At present, most of the thickeners used in printing and dyeing are polymers with only a slight degree of cross-linking, and are often water-insoluble. Therefore, they can only expand through water absorption or moisture absorption, resulting in thickening effect. In addition, in addition to having good thickening performance, the thickener for printing also requires that the particle size of its water absorbent polymer particles is very small, which generally belongs to the micron level. In fact, the smaller the particle size, the better. Therefore, although there are many methods for preparing water absorbent polymers, these methods can also be used to prepare thickeners for printing, it is the best that the polymer latex particles obtained directly through polymerization can meet the particle size requirements. At present, solution polymerization is generally used to synthesize products at home and abroad.
Solution polymerization is a kind of reaction in which monomers and initiators (catalysts) are dissolved in suitable solvents for polymerization. If the generated polymer can be dissolved by the solvent used, the polymerization reaction is called homogeneous solution polymerization. If the generated polymer cannot be dissolved by the solvent used and precipitates or precipitates, the polymerization reaction is called heterogeneous solution polymerization or precipitation polymerization; According to the classification of solvents used, those with water as the solvent for polymerization are called aqueous solution polymerization, and those with oil as the solvent are called oil solution polymerization.
The main advantage of solution polymerization is that its polymerization system is homogeneous, the heat transfer medium is solvent, and is conducive to heat transfer, and is easy to control temperature, and can reduce the gel effect caused by local overheating. The molecular weight distribution of the polymer is also easy to adjust and the product transportation is convenient.
The main disadvantages of solution polymerization: the degree of polymerization of the obtained polymerization products is generally not high because the heat transfer medium solvent will produce chain transfer; The initiator selected for solution polymerization is usually thermal decomposition type. When this initiator is used, it must reach a specific temperature to decompose and produce enough free radicals to initiate the polymerization of monomers, and whether the polymerization temperature is appropriate needs a lot of repeated tests to determine; In addition, the solvent used in the reaction must be recycled, which is usually expensive, and the residual solvent in the polymer is difficult to remove. These do not meet the requirements of environmental protection, and there are some safety problems.
In the 1970s, Shenyang Chemical Research Institute first synthesized thickener by solution polymerization, but the thickening effect of the product is not very good; After the 1990s, Ningbo Chemical Research and Design Institute also used this method to synthesize NBH-1 dispersed thickener. The thickening effect of this product is similar to that of some well-known products produced in western countries at that time, but it has not yet reached the optimal level.
