Exploration and Screening of Rheological Additives in Waterborne Anti-sagging Varnish

LIU Feng, XIA Zheng-ming
(Zhuhai Zhanchen New Materials Co., Ltd., Zhuhai 519090, Guangdong, China)

Abstract: This paper studies the differences in anti-sagging and levelling effect brought by different rheological additive types and different matches in waterborne one-component wood coatings with waterborne acrylic emulsion as the main film forming material. The research results show that based on a given resin system, multiple combinations can achieve prefect balance between the anti-sagging ability and leveling performance of waterborne one-component wood coatings.

0 Preface
One-component water-based paint is the most common water-based paint product in the wood furniture industry today. It is widely used because of its convenient construction and low cost. Furniture is composed of parts, components and accessories, and different combinations form different structures. These different structures lead to different painting methods and painting techniques for wooden furniture. Although there are various differences, the requirements for the decorative and protective properties of the surface coating film are the same, which requires higher workability requirements for wood coatings. Anti-sagging and leveling are core indicators in construction performance. Waterborne wood coatings with high anti-sagging and leveling properties can be applied to simple panel furniture or three-dimensional furniture according to certain construction process parameters. The finished furniture, whether it is a flat surface or a surface with three-dimensional shapes such as grooves and carvings, can finally obtain a uniform and beautiful water-based protective coating.

1 Experimental
1.1 Main raw materials and instruments and equipment
Main raw materials: water-based acrylic emulsion, Zhanchen; film-forming aids, Jiangsu Yida Chemical; surfactants, defoamers, leveling agents, rheological additives (including HEUR thickening Agents, inorganic rheological additives), Hemings-Deqian Chemical, Beike, etc.
Main equipment: fluid viscosity meter: DIN 4 #, Yantian 2 # cup; Stormer viscometer; high-speed disperser; sag meter; rheometer; spray gun (caliber 1.3 mm); electronic scales, etc.
1.2 Experimental scheme
1.2.1 Preparation of semi-finished products
In order to facilitate the addition and dispersion, the two selected raw materials of the inorganic rheological additives a and b were prepared into the inorganic rheological additive dilutions A and B according to the formula in Table 1 before use.

Formulation of Inorganic Rheological Auxiliary Diluent A, B

In order to facilitate the addition and dispersion, the selected six thickeners a, b, c, d, e, and f are prepared into thickener dilution solutions A, B, C, D, E, and F according to the formula in Table 2. stand-by.

Formulation of thickener diluents A, B, C, D, E, F

In order to save the sample preparation process, the water-based one-component varnish is made into a water-based varnish base material according to the formula in Table 3 before use.

Waterborne varnish base formulation

Add emulsion, water, film-forming aid mixture, substrate wetting agent, and defoaming agent a to disperse for 15 min (1,000 to 1 400 r / min) according to the ratio of raw material formula, and adjust the dispersing speed to high-speed dispersing (1 800 ~ 2 500 r / min), add defoaming agent b, until the scraped film has no shrinkage, and meet the quality requirements of the base material formula.
1.2.2 Study on the properties of rheological additives in water-based coatings
1.2.2.1 Rheological properties of inorganic rheological additives
(1) Preparation of sample
design The amount of inorganic rheological additive dilution A / B is 1%, 3%, 5% 3 gradients, prepare water-based varnish samples according to the formula in Table 4.

Waterborne Varnish Sample Formula

(2) Determine the Stormer viscosity and flow curve of the sample to be measured
in a constant temperature and humidity environment. The temperature of the constant temperature and humidity room: (25 ± 2) ℃; relative humidity: 50% ± 5%. The flow curve was measured using a rheometer in rotation mode. The temperature of the sample to be measured was 20 ° C, and it was measured on the second day.

(3) Results and discussion
From the viscosity data and flow curves measured in Table 5, Figure 1, and Figure 2, it can be easily obtained: (1) In the case of the same addition amount, the inorganic rheological additive B is more likely to be improved than A Stormer viscosity of water-based coatings, but this increase in viscosity is not sufficient to meet the construction viscosity requirements of water-based coatings; (2) whether it is a rheological additive A or B, it will bring thixotropy to water-based coatings, and with the addition of As the amount increases, the thixotropic area becomes larger. After the water-based paint has thixotropy, it will greatly improve the spray application performance. It was also found during the experiment that with the increase in the amount of inorganic rheological additives added, the foam of the water-based varnish samples also increased during high-speed dispersion.

Stormer viscosity of water-based varnish samples under different gradients of inorganic rheological additive diluents A and B
Flow curves of water-based varnish samples with different additive gradients of inorganic rheological additive diluent A, and flow curves of water-based varnish samples with different additive gradients of inorganic rheological additive diluent B

1.2.2.2 Rheological properties of thickener
(1) Preparation of sample
design The Stormer viscosity of the water-based one-component varnish to be tested is (70 ± 3) KU, using the thickener diluent A / B / C / D / E / F adjusts the viscosity and prepares water-based varnish samples according to the formula in Table 6.

Water-based one-component clear finish

(2) Determine the Stormer viscosity and flow curve of the sample to be measured
. On day 1d, the Stormer viscosity is measured in a constant temperature and humidity environment, and then cured. On the second day, adjust the Stormer viscosity to (70 ± 3) KU again in a constant temperature and humidity room. Constant temperature and humidity room environment temperature: (25 ± 2) ℃; relative humidity: 50% ± 5%. The flow curve was measured using a rheometer in rotation mode. The temperature of the sample to be measured was 20 ° C, and it was measured on the second day.
(3) Results and conclusions
It can be seen from Table 7 and Figure 3 that even at higher additions of thickeners c and f, the Stormer viscosity value is lower and the viscosity is lower at different shear rates. It is a high-shear thickener or Newton-type thickener; thickeners a and d can provide higher Stormer viscosity at lower additions, and the viscosity becomes significantly lower at high shear rates. It should be a low-shear thickener; the Stormer viscosities brought by thickeners b and e are moderate, and they bring higher viscosity at high shear rates, and have relatively obvious characteristics of medium-shear thickeners. Although the thickeners b and e are both characterized by medium-shear thickeners, the added amounts are very different. Follow-up observations will be made on whether this difference in added amount will cause a difference in anti-sagging performance of water-based coatings.

Stormer viscosity of aqueous varnish samples adjusted by different thickener diluents
 Flow curves of water-based varnish samples with different thickeners at 70 KU viscosity

It is not difficult to see from the flow graph 3 that most HEUR thickeners do not provide significant thixotropy for water-based coatings.
1.3 Follow-up work
Based on the measured data and the phenomena observed in the experiment, select:
(1) The gradient of the addition amount of the inorganic rheological additive diluent A / B is 1% and 3% to ensure thixotropy to the water-based coatings. At the same time, effectively reduce the generation of foam.
(2) Thickener diluent B / E, while ensuring that the required viscosity is brought to the water-based paint, measure the difference caused by the added amount to the anti-sagging performance of the water-based paint.

2 Formulation design of rheological additive for facade anti-sagging and leveling water-based paint
2.1 Preparation of water-based one-component varnish Prepare
water-based varnish according to Table 8 for use.

Waterborne Varnish Sample Formula

Add base material, inorganic rheological additive, water, thickener and disperse in order of 15 minutes (1 000 ~ 1 400 r / min) according to the ratio of raw material formula. Adjust the Stormer viscosity to 77 ~ 83 KU to reach the test sample. Quality requirements.
2.2 Data measurement and results
2.2.1 Viscosity data comparison (see Table 9)

Stormer viscosity and fluid viscosity from different rheological systems

2.2.2 Flow curve comparison (see Figure 4 to Figure 6)

Flow curves (80 KU) of rheological additives A and different thickeners with different addition ratios, flow curves (80 KU) of rheological additives B and different thickeners with different addition ratios
Flow curves of rheological additives A and B with different thickeners at the same 3% addition amount (80 KU)

From the measured viscosity data and flow curve, it can be concluded that the amount of rheological additive added The more the static viscosity of the water-based coating is higher, and the rheological additive B can bring greater thixotropy and higher static viscosity to the topcoat than A. This is the better anti-settling performance of the rheological additive B Match. Thickeners B and E, except for the effective addition of thickener E, other differences are not obvious.
2.2.3 Comparison of thixotropy curves (see Figures 7-9)

Thixotropic curves (80 KU) of rheological additives A and different thickeners with different addition ratios, and 80 KU)
Thixotropic curves of rheological additives A and B with different thickeners and different thickeners (80 KU)

From the measured thixotropy curves, it can be seen that the inorganic rheological additive A can bring faster viscosity recovery speed under the same Stormer viscosity. . Fast viscosity recovery speed can be more conducive to the improvement of anti-sagging performance, slow recovery speed is more conducive to the improvement of leveling effect, and inorganic rheological additive B can provide a higher initial viscosity. Under the same conditions, the initial The higher the viscosity, the better the anti-sagging effect. It can be seen that the balance between sagging and leveling needs to be adjusted according to the actual situation in order to obtain a satisfactory viscosity. The characteristic curves of thickener b and e are still very similar. The only difference is that the shear thinning of thickener b is more obvious than that of thickener e, which may be caused by the amount of addition.
2.2.4 Comparison of anti-sagging effect of board making
Test method: Dilute all water-based varnish samples in Table 8 with water, adjust to the construction viscosity (70 ± 5) s, Yantian 2 # cup. The base material is a wooden board coated with a UV clear primer. The flat spray plate is placed on the floor and dried naturally. The application coating amount is 120 g / m2, the ambient temperature: 27 ° C, and the humidity: 50%.
Judging method: Judging the anti-sagging ability by the thickness of the coating film edge. The flatness of the edge of the coating film and the flatness of the board was used to determine the leveling property.
The anti-sagging effect of the actual board is shown in Figure 10.

Anti-sag effect of actual board
Anti-sag effect of actual board

After several actual spray plate confirmations, the anti-sagging and leveling effect of the additive amount of 3% (mass fraction) of the rheological additive B and the thickener e is the best. According to the surface effect, the anti-sagging effect of the rheological additive B is stronger than that of the rheological additive A, which is consistent with the experimentally determined flow curve and thixotropic curve. The anti-sagging and leveling effect of thickener e is stronger than that of thickener b, which may be caused by the amount of addition.

3 Conclusions
(1) The water-based paint itself is thixotropic, but it is weak enough to meet the requirements of construction performance.
(2) Rheological additives can bring greater thixotropy to water-based coatings, but their increase in viscosity is weak, which is insufficient to meet the requirements for viscosity in construction.
(3) Thickener is the main contributor to the viscosity of water-based coatings, and is the basis of anti-sagging ability. Water-based coatings can achieve the need for sag resistance through high viscosity, which is based on the sacrifice of leveling, especially for facade construction.
(4) After the water-based paint has thixotropy, the balance of sag resistance and leveling can be achieved by adjusting the viscosity level and the viscosity recovery time.
The anti-sagging and leveling performance of water-based coatings is an eternal subject of water-based wood furniture coatings. The realization of their performance depends on the performance of each component in the formula. Rheological additives, which are often called rheological additives and additives Thickener is the most obvious ingredient in anti-sagging and leveling. Other component characteristics must also be considered in the early stages of formulation design, such as the drying speed of aqueous emulsions or dispersions, the influence of the dilution ability of film-forming additives on viscosity, and the effect of surfactants on viscosity response.



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