Introduction of Additives for Paints and Coatings
Coating additives can improve the quality and application of the coating, and the addition of a small amount can change the physical properties and functions of the coating. In the current situation of serious environmental pollution, environmentally friendly coatings and cleaning coatings have become the development direction. This article focuses on the use of thixotropic agents for waterborne coatings and their coating effects.
Additives are one of the raw materials for coatings. A small amount of addition can greatly improve the efficacy and performance of the coating, and can also improve the performance of the coating film, and contribute to the personalization of the product.
Paint coatings should have a variety of properties and special effects. To meet these requirements, the relationship between the various characteristics must be coordinated.
To this end, it is a difficult problem for the coatings industry to fully grasp the characteristics of major raw materials such as resins, pigments, and solvents.
The fluidity of the paint, the dispersibility of the pigment, the leveling and the clarity of the paint are related to the coating effect, and the use of additives is the key to increasing the added value of the product. However, if you use improper methods or add too much, it will have the opposite effect.
1. Environmental Issues Determine the Development Trend of Coatings
In order to prevent environmental pollution, countries around the world are developing a series of prevention regulations and their implementation targets related to air pollution, ozone layer destruction, greenhouse effect, water pollution, and soil pollution.
Developed countries in Europe and the United States have long implemented environmental regulations, such as CAA in the United States and TA-LUT in Germany, and actively formulated volatile organic compound (VOC) emission regulations.
In January 2001, Japan began implementing the “Specific Chemical Substances to Environmental Emissions and Improvement Management Promotion Act” (PRTR). This regulation is used to prevent environmentally-friendly, detrimental to human health and to hinder the survival and reproduction of animals and plants.
In order to prevent environmental pollution, the total output of synthetic resin coatings in Japan was reduced by 15% in 2001 compared with 10 years ago. The proportion of waterborne coatings and solventless coatings has increased significantly, and this trend will continue in the future.
2. Additive Types and Effects
In the coating process, additives can prevent coating defects and defects, and give them special functions and effects. With the development of the coating industry, it is required to develop new products with higher efficiency and better performance.
From the beginning of production, the coating is often in a flowing state after storage to solidification and film formation, and the flow rate range is very large, about 10-2~10°.
At the same time, different coating methods, such as spraying, roller coating, electrostatic spraying, dip coating, require different viscosities. When a thick film is applied, sag, face and brush marks are likely to occur, and orange peel wrinkles are generated, which is often unsuitable for the fluidity and surface tension of the paint.
By adding different additives to control the fluidity and surface tension during coating, it is possible to prevent the lack of coating film and improve the efficacy. A variety of additives are used in the production, storage, and coating of paints, as shown in Table-1.
|Coating Production||wetting agent, dispersing agent, coupling agent, thickener|
|Coating Storage||anti-settling agent, anti-skinning agent, anti-polymerization agent|
|Painting||defoamer, thixotropic agent, electrostatic spray improver|
|When the film is formed||anti-sagging agent, anti-separation agent, antifoaming agent, leveling agent, curing accelerator|
|After the film is formed||anti-blocking agent, ultraviolet absorber, antistatic agent, anti-scratch agent, matting agent, preservative, anti-mold agent, flame retardant, anti-rust agent, plasticizer|
The use of additives is related to the composition of the coating, the method of addition and the amount of addition. First, the mechanism of action should be fully understood and appropriate selection should be made.
For example, if it is desired to adsorb on a surface, it is best to add an additive before the surface adsorbs other substances; if some physical changes are desired, the coating material and additive properties should be fully understood and selected.
Further, if it is necessary to utilize the surface characteristics of the material to make the orientation and the separation effect appropriate, it is necessary to use a polymer resin which is compatible with the polymer. Therefore, the solubility parameters (S•P) of the resin and additive must be compared before use. Different additives have different functions, the main functions are shown in Table-2.
|Fully miscible with the resin, hoping to change physical properties||thickener, anti-sagging agent, anti-settling agent|
|Film-forming material and pigment surface adsorb each other||wetting and dispersing agent, anti-floating agent, thickener, anti-settling agent|
|Ultra-thin layer formed on the surface of the coating film||defoaming leveling agent, anti-scratch agent, matting agent, thickener, anti-sagging agent|
|Addition of surface area and shape effect of ultrafine particles||Matting agent, thickener, anti-sagging agent|
3. Market Trends
Researchers are actively developing new coatings with low organic solvent content and recyclability, including high solids coatings, waterborne coatings, and powder coatings. At present, these coatings have deficiencies, and the existing additives cannot fully meet the environmental protection requirements, and new additive varieties need to be developed.
In high-solids and solvent-free coatings, due to the use of low molecular weight and high polarity resins, they are sensitive to temperature and are prone to sag.
By using a solvent with high polarity, the resin adsorbed on the surface of the pigment particles is easily detached, affecting the dispersion stability of the pigment, and is easily discolored over a long period of time, which adversely affects the appearance of the coating.
In addition, the low molecular high-polarity resin has a large surface tension, and there is a problem of wetting and leveling on the object to be coated, and the coating film is liable to cause a flower face.
Water-based paints use water with extremely strong hydrogen bonds as a special solvent, and thus there are many problems in coating operations and painting techniques.
Under high humidity, waterborne coatings are prone to sag, surface wrinkles, bubbles, and spots. Further, the aqueous resin also has problems such as poor storage stability and low performance of a hydrophilic film-forming material.
To solve these problems, additives need more and better features. Current additives cannot meet these needs.
Therefore, new additives with more functions should be developed. Especially for automotive coatings with unique performance, it is necessary to develop coating additives with low humidity effect, luster and beauty, no spots, no discoloration and good water resistance of coating film.
Further improvements should be made to make aqueous coatings comparable to the coating properties of solventborne coatings.
In particular, it is necessary to improve the level of polymer synthesis, physical and physical resolution to meet the needs of users and the market.
At the same time, it should meet the requirements of environmental friendliness, and constantly improve the human living environment, continuously develop technological innovation, and develop more and better new coating additives with more functions for the benefit of mankind.