塑料中常用的添加剂之紫外线吸收剂

UV Absorbents used as additives in plastics

紫外线吸收剂是塑料制品中非常重要的添加剂，是一种起光稳定作用的稳定剂，其主要是借吸收和转化太阳光中具有破坏性的紫外光部分而产生稳定效果。紫外线吸收剂主要应用于塑料制品中，如板材、线缆、管材等厚制品，在很多情况下，塑料薄膜中也会加入紫外线吸收剂，以抑制或延缓紫外光对被防护物品或物质的负面作用。

UV absorber is a very important additive in plastic products. It is a stabilizer for the stabilization of light. It is mainly a stabilizing effect by absorbing and transforming the ultraviolet light part of the sun light. UV absorbers are mainly used in plastic products, such as plates, cables, pipes and other thick products. In many cases, UV absorbers will also be added to plastic film to suppress or delay the negative effects of ultraviolet light on the protected objects or substances.

紫外线及其对塑料等聚合物的破坏作用

Ultraviolet radiation and its destructive effect on polymers such as plastics

我们都知道，从太阳发射出来的辐射线，其电磁波是非常宽的，能够到达地面的主要包括紫外线、可见光和红外线等。辐射线的能量与波长成反比，波长越短，能量越大。其中290nm-400nm波长范围内的紫外线，波长最短，能量也最高，其对塑料等聚合物的破坏性也最大，有机聚合物的键能通常在290~400kJ/mol范围内，故很容易为紫外线所破坏。因此，紫外线是影响塑料光老化的主要因素。但要注意的是不同结构的高分子化合物对紫外线各种不同长短波段的敏感程度是不一样的。

As we all know, the radiation from the sun is very wide, and it can reach the ground mainly including ultraviolet, visible and infrared light. The energy of the radiation line is inversely proportional to the wavelength, and the shorter the wavelength, the greater the energy. In the 290nm-400nm wavelength range, ultraviolet light has the shortest wavelength and the highest energy. It is also the most destructive to the polymers such as plastics. The bond energy of organic polymers is usually within the range of 290~400kJ/mol, so it is easily destroyed by ultraviolet. Therefore, ultraviolet radiation is the main factor affecting the photoaging of plastics. But it should be noted that different structures of polymer compounds are different in sensitivity to ultraviolet light.

塑料等高分子材料之所以具有许多优良性能，归结于其具有足够长的大分子链，但由于紫外线波长短、能量高，在紫外线作用（大多数还有氧的参与）下，高分子材料吸收紫外线后，容易形成电子激发态，这种激发态的分子可以引起一系列的光化学反应，即自由基链式反应，并同时与氧化相伴发生“光氧老化”或“光氧化反应”。高分子大分子链被切断或产生一定的交联，直接影响到了高分子材料的性能，于是就出现了一系列老化现象。如颜色变深、发脆、变硬、表面龟裂以及机械性能与电性能下降等，以致最后丧失其使用价值。

Polymer materials, such as plastics, have many excellent properties, due to their long chain of large molecules, but because of the UV wave length, high energy and ultraviolet radiation (most of the oxygen involved), the absorption of ultraviolet light by polymer materials is easy to form the excited state of the electron, which can be excited by the molecule. In order to cause a series of photochemical reactions, that is, free radical chain reaction, and at the same time with oxidation, "photooxidative aging" or "photooxidation reaction" occurs. Polymer macromolecule chain was cut off or produced a certain cross-linking, which directly affected the properties of polymer materials, so a series of aging phenomena appeared. Such as color darker, crisp, hardened, cracked surface and mechanical properties and electrical properties, and so on, and ultimately lose its use value.

紫外线吸收剂的概念及其作用

The concept and function of ultraviolet absorbents

高分子材料具有不同的分子结构，对紫外光的抵抗能力也自然不同,也就是说不同高分子材料的“光稳定性”不同。对于ABS、SBS等含有双键等不饱和键的高分子材料，其及容易吸收紫外光而发生光氧化反应，因此它们的光稳定性不好。但对于仅含饱和化学键的纯聚合物来说，则不吸收或几乎不吸收紫外线，因此对紫外光是稳定的。

Polymer materials have different molecular structures, and the resistance to ultraviolet light is naturally different, that is to say, the "light stability" of different polymer materials is different. ABS, SBS and other unsaturated bonds with double bonds, such as double bonds, and easy absorption of ultraviolet light and photooxidation reaction, so their light stability is not good. But for pure polymers containing only saturated chemical bonds, they do not absorb or hardly absorb ultraviolet light, so they are stable for UV light.

ABS紫外老化前后对比图

Contrast diagram of ABS before and after ultraviolet aging

但实际情况是，这种具有饱和键的纯聚合物是不存在的，因为在聚合物的工业化生产过程中，如聚合、挤出造粒、注塑、储存等过程中不可避免的引入催化剂残留、微量氢过氧化物等一些杂质，这些杂质对光敏感，在吸收紫外线后，进而会引发材料的光老化反应。

But the actual situation is that this kind of pure polymer with saturated bonds does not exist, because in the process of industrialized production of the polymer, such as polymerization, extrusion granulation, injection molding, storage and so on, some impurities such as catalyst residue and trace hydroperoxide are inevitably introduced. These impurities are sensitive to light and absorb ultraviolet light. The light aging reaction of the material will be initiated after the line.

紫外线吸收剂是目前应用最广的一类光稳定剂。它能强烈地、选择性地吸收高能量的紫外光，并以能量转换形式，将吸收的能量以热能或无害的低能辐射释放出来或耗掉，从而防止塑料中的发色团吸收紫外线能量随之发生激发。

UV absorber is the most widely used light stabilizer. It can absorb high energy ultraviolet light selectively and selectively, and in the form of energy conversion, the absorbed energy is released or consumed with heat or harmless low energy radiation, which prevents the chromophore from absorbing ultraviolet energy in the plastic.

紫外线吸收剂的分类

Classification of ultraviolet absorbents

紫外线吸收剂所包括的化合物类型比较广泛。按结构来划分，主要包括二苯甲酮类、水杨酸酯类、苯并三唑类、取代丙烯腈类、三嗪类等。塑料工业中应用最多的当属二苯甲酮类和苯并三唑类等。

UV absorbers include a wide range of compounds. According to the structure, it includes two benzophenone, salicylic acid ester, benzo three azole, substituted acrylonitrile, three zine and so on. The most widely used plastics industry is two benzophenone and benzo three azole.

二苯甲酮类紫外线吸收剂是目前应用最广的一类紫外线吸收剂，它对整个紫外光区域几乎都有吸收作用，光稳定机理是其分子中苯环上的羟基氢和相邻的羰基氧之间形成了分子内氢键，构成了一个鳌合环，而当吸收紫外光能量后，分子发生热振动，氢键破坏，鳌合环打开，这样就能把有害的紫外光变成无害的热能而释出来。二笨甲酮类紫外线吸收剂中，必须要有一邻位的羟基，否则不能作为聚合物的光稳定剂。这一类紫外线吸收剂的典型代表品种有UV-531、UV-9等等。

Two benzophenone type ultraviolet absorbents are the most widely used ultraviolet absorbents at present. It has almost all absorption effect on the whole ultraviolet region. The mechanism of light stabilization is that the hydroxyl hydrogen on the benzene ring in the molecule and the adjacent carbonyl oxygen form the intramolecular hydrogen bond, forming a chelation ring, while absorbing the ultraviolet energy. After that, the molecules vibrate, hydrogen bonds destroy, and the chelating rings open, so that harmful ultraviolet rays can be released into harmless heat energy. Two in the UV absorber of the methyl ketone, it is necessary to have a neighboring hydroxyl group, otherwise it can not be used as a light stabilizer of the polymer. Typical representatives of this type of UV absorber are UV-531, UV-9 and so on.

水杨酸酯类紫外线吸收剂为应用最早的一类紫外线吸收剂。它可在分子内形成氢键，其本身对紫外线吸收能力很低，而且吸收的波长范围极窄(小于340nm )。但在吸收一定能量后，由于发生分子重排。形成了吸收紫外线能力强的二苯甲酮结构，从而产生强的光稳定作用。

Salicylate ultraviolet absorbers are the first class of ultraviolet absorbers. It can form hydrogen bonds inside the molecule, and its absorption ability to ultraviolet light is very low, and the wavelength range of absorption is very narrow (less than 340nm). But after absorbing certain energy, molecular rearrangement occurs. The structure of two benzophenone, which absorbs ultraviolet radiation, forms strong light stability.

苯并三唑类紫外线吸收剂，其光稳定机理与二苯甲酮类相似，其分子中也存在氢键鳌合环，由羟基氧与三唑基上的氮所形成。当吸收紫外光后，氢键破坏或变为光互变异构体，把有害的紫外光能变成无害的热能。这一类紫外线吸收剂的典型代表品种有UV-P、UV-326、UV-327、UV-329等等。

The UV Absorbents of benzo three azole are similar to two benzophenones, and there are hydrogen bond chelates in their molecules, which are formed by hydroxyl oxygen and nitrogen on three azolyl groups. When ultraviolet light is absorbed, hydrogen bonds are destroyed or transformed into optical isomers, which turn harmful ultraviolet light energy into harmless heat energy. Typical representatives of this type of UV absorber are UV-P, UV-326, UV-327, UV-329 and so on.

紫外线吸收剂使用建议

Recommendations for the use of ultraviolet absorbents

在实际应用中，为了改善和提高塑料及其制品的光稳定性，单单添加紫外线吸收剂是达不到预期效果的。因为塑料等高分子材料的光老化过程基本上都伴随着氧化，所以我们通常所说的“光老化”称之为

In practical applications, in order to improve and enhance the optical stability of plastics and products, adding UV absorbers alone is not achieving the desired results. Because the aging process of plastics and other polymers is basically accompanied by oxidation, what we usually call "photoaging" is called "light aging".