| Thickening Mechanisms - Why do we need thickening / rheology modifiers?
• the coating to achieve desired viscosity / rheology to meet - the material (spatula, roller, spray), storage and suspension characteristics.
• improved quality of the paper - the better smoothness, gloss, paint coating covering the lower permeability and other properties.
• improve coating performance - to improve water retention, paint evaporation rate, fixed speed paint, coating thickness.
• Reduce adhesive migration, improve the printing uniformity.
• economy - lower costs (liquid, replace expensive raw materials).
• When using synthetic thickeners, above properties are improved significantly. If I am in a coated board machine test showed that when the thickening aquasorb by the CMC into synthetic thickener, coating coverage performance significantly improved smoothness increased by 30 to 50%, significantly improved print uniformity. Costs are significantly reduced.
Thickening Mechanism - synthetic thickeners classification Thickener | Action
| Natural
| Synthetic
| | (HEC)、(CMC)、(alginate)。 | (hydrophobically-modified alkali-swellable emulsion (HASEs))、(acrylate ASEs)。 | Thickening | | (urea)、 (dicyandiamide)、 (polyglycol) | Thick drop |
Thickening Mechanism - the history of synthetic thickeners
• natural thickener - 1800s
• polymer chemistry began to develop ~ 1927
• synthetic rubber (gums) - 1940's
• TS Emulsion - 1970
• ASE / HASE alkali soluble thickener - 1970
Thickening Mechanism
• volume expansion
• molecular chain wrapped
• associative mechanism
• hydrogen adsorption
Thickening Mechanism
Volume expansion
After synthesis of the thickener and an alkali, the repulsion of ions, resulting in expansion and stretching of the polymer structure.
Run-molecular weight polymer was hydrated sheets, occupying the space of the solution, resulting in increased viscosity of the solution.
Molecular chain wrapped
With increasing polymer concentration, physical entanglement between the polymer chains occurs. This leads to a high thickening efficiency.
Or in a homogeneous organic solution, hydrogen bonding occurs between the polymer chains also improved thickening efficiency.
Association
Hydrophobic groups on the polymer can be associated with each other, resulting in increase in viscosity.
These hydrophobic groups may be the same and the coating latex particles, pigment particles and a surfactant to produce association, thereby increasing the viscosity.
Hydrogen bonding
Hydrogen bonding occurs between the solution and the thickening agent can also occur between the thickener and additives.
Temperature, reduced hydrogen bonding, resulting in low solution viscosity.
The thickener molecule capable of binding to the pigment surface is also adsorbed by hydrogen bonding.
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