Question and Answer of Latex Coatings Knowledge and Formulation Design

Generally speaking, we first select the base resin and pigments according to the application requirements of coatings, that is, the performance indicators of coatings in the working environment, then determine the solvents according to the construction requirements and selected base materials, and then consider the additives or other additives of coatings on this basis. Wait, form a preliminary formula. The absolute quantity and relative proportion of each component in coatings have a great influence on the performance of coatings. As long as one component is not properly selected, the performance of the coating will deteriorate on-line coatingol.com. What is the color/base ratio (P/B) of latex coatings? In latex coatings, binder and pigments are important components. When the binder and pigments have been determined, the structure and physical properties of the film basically depend on the ratio of them. The so-called pigments/radicals ratio refers to the mass ratio of pigments (i.e. pigments and fillers) to solid resins (non-volatiles), which is usually expressed by P/B. In formulation design of latex coatings, is often expressed as a percentage of quality. However, the density of resins, pigments, fillers and other solid additives that make up latex coatings varies greatly, so their volume fractions in the whole film are significantly different. Volume fraction is more important than mass fraction in determining the performance of dry film. Especially when the performance of coatings with different formulations is compared, the importance of volume fraction is more prominent. The volume concentration of pigments is the percentage of the volume of pigments in the total volume of the film, which is expressed by PVC. 

Critical Pigment Volume Concentration (CPVC) refers to the volume concentration of pigments when the base polymer just covers the surface of the pigments and fills the space where the pigments accumulate. It is usually expressed by CPVC. What role does P/B play in the design of paint formulation?

In studying the quality relationship between pigments and materials in coatings, it is very practical in the initial design stage of formulation with simple numerical calculation. In practical application, it is feasible to classify latex coatings for internal and external use according to their P/B ratio. Usually, the P/B for external use is (2.0-4.0): 1.0, and the more suitable is 3.0:1.0. The internal latex coating is in the range of (4.0-7.0): 1.0. For glossy latex coatings, P/B is usually less than 1.0.

Some properties of coatings can be roughly inferred from P/B. P/B high formula, its performance is not suitable for outdoor use, because the exterior wall coating requires good durability and weatherability, and fewer materials can not form continuous coating around a large number of pigments and filler particles. The formulation of various types of latex coatings can be designed by using the concept of P/B.

What role does PVC and CPVC play in the design of paint formulation? It is difficult to explain the problem only by using P/B in the comparative test of coatings with different compositions. It is more scientific to interpret the test data by understanding PVC. Because many physical properties of coatings have a very clear correspondence with their composition changes. C.P.V.C. value is an important parameter in paint formulation. When the P.V.C. value in the formulation is lower than C.P.V.C., besides wetting the pigments, the amount of the base material can also make the pigments disperse firmly in the middle of the base, which makes the film with high luster, difficult to rust, low water permeability and low air permeability, and has bubbles.

When low PVC paint is prepared, the pigment particles are dispersed in the continuous phase of the matrix polymer, forming the so-called "sea-island" structure. When the CPVC value is reached, there are just enough wetting particles in the film. However, with the increase of pigments, when PVC exceeds a certain limit value, the matrix polymer can not completely fill the gap between the pigments particles. These unfilled spaces are hidden in the film, so the physical properties of the film begin to decline sharply with the limit value of the PVC. Therefore, the PVC of high performance or external coating formulation should not exceed CPVC, otherwise many physical properties of the coating will be adversely affected. On the contrary, the PVC of general performance or internal coating formulation can exceed CPVC. The PVC of external coatings is generally 30%-55%, and that of internal coatings is larger, generally 45%-70%. In order to save resources and reduce costs, the research of high PVC latex coatings has become one of the important contents of developing architectural coatings. Therefore, attention should be paid to the latex products of high PVC coatings.

Take the design of an interior wall latex paint as an example. 1. Firstly, determine the performance requirements of latex paint to be designed the use environment of latex paint for interior wall has no special requirements for the physical properties of latex paint, but it is easy to clean the dirt with water and detergent. For construction performance, the requirement of interior wall latex paint is to have good leveling, and no brushing joints and too conspicuous brushing marks can occur during construction. In addition, most of the construction habits of latex paint in our country are the combination of rolling and brushing. For this construction method, the viscosity of latex paint (4 cups) should be controlled in the range of 45-55 s.

Regarding the storage performance, it is generally required that good suspension and at least no caking precipitation should be observed in the storage process to facilitate the construction and ensure the coating performance. Finally, attention should also be paid to the film formation of latex paint during low temperature construction and the anti-mildew problem during storage.

2. There are two kinds of binders to choose and determine the dosage of binder paint. One is polyvinyl acetate latex paint, the other is polyvinyl acetate latex paint.