperature is 75-85℃, and the degree of crosslinking is ≥80%.

[0022] The core monomer is the soft monomer butyl acrylate (BA), and the shell monomer is the hard monomer methyl methacrylate (MMA).

[0023] Step 4: Add water-soluble solvent, defoamer, and bactericide to the polymer-coated pigment emulsion prepared in Step 3. The amount of water-soluble solvent is 5%-20% of the mass of the polymer-coated pigment emulsion, and the amounts of defoamer and bactericide are 0.1%-1% of the mass of the polymer-coated pigment emulsion, respectively. The process involves stirring at 800-1200 r / min at room temperature for 30-40 min to completely dissolve the additives; adding deionized water to adjust the solid content of the system to 15%-30%; and finely adjusting the pH to 7-9 with ammonia or citric acid to control the ink viscosity at 2-10 mPa·s (25℃) and the surface tension at 30-40 mN / m. The ink is then finely filtered under negative pressure through 0.8μm, 0.45μm, and 0.22μm filter membranes to obtain polymer-coated self-crosslinking dispersant modified pigment ink.

[0024] In step four, the water-soluble solvent in the prepared polymer-coated self-crosslinking dispersant modified pigment ink is a mixture of propylene glycol and glycerin in a mass ratio of 2:1, or a mixture of propylene glycol and ethylene glycol in a mass ratio of 1:1.

[0025] The carboxylic acid monomers in this article interact with the active groups such as hydroxyl (-OH) and amino (-NH2) exposed on the pigment surface through the carboxyl group (-COOH) in their molecular structure. On the one hand, carboxyl groups can form stable hydrogen bonds with hydroxyl and amino groups through hydrogen atom sharing (such as -COOH…HO- pigment, -COOH…H2N- pigment), constructing a network of weak intermolecular interactions; On the other hand, in an aqueous system, carboxyl groups readily ionize to form carboxyl anions (-COO-). - ), and positively charged sites on the pigment surface due to protonation (such as -NH3), + Strong ionic bonds are formed, enabling electrostatic adsorption. Simultaneously, hydrophobic segments in the carboxylic acid monomer molecular chains can interact with hydrophobic regions on the pigment surface, further aiding anchoring. These three effects work synergistically to ensure that the anchoring groups of the carboxylic acid monomers are tightly and firmly adsorbed onto the pigment surface, significantly improving adsorption stability and effectively preventing desorption of the dispersant during long-term storage, temperature fluctuations, or printing.

[0026] Performance optimization: Dispersant: Adjusts the type of anchoring groups (such as carboxylic acids / sulfonic acids) and the density of crosslinking sites, thereby improving dispersion and crosslinking efficiency.

[0027] Polymerization process: RAFT polymerization precisely controls molecular weight, while fine emulsion polymerization ensures uniform coating.

[0028] Crosslinking timing: Introduce crosslinking monomers in the later stages of polymerization to avoid premature crosslinking that leads to excessively large particle size.

[0029] Compound formulation: Optimizes solvent ratio, balances moisturizing properties and drying speed, and reduces nozzle clogging.

[0030] Depending on the actual situation, a step can be added between step two and step three: pigment purification and stability pre-testing, as detailed below: Purification: The nano-pigment paste obtained from centrifugation in step two is then deeply purified by filtration through a ceramic membrane (pore size 50-100nm). The filtration pressure is 0.1-0.3MPa, and the flow rate is 5-10L / h to remove residual undissolved dispersant, small coarse particles, and zirconium oxide bead debris generated during grinding. After filtration, the paste is washed 2-3 times with deionized water to ensure a purity of ≥99.5%. Stability pre-test: Take 10 mL of purified pigment paste and let it stand in a 50℃ constant temperature oven for 48 h. If the particle size change rate is ≤5% and the PDI fluctuation is ≤0.02, it is considered qualified. Take 5 mL of pigment, dilute it with 1 mL of deionized water, and test the absolute value of the Zeta potential. If it is still ≥28 mV (to avoid potential abrupt changes during subsequent coating process that could lead to aggregation). If the color paste fails to meet the requirements, return it to step two for re-grinding or add an appropriate amount of self-crosslinking dispersant to adjust it. Once it meets the requirements, proceed to step three. Purpose: To address potential defects in existing processes: the centrifugation process in step two may leave behind tiny zirconium oxide bead fragments or incompletely dispersed pigment aggregates, which can lead to uneven polymer coating and fluctuations in crosslinking degree in subsequent processes. Avoid the risk of coating failure in advance: Screen stable color pastes through pre-testing to prevent unqualified color pastes from entering subsequent polymerization processes, thereby reducing raw material loss and process costs; Improved coating quality: The purified pigment surface is cleaner, the anchoring groups are more fully exposed, and the coating layer and pigment are more tightly bonded during subsequent core-shell polymerization.

[0031] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A preparation process for polymer-coated self-crosslinking dispersant modified pigment ink, characterized in that: It includes four steps: synthesis of self-crosslinking dispersants, preparation of nano-pigment pastes, polymer coating and self-crosslinking, and ink compounding and adjustment. Step 1: The self-crosslinking dispersant: Weigh the anchoring monomer, hydrophilic monomer and crosslinking monomer in a mass ratio of 3:5:2, and mix them to obtain a monomer mixture; Step 2: Preparation of the nano pigment paste: Add deionized water and the self-crosslinking dispersant prepared in step 1 to a dispersion tank, stir and dissolve. The amount of self-crosslinking dispersant is 50%-200% of the mass of the pigment added later. Add pigment and zirconia beads. The mass ratio of pigment, self-crosslinking dispersant, zirconia beads and deionized water is 1:1-2:5-10:10-20. Step 3: The polymer coating is carried out by core-shell microemulsion polymerization. The nano pigment paste, core monomer and shell monomer prepared in step 2 are weighed in a mass ratio of 10:3:

2. Step 4: Add water-soluble solvent, defoamer and bactericide to the polymer-coated pigment emulsion prepared in Step 3. The amount of water-soluble solvent is 5%-20% of the mass of the polymer-coated pigment emulsion.

2. The preparation process of the polymer-coated self-crosslinking dispersant modified pigment ink according to claim 1, characterized in that: In step one, the anchoring monomer is a carboxylic acid, sulfonic acid, or carboxylic acid + amide complex group, the hydrophilic monomer is PEGMA or NVP, and the crosslinking monomer is DVB.

3. The preparation process of the polymer-coated self-crosslinking dispersant modified pigment ink according to claim 1, characterized in that: In step two, the particle size of the nano pigment paste is controlled at 70-100nm, PDI<0.2, and absolute value of Zeta potential ≥30mV; the grinding speed is 3000-4500r / min, the grinding time is 4-6h, and ultrasonic treatment and centrifugation are used to remove impurities.

4. The preparation process of the polymer-coated self-crosslinking dispersant modified pigment ink according to claim 1, characterized in that: In step three, the core-shell monomer mass ratio is 3:2, the amount of crosslinking monomer is 5%-15% of the shell monomer mass, the fine emulsion particle size is <200nm, the core polymerization temperature is 60-70℃, the shell polymerization temperature is 75-85℃, and the degree of crosslinking is ≥80%.

5. The preparation process of the polymer-coated self-crosslinking dispersant modified pigment ink according to claim 1, characterized in that: The core monomer is the soft monomer butyl acrylate (BA), and the shell monomer is the hard monomer methyl methacrylate (MMA).

6. The preparation process of the polymer-coated self-crosslinking dispersant modified pigment ink according to claim 1, characterized in that: In step four, the amounts of defoamer and bactericide used are 0.1%-1% of the mass of the polymer-coated pigment emulsion.

7. The preparation process of the polymer-coated self-crosslinking dispersant modified pigment ink according to claim 1, characterized in that: The water-soluble solvent in the prepared polymer-coated self-crosslinking dispersant modified pigment ink is a mixture of propylene glycol and glycerin in a mass ratio of 2:1, or a mixture of propylene glycol and ethylene glycol in a mass ratio of 1:

1.

8. The preparation process of the polymer-coated self-crosslinking dispersant modified pigment ink according to claim 1, characterized in that: Depending on the actual situation, a pre-testing mechanism for pigment purification and stability can be added between steps two and three.