Black water-based ink with low dielectric loss and preparation method thereof

Abstract

The invention belongs to the technical field of water-based ink, and particularly relates to low-dielectric-loss black water-based ink and a preparation method thereof.The preparation method comprises the following steps that aniline black is ground to the nanoscale particle size; the preparation method comprises the following steps: mixing nano aniline black, an emulsifier, a coupling agent, an initiator and deionized water to prepare a pre-dispersion liquid; the preparation method comprises the following steps: mixing and emulsifying an acrylate monomer, an emulsifier, a PH buffer agent and deionized water to prepare a seed emulsion; dropwise adding the pre-dispersion liquid into a seed emulsion, and carrying out a graft polymerization reaction to generate a nigrosine-acrylate hybrid emulsion; and mixing the hybrid emulsion with an auxiliary agent to prepare the black water-based ink. The dielectric loss of the black ink layer is reduced, and the process requirements that the black ink layer is not prone to overheating and scorching when the black ink layer is subjected to microwave drying to remove moisture are met. The compatibility of aniline black powder and water-based resin is improved, and the problems of dispersion and precipitation of high-concentration aniline black powder are solved. And the secondary agglomeration condition of the nigrosine powder is obviously reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of water-based inks, and in particular relates to a low-dielectric-loss black water-based ink and a preparation method thereof. Background Art

[0002] In the printing industry, water-based inks are traditionally dried using heat. However, this method suffers from low energy efficiency, incomplete drying, and a tendency to create a phenomenon known as "dry on the surface but not on the inside." For example, in the traditional paper and film printing industry, increasing oven temperatures and temperature gradients to speed drying can lead to deformation or scorching of the film or paper, resulting in product defects.

[0003] Under microwave drying conditions, wet materials are exposed to a microwave high-frequency electric field with an extremely short oscillation period. Water molecules within the material become polarized and align neatly along the direction of the microwave field. They then rapidly rotate in response to the alternating 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 of the microwave energy is converted into molecular kinetic energy, expressed as heat, raising the water temperature and causing it to leave the material, thereby drying it. In other words, after microwaves enter and are absorbed by the material, their energy is converted into heat within the dielectric medium. Microwave heating allows uniform heat penetration regardless of the material's shape, creating a puffing effect and facilitating pulverization. Household microwave ovens are a typical application of this principle. Therefore, microwave drying is a highly efficient drying method that utilizes electromagnetic waves as the heating source, with the material itself acting as the heat source. It is widely used in drying applications 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) and strongly absorbs energy in microwave fields, converting it into heat [Metaxas, AC, & Meredith, RJ (1983). Industrial microwave heating. Peter Peregrinus Ltd.]. In contrast, colored organic pigments (such as phthalocyanine blue and azo pigments) typically have lower dielectric loss and weaker microwave absorption, resulting in a uniform and slow temperature rise during drying. At 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 water-based inks are printed on paper bags or films, the rapid internal temperature rise of the carbon black coating during microwave drying can exceed the heat resistance limit of the paper or film (typically, the carbonization temperature of paper is around 200°C, while the heat deformation temperature of film is even lower). This can easily cause the black coating to absorb excessive microwave energy, leading to overheating or even burning. Lowering the microwave power can also lead to insufficient microwave energy reaching the colored coatings, resulting in poor drying.

[0005] The significant difference in dielectric loss parameters between traditional carbon black and traditional organic pigments makes it difficult to adjust microwave drying parameters for CMYK prints (i.e., prints composed of overprinted cyan, magenta, yellow, and black inks) on the same page, limiting the application of microwave drying in the printing industry. Aniline black (Pigment Black 1), the only industrialized black organic pigment, has physical properties that are completely different from carbon black. Its dielectric parameters, such as microwave absorption, microwave reflection, microwave scattering, and microwave penetration, are essentially the same as those of organic pigments. Therefore, replacing carbon black with aniline black in water-based black ink can avoid carbon black's shortcomings in microwave drying.

[0006] However, commercially available aniline black is either completely oil-soluble (neither soluble nor dispersible in water) or completely water-soluble (typically a mixture of oil-soluble aniline black and sodium sulfonate, resulting in completely water-resistant printed products and dissolving and discoloring upon contact with water). Therefore, commercially available aniline black cannot be directly applied to water-based inks for printed products. Therefore, the idea is to first grind aniline black powder into a nano-sized powder through a freeze-grinding process, then graft-polymerize it into a water-based resin as a coloring particle, integrating it into the whole. This not only effectively solves the problem of effective dispersion of aniline black, but also further reduces the chance of secondary agglomeration between aniline black particles after polymerization with the water-based resin. The black water-based ink formulated using this process not only solves the overheating and coking problem of traditional carbon black systems during microwave drying, but also addresses the problem of traditional aniline black being unsuitable for water-based inks that require 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 a frequency of 2.45 GHz or 915 GHz) penetrates the material, the microwave electric field causes the polar molecules within the material (primarily water, but also polar material components) to undergo orientation polarization. Under the high-frequency alternating electric field, the reciprocating rotational motion of these molecules lags behind the electric field changes due to internal frictional resistance, resulting in the irreversible conversion of some of the microwave energy into molecular kinetic energy (heat). The efficiency of this conversion of electromagnetic energy into heat is directly quantified by the dielectric loss factor (ε''). Higher ε'' values ​​indicate a greater ability of the material to absorb energy in the microwave field and convert it into heat, resulting in a faster heating rate.

[0008] In CMYK four-color printing, traditional carbon black colorants typically exhibit an extremely high dielectric loss factor (ε'') due to their unique graphitized microcrystalline structure and conjugated π-electron system. In contrast, color organic pigments (such as phthalocyanines and azo pigments) typically have very low ε'' values. This significant difference in ε'' is the core physical cause of microwave drying problems. Under the same microwave power and electric field intensity, the high-ε'' carbon black ink layer absorbs energy intensely and heats 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'' color ink layer will absorb insufficient energy, resulting in inefficient evaporation of internal moisture, leading to problems such as poor drying (false drying) and sticking. Therefore, measuring and comparing the ε'' loss factor of different ink coatings (especially black and color) is a key indicator for evaluating their heat absorption capacity and heating rate in the microwave field. It also provides a core scientific basis for addressing microwave drying compatibility issues for multi-color printed products. Summary of the Invention

[0009] The purpose of the present invention is to solve the problems of easy overheating and coking of traditional carbon black system water-based ink during microwave drying, and the application of aniline black as a colorant in water-based ink.

[0010] In order to achieve the above object, the present invention provides a method for preparing a low dielectric loss black water-based ink, comprising the following steps: S1. Grind aniline black to nano-particle size, D90 < 0.3 μm; S2. The nano-aniline black, emulsifier, coupling agent, initiator, defoamer and deionized water are mixed to prepare a pre-dispersion; S3. The acrylate monomer, emulsifier, PH buffer and deionized water are mixed and emulsified to prepare a seed emulsion; S4. The pre-dispersed liquid is added dropwise to the seed emulsion, and a graft polymerization reaction is carried out at 70 to 90 ° C to generate a nigrosine - acrylate hybrid emulsion; S5. mixing the hybrid emulsion with an additive to prepare a black water-based ink.

[0011] Preferably, the aniline black in S1 is oil-soluble aniline black; and the additives in S5 include a defoamer, a leveling agent, an anti-wear agent, a thickener and a bactericide.

[0012] Preferably, the mass percentage of nano-aniline black in S2 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%.

[0013] Preferably, the mass percentage of the acrylic acid monomer in S3 is 40%-58%; the mass percentage of the emulsifier is 1%-3%; the mass percentage of the pH buffer is 0.1%-1%; and the mass percentage of deionized water is 40%-60%.

[0014] Preferably, the mass percentage of the hybrid emulsion in S5 is 95%-98%; the mass percentage of the defoaming agent 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%.

[0015] Preferably, the emulsifier in S2 and S3 is one or more of sodium dodecylbenzenesulfonate SDS, polyoxyethylene sorbitan monooleate Tween 80, polyoxyethylene cetyl alcohol ether Brij 58, alkylphenol polyoxyethylene ether Triton X-100, polyglycerol monolaurate PGFE, sodium lauryl polyether sulfate AES, and soybean lecithin LHP.

[0016] 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-glycidyloxypropyltrimethoxysilane, 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 dilauroyl peroxide.

[0017] Preferably, the acrylic acid ester 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.

[0018] Preferably, the seed emulsion in S3 further comprises acrylic acid or methacrylic acid.

[0019] Preferably, during the grinding process in S1, the grinding beads of the liquid nitrogen refrigerated ball mill are 95 yttrium-stabilized zirconia beads with a particle size of 0.03-0.3 mm, a bead filling amount of 70%-90%, and the temperature of the liquid nitrogen in the inner tank is controlled at -100°C ± 50°C.

[0020] The invention also provides a low-dielectric-loss black water-based ink.

[0021] Compared with the prior art, the present invention has the following advantages: The present invention uses aniline black as a black colorant, replacing the traditional pigment carbon black in water-based inks and being used in microwave drying applications. This significantly reduces the dielectric loss of the black ink layer, meeting the process requirements of microwave drying to remove moisture from the black ink layer without overheating or burning. Aniline black is grafted onto an acrylic emulsion using an emulsion polymerization device, significantly improving the compatibility of the powder with the resin and solving the dispersion and precipitation issues of high-concentration aniline black powder. Furthermore, because the grafted polymer has excellent coating properties on aniline black, secondary agglomeration of the aniline black powder is significantly reduced. DETAILED DESCRIPTION

[0022] The terms used in the present invention generally have the meanings commonly understood by those skilled in the art unless otherwise specified.

[0023] In the following examples, various processes and methods not described in detail are conventional methods well known in the art.

[0024] The reagents used in the following examples were purchased from common commercial channels. The experimental operations and experimental conditions not specified were based on conventional operations and conditions in the art.

[0025] The specific implementation of the present invention is described below with reference to examples.

[0026] Example 1 Step 1: Load 95 yttrium-stabilized zirconia beads (0.05 mm particle size, 80% bead loading) into a cryogenic ball mill (Cryo / Mill 6870D custom model). Open the inner jacket of the ball mill and pass liquid nitrogen through it while controlling the temperature at -87°C ± 3°C. Pour in 100 g of aniline black powder (Tokyo Color Industry Co., Ltd., Japan, model SUPER BLACK® NO.2) and grind repeatedly until the powder particle size D90 is less than 0.3 μm (laser particle size analyzer measured D90 = 0.18 μm). Filter through a 5000-mesh vibrating sieve to obtain 94.7 g of nano-aniline black.

[0027] Step 2: Add the materials in the following table in the order of deionized water, emulsifier, coupling agent, initiator, defoamer, and nano aniline black, totaling 189.41 g, and simultaneously use a homogenizer at 3000 rpm for 2 hours to disperse evenly and filter with a 2000 mesh filter to prepare 182.20 g aniline black pre-dispersion liquid; Table 1

[0028] Step 3: Add 727.88 g of the materials in the table below into a beaker in sequence and mix at a high speed of 1500 rpm for 40 minutes until a milky white uniform solution is formed and no stratification occurs when the mixture is allowed to stand.

[0029] Table 2

[0030] Step 4: Pour 727.88 g of the seed emulsion from Step 3 into a four-necked flask used for emulsion polymerization, introduce nitrogen, and expel oxygen. Then, add 182.20 g of the nigrosine pre-dispersion prepared in Step 2 dropwise to the seed emulsion. Simultaneously, raise the temperature to 86°C ± 2°C and polymerize for 2.5 hours. After the reaction is complete, cool to room temperature and filter through a 100-mesh filter to produce 893.45 g of a nigrosine-acrylate hybrid black emulsion.

[0031] Step 5: Add the raw materials listed in the following table to a glass beaker in sequence. Disperse the mixture at 300 rpm for 10 minutes, then filter through a 100-mesh filter to obtain 100 g of black water-based ink. The viscosity of the ink was measured at 25°C using a Zahn Cup 4# (Chai's Cup 4) and the pH value was 8.3 using a pH meter.

[0032] Table 3

[0033] Test Example 1 Several commercially available black water-based inks for flexographic printing on paper, all based on carbon black, were selected as reference samples. Printing conditions were: a flexographic proofing machine manufactured by Zhongshan Nuobang, an anilox roller with a 100-line gauge, and 280-gram Sun brand food-grade white cardboard. The test results are listed in Table 4: Table 4

[0034] Storage stability test method and results: According to GB / T 6753.3-1986 "Test method for storage stability of coatings", approximately 90g of the black water-based ink prepared in Example 1 was sampled, placed in a 100ml plastic bottle, sealed, and placed in a 50°C constant temperature oven. After 30 days, the sample was removed and cooled to room temperature. No visible precipitation or delamination was observed. The viscosity was re-measured using a ZahnCup 4# at 25°C and the result was 12.58 seconds. The pH value was measured using a pH meter and was 8.21, indicating minimal fluctuation and within the normal range.

[0035] Example 2 Step 1: Load 95 yttrium-stabilized zirconia beads (0.1 mm particle size, 88% bead loading) into a cryogenic ball mill (Cryo / Mill 6870D custom model). Open the inner jacket of the ball mill and pass liquid nitrogen through it while controlling the temperature at -70°C ± 5°C. Pour in 200 g of aniline black powder (BASF, Germany, model Paliotol Black L0080) and grind repeatedly until the powder particle size D90 is less than 0.3 μm (laser particle size analyzer measured D90 = 0.12 μm). Filter through a 5000-mesh vibrating sieve to obtain 193.75 g of nano-aniline black.

[0036] Step 2: Add the materials in the following table in order, totaling 284.03 g, and use a homogenizer at 3500 rpm for 2.5 hours to disperse evenly, then filter with a 2000 mesh filter to prepare 278.65 g of aniline black pre-dispersion; Table 5

[0037] Step 3: Add 1000 g of the materials in the table below into a beaker in sequence and mix at a high speed of 1000 rpm for 40 minutes until a milky white uniform solution is formed and no stratification occurs when the solution is left standing.

[0038] Table 6

[0039] Step 4: Pour 1000g of the seed emulsion from step 3 into a four-necked flask used for emulsion polymerization, introduce nitrogen, and expel oxygen. Then, dropwise add 278.65g of the nigrosine pre-dispersion prepared in step 2 to the seed emulsion. Simultaneously, raise the temperature to 80°C ± 2°C and polymerize for 3.5 hours. After the reaction is complete, cool to room temperature and filter through a 120-mesh filter to produce 1252.68g of a nigrosine-acrylate hybrid black emulsion.

[0040] Step 5: Add the raw materials listed in the following table to a glass beaker in sequence. Disperse the mixture at 300 rpm for 10 minutes, then filter through a 100-mesh filter to produce 100 g of black water-based ink (theoretical aniline black content: 11.35%). The viscosity was measured at 25°C using a Zahn Cup 4# filter and was 16.20 seconds. The pH was measured using a pH meter and was 8.5.

[0041] Table 7

[0042] Test Example 2 Water-based inks for flexographic printing on paper of various colors were prepared using a conventional method. Specifically, 37.35 g of purified water, 15.00 g of aqueous resin liquid (JONCRYL 196 MEA), 35.00 g of aqueous acrylic emulsion (JONCRYL 631AP), 0.30 g of defoamer (TEGO 810), 1.00 g of dispersant (TEGO 755W), 11.35 g of the colorant to be tested, and 150.00 g of zirconium beads (95 specification / size 0.4-0.6 mm) were added to a 500 ml glass jar, sealed, and shaken at high speed for 2 hours. The jar was then filtered through 100 mesh to obtain conventional water-based inks of various colors. See Table 8 for details: Table 8

[0043] Printing conditions were: a flexographic proofing machine manufactured by Zhongshan Nuobang, an anilox roller with a 100-line screen, and 280gsm Sun brand food-grade white cardboard. The test results are listed in Table 9: Table 9

[0044] Storage stability test method and results: According to GB / T 6753.3-1986 "Test method for storage stability of coatings", approximately 90g of the black water-based ink prepared in Example 1 was sampled, placed in a 100ml plastic bottle, sealed, and placed in a 50°C constant temperature oven. After 30 days, the sample was removed and cooled to room temperature. No visible precipitation or delamination was observed. The viscosity was re-measured using a ZahnCup 4# at 25°C and the result was 17.03 seconds. The pH value was measured using a pH meter and was 8.42, indicating minimal fluctuation and within the normal range.

[0045] In the above-mentioned Examples 1 and 2, and the corresponding Test Examples 1 and 2, the present invention uses an X-Rite densitometer to measure color density. Higher color density values ​​indicate stronger light absorption, resulting in a visually darker appearance and better hiding power. The test results demonstrate that using aniline black as a black colorant, replacing traditional carbon black pigments in water-based inks, not only maintains sufficient print color density without compromising blackness, but also significantly reduces the dielectric constant and dissipation factor of traditional black ink coatings, achieving drying characteristics in microwave environments that are essentially consistent with those of colored organic pigment coatings. This addresses the issue of overheating and scorching of the black ink layer in CMYK prints in traditional microwave drying environments. Furthermore, by grafting aniline black onto an acrylic emulsion via emulsion polymerization, the resulting black water-based ink significantly improves the delamination and precipitation issues of lipophilic aniline black powder at low viscosities.

[0046] The above is a detailed description of the embodiments to facilitate proper understanding and application of the present invention by those skilled in the art. Any improvements or modifications to the technical solutions derived by those skilled in the art based on the present invention, without inventive effort, solely 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, characterized in that: The following steps are involved: S1. Grind aniline black to nano-particle size, D90 < 0.3 μm; S2. The nano-aniline black, emulsifier, coupling agent, initiator, defoamer and deionized water are mixed to prepare a pre-dispersion; S3. The acrylate monomer, emulsifier, pH buffer and deionized water are mixed and emulsified to prepare a seed emulsion; S4. The pre-dispersed liquid is added dropwise to the seed emulsion, and a graft polymerization reaction is carried out at 70 to 90 ° C to generate a nigrosine - acrylate hybrid emulsion; S5. mixing the hybrid emulsion with an additive to prepare a black water-based ink.

2. The method for preparing a low dielectric loss black water-based ink according to claim 1, wherein: The aniline black in S1 is oil-soluble aniline black; the auxiliary agents in S5 include defoaming agent, leveling agent, anti-wear agent, thickener and bactericide.

3. The method for preparing a low dielectric loss black water-based ink according to claim 1, wherein: The mass percentage of nano-aniline black in S2 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 defoaming agent is 0.1%-1%; and the mass percentage of deionized water is 40%-60%.

4. The method for preparing a low dielectric loss black water-based ink according to claim 1, wherein: The mass percentage of the acrylic acid monomer in S3 is 40%-58%; the mass percentage of the emulsifier is 1%-3%; the mass percentage of the pH buffer is 0.1%-1%; and the mass percentage of deionized water is 40%-60%.

5. The method for preparing a low dielectric loss black water-based ink according to claim 2, wherein: The mass percentage of the hybrid emulsion in the S5 is 95%-98%; the mass percentage of the defoaming agent 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 fungicide is 0.1%-1%.

6. The method for preparing a low dielectric loss black water-based ink according to claim 1, wherein: The emulsifier in S2 and S3 is one or more of sodium dodecylbenzenesulfonate SDS, polyoxyethylene sorbitan monooleate Tween 80, polyoxyethylene cetyl alcohol ether Brij 58, alkylphenol polyoxyethylene ether Triton X-100, polyglycerol monolaurate PGFE, sodium lauryl polyether sulfate AES, and soybean lecithin LHP.

7. The method for preparing a low dielectric loss black water-based ink according to claim 1, wherein: 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-glycidyloxypropyltrimethoxysilane, 3-ureapropyltrimethoxysilane, and 3-ureapropyltriethoxysilane; the initiator is one or more of ammonium persulfate, potassium persulfate, benzoyl peroxide, di-tert-butyl hydroperoxide, azobisisobutyronitrile, and dilauroyl peroxide.

8. The method for preparing a low dielectric loss black water-based ink according to claim 1, wherein: The acrylic acid ester 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.

9. The method for preparing a low dielectric loss black water-based ink according to claim 1, wherein: The seed emulsion in S3 further includes acrylic acid or methacrylic acid.

10. The method for preparing a low dielectric loss black water-based ink according to claim 1, wherein: The grinding in S1 is performed using a liquid nitrogen refrigerated ball mill. The grinding beads of the liquid nitrogen refrigerated ball mill are 95 yttrium-stabilized zirconia beads with a particle size of 0.03-0.3 mm, a bead filling amount of 70%-90%, and an inner tank liquid nitrogen temperature controlled at -100°C ± 50°C.

11. A low dielectric loss black water-based ink prepared by the method for preparing a low dielectric loss black water-based ink according to any one of claims 1 to 10.

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