The test criteria for the volume content of non-volatiles in coatings and the factors affecting their determination results are discussed

The volume content of non-volatile material of coating, also known as volume solid content, is an important parameter of coating products. This parameter is very important to guide the coating construction of coating products and estimate the amount of paint products, many construction units and users choose paint products as an important indicator. The determination of the volume content of paint non-volatiles is influenced by many factors, at present, the main standard for measuring the volume content of non-volatiles in China is the international standard ISO 3233-1998 and the national standard GB/T 9272-2007, because many parameters in the standard are not clearly defined, select different parameters, the test results are very different
China
. Therefore, the selection of parameters is critical to obtaining accurate and reliable test results.1 Test Principle
The test of the volume content of the coating without volatiles, the relevant standard is based on the main principle is Archimedes' Law, that is, the force of the object immersed in stationary fluid by the fluid action is equal to the flow weight force of the object discharged, the direction vertical upward, this force is called buoyant. By measuring the quality of the paint pre-test plate m1, the quality of the freshly painted test plate m3 and the mass m4 of the painted test plate after drying in the air, as well as the mass m2 of the paint pre-painting test plate immersed in impregnated liquid solution and the mass of the drying paint test plate m5, the liquid coating applied to the test plate, as well as the quality and volume of the drying coating, and then measure the non-volatile mass of the coating NVm. Based on the density of impregnated liquid and liquid coatings at the test temperature (expressed in ρ1 and ρ2 respectively), the density of the dry coating at the test temperature ρ0 and the non-volatile volume content of the coating NVV can be calculated, and the average of the two parallel measurements is taken as the test result. The calculation formula is as follows:
type: m1 - air unpainted test board quality, g;
m2 - the surface quality of unpainted test plate immersed in impregnated liquid, g;
m3 - air just painted test board quality, g;
m4 - air dry after painting test board quality, g;
m5 - immersion in impregnated liquid after drying The surface mass of the paint test plate, g;
NVm - non-volatile mass content, %;
NVV - non-volatile volume content, %;
ρ0 - density of dry coating at test temperature, g/mL;
ρ1 - density of impregnated liquid at test temperature, g/mL;
ρ2 - density of liquid coating at test temperature, g/mL.
Taking into account the differences in paint varieties, it is sometimes not possible to accurately measure the quality of the newly painted test plate m3, or weighing due to the drop of the paint sample on the test plate and affect the test results, so it is not possible to calculate the non-volatile mass content of the coating NVm according to formula (2), at this time, according to GB/T1725-2007 or ISO 3251 provisions to determine the value.
2 Summary of the relevant test method standard content and its progress
2.1 Existing test method standard
There are two main cases of existing test method standard: one is the actual test method, such as ISO 3233-1998 and GB/T 9272-2007;
2.1.1 ISO 3233-1998 color paint and varnish - measure the volume content of non-volatiles in the coating by measuring the density of the dry coating
The surface mass m2 of the test plate and the surface mass m5 of the painted test plate after drying, according to these five mass values, as well as the density of impregnated liquid and liquid coating at the test temperature ρ1 and ρ2, respectively, according to the formula (1) to (3) to calculate the density of the dry coating at the test temperature ρ0 At present, the standard has just been replaced by ISO 3233-1-2013, but the technical content of the two is basically the same.
2.1.2 GB/T 9272-2007 paint and varnish - the number of non-volatile object integrals of the coating by measuring the density of the dry coating
the standard includes ISO 3233 - All technical content of 1998, taking into account the differences in paint varieties, increased according to GB/T 1725-2007 to determine the quality content of paint non-volatile NVm content, at this time can be painted with round and flat operation.
2.1.3 ISO 23811-2009 color paint and varnish - by measuring the quality content of the paint non-volatiles and coating density to determine the volume content of the coating non-volatiles and calculate the theoretical coating rate
By measuring the density of liquid coatings ρ2, the density of various solvents or major solvents in the coating ρ3, and the non-volatile mass content NVm of coatings measured in accordance with ISO 3251, the density of dry coatings can theoretically be calculated according to formula (4 ρ0:
2 Progress in test method standards
In order to seriesize and facilitate the use of non-volatile volume content testing method standards, the International Organization for Standardization Technical Committee on Color Paint and Varnish (ISO/TC35) decided to integrate existing standards into a set of series standards. The integrated standards are as follows:
2.2.1 ISO 3233-1-2013 color paint and varnish - determination of non-volatile volume content - Part 1
This standard and ISO The testing process prescribed by 3233-1998 is basically the same, the main difference is that 2 parallel measurements are changed to 3 parallel measurements, which increases the calculation method of theoretical coating rate, which is the same as ISO23811-2009. The standard has now replaced ISO 3233-1998.
2.2.2 ISO/DIS 3233-2 color paint and varnish - determination of the volume content of non-volatiles - Part 2
This is a draft international standard for the consultation phase and is not yet a formal text of international standards. Compared with ISO 3233-1-2013, the standard does not measure the quality m3 of the newly painted test plate, but separately determines the non-volatile mass content of the coating NVm according to iso3251, which is basically the same as the increase of GB/T 9272-2007 relative to ISO 3233-1998. Similar to ISO 3233-1-2013, the standard also provides for the calculation method of theoretical coating rate, which is the same as ISO 23811-2009.
2.2.3 ISO/CD 3233-3 color paint and varnish - determination of non-volatile volume content - Part 3
This is also the draft international standard for the consultation stage and is not yet an official international standard text. Its content is the same as ISO 23811-2009, once it is officially released, ISO 23811-2009 will be voided.
3 Factors in the determination of the volume content of non-volatiles in coatings
3.1 Difference between theoretical calculation results and actual test values
The actual test value obtained by other test methods is not necessarily the same, as the volume occupied by the combination of resins or solvents may be the same as that of a single resin or solvent component, or it may be large or small, mainly for the following reasons: (() 1) Resin or solvent may shrink or expand; (2) is related to the degree of gap between paint-based pigment particles; (3) is related to volatile parts used in reactive systems, which are reacted to become non- Volatile film-forming substances are calculated as volatiles, and (4) coatings that exceed or are close to critical pigment volume concentrations will result in a larger dry coating volume than the theoretical volume due to an increase in unfilled voids between pigment particles. Therefore, theoretical calculations can only be used as references and estimates, not as a representation of the actual situation.
3.2 Effect of test plate drying conditions
Test plate can be dried according to different conditions, such as natural drying or drying, drying methods are different, the resulting non-volatile mass content is also different, which will affect the non-volatile volume content of the test results and theoretical coating rate calculation. The test results of the samples measured by ISO 3233-1998 are available in Table 1 under different drying conditions (the rest of the operating procedures are the same).Table
1 Effect of different drying conditions on sample test results
As can be seen from Table 1, the results obtained by drying are smaller than those obtained by drying 7 d at room temperature, which may be due to the relatively volatile solvents in the coating during drying, and therefore the resulting coating quality solid content value is relatively small, so that the non-volatile volume content value is also relatively small. The difference in results between the two dry conditions depends on how easily the solvent evaporates in the sample. In order to better simulate the actual situation, the drying conditions when measuring the volume content of non-volatiles are best in line with the actual situation.
3.3 The effect of selecting different non-volatile quality test methods
The non-volatile mass content of the coating can be calculated by measuring the quality of the pre-paint test plate m1, the quality m3 of the freshly painted test plate, and the mass m4 of the painted test plate after drying, or by iso 3251 or GB/T 1725-2007. The former can simulate the actual construction situation, and with the determination of the volume content of non-volatile test board can be determined, but only if the quality of the newly painted test plate m3 can be correctly weighed, whether the value is measured correctly directly affects the final test results of the volume content of non-volatiles. There are many factors that affect the testing of this value, such as the use of different painting methods, the control of time between the completion of painting and the weighing of the test plate, the control of the thickness of the coating film, etc. The iso3251 or GB/T 1725-2007 test is not affected by these factors, but requires the measurement of non-volatile mass content when the sample size is appropriate, its coating thickness covered in a solid disk is similar to the actual thickness at the time of construction.
effects of the 3.3.1 paint method
The volume content of non-volatiles can be measured by brushing, scraping, or dipping. Paint methods are different, the painting process takes different time, usually brushing time is longer, scraping time is short, and immersion is usually carried out with the flattening operation, in the process of flattening solvent will also be a large amount of volatilization. If the non-volatile mass content of the coating is determined by ISO 3251 or GB/T 1725-2007, these operations have little effect on the test results of the non-volatile volume content under the same drying conditions and the same dry coating thickness. And if the quality m3 of the coating test plate is calculated by weighing the quality of the freshly painted test plate, then the longer the quality weighing of the whole painting process to the newly painted test plate takes, the more material is evaporated before weighing, the longer the test results are. And the use of flattening operation, due to a large number of solvent volatilization in the process of flattening, by weighing m3 to calculate the non-volatile mass content of the coating, the result will be greatly deviated from the actual value, so in this case is not recommended to use this measurement method, but choose to determine the non-volatile mass content of the coating according to ISO3251 or GB/T 1725-2007 method.
3.3.2 Effect of the painting process to the test plate weighing time
visible by 3.3.1: different painting methods, painting time is different; Usually the longer the addition of these two periods, the greater the result. Table 2 shows the difference in test results obtained by USISO 3233-1998 using the same plate conditions (using a wet film preparer plate with a specification of 300 m) and controlling the time it takes to finish painting to read the test plate quality (15 s, 30 s, 45 s, respectively).
can be seen in Table 2: the shorter the time, the closer the result is to the ideal reality, because the shorter the time, the less volatile substances in the paint run away before reading the test plate quality.
effect of 3.3.3 film thickness
different paint film thicknesses are selected when painting, and the results will vary greatly under the same drying conditions. The thicker the coating film, the more difficult the solvent at the bottom of the coating to volatile, especially under natural drying conditions, the resulting non-volatile mass content and volume content are greater. Table 3 shows the test results obtained from the plates made of different wet film preparers (200 m, 300 m and 400 m, respectively) according to ISO 3233-1998, with the same other test conditions.
as can be seen from Table 3: the thinner the film, the smaller the result, because the solvent inside the coating is relatively volatile, and the thicker the film, the greater the result, because the solvent inside the coating is relatively difficult to volatile. In order to better simulate the actual situation, it is suggested that the thickness of the coating film is similar to the thickness of the film when the coating is actually constructed. 4 Conclusion
There are many test method standards at home and abroad for testing coatings without volatile volume content, but there are some differences between different standards, according to the special circumstances of coating products and specific coating construction requirements to choose the appropriate test method standards. In the process of testing the volume content of non-volatiles, there are many factors, such as measuring the quality content of paint non-volatiles, drying conditions, painting method, time control between paint completion and test plate weighing, film thickness, etc. will affect the test results. In order to make the test results more accurate, reliable and reflect the actual construction situation, the choice of these factors is best in line with the actual situation.