HOW TO CHOOSE UV ABSORBER?

HOW TO CHOOSE UV ABSORBER?

In this article, we talk about the key points of polymer anti-UV selection, hoping to inspire you. Polymer photoaging is actually similar to the mechanism of thermal aging, both external energy attacks the molecular chain, and the free radicals produced trigger a chain degradation reaction, resulting in the rupture of the molecular chain, and the external manifestations are problems such as polymer color change, physical property decline, and loss of transparency.

Polymer anti-UV generally starts from two aspects: one is to wear sunscreen clothing for the polymer, add substances with a specific chemical structure (UVA), and convert ultraviolet energy into heat radiation through intramolecular vibration to release, thereby protecting the polymer. The second is to defire the polymer, some groups of the polymer have been excited by UV, resulting in free radicals (fire), through the light stabilizer (HALS) to capture free radicals, to avoid the chain degradation reaction caused by free radicals, thereby avoiding more serious damage to the polymer.

Overall, anti-UV aging additives need to consider 7 factors, as detailed below:

1) Performance – Durability:

After UVA is exposed to light for a long time, its chemical structure will change permanently, losing the ability to absorb ultraviolet rays, which is called the photolife of UVA. Among them, triazine UVA (such as YIHOO UV1064/1577, etc.) is the type with the longest light life, so it is suitable for some applications that require long weather resistance. Of course, the use of common benzotriazoles (such as YIHOO UV234/531, etc.) or benzophenone for general use is sufficient.

2) Performance – color and physical properties are maintained

If you focus on the gloss protection of the product, the effect of HALES is more obvious (HALES does not need to consider the thickness for the effect), if the focus is on the maintenance of physical strength, the UVA effect is better (under the premise that the product has a certain thickness), it is generally shared by the two, and the ratio of the two can be adjusted as needed, and half the work is doubled.

3) Appearance – initial color

UVA absorbs ultraviolet light, but also absorbs some short-wavelength blue light, resulting in the initial color of the product yellow. For applications with high initial color requirements, oxalamide-based UV absorbers are a better choice.

4) Product thickness:

UVA requires a certain thickness to work (Bill Ranbier’s law), and HALES does not need to consider this problem, so 70% of HALES is used in thin products such as film, silk, and paint. We also need to consider this issue when designing plastic UV-resistant formulations. At the same time, thickness will also affect the molecular weight selection of HALS, and generally choose small molecular weight HALS for thin products.

5) Compatibility with resin:

The additives are not compatible with the resin, and precipitation will lead to poor appearance such as surface frosting, and loss of protective properties.

For TPU, which is particularly incompatible with additives, YIHOO POLYMER has developed a reactive ultraviolet absorber, a diol with an ultraviolet absorbing group, which is added during polyurethane synthesis and becomes part of the polymer chain, fundamentally solving the problem of precipitation.

6) Compatibility with the overall formula:

When it comes to compatibility, the first thing is acidity and alkalinity. As a hindered amine, HALES will show different acidity and alkalinity, and the common HALS acidity and alkalinity are as follows (PKb is small and alkaline):

Some resins or additives are acidic, so avoid adding alkaline additives, typical such as PVC (release of acidic HCl during thermal processing), polycarbonate (alkaline additives easily lead to PC degradation), anti-heat aging additives thioesters are also acidic (conflict with alkaline HALS).

7) Special scene requirements: transparency, solvent resistance extraction:

Finally, we talk about a few special UV resistant problems: the first is high transparency UV shielding, some functional drinks contain carotene, caramel color, etc., ultraviolet radiation will cause product deterioration or color change, affecting brand image, we also have products to solve such problems, maintain transparency while shielding ultraviolet rays, sunglasses, electronic products and other uses also have applications.

The second is solvent-resistant extraction, water-resistant extraction is very common for HALES (such as car paint), so there are already many products on the market to correspond. However, some coatings or plastic products that require weathering resistance will be in contact with oily solvents for a long time, and it is not simple to resist solvent extraction, and YIHOO LS119 is a reactive (with -OH group) low alkaline HALS, which can resist the washing of solvents without being extracted, achieving long-lasting weather resistance. The above is our 7 points for the selection of UV-resistant additives, the practical application will be more complicated, sometimes you need to make trade-offs, sometimes you need to take into account, and sometimes you need to know that “there is such a product”, I hope to discuss with you, solve problems together, and grow together.

Qingdao Yihoo Polymer Technology Co., Ltd. is committed to supplying high-quality ultraviolet absorbers, antioxidants, flame retardants and other products, welcome to contact at any time：yihoo@yihoopolymer.com