Analysis of factors affecting the gloss of water-based inks

Gloss is an important performance index of ink, which has a great influence on the appearance quality of printed products. However, in fact, the current water-based inks generally suffer from poor glossiness, which seriously hinders the application of water-based inks in certain fields. This article will analyze some of the major factors affecting the gloss of water-based inks.

1. The effect of water on gloss

Since water-based inks use water as a solvent, their content in water-based inks is generally high, and can be adjusted within the range of 20% to 50% depending on the specific needs. When the content of water in the water-based ink is relatively large, the absorption rate of the ink to the paper during the printing process is increased, the viscosity of the ink is significantly increased, and the ink leveling process is terminated prematurely, resulting in that it is difficult for the ink to form a relatively smooth ink layer. This affects the gloss of the ink.

If the water content of the water-based ink is too low, the solid content increases, and the viscosity of the ink also increases accordingly. Because the same absorption intensity of the paper, its ink absorption rate is inversely proportional to the viscosity of the ink, so the greater the viscosity value, the smaller the absorption rate, the worse the leveling, the ink film surface after printing The worse the flatness is, the less glossy it is.

We performed experiments on A-50 water-based inks. The experimental method was as follows: First divide the water-based ink into 5 equal parts, then add an unequal amount of water to each ink to dilute, and then carry out separately on the proof paper. After scraping, after drying, the gloss of each ink sample was measured in turn according to the method of national standard GB9754. The results are shown in Table 1.

2. The effect of ink fineness on glossiness

The fineness of the ink will directly affect the printing quality and leveling of the ink. The fineness is good, the formed ink film has a high degree of smoothness, and the ink film has a high glossiness. With poor fineness, it is not easy to form a high-quality ink film after printing. When printing dot patterns, it is easy to cause dot expansion or emptiness, the edges of the dots are not clean, and the gloss of printed ink film will be greatly reduced.

3. The effect of co-solvent and polymer monomer on gloss

The speed of evaporation of the co-solvent in the water-based ink also affects the gloss of the water-based ink. When the co-solvent volatilizes too quickly, the ink tends to flow poorly, causing the ink layer to level off into a uniform film surface; and streaks appear. Blisters and other phenomena, and therefore its gloss will be poor. The slow evaporation of the co-solvent can cause the ink to dry poorly. The binder in the ink hardens the conjunctiva and the leveling of the ink is also very poor, and the glossiness is naturally affected.

The type and amount of polymer monomer also have a certain influence on the gloss of the water-based ink. For example, when the amount of methyl methacrylate and styrene is increased, the formed ink film has high hardness and good gloss, but it is relatively brittle, has poor solubility, and is prone to cracking. When the amount of butyl acrylate is increased, the formation of The ink film has good flexibility, water resistance and solubility are also improved, but the gloss is poor. Therefore, in order to ensure the high gloss of the ink film, it is necessary to strictly select the resin binder formed by suitable monomers.

4. Effect of additives on gloss

The additives in water-based inks mainly include defoamers, waxes, leveling agents, etc. They also have a certain influence on the gloss of water-based inks.

(1) Defoamer. Different kinds of defoamers not only have certain differences in defoaming ability, but also have different degrees of influence on the glossiness of ink layers. For this reason, we conducted experiments on five different types of defoamers. The experimental data are shown in Table 2.

From the experimental data in Table 2, it can be seen that using S062 with a good defoaming effect (antifoaming height of 30) will reduce the gloss of the printed ink film, and the defoaming effect of CF246 (defoaming height is 25 ) But it can increase the gloss of the ink film.

At the same time, we also conducted a comparative analysis of the effects of different additions of S062 defoamer on the gloss of water-based inks, as shown in Table 3.

As a result, it was found that the gloss of the ink film gradually decreased as the content of the defoamer used was increased. Therefore, in the formula of 100g water-based ink, the amount of defoamer is preferably 0.5%. Excessive addition will not only affect the gloss of the ink layer, but also affect the service life of the water-based ink.

(2) wax materials. In water-based inks, waxes are generally used as agents or slip agents. When using a wax of the same weight, the larger particle size has less effect on gloss. For example, if a 1% microcrystalline wax with an average particle size of 1 um, ie, 1 g of this microcrystalline wax per 100 g of water-based ink, is used in the formulation, the number of wax particles in the formulation is a certain number. If the average particle size is reduced to 5 μm, the number of wax particles in the water-based ink system will be significantly increased, so that the gloss becomes lower. However, when the particle size of the microcrystalline wax is reduced to 1-2 μm, the influence tends to be opposite. In high gloss applications, the combined use of polyethylene and PTFE is the most promising. In low-gloss water-based inks, they can be used either directly (with higher amounts) or with silica.

5, the impact of emulsion

Practice has proved that the emulsion can make water-based ink gloss. Water resistance and rub resistance have been greatly improved and are an integral part of high-grade water-based inks.

Emulsion generally refers to a polymer that is dispersed as an emulsion in an aqueous medium under the action of an emulsifier under mechanical stirring or vigorous shaking. When the polymer is polymerized, an emulsion such as an initiator and a pH adjuster is used as an emulsion. The emulsifier is the decisive factor, and the emulsifier is actually a surface active agent. The role of the agent is to reduce the surface tension of the monomer and water, so that the monomer and water form a stable homogeneous system. When the water-based ink is added with an emulsion, the pigment can be soaked faster than ordinary binders and permeated into the pores of the pigment particle aggregates, the stability of the ink system is improved, and the substrate surface has better wetting, Adhesion, impregnation, leveling performance will be improved, the film surface will be smoother, and the gloss will be improved.