Coating classification: dissolution of polymer in coating

Core tip: Introduction: In the early stage of coating, natural resins such as tung oil and lacquer were used, almost all of which could be dissolved in hydrocarbon solvent One exception is shellac, which is soluble in ethanol Later introduced nitrocellulose, such as RS, was soluble in esters and ketones, but not in alcohol and hydrocarbon solvents, but in mixtures of esters or ketones and hydrocarbon solvents When ethanol is added to the mixed solvent, the content of hydrocarbon solvent can be higher Therefore, ketone is called the true solvent of nitrocellulose, hydrocarbon solvent is called diluent and alcohol is called latent solvent The mixed solvent used for nitrocellulose shall be at least two esters or ketones Paint agent, top 10 Chinese wall paint brands Recommended introduction: interior wall paint and exterior wall paint can achieve beautiful, clean and pleasant effects, but the effects in different environments are different, so the color of the paint will be different There are ten brands of Chinese paint, ten brands of global paint, ten brands of Chinese wall paint, and ten brands of Chinese paint, Famous trademark of Chinese paint and coating In private rooms, most of us choose according to our own personality, personal hobbies and living habits The younger generation will choose the interior wall paint with rich colors and bright colors, while the older ones will have some working experience Introduction: early coatings used tung oil and other vegetable oils and natural resins such as lacquer, which are almost soluble in hydrocarbon solvents One exception is shellac, which is soluble in ethanol Later introduced nitrocellulose, such as RS, was soluble in esters and ketones, but not in alcohol and hydrocarbon solvents, but in mixtures of esters or ketones and hydrocarbon solvents When ethanol is added to the mixed solvent, the content of hydrocarbon solvent can be higher Therefore, ketone is called true solvent of nitrocellulose, hydrocarbon solvent is called diluent and alcohol is called latent solvent At least two esters or ketones, two hydrocarbon solvents and one alcohol are the mixed solvents for nitrocellulose In order to control the drying speed and solubility of the whole drying process at the lowest cost, more than 10 kinds of solvents can be used In order to control the drying speed under various conditions, mixed solvent is needed, and the used mixed solvent must maintain the solubility of polymer in the whole process of volatilization If the slowest volatile solvent is hydrocarbon solvent, and the last remaining solvent is mainly hydrocarbon solvent, nitrocellulose will be separated, resulting in uneven appearance and poor physical properties of the coating Therefore, the dissolution of polymers in coatings is an important factor affecting the performance of coatings and coating construction Solubility parameter: nonpolar or weak polar compounds are dissolved in nonpolar or weak polar solvents, and polar compounds are dissolved in polar solvents This is an empirical rule of "similar dissolving", which is very useful in coatings In the coating, hydrocarbon solvent is the solvent of hydrocarbon polymer, and oxygenated solvent (ketone and ester) is the solvent of oxygenated resin (cellulose, polyvinyl acetate) The solubility parameter (δ) is a more accurate rule than "the similar dissolves", and the solubility parameter is similar dissolves The solubility parameter can also be related to the cohesive energy, which represents the attraction between the liquid solvent and the solid polymer The cohesive energy is determined by the molecular structure The solubility parameter is calculated as follows: δ = (△ E / V) 1 / 2 △ e is the molar evaporation energy; V is the molar volume; δ can be obtained from the heat of vaporization, as well as from the surface tension data, chemical structure and the method of comparison and matching between solvents The solubility parameter δ has the following functions: if the difference between the solubility parameters of components is too large, they cannot be mixed evenly It is required that the solubility parameter δ of homogeneous components should be similar or the same According to this principle, we can: prepare mixed solvent; judge whether several resins used for paint preparation can be mutually soluble, because the mutual solubility of resins directly affects the transparency, gloss and other properties of the film; judge whether the resin can be dissolved in the solvent or mixed solvent; judge whether the plasticizer can be mutually soluble in the paint; manufacture plastics When using paint, it is required that the solvent can not dissolve the plastic as the base material, and the difference between the solubility parameters of paint solvent and plastic may be large The prediction accuracy of solubility parameter is only 50% Besides solubility parameter, hydrogen bond and solvation should be considered According to the strength of hydrogen bond, the solvents can be divided into three categories: the first category: weak hydrogen bond solvents (hydrocarbons, chlorinated alkanes, nitroalkanes), the average value of hydrogen bond force is 0.3; the second category: medium hydrogen bond solvents (ketones, esters, ethers, alcohol ethers), the average value of hydrogen bond force is 1.0; the third category: strong hydrogen bond solvents (alcohol, water), the average value of hydrogen bond force is 1.7 The solubility parameters of strong hydrogen bond solvent, medium hydrogen bond solvent and weak hydrogen bond solvent are δ s, δ m and δ P respectively When selecting solvent, the hydrogen bond force of resin and solvent should be in the same grade, and the value should be the same or similar In this way, the accuracy of prediction can be increased to 95% Most of the solvents used in coatings are mixed solvents, and their solubility parameter δ can be approximately expressed as follows: δ = φ 1 δ 1 + φ 2 δ 2 + φ 3 δ 3 + Where: φ - volume fraction of a component solvent in the mixed solvent Solubility test method for coating application: solubility parameters predict the solubility of solvents to polymers in theory Developed countries have adopted computer application database to select solvents according to the relevant theory of solubility parameters, so as to cooperate with the test work and reduce the test workload The test methods used in coating industry include shell rosin butanol value (KB value), aniline point, mixed aniline point, solvent index, dilution value, etc They represent the actual viscosity of the solution, which is the result of the combined action of solvent dissolving force and solvent viscosity KB value method is the most commonly used method to measure the solvent solubility of hydrocarbons Prepare the standard solution according to the mass ratio of shell turpentine and butanol 1:5 At 25 ℃± 2 ℃, take 20 g of standard solution and measure it with hydrocarbon solvent until it appears turbid The volume of hydrocarbon solvent required (ML) is the KB value of the solvent The larger the value of KB, the stronger the solubility The KB value of aromatic hydrocarbon is larger than that of aliphatic hydrocarbon, and its solubility is stronger The aniline point method is used to determine the solubility of aliphatic solvents When the same volume of aniline is mixed with the solvent, the lowest temperature of the clear solution is called aniline point The lower this value is, the stronger the solvent solubility is The mixed aniline point method is used to determine the solubility of aromatic solvents 5 ml of solvents to be tested, 5 ml of n-heptane and 10 ml of aniline are used, and the other ones are the same as the aniline point The solvent index method is the ratio of the viscosity of the paint diluted with standard solution to the viscosity of the paint diluted with the solvent to be tested under the same conditions The higher the ratio is, the stronger the dissolving power of the solvent to be tested is Dilution value method is to use different solvents to dilute the ratio of the same amount of paint to the amount of solvent consumed by the same construction viscosity, which is also called constant viscosity method The more solvent consumed, the worse the solubility of the solvent Solvent index method and dilution value method are defined by the viscosity of resin solution, while the viscosity of polymer resin solution depends on the dissolving force of solvent to polymer and the viscosity of solvent itself The stronger the dissolving power of the solvent, the stronger the dissolving power and the lower the viscosity of the resin solution The higher the viscosity of the solvent, the greater the viscosity of the resin solution Home of coatings is specialized in coatings, diatom mud, paint coating, coating technology, fire retardant coating news and coating, diatom mud, paint coating, coating technology, fire retardant coating decoration knowledge and decoration renderings,