Application of film-forming additives in water-based two-group polyurethane coatings.

application of film-forming additives in water-based two-group polyurethane coatings
Fang Bo 1, 2, Li Guojun 1, 2, Zhang Yuguo 1, 2, Wang from the country 1,2
(1. Guangzhou Dynasky Materials Technology Co., Ltd., Guangzhou 510860;2. China Electrical Science Research Institute Co., Ltd., Guangzhou 510080) 0 Foreword
film additives are usually high boiling point solvents, their volatility rate is lower than water, will slowly evaporate after the formation of the coating film. Film-forming additives can promote the plastic flow and elastic deformation of polymer compounds, improve their polymeric properties, help them to form films over a wide range of construction temperatures, and are an easy-to-volatile plasticizer. In the thermoplastic water-based emulsion, in order to ensure the hardness of coating, chemical resistance and other properties, it is necessary to improve the glassing temperature of emulsion polymer, at the same time, the minimum film temperature (MFT) required for coating is relatively high, to the lower temperature coating construction and film-forming trouble, film-forming additives can solve this problem, so that high performance and low construction temperature can not conflict.Water-based two-part polyurethane coating film and thermoplastic water-based emulsion is different, through the water-containing hydroxyprool resin coating and water can disperse the uniform mixing of polycyanate curing agent, with the evaporation of water and solvents, particle spacing gradually reduced, forming a high concentration of accumulation structure, and then form a more tight hexagon structure, and finally through polyol and polycyanate main reaction to produce amethane. The main purpose of adding film additives to water-based two-component polyurethane coatings is also different from thermoplastic water-based emulsions, not to help the coating film, but to help the construction of the coating and enhance the appearance of the coating film through the addition of film-forming additives.In this paper, two different water-based hydroxyprool resins, WD-551 and DSM XK-110, are used as the main film-forming materials of the adjunct, of which WD-551 is a dispersive hydroxypropyl acrylic polyol, with a hydroxy content of 3.3 mg KOH/g, and a solid content of 44%, which is a high hydroxyl resin. Coating film with high gloss, high plumpness, good physical and chemical properties, can be used for the appearance and performance requirements of more stringent medium and high-end finish, and because it is a dispersive type of water-based resin, in the production process is not easy to break milk, easy to operate. XK-110 is a lotion-type hydroxypropyl acrylic polyol, hydroxyl content of 2.5 mg KOH/g, solid content of 46.5%, is a medium hydroxy content resin. Coating film has a higher gloss and fullness, because the hydroxyl content is not high, the cross-link density of the coating film is not enough, its physical and chemical properties than high hydroxy resin are lacking, but in the face of the appearance and performance requirements are not high products, its lower curing agent addition can make in terms of cost-effective advantages. As it is a emulsion-type water-based resin, the selection and use of membrane additives in the formulation need to be more careful to avoid the situation of broken milk. Group B selects Cosco's XP2655, by adding different film-forming additives, the storage stability of coating A-parts, the construction of A-B parts mixed (flat and anti-flow hanging effect), coating film table dry speed and dry film appearance, etc. to provide some reference for the selection of film additives.1 Experimental part
1.1 Raw materials and instruments
Raw materials: WD-551 and DSM XK-110 hydroxyproxol resin, R-98 0 Titanium white powder, BYK2012 dispersant, BYK028 deblister, DEGO4100 humidifier, PW336 leveling agent, OMG0620 thickener, film-forming additives.
table 1 is the basic parameter of several commonly used film-forming additives selected in this paper.equipment: electronic balance, dispersing machine, sander, scraper fine meter, viscosity cup (2 cup), dry film tester, pot spray gun and so on.1.2 Basic Formula (see Table 2)
This experiment was conducted using n (-NCO):n (-OH)=1.5:1, when the water-based hydroxypropyl acrylic polyol resin was WD-551, By m (A- parts): m (B-parts) - 7:1; when the water-based hydroxypropyl acrylic polyol resin is XK-110, by m (A-) m (B-parts) - 10:1.1.3 Experimental Method
Add dispersants and de-foaming agents to deionized water, stir at a low speed of about 5 min, slowly add titanium dioxide under continuous stirring, stir at medium speed about 15min, evenly put into the grinder for grinding, until fine less than 20 5 min Sm, take excellent slurry, in the medium-speed stirring in turn to add water-based hydroxypropyl acrylic polyol resin, wetting agent, leveling agent, diethanolamine, thickener and film-forming aids, all the ingredients added to continue to stir at medium speed 15 min, get A part.
the AB parts are mixed evenly according to the ratio of 1.2, add deionized water to adjust the viscosity of about 40 s (2 cups), sprayed on the horse mouth iron, at room temperature level 5min after 70 degrees C baking 1 h to make the coating film.2 Results and discussion
2.1 Paint A part storage stability
paint storage stability refers to the paint products in the normal packaging state and storage conditions, after a certain storage period, the physical or chemical properties of the product can reach the original requirements of use. Since paint products are manufactured in the production plant, to use often need to go through a period of turnover, often may be stored for several months, or even years after use, the ideal coating products stored in containers should not change in quality. Water-based coatings are more prone to storage instability than solvent-based coatings, especially after the addition of film additives, some of the emulsion will cause damage, resulting in skin, particles, subside and other phenomena. Different water-based emulsions to membrane additives selection and addition volume is not the same, this section of the two selected water-based hydroxy polyol resin according to the above basic formula made of coating acetyles to add different film-forming additives storage stability test, testing based on GB/T 6753.3-1986 national standard, storage temperature of 50 degrees C, 30 d.
test results of water-based hydroxyl polyol resins WD-551 and XK-110 are shown in Tables 3 and 4.. Note: The items in the table are rated according to 6 grades: 10 x N, 8 x very slight, 6 x minor, 4 x medium, 2 x more serious, 0 x severe;note: The items in the table are rated according to 6 grades: 10 , none, 8 , very slight, 6 , slight, 4 , medium, 2 , more serious, 0 , severe;by Table 3, Table 4 can be seen, when not added as a membrane additive, the two water-based hydroxyplor polyol preparation of water-based two-component polyurethane coating component a storage stability is very good, after the addition of membrane additives are most prone to subsidon problems, different membrane additives on the effects of the two are not the same, and the sedation problem with the increase of membrane-assisted dose becomes serious, some particle conditions. Therefore, for different water-based hydroxy polyol resin prepared water-based coatings should be fully tested a variety of film-forming additives used in the stability. As can be seen from Tables 2 and 3, WD-551 may select DPM, TPNB and TPM with a film additive of about 5%, and the film assist dose may be increased to 10% when the 12 alcohol esters are selected, while 5% of the film additives are suitable for XK-110, PNB and alcohol esters 12 can be increased to 10%.2.2 Coating table dry speed
Coating film table dry can also be called finger drying, that is, when the finger touches the coating film feel sticky, but the coating film is not attached to the state of the finger. There are many factors that affect the drying speed of the coating surface, the difference of resin, temperature and humidity, the type and dosage of film-forming additives will cause the difference of the drying speed of the table. In the process of coating construction, the drying time is too short will bring negative effects on the appearance of the coating film, such as poor leveling, foaming, hazelnuts and other phenomena, and too long drying time will bring a lot of inconvenience, but also more prone to hanging problems.
for the above two water-based hydroxy polyol resins made of water-based coatings in the same temperature and humidity conditions to add different film-forming additives, according to the experimental method to prepare the coating film, test its drying speed. During the experiment, the air temperature was 28 to 30 degrees C and the relative humidity was 40%, and the specific test results were shown in Table 5.Combined with Table 1, the slower the evaporation rate and the higher the boiling point of the film-forming additives will make the coating surface drying speed slower, and as the amount of added becomes slower, the coating formulation can be designed according to the need to use the corresponding film-forming additives and the appropriate amount of added to adjust the drying speed of the coating.2.3 Dry film appearance
water-based two-component polyurethane coating can have excellent performance and appearance, but its coating in the drying process is prone to poor leveling, orange peel, foaming, hazelnuts and other problems, not only seriously affect the appearance of the coating film, but also some poor appearance will have a certain degree of impact on the film performance. As described in 2.2, the addition of high-boiling point film-forming additives in the coating formulation can adjust the drying speed of the coating membrane, by extending the drying speed of the coating surface can also make poor leveling, orange peel, foaming, hazelnuts and other problems to be resolved.
But different water-based hydroxyploride resins need membrane additives are not the same, if the film-forming additives are water-based hydroxy polyol resin bad solvents, it is likely to lead to the final coating of loss of light, fog, no plumpness.
the two water-based hydroxy polyol resins involved in this experiment, WD-551 and XK-110, were tested accordingly for luster, leveling, tweezers, etc. after adding 10% of the coating formulation amount to different film additives. During this section of the experiment, the air temperature is 30 to 32 degrees C, the relative humidity is 60%, the specific test results are shown in Table 6, Table 7.. Note: Leveling is assessed on 6 levels: 10-excellent, 8-good, 6-medium, 4-poor, 2-poor, 0-severe orange peel;: leveling is rated according to 6 grades: 10- excellent,
8-good,
6-medium,
4-poor,
2-poor,
0-severe orange peel; The tweezers problem is rated according to 6 grades: 10 s
none,
8 s very slight,
6 s minor,
4 s medium,
2 s more serious,
0 s serious.Table 6, Table 7, do not add a membrane additive, because of poor leveling and the influence of tweezers, the film measured gloss will decline, and with the increase in dry film thickness, tweezers more serious problems, the greater the impact on gloss. Combined with Tables 1, compared to Tables 6 and 7, with the decrease of the evaporation rate of film-forming additives and the increase of boiling point, the leveling effect of the coating film is better, and the problem of tweezers is more minor; Especially reflected in the gloss, part of the gloss does not affect or even will make the gloss to be improved, part of the gloss will have a certain impact, visually can be seen when the coating film has fog shadow, not through. From Table 6 and Table 7, DPM, TPM, alcohol esters 12 pairs of two resins are more suitable film-forming additives.3 Conclusion
This paper on two different water-based hydroxyurea polyol resins in the non-addition and addition of different film additives when the storage stability of the coating, coating table dry speed and dry film appearance has been more in-depth research, design and preparation of water-based two-group polyurethane coating according to the corresponding test, choose one or more film-forming additives with a combination of factors to make the coating can be stable storage, coating appearance and performance..