Preparation method and application of recombinant technical veneer based on water regulation and control

Abstract

The invention discloses a preparation method and application of a recombinant technical veneer based on water regulation and control, and belongs to the technical field of recombinant veneers. The preparation method comprises the following steps: (1) preparing a water-based bio-based adhesive; (2) raw wood is sliced into veneers, the veneers are dried and sorted, and the moisture content of the sorted veneers is 12-15%; (3) a water-based bio-based adhesive is applied to the sorted veneers, the veneers are stacked and then transferred into a pressing machine to be subjected to cold pressing, recombined battens are manufactured, and the water content is 30-40%; (4) atomizing and spraying water on the periphery of the recombined batten, and then wrapping the recombined batten with a preservative film to obtain the recombined batten after water spraying; and (5) the recombined batten subjected to water spraying is subjected to normal-temperature curing and then sliced, the recombined technical wood veneer is obtained, and the water content ranges from 25% to 30%. According to the method, the moisture of the recombined technical veneer in different preparation links is precisely regulated and controlled, the interface environment is optimized, the permeability of the adhesive is improved, and controllable preparation of the high-performance recombined technical veneer is achieved.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method and application of a recombined veneer based on water regulation, and belongs to the technical field of recombined veneer. BACKGROUND

[0002] With the rapid development of China's social economy and the transformation and upgrading of residents' consumption structure, the public's aesthetic demand for high-quality living environment continues to upgrade. Wood, with its unique natural aesthetic properties, has become the first choice for high-end decorative materials. However, according to the 2022 Forestry Report, China's annual consumption of precious wood has reached 6.5 million cubic meters, but the annual average decline rate of natural forest stock volume is 2.3%, and the supply-demand gap has expanded to 37%. Against the background of the increasingly severe contradiction between supply and demand of precious wood, recombined veneer is becoming an important solution to alleviate the shortage of raw wood due to its high utilization rate and replaceability.

[0003] Recombined veneer is a high-value composite material prepared by ordinary plantation or ordinary fast-growing material veneer through veneer preparation, adhesive impregnation, assembly, and press forming processes. Because recombined veneer can increase the utilization rate of veneer to more than 95% and reduce the consumption of precious raw wood by more than 60%, it also has the natural texture of precious wood, and is increasingly valued by the wood processing industry. Currently, recombined veneer is divided into aldehyde-based recombined veneer and formaldehyde-free recombined veneer. Aldehyde-based recombined veneer uses formaldehyde-based adhesives such as melamine formaldehyde resin adhesive or urea formaldehyde resin adhesive, which is low in price but prone to release free formaldehyde, has poor environmental protection, and has poor flexibility and water resistance, making it unsuitable for veneering on complex curved surfaces and relief processes. Formaldehyde-free recombined veneer often uses isocyanate adhesive, which can avoid formaldehyde release, but due to the problems of complex components, low initial adhesion, long curing period, and high production cost, its application is limited, and its main raw materials are mainly derived from non-renewable fossil resources, which does not meet the requirements of sustainable development. It can be seen that the selection of adhesive has a significant impact on the performance and application of recombined veneer.

[0004] In addition, the moisture content of wood has a crucial impact on the quality, processing performance and service life of wood. First, appropriate moisture content can ensure the stability and strength of wood, avoiding cracking, deformation and other problems during processing. Second, the moisture content also affects the finishing effect and adhesion performance of wood, thereby affecting the appearance and use performance of wood products such as furniture and buildings. Especially in the preparation process of reconstituted technical veneer, the moisture content of wood always affects the formability and processing usability of the finished technical veneer, so the regulation of water during the preparation process of reconstituted technical veneer is particularly important, and the whole-process regulation of moisture content is the key to realizing high-quality production of reconstituted technical veneer, especially for improving the dimensional stability, weather resistance and adaptability to downstream processing. With the improvement of environmental protection and quality requirements, such regulation will become an important direction for industry upgrading. However, the existing process of reconstituted technical veneer does not regulate the moisture content of reconstituted technical veneer throughout the process, and it is also unable to achieve strong adhesion of the adhesive with the board under high moisture conditions. Therefore, precise regulation of water at each link in the preparation process of technical veneer and achieving strong adhesion under high humidity conditions are crucial to improving the process and performance of reconstituted technical veneer. SUMMARY

[0005] In view of the deficiencies of the prior art, the purpose of the present application is to provide a preparation method and application of reconstituted technical veneer based on water regulation, which improves the reconstituted technical veneer and its subsequent processing performance by precisely regulating the moisture content at each link in the preparation process.

[0006] To solve the above technical problems, the technical solution provided by the present application is: A preparation method of reconstituted technical veneer based on water regulation, comprising the following steps: (1) preparing a water-based bio-based adhesive; (2) planing the logs into veneers, drying and sorting the veneers to obtain sorted veneers; (3) applying the water-based bio-based adhesive to the sorted veneers, stacking them and then transferring them to a press for cold pressing to obtain reconstituted wood; (4) spraying water around the reconstituted wood and wrapping it with plastic wrap to obtain the reconstituted wood after spraying water; (5) planing the reconstituted wood after spraying water after 5-15 days of normal temperature curing to obtain reconstituted technical veneer.

[0007] Further, in step (1), the preparation method of the water-based bio-based adhesive is as follows: polyvinyl alcohol is dissolved in deionized water, then catechin is added, and under the condition of 50-80℃, stirring until completely dissolved, then adding tannic acid to continue stirring to form a uniform and stable solution, which is the water-based bio-based adhesive.

[0008] Further, the mass ratio of polyvinyl alcohol, tannic acid, catechin, deionized water is (8-15):(0.4-1):(0.05-0.2):(83.8-91.55). Polyvinyl alcohol has excellent film-forming property, mechanical flexibility and biocompatibility, tannic acid has abundant biomimetic groups, can form non-covalent bonds with polyvinyl alcohol, improve the bonding performance and water resistance of the adhesive, but will increase the viscosity of the adhesive, weaken the permeability of the adhesive. Catechin is a small molecule natural polyphenol, can form hydrogen bonds with polyvinyl alcohol, and compete with tannic acid to form hydrogen bonds, weaken the interaction between polyvinyl alcohol and tannic acid, reduce the viscosity of the adhesive, improve the permeability of the adhesive in the veneer; at the same time, together with tannic acid to construct a cross-linked network, further enhance the water resistance, flexibility and crack resistance of the veneer.

[0009] Further, the molecular weight of the polyvinyl alcohol is 20-150 thousand, and the alcoholysis degree of the polyvinyl alcohol is greater than 90%. Polyvinyl alcohol is the largest water-soluble polymer material in the world, which can be produced on a large scale through a non-petroleum route, has good film-forming property, mechanical flexibility and biocompatibility, but has the problems of poor water resistance, large viscosity and poor permeability, and is rarely used in veneer. The present application uses it as a raw material to prepare a water-based bio-based adhesive for veneer, which significantly improves the comprehensive performance of the veneer. The alcoholysis degree affects the hydrophilicity, hydrophobicity and molecular chain integrity of polyvinyl alcohol, and high-alcoholysis-degree polyvinyl alcohol has more hydroxyl groups and strong hydrogen bonding, which is easy to form gel after dissolving at high temperature and cooling, and the molecular chain is arranged regularly, so the adhesive has good water resistance.

[0010] Further, in step (2), the thickness of the veneer is 0.8-1.2 mm; the drying treatment is to put the veneer into a drying kiln for drying, and the water content of the dried veneer is 12-15%. If the water content of the veneer is too high, too much water will cause the formation of a weak interface layer, hindering the effective bonding of the adhesive with the wood fiber unit hydroxyl group, thereby weakening the interfacial bonding force; if the water content of the veneer is too low, the adhesive penetration amount will be too large, resulting in surface adhesive deficiency, unable to form a uniform adhesive interface on the surface, leading to interlayer peeling, thereby reducing the pre-pressing performance. In the existing process, the water content of the veneer is usually less than 12%, while the present application controls the veneer at a suitable high water content, so that the water-based bio-based adhesive can be bonded with the veneer efficiently, and the plasticity of the wood is enhanced, which is beneficial to the compression of the veneer to form a dense structure.

[0011] Further, in step (3), the adhesive amount of the water-based bio-based adhesive is 60-90 g / m 2The single boards after sorting are coated with the sizing agent layer by layer, and the moisture content of the single boards is controlled by the sizing amount. Under high humidity conditions, the water-based bio-based adhesive forms hydrogen bonds and π-π stacking and other supramolecular forces with wood, can more quickly and efficiently break through the weak water interface layer, obtain stronger adhesion, and further improve the cold pressing performance. The two synergistically improve the bonding effect of the adhesive on wood in a high-humidity environment, so that the water-based bio-based adhesive can still maintain good bonding strength in a humid working condition. In addition, water also plays a plasticizing role, can penetrate between the molecular chains of the adhesive and the microstructure of the wood, change the intermolecular forces, reduce the rigidity and hardness of the wood, achieve the softening of the wood, and reduce the pressure required for cold pressing. Moreover, under the same pressure conditions, the plasticizing effect of water makes the adhesive and the wood both in a more deformable state, the contact area between the adhesive and the wood significantly increases, and the interlayer bonding of the single boards is more compact.

[0012] Further, in step (3), the sorted single boards are coated with the water-based bio-based adhesive layer by layer, and after stacking, they are transferred to the press for cold pressing. The time for transferring to the press is controlled to be 8-10 min. If the time for transferring to the press is too long, the water-based bio-based adhesive applied will solidify, dry glue phenomenon will occur before cold pressing, and the bonding performance will decrease.

[0013] Further, in step (3), the pressure of the cold pressing is 15-19 MPa; and the center moisture content of the reconstituted wood square is 30-40%. The moisture content of the reconstituted wood square in the existing process is usually 25-30%, and after aging, the overall moisture content of the wood square is 18-23% when the adhesive is cured and formed, and the moisture content of the reconstituted wood veneer obtained by planing is 18-23%. However, through a large number of experimental explorations, the present application adjusts the moisture content of the reconstituted wood square to 30-40% by applying a water-based bio-based adhesive, and then the wood square is aged at room temperature. The overall moisture content of the wood square is 25-30% when planing, which is the fiber saturation point. The moisture content of the wood square is precisely controlled to the fiber saturation point at this time, and there is sufficient bound water in the cell wall, and there is no free water in the cell lumen, so that the wood achieves a good balance between rigidity and plasticity. The wood has good plasticity, can effectively absorb and disperse the planing stress, and reduce the risk of brittle fracture; at the same time, it also retains sufficient rigidity to support the cutting force of the tool, avoids excessive softening of the tool marks, and is beneficial to realize smooth, flat and defect-free planing surface. When the moisture content is lower than the fiber saturation point, the bound water in the cell wall of the wood is lost in large quantities, resulting in increased hydrogen bonding between cellulose, hemicellulose and lignin, significantly reduced plasticity of the wood, and sharply increased rigidity and brittleness. The brittle wood square is prone to cause micro-cracks, edge collapse or even large-area fracture in the planing process, resulting in single board damage and scrap, and the generated debris is easy to damage the cutting edge.

[0014] Further, in step (4), the water spraying amount is 1.0-2.0 kg / m 2 . The atomized water spraying around the reconstituted wood square can slow down the internal water evaporation speed through uniform and small amount of water supplement, so as to balance the overall moisture content of the reconstituted wood square, reduce the internal stress caused by excessive water gradient, and avoid cracking and surface carbonization in the subsequent process.

[0015] Further, in step (5), the water content of the recombined technology wood veneer is 25-30%. High water content makes the technology wood veneer more plastic, easier to deform and fit the irregular base material (such as curved or carved parts) during hot pressing, reduces the risk of cracking, improves the quality of pressing, and meets the demand for complex modeling. Compared with the traditional technology wood veneer with a water content of 18-23%, the recombined technology wood veneer of the present application has a higher water content, and because the thermal conductivity of water is higher than that of dry veneer, the heat transfer during hot pressing can be accelerated, the pressing time can be shortened, and the production efficiency can be improved. In addition, the presence of water can also increase the activity of reactive groups in the adhesive, enhance the bonding with the wood surface groups, improve the interfacial bonding strength, and reduce the risk of glue failure. However, if the water content is too high, the technology wood veneer is prone to deformation and mold growth, and after the excess water vaporizes during subsequent pressing, it cannot be discharged in time, forming steam pressure in the glue layer or the veneer-substrate interface, causing local bubbling, and the technology wood veneer has a large water content gradient after pressing, which is prone to warping and deformation during subsequent drying, affecting the flatness of the product; if the water content is too low, micro-cracks are prone to occur during subsequent pressing, especially under high pressure or rapid heating conditions during veneer pressing, which can cause surface carbonization.

[0016] An application of a recombined technology wood veneer based on water regulation, the recombined technology wood veneer is used to make a veneered panel through veneer pressing and re-veneering processes, the steps are as follows: melamine impregnated film paper is attached to the recombined technology wood veneer, and after 1-3 days, the recombined technology wood veneer is re-veneered on a substrate to obtain a veneered panel.

[0017] Further, the temperature of the veneer pressing process is 190-200℃, the time is 6-7s, and the pressure is 11-12MPa; the glue application amount of the re-veneering process is 125-135g / m 2 , the cold pressing conditions of the re-veneering process are: pressure 5-6MPa, time 20-30min, and the hot pressing conditions of the re-veneering process are: temperature 95-105℃, pressure 5-6MPa, and time 10-15min.

[0018] Compared with the prior art, the present application has the following advantages: (1) The present application precisely regulates the water content of the recombined technology wood veneer at different preparation stages, optimizes the interface environment, improves the permeability of the adhesive, and realizes the controllable preparation of high-performance recombined technology wood veneer. The recombined technology wood veneer prepared has a high water content, is not prone to cracking during subsequent use, improves the quality of pressing, meets the demand for complex modeling, and shortens the pressing time, improving production efficiency.

[0019] (2) The recombined technology wood veneer prepared by the present application has a high water content, which can reduce the temperature of the veneer pressing process and shorten the time of the veneer pressing process, which is beneficial to reduce production cost, improve production efficiency and increase economic benefit.

[0020] (3) The prepared recombinant science and technology veneer has an environmental protection level of HE NF grade, the raw materials used do not contain formaldehyde, no free formaldehyde is released, harmful substances such as formaldehyde commonly used in traditional adhesives are abandoned, formaldehyde pollution is eliminated from the source, and human health and environmental safety are ensured.

[0021] (4) The prepared recombinant science and technology veneer has high toughness and crack resistance, high water resistance, is suitable for veneering on complex curved surfaces and embossing processes, meets the process and quality requirements of various large-curvature customized furniture, and the surface is not easy to carbonize under high pressure or rapid heating conditions in the process of pasting paper.

[0022] (5) The prepared recombinant science and technology veneer has excellent structure stability, and is not easy to open glue after being boiled in water for 48 h under the condition of 63 DEG C water bath. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a comparison diagram of the density of the recombinant science and technology veneer; Figure 2 is a comparison diagram of the knife mark of the recombinant science and technology veneer; Figure 3 is a scanning electron microscope diagram of the side surface micro-morphology of the recombinant science and technology veneer; Figure 4 is a comparison diagram of the water boiling resistance of the recombinant science and technology veneer. DETAILED DESCRIPTION

[0024] Example 1 A preparation method of a recombinant science and technology veneer based on water regulation comprises the following steps: (1) preparing a water-based biological adhesive: dissolving polyvinyl alcohol in deionized water, then adding tannic acid, stirring at 70 DEG C until completely dissolved, then adding tannic acid and stirring until a uniform and stable solution is formed, the components of the water-based biological adhesive are: by weight, polyvinyl alcohol 10 parts, tannic acid 0.5 parts, tannic acid 0.1 parts, deionized water 89.4 parts; (2) The wood is planed into a veneer with a thickness of 1.0 mm, the veneer is dried in a drying kiln, and then sorted to obtain a sorted veneer with a moisture content of 12%; (3) The sorted veneer is applied with water-based biological adhesive layer by layer, the glue application amount is 75 g / m 2 , after stacking, it is transferred to the press for cold pressing, the transfer time to the press is 9 min, the cold pressing operation is: one mold is placed on the upper and lower surfaces of the reconstituted wood square respectively, and the reconstituted wood square is pressed in the press under a pressure of 17 MPa, and the center moisture content of the reconstituted wood square is 34%; (4) Spraying water on the four sides of the reconstituted wood square at a spraying amount of 1.0 kg / m 2 , and then wrapping it with a preservative film to obtain the reconstituted wood square after spraying water; (5) Planing the reconstituted wood square after spraying water for 10 days at room temperature to obtain reconstituted wood veneer with a water content of 26%.

[0025] Example 2 A preparation method of reconstituted wood veneer based on water regulation, comprising the following steps: (1) Preparing a water-based bio-based adhesive: dissolving polyvinyl alcohol in deionized water, then adding tannic acid, stirring at 70°C until completely dissolved, then adding tannin acid and stirring until a uniform and stable solution is formed, the components of the water-based bio-based adhesive are: by weight, polyvinyl alcohol 15 parts, tannin acid 0.8 parts, tannic acid 0.1 part, deionized water 84.1 parts; (2) Planing the original wood into a veneer with a thickness of 1.0 mm, drying the veneer in a drying kiln, and then sorting to obtain sorted veneer with a water content of 13%; (3) Applying water-based bio-based adhesive to the sorted veneer layer by layer, the glue application amount is 90 g / m 2 , after stacking, it is transferred to the press for cold pressing, the transfer time to the press is 10 min, the cold pressing operation is: placing one mold on the upper and lower surfaces of the reconstituted wood square, transferring it to the press for pressing under a pressure of 19 MPa, to obtain a reconstituted wood square, the center water content of which is 38%; (4) Spraying water on the four sides of the reconstituted wood square at a spraying amount of 2.0 kg / m 2 , and then wrapping it with a preservative film to obtain the reconstituted wood square after spraying water; (5) Planing the reconstituted wood square after spraying water for 15 days at room temperature to obtain reconstituted wood veneer with a water content of 28%.

[0026] Example 3 A preparation method of reconstituted wood veneer based on water regulation, comprising the following steps: (1) Preparing a water-based bio-based adhesive: dissolving polyvinyl alcohol in deionized water, then adding tannic acid, stirring at 70°C until completely dissolved, then adding tannin acid and stirring until a uniform and stable solution is formed, the components of the water-based bio-based adhesive are: by weight, polyvinyl alcohol 8 parts, tannin acid 0.4 parts, tannic acid 0.1 part, deionized water 91.5 parts; (2) Planing the original wood into a veneer with a thickness of 1.0 mm, drying the veneer in a drying kiln, and then sorting to obtain sorted veneer with a water content of 15%; (3) Applying water-based bio-based adhesive to the sorted veneer layer by layer, the glue application amount is 60 g / m2 After stacking, it is transferred to the press for cold pressing, and the transfer time to the press is 10 min. The cold pressing operation is as follows: one mold is placed on each of the upper and lower surfaces of the reconstituted wood square, and the reconstituted wood square is pressed in the press at a pressure of 15 MPa to obtain a reconstituted wood square, the moisture content of the center of which is 32%; (4) The reconstituted wood square is sprayed with water around the periphery, and the spraying amount is 1.0 kg / m 2 Then it is wrapped with a preservative film to obtain the reconstituted wood square after spraying. (5) The reconstituted wood square after spraying is planed after 5 days of normal temperature curing to obtain a reconstituted wood veneer, the moisture content of which is 25%.

[0027] Application Example 1 A reconstituted wood veneer based on water regulation is applied to a decorative panel by a paper pasting and re-pasting process. The steps are as follows: melamine impregnated film paper is pasted on the reconstituted wood veneer at a temperature of 195°C, a time of 6s, and a pressure of 11 MPa, and is placed for 1 day. Then it is re-pasted on the substrate to obtain a decorative panel, and the glue application amount of re-pasting is 128 g / m 2 The cold pressing conditions are: pressure 5 MPa, time 20 min, and the hot pressing conditions are: temperature 95°C, pressure 5 MPa, and time 10 min.

[0028] Application Example 2 A reconstituted wood veneer based on water regulation is applied to a decorative panel by a paper pasting and re-pasting process. The steps are as follows: melamine impregnated film paper is pasted on the reconstituted wood veneer at a temperature of 195°C, a time of 6s, and a pressure of 11 MPa, and is placed for 1 day. Then it is re-pasted on the substrate to obtain a decorative panel, and the glue application amount of re-pasting is 128 g / m 2 The cold pressing conditions are: pressure 5 MPa, time 20 min, and the hot pressing conditions are: temperature 95°C, pressure 5 MPa, and time 10 min.

[0029] Comparative Example 1 The steps are the same as those of Example 1, except that the adhesive in step (1) is a urea-formaldehyde resin adhesive, which is specifically: (1) Prepare a urea-formaldehyde resin adhesive; the urea-formaldehyde resin adhesive is purchased from Shandong Zhongyuan New Material Co., Ltd. Among them, the moisture content of the sorted veneer is 12%, the moisture content of the center of the reconstituted wood square is 28%, and the moisture content of the reconstituted wood veneer is 20%.

[0030] Comparative Example 2 The steps are the same as those of Example 1, except that the aqueous bio-based adhesive in step (1) does not contain catechin, which is specifically: (1) preparing the water-based bio-based adhesive: dissolving polyvinyl alcohol in deionized water, stirring at 70°C until completely dissolved, then adding tannic acid and stirring until a uniform and stable solution is formed, the components of the water-based bio-based adhesive are: by weight, polyvinyl alcohol 10 parts, tannic acid 0.5 parts, deionized water 89.4 parts; Among them, the moisture content of the sorted veneer is 12%, the moisture content of the center of the reconstituted wood square is 39%, and the moisture content of the reconstituted veneer is 31%.

[0031] Comparative Example 3 The same as step of example 1, the difference is that the moisture content of the veneer is different in step (2), specifically: (2) The wood is planed into a veneer with a thickness of 1.0 mm, and the veneer is dried in a drying kiln, and then sorted to obtain a sorted veneer with a moisture content of 20%; Among them, the moisture content of the sorted veneer is 20%, the moisture content of the center of the reconstituted wood square is 42%, and the moisture content of the reconstituted veneer is 33%.

[0032] Comparative Example 4 The same as step of example 1, the difference is that the glue amount is large in step (3), specifically: (3) The sorted veneer is applied with water-based bio-based adhesive layer by layer, and the glue amount is 110 g / m 2 , after stacking, it is transferred to the press for 9 min, and the reconstituted wood square is obtained, and the center moisture content is 47%; Among them, the moisture content of the sorted veneer is 12%, the moisture content of the center of the reconstituted wood square is 47%, and the moisture content of the reconstituted veneer is 38%.

[0033] Comparative Example 5 The same as step of example 1, the difference is that step (4) does not spray water around the wood square, specifically: (4) The reconstituted wood square is wrapped with plastic wrap to obtain a reconstituted wood square without spraying water; Among them, the moisture content of the sorted veneer is 12%, the moisture content of the center of the reconstituted wood square is 30%, and the moisture content of the reconstituted veneer is 25%.

[0034] Comparative Example 6 The same as step of example 1, the difference is that the time of transferring to the press in step (3) is different, specifically: (3) The sorted veneer is applied with water-based bio-based adhesive layer by layer, and the glue amount is 75 g / m 2After stacking, transfer to the press for cold pressing, the transfer time to the press is 25 min, and the cold pressing operation is as follows: place one mold on each of the upper and lower surfaces of the reconstituted wood square, transfer to the press for cold pressing, and the pressure is 17 MPa, to obtain the reconstituted wood square; Among them, the moisture content of the sorted veneer is 12%, the moisture content of the reconstituted wood square is 25%, and the moisture content of the reconstituted wood veneer is 18%.

[0035] Comparative Example 7 The steps are the same as those of Application Example 1, except that the reconstituted wood veneer of Example 1 is replaced by the reconstituted wood veneer of Comparative Example 1.

[0036] Comparative Example 8 The steps are the same as those of Application Example 1, except that the reconstituted wood veneer of Example 1 is replaced by the reconstituted wood veneer of Comparative Example 4.

[0037] Comparative Example 9 The steps are the same as those of Application Example 1, except that the reconstituted wood veneer of Example 1 is replaced by the reconstituted wood veneer of Comparative Example 5.

[0038] Comparative Example 10 The steps are the same as those of Application Example 1, except that the reconstituted wood veneer of Example 1 is replaced by the reconstituted wood veneer of Comparative Example 1; the paper sticking process is changed: the melamine impregnated film paper is stuck on the reconstituted wood veneer at a temperature of 205°C, a time of 9s, and a pressure of 11MPa.

[0039] Experimental Example 1 The moisture contents of each step in the preparation process of the reconstituted wood veneer of Examples 1-3 and Comparative Examples 1-6 are compared, and the results are shown in Table 1.

[0040] Table 1. Comparison of moisture contents of each step In the existing preparation process of reconstituted wood veneer, the moisture content of the veneer is usually less than 12%, the moisture content of the reconstituted wood square is usually 25-30%, and the moisture content of the reconstituted wood veneer is 18-23%. Because the moisture content has a significant impact on the performance and subsequent processing of the reconstituted wood veneer, too high moisture content can easily cause the reconstituted wood veneer to deform and delaminate; too low moisture content can easily cause the reconstituted wood veneer to crack and be unstable in size.

[0041] And from Table 1, each link in the process steps of the application can affect the moisture content of the plate, and by accurately controlling the moisture content in each link within the optimal range defined in the application, the moisture content of the veneer is 12-15%, the moisture content of the reconstituted wood square is 30-40%, thereby obtaining the reconstituted technical wood veneer with a moisture content of 25-30%, which has excellent performance and is not prone to cracking during subsequent use, improves the pressing quality, adapts to complex modeling requirements, and also reduces the temperature of the subsequent pressing process, shortens the pressing process time, and improves the production efficiency.

[0042] Experimental Example 2 The reconstituted technical wood veneers of Examples 1-2 and Comparative Examples 1-6 were tested according to the hole and closed crack test method in GB / T 2899-2012 "Reconstituted Decorative Veneer", and the results are shown in Table 2.

[0043] Table 2. Hole and closed crack statistics From Table 2 and the accompanying Figure 1 It can be seen that the reconstituted technical wood veneers in Examples 1 and 2 have high density and no holes and gaps on the surface, which is due to the control of moisture content and the excellent permeability and initial adhesion of the water-based bio-based adhesive with strong bonding strength; the reconstituted technical wood veneers of Comparative Examples 1-6 have poor density and obvious holes and gaps, especially the reconstituted technical wood veneers of Comparative Examples 2 and 3 have the worst density; Comparative Example 2 has large-area cracks after planing, which is due to the fact that the water-based bio-based adhesive does not contain catechin, resulting in too large viscosity and poor permeability of the adhesive, which cannot penetrate into the veneer and cannot be cured; the main reason for the poor density of Comparative Examples 3, 4 and 5 is that the moisture content in the production process is not reasonable, the veneer in Comparative Example 3 has high moisture content, which dilutes the adhesive and affects the curing effect; the adhesive in Comparative Example 4 has high moisture content due to the increase in adhesive amount, and the adhesive is not fully cured; the wood square in Comparative Example 5 has low moisture content due to the lack of water spraying on the edge, which causes cracks on the edge of the wood square and affects the quality of the technical wood veneer; the veneer in Comparative Example 6 is transferred to the press for a long time after gluing, and the adhesive is slightly dry, which reduces the bonding performance. From the accompanying Figure 2 It can be seen that Comparative Examples 2, 3 and 4 have obvious knife marks, which is mainly due to the fact that the moisture content of the technical wood veneer is too high, and the debris cannot be blown away due to the high humidity during planing, and the debris often needs to be cleaned from the knife head, and the debris also gets stuck in the gap of the knife head, which causes knife marks on the surface of the technical wood veneer and also causes mold and other quality defects.

[0044] Therefore, the water-based bio-based adhesive prepared by adding catechin and combined with the control of moisture content promotes the penetration of the adhesive and improves the quality of the product, and the reconstituted technical wood veneer with excellent performance is prepared.

[0045] Experimental Example 3 Since the test methods of hole and closed crack, the number of holes of the reconstituted technology veneer of Comparative Example 2-3 and Comparative Example 6 is large, and the knife marks of the reconstituted technology veneer of Comparative Example 4 are obvious, the formaldehyde emission of the reconstituted technology veneer of Example 1-2 and Comparative Example 1, Comparative Example 5 is further explored.

[0046] The formaldehyde content of the reconstituted technology veneer of Example 1-2 and Comparative Example 1, Comparative Example 5 is tested by referring to the dryer method in GB / T 17657-2022 “Physicochemical property test method of artificial board and veneered artificial board”, and the test results are listed in Table 3. At the same time, the formaldehyde content of the reconstituted technology veneer of Example 1 is detected at 30°C by referring to the climate chamber method in T / CNFPIA 1003-2022 “Formaldehyde emission of artificial board and its products for heating”, and the test results are listed in Table 4.

[0047] Table 3. Formaldehyde emission Table 4. Formaldehyde emission As can be seen from Table 3, the reconstituted technology veneer of Comparative Example 1 is prepared by using urea-formaldehyde resin adhesive, and the formaldehyde emission thereof is 0.44 mg / L, while the reconstituted technology veneers of Examples 1, 2 and Comparative Example 5 are prepared by using the water-based bio-based adhesive prepared by the present application, and the formaldehyde emissions thereof are all less than 0.05 mg / L, according to the enterprise internal control standard E NF 0 level≤0.2 mg / L, 0.2 mg / L≤E0 level≤0.5 mg / L, 0.5 mg / L≤E1 level≤1.5 mg / L, the reconstituted technology veneers prepared by using the water-based bio-based adhesive of the present application all reach E NF 0 level. As can be seen from Table 4, the detection limit of formaldehyde content detected by the climate chamber method is 0.005 mg / m 3 , and the reconstituted technology veneer prepared by using the water-based bio-based adhesive in Example 1 is not detected for formaldehyde, which is lower than the detection limit. According to the standard, the formaldehyde emission of indoor artificial board and its products is divided into three levels: HE1 level≤0.124 mg / m 3 , HE0 level≤0.050 mg / m 3 , and HE NF 0 level≤0.025 mg / m 3 , it can be seen that the reconstituted technology veneer prepared by the present application reaches HE NF 0 level. It is shown that the water-based bio-based adhesive prepared by the present application is used in the process production of reconstituted technology veneer, no free formaldehyde is released, and the environmental protection level of the product prepared thereby reaches HE NF 0 level.

[0048] Experimental Example 4 The decorative panels of Application Examples 1-2 and Comparative Examples 7-10 were tested with reference to the crack resistance test in GB / T 17657-2022 "Test methods for physical and chemical properties of wood-based panels and veneered wood-based panels" and the appearance quality in GB / T 15102-2017 "Impregnated film paper veneer fiberboard and particleboard", and the test results are listed in Table 5.

[0049] Table 5. Crack resistance and appearance quality of decorative panels As shown in Table 5, after the crack resistance test, the veneers of Examples 1-2 showed no surface defects, while the veneers of Comparative Examples 7-9 all had various surface defects. This is because the conventional laminating process uses a temperature of 205°C for 8-9 seconds, while the laminating process in the present invention uses a temperature of 195°C for 6 seconds, both of which are lower than the conventional process. Furthermore, the present invention limits the moisture content of the recombinant technical veneer to 25-30%, which improves thermal conductivity during the laminating process and enhances adhesive activity. Therefore, the present invention can still maintain good surface quality and crack resistance for the veneer at lower temperatures and shorter times. Delamination occurred in the veneer of Comparative Example 7 due to the inability of the aldehyde adhesive to fully cure at the high-moisture interface in a short time and at a lower temperature. The veneer of Comparative Example 8 exhibited surface wetting due to the excessively high moisture content of the recombinant technical veneer. The veneer of Comparative Example 9 exhibited surface carbonization due to the low surface moisture content of the recombinant technical veneer, resulting in cracking at the ends and affecting the surface quality. The decorative panels of Comparative Example 10 have no defects in appearance quality because the aldehyde adhesive can be cured under the existing process conditions. However, compared with the decorative panels of Application Examples 1 and 2, the crack resistance is poor. This also shows that the excellent performance of the decorative panels of Application Examples 1-2 is the result of the unique toughness of the water-based bio-based adhesive of the present invention and the precise control of the moisture content.

[0050] Therefore, the present invention can reduce the temperature of the pasting process, shorten the time of the pasting process, reduce production costs, ensure production quality, improve production efficiency and increase economic benefits through precise control of the moisture content.

[0051] Experimental Example 5 The recombinant technical veneer of Example 1 was sliced ​​and its side micromorphology was observed under a scanning electron microscope. The observation results are shown in the attached figure. Figure 3 shown.

[0052] By the attached Figure 3 It can be seen that the thickness of the glue layer on the side of the reconstructed technical veneer is uniform, without local fractures or accumulation. The water-based bio-based adhesive can fill the tiny gaps between the fibers, and there is no clear dividing line or gap between the two. This shows that the water-based bio-based adhesive has excellent permeability and formability, which can improve the comprehensive performance of the technical veneer.

[0053] Experimental Example 6 The recombinant technical veneer in Example 1-2 and the recombinant technical veneer in Comparative Example 1-6 were placed in a 63°C water bath for a boiling test. The boiling time was 4 hours. After the test, the state of the technical veneer was observed to determine its boiling resistance. The test results are shown in the attached Figure 4 .

[0054] By the attached Figure 4 As can be seen, the recombinant technical veneers in Examples 1 and 2 did not disperse after being boiled at 63°C for 4 hours, demonstrating the excellent bonding properties of the water-based bio-based adhesive of the present invention. The recombinant technical veneers in Comparative Examples 1-6 all showed signs of disintegration after being boiled at 63°C for 4 hours, with the recombinant technical veneers in Comparative Examples 3, 4, and 6 completely disintegrating after boiling. This is due to the high moisture content of the boards in Comparative Examples 3 and 4, which prevented the adhesive from fully curing. In Comparative Example 6, the time it took to transfer the glued veneer to the press after application was too long, resulting in glue drying before cold pressing. Later experiments revealed that by extending the boiling time, the recombinant technical veneers in Examples 1-2 remained intact even after boiling at 63°C for 48 hours.

[0055] Experimental Example 7 Referring to the steps of Example 1, and following the moisture content limits set by existing processes, the following criteria were used: a moisture content of <12% for the sorted veneer, a center moisture content of 25-30% for the reconstituted wood squares, and a moisture content of 18-23% for the reconstituted technical veneer. Using these as a benchmark, a urea-formaldehyde resin adhesive was used to prepare the reconstituted technical veneer. The properties of the reconstituted veneer were tested using the same testing methods as in the experimental example. The results are listed in Table 6.

[0056] Table 6. Comparison of properties of reconstructed engineered veneer using existing technology and the technology of the present invention As shown in Table 6, the recombinant technical veneer prepared according to the existing process has a moisture content of 10% for the veneer, 25% for the recombinant wood square, and 20% for the recombinant technical veneer. The prepared recombinant technical veneer has a high density and appears loose after being boiled at 63°C for 4 hours. It is pressed and laminated at a temperature of 205°C for 9 seconds to prepare a decorative panel. The appearance quality and crack resistance tests show that the decorative panel has no defects in appearance quality, poor crack resistance, and an environmental protection grade of E0. The recombinant technical veneer of the present invention has a high density, good boiling resistance and crack resistance, and an environmental protection grade of HE NF Compared with existing processes, this invention uses a self-made water-based bio-based adhesive to precisely control the moisture content of the boards at each stage, resulting in a reconstructed high-tech veneer with excellent performance, suitable for the field of high-quality veneer.

Claims

1. A method for preparing recombinant technical veneer based on water regulation, characterized by: The following steps are involved: (1) Preparation of water-based bio-based adhesives; (2) Slicing the logs into veneers, drying and sorting them to obtain the sorted veneers; (3) Applying a water-based bio-based adhesive to the sorted veneers, stacking them and transferring them to a press for cold pressing to produce reconstituted wood; (4) Spray water around the reconstructed wood and then wrap it with plastic wrap to obtain the reconstructed wood after spraying water; (5) After the water spraying, the reconstructed wood is cured at room temperature for 5-15 days and then sliced ​​to obtain the reconstructed technical veneer.

2. The method for preparing recombinant technical veneer based on water regulation according to claim 1, characterized in that: In step (1), the preparation method of the water-based bio-based adhesive is as follows: dissolving polyvinyl alcohol in deionized water, then adding catechin, stirring at 50-80°C until completely dissolved, adding tannic acid and continuing to stir until a uniform and stable solution is formed, which is the water-based bio-based adhesive.

3. The method for preparing recombinant technical veneer based on water regulation according to claim 2, characterized in that: The mass ratio of the polyvinyl alcohol, tannic acid, catechin and deionized water is (8-15): (0.4-1): (0.05-0.2): (83.8-91.55).

4. The method for preparing recombinant technical veneer based on water regulation according to claim 3, characterized in that: The molecular weight of the polyvinyl alcohol is 20,000-150,000, and the alcoholysis degree of the polyvinyl alcohol is greater than 90%.

5. The method for preparing recombinant technical veneer based on water regulation according to claim 1, characterized in that: In step (2), the thickness of the veneer is 0.8-1.2 mm; the drying process is: placing the veneer into a drying kiln for drying, and the moisture content of the veneer after drying is 12-15%.

6. The method for preparing recombinant technical veneer based on water regulation according to claim 5, characterized in that: In step (3), the sorted veneers are layered with water-based bio-based adhesives, and after stacking, they are transferred to a press for cold pressing. The time for transferring to the press is controlled to be 8-10 minutes. The amount of the water-based bio-based adhesive applied is 60-90 g / m 2 The cold pressing pressure is 15-19 MPa; the central moisture content of the reconstructed wood is 30-40%.

7. The method for preparing recombinant technical veneer based on water regulation according to claim 6, characterized in that: In step (4), the water spraying rate is 1.0-2.0 kg / m 2 .

8. The method for preparing recombinant technical veneer based on water regulation according to claim 7, characterized in that: In step (5), the moisture content of the recombinant technical veneer is 25-30%.

9. An application of the water-regulated reconstructed technical veneer according to claim 1, characterized in that: The recombinant technical wood veneer is processed into a veneer through a pasting and laminating process, and the steps are as follows: melamine impregnated film paper is pasted on the recombinant technical wood veneer, left for 1-3 days, and then laminating it on a substrate to obtain a veneer.

10. The method for preparing recombinant technical veneer based on water regulation according to claim 9, characterized in that: The temperature of the pasting process is 190-200℃, the time is 6-7s, and the pressure is 11-12MPa; the glue amount of the pasting process is 125-135g / m 2 The cold pressing conditions of the lamination process are: pressure of 5-6 MPa, time of 20-30 min, and the hot pressing conditions of the lamination process are: temperature of 95-105℃, pressure of 5-6 MPa, time of 10-15 min.

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