Analysis of the Influence of Nano Pigment Particles on the Properties of Coated Paper
We are a big printing company in Shenzhen China . We offer all book publications, hardcover book printing, papercover book printing, hardcover notebook, sprial book printing, saddle stiching book printing, booklet printing,packaging box, calendars, all kinds of PVC, product brochures, notes, Children's book, stickers, all kinds of special paper color printing products, game cardand so on.
For more information please visit
http://www.joyful-printing.com. ENG only
http://www.joyful-printing.net
http://www.joyful-printing.org
email: info@joyful-printing.net
The pigment properties of the coated paper coating determine the printability of the paper to some extent. Pigments such as ultrafine calcium carbonate and ground calcium carbonate are widely used in paper coatings because of their high quality and low price. However, with the development of printing technology, the requirements for paper performance are getting higher and higher, and ordinary coatings can no longer meet the requirements of today. Print quality requirements. The nano-sized particles of these pigments are added to the paper coating system, and because of their small particle size, large specific surface area, and large proportion of atoms in the surface layer, they can be sufficiently adsorbed and bonded with the polymer adhesive in the coating system. The reinforcing particles are bonded to the coated base paper to obtain coated paper with high gloss, high whiteness and high surface strength, and the smoothness of the paper is improved, thereby improving the printing suitability of the paper coating. In this paper, the effects of nanopigment particles on ink absorption, water absorption, whiteness and mechanical properties of coated papers were summarized in combination with the quality index of coated paper.
First. Introduction
Nanomaterial research is currently a hot topic in materials science research. The corresponding development of nanotechnology is recognized as the most promising research field in the 21st century. Nanoparticles have extremely small particle size, large specific surface area, high surface energy and chemical activity, and can produce functionally special products that are different from general molecular substances.
At present, foreign research on coating performance improvement focuses more on the shape of pigment particles in coatings, the improvement of surface properties, and the effect of additives on the performance of the entire coating. In accordance with the research trend, nano-materials can be prepared as additive additives and filler particles into paper coatings to prepare nano-coatings with special functions, thereby greatly improving the paper properties of coated paper.
Second, the quality index of coated paper and its coating
The quality of paper can be summarized as follows: Appearance quality, basic physical properties, mechanical properties, optical properties and chemical properties. The use of paper is different, and the quality requirements are different.
1. Quality index of coated paper
For coated papers, when discussing their quality indicators, they usually refer to those closely related to the operation and purpose of coating processing. These indicators are closely related to the printing quality of coated paper, including smoothness, whiteness and gloss. Degree, opacity, surface strength, ink receptivity and ink absorption.
The smoothness determines the tightness of the contact between the coated paper and the inked printing plate or offset blanket surface at the moment of imprinting, and is an important factor affecting whether the ink transfer is complete and the image is clear. The high smoothness of the coated paper facilitates the formation of a uniform and smooth ink film while also saving ink usage. Whiteness is especially important in multicolor printing because white as a neutral tone eliminates the undertone interference that any ink pigment may be subjected to, giving the print a better hue contrast and enhancing the visual impression. Opacity is the main factor determining whether or not the coated paper produces a print after printing. Under the same printing conditions, the higher the opacity of the coated paper, the less likely it is to produce a print. The surface strength of coated paper refers to the bonding strength between the coating particles and between the coating and the base paper. It reflects the ability of the coated paper to resist ink splitting during the printing process. If the surface strength of the coated paper is not high, during printing The coating may be stuck by the ink, and the white spots on the surface of the paper where there should be ink will not only affect the quality of the printed matter, but also cause printing failure. Printing paper must have a certain ink absorption capacity, but if the ink absorption capacity is too large, it will cause the print to be dull, or even produce offset or chalking phenomenon; if the ink absorption capacity is too small, the ink drying speed will be prolonged, which may lead to The printed surface is dirty.
2. Quality index of coated paper coating
The main purpose of coating processing is to improve the performance of the base paper by coating the base paper and improve the printing quality. Therefore, the quality of the coating plays a decisive role in whether the coated paper can obtain the expected printing quality. Paper coating is a highly concentrated liquid dispersion consisting of pigments, adhesives and water. Pigment is the most important component in coatings. Its main function is to improve the smoothness of coated paper, improve ink absorption, improve coating whiteness, opacity, gloss and improve the appearance of paper. The influence of pigment on the coating structure is mainly reflected in the internal geometry of the pigment particles. The performance indicators mainly include shape, particle size and distribution, refractive index and whiteness.
The main effect of pigment on the optical properties of coated paper is that the higher the whiteness and refractive index of the pigment, the higher the whiteness and opacity of the coated paper. For the same kind of pigment, reducing the particle size is beneficial to improve the gloss of the coated paper. Degree and whiteness. The main influence of pigment on the smoothness of coated paper is: The pigment with a shape of flake or disc has a strong covering power, which is beneficial to improve the smoothness. For the same kind of pigment, reducing the particle size is beneficial to improve the smoothness. The main effects of pigments on the absorbency and surface strength of coated paper inks are: The irregularity of the shape of the pigment, the size and distribution of the pigment determine the porosity of the coating and the amount of adhesive required to form the coating.
The quality of the coating mainly refers to some morphological characteristics of the coating, which is usually referred to as the coating structure, mainly including the distribution of the components in the coating inside and on the coating, the distribution of micropore volume and pore size in the coating. And the thickness, tightness, surface roughness, etc. of the coating. The distribution of the components in the coating structure actually refers mainly to the distribution of the adhesive. The adhesive is distributed in the structure formed by the pigment, and there is a difference in concentration distribution at different positions of the coating. However, because the amount of additives in the coating is small, it is of little significance to study its distribution in the coating.
Third, the application of nanomaterials in paper coating
The application of nanotechnology to processed paper coatings can improve the optical properties of paper, improve the rheological properties of coatings, and improve the aging resistance of paper coatings.
Since the particle size of the nano-material particles is small, the optical properties of the paper can be greatly improved, and the opacity thereof is high. For example, nano-scale alumina is applied as a nano-pigment particle to a coating. Since the particle size of the particle is small and the particle size distribution is narrow, it can be ensured as a pure color of the white material, thereby improving coating into paper. The whiteness of the paper improves the gloss of the paper. In addition, some nano-materials can also produce special optical effects. For example, when scattering occurs, the color of the coated paper changes with the angle of observation, so it can be applied to the production of coatings with special applications. Processing paper.
Applying nanopigment particles to the coating can improve the rheological properties of the coating. Due to the special surface effect and quantum size effect, nano-pigments can control the particle size performance, p H value and Z e t a potential of the coating to obtain a coating with high concentration but low viscosity. In addition, the particle powder of the nano pigment is extremely fine, which is very advantageous for improving the stability of the coating material, and the occurrence of precipitation, delamination and the like can be largely avoided. The addition of nano-pigments to paper coatings, with its strong UV-shielding effect, can significantly improve the aging resistance of paper coatings, resulting in a much lower rate of paper aging due to exposure to light. However, if you want to get the best UV shielding effect, the particle size of the nano-pigment is not as small as possible, but has a certain range of requirements. For example, according to the Ranikemiton and Weber formulas, the anatase titanium dioxide has a particle size ranging from 70 to 180 nm, and the coating has the best scattering ability to ultraviolet light.
Fourth, the effect of nano pigment particles on the properties of coated paper
The addition of nanopigment particles to pigment formulations with better coating properties has been found to improve the properties of the coating, including the viscoelastic properties of the coating, the surface strength of the coating, the water absorption properties of the coating and the mechanical properties. Optical properties of paper, etc.
1. Effect of nano-pigment particles on ink absorption and water absorption of coated paper After adding nano-components, the surface strength of the coating is obviously improved, and the ink absorption and water absorption are decreased. This indicates that the coating is improved due to the addition of nano-components. The bonding force of each component is filled with fine pores in the coating, which results in lower ink absorbency and water absorption.
The main factor affecting the absorbency of coated paper inks is the porous structure of the coating. Due to the change of the adhesive in the coating, the pore structure, pore size, and pore size distribution of the coating are changed to cause changes in ink absorbability. In addition, factors such as tightness of pigment particle arrangement, pore size distribution, pigment structure and lubricant also have a direct impact on ink absorption. The results of studying the ink absorbability showed that the ink absorbability of all the samples was lowered after the addition of the nanosilica component. This indicates that the pores on the surface of the coating are filled with fine particles, the average pore diameter is reduced, and the ink does not penetrate the coating as a blank paper. It has been found that the smaller the average particle size of the nano-components, the more likely it is to block the micropores on the surface of the coating, and the capillary action of the permeation is affected.
The sample added with the nano-component has a reduced water absorption weight compared to the surface of the sample to which the nano-component is not added, the tightness of the surface structure of the coating is increased, and the hydrophilic property is lowered. The result is similar to the change in ink absorbability, and the reason is also the same as the mechanism for reducing the ink absorbability, that is, the absorption of the liquid is reduced due to the decrease in the pores of the surface coating of the paper.
2. Effect of nano pigment particles on mechanical properties of coated paper
The mechanical properties of coated paper are manifested in both the strength of the bond between the base paper and the coating and the strength of the coating itself. The strength of the bond between the base paper and the coating is determined by the adhesion of the components of the coating to the base paper. The mechanism by which nano-components improve the mechanical and printing properties of coated papers is primarily due to the nano-effects characteristic of nanomaterials, namely surface effects and small size effects. For example, after the addition of nano-calcium carbonate, the mechanical strength of the coating is increased. The reason for this phenomenon is mainly due to the small particle size, large specific surface area, high activity of the nano-calcium carbonate, and the aqueous polymer molecules and pigments in the coating. The particles have a large contact area and are firmly bonded to them, improving the mechanical properties of the coating.
In the mixed coating system, the nanoparticles, kaolin and calcium carbonate particles are organically combined, and the distance between the particles is reduced after the coating is dried to form a dense network structure, which improves the strength of the coating. In addition, due to the surface effect of nanomaterials, that is, when the particle size is reduced to the nanometer level, the atomic number and surface area of the material are rapidly increased, and it is easily stabilized by combining with other atoms, so that the chemical activity is extremely high and the surface energy is correspondingly It is multiplied, so it is easy to have strong chemical bond with other particles, which improves the strength of the coating composite.
The primary prerequisite for the improvement of the mechanical properties of the paper coating is that the nano-components are uniformly dispersed in the coating and the coating, which not only requires no agglomeration between the nanoparticles, but also is uniformly distributed in the coating and the coating, otherwise the agglomerated state Large particles can become defects in the coating structure, adversely affecting coating properties such as surface strength and coating smoothness.
In summary, the improvement of the mechanical properties of the nano-components on the coated paper is mainly manifested in the improvement of the strength of the coating itself, but has little effect on the strength of the bond between the base paper and the coating and the mechanical strength of the base paper.
3. The effect of nano-pigment particles on the whiteness of coated paper has been found. Under the same coating amount, the whiteness of each sample after adding nano-components is only less than 1%, and some even slightly There is a drop. This indicates that the nano-components have no obvious effect on the optical properties of the coating and do not show differences. Therefore, the nano-components have limited ability to improve the whiteness of the paper and cannot effectively improve the whiteness of the coating. The reason may be that for economic reasons, the amount of nano-components in the coating is small, and the pigment particles in the coating are the majority, and both are opaque particles. Although the nanoparticles have a good scattering effect on visible light, they are only added. When it is increased to a certain extent, it is possible to have a significant effect on whiteness.
However, the nano-sized particles have a small particle size and a large specific surface area, and the nano-coating has good ink absorbing properties and a smooth surface, and is advantageous for improving the optical properties of paper such as opacity, gloss and printing gloss.
V. Conclusion
Nanoparticles have broad application prospects in coatings, but the problem of agglomeration and dispersion of nanopigment particles in coatings is an urgent problem to be solved. On the one hand, it is necessary to prevent further agglomeration of the nanoparticles, and on the other hand, to maintain the special function of the nanoparticles in the coating. From the current technological development trend, the surface modification agent such as a coupling agent is used to treat the nanoparticles, and the interfacial adhesion between the nanoparticles and other component particles in the paper coating is increased, and then dispersed by ultrasonic waves, and a specific surface is used. The active agent enables the nanoparticles to reach a balanced dispersion state in the medium, and can effectively solve the problem of easy agglomeration of the nanoparticles.