Optimization And Interface Regulation Of The UV-digital Printing Processing On Wood-based Materials

UV digital inkjet printing is an emerging furniture surface decoration technique.How to obtain good adhesion and wear resistance is a key issue that researchers need to solve.In this thesis firstly,medium-density fiberboard(MDF)was selected as the research object.The surface roughness and surface contact angle of the MDF were measured after treated by sandpaper with different meshes to understand the effect of sandpaper treatment.By characterizing the performance of UV-digital coatings,the optimal mesh number of sandpapers for MDF treatment was determined,which provides a theoretical basis for the surface treatment of MDF.Nest,the surface of the MDF is painted with four different types of primers to characterize the performance of the UV inkjet coating to achieve the best primer coating process for MDF.Then,the different surfaces of three representative solid wood sawn timbers were selected as the research objects.The morphology,specific surface area and surface pore size distribution of the sawn timber were analyzed,as well as the surface roughness and surface contact angle of the sawn timber surface after grinding.By characterizing the relevant properties of the UV-jet coating,the effect of solid wood species on the performance of the inkjet coating and the interface properties between the coating and the wood were clarified.The results provide theoretical guidance for improving the interface bonding strength of the UV inkjet printing.Finally,plywood was used as the substrate to compare and analyze the performance of the UV inkjet printing and ordinary roller UV coating.Comprehensive evaluation of the advantages and disadvantages of the two finishing processes provides a theoretical basis for the subsequent improvement of the performance of UV inks.The main conclusions of the thesis are give below:(1)Surface roughness has a huge impact on the surface finish of MDF.Treated with five different meshes sandpapers from 60 # to 400 #,the surface roughness of the MDF was gradually reduced with the increase sandpaper mesh number.The lower surface roughness and the smaller surface contact angle of the MDF,which is more conducive to the surface wetting of the MDF.The gloss and adhesion of the coating obtained after UV inkjet printing were better.After 400 # sandpaper sanding pretreatment,UV printing is carried out,and the obtained coating has the highest gloss and adhesion,and have the best inkjet printing effect.(2)Compare four primer treatment methods,including PU white primer,PU varnish,white NE primer,NE varnish treatmt MDF Comparing the four primer,the UV-painted coating of PU varnish has better adhesion,hardness,gloss,wear resistance and hygroscopicity than the other three primers applied.So,the PU varnish treatment was the best.However,the PU varnish was not able to concealthe color of the MDF substrate,and the UV inkjet pattern appeared dim and not beautiful enough.Comparing the UV inkjet coating properties after different primers preatments,pretreatment with a white NE or PU primer was a better choice.Applying two primers can improve the adhesion,gloss and other properties of the UV-coated coating.(3)Using Pinus sylvestris var.mongolica,Betula platyphylla,Suk Fraxinus excelsior L,three surfaces of sawn timber were treated with 400 # sandpaper,then UV inkjet printing.After 400 # sandpaper treatment sawn wood surfaces,the surface roughness of the sawn wood surfaces varied.Comparing all the cross-sections of wood,the roughness of Pinus sylvestris var.mongolica is the largest.Among all the radial section,Betula had the highest roughness.Among all the chord section,the roughness of Betula platyphylla Suk is the largest.The adsorption isotherms of the three sawn timbers belong to the type III isotherm.Mesoporous content of Pinus sylvestris var.mongolica is the largest,Betula platyphylla Suk is the second,Fraxinus excelsior L is the smallest.After UV inkjet printing,the coating on Betula platyphylla Suk had the highestgloss.The Fraxinus excelsior L cross-section had the best coating adhesion.Over all,Fraxinus excelsior L had good abrasion resistance.The chromatic aberration analysis showed Pinus sylvestris var.mongolica exhibited highest brightness,while Betula platyphylla Suk was the lowest.This phenomenon led to better spray painting quality of Pinus sylvestris var.mongolica var.Betula platyphylla Suk sample was poor in painting quality.Due to the presence of the trachea and the vessel opening,the ink penetration was obvious and the pattern was not continuous.For transverse surface,the growth-ring pattern appeared beneath the coating.SEM topography analysis showed that the UV inkjet coating was a thin layer on the surface of the sawn timber,and the coating was only attached to the section.Infrared analysis showed that the ink did not chemically react with wood.It indicated that the UV inkjet coating was only physically attached to the surface of the sawn timber.Comprehensive comparison of the performance,materials lighter color,Solid wood substrate with less pores has a better inkjet effect.(4)The performance of UV lacquer and UV inkjet printing was compared using plywood substrates.Due to uneven thickness and porosity of the plywood surface,the gloss,adhesion and wear resistance of UV inkjet priting were not as good as UV lacquer.The UV inkjet coated specimen and the uncoated plywood specimen show the same effect on theanti-mildew performance.After four weeks,the surface infection area of the specimen was more than 75 percent,the mildew resistance was poor.The UV lacquer samples showed good mildew resistance,and the surface infection area was less than 75 percent after four weeks test,which was suitable for making furniture products.After ultraviolet aging,the surface of the UV paint degrades,resulting in a decrease in brightness ?L*,darkening of the color,and an increase in yellowness.