news

In the paint industry, post thickening is one of the most headache inducing problems in research and production. It usually refers to the abnormal increase in viscosity of the paint after 24 hours of preparation or within a few weeks of storage, even resulting in tofu residue and clumping, making the final paint unusable.

What factors are related to the thickening of our coatings? To summarize, there are roughly the following points.

The first issue is that the thickening agent system is not compatible. For example, alkaline swelling thickeners, closed polyurethane thickeners, and so on, can cause abnormal viscosity increases when applied improperly or added in excessive amounts.

There are also ultra-high molecular weight cellulose thickeners that can easily cause the entire system to flocculate due to their volume limitations, leading to post thickening. Thickener is added too quickly or not stirred enough, resulting in insufficient hydration. Subsequently, continuing to absorb water will also cause thickening afterwards.

The thickening agent or anti settling agent of polyurea will also have high thixotropy under the condition of improper use limit and mismatch, and some will even become like bean curd jelly served with sauce. Its viscosity is still very low when you stir it, but without stirring, it has no fluidity at all.

The second one is the selection of dispersants. Improper selection or the presence of substances that can react with the system in dispersants, improper screening of dispersants, or insufficient addition can cause pigment coagulation. Flocculation can also cause thickening, coarsening, and granulation, and may even become a tofu like substance.

In addition, the anchoring groups of dispersants are basically polar groups, which may contain such groups that react with the resin gas system. A classic case is the use of dispersants with high amine values in epoxy resin systems.

These dispersants with high amine values may have anchoring groups of platinum amine, tertiary amine, or amide. We also know the curing agent for epoxy, which is this type of amine. If stored for a long time, they will undergo cross-linking reactions and even cause self polymerization of epoxy, resulting in thickening or even gelatinization.

The third is the stability of lotion, pigments and fillers. Lotion itself has a problem called calcium ion stability. Pigments, such as heavy calcium and light calcium, contain too much calcium ion, which will also cause demulsification of lotion, resulting in slagging, particles and viscosity abnormalities.

It is not necessary to use deionized water for water-based coating. Tap water or well water or river water are used directly. The water quality in some places is poor, especially in well water. The high ion content in well water may also cause lotion demulsification.

Another problem of lotion is the mechanical stability. For example, if we stir too fast in the production process, the lotion will be demulsified, which will also cause slagging and thickening.

The fourth one is whether the pH value is stable during storage?

There are thickeners in water-based coatings, which are greatly affected by the pH value, which can also cause changes in the viscosity of the system. After the coating is prepared, whether using ammonia water, DMEA, or triethylamine as pH regulators, it may evaporate. If the sealing is not good, it will evaporate.

During the storage process of the system, there may be spoilage, decay, and other issues. Additionally, the raw materials are easily hydrolyzed, which can result in the formation of polyester like compounds that become acidic. This can also affect the pH value of the entire system, leading to changes in its viscosity.

The fifth point is environmental factors. In water-based coatings, hydrophilic resins and cellulose thickeners can easily breed microorganisms and fungi under appropriate temperature and humidity conditions, leading to water separation, delamination, emulsion breaking, thickening, and other spoilage phenomena.

Solvent based and water-based paints also experience an increase in particle movement speed and pigment flocculation in high temperatures, leading to thickening and changes in viscosity.

The sixth issue is the evaporation of solvents or water. If there are coatings, poor packaging sealing, inadequate sealing, or incomplete filling, it can cause solvent overflow. The concentration of the entire system has increased, and the viscosity will definitely increase. Other possible causes include, for example, bactericides such as Casson, which are easy to cause demulsification of lotion. There are formulas and different resins or components are used. The compatibility between these components is not good, that is, the compatibility between resin and resin is not good.

Sometimes it can also cause thickening, viscosity changes, and other issues. Another issue is acid-base reactions. For example, if the acid value of paint is too high, it will undergo a transformation reaction with alkaline pigments such as titanium dioxide and calcium carbonate, producing carboxylate salts and thickening the body.

There is also the use of light calcium to absorb large amounts. This type of powder or silicon calcium powder contains highly active calcium oxide, which is easy to absorb water and react with resin, leading to thickening. The mixing of water or impurities can cause side reactions and also lead to thickening.

The solvent system used is not compatible, for example, a high polarity resin system uses a low polarity solvent, which dissolves poorly. The entire system can also cause flocculation, thickening, viscosity changes, and so on. To solve the problem of thickening of coatings, first of all, we need to understand the reasons for the thickening after it occurs and then prescribe the right medicine.

The most likely cause of thickening after production is improper use of thickeners or anti settling agents. Another main reason is the improper use or insufficient addition of dispersants, which can cause the pigment and filler to flocculate. In most cases, this can be improved by adjusting the thickener or dispersant. If the coating has already experienced slight thickening, we can try adding appropriate diluents or water. Stir it evenly and resume use. But if it is already gelatinized or has particles, it is usually irreversible and is usually scrapped or returned for reprocessing.