Basic knowledge of auxiliaries thickener

thickener
The raw material of latex paint is affected by the performance of the product, and only the thickener has a wider impact on the manufacturing, storage and transportation of latex paint, construction, and coating performance.
1. Rheological properties of latex paint
The viscosity of latex paint is dependent on shear force and time, and with the increase of shear force or the extension of shear time, the viscosity of latex paint will change, which is the rheological property of latex paint. The viscosity of latex paint has an effect on the settling property, brushing property, film fullness property, leveling property and the fluidity of the paint on vertical surfaces. The different rheological physical property curves of paint from storage to application are shown in Figure 3. Latex paint must undergo such rheological process during storage and construction. The viscosity control of this process depends on the combination of different types of thickeners to control.
To ensure the storage and construction of latex paint, it is necessary to control the viscosity at three different shear rates: low shear viscosity is mostly controlled by polymer thickener (cellulose, alkali solution/alkali swelling type) or inorganic thickener (bentonite), etc. The test instrument – rotary viscometer test, the viscosity range is 105~106mPa.s; Medium shear viscosity Stormer viscosity, which can be controlled by thickening rheo-spreading modifier, the viscosity range is 75~100KU; High shear viscosity: ICI viscosity, which is determined by the amount of emulsion, pigment filler and rheological modifier, ranges from 2 to 3P.
The yield value of the coatings thickened by different types of thickeners is not the same, the yield value of the coatings thickened by thickeners such as high score is large, the fluidity is poor, and the anti-settlement is good, while the yield value of the coatings thickened by the association type thickener is small and the fluidity is good. Yield value is also one of the important parameters of latex paint system. Paint static state, yield value > 10dyn/cm2, ensure the film leveling; After the coating construction, the yield value is required to rise quickly, and the yield value is > 2.5dyn/cm2, to ensure that the film leveling is good; After the paint construction, the yield value is required to rise quickly, the yield value is > 5dyn/cm2, and there is no flow hanging phenomenon after construction.
2, thickener types
Thickener can be classified according to different forms, such as the source of thickener, composition, ionic property, solubility and thickening mechanism; The details are as follows:
organic-inorganic
Natural – fully synthetic
Nonionic – anion (alkali soluble)
Dissolve – dissolve
The types of thickeners commonly used for concordant – non-concordant latex paints are as follows:
Inorganic: Bentonite.
Organic: cellulose (non-associated HEC, associated HMEC), alkali-soluble/swollen (non-associated ASE, associated HASE), EO polyamines, etc. Among them, the molecular weight of cellulose and alkali-soluble/alkali-swelling thickener is higher than that of EO polyurethane thickener.
3, thickener thickening mechanism and thickening characteristics
Polymer thickeners can be divided into two types: non-ionic and anionic. These polymer thickeners have high molecular weight and can improve the viscosity of coatings quickly in low shear and medium shear, while the viscosity of ICI increases little. After thickening with polymer thickener, the uniformity of the paint sample system is not good, the yield value of the paint is large, the fluidity is poor, and the gloss of the film is low. The non-ionic thickener has little sensitivity to the formula, and the alkali-soluble thickener is sensitive to the formula pH. The thickening mechanism is shown in Figure 5.
The thickening mechanism and thickening characteristics of EO-polyurethane thickener: This kind of thickener molecule has hydrophobic groups and hydrophilic chains, so it has surface activity, which can form micelles like surfactants in the system, and its hydrophobic groups can be associated with emulsion particles and makeup filler particles to form a thickening network as shown in Figure 6. This kind of thickener is sensitive to the composition of the formula, and the type and amount of emulsion, the type and amount of cosolvent, the type and amount of surfactant, and the type of dispersant will affect the thickening efficiency of EO-polyurethane thickener.
4, thickener evaluation
Thickening agent evaluation items are as follows: thickening efficiency, leveling TI value, temperature sensitivity (2℃/40℃), toning property. The role of thickener is used to thicken, provide latex paint storage, construction, leveling or qualitative, thickening effect and leveling is the main evaluation item.
5. Paint disease caused by improper selection of thickener
When the thickening agent selection is lost, there will be corresponding problems in the construction and storage and transportation of latex paint: there will be settlement delamination in the storage and transportation of latex paint, and there will be problems such as poor leveling in the construction, or poor qualitative ability, and difficult modeling. These problems can be solved by the choice of thickening agent.