Usage methods of fluorescent brighteners for polyester fibers
Release Time:
2010-12-08 13:37
Source:
China Laundry and Dyeing News
Polyester is the trade name for polyester fiber. Polyester fiber is a synthetic fiber made by melt spinning and processing polyester resin, which is produced by ester exchange and polycondensation reactions of no less than 85% by weight of a diol and dimethyl terephthalate. The structure of polyester fiber lacks hydrophilic groups, has a high degree of crystallinity, and a well-ordered structure. Therefore, its dyeing performance is poor, and hydrophilic fluorescent brighteners (hereinafter referred to as FB) cannot be used to whiten it. The methods for whitening polyester can be divided into two categories:
1) Pre-spinning whitening, also called dope whitening. This involves adding certain types of FB to the diol to participate in ester exchange, or adding it after ester exchange to participate in polycondensation, or mixing it before the resin chips are melted during the drying stage.
2) Dyeing and finishing whitening. For already spun polyester fibers and fabrics, certain types of FB are diffused into the fiber surface and evenly distributed. According to the processing technology, it can be further subdivided into high-temperature and high-pressure immersion dyeing, hot-melt padding dyeing, and adsorption fixation aided by certain auxiliaries.
Different whitening methods require different types of FB to achieve ideal whitening effects, although some FB types can be used for different whitening processes. FBs used for polyester should meet the following requirements: First, they should have good chemical and thermal stability, very high sublimation fastness, light fastness, and chlorine bleach fastness. Second, the FB molecular structure should have high fluorescence intensity, and the absorption and emission fluorescence wavelengths of the molecule under ultraviolet light should be within suitable ranges to produce pleasing colors. Generally, the maximum absorption wavelength should be in the 300-400nm range, and the maximum emission wavelength ideally between 420-450nm, because 400-430nm corresponds to violet light, 430-440nm to blue light, 440-470nm to blue-green light, and violet-blue light appears more pleasing to the human eye, making it optimal. Third, FBs used for dope whitening also require good compatibility with polyester resin, good dispersibility, migration resistance, and high purity. FBs used for dyeing and finishing whitening should have good affinity for polyester fibers, high dyeing efficiency, and dyeing fastness.
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