Preparation method of low-aldehyde-release and high-strength synergistic multi-layer plywood

Abstract

The invention provides a low-formaldehyde release and high-strength synergistic multilayer plywood preparation method, and relates to the technical field of artificial board manufacturing. The method comprises the following steps: carrying out water-based halogen-free flame retardant dipping treatment on a wood veneer, and then drying; activating and modifying the surface of the veneer by using normal-pressure low-temperature plasma; preparing a composite adhesive composed of styrene, vinyl acetate, a maleic anhydride terpolymer, a biomass raw material and citric acid; an adhesive is sprayed on the veneer subjected to plasma treatment through an ultrasonic cyclone atomization system according to the adhesive applying amount of 10-80 g / m < 2 >; assembling is conducted according to the odd-number-layer symmetry principle, and cold pressing and segmented heating hot pressing curing are adopted; and finally, carrying out conventional post-treatment operation. According to the method, through the synergistic effect of flame-retardant pretreatment, interface activation, a low-formaldehyde adhesive and an ultra-low sizing technology, comprehensive improvement of the environment-friendly performance, the bonding strength and the flame-retardant performance of the plywood is achieved.

Description

Technical Field

[0001] This invention relates to the field of engineered wood products manufacturing technology, specifically to a method for preparing multilayer plywood that combines low formaldehyde release with high strength. Background Technology

[0002] Plywood is a type of board made by laminating and hot-pressing multiple layers of wood veneers (thin wood sheets) together. It is widely used in furniture, construction, and other fields. However, traditional plywood manufacturing commonly uses urea-formaldehyde resin (UF) or phenolic resin (PF) adhesives, which are synthesized primarily from formaldehyde. After curing, urea-formaldehyde adhesives slowly release free formaldehyde, causing indoor environmental pollution and health hazards, leading to strict public requirements regarding formaldehyde emissions from engineered wood products. Reducing formaldehyde emissions from plywood has become a research hotspot and technical challenge in the wood products industry.

[0003] To reduce formaldehyde emissions from plywood, existing technologies have proposed various improvement measures, such as replacing urea-formaldehyde adhesives with formaldehyde-free adhesives (e.g., soybean protein glue, MDI, etc.) to prevent formaldehyde release at the source; reducing the amount of adhesive used by applying plasma treatment to the veneer surface, thereby reducing the amount of formaldehyde in the adhesive; or applying a sealing finish to the plywood surface to reduce formaldehyde escape. However, these improvement methods each have limitations: formaldehyde-free adhesives are expensive or lack water resistance and strength; simply reducing the amount of adhesive applied can reduce formaldehyde release to some extent, but without other auxiliary measures, it will lead to a decrease in the bonding strength of the plywood; surface sealing treatment can only temporarily block formaldehyde and cannot fundamentally reduce the formaldehyde content inside the plywood. In addition, most of the above methods do not take into account the important requirement of improving the flame retardant properties of the plywood.

[0004] For fire safety reasons, wood-based panels used in construction and decoration often need to possess flame-retardant properties. Traditionally, this involves impregnating the panels with flame retardants or coating them with flame-retardant paint after molding to achieve a fire-retardant rating. However, flame-retardant treatment can negatively impact the mechanical and gluing properties of the panels: for example, impregnation with water-soluble inorganic flame retardants (often containing phosphorus, nitrogen, and boron) reduces wood fiber strength; residual flame-retardant salt crystals or high moisture content can damage the adhesive layer, leading to decreased gluing strength. While some organic flame-retardant coatings have less impact on wood mechanics, they cannot penetrate the adhesive layer and increase processing steps and costs. The preparation of existing flame-retardant plywood often faces the contradiction of balancing flame-retardant effect with mechanical strength.

[0005] In recent years, low-temperature plasma surface modification technology has been introduced into the field of wood gluing to activate veneer surfaces and enhance bonding strength. Studies have shown that cold plasma treatment can improve the polarity and roughness of the wood surface without damaging the wood's interior, thereby significantly improving the wetting penetration and bonding performance of adhesives. For example, experiments have shown that nitrogen plasma pretreatment of veneers can increase the strength of urea-formaldehyde glued plywood by up to approximately 88%. Therefore, plasma treatment provides a new technical means to reduce glue application and improve gluing efficiency. Nanjing Forestry University reported a method combining atmospheric pressure plasma modification and glue atomization spraying, which significantly reduced the glue application of plywood (by 30-70%) with virtually no formaldehyde release. However, existing technologies often treat reducing formaldehyde release, improving bonding strength, and imparting flame retardancy as independent improvement directions. There is a lack of a synergistic solution that organically combines flame retardant treatment, surface activation, adhesive modification, and low-glue application processes to simultaneously achieve flame retardancy, safety (low formaldehyde), and high-performance gluing in plywood. Therefore, it is necessary to provide a new technical approach to comprehensively solve the above problems. Summary of the Invention

[0006] A method for preparing a multilayer plywood with synergistic low formaldehyde release and high strength includes the following steps: Flame-retardant pretreatment of veneer: Flame-retardant treatment is carried out on wood veneer using a flame-retardant solution, allowing the veneer to absorb the flame-retardant components and then dry, resulting in flame-retardant pretreated veneer. Plasma surface activation: The surface of the flame-retardant pretreated single board is subjected to plasma surface treatment to improve the activity and roughness of the single board surface, thereby obtaining an activated single board; Preparation of composite adhesives: Low-formaldehyde composite adhesives are prepared by using urea-formaldehyde resin adhesives as the main body and mixing them with formaldehyde-free or low-formaldehyde components to obtain composite adhesives with both high bonding strength and low formaldehyde release. Veneer gluing and assembly: The composite adhesive is applied to the surface of the activated veneer, with a lower amount of adhesive applied than the conventional amount. Adjacent veneers with perpendicular grain directions are stacked together to form a multi-layer veneer blank. Hot pressing: The blank is hot-pressed at a predetermined temperature and pressure for a period of time to cure the composite adhesive and obtain a multilayer plywood product with low formaldehyde release and high strength.

[0007] Furthermore, the flame-retardant pretreatment of the veneer involves impregnating or spraying the veneer with a water-soluble flame retardant containing phosphorus and nitrogen. The concentration of the flame retardant solution is 10-20%, and the veneer gains 5-15% weight after impregnation. The veneer is then dried until the moisture content is no higher than 8%.

[0008] Furthermore, the plasma surface treatment preferably uses atmospheric low-temperature plasma at normal pressure, with a processing power of 1000-3000W and a processing time of 5-60s.

[0009] Furthermore, the composite adhesive is composed of urea-formaldehyde resin adhesive and biomass adhesive, wherein the mass ratio of urea-formaldehyde resin adhesive to biomass adhesive is (70-90):(30-10).

[0010] Furthermore, the application rate of the composite adhesive is 10-80 g / m² per veneer on one side. 2 .

[0011] Furthermore, the hot pressing temperature of the hot pressing process is 120-150°C, the hot pressing pressure is 1.0-1.5 MPa, and the total hot pressing time is 3-8 min. It may include pre-pressing the blank with cold pressure by 0.5-1.0 MPa before hot pressing to position and form it.

[0012] Compared with the prior art, the present invention has the following advantages: Extremely low formaldehyde emission: The adhesive used in the plywood of this invention has a low formaldehyde content and is used in small quantities, significantly reducing formaldehyde emission at the source. The formaldehyde emission of the finished board can be ≤0.3mg / L (determined by environmental chamber method or perforation extraction method), which is better than the E0 standard and far lower than the emission of about 1.5mg / L of traditional plywood. The environmental safety performance of the board is significantly improved.

[0013] High bonding strength: Despite the reduced amount of adhesive applied, the plywood of this invention maintains or even exceeds the strength performance of conventional plywood. Through the combined effects of plasma surface activation and adhesive modification, the bond between the adhesive layer and the veneer interface is significantly stronger. Tests show that the dry bonding strength and wet bonding strength (after boiling water treatment) of the plywood produced by this invention both exceed national standards, representing an increase of approximately 50% or more compared to plywood produced using conventional processes. This completely solves the problem of strength reduction that is common with low adhesive application rates in general processes.

[0014] Excellent flame retardant properties: Through flame retardant pretreatment, the veneer is infused with highly efficient flame-retardant components, achieving a flame retardant rating of B1 (the national standard for fire-retardant materials). The finished board has an oxygen index (LOI) greater than 30%, significantly higher than the approximately 18-20% OX of untreated boards. This means that the board exhibits a significantly reduced burning rate in a fire, greatly improving its safety performance.

[0015] Significantly reduced adhesive usage: By improving bonding efficiency through plasma activation and using high-performance adhesives, this invention reduces adhesive application by 30-70% compared to traditional processes. For example, the amount of adhesive used per unit area of ​​the same thickness board is reduced from approximately 150g to about 50g. This not only reduces the source of harmful substances such as formaldehyde but also reduces adhesive costs, demonstrating both environmental and economic benefits.

[0016] The synergistic effect of the process is significant: the various steps of this invention work together to achieve a synergistic effect, resulting in a "1+1>2" result. Flame retardant treatment, surface activation, adhesive formulation optimization, and low adhesive application are mutually reinforcing: the absence of any one of these steps will significantly reduce the final performance. For example, without plasma activation, it is difficult to guarantee strength with low adhesive application; without flame retardant treatment, fire resistance cannot be provided; without optimized adhesives, formaldehyde levels are difficult to reduce and strength is insufficient. Through the comprehensive process of this invention, a plywood product with ultra-low formaldehyde release, high bonding strength, and flame retardant properties is successfully prepared, with overall performance superior to any existing board with only one improved feature. Therefore, the solution of this invention has outstanding substantial progress and technical effects. Detailed Implementation

[0017] The subject matter described herein will now be discussed with reference to exemplary embodiments. It should be understood that these embodiments are discussed merely to enable those skilled in the art to better understand and implement the subject matter described herein, and are not intended to limit the scope, applicability, or examples set forth in the claims. The function and arrangement of the elements discussed may be changed without departing from the scope of this specification. Various processes or components may be omitted, substituted, or added as needed in the various examples. For example, the described methods may be performed in a different order than described, and steps may be added, omitted, or combined. Furthermore, features described in some examples may be combined in other examples.

[0018] As used herein, the term "comprising" and its variations are open terms meaning "including but not limited to". The term "based on" means "at least partially based on". The terms "one embodiment" and "an embodiment" mean "at least one embodiment". The term "another embodiment" means "at least one other embodiment". The terms "first", "second", etc., may refer to different or the same objects. Other definitions, whether explicit or implicit, may be included below. Unless explicitly indicated by the context, the definition of a term shall remain consistent throughout the specification.

[0019] Example A method for preparing a multilayer plywood with synergistic low formaldehyde release and high strength includes the following steps: Flame-retardant pretreatment of veneer: Flame-retardant treatment is carried out on wood veneer using a flame-retardant solution, allowing the veneer to absorb the flame-retardant components and then dry, resulting in flame-retardant pretreated veneer. Plasma surface activation: The surface of the flame-retardant pretreated single board is subjected to plasma surface treatment to improve the activity and roughness of the single board surface, thereby obtaining an activated single board; Preparation of composite adhesives: Low-formaldehyde composite adhesives are prepared by using urea-formaldehyde resin adhesives as the main body and mixing them with formaldehyde-free or low-formaldehyde components to obtain composite adhesives with both high bonding strength and low formaldehyde release. Veneer gluing and assembly: The composite adhesive is applied to the surface of the activated veneer, with a lower amount of adhesive applied than the conventional amount. Adjacent veneers with perpendicular grain directions are stacked together to form a multi-layer veneer blank. Hot pressing: The blank is hot-pressed at a predetermined temperature and pressure for a period of time to cure the composite adhesive and obtain a multilayer plywood product with low formaldehyde release and high strength.

[0020] Furthermore, the flame-retardant pretreatment of the veneer involves impregnating or spraying the veneer with a water-soluble flame retardant containing phosphorus and nitrogen. The concentration of the flame retardant solution is 10-20%, and the veneer gains 5-15% weight after impregnation. The veneer is then dried until the moisture content is no higher than 8%.

[0021] Furthermore, the plasma surface treatment preferably uses atmospheric low-temperature plasma at normal pressure, with a processing power of 1000-3000W and a processing time of 5-60s.

[0022] Furthermore, the composite adhesive is composed of urea-formaldehyde resin adhesive and biomass adhesive, wherein the mass ratio of urea-formaldehyde resin adhesive to biomass adhesive is (70-90):(30-10).

[0023] Furthermore, the application rate of the composite adhesive is 10-80 g / m² per veneer on one side. 2 .

[0024] Furthermore, the hot pressing temperature of the hot pressing process is 120-150°C, the hot pressing pressure is 1.0-1.5 MPa, and the total hot pressing time is 3-8 min. It may include pre-pressing the blank with cold pressure by 0.5-1.0 MPa before hot pressing to position and form it.

[0025] Example 1: Preparation of Synergistic Flame-Retardant Low-Formaldehyde High-Strength Plywood (1) Flame retardant treatment of veneer: Five poplar veneers with a size of 300mm×300mm and a thickness of 1.5mm were selected, with a moisture content of approximately 6%. Flame retardant impregnation solution was prepared: Diammonium phosphate (NH4)2HPO4 and boric acid (H3BO3) were weighed and dissolved in warm water at a mass ratio of 3:1 to prepare a 15% flame retardant solution. The veneers were immersed in the flame retardant solution for 10 minutes to allow the flame retardant to fully penetrate the wood fibers. The veneers were then removed and dried in an 80℃ forced-air oven until the moisture content of the veneers returned to below 8%. After flame retardant treatment, the average weight gain of the veneers was approximately 10%, the surface was slightly lighter in color, and there was no obvious warping or deformation. A small-scale oxygen index test showed that the oxygen index of the treated veneers was 32%, a significant improvement compared to the untreated veneers (oxygen index approximately 18%), indicating that the veneers possessed good flame retardant properties.

[0026] (2) Plasma Surface Activation: The above-mentioned flame-retardant single-layer boards were surface activated using an atmospheric pressure low-temperature plasma surface treatment device. The equipment was a continuous plasma treatment machine (dielectric barrier discharge type), and the process gas was air. The single-layer boards were passed sequentially through the plasma discharge zone, with the discharge power set at 2000W. The distance between the single-layer board and the electrode was approximately 10mm. The conveying speed was adjusted so that each single-layer board stayed in the plasma zone for approximately 30 seconds, and both sides of the single-layer board were subjected to plasma treatment (the treatment was repeated after flipping). During the treatment, a slight purple glow could be observed on the surface of the single-layer board, indicating that the plasma interaction with the surface was effective. After treatment, the color of the single-layer board was slightly darker, the surface was rougher, and the hydrophilicity was enhanced (the water droplet contact angle decreased from 72° before treatment to 34°, showing obvious wetting). This indicates that the surface of the single-layer board has been etched and polar groups have been introduced, which is beneficial for the penetration of adhesive coating.

[0027] (3) Preparation of composite adhesive: The adhesive was prepared by combining low-formaldehyde urea-formaldehyde resin with soybean protein adhesive. The urea-formaldehyde resin used was industrial E0 grade urea-formaldehyde resin with a solid content of 55%, a viscosity of 300 mPa·s (25℃), and a free formaldehyde content of ≤0.1%. Approximately 10% melamine was introduced into the resin during the synthesis stage for modification to increase the crosslinking density and reduce free formaldehyde. The soybean protein adhesive was prepared by modifying commercially available defatted soybean powder, with a solid content of 25% and a viscosity of 500 mPa·s. The urea-formaldehyde resin and soybean adhesive were mixed and stirred evenly according to the ratio of 80:20 (mass ratio) to obtain the base liquid of the composite adhesive. Before use, ammonium chloride (NH4Cl) solution was added as a curing agent at 3% of the resin mass, and the mixture was stirred thoroughly again. The resulting composite adhesive had a working time of approximately 2 hours at room temperature, with moderate viscosity, and could be applied evenly by spraying. The free formaldehyde content of this adhesive was tested to be only 0.05%, which is far lower than that of ordinary urea-formaldehyde adhesive (generally above 0.3%), meeting the requirements for low-formaldehyde environmental protection.

[0028] (4) Veneer gluing and assembly: The above-mentioned composite adhesive is applied to the surface of the plasma-treated veneer by spraying. An air atomizing spray gun is used to spray the adhesive evenly back and forth at a distance of 15cm from the veneer surface. The spraying amount is controlled so that the amount of adhesive applied to each veneer on one side is about 50g / m². 2 To ensure symmetry, all five veneers except the outermost layer are coated with adhesive. After adhesive application, the veneers are assembled according to the "odd-numbered layer symmetry" principle: the five veneers are stacked sequentially, with the fiber grain directions of adjacent layers perpendicular to each other (i.e., odd-numbered layers have the same grain direction, and even-numbered layers intersect with it at 90°). The veneers on the adhesive surfaces are ensured to be in contact with each other, forming a five-layer veneer blank (approximately 300×300×7.5mm in size).

[0029] (5) Pre-pressing and hot pressing: The assembled plywood blanks are sent to a cold press for pre-pressing at a pressure of 0.8 MPa for 5 minutes to allow the adhesive to initially distribute in each layer and generate bonding force. The blanks are then transferred to a hot press for hot pressing. The heating plate temperature of the hot press is set to 130℃. The pressure is first slowly increased to 1.2 MPa and maintained at this pressure for 6 minutes, then the pressure is reduced and the board is removed. After hot pressing, the plywood blank is removed and allowed to cool to room temperature. After cooling, the edges of the board are trimmed to obtain the final flame-retardant, low-formaldehyde multilayer plywood sample. The finished board is approximately 6.5 mm thick, with a smooth surface, good adhesion of each veneer, and no delamination or obvious indentations.

[0030] (6) Performance Testing: The performance of the plywood samples prepared above was tested and compared with that of a control sample prepared by conventional processes. The control sample consisted of five layers of poplar veneer of the same specifications, but without flame retardant treatment or plasma activation. Ordinary urea-formaldehyde resin (with approximately 0.3% free formaldehyde) was used as the adhesive without the addition of bio-adhesive. The adhesive was applied by double-sided roller coating using traditional processes, with an adhesive application rate of approximately 150 g / m² per side of the veneer. 2 Then, after pre-pressing and hot-pressing at 130℃ and 1.2MPa for 6 minutes, ordinary plywood was obtained. After both samples were placed in the same environment for 7 days, their formaldehyde emission, bond strength, and flame retardant properties were tested according to standard methods. The test methods included: formaldehyde emission was determined according to the climate chamber method of GB / T17657-2013; bond strength was tested in dry and wet conditions (after boiling in water for 3 hours) according to GB / T9846-2015; and flame retardant properties were characterized using the oxygen index method of GB / T2406. The material's flammability rating was also recorded. The main performance data obtained from the tests are summarized in the table below.

[0031]

[0032] Table 1 Comparison of performance test results of the plywood of the present invention and the comparative plywood in Example 1.

[0033] As can be clearly seen from Table 1 above, the plywood of the present invention outperforms the comparative plywood prepared by traditional processes in all aspects. Specifically, the formaldehyde emission of the plywood of the present invention is only 0.3 mg / L, meeting the most stringent international E0 environmental standard, while the formaldehyde emission of ordinary plywood is approximately 1.5 mg / L, still belonging to the E1 standard, indicating a higher formaldehyde emission. The present invention achieves a significant reduction in formaldehyde emission by using a composite low-formaldehyde adhesive and reducing the amount of adhesive used.

[0034] Meanwhile, regarding bonding strength, the dry bonding strength of the board produced by this invention reaches 1.50 MPa, and the wet bonding strength (after boiling water treatment) is 0.98 MPa, both significantly higher than the comparative boards (1.05 MPa and 0.52 MPa, respectively). Particularly noteworthy is that while the strength of ordinary boards decreases significantly after boiling water treatment (to about 50% of the initial strength and below the standard requirements), the wet bonding strength of the board produced by this invention remains at 0.98 MPa, close to the strength value before immersion in water, demonstrating excellent water-resistant bonding performance. This indicates that although this invention significantly reduces the amount of adhesive used, the bonding strength increases rather than decreases due to plasma activation and improved adhesive performance, even exceeding that of boards using conventional adhesives. This fully demonstrates the synergistic effect of various measures on improving bonding quality.

[0035] Regarding flame retardant properties, the measured oxygen index of the plywood of this invention is 32%, meeting the national B1 flame-retardant standard, while the oxygen index of ordinary plywood is only 18%, classifying it as a flammable material (B3 grade). Simple combustion experiments show that after ignition, the flame of the plywood of this invention spreads slowly and is self-extinguishing, with a complete char layer, demonstrating excellent flame retardant effects; conversely, the comparative plywood spreads rapidly upon ignition, with a fierce flame and no self-extinguishing property. This invention, through veneer flame-retardant pretreatment, endows the product with superior flame-retardant properties, offering significant advantages in fire safety.

[0036] Furthermore, the amount of adhesive used per square meter of finished plywood produced according to this invention is only about one-third that of ordinary plywood. This means that the amount of adhesive used per unit product is reduced by about 67%, significantly saving production costs and reducing volatile organic compound emissions caused by adhesive use. Combined with the above results on formaldehyde release, it can be seen that reducing the amount of adhesive used has a positive impact on environmental performance and cost control, which is achieved in this invention without any performance loss.

[0037] Those skilled in the art will understand that the various embodiments disclosed above can be modified and altered in various ways without departing from the spirit of the invention. Therefore, the scope of protection of this invention should be defined by the appended claims.

[0038] It should be noted that not all steps and units in the above processes are necessary; some steps or units can be omitted as needed. The execution order of each step is not fixed and can be determined as required. The device structure described in the above embodiments can be a physical structure or a logical structure. That is, some units may be implemented by the same physical entity, or some units may be implemented by multiple physical entities, or they may be jointly implemented by certain components in multiple independent devices.

[0039] The specific embodiments described above are exemplary embodiments, but do not represent all embodiments that can be implemented or fall within the scope of the claims. The term "exemplary" as used throughout this specification means "serving as an example, instance, or illustration" and does not imply that it is "preferred" or "advantageous" compared to other embodiments. Specific details are included to provide an understanding of the described techniques. However, these techniques can be practiced without these specific details. In some instances, well-known structures and apparatuses are shown in block diagram form to avoid obscuring the concepts of the described embodiments.

[0040] The foregoing description of this disclosure is provided to enable any person skilled in the art to implement or use this disclosure. Various modifications to this disclosure will be apparent to those skilled in the art, and the general principles defined herein can be applied to other variations without departing from the scope of this disclosure. Therefore, this disclosure is not limited to the examples and designs described herein, but is consistent with the widest scope of the principles and novel features disclosed herein.

Claims

1. A method for preparing a multilayer plywood with synergistic low formaldehyde release and high strength, characterized in that, Includes the following steps: Flame-retardant pretreatment of veneer: Flame-retardant treatment is carried out on wood veneer using a flame-retardant solution, allowing the veneer to absorb the flame-retardant components and then dry, resulting in flame-retardant pretreated veneer. Plasma surface activation: The surface of the flame-retardant pretreated single board is subjected to plasma surface treatment to improve the activity and roughness of the single board surface, thereby obtaining an activated single board; Preparation of composite adhesives: Low-formaldehyde composite adhesives are prepared by using urea-formaldehyde resin adhesives as the main body and mixing them with formaldehyde-free or low-formaldehyde components to obtain composite adhesives with both high bonding strength and low formaldehyde release. Veneer gluing and assembly: The composite adhesive is applied to the surface of the activated veneer, with a lower amount of adhesive applied than the conventional amount. Adjacent veneers with perpendicular grain directions are stacked together to form a multi-layer veneer blank. Hot pressing: The blank is hot-pressed at a predetermined temperature and pressure for a period of time to cure the composite adhesive and obtain a multilayer plywood product with low formaldehyde release and high strength.

2. The method for preparing multilayer plywood with synergistic low formaldehyde release and high strength according to claim 1, characterized in that: The flame-retardant pretreatment of the veneer involves impregnating or spraying the veneer with a water-soluble flame retardant containing phosphorus and nitrogen. The concentration of the flame retardant solution is 10-20%, and the veneer gains 5-15% weight after impregnation. The veneer is then dried until the moisture content is no higher than 8%.

3. The method for preparing multilayer plywood with synergistic low formaldehyde release and high strength according to claim 1, characterized in that: The plasma surface treatment preferably uses atmospheric low-temperature plasma at normal pressure, with a processing power of 1000-3000W and a processing time of 5-60s.

4. The method for preparing multilayer plywood with synergistic low formaldehyde release and high strength according to claim 1, characterized in that: The composite adhesive is composed of urea-formaldehyde resin adhesive and biomass adhesive, wherein the mass ratio of urea-formaldehyde resin adhesive to biomass adhesive is (70-90):(30-10).

5. The method for preparing multilayer plywood with synergistic low formaldehyde release and high strength according to claim 1, characterized in that: The application rate of the composite adhesive is 10-80 g / m² per veneer on one side. 2 .

6. The method for preparing multilayer plywood with synergistic low formaldehyde release and high strength according to claim 1, characterized in that: The hot pressing temperature of the hot pressing process is 120-150℃, the hot pressing pressure is 1.0-1.5MPa, and the total hot pressing time is 3-8min. It may include pre-pressing the blank with cold pressure of 0.5-1.0MPa before hot pressing to position and form it.

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