Study on the Application of Talc Powder Instead of Stripped Kaolin in Light Coated Paper
2020-11-13 11:15:54
With the increasing impact of modern electronic media on cultural paper, traditional cultural paper is facing unprecedented pressure. Light-coated paper, as a kind of cultural paper, is also facing the challenge of this pressure. Under the premise of ensuring product quality, continuously reducing production costs is one of the important measures to cope with this challenge. Light-coated paper, as a kind of paper that is coated once and has a low coating amount, has high requirements for pigment hiding. Widely used in existing coating formulations is stripping kaolin with high hiding property. Mainly imported from Brazil, the price is relatively high. If the tartar powder with the same covering ability and no need to import is replaced by the cost-effective talcum powder, it will play an active role in cost saving.
Table 1 Laboratory topping formula and dosage
Low shear viscosity of the coating: measured by a viscometer, the measured temperature was 25 ° C, and the measured rotational speed was 60 r / min.
High shear viscosity of the coating: measured by a rotary rheometer, plate, shear rate 1-20000 s-1.
Laboratory paper coating: coating on an experimental coater, coating with a doctor blade, and obtaining the required coating amount by adjusting the blade angle, the top coating amount was 10 g/m2.
Laboratory paper calendering: calendering on a 25FC-200E laboratory supercalender with a calendering temperature of 70 ° C and a rotational speed of 30 r/min.
The conventional physical properties of the light coated paper were determined in accordance with the method specified in the standard GB/T 10335.2-2005 coated paper and paperboard lightweight coated paper.
2. Results and Discussion (1) Basic properties of talc Powder For pigments used in paper coatings, pigments are generally required to have high brightness, low impurity content, and easy dispersion. Table 2 shows the basic properties of two pigments, Brazilian kaolin and talc.
Table 2 Basic properties of pigments
It can be seen from Table 2 that compared with Brazilian kaolin, the characteristics of talc powder T90 are mainly characterized by relatively high brightness and high dispersant dosage. In addition, the average particle size of the two pigments is similar, but the 2μm content of the talc powder is significantly higher than that of the Brazilian kaolin.
From the perspective of the granular structure, the kaolin is in the form of a lamellar layered structure, while the talc is in a single sheet structure. Although the two pigments have different morphological structures, they are all flake-like structural pigments, which may provide better coating performance.
(2) Effect of talc powder instead of Brazilian kaolin on coating properties The corresponding coatings were prepared according to the formulations listed in Table 2. The properties of the coatings are shown in Table 3.
Table 3 Performance of coatings
It can be seen from Table 3 that under the condition that the solid content of the coating is similar, as the dosage of talc in the coating formulation increases and the dosage of kaolin decreases continuously, the low shearing diligence of the coating increases, but the increase is limited.
Figure 1 coating high shear viscosity
Figure 2 Viscosity of the coating at a shear rate of 10,000 s-1
Table 4 Cardboard properties after coating
It can be seen from Table 4 that when 22.5 parts of talc is completely substituted for the Brazilian kaolin in the original formula, it does not adversely affect the paper-forming properties of the light-coated paper, and the optical properties and printing surface properties are similar to those of the Brazilian kaolin formula. s level.
From the laboratory evaluation results, the replacement of kaolin in the current light-coating formula with talc does not adversely affect the performance of light-coated paper. Since the talc powder itself has the characteristics of hydrophobic and oleophilic, it is difficult to disperse at a higher solid content without modification (the unmodified talc powder generally has a solid content of about 60%), in order to overcome this defect, the experiment The talc used is properly hydrophilically modified in the processing project so that it can be smoothly dispersed at 70% solid content, and the modification process makes the talc powder have the characteristics of shear thinning, that is, The dispersed pigment dispersion will increase in viscosity without agitation, but will decrease significantly after proper agitation. This feature may also cause the low shear viscosity of the formulated coating to be slightly higher than that of the kaolin formulation. In addition, from the laboratory observations, although talc has the characteristics of shear thinning compared with kaolin, its sedimentation performance is superior to kaolin.
3. Conclusions (1) Compared with kaolin, talc pigment has the characteristics of relatively high whiteness.
(2) When talc replaces kaolin in light-coated paper coating, the high shear viscosity of the coating decreases with the increase of the substitution amount, although the low shear viscosity of the coating increases slightly.
(3) After replacing the kaolin with talc powder, after replacing the kaolin in the formula with talc powder T90, both the optical properties of the paper and the surface properties of the printing are kept close to the original formula.
1. Experiment (1) Experimental raw materials Brazil imported stripped kaolin, 95 grade heavy calcium carbonate (GCC), talc powder T90, styrene-butadiene latex, water retaining agent CMC, dispersant, lubricant, water repellent, defoamer, coating Cloth base paper.
(2) Experimental method Determination of basic properties of pigment: The particle size, whiteness and optimum dispersion conditions of talc and kaolin were determined according to standard GB/T 14563 kaolin and its test method.
Coating preparation and performance determination: Laboratory topcoats were prepared according to the formulation of Table 1, with a solids content of 64.0%.
(2) Experimental method Determination of basic properties of pigment: The particle size, whiteness and optimum dispersion conditions of talc and kaolin were determined according to standard GB/T 14563 kaolin and its test method.
Coating preparation and performance determination: Laboratory topcoats were prepared according to the formulation of Table 1, with a solids content of 64.0%.
Table 1 Laboratory topping formula and dosage
Low shear viscosity of the coating: measured by a viscometer, the measured temperature was 25 ° C, and the measured rotational speed was 60 r / min.
High shear viscosity of the coating: measured by a rotary rheometer, plate, shear rate 1-20000 s-1.
Laboratory paper coating: coating on an experimental coater, coating with a doctor blade, and obtaining the required coating amount by adjusting the blade angle, the top coating amount was 10 g/m2.
Laboratory paper calendering: calendering on a 25FC-200E laboratory supercalender with a calendering temperature of 70 ° C and a rotational speed of 30 r/min.
The conventional physical properties of the light coated paper were determined in accordance with the method specified in the standard GB/T 10335.2-2005 coated paper and paperboard lightweight coated paper.
2. Results and Discussion (1) Basic properties of talc Powder For pigments used in paper coatings, pigments are generally required to have high brightness, low impurity content, and easy dispersion. Table 2 shows the basic properties of two pigments, Brazilian kaolin and talc.
Table 2 Basic properties of pigments
It can be seen from Table 2 that compared with Brazilian kaolin, the characteristics of talc powder T90 are mainly characterized by relatively high brightness and high dispersant dosage. In addition, the average particle size of the two pigments is similar, but the 2μm content of the talc powder is significantly higher than that of the Brazilian kaolin.
From the perspective of the granular structure, the kaolin is in the form of a lamellar layered structure, while the talc is in a single sheet structure. Although the two pigments have different morphological structures, they are all flake-like structural pigments, which may provide better coating performance.
(2) Effect of talc powder instead of Brazilian kaolin on coating properties The corresponding coatings were prepared according to the formulations listed in Table 2. The properties of the coatings are shown in Table 3.
Table 3 Performance of coatings
It can be seen from Table 3 that under the condition that the solid content of the coating is similar, as the dosage of talc in the coating formulation increases and the dosage of kaolin decreases continuously, the low shearing diligence of the coating increases, but the increase is limited.
Figure 1 coating high shear viscosity
It can be seen from Fig. 1 that when the kaolin in the coating formulation is continuously replaced by talc, the shearing rate increases, the high shear viscosity of the coating changes substantially the same; but from the local high shear rate range, The increasing use of talc instead of kaolin increases the high shear viscosity of the coating.
Figure 2 Viscosity of the coating at a shear rate of 10,000 s-1
It can be seen from Fig. 2 that when the shear rate of the paint reaches 10,000 s-1, the viscosity of the coating containing the talc powder formulation is lower than that of the full kaolin formula.
In general, when talc replaces kaolin in light-coated paper coatings, the amount of substitution decreases, although the low shear viscosity of the coating increases slightly, the high shear viscosity of the coating decreases. It shows that the replacement of kaolin with talc will not adversely affect the coating performance of the coating. On the contrary, under the same high shear viscosity, the talc can be used instead of kaolin to further improve the solid content of the coating for better coating. effect.
(3) The effect of talc powder instead of kaolin on the performance of lightweight coated paper was coated by a bar, and the coating amount was controlled at 9-10 g/m2.
In general, when talc replaces kaolin in light-coated paper coatings, the amount of substitution decreases, although the low shear viscosity of the coating increases slightly, the high shear viscosity of the coating decreases. It shows that the replacement of kaolin with talc will not adversely affect the coating performance of the coating. On the contrary, under the same high shear viscosity, the talc can be used instead of kaolin to further improve the solid content of the coating for better coating. effect.
(3) The effect of talc powder instead of kaolin on the performance of lightweight coated paper was coated by a bar, and the coating amount was controlled at 9-10 g/m2.
Table 4 Cardboard properties after coating
It can be seen from Table 4 that when 22.5 parts of talc is completely substituted for the Brazilian kaolin in the original formula, it does not adversely affect the paper-forming properties of the light-coated paper, and the optical properties and printing surface properties are similar to those of the Brazilian kaolin formula. s level.
From the laboratory evaluation results, the replacement of kaolin in the current light-coating formula with talc does not adversely affect the performance of light-coated paper. Since the talc powder itself has the characteristics of hydrophobic and oleophilic, it is difficult to disperse at a higher solid content without modification (the unmodified talc powder generally has a solid content of about 60%), in order to overcome this defect, the experiment The talc used is properly hydrophilically modified in the processing project so that it can be smoothly dispersed at 70% solid content, and the modification process makes the talc powder have the characteristics of shear thinning, that is, The dispersed pigment dispersion will increase in viscosity without agitation, but will decrease significantly after proper agitation. This feature may also cause the low shear viscosity of the formulated coating to be slightly higher than that of the kaolin formulation. In addition, from the laboratory observations, although talc has the characteristics of shear thinning compared with kaolin, its sedimentation performance is superior to kaolin.
3. Conclusions (1) Compared with kaolin, talc pigment has the characteristics of relatively high whiteness.
(2) When talc replaces kaolin in light-coated paper coating, the high shear viscosity of the coating decreases with the increase of the substitution amount, although the low shear viscosity of the coating increases slightly.
(3) After replacing the kaolin with talc powder, after replacing the kaolin in the formula with talc powder T90, both the optical properties of the paper and the surface properties of the printing are kept close to the original formula.
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