Thermochemical and isoconversional kinetic analysis of a polyester–epoxy hybrid powder coating resin for wood based panel finishing

Powder coating is an established technology especially for the surface finishing of metallic substrates for example in the automotive industry. Moreover, powder technology holds also great promises for the coating of non-conventional substrates like plastics or wood due to the lack of solvents and good recoverability. Here, low-temperature curing resins are required and especially mild processing conditions are demanded by the substrates. Advanced characterization methods need to be established that allow the precise balancing of the processing conditions required for adequate melting, flowing and curing of the powder with the process conditions that can be tolerated by the temperature-sensitive substrates. In the present contribution it is shown that differential scanning calorimetry (DSC) in combination with isoconversional kinetic analysis (ICKA) provides great potential for this purpose. DSC is a standard thermo-chemical method that can be successfully used to study both the melting and curing processes of powder coatings and to determine, for example the glass transition temperature of the cured coating directly from the measured thermograms. However, still more information can be extracted from the enthalpy signals when more sophisticated methods of data post-treatment and analysis are employed. Isoconversional kinetic analysis techniques such as the Kissinger–Akahira–Sunose (KAS) or the advanced Vyazovkin (VA) approaches allow calculating the time-dependencies of physical and chemical processes at various temperatures based on the estimates of activation energies which are obtained from DSC raw data. These analyses allow for example to calculate the time required for a certain degree of cross-linking in the coating after processing the coating under specified curing conditions. In the present contribution the application of ICKA of DSC measurements for the analysis of the flowing and curing behaviour of a powder coating based on a polyester–epoxy hybrid resin is illustrated and the potential of this approach to predict optimal curing times for arbitrary curing temperatures is demonstrated. This is especially useful when temperature-sensitive substrates like wood-based panels are coated. Additionally, the potential to relate the thermo-chemical properties of the powder coating to the surface properties of the coated substrates is discussed.     

Influence of thermo-analytical and rheological properties of an epoxy powder coating resin on the quality of coatings on medium density fibreboards (MDF) using in-mould technology

Powder coating of engineered wood panels such as medium density fibreboards (MDF) is gaining industrial interest due to ecological and economic advantages of powder coating technology. For transferring powder coating technology to temperature-sensitive substrates like MDF, a thorough understanding of the melting, flowing and curing behaviour of the used low-bake resins is required. In the present study, thermo-analysis in combination with iso-conversional kinetic data analysis as well as rheometry is applied to characterise the properties of an epoxy-based powder coating. Neat resin and cured powder coating films are examined in order to define an ideal production window within which the resin is preferably applied and processed to yield satisfactory surface performance on the one hand and without exposing the carrier MDF too high a temperature load on the other hand to prevent the panel from deteriorating in mechanical strength. In order to produce powder coated films of high surface gloss – a feature that has not yet successfully been realized on MDF with powder coatings – a new curing technology, in-mould surface finishing, has been applied.     

Powder coating of veneered particle board surfaces by hot pressing

The powder coating of veneered particle boards by the sequence electrostatic powder application – powder curing via hot pressing is studied in order to create high gloss surfaces. To obtain an appealing aspect, veneer sheets were glued by heat and pressure on top of particle boards and the resulting surfaces were used as carrier substrates for powder coat finishing. Prior to the powder coating, the veneered particle board surfaces were pre-treated by sanding to obtain good uniformity and the boards were stored in a climate chamber at controlled temperature and humidity conditions to adjust an appropriate electrical surface resistance. Characterization of surface texture was done by 3D microscopy. The surface electrical resistance was measured for the six veneers before and after their application on the particle board surface. A transparent powder top-coat was applied electrostatically onto the veneered particle board surface. Curing of the powder was done using a heated press at 130 °C for 8 min and a smooth, glossy coating was obtained on the veneered surfaces. By applying different amounts of powder the coating thickness could be varied and the optimum amount of powder was determined for each veneer type.     

New developments in radiation-curable powder coatings

Radiation-curable powder coatings are now in the early stages of commercialization. For years, the coatings industry has sought ways to lower the curing temperature of powder coatings. UV-curable powder coatings offer the possibility of curing powder coatings at temperatures as low as 120°C. Radiation-curable powder coatings also offer high cure speed and relatively low energy consumption. As each application requires its own coating performance, two different maleate-vinyl ether-based binders for UV-curable powder coatings have been developed. With these binders the balance between flexibility and hardness of the coating can be adjusted with proper formulation. In this paper, the curing characteristics and coating performance of several UV-powder coating formulations are described. In addition, a comparison between conventional powder coatings and UV-powder coatings is provided. Presented at the 26th International Waterborne, High-Solids, and Powder Coatings Symposium, February 10–12, 1999, New Orleans, LA. P.O. Box 615, 8000 AP Zwolle, The Netherlands.     

Mechanical strength and wear resistance of protective coatings applied by fluidized bed (FB)

This study deals with the interrelation between the thermo-rheological behaviour of an epoxy-based powder coating system and its mechanical strength and wear endurance.

Matte-finish protective polymeric films deposited by electrostatic fluidized bed (EFB) and conventional hot dipping fluidized bed (CHDFB) on metal substrates were examined. First, the analysis of thermo-rheological behaviour of the epoxy-based powder coating system was detailed. Secondly, the adhesion strength and wear endurance of polymeric films was related to the thermo-rheological behaviour of the starting material formulation. Finally, based on the experimental data, generalized scratch and wear map, in which the overall mechanical performance of the matte-finish polymeric films at different curing levels is reported, was usefully provided.

The experimental findings lead to further advances in the understanding of the mechanisms involved in the establishment of the overall mechanical performances of fluidized bed (FB) deposited polymeric films. They also provide important indications for the settings of curing parameters or preheating temperatures in FB coating processes as well as for the development of new powder coating formulations.     

Characterization of infrared absorption by powder coatings on steel panels

Interest in faster curing systems has led to infrared (IR) curing of powder coatings. The efficiency of IR heating depends on both the coating spectral absorption characteristics and the spectral emissions of the infrared source. Coating spectral absorptivities were measured with an FTIR spectrometer with an integrating sphere. Using the spectral absorptivities and normalized blackbody emissions, integrated average absorptivities and overall radiant efficiencies were calculated for blackbody emitter temperatures ranging from 500 to 3000 K (440 to 4940°F). The effects of several powder coating parameters on spectral absorptivities, integrated average absorptivities, and overall radiant efficiencies were studied. School of Textile & Fiber Engineering, Atlanta, GA 30332-0295. 1079 West Nancy Creek Dr., Atlanta, GA 30319.     

Influence of the curing temperature of a cataphoretic coating on the development of filiform corrosion of aluminium

Aluminium alloys are known to be particularly sensitive to filiform corrosion. The initiation of this particular type of corrosion is related to different parameters such as the presence of defects, the permeability of the coating to water and oxygen, the adherence of the paint system and the presence of salts.In this work, the filiform corrosion resistance of Al 6016 substrates coated with a cataphoretic paint was studied. The curing of the coating was performed at different temperatures (185, 175, 165, 155 and 135 °C) in order to modify its mechanical properties and its permeability to oxygen.The paint properties were studied by different techniques allowing the estimation of the degradation of the metal–primer system and giving some information about intrinsic paint properties.The corrosion protection of the coating was evaluated by a normalized filiform corrosion test and by electrochemical impedance spectroscopy on scratched samples. The glass transition value and the internal stresses of the cataphoretic coatings obtained for different curing temperatures were determined by a stressmeter equipment.This study enabled us to underline the influence of the curing temperature on the intrinsic properties of the coatings such as the glass transition temperature, the internal stresses, the adherence, the permeability and the corrosion protection properties.     

聚酯树脂粉末涂料的固化行为

用差示扫描量热法(DSC)对固态条件下聚酯/TGIC(triglycidyl isocyanurate)体系的非等温固化反应动力学进行了研究。根据DSC和热重（TG）的分析结果,对聚酯粉末的固化过程及热稳定性进行了探讨,通过温度-升温速率图外推法确定了该体系的凝胶温度、固化温度和后固化温度分别为113、146和195℃。采用Kissinger方程、Doyle-Ozawa方程和Crane方程对DSC数据进行分析,得到了固化反应的平均表观活化能65.71 kJ·mol^-1,频率因子8.50×106 min^-1、反应级数0.95,建立了该树脂体系的固化动力学模型。讨论了固化反应速率、固化度、固化温度与时间等关系的变化规律及影响因素,为优化铝型材用粉末涂料聚酯体系的固化工艺提供了理论基础。     

Influence of the curing temperature of a cataphoretic coating on the development of filiform corrosion of aluminium

Aluminium alloys are known to be particularly sensitive to filiform corrosion. The initiation of this particular type of corrosion is related to different parameters such as the presence of defects, the permeability of the coating to water and oxygen, the adherence of the paint system and the presence of salts.

In this work, the filiform corrosion resistance of Al 6016 substrates coated with a cataphoretic paint was studied. The curing of the coating was performed at different temperatures (185, 175, 165, 155 and 135 °C) in order to modify its mechanical properties and its permeability to oxygen.

The paint properties were studied by different techniques allowing the estimation of the degradation of the metal–primer system and giving some information about intrinsic paint properties.

The corrosion protection of the coating was evaluated by a normalized filiform corrosion test and by electrochemical impedance spectroscopy on scratched samples. The glass transition value and the internal stresses of the cataphoretic coatings obtained for different curing temperatures were determined by a stressmeter equipment.

This study enabled us to underline the influence of the curing temperature on the intrinsic properties of the coatings such as the glass transition temperature, the internal stresses, the adherence, the permeability and the corrosion protection properties.     

节能型固化体系在环氧粉末涂料中的应用

本文提出ＬＣＡ－咪唑固化体系在环氧粉末涂料中的应用及其所显示的节能特性,对环氧粉末涂料的几种主要固化体系作了比较,分析了ＬＣＡ－咪唑固化体系显著的节能效果,从而揭示了ＬＣＡ－咪唑固化体系在这一领域广阔的应用前景。     

EB-30防腐环氧粉末涂料体系研究

合成出了一种新型酚类固化剂EB-30，研究其性能。以EB-30为固化剂，配制粉末涂料，研究其固化行为、动力学参数及涂膜性能，旨在提高涂膜防腐蚀性。     

耐候型聚酯粉末涂料的研究进展

针对户外用粉末涂料的老化,介绍了国内外耐候型聚酯粉末涂料的研究进展。阐述了其目前在树脂合成与改性、固化体系和固化剂选择及添加特殊助剂等方面的发展方向,并简要分析了其抗老化机理。指出作为粉末涂料的主要组成物质,聚酯和固化剂的性能对粉末涂料的耐候性起着至关重要的作用,同时添加纳米粒子改性粉末涂料也是提高其耐候性的一种新型有效的方法。     

UG-1紫外光固化粉末涂料研制

用可紫外光固化的星形支化丙烯酸酯树脂作主要成膜物 ,制成了UG 1紫外光固化粉末涂料。对该涂料涂膜理化性能进行了测试 ,考察了影响涂膜性能的重要组分光引发剂、流平剂用量及熔融粘度随温度变化情况 ,确定了熔融流平后紫外光照时间。结果表明 ,UG 1紫外光固化粉末涂料涂膜具有优异的理化性能 ;光引发剂和流平剂较佳用量 (质量分数 )分别为 2 .0 %～ 3.0 %和 0 .6 %～ 0 .9% ;熔融流平温度 110℃ ,熔融流平后紫外光照时间仅为 3s。     

Anticorrosive properties of an epoxy-Meldrum acid cured system catalyzed by erbium III trifluromethanesulfonate

New low curing temperature powder epoxy coatings cured with Meldrum's acid and catalyzed by the use of erbium III trifluoromethanesulfonate have been formulated. Their curing kinetics and anticorrosive properties have been studied and compared with a system commonly used in industry (o-tolylbiguanide/epoxy resin) and with an epoxy powder coating homopolymerized by erbium III trifluoromethanesulfonate. Three different tests of anticorrosive properties (EIS, AC/DC/AC and salt fog spray) have been used together with an adherence test, in order to establish the best system. Results show that systems crosslinked with Meldrum's acid and catalyzed with erbium triflate present very fast curing kinetics and very good anticorrosive properties. The technique AC/DC/AC has shown its ability to evaluate properly and much faster than other techniques the anticorrosive properties of powder coatings.     

环氧涂膜交联密度与耐蚀性

环氧涂膜的交联密度表征涂膜网络结构的致密程度。着重叙述环氧涂膜交联密度与防水蒸汽透过量的关系;高固体分环氧铁红涂料和环氧铁红粉末涂料形成涂膜的交联密度与涂膜耐蚀性的关系。TY650聚酰胺与胺加成物制备复配型固化剂明显提升环氧涂膜的耐蚀性;新开发的快干型固化剂可使环氧粉末涂料在175％／3min实现固化,为节能型环氧粉末涂料品种增添了新成员。     

低温固化环氧粉末涂料制备及性能研究

通过转矩流变仪用E-12型环氧树脂和TC-125固化剂及其他助剂在90℃下熔融混合10min,然后在平板硫化机上冷压3min,最后经过球磨机粉碎制得环氧粉末涂料。制得的粉末涂料和漆膜经过差示扫描量热法和红外光谱分析．并讨论了固化剂用量、升温速率等对涂料性能的影响。结果表明：该粉末涂料可实现低温固化,固化条件为120℃下恒温固化35min;固化剂用量为28％时,涂膜的各项物理性能良好。     

木质地板用环氧树脂粉末涂料研究进展

对木质地板用环氧树脂粉末涂料的研究进展进行分析。主要从三个研究方向即UV固化环氧粉末涂料、双重固化体系和对传统环氧树脂粉末涂料及其固化剂的改性,对木质地板用环氧粉末涂料低温固化技术进行了探讨。     

Properties of powder coatings in load carrying construction

The present study describes the mechanical behavior of powder coatings used under very high compressive loads in clamping force joints. Carboxyl functional polyester powder coatings cured with hydroxyl functional β-hydroxyalkylamides with variations in coating thickness and amount and type of filler, have been studied. The coatings were subjected to conventional tests for coatings and polymers and also to specially designed tests developed to study the behavior of powder coatings in clamping force joints. The specially designed tests were used to study the coatings under compressive loads, and the relation between the results from these test methods and from conventional tests is discussed. The results show the importance of coating thickness in order to achieve the desired mechanical properties of a coating when used under high compressive loads. These loads put high demands on the stability of the coating, and the defects must be kept to a minimum. Increased thickness will give rise to more defects in the coating, especially voids and blisters due to the evaporation of water formed during the curing of the polyester powder coating. The surface roughness of the coating is also affected by the coating thickness, but the main influence originates from the type and amount of filler used. A rough surface will give rise to stress concentrations and increased plastic deformations in the coating, impairing the properties of the clamping force joint.     

A mechanistic study of the effect of pigment loading on the appearance of powder coatings: The effect of surface topography on the optical properties of powder coatings: Modelling and experimental results

Gloss is a critical property for many powder coating applications and is related to the amount of light reflected by the coating layer on a substrate. Gloss of powder coatings can, depending on the composition, vary from excellent to matt. It is well known in the powder coatings industry that increasing loadings of pigment, especially TiO₂, causes a detrimental loss of gloss. In order to understand the cause of this phenomenon two questions have to be addressed: firstly, what is the relation between the optical properties and the surface topography of the powder coating and, secondly, how do the powder coating composition and curing conditions affect the surface topography? In order to answer the first question, the typical features of the surface of a cured powder coating have been studied in detail. Using a white light interferometer, it has been shown that the surface topography consists of both short wave and long wave patterns. Each of these patterns could be described by using two statistical parameters only, the root mean square height of the roughness and its correlation length. The effect of both the short and long wave roughness on the gloss has been simulated with a single wave pattern model, based on an approximation of the Kirchoff scattering theory [9]. These simulations illustrated that neither the short nor the long wave roughness on itself determines the optical properties. In order to quantify the combined effect of the long and short wave surface features a two-scale modelling approach was followed. The predictions of this model were in good agreement with experimental gloss data of coatings containing different amounts and types of pigments.     

Si3N4粉体的表面改性及其对立体光刻成型的影响

传统的陶瓷加工技术成本高、周期长、缺陷多,难以生产高性能陶瓷,立体光刻技术是制造形状复杂陶瓷零件的一种高效手段。纯Si₃N₄粉体的折射率(n=2.1)与树脂(n=1.49)的折射率相差较大,光散射严重,导致其陶瓷浆料的固化深度较低,很难直接利用立体光刻技术成型Si₃N₄陶瓷零件。为解决Si₃N₄粉体难以光固化的难题,本研究采用表面包覆有机物和表面氧化两种方式改性Si₃N₄粉体,并对比两种方式对Si₃N₄粉体光固化特性的影响规律。结果表明,包覆实验后,有机物单体经过一定反应时间后可均匀附着在Si₃N₄粉体表面;氧化处理后,Si₃N₄粉体表面形成非晶SiO₂层,该层均匀附着在粉体表面上。原始Si₃N₄粉体的固化深度仅为20 μm,经过包覆改性和800 ℃氧化4 h后,Si₃N₄粉体的固化深度分别可提高到40 μm和50 μm,两种方式均能有效提高原始Si₃N₄粉体的固化深度。