As a supporting industry in the coating industry, solvents play a vital role in coating formulations. However, The role of solvents in coatings is often overlooked. The industry generally believes that solvents are volatile substances that will eventually evaporate over time and will not remain in the paint film and will have little impact on the quality of the paint film. In fact, coating solvents are a crucial component of coating formulations, accounting for approximately 30-50% of the coating system. Factors such as the solubility and evaporation rate of various solvents will greatly affect the performance of paint production, storage, construction, paint film gloss, adhesion and surface condition. In recent years, with the advent of the low-VOC era, traditional organic solvents have begun to experience a new round of crisis. Due to regulatory and economic reasons, solvents have been limited to unfavorable situations due to their shortcomings as physical substances. They are expensive; tend to flow around and are inconvenient to clean; most are flammable to some extent, and many are toxic. The use of solvents around the world has caused the loss of precious petroleum resources, and when used improperly can cause more harm than good. , so the coating solvent industry is also facing a crisis of reshuffle.
The role of solvents in coatings
The main functions of solvents in coatings are: dissolving and dispersing the resin in the coating, and adjusting its stability and rheology to make it easy to paint; increasing the storage stability of the coating; improving the appearance of the coating film, such as gloss, fullness, etc. ; Increase the wettability of the coating to the substrate being coated and improve adhesion; form a reasonable evaporation rate and give the coating the best fluidity and leveling properties. Different resin series can only be dissolved in different active solvents. In the same special formula, try to use multiple resins, so multiple active agent formulas can achieve better results. Formula principle: Achieve the most stable performance and best balance between active solvents, while adding as much filler as possible to optimize costs and adjust construction viscosity. In order to meet the increasingly stringent requirements of consumers, VOC-free latex paints, water-based paints, UV light-curing paints and powder paints have developed rapidly.
The use and development of solvents for coatings
Judging from the current global usage of coating solvents, coating solvents mainly include three categories The first category of products is hydrocarbon solvents, which are classified according to different boiling points; the second category, which is also the most widely used and mainstream category, is oxygen-containing solvents; and the third category is the most unique solvent - water. Among them, hydrocarbon solvents are toxic solvents and are more harmful to the human body; oxygen-containing solvents refer to solvents containing oxygen atoms in their molecules. They offer a wide range of solubility and volatility, and many resins are insoluble in hydrocarbon solvents but are soluble in oxygenated solvents. Common products include alcohols, ketones, esters and alcohol ethers. A third type of solvent, water, requires more energy to separate molecules and combine them with other materials. This means that water is an efficient solvent for many resin materials, but at the same time it has the disadvantages of high specific energy and high boiling point. Unlike most solvents, the evaporation rate of water is greatly affected by the relative humidity of the surrounding environment at the time of application and the air flow through the wet film. Finally, the equally unique representation of water's low vapor pressureThe molecular structure also contributes to its high surface tension. This directly affects the coating product's wetting ability and adhesion to the substrate. This high surface energy provided by hydrogen ions creates difficulties in water wetting and in obtaining good adhesion bonds to low surface energy substrates.
With the continuous refinement of coating applications and the improvement of technological level , in coating formulations, we will increasingly use composite solvents, usually called co-solvents. This is the main reason why so many solvents are needed in paint manufacturing. For example, ship paint and heavy anti-corrosion coatings will use some propylene glycol methyl ether and isopropyl alcohol as co-solvents; in nitrocellulose wood paint, propylene glycol methyl ether acetate, ketones (butanone, methyl isobutyl ketone) and some Alcohols (n-, isobutyl alcohol, isopropyl alcohol) are mostly used as co-solvents in nitrocellulose paint. We often add alcohols as co-solvents or latent solvents: alcohols cannot be dissolved alone. The nitrogen content is 11.7%-12.2 % of nitrocellulose, but they have potential dissolving power. When combined with active solvents such as esters and ketones within a certain proportion, the "mixed solvent" has the same or even greater dissolving power. For example, the toluene dilution value of one part ethyl acetate is 3.4, and the dilution ratio of half part ethyl acetate plus half part ethanol is also 3.4. The toluene dilution value of butyl acetate is 2.7, while the dilution ratio of half butyl acetate plus half ethanol is as high as 2.95. In most cases, the price of ethanol is much lower than that of butyl acetate. Adding a small amount of n-butanol to the alkyd resin paint can significantly reduce the viscosity; adding a small amount of isobutyl alcohol to the paint can effectively prevent the paint film from whitening, and can also improve the fluidity and gloss. When the type and dosage of co-solvent are appropriately selected, not only the quality is good, but the cost can also be greatly reduced; in coil coatings based on polyester resin, certain esters (n-butyl acetate) and alcohols are often used as co-solvents. (butanol) and certain ketones (butanone); as co-solvents for acrylic resin plastic paints, alcohols (butanol, isopropyl alcohol, n-propanol) and certain alcohol ethers (ethylene glycol butyl ether , propylene glycol methyl ether), also due to toxicity and other reasons, ethylene glycol butyl ether is now partially replaced by diacetone alcohol.
With the development of the coating industry, manufacturers use solvents It has also been improved. The era of formula buying and selling has passed. In China's coatings industry, solvents are developing in the direction of "complexity, high cost performance, high efficiency and low toxicity". Among a series of relatively environmentally friendly solvent products, alcohol ether and alcohol ether ester solvents are increasingly favored by the industry and are developing rapidly.
my country's alcohol ethers and Analysis of the development and current situation of alcohol ether esters
Glycol ethers in my country Product scale development first began in the 1990s, but it was mainly based on the production of glycol ethers. After the European Center for Chemical Industry and Toxicology published a toxicological study report on glycol ethers and alcohol ether esters, the use of glycol ether solvents has been restricted, while propylene glycol ethers and alcohol ether esters have been restricted due to their toxicity. Low, physical and chemical properties are similar to glycol ethers. In recent years, they are gradually replacing glycol ether solvents in many fields. In recent years, the rapid development of my country's automobile, paint, electronics and other industries has also promoted the innovative development of alcohol ether solvents to a certain extent. Among them, propylene glycol ether and alcohol ether ester are developing particularly rapidly. According to statistics, in 1997, the domestic production capacity of glycol ethers was only 22,500 tons. By 2012, my country's production capacity of ethylene glycol ethers and alcohol ether esters was more than 300,000 tons/year, and the production capacity of propylene glycol ethers and alcohol ether esters was as high as 840,000 tons/year. Alcohol ether and alcohol ether ester solvent is a colorless and transparent liquid. It is an excellent solvent with low toxicity produced by the reaction of ethylene oxide or propylene oxide and low carbon alcohol. Because of its chemical structure, it has two relatively The lipophilic covalent ether bond and the hydrophilic alcoholic hydroxyl group of the strong dissolving ability group can dissolve both hydrophobic compounds and water-soluble compounds. Therefore, it is known as the "universal solvent" and is widely used in coatings, Printing, dyeing and pesticide industries, as well as fuel antifreeze, detergents, extractants and organic synthesis intermediates.
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