HIGH SOLID CONTENT AQUEOUS WHITE PIGMENT PASTE

Abstract

A high solid content aqueous white pigment paste includes: TiO.sub.2 powders; an anionic polyelectrolyte; a charge regulator; an pH regulator; and water. Herein, based on a total weight of the aqueous white pigment paste, the content of the TiO.sub.2 powders is 65 to 80 wt %, and a weight ratio of the TiO.sub.2 powders to the anionic polyelectrolyte ranges from 130 to 180.

Claims

1. A high solid content aqueous white pigment paste, comprising: TiO.sub.2 powders; an anionic polyelectrolyte; a charge regulator; an pH regulator; and water, wherein a content of the TiO.sub.2 powders is 65 to 80 wt % based on a total weight of the aqueous white pigment paste, and a weight ratio of the TiO.sub.2 powders to the anionic polyelectrolyte ranges from 130 to 180.

2. The aqueous white pigment paste of claim 1, wherein a content of the anionic polyelectrolyte is 0.3 to 0.7 wt %, a content of the charge regulator is 0.25 to 0.6 wt %, and a content of the pH regulator is 0.1 to 0.4 wt %.

3. The aqueous white pigment paste of claim 1, wherein the anionic polyelectrolyte is an anionic polyelectrolyte comprising phosphate, carboxylate or sulfonate.

4. The aqueous white pigment paste of claim 1, wherein the anionic polyelectrolyte is polyacrylic acid, polystyrene sulfonate, polyacrylamide sulfonate, carboxymethyl cellulose, sulfonated phenolic resin, polyvinyl sulfonic acid, a salt thereof, or a combination thereof.

5. The aqueous white pigment paste of claim 1, wherein the anionic polyelectrolyte is sodium polyacrylate.

6. The aqueous white pigment paste of claim 1, wherein a molecular weight of the anionic polyelectrolyte is 1000 to 15000 g/mol.

7. The aqueous white pigment paste of claim 1, wherein the charge regulator is aluminum oxide hydroxide.

8. The aqueous white pigment paste of claim 1, wherein the pH regulator is sodium metasilicate.

9. The aqueous white pigment paste of claim 1, wherein a surface tension of the aqueous white pigment paste is greater than 60 mN/m.

10. The aqueous white pigment paste of claim 1, wherein an iso-electric point of the aqueous white pigment paste is pH 2.3 to pH 3.2.

11. The aqueous white pigment paste of claim 1, wherein an absolute value of a zeta potential of the aqueous white pigment paste is greater than or equal to 30 mV when the aqueous white pigment paste has pH greater than 4.5.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0024] FIG. 1 is a diagram showing the iso-electric point measurement results of Examples 1 to 3 and Comparative Examples 1 to 2 of the present invention.

[0025] FIG. 2 is a diagram showing the iso-electric point measurement results of Examples 4 to 6 and Comparative Examples 1 to 2 of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0026] The following describes the implementation of the present invention through specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in the present specification can also be modified and changed in various ways according to different viewpoints and applications without departing from the spirit of the present invention.

[0027] Unless otherwise specified herein, the feature A or or and/or the feature B refers to the presence of the feature A alone, the feature B alone, or both the feature A and the feature B. The feature A and the feature B means that the feature A and the feature B exist at the same time. The terms include, comprise, have and contain mean including but not limited to these.

[0028] If a value is between a first value and a second value, the value may be the first value, the second value, or another value between the first value and the second value.

[0029] Moreover, in the present specification, about a numerical value refers to the scope including 10% of the numerical value, particularly the scope of 5% of the numerical value. The quantity given here is an approximate quantity, that is, in the absence of a specific description about, the meaning of about can still be implied.

[0030] The present invention will be described in more detail by way of examples, but these examples are not intended to limit the scope of the present invention. Unless otherwise specified, in the following comparative examples and examples, temperatures are in degrees Celsius, and parts and percentages are by weight. The relationship between parts by weight and parts by volume is similar to the relationship between kilograms and liters.

[0031] The ingredients used in the following examples and comparative examples of the present invention are shown in Table 1 below.

TABLE-US-00001 TABLE 1 Ingredient Surface-modified TiO.sub.2 (TIOXIDE RFDO) Charge regulator Aluminum oxide hydroxide (AlO(OH)) pH regulator Sodium metasilicate (Na.sub.2SiO.sub.3) Anionic polyelectrolyte Sodium polyacrylate (PAAS)

Comparative Example 1

[0032] 60.0 wt % of TiO.sub.2 pigment powders were dissolved in 40.0 wt % of pure water using a mechanical stiffer (NETZSCH MasterMix). Then, the mixture was ground in a bead mill (SUNIN MACHINE CO., LTD. GOLDEN-MILL) using yttrium zirconium grinding beads having a diameter of 0.3 to 0.4 mm to obtain the aqueous white pigment paste of Comparative Example 1.

Comparative Example 2

[0033] 60.0 wt % of TiO.sub.2 pigment powders were dissolved in a premix of 0.18 wt % of sodium metasilicate, 0.37 wt % of aluminum oxide hydroxide and pure water as the remainder, and uniformly mixed using a mechanical stiffer (NETZSCH MasterMix). Then, the mixture was ground in a bead mill (SUNIN MACHINE CO., LTD. GOLDEN-MILL) using yttrium zirconium grinding beads having a diameter of 0.3 to 0.4 mm to obtain the aqueous white pigment paste of Comparative Example 2.

Example 1

[0034] 65.0 wt % of TiO.sub.2 pigment powders were dissolved in a premix of 0.20 wt % of sodium metasilicate, 0.40 wt % of aluminum oxide hydroxide, 0.44 wt % of sodium polyacrylate and pure water as the remainder, and uniformly mixed using a mechanical stirrer (NETZSCH MasterMix). Then, the mixture was ground in a bead mill (SUNIN MACHINE CO., LTD. GOLDEN-MILL) using yttrium zirconium grinding beads having a diameter of 0.3 to 0.4 mm to obtain the aqueous white pigment paste of Example 1.

Examples 2 to 6

[0035] According to the ingredient contents listed in Tables 2 and 3 below, the aqueous white pigment pastes of Examples 2 to 6 were prepared using the preparation method described in Example 1.

Zeta Potential Measurement

[0036] The ground aqueous white pigment paste of the example and comparative examples was formulated into dispersion solutions of 10 ppm. The pH value of the dispersion solution was adjusted to 2 to 12, and 8 to 10 pH points were selected. Zeta potential was measured using MALVERN ZETASIZER NANO ZS and plotted to obtain the isoelectric point (IEP). The results are shown in Tables 2 and 3 below.

Surface Tension

[0037] The ground aqueous white pigment pastes of the examples and comparative examples were diluted with water to a solid content of 10 wt %. The surface tension was measured using a KYOWA SURFACE TENSIOMETER CBVP-A2. The results are shown in Tables 2 and 3 below.

TABLE-US-00002 TABLE 2 (unit: wt %) Comparative Comparative example 1 example 2 Example 1 Example 2 Example 3 TiO.sub.2 60% 60% 65% 70% 75% Na.sub.2SiO.sub.3 0.18% 0.20% 0.21% 0.23% AlO(OH) 0.37% 0.40% 0.43% 0.46% PAAS 0.44% 0.48% 0.51% Water Add to 100% IEP 9.1 7.8 3.0 3.0 3.0 pH value with zeta Less Less Greater Greater Greater potential >|30 mV| than 6.8 than 5.3 than 4.8 than 4.9 than 5.1 (Stabilized range) Greater Greater than 10.3 than 9.1 Surface tension after 71.7 70.4 72.3 71.8 68.2 dilution (mN/m)

[0038] Please refer to the results of Table 2 above and FIG. 1. To meet the pH range of 7 to 9 for white ink applications, Comparative Example 1 used a commercially available surface-modified TiO.sub.2 aqueous solution (iso-electric point 9.1, pH stabilized range less than 6.8 or greater than 10.3) for the charge property adjustment. When the charge regulator (aluminum oxide hydroxide) and the pH regulator (sodium metasilicate) were added, as shown in Comparative Example 2, the IEP was lowered from 9.1 to 7.8, but the pH value for stable suspension still did not fall within the application range of the ink. When the anionic polyelectrolyte (sodium polyacrylate, PAAS) was added, as shown in Examples 1 to 3, the IEP was significantly reduced to 3. In addition, as shown in FIG. 1, when the pH value is greater than 4.5, the aqueous white pigment pastes of Examples 1 to 3 have high and stable suspension stability. Regardless of whether the solid content exceeds 65% (Example 1) or 70% (Example 2), or even when the solid content is increased to 75% (Example 3), the TiO.sub.2 particles in the aqueous white pigment paste of the present invention still maintain high suspension stability and do not delaminate or settle.

[0039] Furthermore, the aqueous white pigment paste of the present invention has excellent surface tension properties. As the surface tension of the aqueous white pigment paste increases (for example, the surface tension of the aqueous white pigment paste of the present invention may be greater than 60 mN/m, and even greater than 70 mN/m), the selectivity of the dispersant (e.g., the dispersant used in ink formulation) becomes more diverse, which helps to improve the splattering problem caused by large differences in surface tension between different substrates when using aqueous white pigment paste.

TABLE-US-00003 TABLE 3 (unit: wt %) Comparative Comparative example 1 example 2 Example 4 Example 5 Example 6 TiO.sub.2 60% 60% 70% 70% 70% Na.sub.2SiO.sub.3 0.18% 0.21% 0.21% 0.21% AlO(OH) 0.37% 0.43% 0.43% 0.43% Molecular weight of 1200 8000 15000 PAAS (0.48%) Water Add to 100% IEP 9.1 7.8 3.1 2.7 2.4 pH value with zeta Less Less Greater Greater Greater potential >|30 mV| than 6.8 than 5.3 than 4.5 than 5.3 than 6.2 (Stabilized range) Greater Greater than 10.3 than 9.1 Surface tension after 71.7 70.4 71.5 71.8 70.4 dilution (mN/m)

[0040] The results in Table 3 above and FIG. 2 verify the effect of the molecular weight of the anionic polyelectrolyte on dispersion stability. In the examples, PAAS with a molecular weight of 1200 (Example 4), 8000 (Example 5), and 15000 (Example 6) were used to adjust the zeta potential/IEP of TiO.sub.2 particles. The results showed that the anionic polyelectrolytes with the aforementioned molecular weights could make IEP to 3.1, 2.7, and 2.4, respectively. However, as the molecular weight of the anionic polyelectrolyte increased, the pH at which the zeta potential fell below 30 mV shifted from 4.5 to 5.3 or even above 6.2. That is to say, when PAAS with a molecular weight of 15,000 is added, the pH needs to be above 6.2 to achieve better suspension stability. The above results show that as the molecular weight of the anionic polyelectrolyte increases, the pH value for achieving better suspension stability also increases. Therefore, when the molecular weight for better suspension stability is within a specific range, good suspension stability can be achieved.

[0041] In view above, the high solid content aqueous white pigment paste provided by the present invention can maintain a good stability (the absolute value of the zeta potential can be greater than or equal to 30 mV (||30 mV)) even when the solid content of the TiO.sub.2 powders exceeds 65 wt %. Thus, the applicability of the aqueous white pigment paste can be significantly improved. On the other hand, the high solid content aqueous white pigment paste provided by the present invention has an iso-electric point (IEP) of approximately pH 3, and can reach an absolute value of the zeta potential greater than or equal to 30 mV (||30 mV) at a pH greater than 4.5. Thus, the pH range of the aqueous white pigment paste can be significantly expanded. Furthermore, the high solid content aqueous white pigment paste provided by the present invention has a high surface tension (>60 mN/m). Thus, the surface tension adjustment capabilities of the aqueous white pigment paste can be significantly improved.

[0042] The above embodiments are merely examples for the convenience of description. The scope of rights claimed by the present disclosure should be based on the scope of the patent application, and is not limited to the above embodiments.

[0043] Although the present disclosure has been explained in relation to its embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the disclosure as hereinafter claimed.