Qiang Zhihua，Cheng Xianglin，Zhao Jianhong，Zhou Pengju，Ma Keke，Li Meng，Jin Jian
（School of Chemical Engineering and Energy，Zhengzhou University，Zhengzhou 450001，China）
Abstract：The title aqueous alkyd resin emulsion was prepared by phase inversion process，and the influence of stirring speed，addition rate of water and the emulsification temperature on the preparation of emulsion were investigated. The results showed that the favorite emulsification condition was as follows：the emulsifier level，200# solvent，and KOH were 5%，3%，and 0.5%，respectively，the stirring speed between 4 000 and 6 000 r/min，the addition rate of water adding 90～120 mL/h，and emulsification temperature 50～60 ℃. The particle size of the emulsion D90≤307 nm. The stability of the emulsion and other properties of the coatings film met the relevant national standards.
There are two methods for water-based alkyd resin coatings: Internal emulsification method and external emulsification method (external emulsification method is also called reverse rotation method). The internal emulsification method is a method of introducing a sufficient amount of carboxyl groups on the molecular chain of an alkyd resin, adding an organic amine to neutralize the salt, and obtaining a uniform dispersion system under the co-action of co-solvent propylene glycol butyl ether and water. However, because it contains free organic amines, it has an unpleasant odor, and requires the addition of a co-solvent (propylene glycol butyl ether), which is not completely water-soluble (the content of the co-solvent is 20% to 30%, which is also VOC), and there is still a certain amount of pollution emissions. At the same time the cost is also higher. The majority of domestic alkyd coating manufacturers currently use the internal emulsification method. The process of the external emulsification method is to add an emulsifier and water to a solvent-free alkyd resin, and emulsify the alkyd resin into small liquid droplets to be uniformly and stably dispersed in the water phase by dispersing. The alkyd resin emulsion prepared by the external emulsification method (reverse conversion method ) has extremely low organic solvent content, and retains the properties of the original solvent-based alkyd resin coating. The paint film dries quickly, and the leveling and gloss are relatively good. it is good. However, this method is still in the laboratory research and development stage in China due to the technical difficulty. In this study, the self-made emulsifier was used to prepare the alkyd resin emulsion by the reverse conversion method, and the relationship between the process conditions and the properties of the emulsion was investigated, in order to achieve the industrial production of the aqueous alkyd resin coating by the external emulsification method.
1 Experimental section
1. 1 Materials and instruments
Alkyd resin: industrial grade, Zhenping Xingbang Paint Co., Ltd., industrial unmixed dilute alkyd paint (solid content above 97%), oil degree 58%, acid value ≤ 8 mgKOH / g; soybean oil: industrial grade , Shandong Defa Chemical Co., Ltd .; Huang Dan: Industrial Grade, Jinan Luhuai Trading Company; Phthalic Anhydride: Industrial Grade, Shanghai Xingmeng Chemical Technology Co., Ltd .; Pentaerythritol: Industrial Grade, Puyang Yong’an Chemical Co., Ltd .; Xylene: Industrial Grade, Shanghai Lu Shi Chemical Co., Ltd .; Antioxidants: Industrial Grade, Jinan Century Lianxing Economic and Trade Co., Ltd .; Sodium Dodecylbenzene Sulfonate: Analytical Pure, Tianjin Kaitong Chemical Reagent Co., Ltd .; OP-10: Industrial Grade, Tianjin Zhonghe Shengtai Chemical Co., Ltd .; Anionic emulsifier: Homemade; KOH: Analytical grade, Tianjin Fengchuan Chemical Reagent Technology Co., Ltd .; 200 # Solvent Oil: National Standard Grade, Wuhan Chaoyang Chemical Co., Ltd .; Drier: Industrial Grade, Jinan Haide Chemical Co., Ltd .; tap water.
High-shear dispersing machine (customized): Shanghai Modern Environmental Engineering Technology Co., Ltd .; Optical microscope: XPF-550C, Shanghai Caikang Optical Instrument Co., Ltd .; Laser particle size analyzer: NanoPlus-3, McMurrick (Shanghai) Instrument Co., Ltd. Company; Synchronous Thermal Analyzer (TGA-DSC): TGA / DSC 1 / 1600HT, METTLER TOLEDO International Limited.
1. 2 Experimental steps
1. 2. 1 Preparation of alkyd emulsion
Emulsifier is the key factor that affects the stability of the emulsion. The preliminary experiments of this research group have explored the use of sodium dodecylbenzenesulfonate, homemade anionic emulsifier and OP- 10 compound is used as emulsifier, which can emulsify non-solvent alkyd resin with different oil and viscosity.
Use an infrared heating furnace to heat the solvent-free alkyd resin to make it flow. In a beaker, weigh 12 g of 200 # solvent oil. Weigh 400 g of resin and solvent oil and pour it into a barrel. The barrel is passed through a constant temperature water bath. Turn on the stirrer to adjust the rotation speed to 2 000 r / min to make the resin mix evenly. Use a digital thermometer to observe the temperature of the resin at any time. When the resin temperature drops to about 75 ℃, add 10 g of 20% KOH solution and continue to stir at low speed for 20 minutes. After it is fully neutralized, add 20 g of composite emulsifier and stir for 30 minutes. After the dispersion is uniform, start adding water. At the same time, the speed of the stirrer is turned to the set value, and the dropping speed of the water is kept at the set value. 5 g portion of drier was added before the inversion of the emulsification process. After the phase inversion, continue to add water dropwise. After the dropwise addition, reduce the speed and quickly cool the water bath to normal temperature, and stop stirring.
1. 3 Performance test
1. 3. 1 Emulsion performance determination
Emulsion pH measurement: Take 10 g of emulsion in a small beaker and measure the pH of the emulsion (solid content 50%) with a precision pH meter; determine the stability of the emulsion: according to GB / T 20623—2006 “Emulsion for Architectural Coatings”; determination of emulsion particle size: measurement of particle size changes with a laser particle size analyzer; determination of emulsion shape: placing a small amount of 3% emulsion on a microscope slide, and then using a cover glass Cover quickly and press the covered sample with your fingers to make it as thin as possible; observe the emulsion morphology with an optical microscope.
3.2 Determination of coating film performance According to GB / T 1729-1979 to determine the appearance of the coating film; to determine the gloss of the coating film according to GB / T1743-1979; to determine the water resistance of the coating film according to GB / T 1733-1993; to GB / T 1728 —1979 Method B (finger touch method) is used to measure the dry time of the coating film; GB / T 1728—1979 Method A (press filter paper method) is used to test the dry time of the coating film; GB / T 1771—2007 is used to measure the resistance to neutral salt spray; Flash rust test: Sand a piece of clean tinplate with sandpaper to remove the protective layer on the surface of the tinplate. After sanding, wipe it with a dry cloth and immediately brush the board. Observe the flash rust condition regularly.
2 Results and discussion
2.1 Selection of emulsification temperature
The drying rate and hardness of alkyd resin paint films are related to the glass transition temperature of the resin. In the process of resin emulsification, the phase inversion temperature of the resin also has a great relationship with it. In general, the higher the glass transition temperature of the resin, the greater the resin viscosity at the same temperature. A large viscosity is not conducive to the uniform dispersion of water in the resin, which is not good for the emulsification process. Therefore, the viscosity of the resin can be reduced by selecting the emulsification temperature segment according to the glass transition temperature to achieve a good dispersion of water in the resin. Figure 1 is the TGA-DSC instrument curve (temperature range: 25 ~ 600 ℃; heating rate: 10 ℃ / min) of alkyd resin. From Figure 1, it can be seen that the glass transition temperature of alkyd resin is about 60 ℃.
The emulsification temperature  (by controlling the temperature of the water bath) directly affects the viscosity of the alkyd resin. The temperature is too low, the resin viscosity is large, it is difficult to disperse the water uniformly in the resin, causing the emulsion particle size to be uneven; the temperature is too high (over the cloud point of the non-ionic emulsifier OP-10, 61 ~ 67 ℃), it will Affects the activity of the emulsifier OP-10, and the viscosity of the resin inside the small droplets of alkyd resin is low at high temperature, which is prone to collision and deformation, resulting in a large particle size.
The effects of emulsification temperature on the properties of emulsions and coatings are shown in Table 1 and Figure 2. From Table 1 and Figure 2, it can be known that the performance of the emulsion is best when the emulsification temperature is controlled in the range of 50 ~ 60 ° C.
2.2 Effect of water addition speed
Add emulsifier to alkyd resin and mix well. Water is continuously added to it to form a water-in-oil (W / O) emulsion. As the water content increases, part of the oil phase is surrounded by the water phase to form oil. In the state of water-in-oil-in-oil (O / W / O), with the continuous addition of water and the effect of stirring shear, the droplets of the O / W / O structure rupture, and the opposite rotation occurs to form the oil-in-water (O / W / O). / W) type emulsion. It can be seen that in the process of phase transformation, the amount of water added plays a key role in the phase transformation process. The reverse conversion method is often used to prepare polymer resin emulsions, especially in alkyd resins. The emulsion inversion mechanism is shown in Figure 3.
The effect of water addition rate on the performance of the emulsion and coating film is shown in Table 2 and Figure 4.
From Table 2 and Figure 4, it can be seen that when the water addition rate is 90 ~ 120 mL / h, the emulsion has the best stability and the smallest particle size. Mainly because the water addition rate is too slow, the phase inversion time will be continuously delayed, and the state of the emulsion will always be maintained at the W / O / W state. The phase inversion cannot be timely, and the phase inversion occurs when the amount of water reaches a certain water-oil ratio (WOR). However, because the water is added too slowly, some W / O / W phase inversion is slow in O / W process, and the phase inversion phase is delayed. In the phase inversion phase, high shear for a long time will cause shear damage to the phase inversion emulsion. , Make the small droplets of the emulsion undergo secondary collision, and the phenomenon of uneven or large particle size (as shown in Figure 4) occurs; the water is added too fast, the emulsion cannot be mixed uniformly in time, that is, W / O / W emulsion When it is too late to fully disperse with water, it will be reversed into an O / W emulsion, resulting in uneven or large particle size. It is advisable to maintain the amount of water at 90 ~ 120 mL / h.
2.3 Influence of stirring speed The influence of
stirring speed on the performance of emulsion and coating film is shown in Table 3 and Figure 5.
It can be seen from Fig. 5 that when the stirring speed is 4 000 to 6 000 r / min, the obtained particle size is small and uniform, which is the optimal stirring speed range. The stirring speed is too small, and the shearing force is also small, making it difficult to mix water evenly in the alkyd resin with high viscosity. Not enough to make the emulsion small enough to cause many large droplets or W / O / W droplets to form during phase inversion; the stirring speed is too large, and small droplets that have formed in the opposite phase will collide during the reverse phase And recombination, the formation of some large droplets will also cause uneven droplets.
2.4 Characterization of particle size
Based on the above experimental results, select the best experimental conditions (additional amount of emulsifier 5%, 200 # solvent oil 3%, stirring speed 4 000 r / min, water addition speed 120 mL / h, emulsification temperature 55 ℃, KOH addition 0.5%, dry feed addition 1.5%) to prepare alkyd resin emulsion, particle size test of the emulsion using a laser particle size analyzer, the results are shown in Figure 6 and Table 4.
0 nm。 The results of Figure 6 and Table 4 show that the particle size distribution is uniform and concentrated, and the particle size is small, D98 is 397.0 nm.
The milky white uniform emulsion made under the best conditions was transparent blue, no precipitation, and no delamination. The properties were tested. The results are shown in Table 5.
It can be known from Table 5 that through multiple experiments, the water addition speed was 90 ~ 120 mL / h, the stirring speed was 4 000 ~ 6 000 r / min, and the emulsion particle size D98≤397 when the emulsification temperature was 50 ~ 60 ℃. The stability of the prepared emulsion was good at 0 nm.
The performance of the paint film is mainly related to the oxidative crosslinking density of the alkyd resin molecules. Since the emulsion is evenly suspended in the aqueous phase with small droplets of the alkyd resin, during the construction process, the emulsion forms a uniform emulsion film on the surface of the coating. The water gradually volatilizes, and the small droplets slowly move closer to each other and aggregate to break the emulsion, leveling into a uniform film. In this process, the evaporation of water inside the paint film is achieved by the microcapillary channels formed between the droplets. The larger the particle size, the more developed the capillary channels between the droplets, the faster the water escapes, and the faster the demulsification. In addition, the emulsion with a larger particle size has a faster demulsification speed, so it shows that the paint film is dry and hard. The paint film formed after the emulsion is demulsified is oxidized and dried to form a film under the action of a drier. The oxidative drying mechanism is the same as that of the solvent-based alkyd resin. Therefore, the various properties of the prepared emulsion after drying are close to those of the solvent-based alkyd resin, that is, most of the advantages of the solvent-based alkyd resin are retained. The paint film formed by the emulsion shows the basic properties of alkyd resin in terms of dryness, gloss, and hardness. The test results of neutral salt spray resistance and the water-based alkyd varnish (neutral salt spray resistance 36) prepared by the internal emulsification method of a well-known brand on the market h) Same.
Water-based alkyd resin emulsion was prepared by the reverse rotation method. The emulsifier was added at 5%, 200 # solvent oil was added at 3%, the stirring speed was 4 000-6 000 r / min, and the water addition speed was 90-120 mL / h, the emulsification temperature is 50 ~ 60 ℃, the amount of KOH added is 0.5%, the amount of the prepared emulsion is 1.5%, the stability of the prepared emulsion is good, and the particle size of the emulsion is D90≤307 nm. After the emulsion is dried and formed into a film, the performance of the coating film retains the excellent properties of the solvent-based alkyd resin, and the properties meet the requirements of relevant national standards.