Manufacturing process of high-water-content low-imbibition floor base material

Abstract

The invention belongs to the technical field of artificial boards, and relates to a manufacturing process of a high-water-content low-imbibition floor base material, which comprises the steps of glue mixing and applying, pre-pressing, hot pressing and the like. When glue is mixed and applied, waterproof low-melamine-proportion modified urea-formaldehyde resin (55-57% of formaldehyde, 31-35% of urea and 8-14% of melamine), a curing agent and a composite formaldehyde reducing agent are applied according to a specific formula. The resin is synthesized by adopting an alkali-acid-alkali-alkali four-stage process. In the pre-pressing step, microwave heating is adopted to heat the slab core layer to 60-70 DEG C; continuous hot pressing is adopted for hot pressing, and five-section temperature partition and four-section pressure distribution are optimized. Through the synergistic effect of a special resin formula, microwave preheating of a plate blank and optimization of a hot pressing process, on the premise that the use amount of melamine is remarkably reduced, the obtained floor base material obtains the low water absorption thickness swelling rate, meanwhile, the water content is increased to 6.0-7.0%, the size stability is better, the formaldehyde release amount is effectively controlled, and the service life of the floor base material is prolonged. The production efficiency is improved; and the cost is reduced.

Description

Technical Field

[0001] This invention belongs to the field of engineered wood products technology, and relates to the preparation of engineered fiberboard, and particularly to a manufacturing process for a flooring substrate with high moisture content and low swelling. Background Technology

[0002] With the development of the social economy and the improvement of residents' living standards, impregnated paper laminate wood flooring (market name: engineered wood flooring) has become a widely used floor decoration material in interior decoration due to its advantages such as high durability, easy maintenance, high stability, beautiful appearance, simple installation and affordable price, and is increasingly favored by consumers.

[0003] Laminate flooring typically uses high-density fiberboard (HDF) as its core material. However, the inherent shrinkage and swelling properties of wood make traditional HDF substrates prone to performance fluctuations when the humidity of the environment changes. Specifically, in humid environments, the flooring substrate absorbs moisture from the air and expands, leading to problems such as warping, deformation, and buckling, severely impacting the user experience and lifespan. Therefore, developing flooring substrate products with low water absorption thickness expansion rate (referred to as low swelling) is key to solving these problems.

[0004] Currently, the core performance requirements for low-absorption flooring substrates in the industry are: water absorption thickness expansion rate ≤6.0% (industry standard requires ≤10.0%). Laminate flooring made from this substrate can have its water absorption thickness expansion rate controlled at ≤10.0%, which is between commercial grade I and commercial grade II in GB / T 18102-2020 "Impregnated Paper Laminate Wood Flooring", and can adapt to a wider range of indoor humidity environments.

[0005] In existing technologies, a common method used by fiberboard manufacturers to produce low-swell flooring substrates is to increase the proportion of melamine in the resin to over 15%. Melamine participates in the polycondensation reaction by introducing triazine heterocyclic structures, which allows the resin to form more three-dimensional structures, increases the crosslinking density, and thereby blocks hydrophilic groups (such as -CH2OH, -CONH-, etc.) in the resin, thus improving the resin's water resistance. However, this technical solution has the following significant drawbacks:

[0006] 1. The addition of melamine accelerates the curing speed of the adhesive, causing the surface of the slab to cure rapidly during hot pressing, forming a thicker, high-density layer. This high-density layer hinders heat transfer from the surface to the core layer, requiring a longer hot pressing time to ensure the core layer reaches its curing temperature.

[0007] 2. Extended hot-pressing time leads to increased moisture generation in the slab during the hot-pressing process, increasing the risk of blistering. To mitigate this risk, manufacturers can only control the fiber moisture content to a lower range (4-5%), creating a vicious cycle.

[0008] 3. Flooring substrates with low moisture content are prone to moisture absorption during subsequent storage, transportation and use, which leads to poor dimensional stability of the substrate and eventually problems such as buckling and deformation.

[0009] 4. The use of a high proportion of melamine and the extension of hot-pressing time significantly increased production costs and reduced production efficiency.

[0010] Therefore, how to increase the moisture content of the flooring substrate while ensuring low swelling performance, and at the same time optimize the production process and reduce costs, has become a technical problem that the fiberboard industry urgently needs to solve.

[0011] To address the aforementioned technical problems, this invention aims to develop a waterproof, low-melamine-ratio modified urea-formaldehyde resin and optimize the manufacturing process of the corresponding low-swelling flooring substrate. Through multi-dimensional synergistic improvements such as resin modification, formaldehyde reduction compounding, board preheating, and hot pressing parameter optimization, the invention overcomes the shortcomings of existing technologies and produces a low-swelling flooring substrate with high moisture content, good dimensional stability, and reasonable production costs, thereby meeting the market demand for high-quality engineered wood flooring. Summary of the Invention

[0012] In view of the technical defects of existing low-swelling flooring substrates, such as low moisture content, poor dimensional stability, and high production cost, the purpose of this invention is to disclose a manufacturing process for a high moisture content, low-swelling flooring substrate, which achieves performance advantages such as high moisture content, good dimensional stability, and low water absorption thickness expansion rate, thus meeting the usage requirements of low-swelling engineered wood flooring.

[0013] Technical solution

[0014] A manufacturing process for a high moisture content, low swelling flooring substrate includes the following steps: log feeding → peeling → chipping → screening → washing → pre-cooking → cooking → hot grinding → adhesive application → drying → sorting → laying → pre-pressing → hot pressing → cooling → curing → sanding → sawing → inspection and grading → packaging and warehousing. The technical parameters and control requirements for the key steps are as follows:

[0015] 1. In the sizing step, waterproof, low-melamine modified urea-formaldehyde resin is uniformly applied through an atomizing sizing device into the pipe from which the fiber is sprayed from the thermoforming mill, with an application rate of 250-300 kg / m³. 3 Simultaneously, ammonium chloride is applied as a curing agent, with an addition amount of 1-2% of the dry resin mass; a composite formaldehyde-reducing agent is applied concurrently, with an addition amount of 2-5% of the liquid resin mass.

[0016] The waterproof, low-melamine-ratio modified urea-formaldehyde resin is synthesized using a four-stage "alkali-acid-alkali-alkali" process. Formaldehyde is added in two stages, urea in three stages, and melamine in one stage. The specific preparation steps are as follows:

[0017] A. Add formaldehyde (90-92% of the total formaldehyde mass) to the reactor for the first time, and adjust the pH value to 8.0-8.5 with a 20% sodium hydroxide solution.

[0018] B. Add the first batch of urea (49-52% of the total mass of urea), turn on the steam heating, and when the temperature reaches 80°C, stop the steam heating and use the exothermic reaction to automatically raise the temperature to 95°C. During this process, monitor the pH value in real time.

[0019] C. Incubate at 95℃±2℃ for 20 minutes, and then measure the pH and viscosity of the system after the incubation period.

[0020] D. Cool the system temperature to 85℃±2℃, add 30% formic acid solution in two portions, adjust the pH to 4.5-4.7, and then keep the reaction at 90-94℃. During this period, continuously monitor the pH and viscosity. The final viscosity at this stage should be controlled at 17.0-19.0 seconds (fort-4 cup, measured at 30℃).

[0021] E. Once the preset viscosity is reached, immediately adjust the pH of the system to 8.5-9.0 with a 20% sodium hydroxide solution. Then add the second batch of formaldehyde (8-10% of the total formaldehyde mass) and adjust the pH to 9.0-9.3 again with a 20% sodium hydroxide solution.

[0022] F. Add the second batch of urea (2-3% of the total mass of urea) and melamine to the system, and simultaneously turn on the steam to heat to 88℃±1℃. During the heating process, continue stirring and check the dissolution of melamine, and measure the pH value and viscosity in real time.

[0023] G. React at 88℃ and pH 7.7-8.0, measuring viscosity every 5-10 minutes. The final viscosity at this stage should be controlled at 21.0-23.0 seconds (Ford cup 4, measured at 30℃).

[0024] H. Adjust the pH of the system to 9.5-9.8 with a 20% sodium hydroxide solution, cool the system to 70℃±2℃, add the third batch of urea (45-49% of the total urea mass), keep the reaction at this temperature for 10 minutes, measure the pH and viscosity, and adjust the pH to 8.8-9.5.

[0025] I. Continue to cool the system to 40℃±2℃, take samples to measure pH value, viscosity, solid content and other indicators. After passing the test, discharge the material to obtain waterproof low melamine ratio modified urea-formaldehyde resin.

[0026] In the aforementioned waterproof, low-melamine-ratio modified urea-formaldehyde resin, the proportions of each raw material to the total resin mass are as follows: formaldehyde 55-57%, urea 31-35%, and melamine 8-14%. The key performance indicators of the resin are: the molar ratio of formaldehyde to urea and melamine F / (U+1.5M) is 1.00-1.10, the pH value is 8.8-9.5, the viscosity is 15.5-17.5 seconds (Ford cup 4, measured at 25℃), the solid content is 52-56%, the curing time is 100-200 seconds, and the free formaldehyde content is 0.15-0.25%.

[0027] The composite formaldehyde depressant is composed of the following components by mass percentage: 10-15 wt% ammonium persulfate, 6-8 wt% cyclopentylamine, 6-8 wt% oxalic acid dihydrazide, and the remainder is water. After mixing, the components are stirred at 30-40°C for 30 minutes, allowed to cool to room temperature, and then sealed and stored for later use.

[0028] 2. Pre-compression step

[0029] Microwave heating equipment is used to preheat the slab after it has been laid. The microwave frequency is 2450MHz, the power is 30-50kW, and the preheating time is 2-5 minutes, so that the core layer temperature of the slab is uniformly raised to 60-70℃. During the preheating process, the surface pressure of the slab is controlled at 0.3-0.5MPa to prevent the slab from delaminating.

[0030] 3. Hot pressing step

[0031] A continuous hot-pressing process is adopted, with a hot-pressing temperature range of 170–240℃ and a pressure factor of 8–10 s / mm. Specific parameter settings are as follows:

[0032] Temperature zones (five sections): Section 1 230±10℃, Section 2 225±10℃, Section 3 215±10℃, Section 4 190±10℃, Section 5 180±10℃;

[0033] Pressure distribution: The pressure in the inlet section gradually increases to 2.4-2.8 MPa (holding pressure for 10-15 seconds), the pressure in the rebound section gradually decreases to 1.3-1.8 MPa (holding pressure for 20-30 seconds), the pressure in the core insulation section gradually decreases to 0.06-0.12 MPa (holding pressure for 30-40 seconds), and the pressure in the fixed thickness section remains at 0.8-1.3 MPa (holding pressure for 15-20 seconds).

[0034] 4. Additional parameters for other key steps

[0035] Hot grinding step: Add molten paraffin or emulsified paraffin into the hot grinding mill, with an application rate of 7-8 kg / m³. 3 The grinding disc gap is controlled at 0.10~0.12mm, and the fiber separation output is 20~22 tons / hour;

[0036] Drying steps: Use an airflow dryer for drying at a temperature of 160–180℃. After drying, the fiber moisture content should be controlled at 9–10%.

[0037] Paving steps: Air-flow paving method is adopted, and the slab paving density is controlled at 820-830 kg / m². 3 The paving thickness is determined based on the finished product thickness and the amount of sand removed.

[0038] Curing steps: After cooling, the boards are stacked and cured. The curing environment temperature is 20-25℃, the relative humidity is 40-60%, and the curing time is not less than 48 hours.

[0039] Sanding process: The process of "two coarse sanding passes + two fine sanding passes" is adopted. The total amount of sanding is 0.8-1.2mm. The sanding amount distribution of each pass is as follows: the first pass (50-mesh sanding belt) accounts for 55-60%, the second pass (80-mesh sanding belt) accounts for 20-25%, the third pass (100-mesh sanding belt) accounts for 10-15%, and the fourth pass (150-mesh sanding belt) accounts for 5-15%. After sanding, the surface roughness Ra of the board is ≤3.2μm.

[0040] Beneficial effects

[0041] The waterproof, low-melamine-ratio modified urea-formaldehyde resin disclosed in this invention, and its application in high-moisture-content, low-swelling flooring substrates, has the following advantages:

[0042] 1. Synergistic Optimization of Resin Performance: The waterproof, low-melamine-ratio modified urea-formaldehyde resin of this invention adopts a four-stage synthesis process of "alkali-acid-alkali-alkali" and a segmented feeding method. While maintaining a high molar ratio (F / (U+1.5M)=1.00~1.10) to ensure adhesive strength, a blend structure of urea-formaldehyde resin and melamine-formaldehyde resin is achieved through secondary formaldehyde feeding. This structure retains the high adhesive strength of urea-formaldehyde resin and also possesses the excellent water resistance of melamine-formaldehyde resin. This allows the melamine addition ratio to be only 8~14% (far lower than the 15% or more of the prior art) to achieve the low swelling requirement of water absorption thickness swelling rate ≤6.0%, significantly reducing raw material costs.

[0043] 2. Highly Efficient Formaldehyde Release Control: The developed composite formaldehyde-reducing agent achieves formaldehyde fixation through a multi-mechanism synergistic effect: ammonium persulfate oxidizes and decomposes formaldehyde, utilizing its reducing properties to achieve chemical fixation; the amine group in cyclopentylamine undergoes an addition reaction with formaldehyde to form a stable compound; and the hydrazide group in oxalic acid dihydrazide reacts with formaldehyde to generate a stable hydrazone link. This composite formaldehyde-reducing agent exhibits high formaldehyde removal efficiency and good stability, effectively solving the formaldehyde release problem caused by high molar ratio resins, controlling the formaldehyde release of the flooring substrate to 0.090–0.110 mg / m³. 3(Meets E1 standard), and there is no formaldehyde rebound phenomenon in the later stage.

[0044] 3. Simultaneous Improvement in Moisture Content and Dimensional Stability: By microwave preheating of the board blank (core layer temperature 60~70℃) and optimizing the hot-pressing pressure distribution (segmented pressure reduction + low-pressure insulation of the core layer), the internal moisture of the board blank is effectively promoted to escape, reducing the thickness of the surface high-density layer, improving heat conduction efficiency, and ensuring full curing of the core layer adhesive. This improvement can shorten the hot-pressing time by 15~20%, reduce the moisture loss of the board blank, and increase the moisture content of the flooring substrate to 6.0~7.0% (compared to only 4~5% in existing technologies). At the same time, the dimensional stability is optimized to 0.60~0.70mm (better than the industry standard requirement of ≤0.80mm), effectively avoiding buckling and deformation problems caused by moisture absorption or humidity changes during use.

[0045] 4. Improved production efficiency and reduced costs: This invention improves production efficiency by 10-15% and reduces unit product production costs by 8-12% by shortening hot pressing time, reducing melamine usage, and decreasing scrap rates such as bubbling. Simultaneously, the optimized sanding process reduces sanding losses, increases board utilization, and further enhances economic benefits.

[0046] 5. Excellent processing adaptability: The high moisture content of the substrate makes it less prone to defects such as dry spots and cracks on the surface during the subsequent laminate flooring pressing process. It can adapt to the pressing needs of different surface textures, resulting in more stable processing performance and a significantly improved product qualification rate. Detailed Implementation

[0047] The present invention will be described in detail below with reference to embodiments, so that those skilled in the art can better understand the present invention, but the present invention is not limited to the following embodiments.

[0048] Example 1

[0049] 1. Waterproof, low-melamine-ratio modified urea-formaldehyde resin

[0050] A waterproof, low-melamine-ratio modified urea-formaldehyde resin has a formaldehyde to urea and melamine molar ratio F / (U+1.5M) of 1.02. Formaldehyde accounts for 55% of the total resin mass, urea for 31%, and melamine for 14%. Formaldehyde is added in two batches, urea in three batches, and melamine in one batch.

[0051] The preparation process is as follows:

[0052] A. Add formaldehyde (91% of the total mass of formaldehyde) to the reactor for the first time, and adjust the pH value to 8.0-8.5 with a 20% sodium hydroxide solution.

[0053] B. Add the first batch of urea (50% of the total mass of urea), turn on the steam to heat to 80°C, then automatically heat to 95°C, and measure the pH value.

[0054] C. Keep warm at around 95℃ for 20 minutes, then measure the pH value and viscosity.

[0055] D. Cool to approximately 85℃, add 30% formic acid solution in two portions to adjust the pH to 4.5-4.7, react at 90-94℃, and measure the pH and viscosity. The final viscosity at this stage should be controlled at 17.0-19.0 seconds (Ford 4-cup, measured at 30℃).

[0056] E. After reaching the desired viscosity, adjust the pH to 8.5-9.0 with a 20% sodium hydroxide solution, add the second batch of formaldehyde (9% of the total formaldehyde mass), and adjust the pH to 9.0-9.3 with a 20% sodium hydroxide solution.

[0057] F. Add the second batch of urea (2% of the total urea mass) and melamine, and simultaneously raise the temperature to 88°C. During the heating process, check the dissolution of melamine, and measure the pH value and viscosity.

[0058] G. React at 88°C and pH 7.7-8.0, measuring viscosity every 5-10 minutes. The final viscosity at this stage should be controlled at 21.0-23.0 seconds (Ford-4 cup, measured at 30°C).

[0059] H. Adjust the pH value to 9.5-9.8 with a 20% sodium hydroxide solution, cool to 70℃, add the third batch of urea (48% of the total mass of urea), measure the pH value and viscosity after 10 minutes, and adjust the pH value to 8.8-9.5.

[0060] I. Continue cooling to 40℃, take samples to measure pH and viscosity, and then dispense the gel.

[0061] The key performance tests of the waterproof, low-melamine-ratio modified urea-formaldehyde resin prepared by this invention are as follows: pH value 9.0-9.5, viscosity 16.5-17.5 seconds (25℃, Forte 4 cup), solid content 54-55%, curing time 140-160 seconds, and free formaldehyde content 0.15-0.20%.

[0062] 2. Manufacturing process of 10mm high moisture content and low swelling floor substrate

[0063] A manufacturing process for a high moisture content, low swelling flooring substrate includes the following steps: log feeding → peeling → chipping → screening → washing → pre-cooking → cooking → hot grinding → adhesive application → drying → sorting → laying → pre-pressing → hot pressing → cooling → curing → sanding → sawing → inspection and grading → packaging and warehousing. The technical parameters and control requirements for the key steps are as follows:

[0064] In the log loading step, mixed hardwood is selected as the raw material.

[0065] In the screening step, qualified wood chips with a length and width of 5 to 40 mm and a thickness of 2 to 5 mm are selected.

[0066] In the water washing step, the wood chips are washed with water to remove impurities such as mud, sand, stones, and metal, ensuring that the wood chips are clean.

[0067] In the pre-cooking step, the pre-cooking temperature is controlled at 90±5℃.

[0068] In the steaming step, the wood chips are softened by steaming at a pressure of 8.8 bar for 3.5 minutes.

[0069] In the hot grinding step, wood chips are fed into the hot grinding mill via a belt screw conveyor, and molten paraffin or emulsified paraffin is added to the mill at a rate of 7-8 kg / m³. 3 The grinding disc gap is controlled at 0.10~0.12mm, and the fiber separation output is 20~22 tons / hour.

[0070] In the sizing step, waterproof, low-melamine modified urea-formaldehyde resin is uniformly applied through an atomizing sizing device into the pipe from which the fibers are ejected from the thermoforming mill, at a rate of 290-300 kg / m². 3 Simultaneously, ammonium chloride is applied as a curing agent, with an addition amount of 1.5% of the dry resin mass; simultaneously, a composite formaldehyde degrading agent is applied, with an addition amount of 5% of the liquid resin mass.

[0071] The composite formaldehyde depressant is composed of the following components by mass percentage: 12wt% ammonium persulfate, 8wt% cyclopentylamine and 8wt% oxalic acid dihydrazide, with the remainder being water.

[0072] During the drying step, the fiber moisture content is between 9% and 10%.

[0073] In the paving step, the density of the slab is 820–830 kg / m³. 3 .

[0074] In the pre-pressing step, the temperature of the core layer of the slab is raised to 60~70℃ using a microwave heating device.

[0075] In the hot pressing step, a continuous hot pressing process is adopted, and the slab is hot-pressed at a temperature of 175-233℃, with a pressure factor of 8s / mm. The hot pressing temperature and pressure are set as follows: five temperature zones are adopted: 233℃, 228℃, 210℃, 192℃, and 175℃; the hot pressing pressure distribution is as follows: the pressure in the inlet section rises to 2.6-2.8MPa, the pressure in the rebound section gradually decreases to 1.5-1.8MPa, the pressure in the core insulation section gradually decreases to 0.08-0.10MPa, and the pressure in the fixed thickness section is 0.8-1.3MPa.

[0076] In the curing process, the cooled boards are stacked and cured for 48 hours to balance their properties.

[0077] In the sanding step, a "two-pass coarse sanding + two-pass fine sanding" method is adopted, and the sanding amount of the four sanding passes is distributed as follows: the first sanding pass accounts for 55-60% (50-mesh sanding belt), the second sanding pass accounts for 20-25% (80-mesh sanding belt), the third sanding pass accounts for 10-15% (100-mesh sanding belt), and the fourth sanding pass accounts for 5-15% (150-mesh sanding belt).

[0078] The 10mm high moisture content, low swelling flooring substrate prepared through the above steps was tested according to the performance requirements of impregnated paper laminate wood flooring substrate (nominal thickness ≥ 8mm) in LY / T 1611-2023 "Fiberboard for Flooring Substrates". The results are as follows:

[0079]

[0080] Example 2

[0081] 1. Waterproof, low-melamine-ratio modified urea-formaldehyde resin

[0082] A waterproof, low-melamine-ratio modified urea-formaldehyde resin has a formaldehyde to urea and melamine molar ratio F / (U+1.5M) of 1.04. Formaldehyde accounts for 57% of the total resin mass, urea for 34%, and melamine for 9%. Formaldehyde is added in two batches, urea in three batches, and melamine in one batch.

[0083] The preparation process is as follows:

[0084] A. Add formaldehyde (91% of the total mass of formaldehyde) to the reactor for the first time, and adjust the pH value to 8.0-8.5 with a 20% sodium hydroxide solution.

[0085] B. Add the first batch of urea (50% of the total mass of urea), turn on the steam to heat to 80°C, then automatically heat to 95°C, and measure the pH value.

[0086] C. Keep warm at around 95℃ for 20 minutes, then measure the pH value and viscosity.

[0087] D. Cool to approximately 85℃, add 30% formic acid solution in two portions to adjust the pH to 4.5-4.7, react at 90-94℃, and measure the pH and viscosity. The final viscosity at this stage should be controlled at 17.0-19.0 seconds (Ford-4 cup, measured at 30℃).

[0088] E. After reaching the desired viscosity, adjust the pH to 8.5-9.0 with a 20% sodium hydroxide solution, add the second batch of formaldehyde (9% of the total formaldehyde mass), and adjust the pH to 9.0-9.3 with a 20% sodium hydroxide solution.

[0089] F. Add the second batch of urea (2% of the total urea mass) and melamine, and simultaneously raise the temperature to 88°C. During the heating process, check the dissolution of melamine and measure the pH and viscosity.

[0090] G. React at 88°C and pH 7.7-8.0, measuring viscosity every 5-10 minutes. The final viscosity at this stage should be controlled at 21.0-23.0 seconds (Ford-4 cup, measured at 30°C).

[0091] H. Adjust the pH value to 9.5-9.8 with a 20% sodium hydroxide solution, cool to 70℃, add the third batch of urea (48% of the total mass of urea), measure the pH value and viscosity after 10 minutes, and adjust the pH value to 8.8-9.5.

[0092] I. Continue cooling to 40℃, take samples to measure pH and viscosity, and then dispense the gel.

[0093] The key performance tests of the waterproof, low-melamine-ratio modified urea-formaldehyde resin prepared by this invention are as follows: pH value 9.0-9.5, viscosity 16.0-17.0 seconds (25℃, Forte 4 cup), solid content 53-54%, curing time 120-130 seconds, and free formaldehyde content 0.18-0.22%.

[0094] 2. Manufacturing process of 12mm high moisture content and low swelling floor substrate

[0095] A manufacturing process for a high moisture content, low swelling flooring substrate includes the following steps: log feeding → peeling → chipping → screening → washing → pre-cooking → cooking → hot grinding → adhesive application → drying → sorting → laying → pre-pressing → hot pressing → cooling → curing → sanding → sawing → inspection and grading → packaging and warehousing. The technical parameters and control requirements for the key steps are as follows:

[0096] In the log loading step, mixed hardwood is selected as the raw material.

[0097] In the screening step, qualified wood chips with a length and width of 5 to 40 mm and a thickness of 2 to 5 mm are selected.

[0098] In the water washing step, the wood chips are washed with water to remove impurities such as mud, sand, stones, and metal, ensuring that the wood chips are clean.

[0099] In the pre-cooking step, the pre-cooking temperature is controlled at 90±5℃.

[0100] In the steaming step, the wood chips are softened by steaming at a pressure of 8.8 bar for 3.5 minutes.

[0101] In the hot grinding step, wood chips are fed into the hot grinding mill via a belt screw conveyor, and molten paraffin or emulsified paraffin is added to the mill at a rate of 7-8 kg / m³. 3 The grinding disc gap is controlled at 0.10~0.12mm, and the fiber separation output is 20~22 tons / hour.

[0102] In the sizing step, waterproof, low-melamine modified urea-formaldehyde resin is uniformly applied through an atomizing sizing device into the pipe from which the fiber is ejected from the thermoforming mill, at a rate of 270-280 kg / m². 3 Simultaneously, ammonium chloride is applied as a curing agent, with an addition amount of 1.2% of the dry resin mass; simultaneously, a composite formaldehyde degrading agent is applied, with an addition amount of 4% of the liquid resin mass.

[0103] The composite formaldehyde depressant is composed of the following components by mass percentage: 12wt% ammonium persulfate, 8wt% cyclopentylamine and 8wt% oxalic acid dihydrazide, with the remainder being water.

[0104] During the drying step, the fiber moisture content is between 9% and 10%.

[0105] In the paving step, the density of the slab is 820–830 kg / m³. 3 .

[0106] In the pre-pressing step, the temperature of the core layer of the slab is raised to 60~70℃ using a microwave heating device.

[0107] In the hot pressing step, a continuous hot pressing process is adopted, and the slab is hot-pressed at a temperature of 185-235℃, with a pressure factor of 8.2s / mm. The hot pressing temperature and pressure are set as follows: five temperature zones are adopted: 235℃, 232℃, 218℃, 198℃, and 185℃; the hot pressing pressure distribution is as follows: the pressure in the inlet section rises to 2.5-2.7MPa, the pressure in the rebound section gradually decreases to 1.4-1.6MPa, the pressure in the core insulation section gradually decreases to 0.06-0.08MPa, and the pressure in the fixed thickness section is 0.8-1.3MPa.

[0108] In the curing process, the cooled boards are stacked and cured for 48 hours to balance their properties.

[0109] In the sanding step, a "two-pass coarse sanding + two-pass fine sanding" method is adopted. The sanding amount of the four sanding passes is distributed as follows: the first sanding pass accounts for 55-60% (50-mesh sanding belt), the second sanding pass accounts for 20-25% (80-mesh sanding belt), the third sanding pass accounts for 10-15% (100-mesh sanding belt), and the fourth sanding pass accounts for 5-15% (150-mesh sanding belt).

[0110] The 12mm high moisture content, low swelling flooring substrate prepared through the above steps was tested according to the performance requirements of impregnated paper laminate wood flooring substrate (nominal thickness ≥ 8mm) in LY / T 1611-2023 "Fiberboard for Flooring Substrates". The results are as follows:

[0111]

[0112] Comparative Example

[0113] The conventional method uses a 15% melamine-modified urea-formaldehyde resin (synthesized using an "alkali-acid-alkali" process). The hot-pressing process is controlled by constant temperature (200℃) and constant pressure (2.0MPa). Other steps are the same as in Example 1. A 10mm low-swelling flooring substrate is prepared, and the performance test results are as follows:

[0114]

[0115] The comparison shows that the flooring substrate prepared by this invention, while maintaining mechanical properties such as static bending strength and internal bond strength comparable to existing technologies, has a moisture content that is increased from 4.5% to 6.5%, dimensional stability that is optimized from 0.76mm to 0.65mm, a slightly reduced water absorption thickness expansion rate, and lower formaldehyde release. At the same time, production efficiency is increased by more than 15%, and production costs are reduced by about 10%, demonstrating significant technical advantages and market competitiveness.

[0116] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A manufacturing process for a high moisture content, low swelling flooring substrate, comprising: log feeding → peeling → chipping → screening → washing → pre-cooking → cooking → hot grinding → gluing → drying → sorting → laying → pre-pressing → hot pressing → cooling → curing → sanding → sawing → inspection and grading → packaging and warehousing, characterized in that, The technical parameters and control requirements for the key steps are as follows: Application steps: Waterproof, low-melamine modified urea-formaldehyde resin is evenly applied through an atomizing sizing device into the pipe from which the fiber is sprayed from the thermoforming mill, at a rate of 250-300 kg / m³; simultaneously, ammonium chloride is applied as a curing agent, at a rate of 1-2% of the dry resin mass; and a composite formaldehyde-reducing agent is applied concurrently, at a rate of 2-5% of the liquid resin mass. The waterproof, low-melamine-ratio modified urea-formaldehyde resin adopts a four-stage synthesis process of "alkali-acid-alkali-alkali". Formaldehyde is added in two batches, urea in three batches, and melamine in one batch. The mass ratio of each raw material to the total mass of the resin is: formaldehyde 55-57%, urea 31-35%, and melamine 8-14%. The molar ratio of formaldehyde to urea and melamine, F / (U+1.5M), is 1.00-1.

10. Pre-pressing step: The temperature of the core layer of the slab is raised to 60-70℃ using microwave heating equipment; Hot pressing step: Continuous hot pressing process is adopted, with a temperature of 170~240℃ and a pressure factor of 8~10s / mm. Five-segment temperature zoning and four-segment pressure distribution control are adopted.

2. The manufacturing process of the high moisture content, low swelling flooring substrate according to claim 1, characterized in that, The specific preparation steps of the waterproof, low-melamine-ratio modified urea-formaldehyde resin are as follows: A. Add formaldehyde to the reactor for the first time, accounting for 90-92% of the total mass of formaldehyde, and adjust the pH value to 8.0-8.5 with a 20% sodium hydroxide solution. B. Add the first batch of urea, accounting for 49-52% of the total urea mass. Heat to 80°C and then automatically heat to 95°C. Measure the pH value. C. Incubate at 95℃±2℃ for 20 minutes, then measure pH and viscosity; D. Cool to 85℃±2℃, add 30% formic acid solution in two batches to adjust the pH to 4.5-4.7, react at 90-94℃, control the final viscosity at 17.0-19.0 seconds, and use a Forte 4 cup at 30℃. E. Adjust the pH to 8.5-9.0, add the second batch of formaldehyde, accounting for 8-10% of the total formaldehyde mass, and adjust the pH to 9.0-9.3; F. Add the second batch of urea, accounting for 2-3% of the total urea mass, and melamine, and heat to 88℃±1℃ to check the dissolution of melamine; G. Reaction at 88℃±1℃ and pH 7.7-8.0, with the final viscosity controlled at 21.0-23.0 seconds, using the Forte 4 cup at 30℃; H. Adjust the pH to 9.5-9.8, cool to 70℃±2℃, add the third batch of urea, accounting for 45-49% of the total urea mass, and adjust the pH to 8.8-9.5 after 10 minutes; I. Cool down to 40℃±2℃, and after sampling and testing, dispense the adhesive.

3. The manufacturing process of the high moisture content, low swelling flooring substrate according to claim 1, characterized in that, The composite formaldehyde depressant is composed of the following components by mass percentage: 10-15 wt% ammonium persulfate, 6-8 wt% cyclopentylamine, 6-8 wt% oxalic acid dihydrazide, and the remainder is water.

4. The manufacturing process of the high moisture content, low swelling flooring substrate according to claim 1, characterized in that: In the pre-pressing step, the microwave frequency is 2450MHz, the power is 30-50kW, the preheating time is 2-5 minutes, and the surface pressure of the slab is controlled at 0.3-0.5MPa.

5. The manufacturing process of the high moisture content, low swelling flooring substrate according to claim 1, characterized in that: The hot pressing step has five temperature zones: 230±10℃, 225±10℃, 215±10℃, 190±10℃, and 180±10℃; and four pressure zones: inlet zone 2.4~2.8MPa, rebound zone 1.3~1.8MPa, core layer insulation 0.06~0.12MPa, and fixed thickness zone 0.8~1.3MPa.

6. The manufacturing process of the high moisture content, low swelling flooring substrate according to claim 1, characterized in that: In the hot grinding step, molten paraffin or emulsified paraffin is added at an application rate of 7–8 kg / m³. 3 The grinding disc gap is 0.10-0.12mm, and the fiber separation output is 20-22 tons / hour.

7. The manufacturing process of the high moisture content, low swelling flooring substrate according to claim 1, characterized in that: After the drying step, the fiber moisture content is controlled at 9-10%; the conditioning step is carried out at 20-25℃ and 40-60% relative humidity for no less than 48 hours.

8. The manufacturing process of the high moisture content, low swelling flooring substrate according to claim 1, characterized in that, The sanding step adopts a "two-pass coarse sanding + two-pass fine sanding" process, with a total sanding amount of 0.8-1.2mm. The sanding amount distribution for each pass is as follows: 50-mesh sanding belt accounts for 55-60%, 80-mesh sanding belt accounts for 20-25%, 100-mesh sanding belt accounts for 10-15%, and 150-mesh sanding belt accounts for 5-15%.

9. A waterproof, low-melamine-ratio modified urea-formaldehyde resin, characterized in that, The resin prepared by the method described in claim 2 has the following key performance indicators: pH value 8.8-9.5, viscosity 15.5-17.5 seconds, Forte 4 cup @ 25℃, solid content 52-56%, curing time 100-200 seconds, and free formaldehyde content 0.15-0.25%.

10. The application of the waterproof, low-melamine-ratio modified urea-formaldehyde resin according to claim 9 in the preparation of a high-moisture-content, low-swelling flooring substrate.

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