Latex paint fluidity adjustment with thickener selection.

adjustment of latex paint fluidity and the choice of thickener . Xu Ling Zhang Advanced Hu Zhibin
(Shenzhen Haichuan Chemical Co., Ltd. Experimental Center 518040)
Wu Xiaotian
Cognis Hong Kong Co., Ltd. 1. Foreword
1.1 Fluidity of latex paint
Fullness leveling and the fluidity of the film on the vertical surface have effects that will eventually manifest them in the quality of the dry film the typical viscosity curve of latex paint under simple shearing must meet the requirements of different operating processes As shown in Figure1
The viscosity curve in the full range can be represented by the Casson empirical equation
D the fluid nature of the coating at the low shear rate is mainly determined by the structural viscosity formed by thickener and pigment latex particles, which makes the latex paint show a certain yield value, i.e. in the low shear rate in the process of settle flow equal flow, although the structure is weak but has a great resistance to flow Force represents the viscosity of the system under infinity shear rate under the condition of medium to high shear force, the structural viscosity caused by the action between the components of the system is easily damaged structure influence can ignore the viscosity of latex paint by the composition and dosage of solid components in the paint determines the appropriate viscosity under high shearing one Generally 2.5 to 5.0P brushing good coating film thickness is best after high shear stop conceding began to restore this feature so that latex paint fluid fluid degeneration with tact denaturation of the false plastic fluid characteristic recovery rate of the thickener viscosity of the function recovery time too fast is not conducive to leveling Too slow to produce flow hanging latex paint production process generally only control the viscosity Stomer viscosity KU value of the same latex paint in the low high shear rate range of viscosity difference tank effect is not good to produce layering of the main reason for pigmentation and volume rejection flocculation.
pigmentation factors include system viscosity low shear range viscosity pigment particle size distribution shape density dispersion state
volume rejection flocculation using HEC cellulose molecule adsorption weak easily replaced by the surface active agent in the moisturizer emulsion in the paint, etc. are replaced in the water phase due to the strong rigid structure of cellulose molecules compression pigment emulsion particles close to each other when the particle interval is smaller than the spiral diameter of the soluble polymer. The interval between extruded particles causes a local low concentration of the polymer, and then an unbalanced osmotic pressure the pressure difference will be caused by the pigment emulsion particles pressed together to create the characteristics of the microflocculant depends on the particle particle size and the volume fraction occupied, as well as the concentration of water-soluble polymer in such a system flow required for a considerable part of the energy required to be used to destroy the particle flocculant that produces yield stress this microflocculation particle plus thickener will be in the storage process to produce large-scale phase separation
Here are some examples that affect storage stability
? Pigment effect 1.2 thickener in latex paint
coating composition affects latex paint fluid change emulsion concentration and the concentration of other solid substances dispersed in latex paint can regulate viscosity but the adjustment range is limited cost higher latex paint viscosity mainly through thickener regulation of commonly used thickeners cellulose ether-based swelling polyacrylate emulsions and so on.
hydroxyethyl cellulose ether thickener mainly increases latex paint's medium-low shear viscosity tactability large cellulose thickener hydrophobic main chain and surrounding water molecules through hydrogen bonding to improve the fluid volume of the polymer itself by reducing the free movement of particles increases the system viscosity between pigments and emulsion particles to form an interconnected mesh structure so that it separates from each other to the pigment emulsion particles rarely adsorption
. Alkaline swelling polypropylene emulsion thickener mainly improves the yield value of medium and low shear viscosity larger tentacles large acrylic emulsion and ammonia or organic alkali start-up and reaction at the same time the basic resin is dissolved nirtine base under the effect of electrostation rejection so that the polymer chain stretches out so that latex paint System viscosity increase and particles in latex paint have weak adsorption such as Cognis SN-636926
non-ion joined polyurethane thickeners divided into two types of hydrophobic strong with false plastic characteristics in increasing high shear adhesion At the same time, the degree can significantly improve the medium and low shear viscosity and the denaturation is larger, such as Cognis SN-612DSX-1550DSX-1514 hydropyrelation shows Newtonian characteristics low shearing and thickening efficiency low mainly increases high shear Viscosity such thickeners such as Cognis SN-621N620DSX-3000DSX-2000 yield value small fluidity and various parts in latex paint have adsorption
. The performance of these three types of thickeners have their own characteristics for the different needs of latex paint formulation can be considered comprehensively to obtain the best application results with the use
2. Experimental results 2.1 high PVC latex paint viscosity control
the market low-cost high PVC latex paint occupies a larger share of engineering paint latex paint pigment dosing is often more than 45% emulsion Dosage as low as 10% PVC up to 80%
due to the high amount of paint filler in the paint to prevent pigmentation to ensure latex paint without layering requirements storage viscosity higher can be applied to higher molecular weight hydroxyethyl cellulose HEC To improve the viscosity of the medium and low shears, but also due to the yield value caused by poor leveling of the paint can also be combined with alkali-soluble thickeners such as Cognis SN-636 to improve the viscosity of the medium and low shears while improving water preservation
. High shear viscosity of hectic and alkali-soluble thickeners is usually not up to the required brushing content and low splashiness can be used to improve leveling brushing plumpness and low emulsion volume in PVC paint The weaker action between the particle coarser non-ion joining thickener and the emulsion can be used newton-type joining thickeners such as Cognis SN-620 and 2000D to improve high shear viscosity and improve brushing fluidity splashy plumpness Under degrees, two kinds of high PVC latex paint as an example to explore the viscosity control of this type of latex paint 2.1.1 PVC - 78% interior wall engineering paint
this kind of lower-cost engineering latex paint requires storage Table 1, which does not water or is less than 10% water before use, lists examples of thickener matching in this type of latex paint
Table 1 PVC , 78% latex paint thickener with example . Note SN-503450403204PE-100N-1005027436 are Cognis' dispersive wetting agent plateThe formation of water-rich HEC thickeners in the upper liquid at the time of the layer is slow and easy to re-mix evenly generally does not affect performance is only the main reason for the poor opening effect of layering pigmentation and volume rejection flocculation
Volume repellent flocculation Using HEC when cellulose molecule adsorption weakly easy to be replaced by surfactants in the moisturizer emulsion in the paint, etc. is free in the water phase due to the role of cellulose molecules strong rigid structure pressure pigment emulsion particles close to each other when the particle interval is less than the spiral diameter of the soluble polymer will be squeezed out of the space between the particles caused by the local low concentration of the polymer so that an unbalanced permeable pressure this pressure difference The properties of microflocculants caused by pressing pigment emulsion particles together depend on particle particle size and volume fractions, as well as a significant portion of the energy required for the flow of water-soluble polymers in such a system, to be used to destroy the particle flocculant, which produces yield stress, and the microflocculation particles, together with thickeners, which will thicken during storage to produce large-scale phase separation
below are some examples of phase separation affecting storage
stability. Pigment effect the particle size and shape of the pigment filler have an effect on the subsiding layering of the pigment particles by seination slower than the surface area, then the amount of adsorption dispersant is larger adsorption relatively stable Lid powder-1 light calcium particle fine Low density suspension is good and Lidl powder-2 heavy calcium density large talc powder kaolin soil filler particles for needle-like or rod-like structure at rest can form a high viscosity of the tactrine structure to prevent pigment sinking ? Wetting agent effect
Table 3 wetting agent effect exampleTable 3 of the two sets of formulations show that the use of more moisturizer on the one hand makes the pigment defuse flocculation on the other hand reduces the adsorption effect of the thickener so that the thickener molecule is easier to free and eventually results in layering 2.1.2 PVC - 64% of the interior wall paint
. This type of latex paint requires storage period of not less than half a year need to adjust the appropriate medium and high shear viscosity so that the coating has a good brushing leveling resistance to splash, but also to improve the low shear viscosity to prevent storage period layered table 4 listed thickener application examples
Table 4 PVC - 6 4% latex paint exampleTable 4 in the total amount of paint fillers to 52% need to improve the low shear viscosity to prevent subsidion profit
Pigment sinking usually adds HEC636 to improve the low shear viscosity may also cause the leveling of the paint to decrease high shear rate viscosity still does not meet the requirements of Table 4 latex paint emulsion dosing 18% add fake plasticity of 612 or 612D to Improving the shear viscosity is more effective in improving the leveling by adding Newtonian fluidizer 2000D to increase the high shear viscosity to improve brushing and improve the paint film plumpness
3 and 4 s paint with more kaolin suspension is not easy to produce layering.2.2 medium PVC latex paint
2.2.1 thickener with
medium PVC latex paint emulsion dosage more use of ordinary HEC alkali swelling emulsion thickener when the shear viscosity meets the requirements of low shear paste High flow level fluidity is poor using false plastic polyurethane-type binding thickener can simultaneously improve the medium and low shear viscosity thickening efficiency high fluidity good but low shear viscosity yield value is low enough to resist flow hanging usually use the above two together
12612D15501550D add less amount of phenyl propylene pure propylene emulsion can simultaneously improve the viscosity of the medium and low shear taking into account a cover and brushing with the use of Newtonian thickeners 620 and 2000D below are some specific examples

Table 5 Medium PVC latex paintTable 5 can be seen only with a joint-type thickener such as 3 in the paint shear viscosity suitable but low shear bonding through the low easy layering easy to flow with HEC or 636 can improve the low shear viscosity anti-flow hanging.
HEC and the combined thickener when used in the ratio system of the two surfactants to help solvents, etc. will affect storage stability so that paint layering phenomena such as Table 5, such as 2 , usually due to volume control flocculation caused by dehydration contraction . 2.2.2 Thickener and emulsion matching
false plastic large non-ionized bonding thickener s4. The efficiency of emulsion thickening is greatly affected by the type of emulsion Generally high efficiency of PHENCR pure propylene emulsion to vinegar C Uncle vinegar emulsion efficiency is lower the same type of emulsion latex particle size surfactant type different thickening efficiency is also different
Example Uncle Vinegar C Vinegar latex paint needs to use a large plastic joint thickener in order to effectively improve the viscosity of medium shear 2.3 low PVC latex paint fluidity adjustment
low PVC latex paint emulsion High use of connective thickener thickener thickening efficiency is high at the same time due to the presence of a joint thickener and latex particles with dry paint film gloss high density good
Table 8 low PVC latex paint example . Data showing that improper use of phenyl propylene pure propylene emulsions and polyplastic joint thickeners does not provide the required performance and can lead to system instability Table 2 and 3 paint data show that high glossy low PV is prepared with fine particle emulsions C latex paint when the false plastic type thickener contracting cooperation with too strong a small amount of added medium and low shear viscosity rose sharply this small amount of thickener will produce bridge flocculation effect to make the system unstable
In areas where flocculation and phase separation exist at very low HEUR thickener and surfactant concentrations, bridge phenomenon occurs when HEUR molecules are adsorbed on more than one emulsion particle because thickeners prefer to adsorption to emulsion particles rather than connect in water there is not enough thickeners at low thickener concentrations to form a stable network between all particles When more thickeners are added, more particles are connected to the flocculation when the thickener is added. Satisfy all particles At this point the thickener molecules begin to connect in the water When the surfactant is added to the flocculant in the bridge flocculation, the thickener will be desusped from the emulsion particles into a free state forming a water phase connected to the bridge flocculation area with flocculants and free latex particles in Brown motion encased in pigment particles that sink up to the water and latex particle mixtures such as table 3
. When a relatively large number of combined thickeners are applied in the system, a certain amount of surfactants will cause the combined thickener to completely remove the non-absorbent thickener from the emulsion particles so that the emulsion particles appear flocculation through the volume limiting process in the case of full desorption requires a large amount of thickener to cause flocculation This is due to the lower molecular weight of the polyurethane thickener the main chain is more flexible when the volume limit area appears flocculation. The two-phase system consisting of liquid does not have emulsion particles in the liquid, such as table 2, paint
Newtonian-type joint thickener and phenyl propylene pure propylene latex particles in cooperation with a weaker and higher amount will not produce flocculation phenomenon at the same time to obtain suitable medium-high shear viscosity and good brushing as in the table of 1 , 4 , 6 , paint 3 conclusion
1 high PVC latex paint viscosity control.