Optical brightening agent

The optical brighteners counteract the yellowness of the fabric by increasing the reflection of blue light rays. They convert invisible short-wave ultraviolet rays of sunlight into visible blue light and has a degree of whiteness which is comparatively more intense. Fig. 10-1 illustrates a comparison of the possible spectral 

OBA for cellulosics and nylon. Recommended for continuous application. Offers good leveling. Neutral/blue cast. 

OBA for polyester and other synthetic fibers. Stable in chlorite or Peroxide bleach systems. Strong bluish cast. 

Nonionic OBA for polyester, polyester/cotton and acetate. Recommended for continuous application. Strong blue cast. 

Polyester OBA, good sublimation properties. May be applied by thermosol or exhaust process. Brilliant white with neutral/ green cast. 

---

OB, OB A Optical brightener, optical brightening agent PVI Pre-vulcanisation inhibitor... 

Detergents. Ultramarine pigments are widely used to enhance the effects of optical brightening agents in improving whiteness of laundered fabrics [3.176], They do not stain or build up with repeated use. 

Colourless molecules with blue fluorescence are optical brightening agents that are used as blue whiteners in paper production and washing powders (see Chapter 7). The two main classes are heterocylics such as pyrazolines and particularly stilbenes (1). 

Acrylics. Manufacturers of acrylic fibers have not generally published or confirmed the chemical composition of their fibers (116). Acrylic fiber will generally contain 85-94% acrylonitrile the balance is made up of comonomers having a specific function, such as to provide dye affinity for specific dye classes or to regulate diffusion of dye into the fiber. A list of typical comonomers has been published (116). Acrylic fibers may also contain heat (117) and light stabilizers (116). They may also contain a delustrant such as titanium dioxide. Some products contain optical brightening agents. These materials probably never exceed 4r-5% of the total composition. The cross-sectional shapes of the fibers vary (116). 

STANSOFT 300 is compatible with all types of optical brightening agents and with dyestuffs of all classes... 

Triazoles and their benzo derivatives have attracted considerable attention because of their theoretical interest, and synthetic value, as well as for their numerous applications in industry and agriculture due to their extensive biological activities and their successful application as fluorescent whiteners, light stabilizers and optical brightening agents. 

The production and consumption of optical brighteners are constantly increasing and the annual increase is amounted to about 10-12%. In addition to textile, detergent and paper industries (Table 10.1), optical brightening agents are also used... 

The saturation limit of an optical brightening agent, however, is also dependent on the method of application to the substrate. Usually exhaust application process gives higher whiteness value then it does when applied by padding technique for a given amount of whitener. 

Generally optical brightening agents have high rate of exhaustion on the substrate and therefore great care is to be taken to avoid unlevel application. Slow exhaustion rate and increased migration time is necessary to produce level whiteness on the fabric. 

The optimum temperatures of optical brightening agents on cellulosic fibres are usually between 40 and 60 C and further rise in temperature tend to lower the exhaustion. However, for synthetic fibres higher temperature is needed for good penetration of the brighteners. 

The chemical stability, solubility and affinity of optical brightening agents depend on effective pH value in solution. For example, for wool and polyamide fibres, optimum pH is on the acidic side for better exhaustion. 

Optical brightening agents are applied to textiles at the time of scouring, bleaching or finishing. When chlorite bleaches are used anti-chlorinating measures must... 

Polyester fibres have no affinity for the water soluble optical brightening agents and thus water insoluble compounds are applied to polyester from dispersion in the same manner as disperse dyes by the formation of a solid solution in the fibre. These brightener particles penetrate into the fibre in a state of molecular dispersion and they are held in the fibre by Van der Waal s forces. A part of the finely dis-... 

In the thermofixation process the fabric is padded with 5-25 g/I dilute suspension of optical brightening agent at room temperature with a liquor pick-up of approximately 50%, dried at about 120°C in an open stenter and then heated for 30-60 sec at 190-200°C. Finally, the goods are washed and dried. This process makes possible higher thoroughput of material with superior dimensional stability. 

---