flooding & floating

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Flooding and Floating in Latex Paint

Huang Ying,

†

_{Cheng Jiang, Wen Xiufang, and Yang Zhuoru—}

_{South China University of Technology*}

*Research Institute of Chemical Engineering, Guangzhou, 510640, China.

†_{Author to whom correspondence should be addressed. Voice/fax: 86.20.87112057.807; [email protected].}

Flooding and floating are problems in many paint applications. If pigment concentration is uniform on the surface but not through the thickness of the film, one refers to ‘flooding’ (horizontal separation). If, however, concentration differences are visible across the surface of the paint film, one refers to ‘floating’ (vertical separation). In this article, the influence of pig-ment, filler, additives, and processing conditions on the flooding and floating of colored latex paint were investigated. It was discovered that too broad a distribution of pigment and filler particle size can lead to flooding and floating. Different lev-els of pigment (TiO₂) or filler (kaolin) loading cause diverse degrees of flooding and floating. Waterborne coatings that do not exhibit flooding or floating may show these conditions when diluted. Using dispersants or thickeners with hydrophobic constituents, increasing viscosity, reducing surface tension, etc., all help to prevent or reduce flooding and floating. Comparison tests revealed little influence of processing conditions on flooding or floating.

Keywords: Flooding, floating, latex paint, exterior wall coating

W

hen pigment and emulsion dispersions in wa-terborne paint are not stable, asymmetric sepa-rations can take place. They are often accompa-nied by flocculation. If there is sufficient dissociation and flocculation, stripe or grid patterns can be seen on films. This defect is called color floating. In other cases, the sep-arations are rather regular, pigments concentrate on the surface, causing a uniform color difference from the nor-mal paint. This is called flooding. Floating may be looked upon as a vertical separation of pigments, and flooding as a horizontal separation. Figures 1 and 2 show floating in a latex paint and its conversion to flooding with the ad-dition of silicon oil. Flooding and floating occur during the application of colored latex paint.1 _{They complicate}

color matching, waste color paste or pigment, and can hurt appearance, flow and leveling, hiding power, tint strength, gloss, and the resistance of the paint film to wa-ter and alkali.2-4

It is widely accepted that there are many components and factors that influence flooding and floating. Among these factors are:

(1) Stability of pigment and emulsion dispersion— Inorganic pigments in aqueous coatings have been inves-tigated using atomic force microscopy and microprobe an-alyzers.5 _{Dispersability of organic pigments aggregation}

degree has been determined,6 _{and rheological,}

electroki-netic properties and surface chemistry of waterborne dis-persions have also been studied.7-8_{When excessive}

floccu-lation and precipitation occur, flooding and floating happen. So absorbing suitable dispersants on pigments and forming an optimum absorption layer will exert a beneficial influence on flooding and floating resistance.

(2) Flow currents within the film9-10_{—In the wet film, as}

water volatilizes, the temperature, surface, and interfacial tension will decline, more hydrophilic pigments will be carried with water to the surface, and Bénard cells are formed.11_{Bénard cells in a wet film are illustrated in Figure}

3. Bénard cells will persist until the coating is too viscous for the particles to move. In many cases, flooding and floating are more likely to occur in humid circumstances than in dry air. Increasing the viscosity and reducing the surface tension of the system can alleviate flooding and floating.12

(3) The emulsion used—Binder, like pigment, requires sur-factants for dispersion and stabilization. If the emulsion and color paste are not compatible, or if the emulsion or color paste is deprived of surfactants, the stability of the dis-persion will be reduced, and flooding and floating may ap-pear.13_{So testing compatibility between emulsion and color}

paste before production is essential. Methods for assessing pigment dispersion have been compared by Van et al.14

Figure 1—Floating and flooding defects. (A) floating, (B) normal, (C) floating converts to flooding after silicon oil is added.

(4) Application conditions—Humidity, temperature, and processing are also influential.15

A variety of approaches have been used to alleviate flooding and floating, such as forming coflocculates,16-17

using leveling agents,18 _{or adding shear thickeners.}19

However, how the essential components in latex paint in-fluence the defects of flooding and floating has seldom been reported.

In this article, the influence of pigment, filler, addi-tives, and processing conditions on flooding and floating is studied. Correlative measures to prevent or alleviate flooding and floating are also proposed.

EXPERIMENTAL

Materials

Primal AC-261, from Rohm and Haas, was used as emulsion. CPS Monicolor universal color pastes were used for color. Dupont TiO₂, kaolin from Jinyang in ShanXi, China, and talc from Longguang in GuangXi, China were used as pigment and fillers. Henkel and BYK additives were used as dispersants and defoamers, etc.

Instruments

An MP200A electronic scale from Shanghai, China and a GFJ-0.4 high speed dispersing plant in Shanghai, China were used to produce the paint. A 480KU viscometer from Sheen Instruments Ltd., U.S. and a Brookfield DV-II vis-cometer from Brookfield Engineering Laboratories, U.S., ICI cone and plate viscometer from Research Equipment Ltd., a QXD-25 to QXD-150 fineness of grind gauge from Tianjin, China, a tensionmeter 70535 surface tension ap-paratus from CSC-Dunouy, and a WGG-B three-angle dig-ital glossmeter from Fujian, China were used to evaluate and survey the experiments.

Experimental Design

The acrylate emulsion and color paste were tested for compatibility. First, the emulsion and color paste were blended at a 50:1 ratio. After storage at 50°C for 30 days, the fineness was measured. If the fineness was below 30 µm, the emulsion and color paste were considered compatible. If the fineness was above 50 µm, they were considered incom-patible. If it was between 30 and 50 µm, they were consid-ered partially compatible. Other ingredients were let-down and the latex paint was produced. Paint was applied on the substrate (asbestine plank) to form films and flooding and floating of the wet films were evaluated.

To study how pigment and filler influence flooding and floating, we designed the following experiments:

(1) Different amounts of TiO₂(4, 10, 23 wt%) and var-ious amounts of monoazo red (0.1, 0.5, 1, 2, 5, and 10 wt%), were added to the basic paint.

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Figure 2—Illustrating diagrams of floating and flooding defects. (A)

normal, (B) floating, (C) floating converts to flooding after silicon oil is added.

(2) Using a formulation with 10 wt% TiO₂in the basic paint, colored by 0.1 wt% monoazo red, we added 5, 10, and 15 wt% water to dilute the paint and stored it natu-rally for seven days.

(3) With no change to the other ingredients in the paint, we used differing kaolin contents; the kaolin contents used were: 8, 11, and 14, and 17 wt%, colored by monoazo red and carbon black both at 0.1 wt%.

(4) We produced three groups of paint with kaolin and talc of various particle sizes, TiO₂, and other ingredients as above:

(a) kaolin (38 µm) + talc (38 µm) (b) kaolin (38 µm) + talc (10 µm) (c) kaolin (10 µm) + talc (10 µm) (d) kaolin (2 µm) + talc (10 µm)

All were colored with monoazo red and carbon black, both at 0.1 wt%.

(5) Several groups of surfactants were investigated to re-veal how the surfactants influence flooding and floating:

(a) 0.8 wt% SN-Dispersant 5040 (b) 0.8 wt% SN-Dispersant 5027

(c) 0.2 wt% SN-Dispersant 5040 + 0.6 wt% SN-Dispersant 5027

Other ingredients were unchanged; the formulations were colored by monoazo red and carbon black, both at 0.1 wt%, and then brushed. After the films dried, we measured the brightness and saturation to compare dis-persion stability.

(6) Three types of thickeners were used to increase vis-cosity: cellulose QP-4400, acrylic CR₂, and polyurethane SN-612. We adjusted the viscosity between 85–95 KU with the three thickeners; QP-4400 was added before other in-gredients, while CR₂ and SN-612 were added in the last phase of production. They were all colored by 0.1 wt% monoazo red and carbon black.

(7) To see whether processing affects flooding and floating of coating, we added 0.1 wt% monoazo red in the coating in four different ways: (a) Dispersed with titanium under high speed agitating; (b) Added after high speed ag-itation dispersion of titanium and filler, and before emul-Table 1—Compatibility of Acrylate Emulsion and Color Paste

Emulsion and Color Paste Only Coatings with Other Ingredients Bin stability Fineness

Color Paste (50°C, 30 days) (µµm) Compatibility Inside Surfacea

Anthraquinone red... Uniform 28 Compatible Uniform Red floating at the brim2_{, flooding}2

Monoazo red ... Uniform 21 Compatible Uniform Floating4_{, flooding}3

Indian red ... Uniform 30 Compatible Uniform Floating1_{, flooding}1

Quinoline yellow... Uniform 26 Compatible Uniform Floating1_{, flooding}1

Monoazo yellow ... Uniform 22 Compatible Uniform Floating1_{, flooding}1

Disazo yellow... Uniform 25 Compatible Uniform Floating2_{, flooding}1

Ferrite yellow ... Uniform 29 Compatible Uniform Floating2_{, flooding}1

Brown iron oxide ... Uniform 28 Compatible Uniform Floating1_{, flooding}1

Phthalocyanine green ... Uniform 28 Compatible Uniform Floating4_{, flooding}3

Phthalocyanine blue... Uniform 26 Compatible Uniform Blue floating at the brim2_{, flooding}2

Quinacridone violet ... Uniform 23 Compatible Uniform White floating1_{, flooding}1

Delphine violet ... Uniform 25 Compatible Uniform White floating1_{, flooding}1

Carbon black ... Flooding2 _{40 Partially compatible Uniform Floating}4_{, flooding}3

(a) Note 1, 2, 3, 4 indicate the degree of floating and flooding: 1 = slightest, 4 = most severe; the same coding scheme is used in all tables.

Table 2—Influence of Titanium Content on Flooding and Floating

Flooding and Floating Condition

TiO₂Content 4 wt% 10 wt% 23 wt%

Color paste 0.1 Floating2_{, flooding}2 _{Uniform Floating}2_{, flooding}2

content (wt%) 0.5 Floating2_{, flooding}2 _{Uniform Floating}2_{, flooding}2

1 Floating1_{, flooding}1 _Floating1_{, flooding}1 _Floating2_{, flooding}2

2 Floating1_{, flooding}1 _Floating1_{, flooding}1 _Floating3_{, flooding}3

5 None Floating2_{, flooding}2 _Floating3_{, flooding}3

10 None Floating2_{, flooding}2 _Floating4_{, flooding}4

Figure 5—The floating results of carbon black with different kaolin contents.

sion addition; (c) Added after the basic paint is produced, that is, the last in order; and (d) Color paste premixed with emulsion, then added into the paint in the usual or-der. Flooding and floating were evaluated for each after natural and accelerated storage at 50° for 30 days.

RESULTS AND DISCUSSION

Influence of Emulsion

The results of the compatibility experiment of acrylate emulsion and color paste are shown in Table 1.

It can be seen that most color pastes are compatible with the emulsion, except that carbon black paste is par-tially compatible. However, in the paint produced with the same emulsion and different paste, flooding and float-ing appear in varyfloat-ing degrees, in which monoazo red and carbon black paint are most severe. That is why we chose monoazo red and carbon black paste for the following ex-periments. In the case of quinacridone violet and del-phine violet, white color floats on the surface. It can be concluded that, in most cases, the emulsion is not the main cause of flooding and floating.

Influence of Pigments and Fillers

The influence of TiO₂content on flooding and floating is shown in Table 2 and Figure 4. It can be seen that paints with different TiO₂content differ in flooding and floating. This is because pigment particles vary in hydrophilicity. While a volatile component like propylene glycol which is used as a cold-resistant agent evaporates, it carries rather more lipophilic particles to the surface, so the scission of color emerges. Usually, 20–30% TiO₂content latex is used

for the preparation of light tint paint, 8–13% TiO₂content latex is used for the preparation of a medium shade coat-ing, and < 4% TiO₂content latex is used in deep color pro-duction. To summarize, high TiO₂ makes flooding and floating worse, especially with high paste content. The 10 wt% level may not be the optimum, but it certainly is bet-ter than the others at low paste content.

The effect of dilution with water on flooding and float-ing is shown in Table 3.

It is observed that, when a nonfloating paint is diluted with water, flooding and floating may occur, or their severity may increase. When more water is added to the paint, the dispersants are diluted and there is compara-tively less dispersant available to stabilize the pigment. The paint becomes more hydrophilic, so lipophilic com-ponents are more likely to phase separate. Last, but by no means least, the decrease of viscosity makes the move-ment of particles easier. The addition of water also tends to raise the surface tension, inducing more severe Bénard cell flows.

The influence of kaolin content on flooding and float-ing is shown in Table 4, and the floatfloat-ing results of carbon black are plotted in Figure 5.

The main component of kaolin is Al₂O₃•2SiO₂•2H₂O. It has some other names, such as hydrated aluminum sili-cate, China clay, white bole, etc. It can engender thixotropic structure, form a kind of spatial network struc-ture, and prevent aggregation of pigment particles, thus alleviating flooding and floating.

It is found that there is an optimum content of kaolin. Increasing concentration favors dispersion stability, but makes dispersion difficult. Application properties and gloss are impaired at high concentrations. Based on Table

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Table 3—Flooding and Floating Difference of Latex Paint Diluted with Water

Flooding and Floating Condition

Dilution ratio ... 5 wt% 10 wt% 15 wt% 0.1 wt% paste + 10 wt% TiO₂... Flooding1_{, floating}1 _Flooding2_{, floating}3 _Flooding3 _{, floating}4

Table 4—Influence of Kaolin Content on Flooding and Floating

Kaolin Content 8 wt% 11 wt% 14 wt% 17 wt%

Carbon black ...Film status after natural setting Floating1 _Floating1 _Floating1 _Floating2

for one week flooding2 _flooding1 _{no flooding floating}2

Film status after accelerated Floating3 _Floating2 _Floating1 _Blocking

storage for one month flooding3 _flooding2 _{no flooding}

Monoazo red ...Film status after natural setting Floating2 _Floating1 _Floating1 _Floating2

for one week flooding2 _flooding1 _{no flooding floating}2

Film status after heat Floating3 _Floating2 _Floating1 _Blocking

accelerating storage for one month flooding3 _flooding2 _{no flooding}

Table 5—Influence of Particle Size on Flooding and Floating

Test Item ... Kaolin (38 µm) Kaolin (38 µm) Kaolin (10 µm) Kaolin (2 µm) +talc (38 µm) +talc (10 µm) +talc (10 µm) +talc (10 µm) Monoazo red (0.1 wt%)... Floating3_{, flooding}2 _Floating3_{, flooding}1 _Floating1_{, no flooding None}

4, 14 wt% is a comparatively effective dosage. In practice, several fillers are often used in combination to meet per-formance requirements.

Small particle size tends to alleviate flooding and float-ing. According to Stokes’ law, the velocity of spherical par-ticles sinking in a liquid is given by:

V = D(d_pi–d_bi)r2_/η

where V: velocity; D: proportional constant; η: viscosity; d_pi: density of pigment; d_bi: density of binder; r: pigment radius. This equation indicates that sinking velocity de-creases when the particle size dede-creases, or the difference between pigment and binder density is reduced, or binder viscosity increases. The effect of particle size on flooding and floating is shown in Table 5.

Influence of Additive Agents

The influence of dispersants on flooding and floating is shown in Table 6. SN-Dispersant 5040 is a special polysodium carboxylate dispersant for latex paint. SN-Dispersant 5027 is a polyammonium carboxylate with higher molecular weight than 5040. 5027 is more lipophilic and has lower

surface tension. For the higher steric hindrance and lower surface tension, 5027 is good at alleviating flooding and floating; but 5040 has higher dispersing efficiency when used alone, so the use of both shows the best effect.

Sedimentation can be adjusted by increasing viscosity. CR₂is an acrylic thickening agent; a schematic of its struc-ture is shown in Figure 6. Its hydrophilic “segment” coa-lesces with water to thicken, and its lipophilic segment’s hydrophobic function keeps the particles detached, and forms a steric network, thus controlling flooding and floating. It can be seen from Table 7 that steric hindrance plays an important role in the control of flooding and floating.

QP4400 is a kind of hydroxyethylcellulose from Cellosize, and SN-612 is another hydroxyethylcellulose from Henkel Ltd. Hydroxyethylcellulose is widely used in paint. However in this case, it is less effective in reducing floating, for CR₂is more similar in structure to and com-patible with the dispersants. So, the compatibility be-tween thickener and dispersant is very important.

The influence of different viscosities (adjusted using CR₂, since it is the most effective thickener among the three) on flooding and floating is elucidated in this exper-Table 7—Influence of Different Thickeners on Flooding and Floating

Thickener

QP4400 CR₂ SN-612

Content... 1.5 wt% 1.2 wt% 1 wt%

Viscosity ... 92.1 92.3 91.8

Monoazo red... Floating3_{, flooding}3 _Floating1_{, flooding}1 _Floating2_{, flooding}2

Carbon black ... Floating3_{, flooding}3 _Floating1_{, flooding}1 _Floating3_{, flooding}3

Table 6—Influence of Dispersants on Flooding and Floating

Dispersants Flooding and Floating Surface Tension (dyn/cm)

Carbon black ... 5027 (0.8 wt%) Floating1_{, flooding}1 _34.5

5040 (0.8 wt%) Floating2_{, flooding}2 _41.5

5027 (0.6 wt%) + 5040 (0.2 wt%) None 37.1

Monoazo red ... 5027 (0.8 wt%) Floating1_{, flooding}1 _34.3

5040 (0.8 wt%) Floating1_{, flooding}2 _41.8

5027 (0.6 wt%) + 5040 (0.2 wt%) None 37.0

Table 8—Influence of Viscosity on Flooding and Floating

CR₂content... 0.8 wt% 0.85 wt% 0.9 wt% 0.95 wt%

Viscosity (KU) ... 89 94 103 112

Monoazo red... Floating3_{, flooding}3 _Floating2_{, flooding}2 _Floating1_{, flooding}1 _Floating1_{, flooding}1

Carbon black ... Floating3_{, flooding}3 _Floating3_{, flooding}3 _Floating1_{, flooding}1 _Floating1_{, flooding}1

Table 9—Influence of Processing on Flooding and Floating

Processing 1 2 3 4

Monoazo red After natural

setting (3 days) None Almost none Floating1_{, flooding}1 _Floating1_{, flooding}1

After natural

setting (7 days) Almost none Almost none Floating1_{, flooding}1 _Floating1_{, flooding}1

After accelerated storage

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iment; the results can be seen in Table 8. It is found that higher viscosity reduces flooding and floating.

Influence of Processing

It can be seen from Table 9 that processing has little in-fluence on flooding and floating. In practice, color paste is added as process number 3 according to the principles of convenience, speediness, and economy.

CONCLUSIONS

In this article, flooding and floating in latex paint were studied and the causes were summarized from the aspect of components. Ways to alleviate flooding and floating in waterborne coatings were explored. The following conclu-sions can be drawn:

(1) Generally, color pastes are compatible or partially compatible with the emulsion. However, in the paint pro-duced with the same emulsion and different paste, flood-ing and floatflood-ing appear in various degrees. So, emulsion is not the main cause of flooding and floating.

(2) Paints with different pigment or filler contents dif-fer in flooding and floating conditions. It is because pig-ment particles are different in hydrophilic property and lipophilic nature. Usually, 20–30% TiO₂ content latex is used for preparing light tint paint; 8-13% TiO₂content la-tex is used for preparing a medium shade coating; and < 4% TiO₂content latex is used in deep colored paint production. Reducing the surface tension, increasing the viscosity, and using finer particles help to prevent flooding and floating.

(3) Steric hindrance in both dispersants and thickeners plays an important role in the control of flooding and floating.

(4) Processing conditions have little influence on flooding and floating.

To sum up, reducing the surface tension, forming spa-tial network structure, decreasing the particle size, mini-mizing the difference between pigment and binder den-sity, and increasing viscosity are helpful in preventing flooding and floating.

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