Dispersant is a kind of dispersant withLipophilicityandHydrophilicityTwo interfacial active agents with opposite properties.But it is difficult to uniformly disperse thosedissolutionIn liquid inorganic, organic pigment solid and liquid particles, it can also prevent particlesettlementandcondensation, forming stableSuspensionRequiredAmphiphilicReagents.
Dispersant is amphiphilicchemical, can increase the oil and water components in the same systemCompatibility。
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Explanation in reference book
A medicament that can promote the uniform dispersion of material particles in the medium to form a stable suspension.Dispersants are generally divided into inorganic dispersants and organic dispersants.Common inorganic dispersants aresilicateClass (such as water glass) and alkali metal phosphate class (such as sodium tripolyphosphate, sodium hexametaphosphate, sodium pyrophosphate, etc.).Organic dispersants include triethylhexyl phosphoric acid, sodium dodecyl sulfate, methyl pentanol, cellulose derivatives, polyacrylamide, Gul gum, fatty acid polyethylene glycol ester, etc.
Interpretation in academic literature
A dispersant is defined as a substance that can reduce the aggregation of solid or liquid particles in a dispersion system.It is easy to form dispersion and suspension when adding dispersants and suspending agents when preparing emulsifiable concentrates and wettable powders, and maintain the relatively stable function of the dispersion system.[1]
Explanation in Chemical Dictionary
Can raise and improve solid orliquidAdditive for material dispersion.When grinding solid dyes, dispersants are added to help particles crush and prevent the agglomeration of crushed particles to keep the dispersion stable.The oil-based liquid that is insoluble in water can be dispersed into very small liquid beads under the stirring of high shear force. After the stirring is stopped, it will soon delaminate under the action of interfacial tension. After the dispersant is added and stirred, it can form a stable emulsion.Its main function is to reduce the interfacial tension between liquid-liquid and solid-liquid.Therefore, dispersants are also surfactants.The species are anionic, cationic, non-ionic, amphoteric and macromolecular.Anionic type is used most frequently.
effect
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The function of dispersant is to use wetting dispersant to reduce the time and energy required to complete the dispersion process, and stabilize the dispersedPigmentDispersion, modifying the surface properties of pigment particles, adjusting the mobility of pigment particles[2]。This is reflected in the following aspects:
1. To improve the gloss and increase the leveling effect, the gloss is mainly determined bycoatingThe scattering of light by the surface (i.e., a certain flatness is enough. Of course, the detection instrument needs to determine whether it is smooth enough, not only considering the number and shape of the original particles, but also their combination mode). When the particle size is less than 1/2 of the incident light (the value is uncertain), it is reflected as refraction light, and the gloss will not be improved,Similarly, the hiding power, which depends on scattering to provide the main hiding power, will not increase (except for carbon black, which mainly depends on light absorption, and organic pigments forget).Note: The incident light refers to the range of visible light, which is not good;However, it should be noted that the decrease in the original number of particles is to reduce its structural viscosity, but the increase in the specific surface will reduce the number of free resins. It is not good to say whether there is a balance point, but generally the finer the powder coating is, the better.
2. Prevent floating color and blooming.
3. Improve the tinting force Note that the higher the tinting force is, the better it is in the automatic color mixing system.
4. Reduce viscosity and increase pigment loading.
5. The way to reduce flocculation is like this, but the finer the particle surface energy is, the higher the dispersant with higher adsorption strength is needed, but the dispersant with too high adsorption strength may cause adverse effects on the performance of the coating film.
6. The reason for increasing storage stability is similar to the above. Once the stability strength of dispersant is not enough, the storage stability will become worse (from your picture, of course).
7. Increase the color development, color saturation, transparency (organic pigment) or hiding power (inorganic pigment).
TEGO Dispers wetting and dispersing agent helps to wet and stabilize pigments, prevent floating, blooming and sedimentation of pigments, maintain stable pigment hiding power and color strength during storage, and ensure maximum color yield and minimum grinding steps.Because these additives can reduce viscosity and increase to the highest pigment concentration when dispersing, the produced coatings and pigment concentrates are more cost-effective.TEGODispers 757 W is recommended for the production of water-based pigment concentrates.It is also the preferred product for corrosion-resistant water-based coatings.Like TEGODispers 750W and TEGODispers 755 W, it can meet the highest optical and rheological performance requirements.For general purpose color pastes that are suitable for both solvent based and water-based formulations, TEGODispers 65x series is the current market standard product without ethoxyalkylphenol.TEGODispers 656, 670 and 685 are particularly suitable for modern solvent based formulations.In UV system, TEGODispers 685 is applicable to all pigments, and TEGODispers 688 is applicable to matting powder.All TEGODispers products do not contain ethoxylated alkyl phenols.
Selection criteria
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An excellent dispersant shall meet the following requirements:
1. Good dispersion performance to prevent mutual aggregation of filler particles;
2. Appropriate compatibility with resin and filler;Good thermal stability;
3. Good fluidity during molding;No color drift;
4. Do not affect the performance of products;Non toxic and inexpensive.
The dosage of dispersant is generallyMasterbatch5% by mass.[2]
type
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Fatty acids, aliphatic amides and esters
StearamideAndHigher alcoholsCombined use can improve the lubricity and thermal stability. The dosage (mass fraction, the same below) is 0.3% - 0.8%polyolefinSmoothing agent;Vinyl Bisstearamide, also known asEthylenebisstearamide(EBS), a high melting pointlubricant, the dosage is 0.5%~2%;Monoglyceride stearate（GMS），Tristearin（HTG）；OleylDosage 0.2%~0.5%;Hydrocarbonsparaffin waxSolid, melting point 57~70 ℃, insoluble in water, soluble in organic solvents,resinThe dispersity, compatibility and thermal stability of are poor, and the dosage is generally below 0.5%.[3]
Liquid paraffin: Freezing point (- 15 ℃)~(- 35 ℃). During extrusion and injection molding, the compatibility with resin is poor, and the addition amount is generally 0.3% - 0.5%. If too much, the processing performance will deteriorate.
Microcrystalline paraffin: obtained from petroleum refining processrelative molecular massLarge, with many isomers, melting point of 65~90 ℃, good lubricity and thermal stability, but poor dispersibility, generally 0.1%~0.2%, preferably mixed with butyl stearateHigher fatty acidsUsed simultaneously.
Metal soaps
Metal salts of higher fatty acids, called metal soaps, such asBarium stearate(BaSt) is applicable to a variety of plastics, the dosage is about 0.5%;Zinc stearate(ZnSt) is suitable for polyolefin, ABS, etc., with the dosage of 0.3%;Calcium stearate (CaSt) is suitable forGeneral purpose plastics, for external lubrication, dosage 0.2%~1.5%;otherStearic acid soapasCadmium stearate（CdSt）、Magnesium stearate（MgSt）、Copper stearate（CuSt）。
Low molecular wax
Low molecular waxIs based on variouspolyethylene（Homopolymerorcopolymer）、polypropylene、polystyreneOr other polymer modified materials as raw materials, which are cracked and oxidized to form a series of oligomers with different properties.Its main products include: homopolymer, oxidized homopolymer, ethylene acrylic acid copolymer, ethylenevinyl acetate Copolymers and low molecular ionomers.Among themPolyethylene waxMost common.[4-5]
Common polyethylene waxAverage relative molecular weight1500~4000, and its softening point is 102 ℃;The average molecular weight of polyethylene wax of other specifications is 10000~20000, and its softening point is 106 ℃;Oxidized polyethylene waxThere is a certain amount of ester or soap group on the long chain molecule of PVC, PE, PP and ABS, so the internal and external lubrication effect is relatively balanced, the effect is good, and the transparency is also good.Since there are many kinds of dispersants and practical application environments, it is important to select appropriate dispersants.
HPMA is a low molecular weight polyelectrolyte, with a general relative molecular weight of 400~800, non-toxic, and easily soluble in water,chemical stabilityHigh thermal stability, decomposition temperature above 330 ℃.It has obvious solution limit effect at high temperature (<350 ℃) and high pH.HPMA is suitable for alkaline water or mixed with other drugs.HPMA below 300 ℃carbonateIt still has good scale inhibition and dispersion effect, and the scale inhibition time can reach 100h.Because HPMA has excellent scale inhibition performance and high temperature resistance, it can neutralize low-pressure boiler, steam locomotiveCrude oil dehydration, water and oil pipelines and industrial circulating cooling water are widely used.In addition, HPMA has a certain corrosion inhibition effect, which is better when combined with zinc salt.
HPMA is usually compounded with organic phosphonate at 1-15ppm for circulating cooling waterOilfield water injectionThe crude oil dehydration treatment and the furnace treatment of the low-pressure boiler can effectively inhibit the formation of scale and peel off the old scale, and the scale inhibition rate can reach 98%.When HPMA is mixed with zinc salt, it can effectively prevent the corrosion of carbon steel.
4. Safety and protection
HPMA is acidic. Avoid contact with skin, eyes, etc. After contact, wash with plenty of water.
mechanism
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1. It is adsorbed on the surface of solid particles to reduce the interfacial tension between liquid-liquid or solid-liquid.The surface of agglomerated solid particles is easy to be wetted.
2. Polymer dispersant forms an adsorption layer on the surface of solid particles, which increases the charge on the surface of solid particles and improves the reaction force between particles that form three-dimensional obstruction.
3. Make the surface of solid particles form a double molecular layer structure. The polar end of the outer layer dispersant has strong affinity with water, which increases the degree of water wetting of solid particles. Solid particles are far away from each other due to electrostatic repulsion.
4. Make the system even, increase the suspension performance, do not precipitate, and make the physical and chemical properties of the whole system the same.
As described above, solid particles in liquid can be stably dispersed by using dispersant.[1]
Fundamentals
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Select dispersant
As its name implies, dispersant is to reasonably disperse various powders in solvent, and make various solids stably suspended in solvent (or dispersion) through certain charge repulsion principle or polymer steric effect.[1]
staycoatingDuring production,PigmentDispersion is a very important production link, which is directly related to the storage, construction, appearance andfilmTherefore, reasonable selection of dispersant is a very important production link.But the dispersion of paint paste is not only related to dispersantPaint formulaThe formulation of and the choice of raw materials are related.
Double electric layer principle
The dispersants used in water-based coatings must be water-soluble, and they are selectively adsorbed on the interface between the powder and water.Anionic type is commonly used. They are ionized in water to form anions and have certain surface activitySurface adsorption。After the dispersant is adsorbed on the surface of powder particles, a double electric layer is formed, and anions are closely adsorbed on the particle surface, which is called surface ions.The ions with opposite charges in the medium are called counter ions.They are passed by surface ionsElectrostatic adsorptionSome of the counter ions are tightly bound to particles and surface ions, which are called bound counter ions.They become a moving whole in the medium, withnegative chargeThe other part of counter ions surround the surroundings, which are called free counter ions and form a diffusion layer.In this way, a double electric layer is formed between the surface ions and counter ions.[6]
Electrokinetic potential: the negative electricity carried by the particles and the positive electricity carried by the diffusion layer form a double electric layer, which is called electrokinetic potential.Thermodynamic potential: Double electric layer formed between all anions and cations, corresponding potential
riseDispersal actionIt is the electrokinetic potential rather than the thermodynamic potential. The charge of the electrokinetic potential is unbalanced, and there is a charge repulsion phenomenon, while the thermodynamic potential belongs to the charge balance phenomenon.If the concentration of counter ions in the medium increases, the free counter ions in the diffusion layer will be forced into the bound counter ion layer due to electrostatic repulsion, so that the electric double layer is compressed and the electrokinetic potential drops. When all free counter ions become bound counter ions, the electrokinetic potential is zero, which is called the isoelectric point.Without charge repulsion, the system has no stability and flocculation occurs.
Steric effect
The formation of a stable dispersion system, in addition to the use of electrostatic repulsion, that is, the negative charges adsorbed on the particle surface repel each other to prevent the adsorption/aggregation between particles and finally form large particles and delamination/sedimentation, also usesSteric effectThe theory that when the particles that have absorbed negative charges are close to each other, they will slide and stagger with each other. Such surfactants that play a steric role are generally non-ionic surfactants.By flexibly applying the theory of electrostatic repulsion and steric hindrance, a highly stable dispersion system can be formed.
The polymer adsorption layer has a certain thickness, which can effectively block the mutual adsorption of particles, mainly relying on the polymerSolvationWhen the adsorption layer on the surface of the powder reaches 8~9nm, the repulsive force between them can protect the particles from flocculation.thereforePolymer dispersantIt is better than ordinary surfactants.[7]
Determination method
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Daniel flow point measurement
Use a dropper to gradually drop the aqueous solvent of dispersant into a certain amount of pigment/pigment mixture, and carefully grind it evenly with a small scraper until the ground pigment slurry can flow down from the scraper as the end point, and calculate the ratio of pigment fraction to pigment.
Dosing curve method
To a thick water slurry made of a certain amount of pigment/pigment mixture, gradually drop a concentrated pigment fraction solution under stirring, and measure the viscosity every time it is added.As the amount/viscosity curve of pigment dispersant, the lowest point is the optimal amount of dispersant.
Concentration/flocculation method
Use a certain amount of pigment/pigment mixture to make thick water slurry, add pigment dispersant solution one by one, and mix evenly until it can flow completely from the scraper.Drop 1ml of ionic thickener on the glass plate lined with black background, and then add a drop of dispersed pigment slurry.Then mix gently.If flocculation occurs, add pigment dispersant in the pigment slurry until no flocculation occurs. Calculate the amount of pigment dispersant at this point according to the pigment, which is called C-A value (concentration flocculation value).
notes: Daniel flow point is suitable for solvent based paint, not suitable for emulsion paint.Dosing curve method is only suitable for the slurry itself, and there is often a shortage of dispersant in latex paint, so it must be added more (up to double) in practical application.C-A value is more comprehensive.The optimal dispersant concentration (ODC) is usually expressed by the amount of dispersant required per unit mass of pigment.The larger the surface area of the pigment per unit volume, the higher the ODC.
Impact on paint
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gloss
This is an indicator to measure the characteristics of the film. The higher the gloss, the stronger the reflection.
For the gloss of high-quality coatings, the particles shall not be larger than 5 microns, and the maximum is 3 microns.Ink cannot exceed 1 micron.Large particles in the coating can not be effectively dispersed, or flocculate, or stimulate crystallization during preparation.The polymer dispersant can also reduce the large particles formed due to flocculation and improve the gloss.
transparent
This is a characteristic of the coating film. The higher the transparency, the easier it is to see the bottom layer.The higher the hiding power, the stronger the hiding power for the bottom layer.
The amount of light reflected and passed through the surface determines the hiding power or transparency of the paint.The type and dispersion of pigments have influence on this.Due to the influence of refractive index and particle size, covering pigments have greater influence on reflected light.
Polymer dispersants improve transparency by influencing the particle size distribution of pigments (more uniform and narrower).For titanium dioxide, high refractive index and large particles can effectively reflect and refract light of various wavelengths.The addition of polymer dispersant can increase the surface area (reduce aggregate and particle size), and further improve the hiding power.For transparent pigments, polymer dispersants improve particle size distribution to allow more light transmission (increase transparency).
compatible
Compatibility is important because good compatibility enables coating manufacturers to produce dispersion systems for many different types of resin products.
Polymer dispersants can increase pigment concentration, not only increase production, but also reduce potential medium incompatibility problems from grinding color paste to final product.Therefore, polymer dispersants expand the application range of basic coatings, especially when high compatibility resins are used.This is very important for the production of mixed colored coatings.
Flow/Leveling
Leveling is the ability of coating to diffuse on a specific surface.Coating surface defects are usually caused by surface tension and occur relatively quickly.Brush marks of decorative coatings are usually caused by insufficient leveling.
The ideal leveling behavior can be explained by Newtonian mechanics.But when pigments are introduced into the system, changes will occur.This is because particles are subject to chemical bond and physical interaction, and are very prone to thixotropy and pseudoplasticity.
Because the pigment particles are more stable under the action of polymer dispersant, and the leveling property is increased, the Newtonian fluid characteristics can be improved.The advection is good.
yield
Output refers to the amount of paint and ink produced by a process.The dispersant can increase the pigment concentration and increase the paint output.Properly adding polymer dispersant can reduce viscosity, increase pigment content of grinding color paste, and thus increase output.
In a fixed time, more pigments can be dispersed, so more products can be produced with the same weight of ground color paste.Obviously accelerating the dispersion speed can also increase the output.As the output increases, the wear of machines will be reduced and the energy consumption will be reduced, especially the labor cost and fixed cost per kilogram of final products.
Tinting intensity
The color intensity of the paint indicates the intensity of the color hue on the application surface.The paint will look brighter and more attractive to customers if the coloring strength is increased.
The best grinding conditions can be created by balancing various opposing factors.Reducing the average particle size of pigments can improve the tinting strength.Increasing the pigment content in the grinding paste will increase the mutual collision of particles and improve the crushing rate of pigments, but also increase the viscosity, reduce the kinetic energy of grinding, and reduce the crushing capacity of abrasive balls or beads on pigments.
The use of polymer dispersants can change this change.The use of dispersant can grind higher pigment concentration, make particles break more quickly, and prevent viscosity increase during grinding.Finally, the dispersant can increase the collision stability of the finer particles and prevent flocculation, so as to give full play to its inherent coloring strength.
