A method for preparing a fiberboard suitable for use in an ultra-flat electrostatic powder spraying process

Abstract

The application discloses a preparation method of a fiberboard suitable for an ultra-flowing calm electric powder spraying process, which comprises the following steps: taking eucalyptus and miscellaneous wood as wood raw materials to obtain fibers after treatment; meanwhile, taking formaldehyde and melamine, mixing and adding urea for three times to prepare melamine modified urea-formaldehyde resin; taking the fibers and applying the obtained melamine modified urea-formaldehyde resin, the sizing amount being 290-300 kg / m 3 , then drying the fibers to obtain a fiberboard blank; taking the fiberboard blank to obtain a board through hot pressing, the density of the board being controlled to be 820-840 kg / m 3 , the core layer proportion being greater than 90% and the minimum density of the core layer being greater than 730 kg / m 3 , then obtaining the fiberboard suitable for the ultra-flowing calm electric powder spraying process after cooling, aging and storage of the board. The fiberboard prepared by the method has the characteristics of anti-hygroscopicity, high strength and excellent structural stability, and solves the problem that the board is easy to crack after powder spraying when the board is subjected to the ultra-flowing process.

Description

Technical Field

[0001] This invention belongs to the field of fiberboard production technology, specifically relating to a method for preparing fiberboard suitable for ultrafluid electrostatic powder coating process. Background Technology

[0002] Traditional electrostatic powder coating for fiberboard involves pre-sealing the edges and top and bottom surfaces of the board, then spraying powder coating, followed by heating and curing at a specific temperature using infrared radiation, typically 110–130℃, to form the desired finished board. With rising living standards and aesthetic preferences, higher demands are being placed on the surface finish of the coated boards, such as a smoother and flatter surface. To meet these increasing customer needs, ultra-leveling electrostatic powder coating technology has emerged. This technology utilizes higher curing temperatures, reaching 130–150℃. This high temperature accelerates both the spreading and curing of the powder coating, thereby enhancing surface smoothness and increasing production speed. Increasing the heating and curing temperature will greatly increase the degree of heat exposure of the board itself during the heating and curing process. The moisture inside the board will escape more quickly during the heating process, causing an impact on the inside of the board and resulting in cracking after powder coating. Therefore, solving the cracking problem of the board during the ultra-fluid electrostatic powder coating process has become increasingly important. Summary of the Invention

[0003] To address the aforementioned shortcomings, this invention discloses a method for preparing fiberboard suitable for ultra-fluid leveling powder coating process, solving the problem that the fiberboard is prone to cracking after powder coating when the fiberboard undergoes ultra-fluid leveling process.

[0004] This invention is achieved using the following technical solution:

[0005] A method for preparing fiberboard suitable for ultrafluid static electro-powder coating process includes the following steps:

[0006] (1) Eucalyptus and miscellaneous wood are used as timber raw materials, and the weight ratio of eucalyptus to miscellaneous wood is (3-4):(6-7); after processing the timber raw materials, fibers are obtained, in which fibers with a diameter ≤0.06mm account for 5-20% of the total weight, fibers with a diameter of 0.06-0.125mm account for 25-40% of the total weight, fibers with a diameter of 0.125-1mm account for 40-70% of the total weight, and fibers with a diameter >1mm account for 0.1-0.3% of the total weight;

[0007] When the fiber thickness of the board is not uniform, coarse fibers will affect the smoothness of the board surface. Uneven fiber thickness will cause water to escape in a disordered way during heating, resulting in uneven internal pressure and cracking at the weak points of the board. Therefore, this invention adjusts the proportion of fibers with different diameters to make the coarse and fine fibers evenly matched, thus avoiding the above problems.

[0008] (2) Apply sizing to the fibers obtained in step (1) at a rate of 290–300 kg / m³. 3 The adhesive used for sizing is urea-formaldehyde resin. After drying the fibers, they are laid out and molded to obtain a fiberboard blank.

[0009] (3) Take the fiberboard blank obtained in step (2) and perform a hot pressing process to obtain a board. The density of the board is controlled at 820-840 kg / m³. 3 The core layer accounts for more than 90% of the total content and the density at the lowest point of the core layer is greater than 730 kg / m³. 3 The press pressure in the hot pressing process is 0.17–1.6 N / mm. 2 The speed is 135-235 mm / s, and a cyclic hot pressing method is adopted. The hot pressing temperature in the first to third cycles is 220-245℃. In the first area, the stability is raised as much as possible to transfer heat to the inside of the board more effectively. The hot pressing temperature in the fourth to sixth cycles is 195-235℃. Under the premise of ensuring heat transfer, the adhesive is gradually cured to obtain the pressed board.

[0010] By using an appropriate board density, the fiber compactness can be increased without increasing the difficulty of subsequent fiberboard milling. The density at the lowest point of the core layer should be controlled to be greater than 730 kg / m³. 3 This ensures that there are no weak points in the overall core layer;

[0011] (4) After cooling the board material that has undergone the hot pressing process in step (3), stack the board material for curing, and then obtain fiberboard suitable for superfluid electrostatic powder coating process by conventional sanding and sawing.

[0012] Furthermore, in step (1), the mixed wood includes large-leaved oak, tung tree and jasmine.

[0013] Furthermore, in step (4), after cooling the board to below 40°C, the board is stacked and stored for 48-72 hours to obtain a fiberboard suitable for the ultrafluid static electro-powder coating process. In the board cooling process, after the board comes out of the press, it is cooled sufficiently by the combined action of multiple flip-plate cooling wheels and a three-dimensional forced convection cooling system, ensuring that the average temperature is reduced to below 40°C before curing, preventing strength degradation due to insufficient dissipation of residual heat. In the curing and storage process, the board is stacked and stored, with a curing period between 48 and 72 hours. This allows for the full release of stress within the board, enabling the components to reach a stable and balanced state; secondly, because the temperature drop in the middle of the board is not significant during stacking, a suitable curing time is ensured to minimize the degradation effect of residual heat on the board.

[0014] Furthermore, in step (2), the urea-formaldehyde resin is a melamine-modified urea-formaldehyde resin, and its preparation method includes the following steps:

[0015] S1. Weigh out formaldehyde, urea, melamine, and polyvinyl alcohol according to the following proportions; the weight of melamine accounts for 3-8% of the total weight of urea-formaldehyde resin, the molar ratio of formaldehyde to the sum of urea and melamine is 0.85-0.95, and the weight of polyvinyl alcohol accounts for 1-5% of the total weight of urea-formaldehyde resin;

[0016] S2. Place formaldehyde in a reaction vessel, add caustic soda solution to adjust the pH value to 6.5-7.5, then add melamine and stir for 15-25 minutes. Then heat to 60°C and measure the pH value. When the pH value is 6.0-7.0, raise the temperature to 65°C and add urea, with the molar ratio of formaldehyde to urea controlled at 2.0-2.5 to obtain mixture A.

[0017] S3. Take the mixture A obtained in step S2, heat it to 85-90℃ and keep it at that temperature for 20 minutes. Then add formic acid solution to adjust the pH value to 5.5-6.5. Check the pH value and viscosity value every 5-10 minutes (using a viscosity cup). When the viscosity reaches 18-20 seconds, add caustic soda solution to adjust the pH value to 6.5-7.5. Then add urea and control the molar ratio of formaldehyde to urea to be 1.6-1.7. Then stir the reaction at 80-85℃. Check the pH value and viscosity value every 5-10 minutes (using a viscosity cup). When the viscosity reaches 20-22 seconds, obtain mixture B.

[0018] S4. Take the mixture B obtained in step S3, add caustic soda solution to adjust the pH value to 7.0-8.0, then add urea and control the molar ratio of formaldehyde to urea to be 0.90-1.05. After stirring for 10-20 minutes, add polyvinyl alcohol to react and obtain mixture C.

[0019] The addition of polyvinyl alcohol (PVA) not only allows it to react with free formaldehyde to form a six-membered ring structure of PVA formal, which is resistant to moisture and impact, but also, because PVA molecules contain polar hydroxyl groups, PVA can cross-link with polar plant fibers through hydrogen bonds to form a denser network structure. This enhances the bonding strength between the adhesive and the fiber, thus solving the problem of insufficient board strength and cracking caused by moisture loss during the high-temperature baking process in super-leveling coating. Furthermore, it also addresses the issue of boards easily absorbing moisture from the air when exposed to air, reducing the risk of cracking during super-leveling coating.

[0020] S5. Take the mixture C obtained in step S4 and cool it to 45°C. Then add caustic soda solution to adjust the pH value to 8.0-8.5. Then cool it to below 40°C and when the viscosity is 16-20s and the solid content is 55.0-58.0%, the melamine-modified urea-formaldehyde resin is obtained.

[0021] Furthermore, the concentration of the caustic soda solution is 25% to 35%, and the concentration of the formic acid solution is 15% to 20%.

[0022] Furthermore, in step S4, after adding polyvinyl alcohol, the mixture is reacted for 15-30 minutes to obtain mixture C.

[0023] Compared with existing technologies, this technical solution has the following advantages:

[0024] 1. The fiberboard prepared by the method of the present invention is conducive to milling. After milling, the board surface has good flatness, which makes the paint surface smooth and flat after the board is sprayed with the super leveling process.

[0025] 2. The method of the present invention improves the moisture resistance of the board, enabling the board to be used normally in environments with high humidity, thereby improving the stability of the product.

[0026] 3. The fiberboard prepared by the method of the present invention can meet the requirements of electrostatic powder coating with super-leveling process under high temperature conditions, which greatly improves the production efficiency of electrostatic powder coating, reduces the risk of product cracking, and improves product quality. Attached Figure Description

[0027] Figure 1 The graph shows the comparison results obtained from the moisture absorption test described in Experimental Example 1, where curve 1 represents the fiberboard obtained by the method described in Comparative Example 1, and curve 2 represents the fiberboard obtained by the method described in Example 1. Detailed Implementation

[0028] The present invention is further illustrated by the following examples, but these are not intended to limit the invention. Specific experimental conditions and methods not specified in the following examples are generally conventional methods well known to those skilled in the art.

[0029] Example 1: A method for preparing a fiberboard suitable for ultrafluid static electrostatic powder coating process, comprising the following steps:

[0030] (1) Eucalyptus and miscellaneous wood are used as timber raw materials, and the weight ratio of eucalyptus and miscellaneous wood is 3.5:6.5; after processing the timber raw materials, fibers are obtained. Among the fibers, fibers with a diameter ≤0.06mm account for 10% of the total weight, fibers with a diameter between 0.06 and 0.125mm account for 30% of the total weight, fibers with a diameter between 0.125 and 1mm account for 59.8% of the total weight, and fibers with a diameter >1mm account for 0.2% of the total weight; the miscellaneous wood is a mixture of large-leaved oak, pine, and sagebrush.

[0031] (2) Apply sizing to the fibers obtained in step (1) at a rate of 295 kg / m². 3 The adhesive used for sizing is urea-formaldehyde resin. After the fibers are dried, they are laid out and shaped to obtain a fiberboard blank.

[0032] (3) Take the fiberboard blank obtained in step (2) and perform a hot pressing process to obtain the board (a Dieffenbacher continuous press can be used, with an effective length of 42.88m, a temperature range of 220~245℃, and the product specifications of the board are 18~22mm). The density of the board is 825kg / m³. 3 The core layer accounts for 92% of the total structure, and the density at the lowest point of the core layer is 759 kg / m³. 3 The press pressure in the hot pressing process is 0.17–1.6 N / mm. 2 The speed is 135-235 mm / s, and a cyclic hot pressing method is adopted. The hot pressing temperature in the first to third cycles is 220-245℃, and the hot pressing temperature in the fourth to sixth cycles is 195-235℃.

[0033] (4) After the board material that has undergone the hot pressing process in step (3) is cooled to below 40°C, the board material is stacked and stored for 60 hours to obtain a fiberboard suitable for the superfluid electrostatic powder coating process.

[0034] The urea-formaldehyde resin is a melamine-modified urea-formaldehyde resin, and its preparation method includes the following steps:

[0035] S1. Weigh out formaldehyde, urea, melamine, and polyvinyl alcohol according to the following proportions; the weight of melamine accounts for 5% of the total weight of urea-formaldehyde resin, the molar ratio of formaldehyde to the sum of urea and melamine is 0.90, and the weight of polyvinyl alcohol accounts for 3% of the total weight of urea-formaldehyde resin;

[0036] S2. Formaldehyde was placed in a reaction vessel, and caustic soda solution was added to adjust the pH to 7.0. Then melamine was added and stirred for 20 minutes. The mixture was then heated to 60°C and the pH was measured. When the pH reached 6.5, the temperature was raised to 65°C and urea was added, with the molar ratio of formaldehyde to urea controlled at 2.2 to obtain mixture A. The concentration of the caustic soda solution was 30%.

[0037] S3. Take the mixture A obtained in step S2, heat it to 86℃ and keep it at that temperature for 20 minutes. Then, add formic acid solution to adjust the pH value to 6.0. Check the pH value and viscosity value every 8 minutes (using a viscosity cup). When the viscosity reaches 19 seconds, add caustic soda solution to adjust the pH value to 7.0. Then, add urea, and control the molar ratio of formaldehyde to urea to be 1.64. Then, stir the reaction at 80-85℃. Check the pH value and viscosity value every 5-10 minutes (using a viscosity cup). When the viscosity reaches 21 seconds, obtain mixture B. The concentration of the formic acid solution is 18%.

[0038] S4. Take the mixture B obtained in step S3, add caustic soda solution to adjust the pH value to 7.5-8.0, then add urea and control the molar ratio of formaldehyde to urea to be 0.95. After stirring for 15 minutes, add polyvinyl alcohol and react for 20 minutes to obtain mixture C.

[0039] S5. Take the mixture C obtained in step S4 and cool it to 45°C. Then add caustic soda solution to adjust the pH value to 8.2. Then cool it to below 40°C and discharge the colloid to obtain melamine-modified urea-formaldehyde resin with a viscosity of 18s and a solid content of 56.0%.

[0040] Example 2: A method for preparing a fiberboard suitable for ultrafluid static electrostatic powder coating process, comprising the following steps:

[0041] (1) Eucalyptus and miscellaneous wood are used as timber raw materials, with a weight ratio of 4:6; after processing the timber raw materials, fibers are obtained, in which fibers with a diameter ≤0.06mm account for 5% of the total weight, fibers with a diameter between 0.06 and 0.125mm account for 25% of the total weight, fibers with a diameter between 0.125 and 1mm account for 69.9% of the total weight, and fibers with a diameter >1mm account for 0.1% of the total weight; the miscellaneous wood includes a mixture of large-leaved oak, pine, and sagebrush.

[0042] (2) Apply sizing to the fibers obtained in step (1) at a rate of 290 kg / m². 3 The adhesive used for sizing is urea-formaldehyde resin. After the fibers are dried, they are laid out and shaped to obtain a fiberboard blank.

[0043] (3) Take the fiberboard blank obtained in step (2) and perform a hot pressing process to obtain a board, the density of which is 820 kg / m³. 3 The core layer accounts for 90% of the total structure, and the density at the lowest point of the core layer is 738 kg / m³. 3 The press pressure in the hot pressing process is 0.17–1.6 N / mm. 2 The speed is 135-235 mm / s, and a cyclic hot pressing method is adopted. The hot pressing temperature in the first to third cycles is 220-235℃, and the hot pressing temperature in the fourth to sixth cycles is 195-228℃.

[0044] (4) After the board material that has undergone the hot pressing process in step (3) is cooled to below 40°C, the board material is stacked and stored for 48 hours to obtain a fiberboard suitable for the superfluid electrostatic powder coating process.

[0045] The urea-formaldehyde resin is a melamine-modified urea-formaldehyde resin, and its preparation method includes the following steps:

[0046] S1. Weigh out formaldehyde, urea, melamine, and polyvinyl alcohol according to the following proportions; the weight of melamine accounts for 3% of the total weight of urea-formaldehyde resin, the molar ratio of formaldehyde to the sum of urea and melamine is 0.85, and the weight of polyvinyl alcohol accounts for 1% of the total weight of urea-formaldehyde resin;

[0047] S2. Formaldehyde was placed in a reaction vessel, and caustic soda solution was added to adjust the pH to 6.5. Then melamine was added and stirred for 15 minutes. The mixture was then heated to 60°C and the pH was measured. When the pH reached 6.0, the temperature was raised to 65°C and urea was added, with the molar ratio of formaldehyde to urea controlled at 2.0 to obtain mixture A. The concentration of the caustic soda solution was 30%.

[0048] S3. Take the mixture A obtained in step S2, heat it to 85℃ and keep it at that temperature for 20 minutes. Then, add formic acid solution to adjust the pH value to 5.5. Check the pH value and viscosity value every 5 minutes (using a viscosity cup). When the viscosity reaches 18 seconds, add caustic soda solution to adjust the pH value to 6.5. Then, add urea, and control the molar ratio of formaldehyde to urea to be 1.6. Then, stir the reaction at 80-85℃. Check the pH value and viscosity value every 5-10 minutes (using a viscosity cup). When the viscosity reaches 20 seconds, obtain mixture B. The concentration of the formic acid solution is 15%.

[0049] S4. Take the mixture B obtained in step S3, add caustic soda solution to adjust the pH value to 7.0, then add urea and control the molar ratio of formaldehyde to urea to be 0.90. After stirring for 10 minutes, add polyvinyl alcohol and react for 15 minutes to obtain mixture C.

[0050] S5. Take the mixture C obtained in step S4 and cool it to 45°C. Then add caustic soda solution to adjust the pH value to 8.0. Then cool it to below 40°C and discharge the granulated material to obtain melamine-modified urea-formaldehyde resin with a viscosity of 16s and a solid content of 55.0%.

[0051] Example 3: A method for preparing a fiberboard suitable for ultrafluid static electrostatic powder coating process, comprising the following steps:

[0052] (1) Eucalyptus and miscellaneous wood are used as timber raw materials, and the weight ratio of eucalyptus to miscellaneous wood is 3.6:6.2; after processing the timber raw materials, fibers are obtained. Among the fibers, fibers with a diameter ≤0.06mm account for 20% of the total weight, fibers with a diameter between 0.06 and 0.125mm account for 40% of the total weight, fibers with a diameter between 0.125 and 1mm account for 39.7% of the total weight, and fibers with a diameter >1mm account for 0.3% of the total weight; the miscellaneous wood is a mixture of large-leaved oak and privet.

[0053] (2) Apply sizing to the fibers obtained in step (1) at a rate of 298 kg / m³. 3 The adhesive used for sizing is urea-formaldehyde resin. After the fibers are dried, they are laid out and shaped to obtain a fiberboard blank.

[0054] (3) Take the sheet material obtained in step (2) and perform a hot pressing process to obtain a sheet material. The density of the sheet material is controlled at 835 kg / m³. 3 The core layer accounts for 91% of the total structure, and the density at the lowest point of the core layer is 760 kg / m³. 3 The press pressure in the hot pressing process is 0.17–1.6 N / mm. 2 The speed is 135-235 mm / s, and a cyclic hot pressing method is adopted. The hot pressing temperature in the first to third cycles is 235-240℃, and the hot pressing temperature in the fourth to sixth cycles is 215-220℃.

[0055] (4) After the board material that has undergone the hot pressing process in step (3) is cooled to below 40°C, the board material is stacked and stored for 66 hours to obtain a fiberboard suitable for the superfluid electrostatic powder coating process.

[0056] The urea-formaldehyde resin is a melamine-modified urea-formaldehyde resin, and its preparation method includes the following steps:

[0057] S1. Weigh out formaldehyde, urea, melamine, and polyvinyl alcohol according to the following proportions; the weight of melamine accounts for 6% of the total weight of urea-formaldehyde resin, the molar ratio of formaldehyde to the sum of urea and melamine is 0.92, and the weight of polyvinyl alcohol accounts for 4% of the total weight of urea-formaldehyde resin;

[0058] S2. Formaldehyde was placed in a reaction vessel, and caustic soda solution was added to adjust the pH to 7.0. Then melamine was added and stirred for 20 minutes. The mixture was then heated to 60°C and the pH was measured. When the pH reached 6.5, the temperature was raised to 65°C and urea was added, with the molar ratio of formaldehyde to urea controlled at 2.4 to obtain mixture A. The concentration of the caustic soda solution was 30%.

[0059] S3. Take the mixture A obtained in step S2, heat it to 88℃ and keep it at that temperature for 20 minutes. Then, add formic acid solution to adjust the pH value to 6.0. Check the pH value and viscosity value every 8 minutes (using a viscosity cup). When the viscosity reaches 18.5s, add caustic soda solution to adjust the pH value to 7.0. Then, add urea, and control the molar ratio of formaldehyde to urea to be 1.68. Then react at 80-85℃. Check the pH value and viscosity value every 5-10 minutes (using a viscosity cup). When the viscosity reaches 21s, obtain mixture B. The concentration of the formic acid solution is 18%.

[0060] S4. Take the mixture B obtained in step S3, add caustic soda solution to adjust the pH value to 7.5, then add urea and control the molar ratio of formaldehyde to urea to be 1.00. After stirring for 15 minutes, add polyvinyl alcohol and react for 25 minutes to obtain mixture C.

[0061] S5. Take the mixture C obtained in step S4 and cool it to 45°C. Then add caustic soda solution to adjust the pH value to 8.3. Then cool it to below 40°C and discharge the granules to obtain melamine-modified urea-formaldehyde resin with a viscosity of 18s and a solid content of 57.0%.

[0062] Example 4: A method for preparing a fiberboard suitable for ultrafluid static electrostatic powder coating process, comprising the following steps:

[0063] (1) Eucalyptus and miscellaneous wood are used as timber raw materials, with a weight ratio of 3:7; after processing the timber raw materials, fibers are obtained, in which fibers with a diameter ≤0.06mm account for 10% of the total weight, fibers with a diameter between 0.06 and 0.125mm account for 29.8% of the total weight, fibers with a diameter between 0.125 and 1mm account for 60% of the total weight, and fibers with a diameter >1mm account for 0.2% of the total weight; the miscellaneous wood includes large-leaved oak, pine, and sagebrush;

[0064] (2) Apply sizing to the fibers obtained in step (1) at a rate of 300 kg / m³. 3 The adhesive used for sizing is urea-formaldehyde resin. After the fibers are dried, they are laid out and shaped to obtain a fiberboard blank.

[0065] (3) The fiberboard blank obtained in step (2) is subjected to a hot pressing process to obtain a board, the density of which is 840 kg / m³.3 The core layer accounts for 92% of the total structure, and the density at the lowest point of the core layer is 740 kg / m³. 3 The press pressure in the hot pressing process is 0.17–1.6 N / mm. 2 The speed is 135-235 mm / s, and a cyclic hot pressing method is adopted. The hot pressing temperature in the first to third cycles is 225-245℃, and the hot pressing temperature in the fourth to sixth cycles is 210-235℃.

[0066] (4) After the board material that has undergone the hot pressing process in step (3) is cooled to below 40°C, the board material is stacked and stored for 72 hours to obtain a fiberboard suitable for the superfluid electrostatic powder coating process.

[0067] The urea-formaldehyde resin is a melamine-modified urea-formaldehyde resin, and its preparation method includes the following steps:

[0068] S1. Weigh out formaldehyde, urea, melamine, and polyvinyl alcohol according to the following proportions; the weight of melamine accounts for 8% of the total weight of urea-formaldehyde resin, the molar ratio of formaldehyde to the sum of urea and melamine is 0.95, and the weight of polyvinyl alcohol accounts for 5% of the total weight of urea-formaldehyde resin.

[0069] S2. Formaldehyde was placed in a reaction vessel, and caustic soda solution was added to adjust the pH to 7.5. Then melamine was added and stirred for 25 minutes. The mixture was then heated to 60°C and the pH was measured. When the pH reached 7.0, the temperature was raised to 65°C and urea was added, with the molar ratio of formaldehyde to urea controlled at 2.5 to obtain mixture A. The concentration of the caustic soda solution was 30%.

[0070] S3. Take the mixture A obtained in step S2, heat it to 90℃ and keep it at that temperature for 20 minutes. Then, add formic acid solution to adjust the pH value to 6.5. Check the pH value and viscosity value every 10 minutes (using a viscosity cup). When the viscosity reaches 20 seconds, add caustic soda solution to adjust the pH value to 7.5. Then, add urea, and control the molar ratio of formaldehyde to urea to be 1.7. Then react at 83-85℃. Check the pH value and viscosity value every 5-10 minutes (using a viscosity cup). When the viscosity reaches 22 seconds, obtain mixture B. The concentration of the formic acid solution is 20%.

[0071] S4. Take the mixture B obtained in step S3, add caustic soda solution to adjust the pH value to 8.0, then add urea and control the molar ratio of formaldehyde to urea to be 1.05. After stirring for 20 minutes, add polyvinyl alcohol and react for 30 minutes to obtain mixture C.

[0072] S5. Take the mixture C obtained in step S4 and cool it to 45°C. Then add caustic soda solution to adjust the pH value to 8.5. Then cool it to below 40°C and discharge the granules to obtain melamine-modified urea-formaldehyde resin with a viscosity of 20s and a solid content of 58.0%.

[0073] Comparative Example 1: The difference between the preparation method of the fiberboard suitable for the superfluid electrostatic powder coating process described in this comparative example and the preparation method described in Example 1 is that the adhesive used in step (2) is conventional urea-formaldehyde resin, that is, it is produced using urea and formaldehyde as raw materials.

[0074] Comparative Example 2: The difference between the preparation method of the fiberboard suitable for the ultrafluid static electrostatic powder coating process described in this comparative example and the preparation method described in Example 1 is only that, in step (2), the density of the board is 750 kg / m³. 3 The core layer accounts for 84% of the total structure, and the density at the lowest point of the core layer is 630 kg / m³. 3 .

[0075] Comparative Example 3: The difference between the preparation method of the fiberboard suitable for the superfluid electrostatic powder coating process described in this comparative example and the preparation method described in Example 1 is only that, in step (2), the density of the board is 800 kg / m³. 3 The core layer accounts for 87% of the total structure, and the density at the lowest point of the core layer is 696 kg / m³. 3 .

[0076] Experimental Example 1: Fiberboard was produced according to the methods described in Example 1 and Comparative Example 1. The fiberboard was then subjected to an accelerated moisture absorption test in an environment of 36°C and 90% humidity. The moisture absorption rate was calculated as follows: Moisture absorption rate = (mass of increased moisture / mass of board after moisture absorption) × 100%. Specific results are shown in [link to results]. Figure 1 The fiberboard obtained by this invention has good moisture resistance.

[0077] Experimental Example 2: Fiberboard was produced according to the methods described in Examples 1-4 and Comparative Examples 1-3. The fiberboard was then subjected to moisture absorption at 36°C and 90% humidity for 1 hour and 2 hours, and then baked at 150°C for 5 minutes for testing. The specific results are shown in Table 1.

[0078] Table 1 Results of fiberboard baking test

[0079]

[0080] As can be seen from the data in Table 1, the fiberboard prepared by this invention has the characteristics of moisture resistance, high strength, and excellent structural stability.

[0081] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing fiberboard suitable for ultrafluid static electrostatic powder coating process, characterized in that: Includes the following steps: (1) Eucalyptus and miscellaneous wood are used as raw materials, and the weight ratio of eucalyptus to miscellaneous wood is (3-4):(6-7); after processing the raw materials, fibers are obtained, in which fibers with a diameter ≤0.06mm account for 5-20% of the total weight, fibers with a diameter of 0.06-0.125mm account for 25-40% of the total weight, fibers with a diameter of 0.125-1mm account for 40-70% of the total weight, and fibers with a diameter >1mm account for 0.1-0.3% of the total weight; (2) Apply sizing to the fibers obtained in step (1) at a rate of 290–300 kg / m³. 3 The adhesive used for sizing is urea-formaldehyde resin. After the fibers are dried, they are laid out and shaped to obtain a fiberboard blank. The urea-formaldehyde resin is a melamine-modified urea-formaldehyde resin, and its preparation method includes the following steps: S1. Weigh out formaldehyde, urea, melamine, and polyvinyl alcohol according to the following proportions; the weight of melamine accounts for 3-8% of the total weight of urea-formaldehyde resin, the molar ratio of formaldehyde to the sum of urea and melamine is 0.85-0.95, and the weight of polyvinyl alcohol accounts for 1-5% of the total weight of urea-formaldehyde resin; S2. Place formaldehyde in a reaction vessel, add caustic soda solution to adjust the pH value to 6.5-7.5, then add melamine and stir for 15-25 minutes. Then heat to 60°C and measure the pH value. When the pH value is 6.0-7.0, raise the temperature to 65°C and add urea, with the molar ratio of formaldehyde to urea controlled at 2.0-2.5 to obtain mixture A. S3. Take the mixture A obtained in step S2, heat it to 85-90℃ and keep it at that temperature for 20 minutes. Then add formic acid solution to adjust the pH value to 5.5-6.

5. Check the pH value and viscosity value every 5-10 minutes. When the viscosity reaches 18-20 seconds, add caustic soda solution to adjust the pH value to 6.5-7.

5. Then add urea and control the molar ratio of formaldehyde to urea to be 1.6-1.

7. Then stir the reaction at 80-85℃. Check the pH value and viscosity value every 5-10 minutes. When the viscosity reaches 20-22 seconds, the mixture B is obtained. S4. Take the mixture B obtained in step S3, add caustic soda solution to adjust the pH value to 7.0-8.0, then add urea and control the molar ratio of formaldehyde to urea to be 0.90-1.

05. After stirring for 10-20 minutes, add polyvinyl alcohol to react and obtain mixture C. S5. Take the mixture C obtained in step S4 and cool it to 45°C. Then add caustic soda solution to adjust the pH value to 8.0-8.

5. Then cool it to below 40°C and when the viscosity is 16-20s and the solid content is 55.0-58.0%, the melamine-modified urea-formaldehyde resin is obtained. (3) Take the fiberboard blank obtained in step (2) and perform a hot pressing process to obtain a board. The density of the board is controlled at 820-840 kg / m³. 3 The core layer accounts for more than 90% of the total content and the density at the lowest point of the core layer is greater than 730 kg / m³. 3 The press pressure in the hot pressing process is 0.17–1.6 N / mm. 2 The speed is 135-235 mm / s, and a cyclic hot pressing method is adopted. The hot pressing temperature in the first to third cycles is 225-240℃, and the hot pressing temperature in the fourth to sixth cycles is 200-232℃. (4) After cooling the board material that has undergone the hot pressing process in step (3), stack the board material for curing, and then sand and saw it in a conventional manner to obtain a fiberboard suitable for the superfluid electrostatic powder coating process.

2. The method for preparing fiberboard suitable for ultrafluid static electrostatic powder coating process according to claim 1, characterized in that: In step (1), the mixed wood includes large-leaved oak, tung tree and jasmine.

3. The method for preparing fiberboard suitable for ultrafluid static electrostatic powder coating process according to claim 1, characterized in that: In step (4), after cooling the board to below 40°C, the board is stacked and stored for 48 to 72 hours to obtain a fiberboard suitable for superfluid electrostatic powder coating process.

4. The method for preparing fiberboard suitable for ultrafluid static electrostatic powder coating process according to claim 1, characterized in that: The concentration of the caustic soda solution is 25% to 35%, and the concentration of the formic acid solution is 15% to 20%.

5. The method for preparing fiberboard suitable for ultrafluid static electrostatic powder coating process according to claim 1, characterized in that: In step S4, after adding polyvinyl alcohol, the mixture is reacted for 15-30 minutes to obtain mixture C.

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