Exterior wood coatings. Part-1: Performance of semitransparent stains on preservative-treated wood

Pressure-treated lumber available for residential applications had been changed from chromated copper arsenate (CCA) treatment to Cu–amine formulations (since January 2004). This change created a need to investigate the performance of coatings on these new Cu-based preservatives as compared with CCA. This study evaluated performance of a number of semitransparent deck stains on CCA, alkaline copper quat (ACQ), copper azole (CA), and untreated wood samples during 3 years of natural weathering. Coatings were evaluated for their ability to reduce water uptake, color change, checking of wood, and mildew growth and to improve general appearance of preservative-treated wood samples. Overall, Cu–amine-treated wood had on average 50% higher water uptake than CCA-treated wood samples. Although solvent-based coatings had better water repellency performance on CCA-treated and untreated wood, there was no significant difference in water-repellent effectiveness (WRE) between water-based and solvent-based coatings on ACQ- or CA-treated wood. All preservative-treated woods had less color change and better visual ratings than those of untreated wood samples. Based on image analysis which was used to determine the total area of surface checking on samples after 3 years, preservative treatments had no significant effect on reducing checking of wood while coatings reduced surface checking by 30–40%.     

Enhancing exterior performance of clear coatings through photostabilization of wood. Part 2: coating and weathering performance

Clear-coated boards have not been recommended for use in exterior conditions since irradiation with visible and UV radiation darkens them and photodegrades the lignin in the wooden surface beneath the coating, leading to delamination and subsequent catastrophic coating failure due to the continued action of sun, rain, and biological factors. Many approaches to rectify this problem have been explored. Chemical modification of the surface with hexavalent chromium, reaction with various anhydrides, grafting of UV absorbers, and esterification are among the methods attempted. A second approach has been via the clear coating itself where UV absorbers, antioxidants, and ultrafine titanium and iron oxides have been added. However, these have had limited or no success in stopping photodegradation processes. Since the main cause of photodegradation is photooxidation of lignin in the wooden surface as a consequence of free radical reactions initiated by UV irradiation, the approach taken in the present study, in an attempt to enhance the weathering performance of clear-coated boards outdoors, was to delignify the surfaces of wooden boards and then apply clear coatings to try and retard possible photodegradation. Two different pretreatments were used. Firstly, chemical surface delignification with a peracetic acid treatment created a partial delignification to a depth of 2–3 mm while still retaining the structural integrity of the surface. Secondly, a preweathering treatment, which resulted in a 100-μm-deep delignification zone, was compared. The coatings applied to the exposure surface of the pretreated boards were either polyurethane or an acrylic varnish. The clear-coated boards were exposed to exterior and accelerated weathering regimes for 3 years or 3000 h, respectively. Pretreated coated boards did not darken and yellow on exposure but untreated coated boards did. However, despite apparently arresting photodegradative processes on board surfaces, there were no significant gains in the performance ratings of coated pretreated boards over those of coated untreated control boards. Explanations for this involve the effectiveness of design factors incorporated into boards for exposure trials. These factors were the fungicidal dipping of boards before coating, precoating the exposure surface with a reactive primer, and applying a full polyurethane system to the back side and edges of boards. Both pretreatments resulted in clear-coated board surfaces that performed very similarly on exposure outperforming systems reported previously. It was surprising to observe that the preweathering treatment, which resulted in a 100-μm-deep delignification zone, performed as effectively as the chemically pretreated boards with 2- to 3-mm treatment zone. However, preweathered surfaces had lost all lignin in the middle lamella and there was cell separation, whereas in peracetic acid-treated boards, there was more or less complete lignin removal from the cell corner middle lamella only and partial lignin removal from other cell wall regions. Furthermore, it is anticipated that refinements in treatment methods and coating formulations will bring desired benefits and future work should focus in this area.     

Experimental and theoretical behavior of exterior wood coatings subjected to artificial weathering

Several solvent- and water-borne exterior wood coatings were artificially weathered to study their performance behavior. Penetration and layer thickness were measured on unweathered samples and compared to theoretical estimates by means of measured basic parameters of coating and substrate. Color, surface roughness, gloss, and adhesion were monitored during aging, and the latter two were also calculated and compared to their experimental values. Theoretical values of gloss, and especially those of adhesion, were less successful on an absolute scale, but were in accordance with practical values on a relative scale. The influence of solid content, drying speed, and viscosity on penetration depth manifested itself clearly both in theory and in practice. In general, solvent-borne coatings performed well, but some water-borne coatings also showed good performance. By measuring the characteristics of a coating as described in this article, it is possible to rank the coatings and follow their weatherability. Finally, calculation of theoretical values proved a promising method for initial screening purpose.     

In-situ growth of MAX phase coatings on carbonised wood and their terahertz shielding properties

Electromagnetic interference (EMI) shielding materials have received considerable attention in recent years. The EMI shielding effectiveness (SE) of materials d...     

UV固化聚丙烯酸系水性木器涂料的合成与性能

研究了一种使用双烯单体来制备水性光固化木器涂料的方法。此方法不但可以简化生产工艺,而且涂膜性能优良。     

Comparisons of weathering performance of two automotive refinish coatings: A case study

The aim of this study was to compare the weathering performance of two commonly refinish coatings used in a domestic car manufacturer based on polyurethane (PU) and acid‐catalyzed alkyd‐melamine resins. The replacement of the alkyd‐melamine refinish with the PU system was shown to largely lower the reported fading behavior of the monocoat system. For better comparison between the refinish coatings, an original equipment manufacturers' (OEM) topcoat, cured at production line, was also used. Different characterization methods including DSC, atomic force microscopy, thermo gravimetric analysis, DMTA, and Fourier transform infrared spectroscopy were performed to elucidate the changes observed in the optical, mechanical, and weathering performance of studied coatings. It was found that the main reason for the inferior behavior of the acid‐catalyzed coatings compared with that of the PU and OEM was due to its low crosslinking density. The poor weathering resistance of the former coatings was attributed to its incomplete curing reaction and therefore, to its immatured film formation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effects of TiO2 and clay nanoparticles loading on weathering performance of coated wood

The weathering performance of Norway spruce coated with acrylic water based paint mixed with TiO₂ and clay nanoparticles were investigated. Uncoated specimens and specimens coated with unmodified paint were used as references. This work describes the effect of the nanoparticles in general and compares the performance of 1 wt% and 3 wt% of nanoparticles in particular on the weathering performance of the coated specimens. Accelerated ageing experiments were performed in an Atlas solar simulator to evaluate the ageing behaviour of the coated wood and characterized through colour measurements and Fourier transform infrared (FTIR) spectroscopy before, during and at the end of the exposure periods. In general, the addition of TiO₂ and clay nanoparticles slightly slowed down the coated specimens degradation compared to specimens coated with unmodified paint.     

Surface properties of impregnated and varnished Scots pine wood after accelerated weathering

In this study, the effect of accelerated weathering on the surface properties of Scots pine specimens impregnated with wolmanit‐CB, tanalith‐E, and adolit‐KD5 and coated with synthetic and polyurethane varnishes was investigated by measuring surface hardness, glossiness, and colour. Results showed that weathering caused an increase in the hardness of impregnated and varnished specimens, while it caused a decrease in the glossiness of specimens. Surfaces became rougher and darker after weathering in comparison with the initial surfaces of wood specimens. Positive values of the chromatic coordinates indicated that the wood surfaces changed from their original colour to a reddish and yellowish colour. The highest colour change was detected in the specimens coated with polyurethane varnish alone. Both copper‐based wood preservative treatment and varnish coating improved the surface properties of specimens in comparison with the surface properties observed on specimens coated with varnish alone.     

在我国经济“转型”发展中木器行业中涂料及涂装如何顺应

该文介绍了水性木器涂料在我国的发展及取得的成就,同时介绍水性涂料的涂装方式为手工和喷,辊、滚、浸印、帘幕等机械涂装;水性涂料的干燥,影响因素及涂膜弊病干燥设施等;指出涂装是涂料性能的体现而涂料配方的设计应满足涂装和施工要求。     

Inorganic/organic nanocomposite coatings: The next step in coating performance

Inorganic/organic hybrid materials have considerable promise and are beginning to become a major area of research for many coating usages, including abrasion and corrosion resistance. Our primary approach is to prepare the inorganic phase in situ within the film formation process of the organic phase. The inorganic phase is introduced via sol-gel chemistry into a thermosetting organic phase. By this method, the size, periodicity, spatial positioning, and density of the inorganic phase can be controlled. An important aspect of the inorganic/organic hybrid materials is the coupling agent. The initial task of the coupling agent is to provide uniform mixing of the oligomeric organic phase with the sol-gel precursors, which are otherwise immiscible. UV-curable inorganic/organic hybrid systems have the advantages of a rapid cure and the ability to be used on heat sensitive substrates such as molded plastics. Also, it is possible to have better control of the growth of the inorganic phase using UV curing. It is our ultimate goal to completely separate the curing of inorganic and organic phases to gain complete control over the morphology, and hence optimization of “all” the coating properties. Thus far, it has been found that concomitant UV curing of the inorganic and organic phases using titanium sol-gel precursors afforded nanocomposite coatings which completely block the substrate from UV light while maintaining a transparent to visible light. Also, it has been found that the morphology of the inorganic phase is highly dependent on the concentration and reactivity of the coupling agent. Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, October 27–29, 2004, in Chicago, IL.     

Surface properties of tannin-impregnated and varnished beech wood after exposure to accelerated weathering

The aim of this study was to determine selected surface properties of varnished beech wood impregnated with natural extracts after exposure to accelerated weathering. Beech wood samples were impregnated with aqueous solutions of 5 and 10% mimosa (Acacia mollissima) and quebracho (Shinopsis lorentzii) tannins. After weathering, colour changes (ΔL*, Δa*, Δb*, and ΔE*) in addition to scratch resistance and surface hardness values were calculated and evaluated. As a result of the weathering process, greater colour changes (ΔE*) were detected in the beech wood samples impregnated with tannins compared with the unimpregnated control samples. The least colour change occurred in the Tanalith-E-impregnated samples. Total colour change was adversely affected with tannin impregnation after the weathering processes. In terms of surface hardness and scratch resistance, the highest values were observed in the mimosa-solution-impregnated and control samples. Furthermore, it was found that scratch resistance and hardness values tended to increase during the first period of weathering and decreased thereafter. Regarding surface properties, the best results were obtained when polyurethane varnish was employed compared with the other varnish types.     

Surface modification of wood fibers using maleic anhydride and isocyanate as coating components and their performance in polystyrene composites

The effect of surface modification of various wood fibers [e.g. woodflour and chemithermomechanical pulp (CTMP) of hardwood aspen, and woodflour of softwood spruce] by precoating with only maleic anhydride (MA) and/or poly[methylene (polyphenyl isocyanate)] (PMPPIC) in the presence of benzoyl peroxide (BPO) on the mechanical performance of modified fiber-filled polystyrene (PS 201 and PS 525) composites has been studied. The effects of the concentration of fiber, MA, PMPPIC, and BPO on the mechanical properties of the composites have also been evaluated. As opposed to unmodified fiber-filled composites, most of the mechanical properties of the modified fiber-filled composites increased with an increase in the concentration of BPO, MA, and/or PMPPIC up to a certain limit, and then either decreased or levelled off. The properties improved even more when both MA and PMPPIC were used as compared with the use of only one of them. The optimum concentrations of BPO, MA, PMPPIC, and fiber vary according to the wood species, the nature of the fiber, and the type of polystyrene. Compared with woodflour, CTMP is believed to be by far the best as far as the mechanical properties of the modified fiber-filled composites are concerned.     

Structure and properties of multiphase particles and their impact on the performance of architectural coatings

Aqueous dispersions used as binders in low-pigmented solvent-free paint formulations have to cope with the challenge to simultaneously guarantee an excellent film formation and appearance as well as good block resistance and hardness. One strategy to fulfill these contradictory requirements is the employment of multiphase particles.

In this work it is proved that the structure of latex particles, synthesized by a two-stage emulsion polymerization process, can be correlated to the morphology and properties of the dispersion films as well as to the application properties of the corresponding paint films.

Two sets of model dispersions were made. In the first set, the hard/soft ratio was varied, in the second set the amount of the AA. The structure of the particles was determined by TEM, and a morphology map was derived. AFM demonstrated a clear correlation between the particle structure and the morphology of the latex film. Dynamic mechanical analyses verified the presence of two distinct polymers with the hard phase acting as a transparent filler. For the hard/soft series, the properties of the dispersion films such as block resistance, gloss and hardness could be attributed to their structure. A closer look on the block behavior revealed that it can be related to the tack and surface roughness of the dispersion film, but not to its internal strength. Solvent free emulsion gloss paints were formulated, and application tests performed. The properties of the paint films correlated very well with those of the dispersion films. The test results clearly show that dispersions of multiphase particles enable the formulation of solvent free paints with excellent film-forming ability in combination with high block resistance, hardness and gloss.     

Mechanical and optical properties of clay-based nanocomposites coatings for wood flooring

Clay-based nanocomposites coatings cured by UV light were prepared by four different types of dispersion equipment: a high-speed mixer, a ball mill, a bead mill and a three-roll mill. For each treatment, formulations were prepared at 1, 3 and 10 wt% of clay. A previous study had established the dispersion efficiency of each treatment and the effect of clay dispersion on UV curing. The present study relates to the effect of clay dispersion on mechanical and optical properties. The mechanical properties studied included abrasion resistance, direct and reverse impact resistance as well as Persoz hardness. Optical properties, such as haze, gloss, color and optical clarity were assessed. An analysis of variance (ANOVA) was conducted to evaluate the effect of clay loading and process type on mechanical and optical properties. A statistical analysis revealed that each property varied with the percentage of clay loading in every treatment. It was found that the quality of the clay dispersion strongly affected both mechanical and optical properties.     

Synthesis and properties of UV-curable waterborne unsaturated polyester for wood coating

UV-curable waterborne unsaturated polyesters for wood coatings were prepared. The effects of different polyols and acids on the properties of the UV-curable waterborne unsaturated polyesters were investigated. Several different unsaturated polyester prepolymers were prepared from three different polyols [ethylene glycol (EG), diethylene glycol (DEG), and propylene glycol (PG)] and three different acids [tetrahydrophthalic anhydride (THPAn), terephthalic acid (TPA), and trimellic anhydride (TMAn)]. UV-curable coating materials were formulated from the prepolymers and 2-hydroxy-2-methylphenyolpropane-1-one as a photoinitiator with distilled water as a diluent. Trimethylolpropane diallyl ether was used as an air inhibitor of cure. The dynamic mechanical studies showed the properties of those unsaturated polyesters were well correlated with their glass transition temperature behaviors. It was found that the unsaturated polyester prepared with 60/40 (mol %) TMAn/THPAn and the equimolar mixture of EG, DEG, and PG showed balanced coating properties such as good tensile properties and weatherability, as well as proper viscosity (ca. 2500 cps) when using distilled water as a diluent. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 695–708, 1998     

Zinc-nickel coatings: Relationship between additives and deposit properties

The electroplating of zinc-nickel alloys from a chloride bath containing two brighteners (a phenolic derivative and an unsaturated aromatic compound) and a levelling agent (an aromatic carboxylate) has been studied under different plating conditions. The composition and morphology of the alloys depended on the concentration of all the additives and also on the temperature. As a general effect, these additives smooth the deposit and refine the grain size. By means of scanning electron microscopy, it was possible to classify the deposit morphologies according to the type and concentration of the additives. The resistance of the alloys to corrosion was studied by means of a neutral salt-spray test.Prema S. A. Company     

新型水基涂料及其膜的性能

1　前言近年来 ,紫外固化水基涂料由于可减少空气污染 ,降低火灾危险 ,改善现场健康条件 ,提高安全性 ,尤其是以水作为紫外固化体系稀释剂 ,降低了有毒气体对环境的污染 ,解决了粘度控制和活性稀释剂影响固化膜性能之间的矛盾 ,而且易于清洗 ,因而得到广泛的工业应用。有 2种水基体系 :含外加表面活性剂的乳液或胶体分散液和水溶性或水分散型含亲水性基团的树脂体系。前者制备时通常加入表面活性剂 ,有助于形成稳定的乳液。但外加的表面活性剂影响最终产品的性能 ,即留在紫外固化膜中的表面活性剂使涂层具有水敏性。后一种体系不用加入表面…