In this paper, a water-based carbon black paste for water-based ink was developed by sanding and dispersing. The dispersion process of aqueous carbon black color paste was optimized by orthogonal test, and the effect of ethylene glycol on dispersion of carbon black was investigated. The results show that the optimal conditions are dispersant content 2.5%, grinding speed 2 000 r/min and grinding time 120 min. The ζ potential of aqueous carbon black paste prepared by adding 10% ethylene glycol was -38.5MeV and the average particle size was 117.1nm. After 90 days of storage, the average particle size was 159.6nm, which had better storage stability and application performance.
The general manufacturing process of ink is similar to that of paint. The selection of suitable and stable color paste is an important condition to improve the stability of finished ink and the quality of products. Due to the particularity of its structure, pigment carbon black has small primary particle size, large specific surface area, strong force between particles, no self-dispersion in water, and the grinding process is easy to swell, resulting in gel, which is one of the most difficult pigments to disperse. At present, has conducted some research at home and abroad, adopted the method including surfactant treatment, surface grafting modification, the carbon black surface oxidation modification, etc., has developed many water-based carbon black color paste, but unlike pigment printing ink, writing ink pigment particle size, stability and compatibility with the formula of the demand is higher, Therefore, the water-based ink suitable for neutral pens on the market has less color paste, which is also one of the key technical problems in the development of water-based ink for neutral pens. The experiment on the basis of fully considering the basic formula of water-based ink, without changing their existing under the premise of, the configuration of the mature technology, using the orthogonal experiment, the analysis of the experiment, the influence factors in the process of preparation technology was optimized and the product formula, suitable for water-based ink was prepared with the ultrafine carbon black color paste, water and preparation process is simple, easy to industrial production.
Ⅰ. The Experiment
1. Main Raw Materials
- 6# High pigment carbon black: Grade A, Shanghai Wujing Carbon black Factory;
- Triethanolamine: analytically pure, Shanghai Lingfeng Chemical Reagent Co., LTD.
- Glycol: analytical pure, Sinopharm Chemical Reagent Co., LTD.
- Dispersant: homemade.
- Zetasizer3000HS dynamic light scattering laser particle size and ζ potential analyzer, MalvernInstrumentsLtd;
- JEM2100F Transmission electron microscope, JEOL Company, Japan;
- Sfj-400c Mixing, dispersing, grinding multipurpose machine, Shanghai Modern Environmental Engineering Co., LTD.
- MiniZeta laboratory pin bar Grinding machine, NETch Instrument (Shanghai) Co., LTD.
- Writing and drawing instrument, Tianjin Ruihang Electric Machinery co., LTD.
3. Pretreatment of Carbon Black
The carbon black was ground in a mortar and dried at 105 ℃ for 24 h. After being removed, it was put into a dryer for later use.
4. Preparation of Carbon Black Aqueous Color Paste
The self-made dispersant was fully dissolved in deionized water, ethylene glycol and other mixed solvents, and stirred at the same time, a certain amount of carbon black was slowly added (solid content of color paste is 20%), and then dispersed at a high speed for 30 min, and then transferred to a sand mill (medium: zirconia ball main =1 mm, filling rate :70%) for a certain time to get water-based carbon black color paste.
5. Determination of Particle Size Distribution
The average particle size and size distribution of the color paste were determined by Zetasizer3000HS dynamic light scattering laser particle size and ζ potential analyzer of malwan instruments co., LTD. The mean particle size was represented by Z-Average, and the particle size distribution was represented by volume distribution.
6. Zeta Potentiometry
The color paste was diluted according to the method of particle size determination, and the ζ potential of the color paste was determined by Zetasizer3000HS dynamic light scattering laser particle size and ζ potential analyzer of malwan instruments co., LTD.
7. Observation of Particle Distribution Morphology
The color paste was diluted about 20 times with deionized water, shaken vigorously, and 3-5 drops of liquid were added to the carbon support film. After drying, it was observed under JEM2100F transmission electron microscope made by JEOL Company in Japan.
8. Application Performance Evaluation of Color Paste
The ink was made from the color paste according to the existing formula and process, and the ink was filled into the pen. According to the requirements of QB/ T2625-2003, the writing performance was tested with the writing instrument of Tianjin Ruihang Electric Machinery Co., LTD., namely, at room temperature (20 ±15)℃ and constant humidity (65 ±20)%, The test pen was loaded at an inclination Angle of (65 ±5)° between the axis and the paper surface, the load was 100 g, and the scribing speed was 4.5m /min. The scribing was made on the scribing instrument and the specified test paper in spiral shape, and a continuous circle with line spacing of 2-5 mm (the circumference was 100 mm) was formed.
Ⅱ. Results and Discussion
1. Orthogonal Test Analysis of Preparation Technology of Color Paste
In order to obtain a set of optimized preparation process conditions of color paste, orthogonal experiment was designed to investigate the mutual influence of each process condition on the dispersion effect of carbon black. For sanding process, according to preliminary results from the experiment and the analysis of the literature showed that the dosage of dispersants and the intensity of the grinding paste in the dispersion and dispersion stability of carbon black are influenced and determined by dispersant dosage, sand grinding speed and grinding time of three factors, investigate the dispersion effect, the influence of each factor in three levels, L9 orthogonal table was used to arrange the experiment. The average particle size and zeta potential of color paste were used to evaluate the dispersion effect. The factors and levels of the selected orthogonal test are listed in Table 1.
The average particle size of color paste was taken as the observed value for orthogonal test, anOVA and significance test, in which the significance level α=0.05 was specified. Table 2 and Table 3 are the results of the orthogonal test and anOVA respectively.
From range analysis in Table 2, it can be seen that the influence degree of the three factors on average particle size is A(dispersant dosage)> C(grinding time)> B(grinding speed), but the significance test in Table 3 shows that none of the three factors has a significant impact on the average particle size. From the perspective of statistics, this may be because the orthogonal test has a large error and a small degree of freedom of error (only 2), which leads to low sensitivity of the test and thus covers the significance of the investigated factors. However, model error is used in this experiment to estimate the experimental error, which may also lead to the significance of the investigated factors being covered in the case of interaction between factors. Since each factor has no significant effect on the average particle size, there is no need to carry out multiple comparison between the levels of each factor. In Table 2, the combination of A2, B2 and C2 with the low average is directly selected as the optimal level combination (A2, B2 and C2), that is, the dosage of dispersant is 2.5% and the grinding speed is 2000 r/min. The grinding time was 120 min as the best technological condition. However, it can be seen from the variance analysis that the influence of the three factors is not significant, so the final process conditions can be adjusted to reduce the raw material consumption and operating cost without reducing the product quality (namely the dispersion of the color paste). Zeta potential was taken as the observed value, and the results of orthogonal test and variance analysis were listed in Table 4 and Table 5 respectively.
From range analysis in Table 4, it can be seen that the influence degree of the three factors on ζ potential is C(grinding time)> B(grinding speed)> A(dispersant dosage), in which C and B have similar effects. The significance test in Table 5 found that at the given significance level, factor B(grinding speed) played A significant role, while factor A(dispersant dosage) and factor C(grinding time) did not. As factor B directly represents the mechanical force applied during particle crushing, it is found that this factor has a great influence on ζ potential in the orthogonal test, which also proves on one hand that ζ potential on particle surface is related to particle size in the dispersion system, which is consistent with the previous experimental results. In Table 4, levels A2, B2 and C1 with large average (absolute value) were selected as the optimal level combination (A2, B2 and C1), that is, the dosage of dispersant was 2.5%, grinding speed was 2 000 r/min and grinding time was 60 min were selected as the optimal technological conditions. Compared with the optimal process conditions obtained from the previous orthogonal test, the selection of factor C(grinding time) is inconsistent. Considering the insignificant influence of factor C on particle size, grinding time of 60min can be selected as the optimal process. If the grinding time is only 60min, it may be due to insufficient grinding time. However, the large particles in the system are not completely opened, and the particle size distribution is not uniform and wide, so the grinding time of 60min is not suitable for the optimal process. Considering the significance test results of influencing factors in the latter orthogonal test, since the effect of factor C is not significant, it can be improved at the level 1 of factor C, that is, grinding time 60 min, and grinding time 120 min as the best process, so that the particles in the system can be guaranteed to achieve smaller particle size. The uniform and narrow particle size distribution can be obtained, and the influence of ζ potential on particle surface can be taken into account.
According to the above orthogonal test analysis, the optimal technological conditions were determined as dispersant content 2.5%, grinding speed 2 000 r/min and grinding time 120 min.
2. Effect of Ethylene Glycol on Dispersion of Carbon Black
In the grinding of pigment, pigment aggregates are broken under the action of mechanical force and produce new surface. Dispersant in slurry medium can be fully wetted and adsorbed on the new surface in time to prevent re-aggregation. In addition, if the selection of appropriate additives, reduce the surface tension of particles, so that the new surface of particles can be more quickly wettable, the role of dispersant can be more obvious, which is very important to improve the efficiency and effect of grinding, but also to improve the consistency of paste and ink thickening system, improve the application performance. In this paper, ethylene glycol (EG) with low surface tension was selected as the main auxiliary agent, and carbon black color paste was prepared by sanding time of 2 h to investigate the influence of the addition of ethylene glycol on dispersion of carbon black. Figure 1 and Figure 2 respectively show the influence of ethylene glycol amount on the average particle size of color paste and surface potential of carbon black particles.
As can be seen from Figure 1, with the increase of glycol dosage, the particle size of the colorant decreases at first and then increases, and when the glycol dosage reaches 10%, the particle size of the colorant is the minimum. This is because with the increase of the dosage of ethylene glycol, reduce the surface tension of the medium, showed better wettability on the surface of a carbon black particles freshman, dispersant effect is more apparent, when the glycol exceeds a certain amount, it is because of ethylene glycol has a certain lubricity, makes the particles on the surface with sand grinding medium in collision skid, As a result, mechanical force cannot be applied to particles completely, so they cannot be effectively crushed, but reduce the grinding efficiency. Contrast figure 2 can also be found that the carbon black surface zeta potential with the increase of the amount of ethylene glycol, present a bigger before the change trend of smaller, when the dosage of ethylene glycol 10%, zeta potential, this is because the anionic dispersant under the synergism of ethylene glycol, better adsorption in the smaller particle size, larger specific surface area of the surface of the particles, Adsorption amount is larger, the zeta potential is bigger also, give the particles in the dispersed system more effective electrostatic repulsion, thus dispersed system more stable, when excessive dosage of ethylene glycol, ethylene glycol and dispersant competitive adsorption in carbon black surface, reduce dispersants on carbon black surface adsorption quantity, leading to the zeta potential is reduced, particle size increases.
3. Test The Properties of Color Paste after Process Optimization
According to the above analysis, the optimal technological conditions were dispersant addition amount of 2.5%, grinding speed of 2 000 r/min and grinding time of 120 min. Aqueous carbon black paste with 20% pigment solid content was prepared by using 10% ethylene glycol as solvent and dispersant and triethanolamine as pH regulator. The test results of various properties of the color paste prepared under the process conditions are as follows:
(1) Average Particle Size and Particle Size Distribution
The average particle size of color paste is 117.4nm, and the particle size distribution is narrow and approximately single peak, as shown in FIG. 3.
(2) ζ Potential
The ζ potential on the surface of the carbon black particles of the colorant is -38.5meV.
(3) Storage Stability
The color paste obtained was stored at room temperature. Figure 4 shows the change of the average particle size of the fresh color paste after storage for 15 d and 90 d. The average particle size was 157.1 nm at 15 days and 159.6 nm at 90 days.
Figure 5 shows transmission electron microscopy (TEM) photos of color paste, in which A is TEM photo of fresh color paste and B is TEM photo of color paste after 90 days storage. The overall distribution of both samples showed good dispersity, and the agglomeration of fresh color paste was very rare. However, the agglomeration of fresh color paste after 90 days storage occurred, but the adhesion between the aggregates was less, the boundary was clear, and the adverse situation of serious agglomeration of particles did not occur. So there is no pigment settlement phenomenon.
(4) Application Performance of Color Paste
The color paste was prepared into neutral ink and pen, and no flocculation or precipitation occurred. The ink was filled with pen for circle test, as shown in Figure 6.
- With the increase of rotor speed N, the average particle size of emulsion decreases gradually and the particle size distribution becomes narrow. At 2 800 r/min, the average particle size of emulsion can reach 2.94422 μm.
- With the increase of emulsifying time te and the amount of emulsifier C, the average particle size of emulsion becomes smaller and the particle size distribution becomes narrower;
- Under the same experimental conditions, the average particle size of emulsion prepared by fixed-rotor reactor is smaller than that prepared by ultrasonic emulsification mechanism, and the particle size distribution is narrow；
The results show that it is feasible to prepare emulsion with fixed rotor reactor. In view of the advantages of fixed-rotor reactor, such as simple structure, stable operation and small amplification effect, it is necessary to carry out more systematic research and lay a foundation for industrial application.