Guided reading
Ultraviolet absorbers can strongly and selectively absorb high-energy ultraviolet rays, and in the form of energy conversion, the absorbed energy is released and consumed as heat energy or harmless low-energy radiation, thereby avoiding damage to the skin and preventing polymer Absorption of ultraviolet energy results in excitation and photophysical and photochemical decomposition.
1.the principle of UV absorber:
The light energy absorption and conversion mechanism of UV absorbers varies with the type, and they are described as follows;
l Benzophenones
Benzophenone UV absorbers are the most widely used class of UV absorbers. This type of UV absorber has a slow absorption effect on uV-A, uV-B, and uV-C. The ketone group and the hydroxyl group in the molecule can generate an internal hydrogen bond to form a chelating ring. After it absorbs the ultraviolet light energy, the thermal vibration of the molecule occurs, the internal hydrogen bond is broken, and the chelate ring is opened. The energy of the ultraviolet light is converted into heat energy and released. In addition, the carbonyl group in the molecule will be absorbed by the ultraviolet light energy. Excited, resulting in tautomerism. Generate enol structure. This also consumes part of the energy. In this type of UV absorber, the strength of the hydrogen bond in the molecule is related to its photostabilization effect. The stronger the oxygen bond, the greater the energy required to destroy it, and the more UV energy absorbed and consumed, the better the effect; otherwise The same is true. The stabilization effect is also related to the length of the alkoxy chain on the benzene ring. If the length is long, the compatibility with the polymer is good. The stabilization effect is just right. In benzophenone UV absorbers, it must contain a hydroxyl group at the ortho position of the carbonyl group, otherwise it cannot form an internal hydrogen bond, and it cannot be used as a UV absorber with an ortho hydroxyl group. It can absorb 290~380~ m ultraviolet rays, almost no visible light absorption, no coloring, and good compatibility with high molecular polymers. If there are two hydroxyl groups in the ortho position of the carbonyl group, it can absorb ultraviolet rays of 300-400fzm, and also absorb part of the visible light. Due to the absorption of visible light, the complementary light is unbalanced. The articles added with this ultraviolet absorber appear yellow. The compatibility of molecular polymers is also poor. Therefore, its use is small. Although benzophenone without o-hydroxyl also has the ability to absorb ultraviolet rays. However, it will cause self-decomposition after being exposed to light, so it is not suitable for use as an ultraviolet absorber.
l Salicylates
Salicylate UV absorbers are the earliest type of UV absorbers, and salicylates also have internal hydrogen bonds in the molecule. The ability of this type of ultraviolet absorber to absorb ultraviolet rays is very low at the beginning, and the absorption range is very narrow (less than 340vm), but after a certain period of ultraviolet irradiation, its absorption gradually increases until the maximum absorption, which is due to its Molecular rearrangement occurs under ultraviolet irradiation, forming a benzophenone structure with strong ultraviolet absorption, thereby strengthening its ultraviolet absorption. Therefore, people call it a pioneer UV absorber. The bishydroxybenzophenone and its derivatives generated after molecular rearrangement can absorb part of the visible light and appear yellow, resulting in the yellowing of the substance added to the ultraviolet absorber.
l Benzotriazoles
The mechanism of action of benzotriazole UV absorbers is similar to that of benzophenones. Benzotriazoles have a wide range of ultraviolet absorption, and can absorb light with a wavelength of 300-400-m. However, it hardly absorbs visible light above 400~m, so the product will not be flooded.
l Other types of UV absorbers
In addition, the substituted acrylonitrile, triazine ultraviolet absorber, its mechanism of action is supposed to be according to cis-trans isomerization, so that the energy conversion of light or the release of harmless energy. Acrylonitrile substituted ultraviolet absorbers can absorb ultraviolet light of 290-320Fm, do not absorb visible light, and will not cause the applied object to flood. Sanhao UV absorber can absorb 300~400~m of UV light. UV absorbers can absorb auxochromic genes (such as -NH, -OH, -SOH, -cOOH, etc.) and chromophores (such as C:N, N:N, N:O, C) with a wavelength below 400~m :O etc.). They are all attached to the aromatic nucleus. Organonickel can also be used as a UV absorber, but it is generally classified as a quencher (also known as a deactivator or a matting agent, or a laser state quencher, energy quencher), and its ability to absorb ultraviolet rays is higher than Connectivity is low, but it can prevent the polymer from freeing due to the absorption of ultraviolet rays.
The organic nickel complexes interact with the molecules that are excited to the excited state of the polymer in the process of ultraviolet light irradiation, so that the excited state returns to the ground state, and the ultraviolet energy is converted into a low-energy spectral emission without destroying it. , so as to protect the polymer from being damaged. Therefore, it is called quencher because its mechanism of action is different from that of general ultraviolet absorbers. The ultraviolet absorber changes the structure of the molecule itself, while the quencher dissipates energy through energy transfer between molecules.
In addition, light shielding agents such as carbon black, titanium dioxide, zinc oxide, zinc barium, etc. are also a kind of substances that can absorb or reflect ultraviolet rays. When it reaches the surface of the polymer, it is absorbed and reflected, preventing ultraviolet rays from going deep into the polymer. The most efficient of them is carbon black.
Radical scavengers are also a class of substances that can produce light stabilization. They are piperidine derivatives with steric hindrance effect, and are called hindered amine light stabilizers.
2. the classification of UV absorbers:
l Benzophenones
Benzophenone UV absorbers are all derivatives of o-hydroxybenzophenone, including monohydroxyl, dihydroxyl, trihydroxyl, tetrahydroxyl derivatives, etc. Such ultraviolet absorbers are widely used in polyethylene and polypropylene. , polyvinyl chloride, ABS, polystyrene, polyamide and other high polymers and the finishing of textile materials, such UV absorbers have good compatibility with most high polymers. Good light and thermal stability. It does not decompose at 200°C, but has strong sublimation. It can be used in paints and plastics, and the addition amount is 0.1 to 0.5.
l Salicylates
The UV absorption rate of salicylate UV absorbers is smaller than that of benzophenones, and the absorption band is narrower (below 3409m), and it is not very stable to UV light itself. Forks can absorb visible light and make the applied object It is yellow, but its price is cheap. It has good compatibility with high polymers, and is used in high polymers such as fiber rope, polyester, PVC, PE, polyvinylidene and polystyrene.
l Benzotriazoles
The performance of benzotriazole ultraviolet absorbers is better than that of benzophenones, which can strongly absorb ultraviolet light of 310-385pm, and hardly absorb visible light. Its stability is also good, but the price is more expensive.
UV-P can absorb ultraviolet light with a wavelength of 270-380nm, hardly absorb visible light, and has low initial coloration. Mainly used in polyvinyl chloride, polystyrene, unsaturated polyester, polycarbonate, polymethyl methacrylate, polyethylene, ABS and other products, especially suitable for colorless, transparent and light-colored products. But not soaping, because it dissolves in alkaline soap, making the fiber color yellow. uV-326 can effectively absorb ultraviolet light with a wavelength of 270-380nm, and is mainly used in polyolefin, polyvinyl chloride, unsaturated polyester, polyamide, epoxy resin, ABS, polyurethane and other products. It stabilizes well. It is insensitive to metal ions, has low volatility, has antioxidant effect, and is easy to color in the initial stage. uV-327 can strongly absorb ultraviolet light with a wavelength of 270-300nm, and is suitable for polyethylene, polypropylene, polyvinyl chloride, polymethyl methacrylate, polyoxymethylene polyurethane, ABS, epoxy resin, etc. It has good chemical stability, low volatility, low toxicity and good compatibility with polyolefins. uV-54l1 absorbs ultraviolet light in a wide range, the maximum absorption peak is 345nm in ethanol) is widely used in polystyrene, polymethyl methacrylate, unsaturated polyester, rigid PVC, polycarbonate, ABS, etc. . Its volatility is small, and the initial coloring property is not large.
l Triazines
Triazine UV absorbers have high absorption capacity for UV light in the range of 280-380nm. Compared with benzotriazole stabilizers, the absorption capacity is a kind of efficient absorption light stabilizer. It is a 2-hydroxyphenyltriazine derivative and contains a hydroxyl group in the ortho position. The ultraviolet absorption effect of these compounds is related to the number of adjacent hydroxyl groups. The more the number of adjacent hydroxyl groups, the stronger the ability to absorb ultraviolet light. The introduction of different substituents can reduce the basicity of the s-triazine ring, but improve the light fastness of the compound and the compatibility with the resin. 327. Disadvantages are poor compatibility with polymers and also coloration of the application. The derivative of o-hydroxyphenyldiphenyltriazine developed by Ciba-Geigy Company is a cationic self-dispersing UV absorber with good sublimation fastness and heat-fixing properties, which can be used for high temperature dyeing, pad dyeing and dyeing. printing.
l Substitute acrylonitrile
This type of UV absorber can absorb 310~320~m of UV light, but the absorption rate is low. It has good chemical stability and compatibility with high polymers. N-53 strongly absorbs ultraviolet rays with a wavelength of 270 to 350 nm. It is suitable for polyvinyl chloride, acetal resin, polyolefin, epoxy resin, polyamide, acrylic acid Resin, polyurethane, urea-formaldehyde resin and nitrocellulose, etc. Especially suitable for polyvinyl chloride products. Good alkali resistance. Soluble in toluene, methyl ethyl ketone, ethyl acetate, etc., slightly soluble in ethanol and methanol, and insoluble in water. The dosage is generally 0.1% to 0.5%. N-539 is a light yellow liquid, soluble in common organic solvents. Insoluble in water, it can give products excellent photothermal stability, and it has good compatibility with resins. It does not color. Can be used for various synthetic materials.
3. the application of UV absorbers in textiles:
There has been a lot of interest in UV-resistant fabrics in recent years. UV-resistant fiber kimonos were first developed in Japan
In China, research has also been carried out to produce anti-ultraviolet sportswear, stockings, hats and sun umbrellas. Place
The basic materials used are the above-mentioned ultraviolet absorbers, the most used of which are benzophenones.
l Manufacture of UV-resistant fibers
Use UV absorbers and shielding agents (such as ZnO, TiO2, etc.) to be mixed into the fibers for spinning to make UV-resistant fibers. The woven fabrics are better than the post-finishing application method in terms of style and washability. . This fiber can shade 60% of the ultraviolet rays in the light. Under direct sunlight, the temperature in the garment can be lowered by 4 ℃, and it has now been commercialized.
l After finishing method to apply UV absorber
The method of applying UV absorbers to clothing or fabrics varies by type of UV absorber. One is to apply ultraviolet absorbers that can form hydrogen bonds with the hydroxyl groups of cellulose, the amide groups of polyamides, the amino groups on wool and silk in the dyeing or softening bath and dye the fibers at the same time. Dip dyeing, pad dyeing or Printing method or soft finish application. Ciba-Geigy and Clariant have all developed such products. If benzophenone UV absorber is used, such as Uvinul DP-uV of BASF, it contains two hydroxyl groups in it. It can form hydrogen bonds with cellulose, wool, silk and polyamide fibers and has affinity. It can dye fibers and can be used for dip dyeing treatment. The dosage is DP-uV 10～20 (O.W.f). Treat at 80℃ for 30min. Pad dyeing method DP-uV 10O～Z00g/L can also be used. Add softener 30g/L, pad dye at 60℃, and dry at 100℃ for 3min. It can also be used in combination with a waterproofing agent. It can be made into an anti-ultraviolet tent, with a waterproofing agent of 60g/L. DP uV 80～150g/L, a catalyst (such as MgCI 2·6H2O) 5g/L. Padding, drying and baking (150°C for 2 min). This application method can achieve the effect of washing resistance, and the shielding rate of ultraviolet rays from 280 to 400vm can reach more than 85%.
l Method of making microcapsules and then applying them to fabrics
The ultraviolet absorber is made into microcapsules by microcapsule technology, and its capsule is preferably made of high molecular polymers, such as styrene and acrylate, and the microcapsules are made by the method of microcapsules while polymerization. The UV absorber is wrapped in the core of the capsule, and then the microcapsules are fixed on the fabric with adhesives and cross-linking agents, which can be made into textiles with a UV shielding rate of more than 85. The microcapsules can release the UV absorber slowly. The purpose of effective UV protection.
l Using the coating application method
The ultraviolet absorber is added to the coating agent. Coating, drying and baking are carried out, and other functional finishing agents can also be added to the coating liquid. Tent and hat made by this method. The method is simple, but the weather resistance and washing resistance are still improved.
