| Impregnated paper veneered blockboard is a decorative board formed by pressing impregnated paper on the blockboard substrate.It has the advantages of stable performance,safety,and environmental protection,and has received extensive attention in the field of customized furniture.An in-depth study of the preparation process of impregnated paper veneered blockboard is of great significance to optimize its performance and improve the quality of its products.Meanwhile,it also helps to broaden the market scale of this decorative board.In the structure of the impregnated paper veneered blockboard,the equilibrium layer is an important part that is used to connect the impregnated paper and the blockboard substrate.Therefore,it is of great importance to explore the effect of the equilibrium layer on the physical properties of impregnated paper veneered blockboard.In this paper,the main object of the research was the equilibrium layer in impregnated paper veneered blockboard.The effects of the equilibrium layer type,equilibrium layer pressing process,and the equilibrium layer pretreatment on the performance of impregnated paper veneered blockboard were analyzed.The main conclusions of the paper were as follows:(1)Poplar veneer(0.7 mm and 1 mm),beech veneer(0.7 mm),paramichelia baillonii veneer(0.5 mm),and multilaminar decorative veneer(0.5 mm)were selected as the equilibrium layers for the preparation of impregnated paper veneered blockboard.The results showed that the surface bonding strength of impregnated paper veneered blockboard prepared from five types of equilibrium layers ranged from 1.14 to 1.5 MPa,which was much higher than the requirements in GB/T 34722-2017.The surface crack resistance of 5 kinds of equilibrium layers prepared by impregnated paper veneered blockboard could only reach the lowest grade(Grade 1).The surface cracks were different depending on the equilibrium layer used,and the specimens prepared with0.7 mm poplar veneer as the equilibrium layer had the least number of cracks.This was because all five types of equilibrium layers exhibit obvious anisotropy.Their total dimensional dry shrinkage was higher than 1.3%,and uneven dimensional dry shrinkage occurred during the crack resistance test.The transverse tensile strength of the five equilibrium layers was lower than 2 MPa,and they were unable to resist the tensile stress of the blockboard substrate during the surface crack resistance test.(2)The impregnated paper veneered blockboard was prepared by two lamination processes,one-time lamination and secondary lamination.The study showed that the two lamination processes had less effect on the surface abrasion resistance,surface scratch resistance,and water absorption thickness swelling rate of impregnated paper veneered blockboard.When using the onetime lamination process,the bonding interface was tight due to the equilibrium layer/the blockboard substrate was experienced twice hot pressing.The surface bonding strength and the transverse static strength of the impregnated paper veneered blockboard were 1.06 MPa and 0.96 MPa,respectively,which were 10% and 12% higher than that of the secondary lamination.However,the surface crack resistance of impregnated paper veneered blockboard prepared by the one-time lamination only reached the lowest grade(Grade 1),which could not meet the requirements in GB/T 34722-2017.When using the secondary lamination process,the impregnated paper was first laminated with the equilibrium layer,and then bonded with the blockboard substrate.Since the impregnated paper/equilibrium layer was thermally pressed twice,its bonding interface structure was more stable.Therefore,the surface crack resistance of impregnated paper veneered blockboard could reach the highest grade(Grade 5).However,the surface cleanliness of the impregnated paper veneered blockboard prepared by the secondary lamination was significantly reduced.(3)The poplar veneer was heat-treated,and the heat-treated poplar veneer was used as the equilibrium layers to prepare the impregnated paper veneered blockboard.The research showed that heat treatment could significantly improve the dimensional stability of poplar veneer.On the one hand,the total dimensional shrinkage of poplar veneer after heat treatment was 82.5% to 98%lower than that of untreated wood.On the other hand,the heat treatment modification reduced the dimensional shrinkage difference of poplar veneer in the direction of the horizontal grain and the parallel grain.However,the improvement of dimensional stability did not improve the ability of the impregnated paper veneered blockboard to resist changes in external temperature and humidity.This was because the transverse tensile strength of poplar veneer generally showed a downward trend with the increase of heat treatment temperature and time,which was 30.1% to 63% lower than that of untreated wood.The reduction of the mechanical properties of poplar veneer made it unable to resist the stress released by the deformation of the blockboard substrate,resulting in surface cracking.The surface bonding strength of the impregnated paper veneered blockboard prepared by using the heat-treated poplar veneer as the equilibrium layer was in the range of 1.12 to 1.4 MPa,which conformed to GB/T 34722-2017.(4)The impregnated paper veneered blockboard was prepared with the equilibrium layer of homogeneous high density fiberboard(HDF).The surface crack resistance grade of the impregnated paper veneered blockboard reached level 5,in line with national standards.The effect of HDF on the surface crack resistance of impregnated paper veneered blockboard was analyzed by testing the dry thermal dimensional stability and mechanical properties of the blockboard substrate and HDF before and after the surface crack resistance test condition(70 ℃,24 h).The results showed that the use of HDF lamination on the blockboard substrate could improve the dry thermal dimensional stability of the blockboard substrate.After the surface crack resistance test,HDF pressing can improve the transverse static bending strength of the blockboard substrate.Therefore,the surface of the impregnated paper veneered blockboard with HDF as equilibrium layer did not crack.Similarly,the dry thermal dimensional stability and mechanical properties of the blockboard substrate and poplar veneer were tested before and after treatment at 70 ℃for 24 h.It was found that the poplar veneer did not have good dimensional stability and mechanical strength,so it did not enhance the dimensional stability and transverse static strength of the blockboard substrate.(5)HDF and poplar veneer were selected as the equilibrium layer to prepare impregnated paper veneered blockboards,and the physical properties of the two impregnated paper veneered blockboards were systematically analyzed.It was found that there was no significant difference in appearance quality,surface scratch resistance,surface abrasion resistance,and immersion peel performance of the impregnated paper veneered blockboard prepared with the two equilibrium layers.The transverse static strength of HDF impregnated paper veneered blockboard was 16.7%higher than that of poplar veneer impregnated paper veneered blockboard.The surface bonding strength and water resistance of poplar veneer impregnated paper veneered blockboard was better than HDF impregnated paper veneered blockboard,and its formaldehyde emission was lower. |
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