The properties that fluorescent whitening agents for plastics should have
Fluorescent whitening agent is a kind of fluorescent dye, and some data call it white dye or colorless dye. Some data call it a plastic coloring special effect pigment based on its main use in plastics to change the appearance characteristics of plastics. There is a type of commercially available fluorescent whitening agent that is insoluble in water but soluble in organic solvents. This type of fluorescent whitening agent is suitable for plastics. However, if it is to be used for plastic whitening, the selected fluorescent whitening agent should also have the following properties according to the performance, processing characteristics and special requirements of use of the plastic:
(1) The whitening effect is better.
High whiteness is the main manifestation of the whitening effect of fluorescent whitening agents. The advantages of high whiteness are not only reflected in the appearance of plastics, but also have many advantages. For example, high whiteness can reduce the amount of use, thereby preventing plastic Changes in strength can also reduce costs.
(2) Excellent high temperature stability.
Because the melting temperature of plastic products generally needs to be between 150 and 280 degrees Celsius, it is required that the fluorescent whitening agent used will not decompose, change color and lose the whitening effect within this temperature range.
(3) It has high sublimation fastness and weather fastness such as sunlight.
Because white plastics have been widely used in the building materials and advertising industries in recent years, this requires the fluorescent whitening agents used to have excellent resistance to heat sublimation and sunlight exposure and other climatic conditions. The weather fastness of optical brighteners is affected by the structure of the optical brighteners and is related to the amount of optical brighteners added.
(4) It has good compatibility with plastics and good dispersion in them.
This is a necessary condition to ensure that the plastic is evenly whitened. The molecular dispersion or complete solubility of optical brighteners is extremely important for achieving high-efficiency optical whitening. If you use a fluorescent whitening agent to dye white products, you first put the fluorescent whitening agent into a resin carrier to make a concentrate. This concentrate is usually called a color masterbatch or masterbatch, and then use the masterbatch to color a large amount of polymers. And the optical effect is much better than adding fluorescent whitening agent directly into the resin. Another example is that after water-insoluble fluorescent whitening agents with very low concentrations are dispersed in water, they will show good optical effects in nylon and polyester fibers; and this fluorescent whitening agent is added directly to the melted polymer ready for spinning. In vivo, it does not show any optical effects. This is because absorption by water dispersion dissolves the fluorescent whitening agent in the form of molecules in the polymer matrix, and the fluorescent whitening agent mixed into the polymer melt can only be dispersed in the form of aggregates at best. Melt inside the body.
For colorants such as fluorescent whitening agents that have poor dispersion in plastics, in order to better disperse them, they generally need to be processed twice, that is, a certain amount of processing agent or dispersant is added to the colorant to make it a Colorant with good dispersing properties. In addition to improving the dispersibility of the fluorescent whitening agent, the selection of processing or dispersing aids must also be careful not to cause a decrease in the physical properties of the plastic.
(5) It has good solvent resistance, migration resistance and chemical stability, and no leakage or extraction.
It will not migrate due to dissolution when in contact with solvents or products containing plasticizers. It has good acid and alkali resistance and does not cause harmful chemical reactions with other additives in plastics.
(6) It has no impact on the processing (such as fluidity, lubrication, printing, coating) and performance (such as electrical properties, physical and mechanical properties, aging resistance, etc.) of plastics.
(7) It should have chemical resistance, electrical insulation, etc.
(8) It should be non-toxic and tasteless.
This requirement is particularly important for fluorescent whitening agents used in the food and toy industries. It is related to people's health and life safety. In some countries, there are strict regulations on optical brighteners used in the food and toy industries.
The above points are relatively comprehensive requirements for fluorescent whitening agents for plastics. Generally, there are very few varieties that meet all these requirements. Therefore, when used, the selection should be based on the purpose of use, environmental factors and other specific circumstances.
