The application of new blocking amine photostabilizers in ultraviolet curing and water-based formulations

The weather resistance of coatings (refers to the stability of coatings against ultraviolet light) has been one of the challenges facing the coating industry for many years. More than 40 years ago, it was discovered that blocked amine light stabilizers (HALS) play an important role in the stability of polymers and resins against ultraviolet light. These compounds are typically 2,2', 6,6'-tetymide derivatives, which oxidize when exposed to peroxy freelance fundamentals, resulting in stable nitrogen oxides . In addition to capturing alkyl free fundamentals, the reaction can also form a circular reaction that makes HALS an excellent class of polymer and resin light stabilizers. In this article, we will discuss how new blocking amine light stabilizers that can be used in UV
curing and water-based coatings can play a good protective role against the harmful effects of UV light.
Introduction
protective coatings are widely used in many products to extend their service life, it is clear that such a demand requires coatings to have a good weather resistance. Coatings are the first line of defense against these factors that lead to structural corrosion and aging. A reliable coating is resistant to water, oxygen, sunlight, contaminants and biological factors. Therefore, it is essential to maintain the flexibility, adhesion, water resistance and impermeability of the coating.
additional requirements for protective coatings in the automotive, construction or home appliance industries. Decorative is important for these applications and is important for properties such as gloss, image clarity (DOI) or anti-change, and biocorrosion.
the coating depends on whether the coating polymer itself can withstand ultraviolet light (UV), humidity, heat, and contaminant erosion for long periods of time. Most polymers or coatings do not meet these requirements on their own, so special additives are needed to protect them from degradation due to aging
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to resist the harmful effects of ultraviolet light and avoid adverse chemical reactions caused by the absorption of ultraviolet light by coating compositions. The following two methods are mainly used in coatings, especially for automotive coatings
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:1, with UV absorbers absorbed in the 290-380nm wavelength range, and used in conjunction with the use;
the UV absorbent as a light stabilizer in automotive varnishes, the UV shielding effect prevents the color change of the pigment and the photochemical degradation of the resin used. In a dual coating system, the photochemical degradation process can result in the complete separation of the varnish layer from the base coating or the complete stripping of the entire coating film from the substrate surface. Blocked amines do not absorb ultraviolet light at wavelengths above 250nm, but can capture free fundamentals, the main role is to maintain the luster of the paint film, to prevent cracking.
since the early 1970s, blocked amines have been a photostabilizer used in polymers and resins, acting as free-based catchers in automatic oxidation cycles and inhibiting photooxidation degradation of polymers. HalS works in a way that is largely independent of the thickness of the coating film, meaning that it can also act as a protective effect on the surface of the coating, where ultraviolet absorbents provide the weakest UV protection. In varnish coatings, HALS prevents surface defects such as loss of gloss or cracking, while in varnish coatings, HALS prevents powdering and color change. These surface defects will eventually increase the permeability of the coating and the loss of the physical and protective properties of the coating, resulting in substrate erosion.
To reduce volatile organic compounds (VOCs), and with increasing end-user expectations of coating performance and functionality, there is a shift in the industry towards water-based and ultraviolet curing coating technologies, prompting resin and additive suppliers to develop new materials or methods to add these hydrophobic materials to low VOC formulations while maintaining the desired performance of
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. Although many of the latest low-VOC technologies have overcome the associated disadvantages of traditional solvent-based systems, UV absorbers and HALS are still needed to avoid coating degradation in daylight exposure and improve weather resistance. The demand for new blocking amine light stabilizers for UV curing and water-based coatings has also become more prominent.
UV curing coating formula
UV curing coating because of its fast curing speed, and can cure at low temperature, has become a class of important products in the paint market
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. UV-curable coating formulations require the use of energy directly from ultraviolet light to trigger photo-curing of monomers and lymers in the formulation. Light triggers absorb ultraviolet light in the 300-400nm range to trigger photo curing mechanisms, while UV absorbers in formulations also absorb ultraviolet light in the same wavelength range. In addition, HALS is a free-snapper and may therefore interfere with the curing mechanism of UV curing coating formulations. Therefore, to add UV absorbers and HALS to the formulation of photo-cured coatings, UV absorbers, HALS and light triggers need to be carefully selected to avoid negative effects on the curing process.
UV curing experiment section
prepares an UV curing formula varnish, which is coated with a scraper stick on a white coil. Use a 120-watt/cm mercury lamp to cure the coating at a line speed of 10 m/min. The dry film thickness of all UV-cured membranes is approximately 40 microns. Unless otherwise noted, all UV curing formulations contain hydroxybenzene UV absorbers relative to 1wt% of the total resin solids. All UV curing formula coatings use a combination of the following light triggers: 2wt% 1-hydroxycychyl phenylbenzone, 2wt% xylene, 0.91wt% ethyl (2,4,1 6-MTH) benzoyl phosphate and 0.09wt% benzene-based double (2,4,6-MTH) oxides, the above-mentioned mass ratio is in the total resin solids.
speed up aging testing on Atlas Weather-Ometer equipment in accordance with DIN EN ISO 16474-2®. Test conditions: Internal and external boron silicate S-type filter, 102 minutes of light and drying, black label temperature (BST): 47±3 degrees C, probe chamber temperature (PRT): 30±2 degrees C, relative Humidity: 40±5%, followed by 18-minute light and front spray, BST:47±3C, PRT:30±2C, relative humidity 40±5%. Xenon lamps have an output of 0.51W/m2 and a wavelength range of 300 to 400nm. CiE Lab Delta E and 60-degree gloss were measured at different intervals during the aging test (see Tables 1 and 2).UV absorbers and HALS in the formulation of photo-cured coatings need to be carefully selected to avoid adverse effects on the coating during the curing process, thus ensuring that the coating curing achieves the desired results. Using the right combination of light stabilizers and an optimized combination of light triggers can improve the weather resistance of UV-cured varnishes. In UV curing formulations, CGL 2049 has good properties and can be used as an option for coating formulaters to achieve light stability in coating performance.
water-based coatings
water-based coatings in many coating applications as a result of changes in legal requirements and reduced demand for volatile organic compounds. As more and more water-based coatings are on the market, challenges are also ensuing, and the long-term stability and weather resistance requirements of water-based coatings are becoming more prominent. Hydrophobic light stabilizers are difficult to add to water-based coatings, and although they can be achieved using cosolt and high-energy dispersion methods, these methods are still limited. The addition of co-solvents may cause problems with the content of some product labels and reduce overall coating performance due to plasticization and seepage. In order to overcome the problem of adding hydrophobic photostabilizers to water-based formulations, a new package additive technology (NEAT) was
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. Using this technique, common hydrophobic light stabilizers are water compatible and can be easily added to coatings without the use of solvents, surface active agents or high shear mixtures. Even at higher concentrations, NEAT technology ensures good compatibness between photostabilizers and water-like dispersants.
the HALS alkalinity and its effects on coating formulations
The role of HALS's stable free fundamentals comes from the tetrome group. The performance of HALS can be controlled by changing the subsotual base on nitrogen atoms to make it suitable for specific types of applications (see Figure 1). The alkalinity of HALS is an important factor to consider when selecting HALS for a specific formulation. Table 3 gives approximate pKb values for various HALS to indicate alkalinity. In general, if the nitrogen atoms in HALS have alternative bases such as hydrogen or alkyl, their pKb value is about 5 and exhibits alkalinity. If HALS's nitrogen atoms have a replacement base such as oxygen alkyl, they do not exhibit
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. The alkaline nature of the HALS molecule may adversely affect different coating formulations, as follows:
A) Adding alkaline HALS to paints that are catalyzed by alkalis can speed up reactions and shorten opening hours. In particular, nitrogen atoms have hydrogen to replace the basis of HALS produced this role is particularly obvious.
B) In amine-neutral water-based systems, adding alkaline HALS can produce drastic pH changes that may cause storage stability problems in coatings.
C) In acid catalytic coatings such as high-solidity thermoo-curing acrylic coatings, as well as high-acid coatings, acids and alkalis react, resulting in insufficient curing of the paint film.
water-
using the above-mentioned NEOT technology, the hydrophobic CGL2049 with 100% active substance content was transformed into a stable water-like dispersant with an active substance content of about 40wt%, CGL 349. The CGL 349, N-Alkyl HALS and NOR-HALS 2 dispersions were added to the water-based coating formulation containing different resin systems with a concentration of HALS actives relative to 1wt% of the total resin solids. Table 4 shows the effects of different HALS on formula pH. As shown in the pH data, CGL 349 and NOR-HALS 2 dispersions have no effect on the final pH of the formulation, while alkaline N-alkyl HALS results in a dramatic increase in the final pH. Fog increases when N-alkyl HALS is added to a multiphate acrylic dispersion. No fog or particles are produced when NOR-HALS 2 dispersion CGL 349 is added to the water-based polyphonyl acrylic dispersion.
is a water-based varnish prepared from anionated acrylic resin and coated with a paint roller with a wet film thickness of 200 g/m2 on a pine substrate pre-treated at a concentration of 80 g/m2 in a nitrate solution that has already passed 2wt%. Let the paint film wind dry naturally for five days before you start measuring the color data. Unless otherwise noted, all water-based formulations contain hydroxybenzene and triamcinolone UV absorbent dispersions relative to the total resin solid 3wt% active substance.
Xe-WOM accelerated aging test is based on DIN EN ISO 16474-2 and is called atlas Weather-Ometer ®. QuV A 340 accelerated aging tests are performed on QUV/SE models in accordance with EN 927-6.
figure 2 shows that the CGL 349 (emulsion-type CGL 2049) is stable in terms of 60 degrees gloss compared to NOR HALS 2. The coating in Figure 2 that does not add a photostatizer cracks and fails after 1500 hours of Xe-WOM accelerated aging. As shown in Figure 3, the CGL 349 performs significantly better than NOR HALS 2 in the QUV A (340 nm) accelerated aging process. The coating in Figure 3, which does not have a light stabilizer added, cracks and fails after 480 hours of accelerated aging.conclusion
the use of the right combination of light stabilizers can significantly improve the outdoor weather resistance of UV-cured coatings and water-based coatings. If the correct combination of HALS and UV absorbent is not added, the combination of light stabilizers is incomplete. In an UV curing formula, CGL 2049 performs well and offers coating formulaters some new options when it is necessary to meet weather resistance requirements in applications. For water-based coatings derived from anionic acrylic dispersions, CGL 349 (NEAT version of CGL 2049) performs better than traditional photostabilizer techniques in the ACCELERATING process of QUV A (340nm) and does not cause fog or particle formation. Compared with other commercial HALS technologies, CGL 2049 has proven to be a versatile and widely applicable HALS. Ultraviolet absorbers and CGL 2049 HALS based on hydroxybenzene-triamcinolone or hydroxybenzene-benzene are ideal for use in a wide range of substrates and coating systems for excellent weather resistance.

1
Schirmann, P., Dexter, M. "Light and Heat Stabilizers for Coatings" in Handbook of Additives, Calbo, L.J., Editor, Marcel Deker, Inc., 1987, 225-268
2
Valet A. Light Stabilizers for Paints, ISBN 3-87870-443-7, C.R. Vincentz Verlag, Hanover, Germany, 1997, 45-128
3
Heller, H.J., Blattmann, H.R., Pure and Applied Chemistry 30 (30) 1972), 145
4
Berner, G., Dexlex, G., Schoof, E., XV FATIPEC-Congress Amsterdam 1980, Congress Handbook Vol. II, 61
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