A method for preparing engraving gravure ink

Abstract

The invention relates to the technical field of inks, and discloses a method for preparing an engraved gravure ink, comprising the steps of preparing a PAMAM dendrimer carrier, loading a pigment, grafting a diisocyanate, chain growth, and post-processing. Compared with the form in which the pigment and the linker need to be fully mixed at the physical level in the traditional ink, the invention embeds the pigment in the dendrimer-modified polyurethane, provides a new combination of dyes and linkers, and fundamentally avoids the problem of pigment agglomeration and precipitation caused by poor compatibility between the pigment and the linker.

Description

Technical Field

[0001] The invention relates to the technical field of inks, and in particular to a method for preparing engraved gravure ink. Background Art

[0002] Ink is a viscous and stable fluid with color, fluidity and drying properties that is made by mechanically mixing and grinding extremely fine pigments, binders, fillers and additives in a certain proportion. The rheology, viscosity, drying, film-forming properties and printing performance of ink mainly depend on the properties of the binder. The solid components in the ink can be ground finely during the manufacturing process by relying on the wetting effect of the binder, and the transfer during the printing process can be completed by relying on its viscosity. The dry film-forming property of the binder allows the imprint to form a glossy and fast ink film to protect the pigment. Among different inks, gravure printing technology is used for printing high-end products due to its unique plate structure and outstanding gravure feel. Gravure printing also has more stringent requirements on inks, and the inks must have good fluidity, adhesion and uniformity. Generally, in order to ensure the uniformity of the ink color, the pigment particles in the ink should be dispersed as much as possible to avoid printing abnormalities and color differences after printing caused by agglomeration. However, similar to coatings with added inorganic particles, there is also a natural interface difficulty in dissolving between the granular inorganic pigments and organic binders in the ink. Pure mechanical grinding and refinement treatment can promote the dispersion of the pigment and prolong the time of pigment agglomeration and precipitation to a certain extent, but it cannot fundamentally avoid the agglomeration and precipitation of inorganic particles in the ink. Summary of the invention

[0003] In order to solve the above problems, the present invention provides a method for preparing an engraving gravure ink, comprising the following steps:

[0004] 1) Preparation of PAMAM dendrimers

[0005] Under nitrogen protection, allylamine at 0°C was added dropwise to methyl acrylate, stirred and heated to 25°C for reaction, the reactant was purified at 40-60°C, the purified reactant was added dropwise to ethylenediamine at 0°C under nitrogen protection, stirred and heated to 25°C for reaction, purified at 40-60°C to obtain PAMAM-G1.0, and the same operation was used to synthesize G2.0 and G3.0 generation PAMAM dendrimers, and G2.0 or G3.0 generation PAMAM dendrimers were selected;

[0006] 2) Loading pigment

[0007] The pigment is added in batches to a mixed solvent of polyethylene glycol and dimethyl sulfoxide, and then added to the PAMAM dendrimer obtained in step 1) after being fully stirred. After being stirred at room temperature for 1 day, the mixture is allowed to stand to separate the aggregated and precipitated pigment, thereby obtaining a PAMAM dendrimer stabilized solution loaded with the pigment.

[0008] 3) Grafted diisocyanate

[0009] Heat the stabilized solution obtained in step 2) to 60-80°C, keep stirring, add diisocyanate and organotin catalyst into the stabilized solution, let it stand after the reaction, and take out the colored mixed solution;

[0010] 4) Chain Growth

[0011] Heat the colored mixed solution obtained in step 3) to 50-80°C, add an organic tin catalyst, add a linear diol under slow stirring, react for 3-5 hours, then add diisocyanate, and repeat the operation 2-6 times;

[0012] 5) Post-processing

[0013] The reaction solution of step 4) is allowed to stand, and after removing the upper clear liquid, a diluent, a stabilizer, a volatile agent or a film-forming agent is added to the filtered lower liquid, and the mixture is slowly stirred and then packaged.

[0014] The present invention uses PAMAM dendrimers as the matrix for loading pigments. PAMAM dendrimers have a hyperbranched branch structure and contain a large number of cavities inside the molecule, which can stably embed pigments in these cavities. In step 1) of the method of the present invention, allylamine, methyl acrylate and ethylenediamine are used as reaction raw materials, and PAMAM dendrimer carriers with di-CONH-functional groups or tri-CONH-functional groups on the side chains are synthesized through repeated addition-substitution reactions. The specific reaction process is as follows:

[0015] .

[0016] In the above reaction, the molar ratio of methyl acrylate (MA) to the amino group is (2.5~9):1, and the molar ratio of ethylenediamine (EDA) to the ester group is (3~9):1.

[0017] The present invention selects G2.0 and G3.0 generation PAMAM dendrimers as carriers of the pigment. The -CONH- functional groups on the dendrimer side chains can form electronic attraction or hydrogen bonds with the functional groups in the pigment, thereby stably adsorbing the pigment inside the dendrimer. In addition, the PAMAM dendrimer side chains are flexible and can form a stable conformation, which is beneficial to preventing the pigment from falling off from the inside.

[0018] In step 2) of the method of the present invention, the particle size of the pigment is 0.2-1 μm, and the pigment is selected from one of carbon black, pigment red 48:2, pigment red 149, pigment yellow 150, pigment yellow 180, pigment blue 27 or pigment blue 60. A mixed solvent of polyethylene glycol and dimethyl sulfoxide is used to promote the movement of the pigment into the PAMAM dendrimer carrier. The amount of polyethylene glycol used is 5%-10% of the weight of the PAMAM dendrimer carrier, and the polyethylene glycol can also be used as a dispersion stabilizer to stably disperse the PAMAM dendrimer loaded with the pigment.

[0019] In step 3) of the method of the present invention, the diisocyanate is one of MDI, HDI, TDI or HMDI, and the diisocyanate and -NH2 at the end of the PAMAM dendrimer carrier undergo a condensation reaction to graft the diisocyanate onto the PAMAM dendrimer. In step 4), a linear diol is further grafted onto the other end of the diisocyanate grafted onto the PAMAM dendrimer, and the structure of the linear diol is HO(CH2) n OH (n is 2, 3, 4 or 5), and then diisocyanate is grafted on another hydroxyl group of the linear diol. After repeating the operation 2 to 6 times, a polyurethane pigment carrier modified by a PAMAM dendrimer is obtained. In its structure, the PAMAM dendrimer part embeds the pigment. The polyurethane part, as an extension of each branch of the PAMAM dendrimer, plays the role of a connecting material in traditional inks on the one hand, so that the pigment can be evenly dispersed and can be firmly attached after drying. On the other hand, it also plays the role of "sealing" the PAMAM dendrimer. The linear diol part in the polyurethane molecular chain has good segment flexibility, which can make the polyurethane molecular chain free conformation. After entanglement with each other, it forms a conical cavity with the PAMAM dendrimer, and the loaded pigment is less likely to fall off.

[0020] Further, add half the amount of linear diol with terminal isocyanate groups to the reaction solution obtained in step 4), and stir and react for 3 to 5 hours while maintaining the temperature. Adding half the amount of linear diol can connect the two terminal isocyanate groups, play the role of chain termination and cross-linking, and make the end-capping effect of polyurethane more obvious.

[0021] Step 5) Adding additives to the modified polyurethane mixed solution loaded with pigments makes the performance of the ink more stable. The polyethylene glycol, dimethyl sulfoxide and linear polyol added in the preparation process will have a certain amount of residue in the product of step 4). These three substances are also additives for the ink. Therefore, additional additives can be added according to the properties of the reaction solution. Specifically, the diluent can be selected from deionized water or organic solvents such as butyl acetate, methyl acetate, butanol, etc.; the stabilizer is sodium dodecyl sulfate or sodium lauryl sulfate; the volatile promoter is one of methanol, ethanol or dimethyl sulfoxide; and the film-forming agent is dodecyl alcohol ester.

[0022] Compared with the form in which the pigment and the binder in traditional inks need to be fully mixed at the physical level, the present invention embeds the pigment in the dendrimer-modified polyurethane, providing a new combination of dye and binder, which fundamentally avoids the problem of pigment agglomeration and precipitation caused by poor compatibility between the pigment and the binder. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the ESEM image of the engraved gravure black ink obtained in Example 1. DETAILED DESCRIPTION

[0024] To make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0025] 1. Preparation of PAMAM dendrimer carrier

[0026] Under nitrogen protection, a mixture of 100 g of allylamine and 100 mL of methanol was placed at 0°C, added dropwise to a mixture of 400 mL of freshly distilled methyl acrylate and 80 mL of methanol, stirred for 1 h, heated to 25°C, and stirred for 3 days. After the reaction was completed, PAMAM-G0.5 was purified at 60°C. Under the same synthetic method, G1.5 and G2.5 PAMAM dendrimers were synthesized at a molar ratio of amino group to methyl acrylate of 1:2.5. Under nitrogen protection, a mixture of G0.5 dendrimer and methanol was added dropwise to a methanol solution of ethylenediamine at 0°C at a molar ratio of ester group to ethylenediamine of 1:8, and stirred for 1 h. h, heated to 25 ° C, stirred for 5 days under nitrogen protection, after the reaction was completed, purified at 40 ° C to obtain PAMAM-G1.0, PAMAM-G1.0 was used as a reactant, and the G2.0 and G3.0 generation PAMAM dendrimers were synthesized by the same method as above, and the G2.0 and G3.0 generation PAMAM dendrimers were used as pigment carriers.

[0027] 2. Preparation of modified polyurethane ink Embodiment 1

[0028] A method for preparing black gravure ink comprises the following steps:

[0029] 1. Add carbon black with a particle size of 0.25 μm in batches to a mixed solvent of polyethylene glycol and dimethyl sulfoxide, stir thoroughly and add to the G3.0 generation PAMAM dendrimer carrier. The amount of polyethylene glycol is 8% of the weight of the G3.0 generation PAMAM dendrimer carrier. Stir at room temperature for 1 day and then let stand to separate the agglomerated and precipitated carbon black to obtain a PAMAM dendrimer stabilized liquid loaded with carbon black.

[0030] 2. Heat the stabilizing liquid to 65°C, keep stirring slowly, add MDI and organotin catalyst to the stabilizing liquid, control the ratio of MDI and PAMAM dendrimer to 8:1, let it stand after the reaction, and take out the black mixed liquid;

[0031] 3. Heat the black mixed liquid to 60°C, add an organic tin catalyst, add 1,4-butanediol while slowly stirring, and add MDI after reacting for 4 hours, wherein the molar ratio of 1,4-butanediol to PAMAM dendrimer is 8:1, and the molar ratio of 1,4-butanediol to MDI is 1:1. Repeat this operation 5 times, then add half the amount of 1,4-butanediol in the previous operation, and continue to react for 4 hours to block and crosslink the terminal diisocyanate groups to obtain a modified polyurethane pigment carrier of G3.0 generation PAMAM dendrimer terminal amino grafted MDI and 1,4-butanediol pentamer;

[0032] 4. Let the reaction solution of step 3 stand, remove the upper clear liquid, add 5% by weight of deionized water, 1% of sodium dodecyl sulfate and 0.5% of dodecyl alcohol ester to the filtered lower liquid, slowly stir evenly and then divide into packages.

[0033] Figure 1 This is the ESEM image of the engraved gravure black ink obtained in Example 1. The large particles in the image are stably suspended modified polyurethane carbon black carriers with a particle size of about 15 μm. The inner cavity of the carrier molecules is filled with carbon black, and the outer surface is evenly coated with long polyurethane chains. The overall structure is relatively regular. Embodiment 2

[0034] A method for preparing red ink for engraving gravure printing comprises the following steps:

[0035] 1. Add Pigment Red 48:2 with a particle size of 1 μm in batches to a mixed solvent of polyethylene glycol and dimethyl sulfoxide, stir thoroughly and add to the G2.0 generation PAMAM dendrimer carrier. The amount of polyethylene glycol used is 10% of the weight of the G2.0 generation PAMAM dendrimer carrier. Stir at room temperature for 1 day and then let stand to separate the aggregated and precipitated Pigment Red 48:2 to obtain a PAMAM dendrimer stabilized liquid loaded with Pigment Red 48:2.

[0036] 2. Heat the stabilizing liquid to 60°C, keep stirring slowly, add HDI and organotin catalyst to the stabilizing liquid, control the ratio of HDI and PAMAM dendrimer to 4:1, let it stand after the reaction, and take out the red mixed liquid;

[0037] 3. Heat the red mixed solution to 60°C, add an organic tin catalyst, add 1,5-pentanediol while slowly stirring, and add HDI after reacting for 4 hours, wherein the molar ratio of 1,5-pentanediol to PAMAM dendrimer is 4:1, and the molar ratio of 1,5-pentanediol to HDI is 1:1. Repeat this operation 6 times, then add half the amount of 1,5-pentanediol in the previous operation, and continue to react for 4 hours to cap the terminal diisocyanate group and cross-link it to obtain a modified polyurethane carrier of G2.0 generation PAMAM dendrimer terminal amino grafted HDI and 1,5-pentanediol hexamer;

[0038] 4. Let the reaction solution in step 3 stand, remove the supernatant, add 3% by weight of sodium lauryl sulfate, 2% by weight of ethanol and 1% by weight of dodecyl alcohol ester to the filtered lower liquid, stir slowly and evenly, and then package. Embodiment 3

[0039] A method for preparing yellow gravure ink comprises the following steps:

[0040] 1. Add Pigment Yellow 150 with a particle size of 0.5 μm in batches to a mixed solvent of polyethylene glycol and dimethyl sulfoxide, stir thoroughly and add to the G3.0 generation PAMAM dendrimer carrier. The amount of polyethylene glycol used is 10% of the weight of the G3.0 generation PAMAM dendrimer carrier. Stir at room temperature for 1 day and then let stand to separate the aggregated and precipitated Pigment Yellow 150 to obtain a PAMAM dendrimer stabilized liquid loaded with Pigment Yellow 150.

[0041] 2. Heat the stabilizing liquid to 60°C, keep stirring slowly, add HMDI and organotin catalyst to the stabilizing liquid, control the ratio of HMDI and PAMAM dendrimer to 8:1, let it stand after the reaction, and take the lower layer of yellow mixed liquid;

[0042] 3. Heat the yellow mixed solution to 70°C, add an organic tin catalyst, add 1,3-propylene glycol while slowly stirring, and add HMDI after reacting for 4 hours, wherein the molar ratio of 1,3-propylene glycol to PAMAM dendrimer is 8:1, and the molar ratio of 1,3-propylene glycol to HMDI is 1:1. Repeat this operation 4 times, then add half the amount of 1,3-propylene glycol in the previous operation, and continue to react for 4 hours to cap and crosslink the terminal diisocyanate groups to obtain a modified polyurethane carrier of G3.0 generation PAMAM dendrimer terminal amino grafted HMDI and 1,3-propylene glycol tetramer;

[0043] 4. Let the reaction solution of step 3 stand, remove the supernatant, add 4% by weight of sodium lauryl sulfate and 2% by weight of dodecyl alcohol ester to the filtered lower liquid, slowly stir evenly and then package.

[0044] Comparative Example 1

[0045] A method for preparing polyurethane carbon black ink comprises the following steps: uniformly mixing carbon black with a particle size of 0.25 μm and MDI powder, adding the mixture into a mixed solvent of polyethylene glycol and dimethyl sulfoxide at 60° C., adding 1,4-butanediol and an organic tin catalyst after sufficient stirring, reacting until the viscosity reaches 600 Pa·s under stirring, adding n-butanol, continuing the reaction until the viscosity no longer changes, adding 2% by weight of the reaction solution of sodium dodecyl sulfate and 1% by weight of the reaction solution of dodecyl alcohol ester, and grinding the reaction solution to obtain the polyurethane carbon black ink.

[0046] Table 1 shows the performance test results of the inks obtained in Examples 1 to 3 and Comparative Example 1. It can be seen from the data in Table 1 that the various properties of the inks in Examples 1 to 3 are consistent with or even improved upon those of traditional polyurethane inks. However, the pigments in Examples 1 to 3 are encapsulated in the molecular space of modified polyurethane, and there is no compatibility problem between the pigment and polyurethane, which is essentially different from the structure of traditional polyurethane inks.

[0047]

[0048] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing an engraving gravure ink, characterized in that: The following steps are involved: 1) Preparation of PAMAM dendrimers Under nitrogen protection, allylamine at 0°C was added dropwise to methyl acrylate, stirred and heated to 25°C for reaction, the reactant was purified at 40-60°C, under nitrogen protection, the purified reactant was added dropwise to ethylenediamine at 0°C, stirred and heated to 25°C for reaction, purified at 40-60°C to obtain PAMAM-G1.0, and the same operation was used to synthesize G2.0 and G3.0 generation PAMAM dendrimers; 2) Loading pigment The pigment is added in batches to a mixed solvent of polyethylene glycol and dimethyl sulfoxide, and then added to the PAMAM dendrimer carrier obtained in step 1) after being fully stirred, and then allowed to stand at room temperature to separate the aggregated and precipitated pigment, thereby obtaining a PAMAM dendrimer stabilized liquid loaded with the pigment; 3) Grafted diisocyanate Heat the stabilized solution obtained in step 2) to 60-80°C, keep stirring, add diisocyanate and organotin catalyst into the stabilized solution, let it stand after the reaction, and take out the colored mixed solution; 4) Chain Growth Heat the colored mixed solution obtained in step 3) to 50-80°C, add an organic tin catalyst, add a linear diol under slow stirring, react for 3-5 hours, then add diisocyanate, and repeat the operation 2-6 times; 5) Post-processing The reaction solution of step 4) is allowed to stand, and after removing the upper clear liquid, a diluent, a stabilizer, a volatile agent or a film-forming agent is added to the filtered lower liquid, and the mixture is slowly stirred and packaged.

2. The method for preparing the engraving gravure ink according to claim 1, characterized in that: In step 1), the molar ratio of methyl acrylate to amino group is (2.5-5):1; the molar ratio of ethylenediamine to ester group in the reactants is (3-9):

1.

3. The method for preparing the engraving gravure ink according to claim 1, characterized in that: In step 2), the particle size of the pigment is 0.2-1 μm, and the pigment is selected from one of carbon black, pigment red 48:2, pigment red 149, pigment yellow 150, pigment yellow 180, pigment blue 27 or pigment blue 60; the amount of polyethylene glycol used is 5%-10% of the weight of the PAMAM dendrimer carrier.

4. The method for preparing the engraving gravure ink according to claim 1, characterized in that: In step 3), the diisocyanate is one of MDI, HDI, TDI or HMDI.

5. The method for preparing the engraving gravure ink according to claim 1, characterized in that: In step 4), the structure of the straight-chain diol is HO(CH2) n OH, wherein n is 2, 3, 4 or 5.

6. The method for preparing the engraving gravure ink according to claim 5, characterized in that: Add half the amount of linear diol of the terminal isocyanate group in the product to the reaction solution of step 4) at once, and stir and react at the maintained temperature for 3 to 5 hours.

7. The method for preparing the engraving gravure ink according to claim 1, characterized in that: In step 5), the diluent is one or more of deionized water, butyl acetate, methyl acetate or butanol; the stabilizer is sodium dodecyl sulfate or sodium lauryl sulfate; the volatile promoter is one of methanol, ethanol or dimethyl sulfoxide; and the film-forming agent is dodecyl alcohol ester.

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