In recent years, with the rapid development of the plastic industry, the plastic coloring technology has also achieved unprecedented development. Among many colored plastic products, white plastic products still occupy the mainstream position. Fluorescent whitening agents are often indispensable in the production of white plastic products.
However, some manufacturers will encounter such problems as adding fluorescent whitening agents, the whiteness and brightness effects of other people's plastic products are good, while their own products cannot achieve the desired results. I sum up for the following reasons:
I. did not choose the appropriate type of fluorescent whitening agent
At present, there are about six or seven kinds of plastic fluorescent whitening agents commonly used in the market. Different fluorescent whitening agents have different properties such as compatibility, melting point and light resistance.
Plastic manufacturers should not choose the corresponding type of whitening agent according to their own products, fluorescent whitening agent is difficult to give full play to its best effect, and even there is a risk of whitening agent precipitation. In addition, it is also necessary to ensure that the quality of fluorescent whitening agents is excellent.
II. excessive (small) addition of fluorescent whitening agent
Although fluorescent whitening agent can improve the whiteness of plastic products, it is not the better to add more fluorescent whitening agent. The added amount of fluorescent whitening agent has a "yellowing point" (as shown in the figure below).
If the added amount exceeds this threshold, it will not only have no whitening effect, but will even turn yellow. In serious cases, fluorescent whitening agent will be precipitated on the surface. Similarly, if the amount of whitening agent added is too small, the whitening agent cannot exert the maximum effect.
III. Effect of UV Absorber
The principle of fluorescent whitening agent is to absorb ultraviolet light and convert it into blue-violet light. Blue violet light and yellow light of plastic cancel each other out, thus achieving whitening effect. The ultraviolet absorber absorbs ultraviolet light, thus reducing the ultraviolet light absorption of fluorescent whitening agent and whitening effect.
IV. Effect of Pigment on Fluorescent Whitening Agent
As mentioned above, the principle of fluorescent whitening agent is that it can absorb ultraviolet light. For example, titanium dioxide in white pigment can absorb light waves of about 380NM in ultraviolet light (whitening agent absorbs ultraviolet light of 300-400nm). If it is present in plastic products, the whitening effect of fluorescent whitening agent will be reduced.
Most of the reasons for the insufficient whiteness of the added fluorescent whitening agent are the above. The following points are suggested:
1. according to the type of plastic products, choose the right type of whitening agent.
2. ask professionals and find out the best dosage of whitening agent through continuous tests.
3. if light stabilizers need to be added in the production process, it is recommended to choose histamine light stabilizers that do not change color.
4. when titanium dioxide is used in combination with fluorescent whitening agent, anatase titanium dioxide is recommended and the amount of fluorescent whitening agent is appropriately increased.