A low dielectric loss black water-based ink and its preparation method

Abstract

This invention belongs to the field of water-based ink technology, specifically relating to a low-dielectric-loss black water-based ink and its preparation method, including the following steps: grinding aniline black to nanoscale particle size; mixing nano-aniline black, emulsifier, coupling agent, initiator, and deionized water to prepare a pre-dispersion; emulsifying acrylate monomer, emulsifier, pH buffer, and deionized water to prepare a seed emulsion; adding the pre-dispersion dropwise to the seed emulsion to carry out a graft polymerization reaction, generating an aniline black-acrylate hybrid emulsion; mixing the hybrid emulsion with additives to obtain the black water-based ink. This invention reduces the dielectric loss of the black ink layer, making it suitable for processes where the black ink layer is not prone to overheating or scorching during microwave drying to remove moisture. It improves the compatibility of aniline black powder with water-based resins, solving the dispersion and precipitation problems of high-concentration aniline black powder. Furthermore, it significantly reduces secondary agglomeration of aniline black powder.

Description

Technical Field

[0001] This invention belongs to the field of water-based ink technology, specifically relating to a low dielectric loss black water-based ink and its preparation method. Background Technology

[0002] In the printing industry, water-based inks are traditionally dried using heat drying. However, this method has drawbacks such as low energy efficiency, incomplete drying, and a tendency to result in a "false dry" state where the surface is dry but the interior remains wet. For example, in the traditional paper and film printing industry, to increase drying speed, the oven temperature needs to be raised and the temperature gradient increased. However, this can easily lead to deformation or scorching of the film or paper, causing product defects.

[0003] Under microwave drying conditions, wet materials are placed within a microwave high-frequency electric field with an extremely short oscillation period. Water molecules within the material become polarized and align themselves neatly along the direction of the microwave electric field. They then rapidly rotate with the alternating changes in the direction of the high-frequency alternating electric field, generating intense collisions and friction (up to hundreds of millions of times per second). As a result, some microwave energy is converted into molecular kinetic energy, manifesting as heat, raising the temperature of the water and causing it to leave the material, thus drying it. In other words, after microwaves enter and are absorbed by the material, their energy is converted into heat energy within the material's dielectric. When using microwave heating, heat can penetrate evenly regardless of the material's shape and can produce a puffing effect, facilitating pulverization. Household microwave ovens are a typical application of this principle. Therefore, microwave drying is a highly efficient drying method that uses electromagnetic waves as a heating source and the material being dried as the heating element, and it is widely used in the drying of many industries such as wood, seeds, and chemicals.

[0004] Traditional black water-based inks use carbon black as a colorant. Carbon black has a high dielectric loss factor (loss tangent), which strongly absorbs energy and rapidly converts it into heat in a microwave field [Metaxas, AC, & Meredith, RJ (1983). Industrial microwave heating. Peter Peregrinus Ltd.]. In contrast, colored organic pigments (such as phthalocyanine blue, azo pigments, etc.) generally have lower dielectric losses and weaker microwave absorption capabilities, resulting in a more uniform and slower temperature rise during drying. Under the same microwave power, the carbon black coating absorbs more energy, causing a sharp increase in local temperature. Therefore, when traditional red / yellow / blue / black four-color water-based inks are printed on paper bags or films, the rapid internal temperature rise of the carbon black coating after microwave drying may exceed the heat resistance limit of the paper or film (the carbonization temperature of paper is usually around 200°C, and the heat distortion temperature of film is even lower). This can easily lead to the black coating overheating or even scorching due to excessive microwave energy absorption. Conversely, reducing the microwave power can easily result in insufficient microwave energy for the colored coating, leading to poor drying.

[0005] Traditional carbon black and traditional organic pigments have significantly different dielectric loss parameters, making it difficult to adjust suitable microwave drying parameters when microwave drying CMYK printed materials (i.e., printed materials formed by overprinting cyan, magenta, yellow, and key / black inks) on the same printing plate. This limits the application of microwave drying in the printing industry. Aniline black (pigment black 1), as the only industrially produced black organic pigment, has completely different physical properties from carbon black. Its dielectric parameters, such as microwave absorption, reflection, scattering, and penetration, are essentially the same as those of organic pigments. Therefore, replacing carbon black with aniline black in water-based black inks can avoid the disadvantages of carbon black in microwave drying.

[0006] However, commercially available aniline black is either completely oil-soluble (it cannot dissolve or disperse in water) or completely water-soluble (generally a mixture of sulfonated sodium salts of oil-soluble aniline black, which is completely water-sensitive and will dissolve and fade upon contact with water). Therefore, commercially available aniline black cannot be directly applied to water-based inks for printing. Therefore, it is proposed to first grind aniline black powder into nano-sized powder using a freeze-milling process, and then graft it onto a water-based resin as coloring particles, fusing them together. This not only effectively solves the problem of aniline black dispersion, but also further reduces the chance of secondary agglomeration between aniline black particles after polymerization with the water-based resin graft. Water-based black inks formulated according to this process not only solve the problem of overheating and charring in traditional carbon black systems during microwave drying, but also address the issue that traditional aniline black is unsuitable for water-based inks requiring water resistance, thus achieving two goals at once.

[0007] The efficiency and uniformity of microwave drying fundamentally depend on the dielectric properties of the material (ink coating), particularly the dielectric loss factor (ε''). When microwave energy (typically at 2.45 GHz or 915 GHz) penetrates the material, the microwave electric field causes the polar molecules within the material (primarily moisture, but also including polar material components) to undergo orientation polarization. Under a high-frequency alternating electric field, the repeated orienting motion of these molecules lags behind the changes in the electric field due to internal frictional resistance, resulting in the irreversible conversion of some microwave energy into molecular kinetic energy (heat). This efficiency of converting electromagnetic energy into heat is directly quantified by the dielectric loss factor (ε''). A higher ε'' value indicates a stronger ability of the material to absorb energy and convert it into heat in the microwave field, and a faster heating rate.

[0008] In CMYK four-color printing, traditional carbon black colorants typically possess extremely high dielectric loss factors (ε'') due to their unique graphitized microcrystalline structure and conjugated π-electron system. In contrast, the ε'' values ​​of colored organic pigments (such as phthalocyanine and azo dyes) are usually very low. This significant difference in ε'' is the core physical reason for microwave drying problems. Under the same microwave power and electric field strength, high-ε'' carbon black ink layers will absorb energy violently and heat up rapidly, easily exceeding the heat resistance limit of the paper or film substrate, leading to overheating and scorching. If the overall microwave power is reduced to protect the carbon black layer, the low-ε'' colored ink layers will absorb insufficient energy, resulting in ineffective evaporation of internal moisture and problems such as poor drying (false drying) and smudging. Therefore, measuring and comparing the loss factors ε'' of different ink coatings (especially black and colored inks) is a key indicator for evaluating their heat absorption capacity and heating rate in a microwave field, and is also the core scientific basis for solving the microwave drying compatibility problem of multicolor printed materials. Summary of the Invention

[0009] The purpose of this invention is to solve the problems of overheating and charring in traditional carbon black-based water-based inks during microwave drying, as well as the application of aniline black as a colorant in water-based inks.

[0010] To achieve the above objectives, the present invention provides a method for preparing a low dielectric loss black water-based ink, comprising the following steps:

[0011] S1. Aniline black is ground to nanoscale particle size, D90 < 0.3 μm;

[0012] S2. Mix nano-aniline black, emulsifier, coupling agent, initiator, defoamer and deionized water to prepare a pre-dispersion;

[0013] S3. Mix and emulsify acrylate monomers, emulsifiers, pH buffers and deionized water to prepare seed emulsion;

[0014] S4. The pre-dispersed liquid is added dropwise to the seed emulsion, and a graft polymerization reaction is carried out at 70~90℃ to generate an aniline black-acrylate hybrid emulsion;

[0015] S5. The hybrid emulsion is mixed with an additive to obtain a black water-based ink.

[0016] Preferably, the aniline black in S1 is oil-soluble aniline black; the additives in S5 include defoamers, leveling agents, anti-wear agents, thickeners, and bactericides.

[0017] Preferably, in S2, the mass percentage of nano-aniline black is 40%-57%; the mass percentage of emulsifier is 1%-10%; the mass percentage of coupling agent is 1%-5%; the mass percentage of initiator is 0.1%-1%; and the mass percentage of deionized water is 40%-60%.

[0018] Preferably, in S3, the mass percentage of acrylate monomer is 40%-58%; the mass percentage of emulsifier is 1%-3%; the mass percentage of pH buffer is 0.1%-1%; and the mass percentage of deionized water is 40%-60%.

[0019] Preferably, in S5, the mass percentage of the hybrid emulsion is 95%-98%; the mass percentage of the defoamer is 0.1%-1%; the mass percentage of the leveling agent is 0.1%-1%; the mass percentage of the anti-wear agent is 0.1%-1%; the mass percentage of the thickener is 0.1%-1%; and the mass percentage of the bactericide is 0.1%-1%.

[0020] Preferably, the emulsifier in S2 and S3 is one or more of sodium dodecylbenzenesulfonate (SDS), polyoxyethylene sorbitan monooleate (Tween 80), polyoxyethylene cetyl ether (Brij 58), alkylphenol polyoxyethylene ether (Triton X-100), polyglycerol monolaurate (PGFE), sodium lauryl ether sulfate (AES), and soybean lecithin (LHP).

[0021] Preferably, the coupling agent in S2 is one or more of 3-aminopropyltriethoxysilane, 3-aminopropylmethyldiethoxysilane, N,N-diethyl-3-aminopropyltrimethoxysilane, bis-(3-trimethoxysilylpropyl)amine, anilinemethyltriethoxysilane, diethylaminomethyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-ureapropyltrimethoxysilane, and 3-ureapropyltriethoxysilane; and the initiator is one or more of ammonium persulfate, potassium persulfate, benzoyl peroxide, di-tert-butyl hydroperoxide, azobisisobutyronitrile, and dilauryl peroxide.

[0022] Preferably, the acrylate monomer in S3 is selected from one or more of methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-butyl acrylate, n-butyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, isooctyl acrylate, isooctyl methacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, and hydroxypropyl methacrylate.

[0023] Preferably, the seed emulsion in S3 further includes acrylic acid or methacrylic acid.

[0024] Preferably, in the grinding process of S1, the grinding beads of the liquid nitrogen-cooled ball mill are 95 yttrium stabilized zirconia beads with a particle size of 0.03~0.3 mm and a bead loading of 70%~90%, and the liquid nitrogen temperature of the inner liner is controlled at -100℃±50℃.

[0025] The present invention also provides a low dielectric loss black water-based ink.

[0026] Compared with the prior art, the advantages of this invention are:

[0027] This invention uses aniline black as a black colorant, replacing traditional carbon black in water-based inks for microwave drying applications. It significantly reduces the dielectric loss of the black ink layer, meeting the process requirements of preventing overheating and scorching during microwave drying of the black ink layer to remove moisture. By using an emulsion polymerization device, aniline black is grafted and polymerized into an acrylic emulsion, greatly improving the compatibility between the powder and the resin and solving the problems of dispersion and sedimentation of high-concentration aniline black powder. Furthermore, due to the excellent coating properties of the grafted polymer on aniline black, secondary agglomeration of the aniline black powder is significantly reduced. Detailed Implementation

[0028] The terms used in this invention, unless otherwise stated, generally have the meanings commonly understood by those skilled in the art.

[0029] In the following embodiments, various processes and methods not described in detail are conventional methods known in the art.

[0030] The reagents used in the following examples were obtained through common commercial channels. Experimental procedures and conditions not specified are in accordance with conventional procedures and conditions in the art.

[0031] The specific implementation of the present invention will be described below with reference to the embodiments.

[0032] Example 1

[0033] Step 1: Load 95% yttrium stabilized zirconia beads (0.05mm particle size, 80% bead load) into a cryogenic ball mill (Cryo / Mill 6870D custom model). Open the inner jacket of the ball mill, circulate liquid nitrogen and control the temperature to -87℃±3℃. Pour in 100g of aniline black powder (Tokyo Color Materials Co., Ltd., Japan, model SUPER BLACK® NO.2). Grind repeatedly until the powder particle size D90 < 0.3μm (actual D90 = 0.18μm measured by laser particle size analyzer). Filter through a 5000-mesh vibrating sieve to obtain 94.7g of nano aniline black.

[0034] Step 2: Add the materials in the table below in the following order: deionized water, emulsifier, coupling agent, initiator, defoamer, and nano aniline black, totaling 189.41g. At the same time, use a homogenizer at 3000rpm for 2 hours to disperse evenly. Then filter through a 2000-mesh filter to prepare 182.20g of aniline black pre-dispersion.

[0035] Table 1

[0036]

[0037] Step 3: Add the total of 727.88g of the materials listed in the table below to the beaker and mix at 1500rpm for 40 minutes until a milky white and homogeneous solution is formed and does not separate into layers when left to stand.

[0038] Table 2

[0039]

[0040] Step 4: Pour 727.88g of the seed emulsion from Step 3 into a four-necked flask for emulsion polymerization, purge with nitrogen to purge oxygen, then add 182.20g of the aniline black pre-dispersion prepared in Step 2 dropwise into the seed emulsion. Simultaneously, raise the temperature to 86℃±2℃ and polymerize for 2.5 hours. After the reaction is complete, cool to room temperature and filter through a 100-mesh filter to obtain 893.45g of aniline black-acrylate hybrid black emulsion.

[0041] Step 5: Add the raw materials listed in the table below to a glass beaker in sequence, then disperse at 300 rpm for 10 minutes, filter through a 100-mesh filter to obtain 100g of black water-based ink. The viscosity was measured to be 12.00 seconds at room temperature (25°C) using a Zahn Cup 4#, and the pH value was measured to be 8.3 using a pH meter.

[0042] Table 3

[0043]

[0044] Test Example 1

[0045] Several commercially available black water-based flexographic inks for paper printing, all carbon black-based, were selected as reference samples. The printing conditions were: a flexographic proofing machine manufactured by Zhongshan Nuobang, 100-line anilox roller, and 280gsm Sun brand food-grade white cardboard. The test results are listed in Table 4.

[0046] Table 4

[0047]

[0048] Storage stability test method and results: According to GB / T 6753.3-1986 "Test method for storage stability of coatings", about 90g of black water-based ink prepared in Example 1 was sampled, placed in a 100ml plastic bottle, sealed, and placed in a 50℃ constant temperature chamber. After 30 days, it was taken out and cooled to room temperature. No visible sedimentation or stratification was observed. The viscosity was retested at 25℃ using ZahnCup 4# and was 12.58 seconds. The pH value was measured to be 8.21 using a pH meter, with minimal fluctuation, which was within the normal range.

[0049] Example 2

[0050] Step 1: Load 95% yttrium stabilized zirconia beads (0.1mm particle size, 88% bead content) into a cryogenic ball mill (Cryo / Mill 6870D custom model). Open the inner jacket of the ball mill, circulate liquid nitrogen and control the temperature to -70℃±5℃. Pour in 200g of aniline black powder (BASF, model Paliotol Black L0080). Grind repeatedly until the powder particle size D90 < 0.3μm (actual D90 = 0.12μm measured by laser particle size analyzer). Filter through a 5000-mesh vibrating sieve to obtain 193.75g of nano aniline black.

[0051] Step 2: Add the materials in the table below in order, totaling 284.03g. At the same time, use a homogenizer at 3500rpm for 2.5 hours to disperse evenly. Then filter with a 2000-mesh filter to prepare 278.65g of aniline black pre-dispersion.

[0052] Table 5

[0053]

[0054] Step 3: Add 1000g of the materials listed in the table below to a beaker and mix at 1000rpm for 40 minutes until a milky white, homogeneous solution is formed and does not separate into layers when left to stand.

[0055] Table 6

[0056]

[0057] Step 4: Pour 1000g of the seed emulsion from Step 3 into a four-necked flask for emulsion polymerization, purge with nitrogen to purge oxygen, then add dropwise 278.65g of the aniline black pre-dispersion prepared in Step 2 to the seed emulsion. Simultaneously, raise the temperature to 80℃±2℃ and polymerize for 3.5 hours. After the reaction is complete, cool to room temperature and filter through a 120-mesh filter to obtain 1252.68g of aniline black-acrylate hybrid black emulsion.

[0058] Step 5: Add the raw materials listed in the table below to a glass beaker in sequence, then disperse at 300 rpm for 10 minutes, and filter through a 100-mesh filter to obtain 100g of black water-based ink (theoretical aniline black content is 11.35%). The viscosity was measured to be 16.20 seconds at room temperature (25℃) using a Zahn Cup 4#, and the pH value was measured to be 8.5 using a pH meter.

[0059] Table 7

[0060]

[0061] Test Example 2

[0062] Water-based inks of various colors for paper flexographic printing were prepared using a standard method. Specifically, 37.35g of purified water, 15.00g of water-based resin solution (JONCRYL 196 MEA), 35.00g of water-based acrylic emulsion (JONCRYL 631AP), 0.30g of defoamer (TEGO 810), 1.00g of dispersant (TEGO 755W), 11.35g of the colorant to be tested, and 150.00g of zirconium beads (95 specification / size 0.4-0.6mm) were added to a 500ml glass jar. After sealing, the jar was shaken at high speed for 2 hours and then filtered through a 100-mesh screen to obtain the standard water-based inks of various colors. See Table 8 for details.

[0063] Table 8

[0064]

[0065] The printing conditions were: a flexographic proofing machine manufactured by Zhongshan Nuobang, a 100-line anilox roller, and 280gsm Sun brand food-grade white cardboard. The test results are listed in Table 9.

[0066] Table 9

[0067]

[0068] Storage stability test method and results: According to GB / T 6753.3-1986 "Test method for storage stability of coatings", about 90g of black water-based ink prepared in Example 1 was sampled, placed in a 100ml plastic bottle, sealed, and placed in a 50℃ constant temperature chamber. After 30 days, it was taken out and cooled to room temperature. No visible sedimentation or stratification was observed. The viscosity was retested at 25℃ using ZahnCup 4# and was 17.03 seconds. The pH value was measured to be 8.42 using a pH meter, with minimal fluctuation, which was within the normal range.

[0069] In the above Examples 1 and 2, and corresponding Test Examples 1 and 2, the present invention uses an X-Rite color density meter to measure color density values. Higher color density values ​​indicate stronger light absorption by the ink layer, resulting in a darker appearance and better opacity. The test results show that using aniline black as a black colorant to replace traditional carbon black in water-based inks not only maintains sufficient printing color density without affecting blackness, but also significantly reduces the dielectric constant and loss factor of traditional black ink coatings. This allows the drying characteristics of the black coating in a microwave environment to be essentially consistent with those of colored organic pigment coatings, solving the problem of overheating and scorching of the black ink layer in CMYK printing under traditional microwave drying environments. Furthermore, by grafting aniline black onto acrylic emulsions through emulsion polymerization, the resulting black water-based ink significantly improves the layering and sedimentation problems of oleophilic aniline black powder under low viscosity conditions.

[0070] The above is a detailed description of the embodiments, which is intended to enable those skilled in the art to correctly understand and use the present invention. Any improvements or modifications to technical solutions obtained by those skilled in the art based on the present invention and on the existing technology, without innovative effort but only through analysis, analogy, or limited enumeration, should be within the scope of protection defined by the claims.

Claims

1. A method for preparing a low dielectric loss black water-based ink coating, characterized in that, The coating is formed by microwave drying of a low-dielectric-loss black water-based ink. The preparation of the low-dielectric-loss black water-based ink includes the following steps: S1. Aniline black is ground to nanoscale particle size, D90 < 0.3 μm; S2. Mix nano-aniline black, emulsifier, coupling agent, initiator, defoamer and deionized water to prepare a pre-dispersion; S3. Mix and emulsify acrylate monomers, emulsifiers, pH buffers and deionized water to prepare seed emulsion; S4. The pre-dispersed liquid is added dropwise to the seed emulsion, and a graft polymerization reaction is carried out at 70~90℃ to generate an aniline black-acrylate hybrid emulsion; S5. The hybrid emulsion is mixed with an additive to prepare a black water-based ink. The dielectric loss factor ε'' of the black water-based ink coating is 0.08 and 0.07 at 25℃ / 2.45GHz using a rotational rheometer. In S1, the grinding beads produced by the liquid nitrogen-cooled ball mill during the grinding process are 95 yttrium stabilized zirconia beads with a particle size of 0.03~0.3 mm and a bead loading of 70%~90%. The liquid nitrogen temperature inside the mill is controlled at -100℃±50℃. In S2, the mass percentage of nano-grade aniline black is 40%~57%; the mass percentage of emulsifier is 1%~10%; the mass percentage of coupling agent is 1%~5%; the mass percentage of initiator is 0.1%~1%; the mass percentage of defoamer is 0.1%~1%; and the mass percentage of deionized water is 40%~60%. In S3, the mass percentage of acrylate monomer is 40%~58%; the mass percentage of emulsifier is 1%~3%; the mass percentage of pH buffer is 0.1%~1%; and the mass percentage of deionized water is 40%~60%.

2. The method for preparing a low dielectric loss black water-based ink coating as described in claim 1, characterized in that, The aniline black in S1 is oil-soluble aniline black; the additives in S5 include defoamers, leveling agents, anti-wear agents, thickeners, and bactericides.

3. The method for preparing a low dielectric loss black water-based ink coating as described in claim 1, characterized in that, The S5 contains 95%-98% by mass of hybrid emulsion; 0.1%-1% by mass of defoamer; 0.1%-1% by mass of leveling agent; 0.1%-1% by mass of anti-wear agent; 0.1%-1% by mass of thickener; and 0.1%-1% by mass of bactericide.

4. The method for preparing a low dielectric loss black water-based ink coating as described in claim 1, characterized in that, The emulsifiers in S2 and S3 are one or more of the following: sodium dodecylbenzenesulfonate (SDS), polyoxyethylene sorbitan monooleate (Tween 80), polyoxyethylene cetyl ether (Brij 58), alkylphenol polyoxyethylene ether (Triton X-100), polyglycerol monolaurate (PGFE), sodium lauryl ether sulfate (AES), and soybean lecithin (LHP).

5. The method for preparing a low dielectric loss black water-based ink coating as described in claim 1, characterized in that, The coupling agent in S2 is one or more of 3-aminopropyltriethoxysilane, 3-aminopropylmethyldiethoxysilane, N,N-diethyl-3-aminopropyltrimethoxysilane, bis-(3-trimethoxysilylpropyl)amine, phenylaminomethyltriethoxysilane, diethylaminomethyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-ureapropyltrimethoxysilane, and 3-ureapropyltriethoxysilane; the initiator is one or more of ammonium persulfate, potassium persulfate, benzoyl peroxide, di-tert-butyl hydroperoxide, azobisisobutyronitrile, and dilauryl peroxide.

6. The method for preparing a low dielectric loss black water-based ink coating as described in claim 1, characterized in that, The acrylate monomer in S3 is one or more of (meth)acrylic acid, (meth)methyl acrylate, (meth)ethyl acrylate, (meth)butyl acrylate, (meth)tert-butyl acrylate, (meth)isooctyl acrylate, (meth)hydroxyethyl acrylate, and (meth)hydroxypropyl acrylate.

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