A low-formaldehyde, high-water-resistance, and high-flame-retardant ultrathin fiberboard and its continuous manufacturing method

Abstract

This invention discloses a low-formaldehyde, high-water-resistance, and high-flame-retardant ultrathin fiberboard and its continuous manufacturing method, belonging to the field of engineered wood processing technology. The manufacturing method mainly includes: a fiber preparation process, softening and hydrophobically modifying the wood fibers; a staged compression process, using heavy-duty pre-compression and wedge-angle venting to pre-compress the rough board blank, followed by humidification and preheating strengthening treatment, and then through humidified hot air impregnation and secondary compression, stabilizing the board blank to 5-6 mm and significantly improving its strength; and a continuous hot pressing process, drying the strengthened board blank and feeding it into a continuous flat press for hot pressing at a high speed of ≥150 m / min. This invention, through material modification and a unique integrated compression-strengthening-hot pressing process, synergistically solves the performance requirements of low formaldehyde, high water resistance, and high flame retardancy in ultrathin fiberboard, as well as the core engineering challenges of board blank transportation and stable forming in industrial continuous production, achieving high-efficiency, high-quality continuous production.

Description

Technical Field

[0001] This invention relates to the field of engineered wood processing technology, particularly to the field of ultra-thin fiberboard processing technology, specifically to a low-formaldehyde, high-water-resistant, and high-flame-retardant ultra-thin fiberboard and its continuous manufacturing method. Background Technology

[0002] With the rapid development of the furniture and decoration industries, structural panels such as solid wood and plywood are widely used. However, solid wood structures exhibit significant physical anisotropy, resulting in a large difference in the longitudinal and transverse expansion rates after absorbing water. This uneven expansion generates internal stress on the surface of the board, easily causing wrinkles or even tears in the overlay decorative layers (such as decorative paper, veneer, etc.), severely affecting the product's aesthetics and lifespan. To solve this problem, an effective approach is to overlay a layer of isotropic material with uniform water absorption and expansion as a buffer and balancing layer onto the surface of the solid wood or plywood substrate. Fiberboard, due to its randomly interwoven internal fibers, possesses good dimensional stability and isotropy, making it an ideal overlay material.

[0003] The market demand for ultra-thin fiberboard (thickness ≤ 1mm) is therefore becoming increasingly urgent. However, more than 90% of the existing fiberboard products in my country are medium-thick boards with a thickness greater than 8mm, and the large-scale production of ultra-thin fiberboard remains a technological bottleneck for the industry. The core challenge lies in continuous industrial production: under laboratory conditions, samples can be produced through simple laying, pre-pressing, and hot pressing, but to stably and continuously feed a fluffy coarse board blank with an initial thickness of 25-35mm into a continuous press with a platen gap of only 1mm or even smaller, and achieve efficient and high-quality hot pressing and curing, involves a series of complex and interrelated engineering problems, such as laying uniformity, board conveying stability, preheating enhancement, and high-speed hot pressing processes, which are far beyond the capabilities of intermittent laboratory production.

[0004] Existing technologies disclose some related solutions, but all have obvious limitations. For example, patent CN 109333900 B proposes a continuous local roll forming process for ultra-thin hemp fiber composite boards, but its process path is completely different from the fiber preparation, gluing, and laying system in the field of engineered wood products, and cannot be directly transplanted and applied. Patent CN 112497414 A discloses a flame-retardant ultra-thin and ultra-thick fiberboard and its preparation method, but does not involve how to achieve integrated and synchronized operation from laying to hot pressing on an industrial continuous production line, lacking guidance on engineering feasibility. Patent CN 116373063 A, a low-formaldehyde ultra-thin fiberboard and its preparation method, although attempting to prepare ultra-thin fiberboard within the framework of a production line, fails to effectively solve the key environmental protection problem of formaldehyde emission control, and also fails to clarify how to ensure uniform laying of ultra-thin specifications (such as 0.8mm) blanks, and how to safely and stably introduce thicker blanks into the extremely narrow press gap—a core engineering bottleneck.

[0005] Therefore, the industry urgently needs an ultra-thin fiberboard that can truly achieve low formaldehyde, high water resistance, and high flame retardancy, along with an efficient, stable, and industrially feasible continuous manufacturing method to overcome the key technological barriers from laboratory to industrial production and meet the urgent needs of downstream industries for high-performance ultra-thin decorative materials. Summary of the Invention

[0006] This invention aims to overcome the shortcomings of existing technologies and provide an ultra-thin fiberboard with low formaldehyde release, high water resistance, and high flame retardancy, as well as its continuous manufacturing method. Specific technical objectives include: First, by modifying the fiber surface, applying specific flame retardants, and designing a three-layer adhesive structure, the board is endowed with comprehensive properties of low formaldehyde release, high water resistance, and high flame retardancy. Second, it addresses the core engineering challenge of how to stably and efficiently compress and feed 25-35mm thick, loose, coarse fiberboard blanks into a continuous press with extremely narrow gaps in the industrial continuous production of ultra-thin fiberboard with a thickness ≤1mm. The key lies in the staged compression process, including pre-compression and humidification / preheating to ensure the strength and integrity of the blank under high-speed (≥150m / min) operation, thereby achieving stable and efficient continuous production.

[0007] To achieve the above-mentioned technical objectives of this invention, the following technical solution is adopted: A low-formaldehyde, high-water-resistant, and high-flame-retardant ultra-thin fiberboard, wherein the thickness of the ultra-thin fiberboard is less than or equal to 1 mm, and it is made of surface-modified wood fibers, adhesives, flame retardants, and is produced by laying, staged compression and hot pressing. The surface of the wood fibers is a sheath structure formed after being modified by silane modifiers.

[0008] Preferably, the silane modifier is selected from one or more combinations of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, 1H,1H,2H,2H-perfluorodecyltrichlorosilane, 1H,1H,2H,2H-perfluorooctyltrichlorosilane, and 1H,1H,2H,2H-perfluorodecyltriethoxysilane, and its addition amount accounts for less than or equal to 3% of the total mass of wood fiber.

[0009] Preferably, the flame retardant is hexachlorocyclotriphosphazene or a derivative thereof, wherein the derivative is selected from at least one of hexa(γ-aminopropyltriethoxysilane)-cyclotriphosphazene, hexa(thiocyanate)-cyclotriphosphazene, hexa(DOPO(9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide))-cyclotriphosphazene, hexa(octaaminocage polysilsesquioxane)-cyclotriphosphazene, hexa(octa(aminophenyl)cage polysilsesquioxane)-cyclotriphosphazene, hexa(aminoethylaminopropylisobutyl polysilsesquioxane)-cyclotriphosphazene, hexa(hydroxycage polysilsesquioxane)-cyclotriphosphazene, and hexa(octa(γ-chloropropyl)cage polysilsesquioxane)-cyclotriphosphazene, and its addition amount accounts for 1% to 15% of the total mass of wood fiber.

[0010] Preferably, the adhesive adopts a three-layer sandwich structure, with the upper and lower layers made of phenolic resin and the amount of adhesive applied to the upper and lower layers being 15-80%, and the middle layer made of at least one selected from urea-formaldehyde resin, melamine-modified urea-formaldehyde resin, and isocyanate adhesive, with the amount of adhesive applied being between 5-15%.

[0011] To achieve the technical objective of this invention, another technical solution adopted by this invention is: a continuous manufacturing method for low-formaldehyde, high-water-resistance, and high-flame-retardant ultra-thin fiberboard, comprising the following steps: S1. Fiber preparation process: Wood fibers are softened by steaming and delignin removal using an alkaline solution, and then the surface of the softened wood fibers is modified with a silane modifier to obtain sheath-structured wood fibers; the sheath-structured wood fibers are then uniformly mixed with adhesives and flame retardants and dried to a moisture content of 5-7%; S2. Phased compression process: including (1) Pre-compression: The mixed wood fibers obtained in S1 are laid into a three-layer sandwich structure of coarse board blanks. After being leveled, they are pressed into 10-15mm thick pre-compressed boards using a double-roller heavy-duty pre-compressor with wedge-angle venting. Specifically, the fiber surface is leveled by a sweeping roller with a piano key structure. The high sensitivity of the piano key structure scrapes off the protrusions and fills the depressions, achieving uniform leveling.

[0012] (2) Humidification and preheating strengthening: The pre-compressed slab is fed into a single-roller humidification and preheating strengthening device. The moisture content of the slab is increased to 10%-12% and the temperature is raised to 70-90℃ through high-pressure atomized jet impregnation. At the same time, the slab is compressed to 5-6mm to obtain a reinforced slab. Specifically, the single-roller refers to the device having a pair of symmetrical upper and lower rollers at the end for secondary compression of the slab. The humidification is achieved by injecting hot and humid air into the slab through the mesh of the steel belt of the device. The preheating is achieved by using hot and humid air to raise the temperature of the slab. The strengthening refers to the plasticization and densification of cellulose under high humidity, high temperature and high pressure, thereby strengthening the slab.

[0013] S3. Continuous hot pressing process: After the reinforced board blank is dried to a moisture content of 7%-8%, it is fed into a continuous flat press for hot pressing to obtain the low-formaldehyde, high-waterproof, and high-flame-retardant ultra-thin fiberboard; wherein, the hot pressing speed of the board blank in the continuous flat press is greater than or equal to 150m / min.

[0014] Preferably, in S1, the alkaline solution is a solution containing one or more of NaOH, KOH, and Ga(OH)2, with a mass fraction of 0.1%-5%, a cooking temperature of 70℃-130℃, a cooking time of 1-10 min, and the removed lignin accounts for 1-10% of the total lignin content.

[0015] Preferably, in S1, the proportion of wood fibers with a length between 0.1-1 mm is greater than or equal to 70%; the length is 1-30 mm, the diameter is 5-10 μm, the melting point is greater than or equal to 200 °C, and the amount added accounts for 1-15% of the total mass of wood fibers.

[0016] Preferably, in S2(1), the thickness of the rough slab is 25-35mm, the upper and lower layers each account for 5-20% of the total slab mass and have the same mass, and the middle layer accounts for 80-95% of the total slab mass; the upper and lower steel belts of the wedge-angle exhaust double-drum heavy pre-press are wedge-angled from the inlet end to the outlet end, and the steel belts are covered with mesh that allows steam to pass through.

[0017] More preferably, in S2(2), the upper and lower symmetrical rollers at the end of the single roller humidification and preheating strengthening device are used to perform secondary compression on the slab. The humidification and preheating are achieved by injecting humid and hot air into the slab through the mesh of the device's steel strip, so that the extension length of the slab stiffness test is greater than or equal to 3cm.

[0018] In a further preferred embodiment, in S3, the continuous flat press is divided into four temperature zones along the slab travel direction, with the temperatures of each zone being: Zone 1 230±5℃, Zone 2 215±5℃, Zone 3 205±5℃, and Zone 4 180±5℃.

[0019] Compared with the prior art, the present invention achieves the following technical effects: This invention employs an alkaline solution to partially remove lignin from wood fibers, softening their rigidity. Ultra-thin fiberboard is very thin, requiring significant pressure to compress it. If the fiber structure itself is soft, it greatly reduces press pressure, thus protecting the equipment. Therefore, this invention proposes an alkaline solution treatment method to solve the problem of excessive pressure. Furthermore, alkaline solution treatment helps reduce cooking time and improves production efficiency.

[0020] This invention employs a sheath structure to coat wood fibers. A silane modifier is used to chemically react with the wood fibers, grafting hydrophobic functional groups of silanes onto the surface of the wood fibers, thereby achieving excellent waterproofing and firmly encapsulating the wood fibers. The other end of the silane modifier is an alkane substance with good polarity and excellent compatibility with adhesives, which is beneficial to improving the bonding strength of the board. Therefore, this sheath structure not only facilitates waterproofing and improves bonding strength, but also facilitates the subsequent flame-retardant effect of silicon.

[0021] This invention employs a three-layer sandwich structure for paving. The upper and lower layers are made of phenolic resin, while the middle layer is made of urea-formaldehyde resin, melamine-modified urea-formaldehyde resin, and isocyanate adhesive. This not only effectively reduces formaldehyde release but also solves the problem of isocyanate easily adhering to the steel belt of a continuous flat press.

[0022] This invention employs a staged compression method for the rough slab, effectively reducing its thickness to 5-6 mm, thus facilitating its smooth feeding into a continuous flat press. If pre-compression is performed in a single step, the slab exiting the pre-press is prone to springback and cannot be immersed in the continuous flat press. However, with staged compression, the first step uses heavy pre-compression and slow wedge-angle venting to compress the slab to a certain thickness. Then, the slab is fed into a humidification and strengthening preheating device. Here, hot steam is drawn into the slab through the mesh of a steel belt, increasing its humidity and thus enhancing the adhesion between fibers, suppressing springback, and simultaneously raising the slab's temperature. At high temperatures, the wood fibers in the slab exhibit excellent plasticity; under pressure, the slab undergoes plastic compression and compaction, thereby increasing its strength. In continuous production, there is a gap between the drying flat press and the continuous hot flat press. If the slab strength is too low, the pre-pressed slab will break at the inlet of the continuous hot flat press due to the initial slab strength. Once this breaks, it will cause fiber backflow and fiber accumulation at the inlet, preventing it from being conveyed into the continuous hot flat press for subsequent production, thus causing downtime and affecting efficiency. Therefore, it is necessary to introduce a humidification and enhanced preheating step to improve the slab strength, thereby facilitating the smooth feeding of the slab into the continuous flat press. Staged compression is an original technology established in this invention that combines pre-pressing, humidification and enhanced preheating, and continuous hot pressing. The pressure involved in the staged compression process is determined by the thickness of the slab after compression. This solution breaks through the original product and process manufacturing methods. By using a humidification and enhanced preheating device, high-temperature mixed gas is immersed in the slab before the hot pressing process, achieving rapid overall heating of the slab, shortening the subsequent hot pressing time, and improving production efficiency.

[0023] The technical solution adopted in this invention is completely different from conventional fiberboard production methods, involving numerous technical challenges. Ultra-thin boards are extremely thin, requiring very short hot-pressing times. This means that the main speed of the production line during the hot-pressing process is very high (≥150m / min), far exceeding the production speed of conventional boards (20-30m / min). The "preheating and humidification strengthening" process of this invention not only increases the humidity of the board to prevent fiber splashing during high-speed operation but also increases the temperature of the board itself, prompting the adhesive to reach its curing gel point. After entering the continuous press, rapid curing can be achieved, promoting continuous production.

[0024] This invention uses silanes as waterproofing modifiers and hexachlorocyclotriphosphazene or its derivatives as flame retardants, achieving a synergistic waterproofing and flame retardant effect. Silanes themselves not only act as waterproofing agents, but silicon is also a flame retardant element, thus endowing ultra-thin fiberboard with a combination of flame-retardant elements such as phosphorus, nitrogen, and silicon, possessing both organic and inorganic flame retardant properties, overcoming the shortcomings of single-performance flame retardants. During the modification process, the silane modifier participates in the chemical reaction of the wood fibers, resulting in good flame retardant effects, preventing flame retardant migration, good stability, and increased bonding strength. Phosphorus and nitrogen are intumescent flame-retardant elements. When fiberboard is exposed to flame, these three flame-retardant elements (phosphorus, nitrogen, and silicon) can undergo a cross-linking reaction with the cured adhesive and wood fibers, forming a three-dimensional network structure. Hexachlorocyclotriphosphazene acts as an acid and nitrogen source during combustion, while the adhesive and wood fibers act as a carbon source, resulting in an intumescent flame-retardant effect. This effect is present in both the condensed and gas phases. In the condensed phase, phosphorus and silicon generate polyphosphoric acid with strong dehydrating properties, rapidly dehydrating and carbonizing the oxygen-containing adhesive and wood fibers, forming a dense, three-dimensional, and non-combustible carbon layer that isolates oxygen and heat. In the gas phase, nitrogen combustion releases flammable gases, diluting the surrounding oxygen concentration and reducing the necessary conditions for combustion. The synergistic effect among the components of this flame retardant is significant, resulting in a noticeable flame-retardant effect. Attached Figure Description

[0025] For ease of explanation, the present invention will be described in detail below with reference to specific embodiments and accompanying drawings.

[0026] Figure 1 This is a flowchart illustrating the preparation process of the continuous manufacturing method for low-formaldehyde, high-water-resistance, and high-flame-retardant ultrathin fiberboard of the present invention.

[0027] Figure 2 This is a schematic diagram of the slab strength testing method of the present invention. Detailed Implementation

[0028] The following are specific embodiments of the present invention, which further describe the technical solutions of the present invention. However, the present invention is not limited to these embodiments. In the following description, specific details such as specific configurations are provided merely to help to fully understand the embodiments of the present invention. Therefore, those skilled in the art should understand that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the present invention.

[0029] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other.

[0030] The strength of a slab is tested based on its stiffness, such as... Figure 2 As shown, the method is characterized by cutting the slab into a cuboid, placing the sample on a horizontal platform with one end coinciding with the front edge of the platform, placing a sliding ruler S on the sample, aligning the zero point of the sliding ruler with the edge of the plane D, and slowly pushing the sliding ruler forward at a uniform speed of 10 mm / s to make the sample extend beyond the edge of the platform. The sample bends downward under its own weight. The sliding ruler is continued to be pushed forward until the front end of the sample reaches the plane formed by the marking lines L1 and L2. The reading of the sliding ruler is the extension length of the sample. The longer the extension length of the sample, the higher the strength of the slab.

[0031] Example 1 Wood fibers from the hot mill are fed into a vertical digester for softening and cooking. The cooking liquor is a 5% sodium hydroxide alkaline solution. The cooking time is 0.5 minutes, and the cooking temperature is 80°C. KH550 ethanol-water solution (ethanol:water = 95:5) is stirred uniformly at room temperature for 30 minutes to ensure complete hydrolysis of the silane modifier. The hydrolysate is then sprayed onto the surface of the softened wood fibers using an atomized spray adhesive method and dried in a 100°C pneumatic conveying duct. During this process, the silanol functional groups and the hydroxyl groups on the wood fiber surface undergo a dehydration reaction, resulting in a sheath structure with the silane modifier coated on the wood fiber surface.

[0032] Wood fibers with a sheath structure are fed into three adhesive application pipes. Phenolic resin is applied to the wood fibers in two of the pipes at a rate of 15%, while isocyanate adhesive is applied to the fibers in the third pipe at a rate of 5%. The fibers from the three pipes and hexa(γ-aminopropyltriethoxysilane)-cyclotriphosphazene flame retardant are laid into a continuous three-layer sandwich structure using a lay-up forming machine. The flame retardant is added at a rate of 5%. The fibers with phenolic resin are laid in the top and bottom layers, and the fibers with isocyanate are laid in the middle layer. The top and bottom layers each account for 10% of the total mass of the slab, and the middle layer accounts for 80%, resulting in a rough slab with a thickness of 25 mm. The slab is pre-compressed through a staged compression process, which involves using a double-drum heavy-duty pre-compressor to compress it to 10mm. The pre-compressed slab is then fed into a single-drum humidification and preheating device for humidification and preheating. Hot steam is drawn into the slab through the mesh on the steel belt, increasing the slab's moisture content to 10% and further compressing it to 5mm. At this point, the slab's temperature reaches 70℃. The pressure involved in the staged compression process is determined by the thickness of the slab after compression.

[0033] The reinforced fiberboard blank is passed through a drying system, and the hot air temperature in the drying press is controlled at 80℃ to dry the moisture in the fibers to 7%. Finally, the dried fiberboard blank is conveyed into a continuous flat press for hot pressing. The continuous hot press has four hot pressing temperature zones: zone one is 230±5℃, zone two is 215±5℃, zone three is 205±5℃, and zone four is 180±5℃. After hot pressing, a 0.5mm thick low-formaldehyde, high-waterproof, and high-flame-retardant ultra-thin fiberboard is obtained. The hot pressing speed of the blank is 180m / min.

[0034] Example 2 Wood fibers from the hot mill are fed into a vertical digester for softening and cooking. The cooking liquor is a 10% sodium hydroxide alkaline solution. The cooking time is 1.0 min, and the cooking temperature is 80℃. KH550 ethanol-water solution (ethanol:water = 95:5) is stirred uniformly at room temperature for 30 min to ensure complete hydrolysis of the silane modifier. The hydrolysate is then sprayed onto the surface of the softened wood fibers using an atomized spray adhesive method and dried in a 100℃ pneumatic conveying pipe. During this process, the silanol functional groups and the hydroxyl groups on the wood fiber surface undergo a dehydration reaction, resulting in a sheath structure with the silane modifier coated on the wood fiber surface.

[0035] Wood fibers with a sheath structure are fed into three adhesive application pipes. Phenolic resin adhesive is applied to the wood fibers in two of the pipes at a rate of 20%, while isocyanate adhesive is applied to the fibers in the other pipe at a rate of 5%. The fibers from the three pipes and hexa(thiocyanate)-cyclotriphosphazene flame retardant are laid into a continuous slab strip with a three-layer sandwich structure using a slab forming machine. The flame retardant is added at a rate of 10%. The fibers with phenolic resin adhesive are laid in the top and bottom layers, and the fibers with isocyanate adhesive are laid in the middle layer. The top and bottom layers each account for 10% of the total mass of the slab, and the middle layer accounts for 80%, resulting in a rough slab with a thickness of 25 mm. The slab is pre-compressed through a staged compression process, which involves using a double-drum heavy-duty pre-compressor to compress it to 15mm. The pre-compressed slab is then fed into a single-drum humidification and preheating device for humidification and preheating. Hot steam is drawn into the slab through the mesh on the steel belt, increasing the slab's moisture content to 10% and further compressing it to 6mm. At this point, the slab's temperature reaches 70℃. The pressure involved in the staged compression process is determined by the thickness of the slab after compression.

[0036] The reinforced fiberboard blank is passed through a drying system, and the hot air temperature in the drying press is controlled at 80℃ to dry the moisture in the fibers to 7%. Finally, the dried fiberboard blank is conveyed into a continuous flat press for hot pressing. The continuous hot press has four hot pressing temperature zones: zone one is 230±5℃, zone two is 215±5℃, zone three is 205±5℃, and zone four is 180±5℃. After hot pressing, a 0.8mm thick low-formaldehyde, high-waterproof, and high-flame-retardant ultra-thin fiberboard is obtained. The hot pressing speed of the blank is 160m / min.

[0037] Example 3 Wood fibers from the hot mill are fed into a vertical digester for softening and cooking. The cooking liquor is a 5% sodium hydroxide alkaline solution. The cooking time is 0.5 minutes, and the cooking temperature is 80°C. KH550 ethanol-water solution (ethanol:water = 95:5) is stirred uniformly at room temperature for 30 minutes to ensure complete hydrolysis of the silane modifier. The hydrolysate is then sprayed onto the surface of the softened wood fibers using an atomized spray adhesive method and dried in a 100°C pneumatic conveying duct. During this process, the silanol functional groups and the hydroxyl groups on the wood fiber surface undergo a dehydration reaction, resulting in a sheath structure with the silane modifier coated on the wood fiber surface.

[0038] Wood fibers with a sheath structure are fed into three adhesive application pipes. Phenolic resin is applied to the wood fibers in two pipes at a rate of 20%, while urea-formaldehyde resin adhesive is applied to the fibers in the third pipe at a rate of 8%. The fibers from the three pipes and a flame retardant (DOPO(9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide))-cyclotriphosphazene are laid into a continuous slab strip with a three-layer sandwich structure using a slab forming machine. The flame retardant addition is 15%. The fibers with phenolic resin are laid in the top and bottom layers, and the fibers with urea-formaldehyde resin adhesive are laid in the middle layer. The top and bottom layers each account for 5% of the total slab mass, and the middle layer accounts for 90%, resulting in a rough slab with a thickness of 35 mm. The slab is pre-compressed through a staged compression process, which involves using a double-drum heavy-duty pre-compressor to compress it to 15mm. The pre-compressed slab is then fed into a single-drum humidification and preheating device for humidification and preheating. Hot steam is drawn into the slab through the mesh on the steel belt, increasing the slab's moisture content to 10% and further compressing it to 6mm. At this point, the slab's temperature reaches 70℃. The pressure involved in the staged compression process is determined by the thickness of the slab after compression.

[0039] The reinforced fiberboard blank is passed through a drying system, and the hot air temperature in the drying press is controlled at 80℃ to dry the moisture in the fibers to 7%. Finally, the dried fiberboard blank is conveyed into a continuous flat press for hot pressing. The continuous hot press has four hot pressing temperature zones: zone one is 230±5℃, zone two is 215±5℃, zone three is 205±5℃, and zone four is 180±5℃. After hot pressing, a 1.0mm thick low-formaldehyde, high-waterproof, and high-flame-retardant ultra-thin fiberboard is obtained. The hot pressing speed of the blank is 150m / min.

[0040] Example 4 Wood fibers from the hot mill are fed into a vertical digester for softening and cooking. The cooking liquor is a 5% sodium hydroxide alkaline solution. The cooking time is 0.5 minutes, and the cooking temperature is 80°C. KH550 ethanol-water solution (ethanol:water = 95:5) is stirred uniformly at room temperature for 30 minutes to ensure complete hydrolysis of the silane modifier. The hydrolysate is then sprayed onto the surface of the softened wood fibers using an atomized spray adhesive method and dried in a 100°C pneumatic conveying duct. During this process, the silanol functional groups and the hydroxyl groups on the wood fiber surface undergo a dehydration reaction, resulting in a sheath structure with the silane modifier coated on the wood fiber surface.

[0041] Wood fibers with a sheath structure are fed into three adhesive application pipes. Phenolic resin is applied to the wood fibers in two pipes at a rate of 15%, while isocyanate adhesive is applied to the fibers in the third pipe at a rate of 8%. The fibers from the three pipes and a flame retardant (DOPO(9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide))-cyclotriphosphazene are laid into a continuous slab strip with a three-layer sandwich structure using a slab forming machine. The flame retardant is added at a rate of 15%. The fibers with phenolic resin are laid in the top and bottom layers, and the fibers with isocyanate are laid in the middle layer. The top and bottom layers each account for 5% of the total mass of the slab, and the middle layer accounts for 90%, resulting in a rough slab with a thickness of 35 mm. The slab is pre-compressed through a staged compression process, which involves using a double-drum heavy-duty pre-compressor to compress it to 15mm. The pre-compressed slab is then fed into a single-drum humidification and preheating device for humidification and preheating. Hot steam is drawn into the slab through the mesh on the steel belt, increasing the slab's moisture content to 10% and further compressing it to 6mm. At this point, the slab's temperature reaches 70℃. The pressure involved in the staged compression process is determined by the thickness of the slab after compression.

[0042] The reinforced fiberboard blank is passed through a drying system, and the hot air temperature in the drying press is controlled at 80℃ to dry the moisture in the fibers to 7%. Finally, the dried fiberboard blank is conveyed into a continuous flat press for hot pressing. The continuous hot press has four hot pressing temperature zones: zone one is 230±5℃, zone two is 215±5℃, zone three is 205±5℃, and zone four is 180±5℃. After hot pressing, a 1.0mm thick low-formaldehyde, high-waterproof, and high-flame-retardant ultra-thin fiberboard is obtained. The hot pressing speed of the blank is 150m / min.

[0043] Example 5 Wood fibers from the hot mill are fed into a vertical digester for softening and cooking. The cooking liquor is a 5% sodium hydroxide alkaline solution. The cooking time is 0.5 minutes, and the cooking temperature is 80°C. KH550 ethanol-water solution (ethanol:water = 95:5) is stirred uniformly at room temperature for 30 minutes to ensure complete hydrolysis of the silane modifier. The hydrolysate is then sprayed onto the surface of the softened wood fibers using an atomized spray adhesive method and dried in a 100°C pneumatic conveying duct. During this process, the silanol functional groups and the hydroxyl groups on the wood fiber surface undergo a dehydration reaction, resulting in a sheath structure with the silane modifier coated on the wood fiber surface.

[0044] Wood fibers with a sheath structure are fed into three adhesive application pipes. Phenolic resin is applied to the wood fibers in two pipes at a rate of 15%, while melamine-modified urea-formaldehyde resin adhesive is applied to the fibers in the third pipe at a rate of 8%. The fibers from the three pipes and a flame retardant (DOPO(9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide))-cyclotriphosphazene are laid into a continuous slab strip with a three-layer sandwich structure using a slab forming machine. The flame retardant is added at a rate of 15%. The fibers with phenolic resin are laid in the top and bottom layers, and the fibers with isocyanate are laid in the middle layer. The top and bottom layers each account for 5% of the total mass of the slab, and the middle layer accounts for 90%, resulting in a rough slab with a thickness of 35 mm. The slab is pre-compressed through a staged compression process, which involves using a double-drum heavy-duty pre-compressor to compress it to 15mm. The pre-compressed slab is then fed into a single-drum humidification and preheating device for humidification and preheating. Hot steam is drawn into the slab through the mesh on the steel belt, increasing the slab's moisture content to 10% and further compressing it to 6mm. At this point, the slab's temperature reaches 70℃. The pressure involved in the staged compression process is determined by the thickness of the slab after compression.

[0045] The reinforced fiberboard blank is passed through a drying system, and the hot air temperature in the drying press is controlled at 80℃ to dry the moisture in the fibers to 7%. Finally, the dried fiberboard blank is conveyed into a continuous flat press for hot pressing. The continuous hot press has four hot pressing temperature zones: zone one is 230±5℃, zone two is 215±5℃, zone three is 205±5℃, and zone four is 180±5℃. After hot pressing, a 1.0mm thick low-formaldehyde, high-waterproof, and high-flame-retardant ultra-thin fiberboard is obtained. The hot pressing speed of the blank is 150m / min.

[0046] Comparative Example 1 The wood fibers from the hot mill are fed into a vertical cooker for cooking and softening. The cooking liquid is a 5% sodium hydroxide alkaline solution. The cooking time is 0.5 minutes and the cooking temperature is 80℃.

[0047] Wood fibers are fed into three separate adhesive application pipes to apply urea-formaldehyde resin adhesive at a rate of 15%. A slab forming machine then lays the fibers from the three pipes and hexa(γ-aminopropyltriethoxysilane)-cyclotriphosphazene flame retardant into three continuous slab strips, each containing urea-formaldehyde resin adhesive, resulting in a rough slab with a thickness of approximately 35 mm. Pre-compression is performed through a staged compression process using a heavy-duty pre-compression machine to reduce the slab thickness to 15 mm. The pre-compressed slab is then fed into a single-roller humidification and preheating strengthening device for further humidification and preheating. Hot steam is drawn into the slab through the mesh of a steel belt, increasing the moisture content to 10% while simultaneously compressing the slab to 6 mm, at which point the slab temperature reaches 70°C. The pressure involved in the staged compression process is determined by the thickness of the compressed slab.

[0048] The reinforced fiberboard blank is passed through a drying system, and the hot air temperature in the drying press is controlled at 80℃ to dry the moisture in the fibers to 7%. Finally, the dried fiberboard blank is conveyed into a continuous flat press for hot pressing. The continuous hot press has four hot pressing temperature zones: zone one is 230±5℃, zone two is 215±5℃, zone three is 205±5℃, and zone four is 180±5℃. After hot pressing, a 1.0mm thick low-formaldehyde, high-waterproof, and high-flame-retardant ultra-thin fiberboard is obtained. The hot pressing speed of the blank is 160m / min.

[0049] Comparative Example 2 The wood fibers from the hot mill are fed into a vertical cooker for cooking and softening. The cooking liquid is a 5% sodium hydroxide alkaline solution. The cooking time is 0.5 minutes and the cooking temperature is 80℃.

[0050] Wood fibers are fed into three sizing pipes to apply isocyanate adhesive at a rate of 10%. A sizing machine then lays the fibers from the three pipes and a hexa(thiocyanate)-cyclotriphosphazene flame retardant into three continuous slab strips, each containing isocyanate adhesive, resulting in a rough slab with a thickness of approximately 35 mm. Pre-compression is achieved through a staged compression process using a heavy-duty pre-compression machine, compressing the slab to 15 mm. The pre-compressed slab is then fed into a humidification and strengthening preheating device. Hot steam is drawn into the slab through the mesh of a steel belt, increasing the moisture content to 10% while further compressing the slab to 6 mm, at which point the slab temperature reaches 70°C. The pressure involved in the staged compression process is determined by the thickness of the compressed slab.

[0051] The reinforced fiberboard is passed through a drying system, with the hot air temperature in the drying press controlled at 80℃ to dry the moisture content of the fibers to 7%. Finally, the dried fiberboard is fed into a continuous flat press for hot pressing. The continuous hot press has four hot pressing temperature zones: Zone 1 at 230±5℃, Zone 2 at 215±5℃, Zone 3 at 205±5℃, and Zone 4 at 180±5℃. The hot pressing speed of the fiberboard is greater than or equal to 150 m / min. After hot pressing, it was found that the isocyanate adhesive on the board directly adhered to the steel strip and could not be detached, forcing the production system to stop and preventing continuous production.

[0052] Comparative Example 3 The wood fibers from the hot mill are fed into a vertical cooker for cooking and softening. The cooking liquid is a 5% sodium hydroxide alkaline solution. The cooking time is 0.5 minutes and the cooking temperature is 80℃.

[0053] Wood fibers are fed into three separate adhesive application pipes to apply urea-formaldehyde resin adhesive at a rate of 15%. A slab forming machine then spreads the fibers from the three pipes and hexa(thiocyanate)-cyclotriphosphazene flame retardant into three continuous slab strips, each containing urea-formaldehyde resin adhesive, resulting in a rough slab with a thickness of approximately 35 mm. A mesh belt pre-compressor is then used to pre-compress the slab to a thickness of 15 mm.

[0054] The results showed that the slabs coming out of the mesh belt pre-press experienced severe springback, returning to a thickness of 20-25mm. This was because the mesh belt pre-press contains multiple pressure rollers. The fibers pressed by the pressure rollers are compressed, and the fibers immediately spring back after leaving the pressure rollers. When the slabs continuously pass through the pressure rollers, they form a cycle of compression-springback-compression-springback similar to breathing. This results in the final slabs not meeting the compression thickness requirements and being unable to enter the humidification, preheating, and strengthening process. After leaving the pre-press, the slabs experience severe backflow and cannot be conveyed into the humidification, preheating, and strengthening equipment, forcing the production line to shut down.

[0055] Comparative Example 4 Wood fibers from the hot mill are fed into a vertical digester for softening and cooking. The cooking liquor is a 5% sodium hydroxide alkaline solution. The cooking time is 0.5 minutes, and the cooking temperature is 80°C. KH550 ethanol-water solution (ethanol:water = 95:5) is stirred uniformly at room temperature for 30 minutes to ensure complete hydrolysis of the silane modifier. The hydrolysate is then sprayed onto the surface of the softened wood fibers using an atomized spray adhesive method and dried in a 100°C pneumatic conveying duct. During this process, the silanol functional groups and the hydroxyl groups on the wood fiber surface undergo a dehydration reaction, resulting in a sheath structure with the silane modifier coated on the wood fiber surface.

[0056] Wood fibers with a sheath structure are fed into three adhesive application pipes. Two pipes apply urea-formaldehyde resin adhesive at a rate of 15%, while the third pipe applies isocyanate adhesive at a rate of 8%. The fibers from the three pipes and the flame retardant hexa(DOPO(9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide))-cyclotriphosphazene are laid into a continuous slab strip with a three-layer sandwich structure using a slab forming machine. The fibers with urea-formaldehyde resin are laid in the top and bottom layers, and the fibers with isocyanate are laid in the middle layer. The top and bottom layers each account for 5% of the total slab mass, and the middle layer accounts for 90%, resulting in a rough slab with a thickness of 35 mm. Heavy-duty pre-compression press is used to pre-compress the slab to 15mm. Instead of sending the pre-compressed slab to a humidification and preheating equipment for humidification and preheating, the slab is directly passed through a drying system. The temperature of the hot air in the drying press is controlled at 80℃ to dry the moisture in the fiber to 7%. Finally, the dried fiber slab is sent to a continuous flat press for hot pressing.

[0057] The results showed that without the humidification and preheating strengthening process, the slab strength was too low. After leaving the pre-press, the slab fractured severely and could not be fed into the inlet of the continuous press, forcing the production line to stop.

[0058] Comparative Example 5 Wood fibers from the hot mill are fed into a vertical digester for softening and cooking. The cooking liquor is a 5% sodium hydroxide alkaline solution. The cooking time is 0.5 minutes, and the cooking temperature is 80°C. KH550 ethanol-water solution (ethanol:water = 95:5) is stirred uniformly at room temperature for 30 minutes to ensure complete hydrolysis of the silane modifier. The hydrolysate is then sprayed onto the surface of the softened wood fibers using an atomized spray adhesive method and dried in a 100°C pneumatic conveying duct. During this process, the silanol functional groups and the hydroxyl groups on the wood fiber surface undergo a dehydration reaction, resulting in a sheath structure with the silane modifier coated on the wood fiber surface.

[0059] Wood fibers with a sheath structure are fed into three adhesive application pipes. Two pipes apply urea-formaldehyde resin adhesive at a rate of 15%, while the third pipe applies isocyanate adhesive at a rate of 8%. The fibers from the three pipes and the flame retardant hexa(DOPO(9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide))-cyclotriphosphazene are laid into a continuous slab strip with a three-layer sandwich structure using a slab forming machine. The fibers with urea-formaldehyde resin are laid in the top and bottom layers, and the fibers with isocyanate are laid in the middle layer. The top and bottom layers each account for 5% of the total slab mass, and the middle layer accounts for 90%, resulting in a rough slab with a thickness of 35 mm.

[0060] The pre-pressing process uses a mesh belt pre-pressing machine to bring the slab thickness back to 20-25mm. The hot pressing speed of the slab on the production line is reduced to 100m / min. It can be stably fed into the humidification and strengthening preheating equipment for humidification and preheating strengthening, and the slab is pre-compressed to 6mm. Then the slab is passed through the drying system, and the hot air temperature in the drying press is controlled at 80℃ to dry the moisture in the fiber to 7%. Finally, the dried fiber slab is fed into the continuous flat press for hot pressing.

[0061] The results showed that continuous production was possible, but the operating speed was very slow, there was no economic value, and the production line was forced to shut down.

[0062] Comparative Example 6 Wood fibers from the hot mill are fed into a vertical digester for softening and cooking. The cooking liquor is a 5% sodium hydroxide alkaline solution. The cooking time is 0.5 minutes, and the cooking temperature is 80°C. KH550 ethanol-water solution (ethanol:water = 95:5) is stirred uniformly at room temperature for 30 minutes to ensure complete hydrolysis of the silane modifier. The hydrolysate is then sprayed onto the surface of the softened wood fibers using an atomized spray adhesive method and dried in a 100°C pneumatic conveying duct. During this process, the silanol functional groups and the hydroxyl groups on the wood fiber surface undergo a dehydration reaction, resulting in a sheath structure with the silane modifier coated on the wood fiber surface.

[0063] Wood fibers with a sheath structure are fed into three adhesive application pipes. Two pipes apply urea-formaldehyde resin adhesive at a rate of 15%, while the third pipe applies isocyanate adhesive at a rate of 8%. The fibers from the three pipes and the flame retardant hexa(DOPO(9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide))-cyclotriphosphazene are laid into a continuous slab strip with a three-layer sandwich structure using a slab forming machine. The fibers with urea-formaldehyde resin are laid in the top and bottom layers, and the fibers with isocyanate are laid in the middle layer. The top and bottom layers each account for 5% of the total slab mass, and the middle layer accounts for 90%, resulting in a rough slab with a thickness of 35 mm.

[0064] The slab is pre-compressed through a staged compression process, which involves using a heavy-duty pre-compressor to compress it to 25mm. The pre-compressed slab is then sent to a humidification and strengthening preheating device for humidification and strengthening. Hot steam is drawn into the slab through the mesh on the steel belt, increasing the slab's moisture content to 10% and further compressing it to 10mm. At this point, the slab's temperature reaches 70℃. The pressure involved in the staged compression process is determined by the thickness of the slab after compression.

[0065] The reinforced fiberboard blanks are passed through a drying system, with the hot air temperature in the drying press controlled at 80℃ to dry the moisture content of the fibers to 7%. Finally, the dried fiberboard blanks are fed into a continuous flat press for hot pressing. The continuous hot press has four hot pressing temperature zones: Zone 1 at 230±5℃, Zone 2 at 215±5℃, Zone 3 at 205±5℃, and Zone 4 at 180±5℃. The hot pressing speed of the production line is 160 m / min. The results showed that the pre-pressing pressure of the blanks in each stage was insufficient (i.e., insufficient compression of the blank thickness), and the production line speed was too high. This caused severe breakage of the blanks at the entrance of the continuous press, preventing them from being fed into the press and forcing the production line to stop. When the hot pressing speed of the production line was reduced to 100 m / min, a 1.0 mm thick low-formaldehyde, high-waterproof, and high-flame-retardant ultrathin fiberboard was obtained after hot pressing; however, the operating speed was too slow and economically unviable.

[0066] Table 1 Comparison of sheet material performance in the examples and comparative examples.

[0067] Those skilled in the art to which this application pertains may modify or supplement the specific embodiments described or use similar methods to replace them, but without departing from the inventive concept of this application or exceeding the scope defined by the appended claims.

Claims

1. A low-formaldehyde, highly waterproof, and highly flame-retardant ultra-thin fiberboard, characterized in that, The ultra-thin fiberboard has a thickness of less than or equal to 1 mm and is made of surface-modified wood fibers, adhesives, and flame retardants through laying, staged compression, and hot pressing. The surface of the wood fibers has a sheath structure formed after being modified by silane modifiers.

2. The low-formaldehyde, high-water-resistance, and high-flame-retardant ultra-thin fiberboard according to claim 1, characterized in that, The silane modifier is selected from one or more combinations of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, 1H,1H,2H,2H-perfluorodecyltrichlorosilane, 1H,1H,2H,2H-perfluorooctyltrichlorosilane, and 1H,1H,2H,2H-perfluorodecyltriethoxysilane, and its addition amount accounts for less than or equal to 3% of the total mass of wood fiber.

3. The low-formaldehyde, high-water-resistance, and high-flame-retardant ultra-thin fiberboard according to claim 1 or 2, characterized in that, The flame retardant is hexachlorocyclotriphosphazene or its derivative, wherein the derivative is selected from at least one of hexa(γ-aminopropyltriethoxysilane)-cyclotriphosphazene, hexa(thiocyanate)-cyclotriphosphazene, hexa(DOPO(9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide))-cyclotriphosphazene, hexa(octaaminocage polysilsesquioxane)-cyclotriphosphazene, hexa(octa(aminophenyl)cage polysilsesquioxane)-cyclotriphosphazene, hexa(aminoethylaminopropylisobutyl polysilsesquioxane)-cyclotriphosphazene, hexa(hydroxycage polysilsesquioxane)-cyclotriphosphazene, and hexa(octa(γ-chloropropyl)cage polysilsesquioxane)-cyclotriphosphazene, and its addition amount accounts for 1% to 15% of the total mass of wood fiber.

4. The low-formaldehyde, high-water-resistance, and high-flame-retardant ultra-thin fiberboard according to claim 1, characterized in that, The adhesive is distributed in a three-layer sandwich structure, with the upper and lower layers made of phenolic resin and the middle layer made of at least one selected from urea-formaldehyde resin, melamine-modified urea-formaldehyde resin, and isocyanate adhesive.

5. A continuous manufacturing method for a low-formaldehyde, highly waterproof, and highly flame-retardant ultrathin fiberboard according to any one of claims 1 to 4, characterized in that, Includes the following steps: S1. Fiber preparation process: Wood fibers are softened by steaming and delignin removal using an alkaline solution, and then the surface of the softened wood fibers is modified with a silane modifier to obtain sheath-structured wood fibers; the sheath-structured wood fibers are then uniformly mixed with adhesives and flame retardants and dried to a moisture content of 5-7%; S2. Phased compression process: including (1) Pre-compression: The mixed wood fibers obtained in S1 are laid into a three-layer sandwich structure of coarse board blanks. After being leveled, they are pressed into 10-15mm thick pre-compressed boards using a double-roller heavy-duty pre-compressor with wedge-angle venting. (2) Humidification and preheating strengthening: The pre-compressed slab is fed into a single-drum humidification and preheating strengthening device. The moisture content of the slab is increased to 10%-12% and the temperature is raised to 70-90℃ by high-pressure atomized jet wetting method. At the same time, the slab is compressed to 5-6mm to obtain a reinforced slab. S3. Continuous hot pressing process: After the reinforced board blank is dried to a moisture content of 7%-8%, it is fed into a continuous flat press for hot pressing to obtain the low-formaldehyde, high-waterproof, and high-flame-retardant ultra-thin fiberboard; wherein, the hot pressing speed of the board blank in the continuous flat press is greater than or equal to 150m / min.

6. The continuous manufacturing method according to claim 5, characterized in that, In S1, the alkaline solution is a solution containing one or more of NaOH, KOH, and Ga(OH)2, with a mass fraction of 0.1%-5%, a cooking temperature of 70℃-130℃, a cooking time of 1-10 min, and the removed lignin accounts for 1-10% of the total lignin content.

7. The continuous manufacturing method according to claim 5, characterized in that, In S1, the proportion of wood fibers with a length between 0.1-1 mm is greater than or equal to 70%; the length is 1-30 mm, the diameter is 5-10 μm, the melting point is greater than or equal to 200 °C, and the amount added accounts for 1-15% of the total mass of wood fibers.

8. The continuous manufacturing method according to claim 5, characterized in that, In S2(1), the thickness of the rough slab is 25-35mm, the upper and lower layers each account for 5-20% of the total slab mass and have the same mass, and the middle layer accounts for 80-95% of the total slab mass; the upper and lower steel belts of the wedge-angle exhaust double-drum heavy pre-press are wedge-angled from the inlet end to the outlet end, and the steel belts are covered with mesh that allows steam to pass through.

9. The continuous manufacturing method according to claim 5, characterized in that, In S2(2), the upper and lower symmetrical rollers at the end of the single roller humidification and preheating strengthening device are used to perform secondary compression on the slab. The humidification and preheating are achieved by injecting humid and hot air into the slab through the mesh of the device's steel strip, so that the extension length of the slab stiffness test is greater than or equal to 3cm.

10. The continuous manufacturing method according to claim 5, characterized in that, In S3, the continuous flat press is divided into four temperature zones along the slab travel direction, with the following temperatures: Zone 1 230±5℃, Zone 2 215±5℃, Zone 3 205±5℃, and Zone 4 180±5℃.

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