Hydroxyphenyl-s-triazines: advanced multipurpose UV-absorbers for coatings.

Introduction

History of light stabilizers

Light stabilization of clearcoats has been a challenge for the paint industry for many years. (1) Automotive clearcoats are, for example, expected to ensure gloss retention and retain a colorless appearance for many years, while protecting the basecoat or coated plastic parts. (1,2) Throughout their service life, these coatings are exposed to light, heat, and temperature changes (i.e., weathering and mechanical stress such as scratch and mar impact). Apart from color deviation and loss of gloss, this may lead to surface defects such as cracking and even delamination. (1-3)

More than three decades ago, it became evident that hindered amine light stabilizers (HALS)--which interact with radicals (4) and retard the photooxidative degradation of polymers--are key additives for the stabilization of clearcoats. (5,6) HALS are mainly derivatives of 2,2,6,6-tetramethylpiperidine and reported to function mainly as chain-breaking antioxidants (7) and, in addition, transition metal complexing agents. (8) A variety of HALS compounds is available where the most important group is difunctional piperidine derivatives linked by diester, as shown in Fig. 1, to increase molecular weight and therefore decrease volatility. The first commercial HALS, still used to a degree, had R = H. Later versions (where R = alkyl) exhibit better long-term stability. Both of these types are basic (e.g., HALS-1: R = C[H.sub.3], p[K.sub.b] ~ 5) and interfere with acid-catalyzed crosslinking reactions such as those involving melamine-formaldehyde or epoxy-carboxy resins and some air-drying alkyd systems. More recently, hydroxylamine ethers have gained wide acceptance in the paint industry. One major advantage is that the aminoether function N-OR lead to a nonbasic and noninteracting HALS (e.g., HALS-2: R = O[C.sub.8][H.sub.17], p[K.sub.b] ~ 10). The low basicity is thus preventing possible interactions with acidic media or other paint components like biocides and does not interfere with the drying process of acid-catalyzed or air-drying systems.

[FIGURE 1 OMITTED]

Since the early 1970s, it has been common practice to combine HALS with UV-absorbers (UVA) to achieve improved synergistic effects. (9) UVAs filter out the harmful wavelengths of the light spectrum before subsequent photochemical reactions can take place (1) and therefore reduce the radical generation rate. On their own, UVAs are inefficient in protecting the surface of a film (Lambert-Beer Law), whereas HALS compounds do effectively scavenge free radicals at the surface and thus help to prevent surface defects.

Two of the early classes of UVA employed commercially were 2-hydroxybenzophenones (BP) and oxalanilides (Ox) (see Fig. 1), both being characterized by poor-spectral coverage and inferior photopermanence. Ox exhibit one absorption maximum at about 300 nm in the range of 280-400 nm, whereas BP show two absorption maxima (in the short-wave UV at about 300 nm and in the longer-wave UV above 320 nm). By the late 1970s, these UVA types had already almost entirely been replaced by various 2-(2-hydroxyphenyl)-benzotriazoles (BTZ). UVAs based on the benzotriazole chemistry were the most important UVA family in the 1980s, and are still today considered the most important class for the stabilization of clearcoats for most paint applications. BTZ have two absorption maxima in the short-wave UV at about 300 nm and in the long-wave UV at about 350 nm. The extinction of the BTZ is mainly governed by the molecular weight (i.e., the BTZ [R.sup.1]) and the [R.sup.2] substituent mainly affects the height and not the wavelength position of the maxima. The absorption spectra of Ox-1, BP-1 and BTZ-2, BTZ-3, and BTZ-4 are shown in Fig. 2. Here it is clearly shown that the difference in the absorbance profile of the used BTZ depends only on the molecular weight (molecular dilution of the active chromophore).

The liquid BTZ-1 can be considered the most versatile benzotriazole UVA, whereas BTZ-2 also finds use in water-based systems due to the hydrophilicity of the polyethylene oxide chain. The value of the solid and historically oldest BTZ-3, although still being used in a variety of applications, is limited due to its pronounced volatility even at moderate temperatures. Therefore, both BTZ-4 and BTZ-5 can be considered the main products representing this chemistry for high-bake applications such as coil and powder coatings. Although useful in a broad range of applications, certain limitations apply to benzotriazole-based UVAs, which will be discussed below. In spite of the high industrial relevance of BTZ (10) in the paint industry, there are still requirements that cannot be satisfactorily met with this chemistry. Therefore, a new UVA of the 2-hydroxyphenyl-s-triazine (HPT) class has recently been successfully introduced to the paint industry. This HPT offers a greater variety of advantages and is mainly used in high-performance applications or where BTZ cannot be used. The spectral properties of the HPT exhibit the strongest absorption in the region of 300 nm, with two absorption maxima; in the shortwave UV at about 300 nm (strong) and in the longwave UV at about 340 nm (less pronounced).

[FIGURE 2 OMITTED]

Properties of UV-absorbers

Besides primary photophysical properties such as absorbance profiles, absorptivity, or extinction, the photochemical stability (i.e., the photopermanence) is a basic requirement for a UVA. The photopermanence (i.e., the loss of stabilizer during light exposure) can be a result of two mechanisms: a physical loss by evaporation due to high-vapor pressures, leaching, migration and/or chemical loss by photochemical reactions of the stabilizer. (11) It was shown previously that mainly HPTs have very low-vapor pressure and show best photopermanence followed by BTZ, BP, and then Ox. (12) Besides the photopermanence, the heat resistance (i.e., the low volatility) is a key point. The poor heat resistance of certain UVAs on baking is well known. The loss rates after challenging bake cycles have shown the superior performance of HPT-1, HPT-2 and HPT-3, compared with standard BTZ, BP, and Ox absorbers. Besides the superior properties in terms of photopermanence and heat stability, HPT shows, in addition, excellent chemical resistance without interaction with metals or strong alkalis. In contrast, the presence of certain amines or metal ions causes yellowing of BTZ due to chemical or complexation reactions. (12) Another big advantage of the triazine chemistry is that simple chemical modification of the HPT chromophore can change photophysical properties like the absorbance profile or the extinction. It will be shown in this paper that the triazine chemistry still provides significant scope for improvement and allows fine-tuning of the chromophores to the required properties and final application. The chemical structures of different substituted HPTs (see Fig. 1) have significant influence on the spectral properties in contrast to BTZ. The absorption spectra of different HPT UVA can be seen in Fig. 3.

HPT-1 and HPT-2 show almost similar absorption spectra due to only a small difference in [R.sup.1]. [R.sup.1] determines the physical state: HPT-1 is liquid and mainly used in industrial and transportation application (see the section headed 'Stabilization of automotive coatings'), whereas the solid HPT-2 is mainly used in powder-coating applications (see the section headed 'Stabilization of powder coatings'). HPT-3 shows by far the highest extinction in the UV-B area ([l.sub.max] = 320 nm). This extreme extinction allows the making of an ideal product for thin- or reduced-film application (see the section headed 'Stabilization of automotive coatings') and to boost the efficiency of other commercial HPT stabilizers such as HPT-1 and HPT-2. HPT-4 is more red-shifted, that is absorbing in both the UV-B, but also strongly in the longer wavelength UV-A radiation area, and is a unique product for protecting substrates sensitive to these radiations such as wood coatings as well as printed materials and substrates (see section headed 'Stabilization of wood coatings').

[FIGURE 3 OMITTED]

Most of the light-stabilizer materials used today were initially developed for solventborne coating systems. Therefore these additives (except BTZ-2) are hydrophobic in nature and not suited for direct use in waterborne systems. However, the number of waterborne systems is constantly increasing in many coating application areas. To this end, the state-of-the-art products are supplied as solid or liquid UVAs dispersed in water using dispersing agents or emulsifiers. Although such products offer the coating formulators full freedom to apply the desired concentration levels, the nonmolecular and inhomogeneous distribution of the UVA in the coating film lead to a reduced efficiency in UV light filtration. Furthermore, these solid UVA dispersions in general cause haze and reduced transparency due to scattering effects of solid particles present in the polymeric film.

Current methods in their usage come with trade-offs in appearance, handling, or high levels of volatile organic compounds (VOCs) because of the use of cosolvents in these formulations. Novel approaches to an optimal solution with full formulation flexibility and performance for waterborne coatings are considered indispensable. Therefore a new encapsulation technology has been developed to render organic water-insoluble UVAs compatible with waterborne coating systems. (13,14)

The preparation of the new product form, being a UVA which is encapsulated in an acrylic polymer matrix (i.e., UVA containing polymer dispersion), is based on two steps: a pre-emulsion with a droplet size below 1 um consisting of a monomer mixture and UVA is produced in water. Second, the polymerization of this emulsion yields a very fine and stable polymer emulsion containing liquid or solid UVAs in the polymeric particles. The polymer matrix is built up with a monomer mixture, which provides a very broad compatibility with aqueous coating formulations. The newly developed product form is hazard warning symbol and organic solvent-free, low in viscosity, containing between 20 and 30% of UVA with droplet sizes below 150 nm, and allows for the postaddition to waterborne coatings (i.e., at the end of the production process under normal stirring conditions without specific equipment). The novel dispersion exhibits long-term storage stability even after being added to the liquid paint without any sedimentation, whereas milled UVA and inorganic UVA dispersions tend to separate after relatively short storage periods. Excellent retention of paint film properties (no or little reduction of hardness, blocking resistance and water impermeability) as well as total dry film clarity is obtained. They exhibit long-term storage stability even in the liquid paint without any sedimentation, whereas milled UVA and inorganic UVA dispersions tend to separate after relatively short-storage periods. This new product form is denoted as, for example, HPT-1 DW, whereas DW stands for dispersible in water.

The aim of this paper is to present application examples, where it is shown that HPT-based UVAs exhibit superior performance in comparison with the state-of-the-art BTZ-based materials.

Experimental

Artificial exposures were performed under different light sources. For automotive applications, Xenon light was required to simulate the entire UV and visible spectrum of daylight using the Xe-WOM CAM 180-cycle with the Atlas Weather-Ometer[R] Ci-65 A/Ci5000 (outer filter borosilicate/inner filter quartz) according to SAE-J-1960 (0.55 W/[m.sup.2]/340 nm: 60 min dark with spray, black panel temperature (BPT) 38 [+ or -] 2[degrees]C, relative humidity (RH) 95 [+ or -] 5%; 40 min light, BPT 70 [+ or -] 2[degrees]C, RH 50 [+ or -] 5% 20 min light and spray, BPT 52 [+ or -] 2[degrees]C, RH 95 [+ or -] 5%; 60 min light, BPT 70 [+ or -] 2[degrees]C, RH 50 [+ or -] 5%). The Xenon test for wood coatings required the use of the Xe-WOM CAM 7 with the Atlas Weather-Ometer Ci-65 A (outer filter borosilicate/inner filter borosilicate) according to DIN EN ISO 11341A (0.35 W/[m.sup.2]/340 nm: 102 min light, BPT 60 [+ or -] 2[degrees]C, RH 50 [+ or -] 5%; 18 min light and spray, BPT 40 [+ or -] 2[degrees]C, RH 95 [+ or -] 5%). The color was measured with a Minolta CM-3600d (gloss included) and the calculation of L*, a*, b*, C*, h, and [DELTA]E* with CGREC software according to DIN 6174. The gloss evaluation was performed at 20[degrees] with BYK-Gardner Micro-Tri-Gloss according to DIN 67530. The cracking evaluation was performed visually according to DIN EN ISO 4628-4.

Results

Stabilization of automotive coatings

The light stabilization of automotive coatings is well known and state-of-the-art. The principles of automotive coatings stabilization are described elsewhere. (1) Light stabilizers have been extensively discussed in an earlier paper. (12) Here it was clearly shown that HPT outperformed BTZ in most automotive applications. The superior photopermanence in terms of the low volatility of HPT correlates with their stabilization performance. Again this is shown in Figs. 4 and 5. Figure 4 shows the remission spectra of a high-solid 2 K clearcoat over a silver metallic basecoat after 54 months 5[degrees] south Florida exposure. Figure 5 shows the visual appearance of the exposed panels stabilized with BTZ-1, HPT-1 and HPT-3 at 20 and 40 [micro]m dry film thickness (DFT).

Based on the Florida exposure, there is clear evidence that the photopermanence of the used UVA correlates well with the overall performance. It is quite obvious that BTZ-1 is almost entirely gone after 54 months of exposure, whereas HPT-1 and HPT-3 are still present in the coating. This result confirms the visual appearance where the nonstabilized panels show severe color deviation, loss of gloss, and a patchy pattern on the surface. The performance can only be slightly improved using BTZ-1. HPT-1 shows an obvious improved performance at 40 [micro]m DFT. Nevertheless, at a reduced DFT of 20 [micro]m, HPT-3 with the highest extinction (see Fig. 3) clearly outperforms HPT-1 as well as BTZ-1.

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

The results of this study (low volatility, high photo-permanence, and UV protection performance of the HPT stabilizer) become much more important if for any reason the film build of the clearcoating has to be decreased or if the total additive concentration has to be reduced. As cost pressures, in particular, drive the paint industry in this direction, future UVA packages will increasingly contain UVAs of the HPT class.

Stabilization of coatings over plastic

The use of car parts in a variety of plastics has been increasing since the early 1990s. One of the most widely used materials for exterior applications are thermoplastic polyolefins (TPO). The painting of these plastic materials offers several challenges not encountered in the painting of conventional steel substrates. These include the adhesion of a polar coating to the nonpolar plastic substrates, and the weathering performance of the applied coating. However, in contrast to coatings applied over steel, it has been found that the UVAs and HALS can migrate through the coatings into the TPO plastic substrate, resulting in inferior durability. (15) To minimize this problem, the use of UVAs with hydroxyl groups (see BTZ-2, HPT-1, and HPT-2 in Fig. 1) which can react with the isocyanate in the clearcoat to bind the stabilizers to the polymer chains are used. An extensive study of the use of similar reactive UVAs and HALS using an acrylic melamine-formaldehyde (MF) basecoat and a 2 K urethane clearcoat also showed marked improvements in performance compared with nonreactive UVAs. (16) In general, reactive UVAs outperform nonreactive UVAs, and reactive HPTs show improved performance compared with reactive BTZs.

Stabilization of powder coatings

The overall development of the powder coating technology is mainly due to the so-called five "E"s: Excellence of finish, Environmental friendliness, Economics, Energy savings, and Ease of application. The latest technology advances in powder coatings further stimulate growth by allowing outlets in applications such as automotive clearcoats or highly durable architectural finishes. Since 1996, powder coatings have been successfully used in automotive series as clear topcoats. This development has been accessible thanks to new binder systems used in combination with light stabilizers like UVAs and HALS. Acrylics are the binder of choice for transparent finishes with general properties such as high transparency, excellent flow, and acceptable durability. Light stabilizers extend the lifetime of such coatings and meet the demands from the automotive industry. Currently the most common powder coatings used for exterior applications in industrial coatings and architectural finishes are based on polyester (PES) binder systems. However, in this area, significant improvement has been achieved with the development of so-called 'super durable' polyesters. The lifetime of these super-durable resins has been enhanced by the use of appropriate light stabilizers. Extended studies have been carried out to show the benefit of using light stabilizers in polyacrylates based on glycidylmethacrylate/dodecane dicarboxylic acid (GMA) and in super-durable polyester/triglycidylisocyanurate (PES/TGIC) powder coatings. (17) For example, the gloss retention of GMA with different light stabilizers during the Florida exposure is shown in Fig. 6.

Based on the results of the exposure tests, the efficiency of the light stabilizers in acrylates and super-durable PES clearcoats was confirmed in both artificial and natural outdoor exposure tests. Again the triazine HPT-2 shows best performance in terms of gloss and color retention followed by BTZ-4, BP-1 and then Ox-1. Due to its ease of incorporation (low-melting point), its minimal contribution to the initial color and its great gloss and color retention performance HPT-2 is dedicated to high-quality powder coatings. (17)

Stabilization of wood coatings

Wood remains a remarkable material for construction and decoration purposes. Displaying the elegance and appearance of the color, grain and texture of natural wood supports the general trend toward natural products. Transparent coatings are desired to highlight and preserve the natural beauty of wood. High performance and durability of the coating systems is mandatory to maintain this look without significant color change. Color change can occur early in the life of indoor applications, especially in pale wood species. More rapid and severe discoloration occurs in exterior applications, with subsequent cracking and flaking of the wood coating film or graying of the wood surface impregnated with wood stains. The key for improving the service lifetime of transparent wood coatings is the optimization of UV light protection of the wood surface itself in addition to the prevention of the alteration processes in the coating film. (18) In order to obtain better performance, it was necessary to develop new screeners with the absorbance spectra extended to the longer-wavelength range (red-shifted UVA) and excellent photopermanence for efficient long-term protection in comparison with the currently used BP and BTZ-type UVA. For wood coatings, two UVAs for solventborne as well as an encapsulated water-based form (HPT-4 DW) of the red-shifted chromophore of HPT-4 are available. The influence of the concentration and the spectral characteristics of the UVA on the wood color protection have been demonstrated in earlier tests on pine and fir substrates. (19,20) One example of the improved performance and long-term stability of the new red-shifted chromophore is given in Fig. 7. Here the retained amount of UVA (i.e., the photopermanence) of UVA in a solventborne long-oil alkyd (LOA) as well as a waterborne acrylic over pine during Xe-WOM CAM 7 exposure is shown.

[FIGURE 6 OMITTED]

Based on these results, it is apparent that the used triazine HPT-4 chromophores significantly outperform the conventional BTZ in terms of photopermanence. After 2000 h of artificial weathering, there is still around 90% of HPT-4 DW and 60% of the used HPT-4/BTZ-1 mix in the coating. Here the loss of around 40% in the HPT/BTZ mix can be related to the loss of BTZ. BTZ-1, and BTZ-2 show very strong loss with only around 20% of UVA remaining in the coating. This improved photopermanence of HPT-4 DW clearly indicates the advantages of the new encapsulated product form over conventional hydrophilic BTZ UVAs like BTZ-2 in aqueous application. It was confirmed earlier that a better performance observed on wood protection is related to the higher photopermanence in the coating films, and keeping in mind the larger absorbance range, the better long-term color protection and overall better performance on wood protection. (18)

[FIGURE 7 OMITTED]

Figure 8 shows clearly the improved performance of HPT-4 in a solventborne LOA (two coats brush-applied over a colorless fungicidal pretreatment) on fir after 18 months 45[degrees] south exposure in Sydney, Australia. Here it is obvious that the HALS as well as the UVA-type play an important role. The unstabilized sample shows strong erosion of the coating and the wood itself. Only a small improvement can be obtained by the use of UVA in combination with HALS-1. Here the nonbasic HALS-2 clearly outperforms the basic HALS-1. In general it could be stated that the use of basic HALS can cause curing retardation, or even inhibition, in air-drying alkyd and oil-based paints. Furthermore, HPT-4 shows a significantly better performance compared with the conventional BTZ-1 in combination with HALS-2 due to the improved photophysical properties.

Nevertheless, the discoloration of the wood cannot be completely suppressed by the use of UVA alone. The reason is that wood as a complex biopolymer discolors on exposure not only to UV-A and UV-B light but also to visible light. The main factor for the light sensitivity of wood is the photodegradation and the breakdown of lignin. Today, three different lignin photodegradation mechanisms are known; the phenoxy and the phenacyl pathways are both induced by UV light and, in addition, the ketyl pathway is induced by visible light. (21) Therefore, a new lignin stabilization concept has recently been presented, which provide an improved wood color stability in interior applications and long-term durability to clear and transparent pigmented wood coatings in exterior applications. (22,23) The concept consists of a new HALS compound acting as an effective lignin stabilizer trapping the radicals at the wood surface formed by visible light not screened by UVA (>400 nm), and a highly photostable red-shifted UVA based on HPT chemistry. According to this new concept, an optimized wood protection can be achieved when the lignin stabilizer is applied as a dilute aqueous solution or in a primer formulation directly on wood. For having a permanent effect the lignin stabilizer has to be used together with a UVA, at best in the subsequently applied coating layers. The effect of the lignin stabilization concept on color and coating protection of pine after 500 h of Xe-WOM CAM 7 exposure is shown in Fig. 9. Here, an aqueous solution of the lignin stabilizer (2%, 1 x 80 g/[m.sup.2]) followed by a waterborne acrylic topcoat (2 x 100 g/[m.sup.2]) containing 5% HPT-4 DW (1% active UVA) and 1% HALS-1 on solids was applied by brush. In general, the single use of UVA decreases the color deviation on most pale wood species approximately by half. It can be seen in Fig. 9 that the lignin stabilizer concept further improves the color retention to retain almost the initial color of the wood.

Conclusions

It has been shown that HPTs represent the top class of UV-absorber for most application areas such as automotive, wood and powder clearcoatings. Combining high photopermanence and high extinction coefficient with very low volatility, this additive family provides an outstanding stabilization potential for high-performance coatings to meet the high demands and expectations of the end-user. Furthermore, it was shown that this chemistry still has the potential for substantial further improvement, which becomes particularly necessary when film build or additive loading has to be reduced to a minimum. In addition, the availability of the mostly hydrophobic additives in a product form compatible with aqueous systems further allows their use in waterborne coatings and helps to close the gap between solventborne and waterborne applications.

References

1. Valet, A, Light Stabilizers for Paints, pp. 45-128, CR Vincentz Verlag, Hannover, (1997) ISBN 3 87870 443 7

2. Pospisil, J, Nespurek, S, "Photostabilisation of Coatings. Mechanisms and Performance." Prog. Polym. Sci., 25 (9) 1261-1335 (2000)

3. Bauer, DR, "Kinetics of Photooxidation and Photostabilisation in Cross-linked Polymer Coatings." Polym. Degrad. Stabil., 48 259-267 (1995)

4. Klemchuk, P, Gande, M, Cordola, E, "Hindered Amine Mechanisms. III: Investigations Using Isotopic Labeling." Polym. Degrad. Stabil., 27 65-74 (1990)

5. Pospisil, J, Klemchuk, PP, "Oxidative Deterioration Processes in Organic Materials." In: Pospisil, J, Klemchuk, PP (eds) Oxidation Inhibition in Organic Materials, vol. 1, pp. 1-10. Boca Raton: CRC Press (1990)

6. Mielewski, DF, Bauer, DR, Gerlock, JL, "Determination of Hydroperoxide Concentrations in Cross-linked Polymer Coatings Containing Hindered Amine Light Stabilizers." Polym. Degrad. Stabil., 41 323-331 (1993)

7. Kramer, HEA, "Wirkungsweise von Stabilisatoren in Polymeren unter Berucksichtigung der 2-Hydroxyphenylbenzo-triazole." Die Angewandte Makromolekulare Chemie, 183 (1) 67-101 (1990)

8. Fairgrieve, SP, MacCallum, JR, "Hindered Amine Light Stabilisers: A Proposed Photo-stabilisation Mechanism." Polym. Degrad. Stabil., 8 107-121 (1984)

9. Gerlock, JL, Bauer, DR, Briggs, LM, Dickie, RA, "A Rapid Method of Predicting Coating Durability Using Electron Spin Resonance." J. Coat. Technol., 57 (722) 37-46 (1985)

10. Keck, J, Stuber, GJ, Kramer, HEA, "Deactivation Processes of 2-Hydroxyphenyl-1,3,5-Triazines: Polymeric and Monomeric UV Absorbers of the Benzotriazole and Triazine Class." Angewandte Macromolekulare Chemie, 252 119-138 (1997)

11. Decker, C, Biry, S, Zahouily, K, "Photostabilisation of Organic Coatings." Polym. Degrad. Stabil., 49 111-119 (1995)

12. Stahrfeld, A, Braig, A, "Advanced UV Protection of Automotive Clear Coatings." Proceedings from XXVI FATIPEC Congress, Dresden, Germany, 2002

13. Peter, W, Schellenberg, C, Rogez, D, Schaller, C, Kalscheur, G, "New Concepts for Improved Durability of Water-Borne Wood Coatings." Proceedings from the Coating Wood and Wood Composites Conference, Charlotte, NC, 2005

14. Peter, W, Schaller, C, Schellenberg, C, Rogez, D, "A New Concept of Aqueous Additive Preparations for Water-Borne Coatings." Proceedings from the Water-borne and High-solids Coatings Conference, Brussels, Belgium, 2006

15. Cliff, N, Adamson, K, Yaneff, P, "Reactable Light Stabilisers for Automotive Coatings Over Plastics." Proceedings from the International Coatings for Plastics Symposium, Troy, MI, 2001

16. Cliff, N, Peters, C, "The Use of Reactable Light Stabilisers to Prevent Migration and Improve Durability of Coatings on Plastic Substrates." Proceedings from the International Coatings for Plastics Symposium, Troy, MI, 2003

17. Zeren, S, "UV Stabilisation of Powder Clear Coats." Proceedings from the XXVI FATIPEC Congress, Dresden, Germany, 2002

18. Rogez, D, "Colour Stabilisation of Wood and Durability Improvement of Wood Coatings." Proceedings form the 2nd Wood Coatings Congress, The Hague, Netherlands, 2000

19. Hayoz, P, Peter, W, Rogez, D, "Improved Photo-protection of Wood and Durability Improvement of Wood Coatings." Proceedings from the 3rd Wood Coatings Congress, The Hague, Netherlands, 2002

20. Rogez, D, "Colour Stabilisation of Wood and Durability Improvement of Wood Coatings." Paint Coating Indust. Magazine, www.pcimag.com (site checked 21st July 2006), March 2002

21. Leary, GJ, "Recent Progress in Understanding and Inhibiting the Light-induced Yellowing of Mechanical Pulps." J. Pulp Paper Sci., 20 (6) 154-160 (1994)

22. Hayoz, P, Peter, W, Rogez, D, "Colour and Light Stabilisation of Untreated and Stained Wood for Indoor Use." Farbe Lack, 109 (7) 26-33 (2003)

23. Hayoz, P, Peter, W, Rogez, D, "Improved Photoprotection of Wood Substrates Part I: Colour Stabilisation of Natural and Stained Wood for Indoor Applications." Asia Pacific Coat. J., 16 (2) 14-20 (2003)

[c] FSCT and OCCA 2007

Presented at XXVIIIth FATIPEC Congress, organized jointly by the Hungarian Chemical Society (MKE) and the Polish Association of Chemical Engineers (SITPCHEM), in Budapest, Hungary, June 12-14, 2006.

C. Schaller ([mailing address]), D. Rogez, A. Braig

Ciba Specialty Chemicals Inc., Klybeckstr 141, CH-4002 Basel, Switzerland

e-mail: [e-mail]

unstabilized  1.5% BTZ-1   2.5% BTZ-1   2.5% BTZ-1   2.5% HPT-4
              1.5% HALS-1  1.0% HALS-1  0.5% HALS-2  0.5% HALS-2

Fig 8: Effect of UVA and HALS on color and coating protection of fir
with long-oil alkyd after 18 months 45[degrees] south exposure in
Sydney, Australia

no additive  5% HPT-4 DW in top coat  2% lignin stabilizer in printer
             (1% active UVA)          5% HPT-4 DW in top coat

Fig. 9: Effect of the lignin stabilization concept on color and coating
protection of pine with waterborne acrylic (including 1% HALS-1) over
impregnation (2% lignin stabilizer in aqueous solution) after 500 h of
Xe-WOM CAM 7 exposure