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Investigation of Roughness and Adhesion Strength Properties of Pine and Poplar Wood Heat Treated in Air and under Vacuum after Artificial Aging
Heat treatment is an eco-friendly and efficient way to improve the defective properties of wood, such as its hygroscopic nature, the lack of dimensional stability, and low resistance against biological degradation, and to produce a green and sustainable wood material for construction and buildings. However, these treatments alter the substrates and could influence the performance of the coating products necessary to maintain the surface features in certain end-use sectors. In this study, the effects of heat treatment in air (HT) and under vacuum (VHT) on the surface properties of Scots pine (Pinus sylvestris L.) and poplar (Populus euramericana) wood were investigated. For this purpose, the samples were exposed to an artificial aging process. After the aging process, surface roughness and the adhesion strength behavior of the samples were measured. After the HT and VHT, poplar and pine wood samples showed different roughness. While the roughness value parallel to the fibers decreased in poplar wood, it increased in pine wood. The roughness value perpendicular to the fibers increased in both tree species. The maximum roughness value after UV aging was 62,622 in the VHT-200 group. Although with the UV ageing treatment, the adhesion strength was decreased in the samples heat treated in air, it was increased in the samples subjected to vacuum heat treatment. A lower loss of adhesion strength was observed in the heat-treated samples processed under vacuum compared to the heat-treated samples processed in air.
Correction: Physical and mechanical properties of wood treated with chitosan-caffeine formulations
Adhesive Bonding of Scots Pine Wood from the Szczecinek Forest District for the Production of Garden Equipment: An Experimental Investigation
This work aimed to determine the gluability of pressure-impregnated pine wood with two protection agents used in production technologies for garden equipment and their effect on the strength, water resistance and thermal resistance of joints, as well as their susceptibility to aging. The tests were carried out on Scots pine wood (Pinus sylvestris L.) purchased from the forest districts of the Regional Directorate of State Forests in Szczecinek town, Poland. For the impregnation, two commercial protection agents were used. The pressure impregnation of the elements and gluing with the PUR adhesive were carried out by a garden furniture manufacturer. The strength and durability after aging tests of glued joints were performed in accordance with the procedure described in Technical Approval No. AT-15-2948/00 and the PN-EN ISO 9142 standard. The collected experimental data can be used in technological solutions, mainly for processes which involve gluing wood after impregnation.
Evaluation of Surface Roughness Parameters of HDF for Finishing under Industrial Conditions
One of the most important properties of the surface of wood-based panels is their roughness. This property determines the way of working with the material in the processes of gluing and surface varnishing. The aim of this study was to determine the effect of various sanding belt configurations and the feeding speed of the conveyor belt during grinding on the surface roughness of high-density fiberboards (HDF). The research material was prepared under industrial conditions. Three types of boards were selected for the tests. After grinding, the roughness parameters were measured both transversely and longitudinally relative to the grinding direction, using a Mitutoyo SJ-210 profilometer and the optical method. Based on ANOVA analysis of the data, it was found that the type of HDF boards used and the configuration of the abrasive belts had a statistically significant impact on the roughness. The samples for which the grinding process was performed with sanding belts of the highest grain size had the lowest roughness. For the amplitude roughness parameters, the direction of roughness measurement had a significant influence. These results may provide valuable guidance for the furniture industry in the preparation of HDF for furniture production.
Adhesion of varnish coatings as a background for analogue and digital printing technologies
In analogue and digital printing technologies, from 3 up to 12 layers of lacquer products are applied. Technological parameters significantly influence the adhesion in the coating system. This article refers to the analysis of the influence of selected technological parameters, such as the number of layers, energy doses distributed by the radiators, and line speed, on the topography and adhesion of varnish coatings formed in the process of varnishing with rollers and UV-curing systems. The appropriately prepared surface can be used as a background layer for the analogue and digital printing technology. Manufacturers must adapt the production process to the particular varnish to obtain finished products with the best possible performance properties. The state of surface free energy and finally adhesion can be assessed by theoretically determining the possibility of an adhesive bonding between the product and the substrate, taking into account the assumptions of the adsorption theory of adhesion and measurement of the contact angle (Θ). An experimental confirmation of adhesion measurements included removing the coatings from the substrate via stamps glued to the coating.
Gloss level, type of paper and colour of HDF boards finished with the energy-saving acrylic paint system
The global drive to eliminate mercury is stimulating the development of LED lamps for UV curing of coatings. Despite its many advantages, the transition to this system in the furniture industry presents technological issues. This paper aimed to determine the impact of the paint line’s individual technological and process parameters on the coating’s optical properties, such as colour and gloss of furniture components made of white-coloured light-weight boards. Samples were prepared under the conditions of an industrial paint line using LED and traditional mercury lamps at the rate of 50 m/min. The colour was tested using the CIELAB system on a BYK GARDNER spectrophotometer, while the gloss was measured using the PICO GLOSS meter. Based on the data obtained, the optical parameters were found to be highly stable irrespective of the power drop in the LED lamps. The coordinates L*, b* and gloss G were affected by the amount of topcoat and basecoat, the number of coats, the mercury lamps’ power and the panel grinding programs used. The results of the tests showed that high L* and b* values could be achieved by increasing the number of overlays. This solution also ensures less basecoat and topcoat consumption, contributing to large material savings.
Gloss of Varnished MDF Panels Veneered with Sanded and Thermally Compressed Veneer
The objective of this study was to investigate the gloss of different types of commercially manufactured varnish systems, including water-based (WB), polyurethane (PUR) and UV-cured (UV), applied on veneered MDF panels with sanded and thermally densified alder and birch wood veneers. The varnishes were applied at various numbers of layers on veneered panels. The gloss was measured at three angles of incident light: 20°, 60° and 85°. Statistical analysis showed that the type of varnish, the number of layers, the pre-treatment process, the wood species and direction of wood fibers significantly affect gloss of the coatings of veneered MDF panels. The type of varnish had a dominant effect on gloss. The highest gloss values were measured for the UV-varnished surface, and the lowest for WB- and PUR-varnished surfaces. Gloss was enhanced with an increase in the number of layers. Birch veneer provided higher gloss values compared to alder veneer. The gloss values measured along the wood fibers were higher than those measured across the fibers. No significant differences were found between the coatings created on sanded and thermally densified veneers for the average gloss values measured along the fibers at angles 60° and 85°. This study could have practical applications for producing value-added furniture elements using low-value wood species pre-treated by thermal compression.
Influence of Finishing Process Parameters of HDF Boards on Selected Properties of Coatings in Modern UV Lines and Their Relation to Energy Consumption
This study analyzes the influence of energy generated by emitters on the adhesive properties of varnish coatings in multilayer UV systems. The experimental material, in the form of a cell board finished with UV varnish products, was prepared on a prototype line under the conditions of Borne Furniture in Gorzów Wielkopolski. The roughness and wettability were measured using a OneAttension tensiometer integrated with a topographic module, taking into account the Wenzel coefficient. The adhesion of the examined systems was verified using the PositiTest AT-A automatic pull-off device. Energy consumption by the prototype production line was compared to the standard line, utilizing mercury emitters and mercury emitters with added gallium. Energy consumption was calculated for selected variants. The influence of the Wenzel coefficient on the wettability angle was observed. Significant differences between contact angles (CA and CAc) were noted for coatings formed with sealers (stages I and II). The largest discrepancies, reaching up to 30 degrees, were recorded at the lowest UVA and UVV doses of 26 mJ/cm2. In adhesion tests, values below 1 MPa were obtained. Insufficient energy doses in the curing process of UV systems led to delamination between the coatings. Five variants were selected where delamination within the substrate predominated (˃90% A) and were characterized by the lowest energy consumption in the processes. Topographic images helped identify the presence of various surface microstructures at different stages of the production cycle. The greatest energy savings, up to 50%, were achieved in stages III and IV of the technological process.
The Impact of Sanding and Thermal Compression of Wood, Varnish Type and Artificial Aging in Indoor Conditions on the Varnished Surface Color
Mechanical and Chemical Resistance of UV Coating Systems Prepared under Industrial Conditions
In the upcoming years, it is expected that more furniture will be built from honeycomb panels due to the growing demand for lightweight, long-lasting furnishings. High-density fiberboard (HDF), previously used in the furniture industry as back walls in box furniture or drawer components, has become a popular facing material used in the production of honeycomb core panels. Varnishing the facing sheets of lightweight honeycomb core boards with the use of analog printing technology and UV lamps is a challenge for the industry. The aim of this study was to determine the effect of selected varnishing parameters on coating resistance by experimentally testing 48 coating variants. It was found that the interactions between the following variables were crucial in achieving adequate resistance: lamp power, the amounts of varnish applied, and the number of layers. The highest scratch, impact, and abrasion resistance values were observed for samples with optimal curing provided by more layers and maximum curing with 90 W/cm lamps. Based on the pareto chart, a model was generated that predicted the optimal settings for the highest scratch resistance. Resistance to cold liquids made with a colorimeter increases with lamp power.
Interlayer Adhesion of Coating System in Analogue and Digital Printing Technologies Formed on Lightweight Honeycomb Furniture Panels
This article concerns research into the influence of the energy dose distributed by UV lamps on selected parameters of varnish coatings formed during the varnishing process of lightweight cellular panels. The lightweight cellular board used in the study was made according to an innovative solution. The surface finishing of the boards was carried out using the roller method in combination with digital and analogue printing under industrial conditions. Contact angle measurements of the obtained varnish coatings were carried out, from which the surface free energy was calculated. In addition, interlayer adhesion was assessed by pull-off tests. Irrespective of the radiation dose, higher contact angle values (54.3–89.9°) were recorded for the last two applied layers (base coat 2 and base coat 3) than for the other coatings (39.6–64.1°). For all systems tested, the γsp component showed lower values (2.25–28.99 mJ/m2) than γsd (28.66–32.80 mJ/m2). The adhesion test results ranged from 0.5 to 0.9 MPa, although with varying types of delamination. Based on the test results, the most favourable variants from the furniture manufacturer’s point of view were selected that provided the desired level of adhesion, in which cohesive damage located within the substrate (A) predominated.
Mechanical and Chemical Resistance of UV Coating Systems Prepared under Industrial Conditions Using LED Radiation
The furniture industry constantly strives to search for ecological and cost-effective solutions in the production of wood-based composites. It is anticipated that furniture with a honeycomb core and HDF-facing will gain market share. Understanding how specific technical and procedural factors on the finishing line affect the resistance of coatings on furniture elements made of honeycomb boards was the main goal of the study. With the use of a digital microscope, the roughness of two different types of HDF was tested. On the industrial UV LED+Hg finishing line, 198 different surface coating variations were produced by applying five or six layers of varnish applied, ranging from 3 to 30 g/m2 and hardening them with various surface power densities. On the basis of statistical tests, the influence of individual factors on abrasion, impact, and scratch resistance was determined. The nanointendence test of the coatings was used to measure the hardness and elasticity modulus. The coloring caused by coffee traces was checked using a colorimeter. The findings confirm the conception that LED+Hg lamp modules can replace mercury and gallium-doped mercury lamps.
Gloss Level of HDF Finished with Different Numbers of Layers and Hardened with UV Hg-Ga Lamps of Selected Power
A key feature of varnish coatings on furniture surfaces is their optical properties, which often determine customers’ purchase choices. Furniture may be produced using various boards, which are much cheaper than wood-based materials. For their finishing, among others, UV-cured varnish products are used. The aim of this study was to determine the effect of different types of HDF boards, the amount of basecoat and topcoat applied, the number of layers, and the different lamp powers used for hardening on the gloss of coatings obtained using UV technology. The gloss was tested with a photoelectric apparatus. An auxiliary parameter in the assessment of the gloss of the coatings was the surface roughness, which was measured with the Mitutoyo SJ-210 Analysis of variance (ANOVA) was used to obtain the results. Statistical considerations showed that the amount of topcoat applied, the power of the lamps, and the interactions between them had the greatest impact on gloss, followed by the number of layers. In general, the gloss of the coating decreased with a decrease in lamp power in the range of 120–60 W/cm and with an increase in the amount of topcoat applied.