Development and Performance Research of Low VOC, Low Odor Waterborne Wood Coatings

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volatile organic compounds (VOCs) emissions are one of the most important causes of photochemical pollution and ozone layer destruction, some of which originate in the coating industry.
, the development and production of low VOC and even zero VOC environmentally friendly coatings has become an important development direction in coating technology.
water-based coatings are water-based coatings that are dispersed mediums and thinners, which have obvious advantages in environmental protection and

.
However, the existing water-based coatings, especially water-based wood coatings still have some shortcomings, such as wood coating polyacrylic emulsion general glass transition temperature (Tg) is higher, need to add a large number of film-forming additives to aid film- and membrane-forming additives are mostly high-boiling point organic solvents, will be partially residual in the coating film, reduce the film's mucousty, chemical resistance, hardness, etc.
addition, most film-forming additives also affect the content of VOC in water-based wood coating formulations, making most water-based wood coatings do not meet environmental standards.
the film-forming substances of water-based wood coatings determine the performance of the final coating, and the film-forming substances currently used in single-group hydrohydrated wood coatings are water-based acrylic emulsions (PA), water-based polyurethane dispersions (PUDs) and acrylic modified polyurethanes (PUAs).
acrylic emulsion has excellent weather resistance, water resistance, but the coating film has the disadvantages of hot, cold and brittle,
water-based polyurethane dispersion has good low temperature film-forming, high-temperature back-to-mucous, high wear-resistant properties, but its self-thickening, low solid content, high price, coating water resistance, solvent resistance, affecting its popular application.
, if the two are combined, overcome their shortcomings and play their respective advantages, the performance of the coating film can be fully improved.
film additives are the largest source of VOC in water-based wood coatings, to reduce the content of wood coating VOC is to reduce the amount of film additives.The addition of
film-forming additives is related to the minimum film-forming temperature (MFFT) of the film-forming system, MFFT low film-forming substances need to be added to the film-forming material with less film-forming dose, good construction tolerance, the VOC content of the formula is relatively low, but the hardness of the coating film is low, chemical resistance is poor, high temperature soft back to the mucous, non-polluting, the comprehensive performance of the coating film is poor.
MFFT high film-forming substances need to be added to the amount of film-forming additives, the voC content of the formula is relatively high, poor construction tolerance, but the hardness of the coating film is higher, chemical resistance is better, the comprehensive performance of the coating film is better.
In order to adjust the minimum film-forming temperature of the film-forming substance and ensure the performance of the coating film, the two film-forming substances of high MFFT and low MFFT are usually mixed, and by adjusting the ratio of the two emulsions, the minimum film-forming temperature of the system can be reduced and the amount of film-forming additives can be reduced.
This project looks forward to optimizing the formulation of water-based wood coatings from both film-forming substances and film-forming additives, and develops a low-odor environment-friendly water-based wood coating with excellent overall performance and a VOC content of less than 30 g/L.
1 Experimental part
1.1 Experimental raw materials and instruments
experimental raw materials:
acrylic emulsion A, acrylic emulsion B, acrylic emulsion C,
polyurethane dispersion H, DSM;
polyurethane dispersant F, polyurethane dispersant G, thickener, Wanhua Chemistry;
humidifiers, dispersants, leveling agents, defoulants, Bick Chemistry;
membrane additives OE-300, OE-400, Eastman.
experimental instrument:
. SZQ Wet Film Preparationer, Shanghai Modern Environmental Engineering Technology Co.,
,
QSJ High-Speed Dispersion Machine, Tianjin Jianyi Experimental Instruments Co., Ltd.
1.2 Basic formula and preparation process
basic formula is found in Table 1.
preparation process:
in the container in turn interval of 5 min to add resin, wetting agent, pH regulator, dispersant, low-speed mixing uniform, add pre-high-speed dispersion of good desiccant, and then add pre-mixed film additives, deionized water, medium-speed dispersion of 15 min after the addition of leveling agent and thickener, and finally low-speed dispersion of 10 min, that is, made of water-based wood coating.
1.3 Experimental Method
1.3.1 Experimental Model Production
According to GB/T 23999-2009 "Indoor Decoration Water-based Wood Coatings" national standard 6.3 in the method of preparation of models.
a 100 m wet film is scraped with a film coater on the glass plate (150 mm ×100 mm ×3 mm) and the hardness is tested after 7 d at constant temperature and humidity.
1.3.2 Film hardness, anti-adhesion, water resistance, alcohol resistance and pollution resistance test
according to GB/T 6739-2006 "color paint and varnish pencil method to determine the hardness of the paint film" provisions using a pencil hardness meter to determine the hardness of the coating film.
test water resistance according to GB/T 4893.1-2005 "Furniture surface cold-resistant liquid determination method."
The test fluid is distilled water, the experimental area takes the middle part of each plate, places 5 layers of paper sheets in each experimental area, the experimental process needs to keep the filter paper moist, if necessary, in the glass cover and test plate contact area coated with Vyslin to seal.
24 h after removing the filter paper, absorbing dry, placed 2 h after visual observation in scattered sunlight, such as 2 of the 3 sample boards did not appear foaming, cracking, peeling and other membrane diseases (but allowed for minor color changes and slight gloss changes) is rated as "no abnormality";
such as the above membrane morbid phenomenon according to GB/T 1766-2008 "color paint and varnish coating aging rating method" described.
test alcohol resistance according to GB/T 4893.1-2005 "Furniture surface cold resistance measurement method."
test and results assessment method with water resistance, the test fluid is 50% (volume fraction) of ethanol solution, the experimental time is 1 h, after the experiment placed 1 h observation.
testing of anti-pollution resistance according to GB/T 4893.1-2005 "Furniture Surface Cold Resistance Measures".
test and results assessment method and water resistance, the experimental time is 1 h, after the experiment placed 1 h observation.
vinegar resistance:
test liquid for brewing vinegar.
:
test liquid green tea, in 2 g green tea to add 250mL boiling water, room temperature placed 5 min immediately with tea for experiments.
testing of dry heat resistance in accordance with GB/T 4893.3-2005 "Furniture surface cold resistance determination method."
the experimental temperature (70±2) and the experimental time was 15 min.
the VOC content of wood coatings is calculated according to GB/T 23986-2009 "Measurement of Volatile Organic Compounds (VOC) Content of Color Paint and Varnish".
specific formula is as follows:
:
ρVOC - VOC content of the sample to be tested, g/L;
mi-1 g mass of the compound i in the experimental sample, g;
ρs - density of the experimental sample at 23 degrees C, g/mL;
1 000 - mass conversion factor.
2 Results and discussion
2.1 Preferred acrylic emulsion
water-based acrylic emulsion with fast drying, good transparency, good color preservation and other advantages, this project first optimizes acrylic film-forming substances Selected, four acrylic emulsions A, B, C and D with MFFT of 5 degrees C, 15 degrees C, 29 degrees C and 43 degrees C were selected to make a water-based wood coating and the performance of the coating film was studied, as shown in Table 2.
can be seen from Table 2, the four acrylic emulsions selected, in terms of film hardness, emulsion C and emulsion D have the highest hardness, emulsion B second, emulsion A is the worst.
This is because the MFFT of emulsion C and emulsion D is higher than room temperature, the polymer chain segment in the dry film is in the glass state at room temperature, the coating film is shown to have a higher hardness, and the polymer chain segment in the dry film formed by emulsion A and emulsion B is in a high emoticon state, and the coating film is shown to be softer.
, emulsion C and emulsion D are also better chemically resistant than emulsions A and emulsion B.
MFFT high acrylic emulsion is usually less film-forming, shown as poor tolerance of construction, easy to crack and other ills.
by adding a certain amount of film-forming additives, emulsion A, emulsion B, emulsion C and emulsion D4 emulsions did not crack when the film was formed at 5 degrees C on the glass plate.
This project further examined the construction tolerance of wood coatings made of different acrylic emulsions on wood, from Table 1, it can be seen that MFFT higher acrylic emulsion C and emulsion D made of wood coating on the birch wood 5 degrees C into the film appeared different degrees of cracking, because acrylic emulsion C and emulsion D formation coating film is relatively brittle, wood easy to absorb water expansion, coating film and wood easy to produce a cracking film.
the hardness, chemical resistance and construction tolerance of the coating film, the acrylic emulsion C was selected as the film-forming substance, and the performance and construction tolerance of the coating film were optimized.
2.2 Preferred
polyurethane molecular structure with hard and soft chain segment, the structure determines its unique performance of both hard and flexible, its two-phase structure makes water-based polyurethane has excellent low temperature film-forming, fluid flatness and flexibility, good resistance to heat back to mucous, due to the presence of hydrogen bonds, it has the advantages of wear resistance, high hardness.
water-based acrylic resin and water-based polyurethane resin have a certain complementary role in nature, the use of organic combination of the two to improve the comprehensive performance of the material, has become an important way to develop a new generation of water-based wood coatings.
Choose the film temperature low polyurethane dispersion and acrylic emulsion C to mix, on the one hand, can adjust the membrane system MFFT, reduce the amount of membrane additives, reduce the content of formula VOC, on the other hand, can use the advantages of complementary, improve the comprehensive performance of wood coating.
project selected 4 MFFT less than 10 degrees C polyurethane dispersions as film-forming substances, respectively, made wood coating, and tested its performance, the results are shown in Table 3.
As can be seen from Table 3, the four polyurethane dispersions selected, in terms of film hardness, the hardness of dispersion G and dispersion H can reach B, the hardness of dispersion E is the lowest, less than B, consistent with the laws of these polyurethane dispersion MFFT.
chemical resistance of each of the four polyurethane dispersions is similar, and they can basically meet the requirements.
In the absence of membrane additives, the choice of 4 polyurethane dispersants on the glass plate of 10 degrees C film-forming is normal, dispersion E, dispersion F, dispersion G on the board of the low-temperature film is also normal, and dispersion H appears slightly cracked, and dispersion G, dispersion H surface dry time than dispersion body E, dispersion F dry time is shorter.
the hardness of the coating film, construction tolerance and table drying time, the polyurethane dispersion G and acrylic emulsion C are selected for mixing.
2.3 Preferred mixing ratio of acrylic emulsion and polyurethane dispersion
Acrylic emulsion C and polyurethane dispersion G have different characteristics, so the ratio of the two mixtures will also have an impact on the final performance of the coating film and VOC content.
project examines the effect of different quality ratios on coating performance, and the results are shown in Table 4.
From Table 4, it can be seen that, with the increase in the proportion of polyurethane dispersion in the emulsion, the hardness of the coating film becomes softer, because the MFFT of the added polyurethane dispersion is relatively low, the formation of the coating film is relatively soft at room temperature, so in order to ensure the hardness of the coating film, the proportion of polyurethane can not be too high.
when the ratio of acrylic emulsion to polyurethane dispersion is 4:1, 3:1 and 2:1, the hardness of the coating film is higher to meet the basic performance requirements.
The chemical resistance of the coating film of the mixed emulsion is basically normal, which shows that the synergy between acrylic emulsion and polyurethane dispersion can significantly improve the comprehensive performance of the coating film, and the combination of the two emulsions achieves the goal of improving the comprehensive performance of the coating film.
acrylic resin coating feel is poor, poor plumpness, poor construction tolerance, and the addition of polyurethane dispersion can improve the film feel and construction tolerance.
the price of polyurethane dispersions is relatively high, so the proportion of polyurethane dispersions should not be too high.
the performance and cost of the integrated coating film, the preferred acrylic emulsion and polyurethane dispersion mix ratio is 3:1.
2.4 Choice of membrane additives
The membrane additives of water-based coatings, also known as polysynthics, solvents or cosolnts, are high boiling point compounds with molecular weight of hundreds, mostly alcohols, alcohol esters, alcohol ethers, etc., and are actually a solvent of polymers.
performance of the film-forming additives selected for this project is shown in Table 4.
EU Directive 2004/42/EC stipulates that the maximum boiling point of VOC is 250 degrees C, as can be seen from Table 5, the boiling point of Coasol, OE-300 and OE-400 is higher than 250 degrees C, not counted in the formulation of VOC, can preferably be low VOC content of wood coating film additives.
DPnB (dipropanol butyl ether) is the most commonly used film-forming additive in water-based wood coating formulation, with high film-forming efficiency, fast drying speed and certain antifreeze resistance.
in order to optimize these three non-VOC film-forming additives, Coasol, OE 300 and OE-400 and DPnB were used as film-forming aids, respectively, and the performance results of the coating were examined as shown in Table 6.
from Table 6, it can be seen that the comprehensive performance of coating film with DPnB as a film-forming additive is better, but its spray construction odor is relatively large.
compared with three non-VOC film-forming additives, wood coating with Coasol and OE-300 as film-forming additives has better film hardness and chemical resistance, but Coasol spray construction odor is relatively large.
to improve the performance of the coating film and reduce V.