Study on Preparation of Zero-VOC Interior Wall Coatings

Abstract: Zero VOC interior wall coating was prepared using the nuclear shell acrylic emulsion of hard core soft shell, and the effect of preparation method, emulsion type, pigment volume concentration and additives on coating film-forming and coating properties was discussed.
Foreword
Building interior wall latex coating volatile organic compound (VOC) content has been relatively small, but still need to add a certain amount of organic solvents to improve the coating film-forming and low temperature stability, construction still exists a certain smell, but also can not fully meet the indoor secondary decoration of decorative materials more environmentally friendly and healthy requirements. Constantly reducing the VOC content of coatings is the goal pursued by coating research staff, the current low VOC or zero VOC interior wall coating research and development has been the majority of paint manufacturers generally concerned about

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This paper uses homemade acrylic nucleus shell emulsion, without any organic solvents, prepared a low VOC content (almost zero) and low temperature film-forming and coating performance of environmentally friendly inner wall latex coating, examined the preparation method, emulsion type, pigment volume concentration (PVC) film-forming ambient temperature and various additives and other factors on the coating film-forming and storage stability and coating performance.
The so-called zero VOC coating in this paper refers to the coating formulation does not involve organic volatile substances and the resin (emulsion) used does not contain organic solvents, is a conceptual term.
technical performance indicators
Table 1 zero vOC interior wall coating technical indicators
2 results and discussion of the impact of
2.1 different types of emulsions
) and foreign well-known companies recommended for the preparation of low VOC or zero VOC coating acrylic emulsion A, B, C to prepare medium PVC (55%) of the inner wall coating, without any film additives, test results can be seen in Table 2.Table
2 different acrylic emulsion preparation of zero VOC interior wall paint performance comparison
For emulsion C-prepared coatings, the hardness and resistance to contamination may be significantly improved due to their high glass transition temperature (Tg), but MFFT increases. The freezing and melting stability of the coating prepared by emulsion B has not passed, which is mainly related to the low temperature stability of the emulsion itself.
2.2 Effect of Pigment Volume Concentration (PVC)
This experiment selected homemade HE-type nuclear shell emulsion, without any film-forming additives and solvents, changed the PVC of the coating, examined the effect of the coating PVC on the film-forming and coating mechanical properties of the inner wall coating, the test results are seen in Table 3Table 3 different PVC on the impact of zero VOC interior wall coating film temperature and coating performance
As can be known from Table 3, the use of homemade nuclear shell emulsion to prepare different PVC zero VOC interior wall coating, the minimum film temperature of the coating is less than 5 degrees C, to meet the actual use requirements.
PVC has a great impact on film hardness and stain resistance. In a certain range of low PVC, with the increase of PVC, the hardness of the coating film gradually increases, when the PVC increases to a certain value (e.g. 50%) the change in the hardness of the coating film has been very small, basically unchanged, because the Tg value of the emulsion used in this coating is relatively low (20 degrees C). Mainly depends on the pigment content in the composition of the coating, so with the increase of pigment fillers, the hardness of the coating film gradually increased, but in the high PVC range, the content of the base material in the coating is relatively small, the hardness of the coating film is mainly provided by the hardness of the pigment itself, so even if the PVC increases again, the hardness of the coating film is basically unchanged.
coating film resistance is mainly affected by the hardness of the coating film and surface finish double factors, in the low PVC range, the coating surface is relatively flat and smooth, at this time the surface hardness of the coating film on the resistance to contamination determines, so with the PVC increase, hardness increases, then the resistance to contamination increases. However, in the high PVC range, the surface hardness of the coating film is basically unchanged and the surface roughness is increased, so the resistance to contamination is reduced.
Overall PVC on washing, hardness, stain resistance (to a certain extent, on behalf of the film's anti-heat back viscosity), the selection of PVC in the range of 45% to 55% can be made to meet the actual use requirements and excellent performance of zero VOC interior wall coating.
2.3 Effects of different preparation methods
This test selected the following 3 different options, without any film-forming additives and solvents, respectively, prepared low, medium and high 3 kinds of PVC interior wall coating. Scenario 1: The he-type nuclear shell structure emulsion is adopted, the scheme 2: the low Tg is used in the ion phase emulsion (Tg value 0-5 degrees C), and the scheme 3: the high Tg and low Tg are used in the flattening of the ion phase emulsion. The performance effect of different preparation schemes on zero VOC interior wall coatings was examined, and the results were found in Table 4.
Table 4 different schemes prepared zero OC interior wall coating performance comparison
by Table 4 can be known, using different methods to prepare zero VOC interior wall coating, without any film additives can be produced MFFT at less than 5 degrees C of the inner wall coating, and with the improvement of PVC, MFFT reduced. From the data in the table, it can be seen that the use of high, low Tg emulsion mixed preparation of zero VOC interior wall coating, in different PVC, although the hardness of the coating film and resistance to contamination are better, but its wash resistance is poor, the reason may be that the high Tg emulsion in this experiment Tg has been very high (>60 degrees) C) is much higher than the actual environment film temperature (25 degrees C), its latex grain is very hard, in the case of membrane additives, only play a filling role in the coating film, equivalent to organic fillers, improve the paint PVC, so that the coating film wash resistance greatly reduced, over time, prone to cracking off. And the simple use of low Tg emulsion preparation zero VOC interior wall coating, in low PVC due to the coating film in the content of the substation is high, low surface hardness, poor anti-fouling, can not meet the requirements of use. However, in the case of high PVC, due to the low content of the substitlysis in the coating system, the hardness of the coating film is mainly determined by the pigment, so the hardness is higher, the resistance to contamination is better, but also to meet the use requirements of some occasions. For HE-type nuclear shell emulsion preparation coatings, in a relatively wide PVC range can be made in line with the actual use of the requirements of the inner wall coating. In addition, it can be seen from the table: the low temperature stability of the emulsion itself has a great impact on the stability of the coating freezing and thawing.
2.4 Wetting agent type and dosage of the effect on paint performance
the internal wall coating is usually selected as a surfactant, does not belong to the VOC category, it can not only improve the pigment moisture to water and paint dispersion stability, but also can improve the stability of the coating freeze-thaw. In addition, adding a certain amount of wetting agent to the zero VOC interior wall coating can extend the opening hours of the paint film and improve the construction of the coating and the smoothness of the coating film.
test selected the nuclear shell emulsion with poor freeze-thaw stability as the base material, and examined the effect of different kinds of wetting agent and its addition on the performance of the inner wall coating, and the results were seen in Table 5.
Table 5 wetting agent type and dosage on the performance of zero VOC interior wall paint
As can be seen from Table 5, adding a certain amount of wetting agent to latex coating can not only improve the stability of the coating freeze and thaw, but also reduce the paint's tacthragm index, increase the fluidity of the coating, improve the smoothness of the coating film, so that the coating film is flat, smooth and delicate. However, since most moisturizers are surfactants, adding paint increases the foaming of the coating, and the larger the addition, the stronger the foaming. It can be found from the experimental results that the anti-foaming resistance of wetting agents I and II is better. Wetting agent III. The improvement of coating freeze-thaw stability is greatly improved, but it will reduce the water resistance of the coating film and make the addition of wash-resistant drop wetting agent will significantly reduce the thickening effect of thickening agent, which is particularly obvious for hydrophobic modified alkali-soluble type (HASE) and polyurethane type (HEUR) thickener.
2.5 film temperature on the coating film-forming and coating performance of the impact
the construction environment temperature of the coating has a direct impact on the performance of the coating film, the preparation of the inner wall coating usually requires its minimum film-forming temperature is less than 5 degrees C (preferably close to 0 degrees C), in order to investigate the impact of the construction temperature on the film's intrinsic performance, this test selected different film-forming temperature, examined the film-forming temperature of various types of coatings The situation and the effect on the coating film wash resistance, the results can be seen in Table 6
Table 6 different film ambient temperature on the zero VOC coating film conditions and the impact on the coating film wash resistance
The coating in the table after drying 7d at a temperature of 2-3 degrees C, its coating film wash resistance is poor, this may be due to the coating film has not been completely dry. This also shows that the use of nuclear shell emulsion prepared by the zero VOC interior wall coating, dried into a film, the internal properties of the coating film and ordinary paint similar.
2.6 Other additives
2.6.1 Dispersant Selection
The dispersant currently commonly used in interior wall latex paint is polycarbonate. These dispersants use water as a dispersion medium without any organic solvents, usually ammonium salts and sodium salts. In order to further reduce VOC, this experiment uses sodium polypropyleneate-type dispersants, which have good dispersion to inormeric pigment fillers and are completely VOC-free, especially suitable for this coating, the dosage of the coating is 0.5%-1.0%.
of 2.6.2 deblisters
A small amount of water-based desulbant must be added to the preparation of the interior wall coating to ensure a good appearance of the coating and its coating. Commonly used desticants are mineral oils, silicones and organic polar compounds. The first two types of defoulants contain less volatile organic compounds, mainly a mixture of silicones, inorganic silicone (SiO2) metal soaps, mineral oils, water and emulsions. Since the amount of desiccant only accounts for 0.1% to 0.3% of the coating, the contribution of selecting these two types of desticants to VOC is negligible. This test selected the inner wall coating commonly used mineral oil deblistering agent, these deblistering agent deblistering, anti-foaming and de-foaming effect is good, and not easy to cause the coating film to produce fish eyes, shrink holes and other ills.
2.6.3 Choice of anti-mold agents
There are many types of anti-mold agents, such as amines that replace alkaloids, heterocyclic compounds (e.g. benzodiaxone), organic metal compounds (e.g. organic mercury, organo tin, organic arsenic) and so on. At present, the main anti-mold agent used in latex paint is formaldehyde release type and isopycin ketone compounds. This project selected a mold-resistant agent free of formaldehyde and heavy metals and organic solvents, the amount of addition of the coating 0.1% to 0.2%.
2.6.4 fluid thickeners
There are three types of thickeners commonly used in latex paint: cellulose, acrylic emulsions, polyurethanes. Most of these polyurethane thickeners usually contain a certain amount of organic solvents, and their effects on VOC must be taken into account when selecting such thickeners. Acrylic emulsion-type thickeners are divided into two types: one is alkali-soluble expansion type (ASE) and the other is hydrophobic modified alkali-soluble expansion type (HASE). The two types of thickeners basically do not contain organic solvents, the latter of which has better leveling and construction. This experiment selected hydroxyethyl cellulose (HEC) and HASE to be used together, so that the prepared coating not only has good storage stability, can opening effect, construction and coating appearance, but also does not increase the VOC of the coating.
2.6.5pH regulator
pH regulator commonly used in latex paint for ammonia, polymeramine compounds (such as AMP95) and sodium hydroxide solution, this experiment selected 25% sodium hydroxide solution to adjust the paint pH of 7-9, which does not increase the VOC of the coating, but also avoid the irritating odor of ammonia excessive.
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