Current status and development trend of defoamers for waterborne coatings in China

 

Current status and development trend of defoamers for waterborne coatings in China

INTRODUCTION of defoamers for waterborne coatings

Although the amount of additives used in water-based coatings is small, its effect is huge. Generally speaking, many problems encountered in the production, construction and application of water-based coatings can be solved by additives, among which defoamers for waterborne coatings are one of the more important additives. China is a major producer of architectural coatings, of which latex paint is the largest and most important variety. Latex paint has a large demand for defoamers, and it is increasing year by year, so the development of defoamers is very important.

Before the German BYK additives entered the Chinese market, China's defoamers for waterborne coatings market was almost blank. At the same time, the magical functions of water-based paint additives began to receive approval, and Japan's Nippon Paint Company launched latex paint in China Later, its performance and application effects were praised by industry insiders, so people in the paint industry developed latex paints, which became a hot spot in the paint industry at that time.

In the development process of latex paint, people have deeply realized from practice that if latex paint is to be made, additives for water-based coatings, especially defoamers, are essential. However, at that time, most of the defoamers came from abroad, and the prices were very expensive, so only by doing it yourself and mastering the manufacturing technology of the defoamers, can latex paint be introduced to the market and occupy a place. Soon, there will be many defoamer products in China. Although there are still some gaps in performance compared with similar foreign products, these defoamers are close to the market and suitable for national conditions, so they are well received by customers.

1 Varieties and limitations of current defoamers

There are many types of defoamers in use, and there are three main types of defoamers for water-based coatings:

• Mineral oils, the market share is 80%;
• Polysiloxanes, with a market share of 17%;
• Polyethers have a market share of 3%.
• Among them, mineral oil defoamers have the highest cost performance and are more commonly used. They can be used in most flat and semi-gloss emulsion paints, but their defoaming and defoaming effects are not as good as polysiloxane and polyether defoamers. Agent. Mineral oil defoamers are basically composed of carriers (mostly hydrocarbon oils or water), hydrophobic particles (wax, silicone oil, hydrophobic silica and fatty acids or polyurethanes, etc.), emulsifiers or expanders (fatty acid esters, It is composed of sorbitan (sugar) alcohol esters, etc.], in which the carrier accounts for 75% to 80%, the hydrophobic particles account for 10% to 15%, and the emulsifier or spreading agent accounts for 5% to 10%.

The role of the carrier is to bring the main defoaming substance into the foam system, so that it diffuses on the foam film, and plays the role of bearing and dilution. It has a great influence on the defoaming performance and durability of the defoamer. It is a low surface tension substance, has suitable incompatibility with the foam system, and is easy to rise to the surface of the foam system; the size of the hydrophobic particles is 0.1 Between ~20 μm, it mainly plays an active role in the formulation; emulsifiers or spreaders are used to adjust the compatibility of the active ingredients in the coating system, to balance the compatibility and incompatibility, and to ensure the active ingredients It diffuses quickly and penetrates the surface of the coating film quickly, so that the active ingredients immediately defoam. In addition, mineral oil defoamers also contain a small amount of stabilizers or preservatives.

• Polysiloxane defoamers include polydimethylsiloxane defoamers and modified polydimethylsiloxane defoamers, collectively referred to as silicone defoamers. Among them, the polydimethylsiloxane antifoaming agent is a non-volatile oily liquid, with a degree of polymerization of tens to hundreds, with stable physical and chemical properties and a very low surface tension; modified polydimethylsiloxane Class defoamers have suitable hydrophilic and lipophilic balance values. For example, polydimethylsiloxane defoamer modified with organic fluorine, which is a defoamer with extremely low surface tension and excellent defoaming ability. Although polysiloxane defoamers have low surface tension, strong defoaming and foam suppression capabilities, and do not affect the gloss, improper use will cause film shrinkage and poor recoatability.
• Polyether defoamers are products with suitable incompatibility obtained by selectively modifying some polymers, and are mainly used in some systems that require higher compatibility. For example, there is incompatibility between acrylate and epoxy resin. For this reason, consciously change the polarity, relative molecular weight and distribution of the polymer to make it a proper balance between "miscible" and "immiscible", so that the obtained defoamer product is compatible with silicone defoamer Compared with other agents, it has better miscibility and does not stabilize foam. This is the characteristic of polyether defoamers, but it often has the problem of weak or no defoaming ability, so its market demand share is small.

 

2 A new generation of defoamers and their characteristics

The above-mentioned defoamers are all traditional defoamers, and their defoaming substances are all water-insoluble substances, and proper amount of emulsifiers, extenders, etc. need to be added to make them quickly and uniformly dispersed in the water-based paint to exert their defoaming effect. If for some reasons, such as the common construction method of adding water to dilute before painting, the emulsifier will be separated from the surface of the defoaming material, so that the water-insoluble defoaming material will easily cause shrinkage on the surface of the coating film. , This is a common disadvantage of traditional defoamers. In addition, it is very difficult for a high-viscosity coating system to achieve an ideal defoaming effect. This is because the high-viscosity system makes it difficult for the liquid to flow between bubbles, and the film wall of the bubbles has a certain thickness, which makes it difficult to make it Rupture, which will cause a lot of pinholes in the paint film. Therefore, it is necessary to develop new defoamers to solve the problems that traditional defoamers cannot solve.

People get inspiration from the structure of a new type of Gemini surfactant, which is a substance formed by linking two or more monomer surfactants together through a chemical bond. For example, two common surfactants with single-chain single-chain single-head groups are connected together by chemical bonds at the ionic head groups, so that the resulting special structure has certain special properties, especially higher surface activity. And other physical and chemical properties.

The structure diagram of Gemini surfactant is as follows:

The characteristics of this structure are:

• At least 2 hydrophobic chains and 2 hydrophilic groups;
• Hydrophobic chains can be hydrocarbon chains of different chain lengths;
• The hydrophilic group can be anionic, cationic or non-ionic, and the two hydrophilic groups in the same molecule can be different;
• According to the difference of the spacer chain, it can be divided into rigid and flexible structures, and because of the heteroatoms, its hydrophobic and hydrophilic abilities are also different, which can be divided into hydrophobic and hydrophilic;
• Most Gemini surfactants have two identical hydrophobic chains and hydrophilic groups.

In view of Gemini surfactant technology, the defoamer is designed into a network-like supramolecular structure, so that it has many anchor points, and also has a certain self-emulsification effect, so there is no need to use emulsifiers. The problem of shrinkage caused by such a structure can make it have a certain wetting effect on the substrate, so the amount of wetting agent can be appropriately reduced. This is a major change in water-based defoamers, which are called molecular defoamers. For example, INVELY’s 8200 defoamer is an enhanced mineral oil-based defoamer, suitable for all kinds of high-gloss pure acrylic, styrene acrylic and vinegar paint, its performance is equivalent to foamaster-st 10.

The advantages are:

• The addition amount is 1/3 or even 1/2 lower than traditional defoamers, and the cost can be reduced by at least 20%;
• During storage, there will be no delamination of ordinary mineral oil defoamers;
• Especially effective when used in vinegar-acrylic and pure acrylic paint;
• The foam breaking speed is faster than ordinary defoamers, especially the effect of breaking fine foam.

3 China's demand for defoamers and their development trends

The total production of defoamers in China is about 2 000 tons. In 2015, the output of China's architectural coatings was 5.38 million tons, a growth rate of 4.2%. Defoamer is an indispensable raw material in architectural coating formulations. Based on an average addition of 0.3%, the defoamer required for architectural coatings in 2015 is 16,000 tons. It is estimated that the amount will increase in the future. The output of the agent is far from meeting the market demand. At the same time, there is still a big gap between China's defoamer technology and foreign countries, especially in terms of high-performance water-based defoamers. Therefore, it is necessary to strengthen research and development work to meet market demand. In view of the current status and market demand of water-based defoamers in my country, research and development in the following aspects are needed in the future:

• Develop new high-activity defoamers, such as molecular defoamers and ultra-stable defoamers;
• Develop multifunctional defoamers, such as defoamers with wetting or emulsifying functions;
• Develop powerful defoamers for high-viscosity and high-elastic coatings;
• Develop compounding technology of defoamer, such as compounding technology of polyether and silicone; compounding technology of water-soluble or oil-soluble polyether and silicon-containing polyether; compounding of organosilicon compound and surfactant Technology etc.;
• New varieties of modified polyether and silicone defoamers.